Microfacies of Carbonate Rocks: Analysis, Interpretation and Application

E. Fliigel Microfacies of Carbonate Rocks Erik Fliigel Microfacies of Carbonate Rocks Analysis, Interpretation and A...

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E. Fliigel Microfacies of Carbonate Rocks

Erik Fliigel

Microfacies of Carbonate Rocks Analysis, Interpretation and Application With 330 Figures and 151 Plates, some in color

a- Springer

PROFESSOR DR.ERIKFLUGEL Institute of Paleontology Loewenichstrasse 28 D-91054 Erlangen Germany E-mail: [email protected]

ISBN 3-540-22016-X Springer Berlin Heidelberg New York Library of Congress Control Number: 2004104816 This work is subject to copyright. All rights are reserved, whether the whole or art of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, repro!uction on microfilm or in any other way, and storage in data banks. Duplication of this publication or parts thereof is permitted on1 under the rovisions of the German Copyright Law of September 9, 1965,in its current version, and permission for use must always ze obtained from Springer-Verlag. Violat~onsare liable to prosecution under the German Copyright Law. Springer is a part of Springer Science+Business Media springeronline.com O Sprmger-Verlag Berlin Heidelberg 2004 Printed In Germany The use of general descriptive names, registered names, trademarks, etc. in this publication does not im ly, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and $ere fore free for general use. Camera-ready by Erentraud Fliigel-Kahler, Erlangen Cover design: E. Kirchner, Heidelberg Production: Almas Schimmel Printed on acid-free paper 32131411as 5 4 3 2 1 0

Preface

The objective of this book is to provide a synthesis of the methods used in microfacies studies of carbonate rocks and to show how the application of microfacies studies has contributed to new developments in carbonate geology. In contrast with other textbooks on carbonate sedimentology this book focuses on those compositional and textural constituents of carbonates that reflect the depositional and diagenetic history and determine the practical usefulness of carbonate rocks. The chapters are written in such a way, that each one can be used as text in upper level undergraduate and graduate courses. The topics of the book also apply to research workers and exploration geologists, looking for current information on developments in the use of microfacies analysis. Since microfacies studies are based on thin sections, instructive plates showing thin-section photographs accompanied by thorough and detailed explanations form a central part of this book. All plates in the book contain a short summary of the topic. An -> sign leads the reader to the figures on the plate. The description of the microphotographs are printed in a smaller type. Care has been taken to add arrows and/or letters (usually the initials of the subject) so that the maximum information can be extracted from the figures. Rather than being a revised version of 'Microfacies Analysis of Limestones' (Fliigel 1982) 'Microfacies of Carbonate Rocks' is a new book, based on a new concept and offering practical advice on the description and interpretation ofmicrofacies data as well as the application of these data to basin analysis. Microfacies analysis has the advantages over traditional sedimentological approaches of being interdisciplinary, and integrating sedimentological, paleontological and geochemical aspects. 'Microfacies of Carbonate Rocks': analyses both the depositional and the diagenetic history of carbonate rocks, describes carbonate sedimentation in various marine and non-marine environments, and considers both tropical warm-water carbonates and non-tropical cool-water carbonates,

presents diagnostic features and highlights the significance of microfacies criteria, stresses the biological controls of carbonate sedimentation and provides an overview on the most common fossils found in thin sections of limestones, discusses the relationships between diagenetic processes, porosity and dolomitization, demonstrates the importance of microfacies for establishing and evaluating sequence stratigraphic frameworks and depositional models, underlines the potential of microfacies in differentiating paleoclimate changes and tracing platform-basin relationships, and demonstrates the value of microfacies analysis in evaluating reservoir rocks and limestone resources, as well as its usefulness in archaeological provenance studies.

Structure of the Book Microfacies of Carbonate Rocks starts with and introductory chaper (Chap. 1) and an overview of modem carbonate deposition (Chap. 2) followed by 17 chapters that have been grouped into 3 major parts. Microfacies Analysis (Chap. 3 to Chap. 10) summarizes the methods used in microfacies studies followed by discussions on descriptive modes and the implications of qualitative and quantitative thin-section criteria. Microfacies Interpretation (Chap. 11 to Chap. 16) demonstrates the significance of microfacies studies in evaluating paleoenvironment and depositional systems and, finally, Practical Use of Microfacies (Chap. 17 to Chap. 19) demonstrates the importance of applied microfacies studies in geological exploration for hydrocarbons and ores, provides examples of the relationships between carbonate rock resources and their facies and physical properties, and also illustrates the value of microfacies studies to archaeologists. Important references are listed at the end of chapters or sections under the heading 'Basics'. The code

numbers K... are keywords leading to references on specific fields of interest (see CD), e.g. KO21 (coldwater carbonates), KO78 (micrite), or K200 (hydrocarbon reservoir rocks). The book is also accompanied by a CD containing an alphabetical list of about 14,000 references on carbonate rocks (see Appendix) as word document, and visual comparison charts for percentage estimation.

Synopsis of the Book's Contents Chapter 1: New Perspectives in Microfacies. Microfacies studies, which were originally restricted to the scale of thin sections, provide an invaluable source of information on the depositional constraints and environmental controls of carbonates, as well as on the properties of carbonate rocks. Microfacies studies assist in understanding sequence stratigraphic patterns and are of economic importance both in reservoir studies and in the evaluation of limestone resources. Chapter 2: Modern Depositional Environments. Knowledge of modem carbonates is a prerequisite for understanding ancient carbonate rocks. Modem carbonates are fortned both on land and in the sea, in shallow- and in deep marine settings, and in tropical and non-tropical regions, but the present is only part a key to the Past.

Microjbcies Analysis Chapter 3: Methodology. Which methods can be used in the field? Which sampling strategy should be applied and how many samples are required? Which laboratory techniques are useful in rnicrofacies analysis? Which other techniques should be combined with microfacies studies? Chapter 4: Microfacies Data: Matrix and Grains. This chapter offers practical advice on how to handle microfacies data, and deals with how to describe and interpret thin-section characteristics. Matrix types and grain categories are discussed with regard to their diagnostic criteria, origin and significance. Chapter 5: Microfacies Data: Fabrics. Typical depositional and diagenetic fabrics in limestones reflect the history of the rock. Microfacies criteria indicating breaks and changes in sedimentation (discontinuity surfaces) are of specific interest in refining sequence stratigraphic boundaries. Variously sized fissures, microcracks and breccias can be used in deciphering synand post-depositional destructive processes.

Chapter 6: Quantitative Microfacies Analysis. Whilst previous chapters focused on qualitative criteria this chapter deals with quantitative data including grain size analysis, frequency analysis and multivariate studies. Constituent analysis and the distribution patterns of specific grain types are valuable tools in the reconstruction of paleoenvironmental controls and depositional settings. Chapter 7: Diagenesis, Porosity and Dolomitization. Understanding diagenetic processes and their products is of high economic importance. The diagenetic microfacies of a rock reflects changes in the course of its lithification history. The main topics discussed in this chapter are porosity types, carbonate cements, diagenetic textures including compaction and pressure solution, and dolomitization/dedolomitizationand dolomite textures. The last part of the chapter deals with thinsection criteria for metamorphic carbonates and marbles. Chapter 8: Classification - chosing a name for your sample. Aclassification is simply a tool for organizing information, and should not be the only source of conclusions. Whilst a name based on texture and composition can not replace a well-defined microfacies type, rock names are essential for the categorization of samples. Textural classifications proposed by Dunham and by Folk have proven to be the most practical. Specific concepts must be adhered to in the naming of reef limestones, non-marine carbonates, recrystallized carbonates rocks and mixed siliciclastic-carbonate rocks. Chapter 9: Limestones are Biological Sediments. In contrast to siliciclastic rocks, both the formation and the destruction of most limestones is directly or indirectly influenced and controlled by biological processes. This chapter stresses the biological controls on carbonate sedimentation. Microbes, encrusting organisms, and macro- and microborers can yield useful information on paleoenvironment, depositional constraints and carbonate production. Chapter 10: Fossils in Thin Sections. It Is Not That Difficult. The recognition of fossils in thin sections is not so difficult once the diagnostic criteria for the main groups have been understood, particularly for algae and foraminifera, sessile invertebrates, and organisms with shells. This chapter provides an overview of the most common fossils found in thin sections of limestones. The text concentrates on identification criteria, environmental and temporal distribution, and on the significance of the fossils. Numerous instructive plates are included to aid in the recognition and differentiation skeletal grains in thin sections.

VII

Microfacies Interpretation Chapter 11:Summarizing Microfacies Criteria:Microfacies Types. How can microfacies data be combined in sensitive and practicable microfacies types? Which criteria should be used, which grain types are of particular importance and, how many microfacies types are reliable? The creation of microfacies types is illustrated by means of examples. Chapter 12: Recognizing Paleoenvironmental Conditions. Carbonate sediments are particularly sensitive to environmental changes. Microfacies and organisms are excellent paleoenvironmental proxies as they reflect hydrodynamic conditions, the impact of storms, substrate conditions, light, oxygenation, seawater temperature and salinity. Significant differences between the compositions of skeletal grain associations for warm-water and cold-water carbonates provide a useful tool for estimating paleoclimatic changes. How deep was the sea? Microfacies studies provide an answer. Chapter 13: Integrated Facies Analysis. Understanding the formation and diagenesis of carbonate rocks requires the combination of microfacies with mineralogical and geochemical data. The chapter deals with acid-insoluble residues and authigenic minerals in carbonate rocks, discusses the value of minor elements and stable isotopes in tracing the depositional and diagenetic history of limestones, and deals with the potential of organic matter in carbonate rocks for facies analysis. Chapter 14: Depositional Models, Facies Zones and Standard Microfacies. Microfacies are essential for defining depositional models and recognizing facies zones. Facies models assist in understanding depositional history. Changes in sedimentological and biological criteria across shelf-slope-basin transects form the basis of generalized models for carbonate platforms, ramps and shelves. Facies belts are reflected by their biotic zonation patterns and the distribution of Standard Microfacies Types (SMF Types). The latter are virtual categories that summarize rnicrofacies with identical criteria. Which criteria are used in differentiating the SMF Types of platform and ramp carbonates? What are the problems involved in the SMF concept? Revised and refined SMF types are a meaningful tool in tracing facies belts, but must be used with care. Common microfacies of carbonate ramps (Ramp Microfacies Types) show only partial correspondence to the SMF Types of rimmed platforms. Chapter 15: Basin Analysis: Recognizing Depositional Settings. Which diagnostic criteria characterize lime-

stones of different carbonate systems? Case studies for non-marine and marine carbonate rocks demonstrate how to translate microfacies into ancient depositional settings. Non-marine settings can be successfully reconstructed for pedogenic carbonates, paleokarst deposits and ancient speleothems, travertine deposits, and lacustrine carbonates, these can be characterized by specific microfacies types. Marine settings can be differentiated into peritidal carbonates, platforms and ramps, platform-slope-basin transects, and pelagic deep-marine carbonates. Grain Composition Logs are particularly effective in tracing platform-basin relations. Chapter 16: Recognizing Depositional Constraintsand Processes. Selected case studies are used to demonstrate the value of microfacies data in interpreting depositional controls. How can microfacies be used in sequence stratigraphy? Cyclic depositional patterns and sequence stratigraphic constraints are documented by microfacies data that assist in recognizing sequence boundaries, parasequences, high-frequency sea-level changes, and systems tracts. Which criteria characterize reef limestones? Major reef types differ in biota, matrix, sediment, and cements. Which methods should be employed in reconstructing former platforms and reefs that are only recorded by eroded relicts deposited on slopes and in basins? Clast analysis can solve this puzzle. Which criteria define ancient cold-water carbonates? Ancient cool-water shelf and reef carbonates are typified by specific biotic, compositional and diagenetic features. Which facies criteria are diagnostic of ancient ventand seep carbonates? Case studies provide answers. How to handle mixed carbonate-siliciclastic sediments and interpret limestone-marl successions? * Constraints on carbonate deposition exhibit secular variations, which are discussed in the last section.

Practical Use of Microfacies Chapter 17: Reservoir Rocks and Host Rocks. Carbonates are the most important reservoir rocks for hydrocarbons as well as forming important host rocks for ores. Limestones and dolomites contain more than 50% of the world's oil and gas reserves. Reservoir potential differs for carbonates formed in different depositional settings and depends on the interplay of depositional processes and diagenetic history. The microfacies of cores and cuttings - assist in the translation of lithological data into petrophysical information. Facies-based outcrop-analogue studies indicate the scale of porosity and

VIII

permeability variations within carbonate bodies. Microfacies analysis also assists in the genetic interpretation of carbonate-hosted base metal deposits controlled by specific facies patterns. Chapter 18: Carbonate Resources, Facies Control and Rock Properties. Carbonate rocks are important raw materials for chemical and construction industries and are high on the list of extracted mineral resources, both in terms of quantity and of value. Both exploration and exploitation can be enhanced by taking into account the relationships between depositional and diagenetic facies that control technologically relevant chemical and physical parameters, as well as the weathering and decay properties of carbonate rocks. Conservation and preservation of works of art and building stones should start with thin-section studies of the textural and diagenetic criteria that describe the porosity and permeability of the material. Chapter 19:Archaeometry. Microfacies analysis, combined with geochemical data has considerable potential in provenance analysis of archaeological materials. Thin sections reveal the source of building stones and of material used for mosaics and works of arts. The microfacies of temper grains in ancient pottery helps in understanding the source and production areas for ceramics. Last but not least, microfacies studies can throw new light at the love affair between Antony and Cleopatra. ...

Acknowledgments Thanks are due to many people who have provided photographs, information and advice: Gernot Arp (Gottingen), Martina Bachmann (Bremen), Benoit Beauchamp (Calgary), Thilo Bechstadt (Heidelberg), Michaela Bemecker (Erlangen), Joachim Blau (Giessen), Florian Bohm (Kiel), Thomas Brachert (Mainz), Ioan Bucur (Cluj-Napoca), Werner Buggisch (Erlangen),Thomas Clausing (Halle), Wolf-Christian Dullo (Kiel), Paul Enos (Lawrence, Kansas), Gerd Flajs (Aachen), Christof Fliigel (Miinchen), Helmut Fliigel (Graz), Beate Fohrer (Erlangen), Holger Forke (Berlin), AndrC Freiwald (Erlangen), Robert van Geldern

(Erlangen), Markus Geiger (Bremen), Gisela Gerdes (Oldenburg), Eberhard Gischler (Frankfurt), Dirk von Gosen (Erlangen), Jiirgen Grotsch (Damascus). HansGeorg Herbig (Koln), Richard Hofling (Erlangen), Bemhard Hubmann (Graz), Andi Imran (Makassar), Michael Joachimski (Erlangen), Josef Kazmierczak (Warszawa), Martin Keller (Erlangen), Stephan Kempe (Darmstadt), Helmut Keupp (Berlin), Wolfgang Kiessling (Berlin), Roman Koch (Erlangen), Karl Krainer (Imsbruck), Jochen Kuss (Bremen), Michael Link (Erlangen), Heinz Lorenz (Erlangen), Ulrich Michel (Nurnberg), Axel Mumecke (Erlangen), Fritz Neuweiler (Gottingen), Alexander Nutzel (Erlangen), Joachim Reitner (Gottingen), Jurgen Remane (Neuchatel), Elias Samankassou (Fribourg), Diethard Sanders (Imsbruck), Chris Schulbert (Erlangen), Baba Senowbari-Daryan (Erlangen), Robert J. Stanton (Thousand Oaks, California), Torsten Steiger (Bad Blankenburg), Thomas Steuber (Bochum), Harald Tragelehn (Koln), Jorg Trappe (Bonn), Dragica Tumsek (Ljubljana), Andreas Wetzel (Tubingen). I am indebted to Birgit Leipner-Mata and Marieluise Neufert (Institute of Paleontology Erlangen) for laboratory work and photography. Chris Schulbert (Institute of Paleontology) was a valuable help with all computer problems. I am sincerely grateful to my friend Johann Georg Haditsch (Graz) for critical reading the text of the book. Special thanks go to Karen Christenson (NiimbergKraftshof) who took care of linguistic problems and pitfalls. Editing, layout, drawings and the preparation of plates and figures have been camed out by my wife Erentraud Fliigel-Kahler. I am most grateful for her encouragement and constant help. Finally, I am obliged to all institutions who gave permission to use published material and to the staff of Springer Verlag, especially to Dr. Wolfgang Engel for his constant encouragement and to Dr. J. Witschel for assistance with the book.

Contents New Perspectives in Microfacies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The Microfacies Concept . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . New Perspectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Depositional Environments . . . . . . . . . . . . . . . . . . . . . . . . . . Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonates are Bom not Made . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . The 'Sorby Principle': Limestones are Predominantly Biogenic Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modem Carbonates: Obligatory Reading . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Sediments Originate on Land and in the Sea . . . . . . . . . . . . . . . Classification of Marine Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . BoundaryLevels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Vertical and Horizontal Zonations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . VerticalZonations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Horizontal Zonations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Review of Modem Carbonate Depositional Environments . . . . . . . . . . . . . Non-Marine Carbonate Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pedogenic Carbonates. Paleosols. and Caliche/Calcretes . . . . . . . . . . . . . . Palustrine Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cave Carbonates. Speleothems and Karst . . . . . . . . . . . . . . . . . . . . . . . . . . Glacialcarbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Travertine. Calcareous Tufa and Calcareous Sinter . . . . . . . . . . . . . . . . . . . Lacustrine Carbonates: Lakes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluvialcarbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Transitional Marginal-Marine Environments: Shorelines and Peritidal Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Beach (Foreshore). Barriers and Coastal Lagoons . . . . . . . . . . . . . . . . . . . . Peritidal Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shallow-Marine Sedimentary Environments: 'Shallow' and 'Deep' . . . . . . Pericontinental vs Epicontinental Shallow Seas . . . . . . . . . . . . . . . . . . . . . Carbonate Shelves. Ramps and Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . ShelfMargins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tropical and Non-Tropical Carbonates: Different in Composition. Controls and Significance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Latitudinal Zonation and Diagnostic Criteria of Tropical and Non-Tropical Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tropical and Subtropical Shallow-Marine Carbonates . . . . . . . . . . . . . . . . Non-Tropical Shelf and Reef Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . Deep-Marine Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sedimentation Processes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pelagic Sedimentation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Resedimentation (' Allochthonous Carbonates') . . . . . . . . . . . . . . . . . . . . .

Contents

Carbonate Plankton and Carbonate Oozes . . . . . . . . . . . . . . . . . . . . . . . . . . Preservation Potential and Dissolution Levels . . . . . . . . . . . . . . . . . . . . . . . Carbonate Slopes. Periplatform Carbonates and Caronate Aprons . . . . . . . Seepandventcarbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Analysis Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Work and Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Lithology. Texture and Rock Colors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bedding and Stratification. Sedimentary Structures and DiageneticFeatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fossils and Biogenic Structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Field Logs and Compositional Logs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Search Sampling and Statistical Sampling . . . . . . . . . . . . . . . . . . . . . . . . . . How Many Samples? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical Advice for Microfacies Sampling . . . . . . . . . . . . . . . . . . . . . . . . . Laboratory Work: Techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Slices. Peels and Thin Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Casts. Etching and Staining . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Petrographic Microscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . StereoscanMicroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluorescence. Cathodoluminescence and Fluid Inclusion Microscopy . . . . Mineralogy and Geochemistry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trace Elements and Stable Isotope Analysis . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Data: Matrix and Grains . . . . . . . . . . . . . . . . . . . . . . . . . . . Fine-Grained Carbonate Matrix: Micrite. Microspar. Calcisiltite . . . . . . . . Micrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modes of Formation of Micrite and Other Fine-Grained Matrix Types . . . Microspar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calcisiltite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical Aids in Describing and Interpreting Fine-Grained Limestones . . Significance of Fine-Grained Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Grains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bioclasts (Skeletal Grains) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peloids: Just a Term of Ignorance? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cortoids - Carbonate Grains Characterized by Micrite Envelope . . . . . . . . Oncoids and Rhodoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oncoids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rhodoids and Macroids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ooids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pisoids and Vadoids - Simply 'Larger Ooids' or Carbonate Grains on their Own? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Aggregate Grains: Grapestones. Lumps and Other Composite Grains . . . . Resediments: Intra.. Extra- and Lithoclasts - Insiders and Foreigners . . . . Intraclasts: Origin and Facies-Diagnostic Types . . . . . . . . . . . . . . . . . . . . . Extraclasts: Strange Foreigners . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Morphometry of Carbonate Grains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Intentions and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance of Morphometric Data for Carbonate Grains . . . . . . . . . . . . .

Contents

Microfacies Data: Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Depositional and Diagenetic Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geopetal Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biofabrics and Grain Orientation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bedding and Lamination Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burrowing and Bioturbation Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Birdseyes. Fenestral Fabrics and Stromatactis . . . . . . . . . . . . . . . . . . . . . . . Birdseyes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fenestral Fabrics ............................................. Stromatactis ................................................. Significance of Birdseyes. Fenestral Fabrics and Stromatactis . . . . . . . . . . Nodular Fabrics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discontinuity Surfaces: From Microfacies to Sequence Stratigraphy . . . . . Classification of Discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Major Criteria of Discontinuities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Criteria and Significance of Exposure Surfaces . . . . . . . . . . . . Microfacies Criteria and Significance of Condensation Surfaces and Hardgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hardgrounds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Condensation Surfaces and Condensed Sections . . . . . . . . . . . . . . . . . . . . . Discontinuities and Sequence Stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . Syn- and Postdepositional Features: Fissures. Veins. Breccias . . . . . . . . . . Sediment-Filled Fissures: Neptunian Dikes and Fissure Fills . . . . . . . . . . . Origin. Development and Filling of Sedimentary Fissures . . . . . . . . . . . . . Microfacies Analysis of Neptunian Dikes . . . . . . . . . . . . . . . . . . . . . . . . . . Case Studies of Neptunian Dikes in Carbonates . . . . . . . . . . . . . . . . . . . . . Significance of Sediment-Filled Fissures . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfractures and Veins (Calcite Veins) . . . . . . . . . . . . . . . . . . . . . . . . . . . Origin and Classification of Calcite Veins . . . . . . . . . . . . . . . . . . . . . . . . . . Descriptive Criteria of Calcite-Filled Microfractures . . . . . . . . . . . . . . . . . Significance of Microfractures in Carbonate Rocks . . . . . . . . . . . . . . . . . . Carbonate Breccias and Conglomerates . . . . . . . . . . . . . . . . . . . . . . . . . . . . Teminology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to Describe Carbonate Breccias? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Breccia Types: Origin. Classification. Criteria . . . . . . . . . . . . . . Carbonate Conglomerates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance of Carbonate Breccias and Conglomerates . . . . . . . . . . . . . . . Quantitative Microfacies Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain-Size Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain-Size Analysis: Methods and Aims . . . . . . . . . . . . . . . . . . . . . . . . . . . Measuring Grain Sizes and Describing Size Distributions . . . . . . . . . . . . . Approaches to the Environmental Interpretation of Grain-Size Data . . . . . Grain-Size Analysis in Thin Sections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain-Size Studies of Modem and Ancient Carbonates . . . . . . . . . . . . . . . . Grain-Size Studies of Modem Carbonate Sediments . . . . . . . . . . . . . . . . . . Application of Grain-Size Analyses to Carbonate Rocks . . . . . . . . . . . . . . Significance of Grain-Size Studies of Carbonate Rocks . . . . . . . . . . . . . . . Frequency Analysis of Microfacies Data . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods of Frequency Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Counting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Image Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Contents

Constituent Ranking. Diversity and Maturity . . . . . . . . . . . . . . . . . . . . . . . Integrated Frequency Studies of Reef Carbonates . . . . . . . . . . . . . . . . . . . . PracticalAdvice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Multivariate Microfacies Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods: Variations between Constituents and between Samples . . . . . . . . Significance of Multivariate Studies: Constituent Analysis as a Clue to Environmental Conditions and Depositional Settings . . . . . . . . . . .

Diagenesis. Porosity. and Dolomitization . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Mineralogy and Diagenetic Processes . . . . . . . . . . . . . . . . . . . . Modem Carbonate Sediments and Ancient Carbonate Rocks . . . . . . . . . . . Common Carbonate Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic Processes and Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . From Soft Sediments to Hard Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Oscillating Trends in Phanerozoic Carbonate Mineralogy . . . . . . . . . . . . . Secularvariations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to Recognize Former Aragonite and Mg-Calcite Mineralogy in Ancient Low-Calcite Limestones? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Major Diagenetic Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Meteoric. Marine and Burial Diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . Meteoric (Freshwater) Diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing Zone and Marine Vadose Environment . . . . . . . . . . . . . . . . . . . . . . MarineDiagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Burial Diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Early and Late Diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Porosity of Carbonate Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Porosity Categories. Pore Geometry and Permeability . . . . . . . . . . . . . . . . Basic Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pore Geometry and Permeability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Porosity Measurements and Pore Types in Thin Sections . . . . . . . . . . . . . . Porosity Terminology and Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . Porosity in Limestones and Dolomites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pore-Filling Processes: Cementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Controls on Carbonate Cementation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Morphology and Fabrics of Cement Types . . . . . . . . . . . . . . . . . . . . . . . . . CementTypes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cen~entFabrics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cement Types and Diagenetic Environments . . . . . . . . . . . . . . . . . . . . . . . Facies-Controlled Diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Platforms and Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cold-Water vs . Warm-Water Diagenesis . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic Pathways and Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic Textures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mechanical Processes: Compaction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Chemical Processes: Pressure Solution and Stylolitization . . . . . . . . . . . . . Significance of Compaction and Pressure Solution . . . . . . . . . . . . . . . . . . . Neomorphic Processes: Alteration and Recrystallization . . . . . . . . . . . . . . Recrystallized Carbonate Rocks: What to do? . . . . . . . . . . . . . . . . . . . . . . . How to DescribeRecrystallized Carbonate Rocks? . . . . . . . . . . . . . . . . . . . Sparite: Recrystallization Product or Carbonate Cement? . . . . . . . . . . . . . . Dolomitization and Dedolomitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Descriptive Criteria and Terminology of Dolomite Fabrics . . . . . . . . . . . . .

Contents

Thin-Section Description and Terminology of Dolomite Rocks . . . . . . . . . Dolomite Cement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Value of Dolomite Textures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Some Dolomitization Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dolomites Associated with Evaporites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mixing-Water and Seawater Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Subsurface Burial Dolomites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dedolomitization . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Textural Criteria for Recognizing Dedolomitization . . . . . . . . . . . . . . . . . . Origin of Dedolomite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance of Dedolomitization. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Metamorphic Carbonate and Marbles . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Classification . A Name for Your Sample . . . . . . . . . . . . . . . . . . . . . . . . Basicconcepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reef Limestones and Microbial Carbonates (Autochthonous Carbonates) . Classifications Based on Depositional Texture . . . . . . . . . . . . . . . . . . . . . . Prerequisites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Original and Expanded Dunham Classification . . . . . . . . . . . . . . . . . . . . . . Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Original and Expanded Folk Classification . . . . . . . . . . . . . . . . . . . . . . . . . Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Specific Classifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic Changes in Depositional Textures . . . . . . . . . . . . . . . . . . . . . . . Some Nonmarine Carbonates Need very Specific Names . . . . . . . . . . . . . . Classification of Mixed Siliciclastic-CarbonateRocks . . . . . . . . . . . . . . . . A Name for Your Samples: Some Practical Advice . . . . . . . . . . . . . . . . . . . Limestones are Biological Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microbial Carbonates and Stromatolites . . . . . . . . . . . . . . . . . . . . . . . . . . . Bacterial Contribution to Carbonate Precipitation . . . . . . . . . . . . . . . . . . . . How to Recognize Microbial Carbonates? . . . . . . . . . . . . . . . . . . . . . . . . . . Describing and Classifying Benthic Microbial Carbonates . . . . . . . . . . . . . Terminology and Descriptive Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classification of Benthic Microbial Carbonates . . . . . . . . . . . . . . . . . . . . . Stromatolites are Laminated Microbialites . . . . . . . . . . . . . . . . . . . . . . . . . Occurrence and Significance of Microbialites and Stromatolites . . . . . . . . Development through Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Paleoenvironmental Significance of Microbial Carbonates . . . . . . . . . . . . . Economic Importance of Stromatolites . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biogenic Encrustations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Criteria and Constraints of Encrusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phanerozoic Encrusters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance of Encrustation Patterns in Recognizing Depositional Settings and Environmental Controls . . . . . . . . . . . . . . . . . . . Bioerosion. Boring and Grazing Organisms . . . . . . . . . . . . . . . . . . . . . . . . Recent and Fossil Microborers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recent and Fossil Macroborers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Micro- and Macroboring through Time . . . . . . . . . . . . . . . . . . . . . . . . . . . . Qualitative Changes in Micro- and Macroborer Groups . . . . . . . . . . . . . . . Quantitative Changes in the Intensity of Macroboring in Coral Reefs . . . .

Contents

XIV

Microborer Associations are Proxies for Paleo-Water Depths . . . . . . . . . . . Practical Advice: How to Describe Microbialites and Stromatolites. Biogenic Encrustations and Borings? . . . . . . . . . . . . . . . . . .

Fossils in Thin Section: It is Not That Difficult . . . . . . . . . . . . . . . . . . . . Specifics of Thin-Section Fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to Determine Fossils in Thin Sections? . . . . . . . . . . . . . . . . . . . . . . . . Which Fossils in which Time Interval? . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical Advice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagnostic Criteria of Fossils in Thin Sections . . . . . . . . . . . . . . . . . . . . . . Cyanobacteria and Calcareous Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyanobacteria and Calcimicrobes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corallinacean and Peyssoneliacean Red Algae . . . . . . . . . . . . . . . . . . . . . . Solenoporacean Red Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ancestral Red Algae and Problematic Red Algae . . . . . . . . . . . . . . . . . . . . Udoteacean Green Algae and Gymnocodiacean Algae . . . . . . . . . . . . . . . . Phylloid Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dasyclad Green Algae . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Charophyta: Fresh-Water and Brackish-Water Algae . . . . . . . . . . . . . . . . . 'Calcispheres' and Algal Cysts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Foraminifera and other Protozoa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Foraminifera . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Radiolaria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Calpionellids . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Benthic Sessile Organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sponges . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrozoans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Corals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bryozoans . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Shells . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Brachiopods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Bivalves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Gastropods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cephalopods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Tentaculitids and Other Conical Shells (Cricoconarida; Hyolithida) . . . . . . Serpulids and Other Worm Tubes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CrustaceanArthropods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Trilobites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Echinoderms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare Thin-Section Fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microproblematica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Inventory of Microproblematica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion of Selected Microproblematica . . . . . . . . . . . . . . . . . . . . . . . . . Biozonation of Platforms with Thin-Section Fossils . . . . . . . . . . . . . . . . . . Where to Look for Thin-Section Pictures of Fossils and Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Microfacies Interpretation Summarizing Microfacies Criteria: Microfacies Types . . . . . . . . . . . . . MFTConcepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to Differentiate Meaningful Microfacies Types . . . . . . . . . . . . . . . . . Making Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Recognizing Paleoenvironmental Conditions . . . . . . . . . . . . . . . . . . . . . Reconstructing Environmental Constraints . . . . . . . . . . . . . . . . . . . . . . . . . Hydrodynamic Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrodynamic Energy Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Classifying Low-Energy and High-Energy Environments . . . . . . . . . . . . . Paleocurrent Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Storm Deposits (Tempestites) on Shelves. Ramps and Platforms . . . . . . . . Impact of Tropical Storms on Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance of Carbonate Storm Deposits . . . . . . . . . . . . . . . . . . . . . . . . . Marine Carbonate Substrates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Substrate Types and Organism-Sediment Interactions . . . . . . . . Recognizing Substrate Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Light . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Zonation and Light Conditions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recognition of Photic and Aphotic Conditions . . . . . . . . . . . . . . . . . . . . . . Oxygen . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Terminology and Classification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recognizing Paleo-Oxygenation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Black Shale Development on a Carbonate Platform . . . . . . . . Seawater Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seawater Temperature: Biotic Proxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geochemical Proxies of Seawater Temperatures . . . . . . . . . . . . . . . . . . . . . Salinity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biotic and Microfacies Proxies of Paleosalinity . . . . . . . . . . . . . . . . . . . . . Geochemical Proxies of Paleosalinity ............................. Microfacies Proxies for Hypersaline and Evaporitic Conditions . . . . . . . . . Productivity and Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Nutrients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Estimating Paleonutrient Levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Effects of Nutrient Excess on Reef and Platform Carbonates . . . . . . . . . . . Estimating Paleoclimatic Conditions: Grain Association Analysis . . . . . . . Concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Practical Advice. Examples and State of Current Information . . . . . . . . . . Distinguishing Grain Association Types . . . . . . . . . . . . . . . . . . . . . . . . . . . Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . State of the Art . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Assessing Water Depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hints to Paleowater Depths . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Assessing the Water Depth of a Carbonate Ramp . . . . . . . . . . Integrated Facies Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non-Carbonate Constituents . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Insoluble Residues (IR): Clay Minerals and Detrital Quartz . . . . . . . . . . . . Authigenic Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Silicification of Carbonates. Authigenic Feldspar and Glauconite . . . . . . . Sulfides: Pyrite . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sulfates: Evaporite Minerals . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Geochemical Proxies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . TraceElements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Strontium and Manganese .Favorite Tools for Facies Studies . . . . . . . . . .

Contents

Significance of Trace Elements in Facies Studies of Carbonate Rocks . . . . Stable Isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Organic Matter in Carbonate Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Depositional Models. Facies Zones and Standard Microfacies . . . . . . . Depositional Facies Models ..................................... Conceptual. Dynamic and Computer Models . . . . . . . . . . . . . . . . . . . . . . . ConceptualModels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . DynamicModels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Numerical Models . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Elements of Carbonate Facies Models . . . . . . . . . . . . . . . . . . . . . . . . Common Facies Belts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common Depositional Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Different Depositional Settings Require Different Facies Models . . . . . . . Facies Zones of Rimmed Carbonate Platforms: The Wilson Model . . . . . . Standard Facies Zones and the Modified Wilson Model ............... Discussion and Use of Standard Facies Zones . . . . . . . . . . . . . . . . . . . . . . . CarbonateRampModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Non-rimmed Shelves and Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Isolated Platforms and Atolls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EpeiricPlatfomModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . EpeiricRampModel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biotic Zonation Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ConceptsandMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Foraminifera1 Distribution in Late Triassic Reefs and Platforms Standard Microfacies Types (SMF) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Revised Standard Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Discussion of Standard Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . . . Stratigraphic Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Common Microfacies Types of Carbonate Ramps . . . . . . . . . . . . . . . . . . . Microfacies Criteria of Carbonate Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Types of Carbonate Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . Tracing Facies Zones with Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . Determining Standard Microfacies Types: A Practical Guide . . . . . . . . . . . Dynamic Microfacies Types and Environmental Changes . . . . . . . . . . . . . Basin Analysis: Recognizing Depositional Settings . . . . . . . . . . . . . . . . . Pedogeniccarbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Criteria of Paleocaliche . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Significance of Paleocaliche and Paleosols . . . . . . . . . . . . . . . . . . . . . . . . . Paleokarst and Ancient Speleothems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagnostic Criteria of Paleokarst and Paleospeleothem Structures . . . . . . . Significance of Paleokarst and Cave Carbonates . . . . . . . . . . . . . . . . . . . . . Travertine. Calcareous Tufa and Calcareous Sinter . . . . . . . . . . . . . . . . . . . Lacustrine and Palustrine Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies of Lacustrine Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Types of Lacustrine Limestones . . . . . . . . . . . . . . . . . . . . . . . . Distribution of Lacustrine Microfacies Types . . . . . . . . . . . . . . . . . . . . . . . Palustrine Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peritidal Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Criteria of Peritidal Limestones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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XVII

Major Facies Criteria of Peritidal Carbonates . . . . . . . . . . . . . . . . . . . . . . . Synopsis of Diagnostic Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Middle Devonian Peritidal Carbonates from Poland . . . . . . . . Carbonate Platforms and Ramps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ecological Controls on Platforms and Ramps . . . . . . . . . . . . . . . . . . . . . . . The Response of Carbonate Platforms to Drowning . . . . . . . . . . . . . . . . . . Microfacies Signals of Drowning History . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Platfonn Drowning Reflected by Microfacies . . . . . . . . . . . . . Case Studies: Platform and Ramp Carbonates . . . . . . . . . . . . . . . . . . . . . . . A Late Jurassic Bahamian-Type Carbonate Platform from the Northern Calcareous Alps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . A Middle Devonian Ramp from Graz. Southern Austria ............... A Late Jurassic/Early Cretaceous Ramp from the Subsurface of Southern Bavaria. Germany . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Platform-Slope-Basin Transects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Types and Composition of Carbonate Slopes . . . . . . . . . . . . . . . . . . . . . . . Allochthonous Slope and Basin Deposits: Diagnostic Criteria . . . . . . . . . . Submarine Rockfalls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Breccias and Megabreccias . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Debris-Flow Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Grain-Flow Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Turbidites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sliding and Slumping . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies of Slope Carbonates: Case Studies . . . . . . . . . . . . . . . . . . . . . . Permian of Sicily: Megablocks and Base-of-Slope Carbonates . . . . . . . . . . Triassic of the Southern Alps: Allochthonous Slope Sediments . . . . . . . . . Jurassic of Morocco: Platform-Slope-Basin Transect . . . . . . . . . . . . . . . . . Jurassic of the Northern Calcareous Alps: Detailed Information from Limestone Turbidites on Source and Deposition Patterns . . . . . . . . . . . . . . Slope Stability Reflected by Texture and Microfacies . . . . . . . . . . . . . . . . . Tracing Platform-Basin Transitions Using Grain Composition Logs . . . . . ConceptandMethods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Late Triassic of the Gosaukamm Region. Austria . . . . . . . . . . Pelagic Deep-Marine Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Setting. Controls and Biota of Pelagic Limestones . . . . . . . . . . . . . . . . . . . Examples and Case Studies of Pelagic Carbonates . . . . . . . . . . . . . . . . . . . Microfacies of Paleozoic Basinal Carbonates . . . . . . . . . . . . . . . . . . . . . . . Microfacies of Mesozoic Basinal Carbonates . . . . . . . . . . . . . . . . . . . . . . . Contourites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Realizing Depositional Constraints and Processes . . . . . . . . . . . . . . . . . Cyclic Carbonates. Microfacies and Sequence Stratigraphy . . . . . . . . . . . . Cyclic Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cyclic Carbonates: Some Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies and Cyclic Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Studies: The Lofer Cycle and the Latemar Cycle (Triassic of the Alps) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Sequence Stratigraphy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sequence Analysis: Some Basics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Data Applied to Sequence Stratigraphy . . . . . . . . . . . . . . . . . . Case Studies: Sea-Level Fluctuations and Systems Tracts Documented by Microfacies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Understanding Reef Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Contents

WhatisaReef'? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reef Types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reef Fossils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reef Biota: Compositional Changes during Time . . . . . . . . . . . . . . . . . . . . Reef Guilds: Ecologic Units . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . How to Classify Reef Carbonates? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies Approach to Reef Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Basic Constituents of Reef and Mound Carbonates . . . . . . . . . . . . . . . . . . . Describing Reef Carbonates: A Practical Guide . . . . . . . . . . . . . . . . . . . . . Case Studies of Some Ancient Reefs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mud Mounds: The Early Devonian 'Kess Kess' Mounds in the Anti.Atlas, Southern Morocco . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waulsortian Mud Mounds: Early Carboniferous (Lower Mississippian) Muleshoe Mound. Sacramento Mountains. New Mexico. U.S.A. . . . . . . . . Reefs: The Capitan Reef. Permian Reef Complex. Guadalupe Mountains. Texas and New Mexico. U.S.A. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fingerprinting Lost Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Casestudies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Platform Facies Patterns Derived from the Microfacies of Early Carboniferous Conglomerates (Southern Spain) . . . . . . . . . . . . . . . . Case Study: Reconstruction of Paleo-Escarpments from Microfacies Data Recognizing Ancient Cool-Water Carbonates . . . . . . . . . . . . . . . . . . . . . . . Microfacies Criteria of Non-Tropical Cold-Water Shelf and Reef Limestones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Case Study: Early Tertiary Cool-Water Coral Reef . . . . . . . . . . . . . . . . . . . Testing for Ancient Vent and Seep Carbonates . . . . . . . . . . . . . . . . . . . . . . Diagnostic Criteria of Ancient Seep and Vent Carbonates . . . . . . . . . . . . . . Casestudies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Late Eocene 'Whiskey Creek' Seep Carbonates of Washington State. U.S.A. Early Cretaceous Seep Carbonates in the Canadian Arctic . . . . . . . . . . . . . Mixed Carbonate-Siliciclastic Settings and Limestonehlarl Sequences . . . Carbonate-Siliciclastic Environments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Modern Carbonate-Siliciclastic Environments . . . . . . . . . . . . . . . . . . . . . . Ancient Mixed Carbonate-Siliciciastic Environments . . . . . . . . . . . . . . . . . Describing Carbonate-Siliciclastic Sediments: Practical Advice . . . . . . . . . Limestone-Marl Sequences: Primary orland Diagenetic Origin? . . . . . . . . Secular Variations in Carbonate Depositional Patterns and Temporal Changes in Microfacies Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Changes of Major Carbonate Depositional Environments During Time . . . Phanerozoic Carbonate Platforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phanerozoic Reef Patterns . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Pelagic Carbonates . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Differences in Phanerozoic Benthic Carbonate Factories . . . . . . . . . . . . . . Temporal Changes in Non-Skeletal and Skeletal Mineralogy . . . . . . . . . . . Temporal Changes in the Abundance and Significance of Microfacies Criteria

Practical Use of Microfacies Reservoir Rocks and Host Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate Hydrocarbon Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Distribution of Carbonate Reservoirs during Time . . . . . . . . . . . . . . . . . . . Depositional Setting and Environmental Controls of Carbonate Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

830 830 831 831 831 833 833 834 836 836 838 842 843 847 847 848 848 849 852 852 856 857 857 858 859 860 862 862 862 864 864 866 868 868 869 870 872 873 874 874

877 877 878 878

Contents

XIX

Depositional Setting . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Environmental Controls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic Controls on Carbonate Reservoirs . . . . . . . . . . . . . . . . . . . . . . . Reservoir Properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic Controls on Reservoir Properties . . . . . . . . . . . . . . . . . . . . . . . . Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Seismic Interpretation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . LogResponse . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cores and Cuttings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reservoir-Related Outcrop Analog Studies . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies. Lithofacies and Reservoir Rock Types . . . . . . . . . . . . . . . . . . Reservoir Heterogeneity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Relevant Microfacies Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Reservoir Rock Types and Facies Criteria . . . . . . . . . . . . . . . . . . . . . . . . . . Carbonate-Hosted Mineral Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ore Deposits and Carbonate Settings . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies and Ore Deposits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Carbonate Rock Resources. Facies. Weathering. Preservation . . . . . . . Industrial Use of Carbonate Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Exploration and Exploitation of Carbonate Rocks . . . . . . . . . . . . . . . . . . . . Facies and Physical-Chemical Properties of Carbonate Rocks . . . . . . . . . . Weathering. Decay and Preservation of Carbonate Rocks . . . . . . . . . . . . . . Weathering of Carbonate Rocks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Preservation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Microfacies and Archaeology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Questions and Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Buildingstones . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Building Stones: Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Building Stones: Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mosaic Material . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mosaic Material: Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mosaic Material: Examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . WorksofArt . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Works of Art: Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Works of Art: Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ceramics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ceramics: Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ceramics: Example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Marble Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Antony and Cleopatra: Tracing a Famous Love Affair . . . . . . . . . . . . . . . . Appendix Answers to Exercises . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Looking at the Attached CD . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Comparisoncharts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Using the List of References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Permissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index

1 New Perspectives in Microfacies

A rapid evolution in our understanding of carbonate rocks was triggered in the mid- to late 50's by the discovery of carbonate reservoirs in various parts of the world, followed by intensive research of recent carbonates. Modem and ancient carbonate environments, diagenetic processes and facies models were studied between about 1955 and 1965. During the late 60's and the 70's microfacies became an essential part of facies analysis and paleoenvironrnentalinterpretation of limestones. The increasing importance of limestones and dolomites as reservoir rocks and the use of thin-section fossils in subdividing carbonate platforms gave substantial impetus to the progress of microfacies research. The 1980's were characterized by an increased application of geochemical techniques with the object of developing predictive models for carbonate diagenesis and porosity. The subsequent period of time has seen the rapid development of sequence stratigraphy which now plays a major role in the characterization of the geometry and reservoir potential of carbonate rocks.

1.I The Microfacies Concept As originally defined by Brown (1943) and again independently by Cuvillier (1952) the term 'microfacies' referred only to petrographic and paleontological criteria studied in thin-sections. Today, however, microfacies is regarded as the total of all sedimentological and paleontological data which can be described and classified from thin sections, peels, polished slabs or rock samples. Field geology, including mapping and profiling, is a prerequisite for successful microfacies analysis. The importance of combined field work and thin-section studies was already emphasized in the earliest thin-section based investigations of carbonate rocks directed towards genetic interpretations of limestones (Peters 1863; Giimbel 1873; Sorby 1879; Hantken 1884). The practical application of thin-section criteria of limestones was demonstrated by Udden and Waite as early

as 1927 by the use of microscopic features of limestones for oil exploration in Texas. Hovelaque and Kilian (1900) published the first illustrated volume of thin-section photographs of carbonates. This approach was continued by the 'Intemational Sedimentary Petrographical Series' initiated by Cuvillier at the Third International World Petroleum Conference in Paris in 1951. The volumes published within this series as well as other comprehensive monographs containing numerous plates with thin-section photographs (see Sect. 10.4) contributed substantially to the rapid adoption of the microfacies approach. During the past decades microfacies has become an established part of the study of carbonate rocks. However, many authors use microfacies criteria in describing and classifying limestones but fail to explore the significance of these criteria for the interpretation of depositional and diagenetic histories of carbonate rocks. Part 2 and 3 of this book demonstrate the great potential of microfacies studies in basin analysis and applied carbonate geology.

1.2 New Perspectives New perspectives in the study and application of microfacies have resulted from the application of new techniques, from the availability of new comparative data on modem and ancient carbonates, from new data concerning the origin and distribution patterns of carbonate grains and the dominant biological control on carbonate sedimentation, from new concepts on defining facies models, and from new ideas concerning the course of carbonate sedimentation through geological time.

New techniques. Whilst microscopy is essential in the study of carbonate rocks there are many additional techniques which should also be utilized to maximize the information offered by microfacies analysis (Tucker 1988). Cathodoluminescence microscopy, fluid inclusion microscopy, scanning electron microscopy as well

A First Glance at a Thin Section

bonates and to recognize 'warm-mode' and 'cold-mode' paleolatitudes are improving rapidly.

Carbonate grains. Increasingly new more information is available concerning the biological and non-biological controls on the origin of carbonate grains, the site of deposition of carbonate grains, and on the distribution and dominance of grain types during the Phanerozoic. Characteristic grain type associations and the specific composition of grain types (e.g. ooids, oncoids, pisoids) provide hints on paleolatitudes and environmental controls for both marine and non-marine carbonate deposition (Sect. 4.2; Sect. 12.2).

Bioerosion. The biological destruction of carbonate substrates by borers, raspers and crushers is currently being intensively studied. Important objectives of these studies, which are also significant in microfacies analysis, are the application of boring morphology and boring patterns for paleobathymetric reconstructions and the estimation of the quantitative contribution of bioeroders for the marine carbonate budget (Sect. 9.3). Microbial carbonates:Carbonate deposits produced or localized by microbial communities are known from marine, marginal-marine, freshwater and terrestrial environments. The role of bacteria and cyanobacteria

Plate 1 A First Glance at a Thin Section The plate exhibits a thin section of a Mesozoic limestone from the Austrian Alps. Although the first appearance may be puzzling, a thorough investigation of the microfacies criteria reveals an amazing history for this rock. 1 The thin section shows fossils and dark-colored areas. The fossils correspond to organisms once living in a reef and contributing to the formation of a reef limestone. The dark-colored areas represent various types of fine-grained sediment. The reef limestone contains calcareous sponges, serpulid worms (SW), tube-like microproblematica (Microtubus, M), and bivalves. Sponges and encrusting Microtubus and serpulids formed an organic framework. The sediment within the framework (S 1) consists of tiny, densely packed microcrystalline particles (peloids) and some ostracods and foraminifera. Both elements can only be seen under greater magnification. The sponges are represented by non-chambered inozoans (IS), chambered sphinctozoans (SS) and chaetetid sponges (CS). Microtubus occurs encrusted on and within sponges, and is concentrated near the periphery of the framework, but the outermost part is a microbial crust (MC) formed by bacterially induced carbonate precipitation. The surface of the microbial crust outlines a distinct relief. The eye-catching large bivalve shell (BI) was heavily attacked by boring organisms including boring bivalves (BB) and microborers drilling tiny holes (MB). The bivalves are infilled with dark calcareous sediment (S2) different in composition from the sediment within the organic reef framework. The conspicuous circular section might represent a pelagic fossil (H, Heterastridium). The reddish fine-grained sediment (S3) yields densely packed skeletal grains including sponge spicules and pelagic shell debris as well as some radiolarians and pelagic ostracods. This sediment and the reef limestones are covered by a thin Fe/Mn crust (arrows) forming small microbial microstromatolites. The overlying sediment S4 contains (white) skeletal elements of crinoids, mostly parts of arms associated with pelagic shell debris. Radiolarians, small ammonites and pelagic algal cysts are too small to be visible on the plate. Interpretation: Microtubus indicates a Late Triassic (Norian to Rhaetian) age for the reef limestone. The composition of the reef-building assemblage characterizes reefs formed in protected low-energy settings. Environmental change is indicated by the peripheral microbial crust covering the reef fabric. The reef limestone and the microbial crust were transected by a fissure that remained open for some time as indicated by the calcite tapestry. Later on the fissure was infilled by the open-marine pelagic sediment S3. The Fe/Mn crust covering both the surface of the microbial crust and the fissure fill marks a discontinuity surface corresponding to a hardground and indicating a gap in the sedimentary record. The microfacies of sediment S4 reflects the renewed onset of pelagic sedimentation. The sediments S3 and S4 are Liassic in age. The time hidden in the pelagic sedimentary record, however, can not be determined from the thin-section data. Solution took place within the reef limestone as shown by solution voids (V) within the originally aragonitic sponges. In contrast primary calcitic fossils, e.g. Microtubus, are well preserved. These voids and the cement type of the calcite tapestry within the fissure point to freshwater diagenesis, an interpretation that also is supported by stable isotope data. The small-scale microfacies data of the thin section reflect the large-scale developments in sedimentation at the TriassicJurassic boundary in the Northern Calcareous Alps: Platform and reef development - platform destruction related to subaerial exposure and drowning - transition to open-marine pelagic sedimentation. The sample comes from the Tropfbruch quarry in Adnet near Salzburg, Austria, where Rhaetian reef limestones (Fig. 8.2) are overlain by Early Jurassic carbonates.

The story behind this thin section is rather difficult, but the following chapters will answer to all of your questions and give the information needed.

in the precipitation of fine-grained carbonate and in the formation of microbialites is becoming increasingly well understood. Laboratory experiments simulating bacterially-controlled carbonate precipitation, the recognition of bacterially constructed carbonate crystals and grains and the study of modem biofilms combine to indicate the importance of microbes in the formation of many items included within the list of microfacies criteria (e.g. micrite, peloids, ooids, oncoids, micrite envelopes, stromatactis, carbonate crusts; Sect. 9.1). Combined studies of microfacies and geobiochemical data are necessary in order to understand constructive microbial contr& (e.g. biogenic crusts and mud mounds), destructive processes (e.g. boring microbes) and carbonate cementation.

Carbonate sequences and cycles. The recognition and interpretation of cyclic patterns is a major objective of modern carbonate sedimentology. Because cyclicity is reflected by systematic changes in biota, grain composition, texture and early diagenetic criteria, microfacies studies are able to contribute to a better understanding of short-term depositional variations (Sect. 16.1.1). The three major prerequisites for sequence stratigraphy - a sound paleoenvironmental interpretation, an estimate of synchronicity, and the differentiation between regional and local effects - may be vigorously supported by microfacies studies which also improve the interpretation of sequence boundaries with regard to origin, timing and location (Sect. 16.1.2). New concepts in defining facies models. The value of 'models' in facies analysis depends largely on the significance attributed to a sedimentary model by the author. The majority of models suggested for the different modes of carbonate sedimentation are based on comparative studies between modem and ancient carbonates. These 'conceptual models' remain important tools because they facilitate the attribution of characteristic sedimentological or paleontological data to specific facies belts (Chap. 14). However, a too rigorous use of conceptual models for one's own facies studies may result in significant errors if the more descriptive, static character of the model is not critically considered. 'Dynamic models', concentrating on processes and controls and computer simulations dealing with the major controlling factors of carbonate buildups, provide a promising platform for the discussion of potential steps in the development of sedimentary bodies (e.g. carbonate platforms), organic structures (e.g. reefs) or individual sequences (e.g. cycles). The evaluation of computer-generated facies models should be strongly de-

pendent on microfacies and paleontological criteria because only these criteria deliver the paleoenvironmental information that can verify, refine or disprove theoretical concepts.

Secular changes during the Phanerozoic. There is considerable evidence for temporal and secular fluctuations in major facies types, the dominant types of carbonate cements, the mineralogy of skeletal grains and probably also in diagenesis and carbonate geochemistry. Some of these fluctuations can be explained by global changes in biological factors (e.g. role of carbonate plankton, nutrients), others by global changes in climate and oceanography. Microfacies criteria for carbonate rocks provide evidence for changes through time as shown by distinct differences in the composition of Phanerozoic bioclastic sands, types of calcareous ooids, composition and size of oncoids, open-space structures etc. (Sect. 16.7). The recognition of these changes has a major impact on depositional and diagenetic models for ancient carbonates. Applied microfacies. Carbonate rocks contain more than 50% of the world's oil and gas reserves, are important hosts to ore deposits and form very important raw materials. Depositional facies and diagenetic patterns determine the physical and chemical properties of these limestones and dolomites which control their reservoir potential (Chap. 17) and their technological attributes (Chap. 18). Microfacies studies assist in understanding the origin and history of these characteristics. Basics: New perspectives in microfacies Brown, J.S. (1943): Suggested use of the word microfacies. - Economic Geology, 38, p. 325 Carozzi, A.V. (1989): Carbonate rock depositional models. A microfacies approach. - 604 pp., Englewood Cliffs (Prentice Hall) Cuvillier, J. (1952): Le notion de 'microfacies' et ses applications. - VIII Congreso Nazionale di Metano e Petroleo, sect. I, 1-7 Cuvillier, J. (1962): ~ t u d eet utilisation rationelle de microfacies. - Revue de Micropal6ontologie, 4, 3-6 Fliigel, E. (1982): Microfacies analysis of limestones. 633 pp., Berlin (Springer) Spence, G.H., Tucker, M. (1999): Modelling carbonate microfacies in the context of high-frequencydynamic relative sea-level and environmental changes. - Journal of Sedimentary Research, 69, 947-961 Udden, J.A., Waite, V.V. (1927): Some microscopic characteristics of the Bend and Ellenburger limestones. - Texas University Bulletin, 27, 8 pp. Wilson, J.L. (1975): Carbonate facies in geologic history. 471 pp., Berlin (Springer) Further reading: KO02

2 Carbonate Depositional Environments

Knowing where modem carbonates occur, what they are composed of, and what their controls are is essential for evaluating microfacies data. The objectives of this chapter are to summarize the settings and environments in which carbonate sediments are formed and to document which classifications are used for differentiating these environments. Emphasis is placed on the definitions of terms. The potential of microfacies analysis in recognizing and interpreting the environments discussed in this chapter will be demonstrated later. If you want to know how to describe paleoenvironmental criteria, and which microfacies criteria can be used in deciphering the biological and depositional constraints on ancient limestones, have a look at Chap. 12 and 15.

Shallow-marine carbonate depositional systems differ fundamentally from siliciclastic depositional systems in their intrinsic controls, i.e. the growth potential including the 'aggregation potential' (the ability to grow vertically and to track sea level) and the 'production potential' (the ability to produce and export sediment). The aggradation potential is critical for the history of carbonate platforms and reefs, the production potential for the progradation and retreat of platforms. These differences are of central importance in the application of sequence stratigraphy to carbonates (Schlager 1992).

2.1.2 The 'Sorby Principle': Limestones are Predominantly Biogenic Sediments

Well over 90% or more of the carbonates found in modem marine environments are biological in origin, i.e. 2.1 Introduction the sediments are biotically induced (by an organic trigger, e.g. microbial micrites) or biotically controlled Microfacies analysis of carbonate rocks requires a (skeletal autotrophic and heterotrophic organisms deknowledge of modern carbonates and an understandtermine the composition, location and timing of caring of biological and geological changes during earth bonate production). Some of the 'abiotic' carbonate prehistory. R.N. Ginsburg's eloquent statement 'carbon- cipitation (represented by marine cements) is also trigate buildups are like Shakespeare; the plays go on - gered by organics or the activity of organisms. The only the actors change' emphasizes the remarkable simi- dominant role of organisms in the formation of limelarities and analogues in the criteria of modem and an- stones was recognized as early as 1879 by Henry Clifton cient carbonates. The aphorism, however, ignores the Sorby. Studying Paleozoic, Mesozoic and Tertiary carguiding role of the stage-managers who often decide bonate rocks in thin sections, he recognized the overthe basic mode of the play, similar to the changing geo- whelming abundance of fossils and their importance in logical and biological earth system parameters which the composition of carbonate sands and muds. The disshape the appearance of carbonate buildups. tribution and frequency of carbonate-producing organisms depend strongly on environmental factors, such as light, water temperature and sedimentary influx. 2.1.1 Carbonates are Born not Made These controls as well as the paleoenvironmental settings are reflected by microfacies criteria and paleonThis simple phrase by Noel James (1979) highlights tological data. the main theme of carbonate sedimentation and the differences between carbonate and siliciclastic sediments. Carbonates are 'born'. They originate as skeletal grains 2.1.3 Modern Carbonates: Obligatory or precipitates within the depositional environment. By Reading contrast, terrigenous clastic sediments are formed primarily by the disintegration of parent rocks and are There is a wealth of well-written reviews and concise transported to the depositional environment. updated syntheses of modem carbonate sediments (see

Marine Environments

8

CONTINENTAL, NON-MARINE

TRANSITIONAL MARGINAL-MARINE

MARINE Deep marine

Terrestrial, subaerially exposed Paleosols, caliche Caves and karst Coastal Eolian dunes lagoons, Glacial deposits Tidal flats Aquatic Freshwater tufa, travertine Freshwater and salt lakes Rivers

and reefs Ridge //// Basin ////////

Fig. 2.1. Settings of carbonate depositional environments.

list at the end of this section). The strength of these papers is that they outline the main criteria of recent marine and non-marine carbonates and their major controls in the context of interpreting ancient carbonate rocks. The information included in these fundamental texts is crucial for microfacies analyses. The 'Microfacies of Carbonate Rocks' does not intend to duplicate this information, but focuses on those data which are specifically relevant for microfacies studies.

2.2 Carbonate Sediments Originate on Land and in the Sea Carbonate sediments originate on land and in the sea. They are formed in three major settings: On the continents, within the transitional area between land and sea, and in the shallow and deep sea. Today only around 10 L;:, of marine carbonate production takes place in shallow seas. 90% of the modem carbonate production is related to the deposition of calcitic plankton in the deep sea. These proportions were very different during most parts of the Phanerozoic. Major depositional environments are shown in Fig. 2.1. Terrestrial and aquatic non-marine carbonates are receiving increasingly more attention from geologists because of their economic importance and their significance in paleoenvironmental analyses. These carbonates are discussed in Sect. 15.1 to 15.4. Owing to their very shallow-water setting, marginal-marine carbonates have been studied in great detail and offer a wealth of information on coastal sedimentation processes and diagenesis. About 70% of microfacies studies dealing with marine carbonates concerns shallow-marine carbonates formed on the shelf and near the shelf break. Future research should be focused on the huge deep-marine carbonate depositional regions on the continental slopes.

2.3 Classification of Marine Environments Marine environments are classified into the benthic, for the sea bottom, and the pelagic, pertaining to the water mass. There is no universally accepted scheme of subdivision of marine environments which is equally acknowledged by biologists, oceanographers and geologists. Fig. 2.2 summarizes categories that are frequently used. The categories are predominantly based on schemes proposed by Hedgpeth (1957) and Edwards (1979), who discuss marine terminology.

2.3.1 Boundary Levels Several levels at the sea bottom and within the water column are commonly used in a vertical subdivision of marginal-marine and marine environments (Box 2.1). Microfacies analysis provides the basic data for recognizing these levels in ancient carbonate rocks (see Chap. 12). Essential critical interfaces that control sedimentary patterns and the distribution of organisms are: (1) The lower and the upper boundaries of the tides (control the distribution of organisms), (2) the base of the photic zone (controls the distribution of light-dependent phototrophic organisms), (3) the base of the zone of wave abrasion (above which bottom currents and wave action may lead to erosion and cementation), (4) the base of the action of storms on the sea bottom, (5) the 0, minimum zone (strongly limiting life on and in the sea bottom), (6) the thermocline (the layer of water that is too cold for most carbonate-producing organisms), and (7) the pycnocline (the layer of water where salinity is too high for most organisms). High and low tide, wave base and storm wave base are used as basic boundaries in the classificationof the major shallow-marine environments.

Marine Zonations

Fig. 2.2. Marine depositional environments. Modified from Kennett (1982).

P E L A G W T E R A L ZONES

PELAGIC DEPTH ZONES

I

'Abyssopelagic \

Hadalpelagic

2.3.2 Vertical and Horizontal Zonations Subdivisions of marine environments are both vertical and horizontal:

2.3.2.1 Vertical Zonations Benthic depth zones: The depth of the sea bottom and critical levels controlling the sedimentation subdivide the benthic environments into six zones: (1) coastal sublittoral zone (above high tide, corresponding to the supratidal zone), (2) littoral (between high and low tide, identical with the intertidal zone), (3) sublittoral (below low tide, corresponding to the major part of the

continental shelf), (4) bathyal (approximately equal to the continental slope), ( 5 ) abyssal (corresponding to the abyssal plains), and (6) the hadal zone (deep-sea trenches). Modem carbonate sedimentation takes place within the range of zone 1 to parts of zone 5.

-> Geologists are in favor of the terms supratidal, intertidal and subtidal instead of the ecologically defined terms supralittoral, littoral and sublittoral. Pelagic depth zones: Five zones are defined by the vertical distribution of floating and swimming life. These are, in descending order, the epipelagic zone (the upper region of the oceans, extending to a depth of about 200 m), the mesopelagic, bathypelagic, abyssopelagic

Box 2.1. Glossary of terms used in the subdivision of marine environments. Fair-weather wave base (FWWB): Intersection of the wave base with submarine topography. The water depth below which surface wave action no longer stirs and moves the sediment. The depth of the wave base varies widely, depending on wave amplitude and fetch, bottom topography, activity of storms, orientation of shelves and ramps, latitudes etc. High tide: High water. The maximum height reached by each rising tide. Low tide: Low water. The minimum height reached by each falling tide. Mean sea level: The average height of the surface of the sea for all stages of the tide for a defined period. Storm wave base: See storm wave weather base. Storm wave weather base (SWWB): The water depth down to which storm-generated waves and resulting bottom currents rework bottom sediments and produce specific texture types (tempestites). The depth of the storm wave base varies strongly and depends on shelf and shelf edge topography, storm intensity and climate zone. Surf: a) The wave activity in the area between the shoreline and the outermost limit of breakers. b) A collective term for breakers. Tidal range: The difference in height between consecutive high and low waters. Tide: The periodic rise and fall of the sea resulting from the gravitational attraction of the moon and the sun acting upon the rotating earth and causing flood and ebb currents. Wave base: See fair-weather wave base.

10

(corresponding to oceanic environments below about 4 000 m), and hadopelagic zone. -> Note that the boundaries of the benthic and pelagic depth zones are not fixed accurately.These boundaries reflect the situation in modem oceans that are not necessarily equivalent to depth zones visualized for ancient oceans.

2.3.2.2 Horizontal Zonations The lateral distribution of pelagic organisms with respect to their distance from the coast characterizes two major zones of the ocean: The neritic zone is the water that overlies the continental shelf, today generally with water depth less than 200 m and covering about 8% of the ocean floor. The term oceanic zone refers to the water column beyond the shelf break, overlying the slope and the deep-sea bottoms, generally with water depths greater than 200 m and down to more than 10 000 m.

Depositional Environments Rao, C.P. (1996): Modem carbonates. Tropical, temperate, polar. - 206 pp., Howrah (Carbonates) Reading, H.E. (1996): Sedimentary environments, processes, stratigraphy.Thiid edition. - 688 pp., Oxford (Blackwell) Scholle, P.A., Bebout, D.G., Moore, C.H. (eds., 1983): Carbonate depositional environments. - Amer. Ass. Petrol. Geol. Mem., 33,708 pp. Scoffi, T.P. (1987): An introduction to carbonate sediments and rocks. - 274 pp., Glasgow (Blackie) Tucker, M.E., Wright, V.P. (1990): Carbonate sedimentology. - 482 pp., Oxford (Blackwell) Varney, M. (1996): The marine carbonate system. - In: Summerhayes, C.P., Thorpe, S.A. (eds.): Oceanography. An illustrated guide. - 182-194, New York (Wiley) Walker, R.G., James N.P. (eds., 1992): Facies models. Response to sea level change. - 409 pp., Ottawa (Geol. Ass. Canada) Wilson, J.L. (1975): Carbonate facies in geologic history. 471 pp., Berlin (Springer)

2.4 Review of Modern Carbonate Depositional Environments

-> Again, keep in mind that these water depths are not compatible with the situation in many ancient oceans. Note that the term 'neritic' is often used to describe sea bottom environments below the neritic water colun~n,or shallow-marine environments characterized by significant terrigenous influx.

The following review is focused on the definitions, main criteria and subdivisions of carbonate settings. The criteria that help recognize these settings and the evaluation of paleoenvironments in ancient carbonate rocks are discussed in Chap. 12 and 15.

Basics: Classification of carbonate environments and obligatory reading

2.4.1 Non-Marine Carbonate Environments

Classificatloiz Edwards, A.R. (1979): Classificationof marine paleoenvironments. - Geol. Soc. New Zealand Newsletter, 48, p. 48 Hedgpeth, J. (1957): Classification of marine environments. - In: Hedgpeth, J.E. (ed.): The treatise on marine ecology and paleoecology. Vol.1, Ecology. - Geol. Soc. America Mem., 67, 17-28 Kennett, J. (1982): Marine geology. - 813 pp., Englewood Cliffs (Prentice Hall) Nybakken, J.W. (1993): Marine biology. An ecological approach. Third edition. - 462 pp., New York (Harper Collins) Summerhayes. C.P., Thorpe, S.A. (eds., 1996): Oceanography. An illustrated guide. - 352 pp., New York (Wiley) Obligatory reading Bathurst, R.G.C. (1994): Carbonate sediments and their diagenesis. 2nd enlarged edition - Developments in Sedimentology, 12,660 pp., Amsterdam (Elsevier) Bosellini, A. (1991): Introduzione a110 studio delle rocce carbonatiche. - 317 pp., Ferrara (Italo Bovolenta) James, N.P., Kendall, A.C. (1992): Introduction to carbonate and evaporite facies models. - In: Walker, R.G., James N.P. (eds.): Facies models. Response to sea level change. - 265-275, Ottawa (Geol. Ass. Canada) Milliman J.D. (1974): Marine carbonates. - 375 pp., Berlin (Springer)

Non-marine carbonates originate in terrestrial and aquatic environments without marine influence. These carbonates, formed by abiotic and/or biotic processes differ in many aspects from marine carbonates, which are much better known to geologists. These carbonates are formed in terrestrial subaerially exposed settings and in submerged aquatic settings (Fig. 2.3). The major non-marine carbonate environments are listed in Box 2.2. Non-marine carbonatesformed in terrestrial subnerially exposed settings comprise pedogenic carbonates, palustrine carbonates, cave carbonates, eolian carbonates and glacial carbonates.

2.4.1 .I Pedogenic Carbonates, Paleosols, and CalichelCalcretes Terminology: The term pedogenic refers to soil genesis. Most pedogenic carbonates are formed withn soils rich in calcium carbonate. The termpaleosol describes 'a buried soil horizon of the geologic past' but is often

Non-Marine Environments

11

Non-marine continental environments Karst

Freshwater

Calcareous tufa

; Marginal marine I I I

environments

Peritidal zones

Fig. 2.3. Non-marine carbonate depositional environments.

used in a broader sense, embracing various descriptive terms associated with horizons of subaerial exposure (e.g. caliche). Important processes are chemical and physical weathering of host carbonate rock, soil development and accumulation of calcium carbonate within the soil by evaporation of saturated porewaters driven to the surface by capillary forces. These processes may result in a physicochemically and microbially controlled formation of hard crusts on the surface or in the upper horizon of soils (duricrusts). Depending on climatic conditions and the host substrate, the duricrusts consist of carbonate (forming calcretes or dolocretes) or other mineral phases (e.g. silica forming silcretes, gypsum -> gypscretes, hematite and goethite -> ferricretes). The following discussion is limited to near-surface accumulations of calcium carbonate (Low-Mg calcite) in terrestrial, alternating wet settings, generally called calcrete or caliche. These distinctive carbonates result

from multiple processes induced by life, climate and exchange between mineral phases: 'Calcrete' was proposed for calcareous-cemented deposits in Africa, the roots of the word caliche are Latin, meaning lime and limestones (Reeves 1976). Calcrete and caliche are used synonymously or separately (calcrete in order to describe highly indurated parts of caliche profiles). Other names are calcareous duricrust, cornstone, kalkar (Agarwal et al. 1992) or 'Krustenkalk'. These calcium-rich .soil accumulations cover an estimated 20 million km2 or about 13% of the total land surface (Yaalon 1988). They are widespread in temperate (e.g. Mediterranean),semiarid and arid climates, particularly in tropical and subtropical latitudes (e.g. Caribbean) with sparse rainfall and a mean annual temperature of about 18 "C. 'Calcicretes (syn. calcretes)' and 'dolocretes' can be differentiated.

Box 2.2. Carbonates originating in non-marine environments. Non-marine carbonates formed in terrestrial subaerially exposed settings Pedogenic carbonates, paleosols, calicheicalcrete: Formed by the accumulation of calcium carbonate within unconsolidated carbonate-rich soils. Palustrine carbonates: Carbonates formed in lacustrine and transitional non-marinelmarine environments originating by short-term oscillations of the water levels and characterized by a mixture of subaerial and freshwater facies criteria. Cave carbonates, karst: Formed by the precipitation of calcium carbonate within caves resulting in 'speleothems' (e.g. flowstones, dripstones). Eolian carbonates: Sedimentation of fine-grained, wind-born sand-sized carbonate material (-> eolianites). Glacial carbonates: Dissolution and recrystallization of glacially transported carbonate debris, occurs in glacial-marine deposits. Non-marine carbonates formed in terrestrial aquatic settings Freshwater carbonates: Travertine, calcareous tufa, calcareous sinter: Formation of carbonate deposits at warm, hot ore cold spring orifices in subaquatious settings (e.g. pools), by combined biotic and abiotic processes. Lacustrine carbonates: Deposition and precipitation of calcium carbonate in lakes of different salinity (freshwater lakes, salt lakes, playa lakes) and different settings. Fluvial carbonates: Carbonate deposits formed in rivers, creeks and waterfalls, originating from the combined activity of biotic and abiotic processes.

12

Important studies of pedogenic carbonates deal with late Pleistocene and Holocene calcretes on the Bahamas, Florida Keys, Yucatan, Barbados, Persian Gulf, Western Australia, and the Mediterranean (see Basics and references with Code K030). Calcareous paleosols typically contain a higher proportion of mineral insoluble residue than the enclosing limestone units. Two models have been developed for explaining the mechanisms that lead to the concentration of insoluble residue: (1) Selective dissolution and removal of calcium carbonate from carbonate host rock, and (2) accretion of wind-driven dust at the limestone exposure surface without major dissolution of the limestones (Multer and Hoffmeister 1968). Most authors favor the first explanation. Calcretes are defined as 'secondary accumulations of calcium carbonate (Low- and High-Mg calcite) in nearsurface settings, which result from the cementation and/or replacement of host material by the precipitation of calcium carbonate from soil water or ground water' (Wright 1990). In addition to the calcium carbonate derived from the host rock, eolian input is still an important factor (Goudie 1973). Currently, two basically different models are being discussed with respect to the formation of calcretes. The commonly held model, that calcretes are pedogene structures resulting from leaching of carbonate from the surface horizon, is questioned by the second model, claiming that calcretes are complex sedimentary formations that have undergone phases of deposition, pedogenesis, and transformation of sediments during early diagenesis heavily related to microbially influenced processes. According to the first model, calcrete is formed in the interior of a soil; according to the second model calcretes are accumulations that build up by aggradation from bottom to top (Verrecchia 1996). Classificafion: Calcretes are classified according (a) to their micromorphology and hydrological setting or (b) dolomite content (Netterberg 1978). Using micromorphological criteria, massive 'alpha calcretes' (exhibiting a dense pseudonodular microfabric with complex microcracks, microsparite and coarse-crystalline calcite, floating sediment grains (Pl. 128/6),and calcretes exhibiting microfabrics of biogenic (particularly fungal) origin, called 'beta calcretes', can be distinguished (Wright 1990).The latter group is characterized by microbial coatings, calcified tubules, Microcodium, alveolar septa1 fabrics, and needle fibre calcite (Pl. 128). Two calcrete types are differentiated according to their hydrologic setting: (1) Pedogenic calcretes derived from vertically percolating soil water and typically occumng in the form

Caliche

of well-horizonted soil profiles. Characteristic features are distinct profiles made up of a succession of different horizons and specific microfacies attesting to the presence of a vegetated soil cover. 'Rhizogenic calcretes' produced by calcification associated with plant roots occur in the fluvial sequences of floodplains (Wright et al. 1995), palustrine and lake margin areas with relatively high water-tables, on subaerially exposed marine carbonates (Wright 1994), in carbonate dunes (Hay and Reeder 1978) or in beachrock deposits. (2) Non-pedogenic calcretes, derived from laterally migrating groundwater and composed of well-indurated, variably extensive sheets of mottled carbonate (Goudie 1983). In contrast to the rather thin pedogenic calcretes (a few meters), these calcretes may have a thickness of more than 10 meters as shown by Australian examples. Compared with pedogenic calcretes, non-pedogenic calcretes are characterized by the absence of rhizoconcretions, black pebbles and peloids, and by more silica than carbonate.

Criticalfactors in theformation of caliche are (1) climate (a significant net annual moisture deficit in the soil; control on dust accretion caused by dust storms), (2) topography, (3) vegetation, (4) presence of carbonate and oxalic phases, (5) carbonate content, texture, porosity and permeability of the hosting substrate (ThCriault and Desrochers 1993), (6) action of microorganisms (Loisy et al. 1999) as well as (7) exposure time (which may range between a few tens of thousands, as shown by Holocene calcretes, and millions of years as suggested by Carboniferous calcretes). Vegetation is the main factor in rhizogenic calcretes (Klappa 1979; Wright et al. 1995) exhibiting textures which can be interpreted as calcification in, on or around roots: Intracellular calcification creates Microcodiumtype microstructures. Extracellular calcification around roots produces laminur rhizolites (Wright et al. 1988) consisting of vertical rhizoconcretions or as calcareous cementation around root mats (Pl. 2016). Incomplete calcification of root mats may be responsible for the formation of rhizogenic calcretes characterized by peloidal and coated grain fabrics (Calvet and Julia 1983). Exposure time, substrate composition and vegetation control the maturiq levels of calcrete profiles. Relatively mature levels can be recognized from the sequence of horizons forming the calcrete profiles and by the number of calcrete microfabrics (which increase with increasing maturity). A number of models for pedogenic calcrete profiles has been developed, focused on the progressive increase in the volume of secondary calcium carbonate within

Cave Carbonates

the host material (soil, sediment or rock) via a combination of cementation, replacement and displacement (Gile et al. 1966; Arakel 1982; Machette 1985; West et al. 1988; Rabenhorst et al. 1990). Diagnostic criteria of caliche andpaleocaliche: see Chap. 13 and P1. 1416, P1. 128, and P1 14119-10.

2.4.1.2 Palustrine Carbonates Palustrine limestones are deposits of shallow freshwater environments exhibiting extensive evidence of pedogenic modification (Pl. 48). These carbonates are common in many ancient continental and marginalmarine sequences. The term (derived from 'paludal', meaning marshy or swampy) was first proposed while describing late Cretaceous-Early Tertiary limestones in southern France (Freytet 1973,1984; Freytet and Plaziat 1982). Palustrine carbonates were originally considered as near-shore deposits of extremely shallow lakes with oscillating lake levels and densely vegetated shorelines. Because of a very low relief on the lake bottom, fluctuation in the water table should result in an interbedding of lacustrine facies (characterized by the occurrence of specific fossils), and pedogenic facies (characterized by textures which indicate a pedogenic overprint of dried-out parts of shores). This interpretation presents problems since many palustrine limestones are not associated with lake deposits. A suitable modern analogue for a palustrine environment may be the freshwater carbonate marshes of the interior Everglades in Florida (seasonal wetland model: Platt and Wright 1992). Seasonal variations in water depth and minor topographic variations across the area could explain the association of soil and calCrete criteria with dissolution features (pseudomicrokarst), and the presence of sublittoral carbonates which were formed in perennial shallow lakes within the wetland.

2.4.1.3 Cave Carbonates, Speleothems and Karst

Speleothems (carbonates formed in caves) are important paleoclimatic recorders documenting short- and long-term climatic fluctuations. Terminology: The term karst refers to physical structures formed by dissolution from meteoric waters. It includes 'all of the diagenetic features - macroscopic and microscopic, surface and subterranean - that are produced during the chemical dissolution and associated modification of a carbonate sequence' (Choquette

13

and James 1988). Karst develops (a) at the air-limestone or soil-limestone interface ('surface karst') and (b) within carbonate bodies ('subsurface karst'). Diagnostic features: Surface karst or exokarst is characterized by surface solution or corrosion features comprising small-scale and large-scale criteria (microkarst, residual paleosols, karren, solution pans or kamenitzas, and dolines or sinkholes). Large-scale geomorphological features (e.g. karst valley and karst towers) are responsible for characteristic landforms. Subsugace karst (see P1. 129) is represented by caves and vugs formed above, at and below the water table. Caves contain (a) secondary mineral deposits (porous calcareous tufa: moonmilk, and hard crystalline sinter or speleothems) precipitated by vadose and shallow phreatic waters and (b) internal cave sediments and karst breccia caused by the collapse of caves. Karst breccias exhibit a wide variety of internal composition depending on the site and the mode of origin (Sect. 5.3.3.3 and Sect. 15.2). Speleothems are precipitated from thin water films flowing over the rock and forming flowstones and dripstones, or in pools of water, forming 'cave pearls' (globoids, pisoids; vadoids: Chafetz and Butler 1980; Peryt 1983. See P1. 1418). Dripstones include stalagmites and stalactites as well as finely curved twiglike structures (helictites). Carbonate sinters are made up of calcite with various amounts of Mg, and/or aragonite,dolomite and rarer minerals (Gonzalez and Lohmann 1988; Tietz 1988). The mineralogical composition is often seasonally controlled; it depends on the MgICa ratio of the percolating pore-fluids, pC02, and evaporative conditions within the cave. Speleothems exhibit diagnostic cave cements (Folk and Assereto 1976; Kendall and Broughton 1978; Assereto and Folk 1980) which can be used in order to recognize ancient cave carbonates (Sect. 15.2.1).Common cement types in speleothems are length-slow and length-fast calcites and dendritic calcite crystals. Changes in mineralogical composition and cement types of vadose-zone speleothems may reflect short and long-ranging cyclic oscillations of climatic factors (Railsback et al. 1994; Shopov et al. 1994). There is increasing evidence for microbial contributions to the growth and fabric of speleothems (Danielli and Edington 1983; Jones and MacDonald 1989). Controls: Prerequisites for the formation of extant karst and cave systems are fluids that are undersaturated with respect to the country rock, and fluid flow transporting dissolution products (Lohmann 1988; Dreybrodt 1990). The most important intrinsic factors influencing karst development are the general lithol-

Travertine

14

ogy (including mineralogy, bulk purity, fabric and texture), stratal permeability, bedding planes, fractures as well as the existence of confined or unconfined aquifers and structural conduits. Limestones are several orders of magnitude more soluble than dolomites in meteoric waters. Major extrinsic factors are climate (rainfall and evaporation, temperature), base level (elevation and relief, sea level or local water bodies), vegetation and the duration of time involved in karstification. Different climatic conditions produce different karst types (James and Choquette 1988). Karst formed in areas of warm temperatures and high rainfall is characterized by the development of soils and terra rossa, abundant sinkholes, and dissolution-collapse breccia. In semiarid and temperate climates both karst and calcrete may occur together, depending on alternating wet and dry conditions (Esteban and Klappa 1983). The potential of microfacies studies for the recognition of ancient speleothems and karst and the significance of paleokarst in basin analyses is discussed in Sect. 15.2.

2.4.1.4 Eolian Carbonates

Terminology: The term eolianite has been coined for bioclastic wind-borne deposits that make up more than 9070 of the Pleistocene deposits of Bermuda (Sayles 1931). The term is now used for eolian sands that have been cemented by calcium carbonate in a subaerial environment. The coalescence of dunes results in linear ridges with large cross-bed sets which may stand a few tens of meters above the source beach. Glacial, interglacial and Holocene eolian carbonate dune deposits are known from Bermuda, the Bahamas, northeast Yucatan, California, the Trucial Coast, the Meditenranean (Mallorca, Tunisia, Israel) and western Australia. Generally modem eolianites are associated with coastal marine deposits and pedogenic carbonates. Wind can transport carbonate particles (ooids, microfossils) over wide distances (e.g. from Africa to the Caribbean). Recognizing carbonate eolianites: Summaries of features common among carbonate eolianites were given by McKee and Ward (1983) and Abegg et al. (2001). Important criteria are: (1) Grain texture - good overall sorting, fine- to medium-grained, fenestrae, sorting differences between laminae or beds. (2) Carbonate cements - vadose and phreatic Low-Mg calcite cements (PI. 212 and PI. 3 1/5,6) meniscus, pendant, needle-fiber, blocky, drusy). (3) Biota - plant structures (rhizoconcretions, calcified root systems of dune plants),

Microcodium, ichnofossils: crustacean and insect burrows, bioturbation; terrestrial gastropods. (4) Stratification - high- to low-angle beds, see Fig. 15.1. (5) Associated facies - upward-shallowing succession, shelf/ reef - beach grainstone - eolian grainstone. Grains are ooids or bioclasts, sometimes accumulations of particular foraminifera1 tests (forming the 'miliolite' of the Trucial Coast, a grainstone composed predominantly of miliolid foraminifera). Significance: The differentiation of wind-borne calcarenites from grainstones formed in marine environments is important because calcareous eolianites indicate carbonate shorelines, sea-level fluctuations (aragonite cements in eolianites indicate a later marine transgression; White 1995, San Salvador Island, Bahamas), paleoclimatic conditions and paleowind directions. 2.4.1.5 Glacial Carbonates The dissolution and recrystallization of glacially transported carbonate debris may result in the formation of micritic and sparitic carbonates, leading to a chemically distinctive carbonate matrix in meltout tills or subglacial crusts within glacial-marine deposits (Hallet 1976; Aharon 1988; Fairchild and Spiro 1990; Fairchild et al. 1993), which are also recorded in Precambrian and Phanerozoic glacial deposits. Enigmatic calcite pseudomorphs, known as glendonites and interpreted as pseudomorphs after ikaite, a metastable hexahydrate of calcium carbonate, were reported from some modem as well as ancient glaciomarine environments. Ikaite occurs in morgenstem-like and stellate aggregates, several centimeters in size, and indicates sub-zero temperatures at the seafloor. Glendonites are typically found in cold-water deposits dating from the Precambrian to the Pleistocene (Suess et al. 1982; Shearman and Smith 1985; Kemper 1987).

Non-marine carbonates formed in aquatic settings comprise freshwater carbonates, lacustrine carbonates and fluvial carbonates.

2.4.1.6 Travertine, Calcareous Tufa and Calcareous Sinter Origin: Travertine and tufa are freshwater carbonates formed as a result of physical and/or biochemical CO, degassing around carbonate- and C02-rich springs, along streams and in pools, and often precipitated together with and on cyanobacteria, bacteria, algae (Pl.

Travertine

2/6), mosses, and higher plants (Pl. 2/7) as well as on various organic and inorganic substrate. Cyanobacteria, bacteria and algae are able to trigger the precipitation of calcite and aragonite forming microbial travertines (Chafetz and Folk 1984; Folk et al. 1985). Millimeter- to centimeter-sized laminae (Pl. 2/1,2), and arborescent shrub-like calcite precipitates (Pl. 2/1), consisting of associations of micrite aggregates and rhombic spar crystals aggregates appear to be microbially controlled (Guo and Riding 1994). Stromatolitic travertine~exhibit alternating sparry and micritic laminae which are interpreted in terms of seasonality (Chafetz et al. 1991), climatic changes as well as changes in microbial and algal growth and sedimentation (Monty 1976). Travertines and tufa are often associated with higher plants (Pentecost 1990), but the ability of macrophytes to induce the precipitation of carbonate during photosynthesis is regarded as controversial. Consumption of CO, leads to carbonate precipitation in the immediate vicinity of photosynthesizing vegetation. Both field and laboratory studies show that the intensity of photosynthesis varies from least effective in springs and waterfalls to highly effective in lakes and rivers (Merz 1992).

inorganic precipitation

A organic precipitation

Fig. 2.4. Practical classificationof travertines, tufa and sinter (after Koban and Schweigert 1993).

2,3,5), tufa (Pl. 2/6,7) or sinter (PI. 214) (Schweigert 1996). Travertine often is used in a rather loose manner to designate hard and compact carbonate deposits; tufa for porous deposits. Many authors use travertine in a rather broad sense, covering all kinds of non-marine carbonates of springs, creeks, streams, pools and lakes, as well as caves (e.g. Julia 1983; Pentecost and Whitton 2000). More precise definitions were offered by Riding (1991): The term travertine is restricted to non-marine, Morphological differentiation: Travertine deposits ex- layered autochthonous carbonates deposited at thermal hibit distinctive morphologies (Chafetz and Folk 1984): springs and commonly exhibiting a bushy fabric (Pl. 21 1). Tufa refers to often conspicuously porous carbonWaterfall deposits, formed at sites of break-in slope ates, whose formation in non-marine cold-waters is of streams by the growth of plants and contempo- strongly controlled by aquatic plants. Calcareous sinraneous calcification, resulting in a massive, irregu- ters are characterized by well-developed lamination and lar contorted tangle of cement crusts and plant lack of visible porosity. Currently there is a tendency molds. to restrict the term travertine to thermal deposits (Ford Lake-fill accumulations, characterized by thick, and Pedley 1996; Fouke et al. 2000) formed at hot and horizontally stratified and laterally extensive trav- warm, often mineralized springs, and calcareous tufa ertine~.These are composed of thin summer layers to settings where calcium-rich waters bubble up from of (bacterial) shrubs intercalated with finely lami- springs to the earth, cool down and precipitate calcium nated winter mud layers and thicker, crudely lami- carbonate, supported by photosynthesizing plants. nated muds. Contorted zones composed of calcite rays, intraclasts and pisoids, represent spring oriHow to classify freshwater carbonates? Koban and fices on the lake bottom. Schweigert (1993) proposed a classification which reSloping mounds, fans and cones, characterized by flects the genetic factors responsible for the fabric of structures paralleling a slope at the time of deposi- non-marine freshwater carbonates (Fig. 2.4): The trition. angle underlines the inferred origin, setting and visible Terraced mounds, exhibiting a step-like morphol- porosity (see P1.2 for examples). ogy. Warm spring waters, flowing down both sides of Thermal travertines: Comparative studies of modfissure ridges. em thermal spring systems (Cady and Farmer 1996; Fouke et al. 2000) provide a basis for constructing faWhich names are appropriate? The terminology of cies frameworks which can assist in the interpretation freshwater-carbonates is controversial because of the of ancient travertines. The spectacular carbonate-premixed use of descriptive and genetic terms. This is par- cipitating thermal springs of the Mammoth Hot Springs ticularly true for carbonates called travertine (Pl. 211, in Yellowstone National Park, Wyoming, demonstrate

16

Travertine,Tufa, Sinter

Plate 2 Terrestrial Freshwater Carbonates: Travertine, Calcareous Tufa and Sinter Travertines, tufa and calcareous sinter are excellent paleoclimatic archives (Andrews et al. 2000). These carbonates and their corresponding water bodies can serve as analogues of Precambrian and Phanerozoic microbialites and their oceans (Arp et al. 2001). Travertines of hot springs are of interest for recognizing potential microbial signatures on Mars (Kempe and Kazmierczak 1997). Travertines are very important building stones that have been used since antique times (Winkler 1994). Many travertines and tufa originated during interglacial phases of the Pleistocene, but in places are still growing today. Terrestrial carbonates produced by precipitation in freshwater occur as travertines (->1-3,5), calcareous tufa (-> 6,7), and calcareous sinter (-> 4). Travertine is a layered deposit of calcium carbonate with moderate to high primary porosity, and often with a dendritic fabric. Calcareous tufa is an originally porous, laminated or massive deposit which commonly originates at cold subaerial springs, but also forms at subaquatic springs in soda lakes and highly alkaline salt lakes ('tufa pinnacles': Kempe et al. 1991; Benson 1994; Arp et al. 1998). Calcareous sinter is characterized by well-developed lamination and the lack of visible porosity. These carbonates orignate from degassing of CO, and HC03-caused by changes in temperature, pressure and photosynthesis. Travertine is often found on warm or mineralized hydrothermal waters, tufa on temperate waters. Tufa precipitation takes place on organic substrates (higher plants, algae, mosses) in freshwater. In both types carbonate chemistry and the temperature of the spring waters, the overall morphology of the accumulation and biologically induced processes are major controls. Characteristic textural criteria of freshwater limestones are (1) macroscopically visible voids (often corresponding to moulds and leaves of higher plants); (2) void-filling radiating calcite (-> 3); (3) small spar-filled cellular structures; (4) wavy and laminar layers (-> 1, 2); (3) concentric structures consisting of smooth and wavy laminae of micrite and sparite (-> 1); (5) alternating dark and light laminae with vertical thin 'filaments' (> 4); (6) layers with bubble structures (-> 1); (7) shrub-like structures (-> 1); (8) ovoid to subangular peloids with diameters from 50 to 300 pm, occurring in clumps or aggregates (-> 5); (9) travertine fragments occurring as intraclasts, and detrital grains derived from underlying or adjacent rocks; (10) pisoids (see P1. 1411). 1 Travertine. The name travertine is derived from the Latin lapis tiburtinus,meaning 'the stone of Tiburnium' (now Tivoli), a locality near Rome where these carbonate rocks have been quarried for more than two thousand years. At the 'type locality', the precipitation of carbonate occurs from spring waters. The importance of inorganic or organic (bacteriallyinduced) modes of precipitation is primarily controlled by water temperature and water chemistry (Chafetz and Folk 1984). In the Bagni di Tivoli locality, travertine occurs as stratified lake-fill deposits formed in shallow ponds.The travertine is composed of laterally continuous and vertical repetitions of layers with micritic shrubs (S; interpreted as result of bacterially induced precipitation) intercalated with laminated muds (-> 3). The shrubs nucleate on a substrate and grow and branch upward, indicating a phototrophic control. The bubbles (B) at the bottom may represent lithified gas-filled vesicles surrounded by bacterially precipitated walls or relics of chironomid insect larvae. The samples (-> 1 and 2) are classified as travertine according to the vadose setting, microbial-induced precipitation, and medium porosity (Fig. 2.4). 2 Travertine. 'Bacterial stromatolite'. Thin laminae aggregate into packets with large lenticular intermat cavities bulged up by large gas bubbles (B). Note the abundant micritic clumps within the mats (arrows) interpreted as bacterial aggregates embedded or surrounded by calcite crystals. Bagni di Tivoli near Rome. 3 Travertine. Laminated micrite layers bordering voids which are partly filled with bladed prismatic ('dogtooth', DC) calcite cement. Same locality as -> 2. 4 Calcareous sinter. The layers consist of fibrous cements arranged in bundles. The low-calcite sinter originated from carbonic acid-rich and calcium-rich mineral waters. The travertine was formed during warm interglacial periods in the Pleistocene. The sample is classified as calcareous sinter owing to inferred inorganic precipitation, low porosity and the vadose setting. Bad Cannstatt-Stuttgart, Germany. 5 Travertine. Peloids and bacterial mud reworked into intraclasts. Same locality as -> 2. 6 Recent freshwater tufa. The fabric is characterized by incrustations of oscillatoriacean cyanobacteria. The threads have a diameter of about 10 pm. Fossil Oscillatoriaceae are indicative of freshwater and brackish water environments. Schleierfalle, Ammer, southern Germany. 7 Modem freshwater tufa. Tufa deposition is controlled by a number of intervening factors including carbonate equilibrium, crystal nucleation, crystal morphology, and diagenesis (Ford and Pedley 1996; Merz-PreiR and Riding 1999: Jamsen et al. 1999). Note the porous texture and the plant stem (P) surrounded by euhedral calcite crystals some of which exhibit dark 'centers' (arrow) commonly interpreted as an indication of bacterial contributions to carbonate precipitation. The sample still fits into the triangle classification (Fig. 2.4) because of its high porosity, considerable organic contributions (-> 6) and origin in a phreatic setting. Same locality as -> 6.

I'latt. 2 T r a \ ' t . r r ~ n e ,T u t a , Sinter

17

Lakes

18

the distinctive control of travertine microfacies types and dominating organisms (eucaryonts, photosynthetic and chemosynthetic bacteria) by water temperatures and pH values (Farmer 2000). Pamukale near Denizli (southeastern Turkey) is another famous locality where thermal spring waters at a hill built, and still build, large rimstone pools of travertine while flowing down in cascades about 100 m of height difference. Because of the large surface of the very thin layer of water, the water looses deep-source carbon dioxide, resulting in carbonate precipitation. The resulting white travertines have been used since Roman times as building stones. The Turkish name Pamrnukale means 'cotton castle' and refers to the strikingly white color of the large steps.

fabric-selective porosity patterns. Changes in porosity, permeability, specific surface, and water sorption due to the dissolution and precipitation of calcite within pores lead to a decrease in porosity and increase in rock hardness with time (Koch et al. 1999). The rapid precipitation of carbonate favors the preservation of fossil faunas and floras, and of archeological artifacts. Chronological dating of Pleistocene travertine~aids greatly in the age determination of prehistoric archeological material (Kahlke 1984).

2.4.1.7

Lacustrine Carbonates: Lakes

Lacustrine environments differ from marine environments in the properties, kinetics, chemistry and productivity of lake waters as well as in the sedimentation Phytoherms: Plant-dominated freshwater calcareous patterns originating in hydrologically open and hydrotufa, formed in river systems, are called 'phytoherms' logically closed lakes. Lakes are dynamic systems. (Cipriani et al. 1977; Pedley 1987, 1992) underlining Short-term and long-term changes in climate, water the dominant role of macrophytes and procaryotechemistry and bathymetry of lakes result in significant microphyte biofilms in the construction of carbonate variations of litho- and biofacies, and their lateral and buildups (Collinson 1988). Phytoherms of river sysvertical distribution patterns. tems, capable of damming the water courses to produce chains of lakes (e.g. Plitvica region, Croatia: Emeis Our review focuses on the carbonates formed in et al. 1987), are characterized by rapid growth in cool, lakes. Carbonates are only a part of lacustrine sediments, agitated waters. Continuous water circulation is neceswhich in addition, often include claystones, mark and sary for bringing in nutrients and providing replenishalso sandstones. The review neglects the siliciclastic ment of CaCO, for the extensive precipitation of Lowsediments as well as some chemical deposits (cherts, Mg-calcite cements within organic frameworks. The phosphorites). primary frameworks are provided by the in-situ growth Lacustrine carbonates are a specific type of terresof erect and trailing hydrophytes and semi-aquatic mactrial carbonate deposited within a lake or at the shorerophytes. Secondary frameworks are formed by oscillalines of a lake. Fluctuating shorelines may result in a toriacean cyanobacteria, diatoms and insect larvae colopedogenic overprint of lacustrine sediments leading to nizing exposed surfaces. The shelly fauna associated the formation of 'palustrine carbonates' (Sect. 2.4.1.2), with the phytoherms contains ostracods, gastropods, which were defined as 'near-shore deposits of extremely rare bivalves and crustaceans. shallow lakes with oscillating lake levels and densely The stability of these bioconstructions and also their vegetated shorelines' (Freytet and Plaziat 1982). Frepreservation in the fossil record is provided by a conquently, lake deposits are associated with paleosols as comitant development of thick Low-Mg calcite calcite well as with fluvial sediments. cements (micrite fringes and bladed calcite spar fringes) Because wind-driven currents and waves often do and by an intra-frame sediment infill. Both micritic not affect the lake bottom, lake waters tend to become fringe cements and the abundant small-scaled peloids permanently or seasonally stratified:Warmer and lighter are interpreted as the product of biological mediation waters (epilimnion) overlie colder and denser waters associated with a procaryote-microphyte biofilm and of the bottom zone (hypolimnion). These zones are the presence of organic detritus. separated by a zone characterized by a rapid rate of Significance: Travertines are important building and change of temperature with depth (mesolimnion). Perdecoration stones, used since antique times. High qual- manent stratification is characteristic of tropical ity travertine possesses a great mechanical strength and oligomictic lakes with temperature stratification and of remarkable resistance to weathering as compared with merornictic lakes in which the bottom water has a higher other building stones. Technological qualities of trav- salinity than the surface water. In both cases, the botertine~are strongly controlled by depositional facies tom water can become completely stagnant and be deand early diagenesis. Differences in technological prop- pleted of nutrients and oxygen, resulting in the accuerties of travertines and tufas are primarily caused by mulation of laminated muds rich in organic matter.

Lakes

Seasonal stratification is common in temperate climates. During the summer, surface waters are warmer and less dense than deeper waters. Cooling of the surface waters during the winter or an underflow by cool waters caused by rivers crossing the lake will produce surface waters of the same or higher density than that of the bottom waters. Consequently, the lake water body is turned over once or twice yearly and mixed (monomictic or dimictic lakes; tropical and polar lakes). Both near-surface waters and bottom waters are well-oxygenated, enabling a seasonal biogenic production (e.g. algae), which may be recorded by annual varves consisting of fine-grained siliciclastics, biogenic silica and carbonate formed in the deeper parts of the lakes. Fine-scale lamination, caused by the seasonal precipitation of carbonates or periodic influxes of sediment into lakes, is a common feature of both freshwater and saltwater lakes. Biologically induced precipitation of light carbonate laminae alternating with dark organic-rich laminae and/or detrital laminae form varved sediments in the deeper parts of many lakes.

Profundal zone: Aphotic zone. Often, but not always corresponds to the zone below the thermocline. Pelagial zone: Open-water, planktic zone.

Carbonates infreshwater lakes result from: Removal of C 0 2 by photosynthesis of plants (microbes, algae, floating phytoplankton, macrophytes), less commonly by changes in temperature, evaporation or mixing of water masses, resulting in the precipitation of Low-Mg calcite. Basin-wide carbonate blankets are produced in larger and deeper stratified lakes resulting from a seasonal change of algal blooms and sedimentationof organic matter, diatoms and detrital components, producing couplets of light carbonate-rich laminae and dark organic-rich laminae. Deposition of 'algal sediments', algally-coated grains (e.g. oncoids; P1. 1215, P1. 13115) and of characean oogonia (Pl. 65) in nearshore shallow parts of the littoral zone and accumulation of carbonate shells (e.g. gastropods, bivalves, or ostracods; P1. 130/2,3) in deeper parts of the littoral zone, resultOpen and closed lakes: Freshwater and salt lakes ing in biogenic sedimentation. Differences in the composition of the algal carbonates may reflect the Lakes are classified according to their salinity. Freshgenerally well-defined zonal distribution of vegetawater lakes usually contain 5 g/ Growth of stromatolitic bioherms (Pl. 13111) or 'al1. The setting of lakes in hydrologically open or hydrogal reefs' (Pl. 13011). logically closed basins as well as the chemistry of lake Input of allochthonous carbonate particles derived waters is used in separating major types of lacustrine from the drainage basin and deposited by debris environments (Allen and Collinson 1986): flows and turbidity currents in deeper part of the lake. (1) Hydrologically open lakes (freshwater lakes) Early diagenetic precipitation of carbonates (nonhave an outlet, relatively stable shorelines and are filled marine carbonate cements; Chafetz et al. 1985). with meteoric lake waters. They are characterized by the input of siliciclastic sediments in nearshore and offCase studies: Europe: Lake Constance, Germany: shore zones as well as by inorganic/biochemica1 and (Miiller 1971; Schafer and Stapf 1978; Dominik 1981); biogenic deposition of calcareous sediments in the shal- Eifel, Maar Lakes, Germany (Negendank et al. 1990); lower littoral zone and the deeper profundal zone. Most Lake Zurich and Lake Biel, Switzerland (Kelts and Hsu freshwater lakes are fed by rainfall; the salinity, there- 1978; Wright et al. 1980); Austria: Behbehani et al. fore, is low. Sedimentation patterns vary in response to (1986); North America: Green Lake, New York State changes in depositional regimes and source areas (Calvo (Eggleston and Dean 1976); Minnesota Lakes (Megard et al. 1989). Hydrologically open freshwater lakes are 1967; Murphy and Wilkinson 1980). The Green Lake normally perennial and occur mainly in temperate hu- exhibits wave-resistant stromatolite bioherms, formed mid climates. The subdivision of lake environments is by cyanobacteria and mosses trapping carbonate sedibased on biological criteria and embraces the follow- ment, and subsequent cementation by precipitated caling zones (Wright 1990): cium carbonate. Lake Michigan is an impressive exLittoral zone: Below the wave base, characterized ample of facies differentiation in a typical northern temby rooted macrophytes. The eulittoral zone is the perate hard-water lake. area between the highest and lowest sea levels, the supralittoral zone corresponds to the landward zone, (2) Hydrologically closed lakes (salt lakes) lack an which is rarely submerged. outlet. They are common in regions with semi-arid Sublittoral zone: Still within the photic zone, colo- warm and hot climates. If evaporation of the lake wanized by algae and cyanobacteria. ter is about equal to inflow, a permanent water body is

Lakes

maintained (perennial lake). If the evaporation exceeds inflow for a long time, salinity and the MgjCa ratio of the water will increase, as Ca is depleted by early-stage precipitates. Finally salts will be precipitated in these shallow 'salt lakes' and 'soda lakes' which normally fall dry, with the exception of a central pond containing highly concentrated brines (ephemeral lakes, playa lakes: Last 1993). High and extreme salinities can originate from a separation of former parts of the sea (e.g. separation of the Caspian Sea from the Mediterranean Sea), prolonged evaporation of lake waters, or increased input of dissolved salts. Case studies: Mono Lake, Death Valley, California; Great Salt Lake, Utah (Eardly 1966; Halley 1976); seamarginal ponds of the eastern Mediterranean e.g. Solar Lake, Israel (Krumbein and Cohen 1974; Friedman 1978); sea-marginal flats in the Red Sea, Gulf of Elat and Aqaba (Sneh and Friedman 1985); Australia: (De Deckker 1988); Lake Clifton (Burne and Moore 1983); Lake Thetis (Grey et al. 1990); Coorong Lagoon (Rosen et al. 1988). One of the most intersting saline lakes is the Dead Sea whose bottom sediments consists of precipitated aragonite, gypsum and halite, and detrital grains (Garber et al. 1987). Many hydrologically closed lakes are characterized by fringes of supralittoral mudflats (commonly termed 'playa' or 'inland sabkha'), sandflats in the nearshore zone, and depositions of mixed siliciclastic-evaporitic sediments as well as organic-rich sediments ('oil shales') within the lakes. Saline minerals are precipitated in perennial brines, as efflorescent crusts and salt pans and as cements within the sediments of the mudflats. Climatic changes may turn freshwater lakes into saline water bodies, as exemplified by the history of the modern Great Salt Lake, Utah, or the great lakes in the East African rift system.

waters on the playa surfaces cause supersaturation with respect to calcite, resulting in the formation of pisoids and carbonate encrustations (Risacher and Eugster 1979), ~ ~ d i o t h e r mfluids a l emerging from the lake bottom may produce sinter crusts consisting of aragonite and magnesium calcite (Lake Tanganyika, East-Central Africa: Cohen and Thouin 1987, Stoffers and Botz 1994).

Compositional characteristics of lake carbonates Similar to marine carbonates, lacustrine carbonates are composed of allochthonous and autochthonous constituents, the former represented by skeletal and nonskeletal grains and fine-grained calcite mud caused by seasonal phytoplankton blooms ('Seekreide': Schafer 1973), the latter by predominantly biogenic structures (stromatolites,bioherms and 'reefs') formed or induced by cyanobacteria and algae. All major grain categories known from marine carbonates also occur in lacustrine settings.

Biota: Differences exist in the inventory of the biota. Common organisms are (a) calcareous algae (charophycean algae, see Sect. 10.2.1.8 and PI. 65; planktonic and benthic green algae, see Pl.l3O/l) and cyanobacteria, siliceous algae (diatoms), (b) gastropods and bivalves, cf. P1. 13012, 3, (c) ostracods (see PI. 130/2), and (d) arthropods that are responsible for the production of abundant peloids. Otherwise marine organisms, e.g. foraminifera, also may occur in salt lakes. These ~narinebiota are transported by wind and may thrive in lakes if environmental conditions are favorable (Lee and Anderson 1991). Bioturbation and bioerosion are very important processes modifying the depositional texture of lacustrine sediments (Schneider 1977, Schroder et al. 1983). Cat-horzates in saltwater lakes are characterized by: Peloids and reworked and redeposited sedimentary Precipitation of High-Mg calcite and aragonite (e.g. fragments (intraclasts,lithoclasts) are common constituDead Sea) or Low-Mg calcite and High-Mg calcite ents. Small ooids and large oncoids (PI. 1311.5) are of (e.g. Lake Balaton, Hungary) because of the increase specific interest in microfacies studies of ancient lacustrine limestones because these grains may aid in the in the MgICa ratio, differentiation of non-marine and marine settings. Formation of carbonate laminites, consisting of CaOoids occur in marine as well in non-marine setMg carbonates, detrital quartz, silicates and organic tings (PI. 13/1), they are known from low- and highlayers, Ooid sands are formed in shallow, near-shore areas saline environments. Ooids are not common in recent of' current- or wave-swept lakes, sometimes ( e g freshwater lakes. Ooids originating in salt lakes have been described from the Great Salt Lake, Utah (Eardley Great Salt Lake, Utah) associated with Algal bioherms, composed of mm-scale laminated 1966; Kahle 1974; Sandberg 1975; Halley 1977; PI. 1312) and the Pyramid Lake, Nevada (Popp and Wilkinmicritic aragonite or of porous carbonate, Loss of COzby degassing or photosynthesis of spring son 1983).Ooids formed in a temperate 'marl' lake were

Fluvial Carbonates

reported from Michigan (Wilkinson et al. 1980). Saltwater and freshwater ooids exhibit differences in the morphology, microfabrics and mineralogy of the cortical layers, and in size ranges. The same is true for oolitic carbonate particles formed in situ in hypersaline algal mats (Friedman et al. 1973). These differences offer the possibility of tracing the development of ancient freshwater- and saltwater lakes (Sect. 4.2.5). Lacustrine oncoids have been described by various names (algal nodules, water biscuits, lake balls, lacustrine pisoliths) for many years (Pia 1926,1933, Schafer and Stapf 1978, Jones and Wilkinson 1978; P1. 1215). The origin of these grains is related to the activity of algae and microbes (Sect. 4.2.4.1). Cyanobacteria are known or assumed to be essential in the formation of these oncoids. Modem oncoids are not restricted to freshwater environments but also occur in brackish and hypersaline waters. Today, oncoids are rare in tidal and shallow subtidal marine environments. Recent marine oncoids are non-lithified, as opposed to modem hard freshwater oncoids that are closely similar to Paleozoic and early Mesozoic marine oncoids. This may be related to the replacement of porostromate oncoids by spongiostromate oncoids in marine settings during the Jurassic. Stromatolites occur both in freshwater and salt lakes. The stromatolites are usually domes, passively paving the relief of the substrate and reacting to environmental controls like currents. Stromatolites of less saline lakes are composed of calcium carbonate whose precipitation is induced by algalbacterial activity. Trapping of clastic particles, widely known from modern stromatolites, appears to be only of secondary importance. Stromatolites of saline lakes are well-known from hypersaline lakes in Utah, Nevada and California as well as from the San Salvador Island, Bahamas (Mann and Nelson 1989). The stromatolites have complicated microstructures consisting of micrite, pellets, filament molds and casts as well as sparry calcite. Lacustrine stromatolites contribute to the growth of 'algal mounds' as demonstrated by the 'reefs' described from the Great Salt Lake in Utah, which exhibit a nonskeletal framework of algally induced aragonite precipitates, internal sediments and carbonate cements, and cover about 100 square kilometers of the nearshore areas. The mounds extend from the shoreline down to a depth of 4 m; they are surrounded by rippled ooid sand. Coccoid bluegreen algae on the present-day living surface are different from the filamentous algae recognizable in the indurated stromatolites. The change in the algal flora may be due to an increase in salinity.A similar pattern is known from the famous intertidal stromato-

21

lites of Shark Bay in western Australia. Spectacular meter-sized strornatolites consisting of hydromagnesite were described from the highly alkaline Salda Golu Lake in Southern Turkey (Braithwaite and Zedef 1996). The composite stromatolites originate from microbially induced precipitation of hydromagnesite, which is possible because of the dissolution of magnesium and calcium during the passage of water through ultramafic rocks.

2.4.1.8 Fluvial Carbonates Carbonate deposits originate in fluvial waters in various settings including small creeks, large rivers or waterfalls where tufa is formed. Stromatolites,oncoids and ooids in present-day creeks and streams are usually formed by the complex activity of algae, mosses and microbes (Nickel 1985; Galli and Sarti 1989). Fluvial oncoids and ooids differ in morphological and compositional criteria as well as in transport patterns (Verrecchia et al. 1997) from marine grains and are, therefore. valuable environmental indicators. Basics: Non-marine carbonates Esteban, M., Klappa, C.F. (1983): Subaerial exposure environment. -In: Scholle, P.A., Bebout, D.G., Moore, C.H. (ed.): Carbonate depositional environments. - Mem. Am. Ass. Petrol. Geol., 33, 1-54 Etheridge, F.G., Flores, R.M. (eds., 1981): Recent and ancient nonmarine depositional environments: models for exploration. - Soc. Econ. Paleont. Min. Spec. Publ., 31, 349 pp. James, N.P., Choquette, P.W. (1990): Limestone - The meteoric diagenetic environment. - In: McIlreath, LA., Morrow, D.W. (eds.): Diagenesis. - Geoscience Canada, Reprint Series, 4,35-73 Pia, J. (1926): Pflanzen als Gesteinsbildner. - 355 pp., Berlin (Borntraeger) Pia, J. (1933): Die rezenten Kalksteine. - MineralogischPetrographische Mitteilungen, Neue Folge, Erganzungsband, 420 pp., Leipzig Further reading: KO28

Pedogenic carbonates, caliche, paleosols Esteban, M.C. (1975): Vadose pisolites and caliche. - Amer. Ass. Petrol. Geol. Bull., 60, 1048-1057 Klappa, C.E (1983): A process-response model for the formation of pedogenic calcretes. - In: Wilson, R.C.C. (ed.): Residualdeposits.-Geol. Soc. London Spec. Publ., 11,211220 Reeves, C.C. (1976): Caliche. Origin, classification, morphology and uses. - 233 pp., Lubbock, Texas (Estacado Books) Reinhardt, J., Sigleo, W.R. (1988): Paleosols and weathering through geologic time: principles and application. - Geol. Soc. America Spec. Paper, 216, 181 pp. Retallak, G.J. (2001): Soils of the past. Second edition. 416 pp., Oxford (Blackwell)

Basics: Non-Marine Carbonates

Wright, V.P. (ed., 1986): Paleosols. Their recognition and interpretation. - 3 15 pp., Oxford (Blackwell) Wright, V.P., Tucker, M.E. (1991): Calcretes. - Reprint Series Int. Ass. Sed., 2,352 p., Oxford (Blackwell) Further reading: KO30 Cave carbonates, speleothems and karst Borsato, A., Frisia S., Jones B., Van der Borg, K. (2000): Calcite moonmilk: crystal morphology and environment of formation in caves in the Italian Alps. - J. Sed. Research, A70, 1171-1182 Chafetz, H.S., Butler, J.C. (1980): Petrology of recent caliche, pisolites, spherulites and speleothem deposits from central Texas. - Sedimentology, 27,497-518 Drybrodt, W. (1988): Processes in karst systems - physics, chemistry, geology. - Springer Series in Physical Environments, 4, 288 pp., New York (Springer) Folk, R.L., Assereto, R. (1976): Comparative fabric of lengthslow and length-fast calcite and calcitized aragonite in a Holocene speleothem, Carlsbad Cavem, New Mexico. J. Sed. Petrol., 46,486-496 Frisia, S., Borsato, A., Fairchild, I.J., McDermott, F. (2000): Calcite fabrics, growth mechanisms, and environments of formations in speleothems from the Italian Alps and southwestern Ireland. - J. Sed. Research, A70, 1183-1196 Choquette, P.W., James, N.P. (eds., 1988): Paleokarst. 4 16 pp., New York (Springer) Fritz, R.D., Wilson, J.L., Yurewicz, D.A. (eds., 1993): Paleokarst related hydrocarbon reservoirs. - Soc. Econ. Paleont. Min. Core Workshop, 275 pp. Klinchouk, A.B., Ford, D.C., Palmer, A.N., Dreybrodt, W. (eds., 2000): Speleogenesis: evolution of karst aquifers. 527 pp., Huntsville (National Speleological Society) Mylroie, J.E., Carew, J.L., Vacher, H.L. (1995): Karst development in the Bahamas and Bermuda. -In: Curran, H.A., White, B. (eds.): Terrestrial and marine geology of Bahamas and Bermuda. - Geol. Soc. America Spec. Paper, 300, 2.5 1-267 Purdy, E.G. Waltham, I). (1999): Reservoir implication of modem karst topography.-Amer. Ass. Petrol. Geol. Bull., 83, 1774-1794 Thrailkill, J. (1976): Speleothems. - In: Walter, M.E. (ed.): Stromatolites. - 73-86, Amsterdam (Elsevier) Tietz, G.F. (1988): Zur Genese rezenter Karbonatbildungen in Dolomithiihlen Frankens. -Karst und Hohle, 1988, 7-79 Further reading: KO3 1

Eoliun carhonutcs Abegg, F.E.R., Harris, P.M., Loope, D.B. (eds., 2001): Modem and ancient carbonate eolianites: sedimentology, sequence stratigraphy and diagenesis. - SEPM Spec. Publ., 71,214 pp. Bigarella. J.J. (1972): Eolian environments: their characteristics, recognition, and importance. - Soc. Econ. Paleont. Min. Spec. Publ., 16, 12-61 Brookfield, M.E. (1992): Eolian systems. - In: Walker, R.G., James, N.P. (eds.): Facies models. Response to sea level change. - 143-156, Ottawa (Geol. Ass. Canada) Caputo, M.V. (1995): Sedimentary architecture of Pleistocene eolian calcarenites, San Salvador Island, Bahamas. - Geol. Soc. America Spec. Paper, 300,63-76 McKee, E., Ward, C.W. (1983): Eolian environment. - In: Scholle, P.A., Bebout, D.G., Moore, C.H. (eds.): Carbon-

ate depositional environments. - Amer. Ass. Petrol. Geol. Mem., 33, 131-170 Pye, K. (1994): Aeolian sediments: ancient and modem. Spec. Publ. Int. Ass. Sedimentologists., 16, 192 pp. Sayles, R.W. (1931): Bermuda during the Ice Age. - American Academy of Arts and Sciences, 66,381-468 Further reading: K 032 Glacial carbonates Edwards, M.(1986): Glacial environments. - In: Reading, H.G. (ed.): Sedimentary environment and facies. - 445470, Oxford (Blackwell) Eyles, N., Eyles, C.H. (1992): Glacial depositional systems. -In: Walker, R.G., James, N.P. (eds.): Facies models. Response to sea level change. - 73-100, Ottawa (Geol. Ass. Canada) Fairchild, I.J., Bradby, L., Spiro, B. (1993): Carbonate diagenesis in ice. - Geology, 21,90 1-904 Fairchild, I.J., Spiro, B. (1990): Carbonate minerals in glacial sediments: Geochemical clues to paleoenvironment. -In: Scource, J.D., Dowdeswell, J.A. (eds.): Glacimarine environments and processes. - Geol. Soc. London Spec. Publ., 53,241-256 Suess, E., Balzer, W., Hesse, K-F., Miiller, P.J., Ungerer, C.A., Wefer, G. (1982): Calcium carbonate hexahydrate from organic rich sediments of the Antarctic shelf: precursors of glendolites. - Science, 216, 1128-1131, Washington Shearman, D.J., Smith, A.J. (1985): Ikaite, the parent mineral of jarrowite-type pseudomorphs. - Proc. Geol. Ass. London, 96,305-314, London Further reading: K210 Calcareous tufa and travertine Andrews, J.E., Pedley, M., Dennis, P.F. (2000): Paleoenvironrnental records in Holocene Spanish tufas: a stable isotope approach in search of reliable climatic archives. Sedimentology, 47,961-97 1 Arp, G., Wedemeyer, N., Reitner, J. (2001): Fluvial tufa formation in a hard-water creek (DeinschwangerBach, Franconian Alb, Germany). - Facies, 44, 1-22 Chafetz, H.S., Folk, R.L. (1984): Travertines: depositional morphology and the bacterially constructed constituents. - J. Sed. Petrol., 54, 289-316 Folk,, R.L., Chafetz, H.S. (1983): Pisoliths (pisoids) in Quaternary travertines of Tivoli, Italy. - In: Peryt, T.M. (ed.): Coated grains. - 47 1-487, Berlin (Springer) Ford, T.D., Pedley, H.M. (1996): Areview of tufa and travertine deposits of the world. - Earth-Science Reviews, 41, 117-175 Irion, G., Miiller, G. (1968): Mineralogy, petrology and chemical composition of calcareous tufa from the Schwabische Alb, Germany. - In: Miiller, G., Friedman, G.M. (eds.): Recent developments in carbonate sedimentology in central Europe. - 157-17 1, Berlin (Springer) Julia, R. (1983): Travertines. -In: Scholle, P.A., Bebout, D.G., Moore, C.H. (eds.): Carbonate depositional environments. - American Association of Petroleum Geologists Mem., 33,64-72 Koban, C.G. (1993): Faziesanalyse und Genese der quartken Sauerwasserkalke von Stuttgart, Baden-Wiirttemberg. Profil, 5,47-118 Koban, C.G., Schweigert, G . (1993): Microbial origin of travertine fabrics. Two examples from southern Germany

Basics: Non-Marine Carbonates (Pleistocene Stuttgart travertines and Miocene Ried- Picard, M.D., High, L.R. (1981): Physical stratigraphy of ancient lacustrine deposits. - In: Ethridge, F.G., Flores, R.M. ijschingen travertine). - Facies, 29,251-264 (eds.): Recent and ancient nonrnarine depositional enviPedley, H.M. (1990): Classificationand environmental modronments: models for exploration. - Soc. Econ. Paleont. els of cool freshwater tufas. - Sed. Geol., 68, 143-154 Pedley, M. (1992): Freshwater (phytoherm) reefs: the role of Min. Spec. Publ., 31,233-259 biofilms and their bearing on marine reef cementation. - Platt, N.H., Wright, V.P. (1991): Lacustrine carbonates: fac i e ~models, facies distribution and hydrocarbon aspects. Sed. Geol., 79,255-274 - In: Anadon, P., Carrera, L., Kelts, K. (eds.,): Lacustrine Pedley, M. (2000): Ambient temperature freshwater microbial tufas. - In: Riding, R.E., Awramik, S.M. (eds.): Mifacies analysis. -Spec. Publ. Intem. Ass. Sedimentologists, crobial sediments. - 177-186, Berlin (Springer) 13,55-74, Oxford Pentecost, A., Whitton, B.A. (2000): Limestones. - In: Renault, R.W., Last, W.M. (eds., 1994): Sedimentology and Whitton, B.A., Potts, M. (4s.): The ecology of cyanobacgeochemistry of modem and ancient saline lakes. - Soc. Econ. Paleont. Min. Spec. Publ., 50,334 pp. teria. - 257-279, Dordrecht (Kluver) Renault, R.W., Jones, B. (2000): Microbial precipitates around Sermya, C., Pollingher, U. (1983): Lakes of the warm belt. 569 pp., New York (Cambridge Univ. Press) continental hot springs and geysers. - In: Riding, R.E., Awramik, S.E. (eds.): Microbial sediments.- 187-195, Ber- Talbot, M.R., Kelts, K. (eds., 1989): The Phanerozoic record lin (Springer) of lacustrine basins and their environmental signals. Palaeogeogr., Palaeoclimat., Palaeoecol., Special Issue, 70, Riding, R. (199 1): Classification of microbial carbonates. In: Riding, R. (ed.): Calcareous algae and stromatolites.304 pp., Amsterdam Torgersen, T. De Deckker, P., Chivas, A.R., Bowler, J.M. 2 1-51, Berlin (Springer) (1986): Salt lakes: a discussion of processes influencing Schweigert, G. (1996): Vergleichende Faziesanalyse, Palaopaleoenvironmental interpretations and recommendation okologie und,palaogeographisches Umfeld tertiiirer SiiBfor future studies. - Palaeogeogr., Palaeoclimat., Palaeowasserkarbonate auf der westlichen SchwabischenAlb und im Hegau (Baden-Wiirttemberg). - Profil, 9, 1-100 ecol., 54,7-19 Wright, V. P. (1990): Lacustrine carbonates. -In: Tucker, M., Further reading: KO29 Wright, V.P. (eds.): Carbonate sedimentology. - 164-189, Lacustrine carbonates Oxford (Blackwell) Allen, P.A., Collinson, J.D. (1986): Lakes. -In: Reading, H.G. Further reading: K025, K026, KO27 (ed.): Sedimentary environments and facies. Second edition. - 63-94, Oxford (Blackwell) Anadon, P., Carrera, L., Kelts, K. (eds., 1991): Lacustrine Fluvial carbonates facies analysis. -Spec. Publ. Intem. Ass. Sed., 13,318 pp. Galli, G., Sarti, C. (1989): Morphology and microstructures of Holocene freshwater-stream cyanobacterial stromatoAnderson, R.Y., Dean, W.E. (1988): Lacustrine varve formalites (Villa Ghigi, Bologna, Italy). - Rev. Paleobiol., 8, 39tion through time. - Palaeogeogr., Palaeoclimat., Palaeo49 ecol., 62,2 15-235,Amsterdam Dean, W.E., Fouch, T.D. (1983): Lacustrine environment. - McGamon, D.E. (1975): Primary fluvial oolites. - J. Sed. Petrol., 45,7 19-727 In: Scholle, P.A., Bebout, D.G., Moore, C.H. (eds.): CarNickel, E. (1985): Carbonates in alluvial fan systems. An apbonate depositional environments. - Amer. Ass. Petrol. proach to physiography, sedimentology and diagenesis. Geol. Mem., 33,97-130 Sed. Geol., 42,83-104 Forester, R.M. (ed., 1987): Paleo-lacustrine theme issue. Ordonez, S., Garcia Del Cura, M.A. (1983): Recent and TerPalaios, 2,412-522 tiary fluvial carbonates in Central Spain. - In: Collinson, Eugster, H.P., Hardie, L.A. (1978): Saline lakes. -In: Lerman, J.D., Lewing, J. (eds.): Modem and ancient fluvial sysA. (ed.): Lakes. Chemistry, geology, physics. - 237-293, Int. Ass. Sedimentologists Spec. Publ., 6,485-497 tems. Berlin (Springer) J. (1999): Fluvial sedimentology VI. Smith, N., Rogers, Friedman, G.M., Krumbein, W. (1984): Hypersaline exoInt. Ass. Sedimentologists Spec.Publ., 28,488 pp., Oxford systems. -Ecological Studies, Analysis and Synthesis, 35, Verrecchia, E.P., Freytet, P., Julien, J., Baltzer, F. (1997): The 500 pp., Berlin (Springer) unusual hydrodynamical behaviour of freshwater oncolites. Hakanson, L., Jansson, M. (1983): Principles of lake sedi- Sed. Geol., 113,225-243 mentation. - 3 16 pp., Berlin (Springer) Katz, B.J. (ed., 1990):Lacustrine basin exploration. Case studies and modem analogs. - Mem. Amer. Ass. Petrol. Geol., Palustrine carbonates 50,340 pp. Freytet, P., Plaziat, J.-C. (1982): Continental carbonate sedimentation and pedogenesis - Late Cretaceous and Early Kelts, K., Talbot, M. (1990): Lacustrine carbonates as geochemical archives of environmentalchange and biotic/abiTertiary of southern France. - Contributions to Sedimenotic interactions. - In: Tilzer, M.M., Sermya, C. (eds.): tology, 12,213 pp., Stuttgart Large lakes: ecological structure and function. - 288-3 14, Monty, C.V., Hardie, L.A. (1976): The geological significance Berlin (Springer) of freshwater bluegreen algal marsh. - In: Walter, M.R. Matter, A., Tucker, M.E. (eds., 1978): Modem and ancient (ed.): Stromatolites. -Developments in Sedimentology, 20, lake sediments. - Int. Ass. Sedimentologists Spec. Publ., 447-477, Amsterdam (Elsevier) 2,290 pp., Oxford Platt, N.H. (1992): Fresh-water carbonates from the Lower Freshwater Molasse (Oligocene, western Switzerland). Picard, M.D., High, L.R. (1972): Criteria for recognizing lacustrine rocks. - In: Rigby, J.K., Hamblin, W.K. (eds.): sedimentology and stable isotopes. - Sed. Geol., 78,8 1-99 Recognition of ancient sedimentary environments. - Soc. Platt, N.H., Wright, V.P. (1992): Palustrine carbonates and the Florida Everglades: towards an exposure index for the Econ. Paleont. Min. Spec. Publ., 16, 108-145

24

Transitional Marginal-Marine Sediments

freshwater environment. - J. Sed. Petrol., 52, 1058-1071 Modem carbonate coastal and offshore environments Wright, V.P., Platt, N.H. (1995): Seasonal wetland carbonate can be described by two models, the beach-banier issequences and dynamic catenas: a re-appraisal of palusland-lagoon model and the beach-strandplain model trine limestones. - Sed. Geol., 99,65-71 (Reinson 1984, Tucker 1990). The first model develFurther reading: K 030 ops inregions with moderate to high wave energy, relatively high tidal range and high carbonate sand production resulting in barriers and sand shoals and ridges. 2.4.2 Transitional Marginal-Marine The beach-strandplain model is also characterized by Environments: Shorelines and Peritidal high wave energy and high sand production rate, but Sediments low tidal range. Most modem carbonate shoreface-foreMarginal-marine environments (deltas, beaches and shore-backshore environments are dominated by skelbarrier-islands, estuaries, coastal lagoons and tidal flats) etal grainstones composed of skeletons of organisms occur in a narrow nearshore zone along the boundary living in these environments and in small coastal patch between continental and marine depositional realms. reefs; ooid grainstones are common in some regions. Coastal lagoons differ in sediment production and The shoreline is marked by great environmental instabiota. Protected lagoons with varying salinities behind bility resulting from intensive interaction between highenergy forces related to waves, tides, wind, and cur- beach bamers (islands or off-shor sand bars) are sites rents and constantly changing sea levels. Water energy, for the deposition of fine-grained sediments forming sediment transport and resulting sediment structures packstone through to mudstones; the biota are low-dichange across the shoreline from offshore to shoreface versity. Open lagoons connected to the open sea via and foreshore environments. Carbonate deposition takes tidal inlets and with a normal salinity contain a diverse place in the coastal shoreline zone at the beach, in fauna and a variety of sediment types. Freshwater coastal lagoons behind bamers, and within the periti- marshes, tidal flats, brackish water and salt ponds or dal zone. Sediments formed in arid and humid shore- sabkhas may occur adjacent to the lagoons. line environments differ in depositional patterns, composition and biota (Sect. 15.5). Key areas for the understanding of modem carbon- 2.4.2.2 Peritidal Environments ate shoreline sedimentation are the Yucatan Peninsula, Florida Bay, the Bahamas, Belize shelf, the Arabian Peritidal carbonates are sediments formed 'around the tides' (Folk 1973, Wright 1984) and include deposits Gulf, and western Australia. Excellent reviews of the environments, depositional formed in supratidal, intertidal and shallow subtidal arpatterns and facies sequences in these areas are given eas (Box 2.3). The term describes sedimentation on lowby Inden and Moore (1983) and Tucker (1990). Par- energy tidal zones, especially on tidal flats accreting ticularly handy overviews of modem peritidal carbon- from the shorelines of land areas or around islands, and ates were presented by Shinn (1983), Hardie and Shinn on shelves, platforms and ramps. Hardie and Shinn (1986) defined ten basic features characterizing tidal(1986), and Pratt et al. (1992). flat deposition:

2.4.2.1 Beach (Foreshore), Barriers and Coastal Lagoons The beach is strongly wave-dominated and constantly changing. Sediments are produced by the influx from rivers, erosion of cliffs and headlands,erosion of the sea floor, accumulation of shells and the depostion of nconsoliated sediment by tides. A common feature of low-ltitude warm-water beaches is the presence of beachrock (Scoffin and Stoddard 1983). Beachrock originates from the rapid cementation of sand grains and gravels by aragonite and Mg-calcite crystals growing in intergranular pores. Beachrocks are formed both in tropical (see PI. 3/7,8; P1.3313, PI. 35/1,2) and temperate environments (Pl. 3 1/3,4, P1. 9212).

(1) Carbonate tidal flats occur in settings which are protected from open ocean waves. Protection from the open ocean can be caused by wide shelf lagoons, dampening the incoming waves (e.g. Andros tidal flats on the Great Bahama Banks), a position behind barrier islands that separates back reef lagoons from the open ocean (e.g. Abu Dhabi, Persian Gulf), or within restricted embayments (e.g. Shark Bay, Australia). (2) The basic physiography of the tidal-flat system is determined by the scale of the tidal ranges. (3) Tidal flats are subdivided into three depositionalecological zones by the daily oscillations of the tides (Box 2.3). (4) Tidal flats are partly sea and partly land. They are affected by steep gradients of environmental con-

25

Peritidal Encironrnents

I

Box 2.3. Criteria of peritidal and subtidal zones. Supratidal zone (supralittoral): Shore zone above normal high tide, flooded only during storms and semi-monthly high spring tides. The zone includes marshes, mangrove forests and diverse coastal ponds of different salinity. May become evaporitic in arid or semiarid climates. Evaporitic supratidal flats are called sabkhas. The width of this zone depends on the relief and dip of the coasts. Intertidal zone (littoral, eulittoral): Near-coast zone between normal high- and low-tide levels which is alternatively flooded and exposed on a diurnal or semi-diurnal basis. Transitional area from marine to terrestrial conditions, dotted with brackish and saline ponds and dissected by subtidal creeks. This zone exhibits a variety of biological, sedimentary and diagenetic criteria. Because many of these criteria are preserved in the geological record, ancient intertidal carbonates are of major importance as key markers in facies studies. Subtidal zone (sublittoral, circalittoral): Marine zone below low-tide level, seaward of the tidal flats, extending down to the edge of the continental shelf and underlying the neritic zone. Water depths between a few decades of meters and 100 to 200 m. Includes low- and high-energy environments. The shallowest parts can be influenced by tidal currents and may be briefly exposed by serni-monthly neap tides. The zone is illuminated and includes shallow and deep subtidal subenvironments. Subdivisions are predominantly based on the distribution and composition of benthic biota.

ditions resulting in an extreme rich variety of sedimen- Basics: Modern transitional environments tary, early diagenetic and paleontological featurs re- Ginsburg, R.N. (ed., 1975): Tidal deposits, a case book of Recent examples and fossil counterparts. - 428 pp., Bercorded in carbonate rocks. lin (Springer) (5) Owing to the large number of combinations of Hardie, L.A. (ed. 1977): Sedimentation on the modem tidal circulation, salinity, tides and climate, care must be flats of Northwest Andros Island. - John opkins University Studies in Geology, 22,202 pp. taken, to use just a sngle 'model' in describing ancient Hardie, L.A., Shim, E.A. (1986): Carbonate depositional entidal deposits. vironments, modem and ancient. Part 3. Tidal flats. - Colo(6) Tidal flats are wave-protected and, therefore prefrado School of Mines Quarterly, 81, 1-74 erential sites for the accumulation of mud. Offshore Inden, R.F., Moore, C.H. (1983): Beach environment. - In: mud is transported shoreward onto tidal flat currents Scholle, P.A., Bebout, D.G., Moore, C.H. (eds.): Carbonate depositional environments. - American Asociation of and storms, and mud can also be produced on supratidal Petroleum Geolists Memoirs, 33, 21 1-265 flats. Pratt, B.R., James, N.P., Cowan, C.A. (1992): Peritidal car(7) Carbonate tidal flats nucleate on a continental bonates. -In: Walker, R.G., James, N.P. (eds.):Facies modmainland (Persian Gulf), isolated islands with a lagoon els. Response to sea level change. - 303-322, Ottawa (Geo(Florida Bay), and platform-margin islands (Great Balogical Association Canada) Shinn, E.A. (1983): Tidal flat environments. - In: Scholle, hama Banks). P.A., Bebout, D.G., Moore, C.H. (eds.): Carbonate depo(8) Warm and clear waters of shallow tropical envisitional environments. - American Association of Petroronments are conducive to the profilific growth of alleum Geolists Memoir, 33, 171-210 gal and microbial mats which influence carbonate depo- Shinn, E.A. (1986): Modem carbonate tidal flats: their disition by binding, trapping and precipitation in supraagnostic features. -Colorado School of Mines Quart. 81,735 and intertidal zones. Neumeier, U. (1999): Experimental modelling of beachrock (9) Early cementation is crucial in the preservation cementation under microbial influence. - Sedimentary Geolof primary structures and textures. ogy, 126,35-46 (10) Carbonate tidal-flat facies typically occur as Wright, V.P. (1984): Peritidal carbonate facies models: a restacked cycles, each ideally composed internally of an view. - Geological Journal, 19,309-325 upward succession of subtidal to intertidal to supratidal Wright, V.P.: (1990): Peritidal carbonates.-In: Tucker, M.E., Wright, V.P.: Carbonate sedimentology. - 137-164, Oxunits. Peritidal environments exhibit a high degree of variability in relation tothe tidal range, mean sea level, topographic position and meteorological factors acting within each zone. To overcome these problems, Ginsburg et al. (1977) have proposed the use of an 'exposure index' defined as the percentage of the time that a specific area is exposed. This approach also can be applied to ancient tidal carbonates (Sect. 15.5).

ford (Blackwell) Further reading: K019, KO20

2.4.3 Shallow-Marine Sedimentary Environments: 'Shallow' and 'Deep' Geologists reconstructing ancient depositional environments like to distinguish between marine 'shallow-water' and 'deep-water' carbonates, but have a lot of

Shelfs, Ramps, Platforms

26

RIMMED PLATFORM

UNRIMMED PLATFORM

Wave

'Deep sea' as used in marine biology to mean that part of the marine environment that lies below the level of effective light penetration for phytoplankton synthesis in the open ocean (photic zone), and deeper than the depth of continental shelves (corresponding approximately to > 200 m). The upper part of the deep sea retains some light (disphotic zone). The permanently dark region below sunlit waters is the aphotic zone which starts in temperate waters at rather shallow depths (about 100 m), and in tropical waters at deeper depths (about 600 m).

2.4.3.1 Pericontinental vs Epicontinental Shallow Seas

Fig. 2.5. Rimmed and non-rimmed carbonate shelves (platjbrms) and ramps (slightly modified after James and Kendall 1992). Note the different position of the 'carbonate factories' at the seafloor. Carbonatefactories (James 1979) are subtidal areas characterized by high carbonate production by predominantly benthic organisms. The optimum autochthonous carbonate production on rimmed platforms occurs near the platform margin and behind the margin. On ramps optimum areas of carbonate production are distributed over the entire extension of the ramp. Rimmed and unrimmed platforms are common in tropical and subtropical sunlit waters, today approximately 30" N and S of the equator, where the carbonate factory is primarily controlled by high water temperatures favoring phototroph carbonate-secreting organisms. Ramps are common in cool-water zones, extending polward from the limit of the tropical factory to polar latitudes, and characterized by the dominance of heterotroph organisms (Sect. 16.4). Schlager (2000) differentiated a third carbonate factory (mud mounds), characterized by the in-situ production of biotically induced and abiotic carbonate mud.

trouble doing so. Microfacies analysis assists in overcoming these difficulties (see Sect. 12.3). Common criteria used by marine geologists and biologists in distinguishing 'shallow-marine' from 'deepmarine' environments in modem oceans are the shelf break and the lower boundary of the well-illuminated zone. Another important boundary level is the storm wave weather base (see Box 2.1). Shallow seas occur above the continental shelf and include marginal-marine and marine environments, both in pericontinental and epicontinental settings. Deep-marine sea bottom environments are located on the slope, at the toe-ofslope and within basins.

Most modem shallow seas cover shelves around the margins of the continents. These pericontinental seas differ strongly from the epicontinental (epeiric) setting of many ancient shallow seas. Epeiric seas occupied extensive areas of the continental interior or the continental shelf. They differ from pericontinental seas with regard to wave and current regimes, sediment input and sea level controls. Modem examples of epeiric shelf seas are rare in contrast to the geological record, where epeiri carbonate platforms and ramps were common. 2.4.3.2 Carbonate Shelves, Ramps and Platforms Carbonate depositional models developed in the 1960s and early 1970s were strongly based on modem analogues from the Bahamas, Florida, the Yucatan and the Persian Gulf (Wilson 1975). These models describe sedimentation patterns onshelves characterize by the deposition of shallow-water sediments on flat platform tops, and by significant rims marked by reefs or shoals near the shelf break. Ahr (1973) noted that the 'rimmed shelf' model does not fit many ancient carbonate successions, and that a different model was necessary, especially for the epeiric shallow-water carbonates (Irwin 1965). The term carbonate ramp was adopted to describe a gently sloping depositional surface which passes gradually without slope break from a shallow, high-energy environment to a deeper, low-energy environment. A ramp is attached to a shoreline at one end and to correlative basinal beds at the other end. Fig. 2.5 exhibits the basic differences between immed and unrimmed shelves (platforms) and ramps with respect to the position of the optimum carbonate production (carbonate factory) and sediment transport.

27

Shelves, Ramps, Platforms

Carbonate Platforms: Broad Categories Rimmed carbonate shelves

Rimmed carbonate shelves (Ginsburg and James 1974): Shallow pericontinental flat-toppedplatforms.Outer wave-agitated edge characterizedby morphological rims (barrier reefs, shoals, islands) that absorb wave action and a pronounced break of slope into deeper waters. Rimmed shelf margins comprise accretionary, bypass and erosional margins. High-energy facies occurs predominantly at the outer shelf margin. Widths typically a few to about 100 km. Modern examples: Queensland Shelf off eastern Australia with the Great Barrier Reef, South Florida Shelf, Belize Shelf, Gulf of Suez.

Non-rimmed carbonate shelves

Non-rimmed carbonate shelves: Shallow platforms without a pronounced marginalbarrier. Characterized by open water circulation. The term includes 'open carbonate platforms' as well as carbonate ramps. Widths a few to more than 100 km. Modern examples: western Florida, Yucatan, Brazil. Atlantic, common in cool-water settings.

.............................

. :.'I:.:::.::. :.: .......... .................... ...... :.....:.. :

z..:.:.

Homoclinal ramps

Homoclinal ramps (Read 1982): Shallow epeiric and pericontinentalplatforms charac::.:;..:: ...,:.::,....;.'...:.:::..:,:;i:.:i.>;..;:::.::' . . . . ..:. terized by gentle uniform depositional slopes, .................. . ..........:.:.Y..~-:.:..+:..... .... passing downwards from a shallow nearshore high-energy facies offshore into a more muddy deeper-water facies without a marked break in slope. The angle of slope is commonly less than 1"(of the order of a few meters per kilometer), but steeper dips may occur. Width between 10 and > 100 km. Modern examples: Trucial Coast of the Arabian Gulf, Shark Bay of Western Australia.

--------------*-----------------M---

Distally steepened ramps

Distally steepened ramps (Read 1982): Similar to homoclinal ramps, but with a distinct increase in gradient in the outer, deep ramp region. Width between 10 and 100 km. Modern examples: Northeastern Yucatan, western Florida.

-1 ........ ...... .. ...:-.:. ....... ..

Epeiric platforms

Epeiric platforms (Shaw 1964): Very extensive, flat, cratonic areas covered by shallow . . . . . . . . . . . . . . ;. . .................... . . . . . " . .;:.. .. : seas. Dmlinated by shalbw subtidal-intertidal low-energy facies and tidal flat cycles. The oceanward margin can be gentle (ramp-like) or steep (shelf-like), and can be rimmed. Width between 100 and 10 000 km. No good modern examples of epeiric platforms exist.

...................................... 23 "C Normal to hypersaline Supersaturated to saturated Restricted to open 50 to >I000 cm/1000 a Common to abundant Common Common to abundant

beyond 30" N and 30"s Open shelf; ramp Stable to unstable Low to high Homoclinal and distally steepened ramps 4 0 "C Normal (to reduced) Saturated to undersaturated Open >1 to >10 cm/1000 a Rare to absent Absent Abundant, strong 50-100% Sands, gravels, muds Rare to abundant Physical and chemical degradation of skeletons Absent Absent Rare or absent Rare to common Abundant Abundant Very rare Rare Abundant Less common Rare Common to abundant Solitary and fasciculate Abundant, low-diversity Abundant Abundant and diverse Common Common Common to abundant Abundant Common to abundant Diverse Moderate to high High Rare to abundant Common Common Rare to common Common to abundant Abundant to common Rare Rare Less common Destructive

290% Muds, sands, gravels Common to abundant Disintegration of algae, microbial Common Common Common Common Common to abundant Common Abundant Common to abundant Rare Abundant Abundant Rare Diverse Common, high-diversity Rare to common Common and diverse Rare Rare to common Rare Common Rare to common Few High Low Rare Rare Rare Rare Rare to common Abundant Aimndant Common Common to abundant Constructive

Subtropical Shelf Carbonates

1~ x a m ~ l ewith s important references

Main features

Great Bahama Bank Anselmetti et al. 2000; Ball 1967; Curran and White 1995; Eberli and Ginsburg 1989; Ginsburg et al. 1991; Hardie 1977; Harris 1979; Hine 1977; Milliman et al. 1993; Newellet al. 1959; Neumann and Land 1975; Purdy l963a; l963b; Schlager and Ginsburg 1981; Shinn et al. 1969; Wanless and Dravis 1989; Ginsburg 2001

>

5

E

Shallow sea floor (-100 m average depth); topographical fringing barriers (reefs, shoals, islands) at the seaward margin; low-energy environments and mud deposition within the shelf lagoon, high-energy environments predominantly at the outer margins

.El

South Florida Shelf Bosence 1989; Enos and Perkins 1977; Ginsburg 1956; Halley et al. 1983; Messing et al. 1990; Multer 1969; Shinn 1963; Shinn 1983; Shinn et al. 1989; Stockman et al. 1967; Turmel and Swanson I976

L

a,

V)

m o

Cuba Bandy 1964; Daetwyler and Kidwell 1959; Bathurst 1975

%

c2

CLI a, 3 L G= Cn

-: .

Great Barrier Reef Drew 1983; Gagan et al. 1990; Larcombe and Woolfe 1999; Maiklem 1968; Maxwell 1968; Maxwell and Swinchatt 1970; Scoffin and Tudhope 1985; Tudhope 1989

,3 2 $$

Northwestern Yucatan Folk 1967; Folk and Robles 1964; Gischler and Lomando 1999; Hoskin 1963; Logan et al. 1969; Viniegra-Osario 1981; Wilson 1970; Ward and Brady 1973

.s E O "

Sea floor gently inclined towards the shelf break; sedimentation controlled by wave action, and tidal and oceanic currents; calcareous sands in shallow settings; mud in deeper settings; wide irregular facies belts; lack of resedimentation by mass flow mechanism

Belize Gischler and Lomando 1999; Gischler et al. 2000; James and Ginsburg 1979; Purdy 1974; Purdy et al. 1975; Scholle and Kling 1972

D

f

2>

O

5 m

1

g

0 a,

, 5% 91 r 3

+

.E

5

Eastern Gulf of Mexico Folk et al. 1962; Gardulski et al. 1986; Rezak et al. 1985; Siringan and Anderson 1994 Persian Gulf Houbolt 1957; Patterson and Kinsman 1981; Purser 1973; Scholle and Kinsman 1974

Fig. 2.10. Major settings of modem subtropical shelf carbonates (based on Sellwood 1986).

glacial stage. Facies distribution and setting of modem reefs and shoals, therefore, are strongly controlled by the Pleistocene topography (Purdy 1974). Excellent reviews and detailed descriptions of modem tropical and subtropical shelf carbonates from different settings can be found in Sellwood (1986), Tucker and Wright (1990), Jones and Desrochers (1992), and Wright and Burchette (1996). In the context of interpreting of microfacies data, these references must be thoroughly consulted.

definitions and significance of these constituents are discussed in Sect. 4.2. Plate 3 offers a first look at the diversity of the grain types.

Reefs Modem tropical and subtropical reefs are situated at shelf and platform margins, and on shelves, platforms and ramps. The distributional pattern of recent coral reefs suggests that reefs are arranged nearly symmetrically in both hemispheres, do not occur at latitudes greater than 34", are concentrated at the western marConzposition of tropical and subtropical shallow-mu- gins of the oceans, are absent in the vicinity of large rine carbonates: Similar to ancient limestones, mod- river mouths, and exhibit two reef realms (Caribbean em warm-water shelf carbonates consist of polygen- and Indo-Pacific realm). etic carbonate mud and different categories of grains. Furthergoing explanation of the distributional patGrains include biogenic material (detrital bioclasts or tern suggests that reefs prefer shallow waters and tropiin situ calcareous organisms), sand-sized grains of mud- cal to subtropical climates, and can grow in land-locked grade carbonate (peloids), various coated grains (oo- settings and in open oceanic settings, and that reefs ids, oncoids, rhodoids), sand-sized aggregates of ag- avoid settings with high clastic input and areas affected glutinated particles (grapestones), and lithified and re- by cool eastern boundary currents and coastal upworked sediment clasts (lithoclasts, intraclasts). The welling. In summary, sea-water temperature, sunlight

Modern and Pleistocene Carbonates

and water depths, and nutrients and siliciclastic input are the major controls on the distribution of modem zooxanthellate coral reefs. Cool-water reefs are discussed in Sect. 16.4.1.

2.4.4.3 Non-Tropical Shelf and Reef Carbonates Shallow-marine temperate carbonate sediments constitute about one third of modem global shelf sediments (Nelson 1988). Modem temperate cool-water carbonates differ from tropical carbonates in the type of skeletal grains, mineralogy and diagenesis, oxygen and carbon isotopes and in the range of trace elements. Nontropical and tropical shallow-marine carbonates differ significantly in their prevailing geometries: The scar-

37

city of rapidly growing calcareous frame-building organisms and the absence of aragonite (which would favor early lithification)hinder the development of platforms with wave-resistent margins and steep flanks. Non-tropical shelf sediments are primarily controlled by bottom currents which distribute the bioclastic sediment over extended areas. The results are homoclinal ramps, developing in low-water energy, and distally steepened ramps in high-energy environments. Non-tropical carbonates are found almost continuously from mid to high latitudes in shelf areas with low or missing clastic input. Similar settings which occur along a latitudinal transect from warm to cold water conditions, may be developed along downslope profiles at any latitude (including tropical carbonate platforms, Brazil shelf).

Plate 3 Modern and Pleistocene Carbonates: Shallow-Marine and Windblown Sands; Beachrocks The samples shown on this plate document the common composition of calcareous sands deposited in shallowmarine (-> 1-3) and subaerially exposed environments (-> 4,5,7,8). Both the Bahamas and the Bermudas offer excellent possibilities for studying the controls on the deposition of calcareous sediments and the processes involved in their transformation into carbonate rocks. The Bahamas are a large isolated platform, 700 x 300 krn in size. The subtidal sediments exhibit specific distributional patterns (see map on next page). Lithofacies characterized by skeletal grains (coralalgal), ooids and reefs (see P1.5 117) occur at the platform margins, whereas sediments rich in aggregate grains (grapestone) or carbonate mud (pellet mud) are platform-interior facies. Modern shallow-marine carbonate sands formed in tropical and subtropical warm-water environments consist predominantly of skeletal grains (foraminifera, -> 6; calcareous algae, -> 5; mollusk shells, -> 2, and other biota), associated with non-skeletal grains including peloids (-> 2), ooids (-> 1,3) and composite grains represented by aggregate grains (-> 1; P1. 1511-3), and reworked and redeposited sediment (intraclasts, -> 1). Grains are usually aragonite or High-Mg calcite. The average size ranges between < 0.5 and about 2.0 mm. Sand accumulations are common on or near the seawards edge of banks, platforms or shelves (Halley et al. 1983). Sand production and the development of modem bank-margin sand bodies are strongly controlled by antecedent topography, physical processes (wind, waves, tides, and storms), and sea-level changes. Various encrusting organisms contribute to the stabilization of the sediment binding of grains and to the formation of beachrocks (-> 8). Submarine cementation within inter- and intragranular pores as well as early diagenetic cementation of subaerially exposed sediments lead to an incipient lithification (-> 4). The microstructure of many grains becomes highly altered due to the activity of microborers (-> 2; 'micritization') and diagenetic alterations. These grains are formed in specific high- and low-energy environments (see map). Eolianites, consisting of windblown marine carbonate grains, are known from modem and ancient tropical and subtropical coastal environments (see Fig. 15.1). Eolianites are commonly associated with coastal marine deposits and paleosols. Because the sediment consists of grains, originally formed in shallow-marineenvironments, eolian grainstones may be confused with marine calcarenites. Important diagnostic criteria of eolianites are lamination and stratification with high- to low-angle beds (see Fig. 15.1), fine- to medium-sized grains, good overall sorting (-> 4), sorting differences between laminae or beds, inverse grading, rounded tabular grains, and meteoric vadose meniscus and microstalactitic calcite cements (-> 4). Other cement types are fibrous cements consisting of long calcite crystals, and rnicrite rim cement that superficially resemble micrite envelopes. Calcified plant root systems in calcarenites associated with paleosols and carbonate crusts (see P1. 128) suggest a pause in sedimentation under subaerial conditions.

38

Plate 3: Description of Figures

Plate 3 Text Continued: Modern and Pleistocene Carbonates: Shallow-Marine and Windblown Sands; Beachrocks 1 Constituents of recent marine calcareous sands: Ooids (0), aggregate grains (grapestones, G; see P1. 1511-3), intraclasts and peneroplid foraminifera(P). Ooid nuclei are large peloids and skeletal grains. Holocene: Exuma Kays, Great Bahama Bank. 2 Skeletal grains (forminifera, algal debris, Halimeda HA) and micritized grains. Note the crossed-lamellar microstructure of the large aragonite gastropod shell. Parts of the shell were destroyed by microborers (arrows; see P1. 5211-4). The sediment in the shell interior was cemented prior to deposition. Subtidal unstable sand of the coralgal facies. Holocene: Bimini Island, Great Bahama Bank. 3 Ooids. Tangentially structured 'normal ooids' (TO) exhibiting a cortex of several aragonite lamellae and 'superficial ooids' (SO), characterized by only a few laminae (see P1. 13). Nuclei are large peloids. Note the small dark micrite-filled spots within some ooids (bottom left) representing microborings. The Bahamian ooid shoals occur along the platform margin. The Joulters ooid shoal north of Andros Island consists of ooid grainstone (formed on current-swept, rippled sea bottoms), ooid packstone (formed on stabilized burrowed bottoms), fine-peloid packstone (formed on stabilized and burrowed bottoms), pellet wackestone and lithoclast packstone (formed in active tidal channels) as well as skeletal grainstone (Hams 1983). Holocene: Joulters Cays, Great Baharna Bank. 4 Constituents of a poorly cemented wind-blown ooid sand (ooid grainstone) forming eolian dunes. Tangentially structured ooids. Cementation has taken place in the meteoric vadose zone. Note rims of Low-Mg calcite cements (arrows) connecting the grains. These 'meniscus cements' and phreatic granular calcite cements indicate freshwater diagenesis (see PI. 32156). Cementation affects densely packed grains more strongly than loosely packed grains. Most pores between the grains are open (but were filled with epoxy during the preparation of the thin section).The grains were formed within a marine environment, but an eolian deposition is indicated by the good overall sorting and vadose cements (Caputo 1995).Late Pleistocene (Grotto Beach Formation; age about 125 000 a): San Salvador Island, Bahamas. 5 Skeletal grains, predominantly fragments of the green alga Halimeda (see P1.57/1,2), few foraminifers and gastropods. The disintegration of Halimeda and other green algae is a major process in the production of carbonate mud (see P1.71 1,2). Late Pleistocene (French Bay Member, Grotto Beach Formation): San Salvador Island, Bahamas. 6 Lithified calcareous sand (calcarenite), deposited in a nearcoastal marine environment during an interglacial phase. Consisting predominantly of skeletal grains (peneroplid foraminifera),peloids, and grains that have been intensively attacked by microborers and transformed into microcrystalline calcite (dark). Late Pleistocene (Belmont Formation): Devonshire Bay, southern Bermuda. 7 Fossil beachrock composed of large micritized aggregate grains (AG) and some skeletal grains (bored shells: arrow points to borehole; foraminifera, F). In contrast to -> 8, all the intergranular pores are filled with cement. Beachrock is formed in the intertidal zone of subtropical or tropical coasts. Late Pleistocene (Grotto Beach Formation): Same locality as -> 5. Juvenile beachrock consisting of well-preserved fragments Andros Island E of Halimeda (HA), composite grains and peloids. Note the still open voids (V). The grains are encrusted by foraminifera (arrows). Beachrock originates from the growth of aragonite and Mg-calcite cements in intergranular pores. Cementation can take place within a few years. Late Pleistocene (Grotto Florida Beach Formation): Same locality as -> 5.

Map and cross-section of Andros Island. Modified from Friedman and Sanders (1978) and Blatt et al. (1972).

Figs. 1-3: Loose grains are embedded in resin which appears white in transmitted light.

Plate 3: Modern and Pleistocene Carbonates

39

1 mm

lmm

-100 urn

-

1rnm

- 1 rnrn

1mm

-

Imm

-

lmm

Temperate and Polar Carbonates

Studies of mid- and high-latitudinal non-tropical carbonates started rather late in the 1970s, but 'temperate' and 'cold-water ' carbonates are becoming continuously better documented (Nelson 1988; Henrich and Freiwald 1995; Rao 1996; James and Clarke 1997) and have become one of the most exciting tools in carbonate research. The importance of non-tropical coral reefs was underlined by Teichert (1958). Chave (1967) pointed out that shelf carbonates could form at all latitudes, regardless of water temperature. Based on a thorough analysis of modem shelf sediments, Lees and Buller (1972) recognized the fundamental differences between tropical and temperate carbonates, and the importance of water temperature and salinity as major controls on the composition of shelf carbonates. The authors emphasized the significance of 'grain association patterns' for distinguishing between tropical and non-tropical carbonates. This concept provides a high potential for evaluating the climatic and oceanographic controls on ancient carbonates using microfacies data (Sect. 12.2). The last twenty years have produced a wealth of papers dealing with non-tropical coastal and shelf carbonates in the Northern and Southern Hemisphere and comprising a latitudinal range of 30 to 80" N and 30 to 70" S. Temperate and cold-water shelf carbonates were studied in the northern Atlantic (northwestern France, England, Ireland, Scotland, Norway), in the Greenland and Barents Sea, on the Canadian Scott Shelf, from various parts of the Mediterranean Sea (Tunisia, Sicily, Adriatic Sea, Eastern Mediterranean)as well as from Pacific regions (Western Canada, India). In the Southem Hemisphere extensive temperate carbonates are forming today off Australia, Tasmania and New Zealand on tidal flats, gulfs, shelves, platforms and ramps. The largest modem temperate-water carbonate shelf production occurs on the outer shelf, shelf edge and upper slope of the southern and southeastern margin of Australia (Boreen and James 1993). The eastern Tasmanian shelf is an excellent example for the deposition and diagenesis of cool-water carbonates. These carbonates have been extensively studied with regard to compositional, mineralogical and geochemical criteria and are, therefore, a reference standard for recognizing and interpreting ancient non-tropical carbonates. Informative reviews and collections of case studies are available (Nelson 1988; Henrich and Freiwald 1995; James and Clarke 1997). Rao (1997) gives an excellent overview on the present state of knowledge and includes a comprehensive bibliography. Controls on temperate carbonates: Major controls on the origin and composition of temperate carbonates are (a) the rate of dilution from ter-

rigenous sources, (b) appropriate sea-water temperatures (which may be relatively 'warm' - the Mediterranean type of parts of southern Australia, or 'cool temperate' - e.g. Otway shelf, southeastern Australia; Tasmania), (c) the relative abundance of calcareous biota, (d) the availability of nutrients, (e) sufficient levels of saturation of CaCO, in seawater (allowing cementation and reducing dissolution), (f) high water energy for accumulating calcareous sands, and (g) the rate of accumulation (approximately an order of magnitude lower in temperate shelves than in tropical shelves). Many non-tropical carbonates form at low CO, levels hregions of upwelling waters, which maintain CaC03saturation and provide nutrients for luxuriant growth of fauna. Lowering of sea level results in wave-base erosion and redistribution of sediments from shallow to deeper water and below the wave base. Temperate and polar carbonates: Bioclastic carbonates of shelfpla$orms: These sediments are represented by moderately to well-sorted accumulations of coarse and fine bioclastic sands (e.g. bryozoan-, mollusc-bryozoan or coralline algal sands; P1. 412, 3, 5) with minor amounts of fines and gravels (e.g. molluscan gravel). The sands consist mainly of bioclasts, some micritic peloids and angular, rounded and bored intraclasts (reworked submarine hardgrounds or semilithified carbonate). Ooids are absent. Sedimentary particles are permanently reworked and swept basinward along the slopes, where the grains mix with autochthonous or older particles. Many sediments are a mixture of modem calcareous sands and Pleistocene relict carbonates. Australian case studies demonstrate the occurrence of two major facies zones: Above the zone of winnowing the sediment consists of coarse skeletal harsh and some relict particles. Below, the deposits are muds, rich in planktonic material and some benthics (Nelson et al. 1988, James and von der Borch 1991). Carbonate mud sedimentation occurs on the temperate shelf of southeastern Australia (Blom and Alsop 1988). The calcitic muds are produced by the accumulation and disintegration of nannoplankton, as well as from the biodegradation of skeletal grains accumulating on the sea floor. Many high-latitude carbonate muds are bioerosional and result from maceration of shells (Farrow and Fyfe 1988). Bioerosion down to about 25 m is intensive in the photic zone. Shelly substrate is affected by e.g. clionid sponges, endolithic algae, bivalves, regular echinoids, crabs, fish. Bioerosional products are angular silt- and gravel-sized chips, or mud-sized disintegration products of fecal pellets.

,,

Cool-Water Reefs

41

Case studies in the northern Atlantic underline the great importance of subtidal kelp forests, which harbor a great number of carbonate-secreting and sediientproducing organisms. These forests occur along the wave-exposed flanks of rocky coastal platforms. In contrast, pure coralline red algal gravel deposits ('maerl') develop in more protected parts of the platforms. 'Maerl' is a Breton term, and refers to unattached crust-forming branched or nodular coralline algae and algal gravel, including their widely distributed deposits (Pl. 412). Maerl is one of the most abundant shallow-water carbonates of cool-temperate environments. Modem maerl beds are found throughout the Mediterranean Sea, and are common on temgenous-free Atlantic coasts in depths < 20-30 m, from Norway and Denmark in the north to Portugal in the south, extending to Morocco and Mauretania on the African coast. Maerl deposits have been studied in detail in Brittany, northwestern France (Henrich and Freiwald 1995, Bader 2001), British Islands (Farnham and Jephson 1977), western Ireland (Bosence 1985) and in the Mediterranean Sea. The French term 'corallig2ne' refers to recent coralline algal buildups of the Mediterranean (Bosence 1985). These carbonates occur in intertidal and sublittoral rocky coasts in water depths between about 20 and 160 m; they are represented by reefs formed by corallinacean frameworks. The coralligkne can be considered to be a good recent analog for some Miocene coralline limestones of the Tethyan region that exhibit a very similar generic composition and similar growth forms of red algae.

Skeletal grains: Common bioclasts are bryozoans (Pi. 4/5),foraminifera, molluscs, echinoids and calcareous red, algae. Other organisms include barnacles, serpulids, brachiopods, ahermatypic corals and sponges. The main groups occur in various proportions, depending on the water temperature, salinity, nutrients and grain size of the sediment. Compositional differences allow 'skeletal grain assemblages' characterized by the dominance of particular grain types to be defined (e.g. bryozoans and mollusks = bryomol association occurring on deep shelf banks of the northern Atlantic; P1.4/4), which are indicative of special environmental conditions and particular parts of the shelf (Sect. 12.2.2.1). Non-skeletal grains (peloids, intraclasts) are rare, ooids are absent. Cool-water reefs: Diverse in composition and distribution: Lower slope deep-water reefs ('lithoherms'): Neumann et al. (1977) described elongate coral bioherms in water depths of several hundred meters, that are axially aligned with the flow field of the Florida current. The upcurrent end of the mounds consists of dense thickets of branching ahermatypic corals; the middle and downcurrent sections are rocky, and strongly bioeroded with attached sponges, alcyonarians, gorgonians, and crinoids. Sediments from this zone are a mixture of planktonic foraminifers and pteropods, with skeletal grains from lithoherm organisms. Large amounts of aragonite mud are trapped in the coral thicket at the upcurrent ends of the mounds or in sponge-boring cavities within the lithoherms. The description of these

Table 2.3. Generalized comparison of modem warm-water shallow-marine reefs and cold/cool-water deeper-marine coral reefs.

Sea water temperature range Bathymetrical range Light Zonation patterns Nutrional regime Trophic modes Diversity of coral framework builders Diversity of associated fauna Diversity of associated flora Biological framework stabilization Bioerosional impact Diagenetic impact Interskeletal cementation Intraskeletal cementation Internal sediment Automicrite

Warm and shallow water reefs

Cold and deeper water reefs

20 - 28 "C -50 m Photic zone Windward-leeward Light zonation Oligotrophic Photo- and heterotrophy High High High Coralline Algae High High Very common Very common Very common Common

4 - 12°C 250 m to >1 000 m Aphotic to dysphotic zones Current zonation Taphonomic zonation Eutrophic Heterotrophy Low High Non existent Encrusting sponges High Low Rare Low to common Very common Very common

4 ?.

structures started a fascinating hunt for Holocene and ancient 'deep-water and cold-water reefs' which is still going on. Non-tropical reefs differ significantly from reefs thriving in shallow warm waters (Table 2.3). High-latitudinal reefs are stressed ecosystems whose biota should be able to tolerate low water temperatures as well as sharp seasonal temperature fluctuations, salinity fluctuations and low light influx. Common reef-building organisms are corals, calcareous red algae, bryozoans, bivalves (e.g. oysters), serpulids and tube-constructing sabellarid polychaetes, vermetids, encrusting forarninifera and sponges. Non-tropical reefs comprise coral reefs, coralline algal reefs, sponge-bryozoan reefs, and mollusk reefs. Examples of coralline algal reefs and maerl pavements have been studied on the northern coast of Brittany (France), and the coast of the Troms District in northern Norway (Freiwald et al. 1991; Freiwald and Henrich 1994). Oyster reefs, vermetid reefs and serpulid reefs occur in different parts of the Atlantic Ocean (Milliman 1974). Corals contribute significantly to the formation of large and extended reef-structures in deeper cold-water settings (Lophelia reefs), but also in relatively shallow warm-temperate environments (Cladocora banks of the eastern Mediterranean: Kiihlmann 1996; Taviani et al. 2001). Lophclia reefs: Huge framework reefs built by the azooxanthellate coral Lophelia cover huge areas of the deep and cold eastern Atlantic shelf bottoms (Scottish shelf: Scoffin et al. 1980; Norwegian shelf: Henrich and Freiwald 1995; Freiwald and Wilson 1998; Faroe Island: Frederiksen et al. 1992, see P1.412). The corals are preserved as frameworks or coarse coral rubble. Hovland and Thomsen (1997) discuss possible causal relations between deep-water coral reefs and hydrocarbon seeps.

Cool-Water Carbonates

tions in light regime, seasonal sea ice cover, ice shelves, currents and circulation patterns. The largest open-shelf cold-water carbonate platform in the Arctic is Spitsbergen Bank in the northwestern Barents Sea (Henrich et al. 1996; Pi. 416). The bank corresponds to a >80 000 km2 wide shallow shelf platform bordered by > 400 m deep troughs. Water depths range from less than 25 m to deeper than 120 m. The bank is completely covered by sea ice for 6 months. Melting sea ice causes strong seasonal variations in surface water salinity. The maximum summer temperature is 2 "C on the bank and 4-6 "C in the marginal zone. Another bioclastic carbonate production area is the southwestern Svalbard shelfwhere skeletal carbonate deposition resting on tillites takes place under glaciomarine conditions in depths between 50 and 80 m (Andruleit et al. 1996). Carbonates are produced by (a) barnacles living on kelp forests and forming mobile sands which are transported over the shallow platform, and (b) benthic communities (infaunal bivalves, balanids, hydrozoans, soft corals, sponges, bryozoans) forming buildups on the deep flanks of the platform. The seamount is covered by extensive sponge-bryozoan bioconstructions exhibiting three distinct facies belts depending on variations in down-slope food transfer. Different communities occurring in these belts are biogenic mats with sponge spicules and bryozoan fragments, sponge bryozoan-serpulid buildups, bryozoan thickets, and sponge-crinoid mounds (Henrich et al. 1992). Basic patterns of sediment distribution are coarse, high-energy bioclastic sands consisting of balanids, bivalves and benthic foraminifera on top of the bank and arctic mollusk coquinat glaciomarine gravel lag deposits over the flanks. These carbonates differ from other high-latitude shelf carbonates with or without glaciomarine controls. Postglacial or interglacial carbonate sediments capping older glaciogenic units and not influenced by glaciomarine settings are known from the Scottish shelf, the Norwegian shelf, off Nova Scotia and Newfoundland, and western Canada. Carbonate deposition associated with glaciomarine environments occurs on Antarctic shelves (Domack 1988; Taviani et al. 1993).

Polar carbonates and arctic sponge-bryozoan mounds: Parameters other than the rather stable water temperature control polar carbonates influenced by glacio~narineconditions (Domack 1988;Henrich et al. 1997): the seasonality of light levels (polar night, polar sum- Signijicance of cool-water carbonates: mer), winter sea ice coverage versus summer open po- 1 Quantitative and qualitative data of high-latitude cool-water carbonates are strongly needed in all lar conditions, seasonality in plankton production, and speculations on regional and global carbonate budseasonality in terrigenous sediment discharge by glaciers, meltwater plumes, rivers and release of sea ice gets. sediment (Henrich et al. 1992,1997). The richness and 2 Because the kind of skeletal and non-skeletal grains, facies, carbonate mineralogy and diagenesis vary diversity of benthic organisms are controlled by relawith sea-water temperatures and other factors, the tively constant (low but stable) temperatures, low flucdifferentiation of tropical and non-tropical carbontuations in salinity, low terrestrial input and fluctua-

Basics: Modern Non-Tropical and Polar Carbonates ates is an important tool in reconstructing paleoclimate and paleolatitudes. Classical concepts, based on grain associations e.g. foramol, Sect. 12.2) must be refined, taking into account not only temperature and salinity as major controls on carbonate composition, but also the negative influence of temgenous input as well as the importance of food supply, biogenic interactions e.g. food transfer from seasonal plankton blooms to benthic communities (benthopelagic coupling) and variable oceanic configurations (Betzler 1995). In addition, differentiation between cold-water and tropical carbonates is complicated by the fact that the occurrence and distribution of cold-water carbonates are controlled not only by lateral latitudes but also by the change in warm to cold conditions along downslope profiles (Carannante et al. 1988). These bathymetrically controlled changes may occur at any latitude and need further study. In contrast to modem tropical carbonates, composed predominantly of aragonite and Mg-calcite, many Phanerozoic limestones are formed from calcitedominated carbonates. Modem cold-water carbonates, therefore, may be good analogues for ancient shelf limestones, e.g. from the Paleozoic or Jurassic (James and Bone 1989, 1991; James and von der Borch, 1991; James et al. 1992). Diagenesis and reservoir potential: It is generally assumed that sea-floor and meteoric cementation are very limited in cool-water carbonates as compared with tropical warm-water carbonates. Carbonate minerals are predominantly High-Mg calcite (and minor aragonite) in shallow warm temperate carbonates and High-Mg to Low-Mg calcites in cool temperate carbonates. The mineralogical composition is controlled by water temperatures and water depths. Carbonate saturation of sea water in non-tropical settings is less pronounced or even undersaturated (Opdyke and Wilkinson 1990). Diagenesis, therefore, is predominantly destructive (Alexandersson 1978). Compared to tropical shallow-marine carbonates the diagenetic potential is low and sediments may remain essentially unlithified for a long period of time. Nevertheless, intraskeletal and intergranular carbonate cementation can be common in some temperate and cold-water carbonates (Rao 1996; James et al. 1992, 1994; Henrich and Freiwald 1995). Basics: Modern non-tropical temperate and polar carbonates Andruleit, H., Freiwald, A., Schafer, P. (1996): Bioclastic carbonate sediments on the southwestern Svalbard shelf. Marine Geology, 134, 163-182 Bader, B. (2001): Modem Bryomol-sediments in a cool-wa-

ter, high-energy setting: the inner shelf off Northern Brittany. - Facies, 44,81-104 Bone, Y., James, N.P. (1993): Bryozoans as carbonate sediment producers on the cool-water Lacepede Shelf, southern Australia. - Sed. Geol., 86,247-271 Boreen, T.D., James, N.P. (1993): Holocene sediment dynamics on a cool-water shelf: Otway, southeastern Australia. - J. Sed. Petrol., 63,574-588 Bosence, D.W. (1985): The Coralligene of the Mediterranean - a Recent analog for Tertiary coralline algal limestones.In: Toomey, D.F., Nitecki, M.H. (eds.): Paleoalgology. 215-225, Berlin (Springer) Briggs, J.C. (1974): Marine zoogeography. - 475 pp., New York (McGrawHill) Cairns, S.D., Stanley, G.D. (1981):Ahermatypic coral banks: living and fossil counterparts. - Proc. 4th Int. Coral Reef Symp. Manila, 1,611-618 Colantoni, P., Cremona, G., Ligi, M., Borsetti ,A.M. , Cate, F. (1985):The Adventure Bank (off Southwestern Sicily): a present day example of carbonate shelf sedimentation. Giorn. Geol. Ser. 3,47, 165-180 Domack, E.W. (1988): Biogenic facies in the Antarctic glacimarine environment: basis for a polar glacimarine summary. - Palaeogeogr., Palaeoclimat., Palaeoecol., 63,357372 Farrow, G.E., Fyfe, J.A. (1988): Bioerosion and carbonate mud production on high-latitude shelves. - In: Nelson, C.S. (ed.): Non-tropical shelf carbonates - modem and ancient. - Sed. Geol., 60,281-297 Fomos, J.J., Forteza, V., Jaume, C., Martinez-Tabemer, A. (1992):Present-day Halimeda carbonate sediments in temperate Mediterranean embayments: Fornells, Balearic Islands. - Sed. Geol., 75,283-293 Freiwald, A. (1993): Coralline algal maerl frameworks - islands within the phaeophytic kelp belt. - Facies, 29, 133148 Freiwald, A. (1998a): Geobiology of Lopheliapertusa in the North Atlantic. - Habilitation Thesis University Bremen, 194 pp. Freiwald, A. (1998b): Modem nearshore cold-temperate calcareous sediments in the Troms District, Northern Norway. - J. Sed. Research, A68,763-776 Freiwald,A., H e ~ c hR., (1994):Reefal coralline algal buildups within the Arctic Circle: morphology and sedimentary dynamics under extreme environmental seasonality. - Sedimentology, 41,963-984 Freiwald, A., Henrich, R., Patzold, J. (1997): Anatomy of a deep-water coral reef mound from the Stjemsund, West Finnmark, Northern Norway. - In: James, N.P., Clarke, J.A.D. (eds.):Cool-water carbonates. - Soc. Econ. Paleont. Min., Spec. Publ., 56, 141-162 Freiwald,A., Henrich, R., Schafer, P., Willkomm, H. (1991): The significance of high-boreal to subarctic maerl deposits in Northern Norway to reconstruct Holocene climatic changes and sea level oscillations. - Facies, 25,315-340 Freiwald, A., Wilson, J.B. (1998): Taphonomy of modem deep, cold-temperate water coral reefs. - Historical Biology, 13, 37-52 Gillespie,J.L., Nelson, C.S. (1997): Mixed siliciclastic-skeleta1 carbonate facies on Wanganui Shelf, New Zealand: a contributionto the temperate carbonate model. -In: James, N.P., Clarke, J.A.D. (eds.): Cool-water carbonates. - Soc. Econ. Paleont. Min., Spec. Publ., 56, 127-140 Halfar, J., Godinez-Orta, L., Ingle, J.C. (2000): Microfacies

44

Modern Non-Tropical Cool-Water Carbonates

Plate 4 Modern Non-Tropical Cool-Water Carbonates: High-Latitudinal Temperate and Polar Shelf and Reef Carbonates from the Northern Atlantic Marine carbonate production is by no means restricted to tropical warm-water environments. Abundant and widespread biogenic carbonate production occurs in non-tropical, mid- and high-latitudinal temperate and coolwater settings with low or missing clastic input, and even in cold water beyond the Arctic Circle. Examples are known from the southern and northern hemispheres. Cool-water carbonates record climatic and paleoceanographic information in their sedimentary deposits and architectures. Microfacies and sedimentary architecture of ancient cool-water carbonates provide basic data for the evaluation of paleoclimate and paleolatitudes. Modem coolwater carbonates are good analogues for limestones formed in calcite-dominated Phanerozoic seas. Widely extended carbonate deposits and even reefal frameworks occur in Subarctic and Arctic seas. Most sediments are bioclastic sands and gravels, formed by balanids, mollusks, foraminifera and coralline red algae. Many of these organisms are epibionts, living on benthic macroalgae which form extended kelp forests in nearshore environments. Kelp and coralline algae are adapted to seasonal climatic perturbations. On the Spitsbergen Bank, the largest open-shelf cold-water carbonate platfonn of the Arctic region, the carbonate production is centered around two main factories: (a) barnacle sands, produced within kelp forests growing on the shallowest part of the platform and transported over the platform, and (b) high biogenic production by infaunal bivalves (-> 6) as well as balanid-hydrozoan-soft coral-sponge-bryozoan buildups on the flanks of the platform (Henrich et al. 1997). Marked differences in the composition of bioclastic grain associations reflect specific environmental conditions on the shelf bottoms; these 'grain association patterns' are powerful indications of the climatic, oceanographic and latitudinal controls of ancient cool-water limestones (see Sect. 12.2). Recognizing reefs in deep, aphotic zones is highly important for interpreting ancient analogues. Different reef types are formed by corals, coralline red algae (-> I), siliceous sponges, bryozoans, and mollusks. These organisms, living in stressed ecosystems, are able to tolerate low watef temperatures, and seasonal fluctuations of light intensity, nutrient availability and salinity. Spectacular reef mounds built by the azooxanthellate coral Lophelia (-> 3) originate at present in eastern Atlantic Ocean of northwestern Europe, at the west Florida and the Bahama Bank slopes, the southeastern Brazilian continental slopes and on eastern Pacific seamounts. Azooxanthellate deep-water corals have the potential to construct large, biologically zoned framework-supported reef mounds below the storm wave base in the aphotic zone (Freiwald 1997). The coral reefs of the Nordic Seas in water depths between 200 and 1200 m can be followed tens of kilometers at lengths and widths of several hundreds of meters. 1 Coralline red algal reef: The reefal framework covers about 125 000 square meters and grows in water depths of 6 to 16 m. Litlzothamnion cf. glaciale is one of the most common framework builders. Note the high density of branching common in turbulent waters. The branches are a prominent source for the producrion of algal gravels and rhodoliths deposited onshore and offshore and producing rhodolith pavements. Troms District, Northern Norway. 2 Near-coast coralline algal gravel ('maerl') facies. Multiple fragmentation of branched rhodoliths caused by storms result in the formation of algal fragment accumulations. The maerl, a mixture of carbonate (skeletal) sand and seaweed is used as agricultural fertilizer. It characterizes cool-water temperate sediments, composed of unattached crusted-forming branched or nodular algae and algal gravel. In turbid, high-energy waters of the cool-temperate northwestern European Atlantic, maerl occurs mostly in the photic zone of wave-protected coasts at depths of 1-10 m (Freiwald et al. 1991). In the warmtemperate Mediterranean Sea, maerl is common in depths down to 40 m. Water depth 5 m. Troms District, Norway. 3 Azooxanthellate reef-forming deep-water coral (Lophelia pertusa). Azooxanthellate corals harbour no photosynthetic symbionts. The corals feed on suspended particles which are seasonally generated in the high-productivity euphotic zone. The corallites of Lophelia exhibit strong variations in the branching pattern, the shape and thickness of corallites, the diameter and the intratentacular budding patterns. These variations support the framebuilding potential of the anastomosing coral. Faroe Island Shelf. Water depth 252 m. 4 Open-shelf skeletal carbonate sediment composed of mollusks, bryozoans and serpulids. Malangsgrumen Bank, off Troms, northern Norway. Water depth 95 m. 5 Selected bioclasts (1-2 mm fraction) of the open-shelf skeletal carbonate shown in Fig. 4. Most bioclasts are bryozoans. The facies corresponds to the 'bryomol grain association' (see PI. 106/2,3) which is common on modem cool-temperate shelves. Water depth 90 m. Malangsgrumen Bank, off Tromso, northern Norway. 6 Arctic-benthic carbonate deposits of the seasonally sea ice-covered Spitsbergenbank (73'30' N and 9'10' W), western Barents Sea. Coquina-gravel lag deposit colonized by abundant bivalves (Mya truncata, - M , note the cylindrical siphones, arrow; Chlamys islandica - C), echinoids (E), hydrozoans, soft corals, balanids, sponges, bryozoans - B) attributed to the initiation of small-scale mounds. The high density of in situ organisms is due to a permanent high productivity zone at the boundary of Atlantic and Arctic surface waters over the flanks of the Spitsbergenbank. Water depth 79 m. -> 1-5: Courtesy of A. Freiwald (Erlangen), 6: Freiwald et al. 1991

Plate 4: Modern Cool-Water Carbonates

45

Deep-Marine Environments analysis of recent carbonate environments in the Southem Gulf of California, Mexico - a model for warrn-temperature to subtropical carbonate formation. - Palaios, 15, 323-342 Henrich, R., Freiwald, A., Schkfer, P. (1997): Evolution of an Arctic open-shelf carbonate platform, Spitsbergen Bank (Barents Sea). - In: James, N.P., Clarke, J.A.D. (eds.): Cool-water carbonates. - Soc. Econ. Paleont. Min., Spec. Publ., 56, 163-181 Henrich, R., Freiwald, A., Wehrmann, A., Schafer, P., Samtleben, C., Zankl, H. (1996): Nordic cold-water carbonates: Occurrences and controls. - GottingerArb. Geol. Palaont., Sonderband, 2, 35-52 Henrich, R., Hartrnann, M., Reitner, J., Schafer, P., Freiwald, A., Steinmetz, S., Dietrich, P., Thiede, J. (1992): Facies belts and communities of the arctic Vestrisbanken Seamount (Central Greenland Sea). - Facies, 27,71-104 James, N.P. (1997): The cool-water carbonate depositional realm. - In: James, N.P., Clarke, J.A.D. (eds.): Cool-water carbonates. - Soc. Econ. Paleont. Min., Spec. Publ., 56, 1-20 James, N.P., Bone, Y. (1989): Petrogenesis of Cenozoic, temperate water calcarenites, South Australia: a model for meteoric/shallow burial diagenesis of shallow water calcite sediments. - J. Sed. Petrol., 59, 191-204 James, N.P., Clarke, A.D. (eds., 1997): Cool-water carbonates. - Soc. Econ. Paleont. Min., Spec. Publ., 56,440 pp. James, N., Collins, L.B., Bone, Y., Hallock, P. (1999): Subtropical carbonates in a temperate realm: modem sediments on the southwest Australian shelf. - J. Sed. Petrol., 69,1297-1321 Lees, A. (1975): Possible influences of salinity and temperature on modem shelf carbonate sedimentation. - Marine Geol., 19, 159-198 Lees, A., Buller, A.T. (1972): Modem temperate-water and warm-water shelf carbonate sediments contrasted. - Marine Geol., 13, M67-M73 Macintyre, I.G. (1988): Modem coral reefs of western Atlantic: new geological perspective. -Amer. Ass. Petrol. Geol. Bull., 72, 1360-1369 Messing, C.G., Neumann, A.C., Lang, J.C. (1990): Biozonation of deep-water lithoherms and associated hardgrounds in the northeastern Straits of Florida. - Palaios, 5, 15-33 Mullins, H.T. (198 1): Modem deep-water coral mounds north of Little Baharna Bank: criteria for recognition of deepwater coral biohems in the rock record. - J. Sed. Petrol., 51,999-1013 Nelson, C.S. (1988): An introductory perspective on nontropical shelf carbonates. - Sed. Geol., 60, 3-12 Nelson, C.S., Bornhold, B.D. (1983):Temperate skeletal carbonate sediments on Scott Shelf, northwestern Vancouver Island, Canada. - Marine Geol., 52,24 1-266 Nelson, C.S., Keane, S.L., Head, P.S. (1988): Non-tropical carbonate deposits on the modem New Zealand shelf. In: Nelson, C.S. (ed.):Non-tropical shelf carbonates - modem and ancient. - Sed. Geol., 60,7 1-94, Neumann, A.C., Kofoed, J.W. , Keller, G.H. (1977): Lithotherms in the Straits of Florida. -Geology, 5,4-10 Rao, C.P. (1996): Modem carbonates, tropical, temperate, polar. Introduction to sedimentology and geochemistry. 206 pp., Howrah (Univ. Tasmania) Rao, C.P. (1997): A colour illustrated guide to sedimentary textures, cold, cool, warm, hot; An introduction to the interpretation of depositional, diagenetic and hydrothermal

temperatures. - 128 pp., Howrah, Tasmania (Rao, C.P.) Rao, C.P. (1999): Cold water polar aragoniticbivalve elemental composition,east Antarctica.-Carbonates and Evaporites, 14,56-63 Schafer, P., Henrich, R., Zankl, H., Bader, B. (1996): Carbonate production and depositional patterns of Bryomolcarbonates on deep shelf banks in mid and high northem latitudes. - Gijttinger Arb. Geol. Palaont., Sonderband, 2, 101-110 Scoffin, T.P., Bowes, G.E. (1988): The facies distribution of carbonate sediments on Porcupine Bank, northeast Atlantic. -In: Nelson, C.S. (ed.): Non-tropical shelf carbonates - modem and ancient. - Sed. Geol., 60, 125-134 Smith, A.M. (1988): Preliminary steps toward formation of a generalized budget for cold-water carbonates. -In: Nelson, C.S. (ed.): Non-tropical shelf carbonates - modem and ancient. - Sed. Geol., 60,323-33 1 Smith, A.M., Nelson, C.S., Spencer, H.G. (1998): Skeletal carbonate mineralogy of New Zealand bryozoans. - Marine Geol., 151,27-46 Teichert,C. (1958): Cold- and deep-water coral banks. -Bull. Amer. Ass. Petrol. Geol., 42, 1064-1082 Walther, J. (1910): Die Sedimente der Taubenbank im Golf von Neapel. - Preuss. Akad. Wiss., phys.-math. Kl., Anhang Abh. 3,1910,49 pp. Further reading: K021, K210 (glacial carbonates)

2.4.5 Deep-Marine Environments 2.4.5.1 Settings Oceanic deep-marine settings beyond the shelf break bordering pericontinental shelves include the slope, the base-of-slope and continental rise, the abyssal plains, mid-oceanic ridges, oceanic rises and volcanic seamounts, as well as deep-sea trenches. Deep-marine environments, however, also comprise parts of the deeper areas of peri- and epicontinental open shelves and of outer ramps, lying below the storm wave water base, and below the lower boundary of the well-lit zone. The bottom of the modem oceans comprises three bathymetrically defined zones (Fig. 2.2;Box 2.6). The bathyal zone lies to the seaward of the shallower subtidal shelf zone and landward of the deeper abyssal zone. The upper limit is marked by the edge of the continental shelf. The abyssal zone seaward of the bathyal zone covers approximately 75% of the total ocean floor. It pertains the nearly flat deep-sea plains. Abyssal plains are usually covered by thin deposits of pelagic ooze or distal turbidites. The lower limit of the zone is bathymetrically only loosely defined. The deepest area of the sea bottom, the hadal zone, lies specifically within the deep-sea trenches below the general level of the abyssal zone, in depths between >6 000 and more than 10 000 m. These marginal trenches are narrow, steepsided troughs running parallel to continental margins at seaward base of a continental platform.

Sedimentation Processes

NNNNNNNUNHNUNNNNNNNNNNNNN

CaC03

0ce

Reropods Foraminifera Coccolidhophores

an Radiolaria

Si02

--

Diatoms

7

Calcite compensation depth

*

In contrast to modem oceanic basins, many basins found in the geological record occur in cratonic positions and represent intra-platform or intra-shelf basins (e.g. pelagic epeiric basins). Note that the term basin as used by carbonate sedimentologists does not necessarily imply that carbonate basins are analogous to deep oceanic basins. Carbonate basins generally lie well above abyssal depth, commonly less than a few hundred meters below sea level. 2.4.5.2

Fig. 2.11. Sources and pathways of modern deep-sea sediments, deposited in tropical, temperate and boreal (polar) zones. Note that only the radiolarian oozes have a fossil record starting in the Paleozoic. Coccoliths (planktonic algae) and planktonic globigerinid foraminifera have become essential constituents of deep-sea sediments since the Cretaceous. The fossil record of deep-sea carbonates formed by pteropods (gastropods adapted to pelagic life) is scanty and limited to the Tertiary and Pleistocene (Buccheri et al. 1980). The earliest records of diatoms (siliceous algae) date from the Middle Cretaceous, but the group did not become important as sediment builders before the Tertiary. Modified from Hay (1974).

Sedimentation Processes

ooze, sediments derived from shallow-marine sources and deposited on slopes and basins, deep-sea clays and volcanic material, and glacial-marine sediments produced by ice-rafting (Fig. 2.1 1). The basic classification of deep-marine sediments considers grain size and composition. Currently used compositional classifications were developed by scientists participating in the DSDP and ODP programs (Berger 1974; Kennett 1982).

2.4.5.3

Pelagic Sedimentation

Biogenic deep-sea sediments are formed by the remains of pelagic organisms contributing to the formation of carbonate or siliceous oozes and muds. The term 'pelagic' means 'of the open sea' and refers to marine nektonic or planktonic organisms whose environment commonly is the open ocean. Large terrigenous sediment input and submarine volcanism cause mixtures of biogenic material and temgenous clays resulting in the formation of fine-grained muddy, 'hemipelagic sediments'. The character of the biogenic sediment depends on the supply of the biogenic material, the dissolution at and near the sea-bottom and in the water column, the dilution of the sediment by non-biogenic components, and alterations during diagenesis: The supply depends on the fertility of the pelagic organisms, which in turn Modem deep-sea deposits comprise biogenic sedi- is related to the availability of nutrients. Both nutrients ments including pelagic siliceous oozes and carbonate and sunlight control the primary production. The dis-

Sedimentation in the deep sea is controlled by four major processes (Cook and Mullins 1983; Cook et al. 1983; Enos and Moore 1983; Pickering et al. 1986; Stow 1985, 1986): (1) settling of marine pelagic and windblown material from the water column, (2) bottom transport by gravity flows including turbidity currents, debris flows, grain flows, and slumping, (3) redeposition of the sediment by geostrophic bottom currents including contour currents, and (4) chemical and biochemical precipitation on the sea floor. The first process is responsible for the deposition of pelagic sediments, the second one for the formation of a broad spectrum of resediments.

48

Glossary for Deep-Water Carbonates

Box 2.6. Glossary of terms used to describe deep-water carbonates Abyssal plains: Area of deep sea bottom below 2000 m and between 4000 and 6000 m, including the nearly flat deepsea plains covered by sediment. Accretionary slope: Adepositional slope, less steep than by-pass slopes. Characterized by net accumulation of sediments. Aragonite compensation depth (ACD): Level in the oceans where aragonite is dissolved. The bathymetrical position of the ACD and the CCD depends on the fertility of the surface waters and the degree of undersaturation of deep waters. Aseismic volcanic ridges: Volcanic seamounts, ridges and plateau, rising several kilometers above the deep ocean floor. Base-of-slope: The lower or lowermost part of slopes, continental rise. Bathyal: Sea bottom between about 200 (continental shelf edge, shelf break) and 2000 (4000) m, encompassing the continental slope and continental rise, down to the deep sea.. Bypass slope: Slopes on which sediment is transported from shallow to deeper water without significant deposition on the slope. Calcite compensation depth (CCD): The level in the deep oceans where the rate of dissolution of calcium carbonate (calcite) balances the rate of deposition and below which carbonate-free sediments accumulate. The level is characterized by a transition from carbonate ooze ro deep-marine clay or siliceous ooze. Today, the CCD has a mean depth of about 4.5 km, but varies between ocean basins. Note that large shifts of up to several thousand of meters of the CCD have occurred during the Meso- and Cenozoic. Chalk: Fine-grained porous carbonate rock, predominantly composed of pelagic nanno- and microfossils, and deposited on deeper shelves and basins. Continental rise: Setting at the foot of the continental slope between the slope and the deep ocean basin, characterized by a gently sloping surface created by coalescing submarine fans. Sedimentation takes place by downward sediment transport and deposition at the slope base. The continental rise may be subdivided by submarine canyons and deepsea channels. Contourite: Sediment deposited on the continental rise by contour-following bottom currents. Debris flow: A sediment gravity flow. Sediment transport by a cohesive matrix. Corresponds to mudflow. Erosional slope: A steep slope. Net sediment loss. Erosion due to rockfalls, sediment gravity flows and the effect of contour currents. Grain flow: A sediment gravity flow. Grains are supported during the sediment transport by dispersive pressure arising from grain collisions. Gravity flows: Downslope flow of sediment. Comprises turbidites, grains flows, and debris flows. Guyot: A type of seamount with a platform top. Hadal: Deepest area of sea bottom, lying specifically within the deep-sea trenches below the general level of the abyssal zone, between 6000 and > 10,000 m. Hemipelagic sediments: Fine-grained muddy sediment consisting of a mixture of calcareous biogenic material and tenigenous clay. More than 25% of the fraction coarser than 5 pm is of temgenous or volcanic origln. The sediment has undergone lateral transport. Deposited near continental margins, on slopes, abyssal plains, and ridges. Lysocline: The level or ocean depth at which the rate of dissolution of calcium carbonate just exceeds its combined rate of deposition and precipitation. The lysocline is characterized by a noticeable decrease in the percentage of deepmarine carbonate sediments and by an interval separating well-preserved from poorly preserved microfossil assemblages. The calcite lysocline is defined by planktonic foraminifera and calcareous nannofossils, the aragonite lysocline by pteropods. Oceanic basin: Comprises various deep-sea settings including abyssal plains, volcanic hills, mid-oceanic ridges and deep-sea trenches. Oceanic plateau: Topographically high area of the ocean floor that rises to within 2-3 km of the sea floor surface above the abyssal floor. Many Pacific plateaus are covered by carbonate ooze overlying volcanic rocks. Pelagic carbonates: Fine-grained calcareous sediments of the open sea, composed chiefly of the skeletal debris of calcareous planktonic organisms, and deposited in a range of deep-water settings (slopes, ocean floor, seamounts, mid-oceanic ridges). Periplatform sediments: Intermixed platform-derived sediments and pelagic carbonate muds (Schlager and James 1978). 1 Resedimented carbonates: Carbonate rocks characterized by redeposition of shallow-water carbonate sediment into deep water. Submarine mass transport and redeposition is related to a variety of processes, including rockfalls, slides, slumps, and gravity flows. Resedimented carbonates may be additionally reworked by deep-marine bottom currents. Rockfalls: Single blocks or many clasts derived from steep slopes of the shelf margins and deposited in talus piles at the base of slopes or as blocks on the slopes. Abundant along fault-bounded platform margins and along fore-reef slopes. Seamount: Elevation of the sea floor, 1000 m or higher, flat-topped (Guyot) or peaked. Slope: Surface which connects the shelf or the shelf break with the continental rise or the deep-sea floor. Turbidite: A sediment laid down by a turbidity current. Characterized by graded bedding, moderate sorting and a vertical sequence of distinct sedimentary structures. Turbidity currents are initiated by the disturbance of the sediment near the shelf margin or on the slope; deposit originally shallow-water sediments on the slope, at the foot of the slope and on abyssal plains. Limestone turbidites are called 'calciturbidites' or 'allodapic limestones'.

I

1

l

Resedimentation

tribution of pelagic sediments on the sea bottoms is controlled by the different dissolution of biogenic grains, produced in the surface waters of the oceans. Most dissolution of siliceous tests (radiolaria, diatoms) occurs in highly silica-undersaturated shallow surface waters. In contrast, most dissolution of carbonate tests takes place on the sea floor as bottom waters become more undersaturated in calcium carbonate. Therefore, siliceous biogenic sediments reflect the biological fertility of the surface waters, whereas carbonate biogenic deep-sea sediments chiefly reflect the preservation potential of carbonate at various depths. The proportions of siliceous and carbonate-rich oozes depend on bottom-water circulation which controls both dissolution pattems, and, through upwelling, fertility pattems (Berger 1970,1974,1976).Differences in the composition of pelagic calcareous plankton reflect differences in oligotrophic, mesotrophic and eutrophic nutrient environments (Henrich et al. 2001).

2.4.5.4 Resedimentation ('Allochthonous Carbonates')

2.4.5.5 Carbonate Plankton and Carbonate Oozes Carbonate oozes cover about 50% of the modem ocean floor. They are deposited on deep-sea plains, submarine rises, ridges and plateaus. Modem carbonate oozes consisting of the shells of minute drifting planktonic organisms comprise foraminifera1 ooze, namofossil ooze and pteropod ooze: Foraminifera1 oozes are dominated by tests of sand-sized planktonic foraminifera (Pl. 73/10) occurring within carbonate mud consisting of calcareous namofossils. Nannofossil oozes or coccolith oozes are very fine-grained muds composed predominantly of remains of planktonic algae (Chrysophyta: Coccolithophorida; P1. 713-5). Pteropod oozes are restricted o shallow tropical areas in depths < 3 000 m. They consist of aragonitic shells of planktonic gastropods (pteropods and heteropods). The carbonate production is greatest in surface waters with high biological productivity caused by upwelling. Production and growh rates of pelagic foraminifera and coccolithophorids are differnt.

Plankton contributes to the sedimentary record by (1) settling of individual tests, (2) fecal pelletization, Downslope gravity transport along deep-marine slopes and (3) the deposition of various biogenic materials (inoccurs by various processes including rockfall, slump- cluding 'marine snow', aggregates, flocks and particuing, sliding, and sediment gravity flows. late organic matter, POM). Individual settling may play Subaqueous rockfalls occur in areas with very steep a role in the deposition of larger microfossils (e.g. foratopography producing talus and scree deposits at the minifera, radiolarians), but fecal pelletization and seabase of slopes. sonally varying sinks of detrital aggregates (e.g. phyA slump is a downslope translocation of a sediment todetritus displaying an important food resource in the parcel along discrete shear planes. In slides, large blocks deep sea, Thiel et al. 1988) play the greatest role in the move on only a few slippage planes. Both slumping transportation of smaller tests (e.g. coccolithophorids; and sliding are controlled and triggered by high rates Honjo 1976). of sedimentation creating oversteep slopes and differential compaction, structural changes (e.g. effect of salt -> A cautionary note: Comparable calcareous plankdomes) as well as by earthquakes. In sediment gravity ton is not known from pre-Mesozoic records and comflows, the sediment is transported downwards under parisons with modem analogues work for pelagic Methe influence of gravity. sozoic-Tertiary carbonates, but not for Paleozoic slope The sediments are transported by different mecha- and basin carbonates (see Sect.15.8). nisms: In 'grain flows', the sediment is supported during transport by direct grain to grain interactions. In 'debris flows' larger grains are supported by a matrix 2.4.5.6 Preservation Potential and Dissolution consisting of a mixture of fine sediment and interstitial Levels fluid. In 'turbidity currents', the sediment is supported In modem oeans carbonate sediments are largely mainly by the upward component of fluid turbulence. absent below depth of about 4500 m. High hydrostatic The resulting deposits differ in grain size, sorting, tex- pressure, low water temperature and high partial presture and sedimentary structures. Because turbidity cur- sure of C02 lead to dissolution and significant diferrents are episodic, the resulting turbidites are interbed- ences in the carbonate preservation potential of deepded with finer pelagic sediments representing the back- sa sediments. These differences have been used to disground sedimentation. tinguish two levels:

50

(1 ) The lysocline, defined as the depth that separates well-preserved from poorly preserved planktonic assemblages and where a noticeable decrease in the percentage of carbonate occurs. Because calcareous microfossils dissolve at different rates, three types of lysoclines are used: the pteropod or aragonite lysocline (ALy), defining significant dissolution of aragonite material occurring in relatively shallow depths; and the foraminifera1lysocline and the coccolith lysocline (calcite lysocline, CLy), defining the significant dissolution of calcite material in greater water depths. (2) The calcite compensation depth (CCD) is defined as the depths at which calcite microfossils and carbonate arelargely absent. The depth of the CCD in modem oceans varies between about 4 200 and 5 400 m, with a mean depth of about 4500 m. At that level, the rate of dissolution balances the rate of accumulation. -> A cautionary note: The depth position of the CCD in Phanerozoic oceans has varied during geological time owing to fluctuations in the amount of carbonate being brought into the oceans from the land, variations in hydrothermal activity, or increased carbonate production on the shelves. Because the calcareous tests of planktonic organisms differ in dissolution susceptibilities, dissolution types can be used to record steps in the formation of diagenetic patterns. Present-day foraminifera species exhibit a dissolution ranking that is strongly controlled by the thickness, size and shape of the tests. Most coccoliths are more resistant than foraminifera with regard to dissolution. First evidence of coccolith dissolution occurs in depths above 3000 m, but changes in the composition of the assemblages become evident in depths between 3000 and about 5000 m.

2.4.5.7 Carbonate Slopes, Periplatform Carbonates and Carbonate Aprons Gravity flows, particularly turidites and debris flow deposits, are common on carbonate slopes, and also occur in basins (Cook et al. 1983; McIlreaii992). These sediments are derived from shallow-water platform and platform-edge settings, sometimes also from the upper slope, and transported to upper, mid and lower slope settings. Carbonate slopes were categorized as: (1) 'by-pass slopes' on which sediment is transported from shallower to deeper water without significant deposition on the slope: gravity flows bypass the slopes nd accumulate in adjacent basins. (2) less steep 'depositional or accretionary slopes' where gravity flow sediments are predominantly deposited in lower slope settings, as dem-

Basics: Deep-Marine Carbonates

onstrated by excellent examples from the Holocene Bahamian slopes. The resulting fine-grained 'periplatform carbonates' (Schlager and James 1978; Boardman and Neumann 1984; Boardman et al. 1986; Pilskaln et al. 1989) form a sequence of resedimented shallow-marine carbonates intercalated within pelagic carbonates. The Bahamian carbonate slopes (Straits of Florida, Little Bahama Bank) offer the possibility of studying the interplay between allochthonous and pelagic sedimentation, and submarine cementation, resulting in the formation of hardgrounds. The periplatform ooze of the upper slope consists of a mixture of bankderived material and pelagic debris. Lower slope and base-of-slope seiments are turbidites and mud- or grain-suported debris flow deposits, interbedded with periplatform ooze, and forming large carbonate aprons. Cyclic variations in the prevailing mineralogy (aragonitic and Mg-calcitic platform-derived grains vs calcitic pelagic grains) of periplatform carbonates and differences in the abundance of platform-derived and pelagic carbonates signalize climate changes, sea-level fluctuations and changes in the rate of carbonate production on the platforms which are reflected by microfacies analysis (Sect. 16.1). Another promising approach of microfacies studies is the evaluation of the controls on the different declivities of carbonate slopes which depends greatly on the primary depositional texture. Basics: Deep-marine carbonates Berger, W.H. (1991): Produktivitat des Ozeans aus geologischer Sicht: Denkmodelle und Beispiele. - Zeitschrift der deutschen geologischen Gesellschaft, 142, 149-178 Cook, E., Enos, P. (eds., 1977): Deep water carbonate environments. - Soc. Econ. Palwnt. MUI.Spec. Publ., 25,336 pp. Cook, H.E., Hine, A.C., Mullins, H.T. (1983): Platform margin and deep water carbonates. - Soc. Econ. Paleont. Min. Short Course, 12,563 pp. Cook, H.E., Mullins, H.T. (1983): Basin margin environment. -In: Scholle, P.A., Bebout, D.G., Moore, C.H.(eds.): Carbonate depositional environments. - Amer. Ass. Petrol. Geol. Mem., 33,539-617 Coniglio, M., Dix, G.R. (1992): Carbonates slopes. - In: Walker, R.G., James, N.P. (eds.): Facies models. Response to sea level change. - 349-373, Ottawa (Geol. Ass. Canada) Crevello, P.D., Harris, P.M. (1985): Deep water carbonates: buildups, turbidites, debris flows and chalks. -Soc. Econ. Paleont. Min. Core Workshop, 6,527 pp. Doyle, L.J., Pilkey, O.H. (eds., 1979): Geology of continental slopes. - Soc. Econ. Paleont. Min. Spec. hbl., 27,374 pp. Enos, P., Moore, C.H. (1983): Fore-reef slope environment. -In: Scholle, P.A., Bebout, D.G., Moore,C.H. (eds.): Carbonate depositional environments. - Amer. Ass. Petrol. Geol. Mem., 33,507-537 Hsii, K.J., Jenkyns, H.C. (eds., 1974): Pelagic sediments: on land and under the sea. -Spec. Publ. Int. Ass. Sedimentol., 1,447 pp.

Seep and Vent Carbonates Leggett, J.K. (1985): Deep-sea pelagic sediments and palaeooceanography: a review of recent progress. -In: Brenchley, P., Williams, B.P.J. (eds.): Sedimentology, recent developments and applied aspects. -95-118, Oxford (Blackwell) Little C.T.S., Campbell, K.A., Herrington, R.J. (2002): Why did ancient chemosynthetic seep and vent assemblages occur in shallower water than they do today? Comment. Int. J. Earth Sciences, 91, 149-153 Macilreath, LA., James, N.P. (1979): Facies models. Carbonate slopes. - Geosci. Canada Reprint Ser., 5, 189-199 Milliman, J.D., Droxler, A.W. (1996): Neritic and pelagic carbonate sedimentation in the marine environment: ignorance is not bliss. - Geol. Rundschau, 85,496-504 Mullins, H.T. (1986): Periplatform carbonates. - Colorado School Mines Quart., 81,63 pp. Mullins, H.T., Cook, H.E. (1986): Carbonate apron models: alternatives to the submarine fan model for paleoenvironmental analysis and hydrocarbonexploration. - Sed. Geol., 48,37-79 Oxburgh, R., Broecker, W.S. (1993): Pacific carbonate dissolution revisited. - Palaeogeogr., Palaeoclimat., Palaeoecol., 103,31-39 Schlager, W., Chermak, A. (1979): Sediment facies of platform-basin transition, Tongue of the Ocean, Bahamas. Soc. Econ. Paleont. Min. Spec. Publ., 27, 193-208 Schlager, W., Camber, 0.(1986): Submarine slope angles, drowning unconformities, an self-erosion of limestone escarpments. - Geology, 14,762-765 Schlanger, S.O., Douglas, R.G. (1974): Pelagic ooze-chalklimestone transition and its implicationsfor marine stratigraphy. -Spec. Publ. Int. Ass. Sedimentol., 1, 117-148 Shanrnugarn, G. (2000): 50 years of the turbidite paradigm (1950s - 1990s): deep-water processes and facies models a critical perspective. - Marine Petroleum Geol., 17, 285342 Stow, D.A.V., FaugCres, J.C. (eds., 1998): Contourites, turbidites and process interaction. - Sed. Geol., 115, 1-386 Westphal, H., Reijmer, J.J.G., Head, M.J. (1999): Sedimentary input and diagenesis on a carbonate slope (Bahamas): response to morphologic evolution of the carbonate platform and sea-level fluctuations.- In: Harris, P.M., Saller, A.H., Simo, J.A.T. (eds.): Advances in carbonate sequence stratigraphy: application to reservoirs, outcrops, and models.- Soc. Econ. Paleont. Min. Spec. Publ., 63,247-274 Further reading: K022, K023, KO24

Kemish 1993). The very first vent site with sea-bed dwelling large benthic organisms was discovered 1977 on the Galapagos rift in the eastern Pacific, where hydrothermal vent organisms are associated with sulfide mineralizations and surround black and white smokers within an area of a few hundreds of square meters. Today, examples of seep and vent communities are known from the Pacific (Fig. 2.12), the Monterey Bay of Califomia, the Gulf of Mexico, the continental slope off Louisiana, the North Sea and the Black Sea (Nybakken 1993). Modem cold-seep communities are nearly always found in oligotroph waters of the aphotic zone, and occur from shallow to deep water down to about 3000 m (Callender and Powell 1999, Little et al. 2002). The success of the low-diversity vent communities (consisting of bivalves, vestimentiferan tube-worms, arthropods) depends on specialized anaerobic bacteria, which build carbon molecules using reduced inorganic compounds (particularly sulfides) that are contained in the heated water gushing from the vents. The low-diversity vent communities depend on these endosymbiontic bacteria. Bivalves (giant vesicomyid clams, infaunal lucinids) are able to exploit directly gas seepage by hosting chemoautotrophic bacteria in symbiosis in the gills. The symbionts produce organic matter via chemosynthesis using methane or sulfur from vented fluids or available in the environment. Hydrothermal vent communities and cold seep communities are phylogenetically related and show similarities in the physiology and anatomy of their dominant organisms.

2.4.6 Seep and Vent Carbonates

Cold-seep communities contribute to the formation of a specific carbonate rock type. Characteristics of these limestones are (1) carbonate beds embedded in shales or mounds exhibiting irregular textures, and occurring within a strongly differing facies, (2) low-diversity but abundant mollusks, and (3) abundant authigenic carbonate cements. Ancient vent and seep carbonates are becoming increasingly more frequently reported from the Phanerozoic rock record (see Sect. 16.5).

One of the most exciting discoveries in the last twenty years is the recognition of authigenic and biogenic carbonates formed in deep-water settings by fluid and gas expulsions near cold seeps and hydrothermal vents (Beauchamp and von Bitter 1992). Biomass concentrations of organisms with calcareous shells occur near hot hydrothermal vents on midocean ridges and cluster around cold seeps of natural gas, brines, hydrocarbon and methane in varying depths of the oceans, particularly within faulted continental margin environments (Tunnicliffe 1992; Lutz and

Basics: Seep and vent carbonates Aharon, P. (2000): Microbial processes and products fueled by hydrocarbons at submarine seeps. - In: Riding, R.E., Awramik, S.M. (eds.): Microbial sediments. - 270-282, Berlin (Springer) Beauchamp, B., von Bitter, P. (eds., 1992): Chemosynthesis: geological processes and products. - Palaios, 7, 337-484 (with papers on modem and ancient chemosynthetic carbonates) Callender, W.R., Powell, E.N. (1997): Autochthonous death assemblages from chemosynthetic communities at petroleum seeps: biomass, energy flow and implications for the fossil record. - Hist. Biology, 12, 165-198

This book consists of three major parts. This first part 'Microfacies Analysis', deals with the methods of microfacies studies (Chap. 3), qualitative and quantitative microfacies data (Chap. 4, 5 and 6), diagenetic criteria (Chap. 7), limestone classification (Chap. 8) and biological controls on the formation of carbonate rocks (Chap. 9 and 10).

3 Methods

This chapter summarizes field work studies, sampling strategies and laboratoy methods relevant to microfacies analysis. A precise field record of geological and paleontological data as well as sampling strategies that consider the vertical and lateral variations in these data are vital for the success of microfacies studies. Laboratory methods study microscopic features and mineralogical and geochemical data.

A highly recommended description of field methods is given by Tucker (1982). The methods used in the study of litho- and biofacies of sedimentary rocks are the subject of several textbooks (Leeder 1982; Lewis 1984; Pettijohn et al. 1987; Miall 1990; Chamley 1990; Blatt 1992,Friedman et al. 1992, Lewis and McConchie 1993; Boggs 1995; Reading 1996; Leeder 1999; Miali 2000; Einsele 2000).

3.1 Field Work and Sampling

3.1.1.1 Lithology, Texture and Rock Colors

Many criteria that are important in facies interpretation can not be recognized sufficiently in small-scale microfacies. Paleoenvironmental interpretations derived from microfacies should be controlled by lithological criteria and sedimentary structures evaluated by the high information potential provided by fossils and biogenic structures. Microfacies sampling requires an understanding of the meaning of bedding and the depositional characters reflected by sedimentary structures.

Lithology: Sedimentary rocks are classified into siliciclastic rocks (claystone/mudstone, siltstone and sandstone), conglomerates and breccias, carbonate rocks (limestone, dolomite), mixed siliciclastic-carbonates (marl, argillaceous and sandy limestones), evaporites (gypsum, anhydrite, salt), siliceous sedimentary rocks (cherts), phosphorites and organic-rich rocks. Carbonate rocks make up 20 to 25 percent of all sedimentary rocks in the geological record and are classified into limestones and dolomites (dolostones); see Fig. 3.1. Limestones consist of more than 50% CaC03. They comprise limestones and dolomitic limestones. Dolomites are composed of more than 50% CaMg(C03), and are subdivided into calcitic dolomites (50-90% dolomite) and dolomites. Although detailed differentiation of carbonate rocks is best performed in the laboratory, field distinctions can also be made, using dilute 10% hydrochloric acid (limestone will fizz strongly, dolomite will show little or no reaction). Alizarin-red-

3.1.1 Field Observations

Field work forms the basis for studying sedimentary deposits. Criteria that can be studied in outcrops and cores in facies analyses are: lithology, texture, rock color, bedding, sedimentary structures and diagenetic features, and fossils and biogenic structures.

Rock Color Carbonate lithologies Dolomite 0

10

Limestone

90

50

Dolomitic limestone

Calcareous

100%

Dolomite

dolomite

Mixed siliciclastic-carbonatel i l o g i e s

Marl

Argillaceous l~mestone

Bituminous argtllaceous hmestone

Sandy

limestone

Fig. 3.1. Common lithologies of carbonate rocks and mixed

carbonate-siliciclasticrocks. The symbols used are those from the standard Shell Legend.

S in weak HC1 stains limestone pink to mauve but leaves dolomite unstained. Mixed siliciclastic-carbonate lithologies include marls (a sediment consisting of 65-35% carbonate and 35-65% clay), argillaceous limestones (a limestone containing an appreciable amount of clay, less than 50%) and sandy limestones (a limestone containing an appreciable amount of quartz sand).

Texture: Attention should be focused on the depositional variability of limestone beds, on depositional processes recorded by characteristic sedimentary patterns, and on the control of microfacies-based paleoenvironmental interpretations using larger-scaled criteria. The texture of major limestone types can be characterized in the field using the classification proposed by Dunham (1962); see Sect. 8.3.2. Much information is provided by the size, shape and sorting of grains, the ratio of matrix to grains, and the fabric. Details are described in Chap. 4. The textural composition of beds and laminae may be characterized by distinct vertical gradations in grain size (graded bedding). 'Normal grading' (coarser grains at the base, finer grains at the top) and 'reverse or inverse grading' (coarser particles at the top grading downwards to finer particles) are important in the interpretation of depositional processes (PI. 1711, PI. 10212, PI. 11512, PI. 1161 1, PI. 12612). Rock color: Many limestones are a shade of gray, but limestones can also display distinctive rock colors which need a more precisive terminology (Folk 1969). Dolomites are often creamy yellow or brown in color. Rock colors can be characterized by simple verbal descriptions (e.g. medium to dark gray) or by comparing fresh rock fracture surfaces with standard color schemes

(e.g. U.S. National Research Council Rock-Color Chart based on the Munsell Color System: Goddard et al. 1948). The use of the Rock Color Chart requires (a) determination of the gradation of color (hue), followed by (b) estimation of light to dark values, and (c) estimation of the degree of saturation (chroma). Colors are indicated by a code (e.g. 5 R 416) or by a descriptive name (e.g. moderate red). Color names used in the Rock Color Chart do not always correspond to the subjective color impression of geologists, which may be adequate for general surveys but not, for example for the characterization of carbonate rocks used in the arts or as building stones. Colorimetric analysis is another approach but relatively rarely used for limestones (Engelbrecht 1992), except when determining technological criteria. Colors of carbonate rocks are strongly controlled by depositional conditions, diagenesis and recent weathering. The amount and composition of the non-carbonate fraction is crucial for the color aspect because the adsorption of iron and manganese on the surface of finely dispersed clay minerals is often responsible for distinct colors. Fe and Mn content, rock color and depositional facies may exhibit distinct correlations, specifically in hemipelagic and pelagic sediments. Of particular significance is the oxidation-reduction balance: Yellow colors, for example, can be caused by the oxidation of FeS as demonstrated by the famous Jurassic Solnhofen Limestone of Southern Germany which appears in fresh samples bluish gray. Comparisons of photometric color measurements with geochemical data of limestones indicate correlations of bluish and yellowish colors with pyrite and goethite contents and dark or light rock color values with clay and silt contents. Green and drab gray colors may be caused by organically derived carbon and Fe2+ compounds such as sulfides in reduced sediments. Various shades of red, yellow and brown colors are due to Fe3+ compounds such as hematite and limonite in oxidized sediments. Yellowish shades of marbles can be caused by small quantities of siderite. Dark colors are also induced by aromatic hydrocarbons (pure solvent-soluble organic matter composed of carbon and hydrogen only). The amount of organic matter and the degree of light reflection are related (Patnode 1941). Black colors can also be caused by thermal heating. Sedimentary limestones may undergo considerable color change during metamorphism (Winkler 1994).

Why is this limestone red? Vivid rock colors generally provoke questions which are difficult to answer.

Bedding

Very generally, the coloration of sediments is regarded as synsedimentary (caused by the input of detrital coloring material or by contributions of ferric bacteria; Mamet et al. 1997) or postsedimentary (caused by diagenetic changes within the sediment or coloration by overlying beds). Red limestones may serve as an example for the problems involved: The red color of marine carbonates is primarily caused by small amounts of ~ e (about ~ + 2%: Franke and Paul 1980). Volcanic emanations provide a direct source of iron in seawater. But the weathering of land masses associated with an input of iron to the sea (as colloids or absorbed on clay minerals) and organic matter provide the major source. Low sedimentation rates, near-bottom waters rich in oxygen, the absence of sulfate-reducing bacteria as well as the local Eh/pH potential within the sediment and at the sedimentlwater interface favor the development of red colors (e.g. by dehydration of goethite to hematite: Rech-Frollo 1971).The intensity of the red coloration may depend on the amount of detrital material and iron (Hallam 1967; Fliigel and Tietz 1971). Because iron is transported from land to sea via several solution/precipitation-phases, the importance of climatic controls for the formation of red limestones must also be considered. The following diagenetic factors promote rock coloration: (a) Compaction facilitates the flow of oxydized pore water through the sediment. (b) Pressure solution and freeing of iron from clay minerals may be responsible for red-colored stylolite seams, often occumng together with burial dolomites (Mattes and Mountjoy 1980). (c) During dedolomitization, Fe originally incorporated in dolomite can be precipitated as FeO(0H) and oxidized to Fe,03, producing reddish rock colors. cm

/

Shell Standard Legend 1995 Meter bedded

1

Colored paleosols (e.g. terra rossa, a residual soil, over limestone bedrock, typically in karst areas) can impact on rock colors. Reddening of paleosol horizons is caused by (a) in situ alterations of iron-rich clays, (b) reddened detritus brought from the exposed surface downward through the soil by percolating waters, (c) dehydration of goethite to limonite and hematite during subaerial exposure in a well-drained environment (Retallack 1981), or (d) concentration of reddish matrix by eluviation within the paleosol profile during alternating wet and dry climate periods (Goldhammer and Elmore 1984). Terra rossa, brought to the sea will not directly cause red colors (Hinze and Meischner 1968). Near-surface cavities in karstified reef limestones may contain red internal sediments, derived from an overlying soil zone, with deeper cavities being filled with green and gray internal sediments (Satterley et al. 1994). Changes of rock colors with depth below the surface indicate changes in the oxidation state within the vadose and phreatic zones (Esteban 1991).

3.1.1.2 Bedding and Stratification, Sedimentary Structures and Diagenetic Features Many of the structures described in this subchapter can also be recognized at a microfacies scale, particularly sedimentary fabrics and diagenetic textures (Fig. 3.4). Bedding and stratzfication: Carbonate rocks are stratified or non-stratified. Non-strat@cation is a result of (a) primary lack of bedding (e.g. in reefs), (b) bed-destructing processes (e.g. intensive burrowing), or (c) diagenetic processes (e.g. dolomitization or strong recrystallization of limestones).

Boggs 1995

Demicco and Hardie 1994

Very thickly bedded

100

Thickly bedded 30

I

Layers greater than 100 mm, thick to very thick beds

Decimeter bedded Medium bedded Thinly bedded

3

Centimeter bedded Very thinly bedded

-1-

Layers 5 mm to 100 mm, Laminae >5 mm Thin beds 4 0 0 mm

Thickly laminated 0.3

Millimeter bedded

Layers >

Fig. 3.5. Standard Shell Legend symbols o f abundant sedimentary, biogenic and diagenetic structures occurring in carbonate rocks. The symbols are useful for a uniform schematic representation.

Checklist for Field Description

59

Box 3.1. Checklist for field description of paleontological data in carbonate rocks. Bedded limestones Bedding and sedimentary structures Bedding types (lithology, thickness, bedding boundaries, texture; see Fig. 3.1, Fig. 3.2) 'Event beds' ? (beds caused by physical and biological events of short duration, e.g. storms, turbidity currents, earthquakes, sudden death of organisms resulting in mass acummulations; see Sect. 5.1.3) Cyclic patterns ? (see Sect. 16.1) Sedimentary structures and diagenetic features (see Fig. 3.4) Types and preservation of fossils Classification of fossils (group, taxa) Evaluation of fossil types with regard to ecological criteria Trace fossils and/or body fossils ? Burrowing and bioturbation (see Sect. 5.1.5) Taphonomic criteria (see Chap. 10) Abundance and distribution of fossils Fossil concentrations Abundance of fossils based on bulk samples or on counts using various grids (see Sect. 6.2.1) Distributional patterns of fossils on bedding planes (random, patchy, oriented) Lateral distribution of fossils within the beds Distribution and type of fossils within underlying and overlying beds

I

I

Massive limestones (e.g. reef limestones) Geometry of the carbonate body Mapping of the boundary and geometry of the buildup Mapping of major litho- and biofacies types Establishing time lines (tracing bedding surfaces in the flank facies), discontinuities and event marker beds, e.g. storm layers, synsedimentary breccias) Look for bottom-top structures (particulary at the flanks of buildups) Types and preservation of fossils Classification of fossils Taphonomic criteria Analysis of the principal fossils with regard to their inferred role in buildup formation (e.g. framebuilders, binding and encrusting organisms) Differentiation of growth forms of sessile organisms Abundance and distribution of fossils Vertical and horizontal cover (density) and size of reefbuilding organisms (using a gridded overlay, the quadrat method orthe line method, see Sect. 6.2.1) Recognition of significant vertical sequential changes in growth forms, taxonomic composition or abundance Relation between sediment, texture and fossils Description of the 'matrix' between and around autochthonous reefbuilders (see Sect. 16.2.5.2) Description of growth cavities, shelter structures, open-space structures and solution voids (see Sect. 5.1.5) with regard to geometry, dimension, distribution and filling (sediment, spar, crystal silt, still open) Description of fissures with regard to setting, size, orientation, filling and fossils Abundance of fine-grained sediment and carbonate cements in relation to benthic fossils Diageneticfeatures: see Sect. 7.4.4.2

3.1.1.3 Fossils and Biogenic Structures Fossils, fossiliferous sediments and biogenic sedimentary structures are key sources of information on paleoenvironments, sedimentation patterns and diagenesis. Strategies necessary for describing paleontological data in the field were summarized by Goldring (1991). Field strategies are different for bedded sediments and for dominantly autochthonous buildups. Box 3.1 is based on afield classification offossiliferous sediments proposed by Goldring (1991). Of special interest are 'fossil concentrations', bioclastic fabrics, and ichnofabrics.

Fossil concentrations are relatively dense accumulation of biologic hardparts (irrespective of taxonomic composition, state of preservation, or degree of postmortem modification). By taking into consideration the taxonomic composition, bioclastic fabric, geometry and internal structure of the deposit, skeletal concentrations can be grouped genetically according to the inferred relative importance of biogenic, sedimentologic and diagenetic processes (Kidwell et al. 1986; Fig. 3.6). This approach is useful for interpreting 'shell beds' composed of mollusks and brachiopods, and understanding the processes

Field Logs

Fig. 3.6. Field description of skeletal concentrations (Modified and completed after Kidwell et al. 1986). Accumulation of shells, echinoderm fragments and other fossils are produced by biogenic (area 1in the triangle), sedimentologic (area 2) and diagenetic processes (area 3). An example of biogenic concentrations are oysters, whose larvae preferentially colonize sites with abundant adults causing reef-like structures in subtidal shelf settings. Photo at top right: Placunopsis, Middle Sedimentolwic Diaoenetic Triassic, Germany. Sedimentobgical concentrations form through hydraulic reworking of hardparts, and/or through non-cleposition of sediment, or selective removal of the sedimentary matrix. These processes result in the formation of conspicuous shell beds (lumachelles, coquinas). An example is shown in the foto at bottom left: Accumulation of looseley packed, bimodal sorted bivalve shells within a storm layer originated in inner shelf position; the inversely graded carbonate mud was infilled subsequent to the deposition of the shells. Late Triassic, Northern Alps, Austria. Diagenetic concentrations originate from the increase of the spatial density of fossils by compaction and selective pressure solution. The photo at bottom right displays a crinoidal limestone, formed on a carbonate ramp and strongly affected by pressure solution. Early Carboniferous: Frank's Slide,Turtle Mountains,Albertafcanada.The triangle can be used to estimate the position of shell beds along an onshore-offshore transect: Tidal flats are characterized by a composition corresponding to the areas 1 and 2; lagoons by the dominance of the areas 1 and 4; shallow shoals by the dominance of the area 2; inner shelf shell beds by the areas 2 and 4; and subtidal outer shelf settings below storm wave base by the abundance of concentrations that correspond to area 1.

and environments responsible for their origination. Fossiliferous carbonates yielding fossils or fossil fragments larger than 2 mm can be readily categorized into macroscopic fabric types using semi-quantitative scales for close-packing and size-sorting of coarse bioclasts (Kidwell and Holland 1991; Fig. 3.7). The fabric types are useful to narrow the possible modes of origin, e.g. accumulations of mollusk shells or crinoidal fragments. Ichnofabrics and trace fossils have a high potential for interpretating of paleoenvironments and depositional processes (Donovan 1994;Bromley 1996).A semiquantitative field classification of bioturbation based on pattern recognition of the percentage of original sedimentary fabric disrupted by biogenic reworking facilitates the explanation of bioturbation structures seen in thin sections (Droser and Bottjer 1986; see Sect. 5.1.4). Distinctive distributional patterns of trace fossils in carbonate shelf environments are useful in delineating environments of deposition and determining sea-level positions.

3.1.1.4 Field Logs and Compositional Logs

Field information originating from stratigraphic sections and mapping is commonly recorded by written descriptions of observed features (field notes: Tucker 1982, Graham 1988). Graphic logs aid in documenting of rock composition and texture and consist generally of a main column showing the lithological sequence (drawn as column or imitating a weathering profile) and adjacent columns showing the occurrence and distribution of sedimentological and paleontological data. These columns may include only field data or a combination of field and laboratory data. Various standard forms for plotting graphic logs and standardized coding systems have been proposed to uniformly describe facies criteria, and to facilitate transforming field and laboratory data into digital data (e.g. Charollais and Davaud 1974; AmStrat-CanStrat system: Miall 1990). Reijers et al. (1993) recommend a hierarchically organized lithofacies coding system allowing macro-

Packing

Fig. 3.7. Classification of coarse bioclasticfabrics characterizedby closepacking of fossils (modified after Kidwell and Holland 1991). The classification can be used in the field as well as in thin section studies. Basic Bioclast supported, Most bioclastswithin Most bioclasts are more than parameters are packing, size sorting of bioclastlbioclast contacts one body length of each other, one body length common a few in dired contact awav from each other the bioclasts larger than 2 mm,and the biofabric which is bioclast-supported ('densely packed') or matrix-supported ('loosely packed and 'dispersed'). The fabrics are well-sorted exhibiting little variations in the size of bioclasts, bimodal sorted (with two discretes modes), or poorly sorted exhibiting great variations in bioclast sizes. The packing and sorting descriptors convey an immediate visual image of the fossiliferous limestone. The criteria have genetic implications. The categorization by close-packing and size-sorting limits the number of possible origins and leads to basic hypotheses that can be tested using taphonomic, palecologic, sedimentologic and stratigraphic features. The sample exhibits a fabric characterized by large gastropod shells and abundant smaller bioclasts consisting of small gastropods and bivalve valves. These bioclasts constitute an overall loosely packed fabric which would be classified as gastropod floatstone following Dunham's classification (see 6.2). The finer bioclasts, however, are densely packed and these parts of the thin section would be classified as fine-bioclastic mollusk packstone. Small gastropods often are regarded as 'dwarf' forms pointing to unfavorable environments. It should be taken in mind, however, that the majority of gastropods is characterized by mm-scale shells. Note the strong recrystallizationof the large gastropods. The originally aragonitic shell has been replaced by coarse-grained calcite crystals.The first whorls are completely obliterated; following whorls exhibit various cement generations or are infilled by micritic sediment. Late Cretaceous pebble in Quaternary deposits: GrazIStyria,Austria. scopic features of sedimentary rocks to be objectively described and the data stored in a computer database. The standard lithologic logging system proposed by Shell International Exploration and Production (Standard Legend 1995) offers a widely used possibility for describing featuresf recognized in .outcrops, cores and microfacies samples. Lithology, texture and composition, rock color, accessory minerals, fossils, stratification and sedimentary structures, postdepositional criteria and diagenetic features as well as physical criteria (e.g. porosity and permeability) are expressed by symbols, standard abbreviations and codes. Too many symbols and criteria will mask trends in the stratigraphic sequence. For the purpose of microfacies studies the most important data should be shown in logs: e.g. depositional textures, fossils, grain types, matrix and carbonate cement. Logs are presented in a variety of scales depending on the problems involved. Detailed microfacies logs may require a scale of 1 cm = 1 m or less. Authors studying depositional patterns of carbonate rocks use a scale of 1 cm =10 m.

3.1.2 Sampling The following comments refer to outcrops and cores. Sampling of cuttings requires specific methods discussed in Sect. 17.1A.2. Sampling depends on the nature of the project (Griffith 1967). The scope of the problem must be defined before collecting samples. Typical research objectives may be depositional texture of carbonate rocks as an aid to classifying rock types and assessing physical properties, type, texture and size of carbonate grains as an aid to determining depositional environment and paleocurrents, studies of grains, matrix, cement and pores for understanding diagenesis and physical/technological properties of carbonate rocks, paleontological criteria, for subdividing and correlating stratigraphical units or providing data which can help with paleoenvironrnental reconstructions.

How Many Samples?

3.1.2.1 Search Sampling and Statistical Sampling

plan, e.g. at equal distances or according to a random distribution. Common methods of sampling are: Simple random sampling: Samples are taken at unSize of samples evenly spaced intervals determined by random numMicrofacies sampling should provide (1) lithological bers, and the variability of the samples is checked samples exhibiting textures, structures and fossils on a by variance tests (Eltgen 1970). hand specimen scale, (2) samples for laboratory analySystematic sampling: Samples are taken at evenly sis (samples for geochemical investigations should conspaced intervals and checked by significance tests; sider induration and degree of weathering!), and (McCammon 1975). Sampling within a constant ver(3) samples for paleontological studies. Because the methods used in laboratory investigations may not yet tical distance facilitates the statistical treatment of be certain at the time of sampling, large-sized samples distributional data (Grotsch et al. 1994). are recommended allowing several medium to largeStratified sampling: At least two samples are taken from each bed; the number of samples should be scale thin sections to be prepared and specific quesproportional to bed thickness. tions to be studied. The sizes 5 x 4,5 x 5, and larger up Cluster sampling: Several adjacent samples are taken to 20 x 15 cm have proved useful as formats for thin in random distribution. This approach was successsections used in microfacies analyses. fully used for microfacies studies of reef limestones and shelf carbonates. Large and oriented samples (showing the position of the samples in spaces and marked in the field) are In practice, real possibilities of microfacies sampling necessary for and theoretical statistical requirements differ widely due determining top-and-bottom criteria, allowing the to the outcrop situation, accessibility and physical condepositional and structural top to be recognized, studying textural variations and fabrics (e.g. grain dition of the student carrying heavy sample bags. 'We orientation; bedding, discontinuity surfaces, biotur- collect what we can...' bation, breccia), Beware ofthe tfamily photo album effect' describing biotic characters (e.g. growth forms, sucIn a family photo album extraordinary events like cession pattems, guilds). Reef limestones require birthdays and holidays are commonly overrepresented large and very large samples because of the high as compared with photos of every day life. Similarly, compositional variations within centimeter and decimany microfacies samples are often selectively taken meter ranges. Only large samples allow synchronous because of a conspicuous abundance of fossils in some and non-synchronous associations to be differentibeds or exceptional textural types. The 'daily life' reated and sediment types and internal features (caviflected by more monotonous lithotypes (e.g. micritic ties, cryptic habitats) within bioherms or biostromes shelf limestones or hemipelagic limestones) is recorded to be discussed. Large samples, sometimes compristo a minor degree, because the vertical sampling dising a whole bed, are also necessary for calciturbidtance is larger and the spacing more irregular.The depoites (Herbig and Mamet 1994). sitional 'trends' (e.g. cycles) derived from samples representing extraordinary events rather than 'daily life' Equipment and first observations Microfacies sampling requires the use of a ham- may display an artificial pattern. mer, chisel and, sometimes specific equipment (angle grinder). Hand lenses as well as a pocket microscope for grain size measurements (Miiller 1967) and textural 3.1.2.2 How Many Samples? observations in the field are important prerequisites. Determine rock color, texture, composition and mean The variability, diversity, and richness of microfacies size of grains, induration and weathering in hand data are related to sample size effects. An increase in sample size may lead to an increase of richness and specimens. diversity. Various analytical techniques are known to estimate sample size in geological, biological, and arStatistical sampling Statistical sampling, based on random samples with cheological studies. Some methods are also valuable the objective of estimating the statistical probability of in microfacies analysis (curves of sample size against facies types and pattems, is a common approach in mod- diversity or richness, regression and simulation techem microfacies studies (Carozzi 1988). Statistics re- niques). There is, of course, no general rule for the numquire that the samples be taken according to a specific ber of microfacies samples that are 'truly representa-

Advices for Sampling

tive' of the limestone studied, but some empirical tendencies do exist:

Shallow-marine bedded carbonate sequences need a detailed sampling program, because they exhibit high microfacies variability due to changing subtidal and tidal depositional sites and the common occurrence of cyclic sedimentation pattems. A very close sampling of cyclic carbonates at an interval of 0.10 m and less is recommended if high-order short-term cycles are to be detected (Buggisch et al. 1994). Thin- to medium-bedded platform and ramp carbonates are commonly sampled at intervals between 0.20 and 0.50 m (corresponding to a bed-to-bed sampling) or at intervals of several meters. Bed-to-bed sampling is advised if the study aims to understand of short-term changes in environmental controls of biota and sedimentation. Novak and Carozzi (1972) studied a 5 m thick section of Late Carboniferous-Permian platform carbonates by using thin section samples taken at intervals of 20 cm and a continuous series of samples.Although continuous sampling provided more information and allowed a better separation of microfacies types, the general trend in the sequence of microfacies types was still recognizable for sampling intervals of 20 cm. Wider intervals are used for (1) search sampling (taking samples preferentially from conspicuous beds noticeable because of a particular composition, structure or cyclic pattern), and (2) obtain pilot studies aiming to a first overall picture of the section studied and recognize lithotypes which may be evaluated later by microfacies data. Cyclothems that are evident already from field observations are often described using only a few samples. This may provide false information because shallowing- or deepening trends of the cycles could be missed. In addition, cyclic sedimentationpattems may be obscured by the amalgamation of beds, thus calling for densely spaced samples (Gischler et al. 1994). Massive to coarse-beddedcarbonates (reefs,mounds) require the study of many samples in order to consider (1) the variability of sediment within and between frame-building and baffling organisms, (2) the various kinds of voids and open-space structures common in mounds and reefs, (3) lateral microfacies changes on a decimeter-scale, and (4) relations between mound fac i e ~and intermound facies. Microfacies analysis of bedded deepwater carbonates often is based on rather few samples because of the assumed 'monotonous' microfacies spectra of these limestones. The calculated sampling interval (profile thicknesslnumber of samples) of most case studies lies between 1.OO and 2.50 m. Wheras the overall qualitative composition of deep-water limestones may indeed be uniform, the quantitative investigation of microfa-

cies criteria and microfossil distribution, based on a 'onetentimeter style' sampling exhibits hidden aspects of environmental controls (No6 1993). Hardgrounds and condensed pelagic limestones should be studied in channel samples covering the total bed thickness and with particular consideration of the bed surfaces,because rnicrofacies types can change within a distance of a few millimeters and centimeters. Collectingsamplesforpaleoecological or biostratigraphical analysis must take into account the strong facies control of the frequency and distribution of fossils. Many microfacies studies aiming for biostratigraphical classifications are based on spot samples taken at regular intervals or over a regular number of event beds (e.g. calciturbidites). Channel samples continuous over the total thickness of limestone beds are necessary to understand fine-scale vertical variations in event beds. These variations describe the hydraulic changes during the formation of the calciturbidites.

3.1.2.3 Practical Advice for Microfacies Sampling 1 Become clear about the principal aim of the investigation and decide whether you will use random sampling or systematic sampling strategies. 2 Start with a test section to understand the scale of microfacies variations and choose the most appropriate vertical sampling distance. 3 Mark the orientation of the sample (sedimentary top and, if necessary dip and strike, which may be important for the interpretation of grain orientation as a current indicator) before removing the sample from the bed. 4 Take samples of an appropriate size allowing for the preparation of thin sections, the study of non-carbonates in acid residues and geochemical analyses. 5 Consider the negative effect of weathering and avoid taking samples for geochemical and diagenetic studies at or near bedding surfaces. 6 Follow a strict sampling strategy, but do not exclude sampling of beds showing rare but conspicuous criteria (e.g. extremely fossiliferous beds, beds exhibiting differences in colors). But be careful not to follow the 'family photo album effect' by samplingpredominantly 'extraordinary' lithotypes. 7 Locate microfacies sampling in those parts of beds which will deliver a maximum potential on information. 8 When working with bedded carbonate sequences, do not forget to sample also non-carbonate interlayers as well.

Practical Advices

Rock colors Wells, N.A. (2002): Quantitative evaluation of color measurements: I. Triaxial stereoscopic satter plats. - Sedirnentary Geology 151, 1-15 Folk, R.C. (1969): Toward greater precision in rock-color terminology. - Geol. Soc. America Bull., 80,725-728 Fliigel, E., Tietz, G.F. (1971): ~ b e die r Ursachen der Buntffiung in Oberrhat-RiKkalken(Adnet, Salzburg). -Neues Basics: Field work Jahrbuch fiir Geologie und Palaontologie, Abhandlungen, Field methods and graphic record 139,2942 Allen, J.R.L. (1982): Sedimentary structures. Their characGoddard, E.N., Trask, P.D., De Ford, R.K., Rove, O.N., ter and physical basis. - Development in Sedirnentology, Singewald, J.T., Overbeck, R.M. (1948): Rock-color chart. 30, 1258 pp., Amsterdam (Elsevier) - Geological Society of America Collinson, J.D., Thompson, D.B. (1988): Sedimentary struc- Patnode, H.W. (1941): Relation of organic matter to color of tures. - 2nd edition, 208 pp., London (Allen and Unwin) sedimentaryrocks. -Amer. Ass. Petrol. Geol. Bull., 25,1921Dietrich, R.V., Dutro, J.T., Foose, R.M. (1982): AGI data 1933 sheets for geology in the field, laboratory, and office. Wright, W.D. (1969): The measurement of color. - 340 pp., 2nd edition, Boulder (American Geological Institute) London (Hilger) Gagliardi, R., Kalin, O., Morreale, E., Pataca, E., Scandone, F., Sprugnole, R. (1980): Una banca dati geologici del Sampling progetto finalizzato geodiiamica. - Consiglio Nazionale Griffith, J.C. (1967): Scientific method in analysis of sedidelle Ricerche. Progetto Finalizzato Geodinamica, Pubments. - 508 pp., New York (McGraw-Hill) blicazione, 393, 1-90 Schindel,D.W. (1980): Microstratigraphicsampling and the Leeder, M.R. (1982): Sedimentology.Process and product. limits of paleontologic resolution. -Paleobiology, 6,408344 pp., Boston (Allen and Unwin) 426 Lewis, D.W., McConchie, D.M. (1994): Practical sedimenFurther reading: K003, K004, K014, K015, KO16 tology. 2nd ed. - 256 pp., New York (Chapman and Hall) Reijers, T.J.A., Mijnlieff, H.F., Pestman, P.J., Kouwe, W.F.P. (1993): Lithofacies and their interpretation: a guide to standardised description of sedimentary deposits. - 3.2 Laboratory Work: Techniques Mededelingen Rijks Geologische Dienst, 49,l-55 Shell International Exploration and Production B.V., The Hague (1995): Standard Legend 1995. - Document and Originally strongly focused on the study of thin sections, peels or slices with the aid of low to medium CD-ROM version Tucker, M.E. (1982): The field description of sedimentary power binocular and petrographical microscopy, the rocks. - Geological Society of London, Handbook Series, combined use of conventional thin-section data and 2, 112 pp., London (Open University Press) more sophisticated detailed microscopy (SEM, cathodoTucker, M.E. (ed., 1988): Techniques in sedimentology. luminescence and fluorescence microscopy) as well as 416 pp., Oxford (Blackwell)

9 Do not restrict sampling to microfacies alone, but also collect macrofossils and specific micropaleontological samples. 10Record the sampling locality and the beds sampled in field photographs and detailed sketches.

mineralogical and geochemical studies have proved to be of high potential in the application of microfacies Bedding, sedimentary and biogenic structures Bromley, R.G. (1996):Trace fossils: biology, taphonomy and analysis. Valuable summaries of techniques are found in Miiller (1967), and especially in Tucker (1981). The applications. - 2nd ed., Dordrecht (Kluwer) Cole, R.D., Picard, M.D. (1975): Primary and secondary sedi- latter book includes excellent overviews of diverse mimentary structures in oil shale and other fine-grainedrocks, croscopical methods, cathodoluminescence microsGreen River Formation (Eocene), Utah and Colorado. copy, scanning electron microscopy, X-ray powder difUtah Geology, 2,49-67 Campbell, C.V. (1967); Lamina, laminaset, bed and bedset. - fraction and chemical analysis of sedimentary rocks. Sedimentology, 8, 7-26 Texts covering the paleontological aspects of microDroser, M.L., Bottjer, D.J. (1986): A semiquantitative field facies studies are listed in Sect. 10.4. classification of ichnofabric. - J. Sed. Petrol., 56,558-599 Goldring, R. (1991): Fossils in the field. Information potential and analysis. - 218 pp., London (Longman) Kendall, C.G.St.C., Warren, J. (1987): Areview of the origin and setting of tepees and their associated fabrics. - Sedimentology, 34, 1007-1027 Kidwell, S.M., Holland, S.M. (1991): Field description of coarse bioclastoc fabrics. - Palaios, 6,426-454 Lewis, D.W., McConchie, D.M. (1993): Practical sedimentology. - 256 pp., London (Chapman and Hall) Lumsden, D.N. (1971): Facies and bed thickness distributions of limestones. - J. Sed. Petrol., 41,593-598 Plummer, P.S., Gostin, V.A. (1981): Shrinkage cracks: desiccation or synaeresis. - J. Sed. Petrol., 51, 1147-1156

3.2.1 Slices, Peels and Thin Sections The composition, fabric and texture of carbonate rocks are studied in slices, peels, or thin sections which may be etched or stained in various phases of preparation in order to emphasize specific criteria. Various techniques and methods are described by Adams et al. (1984) and Miller (1988). Slices: Oiling and gentle etching of cut and smoothened carbonate rock faces exhibit otherwise cryptic fab-

Laboratory Work

rics or show fabrics within apparently homogeneous limestones (Bromley 1981). Peels: The imprint of etched surfaces on transparent plastic films is the most rapid and simplest method for studying cut, polished, and etched samples. Acetate replicas can be made using a dry-peel technique (McCrone 1963; Germann 1965) or by making peel sheets by pouring solutions (ethyl cellulose in trichloroethylene, nitrocellulose) on to glass plates (Davies and Till 1968). The procedure of preparing peels includes (I) cutting, grinding (and polishing) the sample, (2) drying and etching the cut surface, (3) flooding the surface with a solvent and (4) pressing the film onto the surface; the film will settle down into irregularities in the etched surface and produce the replica. After pulling off, the peel should be pressed or mounted between glasses. Peels have many advantages: They offer a rapid and inexpensive method to obtain a first observation of the characteristics of the sample. Peels can be used not only for carbonates but also for cherts, siliceous clastics and sulfates rocks (Mandado and Tena 1986). Peels can be studied just like thin sections using a binocular microscope or a simple microfiche equipment and they can be placed in the negative carrier of a photographic enlarger, producing iarge negative prints by projecting the image directly to bromide paper. These prints may be used as working copies exhibiting locations of areas of particular interest. Replicas can be made of large surfaces, even up to several tenths and hundredths of square centimeters. Serial peels can be produced by regrinding surfaces after each peel, thus allowing the three-dimensional reconstruction of open-space structures or fossils only known from thin sections (Honjo 1963). Staining peels prior to the flooding of rock surfaces allows minerals and fabrics to be differentiated (Katz and Friedman 1965). Since earlier stains can be removed by repolishing, different stains indicating different minerals can be used with good success. Peels are suited for high-magnification studies and phase contrast microscopy (Frank 1965; Honjo and Fischer 1965) and for SEM studies (Brown 1986). Acetate peels have proved to be of value in studying carbonate cements and textural criteria (e.g. grainsize distribution: Gutteridge 1985). Disadvantages of peels are the susceptibility of acetate films to contamination and the danger that porous samples might be difficult to work with, because the film may bulge into the pores, causing blisters. Ac-

etate films are isotropic; the main disadvantage of peels, therefore, is that minerals can not be identified by optical properties, such as relief or birefrigence. Thin sections: The investigation of the composition and fabric of surface and subsurface samples requires standard thin sections with a thickness of approximately 30 pm. These thin sections are usually cut perpendicular to the bedding. Initially, the thin sections should not be covered, allowing later more detailed investigations (staining etc.). Very fine-grained micrites are studied in high-quality ultra-thin sections with a thickness between 0.5 and 5 pm (Lindholm and Dean 1973), allowing observations at magnifications of between x 150 and x 1000. Thin sections may be subject to etching and staining (Friedman 1959; Houghton 1980; Rassineux and Beaufort 1987). These procedures and other more detailed studies (e.g. cathodolurninescence microscopy: Mugridge and Young 1984) only can be applied to uncovered thin sections. Rapid covering can be done using a plastic spray (Moussa 1976). Microfacies thin sections are generally larger and thicker than regular petrographic slides. Commonly used sizes are from 5 x 5 up to 15 x 20 cm. Large thin sections are necessary for studying reef limestones, coarse-grained detrital limestones and carbonates deposited during events (e.g. turbidites, tempestites). Note: Samples are generally cut perpendicularly to bedding planes. Therefore, a thin section comprising a vertical interval of 5 cm records a set of 'microsequences' corresponding to shorter or longer time intervals within a scale of hundreds, thousands or more years.

3.2.2 Casts, Etching and Staining Casts: Impregnation of carbonate rocks and fossils with low viscosity epoxy resin under vacuum and under pressure has a high potential in recognizing micron- and submicron-scaled structures in porous but also moderately porous carbonates and evaporites. Impregnation of carbonate rocks with a mixture of fluorescent dye and epoxy resin enhance the ability to study micro- and macroporosity. SEM observations of artificial casts aid in the study of microporosity and pore geometries of limestones and chalks (Gardner 1980; Beckett and Sellwood 1991; see P1. 6), modem and ancient microborings (Golubic et al. 1975; see P1.5211-4). Etching and staining: Etching of slices or thin sections with hydrochloric acid (1-5% by volume) or acetic acid (about 20% by volume) causes partial dissolu-

Casts, Etching, Staining

66

tion that emphasizes textural criteria and allows subsequent staining, which is one of the most useful techniques in carbonate rock studies. Comparing staining techniques with other methods, e.g. X-ray diffraction, may exhibit discrepancies in estimates of dolomite in limestones (Gensmer and Weiss 1980). The success of etching and staining depends on (a) the strength and temperature of the reagents, (b) etching and staining times, (c) the pre-treatment of the sample, and d) the composition and fabric. An advantage of staining is the possibility using the method already used during field studies (Warne 1962). Staining assists in (1) identifying minerals common in carbonates (aragonite, Mg-calcite, calcite and dolomite, gypsum and anhydrite, feldspars), (2) studying dedolomitization (Evarny 1963), (3) recognizing microporosity (Yanguas and Dravis 1985)

3.2.3 Microscopy The microscopic study of thin sections of carbonate rocks provides the basic microfacies data. The combination of microfacies analysis with the criteria derived from fluorescence, photoluminescence, cathodoluminescene and fluid inclusion studies provide key information on sedimentary and diagenetic processes.

3.2.3.1 Petrographic Microscopy

3.2.3.2

Stereoscan Microscopy

Utilization of Steroscan Electron Microscopy (SEM) in the study of ancient and modem carbonate rocks has brought about major breakthroughs in our understanding of depositional and diagenetic products and processes (Welton 1984; Trewin 1988). The chief advantages of the SEM are the great depth of focus, producing excellent photographs of extremely small (micron- and submicron-sized)three-dimensional surfaces, the high power of resolution and the possibility of very high magnifications in the range between x 10 up to x 100 000. Transmission Electron Microscopy (TEM) of replicas, however,which has been used prior to SEM in the study of carbonate rocks (Fischer et ai. 1967), is still a valuable tool in carbonate investigation (e.g. biomineralization modes, microbial contribution to the formation of carbonates). Today, SEM studies are a part of integrated analyses which combine SEM with energy dispersive X-ray (EDX) data, back-scattered electron images and image analysis,cathodoluminescencemicroscopy and conventional studies of (stained or etched) peels and thin sections. Peels and thin sections can be used directly for SEM studies. EDX studies show element composition and element distribution. Element mapping is used to distinguish mineralogical phases and to elucidate Mg and Sr distributional patterns in cements and fossils. Carbonate SEM samples should be unaffected by weathering. Nonporous limestones and dolomites are studied using untreated fractures of rock chips or slices (size about 5 by 10 by 10 mm) which are polished and etched with dilute hydrochloric acid or formic acid, or Titriplex-111. Samples are mounted on stubs by doublesided sticky tape or various glues. Porous carbonates may need specific sample treatment (Trewin 1988).

Good polarizing microscopes and binocular microscopes are essential tools for microfacies studies. Microscopes should have photographic equipment low and high power magnification and should be equipped with mechanical or computer-interfaced stages for examining modal composition and fabrics (Kobluk and Vyas 1989). The major applications of SEM in investigating carThe speed, thoroughness and accuracy of thin-section analysis can be increased by using integrated com- bonate rocks include studies of the matrix of fine-grained limestones (micrite, chalk) puterized systems (Kobluk and Kim 1991).To provide an overview of the whole thin section, the use of digiand the composition of modem carbonate muds, composition and ultrastructure of fossils and nontal film scanners (De Keyser 1999) and microfiche inbiogenic carbonate grains, struments is strongly recommended. Microfacies obbreakdown of fossils, including the importance of servations should always start with low-power examiendolithic borings in the destruction of grains and nations and continue to high-power magnification. Prithe formation of micritic coatings, mary textural features in dolostones and recrystallized type, sedimentological and biostratigraphical role of limestones can be made visible by using a simple light diiuser (translucent plastic or plain white paper), placed micro- and namofossils, distribution and geometry of micropores, directly under the thin section (Delgado 1977). mineralogy, morphology and spatial relations of carThere are many excellent and colored texts on minbonate cements, eral identification in thin sections (e.g. Scholle 1979; Adam et al. 1984; Carozzi 1993). stages of dolomitization,

Microscopy

type and distribution of non-carbonate minerals, changes taking place during burial diagenesis and incipient metamorphosis.

3.2.3.3 Fluorescence, Cathodoluminescence and Fluid Inclusion Microscopy Fluorescence is a form of luminescence and represents the property of material to emit light when exited by visible or ultraviolet light (Rost 1992). Fluorescence microscopy is a standard technique in coal petrography, paleobotany, and the organic petrography of sediments of mainly organic origin or with a high organic content (e.g. petroleum source rocks). Fluorescence in limestones is probably caused by organic matter (Machel et al. 1991). Samples are studied as polished slices and thick thin sections (Clausing 1991). Epifluorescence in carbonates is used for recognizing hidden microfabrics (Dravis and Yurewicz 1985; Klotz 1989), studying organic constituents of fine-laminatedlimestones (e.g. cyanobacteria,algae, pollen and spores), differentiating automicrites and allomicrites (Neuweiler 1995), understanding biomineralization processes. Cathodolurninescence (CL) microscopy of carbonate rocks, starting with the work of Sippel and Glover (1965), is a significant tool in the petrography of marine and non-marine carbonates (Marshall 1988; Barker and Kopp 1991; Barbin et al. 1991) and in the investigation of primary or diagenetic microstructures of fossils (Amieux 1987; Elorza et al. 2001). CL microscopy stimulates of luminescence on polished thin sections (thickness < 30 pm) and polished rock surfaces by electron borbardment. Luminescence depends on the material characteristics of the excited solid. These characteristics comprise the chemistry, crystal structure, lattice defects and other factors (Hemming et al. 1989). The main activator elements of carbonates are ~ n and PW2.Activation of calcite and dolomite by Rare Earth elements is also a common feature of Phanerozoic marine limestones and sinter calcites (Habermann et al. 1996). The subjective determinationof CLcolors should be supplemented by spectrometricanalyses. CL studies are often combined with petrographic microscopy (Gregg and Karakus 1991) and rare element microanalyses, and have become a significant part of microfacies analyses. The major applications of CL microscopy for carbonate rocks (see P1.5) are for observing and interpreting of diagenetic phases (e.g. zonar structures within crystals reflecting changes in

67

the chemical environment and/or in the growth speed; early diagenetic and burial cements reflecting burial depths; mineral transformations, such as the alteration of calcite to dolomite (Richter 1984), evaluating pore water chemistry, reflected by sector zoning in calcite crystals (Bruckschen et al. 1992), and interpretation of the diagenetic history of reservoir rocks, reconstructing diagenetic events which identify stages of cementation and provide a 'cement stratigraphy' that are used to establish cement-based stratigraphic correlations (Meyers 1991; Sect. 7.7. l), recognizing fabrics (e.g. distinction of recrystallized structures, recognition of microcracks), studying the diagenesis of fossils.

Fluid inclusions in minerals have been studied during the last twenty years with respect to the genesis and migration of hydrocarbons, mineral deposits, diagenesis of sedimentary rocks and problems of structural geology and petrology (Roedder 1984, 1990; Lattanzi 1991). Fundamental for the interpretation of fluid inclusion data is the assumption, that the fluid inclusions still have the same composition and volume as at the time of formation in a closed system. Alterations may be caused by changes in geometry and volume or by a temporary or permanent opening of the inclusions. Carbonate crystals with fluid inclusions appear dark in thin sections and polished sections. Cloudy inclusions of aqueous liquid and vapor within carbonate crystals provide information on the diagenetic environment of cements (vadose zone, low-temperature phreatic zone, high-temperature burial zone) and their thermic history. The size of the inclusion ranges from < 10 pm to 30 pm. Fluid inclusions are caused by primary engulfment of fluids within growing crystals or by secondary entrapment of fluids in microfractures that are subsequently healed. Samples should not have been subjected ~ significant + to overheating beyond the temperature of entrapment or the temperature of homogenization (Barker and Goldstein 1990) and should have been reequilibrated during recrystallizationand deformation. Calcite crystals should display distinct growth zones. Genetic interpretationsand classifications are based on the composition, form, and position of the inclusions as well as their relationship to crystal structures (Roedder 1984; Goldstein 1993). Investigations require a petrographical microscope (with UV epifluorescence capabilities for differentiating aqueous and hydrocarbon inclusions) and a heating and freezing stage. Fluid inclusion studies are com-

Cathodoluminescence

68

Plate 5 Cathodoluminescence (CL): A Possibility to See More Cathodoluminescence microscopy of thin sections has become an important tool of microfacies analysis.It assists in observing diagenetic phases recorded by different cement types (-> 1, 2, 8) and establishing a 'cement stratigraphy'as well as recognizing zonation patterns of calcite crystals and the mode of porosity occlusion (-> 3). CL reveals the original structures of fossils and their growth modes (-> 4) and facilitates the recognition of diagenetic not or little altered shells which can be used for the determination of stable isotopes. Generally CL accentuates diagenetic and sedimentary textures (-> 6,7), thus allowing a more precise observation of microfacies criteria. The combined use of CL and petrographic microscopy is strongly recommended. 1 and 2 Primary interparticle pore in transmitted light (-> 1) and under CL (-> 2). Note the different appearance of

cement successions. The succession consists of a light-brown luminescent radialfibrous cement (A) circumcrusting a grain followed by non-luminescent dogtooth cement (B) and banded yellow to brown luminescent burial coarse mosaic calcspar cement which fills the remaining pore space. Early Jurassic: Carbonate platform of Jbel Bou Dahar, High Atlas, Morocco. Zoned crystal growth. The luminescence pattern exhibits the distinct zonation of a large crystals filling the pore space in a travertine. Quaternary: Tivoli near Rome, Italy. Ulltastructure and growth modes of fossils: Shell of the inoceramid species Antarcticerarnus rabotensis (Crame and Luther). Under cathodoluminescence a distinct yellow luminescent lamina is visible which interrupts the normal sized prisms constructing the shell. A recovery to normal crystal sizes is rather slow as seen by the smaller prisms (here) left of the yellow lamina. This interruption in shell growth is interpreted as the result of a cooling interval or even a freeze shock which influenced the growth of prisms in the shell. Growth direction of the shell is from right to the left in this picture. Late Cretaceous (Campanian): James Ross Island, Antarctica. Grade of diagenetic alterations of shells. Punctate brachiopod. The brachiopod shell appears dark (unaltered) with some luminescent parts (diagenetically altered). The punctae are filled by orange luminescent diagenetic calcite. Sediment in the lower part shows bright orange luminescence due to Mn2+incorporation ('activator' ion) during the diagenetic transformation of metastable aragonite and High-Mg calcite to the stable phase Low-Mg calcite and are therefore relatively stable to diagenetic alteration. Unaltered shells usually show no luminescence. The shell belongs to the genus Sclzizophoria. Devonian: Iowa, USA. Diagenetic stages: Relictic ooids. The ooid layers were dissolved mainly during late burial diagenesis; the preserved core consists of recrystallized shell fragments which show a weak red to orange luminescence. Open moldic porosity appears dark. The outline of the ooids is traced by orange to red luminescent early diagenetic micritic envelopes and fine crystalline cements. Interparticle porosity between ooids is filled by coarse crystalline sparite showing bright orange luminescence. This is interpreted as the result of late diagenetic neomorphism of an original early diagenetic marine-phreatic sparite. Late Cretaceous: Sinai Peninsula, Egypt. Dolomitization and compaction. Dolomite rhomboids. The rhomboids have a non-luminescent to weakly luminescent core surrounded by a bright orange luminescent zone. The weak luminescence of the cores indicates iron-rich diagenetic fluids and the incorporations of Fe2+in the dolomite lattice ('quench' ion) during crystal growth. By contrast, the final bright orange luminescent zone indicates changing pore fluid chemistry with more Mn2+ incorporation in the crystal lattice. Broken cores cemented by the outer luminescent zone indicate ongoing compaction during dolomitization. The rhomboids are interpreted as baroque dolomite typical of late burial diagenesis. Same locality as -> 6 Diagenetic filling of a fossil (brachiopod shell not visible in figure). Left part shows sediment (micrite) with red to orange luminescence due to diagenetic transformation to Low-Mg calcite and the incorporation of Mn2+in the calcite lattice. Remaining porosity was cemented by large calcite crystals (right) formed during late diagenesis. The distinct zoning of the crystals with weak and bright orange luminescent zones indicates slow crystal growth, changing pore water chemistry and/or changing redox conditions during crystal formation. The latest cements exhibits bright orange to yellow luminescence and document the final stage of the diagenetic cements. Middle Devonian: Anti-Atlas, Morocco.

-> 1, 2: Blomeier and Reijmer 1999; 3: Courtesy of R. Koch (Erlangen); 4: Elorza et al. 2001; 5-8: Courtesy of R. von Geldern (Erlangen)

Trace Elements and Stable Isotopes

The most important carbonate minerals are LowMg calcite (LMC), High-Mg calcite (HMC), aragonite and dolomite (Fig. 3.8). The dividing line between LowMg calcite and High-Mg calcite is commonly drawn at 4 mol % MgC03. These groupings can be subdivided into those containing a variable amount of MgCO, Fluid inclusions in carbonates are a powerful tool (4-12 mol 9%) and those containing a consistently high for the amount of MgCO, (12-28 mol %, e.g. corallinacean red history and timing of shallow and burial diagenetic algae, echinoderms). The latter group represents the and low-grade metamorphic processes ( Brockerhoff HMC sensu stricto (hHMC = high High-Mg calcite). The amount of Mg substitution for Ca in the calcite and Friedman 1987; Liedmann 1992), conditions of dolomitization (Goldstein et al. 1990; structure is determined by X-ray diffraction analysis. The composition of carbonate sediments is studied Montanaze and Read 1992), migration processes of paleofluids (Burruss et al. by petrographical microscopy and X-ray diffraction (XRD), which is particularly useful for analyzing fine1985; Ricken 1992; Muchez et al. 1994), uplift and subsidence history of sedimentary rocks grained carbonate rocks. The qualitative and quantita(McLimans 1987), tive methods of XRD whole rock analysis and clay minsubaerial exposure and karst phenonema (Goldstein eral analysis are described by Hardy and Tucker (1988). XRD data provide information on the chemical comet al. 1990), data on pore water chemism and temperature dur- position of carbonate minerals, allow carbonate minerals to be distinguished, and are used to determine the ing the formation of geodes, vugs and veins. ordering of dolomite crystals and the proportions of calcite and dolomite. The 'carbonate bomb' (Miiller and Gastner 1971) offers the possibility of rapidly deter3.2.4 Mineralogy and Geochemistry minating the contents of CaCO, and insoluble residues Carbonate minerals include minerals composed of in limestones. C0,2- and one or more cations. Approximately sixty minerals occur in nature with a C03group in common. Of these the trigonal CaC03 (calcite) and its orthor- 3.2.5 Trace Elements hombic polymorph (aragonite) are the most common and Stable Isotope Analysis in modem sediments. Calcite and dolomite are by far the most common carbonate minerals in ancient car- Section 13.3 summarizes the impact of geochemical bonate rocks. Several cations can substitute in varying studies of ancient limestones and the advantage of comamounts for the Ca2+in the crystal structure: ~ g ~ bined + , investigations of microfacies, stable isotopes and Fe2+and Mn 2+ are more readily accepted in the hex- trace elements. agonal calcite structure, and S$+ and ~ a by~the+aragonite structure. The minor element composition of cal- Trace elements: The elemental analysis of carbonate cite and aragonite is determined by biochemical and rocks provides important data on the sedimentary and diagenetic history. Atom Adsorption Spectrophotometry physical-chemical processes.

monly combined with petrographic and cathodoluminescence microscopy and isotope analysis (Sotak and Lintnerova 1994). Fundamental techniques have been described by Hollister and Crawford (198 I), and Goldstein (1993).

System

Mol % MgCO,

Stability

Calcite CaCO, Low-Mg calcite (LMC)

trigonal

4 to -30 Mg content correlated with water temperature

metastable

very low

metastable, alters readily in calcite under aqueous conditions

40 - 50

stable

Dolomite

I

orthorhombic

trigonal CaM~(CO,),

Fig. 3.8. Common carbonate minerals.

1

Mineralogy

Isotope signal Preservation potential HIGH Good chance of preservation of carbon and oxygen isotope signals

Mineralogy of components

-

Components Skeletal Non-skeletal

Pristine aragonite

Mollusks

Pristine Low-Mg calcite fossils, grains or cements

Brachiopods, belemnites, foraminifera, bivalves

Marine cements, Low-Mg calcite ooids

Pelagic sediments particularly coccolith oozes

Molluscs, foraminifera, corals, echinoderms, calcareous algae

Marine cements, ooids, peloids, intraclasts

Some micrites, some shallowwater carbonates some dolomites

-

Phosphatic fossils

Conodonts, fish teeth

MODERATE

Secondary calcites

Carbon isotope signals may be preserved, oxygen isotope signals are commonly altered

(stabilized in relatively closed systems with low waterlrock ratio)

LOW

Secondary calcites

Carbon and oxygen isotope signals very likely to have been altered

(

Bulk sediments

(stabilized or cemented in relatively open systems with high waterlrock ratio)

Marine cements

Limestones altered by near surface meteoric diagenesis of intensive cementation or recrystallizationduring burial; many dolomites

Fig. 3.9. Preservation potential of carbon and oxygen isotopes in ancient carbonate sediments and skeletal and non-skeletal constituents, and phosphatic fossils. Modified after Marshall (1992).

(AAS) is widely used in the analysis of limestones and dolomites because of elements hidden in minor amounts within the carbonate lattice. Inductively-coupled Plasma Atomic Emission Spectrometry Analysis (ICP-AES) and Neutron Activation Analysis (NAA) are used for determining the contents of trace elements and rare earth elements in carbonate rocks by whole-rock and selective analyses (Fairchild et al. (1988). Minor elements in carbonate rocks and in fossils are important paleoenvironmental indicators. The combined use of microfacies data, trace elements and isotope geochemistry in facies analyses continues to evolve in current studies (see Chap. 13).

sisting of Low-Mg calcite are rather resistant to diagenetic alteration, isotope analyses of brachiopods are enjoying increasing popularity. Stable isotope analyses of ancient carbonates provide proxies for paleoenvironmental constraints (e.g. temperature and salinity variations of the sea water, terrigenous input), unravel changes in carbon cycling of ancient ocean-atmosphere systems and document global fluctuationsin the climate. Isotope abundance measurements for geochemical research are determined on a mass spectrometer. Basics: Laboratory work

Techniques and microscopical methods Beckett, D., Sellwood, B.W. (1991): A simple method for Stable Isotopes: The isotope ratios of '80/160 and 13C/ producing high-quality porecasts of carbonate rocks. - Sed. 12Care very often used to trace processes involved in Geol., 71, 1-4 the production of carbonate grains and their subsequent Brown, R.J. (1986): SEM examination of carbonate microfacies using acetate peels. - J. Sed. Petrol., 56, p. 538 conversion into limestones. Isotope studies are perDelgado, F. (1977): Primary textures in dolostones and reformed as whole-rock bulk analyses or analyses of crystallized limestones: a technique for their microscopy single components (e.g. isolated fossils, carbonate cestudy. - J. Sed. Petrol., 47, 1339-1341 ments) or as microsamples of individual parts of fos- Folk, R.L. (1987): Detection of organic matter in thin-sections using a white card. - Sed. Geol., 54, 193-200 sils (e.g. shells) or cement crystals. The preservation Friedman, G.M. (1959): Identification of carbonate minerals potential of isotope signals depends on the preservaby staining methods. - J. Sed. Petrol., 29.87-97 tion of the primary mineralogy and the degree of di- Gardner, K.L. (1980): Impregnation technique used colored agenetic alterations (see Fig. 3.9). Diagenesis can obepoxy to define porosity in petrographic thin sections. scure the original composition of constituents of carCanadian Journal of Earth Sciences, 17, 1104-1107 bonate rocks, and if undetected, can lead to erroneous Germann, K. (1965): Die Technik des Folienabzuges und ihre Ergiinzung durch Anf&bemethoden. - Neues Jahrbuch fiir conclusions. All samples, therefore, must be tested prior Geologie und Palaontologie Abhandlungen, 121,293-306 to isotope analysis with respect to potential diagenetic Gies, R.M. (1987): An improved method for viewing microoverprinting, using petrographic and CL microscopy, pore systemsin rocks with the polarizing microscope.-Soc. SEM criteria and chemical data. Because shells conPetroleum Engmeers Formation Evaluation, 1987,209-214

72

Gutteridge, P. (1985): Grain-size measurement from acetate peels. - J. Sed. Petrol., 55,595-596 Katz, A., Friedman, G.M. (1965): The preparation of stained acetate peels for the study of carbonate rocks. - J. Sed. Petrol., 35, 248-249 Kobluk, D.R., Kim, K.H. (1991): A new microcomputer-assisted approach to the study of thin sections of carbonate rocks. - Bull.Canadian Petroleum Geology, 39,252-259 Mandado, J.A., Tena, J.M. (1986): A peel technique for sulfate (and carbonate) rocks. - J. Sed. Petrol., 56,548-549 Miller, J. (1989): Microscopic techniques. I. Slices, slides, stains and peels. -In: Tucker, M. (ed.): Techniques in sedimentology. - 86-107, Oxford (Blackwell) Moussa, M.T. (1976): Plastic spray thin-section cover. - J. Sed. Petrol., 46,252-253 Mugridge, S.J., Young, H.R. (1984): Rapid preparation of polished thin sections for cathodoluminescence study. Canadian Mineralogists, 22, 5 13-515 Miiller, G. (1964): Methoden der Sedimentuntersuchung. 303 pp., Stuttgart (Schweizerbart) Murphy, C.P. (1986): Thin section preparation of soils and sediments. - 149 pp., Berkhamsted (Academic Publ.) Ruzyla, K., Jezek, D.I. (1987): Staining method for recognition of pore space in thin and polished sections. - J. Sed. Petrol., 57, 777-778 Trewin, N. (1988): Use of the scanning electron microscopy in sedimentology. - In: Tucker, M. (ed.): Techniques in sedimentology. - 229-273, Oxford (Blackwell) Tucker, M. (ed., 1988): Techniques in sedirnentology. 394 pp., Oxford (Blackwell) Yanguas, J.E., Paxton, S.T. (1986):Anew technique for preparation of petrographic thin-sections using ultraviolet-curing adhesive. - J. Sed. Petrol., 56,539-540 Warne, J. (1962): A quick field or laboratory staining scheme for the differentiation of the major carbonate minerals. J. Sed. Petrol., 32, 29-38 Wolf, K.H., Easton, A.J., Warne, S. (1967): Techniques of examining and analyzing carbonate skeletons, minerals and rocks. -In: Chilingar, G.V., Bissell, H.J., Fairbridge, R.W. (eds.): Carbonate rocks: physical and chemical aspects. - Developments in Sedimentology, 9B, 253-341 Fluorescence and cathodoluminescence microscopy Amieux, P. (1982): La cathodoluminescence: mtthode d'ttude stdimentologique des carbonates. - Bull. Centre Rech. Exp1or.-Prof. Elf-Aquitaine, 6,437-483 Barbin, V. (1995): Cathodoluminescence of carbonates: new applications in geology and archaeology. - Scanning Microscope Supplement, 9, l 13-123 Barker, C.E., Kopp, A.C. (eds., 1991):Luminescence microscopy and spectroscopy. Quantitative and qualitative applications. - SEPM Short Course, 25, 195 pp. Fairchild, I.J. (1983): Chemical controls of cathodoluminescence of natural dolomites and calcites: new data and review. - Sedimentology, 30, 579-583 Gregg, J.M., Karakus, M. (1991): A technique for successive cathodoluminescence and reflected light petrography. J. Sed. Petrol., 61,613-614 Hemming, N.G., Meyers, W.J., Grams, J.C. (1989): Cathodoluminescence in diagenetic calcites: the roles of Fe and Mn as deduced from electron probe and spectrophotometric measurements. - J. Sed. Petrol., 59,401-411 Machel, H.G., Mason, R.A., Marino, A., Mucci, A. (1991):

References Laboratory Work Causes and emission of luminescence in calcite and dolomite. - In: Barker, C.E., Kopp, O.C. (eds.): Luminescence microscopy and spectroscopy: qualitative and quantitative applications. - SEPM Short Course, 25,9-25 Marshall, D.J. (1988): Cathodoluminescence of geological materials. - 146 pp., London (Unwin Hyman) Marshall, D.J. (1991): Combined cathodoluminescence and energy dispersive spectroscopy. - SEPM Short Course, 25,27-35 Meyers, W.J.(1991): Calcite cement stratigraphy: an overview. -In: Barker, C.E., Kopp, O.C. (eds.): Luminescence microscopy and spectroscopy: qualitative and quantitative applications. - SEPM Short Course, 25, 133-148 Miller, J. (1988): Cathodoluminescence microscopy. - In: Tucker, M. (ed.): Techniques in sedimentology. - 174-190, Oxford (Blackwell) Neuser, R.D., Bruhn, F., Gotze, J. Habermann, D., Richter, D.K. (1996): Kathodolumineszenz: Methodik und Anwendung. - Zentralblatt fiir Geologie und Palaontologie. Teil I, 1995,287-306 Pagel, M., Barbin, V., Blanc, P., Ohnenstetter, D. (2002): Cathodoluminescence in geosciences. - 514 pp., Berlin (Springer) Ramseyer, K., Fischer, J., Matter, A., Eberhardt, P., Geiss, J. (1989): A cathodoluminescence microscope for low intensity luminescence. - J. Sed. Petrol., 59,619-622 Richter, D.K., Zinkemagel, U. (1981): Zur Anwendung der Kathodolumineszenz in der Karbonatpetrographie. - Geologische Rundschau, 70, 1276-1302 Rost, F.W.D. (1992): Fluorescence microscopy. Volume I. 253 pp., New York (Cambridge University Press) Mineralogy, geochemistry and stable isotopes Arthur, M.A., Anderson, T.F., Kaplan, I.R., Veizer, J., Land, L.S. (1983): Stable isotopes in sedimentary geology. SEPM Short Course, 10,435 pp. Clauer, N., Chaudhuri, S. (eds., 1992): Isotopic signatures and sedimentary records. - Lecture Notes in Earth Science, 43,529 pp. Dickson, T. (1990): Carbonate mineralogy and chemistry. In: Tucker, M.E., Wright, V.P: Carbonate sedimentology. - 284-313, Oxford (Blackwell) Fairchild, I., Hendry, G., Quest, M., Tucker M. (1988): Chemical analysis of sedimentary rocks. - In: Tucker, M. (ed.): Techniques in sedirnentology. - 274-354, Oxford (Blackwell) Faure, G. (1986): Principles of isotope geology. - 589 pp., New York (Wiley) Hardy, R., Tucker, M. (1988): X-ray powder diffraction of sediments. - In: Tucker, M. (ed.): Techniques in sedimentology. - 191-228, Oxford (Blackwell) Hoefs, J. (1997): Stable isotope geochemistry, 4th edition. 201 pp., Berlin (Springer) Moore, C.H. (1989): Carbonate diagenesis and porosity. Developments in Sedimentology,46,338 pp., Amsterdam (Elsevier) Morse, J.W., Mackenzie, F.T. (1990): Geochemistry of sedimentary carbonates. - Developments in Sedimentology, 48,707 pp., Amsterdam (Elsevier) Veizer, J. (1983): Trace elements and isotopes in sedimentary carbonates.-In: Reeder, R.J. (4.): Carbonates: mineralogy and chemistry. - Reviews in Mineralogy, 11,265-299 Further reading: KO05 to KO12

4 Microfacies Data: Matrix and Grains

The purpose of this chapter is to outline and discuss the criteria used in the description of matrix and grains. Microfacies criteria reflected by fabrics and quantitative microfacies data are discussed in Chap. 5 and 6. Major constituents seen in thin sections of carbonate rocks are 'grains' and 'groundmass', the latter developed as fine-grained carbonate 'matrix' or as spany calcite representing pore-filling cements or recrystallized matrix. A spany calcite groundmass is conventionally called 'sparite' (calcite spar), and discussed in Chap. 7. Grains and matrix are separated at 62.5 pm in terrigenous sediments but at much lower values in carbonate rocks. Here the lower limit is defined differently as larger than 4 ym or >20 ym or >50 pm. SEM studies reveal the arbitrary character of particle size boundaries between grains and matrix, but a conventional definition is necessary for thin-section studies. The physical arrangement of particles, including their texture and structure, forms a fabric which reflects the depositional and diagenetic controls on the formation of carbonate rocks.

terial such as micrite, microspar and calcisiltite.A common generalization is that 'matrix' is synonymous with 'groundmass', but some authors use these terms to designate both fine-grained interstitial material (e.g. micrite) as well as coarse interstitial crystal fabrics (e.g. sparite formed by cementation or neomorphic processes, see Sect. 7.6). This contradicts the limitation of the term matrix to 'mechanically deposited material between particles - as distinct from precipitated cement' (Bathurst 1975). One should be cautious about regarding all fine-grained interstitial material as synsedimentary matrix: Intensive micritization, compaction and neomorphism of mixed carbonate/siliciclastic deposits as well as alterations of peloids may lead to the formation of a carbonate pseudomatrix (Dickinson 1970; Geslin 1994).

Techniques: Genetic interpretation and the understanding of the properties of fine-grained carbonates require the examination of polished and/or etched rock surfaces, thin sections, stereoscan microscope and transmission microscope studies, the investigation of geochemical and isotopical signatures as well as the use of 4.1 Fine-Grained Carbonate Matrix: biomarkers (Sect. 13.3).- Conventional thin sections used in microfacies studies are commonly too thick Micrite, Microspar, Calcisiltite (about 30 pm) to reveal distinct crystal boundaries. Peels Fine-grained matrix constitutes a significant part of the and ultra-thin sections offer better data (Honjo and carbonate record. Despite the importance of micro- Fischer 1965; Wolf et al. 1967; Lindholm and Dean crystalline limestones in basin analysis and as reser- 1973; Murphy 1986; Tucker 1988). voir rocks and limestone resources, classifying and geMicrite textures described only on the basis of light netically interpretating microcrystalline carbonates still microscopy may be inadequate. Epifluorescence miinvolve many problems. However, the advent of the croscopy assists in the discussion of organic material scanning electron microscope and the data provided by preserved in limestones (Dravis and Yurewicz 1985, geo- and biochemical analyses now allow us to take a Neuweiler and Reitner 1995). SEM studies of broken, closer look at modem carbonate muds and ancient fine- polished and etched surfaces provide an insight into grained limestones. the variability of micrites. Polished and etched SEM samples deliver better results than broken surfaces. The Definition: The term matrix denotes the interstitial main data which can be retrieved from SEM studies of material between larger grains. Most definitions refer fine-grained carbonates are summarized in Box 4.1. to the relatively small size of the crystals and/or particles bordering intergranular pores. Hence the matrix Major categories: Micro-grained limestones exhibit of micro-grained limestones includes fine-grained ma- mean sizes commonly between 2 ym to about 30 ym.

74

Micrite Terminology

Box 4.1. SEM criteria used in the distinction of fine-grained microcrystalline limestones of different origin and diagenetic history (based on Fischer et al. 1967; Fliigel 1968; Wise et al. 1970; Minoura 1974; Moshier 1989; Peszat 1991; Lasemi et al. 1993; Munnecke 1997).

Microfabric Grain size: Is measured by counting the longest diameter of 100 to 200 grains. Allows attribution to grain size-based classifications. 'Sorting' in micrites, as the result of competition between space and grain growth, can be used as measure of the textural maturity of fine-crystalline carbonates. Grain size ranges may reflect differences in the depositional environment (e-g. reef micrites and micrites in limestone/shale sequences). Differences in predominant crystal sizes provide indications of the potential aragonite-dominated or calcite-dominated precursors of calcite micrites. Grain contacts: Grain contacts seen under the SEM are straight, curvilinear or serrate. The percentage of specific grain contacts reflects the degree of diagenetic changes (e.g. recrystallization). Grain shape: Differentiation of anhedral, subhedral and euhedral micrite grains. Anhedral and subhedral grains forming a hypidiotopic fabric appear to be common in micritic rocks composed of grains > 4 pm. Irregular, interlocked grains form an 'amoeboid mosaic', in contrast to block-like grains forming a 'pavement mosaic' common in limestones affected by thermal stress. Most rnicrite grains are angular to subangular. Subrounded and rounded grains result from intergranular solution and crystal overgrowth. Inclusions in crystals: Liquid and gas inclusion pits are common in microspar crystals as well as in larger spar crystals. The composition of the inclusions indicates the conditions under which recrystallization took place. Microfenestrae: Some micrites contain round voids, 40 to 80 pm in size, which are filled with blocky calcite. The preservation of this microfenestral fabric is used as evidence against a strong mechanical compaction of the sediment prior to lithification. Boundary between calcite matrix and fossils: Diagenetic stages are distinguished by differences in the boundaries between matrix and fossils: (a) Sharp boundaries between matrix and Low-Mg calcite fossils (e.g. brachiopods, bryozoans, ostracods, trilobites) with well-preserved ultrastructures; (b) moderately sharp boundaries between matrix and fossils (recrystallized tabulate and rugose corals, stromatoporoids); and (c) boundaries between matrix and fossils (e.g. mollusks) which are difficult to recognize. Microporosity: SEM studies reveal numerous types of micropores (5- 10 pm wide) in micritic limestones, including both primary and solution-enhanced intercrystallinepores, as well as micromolds, microvugs and microchannels (PI. 716; see Chap. 5). Microporosity is developed in many subsurface micritic limestones, including significant petroleum reservoirs in Mesozoic and Tertiary deposits of the Middle East, North Africa, and the North American Gulf Coast.

Skeletal grains A main advantage of SEM studies of micrites is the possibility of recognizing the occurrence and abundance of planktonic nannofossils (Pl. 713-5, P1. 77/23) in mudstones and wackestones in both deep-water and shallow-water settings. SEM differentiation of silt-sized and smaller bioclastic grains derived from the breakdown of shells helps to define micrites formed by the accumulation of disintegrated invertebrate skeletons (group 7: Fig. 4.1).

Three categories can be distinguished according to differences in grain size and composition:

4.1.1 Micrite Terminology: The term 'micrite' is the abbrevation of

1 Micrite, characterized by a crypto- to microcrystalline crystal texture. The original definition by Folk (1959) sets a grain-size limit of 1,2, 7: Keupp et al. 1993; 3: Leinfelder 1985; 4: Bohm and Brachert 1993; 5: Fliigel et al. 1984; 6: Hensen et al. 1995

I'l:ttz

8 . blicrohial Carbonates

87

Allomicrites

and Von der Haar 1975; Shark Bay, Australia: Monty 1976; Gulf of Aqaba: Friedman et al. 1973, Gerdes and Krumbein 1987). Interpretation of limestones: The disintegration of externally calcified cyanobacteria is regarded as an important source of micritic reef limestones, especially of Paleozoic age (e.g. Pratt 2001).

Allomicrites Allomicrites (allochthonous micrites) originate from the destruction of calcareous algae and invertebrate skeletons, bioerosion, accumulation of calcareous plankton as well as from the erosion and abrasion of lithified carbonates (Fig. 4.1). In shallow waters, tropical storms and ebb-tidal currents causing a mixing of bank and ocean waters can lead to a redistribution of genetically different carbonate muds. Carbonate muds produced on shallow-marine platforms are also a major source for periplatform sediments deposited on slopes or in basins (periplatform carbonates, see Sect. 2.4.5.7) (5) Disintegration of benthic calcareous algae: The Halimeda model. The disintegration of the skeletons of modem calcareous green algae causes the formation of sand- to clay-sized particles. Processes involved in the disintegration, deposition and redeposition of the algal particles are exemplified by the udoteacean alga Halimeda (Fig. 4.3; P1.711-2, P1.5711-2). The ultrastructural elements of the calcareous skeleton of this and other green algae are aragonite needles. These needles are set free after decomposition of the organic matter. Morphologically similar needles are abundant in carbonate muds of the Great Bahama Bank and Florida Bay as well as in Pacific lagoons (Lowenstam and Epstein 1957; Stockmanet al. 1967; Neumann and Land 1975; Nelsen and Ginsburg 1986). The algal origin of the needles was supported by (a) comparable stable isotope data of muds and algal needles, (b) SEM photomicrographs (Pl. 712) indicating morphological similarities between the aragonite produced by udoteacean algae and the aragonite needles occurring within the aragonite muds, and (c) excess productivity of udoteacean algae in the Bight of Abaco (Little Bahama Bank) where the algae produce more than twice the amount of fine-grained aragonite that has accumulated in the Bight (Neumann and Land 1975). Aragonite muds occumng in the deeper Northwest Providence Channel are, therefore, explained as the result of the extended offbank export of algal muds. These points, however, have to be discussed in the light of new data: (a) Isotope data could also indicate chemi-

cal precipitation of the aragonitic muds, (b) SEM studies show that the aragonite needles in the Great Bahama Bank muds are bladed and have poorly developed pointed ends, in contrast to algal needles with blunt-ended prisms (Loreau 1982; Macintyre and Reid 1992). Nonskeletal aragonite needles are apparently precipitated ubiquitously over the Bahama Bank; they accumulate within the low-energy bank leeward of Andros Island and are exported to the deeper leeward slope (down to -90 m), and even to deep settings, as indicated by the position of the aragonite lysocline in a depth of 1500 m (Droxler et al. 1988), (c) Present-day standing stocks of green algae and carbonate production appear too low to account for the volume of Holocene aragonitic mud on top of the Bahama Bank. Algal mud production is estimated to be greater than an order of magnitude less than the precipitation rate calculated for the mud on the bank. Of course, a significant algal contribution to the submicroscopic needles of the muds can not be ruled out and has to be re-evaluated. Measurements of growth rates of Halimeda and other calcified udoteaceans suggest that these algae renew their standing stocks within a few weeks (Wefer 1980; Multer 1988; Hillis 1991, 1999)and could, therefore, produce tremendous amounts of fine-grained carbonate sediment in shallow lagoonal and reef environments. Halimeda mounds and banks, formed in deeper and shallow slope settings in eastern Australia, Indonesia and the Caribbean, document the enormous sediment-producing potential of these algae (see publications in Coral Reefs, vol. 6, 1988).The disintegration of algae, not only udoteaceans, is an additional important source of fine-grained sediments in modern reefs. Breakage and subsequent diminution of exposed calcified filaments of endolithic (boring) green algae (e.g. Ostreobium) and of filamentous cyanobacteria result in the production of silt- and micrite-size material (Kobluk and Risk 1977). Interpretation of limestones: Green algae, closely comparable with modem Halimeda, have been known since the Late Permian (Poncet 1989), were more common in the Late Triassic (Fliigel 1988; P1. 57/3), and became rock-building constituents of warm-water platform carbonates during the Cretaceous and in the Tertiary (Hillis 2001). Halimediform algae exhibiting a highly identical internal structure, however, occur as early as in the Ordovician and are more common in the Devonian (Pl. 57/4,5).

(6) Disintegration of epibionts living on seagrass and macro-algae: Seagrass (Thalassia, Posidonia, Zostera and others) is abundant in shallow subtidal and inter-

Halimeda Model

F

Filament

G

Fig. 4.3. The Halimeda model. Halimeda, a common calcareous green alga in lagoonal and reef environments, is one of the most prominent producer of modem carbonate muds and sands. The erect plant is several centimeters high and attached with a holdfast of root-like filaments to the sediment (B). The alga is segmented and branching. The segments possess an internal structure composed of interwoven tubular filaments which are differently arranged in the central and peripheral parts of the segments (C and D; P1. 5711, 2). Calcification starts at the surface between the filaments (D to F)) and progresses inwards. The skeleton consists of minute needles of aragonite (5 pm long and 0.3 bm wide; G; Pi. 712) which, on the death of the plant and disintegration of the segments, disperse inthe sediment and provide a source for lime mud. The mud is often redeposited within the shallow-water area or in deeper environments on the slope. Isolated algal segments (Pl. 315) are a major component of calcareous back-reef sands and occur in the talus of many Cenozoic reefs. A: The first species of Halimeda was documented from the Mediterranean Sea in 1599 by the Italian naturalist Imperato. His figure illustrates superbly the characteristic segmentation, the branching pattern and the inconspicuous holdfast of Halimeda tuna. The holdfast of the pantropical species forms a mat that fixes the plant onto the rocks or corals. The width of the thallus is about 10 cm. B: The basic holdfasts of the sand-growing species act as anchors in times of storms. C: Internal structure of a segment. Note the different branching pattern and orientation of the filaments in the central part (medulla) and the peripheral part (cortex). D: Differentiation of cortical filaments. Calcification (gray pattern) takes place around and between the filaments. E: Calcification on and between medulla (left) and cortical filaments. F: Close-up of the cortex exhibiting remains of organic membranes; see also Fig. E. G:Aragonite needles. Sources: A, B and C - modified from Hillis-Colinvaux (1980); D - modified from Hillis (1959).

tidal settings. Seagrass can tolerate a wide range of salinities, it occurs most prolific in water depths between 2 and 15 m. The mud banks of Southern Florida, sometimes regarded as an analogue of ancient mud mounds (Bosence 1985), document four important controls of seagrass on carbonate mud production and energy baffling: (1) The long and dense root systems (rhizomes), extending a few tens of centimeters below the sea bed, stabilize and bind the sediment. (2) The long blades have a baffling effect, can trap passing suspension-trans-

ported particles and reduce current speeds (Ginsburg 1957; Scoffin 1970; Almasi et al. 1987). Depending on the density of the meadows, large amounts of muddy sediment (packstones and wackestones) will accumulate. (3) Seagrass stabilizes the substrate permitting colonization by stable-bottomsediment-producing and sediment-reworkingcommunities, and (4) very importantly, sea-grass blades provide a constantly renewable substrate onto which benthic organisms can attach and grow (Ginsburg and Lowenstam 1958).

90

Epibionts are integral members of seagrass communities. The disintegration of the epibionts is a major source of lime mud in Florida Bay (Turmel and Swanson 1976; Nelsen and Ginsburg 1986) and other areas (Land 1970; Patriquin 1972). Epibionts comprise a variety of encrusters such as coralline algae, foraminifera, bryozoans, bivalves, gastropods and serpulids (Brasier 1975; Ivany et al. 1990). Seagrass is not restricted to tropical environments but is also common in warm- and cool-temperate carbonate settings ( Gostin et al. 1984) where epibiontic bryozoans and foraminifera contribute sigmfkantly to the production of mud-, silt- and sand-sized particles (Collins 1988). Floating seaweeds (large brown macro-algae) provide another habitat for epibionts which contribute to the formation of fine-grained carbonates. The epibionts (mostly bryozoans, coralline algae) occurring on Sargassum and other kelps produce significant amounts of skeletal material, which add much to nearshore and offshore carbonate muds and sands (Pestana 1985; Wehrmann 1998). Interpretation of limestones: Seagrass is known as far back as the Late Cretaceous and floating macroalgae at least since the Jurassic, but perhaps from the Devonian. Fossil seagrasses are extremely rare in the rock record, but can be inferred by examining characteristic lithologies (carbonate lenses enclosed within shales: Petta and Gerhard 1977; fining upwards sequences: Wanless 198l), invertebrate assemblages and associated foraminifera (Eva 1980). A contribution of epibionts to the formation of fine-grained limestones of inner shelf settings, therefore, should not be ruled out.

Bioerosion

compounds on and within the skeletons, and the microstructure of the infested particle. (c) Degradation by microborers (see point 8). (d) Mechanical erosion and abrasion in high-energy environments (Folk and Robles 1964; Swinchatt 1965; Matthews 1966; Stieglitz 1972). Tidal currents and wave action in lagoons may be effective in grinding grains. Experiments (Chave 1964; Folk and Robles 1964) as well as studies of the mud and silt fraction of modem carbonates (Mathews 1966; Stieglitz 1972; Futterer 1979) prove that mechanical abrasion and biological processes work together in the production of muds, whereby bioerosion appears to be of greater importance in low-energy environments. Nearly all marine invertebrates are affected by this destruction process. Impressive examples were reported from benthic forarninifera, corals, bivalves and gastropods, echinoderms,barnacles as well as coralline red algae (Alexandersson 1979; Fitzgerald et al. 1979; Canfield and Raiswell 1991). Shells of modem benthic reefal foraminifera break down into micron-sized needles and rods through combined effects of corrosion, dissolution,abrasion and erosion (Kotler et al. 1992; Debenay et al. 1999). Interpretation of limestones: The formation of allomicrites by the disintegration of invertebrate skeletons appears to be a common mode both in shallow-marine and deep-marine settings (Pl. 11811). Fine-grained micritic sediments may still show the disintegrated basic skeletal elements as demonstrated by fine-grained Cretaceous limestones consisting of calcite prisms of shells of the bivalve Inoceramus (Pl. 8718). Bioclastic micrites originating from the disintegration of corals, stromato(7) Disintegration of invertebrate skeletons (bioclas- poroids, tabulates and crinoids were described from Sitic micrites): Sorby recognized as early as 1879 that lurian reefs (Watts 1981). invertebrate skeletons disintegrate after death by 'maceration' processes into microscopic elements forming (8) Bioerosion and microborings: Bioerosion by macalcareous muds and silt- to sand-sized particles. De- rine and non-marine boring and grazing organisms is a major process in the production of clay- and silt-sized structive processes include: (a) Destructive diagenesis (physicochemical disso- carbonate particles contributing greatly to the formalution due to carbonate undersaturation), common in tion of micrite and calcisiltite. Biological erosion decolder sea water at higher latitudes and characterized stroys organic skeletons, grains and carbonate subby dissolution and breakdown of solid carbonates on strates, and creates cavities. Processes involved in bioerosion are corrosion by endolithic organisms and loosthe sea floor and in contact with sea water. (b) Microbial degradation of skeletal-bindingorganic ening of hard substrates by dissolution. Organisms matter under aerobic conditions at the sedimentlwater which are able to disintegrate hard carbonate substrates interface or just below it (Henrich and Wefer 1986; Frei- and skeletons include microbes, algae, foraminifera, wald 1995). The susceptibility to dissolution of car- sponges, near-shore bryozoans, worms (sipunculids, bonate grains depends on the amount of skeletal bind- polychaetes), mollusks, arthropods (cirripedians) and ing organic matter, as well as on the size, shape and echinoderms (regular echinoids). Chemical-mechaniroughness of the crystallites (Walter 1985). The im- cal borings by clionid siliceous sponges in skeletons or pact of degrading bacteria on biogenic carbonates is rocks, produce large quantities of fine-grained carboncontrolled by the distribution and supply of organic ate sediment (up to 30% of the total sediment) in deeper

Accumulation of Plankton

intertidal and subtidal zones; most boring chips are siltsized (Futterer 1974, Moore and Shedd 1977). Clionids are common in tropical regions, but also occur at high latitudes. Boring bivalves (e.g. Lithophaga, PI. 521 8) and snails occur preferentially in shallow seas. Of particular importance are heterotroph bacteria, cyanobacteria, green and red algae as well as fungi (Pl. 5211-4) producing microborings and causing micritization (Pl. 1212, P1. 1316). Bacterial attacks of organic matter in shells lead to the disintegration of skeletal grains into ultrastructural units. Borings of bacteria and fungi have diameters 50% within the beds). The carbonate deposition in the Solnhofen lagoon was controlled by an alternation of hypersaline conditions favoring the growth of cyanobacteria mats and normal marine conditions with the sedimentation of ultraplankton and the input of allochthonous carbonates. The light-colored bedded Oberalm Limestone (PI. 7611) represents a common Late Jurassic to Early Cretaceous bathyal facies that is widely distributed in the Alpine-Mediterranean region. The limestone is also known as Apfychuslimestone, Majolica, or Biancone. The carbonate production was controlled by the deposition of coccoliths and nannoconids as well as by the input of fine-grained carbonate derived from nearby platforms into open-marine basins. Adapted from Fliigel and Keupp (1979).

(11) Micro- and cryptocrystalline calcite cements: Detailed studies reveal that many 'micrites' are in reality crypto- and microcrystalline calcite or aragonite cements precipitated in very different settings including reef cavities (Friedman 1985; Reid et al. 1990; Scoffin 1993), slope environments (Wilber and Neumann 1993), ocean floors, beachrock (Pl. 3113) or caliche crusts (Sect. 2.4.1.1). A growing number of authors calls these micro- and cryptocrystalline cements 'micrite' or 'micritic cements', not taking into consideration the continuing struggle for clearness in sedimentological terminology (Friedman 1985; Milliman et al. 1985).

Micro- and cryptocrystalline cements are formed in place and, therefore, correspond to 'automicrites' as described above; see (1) to (4). Differentiating these micritic autochthonous microfabrics from allochthonous micrites is essential for accurately interpreting of depositional environments. A 'micritic matrix' occurring in intergranular pores of carbonate slope packstones or in voids of reef carbonates should not be considered a priori as an indication of low energy conditions (Reid et al. 1990; Wilber and Neumann 1993). Bahamian slope carbonates demonstrate the formation of autochthonous 'muddy' carbonates by interstitial precipitation of fine-grained Mg-calcite at the

Microspar

thermocline-layer depths (200 to 800 m) and in areas of strong currents. This process can transform sedimentary grain-support fabrics into diagenetic mudsupport fabrics (see Chap. 6), and thus give the paleoenvironmental interpretation a wrong direction. A cyanobacterial origin of rnicrite cements has been described from Pleistocene carbonates (Kazmierczak and Iryu 1999).

(12) Recrystallization and grain diminution: Recrystallization of grains (e.g. peloids, see Sect. 4.2.2) and grain-diminution (Orme and Brown 1963) of skeletal grains are further possibilities for the formation of a 'micrite' fabric. Grain diminution (degrading neomorphism) takes place both during early diagenetic and burial diagenetic phases (Dixon and Wright 1983). It results in a replacement of former larger crystals by tiny crystals due to changes in crystal texture or changes in mineralogy. Examples are known from modem and ancient algal carbonates, where early diagenetic microcrystalline cements are formed within the algal frarnework (Alexandersson 1977). The dissolution of sparry cements in grain-supported limestones and the precipitation of microcrystalline cement (Wardlaw 1962; sparmicritization, Kahle 1977) can also cause the formation of diagenetic micrite. Alteration of skeletal grains due to a combination of micritization and recrystallization lead to the formation of modem lagoonal muds composed of rnicrite-sized clumps of equant anhedral Mgcalcite crystals about 0.5 pm in size (Reid et al. 1992). 4.1.3 Microspar

Microcrystalline carbonate rocks display a wide range of mean crystal sizes. For examples see P1. 612; P1.4712, PI. 9117). Folk (1959, 1965) distinguished between 'micrites' ( 3) and grain orientation patterns (-> 1,5,7) as well as bedding and lamination (-> 2,4,6) reflect depositional and climatic conditions and indicate biological and diagenetic controls during sedimentation. Internal bedding of limestones is recorded by distinct compositional changes (-> 2) and current-aligned orientation patterns of elongate particles (e.g. imbrications, cross-structures, -> 1, 3). Biolaminated fabrics are characterized by thin laminae differing in grain size, texture, biota (-> 4, P1.50/1), mineral composition, clay content, and the amount of organic material. Ideally, laminae represent 'sedimentation units' formed in short-term intervals. The classification of bedding and lamination is based on structural and textural criteria (Demicco and Hardie 1994, see Sect. 3.1.1.2). 1 Grain orientation: Imbrication structure, indicating current energy. The current 'direction' is from right to left. Most grains are cortoids comprising coated shells (CS), fusulinids (F), and echinoderms (E). Open marine platform. Early Permian: Fomi Avoltri, Carnia, Italy. 2 Bedding: Interlayering of fine wavy laminae consisting of sand-sized grains (peloid packstone, P) and carbonate mud (mudstone, M). This texture is called 'heterolithic bedding' and indicates a depositional environment where current flow varies considerably. Jurassic: Northern Alps. 3 Cross-bedding of foraminiferal shells (Nummulitidae: Assilina and Nummulites). Note the radial hyaline wall structures. The biofabric characterized by chaotically stacked tests, linear contact imbrication und cross-bedding indicate deposition by short-term high energy events. Early Tertiary (Eocene): Agathazell, southern Bavaria, Germany. 4 Biolamination: Alternation of fine wavy laminae corresponding to microbialites (ME), sponges (S), and sediment. Late Triassic (Dachstein limestone, Norian): Begunjscica Mountains, northern Slovenia. 5 Grain orientation: Parallel orientation of tabular limestone clasts caused by current transport. Smaller grains are micrite intraclasts and peloids. Precambrian (Altyn Formation): Logan Pass, Glacier Park, Montana, U.S.A. 6 Lamination consisting of microspar laminae and peloidal laminae. Equant coating of the small peloids by cement rims perhaps points to a bacterial origin of these grains occurring within a peloidJmicrite crust (see PI. 815). Reefal limestones. Middle Triassic (Ladinian): Seiser A h , Dolomites, Italy. 7 Lamination due to parallel oriented densely-packed 'filaments' (arrows, see PI. 11312). The microfabric of undisturbed hemipelagic laminae is often characterized by a preferred horizontal orientation of elongated particles (Krinsley et al. 1998). Early Jurassic: Djebel Assiz, Northern Tunisia.

5 mm

5 mrn

184

provided by King (1948) who used fusulinid orientations for interpretating the directions of ancient shorelines. Tentaculites and styliolinids are often currentaligned, but preferred orientations can vary considerably (Wendt and Belka 1991, Hladil et al. 1996). Other current-aligned microfossils are shown in P1.7418 (foraminifera), P1. 7812 (sponge spicules), P1. 94/7 (trilobites), P1. 5717 (gymnocodiacean algae), P1. 11211 (sponge spicules), P1. 10216 (shells), P1. 10512 (dasyclad algae), and bivalve shells.

Orientation of intraclasts: Penecontemporaneous erosion and redeposition of sediment, indicated by intraclastic beds, is a common feature of peritidal and shallow subtidal carbonates. Measurements of the azimuths of the long axes of intraclasts on bedding planes and in oriented samples assist in reconstructing tidal currents and wave movement (Lindholm 1980).

Bedding and Lamination Fabrics

thin sections that are important in microfacies analyses (see Fig. 3.4).

Depositional controls on fine-scaled lamination and bedding are recorded by conspicuously planar laminae (Fig. 3.3), distinct changes in texture, composition and grain size (Pl. 18/2), parallel orientation of grains (PI. 18/7), or abrupt changes in microfacies (Pl. 1816). The latter can reflect short-term depositional events (e.g . storms, turbidites, mass flows) causing event stratification (Wheatcroft 1990; Seilacher 1991). Depositional processes leading to the formation of laminae are settling-out of grains from suspension, bottom flows and bedload deposition, and debris and grain flows. Common depositional bedding types are parallel bedding, cross-bedding (Pl. 1813) and normal or reverse graded bedding (PI. 1711). For reverse grading see Sect. 5.1.1.

Biological controls are indicated by wavy or crinkled laminae, irregular alternations of micritic and sparry layers (Fig. 3.3, Fig. 3.5, P1. 1814, P1. 50/1), intercalations of sedimentary layers and peloidal fabrics (Pl. 181 6, P1. 50/2), and relicts of cyanobacteria (Pl. 53) and other microbes. Microbial mats form on bedding surfaces. Most mats have a characteristic filamentous morphology, the filaments have rigid walls and polymeric sheets which act as sites of agglutination of sedimentary grains and external calcification. Of major importance for the creation of a laminated pattern (biolaminations, Gerdes and Krumbein 1987; Gerdes et al. 1991) is the capacity of the mat-constructing biota to migrate vertically to escape burial by sediments and to recolonize the newly deposited surface. 5.1.3 Bedding and Lamination Fabrics In terms of ecology, biolaminites correspond to sucBedding and lamination are caused by changes in depo- cessions with formative and consuming stages. Formasitional, biological and diagenetic controls. Depositional tive stages include primary production via photosynfactors primarily include changes in sedimentationrates thesis and chemosynthesis. Consuming stages are charand in the composition of the sediment, and alterna- acterized by anaerobic microbial communities with hettions of sedimentation and non-sedimentation phases. erotrophic and anoxygenic phototrophic bacteria. Heterotrophic bacteria trigger the formation of carBiological controls are predominantly a result of the interaction of microbes and microbial mats with their bonates, silicates and sulfides, and the growth of cephysical and chemical environment and their influence ments which increase the preservation potential of bioon binding and trapping of the sediment. Diagenetic lamination structures. The thickness of biolaminated processes leading to bedding structures are dissolution stacks ranges from millimeters to centimeters and even decimeters. Resulting biolaminated structures have and cementation within the sediment. Types, descriptive criteria and the significance of been called 'cryptalgal' structures (Aitken 1967; Monty bedding and lamination structures are discussed in Sect. 1976). 3.1.1.2. Although bedding and lamination must be studBioturbation commonly alters or destroys bedding ied on an outcrop scale, a thorough investigation of oriented thin sections is important for recognizing hidden and lamination structures and contributes to a homogsedimentary structures (e.g. small-scale cross bedding) enization of the sediment (Reineck 1963, see Sect. and cyclic patterns. This chapter describes some of the 5.1.4). Exceptions exist however: A specific type of biomore common lamination and bedding types seen in logically controlled bedding is biogenic stratification Imbrication of intraclasts or elongated skeletal grains characterized by the preferred dipping of disk-shaped or elongate fragments at an angle to the bedding can be used as indicators of current-flow directions (Pl. 1811, 3). Flat pebble conglomerates containing imbricate intraclasts are typical in modem shallow-marine carbonates, and also known from ancient carbonate platforms (Whisonant 1987). Imbricate intraclasts document episodic events. Microfacies analysis reflects the source sediments of the intraclasts and may indicate whether the material was transported landward or seaward.

Burrowing and Bioturbation Fabrics

produced by infaunal deposit feeders (e.g. worms and crabs living on tidal flats) during feeding and burrow excavation leading to vertical size sorting of the sediment (Meldahl1987). This bedding is distinct from biogenic graded bedding (Rhoads and Stanley 1965)commonly formed in intertidal sediments by the feeding activity of polychaete worms in that the transition from the lower coarse-grained interval is sharp and not graded.

Diagenetic controis are revealed by parallel dissolution seams (Pl. 37/6), horse tail structures (Pl. 37/8), stylolite sets (Pl. 3713) and significant differences in carbonate and clay contents. Stylobedding and stylolamination are common features of shallow and deep marine limestones (Sect. 7.5.2). Other criteria of diagenetically caused or at least enhanced bedding are cemented layers (PI. 50/6), stratified cementation, hardgrounds (Sect. 5.2.4.1, P1. 23) and selective compaction. Diagenetic bedding is a common feature in chalks (Ekdale and Bromley 1988) and in argillaceous limestone and marly sequences of open marine platforms (Bathurst 1987). Diagenetic controls are of major importance in models explaining the origin of marl-limestone alternations in terms of repeating zones of diagenetic carbonate dissolution and cementation (Ricken 1986). These processes considerably enhance primary carbonate variations and can thereby generate rhythmic bedding (Sect. 16.1.1.1). Significance of depositional and biogenic lamination Depositional laminae, produced by variations in sediment input and primary production, are characteristic of hemipelagic sediments and occur in shallow and deep-water settings. Sediment is supplied seasonally andlor episodically. The preservation and composition of laminations of fine-grained carbonate rocks are excellent proxies for paleoclimatic conditions, oxic or anoxic bottom and pore waters, and ecologic constraints of benthic organisms. Thii-section image analysis is a common method of identifying and quantifying sedimentary laminae in the context of paleoclimatic studies of both marine (particularly lagoonal carbonates, Park and Fiirsich 2001) and lacustrine sediments (Francus 2001, Trichet et al. 2001).

185

fabrics (Ekdale et al. 1984; Bromley 1996; Donovan 1994; Fig. 5.4). These organisms occur in niches at different levels above and within the substrate. Tiering of infauna is reflected by vertically changing ichnofossils. Ichnofabrics are recorded by both discrete trace fossils as well as complicated structures, e.g. bioturbation fabrics. Burrowing is a prominent process in modem subtidal environments, often causing a lack of internal layering. Burrows and bioturbation provide information on conditions of life in sediments (Curran 1991) and, thus, about the depositional environment. They are also valuable indications of synsedimentary and diageneticdeformations (Gaillard and Jautee 1987). Compaction can be directly measured from deformed, originally cylindrical bioturbation tubes using the compaction law developed by Ricken (1987), see Sect. 7.5.1 and P1. 4913. Burrows are formed within soft unconsolidated sediments (muds, sands, firmgrounds) by the activity of animals during feeding, resting or migration. The size of burrow structures ranges from millimeters to a few centimeters and up to decacentimeters. The distinction between burrows and borings (biogenic structures drilled into hard sediment or shells) is not always easy to discern (Pl. 2311). Roots molds and casts (caliche, tidal flat, subtidal settings) can be mistaken for burrows (Pl. 2016). Most distinctive is the downward branching pattern where there is a marked and systematic decrease in tube diameter at junctions. Roots may have carbonaceous linings and exhibit branching out into clusters of root hairs. Bioturbation, burrowing and bio-retexturing The term bioturbation was proposed for 'all kinds of displacement within sediments and soils produced by the activity of organisms and plants' (Richter 1936). The term designates the churning and stimng of sediments by organisms resulting in the destruction of sedimentary structures (e.g. bedding). Because bioturbation is often very loosely used, a new term has been

5.1.4 Burrowing and Bioturbation Fabrics

Organisms that across* rest 'POn Or ingest sediment Create trace fossils exhibiting characteristic shapes and patterns and well-defined ichno-

Fig. 5.4. Distinct burrow in a rnudstone destroying the d& organic-richlayers. Siliciclasticcomponents enriched

within the burrow. Late Devonian: Menorca. Scale is 2 mm.

Burrowing and Bioturbation

proposed. Bio-retexturing is defined as the processes by which burrowing biota may modify or transform original textures by relocating significant volumes of unlithified sediment into or out of the sedimentary layers (Pedley 1992).

quiet-water sheltered embayments, e.g. lagoons, muddy tidal flats) and deeper water environments below fairweather and storm-wave base. Recent shallow-marine carbonate environments in Florida and the Bahamas are dominated by burrows of the shrimp Callianassa, which affect up to 75% of the sediment. Repetition of Occurrence and origin of bioturbation burrow excavation and storm infilling results in the forBioturbation occurs in shallow- and deep-marine mation of a storm-derived sediment textures dominated environments as well as in lacustrine settings and even by mottled packstone with coarse skeletal patches in eolian environments (e.g. carbonate dunes: Ahlbrandt (Shinn 1968; Tudhope and Scoffin 1984; Curran and et al. 1978). Burrows are the most common features White 1991; Wanless and Tedesco 1993). observed in shelf limestones (e.g. P1. 13511). BurrowBurrowing is common in many slope sediments ing occurs in carbonates both in intertidal and espe- (Henderson et al. 1999; P1.137/1,6). The occurrence cially subtidal settings, and in deep-marine bathyal en- of pelagic bathyal and abyssal deep-sea bioturbation vironments where a high density of endobionts in con- (Pl. 1912,3; PI. 13911) in the upper few tens of centijunction with low sedimentation rates may cause mul- meters of the sea bottom depends on the nature of the tiple episodes of burrowing and churning-up of the sedi- seafloor sediment, the oxygen content of the bottom ment. Bioturbation is ubiquitous in outer-ramp settings and of the pore waters, and the nutrient resources where crustacean-dominated bioturbation results in in- (Ekdale et al. 1984;Wetzel1984; Meadows and Meadtensive bio-retexturing of the primary depositional fab- ows 1994). Because the rates of deep-sea bioturbation are high, in contrast to the low sedimentation rates, rics and masks inorganic process-related structures. deep-sea bioturbation structures often represent mulInfaunal burrowing organisms are particularly fre- tiple episodes of burrowing (Magwood and Ekdale quent in calcareous muds deposited in shallow-marine 1994).

Plate 19 Burrowing and Bioturbation: Sea-Bottom Conditions and Post-SedimentaryDiagenetic Changes Burrows are formed within soft unconsolidated sediments (muds, sands, firmgrounds) by the activity of animals. The term 'bioturbation' designates the churning and stirring of sediments by organisms resulting in the destruction of sedimentary structures (e.g. bedding). Bioturbation fabrics are typified in terms of spatial arrangement and geometry of burrows, burrow density (using semi-quantitative 'bioturbation indices'), burrow abundance, and texture and filling of burrows. These criteria can be studied in the field but can also be applied to large thinsections. Burrows and bioturbation are the most common features observed in shelf limestones and deep-marine carbonates. The common criteria of burrowed limestones is a mottled appearance differing in color and texture (-> 6), or by dolomitization from the host rock. 1 Indications of bioturbation are the circular swirls (arrows) of skeletal debris (trilobite and echinoderm fragments), the patchy distribution of these structures, and variations in packing densities of grains. Well-oxygenated subtidal mid-shelf environment. Red bedded limestones. SMF 9. Ordovician: Oland Island, Sweden. 2 Burrowed radiolarian wackestone. Note the difference in the packing of radiolarian tests in the infilling of the burrow and outside the burrow. Bathyal environment. Late Jurassic: Northern Alps. 3 Burrowed calcisphere packstone. Note different packing of the spheres (corresponding to calciodinoflagellate cysts). The calcisphere content exceeds 35%. The irregular texture is partly caused by synsedimentary sliding of the sediment (Voigt and Hiintzschel 1964). Open-marine deep-shelf environment. Red bedded limestones alternating with flint layers. Late Cretaceous (Pliiner marl, Late Turonian): Northern Germany. 4 Burrowfilling consisting of benthic foraminifera and shell bioclasts. Note absence of compaction indicating firmground substrate consistency. Late Jurassic (Sequanian): Beze, France. 5 Burrow within microbial crusts, infilled with oncoids and coated grains. Upper slope environment. Late Triassic (Raibl Beds): Schlern, Dolomites, Italy. 6 Distinct mottling due to bioturbation in a deep-shelf lime mudstone with pelagic ostracods (see P1. 93/3,4). Note differences in color shades and compaction of burrows indicating softground substrate consistency. Early Carboniferous (Late Vistan): Betic Cordillera, southern Spain. 7 Burrowing indicated by skeletal grains (predominantly trilobite debris) forming twisted structures. Bedded intermound mid-shelf limestones. Early Devonian (Emsian): Anti-Atlas, southern Morocco.

1'l:ltc.

I9 I3urrowing a n d B ~ o r u r b a t i o n

187

188

Burrowed Limestones

quantitative categories. These categories are divisions between two extremes: 0% bioturbation (no evidence of biogenic mixing of sediments) and 100%bioturbation (complete biogenic mixing of sediments). The categories between these end members in a continuous spectrum of bioturbation are defined by the ranges of biogenic disturbance, e.g. 1-10% bioturbation, 10-40% Diagnostic criteria of bioturbation fabrics in limestones bioturbation, and so on. Names have been given to such Small- to medium-scaled burrows diameter ranges categories reflecting some ordinal scale (e.g. ichnofabfrom 7, 8), often associated with microbial bindstones. Larger millimeter- to centimeter-sized voids with flat bases and digitate roofs are known as strornatactis. These voids are commonly filled with fine-grained sediment at the base and sparry cements at the top. Birdseye limestones are formed preferentially in supratidal and intertidal environments, stromatactis-type voids occur more commonly in subtidal environments. Both types are formed by various processes (Box 5.1 and Box 5.2). Significance: Open-space structures are valuable microfacies criteria for indicating ancient depositional settings and environmental conditions, and controlling the porosity and permeability of carbonate rocks. Stromatactis structure in peloidal wackestone. The cm-sized structures occur within a 1.5 m thick horizon in the uppermost part of slope sediments close to a microbial-sponge reef. They are interpreted as the result of an internal erosion of a laminar organic framework (Matyszkiewicz 1993). The roofs of the cavities are lined with thin, marine phreatic isopachous cements, the center with blocky calcite crystals formed under burial or meteoric conditions. Note the basal internal sediment consisting of tiny peloids. Late Jurassic (Oxfordian): Mlynka quarry NW Crakow, southem Poland. Laminoid fenestral fabric (LF-A fabric) Laterally elongated open spaces within pisoid layers. Supratidal environment. SMF 21. Late Triassic (Carnian): Nesza quarry, Budapest, Hungary. LF-B I1 fabric in bindstones with reworked pisoids. The fabric is characterized by a large amount of detrital sediment. Supratidal/itertidal environment, inner carbonate platform. Early Jurassic (PantokratorLimestone): Peloponnesus, Greece. Fenestral fabrics within cyanobacterial mats. Note the occurrence of filaments (arrow). The association of cryptalgal structures and fenestral fabrics indicates a peritidal environment. Early Carboniferous (Late Toumaisian): Czatkovice quany, Crakow Upland, southern Poland. Fenestral fabric. Note pisoids, black pebbles (center), and internal micrite (gray). Supratidal environment.Early Jurassic (Pantokrator Limestone): Peloponnesus, Greece. Not birdseyes! Open bifurcated voids (plant roots and rootlets) within recent caliche. Root molds can be mistaken for burrows but differ in downward branching and decrease in diameter. French Reef, Bahamas. Birdseyes. Small calcite-filled voids in a laminated dolomite mudstone. Planar fine laminae composed of couplets of peloid-rich layers alternating with continuous dark mudstone layers. This is a common texture in peritidal carbonates. Lagoonal intertidal environment. Late Triassic (Hauptdolomit, Norian): Steinplatte,Tyrol, Austria. Close-up of birdseyes. Note sediment infilling. Late Triassic (Hauptdolomit, Norian): Steinplatte,Austria. -> 1: Matyszkiewicz 1993

Fenestral Fabrics

These cavities and fillings are believed to be predominantly of synsedimentary origin and should not be confused with spar-filled interparticle pores, growthcavities in reefs, solution voids and spar-filled fractures, or mineralized lichens and spar-filled molds of plant roots found in caliche crusts (Klappa 1978). Birdseyes occur predominantly in supratidal and intertidal carbonates, stromatactis in limestones formed in deeper and shallow subtidal environments. Other terms in use for limestones with spar-filled voids are dismicrite (disturbed micrite: Folk 1959), describing a micritic limestone with less than 1%grains and containing many birdseyes, and loferite (Fischer 1964), characterizing a limestone riddled by spar-filled shrinkage pores (Sect. 16.1.l.3). Both terms are partly synonymous with birdseyes limestone but the terms birdseyes and stromatactis should be reserved for describing the shape and geometry of the cavities, whereas loferite may be used for carbonate rocks abundant in various kinds of fenestral fabrics formed in a peritidal environment.

vertical tubular voids filled with calcite, in places associated with birdseyes, are most likely root tubes or burrows and should be named 'pseudo-birdseyes' (Shim 1982). These tubular structures of constant size often occur in tidal and subtidal fine-grained limestones (Wu 1983).

5.1.5.2 Fenestral Fabrics

Birdseyes (but also stromatactis-type structures) are important constituents of fenestral fabrics. Tebbutt et al. (1965) suggested the name fenestra or window to characterize ... 'a primary or penecontemporaneousgap in rock framework, larger than grain-supported interstices'. Fenestrae may be open cavities, or may be completely or partially filled by surface-derived internal sediment, diagenetic intemal sediment (e.g. crystal silt) or cements. Fenestrae have no apparent support in the framework of primary grains composing the sediment. In that respect, they differ from growth-framework pores or from solution voids. The term fenestra is now in use for any kind of a hole of any shape in a rock or unconsolidated sediment 5.1 5 . 1 Birdseyes that is not of an intergranular nature (Demicco and Birdseyes and birdseye limestones (Pl. 20/7,8. P1.1231 Hardie 1994). It seems, however, better to restrict the 2) are old names used by American field geologists to term to fabric-selective textures, and to use the term describe calcite-filled voids that sparkle in the sunlight. void for non-fabric selective cavities. Apparently, the shape and sparkle of these features reminded someone of birds'-eyes. The name was intro- Terminology of fenestral fabrics Fenestrae are arranged concordant to stratification, duced for very small spar-filled voids in Ordovician cross-bedded, or irregularly distributed. Arrangement micritic shelf limestones (Ham 1952). Birdseyes occur as isolated bubble-like vugs 1 to Box 5.1. Proposed origin of birdseyes structures. 3 mm in diameter, or as planar isolated vugs 1 to 3 mm high by several millimeter in width forming fenestral Direct or indirect organic interactions fabrics. The structures are often associated with micro1 Spar-filled interspaces in and between algal and cyanobacterial mats: Ham 1952; Philcox 1963; bial and algal mats. They are found in carbonate rocks Deelman 1972 from the Precambrian to the Recent and originate pre2 Cavities supported by algae and enlarged by receddominantly in supratidal, sometimes in upper intertidal ing tidal waters: Wolf 1965 settings. 3 Cavities formed by burrowing organisms: Fruth and

Origin of birdseyes Birdseyes have different origins (Box 5.1). Modes 1 , 2 , 5 and 6 produce birdseyes arranged more or less concordant to bedding planes. Irregularly distributed open-space structures may originate by modes 3,4 and 7 to 9. Nearly all modes are known from modem shallow-marine environments, some have been verified by experiments (Shinn 1983). The term birdseyes often is rather loosely used, but should be restricted to millimeter-scalespar-filled vugs exhibiting rounded shapes and concentrated in peritidal environments (Shinn 1983).Small vertical to near-

Scherreiks 1975 4 Gas bubbles caused by decaying organisms: Kom 1932; Hodgson 1958; Cloud 1960; Shim 1968

Inorganic 5 Desiccation, shrinkage pores in tidal zones: Fischer 1964 6 Air inclusions formed during subaerial exposure and subsequent tidal reinduration: Bolliger and Burri 1970; Deelman 1972 7 Different behavior of capillary and non-capillary sediment in comparison to water: Deelman 1972 8 Leaching of anhydrite 9 Late diagenetic selective recrystallization ('pseudosparitization'): Wolf 1965; Zorn 1971

Fenestral Fabrics

and shape is used in classifying laminoid-fenestralfabrics (LF fabrics) characterized by elongate horizontal fenestrae within fine-grained or grain-supported sediment (Fig. 5.5): (a) LF-A fabrics - with distinct laminoid fenestrae (Pl. 13216, P1. 142/13), and (b) LF-B fabrics -with irregular laminoid fabrics. The latter type is subdivided into low-detrital fabrics &B-1) with voids embedded in micrite, and high-detrital fabrics with voids occurring in sediment rich in grains (LB-2,P1.816, P1. 12211). Origin and distribution of fenestral fabrics The shape and orientation of fenestrae reflect different origins: (1) Laminoid fenestrae (Pl. 4112) are of polygenic origin and may be caused by (a) wetting and drying of carbonate mud in supratidal settings (Shinn 1968), (b) drying out of the surface of cyanobacterial mats resulting in wrinkling, lifting and separation from the adjacent sediment (Hardie and Ginsburg 1977; Davies 1970; Logan et al. 1974), and (c) degassing of decaying organic material connected with compaction of subspherical gas bubbles. Larninoid fenestrae are common in modern intertidal to supratidal settings. However, these structures Fenestral Fabrics

develop (as do cyanobacterial mats) in a variety of subaqueous marine and non-marine environments, too. (2)Tubularfenestrae originate in modem intertidal and shallow-subtidal environments as burrows or as root holes, but are also formed by upward escape of gas bubbles biogenically produced within the sediment. (3) Spherical to subsphericalfenestrae are produced by air and gas bubbles trapped during the deposition of the host sediment or they are generated by post-depositional decay of organic matter. Air bubbles can be transported within the sediment by rising groundwater. A particular type of mm- to cm-sized spherical and subspherical open fenestrae are keystone vugs (Emery 1945), see P1. 2919. The vugs are larger than ordinary birdseyes and are produced by trapping of air-bubbles during storm deposition in the squash zone on beaches or in the sheetwash zone on tidal flats or playas (Shinn 1968; Dunham 1970; Deelmann 1972). (4) Irregularlyformed and distributed fenestrae (Pl. 4014) may form by (a) desiccation, (b) soft-sediment deformation of other originally more regular-shaped fenestrae, (c) gas bubbles, (d) evaporite molds, (e) burrows, (f) burial of pustular cyanobacterial mats, (g) dewatering of gel-like carbonate muds, and (h) replacement of grains. Some of these 'irregular' structures are not fenestrae but rather intergranular pores of grain- and packstones. Shinn (1983) proposed the term 'pseudo-fenestrae' for these structures. Note that shelter pores in subtidal lithoclast grainstones can strongly resemble vuggy laminoid fenestrae (Goldhammer et al. 1987, Hardie et al. 1986).

LF-A

5.1.5.3 Stromatactis

LF-B I

LF-B I1

Fig. 5.5. Subtypes of laminoid-fenestralfabrics.Type A and type B are distinguished by shape and distribution of the sparfilled fenestral voids (here white), type B-I and B-I1 by the relative amount of voids and sediment. Adapted from Tebbutt et al. (1965) and Miiller-Jungbluth and Toschek (1969).

These structures, characterized by elongated cavities with irregular tops and flat bases, were first observed in Frasnian and Early Carboniferous carbonate mounds of Belgium (Dupont 1881, 1883) and were considered as recrystallized fossils. Most authors now agree, that the name stromatactis should refer to a spar-filled (and sometimes mud-filled) body commonly embedded in micritic limestones that originated from centripetal cementation of cavities by fibrous or radiaxial cements. Some authors restrict the term to a spar network formed by interconnected cavities and exhibiting a reticulate distribution (Bourque and Boulvain 1993), others also incorporate non-interconnected spar bodies occurring underneath platy skeletons of stromatoporoids or corals (Tsien 1983; Flajs and Hiissner 1993). These structures resulted from cementation of synsedimentary shelter cavities or cavi-

Origin of Stromatactis Fabrics

ties formed by the collapse of mud underneath a rigid Common cements occurring within stromatactis object acting as an umbrella during water escape and cavities are radiaxial, fibrous and granular calcite. Fimud compaction. Stromatactis is abundant in micritic brous and radiaxial cements are considered as being of limestones, but geometrically similar open-space struc- early synsedimentaryorigin, formed a few centimeters tures also occur in cemented grainstone crusts or decacentimeters beneath the depositional surface. (Macdonald et al. 1994). Early diagenetic fibrous cements first originate in small The internal sediment in the cavities of stromatac- voids enlarged by erosional and solution processes. tis commonly is fine-grained micrite, sometimes with Other cement types are formed during shallow and microfossils, peloidal micrite, or laminated silt-sized deeper burial phases. Early cementation contributes sediment. Genetically it corresponds to the iddl of fine- greatly to rapid lithification and stabilization of cargrained sediment in a reticulated cavity system or to bonates formed at the flanks of mounds. diagenetic products caused by recrystallization of mud and deposition of solution products (Aissaoui and Stromatactis fabrics occur in patchy distribution or Purser 1983; Flajs and Hiissner 1993; Vigener 1996; as layers which alternate with limestones consisting preAubrecht and Szulc 2000; see Sect. 7.4). A common dominantly of micrite (Fig. 5.6). These alternations,obfeature of internal sediments is a vague and indistinct served in bedded Devonian stromatactis carbonates, lower boundary. have been interpreted as reflecting Milankovitch cycles Box 5.2. Proposed origin of stromatactisfabrics.

Organic 1 Recrystallized fossils: Dupont 1881; Scoffin 1987 2 Permineralized, unfossilizable organism (e.g. algae): Lecomptel937; Tsien 1983 3 Cavities formed after the decay of various soft-bodied organisms in the sediment: Bathurst 1959; Philcox 1963; Otte and Parks 1963; Lees 1964 ; Davies and Nassichuk 1990; Lees and Miller 1985; Warnke and Meischner 1995 4 Burrow network such as Callianassa: Shim 1968 5 Action of various burrowing organisms: Shinn 1968 Non-skeletal algae: Coron and Textoris 1974 6 7 Thrombolites, microbial: Pratt 1982 8 Diagenetic CaC03 replacement of large microbial accretions: Tsien 1985; Weller 1989 9 Winnowing of sediment between microbial framework mats on the sea floor: Pratt 1982, 1986 10 Cementation of cavities left after the decay of microbial mats: Flajs and Hiissner 1993; Kaufmam 1998; Vigener 1996 11 Collapse of material within organic tissue of probable microbial origin: Lees 1964, 1988; Lees and Miller 1985 12 Partial cementation of cavities created by collapse of unlithified sponge tissue: Bourque and Gignac 1983; 1986; Beauchamp 1989; Bourque and Boulvain 1993; Vigener 1996 13 Early marine cementation of cavity networks created by exacavation of uncemented material in partly indurated, decaying sponges and organic mats: Bourque and Boulvain 1993; Dicken 1996 14 Recrystallized bryozoans: Lowenstam 1950; Textoris and Carozzi 1964 15 Sheltering of sediment by bryozoan sheets: Schwarzacher 1961; Lees and Miller 1995 16 Action of plant roots: Bechstadt 1974 Inorganic 17 Primary cavities and/or dissolution cavities: Kukal 197 1 18 Cavities produced by dewatering and compaction of a thixotropic mud: Heckel 1972; Macdonald et al. 1994; Bemet-Rollande et al. 1982 19 Excavations between layers of early-cemented crusts on the sea floor, differential cementation of host peloidal mudstone into successive, closely-spaced hardgrounds: Bathurst 1980, 1982; Wallace 1987 20 Downslope creeping and slumping of partially cemented mud on mound flanks: Schwarzacher 1961; Bathurst 1982; MacDonald et al. 1994 21 Internal erosion of cyanobacterial growth cavities on a partly lithified slope: Matyszkiewicz 1993 22) Enlargement of pre-existing cavities (e.g. vertical water and gas escape structures) in unconsolidated bioclastic lime mud by internal erosion and internal reworking: Wallace 1987; Shen and Zhang 1997; Vennin 1997 23 Forcing apart and fracturing of variably bound and lithified sediment by episodic earthquakes: Pratt 1995 24 Subaerial solution (e.g. karstification) resulting in the formation of voids subsequently filled with carbonate silt and cement: Semeniuk 1971 25 Recrystallized patches of the host lime mud: Black 1952; Orme and Brown 1963; Wolf 1965; Ross et al. 1975 26 Pressure solution connected with low-grade metamorphism: Logan and Semeniuk 1976 27 Creation of cavity systems by hydrothermal endo-upwelling: Beka 1998

Zebra Limestones

1992; Flajs and Hiissner 1993), (d) below storm wave base (Bourque and Boulvain 1993; Kaufmann 1996). A common assumption is that stromatactis structures usually originate in mounds most likely formed below the photic zone, because of the abundant lack of calcareous algae. Stromatactis-bearingmounds are widely distributed in bathymetrically different ramp settings, particularly in the Devonian and Early Carboniferous of Europe, North America and North Africa (e.g. Carboniferous 'Waulsortian' facies, Fig. 5.7), but also originated at the top of submarine volcanic swells. Note that stromatactis is not only restricted to deeper subtidal settings, as shown by the infilliig of shrinkage voids corresponding in shape and structure to stromatactis with 'vadose silt' (PI. 1713) and the association of birdseyes and stromatactis in loferite-type bedded limeFig. 5.7. Stromatactis cavities on the flanks of a Waulsortian stones. mudmound. Section normal to bedding plane. The elongated cavities are filled with gray internal sediment at the base and Zebra rocks recrystallized radiaxial carbonate cements at the top. Early A conspicuous fabric found in peritidal carbonates Carboniferous: Ireland. Scale is 5 mm. of the Lofer cyclothems and somewhat reminescent of layered stromatactis structures has been called zebra A combination of the microbial with the sponge fabric (Fischer 1964). These structures range in width model seems reliable for the genetic interpretation of Early Devonian stromatactis mounds and shelf limeBox 5.3. Selected case studies of stromatactis structures stones (e.g. Dieken 1996; Vigener 1996). High-frein carbonate mounds. Note the apparent absence of Triquency sea-level fluctuations governing nutrient and assic stromatactis mounds and the scarceness of Mesosediment input are considered as major controls for the zoic records as compared with the Paleozoic (see Neuformation of these stromatactis limestones. weiler et al. 2001). Models assuming a predominantly inorganic conCretaceous: Reitner 1986; Camoin and Maurin 1988; trol of the formation of stromatactis cavities (Nos. 19Neuweiler 1993 23 in Box 5.2) concentrate on the frequency of stromJurassic: Matysziewicz 1993, 1997; Mathur 1975 atactis limestones on the flanks of carbonate buildups, Permian: Blendinger et al. 1997; Davies and Nassichuk sometimes underlying mass-flow deposits (Steiger and 1990; Otte and Parks 1963 Jansa 1984; Matyszkiewicz 1993) and thus indicating Late Carboniferous: Keim and Brandner 1999 Early Carboniferous: Bathurst 1959; Black 1952; the possibility that slumping of partly lithified lime mud Dupont 1883; Orme and Browne 1963; Hodgson was of major importance (Bathurst 1982). 1968;Lees 1964; Lees and Miller 1985, 1995; Miller 1986; Schwarzacher 1961; Lees 1964; Warnke and Paleoenvironmental setting of stromatactis Meischner 1995 Devonian stromatactis structures are common in Devonian: Aubert 1989; Bathurst 1980; Belliere 1953; Boulvain and Coen-Aubert 1992; Bourrouilh 1987; mudstones and wackestones of deep-shelf mud mounds, al. 1992;Dieken 1996;Dupont 1881;Flajs Brachertet but also occur in shallow shelf settings (e.g. detrital and Hiissner 1993;Flajs et al. 1996; Gnoli et al. 1981; crinoid limestones). The former type is commonly asHeckel 1972; Kaufmann 1998; Kerans 1986;Kerans sociated with sponge-microbial assemblages, the latter et al. 1986; Kukal 1971; Lecompte 1936, 1937; with trilobites and brachiopods (Dieken 1996). Flanks Macdonald et al. 1994; Monty et al. 1982; Philcox 1963; Playford 1984; Schwarz 1927; Tsien 1983, of Paleozoic and to a minor degree Mesozoic mounds 1985; Vigener 1996; Wallace 1987; Weller 1991; and reefs as well as slopes of platform margins are comWendt et al. 1993 mon settings of subtidal stromatactis formation. Silurian: Bourque and Gignac 1983; Textoris and Mounds with abundant stromatactis structures originate Carozzi 1964; Lowenstam 1950 in different quiet-water environments: (a) below wave Ordovician: Bathurst 1982; Grover and Read 1978;;Middleton 1988; Ross et al. 1975; Stenzel and base (Bourque et al. 1986), (b) near the storm wave James 1995; Krause 2001; Woods 2001 base (Kaufmann 1996), (c) between the fair-weather Cambrian: James and Gravestock 1990 wave base and the storm-wave base (Brachert et al.

Zebra Limestones

197

from microscopic to decimeter-sized, and may be meters long. They may have simple cement fills or complex banding of cement and internal sediment. Interbedded dark micritic limestones and cm-sized, often crinkled white calcite layers produce characteristic zebra-like stripes in the rock. This fabric also occurs in ancient beachrocks (Gray and Adarns 1995) as well as in Paleozoic carbonate mud mounds (Bosence and Bridges 1995, Fig. 5.8). Although originally explained as parallel sets of sheet cracks, current explanations are just as vague as those for stromatactis, and include collapse of thixotropic carbonate gels (Heckel 1972), lithified crusts with winnowed-out intercrust layers, cement-filled sheet cavities (Bathurst 1980), superposed microbial mats (Pratt 1982), or, soft sediment dilation and deformation associated with slumping.

Krause (2001) put forward an interesting interpretation of zebra fabrics and stromatactis structures of a small Ordovician mudmound in Nevada. He compared zebra and stromatactis limestones with structures triggered by gas clathrate hydrates. In this scenario, the carbonate cement layers would have precipitated and stabilized the zebra and stromatactis fabric, both by consolidating and dissociating gas clathrate hydrates, and oxidizing and reduzing associated gases.

Fig. 5.8. Zebra limestone. The spectacular pattern of the rock is characterized by alternations of dark wackestones and white parallel layers consisting of several generations of calcite. Some authors consider this fabric as a variation of stromatactis fabrics, but zebra rocks should be discussed on their own despite coincidences in supposed genetic interpretations and the time range of occurrence (Cambrian to Jurassic). Polished section, Lower Late Devonian Prasnim): Harz, Germany. After Weller (1991). Scale is -1cm.

cantly by dolomitization opening communication between fenestral pores through intercrystalline porosity in the matrix dolomite.

5.1.5.4 Significance of Birdseyes, Fenestral Fabrics and Strornatactis Open-space structures and fenestral fabrics should be evaluated in terms of paleoenvironment and relative water depth, diagenetic history and associated res-

l n d u s h l use offeneslral limestones: ~~~~~i~~ reefs in Belgium and France yield spectacular red-colored stromatactis limestones which are widely used as decorative stones and for works of art.

198

Nodular Fabrics

5.1.6 Nodular Fabrics

processes (PI. 2113). Boundaries between nodules and matrix are inconspicuous or distinct. Distinct boundBedded nodular limestones exhibit a conspicuous fab- aries are often marked by a dark clay-rich seam (Pl. ric characterized by centimeter- and decimeter-sized, 2112).Isolated nodules exhibitingblack fermginous and often 'rounded' nodules floating within a usually mi- manganese coatings often represent 'hardground clasts' . critic matrix. The overall appearance sometimes re- Nodule size (largest diameter) and orientation may be sembles a conglomerate. of interest in the discussion of a possible transport, e.g. along a slope relief. Nodular limestones are usually mud-supported. The Descriptive criteria of nodular fabrics Criteria important for the discussion of the origin matrix corresponds to a mudstone or a wackestone, ofof nodular fabrics relate to nodules, matrix, and spatial ten with small bioclasts. Variations in the color of maarrangement of nodules. CarbonateJclay ratio, grain size trix and nodules are due to differences in the amount of distribution, and burrowing are additional criteria. non-carbonates, Fe-hydroxides, sulfides, and organic Nodules are described with regard to their compo- carbon. sition, shape, boundaries and size. Composition (microfacies,fossils within and at the periphery of the nod- Origin of nodular limestone fabrics ules) can be the same as or different from that of the The origin of the nodular fabric has been explained surrounding matrix. Many nodules appear 'rounded' by diagenetic, sedimentary and tectonic processes. Dito 'subrounded'. 'Subangular' and 'angular' nodules agenetic processes include solution processes as well may indicate reworking and redeposition, these nod- as cementation and nodule growth within the sediment. ules may form conglomerates or even breccias. Appar- Sedimentary models underline the role of transport and ent rounding, however, can also be caused by solution redeposition. Tectonic explanations favor the forma-

Plate 21 Nodular Fabrics Nodular fabrics of limestones exhibit scattered or densely packed nodules within a matrix of like or unlike character. Nodules are generally cm-sized and often have 'rounded' outlines. Contacts between nodules and matrix or between adjacent nodules are indistinct (indicating bioturbation and diagenetic overprint) or sharp (indicating mechanical transport and sorting of nodules, pebbles or lithoclasts) and sometimes accentuated by darker seams (caused by pressure solution). Many nodular limestones exhibit striking red colors which have led to the term 'Rosso Ammonitico' for pelagic and hemipelagic red and variously colored, limestones in the Alpine-Mediterranean region (Farinacci and Elmi 1981). Red nodular limestones often are associated with condensed pelagic limestones and resedimented beds and occur on submarine rises (structural highs and volcanic ridges). Nodular fabrics are common in deeper-marine and slope environments (e.g. Devonian 'griotte facies' and Toumaisian 'calcaire noduleux' of France, Jurassic 'Arnmonitico rosso' facies of the Alpine-Mediterraneanregion) but also can be formed in shallow-marine and non-marine settings. The Early Jurassic nodular Adnet limestone of Salzburg (Austria) shown on this plate is explained by early diagenetic partial cementation and later compactional pressure solution (Bohm 1992, P1. 139). 1 Red nodular limestone. Initial stage of nodule formation, interpreted as local and partial cementation of the lime mud. Note the indistinct boundaries (arrows) between the nodules. Nodules correspond to bioclastic wackestones. Skeletal grains are echinoderms and brachiopod shells. Kiefer-Bruch, Adnet near Salzburg, Austria. 2 Nodular limestone. Boundaries are marked by dark clay seams (arrows) resulting from incipient pressure solution. The sediment is a fine-grained bioclastic wackestone. Larger fossil fragments are brachiopods (B) and bivalve shells. ScheckBruch, Adnet, Austria. 3 Nodular fabric becomes more pronounced by pressure solution. Stylolitization produces an iden-supported fabric (see P1. 3717). Adnet, Austria. 4 Red crinoid-shell wackestone. A nodular fabric is formed by redeposited hardground intraclasts (arrow, see PI. 139110). Kiefer-Bruch, Adnet, Austria. 5 Beginning nodule formation explained as partial cementation within isolated areas of the bioclastic lime mud. Early Jurassic: Wolfgrub-Bruch, Adnet, Austria. 6 Typical nodular limestone. Darker nodules are red-colored due to Fe-oxides and a higher organic content. Note the high degree of rounding. Adnet, Austria.

200

tion of nodular fabrics by shear processes affecting lirnestone-marllclay alternations. Reviews of genetic interpretations were given by Griindel and Rosler (1963) and Bohm (1992). Most models have been developed for Ordovician and Silurian (Moller and Kringan 1988), Devonian (Wendt 1982) and Jurassic (Elsmy 1981) nodular limestones.

Nodular Limestone Fabrics

(e) Local cementation of burrows, partly induced by the organic matter within the burrows (Fiirsich 1973; Abed and Schneider 1980).Bioturbation is regarded as a major process in forming hydroplastic pseudonodules (Elrni and Ameur 1984) and distributing nodules (Moller and Kvingan 1988).

3 Formation of nodules through mechanical processes The models can be classified into three groups: 1 Nodule formation caused by solution processes and explained as (a) Relicts of an intensive submarine dissolution of carbonate at the sea bottom (subsolution: Hollmann 1962, 1964), or (b) Result of the different solubility of clay-rich and carbonate-rich sediments during late diagenetic processes connected with pressure solution (Bathurst 1987).

including (a) Early diagenetic down-slope creeping of limestone/marl sequences and tearing up of partially lithified limestone beds (Seyfried 1978). (b) Tectonicprocesses such as sedirnentvy boudinage (Varol and Gokter 1994) or shearing of limestonel clay sequences due to tectonic (Bourbon 1982; Burkhard 1990; Schweigl and Neubauer 1997).

No single mechanism or sequence of mechanisms can explain how all nodular limestones are formed. 2 Nodule formation caused by localized cementation Therefore, each case should be considered individuwithin the sediment: Explanations of cementation ally. Erosion and redeposition of hardened nodules seeds and the sources of carbonate necessary for ce- formed only a few decimeters below the sediment-wamentation include: ter interface seem to be a reliable interpretation for the (a) Bacterially-induced nodule growth (Jeans 1980) genesis of many ancient nodular limestones. Many au(b) Formation of synsedimentary concretions by con- thors describe nodular fabrics in limestones as resultcentration of carbonate caused by decaying remains ing from early diagenetic concretionary cementation. of organisms (Kukal 1975) However, submarine dissolutionon the seafloor, a com(c) The term pseudonodular limestone. This refers bination of bioturbation, cementation and redeposition to Upper Jurassic sponge limestones composed of as well as pressure-solution should also be taken into densely-packed,rounded-oval to subangular carbon- account as possible factors. ate nodules up to 5 cm in size. The formation of pseudonodules is explained as selective lithification Significance of nodular limestone fabrics of carbonate crusts and associated siliceous sponges, Evaluation of paleowater depth and paleotopofollowed by fragmentation of already lithified frag- graphy: Nodular limestones are bound to particular enments caused by an increase in sedimentary load vironments which developed in specific episodes of rifting of furrows and basins and in specific paleogeo(Matyszkiewicz 1994, 1997). (d) Early diagenetic dissolution of carbonate within graphic situations (Wald et al. 1983; Elmi and Ameur the reduction zone caused by H,S- and NH,-rich pore 1984). waters, followed by an ascendent flow of the pore Settings include flat seamounts, steep slopes and flat water into the oxidation zone due to compaction, bottoms of basins and narrow furrows. Moller and and leading to the precipitation of carbonate around Kvingan (1988) drew attention to the relationships becrystallization centers (Griindel and Rosler 1963). tween paleotopography, paleodepth, depositional enJenkyns (1974) modified this model by explaining vironment and the potential of calcareous sediments the carbonate-rich solution as aragonite dissolution for forming nodular limestones during diagenesis. Many at the sedimentary surface, followed by a descen- Paleozoic and Mesozoic nodular limestones were dent flow of calcite-supersaturatedpore water, caus- formed on subtidal deep swells. Spectacular examples ing calcite precipitation a few centimeters below the are the nodular limestones of the 'Ammonitico rosso' sediment surface. The model is supported by the ob- facies in the Jurassic of the Alpine-Mediterranean reservation of patchy cementation by High-Mg cal- gion (see Sect. 15.8.2.2, P1. 139). cite in subrecent carbonate mud in the Ionian Sea and on Bahamian slopes, and is regarded as a posMost nodular limestones occur in deeper-marine sible precursor to nodular fabrics (Miiller and Fab- depositional settings. Some nodular fabrics, produced ricius 1974; Mullins et al. 1980). in connection with burrowing, however, are formed in

Basics: Depositional and Diagenetic Fabrics

shallow subtidal settings (Abed and Schneider 1980, 1982) or on shallow pelagic ridges (Wendt et al. 1984).

Sedimentation rates: Studies of nodular fabrics, bioturbation patterns and the non-carbonate content of the limestones assist in evaluating sedimentation rates, which should generally be low regardless of the genetic model favored. The time involved in the forming nodular limestone sections is long, as indicated by the common occurrence of condensed faunas representing several biozones (see Sect. 5.2). Basics: Depositional and diagenetic fabrics Geopetal structures Aissaoui, D.M., Purser, B.H. (1983): Nature and origins of internal sediment in Jurassic limestones of Burgundy (France) and Fnoud (Algeria). - Sedimentology,30,273289 Futterer, E. (1978): Studien iiber Eiegelung, Anlagerung und Einbettung biogener Hartteile im Stromungskanal. Neues Jahrbuch fiir Geologie und Palaontologie,Abhandlungen, 156,87-131 Rhoads, D.C., Stanley, D.J. (1965): Biogenic gradded bedding. - J. Sed. Petrol., 35,956-963 Salazar-Jimknez,A., Frey, R.W. (1982): Concavity orientations of bivalve shells in estuarine and nearshore shelf sediments, Georgia. - J. Sed. Petrol., 52,565-586 Sander, B. (1936): Beitrage zur Kenntnis der Anlagerungsgefuge (Rhythmische Kalke und Dolomite aus der Trias). - Tschermaks Mineralogisch-PetrographischeMitteilungen, 48,2X-139, 141-209 Sander, B. (1951): Contributions to the study of depositional fabric. Translated by R.B. Knopf. - 207 pp., Tulsa (American Association of Petroleum Geologists) Shrock, R.P. (1948): Sequence in layered rocks. A study of features and structuresuseful for determining top and bottom or oder of succession in bedded and tabular rock bodies. - 507 pp., New York (McGraw Hill) Wanless, H.R. (1981): Fining-upwards sedimentary sequences generated in seagrass beds. - J. Sed. Petrol., 51, 445-452 Wieczorek, J. (1979): Geopetal structures as indicators of top and bottom. - Annales de la Societt gkologique de Pologne, 49,215-221 Further reading: K105 Biofabrics and grain orientation Aigner, T. (1985): Biofabrics as dynamic indicators in nummulite accumulations. - J. Sed. Petrol., 55, 131-134 Hladil, J., Cejchan, P., Gabasova, A., Tideaborsky, Z., Hladikova, J. (1996): Sedimentology and orientation of tentaculite shells in turbidite mudstone to packstone: Lower Devonian, Barrandian, Bohemia. - J. Sed. Petrol., 66,888-899 Kidwell, S.M., Holland, S. (1991): Field description of coarse bioclastic fabrics. - Palaios, 6,426-434 Lindholm, R.C. (1980): Intraclast orientation in Carnbro-Ordovician limestones in western maryland. -J. Sed. Petrol., 50, 1205-1212

20 1

Potter, P.E., Pettijohn, F.J. (1977): Paleocurrents and basin analysis. Second edition - 425 pp., Berlin (Springer) Racey, A. (1994): Paleoenvironrnental significance of larger foramhiferal biofabrics from the Middle East Seeb L i e stone Formation of Oman: implicationsfor petroleum exploration. - In: Al-Husseini, M.I. (ed.): Geo'94. The Middle East petroleum geosciences, volume 11, Selected Middle East Papers from the Middle East -ewe Conference, Bahrain. - 793-810, Manama, Bahrain (Gulf PetroLink) Schwarzacher, W. (1963): Orientation of crinoids by current action. - J. Sed.Petrol., 33,580-586 Seilacher, A. (1973): Biostratonomy: the sedimentology of biologically standardised particles. - In: Ginsburg, R.N. (ed.): Evolving concepts in sedimentology. - 159-177,Baltimore (Johns Hopkins University Press) Whisonant,R.C. (1987): Paleocumnt and petrographic analysis of imbricate intraclasts in shallow-marine carbonates, Upper Cambrian, SouthwesternVirginia. -J. Sed. Petrol., 57,983-994 Further reading: K099; KO96 and KO97 (Bedding and lamination fabrics) Bioturbationfabrics Bottjer, D.J., Droser, M.L. (1994): The history of Phanerozoic bioturbation. -Ix Donovan, S.K. (4.): Palambiology of trace fossils. - 155-176,5 Figs., Chichester (Wiley) Droser, M.L., Bottjer, D.J. (1986): A semiquantitative field classification of ichnofabric. -J. Sed. Petrol., 56,558-559 Further reading: KO98 Fenestralfabrics Bain, R.J., Kindler, P. (1994): Irregular fenestrae in Bahamian eolianites: a rainstorm-inducedorigin. - J. Sed. Research, A 64, 140-146 Bathurst, R.G.C. (1959): The cavernous structure of some Mississippian Stromatactis reefs in Lancashire, England. -Journal of Geology, 67,506-521 Bathurst, R.G.C. (1980): Stromatactis - origin related to submarine-cemented crusts in Paleozoic mu mounds. - Geology, 8, 131-134 Bathurst, R.G.C. (1982): Genesis of stromatactiscavities between submarine crusts in Paleozoic carbonate mud buildups. - J. Geol. Soc. London, 139, 165-18 Bourque, P.-A., Boulvain, F. (1993): A model for the origin and petrogenesis of Red StromatactisLimestone of Palaeozoic mud mounds. - J. Sed. Petrol., 63,607-619 Bourque, P.-A., Gignac, H.(1983): Sponge-constructed Stromatactis mud-mounds, Silurian of Gaspe, Quebec. - J. Sed. Petrol., 53,521-532 Bourque, P.-A., Raymond, L. (1994): Diagenetic alteration of early marine cements of Upper Silurian stromatactis.Sedimentology, 41,255-269 Deelman, J.C. (1972): On mechanisms causing birdseye structures. - Neues Jahrbuch fiir Geologie und Palaontologie, Monatshefte, 1972,582-595 Dupont, E. (1881): Sur l'origine des calcaires Dkvoniens en Belgique. - Bull. Acad. Roy. Sci. Belgique, (3) 2, 264280 Dupont, E.(1882): Les iles coralliennes de Roly et de Philippeville. -Bull. Mus. Roy. Hist. Nat. Bruxelles, 1, 89-160 Emery, K.O.(1945): Entrapment of air in beach sand. - J. Sed. Petrol., 15,39-49

Basics: Nodular Fabrics

argillaceous platform limestones: stratified cementation Fischer, A.G. (1964): The Lofer cyclothems of the Alpine and selective compaction. - Sedimentology, 34,749-778 Triassic. -Kansas Geol. Surv. Bull., 169, 107-149 Flajs, G., I.liissner, H. (1993): Amicrobial model for the Lower Bohm, F. (1992): Mikrofaziesund Ablagerungsrnilieudes Lias und Dogger der Nordostlichen Kalkalpen. - Erlanger Devonian Stromatactis mud mounds of the Montagne geologische Abhandlungen, 121,57-2 17 Noire (France). - Facies, 29, 179-194 Grover, G., Read, J.F. (1978): Fenestral and associated va- Burkhard, M. (1990): Ductile deformation mechanisms in micritic limestones naturally deformed at low temperadose d~ageneticfabrics of tidal flat carbonates, Middle Ortures (150-350 "C). - In: Knipe, R.J., Rutter, E.H. (eds.): dovician New Market Limestone, southwestern Virginia. Deformation mechanisms, rheology and tectonics. -Spec. - J. Sed. Petrol., 48,453-473 Ham, W.EL (1954): Algal origin of the 'Birdseyes' limestone Publ., Geol. Soc. London, 241-257 in the McLish Formation. - Oklahoma Acad. Sci. Pro- Bourbon, M. (1982): La genkse des calcaires noduleux en Biaconnais (Haute-Alpes): une consdquence de ceed., $33,200-203 Heckel, P. H. (1972): Possible inorganic origin for Stromatactis l'instabilid tectonique de ce domaine au Malm infdrieur. in calcilutite mounds in the Tully Limestone, Devonian - Mdm. Gt5ol. Univ. Dijon, 7, 129-138 of New York. - J. Sed. Petrol., 42,7-18 Cecca, F., Fourcade, E., Azema, J. (1992): The disappearMatyszkie:wicz, J. (1993): Genesis of Stromatactis in an Upance of the 'Ammonitico Rosso'. - Palaeogeography. Palaeoclimatology., Paleoecology., 99, 55-70 per Jurassic carbonate buildup (Mlynka, Cracow region, Southern Poland): Internal reworking and erosion of or- Dvorak, J. (1972): Shallow-water character of nodular limestones and their paleogeographic interpretation. - Neues ganic growth cavities. - Facies, 28, 87-96 Mazzullo, S.J., Birdwell, B.A. (1989): Syngenetic formation Jahrbuch fur Geologie und Palaontologie, Monatshefte, of grainstones and pisolites from fenestral carbonates in 1972,509-511 Elmi, S., Ameur, M. (1984): Quelques environments des faperitidal settings. - J. Sed. Petrol., 59,605-611 Monty, C.L.V. (1995): The rise and nature of carbonate mudc i e ~noduleux mdsogken. - Geol. Romana, 23, 13-22 mounds: an introductionary actualistic approach. - In: Fursich, F.T. (1973): Thalassionides and the origin of noduMonty, C.L.V., Bosence, D.W.J., Bridges, P.H., Pratt, B.R. lar limestone in the Corallian Bed (Upper Jurassic) of (eds.): Carbonate mud-mounds: Their origin and evolusouthern England. - Neues Jahrbuch fur Geologie und tion. - Spec. Publ. Int. Ass. Sed., 23, 11-48 Palaontologie, Monatshefte, 1973, 136-156 Pratt, B.R. (1982): Stromatoliticframework of carbonate mud Grundel, J., Rosler, H.J. (1963): Zur Entstehung der oberdevo~schenKalkknollengesteine Thuringens.- Geologie, mounds. - J. Sed. Petrol., 52, 1203-1227 Pratt, B.R. (1995): The origin, biota and evolution of deep16, 1009-1038 water mud mounds. - In: Monty, C.L.V., Bosence, D.W.J., Hollmann, R. (1962): Subsolutions-Fragmente(Zur BiostratiBridges, P.H., Pratt, B.R. (eds.): Carbonate mud-mounds: nomie der Ammonoidea im Malm des Monte Baldo/Nordtheir origin and evolution.-Spec. Publ. Int. Ass. Sed., 23, italien).- Neues Jahrbuch fur Geologie und Palaontologie, 49-123 Abhandlungen, ll9,22-82 Semeniuk,V. (1971): Subaerial leaching in the limestones of Jenkyns, H.C. (1974): Origin of the red nodular limestones the Bowan Park Group (Ordovician) of Central Western (Ammonitico Rosso, Knollenkalke) on the Mediterranean Jurassic: a diagenetic model. -In: Hsu, K.J., Jenkyns, H.C. New South Wales. - J. Sed. Petrol., 41,939-950 (eds.): Pelagic sediments: on land and under the sea. Shim, E.A. (1968a): Burrowing in recent lime sediments of Spec. Publ. Int. Ass. Sedimentologists, 1,249-271 Florida and the Bahamas. - J. Palaeont., 42,879-894, Pls. 109-112 Kukal, Z. (1975): On the origin of nodular limestones. Casopis pro mineralogii a geologii, 20, 359-368 Shinn, E.A. (1968b): Practical significance of birdseyes structures in carbonate rocks. - J. Sed. Petrol., 38,215-223 Jeans, C.U. (1980): Early submarine lithification in the Red Shinn, E.A. (1983): Birdseyes, fenestrae, shrinkage pores, Chalk of Eastern England. A bacterial control model and and loferites: A reevaluation. - J. Sed. Petrol., 53, 619its implications. - Proc. Yorkshire geol. Soc., 43,81-157 628, 5 Figs., Tulsa Kennedy, W.J., Garrison, R.E. (1975): Morphology and genTebbutt, G.E., Conley, C.D., Boyd, D.W. (1965): Lithogenesis of nodular chalks and hardgrounds in the Upper Creesis of ,I carbonate rock fabric. - Contrib. Geol., 4, 1-13 taceous of southern England. - Sedimentology, 22, 3 11Tsien, H.H. (1985): Origin of stromatactis - a replacement of 386 colonial microbial accretion. -In: Toomey, D.F., Nitecki, Langbein,R., Meinel, G. (1985): Zur Petrologiedes Thuringer Tentakulitenlcnollenkalkes (Devon). - Hallesches Jahrbuch M.H. (eds.): Paleoalgology. - 274-289, Berlin (Springer) Wallace, M.W. (1987): The role of internal erosion and sedider Geowissenschaften, 10, 55-69 mentation in the formation of stromatactis mudstones as- Matyszkiewicz, J. (1994): Remarks on the deposition and disociated lithologies. - J. Sed. Petrol., 57,695-700 agenesis of pseudonodular limestones in the Cracow area Wolf, K.H. (1965): Littoral environments, indicated by open(Oxfordian, southern Poland).- Berliner gewissenschaftspace structures in algal limestones. - Palaeogeogr. Palaeoliche Abhandlungen, E13,4 19-439 Moller, N.K., Kvingan, K. (1988): The genesis of nodular climat., Paleoecol., 1, 183-223 Further reading: K 101 limestones in the Ordovician and Silurian of the Oslo region (Norway). - Sedimentology, 35,405-420 Muller, J., Fabricius, F. (1974): Magnesian-calcite nodules Nodular Fabrics in the Ionian deep sea: an actualistic model for the formaAbed, A.M., Schneider,W. (1982): The Cenomanian nodular tion of some nodular limestones. - In: Hsu, K.J., Jenkyns, limestone member of Jordan - from subtidal to supratidal environments. - Neues Jahrbuch fur Geologie und Pal& H.C. (eds.): Pelagic sediments: on land and under the sea. ontologie, Monatshefte, 1982, 513-522 - Spec. Publ. Int. Ass. Sedimentologists,1,235-247 Bathurst, R.G. (1987): Diagenetically enhanced bedding in Mullins, H.T., Neumam, A.C., Wilber, R.J., Boardman, M.R.

203

Discontinuity Surfaces

(1980): Nodular carbonate sediment on Bahamian slopes: possible precursors to nodular limestones. -J. Sed. Petrol., 50, 117-1.31 Seyfried, H. (1978): Der subbetische Jura von Murcia (Siidost-Spanien). - Geologisches Jahrbuch, Reihe B, 29, 320 1 Tucker, M.E. (1974): Sedimentology of Paleozoic pelagic limestones: the Devonian Griotte (Southern France) and Cephalopodenkalk (Germany). - In: Hsii, K.J., Jenkyns, H.C. (eds.): Pelagic sediments: on land and under the sea. - Spec. Publ. Int. Ass. Sedimentologists, 1,71-92 Wald, S., Kurze, M., Wienholz, R. (1983): Ausbildung und Genese oberdevonischer Kalkknollengesteine irn Siiden der DDR. - Zeitschrift der geologischen Wissenschaften, 11,27-39 Wendt, J., Aigner, T., Neugebauer, J. (1984): Cephalopod limestone deposition on a shallow pelagic ridge: the Tafilalt Platform (upper Devonian, eastern Anti-Atlas, Morocco). - Sedimentology,31,601-625 Further reading: K104

5.2 Discontinuity Surfaces: From Microfacies to Sequence Stratigraphy Sedimentation is inherently a discontinuous process.

A gradual change in environmental conditions may be accompanied by a continuous reaction of the depositional system, but any abrupt change or the passing of a threshold lead to a discontinuity in sedimentation. Discontinuities are commonly marked by a surface in stratigraphic sections and/or by distinct level of facies changes. All surfaces indicating a break in sedimentation and/ or non-deposition in submarine and subaerial environments are called discontinuity surfaces (Heirn 1924, 1934). The use of this term is purely descriptive in being independent of the process causing the formation of the surface and the duration of the break. Consequently, all stratigraphic gaps are included in this broad definition, ranging from millimeter- and centimeterscale breaks in sedimentation revealed by microfacies analysis, to small breaks on the scale of limestone beds commonly marked as bedding planes, to major stratigraphic unconformities which may be accompanied by prolonged subaerial exposure. Recognizing discontinuities and unconformities should be a major goal in microfacies studies. Unconformities represent the key element in sequence stratigraphy. Because sequence boundaries are defined as 'observable discordances in a given stratigraphic section that show evidence of erosion or non-deposition with obvious stratal terminations ...' (Mitchum in Vail et al., 1977), microfacies criteria pointing to breaks in sedimentation (e.g. discontinuity surfaces, condensed deposits, hardgrounds, karst features et al.) are of spe-

cific interest in refining carbonate sequence stratigraphy and the discussion of time involved in stratigraphic breaks. Small-scale and short-lived discontinuities often reflect large-scale variations of relative sea level. Terminology Various names are in use for defining sedimentary breaks and associated substrate types (Box 5.4).

5.2.1 Classification of Discontinuities Practical classifications of the common discontinuity types occurring in carbonate sequences were proposed by Clari et al. (1995) for analyzing shallow- and deepwater carbonates and Hillgaertner (1998) for studying carbonate platforms. The latter classification differentiates four discontinuity surfaces taking into account the importance of allogenic forcing of environmental changes: (1) Exposure surfaces resulting from subaerial exposure, commonly indicated by an overprinting of subtidal carbonates due to a general lowering of sea level. (2) Condensation sugaces comprising all discontinuities related to stratigraphic condensation in subtidal environments, and predominantly dependent on controls by relative sea-level changes and changes in accommodation. (3) Erosion surfaces including discontinuities that show evidence of subaqueous erosion. (4) Change surfaces describing all surfaces indicating changes in facies and/or texture. In most cases small-scale erosion or facies changes are related to locally restricted depositional processes. But allogenic forcing associated with changes in climate and/or relative sea level can trigger changes in wave base and hydrodynamic energy producing erosion surfaces or surfaces characterized by an abrupt change from carbonate to siliciclast-dominated sedimentation.

5.2.2 Major Criteria of Discontinuities Common criteria used to characterize subaerial and/or submarine discontinuities in carbonate rocks include geometry, lateral extent, surface morphology, biological activity, mineralization, facies contrast, early diagenetic contrast, and biostratigraphy (Hillgaertner 1998).The evaluationof these criteria requires the study of the rocks below and above the discontinuity, a thorough analysis of the discontinuity surface in geological

Discontinuity Surfaces

204

Box 5.4,. Glossary of terms used in the context of the discussion of discontinuity surfaces. Condensation: Sedimentation lag characterized by stagnant to low sedimentation rates over long periods of time (Heim 1924) ranging from thousands to several millions of years. Condensed section: Thin marine stratigraphic units consisting of pelagic and hemipelagic sediments characterized by very low sedimentation rates (Loutit et al. 1988). Corrosion surface: A bedding surface in carbonate rocks that exhibits evidence of lithification, followed by partial soluuon, of the underlying bed prior to the deposition of the overlying bed (Weiss 1954). Most criteria of corrosion surfaces correspond to those of hardgrounds, but the term underlines the greater importance of etching and dissolution. Dereption: Physical action of bottom currents leading to submarine erosion and transport of seafloor material (Heim 1934). Diastem: A relatively short interruption in sedimentation involving only a brief interval of time with little or no erosion before deposition is resumed (Barrel1 1917). The depositional break represents less time than a paraconformity. Disconformity: Disconformities are stratigraphic bounding surfaces which possess a gap in time documentationdespite the fact that the beds below and above the discontinuity are parallel. The discontinuity can result from erosion, abrasion, denudation, deflation, dissolution, corrosion, or non-deposition. Discontinuity: A zone at the sea bottom, usually a few cm thick, the sediment of which is lithified to form a hardened surface, often encrusted, discolored, case-hardened, bored and solution ridden (Heim 1934; Clari et al. 1995). It implies a gap in sedimentation and may be preserved stratigraphically as an unconformity. Today the term is not restricted to submarine settings, but also includes subaerial unconformities (Hillgaertner 1998). Emersion: Subaerial exposure of marine areas due to sea-level fall orland uplift. Firmground: A stiff, unconsolidated sedimentary substrate that can be easily broken and shows no signs of compaction (Ekdale 1985). Often representing the initial stages of hardground formation (Ruffell and Wach 1998).Firmgrounds typically contain a network of burrows (Bromley 1990). Hardground: Discontinuous surfaces of synsedimentary lithification, having existed as hard sea floor prior to the deposition of the overlying sediment. Implies a gap in sedimentation and may be preserved stratigraphically as an unconformity. Hiatus: '4 break or interruption in the continuity of the stratigraphic record and a lapse in time such as the time interval not represented by rocks or an unconformity. Hiatus concretions: Early diagenetic concretions that were bored and encrusted subsequent to winnowing of adjacent sediments and exhumation. Hiatus concretions represent discontinuous hardgrounds, and indicate short- and longlived breaks in sedimentation (Voigt 1968). Omission: Non-deposition of sediment related to a significant and long-lasting break in sedimentation (Heim 1924), leading to the formation of hardgrounds. Paraconformity: Obscure unconfomity in which no or only subtile erosional features are discernible and/or in which the contact over large areas appears to be a bedding plane (Dunbar and Rodgers 1957; Longman et al. 1983). Rockground: A sea ground along which well-lithified sediments are exposed. The term was originally proposed in contriist to hardground for 'a rocky sea floor, whose lithification was not synsedimentary,representing older layers of rock which through erosion and submersion formed the sea floor' (Fursich 1979),but is now used as a term describing surfaces which regardless of their origin were hardened before deposition of their immediately overlying sediment (Clari et al. 1995). Stratal discontinuities: Physical surfaces that either separate strata with different angularity or separate parallel strata where a significant hiatus is present (Doglioni et al. 1990). Subsolution: Carbonate dissolution at the bottom of the oceans (Heim 1924), commonly at great depths and in coolwater regions. Dissolution processes are interrelated with cementation, organic erosion and winnowing of sediment during times of non-deposition (Hollmann 1964). Unconformity: A surface of erosion or non-deposition that separates younger strata from older rocks and represents a significant hiatus (Mitchum 1977). In the context of sequence stratigraphy the definition is restricted to a surface separating younger from older strata, along which there is evidence of subaerial truncation (and, in some areas, correlative submarine erosion) or subaerial exposure, with a significant hiatus indicated (Wagoner 1988).

sections, a combined approach of field observations and sedimentological plus paleontological data including microfacies. Geometry: Many discontinuities exhibit an angular relationship between underlying and overlying strata, caused by the erosional truncation of sedimentary and diagenetic features or entire stratigraphic units. Discontinuity surfaces with non-angular, conformable re-

lationships need microfacies studies, geochemical and/ or biostratigraphical evidence for their interpretation. Lateral extent: Single surfaces with wide lateral continuity (>1 km) indicate environmental changes of at least regional importance. Low lateral continuity (several meters only) is commonly related to locally limited depositional processes. Physical correlation of single open-marine discontinuity surfaces over a dis-

Discontinuities

tance of tens of kilometers or more may point to major oceanographic controls (Di Stefano et al. 2002). SurfQce morphology: Flat, sharply-cut surfaces in shallow-marine environmentsare commonly caused by high-energy abrasion of lithified sediment. Irregular wavy and crinkled surfaces may indicate minor erosion or the former existence of microbial mats. Irregular surfaces also can be caused by differential compaction of strata differing in composition and texture. Rough surfaces can originate from burrowing and bioerosion. Stylolitization superimposed on preexisting discontinuity surfaces may lead to jagged surfaces. Biological activity: The distribution of burrowing, boring and encrusting organisms is crucial for understanding changes in sedimentation rates and resulting substrate types. The intensity of bioturbation and the types of trace fossils below and above the discontinuity surface assist greatly in differentiating pre-omission, omission, and post-omission phases (Bromley 1975). Lithification of marine discontinuity surfaces is indicated by boring organisms that cut sharply through fabrics and different microfacies types of underlying rocks. Encrusting microfossils attached to hardgrounds indicate retardation or breaks in sediment input. Mineralization: Discontinuity surfaces showing in situ crusts of iron and manganese oxides and phosphates as well as authigenic glauconite (Pl. 22/2) indicate breaks in sedimentation, commonly in deep subtidal and bathyal environments. In contrast, aluminium-iron oxide crusts are found to be the result of paleosol formation (terra rossa) and alteration during subsequent marine flooding (Wright 1994).Penetrative staining of strata underlying discontinuity surfaces by iron oxides can indicate oxidation due to pedogenesis and karstification. Facies contrast: A sharp change in microfacies across a surface must not necessarily represent an important break in sedimentation. However, a drastic environmental change can be inferred from a superposition contradicting Walther 's law (Clari et al. 1993, e.g. the superposition of limestones exhibiting microfacies associations typical of platform and reef carbonates by limestones showing evidence of pelagic sedimentation. Changes in grain sizes (reflecting changes in water energy) and in the lithologic composition (e.g. siliciclastics versus carbonates) may provide other clues to the discontinuity character of surfaces. Diagenetic contrasts: Diagenetic evidence of discontinuities is given by sharp differences in the diagenetic style at the discontinuity, e.g. vadose diagenesis or early diagenetic changes due to meteoric waters in the underlying and contrasting marine phreatic diagen-

esis in the overlying strata. Cement stratigraphy, different compaction features in the overlying and underlying strata as well as stable isotopes and trace elements offer other clues to the existence of exposure surfaces or breaks in the diagenetic style. Isotope and trace element data assist greatly in recognizing submarine lithifkation of hardgrounds, identifying unconformities and the genetically interpretating subaerial and submarine discontinuities (Marshall and Ashton 1980; Vi&tich and Matthews 1980). Biostratigraphy: Generally biostratigraphic and chronostratigraphic data are the only means for estimating the time involved in discontinuities. In basinal sections with rather monotonous sedimentation patterns, fossils can even be only means of identifying stratigraphical discontinuities. The main limitation, however, is time resolution, which is commonly too low for the majority of discontinuity surfaces occurring in carbonate sequences. Most discontinuities in shallow-marine platform carbonates are below biostratigraphic resolution. Better results have been obtained in the context of studying deep-marine carbonates.

5.2.3 Microfacies Criteria and Significance of Exposure Surfaces Detecting exposure surfaces in limestones by means of microfacies includes the following criteria: Conspicuous differences in facies types reflected by differences in rock color, lithologic composition, texture and fossil content below and above the exposure surface, Meteoric-vadose diagenesis at bounding surfaces, characterized by vadose cements in the underlying rocks and contrasting marine phreatic cements in the overlying rocks. Vadose zones extend downwards in the strata for a few tens of centimeters only. The surface can be accentuated by stylolitization. Stable isotope trends across exposure surfaces exhibit significant shifts (Sect. 13.2.4), Dedolomitized horizons: The alteration of dolomite to calcite takes place in several diagenetic settings (see Sect. 7.8.3) but is a common feature of near-surface vadose zones (Kenny 1992). Open dolomolds may indicate subaerial exposure and dissolution by karst waters (Braun and Friedman 1970), Microkarst caused by dissolution of C0,-enriched meteoric waters is indicated by sharp-cut and intensely stained surfaces displaying a microrelief with millimeter- to centimeter-sized cavities (Sect. 15.2.1).The ab-

206

Hardgrounds

Caverns, breccia and vugs can form in deep subsursence of larger paleokarst solution cavities is explained by the formation of epikarst underneath a soil cover face because of dissolution by basinal fluids or the conduring seasonally humid climates (Wright 1994; trols of shales overlying carbonates. Mylroie and Carew 1995) and limited duration of subaerial eTposure (d' Argenio et al. 1997). Other karst feaOre deposits: Emersion surface-hosted ore depostures are the gravitational infill of cavities by stained its associated with paleokarst are known from the Paand reworked lithoclasts and clayey calcareous silt in leozoic and Mesozoic (Parnell et al. 1990; Scott et al. association with micrite crusts and stalactite cements, 1993; Ruffell et al. 1998). Pedogenic features (Pl. 12814, P1. 14119, 10): DisPb-Zn-Fe sulfide mineralizations are common besolution processes and rhizoturbation during exposure low and/or along and above subaerial exposure surfaces as well as erosion and reworking of the soil during the of carbonate platforms. One such example, interesting subsequent marine flooding, can produce a brecciated in economic terms, is the 'Metallifero' in the southto pebbly appearance of exposure surfaces. Other cri- western part of Sardinia, a Cambrian carbonate comteria are microscopic root molds, soil pisoids and cal- plex, unconfonnably overlainby Ordovician conglomCrete crusts (Sect. 15.1.1). The absence of a vertical erates (Fanni et al. 1981; Bechstadt and Boni 1994). zonation of pedogenic fabrics at these surfaces points Other examples are emersion-bound mineralizations at Devonian-Carboniferous and Triassic disconformities to generally short-lived exposures. All these methods have limits and pitfalls and must in the Alps (Assereto et al. 1976; Hentschel and Kern be combined with a detailed analysis of sequence 1992). stratigraphy, biostratigraphy,facies and diagenetic history in a regional context (Saller et al. 1994; Fouke et al. 1996). 5.2.4 Microfacies Criteria and Significance of Condensation Surfaces and Hardgrounds

Practica,! significance of exposure surfaces and subaerial unconformities: Reservoir rocks: Identifying and predicting subaerial exposure surfaces is essential for understanding the modification of porosity beneath sequence-bounding unconformities and parasequence disconformities on carbonate platforms, the reservoir degradation below subaerial unconformities, and the development of permeability patterns (Read and Horbury 1993; Saller et al. 1994; Budd et al. 1995; Wagner et al. 1995). Controls of subaerial unconfonnities on porosity and permeability include the following points: Carbonate diagenesis during subaerial exposure rearranges the pore network, but does not necessarily increase total porosity. In many cases porosity is reduced under unconformity, but remarkable exceptions exist, Permeability is more strongly changed by subaerial discontinuities than porosity, and may increase or decrease, Pore systems evolve with the time of subaerial exposure. Shorter periods (10 000-400 000 yr) are often associated with higher porosity than long intervals of subaerial exposure (1-20 million yr), Many carbonates subjected to subaerial exposure have little or no porosity in the deep surface due to compaction, cementation and stratal collapse reducing burial porosity. But unconformity-related diagenesis may also enhance reservoir porosity by creating pore systems that are resistant to deeper burial compaction,

Stratigraphically reduced marine carbonates originate from very low sedimentation and alternating deposition and erosion, leading to the formation of condensed sequences. Modem oceanic equivalents have been identified on seamounts. Breaks in the sedimentation caused by non-deposition result in the formation of hardgrounds both in shallow-marine settings and deep-marine oceanic environments. In many ancient open-marine carbonates hardgrounds and condensed sequences are intimately associated.

5.2.4.1 Hardgrounds Hardgrounds are centimeter-sized discontinuous surfaces of synsedimentary lithification, having existed as hardened sea floor prior to the deposition of the overlying sediment. They are related to a combination of non-deposition or low sedimentation rates, and condensation. Hardgrounds denote a submarine sediment surface that became lithified in the ambient depositional environment before the next sediment layer was deposited (Demicco and Hardie 1994). Hardground surfaces are the result of submarine cementation by aragonite and magnesian calcite precipitation directly from seawater circulating through the uppermost few centimeters or tens of centimeters of a porous sandy sea bottom. The basic requirement is a longer-lasting stability of the sediment-waterinterface. The time involved

Ancient Hardgrounds

in the formation of hardgrounds is unclear, Shim (1969) reported antique Greek pottery incorporated into hardground of the Persian Gulf (a few thousand years). Hardgrounds are common but not confined to deeper-marine settings. They also occur in the terrestrial onshore and estuarine zone (tropical lateritic hardpans) throughout supra- and intertidal (beachrocks) and various marine regions. Marine settings include shallow subtidal environments (Pl. 127/4), off-platform pelagic settings, shallow slopes (Mullins et al. 1980), and deep basins. Holocene hardgrounds have been described from the Bahamas (Dravies 1979), the Persian Gulf (Shim 1969), the Red Sea, and the Mediterranean Sea (Aghib et al. 1991; Brornley and Allouc 1992). The majority lies less than a few tens of meters under water. In the Bahamas and in the Persian Gulf the development of hardgrounds is probably related to surface water saturation relative to calcium carbonate. In these shallow-water environments, cessation of sedimentation and development of hardgrounds can form in the space of a few months. Some of the hardgrounds, found in oceanic settings, occur in great depths, sometimes on oceanic ridges and guyots (Pl. 23/64!), between several hundreds of meters to more than 3000 meters (Fischer and Garrison 1967; Bernoulli and McKenzie 1981; Malfait and Van Andel 1980).

Recognizing ancient hardgrounds Fig. 5.9 summarizes some of the most common features of hardgrounds. Important criteria are: Contacts: Sharp upper contact and diffuse lower contact. Grains and cement crystals may be truncated along the upper contacts (Pl. 2312). Upper surface sometimes has a thin micrite rind. Some hardground surfaces are covered by micritic microbial crusts. The overlying sediment may infill cavities (Pl. 22/5), borings or undercut recesses in the hardground. Surfaces: The upper contact is characterized by smooth or irregular surfaces. Many surfaces exhibit irregular protuberances separated by pits and grooves (Pl. 2313). Smooth planar surfaces are formed by abrasion and are more common in shallow-marine highenergy environments. Angular surfaces related to solution processes are more common in deep-marine shelf and basinal settings. The upper surface of shelf hardgrounds may be buckled into tepee-like expansion ridges or may show signs of corrosion. The lack of encrustations on these surfaces indicates relatively short omission phases and high-energy conditions. Mineralization: Uppermost layers may be mineralized in the form of crusts or as impregnations (Pl. 231

Fig. 5.9. Common criteria of carbonate hardgrounds. Modified after James and Choquette (1983).

3,6). The composition, form and intensity of mineralization depend on the environment: Shelf hardgrounds are usually mineralized by glauconite (occurring within grains, burrows - P1. 2214, borings and cracks), calcium phosphate salts (forming phosphate cements as well as phosphatic stromatolites - Pomoni-Papaioannou 1994)and iron hydroxides (goethite,limonite), whereas pelagic hardgrounds in addition also contain a high percentage of manganese oxides (Fiirsich 1979;Lindstrom 1979; Marshall and Ashton 1980). In some hardgrounds, calcium carbonate has been replaced by baryte (Lindstrom 1979). Fermginous crusts covering hardgrounds frequently consist of irregular laminae of iron hydroxide, occasionally forming a cauliflower structure (Pl. 23/5), alternating with laminae of calcareous skeletons of encrusting organisms (e.g. foraminifera - P1.23/3,4, serpulids). Current interpretations favor a strong microbial control on the formation of laminated Fe-Mn crusts. In-place dissolution within microbial carbonates with thin limonitic laminae is explained by a process in which iron crusts acted as a cathode, sea water as an electrolyte, and the underlying carbonate as an anode (Videla 1989; Reitner et al. 1995). The existence of limonite crusts on hardground surfaces is often regarded as indication of relatively long omission phases and low-energy hydrodynamic conditions. Biogenic encrustations: The upper surfaces of hardgrounds are frequently encrusted by organisms who require a hard substrate to settle. Encrusted bryozoans, brachiopods and oysters occur also on the lower surface of hardgrounds. Differences in encrustation indicate the polarization of the fauna according to light in-

Discontinuities and Unconformities

tensity, rates of sedimentation and turbulence levels. Common encrusters restricted to hard substrates including hardgrounds are encrusting calcareous algae, foraminifera - P1. 2314, bryozoans, corals, serpulid polychaetes, cimpeds, and some brachiopods. Note, that some encrustingorganisms occurring on hard substrates can also settle on fm substrates (e.g. some oysters, crinoids and brachiopods). Bryozoans have proved to be of particular value for differentiating Cretaceous hardgrounds (Voigt 1968). Some authors consider the existence of only thin biogenic crusts as an indication of relatively short omission periods. Borings: Macro- and microborings (Pl. 52) are common along the upper surface of many hardgrounds (Pl. 2214). Borings provide sedirnentological information about the: consistency of the ancient sea floor as well as paleoecological information about environmental and depositional conditions (Ekdale 1985; Bromley

1994; Ekdale and Bromley 2001). Borers restricted to hardgrounds and other hard substrates (e.g. rock cobbles, shells, coral colonies) include some bivalves, phoronids, sponges, algae and fungi. Several animals can penetrate both firm and cemented substrates (e.g. bivalves and polychaete worms). Burrowing: The strata underlying and overlying the hardground are characterized by specific associations of trace fossils indicating the changes in substratetypes. Changes from fmground to hardground stages are reflected by the temporal relationship of bioturbation, boring and encrustation. Clasts of cemented limestones: Lithoelasts similar in composition to the hardground occur above the upper surface, along the discontinuities or as infill of depressions. The clasts have sharp edges and are often bored, encrusted or coated with FeMn crusts (Pl. 231 8). These clasts (e.g. 'subsolution lithoclasts', Sect.

Plate 22 Discontinuities and Unconformities Recognizing discontinuities and unconformities is a major goal in microfacies studies, because unconformities represent a key element in sequence stratigraphy and subaerial disconformities have a major impact on the porosity and permeability of carbonate rocks. Stratigraphic discontinuities manifest breaks in sedimentation at unconformities in which bedding planes above and below the break are essentially parallel ('disconformity'). Interruptions can result from various processes including erosion, significant reduction in sedimentation rates, non-deposition, bioerosion, or dissolution below or above carbonate compensation depths. Disconformity surfaces are often connected with variously colored condensed beds and hardgrounds. The latter denote a submarine sediment surface that became lithified in the ambient depositional environment before the next sediment layer was deposited. Hardgrounds are the result of submarine cementation by aragonite or Mg-calcite precipitation directly from seawater circulating through the uppermost part of the sea floor. They are formed in various marine settings (e.g. supratidal and intertidal, shallow subtidal, shallow and deep slopes, deep open-marine environments) but also originate in subaerial settings (e.g. on emersion surfaces). Because of the abundant hiati in deposition and rock-stratigraphic record, very thin condensed beds can represent very large time spans (100 000s to millions of years). 1 Hardground (arrows) separating deep-marinequartz-bearing wackestones with filaments and a wackestone characterized by phosphoritized bioclasts and a glauconite-bearing micrite matrix. The discontinuity surface is marked by FeNn mineralization. Deep subtidal shelf limestones. Jurassic (Callovian-Oxfordian): near Pamplona, Spain. 2 Pkosphoritized ammonites, indicating solution and replacement of the aragonitic shell by phosphate during times of starved sedimentation rates. Most glauconite grains within the micritic matrix are replaced by Fe-calcite. Deep subtidal shelf limestones. Jurassic (early Oxfordian): Ricla southwest of Zaragoza, Spain. 3 Hardground in a condensed sheif limestone with ferruginous ooids (0). The concentric layers consist of goethite, the nucleus of broken ooids, lithoclasts and quartz grains. Note the encrusting foraminifera (F). Jurassic (Early Oxfordian): near Pamplona, Spain. 4 Hardpund. Distinct borings within an erosional relief were filled with glauconitized peloids. Deep shelf. Jurassic (Oxfordian:):near Pamplona, Spain. 5 Microfacies about 50 cm below a distinct disconfomity separating two rock units. The thin section exhibits a cavity within i l foraminifera1 limestone. The cavity walls crosscut the matrix and some of the foraminifera (Lepidocyclina, arrows) indicating that the cavity was formed by dissolution below the discontinuity plane, after lithification of the rock. The cavity is filled with laminated mudstone and skeletal wackestone. The uppermost layer contains imbricated Lepidocyclina tests. Tertiary (Brac Formation and Cayman Formation, Oligocene/Miocene): Cayman Brac Island, British West hdies. -> 1-4: Behnke 198 1,5: Jones and Hunter 1994

210

Hardgrounds

4.2.8) re:presentthe result of a complex intraformational Long-lived formation of hardgrounds requires major reworking of both biological and erosional origin (Pl. changes in environmental conditions including shallowing to the point that seawater circulation be13917, 10). comes too restricted for significant biogenic carbonHiatus concretions: Reworked, encrusted and bored ate production caused by eustatic drop or tectonjc 'hiatus concretions' occumng in carbonate and nonuplift, or filling of shallow-water basins, carbonate sediments reflect multiple phases of deposideepening beyond the effective phototrophic zone tion, burial and excavation and provide insight into substrate conditions and the diagenetic history of harddue to sea-level rise or tectonic subsidence, or significant increase in salinity due to barriers. grounds (Kennedy and Klinger 1972; Fiirsich et al. 1992). Small-scale sedimentary intercalations: Sediments Short-livedformation of hardgrounds can be attributed with marine fossils are interlayered with cements in to local changes in sediment distribution patterns, cavities beneath the upper surface (Pl. 2215). short-term climatic variations affecting the frequency Alternation of hardground sur-j%acesand cement: Many hardgrounds are characterized by multiple surand travel paths of storms. In this case, the subtidal faces spaced millimeters to tens of millimeters apart, sediments may be dominated by lithoclasts derived from fmgrounds. and a high volume of carbonate cement causing laterally continuous cement crusts and layers (Pl. 2313). Carbonate cements: Most hardgrounds yield LowBox 5.5. Selected case studies of ancient hardgrounds. Mg calcite cements occurring as. blocky mosaics, synA comprehensive bibliography of studies related to antaxial rim cement and palisade-like fibrous cement, and cient and modem hardgrounds and other hard surfaces radial crystal aggregates. Microspar (including ant-egg can be found in the Intemet (Wilson 1999: Bibliography spar) is abundant. Often calcite crystals are intergrown of lithologic substrate studies). with glauconite, goethite and pyrite. Tertiary: Bromley and Goldring 1992; Carter et al. 1987: Micr1,facies: Microfacies types of underlying and Glenn and Kronen 1993; Gupta 1995; Lewis and overlying strata may differ in texture and biotic conEkdale 1992; Malaroda 1962; Mikulas and Pek 1995; tent, or may not. Pedley and Bennett 1985

Hardground communities: Clues to lithification stages In addition to cobbles, boulders and invertebrate skeletons hardgrounds are a type of substrate which can be colonized by a wealth of organisms. Here they can thrive as encrusters or as burrowers and borers (Brett 1988). Because the rate of early cementation of substrates imposes considerable constraints upon ecological successions of the burrowing, boring and encrusting biota, the occurrence and abundance of these biota can be used to evaluate lithification stages of hardgrounds (Goldring and Kazmierczak 1974; Gruszczynski '1979). Processes which might trigger 'non-deposition' and the formatioicz of hardgrounds Submarine hardgrounds mark hiatuses in submarine deposition, they are omission or condensation surfaces. Controls on non-deposition include cessation of carbonate mud import through emergence or drowning of platforms supplying it, extreme dissolution of carbonates and silica at the sea bottom, intermittent scouring at the sea bottom caused by changing bottom currents, and depletxon of nutrients.

Cretaceous: Bromley 1967, 1968, 1975; Bryan 1992; Carson and Crowley 1993; Kennedy and Garrison 1975; Lewis and Ekdale 1992; Malaroda 1962; Massari and Medizza 1973; Molenaar and Zijlstra 1997; Pomoni-Papaioannou 1994; Pomoni-Papaioannou and Solakius 1991; Rose 1970; Ruffell and Wach 1998; Voigt 1959, 1974, Zitt and Nekvasilova 1996 Jurassic: Behnke 1981; Bohm et al. 1999; Di Stefano et al. 2002; Fels 1995; Fursich 1971,1979;Fursich et al. 1992; Garcia-Hernandez et al. 1986; Gruszcynski 1979,1986; Hallam 1969; Kazmierczak and Pszczolkowski 1968; Krawinkel and Seyfried 1996; Lehner 1992; Lualdi 1986; Marshall and Ashton 1980; Mensink and Mertmann 1984; Palmer and Fiirslch 1974; Seyfried 1978; Wendt 1970; Wings 2000 Triassic: Bertling 1999; Kazmierczak and Pszczolkowski 1968; Schlager 1974; Wendt 1970 Carboniferous: Dawson and Carozzi 1983; Loope 1994 Devonian: Baird 1981; Bourrouilh et al. 1998; Tucker 1973; Wendt 1988 Silurian: Bridges 1975; Chems 1980; Kobluket al. 1977 Ordovician: Brett and Brookfield 1984; Brett and Liddell 1978; Dronov and Federov 1996; Droser and Bottjer 1989; Ekdale and Bromley 2001; Jaanusson 1961; Lindstrom 1963,1979;Nordlund 1989; Palmu and Palmer 1977; Pickerill and Narbonne 1995, Saadre 1993; Wilkinson et al. 1982; Wilson 1985 Cambrian: Brett et al. 1983; Chow and James 1992, Hessland 1955; Palmer 1982

Condensation

Development of hardgroundformation over time Box 5.5 indicates higher numbers of studies of Ordovician, Jurassic and Cretaceous hardgrounds than other Phanerozoic hardgrounds. This pattern reflects not only the interest in specific time intervals but also the distributional pattern over time (Brett 1988; Wilson and Palmer 1990,1992). Hardgrounds were particularly abundant in Middle and Late Ordovician, Jurassic and Late Cretaceous. Spectacular Ordovician examples are the beautifully colored Orthoceras limestones of Scandinavia and the Baltics (Lindstriim 1979). The general community structure of Ordovician hardgrounds shows relative little change during the Paleozoic. Mesozoic encrusting communities differ strongly in their composition from middle Paleozoic counterparts. The general diversity and guild structures observed in modem hardgrounds were f m e l y established by the Jurassic. Late Cretaceous chalk hardgrounds occur as well as cemented hard beds within a succession of porous, slightly cemented soft chalk. The upper surfaces of these hardgrounds are strongly bored and encrusted, and often show signs of abrasion and corrosion. Glauconitization and phosphatization are common features.The duration of the depositional hiatus associated with the formation of hardgrounds has been estimated at only several hundreds to thousands of years for the chalk, as compared to about 200 000 years for Ordovician hardgrounds. Surprisingly little is known about Late Paleozoic and Tertiary hardgrounds.

5.2.4.2 Condensation Surfaces and Condensed Sections Condensed sections are characterized by strata which are much thinner than their coevally formed stratigraphic equivalents, due to greatly reduced sedimentation rates. Condensed deposits accumulate over a large time span and should have a recognizable and chronological biostratigraphic record. It must be kept in mind that condensation reflects different factors the decrease of the sedimentation rate (stratigraphic condensation: Heim 1924), the decrease of the accumulation rate (sedimentary condensation), and a mixture of different age fossils (taphonomic condensation: Brett and Baird 1986).

Controls on condensed sections: Major processes involved in condensation include mechanical concentration, chemical concentration and biological concentration (Fels and Seyfried 1993):

21 1

Mechanical concentration is achieved by filtering (sieving), screening, bypassing, or scouring sediment. Condensation by sieving is well-known from neptunian dikes (Wendt 1976; Lehner 1992) and from carbonate ramps in times of sea-level rise when the clastic input is reduced (Dromart 1989; Schlager 1989; Leinfelder et al. 1993). Condensation by screening is common across strongly rifted passive continental margins (Bernoulli and Jenkyns 1974; S e w 1980; Bice and Stewart 1990). Condensationby bypassing occurs on carbonate ramps during sea-level lowstands. Condensation by winnowing is a common feature on clastic shelves where burial-exhumation-reworking processes are effective (Fursich 1979; Hallam 1988). A combination of winnowing and filtering processes during rising sea level may lead to shell concentrationson clastic shelves and bonebeds on carbonate platforms (Kidwell 1985,1986,1987;Nurnmedal and Swift 1987; Fursich et al. 1991).Concentrationof lithified bottoms by scouring requires extense current activity (Wilson and Palmer 1992). Chemical condensation can be caused by dissolution below the carbonate compensation depth, as strongly favored by Jurassic cephalopod limestones from the Tethys (Hollmann 1964; Garrison and Fischer 1969). But precisely these examples were questioned with respect to the water depths and the processes involved in the production of the condensed deposits (Schlager 1974). Many authors now favor relatively shallow depositional environments for the Tethyan condensed sections (e.g. Wendt and Aigner 1985; Martire 1992). Relative sea-level fluctuations and a combination of winnowing and bioerosion of differently lithified substrates could be responsible for the condensation features attributed predominantly to dissolution effects at the sea bottom until now. Condensation through biological concentration is caused by bioerosion on hardgrounds as shown by the common record of microborings at pelagic Triassic and Jurassic discontinuity surfaces (Seyfried 1981; Schmidt 1990). Microfacies criteria pointing to condensation and reduced or omitted sedimentation in pelagic environments: Centimeter- to meter-sized rock units consisting of bedded, variously colored limestones and limestonel marl sequences. Alternation of intensively burrowed beds and beds exhibiting current transport and quiet-water deposition. Variously spaced intercalation of hardgrounds ex-

Plate 2.3 Discontinuities: Criteria of Submarine Hardgrounds and Condensed Carbonate Rocks

A hardground is a usually only centimeter-thick zone at the sea bottom, which is lithified to form a hardened wrface It lmplles a gap or retardation of sedimentation and may be preserved as an unconformity. Common crrreria af submarine hardgrounds are sharp upper and diffuse lower contacts, mineralizations (iron hydroxides, manganese oxides, phosphates, glauconite) of upper surfaces in the form of crusts or microstromatolites (-> 2, 4, b: Massan 1981; M a t et al. 1999), fermginous impregnations of grains, cements or within peloids and oncolds, encrustations by microbes, foraminifera. serpulids, brachiopods, bivalves et al., borings and burrows in endured substrates (--> I), e.g. omission surfaces, condensed fauna, lithoclasts resulting from intraformational ren orking of hardgrounds, reworked hiatus concretions, interlayers of marine sediment and cements, dissolut m features, e.g. steinkerns of primarily aragonitic shells. Hardgrounds originate in 'deep-marine' pelagic envirorrmenl5 (slopes, basins, ridges) as shown in the examples on this plate, but are also abundant on the sea t3orron1~of shelves and ramps. I?rz7aX in srdinzcmation. A fine-grained bioniicrite (BM) is covered by dark red argillaceous niicrobioclastic micrite, ;wetrating into a microrelief. Some skeletal grains enter into the lower region as well. Bioturbation (right upper comer) i ;si1o.m by the whorled alignment of shell fragments. Deposition of the dark sediment probably took place subsequent to korings by bioeroding organisms (cf. Ekdale and Bromley 71001) into hardgrounds or firmgrounds. Differentiation of iiardgl-ounds and firmground borings requires criteria such as the shape of endolithic structures (better seen in the field [ban in non-oriented thin sections as in this example) and the type of the boundary between the host sediment and the borin;:s {sharp. truncating fossils or discontinuities surfacex, or indistinct). A break in sedimentation is indicated by ~!ccun~uIations of glauconite grains. These 'Orthncal-as limestones' represent a condensed ca. 50 m thick pelagic sedifilent. deposited under relatively cool-water marine conditions. on the Baltic Shield. extending one-half million square kilometers (Lindstrom 1963). The rocks arc predominantly micritic, fossiliferous and thinly bedded. Complex ichnofabrics itldicatc. that the sea floor ranged from softground to firmground to hardground. Early Ordovician (Limbata limestone. Areiiigian): landIsland, southern Sweden. Irardground; The echinoderm fragments in the bottom half of the picture have been dissolwtl along a discontinuity and ~!~bsecpently truncated. Hardground criteria: Linionitic cauliflower structures iCS, 'deep-water. siromatolite') above the j is continuity surface. Decimeter-sized, dome-shaped microbial microstromatolites growing on discontinuity surfaces, !,thoci;~s~s or shells, are common features of dccp-marine pelagic limestones (Massari 198 L). Early Jurassic (Adnet lime,-,one):Adnet near Salzburg, Austria. The Adnet limestone I.; an example of widely dislrihuted Tethyan 'deepwater iimcstt)ncs' generally summarized as 'Amnionitico rosso' bccauae of thc common occurrcnc~,c\f mmonites and the re\\ ~ . , hofr the rock (see P1. 139). This facies represents the post-drowning facies of 'pelagic carbonate ramps'. The Adnet iirnestl)ne originated on drowned late Triassic carbonate platforms in upper and lower slope settings. Hardgta~rmi:Fe/Mn mineralizations upon and within mm-sized columns constructed by agglutinated sessile foraminifer:^ ! :'lucopilincz d'Orbigny, arrows) growing on lithified microbial substrates and forming minute 'reef' structures (Wendt 1,969').Encrusting agglutinated foraminifera are abundant in modern manganese crusts and nodules. Late Triassic (I-lallc!au limestone. Camian): Feuerkogel near Bad Aussee, Styria. Austria. The Hallstatt limestone originated on the top ot i":iult-boundedridges in water depths of several hundreds of meters. c Feuerkogel Letail of 'dcc7p-llwter stronzatolites' with abundmt sessile foraminifera (arro\ips). Late T r i a ~ s ~(Carnian): r.1 .as Bad Aussec, Styria, Austria. i- i m n ! l j ( ~(J~rownishor yellowish) 'caidiflour~r~ s~uctrrt-e'(originating by migration of colloidal Fe-solutions, CS) into :I a v i t y t?eiow a discontinuity surface (arrow). Note differences in sediment composition: Gray biomicrite with foramini ! m and shells (GB), and red fine-bioclastic biomrcrite with ostracods and other skeletal debris (RB) also occurring in thc ~ . . i \ . ~ below il~ the discontinuity (arrows). E - echinoid spine. Late Triassic (Norian): Hallstatt. Upper Austria. P7lagi8:.l ! c ~ n l ~ r - Note o ~ ~ ~the ~ ithin . upward growing stro~natoliticFe-Mn crust (arrow). Post-drowning micrites above a wnher- :mil. Late Cretaceous?: Isakov Guyot. northwestern Paciiic. Jjal-dgro~u~ti at the top of a drowned carbonate platfomi. Microbial Fe-Mn rnicrostromatolitr (arron.1 growing perpen!hcular to the wall of a dissolved component within a completely phosphatized rock. Middle Cretaceous (Late Albian!: i::larlg Johnson Guyot, northwestem Pacific. P k x p h a t i z a r i o ~Resedimented hemipelagic mudstone clasts with Fe-Mn crusts in a phosphorized matrix. Clasts werc is.insported by submarine currents prior to the formation of the crusts. Cretaceous: Heezen Guyot. northwestcm Pacific (? 7:C?rvtsch and Fliigel 1992

2 mrn

2 mm

1mm

5 cm

Fig. 5.10. Based on thin-section observations of Early and Middle Jurassic limestones. Note variously preserved ammonite shells. various-sized Fe/Mn nodules and sutured discontinuity surfaces above the hardground. The latter exhibits typical micl ite-filied microborings covered by microbial microstromatolites that are often impregnated with Fe and/or manganese oxiclcs. The crusts alternate with micrite layers. A common feature of these crusts in Triassic and Jurassic limestones arc at^ hed foraminifera. After Wendt (1970).

1l1bi"lngspeclfic tract: fossil association on omission surtdces (Beltling 1909). F:cwc~rked hardgrounds and occurrence of poorly WI tt~dI~thoclasti ikxetl and encrusted, early diagenetic. clay-hosted c o m letion\ (Hesselbo and Palmer 1992) -mmonlte pavements, occurring together with mang'u1t.w and iron crusts. Primarily aragonitic cephalopod shell5 are preserved as calcite spar, micrlte or goet h I I< pwudoinorphs. High percentages of broken or p,lr t J dl*,\ol\ed shells (PI. 9013). I lighl? variable nucrofacies type\ occuxrmg only u i t 1 In a t l ~ \ r n n ~ ote3 few centmeters and rmglng from 01amstones rnuciston:, wxhestones, packstones and , 1( I i i l,itwne\ and rudstones. * d o1rli11011 nucrobmta: Attached forammifeia. serpulitl\. \ri~allgastropods, thin-shelled bivalves, and osir.icoti\ High concentrations of planktic and benthlc tc;\s I \ (\ometltne\ constituting mixed assemblages (i;elmng 1986) * .uthlgenlc i n ~ n e ~ a(glauconlte. ls pho\phorite. sldvrirz etc . i e r ~ u ~ r ~ n 'tnic~vstromatolite' oui crusts ( 1 Q 5 . lo), nociide\ i u ~ dFe-ooid\ (PI. 2213): Goetllite crurts (massr ts or c.on\isting of up to 50 vm thlck lam~nae,alterri,itlr,g \\ lrh ca1~1tlclaye~sand forming flat to domek y w i ii~g~rate \tructures. Centimeter-slzed goethite ~ I I L C ) I (Sect ~ \ 4.2 1 1 I Nuclei are lithoclasts fiom adj'icetlt hardgrounds or rockgrounds. Laminae contain la]gr anlount\ of sesslle foraminifera Oncold\ occur rw1,ited or densely packed within a single layer. * ,21dngmese crust5 and scattered manganese nodules iHctner)et.and lyer 1991). * Pilosphat~c'micro~~r~matolites', composed of stratifom?and columnar sheets consisting of alternating dark (phosphatic, with microbes) and light laminae (nonp h o \ d ~ ' ~ t !sediment) ~.. Phosphoritized calcareoui shells I

(PI. 2212).Current induced condensation accompanied by phosphogenesis is often associated with platfoim drowning (Follmi 1989). * Accumulations of organlc mattcr The history of many condensed units often exhibits a three-stage sequence: (1) Reduced sedimentation stage. recorded by shell concentrations (e.g. ammonite pavements), bored and encrusted bio- and lithoclasrs. reworked iron crusts, sometimes indication of current transport, (2) Omission stage, chxactzrizetl by irregular, boi-elf and encrusted hardgrounds as \$ eli as scoured surfaces exhibiting truncation ofpre-omission hulrous. Reworking breccias and large cavilies Ins! bt: common. ( 3 ) Fe and FelMn crust s t a y . 'lime rnvol\wl ri1 decj?-nmi ~irc oi?Lic~~,ahn~l 1101 1:orr , urzd ha~dgrounds Geolog~calcondensation refer5 to n long-lastlnp bleak in the rock-~tratigr~~ph~c lecord commonly as50 cmed w ~ t ha h ~ t u s(Flg 5 I 1) Vc'r! thin rock unit\ may represent xier> large timespm. langlng from huu of years. Excel dreds of thousands to several im~llion~ lent case studies dealmg wlth the pIocesces and the tlmc involved in the formation of condensed carbonate i e I I home Idea of thc quence5 In the Juiassic of S ~ J I glve Immense time spans associated w ~ t hdeep-manne con densation (Seyfried 1978, 1980 1981; Fels and Seyfrieti 1993; Fels 1995). The authors descl~bedan mstructivc example showing that at least 1 0 m~llronyears may bt. concentrated in a one-meter tl-uch condensed carbon ate succession Because the carbonate ~nicrofaciesrypes were de posited relatively rapidly. most ot the time should bc h~ddenwithin the goethite crust\, hardgrounds and thc erosional discont~nultle\ (

2 16

Conventional sequence stratigraphy relates the large-scale stratal architecture of sediment bodies to changes in sea level. Stratal architecture alone, however can be a rather ambiguous guide to sea-level history. A combination of microfacies analysis, the study of diagenetic patterns and stratal geometries is required to single out the role of changes in accommodation and carbonate production for the development of platforms in comparison with sea-level controls. An excellent example was provided by Evarts et al. (1995) while studying early Cretaceous platform margins. Frequency and distributional patterns of environmentally diagnostic grain types and discontinuities in sections covering different parts of the platform and the platform-basin transition allow lowstand and highstand sedimentation phases to be differentiated, resulting in a significant refinement of the sequence stratigraphic model. Other advantages in using microfacies data and particularly the types and distribution of discontinuities have been demonstrated by Hillgaertner (1998). The author compared the distribution of the major discontinuity types in carbonate platform sections with depositional types characterized by microfacies and biota. This resulted in the recognition of 'discontinuity zones' that reflect specific positions within the sequence stratigraphic framework. Most zones with prevailing exposure surfaces correspond to large-scale sequence boundaries. In contrast, discontinuity zones with dominating condensation surfaces fall between the major sequence boundaries. This implies that the occurrence of specific small-scalediscontinuities reflects large-scale second- or third-order sea-level changes. The generalization that condensed sections found in deep-marine carbonates have been developed exclusively during transgressions and that condensation intervals should be interpreted as the result of transgressive maxima is questionable. Gomez and Femandez Lopez (1 994) drew attention to the fact that the relative distribution of unconformities and condensed sections should not be used as unequivocal diagnostic criteria for particular paleogeographical settings (e.g. basinal),or as indicators of maximum regional transgressions, because condensation processes also occur in the shallowest parts of carbonate platforms and during maximum regression periods. Further implications of microfacies studies in the context of sequence stratigraphic investigations are discussed in Sect. 16.1.2. Basics: Discontinuity surfaces in carbonate rocks B e r n , M. (1999): Taphonomy of tracefossils at omission surfaces. - Palaeogeogr. Palaeoclimat., Paleoecol., 149,27-39 Brett, C.E. (1988): Paleoecology and evolution of marine hard substrate communities: an overview. - Palaios, 3,374-378

Basics: Discontinuities Budd, D.A., Saller, A.H. and Harris, P.M. (eds., 1995): Unconformities and porosity in carbonate strata. - Mem. Arner. Ass. Petrol. Geol., 63,313 pp. Clari, P.A., Dela Pierre, F., Martire, I. (1995): Discontinuities in carbonate successions: identification, interpretation and classification of some Italian examples. - Sed. Geol., 100,97-112 Evarts, A.W.E., Staffleu, J., Schlager, W., Fouke, B.W., Zwart, E.W. (1995): Stratal pattern, sediment composition, and sequence stratigraphy at the margin of the Vercors carbonate platform (Lower Cretkous, SE France). - J. Sed. Research, B65, 119-131 Fels, A. (1995): Prozesse und Produkte geologischer Kondensation im Jura der westlichen Tethys. - Profil, 9,363-472 Fiirsich, F.T., Oschmann, W., Singh, B., Jaitly, A.K. (1992): Hardgrounds, reworked concretion levels and condensed horizons in the Jurassic of westemIndia: their significance for basin analysis. - J. Geol. Soc. London, 149,313-331 Goldring, R., Kazmierczak, J. (1974): Ecological successions in intraformational hardground formation. - Palaeontology, 17,942-962 Gomez, J.J., Femandez-Lopez,S. (1994): Condensation processes in shallow platforms. - sed. Geol., 92, 147-159 Heim, A. (1934): StratigraphischeKondensation. - Eclogae geol. Helvetiae, 27, 372-383 Hillgaertner, H. (1998): Discontinuity surfaces on a shallow carbonate plattform (Beniasian, Valangian, France and Switzerland). - J. Sed. Research, B68, 1093-1108 Krawinkel, H., Seyfried, H. (1996): Sedimentologic, paleoecologic, taphonornic and ichnologic criteria for high-resolution sequence analysis: a practical guide for the identification and interpretation in shelf deposits of discontinuities in shelf deposits. - Sed. Geol., 101,79-110 Lindstrom, M. (1979):Diagenesis of Lower Ordovician hardgrounds in Sweden. - Geologica et Palaeontologica, 13,930 Palmer, J.T. (1982): Cambrian to Cretaceous changes in hardground communities. - Lethaia, 15, 309-323 Pedley, H.M., Bennett, S.M. (1985): Phosphorites, hardgrounds and syndepositional subsidence: a paleoenvironmental model from the Miocene of the Maltese Island. Sed. Geol., 45, 1-34 Voigt, E. (1959): Die okologische Bedeutung der Hartgriinde (hardgrounds) in der oberen Kreide. - Palaontologische Zeitschrift, 33, 129-147 Wendt, J. (1988): Condensed carbonate sedimentation in the late Devonian of the eastern Anti-Atlas (Morocco). Eclogae geol. Helvetiae, 81, 155-173 Further reading: K102, K174

5.3 Syn- and Postdepositional Features: Fissures, Veins, Breccias Carbonate rocks are often affected by destructive processes leading to the opening and filling of variously sized fissures, voids and veins, and the formation of limestone breccias and conglomerates. Some of these processes occur syndepositionally, others take place a long time after final lithification.

Neptunian Dikes

5.3.1 Sediment-Filled Fissures: Neptunian Dikes and Fissure Fills Many limestones yield fissures filled with carbonate or other sediment (sedimentary dikes) and with carbonate cements. Fissure walls are commonly subparallel, planar or irregularly undulated. The fissures cut the host rock obliquely or vertically across bedding planes, or parallel to the bedding. The width of vertical or obliques fissures varies between a few centimeters and several meters, they may be several hundreds of meters up. Horizontal sediment-filled fissures can be followed a few tens of centimeters up to several hundreds of meters. Many fissures occur beneath erosional or stratigraphic unconformities. Fissures may extend several tens of meters below unconformity surfaces. The formation and infilling of these fissures can take place both in submarine and subaerial environments. Submarine fissures are common in platform carbonates, particularly at platform margins, but also occur in slope and basinal settings. Terminology Several terms describe submarine and subaerial voids and fissures filled with sediment (see Box 5.6). Definitions of these terms are not consistent, because of differences in the descriptive and/or genetic aspects. Common terms are fissure and dike. Fissure stresses the existence of fractures within rocks, whereas dike relies on the filling with sedimentary material and chemically precipitated cements. The conditions of sediment deposition are conventionally used to define the major types of sediment-filled fissures. Neptunian dikes are defined as fissures within rocks exposed on the sea bottom that have been filled with submarine sediments. Most definitions include discordant cutting of bedding, infill of younger (but also stratigraphically coeval) sediments and infilling from above. If we accept these criteria, then neptunian d i e s represent a specific type of sedimentary dike. The most workable definition of neptunian dikes is probably that of Fischer (1964): 'Discordant dikes of limestones within limestones' parallel to the bedding planes. This definition coincides with that of 'S-fissures'. The names S- and Q-fissures (German: 'S- und Q-Spalten', Q = quer, oblique) describe the geometrical relationship of fissures with the host rock (Wendt 1971). Q-fissures cut the bedding (Pl. M/l, Fig. 5.12), and S-fissures run parallel to it (Pl. 2412, Fig. 5.13). The use of the termfissurefill for continental sediments filling subaerial cavities and fissures (e.g. paleo-

Box 5.6. Glossary of terms used in the context of the study of sediment-filledfissures. Based on Bates and Jackson (1980), V i r (1980), Smart et al. (1994).

Clastic dike: A sedimentary dike, transecting bedded sediments at various angles, and consisting of clastic material derived from underlying or overlying beds. Cavity fill: Subaqueous fills deposited in brackish or phreatic freshwaterenvironments(Swart et al. 1988). Dike (British spelling: dyke): A discordant or concordant fissure filling. Fissure: A fracture or a crack in rocks along which there is a distinct separation of walls. Fissure fill: Terrestrial deposit infilling voids and fissures in older rocks created, e.g. by karstification. The term is the terrestrial equivalent to neptunian dikes referring to submarine infillings. Injection dike: A sedimentary dike cutting vertically through massive or normally bedded strata filled by material through hydrostatically controlled pressure of injection from below or above or from the side. Neptunian dike: A sedimentary d i e formed by infilling of submarine sediment in fissures and cavities of rocks exposed on the sea floor. The term was originally coined by Pavlov (1896) for dikes, occurring in Early Cretaceous clays and filled with Oligocene sandstone. The British term 'neptunian', now commonly used for carbonate rocks, refers to the submarine origin of the fissures and their submarine infillings. Neptunian sill: Fissures that essentially follow bedding planes and are filled with submarine sediments (Playford et al. 1984). Sedimentary dike: A tabular mass of sedimentary material that cuts across the structure of bedding of preexisting rock. It is formed by the filling of a crack or fissure from below, above or laterally,

karst, see Sect. 15.2.1) may be meaningful but sometimes troublesome when mixed infills of terrestrial and marine sediment occur.

5.3.1.1 Origin, Development and Filling of Sedimentary Fissures The initiation, development and sedimentary filling of fissures can take place in a variety of environments and is influenced by various processes such as karst solution in subaerial and vadose settings, solution in phreatic and mixing zones between freshwater and saline waters, and processes occurring in shallow and deep marine settings. Initiation and development offissures Initial fissures can be depositional, synsedimentary or tectonic in origin. Primary depositionalfissures are

Tectonic Fissures

2 18

of some significance only in reef carbonates and forereef breccias. These fissures correspond to cavities between large reef-building organisms or reef blocks. The cavities are largely filled at an early stage by sediment derived from the erosion of the reef itself (Land and Goreau 1970). Synsedimentaryfissures develop by downslope sliding and slumping of early-cemented slope deposits on uncemented interbeds as a result of earthquake shak-

ing (Martire 1996). Shallow-marine lagoonal carbonates can be affected by desiccation and shrinkage leading to the formation of dikes (Fischer 1964). Tectonicfissures are often related to block faulting and rifting. Regional tectonics associated with active block faulting and extensional movements causes the formation of faults and gravity sliding of large sedimentary blocks along unstable slopes due to oversteepening (Fiichtbauer and Richter 1983;Winterer and Sarti

Plate 24 Sediment-Filled Fissures: Neptunian Dikes and Terrestrial Infills Vertical, horizontal or oblique millimeter- to meter-sized fissures filled with carbonate or other sediment-or with carbonate cements can be formed in submarine and subaerial environments. Neptunian dikes are 'discordant dikes of limestones within limestones' filled with submarine sediments. Fissures are common in platform carbonates, particularly in drowned platforms (-> 4) and at platform margins, but also occur in slope and pelagic limestones (-> 1,2,6). Submarine formation of fissures is triggered by synsedimentary tectonics and rifting or differential compaction. Subaerial fissure formation occurs during karstification (-> 5) and vadose dissolution. Internal fillings in neptunian dikes consist of mud, pelagic and benthic fossils and lithoclasts eroded from fissure walls. Microbial crusts can occur. Common cements are early-marine radiaxial-fibrous calcite and later granular calcite covering the walls of fissures. Common fillings of paleokarst fissures are erosional carbonate lithoclasts and relicts of overlying deposits, silt, and pedogenic sediment, carbonate cements are of meteoric-phreatic and burial origin. Analysis of neptunian dikes requires one to study the geological framework, compare the microfacies of fissure sediments and host rocks, evaluate fossils (taphonomy, biotopes, age) and examine the diagenetic criteria. Common microfacies types of submarine fillings are red and gray mudstones and wackestones/packstones containing foraminifera, mollusk and echinoderm coquinas and lithoclasts. The timing of fissure fillings can be determined by microfossils, particularly foraminifera. Differences in texture reflect open or closed fissure systems. Alternations of cement tapestries and sediment infill reflect repeated rupture of fissures. Neptunian dikes indicate breaks in sedimentation and changes in sea level and subsiden-ce.Low sedimentation leads to condensed sequences with condensed faunas, covering a substantial time period. Neptunian dike (outlined in white) within red pelagic limestones with 'filaments' (pelagic bivalves). The host rock is a filament wackeJpackstone, the filling is a fossiliferous mudstone. Note the distinct difference between the microfacies of the host rock and that of the infilling sediment. This difference and the irregular wavy boundary of the fissure (white line) indicate a modification of the fissure system by submarine dissolution and a certain time break. Deep-water limestone. Late Triassic (Camian): Hydra Island, Greece. Internalfilling of a horizontal neptunian dike. The alternations of grain-rich and grain-free laminae and aligned shells point to the existence of bottom currents within the dikes. Jurassic (Rosso Ammonitico Veronese): Altopiano di Asiago, Italy. Repeated rupture and fissure formation. Two generations of fissures (outlined with white ink) in a red pelagic wackestone. An older system is cut by younger fissures filled with radiolarian packstone. Late Triassic (Norian): Epidavros, Greece. Submarine fissures in drowned platform carbonates. The Late Triassic host rock (peloid grainstone, PG) is cut by repeatedly ruptured fissures exhibiting several phases of Liassic fillings: 1: Red echinoderm wackestone, 2: Red mudstone, 3: Calcite vein cutting the red mudstone, 4: Gray crinoid packstone. The arrow points to the youngest fissure. Triassic/ Jurassic: Kirchbruch, Adnet, Austria. Fissure fill. Terrestrial fissure within Jurassic shallow-marine bindstones. The karst fissure has been filled with late Cretaceous angular to subrounded limestone clasts. Note the plane boundary of the fissure and the cracks filled with burial calcite cement. Late Jurassic (Emstbrunn Limestone, Tithonian): Emstbrunn, north of Vienna, Austria. The Emstbrunn limestone is part of a Late Jurassic-Early Cretaceous carbonate platform which was affected by intensive karstification prior to a Late Cretaceous transgression (Hofmann et al. 1999). Pelagic wackestone (PW) withfilaments, radiolarians and Globochaete, cut by synsedimentary subvertical Q-fissures, infilled by fie-grained sediment and juvenile mollusks (M). Note bivalve (Halobia) coquina, C) at the bottom and thin calcite tapestries at the walls of the fissures. Late Triassic (Hallstatt limestone, Norian): Bad Ischl, Upper Austria. -> 1. 3: Diirkoop et al. 1986,2: Martire 1996 1

Fissure Infillings

gence, commonly exhibit changes in shape and dimensions due to solution, bioerosion and karstification. Filling In general, fissure infill occurs much less rapidly in terrestrial than in marine environments. Marine fissure fillings are primarily controlled by the relative rates of autochthonous and allochthonous sedimentation, by the size of the fissures and by the interconnection of the fissure with the external environment. Laminations and crossbedding of internal sediments within neptunian dikes can indicate relatively high flow rates within fissure systems (Pl. 2412; Figs. 5.12,5.13). Neptunian dikes are filled with sediment and fossils derived from variable sources, and carbonate cements formed at different times. Internal sediments comprise allochthonous grains and mud as well as autochthonous elements originating within the fissures. Allochthonous constituents are predominantly fossils (commonly pelagic fossils or organisms living on the sea-bottom nearby) forming densely packed, stratigraphically condensed accumulations of cephalopods, thin-shelled bivalves (e.g. Posidonia, Halobia, 'filaments') and gastropods ('Fossillagerstatten') as demonstrated by Triassic and Jurassic S- and Q-fissures in Austria and Sicily (Krystyn et al. 1971). Many of these 1995). Fissures can also be produced by differential fossils have been swept into and trapped in the fissures compaction of platform and basinal carbonates (Saller but some, characterized by significantly small growth 1996). Rapid extensional tectonic activities and high forms, represent probably cavity dwellers (Wendt hydrostatic pressure can, perhaps, also cause injection 1976). Common cavity-dwelling organisms are ostraof sediments into voids and fissures (Castellarin 1982). cods (Aubrecht 1997),foraminifera, and some brachioHydrothermal effects related to thermochemical effects pods. Autochthonous sediments consists of material (Sotak et al. 1993; Belka 1998) might also result in the formation of neptunian dikes. Opening of fissures in eroded from fissure walls and fossils formerly living at platform carbonates during rifting phases and infilling the edges of or within neptunian dikes (Gonzalezof pelagic sediment during andlor after drowning of Donoso et al. 1983; Playford 1984). Autochthonous the platforms have been repeatedly reported from the biota comprise microbial crusts as well as benthic foraMesozoic of the Alpine-Mediterranean region. Many minifera, ostracods, serpulids and brachiopods. Midikes are associated with regional extensional features, crobes are able to form distinctive morphological strucas shown by the coincidence of the preferred orienta- tures (fissure-dwelling 'endostromatolites': Monty tions of neptunian dikes and tectonic structures (Blen- 1982, see Sect. 9.1). dinger 1986). Neptunian dikes are not restricted to platTerrestrial infill within subaerially formed fissures forms and platform margins but also occur within pelagic carbonates deposited on tilted fault blocks (Martire differs from the internal sediments of neptunian dikes 1996). Opening of bedding planes can occur as a result in the lack of marine fossils (PI. 2415). Internal sedi= of both tectonic and synsedimentary induced fractur- ments of paleokarst fissures consist commonly of fine ing. Fracture orientation parallel or oblique to platform limestone or dolomite lithoclasts eroded from fissure margins can be indicative of synsedimentary or tec- walls, erosional relicts of overlying deposits, calcareous silt, siliciclastics, and redeposited pedogenic seditonic origins of fissures, respectively. ment (MacDonald et al. 1994; PI. 2415, P1.12911). CarMany neptunian dikes show little evidence of dissolutional and mechanical enlargement after the initial bonate cements of paleokarst fissures are often of meopening. Conversely, fissures associated with emer- teoric-phreatic origin (see Sect. 15.2.1).

Fig. 5.12. Early Jurassic neptunian dike (right) within a Late Triassic reef limestone (left). The organic structures of the white Upper Rhaetian reef limestones (Lamellata wahneri Fliigel and Sy, a hydrozoan - L, and a cyanobacterial crust C ) are cut by a vertical fissure (Q-fissure) filled with red Liassic echinoderm packstone. The planar boundary between the host rock and the dike indicates a tectonic origin of the fissure (related to initial rifting of a drowned platform). The peripheral calcite tapestry consisting of radiaxial cement points to a time break between the opening of the fissure and the infilling of the Liassic sediment. Note the solution seams on both sides of the calcite tapestry (arrows). Rofan, SOMwend Mountains, Tyrol, Austria. Scale is 5 mm.

Neptunian Dikes

5.3.1.2 MicrofaciesAnalysis of Neptunian Dikes Field data of neptunian dikes include rock color, orientation, geometry, and size of the fissures as well as the spatial relationships between fissures and breccias (Fiichtbauer and Richter 1983). The color of the neptunian dikes can be distinctly different from that of the host rock (e.g. red Liassic fissure infillings in gray or white Triassic platform and reef carbonates of the Alpine-Mediterranean region, Figs. 5.12 and 5.13), but many synsedimentary fissures are filled with carbonates displaying the same color as the host rocks. Sharp boundaries between the fissure infillings and the host rock indicate a tectonic origin of the fissures (Fig. 5.12), wavy and undulated boundaries can be caused by subaerial or submarine dissolution and erosion (Pl. 2411). Of major importance is the comparison of microfacies types of fissure sediments and host rocks, the evaluation of fossils with regard to taphonomic and ecologic criteria as well as original biotopes and age, and the investigation of carbonate cements using thin sections, cathodoluminescencepetrography, and isotope data. Microfacies data which should be evaluated in thin sections are: Composition and texture of internal sediment: Common microfacies of submarine fillings are red and gray mudstones and bioclastic wackestones and packstones with foraminifera, mollusk shells (ammonites, gastropods, accumulations of pelagic pelecypods, P1. 2416) and echinoderms (accumulations of crinoids, P1.2414, Figs. 5.12 and 5.13). In addition, brachiopods and various pelagic biota, e.g. radiolarians and globochaete algae may occur (Pl. 2413). Lithoclasts, derived from fissure walls, consisting of reworked calcite cements, or resulting from the erosion of host rocks and stratigraphically overlying rocks, may be common. Lithoclasts can represent reworked fragments of hardgrounds (Seyfried 1981; Wendt 1976). Differences in the sorting of particles reflect fissure systems that are more or less open and closed (Winterer et al. 1991). S-,parallel fissure infills are commonly finebedded (Fig. 5.13). The individual beds can differ in color shades, fossil content and stratigraphicage of the fossils included. Depending on the environment the 'internal sediments' are of shallow-marine to pelagic origin. Microfacies of neptunian dikes were described by Gonzalez-Donoso et al. (1983), Vachard et al. (1987) and Vera et al. (1988). Cements: Fissures that were inaccessible to infilling sediments are lined and partly or totally filled with

calcite cement (Fig. 5.13). Common cements are earlymarine radiaxial-fibrous calcite and younger granular calcite. Age-diagnostic micro- and rnacrofossils: Fissure infillings record continuous or interrupted sedimentation over very long time spans. These time spans can often be evaluated with the help of conodonts, foraminifera, and ammonites and by using 'microfacies zones' (see Sect. 10.3). Repeated rupture andfilling: Alternations of cement and sediment infill indicate repeated rupture and filling of the fissures (Pl. 2414, Wiedenmayer 1963). As many as twenty generations of fillings have been observed. Excellent examples are neptunian dikes cutting through Upper Triassic lagoonal limestones and filled with several generations of Liassic sediments at the Loser in the Styrian Northern Alps.

5.3.1.3 Case Studies of Neptunian Dikes in Carbonates Neptunian dikes are particularly associated with carbonate buildups because lithified carbonate responds in a brittle manner to stress and develops fractures at an early stage of lithification, steep carbonate slopes tend to develop fractures due to unloading and mass movements along margins of active and drowned platforms, and the solubility of carbonate favors percolation of undersaturated waters, assisting in void and fissure formation.

Box 5.7. Selected case studies of neptunian dikes.

Tertiary: Premoli Silva et al. 1998; Vachard et al. 1987 Cretaceous: Andrieux 1967; Company et al. 1982, Garcia-Hernandez et al. 1989, Greber 1988

Jurassic:Bohrn et al. 1999; Bouillin and Bellono 1990; Fabricius 1968; Fels and Seyfried 1993; Jurgan 1969; Lantos and Mallarino 2000; Lehner 1991; Martire 1996; Molina et al. 1985; Schijll and Wendt 197 1; Seyfried 1978, 1980; Vera et al. 1984; Wendt 1969; Wiedenmayer 1963; Winterer and Sarti 1994 Triassic: Blendinger 1986; Cozzi 2000; Fabricius 1966; Fischer 1964; Fiichtbauer and Richter 1983; Krystyn et al. 1971; Schlager 1969; Scholl and Wendt 197 1; Wendt 1973; Wiedenmayer 1963 Permian: Pray and Stanton 1992; Stanton and Pray 1993 Devonian: Belka 1989; Gischler 1992; Krebs 1968; Macdonald et al; 1994, Playford et al. 1989; Szulczewski 1973; Tucker 1973; Wendt and Bellca 1991; Wendt et al. 1984

Examples of Neptunian Dikes

Impressive examples of long-ranging graduated fissure fillings have been reported from Devonian, Triassic and Jurassic platform and reef carbonates as well as from slope and basinal carbonates (Box 5.7). The 'Blue Holes' of the Bahamas: a modem example of neptunian dikes Underwater caves formed on synsedimentary fractures paralleling the margin of the Bahama Bank and enlarged by dissolution activity in a mixing zone of fresh and saline waters may represent a modem analogue of neptunian dikes (Smart et al. 1988; Mylroie et al. 1995). These so-called Blue Holes got their name from the seemingly blue water of the surface water. The underwater cavities were formed as a result of erosional and dissolution processes controlled by Pleistocene high and low stand phases of the sea level. Some of the fractures of the Bahama Bank are associated with large submerged cave systems. Steep-sided planar walls, synchronous deposition of erosional and encrusting biota within the cavities, as well as the size and geometry of the cavities indicate that the Blue Holes are a good present-day example of active neptunian dikes, fissures and cavern infill. Neptunian dikes in Devonian reef and platform carbonates, Western Australia Neptunian dikes are frequent along the Frasnian platform margins of the Canning Basin (Playford et al. 1984). They become rarer towards the platform interior in the reef-flat facies and down marginal slopes in reef slope facies. Interestingly, dikes are especially well developed in Famennian back-reef limestones formed subparallel to the Frasnian reef front. Individual dikes may become 6 km long, 80 m deep and 20 m wide. But most of them are less than 100 m long, 20 m deep and about 5 cm wide. S-parallel dikes ('neptunian sills') are very abundant in marginal-slope deposits. Both fissure types show a complex history of fissure development, filling, lithification and refracturing. Early fillings include encrusting organisms, fossil debris, ooids, lime sand and mud, terrigenous sand, cavity peloids and 'spar balls', radiaxial calcite and internal breccias. Synsedimentary dikes in the Late Permian reef complex of Texas and New Mexico Vertical dikes near and parallel to the shelf-edge, composed of encrusting carbonate laminae, as well as dikes with abundant marine biota (algae and/or invertebrates) are known from the Capitan limestone (Stanton and Pray 1993). Fossil-rich dikes are usually 0.3-0.5 m wide and exhibit progressive opening, fill-

Fig. 5.13. Horizontal Liassic fissure (S-fissure) in Late Triassic peloidal grainstones (bottom, PG). Note that the picture does not show the entire width of the fissure. The Upper Rhaetian grainstone originated in a back-reef setting.The neptunian dike exhibits two-fold fillings: (1) alternating infillings of fine-grained crinoidal debris and carbonate mud, followed by (2) occlusion of a younger fissure within the lithified echinoderm packstone by several generations of calcite cement. The lack of calcite tapestries at the boundary (indicated by two short black lines) between the host rock and the fissure and current-induced textures within the fissure (alignment of shells - black arrows, laminations in micrite layers white arrow) points to a rapid infilling of the dike. Both, the Triassic host rock and the neptunian dike were transected by a network of thin microcracks (3), filled by gray calcareous silt possibly of meteoric origin and related to late tectonics. The Early Jurassic age of the echinoderm packstone is indicated by diagnostic foraminifera (In - Involutina liassica Jones). Rofan, Sonnwend Mountains, Tyrol, Austria. Scale is 5 mm.

ing by intact and fragmented skeletal grains and/or cement, and reopening which creates vertical layering. Most bioclasts in the dikes were loose seafloor particles, but some (whole and paired shells and large Tubiphytes) probably were fissure dwellers. The scarcity of rnicritic

Sediment-Filled Fissures

internal sediment in fossil-rich dikes suggests little free mud on the sea floor, bolstering the cemented seafloor concept of the Capitan limestone. Tectonic Jurassic dikes in Triassic limestones of the Northern Calcareous Alps, Austria The Sonnwend Mountains in m o l represent an excellent example of Jurassic fissure infillings of different stratigraphic age in Late Triassic reef limestones (Fabricius 1962; Wendt 1969; P1.2414, Figs. 5.12 and 5.13). The reef limestones are overlain by a condensed Jurassic sequence of red bedded limestones. Identical lithofacies types occur in vertical and oblique fissures starting at the Triassic/Jurassic boundary and transecting the upper part of the reef limestone. In contrast, lithofacies types and fossils in the sedimentary infillings of the horizontal 'S-dikes' within the reef limestones, running parallel to bedding planes, differ strongly from that of the Q-dies. These conspicuous differences have caused considerable problems in deciphering the structure of the mountains prior to the recognition of the red apparent intercalations as sedimentary fissures.

5.3.1.4 Significance of Sediment-Filled Fissures Fissures and neptunian dikes are of major importance in basin analysis: Internal sediments can preserve biota and sediment for periods where other records are lacking. Low sedimentation rates within fissures lead to condensed sequences covering substantial time periods. If sediments are not recognized as the internal sediments of neptunian dikes severe stratigraphical and structural misinterpretations may be the result. Neptunian dikes and fissure fills are sensitive sealevel indicators. Changes in the composition of internal sediments in dikes and fissures can reflect changes between marine nd subaerial settings, e.g. the beginning of transgressions or long-lasting karstification phases (Gonzalez-Donosoet al. 1983). The existence of multiple crosscutting neptunian dikes can be used to reconstruct recurrent syndepositional extensional tectonic activities along drowned platform margins and as paleostress indicators (Lehner 1991, Cozzi 2000). Indications of tensional disruption other than neptunian dikes are fractures, normal faults, shatter breccias and laterally discordant intraformational breccias dissecting platform-margin carbonates.

Basics: Neptunian dikes and fissure fills Cozzi, A. (2000): Synsedimentary tensional features in Upper-Triassic shallow-water carbonates of the Carnian Prealpes (northern Italy) and their importance as paleostress indicators. - Basin Research, 12, 133-146 Fischer, A.G. (1964): The Lofer cyclothems of the Alpine Triassic. - In: Memam, D.F. (ed.): Symposium on cyclic sedimentation. - Kansas Geol. Surv. Bull., 169, 107-149 Fuchtbauer, H., Richter, D.K. (1983): Relations between submarine fissures, internal breccias and mass flow during Triassic and earlier rifting periods. - Geologische Rundschau, 72,53-66 Garcia-Hernandez, M., Rey, J., Vera, J.A. (1989): Disques neptunicos de edad Cretacica en la Sierra de Quipar (Subbetico externo, Prov. Murcia). - Rev. Soc. Geol. Espaiia, 2,85-93 r Krystyn, L., Schaffer, G., Schlager, W. (1971): ~ b eFossillagersatten in den triadischen Hallsaner Kalken der Ostalpen. - Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen, 117,284-304 Lehner, B.L. (199 1): Neptunian dykes along a drowned carbonate platform margin: an indication for recurrent extensional tectonic activity? - Terra Nova, 3,593-606 Martire, L. (1996): Stratigraphy, facies and synsedimentary tectonics in the Jurassic Rosso Ammonitico Veronese (Altopiano di Asiago, NE Italy). - Facies, 35,209-236 Playford, P.E., Kerans, C., Hurley, N.F. (1984): Neptunian d i e s and sills in Devonian reef complexes of the Canning Basin, Western Australia. - Amer. Ass. Petrol. Geol. Bull., 68, p. 5 17 Scholl, W.U., Wendt, J. (1971): Obertriadische und jurassische Spaltenfullungen im Steinernen Meer (Nordliche Kalkalpen). - Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen, 139,82-98 Smart, P.L., Palmer, R.J., Whitaker, F., Wright, V.P. (1988): Neptunian dikes and fissure fills: an overview of some modem examples. - In: James, N.P., Choquette, P.W. (eds.): Paleokarst. - 149-163, Berlin (Springer) Vera, J.A., Ruiz-Ortiz, P.A., Garcia-Hernandez, M., Molina, J.M. (1988): Paleokarst and related pelagic sediments in the Jurassic of the Subbetic zone, southern Spain. - In: James, N.P., Choquette, P.W. (eds.): Paleokarst. - 364384, Berlin (Springer) Wendt, J. (197 1): Genese und Fauna submarinersedimentiirer Spaltenfiillungen im mediterranen Jura. - Palaeontographica, Abteilung A, 136, 122-192, Stuttgart Wmterer, E.L., Sarti, M. (1994): Neptunian dykes and associated features in southern Spain: mechanics of formation and tectonic implications. - Sedimentology, 41, 1109-1132 Further reading: K103

5.3.2 Microfractures and Veins (Calcite Veins) Many carbonate rocks display millimeter- to centimeter-sized, mineral-filled (often calcite-filled)microfractures (veins and veidets, Box 5.8). Fractures are discrete breaks within a rock mass and comprise microfractures, joints and faults. The existence of ductile shear zones, brittle shear zones and brittle-ductileshear

Calcite Veins

zones may be deduced from calcite-filledcracks in lirnestones. The spatial distribution of geological fractures is of particular interest with rgard to reservoir potential, hydrology or slope stability. Microfractures are only a part of largescaled fracture systems, and can therefore, be genetically understood only in the context of regional structural analysis. However, small-scaled fractures should not be overlooked in microfacies studies because of their importance in deciphering tectonic activities, fluid migrations, diagenetic history, reservoir potential and the mechanical properties of carbonate rocks.

5.3.2.1 Veins

Origin and Classification of Calcite

Fracture systems in carbonate rocks form in various stages of sedimentation (e.g. oversteepening of semilithified sediments, network of thin veinlets representing water escape structures: Macdonald et al. 1994) and diagenesis (e.g. compaction load, freshwater dissolution, deep-burial diagenesis: Geiser and Sansone 1981), but most calcite veins are due to brittle failure and tectonic fracturing of lithified carbonate rocks. Tectonic fracturing is caused by stress and shear displacement (Narr and Burruss 1984: Logan 1984; Ramsay and Huber 1987; Roehl and Weinbrandt 1988; Vrolijk and Sheppard 1991), extensional movements, or natural hydraulic fracturing (Sibson et al. 1975; Gretener 1976). Abnormally high natural pore fluid pressures form during (a) rapid sediment burial in basins of high sedimentation rate, (b) tectonic deformation causing closure of pore spaces at one site and high pore pressure due to migrating fluids at some other site, or (c) aquathermal pressure or mineral-phase changes as a result of diagenesis or low-grade regional metamorphosis and contact metamorphism (e.g. smectite-illite transformation). These fractures are characterized by the dominant vertical orientation and parallel nature of the fractures (Longman 1985). Vertical orientation, parallel nature and close vertical spacing of fractures, and the absence of shear offsets can be indicative of hydrofracture origin. Indications of fractures formed by extension are the lack of shear offsets on the fractures and the presence of only a single fracture set. The history and timing of shearinduced fractures in carbonate rocks is elucidated by laboratory experiments providing information on the controls of fracture development by stress, strain, strain

Box 5.8. Terms refering to tectonically induced fissures. Fractures: Discrete breaks in a rock mass where cohesion was lost due to brittle failure bv stress. Fractures include faults, across which shear displacements occur, joints which have an aperture but show no significant shear displacementsat hand specimen scale, and filled fractures, such as veins and dikes (Ramsey and Huber 1987, Gillespie et al. 1993). Microcracks. An opening that occurs in rocks and has one or two dimensions smaller than the third dimension (Simmons and Richter 1976). Generally millimeters to centimeter in size. Microfractures mm- to cm-sized structures developed by brittle failure. Veinlets: Small veins. Veins: Fractures filled with coarse crystalline calcite or various epigenetic minerals. Vein widths range from millimeters to over a meter, vein walls are subparallel, planar or irregular undulating. Contacts with host rock are usually sharp but embayed margins due to solution and/or replacement of host rock are also common (Logan and Semeniuk 1976).

rate, fluid pressure, temperature and lithology (Paterson 1978). Crack pathes observed in carbonate rocks appear to be controlled by texture and composition (e.g. irregular cracks preferentially within the matrix, not through the grains: Hugman and Friedman 1979; Olsson 1974). Fracture abundance often shows an inverse correlation to the amount of argillaceous material. Relations also exist between the carbonate texture type and the frequency of calcite veins. Lime mudstones and wackestones seem to be more strongly affected by shear-induced fracturing than grainstones. Classification of calcite veins Attempts to classify calcite veins rely on fracture types, geometry and morphology of veinlets, mineralogy and cement texture of filling as well as the timing and age relationships of veins. Four types of tensional fracture veins in outcrop and hand specimens have been distinguished (Logan and Semeniuk 1976): (1) parallel sheet (a single subparallel vein set), (2) rhomboidal and (3) rectangular (conjugate veins cutting the host rock idens appearing as rhomboid to rectangular in cross section), and (4) breccioid (caused by irregular and numerous conjugate veins). Misik (1966) distinguished separate veinlets formed by tension from those formed by compression using filling and relationships with microstylolites. He drew attention to a specific veinlet type characterized by a set of thin parallel veinlets separated by micrite and believed to have been formed by repeated cracking and recrystallization (Misik 1998).

Microfactures

5.3.2.2 Descriptive Criteria of Calcite-Filled Microfractures The following criteria are useful in describing and discussing of calcite veins: Spatial relations of fractures and grains (Simmons and Richter 1976; Kranz 1983): (a) more crumbly fractures (breaking around solid particles, intergranular and intercrystalline cracks), or grain boundary cracks associated with grain boundaries, (b) sharp-edged fractures (breaking through particles and intragranular and intracrystalline cracks extending from a grain boundary crossing into one or more other grains, P1. 2511). Sedimentary texture and composition seem to be the essential controls on the main fracture types of carbonate rocks. Occurrence of single microfractures or fracture sets (composite crack-seal veins, P1.2511) characterized by the consistency of orientation. Morphology of fractures (straight, arched, branching, stepped, displaced, P1.25/4,6). Existence of offsets on microfractures (indicating shear, P1.2513). Shape of upper and lower terminations (sharp, pinching out, irregular). Orientation of calcite veins with regard to bedding planes (vertical, oblique, parallel). Occurrence of crosscutting fractures (Pl. 25/1,6). Distribution, spacing and density of microfractures and larger fractures (Gillespie et al. 1993). Microcrack densities are expressed either as the number of cracks per unit area or per grain. Crack densities increase with increasing stress, the ratio of grain boundary cracks to intragranular cracks decreases at higher applied loads. These generalized density patterns, however, observed predominantly in non-carbonate rocks, are not always relevant for carbonate rocks because cracking can be surpressed at higher pressures to the benefit of twinning. Width and length of microfractures. Filling and sealing. Fracture filling should be described with regard to (a) mineralogy, (b) inclusion bands (Ramsay and Huber 1987), (c) cement types (Muchez et ai. 1994), (d) timing of filling generations, (e) mode of vein-growth by various crack-seal mechanisms (e-g. crack-seal fiber growth due to syntaxial overgrowth of grains in microcrack walls and oriented or random nucleation and initial growth of crystals: Cox and Etheridge 1983; Ramsay 1980; solution cleavage, Alvarez et al. 1978),and (f) dynamic effects (e.g. twinning, curving of twin lamellae, undulose extinction). Spatial relations of microfractures with sedimentary grains and structures (Pl. 2512).

Association with stylolites (Nelson 1981; Beach 1982; P1.2514). Volumetric importance of calcite veins related to the total rock. Differences in the occurrence of veins in various beds. Relation of vein abundance and bed thickness (fracture density can have an inverse logarithmic relation to bed thickness, regardless of structural setting (McQuillan 1973). Relative age of joints and calcite-filled fractures. Conventional analysis of geological fracture data considers the orientation and distribution of fractures measured on sample linepines oriented normal to the fracture strike and shown by stereonet projections. Methods are described by McQuillan (1973), Huang and Angelier (1989) and Gillespie et al. (1993). Microfracture density can be expressed by (a) the number of fractures intersecting a line in thin section, hand specimen or core, or (b) the number of vertically and obliquely oriented calcite veins related to a defined thin-section area. Geochemical and mineralogical criteria Microfacies thin sections allow only a first evaluation of calcite vein types, distribution and frequency. Detailed analysis of fracture fillings demands that fluid inclusions, isotopic composition and other geochemical criteria as well as SEM and TEM be investigated (Marshall 1982;Dietrich and McKenzie 1983;Ramsay and Huber 1987; Fairbairn and Ferguson 1992; Migaszewski et al. 1998; Suchy et al. 2000).

5.3.2.3 Significance of Microfractures in Carbonate Rocks Microfractures have great potential for evaluating the postsedimentary history of carbonate rocks. The following points are of particular interest: Laiger and smaller fractures in subsurface rocks are known to impart the permeability necessary for the economic recovery of hydrocarbons from reservoir rocks, and some fractures provide a major part of reservoir storage capacity (Drummond 1964; Narr and Cume 1982; Kulander et al. 1990). Fracturing of carbonate rocks enhancespermeability and porosity, both of which are important in the reservoir potential. Many large hydrocarbon reservoirs are connected with fractures (e.g. Longman 1985; Roehl and Weinbrandt 1985; McQuillan 1985; Irish and Kempthorne 1987).

Microfractures and Calcite Veins

Details of small-scalefracturing assist in understanding relationships between tectonic structures and fracture distribution and their origin within a regional geological frame (Fliigel and Kirchmayer 1962; Logan and Semeniuk 1976; McQuillan 1985). Mineralogical and geochemical data of microfissure fillings associated with larger joints and major faults add to the explanation of the course of mineralization and ore formation (Fairnbairn and Ferguson 1992). Abundance of calcite-filled veins influences technological properties (hardness, strength, breakage, slake durability and weathering) of carbonate rocks,

Basics: Microfractures and 'calcite veins' in carbonate

rocks Al-Aasm, I.S., Coniglio, M., Desrochers, A. (1995): Formation of complex fibrous calcite veins in Upper Triassic strata of the WrangelliaTerrain, British Columbia, Canada. - Sed. Geol., 100,81-95 Antonellini, M., Mollema, P.N. (2000): A natural analog for a fractured and faulted reservoir in dolomite: Triassic Sella Group, Northern Italy. - Arner. Ass. Petrol. Geol. Bull., 84,3 14-344 Boukadi, N., El Ayeb, S., Kjarbachi, S. (2000): Analyse quantitative de la fractuation des calcaires yprksiens en Tunisie: I'exemple de Jebel Ousselat. - Bull. Soc. gCol. France, 171,309-3 17

Plate 25 Microfractures and 'Calcite Veins': Controls on Permeability, Mineralization and Technological Properties of Carbonate Rocks Fractures can raise the permeability of hydrocarbon reservoir rocks. Mineralogical and geochemical data of microfractures assist in explaining ore formation. The abundance and type of calcite-filled veins influences the technological properties of carbonate rocks (e.g. strength, breakage, weathering). Many limestones exhibit millimeter- to decimeter-sized calcite- or sediment-filled microfractures, commonly called 'calcite veins'. These structures are part of large-scaled fracture systems affecting the rock together with joints and faults. Although microfractures can be understood genetically only in the context of a regional structural analysis, the relationships between fractures, faults and folds, 'calcite veins' should not be overlooked in microfacies studies because of their importance in deciphering the postsedimentary history of the rocks, including the tectonic activities, burial diagenesis, fluid migrations, reservoir potential and mechanical properties of carbonate rocks. Useful descriptive criteria of microfractures are (a) spatial relations of fractures and grains (-> I), (b) occurrence of isolated microfractures or fracture sets, (c) morphology (e.g. straight, arched, branching, -> 6), (d) offsets (-> 3), (e) shape of terminations (-> 4,6), (f) filling and crack-sealing (e.g. mineralogy, cement type, inclusions, growth pattern, dynamic structures) and sealing, (g) orientation with regard to bedding planes, (h) crosscutting (-> 1, h), (i) distribution, spacing and density, width and length, volumetric importance, association with stylolites (-> 4), and 6)the relation of vein abundance and bed thickness. Fracture systems in carbonate rocks can form during various stages of sedimentation (e.g. oversteepening of semilithified sediment, water escape structures, -> 5) and diagenesis (compaction load, freshwater dissolution), but most calcite veins are due to brittle failure and tectonic fracturing of lithified carbonates caused by stress and shear displacement (-> 2,3), extensional movements or natural hydraulic fracturing. Attempts to classify calcite veins rely on fracture types, geometry and morphology of veinlets, mineralogy and cement texture of filling (-> 2) as well as the timing and age relationships of the microcracks. 1 Microfracture sets. Radiolaria wackestone. Most larger radiolarians are crossed by calcite-filled cracks. Early Cretaceous (Aptychus beds): Schrecksee, Allgau, Germany. 2 Shear-,fructures.Fusulinid foraminifera (Neoschwagerina),displaced along calcite cement-filled shear systems. Note the difference in cement fillings. Middle Permian: Straza quarry, Bled, Slovenia. 3 Microcracks with offsets. Bioclastic mudstone. Late Triassic (Kossen beds): Schrecksee,Allgau, Germany. 4 Burrowed lime mudstone, crossed by crosscutting calcite veins associated with stylolite seams (arrows). Note the interconnected burrow network (dark appearance) created by sediment-inhabiting organisms. Burrowing took place in aerobe environment. Stylolites are often associated with small-scale calcite-filled fracture sets, which can be used as paleostress indicators. Early Jurassic (Liasbasiskalk): Schrecksee, Allgau, Germany. 5 Early diageneticfractures. Vertical microcracks caused by dewatering of the sediment. The rock is characterized by wavy to crinkled fine laminae composed of couplets of mudstone layers (dark) and layers with quartz grains (light). These couplets are known from peritidal settings and muddy lagoonal environments. Late Triassic (Kossen beds): Schrecksee, Germany. 6 Bedded lagoonal fenestral bindstone. Note the differences in shape, thickness and terminations of calcite veins. Middle Triassic (Wetterstein limestone): Schrecksee,Allgau, Germany.

228

Fairbairn, R.A., Ferguson, J. (1992): The characterisation of calcite-filledfractures from the Northern Pennine orefield. - Proc. Yorkshire Geol. Soc., 49,117-123 Geiser, P.A., Sansone, S. (1981): Joints, microfractures and the formation of solution cleavage in limestone. - Geology, 9,280-285 Gillespie, P.A., Howard, C.B., Walsh, J.J., Watterson, J. (1993): Measurement and characterisation of spatial distribution of fractures. - Tectonophysics, 226, 113-141 Irish, J.P.R., Kempthorne, R.H. (1987): The study of natural fractures in a reef complex, Norman Wells Oil field, Canada. - In: Tillman, R.W., Weber, K.J. (eds.): Reservoir sedimentology. - Soc. Econ. Paleont. Min. Spec. Publ., 40, 153-167 Kranz, R.L. (1983): Microcracks in rocks: a review. - Tectonophysits, 100,449-480 Logan, B.W., Semeniuk,V. (1976): Dynamic metamorphism, process and products in Devonian carbonate rocks: Canning Basin, Western Australia. - Western Australian Geological Society, Spec. Publ., 6, 138 pp. Misik, M. (1966):Tentative classification of veinlets in limestones. - Geol. Sborn. Slov. Akad. Vied, 17,337-344 Misik, M. (1998): Peculiar types of thin veins in the Mesozoic carbonates and silicates of the Western Carpathians. - Geologica Carpathica, 49,27 1-298 Narr, W., Burmss, R.C. (1984): Origin of reservoir fractures in Little Knife field, North Dakota. - Amer. Ass. Petrol. Geol. Bull., 68, 1087-1100 Rarnsey, J.G., Huber, M.I. (1987): The techniques of modem structural geology. Vol. 2: Folds and fractures. - 700 pp., London (Academic Press) Suchy, V., Hejlen, W., Muchez, Ph., Dobes, P., Hladikova, J., Jackova, I., Safanda, J., Zeman, A. (2000): Geochemical study of calcite veins in the Silurian and Devonian of the Barrandian Basin (Czech Republic): evidence for widespread post-Variscan fluid flow in the central part of the Bohemian Massiv. - Sed. Geol., 131,201-219 Troalen, J.-P. (1993): Une mCthode indirecte de quantification de l'kvolution de la microfissuration themiclue dam des roches carbonatkes. -Engineering Geology, 33, 189199 Vemin, E., Moreno-Eiris, E., Perejon,A., Alvaro, J.J. (2001): Fracturaci6n sinsedimentaria y diagenesis precoz en las bioconstrucciones del Cfimbrico inferior di Alconera (Ossa-Morena).- Rev. Soc. Geol. Espafia, 14,75-88 Further reading: KO71

5.3.3 Carbonate Breccias and Conglomerates Carbonate breccias and conglomerates are sedimentary rocks characterized by limestone or dolomite fragments embedded in a groundmass consisting of fine-grained matrix orland cements. Breccias are characterized by abundant angular clasts (usually > 50%), conglomerates by abundant well-rounded clasts of pebble- or gravel size. The word breccia originated in Italy where it has long been used for the crushed rubble used in walls.

Breccias

The Latin word conglomeratus means heaped, rolled and pressed together. The study of breccias and conglomerates requires integrating field observations and laboratory data. Microfacies analysis provides a powerful means of deciphering the provenance of the clasts and understanding the relationships between depositional and tectonic controls on recycled sediments.

5.3.3.1 Terminology A variety of terms is applied to rocks composed of carbonate clasts. Most terms recognize the rock to be genetically interpretated. Breccias related to seismic events (see Sect. 12.4) and impact breccias caused by meteorites will be discussed later. Impact breccias are generally characterized by strongly fractured clasts and a large amount of groundmass consisting of fragmented particles. The rock is twisted, sheared and heavily veined. Cement filled vugs are common (Martinez et al. 1994; Warme and Kuehner 1998). Other terms focus on the dimensions of the clasts, which vary widely: Microbreccias: containing mm- and cm-sized carbonate clasts are often described within the framework of common limestone classifications using the terms intra- or lithoclast, and indicating size ranges by the use of 'calcirudite', 'rudstone' or 'floatstone' (e.g. 'polymict intracalcirudite'). The boundary between lithoclast limestones and breccias is artificial, some authors propose a boundary of about 2 mm. Some microbreccias are extremely diverse with regard to the microfacies types of the carbonate clasts. Auley-Charles (1967) for example, reported a Miocene microbreccia consisting of more than 30 limestone types. Microbreccias are common constituents of slope deposits (Pl. 11411, 3) or represent distal debris-flow deposits (Pl. 2614). Megabreccia are coarse matrix-supported breccias containing individual angular blocks up to a meter to more than 100 meters in size. The breccias result from sedimentary and tectonic processes and develop downslope by large thrusts connected with gravitational sliding, e.g. mega-debris flow deposits (Cook et al. 1972; Mountjoy et al. 1972; Leigh and Hartley (1992). They are formed on a broad range of slope angles and contains coarse-grained as well finer-grained breccias. The latter represent a specific Standard Microfacies Type (Pl. 11411, 3). Explanations for the formation of megabreccias are the release of pore-water overpressure of confined aquifer horizons beneath the sea floor (particularly during falls of sea level) or a catastrophic collapse of high-angle oversteepened carbonate plat-

Describing Breccias

form margins (Spence and Tucker 1997). Diagnostic criteria of megabreccias are (a) the association of megabreccias with various types of mass-flow deposits, (b) mixtures of extrabasinal clasts, intrabasinal clasts and tabular intrabasinal blocks with dimensions of tens of meters to several hundreds of meters, and (c) the common disorientation of geopetal fabrics within blocks (Pl. 2617) or from one block to another block. Spectacular examples are known from toe-of-slope deposits (e.g. Gullo and Vitale 1987;Fliigel et al. 1991; Haas 1999) and in accretionary settings (Sano and Tamada 1994). Decameter-sized constituents of megabreccias should not be mistaken for autochthonous formations. The timing of breccia or conglomerate formation can be indicated by the adjective 'intraformational'. Intraformational breccias are formed by synsedimentary processes and consist of clasts believed to have formed within the depositional basin. The clasts originate from penecontemporaneous reworking and redeposition fairly close to the site of formation. Breakingup takes place subaerially (e.g. drying of mud on tidal flats) or in a submarine setting by tidal currents (Pl. 132/4), storm waves (Pl. 132/2), or gravity flows (Walcott 1894; Assaruri and Langbein 1987).

5.3.3.2 How to Describe Carbonate Breccias? Basic criteria relevant to the microfacies analysis of carbonates breccias include: Field relationships Geometry, thickness and lateral extension: Geometry as well as local or regional extension of breccia bodies are crucial in understanding breccia genesis. Shallow-marine breccia and carbonate conglomerates are characterized by: individual layers usually a few decimeters thick, discontinuous layers ranging from meter-sized lenses to a lateral extension of many tens of kilometers (Grotzinger 1986). Mass-flow breccias can extend laterally several hundreds of meters to tens of kilometers. Stratification,grading and sedimentary structures: Breccias are massive or stratified. Stratification should be described in terms of distinctness, dimensions and sedimentary structures (cross-stratification,high-angle edgewise structures, common in modem beach deposits, occurring in lenses and pockets). Edgewise conglomerates have various origins, they occur as erosional scours in supratidal-flats, as discontinuous layers near linear mounds, and on beach ridges along eroded shorelines. Breccia grading can be normal or inverse.

229

Boundaries and relationships to adjacent rocks:The genetic interpretation of breccias needs data concerning the basal and upper boundaries and the relations to the underlying and adjacent rocks. Lower contacts can be erosional and sharp, gradual or passing into fractures and fissures (e.g. internal breccias). Breccias formed by sliding and slumping often exhibit multiple brecciation phases and reverse gradation of the clasts. Diferences in the color of clasts and groundmass: The color of the clasts and the fine-grained matrix is important in recognizing extra- or intrabasinal origins of the material. Clasts Lithologic composition: The composition of clasts is differentiated with regard to (a) homogeneity or differences in lithology (monomict and polymict breccias, pure carbonate breccias, lithologically mixed breccias), and (b) the quantitativeproportions of different lithologies. Lithology is commonly described in terms of field observations only (e.g: limestone, dolomite or chert clasts) but should be evaluated by thin sections. Commonly, very small clasts are attributed to the matrix during field work, but thin sections might provide evidence that precisely these clasts are the only relicts of stratigraphically older rocks that have suffered repeated erosion and redeposition. Quantitative analysis needs statistical sampling based on line-, ribbon-, area- or point-counting (Sect. 6.2.1). Quantification must consider not only the frequency of lithologic types but also the frequency of clasts which catch the eye by their particular rock color, rounding or size. Compositional clast analysis offers key information on (a) extra- or intrabasinal sources, (b) the environmental controls in the provenance area, (c) multiple redeposition, (d) depositional or non-depositional formation of the breccias and (e) the site of breccia formation (terrestrial, marginal-marine, marine). Fabric: The fabric of breccias is characterized by matrix-support or clast-support. Matrix-supportedbrecc i a ~exhibit clasts floating within fine-grained matrix (Pl. 2612) or a calcarenitic groundmass. Clast-supported breccias consist of clasts supporting each other (Pl. 261 3). This differentiation resembles the distinction between mud-support and grain-support used to characterize depositional structures of limestones (Dunham 1962), but should not be regarded as strictly genetic, because matrix- and clast-support fabrics are caused by depositional as well as non-depositional processes (e.g. solution, brecciation, tectonic shear). Size and sorting: The size of carbonate clasts is highly variable. Clasts can range from arenite to boulder size. Shallow-marinebreccias and mass-flow brec-

Carbonate Breccias

cias formed in upper slope environments often exhibit a bimodal grain size composition, with larger clasts and interstitial well-sorted sand-sized particles (peloids, ooids, skeletal grains, P1. 2617). Size and sorting are essential criteria in discriminating genetic conglomerate types. Shape and sur3'ace of carbonate clasts: The form may vary from sharply angular to more or less rounded, the shape can be isometric, platy, or tabular. Many round

conglomerate pebbles exhibit biogenic encrustations and borings indicating interruptions and resting times during transport processes (Pl. 2617). Roundness: Per definition breccia clasts are angular, but carbonate breccias display all transitions possible from predominantly angular to variously rounded clasts, which relate the latter samples to conglomerate categories (see PI. 2613). The roundness of breccia clasts is determined with the help of comparison charts that

Plate 26 Carbonate Breccias Carbonate breccias and conglomerates, made of angular or rounded rock fragments embedded within a matrix and/or cemented by various minerals, are common in marine and non-marine sequences. Integration of field and laboratory data is necessary for classifying and interpreting these rocks. In polymict breccia, clasts and matrix are not genetically related, and result from transport and depositional processes (e.g. submarine landslide, fluvial transport and deposition, subaerial and subaqueous debris flows (-> 3), slumping and volcanic phenomenons (-> 2). Mechanisms triggering mobilization are gravity, earthquake and water loading that induce overpressure, storms (producing flat-pebble conglomerates), tides, oversteepening of slopes (-> 7), gas hydrate destabilization, and glaciation processes. In autoclastic or intraformational breccias, clasts and matrix are genetically related. In terrestrial or meteoric-vadose environments, these breccias result from in situ deformation or reworking processes (dehydration, karstification). Polymict stylobreccia consisting of tightly packed limestone clasts. The scarce marly matrix is a residue product of pressure solution. The breccia represents a massflow deposit formed by submarine gravity flows and modified by subsequent pressure-solution. Rounding of clasts is caused by burial solution, not by transport. Arrows point to solution seams. Note the different microfacies of the clasts: The dark clasts are pelagic bioclastic wackestone with filaments, ostracods and radiolaria. Light clasts are bioclastic packstones. Early Jurassic (Adnet Limestone): Adnet near Salzburg, Austria. Matrix-supported agglomerate (volcanic breccia) formed by submarine volcanic explosion followed by admixture and massflow transport of volcanic clasts (V) and rounded carbonate extraclasts (E). Middle Triassic (Ladinian): Mt. Agnello, Southern Alps, Italy. Clast-supported monomict limestone breccia. The clasts exhibit different roundness/sphericity values: subangular, subrounded and rounded clasts (fields B, E and I in the Krumbein chart, cf. Fig. 4.30). The clasts are pelagic bioclastic wackestones and packstones. Calcite-filled microfractures are limited to the clasts indicating fracturing prior to brecciation. Interclast voids are filled with several generations of marine fibrous and blocky calcite cements. The breccia is explained as mass-flow breccia resulting from submarine slides of semiconsolidated pelagic sediments on a steep slope of a drowned Triassic reef, triggered by tectonic activities (Hudson and Jenkyns 1969; Bijhrn et al. 1995). Because of the attractive appearance of the red limestone clasts within the white sparry calcite, the breccia has been widely used as decorative stone. Early Jurassic ('Scheck breccia', Piensbachian~Toarcien): Adnet near Salzburg, Austria. Polyrnict clast-supported microbreccia (sandy lithoclast packstone) consisting of angular (gray) dolomite clasts, (dark) limestones clasts and (white) quartz grains. Note the absence of matrix. Debris-flow deposit. Early Cretaceous: Mosaic material of a Roman building, Kraiburg, southern Bavaria, Germany. Monomict tectonicfault breccia. Note the angularity and the complex and strong fracturing of individual clasts as well as the whole rock. Microfractures differ in width, filling and orientation. Some calcite veins clearly postdate brecciation. The matrix consists of small broken and sheared rock fragments bound together by sparry calcite. Late Triassic (Dachstein Limestone, Norian): Northern Alps, Austria. Polymict breccia consisting of extraclasts (left: shallow-marine algal wackestone with dasyclads - AW, bottom right: microbioclastic packstone - P) and alveolinid foraminifera. Interpretation: Massflow deposit. Redeposition of shallowramp bioclasts and lithoclasts in deeper ramp areas caused by regressive events (Kulbrok 1995).Early Tertiary (Eocene): St. Paul Monastery, Wadi Araba, eastern Egyptian Desert. Polymict massflow breccia. The material was eroded from reefs formed on the upper slope of a platform margin. The sample is part of a megabreccia consisting of meter-sized reef- and slope-derived blocks.. Deposition took place in a proximal position on the foreslope. Most clasts are boundstones except for the crinoid packstone (P) representing slope facies. Note biogenic encrustations (arrows) indicating breaks during the transport on the slope. GP: Upside-down geopetal structure (arrow). The interstitialgrainstone 'matrix' (GM) represents platform-derived material infilled subsequent to the deposition of the clasts. Fracturing postdates brecciation. Middle Triassic (Ladinian): Seiser A h , Dolomites, Italy.

Groundmass of Breccias

consider both roundness and shape (Sect. 4.3.1, P1.261 3), or as the percentage of clasts with at least one rounded edge (roundness number: Richter and Fiichtbauer 1981). Breccias formed in place commonly consist of high proportions of angular or only partly subrounded clasts (e.g. internal breccias, karst breccias, pedogenic breccias, P1. 12812, PI. 12911). Roundness can increase with transport (e.g. in mass-flow breccias) and by multiple reworking of breccia beds (Buggisch and Fliigel1980). However note, that rounded carbonate rock fragments are not necessarily products of abrasion during transport but can also be caused by partial dissolution (Pl. 2611) or replacement processes after deposition. In addition, organic encrustations will modify the shape of clasts and transform angular rock fragments into round boulders. Fitting: Fitting (Richter and Fiichtbauer 1981) describes the grain-to-grain relations of clasts - the degree and percentage to which clast boundaries match those of adjacent clasts (PI. 26/1,5). In measurements, each clast is counted only once. Differences in fitting are powerful criteria in distinguishing genetically different breccia types (Fig. 5.14). Orientation: The orientation of clasts may be absent or parallel to bedding or stress, and increasingly or decreasingly parallel to the transport direction. Flatlying orientation in shallow-marinecarbonate breccias is sometimes caused by compaction. Current-controlled deposition is manifested by the imbrication of clasts and partial infilling of interstices between the clasts with sand after the deposition of the gravel framework. However, it should be taken into account that 'pseudo-imbrication' also occur at the foresets of large-scalecrossstratification. Fracturing or veining of clasts occurs prior to brecciation, during the process of brecciation, or subsequent to brecciation (Pl. 26/3,5,7). Fractures and veins within clasts of many mass-flow breccia and reef breccia predate fracturing and veining whereas fracturing during brecciation is common in caliche and solution breccia. Internal breccias and shear breccias exhibit abundant and superposed generations of post-brecciation fractures and veins (Pl. 2615). Internal breccias often show inherited calcite-filled fractures. Microfractures should be described by abundance, orientation, size and filling (see Sect. 5.3.2.2). Clastlmatrix boundary: Most boundaries are sharp (e.g. Pi. 2613, 5) except for diagenetic pseudobreccias and solution-evaporite-collapse breccias, which may exhibit irregular replacement margins. Microfacies: Sampling for microfacies studies of clasts must consider the size, roundness and shape, packing of clasts as well as conspicuous sedimentary

0w

%

Fissure-

o

Fitting

10

Fig. 5.14. Relations betweenfitting of clasts and the amount of groundmass (matrix+ cement).After Fiichtbauer and Richter (1983).

structures (e.g. stratification). Carbonateclasts of breccia~ and conglomerates are classified according to depositional texture, composition and fossils. The frequency and size of clasts give some indication of the proximity or distality of source areas. At the very least, the relative proportions of microfacies types should be estimated or measured (e.g. counting all clasts within a defined thin-section area). A comparison of standard microfacies types (see Sect. 14.3) of breccia clasts with regional or generalized facies models may provide clues to the provenance area. Fossiliferous clasts must be tested with an eye to age determinations. Groundmass Abundance of the matrix and clastlrnatrix ratio: Matrix can be abundant, scarce or even missing due to diagenetic solution (e.g. stylobreccia). Differentiation of breccia types and genetic interpretation requires the quantitative data of the amount of matrix and the clastl matrix ratio. These data are determined in the field (sometimes also in large rock samples and thin sections) using the counting methods mentioned in conjunction with the compositional clast analysis, or estimating the frequency of clasts. Matrix composition: The matrix of carbonate breccias consists of sediment or rock detritus formed by the destruction and attrition of rock material. The descriptive criteria of the sedimentary matrix are color, mineralogy, uniformity, texture (e.g. micrite, calcilutite or calcarenite matrix), and small-scaled sedimentary structures (e.g. grading, lamination). Finegrained matrix is represented by (a) sediment deposited between clasts coeval with the deposition of the

233

Types of Breccias

clasts P1. 26/7), (b) sediment infilled ('sucked in7)after the deposition of the clasts, (c) the residual matrix of beds which have been affected by solution (stylobreccias, P1. 26/1), or (d) fine erosional detritus consisting of rock debris (Pl. 2615) The major aim of the study of matrix composition is to find out if clasts and matrix are different with regard to the environment and timing of breccia formation. Cement minerals: Common chemical precipitates of carbonate breccias are calcite cements. The mineralogical composition, cement types and spatial distribution of pore-filling carbonate cements are important criteria for understanding the course of the diagenetic and tectonic history of breccias. Fossils The fossils occurring within the matrix and in the clasts are the main criteria in (a) reconstructing the environment and facies patterns in the source area of depositional breccias and conglomerates (Pl. 27), and (b) evaluating age and timing of breccia and conglomerate formation. In basin analysis, the microfacies data of isolated pebbles and of breccia clasts assists significantly in recognizing erosion events connected with the breakdown of carbonate platforms (e.g. Fliigel and Kraus 1988) and of allochthonous sedimentation on slopes and in deeper basins (e.g. Herbig 1984). Abundant stratigraphically useful microfossils seen in microfacies thin sections of Phanerozoic conglomerates and breccias include foraminifera, calcareous algae and many microproblematica (see Chap. 10). The combined use of thin-section biota and microfossils recognized in solution residues of limestone pebbles (e.g. conodonts) is highly recommended (e.g. Pohler and James 1989). Because fossils can be reworked several times and set free from surrounding rock material, difficulties can arise in evaluating 'isolated' microfossils found within the matrix. Taphonomic criteria (preservation) should help overcome these pitfalls (Pl. 917).

The following summary of common breccia types is based on the suggestions of Norton (1917), Blount and Moore (1969), Keith and Friedman (1977) and Richter and Fiichtbauer (1981). Major genetic categories include depositional, non-depositional,tectonic and diagenetic breccias (Fig. 5.16). Depositional, nondepositional and tectonic breccias as well as conglomerates differ in composition and the role of transport processes (Fig. 5.15).

Depositional breccias Mass-flow breccia Field observations: Bedded, primary sedimentary structures, stratigraphically concordant, stratabound. Variable thickness, large lateral extension. Lens-shaped bodies, massive laterally extended beds. Variable grading (inverse and normal). Upper and lower boundary sharp or undulated, lower boundary often erosive or channelized. Clasts: Lithologic composition: often polymict (Fig. 5.21). Fabric usually clast-supported, no primary fitting but common boundaries due to pressure solution (Pl. 2611). Close to open packing. Variable shape, all degrees of roundness, subangular and rounded clasts common (Pl. 2611, 3), P1. 2711). Variable size, poor to moderate sorting (Pl. 114/1,3). Fracturing or veining of clasts (if present) predates breccia formation. Clastl matrix boundary sharp. Microfacies variability very

t

Conglomerate

Moraine debris Fanglomerate Forereef breccia Mass-flow and grain-flow breccia Rockfall and talus breccia

Shear breccia Fissurefill breccia Solution/coliapse breccia Internal breccia Shrinkage breccia monomlct

5.3.3.3 Carbonate Breccia Types: Origin, Classification, Criteria Carbonate breccias are of different origins. Their classification is essentially genetic and differs conceptually from those of limesfones. Classification systems are based either on descriptive criteria or inferred from brecciation processes (Spence and Tucker 1997).

-Composition

-

7

poiymict

Fig. 5.15. Relations between the composition of breccias and conglomerates and the relative motion of clam. Note the differences between nondepositional breccias (shrinkage and ~o1ution/co~apse breccias) and tectonic breccias (internal, fissure-fill and shear breccias) as compared with depositional breccias. Conglomerates,including synsedimentary soft-clast conglomerates, appear to be distinctly separated from brecc i a ~but , may act as precursor stages of breccia formation. Modified from Richter and Fiichtbauer (198 1).

234

Types of Breccias

Depositional breccias sulting from the deposition of eroded carbonate material)

Mass-flow breccia: Breccia originating from the downslope transport of shallow-marine and (reslope sediments moving under the force of gravity. Includes breccias formed by slumps and slides, debris flows, grain flows, and turbidity flows. Submarine rockfall breccia: Mass-flow breccia formed by the accumulation of coarse, angular rock fragments derived by falling from a cliff, escarpment or steep rocky slope. Peritidal and shallow-marine breccia: Breccia formed by synsedimntary deposition of eroded peritidal, shallow subtidal as well as subaerial carbonates, often related to storm events. Deposition takes place in inter- and supratidal settings, and at the beach. I

Non-depositional breccias (resulting from in-place dissolution)

Forereef breccia: Breccia deposited on the seaward slope of high-energy reefs. Consisting of eroded reef material and remains of organisms living in the reef or on the foreslope. Caliche breccia: Breccia formed by in-situ brecciation in arid and semiarid climates, controlled by soil-forming processes, and connected with extensive weathering, erosion, solution and shrinkage. Solution-evaporite-collapse breccia: Breccia formed by collapse of beds subsequent to the removal of soluble material within some beds (e.g. evaporites).

Tectonic breccias (resulting from internal dislocation of carbonate rocks)

Fissure fill breccia: Breccia formed within submarine neptunian dikes or subaerial fissure infills and karst fissures. Internal breccia: Breccia formed by rupture and fracturing of carbonates near the depositional surface. These breccias are products of dilation of slightly lithified limestonescaused by tectonics (e.g. hydraulic fracturing, earthquakes). Internal breccias occur in platform and slope carbonates which were brecciated shortly after deposition and before final lithification. Shear breccia: Breccia caused by brittle deformation associated with thrust and sliding displacement.

Diagenetic breccias (resulting from early diagenetic processes)

I

Pseudobreccia: Mottled limestones and dolomites with breccia-like textures caused by patchy recrystallization and cementation, possibly controlled by the distribution of organic compounds. Stylobreccia: Breccia in which fragments are bound by stylolites. Caused by fracturing of carbonate rocks, accompanied by pressure solution between the fragments of the breccia.

Fig. 5.16. Main types of carbonate breccias. Because many breccias are products of multiple processes, the boundaries between some categories are transitional. The formation of fissure fill breccias, for example, depends on the existence of a tectonic framework, but the composition of the breccias i s depositionally controlled.

high to moderate, and may include the entire spectrum of Dunham's texture types (Fig. 5.21). The clasts represent a mixture of material derived from various shallow-water and slope environments and sometimes also from basinal environments. Groundmass: Fine-grained sedimentary matrix (e.g. pelagic micrite) or matrix brought to the basin together with the clasts. Depending on the depositional pattern, the matrix volume is less,than equal to or greater than that of the clasts. Inter-clast carbonate cements are relatively rare (Pl. 2613). Fossils: Common and abundant in clasts and within the primary sedimentary matrix (Pl. 9/7), relatively rare in the allochthonous matrix. Case studies: Bektas et al. 1995; Bernoulli et al. 1987; Braithwaite and Heath 1992; Cook 1979; Engel 1970; Fliigel et al. 1993; Gawlick 1996; Giinther and

Wachsmuth 1969; Leigh and Hartley 1992; Payros et al. 1999; Peryt 1992; Remane 1970; Ruberti 1993; Steiger 1981; Stock 1994; Wachter 1987. Submarine rockfall breccia Field observations: Massive or thick-bedded. Intercalated in bedded limestones and marl/limestone sequences. Thickness ranges between several meters and some tens of meters. Lateral extension can reach more than 100 m. The clasts are often eroded from coastal escarpments or steep submarine slopes. Clasts: Lithological composition often polymict. Limestone clasts may be derived from different lithoor biostratigraphic units. Fabric clast-supported. Close packing. Variable shape, angular and subangular clasts common. Rounded fragments are not caused by abrasion during transport but rather to partial dissolution.

Peritidal Breccias

Variable size, mixtures of m-sized and cm-sized clasts are common. Poor sorting. ClastJmatrix boundary sharp. Microfacies variability of clasts high. Groundmass: Matrix common to abundant, consisting of micrite or fine-grained rock debris. Several phases of matrix infilling in fissures within the semilithified breccia blocks are common. Fossils: Common in clasts and as isolated, often only poorly preserved fragments. Case studies: Prtoljab and Glovacju Jemej 1994; Semeniuk and Johnson 1985; Sanders 1997; Thiedig 1975.

Case studies:Aigner 1985; Craft and Bridge 1987; Einsele and Seilacher 1982; Shim 1986; Waters et al. 1989; Demicco and Hardie 1994.

Forereef breccia Field observations: Meter- to tens of meter thick units consisting of coarsely bedded or massive breccias. Lateral extension tens to hundreds of meters. Considerable differences between proximal and distal parts of the breccia with regard to size and sorting of clasts, clast : matrix ratio, and the occurrence of inter-clast cements. Clasts: Lithological composition monomict but Peritidal and shallow-marine breccia strong microfacies differentiation. Fabric clast-supField observations: Individual layers usually a few ported or mud-supported depending on the position on decimeter thick. Layers discontinuous, ranging from the foreslope. Size strongly variable within millimeter meter-sized lenses to a lateral extension of many tens to decameter range. Sorting poor to moderate. Shape of kilometers. Flat-lying clast orientation, sometimes variable, angular to apparently well-rounded. The latcaused by currents, sometimes caused by compaction. ter clasts may have become round by repeated biogenic True imbrication patterns are indicated by partial in- encrustations. Low or no fitting. Fracturing or veining filling of interstices of gravel clasts with sand after the of clasts prior to deposition. Clast/matrix boundary deposition of the gravel framework. Pseudo-imbrica- sharp. Microfacies variability high because clasts are tion may occur at the foresets of large-scale cross-strati- derived from different parts of the reef complex infication. Cross-stratification and high-angle edgewise cluding reef flat, reef margin and various slope envistructures are common. ronments. In addition, back-reef sands can be deposClasts: Lithological composition monomict, but ited together with forereef clasts. Common microfastrong microfacies differentiation. Fabric clast-sup- cies types of the clasts comprise boundstones, bio- and ported to matrix-supported. Low fitting. Bimodal grain lithoclastic wackestones and floatstones, packstones as size, with interstitial well-sorted sand-sized grains (pe- well as grainstones and rudstones. loids, ooids, skeletal grains). Variable shape, many Groundmass: Fine-grained, usually poorly sorted clasts are highly rounded and form conglomerates. matrix (wackestone,packstone, grainstone), sometimes These conglomerates comprise flat-pebble conglom- graded. Submarine carbonate cements in interclast erates caused by erosional rip-up of intertidal and su- voids, commonly several cement phases (Pl. 2712). Difpratidal laminites during storm events, and subtidal ferential submarine cementation can result in downconglomerates. The latter originate as storm or swell slope displacement of carbonate clasts and sands. lags in shore-face environments, as lateral accretions Fossils: Reef builders and reef dweller are abunat the base of tidal channels (Pl. 132/4), or from a rip- dant and often highly diverse within the clasts. Bioup of underlying older tidal flat sediments during rises genic encrustations and borings are common on clast in sea level (Pl. 13213).The last case results in a dis- surfaces. Isolated fossils occur in the interclast groundtinct polygenic composition of the conglomerate. mass. Cryptic habitats in cavities between reef blocks Microfacies of clasts highly variable. Constituents are characterized by specific microfossil associations. include desiccated and often laminated mud clasts deCase studies: Brachert and Dullo 1990,1994;Enos rived from modem intertidal and supratidal settings and Moore 1983; Hopkins 1977; Krebs 1969; Melim (dessication breccias), clasts derived from subaerial or and Scholle 1995; Stentoft 1994; Gischler 1995; Vecsei submarine cemented hardground (e.g. lithoclasts con- 200 1. sisting of reworked supratidal crusts or of blackened soil crusts), and grainstone intraclasts. Clastlmatrix Non-depositional breccias boundary usually sharp. Caliche breccia Groundmass:Fine-grained carbonate matrix, often Field observations: Related to exposure profiles. dolomitized. Often superimposed on solution-collapsebreccias. BedFossils:Rare in supra- and intertidal clasts, but com- ding dependent on primary clast distribution. mon in subtidal clasts. Matrix with ostracods, foraminClasts: Strong compositional similarity of limestone ifera and mollusk shells. clasts and the limestone underlying beds. Polymict

Non-Depositional Breccias

clasts, representing a mixture of limestone clasts, clay minerals, iron oxides, quartz silt and isolated bioclasts. Solution relics ('lithorelics') of the underlying rocks floating within the matrix. Clasts of variable size within millimeter and centimeter range. Greatly variable shape, rarely rounded, but often 'subrounded' due to dissolution. Extremely poor sorting. Fabric clast-supported. Fitting often high. Sharp clast/matrixboundary. Circumgranular cracks around the clasts. Clay-filled fractures (crypto- and microkarst). Clasdmatrix boundary sharp. Veining commcm, fracturing uncommon. Microfacies: Variability of clasts high including lime mudstones, floatstones and rudstones.

Groundmass:Fine-grained calcitic or dolomitic matrix abundant. Often clayish commonly reddish matrix, corresponding to the insoluble oxidized residue remaining after the dissolution of underlying limestone. Meteoric-vadose and meteoric calcite cements. Fossils: Rare. Case studies: Semeniuk 1986; Wright and Tucker 1991.

Solutionevaporite-collapsebreccia Field observations: Thick, discontinuous breccia bodies. Unstratified or only indistinctly stratified. Some gravity segregation. Usually proximal to evaporite pri-

Plate 27 Carbonate Breccia: Provenance Analysis of Clasts Microfacies analysis of the clasts of carbonate breccias has great potential for basin analysis. Compositional studies of the clasts assist in evaluating intensity and timing of erosion processes and in reconstructing 'lost' carbonate platforms whose material has been deposited in slope and basin positions (Sect. 16.3). Because the destruction of shallow-marine platforms depends on changes in water depths caused by sea-level fluctuations, clast analysis is a promising method in sequence stratigraphy. The samples shown in Fig. 1 of this Plate and in Fig. 5.21 come from the 'Tarvis breccia', a breccia horizon in Early Permian sediments of the Southern Alps which can be followed laterally for a distance of several tens of kilometers. The breccia was studied with regard to the lithologic composition and textural characteristics of the clasts and the matrix, and with respect to the microfacies types and microfossils (Buggisch and Fliigel 1980; Fliigel 1980). The microfacies types of the clasts reflect the erosion of a sequence of shallow-marine platform carbonates formed in restricted and open shelf lagoons. Platform-margin reef limestones are of subordinate importance. Most clasts were deposited as mass-flow breccias (Fig. 5.21) and rockfall breccias in mixed carbonate-siliciclastic settings. Some carbonate clasts are also associated with volcanic material in lacustrine settings (-> 1). Differences in fitting, size and rounding of the clasts, and the change from carbonate and marly matrix types in the lower parts of the breccia sequence to predominantly siliciclastic matrix types in the upper part indicate a regressive shift from a shallow-marine to a coastal and continental depositional environment accompanied by syntectonic events. 1 Lacustrine breccia. The microfacies of the lithoclasts reflects the erosion of shallow-water marine platform carbonates. The bioclastic grainstone clast (left) with dasyclad green algae (Connexia carniapulchra, Mizzia sp., Gyroprella sp.) and fusulinids (Pseudofusulina) was derived from carbonates formed in a protected high-energy environment within a shelflagoon. The high primary interparticle porosity was reduced by submarine radiaxial cements. The bioclastic packstone (right) yields poorly sorted skeletal grains (echinoderms, foraminifera) which underwent selective dolomitization prior to the erosion and deposition of the lithoclast. Fusulinid foraminifera (Pseudoschwagerina - center and Pseudofusulina right) attest to an Early Permian age. Both clasts were deposited together with volcanic pebbles (VP) within a lacustrine mud represented by a dark homogeneous micrite with calcite-filled dewatering structures (arrows). During burial the breccia was affected by strong pressure-solution resulting in distinct penetration of clasts (CP). Early Permian Tarvis Breccia: Sexten Dolomites, Southern Alps, Italy. 2 Clast-supportedforereef breccia. Lithoclast rudstone. Poorly sorted angular, subangular and subrounded clasts of lithified reef carbonates as well as some isolated reef organisms are cemented by submarine fibrous and radiaxial calcite cements (RC), characteristic for upper slope deposits (see Sect. 15.1.8).Roundness/sphericity corresponds to the fields B, D, J and K of the Krumbein visual chart (Fig. 4.30). Reef clasts exhibit diverse microfacies types, indicating erosion in different reef crest areas. Most limestone clasts were eroded from central parts of the reef, others (bottom right) represent sediments originally deposited within cryptic environments of reef cavities (indicated by fine-grained peloidal texture and diagnostic foraminifera). Larger fossils are redeposited sponges, Cheilosporites). Erosion of sediments originally deposited in low-energy protected environments (deeper reef crest or slope) is indicated by the specific biotic association of sphinctozoid sponges (S), spongiomorphid sponges (SP), coral fragments (C) and solenoporacean red algae (SO). Note the microbial coating of frame-building organisms (arrows, cf. P1. 5011). Late Triassic (Dachstein Reef Limestone, Norian): Ciosaukarnm, Austria.

238

mary strata or associated with vanished evaporites (see Sect. 12.1.7 for criteria). Clasts: Often polymict. Commonly dolomite or dedolomite clasts. Weathering of dolomite clasts results in the formation of a cellular structure (Rauhwacken). Unsorted, variously sized, usually angular and subangular clasts. Usually clast-supported fabric. Variable fitting. Clast-matrix boundary sharp except at the replacement margins of some clasts. Often densely packed. Very common pre-breccia veining, fracturing common. Clast microfacies types include lime and dolomitic mudstones with evidence of former evaporites, and replacement dolomites and dedolomites. Groundmass: Fine-grained matrix corresponds to a microbreccia resulting from internal brecciation of coarser clasts, or to microcrystalline calcite. Fossils: Absent or very rare. Case studies: Assereto and Kendall 1977; Beales and Oldershaw 1969; Middleton 1961; Morrow 1982; Karakitsios and Pomoni-Papaioanou 1998; PomoniPapaioanou and Dornsiepen 1987;Stanton 1966;Visser 1986.

Tectonic breccias Movement along a fault surface at high levels within the crust generally results in the fracturing and breaking of wall rock fragments and crystals due to cataclasis. Products of this process are fault breccias (Pl. 26/5), microbreccias (with largest fragments < 1.0 mm) and fine-grained gouges (consisting of fragments diminuated to 0.1-100 pm). Many tectonic breccias are calcite cemented. The terminology of fault-related breccias was discussed by Wise et al. (1984). Fissures filled with breccias are often related to synsedimentarytectonics. Other tectonically controlled breccias are internal breccias and shear breccias formed. Marine fissure-fill breccias Field observations: Fissure-fill breccias occur in karst cavities (see Sect. 15.2.1) and in vertical and obiique submarine dikes. Commonly in strata underlying strata with internal breccia. Clasts: Monomict. Angular or subrounded. Clasts usually small, cm-sized. Unsorted. Cladmatrix boundary sharp. Poor fitting. Microfacies: Lithoclastic floatstones. Groundmass: High matrix percentage consisting of recrystallized fine-grained calcite.

Fossils: and worn mollusk and echinoderms may be associated with breccia clasts. Case studies: Schlager 1969; Richter and Fiichtbauer 1981.

Internal Breccias

Internal breccias Field observations: Strata-bound, but laterally discontinuous. Many internal breccias consist of shallowmarine platform carbonate rocks overlain by basinal sediments (e.g. red pelagic limestones). A characteristic sequence (Fig. 5.17) includes from base to top (a) shallow-water limestones, locally with calcite-cemented joint, (b) shallow-water with fissures, filled with a breccia of the same lithology and exhibiting a red carbonate matrix, (c) internal breccia consisting of shallowwater limestones with a red carbonate matrix filled-in from above, (d) mass-flow breccia consisting of the same shallow-marine limestones and the same red matrix as in (c), and (e) red pelagic limestones. Common in shelf-to-slope transition settings. Clasts: Usually monomict. Angular and subangular clasts. Shape irregular to isometric. High to moderate fitting. Low relative dislocation of clasts. Fracturing of clam characterized by several superimposed generations. The breccia includes fragments of calcite veins as well as of older internal breccias. Variable microfacies types including all common types of platform carbonates. Groundmass: Matrix sucked in from above, or cement. Variously colored, often red. Fossils: Common within clasts and also in the matrix. Other terms used for breccias: Autoclastic breccia (Fairbridge 1978),dilatation breccia (Roehl 1981). Case studies: Richter and Fiichtbauer 1981; Fiichtbauer and Richter 1983; Herbig 1985; Wachter 1987. Shear breccia Field observations: Poorly stratified and discontinuous. Shear faces crossing the breccia and crushed clasts.

--k->esd

Red micrite with filaments Mass flow

gray fragments

Shallow-marinegray limestone with fissures With fractures and joints

Fig. 5.17. Schema of the development of infernal breccias. Fractured shallow-marine limestones are overlain by internal breccia. followed bv mass-flow breccia and ~elagiclimestones. ~odifiedfromkiichtbauer and Richter &(1983).

Diagenetic Breccias

'Clasts' and 'groundmass':The clast-like mottled areas are of different size, have irregular and transitional outlines and appear poorly sorted. The calcite crystals of the mottles are larger than those of the inter-mottle areas. The proportions of 'clasts' and 'matrix' differ widely. No fitting and no veined 'clasts'. The 'groundmass' is more frequently affected by late diagenetic dolornitization than the 'clasts'. This breccia type may appear either 'clast' or 'matrix' supported. Case studies: Bathurst 1959; Blount and Moore 1969; Solomon 1989. Note that the term 'pseudo-breccia' is also applied to breccias consisting of in-place clasts, separated by a network of joints and interpreted as being the result of earthquake loading. Similar breccias can also be caused by wave-induced processes including pseudo-cracking, crack collapse and heterogeneous liquefaction (Bouchette et al. 2001). Stylobreccia caused by variable pressure solution Field observations: Massive or indistinctly bedded limestones, often displaying a 'nodular' fabric. Clasts: The 'clasts' are 'idens' (see Sect. 7.5.2) and comprise resedimented lithoclasts and fossils affected by pressure solution (Pl. 2611). They are separated by thin residual clay seams or microstylolites. Many Fig. 5.18. Internal breccia. The bivalve coquina consisting 'clasts' appear subrounded or subangular. Clast sizes of Halobia shells is brecciated and fractured. Note the corresponding boundaries of many 'clasts' (white arrows) and cal- highly variable. Fabric appears clast-supported Microcite-filled cracks. Late Triassic (Hallstattlimestone, Norian): facies types highly diverse. A specific case are styloconglomerates formed by selective pressure solution Obersalzberg, Berchtesgaden, Germany. Scale is 1 mm. of lime mudstones (Pl. 4716). Groundmass: More or less absent or restricted to Clasts: Usually monomict. Closely packed and dis- small amounts of residual micrite. sected by shear planes. Low fitting. Relative dislocaFossils: Common. tion of clasts high. Different generations of fractured Case studies: Logan and Semeniuk 1976; Steiger sometimes difficult to separate. Flat to lens-shaped 1981. clasts. Clasts closely packed Groundmass: Groundmass consists of cataclastic clasts or cement. 5.3.3.4 Carbonate Conglomerates Fossils: If present poorly preserved. Other terms used for shear breccias: Tectonic brec- Most authors distinguish conglomerates sensu strictu cias (Blunt and Moore 1969). (formed by extraclasts) and synsedimentary soft conCase studies: Roehl 1981. glomerates (formed by intraclasts).The latter comprise flat-pebble conglomerate produced by erosional ripDiagenetic breccia up of intertidal and supratidal larninites during storm Pseudobreccia caused by patchy recrystallization events. Field observations: Fine-grained bedded dolomites Descriptive parameters of conglomerates are fabor limestones displaying a distinct irregularly distrib- ric, stratification and grading, size and sorting of the uted mottled texture, which mimics the appearance of pebbles, lithologic uniformity or variability, and the breccia. The mottles differ in darker color from the ar- amount of matrix. The composition of the groundmass eas in-between. Known predominantly from wacke- is variable (carbonate, siliciclastics, matrix andlor cestones and packstones. ment). Orthoconglomeratesare characterized by clast-

240

Setting

of Carbonate Breccias

Fig. 5.19. Polymict orthoconglomerateconsisting of well-rounded limestone pebbles of different age, quartz pebbles (Q) and completely rounded fossils (worn and recrystallized colonial coral: top left). Note the strong difference in the microfacies and the age of the limestone pebbles: Intraclastic grainstone (IG, Triassic), peloidal packstone (PP, Late Cretaceous), argillaceous mudstone (M, Eocene) with some ostracods. The light gray pebbles are dolomite (D, Triassic). The microfacies of the conglomerate indicates reworking of Northern Alpine rocks, the excellent rounding of the limestones points to a short fluvial transport distance of the material into the Molasse Basin. Interparticle pores are filled with granular calcite. Penetration of adjacent clasts (arrows) indicates strong compaction. Early Tertiary (Oberaudorf Formation, Late Eocene): Florianiberg near Oberaudorf. Bavaria, Germany. Scale is 1 mm.

support or by clasts floating within a sandy matrix. The clasts of paraconglomerates float within a muddy matrix. The main criteria used for the quantification of conglomerates are clast size and rock types. The formation of conglomerate is essentially controlled by transport processes. The larger the pebbles of a conglomerate, the higher is the transport energy. Conglomerates become better sorted during transport and the proportion of matrix decreases. A

Limestone conglomerates originate in nonmarine and shallow- and deep-marine environments, and are common in fluvial and beach settings (Fig. 5.19). Conglomerates composed entirely of limestone pebbles record conditions of rapid erosion and burial, e.g. along a fault scarp (e.g. erosion of coastal limestone cliffs). Transgression of an advancing sea in marginal marine environments can produce limestone conglomerates consisting of beach gravels. Shallow-marine carbon-

Karst Platform

Reef

Deep swell

Slope

Basin

WWffWWWCWWCffWIIffWWNWWCWNCWffCWNCWWCWWCW

3 4 5 6

Rockfall and landslide breccia Peritidal and shallow-marine breccia Fissure-fill breccia Fore-reef breccia 7 Internal breccia 8 Mass-flow breccia 9 Toe-of-slope breccia

8 Carbonate ramp

Fig. 5.20. Environmental setting of depositional carbonate breccias. A: Cross section from land - to platform and platform margin with reefs - to slope and deep swells -down to deepwater basin. B: Cross section across a distally steepened ramp.

Significance of Breccias and Conglomerates

ate conglomerates include (a) storm or swell lags in shore-face environment (Einsele and Seilacher 1982; Nemec and Steel 1984; Aigner 1985; Craft and Bridge 1987), (b) lateral accretionlags at thebase of tidal channels (Shim 1986; Waters et al. 1989), (c) transgressive lags, originating from a rip-up of underlying older tidal flat sediments during rises in sea level (Pl. 917).

5.3.3.5 Significance of Carbonate Breccias and Conglomerates Fig. 5.20 shows the setting of breccias and conglomerates. Box 5.9 summarizes the significance of breccias and conglomerates for facies analyses and economic issues. Basics: Carbonate breccias and conglomerates Bathurst, R.G.C. (1959): Diagenesis in Mississippian calcilutites and pseudobreccias. - J. Sed. Petrol., 29, 365-376 Blount, D.N., Moore, C.H. (1969): Depositional and nondepositional carbonate breccias, Chiantla Quadrangle, Guatemala. - Geol. Soc. Amer. Bull., 80,429-442 Bohm, F., Domrnergues, J.L., Meister, C. (1995): Breccias of the Adnet Formation: indicators of a Mid-Liassic tectonic event in the Northern Calcareous Alps (Salzburgl Austria). - Geol. Rundschau, 84,272-286 Fliigel, E., Kraus, S. (1988): The Lower Permian Sexten breccia (Sexten Dolomites) and the Tarvis breccia (Camic Alps): Microfacies, depositional environment and paleotectonic implications. - Mem. Soc. Geol. Ital., 34, 67-90 Fiichtbauer, H., Richter, D.K. (1983): Carbonate internal breccias: A source of mass flow at early geosynclinal platform margins in Greece. - Soc. Econ. Paleont. Min. Spec. Publ., 33,207-215 Fiichtbauer, H., fichter, D.K. (1983): Relations between submarine fissures, internal breccias and mass flow during Triassic and earlier rifting periods. - Geol. Rundschau, 72,53-66 Koster, E.H., Steel, R.L. (1984): Sedimentology of gravels and conglomerates. - Canadian Soc. Petrol. Geol. Mem., 10,441 pp. Laznicka, P. (1988): Breccias and coarse fragmentites. - Dev. Econ. Geol., 25, 832 pp., Amsterdam (Elsevier) Norton, W.H. (1917): A classification of breccias. - J. Geol., 25, 160-194 Richter, D.K., Fiichtbauer, H. (1981): Merkmale und Genese von Breccien und ihre Bedeutung im Mesozoikum von Hydra (Griechenland).- 2. deutsch. geol. Ges., 132,45150 1 Schaad, W. (1995): Die Entstehung von Rauhwacken durch die Verkarstung von Gips. - Eclogae geol. Helvet., 88, 59-90

Box 5.9. Significance of carbonate breccias and conglomerates. Paleoenvironmental proxies Since the formation of many breccia types is restricted to specific settings (Fig. 5.20), depositional and nondepositional breccias assist in the paleoenvironmental interpretation of non-marine and marine carbonates. Caliche breccias and karst breccias indicate subaerial exposure, solution-evaporite-collapse breccias may point to sea-level lowering (Obrador et al. 1992). Depositional patterns Breccias can mark underlying sequence boundaries (e.g. Biddle 1984, Garcia-Mondejar 1990) and offer information on the geometry of carbonate ramps, e.g. distal steepening. Reconstruction of provenance areas Clast analyses of breccias and rnicrofacies studies of conglomerates provide excellent data which allow detailed reconstructions of the changing sedimentary input into marine or non-marine basins, the provenance of the material and the climatic and tectonic controls of the processes involved (see P1. 27, Fig. 5.21 and 16.3). Tectonic events Breccias can indicate the proximity of faults which may otherwise not be directly detected (e.g. Bosellini 1989; Garcia-Mondejar 1990). Economic importance Reservoir rocks: Fractured carbonate breccias are important hydrocarbon reservoirs. Of particular interest are solution breccias (Loucks and Anderson 1985; Miller 1985),debris-flow breccias (Enos 1988) and karst breccias. Mineralizations: Breccia-hosted karst and collapse breccias host Mississippi Valley-type lead-zinc deposits (Klau and Mostler 1983; Bechstadt et al. 1994; Liaghat et al. 2000). Building stones: Many polymict carbonate conglomerates and breccias are used as building and decoration stones (Pl. 26/3), e.g. 'Nagelfluh' (an interglacial conglomerate), or the socalled 'Untersberg marble' (a Cretaceous mass-flow breccia) in Austria.

Stanton, R.J. (1966): The solution brecciation process. - Geol. Soc. Amer. Bull., 77,843-848 Wise, D.U., DUM,D.E., Engelder, J.T., Geiser, P.A., Hatcher, R.D., Kish, S.A., Odom, A.L., Schamel, S . (1984): Fault related rocks: suggestions for terminology. - Geology 12, 391-394 Further reading: KO72

6 Quantitative Microfacies Analysis

The previous chapters of this book introduced various aspects of recognizing qualitative microfacies criteria and their signifcance, whereas this chapter will treat quantitative criteria. The first part describes selected principles of grain-size analysis and demonstrates the potential of grain size in the context of microfacies studies. The second part deals with methods of frequency analysis and their use in microfacies-based interpretations. The last part discusses the evaluation of microfacies by multivariate statistical analyses.

tending from 41256 mm to >256 mrn.A modification of this scale is the +scale which allows grain-size data to be expressed in units of equal value. The $ size is the negative logarithm to the base 2 of the grain size measured in millimeters (Krumbein 1936).A grain size of 1 mm corresponds to a $ value of zero. Smaller grain sizes are expressed by positive phi values, larger grain sizes by negative $ values. Pierce and Graus (1981) and McManus (1982) have discussed the use and misuse of the +scale. Phi values can be obtained from conversion tables (Page 1955; Griffith 1967) or nomograms (Friedman and Sanders 1978).

6.1 Grain-Size Analysis Grain size is a basic descriptive measure of sediments. Grain-size distribution patterns may be characteristic of sediments deposited in certain environments and can yield information about depositional processes. In turn grain sizes are a major control on porosity and permeability. Various methods are in use ranging from simplistic diagrams of grain-size parameters up to sophisticated analyses of statistically treated data. Measures for characterizing grain-size populations have been reviewed at length in many standard texts (e.g. Boggs 1995) and include a wide spectrum of analytical methods (McManus 1988; Syvitski 1991; Pye 1994). Most descriptive and interpretative concepts are based on studies of modem quartz sands deposited in specific environmental settings. Grain-size criteria of modem carbonate sediments have been examined predominantly for tropical and subtropical inter- and subtidal sands accumulating near beaches, lagoons, on shallowmarine banks and within reef complexes (Box 6.1). Contrary to the abundant grain-size analyses of sandstones, only a few authors have studied grain-size distributions of ancient carbonate rocks. Grain-size scales: The commonly adopted size scales are shown in Fig. 6.1. Sedimentary grains range in size from a few microns to a few meters. Because of this wide range, logarithmic or geometric scales rather than linear scales are more useful for expressing size. The Udden-Wentworthscale is a geometric scale ex-

Grain-size groupings in carbonate rocks: The terms calcilutite, calcarenite and calcirudite, proposed by Grabau (1904), refer to the sizes of carbonateparticles. Calcilutite consists of clay- and silt-sized particles ( 2 mm, but calcirudite considers only grain size whereas rudstone is defined by grain size and the number of grains larger than 2 mm. Note that calciruditic limestones embrace rudstones as well as floatstones, and that the term calcarenite covers grain sizes represented in grainstones and wackestones of the Dunham classification.

6.1.1 .I Measuring Grain Sizes and Describing Size Distributions The size of siliciclastic grains is determined by several techniques. Unconsolidated sediments and disintegrated rocks of clay-, silt-, and sand-size ranges are commonly measured by sieving or sedimentationmethods (Coakley and Syvitski 1991; Matthews 1991). Modem carbonate sands have usually been measured by sieving. Lithified sandstones and limestones require thin-section measurements for silt- and sand-sized rocks and electron microscopy for clay-sized samples. Image analysis is a highly promising method for rapid and accurate measuring of grain sizes, both of loose grains and indurated sediments (Schger 1982; Kennedy and Mazzullo 1991). The interpretation of grain-size patterns requires graphical and mathematical treatment of the data. Common graphic methods for presenting grain-size data are histograms, frequency curves and cumulative curves. Histograms are bar diagrams in which grain size is plotted along the abscissa of the graph and individual weight percent along the ordinate. Frequency curves result from connecting the midpoints of each size class in the histogram with a smooth curve. Cumulative curves are grain-size curves generated by plotting grain size against cumulative weight percent frequency. The curves can be plotted on an arithmetic scale or on a log probability scale in which the arithmetic ordinate is replaced by a log probability ordinate. The latter method allows the important grain-size statistical parameters to be calculated using the 4 values read from the cumulative curve for various percentiles (Tab. 6.1). Breaks and discontinuities in cumulative curves produced by plotting of grain sizes on a log probability scale are interpreted as results of mixing of sediment populations related to different transport processes (Visher 1969). Grain-size data can be plotted statistically, deriving parameters that allow average size and sorting of sedimentary populations to be expressed mathematically:

Sorting

245

very well sorted

well sorted

o = 0.35

o= 0.5

moderately sorted

O = 1.0

poorly sorted

o = 2.0

F i g .6.2. Chartfor visually estimating of sorting (based on Pettijohn et al. 1973). The chart was developed for sandstones and

differs from the charts in Fig. 6.3 by the overrepresentationof larger grains. After Tucker (1981).

Average grain size is the easiest parameter to determine but is sometimes a rather inaccurate value. The average grain size depends on the grain sizes of the material available and the amount of energy in the transport medium. Average grain sizes are measured by mode, median size or mean size distribution.The mode or modal diameter (Mo) describes the most frequently occurring particle size in a population of gains. The modal size diameter corresponds to the diameter represented by the steepest point (inflection point) on the cumulative curve or the highest point on the frequency curve. The median size (Md) is expressed by the midpoint of the grain size distribution and corresponds to the 50% percentile diameter on the cumulative curve. The mean size (Mz) is determined by the arithmetic average of all the particle sizes in a sample.

Beach sands, for example, tend to have negative skewness, since line particles have been removed by the persistent wave action. River sands are often positively skewed, since not much silt and clay is removed by the currents. The degree of the peakedness or sharpness of grainsize curves is expressed by kurtosis values, which are commonly calculated along with the other grain-size parameters. Commonly used formulas for calculating grain-size parameters by graphic methods are shown in Tab. 6.1. Grain-size statisticalparameters can also be calculated without reference to graphic plots by the mathematical method of moments. The parameters obtained by this method are analogous to those of graphical statistics, but because moment measures employ the entire frequency distribution rather than a few selected percenSorting is a measure of the grain sizes present in a tiles, the pararneters are considered to be more repregrain population and describes the magnitude of the sentative for the sample than the graphically derived spread or scatter of these sizes around the mean size. values. For overviews on the various grain-size paraSorting of water-laid sediments is produced by currents, meters see Folk (1966) and Syvitski (1991). wavesand splashing. Sorting canbe described with the help of visual comparison charts (Figs. 6.2 and 6.3) or, Table 6.1. Formulas for calculating statistical parameters s and Ward 1957). more precisely, by parameters which document the for grain sizes by graphic n d ~ o d (Folk The Greek letter 4 (phi) for grain sizes indicates that the pernumber and the percentage of grain-size fractions within centiles were measured using the phi and not the mm-scale. a grain mixture. The @ sorting standard deviation and skewness (Sk) values are determined graphically or by calculation (Tab. 6.1). @ skewness describes the deviaGraphic mean MZ = $16 + $50 + $84 tion from a normal or lognormal grain size distribution 3 and the degree of asymmetry. Skewness reflects sort- Inclusive graphic standard deviation ing in the tails of a grain-size population. Positively = $84-416 + 495 - $5 I skewed populations have a tail of excess fine particles, 4 6.6 negatively skewed populations a tail of excess coarse Inclusive graphic skewness particles. Terms for sorting that correspond to various ($84 + -2$5~) ($95 + 4 5 - 2$51)) values of standard deviations and skewness have been SK, = + proposed by Folk and Ward (1957) and Friedman z! ($95 - $5) (484 - $16) (1962); Fig. 6.5. Skewness is given an environment senKG = (495 - 45) sitive significance by many authors (e.g. Friedman Graphic kurtosis 2.44 ($75 - $25) 1967; Folk and Robles 1964;Valia and Cameron 1977). , ,

Interpretation of Grain-Size Data

Fig. 6.3. Comparison charts for particle sorting afer Longiaru (1987).Labels indicate the degree of sorting (standard deviation) approximated by the comparator and the descriptive terminology of Folk (1966). Visual estimates of sorting can be obtained by comparison with charts, some of which have been developed particularly for calcarenites (e.g. Harrell 1984). Note that visual comparison charts assume a lognormal distribution of grains, which is not always the case, and that in most charts larger grains are overrepresented except in the charts shown in this figure. The bar at the lower right of each diagram indicates the maximum grain size which might occur in the samples.

6.1.1.2 Approaches to the Environmental Interpretation of Grain-Size Data

beach and dune sands (Friedman 1979; Eschner and Kirchner 1984; El-Ella and Coleman 1985; Sutherland and Lee 1994).The Friedman diagrams allow the plots Hydrodynamically controlled covariations of two or to be differentiated into major environmental fields. Passega (1957, 1964. 1977) suggested that the ratio more measures, such as mean size and sorting are commonly available. Following early studies by Friedman of the coarsest one percentile, C, to the median dia(196 1, 1967) and Douglas (1968) the use of bivariate meter, M, and the percentage of grains finer than 3l pm scatter diagrams (e.g. skewness vs. standard deviation (L) are indicators of the dynamics in different deposior mean size vs. standard deviation) has become a com- tional environments. The strongest current should demon approach in attempts to discriminate modem river, fine the largest stable particle size. Different fields in

Grain Size in Thin Sections

the C-M diagram typify deposits from traction currents, from beaches or from various forms of suspension (Rizzini 1968; Fabri et al. 1986). Different environments can be distinguished by examining the patterns produced by plotting a number of samples from the same unit on C-M or L-M diagrams (Fig. 6.6). The Passega diagram allows the type of sediment transport to be differentiated preferentially for sediments with C < 1 mm (Gromoll1992). The diagram has been successfully used both in the interpretation of modem sediments and ancient sedimentary rocks (Faugbres 1974). Other authors have suggested that the depositional environments and different transport dynamics can be interpreted on the basis of the shapes of grain-size cumulative curves plotted on probability paper (Visher 1969; Glaister and Nelson 1974). Several multivariate statistical techniques (factor analysis, discriminant function analysis, log-hyperbolic distribution, entropy analysis) have been successfully applied to the interpretation of grain-size distribution (Klovan 1967; Vincent 1986; Forrest and Clark 1989; Merta 1991).

However, contrary to the information provided by ecology or sedimentary structures, the grain-size evidence provided has the advantage of being universal.

6.1.1.3 Grain-Size Analysis in Thin Sections

In sandstones and limestones grain sizes are usually measured in thin sections, peels or microphotographs. Rocks should be sectioned in a consistent direction. Sections parallel to the bedding plane would be more appropriate but most students use vertical or non-oriented thin sections. Peels can be made of much larger surfaces than conventional thin sections, allowing a large amount of grains to be measured (Gutteridge 1985). Grain size analysis of thin sections requires statistical grain selection according to a well-defined sampling plan. Techniques used include point-, line-, area-, and ribbon-counting (Sect. 6.2.1). Point counting (grains selected at grid points) appears to be the most appropriatemethod for sandstones,ribbon-counting as well as point-counting are commonly used for limestones. The number of grains measured ranges beThe value of nearly all these techniques for identi- tween 150 and 500. Measurement of 300 grains is offying depositional environments has been questioned ten regarded as statistically sufficent for sandstones. in parts or as a whole (e.g. Vandenberghe 1975; Tucker Calcarenitic and calciruditic carbonates must be handled and Vacher 1980; Sengupta et al. 1991). The main rea- differently (Sect. 6.2). sons for these difficulties are related to the variability Measurement errors: Grain sizes derived from thin of depositional conditions within the .major environmental settings and the complexity of depositional pro- sections are apparent, not true grain sizes. The probability that a grain will be cut by a random section is cesses: Hydrodynamic conditions within the sedimentation proportional to the size of the grain. Diameters meaarea can considerably vary, depending on the size of sured in thin sections, therefore are usually smaller than the true grain diameter. Random sections lead to an inthe sedimentary basin. Spatial and temporal grain size distribution within a crease of measurements of small grains. given physiographic setting are highly variable, and Conversion of grain-size data: Basic concepts of demand critical statistical analysis (Piller and grain-size analysis were developed by studying loose Mansour 1990, Medina et al. 1994). Frequency and cumulative curves reflect grain-size sediments or disintegrated sedimentary rocks. Because subpopulations, distinguished by rolling, saltation the commonly used sieve method can not be applied to indurated rocks, a conversion of granulometric data obor suspension transport (Smolka 1990). Primary grain-size distributions can be changed by tained by thin section analysis into sieve data appears bioturbation and episodic high-energy events, e.g. necessary if statistical parameters are also to be evalustrong storms, as well as by variations in sediment ated for sandstones and carbonate rocks. This converinflux caused by sea-level fluctuations. sion has been based on different regression models (Friedman 1958,1962; Harrell and Erikson 1979; Merta In summary, grain-size distributions primarily re- 1991). flect transport and depositional processes which are not Miiller (1964) developed a nomogram from which necessarily unique to a particular environment. Never- the sieve-size distributions can be directly derived. A theless, in the context of facies analyses, grain-size data comparison of sieve and thin-section methods used for assist in environmental interpretation if the data are in- siliciclasticrocks indicates that the two techniques must corporated in the framework of textural and composi- be regarded as mathematically independent methods tional criteria and all lines of evidence are regarded. (Burger and Skala 1979).

Controls on Grains Size

6.1.2 Grain-Size Studies of Modern and Ancient Carbonates The following chapter summarizes the still rather incomplete information about grain-size distributions of recent marine carbonate sands, and discusses the application of grain-size studies to the microfacies analysis of carbonate rocks.

6.1.2.1 Grain-Size Studies of Modern Carbonate Sediments How does sorting of carbonate sediments compare with sorting of siliciclastic sediments?

Differences between siliciclastic and carbonate sands: The grain-size distribution of siliciclastic sands depends on the source, weathering, erosion and transport processes. Marine carbonates are predominantly biogenic sediments (Sect. 2.1.2). Therefore, the size of carbonate particles is highly controlled by the original size and decay of the skeletons, and by size-reduction processes which take place during transport. In subtidal carbonate environments, however, the areal effect of larger transport processes is rather restricted and the sediment is produced nearby or at the site of fmal deposition. Larger transport processes occur if storms and strong currents cause bottom erosion and redeposition of carbonate sands. Many bioclastic carbonates exhibit a bimodal grain-size distribution consisting of silt- and sand-sized grains and mud. Common size range of carbonate grains: The sizes of carbonate grains vary between t ~ \ d o , i d s n gof brqozoans, brachiopodj and serpulid\ ciior8gu I 11 d pos~tlte loxhng of echlnoderms Ahighly nega I \ lo,idsnp 15 \lionri by terngenous components Factor 2 ;\p .i~n\iie,ul) 1 7 ' ~of the varlance and is characterized b) .I , h~glil)positr\ t load~ngof barnacles and ep~faunalhl x.11. e\. 'tad A lughlb nesative loading of foranm~fers 1.: i * , ~ ~it \.oL ~fdctor 4 plot. Factor 3 explalns 14 3% of t h ~ i ,ir I inLe (Y h~nodemls and foraminifers exhibit a h~ghlyp o s ~ II\, loading, the muddl niatrlx a hlghly negatlve loadmg F ,I, o r -Iirpr c\ent\ I 0 4% of the var~anceco~allmealgae art 'ii. I \ pov:i\ el! lcidetl Negat~vetoad~ngI\ \hr)\\.liby ter IO'I c~rnpmcilt~ ti;( i i u ' ;ui10/2 PI i n l q controls rcsporls~hlcfor the con1 ,' 1, ' I I I r l l k ~ ~tmtiori i ~ j i ' i t terrrgenous Input, hytirotiqn~m~c cil l \ s light lntemltq Factor i rc pic I'IILC of w C i g ~ ~ and t l ~ .\ 1111. tfc~tr1rnent~11 eltect of h ~ g hterrtgcnou\ mput to f11 t r 1:ctimrl b~)oco,iri\.hach~opod\and mpulitls Factor 2 t cn t \ l ii'tlcit t i c evposure to high energy uater condl I i i1 l i n t ~ ~ p ~ e t n1st ~supported o~l by the dornindnce ol h iii1~icli'~ m d eplt,lundl b~valvesand the occurrencc of tht\ 1, i t \ i n ,oii\rLllsettlngs Factor 3 should explam the pos1t11c i t ' i , i , r y \ OI ei hinc>dennlij rr~l,~tecl to M ater depth and \uspen51on load\ 4 i kol dl \ L C !1o11m d changes In fdctor \core< durin~r \ I o ~ i i f ~trim, ~ i \etxAwk (1992)

-

.

( I0cJ.ji 11 trojucnon to gt'ologl ial ddt anhydrite, opal C -> opal A-> quartz, smectite -> mixed-layer minerals -> illite). Increasing temperature controls the transformation of stable organic matter into unstable organic matter and hydrocarbons. Free C 0 2 resulting from these processes and organic acids contribute to the dissolution of carbonate minerals and the creation of porosity. 3 Pore water chemistry: Influences on transport and the speed of pressure solution, which is more rapid in Mg-rich pore waters of marine environments than in Mg-poor burial pore waters.

more rapid. Typical rocks originating in this setting are beachrocks (see Sect. 2.4.2.1).

7.2.1.3 Marine Diagenesis Marine phreatic diagenesis takes place at the shallow or deep sea floor or just below, and on tidal flats and beaches. High hydrostatic pressure, low water temperature, and high partial pressure of CO, in the deep sea lead to dissolution and to significant differences in the calcium-carbonate preservation of deep-sea sedi7 ments. These differences are used to distinguish two dissolution levels, the lysocline and the calcite compensation depth (see Sect. 2.4.5.6).

7.2.1.4 Burial Diagenesis Carbonates that have undergone burial diagenesis are 'out of sight' and somehow 'out of mind' (Scholle and Halley 1985). Microfacies criteria indicating burial diagenesis are specific cements (Sect. 7.4.2.1) and diagenetic textures pointing to compaction and pressure solution (Sect. 7.5). The study of burial diagenesis is highly significant in the reconstruction of rock history and the evaluation of rock properties and porosity. Reviews on burial diagenesis have been published by Wanless (1983) and Hutcheon (1989).

Burial environments are conventionally subdivided into shallow burial and deep burial, but the boundary is by no means well defined. The shallow burial zone includes the first few meters to tens of meters of burial. Shallow burial near-surface diagenesis are influenced by changing pore water chemistry in the mixing zone, temperature and pressure processes. Diagenetic processes in the deep burial zone are controlled by conditions summarized below and in Box 7.2. Pore water composition in deep burial environments differs substantially from that of shallow diagenetic environments, where cementation usually takes place in dilute meteoric waters that are oxic or only slightly reducing. Deep-burial subsurface pore waters have elevated salinities and act in a reducing manner. As a consequence redox-sensitive elements are mobilized and Mn and Fe tend to be incorporated in the calcite or dolomite cements. The cements are characterized by distinctive morphologies (Sect. 7.4.2). Changing Mn and Fe compositions of subsurface fluids result in mineral zoning recorded by CL patterns, specific fluid inclusion salinities (Dorobek 1989), and stable isotope signals (Scoffin 1987). Processes in deeper burial environments include: Physical compaction due to sediment overburden: Reduces thickness of sediments, porosity and permeability, leads to breakage and distortion of grains

( r ~,id11\sccn in gramstones), and produces cornpressed I,jtmc'. (Sect -1.5 1

,

Clrt~tmcvicnnzptzction Starts at varlous depths of ill erbu~den (commonly several hundreds and thousands r i i meterr, hut also at an overburden of 100 or 200 m). K d m s thickness of sediments, porosity, and permeallrlity. Produces stylolites and other pressure-solution \t- uctur e;. Pre\sure solution prov tdes carbonate for hbrial i:ementation (Sect. 7.5.2). C'cm~rtc~tron Produces coarse calcite spar cements. The cements are enriched in iron and manganese, poor rn strontrum. Fluid ~nclusionsare common. Coarse or pork~lotopiccalcite drusy and other calcite mosaics, 4,~idlecloloni~tr Mlrroi ~~jlutloit p m s i t y : Caused b j dissolution of s,~rbontte and calclum sulphate minerals. Uiu llli (1o1~miri~~iltion: Anhedral crystalline fabr~c; i:cwra!i\ c c ~ use crystals.

7.2.2

Early and Late Diagenesis

Fig. 7.4. Micr-opomsity i/z n tiuc rriic. !.t~.w~.rvir rock. Porosit). i x caused by equant to equanl-chigatt* or tubular or. p l a ~ y p e s b e t w e e n calcite crystals (ir~t~rtrystallinc porosity). 111 this sample porca are very small (0.5 to 5 jun, nlostly < 1 prn)., but effective porosity is high because r~f‘well-developed pore ~hroatsand good permeability. ?'he rhornhohctiral crystals ;we of different size and have wli-di.wlopcii crystal filcCb,brni.. ing an inequigra~lularidiotoplc c1-j.st31fabric sensu Friedmarl i1965).Micropo:-osity occurs 111 thr im~triiof lime niudstonc.~. ackestones and pachstoiii-s ;IS kt. cii a\ in cashonate p a i n \ . Prc~cessrsinvolved in thc cr-eic:~;):~ i i ! rnicr-oporosity are (115\olirtio~i.dolomltlzatior~uicl irli~ip!c.ritwe:ithcring. SEkl. Subwr-face. Latc Crc.t;lc:eous: K,I\ 41 b;lrrlrali. I !nitid Ar-;rhi.iit F.:nirutcc. Sc;~le1, 11) ~ u i i

7.3.1 Porosity Categories, Pore Geometry and Permeability

7,f! Porosity

of Carbonate Rocks

7.3.1 .I

Basic Definitions

I'oroslty i b the percent,iyc o f tlic hulh volurnc. ot rock thcrt I S occup~edby Intersucv, $4 11etht:r ~solatrd01 c-onnected. Thlr definltlon descrltn the roral po/oslr\ m h ~ c hmust be separated i ~ o mthe c$ct r i i ~ [)oro s i I~ The latter is the percentage ot the total rock ~ o l u r n ~ that consists of mterconncctcd pore4 Many carbonate locks no longer exhib~topen port3s. hut former intc~ rtlc'cs M hiclz h ~ i hce/? l ~ f i ! / t d 1.111/1 i t m ~ An t cstirm ~ im of this n 7 i 1 ~ i ~ - ~ ~ mo~ut .l\ti / representing ), the m n P1. 7). P1. 2912, 7; P1. 6711. Depends on the morphology and microstructure of tests and skeletons of organisms as well as on the ultrastructure of the grains (e.g. ooids or aggregate grains). Common pore sizes are 15% excellent. The quanpores (minus-cementporosity) assists in understand- titative characterization of pore systems is facilitated by digital image analysis (Anselmetti et al. 1998). ing the course of porosity development. Text continued on p. 288

284

Pore Types

Plate 29 Distinguishing Carbonate Pore Types The plate displays different pore types, using the Choquette and Pray classification. See Fig. 7.5 and Box 7.4. 1 Primary (fabric-selective)and secondary (non-fabric-se1ective)porosity.Poorly cemented bryozoan rudstone with different types of bryozoans. Primary pores are pores between particles (interparticle or intergranular pores, IP), and within particles (intraparticle pores, black arrows). Secondary, still open pores appear as vugs (VP) originating from solution enlargement of interparticle pores forming vugs that grade into elongate channel pores. Note that outlines of vuggy pores intersect and destroy grain outlines (white arrows). Primary pores have been partly filled with isopachous equant calcite and calcite blocky cement, and partly reopened by solution. Large idiomorphic calcite crystals (top right) were formed subsequent to equigranular cement. The preservation of open interparticle porosity was favored by the stable mineralogy of the skeletal grains (Low-Mg calcite) and burial solutionenhancement of interparticle pores. The dominance of bryozoans, grain association, and weak primary cementation are common criteria in bryozoan-dominated temperate and coolwater carbonates (see Sect. 16.4.1). Tertiary (Middle Miocene): Albacete near Tobara, Alicante, SE Spain. Use this picture as an exercise! You should find the following answers to the questions summarizedon P1.30: (A) Primary interparticle pores occluded by cement. Open secondary vuggy and intraskeletal pores. (B) Vuggy pores. (C) Primary reduced porosity. Secondary vuggy solution-enlarged porosity. @) Primary pores enlarged and enhanced by solution, grading into irregular vugs. Q Vuggy porosity postdates cementation, no compaction. (F)Open porosity about 20%. 2 Open intraparticle (intraskeletal)porosity (P) within a rugose coral. The oblique section shows septa (S) and horizontal tabulae (T). These skeletal elements consist of recrystallized calcite crystals growing perpendicular to the median line of the original skeletal elements. The coral microstructure is still preserved because of the stability of Low-Mg calcite. Some intraparticle spaces were filled with cements, but most intraskeletal pores are still open. Middle Devonian: Belgium. 3 Fabric-selective oomoldic porosity. Ooid grainstone. The primary aragonitic ooid cortices have been leached (arrows) by vadose meteoric solution. Leaching of cortices can create secondary intraparticle porosity, which is either occluded by cement or leads to oomolds. No evidence for strong compaction. Interparticle pores were filled with thin isopachous cement rims and fie-grained drusy mosaic cement. Early Cretaceous (Purbeck facies, Beniasian): Subsurface, Bavaria, Germany. 4 Fabric-selective oomoldic porosity (OM).Ooid grainstones/packstones are important hydrocarbon reservoirs. Principal effective porosities of carbonate reservoirs in the Four Comers Area of the Colorado Plateau include interparticle, interand intraskeletal (algal blade), oomoldic and intercrystalline dolomite types (Weber et al. 1995). Oomoldic porosity on paleodepositional highs is characterized by high porosity values (average 11.3%, McComas 1963) associated with low permeability (average 3.4 millidarcys). High porosity is caused by meteoric leaching of originally aragonitic ooids. Low permeability is due to the insufficient pore interconnection system because of the scarceness of leached mold walls. Note that some ooids have not been leached. This may indicate differences in the primary mineralogy of the ooids. Middle Pennsylvanian (Paradox Formation): Goosenecks of San Juan, Four Comers Area, Utah, U.S.A. 5 Intercrystalline and interparticle nannofossilporosity. Soft Chalk is a very fme-grained, light-colored and friable carbonate sediment, composed largely of minute Low-Mg calcite skeletons of planktonic coccolithophorids (Cribrosphaerella ehrenbergi (Arkhangelsky); see P1.7/3-5). Porosity occurs between fragments of nannofossils and between calcite crystals. Small cement crystals form overgrowth on coccolith elements. Intraparticle pores are partly filled with coarse blocky cement. High-porosity chalks are characterized by well-preserved nannofossils indicating minimum fragmentation and dissolution, in contrast to lowest-porosity chalks containing poorly preserved nannofossils. The hydrocarbon production of many chalk reservoirs (e.g. in the North Sea) is due to the preservation of high primary porosity (caused by a unique combination of pore fluid overpressuring and exclusion of water from pores by migrating oil) and permeability enhancement by post-lithification fracturing (Feaze1 1985). SEM. Late Cretaceous (Maastrichtian) chalk: Logster, Denmark. 6 Interparticle porosity (IP). Grains are superficial ooids. Note open pores between the grains. Thin white rims around grains are isopachous meteoric cements. Subrecent grainstone: San Salvador, Bahamas. 7 Open interparticle (IP) porosity between skeletal grains (predominantly corallinacean red algae, CA) and intraskeletal porosity within foraminifera (arrows). Corallinacean algal grains are covered by thin isopachous Mg-calcite cement rims. Pleistocene calcarenite: El Haouira, Cap Bon, northern Tunisia. Crossed nicols. 8 Moldic porosity formed by selective dissolution of ooids and bioclasts. Reservoir rock characteristics of dolomitized oolitic grainstones in the Fore-Sudetic area of western Poland are controlled by vadose dissolution of aragonite and Mgcalcite grains. Late Permian (Zechstein Main Dolomite): Subsurface, Laba, Poland. 9 Keystone vugporosity. Keystone vugs (KV) are rnm-sized fenestral pores occurring in tidally influenced carbonate beach sands. They form when tides rise and air or gas bubbles enclosed within the fine-grained sediment try to escape from the sediment. The air bubbles push grains aside, thus creating voids. The grains at the top of the vug form a keystone arch that prevents collapse. Preservation of keystone vugs points to rapid cementation. Keystone vugs are generally larger than birdseyes (see P1.2017,8). Example: Particles are predominantly peloids and micritized ooids as well as a few aggregate grains. Tidal sand bars. Early Cretaceous (Purbeck facies, Bemasian): Subsurface, Kinsau, Bavaria, Germany.

286

Porosity in Thin Sections

Plate 30 Porosity Evaluation in Thin Sections The impregnation of carbonate rocks with blue-dye stained resin before sectioning makes the evaluation of porosity straightforward and facilitates the recognition of pore distribution. Questions which should be answered in evaluating thin sections with regard to porosity are: A Are the pores completely or partially occluded by cement or sediment or are they still open? B Which of the pore types shown in Fig. 7.5 occur and which types dominate? C Classify the sample according to the Choquette and Pray scheme (Fig. 7.5)! D Do primary depositional pores still exhibit their original shape or are they enlarged and enhanced by solution, thus grading into irregular vugs? E Does porosity postdate cementation and compaction (e.g. fracture porosity)? F Estimate the percentage of open (and/or closed) rock porosity! 1 Bioclasric limestone with terrestrial gastropods (Hydrobia,H). A blue color reveals open pores. The snails were deposited near the coast and covered by sediment. The dark particles (bottom left) are micritized algal stems. The primary aragonitic shells were dissolved and replaced by calcite under meteoric conditions. The interior of the shells was filled with peloids prior to the final deposition of the shells. The peloids are fecal pellets exhibiting different preservation; light peloids are calcitized aragonite pellets. The fine-grained sediment exhibits a distinct geopetal fabric consisting of dark micrite at the bottom and lighter, more coarser sediment at the top. The remaining interparticle voids between the shells are lined by thin isopachous cement rims of bladed calcite crystals and blocky spar. Porosity: Moldicporosity is indicated by white arrows. Some pellets show open intraparticle porosity (top right). Black arrows point to vuggy porosity. Brackish-lagoonal environment. Late Tertiary (Early Miocene): Mainz Basin, Germany. Answers: (A) Most pores filled with sediment and cement, some pores open. (B) Moldic, interparticle, vuggy, rare intercrystalline. Moldic porosity now dominates. (C) Primary depositional interparticle porosity mainly filled and reduced, open secondary moldic porosity. (D) Primary pores with original shape. (E) No compaction. (F) Original porosity about 50%, open porosity < 5%. 2 Detail of the sample shown in -> 1. Gastropod shell (Hydrobia)filled with peloids and calcite cement. Note the difference in crystal size and shape of cements within the shell and in the void at the top of the geopetal structure. Many of the peloids and the complete gastropod shell are dissolved. The shape of the gastropod is preserved because of thin protecting organic coatings. 3 Predominantly vuggy porosity (blue) caused partly by solution-enlargement of interparticle pores. Solution enhancement has changed the original fabric-selective porosity to non-fabric-selective porosity. Some intraskeletal porosity is preserved in the whorls of foraminifera1 tests. In terms of the Choquette and Pray classificationthe open porosity is classified as solution enlarged secondary vuggy porosity characterized by mesopores (see Fig. 7.5). This bioclastic grainstone consists of skeletal grains and some micritic intraclasts. Bioclasts are predominantly miliolid foraminifera and a few bryozoans (B). The chambers of the miliolid foraminifera were partly occluded by cement. Non-miliolid foraminifera have been almost completely replaced by calcite (arrows). Tertiary (Miliolid limestone): Cambre Saint-Pierre-Aigle, Paris Basin, France. 4 Fenestral porosity in a travertine formed by spring waters in shallow ponds (see P1. 211-3). Small open fenestral pores occur within a laminated fabric. Note the different cementation within large and small pores: Larger pores are bordered by large scalenohedral calcite crystals, small pores by small bladed crystals. Some scalenohedralcrystals are zoned (arrow). The micritic layers border larger voids that are incompletely filled with blocky calcite crystals. Fenestral porosity occurs in caliche deposits, freshwater tufa, and travertines, but is most common in carbonate mud- and bindstones of tidal flats. Travertine. Terme di Rapolano, north of Rome, Italy. 5 Fenestral porosity in travertine. Isopachous calcite cements lining open pores in places. The crystals are more or less equidimensional, indicating precipitation in a meteoric phreatic environment. Remains of organic-rich laminae are shown as a brown color. Same sample as -> 4. 6 Moldic porosity (blue). Because of the metastability of aragonite the gastropod shell was dissolved, creating moldic porosity. Same locality as -> 4.

Porosity in Limestones and Dolomites

7.3.3 Porosity in Limestones and Dolomites Primary and secondary porosity of carbonate rocks are strongly facies-controlled and depend on the depositional patterns and the diagenetic history (e.g. Sun et al. 1992). Porosity relies upon the composition and fabric of rock constituents, the distribution and quantity of cement as well as the abundance and distribution of fractures and stylolites.

Box 7.5. Porosity and permeability of modern carbonate sediments based on samples from Florida and the Bahamas (Enos and Sawatsky 1981). Interrelationships between porosity and permeability in recent carbonates is largely controlled by depositional texture, particularly the amount of fines 60% at the waterlsedi- average porosities and permeabilities than limestones, ment interface of deep-water calcareous muds to about because of differences in the size, shape and arrange35% at a depth of 1000 m, about 15% at 2000 m and ment of crystals. Porosity tends to increase slightly in 4 % at 3000 m. This curve has many deviations, de- the initial stages of dolomitization of limestones, but pending on pore water pressure, as exhibited e.g. by increases abruptly with higher amounts of dolomite. chalks (Scholle 1977; Feaze1 and Schatzinger 1985). At this stage, the dolomite is characterized by a sucrosic Mechanical compaction can be responsible for about texture composed of equally-sized rhombohedra with one third of porosity in micritic limestones. The total intercrystalline porosity originating by dissolution of porosity of many limestones is often less than 10% associated calcite. Dolomitization is a selective prowhereby grain-supported limestones often exhibit cess and fine-grained constituents tend to be preferenhigher porosities than mud-supported limestones. Com- tially replaced. mon porosities of wackestones formed in inner shelf and lagoonal environments are 1,7), meteoric (-> 5,6) and burial cements (-> 1,3,4). Thin sections allow a first interpretation of crystal morphology and fabric with regard to the diagenetic environment.A critical assessment of the environment requires cathodoluminescencefluid inclusions analyses as well as and stable isotope studies. Bioclastic grainstone. Interparticle pores between fossils enclosed within oncoids (T: trilobite) are filled with submarine calcite cement (thin rim consistingof acicular crystals, black arrow) and blocky burial cement (white arrow). The trilobite fragments show the typical 'shepherd's crook' shape (see P1.9413). Late Silurian (Ludlow):Burgwik, Hobbugen, Gotland Island, Sweden. Radiaxial calcire cement growing on trilobite fragments. The large radiaxial cement crystals have curved boundaries and show a cloudy appearance due to inclusions. Note the distinct pores typical of some trilobite carapaces.The shell consists of prismatic calcite crystals growing with their c-axes perpendicular to the skeleton surface. Early Devonian (Emsian): Erfoud, Anti-Atlas, southern Morocco. Syntaxial overgrowth (arrow) on echinoderm fragments. Because echinoderm fragments act as single crystals, they are commonly nucleation sites of calcite cements. Clear calcite is added in optical continuity to the echinoderm fragment. Sediment adjacent to the monocrystal crinoid may have been dissolved as the syntaxial overgrowth developed. The crinoid fragment at the left side of the photograph shows distinct cleavage lamellae. Syntaxial overgrowth by clear crystals points to burial diagenesis. In contrast, syntaxial overgrowth in near-surface marine, meteoric or mixing-zone environments is generally inclusion-rich and cloudy. Cambrian: Handler Range, Antarctica. Syntaxial overgrowth (arrows) on echinoderms. When viewed under crossed nicols, the cement crystals show the same interference colors as the enclosed single crystal echinoderms and are part of the same crystals typical of syntaxial overgrowth. Prolongation of twin lamellae into the syntaxial cement as well as the inclusion-free clear crystals indicate the continuing growth of the echinoderm calcite under burial conditions. Jurassic: Switzerland. Leached corals, filled with internal sediment and calcite. The walls of the corals are almost completely replaced by calcite. Some septa1 structures are preserved as relicts at the periphery (arrow). Dissolution occurred during the subaerial exposure of a reef and karstification (Bernecker et al. 1999). Infilling of (red) micrite sediment took place subsequent to a renewed change to submarine conditions. Late Triassic: Tropfbmch Adnet, Salzburg, Austria. Gravitational cement represented by pendant cement (arrows) beneath variously shaped vadoids formed in a marinevadose shelf interior environment. Pendant cements reflect growth outward to capillary water-air interfaces of partly filled interparticle pores. Pisoid grainstone. SMF 26. Late Permian: Entrance Carlsbad Cavern, New Mexico, U.S.A. 7 Marine phreatic isopachous bladed calcite cement (arrows) around dasyclad algae and aggregate grains. Remaining interparticle pores were filled with crystal silt. Crystal silt composed of tiny calcite crystals, sometimes associated with microfossils. This internal sediment is often used as an indication of vadose diagenetic conditions (as in this figure), but is also known from burial environments. Middle Permian: Velebit, Croatia. Solution void, occluded by scalenohedral calcite cement (black arrow) and silt-sized sediment (white arrow) consisting of tiny mechanically deposited calcite crystals and broken-off tips of cement crystals (crystal silt). See -> 7. Lowermost Cretaceous: Subsurface, Kinsau, Bavaria, Germany.

Pl'tte i-1 Ma1 ~ n e M , e t e o i ~ c .Burla1 Cements

307

Diagenetic Pathways

308

7.4.4.3 Cold-Water vs. Warm-Water Diagenesis Carbonate minerals are predominantly High-Mg calcite (and minor aragonite) in shallow warm temperate carbonates and High-Mg to Low-Mg calcites in cool temperate carbonates. Mineralogical composition is controlled by water temperatures and water depths. Carbonate saturation of seawater in non-tropical settings is less pronounced or even undersaturated (Opdyke and Wilkinson 1990).Diagenesis, therefore, is predominantly destructive (Alexandersson 1978). In comparison with tropical shallow-marinecarbonates the diagenetic potential is low and sediments may remain essentially unlithified for a long period of time. Nevertheless, intraskeletal and intergranular carbonate cemen-

tation may be common in some temperate and coldwater carbonates (Rao 1981,1993,1994; Rao and Adabi 1992; James et al. 1992, 1994; Freiwald 1998). In contrast to warm-water reefs, Mg-calcite radiaxial cements appear to dominate in cooler waters (Beauchamp 1994; Nelson and James 2000). Dolomite is rare, known from the cool temperate water of the Coorong, South Australia, and locally present in New Zealand.

7.4.5

Diagenetic Pathways and Patterns

Pore waters and their products, including cement and porosity evolve over time resulting in short- and longterm diagenetic sequences and stages. Changes over

Plate 35 Diagenetic Pathways and Spatial Variations A detailed study of diagenetic spatial variations is necessary for understanding porosity development over time and the highly complex diagenetic history of carbonate rocks. Instructive examples of these processes were presented by Schroeder (1988). Spatial variations depend on the individual characteristics of grains and cements (mineral and chemical composition, ultra- and microstructure, surface properties), collective characteristics of sediments and sedimentary rocks (component mix due to ecological and transport selection, fabrics as determined by primary sedimentary and skeletal structures), synsedimentary to early diagenetic processes (internal sedimentation, bioturbation, bioerosion), early to late diagenetic processes (cementation, dissolution, fracturing, decomposition of organic matter), hydrology (wave and tide ranges, sea- and ground-water levels, mixing zones), as well as substrate mobility and solubility. Many of the causal factors are controlled by biologic, meteorologic and oceanographic factors. The samples shown in this plate illustrate a few variations in cements and neomorphic alterations as well as in grain preservation, both between and within particles. Diagenetic pathways are highly complicated. Therefore attributing the depicted diagenetic features to specific diagenetic environments has been restricted to the samples described here and should not be too generalized. 1 Cementation in a Holocene beachrock from Uyombo, Kenia. The photograph shows inherited aragonite spherulitic cement (IAC) within an intraskeletal pore of a coralline red alga (CA) and fibrous marine Mg-calcite palisade cement (MC) surrounding carbonate particles but not the quartz grains (Q). Meteoric sparry calcite cement (SC) fills the remaining pore spaces. Crossed nicols. 2 Particle alteration in a Holocene beachrock from Uyombo, Kenia. A fragment of a mollusk shell exhibits a variety of modes of preservation/alteration: The original fabric is partly preserved and rimmed by a micrite envelope. A secondary solution pore is partly empty and partly filled by blocky sparry calcite cement. Interparticle pores are filled with fibrous Mg-calcite cement. CA: Coralline alga; Q: quartz. Crossed nicols. 3 Modern Bermuda algal cup reef rock. Adjacent skeletal pores within barnacles are filled completely by aragonite needle cement (I), by a basal layer of micrite and subsequent Mg-calcite cements with calcified algal filaments (2,3), or by Mgcalcite cement on calcified algal filaments and subsequent aragonite needle cement (4). Crossed nicols. 4 Branching reef coral Procladocora tenuis. The corallite is filled by micrite (I), fine-grained sediment (2), sparry calcite (3) and neomorphic calcite (4). The Paleocene coral knobs studied passed through a sequence of diagenetic environments ranging from marine to meteoric and back to marine, on to shallow burial conditions at various depths, and then back to the surface. In the course of this development various portions of the corals were affected at different times by neomorphism, replacement, dissolution, cementation, andlor fracturing. As a result of this history, various incomplete diagenetic sequences occurred in spatial proximity, many of which can be recognized in a single thin section. Infilling of intraskeleton pores with fine-grained sediment (2) and micrite (1) occurred in the marine environment.This micrite may be a sedimentary or diagenetic product. The sparry calcite mosaic (3) represents neomorphically altered Low-Mg calcite cements (indicating meteoric processes). The large crystals (4) with irregular boundaries and relicts of septa are caused by neomorphic alterations, probably in the burial environment. Crossed nicols. Paleocene: Bir Abu El Husein area, southern Egypt. -> 1-4 Schroeder (1988)

Plate 3 i : D ~ d g e n e t i cP a t h w a y s

309

310

Diagenetic Textures

Fig. 7.15. Diagenetic changes of coral skeletons over time demonstrated by diagenetic patterns of dendroid scleractinian corals. The sketch summarizes different preservation types and the course of diagenetic processes. The generalized drawings are based on thin sections (see P1. 3614) of Cretaceous coral limestones used as building stones in the giant wall of the Hittite capital Hattusa near Bogazkoy, central Turkey. A: The septa1 structure of the originally aragonitic dendroid corals showing biogenic encrustations is rarely completely preserved, whereby a geopetal indicates toppling of the corallites. C B: Preservation of coral structures can be enhanced by the precipitation of fine-crystalline dmsy calcite mosaics between the septa. More often, however, the interior of the corallites is completely dissolved, producing open molds. The molds are stabilized by variously thick interior cement tapestries. Coral dissolution may occur under meteoric conditions both in subaerial and burial environments. The tapestries at the bottom of some molds are covered by gray crystal silt pointing to dissolution in a near-surface burial setting influenced by meteoric-vadose waters. C: Some of the molds have been completely occluded by blocky burial cements. D: Still open molds are now filled with red internal sediment, in places overlying the gray crystal silt. The red sediment is .. . ... .... ................ . .. . ............................... unfossiliferous weakly laminated micrite that might represent a reworked karstic residual sediment. E: This stage is characterized by the formation of calcite-filled microcracks transecting both corals and packstone matrix during increasing burial conditions. F: Deep burial compaction and shearing produces angular fragments showing plastic bending and grain breakage. G: The last stage is characterized by tectonic fissures filled with clasts consisting of reworked corals and matrix. After Fliigel und Fliigel-Kahler (1997).

time are manifested by cement successions visible on small- and medium scales as well as by large-scale trends in mineralogy, cementation, and porosity due to shifts of diagenetic environments during rock history. Examples are shown in Fig. 7.15 and in P1.35.

ing diagenetic features to changing diagenetic environments (Schroeder 1986; Koch and Schorr 1986) and provides a more profound understanding of porosity evolution.

"Gone are the days when the carbonate petrographers were fully content in distinguishing cement Aand cement B" (Schroeder 1988). For a long time these terms were used in distinguishing first stage cement, generally regarded as early diagenetic, and second stage cement, considered to be late diagenetic in origin (Graf and Lamar 1950). Precise petrographical thin-section analyses and cathodoluminescence studies demonstrate that a simple two-fold classification gives only a very rough and often incorrect picture. Diagenetic stages are indicated by the superposition of different mineral phases, or by differences within cement minerals (Braithwaite 1993). Another pitfall in recognizing small-scale diagenetic successions is spatial variation within carbonate units (PI. 35). Spatial variations increase in the course of diagenesis over time, resulting in a highly complex pattern of cementation, dissolution, and porosity development. The petrogenetogram, a time-space flow diagram ascribes vary-

7.5 Diagenetic Textures The most important processes occurring in subsurface carbonates are compaction and pressure solution. Burial of noncemented carbonate sediments under an increasing burden results in compaction and then in pressure solution. The specific criteria of these processes can be recognized on different scales including thin sections. During mechanical compaction, strain is concentrated at grain contacts. Grains may behave in either a brittle or a ductile fashion. Early cementation protects grains against compaction and pressure solution. Mechanical compaction eventually can continue on to chemical compaction if the grains begin to dissolve at their contacts. Chemical compaction in lithified limestones leads to pressure solution generating dissolution seams and stylolites. References on mechanical and chemical compaction are listed in Box 7.8.

311

Compaction

Box 7.8. Irnportant references on mechanical and chemical compaction of carbonate rocks. Overviews: Chilingarian 1989; Chiliigarian and Wolf 1976; Coogan and Manus 1975; Hutcheon 1989; Choquette and James 1989; Shim et al. 1976; Wanless 1983; Wolf and Chilingarian 1976 Experimental compaction: Bhattacharyyaand Friedman 1983;Deelman 1975; Ebhardt 1968;Fruth et al.1966; Golightly and Hytle 1988; Molenaar and Venmans 1993; Neilson 1990; Pitman and Larese 1991; Robertson 1967; Shim and Robbin 1983; Shinn et al. 1980 Compaction models: Bayer 1978; Carrio-Schafhauser et a1.1990, Ortoleva et al. 1993; Ricken 1987, 1992; Stefaniuk and Mackowski 2000; Temghi 1940 Compaction studies: As-Saruri and Dietrich 1996; Bathurst 1987; Borre and Fabricius 1998; Chanda et al. 1977; Kendall2000, Klotz 1990; Lasemi et al. 1990; Myers 1980; Myers and Hill 1983; Pray 1960; Saller 1996; Scholz 1973; Shim et al. 1983; Tnunit 1980; Wanless 1979; Westphal and Munnecke 1997 Compaction measurement: Coogan 1970; Coogan and Manus 1975;Kahn 1956; Masson 1951; Nicolaides and Wallace 1997; Taylor 1950 Decompaction: Doglioni and Goldhammer 1990, Gnoli 2002; Lang 1989; Martire and Clari 1994; Meder 1987; Monaco et al. 1996; Perrier and Quiblier 1975; Steiger 1981; Wetzel and Aigner 1989 Stylolite studies: Bauerle et al. 2000; Buxton and Sibley 1981; Friedel 1995; Friedman et al. 1981; Garrison and Kennedy 1977; Gillett 1983; Huber 1987; Luczynski 2001; Nelson 1981; Railsback 1993a, 1993b, 1993c, 1993d; Salarneh and Zacher 1982; Steiger 1981 Stylolite models: DeBoer 1977; Deelman 1975; Merino et al. 1983; Park and Schot 1968; Weyl 1959 Compaction, stylolites and hydrocarbon reservoirs: Abu Dhabi National Research Foundation 1984; Amthor et al. 1988; Clunnington 1967; Hunt and Fitchen 1999; Leythhaeuser et al. 1995; Scholle 1977; Shim et al. 1984; Smith 2000. Classification and terminology: Logan 1984; Logan and Semeniuk 1976; Wardlaw 1979.

7.5.1 Mechanical Processes: Compaction

A

'Limestone compaction is an enigma' (Shinn et al. 1977) Mechanical compaction is associated with dehydration, porosity reduction, and significant reduction of sediment thickness which may be reduced to one quarter of the original thickness. Concavo-convex

The initial compaction is characterized by three stages: (1) Deposition of sedimentary grains, dehydration, changes in packing density. Reduction of lime mud to 80-75% of the original porosity. (2) Compaction and dehydration of carbonate mud. The porosity is reduced to about 40%. Reorientation of grains. (3) Plastic deformation of grains. Micrite may be preserved in protected areas. Processes during stages 1 and 2 can occur within a burial depth of just one meter. Compaction of half of the original thickness and a loss of 5040% of the initial porosity often needs a burial depth of at least a hundred meters. Dewatering is the main process in the mechanical compaction of muddy shelf carbonates and grain-supported sands, followed by pressure solution in deeper burial environments. In contrast, porosity loss of pein the upper tens lagic oozes is caused at of meters by a mechanical rearrangement of grains followed by grain crushing and pressure solution.

Tangential contact

Sutured contacts

Line of transverse

Fig. 7.16. Description of grain contact types according to Taylor (1950). Important types are point contacts, tangential contacts, concavo-convex contacts, and sutured contacts. Point contacts indicate initial compaction, tangential contacts increasing compaction, and sutured and concavo-convex contacts point to effects of pressure solution at grain contacts. Measurements taken along traverses assist in quantifyingdifferent grain contact types; the traverses should be vertical to the sedimentary bedding.

Box 7.9. Compaction criteria seen in thin sections. Mud-supported micritic limestones (mudstones, wackestones) elongated and merged peloids forming a clotted structure, closely compressed shells, shell breakage. Note that shells in experimentally compacted lime muds may not show breakage (Shim et al. 1977; Shim and Robbin 1983). Compaction effects on allochems decrease as the matrix percent increases (Fruth et al. 1966), enrichment of skeletal grains in defined patches, degree of burrow deformation (Ricken 1986), distorted fenestral voids and desiccation structures, the abundance of microfenestrae (Lasemi et al. 1990) decreased in experiments with increasing pressure. Describe the porosity evolution in micritic limestones. They can be studied only in SEM and have a maximum diameter of 1.5-15 pm. thinned and wispy laminations, irregular stringers of organic matter draping over rigid grains, forming wispy seams, deformation of thin-walled organic microfossils within the sediment (Westphal and Munnecke 1997). Early cemented limestones contain spherical to slightly deformed microfossils, mechanically compacted carbonates exhibit flattened microfossils. Grain-supported limestones (grainstones,packstones) plastic deformation of peloids (Pl. 3612) and cortoids, collapsing and telescoping of grains, mechanical rearrangement of grains (PI. 36/1,3), grain rotation indicated by rotated geopetal fabrics, overpacking, truncation of grains by adjacent grains, spalled ooids (PI. 3615) and shells, e.g. foraminifera (Pl. 36/1), broken and welded fossils (Pl. 36/1,3), broken micrite envelopes, grain flattening (Pl. 3615, 6), curviplanar parallel grain contacts (Pl. 36/5), stylolites.

Compaction criteria in thin sections Box 7.9 lists common compaction criteria for limestones. The intensity of the compaction of carbonate muds and carbonate sands is different as is the possibility of recognizing all the effects in thin sections. Description and measurement of compaction Measurements of compaction in t h sections require point-counter determinations of grain volume percentage, or the minus-cement porosity expressed by the frequency of cement or grain contact types. The resulting numbers are compared with inferred average porosities of modem carbonate sediments of similar composition. Grain contacts should be described following precise definitions (Taylor 1950; Fig. 7.16). Some cau-

tion is necessary because the original shape of the grains may determine the type of grain contacts and not compaction effects. Several methods have been proposed for quantifying the degree of compaction:

Measuring the increase in grain volume percentage. This can be measured directly in thin sections of grainstones using point counter methods and expressed by Packing Density (Kahn 1956; Coogan 1970). Packing Density is the grain volume percentage as measured in thin section. A Compaction Index based on Packing Density was proposed by Coogan (1970) for oolitic grainstones,grainstones with aggregate grains, and skeletal grainstones. The Compaction Index is a measure of the degree of grain compaction, given as a percentage. It is derived from the grain volume measurement and adjusted for the original volume percentage of the uncompacted sediment according to grain type. Measuring the increase in grain closeness. This is reflected by the increased number of grains that touch each other as compared to the original uncompacted sediment. It is based on grain boundary measurements, requiring measurement of grain-to-grain, grain-to-cement, or grain-to-pore contacts along traverse lines and is expressed by the Packing Index (Masson 1951; Coogan 1970). The Packing Index is determined from the ratio of the number of grains touching each other to the total number of grains in thin sections. The rationale behind the Packing Index is the idea that compacted grainstones should have more grains touching each other than uncompacted grainstones. This index is more quickly determined than packing density, but is less useful because it depends on the total number of grains counted, and is affected by grain shape and interparticle cementation, which may change grain contact configurations. Measuring porosity and cements. In thin sections of grainstones, the degree of compaction is estimated by measuring the percentage of interparticle porosity and interparticle cements and comparing it with modem sediments of similar composition (Nicolaides and Wallace 1996). Measuring the diameters of deformed burrows and comparing it with non-deformed circular burrow diameters (Ricken 1987; Gaillard and Jautee 1987). Open burrows of organisms living within the sediment will be deformed, whereas burrows filled with early sediment or cement will not be. Open burrows are deformed similarly to the neighboring sediment. Measuring deformed fossils with originally circular cross sections, e.g. nautilid cephalopods.

Controls on Compaction

Compaction and decompaction The degree of compaction can be calculated according to the Carbonate Compaction Law (Ricken 1987, 1992).The c:alculation requires quantitative data on the CaCO, conl:ent and insoluble residue contents of the sample, rock porosity measurements, and compaction values derived from deformed burrows. An estimate of compaction percentages is necessary for estimating the precompact ion thickness and the geometry of carbonate units by decompaction (Ricken 1985). Compactilon values are used for decompaction calculations that can restore the original thickness of the limestone sequences. The evaluation of original thickness is nece:ssary in understanding paleorelief geometries and the spatial relationships between reefs, platforms and basins (e.g. Lang 1989). Low compaction is common in reef boundstones, is medium in mudstones, high in packstones and marls, and often high in grainstones. Decompaction is commonly measured by evaluating of spheres deformed into ellipsoids. This technique uses deformed trace fossils that originally had a circular cross section (Wetzel and Aigner 1989), ooids (Coogan 1970) as well as originally spherical microfossils (Martire and Clari 1994; Monaco et al. 1996). Another common method for calculating thickness changes during burial compaction is based on porosity-depth curves (Perrier and Quiblier 1975; Doglioni and Goldharnmer 1990). Algorithms relating compaction and decompaction of carbonates were developed by Goldhammer (1997). Controls on compaction Many dynamic, inherited, and also inhibiting variables influence the degree of compaction:

Dynamic factors overburden subsurface temperature pressure duration of burial stress pore pressure pore-water chemistry: Pore water is of prime importance in chemical compaction but not in mechanical compaction (Weyl 1959).The greater the degree of undersatura1:ion with respect to CaC03, the lesser the amount of overburden needed to cause interparticleand intraparticle pressure solution. The greater the degree of oversaturation, the greater the amount of overburden needed to cause pressure solution. Inherited factors sedimenr.aryfabric skeletal architecture: Microcrystalline skeletal grains

(e.g. bryozoans) are more susceptible to mechanical and chemical diagenesis than single-crystalechinoderm grains (Meyers 1980) skeletal mineralogy: Apparently without major influence on inter- and intraparticle chemical compaction clay content: Clay-bearing rocks are often more susceptible to strong compaction than clay-free rocks. In limestone/marl sequences limestones are not or less compacted, but marls exhibit strong compaction. (Mumecke 1990). The precise effects of clays (e.g. decreasing permeability to cementing pore waters, enhanced diffusion of dissolved CaCOJ require further studies grain size and sorting grain shape.

Inhibiting factors preburial cementation; precompaction diagenesis of interparticle cements may inhibit compaction preburial dolomitization clay content (see inherited factors above). Compaction of carbonate muds and sands Compaction data on sedimentary carbonates have been gathered by Goldhammer (1997). In contrast to muddy siliciclastic beds, which are commonly highly compacted to fissile shales, muddy carbonates preserve sedimentary structures much better, because carbonate muds are far less compacted than clay-rich muds and because precompaction cementation is widespread, at least in shallow-marine carbonate. Modem shallow-marine lime mud, consisting of loosely arranged aggregates of micron-sized aragonite needles, has porosities in the range of 70-80% (Enos and Sawatsky 1981; Shim and Robbin 1983). Squeezing experiments prove that these muds can not be condensed by mechanical compaction below a porosity of about 25%. Initial porosity loss is dominantly a result of dewatering. Grain stabilization is reached under burial conditions of 100 m or less. A fully compacted

Fig. 7.17. Stylolites on a microfacies scale. Stylolites are serrated boundaries between units. The boundary usually has an accumulation of clay, oxides, and/or organic matter. Lowermost Cretaceous carbonate ramp: Subsurface, southern Bavaria, Germany. Scale is 1 mm.

Pressure Solution and Stylolitization

lime mud may then have the porosity of a compacted eralogy, and minimal early cementation and dolomitisand, but differs in the very low permeability. Mechani- zation. Grain-supportedcarbonates may be resistant to cal compaction is particularly important in mud-domi- compaction down to 700 m. nated sediments as proved by studies of pelagic oozes and chalks (Scholle 1971; Neugebauer 1973; Schlanger 7.5.2 Chemical Processes: and Douglas 1974; Scholle et al. 1983). Compaction of carbonate sands is favored by deep Pressure Solution and Stylolititation burial and high effective strength, a low geothermal Following mechanical compaction many sediments gradient, a low rate of loading, low pore pressure, long burial under stress, and water-wet grain surfaces. Fur- are subject to chemical compaction,expressed by presther factors are small average grain size, moderately to sure solution and the formation of stylolites and soluwell sorted grains, close primary packing, stable min- tion seams that are often associated with fracturing

Plate 36 Mechanical Compaction and Deformation Structures Mechanical compaction is a process caused by sediment overburden and resulting in a general reduction of porosity and rock volume. The thickness of the overburden necessary to produce compaction structures is controversial. Overburden results in the mechanical failure of grains. Compaction is commonly followed by pressure solution recorded by stylolites and solution seams (see P1. 37). The degree of mechanical compaction is inhibited or reduced by early precompaction cementation (-> 2) and can be studied in grainstones by cement/ grain ratios (Meyers 1980). 1 Mechanical and chemical compaction resulting in the formation of a diagenetic packstone exhibiting a condensed fabric after Logan and Semeniuk (1976). Overburden stress at grain contacts is accommodated by grain deformation in the form of ductile squeezing and grain fracturing (black arrows). Lime mud within the foraminifera is protected from compaction. Pressure solution is indicated by nonparallel multigrain sutured seams (microstylolites). The diagenetic packstone consists of worn, redeposited, and strongly compacted fusulinid foraminifera (F) and platy algae (A). Some matrix has been lost during compaction and a welded mass of skeletal grains remained. The sequential history of fusulinids includes: (1) Infilling of the tests with gray micrite (GM) and red micrite (RM) prior to compaction. Globular tests of the fusulinids suffered stronger breakage than spindle-shaped shells (top right). Deep burial environment. Early Permian (Rattendorf Formation): Camic Alps, Austria. 2 Dzfferential compaction. Ooid-peloid grainstone. The sample consists of alternating layers with ooids (center and uppermost layer), and layers with peloids, crustacean coprolites (Favreina, F) and ooids (below and above the ooid layer). Compaction is indicated by plastic bending (arrows) of peloids and Favreina grains. Compaction within the ooid layer was inhibited by early cementation and is only indicated by the close packing of the grains. The interparticle cement postdates compaction of grains, pointing to shallow subsurface burial cementation. Early Cretaceous (Purbeck facies, Berriasian): Subsurface, Bavaria, Germany. 3 Crushed fusulinid test, the victim of physical compaction caused by bioclast-to-lithoclast (L) contact. The whorls are broken and rearranged (arrows). Differences in the rigidity of lithoclasts and the fossil caused breakage and splittering of whorls associated with burial fracturing. Note the absence of stylolitization. The limestone is a sedimentary microbreccia generated by the erosion and deposition of platform-derived material. Early Permian (Tressdorf limestone): Camic Alps, Austria. 4 Tectonically deformed limestone with branching scleractinian corals. Preservation stages of corals reflects several of the diagenetic and deformation stages shown in Fig. 7.15: Corallites with well-preserved septa (1); calcite within partially or totally dissolved corallites (2); infilling of red micritic sediment (RM) in hollow corallites (3). Corals were affected by shearing (4) and fracturing of the rock. The diagenetic pattern of aragonitic corals is often related to growth types: The open framework of branching corals favors dissolution, whereas massive corals are completely replaced by neomorphic spar. Cretaceous: Building stone of the Hittite wall, Bogazkoy, central Anatolia. 5 Strong compaction. Ooid grainstone with distinctive compaction features: Flattened grains (FG) and parallel grain contacts (PGC). The nuclei of the ooids are dissolved. Deformation (arrows) of partially dissolved ooids suggests that compaction took place during burial. Late Permian (Main Dolomite, Zechstein): Subsurface, Debki well, northern Poland. 6 Shallow-burial compaction. Diagenetic pisoid grainstone with contorted grains. The concentration of calcite cement below the grains (arrows) points to precipitation in the meteoric-vadose zone subsequent to burial compaction. Another explanation is indicated by the laterally continuous cement garlands underneath the grains, which may mark stylolites filled with burial cements. Late Permian (Main Dolomite, Zechstein): Subsurface, Miloszewo well, northern Poland. -> 4: Fliigel and Fliigel-Kahler 1997; 5 and 6: Peryt 1986.

Plate 3 ( . : C o m p a c t ~ o na n d Deformation

1 crn

315

2

rnm

Chemical Compaction

316

structures (Logan 1984). Pressure solution is caused by load and/or tectonic stress. In more strongly cemented rocks solution takes place along extensive surfaces, forming stylolites. Dissolution often starts along a bedding surface. Mechanisms by which pressure solution occurs are dissolution in a thin solution film as result of compressive stress inside grain-to-grain boundaries (Weyl 1959; Rutter 1983) or dissolution at or just

outside the rims of grain contacts resulting in an undercutting (Bathurst 1975; Tada and Siever 1986). Pressure solution can increase the dissolution of calcite and is believed to be a significant source for the formation of porosity-occluding subsurfacecements in deep burial settings. On the other hand, pressure solution may create conduits for fluids and open migration

Plate 37 Chemical Compaction: Pressure Solution (Stylolites and Seams) Chemical compaction is exemplified by pressure solution resulting in stylolites and solution seams formed under burial conditions. Stylolites are irregular, suture-like contacts produced by differential vertical movement under pressure accompanied by solution. They are marked by irregular and interlocking penetration on two sides: Columns, pits and tooth-like projections on one side fit into their counterparts on the other side (-> 2). Concentrations of insoluble residues along stylolite surfaces are common (-> 5). Solution seams are isolated or swarm-like partings characterized by thin seams, often with accumulations of insoluble residues. Pressure solution processes involve a strong reduction in rock bulk volume with a resultant loss in porosity caused by the occlusion of pores by late diagenetic subsurface cements (Wong and Oldershaw 1981). Volume loss caused by chemical compaction is facies-dependent. Stylolitization changes original depositional textures and produces new diagenetic fabrics. A specific terminology is necessary for describing the type of interfaces between adjacent particles, the structures produced by pressure solution and shear fracture, the fabrics developed by pressure solution, and the resulting rock type (Fig. 7.18). 1 High amplitude columnar stylolites in a peloidal bioclastic wackestone. Stylolite interfaces are partly covered by reactate calcite (arrow). SEM . Late Cretaceous (Mishrif Formation): Middle East. 2 Peaked high amplitude stylolites along a bedding plane separating laminated fie-grained peloid grainstone (LPG) and non-laminated medium-grained peloidal grainstone (PL). Both microfacies types originated in intertidal environments. The lower one is a microbial mat with abundant bacterial peloids (see P1. 815). The upper microfacies corresponds to another mat formed by organically bound peloids and oncoids (0).The limestone was not mechanically compacted prior to stylolitizationowing to early cementation by calcite. Stylolitization has dissolved a high amount of the limestone. Early Cretaceous (Purbeck facies, Berriasian): Subsurface of the Molasse zone, Bavaria, Germany. 3 Bedding-parallelirregular anastomosing sutured seams (microstylolite set) in lime mudstone. Note dark insoluble residue (stylocumulate, SC) along pressure-solution surfaces and calcite, representing styloreactate(material that has crystallized at stylolite interfaces, SR). Pressure solution took place subsequent to leaching of evaporite minerals (black arrows). Late Permian (Zechstein): Harz, Germany. 4 Pressure solution postdates compaction. Grain-to-grain pressure solution of conspicuously large, tangentially structured fractured ooids (TSO) exhibiting jagged surfaces. Nonparallel reticulate grain contacts. Note dark stylocumulate (clay residue, calcite fragments and dolomite). Dolomitization occurs within the stylocumulate, but also in ooids as selective replacement. Arrows point to dolomite crystals. Cambrian: Takkanawa Fall, Yoho Valley, British Columbia, Canada. 5 Widely spaced high-amplitude columnar stylolites in a burrowed ostracod wackestone. The dark stylocumulate consists of clay and pyrite. The limestone has suffered no compaction prior to deep-burial pressure solution. Silurian: Valentintorl, Central Carnic Alps, Austria. 6 Non-sutured wispy parallel sets of dissolution seams producing a stylolaminated fabric. This fabric tends to develop when the clay content is high, larger than at least 10%. Arrows point to individual seam sets. Note that very similar features have been produced by mechanical experimental compaction (Shim and Robbin 1983). L i e mudstone. Jurassic: Peloponnesus, Greece. 7 Stylobreccia. Sutured reticulate multi-grain fabric (Wanless) or condensed fabric (Logan and Semeniuk). Idens (bodies that behave as homogeneous entities under physical or chemical conditions) are densely packed and bound by irregular, anastomosing microstylolites (white arrows). The black arrow points to dissolution of a miliolid foraminifera1shell. RC: Reactate calcite formed by pressure solution. Subsurface of the Molasse zone, Bavaria, Germany. 8 'Horse tail' structure characterized by lateral splitting of seams (arrows). Bedded non-sutured wispy seams (Wanless). Irregular anastomosing sets (Logan and Semeniuk). Estimates of the minimum local extent of chemical compaction can be made by determining the difference in thickness between a solution seam and the laterally equivalent wedge of diagenetically laminate carbonate (horsetails: Kendall2000). Cretaceous: Egypt.

Plate 3 7 : S t y l o l i t e s and S e a m s

3 17

I rnrn

2 mrn

2 mm

1 rnrn

2 rnrn

3 18

paths. Fracturing and pressure solution are prime factors for reservoir rocks in the Middle East. Stylolitizationcontributes to bulk volume reduction, resulting in a marked drop in the original thickness of carbonate units. Stylolitization modifies the primary sedimentary fabric of limestones dramatically and their description, therefore, requires a specific terminology focussing on the fabric and structure of the altered rocks. Criteria of pressure solution in carbonate rocks Chemical compaction (Lloyd 1977) is recorded by dissolution seams (horse tails, wispy stylolites, microstylolites) characterized by surfaces that can be followed across several grains; common in fine-grained and clay-rich limestones, stylolites characterized by greater amplitudes than in dissolution seams; common in more coarse-grained limestones or at lithologic boundaries, stylolites often cross the whole rock, intersecting grains, matrix and cement, stylolites often have a zigzag form, due to differences in the solubility of different components (e.g. skeletal grains may be less soluble than micrite matrix),

Pressure Solution

the less soluble parts of three-dimensional 'fingers', extending into the more soluble parts, amplitudes of stylolites may range from < lrnm to > 1 m. The amplitudes indicate the minimum thickness of the dissolved material, insoluble material (often clay, hydrocarbons) becomes concentrated along the stylolite surface. This material does not appear to reprecipitate in the immediate vicinity of its origin, implying transport by fluids, pressure solution-derived cements, inter- or intragranular dissolution at grain contacts causing sutured boundaries. Terminology and classification of carbonate rocks affected by chemical compaction Diagenetic features of carbonate rocks, even if they are striking, are only rarely recorded in names of limestone types. Exceptions are the modification of the Dunham classification proposed by Wright (1992; Sect. 8.4.1) and the consideration of pressure solution structures in the classification of Logan and Semeniuk (1976). Fig. 7.18 summarizes the main criteria used by Logan and Semeniuk and by Wanless (1979). The terms introduced by Logan and Semeniuk for the description of rocks suffering from pressure solu-

>>> Fig. 7.18. Terminology of pressure solution features. Most of these categories can be derived from thin-section studies (see PI. 37). A - Styles ofpressure-solution features after Wanless (1979) modified by Choquette and James (1987). The non-sutured type is characterized by microstylolites, microstylolite swarms, clay seams and grain contact sutures; it forms in limestones that contain a significant amount of insoluble material (clay, silt, organic matter). The sutured type is typified by stylolites and grain-contact sutures and forms in limestones with very low amounts of insoluble residual material. Bedding-parallel sutured seams correspond to stylolites of different amplitudes, which may occur as single structures or in swarms. Reticulate systems of anastomosing microstylolites(fitted fabrics, see B) and non-sutured seams occur in limestones made up of rigid entities in grain-to-grain contact or surrounded by more soluble sediment. B - Classification of pressure solution features by Logan and Semeniuk (1976). The classification concentrates on the morphology of stylolites (columnar, PI. 3711, 5; high amplitude - P1. 3712 and low amplitude - PI. 37/3 - types, irregular, hummocky or smooth) and differences in stylolite sets (parallel, irregular anastomosing, PI. 3713; conjugate - P1. 37/6), and focuses on fabric types caused by pressure solution and structural types that can be recognized on micro- to macroscales. Note that in rare cases stylolites can also be formed by mechanical compaction without pressure solution (Braithwaite 1986). Fabric types are differentiated according to the behavior of idens (bodies that behave as statistically homogeneous entities under physical and chemical changes). Iden-supportedfabric: Idens form a self-supporting frame and are in contact at grain points. Condensedfabric: Idens are very densely packed, grains contact over a surface. Fitted fabric: Idens produce a puzzle-like fabric. They are surrounded by solution seams and are in contact with their neighbors all along their margins. Stylocumulatelreaction support: Larger idens are supported by fine-grained stylocumulate (insoluble residue accumulated along a pressure-solution surface). Diagenetic structures: Stylobedding: Pseudo-bedding caused by parallel pressure solution that may be parallel to the original horizontal layering. Stylolaminated: Laminated appearance due to swarms of parallel solution seams or low-amplitude stylolites. Stylonodular: Nodules and lenses of limestone idens separated by broad stylolite swarms. The original micritic matrix is more or less dissolved. Stylomottled: Characterized by patchy enrichment of insoluble stylocumulate and reactate (material which has grown at solution interfaces, e.g. calcite, dolomite, or quartz), may be also caused by patchy enrichment of marls due to inhomogeneous pressure solution. Stylobreccoid: Originates from selective pressure solution (PI. 3717).

3 19

Pressure Solution: Terminology

STYLES

IF

NOH-SUTURED SEAMS Bedding parallel Single

PRESSURE SOLUTION SUTURED SEAMS Bedding parallel Non-parallel reticulate

-----

Large amplitude

Grain-contact

Non-parallel reticulate Small amplitude

w Single

TYPES O F STYLOLITES Columnar

Peaks high amplitude

Irregular

Hummocky

Peaks l o w a m p l i t u d e

Smooth

TYPES OF STYLOLITE SETS Parallel sets

I r r e g u l a r anastomosing s e t s

C o n j u g a t e sets

FABRIC TYPES l d e n support

Condensed

Fitted

Stvlocumulate/reactate support St

PRESSURESOLUTIONSTRUCTURES Stylobedded

Stylolaminated

Stylonodular

Stylomottled

Stylobreccioid

Fig. 7.18. Terminology of pressure solution features. Most of these categories can be derived from thin-section studies (see PI. 37). Explanation on the left.

Pressure Soultion: Signifcance

tion were included by Logan (1984) in a more rigorous classification that also considers deformation structures caused by pressure response to burial and/or tectonism. Carbonate rocks affected by compressional stress are accommodated by compaction, pressure solution, and shear fracture. The main response to tensional stress is the formation of strain cavities - represented by veins, vugs, and inter-fragment voids within breccias. Compressional and tensional stress is often associated with dolomitization, silicification, and other mineralization processes. Controls on chemical compaction Chemical compaction is controlled in a complex manner and depends on burial depth with attendant lithostatic load. Pressure solution becomes effective at various depths. Many authors favor burial of several hundreds to thousands of meters, but stylolite formation has also been recorded after only some tens to hundreds of meters. The paradigma of 900 m overload necessary for the formation of stylolites (Dunnington 1967) is out of date. tectonic stress leading to tectonically controlled formation of stylolites (Bathurst 1984), vertical stress caused by overburden pressure resulting in preferential solution of the upper and lower surfaces of grains, via solution films, the chemistry of pore fluids. Mg-poor meteoric pore waters will enhance pressure solution, the formation of stylolites can be retarded and prevented by the presence of oil or organic films between and on grains, pore fluid pressure in overpressing settings may retard or stop pressure solution, original mineralogy controls the early compactional history. Aragonite mineralogy at times of burial (shallow-marine carbonate muds) will enhance chemical compaction; primary calcite mineralogy (e.g. deep-marine carbonate oozes and chalk) will retard pressure solution, insoluble residues (clay, organic matter) seems to enhance pressure solution in fine-grained carbonates (Oldershaw and Scoffin 1967, Sassen et al. 1987), grain size and grain surface properties, early dolomitization can inhibit or preclude stylolitization, clay minerals; the presence or absence of minor amounts of clay minerals appear to be a major control on whether or not pressure solution occurs in carbonate rocks (de Boer 1977).

Box 7.10. Significance of compaction and pressure solution. Thickness and paleotopography of sedimentary units: Stylolitizationresults in a considerable reduction of the thickness of a sequence. Differential compaction may control seafloor relief and reef geometry (Anderson et al. 1996) and reduces the thickness of adjacent facies units, e.g. reef and platform margins (Matyszkiewicz 1999). Burial cements: Pressure solution increases the dissolution of calcite (Maliva and Siever, 1989). The supply of CaCO, from pressure solution along stylolites is a major source of late diagenetic cement and may or may not (Kreutzberger and Peacor 1988) affect also phyllosilicates within carbonate rocks. Dolomitization: Transformation of clay minerals by burial diagenesis could be a source of magnesium and dolomitization (McHargue and Price 1982; Stembach and Friedman 1984). Economic importance: Compaction and stylolitization reduce porosity depending on the degree of precompaction cementation and depending on the textural rock type. Stylolites may enhance and inhibit reservoir quality (Abu Dhabi National Reservoir Research 1984). Stylolite surfaces may be important permeability barriers, influencing the flow in aquifers and petroleum reservoirs. Grain-to-grain pressure solution is the most detrimental process for permeability (Budd 2002), followed by cementation. However, stylolites can act as conduits for fluids (Braithwaite 1989), and permeability may be created by veining activating the connectivity of stylolites (Smith 2000).

Pressure solution and rock types Pressure solution in grain-supported carbonate rocks with minor cementation starts with solution at grainto-grain contacts. Solution affects the more soluble grain causing a ranking of grain solution. Pressure solution subsequent to cementation results in the formation of a fabric that distributes pressure laterally, resulting in distinct stylolites or in a fitted fabric (Buxton and Sibley 1981). Grain-rich carbonates can be stylolitized under shallow burial of not more than 30 m (Railsback 1993). Lime mudstones, wackestones, packstones, and weakly cemented grainstones exhibit preferential solution seams that may indicate diagenetic bedding processes (Ricken 1986). Solution seams can be pre- and post-burial in origin (Bose et al. 1996). Solution resistance of grains? Differences in solution resistance of different grain and matrix types have been observed by various authors (e-g. Trurnit 1968; Logan and Semeniuk 1976; Steiger 1981; Huber 1987). Sandstone and dolomite extraclasts are more resistant

Alteration and Recrytallization

differentiate neomorphic processes. Aggrading neomorphism: A kind of coalescive neomorphism or recrystallization in which the crystal size increases and finer crystal mosaics are replaced by coarser crystal mosaics of the same mineral or its polymorph without the intermediate formation of visible porosity (Blathurst1975).Occurs chiefly in fine-grained limestones and results in rnicrospariticpatches, laminae and beds. See Morse and Mackenzie (1990) for a discussion of aggrading neomorphism. P1.3812.3. Coalescive neomorphism: Larger crystals grow at the expense of :smallercrystals or small crystals grow within a larger crystal. Degrading neomorphisrn: A kind of coalescive neomorphism :in which the crystal size decreases; smaller crystals grow within a larger crystal. Not common, but may occur under stressed or low-metamorphic conditions.

quartz), and recrystallization (changes in crystal size, shape and crystal lattice without a change in mineralogy). The last term is often used rather loosely, since it is not always possible to demonstrate whether or not a mineralogical change has occurred. Neomo~phicprocesses lead to crystal enlargement or diminution (Box 7.11). The transformation of aragonite and High-Mg calcite grains and mud to Low-Mg calcite is one of the most important processes in carbonate diagenesis because it controls the ultimate petrophysical properties of limestones and their geochemical composition (particularly stable isotopes and Sr content: Al-Asam and Veizer 1986a, 1986b; Banner 1995; Maliva 1998). Replacement of aragonite by calcite involves gradual dissolution of the original mineral and precipitation of calcite, so that relicts of original shell or cement structures may be preserved in the neomorphic calcite.

to solution than carbonate grains. Carbonate grains exhibit strong variabilities with regard to pressure solu- 7.6 1 Recrystallized Carbonate Rocks: tion potential. What to do? The only feature common to all case studies is that echinoderm grains seem to be the most resistant grains, Recrystallized limestones are predominantly charand micritic particles (e.g. peloids) and argillaceous mi- acterized by changes in the size, shape and arrangecritic matrix. are the least resistant parts of carbonate ment of crystals, and by the obliteration of the original rocks. depositional textures and constituents. Recrystallization of micritic limestones may be controlled by the clay content of limestones; a clay content > 2% seems 7.5.3 Significance of Compaction and to inhibit or prevent crystal coarsening (Bausch 1968). Enlargement of micrite may create microspar (Sect. Pressure Solution Box 7.10 lists important effects of the mechanical and chemical co~mpactionof carbonate rocks during burial as well as thie influence of dolomitization. It also discusses the economic importance of compaction and pressure solution.

7.6 Neomorphic Processes: Alteration and Recrystallization Carbonate sediments and carbonate rocks are affected by diagenetic processes that alter mineralogical composition and/or crystals and crystal fabrics. The term neomorphism (Folk 1965) relates to transformations of minerals taking place in the presence of water and includes processes of replacement (the dissolution of one mineral and simultaneous formation of another mineral, e.g. silicification of carbonates), inversion (the replacement of a mineral by its polymorph; e.g. aragonite -> calcite (calcitization); opal-A -> opal-CT ->

Fig. 7.19. Recrystallized coral limestone. Arrows point to centers of former corallites of a colonial coral. Note faint radial structures representing the recrystallized coral septa. Aggrading neomorphism has replaced cement crystals between coral calices by a medium to coarse-grained inequigranular, hypidiotopic calcite fabric. Crystals were enlarged at the expense of other crystals (note left side of the figure in particular). Jurassic: Argentina. Scale is 5 mm.

322

Recrystallized Limestones and Marbles

Plate 38 Recrystallized Limestones and Metamorphic Carbonates (Marbles) The original depositional microfacies and early diagenetic textures of limestones are often altered (-> 1) or destroyed by recrystallization and processes acting during burial diagenesis and thermal history in relation to the ups and downs of the rocks.

Recrystallized carbonate rocks (-> 2-3) should not be disregarded in facies analyses, even though depositional criteria are obliterated or completely destroyed. Recrystallization depends on clay content (> 2 % may inhibit recrystallization) and can create microspar (see P1.612) and pseudospar, the latter with crystals measuring tens to even hundreds of microns in diameter. Burial diagenesis and changes in temperature, pressure, and volatile content will favor the formation of carbonate rocks with crystal sizes up to several tens of millimeters. Some of these rocks already correspond to marbles, showing a fine- to coarse-grained granoblastic texture. Marble (-> 4-8; Sect. 7.9) is a metamorphic rock consisting predominantly of fine- to coarse-grained, dynamically recrystallized calcite and/or dolomite, usually with a granoblastic, crystalline texture. Differentiation of marbles in thin section requires the description of mineralogical composition (carbonate and non-carbonate minerals), grain shape, fabric (size and mutual relations of crystals), deformation features like frequency, bending and orientation of twin lamellae with respect to a reference plane (-> 4), and granulation textures (caused by mechanical breakage along gliding planes). Recrystallized limestones 1 Tectonically elongated fusulinid foraminifera (Quasifusulina). Low-grade tectonic deformation can remodel the shape of fossils. The tests were originally deposited parallel to each other and later stretched along their length axis. Fossils of known geometric parameters deformed in this way are important tools in reconstructing shear processes. Permian: Biikk Mountains, northern Hungary. 2 Neomorphized limestone. Note the differences in crystal size and preservation of primarily calcitic micrite clasts (MC) and the aragonitic dasyclad alga (DA). The skeleton of the alga has been replaced by calcite. Arrows point to twin lamellae developed within the segmented algal skeleton.The former micritic matrix is altered by aggrading recrystallization. Early Carboniferous:Anhui, southern China. 3 Neomorphized recrystallized limestone. Dark areas are relicts of former micritic grains (1). Former cement crystals in interparticle (2) and intraparticle pores suffered aggrading neomorphism, indicated by the coarsening of calcite crystals. The outline of the structure marked by (3) suggests a foraminifera1 shell whose central part has been replaced by coarse calcite. Common diagnostic features of the neomorphic sparite (pseudospar)are crystals of conspicuously different sizes, predominantly curved interfaces between crystals, and large crystals in association with smaller crystals. Early Carboniferous: Anhui, southern China. Marbles 4 Inequigranular coarsely crystalline calcite marble with silicate impurities. Xenotopic and poikilotopic fabric (larger calcite crystals enclose smaller silicate mineral crystals: black arrows). White arrows point to an 'enfacial junction' (a joining point of three intercrystalline boundaries where one of the three angles is 180"). The frequency of this type of triple junctions is used in distinguishing neomorphic and metamorphic spar and carbonate cement. Note the abundance of thin twin lamellae indicating deformation at relatively low temperatures (Fenill 1998). As shown by the varying directions of the twin lamellae, and strong differences in grain size, the marble is a protomylonite, caused by multiple deformations. Paleozoic: Roman quany Tentschach, Carinthia, Austria. 5 Inequigranular medium to coarsely crystalline marble, a product of intensive strain recrystallization. Xenotopic fabric. Note smaller crystals (size about 0.16 mm, arrows) between larger crystals (maximum size 1.0 rnrn), indicating grain diminution. Marble used in Roman buildings. Hergla, Gulf of Hammamet, eastern Tunisia. 6 Equigranular finely crystalline marble consisting of anhedral calcite grains, probably resulting from cataclastic granulation. Arrow points to a former shell now consisting of twinned and bent calcite crystals. Twinning is often indicated by a conspicuous strippy pattern. Ghosts of fossils (especially shells, echinoderms)may be preserved even in highly metamorphic carbonates. Jurassic (Chemtou marble): Roman quarries, Chemtou, Tunisia. 7 Inequigranular coarsely to very coarsely crystalline marble. Xenotopic fabric consisting of calcite crystals exhibiting no crystal faces bounding the mineral grains (anhedral crystal shape). Size between 0.9 and 2.5 mm. Note different directions of twin lamellae indicating dynamic recrystallization. Mesozoic marble: Sterzing, South Tyrol, northern Italy. 8 Same thin section as -> 7, crossed nicols. Note extensive twin development. Twin planes are closely spaced. The black arrow points to multiple set twin lamellae, the white arrow to bent and displaced twin lamellae. -> 1: Kahler 1988

Plate 38: Recrystallized Limestones and Marbles

323

Sparite

equigranular

inequigranular xenotopic

hypidiotopic

idiotopic

Fig. 7.20. Crystallizationfabrics of recrystallized carbonates and marbles can be described according to equant or nonequant crystal size and crystal fabric depending on crystal shape (see Box 7.12 for definitions). From Friedman (1965).

4.1.3) and continuing diagenesis may producepseudospar with crystals measuring tens to even hundreds of microns in diameter (Sect. 7.7). Burial diagenesis and changes in temperature, pressure, and volatile content will favor the formation of carbonate rocks with crystal sizes up to several tens of millimeters. Some of these rocks already correspond to marbles, characterized by fine- to coarse-grained granoblastic textures (Fig. 4.20). Recrystallized carbonate rocks are not loved by geologists interested in facies analysis. These rocks show

Box 7.12. Descriptive termsfor crystallization textures and fabrics after Friedman (1964). Compare Fig. 7.20. The scheme can also be used to describe calcite and dolomite marbles. Crystallization textures: Refer to the shape of mineral crystals and the type of crystal faces at crystal boundaries. Descriptive terms are Anhedral: Characterized by the absence of crystal facing bounding the mineral grains. P1. 3813. Sublledral: Characterized by partly developed crystal faces. Euhedval: Characterized by crystals that are bounded by crystal faces.

Crystallization fabrics: Refer to the size and mutual relations of crystals that can be differentiated into Equigranular fabrics: Consist of crystals of approximately the same size (e.g. PI. 3816). Fabrics subdivided into Xenotopic: Predominantly anhedral crystals. Hypidiotopic: Predominantly subhedral crystals. Idiotopic: Predominantly euhedral crystals.

Inequigranular fabrics: Consist of crystals of various sizes (e.g. Pi. 38/4,5,7). Fabrics are subdivided into xenotopic hypidiotpic idiotopic. Each of these inequigranular fabrics is in turn subdivided into Porphyrotopic: Larger crystals are enclosed in a fine-grained matrix. Poikilotopic: Crystals are of more than one size; larger crystals enclose smaller crystals of another mineral.

only a few characteristics that can be used in paleoenvironmental interpretations and they are poor in criteria allowing a reproducible classification. What to do? If no relicts of the primary depositional textures are preserved, a classification can be based only on the attributes of the diagenetic calcite. These features include crystal sizes, crystal shapes, mutual relationships between crystals, types of boundaries between crystals, and crystal foundations.

7.6.2 How to Describe Recrystallized Carbonate Rocks? Textures and fabrics of recrystallized limestones and dolomites as well as carbonate cements can be described using the classification developed by Friedman (1 964, 1965) and summarized in Box 7.12. Hibbard (1994) drew attention to the limited value of the terms anhedral, subhedral, and euhedral where crystal morphology is considered an expression of the conditions under which crystals and rocks are formed.

7.7 Sparite: Recrystallization Product or Carbonate Cement? The non-genetical term sparite (Fig. 7.21) designates a fabric consisting of calcite spar. Genetically, sparite is carbonate cement (corresponding to orthosparite) or a product of recrystallization. Distinguishing the products of aggrading neomorphism from sparite representing carbonate cement is often difficult. Criteria have been discussed by Folk (1965) and Bathurst (1975). Sparite representing cement occurs within pores. Boundaries between sparite and pore limits are sharp. Crystal boundaries are straight and have enfacial junctions. Neomorphic fabrics often exhibit irregular crystals with curved and embayed boundaries, variable crystal size with remnants of micrite, and the presence of grains

Fig. 7.21. Sparite (sparry calcite) represents carbonate cement or products of neomorphic changes. The former have been termed ortlzosparite, the latter pseudosparite. The thin-section photograph displays various early and late diagenetic stages of a lithoclast/bioclast rudstone deposited near a reef. The numbers indicate syn- and postdepositional diagenetic alterations affecting the skeleton of a dasyclad green alga (Macroporella sp.) and its infillings as well as the carbonate precipitated in interparticle pore spaces. 1 : Early diagenesis starts with the micritization of the walls of algal pores. 2: Infilling of algal pores with micrite (now preserved as microspar) and small peloids. 3: Microbial encrustation of the algal surface. 4: Transfomation of the originally aragonitic pore walls to calcite. 5: Infilling of the algal interior by sedimentary grains, some of which are covered by thin marine cement crusts composed of bladed calcite crystals. 6: These grains are incorporated within originally micritic microbial crusts formed in the algal interior and now preserved as microspar. 7: The alga is overgrown by a complex biogenic crust. 8: The interior of the alga is partly filled with larger bioclasts. 9: The boundary between the infilling and the remaining pore space is marked by an irregular microbial crust. 10: Large interparticle pores between (dark) reef-derived lithoclasts are occluded by abundant shallow-marine radiaxial calcite cements (orthosparite). 11: Late diagenetic processes are responsible for the formation of coarse calcite spar (pseudosparite), probably of burial origin. 12: Recrystallization causes coarsening of the walls of algal pores. 13: Tectonic shear is indicated by breaking and dislocation of the radiaxial cement crusts and by 14: a thin calcite-filled veinlet crossing cements and alga. 15: Neomorphic alterations enlarge crystals within the calcite cements. Sparite-producing diagenesis took place under marine near-subsurface conditions (points 4, 5, 10) and burial conditions (points 11, 15). Middle Permian: Straza near Bled, Slovenia. Scale is 2 mm.

apparently 'floating' within sparite. The boundary between sparitic and micritic areas is often poorly defined and can crosscut micritic grains. Larger crystals are often irregularly intergrown. A common neomorphic fabric is microspar characterized by a crystal size between about 5 and 30 um (see Sect. 4.1.3). Coarse neomorphic fabrics originating from aggrading recrystallization and consisting of calcite crystals larger than 30 pm or so are calledpseudosparite (Folk 1965).Metasparite {Kovacs 1987) designates a similar fabric that exhibits indications of metamorphic processes (e.g. granoblsstic texture. complex twinning).

7.8 Dolomitization and Dedolomitization The first part of this chapter deals with the descriptive criteria of dolomites seen in microfacies thin sections. The lack of undisputed modem analogues for ancient dolomites is the core of the 'dolomite problem' and the reason for several competing dolomitization models that are briefly summarized in the second part of this chapter. The third part discusses dedolomitization phenonema.

326

Dolomite and Dedolomite

Plate 39 Dolomite Fabrics, Dolomite Types (Saddle Dolomite) and Dedolomitization The basic terminology of dolomitefabrics used in thin sections considers crystal shape, the mutual relationships of crystals and uniform or non-uniform size distribution (-> 1-3). Saddle dolomite (-> 5) or 'baroque dolomite' is a specific dolomite type, commonly interpreted as having formed under deep burial or hydrothermal conditions. Dedolomitization refers to the early or late diagenetic replacement of dolomite by calcite (-> 4,6-8). Criteria of dolomite fabrics The fabric of dolomite rocks varies between two end-members: Limestones with scattered dolomite rhombs (-> 2) and sucrosic mosaic dolomites (-> 3). 1 Criteria: Inequigranular; non-rhombic crystals; tightly packed anhedral crystals; xenotopic fabric; intercrystalline boundaries usually curved, lobate, irregular; preserved crystaljunctions rare; grain size between 0.4 and 1.5 mrn. Classification: Friedman - Decimicron- to millimeter-sized inequigranular, xenotopic dolomite: Gregg and Sibley - Polymodal nonplanar matrix replacement dolomite; Randazzo and Zachos - Inaequigranular mosaic dolomite. Replacement dolomite. Crystal size scale (Folk) - Coarsely to very coarsely crystalline. Black spots are artifacts. Interpretation: Late burial replacement dolomitization is indicated by the amoeboid fabric and the serrate crystal boundaries. 2 The sample is characterized by clear euhedral and subhedral dolomite crystals (0.2-0.4 mm) exhibiting cloudy centers and clear rims. Cloudy centers can be caused by calcite relicts, non-carbonate or fluid inclusions. The dolomite crystals exhibit straight compromise boundaries. Descriptive criteria: Equigranular; rhombic crystals; crystal-supported, idiotopic fabric. Intercrystalline areas are still microcrystalline calcite. Fenestral voids (FV) are filled with recrystallized fibrous calcite cement. Classification: Friedman - Decimicron-sized idiotopic dolomite. Gregg and Sibley - Unimodal planar partial matrix replacement dolomite. Randazzo and Zachos - Equigranular sieve mosaic dolomite. Size scale - Medium to coarsely crystalline. Interpretation: Dolomite crystals postdate shallow-marine calcite cements of fenestral tidal limestones. Missing evidence of compaction prior to dolomite crystal growth and the restriction of the crystals to fenestral boundaries indicate replacement dolomitization of tidal sediment in a shallow burial setting. 3 Criteria: Inequigranular; non-rhombic crystals; tightly packed anhedral and subhedral crystals; hypidiotopic fabric; intercrystalline boundaries lobate and straight; some crystal-face junctions preserved; grain size between 0.1 and 0.4 mm. Classijication: Friedman - Centimicron-sized inequigranular, hypidiotopic dolomite; Gregg and Sibley - Polymodal nonplanar matrix replacement dolomite; Randazzo and Zachos - Inequigranular mosaic dolomite. Size scale -medium to coarsely crystalline. These fine- to medium-grained mosaic dolomites formed by replacement of fine-grained calcite matrix. The hypidiotopic fabric indicates recrystallization of burial dolomites. -> 1-3: Triassic: Roman mosaic stones, Hemmaberg near Globasnitz, Carinthia, Austria. Dedolomitization (-> 4 , 6 4 ) and Saddle Dolomite (-> 5) 4 I. Rhombohedral dolomite crystals have been dissolved. Molds were filled with equigranular microcrystalline Low-Mg calcite. Preferred solution of the core zones of dolomite rhombohedrons is a common phenomenon, because these zones often are richer in Ca than the periphery of the crystals (Randazzoand Cook 1987). SEM microphotograph. Late Jurassic: Southern Franconian Alb, Germany. 5 Late diagenetic 'saddle dolomite' cement crystals within a vug characterized by curved crystal faces (black arrow). The zonar dolomite has been internally corroded by low-saline formation-watermigrating along rhombohedra1cleavage planes and causing burial dedolomitization and the formation of intracrystalline pores (white arrows). VP: Vuggy porosity. Fluid inclusion analysis provides direct information about fluid movement and the timing of hydrocarbon migration. Saddle dolomites are characterized by large, nun-sized crystals, curved crystal faces and cleavages, undulose extinction, commonly ferroan composition,often fluid inclusions that make the crystals appear cloudy in thin sections and pearly in hand specimens. Saddle dolomites are commonly associated with sulphide mineralization, hydrothermal activity, and the presence of hydrocarbons at relatively deep burial depths. 6 Burial dedolomitization of a late diagenetic dolomite. Calcitization is restricted to the inner Ca-rich zones of former zonar dolomite crystals (white arrows). 7 Near-sugace early meteoric-vadose dedolomitization: Solution-enlarged molds of the former dolomite crystals are filled with meteoric calcite cements (arrows). 8 Near-suiface early meteoric-vadose dedolomitization. Crystals molds are geopetally infilled by gray vadose crystal silt (arrows) and granular meteoric cement. -> 5-8: Jurassic (Kinuneridgian): Subsurface,TB-3 Saulgau well, southwestern Germany. -> 1-3: E. Flugel and Ch. Fliigel 1997; 4-7: Meder 1987

Plate 39: Dolomite and Dedolomite

327

Dolomite Fabrics

Reviews summarizing the state of the art of the dolomite problem and the enigma cowrning the uneven distribution of dolomite rocks during the Precambrian and the Phanerozoic were given by Zenger et al. (1980), Land (1983), Machel and Mountjoy (1986), Hardie (1987), Given and Wllkinson (1987), Shukla and Baker (1988), Morrow (1990a, 1990b), Purser et al. (1994), Sun (1994), Burns et al. (2000), and Warren (2000).

7.8.1 Descriptive Criteria and Terminology of Dolomite Fabrics

lomite crystals as well as their mutual relationships are important for classifying those dolomite rocks whose original textures have been obscured or obliterated (Friedman and Sander 1967). Most dolomite nomenclature systems are descriptive and based on compositional grouping modified by textural terns (Folk 1959; Leighton and Pendexter 1962; Powers 1962; Bissell and Chilingar 1967). A 'coarsely crystalline oolitic dolomite' (Folk 1959), for example, is a dolomite characterized by ooids within a matrix consisting of dolomite crystals 0.25 to 1 mm in size.

The basic terminology used in describing dolomite Similar to limestones, dolomite rocks can be grouped according to mineralogical and chemical composition, rocks was developed by Friedman (1965; see Box 7.12) and expanded by Randazzo and Zachos (1983) and and to textural criteria. Sibley and Gregg (1987). The use of crystal size scales allows more extensive differentiation of dolomite fabVarious terms are in use for describing the amount of dolomite contents in carbonate rocks. The definition rics. Different crystal size limits are used by Friedman (1965), Randazzo and Zachos (1984) and Wright of these terms is not uniform and sometimes vague: The use of the term dolomitized may (a) simply in- (1992). The latter coined the terms dolomicrostone dicate that dolomitization has converted limestones (crystal size 10 pm). stone, or more specifically, (b) that the rock contains Crystal size distributions carry information on nuclemore than 10% replacement dolomite (Folk 1959). ation and growth (Sibley et al. 1993). Dolomitic refers to (a) a dolomite-bearing or doloThe nomenclature proposed by Randazzo and mite-containing rock that contains different amounts of the mineral dolomite. Dolomitic limestones yield a Zachos (Fig. 7.22A) offers a possibility for recognizconspicuous amount of the mineral dolomite, but caling dolostone types originating from 'homogeneous' cite is more important. The opposite is a calcareous and 'heterogeneous' dolomitization. dolomite (see Fig. 3.1). The ill-defined term magnesian limestone designates a rock composed of mixtures Practical use of this classification demands answers of calcite and dolomite or a limestone with some MgO to thefollowing questions: Crystal size: Very fine, fine, medium, or coarse crysbut no dolomite. talline? Dolostones are classified genetically into (1) syngeCrystal size texture: Equigranular, inequigranular netic dolostone (penecontemporaneously formed within (unimodal, polymodal) or extremely fine (aphanotopic)? the depositional environment),(2) diagenetic dolostone (formed by replacement of carbonate sediments or limeFabric: peloidal, mosaic, porphyrotopic, poikilotopic? stones during of following consolidation), and (3) epigenetic dolostone (formed by localized replacement Crystal distribution:Tightly packed, loosely packed, along postdepositional faults and fractures). isolated patches, crystals isolated or floating? Crystal shape: Anhedral, euhedral or subhedral?

7.8.1.1 Thin-Section Description and Terminology of Dolomite Rocks In thin sections, dolomites may or may not exhibit their original depositional and compositional textures. Calcareous dolostones and dolostones having preserved the original depositional components and textures are classified according to textural composition,crystal textures, and crystal fabrics. The shape and the size of do-

Following the Randazzo and Zachos classification an 'inequigranular, idiotopic, floating-rhombporphyrotopic dolomite fabric' is a fabric composed of predominantly euhedral, isolated crystals of different size, floating within a fine-grainedmatrix. An 'equigranular, microxenotopic, sutured mosaic fabric' is a fabric consisting of fine, tightly packed, predominantly anhedral crystals of equant size. Further examples for the use of both classifications are shown on P1. 39 and P1.40.

329

D o l o m i t e Fabrics

A

EQUIGRANULAR: Unimodal crystal size Peloidal

Sharp to diffuse clotting of crystals of uniform size

Sutured: Tightly packed anhedral crystals with no or little intercrystalline porosity

Sieve: Loosely packed anhedral to euhedral crystals; high moldic intercrystalline porosity

INEQUIGRANULAR: Multimodal crystal size

I

Mosaic

Sped Isolated and well-defined spots of fine to very fine crystals in a coarse mosaic groundmass

Porphyrotopic: Larger crystals enclosed in in a finer-grained groundmass

Fogged Irregular or diffuse areas of very fine crystals in a coarsemosaic groundmass

Contact-rhomb Loosely aggregated euor subhedral crystals in a fine-grained matrix

APHANOTOPIC: Crystals ~0.002 mm

Nonplanar: closely packed anhedral crystals with mostly curved, lobate, serrated, or otherwise irregular intercrystalline boundaries. Preserved crystal-face junctions are rare and crystals often have undulatory extinction under crossed nicols.

Planar-e (euhedral):most dolomite crystals are euhedral rhombs; crystal-supportedwith intercrystalline area filled by another mineral or porous (as in sucrosic texture).

Planar-s (subhedral): most dolomite crystals are subhedral to anhedral with straight, compromise boundaries and many crystal-face junctions. Low porosity and/or low intercrystalline matrix.

Poikilotopic

Floating rhomb Finer crystals lsolated euhedral or enclosed in subhedral crystals larger crystals in a fine-grained

.

. . . . .. ._ . . . .... .. . . . .:.. . . . .. . . . . . ._

_

'

'.

.

'

Fig. 7.22. Classification of dolomite fabrics. A: The basic terminology of crystallization textures defined by Friedman (1965) is used in the descriptive classification of Randazzo and Zachos (1983). Friedman's classification has been expanded by a finer distinction of subtypes, particularly of inequigranular fabrics. Size classes used are 0.256-0.016 mm,0.016-0.002 mm (indicated by the prefix micro), and 50% spar of early and late diagenetic as well as neomorphic origin ('Fagerstrom 1987). The cement volume may exceed that of organic framework or internal sediment. PI. 5016, P1. 14511. (b) Limestones composed almost totally of fibrous cement (commonly replaced and/or recrystallized), in which grains or in-situ biogenic material does not constitute a framework (*Wright 1992). Describes a diagenetic fabric! Coverstone - Carbonate rocks dominated by in-situ tabular or lamellar organisms covering, protecting and stabilizing broken debris ("Tsien 1981, 1984). Includes a part of 'bindstone', sensu Embry and Klovan (1971). P1.7814 Cruststone - Reef limestone consisting of densely packed organic crusts growing one upon the other (*Cuffey 1985). P1. 5117 Framestone - (a) Carbonate rocks containing in-situ massive sedentary fossils that built a rigid, three-dimensional supporting framework at the time of deposition (*Embry and Klovan 1971). (b) Reef frameworks dominated by the constructor guild (Fagerstrom 1987). P1.4211, P1. 7911, P1. 11612, P1. 14912 Globstone - Reef carbonate rocks, consisting of colonies attached one upon the other (* Cuffey 1985). Lettucestone - Reef carbonate rocks, built up by calcified organisms characterized by lettuce-like growth forms (e.g. phylloid algae), aiding in the formation of a framework and intra- and interskeletal trapping of sediment. The descriptive name recalls the similarity of the growth form to that of composite plants, e.g. cabbages (*Cuffey 1985). Platestone - A limestone composed of an in-situ accumulation of algal plates, e.g. of phylloid algae (* Davies and Nassichuk 1990). Pl. 58/1 Shellstone - Carbonate rock characterized by shells (e.g. bivalves or brachiopods) cemented upon one another (e.g. oyster banks). Most shells are in contact; there is no or only little sediment between the shells (* Cuffey 1985).Pi. 8714.

344

Bafflestones and Bindstones

Plate 41 Classification of Autochthonous Carbonates: BaMestones and Bindstones Marly textures used in the classifications of limestones are strongly biologically controlled. The term boundstone introduced by Dunham (1962) designates 'carbonate rocks showing signs of being bound during deposition' (e.g. reef limestones or stromatolites).This rather comprehensive term was later split up into several new terms, all of which demand a decision of the user about the potential control of sessile organisms on the formation of specific rock textures. Studying Devonian reef carbonates, Embry and Klovan (1971) proposed three terms to replace the name boundstone (see Fig. 8.5). The terms are widely used by geologists and palecologists interested in ancient reefs, despite considerable problems regarding the genetic meaning. The term boundstone should only be used if no decision on the mode of binding during deposition can be made. Frarnestones (see P1.41; Fig. 8.2) are characterized by massive in-situ fossils that constructed a rigid threedimensional framework during deposition. The in-situ fossils therefore form the supporting framework of the rock, with matrix material occurring in interstices of the fossils. Bina'stones (-> 2) contain in-situ, tabular or lamellar fossils that encrusted and bound sediment during deposition. I[n bindstones the matrix, not the in-sit~fossils, form the supporting framework of the rock. Baffjestones (-> 1) contain in-situ stalk-shaped fossils which trapped sediment during deposition by acting as baffles (i.e. reducing the rate of flow of water, thus causing deposition). The ingredients for recognizing a bafflestone are the presence of a large number of in-situ stalk-shaped fossils, and a good imagination on the part of the geologist. Plates 41 and 42 exemplify the application of the three terms and demonstrate the advantage of using a few more sophisticated reef rock terms. 1 Baflestone. The picture displays a vertical to slightly oblique section of a tabulate coral colony belonging to the group Auloporida and the genus Multithecopora Sokolov. Species of this genus are characterized by colonies composed of cylindrical very thick-walled branching corallites that are not in contact and arranged parallel to each other. The corallites of th43 erect colonies of Multithecopora syrinx (Etheridge) are arranged subparallel to each other or grow in various directions. The corals occur in situ within mini-mounds found in a shelf sequence formed during a relatively sea-level highstand (Fliigel and Krainer 1992). Maximum height of the mounds is 30 cm, maximum width 90 cm. Except for the tabulate corals, the mounds yield only a few foraminifera and ostracods. The fine-grained sediment of the mound is represented by (a) homogeneous micrite (M) within and between the aulo~loridcolonies and in the center of the mounds, and (b) inhomogeneous calcareous siltite (S) between corallites and colonies, reflecting the allochthonous background sedimentation, also indicated by siltstone beds overlying and underlying the mounds. The micrite was formed prior to the siltite, which increases in frequency towards the mound margin. The delicate upwards branching growth form of the coral implies that these organisms were able to filter out carbonate mud, owing to baffling of gentle currents. A slight increase in water energy as indicated by changes in the orientation of corals enabled the siltite sediment to be trapped between the corals leading to a more rapid accumulation of the mound sediment as compared with the adjacent area. The name bafflestone is justified because of (a) the occurrence of stalk-shaped fossils in life position (as shown by the geopetals (GP), and (b) abundant fine-grained sediment baffled and trapped by the organisms. SMF 7-BAFFLESTONE. Middle Carboniferous (Kasimovian): Carnic Alps, Italy. 2 Bind~rone.Vertical section of an irregularly laminated fenestral limestone. The limestone is part of a peritidal cyclic sequence consisting of subtidal, intertidal (this example) and supratidal members. The texture is characterized by altemating peloidal layers (PL), thin clotted micrite layers (ML) and intercalated horizontally elongated, laminate fenestral pores (F). The peloidal layers consist of fine and coarser micrite grains which are grain- or mud-supported. Mud-support occurs in association with micrite layers. Smaller micrite grains are well-rounded, larger grains are subangular. Some larger particles are composite grains (CG) and may represent 'black pebbles' (see Sect. 4.2.8). Spar-filled interspaces between smaller grains correspond to tiny tubes representing relics of microbial and algal filaments (white arrow). Many sparfilled fenestrae exhibit flat bottoms and slightly digitated roofs. Isolated grains within the fenestrae (black arrows) indicate a partial breakdown of the roofs. The vertical intrusion of a large clast (C) as well as the irregular shape of some fenestrae (F) indicate the soft consistence of the sediment. Despite the absence of in-situ lamellar fossils, this limestone is a bindstone because the grains were bound together by microbial activity concentrated in the micritic layers. The binding effect was enhanced by synsedimentary cementation in intergranular pores. SMF 21-BINDSTONE. Late Triassic (Pantokrator limestone, Norian): Didymi Mountains, Peloponnesus, Central Greece.

Autochthonous Carbonates: Framestone

mounds. It is common in protected environments and cryptic habitats. Coverstone refers to a texture characterized by insitu sedentary tabular or lamellar reef organisms covering, protecting, and stabilizing broken debris (Pl. 781 4). This type was included by Embry and Klovan in the bindstone category together with reef carbonates characterized by encrusting organisms that bind debris together, forming a secondary reef framework. For the needs of a field geologist, Cuffey's (1985) expansion of the differences in the relationship of reef organisms and texture may appear to be too rigorous. The terms, however, have the advantage of reminding us of the complexity of reef-building, which could not be described by the use of more widely defined terms such as 'boundstone' or 'framestone'. Cuffey's terms, therefore, will be especially valuable for studies dealing with the biological controls on reef building.

em reefs are gorgonian fans, alcyonarian whips, or the bladelike coenostea of hydrocorallines. Sea grass is also involved in baffling and trapping processes by its blades or roots. However, geologists may be baffled by bafflers. Ancient organisms believed to have acted as bafflers comprise sponges, bryozoans, bivalves and algae as well as some corals (Fagerstrom 1987). It is virtually impossible to demonstrate that the original organisms baffled sediment; therefore, baffling is inferred from functional morphology (erect and dominant upward growth; flexible, semirigid or rigid skeletons) and close intercolonial and intracolonial spacing. But both criteria may be misleading (Fliigel and Krainer 1992). If organisms are attributed to the baffler guild, additional criteria should be considered (e.g. composition of the fine-grained sediment between and around the 'potential bafflers', see PI. 4111; role of extrinsic factors).

Do rock names assist in reliable environmental interpretations ? The question can be discussed by using the term bafflestone, which implies the process of baffling. 'Bafling' refers to current reduction and gravityinduced dropping of sediment grains to the substrate. In reef limestones baffling organisms are rarely found in their growth position. Examples of bafflers in mod-

Controls on growthforms used in limestone classijications: Growth forms of organisms used to define textures of reef carbonate types are commonly thought to be related to water energy. But what controls the organic growth types used in textural carbonate classifications? Common reef fabrics may be placed into four groups, characterized by the morphology of the domi-

Plate 42 Classification of Autochthonous Carbonates: Framestones Framestones (a subdivision of boundstones) are defined by the occurrence of sessile benthic fossils that are densely spaced and preserved in life position. The morphology and distribution of the fossils should fit into an imaginary three-dimensional organic framework. Organisms contributing to the formation of framestones have changed during the Phanerozoic and include corals (Fig. 8.2)' coralline sponges (this example), stromatoporoids, rudist bivalves, and calcareous red algae. Framestone. The thin section of a reef limestone, cut obliquely to the growth direction of most of the sessile organisms, exhibits fossils, cement-filled interspaces and areas with fossils and micrite. Most of the fossils are coralline sponges, except for a few mollusk shells (MS) and crinoid colurnnals (C). Sponges include various 'sclerosponges' (S), inozoid sponges (IS) characterized by the absence of segmentation, as well as segmented sphinctozoid sponges (SS). The growth forms of these sponges correspond somewhat to densely spaced bundles of cylinders united by organic encrustations. Encrusters are sclerosponges,Archaeolithoporella (A)and Tubiphytes (T) - two microfossils of unknown systematic position (see P1.98/8). Isolated sponges as well as the concentrations of fossils were initially bound by microbial crusts and marine carbonate cement. The originally aragonitic cements and the biogenic encrustations formed a rigid, highly porous framework structure (accentuated by white spot lines). Large voids between the organic framework were partly occluded by marine-phreatic, fibrous isopachous cements (IC) and botryoidal cements (BC) as well as spany calcite mosaics (SCM). The remaining intergranular voids were occluded by large calcite crystals (black arrow) formed in a meteoric-vadose zone during exposure of the reef. The composition and diagenesis of these reef rocks are similar to Late Permian reefs in Texas and New Mexico (cf. P1. 145), both of which are very important hydrocarbon reservoirs. The name framestone is substantiated by the existence of an organic framework made by in-situ fossils and forming a rigid structure that was strengthened by coeval marine cementation. A massive growth form, as indicated in the original definition of the name, is not compulsory, because small densely growing sessile organisms can build frameworks as well. This sample comes from one of the very last reefs formed prior to the huge Permian-Triassic mass extinction. SMF 7FRAMESTONE. Uppermost Permian (Changsingian): Jiantinba, western Hubei, South China. Crossed nicols. Courtesy of Fan Jiasong (Beijing)

Dunham and Folk Classifications

nant members of the community (Fig. 8.1). In general, the distribution of growth forms of benthic shallowwater organisms reflect patterns of functional significance. Many authors underline the adaption of growth habits of reef organisms to water energy, e.g. strength, type, and duration of currents and waves. Specific growth forms are used as indicators of the existence of particular or dominating energy stages (see Sect. 12.1.I). There is, however, growing evidence that nutrient levels and resulting predator patterns as well as substrate conditions are major and probably dominating controls on the biogenic fabrics that are used in more sophisticated subdivisions of reef limestones (Wood 1995).

vestigations of cores, and in laboratory studies. The use of Folk's classification is more restricted to laboratory studies based on thin sections or peels.

8.3.1 Prerequisites Before classifying anything, it is necessary to determine what constituents occur (grain categories, matrix

and cement types). The second fundamental principle concerns the question of whether the constituent grains are grain- or mudsupported (see P1.43).

8.3.2 Original and Expanded Dunharn Classification

8.3 Classifications Based on Depositional Texture The most widely used classifications are those of Dunham (1962) and Folk (1959,1962). Dunham's classification can equally well be applied in the field, in in-

Figure 8.4 shows the original version of the Dunham classification, Fig. 8.5 the expanded and revised versions (Embry and Klovan 1971; Wright 1992).The criteria of the rock categories are depicted and discussed in P1.43 and P1.44.

Carbonates Dunham (1962)

Groundmass: Fine carbonate matrix

I

I

sparry cement +spar

Matrix-supported z 10%

Bioconstruction

Grain-supported

Grains: < 10% MUDSTONE

WACKESTONE

PACKSTONE

GRAINSTONE

BOUNDSTONE

Folk (1959, 1962)

Allochems: 50%

I

I packed BlOMlCRlTE

poorly washed I BlOSPARlTE -

BlOLlTHlTE -

-

--

Terrigenous Matrix-supported Sand: < 10% 1 10-25%

sandy MUDSTONE

Grain-supported > 25%

WACKE

;

I

SUBWACKE SANDSTONE

ARENITE

Fig. 8.4. Fossiliferous limestones classiJicationafter Dunham (1962) and Folk (1959,1962). Both classifications distinguish allochthonous limestones (mudstone, wackestone, packstone, grainstone) and autochthonous limestones (here called boundstone or biolithite). Limestones whose components were deposited as discrete grains are grouped according to mud-support or grain-support and the abundance of grains. The Dunham classification stresses the depositional fabric, the Folk classification tries to evaluate hydrodynamic conditions. Both classifications consider the dominating groundmass types. Note the divergent categorizationof limestones with abundant, densely packed grains and a fine-grained matrix or mixed fine-grained1 sparry groundmass (packstone).

349

Dunham Classification o f Limestones CLASSFlCATlON OF LIMESTONES (DUNHAM 1962)

NOT RECOGNIZABLE

I

10% rains MUDSTONE

I

I

10% grains VVACKESTONE 1

I

PACKSTONE

1 GRAINSTONE I

during deposition as shown by intergrown or lamination contrary to gravity, sediment-floored cavities that are roofed over by organic or questionable oraanic matter and are tooiarcle to be interstices BOUNDSTONE

CRYSTALLINE CARBONATE (Subdivide according classification designed to bear on physical texture or diagenesis)

I

EXPANDED CLASSIFICATION (EMBRY and KLOVAN 1971)

I

ALLOCHTHONOUS LIMESTONE ORIGINAL COMPONENTS NOT ORGANICALLY ORIGINAL BOUND DURING DEPOSITION

Less than 10% > 2 mm components contains lime mud (< 0.03 mm) Mud supported less than greater than 10% grains 10% grains ( > 0.03 mm and < 2 mm) MUDSTONE WACKESTONE

no lime mud

Greater than 10% > 2 mm components

Grain-supported

PACKSTONE

I

AUTOCHTHONOUS LIMESTONE COMPONENTS ORGANICALLY BOUND DURING DEPOSITION

GRAINSTONE

by organisms which

Matrixsupported

>2mm component supported

build a rigid framework

encrust and bind

FLOATSTONE

RUDSTONE

FRAME ST ON^

BOUNDSTONE BINDSTONE

act as bafflers

BAFFLES STONE

REVISED CLASSIFICATION (WRIGHT 1992) IDEPOSITIONAL

I

7Mixed supported

< 10%

Grain-supported

> 10% grains with grains matrix

no matrix

CALCIWACKEPACKGRAIN-MUDSTON s o -STONE -STONE FLOATSTONE RUDSTONE

BIOLOGICAL

I

DlAGENETlC Non-obliterative

In situ organisms rigid organisms dominant FRAME-

s

o

encrusting organisms acted to binding baffle organisms BOUND-ITONE

BAFFLE-,ONE

main component in cement CEMENT-STONE

I

many grain most grain contacts ascontacts microare microstylolites stylolites CONDENSED FITTED GRAINSTONE

1

Obliterative crystals > 10 pm SPARSTONE

C~stals< 10 urn

Fig. 8.5. Original, expanded, and revised Dunham classification. Embry and Klovan (1971) introduced the size aspect and distinguished grains smaller or larger than 2 mm. The new categories floatstones and rudstones correspond to wackestones and grainstones and packstones, respectively. Other changes concern the subdivision of the boundstone category (see Sect. 8.2). Wright (I 992) suggested terms describing diagenetic changes of depositional fabrics. The author emphasizes that the fine-grained matrix commonly called 'mud' is not necessarily identical with micrite, but corresponds to a matrix consisting of clay-sized imd silt-sized constituents. Note that in this scheme the term mudstone is replaced by calcimudstone and bindstone by boundstone owing to slight semantic problems.

8.3.2.1 Concepts The original c:lassificationincludes five textural classes. Two major groups are distinguished - (1) carbonates whose origini~lcomponents were organically bound together during deposition (boundstones), and (2) carbonates whose original components were not organically bound. The second group is subdivided according to mud-support (mudstone and wackestone) or grain-support (packstone and grainstone). The subdivision of mud-supported rocks is based on the < or > 10% grain bulk boundary. These rock names can be combined with grain type names in various ways: Ostracocl mudstme (mudstone containing < 10 total rock volume % ostracods), crinoid packstone (packstone containing a high percentage of closely-packed crin-

oids), ooid grainstone (grainstone containing predominantly ooids). Dunham proposed the notation 'lime' or 'dolomite' for characterizing the mineralogy, but only the reference to dolomite rocks (e.g. dolomite mudstone) appears necessary. The classification is highly flexible. The rock names should be complemented by all relevant field or laboratory observations. These can be sedimentary structures (e.g. medium-bedded, cyclic bioclast grainstones) and specific textural criteria (Stromatactis-bearingmicrobial mudstone). Limestones with small-scale mixtures of fabric types may be described by combinations of names: Peloid wackelpackstone corresponds to a sample with > 10% peloids and exhibiting wackestone and, to a lesser degree, packstone textures. Such close occurrence of wackestone and packstone textures may be caused by burrowing.

Grain-Support and Mud-Support

8.3.2.2

Discussion

Dunham's rock names are generally accepted despite some problems in the difficulty of unequivocally differentiating of the textural categories and their inferred environments. The greatest problem is that the classification strongly suggests a 'depositional' character of the textures. It must be kept in mind, however, that l i i e stones exhibiting mudstone, wackestone, packstone and even grainstone fabrics could also be products of diagenetic processes, such as micritization, cryptocrystalline calcite cementation or neomorphism.

What do mudstones and wackestones indicate about paleoenvironmental conditions? Mudstones are per definition 'muddy carbonate rocks containing less than 10 per cent grains'. Grains and grain-producing organisms are rare, possibly reflecting unfavorable environmental conditions. The sparsity of grains, however, could be a matter of scale and method: Many pelagic mudstones correspond to densely packed wackestones or even to packstones if studied with the aid of ultra thin-sections or the stereoscan electron microscope. Linking the deposition of mudstones and wackestones to low-energy settings may be a misinterpretation, be-

Plate 43 Allochthonous Carbonates. Basic Depositional Fabrics: Grain-Support and Mud-Support Major criteria for classifying allochthonous limestones are the depositional fabric, the abundance of various grain categories as discussed in chapter 4, and the type of fine-grained matrix and carbonate cements associated with the grains. The principal feature of the classification proposed by Dunharn (1962) is the distinction between grain-support (particle-support) and mud-support (matrix-support) describing the basic depositional fabrics: Grain-support (-> 1) is defined as a fabric with little or no mud and abundant sand-sized grains that are in three-dimensional contact and able to support each other. The fabric is comparable to that of grains in a pile of sand. Mudsupport (-> 2) is defined as a fabric whose sand-sized grains (at least 10% of the total rock volume) 'float', i.e. are embedded in, and supported by the muddy matrix. The fabric resembles pebbles within a mud puddle. Distinguishing grain-supported packstone from mud-supported wackestone may be difficult, because thin sections of both rock types can show grains 'floating' within a matrix and apparently not in contact. Because of the two-dimensional aspect of thin sections, irregularly shaped grains of a grain-supported fabric often do not appear to be in contact along every surface. Hence the point contact of grains is not necessarily a decisive factor in defining a 'packstone'. The degree of grain packing, grain density, and number of grains can be measured in thin sections using various methods (see Sect. 6.1.1.1). However, the number of grains alone is not conclusive for distinguishing between grain- and mud-support because even 20-30% of irregularly shaped large grains may form a self-supporting framework. Helpful but not unequivocal criteria in recognizing grain-support are: (a) lack of carbonate mud, (b) floored interparticle pores, (c) embowed grains, (d) close and overly close packing, and (e) abundant interparticle cement. The grain-/mud-support concept is fundamental in interpreting depositional controls (e.g. hydrodynamic conditions). The distinction between grain-supported and mud-supported fabrics reflects major differences in primary porosity types (Sect. 7.3) and, in turn, the potential of limestones as reservoir rocks (Sect. 17.1.5.2). Grain-support fabric, indicated by absence of mud, close packing of grains, and abundance of carbonate cement in interparticle pores. Most particles are aggregate grains, followed by some micritized bioclasts (foraminifera, F; mollusks, M), very small gastropods (G)and peloids. The grains are equally sized and very well sorted (standard deviation 0.35), see Fig. 6.3. The calcite cement in the interparticle pores appears white. The fine-grained lithoclastic grainstone forms a capping bed overlying a rudist patch reef. The capping beds correspond to mobile midshelf grain flats. SMF 17. MidCretaceous (Edwards Limestone, Comanche Formation, Albian): Belton, central Texas. Mud-support fabric indicated by grains 'floating' in lime mud. Skeletal grains are echinoderms (E), thin-shelled bivalves (fiarnents, FI), double-valved bivalves (B) and foraminifera. Note that geopetally filled cavities (black arrows) form a distinct horizon, possibly indicating shallow-burial dissolution. Aragonitic shells are dissolved and infilled with sediment (ammonite mold: white arrow). Original calcitic grains (echinoderms, filaments) are well preserved. The sample would be classified as echinodermfloatstone according to the echinodem fragments, which are larger than 2 rnm and comprise more than 10% of the rock. This name would fail to document the conspicuous bimodality of the sample and specific composition of the matrix. The total rock fabric is better described as 'crinoid floatstone with a fine-grained skeletal wackestone matrix rich in filaments'. The red nodular limestones originated in a moderately deep pelagic basin. Late Triassic (Hallstatt limestone, Carnian): Rotelstein, Styria/Austria.

t'1.rtr ii (ira111-Suppori m d Mud-Support

35 1

Dunham's Classification

Evidence of this can be seen in geopetal fabrics. These packstones may exhibit a micritic matrix occumng together with sparite formed as cement within the remainWhat is a 'packstone'? The term packstone is am- ing open pores. Precipitation of microcrystalline carbonate cement biguous with regard to its genetic implications. Packstones are characterized by grain-support as well as by within intergranular pores may result in a packstone mud matrix, indicating different energy levels during fabric. This is common in calcretes or beachrocks but deposition. How can this contradiction be explained? may also occur in marine carbonates. Compaction of wackestones, facilitated by dewaterHow can the matrix be introduced into the grain-supported fabric? Do all packstones represent depositional ing may produce a 'diagenetic packstone' fabric (Shim and Robbin 1983). textures? Uncemented grains may be welded together during Mud from low-energy deposits may filter into empty pressure dissolution resulting in a fabric that is compores of underlying, grain-supported high-energy de- monly classified as 'packstone', even though 'matrix' posits or settle out of the water flowing through pores. is very rare (Pl. 4711). cause binding organisms (e.g. microbes) may also fix mud within higher-energy settings.

Plate 44 Dunham's Classification of Carbonate Rocks: Mudstone, Wackestone and Packstone Mud- and grain-supported limestones (Pl. 43) are subdivided into textural categories according to the abundance of grains (Fig. 8.4). The complete rock name requires the combination of the name of the category with adjectives referring to grain kinds. Texture, mineralogy and frequency criteria can be included in the rock name. Mudstones are muddy carbonate rocks containing less than 10% grains measured as grain-bulk percent. The name is more or less synonymous with calcilutite. Wright (1992) replaced the name mudstone by calcimudstone because mudstone is also used for rocks consisting of silicate silt and clay material. This term refers to 'lithified material composed of greater than 90% by volume, silt and clay-grade calcite'. It is not synonymous with 'micrite'. The usual interpretation of mudstones is that they represent deposition of fine-grained sediment under lowenergy conditions allowing carbonate mud to settle in calm and quiet waters. However, it is now clear, that finegrained carbonates can be also formed by precipitation of microcrystalline carbonate cements (Reid et al. 1990). Examples are known from microbial carbonates (see P1. 8), terrestrial carbonates (caliche, PI. 12816) as well as seep and vent carbonates (Pl. 148). Mudstone is a useful term in the field and also for thin-section studies. It should be noted, however, that the ultrastructure of many mudstones corresponds to extremely fine-grained bioclastic or peloidal packstones and wackestones. Wackestones are mud-supported carbonate rocks containing more than 10% grains. High variations in abundance and type of grains call for a breakdown of this category into informal subcategories (e.g. packed or sparse wackestone, > or < 50% grains; -> 2 and P1. 118/1). Packstones are grain-supported muddy carbonate rocks exhibiting features pointing to deposition in agitated waters (grain-support) and criteria pointing to quiet-water deposition. Packstones have different origins including infiltrating of previously deposited mud-free grainstones, prolific production of grains in calm waters, mixing of sediment by burrowers, partial leaching of mud or compaction and dewatering of original wackestones (Shinn and Robbin 1983). A rather common feature of packstones in thin sections is the co-occurrence of mud (micrite) and irregularly distributed areas with sparry calcite. 1 Mudstone. Radiolaria-spicula mudstone (MS). Note the homogeneous texture of the matrix. The matrix is a fine-bioclastic micrite, corresponding to type 7 in Fig. 4.1. A different fabric is shown near the bottom of the picture (packed radiolaria-spicula wackestone; WS). The sample comes from well-bedded lithographic limestones formed in restricted parts of an open shelf environment. SMF 1. Late Jurassic (Vaca Muerta Formation, Tithonian): Zapala, Neuqutn Basin, Argentina. 2 Wackestone. Packed echinoderm wackestone. Most grains are crinoid plates. White arrows point to ophiurid elements, the black arrow to a foraminifera. The echinoderm grains are very worn. Straight elements are bivalve shell debris. The echinoderm limestone is part of a transgressive unit formed after drowning of Triassic reefs (Bohrn et al. 1999). SMF 9. Early Jurassic (Hettangian): Adnet near Salzburg, Austria. 3 Packstone. Bioclastic coral-algal packstone composed of corals (C), solenoporacean red algae (Pseudochaetetesasvapatii Pia; PS), bivalve shells, and gastropods (G).Arrows point to sediment-binding squamariacean red algae (Pseudolithothamnium album Pfender). The infilling of mud and fine skeletal debris in interstices between larger grains indicates grain-support. SMF 8. Early Tertiary (Kammbiihel limestone, Paleocene): Mooshuben near Mariazell, StyriaJAustria.

l'ldte 44 M u d \ t o n e . Wacheltone, Packstone

5 rnrn

7 - ,

1,

Dunham's Classification

Are grainstone fabrics infallible indicators of highenergy conditions near the depositional interface? Many grainstones represent deposition in current or wave-influenced settings where mud-grade sediment does not accumulate. It should be kept in mind that not all grainstones indicate the existence of high-energy conditions and that some 'grainstones' may be the result of specific depositional or diagenetic processes: Some grainstone fabrics are the product of a local accumulation of grains that have settled out of a flow of a mud-grain mixture while the mud is washed away. Other grainstones develop from the winnowing of mud from previously deposited grainylmuddy sediment. A too rapid production and accumulation of grains will prevent the contamination by mud.

The desiccation of subaerially exposed carbonate muds can produce 'diagenetic grainstones'. This process, called 'grainification' (Mazzullo and Birdwell 1989; Wright 1990) is common in peritidal, paludal, and pedogenic carbonates. Diagenetic grainstones are also produced by pressure solution during burial diagenesis,resulting in 'condensed grainstones' and 'fitted grainstones' (Wright 1992).

Floatstone and rudstone fabrics may be pitfalls in environmental interpretation: A coarse-grained texture can be better seen in larger rock samples and thin sections than in small ones, due to the variability in grain sizes of transported bioclasts.

Plate 45 Dunham's Classification of Carbonate Rocks: Grainstone, Floatstone and Rudstone The terms floatstone and rudstone were proposed for equivalents of wackestones, packstones and grainstones differing from these rock types in their larger mm- to cm-sized grains. Distinguishing floatstone/wackestone and rudstonelgrainstone is particularly meaningful for investigating reef limestones and allochthonous limestones deposited on slopes. Grainstones are grain-supported and mud-free carbonate rocks and consist of skeletal and non-skeletal carbonate grains. The absence of mud has various causes: deposition of grains in high-energy environments (e.g. in intertidal and shallow subtidal environments),rapid accumulation of grains allowing no coeval mud sedimentation (e.g. turbidites), deposition in current-controlled environments, or winnowing of mud from previously deposited grainfmud mixtures. Grainstones are highly variable with regard to grain type, shape, size, and sorting. Significance: Grainstones are common rocks in platform and ramp carbonates. They are usually related to the locus of wave energy absorption such as shorelines, shoals or shelf breaks. Here, grainstones form thick accumulations at the outer shelf margins or in inner ramp settings. 'Bank-margin sands' occur in tidal bar belts, tidal deltas, marine sand belts, back-reef areas, on beaches and in subaerial dunes. Note that accumulations of grainstones can also originate below the wave sweep base owing to current effects. Owing to their high interparticle porosities and the possibility of additional secondary moldic porosity caused by dissolution of grains (Pl. 2913, 4), grainstones are of particular interest as reservoir rocks. Floatstones are matrix-supported carbonate rocks yielding more than 10% grains larger than 2 mm. This 2 mm boundary creates difficulties in applying the term to fossiliferous limestones or limestones with oncoids because the size of skeletal grains and oncoids can only reflect growth stages. The use of a strict terminology would put a gastropod limestone yielding adult snails into the floatstone category and limestones containing the same but juvenile snails into the wackestone category. Note that floatstone and rudstone were originally proposed for reef carbonates and carbonate breccias. The 'matrix' of floatstones does not necessarily correspond to micrite, but often exhibits fine-grained textures that must be described separately (-> 2). Rudstones are grain-supported carbonates rocks containing more than 10% grains larger than 2 mm. Many breccias belong in this category. Rudstones and floatstones must be further characterized by compositional and textural criteria (-> 3). Formation of &tones needs erosion and transport. Erosion can be triggered by shallowwater settings allowing destruction by storms. Slopes are common depositional settings of rudstones. Grainstone. Medium-sorted oolitic grainstone. Note the difference in ooid sizes, indicating some transport. SMF 15-C. Late Triassic (Carnian): Obir, Carinthia/ Austria. Floatstone. Bioclastic coral (C)-gastropod (G) floatstone with a fine-grained calcirnudstone matrix. The originally aragonitic corals are strongly recrystallized. Arrow points to still preserved septae. SMF 8. Late Triassic (Kossen Formation): Allgau, southern Germany. Rudstone. Poorly sorted lithodastic rudstone. The large coated bioclasts are sclerosponges (S). Lithoclasts (L) correspond to reef debris deposited on reef slopes and redeposited as part of a megabreccia. Interparticle pores are filled with submarine and burial carbonate cements. SMF 6. Late Permian: Sosio, western Sicily, Italy.

F".ittx

d:

G i ~ i n , t o n e ,Floatstone, Rudstone

I crn

355

Folk's Classification

The terms have been proposed to characterize transported and resedimented fossils as illustrated by fragments of stromatoporoids. The original definition used was not intended for classifying limestones with large components that owe their size to biological growth processes (e.g. oncoids or colonial fossils). A distinction in the nomenclature of limestones with double-valved bivalves which are either smaller or larger than 2 rnm, will separate different biological growth stages whose size differences are not controlled by transport. This problem is commonly overlooked in the current use of the terms floatstone and rudstone. This is not of great importance as long as the texture types are not interpreted with respect to possible water energy levels or other environmental factors. Coarse-grained bioclastic particles such as phylloid algal plates or Halimeda blades can accumulate, producing a rudstone texture. This term, however, is inappropriate, because it infers transport and allochthonous sedimentation. The algal elements, however, are essentially in-place accumulations. Therefore, the term platestone (Davies and Nassichuk 1990) is more appropriate.

8.3.2 Original and Expanded Folk Classification

Folk (1959) distinguished three end members: (1) discrete carbonate grains ('allochems'), (2) microcrystalline calcite matrix, and (3) spamy calcite, regarded as pore-filling cement. Using the relative proportions of these three end members, the author distinguished 'sparry allochemical rocks' (consisting chiefly of grains cemented by sparry calcite cement), 'microcrystalline allochemical rocks' (consisting of microcrystalline matrix and various amounts of grains) and 'microcrystalline rocks' (consisting of microcrystallinecalcite and few or no grains). Further subdivision of these major groups is based on the ratio of grains to sparite to micrite as well as the type of grains. Quantitative boundaries include grain bulk percentages (> or < 10% grains with differentiation between 1-10% and < 1%) as well as proportions of special grain types related to the total of all grains. The Folk classification was designed to cover limestones, partly dolomitized limestones, 'primary' dolomites and replacement dolomites. Limestones were subdivided into eleven lithotypes, eight of them comprising allochemical rocks, two orthochemical rocks and one autochthonous reef rock. The kind of grains (only intraclasts, ooids, fossils and pellets were differentiated) and the ratio of grains, sparite and micrite are used in classifying and naming rock types.

A strict use of Folk's classification system requires consideration of several points when establishing rock Folk's classification is a useful and practical method names: Non-genetic meaning of grain names: Despite its for describing carbonate rocks, particularly in thin secgenetic definition, Folk (1962) regarded the term intions and peels. traclast for purposes of nomenclature 'as a broad class term without specifying the precise origin'. Using the term in a rock name, says nothing per se about the ori8.3.2.1 Concepts gin of the grain or about the environment. The term The basic philosophy of Folk's classification is that may refer to mud clasts reworked and transported by carbonate rocks are similar to siliciclastic rocks in their tidal currents or hurricanes as well as synsedimentary mode of deposition, because their textures are both con- cemented grain aggregates (grapestones), or merely trolled largely by the water energy in the depositional fragments of weakly lithified sediment that have been area. In calm water with only sluggish currents, car- retectured by burrowing. Similar to intraclasts, the use bonate mud (represented as micrite) with or without of the term pellet has no genetic implications. The disgrains is predominantly deposited. By contrast, vigor- tinction of pellets (i.e. peloids, see Sect. 4.2.2) and inous water energy hinders deposition of fine-grained traclasts is conventional and purely descriptive. material, thus favoring the sedimentationof winnowed Strict ranking of grains (allochems): Basically, sands with large amounts of pore space that is later filled Folk's rock names consist of two prefixes. The first with sparry calcite (sparite). The most important envi- (abbreviated by the prefixes intra-, 00-, bio- or pel-) ronmental break is between limestones with a lime-mud refers to the grain type, the second to the groundmass matrix and those with calcite cement, because this (sparite or micrite), see inset on P1.46). But many limeshould reflect the point where water energy becomes stones exhibit various amounts of different grain types. turbulent enough to wash out (winnow) the lime mud, Folk introduced a ranking system and regarded intrackeep it in suspension and carry it into lower energy lasts as the most important carbonate grains 'because zones (Fig. 8.6). of their implication of shallow water, lowered wave

357

Folk's Class~.fication Over

213 Lime Mud Matrix

-

-

Subequal

Over 213 Spar

Cement

Percent Allochems

0- 1 %

1 - 10 %

10 50 %

over 50%

Spar and Lime Mud

Sorting poor

Sorting good

Rounded and abraded

Representative Rock Terms

Micrite

Fossiliferous Miirite

Sparse

Packed

Unsorted

Sorted

Rounded

Biomicrite

Biomicrite

Pooriy washed Biisparite

Biosparite

Biosparite

Biosparite

1959 Terminology

Micrite

Terrigenou:; Analogues

Fossiliferous Micrite

Claystone

Lime Mud Matrix

Biomicrite Sandy Claystone

Clayey or Immature Sandstone

Biosparite Submature Sandstone

I

Mature Supermature Sandstone

5 Sparry Calcite Matrix

Fig. 8.6. Concept and textural spectrum of the Folk classification. Modified from Folk (1962). Note the increasing textural maturity from left to right. Disrnicrite is omitted in this figure.

base, or possible tectonic uplift'. Ooids are the next important group, followed by fossils and peloids. This ranking implies the knowledge of quantitative data: In 'intraclastic limestones' intraclasts must comprise more than 25% of all grains or in 'oolitic limestones' there must be more than 25% ooids regardless of the percentages of other grain types, which may be more frequent than ooids. However, more than one name-defining grain category may be important for rock naming. 'Fossiliferous oosparite', for example, would indicate that at least 25% of the grains are ooids, but fossils also occur in significant quantities. 'Fossil-bearing oosparite' would indicate that fossils occur, but that they are not frequent. These notations, of course, are not very precise, because both examples could contain between 1 and 74% fossils whose existence is lost in the name ! Grain sizes: Folk distinguished allochemical rocks with larger and smaller grains, using a median size limit of > or 25% of the grains) and the micritic matrix, the rock is called oomicrite. Because this name excludes the rather conspicuous intraclasts (I), some authors would prefer the name 00-intra-micrite or even, loosely, intra-00micrite, emphasizing reworking of the sediment as indicated by the large intraclasts. The sample indicates transport and redeposition of ooid shoals in protected ramp settings (see P1. 136). Lowermost Cretaceous: Subsurface, Kinsau well, southern Bavaria, Germany. 4 Biomicrite. Corresponding name: Red-algae bearing echinodermpackstone Sparry calcite Microcrystalline matrix matrix or Komia-bearing echinoderm packstone. The reference to Komia is important because of the facies-diagnostic value of Late Paleozoic red algae (see PI. 108). All the grains are bioclasts, usually echinoderms associated with a few shells (S) and a red alga (Komia, K; see P1.5616). There are >25% sandsized skeletal grains associated with a micritic matrix. Hence, the rock is a biomicrite. Packing is conspicuous, hence the name 'packed echinoderm biomicrite' is more appropriate (see Fig. 8.6). Pennsylvanian (Homacker Ooids Trail Formation): Limestone Ridge, Goosenecks, San Juan, Utah. 5 Intrasparrudite. Corresponding name: Poorly sorted lithoclast rudstone. Grains are intraclasts consisting of pelmicrite, cemented by various generations of submarine calcite spar. Because the grain size (> 2 mm) is included in the rock name the prefix 'rudite' is a part of the name. Slope environFossils ment. Early Jurassic: Adnet near Salzburg, Austria. (Biota) 6 Oosparite. Corresponding name: Poorly sorted ooid grainstone. Grains are large and small ooids (0;65%), bioclasts (25% bryozoans, B; foraminifera, F; shells, S), and cortoids (10%;C). Strohmenger and Wirsing would classify this sample as oobiosparite (see Fig. 8.7). Early Cretaceous: SubsurPeloids face, Ostermiinchen well, Bavaria, Germany. 7 Classification exercise. Try to find names for this sample, following the Pelsparite Pelmicrite proposal of Folk and Dunham. For explanation see Appendix. Middle TriBasic concept of the Folk classification. assic (Anisian): Karawanken Mountains, Austria.

Plate 4 6 E x a m p l e s for F o l k ' s Classification

359

Modified Folk Classification

Fig. 8.7. Modified Folk classification after Strohmenger and Wirsing (1991).

(Elf-Aquitaine 1975; Fliigel 1982). In reality, Folk's special depositional conditions, e.g. subaerial exposure) classification has often been applied in a rather loose as two new grain groups, adjustment of the percentage of individual grains manner without following the grain ranking concept (resulting in rather monstrous names like 'pelonco- from 25% to 20% for intraclasts, ooids and oncoids biosparmdite'!) or by creating names, not provided for and 40% for fossils and peloids, Incorporation of all the grains into the rock name as within the original classification, by including several grain types in order of increasing importance within long as they comprise >20% (for intraclasts, ooids or the rock name (Friedman and Sanders 1978). 'Intrabio- oncoids) or >40%for fossils and peloids). oncopelmicrite', for example would describe a micritic Owing to the introduction of oncoids as a fifth grain carbonate rock whose grains are predominantly peloids, type - they are in third position in the ranking list (infollowed by oncoids, bioclasts and fewer intraclasts. traclasts, ooids, oncoids, fossils and peloids) - the voluIn order to restore the reproducibility of Folk's clas- metric grain proportions have been changed, except for sification and to strengthen the value of rock names for the fossiVpeloid group. For Strohmenger and Wirsing paleoenvironmental interpretations, an expanded and the ranking list and the grain percentage must be remodified textural classification has been proposed by spected, even if, as a consequence, the most frequent Strohmenger and Wirsing (1991); see Fig. 8.7. grain type is not indicated by the first prefix of the rock name. Major modifications are: the introduction of new grain categories: (1) oncoids A strict use of the modified classification scheme (indicating special environmental conditions, e.g. dif- results in the differentiation of a maximum of 3 1 posferences in sedimentation rates, salinity, or substrate sible rock names. The practical steps involved in aptypes; see Sect. 4.2.4.1) and (2) extraclasts (indicating plying the classification are shown in Fig. 8.7.

Specific Classifications

36 1

8.3.2.2 Discussion

tors but also by the diagenetic history, he added five categories predominantly describing diagenetic rock Folk's classification has many advantages but also some types (Fig. 8.5): Three of these rock types are non-oblitpigalls in that not all the information included in mi- erative with regard to the primary depositional fabric crofacies features is revealed: (cementstone,condensed grainstone and fitted grainThe combined rock names (prefix for grains, suffix stone; P1.4713). Two categories, differentiated by crysfor matrix) are simple to learn and the terms can be tal size (using Folk's 1962 scale), are obliterative beeasily used in a descriptive way. cause they have lost their depositional fabric as a result The rock names can be freely combined with a num- of complete obliterative recrystallization or replaceber of modifying and qualifying adjectives. ment. Sparstones are composed of inequant spany calThe recognition of well-defined rock types facili- cite crystals forming a blocky mosaic, with a crystal tates facies-oriented studies because the basic binary size larger than 10 pm. The term microsparstone apprinciple is (oriented to major differences in the envi- plies to limestones consisting of calcite mosaics with ronmental controls of deposition. However, paleoen- crystals between 4 pm and 10 pm (Pl. 4712). vironmental interpretations which cling too strongly to the idea of low versus high energy controls on the sedimentation, rnay go wrong. The possibility, that low- 8.4.2 Some Nonmarine Carbonates Need energy conditions are only simulated by lime mud trick- very Specific Names ling down into empty pores of high-energy deposits or Many nonrnarine carbonates are characterized by that the fine-grained 'micritic matrix' does not correspond to a low-energy lime mud but instead represents particular components, fabrics, and microfacies types, a cryptocrystalline cement, should always be taken into which are difficult to describe using the standard textural classifications developed for marine carbonate account. A major shortcoming of the original classification is rocks. Some of these difficulties are caused by the strong the loss of information about grain diversity because impact of abiogenic factors on the formation of nonless frequent grain types are not indicated in the rock marine carbonates such as speleothems,travertine, tufa name. This difficulty can be overcome by using the and caliche. Particular rock names have been proposed for these limestones (Gebhardt 1988; Pedley 1990; modified classification of Strohmenger and Wirsing. Limestones containing both groundmass types rep- Riding 1991; Wright 1992; Koban and Schweigert resent problems in all limestone classifications. In 1993). Lacustrine limestones are better suited for apDunham's classification these types are incorporated plying standard classification schemes, especially that within the packstone group. Folk (1962), stressing the of Dunham, because carbonates formed within lakes wide textural spectrum of carbonates, proposed a tran- are more strongly controlled by biotic factors. Folk's sitional class ('poorly washed limestones'), defined as classification is less appropriate because of the strong having 113 to 213 spar and 213 to 113 micrite (Fig. 8.6). emphasis on hydrodynamic aspects, which may have Both Folk's and Dunharn's classifications can be had less influence on the textures of lacustrine carbonsharpened by using additional criteria reflecting pack- ates. Nonmarine carbonates formed at the margins of ing intensity (e.g. densely packed, loosely packed), the existence of large grains (e.g. rudite wackestone), the aquatic environments (e.g. lakes) may be strongly afdegree of winnowing (poorly or strongly winnowed), fected by pedogenic and meteoric processes overprintthe most frequent grain type, and the amount of terrig- ing primary textures. The Miocene carbonates of the Ries crater lake in Southern Germany are excellent obenous particles. jects for testing the efficiency of a classification, by combining descriptive criteria (following the Dunham scheme) and indications of overprinting (Arp 1995). 8.4 Specific Classifications Examples are shown in P1.48.

8.4.1 Diagenetic Changes in Depositional Textures

8.5 Classification of Wright (1992) revised both the Dunham (1962) clas- Mixed Siliciclastic-Carbonate Rocks

sification and its modification by Embry and Klovan (1971). Because the textures of most limestones are controlled not only by depositional and biological fac-

Sediments composed of mixtures of carbonate and siliciclastic material are common in near-coast environ-

Classifying Mixed Siliciclastic-Carbonate Rocks

-

ments, inner shelf settings as well as at high latitudes. Siliciclastic > Sand s Allochems > Name Micrite ? Carbonate ? Marl ? For a long time impure limestones with admixtures of allochemic sandstone siliciclastics have been neglected, in the context of both micritic sandstone no sediment classification as well as facies interpretation. Yes q Yes no qyes allochemic mudrock A descriptive classificationsystem (Fig. 8.8) was prono micritic mudrock posed by Mount (1985) using four components: (1) Sisandy allochem limestone yes sandy micnte liciclastic sand (sand-sized quartz, feldspar etc.), (2) non-carbonate mud (mixtures of silt and clay), muddy allochem limestone (3) carbonate grains or allochems (peloids, ooids, bio--,muddy micrite clasts and intraclasts >20 pm in size) and (4) carbonate mud (or micrite, defined as 2). Sparstones consist of sparry calcite crystals (>lo pm in diameter) forming inequant blocky mosaics. Microsparstones are composed of calcite crystals within the range of 4-10 pm. Non-obliterative textures include diageneticpackstones (-> 1,4) and condensed or jilted grainstones (-> 3) caused by modification of originally grain-supported textures by pressure solution during burial. However, pressure solution can also completely transform textures into new ones (-> 5, 6) and create new fabrics (see PI. 37). Displacive and replacive growth of micrite cements in pedogenic carbonates can result in a complete textural inversion. Diagenetic and biological factors are responsible for the formation of cementstones. The term refers to reef limestones consisting largely of replaced but recognizable marine cements occumng in association with predominantly encrusting organisms (see P1. 145). Conspicuous cementstones forming reefs on the paleoshelf occur in the Neoproterozoic Cap Carbonates, which worldwide cover the glacigene sediments of Early and Late Proterozoic age of the 'snowball earth' (James 2001). Diagenetic echinoderm packstone. Pressure solution has transformed a depositional wackestone into a diagenetic packstone fabric (Pl. 144). Bioclasts are separated by microstylolites. Note the almost complete absence of matrix. Mississippian: Muleshoe Mound, Sacramento Mountains, New Mexico, U.S.A. Microsparstone formed by meteoric recrystallization of a laminated micrite. Note the equant uniform crystals. Mississippian: Big Hill, Cairn, Canada. Condensed grainstone caused by compaction. Grains are flattened and compacted micrite clasts. Clasts are surrounded by thin rims of burial calcite cement. Both rims and grains were dolomitized. The mechanical compaction also affected the cements (arrows). Early Cretaceous (Purbeck facies, Berriasian): Subsurface, Kinsau well, Bavaria, Germany. Diagenetic stromatoporoid packstone. The original close packing of grains has been enhanced by pressure solution. Note stylolite seams (black arrow), grain penetration (GP) and irregular grain boundaries (white arrow). Most fossils are stromatoporoids (Stachyodes, S; Stromatoporella, ST) and thamnoporid tabulate corals (T). C: Rugose corals; B: Brachiopod shells. The matrix is a black argillaceous mudstone. Back-reef environment. Middle Devonian: Brilon, Sauerland, Germany. Mudsrone (M), grading into argillaceous lithoclast-bearing mudstone (LM), caused by pressure solution. Lithoclasts are relicts of former 'tuberoids'. Stylolaminated fabric (see Sect. 7.5.2). Late Jurassic: Subsurface, Saulgau well, southern Germany. Marly diagenetic lithoclast wackestonelJloatstone,caused by continued pressure solution of a former mudstone (-> 5). The former micrite matrix was converted into a marly matrix with up to 60 % insoluble residue. Note concentration of stylolite swarms (arrows) near pressure-solution resistant components floating within the marly matrix. Stylolaminated to stylocumulate fabric. Same locality as -> 5. -> 5 , 6 : Huber 1987

Plate a7 D ~ a g e n e t l cRoch Types

363

364

8.6 A Name for Your Samples: Some Practical Advice Which of the two major groups does your sample fit into? Autochthonous or allochthonous limestone? Autochthonous limestones: Use the classification proposed by Embry and Klovan (Fig. 8.1A and Fig. 8.5; PI. 41 and P1.42), if you are sure that you can imagine

Practical Advices

the role of the sessile benthic organisms in the formation of the reef limestone or of the microbialites. Otherwise use the sackname boundstone. Avoid the name biolithite. Integrate into the name the dominant or ecologically important fossil group, e.g. coral framestone, or more precisely, branched coral framestone, or, if you have good taxonomic data, Retiophyllia coral framestone (see Fig. 8.2).

Plate 48 Modified Textural Dunham Classification for Non-Marine and Palustrine Carbonates Many non-marine carbonates exhibit specific grains, fabrics and microfacies that are difficult to characterize by standard classifications developed for marine limestones. The Dunharn classification, reflecting hydrodynamic and biological controls of textures, can be successfully applied to some lacustrine carbonates, e.g. to those deposited in profundal and infralittoral environments. However, carbonates formed at lake margins as well as terrestrial carbonates (caliche, tufa, travertines, speleothems) are strongly prone to pedogenesis, meteoric diagenesis, and inorganic and microbial carbonate precipitation. Changes in dissolution and reprecipitation by pCO, play an important part. In studying lacustrine carbonates, Arp (1995) developed a modification of the Dunham classification that indicates pedogenic and early meteoric alterations by adding an interpretative attribute to the descriptive Dunham term. Attributes are transformed, neoformed or derived. The classification facilitates the description of 'palustrine carbonates' (shallow fresh-water and marsh deposits showing evidence of pedogenic modification related to subaqueous deposition and subaerial exposure). The term is taken from the French word for swampy or marshy. Diagnostic criteria of palustrine carbonates are an association of shallow-water, bioturbated mudstones and wackestones with a low-salinity biota of ostracods, gastropods and charophytes, intraclastic grainstones and packstones, and brecciated limestones displaying mottling, root tubules and vertically elongate fenestrae (pseudo-mikrokarst: Freytet and Plaziat 1982). Palustrine carbonates, originally described from the Late Cretaceous and Early Tertiary (Freytet 1984) have been reported from a variety of stratigraphic horizons (Carboniferous to Tertiary). The Florida Everglades are taken as a modem model of the development of palustrine conditions (Platt and Wright 1992). Examples on this plate are from the Upper Miocene lacustrine carbonates of the Nordlingen Ries impact crater (southem Germany). 1 Pedogenically transformed skeletal stromatolite (SS). A brownish pedogenic calcite crust (CC) fills up depressions. The vesicular fabric (VF) is caused by subaerial exposure within the supralittoral. Erect cyanobacteria filaments (F).Ehingen. 2 Pedogenically neoformed 'ooid' packlfloatstone. The pedogenic ooids ( 0 0 ) were formed in situ around ostracods (0) and detrital grains. Cladophorites-clast (C) derived from adjacent algal bioherms. The formation of soils in swamps caused pedogenic circumcrustations around former lacustrine grains. Hainsfarth. 3 Pedogenically neoformed nodule wacke/packstone (top and bottom) with horizontal 'craze planes' (CP) distinctive for palustrine facies (cracks caused by desiccation, center). The inverse gradation was formed in-situ by alternation of dissolution and desiccation. V: Multiple, fibrous and microcrystalline pendant cements and internal sediment in voids. Origin: Alternating swamp pedogenesis and prolonged meteoric-vadose conditions. Palustrine facies. Ehingen. 4 Pedogenically derived intraclast grainstone. Brownish pedogenic particles with schlieren-like cortices (arrows). Reworking of pedogenically transformed lacustrine grains and redeposition within the wave-exposed eulittoral. Ehingen. 5 Meteorically transformed intraclast rudstone consisting of reworked algal laminites (AL). Meteoric dissolution is indicated by the reduction of particles to flake-like components (black arrow) and partial replacement of micrite by sparite (white arrows). Note fracturing of meteoric-phreatic cements (FC). CH: Encrusted chiropteran larva. Interpretation: Deposition of coarse carbonate sands within wave-exposed eulittoral followed by meteoric-vadose dissolution during emersions. Ehingen. 6 Meteorically transformed intraclast wackestone. The vesicular structure (VS) is caused by meteoric dissolution. Root cavities (RC) have been enlarged by dissolution and filled with drusy calcite. Supralittoral. Ehingen-Belzheim. 7 Meteorically neoformed cement-framestone. The framework consists of laminated, fibrous sinter cements (SC). The nucleation bases are preserved as a few remnants of microbial micrite (MM). Dendroid sinters (DS) are speleothems. Interpretation: Alternation of the primary thrombolite fabric by meteoric diagenesis and formation of a new fabric. Central part of a spring mound. Ehingen-Belzheim. -> 1-7: Arp 1995

Practical Advises

Specify the composition of bindstones, e.g. fenestral bindstones, micritic bindstones, thrombolitic bindstones. Try to use the terms coverstone and cruststone (Box 8.1) to indicate the role of the organisms in binding. For bafflestones and framestones include clues to the texture of the fine-grained matrix surrounding the reefbuilding organisms, e.g. coral bafflestone with fmebioclastic wackestone matrix. Allochthonous limestones: Use the Dunham classification (Fig. 8.4; Pls. 44 and 45) first to separate your

samples into large groups. Look at grain- or mudlmatrix-support (Pl. 43). Use the term calcimudstone (Fig. 8.4) in order to avoid confusion with argillaceous mudstone. Distinguish between pure calcimudstone with hardly any fossils or other grains and fossiliferous or peloidal calcimudstones. Use the adjectives skeletal or bioclastic, peloidal, oolitic, toncolitic,and lithoclastic to describe the main constituents of your samples - e.g. oolitic grainstone (Pl. 4511). If you can differentiate between intra- and extraclasts use these terms, otherwise use lithoclast.

Distinguish between sparse and packed wackestones considering abundance and packing of grains. Sparse wackestones are characterized by abundant matrix and relatively few grains, packed wackestones by high amounts of grains. Try to distinguish packstones with fine-grained matrix from packstones with a mixed fine-grained and sparry matrix (Fig. 8.4). For grainstones, include additional clues to sorting and grain size - e.g. very well-sorted equally sized oolitic grainstone. These informations are essential for the discussion of porosity evolution. If you use the terms floatstone and rudstone (Fig. 8.5B) for larger grains, remember that the official 2 mm boundary does not reflect specific depositional conditions. The terms are useful if your sample consists of millimeter to centimeter-sized grains (e.g. calcirudites). If you want a more specific and sophisticated separation of your samples, use the Folk classification (Pl. 46), which allows better treatment with multivariate methods in a further step. Determine the abundance of the grain categories using point-counting or estimation methods (see Sect. 6.2). Determine the type of groundmass (micrite, sparite).

Plate 49 Classification of Mixed Siliciclastic-CarbonateRocks Mixed carbonate-siliciclastic deposits have been comprehensivelytreated by Doyle and Roberts (1988). Carbonate rocks containing between 10 and 50% of tenigenous admixtures must be distinguished in nomenclature from pure carbonates. A useful classification scheme was proposed by Mount (1985; Fig. 8.8). The plate shows several examples. A rock containing less siliciclastic than carbonate, more sand-sized siliciclastics than non-carbonate mud and more carbonate grains than rnicrite is termed a 'sandy allochem limestone' (-> 1). Prefixes and adjectives can be added to the rock names to include dolomitic sediments (e.g. dolo-allochemic sandstone), conglomeratic textures, and biogenic constituents. 1 Sandy allochem limestone. Nummulitid forarniniferal floatstone. The matrix consists of angular, fine-sand sized quartz grains (white) and glauconite grains, embedded within calcite micrite. Most nummulitids are represented by oblique and axial sections (see Kleiber 1991 for clues for determining axial sections). Near-coastal inner shelf setting. Early Tertiary (Lutetian, Eocene): Kressenberg, Bavaria, Germany. 2 Allochemic sandstone. Fossils are Nuia (N), mainly regarded as an alga. Note poorly sorted subangular and rounded quartz grains (Q) and carbonate lithoclasts (L). Cambro-Ordovician: Antarctica. 3 Muddy allochem limestone. Packstone. Most carbonate grains are worn and strongly altered foraminifera1tests (fusulinids, F). Note distinct burrowing (B). Burrows are compacted. Middle Carboniferous (Kasimovian): Carnic Alps, Italy. 4 Coarse-grained sandy allochem limestone. Carbonate grains are reworked barnacles (B). Note poor sorting of quartz grains. The limestone was deposited in a high-energy near-coastal temperate setting. Barnacles are highly resistant to abrasion. Late Tertiary (Early Miocene): Burgschleinitz near Eggenburg, Austria. 5 Sandy allochem micrite. Sandy mollusk shell packstone. Note gastropods (GA) and coated bivalve shells (BS). All the primary aragonitic mollusk shells are dissolved. Near-coast mixed siliciclastic-carbonateshelf. Middle Jurassic (Bajocian): Analananga near Sakaraha, southwestern Madagaskar. 6 Micritic sandstone. Note poor sorting of the detrital quartz grains. Carbonate grains are lithoclasts with fermginous coatings (L), echinoderms (E), and coral fragments (C). The high number of angular quartz grains in combination with well-rounded quartz pebbles points to the relatively close proximity of a shallow marginal-marine area to a hinterland. Bioclasts were probably reworked in off-coast positions and redeposited within the siliciclastic sand. Late Jurassic (Oxfordian): Jubera, southwest of Pamplona, Spain. -> 5: Sample provided by M. Geiger, Bremen; -> 6: Benke 1981

368

Be aware that rnicrite and sparite have a priori no genetic significance. The name sparite was designed for 'sparry calcite cement', but the common use also includes sparry calcite mosaics representing recrystallized fine-grained matrix. While constructing the name of your sample, indicate clearly whether you are strictly following the increasing ranking order proposed by Folk or whether you prefer the reversed ranking. Imagine for a minute that about 20% of the particles of your micritic limestone are intraclasts, 75% bioclasts, and 15% peloids would you give your sample the name intrapelbiomicrite or biointrapelrnicrite, as many people do? If the grains exceed sand-size ranges, use the syllable rud-, e.g. intrasparrudite (a limestone consisting of millimeter-sized or larger intraclasts occurring within a sparry groundmass, P1.4615) If you prefer a strict guideline leading you to a welldefined and reproducible name, use the expanded Folk classification proposed by Strohrnenger and Wirsing (Fig. 8.7). Utilize the open-minded character of the original Folk classification, which allows the rock name to be combined with additional descriptive characters - e.g. black, poorly laminated pelmicrite (a common lagoonal limestone), or red nodular pelagic biomicrite (a common open-marine deeper-water limestone). Because of the value of fossils as paleoenvironmental proxies, a specification of the fossil types is desirable - e.g. dasyclad green algal biosparite or pectinid mollusk biomicrudite. Consider diagenetic alterations in depositional fabrics (Pl. 47); Fig. 8.5). The terms proposed by Wright (1992) are useful, particularly those which characterize alterations that have not completely obliterated the original texture. Try to differentiate between transformed and neoformed fabrics in pedogenic or meteoric modified carbonates (PI. 48). Mixed siliciclastic-carbonate rocks require specific names, e.g. those proposed by Mount (Pl. 49, or by Folk (1959), who uses adjectives (e.g. clayey, silty, sandy). And read the quotation at the beginning of this chapter again! Basics: Classification of carbonate rocks

4,G. (1995): Lacustrine biohems, spring mounds and marginal carbonates of the Ries-impact crater (Miocene, Southern Germany. - Facies, 33,35-90 Baisert, D. (1967):Analyse der Nomenklaturen sedimentiirer Kalkgesteine. - Zeitschrift fiir angewandte Geologie, 13, 642-650 Chilingar, G.V. (1960): Notes on classification of carbonate

Basics: Limestone Classification rocks on the basis of chemical composition. - J. Sed. Petrol., 30, 157-158 Cuffey, R.J. (1985): Expanded reef-rock textural classification and the geological history of bryozoan reefs. - Geology, 13,307-310 Davies, G.R., Nassichuk, W.W. (1990): Submarine cements and fabrics in Carboniferous to Lower Permian reefal, shelf-margin and slope carbonates,northwestern Ellesmere Island, Canadian Archipelago. - Geological Survey of Canada, Bulletin, 399, 1-77 Dunham, R.J. (1962): Classification of carbonate rocks according to depositional texture. - In: Ham, W.E. (ed.): Classification of carbonate rocks. A symposium. - Amer. Ass. Petrol. Geol. Mem., 1, 108-171 Embry, A.F., Klovan, J.E. (197 1):A late Devonian reef tract on northeastern Banks Island. N.W.T. - Bull. Canadian Petrol. Geol., 19,730-781 Fagerstrom, J.A. (1987): The evolution of reef communities. - 600 pp., New York (Wiley) Folk, R.L. (1959): Practical classification of limestones. Amer. Ass. Petrol. Geol. Bull., 43, 1-38 Folk, R.L. (1962): Spectral subdivision of limestone types. - In: Ham, W.E. (ed.): Classification of carbonate rocks. A symposium. -Amer. Ass. Petrol. Geol. Mem., 1,62-84 Ham, W.E. (ed., 1962): Classification of limestones. A symposium. -Ass. Petrol. Geol. Mem., 1,279 pp. Leighton, M.W., Pendexter, C. (1962): Carbonate rock types. - In: Ham, W.E. (ed.): Classification of carbonate rocks. Asymposium. -Amer. Ass. Petrol. Geol. Mem., 1,33-61 Mazzullo, S.J., Chilingarian, G.V., Bissell, H.J. (1992): Carbonate rock classification. - In: Chilingarian, G.V., Mazzullo, S.J., Rieke, H.H. (eds.): Carbonate reservoir characterization: a geologic-engineering analysis, part I. - 59-108, Amsterdam (Elsevier) Mount, J. (1985): Mixed siliciclastic and carbonate sediments: a proposed first-order textural and compositional classification. - Sedimentology, 32,435-442 Oates, J. A.H. (1998): Lime and limestone. Chemistry and technology, production and uses. - 474 pp., Weinheim (Wiley-VCH) Plumley, W.J., Risley, G.A., Graves, R.W., ~ a l e M.E. i (1962): Energy index for limestone interpretationand classification. - In: Ham, W.E. (ed.): Classification of carbonate rocks. A symposium. - Amer. Ass. Petrol. Geol. Mem., 1,87-107 Strohmenger, C., Wirsing, G. (199 1): A proposed extension of Folk's textural classification of carbonate rocks. - Carbonates and Evaporites, 6,23-28 Tsien, H. (1994): Contribution of reef building organisms in reef carbonate construction. - Courier Forschungsinstitut Senckenberg, 172,95-102 Wood, R. (1993): Nutrients, predation and the history of reefbuilding. - Palaios, 8,526-543 Wood, R. (1995): The changing biology of reef-building. Palaios, 10,517-529 Wright, V.P. (1992): A revised classification of limestones. Sed. Geol., 76, 177-186 Further reading: K 145

9 Limestones are Biological Sediments

Most limestones are directly or indirectly influenced and control.led by biological processes. The present chapter deals with the formation of carbonates by microbes and benthic encrusting organisms, and with the destructive role of micro- and macroborers. Knowledge of constructive and degrading processes is essential in evaluating carbonate budgets.

algae, (b) extracellularpolymeric substances (EPS; accumulating outside the cells to form a protective and adhesive matrix that attaches microbes to the substrate), (c) biofilms (submillimetric veneers of bacterial communities in an EPS matrix), (d) microbial mats (millimeter-sized complex layers composed of filamentous cyanobacterian algae and diatoms, and able to trap sediment), and (e) organomineralization (precipitation of CaC03 in association with nonliving macromolecules independent of organic activity). See Riding (1 99 1, 9.1 Microbial Carbonates and 2000), Van Gemerden (1993), and Riding and Awramik Stromatcolites (2000) for further explanations. The eminent role of bacteria and other microbes in Microbes encompass bacteria, fungi, small algae and the formation of carbonate rocks was summarized in protozoans. Bacteria comprise two major groups Sect. 4.1.2 and is discussed in the following paragraphs Archaebacteria and Eubacteria, now respectively called which also cover controls and the terminology of miArchaea anti Bacteria (including Cyanobacteria). The sedimentologically important Cyanobacteria crobial carbonates, and examine the importance of stro(Sect. 10.2.1.1) are aerobicphototrophs, living in shal- matolites. low-water and using sunlight as energy. Cyanobacterial calcification is associated with the photosynthetic uptake of CO, and/or HCO; that raises alkalinity (Pente- 9.1.1 Bacterial Contribution to Carbonate cost and Riding 1986; Merz-Preiss 1999) and leads to Precipitation calcificatiorl of the mucilaginous sheaths. Present day, intense cyanobacteria calcificationappears to be essen- Microbial precipitation of calcium carbonates played a tially a freshwater phenomenon and is rare in modern vital role in the development of Proterozoic and Phansubtidal environments, by contrast to ancient cyano- erozoic carbonate platforms and reefs. The importance bacteria which occupied tidal and subtidal environ- of bacteria and cyanobacteria in the formation of finegrained carbonates in natural aquatic environments has ments. Many other bacteria are anaerobic heterotrophs and long been a matter of discussion, starting with the retake their energy from the decomposition of organic search of Drew (1911, 1913) and Black (1933) on the material to inorganic components by redox processes. action of denitrifying bacteria in tropical and in temThese bacteria can occupy lighted and shallow as well perate seas, followed by observations on calcium caras dark and deep-water settings, and are responsible bonate precipitation in seawater and freshwater envifor ammoni hcation, denitrification, sulfate reduction, ronments (Pentecost 1985). Reviews discussing this anaerobic sulphide reduction and methanogenesis pro- topic have been published by Cohen et al. (1984) and cesses. These processes can lead to HC03- concentra- Jones (1985). Many researchers have demonstrated that tion and increasing alkalinity favoring fine-grained life processes of marine bacteria and the decomposiCaC03 precipitation (Knorre and Krumbein 2000) in tion of organic matter by bacteria cause physicochemical changes in the microenvironment that can result in the form of micrite. calcium carbonate precipitation. This has been proved Microbial CaC03 precipitation is triggered by vari- in laboratory experiments and observed in various modous processes associated with (a) bacteria and small em carbonate-producing environments (soils, freshwa-

370

Recognizing Microbial Carbonates

ter and marine realms, particularly in lagoons; Castanier et al. 1989; Chafetz et al. 1991; Folk 1993; Arenas et al. 1993; summary by Buczynski and Chafetz 1993). Experiments indicate that bacteria trigger the precipitation of aragonite and calcite, exhibiting distinct morphologies that seem to be limited to bacterial contribution. The size of individual crystals, spheres and rods ranges between 0.1 and 0.4 pm; that of crystal aggregates between 5 and 100 pm. Comparable morphologies have been observed in laboratory cultures and in modem carbonate sediments. Because most bacteria except for cyanobacteria, are indifferent to light, bacterially-controlled carbonate precipitation is not restricted to shallow environments, but also occurs in deeper subtidal settings, various cryptic habitats and in deep restricted basins. A strong microbial contribution of microbes to the formation of 'mud mounds' is advocated by many authors (e.g. Pratt 1982; Lees and Miller 1985; see Sect. 16.2.2).

to basin traverses (Precambrian: Hoffman 1974; Late Devonian: Playford et al. 1976; Late Jurassic: Leinfelder 1993; Tertiary: Braga et al. 1995).

Biological versus environmental controls:The main processes of microbial carbonate formation are (I) trapping (agglutination) of sedimentary particles, (2) biomineralization (calcification) of organic tissues, and (3) mineralization (superficial precipitation of minerals on organisms and/or sediment). Fine-grained carbonate is trapped and produced within microbial mats, occumng under a wide range of environmental conditions in nonmarine and marine sites. The mats are dominated by various phototrophic, chemotrophic and heterotrophic microorganisms (cyanobacteria dominating in the top layer; colorless sulfur bacteria, purple sulfur bacteria, and sulfate-reducing bacteria harboring the underlying layers). Other numerically less important groups are nitrifying and denitrifying bacteria and methanogenic bacteria. The activity of aerobic heterotrophic organisms leads to oxygen depletion. Fermentative organisms provide growth substrates for sulfate-reducing bacteria. The vertically laminated structures develop as a result of microbial growth and activity sediment trapping and binding in the organic matrix, and sedimentation (Van Gemerderi 1993). The shape and macrofabric of microbial carbonates are strongly influenced by variations in the depositional environment. Important controlling environmental parameters are the grain size of the substrate, the penetration of light, sedimentation and erosion rates, and grazing pressure (Walter 1976). Sedimentation and microbial mat composition are sensitive to water movement and light, respectively, and change with water depth. This is reflected in the morphology, texture and microfabrics. Examples were described from various shelf

Microbial carbonates are recorded by specific textures occurring within a wide range of scales. Common features are dense autochthonousmicrites, micro- to megascaled laminated fabrics (e.g. stromatolites), millimeter- to centimeter-sized micritic crusts, non-laminated micritic and peloidal structures, and limestones exhibiting tiny tubelike microfossils referred to as remains of cyanobacteria.

9.1.2 How to Recognize Microbial Carbonates? Increasingly more authors support the idea of a strong microbial impact on the formation of Paleozoic and Mesozoic limestones, using external appearance, internal fabrics and geochemical signatures as evidence (see Facies, vol. 29, 1993). Box 9.1 lists some criteria which are commonly used as evidence for a bacterial contribution to the formation of limestones.

9.1.3 Describing and Classifying Benthic

Microbial Carbonates

9.1.3.1 Terminology and Descriptive Criteria Microbial carbonates are carbonate deposits produced or localized by benthic microbial communities (Riding 1990) living in marine, marginal-marine,freshwater and terrestrial environments.The complex associations of bacteria, cyanobacteria (cyanophytes, bluegreens) and algae embrace photosynthetic prokaryotes, eucaryotic microalgae and chemoautotrophic as well as chemoheterotrophic microbes. In addition, encrusting invertebrates (e.g. foraminifers) may be of some importance (Sect. 9.2). Communities creating microbial carbonates are termed microbial mats (Gerdes and Krumbein 1987) or algal mats, reflecting the densely interlayered and intertwined orientations of the filamentous and coccoid cells involved and the resulting biolarninated sedimentary structures.

Biolaminites characterized by organic-rich laminae and microbial mats are an essential criterion of microbially induced sedimentary structures (Noffke et al.

Benthic Microbial Carbonates

1996). The term microbialite (Burne and Moore 1987; changed to microbolite by Riding 1991) characterizes 'organosedimentary deposits that have accreted as a result of benthic microbial community trapping and binding deltrital sediment andlor forming the locus of mineral precipitation'. Microbialite is often used as an overall term, but also as a term restricted to non-laminated microbial carbonates only in contrast to stromatolite, which denotes laminated benthic microbial deposits (Riding 1999); see Box 9.11 using the classification deve:loped by Logan et al. (1964; Fig. 9.3). The fabric describes lamination or non-lamination and the spatial coniposition (e.g. clotted). Microstructure refers to the type and fabric of the constituents (commonly mic~iteor microspar, various grains, and fenestral spar-filled voids, sometimes encrusting fossils and borings).

9.1.3.2 Classification of Benthic Microbial Carbonates

Box 9.2 summarizes the current classificationof microbial carbonates (examples in PI. 8 and P1.50). Comments on non-laminated microbialites Thrombolites (PI. 811, 6, P1. 5015, P1. 13115). The term was proposed as a field term for 'cryptalgal structures related to stromatolitesbut lacking lamination and characterized by a macroscopic clotted fabric' (Aitken 1967). The name refers to micrite clots. The clots differ in color, form and/or texture from the intervening area and create a blotchy fabric. Kennard and James (1986) called the components of thrombolites mesoclots, which are typically dark colored and have a microcrystalline texture. They display a variety

Box 9.1. Which thin section and SEPM criteria provide evidence of a microbial contribution to the formation of limestones? Veryfine-grained dense micritic matrix: Dead calcified bacterial cells can become calcified (Knunbein 1979) and form discrete micron-sized bodies. Small varieties found in micritic carbonates have been attributed to nannobacteria (size 0.05 to O.:! pm) because the sphere- and bean-shaped objects seen in SEM exhibit similarities with regard to morphology and cluster-like distribution patterns (Folk 1983). Caution is needed because similar objects can be also formed abiotically (Kirkland et al. 1999, Abbott 1999). Laminated and undulated micritic structures: Comparing of laminated textures of fine-grained limestones with microtextures produced by bacteria in laboratory experiments shows that micritic finely laminated and undulated microstructures (Pl. 615, P1. 5014) can be formed by microbes that contribute to the precipitation of seafloor automicrite (see Sect. 4.1.1). Construct,;vemicrite envelopes: Some of these envelopes (see Sect. 4.2.3) may represent biofilm calcification (Perry 1999). Bacteria adhere to surfaces for stability and create calcifying biofilm communities augmented by other microbes. Clotted fabrics: Clotted fabrics (Pl. 1011) are widespread in stromatolites and thrombolites. The fabric appears to represent EPS calcification.It has been referred to as spongiostrome (Giirich 1906) and structure grumeleuse (Cayeux 1935), and can grade into dense micrite. Diffusely clotted micrite often forms clusters of rounded aggregates within microsparite and is associated with filamentous microfossils (Guo and Riding 1992). Calcimicrobes: Calcification of microbial, extemal polysaccharide-protected, sheets produces calcified fossils (calcimicrobes, e.g. Girvanella, Cayeuxia, P1. 813, P1. 53) which are represented by tiny tubes with micritic walls. Most of these fossils are cyanobacteria, and occur in association with finely peloidal and clotted fabrics. Peloids: Siilt to sand-sized micritic grains and aggregates (20-60 pm) are common constituents of modem tropical carbonates. In-situ precipitation has been observed in Holocene reefs (Lighty 1985).These Mg-calcite components have been regarded as cement (Macintyre 1984, 1985), but also as calcified bacterial aggregates rimmed by euhedral calcite crystals (Clhafetz 1986; P1. 815; see Sect. 4.2.2). Potential microbial peloids are widespread in ancient reefs (PI. 8/6), in stromatoli tes and thrombolites. Microbial ooids: The recognition of bacterially constructed carbonate crystals and grains (Fig. 4/24) in recent environments and the similarity of these grains with particles occumng in ancient carbonates (Gerdes et al. 1994; Reid 1987; see Sect. 4.2.5) offer a clue to the microbial character of some ooids enclosed in laminated textures. Microspar and spar: Fibrous, equant and dendritic spar precipitates (Hofmann and Jackson 1987) occur as extemal crusts on atrganic tissue and mineral surfaces of microbial carbonates, particularly those originating in fresh water (tufas and traventines, karst) and schizohaline settings. These spars also form rosettes and spherulites around cyanobacterial precipitates and on bacterial cells (Guo and Riding 1992; Defarge et al. 1996). Pores and allochthonous grains: Discrete voids ranging from tiny interstices to large growth cavities (Pratt 1995) are often associated with microbial carbonates. They include irregular fenestrae and tidal flat birdseyes. Trapped grains are important constituents of these carbonates (Pl. 2014, P1. 5015, P1. 12411).

Organosedimentary Deposits

Box 9.2. Classifzcation of organosedimentary deposits controlled by benthic microbial communities (after Riding 2000).The classification is based on macro- and microfabric criteria. The presence or absence of lamination is used in distinguishing two major groups. Note that some authors restrict the term rnicrobialite to nonlaminated microbial carbonates, whereas others use the term as a synonym for all microbial carbonates.

Microbialites (Burne and Moore 1987): Non-laminated benthic microbial deposits: Thrombolites (Aitken 1967): Clotted mesofabric. Dendrolites (Riding 1988): Dendritic mesofabric, that may be distinct, crude or diffuse. Leiolites (Braga et al. 1995): Structureless, aphanitic mesofabric. Cryptic microbialites (Riding 1991):Lack distinct mesofabrics, but typically possess micritic,clotted or peloidal microfabrics. Stromatolites (Kalkowsky 1908): Laminated benthic microbial deposits: Agglutinated strornatolites (Riding 1991): Produced by trappingbinding of particulate sediment. Well-laminated and fine-grained, or crudely laminated and coarsegrained. Skeletal strornatolite (Riding 1977):Produced by in-place organisms that are commonly preserved as calcified fossils. Freshwater tufa stromatolites (Riding 1991): Produced by encrustationsof external sheets of cyanobacteria and green algae. Terrestrial stromatolites (Riding 2000):The term refers to fabrics seen in laminar calcretes. of shapes (subrounded, amoeboid, grape-llke, arborescent, digitate, pendant) and occur isolated, interconnected, or amalgamated. The clots can make up in excess of about 40% of the volume of a thrombolite rock. Mesoclots may be lobate, cellular, microspherulitic, grumous, peloidal, vermiform, or mottled. Calcified microfossils such as Renalcis, Girvanella and Nuia are common in Paleozoic thrombolites. The clots are interpreted as a complex of irregular agglutination, insitu calcification of coccoid or coccoid-dominated microbial communities, skeletal encrustation, and erosional processes, but may result also from calcified filaments (Bume and Moore 1987).Walter and Heys (1985) consider some thrombolites as being disturbed stromatolites in which the original laminated structure was disrupted and modified by bioturbation or subsequent diagenesis. In thin sections thrombolites show a complicated microstructure. The individual micrite masses may consist of (1) dense micrite, (2) clotted micrite, (3) peloids of irregular shape and size, sometimes retaining porostromate structures, (4) calcite spherulites consisting of radially-oriented, non-ferroan calcite, typically 1220 pm in diameter with a cloudy micrite core, and

(5) various microfossils encrusting micrite and peloids. Many thrombolites contain micro-encrusters. Riding (2000) distinguished calcified microbial thrombolites typically displaying well-defined clots, coarse agglutinated thrombolites that incorporate sandand even gravel-sized sediment and commonly exhibit complex internal variations (e.g. Shark Bay), some of which are associated with sponge-tissue degradation (Reitner 1993; Reitner et al. 1995); arborescent thrombolites associated with decimetric dendritic fabrics (Schmitt and Monninger 1977, Armella 1994); tufa thrombolites occurring in freshwater lakes and streams (Moore and Burne 1994). Thrombolites are essentially subtidal, common in deeper-water settings, and form columns, domes, layers and thick crusts, typically dome-shaped meter-scale doughnut-like masses (kalyptrae: Luchinina 1975; Rowland and Gangloff 1988). They reflect an irregular and uneven supply of sediment on surfaces that were patchily colonized by microbes. Thrombolites range from the Neoproterozoic to the modem and were important as constituents of smallscaled reefs throughout much of the Cambrian and Early Ordovician (Shapiro and Rowland 2002; Webby 2002). Reports of post-Ordovician thrombolites are rare (Silurian: Kahle 2001; Late Jurassic: Leinfelder and Schrnid 2000; Cretaceous: Neuweiler 1993; Miocene: Riding et al. 1991). Dendrolites (Pl. 814). These microbialites form large domes and columns that may be roughly layered, and exhibiting bush-like dendritic fabrics, either vertically erect or pendant. The fabric differs in color from adjacent areas and is distinct, crude or diffuse. Dendrolites formed by porostromate microfossils (e.g. Epiphyton; P1.8214) are common features of Early Paleozoic reefs, growing at the surface, within dark cavities (endostromatolites: Monty 1982) or in fissures (Pl. 814). Rapid calcification and early cementation between the bushy fossils resulted in the formation of an organic framework that provided hard substrates for attached metazoans (e.g. archaeocyaths, stromatoporoids). Dendrolites were most conspicuous during the Early Cambrian and Early Ordovician, Late Devonian and Early Carboniferous. Bushy fabrics of dendrolites contribute significantly to the formation of nonmarine carbonates, e.g. travertines (Pl. 211). Leiolites form large domes in association with stromatolites and dendrolites. These microbial deposits with structureless micritic fabrics often appear 'homogeneous' or 'massive' and lack clear lamination, clots or dendritic fabrics. Leiolite formation is favored by a

Spongiostromata and Porostromata

steady uniform supply of well-sorted sediment on sur- defined growth forms but without (or very rare) with faces colonized by an even layer of microbes. preserved organic microstructures (Pl. 5014). PoroRecords of leiolites are rather rare (e.g. Late Juras- stromata comprise forms exhibiting tubular microstrucsic: Dupraz and Strasser 1999, Leinfelder and Schmid tures (Pl. 5011). 2000; Miocme: Braga et al. 1995). Spongiostromatemicrostructures are very variable, including micritic, spongious, vermicular, fenestral, and Cryptic microbial carbonates (Pl. 817). Many fine- peloidal textures (Giirich 1906). Comparable textures grained limestones, especially from reefal environ- occur in recent and ancient stromatolites (Monty 1976). ments, may be microbial in origin but lack distinctive Porostromate microstructures are typified by loose macrofabrics. They are characterized by inhomoge- or tangled, variously oriented, straight or sinuous tubes. neous micritic, clotted or peloidal fabrics, showing lo- Because these tubes record organisms of different syscally some traces of filaments. Many of these fabrics tematic position Riding (1977) proposed the term 'skelare also present in stromatolites,dendrolites and throm- etal stromatolites'. The terms spongiostromate and porostromate are used in microfacies studies describing bolites. textural variations of biogenic carbonate crusts and onFurther c1asr;ifications coids (see Sect. 4.2.4.1). Microbialite features can be differentiated at variSpongiostromate refers to a laminated, poorly difous scales (Shapiro 2000) and according to the amount ferentiated micritic and peloidal microfabric (Pl. 2811) of compositionalconstituents (Schmid 1996; Fig. 9.1). that may include various encrusting fossils. Porostromate microfabrics characterized by tiny calcified tubes occur in skeletal stromatolites (Pl. 50/1), Comments on Spongiostromata and Porostromata These groups were proposed by Pia (1927) for but also in non-laminated microbialites (Pl. 124/1), and schizophycean blue-green algae of uncertain affities. as constituents of biogenic nodules (Pl. 12/3,4), in reef Spongiostromata refer to nodules or heads with well- limestones as well as in carbonates formed in nonmarine and marine-nonmarine transitional environments (Pl. 5016).

/ ciotted \

1m

Macrostructure e.g. domical hemispheroi

e.g. peloids and filamentous microbes in spar

Mesostructure e.g. random plylobate and subspherical mesoclots

Fig. 9.1. DifSerentiation of microbialites. A: Thefour scales of microbialite investigation.Microbialites should be diiferentiated according to (1) the megastructure (referring to the large-scale features of microbial limestones, e.g. biostromal buildup), (2) macrostructure (designating the shape of the microbialite, with typical diameters of centimeters to meters, e.g. domal or columnal), (3) mesostructure (describing internal textures of macrostructuralelements visible with the naked eye, e.g. laminated, clotted, or dendritic), and (4) the microstructure (referring to microscopic feature observed under the microscope or in SEM, e.g. peloids, filamentous microbes). The scale bars indicate the magnitude of the criteria described at each of the stages. Slightly modified from Shapiro (2000). B: Classijicatii~nof Mesozoic microbialites (modified from Schmid 1996). This valuable classification relies on microstructures observed in thin sections. The system is apparently not applicable to the morphologically highly variable Precambrian and Early Paleozoic microbialites. See PI. 50 for examples.

374

9.1.4 Stromatolites are Laminated Microbialites

Stromatolites

I recommend the definition proposed by Riding (1999): Stromatolites are laminated benthic microbial deposits. This definition emphases the two main elements included in the original definitionby Kalkowsky: lamination and biogenicity.

In describing the siliciclastic Rogenstein deposit of the Early Triassic Buntsandstein of the German Harz Mountains, Kalkowsky (1908) introduced the term stromatoRecent stromatolites occur predominantly in freshlith for 'limestone masses showing a fine, more or less planar, layered structure' composed of a set of laminae water (Freytet and Verrecchia 1999), marginal marine ('stromatoid') and believed to be of vegetal origin (see (Fig. 9.2) and shallow subtidal environments. Ancient Paul and Peryt 2000). The use and definition of the stromatolites are known from the same settings, but term stromatolite have undergone gradual revisions from deep subtidal and basinal environments. Stroma(Riding 1977; Krumbein 1983) and oscillate strongly tolite fabrics can also form in geothermal systems as between descriptive and genetic approaches (Monty well (Jones et al. 2002) and result from anaerobic meth1977; Semikhatov et al. 1979; Awrarnik 1984, 1990). ane oxidation at cold seeps (Greinert et al. 2002).

Plate 50 Microbialite and Stromatolite Fabrics Biogenic laminated and non-laminated microbialite crusts forming various growth forms and consisting of micrite, grains and fenestral pores occur in different settings of shallow- and deep-marine as well as nonrnarine carbonates. The fabric corresponds to that of stromatolites (skeletal stromatolite,-> 1; agglutinated stromatolite, -> 2) or non-laminated microbialites (e.g. thrombolite, -> 5). The microbialites are built by the combined effect of biota, sedimentation and diagenetic processes. Microbial contributions, rapid cementation as well as the assistance of encrusting organisms (foraminifera, serpulids) are essential in the formation of these microbialites. Skeletal stromatolite crust growing on a colonial reef coral. The crust consists of slightly undulated spongiostromate micritic layers (ML) separated by layers of porostromate cyanobacteria filled with sparry calcite (SC). Late Triassic (Dachsteinriffkalk,Norian): Gosaukamm, Austria. Laminatedfine-grained agglutinated stromatolite produced by trappingbinding of sediment. Detail of microbial crusts consisting of thicker peloid layers (PL) and thinner micrite layers (ML). Peloids are very small and surrounded by calcite rims. They are isolated or occur in amalgamated masses. Micrite layers consist of micritic laminae with peloids and (white) bodies composed of radially arranged calcite crystals (Baccanella, see P1. 9918). Both, calcite-rimmed small peloids and Baccanella point to a microbial origin. These crusts are abundant in mm- to cm-sized framework voids of Triassic reefs. The peloidal texture is characteristic of 'container organomicrites' (see Sect. 4.1.1) formed in semi-restricted cavities. Late Triassic (Norian): Gosaukamm, Austria. Microbial crusts around and between rugose corals (Peneckiella).Microbial circumcrustations around reef-building organisms contribute significantly to the stabilization and preservation of reef structures. The crusts exhibit peloidal and clotted structures. Note that the crust around adjacent corallites is interconnected, forming a framework. This sequence can be explained by the leeward position of the Peneckiella thickets on the forereef slope (Gischler 1995) that hampered a rapid early cementation. Interskeletal pores are filled with burial calcite cements. Black spots between the septa of the corals and between coral c a k e s are ipsonite, an asphaltic probitumen derived from the metamorphism of hydrocarbons due to thermic effects. Atoll reef, formed by stromatoporoids and corals on top of a volcanic seamount. Late Devonian (Frasnian): Iberg, Harz, Germany. 'Spongiostromate' stromatolite crust covering the wall of a cryptic reef cavity. Micritic stromatolite according to the classification by Schmid (1996). The term spongiostromate refers to the variable, undifferentiated microfabric. Note the variable thickness of the micritic laminae. These crusts which are several centimeters thick, are interpreted as microbially induced carbonate precipitation within biofilms coating the interior of semi-closed reef voids and forming autochthonous micrites (container organomicrite).The interior of the cavity is occupied by Baccanella (arrow), supposed to be of bacterial origin or as diagenetic products caused by the recrystallization of micritic High-Mg calcite and aragonite (Pratt 1997). Late Triassic (Norian): Gosaukamm, Austria. Agglutinated microbialite consisting of amalgamated peloids (AP) leaving space for spar-filled cavities (C) forming a 'laminoid fenestral fabric' (see Sect. 5.1.5.2). The absence of a distinct lamination prohibits an assignment as stromatolite. Poorly structured thrombolite according to the classification by Schmid (1996). SMF 21. Late Triassic (Norian): Zelenica, Begunjscica Mountains, Slovenia. Tufa stromatolite. Cementlalgal bindstone, characterized by alternating thick layers of bladed elongate calcite cement crystals (CC) and layers consisting of radiating bundles of algal threads (arrow). The algal character of these threads is supported by distinct bifurcations. Schizohaline near-coastal environment. Tertiary (Miocene): Gulf of Suez, Egypt.

-- :!

rnm

Microbial Mats and Stromatolites

I

Box 9.3. Selected references on modem marginal-marine and marine microbial mats and stromatolites. Most references deal with tidal and subtidal settings which certainly do not represent all the wide variations of the depositional environments of ancient microbialitc:~.In modem reefs laminated microbial crusts occur as coatings on corals and other organisms and can contribute to the formation of high-energy coralalgal-stromatolite frameworks. Bahamas: Bathurst 1967; Black 1933; Cao and Xue 1985; Dill et al. 1986; Dravis 1983; Feldmann and MacKenzie 1998; Gebelein 1976; Ginsburg et al. 1977; H.ardie 1977; Hardie and Ginsburg 1977; Macintyre et al. 1996,2000;Mann and Nelson 1989; Monty 1965,1967,1972,1976;Neumann et al. 1970; Park 1977; Paull et al. 1992; Pickney et al. 1995; Reid and Browne 1991; Reid et al. 1995; Riding 1994; Riding et al. 1991; Scoffin 1970; Shapiro et a1.1995; Visscher et al. 1998 Florida: Frost 1974; Gebelein 1976; Ginsburget al. 1954 Bermuda: ~Gebelein1969,1976; Sharp 1969 Mediterranean: Friedman and Krumbein 1985; Friedman et al. 1973; Gerdes and Krumbein 1984; Gerdes et al. 2000 Red Sea: Friedman 1972 Pacific: Defarge et al. 1994; Kempe and Kazmierczak 1990,1993,1997; Kempe et al. 1996 Shark Baj, western Australia: Bauld 1981, 1984; Chvas et al. 1990; Davies 1970; Golubic 1982,1985, 1992; Hoffman 1976;Logan 1961;Logan and Brown 1986; Logan et al. 1974; Playford 1990; Playford and Cockbain 1976; Riding 1994; Skyring and Bauld 1990; Walter 1984 South Australia: Bauld et al. 1980; Skyring et al. 1983 Reef environments: Cabioch et al. 1999; Camoin and Montaggioni 1994; Carnoin et al. 1999; Macintyre 1993; h4acintyre et al. 1996; Marshall 1983; Montaggioni and Camoin 1993; Reid and Browne 1991; Reitner 1993; Reitner et al. 1995; Scholz 2000; Sorokin 1973; Steneck et al. 1998;Taylor 1977;Thiel et al. 1906; Wood 1962

forms are common in subtidal settings. This interpretation may fit the rough shapes of large stromatolite bodies, but the shape of small stromatolites and their constructional composition depends strongly on the biota involved. Lamination, lamina shape, fabric and texture as well as gross morphology can be substantially controlled by the taxonomic composition of the mat-building community (Awramik and Semikhatov 1979; Hofmann 2000) and reflect the activity of microcommunities living under different microenvironmental conditions (Defarge 1996).Quantitativemethods in the study of stromatolite fabrics facilitate the recognition of microenvironmental changes.

9.1.5 Occurrence and Significance of Microbialites and Stromatolites 9.1 5.1 Development through Time

Stromatolites and other microbialites played an important role in the formation of Precambrian and Phanerozoic limestones originating in various settings including marine, transitional marginal-marine and nonmarine environments.Whereas the microbial contribution to marginal-marine carbonates was uninterrupted through time, the role of microbes varied in the formation of shallow-marine platform and reef carbonates (Fig. 9.5). The Golden Age of stromatolites was the period from 2 800 Ma to 1 000 Ma where stromatolites contributed significantly to the formation of tidal carbonates, platforms and reefs (Fig. 9.4), and during the Proterozoic reached a maximum in abundance, diversity and lateral environmental expansion (Grotzinger 1989;Grotz-

Fig. 9.3. Stronzatolite classification after Logan et al. (1964). The classification is based on basic geometric forms expressed by the vertical and lateral arrangement of hemispheroids. Stromatolitegrowth forms as well as the shape of the lamination is described by symbols and formulas. These symbols can be used in the field and in the laboratory to describe thin sections and polished sections. LLH: Laterally Linked Hemispheroids with laminae whose domes are either Closely packed or Spaced somewhat apart (subtypes LLH-C and LLH-S). SH: Stacked Hemispheroids forming columns that are separated by sediment. The domes of the laminae have either a Constant diameter or Various widths (subtypes SH-C and SH-V). SS: Spheroidal Structures around a nucleus (corresponding to oncoids). Subtypes are SS-C (characterized by a Concentric structure; normal oncoid), SS-R (laminae Randomly overlapping), and SS-I (Inverted; laminae facing each other as concentric hemispheres), see Fig. 4/15. Mixed geometric forms can be indicated by a linear combination of symbols, e.g. LLH-SH. The relations of growth forms and microstructure is expressed by a fraction, whereby the numerator describes the macrostructure seen in the fie,ld and in hand specimens, and the denominator the microstructure seen on a smaller scale as in thin sections.

ter settings can be found in the papers included in the SEPM Special Volume 72 on Phanerozoic Reef Patterns (Kiessling et al. 2002). The decline of stromatolites near the Precambrian1 Cambrian boundary and the development of Cambrian and Ordovician tidal carbonates have been explained by competitive or noncompetitive restriction of strornatolites by grazing and burrowing organisms, e.g. gastropods (Garrett 1970; Mazzullo and Friedman 1977), but this interpretation has been strongly criticized (Pratt 1982; Browne et al. 2000; Rowland and Shapiro 2002). The microbial reef ecosystem flourished after the collapse of the archaeocyath reefs from the Middle Cambrian to the Early Ordovician, covering a period of about 40 Ma. Manv Cambrian inter- and subtidal shelf car-. . bonates and reefs exhibit dendrolitic, stromatolitic or Fig. 9.4. Late Cambrian (La Flecha Formation) stromatolitc thrombolitic textures (Aitken 1967; Ahr 1971; Soudry f r m n the Eastern Precordiliera. betwe en San Juan and hle.ldoza (Argentma) Scale is 50 cm. Courtesy of M'. and Wissbrod 1993; PI. 8212. 4). Stromatolites occur throughout the Ordovician whereas thrombolites had a Bui glrch Erlangerl (.onstant decline during the Early and Middle Ordoviinga and Knoll 1999: Hoffman 2000; James et al. 2000; cian, subsequent to their peah In the Late Cambrian Scrnikhatov and Raaben 2000; Sumner 2000). By the (Webby 2002). The Silurian (Soja 1994) and Devonian enci of the Precambrian, stromatolite development had (Browne and Dernicco 1987)exhibit a marked decrease dec llned. but stromatolites and other microbial carbon- in the frequency of microbial carbonates, except durateb,were still important in the fom~ationof reef struc- ing the upper Late Devonian where calcimicrobes and tun s in various part\ of the Phanerozoic, as shown in stromatolite~contributed significantly to the formation E I 0~ 5 and ~ ~ ~ m i n m by z e dRiding (2000). A wealth of carbonate platforms during times of major envlronc l t lie\\ dat,t on P&ozoic and Mesozoic microb~al car- ~nentalchanges (Playford ct 31. 1976; Whalen et al. LWI ate\ m d their d ~ \ t r ~ b u t ~Ino,hallown and deep-ud- 2002). Mlcrob~alshelf anti lecf carbonates agam bc

I

Fig. 9.5. Changes In the microbial control on limestones during time expressed by the percentage of microbial reefs (based on the evaluation of more than 2800 Phanerozoic reefs; see Kiessling 2002). The contribution of microbes to the formation of n:ef carbonates varied during the Phanerozoic. Stromatolites and calcimicrobes were abundant in Cambrian, Ordovician and Early Carboniferous carbonates, and common to abundant in periods following worldwide extinction events (Famenniar: Early Triassic). The importance of microbial carbonates in reefs decreased after the Jurassic.

Importance of Stromatolites

came important in the Mississippian, as exemplified by the deep-water 'Waulsortian' mud mounds. Stromatolites gave way to thrombolites during the VisCan. Microbial contribution to Pennsylvanian and Early Permian reefs is indicated by the common association of micrite anti carbonate cement crusts with encrusting organisms regarded to be microbial (e.g. Archaeolithoporella; P1.4:2/1). Similar associations occur in Middle and Late Permian shelf-margin reefs, e.g. the Capitan reef of Texas (Pl. 14511). Shallow-water and deeperwater stromatolite reefs are widely distributed in the cratonic Zechstein basins of central Europe and the Kungurian basins of the Urals (Pl. 12611). Comparable to the abundmce of microbial carbonates subsequent to the FrasnistnJFamennian extinction event, microbial carbonates and small microbial reefs dominated after the Permian-Triassic extinction event during the Early Triassic. Mic:robes contributed to the construction of Middle and Late Triassic reef frameworks (Harris 1993; Brachert and 13ullo 1994;P1.2811, P1.11612); some Late Triassic reefs were almost exclusively formed by stromatolites and microbial crusts. The importanceof photic and aphotic inicrobes as reefbuilders increased again during the Late Jurassic, where low-energy microbedominated reefs and platform carbonates were widespread (Keupp and Arp 1990; Schmid 1996; Leinfelder et al. 2002), and continued being constituents of shallow-water and deeper-water environments during the Early Cretaceous (Strasser 1988; Neuweiler 1995). In the Late Cretaceous microbialites were gradually substituted by encrusting red algae. Some microbial-dominated reef carbonates are still known from the Tertiary.

379

cessfully used in recognizing depositionalenvironments of Precambrian and Phanerozoic limestones and discriminating shallow- and deeper-water settings (Hoffman 1974, George 1999, Riding and Awrarnik 2000). Fig. 9.6 illustrates generalized distribution patterns of Mesozoic rnicrobialites based on about thirty case studies. Marine deep-water microbialites, formed on slopes and deeper ramps at water depths of 100 to 150 m, become important in the Late Jurassic (e.g. Gygi 1992), but were already present in the Precambrian and Devonian. Aphotic stromatolitesare known from Late Triassic and Early Jurassic basinal settings (Bohrn and Brachert 1993).

9.1 5.3 Economic Importance of Stromatolites

Microbes contribute significantly to the precipitation of a wide variety of authigenic minerals, including oxides, carbonates, phosphates, sulfides and silicates (see overviews by Mendelsohn 1976; Ferris 2000). Microbial metabolic activity can alter Eh and pH conditions, influence oxidation and reduction processes, and trigger mineral precipitation and fixation of dissolved metal ions, thus contributing to the formation of economically important ore deposits (Dexter-Dyer et al. 1984; Westbroek and DeJong 1983; Schidlowski 1985; Fan et al. 1999). Many ore deposits are closely associated with stromatolites, particularly with stromatolitereefs. Examples are deposits related to the Precambrian Banded Iron Formation in America (James 1992), stratiform copper deposits in Africa, or some lead-zinc deposits of the 9.15.2 Palleoenvironmental Significance of Mississippi Valley type in North America (see papers Microbial Carbonates included in Wolf 1976 and Parnell et al. 1990). Cyanobacteria and other bacteria are directly or indirectly Microbial carbonates, together with associated en- implicated in the genesis of iron and manganese decrusting organisms, offer a high potential for inter- posits (Nealson 1983; Yin 1990). preting ancient environments and their major controls by nutrients, light, water energy and water depth. Nutrification is influenced by relative sea-level changes, 9.2 Biogenic Encrustations which result in shifts from oligotrophic to mesotrophic organisms, including microbes (Wood 1993), an in- Encrusting organisms play a key role in carbonate sedicrease in bioerosion, and platform drowning (Hallock mentation and the development of reefs. and Schlager 1986; Hallock 1988; Hallock et al. 1988). Skeletonized and non-skeletonizedencrusting organEcologic changes indicated by differences in micro- isms grow on various hard substrates represented by bial carbonates allow sequence stratigraphyframeworks hardgrounds (see Sect. 5.2.4.1), cobbles/boulders and of carbonate platforms to be refined and sea-level curves skeletons of organisms. to be evaluated (Whalen et al. 2002). This subchapter addresses biogenic crusts developed Differences in growth forms, morphotypes, micro- on free exposed surfaces of benthic host organisms, e.g. fabrics and the association of microbialites with fossils the upper surface of colonial fossils, or in hidden and and specific sedimentary structures have been very suc- shadow places, e.g. the undersides of colonies, or within

Msozoic Microbialites

380

Middle to Late Cretaceous

and stromatoliies microbial ma in freshwater lakes (loferites) oncoids and rhodoids

incrbsting red algae

coral-ru&\ mud mound

.. siliceous meadows

Late Jurassic

aphotic microbialite:,. patch reef . .'\

Late Triassic

-----.-.-

Middle Triassic

----------

serpulid cement reefs

Fig. 9.6. Generalized distribution of microbialites in Mesozoic platforms and reefs. Microbialites comprise non-laminar and laminar types as well as microbial oncoids (see Sect. 4.2.4.1). Cement crusts refer to quantitatively frequent, microbially induced marine carbonate cements. The Middle Triassic (predominantly Ladinian) and Late Triassic (predominantly Norian) scenarios reflect case studies in the European western Tethys. The Late Jurassic scenario summarizes case studies in the Tethys and in epicontinental settings. The Middle and Late Cretaceous sketch describes the distribution of microbialites in the Tethys. Note similarities in the setting of microbial oncoids, but differences in the microbial contribution to reefs and mud mounds. Modified and expanded from Leinfelder and Schmid (2000).

cavities or in borings (Sect. 9.3). The composition and sequential order of encrustation patterns are important microfacies criteria allowing the study of original ecological relationships and the interactions and competition between encrusters to be studied, environmental paramet:ers, e.g. nutrient constraints to be estimated. Encrusting organisms occur in all shallow- and deepmarine settings, both in warm-water and cold-water environments. Encmsting taxa act as binders and cementing organisms, but also as constructors, and are often initial and early colonizers.

Encrusters are commonly included in the binder guild, but for many encrusting organisms a considerable guild overlap exists (Sect. 16.2.3.2). The dominance of encrusters is used in limestone classifications (Sect. 8.2). Terminology: Organisms living on a substrate can be divided into epibenthic and endobenthic, depending on whether they live above or below the substrate surface. A simple nomenclature system was proposed by Taylor and Wilson (2002) for marine plants and animals that encrust or bore natural hard substrates. The

Encrusters

terms describe the identity of the colonizing organism, the nature of the substrate, and the location of the colonists (on the. surface or within the surface). The classification was inspired by the carbonate classification system used by Folk (Sect. 8.3.2). Each term consists of two or three roots: The last root refers to the identity of the colonizing organism (animal, -zoan; plant, -phyte, or either, -biont). The preceding root describes the type of the subshate (rock,-1itho-, animal, -zoo-; plant, -phyto-; or any organic hardpart of unknown or uncertain status, living or dead, -skeleto). The location of the colonizing organisms is indicated by the prefn epi- or endo-. The collective term sclerobiont is used for any kind of animal or plant fouling any kind of hard substrate. Sclerobionts include encrusters pressed closely to the surface of the substrate (Fig. 9.7), sessile organisms that are cemented or organically anchored to the substrate surfacle and grow into the water column (Fig. 9.9), and borers that enter the substrate.

9.2.1 Criteria and Constraints of Encrusters Biogenic crusts are formed by sessile benthic organisms including microbes, algae, foraminifera, sponges, bryozoans, corals as well as serpulids and mollusks. Encrusting organisms are solitary or colonial. The latter exhibit various growth forms (Jackson 1979, Taylor 1992) comprising runners (linear forms, e.g. some bryozoans), sheets, mounds, plates (with punctuated bases), vines (linear to branched, semierect forms) and trees (erect forms). Sheets and mounds are common growth forms of reefal encrustations, producing crusts oriented parallel to the substrate (Fig. 9.7) and indicating strong competition for space. Erect upright encrustations (Fig. 9.9) point to low sediment input. The success of encrustation depends on a number of factors including the size, structural complexity and stability of the substrate, the biochemical conditioning,

Fig. 9.7. Characteristic hard substrate encrusters. The bivalve shell (B) was first encrusted by an association consisting of sessile foraminifera (SF; Miniacina), serpulids (Ditrupa, D) and squamariacean red algae (SRA; today called peyssonnelaceans). Corallinacean red algae (CRA) form the later phase of the encrustation. Note intensive boring of the shell (black arrows) prior to the biogenic encrustation. Borings are with fine bioclastic sediment. By contrast, the borings in the squamariacean algae are occluded by cement (white mow). Applying the terminology proposed by Taylor and Wilson (2002) for organisms inhabiting hard substrates, the crust sequence consists of more or less synchronous episclerozoans and episclerophytes represented by squamariacean red algae, followed by epizoophytes represented by corallinacean red algae. Late Tertiary (Middle Miocene): St. Margarethen, Burgenland, Austria. Scale is 5 mm.

382

Biogenic Encrustations

Plate 51 Biogenic Encrustations Biogenic encrustations originate from the growth of sessile organisms on various substrates. These epibionts grow on animal hosts (epizoans) or on plant hosts (epiphytes, e.g. sea grass or soft algae). Epibionts from ephemeral substrates are generally rare, in contrast to the considerable record of epibionts from hard substrates. Crust-forming calcareous organisms occur on living and dead surfaces of skeletons, particularly in reef environments, and on lithified rock surfaces (e.g. hardgrounds, see Sect. 5.2.4.1). Calcareous encrusters include microbes and algae (see P1.50), adherent foraminifera, sponges, corals, bryozoans, serpulids and some mollusks. The frequency, composition and diversity of crust-building communities have changed over time. Sessile foraminifera (-> 1,2,4,7,8) belonging to different suborders are common in Mesozoic and Cenozoic reef and shelf faunas (Adams 1962). Some taxa contributed significantly to the formation ofCTertiary reefs (Plaziat and Pemn 1992). Attached foraminifera are valuable proxies for sedimentation rates, water energy and paleo-water depths (Ghose 1977; Martindale 1992). Biogenic encrustations take part in the stabilization of sediment, the rapid lithification of reef slopes (Keim and Schlager 1999), the formation of carbonate grains (-> 2,4) and the construction of rigid reefs (-> 7). Major controls on the occurrence and distribution of encrusters are substrate, availability, water energy and (low) sedimentation rates. Succession analyses of encrusting associations provide clues to substrate types, sedimentation rates, paleo-water depths (Rasser and Piller 1997) and associated sea-level fluctuations (Reid and Macintyre 1988). Biogenic encrustations can be more easily described by using the simple classification system proposed by Taylor and Wilson (2002). Each term consists of two or three roots: The location of the colonizing organisms is indicated by the prefm epi- or endo-. The second root refers to the type of the substrate (rock, -1itho-; animal, -zoo-; plant, -phyto-; or any organic hardpart of unknown or uncertain status, living or dead, -sclero-). The last root describes the identity of the colonizing organism (animal, -zoan; plant, -phyte, or either, -biont). Examples are given on this plate. Attached agglutinated foraminifera (Ammovertella Cushman, Carboniferous-Permian). Note the flat lower surface of the tests representing adaption to an encrusting mode of life (e.g. on not preserved, poorly calcified algal blades). The foraminifera were probably epiphytozoans. Early Permian: Carnic Alps, Austria. Foraminifera1 encrustations (Tolypammina Mumbler) attached to shells. Episkeletozoan crust. Long-lasting encrustation$,lead to the formation of foraminifera1 oncoids. Late Triassic (Carnian): Central Carinthia, Austria. Encrustations of sphinctozoid sponges (Uvanella; arrows) on and between corals facilitate the construction of rigid reef frameworks. Epizoozoan crust. Late Triassic (Hawasina Formation, Norian): Central Oman. Formation of composite grains by encrustation of ooids with nubeculariid foraminifera and cyanobacteria. Nubeculariids are nliliolid porcelaneous foraminifera, often attached to sedimentary grains or shells. They contribute to the formation of oncoids andTertiary reef structures. The crust type can be classified as epilithozoan crust or more precisely as epizoozoan crust. Late Triassic (Late Camian): Central Carinthia, Austria. Encrustations of serpulids around a vanished recrystallized structure, probably a shell infilled with peloids. Episkeletobiont crust. The serpulid encrustation indicates the existence of a hard substrate. Early Cretaceous: Ostermiinchen well, Southem Elavaria, Germany. Repeated biogenic encrustations form characteristic sequences consisting of two and more taxonomically different organisms Example: Cystoporid bryozoans (Dybowskiella, B) growing upon (now recrystallized) solenoporacean red algae (SO) are overgrown by sphinctozoid sponges (S). The relations between encrusting organisms include epiphytozoans followed by episkeletozoan crust types. Middle Permian reef limestone: Straza near Bled, Slovenia. Modem reef limestone. Note the interaction of different encrusting organisms in the formation of an autochthonous boundstone structure: A meshwork resembling the rnicroproblematicumBacinella (B), interpreted as being of cyanobacteria origin is encrusted by corallinacean red algae (RA); followed by attached agglutinated foraminifera (F). The development of the encrusters was disturbed several times by the influx of ooid sand. San Salvador, Bahamas. Encrustation of foraminifera (Palaeonubecularia) on a phylloid alga. Epiphytozoan crust. Note the difference in the preservation of the primary Mg-calcitic foraminifera and the primary aragonitic alga which has lost almost all its significant features due to the recrystallization of its aragonitic skeleton. Early Permian: Forni Avoltri, Camia, Italy. Alternations of calcirnicrobes (Rothpletzella, R, P1. 5318) and fossils interpreted alternatively as foraminifera or cyanobacteria (Wetheredella Wood, W) are important in the formation of Paleozoic oncoids. Many Early Paleozoic biogenic crusts were built predominantly by microbes, sponges and stromatoporoids. Early Devonian (Emsian): Lake Wolaya, Carnic Alps, Austria.

Phanerozoic Encrusters

9.2.2 Phanerozoic Encrusters

Fig. 9.8. Rugose corals (Acanthophyllum sp.) encrusted by stromatoporoids (Clathrocoilona sp.) and thin layers composed of porostromatecyanobacteria(Girvanellasp.; not recognizable in the picture). Stromatoporoids and cyanobacteria form sheetlike crusts around the corals. The wide distribution of this crust pattern in Middle Devonian platform carbonates suggests that encrustation took place during the lifetime of the coral. Middle Devonian: Letmathe, Sauerland, Germany. Scale is 5 mm.

and the presence of biofilms. The available attachment surface area is critical for the survival of crust-building organisms. The biological potential of many encrusters is strongly microbially controlled. Colonizer-inherent faclors are larval recruitment patterns and growth strategises.Ecosystem-inherentfactors include sedimentation rates, water movement, predationlgrazing pressure and disturbance frequency. In general, the dominance of encrusters with skeletons is reduced with depth, leading to complex succession patterns controlled by endogenic and exogenic factors. The former includes reproduction and larval strategies as well as competition for space and nutrients. Exogenic controls are mainly the size of the encrusting surface and predation pressure. Upper and lower surfaces of organisms acting as substrates for encrusters are likely to be subject to different light. intensity, turbulence, grazing pressure and dissolved oxygen. These differences influence the distribution of generalists and specialists and cause faunal polarity between crusts developed upon upper and lower surfaces of host organisms. Lower surfaces often exhibit greater areal cover, higher density and a higher diversity of encrusters than upper surfaces.

Encrusting organisms range in size from less than a millimeter to several millimeters (cyanobacteria, foraminifera, many microproblematica) up to centimeters (red algae, stromatoporoids,corals). Micro-encrusters are encrusting microfossils, often occurring in close association with microbialites and within marine and nonrnarine oncoids (Sect. 4.2.4.1). Cambrian and Ordovician encrusting communities lived predominantly in sheltered reef cavities (Kobluk 1988) and are dominated by microbialites, particularly cyanobacteria. Other common encrusters are bryozoans and sponges. The differentiation between encrusters occurring on exposed surfaces, cryptic habitats or in shadowed cavities seems to have taken place in the Ordovician. In Silurian and Devonian reef limestones, biogenic crusts on the surface of benthic organisms are composed of stromatoporoid sponges (Fig. 9.8), tabulate corals and porostromate cyanobacteria. Strong evidence for spatial competition among ancient marine hard substrate biotas comes from the study of overgrowth networks among Silurian bryozoans (Lidell and Brett 1982;Taylor 1984).=crobes, algae, smaller foraminifera, bryozoans and chaetetid sponges are important constituents of Carboniferous and Permian encrusting communities. Mesozoic reef and platform carbonates yield diverse encruster communities whose taxonomic diversity and ecologic complexity increase in the Late Jurassic and the Cretaceous. Tertiary succession patterns resemble those of modem crust communities, due to the dominance of red algae, foraminifera, bryozoans, barnacles and serpulids (Fig. 9.7 and Fig. 9.9).

9.2.3 Significance of Encrustation Patterns in Recognizing Depositional Settings and Environmental Controls The combined use of encrustation patterns, microbialite types and bioerosion criteria can serve as a guide to identifying inner and outer parts of carbonate platforms and ramps, as well as interpreting paleo-water depths and nutrient levels in ancient reefs. Prerequisites for the successful application of these criteria are (1) the knowledge of changes in the composition of biogenic crusts during time, and (2) the differentiation of rnicroencrusters, if possible at low taxonomic levels. Changes in the composition of Triassic biotic crusts: Middle and Late Triassic crusts exhibit distinct differ-

Encrustation Patterns

Jurassic micro-encruster associations subdividing carbonate ramp depositional environments: Schmid (1996)studying Late Jurassic reef and ramp carbonates in diierent parts of Europe recognized five microencruster associations characterized by composition and diversity (Fig. 9.10).Girvanella associationswithin oncoids are restricted to near coastal settings with fluctuating salinities.The widespread Bacinella-Lithocodium association occurs in shallow lagoonal and reefal settings affected by moderate environmental stress. Balanced environmentalconditions in shallow lagoonal and reefal areas are indicated by high-diversity micro-encruster associations consisting of porostromate microbes (Cayeuxia, Girvanella), red algae (Marinella) and microproblematica(Bacinella, Thaumatoporella). The Tubiphytes-Koskinobullina association is abundant in mid-ramp positions, but also occurs in reef cavities. Low-ramp and middle- to outer-ramp positions are characterized by the low-diversity Terebella (a serpu1id)Tubiphytes association that thrives in low-energy environments and appears to tolerate oxygen deficits at the sea bottom. Nutritional models derivedfrom microbialites, micro-encrusters, bioerosion, and faunal diversity: The paper by Dupraz and Strasser (2002) on coral-microbialite reefs from the Swiss Late Jurassic illustrates the high potential of microbial structures, encrusters and borings for evaluating changes in dominating nutrient regimes. Micro-encrusters associated with microbialites and reef-building corals include here red algae, foraminifera, bryozoans, serpulids and sponges. The semiquantitative micro- and macroscale distribution patterns ences in the association and diversity of organisms that indicate three trophic structures that parallel the differcontributed to the formation of crusts in reef environ- ent siliciclastic influx into the reef areas: Phototrophicments (Fliigt:l2002). Anisian crusts are rare but diverse; dominated structures (indicated by Lithocodium-Bacitheir encrwting organisms comprise sphinctozoid nella and opportunistic serpulids and bryozoans) domisponges, porostromate cyanobacteria, foraminifera, ser- nate in moderately diverse coral reefs growing in poor pulids and some microproblematica.The latter are com- carbonate and nutrient-poor environments with only mon and sometimes abundant in younger Triassic but low bioerosion. Balanced phototrophic-heterotrophic also in Jurassic reef crusts. Crusts are frequent in Ladin- structures developed in mixed siliciclastic platform enian and Early Carnian reefs; they are characterized by vironments and produced the most diversified coral various asscciations of sponges, microbes, and micro- reefs with common thrombolites. Heterotrophic strucbially induced carbonate cement. The composition of tures dominated in the case of strong siliciclastic accuLate Carnian reefs differs significantly in that low- mulation or a strong increase in nutrient availability; growing sponges and porostromate cyanobacteriadorni- thrombolites, Terebella and other serpulids, and bryonate (Pl. 7911). A complete change took place in the zoans are common. Bioerosion is moderate to high. Norian (Late Triassic): Biogenic crusts become highly diverse and mainly built by microbialites (Pl. 116/2), Late Cretaceous encruster associations dependent sphinctozoan and chaetetid sponges (Pl. 81/1), and mi- on the reef type: Different encruster associations occur cro-encruster associations,which also dominate in Late in reefs built by different reef organisms as exempliJurassic and Early Cretaceous reefs (e.g. Lithocodiuml fied by coral-stromatoporoid reefs, coral reefs, rudist Bacinella; E'l. 9914, 5). reefs and algal reefs (Moussavian 1992). Encrusters are Fig. 9.9. Encrustation of colonialscleractinian corals by corallinacean red algae (Archaeolithothamnium gosaviense Rothpletz). B'oth, the corals and the algae were attacked by macroborers. The coral was strongly eroded and bored prior to the overgrowth by the algae. The transition from moundlike to erect growth indicates quiet-water conditions and low and slow sediment input. Lagoonal back-reef environment. Late Cretaceous (Coniacian): Northern Alps, BadReichenhall, Bavaria, Genmany. Scale is 2 mm. Courtesy of R. Hofling, Erlangen.

386

Encrusters in Jurassic Reefs

Inner ramp

;&;Bm

Southern Germany mmmSpain ,... :...

I

Middle ramp

mm-mmmmm - m - m m m - - ~ m m m m m m - - m - m m m -

I

Outer ramp m-m*mm--

h

-mm-m---m

Fair weather wave base

~'1

Storm wave base

=4: Microbial crusts Koskinobullina

y.

High-diversity association 00

Siliceous sponges Desiccation cracks Bioclasts

Tubiphytes-Koskinobullina

association

"S

Terebella

Terebella-Tubiphytes association

Fig. 9.10. Distribution patterns of micro-encruster associations in Late Jurassic reefs developed in different parts of carbonate ramp:;. Modified from Schmid (1996).

cyanobacteria, rhodophycean algae, various groups of al. 1983), and affects carbonate rocks, life or dead skelsessile foraminifera (e.g. acervulinids), corals, hydro- etons as well as hardened sea floors. Endolithic borers zoans, sponges including stromatoporoids and chaet- (algae, polychaetes) and grazers (e.g. herbivorous fishes etids, bryozoans, and microproblematica (e.g. Litho- and sea urchins) modify and redistribute carbonate procodium and Bacinella). duced by reef-building organisms. The relative importance of endolithic borers and grazers varies between reef environments and with time of exposure (Kiene 9.3 Bioerosion, Boring and Grazing and Hutchins 1994). Macroborers are responsible for extensive substrate erosion, sediment production and Organisms the generation of secondary porosity in reef frameThis chapter deals with the destruction of carbonates works. substrate:by boring organisms and with the nature, inBioerosion occurs in marine warm-water and coldtensity and significance of bioerosion. The term bio- water carbonate environments and is controlled by ilerosion (Neumann 1966) describes the processes by lumination, nutrients, sedimentation rate, siliciclastic which bimological activity destroys hard substrates. Bio- influx and water depth, as drastically shown by the comerosion contributes significantly to sediment produc- positional difference of boring associations in shallow tion, controls early diagenetic processes, and the tapho- warm and deep cold-water environments. The latter, nomic history of fossils. exemplified by deep-water Lophelia reefs in the AtlanMany fine-grained carbonate particles, seen in thin tic are characterized by the abundance of non-autosections,may be the result of biodegradation by bor- trophic bacteria, heterotrophic fungi as well as clionid ing. Especially particles in the silt-size range are can- sponges and bryozoans. Sediment production is high didates for this interpretation, as shown by SEM stud- (Freiwald 1998), sometimes competing with figures ies. In coral reefs, bioerosion depends on numerous known from shallow tropical environments (up to 0.5 environmental factors such as light availability, nutri- to 2.5 cmlyear). ent supply, and water depth. Boring occurs in shallowThe interest in bioerosion and boring organisms has and deep-marine, freshwater and terrestrial environ- increased significantly during the last few decades. A ments (contributing to phytokarst formation and the bibliography of papers dealing with modem and fossil degradatron of limestones and marbles used as build- micro- and macroborers includes more than 800 refering st0ne.s and for art sculptures (e.g. Anagnostidis et ences (Radtke et al. 1997).

Bioerosion, Boring, Grazing

Micro- and macroborers produce trace fossils The traces of micro- and macroborers are known throughout the Phanerozoic. Microborers at a scale < 1 pm to about 100 pn tunnel their way into the substrate using weak acids. They include bacteria, cyanobacteria, fungi as well as foraminifera and bryozoans. Macroborcm are visible with the naked eye, and have diameters of 1 mm and greater. They use physical and physicochemical techniques for boring. Endolithic microborers attack hard substrates (skeletons, hardgrounds, carbonate grains, rocks) and produce borings that are filled with cement or sediment, or remain open. The products of boring activities are tunnels and caves whose shape may correspond to the morphology of the borers, thus allowing taxonomic assignments of the trace fossils. Most borings excavated by bacteria, algae or fungi are too small to be successfully studied in thin sections. Studies dealing with modem and ancient microborers are mainly based on SEM investigations of artificial casts produced by filling the boreholes with resin (Golubic et al. 1970,1983;P1.521 1-4). Some of the macroborings can be morphologically differentiated in thin sections and attributed to systematic groups (Box 9.4).

Fig. 9.11. Sponge borings dominate in modem and Neogene environments, but are already known in the Cambrian. Sponges are capable of destroying large amounts of reef frameworks. The Modiola mussel is intensively bored by a sponge (Cliona) characterized by a network structure. The borings consist of a series of galleries branching and anastomosing within the substrate and communicating with the surface via numerous small round pores that house the inhalant and exhalant papillae of the sponge. The sponge tissue has specialized etching edges responsible for boring, which results in freeing of characteristically shaped chips.These chips with a size of 40-60 pm are expelled by the oscula und carried away by currents. Clionid borings preserved as trace fossils are called Entobia. X-ray photograph. Scale is 2 cm.

pact on the destruction of modem reef surfaces. The first unequivocal fossil representative of the Scaridae is known from the Middle Miocene (Bellwood and Schultz 1991); scarids may represent 'the reefs latest trophic innovation' (Bruggemann 1994).

Grazers, scra.pers and swallowers Bioeroding organisms include not only borers, but Scrapers (e.g. regular echinoids, limpids, some paralso grazers, scrapers and swallowers, which have a major impact on the bioerosion of modern shallow- rot fishes) use beaks or claws to scratch skeletons in order to remove microbial nutrients or algal/microbial marine carbonates (Hutchins 1986). Grazers (e.g. echinoids, gastropods, chitons, and cover. Regular echinoids are known since the Carbonfishes) are organisms feeding mainly on plants, e.g. al- iferous. gal and microbial mats. Most grazers search for algae Swallowers are detritus feeders that swallow sediin living or dead substrates. Grazing echinoids are major eroders of modern coral reefs. Chitons, already ment grains that are comminuted through their digesknown from the Late Cambrian, are common grazers tive tracks, usually producing pellets (e.g. holothuriof endo- and epilithic algae along carbonate coastlines ans, jawed fishes). Holothurians are known since the (Rasmussen and Frankenberg 1990). Carbonate re- Middle Cambrian, jawed fishes since the Wenlockian. moval by grazers may be responsible for a high percentage of the total bioerosion (Chazottes et al. 1995). Intensive microbial mat grazing started in the Late Pre- 9.3.1 Recent and Fossil Microborers cambrian. Grazing by conodontophoridsand fishes may Microboring is not only a product of light-depenhave become more intensive in the Middle and Late dent photosynthetic algae but also of heterotroph bacCambrian. Grazing fl~shesare the dominant herbivores in most teria and fungi. Therefore, microborings have a wide tropical environments. Herbivorous grazing fish spe- bathymetric distribution ranging from supratidal and cies are important bioeroders on tropical shallow reefs intertidal environments to subtidal and deeper-water (up to 7 kg/m2/year). Substrates already infested by bor- environments. Many microborers are concentrated within shallow ing algae and of low skeletal density are eroded fastest (Bruggemann et al. 1995). Scarid parrotfish and acan- subtidal and intertidal depths and exhibit distinct zonathurid surgeonfish, feeding by scraping off algae that tion patterns. Endolithic biodegradation is common and grow on and in dead coral skeletons, have a major im- highly diverse in near-coastal environments and warm

Microborers

shallow seas, but is also important in cool-water skeletal shelf carbonates (Akpan and Farrow 1984; Young and Nelson 1988). Microborers are studied in order to understand destructive processes resulting in the degradation of skeletal elements and the production and accumulation of fine-,gained carbonate sediment, processes responsible for the formation of micrite envelopes (cortoids; P1.52/6), distributionalpatterns that can be used to differentiate modem and ancient marine environments (e.g. intertidal and supratidal sequences, Hoffman 1985), the role of microborers as (paleo-)bathymetric and (paleo-)ecologic indicators, the role of increased nutrient input to reefs that might result in reef demise (Hallock 1988; Wood 1993).

Fig. 9.12. Recent cold-water microborings produced by marine fungi attacking the deep-watercoral Lophelia. Microborings are not restricted to shallow-marine environments (see P1. 51/14), but also occur in the deep sea where bacteria, fungi and bryozoans act as borers (Freiwald and Wilson 1998). The abundance of fungal borings increases with water depth from deeper subtidal to bathyal environments (see Fig. 9.16). The SEM photograph of the resin cast shows linear fungal borings and globular sporocysts developed within 70 Frn below the surface of the coral. Propeller Mound, Northern Atlantic, west of Ireland. Water depth about 700 m, water temperature 10 "C.Courtesy of L. Beuck, Erlangen.

Microboring groups Microborers include bacteria, algae and fungi that penetrate substrate by etching. Boring foraminifera and bryozoans are attributed to microborers, because the dimensions of the trace fossils are smaller than 100 ym. Bactev-ia: Non-photosynthetic bacteria and photosynthetic cyanobacteria occur in marine, limnic, fluvial and terrestrial environments. Both groups include Schonfeld 1996). They occur in groups characterized the oldest microborers known since the Precambrian by agglutinated and calcareous perforate tests; they are and recorded in carbonate rocks as old as 1700 Ma known from cold-water and warm-water environments, (Zhang and Golubic 1987). Bacteria have various and are reported from Jurassic to Quaternary carbonshapes (spheres, bars, bent bars and spirals). The size ates (Venec-Pyre 1987; Baumfalk et al. 1983; Smyth of non-photosynthetic bacteria ranges between 1 and 1988; Cherchi et al. 1990;Cherchi and Schroeder 1991). 5 pm with diameters between 0.2 and 1 ym. Modem Bryozoans: Trace fossils of boring bryozoans can endolithic cyanobacteria are represented by more than be easily recognized in SEM images, because the trace 20 genera (Budd and Perkins 1980). Green algae occur in marine and non-marine envi- closely resembles the producer morphology and reflects ronments. Some chlorophycean algae live within car- the shape of the body fossil. The trace corresponds to a bonate substrates or have endolithic stages (Golubic et network that connects elongated chambers. These bryoal. 19751; they are already recorded from Early Paleo- zoans are differentiated by the shape, size and position zoic skeletal grains and ooids (Podhalanska 1984) and of the zooids, the relation between zooids and the stolonial system, and the size of surface openings possibly also from Precambrian rocks. Red algae are predominantly marine. Endolithic life (Pohowsky 1978). The diameter of the non-calcified stages are known from only a few marine genera that slender structural elements is less than 10 pm. Most boring bryozoans known from Jurassic to Quaternary already occur in Early Paleozoic rocks. Fungi are heterotroph organisms without photosyn- limestones are attributed to the Ctenostomata. The Pathetic pigments. Boring fungi occur in shallow and deep leozoic record of boring bryozoans is scanty. marine environments down to 5000 m. Their trace fossils are differentiated by the shape, size, mode of branching and aporangia (Glaub 1994).The oldest records of 9.3.2 Recent and Fossil Macroborers boring fungi are from the Middle Ordovician. Macroborings occur in marine and non-marine enviForaminifera:Boring endolithic foraminifera appear ronments and contribute considerably to bioerosion in to be of greater importance for the degradation of skel- marine shallow- and deeper-water, warm- and coldetal grains than previously assumed (Freiwald and water settings (Ekdale et al. 1989). The most effective

Macroborers

38

Fig. 9.13. Mmroborings produced by cinipedians of the group Acrothoracica. The brings are characterized by a amphoralike shape with a narrow neck at the anterior end. The borings occur within a reef limestone with abundant bryozoans (celllike structures). Note the reversed geopetal fabric in the brings indicating overturning of parts of the reef mound. These are the oldest Mesozoic cimpedian borings subsequent to the Permian-Triassic extinction event. The association of ascothoracid & reefs and in the Anisian underlines the Paleozoic aspect of the early borings and wepostomate bryozoans in the ~ a Permian Middle Triassic. Middle Triassic (Anisian): Olang Dolomites, Southern Alps, Italy. Modified from Senowbari-Daryan et al. (1993). Scale is 2 mm.

Bivalves: Boring into reef-building organisms by groups in modem environments are sponges, bivalves and 'worms ', followed by specialized cinipedians (Fig. shells is extremely well developed within three fami9.13). These groups were also the principal macroborers lies of bivalves ( W m e 1975; Kleemann 1980, 1983, in the Mesozoic and Cenozoic. The identification of 1990; Bromley 1981). The Pholadidae are exclusively the producer of macroborings in thin sections is diffi- borers primarily using mechanical means of penetracult, but should by tried using the morphological crite- tion. The Gastrochaeniidae and some Mytilidae penria summarized in Box 9.4. etrate predominantly calcareous substrates using meMacroborers are responsible for extensive substrate chanical and chemical means. Bivalve borings have a destruction, sediment production and the generation of major impact on the destruction of littoral sediments, secondary porosity in reef frameworks. Macroboring groups Sponges: Boring sponges have received the most attention of all groups of boring groups because of their role in bioerosion processes, sediment production and calcium carbonate dissolution (Neumann 1966; Futterer 1974; Riitzler 1975; Torunski 1979; Reitner and Keupp 1991; Ackes and Risk 1985). Boring sponges (Fig. 9.11) form large chambers, with smal1e:r galleries branching off the main charnbers. Bromley (1978) noted that the cavities can be identified even after fossilization, allowing sponge borings to be distinguished from other borings. Demospongid borings are differentiated according to the size of the external openings and the chamber system (Bromley and D' Alessandro 1984). Traces of sponge borings resembling present day Demospongiae have been found in Early Cambrian archaeocyathid reefs and are common in Permian to Cenozoic carbonates.

Box 9.4. Some morphological trace fossil criteria of macroborer groups (after Perry and Bertling 2000). Reviews assisting in the identification of borings were published by Warme (1975), Bromley (1978), Bromley and D'Alessandro (1984, 1987), Pleydell and Jones (1988), and Fiirsich et al. (1994).

Sponges: Complex branched multi-apertured networks of large chambers; multi-apertured irregular network without chambers; stellate structures with single aperture. Polychaete worms: Cylindrical brings. Round or dumbbell-shaped cross section. Mostly single-apertured. Sipunculids:Cylindrical,straight to gently curved, round cross sections, single aperture. Phoronids: Cylindrical and U-shaped, multi-aperhues, or small, branched with cylindrical branches, multiapertured. Bivalves: Flask-shaped. Single apertured. Cirripedians: Small amphora-like brings with a slitlike apertura in the narrow exterior part.

Bioerosion

the degradation of reefs (Scott and Risk 1988), and diagenetic processes affecting reef organisms (Jones and Pemberton 1988). Bivalve borings can be recognized in thin sections by vertical or oblique boreholes that often contain remains of the rock-boring shell (Pl. 5218). Records of bivalve borings in hardgrounds, reefs and fossils are known fiom the Ordovician to the Quaternary, but do not became more abundant until the Triassic.

contribute to bioerosion. Millimeter-sized holes believed to have been made by gastropods have been reported from the Paleozoic, but these data are controversially discussed. Undisputable drill holes of carnivorous naticid gastropods occur in the Late Triassic. Gastropod drilling is very rare in the Jurassic to the Early Cretaceous interval. Starting with the Late Cretaceous gastropod drilling in mollusk shells become abundant (Kowalewski et al. 1998).

Gastropods: Carnivorous gastropods drilling into various fossils are predators rather than borers, but still

'Worms': Trace fossils referred to boring activities of worms occur throughout the Phanerozoic and are

Plate 52, Bioerosion and Boring Organisms Bioerosion has a tremendous impact on carbonate sedimentation and carbonate diagenesis. The destruction of hard substrates by boring, rasping, grazing and browsing organisms is substantial in the breakdown of carbonate skeletons and for the production of fine-grained to sand-sized sediments both in warm-water and cool-water environments. A huge variety of microbes, plants and animals penetrate hard surfaces. Submarine bioerosion increases the porosity and surface area of skeletons and makes them more susceptible to dissolution. Microborers are highly effective in the biological degradation of subaerially exposed carbonate rocks (e.g. karst) and of limestones used as building stones. Microborers (-> 1-4) include autotroph (-> 1,2) and heterotroph bacteria, green algae (-> 3) and red algae, fungi (-> 4), as well as foraminifera and bryozoans. Important macroborers are sponges (e.g.clionids; Fig. 9.I), bivalves, 'worms' and cinipedian arthropods (Fig. 9.13). Microborers are known since the Proterozoic, the oldest macroborers have been reported from the Early Cambrian. Microborings are studied by stereoscan electron microscopy. SEM photos (-> 1-4) exhibit microborings of recent bivalve shells which were collected from an upper shelf slope covered by reefs and bioclastic sands (Giinther 1990). The samples were first impregnated by plastic material, followed by dissolution of the carbonate so that casts of the boreholes can be studied. Macroborings are described and differentiated in thin sections and rock and fossil samples. Many groups produce morphologically distinct borings which are valuable in evaluating paleoenvironmental conditions. Distribution patterns of microborers provide a highly promising tool for the differentiation of paleodepth zones. Modem shell-boring cyanobacteria (Mastigocoleus testarum Lagerheim). Long arched tunnels ( 0 6-10 pm) growing in all directions and forming a dense network. Short branches with terminal heterocysts (H). Generally, cyanobacterial rnicroborings are concentrated in shallower waters. Cozumel shelf, Yucatan, Mexico. Water depth 42 m. Modem shell-boring cyanobacteria (Hyella gigas Lucas and Golubic). Thick short filaments with rounded tips, arranged in clusters. 0 10-40 pm. Upper and lower photic zone. Cozumel. Water depth 10 m. Modem shell-boring green algae (Phaeophila engleri Reinke). Filaments are characteristically branched exhibiting distinct sporangia (arrows). Boring in the uppermost layer of a bivalve shell. Note the prismatic shell microstructure. Generally, green algal borings are common in shallower waters. Upper part of the photic zone. Cozumel. Water depth 2.5 m. Modern shell-boring fungi. Spherical and stalked sporangia, oriented to the shell surface. Thin hyphae connecting the sporar~gia.Fungal borings occur in shallow-marine and deeper marine environments but increase in abundance in deeper waters. Lower photic zone. Cozumel. Water depth 20 m. Macroborings in a brachiopod shell. The primary mineralogy of the brachiopod shell was Low-Mg calcite. Note differences in size, orientation and shape of the bore holes which may be attributed to the Trypanites group regarded as being excavated by polychaete worms. Early Devonian (Emsian): Anti-Atlas, southern Morocco. Micrite envelope forming cortoids: Reworked rounded echinoderm clasts are surrounded by thin micritic linings, caused by multiple microboring (arrows), and subsequent infilling of the bore holes with microcrystalline calcite cement (see Sect. 4..1.2.3). The microstructure of the echinoderm fragments characterized by reticulate pattern and cleavage planes partly preserved and partly obliterated by recrystallization of High-Mg calcite to Low-Mg calcite. D: Dasyclad green algae. Early Permian: Carnia, Southern Alps, Italy. Borings in crinoid bioclasts. The echinoderm microstructure is still preserved. Note the different infilling and the close setting of the boreholes. Middle Triassic (Muschellcalk): Southwestern Germany. Lithophagid bivalve borings in colonial corals. Remains of the bivalves are still preserved within the boreholes (arrow). Late Jurassic (Kimmeridgian): Lower Saxony, northern Germany.

1 mrn

1 mm

392

abundant in Mesozoic and Cenozoic limestones. The oldest representatives occur in Early Cambrian reefs (James and Debrenne 1980; Rowland and Gangloff 1988). Many fossil records are attributed to marine annelid worms, specificallyto polychaete worms, which include several rock- and wood-boring families. In thin sections borings attributed to polychaete annelids exhibit circular or thumb-shaped cross sections. The boring extends as a long cylindrical tube from a single entrance.

A co~mmontrace fossil often (but not unequivocally) interpreted as borings of polychaete worms is Trypanites, first de;scribed from the German Triassic, and now known .from the Early Cambrian to the recent. These borings may be observed in thin sections of reef-building org;anisms (e.g. stromatoporoids, rugose corals, bryozoans; Pemberton et al. 1988) and reef sediments as well iis in hardgrounds (Palmer 1982) and at discontinuity s~urfaces(Pemberton et al. 1980). Trypanites is charactmized by simple unbranched vertical to sinuous borings with a single opening to the surface, and with or ,without a flared entrance. The diameter (< 1 to about 2 mm) is more or less the same throughout the entire length of the boring which varies between a few millimeters to more than 20 millimeters. Geopetal sediment fil!lings within the boring may bear testimony to a reorientation of the bored fossils.

Evolution of Borers

9.3.3 Micro- and Macroboring through Time Major boring organisms have very long ranges (Fig. 9.14), but the contribution of the groups varied strongly during the Phanerozoic. Older bioerosion processes that can be qualitatively and quantitatively compared with modern processes are relatively young and have been effective since the Late Tertiary. It has been suggested that bioerosion, predation and grazing features were only fully present in modem Mesozoic-Cenozoic reefs (Wood 1998,1999). The biological destruction of recent coral reefs is an impressive example of the overwhelming role of organisms in degradation and recycling of carbonate sediments (Bromley 1978;Hutchings 1986).Although rnicroborers have been known since the Precambrian and macroborers since the Cambrian, processes comparable in quality and quantity with the biological destruction in modem reefs seem to have developed relatively late in the Phanerozoic and did not reach their full intensity in reefs before the Late Tertiary (Fig. 9.15). Examples, indicating strong bioerosion are known however, from Early Paleozoic stromatoporoid reefs (Nield 1984), from Triassic coral reefs (Stanton and Fliigel1989) and from Jurassic sponge and coral reefs (Pisera 1987; Reitner and Keupp 1991; Fliigel 1993).

9.3.3.1 Qualitative Changes in Micro- and Cirripedians: Some ascothoracican Cinipedia liv- Macroborer Groups ing in shallow seas create cavities in skeletons (e.g. corals, bivalves, echinoids) and various carbonate subMicroborers were important in Paleozoic and poststrates including hardgrounds. Records of Paleozoic cir- Paleozoic times, but the impact and the composition of ripedian borings (Webb 1987)are rare as compared with macroborer communities seem to have increased durthe Mesozoic (Fig. 9.13; Fiirsich and Wendt 1977) and ing the Mesozoic and the Cenozoic, as exemplified by the Cenozoic. The millimeter-sized borings are shoe- Fig. 9.15. The oldest macroborers in the Early Camor sack-:like with a narrow opening at a neck to the ex- brian and Ordovician occurred in reef environments. terior. A slit-like extension at the anterior end gives the In contrast, the most intensive boring in the Silurian aperture the shape of a comma. took place not in reefs but in deeper-water muddy ramp settings. Copper (2002) discussed the possibility that Phonmids and sipunculids: Less common macroboring developed in deeper shelf settings before invadborer trace fossils are interpreted as being produced by ing shallow reef platforms. Macroboring occurred in phoronicls and sipunculids.Phoronid borings have been Early and Middle Devonian reefs, but is only poorly described from the German Triassic Muschelkalk and documented in the Farnennian and was not a dominant from the Late Cretaceous chalk. The borings correspond process in Carboniferous and Early Permian reefs to small irregularly winding tubes with diameters less (Webb 2002; Wahlman 2002). The rate of the destructhan 0.5 mm. Modem sipunculid borings are common tion of Late Permian reefs by borers and grazers was in coastal rocks and reef limestones. They appear as low, because free substrates were rapidly occupied by clubs in thin sections (Rice and Macintyre 1972). If all encrusting organisms. Macroborers (predominantly or some Trypanites borings were attributed to spirun- sponges) were more important than microborers culids instead of polychaete worms, the stratigraphic (Weidlich 2002). Interestingly, the composition of record would range from the Cambrian to the Quater- microborers did not change from the Permian to the nary. Triassic, despite significant changes in the reefal host

Macroboring in Reefs

I

I

MICROBORERS MACROBORERS

1

organisms, .and remained similar during the Mesozoic and Cenozoic (Schmidt 1992; Balog 1996; Vogel et al. 1999). No nnacroborers are known from Early Triassic carbonate platforms. Anisian macroborers are bivalves and cirripedians. Macroborer diversity and abundance increased significantly in Norian and Rhaetian reefs,

Fig. 9.14. Fossil record of micro- and macroborers and substrate excavating grazers destroying carbonate skeletons and lithified substrates. The fossil record of boring organisms can be estimated through trace fossils. In many cases a reasonable delineation of the responsible group or borer is possible, but often the assignment of the trace fossils remains controversial. The range chart summarizes borings in different settings (reefs, hardgrounds). In addition, the presence of drill holes in marine invertebrate shells attacked by predators (mainly gastropods) is indicated. Black columns refer to times where the group contributedgreatly to bioerosional processes; open columns refer to times with a less significant influence of borers. Note that the columns also include time intervals with no or questionable records. Based on Kobluk et al. (1978). Vogel (1993), Kowalewski et al. (1998), Perry and Bertling (2000) and other sources.

possibly indicating a parallel evolution of Triassic reefbuilding corals and macroborers (Perry and Bertling 2000). Norian and Rhaetian ieefs were attacked by bivalves; sponge boring activity increased in the Rhaetian. The contribution of macroborers to bioerosion increased strongly during the Jurassic (Leinfelderet al. 2002). In the Liassic bivalves became the dominant group. Middle and Late Jurassic reefs suffered from boring sponges, bivalves and worms. Boring gastro-

Fig. 9.15. Impact of micro- and macroborings on reefs through time: The graph is based on the Erlangen PaleoReef Database (see Kiessling and Fliigel 2002). Bioerosion was low to moderate in Paleozoic reefs, increased significantly during the Triassic, and maintained high but fluctuating levels from the Jurassic to the Recent. The Mesozoic increase may be explained by the coeval diversification of predators. Caution should be exercised when using the graph: The Early Triassic decline is caused by the single occurrence and rare records of microbial reefs, and the complete lack of metazoan reefs. These microbial reefs were not attacked by microborers; macroborers were not described. Grazers were abundant, as indicated by common herbivorous gastropods. The decline of microborers in the Middle Jurassic was probably caused by the low number of reefs in the database. Similarly, the decline in the Paleogene may be due to bias caused by the lack of sufficient data.

Paleobathyrnetry of Microborers - --

Permian-Triassic Sponge, algal, reefs Traces of 2'

"

05 sg

-P 2% EG

5. 'j

O r '

1' 2

3 4 6 7

/ I

II

Today H. caespitosa

H. gigas Masti ocoleus concfocelis Ostreobium ,Plectonema

Silurian Coral-stromatoporoid Traces of 3 5' 6 7

Triassic Bivalve-crinoid reefs Traces of 1 2' 7 Trace of 2 : vertical

II

Jurassic Sponge reefs I Traces of 2' 5' Trace of 2 : vertical

i

Fig. 9.16..Bathymetry of different Phanerozoic reef types inferred from microborer associations. The figure summarizes investigations of modem shallow-water coral reefs of the Bahamas and deep-water coral reefs of the North Atlantic, and case studies of' ancient reefs from the Silurian of Gotland Island, the Permian of Tunisia, the Middle Triassic Muschelkalk of Germany and Late Triassic reefs in the Northern Calcareous Alps and Turkey, and Late Jurassic reefs in southwestern Germany. The bathymetric zones are characterized by (1) the appearance of borings assigned to cyanobacteria (Hyella, Mastigocoleus) versus those affiliated with green algae (Ostreobium) or red algae (Conchocelis), (2) the frequency of algal-related borings perpendicular to the surface of the substrate versus those oriented parallel to the substrate surface, and (3) the occurrence of borings attributed to obligate photoautotrophs (cyanobacteria, algae) versus those produced by obligate or facultative chemoheterotrophs (fungi). Each ichnocoenosis is named after key taxa. Not shown in the figure is the shallow eutrophic zone I corresponding to the supratidal zone. The shallow eutrophic zone I1 covers the intertidal zone and probably the uppermost part of the subtidal zone. The shallow eutrophic zone I11 corresponds to the well illuminated part of the subtidal zone (light intensity 10%of the surface light). The deep eutrophic zone comprises the less to poorly illuminated subtidal zone (light intensity to about 1% of the surface light). The dysphotic zone (light intensity to 0.01 to 0.001% of the surface light) is not yet clearly defined by microborers. Similarly, the microborer associations of the aphotic zone characterized by a dominance of bacteria, fungi as well as sponge and bryozoan borings need further investigation. The asterisks mark the presence of key taxa of the respective photic zone. The use of diagrams showing light intensity versus water depths may lead to a rough estimation of absolute water depths. But note that light intensity depends on many factors, such as latitude, turbidity of the water, or overshadowing of the bored substrate by densely growing organisms. Modified from Vogel et al. (1999).

pods became common in Early Cretaceous reefs. Late Cretaceous rudist reefs exhibit macroborer associations consisting of bivalves, worms, sponges and cimpedians (Johnson et al. 2002). Paleogene macroborer associations are similar to those of the Late Cretaceous. A significant change in the abundance and composition of bioerosion by macroborers took place during the Oligocene and continued in the Miocene. Late Tertiary reefs exhibit boring patterns similar to recent ones (Pleydell and Jones 1988; Penin 2002).

9.3.3.2 Quantitative Changes in the Intensity of Macroboring in Coral Reefs Boring intensity can be measured by the semi-quantitative assessment of ichnospecies abundance using field and laboratory samples, X-ray techniques, serial thin sections and point-counting (Modem coral reefs: Klein et al. 1991; Risk et al. 1995; Perry 1998). Preliminary data provided by Perry and Bertling (2000) suggest that ancient reefs were variously affected by macroborers

Describing Microbialites, Encrusters, and Borings

395

Box 9.5. Describing microbialites, encrustations and borings. Microbial carbonates Micrite: Inhomogeneous or homogeneous texture? Peloidal micrite? Differences in color? With or without undulation? Peloids: Within the micritic matrix? In interskeletal or intraskeletal protected cavities? Silt- or fine sand-sized grains? Peloids with dark center surrounded by a clear rim of euhedral calcite crystals? Clotted fabric: Frequency of micritic and peloidal micritic areas? Relation of the clotted fabrics to non-clotted fabric areas? Remains of tubular and filamentous cyanobacteria? Calcimicrobes: Tiny tubes with micritic walls, often bifurcated. Morphological type (see P1. 53), frequency, irregular occurrence or in layers? Fabric: Non-laminated or laminated fabric (-> microbialites or stromatolites; see Fig. 9.1 and Box 9. I)? Non-laarzinatedfabric: Irregular, sometimes dome-shaped structuresconsisting of mesoclots (-> thrombolites)? Domeshaped, sometimes bushy structuresexhibiting micritic, peloidal and coarsely zoned microstructures (-> dendrolites)? Dome-shaped structures consisting predominantly of undifferentiated micrite (-> leiolites)? Laminated fabric: Macroscopic growth form (dome shaped, columns, high or low forms; fine- or coarse-grained laminae:; agglutinated laminae)? Internal structures (individual laminae composed of micrite peloids or mesoclots)? Disruptions of the lamination by sediment, borings or biogenic encrustations? Geometrical arrangement of basic growth elements (see Logan et al. classification, Fig. 9.3)? Biogenic encrustations Occurrence of the encrusters: On or within substrates (epibenthic or endobenthic)? Location o f the crusts: Upward growing crusts on a surface or pendant crusts in cavities? Thickness $ofthe crust: Uniform or laterally decreasing or increasing? Interruptions of crustbuilding: Layers separated by sediment or cement? Bored surfaces of layers? Substrate: Lithified surface, fossil or other sedimentary grains? Carbonate cement? Boundary encruster/substrate? Growthforms: Thin or thick crusts, sheets, mounds, plates, semi-erect or erect forms)? Sequential patterns: Composition of crusts consisting of different encrusters? Relation between parts formed by specific encrusters? Thickness of the individual crust layers? Relation between encrusters and microbialites: Crusts embedded within microbialites? Distinct or vague boundaries? Encrusting organisms: Identity (encrusting organisms should be differentiated to the lowest possible taxonomic level)? Species diversity and percent cover of upper and undersides of host organisms (e.g. corals, stromatoporoids, shells)? Proportion of autotrophic to heterotrophic encrusters? Bioerosion and borings Microborers: SEM characterization. Which groups (bacteria, cyanobacteria, algae, fungi, foraminifera, bryozoans)? Relative frequency? Growth sequences? Macroboru-s: Thin-section characterization. Simple tubes or branched networks? Shape of the bore holes (cylindrical, dumb-shaped, amphora-like)? Mode of the exterior opening (single or multi-apertured openings; circular, elliptical or slit-like openings)? Assignment of the trace fossils to major groups: Sponges, worms, bivalves or cirripedians? Dominating group? Dimension of the borings: Lengths and diameters of the bore holes? Orientation of the borings: Vertical, oblique, horizontal, irregular, or fluctuating? Substrate type: Rock surfaces? Lithified surface, e.g. hardgrounds and disconformity surfaces? Fossils? Sedimentary grains? Relation borings and substrate: Depth of the penetration below the bored substrate? Borings only in specific fossils? Cross-cutting patterns? Association of boring organisms and the organisms of the host substrate: Repeated co-occurrence of particular borers and specific host fossils? Borings only in specific biofacies types (e.g. only in coral reef limestones)? Quantitative data: Percentage of macroborer groups within a defined area? Density of macroboring measured by pointcounting or image analysis considering macroborers versus the non-bored substrate areas?

depending on reef type, environmental setting and dominant macroborers. The abundance of borings in coral reefs expressed by the ratio of the point counter percentage of borings to the percentage of non-attacked substrate areas per cm2 is low and moderate in the Late Triassic (Northern Alps: 0.01 - dominating macroborers bivalves and sponges, and 0.09 - mainly worms; Nayband Forma-

tion, Iran: 0.14 - worms dominate over bivalves and cirripedians) and in the late Early Jurassic (Morocco: 0.08 and 0.12 - dominated by cirripedians), moderate in the Middle Jurassic (Iran, India, Chile: 0.12 - bivalves and worms equally important), and increases in the Late Jurassic, Oxfordian, and Kimmeridgian microbial-coral reefs (central and western Europe: 0.330.59 - dominated by bivalves and worms followed by

396

sponges). In contrast, low-energy carbonates of the deep-water turbid facies dominated by bivalves exhibit a low boring intensity of 0.03-0.06. A moderate to high abundance of macroborers is found in Late Cretaceous coral reefs (Coniacian, Bavaria: 0.18 - bivalves and sponges dominate over worms; Turonian, France: 0.44 - worms dominating over bivalves). Factors influencing these patterns are apparently the existence of clear or siliciclastic-influenced water and lagoonal or shallow/deep fore-reef settings. Microfacies analyses of reef limestones but also of platform carbonates should provide more quantitative data that can be used as measures of the changes in macroboring and bioerosional intensity during earth history.

Practical Advices

9.4 Practical Advice: How to Describe Microbialites and Stromatolites, Biogenic Encrustations and Borings? Box 9.5 summarizes the questions which should be kept in mind when studying the biological aspects of the formation and destruction of carbonate sediments.

Basics: Limestones are biological sediments Microbial carbonates and stromatolites Aitken, J.D. (1977): Classification and environmental significance of cryptalgal limestones and dolomites. With illustrations from the Cambrian and Ordovician of southwestern Alberta. - J. Sed. Petrol., 14,405-441 Atlas, R.M., Bartha, T. (1981): Microbial ecology: Fundarnentals and application. -569 pp., Reading (Adisson-Wessley) 9.3.4 Microborer Associations are Proxies Burne, R.V., Moore, I.S. (1987): Microbialites: organofor Palelo-Water Depths sedimentary deposits of benthic microbial communities. - Palaios, 2,241-254 The bathymetric distribution of modern endolithic Castanier, S., Le Metayer-Kevrel, G., Perthuisot, J.-P. (1999): Ca-carbonates precipitation and limestone genesis - the microborm depends predominantly on the intensity and microbiologists point of view. - Sedimentary Geology, spectral composition of light. The association of micro126,9-23 borers is different in the eu-, dys- and aphotic zones. Chavetz, H.S. and Buczynski, C. (1992): Bacterially induced Microborers exhibit strong water depth controls; the lithification of microbial mats. - Palaios, 7,277-293 association patterns therefore represent one of the best Characklis, W.G., Marshall, K.C. (eds., 1990): Biofilms. 796 pp., New York (Wiley) paleobathymetric criterium (Vogel et al. 1999). This apCohen, Y., Castenholz, R.W., Halvorson, H.D. (eds., 1984): proach is based on the Microbial mats: stromatolites. - MBL Lectures in BiolSEM study of the composition and distribution of ogy, 3,498 pp., New York (Alan R. Cis) modern shallow- to deep-marine microborers, Gerdes, G., Krumbein, W.E. (1987): Biolaminated deposits. investigation of trace fossils of microborers from an- Lecture Notes in Earth Sciences, 9, 1-183 cient environments that can be assigned to specific Grey, K. (1989): Handbook for the study of stromatolites and associated structures. - Stromatolite Newsletter, 14,82-171 paleo-water depths according to paleontological and Grotzinger, J.P., Knoll, A.H. (1999): Stromatolites in Precamfacies criteria, brian carbonates: Evolutionary mileposts or environmenmorphological comparison of ancient and modern tal dipsticks. -Annual Review of Earth and Planetary Scimicroborings, which surprisingly exhibit a high deences, 27,313-358 Kalkowsky, E. (1908): Oolith und Stromatolith im nordgree of correspondence, and deutschen Buntsandstein. - Zeitschrift der deutschen establishment of characteristic ichnocoenoses degeologischen Gesellschaft, 60,68- 121 fined by the relative dominance of variously light- Kennard, M.M., James, N.P. (1986): Thrombolites and stroadapteld groups (cyanobacteria, green algae, red almatolites: two distinct types of microbial structures. gae, fungi) and the occurrence of the most common Palaios, 1,492-503 Logan, B.W., Rezak, R., Ginsburg, R.N. (1964): Classificaendoliihs. tion and environmental significance of algal stromatolites. These studies resulted in bathymetric subdivisions - Journal of Geology, 72,68-83 of ancient subtidal, slope and deeper basinal sequences. Monty, C. (ed., 1981): Phanerozoic stromatolites. Case histories. - 249 pp., Berlin (Springer) The subdivisions correspond to bathymetric zones recPaul, J., Peryt, T.M. (2000): Kalkowsky's stromatolites reognized in modern environments (see summary in visited (Lower Triassic Buntsandstein, Harz Mountains, Glaub 1994) and identified in the Silurian (Glaub and Germany).- Palaeogeography, Palaeoclimatology, PalaeoBundschah 1997), Devonian (Vogel et al. 1987), Perecology, 161,435-458 mian (Bal.og 1996) and Triassic (Schmidt 1990, 1992, Pratt, B.R. (1982): Stromatoliticframework of carbonate mudmounds. - J. Sed.Petrol., 52, 1203-1227 1993; Gla.ub and Schmidt 1994; Balog 1996), Jurassic Reid, R.P., Visscher, P.T., Decho, A.W., Stolz, J.F., Bebout, and Cretaceous (Glaub 1994; Hofmann 1996), and TerB.M., Dupraz, C., Macintyre, O.G., Paerl, H.W., Pinkney, tiary (Radtke 1991) The distribution patterns have a J.L., Prufert-Bebout, J.L., Steppe, T.F., DesMarals, D.J. high potential for estimating the water depths of an(2000): The role of microbes in accretion, lamination and early lithification of modem marine stromatolites.- Nacient reef:; (Fig. 9.16).

Basics: Microbes, Encrusters, Borers

ture, 406,989-992 Riding, R.E. ((XI., 1991): Calcareous algae and stromatolites. - 57 1 pp., Berlin (Springer) Riding, R.E. (1999): The term stromatolites: towards an essential defintion. - Lethaia, 32,321-330 Riding, R.E. ((2000):Microbial carbonates: the geological record of cidcified algal mats and biofilms. - Sedimentology, 47, 179-214 Riding, R.E., Awramik, S.M. (eds., 2000): Microbial sediments. - 33 1 pp., Berlin (Springer) Schneider, J., Campion-Alsumard, T. (1999): Construction and destruction of carbonates by marine and freshwater bacteria. -European Journal of Phycology, 34,417-426 Shapiro, R.S. (2000): A comment on the systematic confusion of thrombolites. - Palaios, 15, 166-169 Walter, M.R. (ed., 1976): Stromatolites. - Developments in Sedimento:logy,20,790 pp. Further reading: K038, K137 Biogenic encrustations

Brett, C.A. (1988): Paleoecology andevolution of marine hard substrate communities: an overview.- Palaios, 3,374-378 Dupraz, C., Stsasser, A. (2002): Nutritional models in coralrnicrobialite reefs (Jurassic, Oxfordian, Switzerland):Evolution of trcsphic structure as a response to environmental change. - I'alaios, 17,449-471 Jackson, J.B.C. (1979): Morphological strategies of sessile animals. - In: Larwood, G., Rosen, B.R. (eds.): Biology and systematics of colonial organisms. - 499-556, London (Academic Press) Moussavian, E:. (1992): On Cretaceousbioconstructions: composition ar~devolutionary trends of crust-building associations. - Facies, 26, 117-144 Rasser, M., Piller, W. (1997): Depth distribution of calcareous encrusting associations in northern Red Sea (Safaga, Egypt) and their geological significance. - Proceedings of the 8th [nternational Coral Reef Symposium, 1, 743748 Schmid, D.U. (1996): Marine Mikrobolithe und Mikroinkrustierer aus dem Oberjura. - Profil, 9, 101-251 Taylor, P.D., Wilson, M.A. (2002): A new terminology for marine organisms inhabiting hard substrates. - Palaios, 17,522-525 Walker, S.E., Miller, W. (1992): Organism-substraterelations. Toward a logical terminology. - Palaios, 7, 236-238 Further reading: K2 13 Bioerosion, micro- and macroborers

Anagnostidis, K., Golubic, S., Komarek, J., Lhotsky, 0.(eds., 1988): Cyanophyta (Cyanobacteria). Morphology, Taxonomy, Ec~dogy.- Algological Studies, 5043,584 pp.

397

Bertling, M. (1999): Late Jurassic reef bioerosion - the dawn of a new era. -Bulletin of the Geological Society of Denmark, 45, 173-176 Bromley, R.G. (1970): Borings of trace fossils and Entobia cretacea Portlock, as an example. - In: Crimes, T.P., Harper, J.C.C. (eds.): Trace fossils, 49-90 Bromley, R.G. (1990): Trace fossils: Biology and taphonomy. - Special Topics in Palaeontology, 3,280 pp. Bromley, R.G. (1994): The palaeoecology of bioerosion. In: Donovan, S.K. (4.): The paleobiology of trace fossils. - 133-154, London (Belhaven) Glaub, I, (1994): Mikrobohrspuen in ausgewiihlten Ablagerungsriiumen des europtiischen Jura und der Unterkreide (Klassifikaton und Palokologie). - Courier Forschungsinstitut Senckenberg, 174, 1-324 Golubic, S., Friedman, I., Schneider, J. (1981): The lithobiontic ecological niche, with special reference to microorganisms. - J. Sed. Petrol., 51,475-478 Hallock, P. (1988): The role of nutrient availability in bioerosion. Consequences to carbonate buildups. - Palaeogeography, Palaeoclimatology, Palaeoecology, 63,275-291 Hassan, M. (1997): Modification of carbonate substrate by bioerosion and bioaccretion on coral reefs of the Red Sea. - Ph.D. Thesis Kiel University, 126 pp. Hutchins, P.A. (1983): Biological destruction of coral reefs: a review. -Coral Reefs, 4,239-252 Kobluk, D.R., James, N.P., Pemberton, S.G. (1978): Initial diversification of macroboring ichnofossils and exploitation of the macroboring niche in the lower Paleozoic. Paleobiology, 4, 163-170 Kowalewski M., Dulai, A., Fiirsich, F.T. (1998): A fossil record of holes: the Phanerozoic history of drilling predatory. - Geology, 26, 1001-1004 Perry, C.T., Bertling, M. (2000): Spatial and temporal patterns of macroboring within Mesozoic and Cenozoic coral reef systems. - In: Insalaco, E., Skelton, P.W., Palmer, T.J. (eds.): Carbonate platform components and interactions. - Geol. Soc. London, Spec. Publ., 178,33-50 Lynch, J.M., Hobbie, J.E. (1988): Micro-organisms in action: concepts and applications in microbial ecology. 2nd edition. - 363 pp., Oxford (Blackwell) Radtke, G., Hifmann, K., Golubic, S. (1997):A bibliographic overview of microscopic and macroscopic bioerosion. Courier Forschungsinstitut Senckenberg, 201,307-340 Vogel, K.(1993): Bioeroders in fossil reefs. - Facies, 28, 109-114 Vogel, K., Balog, S.-J., Bundschuh, M., Gektidis, M., Glaub, I., Kruschina, J., Radtke, G. (1999): Bathymetric studies in fossil reefs, with microendoliths as paleoecological indicators. - Profil, 16, 181-191 Further reading: KO38

Chronostratigraphic Time Scale Period1 Epoch

EpochIStage

Age

(Ma)

Period1 Epoch

EpochIStage

I

Tcurnaisian

Nman

Famennian

Aquihnian Frasnian

Chalhn Carnian Rupelian Priabonian Bartonian

Ladinian

Eifelian

Luteban Ypresian

1

I

Emsian

I

Ragian Lochkovian

&iddm Ludlowian

Campanian

I

Wenlockian Kungurian Artinskian

T6ychan

Liandoverian

Aeronan

Sakrnarian

RhuMaman

Turonian Asselian Gzhdian Kasirnwian

Barremian

1

4 ate Early

Serpukhovian

rremadocian

I

Tlthonian

Callobian

Tournaisian

Bathmian Bajoclan Aalenian

Slnemurian

Fig. 9.17. Chronostratigraphic time scale for the Phanerozoic (Golonka and Kiessling 2002) used throughout this book.

10 Fossils in Thin Section: It is Not That Difficult

Many students of carbonate rocks are bewildered and sometimes frustrated by the morphological and microstructural diversity of skeletal grains and are satisfied by distinguishing major fossil groups. The present chapter will hopefully demonstrate that more detailed identifications of thin-section fossils are not so diicult and that identifications at lower systematic levels can provide fresh insights into the environmental controls on depositional processes. However, keep in mind, that thin-section fossils present only a part of the biota present in the: rock and that thin-sectiondiversity is not equivalent ts biotic diversity (see Sect. 6.2.1.4). The chapler consists of four parts. The first part discusses specilic problems related to the study of fossils in thin sections. The second part documents the principal criteria used to distinguish fossil groups commonly or abundantly occumng in thin sections of limestones, their distribution in time and their significance with regard to carbonate production, the recognition of paleoenvironments and depositional settings. The fourth part deals with the potential of thin-sections in recognizing assemblage zones Because a good picture may be worth more than a thousand words, the last chapter includes a list of monographs and papers showing useful thin-section microphotographs Many fossils are restricted to specific time intervals. Knowledge of distinct time ranges is necessary for estimating their value as guide fossils or in recognizing time-dependent facies types. Age and time ranges of the fossils discussed in this chapter and throughout the book are noted within the frame of the chronostratigraphic time scale shown in Fig. 9.17, see left page!

10.1 Specifics of Thin-Section Fossils 10.1.1 HOWto Determine Fossils in Thin Sections?

Several well-illustrated books assist in a first identification of skeletal grains: Horowitz and Potter (1971), Majewske (1974), Lucas et al. (1976), Scholle (1978), and Adams and MacKenzie (1998).

Determining fossils in thin sections used in microfacies analysis may be difficult, because: randomly cut sections of rnicrofossils may exhibit very different shapes and outlines, resulting in an often confusing taxonomic situation of 'thin-section fossils' (Racki and Sobon-Podgorska 1992), diagenetic alterations may produce 'diagenetic taxa' as, e.g. exemplified by calcimicrobes (e.g. Renalcis: Pratt 1984), or some foraminifera whose tubular structures are difficult to distinguish from micritized shells or agglutinated worm burrows, the lack of modem counterparts of many extinct fossils may cause very different opinions varying from author to author regarding the systematic position and classification of fossils known only from thin sections. Despite their uncertain position, these 'microproblematica' are often excellent facies indicators and can be used as guide fossils, very small-sized skeletal grains may present problems in attributing the grains to specific systematic groups as demonstrated by the investigation of silt-sized fragmented material from known organisms (Feray et al. 1962;Matthews 1966;Force 1969). In general, skeletal identity is lost when the particle size lies below 62 pm. Additional SEM studies significantly increase systematic assignment, particularly of mollusc shells. Some fossils (e.g. larger foraminifera) common in thin sections require oriented sections to follow defined planes. These sections may be rare in randomly cut microfacies samples, contrary to the opinion of many geologists who believe that thin sections yielding abundant microfossils must be useful in generic or specific determinations. The problem is demonstrated by an Early Permian fusulinid limestone from Oman (Fig. 10.1). The sample was studied in six over-sized thin sections cut in various directions. These thin sections exhibit more than 2000 sections through the spindle-shapedforaminifers. Only a very small number of the sections can be used in systematic assignments as shown by a thin section with 457 sections of fusulinids. 25.5% of the fossils represent broken shells and 10.5% of the samples are

400

Cutting Effects

Fig. 10.1. Highly fossiliferous fusulinid foraminifera1 limestone. The sample yields very abundant shells, but only a few sections exhibit morphological criteria allowing a taxonomic assignment, which is imperative if the age determination of the sample has priority. Early Permian: Baid area, eastern Oman. Scale is 1 cm.

cut extremely obliquely and are therefore not suitable for taxonomic determinations. 64% of the sections can be attributed to specific cutting planes, but most of these sections iun only parallel or oblique to the coiling axis of the shells. These sections exhibit morphological criteria which are of taxonomic value only in combination with axial and sagittal sections showing the arrangement of the whorls around the initial part of the shell (PI. 68). Sections allowing a generic determination (Par-afusdina)are extremely rare: 4.5% of all sections present in the thin section. What can we learn from this example? Be aware of which problems should be solved with your sample. If you are aiming at indications of paleoenvironment, a sample exhibiting the abundance and orientation of the foraminifera1 tests will be sufficient. But if you want to know the age of the sample, you should send a sufficiently large sample that allows oriented thin sections to be prepared by your paleontology colleague, specialized i n the study of larger foraminifera (look for lists In the net), and ask for friendly cooperation. Cutting effects Obviously, the reconstruction of the three-dimensional geometry of fossils from two-dimensional cross sections can be hazardous if only a few sections are examined (Fig. 10.2). Microstructural features are of value in discriminating fragments of mollusks and echinoderms, but other groups (e.g. foraminifera, calcareous algae) require oriented sections along defined planes.

Several attempts have been made to reduce the geometric diversity of organisms with hardparts and the wealth of figures seen in thin sections. The approach used by Horowitz and Potter (1971) concentrates on the basic geometry and distinguishes five major groups: (1) Straight or coiled single cones. tubes or cylinders; (2) colonial tubes; (3) valves; (4) multi-element or multi-plated shells, and (5) reticulate or rectangular and cystose networks. The identification key developed by Fliigel (1982) considers the two-dimensional thin-section figures and distinguishes six groups: (1) Circular and elliptical figures, (2) U and V shaped figures, (3) curved figures, (4) net-like figures, ( 5 )layered structures, and (6) chains of segments. Although both authors underline the pitfalls of these groupings, beginners and people eager to become acquainted with the mysteries of biotic identifications in thin sections, will find these 'cookery books' useful.

10.1.2 Which Fossils in which Time Interval? Most thin-section fossils have wide stratigraphic ranges, but different stages are characterized by the association and abundance of common and dominating fossil groups found in limestones. Fig. 10.3 and Box 10.1 give a rough picture of the larger groups which can be expected in limestones of different age and different depositional settings.

Cutting Effects

/

40 1

7/

Dasycladacean algae

I

-

-- --

Foraminifera

I

@ f (i$ w

a

-

1 rnm

8

Y3

I

Fig. 10.2. Cutting effects. Random cutting of microfossils results in very different figures. Relatively few of these figures show all the morphological criteria necessary for a determination at low taxonomic levels. Generally a combination of several figures and oriented sections are needed for generic or specific determinations of thin-section fossils. In contrast, random cuts can often be assigned to major fossil groups, if additional criteria (e.g. size, microstructure) are considered. A: Different sections through the cylindrical calcareous skeleton of the Late Paleozoic dasyclad green alga Velebitella (see P1. 5911) produce various figures. The diagnostic taxonomic criteria must be derived from longitudinal, oblique, tangential and cross sections. Modified from Kochansky-Devidt (1964). B: The Late Paleozoic smaller foraminifera1 genus Climacanzmina is characterized by a calcareous test whose chambers are biserially arranged in an early stage and uniserially in the last growth stage. The aperture is cribrate. The figure displays oriented sections which in combination exhibit these criteria and allow the generic determination of the microfossil. Modified from Cummings (1958).

10.1.3 Practical Advice

spect to bedding planes and geopetal structures (vertical, parallel, oblique). Consider the size of the grain. It is imperative to The following text summarizes some points which should be considered looking at fossils in thin sections. know the field of view of the microscope at each magniBrowsing among thin-section photographs in books and fication. Evaluate the presence of major fossil groups (e.g. microfacies monographs (the penultimate point) is certainly very tempting, but often misleading. bivalves, echinoderms, calcareous algae) and decide which group should be investigated in detail (e.g. calUse various techques (polarized light, CL staining etc.). careous algae), because they give indications of paleoCheck the orientation of the thin section with re- environmental constraints and the age of the sediment.

Tertiary Cretaceous Jurassic Triassic Permian Carboniferous Devonian Silurian Ordovician Cambrian

-

0

I,

0 Abundant in thin section Fig. 10.3. Gcncralized distribution of the major fossil groups occurring in thin sections of Phanerozoic limestones. No fossil record

Not or rare in thin sections

Common in thin sections

Occurrence ot T h i n - S e c t ~ o nI:os\lis

-

criteria in reconstructing the shape and internal strucPi cJser\~attoti Test the preservation of the fossils. ture of the fossils. Consider the possibility of recrystallization, diagenetic solution or replacement of the original microstruc- Skeletal mineralogy and microstructurr Look at the mineralogical composition of the fost tlre. * Are the fossils complete or fragmented? sils (calcareous, siliceous, phosphatic, organic). Decide whether the original mineralogy of the skelConsider the degree of fragmentation and the reetal grain was aragonitic or calcitic. Preservation of the sulting sizes. bioclast as a mold or cast indicates a primary aragoAre the fossils in place or transported? * In place fossils may need several sections in order nitic mineralogy that has been subsequently altered. Well-preserved microstructures point to a primary caito recognize the variability of internal structures. In-place fossils, particularly colonial reef organisms, citic mineralogy. For shells try to discriminate the original microstrucare often large and their study requires oversized thin tures and structures produced by diagenesis. sections or peels (up to 10 and 20 cm in length). Describe the microstructure by looking at the shape, In-place fossils often have characteristic growth forms which will influence the figures seen in thin sec- size and orientation of the component crystals. tions Advancing systemaric determinations Bear in mind the age of the rock examined, and the Qualiry of the thin sections Compare the thin sections with the rock sample, and likely biota will be encountered. Browse among the thin-section microphotographs if necessary, make additional and better oriented thin in the microfacies monographs (see Sect. 10.3'1. sections, * If you think you have found a reliable assignment Differentiate between random sections and oriented to a specific group or on taxa, look for further infonnasections. = Some fossil groups, particularly sessile benthos (e.g. tion in the relevant parts of Sect. 10.2. corals, coralline and stromatoporoid sponges) need at least two sections (@mallel and perpendicular to the 10.2 Diagnostic Criteria of Fossils in growth direction). Indicate the orientation of the section using defined Thin Sections tcrrns (e.g, ~'ertical,tangential. oblique!. a Look especially for sections that contain defined Thin-sect~onfossils comprise six mfornlal group: morphological criteria necessary for raxonomic detercyanobacteria (calcimicrobes) and calcareous algae. nlinations (e.g. axial structures in larger foraminifera). foraminifera and other protozoa (radiolarians, calpioDecide which of the taxonomically important critenellids). ria are shown by the sections and try to combine these

Box 10.1. E'ossil gi.oups conzrw~zin tlzitz sections of rxarine litmstorws formed in different settings. Ranking indicates the approxiinaic frequency.Note that this list is highly subjective and does not consider specific associations, e.g. in reel limestones and slope sediruentb, as well as microfossils of uncertain systematic position present predominantly in inner and outer platfonn environ~nenrsarid reefs. Late 'firliar! Innel- shullowpla@or-m:Smaller benthic foraminifera, cor-

allinacean red algae, mollusks, bryozoans, barnacles. serpulids. ostracods Eclgc: Reefs with coralli~~acean red algae, corals, bryozoans Slope: Benthic and planktonic foraminifera Basin: Planktonic foraminifera Earl? 'Tertiarj Inner clzullow pla@orrn Smaller and larger benth~cfora-

'

rnmfera, calcareous dasyclad algae and udoteacean green algae, corallinacean and squamariacean red algae

Edge: Larger foraminifera Slope: Planktonic and benthic foraminifera Basin: Planktonic foraminifera Upper Late Cretaceous Inner shallow platform: Benthic foraminifera. mollusks,

bryozoans, echinoderms Edge: Rudists Slope: Planktonic and benthic foraminifera.'calcispheres'.

siliceous sponges Basin: Planktonic foraminifera, 'calcispheres' Continued next pdgi.'

Occurrence ot T h ~ n - S e c t i o nFossils

Box 10.1. Continued Lower Late Cretaceous Inner shallow platform: Benthic foraminifera, gastropods, rudists and other bivalves, Edge: Rudists Outer platform: Benthic foraminifera, echinoderms, cephalopods Basin: Planktonic foraminifera, 'calcispheres', cephalopods Early Cretaceous Inner shallow plarform: Benthic foraminifera, dasyclad and udoteacean green algae, gastropods Edge: Corals, calcimicrobes, benthic foraminifera Outer platform: Benthic foraminifera, sponges, echinoderms, bivalves, cephalopods Basin: Planktonic foraminifera, cephalopods Late Jurassic Inner shallow platform: Benthic foraminifera and dasyclad green algae, solenoporacean red algae, calcimicrobes, gastropods, serpulids Edge: Corals and 'hydrazoans', siliceous sponges, brachiopods, bivalves, echinoderms Slope: Pelagic bivalves, echinoderms, benthic foraminifera, 'calcispheres', cephalopods Basin: Calpionellid tintinnids, radiolarians, pelagic crinoids, pelagic bivalves, 'calcispheres'; siliceous sponges, bivalves, cephalopods Early Jurassic Inno. shnllnw plafol-m: Benthic foraminifera, dasyclad green algae, calcimicrobes, gastropods Edge: Benthic foraminifera Outer plafirm: Benthic foraminifera, bivalves Basitl: Radiolarians, sponge spicula, cephalopods Late Triassic Inner slzullow platform. Benthic foraminifera, dasyclad green algae, calcimicrobes, bivalves Edge: Reefs with scleractinian corals and coralline sponges, foraminifera, solenoporacean red algae Slope: Echinoderms, bivalves, brachiopods Basin: Thin-shelled pelagic bivalves. radiolarians, cephalopods Middle Triassic Inncr s h a l l o ~platform: , Dasyclad green algae, calcimicrobes, gastropods, benthic foraminifera Edge: Reefs with coralline calcareous sponges, scleractinian corals, smaller foraminifera Slope: Reefs with encrusting microfossils (e.g. Tubiphyres), coralline calcareous sponges, brachiopods, echinoderms Basin: Radiolarians. thin-shelled pelagic bivalves Early Triassic Inner shallow platform: Gastropods, bivalves, small benthic foraminifera Edge: Mollusks, echinoderms Basin: Bivalves, cephalopods

403

Late Permian Inner shallow platform: Dasyclad and gyrnnocodiacean green algae, phylloid algae, fusulinid foraminifera, gastropods Edge: Reefs with calcareous coralline sponges, bryozoans, calcimicrobes, rugose corals Slope: Reefs with encrusting microfossils (e.g.Tubiphytes), brachiopods, echinoderms Basin: Radiolarians Early Permian Inner shallow platform: Ancestral red algae, dasyclad green algae, phylloid algae, fusulinid foraminifera, smaller forminifera, bryozoans, gastropods Edge: Reefs with microbes, phylloid and dasyclad green algae Outer platjform: Brachiopods, echinoderms Basin: Radiolarians Late Carboniferous Inner shallowplatform: Ancestral red algae, dasyclad green algae, smaller foraminifera, fusulinid foraminifera, gastropods Edge: Bryozoans, coralline sponges, echinoderms, brachiopods Slope: Echinoderms, bivalves Basin: Radiolarians, echinoderms, bivalves Early Carboniferous Inner shallow platjornt: Smaller benthic foraminifera, dasy clad green algae, various calcareous red algae, 'calcispheres' Edge: Reefs with calcimicrobes, bryozoans Outer platform: Smallcr benthic foraminifera, various red algae, mollusks, echinoderms, rugose corais Basin: Radiolarians Devonian 1nnc.r shallnu, platform: Stromatoporoid sponges, tabulate and rugose corals, 'calcispheres', dasyclad and udoteacean green algae, benthic foraminifera Edge: Reefs with stromatoporoids and tabulate corals, calcimicrobes, rugose corals Slope: Echinoderms, brachiopods Basin: Tentaculitids, cephalopods Silurian Itzner-slzallou~platfort?~: Dayscladacean green algae, calcimicrobes, mollusks Edgc: Reefs with stromatoporoid sponges, tabulate and rugose corals, bryozoans. echinodemls Outc~rplatform:Brachiopods, trilobites, echinoderms Basin: Tentaculitids, cephalopods Ordovician Inner shallow platform: Green and red algae, nlollusks Edgc: Reefs with calcimicrobes, sponges and bryozoans Outerplatjbrm: Trilobites, bryozoans. brachiopods, echinoderms, sponges Basin: Cephalopods Cambrian Inner shallow pla$orm: Calcimicrobes, mollusks Edge: Reefs with archaeocyath sponges and calcimicrobes Outer platjform: Trilobites, sponges, echinoderms Basin: Echinoderms.

404

benthic sessile organisms (sponges, corals, bryozoans), * shell-bearing organisms with valves (brachiopods,

mollusks, serpulids, ostracods) and multi-element1 multi-plate shells (trilobites. crustaceans, echinodem~s), rare thin-section fossils (including vertebrates, conodonts, graptolites, and wood), fossils of uncertain systematic position (microproblematicaj. These groups and their major systematic units are presented by instructive plates and with accompanying text. The text starts with a definition of the group, followed by the diagnostically important morphological criteria, takes a short glance at the classification and discusses the environment and the biofacies, and finally gives an overview of the temporal distribution. The significance of the group as well as hints for avoiding confusions with other fossil groups are summarized in the last part.

10.2.1 Cyanobacteria and Calcareous Algae Dcfl~ritior~: Algae are aquatic photosynthetic benthic and planktonic plants. ranging from micron-sized unicelluiar forms to giant kelps several meters long. These eucaryotic organisms display extremely varied lifecyc1r:s. characterized by different complexes of photosynthetic pigments, which together with other characters are used to distinguish major groups, i.e. red, green and brown algae (Rhodophyta, Chlorophyta, Phaeophyta). in contrast to these groups, the so-called 'bluegreen algae' (Cyanophyta) are procaryotes, lacking a discrete nucleus and membrane-bound organelles w'ithin the cell. They are physiologically more closely related to bacteria and are included within a separate division of thc Procaryota ('Cyanobacteria'). In comparison with eucaryotic algae, the cyanobacteria are adapted to a wider range of environmental conditions (w,hich may include the loss of photosynthetic activily) and occur both in freshwater and marine environ' ments. Because of these differences, the paleoemllronrnental interpretation of 'algae" has to consider the systematic membership of the fossils as well as the differences in the calcification potential. Calc(fii:utii~tr: Calcareous algae constitute a highly artificial group comprising various benthic and planktonic algae belonging to different systematic groups, which are capable of renloving carbon dioxide from the water in which they live and secreting or depositing carbonate around the algal body (thallus). Calcifi-

C y a n o h d ~ t e r l dand ( ' a l c a r e o ~ \ 41g:ir

cation has been interpreted as a light-shading function, protection against predators and epiphytes, or as a means of receiving higher amounts of light and nutrients. The mode and objective of calcification are topics of current research (Borowitzka 1989; Pentecost 1991i. The precipitation of calcium carbonate may occur within the cell (planktonic coccolithophorids), in association with cell walls (coralline red algae), outside the cell (many green algae) or as a surface deposit on the thallus (many blue-greens). The skeleton of calcified green and red algae displays distinct ultrastructures (Flajs 1977). Cyanobacterial calcification results from complex, in places, bacterially-initiated processes within and upon the mucilaginous sheath surrounding the cell wall. Binding and trapping of carbonate at the sheat surface enhance the formation of structures capable of fossilization (calcimicrobes). In all groups, calcification is associated with organic matter, primarily polysaccharide, which may stimulate nucleation and control subsequent growth of calciunl carbonate crystals (Merz 1992). Less than 10% of the total of modem benthic algal species and cyanobacteria exhibit calcification, but the percentage of calcareous algae may increase to about 20% in warm shal1o~~marine environments. In the cyanobacteria, considerably more calcified species are known from freshwater than from marine environments, in contrast to green algae, with a reversed situation. Calcification of rCd algae is almost completely restricted to the oceans. Disregarding the diatoms (a group of the Chrornophyta) whose cell walls are impregnated with silica, modem skeletal algae exhibit skeletons consisting of either aragonite or calcite (see Box 4.9). Aragonite is the exclusive mineral of marine green algae, but also occurs in some red algae (e.g. squamariaceans). The skeletons of corallinacean red algae consist of HighMg calcite containing magnesium amounts ranging up to 30 mole percent. Low-Mg calcite is the common ~ninera1 of nonmarine cyanobacteria as well as of ano~her group of the Chromophyta, the marine planktonic coccolithophorids. The calcified reproductive organs of freshwater charophyceans consist of Low-Mg or HighMg calcite. The first well-calcified cyanobacteria are known from the Late Precambrian, the first calcified algae from the lowermost Cambrian. Since the calcification of cyanobacterians depends strongly on environmental conditions favoring precipitation of calcium carbonate, the abrupt appearance of calcified cyanobacteria near the Precambrian-Cambrian boundary has been interpreted as possibly reflecting a change in seawater chernistry (decrease of the Mg2+/ca2+ratio: Riding 1982).

Distribution of Cyanobacteria and Algae

Environmental contr-01s on algae: Controls on the distribution of recent benthic algae comprise (a) physical factors: intensity and quality of light (necessary for photosynthesis), water temperature, water energy and substrate; (b) chemical factors: water chemistry, salinity, dissolved gases, pH values; and (c) biological factors: nutrients, competing and herbivorous organisms, and ecological successions. Generally, the intensity of light decreases with increasing water depth. About 50 % of the light penetrating clear water is absorbed in the uppermost ten meters. Despite this, photosynthetic algae can occur at greater water depths if they have special pigments that can utilize minimal light intensities and specific wave lengths. Modem red algae, adapted to blue and green light sectors, also occur at greater water depths, whereas calcified green algae assimilate most strongly in the red sector and are, therefore, preferentially limited to shallow seas. Preservation of calc~areousalgae: Because of the widely differing solubilities of calcium carbonate phases, the primary mineralogy of calcareous algae is a critical factor in their diagenesis and in the preservation of algal fossils. Aragonitic skeletons of udoteacean and dasyclad green algae are susceptible to solution and replacement by sparry calcite. Coralline red algae

display differing degrees of diagenetic alterations, depending on varying magnesium contents. Low-Mg calcite algae and calcimicrobes are commonly well-preserved.

Classification: Calcified cyanobacteria have been classified into formal taxonomic units (Chuvashov 1987; Dragastan et al. 1996) or into informal morphological groups (Riding 1991). The latter classification is more practicable (Fig. 10.4). Living algae are classified according to pigments, nature of the food reserve, kind of flagellation, and chloroplast ultrastructure. The presence of skeletal carbonate is not a classification criterium. Fossil calcareous algae are classified according to morphological characteristics used in classification schemes of analogous living forms. These characters include external morphology, preserved tissue, and reproductive bodies. Many fossil algae, however, can not be related to major groups of living algae. These algae are included in non-systematic collective groups (e.g. ancestral red algae, phylloid algae) or in taxonomic units which can only be tentatively assigned to major groups of green or red algae (e.g. gymnocodiacean algae). Still other ancient extant algae exhibit morphological characters that are similar to green or red algae, but do not allow

Cyanobacteria Corallinacean red algae Squarnariacean red algae Ancestral red algae Solenoporacean red algae Udoteacean green algae Gyrnnocodiacear green algae Phylloid algae Dasyclad green algae

Fig. 10.4. Distribution of Phanerozoic calcimicrobes and major calcareous algal groups. Note that the thickness of the bars does not reflect taxonomic diversity, but instead indicates the relative frequency i n thin sections.

Algae and Sedinizni

an attribution to known systematic subgroups (e.g. ungdarellacean algae). Fig. 10.4 exhibits the temporal distribution of major groups of calcareous algae. Further smaller groups are dealt within the discussion of red and green algae. Significance of algae in microfacies analysis Fossil calcified algae are most important in microfacies analysis, because of their high potential in reconstructing paleoenvironments and ecological conditions, their biostratigraphic potential, and their large contribution to the formation of carbonate sediments.

Yaleoen~irontn~nt: Fossil calcified algae are used in reconstructing environmental factors such as water temperature (see PI. lO5), salinity and relative water depths (see P1.108). This approach has to consider several points: (a) Modern calcareous green and red algae exhibit different ecological controls with regard to water depths. Some algal groups occupy wide bathymetric ranges: Coralline red algae and udoteacean green algae are not restricted to 'shallow' depths but also thrive at watcr depths of several tens of meters, corallinaceans even in depths of more than two hundred meters. Paleobathymetric interpretations should be based on specific algal groups rather than on the generalized statement of the occurrence of 'algae'. (bj A few algal groups exhibit dif'ikrences in preferred modern and ancient biotopes. Ancient calcimicrobes are common fossils in marine limestones, whereas modern calcified cyanobacteria flourish in ivaters with nonmarine salinities. Modem dasyclads prefer lagoonal and shelf habitats in contrast to ancient forms common in lagoonal and shelf carbonates, but also occur in reef limestones. The myor factors controllins the distribution of algae may be modified by local factors, e.g. substrate conditions (Fliigel 1983). (c) Not all modern calcified algae are highly Iiglitdependent. Green algae and red algae exist in shadowy habitats. Ancient calcimicrobes are common constituents of cryptic biotopes. (d) Mean annual water temperature has a strong control on the distribution of calcareous algae, but for modern corallinacean red algae this factor is distinctly taxadependent. (e) Algal bioclasts are easily transported and redeposited. They may not represent autochthonous constituents of the sediment, but rather grains transported into other carbonate settings. Downslope and turbidity current transport of green algal debris from modern carbonate platforrns to deep water environments is a com-

mon feature. Transport of shallow-marine algae to deeper subtidal, slope and basinal environments as well as the growth of various red and some green algae at water depths of several tens and even a few hundred meters is also responsible for the possible occurrence of algal material in deep-marine settings. Storms can transport algal debris from open-marine platforms to near-coastal environments. Even a transport of marine algae to nonmarine settings by storms is likely (Pl. 13l/4). To avoid some of these pitfalls, the use of distribution patterns is recommended. This approach relates the composition of algal associations to other microfacies data (limestone textures and structures, additional fossils). The algal associations are characterized with regard to their taxonomic composition, frequency and dominance of specific taxa or groups, and diversities. The distribution patterns of algal associations can not be directly compared with the ecological zonation of living algae, because many ancient taxa are extinct and their relationship to living forms may be unknown. Nevertheless, established empirical distribution patterns have a high potential for reconstructing paleoecological factors, e.g. paleoclimate and paleoceanography and paleoenvironments. Stratigraphic zonation: Calcareous algae are valuable in subdividing rock units and establishing zonations. These zonations are based on the occurrence of characteristic associations of species, or the range of single species, or the abundance and climax of spccies. Commonly used marine algal groups are dasyclad green algae, some red algae, and charophycean algae in nonmarine sediments.

Sedinlr~ztation:Calcareous algae are major producers of carbonate sediments in shallow marine environments as well as in deep-water settings. Modern sediment-producing algal groups in shallow platform and inner ramp environments conlprise predominantly udoteacean green algae (e.g. Hulimcdu; see Sect. 4. I .2j and corallinacean and squamariacean red algae. The contribution of dasyclad algal skeletal grains to recent sediment production is minor as compared with ancient carbonate platforms, particularly of Late Paleozoic and Mesozoic age. Udoteacean green algae were inlportant producers of carbonate mud and sand at least since the Late Triassic, but probably already in the Paleozoic. Common Late Paleozoic sediment producers were ancestral red algae forming rhodoids, and phylloid algae contributing to the accumulation of sediment in reef mounds. The deposition of calcitic planktonic algae (coccolithophorid chrysophyceans, calciodinoflagellate dino-

Basics: ( ~ a l c i m ~ c r o h ea sn d Algae

phyceans, and other related groups) in pelagic deepshelf environments and open-marine basinal settings started during the Triassic, increased in the Jurassic and became a dominant process in Cretaceous and Cenozoic rimes. The influx of shallow-water algal material derived from platforms into slope and basinal settings is known already from the Cambrian, and is a common feature in Mesozoic periplatform carbonates. Cyanobacteria, charophycean algae as well as a f e w green algae are important constituents of nonmarine Mesozoic and Cenozoic lacustrine carbonates.

Basics: Calcimicrobes and algae Far more general texts and overviews deal with calcareous algae than most invertebrate groups. Taxonomically based overviews are listed at the end of the relevant paragraphs. General texts Barattolo, F., de Castro, P., Parente, M. (1993): Studies on fossil benthic algae. - Bolletino della Societi Paleontologica Italiana, Spec. Vol., 1,420 pp. Bassoullet, J.P., Bernier, P., Conrad, M.A., Deloffre, R., Jaffrezo, M. (1 978): Les algues dasycladales du Jurassique et du CrCtacC. - Geobios, M6m. spec., 2,330 pp. Chuvashov, B.I., Shuysky, V.P., Schaikin, I.M.(1987): Iskopaemye izvestkovye vodorosli. - Akademya Nauk SSSR, Sibirskoe otdelenie, Trudy instituta geologii i geofiziki Novosibirsk, Vypusk, 674, 200 pp. Flajs, G. (1977): Die Ultrastrukturen des Kakalgenskelettes. - Palaeontographica, B, 160, 69-128, Stuttgart Fliigel, E. (ed., 1977): Fossil algae. Recent results and developments. - 375 pp., Berlin (Springer) Ginsburg. R.. Rezak, R., Wray, J.L. (1972): Geology of calcareous algae (Notes for a short course). - Sedimenta, I, 70 pp., Miami (Comparative Sedimentology Laboratory, Rosenstiel School of Marine and Atmospheric Science) Hofling, R., Moussavian, E., Piller, W.E. (eds., 1993): Facial development of algae-bearing carbonate sequences in the Eastern Alps. - Intemational Symposium and Field-Meeting 'Alpine Algae '93', Guidebook, 206 pp., MiinchenWien Johnson, J.H. (1961): Limestone-building algae and algal limestones. - 295 pp., 139 Pls., Golden (Colorado School of Mines) Maslov, V.N. (1956): Iskopaemye izvestkovye vodorosli SSSR. - Akademya nauk SSSR, Trudy instituta geologicheskikh Nauk, Vypusk, 297 pp. Monty, C1. (ed., 1981): Phanerozoic stromatolites. Case histories. - 249 pp., Berlin (Springer) Pentecost, A. (1991): Calcification processes in algae and Cyanobacteria. - Riding, R. (ed.): Calcareous algae and stromatolites. - 3-21, Berlin (Springer) Pentecost. A,, Riding, R. (eds., 1978): Biomineralization in lower plants and animals. -The Systematic Association, Spec. Vol., 30,400 pp., London Pia, J. (1926): Pflanzen als Gesteinsbildner. - 355 pp., Berlin (Borntraeger) Piller, W. (ed., 1994): Proceedings of the Intemational Symposium and Field-Meeting 'Alpine Algae '93'. - Beitrage zur Palaontologie, 19, 264 pp., Wien

407

Poignant, A.F., Deloffre, R. (eds., 1979): 2nd Intemational Symposium on Fossil Algae. -Bull. Centres Rech. Exp1or.Prod. Elf-Aquitaine, 3,385-885, Pau Riding, R. (ed., 1991): Calcareous algae and stromatolites. 57 1 pp., Berlin (Springer) Round, F.E. (1981): The ecology of algae. - 653 pp., Cambridge (Univ. Press) Toomey, D.F., Nitecki, M.H.(eds., 1985): Paleoalgology. Contemporary research and applications. - 375 pp., Berlin (Springer) Walter, M.R. (ed., 1976): Stromatolites. - Developments in Sedimentology, 20,790 pp., Amsterdam (Elsevier) Wray, J.L. (1977): Calcareous algae. - Developments in Palaeontology and Stratigraphy, 4, 184 pp., Amsterdam (Elsevier) Reviews of calcareous algae from different time intervals Awramik3.M. (1991): Archaean and Proterozoic stromatolites. - In: Riding, R. (ed.): Calcareous algae and stromatolites. - 289-304, Berlin (Springer) Chuvashov, B., Riding, R. (1984): Principal floras of Palaeozoic marine calcareous algae. - Palaeontology, 27, 487500 Emberger, J. (1976): Les algues (Chlorophyceae, Prasinophyceae, Rhodophyceae) du Carbonifkre et du Pennien. Essai d'un inventaire bibliographique, gCographique, stratigraphique. - Bulletin de 1'Institut de GCologie du Bassin d'Aquitaine, Numero SpCcial, 168 pp. Emberger, J. (1976): Les algues (Chlorophyceae, Prasinophyceae, Rhodophyceae) du DCvonien. Essai d'un inventaire bibliographique, gkographique, stratigraphique. Bulletin de 1'Institut de Gtologie du Bassin d'Aquitaine, Numero Sptcial, 94 pp. Emberger, J. (1979): Les algues (Euchlorophyceae, Prasinophyceae, Rhodophyceae)du Trias. Essai d'un inventaire bibliographique, gCographique, stratigraphique. - Bulletin de 1'Institut de GCologie du Bassin d'Aquitaine, Numero Sp6cia1, 157 pp. Fliigel, E. (1991): Triassic and Jurassic marine calcareous algae: a critical review. -In: Riding, R. (ed.): Calcareous algae and stromatolites. - 481-503, Berlin (Springer) Johnson, J.H. (1961): A review of Ordovician algae. - Quarterly, Colorado School of Mines, 5612, 1-101 Johnson, J.H. (1961):The Jurassic algae. - Quarterly, Colorado School Mines, 59, 129 pp. Johnson, J.H. (1963): Pennsylvanian and Permian algae Quarterly, Colorado School of Mines, 58, 1-218 Johnson, R. (1966): A review of the Cambrian algae. -- Quarterly, Colorado School of Mines, 61, 1-162 Johnson, J.H. (1969): A review of the Lower Cretaceous algae. - Professional Contributions Colorado School of Mines, 6, 180 pp. Johnson, J.H., Konishi, K. (1956): A review of Mississippian algae. -Quarterly, Colorado of School Mines, 5114, 1-84 Johnson. J.H., Konishi, K. (1958): A review of Devonian algae. - Quarterly, Colorado School of Mines, 5312, 1-84 Johnson, J.H., Konishi, K. (1959): A review of Silurian (Gotlandian) calcareous algae. - Quarterly, Colorado School of Mines, 5411, 1-114 Mamet, B. (1991): Carboniferous calcareous algae. - In: Riding, R. (ed.): Calcareous algae and stromatolites.- 37045 1, Berlin (Springer) Riding, R. (1991): Cambrian calcareous Cyanobacteria and algae. - In: Riding, R. (ed.): Calcareous algae and stro-

C y a n o b a c t e r i a a n d Calcirnicrobes

matolltes. - 305-334, Berlin (Springer) growth forms. Laminated growth forms include skelRiding, R., Guo, L. (1991): Permian marine calcareous al- etal stromatolites and oncoids, sometimes exhibiting disgae. - In: Riding, R. (ed.): Calcareous algae and stroma- crete tubular microstructures. Other growth forms are tolites. - 452-480, Berlin (Springer) Roux,A. (1985):Introduction a 1'Ctude des algues fossilesPalko- microbushes, thrombolites and dendrolites. zoiques (de la bacteria a la tectonique des plaques). -Bull. Classification: Cyanobacteria are extremely variCentre Rech. Exp1ora.-Prod. Elf-Aquitaine, 9,465-699 Roux, A. (199 1):Ordovician algae and global tectonics. -In: able with regard to their morphology. Some fossil calciRiding, R. (ed.): Calcareous algae and stromatolites.- 335- microbes exhibit high morphological similarities with 348, Berlin (Springer) groups of modem cyanobacteria, indicating the existRoux, A. (1991): Ordovician to Devonian marine calcareous algae. - In: Riding, R. (ed.): Calcareous algae and stro- ence of very conservative long-range characters. The tubular microstructure was used to define the artificial matolites. - 349-368, Berlin (Springer) Further reading: K129 to K136 group 'Porostromata'. Some authors still prefer the term 'porostromate algae' but one should be aware that this group includes cyanobacterian fossils with close morphological sirni10.2.1.I Cyanobacteria and Calcimicrobes larity to recent calcified blue-greens, but also various Llefinirion, calcification and nzorphology: Cyanobac- green algae. A handy as well as morphological classification of teria are phototroph Procaryota. The cells are arranged calcimicrobes proposed by Riding (1991) is shown in in colonies (coccoid forms; Croococcales) or arranged within threads forming trichomes (filamentous forms; Fig. 10.5. Another approach, based on comparative Hormogonophyceae). The threads can be branched and studies of porostromate taxa and recent cyanobacteria, enclosed in a protecting mucilaginous sheath. The de- results in a classification that relates ancient taxa to velopment of organic sheaths is strongly environmen- recent counterparts (Dragastan 1985, 1988, 1989, 1990; tally controlled. Some modem filamentous and coc- Dragastan et al. 1996). coid cyanobacteria calcify through impregnation within or encrustation upon the extracellular sheaths with carbonate. Encrusted filaments are potential fossils, whereas impregnated filaments commonly disintegrate to carbonate mud. The mineralogy reflects waler chemistry (freshwater: Low-hlg calcite; marine and restricted environments: Aragonite and High-Mg calcite). Calcification is species-specific. Calcification in recent cyanobacteria corresponds to a nucleation of calcium carbonate upon or within the mucilage sheath (Pentecost and Riding 1986; Pentecost 1990). Considerably more cyanobacteria have been observed in modem freshwater lakes and streams compared with the sea. However, calcification occurred widely in marine cyanobacteria during the Paleozoic and Mesozoic. perhaps reflecting temporal changes in oceanic carbonate chemistry. Merz-Preiss and Riding (1999) comparing calcification patterns of cyanobacteria from the Everglades in Florida and from spring tuffs stress the point that the preservation potential of fossilized filamentous cyanobacteria probably depends on the degree of carbonate oversaturation of the ocean water. Calcification of filaments produces tubelike microfossils. varying in external diameter between ten and several tens of microns. The tubes are bordered by microcrystalline calcitic 'walls'. Calcified cyanobacteria occur as millimeterto centimeter-sized discrete microfossils (calcimicrobes) consisting of tubes or irregular bodies, or as amalgamated masses exhibiting laminated or massive

Enviwnnzentul constraints: Modem cyanobacteria have a wide range of habitats. As pioneer settlers in marine freshwater and on terrestrial sedimentary dc posits, benthic cyanobacteria prepare the ground for the successive invasion and expansion of eukaryotic flora and fauna (Golubic et al. 2000). Benthic cyanobacteria are the major constituents of microbial mats. specifically of the topmost oxic layers. 'The mats form in inter- and supratidal, sometimes hypersaline coastal environments as well as in soda and freshwater lakes or hot springs. Mat-building cyanobacteria exhibit significant tolerance to changes in light intensity. anoxic conditions or sporadic drying. Effective environrncntal factors are light, water temperature and nutrients (C, N, P, Fe). Planktonic cyanobacteria are common in freshwater but also occur in open oceans. Ancient benthic cyanobacteria are known both from marine and nonmarine environments. Calcirnicrobes art: common constituents of Mesozoic restricted, lagoonal as well as on open-marine platform carbonates and contributes to the formation of reefs and mud mounds. Distribution: Nonskeletal cyanobacteria were abundant in the Precambrian and have been recorded from rocks as old as 3.5 billion years. Heavily calcified calcimicrobes appeared in the Vendian (1.0-0.85 billion years) coincident with the decline in stromatolites. Vendian reefs are composed of abundant thrombolites and calcimicrobes. Text c o n t i n u e d o n p. 4 1 2

Classification: Calcified Cyanobacteria

Frutexites

Epiphyton

409

toriaceae

Girvanella

Examples: Gi~ane//a:Cambrian to Cretaceous

Hedstroemia Group: Cambrian to Cretaceous Criteria: Branching clusters of tubes; clusters with

fan-like longitudinal sections, radial erect growth. Adjacent tubes may share common walls or may be separate; taxa separated according to patterns of branching. Similar to recent rivulariacean cyanobacteria Examples: Hedsroemlb: Silurian; Ortonella: Carboniferous; Cayeuxia:Triassic to Cretaceous 12.":

C'ayeuxla

.

.

Henalcls

Renalcis Group: Abundant in Cambrian and Early Ordovician; Late Devonian; common in reefs Criteria: Clusters of hollow reniform bodies, usually with thick walls which may be micritic, fibrous or clotted; irregular or erect Examples: Rena/c/s: Cambrian to Early Carboniferous; Shuguria:Cambrian to Carboniferous Garwoodia/Mitcheldeania Group: Late Paleozoic and Mesozoic Criteria: Coarse, thin-walled, radiating clusters of tubes which are commonly juxtaposed (systematic position uncertain, may be green algae) Examples: Garwoodia: Devonian to Cretaceous; MifcMeama:Carboniferous to Cretaceous Rothpletzella Group: Silurian and Devonian Criteria: Flat, curved and encrusting sheets of jux-

taposed tubes which branch dichotomously in one plane, systematic position uncertain Examples: Rofhp/efze//a: Devonian Fig. 10.5. Pmcticnl c1assifi;cation of 1,alcified cyanobacteria based on growth forms and filament patterns appearing as variously oriented tubiforrn structures or irregular bodies (modified from Riding 1991). The tubes occur in clusters within commonly millimeter-sized nodules, bushes or sheets. Preferred growth direction is erect, pendant or prostrate (horizontal. parallel to the substrate). The Hedstr-oemia group and the GaiwoodialMitcheldeania group comprise microfossils, often described as porostromate algae or microbes. The systematic position of these fossils (cyanobacteria or green algae) as well as the generic differentiation is still a matter of discussion. Thin-section pictures: Fr-utexitesoccurring in a deep-water stromatolite. Note the bush-like growth form and the microstructure consisting of radially arranged fibres of Fe-Mn oxides and calcite. Frutexites was probably non-phototrophic and seems to have preferred oxygen deficient, low-energy environments (Bohm and Brachert 1993). Early Jurassic: Near Lunz, Austria. - Epiphyton: The genus appears close to the Precambrian-Cambrian boundary and is widespread in Cambrian reef limestones. Early Cambrian: Southern Sardinia. - Giwanella forms small nodules, oncoids or sheets composed of loosely or densely tangled thin-walled tubes. Early Ordovician: Western Newfoundland. - Cayeuxia and morphologically similar taxa are abundant fossils in Mesozoic platform carbonates. The genus was placed in the synonymy of Rivularia, a modem cyanobacterium occurring in freshwater and marine environments. Late Jurassic (Tithonian): Sulzfluh, Switzerland. - Renalcis often occurs together with Epiphyton (bottom of the picture). Both genera are principal constituents of Cambrian archaeocyath reefs. Early Cambrian: Southern Sardinia. - Garwoodia and other taxa of this group are characterized by coarser tubes than of Hedstroemia and similar genera. The size of the tubes has been used as an argument for assigning these microfossils to udoteacean green algae. Late Jurassic (Tithonian): Sulzfluh, Switzerland. - Rothpletzella occurs in platform and reef carbonates. Early Devonian (Currajong limestone): Canberra, Australia.

Garwoodia

Rothpletzella

Plate 53 Calcified Cyanobacteria: Porostromate Calcimicrobes Cyanobacteria (also known as cyanophytes or blue-green algae) are procaryotes. They contribute to sediment production (microbial mats), sediment construction (e.g. travertines and tufa; reefs), and sediment destruction (boring and micritization). Cyanobacterial microboring is the oldest known form of bioerosion. The first calcimicrobes appeared near the Precambrian-Cambrian boundary. Calcified cyanobacteria were abundant in Paleozoic and Mesozoic shallow-marine carbonates. Late Mesozoic and Early Tertiary calcimicrobes are commonly found in lacustrine or marginal-marine limestones. Calcified cyanobacteria (calcinzicrobes) form millimeter- to centimeter-sized bushy masses, radial fans or tangled masses, often composed of very small 'tubes' (designed by calcification within organic sheaths), or irregularly shaped bodies. Calcimicrobes comprise microfossils consisting of tubes organized in erect radial clusters of branched tubes (e.g. Cayeuxia: -> 1,2), prostrate felts composed of non-oriented intermingled tubes (e.g. Girvanella: -> 7), dendritic micritic filaments, apparently chambered (e.g. Epiphyton; Fig. 10.5)), or aggregates of hollow reniform bodies (e.g. Renalcis; Fig. 10.05). Most recent Cyanobacteria use Low-Mg calcite, but a few also High-Mg calcite or aragonite. Fossil calcimicrobes consist of Low-Mg calcite. At present, intense cyanobacteria calcification appears to be essentially a freshwater phenomenon and is rare in modem subtidal environments, in contrast to ancient cyanobacteria which occupied tidal and subtidal environments and were common in reef and platform setting\. Common criteria used in the differentiation of groups or taxa of tubiform porostromate forms are the arrangctneiit of tubes (e.g. erect, pendant, prostrate; -> 1, 7, 8), branching patterns (e.g. simply dichotomous, polpdichotomous. V-shaped or right-angle branching; -> 1, 3, 6), and the shape and dimensions of the tubes (mner d~ameter,wall thickness and wall structure). Growth forms (hemispherical, -> 1; tufted, -> 4; nodular, > 6; laterally expanded crusts and sheets, -> 7, 8) as well as growth zonation patterns (-> 2,4) reflect environmental and biological constraints. Do not cotzfuse rltbrdar-yorostr-on~urcru1cinzzcrobe.s with other thirz-sectionfossils! Solenoporacean filaments shown in longitudinal sections have smaller dimensions and often exhibit horizontal partitions (Pl. 55). Bryozoan tubes are conspicuously larger and morphologically differentiated (PI. 85). 1 Cuyirsia Frollo. Longitudinal sectron 01' a nodular thallus. The small nodules exhibiting a hemispherical outline arc

2 3

4

5 h

7

8

composed of oulward radiating tubea that originate from a point located peripherally on the thallus. The tubes diverge upward at a narrow angle. Cayc.~rsi~ is very similar to the recent alga Rivular-ia; some authors consider the genera as being identical (Dragastan 1985). Late Jurassic (Tithonian): Kapfelberg, Southern Franconian Alb, Germany. Cajwrxia Frollo. SEM sample. Note growth zonation (GZ) and branching pattern (arrows). Same locality and age as -->1 . Cuycuxia. Note nodular growth form, long branched tubes (arrow) and the difference in tube diameter as compared with Fig. 1. Species of Cnycuxia (and Rivulurin) are differentiated according to divergence angle, tube diameter and branching pattern. Late Jurassic (Tithonian): Sulzfluh Mountains, Graubiinden, Switzerland. tIZ11Porostromate cyanobacteria (Pjc\.c-lzopo,-iili~m fobatlrn~Yabe and Toyarna) are characterized by erect growth and diff-. tiation into marginal tufts (arrow). Late Jurassic: Lower Saxonia, Germany. 01-tonclluGarwood. Cross-section (CS', and longitudinal section (LS) of a globular growth form. Higii-energy grainstones of an inner carborlatc ramp. Early Carboniferous (Kohlenkalk; Visean): Aachen. Gcrrnany. C;al-\zmilia Wood. Note difference in thickness of the tubes (as compared with Fig. 1 and 5) and right-angle branching pattern (anow). Some authors place this genus into the green algae. Garwoodin and morphologically similar taxa art. known from Paleozoic and Mesozoic platform carbonates. Jurassic and Cretaceous species are abundant in back-reef m c l inncr shelf environments. Early Cretaceous: Subsurface, Hohenlinden, Bavaria, Gennany. G~I- ane el la ducii Wethered, characterized by thin-walled tangled, coiled or aligned tubes and prostrate growth. The genus is common in Paleozoic carbonates. Filaments of micrite-walled calcimicrobes as Girvanella might have been a majorsource of lime mud in the Early Paleozoic when the tubes fell apart (Pratt 2001). Middle Devonian (Givetian reef): Sauerland, Germany. Rorlzplerzclla Wood, characterized by flat, curved or encrusting sheets of tubes branching dichotomously in one plane and appearing as 'strings of pearls' in oblique sections. Rorhpletzella is a common Devonian calcimicrobe occuning both in shallow and deep-water settings, and characteristically found at reef-margins and on fore-reef slopes. The genus acted as constructors, but also as crypts within cavities. Early Devonian: Near Canberra, Australia.

Plate 5 3 : Calcified Cydnobacteria

41 1

Coralllne A l g a e

The absence of Proterozoic calcified cyanobacteria and their appearance in the Late Precambrian has been explained by a decrease in the Mg2+/Ca2+ratio near the Precambrian-Cambrian boundary (Riding 1982), extreme calcium carbonate oversaturation of Precambrian ocean waters (Knoll et al. 1993), and biological evolutionary controls (Defarge et al. 1994). Calcified filamentous cyanobacteria are common in marine sediments from the Early Cambrian to the Late Cretaceous. Calcimicrobes flourished in Cambrian and Ordovician reefs and open-marine shelf carbonates; they were less common in Silurian to Permian carbonates, prominent again in lagoonal and reef environments during Middle Triassic to Mid-Cretaceous time, but scarce in the Late Cretaceous. In reefs calcimicrobesacted as frame-builders (e.g. Cambrian and Devonian Renalcis; P1.8214.5) as well as crypts within cavities (e.g. Frutexites; Fig. 10.5). Porostromate calcimicrobes are common constituents of Early Carboniferous ramp deposits (Pl. 531 5) and Mesozoic inner platform and lagoonal carbonates (PI. 5311-4). Depth distribution was not necessarily limited to very shallow environments, as shown by the occurrence of calcinlicrobes in Devonian deeper forereef positions. Starting with the Tertiary, the group became primarily limited to nonmarine and transitional environments (Monty 1973: Pentecost and Riding 1986; Riding 1992). Records of calcified cyanobacteria from Early Cenozoic and modern shallow-marine carbonate environments are rare, probably due to the major change in the prefen-ed biotopes of blue-greens during the Mesozoic. Slarting with the Late Jurassic and Early Cretaceous, calcified cyanobacteria adapted to marginal-marine and freshwater conditions, where they become conspicuous carbonate producers in lacustrine and terrestrial environments.

Pratt, B.R. (1984): Epiphyton and Renalcis -diagenetic microfossils from calcification of coccoid blue-green algae. - J. Sed. Petrol., 54, 948-97 1 Riding, R. (1991): Calcified cyanobacteria. - In: Riding, R. (ed.): Calcareous algae and stromatolites. - 55-87, Berlin (Springer) Further reading: K033, K129-K136

10.2.1.2 Corallinacean and Peyssoneliacean Red Algae Sections 10.2.1.2 to 10.2.1.4 deal with red algae. Calcified red algae are common fossils in thin sections of Phanerozoic limestones (Fig. 10.6). They comprise some well-defined systematic units (Corallinaceae, Peyssoneliaceae,Solenoporaceae),Paleozoic fossils interpreted as 'ancestral corallines' (Archaeolithophyllaceae), and microfossils attributed to red algae but of unknown systematic position (Ungdarellaceae, Stacheinaceae and other Paleozoic groups).

Coralline algae Definition and calcification: Corallinacean algae (also known as coralline algae) are a distinct, exclusively marine group within the Rhodophyta. They represent the most heavily calcified red algae. Calcification occurs intracellularly by High-Mg calcite with varying amounts of MgC03 (up to > 30 ~01%).T h e stabilization of the High-Mg calcite connected with a magnesium loss is interpreted as a congruent dissolution of High-Mg calcite and precipitation of Low-Mg calcite with a definite textural change (Oti and Miiller 1985).

Classification: Traditionally coralline algae have been divided according to growth morphology into two Basics: Calcified cyanobacteria Dragasran, O., Golubic, S., Richter, D.K. (1996): Rivulariu major groups - the non-genlculate (non-articulated) izacrnc~titrs:a case of recent versus fossil morphology. crustose corallines and the geniculate (articulated) corTaxonomical considerations. - Kevista Espaiiola de Microallines (Fig. 10.7). Non-yeniculate encrusting coralpaieontologia, 28,33-73 Dragastan, O., Richter, D.K., Gielisch, H., Kube, B. (1998): lines comprise crusts, a few microns to several centiEnvironmental siginificance of some Mesozoic 'Poro- meter thick, on rocks, coral skeletons, shells, other alstromata' calcareous algac. - Revista Espaiiola de Micro- gae or sea grass. Encrusting corallines vary in size from paleontologia, 30, 59-101 thin crusts to massive, nodular or lamellate thalli sevElicki, 0. (1999): Palaeoecological significance of calcieral tens of centimeters in diameter. Some non-genicumicrobial communities during ramp evolution: an example from the Lower Cambrian of Germany. -Facies, 41, late corallines are free-living and occur as rhodoids. Geniculate corallines are erect branching, tree-like 27-40 Fournie, D. (1967): Les Porostromata du PalCozoique. ~ t u d e plants attached to the substrate by crustose or calcibibliographique. - Bull. Centre Rech. Pau-SNPA, 1,21-45 fied, root-like holdfasts. The plants are flexible owing Merz-Preiss, M. (2000): Calcification in Cyanobacteria. -In: to non-calcified sections (genicula) separating longer Riding, R., Awramik, S.M. (eds.): Microbial sediments. calcified segments. Individual segments vary in shape 50-56, Berlin (Springer) Pia, J. (1927): Thaliophyta. -In: Hirmer, M. (ed.): Handbuch from cylindrical to flattened. The segments consist of der Paliiobotanik. - 1, 3 1-136, Miinchen (Oldenbourg) a central part (medulla) extending upwards to the next

Calcareous R e d A l g a e

413

Thin-section criteria ( Stratigraphic range Corallinaceans Fine net-work structure; cell size < 5 to 15 pm; differentiation according to cell size and Early Cretaceous to arrangement; case-shaped cavities in lines or isolated within the tissue; crusts, nodules, recent, possibly already branches; in transmitted light dark. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .PI. 54 Early Paleozoic Peyssoneliaceans Net-work structure; cell size 20 - 30 pm; basal calcification with botryoids; distinctly set sheets; blades, nodules; in transmitted lght golden, yellowish, gray . . . . . . . . . .PI. 64/10

Early Cretaceous to recent possibly also Late Paleozoic

Solenoporaceans Closely packed vertical filaments, sometimes with horizontal partitions; cell size 10 - 100 pm; no cell differentiation, no case-shaped cavities; nodular and branched . .PI. 55

Cambrian to Tertiary (Miocene)

Ancestral red algae (Archaeolithophyllaceans) Net-work structure; cell size approx. 10 - 30 pm; cell differentiation; blades and nodules; in transmitted light yellowish, gray . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .PI. 5612, 8

Carboniferous and Permian (Visean to Late Permian)

Problematic algae Ungdarellaceans Net-work structure; cell size about 20 pm; cell differentiationyery small encrusting or isolated structures; in transmitted light often golden, yellowish . . PI. 5615-7, PI. 10817-8

Carboniferous and Permian Common: Visean-Moscovian

Stacheinaceans Indistinct network; very small encrusting structures; in transmitted light often golden, yellowish . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . PI. 108110

Carboniferous (Visean to Moscovian)

Fig. 10.6. General thin-section criteria of some common calcareous red algae.

segment and composed of partitioned filaments, and peripheral cellular filaments (cortex) surrounding the medulla (Fig. 10.7G; PI. 6411 1). At present, the morphology and taxonomy of coralline genera are under revision. The identification of species should be reserved for specialists. Both, traditional morphological criteria and neontological features are used in determining coralline taxa. Identification keys have been published by Braga et al. (1993) and Rasser and Piller (1999). Comnlonly used features for identi-

fying fossil genera are growth form, development of cells within different parts of the thallus. and reproductive organs. Morphology: The thallus consists of adjacent calcified filaments. Consecutive cells within core filaments are connected by primary pit connections or by cell fusions. The calcified cellular tissue is characterized by definite arrangements, shapes and sizes of cells. Cells are very small (5-20 pm).

Encrustlnq (crustose) corall~nes B

-P

-H

El

a===Qa single-layered equidimensonal

E

rnultilayered

Art~culatedcorall~nes

medulla filaments cortex lilaments

Fig. 10.7. Internal mot-plzolo~yof c nlr ifled c or all& algae. Both encrusting &d erect articulated corallines exhibit differentiation of the plant tissue into a basal (central) and a peripheral (upper) part differing in the geometry, arrangement and size of the filaments. A: Lithothamnion crust overgrowing an older algal nodule. B to E: Basic types of hypothallus (H) and perithallus (P) organization in encrusting corallines. F: Typical growth form of erect, articulated corallines (Corallina). G: Internal organization of the calcified segments. A: Aftcr Fott (1971), B-G: After Wray (1977').

Corallinc Red Algae

Most encrusting corullincs (PI. 54) are dorsoventrally organized. They have a basal-most (dorsal) part (formerly called the hypothallus) near the substrate, with cells oriented more or less parallel to the substrate, responsible for the lateral growth, and an outer (ventral) part (formerly called the perithallus) with commonly very small cells, developed above and upon the hypothallus and oriented perpendicular to it, responsible for the plant's thickness. The basal part may con-

sist of multilayered or unilayered filaments (Fig. 10.7BE) The cells of the multilayered basal part are described with regard to size, shape, arrangement of cells into single, multilayered and arcuate layers (coaxial; P1.541 8; Fig. 10.7 C) or they are non-coaxial (plumose). A thin surface layer (epithallus) known from modem corallines is very rarely preserved in fossil algae. Additional criteria revealed by SEM and ultrathin section studies (e.g. connections between contiguous cells)

Plate 54 Corallinacean Red Algae Tertiary limestones composed predominantly of red algae are important hydrocarbon reservoir rocks, e . g in Libya and Indonesia. Corallinacean algae (or coralline algae) are a red algal group characterized by a strongly calcified tissue exhibiting a fine net-like structure in thin sections. The group is traditionally subdivided into encrusting (or crustose) corallines and segmented articulate corallines. The former develop millimeter- to centimeter-thick crusts, the latter erect, flexible branches consisting of calcified segments and non-calcified parts. Corallinacean algae are abundant constituents of Cretaceous and Cenozoic shelf and reef carbonates. The plate shows Tertiary and Cretaceous encrusting corallines forming rigid skeletons. The algal body (thailus) consists of adjacent calcified filaments. Corallinacean algae are most valuable paleoecological markers. They are used in assessing paleoclimate, paleolatitudes and paleodepths. But note that the occurrence of corallinacean red algae is not uprioi-i indicative of a shallow tropical warm-water environment; coralline algae grow in temperate and cold-water environments as well. In contrast to calcareous green algae, coralline algae flourish down to several decades of meters even down to about 250 m. 'The study of corallines in thin sections needs high magnifications, otherwise algal fragments appear nonstructured and may be confused ~vithmicrite clasts. Similar confusion may exist for the red alga Marincilrr. TIlis alga (Pl. 116i3.5). abundant in Late Jurassic and Cretaceous (Barattolo and DelRe (1985) and known until thc Oligocene. is characterized by millimeter-sized thalli composed of extremely fine threads (about < 5 to I5 pm 1. ('orallines appear dark in transmitted light and white in hand specimens and polished sections. i

2

Red algal nodule trhodoid) consisting of Lithothanznioil, a member of the rnelobesioid coralline algae. Large spar-filled structures occurring within the thallus are reproductive organs (conceptacles, C). These structures should not be confiised with borings (B). The genus is charactenzed by encrusting growth, a multi-layered internal structure and mukiporate conceptacles (black arrows). Interspaces between algal specimens are filled with sediment (peloids, foraminifera). Angular algal fragnienls (white arrows) are caused by vadose dissolution and breakage of the algal limestone. The growth form of the nodules and peloidal infilling indicate restricted water energy within a reef environment. Late Tertiary (Leithakalh, Miocene): St. Margarethen, Burgenland, Austria. Bioclastic algal debris facies with broken branches of Litl~oplzyllum.Note the different cell size of the hypo- and perithallus. 1 lir: gcnu5 is all important framebuilding coralline alga in Cenozoic reefs. The sample comes from sediments deposited adjacent to small patch reefs. Late Tertiary (Leithakalk, Miocene): Oslip near Rust, Burgenland, Austria. Spot-olirlion (formerly called A1r.hac~t1lithuthan1tzi1~nl). The genus is characterized by a rnultilayered hypothallus and a thick perithallial tissue with individual sporangia arranged in rows ('sori'; arrow). Late Tertiary (Miocene): GroBhiiflein .\vcs[ of Eisenhtaiit. Burgenland, Ausiria. .2li'.\.00hyll~l,1r. ASI-owspoint to conceptacles with a single-pored roof (-> 6). Tertiary (Miocene): Southwestern Turkey. C'oizilliiicr:Articulated coralline alga characterized by erect, jointed thalli consisting of segments. The segments consist of straight central (medullary, M) equant cells and a cortex (C) composed of tiny cells. Quartz-rich algal rudstone. Note the dztrital subangular quartz grains (white). Transgressive near-shore shelf facies (Reijers and Petters 1997). Mid-Crew ceous (Mfamosing Limestone, Middle Albian): Calabar Flank, Niger Delta, Southern Nigeria. Lithuphjllirnz. Conspicuous single-pored conceptacle (arrow). Temperate near-coastal facies. Tertiary (Oligocenej: Pohlkotte. Lower Saxony. Germany. Spo~olitho~r. Conceptacles are borne in 'sori' (S; compare P1.64112). Same locality as Fig. 6. Rhodoid composed of crustose branches of Lithoplzyllunz. Note differences in cell sizes in the basal part (hypothallus, ijT) and the perithallus (PT). Late Tertiary (Miocene): Turkey. Articulated coralline alga. Subterrc~rl(~phpllum. Tertiary (Late OligoceneJEarly Miocene): Drowned reef complex in the Sulu Sea south of Palawan, Philippines. I , 2: Dulh 1983; 5 : Oii and Koch 1990; 6 . 7: Fliigel 1970; 9: Wiedicke 1987 , 7

3

4

5

6

7 8 9 ->

Plate 53: Corailinacean Red Algae

4 16

Significance of Corallinacean Algae

have become increasingly more important (Johansen Coralline bioclasts contribute significantly to the formation of marine warm-water, temperate-water, cold1981; Woelkerling 1988; Bosence 1991). Reproductive organs are borne in calcified case-like water and even polar sand- and gravel-sized carbonates chambers (conceptacles). Conceptacles may be uni- (Pl. 33/2, P1.3511). porate (Pl. 54/4), multiporate (PI. 54/1), or arranged in Reef frameworks are constructed from crustose or rows (sori; P1.5417). The type, the kind of conceptacle roof formation, and the location of conceptacles are dia- branching coralline algae both in high- and low-energy environments, but differ in the density of the crusts and gnostic criteria. branches. Frameworks cemented by fibrous aragonite Environmental constraints: Modem corallines range and microcrystalline High-Mg calcite occur in highfrom tropical to polar oceans and extend from inter- energy coralline algal ridges. Low-energy frameworks tidal areas to depths of about 250 m. Tropical taxa oc- are characterized by intraskeletal cements precipitated cur in depths down to about 80 In, cold-water taxa be- only during the life of the algae. Bioerosion by microtween about 20 and 250 nl (Pl. 411). The distribution of and macroborers is strong in high-energy reefs and less corallines is controlled by environmental factors, pre- common in low-energy reefs. Sediments derived from dation (grazing) and competition. Competitive inter- high-energy reefs comprise coarse particles from breakaction among crustose corallines is influenced by the age by waves and fine particles caused by borers. Quietthickness of the crusts and the height to which the grow- water frameworks are broken by wave action and bioing margin is raised (Steneck et al. 1991). Most coral- turbation; wackestones and packstones are deposited lines prefer hard rough substrates, dim light conditions around the reefs (Bosence 1985). and agitated water. They occur in warm and cold waSignificance of coraliinacean algae: Most Tertiary ters from low to high latitudes and are commonly adapted to normal marine salinities. Growth rates de- genera occur even today. Because of these long-term pend mainly on light conditions. Many corallines are ranges, the study of present-day coralline algae offers shade-adapted. an excellent potential for paleoerzvironmental interp-ctntions. Of particular value are thallus shape and geUisn~iOution:The definite record of abundant coral- ne~icassociations. The morphology of coralline crusts lines begins near the start of the Cretaceous, perhaps and branches reflect d~fferentwater energies (Bosencs already in the latest Jurassic. The recognition of Or- 1983). Rhodoids are sensitive to turbulence in shallou dovician and Silurian fossils with coralline-like features marine environnlents (Bosence and Pedley 1982; Sect. extends the earliest record to the Early Paleozoic (Brooke 4.2.4.2). Because modem cmstose coralline genera have and Riding 1998; Riding ct al. 1998). existed from the Miocene onward, the paleobathyinetr-y can be successfully evaluated at least for the Neogenc. Srdiment production: Coralline algae are one of the (Basso 1998). most abundant marine carbonate producers. Unattached Basics: Corallinacean red algae corallines live on hard and soft sea bottoms and can Adey, W.H., MacIntyre, I.G. (1973): Crustose coralline alform ~fmloirls(Sect. 4.2.4.2; P1. 12/G. PI. 149/6) that gae: a re-evaluation in the geological sciences. - Bull. Geol. Soc. Amer., 84, 883-904 contribute to I-hoclolithpavements and maei-1(composed of branched rhodoids and coralline branches; P1. 412: Basso, D. (1998): Deep rhodolith distribution in the Pontian Islands, Italy: a model for the palenecology of a temperale Sect. 2.4.4.3). Attached corallines form algal ridgcs sea. - Palaeogeogr., Palaeoclimat., Palaeoecol., 137. 171(late successional stage of coral reef development foml187 ing a constructionaI cap over corals as the reef ap- Bnsence, D.W. (1983): Corafline algal reef frameworks. -- J. Geol. Soc. London, 140,365-376 proaches sea level) and algal clip rccf:i (intertidal cupshaped reefs formed by intergrowing coralline algae Bosence, D.W. (1991): Coralline algae: mineralization, taxonomy, and palaeoecology. - In: Riding, R. (ed.): Calcarand invertebrates), trottoin (intertidal buildups, usueous algae and stromatolites. - 98-113, Berlin (Springer) ally growing on steep rock shores, e.g. Mediterranean Bosence, D.W., Pedley, H.M. (1982): Sedimentology and and the Northern Atlantic) and the cur-alligdne de plapalaeoecology of a Miocene coralline algal biostrome from the Maltese Island. - Palaeogeogr.. Palaeoclimat., Palaeoteau (occurring in deeper shelf waters of about 20 to ecol., 39,9-43 160 rn, and passing laterally into carbonate sands and J.C., Bosence, D.W., Steneck, T.S. (1993): New anaBraga, gravels or terrigenous sands). Crustose corallines are tomical characters in fossil coralline algae and their taxoimportant Cenozoic reef builders in tropical and subnomic implications. - Palaeontology, 36, 535-547 tropical regions, as framebuilders and binders, and as Johansen, H.W. (1981): Coralline algae, a first synthesis. 239 pp., Boca Raton, Florida (CRC) cementing agents for bio- and lithoclasts (Pl. 14912).

Peyssorieliacean Red Algae

417

Nebelsick, J.H., Bassi, D. (2000): Diversity, growth forms A and taphonomy: key factors controllingthe fabric of coralline algae dominated shelf carbonates.-In: Insalaco,E., Skelton, P.W., Palmer, T.J. (eds.): Carbonate platform systems: compounds and interactions. - Geol. Soc. London, Spec. Publ., 178, 89-107 Woelkerling, W.J. (1 988): The coralline red algae: an analysis of the genera and subfamilies of non-geniculate Corallinaceae. - 268 pp., British Museum Natural History, London (Oxford Univ. Press) basal tubules (aragonite botryoids) Look at http:llwww.hotany.uwc.ac.zalclineslbibliog/Intro.htm for the bibliography of Rhodophyta (prepared by W.J. Woelkerling with over 4500 references), Coralline News, or Fig- 10-8. Pe~ssoneliaceanred algae. A: Peyssonelia. The thallus is built of thin blades. B: Internal structure of PeysRasser: http:llww~,.paleoweb.ner/rasser/~eI~ome-~. sonelia composed of a thin hypothallium with basal aragonite calcification between downward projecting tubules, and a thick perithallium. A: After Pia (1926). B: After Wray (1964).

Peyssorieliacean red algae

Definition, calcification and morphology: Peyssoneliaceans (formerly called squamariaceans) are a small group of marine calcareous red algae, some of which secrete an aragonitic skeleton. Calcification is both intracellular and extracellular. The latter occurs as a layer of small botryoids below the thallus projecting downwards from basal hypothallus cells. The botryoids are similar to those forming aragonite cements (Sect. 7.4.2.1). The internal structure resembles some crustose corallinaceans. It consists of rectangular hypothallus cells (about 30 y rn high and 20 pm wide) from which vertical or arcuate rows of smaller perithallus ccll3 arise. The algae grow 3s arched millimeter- to centimetersized sheets on soft mud substrates and hard rock surfaces, fonn a bridge-like network between corals in reefs. and occur as concentric layers within nodules (Fig. 9.7, Fig. 10.8).Growth forms are layered and fohose. The former consist of superimposed layers with little or no space between, similar to the growth of encrusting corallines. The latter is an open structure composed of irregularly attached arcuate crusts forming overlappmg sheets with open cavities in-between. In thin sections the crusts of fossil peyssoneliaceans differ from corallinaceans by a transparent golden or yellow-brownish tmt in contrast to the uniform dark appearance typical of coralline algae in general.

Etz~llr-ontnetztal~otzstraint~: Calcified peyssoneliacean algae occur in temperate, and tropical and subtropical waters in depths between a few meters to more than 100 meters. They are common down to 50 meters. Distribution is controlled by light intensity, current regime and sediment input. The algae are often associated w ~ t hcoralline red algae and encrusting foraminifera.

Distribution: The confirmed fossil record starts in the Early Cretaceous. Peyssoneliaceans are widely distributed in Cretaceous and Tertiary warm-water and temperate shelf carbonates. The algae are common in Paleocene and Eocene reef limestones associated with corals, or limited to rhodoid accumulations near reefs. Important genera are: Erhelia (also called Polystrataj, Peyssonelia and Pseudolitlzothanzniunz. Significance: Striking similarities between calcified peyssoneliacean algae and some Late Carboniferous and Permian phylloid algae suggest that the latter may be closely related, thus allowing a less speculative interpretation of economically important phylloid algal buildups (James et al. 1988). Basics: Peyssoneliacean red algae Buchbinder, B., Hailey, R.B. (1983): Occurrence and preservation of Eocene squarnariacean and coralline rhodoliths: Eua. Tonga. - In: Toomey. D.F., Nitecki. M.H. (eds.): Paleoalgology, contemporary research and application. 248-256, Berlin (Springer) Denizot, M. (1968): Les algues FloridCes enwoutantes (i l'exclusion des CorallinacCes). - ThCse, Laboratoire de Cryptogamie, Museum Nationale dlHistoire naturelle Paris, 280 pp. James, P., Wray, J.L., Ginsburg, R.N. (1988): Calcification of encrusting aragonitic algae (Peyssoneliaceae): implications for the origin of late Palaeozoic reefs and cements. - J. Sed. Petrol., 58,291-303 Massieux, M., Denizot, M. (1964): Rapprochement de genre Pseudolithothamnium Pfender avec le genre actuel Etheliu Weber van Bosse (Algues Florideae, Squamariaceae). Revue de MicropalContologie, 7 , 3 1-42 Moussavian, E. (1988): Die Peyssoneliaceen (auct.: Squamariaceae; Rhodophyceae) der Kreide und des Palaogen der Ostalpen. - Mitteilungen der Bayerischen Staatssammlung fiir Palaontologie und historische Geologie, 28. 89124

Solenoporacean Red Algae

10.2.1.3

Solenoporacean Red Algae

Definition, calcijication and morphology: Solenoporaceans are extinct encrusting calcareous algae that developed nodular and branched growth habits ranging in size from several millimeters to a few centimeters. The thalli consist of closely packed threads of vertically divergent calcified cells, which appear circular or polygonal in cross-sections. Solenoporaceans are commonly preserved as Low-Mg calcite, but rare records and the strong and patchy recrystallization indicate a primary aragonitic composition. In contrast to coralline algae no distinct differentiation of the cellular tissue exists. Undisputable reproductive structures are not known. Cell diameter ahd length is con~monly larger than those of corallinaceans (about 10 to 100 ym). is based on zonation patterns, Taxonomic d[ffccl-cr~tiarion the arrangement, shape and size of cells, partitions within the filaments and walls and cell connections. The presencetabsence and regular or irregular spacing of horizontal partitions within the filaments have been

used as generic characteristics. The traditional species differentiation only on the basis of cell dimensions is highly artificial. The group has to be restudied. Vachard et al. (1989) drew attention to the possibility that many solenoporacean 'species' correspond to diagenetic stages rather than to well-founded taxonomic units. Systematic position: The Solenoporaceae are now regarded as a subgroup of the red algal group Florideae because of the existence of pit-like connections between the cells (Moussavian 1989). The group has been considered to represent possible ancestral forms of the Corallinaceae, but still distinct evidence for this interpretation is missing. Distribution: Cambrian to Miocene. Solenoporaceans are constituents of Paleozoic and Mesozoic subtidal open-marine shelf carbonates and reef limestones. In some Silurian, Permian and Late Cretaceous reefs the algae are concentrated near the open-marine reef margin. They are common in Middle and Late Trias-

Plate 55 Solenoporacean Red Algae Solenoporacean algae, known from the Cambrian to the Late Tertiary, are common thin-section fossils in Paleozoic and Mesozoic platform and reef carbonates. The encrusting calcareous algae had nodular and branched growth habits and range in size from several millimeters to a few centimeters. Solenoporaceans have beer1 regarded as possible ancestors of corallinacean red algae. Longitudinal sections show radially or vertically divergent calcified filaments appearing ns long 'tubes' (-> 3) or superposed cells within the filaments (-> 5 ) . Ccll diameter (about 10-100 ~cm)is larger than that of most corallinacean red algae. Taxonomic differentiation is based on zonation patterns, the arrangement, shape and size of cells (-> 3, 5, 8), partitions (-> 4, 5 ) within the filaments and walls and cell connections. The group has to be restudied regarding additional morphological 8). criteria i-> 1 Solenporacean floatstone. The nodular aigal thalli are bored and marginally micritized. Solenoporacean algae, often

associated with porostromate algae, are common constituents of small-scaled Frasnian and Famennian buildups. Latest Devonian (Strunian): Dubic-Debnik near Krakow, southern Poland. 2 S o l e m p u ~ - (Nodular ~. thalli in life positon with distinct growth zonation. They occur together with dentfroid coral.\ ( r m t shown) and form a reef framework with s i ~ e slarger than 1 square meter. Late Triassic: Jabal Kawr, Omall. i Soletwpc~r-uc~ussimuFliigel. Longitudinal (LS) and cross-section (CS). Note distinct filaments exhibiting pearl-sllapcd outlines ( a ~ ~ o that w ) correspond to lateral connections. Reef facies. Late Triassic (Cassian Formation, Camian): Seelard 41m near Cortina d'Arnpezzo, Soutlwn Alps. Italy. -t Par-rrchurtcte.s,joI~r~sotzi Maslov. Note different preservation obscuring the algal structure in the lower part of the thallus. Same locality as -> 1 5 Parnrlzuc~t~.res johnsuni hlaslov. Horizontal partitions are situated at the samc level between tubes, and separate the iong cells. The well-preserved alga is encrusted by foraminifera. Same locality as -> 1. f~ Transported solenoporacean red algae exhibiting the common preservation feature. Recrystallization of the originall!, aragonitic thalli has obliterated the algal structure, which is only recognizable in traces. In contrast, micro- and macrobor-ings (black and white arrows) are well preserved because of early infilling with calcite. Early Permian: Teufelsschlucht. Karawanken Mountains, Slovenia. ? Solenopor-a. Longitudinal section. Note growth zonation and microborings (arrows). Early Cretaceous: Subsurface, United Arabian Emirates. 8 Parnchaetetes asvapatii Pia. The filaments are differentiated into 'long' and 'short' cells (occurring in the dark zones) similar to cell differentiation in modem floridean red algae. The cosmopolitan species is known from the Albian to the Paleocene. Early Tertiary: Italy. 4 2: \'Jzidlich et al. 1993

Plate 5 5 : Solenoporacean Red A l g a e

419

5 rnrn

5 rnrn

420

sic, and locally abundant in Jurassic and Cretaceous patch reefs. Common genera are: Solenopora, Parachuetetes, Colzlilites (Late Cretaceous), Elianella. Basics: Solenoporacean red algae Johnson, J.H. (1960): Palaeozoic Solenoporaceae and related red algae. - Quarterly, Colorado of School Mines, 55, 177

Ancestral Red Algae

Mamet, B., Roux, A. (1977): Algues rouges dkvoniennes et carbonifires de la Tkthys occidentale, part 4. -Revue de MicropalContologie, 19,215-266 Moussavian, E. (1989): Uber die systematische Stellung und Bestimmungskriterien der Solenoporaceen (Rhodophyceae). - Courier Forschungsinst. Senckenberg, 109,51-91 Wright, V.P. (1985): Seasonal banding in the alga Solenopoi-a jurassica from the Middle Jurassic of Gloucestershire, England. - Joumal of Paleontology, 59,721-732

Plate 56 Late Paleozoic Ancestral Red Algae and Problematic Red Algae The terms 'ancestral red algae' or 'ancestral coralline algae' refer to Late Paleozoic algae characterized by differentiated blade-like thalli with hypo- and perithallus structures, thus reminding one of corallinacean algae. Other taxa exhibit branched (-> 6) or irregular, encrusting forms (-> 4). Many taxa exhibit yellowish hyaline structures pointing to a primary aragonite skeletal mineralogy that is also indicated by high strontium concentraSome genera (Archaeolithophyllum; -> 1, 2, 8) contribute to the formation of tions in AI-chaeolithoplzyll~i~~~. mounds, others are common in open-marine shoals but also in restricted lagoonal carbonates. Archaeolithoplzyllun~ appears to be related closely to modem aragonitic Peyssoneliaceae. A few taxa, sometimes called 'pseudoalgae', have been attributed to sponges, but are probably algae (Ungdarella,-> 7; Fasciella, -> 3,4; Komia, -> 6). Some of these taxa are index fossils, particularly useful for biostratigraphic differentiation based on foraminiferal assemblage zones of Early Carboniferous shelf carbonates. Fig. 10.9. Late Paleozoic ungdarellacean algae (Ungdai-ella, Komia) and stacheinacean algae (Aoujgalia, Efluegelia, Stacheoides). The interpretation of these mm-sized encrusting microfossils is controversial, but many workers assign them to red algae because of the structural similarity with genuine rhodophytes. After Chuvashov et al. ( 1987). 1 Ai~chaeolitlzopI~~llirwz Johncon. Anccstml coralline alga. Criteria: Crustose multifoliate sheets of differentiated cells. Promnent hypothallus with large polygonal cells (arrows), poorly developed perithallus. Single high-arched conceptacles in the perithallus tissue. Thalli often recrystallized, yellowish in transmitted light. Originally aragonitic skeleton. Top right: Cross-section lvith distinct cell srructurc. Time range: Early Carboniferous to Early Permian, abundant in Middle and Late Carboniferous. The genus is common in shallow-marine mounds and shoals. Late Pennsylvanian (Auernig Formation): Gugga, Casnic Alps, Austria. 2 At~c~haeolirizoplzyll~~tii Johnson. Note central hypothallus (HT) cells. The perithallus (arrow) is largely destroyed. Same locality as -> 1 3 Fuscielli~Ivanova. Forn~cslyimned Slta~.ryt~~opltyc~~s. Regarded as red or green alga. Criteria: Encrusting nodular thailus. composed of irregular concentric layers of elongated cells. Walls yellowish, hyaline. Time range: Carboniferous (VisCan to Bashkirian). Common in open-marine shelf grainstones. Early Carboniferous (VisCan): Betic Cordillera, Spain. 4 Fusciellu Ivanuva. Note nodular growth and irregular layers (arrow). Middle Carboniferous: Nassfeld, Carnic Alps, Austria. 5 Ej7rwpc~lin\'acharci, enclosed in an oncoid. Probably an ancestral red alga. Criteria: Encrusting thallus consisting of a fsw thin rows of minute, subparallel laminae with quadratic cells. Walls yellowish, hyaline. Commonly enclosed in biogenic crusls. Time range: Carboniferous and Early Pem~ian.Early Pennian (Asselian): Carriic Alps, Austria. 6 Konziu Korde. Criteria: Ramified robust thallus composed of rectangular and quadrangular cells. Walls yellowish, hyaline. Time range: Middle Carboniferous to Early Permian. Common in shelf carbonates. Late Pennsylvanian (Gzhelian): Hiittenkofel, Carnic Alps, Austria. 7 Ur~gdarellrKorde. Criteria: Ramified thallus, perithallus with long thin rows of subquadratic cells. Time range: Carboniferous and Early Permian. Common in Middle Carboniferous shelf carbonates. Carboniferous (VisCanlNamurian): Rif Mountains, northern Morocco. 8 Khodoid with thin crusts of Ai-chaeoiiri~opl~yllum lamellosum Wray. The alga has coated phylloid algae (Eugoizophylllm, E; P1.58/3) as well as a rugose Dibut~ophyllum-typecoral (C). Note the loose organization of the cm-sized oncoid and the inclusion of mud chips (MC), indicating that coating was a nonselective process. Late Pennsylvanian (Leavenworth limestone. Virgilian; transgressive part of a megacyclothem): Osage County, northern Oklahoma. U.S.A. -r 8: Toonley 1983

Plate 56: A n c e s t r a l Red Algae

47 1

Udoteacean Algde

Box 10.2. Late Paleozoic ancestral red algae common in reef limestones, and possible red algae, abundant in platforms and ramps. Although the systematics of the latter are controversial and need substantiation, the fossils have a high potential in microfacies analyses. Specific associations of these algae and of foraminifera allow a detailed biozonation and correlation of Carboniferous shelf carbonates (Armstrong and Mamet 1977, Mamet et al. 1987). Archaeolithophyllacean red algae Central hypothallus coaxial, consisting of large polygonal and rectangular cells. Perithallus poorly developed, cells much smaller. Large conceptacles at the periphery, commonly exhibiting a yellowish color in transmitted light. Often strongly recrystallized. Common taxa: Archaeolithophyllurn (Pl. 56/1,2,8). Vis6an to Late Permian. Cosmopolitan. Abundant in Pennsylvanian and Early Permian reefs (reef mounds and mud mounds). Ungdarellucean I ed algae M~lllmeter-sizedelongated and often ramified encrusting nodules. exhibiting rectangular and subquadratlc cells that are son~etimesdifferentiated according to size and arrangement. Skeletal elements hyaline, often with a golden or yellowish tint in transmitted light. Common taxa: Ungdarellu (Pl. 56/7. P1. 108/7, 8), Konuu (PI. 5616) Early Carboniferous to Permian. Cosmopolitan. Abundant in Late V~stanto Moscovian shelf carbonates. Sfnclzeirzaceuriurzd related red aigae Millimeter-sized rnicrofossils encrusting a central support or a substrate. Characterized by a succession of arched or subquadratic cells arranged irregularly or in rows. Skeletal elements hyaline. Commonly yellowish in transmitted light. Common taxa: Cur~eiphycus, Efluegeliu (Pl. 56/5), Epistacheoides (Pl. 108/9), Stucheia (PI. 108/10),Stacheoides. Early Carboniferous to Permian. Common in Visean to Moscovian platform and ramp carbonates. Rare in Early Pennian shelf carbonates.

10.2.1.4 Ancestral Red Algae and Problematic Red Algae Several thin-section fossils, predominantly of Late Paleozolc age, are believed to be ancestors of younger red algal groups, or are assigned to red algae, more or less persuasively. Some exhibit thalli composed of a cellular tissue known from true red algae taxa (e.g. Alrlzaeolitlzophyllum). Other taxa can not be related to existing red algal groups and are therefore assigned to separate algal groups (e.g. C'ngdareliu) or have been excluded from the algae and compared with foramin-

ifera, hydrozoans or sponges. Two groups of these microfossils are common in Late Paleozoic shallow-marine carbonates and used in the stratigraphic and environmental subdivision of platforms and ramps (Fig. 10.9; Box 10.2). Basics: Ancestral corallines and problematic red algae Armstrong, A.K., Mamet, B. (1977): Carboniferous microfacies, microfossilsand corals, Lisbume Group, Arctic Alaska. - Geological Survery Professional Paper, 849, 144 pp. Johnson, J.H. (1956): Arclzaeolithophyllurn, a new genus of Paleozoic coralline algae. - Journal of Paleontology, 30, 53-55 Mamet, B., Roux, A., Nassichuk, W. (1987): Algues carbonifires et permiennes de 1'Arctique canadien. - Geologica! Survey of Canada, Bulletin, 342, 1-143 Wray, J.L. (1964):Archaeolithophyllum, an abundant calcareous algae in limestones of the Landsing Group (Pennsylvanian), southeastern Kansas. - Kansas Geological Survey Bulletin, 170, 13 pp. Further reading: K129

10.2.1.5 Udoteacean Green Algae and Gymnocodiacean Algae Most modem benthic gl-eel? algae live in freshwater environments, about 10% of the species also occur in marine settings. Ancient green algae are almost exclusively marine fossils. Benthic ctrlcifiecl green algue are represented by the Udoteaceae and the Dasycladareue. The systematic position of the extinct Gprnrrocodiaceae (green or red algae) is still under discussion, but better arguments are in favor of green algae (Mu 1991; Bucur 1994). Other algal groups related to or interpreted as benthic green algae are the Early Paleozoic receptuculitids (common in Ordovician and Silurian, ranging to thc Permian) and ryclo~~rinitids (Ordovician and Silurian). Both groups differ in the size of the globular shape (several centimeters) of typical calcareous algae, but resemble dasyclad green algae in their internal organization. They have a central main axis and radially ananged tightly packed lateral branches forming hexagonal orrhombohedra1 facets on the outer surface (Rietschel 1977; Nitecki et al. 1987; Beadle 1988, 1991). Some of the fossils included within the informal group of 'phylloid algae' are most probably udoteacean green algae (Sect. 10.2.1.6). Fossil records of marine planktonic green algae are known from the Volvocales and Chlorococcales (Sect. 10.2.1.9). Calcifying planktonic green algae also contribute to the formation of modem and Tertiary freshwater carbonates (Miiller and Oti 1981).

Udoteacean Algae

Udoteacean green algae

filamentous (nodular), delicately branched, and phylloid (bladed) growth forms. The basic pattern of the internal organization is differentiated into a central region (medulla)and a peripheral zone (cortex).The medullary filaments are arranged parallel to the axis of the thallus, interwoven or branched, and give rise to lateral cortical filaments. The medulla is poorly calcified. Hence, in thin sections the central region often exhibits no structures and is strongly recrystallized. The thinner cortical filaments differ greatly in shape and are straight, swollen or constricted. Calcification of living udoteaceans varies in intensity and takes place by precipitation of needle-shaped aragonite crystals on the surface of filament membranes within the thallus. In fossil udoteaceans, calcification is mainly recorded in the cortex. Many udoteacean fossils appear as calcareous 'tubes' or blades, exhibiting a peripheral zone perforated by pores and an often strongly recrystallized or spar-filled central region with faint or no filaments. Fossil reproductive structures are commonly absent, reported occurrences are questionable. Bladed udoteaceans are described in the context of the discussion of phylloid algae (Sect. 10.2.1.6).

This algal group is well-known to sedimentologists because of the fundamental importance of Halimeda in the production of carbonate muds and sands in modem shallow seas.

Which name is the right one? Taxonomists like to change systematic categories. Both, erect and filamentous forms were formerly called Codiaceae, a group of the Bryopsidales (formerly Siphonales). Since modem Codiaceae include biologically different types, the group has recently been split up into Udoteaceae, morphologically represented by the genus Halimeda, and into the non-calcified Codiaceae, represented by the genus Codium. Most erect fossil forms are now included within the Udoteaceae. Some authors use the name Halimedaceae which has priority over Udoteaceae (Hillis 1991).Filamentous fossil taxa are attributed to the porostro~nateCyanobacteria or are sometimes regarded as members of separate groups of siphonate green algae. Definition and morphology: Udoteacean algae are plants consisting of cm-sized segmented thalli attached to the substrate by rhizoids. The algae develop erect, Jurassic I

E

I

M

rare

B

I

Ecological constraints: Modem codiacean green algae occur in normal saline warm waters of tropical shelf, Cretaceous

L

!

Tertiary L

E

common

E

-

/

IPbr&ent L

I

frequ

Halimediform udoteaceans in reef environments rare : I -

?-

. common

Halimediformudoteaceans in lagoonal and platform environments

Fig. 10.10. Udoteacean algae. Species richness and sedimentological role. A: The figure shows the number of species of three closely related genera characterized by similar patterns in the differentiation of cortical filaments (Pl. 57). In recent papers some more new species have been described, but the general trend in species richness is the same as shown in the figure. Halimeda was also reported from Permian deposits. B: The contribution of erect udoteaceans to the sand fractions of platform and reef carbonates increased notably during the Tertiary and reached in Miocene lagoons values of more than 75% similar to those of today. PL: Pleistocene. Modified from Fliigel (1991). Pictures of the morphotypes after Elliott (1982).

Gymnocodlacean Algae

lagoonal and reefal environments. They are commonly concentrated in depths of a few meters, but extend to about 100 m (Halinzeda thickets). The plants grow on sand and mud bottoms below intense water agitation. Disrributiorz: Calcified udoteaceans appear in the Ordovician. The algae are common in the Ordovician, abundant in the Early and Middle Devonian, and relatively rare in the Late Paleozoic and Triassic. Calcified udoteacean algae are locally common in Late Triassic and Jurassic limestones and abundant in Early Creta-

ceous carbonate platforms. They became abundant during the Cenozoic. Many taxa appear to be restricted to stage or substage intervals. Udoteaceans related to or identical to Halimeda are common in shallow-marine carbonates of Cretaceous and Early Cenozoic age, where they occur in similar environments as today (Fig. 10.10). For a survey of the Phanerozoic species see Bassoullet et al. (1983). Some rock-building fossils of problematic systematic position that have been tentatively placed in the udoteacean or codiacean algae are discussed in Sect.

Plate 57 Calcareous Udoteacean Green Algae and Gymnocodiacean Algae Modem udoteacean green algae are a major source of calcareous mud from postmortem disintegration of their skeletons. Halimeda contributes to the formation of carbonate muds and sands in shallow environments but also to Halimeda 'reefs' occurring today on deeper slopes. Udoteaceae are calcareous green algae with erect (-> 1-6), nodular or bladed growth forms. The internal organization of erect segmented forms is exemplified by Hnlimeda (-> 1,2; Fig. 10.3). The thallus consists of a central zone (medulla conlposed of filaments arranged parallel to the axis) and the peripheral cortex zone exhibiting smaller branched filaments. Calcification (aragonite) takes place between and around the filaments. Ancient udoteaceans, known since the Ordovician, are predominantly classified according to growth form (branched. unbranched, segmented, non-segmented, bladed), and the structure of the medulla and cortex (size, shape, number, arrangement and branching mode of the filaments). C;ynz~rocodiacearzalguc (-> 7, 8) are extinct (Devonian to Tertiary) cylindrical or sack-like algae comnlonly occurring as mm-sized fragments. They developed erect, branched or unbranched, segmented or non-segmented thalli composed of central filamentous medulla and a peripheral thin cortex zone with pores. The primary mineralogy is considered to have been aragonite. Mass accumulations in Late Pem~ianand Early Cretaceous 'Iethyrtn carbonate platforms are indicative of warm, shallow seas with low to noder rate water energy. 1 Hdimeda. Longitudinal section of a segment. The internal structure is characterized by loosely packed filaments forming an outer cortical (C) zone of thin lateral branches that develops from a broad central zone (medulla, Mj with thicker filaments. Dark areas between the filaments are carbonate. Recent reef lagoon: Florida Bay, U.S.A. 2 Hiriirriedu. Note the differences in the size and arrangement of filaments. The medullary filaments are tangled and form uiricles (swellings; arrow) passing into the cortical zone. Recent reef lagoon: French Reef, Florida Bay, U.S.A. 3 Boueina nzurondei Fliigel. Longitudir~al( L S ) and tangential section (TS). Note the gross similarity of the internal structure with Hczliniedu. M: Central medulla. C: Peripheral cortex. Late Triassic (Norian): Western Thailand. 1 Psrudo~~ulacopor-ella lun~nlatoizctlsis(Elliott). The cortex (C) consists of densely spaced, branched and subparallel filaments. Middle Devonian (Eifelian): Graz, Austria. 5 Litcriruin graerensis Hubmann. Cross sec~ionof a cylindrical thallus, differentiated into central medulla ( M j with thick filaments, and peripheral cortex (C). Note bifurcation and thickening of cortical filaments (arrow). Litanaia and similar kxa ( e . Larzcicula) ~ are common in Early and Middle Devonian shelf carbonates. Inner ramp (see Pi. 135). Middlc Devonian (Eifelian): Graz, Austria. 0 Cross section of Boueina Iloc1zstetrer.i Toula, a cosmopolitan Late Jurassic and Cretaceous species occurring prcdorninantly in Early Cretaceous platform carbonates. Cretaceo~ls(Early Aptian): Southern Carpathians, Romania. 7 Gymnocodiacean grainstonc, consisting of broken Per-mocalculus thalli. Arrows point 10 thin-walled fragments with fine densely spaced branched cortical filaments. Permocalculus is characterized by tightly bound segments with a widz, poorly calcified medulla and a narrow cortex intersected by numerous branched pores (see Fig. 10.11). Parallel alignment Middle Perof algal fragments and some coated shells indicates current deposition. Back-reef facies. SMF 18-GYMNO. mian (Wordian): Djebel Tebaga, southern Tunisia. S Compacted gymnocodiacean floatstone, consisting of densely packed thalli of Gymnocodium. Arrows point to longitudinal sections exhibiting the characteristic irregular outline of the thalli caused by thick peripheral filaments. SMF 18GYMNO. Late Permian: Taurus Mountain Range, Turkey. -.> 4: Courtesy of B. Hubmann (Graz); 5: Hubmaw 1990; 6: Courtesy of I. Bucur (Cluj-Napoca)

Plate 5 7 : Udoteaceans a n d Gyrnnocodiaceans

425

5 0 0 urn

1 mrn

Gymnocodiacean Alagae

426

10.2.1.5 (Nuia, PI. 9811) and Sect. 15.1.2 (Microcodiunz, P1. 12814). Sedimentological significance: In modem shallowmarine, low- to moderate energetic environments udoteaceans are a major source of calcium carbonate mud from postmortem disintegrations of their skeletons.Halirneda is abundant (1) in tropical lagoonal environments (Hillis 1991) similar to fossil counterparts, (2) in reef and forereef environments, and (3) on deep slopes, forming banks and reefs (Drew 1983; Marshall and Davies 1988). Ancient Halimeda-form algae contributed to sediment production, locally in the Late Triassic (PI. 5713) and more commonly in the Cretaceous (Pl. 5716) and significantly since the Early Tertiary. The sedimentological role of Paleozoic udoteaceans seems LObe restricted to some Ordovician and Devonian shelf carbonates (Pl. 5714, 5).

Gymnocodiacean algae Systernutir position: These algae were originally regarded as codiaceans, but later attributed to the red algae because of some similarities of the reproductive structures to those in a genus of recent chaetangiacean red algae (Elliott 1955). The affinity of the group is not yet settled. A red algal affinity has been accepted by many authors, but was recently questioned again In favor of a possible assignment to green algae (Mu 1991; Bucur 1994). The gymnocod~aceansresemble fossil erect udoteaceans in growth form, internal structure, and palecological and paleogeographical distribution, but seem to differ in containing internal reproductive organs (Mu and Riding 1983).

Fig. 10.11. Longitudinal section of Permocalculus. This gymnocodiacean genus is of rock-building importance in Permian and Cretaceous carbonates. Late Permian: Berganla, northwestern Anatolia, Turkey. Scale is 1 mm.

Fig. 10.12. Gymnocodiacean limestone. Various sections through segments of Gymnocodium bellerophontisRothpletz. These algae were poorly calcified in the central part (which is commonly filled with sediment) and strongly calcified in the peripheral cortex, where the branched filaments may terminate in the form of funnels or bowls, appearing as polygonal structures in tangential sections. Faint relics of medullarq filaments occur within the grayish interior of two sections. Middle Permian: Balya, Anatoha, Turkey. Scale is 1 mm.

Molphology: The extinct algae have erect, branched or unbranched, segmented or unsegmented cylindrical thalli, consisting of cylindrical, oval, or pyrifornl segments. The internal structure of these segments is characterized by a medullar zone and peripheral cortical zones. Calcification (primary aragonite) was signilicantly stronger in the cortical than in the nledullar zone: the center of the thalli, therefore is commonly filled with sediment or cement. Medullar filaments run parallel along the axis, cortical filaments are branched several times and form a distinct pattern. Reproductive structures are represented by oval or spherical cavities in the cortex or in the area between the cortex and medulla. Distribution: The records of this group range from the Middle Devonian (Mamet et al. 1994) to the Late Tertiary, with most abundant occurrences at the Latc Permian (Mu 1991) and common occurrences in some Cretaceous carbonates (Elliott 1958; Bucur 1993). Limestoes composed more or less completely of gymnocodiacean algae are common in the Middle and Late Permian of theTethys (e.g. Dolomite Mountains, South Tyol) and most abundant in the Capitanian and the Early Changsiangian stages. Sedimentological significance: During the Late Permian, gymnocodiaceans were important sediment pro-

P h y l l o ~ dAlgae

ducers in shallow, low to moderate energetic shelf seas (Fig. 10.12, P1. 12213). 'They acted as bafflers and contributed to the formation of bioclastic wackestones and packstones in ramp and outer shelf environments through fragmentation and transport of their thalli. Common geographically widespread taxa are Gymnocodiunz (restricted to the Permian) and Permocalculus (Permian to Aptian; Fig. 10.11). Basics: Udoteacean green algae and gymnocodiacean algae Bassoulet, J.P., Bemier, P., Deloffre, R., Genot, P., Poncet, J,, Roux, A., Jaffrezo, M. (1983): Les algues udoteactes du PalCozoique au CCnozoique. - Bull. Centre Recherches Exp1or.-Prod. Elf-Aquitaine, 7,449-621 Bucur, 1.1. (1994): Lower Cretaceous Halimedaceae and Gymnocodiaceae from the Southern Carpathians and Apuseni Mountains (Romania) and the systematic position of the Gymnocodiaceae. - Beitrage zur Palaontologie, 19, 13-37 Deloffre, R. (1992): RCvision des Gymnocodiaceae (Algues rouges, Permien-Miocene). Taxonomie, biostratigraphie, palCogCographie. 32me partie. Inventaire taxonomique critiques des especes de GymnocodiacCes du Permien et du Trias. - Revue de MicropalContologie, 35,23-37 Elliott, G.F. (1955): The Permian alga Gymnocodium. -Micropaleontology, l, 83-!90 Elliott, G.F. (1958): Algal-debris facies in the Cretaceous of the Middle East. - Palaeontology, 1, 254-259 Fliigel, E. (1988): Hulinwdu: paleontological record and paleoenvironmental significance. - Coral Reefs, 6,123- 130, Berlin Hillis, L. (199 1): Recent calcified Halimedaceae. -In: Riding, R . (ed.): Calcareous algae and stromatolites. - 167-188, Berlin (Springer) F-Iubmann,B.(1993): Zur heutigen Situation der Systematik und Taxonomie devonischer Griinalgen am Beispiel 'Lancicula' . - Sitzungsberichte der ~sterreichischenAkademie der Wissenschaf'ten, mathematisch-naturwissenschaftliche Klasse, 200, 151-161 Mamet, B., Roux, A., Shalaby, H. (1984): R6le des Algues calcaires dans la sedimentation Ordovicienne de la platfonne du Saint-Laurent. - Geobios, MCmoir SpCcial, 8. 26 1-209 Mankiewicz, C. (1988): Occulrence and paleoecological significance of Hulin~eduin late Miocene reefs, southeastern Spain. - Coral Reefs, 6, 271-279, Berlin Marshall, J.F., Davies, P.J. (1988): Halimeda bioherms of the Great Barrier Reef. -Coral Reefs, 6, 139-148, Berlin Mu, Xinan (1 99 1): Fossil Udoreaceae and Gymnocodiaceae. - In: Riding, R. (ed.): Calcareous algae and stromatolites. - 146-166, Berlin (Springer) Mu, Xinan, Riding, R. (198:3): Silicified gymnocodiacean algae from the Permian of Nanjing, China. - Palaeontology, 26, 26 1-276 Roux, A. (1991): Revision des Gymnocodiaceae (Algues rouges, Permien-CretacC). Taxonomie, biostratigraphie, palCogCographie. 22me partie. Inventaire taxonomique critiques des espkces de GymnocodiacCes du Permien et du Trias. - Revue de MicropalContologie, 34, 136-173

Fig. 10.13. Reconstruction of a phylloid algal commutzity. The algae dominate the sea bottom. The algal leaves are home to various encrusting foraminifera and polychaete worms. Brachiopods live in sheltered areas below algal blades. Gastropods and echinids graze the algal meadow. Some bivalves occur on and within the sediment. Slightly modified from Toomey (1981). Roux, A., Deloffre, R. (1990): RCvision des Gyrnnocodiaceae (algues rouges, Permien-CrCtacC). Taxonomie, biostratigraphie, palCobiogtographie. Ire partie: GCnCralitCs sur la famille. -Revue de MicropalContologie, 32, 123-137 Further reading: K129

10.2.1.6 Phylloid Algae Definition and morphology: The informal name refers to the leaflike form of the thalli, which consist of variously shaped calcified blades comparable in shape to the modem green alga Udotea and to non-calcified brown algae (Pray and Wray 1963). The fossil record of these algae consists of fragmented blades exhibiting various internal structures. Some phylloid algae are differentiated into central medullary and cortical zones (Anchicodium,Ivanovia, Eugonophyllum) or consist of only one layer of pores (Calcifnli~im).The medullarq zone is commonly replaced by coarse sparite. Primary calcification consists of aragonite. Taxonomic differentiation is based on the structure of the cortex. Some phylloid algae have internal cellular structures that relate them to red algae (Arclzaeolirhophyllum,see Sect. 10.2.1.4). Systematic position: Most authors place genera of 'phylloid algae' into various groups of green or red algae (Udoteaceae; Peyssoneliaceae). The green algal interpretation is, at least for Eugonophyllum, supported by strong arguments (Kirkland et al. 1993). Some authors include Eugonophyllum (Pl. 58/5),Ivanovia (Pl. 5814) and Anchicodium in the separate green algal group Anchicodiaceae.

Phylloid A l g a e

Distribution: Predominantly Middle Carboniferous to Late Permian. A few records are known from the Middle Devonian and the Late Triassic (Reid 1986; Mamet and Preat 1983). The algae flourished during the Late Pennsylvanian and Early Permian (Asselian and Sakmarian). Sedirnentological significance: Phylloid algae are dominant rock constituents in bedded shelf carbonates and contribute significantly to the formation of Pennsylvanian and Early Permian mud mounds, reef mounds, and banks. Mounds and banks dominated in shelf settings and at shelf margins (Wahlman 2002). Phylloid mounds are characterized by flat bases, undulatory surfaces and high micrite content. Rapid growth and recovery rates of phylloid algae were ideal for life in settings strongly controlled by short-term sea-level fluctuations. Stacked mounds reach a thickness of sev-

eral decades of meters. Banks are more extended and may cover areas of more than 50 krn2. Location and development of phylloid algal mounds seems to be controlled by paleocurrent directions and nutrient levels. Phylloid algae acted mainly as important sediment bafflers, but some of them have also built reefs by constructing organic frameworks (Sarnankassou and West 2002). Some phylloid algae (e.g. Eugonophyllum) exhibit a felt of aragonite needles interspersed between small parallel medullar tubes, similar to Halinzeda. These needles might have been a source for carbonate muds of mounds and banks. Laterally extended phylloid algal buildups are major hydrocarbon reservoirs in the southwestern United States (Montgomery et al. 1999)because of high intraskeletal and interskeletal porosities and common subaerial exposure. The depositional texture of the phyl-

Plate 58 Phylloid Algae *Phylloidalgae' is a non-taxonomic term referring to predominantly Late Paleozoic calcareous algae characterized by leaf-like growth forms (Fig. 10.13). The group includes udoteacean green algae (Pl. 57), ancestral red algae (Pl. 56) as well as squamariacean red algae with erect or inclined growth forms. Viewed in cross-sections in limestones, phylloid algae appear as thin sinuous lines. sometimes looking like 'potato-chips'. Many phylloid algae are recrystallized and lack sufficient internal features for taxonomic identification. Epifluorescence perrography assists in overcoming (his difficulty (Dawson 1992). Generally, the central (n~edullary)part of' thc blades is filled with carbonate cement (-> 5). The very poor preservation as well as rare records indicate primary aragonite mineralogy. ?'axonomically important criteria are the shape and arrangement of cortical branches (-> 2 , 4 and 5 ) . Blades can be several centimeters long and up to 1 mm thick. ! Phylloid algal floatstone. All bent. curved and straight elements are recrystallized algal blades. Mollusk shells differ in tllc shape and lack of peripheral pores. Many algal blades are bored (B). Other biotic elements are scarce (gastropods - G , and

rare echinoderm plates - E). The chaotic distribution of the blades resembles the edgewise fabrics of conglomerates, and points to reworking and deposition caused by storm currents. Edgewise fabrics have been described mainly from peritidal environments, but also occur in subtidal settings, e.g. as storm or swell lags deposited in shoreface environments, lateral accretion lags deposited in tidal channels, or as transgressive lags formed by ripping up of the underlying strata a \ the sea Icvel rose d~tringplatfom~drowning (Demicco and Hardie 1994). SMF 5. Late Pennsylvanian (Lower Pseudosch~vagerina beds, Gzhelian): Camic Alps, Austria, 2 ilieoitnchiiodiunz Endo. Blades with poorly calcified tubes and one or two rows of ellipsoidal cells in the peripheral LOIIC appearing as a 'ring of pearls' in transverse sections (arrow). The genus is common in Early Permian open-maririt. platform carbonates. Early Pennian shelf platform: Forni Avoltri, Carnia, Italy. 3 Eugonophyllwn Konishi and Wray, an udoteacean green alga. The thallus consists of large blades standing erect on the substrate. The alga is most conimonly preserved as isolated and often heavily recrystallized fragments. Filaments in thc central medulla are often obliterated by recrystallization. The blades are strongly encrusted by foraminifera (arrows). E: Epirnastopot-a (see PI. 60/4). Early Permian: Camic Alps, Austria. -1- I\sanovia Khvorova. The central (medullary) zone is recrystallized. The well-preserved cortical zone exhibits thin branchc:> oriented perpendicular to the medullary zone. The sample comes from phylloid algal packstones overlying a Alr~l~cre(jlitlzoporella-Tubi[>Izytesreef. Middle Permian (Wordian): Djebel Tebaga, southern Tunisia. 5 Eugonophyllutn mulderi Kacz. Well-preserved cortical zone (C) with crescent-shaped branches. The medulla (M) is obliterated by dissolution and cement filling. E: Echinoderm plate. Late Carboniferous (Gzhelian): Hiittenkofel, Camic Alps, Austria. - -r 4: Toonley 199 1

Plate 58: P h y l l o ~ dAl,o;ie

420

430

Dasyclad Algac

axis) which bears one or more whorls of lateral branches (laterals). These primary branches may subdivide distally forming one to three or more orders of laterals. Basics: Phylloid algae Reproductive organs occur on or between branches, or Cys, J.M. (1985): Lower Permian phylloid algal mounds, southern Tatum basin, southwestern New Mexico, U.S.A. within the central stem. Aragonite is precipitated around - In: Toomey, D.F., Nitecki, M.H. (eds.): Paleoalgology. the stem (or parts of the stem) and between the branches. Contemporaneous research and applications. - 179-187, As a consequence, fossil dasyclads are represented as Berlin (Springer) molds in which the area of the stem cell appears as a Kirkland, B.L., Moore, C.H., Jr,, Dickson, J.A.D. (1993): Well spar- or sediment-filled cavity, surrounded by a calcipreserved, aragonitic phylloid algae (Eugonophyllum, Udoteaceae) from the Pennsylvanian Holder Formation, fied zone exhibiting the branches as pores. The recogSacramento Mountains, New Mexico. - Palaios, 8,111- 120 nition of the diagnostic criteria is controlled by the exMontgomery, S.L., Chidsey, T.C., Eby, D.J., Lorenz, D.M., tent of calcification. For major diagnostic criteria see Culham, W.E. (1999): Pennsylvanian carbonate buildups, Fig. 10.14. loid algal sediment is a principal factor in the localization of effective porosity and permeable zones.

Paradox Basin: increasing reserves in heterogeneous, shallow shelf reservoirs. -American Ass. Petrol. GeoI., Bull., 83, 193-210 Toomey, D.F. (1980): History of a Late Carboniferous phylloid algal bank complex in northeastern New Mexico. Lethaia, 13, 249-267 Toomey, D.F., Winland, H.D. (1973): Rock and biotic facies associated with a middle Pennsylvanian phylloid algal buildup, Nena 1,ucia field, Nolan County, Texas. -American Ass. Petrol. Geol., Bull., 57, 10.54- 1074 Wahlman, G.P. (2002): Upper Carboniferous-Lower Permian (Bashkirian-Kungurian)mounds and reefs. -In: Kiessling, W., Fliigel, E., Golonka, J. (eds.): Phanerozoic reef patterns. - SEPM Special Publication, 72, 271-338 Further reading: K129

10.2.1.7 Dasyclad Green Algae

Dssyclads are the most important fossil calcareous algae used in nlicrofacies analyses. These algae appeared in the Cambrian and were important rock builders during the Late Paleozoic, Mesozoic and Early Cenozoic. Because of their value as palecological proxies and for stratigraphical zonations, dasyclad algae are key elements in interpretating of ancient shallow-marine shelf carbonates. Excellent overviews on the biology of daspclad algae and the methods used in their analysis were provided by Berger and Kaever (1 992) and De Castro (1997). Deloffre (1988) presented a key for the distinction of suprageneric taxonomic units. Most dasyclads are recorded in thin sections as fragments. Generic and specific detemlinations demand the reconstruction of the morphology from random cuts and variously oriented sections (see Fig. 10.2). Definition, calcification and nzorphology: Dasyclads are a group of benthic calcified unicellular green algae. Living dasyclads are nun- to cm-sized, upright growing plants, which are attached to firm or soft substrates by rhizoids. Characteristically, the thallus consists of a long central stem (also called central cylinder or main

(1) Morphology: Most dasyclads form unbranched thalli; only a few form a branched thallus. Unbranched thalli exhibit various shapes including (a) rod-shaped (tubelike; e.g. Macroporella, Gyroporella, Velebitella) and spherical thalli (e.g. Mizzia), (b) clavate thalli (which increase in size during their development rcsulting in pear-shaped forms), and (c) stalked thalli with a spherical or barrel-shaped capitulum (e.g. Bornetclln) or a cap formed by whorls of rays (e.g. Acicularia, Acetabularia). Most of these types may be unsegmented or segmented. Branched thalli are represented by dichotomous tube-like forms (e.g. Anthracoporella) and articulate forms appearing like beads on a string ( e . g Cynopolia). (2) E.Y~~I-nu1 or. internal configuration of rhe thuili e.xpres.sed by undulation and articulation: Undulation refers to ring-shaped swellings at the thallus surface, annulation to ring-like lacing of the thallus surface not separated from each other (Neoteutloporella, P1. 59/3; Salpingopor-clla,P1.62/2), perannulation to pronounced annular lacings in the calcareous skeleton connected by noncalcified segments (Eovelebitella, P1.59Il j, and fissuration to annular fissures in the calcareous skeleton. Intusannulation is a term for more or less pronounced undulations of the main axis diameter engraved into the inner side of the central cylinder.

(3) Arrangement of later-als (primary branchesi ut the main axis: Asporidyl describes an irregular arrangement at the main axis (Anthracoporella, PI. 5916; Teutloporella, P1. 61/3), euspondyl a regular arrangement in whorls like the spokes of a wagon wheel (Neoreurloporella, P1. 59/3; Salpingoporella, P1. 63/2), and metaspondyl an arrangement of primary branches into clusters of regular whorls (Eovelebitella, P1. 59/1, PI. 6013; Diplopora, P1.5912). The arrangement of the laterals is one of the most effective criteria for defining dasyclad families. Text continued on p . 43.4

Ddsyclads: Diagnostic Cnteria

A

43 1

Morphology

rod-shaped spherical rod-shaped unsegmented undulate cap-forming unbranched stalked rod-shaped clavate Capitulum-shaped segmented unsegmented stalked

B

rod-shaped annulate

Undulation and Articulation

undulation

C

capitulumshaped

annulation

perannulation

Arrangement of Laterals at the Main Axis F====-h

aspondyl

euspondyl

E

Number of Order of Laterals

one

two

three

Shape of Laterals

more than three

: Shape of Laterals

ves~cular

rnetaspondy!

phloiophore

urnbrellophore

umbrellophore

acrophore

phloiophore

tr~chophore

Fig. 10.14. Major diagnostic criteria of dasyclad green algae. After Berger and Kaever (1992).

pirifere

clavate annulate

q;;v $-----k $ ---P

43 2

I

I

I I

-----

endospore wtth cysts

-----

~ h ~ r ~ s t o s pwlth o r e cysts

R e p r o d u c t i v e organs of Dasyclaci\

-----

endospore wlthout cysts

cladospore w ~ t hcysts

cladospore wtthout cysts

Position and Mode of Gamete Production

L--l

chor~stosporewlthout cysts

urnbrellospore w ~ t hcysts

Fig. 10.15. Position of the reproductive organs in dasyclad algae. After Berger and Kaever (1992).

Plate 59

Dasyclad Green Algae: Taxonomic Criteria

Main criteria in the differentiation of dasyclads are the growth foml and shape of the thallus and the central stem, the arrangement, shape and the number of branching of laterals, and the position of reproductive organs (see Figs. 10.14 and 10.15). The plate shows examples of some of the diagnostic morphological criteria. l Eovelehitella occirallica Vachard. Cross section (CS), longitudinal (LS) and tangential sections (TS). Rod-shaped, annulate thallus. Primary branches (white arrows) are arranged in clusters of regular whorls (metaspondyl), forming a succession of subspherical articles, black arrows). The laterals increase in size towards the periphery (phloiophore type). The genus is locally abundant in Toumaisian and Viskan shelf carbonates. Early Carboniferous (Visean). Southern Spain. 2 I ) i p l o p u r c l ~ ~ l ~ u / ~ eI'ia. i ~ oCross s ~ ~ oqection ~ ~ ~ and longitudinal section. Club-shaped articulated thallus. Primary poikilophore and vesicular branches of o w single order are grouped into tufts (metaspondyl). Calcified reproductive organs (cysts, xrow) are situated within the maill axis (cndospore type). Late Triassic (Zlambach beds, Rhaetian): Bavarian Alps, (iCr~iim\. 3 Nc~olcutlo~)o~-eliu sociulis (Praturloni. Longitudinal section of densely spaced autochthonous dasycladacean thalii that form algal meadows and biostromes in ouler platfom settings of the Alpine-Mediterranean Tethys (Dragastan et al. 1987; Bodeur 1995). Cylindrical articulated thallus with short primary and long secondary branches (black arrows) arartgcd oblique io the main axis (white arrow) in close-set euspondyl whorls (W). Laterals become thinner at their distal ends (rrichophore type). Stem cell u,ith swellings and narrowings (annulation). The species is conlmonly associated with corals ;mi 'hydrozoans' (e.g. Elli1)sartinicr.--->P!. 8 115).Species range Oxfordian to Tithonian. Late Jurassic (Tithonian): A b r u ~ ~ i National Parh. central Apennincs. Iialy. 4 Mixiir i~lehitcu7irSchuben. Ohlique and tangential sections (TS). The thallus consist5 of spherical articulated segments. The central stem is barrel-shaped and has constrictions at the joints between segments (annulation). Only prilnary branches. ar.r;inged in concentric r0Lt.s. Branches enlarge in diameter near the exterior, producing a honeycomb pattern on the surface. Late Perniian: Berganla, western Turkey. 5 ilf;xin wackestone. Isolated spherical segments. Note the difference in size; indicating transport of the algal fragments. Lale Pcrn~ian:Taurus Mountain Range. Turkey. ( A/~rl~r~uc~oporc~lIn .spcctaDilis Pia. Longitudinal (LS), cross section (CS) and tangential section (TS). Rod-shaped, tube-like thalli. Closely spaced irregularly arranged (aspondyle) primary laterals. The thalli of this species are conspicuously large and are several centimeters long. Late Carboniferous (Lower Pseudoschwagerina beds, Gzhelian): Hiittenkofel, Canlic Alps, Austria. 7 C:lyp~itznjr/t.ils.sii~aFavre. Star-shaped cross sections (CS) and chain-like oblique sections ( 0 s ) of isolated whorls. The cylindrical thallus consists of basket-shaped superposed whorls. The whorls are composed of jointed fertile branches bearing sporangia that almost touch each other, and broadening toward the periphery (arrow). Packstones and wackestones with mass accumulations of Clypcina jurassica are diagnostic of lagoonal inner platform environments with restricted circulation and sometimes also reduced marine salinity (->PI. 2812, PI. 62/56, PI. 13415). The species is widely disrributed from the Late Kirnineridgian to the base of the Late Berriasian. Late Jurassic: Mhnica. Slovenia.

Plate 59: Diagnostic Critcir~aof Dasyclads

433

Determination of Dasyciads

( 4 ) Number and shape of laterals are essential irz distinguishing species and genera of dasyclads: Primary branches arise from the main axis in different arrangements, numbers and forms. The primary laterals may branch distally, producing segments of second (Pl. 6316, PI. 64/4), third (Palaeodasycladus, P1. 6211) or higher order. The number of the segments per lateral and the number of laterals per whorl as well as the shape of the laterals are used as species- and genus-specific criteria. Terms characterizing the shape of the laterals are (a) phloiophore (branches distinctly expanded terminally; genus-specific; e.g. Bornetella; Eovelebitella, PI. 59/1), (b) vesicular (laterals inflated, straight or slightly

bent), (c) pirifere (laterals short, usually straight, inflated, widest diameter at their middle; nearly exclusively as a primary lateral), (d) trichophore (laterals long, pear-shaped, sudden decrease in diameter followed by very thin hairlike forms; restricted to higherorder segments of laterals; Neoteutloporella, PI. 59/3), (e) acrophore (laterals thin, acute; mainly as higherorder laterals), and (f) umbrelloform (laterals inflated forming an umbrella-like whorl (Clypeina,P1.5917) or separated pear-shaped or lanceolate rays; restricted to primary segments of laterals). ( 5 )Position of the reproductive organs (Fig. 10.15j: Gametes (sexual reproductive cells) are produced in

Box 10.3. How to determine dasyclad algae? The table should help in organizing the requisition of data that are necessary to separate dasyclads at least at a generic level. Basic considerations Look at tlze numl~erof dasyclad sections in your sample. Are there many ofjusr a few? Note that determining genera and taxa requires combining criteria seen in longitudinal, cross, oblique and tangential sections of variously shaped three-dimensional objects. Examine the preserwztion of the dasyclads. Are the algae well or poorly preserved? Did recrystallization destroy impor tant taxonomic criteria (e.g. arrangement and shape of pores/laterals)? Are the central stem and pores filled with sediment or cement? Growth of cement may make it difficult to recognize the number of the orders of branches. Dijif'erenriate the sections into longituilinal. tangential, cross and oblique sections. Select those sections that exhibit a maximum of morphological criteria. Morphological criteria Evaluare the shupe of the t1~allu.susing Fig. 10.14.A.Differentiate between unbranched and branched thalli. Unbranched thalli may be tube-like, pear-shaped or stalked. Both unbranched and branched thalli may be segmented. Tvplfi the subdi\~isiorzof the zhtrlli (Fi,?. 10.14B). The external or internal configuration (undulation, annulation, intusannulation) is important in separating genera. Describr the arrangement ofthe primor.,: Orunclzes ur-isingfi-onztlze niaitz axis (Fig. 10.14C). 4 r e the branches irregularly arranged with respect to the main axis (aspondyl)? Are they regularly arranged like the spokes of a wheel (euspondyl), or do they form regular whorls consisting of clusters of primary branches (metaspondyl)? These criteria serve to distinguish families and genera. Look at tlze contucf of the prinzary brur~chrswith the rnain axis. Laterals may form different angles with the axis; they may start from a small platform, or two or more branches may have a joint basis. ?j,p[fi the shape of the ht-anchesipores(Fig.10.14E).Do the diameter and width of the pores increase distally (phloiophorc and vesicular) or decrease distally (acrophore, trichophore)? These criteria are species-specific. E.~ilnlincthe nu111berofhig1lel.-order hru11c11e~ a r i s i n g j m i the primuly blzlnc~lzcs(Fig. 10.141~).The pattern of distal branching of primary lateral into branches of second, third and higher orders is crucial in distinguishing genera a i d species, Look for reproducti~~e organs wit11itz11w central stem or in or between branches (Fig. 10.15). These criteria are important in distinguishing dasyclad groups. Quantitative data Collect nzeasurernents t / m characrrrize the range and variability of the dimensional triter-iu. Comnlonly used in distinguishing species are the diameter of the central cavity of the thallus, the ratio of the outer and inner thallus diameter (total diameter versus diameter of the main axis), the thickness of the 'wall' (representing the calcified zone around the central stem), the diameter of primary and other branches, the angle between branches and main axis, and the siz.e of the whorls and the number of branching participating into whorl formation Relevant references Start with the papers by Berger and Kaever (1992), De Castro (1997) and Bassoullet et al. (1975) in order to understand the terminology and the handling of the morphological criteria. In most cases you will have some idea about the approximate age of your sample. Look at the list given in 'Basics' at the end of this paragraph and select the relevant overviews that will leadyou to other useful papers.

Distribution of Dasyclads

I 7

i Late ~urassic- Earlv Genera 40

30

20

Early and Middle Jurassic Decline and Renewal 10

Early

'

Middle JURASSIC

f.. .'...*: : "*"

Late

Early

Late

I

Fig. 10.16. Frequency of Jut-assic to Cenozoic dasyclad genera. New genera originated predominantly in the Late Jurassic and Paleogene. Data after Bucur (1999). Extinction rates of species were high at the end of the Early and Middle Jurassic, in the Late Aptian and near tlae Cretaceous-Tertiary boundary. Origination rates of Late Cretaceous species are somewhat controversial in comparison to generic origination rates, as shown by the increase in the number of spccies in the Cenomanian (Kuss 1994).

the main axis (endospore, e.g. Diplopora, PI. 59/2), within the laterals, predominantly of primary laterals (cladospore), in cysts that are laterally or terminally attached to the primary laterals (choristospore), and in ray-shaped gametophors (umbrellospore; Acetabularia; Acic~rlar-in.PI. 6419). In addition, up to 30 quantitative parameters are used in discriminating species (e.g. exterior diameter, diameter of the stem cell, height of a segment, number of whorls per segment, distance between whorls, diameter of branches and pores). The biometrical treatment of these measurements assists in evaluating speciesspecific variations. Classification: Modem dasyclads are represented by only about 11 genera and 37 species (Berger and Kaever l992), in contrast to ancient dasyclads comprising about 235 genera and up to 830 species (Bucur 1999). For a long time dasyclads were considered as one family (Dasycladaceae), and were promoted to the rank of an order (Dasycladales) comprising several families and

systematic subunits (tribi). In this book the term dasyclads is used as a name for the entire group. Following Deloffre (1988) and Berger and Kaever (1992) the dasyclads are now subdivided into six families comprising the Seletonellaceae (laterals aspondyl. Reproductive organs endospore, seldom cladospore. Cambrian to Early Cretaceous, predominantly Early Paleozoic. 7 subgroups), Diploporaceae (metaspondyl, endospore, seldom cladospore. Devonian to Early Cretaceous, predominantly Late Paleozoic and Triassic. 4 subgroups), Triploporellaceae (euspondyl, cladospore. Devonian to Early Tertiary. 7 subgroups), Dasycladaceae (euspondyl, choristospore. Jurassic to recent, predominantly Cretaceous and Early Tertiary. 4 subgroups), Acetabulariaceae (euspondyl, umbrellospore. Jurassic to recent. 3 subgroups). Beresellaceae (Late Devonian to Early Permian). Text continued o n p. 438

Late Paleozoic D:tjvcl~id,

4 36

Plate 60 Late Paleozoic Dasyclad Green Algae Dasyclad algae contributed significantly to the formation of extended algal carbonates (grain- and wackestones) and the formation of reef mounds and mud mounds in Carboniferous and Permian shelf environments. The plate displays some globally distributed algal limestones. Baffling effects of algae with small erect cylindrical thalli were important in the formation of Carboniferous mounds (-> 1, 2, 5). Some authors consider these algae as dasyclads (Beresellaceae), from which they differ in a segmentation of the cylinders by horizontal or vertical elements (-> 2); other authors regard them as a separate green algal group (Palaeosiphonocladales),known from the Devonian to the Early Permian and abundant in the Middle Carboniferous. The genera Dvinella, Donezella and Beresella, common in Bashkirian and Moscovian carbonates grew in dense low-lying thickets that baffled stabilized sediment, forming large low-relief mud-rich mounds or banks in relatively quiet normal marine lagoonal settings, landward of grainstone shoal deposits o r of Chiretetes buildups (Riding 1979; Davies and Nassichuk 1989). Some of the banks and buildups form hydrocarbon reservoirs. Many Carboniferous and Permian platform and ramp carbonates were formed by the accumulation of dasyclad algae (-> 6) and their reworked and-transported fragments (-> 3,4, 7).

C

Sabkha Supra-

bdal

Restricted lagoon

Semi-restricted

Barr~er

1- - - - - - - - - - -

Open marine

Open marine

Platform

1I

I

-

i

I

i I

I

I

. .

Porostrornatecyanobacteriaandporostromate

Phylioid algae (Anch~codiaceans)

green algae (Palaeos~phonocladales) Dasyclad green algae I I --Solenoporacean red algael - - Archaeol~thophylhdana ungdarellacean red algae

@ 0 @ -Tubular

-4

---

- --

Stxnziriacean algae

--

"I

algae

-

--

----

-

Fig. 10.17. Distribution of algae and c-ymobacteria on an idealized Carboniferous carbonate platform. Stacheinacean and solenoporacean algae (PI. 55 and P1. 56 ) indicaw the deepest habitats in the photic zone. Higher up in open-marine settings red algae occur together with tubular palaeosiphonoclad algae. Shallow shoals and lagoonal environments are indicated by abundant dasyclads. Dasyclads associated with palaeosiphonoclads and cy anobacteria marl.; a semi-restricted very shallow environment. Similar associations occur in restricted nesrcoastal environments together with algal cysts (calcispheres, see Sect. 10.2.1. I ) ) . Modified from Mamet ( I 99 1 1.

Pscr~tiodonezcllaboundstone. Middle Carboniferous Beresellacean green algae were important in the formation of hindstones and bafflestones as well as of nlounds on open-marine carbonate platforms. The algae are characterized by cylindrical ramified and constricted thalli (arrows). Middle Carboniferous: Southern Spain. Bcre.sel/a boundstone. Beresellids are characterized by a peripheral zone consisting of short, thin, blind-ending cortical branches, separated by 'clear bands' (arrow) of a non-perforated cortex and an outer cement layer (-> 5). Mid-shelf facie\. Early Permiail (Asselian-Sakmarian): Sverdrup Basin, Canadian Archipelago. Coated dasyclad grainstone with E o ~ d ~ b i t c l (see l a PI. 5911). The grains exhibit transitions from cortoids to oncoids. Open-~narincplatform. Early Carboniferous (VisCan): Spain. Etvinrastopora grainstone. The algae are represented by platelike fragments exhibiting numerous cylindrical or durnbbtli shaped branches. Epimastoporids are widely distributed in Late Carboniferous and Early Permian outer shelf cnvii-011ments. Their assignment to dasyclads is a matter of discussion (Flugel and Fliigel-Kahler 1980). Early Permian ( j : i ~ ~ ~ lian): Carnic Alps, Austria. Br~.csriluhcrnziitur Racz. Note continuous calcite layer (arrow) around the thallus, interpreted as carbonate precipitation within the surficial mucilage sheat of the alga. Middle Carboniferous (Valdeteja Formation): Cantabrian Mountain.;, Northern Spain. M i z i u wackestone. The thalli consist of spherical or cylindrical segments. The branches enlarge in diameter near the surface, producing a hexagonal pattern in tangential sections (arrows). Mizzia limestones were widespread in Middle and Late Pennian shelf and back-reef environments of the tropical Paleotethys. Late Permian: Taurus Mountains, southern Turkey. Dasyclad spores. Atractyliopsis carnica Flugel represents the fertile stage of a dasyclad alga that produced spores of various sizes and shapes within spherical sporangial cavities (arrows). Calcified spores occur in rock-building frequency in Late Paleozoic open-marine shelf carbonates. Early Permian: Carnic Alps, Austria. -> 2: Monn et al. 1994; 5: E~chmiiller1985

Plate 60: Late Paleozoic Dasyclads

437

500 urn

Triassic Dasycldds

All the families except the Beresellaceae are nonseptate. Because the Beresellaceae differ from the typical dasyclads by the horizontal and vertical septation of the thalli and the absence of laterals, some authors consider the group as separate order of green algae.

How to determine dasyclad algae? Many people studying the microfacies of carbonate rocks are quite satisfied to attribute algal bioclasts to the dasyclad group, and postulate that the sample indicates deposition in shallow or very shallow warn1 water of normal salinity. This is a very generalized statement that can be significantly enhanced if the dasyclads are differentiated at a genus and/or species level. Further systematic determinations are also necessary if algal-bearing platform carbonates are to be subdivided stratigraph-

ically and correlated. Generic determinations require evaluation of the following criteria: The shape and subdivision of the thalli; aspondyl, euspondyl or metaspondyl arrangement of laterals; the shape of the laterals; and the position of reproductive organs. If these criteria and the extensive stratigraphic overviews of dasyclads are used, nonspecialists will also be able to determine genera and higher systematic groups. A determination of species should be left to specialists.

Distribution of Phanerozoic dasyclads (Fig.10.16): The first dasyclads are known from the Late Cambrian, but the group remains subordinate in contrast to cyanobacterians and other algal groups from the Ordovician to the Devonian. The first diversificationtook place during the Carboniferous and Permian, a total renewal Text continued on p. 442

Plate 61 Triassic Dasyclad Green Algae No calcareous algae are known from the Early Triassic. Dasyclad algae are common in Tethyan Middle and Late Triassic shallow-marine carbonates. Triassic dasyclads display environmentally controlled distribution patterns that are used in the spatial subdivision of lagoonal platform carbonates (Senowbari-Daryan and Schafer 1979; Lobitzer et al. 1990). Middle Triassic dasyclads contributed significantly to the accumulation of grain- and packstones. Regional stratigraphical zonations of Tethyan carbonates are based both on algal assemblages and on the time-range of species (Ott 1972). A revised zonation has been worked out by Piros et al. (1994, 2002)who established a detailed zonation for the Middle Triassic and Camian. 1 Bioclastic grainstone composed of dasyclad algae, aggregate grains (AG), a few solenoporacean algae (S) and corals (0. Daspclads are Diplopor-a arzr~rrlata(Schafhautl) (D) and Teutlopor-rllu her.culea (Stoppani) (T). See Bucur and Enos (2001) for a discussion of the taxonomy of Diplolm-dike dasyclads. Identification of them requires evaluation of the criteria seen in cross sections (CS) and longitudinal sections (LS). Note the occurrence of several marine cement genera-tions. The sample is a good example of SMF 18 (see PI. 122). Paleoenvironmental interpretation: Deposition in highenergy environment (indicated by lack of micrite and grain-support fabric), water depth of a few meters (as compared with depth distribution of modem dasyclads and inferred from the occurrence oiaggregate grains), warm water (related 10 the abundance of dasyclads), unstable sand bottom (high primary intergranular porosity, incipient marine cementation). The sample represents lagoonal platform limestones formed within a back-reef area. SMF 18-DASY.Middle Triassic (Wetterstein Limestone, Late Ladinian): Amtmanngalgen, Gesause Mountains, Styria, Austria. 2 Dasycladad grainstone. Cross sections of Hctcr-opor-ellazunkli (Ott) characterized by large sporangia arranged in rings. Dasyclads (D) are associated with porostromate cyanobacteria (C). Note high primary intergranular porosity now W eluded by isopachous acicular marine-plireatic cements (MPC) and sparry coarse burial cements (CBC). Paleoenvironmental interpretation: High water energy (grainstone fabric, reworked cyanobacteria nodules), water depth a few meters (as compared with the average distribution of modern dasyclads and calcified cyanobacteria), warm water (chloralgal association, see PI. 105/2), instable sand substrate. The sample comes from outer lagoonal carbonates deposited behind :i major reef complex formed by coralline sponges and corals. Late Triassic (Norian to Rhaetian): Cuzzo di Lupo, Palenno Mountains, northwestern Sicily, Italy. 3 Dasyclad grainstone composed of Teutloporella nodosa (Schafhgutl). Diagnostic criteria are shown in longitudinal (LS) and oblique sections. The long thalli are annulated. The aspondyle branches become thinner toward the outside, forming a hairlike structure (white arrow). Note distinct circumgranular isopachous cements (black arrows) consisting of acicular crystals. These cements were formed in marine phreatic environments. Paleoenvironmental interpretation: Shallow-mrine warm-water carbonate, formed in high-energy areas. The high and still open interskeletal porosity (P) can be explained by strong meteoric phreatic diagenesis. The sample comes from platform shoals formed by a parautochthonous accumulation of algae. Teutloporella is a facies-diagnostic fossil; it characterizes subtidal lagoonal deposits as well as proximal reef detritus areas (Ott 1967; Piros et al. 1994).Stratigraphic range of the species: Ladinian and Early Camian. Middle Triassic (Late Ladinian): Calabria. Southem Apennines, Italy.

Plate 61: Triassic Dasyclacls

439

430

Jurassic D a s y c l a d \

Plate 62 Jurassic Dasyclad Green Algae Biozonations developed for Tethyan Jurassic and Cretaceous shallow-marine carbonates are based predominantly on dasyclads and benthic foraminifera. These zonations use combinations of various stratigraphical concepts. Some zones correspond to taxon range and concurrent range zones, but many 'coenozones' are assemblage or abundance zones characterized by the association of several taxa or by a maximum abundance of specific taxa. Coenozone boundaries, therefore, are not necessarily synchronous time lines. The Early and Middle Jurassic represent periods of decline and renewal of dasyclads. Common Early Jurassic and Middle Jurassic dasyclads are Palaeodasycladus (-> 1 ) and Selliporella (-> 4). The Late Jurassic, particularly the Kimmeridgian and Tithonian, was characterized by highly diverse and widely distributed dasyclad associations. Common dasyclads in Late Jurassic-Early Cretaceous times were Salpingoporella (-> 2; P1.63/7), Clypeinn (-> 5, 6), Cylindroporella (Pl. 6318) and Triploporella. Dasyclads occur in rock-building abundance, as exemplified by Clypeina limestones (-> 5 , 6) or limestones with Campbelliella (-> 2, 3) in lagoonal or protected shelf environments. Palaeodasycladus nzediterraneus Pia. Oblique ( 0 s ) and cross sections. The alga was common in Tethyan Early and Middle Liassic (Sinemurian to Domerian) intertidal lagoonal and in outer shelf settings (Sokac 2001) and is used in the biozonation of Liassic platform carbonates. It characterizes a Late Sinemurian acme zone. Elongated club-shaped thalli, up to third-order branches diverge with angles of about 45" from the main axis. The sediment consists of poorly sorted aggregate grains, peloids and micritized algae, sometimes forming nuclei for micrite oncoids (arrows). Note the sparry patches within the oncoids, indicating the contribution of microbial networks to the formation of 'fenestral oncoids'. Early Jurassic (Pantokrator limestone, Sinemurian): Korfu Island, Greece. Salpingoporella annulata Carozzi. Oblique ( 0 s ) and cross sections (CS). Cylindrical annulated thallus. Pores vertically flattened, arranged in whorls (arrow). CA: Transversal-oblique section of Carnpbelliella. Open-marine isolated platform. Late Jurassic (Tithonian): Sulzfluh Range, Graubiinden, Switzerland. 3 Canzpbelliella siriata (Carozzi). Arrows point to different sections. These microfossils were formerly regarded as incertae sedis, pteropod gastropods, large aberrant tintinnids, or pallets of boring teredinid bivalves. They are IIWV recognized as dasyclad algae. The calcareous skeleton consists of a succession of articles interpenetrated into each other. Each funnel-shaped article (A) contains the pores of a single whorl (De Castro 1993). Campbelliella occurs in abundance with small benthic foraminifera and Fa~wiilu in restricted lagoonal platform carbonates. Late Jurassic (Tithonian): Sulzfluh Range, Graubiinden, Switzerland. 4 Selliporella donzellii Sartoni and Crescenti. Oblique longitudinal section. Note double whorls (arrows) with pores thickening outward (phloiophore). Range of the species: Bajocian to Late Bathonian. Late Middle Jurassic: Southe m Apemines, Italy. 5 Clypeina jurassica Favre. Cross sections. Fertile whorls shaped like a wide basket and composed o l broadening sporangial chambers. Note (dark) pores in the center of these chambers. Species range: Late Jurassic to Beninsian, comnlon in Kimmeridgian. Late Jurassic: Vrhnica. Slovenia. 6 Clypeina jurassica Favre. Isolated whorl fragments. Late Fig. 10.18. Reconstructions of Late Jurassic dasyclads Jurassic: Sulzfluh Range, Graubiinden, Switzerland. A: Clypeincr jurassica Favre. After Pia (1920). B: Canzpbclliella striata (Carozzi). After De Castro (1993) -> I: Fliigel 1983

Plate 6 2 : J u r a s s ~ cD a s y c l a d s

44 1

S i g n i f i c a n c e o f Dasyclad\

at a species level during the Middle Triassic (Fliigel 1985). Late Jurassic and Early Cretaceous platforms were characterized by highly diversified associations, both at a genus and species level. Starting in the Aptian, dasyclads decline significantly at a generic level during the Late Cretaceous before reaching high diversities and global distribution again in the Early Tertiary (Fig. 10.16). Critical lists of dasyclad species are available for the Permian and Triassic (Granier and Grgasovic 2001), Jurassic and Cretaceous (Bassoulletet al. 1978;Deloffre 1993), and Tertiary (Deloffre and Genot 1982; Deloffre and Granier 1992). Plates 60 to 64 show some typical and common dasyclads occurring in Carboniferous to Paleocene shallow-marine carbonates.

Environmental constraints: Modem dasyclads occur predominantly in tropical and subtropical environments but are also found in temperate waters, e.g. the Mediterranean. Their distribution is controlled by water temperature (warm waters, ~nostlywithin the 20" isoclyne), substrate (sand and mud), salinity (normal

marine; only a few modern and some Tertiary taxa became adapted to hypersaline and brackish waters), water energy (low, generally subtidal) and depth (below low tide down to about 30 m, commonly < 5 meter). Dasyclads are found in open lagoons, protected but open bays and in the shelter of ridges. The ecological requirements of post-Paleozoicdasyclads are regarded as similar to those of their living descendants (Elliott 1978, 1981). Deviations of distributional patterns of Permian and Triassic dasyclads from the recent shallow-water model have been explained by substrate control (Fliigel 1981). Some algal remains attributed to 'marine' dasyclads have been reported from Early Permian lacustrine sediments and explained by wind drift of cysts from marine environments to terrestrial sites (Schneider and Gebhardt 1992; P1. 13114). Significance of dasyclad algae Sedimentological significance: Since the Carboniferous, the accumulation of dasyclad bioclasts contributed significantly to the formation of shallow-marine.

Plate 63 Early Cretaceous Dasyclad Green Algae Similar to the Late Jurassic, algal carbonates were also essential in the formation of Early Cretaceous platforn~s. More than 150 species have been described from Early Cretaceous deposits. The greatest wealth of species occurs in the Barremian. Berriasian-Valanginian and Barremian-Aptian assemblages differ in species composition and abundance. Dasylad assemblages allow regional biozonations (e.g. Bucur 1994; Bodrogi et a1 1994). The large number of species decreased dramatically from the Aptian to the Albian. Dasyclads assist in differenting thc paleoenvironments of various parts of platforms (Peybernes 1979; Fig. 10.19), and in evaluating cyclostratigraphic units (Schindler and Conrad 1994). Some widely distributed genera in the Tethyan region are shown on this plate. 1 Hakalo~~aella elifzue (Bakalova). Early Cretaceous (Late Barremian-Early Aptian): Southern Romania. 3 Sillpinyopoi-ella ex. gr. mlwhlhrr-yi (Lorcnz). Oblique longitudinal section (OLS) and transverse section (TS). Thallus cylindrical. Only primary branches are arranged perpendicularly to the main axis in euspondyl whorls (arrows). Salpir~gr~po~dla is cornmon in hack-reef and open-lagoonal sediments. Early Cretaceous (Barremian-Aptian): Resitah4oldova Noua zone, southwestern Romania. 3 Salpingoporella ex gr. mclitae Radoicic. Ob!ique longitudinal section. Elongated cylindrical thallus. Same locality as -> 2. 4 P.seztdocynzopoliajur-assica (Dragastan). The oblique longitudinal section through two segments (S) exhibits primary and densely spaced secondary branches (arrows). Note the distinct annulation of the thallus. Same locality as -> 2. 5 Neomeris cr-etacca Steinmann. Arrows point to the sporangia characteristic of the species. Early Cretaceous: Southern Romania. 6 Pseudoactitzoporel1afiagilisConrad. Transverse section. Simple branches increasing in size outwardly (phloiophorc). The distributional pattern of the branches indicates that the branches are arranged obliquely to the central stem. Early Cretaceous (Barremian): Romania. 7 Algal wackestone with Salpingoporellu dinurica Radoicic. This facies is common in restricted parts of Aptian carbonate platforms. The association of the species with ostracods, charophytes and specific foraminifera in the Valanginian indicates pond environments in strongly protected lagoons. Early Cretaceous (Valanginian): Apemines, southern Italy. 8 Shallow-marine algal-foraminifera] limestone with miliolid foraminifera and dasyclad algae (Cylindroporella, note the spherical sporangia growing attached to the main axis, choristospore type; center). Inner shallow platform. Early Cretaceous: Subsurface. United Arabian Emirates.

Plate 63: Early Cretaceous Dasyclads

433

Significance of D a s y c l a d s

sand-sized carbonates on platforms and ramps. Many dasyclad limestones (mostly grainstones and packstones) were formed in open-marine lagoonal or backreef environments. Examples are Permian Mizzia limestones (Pl. 60/6), Middle Triassic Diplopora limestones (Pl. 61/1), Liassic Palaeodasycladus limestones (Pl. 621 l), Late Jurassic Clypeina limestones (PI. 62/5,6), and Early Cretaceous Salpingopoi-ella limestones (Pl. 631 7). Late Paleozoic and Mesozoic dasyclads contributed

to the formation of biogenic mounds (e.g. Late Carboniferous Anthracoporella mounds, PI. 59/6; Late Jurassic Neoteutloporella biostromes, P1. 5913).

Recognition of shallow-marine depositional sites: Different algal groups prefer different depositional sites. Fig. 10.17 and Fig. 10.19 give a rough picture of the environmental distribution of Carboniferous dasyclads and other algal groups.

Plate 64 Late Cretaceous and Paleocene Calcareous Green and Red Algae Dasyclad algae suffered a significant decline during the Late Cretaceous. The number of genera per stage decreased from about 40 in the Early Cretaceous to less than 20 in the Late Cretaceous. A similar drop is shown hy the number of species from the Cenomanian to the Campanian. Maastrichtian dasyclad assemblages exhibit slightly higher species numbers (up to 15). Late Cretaceous dasyclad species are of value in establishing composite biozonations (Kuss and Malchus 1989). Early Tertiary dasyclads are valuable time markers. The Early Cenozoic was a time of high dasyclad species diversity connected with a renewal of the algal associations. Paleocene and Eocene species numbers (81 and 95 respectively) surpass those of the Early Cretaceous. At the end of the Eocene more than 90% of the Paleocene-Eocene species had disappeared. The Neogene represents a marked decline for the dasyclads. 20 species were recorded from the Miocene, 8 from the Pliocene, only one species appears to have survived in recent assemblages, which contain about 35 species, predominantly of the group Acetabulariaceae. Dasyclad green alga: Neorneris (Lar-).aria)sp. Tangentiallaxial longitudinal section. Black arrows point to distinctly differentiated whorls. White arrows indicate the dasyclad alga Aciculella. Paleocene (Thanetian): Mariazell, Styria, Austria. Dasyclad green alga: li-inoc1ad~l.sperplews Ellio~t.Longitudinal section. Shallow subtidal open platform. Late PACocttne: Priglitz, Lower Austria. Udoteacean green alga: Halimeclu rzam Pia. Longitudinal section. Note the distinct differentiation of axial rnedulla ( h l ) and corlex (C). Arrows point to filaments. Open platform. Paleocene: Priglitz, Lower Austria. Dasyclad green alga: Cymopolia elongata (Defrance) Munier-Chalmas. Longitudinal section. Differences in size of the thalli and number of whorls allow low-energetic, moderate or high-energetic (this figure) environments to be differentiated. Same locality as -> 3. L)istichoplilx biserialis (Dietrich). A widely distributed microproblematicum, restricted to Paleocene and Early Eocene carbonates. E: Echinoid spine. Paleocene (Thanetian): Lupina, Western Carpathians, Slovakia. Dasyclad green alga: Cymopolia irzflaturamosa Segonzac. Oblique cross section. Diagnostic criteria are broadened primary branches (black arrows) and thin short secondary branches (white arrow). Paleocene (Late Thanetian): Hricovskc Podlxadie, Slovakia. Composite crust consisting of red algae (top: Archaeolithothattmium, A: below: Psei~dolithothuw~rzi~lm niburn, PA) anti sessile foraminifera (Planoubulii~a,P). Deeper subtidal environment. Late Maastrichtian: Hochschwab, Styria, Austri~i. Dasyclad green alga: Broeckella belgica Munier-Chalmas. Cross-section. Diagnostic criteria is the broadening of the primary branches (arrows). The species is an index fossil (Danian and Early Thanetian). Common in lagoonal and backreef sediments. Paleocene (Thanetian): Mooshuben, Styria, Austria. Dasycladalean green alga: Acicular-ia cf. palaantina dlAchiarc. Note cross sections of ampullae. Sanie locality as --> 8. Squarnariacean red algae (Peysso~zelia, P) and coralline red algae (Anzphiroa,A; Lithophyll~ml,L). Criteria of squamariacean algae: Encrusting aragonitic thalli consisting of a basal layer (hypothallium, HT) from which vertical or arcuate rows of cells arise (perithallium, PT). Note the difference in the preservation of aragonitic squamariacean and High-Mg calcite corallinacean algae. Typical association of high energy shallow-marine environments. Late Maastrichtian: Hochschwab, Austria. Articulated coralline red alga: Anzplziroa sp. Longitudinal section. Criteria: Medullary segments (S) consisting of long cells. Distinctly layered cortical tissue (CT). Same locality as -> 10. Crustose coralline red alga: Sporolithon sp. Note the linear arrangement of conceptacles (C). Late Paleocene: Priglitz, Lower Austria. -> 1-1 I : Courtesy of H. Tragelehn (Koln)

Plate 64: Late Cretaceous and Paleocene Dasyclads

345

446

B

Dasyclad Associ;ltion{

...

Coralline red algae Boueina (erect udoteaceans) Marinella lugeoni Bacinella irregularis and Lithowdium Neomeris cf. cretacea Griphoporella ? aurigerica Cylindroporella benizarensis Salpingoporella urladanasi * 9 Heteroporella aft lepina Clypeina nigra

-..-

-

Salpingoporella hispanica

..... ..... .....

-

Angioporella fouryae Heteroporella paucicalcarea

,upralitoral Freshwater lake

Internal platform

Platform margin

2

Mudstone with

l

1

Mudstone and wackestone with serpulids

3

I

Slope

4

Basin

I

Bioclastic wackestone with orbitolinid foraminifera Wackestones and boundstones with rudists and some corals

Dark mark with ammonites

......... ......... .........

Cylindoporelia cf. barnesii Cylindl-oporella sugdeni Salpk~goporeliamuehlbergii Likanella ? danilovae Cylindroporelia elliptica Pseudoactinoporella fragilis Salpingoporella melitae Acroporella radoicicae Actinoporella podolica Salpingoporella genevensis Montenegreila wrbarica -** Heleroporella israelense Linoporella aff. kapelensis Triploporella 7 uragieNiformis Dissocladella hauteriviana Griphoporelia iailaensis LikaneNa canlpanensis Mac!-oporelia embergeri Macroporelia praturloni Cylindroporella arabica

......... ......... ......... ......... ......... ........ ......... . ..........

.......e .

-

*

( I I

Triploporella ? neocomensis

wkth charophyb

$:ke"One

Fme-grainded dolomite

Marly lmestones with ammon~les

Fig. 10.19. Distributional patterm of dasyclad associations on Early Cretaceous carbonate platforms in the French and Spanish Pyrenees Mountains. Species composition of the association differs significantly in the various parts of the tidal and shallow subtidal shelf environments. A: Berriasian and Valanginian. B: Barremian to Aptian (Urgonian facies). Based on Peybemes (1979). See Masse (1993) for a discussion of facies development during time and the biostratigraphical value of dasyclad species associations. Dotted lines indicate rare occurrences.

Basics Dasyclads

Similar to modem dasyclads, ancient dasyclads exhibit recurrent species assemblages that preferred particular depositional environments on shallow, welllighted shelves. The distribution of these assemblages follows regular patterns, at least for Mesozoic and Cenozoic dasyclads, and can be successfully used in recognizing and subdividing facies belts of platforms and ramps. Fig. 10.19 shows an example from Early Cretaceous platforms. Biozonations: Many dasyclad genera and species

have long stratigraphical ranges, comprising more than one stage (Bucur 1999). However, notable exceptions exist that allow platform carbonates to be dated and subdivided. Platform carbonates are often poor in guide fossils. The only abundant fossils in these limestones are calcareous algae and foraminifera. Both groups are prone to strong facies controls that reflect the change of the major environmental constraints (e.g. sea-level fluctuations, clastic input) over time. These changes are recorded by vertical successions of rock units yielding specific dasyclads and other thin-section fossils that allow Mesozoic platform carbonates to be subdivided into variously defined 'biozones'. These biozones are valuable stratigraphic tools in regional correlations, but their boundaries are often certainly not synchronous. Dasyclads play an important role in defining biozones. First recognized in 1920 by Julius Pia from Vienna, species ranges of dasyclads allow relatively short stratigraphic intervals to be differentiated for time intervals characterized by high origination rates (e.g. Middle and Late Triassic, parts of the Early Cretaceous, Paleocene and Eocerie). Basics: Dasyclad green algae Barattolo, F. (1991): Mesozoic and Cenozoic marine benthic calcareous algae with particular regard to Mesozoic Dasycladalenas. -In: Riding, R. (ed.): Calcareous algae and stromatolites. - 504-540, Berlin (Springer) Bassoullet, J.-P., Bernier, P., Deloffre, R., Genot, P., Jaffrezo, M., Poignant, A.F., Segonzac, G. (1975): Reflexions sur la systtmatique des Dasycladales fossiles - ~ t u d ecritique de la terminologie et importance relative des critkres de classification. - Geobios, 8, 259-290 Bassoullet, J.P., Bernier, P., Conrad, M.A., Deloffre, R., Jaffrezo, M. (1978): Les algues dasycladales du Jurassique et du CrttacC. - Geobios, Mem. Spec., 2, 330 pp. Berger, S., Kaever, M.J. (1992): Dasycladales: an illustrated monograph of a fascinating algal order. - 274 pp., Stuttgart (Thieme) Bucur, 1.1. (1999): Stratigraphic significance of some skeletal algae (Dasycladales, Caulerpales) of the Phanerozoic. - Palaeopelagos Special Publication, 2,53-104 De Castro, P. (1997): Introduzione a110 studio di sezioni sottili delle Dasicladali fossili (An approach to thin-section study of fossil Dasycladales).-- Quademi dell' Accademia Pontaniana Napoli, 22, 261 pp.

Deloffre, R. (1988): Nouvelle taxonomie des algues dasycladales. - Bull. Centres Rech. Exp1or.-Prod. ElfAquitaine, 12, 165-217 Deloffre, R. (1993): Inventaire critique des algues dasycladales fossiles. 2. partie - Les algues dasycladales du Jurassique et du Cr6tac6. -Revue de PalCobiologie, 12, 19-65 Deloffre, R., Genot, P. (1982): Les algues dasycladales du Ctnozoique. - Mem. Centres Rech. Explor. Prod. ElfAquitaine, 4, 247 pp. Deloffre, R., Granier, B. (1992):Inventaire critiquedes algues dasycladales fossiles. - Revue de Paltobiologie, 11,33 1356 Elliott, G.F. (1968): Permian to Paleocene calcareous algae (Dasycladaceae) of the Middle East. - British Mus. Nat. Hist. Bull., Geol. Suppl., 4, I l l pp. Elliott, G.F. (1978): Ecologic significance of post-Palaeozoic green algae. -Geological Magazine, 115,437- 442 Elliott, G.F. (1981): The Tethyan dispersal of some chlorophyte algae subsequent to the Palaeozoic. Palaeogeogr., Palaeoclimat., Palaeoecol., 32,341-358 Fliigel, E. (1985): Diversity and environments of Permian and Triassic dasycladacean algae. - In: Toomey, D.F., Nitecki, M.H. (eds.): Paleoalgology. - 344-351, Berlin (Springer) Genot, P. (1991): Cenozoic and recent dasycladales. - In: Riding, R. (ed.): Calcareous algae and stromatolites. - 131145, Berlin (Springer) Granier, B., Deloffre, R. (1993): Inventaire critique des algues dasycladales fossiles. 2. partie - les algues dasycladales du Jurassique et du CrCtact. - Revue de Paltobiologie, 12, 19-65 Granier, B., Grgasovic, T. (2000): Les algues dasycladales du Permien et du Trias. Nouvelle tentative d'inventaire bibliographique, gkographique et de stratigraphique. - Geologica Croatica, 53, 1-197 Jaffrezo, M. (1973): Essai d'inventaire bibliographique des algues dasycladacees du Jurassique et du Cretact inferieur. - Geobios, 6, 7 1-99 Pia. J. (1920): Die Siphoneae verticillatae vom Karbon bis zur Kreide, - Abhandlungen der zoologisch-botanischen Gesellschaft Wien, 11, 1-263 Further reading: K 129. See also Basics for 10.2.1.

10.2.1.8 Charophyta: Fresh-Water and Brackish-WaterAlgae Definition and morphology: Modem charophytes are regarded as a separate group of macrophytic algae or as a group of green algae. They live submersed and occur predominantly in shallow oligotrophic freshwater environments of lakes and rivers as well as in brackish waters of marginal seas. The erect and branched thallus is divided into a regular succession of nodes, with whorls of small branches, and intemodes. The only calcified parts are the reproductive organs, developing from the nodes during fertile stages of the plant, and vegetative stem nodes and intemodes. The female

Plate 65 Charophyta Charophyta are macrophytic green algae. The plant attains a size ranging from several centimeters to as much as a meter. The erect and branched thallus is divided into a regular succession of nodes with whorls of small branches, and internodes. The reproductive organs develop from the nodes during fertile stages. Ancient charophyte fossils are recorded by the female gametangia (oogonia) and by internode parts (-> 1). The oogonium consists of spiral cells (Fig. 10.20). These cells are partly calcified (Low- or High-Mg calcite). Only the calcified part of the oogonium (called gyrogonite) is preserved as a fossil. Many gyrogonites are elliptical in shape and 0.5 to 1.0 mm in size. Additional calcareous plates can form an envelope (utriculus) for the gyrogonites. The taxonomy of fossil charophytes is based on isolated oogonia. Generic differentiation of gyrogonites in thin sections is rarely possible and requires longitudinal sections exhibiting an apex, basal pore and basal plate. Charophytes have been known since the Silurian and became diversified in the Devonian and during the Late Jurassic, Early Cretaceous and Tertiary. Valuable charophyte-based biozonations have been established for the Late Mesozoic and the Tertiary.

//,

Sycidiales

Trochiliscales

Charales

Fig. 10.20. Charophyta and their calcified parts. A: Charophyte plant. The erect branched thallus is divided into a regular succession of nodes, with whorls of small branches, and internodes. B: Calcification takes place at the nodes only with the elliptical female reproductive organ (oogonium) and near the stem nodes and internodes. C: Oogonium consisting of the internal egg cell, surrounded by spiral cells whose inner p a t is calcified (black). This part, called the gyrogonite, is preserved as a fossil. D: IIigh-le\d systematic units are differentiated according to gyrogonite morphology and sculpture. From left to right: Sycidialcs (Late Silurian to Early Carboniferous). Trochiliscales (Late Silurian to Permian), Charales (Devonian to Recent). A, R after Wray (1977). C, D after Schudack (1993).

Charophyte packstone. Cross sections (white arrows) and longitudinal section (black arrow) of internodia. Thc algae occur in association with thin-shelled ostracods. Brackish-water facies.LMF 7.Lowenrlost Cretaceous (Upper Miinden bcds, lowennost Berriasian): Lower Saxony, Germany. Charophyte gyrogonites (G) and internodia (IN). Fine skeletal elements in the matrix are charophyte debris. Late Cretaceous (Turonian): Divaca, Slovenia. Lacustrine charophyte limestone. Cross sections and oblique sections of internode parts of Characeae. Spinose surface structure (arrows) is caused by internode rips. Black grains are reworked micrite clasts (MC). White areas are open pores (PI. Carbonate sands near green algal bioherms. Late Tertiary (Miocene): Marktoffingen, Ries, Southern Germany. Gyrogonite. Cross section. The interior was originally occupied by the egg cell. The 'wall' consists of the calcified parts (calcine) of the spiral cells (SC) surrouriding the egg cell. Early Cretaceous: Subsurface, southern Bavaria, Germany. Gyrogonite. Oblique tangential section displaying the orientation of the spiral cells. Lowermost Cretaceous (Purbeck facies, Berriasian): Subsurface. Kinsau, southern Germany. Gyrogonite. Lowernlost Cretaceous (Purbeck facies, Berriasian): Same locality as -> 5. Wackestone with gyrogonites. LMF 7. Same locality as -> 2. Sycidiunl. Middle and Upper Devonian lagoonal carbonates can yield microfossils resembling charophyte oogonia and attributed to the genera Sycidium, Karpinskya or Trochiliscus. Middle Devonian: Eifel, Germany. 1,6: Courtesy of M. Schudack (Berlin).

Plate 65: Charophyt.1

1149

Calcispheres and Algal Cysts

reproduction organ (oogonium) is elliptical in shape, 0.2-1.0 mm in size, and exhibits a wall composed of variously arranged tubular cells. The spiral or vertical arrangement of the enveloping cells is recorded in the 'gyrogonites' (Fig. 10.20) corresponding to the calcified parts of the oogonium and representing the essential criteria for the classification of fossil charophytes.

Environnzent: Today the group is restricted to fresh and brackish waters (lakes, rivers and brackish marginal seas). Some species also occur in salt lakes. Charophytes are found in shallow lakes, predominantly in water depths of a few meters only, often exhibiting distinct shore-parallel distributional patterns. Modem charophytes are abundant in w m temperate climates but have a wide geographical range, and also occur in tropical and arctic settings. Major controlling factors on the distribution of charophyta are salinity, the oxygen content and chemistry of the waters as well as substrate type, salinity, nutrient supply and substrate type. Because oogonia can be transported by water and wind, the occurrence of abundant fossil oogonia, therefore, must nor necessarily reflect biocoenoses. Many ancient charophytes are found in association with nonmarine or brackish water biota. Oogonia found in marine sediments are usually interpreted as allochthonous. However. Devonian forms (e.g. Sycidiunl, PI. 6518) are known from shallow-marine open shelf environments.

Thin sections: Taxonomic studies are predominantly based on isolated gyrogonites. Differentiating genera in thin sections is difficult and would need longitudinal sections displaying the apical and the basal part of the gyrogonites. The calcified spiral cells of the gyrogonites exhibit distinct microstructures(Schudack 1987, 1993).The calcified vegetative internodes of the charophycean stems correspond to cylindrical segments making up a hollow central channel. Cross sections exhibit an axial cavity surrounded by a peripheral zone of small, densely arranged circular structures corresponding to sections of external longitudinal grooves. Distribution: Modem charophytes represent a relict group comprising only six genera. Charophytes have been known since the Silurian. Important radiations took place during the Devonian, Late Jurassic and Early Cretaceous ('Purbeck' and 'Wealden' facies of Western Europe: Schudack 1993). Gyrogonites are useful in correlations between marine and nonmarine sediments; they are important zone fossils for the Early Cretaceous and Early Tertiary time interval. Paleoenvironinental significance: Charophyta are used in evaluating paleoclimate, paleolatitudes and paleoenvironmental constraints. Fossil gyrogonites are important paleosalinity indicators. They are often associated with nonmarine and brachsh-water faunas (e.g.

Plate 66 Paleozoic and Mesozoic Calcispheres Calcispheres is a term referring to spherical or egg-shaped n~icrofossilswhich have been regarded for a long time as microprobletnatica with respect to their systematic position. Most authors now agree that most of thcse fossils are algal cysts, some perhaps also planktonic algae. Devonian and Carboniferous calcispheres are abundant in restricted and semi-restricted lagoonal environments and in back-reef settings. Most of the Jurassic and Cretaceous calcispheres occurring in pelagic limestones, and often described in thin sections as pithonellids or cadosinids represent calcareous dinoflagellate algae. 1 Paleozoic calcispheres. Peloidal calcisphere-foraminifera1 grainstone. The sediment consists of calcispheres, peloids, small intraclasts and some endothyrid foraminifera. The calcispheres exhibit different shapes and different wall structures. These differences are used for taxonomic differentiations. This niicrofacies is common in Early Carboniferous inner ramp settings. SMF 16-NON-LAMINATED. Early Carboniferous (Viskan): Basin of Dinant, Belgium. 2 Paleozoic calcispheres. Variously sized thin-walled calcispheres. Note the distinct difference in the size of calcispheres and peloids. Early Carboniferous (Late Visean): Nassfeld, Camic Alps, Austria. 3 Paleozoic calcispheres. Rndiosplzel-a characterized by a radially structured wall. Back-reef facies. Late Devonian (Frasnian): Holy Cross Mountains, Poland. 4 Mesozoic calcispheres. Pithonella, a caicareous dinoflagellate. The SEM photograph shows the regular pattern of the calcite crystals forming the shell surface and the circular exterior pore. Late Cretaceous (Turonian): Switzerland. 5 Mesozoic calcispheres. Pelagic Pithonella packstone. Open-marine deep shelf environment. SMF 3. Late Cretaceous (Seewen limestone, Turonian): Switzerland. 6 Mesozoic calcispheres. Association of calcispheres and pelagic foraminifera (Globotruncana). 'SMF 3. Same locality as -> 5. 7 Mesozoic calcispheres. Strongly burrowed calcisphere packstone. Late Cretaceous ( P l b e r limestone, Cenomanian): Teutoburger Wald, Westphalia. Germany.

Plate 66:Paleozoic and Mesozoic Calcispheres

45 1

ostracods, serpulids, ostreid pelecypods), but have also been reported from marine strata. Marine occurrences were explained by (a) transport of charophytes from coastal areas to the sea, (b) reworking of nonmarine beds with charophytes in connection with transgressions, or (c) adaption of some taxa to normal-marine conditions (e.g. some Devonian genera: Racki and Racki 1989). Common microfacies types associated with charophyte-bearing carbonates are ostracod wackestones and mudstones, lime mudstones with cyanobacteria and shell fragments, wackestones and grainstones with charophytes and a mixture of ooids, lithoclasts and skeletal grains, and carbonate breccia.

coryne). Isolated cysts and aggregates of cysts can be common in limestones. Modern dasyclad cysts are represented by calcareous, thin-walled spherical hollow bodies (Marszalek 1975; Berger and Kaever 1992). Morphologically comparable spheres and aggregates of spheres and egg-shaped bodies, ranging in size between 100 and 500 pm, are known from Permian, Mesozoic and Paleogene carbonates (e.g. Fliigel 1966; Elliott 1986; P1.6017).

Devonian and Carboniferous calcispheres Hollow spheres with simple or differentiated calcitic walls are common constituents of Middle and Late Devonian restricted lagoonal and back-reef carbonates as well as early Carboniferous ramps. Sizes between Basics: Charophyta 100 and 500 ym. The spheres have been taxonomically Feist, M., Grambard-Fessard, M. (1991): The genus concept differentiated according to wall structure, ornamentain Charophyta: evidence from Paleozoic to recent. - In: Riding, R. (ed.):Calcareous algae and stromatolites.- 189- tion and size variation (PI. 6611-3). The fossils have been regarded as dasyclad algae 203, Berlin (Springer) Mojon, P.O., Strasser,A. (1987):Microfacies, ~Ldimentologie (Marszalek 1975) or as planktonic green algae (Volvoet micropalContologie du Purbeckieme de Bienne (Jura cales: Kazmierczak 197.5), but also as single-chambered suisse occidental). - Eclogae geol. Helvetiae, 80, 37-58 foraminifera. The spheres are commonly associated Racki, G., Racki, M. (1989):Ecology of the Devonian charophyte algae from the Holy Cross Mts - Acta Geologica with peloids, amphiporid stromatoporoids (Devonian) or smaller foraminifera (Carboniferous). Paleozoic calPolonica. 31,213-222 Schudack, M. (1987): Charophytenflora and fazielle Ent- cispheres can be used as indicators of paleosalinity. wicklung der Grenzschichten mariner Jura/Wealden in den nordwestlichen Iberischen Ketten (mit Vergleich zu Astu- Mesozoic and Cenozoic 'calcispheres': Calcified dirien und Kantabrien).- Palaeontographica, B, 204, 1-180 Schudack, hl. E. (1993): Die Charophyteu in Oberjura und noflagellate algae Thin sections and SEM studies of Late Jurassic, CreUnterkreide Westeuropas. Mlt einer phylogenetischen Anataceous and Tertiary limestones reveal hollow spherilyse der Gesamtgruppe. - Berliner Gcowls~enschaftliche Abhandlungen, E, 8,209 pp. cal and ovoid microfossils in rock-building abundance Further reading: K 129 (PI. 66/5), often associated with pelagic foraminifera, calpionellids and radiolarians. The sizes of the spheres range between about 10 and 100 pm, usually about 40 pm). The spherical or egg-shaped bodies are char10.2.1.9 'Calcispheres' and Algal Cysts acterized by differentiated calcitic walls, with or withMany Paleozoic and Mesozoic shelf limestones yield out openings and pores. Differences in wall microstrucsmall-sized (diameter commonly < 500 pn), hollow ture have been used to distinguish genera (e.g. Pithospherical microfossils exhibiting calcitic 'walls'. Many pi el la, Stomiosphrrcr-a, Cadosina, Calcisphaer-ulu; of these fossils, often designated as 'calcispheres', are Rehanek and Cecca 1993). SEM studies indicate that interpreted as algal remains, particularly as algal cysts. many taxa separated by thin-section criteria represent True algal spores are very rare in thin sections but red diagenetic forms only and that other 'taxa' refer to the algal spores have been recorded from Jurassic lime- high morphological variation of these fossils. Many single-layered Mesozoic calcispheres are stones (Fay and Dirsche 1975). Paleozoic calcispheres occur in shallow-marine plat- cysts of planktonic algae (Calcidinoflagellata: see form and ramp carbonates. Jurassic and Cretaceous Keupp 198 1). Calcareous dinoflagellate cysts have exspherical n~icrofossilsare predominantly found in pe- isted probably since the Triassic. Mesozoic calcispheres exhibit a wide climatic range and were common in temlagic limestones. perate regions. They have been found predominantly in sediments of the deeper shelf to slope and basinal Dasyclad cysts In living, calcifying dasyclads cysts are formed in settings, sometimes in inner shelf environments. These calcispheres are abundant in association with reproductive branches or chambers. Some dasyclads are poorly calcified except around the cysts (e.g. Hali- other planktonic algae and occur in pelagic upper slope

Introduction to Foraminifera

453

and basinal carbonates as well as in outer shelf carbonates of low and mid latitudinal settings. The fossils can be used as bathymetric indicators of shelf margin and slope environments and in the stratigraphic subdivision of Late Jurassic to mid-Cretaceous Tethyan and subboreal pelagic carbonates (Borza 1969; Bucur 1992). Basics: Calcispheres and algal cysts Dasyclad cysts Elliott, G.F. (1986): Isolated cysts in the Palaeocene-Lower Eocene of Kurdistan. - Palaeontology, 29,739-741 Fliigel, E. (1966): Algen aus dem Perm der Karnischen Alpen. - Carinthia 11, Sonderheft, 25, 3-76 Marszalek, D.S. (1975): Calcisphere ultrastructure and skeletal aragonite from the alga Acetabularia antillana. - J. Sed. Petrol., 45, 266-271

Paleozoic calcisphe~~es Fliigel, E. and Hotzl, H. (1971): Foraminiferen, Calcisphfiren und Kalkalgen aus dem Schwelmer Kalk (Givet) von Letmathe im Sauerland. - Neues Jahrbuch fiir Geologie und Palaontologie, Abhandlungen, 137, 358-395 Kazmierczak, J. (1975): Colonial Volvocales (Chlorophyta) from the Upper Devonian of Poland and their paleogeographical significance. - Acta Palaeont. Polonica. 29, 73-85 Mesozoic calcispl~ews Borza, K. (1969): Die Mikrofazies und Mikrofossilien des Oberjuras und der Unterkreide der Klippenzone der Westkarpaten. - 301 pp., Bratislava (Slov. Akad. Znanosti) Keupp, H. (198 1): Die kalkigen Dinoflagellaten-Zysten der borealen Unter-Kreide (Unter-Hauterivium bis UnterAlbium). - Facies, 5, 1.-190 Keupp, EI. (1991): Fossil calcareous dinoflagellate cysts. In: Riding, R. (ed.): Calcareous algae and stromatolites. 3-67-286, Berlin (Springer) Rehanek, J., Cecca, F. (1993): Calcareous dinoflagellate cysts, biostratigraphy in Upper Kimmeridgian-Lower Tithonian pelagic limestones of Marches Apennines (Central Italy). - Revue de MicropalContologie, 36, 143-163, Villain, J.M. (1977): Les Calcisphaerulidae: Architectures, calcification de la paroi et phylogenbse. - Palaeontographics, A, 159, 139-177 Further reading: K 139, K: 140

the class Rhizopoda. Similar to calcareous algae, foraminifera are of prime importance in microfacies analyses. Foraminifera provide time markers for biozonations of shallow and deep marine carbonates, are excellent environmental proxies and permit ancient depositional systems to be reconstructed. The shells of benthic foraminifera have been major constituents of shelf carbonates at least since the Late Paleozoic and those of planktonic foraminifera formed pelagic limestones from the Late Mesozoic on. Foraminifera1 shelf limestones are important reservoir rocks for hydrocarbons. Most foraminifera1 shells typically range from 0.1 to 1 mm in size, but some groups developed rather large tests. For study purposes a distinction is made between smaller foraminifera and larger foraminifera (about 0.6 mm to 20 cm). Smaller foraminifera with test sizes of approximately 100 pm to 600 pm form the majority of benthic foraminifera. They are usually identified by their external characters, but can be also typified in thin sections. Larger foraminifera are usually large enough that geologists can spot them in the field. Their tests have complex internal structures that need to be studied in thin sections. The two major groups of foraminifera are benthic, living in or on sediments on the sea floor, and planktonic, living in the upper 100 m of the oceans.

10.2.2.1 Foraminifera

Morphology of foraminifera The living cell is made up of protoplasma. Extensions of the protoplasma (pseudopodia) protrude through a single foramen or through minute pores in the test. Pseudopodia assist in locomotion, capturing of food, and removal of waste products. The cell is enclosed by a test consisting of a singlc chamber or several chambers each connected by one or several openings. Most foraminifera are multichambered. The chambers are arranged in whorls. They may be uniserial (forming a single linear series), or multiserial (two or more chambers per whorl). If the test coils in a single plane around the growth axis, it is called planispiral. In trochospiral tests the chambers are arranged in a helical coil. A common arrangement in which five chambers are visible is called quinqueloculine. Internally the chambers are separated by walls called septa. An opening (aperture) in the wall of the final chamber connects external pseudopodia and internal endoplasm. The external surface of the tests is smooth or variously ornamented (e.g. spines and keels).

Foraminifera are small, predominantly marine heterotrophic protists that construct chambered shells (tests). The group belongs to the phylum Sarcodina and

Diagnostic criteria, classification and major groups Diagnostic criteria of foraminifera are (1) wall composition and microstructure, (2) chamber arrangement

,

10.2.2 Foraminifera and other Protozoa

The second prominent category of fossils found in thin sections of carbonate rocks includes small-sized singlecelled protozoan organisms : foraminifera, radiolarians and the calpionellids (an extinct group of the ciliates).

Wall Structures of Foraminifera

Textulariina

Agglutinated test with compact wall

Agglutinated test with alveolar (labyrinthic)wall

Fusulinina

Calcareous test with microgranular wall

Miliolina

Calcareous test with microgranular differentiated wall

Majorforanziniferal wall structures seen in thin sections and studied in SEM are agglutinated, microgranular calcareous, porcelaneous calcareous and hyaline calcareous (Fig. 10.22). Wall composition and microstructures are the most important features for classifying foraminifers on a suprageneric level, and are the subjects of current critical evaluations (Piller 1990). Note that the groups mentioned below are those of more conventional classifications. Loeblich and Tappan (1988) recognized 12 suborders acknowledging specific skeleton mineralogy (e.g. Involutinina originally with aragonitic walls, Fig. 10.27, see P1. 111/15) or specific lamellation pattern (e.g. Globigerinina, PI. 73).

The wall of the agglutinated tcxtulariid foruminifera consists of particles held together by organic material and cement of different composition. The parCalcareous test with porcelaneous wall ticles can be coarse (see Ammobaculites, P1. 6917; Haddonia, P1. 7519; Reophax; Tolypammina. P1.5 112, P1. 111/18) or fine (e.g. Alpinophragrnium, P1. 1 1 111; Chrysalidina,P1.7213). In more complex Mesozoic taxa an outer microgranular wall covers a complex inner Rotaliina layer that may be folded inward into the chambers, producing labyrinthic or alveolar structures (see Alveosepta, P1.6918; 01-0ijolina,P1.70, Pseudocyclamminu, P1.6911). Textulariid foraminifera occur in various maBL rine environments. They are often dominant in trans]Calcareous test with Calcareous test with granular hyaline wall fibroaxial hyaline wall tional environments with brackish and marsh conditions as well as at bathyal and abyssal depths. Fig. 10.21. Major wall sfr~ucti~r.es of for-cnzir~ifcdgt-oups. Agglutinated walls are characterized by individual grains from the sea floor bound together in a cement, which niay be calcareous, ferruginous or organic. Fusulinid foraminifera have a microcrystalline calcitic wall, that is often differentiated into several units. The porcelaneous walls of rniliolinid foraminifera are submicroscopical crystals of magnesian calcite, usually in random orientation. Rotaliinid foraminifera have glassy-looking (hyaline) walls; which may be differentiated into layers. AG - agglutinated grains, ALV - alveoles, BL basal layer, C - cement, IL - inner layers, OL - outer layer, ORL - organic lining. Arrows indicate the optical orientation of calcite crystals. Modified from Brasier (1980) and Bignot (1985).

and septa1 addition, (3) apertural characters and modifications, and (4) chamber form and ornamentation. These criteria are by far the most important characteristics used in the classification and taxonomic differentiation. Further properties particularly important for discriminating modem foraminifera are life habits and habitats, protoplasma features, ontogenetic changes, and genetics. The last criterion has become increasingly more meaningful for higher-level classification of ancient foraminifera as well.

Fusulinid forurninifera with microgranular culcureous wall structures are represented by smaller and larger foraminifera. The wall of the smaller foraminifer consists of microgranular calcite cemented by mlcrocrystalline calcareous cement (see Earlandia, PI. 671 2; Endothyranopsis, P1. 6711 ; Cribrogenerinu, P1. 671 10; Tubel-itina,P1.6712). Larger fusulinid foraminifera, (Fusulinacea; Visean to Late Pemiian; PI. 68) are rnorphological highly differentiated. Millolinidfo~~umin$c~~-a exhibit a porce1ancou.t culcareous wall structure without pores, characterized b) a shiny, smooth appearance of the test. Examples are Austrocolomia, P1. 111/23; Alveolina, P1. 7512; Guleunella, P1. 11 114-5; Hemigordius, P1. 6717).

are characterized by ilpoThe rotaliirzid.fo~-aminiferu line calcareous wall structures. In cross sections organic layers or calcareous laminations may be visible. Lamellar tests can be recognized by thicker early chanibers, thinner later chambers and a single-thickness final chamber. Lamellar walls are characteristic for taxa

Environment of Foraminifera -

-

Wall and microstructure

1

Appearance

Criteria

Group Allogromiina

Organic, proteinaceous material

Poor preservation potential

Tubular, single-chambered round or flask-shaped forms

Various foreign grains glued together by organic, calcareous, ferrugineous or siliceous cement

Dark in transmitted light

Simple agglutinated (arenaceous) Textulariina walls. Advanced Mesozoic forms with outer layer covering complex inner layer forming chambers, alveolar and labyrinthic structures

Microgranular calcite, randomly or normally oriented crystals of unequal size Calcite crystals oriented randomly or in a brick-like pattern, Low-Mg and High-Mg calcite

opaque in reflected light

Dark or amber-colored in transmitted light, milky white and brilliant in reflected light. Under crossed nicols calcite crystals appear as tiny multicolored specks

Advanced forms show differentiation of the wall into two or more layers

Fusulinina (include Carboniferous and Permian larger foraminifera, Fusulinacea)

Miliolina Porcelaneous. Imperforatewall with inner and outer surface layers

Crystals arranged in prisms Light-colored, clear or gray in Hyaline, finely perforate wall. transmitted light, glossy and with c-axes normal to test dark in reflected light lamellar surface radial hyaline or randomly granular hyaline. Low- or High-Mg calcite. Few groups with aragonite

Rotaliina, including

Time range Cambrian to Holocene Early Cambrian to Holocene

Early Silurian to Late Permian Carboniferous to Holocene

Triassic to Holocene

multilamellar and Cenozoi larger foraminifera) and planktonic Globeriginacea (predominantly

Fig. 10.22. Microstructure, wall composition and major systematic categories offoraminifera. Note that the suprageneric high-level classification of the foraminifera is much more complicated than shown in this simple graph.

of the benthic Rotaliacea with multichambered spiral shells (Orbitoides, P1. 72/7-10; Nummulites, P1. 7.512) and the planktonic Globigerinacea with bubble-shaped chambers arranged in expanding spirals (see Globigerinoides, P1. 7319).

Environmental constraints of foraminifera Foraminifera1 environments include shelves, platforms, ramps. reefs, slopes and basins. Most modem foraminifera are marine and benthic and live from the intertidal zone down to the deep sea. Some benthic foraminifera inhabit fresh and brackish waters. Planktonic foraminifera live in the upper part of the open oceans.

(A) Benthic foraminifera are restricted to a narrow range of depths and substrates, and have characteristic tolerances to salinity and temperature: Salinity: Most foraminifera are found in water with a normal marine salinity of 35960.Diversity decreases with decreasing salinity. Low salinities (e.g. in coastal lagoons) favor low-diversity assemblages, rich in agglutinated forms. High carbonate concentrations in hypersaline marine waters favor the occurrence of porcelaneous Miliolina. Triangular plots of the relative proportions of Textulariina, Miliolina and Rotaliina have proved to be valuable indicators of paleosalinity and paleotemperatures and can also be derived from thinsection analysis of foraminiferal limestones. Temperature: Benthic foraminifera enable warmwater, temperate and cool-water environments to be

distinguished. Cold-water foraminiferal associations inhabiting the shallow waters of high latitudes or the cooler waters of the deep ocean are fairly uniform. Because of the lower solubility of calcium carbonate in warmer than in cool waters, accumulations of foraminifera and foraminifera1sediments are more frequent in carbonate platforms of low latitudes. The increasing solubility of carbonate with depth results in a distinct and final drop of calcareous foraminifera at the lysocline and the CCD (see Box 2.9) and results in a dominance of agglutinated foraminifera in deep-water environments. Oxygen and nutrients: Most benthic foraminifera occur in areas of normal oxygen concentration, although deep-water forms may tolerate very low oxygen levels. The composition of slope and outer shelf foraminiferal faunas is considerably influenced by upwelling oxygen-poor and nutrient-rich waters. Specific faunas occur in the oxygen-minimum zone of the continental slope. Substrate: Various types of sea bottom contain distinctive associations differing in shell morphology and taxonomic composition. Microenvironments around the sediment-water interface provide distinct substrate-controlled microhabitats for benthic foraminifera living free or attached to sedimentary grains, algae and sea grass, hard substrates or as infauna at depths between 0.5 to about 10 cm (Langer 1988; Yamano et al. 2000). Water depth: Many foraminifera are limited to the photic zone because of their endosymbiotic associa-

Planktonic Foraminifera

tions, or because they prefer habitats within algal and sea grass meadows. Depth distribution of endosymbiotic foraminifera depends on the type of endosymbionts. Foraminifera with green or red symbionts are restricted to shallower depths than those with diatoms that can occupy greater depths. Near-coastal, lagoonal, and inner and outer shelf environments as well as upper and lower slope and basinal environments differ in foraminifera1 association patterns. Shallow nearshore and lagoonal environments, down to about 50 m, are characterized by porcelaneous miliolid foraminifera. Planktonic foraminifera are absent or rare in shallow-marine environments. Hyaline rotaliinids occur in shallow and deeper waters. Agglutinated tests are ubiquitous but common on the slope and also occur at depths of several thousand meters. In outer shelf environments (about 50 to 200 m) the faunas are dominated by perforate rotaliinid species. Bathyal depths tend to be dominated by biserial and

Single chambered

I

triserial agglutinated foraminifers along with some hyaline rotaliinids and porcelaneous miliolinids.

(B) Planktonic foraminifera are adapted to different oceanic layers with particular temperatures and densities. Temperature-controlled planktonic species exhibit specific morphological characteristics (shape, size and coiling direction). These adaptions are used together with geochemical and isotope data as proxies for paleoceanographic interpretations of Cretaceous and Cenozoic pelagic carbonates. Most planktonic foraminifera are restricted to marine salinities of 30-40%0 and live in defined parts of the water column. The majority occurs in the upper part of the water column within the upper 50 to 100 m near the surface (photic zone). Below 200 m they are virtually absent. The thin-walled spherical, symbiont-bearing globigerinids prefer the surface waters where there is Iight, while those with thicker walls and keeled shells (lacking photosymbiosis) tend to be

Multichambered uniserial

Multichambered pianspiral

Multichambered biserial

E

1

Multichambered triseriai

1

2

3

Multichambered trochospiral

Fig. 10.23. DiSfereizt sections through foranziniferal tests of different shapes. A. Single chambered: I - axial section, 2 longitudinal, 3 - tangential, 4 -transversal, 5 - oblique. B. Multichambered uniserial: 1 - axial, 2 - longitudinal, 3 - transversal, 4 - oblique passing through two chambers. C. Multichambered biserial: 1 - axial sagittal, 2 - axial frontal, 3 - longitudinal, 4 - axial oblique, 5 - transversal, 6 - transversal oblique. D. Multichambered planspiral (a, lateral view; b, peripheral view): 1 - axial, 2 - transversal equatorial. E. Multichambered triserial (a, lateral view; b, oral view): 1 - axial, 2 - longitudinal passing through two chambers, 3 - longitudinal passing through one chamber, 4 - transversal. F. Multichambered trochospiral: 1 axial, 3 - transversal dorsal, 3 - transversal, passing through an embryonal chamber, 4 - transversal ventral. After Neumann ( 1967).

References o n Foraminifera found at slightly greater depths. Planktonic foraminifera avoid terrigenous input. Their shells, therefore, accumulate in the bathyal depths of open-marine ba-

sins. Foraminifera in thin sections Relevant criteria for the taxonomic discrimination of foraminifera in thin sections are wall structure, arrangement of chambers and the form and position of the apertura (Arnaud-Vanneau 1980). Foraminifera should be studied in plane and polarized light.

Taxonomic determination of foraminifera in thin sections of limestones may b e difficult because only randomly oriented sections are commonly available, and wall structures are often obliterated by diagenesis. Some of these problems can be overcome by the following steps: Compare foraminifera dissolved from limestones by acids with those found in thin sections of the limestone (see P1. 911, 2); compare hypothetical figures of geometrically dif-

Box 10.4. Selected references on foraminifera in thin sections. The list includes papers accompanied by plates that are useful for determining foraminifera and that assist in interpreting depositional environments of limestones with foraminifers. Planktonic Cretaceous and Tertiary foraminifera: Atlas 1979; Caron 1985; Lipps 1966; No6 1993; Robaszynski et al. 1984; Sliter 1989; Van Konijnenburg et al. 1998; Radoicic 1995; Weidich 1984, 1990 Tertiary: Bonnefous and Bismuth 1982; Charproniere 1975; Drobne 1974; Drobne et al. 1977; James et al. 1962; Gee1 2000; Ghose 1977; Hallock and Glenn 1986; Hallock et al. 1988; Hottinger 1997; Hottinger and Drobne 1980, 1988; Kenawy 1966; Less 1998; Luterbacher 1984; Moussavian and Hoflingl993; Pemn 1992, 1994; Reiss and Hottinger 1984; Ross 1979; Schaub 1981; Tourmakine and Luterbacher 1985 Late Cretaceous: Beckrnann et al. 1982; Berthou 1973; Berthou and Schroeder 1978; Bilotte 1984, 1985; Carbone et al. 1971; Caus 1988; Chiocchini et al. 1983; De Castro 1971,1980,1988; Eames et al. 1962; Fleury et al. 1985; Gargouri 1988; Gusic et al. 1988; Hamaoui and Brun 1974; Hamaoui and Saint-Marc 1970; Hart 1988; Hofling 1988; Hottinger 1966; Krijnen et al. 1993; Kuss 1994; Kuss and Conrad 1991; Kuss and Malchus 1989; Papp 1955; Saint-Marc 1982; Septfontaine 1981; Velic and Vlahovic 1994 Early Cretaceous: Arnaud 198 1; Amaud-Vanneau 1980, 1986; Amaud-Vaunard and Amaud1978: Arnaud-Vanneau and Masse 1989;Arnaud-Vanneau et al. 1988; Bassoullet et al. 1985; Becker 1999; Berthou and Schroeder 1978; Bodrogi et al. 1994; Bucur 1988; Cherchi et al. 1981; Chiocchini and Mancinelli 1978; Chiocchini et al. 1983, 1988; Conrad 1977; Darga and Schlaginweit 1991; De Castro 1988; De Castro and Peybernes 1983; Douglass 1960: Dragastan et al. 1975; Gallagher 1997; Gusic 1975, 1981; Hottinger 1967; Husinec et al. 2000; Kaever 1967; Masse 1976, Moullade et al. 1985: Neumann 1958; Peybemes 1979; Ramalho 1971; Sanchez et al. 1991; Schroeder et al. 1968; Schroeder and Neumann 1985; Septfontaine 1981; Velic 1988 Late Jurassic: Allemann and Schroeder 1972; Altiner and Septfontaine 1979; Bassoullet et al. 1985; Chiocchini and Mancinelli 1978; Chiocchini et al. 1988; Darga and Schlaginweit 1991; Dragastan et al. 1975; Farinacci 1964; Grossowicz et al. 2000; Gusic 1969, 1977; Hottinger 1967, 1973; Misik and Sotak 1998; Pelissie and Peybernes 1984; Peybernes 1979; Ramalho 1971; Schmalzriedt 1991; Septfontaine 1988; Starn 1986 Middle Jurassic: Bernier and Neumann 1970; Blau and Wemli 1999; Cherchi and Schroeder 1981: Ruggieri and Giunta 1965; Furrer and Septfontaine 1977 Early Jurassic: Blau 1987a, 1987b; Gazdzicki 1983; Gusic 1975; Hottinger 1967; Pirini 1965; Septfontaine 1984, 1985 Triassic: Gazdzicki 1983; Hohenegger and Lobitzer 1971; Hohenegger and Piller 1975a, 1975b, 1975c, 1977; KoehnZaninetti 1969; Oravecz-Scheffer 1987; Piller 1978; Rettori 1995; Salaj et al. 1983; Schafer and Senowbari-Daryan 1978; Schott 1983: Zaninetti 1976 Permian: Groves and Wahlman 1997; Henbest 1963; Kahler 1983; Leven, 2003; Okimura et al. 1985; Pasini 1965; Ross 1982, 1995; Wilde 1990 Late Carboniferous: Fliigel 1971; Forke et al. 1998; Groves and Wahlman 1997; Henbest 1963: Pasini 1965: Ross 1982: Toomey 1974; Vachard and Krainer 2001a, 2001b Early Carboniferous: Conil 1964; Conil et al. 1979, 1990; Cossey and Mundy 1990; Fewtrell et al. 1981; Gallagher 1997, 1998; Horbury and Adams 1996; Krainer and Vachard 2002; Marnet 1977; Marnet et al. 1986; Mamet and Pinard 1990; Vachard 1988 Devonian: Chuvashov 1965; Fliigel and Hotzl1971; May 1994; Petrova 1981; Poyarkov 1979; Toomey 1965; Vachard 1988; Vachard and Massa 1989; Zadorozhnyi and Yuferev 1981

Paleozoic Foraminifel a

ferent tests with the random figures displayed in thin sections (Fig. 10.23; Neumann 1967; Hottinger 1971); compare free tests and line drawings of possible sections using a defmed coordinate system (Cummings 19.58); reconstruct three-dimensional tests enclosed in lirnestones using serial peels and computer-assisted designs; use X-ray microradiographic techniques in taxonomic differentiation of pyritized foraminifera occurring within micritic limestones (Mehl and No6 1990)

Larger foraminifera These foraminifera are significant constituents of Late Paleozoic, Jurassic, Cretaceous and Early Tertiary limestones. These foraminifera include systematic groups that are not closely related taxonomically. They are characterized by tests with sizes between about 0.5 Inn1 and several centimeters (up to 20 cm), complicated internal structures, and the often distinct differentiation into sexual and asexual reproductive stages that can be distinguished by the size of the initial chambers and the shells. Larger foraminifera are thin-section fossils per se because of the necessity of studying their endoskeletons in oriented sections. This taxonomic differentiation requires sectlolls exhibiting the size and shape of the test, the morphology of the initial and embryonal chambers, the character of the whorls, the shape and number of septa as well as dimensional criteria. Modem /urgerforanzinifera: About ten recent families of the tropics and subtropics and thirteen additional fossil families include taxa with large calcareous tests, belonging to widely divergent taxa of the suborders Textulariina, Fusulinina, Miliolina and Rotaliina. These foraminifera attain a volume of at least 3 n1m3 before reachmg reproductive maturity and many reach volumes of more than 300 mm3 (Ross 1979). Larger foraminifera are typically associated with tropical and subtropical shallow-water carbonate sediments (Hottinger 1983). They can form a considerable portion of the skeletal debris of reef and platform environments. Their carbonate production rates are comparable to those of calcareous algae and corals (Hallock 1981). Most larger foraminifera live in symbiotic association with unicellular algae. In tropical carbonate shoal and reef environments, calcareous larger foraminifera house various algae, including dinophyceans, diatoms, chlorophyceans and rhodophyceans. The sym-

bioses provide nutrients from photosynthesis, facilitate life in different water depths and favor maximum carbonate precipitation by carbon dioxide uptake. Differences of light attenuation by the water column and of water energy are reflected by different wall structures (Hohenegger et al. 1999). Most larger foraminifera are restricted to relatively shallow well-lighted sea bottom, and if untransported, their presence is generally indicative of depths less than 30 m (Hallock 1986). Symbiont-bearinglarger miliolinid and rotaliinid foraminifera are important constituents of modem reef flat and forereef biota (Hottinger et al. 1993; Hohenegger 1994). In addition to symbioses, the distribution of modem larger foraminifera is controlled by surface water temperature (within the 15" isotherm) and nutrients (oligotrophic, nutrient-poor waters; Langer and Hottinger 2000). Ancient larger foraminifera: The first larger foraminifera appeared late in the Early Carboniferous. The fusulinids (Pl. 68) are useful for biostratigraphically subdividing Late Carboniferous and Permian carbonate rocks and for biogeographical interpretations. Agglutinated larger foraminifera are important index fossils used for regional and global correlations in Jurassic (Pl. 69) and Cretaceous shelf carbonates, particularly in the Early Cretaceous (orbitolinids, PI. 70, Pi. 7 1). Late Cretaceous larger foraminifera are represented by the rotaliinid orbitoideaceans (PI. 7217-1O), Tertiary larger foraminifera by the miliolinid alveolinid and rotaliid nummulitid foraminifera (Pl. 74, PI. 75). Late Paleozoic Fusulinacea as well as other fossil Mesozoic and Cenozoic larger foraminifera are believed

Fig. 10.24. Early Paleozoic foraminifera are characterized by agglutinated or calcareous microgranular, usually singlechambered tests. Parathuramminid foraminifera are common in Middle and early Late Devonian lagoonal limestones. The sample shows Parathurammina dagamarae (Sulei~nanov). Middle Devonian (Givetian): Letmathe, Sauerland, Germany. Scale is 500 pm.

Paleozoic Foraminifera

to have had symbionts (Ross 1972; Hallock 1985). Many larger foraminifera have chambers which are subdivided into smaller chamberlets. Most fusulinids subdivided the chambers by septa1 fluting (folding of septal walls) similar to Tertiary alveolinids. Other larger foraminifera have small bar-like elements starting at the septa and forming additional subdivisions within the shell. These exoskeletal structures are known from the Late Permian verbeekinid fusulinids (Pl. 68/5), but are also very common in Jurassic, Cretaceous and Tertiary agglutinated foraminifera (e.g. P1.6912). Endoskeletal structures are arranged from one septum to the other and reflect the direction of the protoplasma flow. Some Late Cretaceous and Cenozoic larger foraminifera (Rotaliina) have a channel system and a lamellar-perforated wall consisting of inner and other lamellae.

Fig. 10.25. Smaller foraminifera are used for the biozonation and correlation of carbonates deposited on Carboniferous shelves and ramps. The biozones can be correlated both on a regional and a global scale. The sketch exhibits a grainstone with different sections of Endothyranousis and other foraminifera, indicating an Early VisCan age. After Sorby (1879).

Distribution and fossil record of foraminifera Examples of foraminifera common in thin sections of Late Paleozoic, Jurassic, Cretaceous and Tertiary limestones are shown on P1. 67 to P1. 75. For Triassic foraminifera see PI. 111. Box 10.4 lists relevant papers. Benthic foraminifera have been known since the Early Cambrian. During the Carboniferous and Permian minifera taken from different phylogenetic lines (Conil an explosive radiation took place, specially among and Lys 1964; Mamet 1977; Conil et al. 1981; Lys 1988; larger foraminifera (Fusulinacea). Carbonate rocks with Fig. 10.25).These zones were recognized in limestones abundant benthic foraminifera have been common since formed in shallow subtidal parts of platform and ramp the Early Carboniferous and became widely distributed environments. Smaller foraminifera1assemblages also in the Cretaceous and Tertiary. Planktonic foraminifera assist in the zonation of Late Permian shelf carbonates evolved in the Middle Jurassic and became major con- (Okimura et al. 1985; No6 1988). Smaller foraminifera often comprise only less than stituents of the marine plankton during the Cretaceous. 5% of the rock volume, but may increase to more than Early Paleozoic: An overview of Paleozoic fora- 20% in grainstones. Common shallow-marine facies minifera was given by Ross and Ross (1991). Cam- types of bedded VisCan platform carbonates yielding brian foraminifers are poorly documented (e.g. Cherchi benthic smaller foraminifera are (a) grain-, pack- and and Schroeder 1984). Evolution was slow during the wackestones with crinoids, bry ozoans, brachiopods, Ordovician. Silurian populations were rather small and dasyclad green algae and ungdarellacean red algae (Pl. diversity very low. Nearly all Cambrian to Silurian fora- 65/7), (b) fine-grained peloidal grainstones, and (c) laminifera are characterized by agglutinated single-cham- goonal wackestones and packstones. Foraminifera are bered tests. The first major radiation took place in the rare to absent in oolitic limestones (but see Fig. 4.22), Middle Devonian and culminated in the Late Frasnian. deeper-water crinoid limestones and basinal sediments. Devonian microgranular and agglutinated foraminifera In graded calciturbidites intercalated within basinal occur in shallow-marine and basinal facies types. Fusu- sediments, smaller foraminifera are differentiated by h i d Parathuramminacea were common in back-reef size, indicating hydraulic sorting of microbiota derived and lagoonal carbonates (Fig. 10.24). The Devonian from all the parts of adjacent platforms (Herbig and fauna became almost extinct in the Famennian and was Mamet 1994). Statistically-based association patterns of Early Carreplaced by the endothyrid group. This group had a boniferous and Permian foraminifera are indicative of major outburst in the Tournaisian and the VisCan. specific shelf habitats (Gallagher 1998). Distribution Late Paleozoic: Nineteen Tournaisian, VisCan and of taxa, frequency patterns and association types of lower Middle Carboniferous biozones have been es- Paleozoic smaller foraminifera permit various parts of tablished based on assemblages of benthic smaller fora- platforms, ramps and mud mounds to be differentiated Text continued on p. 464

460

Late Paleozoic Smaller Foraminifera

Plate 67 Carboniferous and Permian Smaller Foraminifera Late Paleozoic foraminifera shown on this plate comprise both 'smaller foraminifera' with approximately 0.1 and 0.6 mm tests, and millimeter- to centimeter-sized 'larger foraminifera' (see P1. 68). Foraminifera1 assemblages enable biostratigraphic zonations of Late Paleozoic, particularly Early Carboniferous ramps and platforms (-> 1; P1. 10812) and Permian shelf deposits to be biostratigraphicaily zoned. Distribution of taxa, frequency patterns and association types of Paleozoic smaller foraminifera are used in differentiating the facies depositional settings of ramps and mud mounds as well as recognizing environmental conditions (water energy, paleobathymetry and sedimentation rates). Association patterns are indicative of local shelf habitats. This plate displays taxa common in Carboniferous (-> 1, 6, 11) and Permian (-> 2-5, 7-10) shelf and reef carbonates. Agglutinated foraminifera (-> 9) as well as foraminifera with calcitic microgranular (-> 1, 5,6) or porcelaneous walls (-> 7) are used in paleoecological analyses. Note the different growth forms, including unilocular tests, shells consisting of a proloculus followed by a tubular non-divided chamber (-> 2), multichambered uniserial (-> 4) or coiled tests (-> 11) and conical trochospiral tests (-> 1). Biozonation based on smaller foranzinifcra. The succession of foraminiferal assemblages permits zonation and global correlation of Tournaisian and VisCan ramps and platforms. The sample shows a foraminiferal grainstone with axial sections of Forschiaprisca Mikhailov (center left) and equatorial sections of Endothyranopsis crassa (Brady), top right, indicating the Late VisCan foraminiferal zone 15. Early Carboniferous: Basin of Dinant, Belgium. Encrusting foraminifera and very small tubular microfossils, usually also assigned to foraminifera, are common constituents of Late Paleozoic shelf carbonates. Some of these foraminifera encrusted algal blades, others hard bottoms. Note that recrystallization only affected the matrix, but not the microgranular foraminifera1 tests. Abundant taxa are Tuberitina Galloway and Harlton (T) belonging to the parathuramrninacean Fusulinina, and Earlandia Plummer (E) assigned to the earlandiacean Fusulinina. Both genera occurred in inner and outer shelf environments. The sample is from the top of a meter-scaled cyclothem. Early Pennian (Asselian): Cainic Alps, Austria. Miliolinid attaclzed foraminifera. The initial chamber of Apterinella Cushman and Waters is encircled by uncoiled chanibers planspirally enrolled and later arranged in zigzag bends. The wall appears dark in transmitted light. The sample is from back-reef carbonates deposited in the lceward position of a platfonn margin reef. Middle Permian (Capitmian): Permian Reef Complex, Texas, {J.S.A. Differcrzriated wall st/-ltctur-e.The wall of' Paihy~~l~loiaiLarzgella exhibits a thin dark inner layer (arrow) and a thick hyaline outer layer. The uniserial elongate test consists of strongly overlapping chambers. Middle Pelmian: Pietra di Salomone near Sosio, westem Sicily. Differentiated rest. Axial sections of Lasiotrochus tatoensis Reichel (left) and Lusiorr-ochus minor Reichel. Note initial chamber and microgranular wall. Arrows point to hyaline pillars composed of transparent calcite and tubular chamberlets. Genus range: Pennian. Same locality as -> 4. Differentiated test. Oblique axial section of Howclzenia Cushman. Conical test. The undivided tubular chamber is coiled in a high spire around an umbilical region filled with fibrous calcite. The genus is restricted to Viskan to Moscovian and common in intraclastic wackestones deposited in deep shelf environments affected by storm waves. Early Carboniferous (Badstuben Breccia, Vis6an): Niitsch, Carinthia, Austria. iI.liliolit~idfo/~ur?~iilfer-a1 ~ I ~ U I ' I Z S I O I I with ~ Ncnligor-dius Schubert. The porcelaneous discoidal tests appear dark in transmitted light. The dark tint is intensified by early pyritization of the tests. The sample is from black limestones representing bioclastic shoals within a restricted lagoon. Late Permian (Bellerophon Formation, Dorashamian): Comelico, northern Iialy. T6jtr-atuxisEhrenberg, a common Carboniferous and Permian genus occurring in open-marine subtidal crinoid and bryozoan thickets at or below the fair-weather wave base, which were reworked by currents and storms. The wall consists of an outer microgranular layer and hyaline radiate inner layer. Tetr.ataxis was a loosely attached mobile foraminifer that responded to environmental extremes by attaching onto substrates (Cossey and Mundy 1990). The test is encrusted by Tuberitina, (T). Genus range: Early Carboniferous to Triassic. Early Permian: Carnia, Italy. Agglutinated tcsrulariid foraminifera. Tangential and more central longitudinal sections. The wall is composed of fine sand grains. The chambers are uniserially arranged. Early Permian: Southern Karawanken Mountains, Austria. 10 Cribrogenerina Schubert, a common Permian palaeotextulariid foraminifera. The genus is characterized by initially biserial, later uniserial, broad chambers with multiple and cribrate roofs. The oblique section displays the uniserial part of the test. Late Permian (Zazar Formation): Idrija, Slovenia. 11 Bradyina Moller, an endothyracean fusulinid foraminifer which was common in Carboniferous shallow-marine algal meadows. Planispiral involute test, sutures deeply incised. Calcareous wall, with microgranulate outer layer (tectum, T ) and inner perforate structure (P). Late Carboniferous (Gzhelian): Nassfeld, Camic Alps, Austria. -> 4, 5 : Fliigel et al. 1991: -> 7, 10: Noe 1987

Plate 67: Carboniferous t o Permian Smaller Foraminifera

46 1

Larger Foraminifera: Fusulinlds

402

Plate 68 Late Paleozoic Larger Foraminifera: Fusulinids This plate exhibits characteristics in the morphology and wall structures of fusulinids of different ages. Fusulinids were benthic rock-forming larger foraminifera with a restricted geological range (VisCan to latest Permian), a wide geographic spread and distinct evolutionary lines allowing global biostratigraphic zones to be defined. The mm- to cm-sized tests have spindle-like, subcylindrical or globose shapes (Fig. 10.26). The complex internal structure is caused by variations in coiling, folding patterns of the partitions between chambers (septaj and additional elements projecting from the walls into the chamber interior (-> 9). The walls are microgranular and appear dark in transmitted light and opaque in reflected light. They consist of one to four layers (-> 2,4,6). Pores occur within walls and septa (-> 4). The determination of fusulinid species requires sections in the axis of coiling and passing through the initial chamber (-> 1, 3, 5) and cooperation with micropaleontologists. However, even nonspecialists can use these foraminifera for a very rough dating of shelf carbonates, if they look at the wall structure type: heb ball structures increase in complexity over time, starting with relatively simple multilayered walls (-> 2) in the Early and Middle Carboniferous, and continuing with double-layered walls (-> 4) characteristic of Late Carboniferous and Early Permian schwagerinids (-> 3). Middle and Late Permian neoschwagerinids have two-layered walls and shorter and longer projections into the chambers forming small chamberlets (-> 6). Most fusulinid families became extinct near the end of the Middle Permian (Guadalupian), the last fusulinids at the PermianTriassic boundary. Late Permian taxa are usually small and often characterized by distinct deviations in the coiling planes during individual growth (-> 7,8). Fig. 10.26. Mixture of spherical and spindle-shapedfilsulinidshells derived from different subenvironments. Poorly sorted bioclastic grainstone of an outer carbonate platform. The large spherical test (Zellia heritschi mira Kahler and Kahler) is cut through the initial chamber. Spindle-shaped forms are represented by taro sections cutting the tests tangentially (bottom) and transversially (top). Spindleshaped tests are peripherally rnicritized and often broken. Early Permian (Asszlian): Carnic Alps, Austria. Scale is 1 mm.

Brcdritzu Galloway. Axial section of the fusiform test. Note the initial chamber (proloculus; center) and the strongly fluted septa. Generic range: Middle to Late Moscovian. Middle Carboniferous (Moscovian): Kalinovo, Donets Basin, Ukraine. Beeditza sp. The wall structure exhibits four parts: Dark tectum (t), light diaphano~heca(d) bordered by the upper tectorium (ot) and lower (ut) tectorium. Same locality -> 1. Sphaer-oschwagerina carniolira Kahler and Kahler. Axial section of the spherical test. Note difference between the dimensions of inner and outer whorls. The thin septa are weakly fluted. Wall thin, thickening as the test enlarges. Species range: Early Permian. Asselian (Grenzland Formation): Rudnigsattel, Camic Alps, Austria. Sphaer-uschwuger-inncarniolica Kahler and Kahler. Wallstructure: Tectun~(t) and 'honeycomb-like' alveolar keriotheca (k). The septum (s) is pierced by septa1 pores (sp). Same locality -> 3. Yahcinlr syr-talk (Douville). Axial section of the inflated fusiform test. Note the abundance of whorls, numerous rela-. tively thin septa and short septula (-> 6). Middle Permian sponge-algal reef (Wordian): Bati Beni section, Djebel Tebaga. southern Tunisia. E~heinasyrtalis (Douville). Wall structure consisting of two parts: tectum and keriotheca. The chambers are subdivided by parachomata (pch) and transverse septula (ts) and filled with granular carbonate cement. Same locality -> 5. Rcichelina Erk characterized by a marked difference between an early planispirally enrolled stage and uncoiled final whorl with septa. Late Permian (Wargal Formation, Wuchiapingian): Chidru Nala, Salt Range, Pakistan. Codonojisiella Dunbar and Skinner. Note sharp change in coiling axis. Same locality -> 7. Random cuts: Microfacies thin sections commonly yield only randomly cut tests which are difficult to treat taxononiically. But sometimes specific structures are sufficient for a rough determination. Example: The broad and regularly spaced transverse septula indicate a neoschwagerinid form and points to a Middle Permian age of the sample. Middle Permian: Bohinska Bela near Bled, Slovenia. Random cuts: Sagittal section (perpendicular to the axial section and passing though the initial chamber) and tangential section of fusulinids. Note deformation of the last whorl of the left specimen (arrows) pointing to a pathological disturbance of shell growth rather than a mechanical destruction (Kahler 1988). Same locality as --> 9. 1-8: Courtesy of H. Forke (Erlangen)

Plate 68: Larger Forarnin~fera:Fusulinids

163

Triassic Benthic Foraminifera

as well as environmental conditions (water energy, paleobathymetry and sedimentation rates) to be recognized. The use of Late Paleozoic smaller foraminifera in microfacies studies requires closely spaced sampling (within a distance of < 10 m, often within a distance of less than 1 m), samples displaying the diversity of the foraminifera (e.g. PI. 67/1), systematic determination based on well-defined section plains (Conil et al. 1979), quantitative analysis using the number of different taxa (e.g. per square centimeter of thin-sections), presencelabsence patterns, and statistical treatment of the quantitative data (Gallagher 1997). The millimeter- to centimeter-sized,fusulinid foraminifera (Pl. 68) are excellent biostratigraphic markers on stable, shallow carbonate shelves. The global and regional zonation of the Middle Carboniferous to Late Permian shelf carbonates relies on a succession of genera and species (Ross and Ross 1987). Fusulinids are multichambered. Growth starts with an initial chamber (proloculus). Specimens of sexual generation have a small microspheric proloculus, those of asexual generations a large megalospheric proloculus. Chambers are added to form a coiled shell by extension of the spiral wall (spirotheca). After several chambers are added, a central tunnel is resorbed through the septa allowing free communication between the chambers. Main evolutionary trends are an increase in the size of the initial chamber, an increase in overall size, and an increase in the complexity of the test wall. Note that present classifications differentiate a suborder Fusulinina that includes the large-sized typical Fusulinacca as well as various groups of smaller foraminifera (see P1. 67). Fusulinids were adapted to shallow w a n and warmtemperate waters, usually in tropical and subtropical regions on shelves, platforms and reefs. They lived in normal marine, well-oxygenated environments on subtidal open shelves, in depths between a few meters to a few tens of meters. Variations in test shape indicate specialization to different shallow water subenvironments (e.g. sand bars). Spindle-shaped fusulinids with pole torsions were concentrated in high-energy stress environments, spherical forms in low-energy lagoonal environments (Ross 1982). The life habits and taphonomic history of fusulinids can be derived from shell construction, encrustation patterns, shell damage, and

Fig. 10.27. Invoiutinid foraminifera are abundant elements of reefal Late Triassic carbonate platforms (see PI. 111). A: Triasina hantkeni Majzon defines a Rhaetian biozone. The species occurs in open-marine platform environments. Allgau, southern Bavaria, Germany. B: Ang~rlorliscuspernzodiscoidesOberhauser and related taxa are common in muddy near-reef sediments. Left subaxial scction, right oblique-horizontal section. Note the distinct fibrohyaline wall structure. Late Triassic (Rhaetian): Kendelbachgraben, Austria. Scale is 500 pm. Further Triassic foramin ifera are depicted on PI. 11I .

sedimentary infillings (Kahler 1988). Worn and rounded fusulinid tests as well as mixtures of juvenile and adult specimens are indicative of transport, erosion and redeposition processes that may sometimes produce mixtures of fusulinids derived from different subenvironments (Fig. 10.26), or even different stratigraphic ages. Carboniferous and Early Permian fusulinids are particularly common in bedded medium to light gray grainstones, pack- and wackestones deposited on shallow carbonate shelves, banks and platforms, and in calcareous shales. They mark specific levels in cyclic successions. Middle and Late Permian verbeekinid and neoschwagerinid fusulinids are often associated with platform margin reefs (Pl. 6815, 9). Some species are restricted to back-reef lagoons. Fusulinids also occur as clasts in debris flows and turbidites deposited in deeper-water slope and toe-of-slope settings.

Cretaceous Foraminifera

Fusulinid coquinas (grain- and packstones) may represent parautochthonous assemblages, allochthonous downslope accumulations between buildups, concentrations through storms, or transgressive deposits during times of reduced mud deposition, or they may just be diagenetic packstones caused by intergranular solution. Syn- and postsedimentary changes of test shapes and internal structures (e.g. broken or distorted shells, shells with breaks of septa) are indications of late diagenesis and burial history (see P1.36/1,3).

Triassic: Benthic foraminifera are common in thin sections of Middle and Late Triassic platform and reef carbonates (see P1. 111). Systematic determinations must consider diagenetic changes of wall structures that are particularly frequent in involutinid foraminifera (Hohenegger and Piller 1975). Some taxa are good index fossils and are used for biozonations (Gazdzicki 1983, Salaj et al. 1983; Fig. 10.27). Open and restricted platforms as well as different parts of reefs can be discriminated using distinct foraminiferal associations defined by the occurrence or quantitative predominance of specific taxa (e.g. Schafer and Senowbari-Daryan 1978; Schott 1983). Examples from various parts of the Tethys (Alps, Sicily, Greece, Oman) exhibit corresponding association patterns, proving the usefulness of foraminifera for environmental analysis. Foraminiferal distribution was controlled by substrate conditions, specific life behavior, the topography of the depositional environment and water depth. Common Late Triassic foraminifera include taxa of Textulariina (Pl. 111/1,9, 10, 14, 18, 19,20),Miliolina(Pl. 11112-8, 1517, 22, 23), Rotaliina as well as microgranular foraminifera (PI. 111121). Note that higher systematic groups of Late Triassic foraminifera have been differentiated more deliberately using wall structure types (Hohenegger and Piller 1975, Piller 1978). Involutinid foraminifera offer the possibility for subdividing restricted and open shelf environments. Jurassic: Benthic foraminifera and dasyclad calcareous algae (see PI. 72) assist in biozonations of Jurassic platform, ramp and upper slope carbonates in the Mediterranean Tethys (Sartoni and Crescenti 1962; Jaffrezo 1980; Sartorio and Venturini 1988; Fig. 10.28A). These 'coenozones' are based on various bioevents (e.g. first occurrence and disappearance and total range of taxa, maximum frequency and assemblage patterns; see Sect. 10.3).The first planktonic foraminifera appeared in the Middle Jurassic (Pl. 69/12). Particularly common in thin sections of Jurassic platf o ~ mcarbonates are large lituolinid foraminifera characterized by complex inner structures (Septfontaine

465

1988). In contrast to lituolinid foraminifera without wall differentiation and internal partitions of the chambers, (Pl. 6918) which were common in open-marine environments, lituolinid foraminifera with complex inner structures were restricted to warm lagoonal environments. Widely distributed examples of these Lituolacea are Lituosepra (Early Jurassic), Orbitopsella (Early Jurassic), Haurania (Early and Middle Jurassic), MeyendorfSina (Middle Jurassic), Alveosepta (Late Jurassic, P1. 69/8), Kurnubia (Middle and Late Jurassic, P1. 691 2, 3, and Middle Jurassic to Early Cretaceous; PI. 691 1). Microforaminifera are linings of juvenile parts of foraminiferal tests corresponding to chitinous membranes, and often stained red by diagenetic impregnation of Fe-oxides (Stancliffe 1989; Misik and Sotak 1998). These very small fossils ( 1, 2, 3, 8) are excellent index fossils (Hottinger 1971, Septfontaine 1981) and form the basis for a biozonation of lagoonal platform carbonates. The plate displays some common taxa comprising Textulariina (-> 1-3, 7, 8), porcelaneous Miliolinina (-> 4, 6, 10) as well as lnvolutinina (-> 5,6). Pseudocyclamnzina lituus (Yokoyama). Lituolinid larger foraminifer with complex internal structures. Axial section. Test planspirally enrolled. Note thick honeycombed labyrinthic wall with alveoli and thick septa perforated by large openings. Species range: Middle Jurassic (Domerian) to Early Cretaceous (Valanginian).Late Jurassic (Tithonian):Ernstbrunn, Austria. Kurnuhia palastinensis Henson. Lituolinid foraminifera with complex intemal structures. Oblique section. Important criteria are the subepidermal network (arrow) and the central column (CC). Species range: Oxfordian to Tithonian, abundant in the Oxfordian. Late Jurassic (Kimmeridgian): Central Apennines, Italy. Kur-nubia palastinensis Henson. Transverse section. Diagnostic criteria of the endoskeleton are best shown in sections like this perpendicular to the coiling axis. Late Jurassic (Kimmeridgian): Western High Atlas Mountains, Morocco. Trocholinu alpina Leupold. Oblique axial sections of conical tests. Common in platform and reef carbonates. Early Tithonian: Sulzfluh Mountains, Graubiinden, Switzerland. Spirillinid foraminifer. The characteristic feature of the involutinid group Spirillilina, particularly common in Liassic deep shelf limestones (Blau 1987), are monocrystalline shells (Hohenegger and Piller 1977). Transverse section of the discoidal test. Late Jurassic (sponge-Tubiphytes reef, Tithonian): Altensteig 1 well, western Molasse Basin, southern Germany. Conicospirillinu basiliensis Moehler. Oblique section of the spirillinid foraminifera. Species range: Tithonian to Valanginian. Same locality as -> 4. Anzn~obaculitesCushman. Textulariina. Lituoiacean foraminifera without complex intemal structures. Longitudinal section. Free, elongated test. Early portion coiled, later rectilinear. Note coarsely agglutinated wall structure. Genus range: Mississippian to Holocene. Same locality as -> 5. Alveosepru Hottinger. Lituolinid foraminifer with complex intemal structures. Section slightly oblique to the coiling axis. Exoskeleton with subepidermal network lining the entire chamber including the septa (arrow). Genus range: Oxfordian to Kimmeridgian. Same locality as -> 3. Lcnticulina Lamarck. Rotaliina. Oblique section. Involute planispiral test. Wall calcareous. hyaline, finely perforate. Same locality as -> 5. Protopeneroplis striata Weynschenk. Involutinina. Test enrolled in about two rapidly enlarging and loosely coiled whorls. Wall calcareous lamellar. The species is common in Middle and early Late Jurassic carbonates deposited in shelf-margin and upper slope positions. Same locality as ->4. Frondicularia Defiance. Miliolina, Nodosariacea. Simple uniserial, elongated test consisting of broad, uniform chambers. Sutures are highly arched to angled at the midline of the test. Same locality as -> 5. Planktonic foraminifera: 'Protoglobigerinid', an informal name for probably the oldest planktonic foraminifera, are regionally abundant in Callovian and Oxfordian basinal carbonates (Riegraf 1987). Middle Jurassic: Unken, Austria. -> 8: Hussner 1985

Plate 69: Jurassic Foraminifera

467

46X

Cretaceous Larger Foraminifera

Plate 70 Cretaceous Larger Foraminifera: Orbitolinids Orbitolinids (Textulariina, Orbitolinacea) are large agglutinated foraminifera. They comprise important biostratigraphic markers and are used for biozonations, particularly for Barremian, Aptian, Albian and Cenomanian platforms and ramps. These zonations are based on taxon ranges, assemblage composition and the abundance of species. Identifying orbitolinids requires oriented thin sections. The tests consist of calcareous or non-calcareous particles cemented with a mineral cement (-> 3). The conical forms have uniserial stacks of low, saucershaped chambers following an early trochospiral stage. The chambers grow rapidly in diameter and are subdivided by septula on the periphery, often exhibiting a thin marginal zone of minute cellules, and a reticulate zone in which the radial chamberlets are further subdivided by vertical pillars (-> 8,9). Of diagnostic importance are the shape of the initial and subsequent embryonic chambers (-> 4,7, 13; see figures at the bottom of this page). Preservation: Tests of orbitolinid foraminifera were frequently transported as shown by the various orientations (see -> 15). A common case is downslope transport from subtidal shelf environments into deeper ramp or basinal settings. Cretaceous (Mishrif Formation, Cenomanian): Subsurface, Ras a1 Khaimah, United Arabian Emirates. Recognition and composition: Reworked or worn, finely agglutinated orbitolinid tests can be misinterpreted as micrite clasts if the microcrystalline calcite cement is more conspicuous than the fine-grained particles building the wall. Middle Cretaceous (Aptian): Subsurface, Saudi Arabia. Composition of the test: Agglutinated test composed of angular quartz grains (white) cemented by calcite. Albian: Bavarian Alps, Germany. Dic~gnosticcriteria: Taxonomic differentiation of orbitolinids requires sections showing the initial and embryonic chambers that changed in shape and size from the Albian to the Cenomanian. The axial section of the macrospheric embryonic stage of Ol-bitolina (Orbitolina) duranddelgai Schroeder. Orbitolina (Orbitolina) occurs from the Late Albian to Late Cenomanian. The sample is from the Late Albian of the Sierra de Aulet, Huesca Province, Spain. Orbitolinopsis caprtrnsis (de Castro). Axial section. Genus range: Barremian to Early Aptian. Early Barremian: Djebel Debar, Constantinois, northeastern Algeria. Palorbitolina lenticularis (Blumenbach). Axial section exhibiting the initial chamber. Compare this figure with -> 7 and note the difference in the shape of the initial chamber and the arrangement of the chambers following the initial chambers. The increase in the size of the initial chamber through time can be used for dating (Gusic 1981). Genus and species range: Barremian to Aptian. Early Aptian: Resita Zone, Apuseni Mountains, Romania. Macrospheric embryonic stage of Palor-hitolina lenticularis (Blumenbach). Axial section. Early Aptian: Bari, Puglia, Italy. Palaroilic~tyocotmsurabic~us(Henson). Axial section. Genus range: Valanginian to Bedoulian. Axial section. BarremianEarly Aptian: Resita Zone, Apuseni Mountains, Romania. Palu~odictyoconusarabicus (Henson). Transversal section. Late Barremian-Early Aptian: Grand Banks, Eastern Canadian Shelf (DSDP leg 43). 10 Palaeod~ctyoconusarablcus (Henson). Oblique section. Ap~ian:Subsurface, Ras a1 Khaimah, United Arabian Emirates. 11 Neoiraqia conlcxa Danilova. Axial section of the macrosphere. Genus range: Cenomanian. Early Cenomanian: Caserta, Campania, Italy. 12 Orbitolina (Mesorbirolinaj tcxana Roemer. Tangential axial section. Range of Mesor-bitolirza: Late Aptian to Early Cenomanian. Late Albian: Padurea Craiului. Apuseni Mountains, Romania. 13 Orbitollna (Mesorbitol~na)uperta Schroeder. Obl~que section of the embryonic macrospheric stage. Lowermost 01bltoll17u (Mesurhltolrilu) texann (Roemer) Axial and Cenoman~an:Montagne de Tauch, DCpartenlent Aude, transve~salbasal sections. France. 14 Orhi~olirza(Orbitoliiza)d~iranddelgaiSchroeder. Tangential section of the macrospheric stage exhibiting the embryonic chamber. Same locality as -> 4. 15 Sandy orhitolirzid limestone. Ramp environment. Foraminifera were reworked and eroded (compare -> 1 and 2). Late Aptian: Calizas del Busco, Barranco de las Casillas, Requena, Valencia, Spain. --->4?5, 9, 11 : Courtesy of R. Schrader (Frankfurt).

vu .__-.

Orbitoiina (Mesorbitolina)

Orbitolina (Orb~tolinaj

Left figure: Differences in the morphology of initial and ernOrbitolina (Con/corbitolina)

bryonic chambers of orbitolinid foraminifera. After ArnaudVanneau ( 1980).

Plate 70: Cretaceous Larger Foraminifera

469

Cretaceous Benthic Foraminifera

470

Plate 71 Cretaceous Platform Carbonates: Benthic Foraminifera Thin sections of many Cretaceous platform carbonates are rich in benthic foraminifera, allowing generic or specific identification. Benthic foraminifera are particularly useful for biostratigraphic zonations of Tethyan shallow-marine carbonates (Becker 1999). These biozones exhibit a general trend with regard to the superposition of the zones, but may include different parts of chronostratigraphic units, owing to different paleoenvironmental conditions and regional fluctuations of sea level and subsidence. Conical tests exhibiting chambers subdivided by many septulae and belonging to the textulariid family Cuneolinidae (superfamily Ataxophragmiacea) are index fossils in Early Cretaceous carbonates (-> 1-5, 8, 11). Vercorsella camposauri (Sartoni and Crescenti). Textulariina, Ataxophragmiacea. Transversal-oblique section. The chamber interior is subdivided by radial vertical partitions. Wall agglutinated with fine calcite cement. Vercorsella camposauri and Vercorsella scarsellae (-> 2 ) characterize an Early Aptian biozone. Genus range: Late Hauterivian to Early Aptian. Barremian-Early Aptian (Berdiga limestone): Kircaova south of Trabzon, northern Turkey. Vercorsella scarsellai (de Castro). Transverse section. Vercorsella characterizes the inner platform environment. Same locality as -> 1. Vercursell~ilaurentii (Sartoni and Crescenti). Longitudinal-tangential section. Same locality as -> 1. Vercorsella laurentii (Sartoni and Crescenti). Axial section. Same locality as -> 1. Sabaudia minuta (Hofker). Textulariina, Ataxophragmiacea. Subaxial longitudinal section. Wall agglutinated, imperforate. Small conical test. Trochospiral initial stage with inner microgranular and outer hyaline layer. The biserial chambers are subdivided by vertical partitions forming a network of chamberlets. Genus range: Late Hauterivian to Aptian. Late Aptian: Padurea Craiului, Apuseni Mountains, Romania. Dictyocurzus algerianus Cherchi and Schroeder. Textulariina, Orbitolinacea. Axial section. Conical test, dish-like charnbers with typical convex base. Late Aptian-Early Cenomanian: Gebel Maghara, Sinai, Egypt. Dic~oconusalgerianus Cherchi and Schroeder. Oblique section showing the vertical partitions of the marginal zone (arrows). Same locality as -> 6. Cuneolina ex gr. pavonia d'orbigny. Textulariina, Ataxophragmiacea. Conical test. As shown in this oblique axial section the broad and low chambers are subdivided into chamberlets. Cuneolinid foraminifera are abundant in shallow inner platform deposits associated with miliolinid foraminifera. Genus range: Valanginian to Coniacian. Same locality as -->6. Reophax giganteus Amaud. Textulariina, Hormosinacea. Longitudinal section. Free, elongated test with few chamberb. The coarsely agglutinated wall consists of ooids (0)and foraminifera1 debris (FD). The genus is known from the Middle Ordovician to the Holocene. Early Cretaceous: Subsurface, Hohenlinden-1 well, Molasse zone, Bavaria, Germany. Chuffatella decipiens Schlumberger. Textulariina, Loftusiacea. Transversal equatorial section. Planispiral, enrolled test. The wall is differentiated into a peripheral network (top right). The endoskeleton exhibits thick septa pierced by pores. Genus range: Late Jurassic (Oxfordian) to Late Cretaceous (Cenomanian). Common in the Barremian to Aptian time interval. Early Cretaceous: Spain. Dicycliiza Munier-Chalmas. Textulariina, Ataxophragmiacea. Axial section. The interior of the discoidal test is subdivided by numerous thin radial partitions, perpendicular to the outer wall and aligned from chamber to chamber. The maximum spreading of the Dicyclina microfacies took place during the Coniacian and the Turonian. Senonian: Subsusface, Ras a1 Khaimah, United Arabian Emirates. 12 Rcophax giganteus Amaud. Transverse sections. Walls are coarsely agglutinated. Early Cretaceous: Subsurface, Hofolding-1 well, southern Bavaria, Germany. 13 Rhapydionina liburnica (Stache). Miliolina, Milioliacea. Longitudinal section. Genus range: Cenomanian to Maastrichtian. Senonian: Mesarlek, southern Turkey. 14 Rhapydionina liburnica (Stache). This species often dominated an oligotyp~c assemblage of upper Late Cretaceous inner platform environments characterized by restricted water circulation. Axial section. Same locality as -> 13. a

Left figure: Schematic sections of Dicyclina. Center: planispiral test. A: Axial section passing through the initial chamber. B: Subaxial section exhibiting several peripheral chambers and radial partitions in the central part of the shell. After Neumann (1967). ->I-4: Kirmaci et al. 1996; 5: Courtesy of I. Bucur (Cluj-Napoca); 6-8: Kuss and Schlagintweit 1988

Plate 7 1: C r e t a c e o u s Benthic Foraminifera

47 1

Late Cretaceous Benthic Foraminifera

472

Plate 72 Late Cretaceous Benthic Foraminifera Benthic foraminifera allow the biostratigraphic zonation as well as the facies differentiation of platforms and ramps. Middle and Late Cretaceous miliolinid alveolinids (e.g. Praealveolina, Ovalveolina, Cisalveolina, -> 2 ) are abundant in inner parts of carbonate platforms (De Castro 1980,1988). The large discoidal or lenticular tests of the orbitoidacean foraminifera (-> 5-10) are characterized by radially hyaline and perforated tests, cyclically arranged equatorial chambers and more or less regular lateral chambers arranged in annular cycles (-> 7). Orbitoidacean foraminifera are abundant in Campanian and Maastrichtian outer platform and upper slope carbonates. The Plate exhibits agglutinated textulariid, miliolinid and rotaliinid foraminifera.

W

2

3

4

1 Nezzazata Omara. The systematic position of the genus is doubtful. Oblique section of the trochospiral tesl. Calcitic wall. Genus range: Albian to Turonian. The maximum diversification and spreading of this genus and morphologically related foraminifera occurred in the Cenomanian. The sample is from Cenomanian inner platform deposits in the subsurface of Ras a1 Khaimah, United Arabian Emirates. Left figure: Exterior view of the trochospiral plano-convex test (after Loeblich and Tappan 1964).

Cisalveolina fallax Reichel. Miliolina, Alveolinidae. Right: Oblique equatorial section of a megalospheric test. Left: Tangential section. Note the numerous chamberlets produced by septules. Genus range: Cenomanian. The sample is from the Cenomanian Mishrif Formation: Subsurface, Ras a1 Khaimah, United Arabian Emirates. Agglutinated foraminifera. Chtysalidit~ad'orbigny (bottom, axial section); associated with orbitolinids (top). Note the large initial chamber (arrow) of the conical triserial test and the low and strongly overlapping chambers. Thick, finely agglutinated wall. Time range of Clzrysalidina: Cenomanian-Turonian. Same locality as -> 2. Curzeolina d'orbigny. Textulariina, Ataxophragmiacea. Oblique section. Common in inner shelf platform settings. Genus range: Valanginian to Santonian. Late Cretaceous: Subsurface, Ras a1 Khaimah, United Arabian Emirates.

Siderolites Lamarck. Rotaliina, Kotaliacea. Note the hyaline wall structure and the distinct spines (arrow) arising near the initial chamber in the plane of coiling. White grains are quartz. Common in upper slope environments. Maastrichtian: Subsurface, Saudi Arabia. Lepidorhitoides Silvestri, embedded in an echinoderm packstone. Rotaliina, Orbitoidacea. Oblique section of the flattened, lenticular test. This is an example of poorly preserved tests that are rather common but that can be still determined at higher taxonomic levels, allowing a rough age assignment. Genus range: Campanian to Maastrichtian. Late Crrtaceous: Northern Tunisia. The sample is a mosaic stone, used for the decoration of Punian houses in ancient Carthage. Microfacies and age indicates a source of the material within a distance of at least fifty kilometers. Orbitoides dlOrbigny. Rotaliina, Orbitoidacea. Axial section. Taxonomic criteria of these larger foraminifera are the early ontogenetic stages reflected by the initial chamber and the subsequently fom~edchambers. Siderolites calcitrapoides. Late Maastrichtian Note the differentiation of a median equatorial layer of chambers (El open marine shelf margin facies characterized by an assernblage of larger foraminifera. dasyand lateral chambers (L). Genus range: Latest Santonian to Maastrichclad algae and rudist debris. Salento Peni[lsula, tian. Orbitoidacean foraminifera are common in upper slope en\'IronPuglia, Southern Italy. Scale is 1 mrn. ments. Maastrichtian: Wietersdorf, Carinthia, Austria. 8 Orbitoides. Vertical section. Diagnostic criteria are the arrangemenl anti size of the equatorial chambers and the distribution of the radiating calcite pillars (P) within the lateral part of the test. The pillars give rise to granules on the outer surface. Same locality as -> 7. 9 Orbitoides. Axial section of the megalospheric iuvenarium. The arrow points to the diagnostically important trilocular embryonic chambers, surrounded by a thick perforated wall. Note the equatorial chambers with curved walls and the smaller lateral chambers. Same locality as -> 7. Axial section of Orhitoides displaying the ini- 10 Orbitoides. Vertical section. Note the embryonic chambers and the smaller lateral chambers. Same locality as -> 7. tial chamber and cyclically arranged equatorial chambers, surrounded by rows of lateral chambers. -> 5 and figure on this page: Parente 1997 '

Plate 72: Late Cretaceous Benthic Foraminifera

473

Cretaceous and Tertiary Planktonic Foraminifera

474

Plate 73 Late Cretaceous and Tertiary Planktonic Foraminifera Planktonic foraminifera are Protista that inhabit the upper zones of the pelagic realms of the oceans. Known since the Middle Jurassic (Triassic?), they are rock-building constituents of Cretaceous and Cenozoic deepmarine limestones, important biostratigraphic markers since the Early Cretaceous, and proxies for paleoceanographic, paleoclimatologic and paleobathymetric reconstructions. About 47 % of the modem sea floor is covered by Globigerina ooze. Planktonic foraminifera are characterized by trochospirally coiled tests with inflated, perforated chambers, sometimes with keeled outer margins (e.g. Globotruncanidae and Globorotaliidae). The wall consists of optically radial and bilarnellar low-magnesian calcite. The observation of wall structure and surface ornamentation in thin sections is not practicable in all cases, but is currently refined by the analysis of oriented sections across isolated tests. Widely used in the correlation of Late Cretaceous open-marine carbonates are species of Globotruncana (-> 1,2,5,8), in Cenozoic carbonates Gioborotalia,Globigerina (-> 9 ) and Orbulina (-> 10). Globotruncanais differentiated according to the number of keels that can be recognized in axial sections (singlekeeled -> 8; double-keeled -> 7). Axial and tangential sections of different planktonic foraminifera, including Whiteinella with trochospirally coiled tests and globular chambers. Late Cretaceous (Seewer limestone, Turonian): Glacial boulder, near Bern, Switzerland. The occurrence of planktonic foraminifera (double-keeled Globotruncana - G, Heterohelix - H) associated with abundant 'calcispheres' (Pithonella, see P1.66/4,5) indicates an open-marine deep-shelf depositional environment. Turonian (Seewer limestone): Seewen, Switzerland. Planktonic foraminiferal packstone predominantly with Praeglobotruncana. Late Cretaceous: Siliana near Maktaris, Northern Tunisia. Planktonic foraminiferal packstone with Morozovella McGowran. Genus range: Paleocene to Middle Eocene. Paleogene: Central Apennines, Italy. Globotruncana Cushman (G, axial section) and Heterohelix Ehrenberg (H). High-trochospiral globotruncanids are common in Maastrichtian open-marine pelagic limestones. Genus range of Globotruncana: Santonian to Late Maastrichtian. Single-keeled (arrows) globotruncanids as in this sample are typical of a Carnpanian or Maastrichtian age. Heterohrlis: Late Aptian to Paleocene. Maastrichtian: Delphi, Greece. Ilcter-ohelix Ehrenberg. Note early planispiral and later biserial growth of the high trochospiral test. The maximum development and spreading of large heterohelicid foraminifera occurred in the Maastrichtian. Late Cretaceous: Northern Tunisia. The sample represents rock material used for Roman mosaics in Carthage. Marginotruncata Hofker. Double-keeled form (arrows). Generic range: Turonian to Santonian. Spreading of doublekeeled planktic foraminifera started in the Turonian and Coniacian. Late Cretaceous: Northern Tunisia. Globotruncana stuartiformis Dalbiez and Globotruncana ex gr. area (Cushman) - top right. Axial sections of singlekeeled forms. Note the difference between the infillings of the tests and the dense pelagic carbonate mud. Arrows point tp the diagnostically important keels. Early Maastrichtian: Delphi, Greece. Globigerinid wackestone with Globigerinoides. Coiled tests are cut in all planes. Note the globular chambers and the coarsely perforated calcitic walls. Genus range: Eocene to Holocene. Miocene: Southern Turkey. Orbulirza (0)-Globigerina (G) packstone. Spherical test. Wall calcareous, with numerous smaller pores interspaced among a few larger pores. Orhulina is common in Middle and Late Miocene deep shelf and basinal limestones. SMF 3-FOR. . Miocene: Camposauro, southern Apennines, Italy. Typical planktonic foraminifera. After Ziegler (1983). Globotruncana

Globotruncana

Exterior views and axial sections of Globotruncana. Arrows point to keels. After Bignot (1985).

Plate 73: Cretaceous a n d Tertiary Planktonic Foraminifera

375

476

Tertiary Foraminifera

Plate 74 Tertiary Nummulitid and Alveolinid Limestones Foraminifera are represented in thin sections of Tertiary limestones by benthic and planktonic forms (Pl. 7419, 10). Of particular interest are benthic larger foraminifera, including the Nummulitacea (-> 2-5; P1.75/1,2,6-8; hyaline calcareous rotaliinids, common in shallow inner platform settings and sometimes associated with reefs) and the Alveolinacea (-> 1, 9; P1. 7.513-5; porcelaneous calcareous miliolinids, common in shallow lagoonal platform settings). These groups have millimeter- to centimeter-sized tests with complex endoskeletal structures which must be studied in oriented thin sections. Axial sections show whorls, the character and dimensions of the chambers and the distribution of pillars. Equatorial sections display growth character of whorls, the number and shape of septa and character of initial chambers. Living and extinct taxa evolved in tropical or subtropical habitats. The taxonomic differentiation needs sections showing the size and shape of the test, the morphology of the initial and embryonal chambers, the character of the whorls, shape and number of septa as well as dimensional features. The lenticular and discoidal hyaline Nummulitidae occur in rock-building abundance. A famous example is the carbonate rock used in building the great Cheops pyramide in ancient Egypt. Nummulitids and alveolinids are index fossils for the biozonation of Early Tertiary shallow inner platform and shelf edge carbonates. Other stratigraphically significant groups are the rotaliinids include the Lepidocyclinidae (-> 7-8, Middle Eocene to Early Miocene) and Miogypsinidae (-> 6, Middle Oligocene to Early Miocene). Alveolina d'orbigny. The Alveolinidae, known from the Early Cretaceous up to today, have imperforate calcareous tests of porcelaneous appearance. Coiling is fusiform to ovate planispiral. Chambers are divided by septulae into numerous chamberlets arranged in one or more rows. Genus range: Late Paleocene to Late Eocene. Early Tertiary (Eocene): Slovenia. Nunznzulites Lamarck. Nummulitidae are characterized by radial hyaline and perforate tests with septa. Coiling is biconvex planispiral. Chambers may be Alveolina simple or differentiated into median and lateral layers. The sample is a foraminiferal packstone consisting predominantly of Nummulites. Dense packing, poor sorting and the minor amount of micrite indicate postmortem allochthonous deposition by high energy events. The thin section shows axial sections (A), equatorial sections (E) and random sections. Genus range: Paleocene to Holocene, abundant in Eocene. The maximum distribution of nummulitid facies is in the Middle Eocene. SMF 10. Early Tertiary (Eocene): Southern Bavaria, Germany. Assilina d'Orbigny. Nummulitacea. Large evolute tests with rapidly enlarging whorls and numerous chambers per whorl. Genus range: Paleocene to Holocene, common in Eocene. Early Tertiary (Eocene): Gorica, Slovenia. Discncyclitza Giimbel. Nummulitacea. Tests are radial hyaline and perforate. A median layer of chambers is differentiated from lateral chambers. Rad~ating pillars give rise to granules on the outer surface. Genus range: Late Paleocene to Late Eocene. Example: Discocyclina (D, axial section) associated with Nummulites (N). Early Tertiary (Eocene): Southern Bavaria, Germany. O p e m d i m ~dlOrbigny. Nummulitacea. Planispiral flattened test. Wall calcareous, lamellar, finely perforate. Note imbrication structure indicating current transport. Genus range: Oligocene to Holocene. Miocene: Ekisce, southern Turkey. Miogypsitzcz Sacco. Rotaliina, Rotaliacea. Transverse sections. The Miogypsinidae are excellent index fossils for the Middle Oligocene to Early Miocene time i n t e ~ a l(Abdelghany and Piller 1999). The genus is tolerant of terrigenous influx. It occurs both in lagoon and shallow subtidal environments of open platform. The sample is a foraminifera1 packstone exhibiting an accumulation of foraminifera, bryozoan debris (bottom) and red algal fragments (black). Oligocene: Southern Turkey. Lepidocvclitm (Eulepidina) ephippiniiics Jones and Chapman. Rotaliina, Asteriginacea, Lepidocyclinidae. Vertical section of a macrosphere. Note central initial chambers and densely spaced median chambers. The shape of the median chambers is the diagnostic criterion. Lepidocyclinidae are common in lagoons and shallow subtidal environments. Genus range: Middle Eocene to Early Miocene. Oligocene: Argyrotopos, Epirus, western Greece. Lepidocylina (Eulepidina) eodilarata Douvill6. Vertical section of a microsphere (bottom). Same locality as -> 7. Borelis nzelo (Fichtel and Moll). Tangential section. Miliolina, Alveolinacea. Small spherical test. Note numerous septula aligned from chamber to chamber. Genus range: Eocene to Holocene. Miocene: Kasaba, southern Turkey. Encrusting foraminifera: Miniacina Galloway, arrows (Rotaliina, Acervulinidae) intergrown with coralline red algae (black). Rasbeny-like clusters of globular chambers. Acervulinid foraminifers contribute to the formation of composite rhodoids and reef carbonates. Genus range: Eocene to Holocene. Paleocene: Slovakia. -> 5 , 6.9: Courtesy of M. Link (Erlangen); 7, 8: Bellas et al. 1995. Figure on this page from Bignot (1985)

Plate 74: Tertiary Foraminifera

Significance of Foraminifera

settings (Pl. 73). Although the taxonomic study of Cretaceous and Tertiary planktonic foraminifera is based on isolated specimens from disintegrated samples (Toumarkine and Luterbacher 1985), thin-section analysis is of great importance, both for the biozonation of basinal and slope carbonates and for the interpretation of the environmental constraints of oceanic water masses. Clues for determining planktonic foraminifera in thin sections can be found in many papers (Caron 1985; Nocchi et al. 1988; Sliter 1989; Wemli et al. 1997; Van Konijnenburg et al. 1998).

zoic shelf and ramp carbonates from North Africa to India, and the western Pacific. Productive nummulitid buildups are known from Tunisia and Libya. The taxonomic distributional patterns of larger and smaller foraminifera assist in recognizing paleoenvironrnents and settings. But because the taxonomic composition of Early Tertiary foraminiferal faunas differs considerably from living assemblages, paleoecologic interpretations based only on direct comparisons with recent distributional patterns are somewhat hazardous (Hohenegger 1994). Functional morphology produces better results, as shown by the subdivision of different Cenozoic: Shallow-marine carbonates formed by parts of carbonate ramps using the distribution of larger foraminifera are widely distributed in Early Ter- alveolinids (Gietl 1998). The shape and thickness of tiary sequences. Nummulitid buildups form shoals and the tests as well as distribution trends of modem larger banks in ramp and platform settings. Their biofabrics foraminifera provide a basis for a model (Hallock and are proxies for hydrodynamic processes (Aigner 1985) Glenn 1986) allowing further differentiation of the Stanand show potential trends in reservoir quality within dard Facies Zone model (Sect. 14.2). The model was shallow marine shelf sequences (Racey 1994). Accu- tested for Early Miocene carbonates but can possibly mulations of larger foraminifera are common in Ceno- be applied also to Early Tertiary carbonates.

Plate 75 Rock-Building Early Tertiary Benthic Foraminifera This plate displays thin sections of typical nummulitid and alveolinid limestones. Allochthonous concentrations of rotaliinid and miliolinid larger foraminifera are of rock-building importance. These accumulations are caused by high-energy transport (-> 7,8) or winnowing of finer material forming lag deposits (-> 5). Parautochthonous concentrations are the result of high production rates and in-place sedimentation. Note the different wall structures of agglutinated Textulariina (-> 9), hyaline calcareous Rotaliina (-> 1, 2) and porcelaneous calcareous Miliolina (-> 3-5). 1 Axial sections of Nummulites Lamarck (N) and Discocyclina (D). Poorly sorted foraminifera1 packstone. Outer shelf environment. Early Tertiary (Eocene): Southern Bavaria, Germany. 2 Nummulites. Note the initial chamber (arrow) and the radial fibrous structure of the thick hyaline wall. Early Tertiary: Southern Bavaria, Germany. 3 Alveolina dlOrbigny. Axial section. Note the different wall structure (porcelaneous calcareous) as compared with nummulitid foraminifera (-> 1). The foraminifera are embedded within a calcareous sandstone. Eocene (Lutetian): Southern Bavaria. 4 Alveolina. Equatorial section. Early Tertiary: Divaca, Slovenia. 5 Alveolinid grainstone. The foraminifera association consists predominantly of Alveolina lepidula and miliolid and textulariid foraminifera. Near-coastal sand sheet deposited at the base of a transgressive system originating from reworking of beach wedges during incipient drowning. Early Tertiary (Paleocene, Ilerdian): West of Tremp, northeastern Spain. 6 Sandy glauconite-bearing nummulitid wackestone. Nummulitid tests occur within a fine-grained matrix consisting of angular quartz (white) and micrite clasts. Both large and small tests are well-preserved. Encrustations are absent. These features indicate short transport and rapid embedding within the calcareous sand. SMF 18-FOR.Eocene: Southern Bavaria, Germany. 7 Discocyclina (D)- Amphestigina ( A ) packstone. Predominantly axial sections. The absence of orientation of the flat discocyclinid tests indicates reworking. Larger black constituents are worn coralline algal thalli (CA). Early Tertiary: Southern Bavaria, Germany. 8 Sandy glauconite-bearing Assilina packstone. Note borings in some tests (arrows). Size ranges of tests give some information on the stratigraphic age. The large size in this sample points to a Middle Eocene age. Early Tertiary (Adelholzen beds, Middle Eocene): Agathazell, southern Bavaria, Germany. 9 Encrusting foraminifera: Haddonia heissigi Hagn ( H ) associated with miliolids (M) and textulariids (T). Haddonia and related agglutinated foraminifera are important members of the constructor and binder guilds of Early Tertiary reefs (Darga 1990). Genus range: Late Cretaceous to Eocene. Eocene: Coral patch reef Eisenrichterstein near Reichenhall, southern Bavaria, Germany. -> 6-8: Courtesy of H. Hagn (Miinchen)

Plate 75: Tertiary Foraminifera

479

480

Larger Foraminifera in Limestones

Significance of foraminifera in microfacies analysis ate production of larger foraminifera in the Cretaceous Biozonations: Benthic foraminifera, particularly and Tertiary (Hohenegger 1999). larger foraminifera, are reliable tools in the stratigraphic Reef-adapted encrusting foraminifera are known subdivision and correlation of Late Paleozoic, Meso- from Permian, Jurassic and Early Cretaceous reef limezoic and Tertiary shelf carbonates. Zonations have been stones. Monospecific biostromes built by arenaceous established both for low and high latitude deposits. foraminifera, and surrounded by bioclastic grain- and Biozones of different latitudes have different taxonomic wackestones, occur in the Barremian of Haute Savoie, spectra. Planktonic foraminifera are important in the France. These up to one meter high buildups were interregional correlation of Cretaceous and Cenozoic formed in shallow water on a carbonate platform strata (Bolli et al. 1985). A useful summary of the tim- (Schulte et al. 1993). Other foraminiferal reefs have ing of significant bioevents and changes in platform been reported from the Eocene (Solenomeris reefs: and open-marine pelagic Mesozoic and Cenozoic bio- Plaziat and Perrin 1992) and the Miocene (Jell et al. fazies types characterized by the appearance,disappear- 1965; Ghose 1977; Hallock 1985; Hallock and Glenn ance or abundance of thin-section foraminifera was 1986). given by Sartorio and Venturini (1988). Larger foraminifera have been common constituents of shallow-marine shelf carbonates formed in w a n Paleoenvironnzent: Abundance, diversity and com- water environments since the Late Paleozoic. Extenposition of benthic foraminifera differ in modem sub- sive Cretaceous and Cenozoic shelf carbonates were tropical, warm temperate and cool temperate shelf seas. produced by large, benthic foraminifera. Larger foraComposition patterns of shelf sediments (e.g. 'foramol minifera (e.g. Amphistegina and Calcarina) contribute facies') as well as taxonomic differences in foramin- significantly to the formation of sand-sized carbonate iferal assemblages provide guidelines for distinguish- sediments in reefs and other shallow, carbonate enviing ancient shelf and ramp carbonates deposited in ronments due to the high turnover rates of the populawarm or cold waters and in low or high paleolatitudes tions (Hallock 1981). (see Sect. 12.2). Frequency distribution, species association and diversity of larger foraminifera are strongly Microfacies inzplications of rock-building abunduncc correlated with environmental factors changing along of larger foraminifera: Rock-building concentrations depth gradients. The resulting patterns can be success- of foraminifera (packstones, grainstones) are caused fully used in assessing paleodepths, if the coenocline by * hydrodyamic processes: wave action hindering the concept is applied (Hohenegger 2000). deposition of fmes between the tests or winnowing fines Llepositional settzng andfacies zones: The distribu- and smaller tests; current transport accumulating tests tional patterns of benthic foraminiferal associations as- in protected or deeper environments; storms inducing sist in recognizing and subdividing depositional set- deposition near beaches or in shoals on the shelf; turtings and environments of ancient shelves, if depth bidity currents leading to deposition on slopes or in transport from shelf to basinal environments is consid- basins, high production rates, e.g. in sea grass or sea weed ered (Hohenegger and Yordanova 200 1). Important papers are included in the list of Box 10.4. areas, associated with rapid deposition of epiphytic foraFig. 10.28 gives a very generalized idea of the occur- minifera forming washover deposits or in-place depos~ts rence and abundance of common foraminiferal groups (Davaud and Septfontaine 1995), and bioturbation, e.g. by burrowing echinoids. in Late Jurassic and Eocene carbonate environments. See Sartorio and Venturini (1988) for other Mesozoic In addition, the possibility of 'diagenetic packstonc' and Tertiary distribution patterns of thin-section fosor 'condensed grainstone' fabrics must be considered. sils. Carbonate production: Many tropical beaches are composed almost entirely of tests from shallow-water benthic foraminifera. Benthic foraminifera contribute to the formation of carbonate grains (e.g. oncoids, macroids), reefs and shelf carbonates. The proportion of modem benthic foraminifera is approximately 5% of the global carbonate reef budget (Langer et al. 1997). This is low as compared with the high calcium carbon-

Biofabric analysis of foraminiferal accumulations allows the hydrodynamic and sedimentologic history of foraminiferal limestones to be reconstructed (Aigner 1983,1985; Fig. 5.3). Important criteria for the description of biofabrics are packing, sorting and size of foraminiferal tests, imbrication or bedding structures, and the amount of carbonate mud preserved in interparticle voids. Worn tests can indicate continued transport, as-

48 1

Distribution Patterns of Foraminfera

foraminifera

Large lituolinids with complex inner structures Scale is 500 prn

.:::. ................... . .. .. . ... -. . . . . ... . ..... .. .. .. .. ..... .. .. .. .. .. .. Inner shallow platform

Late Jurassic . . .... .. .. .. .. .. . .

Miliolid

Alveolinids

Discocyclina

Nummulitids

Encrusting foraminifera

Fig. 10.28. Generalized patterns of the distribution of common foraminifera in different sedimentary environments. A: Late Jurassic. Protected muddy inner platform sediments yield many miliolid foraminifera. Agglutinated larger foraminifera, particularly lituolids with complex inner structures (e.g. Alveosepta, Pseudocyclamnzina) and Kurnubia were common in energetically different parts of the inner platform. Trocholinid foraminifera were abundant near or within platform-margin buildups (e.g. reefs formed by corals, ellipsactiniids and many encrusters). Upper slope environments are characterized by hyaline foraminifera, such as Conicospirillina or Protopeneroplis. Planktonic foraminifera appear in the late Middle Jurassic (this picture) and may be found also in Late Jurassic pelagic deep-water limestones, which are otherwise typified by radiolarians and other planktonic niicrofossils (pelagic crinoids and bivalves). B: Early and Middle Eocene. Shallow inner platform areas were inhibited by low-diversity small miliolinids as well as large alveolinids and discocyclinids. Thick-shelled nummulitids lived in shallow waters both in inner and outer platform or ramp settings. Reefs formed by corals and corallinacean red algae contain agglutinated encrusting foraminifera. Agglutinated foraminifera are also common in deeper platform environments and may occur together with planktonic foraminifera. Planktonic globigerinids and globorotaliids contributed to the formation of basinal carbonates.

Radiolaria in Thin Sections

sociated with reworking and redeposition (see P1. 741 6, P1. 118/2). Differences between the infill of worn foraminiferal sediment and the embedding matrix as well as rotated geopetals are criteria in assessing transport processes. Processes leading to the formation of Early Tertiary grain-, pack- and wackestones with nummulitid foraminifera can be derived from the abundance and proportions of large and small tests, their orientation and the amount of carbonate mud occurring together with the foraminifera. Large and small tests reflect sexual and asexual reproduction phases of the life cycle of the foraminifera. Assuming that within natural populations small foraminifera (A-form, with large initial chambers, megalospheric stage) dominate over large tests (B-form, with small initial chamber, microspheric phase), four assemblages can be differentiated that describe the autochthony or redeposition of the foraminiferal tests:

and their classification. - Vols. 1 and 2,970 pp., 847 Pls., New York (Van Nostrand Reinhold) Murray, J.W. (1991): Ecology and paleontology of benthic foraminifera. - 397 pp., London (Longman) Neumam, M. (1967): Manuel de micropaltontologie des forarniniferes(systkmatique-stratigraphic). - 297 pp., Paris (Gauthier-Villas) Further reading: K111. Relevant papers dealing with foraminifera studied in thin sections of Devonian to Tertiary limestones are listed in Box 10.4.

10.2.2.2 Radiolaria

Radiolarians are single-celled marine planktonic protozoans that secrete an amorphous (opaline) silica skeleton composed of a number of architectural elements (radial spicules, internal bars, external spines) that are joined together to form very regular and symmetrical lattices. The shell has a size of usually less than 2 mm and commonly between 100 and 250 pm across. The Relatively undisturbed assemblages: A/B ratio of the unicellular body is divided by a membrane into an insame species 10: 1 or more; matrix-support common, ternal (intracapsular) part (central capsule containing wacke- and mudstones; back-bank environment, the endoplasm and the nucleus) and the surrounding Parautochthonous assemblages: A/B average 7: 1, external (extracapsular) part containing the peripheral poor sorting, packstones; most fines are removed by cytoplasma. Radiolarians may be solitary or colonial. in-situ winnowing caused by wave action; abundant Morphology and classification: The shell morpholin bank facies, ogy is highly variable but typically corresponds to a Residual assemblages: Layers enriched with B-forms but A-forms still commonly present; dominance of hollow sphere or vase containing one or more bars imbricated B-forms suggests selective removal of across the interior. Some forms consist only of simple smaller A-forms and enriching of B-forms, creating tetraradiate or multiradiate branching needles. Radiolaria are a subclass of the class Actinopoda that a residual lag, Allochthonous assemblages: Composed of almost belong to the subphylum Sarcodina and the phylum Proonly A-forms, indicating sorting and selective trans- tista. Modem radiolarians are classified using features of both the skeleton and the soft parts. Separate classiport. fications have been established for Paleozoic, Mesozoic and Cenozoic radiolarians. Recent radiolarians Basics: Foraminifera Benthos '86, 32me Symposium International sur les Foram- comprise two major groups: (1) the polycystines, with ~niferesBenthiques (1988). - Revue de PalCobiologie, solid skeletal elements of opaline silica, and (2) the Volume special, 2, two volumes, 1005 pp., Genkve. phaeodarians with hollow siliceous skeletal elements Bolli, H.M., Saunders, J.B., Perch-Nielsen, K. (1985): Plankton stratigraphy. - 1032 pp., Cambridge (University Press) connected by organic material, which are rapidly disHaq, B.U., Boersma, A. (1998): Introduction to marine mi- solved in seawater, and consequently rarely preserved cropaleontology. 2nd edition. - 376 pp., Amsterdam in the sediments. (Elsevier) The polycystines are subdivided into (1) the basiHemleben, C., Spindler, M.,Anderson, O.R. (1989): Modem cally spherical-shaped Spumellaria, and (2) the basiplanktonic foraminifera. - 363 pp., New York (Springer) Jones, R.W. (1995): Micropaleontology in petroleum explo- cally conical-shaped Nassellaria (Fig. 10.29). Some major groups of extinct radiolarians differ substantially ration. - 432 pp, New York (Clarendon Press) Lee, J.L., Anderson, O.R. (eds., 1991): Biology of foramin- from Spumellaria and Nassellaria and are therefore conifera, 368 pp., Harcourt (Acad. Press) sidered as separate taxonomic units. Spumellarians are Loeblich, A.R.Jr., Tappan, H. (1964): Protista 2. Sarcodina characterized by a pronounced radial symmetry and chiefly 'Thecamoebians' and Foraminiferida. - Treatise on Invertebrate Paleontology, C. - 2 volumes, 900 pp., single or multiple concentric shells connected by radial bars. The skeletons have various shapes ranging Lawrence (Geological Society of America) Loeblich, A.R.Jr., Tappan, H. (1988): Foraminifera1 genera from spherical to ellipsoidal to discoidal. Nassellarian

Diagenesis of Radiolarians

483

Fig. 10.29. Morphology of spumellarian (A, B) and nassellarian (C-F) radiolarians. A - Archaeodictyomitra sixi Yang (Tithonian: Longing Gap,Antarctic Peninsula; height 200 pm), B - Mirifusus minor Baumgartner (Beniasian: Jebel Buwaydah, Oman Mountains; height 500 pm), C - Higumasrra sp. (same locality as A; maximum diameter 500 pn),D - Triactoma kellumi Pessagno and Yang (Tithonian: Southern Alps, Italy; diameter of cortical shell 200 pm), E - Acastea diaphorogona (Foreman) (same locality as B; diameter of cortical shell 130 pm), F - Leugeo hexacubica (Baumgartner) (Callovian: Southem Alps, Italy; pyritic specimen; diameter 175 pm). Courtesy of W. Kiessling (Berlin).

shapes derive from geometrically simple ringlike spicules from which latticed covers are added to form chambers. Methods: Radiolaria are usually studied by separation techniques, but also in thin sections. The fossils are investigated under the light microscope and in SEM. Cathodoluminescence microscopy enhances thin-section criteria. Radiolaria in thin sections: Radiolarians are common to abundant in thin sections of fine-grained openmarine pelagic limestones and radiolarites. Sections through spherical and ellipsoidal tests of spumellarians result in circular figures of different sizes (Pl. 76/1). Circular figures can also be cross sections of nassellarians. Differentiating these two groups in thin sections is in most cases not possible apart from rare exceptions (PI. 7614). Calcitized radiolarian tests exhibit some similarity with calcispheres (Sect. 10.2.1.9), but can be differentiated by a toothed appearance of the peripheral zone of the shell (Pl. 76/2). Unlike from radiolarian tests, the sections of calcispheres commonly show defined calcareous walls. Sections of calpionellids are considerably smaller than those of radiolarians (Pl. 76/8). Biology and ecology: Radiolarians are a part of the zooplankton and capture food from the water column. They consume various zooplankton and phytoplankton as well as bacteria and organic detritus. Some polycystine radiolarians host photosymbiotic dinoflagellate symbionts within their cells. Modem radiolarians are widely distributed in the oceans and occur in the photic surface zone of the ocean as well as in depths of hundreds of meters down to water depths of 4000 m and more. About the same number of modem radiolarian

species occur in tropical and subtropical surface waters and in deeper waters (> 200 m). Fewer species live in high latitudes. Homogeneity in radiolarian assemblages parallel to the latitudes, and heterogeneity across the latitudes indicate that water temperature influences the distributional patterns. Variations in the composition of assemblages depend on the difference of physical, chemical and biological parameters within water masses, e.g. oceanic currents. The composition of radiolarian assemblages and their distributional patterns, therefore, are excellent proxies for paleoclimatic and paleooceanographic interpretations of Meso- and Cenozoic oceans. Distribution: First records are known from the Cambrian. By the Silurian deep-water forms are believed to have evolved. All Early Paleozoic radiolarians are spumellarians or belong to extinct subgroups. Mesozoic and Cenozoic assemblages are characterized by various groups of spumellarians and nassellarians. A rapid diversification took place at the end of the Jurassic. Warm-water faunas have existed since the Cambrian. Cold-water assemblages appear in the Oligocene. Diagenesis and preservation: The fossil radiolarian record is strongly controlled by diagenetic factors. Dissolution of radiolarian tests takes place in the water column, and on and within the upper centimeters of the sea bottom. It depends on the degree of silica undersaturation of pore waters, the intensity of bioturbation and the accumulation rate. High sedimentation rates favor good preservation. The transformation of siliceous muds into siliceous rocks, connected with the maturation of the sediments corresponds to a sequence starting with opal A, followed by opal-CT (porcelanite) and ending with chalcedony or cryptocrystalline quartz (chert). Mesozoic

Radiolarians and Sedimentation

radiolarians consist exclusively of chalcedony or microquartz. The mineralogical composition seems to depend on the time involved in the long-term transformation processes, and is influenced by the lithology of the radiolarian-bearing sediments. Burial transformation of radiolarians in limestones is said to be much faster than in argillaceous sediments. In cherts radiolarian tests are commonly better preserved than in carbonate rocks, but exhibit a wide spectrum in regard to the preservation of morphological structures. This spectrum can be used to estimate recrystallization,corrosion and metasomatic alterations (Kiessling 1996). The preservation of radiolarian tests in limestones is generally poor as compared with radiolarians in cherts or radiolarites, and in concretions. The siliceous radiolarian tests are often replaced by calcite, pyrite or other ore minerals. Calcitization is common in limestones, but also occurs in radiolarites. It leads to poor preservation, which

is evident both in SEM studies of extracted specimens and in thin sections. The replacement of the siliceous skeletons starts as an early diagenetic process but continues under shallow burial conditions (Faupl and Beran 1983). Pyritization is an early diagenetic process that takes place in reducing diagenetic environments. It affects siliceous skeletal grains in different intensities, siliceous sponge spicules more frequently than radiolarians, probably because of their higher organic content, which in turn controls microbial sulphate reduction and the accumulation of iron sulfides at organics. Microfacies of radiolarian-bearing limestones Radiolarians occur predominantly in micritic carbonates and in marls. They are found in lime mudstones, wackestones and packstones. Common Jurassic microfacies types are (Kiessling 1996): Pelagic and hemipelagic marly mudstones with radiolarians and sponge spicules.

Plate 76 Radiolarians and Calpionellids The plate displays Late Jurassic planktonic organisms represented by radiolarians and calpionellids, a group of the ciliate Protista. 1 Pelagic radiolaria packstone. Note the differences in size and preservation of radiolarians. Calcitized spumellarian radiolarians are recorded by circular sections of different size. Sponge spicules (arrows) exhibit parallel orientation, indicnting the intluence of bottom currents. The dark micritic matrix yields abundant coccolithophorids, as proved by SEM studies. Using the abundance of radiolarians and sponge spicules and the radiolaria/spicule ratio within a standard field of the thin section as a measure for the depositional setting (Kiessling 1996), sedimentation in the distal parts of a deep basin influenced by bottom currents appears to be likely. The sample comes from the Oberalm limestone, a representative of widely distributed pelagic carbonates, better known as Aptyclzus limestone in the Alpine region, and Biancone limestone in the Mediterranean area. These limestones are commonly associated with radiolarites. The limestone beds are often separated by mark and contain some cherts and intercalations of allochthonous limestones consisting of material derived from the nearby carbonate platfomls. Radiolarians, sponge spicules, thin shell fragments (filaments) and tiny bioclasts form wackestone and packstone fabrics. SMF 3-RAD.Late Jurassic (Tithonian): Hallein, Salzburg, Austria. 2 Spumellarian radiolaria. The original opaline silica of the spherical test has been replaced by calcite, obscuring structural details. The pores on the surface of the test were partially infilled by carbonate mud, giving the margin a toothed appearance. This feature differentiates circular sections of radiolarian casts from sections of calcispheres or globular foramillifera. Same locality as -> 1. 3 ilca11t1rocircu.ssp., a member of associations which occur in relatively shallow depths. Late Jurassic: Kraiburg, Bavaria, Gern~any.The sample is a white limestone, used in Roman mosaics of southem Bavaria, Germany. 4 Radiolaria packstone. Limestone concretion in mudstones. Concretions are protected with regard to aggressive pore waters and compaction and can, therefore, yield well-preserved microfossils. The densely packed radiolarians are multicyrtoid nassellarians. The sample comes from an osygen-deficient basin in a high paleolatitudinal position. Late Jurassic (Nordenskjdd Formation): Longing Gap, Graham Land, Antarctic Peninsula. 5 Eitrabs e ~ i n g Pessagno. i The radiolarian skeleton is replaced by sparry calcite but has still preserved its morphology. Same locality as -> 3. 6 Podobursa sp. The nassellarian skeleton is preserved as microcrystalline calcite. Same locality as -> 3. 7 Calpionellid wackestone. Arrows point to the few longitudinal sections showing the criteria necessary for the taxonomic determination of calpionellids (Calpionclla sp.). Well-bedded micritic limestones with abundant remains of extinct ciliates are common in Late Jurassic and Early Cretaceous open-marine basinal settings. SMF 3-CALP.Late Jurassic (Tithonian): Seebuhel, Switzerland. 8 Calpionellid-radiolaria wackestone. C: Transversal and longitudinal sections of calpionellids; R: Recrystallized radiolaria. Note the difference in size and preservation between radiolarians and calpionellids. Locality as -> 7. --> 3, 5 , 6 : E. Fliigel and Ch. Flugel 1997. 4: Kiessling 1996

Plate 76: Radiolarians and Calpionellids

485

486 * Hemipelagic radiolaria wackestones with common to abundant, partly or totally calcitized radiolarians and sponge spicules as well as benthic foraminifera. Samples contain up to 20%particles. This microfacies is common in carbonates formed in slope position. Pelagic radiolaria packstones with high amounts of radiolarian tests consisting of microcrystalline calcite, and spicules (Pl. 7611). Peloids and tiny micritic intraclasts are common. Samples contain up to 50% particles. This rnicrofacies is common in current-influenced basinal settings. Hemipelagic filament-radiolarian wacke- and packstones with equal amounts of radiolarians and thin bivalve shells, spicules, and remains of pelagic crinoids. Samples contain up to 60%particles. The microfacies occur in basinal settings, influenced by bottom currents. Microbioclastic/lithoclastic packstones with radiolarians, spicules, filaments, benthic foraminifera and echinoderms, abundant very small lithoclasts, and with up to 70% particles. These microfacies are common in basinal settings; they may be a part of distal turbidites.

Significance of Radiolarians

to the formation of cherts and radiolarites (characterized by at least 30%of radiolarian material). Both lithologies are commonly associated with fine-grained sediments, including biogenic pelagic carbonates, mark and terrigenous mudstones. Modern radiolarians are abundant in deep-sea sediments, particularly in Pacific equatorial regions where productivity is high in the overlying water column. The accumulation of radiolarian mud in high latitude areas is due to high productivity rates, deposition at great depths below the CCD, and low dissolution of radiolarian tests.

Clues to depositional settings: Radiolariansare common to abundant in thin sections of Mesozoic limestones formed on open-marine slopes and in basins of differing bathymetry. Limestones and cherts with abundant radiolarians are generally thought to represent deep-marine deposits. Paleozoic and Mesozoic radiolarians sediments include, however, a wide range of facies, which vary strongly in composition and texture, fossil content, bedding style, sedimentary structure and rock color (O'Dogherty et al. 2001). Many radiolarThese or similar microfacies types are also known ian-rich rocks originated in deep-water upper slope or from Triassic basinal limestones. In Cretaceous lime- basinal positions, but reports describing the associastones, the tests of radiolarians are often overshadowed tion of shallow-water facies and radiolarian limestones by abundant planktonic foraminifera1 tests. (Blendinger 1985) as well as the occurrence of radiolarians in lagoons should be considered in facies interpretations (discussion in Racki and Cordey 2000). Significance of radiolarians Radiolarian assemblages are important biostratiDiscriminatiorz of proximal versus distal basin fugraphic, paleoecological and paleoenvironmental tools and contribute greatly to the formation of marine sedi- cies: Radiolarian abundance, the nassellarian/spumellarian ratio and the frequency of sponge spicules in the ments. siliceous microfauna are used for characterizingbathyal Biozonatiom: Whole-body radiolarians, extracted and abyssal sediments (Kiessling 1996). Nassellarians from limestones and cherts, have proved to be very use- increase in relative abundance in deeper-water sediful for biostratigraphic subdivisions, particularly of ments, whereas the relative abundance of sponge spiMesozoic and Cenozoic open-marine sedimentary rocks cules is inversely correlated with the bathymetry or distance from the shelf. Spicules only make significant (Casey 1993; Jud 1994; Baumgartner et al. 1995). contributions to siliceous microfaunas in slope and Contribution to sedimentation: Radiolarians accu- proximal basin environments. Thin-section analysis mulate on the sea bottom as a consequence of sinking exhibits comparable values regarding the abundance from the overlying water after the death of the organ- of radiolarians and the proportions of radiolarians and isms. Only a fraction of the living population is pre- sponge spicules, as does the analysis of isolated exserved at the sea bottom because silica-deficient sea- tracted radiolarians. Abundance can be better evaluwater dissolves the skeletons during sinking and at the ated from thin sections than from extracted faunas. sea water-sediment interface before burial. Radiolarian tests deposited on the sea bottom may be affected Basics: Radiolaria by contourite bottom currents. Many radiolarian tests Blendinger, W. (1985):Radiolarian limestones interfingering with loferites (Triassic, Dolomites, Italy). - Neues Jatuoccur in distal turbidites. Radiolarian-rich sediments buch fiir Geologie und Palaontologie, Monatshefte, 1985, are formed when the input of non-siliceous components 193-202 is scarce, so that radiolarians are concentrated in the Casey, R.E. (1993): Radiolaria. - In: Lipps, J.H. (ed.): Probottom sediment. Radiolarian skeletons are a major karyotes and protists. - 249-284, Boston (Blackwell) source of silica. Radiolarian accumulation contributes Faupl, P., Beran, A. (1983): Diagenetische Veriinderungen an

487

Calpioriellid Biozonatiori

Fig. 10.30. Calpionellid limestone.The pelagic limestone displays numerous cross sections and some longitudinal sections. Only a small number of the latter shows the diagnostic criteria necessary for taxonomic assignments. The thin section yields three species: Calpionella alpina Lorenz (C; see P1.77/6,7)), Crassicollariapawula Remane (CR; P1.77/4), and Remaniella sp. (R). The assemblage indicates the Calpionella zone, more specifically the elliptica subzone (D2 interval) of the global standard calpionellid biozonation (see Fig. 10.32). Early Cretaceous (Bemasian): Alpe Ra Stua near Cortina d'Ampezzo, northern Italy. Courtesy of J. Blau (Giessen).

10.2.2.3 Calpionellids

Radiolarien- und Schwammspicula-fiihrenden Gesteinen der Strubbergschichten (Jura, Nordliche K a k alpen, Gsterreich). - Neues Jahrbuch fiir Geologie und Palaontologie, Monatshefte, 1983, 129-140 Kiessling, W. (1996): Facies characterization of Mid-Mesozoic deep-water sediments by quantitative analysis of siliceous microfaunas. - Facies, 35,237-274 Kling, S.A. (1978): Radiolaria. - In: Haq, B.U., Boersma, A. (eds.): Introduction to marine micropaleontology. 203-244, Elsevier (New York) O'Dogherty, L., Martin-Algarra, A., Gursky, H.J., Aguado, R. (2001): The Middle Jurassic radiolarites and pelagic limestones of the Nieves Unit (Rondaide Complex, Betic Cordilleres): basin starvation in a rifted marginal slope of the western Tethys. -International Journal of Earth Sciences, 90, 83 1-846 Racki, G., Cordey, F. (2000): Radiolarian palaeoecology and radiolarites: is the present the key to the past? Earth-Science Review, 52,83-120 Further reading: K112

Calpionellids are extinct, bell-shaped very small calcitic microfossils (length about 50-200 ym) that occur abundantly in fine-grained, pelagic limestones of Late Jurassic and Early Cretaceous Tethyan oceans. The group suffered a dramatic decline within the Early Cretaceous age. The planktonic fossils are considered as a group of the subphylum Ciliophora and the class Ciliata. Ciliates are distinguished from other protozoans in having numerous tiny flagella (cilia) serving both for locomotion and food gathering. Calpionellids are regarded as a group of unknown systematic position (Remane 1978), or, more commonly, they are attributed to the Tintinnida with which they have strong morphological similarities and similar sizes, but differ in the material used for building the tests. Modem tintinnids are an important component of the microscopic zooplankton living predominantly in the photic zone of the oceans, but also occur with few taxa in estuaries and lakes. The bell-shaped cells

0ir'"'* -aboral Tintinnopsella

pole

-

alpi ion el la

I

Fig. 10.31. Longitudinal sections and reconstructed morphology of calpionellids. Diagnostic criteria are the morphology of the collar, the type of the aboral pole, and the shape and dimensions of the test. After Brasier (1980).

Plate 77 Calpionellids Calpionellids are very small bell-shaped, amphora-like or cylindrical microfossils restricted to Late Jurassic to lower Early Cretaceous pelagic limestones. The plate displays longitudinal sections of taxa used in the standard biochronology of the Jurassic-Cretaceous time interval (see Fig. 10.32). 1 Chitinoidella boneti Doben. The test has a microgranular calcitic wall and appears dark in transmitted light due to an

ultrastructure that differs from almost all other calpionellids (collected in the family Calpionellidae). Middle Tithonian: Pontaux (DrGme), France. 2 Crassicollaria intermedia (Durand-Delga). Arrows point to the diagnostic criteria of the genus (thickening at the base of the collar caused by oral ring). Late Tithonian, interval A 2 Serres-Montclus, France. 3 Crassicollaria brevis (Remane). Late Tithonian, interval A3: Same locality as -> 1. 4 Crassicolaria parvula Remane. Early Bemasian, interval B: Chevallon, France. 5 Praetintinnopsella andrusovi Borza. Tithonian (Chitinoidella zone): Pointaix (Ishre), France. 6 Calpionella alpina Lorenz. Black arrows point to the short and erect collar characteristic of Calpionella. White arrow indicates the bell-shaped aboral part of the test. Lowermost Berriasian, lower part of interval B: Saint-Penteraix, France. 7 Calpionella alpina Lorenz. Large specimen, characteristic of time interval A21A3. Late Tithonian, interval A2: Same locality as -> 2. 8 Calpionella elliptica Cadisch. Beniasian, interval C: Same locality as -> 2. 9 Remaniella ferasini (Catalano). Early Middle Bemasian, Calpionella zone, interval B: Ra Stua section, Belluno, Italy. 10 Remaniella catalanoi Pop. Early Middle Berriasian, Calpionella zone uppermost interval B or lowermost interval C: Same locality as -> 9. 11 Remaniella duranddelgai Pop. Early Middle Berriasian, Calpionella zone, interval B: Same locality as -> 9. 12 Renlaniella colorni Pop. EarlyMiddIe Bemasian. Calpionella zone, interval C: Same locality as -> 9. 13 Renzaniella colorni Pop. EarlyMiddle Berriasian. Remaniella is characterized by a collar consisting of three elements (arrows). Calpionella zone, interval C: Same locality as -> 9. 14 Renzaniella cadisclziana (Colom). Middle Bemasian, Calpionella zone, interval C. Same locality as -> 9. 15 Calpionellopsis sinzplex (Colom). The arrow points to the simple ringlike collar surrounding the oral opening. Late Berriasian, Calpiotzellopsis zone, interval D: Majorca, Spain. 16 Calpinnellopsis oblonga (Cadisch). Late Berriasian, interval D3: Berrias, France. 17 Sturiella dolotnitica Griin and Blau. Late Berriasian, interval Dl, Calpionellopsis zone, sinzplex subzone: Locality as -> 9. 18 St~m'rllaoblonga Borza. Late Berriasian. Culpionellopsis zone, interval D2; oblonga subzone: Same locality as -> 9. 19 B o ~ . z a i t ~atuws s (Griin and Blau). The arrow points to the ringlike collar. Holotype. Late Berriasian. Calpione1lop.si.s zone, interval D2; oblonga subzone: Same locality as .-> 9. 20 Pmecalpiotzellites hillebrandti Griin and Blau. Praecalpionellites is characterized by a two-fold collar with both elements separated from the lorica (arrow). Late Bemasian. Calpionellopsis zone, oblonga subzone, interval D3. Same locality as -> 9. 21 Cone-in-cone stacking: Outer form is Praecalpionellites murgeanui (Pop), smaller inner form is ?Loretz-.iclla sp. Lats Ben-iasian. Calpionellopsis zone, oblonga subzone, interval D3: Same locality as -> 9. 22 Praecalpionellites siriniaensis Pop. Early Valanginian, Calpionellites zone, interval E: Same locality as -> 9. 23 Praecalpionellitcs filipescui (Pop). The nannomicrite consists of disintegrated elements of Nantzoconus (inset bottom right). Nannoconid assemblages are used to establish biozones. Late Bemasian. Calpionellopsis zone, oblorzga subzonz, interval D.3: Locality as -> 9. 24 Praecalpionellites daduyi (Knauer). Late Beniasian. Calpionellopsis zone, oblotzgu subzone, interval D3: Locality as -> 9. 25 Calpionellites dardcri (Colom). The arrow points to a diagnostic feature of Calpionellites, the arrangement of parts of the collar parallel to the lateral walls. Early Valanginian, Calpionellites zone, interval E: Fanes area, Italy. 26 Culpionellites durderi (Colom). Early Valanginian, Calpionellites zone, interval E: Same locality as -> 25. 27 Calpionellites nzajnr (Colom). Early Valanginian, Calpionellites zone, interval E: Same locality as -> 25. 28 Calpionellitcs col-onatus Trejo. Early Valanginian, Calpionellites zone, interval E: Same locality as -> 25. 29 Tintinnopsella carpathica (Murgeanu and Filipescu). Early Valanginian, Calpioncllites zone, interval E: Same locality as -> 9. 30 Tintinnopsella carpathica (Murgeanu and Filipescu). Black arrows point to the flaring collar, the white arrow to the caudal appendix. Berriasian, interval C: Bemas, France. 31 Tintinnopsella longa (Colom). Early Valanginian, Calpionellites zone, interval E: Same locality as -> 25. 32 Tintinnopsella longa (Colom). Berriasian, interval D2: Bemas, France. 33 Lorenziella plicata Remane. Berriasian, upper part of interval D2: Same locality as -> 32. 34 Lorenziella hungarica Knauer and Nagy. Bemasian, interval D3: Same locality as -> 32. 35 Lorenziella hungarica Knauer and Nagy. Early Valanginian, Calpionellites zone, interval E: Same locality as -> 9. 36 Lorenziel/a ruggierii (Catalano). Early Valanginian, Calpionellites zone, interval E: Same locality as -> 9. -> 1-8, 15, 16,30-34: Courtesy of J. Remane (Neuchbtel); 9-14, 17-29,35,36: Courtesy of J. Blau (Giessen)

Plate 7 7 : Calpionelhds

489

Significance of Calpionellids

l ~ r i i nand Blau 1997 gr. carpathica PI. 77129-3 gr. hungarica PI. 77134-3

l; mjri

PI. 77/27 PI. 77125-2

/ dadayi

PI. 77/24

El ;;:z murgeanui

i

PI. 77/21

,

/simplex

PI. 77115

PI. 7716-7 PI. 77110 Pi. 7712 C

--I remanei

andrusovi

PI. 7715

/ bermudezi

.

I

I- -

/ boneti

- ---

-

PI. 7711

I

appears hyaline except in stratigraphically old taxa which exhibit microgranular, brownish opaque walls (Chitinoidella; P1. 77/1). The fossils are studied in thin sections or peels. Taxonomic differentiation needs sections exhibiting the shape of the test (U- and C-shaped figures), the type of the collar bordering the oral apertura as well the shape of the aboral region. These criteria are shown by longitudinal sections (Pl. 77). Cross sections are circular and statistically more frequent (Fig. 10.30). Geometric variations due to different cutting planes and the possibility of tectonical deformation (Remane 1964) must be thoroughly considered. The length and width of the test are further criteria used in discriminating species.

Significance of calpionellids Biozonation: Calpionellids are excellent index fossils enabling the biozonation of Late Jurassic (Middle Tithonian) to Early Cretaceous (Valanginian) Tethyan pelagic carbonates to be established. The current standard calpionellid biozonation is based on studies by Remane (1964,) Le HCgarat and Remane (1978), Remane et al. (1986), and Pop ( 1994). A revised zonal and subzonal subdivision was proposed by Griin and Blau (1997; Fig. 10.32). Calpionellid stratigraphy is generally combined with biozonations based on calcareous nannoplankton (nannoconids, coccolithophorids) and radiolarians (Weidich and Schairer 1990; Ondrejickova et al. 1993).

j dobeni

Sediment production: Calpionellids were rockbuilding constituents of Late Jurassic and Early Cretaceous fine-grained basinal carbonates in a tropical belt extending from Mexico to eastern Indonesia. The fossils occur in high abundance typically in very fine-grained micritic limestones or marly limestones that are rich in other pelagic microfossils (coccolithophorids, nannoconids; P1.77/23), and radiolarians). Nannoconids are calcitic conical nannofossils particularly common in Tethyan pelagic and hemipelagic limestones ranging from the Late Jurassic (Tithonian) to the Late Cretaceous (Campanian). They usually co-occur with coccoliths, calpionellids and radiolarians, but al~nostpurely nannoconid limestones are also known.

Fig. 10.32. Calpionellid biozonation after Griin and Blau (1997). The zones and subzones reflecting faunal successions and evolution events are used in worldwide correlations. Many of the species used to name the subzones are shown on Plate 77. Note that the generic assignment of these species must not correspond to the genera characterizing the major calpionellid zones. '

are enclosed within an organic test (lorica) exhibiting a large oral opening (apertura) and a differentiated aboral pole. Morphology and thin-section criteria: Calpionellids have a bell-shaped, amphora-like or cylindrical, calcareous test (lorica) with axial symmetry, and a large oral opening (aperture) surrounded by a collar of variable shape and construction (Fig. 10.30, Fig. 10.31). The collar is usually formed by prolongation of the lateral walls, but can also correspond to independent elements. The aboral pole is rounded, pointed or characterized by a caudal appendix. In thin sections the wall

Other tintinnid-like thin-section fossils Morphologically similar microfossils characterized by bell-shaped figures and thought to be tintinnids have been described from the Paleozoic (Silurian: Hermes

Benthic Sessile Organisms

1966, Chennaux 1967; Devonian: Cuvillier and Sacal 1963; VisCan: Cuvillier and Barreyre 1964), elsewhere in the Mesozoic (Eichler 1965; Borza 1972), and from Tertiary limestones (Tappan and Loeblich 1968). Because of their considerably larger size and because of different environmental settings, only a few of these fossils are acknowledged to be true tintinnids.

49 1

10.2.3 Benthic Sessile Organisms

The first two major groups treated in the discussion of thin-section fossils were cyanobacteria and calcareous algae, and foraminifera and other protozoans (Sect. 10.2.1 and Sect. 10.2.2). The third major group comprises sponges, corals and bryozoans as well as some hydrozoans. These groups have a common life-style: Basics: Calpionellids and other tintinnids They are benthic sessile organisms, that contribute Boorova, D., Lobitzer, H., Skupien, P., Vasicek, Z. (1999): greatly to the production of marine carbonate rocks, Biostratigraphy and facies of Upper Jurassic-Lower Cretaceous pelagic sediments (Oberalm-, Schrambach- and particularly by forming reefs and accumulating skelRossfeld Formation) in the Northern Calcareous Alps, etal grains in shallow-marine and deep-marine deposisouth of Salzburg. - Abhandlungen der Geologischen tional settings. The information provided by sponges, Bundesanstalt Wien, 56,273-318 corals and bryozoans greatly enhances our understandGriin, B., Blau, J. (1996): Phylogenie, Systematik und Bio- ing of paleoenvironmental controls and facies belts.

stratigraphie der CalpionellidaeBonet, 1956: Neue Daten aus dem Rosso Ammonitico superiore und dem Biancone (Obejura/Unterkreide):'Iithon-Valangin von Ra Stua (Prov. Belluno, Italien). - Revue de PalContologie, 15, 571-595 10.2.3.1 Sponges Griin, B., Blau, J. (1997): New aspects of calpionellid biochronology: proposal for revised calpionellid zonal and The paleoenvironrnental interpretation of microfacies subzonal division. -Revue de PalCobiologie, 16,197-214 Imbrie, J., Newell, N.D. (eds., 1964):Approaches in paleon- data is often confronted with the need to differentiate and evaluate sponge fossils. Limestones with abundant tology. - 432 pp., New York (Wiley) Rehakova, D., Michalik, J. (1993):Observations of ultrastruc- sponges occur all over the Phanerozoic and in nearly ture of the Upper Jurassic and Lower Cretaceous calpio- all depositional settings from intertidal to deep marine. nellid tests. - Geologica Carpathica, 44,75-79 Sponges (Porifera) are benthic sessile metazoans Remane, J. (1964): Untersuchungen zur Systematik und with a differentiated inhalant and exhalant aquiferous Stratigraphie der Calpionellen in den Jura-Kreide-Grenzsystem with external pores, in which flagellated cells schichten des Vocontischen Troges. - Palaeontographica A, 123, 1-127 (choanocytes) pump a water current through the body. Remane, J. (1985): Calpionellids. - In: Bolli, H.M., Saunders, The water is expelled by canals and the larger exhalant J.B., Perch-Nielsen, K. (eds.): Plankton stratigraphy. - 555osculum. The water flowing through sponges provides 572, Cambridge (University Press) Tappan, H. (1993): Tintimids. -In: Lipps, J.H. (ed.): Fossil food and oxygen, and also functions as waste removal. prokaryotes and protists. - 285-303, Oxford (Blackwell) The firmness of the sponge body is provided by sponFurther reading: K113 gin fibres and a skeleton of silica or calcium carbonate.

Fig. 10.33. Introduction to sponges. A: Niphates digitalis from the reef at 24 m depth in Chan Kanaab, Cozumel, Mexico. Height of the pink sponge approximately 25 cm. B: Needles of Agelas cf. conifera: Slope in 5 1 m depths in Colombia, Cozumel, Mexico. C: Leucetta. Triactine and tetractine needles of a calcareous sponges. Cozumel, Mexico. The sponges shown in A and B are Demospongiae characterized by siliceous spicules. C shows a sponge belonging to the class Calcarea. The spicules consist of calcite. Courtesy of H. Lehnert (Oberottmarshausen).

492

Sponge Ecology

Box 10.5. Describing sponges in microfacies thin sections involves a bewildering number of valid and outdated terms for sponge groups, some of which are systematic units, whereas others are combined by rather loose definitions. The definitions listed in the table are based mainly on the articles included in the comprehensive treatise edited by Hooper and Van Soest (2002). Archaeocyatha: Extinct sponges characterized by calcareous cups and a non-spiculate skeleton consisting of Mg-calcite. Now regarded as a group (class?) of Demospongiae with uncertain affinities. Calcarea: Porifera have a skeleton composed entirely of calcium carbonate. Characterized by free, rarely linked di-, tri-, tetra- and/or polyactine spicules to which a basal skeleton can be added. Comprise less than 5% of mode m sponges. Calcareous sponges: The non-systematic term is used in a rather loose manner for 'calcisponges' exhibiting calcite spicules or a calcareous skeleton. Chaetetida: Formerly regarded as a group of tabulate corals. Now considered as a name for a constructional grade occumng in different sponge groups. In microfacies studies the name is commonly used in an informal way referring to fossils composed of densely packed, thin calcareous tubes with horizontal partitions. Coralline sponges: A polyphyletic group with affinities both to Demospongiae and Calcarea. Demospongiae: Porifera with siliceous spicules and/or fibrous spongin skeleton, or occasionally without a skeleton. Spicules are monaxon (either monactine or diactine) or tetraxon (tetractine), never triaxon. Comprise about 85% of all living sponges. Minor groups have developed a hypercalcified basal skeleton consisting of aragonite or Mg-calcite in addition to other elements, or exhibit a solid aragonite structure lacking free spicules. Hexactinellida: Sponges defined by siliceous triaxon hexactine spicules or derivations from that basic form. Comprise about 7% of the described recent sponges. Important members of deep-marine communities. Inozoa: Originally a name for coralline sponges without segmentation. Now applied to non-segmented calcareous sponges with spicules. Note that the term 'inozoid' is used in a non-systematic context referring to nonsegmented calcareous sponges, but also as the name for a systematic group.

The skeleton consists of discrete, articulated or fused spicules (Fig. 10.33) and/or a hypercalcified mineralized basal skeleton.

Ischyrospongia: A name introduced for a group which should include stromatoporoids, sclerosponges and pharetronids. The term should be abandoned but is still in use in papers dealing with microfacies of Paleozoic limestones. Lithistids: A polyphyletic group of demosponges characterized by articulated spicules (desmas) forming a rigid skeleton. Pharetronids: A term including Sphinctozoa and Inozoa. Also used for calcareous sponges exhibiting spicules. Sometimes considered as a subgroup of the Calcarea. The term is now only rarely used. Sclerosponges: Apolyphyletic group of demosponges characterized by a calcareous basal skeleton with embedded siliceous spicules and different constructionalgrades resembling those of stromatoporoids and chaetetids. Siliceous sponges: Commonly used as an informal term for sponges with a skeleton composed of siliceous spicules. Include demosponges as well as hexactinellids. Sphinctozoa: Originally proposed as a term for chambered sponges with a rigid calcareous skeleton. Now defined by an external rigid skeleton and chambered organization. The name should not be used in a systematic context; it includes sponges that are polyphyletic in origin. Chambered construction has developed independently several times in different sponge groups and occurs in demosponges, Calcarea and hexactinellids. Most 'sphinctozoans' are attributed to the Demospongiae. Stromatoporoideu: Until the 70s of the twentieth century commonly regarded as hydrozoans. Giving credit to the affinities between the stromatoporoid skeletal structure and that of some recent sclerosponges, the group is now placed into the Porifera, and regarded as being related to Demospongiae, or as a separate class of sponges. Thalumida: Synonymous with Sphinctozoa.

terpreted as grades of construction and not phylogenetic clades, although the assignment of these groups and their lower taxa to the established classes is largely unresolved.

Major groups: The subdivision of sponges into sili-

ceous and calcareous sponges is anything but correct, but in the context of facies analyses still in use. In fact, there are three distinct classes (Hexactinellida, Demospongiae, and Calcarea, all appearing in the Late Proterozoic), and the extinct Cambrian class Archaeocyatha having suspected affinities wih Demospongiae. Several predominantly fossil groups including the Sphinctozoa, Stronlatoporoidea and Chaetetida are in-

Ecological constraints o n modern sponges: Sponges are benthic, almost exclusively marine organis~ns.They occur at all latitudes, and from the intertidal to the deep sea, down to more than 5000 meters. A small group of freshwater sponges originated in the Cretaceous. The distribution of modem sponges in shallow and deepmarine environments is controlled by nutrients, substrate, sediment input, and water energy:

Sponge Ecology

Nutrients: Sponges are suspension feeders. Nutrients are planktonic bacteria, organic particles and dissolved organic matter. Deeper-living sponges are exclusively heterotroph, whereas demosponges living in well-lighted environments may be autotroph due to the association with photosynthetic cyanobacteria. Substrate: Most demosponges and hexactinellids need hard substrates (rock surface, shells), but hexactinellids with rhizomes also occur on soft substrates in the deep sea. Sediment input: Deposition of too much sediment will effect sponge distribution negatively. Water energy: Sponges occur predominantly within quiet-water environments; they are rare in high-energy environments (crustose growth forms). Sponges in reefs: In the past, modem sponges were not considered to be major reef-builders (e.g. bioconstructions formed in shallow waters of the Bahama

Bank by demosponges: Wiedenmayer 1W8), but rather more important as cryptic constituents of coral reefs. However, the recent exciting discovery of impressive reefs off British Columbia, formed by hexactinellids in waters 180 to 250 meters deep, has changed this view (Krautter et al. 2002). These reefs are particularly interesting because they may provide a living comparison to extensive reefs created by hexactinellids throughout the Jurassic. Sponges with a soft body occur in cryptic habitats of modern and ancient reefs. These sponges have a low preservation potential, unless the dispersal of the spicules after the decay of the dead sponge can be prevented by an early taphonomic calcification of the sponge tissue. As shown by the preservation of nonrigid sponges in Late Jurassic oyster patch reefs, this calcification may sometimes be induced by heterotrophic, symbiotic bacteria inhabiting the soft parts of the sponges (Delecat et al. 2001).

Fig. 10.34. Siliceous sponges were important in Late Jurassic reefs. The figure shows a marly sponge reef limestone with dish-shaped siliceous sponges carrying thrombolitic microbial crusts at the tops (see Chap. 9.1). This microfacies originated at the base as well as on top of small bioherms formed above sedimentary continuities in relatively deep environments (Brachert 1992). Note fracturing caused by differential compaction. These gray and yellowish sponge limestones are widely used as decorative building stones in central Europe. Late Jurassic (Kimmeridgian): Ludwag near Bayreuth, northern Frankenalb, Bavaria, Germany.

Sponge Spicules

Preservation of non-rigid soft sponges has been recorded from Silurian, Devonian and Jurassic mud mounds (Bourque and Gignac 1983; Flajs and Hiissner 1993; Reitner and Keupp 1991).

Sponge spicules The fossil record of many sponge groups, particularly those of siliceous sponges, consists mainly of spicules which are studied in standard micropaleontological samples, but can sometimes also be recognized in thin sections of limestones (Keupp et al. 1989; see P1. 7812, 3). The composition and general architectureof spicules are used to classify sponges into classes. The form of the spicules and the manner in which they are combined to construct the skeletal structure are the basis for further systematic subdivisions. A complex terminology has been developed to describe the morphological variations of mega- and microscleres. Megascleres (length > 100 Krn to several milli-

meters) are the large principal frame-building elements. Microscleres (typically 10 to 100 Fm long) commonly occur freely within the soft parts of the sponge. Major architectural spicule types differentiated according to the number of axes are monaxons (with a single axis), triaxones (basically consisting of six rays and three axes extending at right angles from a central point; restricted to hexactinellids), tetraxones (four rays radiating from a central point), and polyaxons (several rays approximately of equal length extending from a central point). Desmas are irregularly shaped spicules forming the skeletal network of lithistid sponges. Further morphological differentiations use the number of points or rays on the spicule; resulting terms are often characterized by the root 'actine'. Sponge spicules may show a central canal (PI. 11211). Cross sections of calcitized spicules can be confused with radiolarians. Drawings of common spicule types which help to typify spicules in thin sections and a list of relevant papers can be found in Rigby (1985).

Plate 78 Siliceous Sponges 'Siliceous sponges' is a non-taxonomic term referring to sponges characterized by a skeleton consisting of siliceous (opaline) spicules. These sponges comprise taxa belonging to two polyphyletic systematic units with spicular skeletons, the Hexactinellida and the Demospongiae. Both groups include important reef builders (-> I , 4, 6), include organisms living on soft and firm bottoms, and contribute to the formation of deep-shelf and basinal sediments (-> 2). Spicules can be differentiated according to the number of axes and rays and the shape of the scleres (-> 3). Most figures in the plate display hexactinellid sponges whose siliceous skeletons have been partly replaced by calcite. Sponge reef limestone exhibiting hexactinellid sponges with a rigid skeleton. Hexactinellida (or 'glass sponges') are characterized by triaxon spicules consisting of six rays intersecting at right angles. Arrows point to the canal system. The sponge is strongly bored (B). Late Jurassic (Treuchtlingen limestone, Kimmeridgian): Bonhof, southern Bavaria, Germany. Spiculite composed of predominantly monaxone megascleres. Causes for concentrations of spicules are in-place deposltion of spicules derived from the disintegration of soft-bodied demosponges, or an accumulation of spicules of decaying soft sponges within organic mats. Some current transport is indicated by parallel alignment of the spicules. Early Jurassic: Roman mosaic stone found in Kraiburg, southern Bavaria, Germany. Different types of sponge spicules. Megasclere spicules are classified according to the number of axis and to the number of points or rays on the spicule. C -Monaxon spicule with stalked rings (cricorhabd), M -Monaxon spicule pointed at one end (style), TE -Tetraxon spicule exhibiting one long and three short rays (triaenes), TR -triaxone spicule with three rays in one plane (triactines). The siliceous spicules have been dissolved; the molds are filled with granular calcite cement. The good preservation of the spicules points to slow dissolution and rapid cementation. Late Triassic: North of Isfahan, Iran. Growthform. Tabular platy hexactinellid siliceous sponges covering fine-grained micritic matrix (coverstone). The arrow points to the canal system within the wall. The breccioid texture of the matrix is due to burrowing followed by dissolution. Same locality as -> 1. Constructiotzal grade. Some hexactinellid sponges exhibit internal segmentation similar to sphinctozoid demosponges (see PI. 79). The sample is selectively silicified (white areas). Late Triassic: North of Isfahan, Iran. Preservation of hexactinellid skeleton. A characteristic feature of sponge structures in thin sections is the fine network apparently consisting of discontinuous horizontal and vertical elements. Note the voids within the sponge skeleton caused by dissolution of the skeleton prior to the lithification of the lime mud between the spicules. Same locality as -> 1. -> 3 , s : Courtesy of B. Senowbari-Daryan (Erlangen)

Plate 78: Siliceous S p o n g e s

495

Coralline Calcareous Sponges

497

Fig. 10.36. Cot-ullm,spor~ges.The thin-section photograph shows a characteristic reef assemblage consisting of nonsegmented (inozoan, I) sponges, chambered sponges (sphinctozoans, S), and chaetetid coralline sponges (C). Note the competition for space, a common feature in reefs built by coralline sponges. Late Triassic (Zlambach beds, Rhaetian): Northern Calcareou.; Alps, Austria.

by an interplay of oscillating sea-level and fluctuating oxygen-minimum zones. The former favored the expansion of microbes, the latter in conjunction with successive highstands supported the growth of sponges in deeper water on foreslopes and drowned platforms (Reitner and Neuweiler 1995). Siliceous sponge diayenesis: In many limestones the skeleton of siliceous sponges is preserved as calcite pseudomorphs. As shown for Jurassic hexactinellids, sponges from different depositional environments reflecting different hydrodynamic regimes are preserved differently (Brachert 1991). Preservation is best in lowenergy basinal carbonates and bedded limestones formed between sponge mounds due to slow silica dissolution and rapid micrite cementation. As water turbulence (and water temperature) increases, dissolution accelerates with respect to micrite cementation. This leads to a complete calcitization of spicules in shallow and higher-energy areas, or the dissolution of the skel-

eton, which may then be recorded only as voids containing some relicts of sponge structures. Stagnant basins are suitable environments for the dissolution of spicules, which in turn may be responsible for the chert formation in limestones. The diagenesis of siliceous sponge spicules follows different paths (Gaillard 1983; Lang and Steiger 1984; Brachert et al. 1987). These include the infilling of the axial canals of the spicules with micritic sediment, iron and manganese oxides and cement, followed by the dissolution of spicules and infilling of the molds by HighMg calcite cement (Pl. 7813) or by fine-grained sediment obscuring the former skeleton. Fossil siliceous sponges are frequently enclosed by or associated with micritic or peloidal 'crusts'. Calcification of decaying tissue of siliceous sponges leads to the formation of various automicrite types that may mirror the shape of the sponge body (Warnke 1995). Major processes in sponge diagenesis and in the formation of sponge buildups are (a) early lithification and Text continued on p. 504

4Q8

Sphinctozoan and Inozoan Sponges

Plate 79 Calcareous Sphinctozoan and Inozoan Sponges Many coralline sponges are characterized by chambered, segmented skeletons (-> 4, 8), others are non-segmented (-3 7). The former group has commonly been called Sphinctozoa, the latter Inozoa. These names are now no longer used in a systematic context, but are still applied to separate morphological groups of polyphyletic origin. Sphinctozoans are differentiated according to external and internal morphological features. External features include the shape (cylindrical, club-shaped, sheet-like or irregularly formed), the segmentation of the rigid skeleton, the pattern of chamber arrangement, and the inhalant and exhalant canal system of the outer wall. Internal features seen in thin sections are intemal segmentation (-> 2, 4), chamber shapes (-> 2, 4, 6, 8) and intemal fillings of the chambers (-> 1, 2, 3 , 5 ) separating those parts of the skeleton which have been left behind by the soft parts during growth, intemal walls separating the chambers (-> 4, 8) and the central exhalant system (siphon, spongocoel). The latter corresponds to single or multiple openings appearing as defined central canal or canal bundles (-> 3, 8).The schematic drawings on this page give an idea of the complex internal morphology of a sphinctozoan sponge (A), and demonstrate the possible relationship between the calcareous skeleton (black) and the soft parts (stippled) in a reconstruction (B). A - modified from Senowbari-Daryan (1990), B - after Reitner (1992). Most photographs display sphinctozoans (except -> 7 , which shows a section of an inozoan sponge). Sphinctozoan sponges are abundant in Permian and Triassic reefs where they formed rigid organic frameworks (-> 1, 5), sometimes together with microbial crusts (-> 4). 1 Typical reefframework formed by encrusting sphinctozoans. Cross section of Jablonskya andr~uovi (Jablonsky) - J and Uvanella irregularis Ott ( U ) growing on another sphinctozoan sponge. Both sponges consist of microgranular High-Mg calcite skeleton (black in transmitted light). Note the vesicular filling skeleton of .lahlonskya. Late Triassic (Carnian): Dolomites, Southern Alps, Italy. 2 Morphological criteria ofspizinctozoans. Oblique longitudinal section of Solerzolmia munot1 (Miinster) characterized by segments with a coarsely reticulate filling skeleton. Late Triassic (Carnian): Molignon, Dolomites, Southern Alps, Italy. 3 Sphinctozoan rnotpizology: IJesicocaulis reticuliformis Jablonsky with a central canal bundles (arrow) connecting the catenulate segments and the reticular filling skeleton. Longitudinal section. Late Triassic (Carnian): Huda Juzna, Slovenia. See schematic drawing to the left. 4 Sphinctozoan morphology: Longitudinal section of Colospongia duhia (Laube). The monilifonn stem consists of stalked barrel-shaped segments with differentiated porate walls (PW) and vesicuiae (V) within the chambers. Note the different appearance of the originally aragonitic skeleton as conlpared with originally Mg-calcitic skeletons (-> 1). Late Triassic (Camian) patch reef: Huda Jnzna. Slovenia. 5 Sphinctozoan morphology: Several densely spaced specimens of Solenolinia munon (Miinster). Thc segments contain a coarsely reticular filling skeleton. Internal walls of the segments are perforated. Solenolmia is a common sponge in Middle Triassic and Camian reefs of the Alpine-Mediterranean region. Late Triassic (Carnian): Huda Juzna, Slovenia. "es,coca,,,;s pljcu/rfoim,s 6 Sphinctozoan morphology: Alpinotlzalarniu slovenica (Senowbari-Daryan). Numerous glomerate cyst-like chambers are arranged around the axial spongocoel. The wall consists of High-Mg calcite. Late Triassic (Pantokrator limestone, Carnian): Hydra Island, Greece. 7 Inozoan sponge morphology: Oblique section of Sestrostomella robusta Zittel. Similar to sphinctozoan sponges, inozoans are characterized by the absence of segmentation. The sponge body is transected by axial canal bundles of the exhalant system. Sestrostomella is known from Triassic and Late Jurassic-Early Cretaceous limestones. Late Triassic (Carnian): Dolomites, Southern Alps, Italy. 8 Splzinctozoan and inozoan sponges: Longitudinal section of the sphinctozoan Discosiphonella ler-carensis (SenowbariDaryan and Di Stefano). The central cavity is surrounded by ringlike rows of hollow chambers. The internal walls are perforated. The sphinctozoid sponge was competing for space with the inozoid sponge Maeandrostia (arrows). These sponges occur in shelf habitats, not in reefs. Early Permian: Lercara, Sosio Valley, Western Sicily, Italy. -> 2-8 and Figs. on this page: Courtesy of B. Senowbari-Daryan (Erlangen)

Plate 79: Sphinctozoan and Inozoan Sponges

499

Paleozoic Stromatoporoids

50i)

Plate 80 Paleozoic Stromatoporoids Stromatoporoids are common in thin sections of Ordovician to Late Devonian limestones as well as Jurassic and Cretaceous shelf and reef carbonates (see P1.81/3,5). For a long time regarded as hydrozoans, stromatoporoids are now recognized as sponges. Major points in favor of including the Stromatoporata within the sponges are the similarity of the astrorhizal canal system and the gross skeleton pattems to modem sclerosponges. The basal calcareous skeleton of the Stromatoporataconsists of horizontally continuous elements (laminae, -> 8; cysts, -> 5) and vertical elements (pillars, -> 3, 7, 8; columns, -> 4). Most of the Paleozoic stromatoporoids appear black in transmitted light, some appear hyaline (-> 1) pointing to differences in the original skeletal mineralogy (High-Mg calcite and calcite: Rush and Chavetz 1991; Yoo and Lee 1993; aragonite: Smosna 1984; Steam and Mah 1987; Steam 1989; Tobin and Walker 1998). Much of the hydrocarbon production from Silurian and Devonian carbonates is from stromatoporoid reef and forereef limestones. Growth forms, taphofacies as well as distributional pattems of genera in reef complexes are useful criteria in recognizing environmental conditions (water energy, substrate) and ecologic zonations. The plate displays Devonian strornatoporoids with laminar-encrusting (-> 3), massive-nodular (-> 7, 8) or cylindrical-dendroid (-> 1, 2) growth forms. Stachyodes. Order Syringostromatida. Oblique section. Note the dendroid growth form and the dense packing of skeletal elements. Genus range: Eifelian to Frasnian. The genus is common on reef flats and near-reef platform environments. Late Devonian (Frasnian): Canning Basin, weste m Australia. Amphipora. Transversal (TS) and longitudinal sections (LS). These small, cylindrical, branching organisms lived in calm shallow-marine waters of lagoonal and back-reef environments and were frequently swept into other environments by storms. Black, bituminous Amphipora limestones characterize a widely distributed organic-rich facies type of Devonian reef and shelf carbonates. Diagnostic criStructure and nlicrostructure of stromatoporoids. Cross secteria: Dendroid skeleton, commonly with axial canal, surtion of Stczchyodes (-> 1). The cylindrical branch exhibits rounded by a network formed by pillars and connecting an axial canal. The structure is characterized by a network elements. Frequently peripheral vesicles bounded by a calof radiating pillars and voids. The latter correspond to ircareous membran. Generic range: Late Silurian to Late regular radial canals opening at the margin. Dark microDevonian. Late Devonian (Frasnian): Canning Basin, Auslaminae parallel to growth surfaces form concentric rings. tralia. The originally microreticulate microstructures of the thick 3 Itltergrowtl~of stromatoporoids and corals: Arugose coral skeletal elements appear striated, intensified by recrystalli(RC) is encrusted by a consortium consisting of stromatozation. Late Devonian (Frasnian): Canning Basin, westem poroids (S, Clathrocoilona), alveolitid tabulate corals (TC) Australia. and porostromate cyanobacteria (PC, Rothplet-.ella, see PI. 53/8). Overgrowth of rugose corals by stromatoporoids is a common feature in Devonian and Silurian reef communities. Middle Devonian (Givetian): Letmathe, Sauerland, Germany. Stronlatopomid niiri-ostl-~ture:Longitudinal section of Par-c?llelopotacharacterized by thick superposed but discontintlous vertical skeletal elements (coenostele) with a cellular microstructure. No distinct laminae but upward arched dissepiments. Generic range: Wenlockian to Middle Devonian. Eifelian: Meseta, Morocco. Lcrberhiidstrornatopot-oids:Longitudinal section. The last Devonian stromatoporoids have a similar construction to stromatoporoids appearing during the initial development of the group in the Ordovician. Predominant skeletal elements are cysts. Vertical elements are reduced to spines and short pillars. Some labechiids had aragonitic skeletons. Cyst-dominated skeletons are common in Ordovician and Silurian carbonate banks and reefs. Generic range of Pseudolabechia: Late Devonian (Fan~ennian):Dubic-Debnik, south of Cracow, southem Poland. Irregular nzeslzwork: Oblique section of Harnrnatostronza albertense Steam. Criteria: Persistent laminae; incomplete pillars knotted into irregular tangled structures within the interlaminar space. Generic range: Givetian to Frasnian. Late Devonian (Frasnian): Subsurface, Red Water Reef Complex, Alberta, Canada. Regular meshwork: Vertical (VS) and tangential sections (TS) of Actinostroma. Circular figures correspond to sections through dome-shaped parts (mamelons) of the fossil. Note geopetal fabric in bivalve boring (arrow). Generic range: Lochkovian to Famemian. Late Devonian (Famennian): Same locality as ->5. Growth pattern: Longitudinal section of Actinostroma papillosum (Bargatzky). Variations in laminae spacing indicate growth disturbances (GD). Growth units (latilaminae) offer valuable proxies for paleoclimatic variations. Reef margin. Late Devonian (Frasnian): Canning Basin, western Australia.

.

L

-

Plate SO: Paleozoic Srromaroporoids

50 1

Plate 81

Calcareous Chaetetid Sponges and Other Still Disputed Taxa

The plate shows a selection of Triassic and Jurassic fossils characterized by uniform or differentiated calcareous tubes and sometimes summarized under the name 'tabulozoans'. This term should be forgotten. With the discovery of living, very similar animals (sclerosponges and related forms), it was learned that most of these fossils are sponges although the former systematic assignment of some taxa to hydrozoans (-> 3, 5) has not yet been completely rejected. Figs. (-> 1-4 and 6-8) display some common chaetetid coralline sponges. The skeleton of chaetetids is formed in two steps. Skeleton formation starts with the precipitation of a spicular primary skeleton, followed by the formation of a secondary skeleton consisting of calcareous walls and horizontal partitions (see schematic drawings on this page). Important diagnostic criteria used in taxonomic differentiations are the morphology and mode of the formation of the tubes, the primary mineralogy and microstructure of the walls, the type of the horizontal partitions (tabulae; -> 8) and the mode of the formation of new tubes (-> 7, 8, and schematic drawings on this page). Chaetetids range from Ordovician to Miocene and peaked in the early Late Carboniferous, where they formed shallow-marine biostromal reefs. These reefs were constructed more or less only by chaetetids, in contrast to Late Jurassic reefs where chaetetids played only a small part in the association of stromatoporoid sponges and corals. Ghaetetids in Early Cretaceous rudist reefs were usually dwellers.

skeleton

skeleton

longitudinal parting

intercalicle budding

basal

budding

L)ifj~rcurtypijs ($tor-alliiw c.aIcai~eciirs.rponges. The reef limestone contains an assemblage of spongiomorphids (S), sphinctozoan sponges (SSj, inozoan sponges (IS) and skeletons composed of calcareous tubes (fomlerly surnmarizeti as tabulozoans, T). The latter exhibit the chaetetid constructional type known from sclerosponges. Note the different preservation of spongiomorphids and inozoans as compared with sphinctozoans and chaetetids, pointing to differences in the original skeleton mineralogy. Many Mesozoic chaetetids had an aragonitic skeleton (Wendt 1990;Mastrandrea and Russo 1995). Spongiomorphids have been regarded as corals or hydrozoans but an assignment to sponges is now under discussion. Late Triassic (Dachstein reef iirnestone, Norian): Hoher Goll, Bavarian Alps, Germany. F'n3scrrztioi: qf i,Izartetid skeletons: The infill of micrite into the peripheral part of the skeleton sinlulates the existence of a ruorphological differentiation. Blrrsioc~i~aetetes sp. Same locality as -> 1. i2,sfr;.,.st~iopsis ( A ) .a sponge with Mg-calcite skeleton formerly regarded as hydrozoan, encrusted by a cttaetst~di C ' : l 1. EII~pstrc.rinia(E), sometimes regarded as a hydrozoan, and Astros~lopsis(A) assigned to coralline sponges. The constructional pattern of Ellipsactinia corresponds to the stromatoporoid type. Ellipsactiniids contributed significantly to the Sonnation of Late Jurassic and Early Cretaceous platform-margin reefs. Late Jurassic: Central Apennines, Italy. Pfyc~hocltuctet~.s g l o b o s ~ ~Koechlin s exhibiting distinct growth zonation. Late Jurassic (Tithonian): Krahstein near Mitterndorf, Styria. Austria. Ptychochurreres. Longitudinal section. The mode of the formation of new tubes (here basal budding) is used as a generlc criterion. Late Jurassic (Kimmeridgian): Voksen/Deister, Lower Saxony, Germany. New-opal-a,a chaetetid sclerosponge formerly attributed to bryozoans. Longitudinal section exhibiting densely spaced cross partitions. New tubes are formed by intramural budding. Same locality as -> 6. Spotzgiornol-pha ramosa Frech showing a fine reticulate pattern consisting of crenulated vertical elements. The assignment of spongiomorphids to hydrozoans is now questioned and sponge affinities preferred. Spongiomorphids were common in deeper subtidal parts of Triassic to Early Cretaceous reefs and platforms. Note that the term 'spongiomorphid' ic also loosely ti~edfor sponge-like foss~ls!Late Triassic (Rhaet~an):Steinplatte, Tyrol, Austr~a > F~gureon thls page Crcmer (1993)

Plate 81: Chaetetid Spongcs

-503

replacement of the former sponge tissue by in siru precipitated carbonate cement (automicrite, Sect. 4.1.2) and (b) early or late dissolution and replacement of the siliceous skeleton by calcite. Dissolution depends on pressure, temperature and the type of modification. Skeleton opal is relatively stable under nornlal marine conditions (pH about 8). Dissolution. therefore, requires changes in pH values and an increase in carbonate alkalinities. An increase in pH values may be caused by (1) bacterial degradation of organic matter including ammonification, or desulfurication triggered by sulfur bacteria, or (2) removal of CO, due to changes in physical parameters. The importance of these processes in pH changes is still a matter of discussion (Fritz 1958; Reitner et al. 1995; Rehfeld 1996).

Distribution of siliceous sponges: During the Paleosponges flourished in quiet-water environments. contributing to the Connation of mud mounds. In the h,leso7oic siliceous sponges are abundant in the Jurassic and Cretaceous. Liassic sponges are known L ~ K siliceous

from soft bottom deeper-water environments and are abundant in Late Jurassic ramp and basinal settings where they fom~edextensive and widely distributed reefs. During the Late Cretaceous a major turnover in demosponges took place, as demonstrated by the highly diverse sponge faunas of the Chalk facies in northwzstem Europe. The adaption of siliceous sponges to deepwater environment was continued during the Teniary.

Coralline calcareous sponges Morphology and classificaatiorz: Coralline sponges are defined as sponges with a secondary rigid calcarcous skeleton in addition to a spicular skeleton. Rigid calcareous skeletons occur in different sponge groups including sphinctozoan and inozoan sponges, stromatoporoids and chaetetids as well as archaeocyaths. The great debate on the assignment of these groups to the major sponge classes was strongly triggered by studying modem sclerosponges that exhibit morphological criteria occurring in different fossil groups.

Piate 82 Archaeocyatha Archaeocyaths represent an extinci group of benthic, sessile organisms that lived in Cambrian equatorial openshelf and reef environments. The cup-shaped, vase-like or cylindrical calcareous skeletons are characterized by a large ccntral cavity surrounded by a concentric porous double wall (-> 1,2) or by a porous single wall (-> 3'). The space between the inner and the outer wall (intervallum) is subdivided by radial-longitudinal andlor radialtransverst: partitions (septa. ilat tabulac. curved cysts). The arrangement of these partitions, their pore systcms and the constructional pattern are of taxonomic importance (-> 1, 2). Archaeocyaths are often associatctl with calcirnicrobes (-> 4, 5 ) and form the substrate for microbes and sublnarinc: carbonate cenients. thus contributing to the formation of Early Cambrian reef mounds and reefs. I Donhlc-itsolledui.r~lztrc~oc~~7tI1~~: Variou\ sections of double-walled archaeocyaths. Cross- and oblique sections (CS, OS) s l l o ~thc central cavity bounded by porous inner and outer walls. The intervallurn is subdivided by septa. The septa are finely porous, as shown in a ti~ngentialsection (TS). These structures exhibit the characteristic archaeocyathid construztional type of the skeleton. Other constructional types used in taxonomic differentiations are indicated by black and white rirrows (vesiculx and dictyonid net\vorh respectively). The lower part of the figure below the wavy line shows a pru-allel w i o n to the upper part taken u.ithin a distance of about 2 mm. Note the apparently ciifi'erent filling of the centrill cavity. L%rly Cambrian: Wstzrn Anrarctica. 2 A I - ~ ~ I I ( I L ~mo~phologj: ~ c : ) ' ~ I I I Cross section (CS)of double-walled archaeocyaths and oblique section ( 0 s ) of archaeocyaths corresponding lo another constructional type characterized by septa arranged in a network form. The white arrow points to tubuiar cyanobacteria, the black arroufs to juvenile archaeocyathids. SMF 6. Early Cambrian: Sardinia, Italy. 3 , C i r ~ y l t ~ - ~ !~~-(.lrtrr,oi.~trrlr: ~ t ~ l l ~ ~ t i C)biic~uccross section. The tubelike structures have been described as PI-oaulol?ol-u(Pj and were referred to green and red algae and cyanobacteria as well. This genus indicates an Early Cambrian age. Early Cambrian: Same locality as -> 2. 4 Arsociuteii calc~in~ic~~ul~cs: Many archaeocyaths occur in associatio~lwith calcimicrobes that use the archaeocyaths as a substrate. The figure shows Epiph~tot~. The disintegration of the erect-growing micritic branches of Epiphyton and other calcimicrobes provides coarse silt to very fine sand-sized fragments that lack characteristic microstructures and therefore correspond to peloids. Cyanobacterial peloids contributed greatly to the production of carbonates deposited adjacent to Early Paleozoic reef mounds (Coniglio and James 1985). Same locality as -> 2. 5 ,4ssociatc~icnlrirtzicmhes: Widely distributed Cambrian calcimicrobes are Ker~ulcis(R) and Epiphyton (E). Kentrlcis is charxterized by clusters of thick-walled botryoidal chambers, with the larger ones enveloping smaller ones. Epipizyton exhibits micritic, narrcxv dendritic filaments. Both taxa are known from Early Cambrian to Late Devonian. Same locality it', --->2 --; 2-5: . Courtesy of bl. Boni (Napoli) and 7'. Bechstadt (Heidelberg)

Plate 82: .4rchaeocyatha

505

D~vingin tropical coral reefs resulted in the discovery of puzzling sponges restricted to reef caves and deep forereef areas with low light and strict oligotrophic conditions in the West Atlantic and Indo-Pacific region (Fig. 10.35). These sponge, called sclerosponges by Hartman and Goreau (1972), are characterized by a basal calcareous skeleton by which the animals are attached to the substrate (Fig. 10.35). The living tissue is restricted to a thin veneer upon or within the uppermost few millinleters of the skeleton and contains, usually but not always, tiny siliceous spicules. The taxa were first regarded as a separate class of the Demospongiae, but subsequent to the recognition of the polyphyletic character of these sponges, they are now attributed to different fanlilies of coralline sponges. The skeleton of these sponges consists of aragonite or Mg-calcite. It is organized into tubes and calyces (ceratoporell~dtype), tabulated tubes (chaetetid type), a more or less regular network of the primary skeleton ~71thhorizontal and vertical elements (stromatoporold type), or a chambered skeleton (sphinctozoid or thalamid type). Comparing the morphological criteria of sclerosponges and other 'living fossils' with the criteria of fossil groups of until then unassigned systema t ~ cposition, such as the stromatoporoids and chaetetids, has now led to the assignment of these groups a5 well as sphinctozoans and inozoans to the demosponges. Some authors oppose this systematic treatment and regard these groups primarily as different grades of the ~norphologicalorgani~ationof skeleton\ occurring independently in different sponge classes (Keitner 1989; Wood 1991; Reitne~and Worheide 2003) Overvzen ofnlujor groups ofcolczilme sponges: The following text and the plates summarize the criteria, distribution and significance of sphinctozoan and inozoan sponges (PI. 79). strornatoporoldi (PI. 80) and chaetetdc (Pi. 81) as well as archacocyaths (Pl. 82)

Sphinctozoans and inozoans Diagnostic morphological criteria of chambered sponges (sphinctozoans) and non-chambered calcareous sponges (inomans) are shown in Plate 79. SphinctoLoans appear early in the Paleozoic, diversified and dom~natedduring the Permian and Triassic, and became nearly extinct after the Cretaceous (Senowbari-Daryan 1990: review and extensive bibliography in SenowbariDaryan and Garcia-Bellido 2002). Sphinctozoans and inozoans as well as other coralline sponges contributed significantly to the formation of Late Paleozoic (e.g. Permian Reef Complex in Texas, P1. 14511) and Middle and Late Triassic reefs (cg. Middle Triassic Wetterstein

reefs and Late Triassic Dachstein reefs in the Northern Calcareous Alps; Fig. 10.36, P1. 11612). The first inozoans are known from the Carboniferous. Permian inozoan sponges were common both in non-reef and reef environments (Rigby et al. 1989, Fan et al. 1991, Rigby and Senowbari-Daryan 1996). The group reached a maximum in the Late Triassic (Senowbari-Daryan et al. 1997) and again in the Middle and Late Jurassic (Miiller 1984). The last inozoans with a rigid non-spicular skeleton were described from the latest Cretaceous.

Stromatoporoids Stromatoporoids are extinct fossils known from the Early Ordovician to the Late Devonian and again in the Mesozoic. The relations between Paleozoic and Mesozoic taxa are still open to discussion. Both Paleozoic and Mesozoic stromatoporoids have been placed into the Hydrozoa but are now recognized as Porifera. The fossils are represented by calcified skeletons of domical? bulbous, branching or colunlnar form, and ranging front a few centimeters to meters in diameter. Internally the skeleton exhibits elements more or less parallel and perpendicular to the surface. Distinct aquiferous canal systems (astrorhizae) occur at the surface and internally. The canals converge towards a center and are radially arranged. No traces of spicules have been found in Early and Mid-Paleozoic stromatoporoids. In this feature Paleozoic stromatoporoidsdiffer from Mesozoic stromatoporoids, some of which contain spicules. Thebe tasu. including many former 'hydrozoans' (see P1. 8 1 ). arc' placed into the Dernospongiae. Many authors reprd the Paleozoic stromatoporoids as a separate class of the Porifera with close relationships to other poriferans secreting calcareous skeletons. Morphology and clussification: A glossary of the morphological terms applied to the Paleozoic Strornatoporoidea and a comprehensive overview of the current state of classification, including a critical list ofthe gen-era was provided by Steam et a]. (1999). Criteria 11sed in the taxonomic discrimination include the type of skeletal elements, their microstructure and features of the exhalant water system represented by astrorhizal canals and central tubes. Some microstructural types are identical with those of other coralline sponges and are therefore regarded as primary skeletal structures.

Chaetetid coralline sponges and 'tabulozoans' Thin sections of Late Paleozoic and Mesozoic reef limestones may exhibit sections of fossils composed of calcareous tubes, sometimes with tabula-like horizontal partitions. In the context of microfacies stud~es

Archaeocyaths

these fossils have often been called 'tabulozoans', using a non-systematic term proposed by Kiihn (1942). Plate 8 1 displays some of these taxa that were formerly assigned to various fossil groups, including hydrozoans, tabulate corals and sponges. Most taxa, particularly the chaetetids, are now recognized as sponges related to calcified Demospongiae. The chaetetids compose a small group of organisms that was presumed to be tabulate corals, but are now attributed to sponges as a result of the discovery of a recent representative. The rigid skeleton corresponds to a cluster of closely packed nonporous calcareous tubes with horizontal floors (tabulae). Spicules have been described from Mesozoic chaetetids. Fossil chaetetids appear in the Ordovician. They contributed to the development of Paleozoic (particularly Late Carboniferous) and Mesozoic reefs, both overgrowing and serving as substrate for other reefbuilding organisms. Chaetetid coralline sponges were important reefbuilders both in the Paleozoic and Mesozoic. In Middle Carboniferous platform and platform-margin settings they formed small mounds and broad low banks where they were often associated with beresellid and ungdarellid algae (see P1.56/6,7 and P1.60/2,5). In the Triassic, Late Jurassic and Early Cretaceous chaetetids lived in open-marine platform environments and in reefs. Archaeocyaths This is an extinct group of Cambrian fossils now regarded as Demospongiae with uncertain affinities (Pl. 8211-3). The group appears near the base of the Cambrian (Early Tommotian) and had a worldwide distribution in the Early Cambrian (Atdabanian and Botomian). Some relicts persisted in Middle and Late Cambrian. Compositional differences of faunas from Siberia, Europe, Northern America, North Africa and Australia indicate distinct provincialism. Morphology and classification: The skeleton consisting of microgranular Mg-calcite corresponds to inverted cones or cups exhibiting a distinct central cavity surrounded by porous walls formed by one or two elements . The 'intervallum' between the outer wall and the highly variable inner wall contains a variety of radially or irregularly arranged partitions (blade-like septa; irregular curved plates or subradial pseudosepta). These elements can be connected by bars. The lower end (tip) of the cone was buried in soft sediment or, more commonly, rooted or encrusted onto hard substrates. The diameter of the cups changes with the ontogenetic stages and varies between a few millimeter

507

and about 600 mrn. The average diameter of adult forms is 5 to 25 mm. The height can be more than 300 mm. The classification is based on ontogenic development stages, intervallum structures and pore systems. Generic determination needs oriented transverse, longitudinal and tangential thin sections. Transverse sections can be confused with corals and dasyclad green algae, but most corals lack a distinct double wall. Transverse sections of dasyclads are smaller, and the simple calcareous walls of the algae are penetrated by small pores. Ecology andfacies: Archaeocyaths were exclusively marine filter-feeders living on fairly energetic ramps and platforms. Solitary and colonial archaeocyaths were important constituents of the first metazoan reef communities but also occur in subtidal bottom-level associations. Biohermal and biostromal reefs are believed to have been formed in shallow water depths (about 20-50 m). Depth estimates are based on the abundant association of archaeocyaths and various calcimicrobes (Renalcis, Epiphyton; sometimes quantitatively more important than archaeocyaths), current-produced sedimentary structures, and the abundant fragmentation and resedimentation of archaeocyathan skeletons. Associated biota include trilobites, hyalithids, various shells and fossils with supposed cnidarian affinities. Many limestones with archaeocyaths are boundstones or bioclastic and peloidal floatstones and wackestones,

Basics: Sponges (publications which assist in taxonomic differentiation are marked by an asterisk) Overviews Broadhead, T.W. (ed., 1983): Sponges and spongiomorphs. Notes for a short course. - 220 pp., Knoxville (University of Tennessee) Hartman, W.D., Wendt, J., Wiedenmayer, F. (1980): Living and fossil sponges. - Sedimenta, 8, 274 pp. Hooper, J.N.A., Van Soest, R.W.M. (eds., 2002): S y s t e m Porifera. A guide to the classifications of sponges. 2 volumes. - 1708 pp., New York (KluwerAcademic/Plenum) Reitner, J., Keupp, H. (eds., 1991): Fossil and recent sponges. - 595 pp., Berlin (Springer) Siliceous sponges Brachert, T. (1991): Environmental control on fossilization and siliceous sponge assemblages: a proposal. - In: Reitner, J., Keupp, H. (eds.): Fossil and recent sponges. - 543-553, Berlin (Springer) "Krautter, M. (1997): Aspekte zur Palaokologie postpalaozoischer Kieselschwamme. - Profil, 11, 199-324 Krautter, M. (2002): Fossil Hexactinellida: an overview. In: Hooper, J.N.A., Van Soest, R.W.M. (eds.): Systema Porifera. A guide to the classifications of sponges, 2. 1211-1222, New York (Kluwer Academic/Plenum)

*Mostler, 1-1. (1 976): Poriferenspiculae aus der alpinenTrias. -- Geologisch-Palaontologische Mitteilungen Innsbruck, 6 , 1-42 Mostler, H. (1990): Hexactinellide Poriferen aus pelagischen Kiesekaken (Unterer Lias, Nordliche Kalkalpen). - Geologisch-PalaontologischeMitteilungen Innsbruck, 17,143178 Pisera, A. (2002): Fossil 'lithistids'. - In: Hooper, J.N.A., Van Soest, R.W.M. (eds.): Systema Porifera. A guide to the classifications of sponges, 1. - 388-402, New York (Kluwer Academic/Plenum) *Rigby, J.K. (1995): Sponges as microfossils. -In: Blome, C.D. (ed.): Siliceous microfossils. - Short Course in Paleontology, 8, 1-17 (The Paleontological Society) Warnke. K. (1995): Calcification processes of siliceous sponges in VisCan limestones (Counties Sligo and Leitrim. Northwestern Ireland). - Facies, 33, 215-228

fied demosponges. - In: Reitner, J., Keupp, H. (eds.): Fossil and recent sponges. - 322-340, Berlin (Springer) Archaeocyaths "Debrenne, F., Rozanov, A., Zhuravlev, A. (1990): Regular archaeocyaths. Morphology, systematic, biostratigraphy, paleogeography, biological affinities. - Cahiers de PaEontologie, 2 18 pp. *Debrenne, F., Zhuravlev, A. (1992): Irregular archaeocyaths. Morphology, ontogeny, systematics, biostratigraphy, palaeoecology. - Cahiers de PalContologie, 212 pp. *Debreme, F., Zhuravlev, A.Yu., Kruse, P.D. (2002): Class Archaeocyatha Bomemann. - In: Hooper, J.N.A., Van Soest, R.W.M. (eds.): Systema Porifera. A guide to the classifications of sponges, 2. - 388-402, New York (Kluwer Academic/Plenum) Rowland, S.M., Gangloff, R.A. (1988): Structure and palaeoecology of Lower Cambrian reefs. - Palaios, 3, 1 11-135 Zhuravlev, A., Wood, R. (1995): Lower Cambrian reefal cryptic communities. - Palaeontology, 38,443-470 Further reading: Sponges K114, siliceous sponges K115, sphinctozoan and inozoan sponges K116, stromatoporoids K117, chaetetid sponges K118, archaeocyaths K214

GOI-alliizesponges, stronlatopoi.oid.s m d cha~tetids Hartman, W.D., Goreau, T.F. (1970): Jamaican coralline sponges: their morphology, ecology and fossil relatives. Symposium of the Zoological Society London, 25,205-243 lieitner, J. (1992): 'Coralline Spongien'. Der Versuch einer phylogenetisch-taxonomischenAnalyse. -Berliner Gcowissenschaftliche Abhandlungen, E, 1, 1-352 Rcitner, 3 .,Worheide, G. (2002): Non-lithistid fossil Demospongiae. Origin of their paleobiodiversity and highlights in the history of preservation. -- In: Hooper. J.N.A., Van Soest, R.W.M. (eds.): Systerna Porifera. A guide to the classifications of sponges, 1 . - 52-68, New York (Kluwer Academic/Plenum) "Senowbari-Daryan, B. (1990): Die systematische Stellung der thalamiden Schwanlme und ihre Bedeutung in der Erdgcschichtz. - Miinchncr Geowisscn.schaftlicl~eAbhandlungen, A: 21, 1-326 Seno\vhari-Llaryan, I3., Garcia-Rellido, U.C. (2003): Fossil 'Sphinctozoa': chambered sponges (polyphyletic). - 111: IIooper, J.N.A., Van Soest. K.W.M. (eds.): Systema Porifern. A guide to the classifications of sponges, 2. - 15 111533, New York (Kluwer Acadeniic/?lenum j "Stearn, C.W'., Webby, B.D.. Nestor, [I., Stock. C.bJ. (1999): Revisited classification and tertninology of Palaeozoic

-,

Turnsek, D., Buser. S., Ogorelec, B. (1981): An Upper Jurassic reef complex from Slovenia. - In: Toomey, D.F. (4. European ): fossil reef models. -Society of Economic Paleontology and Mineralogy, Special Publications, 30, 361 -369 Y'urnsek, D.. Masse, J.P. (1973): The lower Cretaceous Hyt l r o ~ o aand Chaetetidae from Provei~ce(south-eastern Frmce) - Slovemka Akademija Znanosti In Umetnost~, Razp~d\c, 16, 317-243 \Vendt.^~.(1983): Skeletal and spicular mineralogy microstructure and diagenesis of coralline calcareous sponges. - Palaeontographica Americana, 54, 326-336 Wiirheide. G. (1998): The reef cave dwelling ultraconservative coralline demosponge Astr.osi.1er.a vtilleyuna Lister 1900 fi-om the Indo-Pacific. - Facies, 38, 1-88 Wood, R.A. (1987): Biology and revised system of some late Mesozoic stromatoporoids. - Special Papers in Paiaeontology. 37, 1-89 Wood, R.A. (1 99 1 ): Non-spicular mineralization in calci-

Fig. 10.37. Heterastridiun~Reuss. The globular or noJul;i~fossil ranges in size between a few centimeters to tens of centimeters. It consists of radially arranged tubes of difkrent morphology, some of which are reflected by pustules on the surface. Mass occurrences of Hetrrastr-idiunr have bcen described from Norian basinal limestones all over the Tethyan ocean. The genus was considered to be a hydrozoan - but who knows? Late Triassic (Nayband Formation, Norian): Kuh-e-Nayband, central Iran. Courtesy of B. SenowbariDaryan (Erlangen).

10.2.3.2 Hydrozoans If Paleozoic stromatoporoids and most Meso~oicfossils previously described as 'hydrozoans' or 'stron~aloporoids' now are to be assigned to the sponges, the fossil record of true calcareous hydrozoans found in thin sections of limestones is meager and restricted to Cretaceous and Tertiary Milleporidae, Stylastericlae (PI. 147153, and some Hydractiniidae. Still one hydrozoan candidate is Hetc.rusrl~idiuni,a puzzling fossil know11only from the Late Trlassic and occurring abundantly in open-marine limestones (Cuif 1971: Fig. 10.37).

Major Coral Groups

10.2.3.3 Corals Corals are common constituents of limestones. Paleozoic rugose corals and tabulate corals are widely distributed in shelf and ramp environments and contribute to the formation of reefs. Mesozoic and Cenozoic scleractinian corals are important reef builders in tropical and subtropical warni-water zones but also occur in temperate and cold-water environments.

Major groups: Corals are Cnidaria comprising the hydrozoans, scyphozoans and anthozoans. Corals are

members of the exclusively marine, usually sedentary Anthozoa. The number and symmetry of vertically arranged infoldings of the gut wall in the body cavity of the polyps and the type and composition of the skeleton serve to divide the class into various groups, such as the soft corals, sea fans (Octocorallia), sea anemones, and the stony or true corals. Octocorals occur from tropical to polar regions and from tidal zones to deep sea. The skeleton of octocorals consists of small calcitic sclerites (0.10 to l mrn) that are common in recent sediments but very rare in the fossil record. True corals, commonly collected in the subclass Zoantharia,

Box 10.6. Major coral groups. Technical terms used are: axial structure - structural element occurring in the center of corallites; corallun? - the skeleton of a coral colony; corallite - the skeleton of an individual coral polyp; coenosteum colonial skeletal deposits formed between corallites; dissepiments - blister-like calcareous elements between septa; edge zone - a fold in the body wall extending over the edge of the corallum; epitheca - outer skeletal sheet laid down by the edge zone; microarchitecture - the spatial arrangement of microstructural elements; microstructure - basic elements of septa and walls; protosepta - initial septa formed at first; septa - radial and vertical element extending from the wall toward the center of corallites; tabulae - horizontal elements within the whole or a part of the corallite; trabecula fibrous rnicrostructural element corresponding to vertically stacked cones and related to skeleton fonnation; wall peripheral calcareous element bounding the c&allites Rugosa - P1. 83/3,8, 10 Criteria: Calcitic skeleton. Solitary or colonial. Cupshaped, conical or cylindrical solitary corals ranging in diameter from a few millimeters to several centimeters. Centimeter- to meter-sized massive or dendroid colonies with variously integrated corallites. Major and minor septa. Long major septa inserted serially in four positions; shorter minor septa inserted between major septa. Septa usually with trabecular microstructure. Dissepiments and tabulae always present. Axial structures present or absent, often of septal origin. Walls formed by laterally fused septa dissepiments of additional thickened stereoplasm. Sigrzificance: Many rugose corals serve as good indicators of paleoenvironment and age. Distribution: Ordovician to Late Permian. Tabulata - PI. 4111; P1. 8311, 4, 7, 9, 11; PI. 13511, 2, 4; PI. 14317, 8 Criterm: Calc~ticskeleton. Exclusively colonial. Sheetlike to dome-shaped, or erect-branched, or chain-like forms. Colonies generally small, but colonies with a diameter of several meters are also known. Slender tubelike corallites ranging in size between 0.5 to about 5 mm. Pores or tubes between corallites. Septa absent or short, commonly expressed iis rows of spines or low ridges. Tabulae common and numerous. Dissepiments present or absent. Significance: Important reef-building organisms in the Silurian and Devonian, often together with stromatoporoid sponges. Distribution: Early Ordovician to Late Permian. Common in Middle Ordovician, Silurian, and Devonian. Less common in the Carboniferous and Permian.

Heliolitida - PI. 8315, 6 Ci-iteria: Calcitic skeleton. Exclusively colonial. Massive, dome-shaped or laminar forms. Slender corallites are separated by extensive coenosteum consisting of smaller tubes. Septa generally present, commonly 12 in number. either spinose or laminar. Tabulae common. No evidence of communication between corallites. Similar to tabulate corals in having corallites with tabulae but different in having corallites embedded apparently within a colonial tissue developed between the polyps. Significance: Sometimes reef builders. Distribution: Late Ordovician to Middle Devonian. Heterocorallia - P1. 8312 Criteria: Calcitic skeleton. Elongate solitary corallites with four axially connected protosepta. Subsequent septa in each quadrant remain attached to earlier septa, dividing successively to form characteristic Y-shaped patterns. Tabulae present. Significance: Predominantly restricted to the VisCan, useful as index fossils. Distribution: Uppermost Devonian and Early Carboniferous. Scleractinia - PI. 8411-6, PI. 11511, Pi. 11613, Pi. 11711; PI. 13412; P1. 14711, 2 , 4 Criteria: Aragonitic skeleton. Solitary or colonial. Varying strongly in shape and colony form. Sixfold symmetry of septal insertion (hence the name hexacorals). Complex microarchitecture and microstructure of septa and walls. Significance: Prominent reef builders since the Late Triassic and even more since the Late Jurassic. High carbonate production in shallow-marine environments and periplatform areas by accumulation of coral debris. Distribution: Middle Triassic to Holocene.

Plate 83 Paleozoic Coral Groups The plate displays examples of the two major Paleozoic coral groups and another small group (see Box 10.6 for definitions). Rugose corals (-> 3, 8, 10) are known from the Middle Ordovician to the Late Permian. Rugose corals were widespread and common by the Silurian and increased in number and diversity in the Devonian. Following a marked extinction event at the Frasnian-Famennian boundary and at the end of the Devonian, new families with new morphological features (e.g. complex axial structures, -> 10) arrived in the Early Carboniferous and persisted until the end of the Permian. Tab~datecorals (-> 1 , 4 , 7 , 9 , 11) received their name from horizontal partitions within the corallites, known as tabulae. The group was common from the Early Ordovician to the Late Permian. Diversification took place at the end of the Ordovician. Tabulate corals played a significant role in the formation of Silurian and Devonian reefs. Many tabulate coral taxa disappeared in the Late Devonian. Late Paleozoic tabulates are rare. Heterocorallia (-> 2) restricted to the latest Devonian and Early Carboniferous differ from all other corals by a specific pattern of septa insertion. All these groups apparently had primarily calcitic skeletons. Tabulate corals. Encrusting colony of Alveolites (A) intergrown with stromatoporoids (S). The colony consists of inclined corallites opening obliquely at the surface and appearing rounded polygonal in transverse section. Adjacent corallites are connected by mural pores. Matrix is a peloidal packstone. Reef facies. Late Devonian (Frasnian): Canning Basin, western Australia. fletcrocor-als.The solitary corallites of this small group are characterized by a specific shape and arrangement of the septa with four axially joined initial septa and later septa forming a Y-shaped pattern. The thin wall consists of microgranular calcite. Three cross-sections of Hexaplzyllia mirahilis Duncan. Heterocorals are common fossils of VisCan inner shelf environments but are also known from the latest Devonian. Matrix is a peloidal micrite with benthic foraminifera (bottom right). Early Carboniferous (Marbella Formation, Late Viskan): Betic Cordillera, southern Spain. Colonial rugose coral. Cross section of Argustrea quadrigernirza Crickmay. The walls of adjacent corallites are united, forming a massive cerioid corallum (coral skeleton). The blister-like elements between the septa are dissepiments corresponding to small convex plates. Middle Devonian (Givetian): Ermberg, Rheinisches Schiefergebirge, Germany. Tubdate co~.als.Oblique and longitudinal sections of Thamnopora sp., a widely distributed tabulate in Devonian lagoona or restricted back-reef environments. Note the conspicuously black matrix. This is a common feature of Devonian shell carbonates, deposited in protected environments rich in organic matter. Early Devonian (Emsian): Cantabrian Mountains. Spain. H~iioliliiiCOI-01. Heteromorph colony of Puchyranaliculata burrandei (Penecke). The slender corallites are separated by 3 zone (coenosteum) composed of narrow polygonal tubes. Heliolitids have been included within the tabulate corals because of the existence of tabulae both in broad corallites and narrow tubes, but are now considered to represent a separate coral group because of the development of distinct equal septa. Middle Devonian (Eifelian): Graz, Austritt. liirliolitid c,oral.Longitudinal section. Corallites and the smaller tubes of the coenosteum differ in the size and frequency of the tabulae. Late Devonian (Frasnian): St.Barbe Quarry, Dinant Basin, Belgium. lhhuiate coral. Longitudinal section of Favosires styriacus Penecke. The corallites are subdivided by numerous, evenly spaced horizontal partitions (tabulae). Adjacent corallites communicate through mural pores (arrows) arranged in rows. S'me locality as --> 5. Cnforziulr~tgosccoral. The cross section of Multimurinus shows a cerioid growth pattern characterized by corallites [hiit are touching each other. Note the distinct axial structure (arrow), a common feature of Late Paleozoic Rugosa. Tethyan Middle and Late Permian bedded shelf sediments often contain intercalated banks consisting of these tens of centimeters i ~ e dcompound corals, which in places can form frame- and bafflestones (Weidlich and Fliigel 1995). Middle Permian (Wurdian): Widi Aday, southwesiern Muscat, Oman. 'Ii~hitlntccorals. Favositid ( F ) and thick-walled encrusting auloporid (A) corals. Auloporid corals acted as bafflers, contributing to mound formation, C: Crinoid ossicle, T: Trilobite debris. Late Carboniferous (Kasimovian): Carnic Alps, Italy. Rugosc~coral. The cylindrical corallites of Siphonodendron are not in contact and form a fasciculate structure. Note the peripheral zone formed by dissepiments and the distinct axial structure. The latter is a characteristic feature of Late Paleozoic rugose corals. Cross section. Early Carboniferous: Western Anatolia, Turkey. Tabulare coral: Parasfriatopor-a.The peripheral margins of the coral have been destroyed. This might indicate abrasion during transport or dissolution within the sediment. Early Devonian (Emsian): Erfoud, Anti-Atlas, Morocco.

Plate 83: Paleozoic Corals

51 1

are defined as those anthozoans that secrete massive external calcium carbonate skeletons. These corals include the Rugosa, Tabulata and Scleractinia as well as some minor groups. For definitions of these groups see Box 10.6.

Ecology: Major controls on the distribution of modem scleractinian corals include surface water temperature, light, symbiosis, and surface circulation (see Veron 1995 for a critical discussion). The symbiosis of corals and endosymbiotic algae has many physiological advantages for corals: enhancement of calcification, removal of metabolic waste, and concentration and recycling of nutrients. The term zooxantellae refers to endosy~nbioticphotosynthesizing dinoflagellates, red and green algae as well as cyanobacteria. The terms zooxanthellate and azooxanthellate applies to corals liv-

ing with or without benefit of algal symbiosis (Schuhmacher and Zibrowius 1985).Zooxanthellate corals are restricted both bathymetrically and geographically by their algal symbionts and are therefore concentrated in shallow tropical and subtropical waters where they build coral reefs. Azooxanthellate corals (Pl. l47/l, 2,4) occur both in shallow and deep environments,but are more abundant at greater water depths of several hundreds of meters and more. Deep-water scleractinian corals with constructional frameworks (e.g. Lophelia, P1. 4/ 3) form extended reef structures (Sect. 2.4.4.3). Azooxanthellate deep-water corals may have existed since the Early Mesozoic (Stanley and Cairns 1988).

Skeletal mineralogy, microstructure and prescnatian: The originally aragonitic skeletons of scleractinian corals become unstable once removed from marine

Plate 84 Jurassic Scleractinian Corals Scleractinia or hexacorals (because of the sixfold symmetry of septa1 insertion) are colonial or solitary corals with an aragonitic skeleton. The group became diversified and widely distributed in reefs and shelf environments in the Late Triassic and continued to expand during the Jurassic and Cretaceous. They were important reef builders in the Late Jurassic and during the mid and Late Cretaceous. The diversity and importance as r e d builders increased starting with the Eocene and reached a peak in the Miocene, when most of the modern reef corals originated The plate displays growth typcs rind n?orphoiogical clzaracteristics of Jurassic scleractinian colonial corals. In massive skeletons adjacent corallites may correspond to the astraeoid type (without walls separating individual corallites, septa in contact), maeandroid type (-> 3 ) or cerioid type (-> 6). The corailites ol' bushy, fascicxlate colonies niay be arranged parallel to each other (phaceloid, -> 1,5) or branch irregularly in a tree-like pattern. Jurassic corals, constructing frameworks and baffling fine-grained sediment, contributed to the formation of reefs in high-energy shelf and platforni-margin environments as well as on ramps. Environmental demands on Jurassic corals might have been considerably different from those of modem scleractinians (Leinfelder el al. 2002). I Gi-ott.fiifypc. Transversal section of S~ylosnziliucorallirza Koby. The colony consists of separated non-integrated coral-lites which are more or less parallel (phaceloid growth type). Late Jurassic (Tithonian): Madonie Mountains, Sicily, Italy. 2 Rclfc.c?i-ois: Transversal section of Calan~o~~hyllio~~sisflubcll~rnz (Michelin). The coral colony is encrusted (black arrows) irlici horeil (B). The peloidal bindstone texture with spar-filled fenestrae (F) between the corallites indicates microb~al binding of bioclaslic material. Middle to Late Jurassic. Pierre Chatel, south of Grenoble, France. ; G ! - o I ~r yLl x . Oblique section of Myiophyllia I-usrellinu (Michelin). The closely integrated chains of corallites of the maeandroid colony are arranged in linear series (black arrows) within the same walls. The exsert edges of the septa and walls form a ridge (white arrows). The structure is caused by intratentacular budding where ncw polypes and corallites are formed through division within the parent corallites. Same locality as -> 1. 4 Rr~u,c>i-k~d corals. The thin section exhibits an allochthonous assemblage of broken and redeposited colonial corals, incl~~tiing Istrstrtrcu sp., I, Mcsonzorplza sp., M, and Thanmasteriu gracilis (Miinster), T. Note the absence of definite walls in Tl~ilnlizasic~-iu and Mesornorplla; the corallite centers are closely united by confluent septa. In thin sections coral debris can be recognized not only in fragments exhibiting skeletal elements but also in bioclasts smaller than 0.20 mm (Stanton and Fiiigel 1989). Jurassic exotic blocks floating in Cenozoic deposits: Northern margin of the Alps, Salzburg, Austria. 5 h ' c ~ e f ( . o t u lTransversal ~: section of Tl~ecosnrilialnnginlana (Quenstedt). The bushy colony consists of laterally free corallites forming tufts of parallel corallites (phaceloid growth type). Note the biogenic encrustation (arrows) and the complctc filling of the interspaces between the corallites by binding and encrusting organisms contributing to the formation of an organic framework. Late Jurassic: Same locality as -> 1. 6 C , v b $ ~type. l ~ Transversal section of Latisrr-aeafoulassensis Beauvais characterized by closely appressed prismatic corallites whose walls are fused to each other (ccrioid growth type). Late Jurassic: Untersberg, Salzburg, Austria. >: 1--6: Dctennination by D. Turnsek (Ljubl.jar~a)

Plate 84: Jurassic Scleractinian Corals

513

Fig. 10.38. Preservation of rugose corals compared with that of scleractinian corals. A: Late Permian rugose coral from Oman. All the diagnostic skeletal elements (septa, dissepiments, axial structure, external wall) are well preserved. B: Late Jurassic scleractinian coral from the Northern Calcareous Alps. Diagnostically important skeletal elements are only partly preserved. The thickness and shape of the septa are moderately modified by diagenesis, but the center and the periphery of 7he corallites are strongly affected. Scale is 2 mrn. environments and are susceptible to dissolution and neomorphism under burial or subaerial conditions. Dissolved skeletal elements may be preserved as spar-filled or sediment-filled molds. Identification of scleractinian corals requires recognizing the microstructures of calices and septa, but these fine structures are often destroyed by diagenesis. Sometimes weak neomorphisin of' coral skeletons can lead to the preservation of the internal microstructures. Common diagenetic modifications of scleractinian coral skeletons ~ncludethe thickening of skeletal elements and the format~onof pseudoskeletal elements. Rugose corals apparently secreted a calcitic skeleton and are therefore not as strongly affected by diagenetic modifications as scleractinians (Pl. 29/2; Fig.

10 38). Cot a1 stt UCILLICJ 111 thin scrtio~ls Plate 83 and 84 shob \oinc of the cha~acteristicfeature5 of rugose and tabulate coral$. heterocoials and \clerac~lniansseen in thin \cct:ons Basics: Corals Hill, D. ( I 98 1): KugusaandrTabulata.-Treatiseon Invertcbrate Paleontology,Coelenterata,supplement 1. -762 pp., Lawrence (Geological Society of America) Oliver, W.A., Coates, A.G. (1987): Phylum Cnidaria. - In: Boardman, R.S., Cheetham, A.H., Rowell, A.J. (eds.): Fossil invertebrates. - 140-193, Palo Alto (Blackwell) Schuhmacher, H., Zibrowius, H. (1985): What is hermatypic? A redefinition of ecological groups in corals and other organisms. - Coral Reefs, 4, 1-9 Scrutton, C. (1999): Palaeozoic corals: their evolution and palaeoecology. - Geology Today, 15, 184-193 Sorauf, J.E. (1993): The coral skeleton: analogy and comparisons. Scleractinia, Rugosa and Tabulata. - Courier For-

schungsinstitut Senckenberg, 164,63-70 Veron, J.E.N. (1995): Corals in space and time. The biogeography and evolution of the Scleractinia. - 321 pp.. Sidney (UNSW Press) Wells, J.W. (1956): Scleractinia. - Treatise on lnvertebratc Paleontology,F, Coelenterata. - 328-440, Lawrence (Geological Society of America) Further reading: K119, K120. K121

10.2.3.4 Bryozoans Bryozoan carbonates reflect specific depos~tionalsettings and paleocliinatic conditions. Bryozoans are pr edominantly marine, active suspension feeders forming ~nillimeter-to a several centimeter-sized colonies occurring from tidal level down to bathyal depths. They dominate in shelf seas, are abundant in depths between the intertidal zone and about 80 m and live both rn 10% and high latitudes.

Morphology: The colony (zoarium) consists of intctconnected individuals (zooids) usually living wlthin calcareous tube- or boxlike chambers (zooecia) that mdy or may not exhibit a number of transverse plates. A11 opening (apertura) is developed at one end of the zooecia. Zooecia and apertures exhibit strong polymorphisn~reflecting different vital functions of zooids. The colonies have wide ranges in fonn and size. They may be massive, encrusting, stick-like or correspond to a delicate branching network. The taxonomic differentiation of bryozoans requires thin-section studies. The skeleton of modern marine bryozoans consists of Low-Mg calcite or intermediate-Mg calcite (Cyclo-

Bryozoans

stomata) or aragonite (Cheilostomata). Differences in skeletal mineralogy may control diagenetic pathways of bryozoan cold-water carbonates (Bone and James 1993). Classification: Modem Bryozoa include the marine classes Stenolaemata and Gymnolaemata and the freshwater class Phylactolaemata, the first two with skeletons, the last without a skeleton. The Stenolaemata are characterized by elongated tubular or conical zooids and tube-like zooecia. The class covers the wealth of bryozoans found in limestones of Ordovician through the mid-Cretaceous age. By the Late Cretaceous the stenolaemates were exceeded in diversity by the gymnolaemates but continue to flourish in marine communities. The Stenolaemata include the orders Trepostomata (Early Ordovician to Triassic), Cystoporata (Early Ordovician to Triassic), Cryptostomata (Early Ordovician to Late Permian), Fenestrata (Early Ordovician to Triassic), and Tubuliporata (Early Ordovician to Holocene). The Gymnolaemata are the morphologically most varied class and exhibit box-shaped zooecia. It includes the orders Ctei~ostonzatiz(uncalcified, Ordovician to Holocene) and Cheilostomata (calcified, Late Jurassic to Holocene). The greater part of the gymnolaemate diversity has evolved since the mid-Cretaceous.

5 15

Bone 1991; James et al. 1993). These differences are used in interpreting the water energy, substrate and temperature conditions of ancient bryozoan-bearing carbonates. Differences in colony growth forms are used as paleobathymetrical proxies (for shallow and deep shelf environments) and indicators of substrate stability (Hageman et al. 1998). This approach is successful in the study of Cenozoic bryozoan carbonates (Herbig 1991) and sometimes also Mesozoic carbonates, but has limitations in the study of Paleozoic bryozoans (Kelly and Horrowitz 1987), see also Pi. 85/3.

Carbonate production: Recent bryozoans are common in sediments of the continental shelves, but also occur in reefal environments (Cuffey 1972). Bryozoan bioclasts are abundant constituents of modem and ancient cool-water shelf carbonates contributing to the formation of carbonate particles of all grain sizes. Grain sizes of bryozoan carbonates are strongly controlled by skeletal architecture, as shown by the bryozoan sands, muds and gravels on the southern Australia Lacepede Shelf. Skeletal architecture is related to the strength and disintegration potential of bryozoan skeletons (Cheetham and Thomsen 1981).A significant number of modem bryozoans live attached to sessile, benthic invertebrate hosts, which are not or only slightly calcified and leave no or little body fossil record. Bryozoan sediEc,oluyy: Most colonies are attached to hard material ment production from epizoans on ephemeral substrates such as rock, shells or sediment grains. Intertidal and may have been important in the Tertiary (Hagernan et upper subtidal encrusters are common on the under- al. 2000). sides of hard substrates. Other habitats of encrusting Bryozoans can contribute to Cenozoic shelf deposbryozoans are long-lived stable hard substrates (reefs, its with a quantity of up to 95% (e.g. off New Zealand). rock walls). Bryozoans adhere also to flexible soft sub- Huge areas of the Pacific deep shelf bottom between strates, e.g. sea weeds and algal fronds. The majority western Australia, New Zealand and the Chatham Isof bryozoan habitats is found in areas of low sedimen- lands extending about 6000 km are dominated by bryotation. zoan sediments. This 'bryomolfacies' is a characteristic feature of non-tropical carbonates (see Sect. 12.2). Paleoenr~iro~lmetztal significance of bryozoans: Bryozoan-richmicrofacies types are common in platB~yozoansare excellent paleoenvironmental and paleo- form and ramp carbonates throughout the geological climatic indicators particularly for temperate and cold- past, particularly in Paleozoic shelf limestones and may water carbonates. The presence or absence of bryozo- contribute to the formation of reefs (e.g. Permian Zechans, diversity and abundance, zooid morphology, colo- stein reefs; PI. 85/11; Early Tertiary Danian reefs, P1. nial plasticity and growth form as well as reef-like struc- 147/2,3). tures provide information on the physical controls on the habitat. Paleoenvironmental parameters, such as as Distribution: Bryozoans are known since the Ordovitemperature, salinity, water energy, character of the sub- cian. Five of six known Paleozoic orders became exstrate, and sedimentation rate may be indicated by bryo- tinct in the Triassic, but the Cyclostomatapersisted from zoans (Smith 1995). the Ordovician to the present, dominating many fauModem cyclostome and cheilostome bryozoans show nas in the Mesozoic. The Cheilostomata are the other distinct zonation of growth form assemblages and spe- important modem marine group. They arose in the Late cial growth-form morphologies depending on the en- Jurassic and became dominant in the Late Cretaceous vironment (Stach 1936: Nelson et al. 1988; James and and Cenozoic.

B ~ y o z o u n s112 thw sections (Pl. 85): Bryozoan sections can be distinguished from other fossils consisting of calcareous tubes (e.g. chaetetid sponges) by the presence of polymorphic tubes of various widths, and by a characteristic fanlike pattern in longitudinal and oblique sections, resulting from a different arrangement of the zooecia in the inner axial zone of the colony and near the surface (PI. X5/2,7). Paleozoic trepostome bryozoans may display morphologically different tubes in addition to the zooecia, differing in the diameter and the development of horizontal elements. Small acanthopores have a laminated cone-in-cone structure pointing outward within the laminated wall. Mesopores of Early Paleozoic trepostonle bryozoan contain numerous transverse plates, in contrast to the mesopores of Lare Paleozoic tam. Many Paleozoic trepostome and cryptostome tubular bryozoans exhib~tzooecia walls that are thin In the inner zone of the colony and thick in

the outer zone. Paleozoic cyclostome bryozoans are characterized by simple tests with walls of constant thickness and generally without internal structures. Post-Paleozoic cyclostomes exhibit a thick finely laminated wall structure in the outer zone of the colony and minutely porous walls. Paleozoic cystoporate bryozoans have a vesicular to cystose framework between the zooecia and simple tubes which are commonly modified by a hood (lunarium) at their outer ends. This structure is reflected internally in tangential sections by a crescent-shaped notch in the wall and a thickening of the wall tissue behind the notch (Pl. 8514). Bryozoan wall microstructure may be laminated, granular or fibrous. The laminated structure occurs in many bryozoan groups and is one of the distinctive features of bryozoan debris (Pl. 85/41. Details of the rnicrostructural types can be found in Horowitz and Potter (1971).

Plate 85 Bryozoans The plate displays thin sections of bryozoans belonging to different systematic units. Characteristic thin-section features of bryozoans are (a) colonies consisting of variously sized tubes (-> I), (b) different arrangement of tubes in the inner and outer part of the colony (-> 3) resulting in a fan-like pattern (-> 7), (c) window-frame network structures (-> lo), and (d) finely laminated wall structures (-> 4, 10). See also P1.415; P1.9/5,6; PI. 5 11 6: Pi, i 0611-3; PI. lO7/l, 2; PI. 144/7. and P1. 14712, 3 for further photographs. 7 i ~ q ~ ) . s~ r~ oO ~: O~ L~( ~I (/i('/~[otioditr~~[)ii IS ~.(iuticu Schafer and Fois), characteri~edby polymorph tubes (~ooecia).Ob!iy~~i. sections. Sections of trepostome bryomans are characterized by robust massive or dendroid colonies and s~nnlllubi.5 between larger ones. Middle TI-iassic(Anisian): Olang Dolomites, Southern Alps, Italy. Cysfop.)i-idhryozoat~are characteri~cdby encrusting or massive colonies consisting of large zooecia (Z) embedtied uritl-iina framework of smaller tubes (cystopores (C). Oblique section. Early Carboniferous: Niitsch, Austria K(fi)liorc cyclostornid hr-yo,-oati.Note the differentiation of central and peripheral parts of the colonies. The vinculariid erect growth form with dichoton~ouslpbranched zooecia indicates a protected environment. Late Tertiary (hlioccnt.): Subsurface, Suez region, Egypt. Broken branch of a cystoporid bryozoctn. The cross section of zooecia (Z) showing the typical crescent-shaped notch In the wall is infilled with micrite and einbedded in a thickened wall exhibiting a lamellar structure (arrow). Mississipi7in~: Turtle Mountains, Frank Slide, soutltcastem Alberta, Canadian Rocky Mountains. C'r~ptc~s~rc~rrir 6ryu:oar~Crypostonie br>~ozoans are characterized by delicate dendroid or bifoliate colonies, axial zooeci;r hundles and in cross sections short elliptical zooecia in the peripheral zones. Oblique section. Ordovician (Caracloc. Macrourus limestone): Oland Island, Sweden. Fcncsrrcite br:yozout~exhibiting cross sections of zooecia and lamellar wall structure. Middle Permian: Stram, Slowilla C~ry?riisrot?ic ht.yo:oizlz. Transverse [I')and longitudinal (L) section. Note radial distribution and the curvature of zoc)~i;1 toweardthe outer margin and the thickened wall structure at the exterior margin (arrow). Cold-water carbonate. Late Ordovician (Berindale lin~estone):Southeastern Tasmania, Australia. Ferws~rut~~ br)'o:ouri with serially arranged zooecia on the surface of a broken frond. Mississippian (Toumaisiani: Mouse Mountains near Calgary, Alberta, Canada. Cystoporid bt-yozoan (Fist~dipora). Oblique section of a broken colony. Note zooecia (Z) separated by vesicular t i s s ~ (cystopores. C). Early Pem~ian:Powoni Canyon, Hueco Mountains, Texas, U.S.A. 10 Fcnc'.srrate bryo.wczn. Outer part of a fan-shaped colony. Zooecia occurring on the surface of the colony (inner part of the fan) can not be seen in this section. Fenestrate bryozoans are characterized by erect rigid fronds connected by cross bars forming a characteristic network with open meshes (fenestrulae, F). Note lamellar wall structure. Most members of ttii.; group preferred quiet sheltered environments. Mississippian: Turtle Mountains, Frank Slide, Alberta, Canada. I I Bryoman debris consisting of fragments of fenestrate bryozoans. Reef facies. Late Permian (Zechstein): Bartolsfeitie, I m v e r Saxony, Germany.

Plate 85. Bryozoans

517

Shell Microstructur.cs

Basics: Brjozoans Boardman, R.S., Cheetham, A.H. (1987): Phylum Bryozoa. --In: Boardman, R.S., Cheetham, A.H., Rowell, A.J. (eds.): Fossil invertebrates. - 497-549, Palo Alto (Blackwell) Bone, Y., James. N. (1993): Bryozoans as carbonate sediment producers on the cool-water Lacepede shelf, southe m Australia. - Sedimentary Geology, 86,247-271 Brood, K. (1978): Bryozoa. - In: Haq, B.U., Boersma, A. (eds.): Introduction to marine micropaleontology. - 189201, New York (Elsevier) Conti, S., Serpagli, E. (1988): Bimineralic (calcareous and phosphatic) skeleton in Late Ordovician bryozoa from Sardinia: geological implications. - Bolletino della Societa Paleontologica Italiana, 27, 129-162 Cuffey, R.J. (1972): The role of bryozoans in modem coral reefs. - Geologische Rundschau, 61,542-550 Gordon, D.P., Smith, A.M., Grant-Mackie, J.A. (eds., 1996): Rryozoans in space and time. - 442 pp., Wellington (National Institute of Water and Atmospheric Research) Hageman, S.J., Bock, P.E., Bone, Y., McGowran, B. (1998): Bryozoan growth habits: classification and analysis. - Journal of Paleontology, 72,418-436 Hageman, S.J., James, N.P., Bone, Y. (2000): Cool-water carbonate production from epizoic bryozoans on ephemeral substrates. - Palaios, 15, 33-48 McKinney. EK., Jaklin, A. (2001): Sediment accumulat~on in a shallow-water meadow carpeted by a small erect bryozoa. -- Sedimentary Geology, 145, 397-410 Robison, R.A (ed , 1983): Bryozoa (revised): introduction, order Cystoporata, order Cryptoporata. - Treatise on Invertebrate Paleontology, 644 pp., Lawrence (Geological Society of America and University of Kansas)

Scholz, J. (2000): Eine Feldtheorie der Bryozoen, Mikrobenmatten und Sedimentoberflachen. - Abhandlungen der Senckenbergischen naturforschenden Gesellschaft, 552, 1-193 Smith, A.M. (1995): Paleoenvironmental interpretation using bryozoans: a review. - In: Bosence, D.W., Allison, P.E. (eds.): Marine paleoenvironmental analysis from fossils. -Geological Society of London, Special Publication, 83,231-243 Stach, L.W. (1936): Correlation of zooarial form with habitat. -Journal of Geology, 44, 60-65 Taylor, P.D. (1998): Bryozoan carbonates through time and space. -Geology, 26,459-462 Further reading: K122

10.2.4 Shells The fourth part of the discussion of thin-section fossils deals with shell-bearing organisms characterized by bivalved or univalved shells (brachiopods, mollusks, serpulids, ostracods) or by multi-elementJmulti-plateshells (trilobites, crustaceans, echinoderms). Most of these fossils are too large to be included in a standard microfacies thin section that will most commonly only exhibit parts or fragments of the skeletons. An identification of these bioclasts as to higher systematic levels is possible when original shell microstructures are still preserved or unique diagnostic criteria are visible. 'The

Box 10.7. Some microstructure types occur^-ing in shells of brachiopods. mollusks, serpulids and ostracods. Definitions based on Majewske (1969) and Carter (1980) Conzplw a-ossed-lamellar:Characterized by a disorderly arrangement of the elements of the crossed-lamellar microstructure. Found in bivalves and gastropods. Crossed: Consisting of elongate structural subunits organized into adjacent, interdigitating aggregations referred to as first-order lamellae. Includes crossed-lamellar and complex crossed-lamellar ~nicrostructures.Common in bivalves and gastropods. Crossrd-ltrmellar.. Consisting of numerous branching and wedging lamellae oriented perpendicular or slightly inclined to the plane of the sheli layer. Each lamella consists of small crystals inclined at a constant angle and inclined in opposite directions in adjacent lamellae. Most perfectly developed in aragonitic shells but also occurring in calcitic shells. May constitute all microstructural layers in mollusk shells or may alternate with other microstructures. Common in gastropods and bivalves. Foliated: Composed of numerous very thin calcite lamellae which may be uniformly oriented over long distances or randomly oriented over short distances. Common in brachiopods, some bivalves and gastropods, and some serpulids.

Homogeneous: Characterized by orderly arrangement of uniformly small crystals. Appears bright in transmitted light and will progressively extinguish under crossed nicols if the stage is rotated. Common in ostracods and aragonitic mollusk shells. Laminar: Characterized by sheets of strongly flattened structural units developed uniformly parallel or oblique to the surface. Includes aragonitic nacreous microstructures and calcitic foliated microstructures. Brachiopods. bivalves, gastropods. il'acr-ems: Refers to an orderly arrangement of numerous thin aragonitic laminae, each separated by thin films of organic material and uniform orientation ('mother-ofpearl'). Common in bivalves, gastropods and cephalopods. Prisnzatic: Consisting of closely packed, generally parallel prisms of calcite or aragonite, generally oriented with their length perpendicular or slightly inclined to the plane of shell layers. Prism columns are mostly longer than wide. Common in bivalves. Spherulitic: Consisting of densely packed spherical to subspherical aggregates of elongate structural subunits which radiate in all directions from a central nucleation site. Rare in aragonitic bivalve shells.

Brachiopods

study of microstructures in thin sections requires magnifications of at least x30 and the use of polarized light. Staining techniques (Adams and MacKenzie 1998) and cathodoluminescence microscopy are strongly recommended. In-depth evaluations of microstructural features are based on SEM data. A comparison of these data with thin-section observations is sometimes difficult, partially because of different definitions of microstructures seen in SEM and in thin sections. The terms listed in Box 10.7 are those commonly applied to microstructures exhibited in thin sections.

10.2.4.1 Brachiopods Brachiopods are bilaterally symmetrical sessile marine organisms with an external shell consisting of two dissimilar but equilateral valves. Brachiopods are major contributors to the bioclastic content of shallow-marine limestones, particularly in the Paleozoic. Morphology and classification: Traditionally brachiopods have been split up into two major groups, the Inarticulata and the Articulata. The Inarticulata dominated in the Cambrian and Ordovician; they received their name from the fact that the two valves do not have an articulating hinge and are united by muscles. Their shells are composed of alternating layers of calcium phosphate and chitin. All other brachiopods included within the Articulata have articulating hinges and calcitic shells. The main groups of the Articulata are the Strophomenida (Ordovician to Middle Jurassic; including the Late Paleozoic productids and brachiopods that are attached with one cone-shaped valve at the substrate, while the other valve acts as a lid; P1. 86/2), Orthida

(Middle Cambrian to Permian), Pentamerida (Late Cambrian to Devonian), Rhynchonellida (Ordovician to Holocene, abundant in the Mesozoic), Spiriferida (Ordovician to Early Jurassic, extremely diverse during the Devonian), and the Terebratulida (Carboniferous to Holocene), the most common brachiopods today. The body of brachiopods is enclosed by a valve except for the pedicle which serves to attach the animal to the substrate. The larger valve on the ventral side of the body is the pedicle valve, the smaller valve on the dorsal side the brachial valve, taking its name from the brachia. These are am-like projections of the lophophore, a feeding organ that also carries them. Shell structures: All articulate brachiopods have Low-Mg calcite shells. The shell grows continually throughout the life of the animal; new material is laid down around the larger rounded edge of the shell. The original wall structure is commonly well preserved. The calcitic shell is overlain by a thin chitinous layer (periostracum), never preserved in fossil shells. The calcitic shell consists of two layers - (1) a thin outer primary cryptocrystalline layer of fairly constant thickness, and (2) an inner, thicker layer that thickens with growth and from which all internal structures are formed. The primary layer is difficult to detect, but i t may be recognizable in shells of different brachiopod groups. The boundary between primary and secondary layers is commonly sharp. The characteristic feature of brachiopod shells is a foliated lamellar structure of the secondary layer appearing as thin parallel laths of calcite which are variably fused and amalgamated, commonly having a wavy banded appearance (Fig. 10.39). The laminae are oriented roughly parallel to the outer surface of the valve.

Fig. 10.39. Laminar microstructure of strophomenid brachiopod shells characterized by wavy iamellae that are buckled adjacent to the pseudopunctae. The latter feature distinguishes the shell from bivalve shells, which may exhibit laminar microstructures as well. Middle Devonian (Givetian): Letmathe, Sauerland, Germany. Scale is 1 mm.

Shells consisting of calcite prisms are a common feature of rhynchonellid brachiopods. The basic types of brachiopod shell microstructures were summarized by Williams (1990). In punctate brachiopods the shells are perforated by tiny open tubes extending almost to the outer surface (e.g. terebratulids). In pseudopunctate brachiopods (most strophomenids, including productids and chonetids) the shell has solid rods of calcite reminiscent of true punctation that end within the fibrous layer; the fibers contributing to the formation of pseudopunctae are buckled into a series of superi~nposedcones. In irnpurzctate brachiopods the shells are imperforate and dense all the way through (pentamerids, most rhynchonellids and spiriferids). The first punctated (endopunctated) shells occur in the Ordovician. Pseudopunctate and impunctate shells are already known from the Cambrian.

Erolog): Brachiopods are active filter feeders commonly attached to hard and firm substrates. Modem brachiopods live in all parts of the sea as sessile organisms attached to the substrate by a pedicle. Today bra-

chiopods are also found in temperate and cool waters of normal salinity. Many articulate species are deepwater specialists and occur in depths down to several hundreds of meters and more. Inarticulate forms, e.g. Lingula, live in relatively shallow coastal waters. Brachiopod shells as environmental recorders: Brachiopod shells are widely used as paleoenvironmental indicators in the reconstruction of ancient seawater temperatures (Veizer et al. 1986; Curry and Fallick 2003). Because Low-Mg calcite is less susceptible to diagenetic alteration, it is more likely that brachiopod shells have retained the isotopic composition in equilibrium with the environment in which the organisms lived. Possible diagenetic alterations are commonly determined by cathodoluminescence (Barbin and Gaspard 1995). Distribution: Brachiopods appeared in the Cambrian, were abundant in the Paleozoic and most diversified in the Devonian. There was a distinct drop in the number of taxa following the Pem~ian-Triassicextinction event, but brachiopods continued to be part of the shelf fau-

Piate 86 Brachiopods 'l'he plate displays thin sections of articulate brachiopods characterized by two valves that are bilaterally synmetrical but dissimilar in size and shapc (-> 1, 3). Internal structures are represented by a calcareous framework (brachidium) that supports the food-gathering sysrcm of the soft body. This framework takes several forms, e.g. calcareous ribbons coiled in helical spirals > 1 ), or elements supporting the brachidium (-> 3). Characteristic microstructures distinguish brachiopod shells from bivalve shells (-> 1, 5 ) . Micwsrru~~riri-u wzd inrerrzal ~ltvncnts:Cross sections of articulate spiriferid brachiopods. Note the well-preserved internal brachialia (B), the median septum (MS) and the low-angle finely layered ~nicrostructureof the calcitic impunctatc shell (arrow) characteristic of brachiopods. SMF 8. Middle Triassic (Anisian): Olang Dolomites, Southern Alps, Italy. Rkhtl~ofi~~litr. Kichthofeniaccan brachiopods (order Strophomenida) differ from other brachiopods by a cone-shaped petliclc valve fixed hy the apex to the scafloor and anchored by spines. The brachial valve acts as a lid-like structure. These brachiopods, together with sponges and microbes, contributed to the formation of Permian reefs in tropical and tenlpzrate paleolatitudes. The group is restricted to the Permian. Oblique section exhibiting the open framework of the pedicle valve. Late Permian: Chios Island, Greece. Infer-iw1 denwnts. Cross section of a smooth brachiopod shell cut parallel to the hinge line exhibiting the larger petliclc valve (right) and the srnaller brachial valve. Note the broken interior double plates (arrows) corresponding to supporting elements of the brachialia. Bioclastic wackestone. Early Devonian (Emsian): Erfoud, southern Anti-Atlas, Morocco. BI-nclziopodcoquitza. Most shells are cut longitudinally. Note microbial encrustations (arrow). Rock-building accumubtions of brachiopod shells are common on shelves and in slope settings. Flanking beds of a microbial-stromatoporoid buildup. Late Devonian (Frasnian): Kielce, Holy Cross Mountains, Poland. Ilfiimsrrlrc~twe.Tangential section of a punctate articulate brachiopod exhibiting very small tubules (punctae, Pi within the shell. Early Jurassic (Hierlatz limestone): Maurach near Innsbruck, Tyrol, Austria. Brachiopnd spines: Some pseudopunctate brachiopods yield spines that are found as displaced elements in the sediment. Diagnostic criteria are the hollow central canal surrounded by concentric inner and thick radial-fibrous outer layers. l'ransverse section. These spines are conlnlon in Carboniferous and Permian shelf carbonates. Early Carboniferous: I b l y Cmss Mountains, Poland.

Plate 86: B r a c h i o p o d s

521

Bivalves

nas in the Mesozoic. From about the midJurassic onwards, the articulate brachiopods retreated to cryptic tropical reef niches, or were confined to colder and deeper waters. Only three groups (rhynchonellids and terebratulids and the inarticulate Lingulata) crossed the Cretaceous-Tertiary boundary and are still present today.

Brachiopod limestones: Accumulations of brachiopod shells are abundant in Paleozoic limestones (Pl. 102/1, P1.132/10) and common in Mesozoic limestones. Brachiopod limestones originated in different depositional environments (shelves, ramps, slopes) and became more frequent in the Silurian and Devonian. Shell beds composed of brachiopods can not be compared with bivalve shell beds because of differences in skeletal mineralogy (Low-Mg calcite vs. aragonite), a stronger tooth-socket hinge (holding the valves together after death), lack of ligament forcing the valves apart like bivalves, and low vulnerability to predators and boring organisms (Copper 1997). Some brachiopod shell beds are composed of in-situ assemblages of life and dead shells, others by transported assemblages deposited by currents within depressions of the sedimentary surface or accumulated on the surface as 'dunes' (Hagdom and Mundlos 1982). The accumulation of shells related to a transport of brachiopods from shallow to deep-water environments is demonstrated by the Jurassic Hierlnrz jucies of the Calcareous Alps and the Carpatliians. This facies is one of the most characteristic Early Jurassic facies in the western 'Fethys. It con~prisestypically variegated predominantly brachiopod limestones and crinoid-brachiopod limestones that overlie drowned Late Triassic carbonate platforms or occur as fillings of neptunian dikes. Associated biota are bivalves, gastropods and small ammonites. Brachiopods and crinoids l i d originally in moderate water depths on the top of seamounts, from where they were transported as a bypass margin deposit to the slopes and foot of the seamounts (Voros 1986; Uchman and Tchoumatchenco 1994). Basics: Brachiopods Cambell, J.D., Lee, D.E., MacKinnon, D.I. (eds.. 1990): Brachiopods through time. - Proceedings of the second International Brachiopods Congress, University of Otago, Dunedin, New Zealand. 580 pp., Rotterdam (Balkema) Copper, P. (1997): Articulate brachiopod shell beds: Silurian examples from Anticosti, eastern Canada. - Geobios, 29, 133-148 Copper, P., Jin, J.S. (eds., 1996): Brachiopods. - 373 pp., Rotterdam (Balkema) Broadhead, T.W. (ed., 1981): Lophophorates. Notes for a short course. - 25 1 pp., Cincinnati (Paleontological Society) Popov. E.L,.Bas$etl, M.G , Holmer, L.E.. L,aurie, J. (1993):

Phylogenetic analysis of higher taxa of brachiopods. Lethaia, 26, 1-5 Kaesler, R.L. (ed., 1997): Brachiopoda (revised), part 1. Treatise on Invertebrate Paleontology, 60 pp., Lawrence (Geological Society of America) Kaesler, R.L. (ed., 2000): Brachiopoda (revised), part 2 and 3. - Treatise on Invertebrate Paleontology, 960 pp., Lawrence (Geological Society of America) Rowell, A.J., Grant, R.E. (1987): Brachiopoda. - In: Boardman, R.S., Cheetham, A.H., Rowell, A.J. (eds.): Fossil invertebrates. - 445-496, Palo Alto (Blackwell) Voros, A. (1986): Brachiopod palaeoecology on a Tethyan Jurassic seamount (Pliensbachian, Balcony Mountains, Hungary). - Palaeogeography,Palaeoclimatology, Palaeo ecology, 57,241-27 1 Williams, A. (1990): Biomineralization in the lophophorates. - In: Carter, J.G. (ed.): Skeletal biomineralization: patterns, processes and evolutionary trends. - Volume I, 6783,volume I1 (atlas), pls. 141-156, New York (Van Nostrand) Williams, A., Rowell, A.J. (1965a): Brachiopod anatomy. -Treatise on Invertebrate Paleontology, part H, volume I, 6-57, Lawrence (Geological Society of America) Williams, A., Rowell, A.J. (1965b): Brachiopod morphology. -Treatise on Lnvertebrate Paleontology, part H, volume I, 57- 138, Lawrence (Geological Society of America) Further reading: K123

10.2.4.2 Bivalves

Bivalves are the most important mollusks contributing to the bioclast content of li~nestones,both in marinc environments (since the Cambrian, and abundant in the Mesozoic and Cenozoic) and in freshwater and brackish environments (since the Carboniferous).

Morphology and class$cation: Bivalves (also called pelecypods or lamellibranchs) have a layered shell consisting of two valves. The valves may be either equal or unequal in shape and size. Most bivalves articulate along a hinge line by means of teeth and socketc. The plan of symmetry passes between the two valves par allel to the hinge line. Each valve contains a thin organic covering (periostracum) and multiple layers of carbonate. The carbonate shell layers consist entirel) of calcite, entirely of aragonite or of a mixture of aragonite and calcite in alternating layers. Shell structure: Common calcitic microstructures are foliated, prismatic, crossed-laminar and homogeneous. Microstructures can sometimes be used to attribute shell fragments seen in thin sections to major taxonomic units. Excellent summaries of microstructural types can be found in Majewske (1974) and Carter (1980,1990). Majewske provides a key which should enable families with related microstructures to be identified.

Shell Beds

disarticulation, plan-view and side-view orientation, fragmentation, abrasion, bioerosion and encrustation, sorting, species diversity. Many of these criteria can only be seen in large thin sections if shell accumulations should be genetically interpreted. Shell concenBivalve limestones Many limestones yield high numbers of bivalve trations (lumachelles,coquinas) can be formed by varishells contributing to the formation of bioclastic wacke- ous processes (Kidwell 1991). Event concentrations stones, packstones, floatstones, and rudstones. Bivalve originate from short-term events, e.g. storm deposits limestones originate in a variety of marine depositional (Pl. 102/3,5), composite concentrations are caused by settings, from the beach across the shelf and the shelf multiple reworking and transport), condensed concenmargin to the slope. To interpret these limestones basic trations are formed by multiple reworking and transconcepts developed for the discussion of shell beds must port of long duration associated with low sedimentabe taken into account. tion rates, and lag concentrations as a result of multiple reworking associated with the winnowing of fineShell beds: Biofabric and taphonomic signatures of grained sediment and corrosion. Shell beds should be studied in detail because they shell accumulations provide information on sedimentary processes, such as fair weather and storm waves, may be used as markers for recognizing the developstorm flows, and long-telm currents as well as rates of ment of sequences and cyclothems (Carter et al. 1991). sedimentation. Fiirsich and Oschrnann (1993) distin- Transgressive system tracts and nearshore highstand guished nine types of skeletal concentrations. Essen- system tracts contain either worn and transported bitial criteria are sedimentary structures (e.g. cross bed- valve shells, or in-situ faunas diagnostic of intertidal ding, planar lamination), erosive base, grading, intra- and shallow subtidal conditions. In contrast, the maxiformational pebbles, bioturbation, matrix, packing of mum flooding surface is characterized by an offshore skeletal elements (bioclast-support or matrix-support), fauna.

Ecology: Bivalves live predominantly marine as endobenthic suspension feeders on soft bottoms and as epibenthos on the sediment. Some bivalves are borers.

Fig. 10.40. Megalodon limestones. The fine-grained bioclastic wackestone contains abundant molds of bivalves, most of which are double-valved and still in life position. The megalodontids lived on shallow muddy substrates in lagoonal lowenergy environments. The well-bedded Megalodon limestones are a part of cyclic platform sequences in Oman as well as in other parts of the Triassic Tethys recorded by alternations of bivalve limestones and microbial/algal carbonates. Late Triassic (Mishrif Formation, Norian): Wadi Ala, Jabal Kawr, Oman Mountains. Coin for scale. Courtesy of M. Bernecker (Erlangen).

Limestones with abundant bivalves representing allochthonous shell concentrations or autochthonous occurrences of bivalves (Pl. 87/4, PI. 11911) are key elements of characteristic facies types which sometimes can be found in worldwide distribution as demonstrated by the following examples:

Triussic Megalodon limestones: The Late Triassic Dachstein limestone of the Northern Calcareous Alps as well as time-equivalent platform carbonates all over the Tethys (Fig. 10.40) are characterized by cyclic platform carbonates containing thick-bedded limestones with abundant shells of pachydont megalodontids. These equal-sized bivalves may become several tens of centimeters in size. They occur commonly in life

position within a fine-grained sediment corresponding to wackestone and packstone with bioclastic debris and in places with some corals and dasyclad green algae. The Megalodon limestones represent the subtidal part of the Lofer cycles (see P1. 14014) . The depositional setting of Late Triassic megalodontid limestones is confined to the standard facies zone 8 (see Sect. 14.3).

Liassic Lithiotis limestones: A specific limestone type characterized by the mass occurrence of Lithiotis, a thick-shelled heterodont bivalve several centimeters in size, and related genera, developed during the Early Liassic (Sinemurian, abundant in Pliensbachian and Toarcian) in carbonate platforms of Tethys and Panthalassa forming a low-latitude belt (Nauss and Smith

Plate 87 Bivalves This plate displays thin sections of Mesozoic and Cenozoic bivalve shells. Shell shape (-> 1) and m~crostr-uctures (-> 5-7. 9) are used to differentiate bivalve shells from other mollusk shells and brachiopods. 1 Conzplete bi~uhle.Radial section through joined calcitic valves of an equivalved megalodontid bivalve. D: Dorsal, V: Ventral. The interior of the shell is filled partly with sediment, partly with recrystallized calcite cement. Late Triassic: Northern A ! p , Austria. 2 Grow~hlines. Radial section through a recent aragonitic Donax shell. Note the widely and densely spaced growth lines (GL) and the crystals of the prismatic microstructure (white arrow). R: Rib area. Recent: North Sea. 3 'Filmlents' . The fossils are larval or juvenile shells of pelagic bivalves. Filaments are common constituents of Mesozoic deep-marine basinal limes~ones,e.g. in the Ammonitico Rosso facies of the Mediterranean region. Note dense packing. bioclast-support and common bioclast/bioclast contacts. More than 70% of bioclasts lie within two adjacent size cl;~sscs. Iligh degree of close packing reflects episodes of gregarious deposition of pelagic shells on the sea bottom within a very short time interval. Early Jurassic: Korfu Island, Greece. 4 Bi~ulvereef. Densely spaced calcitic valves of fossil 'oysters' (Placutzopsis nstracina) forming reef-like structures by attachment of the right valve to hard substrate. Example of a 'primary biogenic shell concentration' (Fiirsich and Oschmann 1993) resulting from a gregarious habit and characterized by epifaunal bivalves growing one shell above the other. Note growth larnellae (GL) characterizing the 'foliated microstructure' of the shells, and sediment-filled borings (B). The high frequency of life-positioned oysters in the densely packed well sorted fabric together with the lenticular shape of the deposit indicates an accretionary buildup. Compare this fabric with the example shown in -> 3 and note the alnlost complete absence of carbonate mud due to failure in sediment supply. Middle Triassic (Muschelkalk): Berlichingen, southwestern Germany. 5 :Ilic~r-osr~-~rcti~~-c~. Bivalve shell fragment showing a finely prismatic calcite microstructure. Small circular black structures are microborings. Late Jurassic: Untersberg, Salzburg, Austria. 6 Miuostr-ucturc. Fossil 'oysters'. Note the microstructural differentiation of the calcitic valve into a prismatic outer layer and a foliated layer. Late Tertiary (Miocene): Ekisce, southern Turkey. 7 Microsir-~~crurc~. The Ostwa shell exhibits alternating foliated (F) and vesicular (V) layers characteristic of pycnodonr bivalves. Late Tertiary (Miocene): Mesarevlev, southern Turkey. X Inocer-anlid bivalves: Longitudinal and cross sections through the outer layers (ostracum) of calcitic Inocer-arnus shells exhibiting the characteristic prismatic microstructure. Note the honeycomb pattern in plan view (center top) and the difference in prism size in the outer and inner shell layer. Individual prisms act as single crystals displaying unit extinction between crossed nicols. Inoceramid bivalves are known from the Jurassic to the Late Cretaceous. They were cornmon during the Late Cretaceous and became extinct in the Maastrichtian well before the Cretaceous-Tertiary boundary. The fossils are important Cretaceous index fossils (McLeod and Ward 19901, provide interesting paleoclimatic proxies (Dhondt and Dieni 1992) and are used as diagenetjc markers (Elorza and Garcia-Garmilla 1998). Disarticulated calcitic prisms of the ostracum are important constituents of Cretaceous open-marine limestones. Note growth lines (top left). Small sparfilled structures in the micritic matrix are calcispheres (see PI. 6617). Late Cretaceous (Cenomanian): Teutoburger Wald, Germany. 9 Micwstructlrl-e. Bivalve wackestone with angular fragments of pycnodont shells showing vesicular and foliated microstructures. Middle Cretaceous (Aptian): Subsurface, Ras al Khaimah, IJnited Arabian Emirates.

Plate 87: Bivalves

525

Limestones with Filaments

1988; Scheibner and Reijmer 1999; Monaco 2000). The bivalves preferred different subenvironments and lived in intertidal and subtidal low energy, marginal marine as well as in high energy shelf-margin settings comprising the standard facies zones 4, 5, 7 and 8. Shell concentrations were controlled by physical and biological agents such as shell transport by currents and waves, winnowing fine-grained material leaving behind shell coquinas, bioturbation resulting in shell concentration, and in-situ growth contributing to the formation of lowdiversity bivalve reefs near platform margins and on upper slopes (Fig. 10.41). Fig. 10.41. Lithiotis limestone contributing to the formation of mounds near a platform-upper slope margin. The dark finegrained sediment corresponds to bioclastic pack- and wack&tones. Early Jurassic: Jebel Bou Dahar, High Atlas Mountains, Morocco. Coin for scale. From Scheibner and Reijmer (1999).

Middle and Late Jurassic limestones with 'jilaments': The name refers to fossils first recognized in thin sections of Jurassic limestones and later also in rock-building quantities in other Mesozoic open-marine limestones, e.g. the Late Triassic Hallstatt Iime-

Plate 88 Cretaceous Rudist Bivalves

Kudists are sessile gregarious bivalves characterized by a lower attached and an upper opercular valve of different sizes. The group appeared in the Late Jurassic and disappeared at the end of the Cretaceous. Rudists were common throughout the Cretaceous. Diversity dropped during the Early Aptian and the latest Cenomanian and increased significantly in the Early Maastrichtian. Major subgroups are differentiated by she11 morphology, the number and position of teeth, accessory cavities, canals (--->2), pores and pillars. 'Thin sections exhibit characteristic n~icrostructuralpatterns. The shells consist of a n inner and middle aragonitic layer (nearly always recrystallized and replaced by blocky calcite, ->5) and an 2; outer Low-Mg calcite layer with compact (-> 1, 6) and/or cellular microstructures (-> 1, 4, 5). Cap-iniduc (--i Aptian to Maastrichtian, cottunon in Cenomanian) are characterized by characteristic canals within thc shell. The shells of Radiolitidae (-> 1,4, 5 , 6 ; Late Aptian to Maastrichtian, common from the Late Albian onwards, abundant from Santonian to Maastrichtian) exhibit a reticulate pattern caused by the calcitic cellular prisnlatic outer layer, and a compact inner layer. Both groups were abundant in outer and mid-shelf environments. The Nippiuifidu~(-> 3; Turonian to Maastrichtian), forming densely packed biostromes, are characterized by pillars within the shell wall.

>

Kadioliticl'ne. Lower valves of Lupcir-uusia sp. Oblique cross-section. Note pseudopillars (P) and thick outer layers shawing the diagnostic alternation of the thick cellular boxwork ostracum and thinner compact microstructures. The interspaces hetween the shells are infilled with siit-sized prismatic calcite crystals (CC) resulting from the disintegration and spalling of parts of the shells. Radiolitids are common in outer to mid-shelf environments. SMF 8. Late Cretaceous (Campanian j: Greece. Cupri~ziLiLI~. [Jpper valve of Spl~ue~ocirpriiza sp. Transverse section. Note the inner shell layer exhibiting a system of morphologically differentiated polygonal and pyrifonn canals (C). The interior cavities of the shell are filled with bioclasts, coated grains and rounded intraclasts. Caprinids are common in outer to mid-shelf deposits. Late Cretaceous (Cenomanian): Northern Greece. Hippui.itidat,. Transverse section of the cylindrical lower valve of Hippurites colliciatus Woodward. Hippuritid rudists are characterized by a thick outer compact calcite layer (CL), a thin inner aragonite layer (AL) and two pillars (P) projecting towards the general cavity. Late Cretaceous (Early Campanian): Pontides, northern Turkey. Kadiolitidac. Radial section. Note the folded cellular network made of horizontal laminae and vertical elements. Late Cretaceous: Lake Belton, Texas, U.S.A. Kudiolitidac. Snu~,agesiasp. The primarily aragonitic inner layer is replaced by blocky calcite. The thick, finely cellular calcitic outer layer consists of prismatic cells. Late Cretaceous (Cenomanian): Greece. Radiolitidae. The outer layer of the upper valve consists of compact calcite. Note the degradation of the shell by boring (arrow j. These Cretaceous rudist limestones in the Italian and Slovenian part of the Trieste area are famous decorative building stones. Late Cretaceous (Santonian): Duino near Trieste, Italy. 1 5: Courtesy of T. Steuber (Bochnrn:

Plate 88: Cretaceous R u d i s t Bivalves

1 cm

5 17

1 crn

stoncs. The thin. C L I ~ \ , Ce l~e m e m exhibit a single-layesed or multilayer-ed calcitic psismatic microstructure. These a c c u m u l a t i o ~ iwithin distinctly defined beds were originally regartled as algal l'ilanients and tlierefore termed 'filaments'. The fossils have been now proved to he protoconchs or juvenile valves of thinshelled bivalves (Peyre 1959: Conti and Monari 1992). Most authors ascribe Jurassic filaments to juvenile shells of posidoniid blvalves (Bositr-(I,Posick,rzicc) and Tsinssic findings to halobiid bivalves. Interpretations of' the life huhits of Rosirro and related taxa are still controversial aticl include nektoplanktonic or pseudoplanktonic as well as benthic liiodes of life. 'Limestone with filaments' is colnmon and widely distributed in the Jurassic (ranging Srom Toascian to Kimmeridgian: abundant in the Middle Jusassic and early Late Jurassic) of the Tetliys (PI. 8713: PI. 11 313; P1. 13711 ). The c.lepositional settings of' filament-sic11 limestones correspond to the standard facies zones 1 , 2 and 3 .

C'ro/ccc,oori.s~.rltli.s/lin~c~.sto~~r,r: Rudists are sessile gsegarious bivalves known Srom Late Jurassic (e.g. Diccr.cl.s limestones) until the end of the Cretaceous. clinracterizecl by :I lower attachcd and an upper opercular valve of different sizes. Three morphotypes are distinguished based on life orientation (Skelton and Gili 199I ): conical or cylindrical elevators (vertical upward growth: growing alone. or in close associations or in

dense clusters \villi mutual ccmcntationl. clinger.. (grouring alone. in close associatio~~s or in dense cluatcrs with ~ L I ~ L I ; I Icementation. Attached to other sutfists. corals or Iiard~rounds).and rec~umbents(hosscshoe-like fosms with the long axis of both valves lying pasallel to the seciimcnt-water interl'ace). There is cu-sently a lively discussion on whether or not sudists formed rigid I-eel.frameworks os were hal'flers Sorming bafflestones. The clepositional settings of sudist lin~estonesusually correspond to the standartl facies m n e s 3. 7 and X . Rudists ;u-e common in Crc!taccous platforni, ramp and reef carbonates exhibiting a biolkies scsponse to the windward/leewasd position and shallowing-up wards cycles. Their habitats stretched from protected and open-marine parts of platforms to shell' margins where they produced huge ;111~)unts of bioclastic r i d ist smds. Rudists formed small houcluets. larger clusters or extended thickets. and contributed significantly to the formation of extended reef belts (c.g. Oman: Fig. 10.42). Rudist density reflects diff'esences in sedimentation rates. Elevator rudists were efficient prociuccrs of bioclaxtic sands that accumulated near Late Csetaceous o x honate platform margins. Boundstones and associated bioclnstic sand piles fosm m~i,joroil and gas seservoirs along shelf margins (Mexico. Dubai. Abu Dhabi. Oman). Rudist shells have a high intraskeletal porosity. Additional fracturing increases the reservoir potential. Leaching of the aragonitic parts or of the whole shell during freshwater diagenesis can cause molclic porosity (Cestasi and Sartorio 1995 ). Rudist limestones ase witlcly used :IS decorative building stones all over the w(~r1d. Basics: Bivalves Carter. J.C. (1980): Guide to bivalve microstructi~res.- In: Rhoads. D.C.. Lutz. R.A. (cds.): Skeletal growth ol' aquatic organisms. - 645-673. New Yorh (Plenum Press) Carter. J.C. ( I99O): Evolutionary significance of' shell microstructure in the Pnlaeo~asodonta.Plcroniorpha iuncl Isofilibranchia (Bivalvia: Moliusca). - I n : Carter. J.C. (ed.): Skeletal biomineralization: patterns. procrsscs and evolutionary trends. - Volume 1. 136- 199: volume 11 ( a t las). pls. 1 - 12 1 . Nen. Yo& (Xi11Nostrand) Cestari. R.. Sartorio. D. ( 1995): Ruclists and facies ol' ~lic Pcsiadriatic domain. -- 707 pp.. S. Donato hlilancse (Ayip~ Conti. M.A.. Monari. S. ( 1992):Thin-slicllcd hi\.alves from the Jurassic Rosso Alnmonitico and Calcari a Positlonia l'ormations from the Ir~nbrian-Marcclie:~~~ Apenninc (Central Italy). - Palaeopclagos. 2. 193-3.1.? Elorza. G..Garcia-G:wmiila. F. ( I W S ) : Paleuen\~irc11i111~11tnI i~nplicxtionsand tliagencsi ol'i~~ocer;rmitl shclls ( H i v a l \ . i a ) i l l the ~nicl-~\l:iastricliiiai~ lwcls of' Sopclana. %unia>.aam1 Bitlard ac'c.tion\ i c , ~ : a \ toI'[lie Ba!. 01' Risca!..

Basque Country). - Palaeogeography, Palaeoclimatology, Palaeoecology, 141, 303-328 Fiirsich, F.T., Oschmann, W. (1993): Shell beds as tools in basin analysis: the Jurassic of Kachchh, western India. Journal of the Geological Society London, 150, 169-185 Gill, E., La Barbera. M. (1998): Hydrodynamic behaviour of long cylindrical rudist shells: ecological consequences. - Geobios, 22, 137-1458 Hagdom, H., Mundlos, R. (1982): Autochthonschille im Oberen Muschelkalk (Mitteltrias) Siidwestdeutschlands. - Neues Jahrbuch fiir Geologie und Palaontologie, Abhandlungen, 162,332-351 Kidwell, S.M. (1991): The stratigraphy of shell concentrations. - In: Allison, P.A., Briggs, D.E.G. (eds.): Taphonomy: releasing the data locked in the fossil record. -Topics in Geobiology, 9 , 2 11-290, New York (Plenum) Kidwell, S.M., Tothfus, D.A., Best, M.M.R. (2001): Sensitivity of taphononiic signatures to sample size, sieve size, damage scoring systems, and target taxa. - Palaios, 16, 26-52 Lee, C.W. (1983): Bivalve mounds and reefs of the Central High Atlas, Morocco. - Palaeogeography,Palaeoclimatology, Palaeoecology, 43, 154-168 McLeod, K.G., Ward, P.D. (1990): Extinction pattern of Itzoccr-atms (Rivalvia) based on shell fragment biostratigraphy. - In: Sharpton, V.L., Ward, P.D. (eds.): Global catastrophs in earth history. An interdisciplinary conference on impacts, volcanism and mass mortality. - Geological Society of America, Special Paper, 247,509-5 18 Monaco, P. (1-000): Biological and physical agents of shell concentrations of Lithiotis facies enhanced by microstratigraphy and taphooomy, Early Jurassic, Trento Area (Northern Italy ). - - GeoKesearch Forum, 6,473-486 Moore, R.C. (ed.. 1969): Mollusca 6 (Bivalvia). Volumes 1 and 2 - Treatise on Invertebrate Paleontology, part N, 952 pp.. 6 13 1111.. La~vrence(Geologica1 Society of America) Schumann, D. ( 1 9951: Upper Cretaceous rudists and stromatoporoid associations of Central Oman (Arabian Peninsula). - Facies, 32, 180-202 Stenzel, 1I.B. (ed.. 1971): Mollusca 6, Bivalvia (Oysters). Volun~e3 - Treatise on Invertebrate Paleontology, part N.- 275 pp.. Lawrenct: (Geological Society of America) Further reading: K 124

10.2.4.3 Gastropods Gastropods are abundant constituents of limestones ( F I ~10.43). . They are known throughout the Phanero~ o i cbut . are most ahundant in the Mesozoic and Cenozoic. Molphology: Most gastropods have an external univalved, usually unchambered shell that is usually coiled. Coiling may be either in a single plane or a helical spiral about an imaginary axis. The whorls are tightly wrapped about the preceding whorl to form a central pillar (columella, PI. 89/5), or the whorls are closely wrapped to form a central cavity. The exterior of the shells may be smooth or ornamented with ribs, nodes and spines.

Skeletal mineralogy and rnici-osn-nctui-e:The calcareous shell (ostracum) is covered by an organic layer (periostracum). Most gastropod shells consist completely of aragonite; a few families have a mixed mineralogy, with an outer layer of calcite and an inner layer of aragonite. Conchiolin forms a thin external cover over the shell (periostracum). The whorls are composed of one to several layers of calcium carbonate, which are distinguished by differences in mineral composition and microstructure. The most abundant microstructure in aragonitic layers is crossed-lamellar, characterized by layers of crystals oriented in different directions. Other common microstructures are the normal prismatic found in calcitic layers ( f i e calcite prisms oriented normal or inclined to the outer surface), complex crossed-lamellar, and nacreous (aragonite crystals arranged in thin sheets and separated by sheets of organic material; e.g. some Archaeogastropoda). Photographs of gastropod microstructures can be found in Majewske (1974). Small fragments of gastropods are distinguished from bivalves by the existence of multiple layers of well-developed crossed-lamellar microstructures, small conlposite prisms, and nacreous layers associated with layers exhibiting dissimilar microstructures. Preservation: Most gastropods are preserved as molds and casts (Pl. 89/8). Shells composed of aragonite are subject to two main fates: they are either dissolved to form complete or partial molds that may bc subsequently filled with cement, or they may be trans-formed during recrystallization to Low-h4g calcite bj. the simultaneous volume per volume dissolution of ara gonite and precipitation of calcite along intervening solution films. In recrystallized shells some trace of the original microstructures can be retained (PI. 89/4, 7 ) . Students may confuse small gastropods with forarninifera but the tests of the latter consisting of calcite are rarely preserved as casts. ('lassification: Three subclasses are differentiated based on the respirative system comprisuig the Prosobranchia, with more than half of all gastropods, the Archaeogastropoda, Mesogastropoda and Neogastropoda (Cambrian to Holocene), the h ~ g h l yd ~ v e r s e Opisthobranchia (Mississippian to Holocene) and the terrestrial Pulmonata (Pennsylvanian to Holocene). The Opisthobranchia and Pulmonata have aragonitic shells. Most calcite-bearing shells belong to the Prosobranchia. Ecology: Gastropods live in marine, freshwater and terrestrial environments. Most gastropods are mobile benthic organisms, but some have become adapted to sedentary life and to pelagic life (pteropods).

Plate 89 Gastropods The gastropod shell corresponds to a conical tube, closed at the pointed end and open at the wide end (apertura). Whorls are wrapped about the preceding whorls forming a central pillar (columella, -> 5) or an axial cavity. The exterior of the shells is smooth or variously ornamented (-> 5). Many gastropod shells are infilled with sediment. Infilling may occur (a) within the environment of the deposition of the shells (as shown by the sediment type within the shell and in the matrix; -> 1,2,5), or (b) prior to the deposition of the shells (different sediment in the shell and the matrix; -> 3, 4). Some small, encrusting tubelike fossils, formerly assigned to 'vermetid gastropods', are now included within a separate mollusk group - the Microconchida (-> 9, 10). Gastropod wackestone. Longitudinal section (LS) parallel to the axis of coiling, transverse section through the upper whorls (TS), and oblique sections ( 0 s ) . Black coating of the shells corresponds to the exceptionally well-preserved external organic cover (black arrow). Note different preservation of originally calcitic outer part and the primarily aragonitic and now recrystallized part (white arrow) of the mollusk shell. The sample is an example of a 'loosely packed, bimodal sorted, biofabric', following the classification of Kidwell and Holland (1991). The fabric is characterized by matrix-support, closely spaced coarse shells and large bioclasts associated with finer bioclasts. SMF 8. Early Triassic (Scythian, Werfen Formation): Gartnerkofel, Camic Alps, Austria. Preservation. High-spired gastropod. Note double-layered shell construction (white arrow) and displacement of the shell along microfractures (black arrow). Longitudinal section. Late Triassic: Northern Alps, Austria. Preservation. Longitudinal section of a high-spired gastropod. Outlines of the shell are well preserved due to the enciosure within an oncoid. The facies corresponds to a peri-reef environment with some terrigenous influx. Note the angular quartz grains within the gastropod infilling. Late Tertiary (Sarmatian): Prut Valley, Simleu Basin, Romania. Pi-esenlatior~.Oblique section. Note the still preserved growth lines (arrow). Silurian (Ludlowian): Hobuggen, Gotland Island, Sweden. Shell cxfcr-ioe Longitudinal section. The shell is coiled tightly about its axis, forming a solid central pillar (columella, CO). Note outline of ornamentation (arrow) consisting of strong spiral ribs. Jurassic: Northern margin of the Alps near Salzburg?Austria. /Ictaroizellid gastropod. Cross section. Actaeonellids are common in brackish-influenced Cretaceous sediments. Early Cretaceous: Subsurface, southern Bavaria, Germany. 7 Low-snir-edshell. Note entire holostome anertura (A 1. Arrow points to relicts of prismatic microstructure. Note the geopetal structure. Late Jurassic: Northern margin of the Alps near Salzburg, Austria. Diagnostic criteria. Typical appearance of a gastropod section perpendicular to the axis of coiling characterized by a 'projection' of the wall into the central cavity. Cross sections of high-spired gastropod shells have been used to differentiate Tertiary gastropod genera (Strausz 1959). The original wall structure was obliterated during inversion to calcite, but the diagnostic morphological criteria (spire) are still recognizable. The mold is filled by drusy calcite cement. The sediment is pelmicrite or peloid packstone, respectively. Lagoonal facies (see P1. 11712). Early Tertiary (Eocene): Monte Bolca,Verona, Italy. 10 'Microconchids', formerly considered to be 'vermetid gastropods' or spirorbid worms, are tiny coiled tubes with differentiated walls. Erect, helicoidal, gregarious forms are frame builders in peritidal schizohaline lagoonal settings (Burchette and Riding 1977). Prostrate, discoidal forms are encrusters, commonly associated with porostromate algae, forming oncoids in high-energy settings. Microconchus is now assigned to a separate group of mollusks (Microconchida). The group is known from Silurian to the This figure shows a gastropod limestone composed of densely Jurassic (Dreesen and Jux 1995), but more commonly packed shells still exhibiting the original layered microstructure found in Devonian and Early Carboniferous limepreserved as aragonite. Late Triassic Zlambach beds, a near-reef stones. Late Jurassic: Argentina. fdcies, Austrian Northern Calcareous A l p . Scale is 5 mm.

2 rnrn

2 mm

2 rnm

2 mrn

2 rnrn

2 rnrnl

2 mrn

5 32

Basics: Gaqtropod..

Fig. 10.43. Oolitic gustr~pod-bivulvegruitlstor~e.Gastropods are represented by Hnlopclla grircilior Schauroth. The skeletal grains have thin oolitic coatings exhibiting a reddish color. This microfacies is widely distributed in Early Triassic platform carbonates and known from the Al~ine-Mcditmxneanregion (see P1. 8911) to Iran and China. Early Triassic (Scythian:: " Subsurface, Precaucasian foredeep, Russia. Scale is 1 rnrn.

Marine species are predominantly benthic herbivores and detritus feeders, some species are carnivore. Planktonic pteropods and heteropods known since the Early Tertiary contribute to the formation of aragonitic muds in the deep sea. Basics: Gastropods Bandel, K.J. (1990): Shell structure of Gastropoda excluding Archaeogastropoda. - In: Carter, J.G. (ed.): Skeletal biomineralization: patterns, processes and evolutionary trends. Volume I. - 117-134, New Yorh (Van Nostrand) Dreesen, R., Jux, U. (1995): Microconchid buildups from Late Famennian peritidal-lagoonal settings (Evieux Formation, Ourthe Valley, Belgium). - Neues Jahrbuch fiir Geologie und Palaontologie, Abhandlungen, 198, 107121 Iiennan, Y. (1978): Pteropods. - In: Haq, B.U., Boersma, A. (eds.): Introduction to marine n~icropaleontology.151 - 159, New York (Elsevier) Moore, R.C., Pitrat, C.W. (eds., 1960): Mollusca 1 (Mollusca general features, Scaphopoda, Arnphineura, Monoplacophora, Gastropoda general features, Archaeogastropoda, mainly Palaeozoic Caenogastropoda and Opisthobranchia). - Treatise on Invertebrate Paleontology, part I, 35 1 pp., Lawrence (Geological Society of America)

Strausz, L. (1959): Uber Gastropoden-Gehauseschnittc Acta Geologica Budapest, 6, 219-229 Weedon, M.J. (1990): Shell structure and affinity of vermlform 'gastropods'. - Lethaia, 23, 297-309 Further reading: K 124

Although this picture is only included to fill this page, it can tell a story about a sculptured gastropod. Please continue! Triassic: Carinthia, Austria.

10.2.4.4 Cephalopods Cephalopods are mobile marine mollusks that have adapted to a swimming mode of life. Major groups are distinguished by their soft parts and shell morphology: Nautiloidea (Late Cambrian to Holocene) and some related Paleozoic groups, Ammonoidea (Early Devonian to Cretaceous) and Coleoidea (Early Devonian to Holocene) with the extinct belemnites (Carboniferous to Eocene but most abundant in the Jurassic and Cretaceous where the group is used as index fossils).

Morphology: The skeleton of nautiloids and ammonoids consists basically of a straight, curved, spiral or coiled calcareous cone. The cone is chambered by curved, transverse partitions (septa) that unite the inner shell walls. The lines of junction of the septa and the shell walls (sutures) are simple, circular or undulated in natutiloids and related groups, but fluted, crenulated and complex in ammonoids. The first spherical or ovoid chamber is called protoconch, the remaining chambers of the shell form the phragmocone, and the large unchambered space between the last septum and the apertura is the body chamber. The chambers of the phragmocone communicated via a tube (sipho) passing through a perforation rn the septa and positioned in the center or at the margin of the shell. The belemnites are characterized by an intemal skeleton consistmg ot the chambered phragmocone. which n as partly contained w~thina cavity at one end of a 40hd calclt~cguard (ro5trurn). The latter is commonly the only prewrved part. Shell S ~ ~ - L L ( . ~ L a'iagc~wsis IIY, a12d preservation: The shells of nautiloids and arnmonoids were aragonitic. The wall is layered, exhibiting an outer prismatic layer and inner nacreous and prismatic layers. The shells are frequently recrystallized or leached and subsequently infilled b y calcite cell-ten1or sediment. Aptychi of ammonoids and the rostra of belemnites consist of calcite (Pl. 90/4, 6 ) . The diagenesis of cephalopod shells has been studied by Dullo and Bandel ( 1988): Preburial diagenesis is characterized by the rapid decomposition of the organic tissue and the settlement of endolithic organisms, which produces a highly porous structure or micritic envelopes. The decay of organic shell material (e.g. of the siphuncular tube) leads to accessibility for sediment infilling. Aragonitic cements grow syntaxially upon aragonitic microstructural parts of the shell. Burial diagenesis comprises the dissolution of aragonite and the loss of the mineralized shell, often long before the sediment is compacted. If the intercrystalline organic tissue is

still preserved after dissolution of the aragonite shell crystals, compaction may result in the flattening of cephalopod shells (PI. 9013) or replacement of the aragonite biocrystals by phosphate, silica or pyrite. Finally, the organic shell may disappear, leaving a mold that can later be infilled by sediment of cements (Pl. 9015). In a meteoric environment, the aragonitic shells of cephalopods are greatly affected by dissolution. Leached shells with High-Mg calcite micrite envelopes create molds; the molds are cemented by Low-Mg calcite crystals coarsening towards the center of the cavity or by blocky calcite.

Cephalopods in thin secrioru: Fossil cephalopods have coiled or straight chambered external shells (ammonoids, nautiloids), or intemal shells (belemnoids). Coiled forms are usually planispiral forming thin-section patterns comparable to those in planispirally coiled gastropods (PI. 8914). However, cephalopod shells are distinguished by having involute coiling (last spiral covers almost all previous ones). In thin sections ammonites are represented by random sections through fragments (PI. 90) and sometimes abundant sections of juvenile ammonites. Due 10 the primary aragonitic mineralogy larger shells are usually recrystallized or completely dissolved. Juvenile ammonites i.e. embryonal or larval stages are more common, particularly in Devonian and Mesozoic open-marine wackestones. Sections of these very snlall tssils (diameter of the shell about 0.5 mm) are characterized by a large globular protoconch followed by one. rarely two whorls subdivided by thin septa. Sections lacking septa, can hardly be distinguished from those of trochospiral dwarf gastropods. The occurrences of abundant juvenile ammonites can indicate the rapid death of plankton. Cephalopod limestones L~n~esrones char-ncrerizcd hj' i r h ~ d ~ icrnmoi~ord i ~ t arzd na~rtiloldshells are common In the P~leozoicand Mesozoic (Pl. 9011, 2). The limestones or~ginatedon pelag~cplatforms, deep shelves or r~dgcsof various origin (submarine volcanoes, drowned reef\, structural highs), platform slopes and basins. Estimates of depositional depths of Paleozoic and Mesozo~copen-marine ammonoid limestones are controversirtl and range between some tens and several hundreds of meters to several thousands of meters. There is good evidence, that the depths of platfornls on which Devonian cephalopod limestones in Europe and North Africa accumulated reached an order of several tens to about one hundred meters (Wendt and Aigner 1985). Commonly these carbonates were formed during ti~nesof reduced scdi-

mentation rates and periods of non-deposition. Silurian cephalopod limestones ('Orthoceras limestones') accumulated on paleo-highs below wave base at depths of several tens to several hundreds of meters (Ferretti and Kriz 1996). Paleozoic cephalopod limestones are bioclastic wackestones characterized by the predominance of pelagic organisms including ammonoids and nautiloids, dacryoconarids, and thin-shelled ostracods. Mesozoic cephalopod wackestones exhibit ammonoids, thinshelled pelagic bivalves and ostracods as well as radiolarians.

Aptychus limestones: Basinal sequences consisting of fine-grained pelagic limestones with aptychi are common in Late Jurassic and Early Cretaceous sediments of the Alpine-Mediterranean region. Aptychi are present throughout the sequence although not present in all beds. The fossils are concentrated at the base of some beds in striking shell pavements (Zapfe 1963), indicating the existence of bottom currents, or they occur irregularly distributed as debris (Fig. 10.44). The carbonates originated from the deposition of n a ~ o p l a n k ton at depths of several hundreds of meters and more (see Fig. 4.4). The depositional setting of the Aptych~~t

Plate 90 Cephalopods The plate demonstrates the appearance and common preservation of ammonoid shells (-> 1-3,5), aptychi (-> 4, 61, nautiloid shells (-> 8) and belemnites (-> 7) as seen in thin sections of Paleozoic and Mesozoic limestones. M c s o x k cepilalopnd linwsrorle. The sample shows various sections through internal molds of ammonoid shells embedded within micrite (black): (1) Median section through the early whorls, (2) transverse section to the plane of the planispirally coiled shell, (3) oblique section, (4) relicts of the shell. Earlier chambers of the shell are filled with calcite cement, later chambers with micritic sediment. Note that the sedimentary infilling of the chambers with pelagic micrite is the same as the enclosing matrix. This indicates infilling of the shells on the substrate surface before burial (Ferdinandez-Lopez and Melendez 1993).The diagnostically important lines of junction of septa and shell walls (suture, S) are still preserved. The originally aragonitic walls and septa have recrystallized to a calcite mosaic. Basinal facies. Late Triassic (Norian, Hallstatt limestone): Northern Alps, Austria. f'aleoroir. c~phalopodlinl~stoiw.Bedding-parallel surface of a cephalopod coquina consisting of ammonoids (goniatites: ?brxoc.r~r-us. T ) and orthocone nautiloids (ON). Note the preservation of the inner prismatic microstructure of the xlicil (center). The sample characterizes a 'condensed shell concentration' defined by high-diversity skeletal elements carryin:l different taphonomic signatures (pristine shells as well as abraded shells, various stages of shell solution). Open-marinc pelagic platform. Late Devonian (Early Famennian): Tafilalt, eastern Anti-Atlas, Morocco. Anmnizite ~ I P . S ~ I ~ I ~ UHardground ~~'OM. with molds of animonoid shells. The sections are transverse to the plane of coiling. Early Jurassic: Murcia region, southern Spain. Aptychi. These Low-Mg calcitic plates are found associated with ammonites and interpreted as parts of the jaws 01- an opercular structure. Normally the plates occur as pairs and have an ornamented outer surface. Note the cellular-tubular microstructure (white arrow) and the ornamentation of the shell surface (black arrow). Classification of aptychi is based on the kind of ornamentation formed by fine lines, ribs (this sample), tubercles or spines. The matrix of the radiolarian mudstone and the aptychi are seleclively silicified (white). Late Jurassic: Monte Generoso, Ticino, Switzerland. ihtmvlire pr-esci-~utiotz. The shell has been infilled with dark pelagic micrite (PC) and aftcr breakage and dissolulion o f the shell. was later embedded in forereef carbonates (FC) with fine-grained bioclastic sediment. The septa were rep1:tcetf by coarse granular calcite cements followed by the burial filling of the chambers with blocky calcite. 0: Ophiurid element. The sample comes from a locality showing the interfingering between basinal sediments and forereef facies. Late Triassic (Norian): Hoher Giill, Northern Alps, Bavaria, Gennany. A p ~ c l z ~ iThe s . thin section shows the characteristic ornamentation. White spheres are radiolarians. This microfacies i > common in liinestones deposited during prc- or post-radiolarite phases of deep-sea sedimentation. Same locality as -> 4. Belcrr~rlite~ L I U I Z J S .Transverse section (TS) and longitudinal section (LS) of the Low-Mg calcite guards (rostrum). In transverse section the rostrum shows a fibrous structure with tiny calcite prisms radiating from an eccentric point. Rings concentric about this point indicate growth stages. Under crossed nicols an extinction cross can be seen resulting from the radial orientation of the individual prisms making up the rostrum. The microstructure of belemnite shells seen in SEM can be used to distinguish belemnite fragments from other mollusk remains (Dauphin 1986). Late Jurassic (Late Oxfordim): High Atlas Mountains, Morocco. Nautiloid shell. Longitudinal section of a straight orthocone shell embedded within a bioclastic wackestone matrix. Note preservation similar to the ammonite shell shown in -> 5. Open-marine deep-water ramp. Early Devonian (Emsian): Erfoud, Morocco. -> 2: Wendt and Belka 1991; 6: Kiessling 1996

Sih

Aptychus L1rnestonc.5

Fig. 10.44. Aptyclzus limestone. The thin section displays numerous fragments of aptychi within a fine-grained matrix. The fragments appear curved due to the slightly domal character of the plates. The exterior ornamentation (white arrows: T: tangential section of ribbed shell surface) is shown by uniformly oriented ribs. Small dark dots in the shells (black arrows) are caused by the porous microstructure. The concentration of the shells in particular areas and their irregular distribution within the sample are characteristics of strong burrowing. Late Jurassic: Karawanken Mountains. Austria. Scale is 1 mm.

limestones corresponds to the standard facies zones 1 and 2 (see Chap.14).

'Bclenznite battleji'elu's': Accumulations of belemnite rostra (Pl. 9017) on bedding planes (Fig. 10.45) are important facies criteria indicating current directions and the type of near-bottom water energy in shelf settings (Urlichs 1971; Doyle and Macdonald 1993), reduced and condensed sedimentation and lag deposition. A common feature of belemnite battlefields is the monospecific composition and the predominance of adult individuals. The most likely explanation of the battlefield is post-spawning mortality in shelf areas followed by current transport. Basics: Cephalopods Blendinger, W. (1991): Upper Triassic (Norian) cephalopod limestones of the Hallstatt type. Oman. - Sedimentology, 38, 223-242 Doyle, P., Macdonald,D.I.M. (1997): Belemnite battlefields. -- Lethaia, 26, 65-80 Dullo, W.C., Bandel, K. (1988): Diagenesis in molluscan shells: a case study from cephalopods. - In: Wiedmam, J., Kull~nann,J. (eds.): Cephalopods. Present and past. 7 19-729, Stuttgart (Schweizerbart) Fernandez-Lopez, S., Melendez, G. (1994): Abrasion surfaces

on internal moulds of ammonites as palaeobathymetric indicators. - Palaeogeography, Palaeoclimatology, PaIaeoecology, 110,29-42 Ferretti, A. (1989): Microbiofacies and constituent analysis of Upper Silurian-Lower Devonian limestones from southwestern Sardinia. - Bolletino della SocietL Geologica Italiana, 28,87- 100 Kaesler, R.L. (ed., 1996): Mollusca 4. Cretaceous Ammonoidea. -Treatise on Invertebrate Paleontology, part L (revised), 362 pp., Lawrence (Geological Society of America) Moore, R.C. (ed., 1957): Mollusca 4 (Ammonoidea). --Treatise on Invertebrate Paleontology, part L, 490 pp.. Lawrence (Geological Society of America) Moore, R.C. (ed., 1964): Mollusca 3 (Cephalopoda general features, Endoceratoidea, Actinoceratoidea, Nautiloidea, Bactritoidea). -Treatise on Invertebrate Paleontology, part L, 519 pp., Lawrence (Geological Society of America) Schlager, W. (1974): Preservation of cephalopod skeletons and carbonate dissolution on ancient Tethyan sea floors. International Association of Sedimentologists, Special Publication, 1,49-70 Tucker, M. ( 1974):Sedimentology of Palaeozoic pelagic limestones: the Devonian Griotte (Southern France) and Cephalopodenkalk (Germany). - International Association of Sedimentologists, Special Publication, 1, 71-92 Urlichs, M. (197 1):Alter und Genese des Belemnitenschlachtfelds im Toarcian von Franken. - Geologische Blatter fiir Nordost-Bayem, 2 1 , 6 5 8 3 Wendt, J., Aigner, T. (1985): Facies patterns and depositional

Fig. 10.45. Accur?z~ilatiotzsof belemnite rostra (predominantlyDactyloteuthis) on a marly-calcareous bedding surface accurately named 'belemnite battlefield'. The bed overlies the black organic-rich Posidonia shales, interpreted as deposition in dysaerobic-anaerobic basins with fluctuating oxygen conditions at the sediment-water interface. Early Jurassic (boundary Early/Late Toarclan): Mistelgau, southwest of Bayreuth, northern Franconian Alb, Germany. Large specimens up to 10 c n ~ long. Courtesy of C. 9chulbert (Erlangen).

env~ronmentsof I'alaco~oic cephalopod limestones \eclment,ir y Geologj. 44, 263-300 Lap1e, I I (1963) Apt) chenlumachellen -Annalen des NaturIlistor~\chenMuseum4 l4J1en,66. 261-266 Further reading: K 124

10.2.4.5 Tentaculitids and Other Conical Shells (Cricoconarida; Hyolithida) Ientaculitids are extinct millimeter- to a few centimeter-hiked exclusively Paleozoic fossils of uncertain affinities but now considered as a class of the Molluscs. They are characterized by slender conicalcalcitic shells occurring in rock-building abundance in Ordovician to Late Devonian open-marine and basinal carbonates. Tentaculitids and related fossils are common constituents of Devonian pelagic and hemipelagic limestones. Morphology u~zdclussijicntiorz: The conical shells have a pointed apex, some groups are chambered. Classification is based on the shell sculpture, type and angle of the apex and shell microstructure. The class Cricoconarida is defined by having conical calcareous shells with ringlike exterior sculptures. The exterior of the shell is characterized by periodic concentric thicken-

ings (annular rings) and fine concen~t-icor longitudinal striations. Imngitudinal sections show nan-ow V-shaped figures (apical angle up to 20"); in cross sections circular. el liptical or polyhedral figures can be observed. Excellent thin-section microphotographs can he found in Farsan (1994). Tetztaculitcs may be confused with brachiopod spines (see P1. 8616). The class includes two orderc - the Tentacul~tldaand the Dacryconarida. The tr~iltrrc~illitrti\(Ordovic~anto Late Devonian 11) havc concentric ling-11ke th~ckenings at the exterior surface but a w ~ o o t hinterior wall surface. The shells (length commonly 15-30 nim) are pointed, the initial part is chambered. The microstructure is finely laminated and canerit havc fine perforations near the apertura. The d u c ~ ~ ~ c o n ~ r(Ordovicim i~iils to Late Devonian II), comprising the nowakiids and styliolinids, are characterized by small shells, apical angles larger than in tentaculitids, a bubble-shaped and unchambered initial shell section, and smooth or longitudinally striated, shell surfaces. This groups comprises the styliolinids and nowakiids, the latter characterized by ringed exterior and interior surfaces. The styliolinids have smooth exterior and interior shell surfaces. Styliolim differs from E n -

Fig. 10.46. Pelagic limestones with cricoconarid shells. A: Styliolinid grainstone. Telescoping in some shells is caused by currents (arrows). Late Devonian (Frasnian): Eastern AntiAtlas, Morocco. After Wendt and Belka (1991). B: Tentaculitid wackestone with longitudinal and cross sections of Nowakia characterized by ringed exterior and interior surfaces. Middle Devonian (Eifelian): Prague Basin, Czech Republic. Scale is 1 mm.

taculites in possessing a smooth, unchambered, imperforate shell without concentric thickenings. The shell usually terminates in a small bulbous extremity. The microstructure is clear homogeneous calcite.Transverse sections show an extinction cross under crossed nicols. The tentaculitids are valuable index fossils used in regional zonations (particularly Devonian). Ecology andpaleoenvironment: The styliolinids and dacryoconarids were pelagic (mainly planktonic) inhabitants of the upper reaches of the oceans contributing to the formation of pelagic carbonates in basins and deep ramp settings (Fig. 10.46).The tentaculitids sensu strictu lived probably as nektobenthos; they are abundant in slightly argillaceous, sometimes nodular packstones and wackestones (e.g. 'Flaserkalk' of the German Devonian cephalopod limestone) as well as in shales formed on deep shelves, submarine highs (swells) Plate 91

Devonian Tentaculitids and Styliolinids

Small conical calcitic shells including thc tentaculitids, styliolinids and other morphologically similar fossils are common and rock-building constituents of Paleozoic, particularly Silurian and Devonian limestones formed in open-marine environments. The fossils are interpreted as presumably planktonic organisms allowing regional and global biozonations e.g. of the upper Late Devonian. Diagnostic criteria are the shell sculpture (-> 2), type and angle of the apex (-> 3, 5 ) and shell microstructure (-> 7). Bioclastic \vackestone with tentaculitids (T) and trilobites (TR). The sample is from bedded carbonates deposited on a deep platform. Early Devonian (Enisian): Erfoud, Anti-Atlas, Morocco. Longitudinal section (LS) of No~lakiu(N) with characteristic ribs on the exterior and interior shell surfaces, and transversr. section of Styliolitzcr (S). Note stacked cone-in-cone cross section of Styliolinn (center bottom). The micritic matrix is rich in Sine-grained bioclastic debris (white spots). Middle Devonian (Eifelian): Prague Basin, Czech Republic. 'Tentaculitid packstone. Variously sized circular and polyhedral cross sections and V-shaped longitudinal sections. Note 'cone-in-cone structure' of some shells (arrows) indicating current activity (Larsson 1979) and the delicate external transversal ornamentation of the shells typical for tentaculitids. ShlF 3-TENT.Early Devonian: Frankenwald, Gennany. ?>ntnc~tlit~.s. Note shells stacked one within the other (arrow) and the current-controlled unidirectional orientation of some shells. Same locality as -> 3. Sryliolitzcr microcoquina packstone deposited after current transport on a pelagic swell. Note the late diagenetic calcite cement covering the shells (arrows). Styliolinid coquinas occur in pelagic to hemipelagic settings and are known from the Lochkovian to the Late Frasnian. Early Devonian (Emsian): Erfoud, Anti-Atlas, southern Morocco. Pclagic styliolinid wackesronc, Styliolinids (arrow) range from the Early Devonian to the Frasnian. The group is characterized by the absence of peripheral ornamentation. Limestones composed entirely of styliolinids are believed to be ancient analogues of modem pteropod-rich carbonates. E: Echinoderm fragment; 0: ostracod. White curved shells are trilobite fragments. Middle Devonian (Givetian): Menorca Island, Spain. Preservation of styliolinid shells: The original microstructure of the shell walls is completely replaced by a fibrous calcite displaying distinct curved twin-lamellae (arrows), probably indicating low-grade metamorphism (Tucker and Kendalf 1973). This preservation is common in many styliolinid limestones. The fine-grained matrix is microspar. Middle Devonian pebble within Lower Carboniferous flysch deposits: Betic Cordillera, southern Spain.

Plate 91: Tentaculitlds a n d Styliolinids

539

Fig. 10.47. Hyolithid shells. A: cross section. B: section along the longest axis. Both photographs show telescoping of various shells explained by wave transport in nearcoast shallow setting. Uppermost Early Cambrian: Northeastern shore of the Dead Sea, Jordan. Scale is 1 mm. After Shinaq and Bandel (1992).

or in basins. Tentaculitids can reflect paleocurrent bottom water patterns. Criteria used are frequency distributions on bedding surfaces, or graded bedding, imbrication and abundance of calcisiltite components (tentaculites) in the lower parts of turbidite beds (Hladil et al. 1996). Very small-sized cones will roll downcurrent, larger cones will point with the apex into the currents. Presupposing a planktonic life habitat, mass accumulations of dacryoconarids (Pl. 9113) and stylolinids in packstones characterize the Standard Microfacies Type 3 common in open-marine deep shelf and basinal settings. Hyolithids Other conical shells restricted to the Paleozoic and most abundant in the Cambrian are included within the Hyolithida (Fig. 10.47).The group is considered to be a class of the Mollusca or related to annelid worms. The probably aragonitic shells is cone- or pyramidshaped and was closed by an operculum. Sizes range between a few niillimeters and about 200 mm. The microstructure corresponds to the crossed-lamellar type. Iiyolithids can be abundant in Can~brianshelf carbonates. Basics: Tentaculitids, styliolinids and hyolithids Farsan, N.M. (1994): Tentaculiten: Ontogenese, Systematik, Phylogenese, Biostratonomie und Morphologie. - Abhandlungen der Senckenbergischen naturforschenden Gesellschaft, 547, l - 128 Fisher, D.W. (1962): Small conoidal shells of uncertain affinities - calyptoptomatids. -Treatise on Invertebrate Paleontology, part W, 116-130, Lawrence (Geological Society of America) Hladil, J.. Cechan, P., Gabasova,A.,Taborsky, Z., Hladikova,

J. (1996): Sedimentology and orientation of tentaculite shells in turbidite lime mudstone to packstone: Lower Devonian, Barrandian, Bohemia. - Journal of Sedimentary Research, 66, 888-899 Larsson, I(. (1979): Silurian tentaculitids from Gotland and Scania. - Fossils and Strata, 11, 1-180 Poijeta, J. (1987): Phylum Hyolitha. -In: Boardman, R.S., Cheetham, A.H., Rowell, A.J. (eds.): Fossil invertebrates. - 416-444, Palo Alto (Blackwell) Shinaq, R., Bandel, K. (1992): Microfacies of Cambrian limestones in Jordan. - Facies, 27, 263-284 Tucker, M., Kendall, A.C. (1973): The diagenesis and !mvgrade metamorphism of Devonian styliolinid-rich pelagic carbonates from West Germany: possible analogues of recent pteropod ooze. - Journal of Sedimentary Petrology, 43,672-683 Further reading: K 124

10.2.4.6 Serpulids and Other Worm Tubes Fossils referred to as worm tubes are known from throughout the Phanerozoic and common in thin scctions of marine and marginal-rnarine limestones. These tubes may be calcareous (PI. 92/14) or agglutinated (PI. 9219, 10). Most calcareous tubes are assigned to annelid Polychaeta. Annelids are known since the Ordovician. Morphology: Calcareous worm shells are straight. curved or spirally coiled unpartioned tubes, a few millimeters in maximum diameter and up to several centimeters in maximum length. The tubes consist of Mgcalcite or aragonite or both. The skeletal mineralogy is related to mean water temperature. The tubes can form rock-building gregarious associations (Pl. 9213, 4) as

Worm Tube\

53 1

well as serpulid 'colonies' which attribute in the construction of 'reef' structures. Many serpulids are characterized by a microstructure consisting of two layers which in longitudinal sections show an outer cone-incone pattern and a clear or laminated inner layer (Pl. 9216, 7). In tangential sections the shell layers appear as concentric rings (Pl. 9218). Spirorbid calcareous worms are fixed with supporting structures on hard or soft substrates (Pl. 9215). Paleoenvironrnental significance: Serpulids occur in very different environments (including shallow and rocky coasts, sea grass areas, hard and firm sea bottoms, deep-marine habitats). They can live in warm and temperate seas, and are adapted to various salinities. The fossil record comprises scattered bioclasts, rockbuilding accumulations of serpulid tubes or autochthonous reef-like structures (Fig. 10.48). Modem serpulid 'reqfs' are represented by banks deposited in instable marine habitats (commonly nearcoastal environments; often mixo- or hypersaline) on shallow parts of continental shelves, and by meter-sized framework reefs at intertidal and subtidal depths, down to 30 m depths, mainly in sheltered coastal lagoonal conditions (Ten Hove and Van Den Hurk 1993; Fornos et al. 1997). Buildups dominated by masses of serpulid tubes associated with coralline red algae are known from lagoonal environments of the Bermudas (PI. 921 1 ), but also occur in cold-water environments of Antarctic21. Ancient serpulid reefs are known from the Early Carboniferous of England (Wright and Wright 1981), from the Early Cretaceous of Argentina (Palma 1992) and of cehtral Europe (Beniasian: hypersaline 'Serpulit' beds) as well as from Miocene lagoonal or brackishwater environments (PI. 9213). Associations of semulids and microbial carbonates are common. Examples are Late Triassic serpulid/microbial reefs consisting of serpulid aggregates, microbial crusts and abundant synsedmentary carbonate cements (Fliigel 2002). In the Late Tertiary. serpulids in association with microbes formed small-scaled reefs in near-coastal environments (Jasionowski and Wysocka 1997).

Agglutinated worm tubes are constructed by siliciclastic sand and silt grains, carbonate and organic material (PI. 9219,lO). These tubes have been known since the Early Carboniferous, often associated with reef environments. Different names are in use for designating annelid agglutinated mucous sheats tending to early cementation and reworking from the enclosing sediment (Terehella,Tluzrthnr-ella.Prethocoprolithus; see DelvolvC et al. 1993).

Fig. 10.48. Allochthonous and autoclrthonords serpulid records. A: Scattered and broken serpulid tubes redeposited in quartz sand. Early Cretaceous: Subsurfrtce, end el ha user^ 1, southern Bavaria. B: Rock-building concentration of serpulid tubes. Middle Jurassic: Wiirgau, Northern Franconian Alb, Germany. C: Serpulid 'colony' contributing to the formation of centimeter- to meter-sized reefs in near-coast. often brackish settings. Late Tertiary (Miocene): Poland. Scalt. is 2 mm.

Basics: Serpulid worms Bromimann, P., Zaninetti, L. (1972): On the occurrence of the serpulid Spirorbis Daudin, 1800 (Annelida. Polychaeta, Sedentaria) in thin sections of Triassic rocks of Europe and Iran. - Rivista Italiana di Paleontologia r: Stratigrafia, 78, 67-90 Gotz, G. (1931): Bau und Biologie fossiler Serpuliden. Neues Jahrbuch fiir Mineralogie, Geologie und Palaontologie, R. 66, 385-438

Serpulids

Misik, M., Sotak, J., Ziegler, V. (1999): Serpulid worms Mercierella Fauvel, Durandella Dragastan and Carpathiella nov. gen., from the Jurassic, Cretaceous and Paleogene of the Western Carpathians. - Geologica Carpathica, 50, 305-332 Moore, R.C. (1962): Miscellanea (Conodonts, conoidal shells of uncertain affinities, worms, trace fossils, problematica). - Treatise on Invertebrate Paleontology, part W, 259 pp., Lawrence (Geological Society of America) Railsback, L.B. (1993): Original mineralogy of Carboniferous worm tubes: evidence for changing marine chemistry and biomineralization. - Geology, 21, 703-706 Schmidt, W.J. (195 1): Die Unterscheidung der Rohren von Scaphopoda, Vermetidae und Serpulidae mittels mikroskopischer Methoden. - Mikroskopie, 6,373-38 1 Ten Hove, H.A., Van Den Hurk, A.M. (1993): A review of Recent and fossil serpulid 'reefs', actuopalaeontology and the 'Upper Malm' serpulid limestones in NW Germany. - Geol. Mijnbouw, 72,23-72 Weedon, M.J. (1994): Tube microstructure of Recent and Jurassic serpulid polychaetes and the question of Paleozoic 'spirorbids'. - Acta Palaeont. Polonica, 39, 1-15. Further reading: K125

10.2.4.7 Crustacean Arthropods Arthropods are characterized b y segmentation, specialized appendices a n d a rigid exoskeleton that must be shed or molted if the organisms change size or shape. T h e skeletons of s o m e arthropod groups also have a good fossil record in carbonate rocks. Three o f these groups belong to the superclass Crustacea, a fourth and most important group are the trilobites, regarded as a n extinct superclass (see Sect. 10.2.4.8). Crustaceans recorded in limestones include ostracods, cirripedians represented b y balanids, a n d microcoprolites of decapod crabs.

Ostracods Ostracods are bivalved m m - to cm-sized crustacean arthropods, known since the Late Cambrian to occur in nearly all types of aquatic environments. They are valuable proxies f o r paleoenvironmental conditions

Plate 92 Serpulids and Other Worm Tubes T h e p l a t e displays calcareous w o r m tubes (-> 1-8) a n d w o r m tubes with walls consisting of agglutinated grains (-> 9, 10).

Seiplirls m d coralline red algae. Modem aragonitic serpulid tubes. Note distinct differences in tube diameter. Arrow points to sessile foraminifera enclosed in crusts made by coralline red algae (black). Reef environment, Bermuda. Temper-atesetting. Serpulids occurring in modem beachrock, formed in temperate water. Serpulids are common constituents of temperate and cold-water carbonates. Note concentric shell structure (arrows). Black grains are volcaniclastics. Fuerteventura, Canary Island, Spain. Reefs. Serpulids forming small-scale reefs in near-coast settings. Note fibrous cement rim around the annelid tubes. Late Tertiary (Early Sarmatian, Miocene): Prut Valley, Romania. Kork building. Gregarious growth of serpulids in brackish-water environments may result in the formation of serpuliil boundstones (serpulite) characterized by monospecific associations (here: Serpula socialis Goldfuss). Late Jurassic: Pinkerdorf, Lower Saxony, Germany. Spir-obids.These calcareous worms have distinct supporting structures (SS). The sample comes from a shallow-marine limestone block that was transported into the deeper ocean. During deposition the block was overturned, as indicatctf by the geopetal infill. Late Jurassic: Northern margin of the Calcareous Alps near Salzburg, Austria. Mic~ostr-ucturc:Serpulid shells exhibiting the characteristic two-layered foliated microstructure with the cone-in-cow pattern. Cretaceous: San Pietro, Mussolino, Apennines, Italy. Miel-ostr-ucture.The walls of the serpulid tubes consist of two microstructurally different layers (arrows). Midtile Jurassic: Wiirgau, northern Franconian Alb, Germany. Mici~srixcrure.Characteristic cross section of a serpulid shell. Note the concentric. finely laminated structure. Ensly Cretaceous: Ras a1 Khaimah, United Arabian Emirates. Agglutirzated worm tube. Oblique section. Late Jurassic: Subsurface, Kinsau near Augsburg, southern Ckmlany. 10 il&lutinared war-nzs. ~ o n ~ i t u d i n (LS) a l and cross section (CS) of Terebclla lapilloides Miinster or P i - e t h o c c ~ ~ ~ r ~ ~ l i r l ~ f ! . ~ Elliott. The silt-sized wall material is bound together by microcrystalline carbonate. Note the intensive darkcolor reflecting the organic content of the 'wall'. The supporting lining to the burrow is typical of a loose-ground consistency of the sediment. These worms are common in flanking beds of Upper Jurassic sponge reefs and in wackestones of deeper ramp settings. Associations of Terebella and Tubiphytes characterize deeper, low-energy environments and are diagnostic of regionally lowered sedimentation rates (Leinfelder et al. 1993; Schmid 1996; Schlaginweit and Ebli 1999). The burrows are also found as reworked particles in grain- and rudstones (see PI. 11611). Late Jurassic: Schammental, Suebian A h southem Gemlany.

54 3

Platc 9 7 . S e r p t ~ l l d 1-4) can be recognized in thin sections of limestones by small calcitic shells consisting of more or less equally shaped but slightly differently sized valves (-> I), sometimes showing finely prismatic microstructures (-> 2) or shell ornamentation (-> 3, 4). Baianids (barnacles) are sessile cirripedians protected by a calcitic multi-plate skeleton consisting of a massive or hollow basal plate (-> 6) and articulated wall plates (-> 6, 7). Balanid shells are often associated with bryozoans and coralline algae (-> 7) as well as benthic foraminifera. Favreinids (-> 5 ) are fecal pellets of decapod crabs. These microcoprolites can be easily recognized by their sieve-like structure caused by calcite-filled canals that form specific patterns. 1 Ostracod-bivull~wackastone. Ostracods are represented by disarticulated valves (black arrows) and complete tests (white arrows). The percentage of disarticulated carapaces provides a measure of post-mortem modification by taphonomic processes. The bivalve shells (BS) are replaced by coarse calcite. Late Jurassic: Margas de Terenas, Kibadresella, Spain. 2 Ostracod niicrostruc.ture. The thick shell consists of two valves showing distinct overlap (0). The carapace exhibits a finely prismatic microstructure. Note the contrast between the well-preserved ostracod shell and the strongly recrystallized sedimentary matrix. Silurian: Gotland Island, Sweden. 3 Paleozoic pelagic ostracods. The thin section shows complete and disarticulated valves of highly spinose ostracods belonging to the Entomozoacea (Myodocopida). Entomozoans are common in Devonian basinal sediments and arc interpreted as having been planktonic. The sample comes from limestones deposited in an open-marine deep-shelf environment. Late Devonian (Famennian): Menorca Island, Spain. 4 Pelagic entonzozoan ostracods. Note the spinose ornamentation (arrows) of the shells. Same locality as -> 3. 5 Favreinids. Fecal pellets of decapod crabs. Poorly sorted grainstone consisting of Favr-eina (cross sections, CS. and longitudinal sections, LS), tiny peloids and large rounded intraclasts. This microfacies is common in the lagoonal environments of inner ramps affected periodically by storms. Lowermost Cretaceous (Purbeck facies, Berriasian): Subsurface, Kinsau well, Bavaria, Germany. 6 Balanid shell. Cross section of the basal plate. The hollow plate is subdivided by partitions (black arrows). Some wall plates are displayed in the upper part of the cross section. The barnacle and bryozoans (B) are encrusted by coralline red algae (white arrows) forming a macroid. Multitaxon macroids indicate unstable substrates. The sample comes from warm-temperate carbonates (Nebelsick 1989). Late Tertiary (Early Miocene): Eggenburg, Austria. 7 Balanid-bryozoan-coralline algal association. The poorly sorted bioclastic packstone consists of balanids (while arrow pointing to an oblique section showing some wall plates), bryozoans (B) and coralline red algae (black arrow). This association is a common attribute of Cenozoic temperate and cold-water carbonates. The irregularly shaped open vugs (white) are caused by freshwater leaching. Late Tertiary (Early Miocene): Zogelsdorf near Eggenburg, Austria.

Plate 9 1 : Crustacean Arthropods

535

Balanids

Fig. 10.49. Cross sections of ostracod shells. A: Shell showing the duplicature. The excellent preservation is due to an early diagenetic silicification of the test. Late Carboniferous (Gzhelian): Auemig, Camic Alps, Austria/ltaly. B: Slightly displaced smooth-shelled test exhibiting the finely prismatic microstructure. Early Carboniferous: Poland. C: Sculptured shell of an entomozoan pelagic ostracod. Late Devonian: Menorca Island, Spain.

ture is layered, homogeneous or finely prismatic. The microstructures commonly form only one shell layer, except in some Paleozoic ostracods (e.g. Leperditiidae).

Ecology: Most ostracods are found crawling on or burrowing into the sediments at the bottoms of the ocean (Fig. 10.50) or lakes. A few modem ostracods have a pelagic swimming life style.

Distribution: Ostracods appeared in the Cambrian, diversified in the Ordovician and were abundant in the Silurian and Devonian, where they are successfully used for biozonations. Late Devonian and lowermost Carboniferous sediments yield the entomozoan ostracods that can also be recognized in thin sections. New groups also including deep-water ostracods (Fig. 10.50) appeared in the Late Paleozoic, Mesozoic and Cenozoic. Ostracods in thin sections: Ostracods are common in many thin sections due to the repeated shedding that result in accumulations of high numbers of disarticulated valves (Pl. 9311). Complete shells are small; they rarely exceed a length of 1 mm. Criteria in thin sections include shape, size, shell overlap (Pl. 93/2), exterior ornamentation (Pl. 9314; Fig. 10.49C) and the prismatic shell microstructure (Pl. 9312). The duplicature is rarely shown (Fig. 10.49B).In general, these criteria do not allow systematic assignments, except where characteristic shell ornamentation patterns can be recognized.

Balanids

Fig. 10.50. Deep-marine osti~~cods associated with benthic foraminifera, mollusk debris and echinoderm fragments exhibiting the characteristic fine net-like structure. The ostracod near the top (infilled with red micrite) displays the duplicature. The large particle near the bottom is a hardground intraclast (see Sect. 4.2.8.1). Early Jurassic: Adnet, south of Salzburg, Austria. Scale is 1 mm.

Balanids or barnacles (Pl. 93/6,7) are sessile crustacean arthropods belonging to the Cirripedia. Cirripedians are highly unusual crustaceans that loose many of their typical arthropod features during ontogeny. All adults are sessile. The carapace of the larvae is replaced by a series of calcified plates that form a protective compartment for the body and the appendages. Balanids occur attached to various substrates including rocky coasts, shells, drifting wood or swimming organisms. Attachment is made by a broad basal plate (Pl. 9316) that is a part of the calcitic test. The shell forms a truncated cone consisting of up to eight calcareous wall plates and other plates that can close the aperture. Modem balanids are abundant in temperate and cold-water environments and occur from intertidal

to mid- and high-latitudinal shelf settings. Balanid shells form a large part of 'bryomol' and 'barnarnol' sediments (Sect. 12.2.2.1). Fossil balanids have been known since the Cretaceous and are common constituents of Late Tertiary nontropical carbonates (Karnp et al. 1988; P1. 10613).

Favreinids A somewhat curious microfossil characterized by small micritic bodies with numerous spar-filled eyes has been described frorn Mesozoic shallow-marine limestones as Favrzina (Fig. 10.51), which is a microcoprolite. Some thalassinid decapod crabs produce fecal pellets exhibiting characteristic sieve-like patterns of tubules formed by projections from the intestine walls. The shape, arrangement and size of the calcitefilled tubules are used for taxonomic differentiation. Mass accumulations of these fecal peloids, commonly associated with smaller peloids or ooids, contributed significantly to the formation of extended sheats of carbonate sands in the latest Jurassic and earliest Cretaceous restricted lagoons (Pl. 9315, P1. 136/ 9). Fossil decapod coprolites assigned to Favreina and similar genera have been reported from Devonian to Tertiary limestones. Most reports deal with Jurassic and Cretaceo~~s favreinids, followed by Triassic findings. Rock-building occurrences are abundant during the Late Jurassic-Early Cretaceous time interval. A bikliography prepared by J. Blau can be found on the Internet. Basics: Crustacean arthropods Hourget, E. (1980): Bxnacle shell growth and the relationship to environmental factors. - In: Rhoads, D.C., Lutz, R.A. (eds.): Skeletal growth of aquatic organisms. -Topics in Geobiology, 1,469-492, New York (Plenum Press) Dall, W.. Moriarty. D.1.W. (1983): Functional aspects of nutrition and digestion. - In: Bliss, D.E. (ed.): The biology of' Crustacea. Volume 5. Internal anatomy and physiological regulation. - 215-261, New York (Academic PI-ess) Kaesler, K.1. ( 1987): Superclass Crustacea. -In: Boardman, R.S., Cheetham, A.H., Kowell, A.J. (eds.): Fossil invertebrates. - 24 1-257, Paio Alto (Blackwell) Molinari l'aganelli, V.. Pichezzi, R., Tilia Zucchari,A. (1980 and 1984): 1 coprolithi di crostacei. Rassegna bibliografica e annotazioni tassonomiche. Parte I. Genere Fmrc~ina. Parte 11. Ger~eriHelicerina, Palaxius, Para,fuvr-einue Tl~orot~ctiaBolletino del Servizio geologic0 d'Italia, 100 (19791, 409-454 and 104 (1983), 309-344 Moore, R.C., Pitrat, C.W. (eds., 1961):Arthropoda 3. Crustacea Ostracoda. - Treatise on Invertebrate Paleontology, part Q, 442 pp.. Lawrence (Geological Society of Americaj Pokorny, V. (1978): Ostracodes. - In: Haq, B.U., Boersma,

.

.

Fig. 10.51. Longitudinal (A) and cross section (B) of Favreina, a microcoprolite of decapod crabs. The patterns caused by the arrangement of the calcite-filled canals are used for taxonomic differentiation. Lowermost Cretaceous (Bemasian): Kinsau well, Bavaria, Germany. Scale is 500 pm.

A. (eds.): Introduction to marine micropaleontology. 109-149, New York (Elsevier) Schweigert, G., Seegis, D., Fels, A., Leinfelder, R. (1997): New internally structured microcoprolites from Germany (Late Triassic/Early Miocene), Southern Spain (Early1 Middle Jurassic) and Portugal (Late Jurassic): Taxonomy. palaeoecology and evolutionary implications. - Palaontologische Zeitschrift, 71, 51-69 Further reading: K127 (ostracods), K139 (favreinids)

10.2.4.8 Trilobites Fragments of trilobites may be common in Early Paleozoic shelf limestones. Trilobites are extinct, exclusively marine arthropods restricted to the Early Cambrian to Late Permian time interval. Most trilobites lived in fairly shallow water and were benthic: a few may have been pelagic, floating in the water column. Benthic forms walked on the sea bottom and fed on detritus. The segmented dorsal exoskeleton is longitudinally differentiated into an anterior head shield (cephalon). the thorax consisting of a few to many segments, and a tail shield (pygidium). Laterally the skeleton is subdivided into a raised axial portion and t\vo laterill portions. The surface of the skeleton is smooth or variously ornamented with tubercles, spines and other elements.

Shell structure: The skeleton consists of chitin hsrdened by impregnation with calcium phosphate and calcite. The microstructure of the finely layered shell is homogeneous prismatic (Pl. 9416). Some trilobite fragments are characterized by fine pores or canals oriented perpendicular to the surface (Pl. 94/1, 3). Triiobite spines may be confused with brachiopod spines, but the latter consist of two calcite layers showing concentric foliated structures in contrast to homogeneous pris.matic trilobite spines.

Trilobites

Trilobites in thin sections: The most common trilobite fragments seen in thin sections are dissociated thorax fragments (Pl. 9412, 4). Because the shields and segments are turned under on the ventral side, in thin sections the inflected margins of the segments look like tiny hooks causing the appearance of 'shepherd's crooks' (Pl. 94/l, 3).

Microstructure and recognition ofechinoderms in thin sections: The echinoderm skeleton is made of plates, spines or sclerites. Each skeleton element consists of a three-dimensional,porous network composed of crystallographically uniformly oriented carbonate crystals (stereom: a latticework constructed from lathes of HighMg calcite) and organic tissue (stroma) within the meshes of the network (Fig. 10.52). Skeleton elements Basics: Trilobites exhibit unit extinction between crossed nicols and corKaesler, R.L. (1987): Trilobitomorpha. -In: Boardman, R.S., respond to a single calcite crystal. The Mg-calcite eleCheetham, AH., Rowell, A.J. (eds.): Fossil invertebrates. ments transform to calcite with some changes in the - 22 1-240, Palo Alto (Blackwell) preservation of the original microstructure (Dickson Moore, R.C. (1959): Arthropoda 1. Trilobita. -Treatise on Invertebrate Paleontology. Part 1,560pp., Lawrence (Geo- 2001). logical Society of America) Echinoderm grains are usually preserved as large Further reading: K 126 single crystals of calcite. The sparry preservation is found irrespective of whether the primary porous network is filled with syntaxial calcite or with pyrite, he10.2.4.9 Echinoderms matite, glauconite or other minerals. Micritic preservation of echinoderm fragments is related to crystal Echinoderms are marine invertebrates with a multi-plate diminution by diagenetic dissolution (Evamy and calcareous internal skeleton embedded in the skin, a Shearman 1965; Neugebauer 1978; Neugebauer and marked five-rayed symmetry and a water vascular sys- Ruhrmann 1978; Richter 1974). tem through which the water is circulated in the body. With few exceptions, modem echinodernls are benthic Usually echinoderm skeletons disarticulate and the bottom dwellers. A few can swim or float. skeletal plates are scattered in the sediment. Individual The phylum Echinodermata, known since the Cam- plates are commonly millimeter-sized to a few centibrian, embraces many major subgroups, some of which meters in maximum dimension. In thin sections, echiare important rock builders during the Phanerozoic (e.g. noderm fragments are easily recognized by the uniform crinoids, echinoids). Echinodernl fragrnents are present extinction, the dusty appearance and often gray or yelin limestones formed in shallow-marine as well as in lowish colors in transmitted light, and the calcite latdeep-marine environments. Most Paleozoic echino- ticework. Many echinoderm plates exhibit a finer more derms were sessile. dense meshwork towards the plate surfaces, appearing

Plate 94 Trilobites The plate displays trilobite limestones formed in low- and high-energy settings of open-marine platforms. Different skeletal parts occur in texturally different limestones, pointing to transport sorting. Grainstones yield head-shield and thoracal fragments (--> 1, 3). Wackestones commonly contain variously sized thoracal fragments (-> 2). Packstones are formed by accumulations of pygidia (-> 7). fidohirc I-utlstoizc.Various trilobite sections: Semicircular section (1) of a trilobite head shield (cephalon). Note welldifferentiated axial region (glabella, G ) and long spines (S). Recurved thoracal segments (2). Open-marine platform. Early Devonian: Hamar Laghdad, Erfoud, southern Anti-Atlas, Morocco. Trilobite ~*ackestone. Poorly sorted trilobite debris in micritic matrix. Same locality as -> 1. Microstn~cture.Characteristic 'shepherd's crook' structure, caused by recurved lateral borders of thoracic segments. The homogeneous prismatic microstructure encloses fine pores (arrows) running perpendicular to the surface. Intergranular spaces between the trilobite fragments are filled with radiaxial calcite cement (RC). Same locality as -> 1. Typical criteria. Recurved trilobite fragment (T) and echinoderm (E) bioclast within a micritic matrix. Same locality as -> 1. Taphonon~y.Microbially encrusted trilobite fragment. Late Silurian: Valentin-Torl, central Camic Alps, Austria. Typical criteria. Trilobite spines within a fine-grained quartz sandstone. Note the fine prismatic microstructure of the thin elements. Middle Cambrian (Paradoxides Sandstone): Oland Island, Sweden. Trilobite packstone. Densely packed and parallel arrangement of trilobite fragments forming a coquina. Most fragments Same locality as -> 1. are parts of tail shields of trilobites living near mud mounds. SMF 12-TRILO.

Plate 94 'I rllobltc.\

549

Crinoidea

gray in thin sections, and an open meshwork within the plates. Pore-filling cement occurs commonly within the host skeleton. Many echinoderm bioclasts, particularly those in micritic limestones, exhibit syntaxial overgrowth of clear calcite cement, because the echinoderm plates act as nucleation sites for calcite cement (Pl. 341 3,4). The genetic interpretation of this cement is discussed in Sect. 7.4.2.1. Many echinoderm limestones are cemented accumulations of echinoderm plates that have broken along the calcite cleavage planes. Some echinoderm fragments show characteristic shapes in thin sections (Fig. 10.53). Columnal plates of stalked echinoderms (crinoids, cystoids, blastoids) appear round or pentagonal in cross sections (Fig. 10.54). Stem plates are centrally perforated by one or several holes that may have circular, elliptical or pentagonal outlines. Sections parallel to the stem exhibit rectangular figures. Stem plates still preserved in series are subdivided by crenulated joint surfaces. Crinoid arm plates may reveal lunate patterns when cut perpendicular to the arm axis and rectangular patterns or two parallel plates when cut parallel to the arm axis. Fig. 10.52. Criteria of echinoderm fragments in thin sections. Pore plates of echinoids cut parallel to the plate sur- A: Oblique tangential section of a crinoid stem exhibiting face show characteristic patterns (Durham et al. 1966). three columnal plates and a side view of the serrate surface Class$cation: Echinoderms fall into two major groups including forms attached to the seafloor (Pelmatozoa) and crawling and burrowing fornls (Eleutherozoa). The Pelmatozoa include the Crinozoa with the Crinoidea (sea lilies) and the exclusively Paleozoic Blastozoa. The Eleutherozoa comprise the Asterozoa with the Asteroidea (starfish) and the Ophiuroidea, the Paleozoic Ilomalozoa and the Echinozoa with the Echinoidea (sea urchins), Holothuroidea and further extinct groups. Most of these groups appeared in the Ordovician, the crinoids and the Homalozoa already in the Cambrian. Modern echinoderms comprise crinoids, asteroids, ophiuroids and echinoids, holothurians. Identification of dissociated echinodermfragments: The elements of echinoderm skeletons are commonly disarticulated by taphonomic processes. Echinoderm fragments are frequent constituents of many Phanerozoic carbonates, but generally they are listed without any further assessment except as 'crinoids' or 'echinoids'. Microfacies analyses, however, require more detailed differentiations. This is possible if specific classification systems developed for isolated skeletal elements of crinoids and echinoids are used (Moore and Jeffords 1968; Termier and Termier 1974; see Fig. 10.55, P1. 13515-7).

between them. Note the parallel cleavage planes caused by recrystallization. Mississippian: Frank's land slide, Alberta. Canada. B: Side view of two crinoid columnals still exhibiting the original meshwork microstructure. Early Pem~ian: Camic Alps, Austria. Scale is 1 nun.

Crinoidea Crinoids are passive filter-feeding organisms. The cup-shaped body (theca) with five simple or branched flexible arms is connected to the bottom via a stem located on the underside of the body. The stem is constructed of a series of interlocking disks called columnals each of which is centrally perforated forming a lumen. The lumen houses the nerves involved in the movement of the animal. Stemmed forms frequently have holdfasts composed of small polygonal plates. The calyx carries long mobile arms which support featherl k e structures (pinnules) acting as filtration fan. Staked crinoids were abundant in shelf environments of the Paleozoic and Mesozoic. Crinoids were the most abundant group of echinoderms from the Early Ordovician to the Late Paleozoic. Today the group is common in deep oceans. The common fossil record of crinoid skeletons are dissociated elements, usually of the stems or the arms. Crinoids disintegrate in a mass of arm and cirri fragments (Allison 1990). Highly porous crinoid ossicles are entrained at lower current velocities than

E c h i n o d c r m s in Thin Sections

55 1

hydraulically sorted components of tempestites, in crinoidal mounds (Becker and Dodd 1994) on slopes and in basins. Widely extended 'regional encrinites' (Ausich 1997) were deposited below normal wave base but within storm wave base. Crinoid limestones are regarded as a specific standard microfacies type (see P1. 11912,PI. 13916). Post-Cretaceous crinoid deposits are rare, because of the change in the habitat of stalked crinoids from shallow shelf and upper slope environFig. 10.53. Schematic drawings of common sections of echi- ments to deeper-water basinal environments. noderm plates. A and B: Cross sections of crinoid columnals Crinoids thrived in carbonate settings to siliciclasdiffering in the shape of the central lumina. C : Colurnnal diftic-dominated settings. Limestones rich in crinoids exfering from A and B in the pentagonal outline of the stem hibit differences in the abundance and composition of plate. D: Section of a stem showing the serrate outline of the articulated surfaces. E: Series of stem plates displaying ser- crinoidal elements, indicating various taphonomic prorated outlines of stem surfaces. F: Same as E but section pass- cesses and differences in the depositional environment: ing through the lumen. G : Oblique section through a crinoid (a) Many primary crinoid packstones consist almost stem. H: Lunate crinoid arm plate. Sections along a-a' and I>-b' will create different pictures, I: Echinoid pore plates par- exclusively of isolated, often worn disks and plates. allel to the surface of the plates. Modified from Horowitz These packstones (encrinites) can form thick beds. (b) Crinoid ossicles may also occur within bioclastic and Potter (1971). wackestones and marly limestones, but to a minor persolid carbonate particles of the same size (Savarese et centage and admixed with other skeletal grains. (c) Long al. 1997). stems and even well-preserved crowns occur in marly Stalkless crinoids (feather stars) appeared in the Me- limestones and marls. Type a may indicate in-place sozoic. Today they live in shallow-marine waters, e.g. degradation or deposition subsequent to transport. reefs. Their isolated elements may be conspicuous con- Type b may indicate transport prior to deposition. stituents of Mesozoic open-marine limestones. Type c characterizes more or less autochthonous burial in quiet-water settings. Crinoid 111nestoner Crinoidal limestones (usually wackestones and packCrino~dIlii~emnesare com~nonlyformed by mas< stones, rarely grainstones) originated in place by auaccumulation\ of benthic crinoid elements, but can also tochthonous or parautochtl~onousdeposition of crinorxglnate from the depomon of fiagments of pelagic oidal elements or allochthonous subsequent to transfree-11v1n~ crinordj port (Cain 1968): Berlthic cl-itzoidu! limc~stonesare formed in different In-place deposition occurred in reef, near-reef (Fig. marine depositional environments. Mass accun~ulations 10.55; P1.143/1), and far-reef settings (Ruhrmann of crinoids occur in reef flank beds (Pl. 14414-6), as 197la, 1971b), in crinoidal mounds (Becker and Dodd

Fig. 10.54. lsolated crinoid columnals in thin sections differing in outlines and surface ornamentation. A: Pentagonal stem plate with several ringlike cirri sockets. Early Jurassic (Sinemurim): Klauskogel near Hallstatt, Austria. B: Penracrinus exhibiting the original meshlike microstructure especially in the center. Early Permian: Southern Anatolia, Turkey. C : Circular stem plate. The original microstructure has largely vanished. Note cleavage planes. The columnal is encrusted by fora~ninitera.Late Carboniferoi~s:Rosskofel, Camic Alps, Austria. Scale is 1 mm.

552

Crinoid Limestones

Fig. 10.55. Crinoid limestone. Most authors reject a more detailed morphologic differentiation of disarticulated elements of benthic crinoids in thin sections. However, the differentiation of dissociated crinoid elements (Moore and Jeffords 1968) in washed samples and thin sections can assist in answering both stratigraphic and sedimentological problems (Stukalina 1988; lJres et al. 1999). The thin section exhibits several morphological features important for the taxonomic differentiation of dissociated parts of crinoid stems. (1) Columnals: Individual components of the crinoid stalk. (2) Pluricolumnals: Two or more colunlnals attached to each other. (3) Latera: Outer surface of crinoid columnals with variously shaped profiles. (4N) and (4IN): Nodals and intemodals: Larger and intercalated smaller columnals of a crinoid stalk. ( 5 ) Articula: Smooth or sculptured surface of coIurnnals serving for articulation with contiguous stem element. (6) Sutures of columnal articulation: Externally visible edges of articula. (7) Axial canals: Longitudinal passageway penetrating the columnals, varying in transverse shape and median longitudinal sections; complex axial canals are characterized by successive alternating columnal restrictions and intercolumnal expansion. This sediment was deposited adjacent to biostromal stromatoporoid-coral reefs. Crinoids lived at the flanks of the reefs. The very poor sorting of crinoid fragments associated with well-preserved crinoid columnals indicates burial in quiet-warcr settings without longer transport. Large angular stromatoporoid fragments (S) were admixed with the echinoderm detritus. Late Silurian (Hoburgen limestone, Hamra/Sundre Beds, Ludlowian): Grotlinbo quarry, Hoburgen, Gotland Island, Sweden.

1 994; PI. 11912) and also in slope environments (Michalik et al. 1993). Parautochthonous crinoid accun~ulationswere formed in Silurian and Devonian forereef areas. Crinoids were major contributors to the pioneer stage of Paleozoic reefs (see Sect. 16.2.6.2). Another type of autochthonous deposits are regionally extended accumulations of crinoids ('regional encrinites'; Ausich 1997). Allochthono~~s deposits formed on subtidal ramps (e.g. in the Early Carboniferous Waulsortian crinoid-

bryozoan facies behind autochthonous accumulations in mud mounds), on platforms, slopes, basins as well as on seamounts. Deposition in subtidal environments is frequently connected with storm-induced transport of crinoid elements contributing to tempestites (Aigner 1984, 1985; P1. 9512). Slope and basinal setting of crinoid accumulations may be associated with a downward transport of crinoids from shallow or upper slope environments leading to the formation of crinoidal turbidites (Tucker 1969; P1. 13913).An upslope transport of off-reef crinoids owing to the fact that crinoids can

Crinoid Limestone5

Are the crinoid elements broken, worn, abraded or conspicuously altered (Pl. 95/3,4)? Do crinoid stems show signs of current orientation? Are the elements bored or encrusted (Pl. 5216, 7)? How abundant are the crinoids with regard to the rock volume? Are the crinoid elements grain- or mud-supported'? What about the sorting of crinoids and other grains? Do crinoids contribute to specific depositional fabrics (e.g. gradation. lamination)? What other skeletal and non-skeletal grains are associated with the crinoids (PI. 95/1)? Other imnortant auestions in the context of the " eenetic interpretation of crinoid limestones refer to field criteria (geometry, sedimentary structures), lateral and vertical extension of the crinoid limestones, and interbedding with other facies types.

Planktonic crinoids Elements of non-stalked planktonic crinoids are important, sometimes rock-forming constituents of pelagic carbonates. These crinoids are known from the Triassic of the Alpine-Mediterranean region (roveocrinoids)

553

Fig. 10.56. Saccocoma limestone. A: This microfacies is characterized by numerous antler-shaped calcitic structures floating in a fine-grained matrix of pelagic micrite. Late Jurassic (Kirnmeridgian): Central Apennines, Italy. B: Cross section of a Saccoconza arm element (brachialia). Late Jurassic: Thurburo majus, northern Tunisia.

and occur with Saccocotna Agassiz in great abundance in Tethyan Jurassic open-marine limestones as well as in epicontinental shelf carbonates (Fig. 10.56).

li-iassic roveocrinoids (PI. 96/1) occur i n wide distribution in the Tethys within a specific tlme interval comprising the Late Ladinian and the Early Carnian (Kristan-Tollmann 1970). The first record of Saccocoma is from late Middle Jurassic, mass occurrences are abundant within the time interval Kimmeridgian to middle Tithonian. The planktonic life-style of Saccocoma was questioned by Manni et al. (1997) who favored a possible benthic mode of life. Anatomical and taphonomical criteria as uell as the distributional pattern argue against this interpretation (Keupp and Matyszkiewicz 1997j. Fig. 10.57. Echrr~oicispines ~c.itlz stereorn-filled center. The pattern corresponds to the Cidaris type distinguished by Hesse (1900). A: The reticulate structure of the central zone is surrounded by a zone of densely arranged radial septa. The septa are connected by rings of interseptal bars. B: The general structural pattern resembles that of A but the spine is covered by a distinct peripheral border. A and B: Early Permian: Forni Avoltri, Carnia, Italy. Scale is 500 um.

554

Echinoids

Fig. 10.58. Holothuriatl sclerires. A: Thin section exhibiting two different sclerites. Early Cretaceous: Subsurface, Bahama Bank. B: SEM photograph of Theelia jloiida (Terquem and Bertelin). Early Jurassic: Ernpede near Hannover, Gcrmany. B: After Fischer et al. (1986). Scale is 100 pm.

Thin sections of Saccocoma elements were described as Eothrix and Lombardia. Verniory (1955) proved that these fossils were sections of facetalia and brachialia of Saccocoma and closely related taxa. Characteristic sections exhibit antler-like shapes (Fig. 10.56; PI. 96/2,

3). In the Upper Jurassic central European epicontinental platforms, the Saccocoma facies characterizes late transgressive system tract and highstand deposits. Within the Tethyan region, the Saccoconla facies is common in deep-marine basinal sequences. Allochthonous deposition by turbidites on slopes forming Saccocoma packstones/wackestones are known from deep-water settings as well as epicontinental positions (Matyszkiewicz 1996).

Echinoidea Modem echinoids occur in almost every major marine habitat from intertidal zones to depths of more than 5000 meters, and from the poles to the equator. Regularia are epibenthic detritus feeders living especially on hard bottoms. Irregularia occur within or on soft bottoms.

Morphology and classification:The skeleton is made of tightly interlocking plates that form a rigid structure (test) whose shape ranges from globular to flattened. Echinoids are traditionally divided into two subgroups. The regular echinoids with almost perfect pentameral symmetry include the Cidaroidea (since Late Paleozoic) and the Echinoidea s.str. (sea urchins:

Plate 95 Echinoderms The plate exhibits Paleozoic limestones rich in crinoid plates (-> 1-4) and remains of cystoidean echinoderms (-> 6) as well as a Triassic limestone with echinoid fragments (-> 5). The figure on this page demonstrates the morphology of a stalked crinoid (after Black 1988). Crinoidfi.agments. Bioclastic wackestone with echinoderms (E; predominantly crinoids) and shells of pelagic bivalves ('filaments', F). The crinoid sections correspond to the sections A, D and H shown in Fig. 10.53.The biofabric is characterized by loose and disperse packing and bimodal sorting; see -> 4. Open-marine deep slope environment. Early Jurassic: Adnet near Salzburg, Austria. Crinoid acci~mulation.Crinoid stem plates (columnals) within a tempestite. Some crinoids exhibit Early L)esyntaxial cement rims. Most cementation, however, is related to fractures. SMF 12-CRINO. vonian (Emsian): Erfoud, southern Anti-Atlas, Morocco. Crinoidstenz. Longitudinal section through three colurnnals. Note grayish color and distinct twin lameilac. Early Carboniferous open-marine carbonate ramp (Visean):Debnik, Cracov Upland, central-south Poland. Crinoid packstone. The columnal (C) is completely recrystallized. Black arrow points to niicroborings, white arrows to the serrate boundary between stem plates. B: Bryozoan. The biofabric is densely packed and well-sorted. The sample is from the deeper part of a carbonate ramp. Mississippian: Turtle Mountains, Frank Slide, Alberta, Canada. Echinoids. Bored echinoid plates (EP) and echinoid spines (ES) associated with gastropods (G). White grains are quartz. Late Triassic: Gurumugl, Mount Hagen, central Papua New Guinea. Cystoid wackestone. Cystoids were important Early Paleozoic rock builders (Cambrian-Devonian). The thin section shows broken and eroded plates occurring in a strongly recrystallized limestone rich in cystoids. Black arrows point to syntaxial overgrowth rim cement. B: Bryozoan. Note the difference in color between echinoderms (dusty gray) and bryozoans (dark). Late Ordovician (Ashgillian): Central Carnic Alps, Austria.

Echinoid Spines

since Late Triassic). In the irregular echinoids a secondary bilateral symmetry is superimposedupon the primary pentaradiate pattern. This group includes the Cidaroidea (pencil urchins), Clypasteroidea (sand dollars; since the Paleocene), Spatangoidea (heart urchins; since the Cretaceous) and Cassiduolidea (since Jurassic).

Echinoid spines in thin sections: Echinoid fragments can be identified using a combination of morphological criteria (Durham et al. 1966; Smith 1984; Nebelsick 1992). Common constituents in thin sections of limestones are echinoid spines. Living echinoids are covered with movable spines, which are anchored in sockets on the top of tubercles in the test and serve for protection, walking and burrowing.

Echinoid spines show a great variety in shape and size. The spines are long and prominent in regular echinoids, but very short and stubby, forming an almost felt-like covering, in irregular echinoids. These spines are hollow and without a cortex. A spine consists of three parts, a long shaft, a short neck and a base. The concave articulation surface that attaches onto the mamelon of the tubercle is the acetabulum which may be either perforate or imperforate. Each spine can be moved individually. The shaft may be smooth, very finely striated or ornamented by ribs, thorns or granules. Sections of echinoid spines exhibit characteristic internal radial patterns that are useful taxonomically. In cross section spines may be hollow (diadematoid type)

Plate 96 Echinoderms The plate displays skeletal elements of non-stalked pelagic crinoids (-> 1-3) and stalked crinoids (-> l l ) , echinoid spines (-> 6-10, 12, 13), and a holothurian sclerite (-> 4). Taphonomic criteria of echinoderms are shown in -> 14 and 15. The figure on this page shows a recent non-stalked crinoid. After Black (1988). 1-3 Pelagic 'free-swimming' crinoids. Skeletal elements of planktonic crinoids are important constituents of Mesozoic open-marine carbonates. Most common elements seen in thin sections are brachial extensions used for swimming. Roveocrinoids. Oblique sections of thin arm plates (brachialia) of Osteocrinus rectus (Frizell and Exline). Late Triassic (Camian): Feuerkogel near Aussee, Austria. Mictofacies with Saccocoma. Accumulation of antler-like brachial plates and other elements of the non-stalked crinoici. Note the fine meshwork structure (white arrow) diagnostic for echinoderms. Black arrows point to zoospores of planktonic algae (Glohoclzaete;see Sect. 10.2.6). This microfacies is widely distributed in Kimmeridgian to Tithonian basinal limestones of the Tethys. Late Jurassic: Margin of the Northern Alps near Salzburg, Austria. Saccocoma. Arm plate. Late Jurassic (Saccocoma limestone, Kimmeridgian): Central Apennines, Italy. Holotkurian sc.lrrite. Skeletal elements of holothurians differ from those of other echinoderm groups in that they consist of isolated microscopic single-crystal calcite pieces. Morphology is highly variable and includes anchors, hooks, tables, rods, wheels (this figure) and others. Early Cretaceous: Subsurface, Bahamas. 5-10, 12, 13 Echinoid spines: The tests of echinoids are covered by spines of different size, sewing as protection, locomotion, or as means of anchoring. Cross sections exhibit a radial pattern around a hollow or irregularly fabricated center. Differences in radial patterns may be useful taxonomically and for stratigraphic zonation. 5 Echinoid spines. Longitudinal section. The spine projects outward from a tubercle (T) on a plate. Late Triassic: Kuta, Papua New Guinea. 6---8Echinoid sj~ines.Cross sections. The three sections correspond to each other in the perforated thin zone surrounding the lumen. and the general pattern of the wall zone. The wall zone consists of wedge-shaped radial elements which widen toward the periphery. The cross sections differ in the shape and the number of the radial septa. The general pattern corresponds to the Diadenla type distinguished by Hesse (1900). Cross sections exhibit either low birefringent colors or extinction under crossed nicols. Same locality as -> 5. Echinoid spine. Cross-section and oblique section. Same locality as -> 5. Echinoid spine. Note the syntaxial overgrowth cement. Late Jurassic (Tithonian): Subsurface, Kinsau, Germany. Crinoid a m rlcnzcn~s(brachial fragments), characterized by bifurcated lunate patterns (see Fig. 10.53). Early Jurassic: Adnet, Salzburg, Austria. Echinoid spine. Cross section. The spine differs from those shown in -> 6-8 and 13 by the arrangement of the radial septa, distinct ring-like interseptal connections and by the larger size of the spine. Late Permian: Bergama, western Anatolia, Turkey. Echinoid spine. Cross section. Same locality as -> 5. Destrucrion of echinoderm plates by boring. Arrows point to cross sections of cricoconarid shells (see PI. 91). Early Devonian (Emsian): Erfoud, Anti-Atlas, Morocco. Echinoderms and mollusks compared. In thin sections, echinoderm (E) elements differ from mollusk (M) shells in color and net-like microstructure. Mollusk shells are commonly replaced by a coarse calcitic mosaic. Same locality as -) 5.

Piate 96: Echinoderms

558

or solid (cidaroid type). The hollow center is called the lumen. The solid center filled with stereom is termed the medulla (Fig. 10.57), the surrounding zone is the cortex. A still useful classification of echinoid spines based on the microstructure was established by Hesse (1900) who distinguished six major groups (see P1.96/ 6-8, 12, 13 for examples).

Distribution: The oldest echinoids appeared in the Late Ordovician but were only a minor element of the benthos throughcut the Paleozoic. The roots of modem echinoids can be traced back to the Permian where the first cidaroids appeared and started to diversify in the Triassic. A major diversification of echinoids took place in the Jurassic. The first irregular echinoids specialized in deposit feeding appeared in the Jurassic. Echinoids generally became a major constituent of the shallow-water benthos during the Jurassic and Cretaceous, also in deep-water environments (chalk) in the Late Cretaceous.

Ophiuroidea and Holothuroidea Remains of echinoderm groups other than crinoids and echinoids are extremely rare in thin sections of limestones, although skeletal elements of holothurians and ophiuroids are often abundant it1 acid residues of carbonates. Cross sections of ophiuro-oid vertebrae from Mesozoic and Late Tertiary limestones exhibit two coalesced calcite plates. each of which constitutes a single crystal, forming a mirrowed reflection pattern (Glazek and Radwanski 1968). Holothurian sclerites may be represented in thin sections by wheel-like structures (Fig. 10.58; PI. 9614) or sieve plates. Basics: Echinoderms Donovan. S.K. (1991): The taphonomy of echinodern~s; calcareous multi-element skeletons in the marine environment. - In: Donovan, S.K. (ed.): The process of fossilization. - 241-269, London (Belhaven I'ress) Glazek, J., Radwanski, A. (1968): Determination of brittle star vertebrae in thin sections. - Bulletin de 1'AcadCmie polonaise des Sciences, S6rie des Sciences gkologique et gkographique, 16,91-96 Guensburg, T.E., Sprinkle, J. (1992): Rise of echinoderms in the Paleozoic evolutionary fauna: significance of paleoenvironmental controls. - Geology, 20, 407-410 Hess, H., Ausich, W.E., Brett, C.E., Simms, M.J. (1999): Fossil crinoids. - 275 pp., Cambridge (University Press) Hesse, W. (1900): Die Mikrostruktur der fossilen Echinoideenstacheln und deren systematische Bedeutung. - Neues Jahrbuch fiir Mineralogie, Geologie und Palaontologie, Abhandlungen, 13, 185-264

Rare Thin-Section Fossils

Keupp, H., Matyszkiewicz, J. (1997): Zur Fazies-Relevanz von Saccocoma-Resten (Schwebcrinoiden) in OberjuraKalken des nordlichen Tethys-Schelfs. - Geologische Blatter fiir Nordost-Bayem, 47,53-70 Kiaer, P.M. (1987): Class Echinoidea. -In: Boardman, R.S., Cheetham, A.M., Rowell, A.J. (eds.): Invertebrate fossils. - 596-611, Palo Alto (Blackwell) Kristan-Tollmann, E. (1977): Zur Gattungsunterscheidung und Rekonstruktion der triadischen Schwebcrinoiden. Palaontologische Zeitschrift, 51, 195-198 Moffat, H.A., Bottjer, D.J. (1999): Echinoid concentration beds: two examples from the stratigraphic spectrum. Palaeogeography,Palaeoclimatology, Palaeoecology, 149, 329-348 Moore, R.C. (ed., 1966): Echinodermata 2. AsterozoaEchinozoa. - Treatise on Invertebrate Paleontology, part U, 725 pp., Lawrence (Geological Society of America) Moore, R.C. (ed., 1967): Echinodermata 1. General characters Homalozoa-Crinozoa (except C ~ o i d e a ) . Treatise on Invertebrate Paleontology, part S, 679 pp., Lawrence (Geological Society of America) Moore, R.C., Jeffords, R.M. (1968): Classification and nomenclature of fossil crinoids based on dissociated parts of their columns. -University of Kansas PaleontologicalContributions, 9, 1-86 Moore, R.C., Teichert, C. (eds., 1978): Echinodermata 2. Crinoidea. -Treatise on Invertebrate Paleontology, part T, 41 1 pp., Lawrence (Geological Society of America) Nebelsick, J. (1992): Echinoid distribution by fragment identification in the Northern Bay of Safaga, Red Sea, Egypt. - Palaios, 7, 3 16-328 Nebelsick, J. (1995): Uses and limitations of actuopaleontological investigations on echinoids. - Geobios, 18, 329338 Savarese, M., Dodd, J.R., Lane, N.G. (1997): Taphonomic and sedi~nentologicimplications of crinoid skeletal porosity. - Lethaia, 29, 141-156 Smith, A.B. (1990): Biomineralization in echinoderms. - In: Carter, J.G. (ed.): Skeletal biomineralization:patterns, processes and evolutionary trends. Volume I. - 413-443, Neu York (Van Nostrand) Stukalina, G.A. (1988): Studies in Palaeozoic crinoid-columnals and stems. - Palaeontographica, A, 204, 1-66 Further reading: K128

10.2.5 Rare Thin-Section Fossils In contrast to the preceding chapters, this chapter and plate 97 deal with fossils that may be recognized in thin sections of limestones, but are generally rare.

Vertebrate remains seen in thin-sections are predominantly bones, scales and teeth of fish. Bones may have ovate, rectangular or round shapes. Remains of amphibians and reptiles are very rare but may occur in lacustrine carbonates. These phosphatic vertebrate grains display clear, amber or brownish, sometimes black colors in thin sections under ordinary light. Be-

tween crossed nicols they may exhibit very low birefringence and undulose extinction. Many fish bones show an interior vesicular or open-network structure and a dense more compact outer structure (Pl. 9712). Fine lamellar microstructures, sometimes with fine tubular pores, are common in bones, teeth and scales (Pl. 9719).

Conodonts (Cambrian to Late Triassic) are small (about 0.2 to about 3 mm in length) tooth-like microfossils consisting of calcium phosphate. They have the shape of serrated bars, ornamented platforms, and blades. They are characteristically brown, gray or black in thin sections (PI. 9'716-8) and sometimes show a lamellar microstructure. Conodonts are generally rare in thin sections, but may be a minor constituent in limestones occurring in condensation sequences. Graptolites (Cambrian to Early Devonian) are usually found in black shales, but specimens may also be preserved in limestones or cherts (9715). The skeleton consists of collagen, a fibrous scleroprotein, showing brown or honey colors in transmitted light . Wood can be preserved by infiltration of calcite, silica iP1. 97/10) or pyrite. leading to preservation of the oreanlc or carbonized mater~alconsisting of cells, sometimes wlth \econdaril~thickened walls. Wood fragments may be minor constituents of lacustrine and n1drlne near-coastal carl-mates.

-

10.2.6 Microproblematica The last part dealing with the criteria of fossils found in thin sections concerns microfossils that are enigmatic with respect to their systematic position. Microprohlematica are micron- and millimeter-sized fossils knonm from acid residues, washed samples and thin sections. that cannot readily be placed in established phyla or major groups. Some microproblematica, described from thin sections may result from difficulties in recognizing threedimensional geometries from two-dimensional views. But many 'thin-section microproblematica' exhibit distinct morphologies, allowing them to be treated taxonomically. Some of these enigmatic fossils have been potentially assigned to the algae, but this assignment is still controversial (Babcock 1986). Some taxa are restricted to specific paleoenvironments and some even represent index fossils (Hoffnxan and Nitecki 1986).

10.2.6.1

Inventory of Microproblernatica

Box 10.8 gives a list of fossils that have been described only from thin sections and are regarded as microproblematica by many authors. Most Mesozoic taxa are benthic and occur in reef limestones and shallow-marine platform carbonates. Some taxa are planktonic and may be common in pelagic open-marine limestones (e.g. Globochaete; PI. 9911). Microproblematica are remarkably abundant in reef communities, predominantly acting as encrusters (see Sect. 9.2.3). Encrusting microproblematica are particularly abundant in reef carbonates, occurring both at the reef surface between and upon reef builders (e.g. Bacinella and Lithocodium; PI. 9914, 5 ) or in small cryptic. habitats of reef cavities (e.g. Baccanella and Kadiomura; P1. 9918, 9). Cavities in modem reefs comprise between 30 and 75 % of the total reef volume. They are inhabited by sessile, boring and encrusting 'coclobiotzts' that contribute greatly to the recycling of nutrients, the production of fine-grained internal sediments and the rapid cementation of reef rocks (Ginsburg 1 983; Hutchins 1983; Choi 1984).The composition and abundance of coelobionts are related to water energy and flushing within the reef body. Common coelobionts that are preserved in the fossil record include foraminifera. sponges, bryozoans, mollusks, serpulids, algae, microbes and many microproblematica (Kobluk 1988). The taxonomic composition of microproblematica contributing to coelobiont assemblages has changed over times as demonstrated by Triassic and Jurassic reef cornmunities. Common microproblematica of Middle Triassic and Carnian reefs in the entire Tethyan region are distinctly different from those of Norian and Rhaetian reefs (Fliigel 2002). The former are represented by Aeolisaccus, Baccanella, Bacinellrr, Burbaferu, Lad inella, Lamellitubus, Radionzura and Tubip11yrc.s;the latter by Lithocodium, Microtuhrrs. Radionzur-(1and Thaunzatoporella. Abundant Late Jurassic encrusting rnicroproblematica are Bacinella, Lithocodi~~nz-T~.oglotella and Tubiphytes (Schmid 1996). The differences become more striking at a species level. Many microproblematica can be assigned to informal groups characterized by the dominating morphology: Hollow tubes (e.g. Aeolisaccus, Koivaella, Lamcllitubus, Macrotubus, Microt~1b~is, Paraeolisaccus) Isolated or closely packed spheroids consisting of radially arranged calcite crystals or spheroids (e.g. Baccanella, Fusanella, Gerneridella, Gfobochaete, Muranella, Microcodium, Nuiu)

Rare Thin-Section Fossils

Cell assemblages (e.g. Bacinella, Ladinella, Thauma foporella) Differentiated crusts and plates (e.g. Lithocodium, Palaeoaplysina).

10.2.6.2 Discussion of Selected Microproblematica The foIlowing alphabetic discussion of the morphology and systematic assignment is restricted to some microproblematica that are of importance for paleoenvironmental and sedimentological interpretations.

Ar-chaeolithoporellaEndo (PI. 4211, P1.9818, P1. 14511) Morphology: Millimeter- to centimeter thick encrustations on hard substrates (fossils, clasts, marine carbonate cement) consisting of alternating couplets of dark micritic layers and slightly thicker layers of fibrous or blocky calcite. Micritic layers may contain

organic matter. Archaeolithoporella also occurs as nodules ('tebagite': Razgallah and Vachard 1991). Distribution: Archaeolithoporella is known from the Sakmarian to the Latest Permian. The genus is widely distributed in the western and southwestern Tethys (Slovenia, Sicily, Greece, Tunisia, Oman), in oceanic microcontinent settings (Japan, China), and in marginal basins of Panthalassa (Texas and New Mexico). The genus is a common constituent of Permian shallow subtidal reefs (e.g. Permian Reef Complex in Texas; Pi. 145/1), often associated with coralline sponges (Fig. 10.59) and with Tubiphytes. Together with syngenetic aragonitic cements, Archaeolithoporella formed waveresistant structures (Fig. 10.59). Archaeolithoporella crusts originated in various settings, including shelf edge, platform margin, forereef, and upper slope. Archaeolithoporella does not seem to be totally dependent on lightened areas, as shown by the occurrence within syngenetic fissures and cryptic cavities. Interpretation: The genus has been interpreted as red algae, stromatolitic algae, remains of microbial mats

Plate 97 Rare Thin-Section Fossils The plate displays fossils which are not common in thin sections of limestones, but, if present, may be important in microfacies analysis. Placod~.r.nlborzrbed. Placodems are a group of fresh-water and marine fishes with primitive jaws bearing tooth-like body plates and variously armored heads and bodies. The group appeared in the Late Devonian, flourished in the Devonian and disappeared in the Early Carboniferous. Thin sections of limestones yield bone plates exhibiting characteristic double-layered microstructures. The sample is a calcareous sandstone. Early Devonian (Odenspieler bed): Bergisches Land, Gem~any. Placoderm nzicrostruct~(re. The placoderm plates are characterized by two layers represented by an inner vesicular (white arrows) and an outer, more compact finely vesicular structure (black arrows). Same locality as -> 1. Fish scales. Cross section of numerous thin and flat scales appearing black in transmitted light. The arrows point to shapes that are characteristic in thin sections. Early Jurassic (Lias epsilon): Hetzles near Erlangen, Germany. Fish tooth andfish bones. The black arrow points to a longitudinal section of a tooth of predatory sharks, the white arrow to oblique sections of fish bones. Shark teeth are characterized by sharply pointed shapes. Late Tertiary (Miocene): Saykamt, Turkey. GI-aptolites.In contrast to the common deposition of graptolites in euxinic basins, graptolites may also accumulate in shallow-marine pelagic carbonate environments. Silurian (Fluminimaggiore Formation, Wenlock): Southwestern Sardinia. Italy. Conodonu: Oblique section of Polygnathus. The sample comes from a strongly recrystallized limestone consisting predominantly of reef debris. Late Devonian: Rugendorf, Frankenwald, Germany. Corzodonts morphology. Free blade (arrow) and platform posterior of Polygnathus. The phosphatic conodonts appear black or brown in transmitted light . The sample is from a pelagic cephalopod limestone. Late Devonian: Elbersreuth. Frankenwald, Gennany. Conodorzt morphology. Oblique section of Polygnathus ex gr. P. glabra. Note carina (ridge with small denticles) and parts of the platform. Late Devonian (Famemian): Drewer, Sauerland, Germany. Fish scale. Note distinctive layering (arrow). Middle Triassic (Muschelkalk, Ladinian): Eschenbach, southwestern Germany. Wood. Length and oblique sections of wood fragments, with a well-defined cellular pattern. Preservation of wood is facilitated by carbonification or silicification (this example). Small grains within the micritic matrix are temgenous quartz. Near-coast mixed siliciclastic-carbonate environment. Middle Jurassic (Bajocian): Morondava Basin, Madagascar. -> 10: Sample provided by M. Geiger (Bremen)

Plate 97: R a r e Thin Secrlon Fossils

501

Microproblematica

Box 10.8. Generic list of thin-section microproblemalica. Many taxa may be cyanobacteriaor algae but their systematic position is not yet fully acknowledged. More than 90% of thin-section fossils designated as microproblematica have been described from shallow-marine reef or platform carbonates. Taxa found predominantly or exclusively in open-marine pelagic 'deep-water' limestones are marked by an asterisk. Tertiary: Codiomorpha Andrusov and Schalekova 1972, Microcodium Gluck 1912, *Pieninia Borza and Misik 1976, Thaumatoporella Raineri 1922 Cretaceous:AeolisaccusElliott 1958,Bacinella Radoicic 1959, Carpathoporella Dragastan 1967, Ciprocampylodon Elliott 1963, Cretacicrusta Elliott 1972, *Diademnoides Bonet and Benviniste-Velasquez 1971, *Didemnum Savigny 1816, *Gemeridella Borza and Misik 1975, Getaia Dragastan 1972, *Globochaete Lombard 1945, Koskinobullina Cherchi and Schroder 1979, Laciymorphus Elliott 1958, Lithocodium Elliott 1956, Microcodium Gluck 1912, *Microlaminoides Bonet 1956, Palaeosiphonium Elliott 1985, *Pieninia Borza and Misik 1976, Thaumatoporella Raineri 1922, Tubiphytes Maslov 1956 Jurassic:Aeolisaccus Elliott 1958,Axothrix Nagy 1971, Bacinella Radoicic 1959, *Diademnoides Bonet and Benviniste-Velasquez 1971, *Didemnum Savigny 1816, Enigma Eliasova 1981, Fusanella Eliosova 1981 , *Gerneridella Borza and Misik 1975, *Globochaetc Lombard 1945, Koskinobullina Cherchi and Schroder 1979, Lithocodium Elliott 1956, Microcodium Gliick 1912, Muranella Borza 1975, Palaeosiphonium Elliott 1985, *Palaeothr-ix Ferasin 1956, Polygonella Elliott 1957, Thaumatoporella Raineri 1922. Tubiphytes Maslov 1956, *VerticillodesmisDragastan and Borza 1975 Triassic: Actinotubella Senowbari-Daryan 1984, Aeolisaccus Elliott 1958, Baccanella Pantic 1971, Bacinella Radoicic 1959,Barbafera Senowbari-Daryan 1984,*Diademnoides Bonet and Benviniste-Velasquez 1971, *Didemnum Savigny 1816, *Genzerrdella Borza and Misik 1975, *Globochaete Lombard 1945, Ladirzella Ott 1968, Ladinosphaera Oberhauser 1960, Lamellitubus Ott 1968, Llthocodiunz Elliott 1956, Macrotubus Fois and Gaetani 1981, Messopotanzellu Dragastan et al. 1985, Microcodium Gluck 1912, Microtubus Fliigel 1964, Muranella Borza 1975, Panormidella Senowbari-Daryan 1984,Paraeolisaccus Senowbari-Daryan and Schafer 1980, Plexoramea Mello 1977, Porferitubus Senowbari-Daryan 1984, Radiomura Senowbari-Daryan and Schgfer 1978, Thaumatoporella Raineri 1922,Tubiphytes Maslov 1956 Permian: Aeolisaccus Elliott 1958.Archaeolithoporella Endo 1959, Koivaella Chuvashov 1974, *Globochaete Lombard 1945, Palaeoaplysina Krotow 1888,Pseudovermiporella Elliott 1958, Tubiphytes Maslov 1956 I

I

Carboniferous: Archaeolithoporella Endo 1959, *Globochaete Lombard 1945, Koivaella Chuvashov 1974,Palaeoaplysina Krotow 1888,Tubiphytes Maslov 1956

and as inorganic structures (Mazzullo and Cys 1977; Wang et al. 1994; Grotzinger and Knoll 1995; Kendall and Iannace 2001). A microbial origin is reliable. Baccanella Pantic 1971 (PI. 9918) Morphology: The genus is characterized by small regularly or irregularly developed spheres consisting of radially arranged aggregates of calcite crystals starting from a central point. The spheres are commonly densely packed side by side. The calcite crystal aggregates exhibit shapes resembling leaves of flowers. They have been interpreted as branches that divide into smaller ones near the periphery. The diameter of the individual spheres varies between about 50 and 500 pm. Distribution: The genus is a common constituent of cryptic cavities in the central parts of Middle and Late Triassic reefs. Interpretation: Baccanella has been regarded as algae, bacteria, bacterially induced carbonate precipitate or diagenetic product caused by recrystallization of micritic High-Mg calcite and aragonite on the sea floor (Pratt 1997). The last two explanations are reliable. Bacinella Radoicic 1959 (Pl. 9914) Morphology: Epibenthic cell assemblages forming crusts or nodules consisting of relatively regular, sometimes parallel irregularly shaped cells. The assemblage is surrounded by an exterior wall. The cells may be circular, rectangular or triangular in cross section. They are filled with sparry calcite. Cell walls are thin. Cell diameter between 100 and 500 pm. Distribution: The genus is known from Middle Triassic to Late Cretaceous deposits. It was originally described from the Cretaceous. Bacinella is a common fossil in Ladinian reef limestones, but occurs also in Late Triassic reef carbonates and is abundant in Jurassic and Early Cretaceous platform carbonates. Bacinella is often intimately associated with Lithocodium. Interpretation: The genus is still enigmatic. It was interpreted as codiacean alga, compared with hydrozoans, and explained as ecotypes of bacterial associations (Neuweiler and Reitner 1992) or as cyanobacteria. Globochaete Lombard 1945 (Pl. 9911) Morphology: The genus is characterized by spherical and kidney-shaped calcitic bodies with a micritic nucleus, about 30 to 100 pm in size, occurring in clusters, isolated or serially arranged, sometimes attached to thin calcitic plates corresponding to 'filaments'. An axial cross between crossed nicols indicates a constmction of radially arranged calcite fibers. The bodies exhibit a sparry wall, appearing yellowish in transmitted light, and sometimes showing a micritic boundary.

hficroproblematica

5 h -3

Fig. 10.59.Archaeolitlzoporella crusts associated with sphinctozoan coralline sponges. The crusts consist of couplets of dark and light irregular and sometimes disturbed layers without distinct microstructures. Note the difference in the preservation of the originally aragonitic sponges and Archaeolithoporella. Both organisms contributed greatly to the fornution of extensive Permian reef structures. Middle Permian (Wordian): Oman. Scale is 1 cm.

Globochuete is similar to Gemeridella Borza and Misik, but the latter genus displays a petaloid arrangement of the radial calcitic elements. Disrrihuriorl: The genus is reported from Silurian lo Early Tertiary limestones. Glohoc.harreis abundant in open-marine pelagic carbonates ( c g . in Late Jurassic deep-water carbonates, often associated with Saccocoma), but also occurs in shallow-marine environments (Schafer and SenowbariDaryan 1980; Bachmann 1987). Infcrpretation: Originally interpreted as calcified zoospores of chlorophycean alga Globoclzaete is now regarded as a planktonic single-celled green alga (Skompski 1982).

Nulysis Hoeg 1932 (PI. 9812) Mo~pholog~l: T h e genus is characterized by a fanshaped structure forming palisades and chains in cross sections. Distribution: Common in Ordovician boundstones (Munnecke et al. 2001) but also known from Silurian to Middle Devonian reefs and lagoonal limestones. lrlfe~pretation:Originally regarded as enigmatic alga, but now assigned to cyanobacteria. Koivaella Chuvashov 1974 (PI. 98/3) Morphology: The genus is characterized by small, sometimes irregularly shaped tubes with micritic walls and indications of bifurcations.

Distribution: The microproblematicu~nis abundant in Late Carboniferous and Permian reef and platform carbonates. Ii~tcvpretutron:Commonly interpreted :is calc~fied cyanohacterial tube or attributed to yreen algae Lithocodiunz Elliott 1956 (Pl. 0915) :Morphology: The encrusted partly coiled test exhibits microgranular (calcitic, partly agglutinating) inlperforate walls that appear dark in transmitted and brownish in reflected light. The wall has filament-like alveoli (originally probably containing endosymbionts), and is covered by a thin epidermal layer. Chambers show 'bubble-like' structures, originally interpreted as algal sporangia but now representing cryptic boring foraminifera. Distr-ibution:Anisian to Late Cretaceous. Often oc.curring together with Baccunelirr irrcg~rlaris.The genus is common in reef limestones. Lirhocociium/Bucinellu associations contribute to the formation of mud mounds through baffling, binding. frame building and automicrite production (Alsharhan 1987; Neuweiler and Reitner 1992; Schmid 1996). Interpretation: Originally regarded as an encrusting codiacean green alga, the genus is now considered to be a loftusian foraminifera, probably containing photoautotrophic endosymbiotic algae and boring foraminifera (Troglotella incl-ustansWemli and Fookes) within the chambers (Schmid and Leinfelder 1995).

Microproblematica

Microcodium Gliick 1912 (Pl. 12814) Morphology: The name Microcodium refers to structures consisting of aggregates of up to 1 mm long prismatic to pyramidal monocrystalline laths of calcite, with a central cavity in each lath. Depending on the arrangement of the basic units, two types can be distinguished: (a) the units may be radially distributed around a central axis producing a structure resembling an ear of maize, or (b) the units are stacked parallel to each other, along axes that branch in successive planes, thus forming thick crusts. Distribution: First described from Miocene deposits, Microcodium and closely related taxa (Microcodiaceae) have been found in carbonates as old as the Devonian. Many authors consider Microcodium to be restricted to the Cenozoic, associated with lacustrine environments and indicative of pedogenic origin. Interpretation: Older records explained Microcodiunz as a product of per descensum contamination. However, Paleozoic occurrences demonstrate that microcodiaceans thrived in shallow-marine and supratidal as well as in lacustrine environments (Nassichuk et al. 1986). Microcodium has been assigned to green alga, 'blue-green alga' or bacteria (Mamet and Roux 1982).

Some authors have suggested a diagenetic origin. Non-marine occurrences in paleosols and caliche were explained as products of calcite-secreting filamental bacteria living in symbiosis with other organisms (fungi) within the soil (Esteban 1974; Bodergat 1974) or as calcified roots (Klappa 1978; Jaillard et al. 1991). Microtubus Fliigel 1964 (PI. 9913) Morphology: Small straight or slightly bent hollow tubes with thin walls of microcrystalline calcite. One end of many tubes appear to be enclosed within micritic matrix. The tubes occur isolated or more commonly in aggregates. Tube diameter 0.05 to 0.20 mm, mostly 0.10 mm. Distribution: Abundant in Late Triassic (Norian and Rhaetian) reef limestones, often associated with micritic spongiostromate crusts. Microtubus is known from all parts of the Tethys. It characterizes the central reef facies. Interpretation: The genus was tentatively assigned to serpulid worms but may have cyanobacterial affinity. Nuia Maslov 1956 (PI. 9811) Morphology: The genus is characterized by cylindrical bodies consisting of transparent fibrous calcite crystals growing in zones around micritic centers.

Plate 98 Paleozoic Microproblematica Shown on this plate are common Paleozoic thin-section fossils whose systematic assignment is disputed. 1 Nuia. The arrows point to longitudinal and cross sections of cylindrical bodies characterized by transparent fibrous calcite crystals growing in zones around niicritic centers. The fossil is interpreted as a bacterial or cyanobacterial growth form. Nuia is a common constituent of Late Cambrian and Early Ordovician reef mounds. Ordovician: Antarctica. 2 Halysis. The fan-shaped structure exhibiting palisades and chains in cross-sections is now regarded as a cyanophycean taxon. Early Ordovician (Arenigian): Megaconglomerate unit of Cow Head Peninsula, western Newfoundland. 3 Koivaella. Small hollow tubes with well-defined micritic walls are common microfossils in Late Paleozoic reef' and platform carbonates. They are interpreted as cyanobacteria or green alga. Early Permian (Sakmarian): Fomi Avolrri, Carnia, Italy. 4 Pseudovcrmi~~oreh sodalica Elliott characterized by attached tubes with perforated walls. The fossil is considered to be a dasyclad alga, a foraminifera or of cyanobacterial origin. Pseudovermiporella is abundant in Late Permian shelf carhonates. Permian: Taurus Range, Turkey. 5 Tubiplryres ohscur-usMaslov, encrusted by Archaeolithoporella (A).The longitudinal section shows the segmentation of the fossil, the spar-filled cavities (arrows) and the surrounding spider-like network. The current explanation of Late Paleozoic Tubiphytes is a commensalism of different organisms responsible for the intemal cavities and tubes and cyanobacteria or other bacteria responsible for the network (see Fig. 10.60). Tubiphytes obscurus is characterized by tubes in each segment. Middle Permian (Murgabian): Sosio, Sicily, Italy. h Tuhiphytes obscurus Maslov. Cross section. Same locality as -> 5. 7 Palueoaplysina Krotow, a common Late Carboniferous to Early Permian reef-building organism. The calcareous plates are characterized by an internal differentiation and a canal system. The fossil is regarded as an alga or a sponge. Early Permian (Asselian): Duvansk reef complex, central Urals, Russia. 8 Archaeolithoporella hidensis Endo, an abundant organism in Permian reefs acting as encruster, binder and frame builder. The characteristic criteria are couplets of micritic and microsparitic or sparry irregularly undulated layers. Middle Permian (Wordian): Oman. -> 2: Pohler and James 1989

Plate 98. Paleozoic h l ~ c ~ o p r o b l e m a t ~ c a

565

Microproblematica

Distribution: Cambrian to Silurian, possibly also Devonian. Nuia is an important rock builder in Late Cambrian and Early Ordovician carbonate mounds. Interpretation: The fossil has been interpreted as codiacean alga, but is now regarded as bacterial or cyanobacterial growth form. Palaeoaplysina Krotow 1888 (Pl. 98/7) Morphology: The genus is characterized by calcareous, originally aragonitic broad tabular plates that appear, wavy in cross sections, with external protuberances and an internal cellular fabric with branched tubes. Length usually 3-10 cm, thickness 0.5-7.0 mm. The plates often occur as parallel layered accumulations. Distribution: Late Carboniferous to Early Permian (Moscovian to Artinskian). Palaeoaplysina built shal-

low-water mounds in subtropical to temperate paleolatitudes on platforms and in platform-margin areas around the northern margin of Pangea. Some of the reefs are reservoir rocks (e.g. Barents Sea; Stemmerick and Larsen 1993; Ehrenberg et al. 1986). The genus is often associated with phylloid algae. Interpretation: The fossil has been attributed to alga, hydrozoans, and sponges. Most authors prefer an algal interpretation, but a sponge interpretation should be considered as well.

Thaumatoporella Raineri 1924 (Pl. 99/21 Morphology: The genus is characterized by small cells arranged in chains forming closed or open irregularly shaped structures, sometimes constructing bridges between sessile organisms, e.g. corals. Some thaumatoporellids exhibit only one chamber, others form sev-

Plate 99 Mesozoic Microproblematica Microproblematica are common in thin sections of Mesozoic limestones and known from shallow-marine and deep-marine carbonates (-> 1, 10). Many taxa are benthic, others planktonic (-> 1, 10). Encrusting microproblematica are particularly abundant in reef carbonates, occurring both, at the reef surface between and upon reefbuilders (-> 4,5) or in small cryptic habitats of reef cavities (-> 8,9). The plate shows thin sections of microfossils, whose systematic position is still under discussion, with exception of the calcispheres (-> 10). Globoclzaete Lombard. These spherical hollow calcitic bodies occur as aggregates or in clusters. They are interpreted as planktonic green algae. The arrows point to a typical serial arrangement. Middle Jurassic (Klauskalk): Grimming, Austria. Thaurnatopotz.ll Raineri, characterized by fine cells (black arrow) arranged in chains or enclosing chamber-like structures. White arrows point to globular inner structures. Thaumatoporella is now enclosed within a separate green algal group. Early Jurassic (Pantokrator Limestone): Korfu Island, Greece. Microrubus conznlunis Fliigel. These small open tubes commonly occur in aggregates, often embedded within micritic crusts developed on reef builders. Microtubus is a marker fossil indicating the central parts of Norian and Rhaetian reefs. Late Triassic (Oberrhatkalk, Rhaetian): Feichtenstein, Salzburg, Austria. Bacinella. The fossil is characterized by an assemblage of variously formed cells that are sometimes arranged in rows. Bacinella is common in Mesozoic reefs. Late Triassic (Norian): Jabal Kawr, Oman. Lithocodiunz, encrusting a shell fragment (SF). The peripheral structures indicated by the arrow are considered as 'pores' or 'cortical filaments' depending on the systematic assignment (foraminifera or udoteacean algae). Lithocodium is now regarded as a foraminifera1 consortium, It is often associated with Bacinella (see PI. 13412) and occurs in Triassic, Jurassic and Cretaceous reefs. Late Jurassic (Kimmeridgian): Ota. west-central Portugal. Tubiplzptes surrounded by a similar but more open network structure called Plexoramea. These fossils are abundant in Middle Triassic and Camian reef limestones. Middle Triassic (Wettersteinkalk, Ladinian): Blumautal, Germany. Tubiplzytes /nor-ronensisCrescenti. This species, associated with Terebella (see P1. 92/10), is abundant in Late Jurassic and Early Cretaceous platform and slope deposits and in limestones with siliceous sponges. The arrow points to a miliolid foraminifera commonly found in the center of the fossil. The Tubijdzyres network is interpreted as part of the foraminiferal wall. Late Jurassic (Treuchtlinger Kalk, Kimmeridgian): Southern Franconian Alb, Germany. Baccanellafloriformis Pantic. These microfossils (arrow) are common in cryptic cavities of Triassic reefs. They represent most probably bacterially induced carbonate precipitates. Late Triassic (Dachsteinriffkalk, Norian): Gosaukarnm, Austria. Radiomura cautica Senowbari-Daryan and Schafer. The fossil is found commonly attached to frame builders or within micritic cryptic habitats of Triassic and Jurassic reefs. Late Triassic (Oberrhatkalk): Feichtenstein, Salzburg, Austria. Some fossils formerly considered to be microproblematica are no longer problematic with regard to their position. .An example are 'calcispheres'. The thin section shows Stonliosphaera sphaerica (Kaufmann) characterized by spheres, 10100 pm in diameter, with calcitic and organic walls. SEM studies reveal strong morphological differentiation of the wall supporting an interpretation as calcareous dinoflagellate cysts (Sect. 10.2.1.9). Late Cretaceous (Turonian, Seewen limestone): Seewen, Switzerland. -> 8: Gaetani and Gorza 1989

Plate 9 9 . Mesozoic Microproblematica

567

5 0 0 urn

5 0 0 prn

Microproblematica: Tuhiphyrcs

Fig. 10.60. Schematic drawing of the internal, commonly spar-filled cavities in Permian Tubiphytes based on thin-section investigations and SEM studies. The network structure is shown in black. Tubiphytes can be differentiated according to the presence (A to C ) or absence (D to F) of segmentation and the nature of the axial tube. The latter may correspond to hollow unmineralized cavities restricted to individual segments (A, B) or to multibranched primarily mineralized stems of Rigidocaulis (possibly a calcimicrobe) passing through all segments (C) or the whole non-segmented body (D). In some Tubiphytes the central spar-filled 'tube' is a palaeonubeculariid foraminifera (E) or a hollow branched tube with a defined wall, probably identical with Koivaella (F; P1. 98/3). Type A agrees with the structure of Tubiphytes obscurus Maslov. The Tubiphytes network of the other types differs in the microfabric used for taxonomic discrimination. Not to scale. After SenowbariDaryan and Flugel (1993).

era1 chambers and still others are developed as chains without well defined encircled structures (Dragastan et al. 1994). Distribution: The genus is known from Middle Triassic to Late Cretaceous deposits. It is widely distributed in Mesozoic platform carbonates and occurs in lagoonal and reefal settings, frequently with Bacinella. Interpretation: Originally regarded as red alga and later as dasyclad algae or possible sponges, Thaumatopurellu is now interpreted as belonging to a separate group of green algae (DeCastro 1990).

Tubiphytes Maslov 1960 (Pl. 98/5,6, P1.99/6,7) Tubiphytes is one of the most common microproblematica in Late Paleozoic and Mesozoic limestones. The name should be replaced by Shamovella for reasons of priority (Riding 1993) but most people still use the familiar old name. Morphology: Oval, lobate, elongated dark encrusting structures exhibiting a fine irregular web-like network surrounding spar-filled cavities (tubes). The fossil appears dark gray in transmitted light and milky white in direct light. The size of individual elements is commonly up to 1.0 mm but may be greater. Taxonomic differentiation is based on central cavities, segmentation and network differentiation (Senowbari-Daryan and Fliigel 1993). Vennin et al. (1997) distinguished three morphotypes. Paleozoic and Mesozoic Tubiphytes appear to be different in construction and in the type of the tubes and cavities surrounded by the web-like network. Fig. 10.60 shows the differentiationsfound in Pefian Tubiphytes. In contrast to the Paleozoic Tubiphytes where the spider network surrounding the internal cavities is re-

garded as functionally different from the cavities, the interpretationof Jurassic 'Tubiphytes' considers the network as the exterior part of a micropeloidal foraminiferal wall formed by endosymbiotic algae or cyanobacteria (Schmid 1995). Distribution: The Tubiphytes group is a cosmopolitan reef builder ranging from the Carboniferous to the Cretaceous (Fig. 10.61) and abundant in the Permian, Middle Triassic and Late Jurassic.

...................

................... ............. ............. ................... Early ...................

a

NoriadRhaetian .............. Carnian

..............

m

Ladinian

...............

Anisian

..................

Scythian

...........

Permian

.......... Carboniferous ..-

..

Fig. 10.61. Distribution and frequency of fossils attributed to Tubjphytes. Frequency is expressed by the relative nulnber of publications dealing with the taxa. After SenowbariDaryan and Flugel (1993)

Permian Tubiphyres are encrusters, binders, bafflers and frame builders in reefs (LeMone 1995; Wahlman 2002; Weidlich 2002) but are also known from bedded shelf carbonates. Tubiphytes occurs in shallow subtidal (and intertidal) settings as well as in submarine fissures indicating relatively large tolerance levels with regard to light, salinity and substrate. Tubiphytes is commonly associated with At-chaeolithoporella, sponges and bryozoans. The group flourished in warm-water tropical settings but also lived in deeper shelf and slope environments as well as in cooler settings. Triassic Tubiphytes are major constituents of Middle Triassic reefs but minor elements in Late Triassic reefs. Late Jurassic and Early Cretaceous Tubiphytes occurred in different environments as compared with Paleozoic Tubiphytes, including shallow outer ramp environments where thick specimens lived, and deepermarine and cryptic habitats characterized by thinner specimens (Schmid 1996). Various growth forms reflect different water energies (Kott 1989). Intergrown Tuhiphyres nzonorzemis associated with Terebella (see PI. 92/10) is abundant in Late Jurassic and Early Cretaceous proximal platform talus and slope deposits as well as in siliceous sponge 'reefs' formed in deeper ramp settings. Paleowater depths of about 100 to 200 m have been considered for mass occurrences. The species also contributed to the formation of organic frameworks (Pomoni-Papaioannou et al. 1989). lr~tr/pi~rtutio/~: 7i~Diphytcshas been attributed to various algal groups. cyanobacteria as well as sponges, hydrozoans and foraminifera (Riding and Guo 1992). The current explanation for Paleozoic and some Triassic Tuhiphytcs is a symbiotic commensalism of different organisms recorded by the spar-filled 'cavities' and tubes and calcified cyanobacteria represented by the surrounding network. Jurassic Tubiphytes are explained as foraminifera. Basics: Microproblenlatica Babcock, J.A. (1986): The puzzle of alga-like problematica, or rummaging around in the algal wastebasket. - In: Ihfman, A,, Nitecki. M.H. (eds.): Problematic fossil taxa. -- Oxford Monographs Ion Geology and Geophysics. 12-26. New Kork (Oxford University Press) Banner, F.T., Finch, E.M., Simmons, M.D. (1990): On l,irlzor~ctdiumElliott (calcareous green algae): its paleobiological and stratigraphical significance. - Journal of Micropaleontology, 9, 21-36 Bengtson. S. (1990): Problematic fossil taxa. - In: Briggs, D.E., Crowther, P.R. (eds.): Palaeobiology. Asynthesis. 442-445, Oxford (Blackwell) Cherchi, A., Schroeder, R. ( 1988): Osservazioni sui microproblematica Paronipora Capeder, Microcodium Gluck, Baccanella Pantic et Paleomicrocodium Mamet and Roux. - Bolletino della SocietB Paleontologica Italiana, 27, 79-

X1

De Castro, P. (1990): Thaumatoporelle: conoscenze attuale a appoccio all'interpretazione. - Bolletino della Societa Paleontologica Italiana, 29, 176-206 Elliott, G.F. (1958): Fossil rnicroproblematicafrom the Middle East. - Micropaleontology, 4 , 4 19-428 Elliott, G.F. (1963): Problematical microfossils from the Cretaceous and Paleocene of the Middle East. -Palaeontology, 6,293-200 Flugel, E. (1964): Mikroproblematika aus rhatischen Riffkalken der Nordalpen. - Palaontologische Zeitschrift, 38,74-87 Flugel, E. (1972): Mikroproblematika in Dunnschliffen von Triaskalken.- Mitteilungen der Gesellschaft der Geologieund Bergbaustudenten in Osterreich, 21, 857-988 Gliick, H. (1912): Eine neue gesteinsbildende Siphonee (Codiacee) aus dem marinen Tertiiir von Suddeutschland. - Mitteilungen der badischen Geologischen Landesanstalt. 4,3-24 Henssel, K., Schmid, D.U., Leinfelder, R. (2002): Computergestiitzte 3D-Rekonstruktionen in der Palaontologie an Hand von Serienschnitten. - Mathematische Geologie, 6, 131-142 Hoffman, A., Nitecki, M.H. (eds., 1986): Problematic fossil taxa. - Oxford Monographs on Geology and Geophysics 5, 267 pp., New York (Oxford University Press) Klappa, C.F. (1978): Biolithogenesis of Microcodium: elucidation. - Sedimentology, 25,489-522 Kobluk, D.R. (1988): Cryptic faunas in reefs: ecologic and geologic importance. - Palaios, 3, 379-390 Munnecke, A. (2001): Halysis Hoeg, 1932 - a problematic Cyanophyceae: new evidence from the Silurian of Gotland (Sweden). - Neues Jahrbuch fiir Geologie und Palaontologie, Monatshefte, 2001, 21-42 Nassichuk, W.W., Davies, G.R., Mamet, B.L. (1986): Microcodiaceans in the VisCan Emma Fjord Formation, Devon Island, Arctic Canada. - Current Research, part B, Geological Survey of Canada, Paper 86-18,467-470 Perret, M.F., Vachard, D., Aguirre, P., Crasquin-Soleau, S. (1994): Micropaltontologie des calcaires epibathyaux a Globochaete (algue problkmatique) du Carbonifkre des PyrCnCes. - Geobios, 27, 659-675 Riding, R., Guo, L. (1992): Affinity of Tubiphjtes. - Palaeontology, 35,37-49 Schmid, D.U.: (1995): 'Tubiphytes'mor~ronensis - eine fakultativ inkrustierende Foraminifere mit endosymbiontischen Algen. - Profil, 8,305-317 Schmid, D.U. (1996): Marine Mikrobolithe und Mikroinkrustierer aus dem Oberjura. - Profil, 9, 10 1-251 Schmid, D.U., Leinfelder, R. (1996): The Jurassic Litlzocodiurn aggregatum-Troglotella incrustans foraminifera1 consortium. - Palaeontology, 39, 21 -52 Senowbari-Daryan, B. (1984): Mikroproblematika aus den obertriadischen Riffkalken von Sizilien. - Miinstersche Forschungen zur Geologie und Palaontologie, 61, 1-8 1 Senowbari-Daryan, B., Flugel, E. (19931: Tubiphytes Maslov, an enigmatic fossil: Classification, fossil record and significance through time. Part I: Discussion of Late Palaeozoic material. - In: Barattolo, F., DeCastro, P., Parente, M. (eds.): Studies on fossil benthic algae. - Bolletino della Societh Paleontologica Italiana, Special Volume, 1.353-382 Skompski, P. (1982): The nature and systematic position of the microfossil Globochaete alpina Lombard, 1945.-Acta Geologica Polonica, 32,47-56 Vennin, E., Vachard, D., Proust, J.-N. (1997):Taphonomie et synCcologie d u 'genre' Tubiphytcs dam les biocon-

570

structions de Tratau et de Nizhni-Irginsk (Permien infkrieur de l'Oural, Russie). - Geobios, 30, 635-649

Further reading: K138 (general), K139 (Paleozoic), K140 (Mesozoic),K 141 (Cenozoic)

10.3 Biozonation of Platforms with Thin-Section Fossils

Biozonation of Platform Carbonarcs

stratigraphicranges of benthic shallow-water organisms must be calibrated with global pelagic biozones (based, e.g., on cephalopods, calpionellids, radiolarians). Isolated skeletal grains, reworked on platforms, transported to basinal environments and deposited within calciturbidites may aid in this calibration. Care must be taken in using microfossils enclosed in reworked platform lithoclasts because this material might represent older, non-synchronous sediment. Using the cenozone concept must consider the following points:

The section discusses the potential of microfacies in subdividing platforms sections that are generally poor in guide fossils into biozones. The example used is from Environmental control. Dasyclad algae and benthic the Late Mesozoic, but similar problems exist for Pa- foraminifera are strongly controlled by environmental leozoic, Early Mesozoic and Tertiary platforms. conditions. Biostratigraphic interpretations based on Starting in the 60s of the last century many attempts dasyclads generally suffer from an apparently slow have been made in subdividing the thick Jurassic and evolution rate, facies-dependence, and poor knowledge Cretaceous carbonate platform sequences in the circum- of the stratigraphic range of many taxa. Mediterranean and Alpine regions and in stratigEnvironmental conditions (e.g. substrate, nutrients, raphically using thin-section fossils, predominantly cal- water energy) are different in different parts of carboncareous algae and benthic foraminifera. Sartoni and ate platforms or ramps, and different zonation patterns Crescenti (1962) studying Mesozoic platforms in the may be developed in restricted inner platform settings southern Apennines introduced the concept of 'ceno- (e.g. shelf lagoons), open-marine parts of platforms and zones'. The authors defined a cenozone as strata con- at platform margins (Crescenti 1971; De Castro 1987; taining a characteristic association of microfossils. Later Dya 1992). authors combined characteristic association with conMesozoic and Cenozoic dasyclads and also benthic spicuous abundance of specific taxa. Doing this, the foraminiferaexhibit strong provincialism. Biozonations definition of cenozones and the practical use of these established in one paleogeographical province may not units include both characteristics of assemblage zones be found again in another province. as well as abundance zones. Characteristics of assemblage zones and abundance zones arc enclosed in the Future dc~lelopnzents.Many current microfacies modern definition of biozones which are determined studies of platform carbonates devoid establishing by the stratigraphic and geographic distribution of (1) biozones within a stratigraphic framework and use the a single taxon, (2) an diagnostic association, or (3) the range of single taxa in deliminating stratigraphic units. relative abundance of taxa (Salvador 1994). However, biozones based on occurrence, association and abundance of algae and foraminifera provide still In earlier studies, zones have been set up for Juras- an important tool in microfacies analysis of carbonate sic and Early Cretaceous platforms, predominantly platforms if the definition of formal biozones considers: based on dasyclad algae and associated benthic foraDepositional environment controls. Sections used in minifers: Plate 62 and P1.69 display dasyclad and fora- studying changes in the composition of algal and foraminiferal taxa used in defining Jurassic biozones. PI. 63, miniferal assemblages must be differentiated with reP1.70 and PI. 7 1 show taxa characterizing Early Creta- gard to depositional setting (restricted or open platform, ceous zones. The zonations developed in the Apennines platform margin). were compared with biozones recognized in the NorthProvincialism of the fossil used in establishing bioem Calcareous Alps, the Dinarides, eastern and south- zones demands rigorous statistical tests indicating ern Carpathians, Switzerland, Spain, South France and which geographical areas can be included within one Greece (see basics and references in K142 and K144). paleogeographical site and which not. The Jaccard simiJaffrezo (1980) tried to correlate the local biozones and larity index has been found very useful in comparing suggested a general biozonation of Jurassic and Early Late Jurassic dasyclads from various localities in the Cretaceous platforms in the western Tethys. Northern Calcareous Alps, and recognizing high or low similarities (Rasser and Fenninger 2002). Pitfalls. The cenozone approach was widely used Only paleogeographical sites having high similarity until about 1990 despite serious pitfalls causing diffi- indices should be used in correlating biozones within a culties in correlating and determining the chrono- chronostratigraphic framework. In the case of the Late stratigraphic age. The age of the biozones and the bio- Jurassic platforms of the Northern Calcareous Alps, the

Uiozonation of Platform Carbonates

Carpathians, the Apuseni Mountains in Romania and the Central Apennines form one region in which the platforms appear to exhibit identical or similar biozonation sequences. Basics: Biozonation of platform carbonates based on thinsection fossils Azema, J, Chabrier, G., Fourcade, E., Jaffrezo M. (1977): Nouvelles donnCes rnicropalContologiques stratigraphiques et paltogtographiques sur le Portlandiien et le NCocornian de Sardaigne. - Revue des MicropalContologie, 20, 125- 139 Arnaud-Vanneau,A. (1980): MicropalContologie, palCcologie et ~Cdimentologied'un platforme carbonatke de la rnarge passive de la ThCthys: 1'Urgonian du Vercors septentrional et de la Chatreuse (Alpes occidentales). - Gtologie Alpine, MCrnoire, 11, part l , 267 pp., part 2,874 pp., part 3, 119 pp. Bodrogi. I., Bona, J., Lobitzer, H. (1994): Vergleichende Untersuchung der Foraminiferen- und Kalkalgen-Assoziationen der Urgon-Entwicklung des Schrattenkalkes in Vorarlberg (Osterreich) und der Nagyharsshy Kalkstein Formation des Viliny-Gebirges (Ungarn). - Jubilaurnsschrift 20 Jahre Geologische Zusamrnenarbeit OsterreichUngarn, Geologische Bundesanstalt Wien, Teil2,225-283 De Castro, P. (1987): Le facies di piattaforma carbonatica del Giurassico italiano: diffusione areale e linearnente biostratigrafici. - Bolletino della Societl Paleontologica Italiana, 26, 309-325 Dragastan, 0. (1975): Llpper Jurassic and Lower Cretaceous microfacies from the Bicaz Valley Basin (East Carpathians). - Institut de GCologie et GCophysics Bucuresti, Memoir, 21. 87 pp. Farinacci. A,, Radoicic, R. (1964): Correlazione tra serie giurese e cretacee del'Apennino centrale e Dinaridi esterne. - Ricerche Scientifiche, Anno 34 (IIA), 169-300 Garcia-Hernandez, M. (1981): Biozonation du CretacC infkrieur a l'aide des foraminifkres benthiques et algues dasycladacCs dand le Prebetique occidental (Cordilleres Betiques, Espagne). - Geobios, 14, 261-267 Jaffrezo, M. (1980): Les formations carbonatkesdes CorbiCres (France du Dogger a 1'Aptien: micropalContologie stratigraphique, biozonation, palCcologie. Extension des resultats a la MeCsogC. - These Doctorat d'Etat, UniversitC Pierre et Marie Curie. Paris VI, 613 pp. Kasser, M.W., Fenninger, A. (2002): Jurassic/Cretaceous Dasycladalean algal stratigraphy in the Northern Calcarcous Alps: a critical review and a paleobiogeographcal approach using similarity indices. -In: Bucur, I.U., Filipescu, S. (eds.): Research advances in calcareous algae and ~nicrobialcarbonates. - Proceedings of the 4th IFAA Regional Meeting, Cluj-Napoca 2001, 167-190 Salvador, A. (ed., 1994): International stratigraphic guide. 214 pp., Boulder (Geological Society of America) Sartorio. D., Venturini, S. (1988): Southern Tethys biofacies. - 235 pp., San Donato Milanese (Agip) Sartorio, S., Crescenti, LJ. (1962): Ricerche biostratigrafiche nel Mesozoico delllAppennino meridionale. - Giornale di Geologia, 29, 16 1-304 Schlagintweit, F., Ebli, 0.(1999): New results on rnicrofacies, biostratigraphy and sedirnentology of the Late Jurassic-. Early Cretaceous platform carbonates of the Northern

57 1

Calcareous Alps. - Abhandlungen der Geologischen Bundesanstalt Wien, 56,379-418 Schroder, R., Neurnam, M. (1985): Les Grand ForarninifCres du Cretact moyen de la r6gion m t d i t e r r a ~ e-. Geobios, MCmoire sgcial, 7, 161 pp. Septfontaine, M. (1980): Les foraminiferes impexforks des rnileux des rnileux plate-forme au MCsozoique: d6terrnination pratique, interprktation phylogCnetique et utilisation biostratigraphique. -Revue de Micropaltontologie. 23, 169-203 Tisljar, J., Velic, I. (1993): Upper Jurassic (Malrn) shallowwater carbonates in western Gorski Kotar area: facies and depoistional environments (western Croatia). - Geologia Croatica, 46, 263-279 Further reading: K111, K129, K142, K144

10.4 Where to Look for Thin-Section Pictures of Fossils and Microfacies Types Agood picture may say more than many words. Therefore, the survey given in Sect. 10.2 on the various groups of thin-section fossils is supplen~entedin a more practical way by the following list, which should assist in finding appropriate thin-section photographs. Sect. 10.3 presents a bibliography of books and papers that include good and instructive photographs (at least 10 plates) of skeletal grains and common microfacies types in Phanerozoic carbonates. Not included are specific publications on the major groups of thin-section fossils (foraminifera, calcareous algae 1. The references are marked by letters that characterize the main topics dealt with: BZ - biozonations based on thin-section fossils, E - environmental conditions, F - facies characteristics and sedimentological criteria, FM - facies models, P - valuable paleontological informations, PD - paleontological determinations that can be used in the generic and/or specific assignment of thin-section fossils. Books covering several time units Bozorgnia, F., Banafti, S. ( 1 964): Microfacies and microorganisms of Paleozoic through Tertiary sediments of some parts of Iran. - 22 pp., 158 Pls., Tehran (Iranian Oil Company). Cambrian, Devonian ro Terriat-J(Miocen~). PD Chiocchini, M., Mancinelli, A. (1977): Microbiostratigrafi:i del Mesozoico in facies di piattaforma carbonatica dei Monti Aurunci (Lazio Meridionale).- Studi tieol. Camerti. 3, 109-152,48 Pls., Camerino. Lotr Triassic. to Miocene. LIZ, P Cita, M.B. (1965): Jurassic, Cretaceous and Tertiary microfacies from the Southern Alps (Northern Italy). - International Sedimentary Petrographical Series, 8, 99 pp.. 117 Pls., Leiden (Brill). Early Jurassic- ro Lotr Terrian (Miocene). PD Christodoulou, G., Tsaila-Monopolis, St. ( 1 975): Eastern Hellenic zone microfacies. - National Institute of Geological

5'12

and Mining Research, 17, 63 pp., 75 Pis., Athens. Early Triassic to Early Tertiary. P Cuvillier, J., Sacal, V. (1951): CorrClations stratigraphiques par microfacies en Aquitaine Occidental. - International Sedimentary Petrographical Series, 2, 16 pp., 90 Pls., Leiden (Brill). Jurassic to Tertiary. P Hagn, H. (1955): Fazies und Mikrofauna der Gesteine der Bayerischen Alpen. - International Sedimentary Petrographical Series, l , 20 pp., 71 Pls., Leiden (Brill). Triassic to Tertiary. P Hanzawa, S. (196 1): Facies and micro-organisms of the Paleozoic, Mesozoic and Cenozoic sediments of Japan and her adjacent islands. -International Sedimentary and Petrographical Series, 5, 117 pp., 148 Pls., Leiden (Brill). Silurian to Cenozoic, PD Lehmann, E.P. et al. (1957): Microfacies of Libya. - 80 pp., 37 Pls., Tripoli (Petroleum Exploration Society of Libya). Cambrian to Miocene. P Mehrnush, M., Partoazar, H. (1977): Selected microfauna of Iran. - Geol. Min. Survey Iran Report, 33, 396 pp., 117 Pls., Tehran. Late Devonian to Miocene. PD Microfacies italiane (1959): Microfacies italiane (dal Carbonifero a1 Miocene medio). - 35 pp., 145 Pls., Milano (Agip Mineraria). Late Carboniferous to Miocene. P. Misik, M. (1966): Microfacies of the Mesozoic and Tertiary limestones of the West Carpathians. - 269 pp., 191 Pls., Bratislava (Slovenska Akademia Vied). Early Triassic to Miocene. P, F Papp, A., Turnovsky, K. (1970): Anleitung zur biostratigraphischen Auswertung von Gesteinsdiinnschliffen (Microfacies Austriaca).- Jahrbuch der GeologischenBundesanstalt, Sonderband, 16, 50 pp., 88 Pls., Wien. Late Carbotz 50% transported grains is considered as evidence for intermittent water energy. Fossil assemblages are more highly complex than those of Type I. Subtype 11-1 (PI. 4412) and 11-2 (Pl. 4413) differ in the size of transported grains (fine- to medium-grained grains and coarse- to very coarse transported grains, respectively). Grains are subangular to rounded. Subtype 11-3 (PI. 1812) is characterized by alternating laminae composed of lime mud and coarser clastic particles. Clay content is below 15%. Tjpe III describes deposition in slightly agitated water. The size of the transported grains varies from silt through fine-grained sand. Subtype 111-1 (Pl. 1181 1) corresponds to a calcisiltite, subtype 111-2 to a very fine-grained calcarenite and subtype 111-3 (PI. 12111) to a fine-grained calcarenite. Matrix (homogeneous microcrystalline in 111-1 and 111-2; inhomogeneous and varying in size) may constitute < 50 percent of the rock bulk. Type I11 includes nonfossiliferous, sparsely or moderately fossiliferous limestones (111-1 and 111-2) as well as limestones with abundant and diverse fossils (111-3). Grains are subrounded to rounded. No conspicuous clay content. Type I$' indicates deposition in rnoderateljl agitated water. The limestones are medium-grained to very coarse-grained calcarenites. The matrix is poorly sorted. Fossils are more common than in Type 111. Subtypes (IV-1: P1. 12211; IV-2: P1. 11813; Fig. 4.32; IV-3: P1. 4513) differ predominantly in the grain size of transported particles which are generally broken and abraded fossils. Grains are subrounded to well rounded. No conspicuous clay content. Type V characterizes deposition and growth in strongly agitated water Fossil fragments and rock debris are coarse-grained and lie within the range of calcirudites. Subtype V-1 (PI. 11512) corresponds to a limestone consisting of subrounded to rounded gravelsized fossils and rock fragments. Subtype V-2 (Pl. 917) is described as being 'composed predominantly of conglomeratic and brecciated rock fragments'. Grains are angular to well rounded. Some clay may be present. Subtype V-3 corresponds to a 'reef' limestone with in situ frame-building organisms'. Modified energy classification: While studying Triassic limestones of Bulgaria, Catalov (1972) differentiated between the energy index log of the energy minima and the energy index log of the energy maxima. These logs are obtained by connecting the respective

points of EI logmax and EI logmin of a geological section. The field between these points is called the differential energy index field (DEI field). It describes the textural variation of carbonate rocks. A wide DEI field indicates large variations, a narrow field smaller variations. In contrast to Plumley et al. (1962), Catalov distinguished only four limestone types: Type I (deposited in quiet water), type I1 (deposited in slightly agitated water), type I11 (deposited in moderately agitated water), and type IV (deposited in strongly agitated water). The differences are indicated by different degrees of winnowing as well as frequency, size, sorting and roundness of grains; type and frequency of temgenous admixtures, fossil associations and substrate (muddy, sandy). The main difference between the classification of Plumley et al. and Catalov is that the frequency and size of grains as well as fossils are much more pronounced in Catalov's classification. Discussion: The original and the modified Energy Classification have proved successful in describing lithologic variations in time and space, changes in energy levels during time as well as in correlating outcrops and boreholes (e.g. Bolliger and Burri 1970; Skupin 1973; Rasser 1994). Assessment of subgroups may sometimes be difficult, if information on non-carbonate contents of the limestones is missing. Pitfalls in the use of the Energy Index can arise because the size of grains depends on water energy, but also on the original size ranges (e.g. of fragmented green algae), the growth rates of organisms (e.g. in oncoid formation) or the cementation stages of grains, the abundance of detrital quartz and clay is not necessarily dependent on water energy. Quiet-water carbonates may exhibit much higher quartz contents than suggested by Plumley et al., due to eolian input, the occurrence of microcrystalline calcite matrix does not prove a priori quiet-water conditions, because rnud can be fixed by organisms also in high-energy settings as well, the use of 'characteristic fossils' in determining energy index types is dangerous as long as only groups or higher taxonomic categories are considered. Energy levels and resulting limestone types are not necessarily related to water depth: Quiet-water Type I limestones may occur in either deep (e.g. basinal) or shallow (e.g. lagoonal) water. Intermittently agitated carbonates of Type I1 should be more common in the transition zone between deep water (depositional interface below wave base) and very shallow water, where

the depositional interface is constantly above wave base. on bedding planes). Paleocurrent analysis is primarily Agitated-water sediments corresponding to Types 111, an outcrop study, but some textural criteria can also be IV and V are more typical of the shallow water of shelf studied in thin sections of oriented rock samples. Paleoareas, reef and bank settings as well as coastal regions. current patterns of ancient shoreline grainstones based on cross-bedding data were described by Knewtson and The differences between the more generalized Hubert (1969), and Stricklin and Smith (1973). The Plumley et al. classification and the more detailed En- orientation of clasts (Pl. 1614, 7; P1. 1812; P1. 13918) ergy Index Classification developed by Catalov (1972) and fossils are useful criteria (Sect. 5.1.2). Look for microphotographs showing the orientation point to the necessity of revising the energy index concept by considering those microfacies criteria that in- patterns of calcareous algae (Pl. 5717, Pi. 58/1), foradicate the degree of energy levels at the depositional minifera (Pl. 7415, 8; P1. 113/2), sponge spicules (Pl. interface with reasonable safety. An attempt in this di- 7812; P1.112/1), mollusk shells (Pl. 1811; P1. 102/1,6; rection was made by Bissell and Chilingar (1967), who P1. 113/2), and tentaculitids (Pl. 91/3,4). combined the Energy Index Classification with the Basics: Hydrodynamic controls grainlmicrite ratio, proposed by Leighton and Pen- Bollinger, W., Buni, P. (1970): Sedimentologie von Schelfdexter (1962) as well as with grain percentages. The Garbonaten und Beckenablagerungen im Oxfordian des grain-micrite ratio is the sum of the percentages of all zentralen Schweizer Jura. Mit Beitragen zur Stratigraphic und Okologie. - Beitrage zur Geologischen Karte der grains divided by the percentage of micrite.

F a c i ~ sn~lmbet-:Based on the system proposed by Plumley et al. (1962), Grotsch (1993) introduced 'fac i e ~numbers' characterizing the degree of water energy and subdividing the mudstone to grainstone spectrum. Facies numbers are successfully used together with compositional data in statistical analysis, e.g. of cyclic carbonates (Griitsch et al. 1994). 12.1 .I .3 Paleocurrent Data Currents are major factors influencing the distribution of sediment and of organisms. Global currents control the distribution of larvae and of nutrients and water temperature (scale: up to >lo00 km). Currents control the geometry of reefs (e.g. spur and groove structures), influence the growth fonns of reef builders (scale: about 10 to 1000 In, lateral; up to 100 m, vertical) and assist in the transport of sand-grade sediment. Small-scale currents are responsible for the transport of nutrients and waste, and control the settlement of larvae (scale: 0.1-1.0 cm). Smallest scale currents are produced by filtering organisms (scale: 0.1-10 cm). Both small-scale and smallest-scale currents may also be common in lowenergy 'quiet-water' environments. Paleocurrent indicators used in facies studies of carbonate rocks are essentially the same as those applied to siliciclastic rocks (Potter and Pettijohn 1977; Miall 1990). Criteria allowing the existence and directions of paleocurrents to be mterpreted may indicate only the sense of current flows (groove marks, channel structures, parting lineation) or both the sense and direction of currents (cross-bedding, cross-lamination and ripple marks, flute marks. slurnp folds; orientation of fossils

Schweiz, Neue Folge, 140, 1-96 Catalov, G.A. (1972): An attempt at energy index (EI) analysis of the Upper Anisian, Ladinian and Camian carbonate rocks in the Teteven Anticlinorium (Bulgaria). - Sedimentary Geology, 8, 159-175 Grotsch, J., Koch, R., Buser, S. (1994): Fazies, Gildenstruktur und Diagenese des nordlichen Randes der Dinarischen Karbonatplattform (Barreme-Apt, W-Slowenien). - Abhandlungen der Geologischen Bundesanstalt Wien, 50, 125-153 Hamblin, W.K. (1969): Marine paleocurrent directions in limestones of the Kansas City Group (Upper Pennsylvanian) in Eastern Kansas. - Geological Survey of' Kansas Bulletin, 194, 3-25 Skupin, K. (1973): Stratigraphy and nlicrofacies in the crinoidal limestones (Trochiten limestone, Triassic) of SW Germany. - Sedimentary Geology, 9, 1- 19 Plumley, W.J., Risley, G.A., Graves, R.W., Kaley, M.E. (1962): Energy index for limestone interpretation and c l a s sification. - In: Ham, W.E. (ed.): Classification of carbonate rocks. - Anerican Association of Petroleum Geologists, Memoir, l, 85-107 Potter, P.E., Pettijohn, F.J. (1977): Paleocurrents and basin analysis. 2nd edition. - 425 pp.. Berlin (Springer) Riedl, R. (1969): Marinbiologische Aspekte der Wasserbewegung. -Marine Biology, 4, 62-78 Steam, C.W. (1982): The shapes of Paleozoic and modern reef builders: a critical review. - Paleobiology, 8,228-24 1 Further reading: K164, K165

12.1.2 Storms

Storms leave distinct facies criteria in marine coldwater carbonates (examples in James and Clarke 1997) and warm-water carbonates as well as in coastal lake sediments (e.g. Liu and Fearn 1993). The distribution and taphonomic characters of fossils may be indicative of storm events, because of a specific response of animals and plants to hurricanes (Walker et al. 1991).

Storm Deposits

High-energy storms generate waves and currents that affect sea bottoms, stir up sediment and create characteristic sedimentary structures (e.g. hummocky crossstratification) and textures (e.g. tempestites). Severe storms erode coasts, destroy tropical islands and reefs, take part in onshore and offshore sediment transport and may contribute to extensive supratidal sedimentation. Shallow-marine waters respond to wind energy by coastal swell (storm floods) resulting from upland winds that raise the sea level, * surface waves producing breakers at the coast, and ground waves that become transformed into onshore and offshore bottom currents. Severe storms are represented by cyclones and hurricanes, occurring in tropical latitudes, and by intense winter storms (blizzards) in middle and high latitudes forming at fronts between cold and warm air masses. The development of strong storms is controlled by changes in atmospheric pressure and wind intensity. The importance of storm deposits in the geological record has attracted the attention of many workers. The papers listed in Box 12.2 describe the effects of modem storms known as cyclones, humcanes and typhoons. A cyclorze is an intense cell of low atmospheric pressure with a central eye surrounded by a circular wind system that rotates clockwise in the Southern Hemisphere and anti-clockwise in the Northern Hemisphere. The system follows tracks that generally curve away from the equator. Tropical cyclones form over the tropical oceans and range from 100 to 1000 km in diameter. Wind velocity may increase to up 230 mph and more. Tropical cyclones transport fine sediments and nutrients from shore to reef zones. The term typhoon designates a tropical cyclone occurring in the Pacific region. A hurricane is a tropical cyclone in which the wind speed equals or exceeds 118 km/h and may reach more than 300 k m h as in the example of Hurricane Gilbert described below. Locations crossed by the central eye experience winds from different directions that generate storm surges causing catastrophic damages within a zone of approximately 30 krn on either side of the eye. The varying intensity, size and strength as well as the forward speed and duration of strong storms are critical constraints on the storm's capacity to modify shallow-marine environments (Boss and Neumann 1993). Impacts from hurricanes are proportional to the area and the period over which hurricane conditions persist. Slower-moving hurricanes will cause more extensive and geologically relevant surface damage and

Box 12.2. Selected references discussing the impacts of humcanes on organisms and sediments in modem shallow-marine carbonateenvironments.Frequent humcanes occur today in belts 7" to 25 ON and S of the equator. Major reef areas suffering regular hurricanes occur in the northwestem and southwestern Pacific, the northern and southern Indian Ocean, and the northwestern Atlantic Oceran including the Caribbean Sea. Reefs: Many papers compare pre- and post-humcane situations of specific reefs. A recent overview was given by Scoffin (1993). The list here includes only papers not cited by Scoffin: Blanchon and Jones 1997; Braithwaite et al. 2000; Davis and Hughes 1983; Gagan et al. 1987, 1988, 1990; Guozhong 1998; Heap et al. 1999; Hubbard 1992; Kaufman 1983; Knowlton et al. 1988; Kobluk and Lysenko 1987; Lugo-Femandez et al. 1994; Moran and Reaka-Kudla 1991;Rogers et al. 1982; Russ and McCook 1992; Schonberger 1989; Woodley 1981; Yarnano et al. 2001; Young et al. 1999. Carbonate platforms and ramps: Aigner 1985; Boss and Neumann 1993; Bourrouilh-Le Jan 1979, 1980, 1998; Davaud and Strasser 1984; Galli 1989; Hine 1982; Seguret et al. 2001; Vermeer 1963; Wanless et al. 1988. Beaches: Ball et al. 1967; Coch 1994; Collins et al. 1999; Davis et al. 1982; Knowles and Davies 1991; Lee et al. 1994; Siringan and Anderson 1994.

sediment redistribution than the quick passage of a weakened hurricane. The major outcomes of severe storms are (a) transport and deposition of storm sediments on shelves and export to slope and basinal environments, and (b) the destruction of reef structures. These processes are discussed in the following two sections.

12.1. 2.1 Storm Deposits (Tempestites) on Shelves, Ramps and Platforms Storm beds are most common on shelves and ramps in windward settings, because of the generation of sediment-laden storm surges that transport sediment from onshore to deeper offshore outer ramp settings via unidirectional return flows. After the storm is over, the sediment is redistributed across the ramp and finally deposited in the form of sheets of limited extension in low-energy environments below storm-wave base (Fig. 12.3). These storm deposits exhibit distinct proximalitydistality trends as shown, for example, in the Arabian Gulf. Storm deposits of attached platforms (e.g. Florida) display strong variations in internal composition. The effects of storms on isolated platforms (e.g. Bahamas) are concentrated at platform margins (Hine et al. 1981). Sediment transport and redeposition produce millimeter- to meter-thick storm layers, contribute to the

Tempest ire. Wave set-up

L W c L . 1 u -

"

Hummocky

-.

cross stratifcation Storm waves and currents

-

-

ameather - - - - - -wave - - - base - - ...,f

...... .

adtent bottom currents - - - -S_to_rm_ w_av_ebb_ase .- .-:.- ..,..wl3enGty current

TempeStiteS

'"y."": y:.

Fig. 12.3. Stornz processes and storm beds. Major storms will interact with the seafloor down to the to storm wave base occurring in depths of several tens of meters. Storms directed onshore lead to a buildup of water masses and, when the storm abates, to the generation of offshore-directed return flows causing bottom currents that transport sediment down below the storm wave base into low-energy depositional environments forming tempestite beds. Shoreface sediment put into suspension can be transported offshore by density currents down to beyond storm wave base. The figure displays storm processes affecting ramps and platforms. Reefs are different (see Sect. 11.1.1.2). After Tucker and Wright (1990).

formation of lag deposits, and change the distribution patterns of benthic organisms. The effect of storms on sedimentation is controlled by water depths and the locations of the fair-wealher wave base and the stormweather wave base. Storms set up waves and currents below the fair-weather wave base, cause reworking of sediment and develop characteristic bed forms. Onshore-directed storms generate currents leading to the buildup of water in nearshore regions or in lagoons. During the decline of storm intensity, offshore-directed bottom currents transport shallow shoreface sediment to deeper offshore settings (Fig. 12.3).

Tempestitcs Li~rlestoneand sandstone beds deposited by storms are called rcmpcsfirrs (Kelling in Ager 1974). The base of these storm beds is sharp and erosional, and exhibits a variety of sole marks. Common internal structures include accumulations of shells, graded bedding, flat bedding, parallel and cross lamination. Ripple bedding and burrowing may be common at the top of the layer.

Prmimc~lurld di.srnl renzpestites: Storm beds exhibit much variation in thickness, grain size and internal structures, depending on the proximity and the intensity of the storm (Aigner 1985; Myrow and Southerd 1996). Similar to turbidites, tempestite bed thickness varies proportionally with the maximum grain size of the bed. Proximal storm beds are thick-bedded, bioclast-dominated and coarse grained, and include many amalgamated and composite beds containing ecologically and stratigraphically mixed biota. The base of the beds is an erosion surface. Distal tempesrite beds tend to become thinner, finer, rarer, better preserved and more biogenic in composition toward deeper depositional environments. They are

commonly mud-dominated. The base of the distal tempestite beds is plane. Proximal tempestites often contain many shell layers, distal tempestites only few.

Criteria of ancient tempestitrs: The following text summarizes field and laboratory criteria denoting the storm-related deposition of carbonate sediments. The facies analysis of ancient storm deposits requires the integration of lithofacies, biofacies and microfacies. Diagnostic features of carbonate tempestires can be derived from observations of modem storm sediments. Some of the criteria listed in the following text are often difficult to recognize in ancient calcareous s t o m deposits, e.g. erosive soles and rippled tops of the tempestite beds, because of bioturbation and diagenetic overprint. Sedimentary structures and sequences of tempestites . Tempestite beds are intercalated in marly, shaly or carbonate beds. They are common in shallowing-up sequences. Storm beds range in thickness between a few millimeters and several tens of centimeter. Thichness often differs markedly from that of underlying and overlying beds. Storm waves and currents deposit layers of packstones and grainstones often exhibiting characteristic undulated bedding. This humnzocky cross stratzfication (HCS; Harms et al. 1975; Swift et al. 1983; Duke 1987) shows gently curved, low-angle cross lamination and laminae with convex-upward (hummock) and concaveupward (swale) developed curvatures. Hummocky cross-stratified pack- and grainstones occur as 0.1 to about 2 m thick units interbedded with lime mudstones and wackestones or shales. Many storm sediments form amalgamated beds. Hummocky limestone beds exhibiting packstone and grainstone textures are common in

596

outer ramp settings (Markello and Read 1981; Kreisa 1981; Wu 1982; Aigner 1982; Wright 1986). Base of storm beds: The base is erosional and sharp. Erosive contacts of tempestites composed of packstones with the underlying bed indicate erosion of the sea bottom (commonly mudstone and wackestone; see PI. 1021 1,3).Sharp and plane boundaries between graded packstone of tempestites and the underbeds point to reworking by storms followed by rapid transport of reworked material into muddy areas (PI. 10212). Sole marks: Channels and scours cutting into finegrained limestones and filled with skeletal packstones and grainstones are often associated with hummocky beds. Infilling material is heterogeneous and unsorted. Gutter casts (U-shaped depressions) indicate paleocurrent directions. Burrowing is common at the top of storm beds. Strong bioturbation indicates breaks in storm activity. Internal structures: Storm beds may exhibit characteristic vertical sequences (Dott and Burgeois 1982; Duke 1985; Aigner 1985; Monaco 1992). A complete storm wave sequence consists of a basal lag unit characterized by an erosional base and coarse-grained resediments and skeletal grains, overlain by parallellaminated, hummocky, flat-laminated, cross-laminated and mudstone units (Pl. 10212).This sequence reflects deposition during waning flows. Note that this sequence is an ideal one that is by no means developed in all tenlpestites and differs for proximal and distal parts. Proximal storm layers comprise beds consisting from bottom to top of an erosional base, parallel to low-angle lamination with ~ninorinternal discordances, wave ripples, and a mud layer. Acommon variation is an erosive basal coarse-grained lag layer, a central well-sorted and matrix-poor calcisiltite or fine-grained calcarenite layer, and an upper fine-grained rippled calcilutite layer. Distal storm layers exhibit erosive or non-erosive bases, internal flat layers, rare grading, and parautochthonous accumulations of shells.

Tempestites: Microfacies

the tempestite. Parallel lamination may indicate unidirectional flows (PI. 10213). Millimeter- to decimeter-sized micrite c l a m and intraclasts (Pl. 611) in wackestones, packstones and grainstones may indicate redeposition of storm-derived material. Lithoclasts comprising distinctly different microfacies, e.g. fenestral bindstones and coral boundstones, pointing to high-energy events and erosion in peritidal and reefal environments. Reworked black pebbles (Pl. 1611) can indicate storm-induced coastal erosion. Non-carbonate extraclasts may represent storm-derived material (Pl. 1614). Flat-pebble conglomerate fabrics. Clast-supported calcirudites composed of coarse flat-shaped intraclasts typically occur in subtidal environments together with storm deposits, but also originate in storm-affected tidal environments (PI. 12513). Many examples have been described from Cambrian and Ordovician storm deposits. The preservation of flat-pebble structures is facilitated by early lithification enhanced by microbial activity (Ito and Matsumoto 2001). Edgewise conglomerate fabrics (Pl. 5811) may indicate storm-influenced sedimentation.

Fossils in ternpestites Distinct quantitative differences exist in the conzposition of tempestite beds and under- and overlying beds (Stel 1975). Skeletal concentrations are common features of many modem and ancient carbonate and siliciclastic shelves. Diagnostic criteria of storm-controlled bivalve shell layers are mixtures of epifaunal and endofaunal elements, bimodal sorting of complete shells and comminuted shell debris (PI. 102/5), random orientation, packstone and grainstone matrix between the shells and an erosive base of the millimeter- to decimeter-thick shell layers (Pl. 102/1, 3). The complete or disarticulated shells are well preserved (PI. 1714).Abrasion, bioMicrofacies criteria erosion and encrustations are absent. Distal tempestites Distinct diflerences in grain sizes of tempestites and often exhibit telescoped mollusk valves (PI. 10215). of under- and overlying beds (grain- and packstones Common fossil groups contributing to the formation intercalated within mudstones or wackestones). The of storm-related skeletal concentrations are bivalves. primary grain-size spectra may be obscured due to bio- brachiopods and crinoids. turbation. Trace fossils and different types of bioturbation in Graded bedding is often common. The graded parts storm-induced beds provide clues to the estimation of of the tempestite beds are commonly succeeded by the depositional water depths of tempestites (Wu 1982; finely laminated bioclastic packstones and wackestones Aigner 1985). Bioturbation is commonly strong in the (Pi. 10213) which in turn are overlain by dark lime mud- upper part of storm beds. stones or marls. Parallel lamination associated with ripple laminated The rnicrofacies of tempestites is characterized by intervuls in beds with hummocky cross stratification packstone textures, densely packed grainstones and indicate a high current regime during the deposition of rudstones. Abundant grains are reworked bioclasts and

Ancient Storm Depoqits

lithoclasts. Shell beds are common. Frequent microfacies types are Non-graded, poorly sorted skeletal packstones and densely packed grainstones and rudstones, consisting of coarse skeletal debris, e.g. shell accumulations (bivalves, brachiopods; P1. 10211) or accumulations of clinoids (Pl. 9512). The limestone is often dark-colored. Graded skeletal packstones, grainstones and rudstones consisting of skeletal debris including mollusks, brachiopods and echinoderms. Biolithoclastic graded, densely packed floatstones and rudstones with coarse fragments of mollusks and echinoderms, together with centimeter-sized intraclasts. Lithoclastic packstones, rudstones and densely packed floatstones. A common microfacies of proximal tempestites is characterized by angular micritic clasts resulting from reworking of beds underlying the storm bed. Thinly-laminated bioclastic mudstones and wackestones, sometimes with pelsparite laminae and graded fine shell debris (Pl. 102/2). Some of the characteristic microfacies criteria of tempestites are shown in Plate 102. Phanerozoic storm patterns: Indications of stomlrelated sedimentation are abundant in Phanerozoic limestones formed on ramps and in mixed carbonate-siliciclastic environments (E)ox 12.3). Fluctuations in the number and intensity of storms during the Phanerozoic have been suggested, based on global paleogeographical distributional patterns of storm deposits (Marsaglia and Klein 1983), paleoclimatic models (Parrish and Curtis 1982; Barron 1989) and variations in the wavelength of hummocky cross stratification (Ito 2001). Surprisingly, the overlap between the spatial distribution of ancient reefs with large amounts of fore-reef detritus and inferred paleowind directions is rare for most of the Phanerozoic except for the Late Triassic (Kiessling 2002). Event Deposits and Eventstones Tempestites are a class of event deposits. Event deposits include tempestites, turbidites, mass flow deposits, inundites (flood deposits) as well as seismites described in Sect. 12.4 (see Seilacher 1991 for a discussion of concepts). Event beds are the result of shortterm sedimentation processes that produce characteristic sedimentary signatures. These signatures may bear considerable similarities. Differentiation of tempestites and turbidites: Storm deposits are physically similar to deposits from other

Box 12.3. Selected case studies of storm deposits in ancient carbonate environments. Most papers deal with tempestites in ramp settings. Tertiary: Martin et al. 1993 Cretaceous: Banerjee 1981; Chel and Leckie 1992; Garcia-Ramos et al. 1989; Hunter and Clifton 1982; James 1979,1980; Valecka 1984 Jurassic: Ager 1974; Badenas and Aurell2001; Fursich and Oschmann 1986, 1993; Galli 1990; Ghosh et al. 1986; Hamblin and Walker 1979; Hussner 1985; Molina et al. 1997; Monaco 1992; Moore et al. 1992a, 1992b; Specht and Brenner 1979 Triassic: Aigner 1979, 1982, 1985; Aigner et al. 1978; Aljinovic 1995; Blendinger and Blendinger 1989; Calvet and Tucker 1988; Duringer 1984; Galli 1989; Hagdom 1982; Hips 1998; Masetti et al. 1988; Michalik 1997; Michalik et al. 1992; Perez-Lopez 2001; Rohl 1986; Torok 1993 Permian: McKie 1994 Carboniferous: Ball 1971; Buatois and Mangano 1994; Engelbrecht 2000; Graham 1982; Handford 1986; Kelling and Mullin 1975; Reynolds 1992; Simpson 1987; Stevens 1971; Wright 1986; Wu 1982 Devonian: Dreesen 1982; Gischler 1995; Hubmann 1999; Kazmierczak and Goldring 1978; Lavoie 1992; Miller et al. 1988; Rehfeld 1986; Stel 1975 Silurian: Brunton and Copper 1994; Cotter 1990; Johnson 1989; Sami and Descrochers 1992 Ordovician: Bakush and Carozzi 1986; Brenchley and Newall 1982; Brookfield and Brett 1988; Drummond and Sheets 2001; Jennette and Pryor 1993: Kreisa 1981; Lee 1988; Lee and Kim 1992; Lehnmn and Pope 1989; Paik and Lee 1989 Cambrian: Liang and Friedman 1993, Markello and Read 1981; Mount 1982; Mount 2nd Kidder 1993; Sepkoski 1962

genetically unrelated processes, such as turbidity or slump events. Turbidite sedimentation may be storminduced (Wu 1982). A table summarizing the distinguishing criteria of tempestites and turbidites (Einsele and Seilacher 1991) as well as a discussion of diagnostic thin-section criteria can be found In Sect. 15.7.2.5. Erosional sole marks, gradation, lamination and ripple bedding occur in both types of event beds, but differ in their frequency. The main discriminating criteria of proximal ~empestitesand proximal turbidites are biofaces, fossils and stratigraphic context. fi~rentstones:The term designates carbonate sediments whose deposition took place in rapid short-tern1 events as compared to the long-term average background sedimentation (Hiissner 1985). Eventstones include tempestites and turbidites and imply the existence of a relief and gravitative sediment transport (turbidites) or of episodically high water energy (e.g. stolms; tempestites).The important criteria of event-

598

Tempestites

Plate 102 Storm Deposits (Tempestites) Limestone and sandstone beds deposited by storms are called tempestites. These storm deposits form beds and lenses intercalated in mads and shales or in limestones of different texture and microfacies. Tempestites are common in subtidal ramp sediments. The plate displays fabrics of tempestites formed under high-energy (proximal) and low-energy (distal) conditions. Pr-oximal tempestites (-> 1,3,4) are often bioclast-dominated and coarse-grained, and composed of many amalgamated and composite beds. Distal storm beds (-> 2, 5,6) are thin-bedded and mud-dominated. The figures 1-3 and 5 show thin sections of a case study. The Late Triassic limestonesfonned in the intraplatform setting of the Kossen Basin (Northern Calcareous Alps) contain many limestone beds interpreted as tempestites (Kuss 1983). The samples are from a sequence consisting of alternating mark and limestones. Sedimentation took place in subtidal low-energy environments of a protected platform influenced by storm events. Some of the limestone beds exhibit erosional sedimentary structures (gutter casts and pot casts), cross bedding, lamination and ripple marks as well as distinct accumulations of shells. The latter occur together with thin, fine-grained peloidal grainstone layers. Field criteria and microfacies suggest high- and low-energy storm sedimentation. High-energy deposition is indicated by the deposition of complete and disarticulated shells (-> 4). Low-energy deposition by the lamination textures of fine-grained peloidal grainstones (-> 4,6). The shell accumulations (lumachelles, coquinas) are caused by storm-induced bottom flows. Tempestite. Brachiopod coquina formed by storms. An interpretation as proximal tempestite is supported by the preservation of complete shells, the current orientation of shells as well as a sharp lower erosive boundary and an irregular upper boundary. Brachiopod shells are geopetally infilled with micrite. The lower part of the figure shows a mudstone matrix with parallel laminae composed of very small peloids and thin compacted shells. The joint occurrence of these low-energy laminae and the high-energy fabric of the coquina layer points to rapidly changing depositional conditions. Late Triassic (Kossen Formation, Rhaetian): Loferbachgraben, Salzburg, Austria. Distal tempestite bed intercalated within calcimudstone (CM). Both the lower and the upper surface of the tempestite are flat. Slight compositional differences occur from bottom to top: a - densely-packed wackestone with abundant recrystallized involutinid foraminifera (white) and small peloids; b - wackestone with bivalve shells, involutinid foraminifera and peloids; c - wackestone with sparse bivalve shells and peloids. The involutinid foraminifera indicate sedimentation as platform-derived sediment. The low-angle cross-bedding boundary between a and b (arrows) suggests the effect of strong currents in the upper flow regime. Same locality as -> 1. Proximal tenzpestite. Storm layer intercalated in lime mudstone. A cross-bedded coquina (CBC) at the base is overlain by thin parallel laminae (GL) grading up into mudstone (M). The discontinuous lens-like geometry of the laminae suggests deposition from unidirectional flows. The arrows point to the distinct erosional basal boundary. Note the chaotic texture of the upper coquina consisting of disarticulated bivalves and gastropods (G). Broken shells point to deposition of material that has been fragmented prior to the storm event. Late Triassic (Kossen Formation, Rhaetian): Gaissau near Hallein. Austria. Storm layer intercalated within bioclastic shelf carbonates adjacent to organic mud mounds (see PI. 143). The tempestite layer differs from the background sediment by the composition and grain size. From bottom to top: a - bioclastic wackestone (below and above the tempestite layer) with fine-grained skeletai debris consisting of ostracods, styiiolinids, trilobites and echinoderms, b - coarse-grained echinoderm packstone representing the lower part of the tempestite layer. Arrows point to syntaxial rim cement around echinodenn fragments. c - bioclastic packstone with echinoderms and tabulate corals (TC). Note the stromatactis-like fabric (S) at the upper boundary of the storm layer. Compare P1.9417 and PI. 143. Early Devonian (Emsian): Erfoud, southern Morocco. Concentration of thin-shelled bivalves and a few gastropods within the distal tenlpestite bed. Densely-packed, wellsorted, bioclast-supported fabric. The carbonate mud is only preserved as post-storm infillings between the bioclasts. Compare the very similar fabric formed by trilobite shells shown in P1.9419. Late Triassic (Kossen Formation, Rhaetian): Steinplatte, Tyrol, Austria. Uppermost part of a thin distal tempestite layer. The parallel orientation of the shells indicates control by weak bottom currents. Note similarities with -> 2. Middle Triassic (Hauptmuschelkalk): Garnberg, Kiinzelsau, Germany.

Plate 101: Storm Deposits !Ternpestites)

599

600

stones are (a) mixing of grains derived from source areas that may be different with regard to facies and age, and (b) vertical sequence of sedimentary structures and textural types indicating changes in energy levels during deposition.

12.1.2.2 Impact of Tropical Storms on Reefs Geologists like to relate the origin of allochthonousreef material, e.g. fore-reef breccias (PI. 27/2) or isolated reef boulders found in slope position to catastrophic storms devastating the reefs. This is a pleasant interpretation, but how do severe storms actually affect reefs and how can we trace their activity in the geological record? Modem tropical storms and hurricanes cause significant perturbations that affect reef communities and destroy reef architecture (Hughes 1993; Scoffin 1993). Damage by hurricanes is common in shallow reefs. The effect of hurricanes and cyclones may be significant over tens to hundreds of square kilometers, but reef destruction is often patchy. Hurricane waves and storm surges erode reef crest, corals, reef rocks and sediments down to more than 20 m depths and produce mud- to boulder-sized fragmented reef material. This material accumulates as talus on and at the foot of the forereef slope, in grooves on the reef front and on submarine terraces, as storm ridges consisting of shingle, boulders or single blocks deposited on intertidal reef flats, as beach ridges formed by leeward migrating shingle, as scattered debris in back-reef lagoons, and as drapes of carbonate sand and mud in forereef and in lagoonal areas.

Impact of Tropical Storms

the growth form, tendency of attachment, strength and community composition of reef-building organisms, the length of time after a hurricane before a subsequent storm disturbs reef recovery. Recurring storms may selectively destroy fragile corals. This can result in gaps in otherwise distinct ecological zonations (Geister 1992). The recoveryperiod of modem reefs (the time taken for the reef to return to pre-hurricane conditions) lasts between a few years and some tens of years. Scoffin (1993) reports numbers between 5 and 40 years. Resettlement is selective and depends on the available substrates. On soft muddy substrates resettlement often starts with sponges and soft corals, on hard substrates with cyanobacteria and sponges. Changes in diversity over time influenced by severe storms have been explained in the context of the 'intermediate disturbance hypothesis' (Connell 1978), suggesting that the highest number of corals species will be reached at intermediate levels of the frequency and size of natural disturbances. The effects of hurricanes on reef diversity vary with depths, reef zones, the time since the last disturbance of the ecosystem, and the morphology of dominant species (Rogers 1993). Application of the intermediate disturbance hypothesis to modem ancient reefs struck by severe storms requires data on pre- and post-hurricane species number and cover.

The Hurricane Gilbert - Cozumel Case Study In September 1988, Hurricane Gilbert, on its devastating path through the western Caribbean, passed directly across the Mexican Island of Cozumel, off the eastern shore of Yucatan Peninsula. The eye of the hurCommon and in the geological record recognizable ricane was situated directly over the northernmost tip results of strong storms are the disintegration of reef of the island. The storm reached an extraordinary framework, coral breakage, dislodgment of heads of strength (about 320 krn/h)and a minimum surface presmassive corals, transport of variously-sized reef blocks sure (885 hPa), damaged coral reefs on the shelf and at and of carbonate sand, and scarring on standing corals the shelf margin, and also destroyed the tropical forest caused by waterborne debris. on the island (Sanchez et al. 1999). The extent of damage that will in turn influence the The shelf of Cozumel Island had been intensively chance of recognizing storm effects in ancient reefs de- studied only a few months before with regard to platpends on many factors including form and reef morphology and distribution patterns of the morphology and size of the reefs. benthic organisms. Priority was given to the carbonthe violence of strong storms relative to fair-weather ate-producing fauna and flora, and the quantitative aseffects and the state of tides, sessment of the shallow-water biotopes on the insular the angle under which the cyclone affects the reef shelf (Muckelbauer 1990). With these detailed obserslope, vations of the pre-hurricane situation at hand, a new the shelter afforded by differences in water depths, survey was started (Muckelbauer 1991, unpublished topography or by the structure of the reefs, research report, Institute of Paleontology Erlangen) in

Fig. 12.5. Cozumel Island east of YuccaranPeninsuln, Mexico. A: Map showing the narrow shelf region. Most coral reefs are situated on the western shelf and at the shelf margin, only a few on the near-coast eastern shelf. B: Schematic profile of the western shelf of Cozumel Island. The reefs are located on the morphological steps (after Muckelbauer 1990).

Reef Ill

Reef II

Terrace 3

order to compare the post- and pre-hurrtcane situations one year after Gilbert. Locafiorz: Cozumel is located approximately 18 km offshore the northeastern coast of Yucatan Peninsula. The narrow shelf (width 200 to 1500 nl; Fig. 12.5A) is organized into steps and terraces (Fip. 12.5R). The insular slope drops down at very steep angles to depths of 400 m and more ~ h a n1000 m. The steps are situated at depths of about 4 111. 10 1x1, 20 m, and in places 30 In and 50 m. The terraces between the steps vary in extension from a few meters to some hundreds of meters. Most coral reefs occur on hard bottoms along the steps and at the shelf edge on the wcsteni shelf. The terraces :ire covered with calcareous sands and sea grass. Reef distribution is controlled by the topography of the shelf. which originated in the Pleistocene and was changed during the Holocene, by tie distribution of hardground and softground substrates, and by strong ocean currents (2 rn/secj from southern directions representing an offshoot of the Caribbean Curren~.

c- m d p o ~ t - h w LCUIIC ~ ( . O ? l i p / i w:i Cornparirons oi damages caused by hurricmeh ~ ~ thet pre-humh cane sltiiat~onhave been made In the C'ar~bbeanand other regions (e.g Endean 1976; Stoddard 1985: Mergner 1985; Mah and Stearn 1986, Hubbard 1992; Boss and Neuman 1993). but nwst teports are focused only on certain organism groups, or u\e d~fferentquant~fyingmethods that can significantly affect the outcome of pre- and post-humcane comparisons.

Reef i Terrace 2

Terrace 1

These drawbacks are avoided in the Cozutnel study, which is based on identicai methods both in the field and for the statistical evaluation of quantita~ivedata. The studied locations were grouped to represent morphological sites of reef growth in different water depths (reefs 1, 11 and 111) at the steps between terraces I , 2, and 3. Patch reefs and the upper insular slope were also studied. Using the photographic transect n ~ e t h o d (Dodge et al. 1982), numerous photographs taken along transects running parallel to the reef structures ursre evaluated by point-counter analyses. Corals were identified down to species, forms and even morphotypes. Algae could be classified to the generic or species level. Altogether a total of 95 taxonomic categories was distinguished, and the percentage of coverage was cal-culated for each one. The resulting data were sumnliirized for the whole transect, thus obtaining the n~eari coverage as well as the standard deviation for differznt reefs. Coverage, diversity and species richness wcrc computed by statistical tests.

t'f

Post-hurricatze clzanges: Hurricane Gilbert devastated the shelf-edge reefs and many smaller reefs located on the shallow shelf. The reef structures were destroyed and eroded. Large areas were abraded by finegrained calcareous sand flushing over the newly created bare hard bottoms. Broken corals and up to metersized reef blocks were transported onshore as well as offshore.

Hard bottom

I

Corals

Soft bottom

Non-calcareous fauna (octocorals, sponges)

Algae Sponges

Non-calcareous algae

Cnidsria I

13

Coveraqe

20

10

30 %

I

I

5

10

I

I

~oderaoe 2b

I

25 "'0

Fig. 12.6. Changes in the substrate, coverage and composition of shelf-edge and shelf reefs off Cozumel caused by Hurricane Gilbert. A: Overall changes. B: Changes in the coverage of calcareous and non-calcareous organisms.

The inlpact of the humcane on substrate conditions, coverage and biotic composition are summarized in Figs. 12.6 and 12.7. The histograms give an idea of the overall changes in the reefs studied (Fig. 12.6) and of the variations in the changes in reefs located in different water depths (Fig. 12.7). Major changes with implication:, for the interpretation of ancient reef destructions relate to the frequency of hard and soft substrates, the distribution of sediments, and the abundance of carbonate-producing and other organisms.

Reef I

Reef II

Statistically significant results of the comparison of the pre-hurricane and the post-hurricane situation are: The size and frequency of bare hard bottoms (reef rocks), not yet resettled by organisms have dramatically increased in shallow subtidal settings (Fig. 12.6A). These hardground areas were almost doubled in some reefs as a result of the hurricane (Fig. 12.7A). The frequency of sand-sized loose sediment (soft bottoms) has increased in shelf-edge reefs (Fig. 12.7A)

Reef Ill

Patch reefs

Upper Slope

Hard bottom

I l l

Soft bottom Algae Sponges Cnidaria

a

O

1987

lo

.

2O 30 40

Reef I

0

.

.

.

1 0 2 0 3 0 40

Reef II

Reef III

Patch reefs

Upper Slope

branched

Pi

platy ,

i

Fig. 12.7. Changes caused b y Hurricane Gilbert in shelf-edge reefs (111), shelf reefs (I and 11, isolated patch reefs) and reefs on the upper slope (15-30 m). A: Coverage changes. B: Changes in the frequency and coverage of coral morphotypes.

h0-l

due to the current-transport of sediment from the shelf to the shelf margin during and after the hurricane. Shelf reefs show no notable changes in the frequency of soft sediments. * Carbonate-producing organisms are distinctly reduced in frequency (Fig. 12.6B). Corals and hydrozoans are reduced to almost one half their pre-hurricane level (Fig. 12.6A). Growth fonns of corals: Branched corals exhibit a decisive reduction in all reef sites (Fig. 12.7B). The coverage of massive and platy corals has not been reduced except platy corals in shelf-edge reefs. * Considering all corals in regard to the relative coverage of all corals dendroid corals have lost out to massive corals. Total coral diversity (species richness) has been maintained, but the ranking of species according to their frequency in the reefs has changed considerably. * Differences in coral diversity between reefs located in different water depths have become more pronounced due to great reductions in species dominating in prehurricane time. * Reefs in deeper water are more greatly destroyed than those in shallow water, due to the higher vulnei-ability of dendroid corals dominating in deeper water. Different algal groups reacted differently: The coverage of brown algae has increased significantly, that of green algae decreased. Red algae show no significant change. C'alcareous algae have not cieclincd clulte as drastically as corals but still significantiy. The frequency of calcareous green algae has been variously reduced. HalirneJa is reduced by one half. Other calcareous green algae show a slight increase. Surprisingly. the coverage of calcareous red algae has nor changed. * The coverage of cyanobacteria growing on transported coral fragments and dead coral heads has increased significant1y. * The destrucrion of the nor]-calcareous sessile reef organisms (mainly sponges. octocorals, hydroids, soft algae) has been hit by the hurricane similar to that of the scleractinian coral fauna. * High-growing finger-, bowl-, tuhe- and vase-shaped sponges have clearly lost ground. Low-growing encrusting and boring sponges have gained in distribution both in near-coast reefs and in shelf-edge reefs, because many of these sponges live in protected cryptic habitats.

-

The Cozumel study describes the s~tuationjust one year after the hurricane. Most of the changes observed reflect the biotic loss and shifts in the dominant taxa

S t o r m Deposits: Significance

rather than the reestablishment of the reef community. The shifts as well as the creation of large no longer organically covered areas show that the impact of hurricanes on reefs is not solely destructive, but that the ecosystem also benefits from severe storms. The initial recovery stage is indicated by the strong increase in the frequency and distribution of cyanobacteria. How to recognize storm effects in ancient reefs !' Box 12.4 reviews criteria that indicate disruption of' reef growth by severe storms. Most criteria must be evaluated in the outcrop, but some should also be evident on a microfacies scale.

12.1.2.3 Significance of Carbonate Storm Deposits Severe storms acting in shallow-marine environments change sedimentation patterns, influence the dl+ tribution of organisms, and modify the course of d agenesis. Ancient storm sediments provide informal~on on the following topics:

Depositional processes: Tempestites and reefs offer the possibility of understanding the physical controls on debris production. Strntigr.uphj: The recognition of the imprint ot 1 ~ ricanes and other strong storms on the sediment rcxol-tf provides a useful stratigraphic marker for the s ~ u d yo?' ancient reef systems. Paleoclimatc: Because the frequency and the predomnant tracks of intense hurricanes are expected t o h a w varied in time as a function of global climatic change5 (Emanuel 1987; Barron, 1989; Gray 1990), hurricanerelated tempestites are used as paleoclimatic proxics. Pa1cogrog1-aphy:Stonn-dominated, windward plaform margins arc characterized by sand bodics trvrlding parallel to the platfom~margin. Windward-leewari! orientations of ancient reef complexes can be deduccd from distributional patterns of fore-reef sediments. These criteria as well as nlodeling of windwarti-levward eft'ects based on paleowind directions allo\v largescale and medium-scale paleogeographic maps tv bc reconstructed. Diagenesis: Hurricanes are frequently accompanied by heavy falls of rain. Strong rain may trigger vadosc dissolution and karstification processes of carbonate platforms (Bourrouilh-Le Jan 1998) and influence dolomitization in tidal flats (Bourrouilh-Le Jan 1979). Reservoir- I-ocks:Onshore directed storms can accumulate shoals and sheets of porous carbonate sands of reservoir quality along coastlines. Draping of stoml-

Basics: S t o r m s

Box 12.4. Diugnostic features of storm effects on ancient reefs. Criteria that have also become evident in the Cozumel study are marked by an asterisk. Reef d~>tritus Fore-reef detritus: Extended slopes and aprons consisting predominantly of reef-derived material are valuable indicators of storm effects on reefs growing in shallow waters. The limestones are breccias, rudstones or floatstones. Angular and rounded clasts are intermixed with isolated fossils. Marked differences in the microfacies of the clasts are due to different source areas of the eroded material. Reef breccias, rudstones and floatstones deposited in near-coast position (*). Large, variously sized coral blocks or reef blocks occurring within fine-grained lagoonal sediments (*). Accumulation of fragments of corals or other reefbuilders acting as a base for encrusting organisms (*). Compositional biotic changes * Striking vertical and lateral differences of paleontological criteria on a decimeter or meter scale. * Conspicuous reduction of branching growth forms in favor of massive growth forms (*). High-growing reefbuilders followed by alevel of lowgrowing reefbuilders along a conspicuous boundary. Abrupt differences in the taxonomic composition and frequency of reefbuilder associations (*). Di.sc~oniitzuiri~s und tcxtur-a1changes Discontinuity planes and fissures disrupting the reef structure. * Bed:; with abundant, poorly sorted coral debris overlain by nticrobiai carbonates (*). Conspicuous chmges in the composition and grain size of the sediment deposited between and within reetl~uilders(*). Finegrained fossil-fwe layers that may correspond to carbonate niud settled down after the abatement of storms. Layers or lenses with high organic content can be caused by accumulation of destroyed plants.

intfuced porou\ skeletal a n d waves over dense mound facies can fonn h)rdrocarlm~traps, as shown by hydrocarbon reservoirs 111 capping bed\ of Carboniferous Waulsortian mound,. Ilasics: Storms Aigner. T. (1985): Stonn depositional systems. -Lecture Notes in Earth-Science, 3. 174 pp., Stuttgart (Schweizerbart) Barron, E.C. (1989): Severe storms during earth history. Geological Society of America, Bulletin, 101, 601-612 Bourrouilh-Le Jan. F.G. (1998): The role of high-energy events (hurricanes andlor tsunamis) in the sedimentation, diagenesis and karst initiation of tropical shallow water carbonate platforms and atolls. - Sedimentary Geology. 118, 3-36 Dott, R.H., Bourgeois, J. (1982): Hummocky stratification: significance of variable bedding sequences. - Geological Society of America. Bulletin, 93. 663-680

Duke, W.L. (1985): Hummocky cross stratification: tropical humcanes, and intense winter storms. - Sedimentology, 32, 167-194 Gischler, E. (1995): Current and wind induced facies patterns in a Devonian atoll: berg reef, Harz Mts., Germany. - Palaios, 10, 180- 189 Harms, J.C., Southard, J.B., Spearing, D.R., Walker. R.G. (1975): Depositional environments as interpreted from primary sedimentary structures and stratification sequences. - Society of Economic Paleontologists and Mineralogists, Short Course, 2, 161 pp. Hubbard, D.K. (1992): Humcane-induced sediment transport in open-shelf tropical systems - an example from St.Croix, U.S. Virgin Islands. - J. Sed. Petrol., 62,946-960 Hughes, T. (ed., 1993): Special issue: Disturbance: effects on coral reef dynamics. - Coral Reefs, 1.2, 117-233 Ito, M., Ishigaki, A., Nihikawa, T., Saito, T.: (2001): Temporal variations in the wave lengths of hummocky crossstratification. Implications for storm intensity through Mesozoic and Cenozoic. - Geology, 29,87-89 Myrow, P.M., Southard, J.B. (1996): Tempestite deposition. - Journal of Sedimentary Research, A, 66,875-887 Nummedal, D. (1991): Shallow marine storm sedimentation - the oceanographic perspective. -In: Einsele, G., Riecken, W., Seilacher, A. (eds.): Cycles and events in stratigraphy. - 227-248, Berlin (Springer) Pielke, R.A. (1990): The hurricane. - 228 pp., London (Routledge) Rogers, C.S. (1993): Hurricanes and coral reefs: the intermediate disturbance hypothesis revisited. --Coral Reefs, 12, 127- 137 Scoffin, T.P. (1993): The geological effects of hurricanes on coral reefs and the interpretation of storm deposits. - Coral Reefs, 12, 203-221 Seilacher, A,, Aigner, T. (1991): Stonn deposits at the bed, facies, and basin scale: the geologic perspective. - In: Einsele, G., Riecken, W., Seilacher. .4. (eds.): Cycles and events in stratigraphy. - 227-248, Berlin (Springer) Shinn, E.A., Steinen, R.P., Dill, R.F., Major, R. (1993): Limemud layers in high-energy tidal channels: a record of hurricane deposition. - Geology, 21, 603-605 Further reading: K032, K165

12.1.3 Marine Carbonate Substrates The composition and type of carbonate substrates depend on depositional, biological and diagenetic factors. The substrate type affects feeding modes as aell as the penetration and attachment of benthic organisms. Limestones represent former soft substrates and former hard substrates and various modifications of these two basic categories. Soft bottoms consist of loose grains exhibiting different consistencies depending on the grain size and water content. Hard bottoms are immobile substrates that are firm or hard enough to take encrusting and boring organisms (Sect. 5.2.4.1 and Sect. 9.2). They represent a non-depositional surface and are resistant to submarine erosion. Differences rn the states of con-

hlin

Car bonate Substrate f ) p r \

Shell bed bottoms: Autochthonous (biological) or allochthonous (physical) concentrations of the skeletons of shelly organisms. Hydraulic accumulations may be enhanced by storm events, tidal currents and turbidity currents. Common in inter-supratidal and shallow subtidal environments. Known since the Cambrian. Carbonate sand to gravel bottoms: Mobile and unstable substrates, formed by bioclastic and non-bioclastic carbonate grains. Redistribution of the grains by currents and waves and winnowing of the fines are conimon. Burrowing deposit feeders as well as vagile epibionts may be abundant. Oolitic bottoms are known since the Precambrian, bioclastic sand bottoms since the Cambrian. Col-al-sponge-blyozoan-algae-dominated st&stl-ates: Muddy to sandy carbonate substrates in quiet waters, covered by basal skeletons of 'coralline' organisms, most of which are clones of the first individual resulting from initial larval settlement. Platy, hemispherical and cylindrical growth forms act in prorecting and baffling sediment. The skeletons form hard substrates for epibionts and cryptic organisms. Known since the Ordovician. Hard bottonzs: Substrates that are firm enough to become encrusted and bored and that are resistant to normal erosion (include firm grounds, hardgrounds. and conglomeratic to skeletal and rocky grounds). Sedin~txtation rates are low to very low. Known since the Canl12.1.3.1 Carbonate Substrate 'Types and brian. Koc,k,~hotroirzs: Hard substrates formed by rocks Organism-Sediment Interactions exposed at the sea floor, large boulders and bedrock Copper (1993) differentiated seven types of con~mon surfaces; predoniinantly in shoreline environments. 'The cofi and hard bottoms. specialized biota is characterized by abundant borers and encrusters. Known since the Cambrian bur mo:-c Muddy soft bottoms: Formed by sedimentation of records known since the Late Mesozoic. microorganisms or breakdown of larger skeletons. Bot10111dwellers are predominantly epibenthic deposit feedInteractions between organisms and carbonate substrate ers because of high mud fractions associated with osBenthic organisms require the organic matter within ganic nlatter. Species diversity is ofren low. Fine lami- substrates as food resources and the sediment as 1~irv:tl ii:ition may be common. Often occur at the base of sedi- settlement sites: shelter and for anchoring and fixation. mentary cycles, in protected quiet-water environments, Suspension-feeders (e.g. many bivalves, sponbe s,. COTin lagoons, and in deep-water environments. Known als, bryozoans, brachiopods, crinoids) favor firm and since the Can~brian. hard or coarse-grained substrates whereas deposit feedMarzgmt~r-scwgrass 1?11.4d~iy bot[oi~z~ (a) : Man- ers (e.g. worms. echinids, some bivalves, many gastrogroves: Fine-grained muds, formed in Iow-energy in- pods) prefer silty and muddy bottoms, probably hecaube tertidal-supratidal tropical or temperate coastal envi- of the higher organic content of muds. Organisms in-. ronments by baffling of sediment, and deposition of fluence substrates through bioturbation and by providepibionts and organic matter (Plaziat 1995). The man- ing skeletons, sot organic tissues and fecal pellets. wove ecosystem is also called 'mangal'. Known since Organisms may have a strong impact on ( I ) grain size the. Late Cretaceous. (b) Sea grass: Fine-grained muds, and grain textures (by digestive activity and burrowformed by baffling, and deposition of epibionts. Car- ing), (2) grain composition (by providing different types bonate grains are stabilized by sea grasses. The sea grass of bioclasts and by selective feeding), (3) sedimentary structures (by destroying bedding through bioturbation; ecosystem dates back to the Late Eocene. b~stencyand stability of soft and hard substrates have been designated by the terms soupground, softground, looseground, firmground, hardground, rockground (rocky sea bottom), and shellground (Ekdale 1985; Coldring 1995; see Sect. 5.1.4 for definitions). Softground refers to a muddy sediment, looseground to a silt or sand grade sediment, the first type with indefinite burrows with irregular outlines, the second type with well-defined burrows. The last three names describe hard bottoms characterized by encrusting and boring biota, and frequently a mineralized crust. Firrngrounds are stiff carbonate substrates in which the sediment has begun to consolidate through initial conipaction, physical cohesiveness of fine particles, biological agglutinants (e.g. biofilms, organic mucus), or from early cementation. Firmgrounds may be initial stages of hardgrounds; they require some effort to become eroded, but can be ripped up by storms resulting In the formation of lithoclastic limestones. Hardgrounds are formed at times of extremely slow or intennittent sedimentation by lithification of the nondeposttional surface prior to the depo\ition of the overiying bed. The hard surface requires substantial mechanical effort to break down and can be destroyed only by borlng or by chemical processes (Sect. 9.3; P1. 51).

J

G

Kecognltion of S u b s t r a t e Types ---

A

BASIN GEOMETRY Topography and hyfiography

BASIN ENERGY Waves and currents

Circulation

B

.

- --

Increasing bottom current velocity

7

lncreasing substrate Decreasing content of mud and organic matter

Decreasing number of plants

Few deposit feeders

Few herbivores

Benthos dominated by vagile suspension feeders and carnivores feedmg on them -

-. -

Fig. 12.8. Inferred relationships among the major environmentalfactors of the Great Bahama Bank determining the relations between substrate and bottom-dwelling organisms. A: All ecologic factors depend on basin geometry and basin energy. Substrate types are predominantly controlled by water turbulence, circulation and salinity. After Newell et al. 1959. B: Relationships between feeding types, substrate and water energy in oolitic shoals. Increasing substrate mobility has two major ecologic consequences: (1) Increase in bottom current velocity results in an increase of substrate mobility, which in turn causes winnowing of organic matter from the sediment and prevents deposition of organic detritus. Consequently, the substrate contains only a relatively low percentage of organic matter. The low organic content limits the number of depositfeeding individuals and taxa. (2) Shifting bottoms inhibit colonization of the substrate by many marine plants. This limits the taxonomic and numerical abundance of the vegetal-matter consuming herbivores. The scarceness of organic nutrients in the substrate and the poorly deweloped flora on the substrate are reflected by a bottom fauna characterized by low-diversity suspension feeders represented by vagile forms (e.g. mollusks) on highly mobile substrates (such as oolite shoals), or sessile forms ( e . ~ sponges) ,. on moderately mobile substrates (such as fine-grained sands). After Purdy (1964).

or installation of lamination through organic mats), and (4) water content and fluid movement within intergranular pores as well as sediment chemistry (thus influencing early diagenesis: see Meadows 1986). The ncti~?ity uf hcnthic, organisms can change grain size. sorting and shape, usually by digestive activity. texture and fabric of the sediment, by mechanical displacement of the sediment, sedimentary structures (bedding, lamination, topography), water content and fluid movement in pores, by respiration and excretion, conlpaction, shear stress and stability (softness and hardness), and sediment chemistry. Substrate and feeding types Basically four feeding types can be recognized: (1) suspension feeders feeding on microorganisms and organic detritus suspended in water, (2) depositfeeders feeding on the same material in or on the sedi~nent, (3) carnivores feeding on other animals, and (4) her-bi~voi-es, feeding on plant material. Omnivores employ two or more of the listed feeding types.

Bottom-dwelling organisms are deposit feeders and suspension feeders as well as carnivores and herbivores. The distribution of the various feeding types depends on the distribution of the requisite food source. Deposit feeders, which feed or; the organic debris and detritus accumulated on or within the substrate. occur predominantly in fine-grained sediments. Suspension-feeders, which filter or strain suspended organic matter or microscopic organisms out of the water are common in medium- to coarse-grained silty and sandy sediments. Suspension feeders depend on the amount of food in the surrounding water; deposit feeclers depend on the amount of food in and on the sediment. The distribution of nutrients at sea bottom and in the water column is controlled by differences in water energy. Fig. 12.8 summarizes the basic relationships between water energy, nutrient source and organisms with different feeding strategies.

12.1.3.2 Recognizing Substrate Types Thin-section criteria that allow primary substrate types to be differentiated are listed in Box 12.5. The main criteria of soft bottoms are ichnofabric and the composition of bottom and sediment dwellers. Hard bottoms can be recognized from borings and encrustations.

Fig. 12.9. Kci~o~t~itiorz of substl-atestability b y ber~tlzicassemblages. The sample exhibits a skeletal grainstone with bryozoans (13j and crinoids (CR). This assemblage is typical for many Mississippian open-marine shelf limestones. The grain-supported xxture indicates deposition of skeletal sand forming a firmground substrate. Most grains are not significantly abraded. The skeletal grains are of different sizes. Bryozoans represent two morphotypes (fenestrate fomis - FB, and ramose cryptostornid forms - CB). Most cryptostomid bryozoans are well preserved. indicating only limited reworking. These bryozoanr arc regardctl as autochtl~ono~ls components of the assemblage. Fenestrate bryozoans grew as loose sheets over the substr;~te.The preservation of crinoids as isolated elements showing 110 signs of strong reworking and the dominance of sessile organisrt)\ unable to tolerate shifting substrates suggest stable substrate conditions. Similar pattenis were described by Feldrnan el i l l . ( 1993). Early Carboniferous: Calgary. Canadian Rocky Mountains.

E91ate 103 Soft Bottoms and Hard Substrates 'l'hc sea hottonl differs in consistency and stability of the sediment. Non-cemented carbonate muds and sands f o m ~soft bottoms, lithified carbonate sedi~nentsform hard bottoms. The state of consistency and stability prior to lithification can be inferred from paleontological and textural criteria. 1 Sofi hortonzs N ~ Z L Jh i d . ~ u h s t r a tdemonstrated ~s by a poorly sorted skeletal tloatstone. The fine-grained micritic milti.is

15

strongly burrowed bioclastic wsckestone with shell debris. Larger fossils are radiolitid rudist bivalves (R), corals ((-) and siliceous sponges (S). Rudists and corals are encrusted by coralline red algae (A). Criteria indicating suhtrate c o n d ;ions art. burrows and borings. Burrows (U) within the wackestone matrix are common but hard to recognize at a first view. Look at the typical, here only faintly visible, subrounded outline (white arrows), the slightly darker color and the close setting of the burrows. These criteria characterize a soft silty looseground substrate (Goldring 1995) with slight stabilization enabling the settlement o i serpulid worms (SER). Corals and rudist shells form local hard substrates as indicated by borings and biogenic encrustation. The borings (BO) in the rudists have affected both the inner aragonilii and the outer calcitic shell layers. The borings marked by black arrows tell a different story. They transect the sedimentary fabric and are filled with gray crystal silt. These criteria show that the borers did not attack individual fossils but the whole rock and that this attack took place in a meteorically influenced post-lithification stage. The sample comes from a sniall reef mound consisting of floatstones and rudstones, and local coral and rudist boundstones. Late Cretaceous: Haidach near Brandenberg. Tyrol, Austria. Courtesy of D. Sanders (Innsbruck). :1

Plate 103 Soft Bottom\ a n d Hard Substrates

600

Box 12.5. Criteria for recognizing carbonate substrate types (for trace fossils see Goldring 1991,1995; Bromley 1996). Biota Distribution of deposit feeders and suspension feeders. * The ratio of epifauna and endofauna provides information on substrate stability. The mode of feeding is controlled by grain size: Fine-grained soft substrates are dominated by endobenthos; increase of substrate stability with increasing grain size results in an increase in epibiontic elements, deposit feeders decrease in coarse-grained sediments due to the early decomposition of organic matter. * Mode of life (e.g. cemented versus burrowing or boring; provides information on the consistency of the substrate). E m c jossi!.~ Burrowing, bioturbation and ichnofabric pointing to soft bottonis (Sect. 5.1.4; Fig. 5.4; PI. 103). Burrows are formed in muds, sands and firmgrounds (PI. 191 I . 3,7j. Stages in the preservation of trace fossils provide information of different stages of hardening. * Tiering. Animals producing trace fossils live at different levels (tiers) in the sediment and colonize newly deposited sediment at different rate in different ways. Tiering patterns offer information on substrate conditions. sedimentation rates and oxygenation levels (Brornley and Ekdale 1986; WetzeI 1991: Uchnian

,.

1995 Abundant macro- and ~nicrobo~ings on bed surfaces (Sect. 9.3). poinfing to hardgrounds and fim~_grounds

hlicr-ojirc.ic..rr.ritc~ii7 Depositional texture types (lime mudstones versus grainstones). Biofahrics and current orientation of grains (Sect. 5.1.2) pointing to iooseground conditions. Biolarnination point to fimiground conditions (Sect. 5.1.3). Mineralized crusts on bed surfaces point to hardgrounds (Scct. 5.2.3.Iand Sect. 9.1; PI. 23/2,3, 7). *

D~sturbanczsof sedimentary fabrics and structures. Differences in grain size, sorting an3 packing.

Bioturbation and substrate type\ Because fine-grained sediment contains more organic matter than coarse-grained sediment. burrowing and bioturbation fabrics are common in micritic limestones (Sect. 5.1.4). The differentiation of soft-, looseand firmgrounds is primarily based on the preservation of burrows (Goldring 1995). An example is shown in PI. ti)?.

Substrate types of cold-water carbonates Carbonate sands formed in temperate and cold-waters of shelf platforms are characterized by the predominance of calcitic skeletal grains that are permanently reworked (Sect. 2.4.4.3). Cements are usually restricted to intraskeletal pores. Interskeletal cementation is weak due to the scarceness of primary aragonitic grains that could provide carbonate for cementation after dissolution. Sands remain unlithified for long periods, therefore many substrates are loosegrounds or firmgrounds. Basics: Carbonate substrates Bottjer, D.J., Ausich, W.I. (1986): Phanerozoic developmeiit of tiering in soft substrate suspension-feeding comniuuities. -Paleobiology, 12,400-420 Brett, C.E. (1988): Paleoecology and evolution of marine hard substrate communities: an overview. - Palaios, 3, 374-3711 Copper, P. (1992): Organisms and carbonate substrates in marine environments. - Geoscience Canada, 19,97-1 12 Ekdale, A.A. (1985): Paleoecology of the marine endobenthos. - Palaeogeography, Palaeoclimatology, Pahcoecology, 50, 63-8 1 Fabricius, F. (1968): Calcareous sea bottonis of the Rhaetian and Lower Jurassic sea from the west part of the Northern Calcareous Alps. - In: Miiller, G., Friednian, C;. (eds.): Recent developments in carbonate sedimentology in central Europe. - 240-249, Berlin (Springer) Feldman, H.R., Brown, M.A., Archer, A.W. (1993): Benlhic assemblages as indicators of sediment stability: evidmct. from grainstones of the Harrodsburg and Salem limestones (Mississippian, Indiana). -In: Keith, B.D., Zuppann. C.G< (eds.): Mississippian oolites and modem a~mlogs.-Anm i can Association of Petroleum Geologists, Studies ill (k-ology, 35, 115-128 Goldring, R. (1995): Organisms and the substrate response and effect. - In: Bosence, D.W.J., Allison, P.A. (ed5.j: Marine paleoenvironmental analysis from fossils. - Geological Society, London, Special Publications, 83, 15I 180 Purdy, E.G. (1964): Sediments as substrates. -In: Inibi-ie,.I.. Newell, N.D. (eds.): .Approaches to paleoecology. 23527 1, New York (Wileyj Further reading: K 172

12.1.4 Light Large-scale reductions in the incident light of benth~c calcareous red algae have been suggested as cause:, tor the mass extinction at the end of the Cretaceous (Agumt' et al. 2000), The functioning of the oceanic ecosysteln is dependent for energy to a high degree on the photosynthetic activity of phytoplankton confined to a thln zone of lighted surface water. Light-dependent photo synthesis is also of fundamental importance for marine benthic plants (algae and sea grass), and for the 11feof many benthic invertebrates harboring photosynthet~c endosymbionts

Zonation of Light I r l t e n s ~ l ) .

Solar incident light at the water surface is closely dependent on latitude. Once the light has entered the water, its rate of penetration depends on the extinction coefficient of the water. Since this varies, subsurface illumination shows little correlation with a simple latitudinal pattern. To broadly generalized, light penetration decreases from the open ocean to the coasts, and from the tropics toward the poles. The amount of light depends on the angle at which the light strikes the water surface. A maximum angle producing a maximum penetration of light occurs in the tropics where light conditions are optimal all year long and photosynthesis works in all seasons. Approaching the poles, the amount of light penetrating the water surface and photosynthesis rates differ significantly with the season. About 50% of the light penetrating clear water is absorbed in the upper tens of meters. The depth to which light penetrates depends on the absorption of light by the water, wavelength, transparency, reflection from the surface of the water, reflection from suspended particles, season of the year and latitude. Large numbers of suspended particles in the water, e.g. in coastal waters, severly reduce light penetration; photosynthesis is possible only within a range of a few meters. In clear tropical waters, where interfering particles are rare, light intensity may be sufficient for photosynthesis down to 100- I 50 I l l . Sunlight is composed of radiation in a spectrum of wavelengths. As these wavelengths enter the seawater, violet and red components are quickly absorbed within the first few meters. Green and blue components are absorbed less rapidly and hence penetrate more deeply, although the intensity of light decreases. These differences control the distribution of photosynthetic organisms.

12.1.4.1 Zonation and Light Conditions Distribution patterns of light-dependent organisms are used in ecological and bathymetric zonations of the oceans (Liebau 1984; 1-iining 1985). One common method distinguishes the illuminated photic and the non-illuminated aphotic zone. Other concepts differentiate three zones:

In the euphotlc zone or photic zone there is sufficient penetration of light to support photosynthesis. Its lower boundary is the water depth at which the visible light is reduced to 1% of the light touching the water surface. This boundary corresponds approximately to the maximum compensation depth of algae and the lower limit of the chlorocline. The euphotic zone com*

prises the supratidal, the intertidal and parts of the subtidal zones. The zone can be further subdivided into a shallow and a deeper euphotic zone using differences in light intensity and wavelength recorded by specific assemblages of endolithic cyanobacteria and algae (Budd and Perkins 1980; Glaub 1994) The dysphotic zone is the twilight zone characterized by dim light and little photosynthesis. The boundary between the dysphotic zone and the aphotic zone is defined by the existence of obligate photoautotroph multicellular organisms. This boundary corresponds to the lower limit of the rhodocline, which receives 0.01 to 0.001 % of the surface light and corresponds to the occurrence of crustose coralline algae. The zone is sometimes regarded as the lower part of the euphotic zone. Twilight is common in shadowy places, e.g. submarine caves and reefs. In the aphotic zone there is not enough light for photosynthesis. Endolithic microborers are restricted to chemoheterotroph taxa. The zone comprises parts of the deep shelf and the deep-sea bottoms. These zones can be further differentiated into vertically arranged units whose boundaries are defined by the distributional limits for specific organisms (Liebau 1984): The limit of the uppermost unit, the c,hloroclme, i\ characterized by the last occurrence of green algae. The hermacline is defined by the lower l~mitof reef-building organisms with photosymbiot~calgac. The I-hodocline can be recognized by the lower limit of encrusting calcareous red algae. The lower lirnit of the chrysocline is defined by the last occurrence of autotroph single-celled algae, particularly diatoms. The deep-lying ophthalmoclinc zone is typified by blind arthropods, particularly ostracods. The depths of these boundaries depend on the optlcal quality of the water and the latitudinal position (see Sect. 12.3).

12.1.4.2 Recognition of Photic and Aphotic Conditions The following criteria are useful for estimating paleo light conditions.

Microfacies criteria The formation of some carbonate grain types is influenced by light conditions. Most cortoids (Sect. 4.2.3) and porostromate skeletal oncoids (cyanoids; Sect. 4.2.4.1) originate in the well-lighted euphotic zone.

r: 1 2 Aggregate grains (Sect. 4.2.7) are abundant in the upper euphotic zone.

Algae and cyanobacteria * Occurrence of calcareous algae. Depth distribution patterns of green algae are much narrower than those of red algae, which can utilize minimal light intensities and specific wave lengths. Corallinacean red algae, therefore, may also occur in deeper waters down to more than 200 meters. * Dasyclad algae are restricted to a few meters in depth; the depth range of udoteacean green algae varies between a few tens of centimeters to about 80 meters. Since the fragments of calcareous green algae are often transported, some caution is needed when using the occurrence of dasyclads as an indicator of the upper euphotic zone. * Because light conditions control the growth rates of encrusting coralline algae, the thickness of the calcified algal body can be used in evaluating relative water depths (Sect. 10.2.1.2). The taxonomic composition of red algal oncoids (rhodoids) reflects differences in light conditions. Rhodoids offer a possibility of distinguishing shallower and deeper parts of the euphotic zone. * Cyanobacteria are aerobic phototrophs. They occur in illuminated as well as in shadowy habitats and can better tolerate changes in light, salinity. water temperature and other ecological factors than algae (Sect. 9.1 ). !\fic~t-o/>ul~6~t-.\ * Microorganisms boring in shells or hard lithified substrates are excellent indicators of light conditions and water depths (Fig. 9.16j. Boring cyanobacteria, algae and fungi are used to subdivide the euphotic and dysphotic zones. 0qaniswl.r wit/?photos~rr7hionts Benthic larger foraminifera with green and red algal synlbionts are restricted to shallow euphotic areas (Sect. 10.2.2.1). Differences in light attenuation by the water coiumn are reflected by different ~ r a l lstructures (Hohenegger 1999). Planktonic: foraminifera with algal endosymbionts occur in water depths down to 50 and 100 nl . Various invertebrates (e.g. corals, some bivalves) are characterized by photosymbiotic algae. Calcification and distribution of zooxanthellate reef corals is greatly determined by endosymbiotic algae. The symbiosis of ancient corals and algae is inferred from the morphological criteria of the corals (e.g. integration and size of corallites) and from stable isotope data.

Recognizing Oxygen

Morphological adaptions Morphological features that may be interpreted as adaptions to light conditions occur in various invertebrates (e.g. eye reduction in ostracods and trilobites). Basics: Light Aguirre, J., Riding, R., Braga, J.C. (2000): Late Cretaceous incident light reduction: evidence from benthic algae. Lethaia, 33, 205-213 Budd, D.A., Perkins, R.D. (1980): Bathymetric zonation and paleoecological significance in Puerto Rican shelf and slope sediments. - Journal of Sedimentary Petrology. 50, 881-553 Glaub, I. (1994): Mikrobohrspuren in ausgewahlten Ablagerungsraumen des europaischen Jura und der Unterkreide (Klassifikation und Palokologie). - Courier Forschungsinstitut Senckenberg, 174, 1-324 Jerlov, N.G. (1970): Light. -In: Kinne, 0.(ed.): Marine ecology. Vol. I (Environmental factors), part 1. - 95- 1 0 2 , 1 ~ n don (Wiley) Liebau, A. (1980): Palaobathymetrie und ~kofaktoren:Flaclimeerzonierungen. - Neues Jahrbuch fiir Geologie u r d Palaontologie, Abhandlungen. 160, 173-2 16 - I'alYLiebau, A. (1984): Grundlagen der Ok~bath~metrie. ontologische Kursbiicher, 2, 149-184 Liining, K. (1985): Meesesbotanik. Verbreitung, Okophysiologie und Nutzung der marinen Makroalgen. - 375 pp.. Stuttgart (Thieme) Riedl, R. (1966): Biologie der Meereshohlen. - 636 pp.. Hamburg (Pasey) Further reading: K 168

12.1.5 Oxygen Oxygen is a bio-limiting element for marine metazoa and one of the most important factors influencing spccies diversity and abundance. The absence of oxygen is generally considered to be essential for inhibiting microbial decay and forming organic-rich sediments (Allison et al. 1495). Oxygen-controlled environments occur-in tidal Ilats, open to poorly enclosed shelf seas, upwelling area.;, filled basins, and hydrothernlal vent and cold seep x eas (Oschmann 1995). All these environments show cyclic oxygen fluctuations. Estimates of dissolved-oxygen levels in ancient oceans contribute towards an understanding of the history of ocean circulation and paleoclimate. Paleo-oxygenation levels are based on fabrics (intensity of binturbation), biota (foraminifera, bivalves) and geochemical criteria (organic carbon/sulfur ratio, sulfur isotopes, rare element concentrations). The oxygen content is generally high in the surface waters of the oceans. A shallow oxygen m a ~ i n l u ~ t i ( S O M ) occurs in the upper ocean layers (Hayward

613

Oxygen i n the Water Column

1994), developing largely from photosynthetic oxygen production. The SOM forms on two different time scales, episodic (by physical events in which nutricline water is transported into the mixed layer and then ventilated to the atmosphere, producing a phytoplankton bloom) and gradual (developing from an input of 'new' nutrients transported from the depths orland by sinking particles). Oxygen-minimum zone: Decomposition of organic matter produced in the surface waters causes a decrease in oxygen in many intermediate waters. The depth of that layer ranges in the Pacific Ocean and in the Indian Ocean from 100 to 1500 m, but oxygen values less than 0.5 ml/l water occur only between 500 and 1000 m. Benthic environments are only affected where the minimum layer intersects with shelf and slope environments. In ancient times, the oxygen minimum layer was of variable thickness and intensity. Reduced or expanded oxygen minimum zones are caused by variations in primary production and density stratification within the water body, which in turn control the advection and diffusion of oxygen. Expanded oxygen minimum zones have berm reported from the Cretaceous.

12.1.5.1 Terminology and Classification Declmng oxygen grad~entscause a decrease in benthic faunal diver\ity until the oxygen-free anaerobic zone I S reached (Rhoads and Morse 1971; Byers 1977; Savrda and HOtljer 1987 ). Ranking by diversity reveals paleo-oxygenat~ongradients (Wignall 1990). LP\Y/.sufdi~sol\.edfifj.eeoxygen are classified by the content of free oxygen in the water expressed as ml/l, and indicated by the terms * oxic: > 1 ml/l O 2 dysoxic: 1.0 tt; 0.2 ml/l O2 * suboxic: 0 to 0.2 ml/l O2 * anoxi~:: 40%0) are called hypersulinc. They occur in arid

hih - --

Paleosal~ntt~ -

~ireshwaterl-I

i

+ I

0.5%0 limnic brackish oligohaline

brackish 5%0 1 O%,

brackish

marine

l8%,

30%,

marine brackish restricted marine brachyhaline

mesohaline Cyanobacteria .......................... ...+++++++++ ....................................................... Dasyclad green algae .................. Udoteacean green algae ............. Charophycean algae ............................

i -

normal marine euhaline

40%,

++++++

Calcareous benthic foraminifera Radioiaria ++++++ Coralline demosponges ............ +++++ Hexactinellid sponges ............... I ................ ............... .............................................................. + + + + + + . Corals ................................. . ++++++ Bryozoans ............................... Brachiopods Serpulids ..................................... Gastropods .................................. Bivalves ........................... . ........ Cephalopods ...... . Ostracods ................................... ++++++++++++ ++++++++ Balanid crustaceans .................... ++++++ Echinoderms ...............................j .......................J................... ............I.... ................ ........I..........

..,.

i..

restricted marine hypersaline

..I

1

I

I

+++L++++++ i

Fig. 12.11. Approximate distribution of some recent organisms relative to salinity. The figure does not include rare excrpL I U I E (e.g. freshmater sponges). The subdivisions follows the Venice System (Oertli 1963).

evaporitic settings (e.g. pans of the Red Sea; Persian Gulf), in salinas and restricted lagoons as well as in semiclosed basins and bays. The term schizohalinc describes strongly fluctuating salinity conditions which may be caused by episodic flushing of hypersaline environments by freshu~ater(Folk and Siedlecka 1974: P1. 50/6j. Estimations of paleosalinity are based predominantly on biotic: microfacies and geochemical data.

12.1.7.1 Biotic and Microfacies Proxies of Paleosalinity I'ill~of~ri~logi(.~ll clirttr are heavily used in reconstruct111gpaleosalinities and discriminating normal marine, brackish and freshwater environments. although salinity is rarely the only parameter influencing faunal composition and diversity. Hut if salinity is the dominant i'actor, salinity gradients can be determined using benthic associations, particularly of mollusks (Fiirsich and Werner 1986). Some difficulties arise in differentiating hypersaline and brackish conditions using paleontological data alone. The capability to regulate the osmotic pressure may allow organisms to thrive both in hypersaline and brackish waters and biota as well as microfacies types may exhibit considerable similarities (e.g. Fiirsich et A. 1995).

Organisms are stenohaline or euryhaline. Stenohtrline organisms do not or are only able to tolerate a narrow range of salinity. Euryhalinc organisms toleratc wide fluctuations in salinity. The differentiation of euryhaline and stenohaline organisms on a higher taxonomic level is a widely used approach in estimating. paleosalinities. Stenohaline are planktonic foraminifera, radiolarians, corals, most bryozoans, brachiopods, cephalopods, and with a few exceptions echinoderms. Common euryhaline are cyanobacteria, sponges, many bivalves. gastropods, and ostracods. Important paleontological criteria that can be used in estimating paleosalinities are Salinity ranges. Comparison of the salinity depcridence of modem and ancient organisms. Fig. 12.1 i shows the salinity ranges of some groups. The distribution of major taxonomic units within these groups may be more specific than the range of the whole group as demonstrated by the foraminifera. Textulariina are abundant in brackish waters, Miliolina occur in waters of normal to hypersaline salinity and Rotaliina are cornmon in waters of normal salinity. Faunal composition. The lack or scarcity of stenohaline invertebrates is characteristic of environments with fluctuating salinity conditions. Extended microbial mats and stromatolites (e.g. Persian Gulf; Shark Ray, Australia).

Paleosalinity: Geochenllcal Proxies

Ostracods are most valuable indicators of paleo- Stable isotopes Differences in the stable carbon and oxygen comsalinities (Pl. 4812; P1.9311; P1. 13012).They occur with facies-diagnostic species and assemblages in freshwa- position from either fossil or rock samples between marine and nonmarine carbonates (Keith and Weber 1964) ter, brackish water and marine environments. * Charophycean algae (PI. 65/1,3; P1.13014) are used can be used to reconstruct paleosalinities (Mook 1971; as indicators of freshwater and brackish water envi- Dodd and Stanton 1990; Yin 1991; Joachimski 1991). ronments (Sect. 10.2.1.8). Alternations of limestones The results, usually based on 613C data, should howwith charophyta, ostracod limestones and intercalations ever be checked by paleontological criteria (Yin et al. of evaporites may reflect seasonally varying salinities. 1995, Mityis et al. 1996). * Faunal diversity (species richness and evenness) can reflect high-stress conditions. A diversity minimum Trace elements Trace elements in skeletons, both of fossils and in exists around a salinity of 5%0. Diversity decreases away from the species minimum toward both the freshwater carbonate rocks provide a possibility for estimating end and the marine end of the salinity range (Remane paleosalinities: 1958). Similarly, the number of individuals often deThe favorite fossils used in paleosalinity interpretacreases from normal marine environments to both tions are ostracods because these organisms occur in brackish or hypersaline restricted environments. See continental, estuarine, marine and hypersaline waters, because their Low-Mg calcite valves are relatively reCroghan (1983) for critical remarks. * Shell size and thickness: The thickness and size of sistant to diagenetic changes influencing the geochemifreshwater and brackish shells is often smaller than that cal data, and because the relationships between the of marine shells. Decreasing and increasing salinities uptake of elements and chemical conditions of the are often related to a decrease in the maximum size. aquatic environment are well studied (Bodergat 1983). Taphonomic features. Burrowers and grazers norContrary to mollusk shells, which represent a whole mally destroy microbial mats in marine waters of nor- lifi growth pattern, ostracod tests - corresponding to mal salinity. These organisms are absent in high salin- molts - may record water chemistry during just a very ity areas. Microbial mats formed in hypersaline envi- short interval of a few days only ronments therefore have a greater chance for preservation. In tropical seawater, the concentrations of M g , SI. andNa increase with increasing salinity.These elements Micr-cfaries data reflecting paleosalinity deviating and their ratios are commonly studied in the context of from that of the normal marine seawater include spe- paleosalinity (e.g. Dodd 1967; Chivas et al. 1986). Socific grain types: dium in carbonate rocks has been used as a possible Radial-fibrous ooids are common, but not restricted index to the salinity of diagenetic solutions (Land and to freshwater, brackish and hypersaline environments Hoops 1973) as well as a paleosalinity indicator (Veizer (Sect. 4.2.5; Fig. 4.20; Fig. 4.26). et al. 1977; Ogorolec and Rothe 1979; Sass and Bein Distorted ooids and half-moon ooids (Fig. 4.23). 1988). Pisoids/vadoids (Sect. 4.2.6; Box 4.19; P1. 14). Changes in salinity during the deposition of subtidal Microbial peloids are abundant in hypersaline envi- to supratidal limestone/dolomite cycles are reflected by ronments. decreasing Sr and increasing Na, Fe and Mn contents Freshwater- and brackish oncoids (Sect. 4.2.4.1) dif- (Buggisch et al. 1994). fer from marine oncoids by specific nuclei and laminaSince rare element concentrations and the MgICa, tion, and by better preservation (Box 4.10; P1. 1217; P1. Sr/Mg and the SrICa ratios of fossil shells and carbon13115). ate rocks depend on many other factors than salinity, The case study displayed in P1. 104 demonstrates their implication for paleosalinity interpretations is the controls of alkalini1.y and salinity on carbonate for- much debated (Dodd and Stanton 1990; Rosenberg mation and lithification. 1990; Carpenter and Lohrnann 1992; Holmes et al. 1992; Rao 1996). 12.1.7.2 Geochemical Proxies of Paleosalinity

Common criteria used in recognizing differences in the salinity of waters and diagenetic fluids are stable isotopes and trace elements.

Boron: Another tool studied in determining paleosalinities is the boron content of argillaceous sediments (Harder 1970; Perry 1972). Spivack et al. (1987) have shown that the bulk of boron in clay minerals is not in isotopic equilibrium with seawater and can, therefore

6211

Satonda Modc!

Plate 104 Salinity and Alkalinity Controls: The Satonda Model Satonda is a small volcanic Indonesian island north of Sumbawa. The island is unique in that the crater lake is filled with seawater with increased alkalinity. Because lake and ocean waters cannot communicate, the lake water acquired higher alkalinity, pH and carbonate mineral saturation than in the open ocean. These conditions exclude most marine macrobiota but favor reef-like structures composed of red algae, serpulids and foraminifera, and biogenic mats built by in situ calcifying cyanobacteria and green algae. Morphology and microstructure of these deposits are similar to certain types of microbialites that are common in the Late Precambrian and Early Phanerozoic oceans. The conditions exemplified by the Satonda case study have been used to establish a new model focused on the role of alkalinity for calcification processes in early Phanerozoic oceans (Kempe and Kazmierczak 1990). The formation of carbonates was controlled by changes in salinity and alkalinity (Kempe and Kazmierczah 1993). Salinity changes are reflected by the composition of the ostracod fauna (Schudack and Reitner 1996).The crater lake was originally filled with freshwater. Shortly after the lake was flooded with seawater. During this phase marine organisms colonized the lake starting with serpulids. Large input of organic matter from the crater walls caused intense oxygen consumption. As a result, the bottom water of the lake became anaerobic and sulfate reduction led to the precipitation of carbonates. The lake became stratified into water bodies of different salinity and high alkalinity. A significantly increased carbonate mineral supersaturation caused a in situ calcification of cyanobacterial microbialites forming microstromatolites (-> 1) and to the lithification of red algal crusts (-->7). 1 Macroscopic view of microstronlatolites exhibiting subcolumnar structures. The stromatolites were formed by cyanobacteria in association with non-calcifying green algae Cladoplzorn in a water depth of 13 m and waters with a salinity of about 30 %. 2 In-situ calcification of cyanobacteria. The SEM view of the surface of a coccoid cyanobacterial mat shows the capsular character of gelatinous sheats surrounding Pleurocapsales cells embedded within a microgranular Mg-calcite matrix precipitated in vivo by the mat itself. The lower part of the photograph comesponds to a dark lamina of the microstromatolitc. the upper part to a fibrous aragonitic lamina (compare -> 3 ) . 3 The internal fabrics of the nlicrostrornatolites are laminated (this figure) or cystose (-> 6). The light aragonite laminae alternating with dark Mg-calcite cyanobacterial laminae overgrow filaments of non-calciijing siphonocladalean grecn algae (empty molds). 4 The vertical section of he microstromatolitic structure shows sparry (light) laminae consisting of fibrous aragonite anti rnicrocryslalline (dark) laminae composed of High-Mg calcite. The differences in the mineralogical composition are interpreted by seasonally changing supcrsaturation in the lake. During the wet season the supersaturation is lowered due to rain allowing the growth of the mats. 'The carbonate supersaturation rises during the dry season resulting in an in vi\,o precipitation of High-Mg calcite at the surface mat. Decay of the mat below the permineralized surface triggered by suifate-reducing bacteria connected with increase in alkalinity and of the Mg/Ca ratio causes the post mortem precipitation of aragonite instead of Mg-calcite. Similar alternations of thin microgranular and thicker fibrous laminae are c o n mon features of ancient fabrics interpreted as microbialites. .i 'The upper part of the calcareous crust consists of intergrown corallinacean red algae and variously calcified p1eurocapsaic;irl cyanubactcria. The lower part consists o f squamariacexl red algae. h The cystuse microbialite structure reminds on a common Palaeozoic fossil (Uet1w1-~~hlla. see PI. 5119) whose syslematic position is not settled (Kazmierczak and Kempe 1992). 7 Parts of the reef framework consist of encrusting squaniariacean red algae (Peyssorzcliil) and accumulations of dark peioids of fecal and cyanobacterial origin. Present-day Squamariaceae grow as flattened crusts or petaloid forms on soft substrates (e.g. circundittoral soft-bottoms of the Mediterranean). The internal structure is characterized by closely packed bssal cells from which vertical rows of cells arise. Note the attached fans of aragonite (arrows). Fossil squamariaceans show in thin sections a yellow-brown tint in contrast to corallinacean red algae (PI. 5411, 3) exhibiting a dark grey tint. X Green algal meadows with Cladophora occur in the upper parts of the lake down to 16 m. Red algal crusts are also found in deeper positions. The photograph shows longitudinal and cross sections of algal filaments (arrows) and irregularly shaped open voids. Cotnpare the picture with the Tertiary algal structures 4hown in PI. 13011. -> 1--8:Courtesy of S. Kempe (Damnlstadt)

Plate 104: Salinity and Alkalinity Controls: The Satonda Model

62 1

H y p e r s a l m e and Evaporitrc Cond:r~o:i,

not be used in salinity analysis. In contrast, the abundance and isotopic composition of boron incorporated in biogenic carbonate skeletons may be useful in tracing changing paleoenvironmental conditions (Vengosh e t al. 1991).

12.1.7.3 Microfacies Proxies for Hypersaline and Evaporitic Conditions High salinities are c o m m o n in arid shallow-marine environments, e.g. evaporite-carbonate shorelines o r lagoons, and can be inferred for ancient sediments by lithologic and mineralogical criteria (e.g. evaporites). Box 12.7 summarizes criteria signaling hypersaline and saline conditions that c a n also be recognized in microfacies studies. Basics: Salinity Buggisch, W.. No6, S.. Krurnm, S. (1994): Geochemische und fazielle Muster in peritidalen KalkJDolomit-Zyklen der oberen Bellerophon-Schichten (Oberperm) in den Siidalpen. -- Abhandlungen der Geologischen Bundesanstalt Wien, 50, 69-87 Chivas, A.R., Dc Deckker, P., Shelley, J.M.G. (1986): Magnesiurn content of non-marine ostracod shells: a new palaeosalinometer and palaeothermometer. - Palaeogeography, Palaeoclimatology, Palaeoecology, 54,43-61 Folk, R.L., Siedlccka, A. (1974): The 'schizohaline'environtilent: its sedimcntary and diagenetic fabrics as exemplified hy Late Paleozoic rocks of Bear Island, Svalbard. Scdimcntary Geology, 11, 1 - 15 Friedman,G.M., Shukla, V. (1 980): Significance of authigenic quartz euhedra after sulfates: example from the Lockport Formation (Middle Silurian of New York). - Journal of Sedimentary Petrology, 50, 1299-1304 Fiirsich, F.T. (1994): Palaeoecology and evolution of Mesozoic salinity-controlled benthic macroinvertebrate associations. - Lethaia, 26, 327-346 Grimm, W.D. (1964): Ausfiillung von Kieselsaure in salinar beeinflufiten Sedimentcn. - Zeitschrift der deutschen gcologischen Gesellschaft. 1962, 589-619 Jacobs. L., Swennen, R., Van Orsmael, I., Notebaert, L., Vicaene, W. (1982): Occurrences of pseudomorphs after cvaporitic minerals in the Dinantian carbonate rocks of the eastern parts of Belgium. --Bulletin de la SociCtC belge dz GCologie, 91, 105-123 Kernpe, R., Kazmierczak, J. (1993): Satonda Crater Lake, Indonesia: hydrogeochemistry and bicarbonates. - Facies, 28, 1-32 Kenipe, S., Kazmierczak, J. (1 994): The role of alkalinity in the evolution of ocean chemistry, organization of living systems and biocalcification processes. - Bulletin de l'hstitut oceanographique, Monaco, no. spec., 13,61-117 Matyis, J., Bums, S.J., Miiller, P., Magyar, 1. (1996): What can stable isotopes say about salinity? An example from the Late Miocene Pannonian lake. - Palaios, 11,31-39 Mook, W.G. (197 1): Paleotemperatures and chlorinities from stable carbon and oxygen isotopes in shell carbonate. -

Box 12.7. Microfacies criteria pointing to hypersaline and saline depositional andlor diagenetic conditions. Interbedded lime mudstones and layers with anhydrite or gypsum crystals (Pl. 10919). Common in supratidal sabkha environments. Microfolds in fine-grained dolomites resulting from dehydration of primary gypsum or hydration of anhydrite (Pi. 12514). Collapse breccias may result from the dissolution of evaporites interbedded with limestones. The breccia beds are characterized by stratiform geometries with welldefined lower boundaries. Silicijied or calcitized nodules formed by replacement of anhydrite nodules (Hennebert and Hance 1980). Common in carbonates formed in intertidal environments or on supratidal sabkha flats. Half-moon ooids (Fig. 4/23) may owe their shape to a collapse of insoluble parts following the dissolution of envelopes composed of anhydrite or gypsum. The grains can indicate vanished evauorites. * Pseudonzorplzs of evaporite minerals in limestones (Paszkowski and Szydlak 1986). Palisade calcites. Millimeter- to centimeter-smd, conical calcite rosettes (PI. 12512) or clusters representing pseudomorphs after gypsum formed in restricted environments (Swennen et al. 1981). Length-slow chalcedony after sulfate evaporite mirierals (Pittman and Folk 1971). Length-slow means that the slower polarized light component produced in double refraction is the one vibrating parallel to the crystal length. Formed when silica replaces a sulfate mineral or when it replaces carbonate minerals in an evaporite milieu. May originate early after deposition of the sediment or after lithification. Authigenic idiomorphic and double-ter.nzinntctl cuhedr-a1quartz c~ystals(Pl. 10915, 6) are common in micritic limestones formed in hypersalinc cnvironmenls. The carbonates are often associated with evaporites and salt deposits (Grimm 1962, 1964). These quartz crystals are formed both during early and late diagenetic phases (Richter 197 1). Authigenic euhedrnl feldspnr. The association of a1 bite-bearing carbonates and evaporites and saline fluid inclusions in albite are considered as tracers of palrobrine-carbonate reactions. These reactions may take placc shortly after the deposition of carbonate mud in hypcssaline environments, but also post-depositionally in deep burial and incipient metamorphic settings (Misik 1994; Spot1 et al. 1999). Low-diversi~hut ahundunt skcleral gr-uins. Lirnestones with accumulations of ostracods (Pl. 130/2,3). or of monospecific bivalves and gastropods may have been formed in environments with significant departures frorn normal marine salinities.

Palaeogeography, Palaeoclimatology, Palaeoecology, 9. 245-263 Oertli, H.J. (1964): The Venice system for the classification of marine waters according to salinity. - Pubblicazionl della Stazione Zoologicadi Napoli, 33, Supplement, p. 6 1 1

N u t r ~ e n tLevel C r ~ t e r l ; ,

can raise or lower nutrient levels and primary production, and encourage or reduce eutrophic conditions were summarized by Follmi et al. (1994) and Brasier (1995).

12.1.8.2 Estimating Paleonutrient Levels Several factors triggering higher or lower nutrient levels are recorded by facies, paleontological and geochemical criteria (Box 12.8).

12.1.8.3 Effects of Nutrient Excess on Reef and Platform Carbonates 'The primary carbonate sediment producers of coral reef communities and of shallow carbonate platforms are

highly adapted to nutrient-deficient environments. Changes in nutrient concentration are regarded as a major control on the demise of coral reefs and drowning of platfornx (Schlager 1981; Hallock and Schlager 1986; Follmi et al. 1994; Dupraz and Strasser 2002) and on the biotic composition of reefs (Birkeland 1988). The input of phosphates and nitrates stimulates the growth of plankton, which reduces water transparency, limiting depth ranges of zooxanthellate corals and calcareous green algae and thereby reducing carbonate production. Higher nutrient concentrations and plankton densities stimulate the growth of fast-growing soft algae and ahermatypic suspension-feedingbenthic organisms, and increase bioerosion by microborers. Many ancient drowned platforms and reefs exhibit evidence of nondeposition, bioerosion and reduced redox potential, pointing to excess nutrient availability

Box 12.8. Criteria of carbonates reflecting possible differences in nutrient levels. Note that some of the facies criteria can also be cau5ed by other environmental constraints. Based on Brasier (1995a, 1995b), Wood (1999) and other sources. * Benthic nutricnt types. Suspension feeders are comFacies criteria Basic types of autochthonous Ilmcstones The dominant mon in eutrophic environments, symbiotic forms and grazrecf biota and the resulting carbonate types are related to ers are more common in oligotrophic environments. Biotic diversity is often low in eutrophic and higher in nutrierit levels. Bindstones and frarnestones originate in low-nutrient environments; mud mounds formed by fine- oligotrophic environments. Density aizd abundance of sessile benthic fossils may grained micrite with weakly calcified heterotrophs, and bafflestones originate in areas of higher and high nutrient reflect differences in nutrient levels. An example are Mesozoic siliceous sponges exhibiting high densities in low levels (Fig. 8.1; Wood 1993). * Microbial nuts. Abundant mats may point to eutrophic nutrient areas and low densities in high nutrient environconditions due to increased nitrate fixalion by cyanobacte- ments. ria and other microbes (see Sect. 9.2.). Changes it7 c~i'oiogicsr~cressiotzsand guilds in reeji. A Riocrosiotl. Levels of bioerosion are high in eutrophic vertical succession from frame-building to baffling and areas, and relatively low in oligotrophic environments.An from high-growing to low-growing sessile organisms ma) increase in nutrient supply (C. N,P and trace metals such indicate an increase in nutrients. as Fe and Mo) in oligotrophic environments influences the * Planktonic organisnzs. Accumulations of radiolarians, population of bioeroders and niay ~nhibitreef growth diatoms, and organic-walled phytoplankton as well as the (Peterhamel and Pratt 2001). The relat~onsbetween bio- occurrence of cold-water planktonic foraminifera may inerosion and micro-encrusters reflect changes from olig- dicate upwelling and high bio-productivity. otrophic to mesotrophic and eutrophic conditions. Mineralogy * Biotui~bariorr.Intensive burrowing of fine-grained carPhosphaticfossils. Accumulations of phosphatic grains. bonates may indicate eutrophic conditions caused by the Formation of phosphorites (see Sect. 13.1.2.4). transport of nutrient elements and orgaliic matter from * Gluuconite formation. Phosphogenesis associated with deeper sedment layers to the sed~nicnt-uatermterface. minimal carbonate accun~ulationmay indicate eutrophic Oncnids and i'ortozds. Common and autochthonous cyanobacterial oncoids and cortoids fonnrd by microborers conditions (Follmi et al. 1994). ind~catehigher nutrient levels. 7i'~-~igenou.s grains. Increased fluvial runoff (e.g. during regression) will deliver nutrients and lead to higher nutrient levels than a reduced input of terrigenous material into shallow-marine carbonate environnients (Erlich et al. 1990) Biota Trophic coniposltiotz ofpaleocomrr~ut~~ties. A dominance of deposit-feeders indicates a preferred accumulation of nutrients within the sediment. A dominance of suspension feeders points to food particles largely suspended in the water column.

Geochemistry Organic muttr,/-atxi olgunic carbon i1z carbonate rocis Intercalation of bedded carbonates and laminated organicrich sediments and fluctuations in organic carbon may reflect fluctuations in bio-productivity and nutrients or they reflect preservation differences (Parrish 1995). Geochemical criteria. Ba/Ca ratios as well as positive 6's0 and more negative bl" values in planktonic shell5 of upwelling areas are valuable indicators of nutrient conditions (see Sect. 13.2). Phosphate grains and phosphorites. Both criteria are used in the context of the discussion on bio-productivity (Follmi 1996; see Sect. 13.1.2.4).

C;r;ri~i A s s o c i a t i o n Anxlysi

625

>

during drowning. Nutrient excess has various causes. Reef carbonates that are overlain by shales may be victims of nutrients in terrestrial runoff. Rapid transgression that flooded subaerially exposed platforms and ramps may have supported the influx of soils and nutrients to areas of reef growth. Other mechanisms for drowning by excess nutrients include rapid pulses of sea-level fluctuations and local or regional upwelling. Studies of modem coral reefs indicate that an increase in nutrient input and the related increase in productivity lead to changes in dominant species, in an increase in fast-growing and smaller taxa, and in greater competition for space. Corals may be less abundant than algae, sponges and bryozoans. This change can be recorded in ancient reefs by distinct differences in successions and growth types. Note that the relations between reef builders and nutrients summarized by the Hallock and Schlager model can be used to explain changes in ancient reefs fornled by zooxanthellate corals, but can not be applied to reefs formed by siliceous sponges, bryozoans or microbes.

mise of coral reefs and carbonate platforms. - Palaios, 1. 389-398 Hottinger, L. (1987): Conditions for generating carbonate platforms. - Memorie della Societii Geologica Italiana, 40,265-271 Peterhansel, A., Pratt, B.R. (2001): Nutrient-triggered bioerosion on a giant carbonate platform making the postextinction Famennian benthic community. - Geology, 29, 1079-1082 Rougerie, F., Fagerstrom, J.A. (1994): Cretaceous history of Pacific basin guyot reefs: a reappraisal based on geothermal endo-upwelling. - Palaeogeography, Palaeoclimatology, Palaeoecology, 112,239-260 Summerhayes, C.P., Prell, W.L., Emeis. K. (eds., 1992): Upwelling systems: evolution since the early Miocene. - Geological Society, London, Special Publication, 64 Thiede, J., Suess, E. (eds., 1983): Coastal upwelling. Its sediment record. Part B. -NATO Conference Series, IV, lob, New York (Plenum) Whelm, W.K., Farrington, J.W. (eds., 1992): Organic matter: productivity, accumulation and preservation in recent and ancient sediments. - 550 pp., New York (Columbia University Press) Wood, R.(1993): Nutrients. predation and the history of reefbuilding. - Palaios, 8,526-543 Further reading: K2 12

Basics: Productivity and nutrients Berger, W.H., Srnetacek, V.S., Wefer, G. (eds., 1989): Productivity of the ocean: present and past. - 470 pp., .. Chichester (Wiley) Hirkeland, C. ( 1 988): Second-order ecological effects of nutrient input into coral communities. - Galaxea. 7,91-100 Hornbardiere, L., Gorin, G.E. (2000): Stratigraphical and lateral distribution of sedimentary organic matter in Upper Jurassic carbonates of SE France. - Sedimentary Gee]ogy, 132. 177-203 Brasler, M.D. (1995a): Fossil indicators of nutrient levels. 1. Eutrophication and climate change. - In: Bosence, D.W.J., Allison, P.A. (eds.): Marine Palaeoenvironmental analysis from fossils. - Ckological Society, London, Specia1 Publications, 83, 113-132 Brasier, M.D. (1995b). Fossil indicators of nutrient levels. 2. Evolution and extinction in relation to oligotrophy. - In: Bosence. D.W.J., Allison, P.A. (eds.): Marine palaeoenvironmental analysis from fossils. - Geological Society, London, Special Publications, 83, 133-150 Caplan, M.L., Bustin, R.M., Grimrn, K.A. (1996): Demise of a Devonian-Carboniferous carbonate ramp by eutrophication. - Geology, 34, 715-718 Dupraz, C., Strasser, A. (2002): Nutritional modes in coralrnicrobialite reefs (Jurassic, Oxfordian, Switzerland): evolution of trophic structure as response to an environmental change. - Palaios, 17,449-471 Follmi, K.B., Weissert, H., Bisping, M., Funk, H. (1994): Phosphogenesis, carbon-isotope stratigraphy, and carbonate-platform evolution along the Lower Cretaceous northem Teth~anmargin. -Geological Society of b e r i c a , Bulletin, 106, 729-746 Hallock, P. (1988): The role of nutrient availability in bioerosion: consequences to carbonate buildups. - Palaeogeography, Palaeoclirnatology, Palaeoecology, 63, 275-29 1 Hallock, P., Schlager. W. (1986): Nutrient excess and the de-

12.2 Estimating Paleoclimatic Conditions: Grain Association Analysis Shelf carbonates from warm- and cooI-waterregimes can be recognized by identifying skeletal constituents. Grain association analysis is one of the most promising tools of mlcrofacies studies, but the results should be verified on the basis of accumulated evidence (James 1997). Cold climatic settings, for example, are indicated by specific grain associations, bllt are more clearly proven by ice-rafted dropstones 01 calcite pseudomorphs after ikaite, a neta astable hexahydrate of calcium carbonate (see Sect. 2.4.1.5). Grain association patterns have a high potential in understanding climate change and paleolatitude shifts of carbonate ramps and platforms. The following text deals w ~ t hthe grain composi tion patterns of modem and ancient shelf carbonates. Examples of facies models deduced from these patterns are described in Chap. 14. 12.2.1 Concepts Modem shelf carbonates are formed in tropical and nor1 tropical zones. The criteria of these sediments were already discussed in Sect. 2.4.4. Tropical carbonate sedimentation at low latitudes takes place in warm-water environments. Non-tropical sedimentation occurs at mid- and high latitudes in warm-temperate and cool-

tl

20

temperate, and in polar cold-water environments (Fig. 2.9). The warm-temperate zone running roughly parallel to the equator at latitudes of approximately 30" S and 30" N forms the link between the tropical zone and the cool-temperate zone. Basic differences between tropical and non-tropical shelf carbonates relate to biota and diagenetic patterns (Tab. 2.7) as well as to the composition of grain associations. Grain association analysis Grain associations (sometimes also called grain assemblages) are characterized by the dominating skeletal and non-skeletal grains. Ooids, aggregate grains and peloids are abundant constituents of warm-water carbonates, but are absent in cool-water carbonates except for the peloids. The abundance and association of skeletal grains are controlled by the dependence of benthic organisms on environmental factors discussed in the preceding sections. The composition of skeletal grain associations is influenced by many factors including light, water temperature, salinity, and the rate of carbonate production versus the rate of siliciclastic input. Lees and Buller (1972) and Lees j 1975) tied the composition of modern low- and high-latitude shelf carbonates to temperature and salinity. The authors introduced the term clziorozoan skeletal association for tropical carbonates con~posedof calcareous green algae (Chior-ophyta)and hermatypic corals (Zoantharia). 'She name chlor-dgnl refers to tropical carbonates dominated by rhlomphycean rrlgae. The terinj~l-am01skeletal association was introduced for non-tropical carbonates consisting predominantly offomminifera and nwllusks. The term has proven to be less useful because of the wide compositional spectrum of non-tropical cool-water sedin1ents.A~a result, other expressions have come in use, partly based on the investigation of recent sediments (e.g. bryomol; Nelson 1988), partly on studies o f Tertiary (Hayton et al. 1005j. Cretaceous (Carannanteet al. 1988) and Late Paleozoic (~Reauchamp 1994; Beauchamp and Desrochers 1997) shelf limestones. The original concept favoring water temperature and, to 3 lesser content, salinity as the main controls on [he global distribution of chiorozoan (chloralgal) and foramol associations draws the boundary between both associations at the 15 "C to 18 "C or more generally at the 20 "C annual isotherm, which parallels the tropical zone in most parts of the world, except in areas affected by Coriolis-driven cold-water currents. In these areas, upwelling of nutrient-rich cold water favors the dominance of autotrophs (e.g. calcareous red algae) over heterotrophs. A significant impoverishment in the foramol association at the 10 "C and 5 "C isotherms leads to differentiation of temperate carbonates into

Photozoan and Heterozoan A s s o c ~ a t i o n \

warm-temperate and cold-temperate carbonates (Brookfield 1988). The predominantly siliceous polar hyalosponge sediments lie beyond the 5 "C isotherm, often in areas with semipermanent or permanent ice cover (Henrich et al. 1992). Photozoan and Heterozoan Associations James (1997) accentuating the light dependencelindependence of benthic carbonate-producing organisms introduced two major association categories: The Photozoan Association is characterized by an association of benthic carbonate grains including (1) skeletons of light-dependent organisms (algae; invertebrates, e.g. scleractinian corals and foraminifera, containing photosymbionts), and/or (2) non-skeletal grains (ooids, peloids and others), and (3) skeletons from the Heterozoan Association. The term replaces the term clllorozoan association and covers the chloralgal as well as many association types based on allcient limestones (see Box 12.9). It reflects the exisrence of shallow, warm-water, benthic calcareous communities and their resulting sediments, today mostly confined to tropical and subtropical settings. The Heterozoarz Association consists of benth~c carbonate particles produced by (1) organisms that arc light-independent, and plus or minus (2) calcareous red algae. The Heterozoan Association comprises man!, grain associations established for Cenozoic shelf casbonates (Box 12.9).It occurs from the poles to the equator and from the intertidal zone to the deep ocean. Cool-water carbonates are always heterozoan. But the Heterozoan Association does not necessarily inclicate cool-water sediments! Heterozoan associations predominate where the supply of other sediments (photozoan, pelagic or siliciclastic) is limited by environmental constraints. In warm water the Heterozoan Association characterizes environments below the photic zone. But hetcroLoan grain associations can also be produced in the photic zone as demonstrated by the Mediterranean Sea, where heterozoan-type organisms living on sea grass form carbonates in warm-temperate settings iBetzlcr et al. 1997). The photozoan and heterozoan concept is useful in tracing major and prolonged paleoclimate trends and1 or paleolatitudinal shifts. A rigorous use of the concept, however, can mask differences better indicated by the individual grain associations listed in Box 12.9. Grain association types Box 12.9 summarizes the criteria of grain association types of modem and ancient shelf carbonates. All

Grain Association I ype\

627

Box 12.9. Grain associlztion types of warm-water and cool-water shelf carbonates. The list records the name, author and age of the material used, followed by the abundant and (separated by a hyphen) minor constituents, and the observed or inferred setting. H (heterozoan) and P (photozoan) at the end of the paragraph indicate the position within the major Grain Associations distinguished by James (1997). Percentage composition corresponds to average values for grains not for bulk samples. Chlorosponge (Beauchamp 1994: Permian). Green alBarnamol (Hayton et al. 1995; Tertiary). Barnacles (-60%), bivalve mollusks (-20%). - Bryozoans, echino- gae, coralline calcareous sponges. - Benthic foraminifera, derms, benthic foraminifera. Non-tropical coastal and open- oncoids. Warm-water. Low latitudes. P. Chlorozoan (Lees and Buller 1972; modem). Calcaremarine shelf environments. H. Bimol (Hayton et al. 1995; Tertiary). Bivalve mollusks ous green algae, zooxanthellate corals. - Benthic foramin(infaunal and/or epifaunal; > 60%, up to 80%). - Bryozo- ifera, articulated coralline red algae, mollusks, non-skelans, benthic foraminifera, echinoderms, calcareous red al- eta1 grains. Tropical. Warm-water. P. Echinofor (Hayton et al. 1995; Tertiary). Echinoderms gae, barnacles. Non-tropical, but also tropical. H. Bryomol (Nelson 1988; modem and Tertiary). Bryo- (about 40%; mainly echinoids), benthic foraminifera zoans (> 50%), bivalve mollusks (infaunal and epifaunal). (-35%; foraminifera may outspace the echinoderms). - Benthic foraminifera, echinoderms, calcareous red al- Bryozoans, planktonic foraminifera. Non-tropical. H. Foramol (Lees and Buller 1972; modem). Benthic foragae, barnacles. Abundant in non-tropical, mostly cool- and cold-water environments, but also occurring in subtropi- minifera, mollusks. - Bryozoans. The term is now somecal and some tropical environments. High-energy open what outdated and replaced by new terms, including the shelves and ramps. Analysis of bryozoan growth form as- rhodalgal and molechfor associations. - Non-tropical. Temsists in distinguishing shallow and deeper settings (see over- perate and cool-water. H. Hyalosponge (Beauchamp 1994; Permian). Siliceous view by Smith 1995). 13. See PI. 10612, 3. Bryonoderm (Beauchamp 1994; Beauchamp and sponge spicules. The name is taken from modem exan~ples Desrochers 1997; Permian). Bryozoans, echinoderms (usu- (Henrich et al. 1992). Deep-water sediments (carbonates ally crinoids). - Brachiopods; rare peloids. Regarded as and cherts) at low latitudes, or shallow to deeper-water the equivalent of modern bryomol associations. Low-lati- settings at high latitudes. H. Molechfor (Carannante et al. 1988; Tertiary). Mollusks, tude deeper-water shelves to high-latitude, deep- to shallow-water shelves. Shallow and deep cool-water carbon- benthic foraminifera. Non-tropical, warm-temperate enviates are biotically alike, but differ in depositional texture ronments. H. Nannofor (Hayton et al. 1995; Tertiary). Planktonic (grainstone versus packstone). Cool-water and cold-water. foraminifera (-go%), nannofossils (coccolithophorids). H. See PI. 10611. Bryonoderm extended (Beauchamp 1994; Permian). Echinoderm spines, sponge spicules, benthlc foraminifera, Bryozoans, echinoderms. -The main composition corre- bryozoans. Not a typical shelf assemblage. Usually in offsponds to that of the bryonoder~nassociation, but addi- shelf deeper waters, but also in shallow, p,irtly enclosed tional biota elements (solitary and colonial corals, benthic basins. smaller foraminifera, larger foraminifera, brachiopods) may Rhodalgal (Carannante et al. 1986; Tert~ary).Calcareous crustose red algae (> 80%; commonly rhodoids), bryobe common. Non-tropical and tropical environments. H. Chloralgal (Lees 19'75; modern). Calcareous green al- zoans, benthic foraminifera, barnacles, bivalves, ecliinogae. - Benthic foraminifera, branching coralline algae, mol- derms. -Common in non-tropical warm-temperate settings. lusks. Tropical and wann-temperate zones. Controlled by High-energetic photic zone. Transitional between chlorozoan-dominated tropical areas and cold-temperate ones. salinity and water temperature. P. See P1. 105/2. Chloroforam (Beauchamp 1994; Permian).- Calcare- Also in tropical zones where environmental conditions preous green algae (dasyclads, udoteaceans), benthic foramin- vent the development of a chlorozoan facies. H. Rhodechfor (Hayton et al. 1995; Tertiary). Calcareous ifera (encrusting and free forms, smaller and larger foraminifera), non-skeletal grains (ooids, aggregate grains) and red algae (up to 80%), echinoderms (mostly echinoids). benthic foraminifera, bryozoans. - Barnacle$. bivalves. oncoids. Warn-water. Low latitudes. P. See PI. 105/1. Non-tropical temperate settings. H.

associations consider the most abundant skeletal constituents in wackestones, packstones, and grainstones. Some definitions are sat.isfied with the qualitative aspect, but most of them use quantitative data derived from point-counter measurements. Hayton et al. (1995) subjected the skeletal abundance data to cluster analyses that indicate the dominant groups and their variations. Grain association analysis is an essential element in categorizing Standard :MicrofaciesTypes (Sect. 14.3) and interpreting Standard Facies Models (Sect. 14.1.3).

12.2.2 Practical Advice, Examples and State of Current Information

12.2.2.1 Distinguishing Grain Association Types Attributing unknown samples to the associations summarized in Box 12.9 requires the following steps: Check criteria that point to autochthonous grain assemblages or to mixing and resedimentation of environmentally different grains.

-

Identify skeletal grains in thin sections. Determine their abundance, i.e. major and minor constituents, using semi-quantitative or point-counter techniques. Compare the results with the grain association types listed in Box 12.9. Note that these types are rather loosely defined and that sometimes 'minor' skeletal grains wili appear at a first rank position. Assign your grain associations to statistically based assemblages, using cluster analysis or more sophisticated methods (see Sect. 6.3). For Cenozoic carbonates consider larger foraminifera for differentiating warm-temperate and tropical zones (Betzler et al. 1997; Halfar et al. 2000). Of particular value in determining the skeletal grain assemblage of Cenozoic shelf carbonates is the composite triangular diagrarn developed by Hayton et al. (1095).

12.2.2.2 Examples Plates 105, 106 and 107 display Paleozoic, Cretaceous and Tertiary grain association types used to evaluate paleoclimatic conditions. The examples consider tropical and non-tropical shelf carbonates. Yon-tropical reef

Warm-Water Grain as so cia ti or:^

carbonates will be discussed in Sect. 16.2.5.2. The samples were selected from case studies whose paleolatitudinal position (derived from the paleomaps in Kiessling et al. 2002) is in fair accordance with the attribution of the sample to tropical, temperate or coldwater zones.

12.2.2.3 State of the Art The composition of Cenozoic warm-water carbonates is well known, although more studies are needed based on thorough quantitative data. Nearly all the studies of ancient temperate and cool-water carbonates deal with Ordovician, Late Paleozoic, Late Cretaceous and Tertiary examples (Box 12.10). Ordovician and Late Paleozoic case studies reflect the influence of glaciation on climate-dependent cold-water carbonates fom~edin periods of deglaciation. Regional climatic variations and the occurrence of tropical cold-water grain associations in warm-watei environments are discussed in papers on Cretaceous shelf carbonates (e.g. Gischler et al. 1994). Tertiary examples from southern Australia and New Zealand are of particular interest, because of the continuous record of temperate sedimentation in these s+ gions.

Plate 105 Skeletal Grain Association Analysis: 'Tropical Warm-Water Shelf Carbonates Modem low-latitude tropical and mid- to high-latitude non-tropical shelf carbonates differ in the overall composition of abundant and dominating skeletal grains. Common constituents in tropical warm-water settings are calcareous green algae, benthic foraminifera, mollusks and hermatypic corals. This gross composition can also be recognized in Mesozoic carbonates. Corals, larger foraminifera and some bivalves harbor endosymbionts that require light and are therefore limited to water depths of only a few meters. Non-skeletal particles are ooids, peloids and aggregate grains. The plate displays common warm-water grain assemblages of the Photozotr~~ Associtri~ontjpc. 1 Chlori$or~iinz gr-uin associatiori. This association is typified by the abundance of calcareous green algae and benthic foraminifera, often accompanied by non-skeletal grains. Characteristic chloroforam associations occur as early as rhe Paleozoic and are common in the warm waters of tropical platforms and shallow ramps. The sample is from the inner part of a Cretaceous extended ramp whose paleoposition was approximately 10" S. Algae are dasyclads (I);Cylindropor.ellu and others) and udoteaceans (11: Ai.ahic~ijrliunl).Foraminifera are represented by miliolids (M) and biserial textu!ariids (T). Other grains include cortoids and peloids (left corner). Note early marine and shallow burial interskeletal cements, a common feature of warm-water carbonates. Middle Cretaceous: Subsurface, Arabia. 2 Chloralgal grain association characterized by the abundance of calcareous green algae. This association has beer1 known since the Cambrian. Modem examples occur in protected areas of tropical and subtropical platforms. The plate-like fragments are Epimustopora Pia, an alga commonly assigned to the dasyclads. Some dasyclads are partly encrusted by foraminifera. Additional biota in modem chloralgal associations are benthic foraminifera and mollusks. Late Paleozoic associations commonly exhibit brachiopods (BR) instead of mollusks. The letter 0 indicates rare ostracods. The sample Early comes from the inner part of a locally restricted carbonate platform with a paleolatitude of -10" S. SMF 18-DASY. Permian: Carnie Alps. Austria.

Plate 105. W a r m - W a ~ e rG r a i n A s s o c i a t i o n s

629

Aspects of C i r n ~ nAssociat~ori,

Positive aspects of grain association analysis of repeated intervals of bryonodenn and chloroforam * Compositional analysis assists in recognizing long- carbonates in Late Pennsylvanian cyclothems (Samanterm climate changes and short-term climate fluctua- kassou 2002), and bryomol and chlorozoan carbonates tions. Long-term changes were studied by Beauchamp in the Upper Miocene ramps in southern Spain (Brachert (1994) in the Canadian Sverdrup Basin. Benthic grain et al. 1997). The evaluation of grain type associations is imporassociations, their biota and mineralogical criteria indicate a significant cooling for the Permian of the Ca- tant in understanding the drowning of carbonate platnadian Arctic. Other examples are known from the Late forms. Foramol platforms are characterized by low sediCretaceous of Sardinia (Carannante et al. 1995). Short- mentation rates. Rising sea level will cause drowning term variations of climate and sea level (cool lowstands of these platforms, whereas tropical chlorozoan platand warm highstands) are documented by successions forms may persist (Simone and Carannante 1988).

Plate 106 Skeletal Grain Association Analysis: Cold-Water and Temperate Shelf Carbonates Bryozoans are often the most abundant carbonate grains in non-tropical carbonates. They contribute to characteristic skeletal grain associations (e.g. bryomol association or bryonoderm association). Modem bryozoans are common in cool-water environments ranging from temperate to subpolar settings, but also live in tropical settmgs and reefs (Sect.10.2.3.4). Bryozoan sands originate in water depths of several tens of meters. The site o i active carbonate production and the accumulation of sands and muds is the deep shelf down to several hundreds of meters. Paleoenvironmental inferences to be drawn from bryozoan sediments of different ages must be handled with care because Paleozoic and post-Paleozoic bryozoan-rich carbonate deposits have strikingly different global distribution patterns. Paleozoic deposits spread through a wide range of latitudes, but were more common in the tropics except in times of significant cooling (Ordovician, -> 1; Late Paleozoic, -> 2). Post-Paleozoic and particularly Cenozoic deposits (-> 3) accumulated mainly in belts north and south of the equatorial zone. The plate displays examples of the Hetcrozourz Association. ! flryotzoder-nzgrain associafiorz: Characterized by abundant trepostomid bryozoans (B) associated with echinoderm frag

ments. Most echinodenns are cys~oidplates (C). In this example the different size of the echinoderm grains is not caused by transport, but reflects primarily different sizes of morphologic elements of cystoids (Dullo 1992). Heterozoan sediments consisting of bryozoans and echinodenns were widely distributed in platforms and ramps during the mid- to Late Ordovician cooling episodes related to continental glaciations. Bryonoderm associations occur in cool-temperate and cold waters of low-latitude deeper-water shelves and high-latitude, deep- to shallow-water shelves. The sample coincs from small bryozoan-cysioid mounds formed in paleolatitudes of > 60" S, most probably in cold-water environments. Late Ordovician (Wolaya Forn~ation):Valentintorl, Carnic Alps, Austria. 2 Bryomol grain association in cold-water carbonates of Gondwana sediments. Modem bryomol associations are typified by a high percentage of bryozoans and mollusk shells. Pre-Cenozoic bryomol associations are characterized by abundant bryozoans associated with brachiopods. The skeletal packstone consists of bryozoans (B) sometimes growing on mollusk shells, brachiopods (BR), a few echinodemi fragments (E) and rare bivalve shells (not in the photograph). The sedirnt.nt is strongly burrowed. Burrows are not compacted. Early cementation is missing, possibly because of the lack of aragonitr: particles providing the carbonate for cement formation. During the Permian, Tasmania lay at about 70" S in subpolar regions. The sea was periodically covered by sea-level ice. Terrigenous tillites pass laterally into marine carbonates that are associated with dropstones (Rao 1981). A cold-water-environment is reflected by the bryozoan-dominated heterozo:iri grain association, the prevailing original calcite mineralogy of the bioclasts, the low-diversity fauna, and the abundancs of bored brachiopods and echinodern~s.Early Permian (Berriedale limestone): Southeastern Tasmania, Australia. 3 Brynnzol grain association. The Tertiary sample exhibits the high abundance of bryozoans (B) and the common association of bryozoans with barnacles (BA) and corallinacean red algae (RA) characteristic of many Cenozoic bryomol cat-bonates. The limestone displayed in the thin section is an example of warm-temperate carbonates (Nebelsick 1989).This specific bryozoan-rich microfacies is limited to environments with low terrigenous input and low sedimentation rates. Bryozoans are represented by nodular encrusting celleporiform growth forms (CB) and thinner encrusting membranifonn growth forms (MB). Most skeletal grains consist of calcite and High-Mg calcite. Aragonitic grains (gastropods, cheilostorne bryozoans) have been leached, resulting in high moldic and open vuggy porosity (irregular white areas, e.g. at the top). 111 contrast to the sample shown in -> 2, early cementation was possible due to the dissolution of aragonitic skeletal grains. Paleolatitude was approximately 45" N. Late Tertiary (Eggenburgian, Early Miocene): Zogelsdorf, NW Vienna, Austria. -> 2: Sample provided by C.P. Ran (Hobart. Tasmania)

Plate 106. Cold-Watet a n d Temperate Grain Associations

631

632

Non-Tropical Grain A5sociarions

Box 12.10. Selected studies on ancient non-tropical carbonates. Most studies use grain-association patterns to differentiate non-tropical and tropical carbonates. Papers that can serve as a guide in comparing samples with established grain association types are marked by an asterisk. Tertiary: *Bemecker and Weidlich 1990; Bemecker et al. 1997; Betzler 1995, 1997; Betzler et al. 1993, 1995, *1996, "1997, "2000; *Boreen and James 1992, 1995; "Brachert et at. 1993, *2001; *Braga et al. 2001; Burgess and Anderson 1983; Carannante et al. 1996; Clarke et al. 1996; *Cunningham and Collins 2002; *Frameen et al. 1997; *Friebe 1994; *Gammon et al. 2000; Gordon et al. 1994; *Hayton et al. 1995; *Holdgate and Gallagher 1997; James 1991, * 1997; James and Bone 1992a, 1992b, *1994, *2000; Kamp et al. 1988; *Krautworst 1999; Lauriat-Rage et al. 1993; *Lukasik et al. 2000; MacGregor 1983; McGowran et al. 1997; *Mutti et al. 1999;Nebelsick * 1989, "1992,2000; Nelson 1978,1999; *Nelson and James 2000; Nelson et al. *1988; Nicolaides and Wallace 1997; "Randazzo et al. 1999; Scudeler Bacelle and Renato 1988; Unexpected grain associations and a few warnings: Many carbonate environments display a specific grain association related primarily to water temperature and associated biota. Nevertheless, unexpected grain associations are rather common in environments, where the prevailing temperature would point to a different association.

Shubber et al. 1997; Simone and Carannante 1988; Spjeldnaes and Moisette 1997; Vecsei and Sanders 1999 Cretaceous: Carannante and Simone 1987; Carannante et al. * 1988, 1995, * 1997; Gischler et al. 1994; *Sirnone and Carannante 1988; *Surlyk 1997 Carboniferous and Permian: *Beauchamp 1994; *Beauchamp and Desrochers 1997; *Brandley and Krause 1997; Draper 1988; *Ezaki et al. 1994; FanYingnian 1988; Hiineke et al. 2001; Martindale and Boreen 1997; *Rao 1981, 1988a, 1988b, "1991; Rao and Green 1982; *Samankassou 2002, *Stemmerik 1997, 2001; Weidlich 2002 Ordovician: *Brookfield 1988; *Dull0 1992; *Lavoie 1995; *Pope and Read 1997; Rao 1990, *1991; Rao and Wang 1990; Grimwood et al. 1999; Webby 2002

Several points must be taken into consideration when using grain associations as paleoclimatic proxies. Cool-water associations may be controlled by factors other than just water temperature. (1) Salinity control: The fora~nolsediments of the western Florida shelf situated approximately 25" N in tropical to subtropical warm waters can be explained

Plate 107 Skeletal Grain Association of Warm-Temperate and Tropical Warm-Water Shelf Carbonates Wann-temperate carbonates orig~naterti a zone between the tropical warm-water zone with mean bottom water temperatures > 22 "C and the mid- to high-latitude cool-temperate zone with mean temperatures from about 10 to 18 "C. The first zone is aragonite/High-Mg calcite-dominated and characterized by calcareous green algae and coral reefs, benthic foraminifera, and strong early cementation. The second zone is calcite-dominated and characterized by abundant bryozoans, bivalves, barnacles, echinids and foraminifera, and only weak cenienlation. For the Cenozoic, the boundary between the tropical zone and the warm-temperate zone is commonly drawn at the occurrence/absence of coral reefs and distribution patterns of larger foraminifera genera (Halloch 1986: tropical zone; Halfar et al. 2000: waml-temperate zone. See Sect. 10.2.2). The boundary between the warm-temperate and the cold-temperate zone is indicated by a marked decrease in biotic diversity and the coalplete absence of green algae and ooids. i

BI-yozoa-For-anzi~zifera association. Many Miocene shallow-marine carbonates are characterized by an assemblage or bryozoans, benthic foraminifera and corallinacean red algae. The thin section exhibits a bryozoan packstone rich irr celleporiform and branching zoaria. Bryozoans (B) are competing with coralline red algae (RA). Other fossils are rolaliid larger foraminifera (Heterostegina;H) and serpulid worms (S; Ditrupa). Heterosteginid foraminifera occur both in tropical and warm-temperate environments. The Heterozoan Association with corallinacean red algae and serpulids points lo warm-temperate conditions. This is in agreement with the approximate paleolatitude of 45" N. Late Tertiary (Middle Miocene): Holy Cross Mountains, central Poland. 2 Foraminifer-a-Bryozou association. The floatstone exhibits larger foraminifera considered as light-dependent because ( ~ f inferred algal endosymbionts. Orbitoid foraminifera are Orbitoides apiculata Schlumberger (0), Lepidorbitoides socinli.\ (Leymerie) - L, and Siderolites (SI); alveolinids are Nummufallotia cretacea (Schlumberger) - N. Other skeletal grains are bryozoans (B) and serpulids (Ditrupa; S). Black grains are nodular corallinacean red algae (RA). The sample comes from carbonates formed in subtidal areas between rudist reefs. The biotic composition of the Heterozoan Association as well as the paleolatitudinal position (>30°N) point to warm-water conditions in the transition zone between tropical and warm-temperate regions. Late Cretaceous (Late Maastrichtian): Sierra de Urbasa, Province Navarra, northern Spain. -> 1: Studencki 1988: 2: Schwentke and Wiedmann 1985

Plate 1 0 7 : W a r m - T e m p e r a t e a n d T r o p i c a l Skeletal G r a i n Associations

633

Paleownter Depth

by high or variable salinity controlling the biotic spectrum and producing a 'foramol' association in warmwater environments (Hallock and Schlager 1986). (2) Nutrient control: A nutrient-surplus caused by local upwelling can prevent the development of a characteristic chlorozoan biota with corals and calcareous green algae (Hallock and Schlager 1986). An ancient example is the foramol facies of the Late Cretaceous Lacazina limestone of northern Spain (Gischler et al. 1994). (3) Depth control: One of the major problems in the use of skeletal grain associations as indicators of paleoclimatic or paleolatitudinal conditions is the fact that water temperature changes observed from low to high latitudes can also be observed with increasing water depths (Brookfield 1988: Carannante et al. 1988). At low latitudes the 15 "C, 10 "C and 5 "C isotherms used as boundaries between tropical, warm-temperate and cold-ternperate shelf carbonates lie at increasing water depths beneath the sea surface. As a consequence, deep-water shelf carbonates fomled at low latitudes may be similar in grain association to shallow-water carbonates forming at high latitudes (Beauchamp 1994). (4) Trunsport control and mixing of grain types: Any evaluation of grain associations of non-tropical shelf carbonates should take into account the possibility of up- and downslope transport and resedimentation of grains on open high-energy shelves or ramps which are often affected by currents. Particular caution is nceded for grainstones and packstones formed in temperate and cool-water shelves whose composition might reflect a mixtu~eof grains originating from bathymetricaily and climatically different sources or may include relict grains of different age. Basics: Grain association analysis Beauchamp, B. (1994): Permian climatic cooling in the Canadian Arctic. - Geological Society of America, Special Paper, 288.295-246 Weauchamp. B., Uesrochcrs, A. (1997): Permian warm-to very cold-water carbonates and cherts in Northwest Pangea. In: James, N.P., Clarke, A.D. (eds.): Cool-water carbonates. --- SEPM Special Publications, 56, 327-347 Betzler, C., Brachert, T., Nebelsick, T.C. (1997): The warm temperate carbonate province. A review of facies, zonations: and deliminations. - Courier Forschungsinstitut Senckenberg. 201,83-99 Brachert, T.C.. Hultzsch, N., Knoerich, A.C., Krautworst, U.M.R., Stiickrad, O.M. (2001): Climatic signatures in shallowwater carbonates: high-resolution stratigraphic markers in structurally controlled carbonate buildups (Late Miocene, Southern Spain).- Palaeogeography,Palaeoclirnatology, Palaeoecology, 175,211-237 Brookfield, M.E. (1988): A mid-Ordovician temperate carbonate shelf: the Black River and Trenton Limestone Croups of southern Ontario, Canada. - Sedimentary Geology, 60. 137-151

Carannante, G., Cherchi, A., Sirnone, L. (1995): Chlorozoan versus forarnol lithofacies in Upper Cretaceous rudist limestones. - Palaeogeography, Palaeoclimatology, Palaeoecology, 119, 137-154 Carannante, G., Esteban, M., Milliman, J.D., Simone, L. (1988): Carbonate lithofacies as paleolatitude indicators: problems and limitations.- ~edimkntaqGeology, 60,333346 Halfar, J., Godinez-Orta, L., Ingle, J.C. (2000): Microfacies analysis of recent carbonate environments in the Southem Gulf of California, Mexico - a model for warm-temperate to subtropical carbonate formation. - Palaios, 15, 323-342 Hayton, S., Nelson, C.S., Hood, S.D. (1995): A skeletal assemblage classification system for non-tropical carbonate deposits based on New Zealand Cenozoic limestones. -Sedimentary Geology, 100, 123-141 Hiineke, H., Joachimski, M., Buggisch, W., Liitzner, 13. (2001): Marine carbonate facies in response to climate and nutrient level: The Upper Carboniferous and Permian of Central Spitsbergen (Svalbard). - Facies, 45, 93-136 James, N.P. (1997): The cool-water carbonate depositional realm. - In: James, N.P., Clarke, A.D. (eds.): Cool-water carbonates. - SEPM Special Publications, 56,l-20 Lees, A. (1975): Possible influences of salinity and temperature on modem shelf carbonate sedimentation. - Marine Geology, 19, 159-198 Lees, A,, Buller, A.T. (1972): Modern temperate-water and warm-water shelf carbonate sediments contrasted. - Marine Geology, 13, M67-M73 Nelson, C.S. (1988): An introductionary perspective on nontropical shelf carbonates. - Sedimentary Geology, 60,3-12 Randazzo, A.E, Miiller, P., Lelkes. G.. Juhisz, E., Hamor, T. (1999): Cool-water limestones of the Pannonian basin31 system, Middle Miocene, Hungary. -Journal of Sedimentary Research, A69,283-293 Schlanger, S.O. (1975): The geographic boundary between the coral-algal and the bryozoan-algal facies: a paleolatitude indicator. - 9th International Congress of Sedimentology, Nice, 187-193 Simone, L., Carannante, G. (1988): The fate of foramol ('tcmperate-type') carbonate platforms. - Sedimentary Geology, 60, 347-354 Further reading: KO21 (cold-water carbonates), K t 7 1 (wa ter temperature)

12.3 Assessing Water Depths In biological and ecological textbooks water depth i i discussed in terms of environmental constraints affecting the organisms or zonation patterns of benthic cornmunities. A separate chapter on water depths is generally missing, as opposed to geologicaI textbooks that try to answer the geologist's favorite question: 'Hou deep was the water?' The simple answer 'shallow' or 'deep' is no longer sufficient for sequence stratigraphy and should be replaced by more precise statements on the water depth within the shallow or deep depositional settings. A reliable sequence stratigraphy depends

Recogn171ng Water Depth

greatly upon the reliability of water-depth indicators and needs bathyn~etricallywell-characterized reference beds that reflect a defined sea-level position. The interpretation of cyclic sedimentation patterns requires paleobathymetric pinpoints. Bathymetric subdivision of benthic marine settings The morphology of the sea bottom and physically or biologically defined boundaries are used to differentiate environments situated at various water depths (Sect. 2.3.1). Physicaily defined boundaries are given by the tidal range, the fair-weather wave base and the storm wave base. These levels are characterized by changes in sediment conlposition and texture. Biological boundaries are given by environmental constraints that govern the depth distribution and zonation of benthic organisms. The most important limiting ecological factors are light (Sect. 12.1.4.1) and seawater temperature (Sect. 12.1.6). The absolute depth of these boundaries is exceedingly variable. Hydrostatic pressure may be a major control in depth distribution of benthic organsms when other parameters do not vary.

12.3.1 Hints to Paieowater Depths Paleowater depths car1 be deduced from various evidence, including paleontological and microfacies criteria, nlineralogical and geochemistry data, sedimentological features. and \tratigraphic and geomorphological aspects. Bathymetry and shallow-marine zonation patterns were summarized by Liebau (1980), various methodological approaches to paleobathymetric interpretations by Hallam ( 1967) and Luterbacher (1984). The following text lists some criteria that assist in the assessment of bathymetric zones. Most features characterize 'shallow' erivironments comprising intertidal and subtidal shelves. Specific criteria of 'deep-water' carbonate\ are discussed in Sect. 15.8. Biological evidence The evaluation of some of the criteria listed below is an integratal part of n~icrofaciesanalysis and SEM studies (calcareous algae, larger foraminifera, microborers, micro-encrusters). Other criteria require extensive palecologically-oriented investigations.

Calcareous algae: Depth distribution patterns of green and red algae are one of the best indicators of ancient depositional depths because of their strong light dependence. Untransported dasyclad green algae point to very shallow depths (tens of centimeters) down to only a few meters (Sect. 10.2.1.7). They record photic bottom conditions and occur within the tidal zone and

63 5

the upper subtidal zone. Depth range of udoteacean green algae is broader and extends from a few tens of centimeters to some tens of meters (Sect. 10.2.1.5).The lower limit of the chlorocline (defined by the range of modem non-dasyclad green algae) is about 100 m. In the context of the facies interpretation of limestones, this boundary is sometimes used to separate upper and lower subtidal depositional settings. Corallinacean red algae, common in Cretaceous and Cenozoic limestones, occur both in shallow and deeper waters, in tropical settings between 20 and 80 m, in cool-water settings down to more than 200 m (Sect. 10.2.1.2). Squamariacean red algae, known since the Early Cretaceous, occur at water depths down to about 50 m. Stromatolites: The formation of laminated microbial deposits is not as strongly light-dependent as the depth distribution of calcareous green and red algae. Ancient stromatolites were formed in depth ranges of meters to tens of meters. Growth forms, the composition and lamination of stromatolites is used to differentiate intertidal/subtidal and deeper subtidal environments (Sect. 9.1.4). Benthic foraminifera1 biofacies is useful for estimating paleobathymetry in Cenozoic and Mesozoic subtidal shelf carbonates (Sect. 10.2.2). The estimates are made based on biofacies models reflecting distribution in the modem ocean. The bathymetric arrangement of biofacies is regarded as a response to oceanic watermass structure. Some caution, however, is necessary because ancient taxa may have had broader bathymetric ranges. Larger foraminifera: Many larger foraminifera can be taken as good evidence of shallow photic environments because of their endosymbiotic associations (Hottinger 1988). Ratio of foraminifera1 groups: Various diagrams describing the proportion of benthic foraminifera (calcareous versus agglutinated groups; ratio of agglutinated, calcareous and planktonic groups; planktoni benthos ratio) are successfully used in estimating paleodepth conditions in shelf and deep-sea environments. Ostracods: The group occurs from very shallow waters to bathyal regions (Secl. 10.2.4.7).Many benthic groups have developed morphological adaptions to life on the deep and very deep aphotic ocean bottom, allowing bathymetric zones to be distinguished (Benson 1984). Zooxanthellate corals: Most modern scleractinian corals with endosymbiotic primary producers occur in shallow depths of a few tens of meters in water generally less than 100 m (Sect. 10.2.3.3). Fossil scleractinian reef corals and coral reefs are often regarded as evidence of well-lighted shallow environments. Considering the strong control of reef corals by factors other

636

than light and symbiosis, these interpretations argue for support by additional criteria (e.g. growth form patterns, community structure). Zooxanthellate symbiosis may have been independently established several rimes in scleractinian coral groups. The existence of zooxanthellate symbiosis in Paleozoic rugose corals is strongly debated. SEPM Special Publication 72 (Kiessling et al. 2002) contains much data on paleolatitudinal distribution and the occurrence of Phanerozoic reef corals in shaIlow or non-shallow environments. These data should be checked. Distribufiorzalpatte~-ns: Water depth on its own does not directly control distributional patterns, but bathymetric inferences may exist from environmental variables (e.g. temperature, salinity, substrate) that limit distribution with increasing depth. Benthic organisms exhibit distinct distributional patterns from the shoreline over the shelf to the shelf break. Gradient analyses of fossil benthic assemblages (e.g. n~ollusks,brachiopods) provide indications of relative water depths. Zorzatiorz pattel-17s of microbor-ers:Endolithic microborers are excellent paleobathyrnetric indicators for euphotic and dysphotic depths of shelves, reefs and ramps and also allow aphotic regions to be recognized (Sect. 9.3.4: Fig. 9.16). Zonation patterns of ancient endoliihs show a high coincidence between paleodepths derived from the composition of the endolithic associations and the paleodepths accounting for the paleogeographical situation and facies distribution, independent of the age of the examples. Comparative associations occurring in comparative paleowater depths are known from the Early Paleozoic to the recent. * Micr-o-ci7ci.uste1~s: Distributional patterns of millimeter- to centimeter-sized encrustations resulting from the growth of various heterotrophic and autotrophic organisms offer a good chance for rccognizing bathymetrically different environments of carbonate ramps above the fair-weather wave base, bc~weenthe wave base and the storm mkre basc, and belo~vthe storm wave base (Sect. 9.3.3; Fig. 9.10). Trace:fos.~ilc.owzn2unirie.s are strongly bathymetrically controlled ciue to their behavioral response to a bathymetric gradient in the food supply and oxygen. Paleobathyrnetric estimations based solely on trace fossil assemblages can have pitfalls, because factors other than nutrients (e.g. oxygenation and sedimentation rates) art' also major controls on the composition of the communities (see Frey et al. 1990 for a discussion). M~crofaciesevidence Specific grain types and fabrics can be used to differentiate very shallow, shallow, deeper and deep depositional settings. Fine-grained micritic matrix originates

Rccognizing Water Depth

everywhere. If you use the prevailing grain types of a limestone as bathymetric indicators, you should consider that the place of origin of sedimentary particles and the depth of the final resting place can differ. Ooids: Accumulations of calcareous tangentiallystructured ooids originate today in very shallow and shallow tropical waters down to a few meters of water depth (down to about 15 m). See Sect. 4.2.5. Aggregate grains: Depth distribution is similar to that of ooids. Many grapestones are formed in very shallow depths of only a few tens of centimeters. Cortoids: The existence of micrite envelopes around skeletal grains is not an unmistakable indication of shallow-water deposition (Sect. 4.2.3), but ancient grainstones consisting of a high percentage of cortoids occurring in association with calcareous green algae and mollusk grains can be taken as proof of shallow subtidal depths in euphotic and dysphotic environments within a range of some tens of centimeter to a few meterb. Oncoids: Marine carbonate oncoids are formed in the shallow euphotic and dysphotic zone, both in intertidal and subtidal environments (Sect. 4.2.4.1). Cyanoids point to water depths within the meter range. Ditferences in biotic composition (algae, microbes. foraminifera), lamination and nuclei offer possibilities of distinguishing oncoids formed in shallow or deeper set tings (Box 4.10). Ferruginous or phosphatic non-carbonate oncoids arc candidates for 'deepwater' but not all candidates pass the test. Khodoirls occur from intertidal to deep subtidal environments (Sect. 4.2.4.2). They originate in shallou and deep settings and often characterize the deeper part of the photic zone and the dysphotic zone below the wave base. The depth range of modem tropical rhodo~tls comprises tens of meters, often around 80 m, but may be extended to more than 180 m. Macroids are common at depths of several lens of meters. Non-trop~calrhodoids are foinied at varlous depths. Temperate-cool water rhodoids occur between about 5 and 150 nl with a maximum between 20-40 ni; polar cold-water rhodoids are known from depthr of about 60 to 100 m. Ancient rhodoids bear a high potential as paleodepth indicators, if the biotic composition and the growth strategies are thoroughly analyzed. Depositional fabrics Open-space und fenestral fabrics are excellent paleodepth indicators, but require detailed studies of the subcategories and the fabric types (Sect. 5.1.5). Birdseyes are good clues to water depths within a centimeter range; stromatactis-type structures have a wider

W a t e r D e p t h on a Carbonate Ramp

bathymetric range most probably comprising both photic and dysphotic settings. The common occurrence of Stromatactis mounds on deep ramps is regarded as clue for water depths of more than 100 m. Bioturbation fabrics reflect differences in nutrients, oxygen and substrate that may differ at different water depths. Abundance and burrowing types are used to distinguish shallow- and deep-water environments (Sect. 5.1.4). Mineralogical evidence Carbonate minerals: High hydrostatic pressure, low water temperature and high partial pressure of CO, lead to dissolution patterns of aragonite and calcite that characterize deep-water levels (Sect. 2.4.5.6). Authigenic minerals: Syndepositional diagenetic minerals, e.g. glauconite, charnosite or phosphorite are often used in defining water depths although this approach is strongly disputed (Amorosi 1992).

Sedimentological evidence Sedimentary structures: Physical depth boundaries, e.g, wave base and storm wave base are reflected by specific sedimentary structures as well as microfacies criteria (Sect. 12.1.2.1; Demicco and Hardie 1994). Stratigraphic evidence Estimates of absolute paleowater depth values are rare, but may be calculated using stratigraphic evidence if the original paleorelief between the platform and the basin is preserved and compaction is considered (Kenter 1990).

12.3.2 Case Study: Assessing the Water Depth of a Carbonate Ramp Fig. 12.12 and P1. 108 demonstrate the potential of calcareous algae and other biota in recognizing rela-

Fig. 12.12. Depth zonation along a Late Viskan ramp profile in the BCchar Basin, Western Algeria. The depth zonation is based on the distribution of algal assemblages and other biota and the recurrence of distinct associations in an analogue outcrop study of microfacies, paleontological data and limestone texture. Note the different distribution of green and red algae. Most bedded grainstones and packstones overlying the mound facies originated in the euphotic zone correI sponding to water depths I within the meter- to about 20 m range. Most mounds : Rarnose Bryozoans consisting of bafflestones, wackestones and mudstones werc formed in the aphotic zone characterized by the absence of algae. The numbers refer to bathymetric zones defined by qualitative and quantitative biotic composition. Oolitic and bioclastic carbonates formed in zone 1 exhibit large-scale cross stratification. zone 2 was dominated by crinoids which were frequently reworked by storms. Zone 3 is characterized by brachiopod shell banks above the coral thicket of zone 4. The upper part of zone 5 shows evidence of reworking. The zones 5 to 7 are parts of the mound facies. The ramp is differentiated not only by biota but also by the dominant sediment: Oolitic and bioclastic sands prevail on the upper ramp, crinoid banks on the mid ramp, and massive dome-shaped mounds on the deep ramp. The reservoir potential occurs in ooid and crinoid grainstones overlying the mounds, formed in the bathymetric zones 1 and 2 (Madi et al. 2000). Width of the bars indicate relative abundance of major fossil groups. FWB - fair-weather wave base, SWB - storm wave base. After Madi et al. (1996).

h iX

tive water depths. The western part of the Algerian BCchar Basin contains Mississippian carbonates that form superposed shoaling-upward sequences consisting of sponge-bryozoan-crinoid reef mounds and bedded shelf carbonates deposited on a ramp. Recognizing paleobathymetric zones is the basis for a facies model that assists in the hydrocarbon exploration of the up to 1200 m thick sequence (Bourque et al. 1995; Madi et al. 1996). Basics: Paleowater depths Bathurst, R.G.C. (1967): Depth indicators in sedimentary carbonates. - Marine Geology, 5 , 4 4 7 4 7 1

Water Depth o n a Carbonate R a m p

Benson, K.H. (1984): Estimating greater paleodepths ulth ostracodes, especially in past thermospherics oceans. -Palaeogeography, Palaeoclimatology, Palaeoecology, 48, 61-106 Cisne, J.I., Gildner, R.F. (1988): Measurement of sea level change in epeiric seas: The Middle Ordovician Transgression in the North American Midcontinent. - SEPM Special Publication, 42,217-225 Ekdale, A.A. (1988): Pitfalls of paleobathymetric interpretations based on on trace fossils assemblages. - Palaios, 3, 464-472 Geister, J. (1984): Die palaobathymetrische Verwertbarkelt der scleractinen Korallen. - Palaontologische Kursbiicher, 2,46-95 Hallam, A. (ed., 1967): Depth indicators in marine sedimen-

Plate 108 Recognizing Paleowater Depths The Eur-IJ Cui-boizifei-ouscm-bonatc rump of the Be'clzul-Basin in westein Algeria offers the possibility of checking the value of algae and other microfossils as indicators of bathymetric zones and in distinguishing different parts of a homoclinal ramp. Because of their sensitivity to the various spectra of visible light, the distribution of small encrusting green and red algae can be used to determine depth-related zones. The absence of green algae is interpreted as indicating deposition within the aphotic zone, whereas the presence of red algae combined with thc absence of green algae is thought to indicate the lower part of the photic zone with little light (dysphotic). Thc abundance of dasyclad green algae is indicative of the upper part of the pl~oticzone. The example reflects the profile of many other Early Carboniferous ramps with low-energy mud-rich 'Waulsortian' mounds in the lower part (see PI. 144), crinoid banks in the central part and high-energy calcareous sands in the upper part (Wright 1986; Jeffery and Stanton 1996). The plate displays facies-diagnostic algae and foraminifera characterizing the shallow photic and dysphotic partsof the Viskan ramp. Not shown are facies-diagnostic biota of the mound facies (cf. Fig. 12.12). lingdarcllacean and stachcinacean red alga are characteristic constituents of Carboniferous platforms and ramps (see Sect. 16.3.2.11 Box 10.2). The fossils shown on the plate occur in bedded skeletal grainstones and packstones deposited at shallow well-illuminated watcr depths (-> 1 and 9) and in somewhat deeper, less illuminated envir-onments below the fair-weather wave base (--> 2-8, 10). .!

Algai7foi-an~irziferal grainstone with the dasyclad alga Koninckopoi-u. Upper ramp. Photic bathymetric zone 1 . Foi-nmit7ifer.al gminstonc~~ ' i t hSu(~i-atninopsis.The uniserial test consists of globular and ovate chambers. 'l'hc Saccarninopsis microfacies is common in Early Carboniferous shelf carbonates. Massive skeletal grainstone forming a cap on the top of the mounds. Dysphotic bathymetric zone 5. 3-4 Gwen alga E.n~oturiselluElliott. The rhallus corresponds to a cylindrical tubc. The central part is subdivided by irregular. cavities f o m e d by thick pseudosepta ( 1 3 ) . The alga is a common element of Late Visean-Namurian shelf carhonale. lxwer ramp. Dysphotic bathyrnecric mni. 5. alga Issinella characterized by an erect cyliridrical shape and a fibro-radial wall, perforated by thin unramil'ted 5 C;I.WIZ branches. The alga is knou.11 frorn the Middle Devonian to the Late Viskan. Lower ramp. Upper part of the dysphotic bathymetric zone 5. 6 Red ulgul grnit7srorw with F~rsc~iclla cncrustirig bryozoans (B). Characteristic criteria of the alga are irregular concentric layers of elongated, undulating cells and a yellowish hyaline structure. Known from the VisCan to the Bashkirian. Fasi~icllir is comrnon in high-energy environments. Lower ramp. Dysphotic bathymetric zone 4. 7-8 Red nlgu Ungdar-ella Maslov with microbial encrustations (ME) characterized by ramified growth, rectangular and subquadratic cells and yellowish-hyaline structure. Known from the latest VisCan to the Early Permian. Massive crinoid mound facies. Lower ramp. Dysphotic bathymetric zone 4. Red alga Epistachcoidcs Petryk and Mamet. The encrusting form resembles Uqdui-ella, but differs in the vesicular central and the rectangular peripheral cells. This alga and similar taxa are common constituents of VisCan and Middle Carboniferous carbonate ramps. Upper ramp. Photic bathymetric zonc 1. Redalga Stacheia Brady, a thin encrusting form consisting of one or two rows of cells. Wall structure yellowish-hyaline. Known from the Vis6an and the Middle Carboniferous. Massive skeletal grainstone forming a cap on top of the mounds. Lower ramp. Dysphotic bathymetric zonc 3. 1-1 0 frorn Madi et al. 1990 3,

Plate I 0 8 Recognizlrlg P,ileowater Depth

639

Influence of Earthquakes

tary environments.-Marine Geology, 5,327-567 Hottinger, L. (1984): Zur Tiefenverbreitung von GroBforaminiferen - Palaontologische Kursbucher, 2, 140-147 Kenter, J.A.M. (1990): Carbonate platform flanks: slope angle and sediment fabric. - Sedirnentology,37,777-794 Liebau, A. (1980): Palaobathymetrieund ~kofaktoren:Flachmeer-Zonierungen. - Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen, 160, 173-216 Luterbacher, H.P. (ed., 1984): Palbbathyrnetrie: Konzepte, Methoden, Moglichkeiten, Probleme. - Palbntologische Kursbucher, 2,225 pp. Luterbacher, H.P., Van Hinte, J.E. (eds., 1984): Deep-water paleobathymety. - Palaeogeography,Palaeoclimatology, Palaeoecology, Special Issue, 48 Madi, A,, Bourque, P.A., Mamet, B.I. (1996): Depth-related ecological zonation of a Carboniferous carbonate ramp: Upper VisCan of BCchar Basin, Western Algeria. - Facies, 35,59430 Oberhansli, H. (1984): Stabile Isotopen: Hilfsmittel fur die Palaobathymetrie. - Palaontologische Kursbucher, 2,96103 Porrenga, D.H. (1967): Glauconite and chamosite as depth indicators in marine sediments. - Marine Geology, 5,49550 1 Seilacher, A. (1984): Bathymetrie von Spurenfossilien. Palaontologische Kursbucher, 2, lO4- 123 Vogel, K., Balog, S.-J., Bundschuh, M., Gektidis, M., Glaub, I., Kutschinna, J., Radtke, G. (1999): Bathymetrical studies in fossil reefs, with rnicroendoliths as paleoecological indicators. - Profil, 16, 181-191 Further reading: K 169

12.4 Looking for Seismic Events Earthquakes contribute to the destruction of carbonate sequences, soft sediment defonnation and dewatering, and the redeposition of marine sediment (Shiki and Cita 2000). Seismic shocks provoke limited internal fracluring of semi-lithified limestone beds, resulting in seismites characterized by a progressively higher degree of disruption and brecciation from the bottom to the top of the bed (Seilacher 1984; Plaziat et al. 1990; Martire 1996). Earthquakes can cause sediment deformation, create water escape structures, sedimentary dikes, sedimentary breccias, recumbent folds, ball-andpillow structures, and convolute bedding. But it must be noted that many of these features also originate in shallow-marine high-energy settings without earthquake-driven causes. Criteria used in evaluating ancient seismic activity in carbonate rocks are intraclast and breccia beds, and micro-scale dewatering structures. Intraclast linzesrones: Laterally continuous limestone beds composed of intraclast wackestones and packstones, and associated with deformation structures, intraformational conglomerates and breccias may point

to earthquake activity. Interesting case studies interprete Late Devonian intraclast carbonate parabreccias consisting of protointraclasts and interpreted as seismites (Spalleta and Vai 1984), and extended stratigraphic carbonate breccia beds in the Triassic Muschelkalk as seismites (Ruffer 1996). Unusual intraclastic limestones in Early Triassic carbonates formed after the end-Permian mass extinction have been explained as the result of tsunami waves related to seismic catastrophes (Wignall and Twitchett 1999).

Small-scaled dewatering structures possibly triggered by submarine earthquakes have been described from micritic limestones, and may be recorded by patchily distributed very small spar-filled voids within microbioclastic wackestones or mudstones. These structures have been interpreted as result of pore-water escape during partial sediment consolidation, spar- or sediment-filled flame structures (Plaziat et al. 1990), vertical, crinkled spar-filled micro-cracks, width about 1 mm or less, close-set parallel vertical micro-faults. Most examples described deal with carbonates formed on epeiric ramps, at platfonn-edges or on upper slopes. Basics: Paleoseismic events Ettensohn, F.R., Rost, N., Brett, C.E. (eds., 2002): Ancient seismites. - Geological Society of America, Special Paper, 359, 190 pp. Kullberg, J.C.,Oloriz, F., Marques, B., Caetano, P.S., Rocha, R.B. (2001): Flat-pebble conglomerates: a local marker for Early Jurassic seismicity related to syn-rift tectonics in the Sesimbracea (Lusitanian, Portugal). - Sedimentary Geology, 139,49-70 Plaziat, J.-C., Purser, B.H., Philobbos, E. (1990): Seismic deformation structures (seismites) in the syn-rift sed~ments of the NW Red Sea (Egypt). - Bull. Soc. GCol. France, ser. 8,6,419-434, Paris Pratt, B.R. (2002): Tepees in peritidal carbonates: origin via earthquake-induced deformation, with examples from the Middle Cambrian of western Canada. - Sedimentary Geology, 153,57-64 Ruffer, T. (1996): Seismite im Unteren Muschelkalk westlich von Halle (Saale). - Hallesches Jahrbuch fiir Geowissenschaften, B18, 119-130 Seilacher, A. (1984): Sedimentary structures tentatively attributed to seismic events. - Marine Geology, 55, 1-12 Shiki, T., Cita, D.S. (2000):Sedimentary features of seismites. seismo-turbiditesand tsunamiites - an introduction.- Sedimentary Geology, 135,7-9 Spalleta, C., Vai, B. (1984): Upper Devonian intraclast parabreccias interpreted as seismites. - Marine Geology, 55. 133-144 Further reading: KO86

13 Integrated Facies Analysis

To understand the formation and diagenesis of carbonate rocks mineralogical and geochemical data derived from the study of non-carbonate constituents, trace elements, and stable isotopes must be integrated. Other indicators for depositional and diagenetic conditions are organic matter and organic carbon. The, following shows how these data can be successfully combined with data based on rnicrofacies analyses. The first section deals with acid-insoluble residues in carbonate rocks and with authigenic minerals (oxides, silicates, sulfides, sulfates and phosphorites) formed after the deposition of the sediment. The second section discusses the value of trace elements in tracing the depositional and diagenetic history of limestones, and the importance of stable isotopes studied in the context of microfacies analyses. The third section gives a brief overview of organic matter in carbonate rocks.

13.1 Non-Carbonate Constituents Non-carbonate constituents of limestones and dolomites include clastic temgenous minerals as well as authigenic minerals. The study of clay minerals in acidinsoluble residues has a high potential for recognizing changes in erosion, climate changes and sea level and estimating the influx of siliciclastic material into shallow and deep-marine carbonate basins. Authigenic minerals grow after sediment deposition during diagenesis. They describe the course of diagenesis and are proxies for varying chemical and physical conditions.

13.1 .I insoluble Residues (IR): Clay Minerals and Detrital Quartz The input of terrigenous material into carbonate environments takes place by eolian transport, fluvial transport (e.g. during flash-floods from wadis), or by erosion of underlying rocks (e.g. in tidal zones).

Common clay minerals in mudstones and also in limestones are those of the smectite group, kaolinite, illite and mixed-layer illitefsmectites and chlorite. Kaolinite and other clay minerals are often used as paleoclimatic proxies, but the post-depositional diagenetic alteration of clays related to the depth of burial and the pore-water geochemistry must be thoroughly considered (see review by Ruffell et al. 2002). As a consequence of different transport behavior clay minerals are deposited in the ocean at different distances from the coast. The relative abundance of kaolinite as a detrital mineral may reflect proximity to the sediment source and deposition in relatively nearshore settings, whereas smectite may be deposited in deeper more offshore settings. The relative proportions of illitekaolinite to smectite in marine deposits have been used to infer shal1owing1regressive and deepeningltransgressive episodes. Techniques: The use of IR as paleoenvironmental indicators requires data on the amount of non-carbonate constituents and the mineralogical composition. The non-carbonate fraction of carbonate rocks is commonly extracted by acid digestion with a variety of acids and chelating agents (Miiller 1967), or by the use of acidic ion exchange resins (French et al. 1984).All these treatments may attack or even dissolve clay minerals. Weak organic acids may be more useful than diluted mineral acids. Clay and silt fractions are separated by sedimentation methods (see McManus 1988). Irzsoluble residues in carbonate rocks: All the clay minerals occurring in clays or sandstones are also known from limestones. A diagenetic origin of kaolinite found in limestones can be neglected because of the protective effect of the carbonate matrix against the formation of an acid milieu. The most common marine clay mineral is illite, which may be subjected to multiple redeposition. A diagenetic origin of illites found in limestones can not be excluded. Mixed-layer minerals are often the result of the transformation of illite to smectites in soils and subsequent transport to marine

I~isolubleResidues

basins. Detrital quartz grains within the silt fraction should be specifically studied with respect to crystal habit and surface features (Krinsley and Doornkamp 1973).

Signijlcance. The mineralogical composition of insoluble residues of carbonate rocks is commonly explained as the result of terrigenous input. However, the possibility of transformation or neoformation of minerals in the course of burial diagenesis must be kept in mind. The amount of clay in limestones varies strongly within a range of less than 1% and more than 10%. Clay content is often higher in micritic rocks than in high-energy grain-supported limestones that are winnowed with respect to fine-grained constituents. These differences are controlled by hydrodynamic conditions and depositional settings. Combined investigations of insoluble residues and microfacies have been successfully applied to facies analysis (Box 13.1) as well as to applied studies of carbonate rocks (see Chap. 17). Basics: Insoluble residues in limestones Adatte, T., Rumley, G. (1984): Microfacibs, minkralogie, stratigraphic et Cvolution des milieux de dep6ts de la platefornle berriaso-valanginienne des rCgions de Sainte-Croix (VD), Cressier et du Landeron (NE). - Bulletin de la Societt5 Neuchliteloise des Sciences Naturelles, 107,221-239 Bausch, NT.(1980): Tonmineralprovinzen in Malmkalken. Erlanger Forschungen, Reihe B, 8 , 7 8 pp. Bausch, W. (1996): Noncarbonates as controlling factor in reef growth and as a tool in reef stratigraphy (with examples from the Upper Jurassic of southern Germany). GottingerArbeiten zur Geologie und Palaontologie,Sonderband, 2,203-205 Bolliger, W., Burri, P. (1967): Versuch einer Zeitkorrelation zwischen Plattforrnkarbonaten und tiefermarinen Sedimenten mit EIilfe von Quarz-Feldspat-Schuttungen (mittlerer Malm des Schweizer Jura). - Eclogae geologicae Ilelvetiae, 60,491-507 Cater, J.M.L. (1984): An application of scanning electron microscopy of quartz sand surface textures to the environmental diagnosis of Neogene carbonate sediments, Finestrat Basin, south-east Spain. - Sedimentology, 31, 717-731 Chamley, H. (1989): Clay sedimentology. - 623 pp., Berlin (Springer) Chamley, H., Proust, N.-J., Mansy, J.-L., Boulvain, F. (1997): Diagenetic and paleogeographic significance of clay, carbonate and other sedimentary componentes in the Middle Devonian limestones of the western Ardennes, France. Palaeogeography, Palaeoclimatology,Palaeoecology, 129, 369-385 Diirkoop, A., Richter, D.K., Stritzke, R. (1986): Fazies, Alter und Korrelation der triadischen Rotkalke von Epidauros, Adhami und Hydra /Griechenland). - Facies, 24,105- 150 Piller, W., Mansour,A.M. (1994): Origin and transport mechanisms of non-carbonate sediments in carbonate-dominated

Box 13.1. Use of insoluble residues (IR) of limestones in facies analysis. Differentiating carbonate plalforms and ramps. Landlocked platforms are more commonly affected by siliciclastic input than open-marine oceanic platforms whose carbonates are generally very poor in non-carbonate residues. Different parts of carbonate platforms can be characterized by different mineralogical composition of the insoluble residues (Adatte and Rurnley 1984). Distinguishing depositional settings. Diagrams of IR content versus the siltlclay ratios of limestones can separate limestones formed in different basins (Bausch 1987). IR contents increase in platform-slope-basin transverses from platform-edge reefs to near-reef basinal facies and to off-reef basinal sediments (Durkoop et al. 1986). Assessing sedimentation patterns. Bed-per-bed studies of limestone sequences reveal quantitative differences in the composition of IR that may reflect cyclic depositional patterns and allow regressive and transgressive phases to be defied. Quantifying sedimentation rates. The proportion of carbonate and non-carbonate within limestone beds and bed thickness are useful for describing depositional rates. Recognizing hidden discontinuities in limestone sequences. Abrupt and significant changes in IR contents and marked differences in the mineralogical composition and in grain sizes from bed to bed may indicate depositional breaks. understanding source areas and hinterland ero~iort. Changes in erosion and the topography of the source areas are reflected by clay mineral composition, the illitekaolinite proportions, grain sizes and IR amounts (e.g. Weaver and Stevenson 1971). Understanding conditions in transitional terrestrialmarine areas. Clay-mineralogical assemblages of mark at the top of shallowing-upward sequences reflect fluctuating freshwater and marine conditions affecting shallow-water carbonates (Deconinck and Strasser 1987). Reconstructing transport mechanisms. SEM surface features of quartz grains are helpful in reconstructing source area and transport mechanisms of terrigenous input into carbonate environments (Cater 1984; Piller and Mansour 1994). Correlating platform and busin curbonutes: Compositional patterns of IR are used for stratigraphic correlation of shallow- to deep-marine carbonates on a regional scale (Gygi and Persoz 1986; Bausch 1996; Schweizer 1996). Changes in the amount of quartz and feldspars studied in IR and in thin sections of carbonates offer a possibility for recognizing time lines and time units (Bolliger and Burri 1967). * Approaching an understanding of major palcoclimatic differences. The abundance and composition of specific clay minerals in association with other proxies are used as key indicators for humid versus arid climates. The criteria used to define humid climate are the abundance of kaolinite, Th-enriched clays, siliciclastics, positive 613C values and wood. Arid climate may be indicated by the abundance of illite, U and K-rich clays, evaporites and carbonates, and negative 6I3C values (Ruffell et al. 2002).

-

Authigenic Mineral\

environments (Northern Safaga Bay, Red Sea, Egypt). Abhandlungen der GeologischenBundesanstalt Wien, 50, 369-379

Ruffell, A., McKimley, J.M., Worden, R.H. (2002): Comparison of clay mineral stratigraphy to other proxy paleoclimate indicators in the Mesozoic of NW Europe. -PhilosophicalTransactions of the Royal Society London, A360, 675-693

Singer, A. (1984): The paleoclimatic interpretation of clays in sediments - a review. -Earth Science Review, 21,251293

Velde, B. (1992): Introduction to clay minerals. Chemistry, origins, uses and environmental significance. - 208 pp., New York (Chapman and Hall) Further reading: K068, K153

13.1.2 Authigenic Minerals Authigenic minerals grow after sediment deposition during diagenesis. They include both replacive minerals and cements. Replacive minerals grow in the place of pre-existing minerals; they are formed from circulating pore fluids or they are alteration products of primary detrital grains. In contrast, cements are crystals growing within existing pore spaces. Excellent thinsection photographs of authigenic minerals can be found in Scholle (1979).

Fig. 13.1. Authigenic idiomorphic quartz crystals in a lime mudstone formed in a hypersaline environment. Note the well developed euhedral crystal shape. Compare P1. 10915 for a

SEM photograph. Late Cretaceous: Subsurface. Ras a1 Khaimah, United Arabian Emirates. Selectiveor pronounced silicification of fossils or other carbonate grains is a common feature (Maliva and Siever 1988; Herrig 1993; Whittle and Alsharhan 1994: Martin Penela 1995).

In thin sections silicification is recorded by idiomorphic quartz crystals or as chert appearing as a colorless microcrystalline aggregate similar in appearance to mi13.1.2.1 Silicification of Carbonates, Authigenic crite or microspar, but with much lower birefringence. Feldspar and Glauconite The term chert refers to a rock composed largely or entirely of fine-grained quartz. Cherts are formed in Silicification and idiomorphic quartz various environments including marine and freshwater A wide variety of sediments is commonly affected (hypersaline lakes) and at subaerial exposure surfaces by silicification in deep-marine as well as in shallow- (Knauth 1979). Marine environments can be differenmarine limestones. The major sources of silica in sedi- tiated using microfacies criteria (Affolter 1997). Many ments are: ( I ) siliceous tests and skeletal elements of chert nodules exhibit ghost structures after depositional organisms, (2) river input of solutions from the weath- textures and biota. In marine settings cherts occur as ering of continents in semi-arid climates (Laschet 1984), nodules varying in size from a few centimeters to about and (3) silica supplied in solution by hydrothermal vol- 30 cm, or in layers, often interbedded with shales or canic systems. limestones. Most chert nodules were formed early durSilicification of carbonate rocks involves replace- ing diagenesis. They are common in pelagic chalks. In ment of carbonate by silica as well as precipitation of shallow-marine areas (ramps, platforms) the input of pore-filling silica cement (e.g. Noble and Van Stemp- silica from land is an important source (Laschet 1984). voort 1989). Studies of silicified carbonates usually In shallow-marine settings chert nodules are sometimes focus on the description of fabrics (e.g. Wilson 1966), related to mixing zones. The silica for nodules and bedthe extent of silicification (minor, selective, pervasive), ded cherts occurring in pelagic deep-marine limestones and the relative timing of silicification with respect to is usually supplied by dissolution of sponge spicules diagenetic events affecting the carbonate host rock (see and radiolarians. Recent pure siliceous ooze of the South Hesse 1990b for an overview; P1.10917, 8). Silicifica- Atlantic may be an example of a diagenetic environtion fabrics may take the form of euhedral quartz (comment with early chert formation (Bohrmann et al. 1994). monly >0.5 mm), drusy megaquartz (0.5 to 10s mm), microquartz ( 1-4),quartz (-> 5 , 6 ) and gypsumfanhydrite (-> 9). Aspects of silicification are shown in -> 7 and 8. 1 Pyrite: Framboidal pyrite in residual clay seams of stylolites. The rounded aggregates consist of many tiny euhedral crystals. The size distribution of framboidal pyrite is a measure of redox conditions within sediments (Wilkin et al. 1996). Compare Fig. 13.1. SEM photograph. Late Cretaceous: Subsurface, Ras a1 Khaimah, United Arab Emirates. 2 Pyrite: Well-crystallized pyrite in residual clay seams of stylolites. Compare Fig. 13.2. SEM photograph. Same locality as -> 1. 3 Pyrirization of fossils. Monaxon sponge spicula. Parts of the siliceous spicula is replaced by pyrite, other parts by calcite. Late Jurassic: Northern Alps. Roman mosaic stone, Kraiburg am Inn, Bavaria, Germany. 4 Pyrite. Scattered pyrite crystals in a dolomitic mudstone. Same locality as -> 1. 5 Silicification. Authigenic quartz crystals in a lagoonal lime mudstone. Scattered 'hexagonal' replacement quartz crystals are not uncommon in fine-grained micritic limestones, and have been regarded as indications of hypersaline fluids (see Box 12.7). SEM photograph. Same locality as -> 1. 6 Silicijkution. The authigenic quartz crystals exhibit inclusions (arrows) of biogenic structures pointing to an early diagenetic replacement of the limestone. Middle/Upper Jurassic: Argelita north of Valencia, Spain. 7 Timing ofsilicificurion. The reef-building fossil Zondarella communis Keller and Flugel (stromatoporoid or stromatolite) is characterized by dome-shaped growth layers. The layers consist of densely-spaced discontinuous laminae (arrows) separated by micritic layers that have been replaced by blocky calcite (C) and euhedral dolomite crystals (D). Silicification (S) took place subsequent to dolomitization within solution voids. Silicification (chertification) of carbonate rocks, subsequent to dolomitization is a common feature (Whittle and Alsharhan 1994). Replacement of calcite by chert may occur at a much more rapid rate than that of dolomite (indicated by floating dolomite within chertified matrix). Ordovician (San Juan Fonnation, Late Arenigian): Las Lajas, Precordillera, western Argentina. 8 SiliciJication of rotaliid foraminifera: The silicification of the aragonitic shells took place subsequent to the redeposition of the shallow-marine bioclasts in deeper parts of a ramp, probably under shallow burial conditions. Early Tertiary: Southern Galala Basin, Egypt. 9 Evaporite-dolomite couplets formed within a sabkha environment. Alternating layers consisting of fine-grained dolomite (black) and gypsum. Requirements for the formation of supratidal sabkhas: (1) hot and arid climate, (2) sea-marginal location with adequate supply of saline water to the sabkha to develop evaporites, (3) supply of tenigenous mud, (4) protection from winds, and (5) low tidal range, allowing the groundwater level to be maintained within the zone of capillary rise. Crossed nicols. Early Tertiary (Eocene): Paris Basin, France. -> 8: Courtesy of J. Kuss (Bremen)

10 urn

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10 mn

100 urn

500 urn

2 mrn

2

rnrn

Pyrite in Limestones

636

coatings on hard substrates. Rounded glauconite grains reflect the original shape of fecal pellets or rounding by transport. The bulk of glauconite pellets may be clay debris from the sea floor, that passed through the digestive tract of burrowing organisms. In thin sections glauconite grains are easily identifiable by (a) green, blue-green, yellowish-green or brownish-green colors both in ordinary and polarized light. (b) speckled greenish birefringence and (c) a very fine granular texture. Significance. Glauconite is usually regarded as an indicator of marine environment, relatively shallow deposition and slow sedimentation. The mineral is often concentrated at discontinuity surfaces indicating depositional breaks (PI. 22/1,2). Different mineralogical compositions of glauconites, distinguished by diffractometric parameters, appear to be related to specific sequence system tracts (Amorosi 1993).

13.1.2.2 Sulfides: Pyrite

Opaque in transmitted light, pyrite is most readily identified by reflecting light owing to its characteristic yellow-gold appearance. Authigenic pyrites in limestones are usually developed in the form of cubic euhedral crystals (Fig. 13.2; P1. 10912). Pyrite attracts sedimentologists, for the mineral is a valuable indicator of chemical processes (Wilkin et al. 1996) and diagenetic stages (Hudson 1992). Fossils preserved in pyrite are attractive for their beauty and for morphological details revealed by pyritization (PI. 10913; Canfield and Raiswell 1991). Most of the pyrite in sedimentary rocks is of diagenetic origin, although detrital and synsedimentary pyrite occurs, too. Authigenic pyrite commonly forms under reducing conditions replacing organic material or in close proximity to organic material. Pyrite is formed in nonnal marine, euxinic, and freshAny use of glauconite as an environmental proxy water environments. Three principal factors limit ultimately how much pyrite is formed in sediments (Berner should consider three points: * Differentiation of authigenic and detrital glauconite 1985): (1) the amount and reactivity toward bacterial grains. Glauconites are formed coevally or non-coe- sulfate reduction of organic matter supplied to the sedivally with sedimentation, and intrabasinal or extra- ments; (2) the amount and reactivity toward H,S of detrital minerals supplied to the sediment; and (3) the basinal. availability of dissolved sulfate. The primary factor limAmorosi (1993) distinguished four major groups: (1) Intrabasinal authigenic glauconites formed in situ iting pyrite formation in normal marine sediments, e . g that have not undergone transport. those deposited in oxygenated bottom waters, is organic (2) Intrabasinal detrital glauconite grains transported matter. In euxinic environments pyrite can form at lofrom submerged structural highs or derived from in cations where no organic matter is deposited, because situ reworking processes. H,S is present everywhere in the bottom waters. Pyrite (3) Extrabasinal detrital glauconite grains eroded from formation in euxinic basins is limited by the amount older stratigraphic levels. Glauconite grains occur- and reactivity of detritic iron minerals. Very little pyring in association with terrigenous quartz may point rite is formed in freshwater lake and swamp sediments to this possibility (Pl. 4911; PI. 7516, 8). (4) Perigenic authigenic glauconites dispersed in an unconsolidated sediment on the sea floor, that have undergone transport from the area where they were fornled by tides, stomx or turbidity currents. * Glauconite gmins are particulariy common in ramp and platform carbonates of Cambro-Ordovician and Cretaceous age. This concentration points to specific and possibly non-actualistic conditions controlling the formation of the mineral. Differences between modern and ancient environments. The occurrence of glauconite cannot be used a priori as an environmental indicator of either mid-shelf and deeper water andlor a slow rate of sedimentation because of striking differences between modem and ancient glauconite-bearing limestones. Chafetz and Fig. 13.2. Authigenic pyrite crystals grown within layers of Reid (2000) showed that Cambro-Ordovician glauco- cyanobacterial oncoids rich in organic matter. Note the wellnite-rich strata were formed under shallow-water to tidal developed crystal shape. SEM photograph. Late Cretaceous: conditions. Subsurface, Ras a1 Khaimah, United Arabian Emirates.

seal rocks and assist in the understanding of climatically controlled cyclic sedimentation patterns. Abundant evaporite minerals are chlorides (halite) and sulfates (gypsum and anhydrite). Gypsum only occurs near the earth's surface, whereas anhydrite is formed at the surface and in the subsurface where it replaces gypsum. Gypsum may replace anhydrite on the uplift of evaporite sequences or after removal of overburden sediments. Fig. 13.3. Framboidalpyrite consisting of tiny euhedral crystals, formed within residual clays of stylolites. The clay lay- Depositional settings of evaporites ers are distinctly displaced by the growing pyrite. Compare Evaporites originate in a number of environments: P1. 10911. SEM photograph. Cretaceous: Subsurface, Ras a1 Continental (subaerial and subaqueous) settings are Khaimah, United Arabian Emirates. characterized by rapid variations in basinal flooding because of the rarely dissolved sulfate, which is a hun- and mineralogically and geochemically enormously varied deposits (e.g. playa deposits) originating from dred times lower than in sea water. Microscopic spheroidal clusters of interlocking crys- the waters of inland desert basins. Supratidal (marine sabkha). These evaporite depostals, termed framboidal pyrite because of the resemits form by evaporation in marginal-marine arid enviblance to raspberries, are known from shelf carbonates and deep-marine limestones (Fabricius 1961; Honjo et ronments (e.g. Persian Gulf and Red Sea). They are al. 1965). They have been explained as petrified sulfur characterized by eitherlor both siliciclastic and marine bacteria; these are crystal aggregates whose formation carbonate matrices and affected by meteoric and subwas triggered by bacterially controlled processes, or as aerial conditions. Distinct facies belts from seaward to inorganic crystallization out of iron sulfide gels. landward or from the base of the sedimentary sequence Framboidal pyrite occurs scattered or as rounded clus- upward are common (Alsharhan and Kendall1994). A ters within fine-grained micritic limestones (Pl. 10911) normal sabkha deposit consists of marine microbially and marls and residual clays (Fig. 13.3) as well as in controlled laminated carbonate or siliciclastic muds, the form of pyrite fillings within fossils (e.g. radiolar- nodular sulfates, desiccation crusts and windblown ians) and synsedimentary cavities. Early diagenetic geo- sands. The sulfates are usually gypsum or anhydrite petal fillings are potential tools for recognizing top and and occur in microbial beds as well as in beds characterized by nodular or enterolithic masses. The finebottom structures and tectonic overturning. grained carbonates are commonly dolomitized. Well Xewvrked pyrite (nodules, tubes and fossil stein- preserved gypsum and anhydrite can be distinguished kerns) is believed to occur widely through the Phan- in thin sections by their crystal morphology (Schreiber erozoic, where currents eroded muddy shelves or slopes et al. 1982). Intertidal to shallow subaqueous settings (hypersain anaerobic to minimally dysaerobic settings and exline sea). Evaporites occur as isolated crystals within humed pyrite grains from the underlying beds (Baird microbial mats, or build gypsum beds. The morpholand Brett 1986). ogy of the gypsum crystals and the mats is commonly well preserved as described from ancient examples. 13.1.2.3 Sulfates: Evaporite Minerals Deep subaqueous settings below the wave base and photic zone. These evaporites are characterized by a Authigenic evaporite minerals are common in lime- long-distance continuity of laminar beds consisting of stones and dolomites. Evaporites are often interbedded gypsum, anhydrite or halite, sometimes by co-occurwith dolomite, limestone and fine-grained siliciclastic rence with turbidites. shales, e.g. thin red beds. Gypsum crystals can be idenMarine evaporites originate from ocean waters in tified by characteristic lath-like crystal shapes, weak barred basins, shallow epeiric seas, or in deep-marine birefringence and low reliefs. Anhydrite is distinguished settings. For case studies of ancient evaporites see from gypsum by a higher relief and stronger birefrin- Handford et al. (1982) and Rouchy et al. (2001). gence. For thin sections of evaporites see Garrison et al. (1978), Scholle (1979) and Adams et al. (1984). Criteria Evaporites are sedimentary deposits composed of Primary sedimentary structures of evaporites include minerals precipitated from brines concentrated by ex- lamination, cross bedding, graded bedding, ripple marks tensive or total evaporation of water. Evaporites form and mud cracks. A laminated anhydrite or gypsum se-

Phosphates

Fig. 13.4. Calcitepseudomorphs after idiomorphic euhedral evaporite crystals formed in a near-coastal hypersaline lagoonal environment. Dark micritic grains correspond partly to black pebbles. Late Jurassic (Kimmeridgian): Imrnouzzer, western High Atlas, Morocco. After Hiissner (1985).

quence consists of alternating laminae of white calcium sulfate mineral and gray lamellae rich in dolomite and organic carbon. Another common fabric is the alternating occurrence of dolomite layers and layers of gypsum crystals. Diagenetic structures are abundant due to the extreme solubility of evaporite minerals. A common diagenetic structure is chicken-wire unhydrite consisting of elongated white anhydrite in a dark microcrystalline anhydrite matrix. Nodular gypsum or anhydrite structures are common in sabkha environments, but should be used with caution for environmental interpretations. Enterolithic folding is a structure characterized by an intralayer crumbling (PI. 12514). Evaporite-solution breccias have a well-defined base and may extend upward through many beds of different lithology (Sect. 5.3.3.3). Most primary and diagenetic structures, e.g. lamination patterns, chicken-wire and nodular structures as well as the replacement of anhydrite after gypsum or calcite after evaporite minerals (Fig. 13.4) can be studied in thin sections.

overprints (Schreiber et al. 1982). Both features can be observed on the scale of outcrops and cores as well as in rnicrofacies samples. The studies must consider the lateral and vertical development of depositional patterns, depositional cycles, e.g. shallowing-upward sequences, and the rapid changes in physico-chemical environmental controls. Common small-scale microfacies include stratification, massive sulfates with gypsum crystals, intercalation of thin marine carbonates, intervals with reworked gypsum grains, and claystones with nodular gypsum features (Aigner and Bachrnann 1989; Balzer 1997). Other thin-section criteria are: Depositional and diagenetic fabric lamination types, relation of layers (couplets, successive, unrelated, disrupted), microfolds, microbial relicts, quiet-water ooids, peloids or siliciclastic grains enclosed within evaporite layers, arenitic or ruditic resedimented gypsum. Crystal fabric morphology and growing habits of gypsum crystals e.g. single, twins (swallow tail), stellate clusters (Pl. 12512, or in massive beds. For classifications of evaporites based on structural and textural criteria see Maiklem et al. (1969), Langbein (1979) and Balzer (1997).

13.1.2.4 Phosphates

Phosphatic sediments form in different environments - not only beneath upwelling systems, but also atop seamounts,guyots and plateaus, on oceanic islands, and on some shelves and in epeiric environments. The formation of phosphorites includes two basic processes: (1) Physicochemical or biochemical precipitation of carbonate fluorapatite within the sediment, at the sediment/water interface and/or during diagenesis. Microbial contribution is important (Krajewski et al. Facies and microfacies studies of evaporites 1994). (2) Hydraulic and biological reworking of priThe different environments in which evaporite for- mary phosphorites by which phosphatic grains are conmation takes place are characterized by a great number centrated to form granular phosphorite. of sedimentary structures that are controlled by the conNon-transported phosphorites may occur in any or centration of various ions, temperature and organic all of the principal phosphorite settings; many of them components present, and reflected by nlicrofacies types. are associated with stratigraphic condensation, deposiEach variation produces differences in the style and tional breaks andlor unconformities. rates of sedimentation, no matter which evaporite minGranular phosphorites developed on shelves and in erals are present. Facies analyses of evaporite rocks and epeiric seas and appear to dominate phosphorite ocevaporite-carbonate sequences require differenting be- currences in the Phanerozoic record (Glenn et al. 1994). tween primary facies characteristics and diagenetic Phosphatic grains include peloids, compound grains,

Phosphatization

oncoids, and intraclasts. Primary phosphatic bioclasts (vertebrate bones, fish scales and teeth) are common. Phosphatization of carbonates Phosphatic particles also form by replacement of carbonate substrates, skeletal and non-skeletal carbonate particles (Fig. 4.16) as well as microbial structures, e.g. microstromatolites. These particles are characterized by marginal or complete impregnation/replacement showing various degrees of preservation of the primary structures (Swett and Crowder 1982; Rodgers 1994). Extensive interparticle, intraparticlecementation and rim cementation by cryptocrystalline carbonate fluorapatite, starting from the sediment-water interface and penetrating pelagic carbonates up to a few centimeters takes place during interruptions in sedimentation. Intraparticle cements occur within skeletal pores and boring pores. Skeletal material may be totally transformed to structureless carbonate fluorapatite peloids. Growth of gradually thickened phosphate coatings (rim cement) around a single or, more commonly, several phosphatized skeletal grains or lithoclasts may produce large coated composite grains. Interparticle cements and grains appear brownish and isotropic between crossed nicols, due to the presence of organic matter and iron oxides (Pl. 110).

649

Glauconite Amorosi, A. (1993): Use of glauconites for stratigraphic correlation: a review and case studies.- Giomale di Geologia, 55,117-137 Chafetz, H.S., Reid, A. (2000): Syndepositionalshallow-water precipitation of glauconite minerals. - Sedimentary Geology, 136,29-42 Odin, G.S., Matter, A. (198 1): De glauconiarum origine. Sedimentology, 28,611-641 Triplehorn, D.E. (1966): Morphology, internal structure, and origin of glauconite pellets. - Sedimentology, 6,247-266 Further reading: KO93

Pyrite Baird, G.C., Brett, C.E. (1986): Erosion of an anaerobic seafloor: significance of reworked pyrite deposits from the Devonian of New York State. - Palaeogeography,Palaeoclimatology, Palaeoecology, 57,157-193 Berner, R.A. (1985): Sulphate reduction, organic matter decomposition and pyrite formation. - Philosophical Transactions of the Royal Society of London, A315,25-38 W i e l d , D.R., Raiswell, R. (1991): Pynte formation and fossil preservation. -In: Allison, P.A., Briggs, D.E.G. (eds.): Taphonomy: releasing the data locked in the fossil record. - 337-387, New York (Plenum) Hudson, J.D. (1982): Pyrite in ammonite-bearing shales from the Jurassic of England and Germany. - Sedimentology, 29,639-667 Schallreuther, R. (1984): Framboidal pyrite in deep-sea sediments. - Initial Reports of the Deep Sea Drilling Project, 75,875-891 Schieber, J. (2002): Sedimentary pyrite: a window into the microbial past. -Geology, 30,531-534 Basics: Authigenic minerals in carbonate rocks Wilkin, R.T., Barnes, H.L., Brantley, S.L. (1996): The size Silicification of carbonates, authigenic quartz and feldspar distribution of framboidal pyrite in modem sediments: an DeMaster,D.J. (1981): The supply and accumulation of silica indicator of redox conditions. - Geochimica et Cosmoin the marine environment.-Geochimica et Cosmochimica chimica Acta, 60,3897-3912 Acta, 45, 1715-1732 Hesse, R. (1990a): Origin of chert: diagenesis of biogenic Further reading: KO67 siliceous sediments. - In: McIllreath, LA., Morrow, D.W. (eds.): Diagenesis. - Geoscience Canada, Reprint Series, Sulfates: Evaporites 4,227-252 Aigner, T., Bachrnann, G.H. (1989): Dynamic stratigraphy Hesse, R. (1990b): Silica diagenesis: origin of inorganic and of an evaporite-to-red bed sequence, Gipskeuper (Triasreplacement cherts. - In: McIllreath, LA., Morrow, D.W. sic), southwest German Basin. - Sedimentary Geology, (eds.): Diagenesis. - Geoscience Canada, Reprint Series, 62,5-25 4,253-276 Balzer, D. (1997): Mikrofazies-Analyse von Ca-SulfatgeKastner M., Siever, R. (1979): Low temperate feldspars in steinen des Zechstein. - Geologisches Jahrbuch, D, 106, sedimentary rocks. - American Journal of Science, 279, 3-99 435-479 Handford, C.R., Loucks, R.G., Davies, G.R. (1982): DeposiLaschet, C. (1984): On the origin of cherts. - Facies, 10, tional and diagenetic spectra of evaporites - a core work257-289 shop. - SEPM Core Workshop, 3,395 pp. Maliva, R., Siever, R. (1988): Mechanisms and controls of Renault, R.W. (ed., 1989): Sedimentology and diagenesis of silicification of fossils in limestones. - Journal of Geolevaporites. - Sedimentary Geology, 64,207ogy, 96,387-398 Richter-Bernburg, G. (1985): Zechstein-Anhydrite. Fazies Martin Penela, A.J. (1995): Silicification of carbonate clasts und Genese. - Geologisches Jahrbuch, A85, 1-82 in a marine environment (Upper Miocene, Vera Basin, SE Rouchy, J.M., Tabemer, C., Peryt, D. (eds., 2001): SedimenSpain). - Sedimentary Geology, 97, 21-32 tary and diagenetic transitions between carbonates and Molenaar, N., de Jong, A.F.M. (1987): Authigenic quartz and evaporites. - Sedimentary Geology, 140, 1- 189 albite in Devonian limestones: origin and significance. - Sarg, J.F. (2001): The sequence stratigraphy, sedirnentology Sedimentology, 34, 623-640 and economic importance of evaporite-carbonate transiWilson, R.G.C. (1966): Silica diagenesis in Upper Jurassic tions. - Sedimentary Geology, 140,9-34 limestones of southern England. - Joumal of Sedimen- Shearman, D.J. (1991): Evaporite sediments and rocks: the tary Petrology, 36,1036- 1049 calcium sulphate and halite facies. - 304 pp., New York Further reading: K064, K091, KO92 (Van Nostrand)

650

Warren, J. (1999): Evaporites. Their evolution and economics. - 448 pp., Oxford (Blackwell) Further reading: KO65 Phosphates and phosphorites Baturin, G.N. (1982): Stages of phosphorite formation. Developments in Sedimentology, 33,344 pp. Bentor, Y.K. (ed., 1980): Marine phosphorites. - Society of Economic Paleontologists and Mineralogists, Special Publications, 29, 259 pp. Follmi, K.B. (1996): The phosphorus cycle, phosphogenesis and marine phosphate-rich deposits. - Earth Science Reviews, 40,55-124 Glenn. C.R., Follmi, K.B., Riggs, S.R., B a t u ~G.N., , Grimm, K.A., Trappe, J., Abed, A.M., Galli-Oliver, C., Garrison, R.E., Ilyin, A.V., Jahl, C., Roehrlich, V., Sadaqah, R.M.Y., Schidlowski, M., Sheldon, R.E., Siegmund, H. (1994): Phosphorus and phosphorites: sedimentology and environments of formation. - Eclogae geologicae Helvetiae, 87,747-788

Phosphatization of Carbonate Rocks Lucas, J., Privost-Lucas, L. (2002): Phosphorite and limestone, two independent end-member products of the range of bio-productivity in shallow-marine environments. -In: Glenn, C.R., Prkvost-Lucas, L., Lucas, J. (eds.): Marine authigenesis: from global to microbial. - SEPM, Special Publications, 66, 117-127 Nothold, A.J.G., Jarvis, I. (eds., 1990): Phosphorite research and development. - Geological Society of America, Spccial Publications, 52,326 pp. Soudry, D. (2000): Microbial phosphate sediments. - In: Riding, R., Awramik, S.E. (eds.): Microbial sediments, 127-136, Berlin (Springer) Trappe, J. (1998): Phanerozoic phosphorite depositional systems. A dynamic model for a sedimentary resource system. - Lecture Notes in Earth Sciences, 76,316 pp. Trappe, J. (2001): A nomenclature system for granular phosphate rocks according to depositional texture. - Sedimentary Geology, 145, 135-150 Further reading: KO66

Plate 110 Phosphatization of Carbonate Rocks Microfacies studies of phosphate rocks and phosphorites reveal striking textural similarities within carbonate rocks. Phosphate fabrics are the result of biologic and authigenic processes as well as replacement of carbonate particles and sediment. The term phosphate rock defines a rock composition with less than 50% phosphate components, and phosphorite those of more than 50% phosphate components. Most ancient phosphate deposits consist of granular phosphoritic rocks (Soudry and Nathan 1980). Paralleling the texture-based carbonate classification of Dunham (1962), orthochemical/microbial phosphorites, characterized by in situ phosphatic precipitates. and granular f'abrics with alloche~nicalphosphate grains can be distinguished (Trappe 2001). The grains are derived from: (a) the reworking of orthochemical/microbial phosphorites resulting in structureless phosphate grains, variously called pellets, peloids or ovoids. The spectrum of these grains also includes phosphatic ooids, oncoids, pisoids, and fecal pellets. (b) Epigenetic replacement of carbonate grains, mostly bioclasts and intraclasts; (c) phosphatic bioclasts, e.g. vertebrates and inarticulate brachiopods, some arthropods, and conodonts (see Fig. 4.9). Strong phosphat~zationof grains may be characteristic of lag deposits (-> 2,3, 5); see the Standard Microfacies Type 14. Except for the difference in mineral composition, thin sections of phosphorites look very much like thin sections of limestones. Thc plate displays texture types and grain types of granular phosphorites and phosphatized carbonates. Rock and grain names follow the suggestions of Trappe (2001). 1 Phosclast gr-uinstonp. Silicified bone bed. Phosphatic skeletal grains ('phosbioclasts'; predominantly fish bones ani!

shark teeth, S), reworked and redeposited phosphate concretions (RPC) and black rounded lithoclasts ('phosclasts', PC) derived from the reworking of phosphatized hard grounds. Cretaceousnertiary (Maastrichtian-Ypres): Imi-n-Tanoute, Morocco. 2 Phosooid packsro~zcwith layers of fish bones (FB) and phosphatized lithoclasts and phosooids within a carbonate matrix. Note the open internal meshwork (arrow) and the solid exterior covering of the fish bones. Cretaceous/Tertiary (Maastrichtian-Ypres): Chichaoua, Morocco. 3 Phosclast rudstorle. Large phosphatized lithoclasts (L) and phosphatic skeletal grains. Early Tertiary (Thersirea Formation, Lutetian): Chichaoua, Morocco. 4 Phosphatized ooids ( 0 0 ) and small rounded skeletal grains. Same locality as -> 3. 5 Phosplzutized lithoclasts. Grains exhibit complete or only marginal phosphatization. Early Carboniferous (Delle Phosphatic Member, Oseagean-Meramecian): Eureka Mining District, Mammoth Mountain, U.S.A. 6 Hardground with microbial phosphate crusts (arrows). The rock is a phoslitho/bioclastic packstone. Note the high compositional variability of grains comprising lithoclasts, ooids, quartz grains and skeletal grains including bryozoans (B), echinoids (E) and serpulids (S). Early Tertiary (Amniter Formation, Thanet-Ypres): Iris-n-Sebt, Morocco. -> 1-6: Courtesy of J. Trappe (Bonn)

Trace Elements

13.2 Geochemical Proxies 'This section summarizes trace element analysis and the use of stable isotopes in evaluating paleoenvironrnents and the diagenetic development of carbonate rocks. The text focuses on the potential of combined geochemical and microfacies studies. See Brand and Veizer (1980) and Morse and Mackenzie (1990) for basic information on the geochemistry of sedimentary carbonates.

13.2.1 Trace Elements Trace elements in carbonate rocks occurring at concentrations between and wt.%, or less, are either bound to the carbonate phase studied in RFA analyses, or to the non-carbonate phase represented by acidresistent residues and measured by AAS and ICP (Bausch 1994). For a time trace elements of limestones were usually investigated in bulk samples, but are now studied in samples differentiating micritic matrix, carbonate cements, fossils and other grains using various microsampling techniques. Trace element studies concentrate on specific trace elements (e.g. strontium or manganese) or investigate a large set of elements followed by statistical analyses. Multivariate analyses are a fundamental prerequisite in testing possible relations between microfacies types and chemical data (e.g. Rijhl and Strasser 1995; Kiihl et al. 1996) In the 1970s many authors stated that rare element variations in carbonate rocks were controlled by variations in lithology, skeletal composition and diagenesis and that rare element patterns might reflect sedimentary facies patterns (Wedepohl1970;Veizer and Demovic 1974). A more skeptical view is expressed in modem studies concluding that geochemical data can be used in facies diagnoses only when the lithologic and diagenetic development of the rock unit are well known (Oesterreich 1992). This view results partly from the difficulties relating geochemical data to microfacies types based on minor paleontological or textural differences. A crltical combination of microfacies types and trace elements is successful if microfacies types are defined using the major compositional criteria (e.g. Lintnerova and Hladikova 1992; Masaryk et al. 1993).

linked to the carbonate phase, depending on the similarity of the crystal chemistry of Sr and Ca, and Mg and Mn and the substitution of CaCO, by MgCO, in calcite and aragonite. The major proportion of limestone studies using trace elements as facies indicators is concerned with these elements. Examples of the application of strontium and manganese distribution to the facies analyses of carbonates are listed in Box 13.2. Strontium Starting with the investigations by Veizer and Demovic (1973), who recognized an apparently facies-controlled bimodal distribution of Sr in Mesozoic micrites, strontium is used as a proxy for paleoenvironmental and diagenetic conditions of carbonate sediments. A common approach aims at recognizing significant correlations between specific strontium contents and carbonate rock types (expressed by microfacies or lithology) and/or depositional settings (e.g. shallow-marine versus basinal). Sr values decrease from modem sediments to ancient limestones and to dolomites. Modem shallowmarine aragonite is characterized by high Sr values (up to 10 000 pprn). Calcite has lower amounts of strontium. The incorporation of Sr in carbonates depends on the primary mineralogy, water temperature, salinity, vital effects, and average CaISr content of seawater. Most ancient limestones have only a few hundred ppm Sr, mainly due to the loss of Sr during neomorphic processes, such as transformation of aragonite to calcite, repeated dissolution-precip~tationprocesses and recrystallization causing a progressive diagenetic elimination of Sr over time. Diagenesis in an open system influenced by freshwater results in decreasing, low and homogeneous values. Manganese The incorporation of Mn into marine carbonates depends on the primary mineralogy, crystallographic conBox 13.2. Selected reference? dealing with combined facies and trace element analycec of carbonate rocks.

13.2.2 Strontium and Manganese Favorite Tools for Facies Studies

Strontium: Al-Hashimi 1976;Auernheimer 1983; Bausch 1968; Cerny 1978; Cioni et al. 1973; H.W. Fliigel and Wedepohl1967; Gittinger 1969; Imrehet al. 1965; Kranz 1976; Krejci-Graf 1965;Jorgenson 1981,1986; Llavador et al. 1983; Masaryk et al. 1993; Matheos et al. 1990; Oesterreich 1992; Prasada and Naqvi 1977; Sakae et al. 1981; Santos Garcia 1992; Strohmenger and Dozet 1991 ; Veizer and Demovic 1973, 1974: Veizer et al. 1971

Many studies deal with common elements such as Sr, Mn or Mg. A relatively new approach is the use of Rare Earth Elements. Mg, Sr and and sometimes Mn are

Manganese: Bencini and Turi 1974; Corbin et al. 2000; Oesterreich 1992; Pingitore 1978; Santos Garcia 1992; Shanmugam and Benedict 1983; Shimmield and Price 1986; Turi et al. 1980

-

S ~ g n l f l c a n c eof ? r a c e Elements

trols, the concentration of manganese in seawater, Eh conditions, organic matter and microbial processes. The behavior and the vertical distribution of solid-phase and dissolved manganese and iron in modem marine sediments are well known for pelagic and hemipelagic deepsea sediments (e.g. Aller 1990) and for anoxic coastal muds of temperate shelf environments (references in Berner 1980 and Chester 1990). Geochemical data from tropical shelf sediments, particularly reef-derived carbonates and shallow-marine carbonate muds are less common (Alongi et al. 1992).

13.2.3 Significance of Trace Elements in Facies Studies of Carbonate Rocks A basic assumption in the use of trace elements for facies interpretation is that a relationship exists between the trace element content of a carbonate and the concentration of this element in the water where precipitation takes place. Trace elements are applied to a wide range of topics but many applications need further refinement. Depositional condition,^ Differentiating depositional and post-depositional physico-chemical conditions. Pu/eot~~i~~i~~o~zrr~c~~~tuI,fui tor5

Recognizing paleosalinity. In neritic and coastal marine environments, the Sr and Mg contents of fossil carbonates are correlated, allowing these elements to be used as indicators for the influence of continental and marine waters (Renard 1986). Sr has been used as a salinity indicator in 'Triassic lagoonal-reef systems (Kranz 1976). The value of Na as a paleosalinity indicator (Masaryk et al. 1993) is somewhat problematic (Hardie 1987; Buggisch et al. 1994) but sodium is a possible index to the salinity of diagenetic solutions. Recogniz~ngpaleowater depths (Shanmugam and Benedict 1983). Differentiating low and high energy sediments, e.g. low values in micr~ticlagoonal carbonates; high values in grainstones (Strohmenger and Dozet 1991).

originally of aragonite are usually Sr-rich; those consisting of calcite are poor in Sr. Recognizing the primary aragonite and calcite mineralogy of fossils (Veizer 1983; Dodd and Stanton 1990). Diagenesis Tracing marine, meteoric and burial diagenesis (e.g . Al-Hashimi 1982). Commonly used elements are strontium, manganese and magnesium. Recognizing meteoric diagenesis, typically with enrichment of Fe and Mn and depletion in Sr and Na (e.g. Pingitore 1978; Brand and Veizer 1980; Al-Aasm and Veizer 1982). Checking possible diagenetic alterations of shells used for stable isotopic studies (Grossman et al. 1996). Sedimentation patterns Recognizing the shallowing of basins, reflected by decreasing Sr contents (Lintnerova et al. 1988). Recognizing breaks in sedimentation, discontinuities, hardgrounds (Marshall and Ashton 1980). Distinguishing allochthonous input and autochthonous sedimentation input. Indication of the input of allochthonous sediment (versus autochthonous origin). Detrital input is indicated by elements related to silicate minerals (e.g. Si, Al, K, Fe). Understanding bedded limestone sequences. Geochemical analysis of bedded lin~estonescan be in1 proved by sampling bed per bed, also analyzing the intercalated marls and evaluating trace elements against the background of overall non-carbonate contents (Bausch 1994). Two-component diagrams are useful in distinguishing clastic, semiclastic and diagenetic elements and correlating profiles. Reefs and carbonate platform Differentiating carbonate sed~mentsformed in different parts of ancient reef complexes (Chester 1965; Davies 1972; Fliigel and Flugel-Kahler 1963; Matheos and Morsch 1990; Oesterreich 1992). Differentiating inner and outer platforms (e.g. Orehek and Ogorelec 1981).

Stratigraphy Prirrzczi-y mineralogy Assessing stratigraphic boundaries (Jorgensen 1981). Recognizing the original mineralogical composition Establishing chemostratigraphical correlations for of micrites and microspar. Sr and Mg concentrations in Mesozoic and Cenozoic pelagic carbonates based on micrites mimic the concentrations in the precursor ara- regional (and global) trace-element stratigraphy using gonite or Mg-calcite (Wiggins 1986), because these el- Sr and Mg contents (Renard 1986). ements are incorporated into calcite at equal rates during diagenesis. During aragonite dissolution and cal- Long- and short-term paleoceanographic j7~ictuation.s The Sr content of pelagic carbonates varies with cite precipitation Sr is excluded from aragonite and builds up in solution. Phanerozoic micrites consisting time (Renard 1986). Long-term variations are influ-

enced by diagenesis, variation of the distribution coefficient and Sr/Ca ratio in seawater,e.g. caused by variations in hydrothermal activity. Short-term variations are controlled by sea-level fluctuations. Basics: Trace elements in carbonates Brand, U. and Veizer, J. (1980): Chemical diagenesis of a multicompone~ltcarbonate system - I. Trace elements. Journal of Sedimentary Petrology, 50, 1219-1236 Carpenter, S.J. and Lohrnann, K.C. (1992): Sr/Mg ratios of modern marine calcite: empirical indicators of ocean chemistry and precipitation rate. - Geochimica et Cosmochimica Acta, 56, 1837-1849 Churnet, H.G., Misra, K.C. (1981): Genetic implications of the trace distribution pattern in the upper Knox carbonate rocks, Copper Ridge District, East Tennessee. - Sedimentary Geology, 30, 173-194 Kiihl, A., Schreiber, A., Scheffler, E. (1996): Faziesanalyse mit multivariatstatistischenund geostatistischen Methoden des Dunklen Knotenkalkes von Wildenfels. - Freiberger Forschungshefte, C, 462,212 pp. Morse, J.W.. Mackenzie, F.T. (1990): Geochemistry of sedimentary carbonates. - 707 pp., Amsterdam (Elsevier) Popp. B., Anderson, F.T., Sandberg, P.A. (1986): Textural, elemental and isotopic variations among constituents in Middle Devonian limestones, North America. - Journal of Sedimentary Petrology, 56, 715-727 Renard, M. (1986):Pelagic carbonate chemostratigraphy (Sr, Mg, I", '"c). -Marine Micropaleontology, 16, 117-164 Veizer, J. ( 1 983): Chemical diagenesis of carbonates: theory and application of trace element techniques. -In: Arthur, M.A., Anderson, T.E, Kaplan, I.R., VJeizer.J., Land, L.S. (eds.): Stable isotopes in sedimentary geology. - Soc. Econom. Paleunt. Miner., Short Course, 10, 3.1 - 3.100 Further reading: K 153, K 1%. K 156

emphasize some applications in the context of integrated facies analyses. Current stable isotope analyses of carbonate rocks aiming for paleoenvironmental or diagenetic interpretations are based on the investigation of micrites, carbonate cements or fossils. Stable isotopes in fossils (predominantly foraminifera, mollusks and corals) are used in reconstructing growth rates of organisms (Wefer and Berger 1991), paleoclimatic fluctuations and paleooceanographic circulation patterns. Isotope signals recorded in planktonic foraminifera offer excellent possibilities for recognizing climate cycles, paleoproductivity and changes in ocean circulation. Carbonate oxygen isotope paleothennometry offers a possibility to evaluate paleo-seawater temperatures. The fractionation of oxygen isotopes is temperature dependent. The ratio of the two most common isotopes (160 and l80) in carbonate fossils can, in principle, be used to reconstruct the temperatures of ancient oceans. Cenozoic and Mesozoic foraminifera are commonly analyzed in order to determine sea-surface, deep-water and bottom-water temperatures but mollusk and brachiopod shells and carbonate cements are used as well (see Corfield 1995 for discussion).

Over the past forty years, the '60/180record in micro-organisms preserved in deep-sea sediments has provided basic data in establishing a history of long-term oceanic temperature and global ice volume during the Quaternary. Many investigations are concentrated on the Cenozoic, but increasingly more studies are dcciphering the isotopic history of Mesozoic and Palco13.2.4 Stable Isotopes zoic oceans and carbonates. 613Cshifts during the PhanMarine and non-marine carbonates have been used ex- erozoic and excursions at or near boundaries are betensively in documenting changes in the ratios of iso- lieved to represent changes in the global carbon cycle. topic species. Stable isotope analysis is one of the most Phanerozoic isotope carbon curves are used for correpowerful tools in deciphering the depositional and di- lations identifying climate variations, determining the agenetic history of carbonate rocks and fossils, and un- isotopic composition of seawater, and recognizing secuderstanding environmental controls and global changes lar variations of organic carbon and carbonate organic o f climate and oceanography. The studies are based on production/burial rates. Cenozoic and ancient (particuoxygen isotopes (180, '"0). carbon isolopes (13c, 12c) larly Paleozoic) isotope patterns exhibit considerable and strontium isotopes (87Sr,'%r: Elderfield 1987). differences, possibly due to primary differences in the Deita values (%c) describe the difference in isotope ra- isotopic composition, e.g. caused by exchange betwcen t ~ o between s samples and standards. Standards are usu- sea water and oceanic ridges; differences in water ternally based on CaC03 (PDB standard; Pedee Formation peratures; different biological fractionation of ancient Belemnite) or H,O (SMOW standard; Standard Mean organisms as compared with modern organisms; Ocean Water). Measurements are whole rock data or changes in productivity, and diagenetic alterations. individual constituent data (crystals,grains) that require microsampling techniques. Well-preserved brachiopods (Wadleigh and Veizer Basic information on the methods and use of stable 1992; Wenzel 1997; Samtleben et al. 2000) and carisotope analyses can be found in Arthur et al. (1983), bonate cements (Lohrnann 1985; Carpenter et al. 1991) Faure (1986) and Hoefs (1 997). The following notes are assumed to be the most suitable phases for deci-

USCof Stable Ihotopes

phering the original oxygen and carbon isotope signatures of carbonate rocks. The value of stable isotope data in paleoenvironmental and facies interpretation of ancient carbonates and carbonate skeletons depends strongly on the critical assessment of possible diagenetic alterations of the material investigated (Fig. 3.9). Diagenetic alterations of shells may be identified by investigating trace elements, cathodoluminescence and shell microstructures (critical remarks in Barbin and Gaspard 1995). Early meteoric diagenesis and burial diagenesis can greatly alter the original isotope ratios incorporated in skeletons or carbonate rocks (Censi and Montana 1994). Diagenetic alterations of micrites may be reflected by strontium and carbonate contents as well as by SEM and cathodolun~inescencedata. The use of stable isotopes in facies analyses of ancient carbonates Stable isotope studies have been successfully applied to Phanerozoic carbonates of all ages and to carbonates formed on ramps (Joachimski 1991) and platforms (Weis and Preat 1994; Rasser and Fenninger 2002), reefs (Aharon 199I), slopes and basins (Jenkyns and Clayton 1986; Masaryk et al. 1993). Measurements cover whole rock samples, the micritic matrix (aiming at differentiating allomicrites and automicritcs), inter- and intraparticle cements (aiming at differentiating shallow-marine. burial and meteoric conditions), as well as individual grains (e.g. oncoids, ooids) and well-preserved shells. A common tool of these studies is the search for isotopic signals that would indicate changes from marine to meteoric conditions and subaerial exposure of the depositional environment, or depositional breaks. The basic prerequisite for the successful application of stable isotopes to facies analyses of limestones is the combinarioiz of the geochenliCLZI data with field observations, paleontological features and microfacies criteria (Samtleben 2000; Munnecke et al. 2003). Basics: Stable isotopes Arthur, M.A., Anderson, TE, Kaplan, I.R., Veizer, J., Land, L.S. (1983): Stable isotopes in sedimentary geology.- Soc. Econom. Paleont. Miner., Short Course, 10, 1-151 Banner, J.J. (1995): Application of the trace element and isotope geochemistry of strontium to studies of carbonate diagenesis. - Sedimentology, 42, 805-824 Barrera, E., Tevesz, M.J.S. (1990): Oxygen and carbon isotopes: utility for environmental interpretation of recent and fossil invertebrate skeletons. -In: Carter, J.G. (ed.): Skeletal biomineralization: patterns, processes and evolutionary trends. Volume I. - 557-566, New York (Van Nostrand) Berger, H., Vincent, E. (1986): Deep-sea carbonates: Reading the carbon-isotope signal. - Geologische Rundschau, 75,249-269

Brand, U., Veizer, J. (198 1): Chemical diagenesis of a multicomponent carbonate system. - 2: Stable isotopes. - Journal of Sedimentary Petrology, 51,987-997 Clauer, N., ChaudhuriS (eds., 1992): Isotopic signatures and sedimentary records. - Lecture Notes in Earth Sciences, 43,529 pp. Elderfield, H. (1986): Strontium isotope stratigraphy. Palaeogeography, Palaeoclimatology, Palaeoecology, 57, 71-90 Faure, G. (1986): Principles of isotope geology. - 589 pp., New York (Wiley) Hoefs, J. (1997): Stable isotope geochemistry. 4th edition. 201 pp., Berlin (Springer) Hudson, J.D., Anderson, T.F. (1989): Ocean temperatures and isotopic compositions through time. -Transactions of the Royal Society Edinburgh, 80, 183-192 Joachimski,M. (1991): Stabile Isotopen (C, 0 ) und Geochemie der Purbeck-Mikrite in Abhangigkeit von Fazies und Diagenese (BemasianlSchweizer und Franzosischer Jura, Siidengland). - Erlanger Geologische Abhandlungen, 119, 1-'114 Marshall, J.D. (1992): Climatic and oceanographic signals from the carbonate rock record and their preservation. Geological Magazine, 129, 143-160 Morse, J.W., Mackenzie, F.T. (1990): Geochemistry of sedimentary carbonates. - Developments in Sedimentology, 48,707 pp., Amsterdam (Elsevier) Munnecke,A., Samtleben, C., Bickert, T. (2003): The Ireviken event in the lower Silurian of Gotland, Sweden - relations to similar Palaeozoic and Proterozoic events. - Palaeogeography, Palaeoclimatology,Palaeoecology, 195,99-124 Popp, B.N., Anderson, T.F., Sandberg, P.A. (1986): Brachiopods as indicators of original isotopic compositions in some Palaeozoic limestones. -- Geological Society of America, Bulletin, 97, 1262- 1269 Rasser, M., Fenninger, A. (2002): Paleoenvironmental and diagenetic implications of 6180 and 613C isotope ratios from the Upper Jurassic Plassen limestone (Northern Calcareous Alps, Austria). - Geobios, 35,41-49 Schidlowski, M. (2000): Carbon isotopes and microbial sediments. - In: Riding, R.: Awramik, S.M. (eds.): Microbial sediments. - 84-95, Berlin (Springer) Schulz, H.D., Zabel, M. (eds., 2000): Marine geochemistry. - 455 pp., Berlin (Springer) Veizer, J., Hoefs, J. (1976): The nature of 0 1 s / 0 1 6and Cii/ Ci' secular trends in sedimentary carbonate rocks. - Geochimica et Cosmochimica Acta, 40, 1387-1395 Veizer, J., Fritz, P., Jones, B. (1986): Geochemistry of brachiopods: Oxygen and carbon isotope records of Paleozoic oceans. - Geochimica et Cosmochimica Acta, 50. 1679-1696 Wadleigh, M.A., Veizer, J . (1992): %/160 and 13C/"C in lower Paleozoic articulate brachiopods: Implications for the isotopic composition of seawater, - Geochimica et Cosmochimica Acta, 5 6 , 4 31-443 Wefer, G., Berger, W.H. (1991): Isotope paleontology: growth and composition of extant calcareous species. - Marine Geology, 100,207-248 Wenzel, B,C. (1997): Isotopenstratigrapische Untersuchungen an silurischen Abfolgen und deren palaoozeanographische Interpretation. - Erlanger Geologische Abhandlungen, 129, 1-117 (cum lit. !) Further reading: K157, K158 (stable isotopes in sediments), K159 (stable isotopes in organisms and fossils)

6 5 (>

13.3 Organic Matter in Carbonate Rocks The formation of carbonate rocks can be considered as a part of a three-component system (Ricken 1993). Organic matter, carbonate and siliciclastic sediment may settle concurrently, but at different rates, and intermix at the sea floor resulting in a particular sediment composition. A change in the flux of one component can cause diluting or concentrating of the other two components expressed by the ratio of organic carbon to carbonate. Organic matter is a trace constituent of calcareous skeletons (Crick 1989), carbonate cements (Dravies and Yurewicz 1985),carbonate particles (Davies et al. 1978) and speleothems (Shopov et al. 1994). The presence and composition of organic matter in carbonates is used as a tool in estimating the productivity and the origin of 'black shales'. recognizing depositional facies and delineate diagenetic fabrics, understanding the controlling effect of organic constituents on mineral growth, providing fingerprints for the source of organic matter in sediments and the origin of source rocks, and determining the txming of hydrocarbon migration.

The ~nolecularstructure of organic matter controls mineral growth (Ramseyer et al. 1997). Inorganically precipitated carbonates (speleothems, cements; Dravies and Yurewicz 1985)incorporate during growth adsorbed organic matter bet~veensubmicroscopic subunits of crystals. Biologically secreted carbonates incorporate biogenic tissue between crystals. The organic matter is derived from soils (speleothem calcite), dissolved organic matter (marine carbonates) and biological decay products (aragonitic coral skeletons). Biogtochcrtiir~illpmxies: Sedimentary compounds within sedimentary rocks supply important biomarkers and paleoenvironmental indicators (de Leeuw et al. 1995).Marine as well as non-marine environments are characterized b5. thc combined presence of specific compounds. Biornarkers are (aj proxies for various groups of bacteria. cyanobacteria, algae, vascular higher plants, and animals (Peters and Moldovan 1993); (b) assist in estimating shoreline proximity of modem carbonates, and allow paralic margins dominated by mangroves, and subtidal mud-banks characterized by sea grass to be distinguished; and (cj are fundamental for evaluating of organic-rich carbonate rocks (Hopf et al. 2001). Paleoenvironmental characteristics, such as photic zone,

Organrc M a t t e r

anoxia, hypersalinity, microbial sulfate-reducing activity, algal blooming, paleo-upwelling and paleo-surface seawater temperature are indicated by molecular and/ or isotopic characteristics. Most work on organic petrology and palynofacies concerns siliciclastic rocks. But biomarkers are also promising and sensitive paleoenvironmental and depositional indicators in carbonate rocks as demonstrated by the distinct differences in autochthonous biomarkers in reef, platform and basin carbonates allowing facies interpretations to be refined with respect to salinity, oxygenation and water stratification (Marynowski et al. 2000). Cyclicity and its bearing on sequence stratigraphy is another tool that can be elucidated by organic matter distribution in limestones (Bombardiere and Gorin 2000).The identification of silt-sized remains of organisms may be facilitated by biornarkers as well, e.g. the differentiation of grains derived from calcareous algae and from corals (Bbhm et al. 1980). Basics: Organic matter Crick, R.E. (ed., 1989): Origin, evolution and modern aspects of biomineralization in plants and animals. -- 536 pp., New York (Plenum Press! De Leeuw, J.W., Frewin, N.L., Van Bergen, P.F., Sinninghe Damste, J.S., Collinson, M.E. (1995): Organic carbon as a paleoenvironmental indicator in the marine realm. -- In: Bosence, D.W.,Allison, P.A. (eds.): Marine paleoenvironmental analysis from fossils. --Geological Society of L,ondon, Special Publication, 83. 43-71 Gautier. D.L. (ed., 1986): Roles of organic niatter in sediment diagenesis. - Soc. Econ. P:iIeont. Mi~xs..Special Publications, 38, 203 pp. Huc, A.Y. (1990): Deposition of organic facics. -- American Association of Petroleum Geologists. Studies in Geology, 30, 234 pp. Marynowski, L., Narkiewicz, M.. (I;relowski, C. (2000): Biomarkers as environmental indicators in a carbonate complex, example from the Middle to Upper Devonian, Ilol>, Cross Mountains, Poland. - Sedimentary Geology. 137. 187-211 Peters, K.E., Moldovan, J.M. (19'9.3): The biornarker guide interpreting molecular fossils in petroleum and ancient sediments. - 363 pp., Englewood Cliffs (Prentice Hall) Ramseyer, K., Miano, T.M., D'Orazio, V., Wildberger, A,. U7agner, T., Geiste~;J. (1997): Nature and origin of 01.ganic matter in carbonates from speleothems, nlaririe cements and coral skeletons. - Organic Geochemistry. 2.6. 361-378 Ricken, W. (1993): Sedimentation as a three-component system. -Lecture Notes in Earth Science. 5 1 , 2 1 1 pp.. Berlin (Springer) Tyson, R.V. (1995): Sedimentary organic matter. Organic fac i e ~and palynofacies. - 6 15 pp , London (Chapman and Hall) Whelan, J.K., Farrington, J.W. (eds., 1992): Organic matter: productivity, accumulation and preservation in recent and ancient sediments. - 533 pp., New York (Columbia Press) Further reading: KO69

14 Depositional Models, Facies Zones and Standard Microfacies

Preceding chapters of part 2 of this book were focused on defining microfacies types, recognizing paleoenvironmental constraints and using an integrated approach to facies analysis. Chapter 14 introduces carbonate facie~ models, underlines the importance of environmentcontrolled distribution patterns of organisms, and gives an overview of Standard Microfacies Types and their application to the facies analysis of limestones. The latter topic is expanded in the case studies described in Chap. 15. A depositionnl faiies model is the essence of the criteria and controls extracted from case studies of modem and ancient sediments. Facies z m e s ( F Z )are belts differentiated according to the changes of' sedimentological and biological criteria across shelf-slope-basin transects. Standur-d r?~icr;qfucicstypes (SMF) are derived from local microfacies types looking at joint paleontological and/or sedimentological criteria. Associations of SMFs are additional criteria for recognizing ancient facies zones.

14.1 Depositional Facies Models A facies model is a generalized summary of a given depositional system (Walker 1992). The information required for this summary is taken from Iocal case studies of modern and ancient examples. Facies models should act as norms for purposes of comparison, as a frame\vork and guideline for future observations, as a predictor of new geological situations, and as an integrated basis for the system that it represents. Sensitive and predictive facies models are important in the exploration of hydrocarbons and limestone resources (see Chap. 17 and 18).

14.1.I Conceptual, Dynamic and Computer Models Carbonate facies models correspond to different categories and comprise conceptual, dynamic and numerical models.

14.1.1.I Conceptual Models The first facies models proposed for carbonate rocks were conceptual models trying to show spatial distribution patterns of rock types and biota, usually along a coast-basin traverse. These static models were strongly influenced by the investigation of modem subtropical and tropical carbonates. For a long time the Bahamas, Florida and the Persian Gulf served as paradigms for shallow-marine carbonate platforms. Starting with the 'X-Y-Z model' by Irwin (1965) new ideas were introduced into carbonate models that were supposed to reflect the overall environmental controls on carbonate deposition on shelves and include the differences between ancient depositional settings and modem settings. Using the commonly observed successions of facies belts of Holocene and Phanerozoic carbonates, Wilson (1975) established a Standard Furies Mo&l that describes Standard Facies Zones (FZ) of a I-itnnreJtropical carbonate plarfornz along a strongly generalized shore-to-basin transect. This Wlron morl~l(see Sect. 14.1.3) had a strong impact not only on the interpretation of the litho- and biofacies of carbonate rocks but also on the use of microfacies types as indicators of facies zones and depositional conditions. Extending the generalizations made by Fliigel (1972) for common microfacies types of Triassic carbonates, Wilson introS' duced a set of 'Standard Mic~-&cic.s T Y ~ P (SMFI which aimed at categorizing common and widely distributed Phanerozoic microfacies types. About the same time, Ahr (1973) recognized the difficulties related to the application of' the rimmed platform concept to the facies distribution of many Paleozoic and Mesozoic shelf carbonates and proposed the carbonate ramp model. This model summarizes the facies distribution on a gently sloping surface from the coast to deeper water without a morphological break at the shelf edge. Ramps differ from rimmed shelves in the absence of continuous shelf-marginal reef trends, the location of high-energy deposits near the shoreline and not at the shelf edge, and the lack of shallow-water derived clasts in deep-water parts of the ramp. Ginsburg and James (1974), Kendall and Schlager (1981), Schlager (198 1, 1992, 2000). Read (1 982,

Numerical Models

1985),Tucker (1985), Tucker and Wright (l990), James and Kendall (1992), Handford and Loucks (1993), Sanantonio (1993), Read et al. (1995) and Lukasik et al. (2000) provided enlarged and more differentiated models ofcarbonate depositionnl envir-onnzents.These papers discuss the subdivision and internal subdivision of ramps and emphasize the importance of non-rimmed shelves, drowned and pelagic platforms, as well as epeiric platforms and ramps. Some of these models are discussed in Sections 14.1.4 to 14.1.8.

14.1.1.2Dynamic Models Depositional systems are inherently complex, yet ancient successions are often reduced to very simple models considering just one major control factor, most commonly sea level. These dynamic models stress the changes in depositional systems and environmental controls through time and combine different scales of observations from microfacies to sedimentary sequences (Aigner 1984). Dynamic models have their merits because they try to avoid strict categorizations such as those involved in the Wilson model and because dynamic models describe the development of facies zones during time. Systems tracts deciphered by sequence stratigraphy are the result of gradual changes in marine environments caused by variations in water depths related to sea-level fluctuations, accornmodation space and biogenic production. These changes are characterized by shifts in the relative importance of limestone grain types. The shifts reflect temporal continua or relays that can be derived from optimized similarity matrices (see Sect. 14.4).

14.1.I .3 Numerical Models A third category of facies nlodels are c u n p t e r modcls conditioned with appropriate geometric and stratigraphic data from outcrops or wells arid process data fro111 modern carbonate depositional environments. These models simulate temporal development, stratal geometries and the architecture of carbonate buildups, and evaluate the rates of processes responsible for the formation of carbonate platforms and slopes. Computer models provide a visual image of the internal architecture of carbonate platforms (e.g. Bosence and Waltham 1990) and platform-slope geometries and the shape of slopes (Aigner et al. 1989; Bosscher and Southam 1992). Modeling allows quantification and evaluation of the major controls on the evolution of platforms and ramps studied in outcrops and derived from seismic

sections. The value of the models is usually tested by comparison with well-studied outcrops (e.g. Harris 1991). Most computer models are based on algorithms that simulate processes acting during the development of carbonate buildups and determining their shape and internal structure. Simulations are performed on a spatial grid in a sequence of time steps from a prescribed set of initial conditions defined by various input parameters. During program application, these parameters are varied within the limits of known geological and sedimentological constraints until the model is consistent with all available data and observations. The programs developed for modeling carbonate and/or carbonate-siliciclastic depositional systems differ in their main goals, input parameters used, and the way modeling results are shown. Carbonate computer models are two-dimensional or uj three-dimensional. Principal key input paran~et~is 2 - 0 nzodelirzg (see Enos 1991) are sea-level fluctuations, subsidence, clastic sediment input and depth-related carbonate growth potential. Other parameters are sedimentation and erosion rates (Bosence et al. 1994), platform shape and slope angle, and early diagenetic processes and compaction (e.g. Strobe1 et al. 1990).

Model outputs are 2-D cross sections explaining internal and external platform geometries (Bosence and Waltham 1990; Read et al. 19911, the growth and geometry of reef structures (Gerhard 1991; Bosscher and Schlager 1992; Hiissner 19g7), the evolution and geometry of shelf-basin transitio~ls (Aigner et al. 1990; Kendall et al. 1991; Bosence et al. 1994), the developnlent of carbonate slopes (Bosscher and Southam 1992). the estimation of paleobathymetric conditions (Aurell et al. 1995), the sea-level control on cyclic sedimentation (Goldhammer et al. 19911, the evaluation of depositional models based on sequence stratigraphic concepts (Burgess 2001 ). Problems involved in computer models are the dii'ficulty in separating global sea-level signals from local or regional processes, obtaining a high time resolution, and quantifying the controls on the biogenic carbonate production potential. In addition, many models provide only rough lithologies or strongly generalized lithofucies types. Thin-section data on niicrofacies scale arc important parameters in modeling component cycle\ (see papers in Franseen et al. 199 1).

Common Facies Belts

659

with supratidal microbial laminites, sometimes with inland freshwater marsh deposits, coal, or siliciclastics. Lagoonal facies. Developed behind barrier complexes. Mainly bedded limestones with micritic or peloidal lime mudstones, or cherty burrowed skeletal packstones to mudstones, sometimes with local patch reefs of colonial metazoans. Minor, thin interbeds of fenestral or cryptalgal carbonates reflect periods of shallowing of the lagoon to tide level. Shoal-water sediments consisting of banks, reefs and ooidlpellet shoals. Occurring as shallow-ramp skeletal banks or lime-sand shoals, or as shelf-edge skeletal reefs and lime sands that may pass gradually downslope into deep ramp facies. On deeply sloping platform edges, the facies passes downslope into foreslope and slope deposits adjacent to deep shelves or basins. Deep shelf and ramp facies. Nodular, sometimes cherty bedded skeletal packstone and wackestone with abundant whole fossils and diverse open-marine biota. The limestones may have upward-fining and storm14.1.2 Basic Elements of Carbonate Facies generated beds. Water depths range from some tens to Models more than 100 m. The depositional base is largely beBasic elements used in carbonate facies models describ- low the fair-weather wave base, but may be influenced ing transects from shallow-marine to deep-marine set- by storms. Slope and basin facies. Foreslope and slope depostings are changes in the relief of the sea bottom expressed by its adjacent to steeply sloping platforms have abundant differently dipping shelf slopes and the shallow-water breccias and turbidites interbedded with periplatform or deeper-water position of a distinct break in the mor- lime muds and terrigenous muds. Adjacent to most phology of the shelf, ramps, slope and basin deposits are thin-bedded perivertical boundaries affecting the sea bottom, and rep- platform lime muds or terrigenous muds with generresented by high and low tide levels, the fair-weather ally only few sediment-gravity flow deposits. Paleozoic basinal deposits are commonly shales, with carwave base and the storm wave base, and lateral differences in the composition of sediments bonate content increasing toward the platform. Mesoand benthic biota allowing facies zones to be distin- zoic and Cenozoic basinal deposits map be pelagic limestones or shales. The slope and basin floor can be anguished. These basic elements have been discussed in Chap. 2 oxic and lacking benthic organisms. These deposits are of this book. laminated and non-burrowed. Oxic slope and basin deposits are burrowed and fossiliferous.

Current 3 - 0 modeling incorporates the basic processes of carbonate accumulation and diagenesis in relation to sea-floor flucluations, basement subsidence, wave-base erosion and transport of sediment. Common input parameters are initial bathymetry and sea-floor geometry, sea-level changes, changes in paleoenvironmental conditions (e.g. salinity, temperature), and paleoclimate. 3-D modeling of carbonate basins has become a very successful technique in reservoir modeling, particularly where the geological and physical reservoir parameters show extreme heterogeneities (e.g. Vahrenkamp and Grotsch 1994). Modeling of the relationships between reservoir lithofacies and petrophysical criteria reflected by logs requires the differentiation of well-strained lithofacies units. The consideration of microfacies types is an important tool in defining these units.

14.1.2.1 Common Facies Belts 14.1.2.2 Common Depositional Patterns Most models used in interpreting ancient shallowmarine to deep-marine carbonate rocks consider five major fucies belts along a shoreline-to-basin transect that include platforms or ramps and continue via a slope into basins (Read 1995): Tidalput jucies. Generally arranged in cyclic, shallowing-upward units. Sequences in arid climate exhibit burrowed to non-burrowed lagoonal limestones overlain by intertidal microbial and algal laminites, supratidal evaporites, or eolian-fluvial clastics. Humid sequences are burrowed subtidal-intertidal litnestones

Sedimentation on sheives often results in meter-scale shallowing-upward sequences, because the accumulation rates commonly outspace the combined rates of subsidence and sea-level rise (James 1984; Osleger and Read 1991). Consequently, the tops of these sequences show signs of intertidal to supratidal exposure, or they are eroded. Such small-scale cycles can be stacked to form larger sequences displaying transgressive and regressive trends. Stacking of sequences is a characteristic criterium of many ancient platforms. Larger-scaled sequences are commonly attributed to third-order sea-

Standard Facies Zones

level fluctuations, small-scale sequences to sea-level and space. Platforms may expand as their margins grow fluctuations in the Milankovitch band (e.g. Read and outward; grow upward while their margins remain staGoldhammer 1988; Goldhammer and Harris 1989; tionary; or retreat at their margins backward (e.g. Jansa Strasser 1994). However, autocyclic processes such as 1981; Blendinger 1986). Platforms are born, grow and migration of bars and islands, delta-switching and lo- die. Growth is caused by aggradation and/or progradcal progradation may also create shallowing-upward ation. Demise is connected with the decrease in and sequences in shallow-marine environments (Strasser cessation of carbonate production due to (1) drowning 1991; Goldhammer et al. 1993). These processes are caused by rapid eustatic sea-level rise or tectonic sublocal and can not be followed over large lateral dis- sidence, (2) subaerial exposure caused by sea-level fall tances. or tectonic uplift, (3) high siliciclastic input, or (4) paleooceanographic effects causing changes in water circulation, temperature and salinity. 14.1.2.3 Different Depositional Settings Major variables influencing the evolution of platRequire Different Facies Models forms are tectonic setting and subsidence,sea-level fluctuations, carbonate productivity and sediment transport, The basic differences of carbonate depositional settings the nature of the sedimentation at platform margins, were discussed in Chap. 2 of this book. Fig. 2.6 gives a the evolution of reef-building organisms through time, brief survey of some of these settings. The discussion and variations in diagenetic processes. in the present chapter is focused on facies zones and models forming the base for the interpretation of anMany platforms are 'rimmed' at their platform-ocean cient carbonate environments. margins (e.g. South Florida Shelf, the Belize Shelf, or The discussion starts with facies zones occurring on the Queensland Shelf with the Great Barrier Reef) or rimmed shelves (platforms) and adjacent slopes and ba- they are 'non-rimmed' (e.g. Western Florida Shelf). sins (Sect. 14.1.3).This Wilson model is contrasted with Both rimmed and non-rimmed platforms may be atthe ramp model (Sect. 14.1.4) describing sedimenta- tached to the continent or occur detached from the contion on a gently dipping slope, and with the non-rimmed tinent as isolated platforms and atolls. Rimmed carbonplatform model (Sect. 14.1S ) .The specific conditions ate s1zel~~e.s und platfoims are characterized by a nearly flat platform top, of isolated platforms and atolls are examined in Sect. 14.1.6. The sedimentation on extremely extended a landward low-energy lagoon, epeiric platforms and epeiric ramps is the topic of Sects. an outer wave-agitated depositional, bypass or ero14.1.7 and 14.12 . sional margin, marked by a continuous to seniicontinuous reef-dominated or - > .Vote that tl~esc jacies nmdels are lrnzited ~ ~ rr-t h sand-shoal dominated rim along the margin that regard to tlzeiryr-edictivecapacity owing to tlzeir statlc stricts circulation and wave action, a pronounced increase in slope, ranging from a feu v i t ~ of ~ t time ~ arzd of the relath~csea-level change:, [ha: cotztr-ol facies shifts These difiic~tlltiescan be degrees to 60" and more, and pur-tly 01-el-come by n l o d ~ l sbased 011 sequence abundant mass-flow deposits ( e g debris flows, mega\tratrgraphy dcnzonstr-atil~gh o ~deposltrorzal , Jrbreccias. turbidites, slumps) downslope from the quc'mer i.espo~zd to I O I I ~ S ~ L L I I ~I II. . ( I M S ~ ~ C S SU I IV ~I ~ shelf edge containing platform-derived material. Irrghstanil c o ~ d r t ~ oojf lr-elatr~'e ~ seir level ~ind'ei-1111rtzid and a n d co/rditiotrs (Handford arld L ~ L ~ C X J 1993) Scquerzce str-atigraphynzodels car1 tlor replace 14.1.3.1 Standard Facies Zones and the the static models whiclz have their o h x merits, hut Modified Wilson Model tlley con~plcte0141. understarzdlny of facres development througlz time (see Sect. 16.1 2 ) The succession of major facies belts on rimmed tropical carbonate platforms was used by Wilson (1975) to establish a Standard Facies Model depicted as a basin14.1.3 Facies Zones of Rimmed Carbonate to-shore transect and comprising Standard Facies Zones Platforms: The Wilson Model (Fig. 14.1). The basis of the model is the recognition of consistently recurrent patterns of carbonate facies in The most frequently used facies models are those hy- the Phanerozoic record and the environmental interpothesizing on platforms and ramps. Carbonate plat- pretation of these patterns by using characteristics of forms are dynamic systems that change through time Holocene sedimentation patterns.

S t a n d a r d Facies Zones

The Standard Facies Zones (FZ) defined in Box 14.1 describe idealized facies belts along an abstract transect from open-marine deep basins across a slope, a pronounced platform marginal rim (characterized by reefs or/and a zone with sand shoals), and an inner platform to the coast. The Facies Zones differ in setting, dominant sediments and prevailing biota, and common lithofacies. Carbonates formed within these Facies Zones often exhibit specific Standard Microfacies Types (SMF) assemblages that are used as additional criteria in recognizing the major facies belts (see Sect. 14.3). The definitions of the Facies Zones in Box 14.1 consider Wilson (1970, 1 9 7 9 , recent suggestions by Schlager (2002) and modifications regarding the diagnostic criteria. Facies Zone 9 is subdivided into 9A and 9B to distinguish the significant differences in arid evaporitic and in humid climates. A new Facies Zone 10 is introduced for limestones affected by freshwater dissolution and precipitation processes (e.g. in karstic and pedogenic settings).

The model does not show the effects of sea-level fluctuations. It fits predominantly sedimentation patterns formed during transgressive highstand and stillstand phases. The model is limited to tropical and subtropical platforms and does not include climatic controls, except for the Facies Zones 9A and 9B. Facies distribution of temperate and cool-water platforms can not be interpreted with the model and are better described using models dealing with non-rimmed platforms or carbonate ramps. The model does not sufficiently consider the changes in the organic platform rims that took place over time in the evblution of reefs. Facies Zone 5, comprising platform-margin reefs and upper slope reefs of various construction, composition and development stages, is too generalized and must be analyzed independently of the other Facies Zones. The specific methods are discussed in Sect. 16.2. The model says nothing about windward-leeward differentiation resulting in distinct geometrical asymmetries that can be revealed by seismic surveys. The model neglects the wide facies spectrum of oceanic deep-water settings and gives a much too generalized picture of slope sedimentation.

-> Note that these facies belts are limited to tropical platforms and do not consider pla$orms in cool\cater settings that qften correspond better to nonrimmed plagorms or ramps. The Wilson model contains more Facies Zones than can normally befound Application of the Standard Facies Zone concept on one platform. Rimmed platforms usually exhibit Despite the pitfalls listed above, the facies zonation rr reduced nlimber of Farics Zones and often a dif- established by Wilson has been successfully used by ferent luferal arr.nngt1merztoffacies belts (Fig.14.2). many authors involved in basin analyses and reservoir studies, e.g. Hubmann (1992, Devonian), Herbig (1984, Carboniferous), Schott (1984, Late Tnassic and Early 14.1.3.2 Discussion and Use of Standard Liassic), Fezer (1988, Late Jurassic), Morrow and Webster (1991, Mississippian-Pennsylvanian), Mette Facies Zones (1993, Jurassic), Steuber et al. (1993, Cretaceous). The Wilson model has passed the test of time with fly- Braun (1998, Triassic), Blomeier and Reijmer (1999, ing colors despite its static approach and the broad gen- Jurassic), and Scheibner and Reijmer (1999, Jurassic). eralizations of the original concept. However, one should be, however. aware that the model is just a snapThe Wilson model assists In evaluating outcrops with regard to their paleogeoshot illuminating potential depositional patterns and their lateral relationships. Critical points which must graphical position within a likely shelf-to-basin transect; recognizing potential depositional and environmenbe considered are: tal relationships between widely spaced stratigraphic The model is ovescomplete. Platforms with a reduced sections, particularly in remote areas: attributing core samples to depositional sites that number of Facies Zones are the common case (Fig. 14.2). allow the evaluation of economically interesting facies The model prefers sharp boundaries between Facies zones (e.g. within reef or shoal complexes or at platZones. Lateral facies boundaries, however, are often form margins) and of depositional conditions that might very gradual (e.g. between the Facies Zones 7 and 8) have created appropriate poroperm values; reconstructing 'lost' depositional sites by looking for or can not be distinguished at all (e.g. FZ 3 and 4). The model underlines the occurrence of litho- and source areas of carbonate clasts found in slope and babiofacies within specific Facies Zones, but does not con- sinal sediments, and derived from the destruction of sider the development of Facies Zones over time. carbonate platforms.

-

662

D e f i n ~ t ~ oofn Standard F a c ~ e sZ o n e > Platform intertor or cratonfc

deep-water

basm

waie base

Fig. 14.1. Rmnzed carbonate platfor m The Standard Facles Zones of the modified W~lsonmodel.

Box 14.1. Standard Facies Zones (FZ) of the modified Wilson model describing a rimmed carbonate platform. Basin and deep shelf

FZ l A Deep Sea Setting: Below wave base and below the euphotic zone in oceanic deep water. Water depth several hundreds to several thousands of meters. Wide facies belt. Sediments: Entire suite of deep-sea sediments including pelagic clay, siliceous and carbonate ooze, hemipelagic muds, turbidites. Adjacent to platforms mixtures of pelagic and platform-derived material (peri-platform oozes and muds). Bedding highly variable, often thin-bedded. Rock color: dark, reddish or light depending on differences in oxidizing and reducing conditions. Hiotu: Predominantly plankton, typical oceanic assemblages, sometimes associated with autochthonous benthic fossils. In peri-platform sediments up to 75% shallow-water benthos, Conzmor?lithofacies: Pelagic mudstone and wackestone; marts: allochthonous packstone, grainstone, breccia.

FZ I B Cratonic deep-water basin Setting: Below wave base, below the euphotic zone. Warer depth about 30 m to several 100s In. Wide facies belt. S~dimcnts:Similar to I A. Hemipelagic muds very common. Occasionally anhydrite. Sometimes common cherts. .4noxic conditions fairly common (high organic content; lack of bioturbation). Dark thin limestone beds and dark shale beds. Lime mudstones, calcisiltites. Rock color: dark brown and black (due to organic matter) and reddish (due t o slow sedimentation). Biota: Predominantly nekton (e.g. ammonites) and plankton (radiolarians, pelagic foraminifera, calpionellids, of thin-shelled bivalves). Occasionally benthos coqui~~as (abundant sponge spicules). Co~iiniotzlirhujkcics: Lime mudstone, wackestone, packstones. Marls. Anhydrite.

F% 2 Deep shelf S~tling:Bclow fair-weather wave base but within the rsach of extreme storm waves. Within or just below the euphotic zone. Forming plateaus between active platforms and deeper basins. The plateaus are commonly established on top of drowned platforms. Water depth tens of meters to hundreds of meters. Normal salinity, oxygenated waters with good current circulation. Wide facies belt. Sediments: Mostly carbonate (highly fossiliferous limestone) interbedded with marl beds. Skeletal wackestone and whole fossil wackestone; some grainstone and coquinas. Matrix commonly pelmicrite. Some silica. Well bioturbated. Well bedded. Bedding thin to medium, wavy to nodular. Rock color: gray, green, red and brown depending on variable oxidizing and reducing conditions.

Biota: Diverse shelly fauna indicating normal marine conditions. Infauna and epifauna. Minor plankton. Stenohaline biota conspicuous (e.g. brachiopods, echinoderms). Common lithofacies: Wackestone. Occasional grainstones. Marls and shales. Toe-of-slope and slope

FZ 3 Toe-of-slope apron (deep shelf margin) Setting: Below wave base and barely at oxygen level. Moderately inclined sea floor (over 1.5") basinward of steeper slopes. Water depths similar to FZ 2 and perhaps 200 to 300 m. Narrow facies belt. Sediments: Mostly pure fine-grained carbonates, in some places cherty, rare intercalations of terrigenous muds. Pelagic material admixed with fine-grained detritus moved off from adjacent shallow shelves. Grain size highly variable. Typical are well-defined graded beds or breccia layers (turbidites, debris-flow deposits) intercalated in finegrained background sediment. Rock color: dark to light. Biota: Mostly redeposited shallow-water benthos; some deep-water benthos and plankton. Common lithofucics: Lime mudstones; allochthonou.; packstones and grainstones. Shale partings.

FZ 4 Slope Setting: Distinctly inclined sea floor (commonly 5" to nearly vertical) seaward of platfonn margins. Very narrow facies belt. Sediments: Predominantly reworked platform material and pelagic admixtures. Highly variable grain size. End members are gentle muddy slopes with much slumping, and sandy or mbbly slopes with steep foresets. Rock color: dark to light. Biota: Mostly redeposited shallow-water benthos, encrusting slope benthos and some deep-water benthos and plankton. The facies may be very fossiliferous. Common lithofacies: Mudstone; allochthonous packstone and grainstone; mdstone and floatstone. Breccia. Upper slope reefs and platform-margin reefs FZ 5 Platform-margin reefs Setting: (a) Organically stabilized mud mounds on upper slope; (b) ramps with knoll reefs and sand shoals: (c) wave-resistant barrier reefs rimming the platform (see Sect. 16.1.2).Water depths generally some metembut some hundred meters for mud mounds. Very narrow facies belt. Sediments: Almost pure carbonates of very variable grain size. Massive limestones and dolomites. Masses or patches of various types of boundstones. Reef cavities filled with internal sediment or carbonate cements; multiple generations of construction, encrustation, boring and destruction. Rock color: light.

663

Definition of Standard Facies Zones

Box 14.1. Definitions of Standard Facies Zones (continued). Biota: Almost exclusively benthos. Colonies of framebuilders, encrusters, and bafflers along with large volumes of loose skeletal rubble and sand containing benthic microfossils (e.g. foraminifera, algae). Common lithofacies: Framestone, bafflestone, bindstone, wackestone and floatstone, grainstone and rudstone. Platform-edge and platform sand shoals

FZ 6 Platform-margin sand shoals Setting: Elongate shoals, tidal bars and beaches, sometimes with eolianite islands. Above fair-weather wave base and within the euphotic zone, strongly influenced by tidal currents. Very narrow facies belt. Sediments: Clean calcareous, often rounded, coated and well-sorted sands, occasionally with quartz. Sand grains are skeletal grains, or ooids and peloids. Partly with wellpreserved cross-bedding, sometimes bioturbated. Susceptible to subaerial exposure. Rock color: light. Biota: Worn and abraded biota from reefs and associated environments. Low-diversity infauna adjusted to mobile substrate. Common biota are large bivalves and gastropods and special types of foraminifera and dasyclads. Common lithoft-rcies:Grainstone, packstone. Open-marine platform FZ 7 Platform interior - normal marine (open marine) Setting: Flat platform top within euphotic zone, normally above fair-weather wave base. Called lagoon when protected by sand shoals, islands or reefs of the platform margin. Sufficiently connected with the open sea to maintain salinity and temperature close to that of the adjacent ocean. Maderate circulation. Water depths a few meters to tens of meters. Wide facies belt. Sediment: Lime mud, muddy sand and clean sands, depending on the grain size of local sediment production and the efficiency of wmnowing by waves and tidal currents. Medium to coarse bedded. Locally patch reefs or organic banks. Terrigenous sand and mud may be common in attached platforms, but are generally absent in detached platforms such as oceanic atolls. Rock color: light and dark. Biota: Shallow-water benthos with algae, foraminifera, and bivalves; gastropods, particularly common. Areas with marine grasses and with patch reefs. Common lithofucies. Lime mudstone, wackestone and float~tone,packstone, grainstone. Restricted-marine platform

FZ 8 Platform interior - restricted

Setting: As for Facies Zone 7, but less well connected with the open ocean, causing large variations in salinities and temperatures. Within the euphotic zone. Typically strongly differentiated tidal zones with freshwater, saltwater and hypersaline conditions as well as subaerially exposed areas. Shallow, cut-off ponds and lagoons with restricted circulation and hypersaline water. Lagoons behind barrier reefs, within atolls or behind coastal splits. Water depths below one meter and a few meters to a few tens of meters. Wide facies belts. Sediments: Mostly lime mud and muddy sand; some clean sand. Terrigenous influx common. Early diagenetic cementation common. Linestones and dolomites. Rock color: light.

Biota: Shallow-water biota of reduced diversity, but commonly with high number of individuals. Typical are miliolid foraminifera, ostracods, gastropods, algae and cyanobacteria. Marine and freshwater vegetation. Common lithofacies: Lime mudstone and dolomite mudstone, wackestone, grainstone, bindstone. Sedimentary breccia.

Arid near-coast evaporitic platforms

FZ 9A Arid platform interior - evaporitic

Setting: As in Facies Zone 7 and 8, yet with only episodic influx of normal marine waters and arid climate so that gypsum, anhydrite or halite may be deposited beside carbonates. Supratidal. Sabkhas, salt marshes, salt ponds. Wide facies belt. Sediments: Calcareous or dolomitic mud or sands, with nodular, wavy or coarse-crystalline gypsum or anhydrite. Intercalations of red beds and terrigenous eolianites in landattached platforms. Rock color: highly variable; light, yellow, brown, red. Biota: Little indigenous biota except cyanobacteria; ostracods, mollusks, brine shrimps adapted to high salinities. Common lithofacies: Laminated lime and dolomitic mudstones and bindstones alternating layers with layers of gypsum or anhydrite. Humid near-coast brackish regions

FZ 9B Humid platform interior - brackish (humid) Setting: Poor connection with the open sea as in FZ 9A but with a humid climate so that water runoff dilutes small bodies of ponded seawater and marsh vegetation spreads in the supratidal flats. Narrow facies belt. Sediments: Calcareous marine muds or sand with occasional freshwater lime mud and peat layers. Rock color: gray, light, brown, dark. Biota: Shoalwater marine organisms washed in with storms plus organisms adapted to brackish-water and freshwater (ostracods; freshwater snails; charophycean algae). Paleokarst, caliche and other terrestrial and terrestrialmarine settings FZ 10 Humid and arid often subaerially exposed, meteorically influenced limestones Setting: Subaerial or subaquatic, formed under meteoric-vadose and marine-vadose conditions. Abundant in karst settings and pedogenic carbonates (continental and near-coast areas), and supratidal and intertidal environments. Sediments: Limestones affected by early diagenetic meteoric dissolution predominantly during phases of subaerial exposure (e.g. paleokarst). Common in caliche crusts. Typically occurring in limestones rich in carbonate cement crusts, but also occurring in micritic caliche or as reworked grains in restricted environments (e.g. coastal ponds or lagoons). Biota: Lndigenous biota lacking except cyanobacteria and microbes.

Carbonate Ramp hlodcl

664

B

A Open-marine inner platform

Platform-margin reef

C

Openmarine mner platform

Platform-margin reef

7

5

ppen-marine mner olatform

Marginal sand shoals

Fig. 14.2. Comnzon variations In the lateral arrangement of facies zones distinguished in the rimmed platform model (see Fig. 14.1). The arrangement of the facies belts is controlled by the position of the sea level (A highstand, B stillstand, C lowstand). A: The platform margin is characterized by a bamer reef zone (FZ 5) interfingering with an open-marine back-reef zone (FZ 7) of the inner platform. Facies zones bZ 3 and FZ 4 of the Wilson model are not distinctly differentiated due to the mixture of coarse reef debris and calcareous sand from the platform interior. Note the absence of the deep shelf facies zone FZ 2. B: The reef zone (FZ 5) is part of a reef complex consisting of lagoonal back-reef sediments and a slope whose upper part is supplied with talus forming a forereef zone. C: The sketch shows a common case whereby marginal sand shoals interfinger with slope sediments consisting of bioclast~c sand transported from the shoals to gentle slopes. Adapted from Schlager (2002).

> Most stridzes conhirw the evuluution ojFacies Zones

ter outer ramp deposits. High-energy carbonates are with thc. detet-mznntioil cf Standard Microfacies formed near the shoreline in inner-ramp settings or in 7jpcs. I'he tnethods and potential qf thrs npproacl~ shoal areas of inner and mid-ramp settings, and not at are cie~rt-ibedrtz Sect. 14 3 the shelf edge. Windward ramps are storm- and wavedominated and characterized by grainy sediment at the shoreline. Leeward ramps are characterized by muddy 14.1.4 Carbonate Ramp Model sediments with low grainstone content.

-

A carbonate ramp is a gently dipping sedimentary surface on the sea floor. The facies belts are controlled primarily by energy levels (fair-weather wave base and storm wave base), variations in ramp topography, and material transport by stonns, waves and tides. The depositional slope gradient from the shallow-water shoreline or lagoon to the basin floor is of the order of a few meters per kilometer and usually less than l o . Nearshore, wave-agitated shallow-water carbonates pass gradually offshore into deeper-water, low-energy deposits and then into basinal sediments. Ramps were common during the Phanerozoic, parlicularly in times when frame- and reef-building organisms were tnissing or rare. Most ramps have been described from the Cambrian and Early Ordovician, Early Devonian, Early Carboniferous, Early and Middle Triassic, Middle and Late Jurassic, Early Cretaceous and Early Tertiary. Carbonate ramps can develop during the drowning of shelves and during the early stages of platform forma~ion.Often they evolve into rimmed platforms. Contrasted with rimmed shelves, ramps lack the steep slope at the shelf edge, show no continuous reef trends and exhibit no shallow-water derived clasts in deeper-wa-

Dimension of ramps The widths and lengths of ancient carbonate ramps vary within a wide range. Maximum width ranges between less than 10 km to about 800 km. Most values are below 200 km and many ramps have widths of only 800 km; Trucial Coast, recent: width 200 km, length > 400 km; Shark Bay, Western Australia, recent: width 100 km, length 200 km; Yucatan Peninsula, Tertiary to present: width 200 krn, length more than 600 km). Yet smaller Holocene wave-dominated ramps with a length of only about 50 km are known (Kuwait, northern Arabian-Persian Gulf). Characteristics of ramps The principal criteria of carbonate ramps are Gentle slopes on which updip nearshore shallow-

Classification of R a m p s

water deposits (mainly grainstones) pass gradually downslope without a marked break into progressively deeper water and low-energy deposits, and finally into basinal muddy sediments. Because oceanic waves and swells sweep directly onto and across the shallow sea floor, the energy level of the shallow-water environments is high. Complex and differentiated nearshore facies. Continuous carbonate production takes place in shallow inner and mid ramp settings. Storm-generated high-energy sediments are commonly deposited in inner and mid-ramp settings. Autochthonous carbonate production by benthic organisms occurs in outer and deeper ramp settings. Shallow-water sediments are transported into deeper water ramp parts. Separate and discrete buildups (e.g. mud mounds or pinnacle reefs) may exist on mid- and outer ramps.

ramps are characterized by fossiliferous wackestonesl lime mudstones and marls with open-marine diverse biota. Deeper distally steepened ramps exhibit similar facies but may have slumps, breccias and turbidites along ramp-to-basin margin. Slumps and channeled or sheet-like breccias with clasts derived from the deepwater slopes are also common in the basin sediments consisting of lime mudstones and wackestones with interbedded marls.

Ramp types: Read (1985) recognized six major ramp types based on the character of the facies formed under the highest energy conditions in shallow parts of the ramp. The author distinguished ramps with fringing banks, with barrier-bank complexes, with isolated shallow and downslope buildups, with fringing ooid shoals, with ooid-peloid barrier, and coastal beachldune complexes. This classification addresses the essential role of sand bodies in the formation of ramps and considers the role of sessile organisms contributing to the formaClassifications of ramps Several classifications have been proposed for ramp tion of mounds and small patch reefs within ramp engeometry, water depth and the controls on ramps by vironments. Similar ideas are included in the concept used by storm wave base and fair-weather wave base (Ahr 1973; Read 1982, 1985; Aigner 1984; Carozzi 1989; Calvet Carozzi (1989) to describe the microfacies of ancient and Tucker 1988). Read (1982, 1985) divided ramps ramps. The author distinguished between simple ramps, into two major groups on the basis of the sea bottom ramps with bioaccumulated to hydrodynamic buildups, profile (Fig. 14.3) and ramps with bioconstructed buildups. The term 'bioaccumulated' refers to the accumulation of loose Hor~~oc~lrnal rc~nzpswith gentle, relatively uniform skeletal fragments (e.g. of crinoids), the term 'bioconslopes without a shelf break exhibiting the same gradi- strutted' to frameworks formed by colonial organisms. ent from shoreline to deeper water, and Hydrodynamic buildups are formed by the deposition Distally str3epcned ramps with an offshore slope of skeletal grains and ooids, subsequent to storms and break between shallow ramp and the basin in relatively current transport. Carozzi's book summarizes the redeep water. Distally steepened ramps have characteris- sults of many case studies of ramp and platform cartics of ramps and of ri~nmedshelves, but they differ bonates, predominantly from the Paleozoic. from the latter in that the major break in slope does not occur at the seaward margin of a high-energy rim but Most ramp classifications recognize two cr-iticul instead many kilometers seaward of high-energy shoals hydrodynamical intafaces - the fair-weatherwave base in around the mid- or outer ramp. The ramp builds lat- and the storm wave base. These boundar~escan be erally seaward with turbidites and slumps along the recognized from sedimentary structures, microfacies steepened slope. criteria and biota. Diagnostic criteria are discussed in Sect.12.1.1.1 andsect. 12.1.2.1. The processes of shaping ramps is aggradational in Combining the fair-weather wave base and the storm homoclinal and progradational in distally steepened wave base, Burchette and Wright (1992) have suggested ramps (Gardulski et al. 1991). Homoclinal and distally the subdivision shown in Fig. 14.3 and described in steepened ramps are often successive stages in the de- Box 14.2. This model is based on the influence of velopment of carbonate buildups, resulting in the storms, waves and tides on the sediments in mid- and growth of rimmed carbonate platforms. inner ramp zones. Many Phanerozoic ramps were Both homoclinal and distally steepened ramps com- strongly storm-controlled and therefore exhibit a tlueeprise tidal flat and lagoonal facies and foreshore or off- fold subdivision. In the case of missing indications of shore complexes of shallow-water oolitic and bioclas- storms, inner and outer ramps can be differentiated by tic sand shoals, but differ in the sediments of deeper- using wave base, biotic composition and dominant limewater and basinal environments. Deeper homoclinal stone textures.

Carbonate R a m p Model

Outer ramp

Fig. 14.3. Carbonate Ramp Model of a homoclinal ramp, modified from Burchette and Wright (1992). The differentiation into an inner, mid- and outer ramp can be applied both to homoclinal and distally-steepened ramps (see inset). Sediment texture, grain size, and biotic criteria depend on the water energy at the sea bottom differing above the fair-weather wave base, between the fair-weather wave base and the storm wave base, and below the storm wave base. The slopedip is strongly exaggerated. Not to scale. Ramp lengths vary between some tens and some hundreds of kilometers.

Box 14.2. Carbonate Rump Model (Burchette and Wright 1992). Criteria of inner, mid- and outer parts of ramps ~ J Z I Z Pran111 I.

The inner ramp comprises the euphotic zone between the upper shoreface (beach or lagoonal shoreline) and the fair-weather wave base.The sea floor is almost constantly affected by wave action. The zone is dominated by sand shoals or organic barriers and shoreface deposits. The shallow inner ramp may consist of (1) a beach barrier-tidal delta complex with lagoons and tidal flats behind (backramp), or (2) fringing sand banks and shoal complexes with intertidal and supratidal flats, but no lagoons behind, or (3) a strandplain of linear beach ridges with depressions. Characteristic sediments are carbonate lime sand bodies fornxxi in agitated, shallow subtidal shoreface areas above the fair-weather wave base. The sands consist predominantly of ooids or various skeletal grains, usually foraminifera, calcareous algae, or mollusks. Peloids may be common in places. Storms contribute to the formation of extended sheet-like sand bodies and sand beaches that may grade into eolian dunes. Offshore storm surges transport shoreface sands to deeper, outer ramp settings. Organic buildups in inner-ramp environments are biostromes and small patch reefs characterized by low-diversity biota (e.g. corals, rudists, oysters). Frequent limestone types are grainstones and pa-k L stones. Buck-r-unlp sediments originate in peritidal settings similar to those of inner platforms (comprising mudstones, bindstones and wackestones), and in restricted lagoonal areas (mudstones, wackestones, packstones). Mid-r-atup The mid-ramp is the zone between fair-weather wave base and the storm wave base. Water depths reach some tens of meters. The bottom sediment is frequently reworked by stom1 waves and swells. The sediments reflect varying degrees of storm influence depending on the water depth and bottom relief. Intraclast and breccia beds may be common.

Thick oolitic and bioclastic sand shoals are common. Storm-related features are graded packstone, grainstone beds, hummocky cross-stratification, and tempestite couplets. Skeletal grains exhibit signs of transport. Fair-weather phases are represented by burrowed sediments dominated by lime mud or temgenous mud forming lime mudstones and m a r k Much of the fine-grained sediment might be caused by lateral sediment transport in offshore zones or by transport from the shoreline to midand outer ramp areas. Mid-ramp deposits are often thicher than coeval inner ramp deposits. Organic buildups are represented by pinnacle reefs and mounds. Outer rump The outer ramp is the zone below normal stonn wa\.i: base. Water depths vary between tens of meters and several hundreds of meters. The zone is characterized by lowenergy allochthonous and autochthonous carbonates, and hemipelagic sedimentation. Little evidence of direct storm reworking exists, but various storm-related deposits ( c . g . graded distal tempestite beds) niny occur. Common lithofacies types are bedded, fine-grained limestones jargil laceous lime mudstone and wackestone) associated and interbedded with marl or shale beds, Calcisiltite matrix is abundant. Biota comprise normal marine diverse benthos, sometimes associated with plankton and nekton. Renrhic organisms include foraminifera, sponges, bryozoans, brnchiopods, mollusks, and echinoderms. Algae may be represented by red algae. Burrows are common. In deeper outer ramp settings restricted botton~conditions may develop. Common organic buildups are mud mounds.

The slope break of distallj steepened ramps is usually located in a position around the mid- or outer ramp boundary or within the outer ramp. Deposition of slope-derived material may dominate proximal to the break.

Non-Rimmed P l a t f o r m s

14.1.5 Non-rimmed Shelves and Platforms

14.1.6 Isolated Platforms and Atolls

A non-rimmed shelf or open platform is characterized by the lack of a barrier at the shelf break. Non-rimmed platforms and ramps are similar in the absence of a rim at the shelf edge. In both systems sediment transport occurs onshore and downslope, and carbonate production takes place in all parts. The major difference, however, is the very gentle slope angle of the ramp, producing different distribution patterns and sizes of fac i e ~zones as compared with unrimmed platforms. Non-rimmed shelves occur at the leeward side of large tropical banks and are abundant in all cool-water settings. Fig. 14.4 displays the subdivision of a nonrimmed carbonate cool-water shelf. Box 14.3 summarizes the characteristics. Mid-shelf and outer shelf sediments of cool-water carbonates differ in the composition of the bioclastic sands (see James and Clarke 1997 for case studies).

Isolated platforms are accumulations of shallow-marine carbonates surrounded by deep-water sediments. This non-attached platform type includes very large structures as well as small platforms found on submarine highs and reef atolls growing upon volcanic basements. Most isolated platforms have steep margins and slopes reaching into deep or very deep water. Outer high-energy parts are characterized by marginal reefs and/or sand bodies. Common features of the platform interior are muddy and sandy calcareous sediments. These sediments differ in composition, sedimentary structures, biota and microfacies. High carbonate production around the platform margins and a steady background subsidence may lead to the formation of a rimmed isolated platform with a lagoon in the center. This pattern has been called an 'empty bucket' by Schlager (1993).

Gravels and hard substrates

Coarse skeletal sand

F~neskeletal sand

Benth~cskeletal mud

Pelaglc mud

Sediment transport Wave abrasion zone beach-dunes t~dalflats

I

Inner shelf constant wave agltatton

Swell wave base frequent storm reworkmg eplsod~cstorm Storm wave base

Fig. 14.4. Hydwdyrztmi( zotzes and subdwision of a non-rimmed cool-w.ater (temper-(ire)shelf. Base of wave abrasion ranges from 30 In to 70 m, swell wave base may reach 120 m, storm wave base about 250 m. Modifled from James (1997).

Box 14.3. Criteria used in the subdivision of a non-rimmed carbonate cool-water shelf. After James (1997). I~vwr-shelf' Dcpositiotzul PI-ocesses:Constant wave agitation. Particle abrasion and bioerosion. Winnowing. Sediment: Zone of sediment movement and active sediment production. Gravels, lithoclastic sands and hard substrates. Subaqueous dunes. Shaved shelf areas. Biota: Coralline red algae, benthic foraminifera, bryozoans, sponges, bivalves, gastropods, serpulids, echinoids. Deposition of epibionts from high-energy kelp forests and low-energy sea grass. Mid-shelf' Depositional PI-ocesscs:Frequent storm reworking. Particle abrasion. Sediment transport to outer and inner shelf areas results in sediment-free areas. Bioerosion and burrowing common. Sediment: Zone of active sediment production. Thin

sediment veneer over lithified bedrock. Coarse bioclastic sand. Rippled sands, subaqueous dunes. Biota: Coralline red algae, mollusks, benthic and planktonic foraminifera, bryozoans, brachiopods, sponges, barnacles. echinoids. Outer shelf Depositional processes: Sea bottom reworked by episodic storms. Suspension settling. Bioerosion and burrowing common. Sediment: Zone of carbonate production and accumulation. Fine bioclastic sands. In deeper parts mud (consisting of a mixture of calcitic plankton and skeletal fragments, siliceous sponge spicules, and clay). Burrowed sediments and storm beds. Biota: Bryozoans, sponges, mollusks, brachiopods, benthic and planktonic foraminifera.

Isolated Carbonate Platlor111

668

A well-known example of an isolated platform is the Great Bahama Bank (see PI. 3). Controls on facies distribution are the windward or leeward orientation, open or protected water circulation, or tide- or stormdominated conditions.

A Environments

An example of a smaller isolated platform in the Caribbean is shown in Fig. 14.5. The study is based on the thin-section investigation of the grain composition, grain size, and texture of plastic-impregnated sieve samples.

B Sediment composition

C Dunham eauivalent

% < 1 25 pm

Windward reef

Restricted lagoon

M~xedpeloidalskeletal Mollusk-ForamHalimeda

Leeward reef

Ponds

Halimeda

Packstone

Sand apron

Cays

Cays

Wackestone

Deep lagoon

Boundstone

8)

Disconhnuous trends

Grainstone

Cays

Fig. 14.5. Facics disrriDutiorz an an isolurcd co/-Donarcplaqor-nz.Tumeffe Islands, Belize, Central America. Tumeffe Islands are surrounded by deep waters. The distribution of the sedimentary fxies is controlled by antecedent topography and exposure to waves and currents. The maps show the relationships between environment, facies types and carbonate texture. A: En~~imrlnwrlts. The platform has an almost continuous surface-breaking wcf rim at the windward side. The reef margin is characterized by a cemented coral rubble pavement transected by tidal passes and channels. Windward and leeward j'oi-t~ct.i areas dip toward the open ocean. Sund u p o n s are developed in water depths down to 2 m. The bottom of shallow lagoons and deep lagoons (> 5 m) consists of unconsolidated sediment and is either barren or covered with sea grass and udoteacean green algae. Restricted lagoons with depths of 8 m and 3 m are enclosed by mangrove swamps and islands. The bottom of the lagoons is covered by sea grass, Huli~ncdu:ind sponges. Subtidal ponds are located within mangrove rims. The cays/islands consist of sand and mangroves. B: Fucirs types expressed by the composition of the sediment. The coral-red algae-Halinzeda facies is most abundant in tile marginal platform areas as well as in platform interior patch reefs. The mixedpeloidaliskeletal facies is characterized by the abundance of non-skeletal grains (predominantly peloids of fecal origin). The mollusk-foraminifera-Halimedafacies is common in platform interior environments. It is characterized by high concentrations of bivalve shells, miliolids and algal fragments. The sediments of the Halimeda facies contain more than 50% algal fragments. It is confined to the restricted lagoons. C: The texture of the surface sediments (using a rnodified Dunharn classification) reflects the hydrodynamic conditions. The distribution of the texture types is similar to the distribution of facies types in ancient isolated reefal platforms. Bo~tndstorl~s characterize the windward reef rim. Grainstone textures are abundant in the reef and forereef environments of the coral-red algae-Halirneda facies. Packstones are tnost common in this facies in the sand apron, shallow lagoon, and patch reef environments. and occur in the mollusk-foraminifera-Halimeda facies. The mixed peloidal-skeletal facies is characterized by wnckrsroiw and packsrotw text-rurcs.After Gischier and Lomando (1999).

Epeiric Platform and Epeiric Ramp

14.1.7 Epeiric Platform Model During the Phanerozoic epeiric seas covered extensive areas of the cratons. These very shallow, low-energy seas extended for hundreds to thousands of kilometers. Epeiric seas first flooded the margins and later the interior of tectonically stable cratons. Modem epeiric seas are rare. Examples of warm-water epeiric seas are the Sunda Sea and Java Sea, cool-water examples are the Baltic Sea, the North Sea, and the Hudson Bay (Edinger et al. 2002). Depositional patterns in epeiric seas are discussed in the epeiric platform model and the epeiric ramp model (Fig. 14.6). The epeiric platform model postulates clear-water sedimentation extending over vast regions from hundreds to thousands of kilometers wide, assuming that tides were damped out by friction with the shallow sea bottom and salinities increased seaward (Irwin 1965). The depositional site should be characterized by a more or less negligible, extremely low slope angle and regionally extended low-energy conditions and distinct salinity gradients. The inner platform is believed to have been characterized by subtidal to intertidal mud flats with widths of tens to hundreds of kilometers, and water depths generally less than 10 rn. The model differentiates a low-energy, below wave base zone X of the open sea, a relatively narrow zone Y of higher energy where waves impinge on the sea floor and strong tidal currents develop, and an extended Lone Z with restricted water circulation, minimal tidal effects, only periodic storm effects, and hyper- and/or hypo-salinity conditions. The tideless mode of the model in zone Z was questioned by Pratt and James

(1986) who proposed a 'tidal flat island model' assuming the existence of small supratidal low-relief islands and intertidal banks surrounded by open subtidal waters. This model overcomes many contradictions inherent in fitting facies criteria to the epeiric platform model, and adapts the tideless model to many Early Paleozoic limestones and dolostones characterized by supra-, inter- and subtidal cycles.

14.1.8 Epeiric Ramp Model The epeiric ramp model was proposed by Lukasik et al. (2000) to describe temperate Tertiary carbonates from the Murray Basin in Australia (Fig. 14.6B). Epeiric ramps and normal carbonate ramps differ in the widths that may reach hundreds of kilometers (normal ramp 1-100 km), very low and negligible slope angles (ramp -> -> intraparticle, intraparticle, shelter interparticle, fenestral voids, intraparticle, fenestral interparticle medium to small

small

up to 10%

up to 20%

up to 30°h

1

mostly < 5% small

matrix: matrix: good angular fragmoderate fossils: poor ments if fossils: mod- to good broken erate to good

large

crinoids, tabular stromatorachiopod: poroids

crinoids 1goniatites Ibrachiopods

bulbous + massive stromato- &Mm poroids. micrite envelopes, syntaxial rim cemer

mha, ostracods

pores)

aminites)

crinoids, So/enopora, Keega

Fig. 14.9. i.'tic-ies nlodelfor Middle m d Late Delwziun reef ccul-honatesafter Machel and Hunter ( 1994).The model differentiares five water energy zones with increasing water energy from I to V, designated as either f (forereef) o r b (baclueeo. Use of the nod el requires an estimation of frequencies, differentiation of growth forms and some knowledge of fossils. Part A estimates water energy by noting rounding and sorting. Part B refers to the limestone texture. Part C records the amount of micrite. Part D lists the amount, size and the predominant type of porosity. Part E lists assemblages that are common in the different facies zones and have their distributional nyaxin~awithin the zone(s). Part F lists 'indicator fossils' which are usually found only in bnckreef, forereef, or reef core settings. The criteria used in distinguishing facies zones can be observed in outcrops. cores as well as in large thin sections. See Fig. 14.8 to see how the model is applied.

Fig. 14.10. The location ofreef gl-owrh and the development of the reef zones depend on the submarine topography. In the case of a more gently dipping slope, maximum reef growth is located deeper than in the example shown in Fig. 14.9 The shallow forereef zone IV-f is missing or only incompletely developed. After Machel and Hunter (1994).

Biotic R a m p Zonation

Fig. 14.11. Integrated reeflramp model for Devonian carbonates (modified from Machel and Hunter 1994). The reef model explained in Fig. 14.9 (facies zones indicated by Roman numbers) and the ramp model (facies indicated by small letters) are complementary. They overlap in space and partially substitute for one another. An integration of the models shows the facies distribution from the supratidal zones across a hypothetical carbonate shelf to the basin. The main differences occur in the outer shelf region where reefs develop in the case of a distinct shelf break. In the case of a gently sloping ramp, the lithol biofacies a and b will develop. Patch reefs (c) are most likely to form within facies b and d. a - Burrowed argillaceous mudstones and wackestones; fossils rare; scattered brachiopods and crinoids. b - Mudstone with carbonate nodules in shaly matrix. c - Patch reefs exhibiting stromatoporoid-coral floatstones to rudstones with bulbous and tabular stromatoporoids; and a wackestone-packstone matrix. d - Amplzipora floatstones and grainstones. e - Vuggy, poorly fossiliferous mudstones. f - Laminated and fenestral dolomite. g - Mudstone breccia, clasts correspond to reworked facies f.

Fig. 14.12. Drfleient/at~oizand sequence stratigraplzic interpretation of an outer homoclinal carbonate ramp bused 011 miuofossil assemblages. The figure displays the biotic gradients of Early Mississippian ramp carbonates in the Sacramento Mountains of south-central New Mexico (Jeffery and Stanton 1996). Black dots on the horizontal line show the position of measured and sampled stratigraphic sections. The length of the bars indicates the lateral extent of fossil assemblages. The letter S indicates the southernmost occurrence of sponge spicules generally regarded as an indication of relative deep-water environments The gently dipping thin- to medium bedded carbonates (mostly bioclastic wackestones) of the Alamogordo Member can be laterally traced bed-per-bed for more than 30 km. The thickness of the member is 1.5 m in the North and 10.5 m in the South. The sediment is interpreted as an autochthonous deposition because of the lack of structures indicative of transport. the presence of well preserved non-abraded fossils, patchy distributions of rock types in contrast to down-ramp gradients of depth-sensitive assemblages, common occurrence of fossils in life position, geopetals in undisturbed position, and beds traceable into and through mud mounds formed on the deeper ramp. The biotic components (hexactinellid sponge spicules, crinoid and other echinoderm debris, fenestellid bryozoan hash, and ostracods) are used to define assemblages that vary in relation to their shoreward and basinward ramp position. Assemblage I of the deepest water consists of crinoid/echinoderm debris, fenestellid hash and ostracods. Assemblage I1 contains the biota of assemblage I1 plus stacheiins (possible algae), rare salebrids (possible bryozoans) and commonly abundant sponge spicules. Assemblage I11 is characterized by members of assemblage I1 plus plurilocular foraminifera. The shallowest assemblage IV consists of assemblage I11 plus green algae. Within any bed, assemblage I is farthest down-ramp (south) and assemblages I11 or IV are the farthest up-ramp (north). The positions of the assemblages on the ramp shift laterally in successive beds of the stratigraphic sections, indicating variations in sea level and water depth. The beds 1-6 contain the deepest and deep assemblages I, I1 and 111; in the middle beds 7, 8 , 9 , 10 and 12 the assemblages shift up-ramp (from right to left of the figure), with the greatest shifts in bed 8. This bed represents the maximum flooding interval within the aggradational sediments of the Alamogordo Member. In beds 11,13 and 14 the assemblages shift back down-ramp, leaving space for the shallowest assemblage IV in the north. The beds below bed 8 represent a part of the transgressive system tract, the beds above bed 8 document the initial highstand tract. Modified from Jeffery and Stanton (1996).

Case Study: Triassic Foraminifera

676

14.2.2 Case Study: Foraminifera1Distribution in Late Triassic Reefs and Platforms Distributional patterns of benthic foraminifera evaluated in thin sections of shelf carbonates are important tools in subdividing facies zones of platform, ramp and reef environments, particularly in Mesozoic and Early Tertiary sediments.

Terrqenous-mud Reef-detntus-mud facles

facies

Benthic foraminifera are common constituents of Late Triassic platform and reef carbonates. They have proved to be extremely useful in recognizing facies zones. Open and restricted platforms (Facies Zones FZ 7 and FZ 8), platform margins and foreslope environments (FZ 6 , 5 and 4) as well as individual parts of reef complexes can be differentiated and subdivided by distinct foraminifera1assemblages. The concept was

Coqu~nas Corakponge facies Oncollbc facies Algal-foraminileral Reef-detritus-mud facies facles

Terrigenous-mud

facies

Absolute abundance of all foramin~fera Alpinophragmium

Sessile textulariids Sessile rniliolids Lagenids Involutina Trochoiina Triasina Ophthalm~cciium Sigmoilina Galear~eilapanticae Galeanella sp. Quinqueloculina Glomospira 7Yochammina Agathammrna "Tetrataxis" tldothyra ,' €ndothyrat~e/la

Duostorn~ds Coarse agglutmated textulariids Fine agglutinated textulari~ds

Fig. 14.13. Distributionalpattems ofbcnthir foraminifera are successfully used in recognizing and subdividing facies zones and enviromlents of carbonate platform and reef complexes. The example from the Rotelwand near Adnet (Austria) shows the distribution of foraminiferal assemblages in a small patch reef formed on a swell within a muddy shallow intraplatforrn basin. The facies zones of these Late Triassic limestones are defined by dominating grain types, biota and limestone textures. The central reef facies is characterized by coralline sponges, scleractinian corals and interstitial reef debris. Note the asymmetric facies pattern, comprising bioclastic grainstones of a near-reef oncolithic grapestone facies and an algal-foraminifera1 fdcies at the leeward side, and a mud facies with reef detritus (packstones, wackestones) grading into a marly lime mud facies (wackestones, mudstones) surrounding the reef. The facies zones are distinguished by specific taxa, assemblage composilion and relative frequency of taxa. Some of the diagnostic foraminifera are depicted in P1. 111. Length of the section about 1.5 km. Modified from Schafer and Senowbari-Daryan (1981).

Basics: Biotic Zonation Patterns

developed for the Northern Calcareous Alps. Studies in other parts of the Tethys (Carpathians, Sicily, Greece, Oman, Papua New Guinea) confirmed the general usefulness of the method in facies studies of outcrop and subsurface samples. Fig. 14.13 and P1. 111 show the potential of foraminifera1patterns in distinguishing reef environments and adjacent areas. Tethyan Norian and Rhaetian platform and reef carbonates are characterized by specific foraminifera1 assemblages. The distribution was controlled by substrate conditions and salinity, nutrient requirements, specific life behavior, the topography of the depositional environment, water depth, and light. The facies-diagnostic foraminifera shown in P1. 111 are members of various high systematic units (see Sect. 10.2.2.1 for criteria). They include Textulariina characterized by shells with agglutinated walls (Pl. 11111, 9, 10, 13, 14, 18,20), Miliolina withporcelaneous walls (PI. 111/24), Involutinina with hyaline aragonitic walls (PI. 111/15, 16, 17, 19,22), Rotaliina with hyaline walls P1. 1111 23) as well as Fusulinina with microgranular walls (Pl. 111/11. 12,21,24). The application of the method requires the following steps: Quantify the essential microfacies criteria (grain types, fossils, micrite, intergranular cement). Determine the foraminifera on a genus level, if possible on a species level. Examine the frequency of the foraminifera by pointcounting, for both the whole sample and the skeletal grains Check the number of foraminiferal tests representing different genera and species within an area of nine square centimeters. This area was successfully used the studies of Triassic foraminifera. The shell size and density of the shells in thin sections require relatively large fields. Evaluate the significance of the composition of fora~niniferalassemblages using chi-square tests, cluster or ordination analysis (Hohenegger 1974; Dullo 1980)! Compare your results with the distribution patterns described by Hohenegger and Piller (1975), Piller (1W8), Schiifer and Senowbari-Daryan (I98 l ) , Gazdzicki (1983) and other relevant papers listed under the Code Kill! Basics: Biotic zonation patterns Geel, T. (2000): Recognition of stratigraphic sequences in carbonate platform and slope deposits: empirical models

based on microfacies analysis of Paleogene deposits in southeastern Spain. - Palaeogeography, Palaeoclimatology, Palaeoecology, 155,211-238 Hallock, P., Glenn, E.C. (1986): Larger foraminifera: a tool for palaeoenvironmental analysis for Cenozoic depositional carbonate facies. - Palaios, 1,55-64 Hladil, J. (1986): Trends in the development and cyclic patterns of Middle and Upper Devonian buildups. - Facies, 15, 1-34 Hohenegger, J. (1999): Larger foraminifera - microscopical greenhouses indicating shallow-water tropical and subtropical environments in the present and past. - Occasional Papers of the Kagoshima University Research Center for the Pacific Islands, 32, 19-45 Hohenegger, J., Lobitzer, H. (1971): Die ForaminiferenVerteilung in einem obertriadischen KarbonatplattformBecken-Komplex der ostlichen Kalkalpen. - Verhandlungen der Geologischen Bundesanstalt Wien, 1971,458-485 Hohenegger, J., Piller, W. (1975): Okologie und systematische Stellung der Foraminiferen im gebankten Dachsteinkalk (Obertrias) des nordlichen Toten Gebirges (Oberosterreich). - Palaeogeography, Palaeoclimatology, Palaeoecology, 18,241-276 Jeffery, D.L., Stanton, R.J. (1996): Biotic gradients on a homoclinal ramp: the Alamogordo Member of the Lake Valley Formation, Lower Mississippian, New Mexico, U.S.A. - In: Strogen, P., Sommerville, I.D., Jones, G. L. (eds.): Recent advances in Lower Carboniferous Geology. .- Geological Society London, Special Publication, 107, 111-126 Kumar, A., Saraswati, P.K. (1997): Response of larger foraminifera to mixed carbonate - siliciclastic environments: an example from the Oligocene - Miocene sequence of Kutch, India. - Palaeogeography, Palaeoclimatology, Palaeoecology, 136. 53-65 Machel, H.G., Hunter, I.G. (I 994): Facies models for Middle to Late Devonian shallow-marine carbonates, with comparisons to modem reefs: a guide for facies analysis. Facies, 30, 155-176 Moody, R.T.J. (1987): The Ypresian carbonates of Tunisia a model of foraminifera1 facies distribution. -- In: Hart, M.B. (ed.): Micropalaeontology of carbonate environments. - 82-92, Chichester (Harwood) Murray, J.W. (1991): Ecology and palaeocology of benthic foraminifera. - 397 pp., New York (Longman) Pautal, L. (1987): Foraminifera1 assemblages of some early Tertiary environments (bays) of the northern Corbikres, France. -In: Hart, M.B. (ed.): Micropalaeontology of carbonate environments. - 74-8 1, Chichester (Hanvood) Piller, W. (1978): Involutinacea (Foraminifera) der Trias und des Lias. - Beitrage zur Palaontologie von Osterreich, 5, 1-164 Schafer, P., Senowbari-Daryan, B. (1981): Facies development and paleoecologic zonation of four Upper Triassic patch reefs, Northern Calcareous Alps near Salzburg, Austria. - In: Toomey, D.F. (ed.): European reef models. Society of Economic Paleontologists and Mineralogists, Special Publications, 30, 241-259 Venec-Peyre, M.T. (199 1): Distribution of living benthic foraminifera on the back-reef and outer slopes of high island (Moorea, French Polynesia). -Coral Reefs, 9, 193-203

Further reading: Kl 1 I

678

Biotic Zonation: Triassic Foraminifera

Plate 111 Biotic Zonation of Shallow-Marine Facies Zones with Benthic Foraminifera: Late Triassic Platform and Reef Limestones Reef: Foraminifera of higlz-growing coral communities 1 Alpinophragmium petforatum Fliigel. The species, known all over the Tethys and from Panthalassan terranes, is characteristic for the central part of Norian and Rhaetian reefs. The fine-agglutinated foraminifer encrusts high-growing corals. Reef limestone, coral framestone. Triassic (Misfah Formation, Hawasina Group, Norian): Oman Mountains. Reef: Foraminifera living in millinzeter- to centimeter-sized growth cavities and on low-growing reefbuilders (e.g. sphinctozoid sponges, solenoporacean red algae) 2 Typical reef cavity microfacies with miliolinid foraminifera (1: Ophthalmidium carinaturn (Leischner); 2: Galeanella) and peloids. Late Rhaetian patch reef: Feichtenstein, Salzburg, Austria. 3 Reef cavity with Galeanella (1: Galeanella sp.; 2: Galeanella panticae Bronnimam et al.) and micrite clasts. This microfacies occurs in small patch reefs at the margins of intraplatform basins as well as in large platform-marginal reefs. Same locality as -> 2. 4-5 Galeanellapanticue Bronnimann et al. This miliolinid foraminifer i s abundant in protected parts within central reef parts and occurs also in bioclastic sands deposited in the leeward position of Late Triassic reefs (Facies Zone FZ 7). Norian (Dachstein reef limestone): Gosaukamm, Austria. 6 'Sigmoilina', a common miliolinid foraminifer in the central reef facies. Same locality as -> 4. 7 Ophtlzalrnidiurn sp. Common in protected areas between reefbuilders and in mud-rich reefs formed at the upper slope (Facies Zone FZ 4). Same locality as -> 4. 8 Opl~tlzalnzidiunitriadirun? (Kristan). Oblique section showing the characteristic trumpet-shaped apertura. Common in boundstones but also in muddy platform areas with reef-derived material (Facies Zone FZ 7). Same locality as -> 5. 9 'Lituosepta' sp. Common in reef cavitiy sediments and in sediments between reef patches. Rhaetian: Same locality as -> 2. 10 Kaeveriaflugeli (Zaninetti et al.) Common agglutinated foraminifera in protected reef areas. Same locality as -> 3. Rack-reef and near-r-eefcarbonate platform I 1 Duostominidae. These foraminifera, characterized by trochospiral tests with microgranular walls, are concentrated in platform carbonate sands (Facies Zone FZ 7). They are associated with involutinid foraminifera and dasyclad grcen algae. Norian (Bedded Dachstein limestone): Dachstein area, Austria. 12 'Tetrataxis' nanus Kristan-Tollniann. The genus is most common in platform environments. but also occurs in muddy shelf limestones (Facies Zone FZ 8). Rhaetian (Kossen beds): Steinplatte, Tyrol, Austria. 13 Glornospira and Glomospirella are difficult to discriminate in thin sections. The genera are characterized by a streptospirally enrolled second chamber that later becomes planspirally coiled, forming a discoidal test. Glomospirella has been regarded as agglutinated foraminifera but has now been assigned to the involutinids. Common in platfonn and backreef carbonates (FZ 7), associated with other involutinids and dasyclads. Same locality as -> 3. 14 Biserial agglutinated foraminifera, attributed to Textuluria, are more common in platform sediments than in the reef facies. Same locality as --> 12. Plutjorol-rn~ni~irotlnwtm 15 Triasinu grainstone. Triasirza Majzon is a widely distributed involutinid foraminifer in open-marine far-reef platform carbonates (FZ 7). Note the different preservation of the primarily aragonitic tests. Late Triassic (Rhaetian): Extraclast within an Upper Jurassic breccia. Gschollkopf, Sonnwendgebirge, Northern Alps, Austria. 16 Aulotortus comrnunis (Kristan-Tollmann), an abundant involutinid foraminifera in grainstones of Late Triassic platforms (FZ 7). Norian (bedded Dachstein limestone): Gosaukamm, Austria. 17 Aulotortus sinuosus Weynschenk. Subaxial-axial section. The species occurs in backreef sands as well as in platform calcarenites and shallow basins. Note the characteristic sickle-shaped chambers. Rhaetian (Kossen beds): Loferbachgraben. Salzbusg, Austria. Drepri- shelf'c.clr-bonu!cs 18 Encrusting textularinid foraminifera. Iblypainnzina gregaria Wendt. Various attached foraminifera are common constituents of peloidal muddy carbonates deposited in deeper areas in front of reefs (FZ 4) or in low-energy platform areas (FZ 8). The foraminifer encrusts bioclasts and acts as binder of sediment grains, sometimes forming oncoids. Rhaetian: Ehrenreit, Bavaria. 19 Planiin~dutit~a curinata Leischner. Attached, probably miliolinid foraminifera. Intraplatfor~nshelf limestone. Same 10cality as -> 13. 20 Trorlzanzmina ulpina Kristan. The trochospiral tests of this agglutinated foraminifer is most common in micritic limestones (deeper shelf carbonates and protected micritic parts of the inner platform (FZ 8), mud-rich reefs of the upper slope, FZ 4). Rhaetian: Gruber reef near Hallein, Austria. 7, I 'Endothyranella'. Muddy shallow-basinal limestones. Rhaetian (Kossen beds): Hochalm, Tyrol, Austria. Fnr-reef ccabonatcs 22 Agatlzammina austroalpina Kristan-Tollmann and Tollmann. This miliolinid or finely agglutinated textulariniid foraminifer is abundant in far-reef peloidal muddy settings (FZ 8) and in open-marine inner platform areas (FZ 7). Same locality as -> 17. 23 Austrocolonzia marschalii Leischner, a lagenid foraminifer. Note the gradually enlarging chambers and wall with costae. Rhaetian (Kossen beds): Gaissau, Salzburg, Austria. 24 'Turrispirillina' sp. Muddy slope (FZ 4) and basinal facies. Norian (Plattenkalk): Gosaukamm, Austria.

Plate 1 I I : Late Triassic Foraminifera

679

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200 urn

-

100 urn

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200 urn

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200 urn

200 urn

200 urn

200 urn

200 urn

200 urn

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200 urn

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300 urn

580

14.3 Standard Microfacies Types (SMF)

Standard M i c r o f a c ~ e s1')p e z

Depositional texture types. Only a few SMF Types correspond to just one texture type; most SMF Types occur in two or more texture types of the Dunham classification and its modifications (Box 14.7).

Facies of carbonate rocks is studied on different scales. Stratigraphic relationships of rock bodies?sedimentary Some SMF Types are very simply defined and rely structures, and litho- and biofacies are the main targets on the principal and quantitatively dominant kind of of outcrop studies. In the subsurface, rock bodies and grains. For example, limestones with abundant aggrefacies units are seismcally differentiated,using log char- gate grains represent a specific SMF Type (PI. 12114). acteristics and investigating cores and cuttings. Limestones with abundant ooids, or limestones with Microfacies based on thin-section studies subdivides abundant peloids, or with dominating benthic foraminfacies into units of similar compositional aspect that ifera are attributed to three other SMF Types (see P1. reflect specific depositional environments and controls. 120, PI. 12111-3, and PI. 12211). These types are easy This target requires integrating small-scale microfacies to determine but somewhat dangerous in their use as data and larger-scale litho- and biofacies criteria. This indicators of paleoenvironmental conditions. A thorcan be done when the criteria of textures, composition ough inspection of oolitic, peloidal or foraminifera1 and fossils of the limestones are considered jointly with limestones will reveal structural, textural or composithe help of Standard Microfacies Types. tional differences that must be included in the discrimination of SMF Types, because these differences conStandard Microfacies Types are virtual categories tain essential information on depositional settings and that summarize microfacies with identical criteria. environmental controls. Oolite grainstones consisting These criteria are simple, non- or semi-quantitative,and of abundant and well-sorted concentric ooids indicate easy to recognize. Most SMF Types are based on only shallow-marine, high-energy conditions. Grainstones a few dominant characteristics comprising grain types, and wackestones with poorly sorted radial ooids indibiota or depositional textures. cate low-energy conditions, common in transitionalmarine and also non-marine environments. In the folThe SMF concept arose from the recognition of the lowing revision of the SMF Type classification these astonishing compositional and textural similarity of differences are annotated by the introduction of suhlimestones of different age formed in analogous cnvi- types (e.g. SMF 15-C and SMF 15-R for oolite limeronments (see Fig. 14.28). Originally developed for cat- stones) in order to avoid an inflation of SMF types. egorizing common Late Triassic platform and reef car- Subtypes were also proposed for peloid limestones. bonates, and based on the combination of texture and using differences in the fabrics, and for limestones conpaleontological criteria (Fliigel 1972). the classifica- sisting of foraminifera or calcareous green algae in rochtion was expanded and more strictly defined by Wil- building abundance. son (1975) for the history of carbonate facies over time. Other limestones having in common the same domiWilson distinguished 24 SMF Types and used these nant grain types (e.g. oncoids) are attributed to differtypes as additional criteria in differentiating the major ent SMF Types because of unlike carbonate te,Wi-Cs facies belts of an idealized rimmed carbonate shelf (Fig. and different grain structures, indicating differences in 14.29). environment and depositional setting (cf. P1. 1 19/3 and PI. 12412). I.Zrhic11 critet-la are used to diflerenriate SMF Types? Some SMFTypes are defined by characteristic ecoThe main criteria used in differentiating SMFs comlogic groups, e.g. the abundance of planktonic microprlse: Grain types, grain frequency (prevailing grain types) fossils (PI. 1l3), or the occurrence of reef-building fosand grain associations. sils (Pl. 116/2,3). These categorizations are very broad Matrix types (e.g. micrite, calcisiltite). and include many pitfalls. Pelagic limestones with abunDepositional fabrics (e.g. lamination, grading, open- dant planktonic fossils must be subdivided at least acspace structures. burrowing, reworking. and redepos- cording to the prevailing systematic groups. The use of 'reef-building fossils' as diagnostic criteria requires ition). Fossils (dominant groups, assemblages, autochtho- interpretating the reef- and sediment-building potennous/allochthonous occurrence, skeletal concentrations tial of benthic organisms. Thin sections with corals are e.g. shell accumulations, specific ecologic groups e.g. no evidence for the existence of reefs. Corals may be planktonic organisms, taphonomic features e.g. pres- members of the constructor guild and contribute to organic frameworks, but are also bafflers that might or ervation: mlcrite envelopes).

Standard Microfacies Types

might not take part in reefbuilding, and they are also members of the dweller guild of level-bottom communities. Despite these difficulties, the SMF Types based on ecologic groups have been retained, since they allow a first approximate assignment of samples. Other criteria used in defining SMF Types are spec$ic fabrics, e.g. lamination or fenestral structures (PI. 123), or combinations of diagenetic and depositional features (laminated evaporitic carbonates, P1.12514; pisolitic carbonates, PI. 12611, 2).

Can the SMF Types be used for other carbonate depositional models? The SMF Types were defined for a model describing the sedimentation on a rimmed carbonate shelf and warm-water platform-reef environments in tropical latitudes. The occurrence and distribution of the SMF Types are strongly dependent on water depth, and that in turn depends on the configuration and topography of the shelf. Some microfacies types of inner and shallow parts of carbonate ramps correspond to SMF Types of platform interior sediments. Back-ramp tidal and lagoonal areas are similar in microfacies associations to tidal flat and lagoonal environments of platforms. Other microfacies types on ramps and platforms, however, differ in their location. SMF 15, characterized by concentric ooids, occurs in the platform model in a platform-edge position, in the ramp model in an inner and mid-ramp position. Outer ramp microfacies types include SMF Types known from the Wilson model, but also types not specifically distinguished in the platform model. Similar situations exist in comparing microfacies types of non-rimmed platforms and epeiric platforms and ramps with SMF Types of rimmed platforms. Major discrepancies exist between the Standard Microfacies Types and microfacies types of cold-water carbonates. The latter differ in composition (lack of ooids, aggregate grains), skeletal grain associations and skeletal mineralogy (see Sect. 12.2), texture and weak cementation. Many temperate and cool-water microfacies types hardly correlate with SMF Types at all. Look at the pictures of cool-water limestones on P1. 10611-3 and try to find comparable microfacies types in the SMF classification that were set up for warmwater platform carbonates! The only SMF Type with an approximately similar biotic composition is SMF 9. This SMF is defined by strongly burrowed skeletal wackestones and a wide spectrum of fossil groups also comprising the fossils of these cool-water samples. Because of the too generalized definition of SMF 9, this assignment provides little help in interpreting the environment of the samples. A comparison with microfacies types of ramps is much more advisable.

14.3.1 Revised Standard Microfacies Types The following pages summarize the diagnostic criteria of the Standard Microfacies Types and indicate their distribution in the Facies Zones of the Wilson model and in the different part of carbonate ramps. Let us start with a short list (Box 14.4).

Box 14.4. List of Standard Microfacies Types. The order of the SMF numbers follows approximately the order of the Standard Facies Zones in the Wilson Model going from the basinal SMF Type 1 to SMF 26 that characterizes subaerial exposed areas.

SMF 1: Spiculitic wackestone or packstone, often with calcisiltite matrix. Subtype emphasizes burrowing.

SMF 2: Microbioclastic peloidal calcisiltite with fine grainstone and packstone fabrics.

SMF 3: Pelagic lime mudstone and wackestones with abundant pelagic microfossils. Subtypes differentiate the groups of planktonic organisms. SMF 4: Microbreccia, bio- and lithoclastic packstone or rudstone. SMF 5: Allochthonous bioclastic grainstone, rudstone, packstone, floatstone, breccia with reef-derived biota. SMF 6: Densely packed reef rudstone. SMF 7: Organic boundstone. Subtypes try to differentiate the kind of contribution by potential reefbuilders to the formation of reefs and other buildups. SMF 8: Wackestones and floatstones with whole fossils and well-preserved endo- and epibiota. SMF 9: Strongly burrowed bioclastic wackestone. SMF 10: Bioclastic packstone and wackestone with abraded and worn skeletal grains. SMF 11: Coated bioclastic grainstone. SMF 12: Limestone with shell concentrations. Subtypes characterize shell-providing fossils. SMF 13: Oncoid rudstone and grainstone. SMF 14: Lag deposit. SMF 15: Oolite, commonly grainstone but also wackestone. Subtypes highlight the structure of ooids. SMF 16: Peloid grainstone and packstone. Subtypes differentiate non-laminated and laminated rocks. SMF 17: Grainstone with aggregate grains (grapestones). SMF 18: Bioclastic grainstone and packstone with abundant and rock-building benthic foraminifera or calcareous green algae. Subtypes describe the systematic assignment of the various groups. SMF 19: Densely laminated bindstone. SMF 20: Laminated stromatolitic bindstone/boundstone. SMF 21: Fenestral packstone and bindstone. Subtypes characterize fenestral voids and the contribution of calcimicrobes. SMF 22: Oncoid floatstone and wackestone. SMF 23: Non-laminated homogenous micrite or microsparite without fossils. SMF 24: Lithoclastic floatstone, rudstone or breccia. SMF 25: Laminated evaporite-carbonate mudstone. SMF 26: Pisoid cementstone, rudstone or packstone. Text continued o n p. 717

Standard M ~ c r o t a c i e sTypes

682

Plate 112 Standard Microfacies Types: SMF 1 and SMF 2 This plate and the following plates up to P1. 126 start with a general text explaining the diagnostic criteria and the occurrence of the SMF Type in the different depositional settings. The description of thin sections is focused on characteristics of the SMF Types and indicates their more frequent distribution in generalized facies zones.

SMF I : Spiculite wackestone or packstone, often with a calcisiltite matrix Criteria: Dark, bedded limestones (mudstone, wackestone), commonly argillaceous and organic-rich. Abundant siliceous (or calcified) sponge spicules, often oriented. Parallel orientation of spicules and clay laminae may cause a very fine depositional 'lamination' pattern (Wilson 1969). In addition pelagic microfossils (e.g. radiolarians) may occur. The microfossils may be densely packed (-> 1) or sparsely distributed due to intensive -> 2). Occurrence: Basinal deep-water environment with slow sedimentation. burrowing (SMF 1-BURROWED: This microfacies is common in Paleozoic and Mesozoic basinal carbonates (FZ I), deeper shelf carbonates (FZ 2) as well as in mid-ramp and outer ramp settings. Spiculites are common in deep cold-water settings, but also occur in shallow-marine environments (Gammon and James 2001). Additional pictures: P1.4411, PI. 13911. SMF I-BURROU~ED: Burrowed hioclastic wackestone with abundant fine pelagic and benthic biodetritus. Criteria: Very small bioclasts, conlmonly shell debris, scattered within a dense, strongly burrowed matrix. SMF 1-BURROWED differs from SMF 1 in the dominance of sparsely distributed skeletal grains representing a mixture of benthic and planktonic elements. Occurrence: Basin (FZ I), open sea shelf (FZ 2), and outer ramp. SMF 2: Microbioclastic peloidal calcisiltite. Criteria: Thin- to medium bedded limestones. Very fine-grained packstones or grainstones consisting of peloids and small litho- and bioclasts. 'The grains are a mixture of off-bank debris and reworked sediment. Common bioclasts are echinoderms and mollusks. Small-scale ripple cross-lamination and laminae exhibiting millimeter-scale gradation are common. Occurrence: Common in deeper basins (FZ 1 ) and open-marine shelf (FZ 2) as well as in deep-shelf toe-of-slope position (FZ 3). Abundant in outer ramp settings. 1 S M F 1. Radiolaria-bearing spirulite packstone. The bioclastic packstone consists predominantly of accun~ulationsof nmnason and other hexactinellid sponge spicules. Some of the spicules are partly calcified. Larger circular structures art. cross-sections of radiolarians (arrows). Note parallel orientation of spicules indicating bottom currents. The matrix is organic-rich micrite. Water energy was sufficient to orientate the spicules, but not to winnow the carbonate mud. Deep basin (FZ 1A). Jurassic of the Northern Calcareous Alps (Roman mosaic stone): Kraiburg, southern Bavaria, Germany. 2 S M F 1-BURROWED. Burrowed wuckestonc. Skeletal grains are conspicuously small and comprise shell debris, sponge spicules (SP), radiolarians, and small echinoderm fragments (E). Burrowing (B) is abundant, corresponding to the bioturbation grade 4 of Taylor and Goldring (1993). This index describes burrow abundance, amount of burrow overlap and

sharpness of primary sedimentary fabric. Grade 4 is characterized by high burrow density with common overlap. Burrowing contributes to the diminution of skeletal grains. Deep open shelf (FZ 2). Early Jurassic (Sinemurian): Korfu Island, Greece. 3 S M F 2. Fine-grained peloid grainstone (FPC)and peloid-hioclast packstone ( P B P ) . Most bioclasts are echinoderms with syntaxial rim cements. The sediment consists of peloids and skeletal debris. White arrow points to a shell fragment, the black arrow to serpulid tubes. The currents that deposited the silt-sized grains also winnowed most of the lime mud. Off-bank facies of an outer ramp. Cretaceous: Switzerland

Fig. 14.14. S M F 2: Cross-bedded fine-gralned quartz-peloici packstone. Dark layers consist of densely packed micritic peioids (redeposited intraclasts). Light layers contain angular, silt-sized terrigenous quartz grains. Note the brachiopod shell (arrow). The sample represents a basinal facies. The sediment was deposited in deep-water canyons (see Buchroithner et al. 1980). Note the vertical calcite-filled microcracks displacing an earlier oblique calcite vein. Standard Facies Zone (FZ 2). Late Devonian: Ferragut Vell, Menorca Island, Spain. Scale is 5 mm.

Plate 112: SMF 1 a n d S M F 2

68.3

I mm

SMF 1

Standard Microfacies T y p e s

Plate 113 Standard Microfacies Type: SMF 3

SMF 3: Pelagic lime mudstone and wackestone with planktonic microfossils Criteria: Micrite matrix with common to abundant pelagic microfossils (e.g. foraminifera, radiolarians, calpionellids) or macrofossils (e.g. 'filaments' -Triassic to Jurassic, pelagic crinoids, graptolites). As shown by SEM photographs, the micritic matrix of many Mesozoic limestones consists of accumulations of disintegrated caicareous ultraplankton (e.g. coccolithophorids, P1.713; namoconids, PI. 77/23). The type of the dominant pelagic fossils should be indicated by letters e.g. SMF 3-CALP(calpionellids), SMF 3 -FOR(pelagic foraminifera), SMF 3-RAD(radiolarians), SMF 3-TENT(tentaculitids). Occurrence: Basin (FZ I-B) and open deep shelf (FZ 3). Additional pictures: P1. 6/6, P1. 6615, P1. 7313 (SMF 3-FOR),P1. 7611 (SMF 3-RAD),P1. 76/7 (SMF 3-CALP),PI. 9 l/3 (SMF 3-TENT). SMF 3 4 0 ~Pelagic . foranzinifera wackestone with single-keeled globotruncanids. Tests are generally well-preserved due to the primary Low-Mg calcite skeletal mineralogy. Pelagic deep-water basinal facies (FZ 1). Late Cretaceous (Scaglia rossa): Central Apennines, Italy. SMF 3-FIL.Thin-shelled pelagic bivalve ('Jilaments')wackestone. The thin, curved calcitic shells were originally regarded as planktonic algae and therefore called 'filaments' (see Sect. 10.2.4.2).The fossils are pelagic bivalves representing in parts shells of planktonic larval stages. Note the parallel arrangement of the shells pointing to some current control. Dense accun~ulations(arrows) are caused by burrowing. The biofabric is characterized by dense and loose packing; little variations in the sizes of the bioclasts, and good sorting. The paleobathymetric position of limestones with filaments 1s controversial. Many authors regard the facies as an indication of bathyal deep-water settings, but others go for a littoral environment. Deep shelf facies (FZ 3). Early Jurassic: Korfu Island, Greece. SMF 3-CALP.Calpiunellld wackestone. Arrows point to the few sections which can be used in taxonomic differentiation. The fine-grained matrix consists predominantly of nannofossils and micropeloids better to be seen in SEM. Black patche:, are bitummous matter. Deep basinal facies (FZ 1). Late Jurassic (Tithonian): Seebiihel, Switzerland.

Fig. 14.15. SMF 3-TENT.Densely packed tentaculitid wackestone. All skeletal grains are shells of pelagic mollusks. Tentaculitids contributed largely to the formation of Ordovician to Late Devonian open-marine and basinal micritic carbonates (see Sect. 10.2.4.5). Deep basin (FZ 3A). Early Devonian: Frankenwald, Germany.

Plate 113: SMF 3

685

Standard Microfacles Types

686

Plate 114 Standard Microfacies Types: SMF 4 and SMF 5

SMF 4. Microbreccia, bioclastic-lithoclastic packstone or rudstone Criteria: Fine-grained breccias, debrites and turbidites consisting of grains of various origin. Grains are cornmonly worn and rounded and may consist of both locally derived bioclasts, imported shallow-water material and previously cemented lithoclasts. Grains may be either polymict in origin or of uniform composition. Grading textures are common. Grains can be mixed with quartz, cherts and extraclasts. This rock type includes both fine talus and also debris laid down by turbidites (e.g. in 'allodapic limestones', Meischner 1965). Occurrence: Foreslope talus, resedimented limestones. Basinal settings (FZ 1) and toe-of-slope settings (FZ 3). SMF 5. Allochthonous bioclastic grainstone, rudstone, packstone and floatstone or breccia Criteria: Densely packed whole fossils and fossil fragments with a high percentage of reef-derived organisms. The bioclasts occur in a chaotic order or they form depositional structures with characteristic patterns (e.g. turbidite sequences). Occurrence: Reef-flank facies, slope (FZ 4), adjacent to reefs. Deposited in forereef position and reef slopes, or in backreef settings and in lagoons. Inner ramps. Additional picture: PI. 5811.

SMF 4. Polymict clast-supported microi'lrei-cia,consisting of carbonate litho- and bioclasts and quartz grains (most white particles). Carbonate grains are subangular to subrounded (fields G, I and L of the Krumbein chart; see Fig. 4.30). Most quartz grains correspond to the fields P and Q (low sphericity and low roundness). Carbonate grains are lithoclasts (L) and bioclasts including bivalves (B), bryozoans (BR), echinodenns (E), foraminifera (F), finely agglutinated orbitolinid foraminifera (OF), and rudist bivalves (R). Debris flow. Toe-of-slope (FZ 3). Late Cretaceous: Northern Calcareous Alps. SMF 4, SMF 2 and SMF 1. Alloclzthonous and autochthonous deep-water sedimentation. The coarse-grained lower part of the basal unit yields thin brachiopod shells (B) deposited in 'convex-up' positions. The center part (packstone, PS) consists of micrite clasts and thin, parallel arranged shells. The overlying layer is a fine-grained grainstone (GS) deposited within a relief (arrows) of the underlying packstone. Packstone and grainstone display indistinct lamination caused by parallel arranged thin shells. Note the differences in grain sizes and the sharp boundary between the fine-grained grainstone and the overlying brachiopod-bearing lime mudstone (M). Shell orientation patterns indicate the existence of weak currents. The sample exhibits three SMF Types: The basal layer with brachiopod shells represents SMF 4. The packstone and grainstone layers correspond to SMF 2. The uppermost part reflects the basinal background sedimentation (lime rnudstone with scattered fossils, SMF 1). Sedimentation took place in a deep shelf environment (FZ 3), see Fig. 14.16. Uppennost Silurian (Lochkovian): Klonk near Suchomasty, southwest of Prague, Czech Republic. SMF 5. Phylloid algalf7outstone. Characteristic criteria of SMF 5 are the abundance of reef-derived fossils, the chaotic fabric and the packstone texture of the matrix. Most bioclasts of the sample shown here are fragmented plates of udoteacean green algae (see Sect. 10.2.1.6). Somc fragments are coated and encrusted by foraminifera. The plates are jumbled together and form a self-supporting framework that was infilled by the matrix. Shells (S) of gastropods and bivalves and fusulinid foraminifera (F) are of minor importance. The matrix is an organic-rich packstone consisting of silt-sized peloids and some quartz grains. The sample comes from flank beds of a shelf-margin mound that was subaerially exposed several times. The mound material was redeposited near the mound core. The algal plates are strongly leached and partly filled with gray micritic sedinlett (black arrow). The original algal structures are completely destroyed. Many phylloid algal buildups of the southweslern U.S.A. are excellent reservoir rocks. Porosity developed through early vadose leaching of skeletal grains and dissolution of parts of the matrix, combined with fracturing and brecciation. Late Pennsylvanian (Holder Formation): Yucca Mound, northern Sacramento Mountains, New Mexico, U.S.A.

Devonian

Silurian

Fig. 14.16. Microfacies assists in dlfferetztiating allochthonous and background sedinzentation in deep-marine environments. The sample on P1. 11412 comes from the international stratotype of the Silurian-Devonian boundary. Questions concerning a possible turbiditic origin of the boundary bed have been clarified by a microfacies study (Hladil 1992). Common microfacies types are hemipelagic laminites, currentderived laminites and lime shale and muddy limestones with graptolites. Coarse calciturbidites are rare. The microfacies of bed 14 exhibits criteria of currentcontrolled deposition (packstones and grainstones; SMF 2), deposition of argillaceous and calcareous material (mudstone, SMF I), and only minor allochthonous sedimentation (brachiopod accumulation at the base of the bed, SMF 4). Most of the other limestone beds of the Klonk section exhibit similar microfacies composition. Modified from Hladil (1992). A: Laminite; B: Current-generated limestone; C: Coarse turbidite; D: Lime shale and muddy limestones with graptolites.

Plate 114: SMF 4 and SMF 5

6x7



SMF 5. For a general explanation of SMF 5, see P1. 114. SMF 6.Densely packed reef rudstone Criteria: Coarse gravels of biogenic material and lithified sediment derived from 'reef' tops or flanks and deposited in high-energy or low-energy slope settings by rock fall and various mass-flow processes. The size of the clasts ranges from some millimeters to tens of centimeters. Often with low matrix content. Sorting is poor (debris flows) or good (turbidites). Occurrence: Slope (FZ 4). SMF 6 is common within and adjacent to reef complexes, at platform margins, or in foreslope sediments. Additional pictures: P1.45/3, P1. 8212. 1 S M F 5. Turbidite. The sample is a graded turbidite consisting of reef-derived material, and deposited in a basin adjacent to small coral reefs. Reworked grains are bioclasts including bivalve shells (BS), corals (C), echinoderms (E), gastropods (G) and algae (A). The 3.5 cm thick bed exhibits the characteristic calciturbidite sequence: An erosive base (black arrows), graded bedding consisting of a thicker floatstone layer (FS) and a thinner grainstone layer (GS), and a planar (even) top (white arrows). The bed is covered by marls (M). Shallow slope (FZ 5). Late Triassic (Zlambach Formation. Rhaetian): Northern Calcareous Alps, Austria. 2 SMF 6. Debrisflow. Lithoclastic rudstone. The sample is from the lower part of a debris flow eroded from small reefs located on an upper slope (FZ 4). Note the apparently good rounding and high sphericity of both large and small micrit~c grains (fields C, D, M and 0 of the Krumbein chart; Fig. 4.30). Many grains are clasts of packstone sediment (PS) yielding reef microfossils, cemented lithoclasts (L) and isolated fossils including the microproblematicum Plexoi-anmr (P), echinoderms ( E ) ,shells (S) and some porostromate algae (A). Lithoclasts are biogenically encrusted (arrows). Middle Triassic (Ladinian): Mahlhecht cliff, Seiser Alm, Dolomites, Italy. -> 1: Matzner 1986

I

Inner platform

Outer platforn1

,-.rhnnltnc

Model 1: Lowstand

i x

I

h Margmal reefs

1

(edgesof glomerate

ngues of carbonate reslope t;31us

Major eroron surface

Model 2: Highstand M~xedcarbonates and volcan~clastics

snglomerale!

!Tongues of carbonate foreslope talus

Fig. 14.17. Highstand or lo,~,stundslope depositiorz? Evidence fi-onz microfacies analysis: The figure shows two model5 describing the possible influence of sea level on the formation of allochthonous foreslope deposits in the Middle Triassic SchlerntSciliar-Rosengarten/Catinaccioplatform of the Dolomites (modified from Yose 1991). Two tongues of carbonate foreslope talus are separated by an onlapping wedge of volcaniclastic conglomerates. The carbonate nlegabreccias are cited as a type of allochthonous lowstand wedge (model 1; Sarg 1987). However, megabreccias may also record platform progradation and shedding of platform material during relative sea-level highstands (model 2; Schlager 1994). Slope deposits recording third-order sea-level lowstands and related subaerial erosion of platforms should be characterized by a mixture of limestone clasts derived from the upper slope, platform margin, backreef and platform interior showing evidence of subaerial diagenesis. Foreslope talus accumulating adjacent to productive platforms during third-order sea-level highstands should principally be composed of margin-derived clasts characterized by marine diagenesis. Microfacies analysis of the clasts of the lower talus tongue (black) strongly supports model 2 (Brandner et al. 1991). Clast composition and biota as well as early diagenetic marine cements within the clasts indicate reworking of platform margintupper slope buildups (-> 2) perhaps triggered by earthquakes of volcano-tectonic origin. Inter-clast pores were occluded by burial cements.

Plate 115: S M F 5 a n d S M F 6

689



SMF 6: For general explanation of SMF 6 see P1. 115.

SMF 7. Organic boundstones In the Standard Microfacies classification, the multifold kinds of reef limestones have been amalgamated within a single SMF Type (boundstone) characterized by in-situ organic growth of potential reefbuilders. The type was subdivided by growth forms and assumed growth patterns (framestone, bafflestone, bindstone; see Sect. 8.2). SMF 7 and also the subdivisions are of limited value for microfacies studies. 'Reef limestones' look very different! Compare PI. 116/2 and P1. 11613, Fig. 14.18 and the reef limestones depicted in Figs. 8.2,8.3 and P1. 41/1 and PI. 42. Reef limestones require specific investigation methods that are discussed in Sect. 15.2. Additional pictures: PI. 4 1/1 (SMF 7-BAFFLESTONE), PI. 42 (SMF 7-FRAMESTONE). SMF 6. Mass-flow deposit. Reef rudstone. The sample shows grains eroded from 'sponge reefs' and redeposited on a slope. Grains are subrounded, micritic lithoclasts, reef dwellers and peloids, sometimes representing 'tuberoids' (interpreted as result of carbonate deposition during the decay of sponges and microbial crusts). Arrows point at longitudinal and cross-sections of Terebella lapilloides. This name designates an annelid worm tube characterized by thick agglutinated micritic walls. Terebelln is a facies-diagnostic fossil in Late Jurassic sponge reefs. Originally living on the lower macerated surfaces of siliceous sponges, the tubes became transported from the reef to the near-reef detrital facies. The fossil is diagnostic of near reef deposits. Black structures with white 'eyes' (left margin) are reworked sessile foraminifera. Late Jurassic (Kimmeridgian): Ludwag quarry northeast Bamberg, Northern Franconian Alb, Germany. SMF 7-FRAMESTONE. Car-allitze sponge-microbe crustfi-arnestone characterized by in-situ growth of sessile organisms. The upright growth form of the sponges (SP) and the close intergrowth with microbial crusts (MC) resulted in the formation of an organic framework. The framework exhibits a large number of cryptic habitats between and below reef-building organisms and in small reef cavities. Cavity-dwelling microfossils (foraminifera, microproblematica, microbes, sponges and others) are common criteria of this SMF 'Qpe, known since the Cambrian. Late Triassic (Dachstein limestone, Norian): Gosaukamm, Austria. SMF 7-BAFFLESTONE. Coral bafflestme. Cross-section of a fasciculate coral colony (Retiophyllia) showing trapping of sediment between the delicate coral branches. Solution cavities are filled with internal sediment (arrows). Note the excel lent preservation of the corals. Late Triassic (Zlarnbach Formation, Rhaetian): Gosaukamm, Austria.

Fig. 14.18. SMF 7. Microlfi.arnework reef linzestone. Many Permian reefs were formed by a micro-framework consisting of very small, encrusting and low-growing organisms, abundant fine-grained trapped bioclastic sediment (often more than 50%) and marine carbonate cement (Weidlich 2002). Large reefbuilders are of minor or no importance in these reefs formed in platform-marginal or upper slope positions. The sample shows 'Tubiphytes' (T), trapped fine-bioclastic and peloidal sediment (S), and recrystallized calcite cement (C). Middle Permian (Wordian-Early Capitanian): Hawasina Complex, eastern Oman Mountains.

Plate 116: SMF 6 and S M F 7

69 1

60 1

Standard Microfacies Type5


SMF 8. Wackestones andfloatstones with whole fossils and well preserved infauna and epifauna Criteria: Predominantly sessile organisms rooted in micrite and some mobile organisms. The micrite contains scattered, often very small skeletal debris contributing to a finely bioclastic matrix. Burrowing is common. Many fossils are well preserved (e.g. double-valved mollusks), but some isolated fragments may occur. Characteristic organisms are mollusks, sponges, corals and some calcareous algae. Occurrence: Shelf lagoon with circulation. Low-energy environments below wave base (FZ 2 and FZ 7). Outer and mid-ramp settings. The sediment is formed in quiet water below the fair-weather wave base. Additionalpictures: P1. 4413, P1. 8611, P1. 8811, P1. 8911. SMF 9. Strongly burrowed bioclastic wackestone Criteria: Micrite with common to abundant fragmented fossils that are jumbled through burrowing. Bioclasts often micritized. Common fossils in Paleozoic limestones are crinoids, brachiopods, bryozoans, and scattered rugose corals. Mesozoic and Tertiary examples are characterized by bivalves, gastropods, and echinoderms. Occurrence: Shallow lagoon with open circulation at or just below the fair-weather wave base (FZ 7) and deep shelf (FZ 2); outer and mid ramp settings. Additonal pictures: P1. 1911, PI. 4412. 1 SMF 8. Wlzolefossil wackestonel'oatstone. The sample shows solenoporacean red algae (SA, Parachaetetes), corals (C) and a few dasyclad algae (DA, Jodotella), as well as foraminifera (F) and bored shells (S). Most fossils are well preserved and show no signs of reworking. This SMF is common both in the deep open shelf environment (FZ 2) and in shallow open shelf lagoons (FZ 7). The presence of calcareous algae supports the attribution to FZ 7. Early Tertiary (Paleocene): Kamrnbiihl near Ternitz, Austria. 2 SMF 9. Burrowed bioclasric wctckestonefloatstone. Fossils are fragments of gastropods (G), corals (C), and foraminifera (F). White arrows point at burrows filled with fecal pellets and foraminifera. The interpretation as fecal pellets is supported by the dark color and the marked bimodal grain size. The matrix is a fine-grained pelmicrite, in parts pelsparitc. The stratigraphic sequence reflects a tropical lagoon surrounded by coral reefs. Thin-bedded, platy bituminous n~icrites without benthic fossils but rich in fishes represent the lagoonal center. Bedded limestones with larger foraminifera and n~oliusks(this sample) represent the shallow part of the lagoon. The composition of the gastropod fauna reflects cl~anges from open-marine to more restricted conditions. Early Tertiary (Eocene): Pesciara, Monte Bolca. Verona, northern Italy. Fig. 14.19. SMF 8: Uioc~lu.sri~. I I . kc ~ stones uiiclflotrt.~ront.~. hlar~ysrtmpl~~s of the SMF Type 8 arc charactcrizcd by bioclastic wackestones and Ilo:~rstones with various shells ( A , B, C J and/or by nearly monospecific biota ( D l An other common criterion is rlw fine-bioclastic micrite matrix. A: Bivalvc-gastropod wackestonc.. Normal nurinc, low-energy, shallou subtidal envlronment. Fasits Lonc I-'% 7. Late C r c t a c w ~ ~(Turunian): s S111.11. k y PI. B: Bivalve floatstone. 'I'he shells occur together with rounded niicritic intraclasts (center). Note large burscniz thc top right. Protected shallon s h tidal en\,ironmcnt. Mid-ramp scrtlng (FZ 7). Locality as in A. C : Bioclastic floatstone with hyohthid shells (see Fig. 10.47) and trilohitc. fragments (bottom right). The matrix is a quartz-bearing burrou~cdpcimicrite. Dcep shelf environnlrnt (F% 2). Cambrian (b'adi Nasb Limestone Formation): Midi Al Ghadaf ~ ~ c . 1 1 , eastern Jordan. D: Wackebtone with the tabulate coral Tharnnopora. The matrix is a fine-bioclastic pelmicrite. FZ 7, opeiimanne lagoon behind a stromatoporoid-coral reef. Late Devonian (Frasnian): Carnic Alps, Italy. Scale for all figures 2 mm. A and B: Bauer et al. (2002); C: Shinaq and Bandel (1992); D: Galli (1985).

Plate l 1/: S M F 8 a n d S M F 9

693

S t a n d a r d Microfacie5 Type\

694

Plate 118 Standard Microfacies Types: SMF 10 and SMF 11 SMF 10. Bioclastic packstones and grainstones with coated and abraded skeletal grains Criteria: Worn and coated bioclasts deposited within a fine-grained matrix. Forming packstones and wackestones, sometimes also fine-grained grainstones. This type indicates textural inversion. The dominant particles have been transported from high-energy to low-energy environments (e.g. from shoals to swales in the proximity). Occurrerzce: Shelf lagoon with open circulation (FZ 2) and open sea shelf (FZ 7). Common in inner and mid-ramp settings. Additional picture: P1. 7412. SMF 11. Coated bioclastic grainstone with sparry cement Criteria: Most grains are coated bioclasts, exhibit micrite envelopes or are completely micritized. Additional grain types may be rounded intraclasts, peloids and some ooids. Occurrerzce: FZ 6 (winnowed platform edge sands) and in reefs (FZ 5). Rare in inner ramp and mid-ramp settings. The sediment formed in areas with normal marine salinity, constant wave action at or above the fair-weather wave base or between the wave base and the storm wave base. Coating due to micritization by microborers occurs preferentially in very shallow environments (see Sect. 4.2.3 and Sect. 9.3.4). SMF 10. Worn furanlinifcral (fusulinid) packstone. The foraminifera1 shells (Triticites) are worn and micritized indicating transport before deposition. Note Iithoclasts (black arrows). The matrix consists of silt- to fine-sand sized peloids, micrite and sparite. The sample consists of 8 1% skeletal grains and 19% matrix according to point-counter analysis. Only very few fusulinids show axial sections (white arrow) necessary for species determination. The mass occurrence of foraminifera is a diagnostic criteria of SMF 1 %FOR.The attribution of the sample to SMF 10 regards the textural inversion of the biofabric. Fusulinids living under high-energy conditions were transported downslope to local protected low-energy areas. Textural inversion and transport are indicated by infilling of outer whorls with sediment and by the loss of outer whorls in many tests. Open platform (FZ 7). Early Permian (Leavenwoyth limestone): Osage County, Oklahoma, U.S.A. The Leavenworth limestone is a uniform sheet, 500 km long and at least many tens of kilometers broad. The mid-shelf limestone unit represents the transgressive part of a megacyclothem, and comprises skeletal wackestones, sonletimcs associated with mudstone, oncoid wackestones, and the fusulinid packstones shown in this figure. SMF 11. C w t r d biocluslic. gi-oinsronr. Most grains are strongly micritized coated skeletal grains associated with scmr smail-sized benthic foraminifera. The sample comes from an isolated Bahamian-type carbonate platform affected 11) incipient drowning. h4iddle Jurassic: Monte Kumeta, western Sicily, Italy. SMF 11. C'oufctl hioc~lusricyrairzstoizc~.Most skeletal grains have micrite envelopes or biogenic encrustations and colrcspond to cortoids and small oncoids (black grains). Lime mud with peloids occurs as infilling in the grain-supported fabric (arrows), but most intergranular pores are occluded by calcite cement. Note the conspicuous wavy boundary between areas with micrite and small peloids and areas characterized by calcite cement. The boundary reflects differences in the lithification within the sandy sediment. Bioclastic grains are mollusk shells, dasyclad green algae (DA) and foraminifera (F). In the Late Triassic the association of involutinid foraminifera and dasyclads characterizes open-marine parts of platform interior settings (see Sect. 14.2.2). In addition to the small coated grains, larger 'fenestral oncoids' (ON) occur. formed by microbes (Rcrc~irzella).The sediment originated in the high-energy area of backreef sands deposited on an outelplatform. Late Triassic (Dachstein limestone, Norian): Gosaukamm, Austria. --->I : Toonley 1983: 2: Di Stefano 2002; 3: Wurnl 1982

Fig. 14.20. SMF 11. Coated grainstone. Cortoids are associated with ooids and strongly micritized bioclasts. The pore space between the grains is filled with stubby fibrous rim cement (arrow) and crystal silt, indicatirlg a post-compactional vadose overprint of the p l a t f o n sediment. The sample comes from platform-marginal sand shoals adjacent to a grapestone facies. Middle Jurassic (Esfandiar limestone): Shotori Mountains, Tabas area, Iran. Crossed nicols. After Fiirsich et al. (2003).

Plate 1 1 8: S M F 10 a n d S M F 1 1

695

Standard Microfaciea Typcs

Plate 119 Standard Microfacies Types: SMF 12 and SMF 13 SMF 12. Limestones with shell concentrations Criteria: Bioclastic rudstones or densely packed floatstones characterized by accumulations of commonly one-type shells or echinoderm fragments. Shells may be bivalves, brachiopods, gastropods, or crinoids. The prevailing fossil group should be noted by additional letters: SMF 12-S (coquina composed of shells without specific assignment), SMF 12-Bs (coquina composed of bivalve shells), SMF 12-BRACH (brachiopods), SMF 12-GASTRO (gastropods). Most echinoderm accumulations occur from crinoids (SMF 12-CRIN).Occurrence: Rock-building concentrations of shells originate in various environments, from the coast to the deep sea. Bivalve shell beds are formed in platform interior settings including restricted platforms and tidal flats (FZ 8) and open platfom~s(FZ 7), reefs and slopes (FZ 5 and FZ 4), and toe-of-slope and deep-marine settings (FZ 3, FZ 2 and FZ 1). Shell concentrations are very common in mid-ramp settings. Accumulations of bivalve shells are caused by various processes including current concentrations, storm wave and tempestite concentrations. transgressive lag and condensation concentrations, or prolonged continuous accumulation of shells, because sedimentation fails to keep up with hardpart accumulation (see Fig. 3.6 and Fig. 3.7). Crinoid concentrations: Limestones consisting of abundant and densely packed echinoderm fragments (e.g. 'encrinites') represent a specific facies type formed in various settings including slopes, protected platforms. reefs and mounds. This type has been included by Wilson in SMF 12, but should be specifically differentiated because of its paleoenvironmental significance. Be aware that crinoid packstones also may be the result of chemical conlpaction (indicated by clay seams, stylolites, and corroded bioclasts). Crinoid accumulations occur both in micritic limestones or they form packstones in which the crinoid columnals are cemented by syntaxial calcite. The accumulations may be autochthonous (open sea shelf - FZ 2; foreslope - FZ 4; mounds - FZ 5) or allochthonous (deep shelf margin - FZ 3; foreslope - FZ 4). Allochthonous accumulations often are debris flows or turbidites. Crinoid concentrations are common in mid-ramp settings. Additional pictures: P1.9417 (SMF 12PI. 95/2 (SMF ~ ~ - C R I N ) . TRILO), The original definition of SMF 12 was restricted to bioclastic rudstones or grainstones characterized by abundant shell hash, and deposited in an en\ lronment of constant wave or current action that removed carbonate mud by winnowing. Actually, mud may be removed by winnowing (bioclastic rudstones), but can be still preserved floatstone, -> I). Winnowing, therefore, should not be regarded a, a within and between the shells (b~oclast~c critical definition cr~terion.

SMF 13. Oncoid rudstones and grainstones Criteria: Millimeter- to centimeter-sized oncoids, predominantly cyanoids and porostromate oncoids, forming a grain-supported fabric, sometimes in association with ooids and fine-grained bioclasts. Bimodal grain-size distributions are common. Note that t h ~ sSMF does not categorize oncoid floatstones (see SMF 22!). OccurrPnce:Ancient oncoids were formed in different settings (see Sect. 4.2.4. l), both in high-energy and low-energy environments. Oncotd rudstones and grainstones were common in open-marine winnowed edge sand areas (FZ 6). open shelf lagoons (FZ 7), the environs of platform patch reefs, and in backreef areas behind larger reef complexes. On lamps grain-supported oncoid\ originated predomlnantly in shallow inner ramp settings. Addltinrzcil l u r e . PI. 1211. I SMF 12-Hs.B i ~ d i ~ ~ f l o u t s t oConcentration nc. of bivalve shells resulting from high population density on a slope (FL 4). The absence of bioerosion, abrasion and encrustation contradicts transport. The recrystallized bivalves are double-valved (center) or occur as single valves. Matrix is a lime mudstone. Late Triassic: Steinplatte, Tyrol, Northern Alps, Austria. 2 SMF ~ ~ - C R Crinoidfloatstonc. IN. Crinoid stem fragments and arm plates (arrows) are embedded within a bioclastic wackestone matrix containing fine-grained echinoderm debris. Note the mixture of complete and broken elements. This 5; see PI. 144). Mississippian (Waulsortian facies): Muleshoe crinoid limestones originated at the flanks of a mud mound (E Mound, Sacramento Mountains, New Mexico, U.S.A. 3 SMF 13.Oncoid-ooid rudsronc. Large oncoids formed by skeletal and non-skeletal cyanobacteria and encrusting foraminifera (white arrows) in association with smaller bioclasts and radially-structured ooids. The ellipsoidal shape of the oncoids is controlled by the shape of the cores (bivalve shells). Note the irregular knobby surface (black arrows), indicating the absence of reworking of the oncoids. The oncoids shown at the bottom right are compacted and dissolved at their boundary. The oncoids formed in moderately high-energy, shallow waters near a platform edge (FZ 6). The radiallystructured ooids were swept into the environment of oncoid formation from protected parts of the platform. Late Jurassic: Switzerland.

Plate 119: S M F 12 and SMF 13

697

60s

Standard Microfacies T y p e ,

Please note: SMF 14 has not been forgotten. This type is different from all other SMF Types. It characterizes lag deposits originating during periods of reduced sedimentation or non-deposition. You can find a discussion and a picture of it on P1. 917. Plate 120 Standard Microfacies Types: SMF 15

SMF 15. Oolite (commonly ooid grainstones but also oolitic wackestones) Carbonate sand accumulations with a high percentage of ooids occur on or near the seaward edge of platforms, h n k s and shelves and they form within the platform interiors and in inner and mid-ramps (Halley et al. 1983). Ooid-rich limestones were originally regarded as one SMF Type characterized by grainstones consisting of abundant, well-sorted and often overpacked ooids, usually occurring in cross-bedded units formed in highenergy environments of oolitic shoals, tidal bars and beaches (FZ 6, winnowed edge sands). This definition did not consider significant differences in the microfabric of the ooid cortices (Fig. 4.20) reflecting differences in environmental conditions and depositional settings (see Sect. 4.2.5; Fig. 4.26 and Fig. 14.22). Concentric ooids with laminae composed of tangentially arranged crystals commonly originate in high-energy marine settings on oolitic shoals, tidal bars and beaches (FZ 6 and FZ 7; mid- and outer ramp settings). Radial ooids characterized by laminae consisting of radially arranged crystals are formed under moderate to low-energy conditions, often in sea-marginal or lacustrine environments with elevated or lowered salinities. Many of these ooids originate in restricted environments (e.g. lagoons, lagoonal ponds; FZ 8). Micritic ooids can be generated by random growth of crystals in marine environments characterized by reduced sedimentation (e.g. outer ramps), growth within biofilms (=8. FZ 9B), or are the result of pervasive micritization. These categories should be distinguished within SMF 15 by using additional letters: SMF 15-C (concentric),SMF 15-R (radial) and SMF 15-M(micritized). More than other carbonate grains, ooids are easily reworked and transported. Oolitic limestones, therefore must be checked to see whether the ooids are autochthonous or parautochthonous, or whether they have been transported by gravity-mass flows and turbidity currents (forming calciturbidite beds in slope and basin sediments; FZ I and FZ 4) or whether they were accumulated by wind action (forming eolian dune carbonates; see Fig. 15.1).Addirio~zulpictur-es:P1. 1314 (SMF 15-R), P1. 1316 (SMF 15-C), P1.4511 (SMF 15-C). SMF 15-C. Ooid gr-ainstonc with concuntr.icaoids. The ooids exhibit distinct tangential structures (arrows), are multiplecoated and well-sorted. Some ooids are micritized and a few are dissolved (boltom left). Interparticle pores are filled with drusy cement. Ooid shoals near an outer platform margin (FZ 6). Late Triassic (Upper Rhaetian): Northern Alps, Austria. SMF 15-R. Ooid grairzstone with radial ooids. In contrast to SMF 15-C, the laminae of the ooid cortices are radially s~ructured(arrow) or exhibit tangential/radial structures. Other features different from SMF-C are poor sorting, the abundance of non-spherical, highly irregularly shaped grains, abundant reworked and broken ooids, the occurrence of composite grains acting as cores for renewed ooid coatings, and the rareness of fossils associated with the ooids. Limestones with abundant radial ooids occur as ooid wackestones or packstones with ooids within micrite matrix, or ooid grainstoncs composed of transported, broken and sometimes regenerated radially-structured ooids (this figure). The sample comes from restricted near-coast marginal-marine parts of a carbonate platform (FZ 8). Early Cretaceous: Apennines, Italy. SMF 25-h4. Quarfz-hearingooid wac.kcstonc with rnicritc 0oid.s. Characteristic features of these ooids are the wide mngc in sizes and shapes, poor sorting and ferruginous coatings (black). The ooids are allochthonous grains. They uperere\+,orliedand redeposited in deep outer ramp environments with discontinuous sedimentation. Sparse fossils are gastropods. Late Jurassic (Oxfordian): Torrecilla-Barranco near Zaragoza, Spain. , Caues &Y--C , actlhe

'b

0

Ee!iai. Lakes dunes

~

TwREsTR>

A

Attached platform

B

Homoclinal ramp

e-

SLOPE Eoim

TERRESTRIAL

INNER RAMP

@

Ooids

0 Pisoids

MID-RAMP

Fig. 14.21. Sites of m i d nnd pisoid fol-nioiiotl. Ooids accumulate on land in eolian dunes, and subaqueously in marine shoals, banks and shecrlike bodies on attached and isolated platfotms. Allochthonous accumulations occur in lurbidites and debris flows deposited on slopes and in basins. On homoclinal ramps ooid accumulation is common near the shoreline in inner ramps and in mid-ramp shoals. Note the different setting of SMF 15 in platforms and ramps! Pisoids and pisolites (SMF 25) occur in terrestrial settings, e.g. caves and caliche, on the shores of some lakes, and in tidal ponds.

Plate 120: S M F 15

699

-

SMF 15-M

700


Plate 121 Standard Microfacies Types: SMF 16 and SMF 17 SMF 16. Non-laminated peloidal grainstone and packstone and laminated peloidal bindstone Criteria: Accumulations of very small, grain-supported, subrounded or subangular peloids. Two subtypes are characterized by tiny, equal-sized peloids associated with benthic foramincommon: SMF 16-NON-LAMINATED, ifera, ostracods or calcispheres. SMF 16-LAMINATED is characterized by peloids of different size, forming irregularly distributed fine-grained packstone (pelmicrite), grainstone (pelsparite) and sometimes also packstone fabrics. An other criterion are wavy micritic laminations. The peloids of SMF 16 are mud peloids, fine-grained fecal pellets (definitions in Fig. 4.11), and microbial peloids (SMF 16-LAMINATED). Occurrence: SMF 16-NONLAMINATED is common in shallow platform interiors comprising protected shallow-marine environments with moderate water circulation (FZ 8) and in inner ramp settings, and may also occur in evaporitic arid platform interiors (FZ 9A).SMF 16-LAMINATED contributes to the formation of mud mounds and the stabilization of PI. 6611 (SMF 16-NON-LAMINATED). platform slopes. Additional pictures: PI. 1012 (SMF 16-NON-LAMINATED), SMF 17. Aggregate-grain (grapestone)grainstone Criteria: Aggregate-grain grainstone. The grainstones and grainstone-rudstones consist predominantly of arenitic and ruditic lumps and grapestones (see Sect. 4.2.7 for definitions), associated with peloids and some coated and micritized skeletal grains. Fossils are usually rare, except for a few foraminifera and algae. Occurrence: Characteristic for platforms, very rare in ramp settings. FZ 7 and FZ 8 (open and,restricted shallow platforms). Very abundant in isolated platforms of the Baharna type but also occurring in attached platforn~ settings. Additional pictures: P1. 1514. P1. 1515, PI. 1518, P1.4311. SMF 16-NON-LAMINATED. Fine-grainedpeloid grainstone. Some of the peloids correspond to tiny rounded micrite clasts. Fossils are very rare except for a few smaller foraminifera. The sample comes from a grainstone bed at the top of a sedimentary cycle. It represents the shallowest subtidal deposition on a relief formed by algal mounds (see PI. 11413j. Pennsylvanian (Holder Formation, Virgilian): Alamogordo, Sacramento Mountains, New Mexico, U.S.A. SMF 16-NON-LAMINATED. Fiizc-grainedpeloidal grainstone. Note the similarity with Fig. 1.Arrows point to 'calcispheres' (see Sect. 10.2.1.9). The peloids are angular and rounded micrite clasts. The paleoenvironment was a restricted inner platform lagoon (FZ 8) adjacent to an inner ramp. Early Carboniferous: Belgium. SMF 16-LAMINATED. Birldsfo~~e consisting offine-grained lunzinatedpeloidal grainstone grading into laminated peloidd parksro~le.The sample exhibits distinct alternations of thicker pelsparite layers (PS) and thin pelmicrite (PM) layers separated by irregular, probably microbial, micrite laminae. This texture is characteristic for mud mounds, slopes, and protected platfonti interior environments (FZ 8). Late Jurassic (Oxfordian): High Atlas Mountains, Morocco. SMF 17. Aggregate-grain graimtone. Most grains are micritized aggregate grains (lumps) exhibiting the characteristic lobate outline. Angular lumps indicate some transport and reworking. The composite grains consist predominantly of peloids and some bioclasts bound together by microcrystalline calcite. Most grains have rims of thin early-marine cement. Remaining interparticle pores of the grain-supported fabric were occluded by coarse burial calcite. The sample comes from a rimmed carbonate platform (FZ 6). This grapestone facies originated within a distance of only a few kilometers behind the platform edge. Late Triassic (Rhaetian): Steinplatte, Tyrol, Austria. CaCO?

Fig. 14.22.Re[utionsh~pbemeen grapestonefacies (SMF 17)and lirnesto~zeresources. Aggregate grains originate preferentially in platform settings with moderate but fluctuating water energy, low sedimentation rates and low terrigenous input. The latter condition and the high amount of interparticle calcite cement are the reason for the formation of chemically high-quality limestones. The figure shows an example. A: The Late Triassic Dachstein limestones of the Northern Calcareous Alps were formed on an attached platform (FZ 9 and FZ 8) rimmed by marginal reef complexes (FZ 5 , FZ 4, and parts of FZ 7). Grapestones originated in the back of the reef zone. B: A survey of the Triassic Dachstein limestones revealed that the reef facies and the grapestone facies have the highest calcium carbonate content, are relatively low in MgC03 and contain very little insoluble residue. These criteria characterize both facies types, particularly the grapestones facies, as targets for the successful exploration of industrially used pure limestone resources. A and B: Modified from Fliigel(1977 and 198 1).

Plate 121: S M F 16 and ShIF 17

70 I

2 mm

2 mm

SMF 16-LAMINATED

SMF 17

Plate 122 Standard Microfacies Type: SMF 18 SMF 18. Bioclastic grainstones and packstones with abundant benthic foraminifera or calcareous green algae Criteria: The main feature of this SMF Type is the high abundance of benthic foraminifera or calcareous green algae. Other grains are peloids, cortoids and composite grains. Common textures are grainstones and packstones. Species diversity is low to moderate. The dominant biota should be indicated by additional letters (SMF 18-FOR,foraminifera; SMF ~ ~ - D A sdasyclad Y, algae; SMF 18-UDO,udoteacean green algae; SMF 18GYMNO, gymnocodiacean algae). Occurrence: Sediments of SMF 18 occur as bars and channels, and in sand shoals heaped up by tidal currents in shallow lagoons and bays (restricted platform, FZ 8) and in shelf lagoons with open circulation (FZ 7). Foraminifera1 sands form also in backreef areas and on reef flats (Fig. 14.23). SMF 18 sediments are common in inner ramp settings. Additional pictures: PI. 5717 (SMF 18-GYMNO), P1. 5717 (SMF 18-GYMNO), PI, 6111 (SMF 18-DASY),PI. 7.515 (SMF 18-FOR),PI. 10512 (SMF 18-DASY),PI. 14514 (SMF 18-DASY). SMF 1 8 - F o ~Foraminifera1 . grainstone with abundant miliolids. Miliolid foraminifera are very common in lagoonal environments (sometimes with elevated salinity) of Mesozoic and Cenozoic restricted inner platforn~sand inner ramps. Most associated particles are aggregate grains (AG). The sample comes from a restricted platform lagoon (FL 8j. Late Cretaceous (Albian to Cenonianian): Trnovo, Dinaric Platform, Slovenia. SMF 18-DASY. Dusyclad graitzston~characterized by concentrations of Spinaporella andalusica Fliigel and FliigelKahler. Spinaporellu is characterized by long spines. Most of the smaller particles (e.g. bottom center) are broken algal elements. Note the geopetal infilling of the algal thalli (arrows). The sample comes from a backreef lagoon behind a reef' formed predominantly of serpulids and synsedimentary carbonate cement. Open-marine platform environment (FZ 7j. Late Triassic (Norian): Sierra Nevada near Granada, southern Spain. SMF 18-GYMNO. Gymnocodiucean algal packstonc characterized by the concentration of debris of gymnocodiacean algae (see Sect. 10.2.1.5,).The micritic matrix was formed by disintegration of the algae, a mode that corresponds to the ' H a l i n ~ ~ model' da (see Sect. 4.1.2; Fig. 4.3). The limestone originated in a low-energy, lagoonal inner ramp environment. Permian (Yeso Fonnationj: Cloudcroft east of Alarnogordo, New Mexico, U.S.A.

Fig. 14.23. SMF 18-FOR.Formninfirul grainstorzc. The massive calcarenite consists of densely packed rotaliid and lepidocycliriid foraminifera with Neplzrolepidina praemarginata. The skeletal sand is part o f a reef flat situated between the back reef area and the front of a fringing reef. The strongly varying orientation of the tests, poor sorting and the admixture of' some corallinacean material (grains here white, because negative print!) indicate high-energy deposition by storms. The sample would be attributed to Facies Zone FZ 7 according to the abundance of benthic foraminifera, but to Facies Zone FZ 5 ('reef') if one would only consider the place from where this sample was taken. Negative print. Tertiary (Castro Limestone, Late Oligocene): Salento Peninsula, southern Italy. After Bosellini and Russo (1992).

Plate 1 2 2 : S M F 1 8

70:

70.4

Standard Microtacies T ~ , p t . s

Plate 123 Standard Microfacies Types: SMF 19, SMF 20 and SMF 21 SMF 19. Densely laminated bindstone Criteria: Bindstone with a laminated fabric consisting of millimeter thick laminae that differ in internal conlposition. Finer laminae correspond to micrite layers. Somewhat coarser laminae consist of densely spaced, very small peloids or spany calcite. The biofabric is characterized by couplets with irregular, sometimes wavy boundaries. Fossils are rare except ostracods and some foraminifera, gastropods and a few algae. Occurrencc: Near-coast platform interior (FZ 8 and FZ 9). Tidal flats of attached and isolated platforms and inner ramps. Additional picture: PI. 132/l. SMF 20. Laminated stromatolitic bindstoneslmudstones Criteria: Planar or variously dome-shaped laminated bindstones composed of fine- or coarse-grained laminae sometimes exhibiting microbial or algal structures (see Sect. 9.1.4; P1.50). Occurrence: Very common in the intertidal zone, but also in supratidal and shallow subtidal environments. Open platforms (subtidal, FZ 7), tidal zones of restricted lagoons (FZ 8) and arid coasts (FZ 9A, supratidal). Additional picture: P1. 132/5. SMF 21 -FEN.Fenestral packstones and bindstones SMF Type 21 was originally defined by a 'spongiostrome mudstone fabric' with algal tufts. Relicts of porostromate algae or calcimicrobes may be preserved (SMF 21-PORO;see PI. 124/1) or not. More useful criter~am distingui\hing this microfacies are fenestral fabrics (SMF FEN) typically developed in FZ 8 and FZ 911. 1'1. 123/3 and PI. 124/1 display two common variants of SMF 21 occurring in association or separated. Criter-la: Bindstone characterized by variously sized fenestral cavities within a framework fornled by sedimentary and biogenic grains. Smaller fenestrae correspond to birdseyes, larger structures may have stromatactoid shapes (compare Sect. 5.1.5 and PI. 20). Occurrence: Supratidal and intertidal environments (restricted lagoons, I;% 8) and evaporitic lagoons (FZ 9A). Additional pictures: PI. 20/2, PI. 41/2, P1. 4612, P1. 50/5, PI. 13216. SMF 19, SMF 20 and SMF 21 are common and in facies analyses often used as indicators for intertidal and supratidal environments. The main criteria are lamination textures caused by microbiallalgal mats and fenestral fabrics. Differences in the morphology of the mats (-> I and 3) in combination with other sedimentary, organic and mineralogical features are used in estimating the 'exposure index' within the peritidal zone. This index reflects the percentage of time during which the area where the laminated sediment was formed was exposed (Ginsburg et al. 1977). This approach also can be applied to ancient peritidal carbonates and allows nlicrofacies samples to be allocated to predominantly intertidal, mostly supratidal but with some intertidal, or only supratidal subenvironnients (Smosna and Warshauer 1981). i S M F 19. Lanlinuted hirzdsfotleconsisting of alternating couplets of micritic and peloidal layers (FZ 8). This microfacics

may grade into bindstones with feneslral fabrics. Late Permian (Main Dolomite, Zechstein): Subsurface, Milosaewo wcll. Northern Poland. 2 SMl" 20. Lntnit~utcdstromcrtolitc hitdstnne. The sample shows finely wrinkled laminae arranged in dense and closc.1y. spaced growth pattenis exhibiting vertically stacked protuberances (arrows). This fabric meets the definition of stromatc~-lite.i, i'avored by Riding (1999): 'A stromatolite is a laminated benthic deposit'. The irregular extended structure markcti by SP probably represents soft non-rigid sponges. The irregularly-shaped white calcite-filled structures indicate burro~v-ing and disintegration of the microbial mats by grazing organisms. The sample comes from cyclic bedded limestones (member B of the 'Lofer cycle'). Intertidal environment (FZ 8). Late Triassic (Dachstein limestone, Norian): Zelenica. Begunjscica hiIountains, northern Slovenia. 3 ShlF ~ ~ - F EF~ttestt-alpac:k.stone K. characterized by small spar-filled cavities (birdseyes, white arrows) and larger irregiilar voids some of which are filled with fine-grained sediment at the bottom (stromatactoid fabric, black arrow). 'The sedimentary framework fomled by peloids and cyanobacteria tufts (CB) encloses transported dasyclads (D). Porostromate cyanobacteria tufts are characteristic constituents of micritic, non-laminated intertidal carbonates (Pi. 13911). The sample comes from the intertidal member of a Lofer cycle (see Sect. 16.1.2). Early Jurassic: Korfu Island, Greece. -> 1: Peryt 1986

Plate 123: S M F 19. S M F 2 0 and SMF 21

2

mm

SMFlQ

705

- mm 2

SMF 20

Standard M ~ c r o f a c i c sl ype\

-(16


SMF 21-PORO.Fenestral bindstones, mudstones and packstones with porostromate microstructures Criteria: Like the S M F FEN, the fabric exhibits small fenestrae, but unlike this type the sedimentary framework consists of densely growing tufts of porostromate cyanobacteria and algae (see Sect. 10.2.1.1). Ostracods and a few foraminifera may be present. Occurrence: Platform interior (FZ 8). Common in intertidal pools and very shallow subtidal environments. SMF 22 Oncoidfloatstones or wackestones Criteria: Millimeter- to centimeter-sized agglutinated oncoids, consisting of sedimentary grains (e.g. tiny skeletal grains, terrigenous quartz) trapped and bound together by non-skeletal microbes and algae (compare P1. 11/1,2). Occurrence: Low-energy environments of shallow lagoons and tidal zones (FZ 8). Typically found on the edges of ponds with brackish water. Additiotlal picture: P1. 12/7. I SMF 21-PORO. Fenestral hindstone with porostromate microfossils. A framework consisting predominantly of cyanobacteria (arrows) is well-preserved. Some of the large voids (V) may represent desiccation structures. The sample comes from a very shallow backreef lagoon behind platform-edge reefs. Late Triassic (Dachstein limestone, Norian): Gosaukamm, Austria. 2 SMF 22. Oncoid~loatstone.The oncoids were fonned by trapping and binding of sedimentary grains (quartz silt, tiny bioclasts). Note the differences in organic matter (black) and in the frequency of grains within the irregularly developed laminae. The cores of the oncoids are gastropods. The oncoids correspond to the 'spongiostromate' oncoid type. Compare the distinctly different structure of oncoids fonned in subtidal normal-marine environments (SMF 13; PI. 119/3). The sample comes from trarrsitional-marirle backwater deposits. Cretaceous: Switzerland. -> I : Wurm 1982

Fig. 14.24. Many fenestrae originate ji.om the decomposition of algae and cynnobacteria. A: Layers with carbonate grains and layers with filaments of Scytonema are common features of tidal algal mats in the Bahamas. B: Oxidation of the mat destroys the non-calcified cyanobacteria, leaving the fenestrae (black) within the grain-supported framework. Depending on algal growth patterns, 'strornatactoid' voids with irregular roofs (this figure) or isolated spar-fillcd voids (Fig. 14.25A) will develop. Modified from Monty (1976).

- ...... Fig. 14.25. SMF ~ ~ - F EA:NFenesfral . packstone characterized by birdseyes and a pelmicritic framework. Note the thin cement rim within the birdseye structures. B: Red fenestral limestone. The red rock color is caused by the geopetal infilling of many birdeyes with red vadose silt indicating intermittent subaerial exposure of tidal platform interior carbonates. Protected part of FZ 7. Early Jurassic: Djbel Bou Dahar, High Atlas, Morocco. After Scheibner and Reijmer (1999).

5 mm

SMF 21-PORO

5 mm

SMF 22

Standard Mlcrofacies T y p e \

7~18

Plate 125 Standard Microfacies Types: SMF 23, SMF 24 and SMF 25 The plate displays two SMF Types distinguished by Wilson (1975) and the new SMF Type 25 characterizing carbonate-evaporite transitional environments. SMF 23. Non-laminated homogeneous micrite and microsparite withoutfossils Criteria: Unfossiliferous lime mudstone or fine-grained dolomicrite, sometimes with authigenic evaporite minerals. Occurrence: Tidal flats (FZ 8) and arid evaporitic coasts (FZ 9A). Deposited in saline or evaporative environments, e.g. in tidal ponds. Remarks: Note that micrites without fossils or other grains may also occur in anoxic deep basins (FZ lB), and that the 'lack' of fossils can only be a sampling effect. SMF 24. Lithoclastic floatstones, rudstones and breccias Criteria: Coarse, up to several centimeter-sized angular carbonate lithoclasts. Elongated micrite clasts are abundant, often edgewise arranged, and sometimes cross-bedded, forming an intraformational breccia. Occurrence: Platform interior (FZ 8). Lag deposits in tidal channels and on tidal flats. SMF 25. Laminated evaporite-carbonate mudstone Criterin: Alternation of fine-crystalline carbonate (limestone, dolomite) which might be microbially induced, and diagenetically deformed layers with evaporite crystals (gypsum). Occurrerzce: Upper intertidal to supratidal sabkha facies (FZ 9A) in arid and semiarid coastal plains and evaporitic lacustrine basins. S M F 23. NOH-lanzinatedutlfossilq2rozrs mudstone. Irregularly distributed voids result from the replacement of evaporite minerals by calcite. FZ 9A. Middle Triassic: Northern Calcareous Alps, Austria. SMF 23. Nun-laminated ur$ossil~~~rous dolonlit~mudstone. Note the calcitized anhydrite rosettes within the fine-grained idiotopic dolomite matrix. The micrite matrix corresponds to type 1 distinguished in Fig. 4.1! and is probably of physicochemical origin, as indicated by the very fine crystal size, the evaporite minerals, and the complete lack of fossils. Supratidal environment. FZ 9A. Late Tertiary (Nullipore Formation, Miocene): Subsurface, Gulf of Suez, Egypt. SMF 24. Coirrxc,litlzoclastic iud.stom-f(out.stone. Imbricated flat pebble conglomerate consisting of partially dolomiti~ed, laminated 'algal' clasts (AC; algal mat chips) and exhibiting desiccation cracks (DC). Note the stylolitic joints of the pebbles, indicating compaction and consolidation of the sediment prior to erosion and redeposition. The matrix is formed by skeletal grains and neomorpliic sparite. The conglomerate has been interpreted as storm sediment deposited within tidal flat areas (FZ 8). Late Triassic (Calcare di Zu, Rhaetian): Denti della Vecchia, Lombardian Basin, northern Italy. SMF 25. Lnnzirznted evapol-itic-lime rnLdsrone composed of alternating layers of organic-rich calcimudstone (Mi, and evaporitic layers (E) with tiny gypsum crystals. Some layers show early diagenetic entherolitic folds characterized by antiform buckles. Note the deformation of folded and non-folded layers by the growth of large gypsum crystals (arrows). 'The sample comes from the deep evaporitic part of a lacustrine basin. Early Tertiary (Eocene): Mormoiron Basin, France.

Sabkha surface

Fig. 14.26. SMF 25 is a characteristic of sabkhaf&~ic~s originally described from the Abu Dhabi coast on the Arabian Gulf. Sabkha is an Arabian word for a salt flat Lammated algal mat found near sand dunes. The sabkha cycles start with with gypsum crystals subtidal shelly lime mud and muddy skeletal sands commonly deposited in a lagoonal environment, overlain by intertidal laminated sediments characterized Lime mud with by algal/microbial mats containing gypsum. The supratidal part of the cycle consists of anhydrite layers whose nodules display a 'chickenwire' texture as thc result of displacive growth. The ancient counterpart of this cycle is represented by subtidal fine-grained dolomites or lime mudstones with rare fossils (mudstones. sparse wackestones), followed by intertidal layered dolomicrites or micritic limestones exhibiting parallel and/or irregular, wavy laminations, and sometimes vanished evaporites. The supratidal sabkha facies can be recorded by anhydrite beds. See Warren and Kendall(1985) for a review of sabkha criteria. Modified from Achauer (1982).

7i0

Standard hlicrofacies Types

Plate 126 Standard Microfacies Types: SMF 26 Figs. 1 and 2 of this plate show a SMF Type introduced here. Main criteria are abundant calcareous pisoidsj vadoids (see Sect. 4.2.6), formed by early diagenetic meteoric carbonate precipitation, predominantly but not always, during phases of subaerial exposure (-> 2). This microfacies is abundant in humid and tropical settings, e.g. paleokarst limestones, caliche carbonates, and travertines. It is associated with SMF 9A in evaporitic settings (FZ 9B). Figs. 3 and 4 show non-carbonate pisolitic structures. Additional pictures: P1. 14/1, Pi. 1413, P1. 3416, PI. 12816.

SMF 26. Pisoid cementstones, rudstones and packstones Criteria: Accumulations of pisoids both autochthonous or allochthonous characterize this important faciesdiagnostic SMF Type. Diagnostic criteria are variously shaped, millimeter- to centimeter-sized, densely packed pisoids, commonly cemented by meteoric cements. The cores of the pisoids are usually broken pisoids or cement crusts. Reworking and redeposition is common. Many pisoids are inversely graded, exhibit polygonal fitting, and are associated with tepee structures. Indigenous biota are usually lacking. Occurrence: Terrestrial subaerial, or terrestrial and transitional terrestrial-marine subaquatic settings, formed under meteoric-vadose and marinevadose conditions (FZ 10). 1 SMF 26. Pisoid ludstone. These pisoids are the grains described in the classical paper by Dunham (1969; see Sect. 4.2.6

and P1. 1411) and interpreted as caliche soil pisoids formed by subaerial vadose diagenesis during episodic lowstands of sea level. At present, the range of depositional interpretations of these pisoids includes caliche formation in continental or coastal-spray-zone supratidal settings, vadose-marine inorganic precipitation in inter- and subtidal environments or formation in marine seepage or groundwater springs (Handford et al. 1984). The pisolitic cementstone consists of large pisoids/vadoids linked by outer laminae and meniscus cement. Most pisoids are well-laminated, their cortices consist of accretionary, essentially isopachous cement laminae. The non-skeletal nuclei are preexisting pisoids or peloids. Arrows point to vadose cements. Successive laminae differ in thinner darker micritic and clearer microspar lamellae. Most black nuclei are broken fragments of preexisting pisoids. White nuclei correspond to reworked pieces of laminated interpisoid cement. Late Permian (Carlsbad Group, Guadalupian): Entrance to the Carlsbad Cavern, New Mexico, U.S.A. 2 S M F 26. Vadosc pisolitic crusts indicating cyclic exposure of lagoonal carbonates. The thin section displays inversely graded pisoids (also called vadoids because of their formation within vadose diagenetic environments) made of pisoid fragments, which in turn are cores of younger vadoids (V). Some vadoids exhibit radial cracks (RC), indicating sporadic. desiccation. The pisoids originated during subaerial exposure phases of parts of intertidal and shallow subtidal lagoonal sediments in the back of platform-margin sponge-coral reefs. The pisolitic crusts may form beds reaching a thickness of tens of centimeters to a f e u meters. Middle Triassic (Wetterstein limestone, Ladinian): Scharnkopf near Reichenhall, Northern Calcareous Alps, Germany. Non-carbonate yisoids 3 Silicified pisolite br-rcciu. Cretaceous: Subsurface. Ras A1 Khaimah, United Arabian Emirates. 4 Prdogenicpisoids. Pisoids occur both in carbonate and non-carbonate rocks. The sample is a lateritic pisolite representing a pedogenic sediment. The pisoids have a diameter up to 5 mm and consist of a kaolinitic or pisolitic core and a cortex composed of iron oxide. Note the shrinkage cracks within the cores (arrows). The matrix consists of hematite (black) and kaolinite (white) representing reworked material of a weathered Precambrian basement (crystalline rocks). Sedinlentary structures indicate mass-wasting and fluviatile transport mechanisms. Late Cretaceous (Nubian Group): Wadi Kaiabsha southwest of Assuan, Egypt. -> 2: Henrich 1984; 4: Flscher and Gernlann 1987

Fig. 14.27. Genetically differentpisoids differ in their nzorphology. A: Phreatic-vadose pisoids often exhibit irregular shapes, polygonal fitting, abundant laminae and downward bulging. B: Caliche pisoids are characterized by centrifugal and accretional growth, and a few discontiuous laminae. A: Modified from Esteban and Pray 1983. B: After Calvet and Julia 1983.

Standard Microfacies Types: D i s c u c s i u n

14.3.2 Discussion of Standard Microfacies TYpes How many samples fit into the SMF Type categories? A common experience is that not all thin sections can be precisely assigned to a specific SMF Type. A review of fifty papers describing and illustrating the microfacies of Paleozoic and Mesozoic carbonate rocks shows that about 70% of the local microfacies distinguished by the authors correspond to established SMF Types. Difficulties occur with local microfacies types represented by wackestones and grainstones containing various types of grains and of fossils. Many of these samples are sediments of the platform interior (FZ 6FZ 8) and of the deep shelf (FZ 2). In these environments mixing of grains by burrowing has a strong impact on the composition of the sediment. In addition, storms frequently contribute to sediment mixing in interior platform environments. 'Mixed grain compositions' are also common in ramp carbonates (Sect. 14.3.4.2). 'These samples should be studied using the 'compositional maturity' concept proposed by Smosna 11987j, see Sect. 6.2.1.4.

SMF Types assist iiz facies interpretations but must be refincd More than two third of the SMFTypes distinguished by Wilson (1975) describe sediments deposited above the fair-weather wave base and between the wave base and the slonn wave base. Microfacies types of deepwater sediments are clearly underrepresented. SMF types comprise autochthonous and parautochthonous sediments deposited more or less within the place of their origin, and allochthonous sediments, transportcd from shallow to deeper depositional environments. The autochthonous background sedimentation i n basinal and deep shelf settings is represented by SMF 1 and SMF 3. SMF 2 indicates mixing of autochthonous sediment and fine-grained eroded and redeposited material. The muddy and often burrowed sediments of SMF 1 and SMF 3 may present indications for bottom currents. The microfacies of these bioclastic wackestones is common in lin~estonescharacterized by nodular fabr~cs(see Sect. 5.1.6). SMF 4, SMF 5 and SMF 6 are allochthonous sediments, whereby the composition of SMF 5 and SMF 6 provide some hints to the existence of reefs. These reefs might have developed at platform margins, in an upper slope position, or on non-rimmed platforms. Microfacies and fossils in clasts of breccias or foreslope rudstones allow source areas to be recognized (see Sect. 16.2.5). Note that reef material as well as lithified sand

shoal material may be transported by storms onshore as well. The interpretation of SMF4 sediments requires information on the geometry and thickness of the allochthonous limestone beds and their position within the sequence. One of the difficulties of the Standard Microfacies concept is the highly generalized definition of SMF Types of fossiliferous limestones. These limestones, represented by SMF 8, SMF 9, SMF 10 and SMF i 1, form the bulk of bedded shelf carbonates. SMF 8 to SMF 11 are common both in the Facies Zone FZ 7 of the open shelf lagoon in euphotic depths, and in the Facies Zone FZ 2 of the deep shelf within depths of tens to hundreds of meters. Environmental interpretations derived from these SMF Types must be checked by palecological and biofacies criteria (see Chap. 15 for examples). The assignment of samples to SMF 8 and SMF 9 can be difficult, because both microfacies types may show strong variations in the frequency of skeletal grains and other grain types. SMF 12 summarizes accumulations of various shells formed in different ways. A sound interpretation ol samples attributed to this SMF depends on information on the stratigraphic and geometric characteristic^ of the shell bed, thickness and lateral extension, position within the sedimentary sequence, and the kind and taphonomy of fossils (Kidwell et al. 1991; Fiirsich and Oschmann 1993; Fursich 1995). SMF 13 and SMF 22 are characterized by o~ico~ds These types are well-defined. Most of the environnlental information is included in the composition of the oncoid cortices. Take a look at the organisms contnbuting to the growth of the oncoids, the type of the lanunation, and consider breaks in growth indicated by encrusting and boring organisms. SMF 14: A very specific SMF Type is SMF 14 (PI. 917) introduced by Wilson for lag deposits. Lag deposits are residual accuinulations remaining on a surface after the finer material has been removed. Lags reprcsent slow accumulations of coarse material in the winnowing zone. The particles are chemically and physically resistent through long periods of non-dcposition and persistent winnowing of sediment on the sea floor. The criteria of carbonate lag deposits are coated. rounded and worn particles, in places mixed with peloids or ooids that are blackened and iron-stained. Phosphate grains e.g. fish bones and teeth and phosphatized organic remains are common (Pl. 11012, 3, 5) as well as glauconite and quartz grains. Coarse lithoclasts may be present, sometimes forming lag conglomerates. Fossil shells are often leached; steinkern preservation is common. Lag deposits are characteristically thin beds.

S M F Types: Discussion

71 3

Fig. 14.28. SMF Tjyes assist in recognizing facies belts independently of the age of the rocks. Note the amazing similarity in

grain composition and depositional texture of the two samples from Jurassic and Cretaceous limestones. Both samples represent SMF 17, characteristic for sediments formed in platform interior environments when water depth has remained relatively constant (late highstand phase). The similarity includes not only the grainstone texture and the dominance of aggregate grains but also the occurrence of benthic foraminifera and algae, indicating very shallow warm-water sedimentation. A: Thick-bedded limestone within a subtidal shallowing-upward sequence. Foraminifera are textulariids and Troclzolirza (T) Green algae are represented by fragments of Clypeina (arrow). Late Jurassic: Sulzfluh, Graubiinden, Switzerland. H: Thin-bedded lagoonal limestone at the base of a mixed siliciclastic-carbonate sequence. Miliolid foraminiferaare Cyclogyra (right) and Quinyuclociclma (center top). Late Cretaceous (Cenomanian): Monastery St.Anthony. Eastern Desert, Egypt After Kuss (1986)

0 c c u 1 ~ c n c . cRemoval . of fine-grained sediment by thonouc sedimenr as indicated by the good preservastrong winnowing occurs in high-energy near-coast en- tion of the foraminiferal tests and their association with vironments (FZ 7). but also through bottom currents, aggregate grains. P1. 12212 demonstrates the formation e,g. in deep shelf and basinal environments (FZ 2 and of a coarse algal sand through the disintegration of dasyFZ I ) . clad thalli. Disintegration was stronger for the gymnoSMF 15 characterized by ooids, SMF 16 defined by codiacean algae (Pl. 12213) that fell apart into smaller accumulations of peloids, and SMF 17 typifying car- particles than the dasyclad algae. Both samples show bonates rich in aggregate grains are frequent constitu- how algae contribute to in-place sediment production, ents of shallow platform carbonates. SMF 15 and SMF but the dasyclad living in high-energy areas, where most 16 are also common in inner- and mid-ramps in con- of the mud has been winnowed, produced skeletal sand trast to SMF 17 that appears to be very rare in ramp recorded by a grainstone fabric, whereas the gymnocarbonates, but is an excellent indicator for platform codiacean algae living in a low-energy environment prointerior environments (Fig. 14.28). These three SMF duced lime mud. Contrasting these examples, the CreTypes are easy to recognize if the diagnostic grains taceous foraminiferal grainstone depicted in Fig. 14.23 don~inarequantitatively. Many samples, however, con- was formed by a short storm event that may have octain mixtures of aggregate grains and peloids, or ag- curred in different parts of the platforms and ramps. A gregate grains, peloids and skeletal grains. The assign- closer look at the taxonomic composition of the forament of these samples to one of the SMF Types may be miniferal fauna may tell you in which ecological zones somewhat tricky. the tests have been reworked (see Fig. 14.7). SMF 18 characterizing accumulations of foraminThe joint characteristic of SMF 19, SMF 20 and iferal shells or calcareous green algae is well-defined sometimes also of SMF 21 is a fine biogenic laminabut unites accumulations having different origins. The tion whose origin is related to trapping and binding acnliliolid foraminiferal sand of PI. L22/1 is an autoch- tivities of microbes and algae, and to the precipitation

Plate 127 Problems with Standard Microfacies Types: Textural Changes in Bedded Limestones Fluctuations in water energy and sediment transport can result in the formation of sedimentary layers differing in depositional texture, constituent composition as well as the size and packing of grains. These differences might give rise to SMF Type assignments that do not necessarily reflect the factual sedimentary environments. To recognize these environments you need a combination of field data, paleontological criteria, and microfacies. Small-scaIed, short-time changes in depositional texture and the association of grain types are common in platform interior areas and in inner and mid-ramp environments influenced by storm-induced currents. These changes in texture and fabric differ from changes caused by turbidity currents and documented by distinct vertical succession patterns and wide areal extensions of sedimentary structures. 1 Changes in depositional energy. The conspicuous characteristic of the sample is the alternation of cortoid grainstone (G) and peloid packstone (P) fabrics. The lower grainstone layer (Gl) and upper layer top (G3) consist of skeletal grains (mostly corals - C, some dasyclad algae, DA, and a few mollusk shells, MS). Larger black grains are porostromate oncoids (0). All skeletal grains are coated by micrite envelopes. Some grains are encrusted by foraminifera. Intergranular pores are occluded by thin rims of early marine cements surrounding the grains, and late diagenetic cements (white) occluding the remaining pore space. The intercalated packstone layer (2) consists of small peloids, most of which are reworked and transported micrite clasts. The coated grainstone shows criteria of SMF 11, the packstone of SMF ~~-NON-LAMINATED. The assignment to SMF 11 is supported by field data and paleontological criteria. The sample comes from bedded carbonates corresponding to calcareous sands formed ar the margin of a platform in a backreef position. An assignment of the packstone, however, to SMF 16 would suggest tidal flat sedimentation and not reflect the genuine depositional environment. The packstone layer originated from a very short high-energy event causing a redeposition of peloids from nearby protected areas. Note the transitional character of the lower boundary of the packstone layer and the infilling of peloids in the underlying grainstone. White a m w s point to geopetals (,deposition of grains on top of shells). Strong shearing of the limestones is indicated by different orientation and filling of microfractures. Late Triassic (Dachstein limestone, Norian): Loser, Styria, Austria. 2 Storm sedirizcrltcztion.Transition of ooid grainstone (OG, 1) to bivalve shell- ooid rudstone (BOR, 2) at the top. Ooids are conspicuously small and more or less the same size, indicating a pre-depositional sorting of the grains. The microstructure of thc shells shows rework in^ of ostrcid bivalves. The blurred boundary between the two textures suggests that deposition of both layers occurred during a single went. Ooids have settled down, coming to rest in the cup-shaped valves (note the geopetals indicated by arrows), and filling shelter pores beneath the shells. The pores were occluded by calcite cement. The upper part of the sample shows similarities with SMF 12-Bs (bivalve shell hash). The dominance of ooids would suggest an assignment to SMF 15 pointing to deposition in ooid shoals. However, the intimate relations between ooids and shells as well as the chaotic orientation of the shell fragments characterize the sample as a storm deposit which can noi be categorized by a specific SMF Type. The sample comes from a storm-dominated inner ramp. Late Jurassic (Oxfordian): Osterwald. Lower Saxony, Germany. 3 Cl~ar~ges it1 1ctarer crzergy calrsing differences in gr-czin packing. The succession exhibits a lower packstonejbindstone fabric ( P B , I), separated by a distinct boundary (arrows) from an upper grainstone fabric (G, 2), which again grades into a packstoneibindstone fabric (P/B, 3 ) .The densely packed peloids, coated grains, oncoids and algae of the lower part are bound together by microbial crusts. The grainstone of the upper part contains reworked fragments of porostromiltc algae (PA:) a~lcigastropod shells (GA). Note oblique microfractures (MF) occluded with spar and gray silt. The sharp boundary between the t\vo textures suggests a more rapid stabilization and cementation of the bindatone than the grainstone. The textural changes reflect short-term changes in water energy conditions. The packstone/bindstone texture corresponds approximately to ShlF 16, indicating deposition within a shelf lagoon (Facies Zone FZ 7). Paleontological data support this interpretation. 'I'he sample comes from an isolated Bahamian-type platform (see 1'1. 1.34). I A e Jurassic (Tithonianj: Sulzfluh, Graubiindcn. Switzerland. 4 Brcwk in shallorz,-marine sedimentation. The lower part of the succession (1) consists of variously sized, angular and rounded lithoclasts embedded within a fine organic network formed by microbes and synsedimentary cements. The upper part (3) exhibits a similar fabric but the lithoclasts are larger and of different composition. Some clasts are reworked aggregate grains, others are extraclasts. The gray central part (2) consists of micritic cement, and differs from the lower and upper layers by the absence of lithoclasts. The erosion at the top of the cement layer (arrows) and micro-encrusters (ME) characterize a hardground evidencing sporadic breaks in deposition. Attribution of the sample to SMF Types might lead to SMF 4 (microbreccia deposited on slopes) or SMF 5 (forereef slope). Neither designation fits the real paleoenvironment. As shown by field data, the sediment originated in a near-coast environment where semi-indurated muds with algal and aggregate grains were reworked and stabilized by microbiai mats. Lithoclasts are storm-transported chips. Late Cretaceous: Central Apemines: Italy.

Plate 1 2 7 : P ~ o b l e m svr ~ t hStandard Evlicrofacies Types

71'

iih

Microfacies Typcs of Carbonate R a m p s

of carbonate induced by the life cycle and the decay of these organisms. The environmental interpretation of these SMF Types should consider the classification of benthic microbial carbonates described in Sect. 9.1.5 and summarized in Fig. 9.1. SMF 23 is a poorly constrained type. The lack of fossils in micritic limestones or dolomites may have many reasons, one of which could be an elevated salinity. SMF 23 should only be considered if pseudomorphs after gypsum, anhydrite or halite crystals, or the stratigraphic position of the micritic beds support the interpretation. SMF 24 represents a common characteristic of tidal deposition but can also originate from storms in shoreface settings. Coastal and inland sabkhas are characterized by SMF 25, subaerially exposed areas in various climate Lones by SMF 26. Both types reflect non-marine conditions. l~epositionnlvariability arzd Standard Microfacies The depositional texture and composition of bedded limestones can change within a scale of some millimeters and a few centimeters. These changes are reflected by different microfacies that are of local importance only. However, some of these small-scale microfacies types indicate substantial changes that are reflected by Standard Microfacies Types. Examples are si~ownin PI. 127.

SMF

T

~

~

,

~

J ~ cnl.Pr ,lor

tile bvholc hpccnunl ofmiuo-

fcic 1c.c

Some samples characterized by conspicuous microfac~escriter~acan not be attributed to an SMF Type of the rimmed platform model, owing to the lack of appropriate SMF Types. Examples are burrowed lime rnudstones (e.g. PI. 2514) common in deep shelf and deep-shelf margin environments, and intraclast packhiones and wackestones occurring in restricted platform Interior. in toe-of-slope settings and common in disrally steepened ramps. Nodular limestones (Pl. 21 and Pi. 139) represent another example. Some of these ;i~icrofaciestypes are included in 'Stratigraphic Microfacies Types' 14.3.3 Stratigraphic Microfacies Types Cieologists working in different parts of the world know the amazing similarities of the facies of carbonate rocks of similar age. Limestones of specific long-range time intervals are characterized by recurrent microfacies types exhibiting a wide geographic distribution and a limitation to particular major facies belts. The significant global coincidences of some of these 'stratigraphic

microfacies types' are sometimes caused by climatic controls determining biogeographical distribution patterns of shelf organisms. One example is the congruent microfacies types of Late Triassic platform and reef carbonates in different parts of the Tethys. Other reasons for time-dependent microfacies types are the combined effects of specific oceanographic conditions and evolutionary stages, exemplified by the worldwide distribution of nodular deep-shelf carbonates in the Jurassic, and the Late Cretaceous pelagic chalk facies triggered by evolutionary bursts of the calcareous plankton. Lists of the common stratigraphic microfacies types for the Devonian, Late Paleozoic, Late Triassic, Jurassic and Cretaceous can be found in Wilson (1975).

14.3.4 Common Microfacies Types of Carbonate Ramps The SMF Types, describing sediments of trop~cal rimmed shelves, can only be sometimes found in carbonate shelves formed in differing latitudinal and climatic settings and developing different geometries. Tht. following sections compare the common microfacics criteria of carbonate ramps with those of rimmed platforms and summarize the common and recurrent rnicrofacies types of ramp carbonates. Many ~nicrofaciescriteria of platform carbonates can also be seen in thin sections of limestones formed ~n ramp settings. However, there exist differences concerning the distribution and type of the prevailing matrix, grains and fabrics. The occurrence of these criteria on inner, mid- and outer ramps is controlled by offshore and onshore transport by storms, the growth of mud mounds and reefs in different parts of the ramps. and the bathynletric dependence of benthic organimf that contribute to carbonate production.

14.3.4.1 Microfacies Criteria of Carbonate Ramps The fine-grained matrix is micrite and calcisiltite. Mic-rite is common in deeper outer ramps and in protected areas of inner ramps. Both allomicrites and automicrites contribute to carbonate production. Allomicrites are characterized by poorly sorted matrix exhibiting very fine peloids within a matrix, with small bioclastic debris probably caused by bioerosion, variations in packing and mixed microfossil faunas. Automicrite matrix is a common constituent of mud mounds. Clues to inplace carbonate production in deeper ramps (Jeffery

Microfacies of Carbonate R a m p s

7 17

and Stanton 1996) are down-ramp sequential distribu- isms by bottom currents is indicated by fossils that are tion of depth-sensitive organisms (see Fig. l4.l2), well uncommon in the depositional environments where they preserved and unabraded fossils, beds and bed sets that are found (e.g. larger foraminifera in outer ramp setare traceable along ramp slopes for tens of kilometers, tings). and that are also traceable through ~noundsgrowing on Ooid accumulations originate in three ramp settings: the ramps, geopetals in original position, and lack of sedimentary structures indicative of transport. Calci- (1) in inner ramps near shorelines and at coasts (here siltite is abundant in outer ramps, characterizing a paralso contributing to eolian sand dunes), (2) in mid-ramp ticular microfacies type (RMF I). The origin of these and inner ramp settings forming shoals and thick graincalcisiltites is enigmatic. Abrasion in storm-influenced stone sheets; and (3) as grains having been transported ramp parts and transport to deeper ramp parts may be from mid-ramps to outer ramps and deposited in thin one of the sources in Paleozoic ramps. Pelagic fallout tempestite beds intercalated with lime mudstones and contributed to the formation of calcisilite and allomi- wackestones, marls or shales. Most of the spherical crite of Mesozoic and Cenozoic ramps. Skeletal min- ooids correspond to concentric or micritc ooids. Paraueralogy might have had some influence on the devel- tochthonous spherical and non-spherical radial ooids opment of ramps that are more abundant in calcite- may occur in inner ramps. Relations between water dominated times with maxima in the Cambrian-Ordovi- energy, ooid size and sorting and the thickness of ooid cian, Mississippian and Jurassic than in aragonite-domi- cortices are indicators of transport mechanisms (see Fig. nated times. 4.25 and Fig. 4.26). The dominant grain types of carbonate ramps are skeletal grains and ooids, followed by peloids and intraclasts. Other grain types are quantitatively of minor importance (cortoids, oncoids), or arc: very rare or totally absent (pisoids, aggregate grains). Abundant aggregate grains are characteristic of carbonate platforms but missing in ramp settings.

Peloids occur as fecal pellets in inner ramps and as mud peloids in outer ramps. Cot-toids are present in current-washed sand shoals of inner ramps, but appear to have not the same importance as in rimmed platform carbonates. Oncoids occur in inner and outer ramps. Oncoids from shallow and deep environments differ in nuclei, organisms contributing to the cortices, lamination type, and the conlposition of the encruster association. Oncoids built by cyanobacteria and algae are present in inner ramps; those built by red algae (rhodoids) in inner ramp, but more frequently in outer ramp settings. Micrite oncoids are common in outer ramps and basins.

Common sXelc~tu1gmirzs in outer ramps are calcimicrobes, smaller foraminifera, sponge spicules, bryozoans, brachiopod and mollusk as well as arthropod shells, serpulids and echinoderms. Shallow inner ramp sediments exhibit similar bioclasts in comparison to the normal marine and restricted platform interior facies of platforms: Calcimicrobes, benthic smaller and larger lntraclasts may occur in all ramp settings, but are foraminifera, calcareous green algae, mollusks, ser- abundant in distally steepened ramps (RMF 9) within pulids, ostracods and echinoderms. These shells are also debris flows accumulating near to the outer ramp slopes. major constituents of storm and current induced skel- These intraclasts are micritic, poorly sorted, angular to etal shoals in mid-ramp and innerramp settings. subrounded grains embedded with~na nlicritc matnx. Organisms taking part in the formation of mud Sedimentary mass flow hrCcrias der~vedfrom ramp mounds, reef mounds or patch reefs are microbes, some slopes are monomict, with medium to high matrix congreen and red algae, sponges including archaeocyathids. tents and clast-supported fabrics. The decimeter- to stromatoporoids, coralline and siliceous sponges, tabu- meter-thick breccia beds have sharp boundaries late and scleractinian corals, and some pelecypods (rudists). Burchette and Wright (1992) suggest that the main Important depositionulfabrics in differentiating insediment producers both in organic buildups and in ner, mid- and outer ramps are bioturbation and laminalevel-bottom communities have migrated from outer tion. Burrows occur all over the ramps, but are particuand mid-ramp settings to inner ramp settings since the larly abundant below the wave base and below the storm Late Jurassic. wave base. Mid-ramp and outer ramp burrows exhibit Taphonomic and preservation criteria including differences in density, spatial distribution and ichnotaxa shape, rounding, breakage, and size and sorting of fos- association. Burrows that have not caused major breaksils are good indications of transpofl. artd allochthonous age of shells, and burrows that have produced extendeposition. Out-of-habitat transport of benthic organ- sive breakage are proxies for the intensity of burrow-

h l ~ c r o f n c ~ Types es of Carbonate R a n i p i

ing, which is greater in the second type that is common in outer ramp settings. Depositional lamination is frequent in deep ramp settings with hemipelagic sedimentation. Fenestral fabrics are common in tidal areas in back-ramp regions (RMF 23). Mid-ramp sediments are characterized by biofabrics indicating storm deposits (cross-bedding, imbrication patterns, reverse grading bedding; see Sect. 12.1.2.1). Good characteristics are disordered fabrics typified by chaotic arrangement of non-sorted, variously sized, commonly fragmented and broken bioclasts whose interspaces are infilled with calcisiltite or bioclastic micrite (RMF 28). Many ramp carbonates, particularly packstones and grainstones, show low compositional nzuturity (see Sect. 6.2.1.4) expressed by a mixture of different skeletal grains, peloids, intraclasts and sometimes also ooids. This m~crofaciesis common in packstones and grainstones of mid-ramp- and inner ramp settings. Characteristic microfacies types are RMF 8 and RMF 14.

14.3.4.2 Microfacies Types of Carbonate Ramps Detailed studies of carbonate ramps are biased with regard to the Early Carboniferous ramps of the 'Waulsortian facies'. and Late Mesozoic and Tertiary ramps. Mriny of the papers listed in Box 14.5 contain data on microfacies criteria. But relatively few investigations define microi'acies types, describe their distribution in different parts of ramps, and usc the microfacies types to subdivide ramp environments or evaluate the sequence stratigraphic development (e.g. Bachmann 1994; Bakush and Carozzi 1'386; Ruffer 1995; Bachmann and Kuss 1998). A survey of some of the papers listed in Box 14.5 allow the existence of several microfacies types that appear t o dominate in specific parts of the ramp model (Box 14.6). The distribution and frequency of these rnicrofacies type:, are different in low-energy, muddominated ramps that are mainly controlled by waves 2nd tides, and in high-energy, grain-dominated ramps srrongly controlled by storms. Low-energy ramps have a low, high-energy ramps a good reservoir potential. Some of these Ramp Microfacies Types (RMF) correspond in their criteria to SMF Types of carbonate platforms, but other RMF Types do not. The RMF Types should not be regarded as obligatory categories comparable with the SMF Types. 'The latler are better defined and are based on more case studies than the RMF Types, which only reflect a summary of the current state of the art.

Box 14.5. Selected case studies on Phanerozoir carbonate ramps. More references, specifically on the importance of carbonate ramps as reservoir rocks, can be found in Burchette and Wright (1992).

Tertiary: Betzler et al. 1999, Buxton and Pedley 1989; Cunningham 2002; Cunningham and Collins 2002; Danese 1999; Franseen et al. 1997; Gietl 1998; Kulbrok 1996; Obrador et al. 19%; Pedley 1992; Pedley et al. 1993; Pomar 2001; Surlyk 1997 Cretaceous: Bachmann 1994; Bachmann and Kuss 1998; Caranannte et al. 2000; El Gadi and Brookfield 1999; Gomez-Perez 1998; Harris et al. 1984; Kulbrok 1996; Pascal et al. 1993; Scott and Warzeski 1993; Surlyk 1997 Jurassic: Aurell et al. 1998; Azaredo 1998; Badenas and Aurell 2001; Baumgartner and Reyle 1995; Braun 1998; Budd and Loucks 1981; Herrmann 1996; Schrnid and Jonischkeit 1995 Triassic: Aigner 1984; Calvet and Tucker 1988; Calvet et al. 1990; Hips 1998; Michalik et al. 1992; Riiffer 1995; Torok 1997; Tucker et al. 1993 Permian: GCrard and Buhrig 1990 Pennsylvanian: Fliigel and Zhou 1986; Harris 1990 Mississippian: Ahr 1989; Bachtel and Dorobek 1998; Bakush and Carozzi 1986; Brandley and Krause 1997; Burchette et al. 1990; Caplan et al. 1996; Chatellier 1988; 1992; Chen and Webster 1994; Diaby and Carozzi 1984; Elrick et al. 1991; Faulkner 1988; Gawthorpe 1989; Gawthorpe and Gutteridge 1990; Handford 1988;Jeffery and Stanton 1996; Lasemi et al. 1998; Rankey 2003; Reid and Dorobek 1993; Sebbar et al. 2000; Simpson 1987; Sommerville and Strogen 1992; Wright 1986; Wright and Faulkner 1990 Devonian: Doring and Kazmierczak 2001; Kaufmann 1998 Silurian: Coburn 1986; Dixon and Graf 1992; Frykman 1989; IIurst and Surlyk 1983; Lavoie and Bourque 1993; Sanli and Desrochers 1993; Whitaker 1988 Ordovician: Bova and Read 1987; Grimwood et al. 1999; Lavoie 1995; Lee and Kim 1992; Lee et al. 2001; Read 1980, 1982 Cambrian: Ahr 1973; Barnaby and Read 1990; Markello and Read 1981

14.3.5 Tracing Facies Zones with Microfacies Types Since common microfacies types reflect the environmental conditions controlling depositional patterns and the distribution of organisms, the assemblage of character-istic Standard Microfacies Types can be used as a proxy for specific facies belts. Fig. 14.29 shows the distribution of SMF Types in the rimmed carbonate platform model. Fig. 14.30 displays the approximate distribution of the more common microfacies types over a carbonate ramp.

M r c r o f a c ~ e sT y p e \ of Carbonate R a m p s

7 19

Box 14.6. Common microfacies type:;ofPaleozoic and Mesozoic rump carbonates. The list starts with microfacies types of the deeper outer ramp zones, anti continues with microfacies types of mid-ramps and shallow inner ramp zones. Microfacies types of the bioclastic and oolitic carbonate sand shoals and banks formed in inner and mid-ramp settings are listed at the end of the box. Numbers in brackets indicate corresponding SMF types. Outer ram/? Thin- to medium-bedded, fine-grained, often burrowed limestones and marls. Laminated karls alternate with lime mudstones. Skeletal grains commonly well preserved, not worn. Mudstones, wackestones, packstones. Some tempestite beds (grainstones). Mud mounds (see Sect. 16.1.2). RMF 1: Calcisiltite and mudstone with peloids, very fine skeletal debris, sponge spicules, sometimes fine-laminated (SMF 1). RMF 2: Argillaceous burrowed mudstone and wackestone; rare agglutinated foraminifera, ostracods, echinoderms. RMF 3: Burrowed bioclastic wackestone and packstone with diverse, common to abundant fossils (bivalves, brachiopods, echinoderms) and peloids. Skeletal grains not worn; whole fossil preservation common (SMF 8). RMF 4: Peloidal wackestone and packstone (- SMF 2). RMF 5: Pelagic mudstone with planktonic microfossils and open-marine nektonic fossils (e.g. ammonites) (SMF 3). RMF 6: Graded, laminated and finely cross-bedded bioclastic and peloidal grainstone (tempestite).

~edium-bedded,fine-grained bioclastic limestones and marls, often burrowed. Skeletal grains often worn. Echinoderms common. Mudstone, wackestone, packstone, some grainstones. Distally steepened ramps exhibit slumps and various signs of reworking and transport of fine-grained ramp material. Distal steepening occurs in outer ramp settings or near the mid-ramp-outer ramp boundary. Calcareous sand shoals and sand banks (see below). Various kinds of reefs occur in tnid-ramp and inner ramp settings (e.g. coral patch reefs, coral-red algal reefs). RMF 2 , RMF 3 , RMF 5 and RMF 7: Bioclastic packstone with abundant echinoderms and common bivalves and foraminifera. Skeletal grains worn (SMF 10). RMF 8: Burrowed packstone and grainstone with various skeletal grains, intraclasts, oncoids and peloids. RMF 9: Wackestone, packstone, floatstone with micritic intraclasts and ramp-derived bioclasts; sometimes microbreccias (distally steepened ramps) (-SMF 5). RMF 10: Limestone conglomerates (distally steepened). RMF 11: Marls with intraclasts and limestone pebbles (distally steepened). RMF 12: Boundstones comprising coral and coral-crust framestone. red alga! framestone (SR4F 7). Inner- ramp Inner ramp sediments are bedded, microfacially differentiated lin~estonesand dolomites forming relatively thin sequences. Marls are of minor importance. The inner ramp comprises open-marine environments wnth good water circulation, protected environments with restricted water circulation, sand shoal and bank environments characterized by oolitic and bioclastic grainstones and packstones (see below), lagoonal environments behind shoals or islands and peritidal environments. The latter are separated from other inner ramp parts as back-ramp environments (Fig. 14.3). Common texture types of open and protected inner ramps are bioclastic packstones and wackestones. Coral and coral-

ed algal boundstones (RMF 12) and other reef limestones (bivalve reefs) are common in open inner ramps. Other reefs, e.g. serpulid biostromes, occur in protected innerramp settings. Open inner ramp environments RMF 13: Bioclastic wackestone and packstone with abundant larger foraminifera (e.g. orbitolinids) (SMF 18-FOR). RMF 14: Bioclastic packstone and wackestone with skeletal grains, various amounts of intraclasts and some ooids (near-shoal). RMF 15: Bioclastic floatstone with various reef-derived material (near-reef coral-, algal- or bivalve-debris) (-SMF 6). Protected and low-energy inner ramp environments A common microfacies type in these environments is RMF 7 characterized by common to abundant echinoderm fragments. Associate skeletal grains occurring in different quantity are bivalve shells, gastropods, bryozoans, and benthic foraminifera. Other microfacies types are packstones and grainstones with larger foraminifera (RMF 13). RMF 16: Mudstone, wackestone or packstone with abundant miliolid foraminifera (SMF 18-FOR). RMF 17: Bioclastic wackestone with dasyclad green algae (SMF l 8-DASY). RMF 18: Bioclastic wackestone with ostracods Lagoonal environments RMF 17 (low-diverse flora) and RMF 19: Non-burrowed llme mudstone RMP 20: Bioclastic wackestone and packstone with calcareous algae and benthic foraminifera RMF 21: Oncoid packstone and floatstone (SMF 32) Perit~dalzones RMF 19 and RMF 21 and RMF 22: Fine-laminated dolomitic/linie rnudstone (SMF 19). RMF 23: Fenestral bindstone (SMF 21). RMF 24: Intraclast mudstone and packstons. RME' 25: Laminated evaporite-cahonate bindstone (SMF 25). Carbonate sand shoals and banks Storm-dominated ramps are characterized by accumulations of ooids, skeletal grains and peloids. These grains occurring separately or associated, form grainstone and packstone textures. Bedding and cross bedding are cornLon. These sediments originate in mid-ramp and innerramp settings. Bioclastic banks may be formed by storminduced but also by coast-parallel bottom currents. RMF 26: Medium- and coarse-grained bioclastic grainstone and packstone with various benthic skeletal grains. RMF 27: Bioclastic grainstone and packstone composed of few dominant skeletal grains (e.g. predominantly echinoderms, or predominantly foraminifera). RMF 28: Bioclastic floatstone and rudstone exhibiting a strongly disorganized fabric. RMF 29: Ooid grainstone with densely packed concentric ooids (common in shoals and banks) (SMF 15-C). RMF 30: Shelly ooid grainstone and packstone (common in banks).

720

Key for Determining SMF Types

SMF Types are valuable tools in facies analysis but do not demand too much from these virtual units. Be careful in solely using distribution patterns of SMF and RMF assemblages to recognize and trace facies zones of shelf-basin transects and * check your interpretations based on microfacies types against outcrop criteria (e.g. lithofacies, sedimentary structures), * examine the assignment to specific facies zones in the context of paleontological and palecological data, and * do not fit your data to the model instead of doing the other way round!

14.3.6 Determining Standard Microfacies Types: A Practical Guide Having avoided the pitfalls shown in P1. 127 and discussed in Sect. 14.3.2, you are ready to determine the SMF Type of your samples. Take the following steps!

/

Discriminate samples showing bindstone/lamination fabrics, breccia fabrics, shell and echinoderm concentrations, and signs of autochthonous reef growths from other samples. -- Bindstone and lamination fabrics: These fabrics (ircharacterize the SMF Types SMF I 6-LAMINATED regular pel~nicriteand pelsparite layers consisting of peloids of different size), SMF 19 (consisting of couplets of finer micritic laminae and somewhat coarser pelsparitic laminae), SMF 20 (planar or variously dome-shaped fine- and coarse-grained laminae), SMF 21 (laminated fenestral spar-filled cavities within a framework formed by sedimentary and biogenic grains; note that the fenestral fabrics also occur in limestones without lamination) and SMF 25 (alternation of fine-crystalline calcimudstone or dolomicrite layers and evaporitic layers with gypsum or anhydrite). -- Breccia fabrics are developed in SMF 4 (microbreccia consisting of skeletal grains and lithoclasts, often graded), SMF 5 (fine-grained breccia with a

Wackestone Floatstone 3 Abundant planktonic microfossils microsparite without fossils -

! Micro)ioclastic ~eloidal ine-grained )ackstone/ jrainstone abric

/ Packstone

Grainstone

5 Densely packec 4 Microbreccia, small bio- and whole fossils lithoclasts and fragments, 5 Denselyoften reef- or platform-derived packed whole fossils, often 11 Abundant planktonic reef-derived lithoclasts reef- or plat8 Whole fossils, 5 Densely packel coated skeletal microfossils grains 8 Whole fossils, fine bioclastic whole fossils 13 Millimeter- to micrite matrix I and fraaments, fine bioclastic centimeter-sized centimetersized reefoncoids with derived biotube-like clasts and structures bioturbation 15-C Ooids with concentric to centimeterstructures Very small sized lithosized oncoids 15-R Ooids with eauallv-sized with tube-like radial or radialmicritic ooids structures concentric rock-building structures centimeter-sized to centimeterbenthic foramin- 16-NON-LAMINATED agglutinated sized lithoifera or calcaroncoids peioids eous algae 17 Abundant voids within a aggregate grains micritic or pelmi- 18 Abundant rock I critic framework building benthic foraminifera or calcareous algae 5 Densely 1 Sponge packed whole spicules, often fossils and fraa- calcisiltite matrix ments of

1 Sponge spicules, often calcisiltite

_I

I

1 i

7

Tab. 14.1. Key to the deternzinution ofstundard Microfacies Types. The key does not include reef limestones, carbonates with bindstone~laminationfabrics, and limestones exhibiting concentrations of shells or echinoderms (see text for explanation). Start with attributing your sample to texture types and continue with the search for SMF Types characterized by adequate criteria.

S M F Types of Rimmed Platform

Platform interior

I

I

I

FWWB

SMF 1: SMF 2: SMF 3: SMF 4: SMF 5:

Spiculite wackestone/packstone Microbioclastic peloidal calcisiltite Pelagic mudstone/wackestone Microbreccia, bio-lithodastic packstone Allochthonous bioclastic grain:;tonel rudstonelpackstone~atstone,breccia SMF 6: Densely packed reef nrdstone SMF 7 : Organic boundstone. platform-margin 'reef' SMF 8: Whole fossil wackestane/floatstorie SMF 9: Burrowed bioclastic wackestone SMF 10: Bioclastic packstone/wackestone with worn skeletal grains SMF 11: Coated bioclastic grainstone SMF 12-5: Limestone with shell concentriltions SMF I2-CRIN:Limestones with crinoid concentrations SMF 13: Oncoid rudstonelgrainstone SMF 14: Lag deposits (found in different facies zones) SMF 15-C: Ooid grainstone with concentric ooids SMF 1 5 4 : Ooid grainstone with radial ooids SMF 15-M: Ooid grainstone with micritic ooids Peloidal grainstonelpackstone SMF 16-NON-LAMINATED: Peloidal bindstone SMF 16-LAMINATED: SMF 17: Aggregate-grain grainstone SMF 18: Grainstone/packstonewith abundant foraminifera or algae SMF 19: Densely laminated bindstone SMF 20: Laminated stromatolitic bindstonelmudstone SMF 21 : Fenestral packstone/bindstone SMF 22: Oncoid floatstonelpackstone SMF 23: Homogeneous, non-fossiliferous micrite SMF 24: Lithoclastic floatstonehudstonelbreccia SMF 25: Laminated evaporitecarbonate mudstone SMF 26: Pisoid cementstonelnrdstone1packstone

Fig. 14.29. Distribution of SMF Types in the Facies Zones (FZ) of the rimmed iarbonate platform model. Nearly all facie~ belts are characterized by assemblages consisting o f several SMF Types. The distribution o f SMF 14 (lag deposit) is not specially indicated, because non-depositionor strongly reducedsedimentation occurs in many deep-marin? as well as shallowmarine facies zones. A: evaporitic, B: brackish.

S M F Types of a Carbonate R a m p

Inner ramp

Outer ramp

Basin

RMF I: Peloidal calcisiltite with spicules RMF 2: Argillaceous burrowed rnudstoneiwackestone RMF 3: Burrowed bioclastic wacke-ipackstone with diverse fossils RMF 4: Peloidal wackestonelpackstone RMF 5: Pelagic rnudstone RMF 6: Graded, laminated bioclastic grainstone RMF 7: Bioclastic packstone, abundant echinoderms RMF 8: Burrowed multigrain packstonelwackestone RMF 9: Wackestone/packstone/floatstonewith rampderived intra- and bioclasts RMF i O : Limestone conglomerates RMF 11: Mark with intraclasts and limestone pebbles RMF 12: Boundstone RMF 13. Wackestoneipackstone with larger foraminifera RMF 14: Packstonelgrainstone with various bioclasts RMF 15: Bioclastic floatstone, reef-derived material RMF 16: Ejludstonelwackestonewith milioiids RMF 17: Bioclastic wackestone with dasyclads RMF 18: Bioclastic wackestone with ostracods RMF 19: Non-burrowed lime mudstone RMF 20: Bioclastic wackestoneipackstone with algae and benthic foraminifera RMF 21: Oncoid packstoneifloatstone RMF 22: Finely laminated dolomitic or lime mudstone RMF 23: Fenestral bindstone RMF 24: lntraclast mudstonelwackestone RMF 25: Laminated evaporite-carbonate bindstone RMF 26: Bioclastic grainstone/packstone with diverse skeletal grains RMF 27: Bioclastic grainstonelpackstone with a few dominant skeletal grains RMF 28: Bioclastic grain-Ifloatstone, disorganized fabric RMF 29: Ooid grainstone with concentric ooids RMF 30: Shelly ooid grainstone and packstone

Fig. 14.30. Strongly generalized distribution of rnicrofacies types in different parts of a honzoclinal carbonate ~-amp. This is

not a 'model' and the Ramp Microfacies Types do not have the character of Standard Microfacies Types. The figure just shows some microfacies types frequently described in studies dealing with Paleozoic and Mesozoic carbonate ramps. R M F 9, R M F 10 and R M F 11 occur predominantly i n distally steepened ramps. See text for the correlation o f some o f these RMF Types with SMF Types o f platform carbonates.

Determining SMF Types: Advices

high percentage of reef-derived ~naterial),SMF 6 (reef talus, fossils and lithoclasts) and SMF 24 (consisting of coarse micrite clasts and laminated clasts, 'flat pebble conglomerate'). All these SMF types also develop other textures and are, therefore, also included in Tab. 14.1, -- Concentrations of shells and echinoderms (mostly crinoids): Shell beds and coquinas are represented by SMF 12. The fossils form packstone, rudstone and floatstone fabrics. The type needs further subdivision. -- Reef limestones are assembled in SMF 7 characterized by sessile reefbuilders and framestone, bafflestone or bindstone fabrics. These limestones require specific investigations of the role of organisms in the formation of reefs, growth fabrics, internal sedimentation and cement types (see Sect.16.2). Distinguish remaining samples according to textural types using the Dunham classification. Use Tab. 14.1 to differentiate the samples, considering common and abundant grain types. Note that samples with identical grain composil.ion can show different depositional textures.

lasts may create problenls in the accurate classification of SMF Types. The SMF Types SMF 8, SMF 9, SMF 10 and SMF 11 often exhibit a multigrain composition without a pronounced quantitative dominance of a specific grain category. Your problem may be related to this shortcoming in the SMF classification. -- Finally, your assignment may not fit because you have relied on the wrong depositional model. Consider the possibilities of the carbonate ramp model (Fig. 14.3). Perhaps you will find the microfacies characteristics of your sample in one of the RMF Types listed in Sect. 14.3.4.2 and summarized with regard to their more common distribution in Fig. 14.30. Note that several of these RMF Types correspond in their composition and texture to SMFTypes, but that the distributional pattern of some of these corresponding types differs from that on carbonate platforms.

14.4 Dynamic Microfacies Types and

Environmental Changes

The concept of microfacies types includes a strong tendency to categorize. Strict categorization, however, may obscure the question of whether or not the microfacies data set consists of components that vary in a continuous fashion, or of discontinuous grain associations. If the spatial distribution is discontinuous, the stratigraphic Check the occurrence of the SMF Type in the con- or geographical representation of various microfacies text of the rimmed platform facies model (Fig. 14.29) types as a mosaic of 'cells' is justified and can provide and think about the reliability of attributing your sample a basis for the interpretation of sedimentary environvia the SMF classification to a specific facies zone. If ments. This approach is followed by the SMF concept. you find that your sample can not have originated in However, if the distribution is continuous, the facies the facies zone indicated by the model, have faith in mosaic gives only a rough picture of nature. This is your interpretation and consider the following possi- specifically important in the facies interpretation of bilities: carbonate ramps where environmental changes are pro-- The composition and texture may not reflect cri- gressive and gradual rather than abrupt. tcria caused by autochthonous deposition, but rather criteria caused by transport from the original depoMost grain analyses are descriptive with little analysitional site to other facies belts. Oolite beds inter- sis of relationships in'grain composition or grain abuncalated within basinal sediments and representing dance of samples. One way to detect relationships and turbidites or debris flow deposits may display all the patterns in grain-type distributions are ordination methcharacteristic criteria of SMF 15. Concentrations of ods that explore relationships between the components shells (SMF 12) are often allochthonous deposits and detect and analyze relays in carbonate rocks. Ref o m ~ e dfar from the living sites of the organisms. lays are spatial or temporal systematic shifts in the relaStorms can transport skeletal grains in offshore and tive importance of component grains answering to unionshore directions, and form multigrain bio- and directional changes of major environmental conditions lithoclastic calcarenites distant from the carbonate- (Hennebert and Lees 1985).The application of ordinaproducing area. tion methods to the study of relay phenonema facili-- Different mixtures of various skeletal grains, tates the recognition of environmental gradients coated grains, composite grains, peloids and intrac- (Hennebert and Lees 1991). Compare your favorite SMF designation with the definition of the SMF Type and with the pictures of the examples. But note that the pictures can not show the whole spectrum of microfacies variations.

Dynamic Microfacies 'Types

b In Q Q %

-

-c

s

d e

- -+ Facies A

Facies B

Facies C

D e p o s i t i o n a l environments

Environmental gradient

e

Fig. 14.31. Microfacies relays. A: Traditional microfacies types based on the abundance of grain types are generally considered as discrete units caused by a discontinuous distribution of the grain types across depositional environments or within a stratigraphic section. Differences in grain abundance are used to distinguish facies which seem to be genetically unrelated. B: The relay method shows the distribution and relative abundance of grain types formed in response to a unidirectional environmental gradient, e.g. water depth or decreasing water energy in shallowing-upward sequences. After Spence and Tucker (1999).

Relays reflecting environmentally controlled compositional changes document the effects of relative third-order sea-level fluctuations and can, therefore, successfully be used in identifying system tracts and hidden sequence boundaries and evaluating microfacies types (Spence and Tucker 1999; Fig. 14.31). Ordination methods use coefficients giving a measure of' similarity in sample composition or in grain distributions. Relays are detected using computer-optimized similarity coefficient matrices (e.g. the Jaccard similarity coefficient) based on presencelabsence compositional data or applying correspondence analysis techniques (Hennebert and Lees 1985). The latter method can consider absolute frequencies, relative frequencies (percentages), ranked values (e.g. low, medium, high) and binary data (presencelabsence) as well.

Basics: Standard microfacies Bonham-Carter, G.F., Gradstein, F.M., D'Iorio, M.A. (1986): Distribution of Cenozoic foraminifera from the northwestem Atlantic margin analyzed by correspondence analysis. - Computer and Geoscience, 12,621-635 Carozzi, A.V. (1989): Carbonate rock depositional models. A microfacies approach. - 604 pp., Englewood Cliffs (Prentice Hall) Cheetham, A.H., Hazel, E.J. (1969): Binary (presence-absence) similarity coefficients. - Journal of Paleontology, 43, 1130-1136 Fliigel, E. (1972): Mikrofazielle Untersuchungen in der alpinen Trias: Methoden und Probleme. - Mitteilungen der Gesellschaft der Geologie- und Bergbaustudenten in Osterreich, 21, 6-64 Hemebert, M., Lees, A. (1985): Optimized similarity matrices applied to the study of carbonate rocks. - Geological Journal, 20, 123-131 Hennebert, M., Lees, A. (1991): Environmental gradients in carbonate sediments and rocks detected by correspondence analysis: examples from the Recent of Norway and the Dinantian of southwest England. - Sedimentology, 38, 623-642 Koopman, B.J., Lees, A., Piessens, P., Sarnthein. M. (1979): Skeletal carbonate sands and wind-derived silty mark off the Sahara coast: Baie de Levrier, Arguin platform, Mauritania. - Meteor Forschungsergebnisse, C, 30, 15-57 Spence, G.H., Tucker, M. (1999): Modelling carbonate microfacies in the context of high-frequency dynamic relative sea-level and environmental changes. - Journal of Sedimentary Research, 69, 947-961 Wilson, J.L. (1975): Carbonate facies in geologic history. 471 pp., Berlin (Springer) Further reading: K148, K190

Fig. 14.32. Exercise: Try to determine the SMF Type for this sample using the Guide in Sect. 14.3.6. How old is the limestone (see Chap. 10) and from which environment does it come? Answers can be found in the Appendix.

15 Basin Analysis: Recognizing Depositional Settings

This chapter is an overview of tools for translating microfacies data into depositional settings. Using case studies of non-marine and marine carbonate rocks, we focus on the diagnostic criteria for recognizing the fac i e ~characteristics needed in basin analysis studies. Microfacies is an important element of basin analysis, but must be applied along with all the other field and laboratory observations available for reconstructing depositional conditions. This is exemplified by Fig. 15.1.

15.1 Pedogenic Carbonates

Pedogenic carbonates are formed by the accumulation of CaC03 within carbonate-rich soils. Ancient pedogenic carbonates are studied by means of microscopy, stable isotopes and geochemistry. The term paleosol (or paleosoil) refers to a soil formed on a landscape of the past. Calcite accumulations in terrestrial, near-surface soil horizons, formed in semiarid climate under conditions of sparse rainfall, are called caliche

Fig. 15.1. At first slght this sample would be referred to the Standard Microfacies Type SMF 10, indicating a shallow-marme depositional environment. But the sample is a sandy grainstone formed in eolian dunes. The highly porous sediment consists predominantly of chips of coralline red algae (all black grains), temgenous quartz grains (Q), bryozoans (B) and bivalve shells (BS), most of which are completely leached and only preserved by the circumcrusts of micrite rlms forming cortoids. Additional skeletal grains are echinoid spines (E), gastropods (GA) and miliolid foraminifera (F). The association of coralline red algae, bryozoans and echinoids is typical for shallow-marine carbonates, deposited in temperate seas. But what criteria characterize the sample as an eolian deposit? Diagnostic features are the narrow size range of the grains, good sorting, winnowing out of fine particles, high grain diversity (as compared to marine oolites), weak cementation (see PI. 291 7, PI. 3312) and cross-bedding observed in the outcrops. Small-scale cross-bedding is indicated by the white lines. This rock was used by the Punians in ancient Carthage for building stones (E. Flugel and Ch. Flugel 1997). Pleistocene (Tyrrhenian): El Haouria, Cap Bon Peninsula, northeastern Tunisia.

or culcrete. Caliche has a variety of origins ranging from a purely pedogenic formation to cementation in the phreatic zone. Calichification modifies the original sedimentary features of carbonate rocks and produces new textures and structures (see Sect. 2.4.1.1 for further information). Caliche originates via a combination of cementation, replacement and displacement, leading to the substitution of the host material. If time permits, a calciterich hard horizon (hardpan layer) will develop, acting as a barrier to further movement of calcium carbonate and favoring the formation of laminar units on the impernleable horizon. The horizon eventually fractures and brecciates, leading to the formation of distinct textures, often associated with pisoids. Paleocaliche are typically micritic deposits that can be laminated or non-laminated. Caliche profiles developing from shallow-marine limestones often exhibit a sequence of massive/brecciated and laminar/pisolitic horizons.

15.1.1 Microfacies Criteria of Paieocaliche A well-illustrated review of rnicromorphological criteria of caliche was provided by Esteban and Klappa (1983). Note that descriptive terms used by geologists and pedologists differ (Ettensohn et al. 1988)! Cnliche cshibits microfabrics of non-biogenic and biogenic origin. Thc latter, summarized as beta cal(Wright 1990), includes microbial coatc~~~~fc~fafitD~-ics ings. calcified tubules, rhizoliths, alveolar-septa1 fabrics, and Micr-ocodizim. Microbial and fungal contributions are evident in many calcretes (Verrecchia 2001). .4ipi2cr cnliche ,fabrics originate from the replacive growth of carbonate (e.g. dense micrite, microspar, nodules. complex cracks and crystal-filled fractures, rhonlbic. calcite crystals). Some of the criteria listed below reflect the development of soil profiles over time, e.g. an open micrite network can develop to dense laminar secondary lime mudstone. and then to brecciated caliche. Common tliirl-section criteria are:

( I ) Ttxtule C'arholzarc tcxturc. The general texture of paleocalrche corresponds to lime mudstones, packstones or bindstones. Note that these textures are no depositional hut secondary textures!

(2) Matrix and constituents Drtzsc nzicritc (Pl. 12815; Fig. 15.2) concentrated eirhei- into dark isolated, small subspherical nodules, or

into ring-like or irregular masses forming a secondary lime mudstone developing from micritic parent limestone. The often used term 'glaebuie' refers to const~tuents of soils (e.g. nodules) whose shape, color or composition are different than the surrounding soil matrix. Clotted micrite consists of rounded to angular micrite peloids, separated by blocky calcite. The clotted texture can lead to total obliteration of the original sedimentary textures and fabrics. A grainstone composed of well-sorted, sand-sized grains may be altered to clotted micrite with peloids (diameter from 0.5 to 1.0 mm). Micritic peloids. Spherical particles, 0.05-0.5 mm in size. Occur in great abundance, isolated or as densely packed aggregates forming a clotted texture. Interpreted as being of near-surface diagenetic origin ('grainification' of a lime mudstone), or as calcified fecal pellets of small soil arthropods. Peloidal and coated fabrics have also been interpreted as calcification products related to root mats (Calvet and Julia 1983). * Micrite coatings (Fig. 1512; PI. 12816). Sand-sized to pebble-sized detrital carbonate grains and bioclasts coated with thin regular to highly irregular laminae of brownish or yellowish micrite, microsparite or fine sparite. Coatings vary laterally in thickness or only occur on one side of the grain. Coated grains may be connected by micritic bridges. Micrite coatings are particularly common in limestone-hosted caliche characterizing initial phases of cal~chification. Pisifornl accretionary bodic~of micrite or mlclo sparite with a nucleus of carbonate silt. Associated .M.it11 laminar caliche horizons. Pisoids. Soil pisoids (PI. 12816; Fig. 4.27) are sphaerical or subsphaerical, irregularly laminated concentric micritic grains, formed by chemical or biochemcal precipitation of microcrystalline carbonate on a nucleus (Fig. 14.27B; P1. 13,614). See Sect. 4.2.6 lor more information. Commonly associated with laminar caliche crusts. (3) Fabric Laminar crusts (Pl. 12811, 6). Laminated or banded millimeter-thick crusts of slightly undulated carbonate laminae alternating in color (yellowish/grayish) and composition (micrite, microsparite, sparite). Lamina thickness varies between 50 pm and about 500 km. 7'hc laminae may form a complex network. The laminae follow the topography of the substrate. See Read (1976) for criteria distinguishing laminar caliche from microbial laminated structures. Circumgranular cracking (Fig. 15.2; P1. 12812, 3 ) . Micrite nodules, up to 10 mm, bounded and locally dissected by crescentic and circular veins of sparite, up to 0.5 mm thick. Formed by alternating shrinkage

Caliche: Root-Related Structures

727

Fig. 15.2. Diagnostic features of paleocaliche. One of the most significant features of caliche seen in thin sections is their inhomogeneous texture and the lack of fossils. Characteristic criteria shown in this picture are the breccia-like texture, nodular fabrics (N), clotted fabrics with micritic peloids (PEL), grains coated by variously thick micrite (MC), and spar-filled wrinkled microcracks (white arrows). 'The latter occur as straight or wrinkled cracks, or surround the nodules (circumgranular cracking).The coatings surround alveolar structures (A; irregular pores infilled with sparite and separated by interconnecting micritic bridges; interpreted as root structures). Black arrows point to rhizogenic structures. The rock is strongly fractured. Early Tertiary (Ilerdian, Paleocene): Serraduy, Tremp Basin, Southern Pyrenees, Spain. After Eichenseer and Luterhacher (1992) and expansion processes in soils induced by seasonal dryingJwetting cycles.

(4) Root-related features Rhizoliths, Microcodium, calcified root hairs, pedotubules, and alveolar structures can be combined under the term 'root-related structures'. Examples of carbonate rocks with evidence of the farnler activity of plant roots forming 'rhizogetzic calcr~tes'(Wright et al. 1995) are known from various Phanerozoic time intervals, particularly from the Late Paleozoic, Jurassic, Cretaceous and from the Tertiary and Quaternary. Root structures (rhizoliths) occur as root casts or rhizoconcretions. Rhizogenic calcretes are formed by the calcification on, in, or around roots of higher plants. Root casts consist of tubular branched voids (pedotubules; P1. 1281.5) of decayed roots infilled with fine sparite. They are generally less than 1 mm in diameter. Rhizoconcretions are characterized by concentric accumulations of tangential to random fibers of micrite. They are typically 0.5 to 2 mm in diameter, often surrounding root casts or alveolar structures. See Klappa (1980) for a classification of root structures.

Micl.ocodiunz (PI. 128/4). Aggregates of 0.1-1 Inn1 long prismatic petal-like sparry calcite crystals, with a central cavity in each one. The cavity is filled with dark material. The calcite crystals are radially arranged around an axis, or are grouped into irregular masses and crusts. Interpreted as calcified mycorrhizae, a symbiotic association between soil fungi and cortical cells of plant roots, or as bacteria or algae (see Sect. 10.2.6.2). Alvcolar srr-uctut-cs(Fig. 15.2). Tubular to irregular pores infilled with sparite and separated by straight or various sinuous interconnecting bridgzs of micrite. The bridges consist of tangentially or randomly oriented micrite and/or microsparite. The pores may contain arcuate micritic septae (alveolar-septa1 structure). Individual pores reach 1 mm in width and 20 mm in length. Interpreted as entwined rhizoliths, resulting from the calcification of root hairs

(5) Breccia structures In-situ hrecciation (Fig. 15.2, P1. 128/6). Micrite fragmented in place, forming a polygonal fracture network infilled with sparite. Infilled micrite polygons are millimeters to several centimeters in size. Brecciation

Microfacies of Paleocallchc

is induced by desiccation, displacive crystallization of calcite, root activity and/or extensive periods of dissolution.

(6) Carbonate cement * Cement and microsparite. Common cement types in caliche are vadose micritic cement, blocky calcite cement and meniscus cement. Microsparry fabrics are common. 15.1.2 Significance of Paleocaliche and Paleosols Paleosols have been known since the Precambrian. Most case studies deal with examples from the Quaternary and Tertiary, but other papers deal with the Cretaceous, Jurassic, and Late Paleozoic. The recognition of paleosols and paleocaliche is of paramount importance in interpretating past climate (Mack and James 1994; Theriault and Desrochers 1994), the evolution of the atmosphere (Cerling 1991; Ekart et al. 1999),and weathering (Martini and Chesworth 1992). Most geological studies of paleosols focus on caliche. Paleocaliche is hosted by sandstones, alluvial

sediments, and lacustrine carbonates and shallow-marine carbonates. Different host sediments cause different associations of calcrete profiles, horizons and associations (Theriault and Desrochers 1994). Since paleosols can form on limestones of marine origin only when the relative sea level is lowered, paleosols are key criteria for bounding surfaces in sequence stratigraphy. The combined use of paleocaliche and paleokarst criteria gives us a detailed picture of the emergence evolution of platforms (Davies 1991;Webb 1994). Basics: Pedogenic carbonates and paleocaliche Bain, R.J., Foos, A.M. (1993): Carbonate microfabrics related to subaerial exposure and paleosol formation. - In: Rhezak, R., Lavoie, D.L. (eds.): Carbonate microfabrics. - 19-27, New York (Springer) Bullock, P., Fedoroff, N., Jongerius, A., Stoops, G., Tursina. G., Babel, U. (1985): Handbook of soil thin section description. - 152 pp., Wolverhampton (Waine Research Publications) Davies, J.R. (1991): Karstification and pedogenesis on a late Dinantian carbonate platform, Anglesey, North Wales. --Proceedings of the Yorkshire Geological Society, 48,297321 Esteban, M., Klappa, C.F. (1983): Subaerial exposure envlronment. -In: Scholle, P.A., Bebout, D.G., Moore, C.H. (eds.): Carbonate depositional environments. -American

Plate 128 Carbonate Paleocalicl~eand Paleosols: Microfacies Criteria The plate dlsplays a few diagnos!ic criteria including MICI-oc.ocfrwn (-> 4), laminar crusts (-> 1, h), inicrltic nodular structures (-> 2. 3 , 6 ) , spar-filled branching pedotubules (-> 5 ) , circumgranuiar cracks (-> 3) and psoids (-> 6). Lamitzar paleocaliche crust. The foraminifera1 grainstone, formed in a platform interior environment, is disconformably overlain by a pedogenic crust consisting of light sparry and dark micritic, slightly undulated laminae. The caliche crust represents a sequence boundary. Early Tertiary: Southern border of the Galala Basin, Egypt. Nodular paleocaliche formed on marginal carbonates of an episodically drying lake. The lacustrine carbonates were pedogenically modified, resulting in the formation of palustrine limestones (see Sect. 2.4.1.2). Caliche criteria arc circumgranular cracks (white arrows) around nodules (N) consisting of dense micrite. The black arrow points to sparfilled shrinkage cracks. Evidence of the lacustrine host rock are charophyte algae (CA). Early Tertiary (Claron Formation, Paleocene): Brice Canyon National Park, Utah, U.S.A. Cirrumgrarzulur crucking around a quartz-bearing nodule caused by alternating shrinkage and expansion processes in soils. The circumgranular crack is filled with calcite. Same locality as -> 2. Microcodium Gliick, characterized by elongate, radiating and petal-like calcitic eletnents grouped into ring-like structures. The structure is indicative of a meteorically influenced environment, e.g. a paleosol, and hence is a criterion for the recognizing continental conditions, cessation of marine sedimentation, and subaerial exposure. Findings of isolated hfirrorodiunz within marine strata may be explained by the reworking of paleosols. Microcodium is abundant in many Late Pennsylvanian to Pennian, Late Cretaceous, Paleocene, Eocene, and Miocene paleosols. Pleistocene: Crete Island, Greece. C a l i c h ~nodule containing irregularly bent and branching voids infilled with fine sparite (pedotubules, arrows) corresponding to decayed root elements of higher plants. Early Cretaceous: Subsurface, Ostenniinchen well, southern Bavaria. Germany. Paleocaliche. The sample exhibits several criteria that are diagnostic for alpha fabric caliche: Clotted and inhomogeneous micrite, irregular nodular texture (N), fracturing and incipient brecciations (white arrows), undulating laminar crusts (black arrow), and pisoid grains (P). Note the difference in the size, shape and internal lamination of these grains as well as their irregular grading. Most of the pisoids consist of microspar and exhibit numerous fine pores. SMF 26. Quaternary: Agadir, Morocco.

Paleokarst and Speleothcrns

Association of Petroleum Geologists, Memoir, 33, 1-54 Freytet, P., Plaziat, J.-C. (1982): Continental carbonate sedimentation and pedogenesis. Late Cretaceous and Early Tertiary of southern France. - Contributions to Sedimentology, 12, 1-213 Klappa, C.F. (1980): Rhizoliths in terrestrial carbonates: classification, recognition, genesis and significance. - Sedimentology, 27, 613-629 Klappa, C.F. (1983): A process-response model for the formation of pedogenic calcretes. -In: Wilson, R.C.L. (ed.): Residual deposits. -Geological Society, London, Special Publication, 11, 21 1-220 Gebhardt, U. (1988). Mikrofaziesanalyseund stratigraphischregionale Interpretation terrestrischer Karbonate der variszischen ~ o l a s s e(Mitteleuropa, Permokarbon). - Freiberger Forschungshefte, C 427, 30-59 Reinhardt, J., Sigleo, W.R. (eds., 1988): Paleosols and weathering through geologic time: principles and application. - Geological Society of America, Special Paper, 216, 181 pp. Read, J.F. (1976): Calcretes and their distinction from stromatolites. - In: Walter, M.R. (ed.): Stromatolites. - 557 1, New York (Elsevier) Retallak, G.J. (2001): Soils of the past. Second edition. 416 pp., Oxford (Blackwell Sciences) 'Iheriault, P., Desrochers, A. (1993): Carboniferous calcretes in the Canadian Arctic. - Sedintentology, 40,449-465 Wright, V.P. (ed.. 1986): Paleosols. Their recognition and interpretation. - 3 15 pp., Oxford (Blackwell) Wright, V.P. (1994): Paleosols in shallow marine carbonate sequences. - Earth Science Review, 35, 367-395 Wright, V.P., Tucker, M.E. (eds., 1991): Calcretes. -1ntemational Association of Sedimentologists, Reprint Series, 2, 352 pp. Wright, V.P., Platt, N.H., Marriott, S.B., Beck, V.H. (1995): A classification of rhizogenic (root-formed)calcretes, with examples from Upper Jurassic-Lower Cretaceous of Spain and Upper Cretaceous of southern France. - Sedimentary Geology, 100, 143-158 Further reading: KO30

sols, discolored rocks, terra rossa, breccias, and specific cavity fills. The recognition of paleokarst-related disconfonnities has major implications for the interpreting sea-level history and defining a sequence-stratigraphic framework. One of the most spectacular features of subsuifuce karst is the development of cave systems and voids originating from meteoric dissolution. These caves are places where the formation of various types of carbonates (speleothems) and the precipitation of aragonite and/or calcite in smaller voids (PI. 12914) take place. Many caves exhibit infilling by cave sediments (Pl. l29/ 2, 3) whose composition and fabric provide clues to climate and hydrological conditions. A major feature of surface and subsurface paleokarst are intraformational karst breccias (Fig. 15.4; P1. 129/1), which may be hosts for mineral deposits, particularly lead-zincsulfide deposits (see Sect. 17.2). Paleokarst develops as depositional, local or intcrregional paleokarst (see case studies in Choquette and James 1988). Depositional paleokarst is commonly associated with meter-scale carbonate platform cycles. Local paleokarst develops when only parts of platforms (e.g. platform rims) are exposed, due to synsedimentary block faulting or small drops in sea level. This is documented by the case study shown in P1. 129. Interregional paleokarst is related to major eustatic-tecton~c events and characterized by widespread karst terranes. Distribution: Paleokarst features have been reported since the Archean, but became abundant in carbonate

15.2 Paleokarst and Ancient Speleothems I'aleokarst IS an ancient karst (see Sect. 2.4.1.3), commonly buried by younger sediments or sedimentary rocks. Speleothems are carbonate sediments formed in cave systems. Karst is an aspect of lowstand conditions in the carbonate system. Humid climate favors karstification of exposed carbonate platforms during sea level lowstands. Rainwater charged with C03penetrates fissures and voids creating a karst landscape with collapse and solution sinkholes, solution caves, dolines and underground rivers. Karst features indicative of subaerially exposed karst are dolines, rundkarren (rounded solution tunnels), kamnitzas (solution basins with circular to oval outlines, flat bottoms and rounded edges), paleo-

Fig. 15.3. Paleokarst breccias caused by the collapse of cave rocks and speleothem carbonates are characterized by a disorganized fabric, and clast-supported angular limestone clam in a size range of a few millimeters up to boulders more than several tens of centimeters across. The thin section shows a breccia consisting of angular clasts of pisolitic and fine-laminated speleothem calcite of a paleokarst cave. Early Carboniferous (Viskan): Holy Cross Mountains, Poland.

Palmkarst: Criteria

rocks from the Upper Proterozoic onward (Bosak et al. 1989). Large-scale products of subaerial.exposure have remained rather similar since the Mid-Proterozoic. However, the amount of karst formation per time unit should have been lower during the Cambro-Devonian, owing to the absence of terrestrial vegetation cover prior to the Carboniferous.

15.2.1 Diagnostic Criteria of Paleokarst and Paleospeleothem Structures Common features of paleokarst include geomorphicstratigraphic characteristics, field-scale obseryations and microscopic criteria (Choquette and James 1988; Esteban and Klappa 1983; Wright 199I). The study of paleokarst requires observations at outcrop, macroscopic and microscopic scales as well as geochemical studies. Valuable criteria include breccias, dikes and fissures, cave infill sediments, speleothems, carbonate cements, and silcretes andi calcretes. Breccia: Collapse breccia (Pl. 12911; Fig. 15.3) formed in ancient caves are clast-supported mega- and ~nicro-brecciasconsisting of angular, sometimes also subrounded millimeter- to tens of centimeter-sized limestone clasts. Sorting is generally poor. Fitting may be good or poor. The matrix is calcareous or siliciclastic depending on the lithology of the host rock and that of the overlying beds. Karst collapse breccia should not be confused with breccia produced by interstratal dissolution of interbedded sulfates (see Sect. 5.3.3.3). Dikes undfissures: Filled and cemented fissures (Pl. 12911) with widths ranging from millimeters to decimeters are common features of paleokarst. Fissures may be cemented by several generations of isopachous and granular coarse calcite cement and filled with internal sediment, consisting of crystal silt, and clasts derived from c a w walls as well as from overlying beds. Corrugated marine radial fibrous cement crystals may indicate karst phases (Aubrecht 1997). Fissure filling occurs subaerially by continental sediments or, subsequent to marine transgressions, by marine sediments yielding characteristic cavity-dwelling micro fossils (e.g. 0stracods). The fossils within the ~narineinfill of fissures and solution cavities arc of enormous importance in recognizing the age and timing of emergence and karstification. Ca~leinfill sediments: Caves can function as giant sediment traps accumulating various sediments and debris. Common structures are (a) lamination (sub-millimeter densely and widely spaced, light and dark parallel laminae; fining-upward: laminations of locally de-

formed laminae; PI. 129/2,3,5), (b) microbreccias (consisting of angular rock clasts and broken crystals embedded within a microgranular matrix; P1. 129/1), (c) coarse redeposited calcite crystals and fine crystal silt, and (d) internal vadose sediments as partial fillings on floors of cavities or as matrix sediment in collapse breccias; often grayish-yellow, silty and laminated. Speleothems are among the more useful features for recognizing karstification (Dreybrodt 1988; Frisia et al. 2000). The surface of cave bedrocks may be coated with white layers consisting of coarse spany calcite and explained as precipitation from phreatic conduits. Distinctive criteria of paleospeleothems are (a) laminar flowstones consisting of several cement layers, growing directly on host rocks and associated with geopetal vadose internal sediment, (b) dendroid calcite sinter crusts forming stalagmite and stalactite structures (Fig. 15.4), (c) fibrous calcite cement crystals developed as optically length-slow 'coconut-meat calcite' (Folk and Assereto 1976) or palisade calcite, often as radiaxial crystals, (d) helictites (excentriques) in fissures (Reinhold 1998), (e) alterations of large and small crystal layers, and (f) coarse blocky calcite. occluding voids. Carbonate cements associated with local paleokarst were studied by Dunham (1969), Steinen and Matthews (1973) and Schonlaub et al. (1991), those of interregional paleokarst by Meyers (1974. 197%.1988). Most

Fig. 15.4. Spefeothem carbonate. Fingerlike, radiating, cmthick sinter crusts lining tens of cm-sized cavities within a highly porous limestone characterized by 'sickle cell' structures (see Fig. 15.6). The speleothem structures are directed upward here, but downward and sideward growth occurs as well. The crusts consist of layers of fibrous calcite. Interframework pores are filled by stalactitic cement followed by drusy calcite mosaic. The sinter crusts fom~edduring subaerial exposure of lacustrine carbonates related to a lake level lowstand phase. Late Tertiary (Miocene): Wallerstein, Nordlingen Ries, Germany. From Pache et al. (2001).

7 32

Paleokarst: Case Stud:,,

Plate 129 Paleokarst and Cave Carbonates: An Early Carboniferous Case Study The plate exhibits samples documenting microfacies criteria of a paleokarst breccia (-> I), cave sediment infillings (-> 2, 3 , 5 ) and relicts of calcite speleothems developed within caves (-> 4). Extensive subsurface karstification of Late Devonian limestones took place during the Early Carboniferous in the central Carnic Alps, a part of the SouthernAlps (Schonlaub et al. 1991) as a result of drops in sea level during the Late Toumaisian and synsedimentary block faulting. The paleokarst is associated with an unconformity separating Famennian to Early Carboniferous limestones from overlying siliciclastic sediments (Hochwipfel Formation). The Famennian to Early Carboniferous sections comprise pelagic limestones and shelf limestones, separated from the Hochwipfel Formation by a disorganized collapse breccia (-> 1). The breccia consists of angular, mm to 0.5 m-sized clast-supported and matrix-supported clasts exhibiting different microfacies types. The succession of events documented by field data, microfacies and geochemical signals is shown in Fig. 15.5B. Polymetallic strata-bound sulfide ore deposits are thought to be genetically related to the Late Devonian paleorelief and connected with the process of karstification. 1 Paleokarst collapse breccia formed by subaerial dissolution leading to the development of a cave system. The breccia consists of angular and subrounded limestone and chert clasts (C). The limestone clasts are Famennian fenestral mudstones (FM) and nodular pelagic wackestones (NW). The Early Carboniferous fine-grained matrix is a microbreccia (MB) conlposed of detrital quartz, sandstone, shale clasts, and cherts. The large limestone clast at the right bears a fissure infilled with radiaxial cements (a~row),pointing to a pre-breccia formation of fissures associated with synsedimentary block faulting processes. C a w di M a n o southeast of the Plocken Pass, near the Italian/Austrian boundary. 2 Densely laminated internal sediment within karst cavities. The parallel siltstone laminae consist of quartz, calcite and illite/muscovite. Arrows point to rock debris. Each couplet of dark and light laminae originate from one flooding of the cavities (Ford 1985).Early Carboniferous (Middle Dinantian): Malpasso quarry, central Carnic Alps, Italy. 3 Laminuted internal sedimerit composed of calcite, authigenic quartz and mica deposited in karst cavities. Note parallel planar bedding and flame and load structures (arrows). Cava Val di Collina west of the Plocken Pass, Camic Alps, Italy. 4 Eulwtlr-czl calcite crystals lining the cmfe walls (spcleatherns). Cathodoluminescence criteria indicate that these nonluminescent cement crystals were fonned in a freshwater phreatic environment. Same locality as -> 3. 5 Cu\,r sedimrnt infilli~lgin palcnkai-st cwities. Laminated filling between fractured scalenohedral calcite crystals fonned on the walls of the karst cavities. The spas calcite coating predates the densely laminated infilling. Same locality as -> 3. > 2-5 Schooluub CI al. (1991 ) Sedimentary Event Bedded sandstone

Diagenetic environment

Transgression of the Hochwipfel Fm. marine phreatic

Shale

Formation of collapse breccia - PI. 12911

freshwater phreatic

Clasts Cephalopod-trilobite wackestone Fenestral limestone Black chert Brachiopod-crinoid lmestone

First generation of isopachous radial cements - PI. 12911

marine phreatic

Matrix Siliciclastic, derived from overlying Hochwipfel Formation

1I

Formation of cave sediment - PI. 12912,3, 5 - - - - - - - - - - - - -- - - - - - -- Formation of caves with freshwater phreatic calcite coating - PI. 12914, 5 Formation of fissures

Fenestral limestone

Ore concentration - - - - - - - - - - - - - - Local silcretes and cherts Extensive karst erosion and limestone solution Limestone sedimentation up to

.

I

f

surface karstlvadose

marine phreatic

Fig. 15.5. Case study 'paleokarst'. Timing of sedimentary events and changes in the diagenetic enhronments in the Early Carboniferous succession of the central Carnic Alps, Austria/Italy. Numbers refer to figures in P1. 129.Modified from Schonlaub (1991)

7.34

cements beneath unconformities seem to be of meteoric-phreatic or deeper-burial origin. Shallow phreatic cements are clear, iron-poor, blocky or sparry calcite (Pl. 12914, 5), commonly non-luminescent with thin zones of bright luminescence. Burial cements are ironrich and commonly inclusion-rich blocky calcite with dull, variably zoned cathodoluminescence. Calcretes and silcretes: Many paleokarst surfaces are overlain by calcretes. Siliceous breccias and layers of white weathered cherts on top of surface karst have been interpreted as silcretes (Mustard and Donaldson 1990; Schonlaub et al. 1991). Diagnostic criteria of significant dissolution and successive pervasive silica cementation are (a) abundant micropores, (b) needle fiber fabrics, (c) a network of anastomosing walls, and (d) composite void fillings by euhedrally terminated megaquartz, radiating chalcedony and coarse mosaic quartz in the center of voids.

15.2.2 Significance of Paleokarst and Cave Carbonates Karstification may affect various types of carbonate buildups, including carbonate platforms, reefs, carbonate ramps and pelagic swells. Paleokarst structures assist in recognizing unconformities, subaerial exposure and stratigraphic breaks (Mussman et al. 1988; Vanstone 1998; Haas 1999; Turgeon and Lundberg 2001), * correlating stratigraphic units (Charcosset et al. 2000), * evaluating sea-level fluctuations (Satterley et al. 1994; Calner 2002; compare the case study, P1. 129), identifying paleoclimates. Paleokarst, used in conjunction with other subaerial exposure features (specifically paleosols of humid and semiarid phases) to be distinguished can be critically compared with modern karst phenonema, to provide an excellent indicator of paleoclimatic conditions (Jimenez de Cisneros et al. 1993; Wright 1980, 1982, 1988; Rums et al. 1998). However, because of the complex history of subaerial weathering processes, paleo-data regarded as indicators should be analyzed within a detailed microstratigraphic setting. High-resolution of paleoclimatic variations are possible by comparing annual variation patterns in speleothems (Railsback et al. 1994; Shopov et al. 1994; Genty and Quinif 1996). * understanding hydrological conduits (Klimchouk et al. 2000). Paleokarst features describe the long-range effect of descending and ascending waters. * exploring hydrocarbon reservoir rocks and mineral deposits (see Chap. 17).

Travertine

Basics: Paleokarst Bosak, P., Ford, D.C., Horacek, I., Glazek, J. (eds., 1989): Paleokarst - a systematic and regional review. - Developments in Earth Surface Processes, 1,726 pp., (Artia) Choquette, P.W., James, N.P. (eds., 1988): Paleokarst. 4 16 pp., New York (Springer) Choquette, P.W., James, N.P. (1988): Introduction. - In: Choquette, P.W., James, N.P. (eds.): Paleokarst. - 1-21, New York (Springer) Ford, D.C. (1988): Characteristics of dissolutional cave systems in carbonate rocks. - In: Choquette, P.W., James, N.P. (eds.): Paleokarst. - 25-57, New York (Springer) Ford, D.C. (1995): Paleokarst as a target for modem karstification. - Carbonates and Evaporites, 10, 138-147 Ford, D.C., Williams, P.W. (1989): Karst geomorphology and hydrology. - 60 1 pp., London (Unwin) Playford, P. (2002): Palaeokarst, pseudokarst, and sequence stratigraphy in Devonian reef complexes of the Camling Basin, Western Australia. -In: Keep, M., Moss, S.J. (eds.): The sedimentary basins of westem Australia, 3. - Proceedings of the Petroleum Exploration Society of Australia Symposium, Perth, 763-793 Reinhold, C. (1998): Ancient helictites and the formation of vadose crystal silt in Upper Jurassic carbonates (southern Germany). -Journal of SedimentaryResearch, 68,378-390 Schonlaub, H.P., Klein, P., Magaritz, M., Rantitsch, G., Scharbert, S. (199 1): Lower Carboniferous paleokarst in the Carnic Alps (Austria, Italy). - Facies, 25,91-118 Smart, P.L., Whitaker, F.F. (1991): Karst processes, hydrology, and porosity evolution.- In: Wright, V.P. (ed.):Palaeokarsts, and palaeokarstic reservoirs. - Postgraduate Research Institute of Sedimentology,Occasional Publication Series, 2, 1-55 Wright, V.P. (1 99 1): Palaeokarst. Types, recognition, controls and associations. - In: Wright, V.P. (ed.): Palaeokarsts, and palaeokarstic reservoirs. - Postgraduate Research Institute of Sedirnentology, Occasional Publication Series, 2,56-88 Further reading: K031. An 'Atlas of Speleothem Mmofabrics' by L. Bruce Railsback, including a glossary of relevant terms and a bibliography, can be found in the Internet (www.gly.uga.edu/raiIsback/speleoatlas).

15.3 Travertine, Calcareous Tufa and Calcareous Sinter Travertine and calcareous tufa are freshwater carbonates. The criteria and origin of travertines (layered carbonates deposited from mineralized waters at thermal springs) and tufas (porous carbonates deposited from cool running waters at springs, in creeks, in zones of ascending groundwater) were discussed in Sect. 2.4.1.6. Calcareous sinter is characterized by well developed lamination and a lack of porosity. These freshwater carbonates were already known in the Precambrian, but the number of Phanerozoic records is low, except for the Quaternary and Tertiary. Techniques used to study travertines and tufa include

T r a v ~ = r t i n eTufa . SIII~CI

(a) petrographical investigation of thin sections and polished slabs combined with staining and XRD analysis to determine mineralogical composition, (b) rare element analysis (e.g. Sr in order to check diagenetic alterations), and (c) stable isotope analysis, to distinguish between biologically and inorganically controlled precipitation. Diagnostic criteria The following overview of diagnostic criteria is based mainly on Schweigert (1996), who studied and illustrated the microfacies, and the sedimentological and paleontological criteria of 'Tertiary limestones fonned in terrestrial and various freshwater settings. Many calcareous tufa and travertine deposits as well as lacustrine carbonates are modified by pedogenic processes. Therefore, microfacies types of non-marine 1imestones can vary within wide boundaries. Trm~ertinc Ancient travertine deposits are characterized by massive or coarse-bedded, layered carbonates. Biota are restricted to cyanobacteria and bacteria. Fossils enclosed within the travertine (e.g. terrestrial snails, vertebrates, plants) are allochthonous. Common features are laminar crusts consisting of large crystals, banding expressed by changes in color and texture, cyclic bedding caused by seasonal climatic fluctuations, tepee structures, pores filled with vadose cements, desiccation cracks, and brecciation. Micr-of~c,ie.st ~ ~ p are c ~ scontrolled by distinct microbial associations, and include: Laminar cementstones (calcareous sinter) consisting of coarse feather-like arrangements of calcite or aragonite crystals (ray crystal 1aye:rs;Chafetz and Folk 1984). Laminar microbial bindstones with a planar upper surface, consisting of 1.e1-ythin micritic and sparry, often discontinuous and broken laminae. Micritic layers with abundant bushy structures consisting of branched filaments, interpreted having a cyanobacterial origin (Dichotlzrixmorphotype; Guo and Riding 1994). They are often associated with laminar bindstone crusts (PI. 211). Micrite layers, sometimes with peloidal and clotted fabrics. Microcrystalline and fine-sparitic layers composed of fibrous cement crystals enclosing large and small open or closed voids ('sickle cell' limestones; Fig. 15.6). Layers with globular or vertically elongated open or closed voids interpreted as gas bubbles (Pl. 212). Detrital layers intercalated between the other microfacies types, formed by reworking of microbial bindstones forming an intraclastic texl.ure (PI. 215).

Fig. 15.6. 'Travertine'fabl-ic. 'Sickle-cell' limestone exhibiting microcrystalline sheets of inclusion-rich,fibrous cements spanning over lenticular voids. Highly porous limestone characterized by irregular, wavy laminae enclosing lenticular to sickle-shaped voids. These structures are only known from spring mounds in highly alkaline lakes. Miocene: Wallerstein castle, Ries, Germany. After Pache el al. (2001).

Pisolitic layers composed of densely packed pisoids of different sizes. Inter-pisoid pores are partly or completely filled with aragonite cement (Fig. 15.7). Pisoid accumulations may be intercalated with micrite layers. C'alcureous tufa Freshwater tufas are characterized by h~ghlyporous fabrics because of the great number of enclosed plant remains. Depending on the plants, a variety of facies types may develop, including leaf tufas, reed tufas, moss tufas (characterized by peloidal textures and sparry fabrics), characean tufas, \'aucheria tufas (tufa formed by xanthophycean green algae), and Cludophorites tufas. Microbial activity is very important for the precipitation of the carbonates but of minor importance for thc de1,elopment of the pores. Plant remains have sheetlike or tubular shapes and are commonly coated by micritic calcite crystals. Algal filaments vary In size from 50 to 100 pm. Different parts of mosses range in size from a few microns to several millimeters. Euhedral calcite crystals growing on the surface of mosses have similar size ranges (Irion and Muller 1968).

Calcareous sintcr Sinters differ from typical travertines and tufas in that they are predominantly inorganic in origin. They are controlled by high water temperatures in thermal springs, high ion content in mineral springs, high running rates of water, and by the absence or rareness of light leading to microbial settling in caves. This type of sinter occurs in different settings (e.g. thermal travertines, carbonate geyserites, and speleothems).

1,acustrine Carbonates

zonation of the biota and the biotic controls on carbonate production. Epilithic and endolithic organisms con-

Fig. 15.8. Lacustrine microfacies types. The pictures show microfacies types of Early Pennian lacustrine limestones of the Saar-Nahe region in southwestern Germany. The limestones comprise only a minor part of the predominantly siliciclastic sedimentary sequence and occur as thin units called 'Floz' because of their association with coal beds. Carbonate beds may have a thickness of only a few tens of centimeters. Nevertheless, the microfacies types reflect distinct differences in depositional settings (see Fig. 15.10). A: Laminated nzudstone (LMF 2 ) charact.erized by dark and light layers that can be better recognized at lower magnification. The laminae consist of carbonate and quartz grains. Shallow eutrophic lake. Odenbach Floz, Lauterecken beds. B: Bivalve floatstone (LMF 9). Leached and recrystallized shells of anthaconaiid bivalves were accumulated by bottom currents. These shells bear some similarity to trilobite fragments and phylloid algae. The former are differentiated by calcium phosphatic shells (see P1. 94), the latter by thicker plates with relicts of cortical pores (Pl. 58). Odenbach Floz. C: Micro-otzcoidpackstone (LMF IOB). Note the distinct differences in size, shape and core/coating ratios. Wiesweil bed. D: Intraclast wackestone (LMF 4 ) consisting of reworked mudstones (irregularly shaped white grains). Arrows point to corroded fish scales. Odenbach Floz. After Clausing(l990).

7.37

738

hlicrofacies o f Lacustrine Carbonate5

Fig. 15.9. Lacusrrine microfocies types from the Early Devonian Old Red Sandstone (Woodbay Formation) in central North Spitsbergen. A: Strongly bioturbated mudstone-wackestone (LMF 1). Sand-sized quartz grains and various skeletal grains (ostracods, charophycean oogonia, fish fragments) are embedded within a micritic matrix. B: Bioclastic ostracod packstone (LMF 6). Densely packed, thin ostracod valves forming a coquina. The accumulation is interpreted as population spread under favorable conditions. C: Bioclastic gastropod grainstone (LMF 8). The gastropods are associated with thick-shelled ostracods. Littoral lake environment. D: Lithoclastic rudstone (LMF 13). Most grains are very well rounded. The granule- to pebble-sized mudstone clasts were accumulated by storms. Scale is 1 cm. After Blomeier et al. (2003).

tribute to carbonate formation and destruction. Carbonate formation in lakes by algae and cyanobacteria is triggered by the trapping and binding of particles, cementation by and encrustation with CaC03. and secretion of C a C 0 3 within algal mucus. Cyanobacteria and algae assist in the growth of oncoids, stromatolites and reefs. In addition, accumulations of benthic and pianktonic algae as well as invertebrate shells contribute to the formation of lacustrine carbonates. Destruction of carbonates occurs by means of endolithic algae and bacteria loosening carbonate surfaces and producing finegrained sediment.

fossils. In addition, accumulations of lithoclasts and intraclasts may be common. Fossils include cyanobacteria, algae, gastropods and bivalves, ostracods, fish bones, scales and teeth, and amphibian remains. Algae are represented by green algae (Cladophorales) and occasionally also by calcareous algae known predominantly from marine environments (Pl. 13114). Saltwater lake carbonates are poor in fossils but may yield ostracods and some remains of crabs. Other common criteria include stromatolites, oncoids and ooids (PI. 1311). Common fabrics of lacustrine carbonates art: lamination and varves, nodular structures and bioturbation.

15.4.1 Microfacies of Lacustrine Carbonates

Stromatolites Cyanobacteria contributing to the formation of stromatolites are strongly salinity-controlled. Stromatolites originate in marine and marginal-marine environments of normal and hypersaline salinities as well as in nonmarine environments including freshwater and brackish lakes, and salt and soda lakes (Riding 2000).

15.4.1.I Microfacies Criteria Common microfacies criteria of freshwater lake carbonates are micrite, peloids, radial ooids (see Boxes 4.15 and 4.16), oncoids and stromatolites, and various

Lacustrine M ~ c r o f a c i e sTypes

Lacustrine stromatolites are already known from Archean and Proterozoic sediments. Common features of Phanerozoic stromatolites are a significant morphological variety (undulations, columns, domes, arborescent growth forms), light and dark macrolaminae composed of many dark and light micritic and microsparitic laminae, and radial fibrous textures reflecting growth pattems of cyanobacterial and algal threads. A survey of ancient lacustrine stromatolites was given by Stapf (1989). Oncoids Freshwater oncoids have been discussed in Sect. 4.2.4.1. The subspherical or concave-convex oncoids are scattered or densely packed within a micrite matrix or in marls. Sizes vary between less than 1 mm and several centimeters (see Fig. 15.8C; P1. 13115). Very

large oncoids (up to 20 cm) occur at the margins of fluvial channels (Anadon and Zamarreno 1981). Many oncoids are irregularly shaped. The cores may be very small and formed by sedimentary grains or rock fragments, or smaller oncoids, or they may consist of gastropods and bivalve shells. The cores are surrounded by often densely spaced, irregularly concentric, up to 1 mm thick macrolaminae. These macrolaminae are composed of dark micritic and bright microsparitic microlaminae. The laminae are arranged in parallel, often crinkled, dome-shaped or columnar layers. Spongy and thrombolitic fabrics are common. Radial, fan-shaped microstructures are caused by the growth pattems of cyanobacteria (see Monty and Hardy 1976 for illustrations). Microstructures of lacustrine oncoids are often better preserved than marine oncoids.

Box 15.1. Common lacustrine microfacies types (LMF).

LMF 1: Lime mudstone consisting of very fine-grained micrite crystals. Can originate from cyanobacterial and algal blooms or by abrasion of limestones. Sometimes strongly bioturbated (Fig. 15.9A). Occurs in deeper and protected lake parts, but the sediment may be reworked by storms and redistributed also in shallow areas. LMF 2: Inhomogeneous laminated lime mudstone with very rare or no fossils (Fig. 15.8A). The laminated fabric is caused by the alternation of light and dark layers, the latter often rich in organic matter, plant debris and/or cyanobacteria forming very thin laminae that can be recognlzed by means of fluorescence microscopy. Clay and fine, s~lt-slzedterrigenous quartz may be common and contribute to the lamination. LMF 2 characterizes a relatively deep quiet-water basin with stratified water column and seasonal variations. Poor oxygenation is indicated by the lack of benthic organisms and burrowing. Fossils may be represented by rare fish remains, ostracods and conchostrakes. LMF 3: Lime ml~dstoneand wackestone with leaves of plants accumulated on bedding planes. The leaves may be encrusted by carbonate. This microfacies is common in Late Paleozoic and Cenozoic lacustrine sediments (e.g. Poromogeion layers. Miocene). LMF 3 characterizes a quiet-water far-shore or near-shore environment. LMF 4: Inhomogencousfine-bedded intraclast wackestone (Fig. 15.8D) characterized by reworked laminated mudstone; LMF 2) and nektonic fossils. Frequent in nearshore and shore lake-floor areas affected by waves. LMF 5: Densely parked nodular: peloidal wackestone orfloatstone with reworked lacustrine grains and with black pebbles of lacustrine limestone, sometimes also with extraclasts. Common near the shoreline of large lakes. Formed by storm events. LMF 6: Ostracod mudstone, wackestone, packstone or grainstone characterized by double-valved or disarticulated thin or thick ostracod shells, often monospecific (Pl. 1301 2; Fig. 15.9B). This type occurs in different near-shore, far-shore and basinal parts of lakes. LMF 7: Chmophycean mudstone or wackestone (Pl.

13014; PI. 65/1,3) with abundant oogonia and stem remains. Often associated with ostracods or ostracod debris. This microfacies characterizes the shore region of many humid and semiarid lakes and brackish environments of coastal regions. LMF 8: Gastropod packstone and grainstone (Pl. 1301 3; Fig. 15.9C). Often composed of monospecific communities. The gastropods may be associated with bivalves and ostracods. LMF 9: Bivalve floatstone (Fig. l5.8B) composed of centimeter-sized, often parallel arranged shells. LMF 9 occurs on near-shore lake floors and is rarely affected by waves. Coquinas may represent storm deposits. LMF 10: Oncoid floatstone, packstone and wackestone. Two subtypes: Large oncoids (commonly porostromate or agglutinated oncoids; P1. 13 115; LMF 10A) occur either associated with stromatolites or separately. Microoncoids with submillimeter sizes (Fig. 15.8C; LMF 10B) accumulate in packstones. These oncoids have nuclei of quartz or silt grains, surrounded by only a few micritic laminae. The large oncoids exhibit various microfabrics reflecting different growth forms of different cyanobacteria and algae. The micro-oncoid packstone facies occurs in near-shore and shore areas. Floatstones with centimeter-sized oncoids are common in higher-energy fluviallacustrine and brackish-water settings. LMF 11: Stromatolite bindstone (Pl. 13 111, 3). Very variable in geometry, shape and internal fabrics (see above and Sect. 9.1 for more information). Contribute to the formation of 'algal reefs'. LMF 12: Green algal baflestone and wackestone (Pl. 13011). Tubular green algae (e.g. Cladophorites) living in near-shore and shore-settings contribute to the accumulation of sediment and the formation of lacustrine 'algal reefs'. LMF 13:Lithobioclast rudstone (Fig. 15.9D) composed of reworked, poorly sorted and sometimes strongly rounded carbonate lithoclasts and worn fossil fragments. Storm deposits.

The shape of freshwater oncoids seems to be controlled to a lesser degree by environmental factors (e.g. water energy, tenigenous input) than texture and microfabrics (Abell et al. 1982). The best way to gain a high paleoenvironrnental resolution is the taxonomic differentiation of cyanobacterial and algal associations (see P1. 8J4).Cyanobacteria communities in lacustrine oncoids and stromatolites have remained stable at least since the Cretaceous (Monty and Mas 1981).

15.4.1.2 Microfacies Types of Lacustrine Limestones

Thirteen cotnmon and widely distributed microfacies types can be recognized when the facies of lacustrine limestones of different age are compared (see Box 15.2). These LMF Types are listed in Box 15.1 and shown in P1. 130, PI. 131 and in Figs. 15.8 and 15.9.

15.4.1.3 Distribution of Lacustrine Microfacies Types Fig. 15.10 is a rough sketch showing the occurrence of more frequent microfacies types of freshwater carbonates. More facies types exist, of course, depending on the climatic setting, the size and depth of the lake basin, and the topography of the surrounding regions.

A strict actuogeological approach to the environmental interpretation of ancient lake sediments is difficult, in that most present-day lakes are shaped by glaciers and therefore provide poor analogs for ancient lacustrine sedimentation. This was predominantly controlled by tectonic movements, and only few modern lakes have an areal extent and a sediment thickness comparable with those of ancient counterparts, particularly in the Paleozoic.

Plate 130 Lacustrine Limestones: Common Microfacies Types The plate displays Tertiary and Cretaceous lake carbonates. The Tertiary samples (-> 1-3) are taken from the Miocene Ries Lake, which fonned within a large impact crater. Bioherms were built by green algae and cyanobacteria, and multiple lacustrine-vadose sinter veneers at the margin of the humid, hydrologically closed soda lake basin (Arp 1995). The lacustrine sediments are overprinted by pedogenic and early diagenetic procesves modifying the primary depositional fabric and implying an adaption of traditional limestone classifications (see Scct. 8.3.2; PI. 38). Algal limestone, ostracod grainslones, wackestones and packstones, as well as gastropod grainstones and wackestones are common microfacies types in lacustrine sediments. Unlike marine limestones, gastropods and ostracods are represented by very low-diversity associations, often by just one or two species. Other common type of' lacustrine limestones formed in oligotrophic or brackish lakes are wackestones and mudstones with charophycean algae (-:, 4). Lacustrine microfacies types (LMF) are defined in Box 15.1. Gtmw al,@ ~~~~~~~~~~~~~~it~s) bufjlestotw: L M F 12. The basic elements of the algae are erect and branched tubes, arrangeci in cushion- or tuft-like thalli that sometimes coalescence forming meter-sized structures. Rhythmic growth patterns intlicate scasonal controls. The tube walls consist of micrite. Cladophorites (C) is regarded as a green alga identical with or closely related to the modern genus Cltdopl~oru.Note associated gastropods (G) and charophycean oogonia (CHI. Tertiary (Miocene): Hainsfarth, Ries Basin, southern Germany. Ostr-crroilj y u i ~ ~ s f o m LMF : 6. Some valves are stacked into each other (white arrows). The ostracods comprise 40--50% of the very porous rock. The shell interior is filled with sinter cement and meteoric-phreatic sparite. The shells are covered by a clear dolomite cement (black arrows). Calcite appears black due to staining with Alizarin-S. Paleoenvironment: Wave-exposed eulittoral zone, sands near the algal bioherm. Note that comparable microfacies types occur in shallowmarine hypersaline environments as well. Same locality as -> 1. Gasm'pod grainstone with some ooids: LMF &The gastropod shells (Hydrobia) are leached and preserved as micrite envelopes only. The envelopes are covered by thin layers of microcrystalline cement. Hydr-obia was the only aquatic gastropod that flourished in the soda lake. Some calcitic ooids exhibit a radial structure (white arrow), other ooids are dolomitized and appear black (black arrow). Paleoenvironment: Wave-exposed shallow eulittoral zone near the algal bioherms. Same locality as -> 1. Charophycean algul wackestone: LMF 7. Most algal fragments are internode parts (arrows), see PI. 65. Fig. 10.20, and Sect. 10.2.1.8. Thin shells are ostracod fragments. Paleoenvironment: Brackish-water lagoon. Cretaceous: Spain. ->2 and 3: Arp (1995)

74 1

Plate 130: L a c u s t r ~ n eL i ~ n e \ t o n e s

1

mm

1 rnrn

Palustrine Carbonates

742

Box 15.2. Selected case studies of ancient lacustrine and palustrine carbonates. Case studies on freshwater oncoids and stromatolites are listed in Box 4.8. References dealing with salt and soda lakes are marked by +,those on palustrine carbonates by *. I

Tertiary:Alonso-Zarza and Calvo 2000*; Anodon and Utrilla 1993; Anodon and Zamarreno 1981; Anodon et al. 2000; Arenas et al. 1992; Armenteros et al. 1997*; Arp 1995; Bellanca et al. 1992; Bradley 1929; Bustillo et al. 2002; Cabrera and Saez 1987*; Calvo et al. 1989, 1995, 2000; Fouch et al. 1976; Herbig 1988*, 1994"; Leinfelder and Hartkopf-Froder 1990; Krylov 1982; Nickel 1983; Platt 1992+; Reggiani 1989; Riding 1979; Rouchy and Monty 1981f; Schweigert 1996; Stanley and Collinson 1979*; Straccia et al. 1990; Surdam et al. 197.5'; Surdam and Wray 1976; Szulc et al. 1991+;Szulc 1992; Trappe 1992+;Wells 1983*; Willems and Wuttke 1987; Wright 1990*. Cretaceous: Alonson et al. 1991; Bell 1989+;Buatois et al. 2000; Carozzi 1989; Fouch 1979; Fregenal-Martinez and Melendez 1994; Freytet 1984+; Freytet and Plaziat 1982*; Martin-Chivelet and Gimenez 1992"; Misik and

15.4.2 Palustrine Carbonates Palustrine limestones assist in recognizing seasonal wetland environments in the geological record (Wright and Platt 1995). These limestones (Sect. 2.4.1.2) exhibit criteria that also occur in pedogenic carbonates (pseudo-microkarst associated with fenestrae, circumgranular cracks and peloidal fabrics; Plaziat and Freytet 1978) and caliche horizons (rhizolites, rhizoconcre-

Sykora 1980;Monty and Mas 1981; Nonnati and Salomon 1989*; Platt 1989. Jurassic: Bell 1989'; Leinfelder 1985. Triassic: Carozzi 1964; Clemmensen 1978; Gore 1989; Milroy and Wright 2000; Olsen 1986; Seegis and Goerigk 1992*; Tucker 1978; Wright and Mayall 1981. Permian: Clausing 1990, 1992; Clausing et al. 1992; Freytet and Lebreton 1992; Gebhardt 1988; Gebhardt et ai. 2000; Guy-Ohlson and Lindstrom 1994; Schafer and Stapf 1978; Schneider and Gebhardt 1993; Stapf 1973, 1989; Warren 1983. Carboniferous: Buatois and Mangano 1994; Driese 1985; Gebhardt 1988; Valero-Garcis et al. 1994". Devonian: Blomeier et al. 2003, Demicco et al. 1987; Donavan 1975; Duncan and Hamilton 1988.

tions, coated grains; Seegis 1993).The main difference, however, is the close association of these features with lacustrine sublittoral limestones. Palustrine carbonates are paleosols reflecting pedogenic effects, such as the repeated drying of the sediment in carbonate swamps bordering lakes, or in episodically drying shallow lakes. Examples are shown in P1.48/2,3. The carbonate beds are commonly associated with claystones, marls, sandstones, cherts and coals. Stable isotopes of the micritic

Plate 131 Lacustrine Carbonates from the Early Permian (Rotliegend) of Germany

The plate displays the microfacies of lowermost Permian lacustrine limestones, formed in intracontinental basins filled predomiantly with fluviatile-deltaic and lacustrine siliciclastic sediments. Limestones are rare. Most carbonates are of algal and microbial origin or formed by the accumulation of ostracods and mollusks. Sporadic subaerial exposure is indicated by pedogenic horizons rich in caliche pisoids (Pl. 1416) at the top of stromatolites. Other facies types are shown in Fig. 15.8. Facies-diagnostic criteria of these carbonates are various types of biogenic laminations (-> 2), stromatolites (-> 1, 3) and oncoids (-> 5) formed in shallow marginal parts of the lakes. Lacustrrne columrzal- stromatolites: LMF i l. These structures occur in limestones and marls with a thickness of up to several meters. The colurnns are distinctly laminated. Larger columns consist of small-scaled stromatolites (black arrow). Early Permian (Lower Rotliegend): Altenglan, Saar-Nahe Basin, Southwestern Germany. 2 Irregularly laminated nzudstone andpeloid nzud~,tone.Note the small-scale alternations of syngenetically deformed layers. These limestones yield 'marine' algae (-> 4). Early Permian (Lower Rotliegend): Birkigt near Freital, Dohlen Bas~n, Thuringia, Germany. 3 Stromatollte boundstone: LMF 11. Note the infilling of micro-oncoids (arrows) between the columns, indicating a sometimes turbulent shoreline/nearshore environment. Early Permian (Upper Kusel Group): Saar-Nahe Basin, Gennany. 4 'Marine' green and red algae can occur in lacustrine sediments as seen in examples from Thuringia (Schneider and Gebhardt 1992). The fossil was assigned to the dasyclad genus Macroporella. The occurrence of these algae has been explained by wind drift of algal cysts or acinetes from marine environments to relatively saline lakes. Same locality as -> 2. 5 Lacustrine oncoid with thrombolite (T) microstructure: LMF 10. Thrombolites are characterized by clotted structures and the absence of conspicuous lamination. The clots are interpreted as being formed by coccoid and filamentous microbes. Early Permian (Upper Rotliegend): Dannenfels, Saar-Nahe Basin, Germany. -> 1,s: Stapf 1989; 3: Clausing 1990; 2,4: Courtesy of J. Schneider (Freiberg) I

743

Plate 13 1 : Early Permian Lacustrine Carbonates

1 rnm

1 crn

744

Lacustrine Carbonates: Microfacies Distrihurion

Shore I Nearshore area 1 Input and influence of clastic material Lake floor affected by waves partly turbulence

)

Offshore

Nearshore area

Shore

-

Lake floor rarely affected by waves

Quiet water

Lake floor rarely affected by waves

]

Sediments with carbonates

Lake floor affected by waves partly turbulence

I

-

Green algal bafflestoneEwackestone:LMF 12

Charophycean mudstone/wackestone:LMF 7

I-

Nodular peloidal wackestonelfloatstone: LMF 5 lnhomogeneous intraclast wackestone: LMF 4

I

-

Oncoid floatstone: LMF 10A

Stromatolite boundstone: LMF 11

I

1

~

I I

I

Micro-oncoid packstone: LMF 10B

,

I

Bivalve floatstone: LMF 9

Ostracod mark

J

K

I

1 Humic coal I

Gastropod packstonelgrainstone: LMF 8

II

Micro-oncoidwackestone: LMF 10B

I I

L

~

1 I

/

z

~

Oncoid floatstone: LMF 1OA

z

~

_

z

L

Ostracod mudstonelwackestone, packstonelgra~nstoneLMF 6 ~ ~Plant / mudstonelwackestone / / / / / LMF ~ 3

Z

~

I

I

Laminated mudstonelwackestone LMF 2 Claylsiltstone Hurnlc coal

I

I

1 '

z7

/

I

Boghead coal

Fig. 15.10. Schcmutir. distrihr~tionof common nzicrofacies types of lacustrine freshwuter- limestones. Based on Clausing (1990) and supplemented after Stapf (1989), Arp (1995), Schweigert (1996) and other sources (see Box 15.2). Dark bal-5 indicate main distributions.

matrix and of carbonate cements offer a possibility for recognizing pedogenic overprinting associated with subaerial exposure of lab ('latt 1992).

Cornnlon micr.of~~c ies types are * mudstone with detrital quartz floating within a micrrtc carbonate matrix; some quartz grains may be surrounded by calcitic aureoles; nodular dolom~licnludstone with irregular tube-like mlllirneter-sized voids, sometimes filled with sediment or quartz grains: common on top of lacustrine limestones; ~uudstonewith micritic nodules and voids, curved planes surrounding nodules. Basics: Lacustrine and palustrine carbonates Allen, P.A., Collison, J.D. (1986): Lakes. -In: Reading, H.G. (ed.): Sedimentary environments and facies. 2nd edition. - 63-93, Oxford (Blackwell) Anadon, P., Cabrera, L., Kelts, K. (eds., 1991): Lacustrine facies analysis. - International Association of Sedimentologists, Special Publication, 13, 336 pp., Amsterdam (Elsevier)

Arp, G. (1995): Lacustrine bloherms, spring nlounds, and marginal carbonates of the Ries-Impact-Crater (Miocene, Southern Germany). - Facies, 33, 35-90 Blomeier, D., Wisshak, M., DullmaIln,W,, ~o]ohonsky,E,, Freiwald, A. (2003): Facies analysis of the Old Red Sandstone of Spitsbergen (Wood ~ a Formation): y reconstruction of depositional environments and implication of basin development. - Facies, 49, 1.5 1- 174 Clausing, A. (1990): Mikrofazies lakustriner Karbonathorizonte des Saar-Nahe-Beckens (Unterperm, Rotliegend, SW-Deutschland). - Facies, 23, 12 1-140 Friedman, G.M., Krumbein, W. (eds., 1985): Hypersaline ecosystems. - Ecological Studies, Analysis and Synthesis, 35,500 pp. Gebhardt, U., Merkel, T., Szabados, A. (2000): Karbonatsedimentation in siliziklastischen fluviatilen Abfolgen. -Freiberger Forschungshefte, C490, 133-168 Gierlowski-Kordesch, E.H., Kelts, K.R. (eds., 2000): Lake basins through space and time. - American Association of Petroleum Geologists, Studies in Geology, 46,648 pp Katz, B. (ed., 1990): Lacustrine basin exploration -case studies and modem analogues. -AmericanAssociation of PCtroleum Geologists, Memoir, 50, 340 pp. Matter, A., Tucker, M. (eds., 1978): Modem and ancient lake sediments. - International Association of Sedimentologists, Special Publication, 2, 290 pp. Monty, Cl., Mas, J.R. (1981): Lower Cretaceous (Wealden)

7-15

Peritrdal Carbonates

blue-green algal deposits of the Province of Valencia, Eastem Spain. - In: Monty, C1. (ed.): Pharierozoic stromatolites. Case studies. - 85-120, Berlin (Springer) Picard, M.D., High, L.R. (1972): Criteria for recognizing lacustrine rocks. -In: Rigby, J.K., Hamblin, W.K. (eds.): Recognition of ancient sedimentary environments. - Society of Economic Paleontologists and Mineralogists, Special Publication, 16, 108-145 Stapf, K.R.G. (1989): Biogene fluvio-lakustrineSedimentation im Rotliegend des permokarbonen Saar-NaheBeckens (SW-Deutschland). - Facies 20, 169-198 Talbot, M.R. (1990): A review of the palaeohydrological interpretation of carbon and oxygen isotope ratios in primary lacustrine carbonates. - Chemical Geology (Isotope Geoscience Section), 80,261-279 Talbot, M.R., Kelts, K. (eds., 1989): The Phanerozoic record of lacustrine basins and their envirom~entalsignal. -Paleogeography, Palaeoclimatology, Palaeoecology,Special Issue, 70, 304 pp. Wright, V.P. (1990): Lacustrine carbonates. -In: Tucker, M., Wright, V.P. (eds.): Carbonate sedimeritology. - 164-189. Oxford (Blackwell) Wright, V.P., Platt, N.H. (1995): Seasonal wetland carbonate sequence and dynamic catenas: a re-appraisal of palustrine limestones. - Sedimentary Geology, 99,65-7 1 Further reading: K02.5. K026, K027, K176, K188

15.5 Peritidal Carbonates Peritidal (1iterally:'around tides') carbonates are shallow-subtidal, intertidal and supratidal :sedimentsformed in marginal-marine and shoreline depositional en1wonments. Sediments formed in inter~idal-supratidalflats are summarized as ticlalites (see Alexander et al. 1998). Major criteria were discussed in Sect. 2.4.2.2 and Sect. 14.1.2.1.These carbonates are easy to recognize in outcrops and in thin sections. They are important paleobathymetric indicators, reflect sea-level fluctuations, and form the basis for the evaluation of sedimentary cycles and stratigraphic sequences (see Sect. 16.1). The facies types are vertically arranged in (regressive) shallowing-upward successions consisting of shallow-marine sediments overlain by intertidal and supratidal carbonates that are subject to periods of subaerial exposure. The subtidal zone is permanently submerged. The intertidal or littoral zone between normal low- and high-tide levels is submerged on a diurnal or semidiurnal basis. Tidal flats are repositories of allochthonous sediment transported by currents and storms from the subtidal carbonate factory. '

The Holocene tidal and stonn dleposits along the western shores of Andros Island in the Bahamas have become a diagnostic guideline for a humid tidally influenced carbonate environment (Shinn et al. 1965, 1969). The tidal flats, sabkhas and lagoons of Abu

Dhabi in the Arabian Gulf serve as recent models for the accumulation of supratidal, intertidal and shallow subtidal sediments in an arid climate (Evans et al. 1969; Schneider 1975). The following section summarizes diagnostic microfacies criteria, and describes a case study from the Devonian.

15.5.1 Criteria of Peritidal Limestones This section lists the criteria of peritidal and shallowsubtidal carbonates and discusses the merits of the criteria in the context of facies analyses. Unlike marine limestones, the recognition and interpretation of ancient marginal-marine limestones is fundamentally dependent on comparison with modem transitional-marine carbonate environments. This approach is very successful, but should be applied cautiously. Fine-laminated carbonates do not necessarily originate in tidal zones, and spar-filled voids in micritic rocks could have been formed in tidal zones as well as in various subtidal environments. The best way to overcome these difficulties is to use the whole set of facies criteria and take into consideration the changes in microfacies and the sedimentary structures within vertical sequences. Ancient carbonate rocks are traditionally studied by divtding peritidal environments into subtidal, intertidal and supratidal zones, despite the problems involved. Whether an area is subtidal, intertidal or supratidal depends on the tidal range, mean sea level and its topographic position relative to sea level. To avoid these difficulties, the exposure index (percentage of the time that a particular area is exposed) proposed by Ginsburg et al. (1977) should be used (see Wright 1990 for discussion).

15.5.1.I

Definitions

Tidal flat carbonates are predominantly micrites, often peloidal micrites. Common limestone types are mudstones, wackestones and bindstones. Intercalations of grainstones may be present, e.g. in tidal channels, or as storm deposits. Supratidal This is the most diagnostic zone in humid and arid tidal flats and represents the splash zone above high tide; it is flooded only a few times each month by spring tides or storms. Most of the sedimentation occurs above

'7 4 6

normal high tide during storm flooding. Diagnostic criteria for supratidal environments are evidence of subaerial exposure and pedogenic influence, * evidence of cementation in the vadose zone. Intertidal This zone is alternately flooded and exposed. Intermittent exposure is indicated by desiccation features, muddy surfaces with animal tracks and trails, and pores filled with vadose cement. Characteristic features of the intertidal regime are alternating erosion and deposition and rapid changes in current and wave velocity. These processes result in discontinuous sedimentation associated with scour-and-fill and the formation of channels, accumulation of reworked sediment (e.g. intraformational conglomerates), and substantial changes in grain size from lamina to lamina and bed to bed. Subtidal This zone below the intertidal zone is permanently submerged. Water depth is a few meters. The subtidal zone is conventionally subdivided into a shallow and a deeper subtidal zone. The .shullou~subtidal zone is characterized by calcareous algae and invertebrates adapted to the phytal (e.g. foraminifera, bryozoans, worms; see Voigt 1956). Epiphytes are common. Important indicators are the occurrence of dasyclad algae and encrustmg organisms. The lower boundary, after comparison with recent zonations, can be drawn at approximately 30 m. The deeper subticid zone is characterized by high-diversity benthic organisms. Calcareous algae still occur (red algae). Dasyclads, however, are absent.

15.5.1.2 Major Facies Criteria of Peritidal Carbonates Bedding Lnminarioiz (PI. 18/2; PI. I W I ): A very common feature of tidal carbonates is fine-scale lamination, usually on a millimeter scale (Sect. 5.1.3). Lamination often occurs associated with fenestral pores. The sediment may be trapped and bound by niicrobial mats, giving rise to the alternation of fine-grained sediment layers and irregular crinkled layers. Many ancient peritidal liinestones exhibit a lamination consisting of millimeter micrite or dolomicrite layers with thin organic or bituminous seams, and thicker, up to several centimeters, layers composed of grainstone or packstone with intraclasts and peloids. The latter represent storm deposits.

Peritidal Carbonates: C r i t r r i : ~

Lamination should be studied with regard to the (1) lithologic composition (only limestone or dolomite, or limestone-dolomite couplets), (2) geometry of the laminae (undulation; parallel laminae; cross-bedded laminae), (3) extension of laminae (continuous, disrupted), (4) microfacies of the laminae (micrite, peimicrite, pelsparite), ( 5 ) type and frequency of associated fenestral pores. See Read (1975) for a classification of lamination types. ->Note: Parallel lamination occurs in subtidal, intertidal and supratidal environments, but is especially abundant in the intertidal zone. Stratification: Bedforms and stratifications made by waves and currents (ripples, planar and cross stra~ification, winnowed sand lenses; flat and cross-bedded calcarenites) exhibit a wide variety of types. Further information can be found in Demicco and Hardie (1994). -> Note: Common in the shallow subtidal and lower intertidal zone. Desiccation features Desiccation and shrinkage cracks seen on bedding surfaces are considered as one of the most useful sed1mentary structures for identifying subaerial exposure and ancient carbonate tidal flats. Desiccation cracks formed by drying out of subaerially exposed mud have different forms depending on the rate of drying, presence or absence of protecting microbial mats, exposure time and bed thickness, and comprise three types: M ~ l dcracks (PI. 25/5) and mud polygons. Prism crocks: Polygonal network of cracks, essential normal to bedding, that breaks up the sediment into vertical prisms. Sheet cracks: Planar to gently undulatory cracks, commonly parallel to the bedding and filled with sparry calcite or micrite. ->Note: Desiccation mud polygons are common in the supratidal and upper intertidal zone. Because mud cracks can also form by substrata1 and subaqueous processes, much care must be taken in interpreting mud crack structures in ancient carbonates (see Demicco and Hardie 1994). Tepees A special form of polygonal structures are tepees (similar to inverted depressed Vs resembling Red Indian tents) characterized by antiformal structures with sharp apices. Tepees originate from desiccation, but the formation of large peritidal tepees is also controlled by fluctuating groundwater conditions. They are associated with fractured and bedded tidal carbonates. The fractures are filled with marine-vadose travertines andl or terra rossa.

Peritidal Carbonates: Criteria

Other processes creating tepees are the crystallization of minerals (e.g. evaporites) and thermal contraction and expansion. See Assereto imd Kendall (1977) and Kendall and Warren (1987) for details. ->Note: Tepees are common features of supratidal environments. Peritidal tepees (Assereto and Kendall 197 1) are strandline indicators.

distribution of the larninoid fenestrae is closely related to that of microbial mats. Note that the often used term loferite (Fischer 1964) is not fully identical with birdseye limestone. Loferite refers to bedded or massive micritic limestones containing millimeter-sized pores that correspond to birdseyes as well as shrinkage pores, sheet cracks and tubular fenestrae.

Intraclasts and breccias Intraclasts (Pl. 16/7): Millimeter and centimetersized, and angular to rounded clasts of lime mudstones, packstone, bindstones and grainstones are common constituents of tidal carbonates. -> Note: Rip-up intraclasts are abundant in the intertidal zone and the lower part of supratidal zones. Storms affecting supratidal flats and coast lines produce intraclast rudstones and floatstones containing reworked indurated carbonate crusts and black pebbles. Flat-pebble and edgewise conglomerates: Many tidal and shallow subtidal carbonates contain beds composed of flat-lying and imbricated carbonate rounded clasts exhibiting different microfacies types. The clasts are produced by storms eroding the shallow sea bottom (see Sect. 5.3.3.3). -> Note: Flat-pebble conglomerates occur in supratidal, intertidal and subtidal settings bur are more common in the intertidal zone. Black pebbles (Pl. 1613): Millimeter- to centimetersized black lithoclasts are a valuable tool for identifying partial or complete subaerial exposure (see Sect. 4.2.8.1). Brecciu~:Solution-evaporite-collapsebreccias (Sect. 5.3.3.3) may be common in supratidal limestones formed under arid or semiarid corrditions.

Microbiallalgal mats Algal-laminated ('cryptalgal') structures characterized by crinkled or flat rnicritic or pelmicritic laminae (Pl. 18/4; P1. 123/2), and relicts of cyanobacterial or algal filaments are common criteria of ancient tidal carbonates (see Sect. 9.1.3.1). These bindstones and peloidal packstones are associated with fenestral limestones and lime mudstones. A characteristic feature is a frequent and abrupt interruption of continuous laminations and mats by lenses, channels or beds of coarsegrained sediment (intraformational conglomerate, ooid sand, skeletal sand). Because mats are often formed on more frequently exposed parts of tidal flats, the association of mats, fenestral pores, mud cracks and evapori t e ~is a common feature. Microbial and algal mats may indicate destruction. Criteria for the existence of former biofilms and microbial mats are local doming of sedimentary surfaces; fenestral pores; clasts derived from microbial mars: textures indicating baffling or trapping effects (selective accumulations of fine sediment between coarser sediment; selective accumulations of coarser grains; orientation of grains parallel to the surface of microbial mats); enrichment of terrigenous clay minerals in layers; enrichment of Fe. S, P, Cog and various other elements in layers. Element mapplng offers a good method for recognizing former microbial mats (Kropp et al. 1996). -> Note: Microbial mats occur in intertidal and supratidal settings, but may also form in subtidal environments if high salinities or other factors prevent grazing organisms from destroying the mats. Grazing organisms, particularly cerithid gastropods, are common constituents of well-laminated sediments consisting of smooth mats with laminoid fenestrae which are distinct features of the lower intertidal zone. The middle and the upper tidal zones are characterized by poorly laminated sediments with an irregular fenestral fabric lying below pustular mats. Records of microbial mats are abundant in the carbonates formed in the upper intertidal and the supratidal zone, probably because grazing is limited by prolonged exposure.

Fenestral structures Fenestral cavity structures (birdseyes; Sect. 5.1.5; P1. 2017; Fig. 14.25) are voids in peloidal and micritic mudstones and wackestones, and in packstones and grainstones. The voids are larger than the intergranular pores and partially or completely filled with sediment or cement. According to Groover and Read (1978), three types can be distinguished: Irregular fenestrae (Pl. 5015; PI. 123/3), typical birdseyes: equidimensional to irregular in shape, several millimeters across. Larninoid fenestrae developed in laminated sediments (PI. 41/2), particularly microbial carbonates. Tzibular.fenestrae,formed mainly by burrowing organisms or plant rootlets (PI. 20/4). -> Note: Abundant in intertidal and supratidal environments. Irregular and laminoid fenestrae are characteristic of the upper intertidal and supratidal zones. The

'38

Stromatolites Spectacular stromatolites (Sect. 9.1.4; Fig. 9.2) consisting of laterally linked hemispheroidal growth forms and stacked hemispheroids are known from recent and ancient intertidal settings, but the existence of stromatolites does not necessarily indicate intertidal paleoenvironments. Many ancient stromatolites, particularly those with vertically pronounced reliefs, were formed in subtidal settings and are also known in modem subtidal environments.

I ' e r ~ t ~ d aCarbonates: l Crttcr la

versity is generally high. Low faunal diversity may indicate stressed environmental conditions. Most common invertebrates and many calcareous algae live in the illuminated, shallow upper part of the subtidal zone.

Riogenic structures Root sfructur-es: Submillimeter- and millimetersized, spar-filled branched tubular structures, different from fenestral structures, may represent relicts of plant roots (PI. 20/6). -> Note: Root molds of land plants are common in suprdtidal environments, but morphologically similar molds are produced by subtidal aquatic plants. Structures interpreted as molds of plant roots, are no definitive characteristics for subaerial or subaquatic settings. Bur-r-o~vs (Pl. 19) are common in all marine settings, but show differences with regard to shape, size and distribution patterns in different parts of shelf environments (Sect. 5.1.3). --> Note: Variously arranged burrows are rare in supratidal environments. The lower intertidal zone is commonly heavily burrowed and often characterized by millimeter-sized vertical burrows. Note that strong burrowing occurs also in shallow and deeper parts of the subtidal zone.

Sea grass Today, sea grass meadows are located in the intertidal and the shallow subtidal zone. Since the vegetation determines the nature and distribution of carbonate sediment types, each zone has its own distinctive skeletal communities (Cann and Gostin 1985) and is reflected by calcareous epiphytes and organisms living in protected niches below and between the aquatic plants. The subtidal Posidoniu meadows occurring in shoreline-attached platforms or offshore banks can be recognized by foraminifera, coralline algae, bivalves and gastropods living on the blades. The corresponding sediment is a poorly sorted skeletal packstone. Intertidal flats may be covered by meadows of the sea grass Zostera, that grows in loose communities in lower intertidal settings and in dense meadows in the upper intertidal zone. The sediment is a poorly sorted mixture of skeletal sand with molluscan infauna, and terrigenous mud and sand. These sand flats merge landward into the upper intertidal mangrove zone, characterized by laminar nludstones, pseudobreccias and 'root rocks' (Galli 1991). The latter exhibits a dense, irregular network of circular voids and vertical cavities exhibitin? downward bifurcations.

Biota The biotic diversity and the composition of benthic assemblages offer the best criteria for distinguishing and subdividing tidal and subtidal carbonates. * Sup-rttidal erzvir-oiznzeiztsare characterized by very low diversity, rare well-preserved fossils and the dominance of only a few organism groups (cyanobacteria, ostracods, some foraminifera, a few mollusks). Plant littcr may be common. Inrcr-tidal envii-onmenrs are characterized by low diversity organisms that adapted to rapidly changing stress conditions. More frequent organisms are (cerithid) gastropods, ostracods, benthic foraminifera and bivalves. Plant litter is common. Cyanobacteria are abundant (coastal and interior algal/~nicrobialmarshes in humid climate). Calcareous algae are represented by dasyclads. S t o m layers may contain transported subtidal organisms. * Subtidal environments are characterized by normal marine biota including skeletal invertebrates and shell debris as well as trace fossils?especially burrows. Di-

Diagenetic features Cementation: Some early diagenetic criteria occur preferentially in tidal limestones (see Sect. 7.4.2 and Sect. 7.4.3). These criteria include: Gravitational (microstalaktitic) cements, e.g. dripstone cements in intertidal birdseyes (PI. 3314). Meniscus cement between grains of supratidal beachrock (Pl. 3314). Meteoric-vadose pisoids (Pl. 14/1; P1. 126/1, 7 ) . Calcite or aragonite sinter crusts formed on intertidal and supratidal surfaces. Irregular carbonate encrustations on substrates affected by surf sprays; associated with pisoids (coniatolites; Purser and Loreau 1973; Pi. 14/2). Dolornitization: Intertidal and supratidal carbonates may be characterized by very early diagenetic fine-crystalline dolomicrite formed under conditions described by the sabkha evaporation model and the mixing zone model (see Sect. 7.8.2). Early diagenetic origin is indicated by dolomite chips occurring in tidal breccias. Often associated with fenestral voids (PI. 39/2).

Criteria of Tidal Carbonates

749

Table 15.1. General summary of criteria used in differentiating supratidal, intertidal and shallow subtidal carbonates. The relative frequencies of diagnostic features should not be taken as the only possible truth! Supratidal

Intertidal

Shallow subtidal

Sedimentary structures Fine-scale lamination Desiccation structures Tepees Flat-pebble conglonlerates Collapse breccias

cotnmon abundant abundant rare ab~~ndant

abundant abundant rare common abundant

rare absent absent rare absent

Biogenic structures MicrobiaValgal mats Stromatolites Burrows

abundant rare rare

abundant abundant abundant

rare common abundant

Fenestral fabrics Irregular and laminoid birdseyes Tubular root voids

abundant abundant

abundant common

rare rare

Sedimentary grains Peloids Fecal pellets Benthic peloids Mud intraclasts Black lithoclasts Non-skeletal oncoids Skeletal oncoids Ooids Cortoids Aggregate grains

common rare rare common common rare rare absent absent absent

abundant abundant common abundant common common common common common common

common abundant absent common absent common common to abundant common abundant abundant

Biota: Characteristic groups Benthic foraminifera Ostracods Gastropods Bivalves Calcareous algac Cyanobacteria

very rare rare rare absent absent common

rare to common ral-e common to abundant rue rare abundant

common to abundant common common to abundaril common common to abundan~ comnlon

Biota: Diversity

very low

low

high

Diagenetic criteria Gravitational cement Meniscus cement Vadose pisoids Carbonate surface crush Fine-grained dolomite Gypsum/anhydrite-carbo~~i~te associations

abundant common abundant abundant common abundant

common common rare common common abundant

absent absent absent absent common rartx

Pedogenic structures

abundant

rare

absent

Evaporites Gypsurn, anhydrite and halite occurring in association with peritidal carbonates are common in arid and semiarid areas. Upper intertidal and supratidal sabkha sediments are characterized by gypsum, landward areas by anhydrite nodules and chicken-wire anhydrite, often hydrated to gypsum. See PI. 125/2,4. Pedogenic structures Supratidal conditions charactenzed by prolonged subaerial exposure are reflected by dissolution and soil

formation connected with karstification in humid zones and calichification in arid and semiarid zones (see Sect. 15.1 and 15.2).

15.5.1.3 Synopsis of Diagnostic Criteria Lists of diagnostic peritidal features provided by various authors including Shinn (1983), Hardie and Shinn (1986) and Demicco and Hardie (1994), and the information in the preceding section show that it is difficult

75 0

D e v o n ~ a nPeritidal Limestones

Plate 132 Peritidal Limestones: A Case Study from the Devonian The plate shows common facies-diagnostic criteria of cyclic peritidal and subtidal limestones forming shallowing-upward cycles. Important criteria of the intertidal and supratidal conditions are laminites and laminated microbial mats (-> l), stromatolites (-> 5), fenestral fabrics (-> 6), reworked sediment and intraclasts (-> 4), and desiccation structures, e.g. mud cracks (-> 1). Synsedimentary reworking by tidal currents and by storms is a common feature (-> 2,4). Intertidal mudstones and wackestones are frequently strongly burrowed (-> 3). The subtidal parts of the cycle can be recognized by fossils: Green algae (-> 7), ostracods (-> 8) and gastropods (-> 9) are common constituents of wackestones and packstones formed in the shallow subtidal environments. The taxonomic composition of the brachiopod fauna characterizes somewhat deeper parts of the subtidal zone. All samples are from the Eifelian Wojciechowice Formation of the Skaly quarry of the Holy Cross Mountains in central Poland. Supratidal and intertidal Fine-laminuted iinze rnudstorze (bindstone) with small vertical desiccation cracks (arrows) indicating the shallowest supratidal parts of the cycle.The microfacies corresponds to Standard Microfacies Type SMF 19. Intrafornzutiorzal breccia from topn~ostparts of intertidal laminites. The mixing of biotic elements from different habitats (ostracods in the micritic clasts, white arrow; brachiopod shells in the micritic matrix, black arrow) suggests a tempestite origin rather than an interpretation as tidal-channel deposit. limsgressive basal br-eccia occurring at the sole of the subtidal part of the cycles. Micrite lithoclasts within a coarsegrained, dolomitized gastropod packstone matrix. Arrows point to burrows. The breccia is interpreted as surf-zone deposit formed during the initial phase of a transgressive episode. Tidal-clzarznel deposit. Interfingering of an intrafonnatiorial tidal-channel breccia (BR) with intertidal laminated sediments (LS). Topmost part of intertidal laminites. Detail of a hemispheroidai srr-orriurolirc.occurring in well-defined horizons. Note the crinkled laminae consisting of niicrite and peloids. Fetzcsrr-a1algal hirzdstorzcs occur in the lowermost part of the tidal sequence. The bindstone exhibits subhorizontal sparfilled voids bridged by microbial mats. The arrow points to planar fenestral structure. Note the oblique position of parts of the mat indicating incipient reworking. Intertidal. Shallo\+*subtidal A l g d ~mkestorlc. The tubular structures are palaeoberesellid green algae regarded as dasyclad algae or as an independent green algal group (palaeosiphonoclads. see Fig. 10.17 ). This Devonian and Carboniferous group was usually restricted to calm, lagoonal shelf en\l ~ r ~ n ~ i ~ e n t s . O . ~ u c o d~~uckestonc. Non-disarticulated smooth-shelled ostracods (arrows) are abundant. Dissolution of the thin shells would result in the formation of 'mold peloids' (see Fig. 4.11). Gastr-opd ~+~ackcstorze, slightly dolomitized. The shallower part of the subtidal unit of the cyclothem is dominated by gastropods in association with amphiporids (stromatoporoids, see P1. 8012). Devonian amphiporid stromatoporoids are abundant in black. bitun~inouslimestones. The organisms were adapted to tranquil, reef-lagoon and back-reef habitat:, with diminished oxygen in boltom waters. '

Intertidal1 supratidal

Shallow subtidal

7

@

Deeper subtidal

strornatoporoids

4gastropods

8 amphiporids

calcareous algae (palaeoberesellids)

O brachiopods

7 bioturbation

,ostraods

Deeper subtidal 1 0 .GI-uchiupodwackcstcme. Some Devonian brachiopods (e.g. Bortzhar-drincl, shown here) and also Mesozoic bivalves (Fiirsich 1993) were adapted to euryhaline conditions. Dense packing and stacking of shells is caused by high-energy events. Note the difference of the matrix type as compared with -> 9 (homogeneous micrite and calcisiltite). Deeper part of the cyclothem. -> 1-10: Skompski and Szulczewski 1994

Fig. 15.11. Idealized shallowing-upward succession in Middle Devonian platform interior carbonates showing main characteristics of intertidal-supratidal and shallow and somewhat deeper subtidal carbonates. See P1. 132 for characteristic microfacies types. After Skompski and Szulczewski (1994).

751

Plate 1 3 2 : Devonian Peritidal Limesta'nes

5 mrn

5 mrn

752

to distinguish between intertidal and supratidal carbonates if only a few facies criteria are used. You must try to find as many criteria as possible. Table 15.1 summarizes the main criteria of peritidal carbonates and gives an idea of the relative abundance of these criteria.

Basics: Peritidal Carbonates

15.5.2 Case Study: Middle Devonian Peritidal Carbonates from Poland

and fossils. Most peritidal carbonates are fine-grained bedded dolomites, differing in their yellow to brown rock color from the dark gray subtidal carbonates. This difference is also known from recent tidal carbonates, both in humid and arid settings. Facies-diagnostic criteria are small-scale p.arallel and crinkled lamination, hemispheroidal and isolated domal stromatolites, intraformational breccias, polygonal networks of up to 20 cm deep desiccation cracks, and small-scale channel-fill cross bedding.

Meter- to tens-of-meter-thick shallowing-upward cyclothems are common features of platform carbonates. Shallowing is indicated by changes in fossils, sedimentary structures and microfacies types. The case study from the Devonian of the Holy Cross Mountains in Poland (Skompski and Szulczewski 1994), documented in P1. 132, describes a typical facies pattern showing some of the diagnostic facies criteria that allow subtidal and intertidal-supratidal carbonates to be differentiated. The Eifelian Wojciechowice Fornlation consists of lagoonal dolomites and limestones. Cyclic sedimentation is evident both in the limestone and dolomite part of the section studied (Fig. 15.11). The succession was formed in low-energy environments, as seen in the dominance of lime mudstones, wackestones and bindstones, arid the rarity of grainstones and packstones. Rare high-energy episodes are indicated only by a brachiopod coquina (interpreted as a storm deposit), a basal breccia of one of the cycles, and few intraformational breccias at the top of intertidal laminites. Subtidol environments are derived from the composition and diversity of the biota comprising brachiopods, massive stromatoporoids, dendroid arnphiporids, gastropods, ostracods, dasyclad calcareous algae as well as very rare trilobites and solitary rugose corals. Shallow subtidal and deeper subtidal assemblages have been differentiated by looking at the inferred ecological requirements of the biota. Shallow subtidal assemblages are characterized by amphiporids, gastropods, ostracod5 and calcareous algae. Deeper subtidal assemblages consist of large brachiopods (Bornhardtino,Emanuella) and massive stronlatoporoid heads, and only subordinate gastropods and amphiporids. Six microfacies types can be distinguished based on the dominant fossils: (I) Brachiopod-stromatoporoidmudstone/wackestone, (2) brachiopod-peloid packstone, (3) Amphipora floatstone, ( 4 ) gastropod wackestone/packstone, ( 5 ) algal wackestone, and (6) ostracod wackestone. All the microfacies types are strongly burrowed. Carbonates interpreted as intertidal-supratidal are distinguished from the subtidal limestones by texture

Basics: Peritidal carbonates Alexander, C.R., Davis, R.A., Henry, V.J. (eds., 1998): Tidalites: processes and products. - Society of Economic Paleontologists and Mineralogists, Short Course Notes, 61,171 pp. Fischer, A.G. (1964): The Lofer cyclothems of the Alpine Triassic. -In: Merriam, D.F. (ed.): Symposium on cyclic sedimentation. - State Geological Survey of Kansas, Bulletin, 169, 107-169 Ginsburg, R.N. (ed., 1975): Tidal deposits: a case book of Recent examples and fossil counterparts. - 428 pp., New York (Springer) Ginsburg, R.N., Hardie, L.A., Bricker, P.P., Garrett, I-'., Wanless, H.R. (1977): Exposure index: a quantitative approach to defining position within the tidal zone. - In: Hardie, L.A. (ed.): Sedimentation on the modern carbonate tidal flats of Northwest Andros Island, Bahamas. - 7 11, Baltimore (John Hopkins University Press) Galli, G. (1 991): Mangrove-generated structures and depositional model of the Pleistocene Fort Thompson Fonnation (Florida Plateau). - Facies, 25, 297-3 13 Joachimski, M.M. (1994): Subaerial exposure and deposition of shallowing upward sequences: evidence from stable isotopes of Purbeckian peritidal carbonates (basal Cretaceous), Swiss and French Jura Mountains. - Sedimentology, 41,805-824 Laporte, L.F. (1967): Carbonate deposition near mean sealevel and resultant facies mosaic: Manlius Formation (Lower Devonian) of New York State. -American Association of Petroleum Geologists, Bulletin, 51,73-101 Hardie, L.A. (1986): Stratigraphic models for carbonate tidal deposition. - In: Hardie, L.A., Shinn, E.A. (eds.): Carbonate depositional environments, modem and ancient. Part 3: tidal flats. - Colorado School of Mines, Quarterly. 81,59-74 Hardie, L.A., Shinn, E.A. (eds., 1986): Carbonate depositional environments, modem and ancient. Part 3: tidal flats. - Colorado School of Mines, Quarterly, 81,74 pp. James, N.P. (1984): Shallowing-upward sequences in carbonates. - In: Walker, R.G. (ed.): Facies models. - Geological Association of Canada, Geoscience Reprint Series, 1, 213-288 Kendall, C.G.St.C. (1987): Areview of the origin and setting of tepees and their associated facies. - Sedimentology, 34,1007-1027 Klein, G. deV. (1971): A sedimentary model for determining paleotidal range. - Geological Society of America, Bulletin, 82,2585-2592 Pratt, R., James, N.P., Cowan, C.A. (1992): Peritidal carbonates. - In: Walker, R.G., James, N.P. (eds.): Facies mod-

Carbonate Platforms and R a m p s

els. Response to sea level change. -- 303-322, Geological Association of Canada Sadler, P.M. (1994): The suspected duration of upward-shallowing peritidal carbonate cycles and their terminal hiatuses. -Geological Society of America, Bulletin, 106,791802 Shim, E.A. (1983): Tidal flat envirorunents. - In: Scholle, P.A., Bebout, D.G.. Moore, C.H. (eds.): Carbonate depositional environments. - American Association of Petroleum Geologists, Memoir, 33, 171-210 Strasser, A. (1988): Shallowing-upward sequences in Purbeckian tidal carbonates (lowermost Cretaceous, Swiss and French Jura). - Sedimentology, 35,369-383 Skompski, S., Szulszewski, M. (1994): Tide-dominated Middle Devonian sequence from the northern part of the Holy Cross Mountains (Central Poland). - Facies 30,247266 Wright, V.O. (1984): Peritidal carbonate facies models: a review. - Geological Journal, 19, 309-325 Wright, V.O. (1990): Peritidal carbonates. -In: Tucker, M.E., Wright, V.O. (eds.): Carbonate sedimentology. - 137-164 Further reading: K020, K177

15.6 Carbonate Platforms and Ramps Facies models and microfacies types of rimmed carbonate platforms and carbonate ramps were discussed in Chapter 14. The objective of this section is to demonstrate the potential of microfacies analyses for differentiating and interpreting platforms and ramps by using selected case studies.

15.6.1 Ecological Controls on Platforms and Ramps The geometry and accumulation of sediment on carbonate platforms depend strongly on the biota living on the platforms, and the interplay of benthic organisms and physico-chemical environmental factors (Fig. 15.12, Fig. 15.13): Ecologic factor., control the l~ocutionand rate of organic sediment production. The depth of the main carbonate production and its position in relation to platform margins affects the geometric evolution of platforms. Both parameters depend on the ecology of carbonate-producing organisms as reflected by their life habit. Carbonate production depth is controlled by illumination, and the lateral distribution of organisms across the platform is dependent on hydrodynamics, substrate and nutrients. The presence or absence of a biogenic framework influence the stabilization and geometry of platform margins, and the composition and location of facies

units. The presence of frameworks and reefs assists in coping with a rapidly rising sea level. The absence of frameworks may promote high rates of sediment reworking and export. Sea-levelfluctuations influence growth potential and the abundance of biogenic carbonate production on platforms. The frequency and growth potential of sediment-producing organisms may be different during transgressive and regressive phases. During transgressions large areas are flooded and biogenic production is high. During regressive phases, when large areas have emerged, the productive depth range is small. The composition of skeletal grain associations depends strongly on the relativefrequency and the taphononzic stability of skeletal grains. The amount of biogenic sediment production influences the growth rates of platforms. Sediment produced on the platform is either deposited on the platform or exported. Maximum sediment production will normally occur, where the environmental parameters meet best the ecologic requirements of sediment producers and where environmental parameters remain constant over a longer time. The early diagenesis of platfom~sediments is influenced by biofabrics that control the primary permeability and porosity, and by the mineralogy of skeletal grains. Sediments consisting nlainly of aragonite and High-Mg calcite have a higher diagenetic potential than sediments dominated by Low-Mg calcite. Resulting differences in dissolution and reprecipitation will be particularly conspicuous in platforms and inner ramps affected by meteoric diagenesis. The Pomar Model: Carbotzate-produciljg organisms and depositional profiles Facies models of platfonns and ramps describing the depositional zones of shallow-marine lo deep-marine transects were discussed in Chap. 14. Anew model, developed by Pomar (2001a), emphasizes the interaction between the different sediment types being produced by organisms and the hydraulic energy acting in the diverse loci of production (Fig. 15.13). The basic ideas of the model are:

( I ) The differences between rimmed platforms, nonrimmed plarforms, distally steepened ramps and homoclinal ramps, can be considered as a balance between ( a ) the type (basically the grain size) of the sediment produced, (b)the locus of the sediment production, and ( c ) the hydrodynamic energy. The carbonate production (sediment supply) of platforms and ramps depends mainly on biological sys-

Ecological Controls on Platforms -

-

-

I

- --

-- -- --I Envfronrnent (clmate, sea level,

delation of sediment production lo sea level

Presence or absence of a biogenic framework

Fig. 15.12. Controlson platform development. Platform evolution and facies distribution depend to a large extent on the environment. The environmental controls are modulated by the ecosystemson the platform. Their impact affects parameters that are documented by microfacies criteria. The parameters emphasized in this sketch are derived from an analysis of Late Cretaceous platform carbonates,but are valid for most other tropical platforms. Modified from Stoessel (1999).

terns, and consequently on ecological factors governing the existence and distribution of organisms. These factors predominantly include light, nutrient availability, water energy, water temperature and salinity. Sediment dispersal including the export and redistribution of mud-, silt-, sand- and gravel-sized sediment, depends on the interaction between the sediment type (relati~~e density, size and shape of skeletal grains) and the hydrodynamic energy existing instead of sediment production. Sediment dispersal is frequently modified by biological processes (e.g. binding and baffling) and cementation.

shelves similar to modem reef platforms (Fig. 15.13A). Gravel-producing biota living on soft substrates in the shallow euphotic zone create flat-topped open shelves (Fig. l5.13B). Gravel-producing biota such as some larger foraminifera and red algae living in the oligophotic zone generate distally steepened ramps (Fig. 15.13C). Mud-producing biota living in either euphotic or oligophotic zones generate homoclinal ramps. Photo-independent carbonate-producing biota living above the wave-base give rise to open non-rimmed shelves and ramps, depending on the grain size, but may produce mounds if carbonate production occurs below wave base or sweeping current.

( 2 ) C~rrhonate-11l-o~-I~1 4, indicating the existence of two species (-> 4: Thamnopora boloniensis; -> 5: Thanznopora reticulala). 6 Diflerentiation of crinoid elements. Crinoid columnal exhibiting the canal pattern of Cupressocrinites characterized by four peripheral canals separated from the central lumen. Cupressocrinites is a widely distributed genus known from the Late Emsian to the Early Frasnian (Ures et al. 1999). 7 Crinoid packstone. Accumulation of small crinoidal columnals with two small, closely set canals of equal size.

Microfacies of Ramp Carbonate(

766

Plate 136 Microfacies of a Late Jurassic to Early Cretaceous Ramp: Subsurface of Bavaria (Germany) The plate exhibits the microfacies of ramp carbonates in the Kinsau well near Augsburg in southern Bavaria. Fig. 1 on P1. 136 is the lowermost, Fig. 10 the topmost sample. The sequence starts with Tithonian shallow-marine, sometimes lagoonal carbonates (-> 1,3-5), and coral reef limestones (-> 2; maximum size of the patch reefs in outcrops 20 m), overlain by ramp deposits representing the Early Cretaceous 'Purbeck facies' (Berriasian; -> 6-10). This facies known from England, France and Switzerland, occurs in southern Germany and northern Austria in the subsurface. Purbeck sediments formed in strongly varying environments, and comprise marine, brackish, freshwater and hypersaline sediments (see Fig. 4.26 for an example). Other microphotographs can be found on P1. 16/7 (tidal intraclasts), PI. 2913 (fabric-selective oomoldic porosity), PI. 65/5,6 (charophycean brackish-water algae), and P1.9315 (Favreina-peloid sand). The shallowing-upward sequence consists of outer, mid- and inner ramp deposits (Fig. 15.16). Outer ramp sediments, deposited below the normal storm wave base, comprise mud-rich subtidal carbonates and marls (-> I), small patch reefs (-> 2), and shallow subtidal limestones with red algae (-> 3 and 5). The existence of midramp sediments is indicated by Larger foraminifera (compare P1.6911) and micrite oncoids (-> 6). Low-energy inner ramp deposits are indicated by oncoid grainstones with porostromate cyanobacteria (-> 4). High-energy inner-ramp sediments are represented by sand shoals and sheets (-> 7-9) controlled by tidal currents. For a coastal sabkha see ->lo. Porosity and reservoir qualities are controlled by primary depositional facies (geometry and grain composition of high-energy shoals; micritic seals) and facies-selective diagenesis (freshwater dissolution of ooids, repeated dolomitization). 1 Deeper outer ramp ( Ain Fig. 15.16): Fine-grained bioclastic packstone. Grains are echinoderms (white), red algal clash (black) and coated shell fragments. The packstone is intercalated within mud- and wackestones, pointing to downslope sediment transport. 2 Patch reef (B in Fig. 15.16): Framestone consisting of intergrown corals (C), chaetetid coralline sponges (CH) and foraminiferal crusts (F). Arrows point to boring. Outer ramp. Ramp microfacies RMF 12 (see Fig. 14.30 for definitions). 3 Deeper outer ramp (C in Fig. 15.16): Red algalpackstone composed of rhodoids formed by Marinella Pfender. This alga has millimeter-sized thalli and extremely fine threads (< 5 to 12 pm). The alga is known from the Late Jurassic to the Oligocene, and is common in Jurassic and Early Cretaceous platform and reef carbonates (Leinfelder and Werner 1993). At smaller magnifications, the nlicritic thalli can be mistaken for micritic clasts. Note intergranular dissolution (white) due to strong compaction. 4 Inner rump (D in Fig. 15.16): Oncoid rudstone. Larger grains are filamentous cyanobacteria (C) and gastropods (C;), small grains are algal peloids. Biocky cements and infill of intergranular voids with crystal silt (arrow) indicate meteoric overprint. Restricted intertidal environment. RMF 21. 5 Outer ralnp (C in Fig. 15.16): Rhodoidpackstone with Marinella (M). The facies interfingers with facies D. Low-energy subtidal environment. RMF 9. 6 Protected lagoonal environment ( E in Fig. 15.16): Oncoid wackestone with micrite oncoids and large lituolinid foraminifera (Pseudocyclamrnina, P), indicating a mid-ramp position. The micritic matrix is selectively dolomitized. RMF 13. 7 Inner ramp (F in Fig. 15.16): Ooid grainstone with simple and compound, tangential ooids. Intergranular pores are occluded by calcite cement, some of which exhibits gravitative textures indicating vadose meteoric diagenesis. High energy inter- and subtidal shoals. RMF 29. 8 Inlo-ridd Lshoolson tile inner. ramp (G in Fig. 15.16): Fine-grained peloid grainstone. Most grains are fecal pellets as indicated by their rodlike shape. 9 High-energetic shoals of the inner ramp ( H in Fig. 15.16): Favreina grainstone consisting predominantly of fecal pellets of decapod crustaceans (see Sect. 10.2.4.7). RMF 27. 10 Back-ramp sahklza (I in Fig. 15.16): Evaporitic argillaceous mudstone composed of alternating mudstone and layers with anhydrite (white). Supratidal environment. Standard Microfacies Type SMF 25.

I

H

G

F

€

C

D

C

B

A

Fig. 15.16. Generalized facies distribution of a Late Jurassic/Early Cretaceous carbonate ramp based on data from the subsurface of southem Bavaria, Germany.

TOP

5 mm

5 mm

BASE

5 rnm

Basics: Carbonate Platforms and R a m p s

carbonate residues. The platform exhibits two major facies, mud-dominated and grain-dominated limestones. Maximum thickness is 150 m. The size of the platform is difficult to evaluate owing to the strong tectonic faulting in the whole region, but might be within the range of several kilometers. Fig. 15.15 shows the distribution of facies and subfacies types representing Facies Zones FZ 9A (tidal flat), FZ 8 (lagoon), FZ 7 (open platform) and FZ 6 (platform margin sands) of the Wilson Model. Other photographs of Sulzfluh limestone samples can be found on P1.5313 (porostromate cyanobacteria), P1.621 2, 3, 6 (dasyclad algae), P1. 69/4,6, 10 (foraminifera) and PI. 12713 (microfacies). The facies and biota of the isolated Sulzfluh platform are similar in many respects to the Late Jurassic Plassen platforms of the Northern Calcareous Alps, although the Sulzfluh and Plassen platforms originated in different paleo-oceans.

15.6.3.2 A Middle Devonian Ramp from Graz, Southern Austria Many Devonian shallow-marine limestones are amazingly uniform all over the world with regard to their gross biotic composition, which includes predominantly tabulate and rugose corals, stromatoporoids, brachiopods and crinoids. These organisms occur in platfonn and ramp settings as well in large reefs formed at the margins of attached and isolated platforms and in smaller reefs formed on platforms. P1. 135 exhibits some common and widely distributed types of Devonian limestones formed in ramp settings. Ramp deposits can be differentiated in more detail using the taxonomic composition of fossil assemblages.

15.6.3.3 A Late Jurassic/Eariy Cretaceous Ramp from the Subsurface of Southern Bavaria, Germany Late Jurassic/earliest Cretaceous homoclinal carbonate ramps covered by Tertiary sediments of the Molasse trough have been studied in the course hydrocarbon exploration in southern Germany. The main targets were reef structures and shallow-marine sand bodies. Common microfacies types are shown on PI. 136. Basics: Carbonate platforms and ramps Blomeier, D.P.G., Reijmer, J.J.G. (1999): Drowning of a Lower Jurassic carbonate platform: Jbel Bou Dahar, High Atlas, Morocco. - Facies, 41,81-110 Erlich, R.N., Barrett, S.E., Ju, G.B. (1990): Seismic and geologic characteristics of drowning events on carbonate plat-

forms. - American Association of Petroleum Geologists, Bulletin, 74, 1523-1537 Erlich, R.N., Longo, A.P., Hyare, S. (1993): Response of carbonate platform margins to drowning: evidence of environmental collapse. -American Association of Petroleum Geologists, Memoir, 57,241-266 Fliigel, E. (1979): Paleoecology and microfacies of Permian, Triassic and Jurassic algal communities of platform and reef carbonates from the Alps. - Bulletin, Centres des Recherches Exploration-Production Elf-Aquitaine, 3, 569-587 Grotsch, I., Fliigel, E. (1992): Facies of sunken Early Cretaceous atoll reefs and their capping Late Albian drowning succession (Northwestern Pacific). - Facies, 27, 153- 174 Handford, C.R., b u c k s , R.G. (1993): Carbonate depositional sequences and system tracts -responses of carbonate platforms to relative sea-level changes. - American Association of Petroleum Geologists, Memoir, 57, 3-41 Hubmann, B. (2000): Die Rannach- und Schiickel-Decke des Grazer Palbzoikums. - Mitteilungen der Gesellschaft der Geologie- und Bergbaustudenten in ~sterreich,44, 1-44 Pomar, L. (2001a): Types of carbonate platforms: a genetic approach. -Basin Research, 13,313-334 Pomar, L. (2001b): Ecological control of sedimentary accommodation: evolution from a carbonate ramp to a rimmed shelf. Upper Miocene, Balearic Islands. - Palaeogeography, Palaeoclirnatology, Palaeoecology, 175,249-272 Schlager, W. (198 1): The paradox of drowned reefs and carbonate platforms. - Geological Society of America, Bulletin, 92, 197-21l Schlager, W. (1989): Drowning unconformities on carbonate platforms. - In: Crevello, P.D., Wilson, J.L., Sarg, J.F.. Read, J.F. (eds.): Controls on carbonate platforms and basin development.- SEPM Special Publication, 44. 15-25 Schlager, W. (1998): Exposure, drowning and sequence boundaries on carbonate platforms. - In: Camoin, G.. Davies, P. (eds.): Reefs and carbonate platforms of the W Pacific and Indian Oceans. - Intemational Association of Sedimentologists, Special Publication, 25,3-21 Schlager, W. (1999): Scaling of sedimentation rates and drowning of reefs and platforms. -Geology, 27, 183-186 Stoessel, I. (1999): Rudists and carbonate platform evolution: the Late Cretaceous Maiella carbonate platform margin, Abruzzi, Italy. - Memorie di Scienze Geologiche. 51,333-413 Swift, D.J.P., Thorne, J.A. (1991): Sedimentation on continental margins, I: a general model for shelf sedimentation. - In: Swift, D.J.P., Oertel, G.F., Tillman, R.W., Thorne, J.A. (eds.): Shelf sand and sandstone bodies. Intemational Association of Sedimentologists, Special Publications, 14, 3-3 1 Szulczewski, M., Belka, Z., Skompslu, S. (1996):The drowning of a carbonate platform: an example from the Devonian-Carboniferousof the southwestern Holy Cross Mountains, Poland. - Sedimentary Geology, 106,21-49 Wilmsen, M. (2000): Evolution and demise of a mid-Cretaceous carbonate shelf: the Altamira Limestones (Cenomanian) of northern Cantabria (Spain). - Sedimentary Geology, 133, 195-226 Wilson, P.A., Jenkyns, H.C., Elderfield, H., Larson, R.L. (1998): The paradox of drowned carbonate platforms and the origin of Cretaceous Pacific guyots. - Nature, 192, 889-894 Further reading: K177, K190

Transects: Platform to H a s ~ n

15.7 Platform-Slope-Basin Transects Deep-marine carbonates comprise two major sedimentary groups differing in depositional criteria and diagenetic development: Pelagic carbonates characterized by fine-grained sediments formed by pelagic planktonic and nektonic organisms (Sect. 2.4.5.3), and Resedimented allochthonous carbonates (Sect. 2.4.5.4), whose constituents are derived from platform and slope settings and exported to slopes and into basins. Microfacies criteria of the first group are discussed in Sect. 15.8. This section deals with the second group, specifically with carbonates produced by gravity mass transport and consisting of resediments. The first part gives a summary of the origin, the composition and the diagnostic criteria of carbonate slopes. The second part describes case studies and demonstrates the potential of microfacies analyses for understanding slope history and slope geometries.

Significance: Recent research on fossil and recent submarine slope systems has provided new insights into the relationships between sediment composition and slope morphology. Declivity and stabilization stages are reflected in the depositional texture, grain types. and biota, and revealed by microfacies features, including compositional data, diagenetic criteria and paleontological proxies. Sea-level fluctuations leading to different kinds of carbonate shedding are reflected by grain compositional logs that can be successfully used in correlating platform-, slope- and basin sediments. Carbonate slopes pass seawards from shallow-water to deeper-water environments. Their development is controlled by extrinsic and intrinsic factors. Extrinsic factors are sea level, tectonics, oceanography, siliciclastic input and climate. Intrinsic factors are biological productivity, sediment transport and erosion, biological stabilization and cementation, the growth of mounds and reefs, and bioerosion and dissolution. A concise synthesis of these controls and an overview of the large-scale patterns of carbonate slopes was given by Coniglio and Dix (1992). Modern slopes: Carbonate slopes are deep-water depositional environments. They exhibit a variety of depositional angles and sediment types that are different for erosional slopes, bypass slopes, and accretionary or depositional slopes. Modem carbonate slope models have been intensively studied in the Bahamas

and Florida (Mullins and Neumann 1979; Mullins et al. 1980,1984,1986; Mullins and Cook 1986) and off Jamaica (Land and Moore 1977), Belize (James and Ginsburg 1979) and Grand Cayman (Rigby and Roberts 1976). The accretionary Bahamian slopes are differentiated into an upper gullied slopes and lower nongullied slopes or a basin-margin rise that passes laterally to the flat ocean floor. The sediment of the upper slope consists of periplatform oozes composed of platform-derived material and pelagic debris. Cementation and hardground formation takes place in the shallow part of the upper slope. The oozes are strongly bioturbated in the deeper part. Differences in the composition and the dominant mineralogy of periplatform ooze layers are explained by changes in the submergence and exposure of the platform, and by differences in the dissolution of aragonitic grains. Lower slope deposits are gravity deposits, interbedded with periplatform ooze. Mud- and grain-supported debris flows and turbidites contribute to the formation of aprons near the base of the slopes. Particular elements of the lower slope are deep-water reefs (lithoherms) with ahermatypic corals (see Sect. 2.4.4.3).

15.7.1 Types and Composition of Carbonate Slopes

Slope types and facics models of slopes have been summarized by (I) Cook et al. (1972). with regard to the sediment wedge underlying the slopes and fomling aprons adjacent to the shallow-water platform; (2) James and Mountjoy (1983) and McIlreath and James (1984), distinguishing bypass and depositional slopes based on the nature of the platform margin and the relief between platform and basin; (3) Mullins and Cook (1986), emphasizing similarities and differences between siliciclastic fans and carbonate aprons, and (4) Coniglio and Dix (1992). Commonly used classifications are those by McIlreath and James, and Coniglio and Dix. The models described by the latter are based primarily upon the geometry of shelf deposits and the adjacent platform margin, but also consider the essential factors listed below: The intensity and location of the carbonate production on the platfom~. The type of the carbonate production and the morphology of the platform margin. * The feeding areas of the exported carbonates (line source and a multitude of feeding channels). The line source of platform-derived sediments originates from numerous channels dissecting oolitic and bioclastic shoals, reefs and islands along margins of

Platform Margin Types

rimmed platforms (depositional slope). Downslope sediment transport occurs predominantly via nonchannelized sheet flow. Carbonate slope sediments extend without interruption from the basin along gentle gradients (< 4") up to a shallow platform margin. The existence of erosional slopes. Steep to vertical escarpment walls can be formed during sea-level lowstands and by tectonics. The upper part of these walls may be settled by luxuriant reef-building communities. The lower part of the cemented rock can exhibit ledges and ridges acting as a base for sediment deposition and the formation of microbially induced micrite crusts that can also be recognized in ancient slopes (Brachert and Dullo 1994). Incised parallel gullies, oriented perpendicular to the platfonn margin, and formed by erosion associated with downslope gravity flows. These gullies are a line source of sediment supply from the platform and upper slope to the lower slope. * The angle between the platform margin and the slope controlling the facies belts parallel to the platform margin. Slope angles of modem slopes may be low (5"lSO),but are often relatively high ( 1-6). The basinal Buchenstein (Livinallongo) Formation consists of flat, medium- to thin-bedded marls and limestones that intergrade upslope with allochthonous limestones consisting of material shed from the margins of a platform. The carbonates of the Buchenstein Formation exhibit several microfacies types, including radiolarian packstones and wackestones, fine-laminated dark mudstones, and calciturbidites with shallow-marine and slopederived lithoclasts and fossils. The varying composition of the calciturbidites reflects platform progradation and high-frequency eustatic oscillations (Maurer et al. 2003). I lkrtical sequence consisting of resedimentcd shallow-marine carbonate grains and pelagic deep-marine sediment. Unit Al: The basal lithobioclastic grainstone consists of lithoclasts, skeletal grains and peloids. Larger lithoclasts are peloid packstones (PP) as well as bindstones (B). Both microfacies are common in Middle Triassic platform interior and reef mound settings. Bioclasts are dasyclad green algae (D), foraminifera, ostracods, and rare echinoderm debris, 'Tubiphytes' (T) and small coated debris. Note fining-upward pattern. The unit corresponds to part of a proximal calciturbidite. Unit A2: The upper part of unit A differs from the lower part by the admixture of pelagic biota ('filaments', e.g. thin pelagic bivalve shells; see PI. 11312) and echinoderm fragments. Unit 8: Radiolaria packstone. The abundant spumellarians occur with some broken filaments, a few monaxon sponge spicules (SS) and rare ostracods (0).Darker patches are caused by burrowing. Unit C: Lithobioclastic packstone. In con~parisonto unit A, lithoclasts (L) are smaller and better sorted. Rioclasts are represented by some mollusk shells (S) arid rare echinoderms. Larger grains are strongly micritized bindstone clasts. Unit Dl: This unit is characterized by a chaotic accumulation of densely packed pelagic bivalve shells (coquina floatstone). Platform clasts, including thick-shelled bivalves (B), bindstone lithoclasts and coated grains, a1-c subordinate. Unit D2: Alternation of platform-derived material and pelagic grains. Platfonn-derived grains are bindstonc lithoclasts and thick-shelled bivalves (B). Parallel alignment of filaments and sponge spicules point to the existence of weak bottom currents. A part of the variations in turbidite composition is related to hydrodynamic sorting. 2 Detail ofpnrt A1 (not shown in -> 1). Lithobioclastic grainstone. Grains are fragments of the enigmatic encrusting fossil 'Tribiphytes' (T; see Sect. 10.2.6),pelmicrite clasts and small echinoderms (top left comer). 3 Dctail ofpart A2 (not shown in -> I j. Characteristic sections of 'Tubiphptes', variously sized peloids, filaments (black arrow) and a few radiolarians (white arrow). 4 Detail oj'part B . Radiolaria packstone. Densely packed, variously sized spu~nellarianradiolaria, rare ostracods (0)and monaxon sponge spicules (SSj. 5 Detail of the upper part of unit C and the lower part of unit D l . Micritic platform clasts overlain by pelagic filaments. 6 Detail of the upper part of unit D l and tlze lower part of unit 0 2 . The irregular orientation pattern of the filaments indicates burrowing (BU),

Plate 117: Triassic Rase-of-Slope Carbonates

783

784

Slope Carbonates: Jurassic Case S t u d v

Fig. 15.24.Microfacies of bodders of carbonute slope wedges (see Fig. 14.17). A: Boundstone consisting of microbial crusts. Growth cavities are lined by isopachous fibrous calcite cement (former magnesian calcite cement; white arrow) and filled with early marine botryoidal calcite (originally aragonite) cement. Note throrribolitic microfabric (black arrow) characterized by clots of small peloids surrounded by a thin calcite cement rim. The samplc typifies a reef limestone formed at the transition of a platform margin to an upper slope. R: Polymict breccia consisting of poorly sorted carbonate clasts. Differences in shape, roundness and size of the clasts point to reworking and redeposition of lithified and semi-lithified material. The clasts are peloidal packstones eroded in platform interior environments. Arrow points to associated volcaniclastic particles. Rare fossils are an echinoid spine (E) and shells. Matching boundaries of some clasts point to in-situ brecciation and displacive cement growth subsequent to the ~nechanical integration of the allochthonous carbonate (see Blendinger - 2001). Middle Triassic (Ladinian): Mahlknecht Cliff, Dolomites, ltal?. After Brandner et al. (1991).

lithoclast grainstone and packstone) and flat graded grainstones consisting of redeposited platform-interior and platform-margin carbonate sands at the toe-ofslope. Turbidites exhibiting units of the Bouma Sequence occur in a proximal and distal position. The latter are characterized by thin grainstone and packstone beds with skeletal grains and peloids. The samples shown in Fig. 15.24 are constituents of foreslope breccias forming platform margin to basin intercalations within slope sediments (See Fig. 14.17). Most of the allochthonous material was eroded from platform and platform-margin limestones. The eroded material was transported by debris flows and rockfalls to the slope. Erosion was triggered by sea-level fluctuations. See PI. 11512 for another picture of these allochthonous carbonates.

15.7.3.3 Jurassic of Morocco: Platform-SlopeBasin Transect A platform-slope-basin system formed during the Late Jurassic in the Tabas area of eastern central Iran is a good example of microfacies types of low-angle slope carbonates (Fiirsich et al. 2003; Fig. 15.25). The export of platform material into the slope and basin is interpreted as highstand shedding related to relative sealevel fluctuations. The slope contains a mixture of allochthonous and autochthonous sediments. Autochthonous sediments are oncolitic floatstones and rudstones, and spiculitic wackestones. Mud flow deposits are characterized by large, fragmented or complete fossils floating in a wackestone to packstone matrix, and by bioclastic grainstones (debris flows).

Jurassic Slope Carbonates

Fig. 15.25. Microfacies of Jurassic slopt. carbonates. The samples come from the Jurassic Qal'ch Limestone Formation: east of Koron, Shotori Mountains (Tabas area; central Iran). The unit is Middle Callovian to Late Oxfordian in age. The unit includes slope-to-basin sediments adjacent to the Esfandiar platform, consisting of an extended platform interior and a small high-energy platform margin. The slope varies laterally from a low-angle depositional slope to a steeper bypass slope. Common autochthonous microfacies types are microbe-sponge carbonates with strong biogenic encrustations (->A) formed on the upper and middle slope; packstones with encrusting Tubiphyres (-> B) occurring in close association with the microbialites; and oncolitic carbonates fonned in protected areas on the upper slope (-> E). Allochthonous grains shed from the platform margin are ooids (-> C) and bioclasts (-> D). This material occurs in calciturbidites and debris flows intercalated in slope and basin deposits. The autochrhonous background sedimentation is represented by spiculitic wackestones (-> F). A: Microbialite with serpulids (S). The black arrow points to smaller calcareous worm tubes (Terebella),the white arrow to an internal growth cavity filled with peloidal sediment. B: Skeletal packstone with Tubiphytes (T), crinoid fragments (white) and bryozoans (N: Neuropora). Neuropora is a common bryozoan inmany Late Jurassic platform carbonates. C: Ooid packstone with aggregate grains (bottom), crinoid fragments and encrusted and coated shells. Calciturbidite. Highstand shedding. D: Poorly sorted, lithoclastic bio-rudstone. Calciturbidite. Mid-slope lowstand wedge. E: Oncoid within an oncolithic floatstone. Note the abundant bioclastic debris and foraminifera incorporated in microbial laminae. F: Fine-bioclastic wackestone with sponge spicules and some ostracods (arrows). Scale is 1 mm. All pictures from Fiirsich et al. (2003).

Slope Stability

15.7.3.4 Jurassic of the Northern Calcareous Alps: Detailed Information from Limestone Turbidites on Source and Deposition Patterns Late Jurassic sedimentation in the Northern Calcareous Alps is characterized by carbonate platforms with reefs (Plassen Formation), and pelagic carbonates deposited in deep-marine basins (Oberalm Formation). Slope carbonates are characterized by a mixture of allochthonous and autochthonous sediments. Autochthonous sediments are formed by benthic organisms growing on lithified surfaces. Allochthonous carbonates consist of fine-grained and sand- and gravel-sized material exported from the platform and platform margins to the slope and the basin. One of the best studied examples of allochthonous carbonates is the Tithonian Barmsteirz Formation (Steiger 1981). The Barmstein limestones are exposed between Hallein near Salzburg, Austria, and Berchtesgaden, Bavaria. The thick-bedded carbonates are predominantly turbidites, sometimes with a fluxoturbidite at the base. Most of the coarseand fine-grained resedimented material was eroded from the Plassen platforms that originated on isolated highs. The limestones were investigated by means of qualitative and quantitative microfacies analysis, texture analysis describing the composition of the sedimentary sequences, grain-size analysis including the statistical evaluation of grain-size parameters, and paleontological analysis. The latter comprises a systematic treatment and paleoenvironmental interpretation of thin-section fossils. Microfacies data on rock fragments and lithoclasts, diagenetic criteria and the abundance, association and taphonomic features of fossils were used in reconstructing the facies types of the Plassen platforms acting as source areas. The microfacies of Triassic and Jurassic extraclasts from the section below the Late Jurassic platfonn carbonates reveals the intensity and course of submarine erosion over time. The destruction of the platforms and the increase in slope sediments was triggered by diapirism and related tectonics. 'The study shows the great potential of the combined study of microfacies, fossils and sedimentological criteria. Of particular interest is the differentiation of platform material that was lithified at the time of erosion and redeposition, non-lithified platform sediments and organisms living in various parts of the destroyed platfornls, and limestone clasts representing input from subaerially exposed parts of the source area. The study of field logs and the consideration of the geometry and extension of the turbidites and their distribution within the small depositional basins (a few tens of kilometers in size) result in a conclusive model of deep-water sedi-

mentation in basins with strong input from intrabasinal platforms and reefs. The methodological approach of the study and of this model is recommended.

15.7.4 Slope Stability Reflected by Texture and Microfacies Carbonate platform flanks are almost exclusively made up of sediments shed by the platform itself. The composition of this platform overproductiondetermines the angle that the sediment can maintain (Kenter and

canning Basin

SellaDolomite

(Devonian) Capitan Reef (Permian) 20

1:

---

Austria (Triassic)

(Mississippiar Germany

/

---I

-I

Little Baham; ,m o m 1

Fig. 15.26. Slope angles of carbonate platforms am controlled by the donzinant depositional fabric. Grainy, non-cohesive mud-free buildups form steeper slopes than muddy, cohesive sediments. Grain-supported fabrics with minor or no matrix (grainstones, rudstones, clast-supported breccias; e.g. Gosaukamm; P1.2712) build slope angles varying up to about 40". Grain-supported textures with matrix (packstones; e.g. Late Jurassic mounds in Germany) and mud-supported fabrics exhibit slope angles up to 15'. Mudstones (e.g. modern Little Baharna Bank or Late Paleozoic algal mounds) have low slope angles up to 5', mud-supported wackestones and floatstones up to about 15". Well-documented examples are marked by circles; examples lacking precise control of geometry by squares; and examples whose flanks are stabilized by microbial automicrite ( c g . Waulsortian mounds, or the Sella Platform in the Dolomites) and/or synsedimentary carbonate cements or organic framework by triangles. Eurly srabilization results in medium to steep slope angles. The range of fabric and slope angles is shown by bars for each data point. These data indicate that the physical behavior of the sediments in the gravity field, angle of shearing and readjustment processes are linked to the composition of the slope sediment. Textural composition appears to be the major control on slope angle and slope curvature besides windwardleeward setting, sea level and climate. Based and slightly modified from Kenter (1990), with additional data for the Gosaukamm (own observations) and for the Sella (Keim and Schlager 1999). A list of localities and references can be found in Kenter (1990).

thc important role of niicrobially mediated, in-situ precipitated micritic carbonate in the early lithificatio~iof steeply dipping slopes. Honwcr, slope geometry is ultimately controlled by the angle of repose of layers differing in ncuiiir? iind grain . ; i x (see Fig. 15.26~. 'I'i-i;~h\ic([.:ire Ladinian to Early Camian): Slope of the Sella Platfomi, Sot~thTyrol.

\.c.~-tic;]I cfistrrnc.t.froni c.orrc!;itive horizontal topset beds. Automicrite can be followed down t o water d i ~ l ? ~ot'ahout h\ 100 i n . I . Bivalvej7oatstotze with recrystallized megalodontid shells (compare Fig. 10.40).The matrix is a fine-grained packstone with variously sized peloids, aggregate grains and a few benthic foraminifera. Small white sections are ostracod and gastropod shells. The fine-grained matrix indicates a protected platform interior environment. Member C. Subtidal part of the Lofer cycle. Same locality as -> I . Coral floutstone. Dendroid corals (Rctioplzyllia) embedded within a bioclastic packstone matrix containing abundant fine-grained shell and coral debris. Note the difference in the composition of the matrix as compared with -> 4, indicating the existence of small coral patches in the outer zone of the platform. Member C. Subtidal part of the Lofer cycle. Late Triassic (bedded Dachstein limestone, Norian): North of Riemannhaus, Steinemes Meer, Salzburg, Austria. 1-5: Thin sections courtesy of E. Sarnankassou (Fribourg).

Plate 140: Cyclic Carbonates: The 'Lofer Cyclothem'

81 1

Fig. 16.2 D m 12 r t t i n (Lojer) cycle A: Laminated mudstone of the Intertidal Member B. The 10% es part of r he p ~ ~ t u sho r e '. ,t pelo~dalpack~tonelayer (pcllet loferite). Sand-sized particles forn~ing a gramstone texture wttrc. Jcposltcd within pocbct\ of the loferite l'iyer The grainstone is separated from an upper mudstone layer by spar-filled sheet crack\ penphcially hlled \kith recr\stj.lii~etlrnd~ax~al-t~brous cement B: Detail of -> A showing the composition of t11t _rrairirtone Lqer Gr,tln\ coinprle pelold\ n i ~ i ~ cla\ts, re coated grains and foss~lsThe lattei are represented by drfteren~txpcL\.'

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Rocks

Carbonate Reservoirs

Gravity Interpretation: Fundamentals and Application of Gravity Inversion and Geological Interpretation

Gravity Interpretation: Fundamentals and Application of Gravity Inversion and Geological Interpretation

Rocks (Geology: Landforms, Minerals, and Rocks)

Rocks

Stability Analysis and Modelling of Underground Excavations in Fractured Rocks

Geology and Hydrogeology of Carbonate Islands

Canonical correlation analysis: uses and interpretation

ECG Interpretation: From Pathophysiology to Clinical Application

Analysis and Interpretation in Qualitative Market Research

Rocks, Minerals, and Soil

Carbonate Sedimentology

Petrology of Sedimentary Rocks

Igneous Rocks and Processes

Linear models: The theory and application of analysis of variance

Nonlinear Digital Filters Analysis and Application

Rocks and Hard Places

Percolation and rocks

Microfacies of Carbonate Rocks: Analysis, Interpretation and Application