The Application of Ichnology to Palaeoenvironmental And Stratigraphic Analysis (Geological Society Special Publication No. 228)

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The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis

Geological Society Special Publications Society Book Editors R. J. PANKHURST (CHIEF EDITOR) P. DOYLE F. J. GREGORY J. S. GRIFFITHS A. J. HARTLEY R. E. HOLDSWORTH

J. A. HOWE P. T. LEAT A. C. MORTON N. S. ROBINS J. P. TURNER

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It is recommended that reference to all or part of this book should be made in one of the following ways: MclLROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228. MANGANO, M. G. & BUATOIS, L. A. 2004. Ichnology of Carboniferous tide-influenced environments and tidal flat variability in the North American Midcontinent. In: MC!LROY, D. (ed.) The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 157-178.

GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO. 228

The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis

EDITED BY

D. McILROY Sedimentology & Internet Solutions Ltd, UK

2004

Published by The Geological Society London

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Contents MclLROY, D. The application of ichnology to palaeoenvironmental and stratigraphic analysis: introduction

1

MclLROY, D. Some ichnological concepts, methodologies, applications and frontiers

3

PEMBERTON, S. G., MACEACHERN, J. A. & SAUNDERS, T. Stratigraphic applications of substrate-specific ichnofacies: delineating discontinuities in the rock record

29

GLAUB, I. Recent and sub-recent microborings from the up welling area off Mauritania (West Africa) and their implications for palaeoecology

63

GOLDRING, R., CADEE, G. C, D'ALESSANDRO, A., DE GIBERT, J. M., JENKINS, R. & POLLARD, J. E. Climatic control of trace fossil distribution in the marine realm

77

MANNING, P. L. A new approach to the analysis and interpretation of tracks: examples from the Dinosauria

93

UCHMAN, A. Phanerozoic history of deep-sea trace fossils

125

MARTIN, K. D. A re-evaluation of the relationship between trace fossils and dysoxia

141

MANGANO, M. G. & BUATOIS, L. A. Ichnology of Carboniferous tide-influenced environments and tidal flat variability in the North American Midcontinent

157

BANN, K. L., FIELDING, C. R., MACEACHERN, J. A. & TYE, S. C. Differentiation of estuarine and offshore marine deposits using integrated ichnology and sedimentology: Permian Pebbley Beach Formation, Sydney Basin, Australia

179

BALDWIN, C. T., STROTHER, P. K., BECK, J. H. & ROSE, E. Palaeoecology of the Bright Angel Shale in the eastern Grand Canyon, Arizona, USA, incorporating sedimentological, ichnological and palynological data

213

MclLROY, D. Ichnofabrics and sedimentary facies of a tide-dominated delta: Jurassic He Formation of Kristin Field, Haltenbanken, offshore Mid-Norway

237

BANN, K. L. & FIELDING, C. R. An integrated ichnological and sedimentological comparison of non-deltaic shoreface and subaqueous delta deposits in Permian reservoir units of Australia

273

BUATOIS, L. A. & MANGANO, M. G. Animal-substrate interactions in freshwater environments: applications of ichnology in facies and sequence stratigraphic analysis of fluvio-lacustrine successions

311

MELCHOR, R. N. Trace fossil distribution in lacustrine deltas: examples from the Triassic rift lakes of the Ischigualasto-Villa Union Basin, Argentina

335

GENISE, J. F., BELLOSI, E. S. & GONZALEZ, M. G. An approach to the description and interpretation of ichnofabrics in palaeosols

355

DROSER, M. L., JENSEN, S. & GEHLING, J. G. Development of early Palaeozoic ichnofabrics: evidence from shallow marine siliciclastics

383

TWITCHETT, R. J. & BARRAS, C. G. Trace fossils in the aftermath of mass extinction events

397

GENISE, J. F. Ichnotaxonomy and ichnostratigraphy of chambered trace fossils in palaeosols attributed to coleopterans, ants and termites

419

BROMLEY, R. G. A stratigraphy of marine bioerosion

455

Index

481

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The application of ichnology to palaeoenvironmental and stratigraphic analysis: introduction DUNCAN McILROY Sedimentology & Internet Solutions Ltd, 29 Proctor Road, Hoylake, Wirral CH47 4BE, UK (e-mail: [email protected])

Ichnology is the study of trace fossils, which preserve the activity of animals as recorded by their tracks, trails, burrows and borings. Rather than giving information about the taxonomic affinities of a given type of organism, trace fossils yield information about an animal's behaviour in response to its environment. Trace fossils are almost always in situ, are commonly specific to a particular suite of environmental conditions, can be readily studied in core and may be common in strata devoid of body fossils. They are invaluable in thorough sedimentological analysis and are thus of great utility to petroleum geologists, sedimentologists and palaeontologists alike. Over the last 30 years or so, ichnology has been a rapidly developing branch of palaeontology that not only has important applications in classical palaeobiology (e.g. Donovan 1994; Bromley 1996), but is also of great value in the more applied disciplines of palaeoenvironmental and stratigraphical analysis. Much progress has been made in the development of this discipline, but there remain many fascinating and challenging issues, particularly in combining ichnology and sedimentology. This book aims to provide a summary of recent progress, with an up-todate summary of most themes in modern ichnology. The volume stems from the 2003 Lyell Meeting sponsored by The Geological Society, The Palaeontological Association, BP, Shell, Exxon Mobil, Statoil, Total and Amerada Hess. The introductory paper by Mcllroy (a) provides a condensed summary of some ichnological themes and frontiers, and outlines a practical approach for the description of trace fossils and identification of key stratigraphic surfaces. The sequence stratigraphic theme is taken up by Pemberton et «/., illustrated by their work on the Mesozoic of Canada, both in outcrop and in core. The recognition of key (sequence) stratigraphical surfaces is addressed in part by the detailed studies of Bann et a/., Mcllroy (b) and Bann & Fielding in shallow to marginal marine depositional systems, and by Buatois & Mangano in their review of non-marine systems. One of the earliest applications of ichnology with widespread use was that of the ichnofacies

concept (Seilacher 1964, 1967), which was widely used to determine palaeobathymetry. Recent work detailed in the paper by Glaub extends the use of trace fossils to determine bathymetry to include microborings in shells. The use of ichnology to determine ancient nonmarine environments has been taken on in recent years largely through the work of the Argentine ichnology groups, as reviewed by Buatois & Mangano and furthered by the detailed study of lacustrine deltas by Melchor. Complementary to the ichnofacies approach to the study of trace fossils is the study of ichnofabrics as developed in sedimentary rocks. Among these, the most complex fabrics probably arise from the combination of pedogenic and biogenie processes found in soils. A new approach to the description of such complex fabrics is proposed by Genise et «/., with illustrated examples from their recent work. In addition, an ichnofabric approach to detailed facies characterization of tidal deltaic facies is adopted by Mcllroy (b). Ancient depositional environments are reviewed from the 'bottom up' from deep water environments - both oxygen rich (Uchman) and oxygen poor (Martin) - through shallow marine (Bann & Fielding) and marginal marine (Baldwin & Strother; Bann et aL\ Mangano & Buatois; Mcllroy (b)) to non-marine settings (Buatois & Mangano). Insights into the formation and preservation of fossil tracks by Manning stand to revolutionize the way that ichnologists interpret vertebrate tracks, and demonstrate how trace fossils may be used to determine the saturation of ancient non-marine deposits. The last theme addressed in the book is how trace fossil assemblages have changed through time. Evolutionary ichnofaunas are reviewed from the Cambrian by Droser et al. with respect to ichnofabrics and substrate changes, and in the aftermath of extinction events by Twitchett & Barras. Comprehensive Phanerozoic-long reviews of borers and traces of the 'denizens of the deep' are provided by Bromley and Uchman respectively. The stratigraphic record of the radiation of bees, termites, ants and other progenitors of chambered burrows is reviewed by Genise, who also organizes them into ichnofamilies.

From: MC!LROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 1-2. 0305-8719/04/S15.00 © The Geological Society of London.

2 References

D. McILROY

SEILACHER, A. 1964. Biogenic sedimentary structures. In: IMBRIE, J. & NEWELL, N. (eds) Approaches to BROMLEY, R. G. 1996.Trace Fossils: Biology, Taphon-Paleoecology. Wiley, New York, 296-316. omy and Applications. Chapman & Hall, London. SEILACHER, A. 1967. Bathymetry of trace fossils. DONOVAN, S. K. (ed.) 1994. The Palaeobiology of Trace Marine Geology, 5, 413^28. Fossils. Wiley, Chichester.

Some ichnological concepts, methodologies, applications and frontiers DUNCAN McILROY Sedimentology & Internet Solutions Ltd, 29 Proctor Road, Hoylake, Wirral CH47 4BB, UK (e-mail: [email protected]) Abstract: Ichnology straddles the boundary between palaeontology and sedimentology, and is becoming an increasingly important tool in both fields. For the palaeontologist, trace fossils allow insight into behaviour and biomechanics of animals that would otherwise be the subject of conjecture. For the sedimentologist, trace fossils have a marked impact on the interpretation of sedimentary rocks in that they destroy primary sedimentary structures, but can also reveal subtle palaeoenvironmental information beyond the resolution attainable by analysis of primary physical sedimentary structures. This contribution aims to review the major developments in the field of ichnology, and to highlight some of the tools and approaches currently used by ichnologists. A personal ethos for the study of trace fossils in core is outlined as a model ichnological protocol, and some of the frontiers of the science as a whole are briefly discussed.

Some landmarks in the history of ichnological research From nomenclatural chaos to stability (ICZN) Structures that we now recognize as trace fossils have been recorded and named in the literature for centuries. In the early history of palaeontology, a profusion of names was created for shapes preserved in rocks. In many subdisciplines of palaeontology, resolving these early names was a comparatively simple process. For ichnologists, however, sifting through the plethora of names of taxa commonly misidentified as sponges, seaweeds and plants has been a monumental task. The individual to whom we owe the greatest debt is Hantzschel (1962, 1965, 1975) for his monographic works on the numerous synonymies of many forms that were originally poorly documented and illustrated. The task of ichnotaxonomy was made even more difficult by the International Zoological Congress (to whom all taxonomists look for guidance in taxonomic procedure), who initially insisted that, to be valid, all trace fossil names erected after 1930 were to be accompanied by a statement identifying the trace-making animal (ICZN 1964). The net effect of this was to render most post-1930 trace fossil names invalid. This is because ichnologists can seldom identify trace-making organisms; indeed a single trace may be made by many different taxa and - in the case of compound trace fossils - a single trace may be the work of several organisms (e.g. Pickerill & Narbonne 1995; Rindsberg & Martin 2003).

The approach taken by most ichnologists in response to the 1964 decision of the ICZN was to continue to apply the rules of the ICZN without the blessing of officialdom. However, in anticipation of a revised version of the ICZN, Sarjeant & Kennedy (1973) published a draft proposal for a separate ichnological code, adapted from the ICZN and its sister publication, the ICBN (International Code for Botanical Nomenclature). A less radical approach was taken by Hantzschel & Kraus (1972) and Sarjeant (1979), who proposed specific amendments to the pre-existing ICZN, which were eventually integrated into the subsequent version (Melville 1979; ICZN 1985) despite some fierce opposition to the inclusion of non-reproducing forms (e.g. Lemeche 1973). The ICZN (1985) therefore overturned the original ruling regarding the identification of trace-making organisms, rendering post-1930 ichnotaxa valid under the code regardless of whether a trace-maker could be identified, and vilifying the personal decision of most ichnotaxonomists to persist with applying the rules of the ICZN despite not being bound by them. In the most recent edition of the ICZN (1999) ichnology seems to have been largely embraced by the zoological community. Trace fossil genera (ichnogenera) established after 1999 must have a designated type species (ichnospecies) (ICZN 1999, Article 66.1); for earlier established ichnotaxa no type species need be designated but may be assigned at a later date according to the rules (ICZN 1999, Article 69). The status of ichnotaxonomy is thus now firmly established as a subdiscipline of taxonomy and - thanks to the new provisions within the

From: MclLROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 3-27. 0305-8719/04/S15.00 © The Geological Society of London.

4

D. McILROY

Table 1. The archetypal Seilacherian ichnofacies Ichnofacies

Predominant trace fossil types

Inferred control (Seilacher)

Skolithos

Vertical traces of suspension feeders

Cruziana

Horizontal and vertical deposit feeders

Zoophycos Nereites

Pervasive deposit feeders Shallow burrows with complex morphologies showing highly programmed behaviours Traces characteristically preserving scratches, mostly of suspension feeders Non-marine traces

Bathymetry (above fair-weather wavebase, FWWB) Bathymetry (between FWWB and storm wavebase, SWB) Bathymetry (shelf and slope below SWB) Bathymetry (basin-floor with turbidites)

Glossifungites Scoyenia

ICZN (1999) and the sensible taxonomic practices of ichnologists over the last 3(MK) years ichnology can only grow as a rigorous science. Among the problems that do remain is the exclusion of modern traces by the International Code of Zoological Nomenclature (ICZN 1999, article 1.2.1), which restricts the use of ichnotaxa to fossil and not to modern traces. This regulation complicates the description of modern borings and burrows, but, as such incipient trace fossils may be incomplete, some taxonomic problems may thereby be avoided. The simplest means of making comparisons between modern traces and their ancient counterparts is to use the prefix 'aff.' to denote their affinity to a trace fossil while acknowledging that modern traces have no validity under the current ICZN. A grey area also exists in defining when a modern trace becomes a trace fossil: at abandonment of the burrow, at burial, or at lithification? Other issues, particularly the exact definition of what constitutes a trace fossil, are currently under discussion (see Bertling et al. 2003). Most modern ichnologists consider rootlets and other plant traces as trace fossils, though the ICZN is reluctant to include non-animal taxa for obvious reasons. It may therefore be that the simplest solution to these issues is for a separate ichnological code to be created and given some form of approval by the ICZN and ICBN. Such issues are as yet unresolved and remain a challenge.

Ichnofacies approach The observations of Seilacher (1964, 1967) that recurrent associations of trace fossils could be recognized in the rock record represents the first widely applicable use of ichnology. Initially, six recurrent sets of trace fossils (named ichnofacies) were recognized by Seilacher (1967) and named for a characteristic trace fossil. The eponymous trace fossil need not be present for

Firm surfaces associated with incipient submarine lithification Freshwater conditions (red-bed deposition)

identification of an ichnofacies, with the types of trace fossils/feeding strategy being diagnostic. These ichnofacies are widely used in palaeoenvironmental interpretation (Table 1). The archetypal Seilacherian ichnofacies (Table 1) were based largely on assemblages of traces in a particular lithofacies and related to a bathymetric gradient from shallow Skolithos to deep Nereites ichnofacies. The Scoyenia ichnofacies was however created differently, being an environment-led definition in contrast to the other behaviourally defined ichnofacies. The recognition of these basic ichnofacies groupings was of great utility to sedimentologists as an aid to palaeoenvironmental interpretation. This work was immediately grasped by both the palaeontological and sedimentological communities, and was seminal in inspiring refined sedimentary facies models and in stimulating further classification of associations of trace fossils into additional ichnofacies. The subsequent proliferation of ichnofacies has been reviewed recently (Bromley 1996; Pemberton et al. 2001), and the most important are listed in Table 2. The controls on the distribution of ichnofacies have been conclusively demonstrated to be more than simply bathymetric (Ftirsich 1975; Ekdale et al 1984; Frey et al 1990; Bromley & Asgaard 1991; Gierlowski-Kordesch 1991; Wetzel 1991; Fig. 1), but the ichnofacies themselves retain their usefulness albeit in modified form. As can be seen from Table 2 there is no consistent ethos behind the creation of ichnofacies. The most anomalous of these are the vertebrate footprint ichnofacies and coprofacies, which are more likely to be trace fossil assemblages related to local palaeoecology and palaeobiology of producers than ichnofacies of inter-regional applicability. In addition, Bromley's proposed Fuersichnus ichnofacies has been demonstrated from a variety of non-marine environments (Buatois & Mangano 2004).

ICHNOLOGY & PALAEOENVIRONMENTAL ANALYSIS

5

Table 2. History of the development of the ichnofacies concept, highlighting the inferred palaeoenvironments of the later ichnofacies Ichnofacies

Palaeoenvironment

Author(s)

Paleodictyon and Nereites ichnosubfacies

The deep marine ichnofacies was subdivided into Paleodictyon for sand-rich proximal turbidites and Nereites for mud-rich distal turbidites

Rusophycus

Fluvial/shallow lacustrine

Fuersiehnus

Originally inferred to be representative of shallow lacustrine settings, below FWWB. Has subsequently been shown to extent to a variety of freshwater settings (Buatois & Mangano 2004) Lithic/hardground substrates Woody (xylic) substrates Freshwater shallow lacustrine and fluviatile settings

Seilacher (1974) recognizes the first subdivision of one of the archetypal ichnofacies. Building on the work of Ksiazkiewicz (1970); Crimes (1973) Bromley & Asgaard (1979) as an ichnocoenosis, and as an ichnofacies by Bromley (1996) Bromley & Asgaard (1979) as an ichnocoenosis and as an ichnofacies by Bromley (1996)

Trypanites Teredolites Redefined Scoyenia Curvolithus Psilonichnus Arenicolites Mermia Entobia Gnathichnus Termitichnus Laoporus Brasilichnium Brontopodus Caririchnium and 'Shorebird ichnofacies' Coprofacies Coprinisphaera Ophiomorpha rudis ichnosubfacies

A subset of the Cruziana ichnofacies, found in settings with high sedimentation rates. Particularly delta and fan delta deposits Coastal dunes A subset of Cruziana ichnofacies (opportunistic colonization of event beds) Lacustrine turbidites Subdivision of Trypanites (boring traces) Subdivision of Trypanites (rasping traces of organisms feeding on the surface of lithic substrates) Palaeosol ichnofacies including coprolites, rhizoliths and traces in xylic matter e.g. leaves The variety of footprint assemblages represent a diverse array of palaeoenvironments, though their facies specificity is in doubt, and the separation of Laoporus and Brasilichnium on stratigraphic grounds is not well founded Based on the distribution of various coprolite types. The facies-specificity of coprolites is in doubt and has not been widely used to date Palaeosols with insect nests Subdivision of Nereites ichnofacies proposed for channel and lobe to lobe fringe environments but is only recognized from Eocene and younger strata

The similarities between some non-marine and marine ichnofacies, as highlighted by Bromley (1996), demonstrates parallel behavioural evolution in the non-marine and marine realms, presumably due to comparable environmental controls. The notable exception is the nearabsence of a deepwater mudstone ichnofacies in non-marine settings, which is probably due - at

Frey & Seilacher (1980) Bromley et al (1984) See emendation of original definition by Frey et al. (1984); Buatois & Mangano (1995) Lockley et al. (1987) based on the earlier Curvolithus ichnocoenose of Heinberg & Birkelund (1984) Frey & Pemberton (1987) Bromley & Asgaard (1991) Buatois & Mangano (1993) Bromley & Asgaard (1993) Bromley & Asgaard (1993) Smith et al (1993), replaced by Coprinisphaera of Genise et al. (2000) Lockley et al. 1994

Hunt et al. (1994) Genise et al. (2000) Uchman (2001)

least in part - to the predominance of anoxia resulting from thermal stratification in lakes (Buatois & Mangano 2004). This increased reliance upon interpretation of sedimentary environment before ichnological characterization (subjective ichnofacies sensu Reading 1978) suggests that there is little utility in continuing to create archetypal ichnofacies - a stance

Fig. 1. Summary diagram showing current thinking on the likely distribution of the main soft/loose and firmground ichnofacies (based on Bromley 1996) and based on condition of still-stand of sea-level. Ar, Arenicolites ichnofacies; Cu, Curvolithos ichnofacies; Co, Coprinisphaera ichnofacies; Cr, Cruziana ichnofacies; Fu, Fuersichnus ichnofacies; Gl, Glossifungites ichnofacies; Ne, Nereites ichnofacies; Ps, Psilonichnus ichnofacies; Ru, Rusophycus ichnofacies; Sc, Scoyenia ichnofacies; Sk, Skolithos ichnofacies; Zo, Zoophycos ichnofacies. During marine flooding events and sea-level fall some ichnofacies become more widespread (e.g. Glossifungites ichnofacies).


7

Table 3. Characteristics that make fossils good zone fossils; the ideal zone fossil would fulfil all criteria Characteristic

Rationale

Rapidly evolving, i.e. narrow stratigraphic range Widespread distribution Good preservation potential Abundance Facies independence Easy identification

Improves resolution of biozone Eases interregional correlation Improves chances of occurrence in a given rock unit Improves chances of occurrence in a given unit Allows correlation independent of palaeoenvironment Allows use by non-experts

supported by Goldring (1993, 1995) and discussed further below in terms of ichnofabric analysis and ichnocoenoses.

robust of these have been the schemes of Crimes (1975, 1987, 1992), which included a vast dataset of Neoproterozoic to Cambrian occurrences but rely on unpublished stratigraphic inferences. The most widely used ichnozones are those based on the Neoproterozoic-Cambrian type section in southeastern Newfoundland erected by Narbonne et al. (1987). Indeed the boundary itself was defined at the junction between the Harlaniella podolica and Phycodes pedum ichnozones (Brasier et al. 1994). Other radiation events. The early terrestrialization event has the potential to yield biostratigraphic data, but such sections do not yield abundant ichnological data and there is a potential problem with likely endemicity and diachroneity of early non-marine faunas/ichnofaunas. Rapid radiation is also recorded after major extinction events (see Twitchett & Barras 2004), such as the Permo-Triassic extinction event, which is estimated to have eradicated 96% of all family-level diversity (Jablonski 1991). Importantly, however, no phylum is known to have become extinct at that particular stratigraphic level so - although there was rapid radiation - no fundamentally new body plans evolved or died out, which limits the potential usefulness of ichnostratigraphy, but the stepwise reappearance of ichnotaxa can be of stratigraphic utility (Twitchett & Barras 2004).

Ichnostratigraphy Biostratigraphy is the methodology by which stratigraphers can subdivide the rock record, and correlate from region to region using the record of evolution and extinction of fossil taxa. The basic subdivision of stratigraphic time is the zone, and the fossils that define those zones are known as zone fossils. In accordance with the criteria in Table 3, the best zone fossils are likely to be rapidly evolving organisms with a pelagic portion to their lifecycle (improves distribution), and should comprise distinctive hard body parts. Thus trace fossils generally make poor zone fossils - due largely to the benthic lifestyle of trace-making organisms - except during intervals where benthic organisms that produce distinctive burrows evolve rapidly. Convergent behavioural evolution is the norm in ichnology, which accounts for the longevity of most ichnotaxa; convergent evolution of burrowing organisms has also been demonstrated (cf. Seilacher 1994). Bio-events that have the potential to include trace fossils of biostratigraphic significance include radiation events, and the evolution of distinct tracemaking groups. Radiation events Neoproterozoic-Cambrian. The Cambrian Radiation is perhaps the most dramatic of all the radiation events in the stratigraphic record, being the period of time in which most anatomical design becomes established. Many of the taxa represented by this diversification of body form were benthic in nature, and 'experimentation' in body form and behaviour are to be expected. It is thus unsurprising that this period has been identified by a number of authors as having excellent potential for ichnostratigraphy (Crimes 1975, 1987, 1992; Alpert 1977; Fedonkin et al 1983; Narbonne et al. 1987). The most

Evolution of distinct trace-making groups Palaeozoic arthropods. One of the first direct applications of ichnology to petroleum geology was the development of an ichnostratigraphic scheme for the correlation of peri-Gondwanan shallow marine 'unfossiliferous' quartzites (Seilacher 1970, 1985, 1992, 1993; Fig. 2), which are important reservoir intervals throughout the Middle East and North Africa. The main trace fossils involved in this ichnostratigraphic scheme are ichnospecies of Cruziana and related arthropod trace fossils. Such traces are abundant both in core and in outcrop, but body fossils are notoriously rare. The concept of basing an ichnostratigraphic scheme on Lower Palaeozoic arthropod traces is thus well founded in that

8

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Fig. 2. The Cruziana ichnostratigraphy of Gondwana (redrawn from Seilacher 1992).

they are abundant and widely distributed, and the trace-makers (trilobites and other arthropods) were rapidly evolving during this phase in their history. The drawback with the use of the scheme is that the trace-making arthropods are benthic and thus prone to provincialism (cf. Magwood & Pemberton 1988). In addition, many of the characters used to define the ichnospecies upon which the scheme relies are only rarely seen in material other than the exquisitely preserved type material. The majority of material examined in the field can thus be difficult to identify by the non-expert. Trias sic—Jurassic. During the Permian through to the Jurassic footprints of the archosaurs are comparatively common, particularly in Europe (Haubold 1984), North America (e.g. Olsen 1980) and South Africa (Ellenberger et al. 1970). The rapid evolution of the archosaur faunas is reflected in their changing footprint morphologies from early (Triassic) Cheirotherium-type footprints to later (Jurassic) tridactyl footprints such as the ichnogenus Grallator. Such schemes are reliant upon an abundance of well-preserved surface tracks, and have been well calibrated by accessory biostratigraphic data (e.g. Cornet & Traverse 1975). The difficulties of recognizing surface tracks make an awareness of possible under-track artefacts an invaluable skill (Manning 2004). In particular, features such as detached heel-like structures and 'spurs' in some ichnospecies of Brachycheirotherium may be related to transmitted heel structures (see Manning 2004, figs 17c, 21b,

22c). Vertebrate footprint ichnotaxonomy is a particularly difficult field, and much work needs to be done to fully appreciate which characters are useful for ichnotaxonomy. Tertiary. The radiation of terrestrial insects is well reflected in the fossil record of their burrow chambers, which is a taxonomic character widely used to identify modern insect taxa. The radiation of insects in the Tertiary was extremely rapid, and their distribution is highly sensitive to regional climatic shifts (Genise 2004). The Insecta are widely dispersed owing to their commonly airborne adult phase, presence in a range of non-marine environments, and their easily characterized egg chambers that have a high preservation potential. The Insecta with their staggered first occurrence datums thus fit the optimal characteristics of a zone fossil (see Table 3).

Seafloor and sediment oxygenation One of the most fundamental controls on the distribution of benthic animals and their trace fossils in aqueous environments is the availability of dissolved oxygen. This may be present either in bottom waters or in porewaters, but is essential for all metazoan life. The links between ichnological/benthic macrofossil distributions and bottom water oxygenation are well established (Bromley & Ekdale 1984; Savrda & Bottjer 1987; Ekdale & Mason 1988), though recent work (Schieber 2003) has demonstrated the need for


careful assessment of apparently unbioturbated sediments through work with image analysis. Appreciation of the role of sediment anoxia in ancient successions is immature, though the impact of sediment anoxia on modern shallow marine taxa is well known (e.g. Pike et al. 2001 and references therein). Likewise, Wignall (1993) has correctly highlighted the fact that changing substrate conditions can favour depauperate ichnofaunas similar to those that typify anoxic bottom-water conditions. Sediments deposited in low-oxygen settings results are generally rich in organic carbon and thus have a high source rock potential to petroleum systems (e.g. Oschmann 199la, b; Wignall 1994). Determination of the palaeo-oxygenation of such sediments can be approached by geochemical means as well as through ichnology and palaeoecology (Wignall & Myers 1988; Wilkins et al. 1996; Wignall & Newton 2001). The organically rich nature of these facies also means that they are a potential treasure-trove of nutrients for deposit-feeding organisms (Diego & Douglas 1999). Colonization during amelioration of low-oxygen conditions by an opportunistic fauna is a common phenomenon that is documented in both modern and ancient sediments (e.g. Sagemann et al. 1991; Savrda & Bottjer 1991; Wignall & Pickering 1993; Bromley et al. 1995; Smith et al. 2000; Martin 2004; Fig. 9). Indeed, the ecology of deep-sea sites in general is now becoming much better known (e.g. Kaufmann & Smith 1997). Recent work has also highlighted the role of chemosymbiosis as a feeding strategy in such settings (Paull et al. 1984; Hovland & Thomsen 1989) and has led to the reinterpretation of some trace fossils as being the result of such behaviour (Seilacher 1990; Fu 1991).

Sequence stratigraphy Perhaps the most significant predictive stratigraphic tool developed in recent years is that of sequence (seismic) stratigraphy, which was developed by Exxon Production Research Co. in the late 1970s (Vail et al. 1977), and has since been further refined and debated (see the excellent review of Nystuen 1998). The basic model involves the recognition of unconformity-bound packages of sediment (sequences), which can be related to cycles of relative sealevel change. Within these sequences higher frequency increases in relative sea-level can be recognized (flooding surfaces), which (envelope) progradational sedimentary packages known as parasequences. The study and correlation of

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these parasequences is known as high-resolution sequence stratigraphy (Howell & Aitken 1996). The majority of integrated ichnological/ sequence stratigraphic approaches have employed the use of trace fossils, either in the recognition of key stratigraphic surfaces (e.g. Bromley & Goldring 1992; Taylor & Gawthorpe 1993; Ghibaudo et al. 1996; Oloriz & RodriguezTovar 1999; MacEachern et al. 1999; Malpas 2000; Pemberton et al. 2000; Uchman et al. 2000) or for improved broad-scale facies interpretations based on a refined ichnofacies-based approach (e.g. Vossler & Pemberton 1988; Frey & Howard 1990; Savrda 1991; Brett 1998; Siggerud & Steel 1999; Pemberton et al. 2001). Despite the firm establishment of the ichnofabric/ichnocoenosis approach to improved facies and stratigraphic analysis (Bockelie 1991; Taylor & Gawthorpe 1993; Taylor & Goldring 1993; Taylor et al. 2003; Schlirf 2003), this methodology has been underused (but see Bockelie 1991; Martin & Pollard 1996; Schlirf 2003; Mcllroy 2004). The advantage of the ichnofabric/ichnocoenosis approach is that its focus is improved characterization of facies - the fundamental building block of sequence stratigraphy - through improved understanding of trace fossil fabrics and seafloor ecology with respect to the host sediments. Once established, an ichnofabric scheme can be used to assess stacking patterns, while simultaneously enhancing ichnological characterization of key stratigraphic surfaces (Mcllroy 2004). It is regrettable that most sedimentology textbooks focus on Seilacherian ichnofacies (e.g. Frey & Pemberton 1984; Pemberton et al. 1992, 2001), rather than also encompassing the more flexible ichnofabric/ichnocoenosis approach outlined below (the notable exception being Goldring 1999). An ichnological ethos What follows is a personal approach to the study of trace fossils and ichnofabric, which is designed largely for the study of marine clastic depositional systems (the author's own main focus of research). The basic methodology is of wider application, but should be adapted to the needs of the particular ichnological/sedimentological problem addressed, e.g. non-marine terrestrial systems (see Genise et al. 2004) and carbonate systems (e.g. Curran 1994). The reader should be aware that there are many ways to approach ichnological studies, and that no single approach is correct. All have their strengths.

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Fig. 3. Comparison of two cross-bedded sandstones with the bivalve escape burrow aff. Lockeia (arrowed): (a) represents a non-marine crevasse splay sandstone from the Carboniferous of Northumberland, England (scale bar in mm); and (b) a tidally deposited sandstone Jurassic, Neuquen Basin, Argentina. Ichnotaxonomically, the two specimens are ichnologically similar but sedimentological observations allow recognition of a tidal depositional environment through tidal bundling.

Scale of observation As with most sedimentological studies, the ultimate aim of an ichnological study commonly determines the resolution at which data are recorded. For example, when looking for long timescale changes in bioturbation, in a thick, sedimentologically homogeneous Neoproterozoic-Cambrian succession, Mcllroy & Logan (1999) used decimetre-scale observations of ichnofabric index (sensu Droser & Bottjer 1986, 1989, 1991). In contrast, when studying the highly heterogeneous tidal deposits of a tidedominated deltaic system, the same author made ichnological and sedimentological observations on a centimetre scale (Mcllroy 2004). The key to producing scientifically valid, usable, data is thus to choose an appropriate scale at which to collect ichnological and sedimentological data. The constraints are commonly time available (often a problem when working to industry deadlines), volume of data required/desired, and the inherent variability of the sedimentary succession. Observations should of course always be made in close detail if possible, but if nothing is found in a thick package of homogeneous sand there is little advantage in making numerous statements describing the lack of sedimentological/ichnological features. A conspicuous lack of trace fossils is in itself revealing though, and an important observation in need of explanation.

Sedimentological context In getting the maximum amount of information from a sedimentary rock it is imperative that

no information is disregarded. In the same way that many sedimentologists record trace fossils as 'bioturbation', so many palaeontologists/ ichnologists record the host sediment as sandstone/shale etc. without due regard to the physical sedimentary structures contained therein (Fig. 3). The sedimentologist should look to ichnology to help understand sedimentologically homogeneous rocks (e.g. Gowland 1996; Martin & Pollard 1996; Mcllroy 2004). Likewise, the ichnologist may learn about the likely spatiotemporal distribution of ichnofabrics by full consideration of likely sandstone body geometries and stacking based on sedimentological information. Although ideally we should all be transdisciplinary geoscientists, the reality is that for most geologists collaboration and open discussion is the way forward; this is especially so between sedimentologists and ichnologists.

Quantification of bioturbation The need to quantify the extent to which animals modify sedimentary fabrics has been recognized since the early days of modern ichnology. Many attempts to produce an easy-to-use scheme for the documentation of this bioturbation have been proposed (e.g. Moore & Scrutton 1957; Reineck 1963; Howard & Frey 1975; Frey & Pemberton 1984; Droser & Bottjer 1986, 1989, 1991; Taylor & Goldring 1993). Most of these rely upon estimating the proportion of sedimentary fabric/laminations destroyed by the burrowing activity of animals (i.e. bioturbation). These need to quantify the fabric as seen in vertical cross-section is a bias introduced by the predominance of studies of shallow box


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Fig. 4. Ichnofabric indices exemplified by flashcards according to the scheme of Droser & Bottjer (1989); redrawn with permission. Shows the proportions of sediment reworked by bioturbation as seen in vertical cross-section.

cores (modern sediments) and sediment/rock cores (e.g. in oil field studies). The most usable of these schemes is the semiquantitative flashcards of Droser & Bottjer (1986, 1989, 1991; Fig. 4), which have been used with success by a number of authors (e.g. Droser & O'Connell 1992; Mcllroy & Logan 1999). This approach has recently been extended to include a flashcard methodology for quantification of the extent of bioturbation on bedding planes (Miller & Smail 1997; Fig. 5). A similar, but more sophisticated, means of graphically representing quantitative and semi-quantitative aspects of trace fossil fabrics in vertical section has been proposed by Taylor & Goldring (1993), and is discussed in detail below (Fig. 6).

Ichnofabric analysis The component of a sediments texture created by the action of animals is known as its ichnofabric. Ichnofabric may be created either by bioturbation (in loose sediment) or by bioerosion (in lithified sediment) by a diverse array of organisms from microbes (e.g. Glaub 2004; Fig. 7a) to dinosaurs (e.g. Manning 2004; Fig. 7b). One of the features of trace-making organisms is that they are commonly highly sensitive to their environment and can thus provide a record of

Fig. 5. Flashcards showing the proportion of bedding planes covered by trace fossils from Miller & Smail (1997), as classified into 'bedding plane bioturbation indices'. Column A represents example bedding planes covered by trace fossils of even size and shape with even distribution; Column B represents example bedding planes covered by trace fossils of different sizes and shapes and with uneven distributions (redrawn with permission).

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Fig. 6. Example of a modified ichnofabric constituent diagram adapted from Taylor & Goldring (1993) expressing the ichnofabric of an outcrop from the Lajas Formation, Neuquen Basin, Argentina. Ast, Asterosoma; Pa, cf. Parahaentzchelinia; Th, Thalassinoides. Note that the horizontal scale is used at the base of the diagram, which is the author's personal preference.

palaeoenvironmental conditions before, during and after deposition of a bed (Fig. 8). When considering physical sedimentary structures alone, information can be gleaned only about conditions at the time of deposition, which in many cases (e.g. hurricane-deposited sandstone beds on the normally quiescent proximal shelf) can be anomalous. The modern sedimentologist should therefore not only be able to record the presence of bioturbation but also be able to combine information from sedimentary structures and other macro/micropalaeontological data in

order to fully characterize their facies and understand their palaeoenvironment of deposition. As discussed above, ichnofabrics are best investigated on a bed-by-bed scale, which normally requires sedimentary logging at a scale of at least 1:50. The features of ichnofabric that should be recorded during routine investigation of sedimentary rocks include: intensity of bioturbation; diversity; relative abundance;

Fig. 7. Different scales of ichnofabric development: (a) artificial casts of microborings similar to Fasciculus in a shell clast (Recent of Mauritania courtesy of I. Glaub); (b) vertical cross-section through a dinosaur track showing bioturbation by a large bipedal dinosaur from the Jurassic Scalby Formation of Yorkshire, UK ('dinoturbation' of some authors) (courtesy of P. Manning).


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Fig. 8. Cored section with Diplocraterion parallelum seen in (a) longitudinal and (b) transverse cross-sections. The greatly different proportions of the cut surface covered by traces is dependent on the section taken. The percentage by volume of core bioturbated is in both cases c. 40%.

ichnometry; infaunal tiering; succession of bioturbation; colonization styles. Intensity of bioturbation Sedimentologists should approach this using one of the many 'bioturbation index' schemes as

described in the section above. The present author recommends either the ichnofabric index schemes of Droser & Bottjer (1986, 1989, 1991), or bed-by-bed estimation of bioturbation as a percentage. It is emphasized, however, that the parameters outlined below should also be investigated in order to make the most of the available ichnological data. It must also be remembered

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Fig. 9. Example ichnofabrics as developed under a range of palaeoenvironmental and sedimentological conditions.

that ichnofabric is a 3D phenomenon, and that examination of a 2D surface (e.g. a cut surface of a core) can be misleading; if possible, an impression of ichnofabric in the opposite plane should be sought in order to estimate the percentage bioturbation as a volume (see Fig. 8). Diversity Ichnological diversity is comparatively simple to measure from both core and outcrop sections, with experience. The number of trace fossils

present within a rock unit can be simply quantified, though care must be taken (especially in core) to ensure that a single trace in different orientations (e.g. different cross-sections of the same trace) is not counted twice. Although trace fossil diversity cannot be directly related to biological diversity it is usually considered as a reasonable proxy. For example, a diverse fauna of shallow infaunal bivalves may only produce two trace fossils (Lockeia as the resting trace and Protovirgularia as the locomotory


trace). In most cases, however, high ichnological diversity corresponds to amenable palaeoenvironmental conditions, and low diversity or lack of bioturbation to harsh palaeoenvironments. The exact causes of environmental stress are diverse and must be assessed on a case-by case basis using ichnological, palaeontological, sedimentological and sometimes geochemical/ palynological means. It is also observed that ichnological diversity is more difficult to assess in core materials where identification below the level of ichnogenus is seldom possible and the morphology of complex branching forms is difficult if not impossible to recognize (except on the limited number of bedding surfaces). Relative abundance Merely presenting the number of different trace fossils present within a rock unit can be a misleading piece of information where the assemblage is dominated by a single ichnotaxon with minor accessory components. Documentation of the relative volumetric proportions of all traces within an ichnofabric and their relative chronology is the fundamental procedure behind good ichnofabric analysis. This can be particularly instructive if combined with simple

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(but tentative) interpretation of the likely trophic niche of the trace-maker. Ichnometry In addition to documenting the diversity and abundance of traces, the dimensions of the burrows themselves can be of great importance. The parameter that is most easily recorded is burrow diameter. Studies have shown that trace fossils become narrower with increased salinity stress (Hakes 1976; Gingras et al 1999) and decreasing dissolved oxygen in porewaters/ bottom waters (e.g. Bromley & Ekdale 1984). This reflects well-known biological trends in such settings (e.g. Milne 1940; Remane & Schlieper 1971). In addition, during some periods of rapid evolution there is a stratigraphic component, in which burrow size increases with time, e.g. the Cambrian explosion (Mcllroy & Logan 1999). Infaunal tiering The distribution of organisms (and their traces) below the sediment is known as tiering. The preservation of a tiering profile is reliant upon rapid killing off of the community (e.g. burial under an event bed or death of the community

Fig. 10. Ichnofabrics in outcrops of the Pacoota Sandstone, Amadeus Basin, central Australia showing: (a) environmental deterioration represented by a decrease in burrow size of Skolithos', (b) development of an early Arenicolites-dommated ichnocoenosis (Arenicolites ichnofacies) cross-cut by a later, Skolithos-domm&ted, ichnocoenosis (Skolithos ichnofacies). The upper bed probably represents a single spatfall as all burrows are the same (small) size. The small size of traces may represent burrows of juveniles buried during a phase of gradually increasing bioturbation.

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due to an anoxic event), because - with continuing deposition - deeper burrows tend to overprint shallower ones (Fig. lOb). This tiering of the infaunal community is typically considered to be a response to partitioning of the infaunal realm into different niches occupied by organisms with different feeding strategies (Bottjer & Ausich 1982; Bromley 1990, 1996; Wetzel & Uchman 1998). The occupants of these different niches, which share similar feeding strategies, have been grouped into 'ichnoguilds' by Bromley (1990), though these rely to a large degree on interpretation of behaviour, which is notoriously difficult to determine with accuracy for most trace fossils. Diagrammatic representation of tiering may be done using either the tiering diagrams of Bromley (1996, p. 295, fig. 12.11) and Wetzel & Uchman (2001) or the more integrated ichnofabric constituent diagrams (ICD) of Taylor & Goldring (1993; see the modified ICD in Fig. 6). More importantly however, several authors appear to use 'complex tiering' for all visually complex ichnofabrics (Taylor & Goldring 1993; Taylor et al. 2003). Complex ichnological tiering is defined herein as being formed

in a sediment in which the trace-making organisms are vertically partitioned into tiers containing more than one trace fossil (see Fig. 9). Multiple occupancy of a given tier should be demonstrable by mutual cross-cutting of the tier's occupant traces (see below). Succession of bioturbation Understanding the order of emplacement of burrows and tracks is a fundamental skill that all modern ichnologists should incorporate into studies aimed at palaeoenvironmental analysis. The recognition of successive cross-cutting palaeocommunities (ichnocoenoses, see below) associated with the same sedimentary unit can lead to an improved understanding of the colonization history and/or changing palaeoenvironmental conditions subsequent to the deposition of a given bed (cf. Wetzel & Uchman 2001). One of the features of such cross-cutting relationships is that later burrows or tracks tend to obscure earlier burrows, and deeper burrows tend to overprint shallower ones with continuing sedimentation (see Figs 9, lOb). In many cases one or a few trace fossils (termed elite trace

Fig. 11. Styles of colonization of sedimentary surfaces: (a) transport of adult and colonization from above; (b) spatfall; (c) equilibration and colonization from below.


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fossils by Bromley 1996) visually dominate an ichnofabric. The elite trace fossil is often produced by a late-stage bioturbator(s), or may be visually striking due to a prominent fill/burrow lining. Colonization styles The colonization of sedimentary surfaces may be achieved in a variety of ways, which can be basically summarized as being from: (a) a depositional surface; (b) an eroded surface; (c) beneath the sediment surface (usually of a migrating bedform); (d) a higher stratigraphic level (Fig. 11). Options (a) and (b) can be difficult to distinguish if the eroded sediment is unlithified and thus not a classical 'Glossifungites surface' (cf. MacEachern et al. 1992; Fig. 6). Option (c) represents the behaviour of a fauna well adapted to conditions with high sedimentation rates (cf. the mouth-bar facies of Mcllroy 2004). Colonization of sediments from a higher stratigraphic level is a common feature of turbidites (e.g. Kern 1980; Buatois & Mangano 2004), though colonization can be from below (e.g. Uchman 1995). The ecology of colonization of disturbed/ defaunated sediment has been a focus of marine ecological research for many years, and has many applications in understanding the palaeoecology of marine event beds. The colonization of marine hardgrounds is generally considered by ecologists to be largely by larval settling (Roughgarden et al. 1985). In soft marine sediments, however, colonization by larval stages is also supplemented by passive (currents) or active (locomotion) relocation of adults (Hall 1994; Snelgrove & Butman 1994; Cummings et al. 1995; Shull 1997). The potential contribution to the sediments ichnofabric of relocated adults is much greater than larval settling (spatfall; see Fig. 1 Ib), and is best developed in regions with high flow strengths where hydraulic transport of adults is common. In addition, spatfall may be seasonal in nature, in which case the colonization window (sensu Pollard et al. 1993) may be controlled by biological rather than physical phenomena. A sedimentological/ichnological description that encompasses all the points above should correspond to an excellent basis for further interpretation. The process of interpreting ichnofabrics and bioturbated sediments is an important step, which should involve careful appraisal of the succession studied. Caution should be exercised when assessing such detailed datasets, so that over-interpretation is avoided.

Fig. 12. Coarse-grained multi-storey tidal channel sandstones with rip-up clasts (upper arrow) with anomalously intense bioturbation (from arrowed surface) by Diplocraterion with a well-developed teardrop shape reflecting ontogenetic growth. From the Tilje Formation, Norwegian Shelf. Core is 10cm wide.

For example, it is well known that modern marine communities are highly patchy in distribution and not predictable relative to prevailing currents etc. This is demonstrated in the few studies of spatial distributions of ichnofaunas

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and ichnofabrics that have been performed thus far (Palmer & Palmer 1977; Goldring et al. 1998; Uchman 2001)

Ichnocoenoses The term 'ichnocoenose' was originally introduced by Davitashvili (1945) to mean the traces of a biological community or biocoenose (fide Radwanski & Roniewicz 1970); ichnocoenose in its original sense thus means the ichnological equivalent of standing crop. Terms for the buried and fossilized ichnocoenose - taphocoenose and orictocoenose respectively - were also introduced by Davitashvili (1945), but have fallen into disuse. The term 'ichnocoenosis' was subsequently independently introduced by Lessertisseur (1955) to encompass fossil assemblages of ichnotaxa equivalent to biocoenose, and was adopted in the latter sense by several authors (Hantzschel 1962; Radwanski & Roniewicz 1970). As noted by Pickerill (1992), communities can rarely, if ever, be recognized in the fossil record, owing to the effects of time averaging. Trace fossils - though study of their cross-cutting relationships (ichnofabric analysis) - can give a detailed impression of the work of several successive communities within a bed. It is useful, therefore, to retain ichnocoenosis as an approximation of its original meaning of the traces of a biological community. Ichnocoenoses should therefore ideally be considered as comprising a group of trace fossils that can be demonstrated - by ichnofabric analysis - to have been formed by the action of what approximates to a single benthic community or a succession of similar communities (based on Ekdale et al. 1984). The normal condition in the stratigraphic record is that beds are colonized by a succession of different communities, and that several superimposed ichnocoenoses can be recognized. Such time-averaged trace fossil fabrics are probably best known as assemblages. An ichnological assemblage is thus made up of all the trace fossils found within a given rock unit (usually a bed), regardless of their relative chronology, and may be composed of one or more ichnocoenoses. Ichnocoenoses and Seilacherian ichnofacies As highlighted by Bromley (1990, 1996), the use of ichnocoenosis as being synonymous with Seilacherian ichnofacies (Dorjes & Hertweck 1975; Frey & Pemberton 1987) is erroneous and problematic. Seilacherian ichnofacies were founded on the recognition of ichnological

assemblages, not ichnocoenoses, and it is important that the two are not confused. An element of ichnofabric analysis is needed to recognize the presence of the Arenicolites ichnofacies (Bromley & Asgaard 1991), which is commonly overprinted by the Cruziana or Skolithos ichnofacies (Fig. 11 a). A number of marine ichnofacies rely upon ichnofabric analysis to distinguish palimpsest fabrics representing different ichnofacies. Some authors, however, do not generally use these more subtle ichnofacies (e.g. Pemberton et al. 1992, 2001, who do not discuss the Arenicolites and Curvolithus ichnofacies). In addition, the use of the prefixes proximal/distal/depauperate is increasingly common (e.g. Pemberton et al. 2001; Bann & Fielding 2004; Buatois & Mangano 2004). It would seem therefore that although ichnofacies are useful as a starting point for ichnological studies - ichnologists working on shallow marine systems have outgrown ichnofacies, and indeed some ichnofacies actually hide important palaeoenvironmental information (cf. Frey & Goldring 1992). The future direction of ichnological work in the shallow marine and ultimately the non-marine is probably through the creation of bespoke ichnological models on a basin-by-basin scale, incorporating description of assemblages (cf. Fursich 1976 for discussion of assemblages) and ichnocoenoses (as resolved by ichnofabric analysis) rather than a reliance on the creation and application of ever more Seilacherian ichnofacies. The study of the non-marine is, however, still in its comparative infancy, and there is still much merit in using an ichnofacies-type approach (cf. Buatois & Mangano 2004; Genise 2004).

Ichnofabric stacking patterns as a correlative tool Having used some variety of the protocol outlined above to describe and understand the ichnology of the stratigraphic succession in question, the next challenge is to use these data in a meaningful manner. As described above, ichnocoenoses are the building block of applied ichnological studies, in both outcrop and core. In many cases beds may contain more than one ichnocoenosis - i.e. comprise an assemblage or association that makes up the sediment's ichnofabric. In core studies, ichnofabric is the most usable stratigraphic unit. In outcrop, however, where good vertical sections are not always available, associations/assemblages of interface traces and the more prominent of the pervasive traces should suffice; quantification of the ichnology is nonetheless still important.


By integrating ichnological and sedimentological data, a sedimentologist should be able to produce a refined fades model, which may then form the basis for stacking pattern analysis at a variety of scales. Through application of Walther's law (Walther 1894), trends in relative sea-level within a given sedimentary package can be established, progradational trends being recorded by deeper water facies/ichnofabrics/ associations being overlain by shallower water facies/ichnofabrics/associations (as resolved in the integrated conceptual facies/ichnofabric model). Analysis of ichnofabric stacking patterns in such a way has been used to great effect to understand complex or difficult bioturbated successions (Bockelie 1991; Taylor & Gawthorpe 1993; Martin & Pollard 1996; Mcllroy 2004) at either the sequence or parasequence scale. The methodology is identical to that used by sedimentologists in routine stratigraphic studies, but incorporates both palaeontological and sedimentological data for improved facies characterization. The above approach may also be used at a coarser scale with ichnofacies as the building blocks. Departures from the expected succession of facies predicted by applying Walther's law (Walther 1894) to the conceptual facies model need to be explained by either autocyclic or allocyclic means. The surfaces thus identified are known as key stratigraphic surfaces and are discussed below.

Recognition of key stratigraphic surfaces The recognition of key stratigraphic surfaces lies at the heart of the sequence stratigraphic approach to understanding and predicting sedimentological phenomena. The classification of such surfaces has been gradually refined, partly through the recognition of the Glossifungites ichnofacies (e.g. MacEachern et al. 1992; Pemberton et al. 2004), but also through other styles of facies dislocation (Taylor & Gawthorpe 1993; Taylor & Goldring 1993; Goldring 1999; Schlirf 2003; Taylor et al. 2003). Noteworthy phenomena are generally changes to the normal ichnological patterns of a given sedimentological succession, such as: horizons with anomalously intense bioturbation (Fig. 13); horizons with anomalously low or high ichnodiversity (Fig. 13); horizons with anomalous ichnofauna, e.g. a horizon with marine trace fossils in an otherwise non-marine succession (Fig. 13);

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horizons that, by ichnofabric/ichnofacies analysis, can be demonstrated to be host to a succession of ichnofaunas recording gradual deepening or shallowing events (Fig. 13); horizons showing anomalously large burrows that evince growth to adult size while living at a single horizon, e.g. loop-shaped Diplocraterion (Fig. 12); horizons across which there is a dislocation of facies as evinced by ichnological and/or sedimentological analysis (Fig. 6). Hypothetical model examples of the ichnological expression of key stratigraphic surfaces are by no means intended to be exhaustive. Each depositional system has its own unique character, and models such as that of Taylor et al. (2003) should be used for guidance, but departures from such idealized cases are to be expected.

Ichnological frontiers Progress As outlined above, the field of ichnology has progressed apace, especially since the early 1970s when the seminal compilations of Crimes & Harper (1970, 1977) exemplify the state of rapid advancement of the subject and the burgeoning interest in its applicability. Since the early 1970s ichnology has become increasingly relevant to a variety of related disciplines, including zoology, ecology, archaeology, geochemistry, diagenesis, sedimentology, sequence stratigraphy, petroleum reservoir characterization and petroleum exploration. In recent years the ichnological understanding of non-marine depositional systems has improved enormously, largely through the work of South American ichnological research groups (e.g. Buatois & Mangano 1993, 2004; Genise et al. 2000, 2004). There is, however, still much to do by way of integrating this improved understanding with sedimentological and sequence stratigraphic work, as outlined by Buatois & Mangano (2004).

Ichnology and the petroleum industry The most applied aspect of ichnological work involves studies that are of relevance to the petroleum industry. The utility of trace fossils stems from the comparatively simple study of ichnofabrics in core, and the excellent palaeoenvironmental information that they hold (cf.

Fig. 13. Intercalation of marine and non-marine ichnofabrics from the Cloughton Formation, Jurassic, Yorkshire Coast, UK: (a) field photograph of the interval with marine flooding and bioturbation; (b) ichnofabrics associated with the marine flooding surface; (c) ichnofabric constituent diagram of the ichnofabric in (b) above.


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Chamberlain 1978 and many authors since) is thus invaluable to industry. The demands of the modern petroleum industry on accurate characterization of facies are highly exacting. With the increased use of reservoir modelling of sedimentary facies and highly detailed petrophysical studies of reservoir units, the need for high-quality interpretation of sedimentary facies is greater than ever. If facies are misidentified, the foundation stone of most other elements of the reservoir characterization process falls down, and nasty surprises may lie in store during field development. By using all information available to interpret sedimentary facies, such risks are minimised.

the sediment, which can be involved in diagenetic reactions that may reduce porosity and permeability after diagenesis (Worden & Morad 2003). Trace fossils may also connect sand layers separated by impermeable mudstones, thereby improving reservoir characteristics (Gingras et al. 1999; Pemberton et al. 2001, 2004) and systematically clean sandstones of clay (Frey & Wheatcroft 1989; Prosser et al 1993). Recent experimental ichnology has also demonstrated that clay mineral authigenesis can occur in the guts of organisms, making the clay mineral assemblage of sediments metastable, and thereby influencing the of creation of clay mineral cements upon burial (Mcllroy et al. 2003).

Facies characterization The use of ichnology to characterize sedimentary facies is well developed in shallow and marginal marine depositional systems (e.g. Bockelie 1991; Mcllroy 2004) but is much less so in the nonmarine (see the recent inroads made by Genise 2004; Buatois & Mangano 2004), where depositional systems are much more variable and prone to the variable effects of climate and the preservation potential of many trace fossils is comparatively low. Future work on non-marine ichnology should work towards incorporating animal and plant trace fossils (Bockelie 1994) in sedimentological and sequence stratigraphic models. In recent years much exploration effort has been directed toward deep water turbidite plays, e.g. Gulf of Mexico, west of Shetland, west of Africa. This trend has been reflected in the increased research into characterization of turbidite architectural elements. These data have not, however, been well integrated with ichnological studies despite there being many ichnologists specializing in the ichnology of deep marine facies. The potential for combination studies involving sedimentology and ichnology alongside data from provenance techniques, palynological techniques (biostratigraphic and palynofacies; see MacEachern et al. 1999) and geochemical techniques (especially in carbonates) is massively underused at present, and provides yet another rich source of potential information for petroleum geologists to use.

New technologies Of the burgeoning technologies being developed by the petroleum industry perhaps the most exciting for the ichnologist is that downhole imaging (FMI) is now just bordering on a resolution whereby ichnology may become useful (e.g. Bourke 1992; Salimullah & Stow 1995), and can only get better. Advantages include the potential for recovery of image data down the full length of the well, which means that the sedimentologist/ ichnologist need not work exclusively on cored intervals. The image data are challenging to interpret, but ichnologists have been working with difficult sections of trace fossils in core for many years, and should be adaptable enough to exploit this potentially rich data source.

Reservoir quality Parameters of interest to the petroleum geologist are the porosity and permeability of potential reservoir intervals. These two parameters are to a large extent controlled by sedimentological heterogeneity but also by diagenesis. One feature of bioturbated sandstones is that clay-grade material is commonly mixed into the matrix of

Experimental and neoichnological studies Experimental and neoichnological studies have a rich history, including the classical studies of modern sediments of both intertidal and subtidal settings using box-coring and serial sectioning or X-ray analysis (e.g. Reineck 1958; Howard & Reineck 1972). Such techniques need to be improved and more closely related to depositional events in modern settings to facilitate more informed interpretation of ancient environments. Facilities for visualizing such data, including tomography of serial sections (e.g. Fu et al. 1994; Sutton et al. 2001), X-ray and NMR imaging techniques, have improved. In addition, time-series X-rays of ichnofabrics in laboratory experiments has never been fully exploited and should be very revealing. In addition, ecological information concerning infauna of many modern environments is well established and ideal for incorporation into models of ancient depositional environments (e.g. Reed 2002 on deep marine traces; Mcllroy 2004 on tidal depositional environments).

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D. McILROY

A. Martinius, P. Manning and M. Carton are thanked for their reading of an early version of this manuscript. The critical reviews of A. Uchman and M. Schlirf are acknowledged with thanks. A. Taylor and S. Gowland are thanked for discussion prior to writing of this manuscript. Statoil asa and its employees past and present are also thanked for nurturing my involvement in the challenges of the modern petroleum geologist and for presenting me with interesting and pertinent challenges over the last six years or so.

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nology and Sedimentology of Shallow to Marginal Marine Systems. Geological Association of Canada Short Course Volume 15. PEMBERTON, G. S., MACEACHERN, J. A. & SAUNDERS, T. 2004. Stratigraphic applications of substratespecific ichnofacies: delineating discontinuities in the rock record. In: MC!LROY, D. (ed.) The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 29-62. PICKERILL, R. K. 1992. Carboniferous nonmarine invertebrate ichnocoenoses from southern New Brunswick, eastern Canada. Ichnos, 2, 21-35. PICKERILL, R. K. & NARBONNE, G. M. 1995. Composite and compound ichnotaxa: a case example from the Ordovician of Quebec, eastern Canada. Ichnos, 4, 53-71. PIKE, J., BERNARD, J. M., MORETON, S. G. & BUTLER, I. B. 2001. Microbioirrigation of marine sediments in dysoxic environments: implications for early sediment fabric formation and diagenetic processes. Geology, 29, 923-926. POLLARD, J. E., GOLDRING, R. & BUCK, S. G. 1993. Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretations. Journal of the Geological Society, London, 150, 149-164. PROSSER, D. J., DAWS, J. A., FALLICK, A. E. & WILLIAMS, B. P. J. 1993. Geochemistry and diagenesis of stratabound calcite cement layers within the Rannoch Formation of the Brent Group, Murchinson Field, North Viking Graben (Northern North Sea). Sedimentary Geology, 87, 139-164. RADWANSKI, A. & RONIEWICZ, P. 1970. General remarks on the ichnocoenose concept. Bulletin de I'Academic Polonaise des Sciences, Serie des Sciences Geologiques et Geographiques, 18, 51-56. READING, H. G. (ed.) 1978. Sedimentary Environments and Facies. Blackwell, Oxford. REED, C. 2002. Lighting the mysteries of the abyss. Geotimes, 47, 24-25, REINECK, H. E. 1958. Kastengreifer und Lotrohre 'Schnepfe' Gerate zur Entnahme ungrestorter, orientierter Meeresgrundproben. Senckenbergiana Lethaea, 39, 42^8, 54-56. REINECK, H. E. 1963. Sedimentgefiige im Bereich der siidlichen Nordsee. Abhandlungen der Senckenbergischen Naturforschenden Gesellschaft, 505, 1-107. REMANE, A. & SCHLIEPER, C. 1971. Biology of Brackish Water. Wiley, New York. RINDSBERG, A. K. & MARTIN, A. J. 2003. Arthrophycus in the Silurian of Alabama (USA) and the problem of compound trace fossils. Palaeogeography, Palaeoclimatology, Palaeoecology, 192, 187-219. ROUGHGARDEN, J., IWASA, Y. & BAXTER, C,

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SAGEMANN, B. B., WIGNALL, P. B. & KAUFFMANN, E. G. 1991. Biofacies models for oxygen deficient facies in epicontinental seas: a tool for palaeoenvironmental analysis. In: EINSELE, G., RICKEN, W. & SEILACHER, A. (eds) Cycles and Events in Stratigraphy. Springer, Berlin, 542-564. SALIMULLAH, A. R. M. & STOW, D. A. V. 1995. Ichnofacies recognition in turbidites/hemipelagites using enhanced FMS images: examples from ODP Leg 129. The Log Analyst, 36, 38-49. SARJEANT, W. A. S. 1979. Code for trace fossil nomenclature Palaeogeography, Palaeoclimatology, Palaeoecology, 28, 147-166. SARJEANT, W. A. S. & KENNEDY, W. J. 1973. Proposal for a code for the nomenclature of trace fossils. Canadian Journal of Earth Science, 10, 460-475. SAVRDA, C. E. 1991. Ichnology in sequence stratigraphic studies: an example from the Lower Paleocene of Alabama. Palaios, 6, 39-53. SAVRDA, C. E. & BOTTJER, D. J. 1987. The exaerobic zone, a new oxygen deficient marine biofacies. Nature, 327, 54-56. SAVRDA, C. E. & BOTTJER, D. J. 1991.Oxygen-related biofacies in maritime strata: an overview and update. In: TYSON, R. & PEARSON, T. H. (eds) Modern and Ancient Continental Shelf Anoxia. Geological Society, London, Special Publications, 58, 201-219. SCHIEBER, J. 2003. Simple gifts and buried treasures: implications of finding bioturbation and erosion surfaces in black shales. The Sedimentary Record, 1,4^8. SCHLIRF, M. 2003. Palaeoecologic significance of Late Jurassic trace fossils from the Boulonnais, N. France. Ada Geologica Polonica, 53, 123-142. SEILACHER, A. 1964. Biogenic sedimentary structures. In: IMBRIE, J. & NEWELL, N. (eds) Approaches to Paleoecology. Wiley, New York, 296-316. SEILACHER, A. 1967. Bathymetry of trace fossils. Marine Geology, 5, 413-428. SEILACHER, A. 1970. Cruziana stratigraphy of 'non fossiliferous' Palaeozoic sandstones. In: CRIMES, T. P. & HARPER, J. C. (eds) Trace Fossils. Geological Journal Special Issue, 3, 447-476. SEILACHER, A. 1974. Flysch trace fossils: evaluation of behavioural diversity in the deep-sea. Neues Jarbruchfur Geologic und Paldontologie Monatshefte, 4, 233-245 SEILACHER, A. 1985. Trilobite palaeobiology and substrate relationships. Transactions of the Royal Society of Edinburgh, 76, 231-237. SEILACHER, A. 1990. Aberrations in bivalve evolution related to photo- and chemosymbiosis. Historical Biology, 3, 289-311. SEILACHER, A. 1992. An updated Cruziana stratigraphy of Gondwanian Palaeozoic sandstones. In: SALEM, M. J. (ed.) The Geology of Libya. Elsevier, Amsterdam, 1565-1580. SEILACHER, A. 1993. Problems of correlation in the Nubian Sandstone facies. In: THORWEIHE, U. & SCHANDELMEIR, H. (eds) Geoscientific Research in Northwest Africa. Balkema, Rotterdam, 329-333. SEILACHER, A. 1994. How valid is Cruziana stratigraphy? Geologische Rundschau, 83, 752-758.

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VAIL, P. R., MITCHUM, R. M. et al. 1977. Seismic stratigraphy and global changes of sealevel. In: Pay ton, C. (ed.) Seismic stratigraphy: Applications to Hydrocarbon Exploration. American Association of Petroleum Geologists, Memoirs, 26, 49-212. VOSSLER, S. M. & PEMBERTON, S. G. 1988. Skolithos in the Upper Cretaceous Cardium Formation: an ichnological example of opportunistic ecology. Lethaia, 21, 351-362. WALTHER, J. 1894. Einleitung in die Geologic als Historische Wissenschaft, Bd. 3. Lithogenesis der Gegenwart. G. Fischer, Jena, 535-1055. WETZEL, A. 1991. Ecologic interpretation of deep-sea trace fossil communities. Palaeogeography, Palaeoclimatology, Palaeoecology, 85, 47-69. WETZEL, A. & UCHMAN, A. 1998. Deep-sea benthic food content recorded by ichnofabrics: a conceptual model based on observations from Paleogene flysch, Carpathians, Poland. Palaios, 13, 533-546. WETZEL, A. & UCHMAN, A. 2001. Sequential colonization of muddy turbidites in the Eocene Beloveza Formation, Carpathians, Poland. Palaeogeography, Palaeoclimatology, Palaeoecology, 168, 171186. WIGNALL, P. B. 1993. Distinguishing between oxygen and substrate control in fossil benthic assemblages. Journal of the Geological Society, London, 150, 193-196. WIGNALL, P. B. 1994. Black Shales. Clarendon Press, Oxford. WIGNALL, P. B. & MYERS, K. 1998. Interpreting benthic oxygenation levels in mudrocks: a new approach. Geology, 16, 452-455. WIGNALL, P. B. & NEWTON, R. 2001. Black shales on the basin margin: a model based on examples from the Upper Jurassic of the Boulonnais, northern France. Sedimentary Geology, 144, 335356. WIGNALL, P. B. & PICKERING, K. T. 1993. Palaeoecology and sedimentology across a Jurassic fault scarp, NE Scotland. Journal of the Geological Society, London, 150, 323-340. WILKINS, R., BARNES, H. & BRANTLEY, S. 1996. The size distribution of framboidal pyrite in modern sediments: an indicator of redox conditions. Geochimica et Cosmochimica Acta, 60, 38973912. WORDEN, R. H. & MORAD, S. 2003. Clay minerals in sandstones: controls on formation distribution and evolution. In: WORDEN, R. H. & MORAD, S. (eds) Clay Mineral Cements in Sandstones. International Association of Sedimentologists, Special Publications, 34, 3-41.

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Stratigraphic applications of substrate-specific ichnofacies: delineating discontinuities in the rock record S. GEORGE PEMBERTON1, JAMES A. MAcEACHERN2 & TOM SAUNDERS1 1

Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta, Canada, T6G 2E3 2 Department of Earth Sciences, Simon Eraser University, Burnaby, British Columbia, Canada, V5A 1S6 Abstract: Trace fossils represent both sedimentological and palaeontological entities, providing a unique blending of potential environmental indicators in the rock record. Trace fossils and trace fossil suites can be employed effectively to aid in the recognition of various discontinuity types and to assist in their genetic interpretation. Ichnology may be employed to resolve surfaces of Stratigraphic significance in two main ways: (1) through the identification of discontinuities using substrate-controlled ichnofacies (the firmground Glossifungites ichnofacies, the hardground Trypanites ichnofacies and the woodground Teredolites ichnofacies); and (2) through careful analysis of trace fossils in vertical (softground) successions (analogous to facies successions). Integrating the data derived from substrate-controlled ichnofacies (so-called omission suites) with palaeoecological data from vertically and laterally juxtaposed softground ichnological successions greatly enhances the recognition and interpretation of a wide variety of stratigraphically significant surfaces. When this is coupled with conventional sedimentary facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated.

Trace fossil assemblages can be employed effectively to aid in the recognition of various discontinuity types, as well as to assist in their genetic interpretations. Ichnology can be utilized to resolve surfaces that may have Stratigraphic significance in two main ways: (1) through the identification of discontinuities using substratecontrolled ichnofacies; and (2) through careful analysis of trace fossils in vertical (softground) successions (accomplished by using either ichnofacies or ichnofabric analysis). Though ichnological analysis is a valuable tool, it continues to remain highly under-utilized in most sedimentologically driven genetic stratigraphic studies. Integrating the data derived from substrate-controlled, omission-related ichnofacies with palaeoecological data from vertical ichnological successions greatly enhances the ability to recognize and interpret a wide variety of Stratigraphic surface types. When this is coupled with conventional facies analysis and sequence stratigraphy, a powerful approach to the interpretation of the rock record is generated. Trace fossils have proven to be one of the most important groups of fossils in assisting in the delineation of stratigraphically important boundaries related to genetic stratigraphy (e.g. MacEachern et al 1991, 1992, 1998, 1999b; Savrda 199la, 1991b, 1995; Pemberton et al 1992a, 2001; Taylor & Gawthorpe 1993; Pemberton & MacEachern 1995; Ghibaudo et al 1996;

MacEachern & Burton 2000; Savrda et al 2001; Taylor et al 2003) and event stratigraphy (Seilacher 1962, 1982; Vossler & Pemberton 1988; Frey & Goldring 1992; Pemberton & MacEachern 1997). Genetic stratigraphy lies at the core of three main Stratigraphic paradigms: genetic Stratigraphic sequences (Galloway 1989a, 1989b), allostratigraphy (Walker & James 1992), and sequence stratigraphy (Van Wagoner et al 1990). The recognition of Stratigraphic breaks is essential in any genetic Stratigraphic paradigm, but also is commonly a difficult task, particularly in subsurface analysis. Discontinuities may reflect processes that are external to the depositional system (allocyclic), which may initiate or terminate deposition of sedimentologically related facies successions (Walker 1990). Interpreting the origin of the discontinuity, essential to sequence stratigraphy and to genetic Stratigraphic sequences, is vital in resolving the depositional environments of associated deposits and in determining the allocyclic controls on the depositional systems. To accomplish this requires the integration of ichnofacies relationships (Pemberton et al 2001) or ichnofabrics analysis (Taylor et al 2003; Mcllroy 2004), physical sedimentology and sequence Stratigraphic techniques. Ichnofacies and reconstructed ichnocoenoses are part of the total aspect of the rock, imparted by the depositional environment, and therefore - like lithofacies -

From: MclLROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 29-62. 0305-8719/04/$ 15.00 © The Geological Society of London.

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S. G. PEMBERTON ET AL.

are subject to Walther's law. For example, isolated bored shells or clasts do not, in themselves, constitute the Trypanites ichnofacies. Rather, there must be some semblance of stratification, lateral continuity and/or vertical succession before an ichnofacies can be applied. This paper expands upon and updates the work already published in Pemberton et al. (2001).

Substrate-controlled ichnofacies and the recognition of stratigraphic discontinuities: the use of omission suites One of the most important factors in the distribution of organisms in modern environments is substrate type. In their recent review Taylor et al. (2003) summarized the different substrate types (Fig. 1) as: soupground (water-saturated mudrocks and micrites); softgrounds (muddy and micritic sediment with some dewatering); loosegrounds (sandy sediments where permanent burrows require stabilized margins); stiffground (stabilized sediment where burrows are unlined); firmground (firm dewatered, often compacted sediment); hardgrounds (lithified substrate surface; variations can be shellground, a cemented shell bed; and rockground, with tectonic omission). To this list could also be added woodgrounds (xylic substrates) and the closely related loggrounds (substrate composed of distinct logs) (Bromley et al 1984; Savrda et al 1993). Three substrate-controlled ichnofacies have been

established (Ekdale et al 1984): Glossifungites (firmground), Trypanites (hardground) and Teredolites (woodground). In clastic settings, most of these trace assemblages are associated with erosionally exhumed (dewatered and compacted or cemented) substrates, and hence correspond to erosional discontinuities. Depositional breaks, in particular condensed sections, may also be semi-lithified or lithified, presumably at their upper contacts (or downlap surfaces), and may be colonized without associated erosion. In general, however, the recognition of substrate-controlled ichnofacies may be regarded as being equivalent to the recognition of discontinuities in the stratigraphic record. Determining whether these discontinuities are autocyclically generated or allocyclically generated, and hence stratigraphically important, is considerably more problematic. Although certain insect and vertebrate burrows in the terrestrial realm may be properly regarded as firmground in character (e.g. Voorhies 1975; Fursich & Mayr 1981; Smith 1987; Groenewald et al 2001) or, more rarely, hardground suites, they have a low preservation potential and are relatively minor in the geologic record. The overwhelming majority of these assemblages originate in marine or marginal marine settings. A discontinuity may be generated in either subaerial or submarine settings, but colonization of the discontinuity is most likely to occur in association with marine influence, particularly in pre-Tertiary intervals. This circumstance has important implications for the interpretation of the discontinuity's genesis. Substrate-controlled ichnocoenoses typically cross-cut the pre-existing softground suites, and hence reflect conditions that post-date both the initial deposition of the unit and the erosion of

Fig. 1. Relationship of substrate type and the distribution of the named ichnofacies.

KEY STRATIGRAPHIC SURFACES

that unit. These omission suites actually correspond to the period of time between the erosional event (which exhumes the substrate) and final burial of the discontinuity beyond reach of the benthic community of the overlying unit. During such a hiatus infaunal organisms are free to colonize the substrates: the specific

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characteristics of the ichnofauna are thus determined by the nature of the substrate and the palaeoenvironmental conditions prevailing during the hiatus. By observing (a) the underlying and cross-cut softground trace fossil suite (contemporaneous with deposition of the underlying unit), (b) the omission suite and ichnofacies

Fig. 2. Schematic development of a Glossifungites demarcated erosional discontinuity based on the Jurassic Arab D interval in Saudi Arabia. 1: The muddy carbonate substrate is deposited and buried. 2: A transgressive surface of erosion is generated by a sea-level rise. This exposes previously deposited dewatered sediment to the sediment-water interface, where it is burrowed by firmground organisms. The burrows are filled with grainstone that is deposited on the surface as a ravinement deposit. 3: After several rises in sea-level a complex framework results that is characterized by mappable surfaces that are characterized by a Glossifungites assemblage.


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associated with the exhumed substrate and (c) the ichnocoenosis of the overlying unit, it is possible to make some interpretation regarding the origin of the discontinuity and the allocyclic or autocyclic mechanisms responsible (Fig. 2).

The Trypanites ichnofacies The Trypanites ichnofacies (Fig. 3) develops in fully lithified substrates such as hardgrounds, reefs, rocky coasts, 'beach rock' and other omission surfaces (Pemberton et al. 1980; Gruszczyhski 1986, 1998). Development of this ichnofacies therefore also corresponds to discontinuities that have major sequence stratigraphic significance. Bromley & Asgaard (1993) subdivided the Trypanites ichnofacies into two ichnofacies: the Entobia ichnofacies for rocky shorelines (see also De Gibert et al. 1998), and the Gnathichnus ichnofacies for bored shells and boulders found further offshore. Bored shells and boulders, however, are not substrates that can be correlated, because it is difficult to ascertain when the boring activity was initiated. The traces in the Trypanites ichnofacies are characterized by: cylindrical to vase, tear- or U-shaped to irregular domiciles of suspension feeders or passive carnivores; raspings and gnawings of algal grazers and similar organisms (mainly chitons, limpets and echinoids);

moderately low diversity, although the borings and scrapings of individual ichnogenera may be abundant; borings oriented perpendicular to the substrate that may include large numbers of overhangs. In contrast to the Glossifungites ichnofacies, the walls of the borings cut through hard portions of the substrate rather than skirting around them.

The Teredolites ichnofacies The Teredolites ichnofacies (Fig. 4) consists of a characteristic assemblage of borings or burrows in woody or highly carbonaceous substrates. Woodgrounds differ from lithic substrates in three main ways: They may be flexible instead of rigid; They are composed of carbonaceous material instead of mineral matter; They are readily biodegradable (Bromley et al. 1984). Such differences dictate that the means by which, as well as the reasons for which, these two types of substrate are penetrated are also different. As currents can raft woody substrates, it is important to determine whether the bored substrates are autochthonous or allochthonous. Only the autochthonous forms are true members of the Teredolites ichnofacies. These assemblages may also be important in defining sequence and

Fig. 3. Trace fossil association characteristic of the Trypanites ichnofacies.


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Fig. 4. Trace fossil association characteristic of the Teredolites ichnofacies.

parasequence boundaries (Savrda 199la). The use of bored logs to define bounding surfaces, as in the concept of log-grounds (Savrda et al. 1993) should be avoided, because it is very difficult to ascertain when the logs were bored. Such logs are clasts and should not be treated in the same manner as the Teredolites ichnofacies sensu strieto. The Teredolites ichnofacies is characterized by: sparse to profuse, club-shaped borings; boring walls that are generally ornamented with the texture of the host substrate (i.e. tree ring impressions and other xyloglyphs); stumpy to elongate subcylindrical excavations in marine or marginal marine settings; shallower, sparse to profuse non-clavate excavations (isopod borings) in freshwater settings.

The Glossifungites ichnofacies The Glossifungites ichnofacies is environmentally wide ranging, but develops only in firm, unlithified substrates such as dewatered muds or highly compacted sands (Fig. 5). Dewatering results from burial, and the substrates are made available to trace-makers if exhumed by later erosion (e.g. Pemberton & Frey 1985).

Exhumation can occur in terrestrial environments, as a result of channel meandering or valley incision; and in shallow-water environments, as a result of meandering tidal channels, tidal scour erosion, erosive shoreface retreat associated with wave ravinement, or as a result of submarine channels cutting through previously deposited sediments. Such exhumed surfaces commonly correspond to stratigraphic discontinuities, and the specific characteristics of their colonization are critical to their sequence stratigraphic interpretation (Saunders & Pemberton 1986; MacEachern et al. 1992, 1998, 1999a, 1999b; Pemberton et al. 1992b, 2001; Pemberton & MacEachern 1995; MacEachern & Burton 2000; Gingras and Pemberton 2000; Taylor et al. 2003; Mcllroy 2004). The Glossifungites ichnofacies (Fig. 6) is characterized by: vertical, cylindrical, U- or tear-shaped, commonly scratch-marked burrows and sparsely to densely branching dwelling burrows; protrusive spreite in some burrows that develop mostly through animal growth (funnel-shaped Rhizocorallium and Diplocraterion [formerlyGlossifungites})', animals that leave the burrow to feed (e.g. crabs) as well as suspension feeders; low diversity, but commonly high abundance.

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Fig. 5. The Glossifungites ichnofacies is environmentally wide ranging, but develops only in firm, unlithified substrates. (A) Develops in dewatered exhumed muds, Albian Viking Formation, Willesden Green Field, Alberta, 10-35-40-7W5, 2327m or (B) highly compacted sands. (B) Develops in compacted sandstone where an inclined Thalassinoides (T) crosscuts a lined Ophiomorpha (O) in the Price River A core. (C) Gallup Sandstone, San Juan Basin, New Mexico with multiple incision surfaces seen in the top metre of the unit.

Firmground traces are dominated by vertical to subvertical dwelling structures of suspensionfeeding organisms (Fig. 7). The most common structures correspond to the ichnogenera Diplocraterion, Skolithos, Psilonichnus, Arenicolites and unnamed flask-shaped domichnia comparable to Gastrochaenolites (Fig. 8). Dwelling structures of deposit-feeding organisms are also constituents of the ichnofacies, particularly where exhumed substrates occupied more sheltered or distal settings during colonization, and include firmground Thalassinoides, Spongeliomorpha and Rhizocorallium. More recently,

MacEachern & Burton (2000) and Savrda et al (2001) have shown omission-related firmground Zoophycos associated with discontinuities colonized in very distal settings of the shelf and slope. Caution should be exercised in distinguishing firmground assemblages from stiffground assemblages (Wetzel & Uchman 1998) that can be localized and may be related to deep tiers. In proximal, high-energy settings, the assemblages attributable to the Glossifungites ichnofacies are dominated by vertical domichnia. The presence of vertical shafts within shaly intervals is anomalous, as these structures are not capable of being maintained in soft muddy substrates. Glossifungites ichnofacies elements are typically robust, commonly penetrating 20-100 cm below the bed junction. Many shafts tend to be large in diameter (e.g. 0.5-1.Ocm), in particular Diplocraterion habichi and Arenicolites. This scale of burrowing contrasts markedly with the predominantly horizontal and diminutive ichnogenera that typify the exhumed shaly intervals. The firmground traces are generally sharp-walled and unlined, reflecting the stable, cohesive nature of the substrate at the time of colonization and burrow excavation. Further evidence of substrate resilience, atypical of soft muddy beds, is the passive nature of most burrow fills. This demonstrates that the structure remained open after the trace-maker vacated the domicile, thus allowing material from subsequent depositional events to infiltrate the open tube. The post-depositional origin of the Glossifungites ichnofacies is clearly demonstrated by the ubiquitous cross-cutting relationships with the previous softground assemblage. The final characteristic of the suite is the tendency to reflect colonization in large numbers (Fig. 7). In numerous examples, 7-15 firmground traces, most commonly Diplocraterion habichi, have been observed on the bedding plane of 9 cm (3.5 in) diameter cores, corresponding to a density of between 1100 and 2300 shafts per m2. Similar populations have been observed from the modern coast of Germany (Schafer 1972), the modern Georgia coast (Basan & Frey 1977; Morris & Rollins 1977; Pemberton & Frey 1985), and Willapa Bay (Gingras et al. 1999). Selected case studies of ichnological applications to sequence stratigraphy

Regressive surfaces of erosion (RSE) and sequence boundaries (SB) Although subaerial exposure and/or erosion during relative sea-level lowstand may produce


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Fig. 6. Trace fossil association characteristic of the Glossifungites ichnofacies.

Fig. 7. Characteristics of trace fossils that are associated with the Glossifungites ichnofacies: (A) the burrows tend to be robust, unlined domiciles; (B) are found in very high densities; (C) commonly display scratch marks; and (D) cross-cut the original softground trace fossil assemblage.

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Fig. 8. Glossifungites assemblages: (A) Skolithos from the sequence boundary at the base of an interpreted forced regression, Kaybob Field, Viking Formation, 11-35-61-20W5, depth 1759.1m; (B) Glossifungites suite of conglomerate-filled Thalassinoides, Cardium Formation, Pembina Field, 12-9-51-10W5, depth 1596.2m; (C) firmground Arenicolites marking a transgressive surface of erosion (TSE), Cretaceous Viking Formation, 07-19-62-19W5, 1652m; (D) Thalassinoides at surface in the Lower Cretaceous Dun vegan Formation, Jayar Field, 6-11-62-3W6, 2523.6m; (E) Diplocraterion at transgressive surface in the Upper Cretaceous Horeseshoe Canyon Formation in outcrops near East Coulee, Alberta; (F) Glossifungites ichnofacies consisting of Rhizocorallium excavated into offshore shales and cross-cutting a resident softground suite of Helminthopsis, Planolites, Schaubcylindrichnus, Chondrites and Zoophycos. Albian Viking Formation, Willesden Green Field, Alberta, 10-35-40-7W5, 2327m.


widespread development of dewatered, firm or cemented substrates (corresponding to regressive surfaces of erosion and sequence boundaries), most are unlikely to become colonized by substrate-controlled trace fossil suites unless the surfaces are subsequently exposed to marine or marginal marine conditions prior to burial. In most cases, deposition of significant thicknesses of non-marine strata generally precludes development of these omission suites on the RSE or SB themselves. There are a number of scenarios, however, where such discontinuities may be preferentially colonized by trace-makers of substrate-controlled assemblages. Such settings include RSE developed beneath forced regressive shorefaces, SB underlying lowstand shorefaces, SB comprising submarine canyon margins, and SB lying at the estuarine mouths of incised valleys, prior to transgressive infill. All of these settings are conducive to colonization of the discontinuity because the surfaces were excavated subaqueously in a marine or marginal marine environment. The marginal marine component of the sequence boundary within an incised valley is aerially restricted and difficult to discern from the transgressively modified sequence boundary during initial transgression. For that reason, this latter scenario is discussed in the context of amalgamated sequence boundaries and flooding surfaces (FS/SB) of incised valleys. Incised submarine canyons There are few published ichnological assessments of an ancient submarine canyon margin. Outcrops of the lower Miocene Nihotupu and Tirikohua formations in Northland, New Zealand, contain a noteworthy firmground trace fossil assemblage of the Glossifungites ichnofacies related to submarine canyon incision (Hayward 1976). The underlying Nihotupu Formation consists of volcanogenically derived siltstones, sandstones and subaqueous mass flow conglomerates, together with submarine andesite pillow-pile complexes. The underlying softground assemblage is sparse and sporadically distributed, characterized by localized individual occurrences of Thalassinoides, Planolites and Scalarituba. These deposits are interpreted as turbidites that were emplaced at bathyal water depths (based on body fossil content) within an inter-arc basin on the lower eastern flanks of the west Northland volcanic arc. The contact with the overlying Tirikohua Formation is sharp and erosional and exhibits visible relief. The exhumed substrate is demarcated by a firmground omission assemblage consisting of Skolithos, Rhizocorallium and ?Thalassinoides attributable to the Glossifungites ichnofacies.

37

Hayward (1976) interpreted the erosional discontinuity as a submarine canyon wall, excavated into bathyal to neritic inter-arc sediment gravity flow deposits as a result of basin margin tectonic uplift. Colonization of the canyon walls by the firmground trace-makers preceded the gradual burial of the canyon margins by neritic turbidite deposits of the Tirikohua Formation. The infill of the submarine canyon probably corresponds to late stage relative sea-level lowstand and early transgression. In the subsurface, examples of submarine canyon incision with the development of trace fossil assemblages of the Glossifungites ichnofacies have been recognized in the Miocene of the Nile Delta (Fig. 9). The canyon walls were excavated during lowstand incision and colonized by shrimps that constructed robust Thalassinoides. The interpretation of the surface is critical to correct correlation of the canyon fill and to the recognition of point source turbidites. Fine-grained facies outside the canyons are totally bioturbated by Phycosiphon, Planolites and Helminthoida. Similar facies within the canyon system reflect episodic mud turbidites and remain virtually unburrowed. Forced regressive and lowstand incised shorefaces Forced regressive and lowstand shorefaces constitute two sequence stratigraphic scenarios by which sharp-based shoreline sandstones may form, and both are associated with falling limbs of relative sea-level. Sharp-based shoreface sand bodies, however, have been variably assigned to the progradation of late highstand successions (e.g. Van Wagoner 1995), forced regressive (falling stage) systems (e.g. Hunt & Tucker 1992; Walker & Bergman 1993; Bergman 1994; Davies & Walker 1993), lowstand systems (e.g. Flint et al 1988; Posamentier et al 1992; Posamentier & Chamberlain 1993; Mellere & Steel 1995; Walker & Wiseman 1995), and transgressively incised complexes (e.g. Downing & Walker 1988; Raychaudhuri et al 1992; MacEachern et al 1998, 1999b). Despite the wide range of sequence stratigraphic contexts that facilitate such deposits, many workers continue to regard sharp-based shoreface sandstone bodies to be exclusively of falling stage or lowstand origin. From a facies perspective, however, the sharpbased shoreface successions generated in all three systems tracts are virtually identical. Their principal difference lies in the character of the basal contact with the underlying facies. One distinction, however, is that highstand examples overlie autocyclic basal surfaces that lack evidence of incision into and concomitant truncation of

38

S. G. PEMBERTON ET AL

Fig. 9. Glossifungites assemblage associated with submarine canyon incision, West Ahken Field, Nile Delta: (A) Skolithos filled with anomalous sediment, West Ahken-1 core, 4379.8ft; (B) sequence boundary at base of submarine canyon fill characterized by a Glossifungites assemblage with Thalassinoides, West Ahken-1 core, 4375.3ft. regional markers in the underlying succession. Such sharp-based but non-incised highstand shoreface deposits also display a genetic affinity of facies across the autocyclic basal surface that commonly corresponds to the erosional bases of individual storm beds. In contrast, forced regressive, lowstand and transgressive shorefaces overlie allocyclic discontinuities that truncate regional markers, reflecting incision into underlying units. Incised-shoreface deposits may correspond to forced regressive, lowstand or transgressively incised systems (Fig. 10). The forced-regressive shoreface overlies a regressive surface of erosion (RSE) cut by wave action during the falling stage

of relative sea-level. Likewise, the lowstand shoreline overlies the marine part of the sequence boundary (SB) and is also cut by wave erosion. The transgressively incised shoreface, however, overlies a wave ravinement surface, cut during relative sea-level rise. The wave ravinement surface commonly amalgamates with or truncates the earlier sequence boundary (FS/SB). This succession reflects a period of shoreline progradation during overall transgression, when sediment supply outpaced relative rise of sea-level. All three scenarios favour the development of substrate-controlled omission suites on the basal discontinuities, as each is excavated within a marine setting, and permit early

Fig. 10. Differentiation of forced-regressive, lowstand, and transgressively incised shoreface complexes. Sharpbased, discontinuity-bound (incised) shoreface successions can be ascribed to one of three main sequence stratigraphic settings. Model 1 reflects forced regression (falling stage), showing the initial fall of relative sea-level and the development of successive shorefaces sitting on regressive surfaces of erosion (RSE). Note that although a correlative conformity (CC) may be produced seaward of each RSE, successive sea-level fall makes these susceptible to erosional removal, and therefore they have a low preservation potential. Model 2 shows the development of the lowstand shoreface, which reflects the most seaward position of the shoreline associated with the lowest position of sea-level. Note that the erosional component of the sequence boundary extends only as far seaward as fair-weather wavebase (FWWB), where it passes into a correlative conformity (CC). In model 3, rise of relative sea-level generates a low-energy flooding surface in basinal positions that passes landward into a transgressive ravinement surface, as it floods across the lowstand and forced-regressive shorefaces. Where the surface cuts across or incises through the old sequence boundary, it produces an FS/SB. Note that the rise of sea-level drowns and preserves the CC of the lowstand shoreface. During a pause in transgression, shoreface progradation occurs, producing a transgressively incised shoreface. In basinward positions, offshore mudstones deposited below fair-weather wavebase may directly overlie the erosional component of the FS/SB because the surface was cut while sea-level occupied a lower position but deposition did not occur until after significant deepening. (Modified from MacEachern et al. 1998)

40


colonization of the exhumed substrate. Differentiation between these incised complexes is difficult, but can be achieved through careful documentation of the erosional extent of the basal discontinuity (MacEachern et al. 1999b). Considerable discussion surrounds the validity of differentiating lowstand from forced regressive deposits (e.g. Hunt & Tucker 1992, 1995; Kolla et al. 1995). The work of Helland-Hansen & Gjelberg (1994) and Mellere & Steel (1995), however, illustrates the utility of discriminating falling-stage systems tracts associated with forced regression from the final lowstand shoreline corresponding to maximum fall of sea-level, but prior to transgression. A forced-regressive or falling-stage origin has been proposed for sharp-based sandstone bodies of the Viking Formation in the Garrington Field (Davies & Walker 1993) and Kaybob Field (Pemberton & MacEachern 1995). Posamentier et al. (1992) and Posamentier & Chamberlain (1993) interpreted sharp-based sandstone deposits at Joarcam to reflect a lowstand shoreface deposit. Lowstand shoreface deposits have also been interpreted in the Lindbrook and Beaverhill Lake fields (Walker & Wiseman 1995), although their figure 6 suggests that the 'Lindbrook a' deposit probably reflects a falling-stage shoreface, given that the 'Lindbrook b' shoreface lies farther basinward and likewise overlies a regressive surface of erosion. The Judy Creek Field, which lies along strike to these deposits, contains a lowstand incised shoreface deposit as well. The differentiation between sharp-based, incised shorefaces and deltas of forced regressive versus lowstand origin, however, is problematic. Both forced regressive and lowstand shoreface deposits tend to be fairly thin, in response to the diminished accommodation space associated with relative lowstand of sea-level (Flint 1988; Posamentier et al. 1992; Van Wagoner 1995). Walker & Wiseman (1995) have further suggested that the damping of wave energy across broad shallow platforms lying outboard of these shorefaces contributes to this, because it inhibits incision into the underlying firmly compacted mud. As a result, facies tracts within these shoreface types may be attenuated or even absent. Lowstand shorefaces may be slightly thicker because they may be developed during late lowstand, where a slow rise in relative sea-level may be initiated with associated increased accommodation space. Sandbody widths and width/thickness ratios have also received some consideration as a means of discriminating between these systems, but because of the effects of such controls as variations in

sediment supply, rate of change of accommodation space, basin gradient and duration of shoreline progradation, caution must clearly be exercised. The perceived regional stratigraphic context of the sharp-based shoreface and/or delta deposits has principally been used as a basis for their interpretation. Ainsworth & Pattison (1994) have discussed the problem of attached versus detached lowstand complexes, highlighting some of the difficulties in differentiating between the two scenarios. Falling-stage (forced regressive) interpretations are most commonly based on the presence of additional incised shoreface and/or delta deposits lying basinward of them within the same sequence. Lowstand deposits, on the other hand, tend to be identified mainly on the basis of the absence of additional basinward shorefaces. Given that such deposits may be detached and lying considerably basinward, the sequence stratigraphic interpretation of these intervals may, in some cases, be highly suspect. Walker & Wiseman (1995) concede this uncertainty with respect to the Viking Formation Lindbrook shorefaces of Alberta. MacEachern et al. (1999b) have argued, however, that there are distinctive facies relationships that can also be employed in order to differentiate the various sequence stratigraphic scenarios. Forced-regressive shoreface and/or deltaic deposits overlie regressive surfaces of erosion (RSE). These surfaces are cut in submarine conditions and pass basinward into conformable surfaces analogous to correlative conformities (Fig. 10). The RSE are cut by wave erosion as relative sea-level falls, bringing more basinal facies into the zone of wave attack. Continued sea-level fall results in the subaerial exposure of the falling-stage shorefaces, and their subsequent cannibalization by later regressive surfaces of erosion and, ultimately, the sequence boundary. The preservation potential of these deposits is considerably less than that of the lowstand shoreface, and the correlative conformities of the RSE are, in particular, unlikely to be preserved in the rock record. Kolla et al. (1995) regard the RSE that bound falling-stage deposits merely as higher-order sequence boundaries reflecting incremental rather than continuous fall of relative sea-level. Lowstand shorefaces directly overlie sequence boundaries and, basinward, their correlative conformities (Plint et al. 1988; Posamentier et al. 1992). Landward of the shoreface, the sequence boundaries are cut by subaerial erosion. At the base of the shoreface, however, sequence boundaries are cut within a marine setting and therefore favour colonization by


substrate-controlled assemblages, particularly where they incise into dewatered offshore muds. As the lowstand shoreface lies in the most seaward position prior to ensuing sea-level rise, the marine expression of the sequence boundary and the correlative conformity have a high preservation potential, facilitating their differentiation from forced regressive and transgressively incised counterparts (MacEachern et al. 1999b). In weakly storm-influenced settings, the erosional component of the RSE and sequence boundaries is unlikely to persist basinward of fair-weather wavebase and therefore defines a sharp base to the lower shoreface. Basinward of this position, finer-grained offshore deposits overlie the correlative conformity and during progradation grade upwards into lower shoreface muddy sandstones. As a result, the Glossifungites ichnofacies and other omission suites are unlikely to occur in positions below fairweather wavebase. In these basinal positions, coarse-grained lag deposits are likely to be absent as well. The correlative conformity may, however, represent a sharp but depositional facies contact, marked by an abrupt change in proximality of facies, grain size and trace-fossil assemblage. In storm-dominated shorefaces, however, the extent of the allocyclically generated marine expression of the RSE or sequence boundary may be masked by autocyclic storm erosion surfaces and appear to extend to stormweather wavebase. This scenario results in the development of a series of vertically stacked and offlapping, aerially restricted autocyclic surfaces, rather than a single allocyclic surface, but recognition of this condition may be problematic unless outcrop exposure is exceptional. In the subsurface, recognition of this situation would be extremely difficult. However, these autocyclic surfaces are rapidly buried by tempestites and are therefore not readily colonized by trace-makers of substrate-controlled ichnofacies. Both forced regressive and lowstand complexes are typically sharp based in proximal positions and gradationally based in basinal positions. Consequently, only the lower shoreface, middle shoreface and upper shoreface deposits directly overlie the erosional expression of the sequence boundary or the RSE and may be demarcated by the Glossifungites ichnofacies. Landward, a ravinement surface may become amalgamated with the sequence boundary and RSE during the ensuing transgression (e.g. Flint et al. 1986; Flint 1988; Pemberton & MacEachern 1995). It appears reasonable that the correlative conformity of the RSE has an exceedingly low preservation potential in falling-stage deposits, in contrast to that of lowstand-

41

shoreface deposits. The forced-regressive deposits are subjected to subsequent erosion and subaerial exposure during continued fall of relative sea-level, as well as the potential of transgressive ravinement during ensuing rise of relative sealevel (Fig. 10). The lowstand deposits, on the other hand, are produced at the lowest position of relative sea-level fall and are unlikely to be subsequently ravined, because water depths are deepened and fair-weather wavebase shifted landward during later transgression. The presence of a correlative conformity might be taken as a significant support for a lowstand interpretation of a deposit. The subsurface Viking Formation of the Kaybob and Judy Creek fields highlights the similarities between a forced regressive shoreface succession and a lowstand one. The Kaybob Field of central Alberta contains a sharp-based, incised shoreface excavated into underlying open marine distal parasequences (Pemberton & MacEachern 1995; MacEachern & Pemberton 1997; Fig. 11). The underlying distal parasequences consist of moderately to abundantly bioturbated (BI4-5) mudstones, silty mudstones and sandy siltstones, displaying diverse trace fossil assemblages attributable to the Zoophycos ichnofacies and distal and archetypal expressions of the Cruziana ichnofacies, respectively. The parasequences reflect progradation of shelf to upper offshore cycles of an underlying highstand systems tract. The erosional discontinuity is principally demarcated by firmground omission suites of Skolithos, Diplocraterion and Thalassinoides of the Glossifungites ichnofacies (Fig. 11C, D). Where the discontinuity is excavated into sandier expressions of the underlying facies, the surface is demarcated by a palimpsest softground suite of Diplocraterion habichi and Skolithos (Fig. 11 A, B). In all cored intervals where the discontinuity is preserved, it is erosional and is overlain by silty to muddy sandstones, interpreted to reflect lower shoreface and middle shoreface deposits (Fig. 11B, D). The sandstones are moderately and sporadically bioturbated (BI 2-3), characterized by abundant, remnant hummocky cross-stratified beds separated by burrowed beds. The succession shows an upward decrease in the number and thickness of burrowed beds and a concomitant increase in the number and thickness of hummocky crossstratified beds, consistent with upward shallowing (Fig. 11 A). A fully marine, diverse, proximal expression of the Cruziana ichnofacies dominates the more thoroughly burrowed successions and passes upwards into suites consistent with the Skolithos ichnofacies. Locally, trough crossbedded sandstones containing sporadically

42


Fig. 11. Forced regressive shoreface. (A) Box shot of core from the Kaybob incised shoreface; base of the interval is to the lower left, and top to the upper right (T). The lower unit consists of bioturbated (BI5—6) silty and sandy mudstones, and (in column 4) muddy sandstones of the underlying regional Viking Formation, reflecting progradation of lower offshore, upper offshore and lower shoreface environments respectively. These are truncated by a regressive surface of erosion (RSE), and overlain by coarser-grained lower and middle shoreface laminated to bioturbated sandstones of a moderately storm-influenced shoreface. Well 11-35-61-20W5; 1757.6-1762.1 m. (B) Close-up photo of the RSE in photo A, showing a palimpsest softground suite consisting of Skolithos (S) demarcating the stratigraphic discontinuity. The incised shoreface in this locality has cut into bioturbated (BI 5) muddy sandstones with softground Ophiomorpha (O), and Palaeophycus (Pa), reflecting a proximal expression of the Cruziana ichnofacies. The overlying lower shoreface sandstones of the forced regressive shoreface contain sideritized mudstone rip-up clasts and Palaeophycus (Pa). Well 11-35-61-20W5, 1759.2m. (C) Box shot of core from the Kaybob incised shoreface in a position more distal than that of photo A. Base of the interval is to the lower left, and top to the upper right (T). The lower unit consists of bioturbated (BI 5-6) silty and sandy mudstones of the underlying regional Viking Formation, reflecting progradation of lower to upper offshore environments. These mudstones are truncated by an RSE, and overlain by lower shoreface muddy sandstones, passing into middle shoreface sandstones. Well 10-15-6219W5; 1667.3-1673.0m. (D) Close-up photo of the RSE in photo C, showing nrmground Thalassinoides (Th) of the Glossifungites ichnofacies demarcating the discontinuity. The discontinuity in this position is incised into bioturbated (BI 6) sandy mudstones containing the archetypal Cruziana ichnofacies with Phycosiphon (Ph) and Chondrites (Ch). The overlying lower shoreface muddy sandstone contains a proximal expression of the Cruziana ichnofacies with Diplocraterion (D) and Palaeophycus (Pa). Well 10-15-62-19W5, 1671.8m.


distributed assemblages of the Skolithos ichnofacies may directly overlie the sequence boundary or grade upward from the middle shoreface sandstones, and are interpreted as upper shoreface deposits. The upper contact of the succession is truncated and, locally, cemented with haematite-stained siderite, interpreted to reflect subaerial exposure. In basinward positions, where one might expect to find the offshore sandy mudstones and siltstones equivalent to the Kaybob lower shoreface sandstones, the interval has been removed by later cycles of incision. The basal discontinuity is not preserved seaward of fairweather wavebase, making sequence stratigraphic interpretation of the surface and therefore of the overlying deposit problematic. The succession is consistent with an incised shoreface, but whether forced regressive, lowstand or transgressively incised cannot be unequivocally demonstrated on the basis of the deposits themselves. The presence of additional shorefaces lying basinward of the Kaybob deposit strongly suggests that the deposit cannot reflect the lowstand shoreface of the sequence (Fig. 10). Furthermore, preferential removal of the discontinuity in a seaward position would be difficult to accomplish during transgression, and appears inconsistent with observed relationships in transgressively incised examples (e.g. Downing & Walker 1988; Raychaudhuri et al. 1992; MacEachern et al 1998, 1999b). Additionally, the iron-stained, siderite cemented sandstone at the upper truncated margin of the interval is consistent with continued relative sea-level fall, exposure and subaerial erosion of a forced regressive shoreface. As such, the basal discontinuity is interpreted to reflect a regressive surface of erosion (RSE). By comparison, further basinward of the Kaybob forced regressive shoreface lies an incised shoreface sandstone in the Judy Creek Field. In contrast to the more storm-influenced successions of the Kaybob deposit (MacEachern & Pemberton 1992), the Judy Creek deposit is weakly storm affected and is characterized by thoroughly bioturbated (BI5), pebble- and granule-bearing sandy mudstones, muddy sandstones and silty sandstones of the upper offshore, lower shoreface and middle shoreface respectively (Fig. 12). Bioturbation within these facies is generally uniformly distributed. All facies contain highly diverse trace fossil assemblages. The upper offshore sandy mudstones display suites consistent with the archetypal Cruziana ichnofacies. The lower shoreface muddy sandstones contain trace fossil assemblages corresponding to proximal expressions of the Cruziana ichnofacies.

43

The middle shoreface silty sandstones, however, contain trace fossils recording a distal expression of the Skolithos ichnofacies. The Judy Creek incised shoreface deposits clean and coarsen upward, and erosionally overlie the distal counterparts of the same shelf to offshore parasequences truncated by the landward-lying Kaybob forced regressive shoreface. The erosional discontinuity is locally demarcated by well-developed firmground Thalassinoides and less commonly by Spongeliomorpha, attributable to the Glossifungites ichnofacies. In all cored intervals containing an erosional expression of the discontinuity, the overlying facies comprise bioturbated muddy sandstones or silty sandstones, interpreted to reflect deposition above fair-weather wavebase (Fig. 12A, B). In the few instances, however, where the Judy Creek deposit is initiated by upper offshore sandy mudstones, the bounding surface shows no evidence of erosional truncation of the underlying parasequences (Fig. 12C, D). This is significant, as it records the character of the bounding surface in positions below fair-weather wavebase. This non-erosional surface shows an increase in grain size associated with progradation of the Judy Creek incised shoreface, but lying seaward of erosional modification by waves. The surface in this position is interpreted as the preserved correlative conformity of the discontinuity lying landward beneath the incised shoreface sensu stricto (Fig. 12D). In even more distal positions the correlative conformity is difficult to identify, and the succession appears to reflect simple progradation. The correlative conformity survived in this position because, after this cycle of progradation, relative sealevel rose again, thereby flooding the area and causing erosional back-stepping of the shoreline. This is consistent with a lowstand shoreface interpretation, and indicates that the underlying erosional discontinuity corresponds to the sequence boundary, rather than the RSE of a forced regressive shoreface (Fig. 10).

Transgressive surfaces Transgressive surfaces are manifest by (1) mainly non-erosional marine flooding surfaces (MFS) and bay margin flooding surfaces, and (2) lowrelief, erosional (ravinement) surfaces. The ravinement surfaces may be produced by either wave or tidal scour processes, and are referred to as transgressive surfaces of erosion (TSE). Analysis of transgressive surfaces of erosion has had a relatively long history since Stamp (1921) originally defined the term 'ravinement'. A

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Fig. 12. Lowstand shoreface. (A) Box shot of core from the Viking Formation incised shoreface at Judy Creek. Base of the interval is to the lower left, and top to the upper right (T). In this proximal position, bioturbated silty mudstones of the regional Viking parasequences, interpreted as lower offshore deposits, are incised into by moderately to intensely bioturbated (BI4—5) silty sandstones of the Judy Creek lowstand shoreface. The discontinuity is interpreted as a sequence boundary (SB). Well 02/10-19-63-11W5; 1423.4-1427.1 m. (B) Box shot of core from the Viking Formation incised shoreface at Judy Creek, slightly distal of that in photo A. Base of the interval is to the lower left, and top to the upper right (T). The interval shows storm-influenced lower offshore silty mudstones with rare tempestites (lower offshore) incised into by bioturbated (BI 5) muddy sandstones of the Judy Creek lowstand shoreface. The discontinuity (SB) corresponds to the same sequence boundary in photo A. The Judy Creek shoreface sandstones in this position are muddier than those of photo A, and reflect lower shoreface deposition. Well 12-26-63-11W5; 1453.3-1457.6m. (C) Box shot of core from the Viking Formation incised shoreface at Judy Creek, distal of the position indicated in photo B. Base of the interval is to the lower right (B), and top to the upper left (T). The succession shows shelf through upper offshore mudstones at the base, sharply overlain by coarser-grained upper offshore sandy mudstones and muddy sandstones of the Judy Creek lowstand shoreface. The sharp contact corresponds to the correlative conformity (CC) of the sequence boundary present in photos A and B. Well 10-35-64-13W5; 1482.3-1486.7 m. (D) Close-up of the correlative conformity (CC) in photo C, separating a finer-grained sandy mudstone facies below from a pebble bearing (Pe), coarser-grained sandy mudstone above. Both facies contain an open-marine, archetypal Cruziana assemblage with Helminthopsis (H), Terebellina (T), Planolites (P), Phycosiphon (Ph), and Asterosoma (As), interpreted to reflect upper-offshore environments. Well 10-35-64-13W5; 1483.0m. number of landmark papers have discussed the characteristics and implications of ravinement surfaces, particularly with respect to their processes of formation, their depths of incision, the interplay of rate of relative sea-level rise with

pre-existing topography and shoreface depth on the preservation potential of coastal-plain deposits, surface diachroneity and associated facies (e.g. Fischer 1961; Swift 1968; Belknap & Kraft 1981; Pilkey et al 1981; Nummendal & Swift


1987). MacEachern et al. (1992) discussed the ichnological suites associated with ravinement surfaces and their associated facies. Marine flooding surfaces Marine flooding surfaces (MFS) are typically abrupt contacts across which there is evidence of an increase in water depth. These surfaces are mantled with dispersed sand, granules or intraformationally derived rip-up clasts, indicating some erosion. The preservation of underlying markers indicates, however, that the degree of erosion is minimal. MFS are typically characterized by the abrupt juxtaposition of offshore, shelf or prodelta shales onto shallow marine sandstones, and are easily identified on geophysical well logs. Such surfaces may demarcate parasequence boundaries, parasequence sets or even systems tracts, depending upon their regional extent (Bhattacharya 1993). The Lower Cretaceous Viking Formation in western Canada contains numerous MFS separating coarsening-upward, regionally extensive parasequences. These parasequences are interpreted to reflect shelf through distal lower shoreface progradation under fully marine conditions. Three facies comprise a complete coarsening cycle, although the minor cycles rarely comprise a complete cycle. The basal facies consists of intensely bioturbated (BI5) silty mudstone. Trace fossils are uniformly distributed and diverse (eight ichnogenera), constituting the archetypal Zoophycos ichnofacies to a distal expression of the Cruziana ichnofacies. Bioturbated sandy mudstone facies grade upward from the silty mudstones and are intensely burrowed (BI5) with a uniformly distributed and highly diverse suite (18-21 ichnogenera) of the archetypal Cruziana ichnofacies. Muddy sandstone facies grade upward from the sandy shale facies and are intensely bioturbated (BI5) with a diverse (18 ichnogenera) and uniformly distributed, proximal expression of the Cruziana ichnofacies. The cycles reflect coarsening upward of facies associated with shoaling, under fully marine conditions, developed during a highstand systems tract. The marine flooding surfaces (MFS) in the major cycles are commonly marked by the return to lower offshore or shelf deposition, and are typically abrupt (Fig. 13A). These flooding surfaces are rarely significantly disrupted by the diminutive trace-makers that characterize the lower offshore and shelf settings. In other cases, cycles may show considerable biogenic modification of the MFS or transgressive surface of erosion (TSE), particularly where lower shoreface deposits are overlain by upper offshore

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sandy mudstones (Fig. 13B). Such contacts may appear gradational, owing to the biogenic homogenization of the surface by the more robust and penetrative trace-makers common in these settings. Elsewhere, the upward transition from shallow to deeper water deposits may occur over intervals of several decimetres or more, reflecting very gradual relative sea-level rise. Similar stacking of such coarsening upward, but thoroughly bioturbated, parasequences separated by pronounced marine flooding surfaces occurs in the Early Permian of the Sydney Basin (Bann 1998; Bann et al. 2004), the Jurassic Heather Formation of the Norwegian North Sea (MacEachern & L0seth 2003), and the Turonian Cardium Formation of Alberta (Vossler & Pemberton 1988, 1989). Transgressive surfaces of erosion Transgressive surfaces of erosion (i.e. ravinement surfaces) afford the most elegant manner of generating widespread substrate-controlled trace fossil assemblages and palimpsest softground suites, because the exhumed surfaces are both widespread and produced within a marine or marginal marine environment. This favours colonization by organisms as the ravinement surface is excavated prior to accumulation of significant thicknesses of overlying sediment (MacEachern et al. 1992a,b; Pemberton & MacEachern 1995). The upper portion of the Albian Viking Formation in the subsurface of central Alberta contains numerous transgressive surfaces of erosion (TSE), recording a complex history of transgression, which culminated in maximum flooding of the Western Interior Seaway. Bann (1998) and Bann et al. (2004) have assessed the ichnological characteristics of TSE from the Early Permian Pebbley Beach Formation of the Sydney Basin and found comparable characteristics to those of the Mesozoic successions of the Western Interior Seaway. The recognition of discrete TSE is difficult on the basis of sedimentology alone, particularly when dealing with the upper Viking Formation, where there exist abundant, sharp-based pebble stringers and thin, trough cross-stratified, coarse-grained sandstones, intercalated with interbedded sandstones, siltstones and shales. A few of these coarse stringers could reflect the veneer on transgressive ravinement surfaces, but owing to their abundance it is difficult to pick those that have regional stratigraphic significance. Similar complexities have been encountered in the Early Permian Pebbly Beach Formation of the Sydney Basin, Australia (Bann 1998), the Middle Jurassic Oseberg Formation (Soegaard & MacEachern 2003),

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Fig. 13. Marine flooding surface/transgressive surface of erosion. (A) Non-erosional marine flooding surface (MFS) separating upper offshore sandy mudstones below from lower offshore/shelf silty mudstones above. The sandy mudstones contain the archetypal Cruziana ichnofacies, with Palaeophycus (Pa), Diplocraterion (D), Asterosoma (As), Planolites (P), Phycosiphon (Ph), Teichichnus (Te) and Rosselia (Ro). The overlying silty mudstones contain a distal expression of Cruziana ichnofacies and show Phycosiphon (Ph) and Teichichnus (Te) Well 12-17-39-27W4; 1604.6m. (B) Bioturbated transgressive contact with palimpsest softground Thalassinoides (Th), subtending into muddy sandstones of the lower shoreface, abruptly overlain by gritty, pebble (Pe) bearing sandy mudstones and silty mudstones with thin tempestites. The contact probably reflects a TSE with only minor erosion. The underlying muddy sandstones contain a proximal suite of the Cruziana ichnofacies with Skolithos (S), Asterosoma (As), Planolites (P), and Phycosiphon (Ph). The overlying mudstones display the


and the Tarbert and Heather formations (MacEachern & L0seth 2003) of the Norwegian North Sea. However, in each of these units, virtually every TSE incised into, or ravined across, shaly sediments exhibits an omission suite attributable to the Glossifungites ichnofacies (Fig. 13D, E F) or palimpsest softground suites of the Skolithos ichnofacies (Fig.ISC). Many firmgrounds also appear to have been developed on sideritecemented intervals within the shales (Fig. 13D). Whether the siderite is formed during ravinement, as a chemical response related to deep substrate penetration by the firmground tracemakers, or whether pre-existing, siderite-cemented bands formed resistant layers through which the TSE could not incise, is uncertain. In the latter scenario, however, soft-bodied fauna would have to have been capable of penetrating a highly compacted or cemented layer. Elsewhere, the TSE have been developed on sandy substrates and are marked by palimpsest softground omission suites (Fig. 13C), typically dominated by Diplocraterion habichi and Skolithos (e.g. Middle Jurassic Heather Formation, Norwegian North Sea, MacEachern & L0seth 2003; Early Permian Pebbley Beach Formation, Australia, Bann et al 2004). In a few exceptional cases, TSE excavated across coal layers (Fig. 14) are demarcated by Teredolites longissimus, Diplocraterion parallelum and, more rarely, Diplocraterion habichi, attributable to the Teredolites ichnofacies (e.g. Campanian Horseshoe Canyon-Bearpaw transition, Drumheller Alberta, Saunders & Pemberton 1986; Lower Jurassic Neil Klinter Formation, East Greenland, Dam 1990; and Lower Palaeocene Clayton Formation, Alabama, Savrda 1991b). The firmground omission suites are predominantly manifest by Diplocraterion (typically D.

47

habichi), Skolithos, Arenicolites, Rhizocorallium and Thalassinoides (Fig. 13D, E), attributable to the Glossifungites ichnofacies. In some Viking Formation TSE, firmground Zoophycos with associated Thalassinoides and Rhizocorallium have also been identified (Fig. 13F), where initial colonization of the discontinuity occurred in more distal or sheltered settings during continued sea-level rise (MacEachern & Burton 2000). Savrda (2001) has also identified Zoophycos as part of an omission suite in the shelf and slope deposits of New Jersey. The proximal omission assemblages record predominantly suspensionfeeding behaviours associated with the period of higher energy prevalent during active ravinement and/or the energy conditions at the substrate during substrate colonization (Fig. 13C, D, E). Colonization of these exhumed surfaces post-dates erosive shoreface retreat but presumably occurs prior to significant deepening. These higher-energy (proximal) TSE are commonly overlain by conglomeratic lags. Transgressive surfaces of erosion that are not colonized until after deepening record higher proportions of domichnia of deposit-feeding organisms and are typically overlain by marine pebbly and sandy shales or muddy sandstones. In the most distal settings, the omission suite may consist entirely of firmground domichnia and feeding structures of deposit-feeding organisms (Fig. 13F; MacEachern & Burton 2000). Transgressively incised shorefaces Several Viking Formation oil and gas fields in central Alberta produce hydrocarbons from NW-SE trending, sharp-based sandstones, interpreted to rest upon transgressive surfaces of erosion incised into underlying facies. These include Chigwell (Raychaudhuri et al. 1992),

archetypal Cruziana ichnofacies with Chondrites (Ch), Helminthopsis (H), Phycosiphon (Ph), and Diplocraterion (D). Well 11-24-65-18W5; 1358.0m. (C) A palimpsest softground of Diplocraterion (D), subtending from a regionally extensive TSE excavated landward of the Joffre Embayment Complex. The palimpsest suite cross-cuts remnant lower shoreface sandstones of the regional Viking Fm parasequences. The underlying sandstones contain a proximal expression of the Cruziana ichnofacies, with Helminthopsis (H), Siphonichnus (Si), and Zoophycos (Z). Well 16-34-38-25W4; 1433.9m. (D) A proximal expression of a regionally extensive TSE in the Viking Formation with a pebble lag passively infilling firmground Diplocraterion (D) and Skolithos of the Glossifungites ichnofacies. The omission suite penetrates siderite cemented silty mudstones with visible Palaeophycus (Pa) and Chondrites (Ch). Well 12-31-40-02w5; 1860.8m. (E) A proximal TSE overlain by a pebble lag that passively infills firmground Diplocraterion (D). The omission suite cross-cuts lower offshore silty mudstones with stacked tempestites, containing abundant Phycosiphon (Ph), Helminthopsis (H), and Chondrites (Ch), comprising a distal expression of the Cruziana ichnofacies. Well 09-15-39-27W4; 1549.4m. (F) A distal TSE from the Viking Formation of the Hamilton Field. The underlying mudstones correspond to shelf deposits and contain the Zoophycos ichnofacies. The TSE is demarcated by a firmground omission suite, consisting of Thalassinoides and Zoophycos of the Glossifungites ichnofacies. The overlying sandy mudstones are pebble bearing (Pe) and show the archetypal Cruziana ichnofacies containing Zoophycos (Z), Thalassinoides (Th), Planolites (P), Helminthopsis (H), and Palaeophycus (Pa). Well 06-13-35-09W4; 904.6m.

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afkldjfhjsdkfhjksdfhdkajsfhksdjfhakdjlfhlaskd asdfasdfasdfadsfadfadfadfadfadfadsfadfadsfadsf

Fig. 14. Summary diagram showing multiple sites of compacted mud/peat exhumation in a transgressive barrier-island setting. These include: back-barrier tidal creeks (1) and channels (2), tidal inlets (3), and the open shoreface (4). In all of these settings, developments of the Glossifungites and Teredolites ichnofacies can intermingle in response to localized change's in xylic properties. As shown, the erosional resistance of compacted peat can exert an overriding control on the depths of both channel erosion and shoreface ravinement. Trace fossil assemblages may therefore reflect complex histories repeated burial and re-exhumation.

Joffre (Downing & Walker 1988; MacEachern et al 1998, 1999b), Gilby (Raddysh 1988) and Giroux Lake (Stelck et al 2000). These successions can be regarded as high-energy parasequences bounded by ravinement surfaces. Although transgressively incised shorefaces tend to display thicker successions than do falling-stage systems, reflecting the increased accommodation space available, the 'transgressive' interpretation has rested mainly with the perceived position of the deposits in the regional stratigrapnic framework rather than with any intrinsic characteristics of the succession itself. For example, Posamentier et al. (1992) and Posamentier & Chamberlain (1993) interpreted the Joarcam deposit as a lowstand shoreface. In

contrast, Walker & Wiseman (1995) reinterpreted it as a transgressive shoreface, primarily on the basis of the observation of underlying and basinward shoreface deposits at Lindbrook that they regarded as lowstand in origin. Furthermore, despite the Lindbrook deposits being given a lowstand interpretation, Walker & Wiseman (1995) indicated that should an additional shoreface deposit within their sequence 1 be discovered farther to the northeast, the 'incision at Lindbrook a would then represent a transgressive incision formed during movement of the shoreline to the southwest' (Walker & Wiseman 1995, p. 136). It has, however, been suggested by MacEachern et al. (1999b) that this uncertainty


could be alleviated through evaluation of the erosional extent of the underlying discontinuity. Transgressive ravinement causes an erosional discontinuity that ultimately lies seaward of fair-weather wavebase during subsequent periodic progradation. This is because the modified surface was cut prior to shoreface progradation, while sea-level lay at a stratigraphically lower position (Fig. 10). Consequently, in the transgressive scenario, lower offshore and upper offshore deposits, reflecting deposition below fair-weather wavebase, can overlie the erosional component of the basal discontinuity. This is a situation that cannot be accommodated by either a forced regressive or a lowstand scenario (MacEachern et al. 1999a), and is diagnostic of transgressively incised systems. In fact, Walker & Wiseman (1995) noted that an erosional surface always underlies the offshore transition mudstone in such settings, though the implications of that observation were not explored further. As transgressive surfaces of erosion are commonly colonized by firmground omission suites, widespread firmground assemblages attributable to the Glossifungites ichnofacies can be generated, directly overlain by thin gravel lags and basinal facies reflecting offshore and shelf deposition. This facies relationship stands in marked contrast to either forced-regression or lowstand systems where basinal facies overlie the nonerosional correlative conformity and lack demarcation by the Glossifungites ichnofacies. Ultimately, the ravinement surfaces of transgressively incised shorefaces pass seaward into nonerosional marine flooding surfaces (Fig. 10). The Viking Joffre Shoreface Complex (Sequence 2) of the Gilby-JofTre trend (MacEachern et al 1998, 1999b) contains a sharpbased transgressively incised shoreface, excavated into underlying stacked marine parasequences. The incision surface (interpreted as an FS/SB) slopes steeply seaward along its landward edge and flattens out basinward, forming an asymmetric, one-sided erosional scarp. Granules and small pebbles of chert locally mantle the erosional discontinuity. More commonly, the surface is demarcated by firmground Thalassinoides, Diplocraterion and Skolithos of the Glossifungites ichnofacies, in both proximal and distal positions (Fig. 15). The FS/SB is overlain by a coarsening-upward (shallowingupward) succession of gritty sandy shales and muddy sandstones containing a fully marine, diverse and uniformly distributed trace fossil assemblage that corresponds to an archetypal to proximal expression of the Cruziana ichnofacies, respectively. These facies reflect the

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short-lived progradation of upper offshore and lower shoreface environments of a transgressively incised, weakly storm-influenced shoreface complex. In proximal positions (Fig. 15A, B), the transgressively incised shoreface is virtually indistinguishable from either the forced regressive (Fig. 10) or lowstand incised shorefaces (Fig. 10); the basal discontinuity shows firmground suites directly overlain by lower shoreface sandstones. The transgressive origin of an incised shoreface's basal discontinuity is demonstrated, instead, in distal positions. Distally, firmground omission suites of the .Glossifungites ichnofacies demarcate the discontinuity, indicating that it continues to be erosional, even where it is overlain by deposits that accumulated below fair-weather wavebase (Fig. 15 C, D). This indicates that the surface was cut while sea-level was lower and the area within the zone of wave attack and was colonized during transgressive deepening. Ultimate burial of the discontinuity occurred either during a pause in the rate of transgression, or when sediment supply to the shoreline outpaced deepening and a period of shoreline progradation ensued. In distal positions, the transgressively ravined discontinuity was buried beneath offshore sandy mudstone prior to shoreface deposition (Fig. 10), as is diagnostic of a transgressively incised origin. A comparable succession was described from the Viking Formation of the Chigwell Field by Raychaudhuri et al (1992). The Turonian Cardium Formation of the Pembina field, central Alberta, also contains a series of conglomeratic bodies associated with underlying transgressive surfaces of erosion, interpreted as transgressively incised shorefaces (cf. Vossler & Pemberton 1989; Walker & Eyles 1991). Below this erosion surface, lower offshore silty shales are abundantly bioturbated (BI5) and contain a diverse ichnological assemblage corresponding to a distal expression of the Cruziana ichnofacies. The erosional discontinuity is incised into these silty shales and is marked by robust, pebble-filled firmground Thalassinoides (Fig. 16) and rare Skolithos of the Glossifungites ichnofacies. The conglomerates are largely devoid of bioturbation but pass upward into overlying marine shelf shales that contain trace fossil suites attributable to the Zoophycos ichnofacies. The erosional discontinuity corresponds to the E5 surface of Plint et al. (1986), interpreted as a surface of initial transgression (Plint 1988; Plint et al. 1988), upon which the conglomerates rest. Firmground colonization of the E5 surface corresponds to a hiatus in deposition between the initial transgressive generation of E5 and shoreface progradation of the conglomerates

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Fig. 15. Transgressively incised shoreface. (A) Box shot of core from the Joffre Shoreface Complex. Base of the interval is to the lower left, and top to the upper right (T). The FS/SB here lies in a proximal position. Silty and sandy mudstones of the regional Viking Formation, reflecting lower offshore and upper offshore conditions respectively, are erosionally truncated by the basal discontinuity, Overlying the FS/SB are conglomeratic sandstones of the transgressive lag, passing into bioturbated muddy sandstones of the lower shoreface. Well 09-16-39-27W4; 1560.8-1565.1 m. (B) Close-up photo of the FS/SB from photo A, demarcated by firmground Thalassinoides (Th) of the Glossifungites ichnofacies. The discontinuity is overlain by a pebble (Pe) lag and muddy sandstones of the lower shoreface containing a proximal expression of the Cruziana ichnofacies. Skolithos (S), Planolites (P), Asterosoma (As), Palaeophycus (Pa), and Siphonichnus (Si) are visible. Well 09-1639-27W4; 1562.5m. (C) Box shot of core from the Joffre Shoreface Complex, in a position distal to that of photos A and B. Base of the interval is to the lower left, and top to the upper right (T). Here, lower and upper offshore mudstones of the regional Viking Formation are erosionally truncated by the FS/SB, but overlain by upper offshore sandy mudstones of the Joffre Shoreface Complex. Well 08-14-38-25W4, 1431.6-1434.5 m. (D) Close-up photo of the FS/SB of photo C, showing the distal expression of the FS/SB. Here, the omission suite demarcating the discontinuity also consists of firmground Thalassinoides (Th) of the Glossifungites ichnofacies. However, it is overlain by bioturbated (BI5) gritty, pebble (Pe) bearing sandy mudstones of the upper offshore, with Phycosiphon (Ph), Chondrites (Ch), Asterosoma (As), Cylindrichnus (Cy), Palaeophycus (Pa), and Planolites (P) corresponding to the archetypal Cruziana ichnofacies. Well 08-14-38-25W4, 1434.0m.


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such surfaces may also include the discontinuities at the bases of some transgressively incised shorefaces (e.g. E-T surfaces of Flint 1988; Flint et al 1986, 1988; FS/SB of MacEachern et al. 1992, 1998, 1999a, 1999b), the majority are associated with incised valley systems. Incised valley discontinuities may correspond to subaerially exposed areas, such as delta plains, fluvial floodplains, interfluves, or transgressively modified sequence boundaries within the estuarine valley fills themselves. Some reserve the term TS/SB' for discontinuities developed on valley interfluves, where deposition did not occur until the valley was filled and the area transgressively ravined during ensuing relative sea-level rise (e.g. Van Wagoner et al. 1990).

Fig. 16. Transgressively incised Cardium shoreface. (A) The FS/SB marking the base of the Cardium Formation conglomeratic shoreface of the Pembina field. Moderately bioturbated (BI4-5) sandy mudstones of the upper offshore, containing Chondrites (Ch) and Helminthopsis (H), are erosionally truncated by overlying pebble conglomerates. The discontinuity is demarcated by gravel-filled firmground Thalassinoides (Th) of the Glossifungites ichnofacies. Well 04-13-51-11W5, 1636.1 m. (B) The same discontinuity in a nearby core, showing lower offshore silty mudstones truncated by pebble conglomerates of the Cardium Formation incised shoreface. The firmground omission suite also consists of gravel-filled Thalassinoides (Th) of the Glossifungites ichnofacies. Well 12-09-51-10W5, 1596.8m.

during a pause in the rate of transgression. The conglomeratic shoreface was ultimately drowned (MFS), and locally removed (TSE), during resumed transgression. Amalgamated sequence boundaries and marine flooding surfaces Amalgamated sequence boundaries and transgressive surfaces are commonly colonized by substrate-controlled trace-makers. The lowstand erosion event typically produces widespread firmground, hardground and woodground surfaces, corresponding to RSE or SB. The following transgressive event, commonly accompanied by erosion, generates a TSE that tends to remove most or all of the lowstand deposits and exposes the original discontinuity to marine or marginal marine conditions. During this phase of transgression, organisms are able to colonize the re-exhumed substrate. Although

TSE across subaerially exposed surfaces or interfluves Numerous units in coastal margin (delta plain and coastal plain) settings display initially subaerial surfaces subsequently flooded and eroded during transgressive influx of brackish to marine waters. Such scenarios are conducive to the development of substrate-controlled ichnofacies demarcating the discontinuities. The Cenomanian Dunvegan Formation consists of a stacked succession of prograding delta lobes that varied during its history of deposition from river-dominated to wave-dominated in character (Bhattacharya & Walker 1991). The stacked delta lobes and individual shingles within the lobes are separated by marine flooding surfaces of varying scales and which are locally erosional (Bhattacharya 1993). In the subsurface of the Jayar Field, central Alberta, a TSE, overlain by a transgressive sandstone, cuts across rooted and subaerially exposed delta plain deposits of the underlying delta lobe (Bhattacharya & Walker 1991). The erosional discontinuity is demarcated by a firmground Thalassinoides of the Glossifungites ichnofacies, passively filled with coarse-grained sand derived from the overlying transgressive sand sheet. Similarly, the Lower Albian Mannville GroupJoli Fou Formation contact in the Kaybob Field of central Alberta is manifest by a regionally developed FS/SB. In this case, rooted incipient palaeosols developed on floodplain mudstones of the Mannville Group are crosscut by robust, firmground Thalassinoides, reflecting the Glossifungites ichnofacies (Fig. 17A), passively filled with muddy sand and large siderite-cemented clasts. The overlying silty shales contain a distal expression of the Cruziana ichnofacies and, more rarely, the Zoophycos

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Fig. 17. FS/SB Interfluve. (A) Glossifungites ichnofacies-demarcated FS/SB at the Mannville Group-Joli Fou Formation contact, reflecting an interfluve area. Rooted incipient palaeosols are colonized with firmground Thalassinoides (Th), and capped by a transgressive lag. Overlying facies reflect offshore to shelf deposition. Well 11-03-60-19W5; 1894.3m. (B) Rooted (r), incipient palaeosols of the Upper Boulder Creek Formation, corresponding to floodplain conditions, are transgressively eroded and overlain by a thin transgressive lag and brackishwater bay mudstones of the Paddy Formation. The FS/SB of the interfluve is demarcated by firmground Thalassinoides (Th) of the Glossifungites ichnofacies. The overlying brackish-water mudstones contain an impoverished Cruziana ichnofacies, with visible Planolites (P) and exceedingly rare Helminthopsis (H). Well 08-13-69-11W6; 1907.2m.

ichnofacies, recording deposition in lower offshore to outer shelf environments. The amalgamated surface corresponds to an interfluve (Van Wagoner et al. 1990) that was transgressively overrun during basin-wide flooding of the Joli Fou Seaway. This transgression marks a major period of marine inundation of the Western Interior Seaway of North America. The Upper Albian Paddy Member is separated from the underlying Cadotte Member in the Peace River area of Alberta by a regionally extensive disconformity that was excavated during a relative sea-level fall and subsequently transgressively modified during flooding of the basin (Leckie & Singh 1991). This continued flooding eventually led to the return of offshore to shelf conditions reflected by the overlying Shaftesbury Formation (Leckie et al. 1990). In

the subsurface, coastal plain to floodplain mudstones and siltstones, alternating with palaeosols, correspond to the Upper Boulder Creek Formation (post-Cadotte Member but pre-Paddy Member). These represent the preserved terrestrial deposits that accumulated during late Cadotte Member highstand conditions and initial sea-level fall, which survived incision during generation of the Paddy Member disconformity. The Upper Boulder Creek palaeosols locally consist of rooted silty light grey mudstones with hematite-stained spherulitic siderite (Leckie et al. 1989). These palaeosols are truncated by a transgressive surface of erosion that locally displays an omission suite of thin, sharp-walled Skolithos and more rarely Rhizocorallium of the Glossifungites ichnofacies (Fig. 17B). The overlying granule-bearing, sandy mudstones of the Paddy Member are of low diversity, archetypal to distal expressions of the Cruziana ichnofacies, and reflect restricted bay conditions during regional flooding of the coastal margin. Regionally, the Paddy Member occupies a major estuarine valley excavated during initial lowstand conditions (Leckie & Singh 1991). The flooding of the estuary margins during late Paddy time resulted in transgressive modification of the interfluve area. Continued transgression resulted in the deposition of open marine mudstones of the Shaftesbury Formation and the return to shelf al conditions (Leckie et al. 1991). Incised valley complexes: demarcation of valley surfaces For the most part, lowstand deposits rarely dominate incised valley complexes, as the system is largely a zone of sediment bypass during incision (Van Wagoner et al. 1990). Much of the sediment accumulation in these systems occurs during late lowstand and transgression, and is therefore characterized by estuarine infill. The juxtaposition of facies into which the valley is incised, the presence of remnant fluvial deposits within the valley, accumulations of estuarine intervals during ensuing transgression, and the excavation of numerous internal discontinuities within the valley fill, result in highly complex successions that ichnology is ideally suited to help resolve. Ichnological suites are also effective at differentiating salinity changes and, more specifically, salinity reductions, assisting in the differentiation of fully marine, brackish and freshwater deposits (e.g. Pemberton et al. 1982; Beynon et al. 1988; Ranger & Pemberton 1992, 1997; MacEachern & Pemberton 1994; MacEachern et al. 1999a).


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Fig. 18. Schematic model of incised valley surface types commonly demarcated by the Glossifungites ichnofacies (modified after MacEachern & Pemberton 1994).

This, coupled with the presence of substratecontrolled assemblages associated with erosional discontinuities within the valley fill, allows detailed mapping of valley components and assists in the resolution of the sequence stratigraphic history of valley excavation and infill. The Viking Formation produces hydrocarbons from estuarine incised valley fills in at least five fields of central Alberta. The facies successions and their distributions indicate that they accumulated in a barrier estuary or wave-dominated embayed estuary setting, in the sense of Roy et al (1980) and Dalrymple et al. (1992). In most of the incised valley systems of the Viking Formation the valley margins are demarcated trace fossil suites of the Glossifungites ichnofacies, indicating that the valley probably did not fill until active transgression (i.e. no lowstand deposits are preserved). Either the valley served as a zone of sediment bypass and possessed no fluvial deposits, or any lowstand deposits were subsequently eroded and reworked during the subsequent transgression, producing an amalgamated (co-planar) sequence boundary and initial transgressive surface. This initial transgressive surface of erosion most likely reflects tidalscour ravinement. The base of the estuarine valley fill therefore serves both as the sequence boundary and as the base of the transgressive systems tract. The valley fill, as well, contains a number of internal stratigraphic discontinuities, locally reflecting re-incision of the valley, erosive back-stepping of the barred mouth, lateral and landward shift of the tidal inlets at the barrier mouth, and lateral shift of tidal creeks and tidal

channels within the valley (Fig. 18). The valley margins are excavated into coarsening upward, regional Viking highstand marine parasequences. These parasequences contain fully marine, high diversity and abundantly burrowed (BI5) distal to proximal expressions of the Cruziana ichnofacies. This contrasts markedly with the ichnological suites developed within the valley fills. In the Crystal Field the valley margins are demarcated by firmground Diplocraterion, Thalassinoides and unnamed clavate burrows similar in morphology to Gastrochaenolites, assigned to the Glossifungites ichnofacies (Fig. 19B, C). At Willesden Green, the valley base contains firmground Arenicolites, Skolithos, Diplocraterion, Rhizocorallium and Thalassinoides (Fig. 19F).

Incised valley complexes: ichnology of estuarine valley fills The wave-dominated barred estuary systems can be separated into the bay-head delta, including the active channels and distributary channels, the central basin or lagoon, and the estuary mouth. The bay-head delta complex (Fig. 19A) is generally characterized by weakly and sporadically burrowed, parallel-laminated sandstones. Trace fossil diversities can be high (up to 16 ichnogenera), although burrow concentrations are irregular and the numbers of individual forms are low. Bioturbation intensities are also generally low (BI 1-2). The trace fossils comprise an impoverished expression of the Skolithos

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Fig. 19. Incised Valley Complex. (A) Parallel-laminated sandstone of the bayhead delta front, Crystal Field. The sandstone is sporadically burrowed with a low-diversity expression of the Skolithos ichnofacies. Unit shows Bergaueria (Be) and Diplocraterion (D). Well 16-24-45-04W5; 1801.3m. (B) Box shot of core from the incised valley of the Crystal Field. Base of the core is to the lower left, and top to the upper right (T). Underlying lower offshore silty mudstones of the regional Viking Formation parasequences have been truncated by an amalgamated flooding surface and sequence boundary (FS/SB) along the margins of the Crystal incised valley. The valley fill at this locality consists of sandstone-dominated central basin deposits that have onlapped the valley margins. Well 04-01-46-04W5; 1802.1-1806.2 m. (C) Close-up of the contact visible in photo B. Lower offshore silty mudstones of the regional Viking contain a distal expression of the Cruziana ichnofacies with Helminthopsis (H), Asterosoma (As), and Palaeophycus (Pa). The FS/SB is demarcated by a firmground omission suite of Skolithos (S), and unnamed flask-shaped domichnia similar to Gastrochaenolites (G). The overlying bay deposits show dispersed pebbles (pe) at the base with a low-diversity suite attributable to the mixed Skolithos-Cruziana ichnofacies. Well 04-01-46-04W5; 1804.5m. (D) Sandy central basin deposits from the Willesden Green incised valley. Current ripple laminated sandstone is intercalated with strongly burrowed (BI4-5) muddy sandstone showing a low-diversity suite of the mixed Skolithos-Cruziana ichnofacies. The facies displays Thalassinoides (Th), Macaronichnus (Ma), Palaeophycus (Pa), Siphonichnus (Si), Bergaueria (Be), Rosselia (Ro) and Planolites (P). Well 06-36-40-07W5; 2322.7m. (E) Bioturbated (BI4) muddy sandstone from the estuary mouth complex of the Crystal incised valley. The suite corresponds to the Skolithos ichnofacies, comprising Thalassinoides (Th), Ophiomorpha (O), Skolithos (S), Diplocraterion (D), Planolites (P), Helminthopsis (H), Palaeophycus (Pa), Siphonichnus (Si), and Teichichnus (Te). Well 08-16-48-03W5; 1529.1 m. (F) Tidal inlet channel fill deposit from the Willesden Green incised valley. Lower offshore, silty mudstones of the regional Viking Formation parasequences with visible Phycosiphon (Ph), and Chondrites (Ch). The discontinuity corresponds to a transgressive scour ravinement (TSR) surface, demarcated by a firmground omission suite of Rhizocorallium (Rh), and Thalassinoides (Th). The channel fill sandstone displays dispersed pebbles (pe), and isolated, robust Ophiomorpha (O). Well 11-31-40-06W5; 2285.6m.


ichnofacies. The central basin complex (Fig. 19B, C, D) consists of delicately interstratified sandy mudstones, dark mudstones and thin sandstones. Synaeresis cracks are present throughout and are locally common. The trace fossil assemblages show moderate to low diversities of ichnogenera, moderate though variable bioturbation intensities (BI2-5; typically BI4), and reflect the mixed Skolithos-Cruziana ichnofacies. Trace fossil suites in the central basins are dominated by Teichichnus, Planolites, diminutive Rosselia, Cylindrichnus and Palaeophycus (Fig. 19D). Salinity fluctuations, episodic deposition and variable substrate consistency appear to be the dominant stresses imparted on the infauna. The estuary mouth complex (Fig. 19E) consists of moderately to abundantly burrowed (BI3-5) current and oscillation ripple-laminated sandstones, with minor intercalated mud beds. The trace fossil suites show high diversities of ichnogenera, corresponding to the Skolithos ichnofacies, but the distribution of individual elements reflects the presence of environmental stresses, in particular, episodic deposition. Channel-fill fades associations (Fig. 19F) predominantly consist of the deposits of relatively small, migrating subaqueous dunes. The amalgamation of the trough cross-beds into thick intervals supports a high sediment aggradation rate. The trace fossil suite is sporadically distributed, low in diversity (seven ichnogenera) and corresponds to the Skolithos ichnofacies. The most common elements include Ophiomorpha, Cylindrichnus, Palaeophycus and Diplocraterion. The burrowing demonstrates that most of the channel complexes accumulated in marine or marginal marine conditions, although the degree of salinity stress is difficult to determine. The main stress imposed on the trace fossil suite appears to be related to migration of bedforms and avalanching of sand into the dwelling structures. In the more tidally influenced estuaries of the Alberta Basin [e.g. the McMurray Formation (Pemberton et al. 1982; Ranger & Pemberton 1992, 1997; Bechtel et al. 1994); the Grand Rapids Formation (Wightman et al. 1987; Beynon et al. 1988); and the Glauconite Formation (Leroux et al. 1999)], the valley fills consist predominantly of channel sandstones and lateral accretion deposits manifest by inclined heterolithic stratification (IHS). The channel sandstones are dominated by stacked trough cross-stratified beds, lesser low-angle planar cross-stratified units, and thin current ripple laminated beds. Bioturbation is generally very low (BI1-2) and sporadically distributed, and typically is associated with thin mudstone

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interbeds. Suites are characterized by sparse Planolites, Palaeophycus and Skolithos, with rare Cylindrichnus, Teichichnus and Arenicolites comprising the secondary elements. Very uncommon ichnogenera include Conichnus, Gyrolithes and fugichnia. IHS intervals are characterized by stacked, trough cross-stratified beds and current-rippled beds alternating with thin, depositionally inclined (3-7°) mudstone beds, interpreted to reflect tidal modification of river flow through the channel system. Bioturbation intensities are variable but moderate to low (BI2-4), and ichnogenera are sporadically distributed. Trace fossil suites are dominated by moderate to common Planolites, with moderately common to rare Teichichnus, Cylindrichnus and Skolithos. Secondary elements comprise rare Gyrolithes, Palaeophycus, fugichnia and roots. Accessory elements include very rare Arenicolites, Rosselia, Thalassinoides, Chondrites, Bergaueria, Rhizocorallium, Lockeia and Ophiomorpha. Some intervals consist of monogeneric assemblages of Planolites, Cylindrichnus or Gyrolithes, particularly within the betterstudied McMurray Formation palaeo-valleys. More saline elements of the suite comprise Chondrites, Rosselia, Rhizocorallium, Bergaueria and Ophiomorpha, all of which have only been described from McMurray Formation intervals (Bechtel et al. 1994; Ranger & Pemberton 1997). The trace fossil assemblages within the incised valley facies associations correspond to simple structures produced by trophic generalists. These are referred to as r-selected (opportunistic) behaviours, and are characteristic of stressed environmental settings (Pianka 1970), particularly those subject to salinity fluctuations. The episodic nature of deposition and the variability in substrate consistency lead to the development of trace fossil assemblages that constitute an impoverished expression of the mixed Skolithos-Cruziana ichnofacies (Pemberton et al. 1992a).

Bay-head delta, channel and embayment deposits In the Viking Formation of the JofTre Field, an amalgamated sequence boundary and flooding surface with a scarp-like geometry truncates underlying regional Viking marine parasequences and, locally, the transgressively incised Joffre Shoreface Complex (MacEachern et al. 1998, 1999a). The Glossifungites ichnofacies, characterized by firmground Skolithos, Diplocraterion and Thalassinoides, locally helps to demarcate this erosional discontinuity (Fig. 20A).

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Fig. 20. Joffre Embayment. (A) Joffre Embayment Complex showing regional Viking Formation lower offshore silty mudstones with Phycosiphon (Ph) and Planolites (P), truncated by a regionally extensive FS/SB, and overlain by embayment sandstones. The discontinuity is demarcated by firmground Thalassinoides (Th) of the Glossifungites ichnofacies. Well 14-11-39-27W4; 1572.7m. (B) Glauconitic pebbly (pe) muddy sandstones of the Joffre Embayment Complex corresponding to a transgressive sand sheet at the base of the regional FS/SB. The sandstone is moderately well bioturbated (BI4) containing a proximal expression of the Cruziana ichnofacies. The sandstone contains Planolites (P), Rosselia (Ro), Helminthopsis (H), Palaeophycus (Pa), and Chondrites (Ch). Well 14-05-38-24W4; 1372.3m. (C) Trough cross-stratified sandstone of the Joffre Embayment


The deposits overlying the discontinuity constitute the Viking reservoir facies at Joffre and reflect three stacked, conglomeratic embayment parasequences that prograded toward the northeast. The reservoir facies are dominated by trough cross-stratified and low-angle planar stratified sandstones, pebbly sandstones and conglomerates, concentrated along the southern margin of the amalgamated sequence boundary and flooding surface. The coarse elastics progressively inter-finger with, and ultimately pass into, interbedded mudstones and fine-grained sandstones in a northward and eastward direction. Near the base, the coarse elastics contain glauconite, siderite-cemented mudstone interbeds, mud inter-laminae and resistant mudstone rip-up clasts, and display moderate to low degrees of burrowing, diminishing in intensity upward (Fig. 20B). The trace fossil suite corresponds to the Skolithos ichnofacies. Overlying facies are dominated by well-sorted, unidirectional trough cross-bedded and low-angle planar stratified coarse elastics, locally in fining upward cycles with scoured bases (Fig. 20C, D). The elastics contain mudstone rip-up clasts and thin mudstone interbeds. Burrowing is of low abundance (BI1-2), and reduced diversity, with Diplocraterion, Skolithos, Palaeophycus and Ophiomorpha of the Skolithos ichnofacies. The interbedded mudstone and sandstone deposits contain oscillation ripples, wavy lamination, combined flow ripples and rare current ripples (Fig. 20E, F). These heterolithic intervals are weakly burrowed (BI 1-3) with a sporadically distributed, lowdiversity (salinity stressed?) trace fossil suite of the mixed Skolithos-Cruziana ichnofacies (MacEachern et al 1998, 1999a). Dominant elements comprise Teichichnus, Cylindrichnus, Planolites and Palaeophycus. Detailed ichnological, sedimentological and stratigraphic analyses demonstrate that the coarse elastics overlying the discontinuity comprise at least three parasequences. These parasequences onlap the discontinuity in a southwest direction and inter-finger with mudstones to the northeast. Toward the north end of the field, erosional amalgamation of the coarse elastics is

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more pronounced, and parasequence boundaries cannot be delineated easily. Near the southern end of the field, these parasequences partition the reservoir along the seaward (and structurally up-dip) edge of the deposit. Amalgamation of the reservoir facies at the north end limits the degree of partitioning. The final parasequence of the embayment complex is truncated by a regionally extensive flooding surface, typically manifest as a wave ravinement surface. The wave ravinement surface is commonly demarcated by the Glossifungites ichnofacies, or where excavated across sandy underlying facies, a palimpsest softground suite of Diplocraterion (Fig. 13C). Facies overlying the marine flooding surface reflect fully marine conditions. Conclusions The main applications of ichnology to genetic stratigraphy are twofold. The most obvious use lies in the demarcation of erosional discontinuities. To date, substrate-controlled ichnofacies have been underutilized but are gaining recognition as a viable means of recognizing and mapping these stratigraphically important surfaces, both in outcrop and subsurface. Locally, many surfaces are obvious on the basis of sedimentology alone; however, their appearance can change markedly across the study area, making correlation difficult. Substrate-controlled ichnofacies, such as the Glossifungites ichnofacies, are also important to the genetic interpretation of erosional discontinuities in marine-influenced siliciclastic intervals, as the many examples cited in the paper demonstrate. Hence, even where discontinuities can be recognized purely sedimentologically or stratigraphically, the associated trace fossils enhance their sequence stratigraphic interpretation. In many cases, the genetic interpretation of the discontinuity has come principally from the trace fossil assemblages that are associated with the discontinuity and the overlying units. The continued integration of substrate-controlled ichnofacies with detailed

Complex with sporadically distributed lined Diplocraterion (D). Well 02-05-39-26W4; 1573.3m. (D) Trough cross-stratified sandstone of the Joffre Embayment Complex with sporadically distributed lined Diplocraterion (D). Well 11-07-39-26W4; 1548.1 m. (E) Heterolithic succession of oscillation rippled, combined flow rippled and low-angle parallel-laminated sandstone and dark, weakly burrowed (BI 2-3) mudstone corresponding to open bay deposits. Trace fossils reflect a stressed, low-diversity expression of the mixed Skolithos-Cruziana ichnofacies, characterized by Teichichnus (Te), Cylindrichnus (Cy), and Planolites (P). Well 02-18-38-24W4; 1459.2m. F) Heterolithic succession of oscillation rippled (osc), current-rippled (cr), and low-angle parallellaminated sandstone, with dark, weakly burrowed (BI 2) mudstone corresponding to open bay deposition. Trace fossils reflect a stressed, low-diversity expression of the mixed Skolithos-Cruziana ichnofacies, characterized by Teichichnus (Te), and Planolites (P). Well 03-24-38-25W4; 1437.7m.

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stratigraphic and sedimentological analysis will undoubtedly enhance and refine the developing genetic stratigraphic paradigms. The second use is more subtle, and is concerned with trace fossil behaviours and their palaeoenvironmental implications. Trace fossils, when used in conjunction with primary sedimentary structures, are useful in the delineation and interpretation of facies and facies associations. When these behavioural and substrate-controlled aspects of ichnology are integrated fully with other sedimentological and stratigraphic analyses, the result is a powerful approach to the recognition and genetic interpretation of discontinuities in the rock record.

USA) reinterpreted as lowstand shoreface deposits. American Association of Petroleum Geologists Bulletin, 64, 184-201. BEYNON, B. M., PEMBERTON, S. G., BELL, D. A. & LOGAN, C. A. 1988. Environmental implications of ichnofossils from the Lower Cretaceous Grand Rapids Formation, Cold Lake Oil Sands Deposit. In: JAMES, D. R. & LECKIE, D. A. (eds) Sequences, Stratigraphy, Sedimentology: Surface and Subsurface. Canadian Society of Petroleum Geologists, Memoirs, Calgary, Alberta, 15, 275290. BHATTACHARYA, J. P. 1993. The expression and interpretation of marine flooding surfaces and erosional surfaces in core: examples from the Upper Cretaceous Dunvegan Formation, Alberta foreland basin, Canada. In: POSAMENTIER, H. W.,

The authors would like to thank the Natural Science and Engineering Research Council of Canada (NSERC) for research funding. The senior author would like to acknowledge the Canada Research Chairs programme for their support of his research. D. Robbins assisted with some of the drafting, and we are grateful for his contribution.

(eds) Stratigraphy and Facies Associations in a Sequence Stratigraphic Framework. International Association of Sedimentologists, Special Publications, Oxford, 18, 125-160. BHATTACHARYA, J. & WALKER, R. G. 1991. Allostratigraphic subdivision of the Upper Cretaceous Dunvegan, Shaftesbury and Kaskapau formations, northwestern Alberta subsurface. Bulletin of Canadian Petroleum Geology, 39, 145-164. BROMLEY, R. G. & ASGAARD, U. 1993. Two bioerosion ichnofacies produced by early and late burial associated with sea level change. Geologische Rundschau, 82, 276-280. BROMLEY, R. G., PEMBERTON, S. G. & RAHMANI, R. A. 1984. A Cretaceous woodground: the Teredolites ichnofacies. Journal of Paleontology, 58, 488-498. DALRYMPLE, R. W., ZAITLIN, B. A. & BOYD, R. 1992. Estuarine facies models: conceptual basis and stratigraphic implications. Journal of Sedimentary Petrology, 62, 1130-1146. DAM, G. 1990. Paleoenvironmental significance of trace fossils from the shallow marine Lower Jurassic Neill Klinter Formation, East Greenland. Palaeogeography, Palaeoclimatology, Palaeoecology, 79, 221-248. DAVIES, S. D. & WALKER, R. G. 1993. Reservoir geometry influenced by high-frequency forced regressions within an overall transgression: Caroline and Garrington fields, Viking Formation (Lower Cretaceous), Alberta. Bulletin of Canadian Petroleum Geology, 41, 407-421. DE GIBERT, J. M., MARTINELL, J. & DOMENECH, R. 1998. Entobia ichnofacies in fossil rocky shores, Lower Pliocene, northwestern Mediterranean. Palaios, 13, 476-487. DOWNING, K. P. & WALKER, R. G. 1988. Viking Formation, Joffre Field, Alberta: shoreface origin of long, narrow sand body encased in marine mudstones. Bulletin American Association Petroleum Geologists, 72, 1212-1228. EKDALE, A. A., BROMLEY, R. G. & PEMBERTON, S. G. 1984. Ichnology: Trace Fossils in Sedimentology and Stratigraphy. Society of Economic Paleontologists and Mineralogists, Short Course Notes, Tulsa, Oklahoma, 15.

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SAUNDERS, T. & PEMBERTON, S. G 1986. Trace Fossils and Sedimentology of the Appaloosa Sandstone: Bearpaw-Horseshoe Canyon Formation Transition, Dorothy, Alberta. Canadian Society of Petroleum Geologists, Field Trip Guide Book, Calgary, Alberta. SAVRDA, C. E. 199la. Teredolites, wood substrates, and sea-level dynamics. Geology, 19, 905-908. SAVRDA, C. E. 1991b. Ichnology in sequence stratigraphic studies: an example from the lower Paleocene of Alabama. Palaios, 6, 39-53. SAVRDA, C. E. 1995. Ichnologic applications in paleoceanographic, paleoclimatic, and sea-level studies. Palaios, 10, 565-577. SAVRDA, C. E., OZALAS, K., DEMKO, T. H., HUTCHINPOSAMENTIER, H. W. & CHAMBERLAIN, C. J. 1993. SON, R. A. & SCHEIWE, T. D 1993. Log grounds Sequence Stratigraphic analysis of Viking Formaand the ichnofossil Teredolites in transgressive tion lowstand beach deposits at Joarcam field, deposits of the Clayton Formation (Lower PaleoAlberta, Canada. In: POSAMENTIER, H. W., cene), western Alabama. Palaios, 8, 311-324. SUMMERHAYES, C. P., HAQ, B. U. & ALLEN, G. P. SAVRDA, C. E., BROWNING, J. V., KRAWINKLE, H. & (eds) Stratigraphy and Fades Associations in a HESSELBO, S. P. 2001. Firmground ichnofabrics in deepwater sequence stratigraphy, Tertiary Sequence Stratigraphic Framework. International Association of Sedimentologists, Special Publicaclinoform-toe deposits, New Jersey slope. Palaios, tions, Oxford, 18, 469-485. 16, 294-305. POSAMENTIER, H. W., ALLEN, G. P., JAMES, D. P. & SCHAFER, W. 1972. Ecology and Palaeoecology of Marine Environments. Oliver & Boyd, EdinTESSON, M. 1992. Forced regressions in a sequence Stratigraphic framework: concepts, examples, and burgh/University of Chicago Press, Chicago. exploration significance. American Association of SEILACHER, A. 1962. Paleontological studies in turbidite Petroleum Geologists Bulletin, 76, 1687-1709. sedimentation and erosion. Journal of Geology, 70, RADDYSH, H. K. 1988. Sedimentology and 'geometry' 227-234. of the Lower Cretaceous Viking Formation, SEILACHER, A. 1982. Distinctive features of sandy tempesGilby A and B Fields, Albert. In: JAMES, D. P. tites. In: EINSELE G. & SEILACHER, A. (eds) Cyclic and Event Stratification. Springer, Berlin, 333-349. & LECKIE, D. A. (eds) Sequences, Stratigraphy, Sedimentology: Surface and Subsurface. Canadian SMITH, R. M. H. 1987. Helical burrow casts of therapSociety of Petroleum Geologists, Memoirs, sid origin from the Beaufort Group (Permian) of Calgary, Alberta, 15, 417^30. South Africa. Palaeogeography, Palaeoclimatol. RANGER, M. J. & PEMBERTON, S. G. 1992. The sedimentology and ichnology of estuarine point bars in the SOEGAARD, K. & MACEACHERN, J. A. 2003. Integrated McMurray Formation of the Athabasca Oil Sands sedimentological, ichnological and sequence Deposit, northeastern Alberta, Canada. In: PEMStratigraphic model of a coarse clastic fan delta reservoir: Middle Jurassic Oseberg Formation, BERTON, S. G. (ed.) Applications of Ichnology to Petroleum Exploration: A Core Workshop. Society North Sea, Norway. Abstract Volume, AAPG Annual Convention, Salt Lake City, Utah, May of Economic Paleontologists and Mineralogists, Core Workshops, Tulsa, Oklahoma, 17, 401-421. 2003, p. A160. RANGER, M. J. & PEMBERTON, S. G. 1997. Elements of a STAMP, L. D. 1921. On cycles of sedimentation in the Stratigraphic framework for the McMurray Eocene strata of the Anglo-Franco-Belgian basin. Geological Magazine, 58, 108-114, 146-157, 194Formation in south Athabasca. In: PEMBERTON, 200. S. G. & JAMES, D. P. (eds) Petroleum Geology of the Cretaceous Mannville Group, Western STELCK, C. R., MACEACHERN, J. A. & PEMBERTON, S. G. Canada. Canadian Society of Petroleum Geolo2000. Foraminiferal biostratigraphic analysis of gists, Memoirs, Calgary, Alberta, 18, 263-291. the Viking Formation, Kaybob North and RAYCHAUDHURI, I., BREKKE, H. G., PEMBERTON, S. G. Giroux Lake fields, central Alberta: a comparison & MACEACHERN, J. A. 1992. Depositional facies with the Hasler Formation biostratigraphy of and trace fossils of a low wave energy shoreface northeastern British Columbia. Canadian Journal succession, Albian Viking Formation, Chigwell of Earth Science, 37, 1389-1410. Field, Alberta, Canada. In: PEMBERTON, S. G. SWIFT, D. J. P. 1968. Coastal erosion and transgressive (ed.) Applications of Ichnology to Petroleum stratigraphy. Journal of Geology, 76, 444-456. Exploration: A Core Workshop. Society of TAYLOR, A. M. & GAWTHORPE, R. L. 1993. Application Economic Paleontologists and Mineralogists, of sequence stratigraphy and trace fossil analysis Core Workshops, Tulsa, Oklahoma, 17, 319-337. to reservoir description: examples from the ROY, P. S., THOM, B. G. & WRIGHT, L. D. 1980. HoloJurassic of the North Sea. In: PARKER, J. R. (ed.) cene sequences on an embayed high-energy coast: Petroleum Geology of Northwest Europe, Proceedan evolutionary model. Sedimentary Geology, 26, ings of the 4th Conference. Geological Society of 1-19. London, 317-335.

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TAYLOR, A. M., GOLDRING, R. & GOWLAND, S. 2003. Analysis and application of ichnofabric. Earth Science Reviews, 60, 227-259. VAN WAGONER, J. C. 1995. Overview of sequence stratigraphy of foreland basin deposits: terminology, summary of papers and glossary of sequence stratigraphy. In: VAN WAGONER, J. C. & BERTRAM, G. T. (eds) Sequence Stratigraphy of Foreland Basins. American Association of Petroleum Geologists, Memoirs, Tulsa, Oklahoma, 64, 9-21. VAN WAGONER, J. C., MITCHUM, R. M. JR, CAMPION, K. M. & RAHMANIAN, V. D. 1990. Siliciclastic Sequences, Stratigraphy in Well Logs, Cores and Outcrops. American Association of Petroleum Geologists, Methods in Exploration, Review 7, Tulsa, Oklahoma. VOORHIES, M. R. 1975. Vertebrate burrows. In: FREY, R. W. (ed.) The Study of Trace Fossils. Springer, New York, 325-350. VOSSLER, S. M. & PEMBERTON, S. G. 1988. Skolithos in the Upper Cretaceous Cardium Formation: an ichnofossil example of opportunistic ecology. Lethaia, 21, 351-362. VOSSLER, S. M. & PEMBERTON, S. G. 1989. Ichnology and paleoecology of the offshore siliciclastic deposits (Cardium Formation). Palaeogeography, Palaeoclimatology, Palaeoecology, 74, 217-239. WALKER, R. G. 1990. Facies modeling and sequence stratigraphy. Journal of Sedimentary Petrology, 60, 777-786.

WALKER, R. G. & BERGMAN, K. M. 1993. Shannon sandstone in Wyoming: a shelf ridge complex reinterpreted as lowstand shoreface deposits. Journal of Sedimentary Petrology, 63, 839-851. WALKER, R. G. & EYLES, C. H. 1991. Topography and significance of a basin wide sequence-bounding erosion surface in the Cretaceous Cardium Formation, Alberta, Canada. Journal of Sedimentary Petrology, 61, 473-496. WALKER, R. G. & JAMES, N. P. (eds) 1992. Facies Models: Response to Sea Level Change. Geological Association of Canada, St John's, Newfoundland. WALKER, R. G. & WISEMAN, T. R. 1995. Lowstand shorefaces, transgressive incised shorefaces, and forced regressions: examples from the Viking Formation, Joarcam area, Alberta. Journal of Sedimentary Research, 65, 132-141. WETZEL, A. & UCHMAN, A. 1998. Biogenic sedimentary structures in mudstones: an overview. In: SCHIEBER, J., ZlMMERLE, W.

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Shales and Mudstones 1. E. Schweizerbart'sche Verlagsbuchhandling, Stuttgart, 351-369. WIGHTMAN, D. M., PEMBERTON, S. G. & SINGH, C. 1987. Depositional modeling of the Upper Mannville (Lower Cretaceous), central Alberta. Implications for the recognition of brackish water deposits. In: TILLMAN, R. W. & WEBER, K. J. (eds) Reservoir Sedimentology. Society of Economic Paleontologists and Mineralogists, Special Publications, Tulsa, Oklahoma, 40, 189-220.

Recent and sub-recent microborings from the upwelling area off Mauritania (West Africa) and their implications for palaeoecology INGRID GLAUB Geologisch-Palaontologisches Institut, Senckenberganlage 32-34, D-60325 Frankfurt am Main, Germany (e-mail: [email protected]) Abstract: Late Quaternary dead molluscan shells off Mauritania (West Africa) from the intertidal zone to 220-300 m water depth were studied for microborings. The study gives preliminary data on microborings in upwelling areas and their implications for the fossil record. In total 18 ichnotaxa are described. They are considered to be produced by cyanobacteria, green algae, red algae, fungi and foraminifera. The ichnotaxonomic composition shows minor differences relative to tropical/subtropical areas of investigation. No ichnotaxa are believed to be specific to upwelling areas. Bathymetrical distribution patterns revealed different depth ranges for individual ichnotaxa. Relative to areas with similar latitude but not influenced by upwelling, the absolute depth of the photic zone is shallower. The majority of ichnotaxa observed are already known from the fossil record (tropical and subtropical study areas) and should also be expected from ancient upwelling areas.

The term 'microborings' is used for boring systems in hard substrates with individual tunnel diameters of less than 100 urn. They are commonly found in calcareous substrates, such as shells and ooids (e.g. Golubic et al 1975; Budd & Perkins 1980; Glaub 1994; Bundschuh 2000; Vogel et al. 2000), but are also rarely observed in phosphatic substrates, such as teeth and bones (e.g. Konigshof & Glaub in press). Research on modern and fossil microborings has intensified since the development of the casting embedding technique (Golubic et al. 1970). This preparation method is based on the filling of boring systems by polymer resin and subsequent dissolution of the infested substrate. The resulting artificial casts allow a three-dimensional visualization of the various borings by SEM. The fully detailed morphology of microborings yields information on the producing microbial endoliths (belonging to cyanobacteria, green algae, red algae, fungi etc.) and provides the basis for comparison with other fossil and recent microborings. Studies of tropical to subtropical modern and fossil microborings are numerous (e.g. Radtke et al. 1997 and references therein; Gektidis 1997; Vogel et al. 1999). In contrast, studies on modern and fossil microborings from high latitudes are still rare (Bromley & Hanken 1981; Akpan & Farrow 1984; Akpan 1986; Young & Nelson 1988; Schmidt & Freiwald 1993; Glaub et al. 2002; Vogel & Marincovich in press). In this context, microborings from upwelling areas in low latitudes are of great interest. They are considered to display the influence of temperature on microboring distribution patterns under a similar angle of light incidence as in tropical to subtropical study areas.

The sampling activity of the Meteor Cruise 25/ 1971 off Mauritania (West Africa) provided an excellent database from which to obtain an initial impression of the microboring inventory in an upwelling area (initial documentation in Glaub et al. 2002), A great amount of Quaternary shell material (mainly molluscan shells) was collected, ranging from the intertidal down to 300 m water depth. The present study addresses the following questions: (1) Does the ichnotaxonomic composition differ from non-upwelling localities? (2) What information do the samples give on bathymetric distribution patterns of microborings in upwelling areas? (3) What are the palaeoecological implications? Material and methods The cruise 25/1971 of R.V. Meteor collected molluscan shells at 24 stations (Fig. 1). The activity of the scientific crew members included additional coastal field trips. Sampling depths range from the intertidal to 300m water depth. Samples were taken by dredges, grab samplers, box samplers and vibrocorers (Einsele et al. 1977). The present investigation is based on approximately 150 Holocene molluscan shells, examined by SEM after application of the casting embedding technique (Golubic et al. 1970). The first intention was to focus on Recent material, because of the good quality hydrographic data (light, temperature, currents) available. However, study of the upper layers of profiles (box sampler, vibrocorers) produced

From\ MclLROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 63-76. 0305-8719/04/S 15.00 © The Geological Society of London.

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Fig. 1. Left: area of investigation. Right: ship track of sampling stations and bathymetry (in metres). Below: shelf zonation, stations and sampling equipment (GS, grab sampler; BS, box sampler; Dr, dredge; VC, vibrocorer). Reproduced with permission from Einsele et al (1977).

MICROBORINGS IN UPWELLING AREAS

no results, even from fresh-looking samples. As a result the studied substrates derive from sampling with a dredge and grab sampler and thus represent a time interval of some thousands of years (Einsele et al. 1977). This revised sampling method is, however, a more realistic analogue for fossil assemblages, which tend to be time-averaged to some degree. The area of investigation is characterized by upwelling water masses and by a cold, mainly south-directed surface current belonging to the Canary current system. Water temperatures of about 15°C to 17°C are reported from 50m water depth and salinity values are about 35.7%o (Mittelstaedt 1972). The area currently belongs to the cold-temperate region. Near the coast the suspension load is high. Plankton blooms may also cause local, temporary reduction of light transparency conditions in the water column. For the naming of the borings observed, established ichnotaxa were used where available. As for the remaining taxa, informal names were

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given (e.g. 'Tripartitum Form'). It was decided to apply the names of existing ichnotaxa to modern traces for the following reasons: (1) if a modern trace and a fossil trace are identical, it is consistent to give both the same name; and (2) ichnological studies on modern microborings have a high potential to aid palaeoecological reconstructions, even if the producer is unknown. As long as the trace-maker is not identified, one has to find a name for the trace observed and cannot use biotaxonomy. In this case the application of established ichnotaxa is more precise and less wordy than informal names (e.g. Tripartitum Form', 'Fasciculus dactylus-lis should not be used in establishing new ichnotaxa, because there is still the opportunity to find the trace-maker in future and to use a biological binomen. This approach serves to avoid the creation of ichnotaxa based on parallel taxonomy that could otherwise increase in an irresponsible way.

Fig. 2. Artificial casts of microborings in molluscan shells off Mauritania; SEM pictures. Simplified drawings are added where needed, (a) Caverna pediculata. Station 69 (41 m water depth), (b) Saccomorpha clava. Station 66 (88-89 m water depth), (c) Fasciculus acinosus. Intertidal Baie de St Jean, (d) Fasciculus dactylus together with Tripartitum Form (thinner tunnels). Station 70 (20m water depth), (e) Fasciculus isp. 1. Station 69 (41 m water depth), (f) Fasciculus isp. 2. Station 58 (74m water depth), (g) Polyactina araneola. Station 69 (41 m water depth), (h) Orthogonum fusiferum. Station 70 (20m water depth), (i) Orthogonum lineare together with Saccomorpha clava. Station 77 (151m water depth).

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Description In total, 18 ichnotaxa are characterized by a brief morphological description, complemented by taxonomic comments and data on their geographical distribution and stratigraphic range. There are several other borings that are not described herein because their rarity precludes confident characterization of their morphology. In addition, borings similar to those of endolithic bryozoa and endolithic sponges are observed. Cavernula pediculata Radtke 1991 (Fig. 2a) Description. Cavernula pediculata is characterized by bag-shaped cavities orientated perpendicular to the substrate surface. The borings

measure 20-30 um in diameter at their greatest width and are 30-60 um in length. They are connected to the substrate surface by thin, short, occasionally ramified tunnels. One of these tunnels is usually 6-7 um wide and 6-7 um long, whereas the others display 1-2 um in diameter and are of similar length. Taxonomic comment. Similar modern borings are affiliated to Codiolum-stages of the green alga Gomontia polyrhiza (Lagerheim) Bornet & Flahault 1889. Distribution in modern and ancient environments. Records of its modern geographic distribution concentrate on the northern hemisphere, where it inhabits tropical to non-tropical environments (e.g. Nielsen 1972; Radtke 1993; Guiry & Nic Dhonncha 2002). The oldest fossil record

Fig. 3. Distribution of microborings at different stations, sorted by water depth.


dates back to the Triassic (Schmidt 1992). The occurrence of Cavernula pediculata off Mauritania is rare (Fig. 3). Saccomorpha clava Radtke 1991 (Fig. 2b) Description. The boring system consists of clubshaped borings (10-30 jam in diameter at their greatest width, interconnected by small tunnels 1 um in diameter). Several varieties of clubshaped borings are developed, in some cases occurring within a single branching system: some clubs show gradually increasing width from the proximal area near the substrate surface to the distal tips, whereas others look like a ball or an ellipsoid on a stem, and still other clubs are heart-shaped, caused by a small distal notch. A branching system mainly connects the club-shaped borings in their proximal portions, but some tunnels branch off at the distal part of the club. No collar was observed. Taxonomic comment. The ichnotaxon Saccomorpha clava Radtke 1991 is used for borings morphologically similar to those of the modern fungus Dodgella priscus Zebrowski 1936. Distribution in modern and ancient environments. Dodgella priscus is known from tropical and non-tropical modern environments down to 2350m water depth (Hohnk 1969; Zeff & Perkins 1979; Budd & Perkins 1980; Golubic et al. 1984). Saccomorpha clava is recorded from the Triassic (Schmidt 1992), Jurassic (Glaub 1994), Cretaceous (Hofmann 1996) and Tertiary (Radtke 1991). Saccomorpha clava borings are very abundant in the sampling area off Mauritania. These findings confirm earlier data, which indicate that Saccomorpha clava borings usually become more common with increasing water depth. Saccomorpha clava is a key ichnotaxon of the index microboring ichnocoenosis for the aphotic zone (Glaub 1994; see below). Fasciculus acinosus Glaub 1994 (Fig. 2c) Description. The most characteristic feature of Fasciculus acinosus is that small sphaeroid cavities (4-8 um in diameter) are arranged close to each other, so as to resemble a bunch of grapes. At the distal portion a prominent tunnel is developed (6-8 jam in diameter, 2040 jim in length). Taxonomic comment. Fasciculus acinosus Glaub 1994 is an ichnotaxon displaying a similar boring pattern to the modern cyanobacterial species Hyella balani Lehmann 1903. Distribution in modern and ancient environments. Hyella balani is widely reported from the Indian Ocean (Guiry & Nic Dhonncha 2002), NE Atlantic (Nielsen 1972), Caribbean (Gektidis

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1997) and Mediterranean (Le CampionAlsumard 1978). The fossil record of Fasciculus acinosus dates back to the Permian (Glaub et al. 1999). Fasciculus acinosus is mainly restricted to the shallow euphotic zone II, which corresponds to the intertidal (sensu Glaub 1994). Observations in Mauritanian sample material confirm this environmental restriction and extend the geographic distribution of the ichnotaxon to up welling areas. Fasciculus dactylus Radtke 1991 (Fig. 2d) Description. The Fasciculus dactylus borings are bunches of tunnels radiating from an area of entry into the substrate. Individual tunnels measure 5-9 jam in diameter. Tunnels usually display rounded tips and can only rarely be demonstrated to branch. Fasciculus dactylus may also be developed spreading parallel to the substrate surface with smaller (5-6 jam), commonly branching tunnels. Taxonomic comment. The boring pattern is known to be produced by Hyella caespitosa Bornet & Flahault 1889 in the Recent, but may also be produced by other Hyella or Solentia species (cyanobacteria). Fasciculus dactylus was introduced by Radtke (1991). Distribution in modern and ancient environments. Hyella caespitosa is known from many tropical and non-tropical study areas: NE Atlantic, SE Pacific, Indian Ocean (Guiry & Nic Dhonncha 2002). Fasciculus dactylus is quite abundant off Mauritania (Fig. 3). It is index ichnotaxon for two subzones of the euphotic zone: Fasciculus acinosus j Fasciculus dactylus ichnocoenosis of the upper euphotic zone II for the intertidal and Fasciculus dactylus jPalaeoconchocelis starmachii - ichnocoenosis for the well-illuminated subtidal (Glaub 1994). It is known since the Permian (Balog 1996; Glaub et al. 1999). Fasciculus isp. 1 (Fig. 2e) Description. Fasciculus isp. 1 is a unique clusterforming boring system characterized by tunnels radiating from a central area of penetration. The tunnels of some clusters display perpendicular to parallel orientation to the substrate surface, whereas other clusters are typified by only substrate-parallel tunnels. In both cases, three tunnels are typically visible at the entrance area. The tunnels measure 7-9 jim in diameter. Tunnel constrictions are present in some cases. The commonly developed regular dichotomous branching is distinctive. Taxonomic comment. Fasciculus isp. 1 is probably produced by Hyella Stella, a modern cyanobacterium classified in the order Pleurocapsales

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and first described by Al-Thukair & Golubic (1991). Distribution in modern and ancient environments. The first description of Hyella Stella was based on specimens in modern ooids from the Arabian Gulf, Indian Ocean (Al-Thukair & Golubic 1991). Gektidis (1997) registered Hyella Stella rarely while evaluating study experiments off the Bahamas. A further report from modern environments is given for similar borings (Radtke 1993, Fasciculus sp). For records from ancient environments, refer to Green et al. (1988). They reported findings of microborings with preserved organic remains similar to Hyella Stella, named Eohyella dichotoma Green et al. 1988. Their studies are based on Proterozoic (700-800 Ma) silicified pisoliths in Greenland. Fasciculus isp. 2 (Fig. 2f) Description. Tunnels 1—4 um in diameter are developed parallel to the substrate surface (rarely observed in perpendicular position). Ramification abundantly occurs, following angles of up to 90°. The boring system forms densely infested patches. Poorly developed tunnel constrictions are visible every 2-8 um. Taxonomic comment. Fasciculus isp. 2 displays the characteristics described by Radtke (1991) for the ichnogenus Fasciculus. The producer of this boring is unknown, but the size and ramification pattern suggest a bacterium. Distribution in modern and ancient environments. The record in modern and ancient environments is confused. In some respects, borings of the Tertiary Fasciculus parvus (Radtke 1991, taf. 10, fig. 6), orientated parallel to the substrate surface, look similar. In addition, Radtke (1993) observed borings called Fasciculus parvus showing parallel development in modern substrates off Lee Stocking Island (Bahamas). Fasciculus isp. 2 is very abundant off Mauritania (Fig. 3) Polyactina araneola Radtke 1991 (Fig. 2g) Description. The Polyactina araneola boring is composed of three morphological elements: entry tunnel; distal globular enlargement; and thinner tunnels with tapering ends. The entry tunnel (8-10 jam in diameter) is orientated perpendicular to the substrate surface. Deeper in the substrate the tunnel extends its diameter to a nearly globular enlargement 30-40 jam in diameter. All around this widening, thinner tunnels (8-10 jam in diameter) radiate in different directions. These tunnels are characterized by gradually decreasing diameters and tapering ends 1-2 um in diameter. Many tunnels turn back towards the substrate surface, where they

run parallel to the surface for several lOOum, to be connected with another Polyactina araneola boring. Together with boring systems clearly identifiable as being Polyactina araneola are those that might represent initial stages. These possible initial stages are stemmed globular borings that widen distally, where one to four thinner tunnels are developed. Taxonomic comment. Conchyliastrum enderi Zebrowski 1936, a lower fungus (order Chytridiales), has been proposed as the producer of the boring Polyactina araneola by Radtke (1991). Distribution in modern and ancient environments. Conchyliastrum is known from tropical and non-tropical environments (Hohnk 1969; Zeff & Perkins 1979; Budd & Perkins 1980). The corresponding ichnotaxon Polyactina araneola has a long geological record back to the Silurian (Bundschuh 2000). Boring activity of marine endolithic Conchyliastrum species seems to increase in the deep euphotic zone and deeper parts of the water column. Off Mauritania, its distribution is exclusive to samples from station 58, 59, 68, and 69 (Fig. 3) Orthogonum fusiferum Radtke 1991 (Fig. 2h) Description. Orthogonum fusiferum borings are characterized by thin tunnels (l-2um in diameter) with typical spindle-shaped enlargements (5-7um in diameter, lOum long). Besides this type of development there is a smaller one. It displays tunnel diameters of approximately 0.5 jam and enlargements 4um in diameter and 6um long. The smaller version shows up to four tunnels branching off at the spindle-shaped broadening, whereas the bigger variety is unbranched at widenings, or a single tunnel may originate. Taxonomic comment. Orthogonum fusiferum Radtke 1991 is the ichnotaxon for borings similar to those of the modern lower fungus Ostracoblabe implexa Bornet & Flahault 1889. Distribution in modern and ancient environments. Ostracoblabe implexa is known from studies in the southern part of the NW Atlantic (e.g. Radtke 1993) and the Mediterranean (Le Campion-Alsumard 1978). According to studies of Le Campion-Alsumard, the boring activity of Ostracoblabe implexa extends down to 200 m water depth. Orthogonum fusiferum is only rarely documented off Mauritania (Fig. 3). As for ancient environments, the oldest record of Orthogonum fusiferum is that of Bundschuh (2000) from the Silurian. Orthogonum lineare Glaub 1994 (Fig. 2i) Description. Tubular borings, 5-15 um in diameter, display a highly organized boring


system, orientated parallel to the substrate surface, dominated by ramification angles of 90°. Tunnels running parallel to each other are common. Taxonomic comment. The ichnotaxon Orthogonum lineare was erected by Glaub (1994) for fossil borings. Its producer is unknown (see below). Distribution in modern and ancient environments. Boring patterns similar to that of Orthogonum lineare are reported from several places under numerous informal names - modern and fossil, topical and non-tropical - mainly from the aphotic zone. Reports on modern borings are given by: Zeff& Perkins (1979) from the Caribbean at 435-775 m as Tubular branching borings'; Budd & Perkins (1980) from the Caribbean at 119-530 m as Tubular-Form F; Schmidt & Freiwald (1993) from Norway as Type C at 20-90 m; and Krutschinna (1997) from Norway at 230-300 m as Tubulare Spur 1'. Fossil forms have been described by Glaub (1994) from the Jurassic of Europe (inferred to be from the deep euphotic zone to aphotic zone) and by

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Hofmann (1996, taf. X, fig. 5-6, taf. XI, fig. 1) from the Cretaceous of northern Europe. Orthogonum lineare is, together with Saccomorpha clava, a key ichnotaxon for recognition of the aphotic zone ichnocoenosis (of Glaub 1994). Off Mauritania, Orthogonum lineare is common in samples from station 77 (151m) (Fig. 3). Orthogonum spinosum Radtke 1991 (Fig. 4a) Description. Tubular tunnels, characterized by diameters of 10-3 8 um and mainly rectangular ramifications. The tunnels are in some cases developed in some distance to the substrate surface and are in that case abundantly connected with it by perpendicular tunnel junctions. They display a conspicuous boring surface, which is surrounded by short hair-like extensions (1-2 jam in diameter, 10-15 um maximum length) all around the tunnels, but in some cases restricted to distinct portions of the tunnel (Fig.4a). Taxonomic comment. The first description of Orthogonum spinosum was given by Radtke

Fig. 4. Artificial casts of microborings in molluscan shells off Mauritania; SEM pictures. Simplified drawings are added where needed, (a) Orthogonum spinosum. Station 66 (88-89 m water depth), (b) Orthogonum tubulare. Station 77 (151 m water depth), (c) Reticulina elegans. Station 69 (41 m water depth), (d) Scolecia filosa. Station 69 (41 m water depth), (e) Scolecia serrata. Station 69 (41 m water depth), (f) Globodendrina monile; thinner tunnels belong to other taxa. Station 70 (20m water depth), (g) Tripartite Form. Station 69 (41 m water depth).

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(1991) based on Tertiary samples. Similar modern borings are known, but yet not attributed to a distinct producer. Distribution in modern and ancient environments. Spinose borings, usually characterized by longer hairs than described above, are very abundant in modern waters, mainly in deep water (e.g. Zeff& Perkins 1979; Budd & Perkins 1980; Glaub 1994; Krutschinna 1997). In contrast, records of fossil spinose borings are rare: Radtke (1991, Tertiary), Schmidt (1992, Triassic). Orthogonum tubulare Radtke 1991 (Fig. 4b) Description. The boring systems usually spread parallel to the substrate surface, branching rectangular. The main characteristic feature is the extremely varying tunnel diameter. At the point of ramification irregularly-shaped enlargements are developed. The diameters of the interconnecting tunnels measure 10-30|im, whereas the enlargements reach more than 40 jim in diameter. The tunnel surface of both elements, which is more clearly visible at the enlargements, is verrucose. Taxonomic comment. The ichnotaxon Orthogonum tubulare Radtke 1991 was established from Tertiary study material. The biological identity of its producer is as yet unknown. Distribution in modern and ancient environments. Borings with similar morphology but smaller dimensions have been documented in foraminiferan tests from the Atlantic Ocean at 21952323m water depth (Golubic et al. 1984). As for the fossil record, besides the description of Orthogonum tubulare from the Tertiary (Radtke 1991), it is known from the Cretaceous (Hofmann 1996) and the Jurassic (Glaub 1994). Off Mauritania, Orthogonum tubulare borings were observed in samples from five stations (Fig. 3). Reticulina elegans (Radtke) Bundschuh 2000 (Fig. 4c) Description. Reticulina elegans borings occur as densely ramified tunnel networks. They are characterized by dichotomous branching, which gives the boring system a zigzag pattern. The tunnel diameter ranges from 2um to 5|im. In the Mauritanian samples studied, Reticulina elegans was generally developed in the substrate around sponge macroborings. There is no clear explanation for this, but it seems as though Reticulina elegans borings were developed after the sponge tissue decomposition. Taxonomic comment. The characteristics of the ichnotaxon Reticulina elegans (Radtke) Bundschuh 2000 correspond to those of the boring pattern known from the modern siphon-

ally organized green alga Ostreobium quekettii Bornet & Flahault 1889. Distribution in modern and ancient environments. A long list of distributional data exists for Ostreobium quekettii, which indicates nearly global distribution. This endolithic chlorophyte is eurybathic and can survive in euphotic intertidal habitats (shaded positions) as well as under dysphotic conditions (deepest record in 220 m water depth near the Bahamas at approximately 0.01 % of surface light; Fredj & Falconetti 1977). The maximum density of occurrence is recorded from the deep euphotic zone. The corresponding ichnotaxon Reticulina elegans is known from Silurian times (Bundschuh 2000). Reticulina elegans is key ichnotaxon of the index ichnocoenosis for the deep euphotic zone (Glaub 1994). Scolecia filosa Radtke 1991 (Fig. 4d) Description. Scolecia filosa is characterized by curved running tunnels of 1-3 jam in diameter. The borings may form dense networks commonly displaying loops. Ramification rarely occurs but, if observed, it shows the typical Xor Y-ramification patterns. Taxonomic comment. The ichnotaxon Scolecia filosa was named by Radtke (1991). Its boring pattern is comparable with that of the modern cyanobacterium Plectonema terebrans Bornet & Flahault 1889. Distribution in modern and ancient environments. In modern environments Plectonema terebrans is abundantly observed. Its bathymetrical distribution ranges from the intertidal to 370m (Lukas 1978). It has been suggested that Plectonema terebrans may live as a facultative heterotroph (Glaub 1994; Glaub et al. 2001). Fossil borings classified as Scolecia filosa are known from deposits as old as the Silurian (Glaub et al. 1999; Bundschuh 2000). The general observation that the boring pattern described is widespread in modern as well as in ancient environments is confirmed by the findings off Mauritania. Also in good accordance with earlier observations (see discussion in Glaub et al. 2001) is the fact that these borings represent bathymetrically the deepest cyanobacterium off Mauritania. Scolecia serrata Radtke 1991 (Fig. 4e) Description. The boring system is identified by thin tunnels 0.5-2um in diameter, running in a slightly zigzag pattern. The borings may form mat-like patches, caused by meandering tunnels developed close to each other. In general, the boring systems are arranged parallel to the substrate surface.


Taxonomic comment. Boring systems in fossil substrates developed similarly to those described above were called S cole da serrata by Radtke (1991). According to her study the producer is unknown, but most probably a bacterium. Distribution in modern and ancient environments. Scolecia serrata is known from different modern environments. Radtke (1991) gives citations for observations in the Atlantic and the Pacific Ocean. According to Radtke (1993), Scolecia serrata is found as deep as 1600m water depth. Although modern borings like Scolecia serrata are recorded from many places (tropical and non-tropical), its taxonomic affinity remains unknown. Findings in ancient deposits are so far restricted to the Tertiary Period (Radtke 1991; Glaub et al 2002). Globodendrina monile Plewes et al. 1993 (Fig. 4f) Description. The boring consists of a spheroid, verrucose swelling (60-100 um in diameter) from which a single tunnel (20-30 um in diameter) branches off, running parallel to the substrate surface. This tunnel continues branching at low angles, forming anastomosing tunnel fusions in some cases. The branching system developed on one side of the globular swelling may be 400 um wide and 500 um long. Hair-like extensions are observed all over the boring system and are also developed as connections to the substrate surface. Taxonomic comment. The taxon Globodendrina monile was erected by Plewes et al. (1993) for borings of a foraminifer. The modern analogue is so far not identified at genus or species level (Cherchi & Schroeder 1991). Distribution in modern and ancient environments. There are a few reports on modern boring foraminifera (e.g. Smyth 1988; Cherchi & Schroeder 1991; Freiwald & Schonfeld 1996). The X-ray documentation of Cherchi & Schroeder (1991) shows both the globular boring system and the producing foraminifera within, although fine details such as hair-like extensions are not visible. Their sample material derives from 180m water depth off Scotland. Hitherto, the casting embedding technique has rarely been used for documentation of modern foraminifera and their borings, which makes comparison of modern and fossil boreholes hard to access. The data on the fossil record of Globodendrina monile date back to the Jurassic (Plewes et al. 1993; Glaub 1994, see 'Semidendrina Form') or even the Carboniferous (personal communication K. P. Vogel, Frankfurt). Future studies should focus on determining its geographic distribution more precisely as it has considerable potential to aid palaeoecological reconstructions.

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Tripartitum Form (Fig. 4g) Description. The boring system is composed of three parts: (a) interwoven tunnels 1-8 um in diameter; with (b) episodically integrated ellipsoidal to globular enlargements 3-12um in diameter; and (c) in some cases connected to perpendicularly orientated clusters of three or more tunnels (8-20 um in diameter) with slightly pointed tips. Taxonomic comment. The informal name Tripartitum Form' was chosen to describe boring patterns known from the endolithic conchocelis stage of the modern rhodophyte taxa Porphyra and Bangia. Variations of tunnel diameters suggest that different species may have caused the borings observed. Chain-like arrangements of ellipsoidal to globular widenings, which are typical for the fossil biotaxon Palaeoconchocelis starmachii Campbell et al. 1979 and its modern counterpart Porphyra nereocystis Anderson 1892 (in Blankinship & Keeler 1892), were observed only in one sample of the Mauritanian study material. Distribution in modern and ancient environments. As for endolithic red algae, more than 100 modern Porphyra and some Bangia species are known (Guiry & Nic Dhonncha 2002), but their endolithic conchocelis stages are usually not documented with the help of the casting embedding technique. Therefore the comparison of modern and ancient red algal borings is usually performed only for Porphyra nereocystis and Palaeoconchocelis starmachii. Borings, so far summarized under the term Tripartitum Form, occur abundantly off Mauritania (Fig. 3). Pygmy Form (Fig. 4h) Description. Thin tunnels approximately 0.3— 0.5um in diameter running parallel to the substrate surface. They display ramification at different angles, mainly between 60° and 90°, and are slightly curved. Taxonomic comment. The name 'Pygmy Form' was chosen according to the term for those borings observed near the Bahamas (Radtke 1993). The boring organism is yet not identified, but a bacterium is suggested, owing to the extremely small tunnel diameter. Distribution in modern and ancient environments. The Pygmy Form is commonly observed in the Mauritanian samples. It holds the deepest boring record in the Mauritanian samples (station 62, 220-300 m). Together with Radtke's observation near the Bahamas this seems to be only the second record. No fossil record of the Pygmy Form is known, and it is most probable that the extreme small tunnel diameter reduces its preservation potential.

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Echinoid Form (Fig. 4i) Description. The boring system consists of an entry tunnel connected with a fan-like widening. The entry tunnel measures 15-30 um in diameter and is up to 60-70 um long. At the point of entry it is usually orientated at a high angle to the substrate surface, and is recurved back to the surface. Near the latter contact to the surface the tunnel broadens to a flat, lobed, fan-like widening (60-120 um wide and 45-80 um long). The Echinoid Form is characterized by a slightly verrucose surface texture to the boring and has hair-like extensions, which may occur all over the boring, including the contact between the fan-like area and the substrate surface. Taxonomic comment. The informal name 'Echinoid Form' was used by Radtke (1993) for similar modern borings. So far nothing is known about either the taxonomic affinity of the borer or the fossil record of the trace. Distribution in modern and ancient environments. Besides its occurrence off Mauritania, the Echinoid Form is so far only recorded from modern environments near Mexico (Giinther 1990) and near the Bahamas (Radtke 1993). Interpretation

Ichnotaxonomic composition The ichnotaxonomic composition is in good accordance with data from tropical study areas (e.g. Puerto Rico, Budd & Perkins 1980; Bahamas, Radtke 1993). All ichnotaxa described were also found by Radtke in the Bahamas except Orthogonum spinosum. In contrast to her studies, borings similar to the following ichnotaxa are lacking off Mauritania: Scolecia maeandria, Fasciculus parvus, Fasciculus grandis, Eurygonum nodosum and Saccomorpha sphaerula. Comparison with high-latitude assemblages is not possible, because of the small database available. As a result, none of the ichnotaxa observed can be considered to be restricted to the up welling area. The taxonomic inventory of inferred tracemakers is dominated by heterotrophs. Three ichnotaxa are considered to be produced by fungi, whereas one is believed to originate from foraminiferal boring and seven are of unknown origin (most probably bacterial or fungal heterotrophs). In addition, the endolith producing Scolecia filosa borings is suspected to live as a facultative heterotroph, among other reasons because of its deep occurrence (see discussion in Glaub 1994, Glaub et al. 2001). Six ichnotaxa are attributed to photoautotrophs (three to

cyanobacteria, two to green algae, one to a red alga).

Borings and bathymetric interpretation Microborings have been demonstrated to be important tools for palaeobathymetric reconstruction (Glaub 1994, 1999; Vogel et al. 1995; Gektidis 1997). This scheme is based on depthrelated assemblages of traces made by microendoliths. Such assemblages have enabled the identification of subzones of the euphotic zone and the aphotic zone. Subsequent studies have demonstrated the applicability of the scheme to sedimentary basins from the Palaeozoic onwards (e.g. Vogel et al. 1995, 1999; Glaub & Bundschuh 1997; Bundschuh 2000). The euphotic zone covers the supratidal, the intertidal and the well-illuminated sub tidal. The lower limit of the euphotic zone is defined as the depth where the surface light (between 350 and 700 nm wavelength) is reduced to approximately 1% (for definition and further literature see Glaub 1994). This depth is almost identical with the depth at which the photosynthesis rate equals the respiration rate of photoautotrophic organisms. Photoautotrophic endoliths dominate the euphotic zone (e.g. Golubic et al. 1975), many of them being obligate photoautotrophs. However, one living cyanobacterial species (Plectonema terebrans, which produces a boring similar to the ichnotaxon Scolecia filosa) and one living chlorophycean species (Ostreobium quekettii, with its boring being comparable to the ichnotaxon Reticulina elegans) can cope with less than 1% of surface light (between 350 and 700 nm wavelength). Consequently, they are not restricted to the euphotic zone (Glaub 1994, Gektidis 1997, Vogel et al. 1999, Glaub et al. 2001). It demands further investigations to understand how Plectonema terebrans and Ostreobium quekettii can exist under these low light conditions (see discussion in Glaub 1994). On the basis of microboring assemblages, a subdivision of the euphotic zone is given. The shallow euphotic zone I is equivalent to the supratidal zone. In modern environments this is dominated by cyanobacteria capable of protecting themselves from sunburn damage by sheath pigmentation. No index ichnocoenosis for microborings was defined for this zone, because sampling has not been extended to this euphotic subzone so far. The shallow euphotic zone II corresponds to the intertidal zone; its microboring index ichnocoenosis is called the Fasciculus acinosus I Fasciculus dactylus-ichnocoenosis. It is


characterized mainly by cyanobacterial borings orientated perpendicular to the substrate surface, which are able to deal with the changing hydrographic conditions in the intertidal. For shallow euphotic zones I and II the endolithic communities are influenced by both photic and hydrodynamic factors. For this reason, the photic and hydrodynamic zonation units are identical. Shallow euphotic zone III encompasses wellilluminated sub tidal settings. In contrast to the aforementioned subzones, its microboring community is characterized by cyanobacteria along with borings of red and green algae. The predominant boring pattern is perpendicular to the substrate surface. The Fasciculus dactylus/ Palaeoconchocelis starmachii-ichnocoQnosis is the corresponding index assemblage. The deep euphotic zone is defined as the lessilluminated part of the euphotic zone down to approximately 1% of surface light. The endolithic community is dominated by red and green algae. Boring parallel to the substrate surface typifies this association. The index assemblage of this euphotic subzone is called Palaeoconchocelis starmachii/Reticulina elegansichnocoenosis. The dysphotic zone extends from the 1 % level to about 0.01% or 0.001% of surface light. The most characteristic feature of the dysphotic zone is the dominance of chemoheterotrophic endoliths (mainly fungi), which are accompanied by Scolecia filosa and Reticulina elegans. The endolithic assemblage of the aphotic zone consists of heterotrophs only. The index assemblage for this zone is called the Saccomorpha clava/ Orthogonum lineare-ichnocoenosis.

Application of the bathymetric model Several samples collected in the intertidal zone by the land excursion related to the Meteor cruise were considered to be recent. Their microboring assemblage shows the typical elements of the Fasciculus acinosus/Fasciculus dactylus-ichnocoenosis (Glaub 1994). In total, 11 microboring ichnotaxa are observed (three affiliated to cyanobacteria, three to algae, four to heterotrophs and the probably facultative heterotroph producer of Scolecia filosa) (Fig. 3). Thus the identification of the upper euphotic zone II by means of microborings is clearly applicable. Demonstration of upper euphotic zone III is, however, more problematic. Only three samples from station 70 (20 m) clearly show the typical composition of the Fasciculus dactylus/ Palaeoconchocelis starmachii-ichnocoQnosis. For further confirmation, Fasciculus dactylus is

73

developed perpendicular to the substrate surface, and a decrease in cyanobacterial borings is observed compared with the intertidal zone. In contrast to data from tropical study areas (summarized in Glaub 1994), off Mauritania heterotrophs dominate over photoautotrophs (one cyanobacterium, two algae, six heterotrophs and the probably facultative heterotroph producer of Scolecia filosa). The typical change in microendolithic association from the shallow euphotic zone to the deep euphotic zone is also hard to follow off Mauritania. Only one sample from station 55 (25m) clearly shows the Palaeoconchocelis starmachii/ Reticulina elegans-ichnocoQnosis of the deep euphotic zone with parallel development of Fasciculus dactylus. Samples from 41 m water depth down to 74m water depth display a rather confused distribution pattern of microborings. These stations are characterized by Einsele et al. (1977) as mixed assemblages. Older shell material indicating lower water depth is mixed with remains of modern shell-bearing organisms. This fact is confirmed by the findings of the present study. Several samples show a mixture of ichnocoenoses from the shallow euphotic zone, the deep euphotic zone and probably the dysphotic zone, which reflect exposure to different light conditions. Despite this diffuse picture, the occurrence of some microboring taxa is restricted to this bathymetric interval (the borings affiliated to heterotrophs: Polyactina araneola and the Echinoid Form), whereas others have their shallowest occurrence in this mixing zone (the borings affiliated to heterotrophs: Orthogonum spinosum and Orthogonum tubulare) or disappear here (the borings affiliated to photoautotrophs: Cavernula pediculata, Fasciculus dactylus. Fasciculus isp. 1, Reticulina elegans and Tripartitum or lineare, which are considered to have heterotrophic trace-makers, are observed in samples from shallower stations as well as in those from deeper stations, but not in the mixing zone. The zone between 41 m and 74 m shows the usually observed displacement of photoautotrophs by heterotrophs, but there is no clear gradient visible within this zone. The lower boundary of the euphotic zone is expected most probably at the top of the mixing zone or between the 25m and the 41m station. The parallel development of Fasciculus dactylus is considered as an indicator of this boundary. Further support derives from light measurements (Morel 1982) (see below). Samples deriving from 88-89 m (station 66) down to sampling depth 220-300 m (station 62)

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clearly display the characteristics of the Saccomorpha clava/Orthogonum linear e-ichnocoenosis. A variety of borings known from heterotrophs (mainly fungi) were identified, associated by Scolecia filosa (down to 148-149 m). Two samples from 74m (station 58) displaying no features of reworking, in contrast to the other samples from this depth, indicate aphotic conditions. Thus the boundary between the dysphotic zone and the aphotic zone is inferred between 74m and 88-89 m water depth. The absolute depths estimated for the boundaries between the individual zones and subzones are in good accordance with measurements of the optical properties off Mauritania (Morel 1982). Remarkably, they are shallower than those found in other areas of similar latitudinal position. One explanation for this observation is a high load of planktic content and resuspended sediment. Morel's long-term light measurements off Mauritania record 10-60 m for the lower limit of the euphotic zone. According to Jerlov's water type III (Jerlov 1976) the euphotic zone extends to approximately 30 m water depth, whereas the aphotic zone onset is in approximately 70m water depth. Geological significance Most of the ichnotaxa observed in this study are known from the fossil record (14 taxa). Only for the following ichnotaxa are there no clear data or no data at all from ancient deposits: Fasciculus isp. 2, Tripartitum Form, Pygmy Form and Echinoid Form. The high number of Mauritanian ichnotaxa with fossil equivalents makes the results meaningful for palaeoenvironmental studies. As for palaeo-depth reconstructions by microborings, the main requirement is the autochthony of the samples studied, because only in this case do borings of photoautotrophic endoliths reflect light conditions at the depth at which bioerosion occurred. The studies of Mauritanian samples demonstrate that investigations on microboring itself can aid in identification of allochthonous samples, if mixing of ichnocoenoses is observed. I am very indebted to D. Herm, K. Vogel, M. Gektidis and G. Radtke for information, discussion and for making available important samples. My gratitude is extended to A. Mutter, O. Sagert, R. Schade and J. Tochtenhagen for their technical assistance. The investigations were kindly funded by the German Research Foundation (DFG-Projekt Vo 90/21). Sincere thanks go to D. Mcllroy and R. Bromley. The manuscript was very much improved by an intensive, friendly discussion on

ichnotaxonomy with them and by their competent suggestions. An anonymous reviewer also deserves my appreciation.

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GUIRY, M. D. & NIC DHONNCHA, E. 2002. AlgaeBase. www. algaebase. org GUNTHER, A. 1990. Distribution and bathymetric zonation of shell-boring endoliths in recent reefs and shelf environments. Cozumel, Yucatan (Mexico). Fades, 22, 233-262. HOFMANN, K. 1996. Die mikro-endolithischen Spurenfossilien der borealen Oberkreide NordwestEuropas. Geologisches Jahrbuch, A 136, 1-151. HOHNK, W. 1969. Uber den pilzlichen Befall kalkiger Hartteile von Meerestieren. Bericht Deutsche Wissenschaftliche Kommission fur Meeresforschung, 20, 129-140. JERLOV, N. G. 1976. Marine Optics. Elsevier, Amsterdam, 1-231. KONIGSHOF, P. & GLAUB, I. (in press). Traces of microboring organisms in Palaeozoic conodont elements. Geobios. KRUTSCHINNA, J. 1997. Untersuchungen an der Tiefwasserkoralle Lophelia pertusa in verschiedenen pra- und postmortalen Stadien unter besonderer Beriicksichtigung des mikroendolithischen Befalls. Diploma thesis, FB Biologic, Johann Wolfgang Goethe-Universitat, Frankfurt am Main. LE CAMPION-ALSUMARD, T. 1978. Les eyanophycees endolithes marines. Systematique, ultrastructure, ecologie et biodestruction. PhD thesis, Universite d'Aix-Marseille II, Marseille. LEHMANN, E. 1903. Uber Hyella balani nov. spec. Nyt Magazinfor Naturvidenskap, 41, 77-87. LUKAS, K. J. 1978. Depth distribution and form among common microboring algae from the Florida continental shelf. Geological Society of America, Abstracts, 10, 448. MITTELSTAEDT, E. 1972. Der hydrographische Aufbau und die zeitliche Variabilitat der Schichtung und Stromung im nordwestafrikanischen Auftriebsgebiet im Fruhjahr 1968. 'Meteor'-Forschungsergebnisse, A, 11, 1—57. MOREL, A. 1982. Optical properties and radiant energy in the waters of the Guinea Dome and the Mauritanian upwelling area in relation to primary production. Rapports et Proces-Verbaux des Reunions, 180, 94-107. NIELSEN, R. 1972. A study of shell-boring marine algae around the Danish island Laeso. Botanisk Tidsskrift, 67, 245-269. PLEWES, C. R., PALMER, T. J. & HAYNES, J. R. 1993. A boring foraminiferan from the Upper Jurassic of England and Northern France. Journal of Micropalaeontology, 12, 83-89. RADTKE, G. 1991. Die mikroendolithischen Spurenfossilien im Alt-Tertiar West-Europas und ihre palokologische Bedeutung. Courier Forschungsinstitut Senckenberg, 138, 1-185. RADTKE, G. 1993. The distribution of microborings in molluscan shells from recent reef environments at Lee Stocking Island, Bahamas. Fades, 29, 8192. RADTKE, G., HOFMANN, K. & GOLUBIC, S. 1997. A bibliographic overview of micro- and macroscopic bioerosion. Courier Forschungsinstitut Senckenberg, 201, 307-340.

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SCHMIDT, H. 1992. Mikrobohrspuren ausgewahlter Faziesbereiche der tethyalen und germanischen Trias (Beschreibung, Vergleich und bathymetrischen Interpretation). Frankfurter geowis12, 1-228. SCHMIDT, H. & FREIWALD, A. 1993. Rezente gesteinsbohrende Kleinorganismen des norwegischen Schelfs. Natur und Museum, 123, 149-155. SMYTH, M. J. 1988. The foraminifer Cymbaloporella tabellaef shells. Journal of Foraminiferal Research, 18, 277-285. VOGEL, K. & MARINCOVICH, L. in press. Paleobathymetric implications of microborings in Tertiary strata of Alaska, USA. Palaeogeography, Palaeoclimatology, Palaeoecology. VOGEL, K., BUNDSCHUH, M., GLAUB, L, HOFMANN, K., RADTKE, G. & SCHMIDT, H. 1995. Hard substrate ichnocoenoses and their relations to light intensity and marine bathymetry. Neues Jahrbuch fur Geologie und Palaontologie, Abh., 195, 49-61.

VOGEL, K., BALOG, S.-J., BUNDSCHUH, M., GEKTIDIS, M., GLAUB, I., KRUTSCHINNA, J. & RADTKE, G. 1999. Bathymetrical studies in fossil reefs with microendoliths as paleoecological indicators. Profil, 16, 181-191. VOGEL, K., GEKTIDIS, M., GOLUBIC, S., KIENE, W. E. & RADTKE, G. 2000. Experimental studies on microbial bioerosion at Lee Stocking Island, Bahamas and One Tree Island, Great Barrier Reef, Australia: implications for paleoecological reconstructions. Lethaia, 33, 190-204. YOUNG, H. & NELSON, C. 1988. Endolithic biodegradation of cool-water skeletal carbonates on Scott shelf, northwestern Vancouver Island, Canada. Sedimentary Geology, 60, 251-267. ZEBROWSKI, G. 1936. New genera of Cladochytriaceae. Annals of the Missouri Botanical Garden, 23, 553564. ZEFF, M. L. & PERKINS, R. D. 1979. Microbial alteration of Bahamian deepsea carbonates. Sedimentology,26, 175-201.

Climatic control of trace fossil distribution in the marine realm ROLAND GOLDRING1, GERHARD C. CADEE2, ASSUNTA D'ALESSANDRO3, JORDI M. DE GIBERT4, RICHARD JENKINS5 & JOHN E. POLLARD6 l

Geoscience Building, School of Human and Environmental Sciences, University of Reading, Whiteknights, PO Box 227, Reading RG6 6AB, UK (e-mail: [email protected]) 2 Netherlands Institute for Sea Research, NIOZ, Paleobiology Department, PO Box 59, 1790 AB Den Burg, Texel, The Netherlands (e-mail: [email protected]) 3 Dipartimento di Geologia e Geofisica, Universita di Bari, Campus universitario, Via E. Orabona 4, 70125 Bari, Italy (e-mail: [email protected]) 4Departament d'Estratigrafia, Paleontologia i Geociencies Marines, Universitat de Barcelona, Marti Franques s/n, 08028, Barcelona, Spain (e-mail: [email protected]) 5 The South Australian Museum, North Terrace, Adelaide, South Australia 5000 (e-mail: [email protected]) 6Department of Earth Sciences, University of Manchester, Manchester Ml 3 9 PL, UK (e-mail: John .pollard@ man.ac. uk) Abstract: Modern coastal and shoreface faunas exhibit strong latitude (climate) controlled distributions. In contrast, most ichnotaxa are long-ranging, and ichnofacies are widely distributed geographically. This is readily explained by the dominantly warmer and more equable climates of much of the past, as well as the diversity of the producers of most ichnotaxa. Nevertheless, in the Pleistocene, and in the Eocene, cool-water ichnofabrics can be recognized. The latitudinal distributions of thalassinidean crustaceans and infaunal spatangoid echinoids are examined because of their propensity to form distinctive and often abundant trace fossils. Three climatic zones are tentatively recognized from modern shore and shoreface sediments, and which are considered to extend back to the Mesozoic: tropical and subtropical with pellet-lined burrows (Ophiomorphd), echinoid burrows and other traces; temperate with echinoid burrows and mud-lined or non-lined thalassinidean burrows (Thalassinoides), but without Ophiomorpha; and arctic (cold waters) with only a molluscan and annelid trace fossil association. Examples demonstrating this climatic trend are drawn from the Cenozoic and Pleistocene.

Trace fossils, with the exception of those utilized in Palaeozoic ichnostratigraphy and footprint stratigraphy, are well known for their long stratigraphic ranges, and sedimentological research has focused on the ichnofacies concept and the relative constancy of the Seilacherian ichnofacies through the Phanerozoic. Ichnotaxa are generally regarded as having wide geographical extent as well as long time ranges. This is undoubtedly, in part, attributable to the more equable climates that prevailed over much of the Phanerozoic, as well as the recognition that individual longranging ichnotaxa were formed by a variety of different animals. However, there are rare to uncommon ichnotaxa, and others that are more common, that have more restricted distributions, For example, Diplocraterion of decimetre depth and width, are known from the Cambrian to the Miocene. Taylor et al. (2003) pointed out that specimens with these dimensions are unknown from modern environments, and hinted that the originator may be known off tropical deltas, but

not its burrow. Diplocraterion is, of course, generally recognized as the work of a range of animals, and at present it is impossible to recognize any general climatic control in its distribution. Differences in trace fossil suites of climatically distinct continental sediments are well established for the Permian (e.g. desert sandstones, Brady 1947; Braddy 1999), lacustrine red-beds (Walter 1980, 1982, 1983), proglacial lakes (Savage 1971; Anderson 1981), and Triassic lacustrine red-beds (Clemmensen 1979). The evolutionary trends in environmental expansion and ecospace utilization seen in continental ichnofaunas (Buatois & Mangano 1993; Buatois et al. 1998), especially insect trace fossils in palaeosols (Genise et al. 2000), in part reflect their response to climate. Pemberton et al. (1992) referred to the distinctions between early Cretaceous, late Cretaceous and Cenozoic suites of trace fossils in non-marine environments, which may be readily attributable to the evolution of angiosperms, insects and crustaceans rather than climate per se. Savrda (1995) discussed the

From: MclLROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 77-92. 0305-8719/04/S15.00 © The Geological Society of London.

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application of ichnology to understanding climatically controlled decimetre-scale bedding rhythms, scour and redox cycles. Stratigraphic facies shifts of Ophiomorpha and Zoophycos have been documented (Bottjer et al 1987, 1988), but these do not refer to climatic control; rather Glaub (1994, 1999, 2004), Perry (1998) and Vogel et al (1995) showed how the distribution of microborings in skeletal carbonates is determined by photic control (depth), and Glaub et al (2002) and Vogel & Marincovich (in press) were able to extend this to latitudinal trends. Climatic effects on trace fossil distributions will obviously be most apparent in continental, marginal marine and neritic facies, because of the greater diversity and disparity present in the equivalent environments than in pelagic facies. To establish such effects in the fossil record it is necessary to show that one is dealing with ichnological differences between similar depositional environments that are of similar age. It is also important to attempt to demonstrate that absence of an ichnotaxon is due to climatic rather than to other palaeoecological factors. Absence of an ichnotaxon from a facies in which it would be expected to occur may be due to real absence (impossible to prove positively), or apparent absence due to hydraulic factors (i.e. it was once there, but was removed by penecontemporaneous erosion), or apparent absence due to loss of identity by reworking. It is in the last situation that the role of tiering in aggradational settings is significant, because the traces of deeper-tier burrows tend to overprint and eliminate the activities of shallow-tier bioturbators from the rock record, leading to a distinct bias in the ichnofabric and preferential preservation as elite traces (Bromley 1996; Goldring et al. 2002). Cadee (2001), in a section of his review paper on the sediment dynamics of bioturbating organisms in the coastal zone, drew attention to the modern latitudinal variation in bioturbation, and certain changes in the diversity of groups of organisms with latitude. The purpose of our contribution is to demonstrate that such changes may with confidence be related to climatically induced latitudinal change, and can be recognized in the fossil record. We extend this discussion to include the shoreface, which is of greater geological significance, but lack of information prevents extension to arctic shoreface settings. Cadee (2001) considered two aspects that might be applied to modern bioturbated sediments: first, that the overall degree of sediment reworking between arctic coasts and warm coasts increased more than fivefold. But such measurements cannot be applied to fossil examples, where sedimentation rate and event

stratigraphy greatly influence the degree of bioturbation, as discussed by Taylor et al. (2003) and Mcllroy (2004). Ausich & Bottjer (1982) and Bottjer & Ausich (1982) showed that the beginning of the Mesozoic witnessed a massive increase in the depth of bioturbation, though this may be somewhat modified if the 1 m depth of Thalassinoides reported by Droser & Bottjer (1989) in Ordovician limestones is included. Droser & Bottjer (1988, 1993) and Bottjer et al (2000) considered that they could detect a general increase in the degree of bioturbation seen between late Neoproterozoic-Cambrian and Ordovician sediments of the shoreface, which they attributed to the increase in diversity and abundance of the infauna. Secondly, Cadee (2001) referred to, and expanded on, the increase in diversity of coastal life from high to low latitudes. Diversity is not readily or reliably applied to ancient bioturbated sediments, because the effects of salinity and the colonization window have to be eliminated (Taylor et al. 2003), and because ichnodiversity is quite distinct from the diversity of body fossils. But changes in diversity through a succession are most useful, especially when applied to the recognition of marginal marine facies. To apply diversity change to ancient sediments requires extensive examples of more or less contemporaneity. Cadee (2001) drew attention to the lack of a diverse fauna of callianassids and crabs and their activities from arctic and temperate coasts in contrast to their richness in warm waters. This is of much geological interest because the trace fossils formed by these crustaceans are so conspicuous in the fossil record. But body fossils are very uncommon, and there are only a few distinctive types of burrow. Independent criteria that may be used to assess palaeoclimate of an ichnological section are: overall palaeogeography and regional climate; facies, especially those that are climatically sensitive - glaciogenic, desert; information from associated body fossils, particularly diversity, and information from modern and ancient associations in carbonates (foramol, chlorozoan, Lees & Buller 1972; Lees 1975); morphological factors such as shell thickness, growth banding in plants, corals and shells (Insalaco 1996), and geochemistry/isotope geochemistry of shells; abundance (frequency) - a complex ecological factor, but one that may be of value when the overall picture is taken. We first discuss aspects of the distributions and ichnology of typical crustaceans and spatangoid

CLIMATIC CONTROLS ON MARINE ICHNOLOGY

echinoids, before considering some case studies and drawing conclusions. Ichnology of certain crustaceans Dworschak (2000) reviewed the present-day latitudinal distribution of thalassinidean species, which show the highest diversity between 3040°N and 20-30°S (Fig. 1). Thalassinideans are unknown from coastal and shoreface sediments in latitudes higher than about 70°N and 50°S. Many species construct substantial burrow systems to appreciable depths (partially reviewed by Bromley 1996). Griffis and Suchanek (1991) recognized four types of thalassinidean burrow, to which we add additional types (of unproven thalassinidean origin) from the fossil record (below). The burrows are commonly, but not invariably, lined (when excavating a relatively loose substrate). The lining can be of several types: mucus, which is unlikely to be preserved fossil; a mud lining (see Bromley 1996), which may be of different thickness in different taxa; a mud lining pressed into the burrow margin (tamping, Stamhuis et al 1996); or a pelleted lining (the hard lining of Griffis & Suchanek 1991), associated with type 4 burrows (Griffis & Suchanek 1991). The pellets are inserted by the animal into the

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burrow margin, and then smoothed off on the inside (Frey et al. 1978). Type 4 burrows are distinguished by the absence of sediment mounds, but with restricted apertures, and a deep reticulate system of galleries. It is the pelletal lining that is so readily observed in the fossil record. Such traces are often referred to Ophiomorpha, even though the diagnostic burrow morphology of Ophiomorpha may not be apparent. The pellets of Ophiomorpha vary considerably in composition between occurrences, though without apparent facies change. Most commonly they are of muddy sand (as described by Frey et al. 1978), in which case they do not compact. In other cases they may be more muddy, or rich in plant debris, and may become strongly compacted on burial (Pollard et al. 1993). Frey et al. (1987) also described a combination of a pelletal lining, and a further mud inner lining. Other crustaceans make lined burrows, and in the stomatopod Squilla, the mud lining may be up to 5 mm thick for a burrow 10-20 mm diameter (Hertweck 1972). Unattributed crustacean burrows constructed in Cretaceous Chalk, representing a lithified coccolith ooze, may also be lined by fish bones and scales (Bromley 1996), gymnospermous leaves or echinoderm elements (Bather 1911), or remain unlined. It is the lining, or its absence, as well as the overall burrow morphology, that is of

Fig. 1. Global map with indications of latitudinal distributions of Callichurus major, thalassinideans and infaunal echinoids. (1) 70°N to 50°S, northern and southern limits of thalassinidean, and northern limit of infaunal echinoids. (2) 34°N to 27°S, northern and southern limits of Callichurus major. (3) 42°S probable southern limit of infaunal echinoids.

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main concern to palaeontology, and it is unfortunate that these features have been less considered by biologists, for obvious practical considerations. Three ichnogenera are widely recognized, and attributed to the work of thalassinidean, or thalassinidean-like crustaceans: Ophiomorpha, Thalassinoides and Spongeliomorpha (but see Fursich 1973; Schlirf 2000). The overall burrow morphology generally relates to type 4 of Griffis & Suchanek (1991). In Thalassinoides the margin of the burrow is smooth, whereas in Spongeliomorpha the margin displays distinct bioglyphs. Other features used to distinguish crustacean ichnotaxa are discussed by Schlirf (2000, and references therein). Five other crustacean ichnotaxa may also be considered. The upright spiral Gyrolithes may lead into one or other of the three ichnotaxa. It generally does not have a pelletal lining. The sinuous Sinusichnus (Gibert 1996a, Gibert et al 1999) from the Pliocene of the northwestern Mediterranean, which has an unlined burrow, was probably constructed by a decapod crustacean. Pliocene examples of Psilonichnus (Fursich 1981), with a Y-, J- or Uform burrow, were linked to Pholeus (Nesbitt & Campbell 2002), and to thalassinideans (Gingras et al 2000), though Frey et al. (1984) interpreted

similar burrows as the work of the ghost crab Ocypode (ocypodid). The upright bow-form burrow Glyphichnus (Bromley & Goldring 1992), with crustacean-type bioglyphs, from lower Cenozoic sediments, may be linked with certain Cylindrichnus (Goldring et al. 2002). Associated Meyeria sp. (Glypheoidea) were probably responsible for Lower Cretaceous examples (Goldring 1996). Thalassinoides, Ophiomorpha and Spongeliomorpha may all be present in one specimen to form a compound trace fossil, reflecting the need of the constructor to deal with the burrow margin in different ways. Clearly, with a firm substrate the organism needs only to render the margin attractive/unattractive to intruders or microorganisms. The common observation in sandy sediments is for a pellet-lined upper section of the burrow system to pass down to unlined or top-lined galleries, reflecting passage into a firmer level. Some species of callianassid thalassinideans appear to colonize a range of substrates: sand, sandy mud, silty mud. Those that pellet-line their burrows and live in coastal sands, or in sandy shoreface settings (Fig. 2 right), appear to have a restricted latitudinal range. Thus, on western Atlantic coasts, Callichurus major,

Fig. 2. (a) Diagram to show the formation of meniscate backfill by the modern, globular echinoid (Echinocardium cordatum) in longitudinal and transverse (centre) section (modified from Bromley & Asgaard 1975), and a wedge-shaped echinoid (Schizaster). Spines are shown diagrammatically. An active respiratory shaft (funnel) and an abandoned shaft indicate advance of Echinocardium. (b) Composite diagram of an Ophiomorpha-Planolites-mottlQd ichnofabric, with restricted shaft, constricted aperture, and lined, top-lined and unlined portions of shafts and galleries.


forming Ophiomorpha-typeburrows, does not today extend north of the North CarolinaSouth Carolina state boundary (about 34°N) (personal communication Curran 2002) or south of southern Brazil (about 27° S) (Dworschak 2000). Thalassinideans in muddier sediment are present to higher latitudes: e.g. Callianassa subterranea in the North Sea (Reineck 1963; Stamhuis et al 1997) and their burrows, which are not pellet-lined, may be referred to Thalassinoides or Spongeliomorpha. For fossil distributions the question to be raised is whether modern distributions can be applied to ancient occurrences, because different taxa will have been responsible (at least at lower orders). The question that must also be posed is whether the recognized ichnospecies of Ophiomorpha, distinguished on the form and arrangement of the pellets lining the burrow margin, had the same or different ecologies, e.g. O. nodosa, O. annulata and O. irregulaire. Tentatively, we suggest that occurrences of pelletlined burrows in shoreface, lower beach and estuarine sandy sediments represent complex constructions in warm tropical to subtropical environments by decapod crustaceans. Although there is little likelihood for confusing Ophiomorpha and Thalassinoides, it is useful to keep in mind the nature of the substrate associated with each occurrence. The Upogebiidae appear to have a similar latitudinal range to the Callianassidae (Dworschak 2000). The burrows are of type 5 (Griffis & Suchanek 1991), and of the form generally referred to the ichnotaxon Psilonichnus. The type ichnospecies, P. tubiformis, is unlined, as are other ichnospecies, though P. upsila (Frey et al. 1984) and P. lutimuratus (Nesbitt & Campbell 2002) have a distinctive mud lining. Spatangoid echinoid ichnology Burrowing echinoids evolved rapidly in the Cenozoic, though many Mesozoic echinoids were able to plough through the sediment. Tchoumatchenco & Uchman (2001) record the oldest deepwater Scolicia that is reasonably attributable to an echinoid, from the Tithonian (latest Jurassic), though the age of the oldest shallow-water three-dimensional backfilled burrow that can be related to an echinoid is much less certain, probably because of the low preservation potential (below). Spatangoid echinoids burrow to depths no greater than 20cm, and mostly shallower (reviewed by Bromley & Asgaard 1975) (Fig. 2 left). Their burrows can be very abundant as well as prominent, especially in

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relatively poorly sorted sandy sediment (Kanazawa 1992, 1995). Sand dollar activity has not yet been recorded from ancient sediments. Echinoid burrows are found in lower beach, upper and middle shoreface settings, and, off the Georgia coast (Dorjes 1972), in offshore relict sands, as well as deeper-water environments (below). The latitudinal distribution of shallow marine infaunal spatangoids extends from the tropics to 70°N (North Cape) for African and European species (Hayward & Ryland 1990), and to at least 42°S (Fell 1948) (Fig. 1), thus considerably greater than that of crustaceans forming pellet-lined burrows. The ichnotaxonomy of spatangoid locomotion-feeding trace fossils was reviewed by Uchman (1995). Bichordites refers to traces made by Echinocardium-typQ spatangoids, with a single drain, and Scolicia (and associated preservational variants) to Spatangus-typQ echinoids, with a double drain (Fig. 2 left). The resting trace Cardioichnus may be found in close association with Scolicia or Bichordites (Smith & Crimes 1983). Discussion on modern distributions of infaunal echinoids and Ophiomorphaforming crustaceans The present latitudinal distributions of infaunal echinoids and burrowing crustaceans would seem to offer opportunities for application to fossil occurrences, especially because of their distinctive traces. But there are several problems, not only with respect to the well-known difficulty of extending modern ecologies to those of fossil taxa. It is important to understand the preservation potential and regional facies distribution of the traces. We thus address ecological aspects, and the sedimentologically related aspects of tiering and tier preservation. Perhaps the first consideration is in respect of the salinity tolerance of each group: echinoids, being stenohaline, are normally excluded from estuarine environments, whereas crustaceans enjoy a wider salinity tolerance. Where infaunal echinoids and burrowing crustaceans are present in the same general area, such as the southern North Sea (Reineck 1963) and Georgia coast (Dorjes 1972), they tend to occupy different specific areas, with different sediment characteristics, and penetrate to different tier levels. Two distinct infaunal activities are represented: locomotion/feeding traces by echinoids, and more or less permanent to semi-permanent dwelling structures by crustaceans. The latter require wall stabilization and thus the availability,

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amensalism by other bioturbators. Although forming relatively deep burrows in the lower beach and shoreface they must maintain a connection with the substrate surface by constructing a ventilation shaft, which must be regularly replaced as the animal progresses forward (Fig. 2 left). Any obstruction to this upwardly built shaft is disadvantageous to the animal below. Burrowing echinoids would be inhibited from colonizing areas with pellet (hard)-lined shafts of Ophiomorpha, or lined tubes of Skolithos (cf. sand mason Lanice). On the other hand, population disturbance by the activity of the burrowing echinoid Brissopsis lyrifera (Widdicombe & Austen 1998) had a marked negative effect on overall diversity. We also note the effect on deepwater spatangoids on the preservation of Zoophycos, with truncation of the initial stages of construction (Kotake 1989). We restrict our discussion to shallow marine environments and facies, because arthropod and echinoid distributions in modern deepwater, basinal environments have not yet been fully analysed in respect of ecological parameters. Mesozoic and younger turbidites yield many examples of Ophiomorpha and Scolicia, but the environmental factors that determine their distriBelow a distal turbiditic event bed, or storm butions are largely unknown. Furthermore it is event bed, where little (minimal) penecontemnot clear whether constructor populations were poraneous erosion had taken place prior to necessarily endemic. Occurrences of Ophiomorthe event sedimentation. This is the classic pha in basin-floor settings have been frequently situation for the preservation and casting of regarded as the work of relocated individuals pre-event, shallow graphoglyptids on the (e.g. Follmi & Grimm 1990), though Uchman soles of distal turbidites (Orr 1994; Uchman (1995) showed that Ophiomorpha in Miocene 1995). flysch must be regarded as a normal component Close to the upper surface of event beds, where of the deep-sea trace fossil assemblage. The the event bed was colonized temporarily prior same problem applies to deep-sea echinoids, to the renewal of 'normal' sedimentation. but it may be considered that, following initial In inclined heterolithic sedimentation, with relocation from the shelf, populations became thin amalgamated or closely spaced event adapted to the deep seafloor (Wetzel & beds, where little erosion and little sedimentaUchman 2001). Trace fossils are notoriously tion took place between successive events. poorly preserved in hemipelagic mudrocks Gibert (1996b) described this situation from between turbidite beds. But photographic studies the Middle Jurassic of Central England, in and modern deep-sea cores (Fu & Werner 2000), oolitic and bioclastic grainstones, where each from coarse silts and fine sands from the north'event' is capped by a thin micrite. Deposition east Atlantic, show that infaunal echinoids, and took place in a marginal marine environment, their activity, are of common occurrence. Overpossibly representing lateral deposition on a printing of shallower tiers is to be expected, 'point bar'. though Baldwin & McCave (1999) recorded In association with large-scale cross-stratificafrom their sampled area off Nova Scotia the tion, with impure packstone event units (0.1ephemeral nature of the shallower tiers due to 1.0m thick), as described from Rhodes and penecontemporaneous erosion associated with Italy (below), where the 'events' represent frequent benthic storm events. Fu (personal comgrain-flow avalanching off the edge of a promunication 2000) suggested that the tiering in grading platform. Similar preservation is to be deep-sea sediments is often a temporal matter, expected under avalanching in other situations. and deeper-tier burrowing organisms are inhibA further problem for the preservation of ited by an abundance of burrowing echinoids. echinoid burrows is that they are subject to Temporal aspects, amensalism and population

either in suspension, within the sediment, or at or at the sediment-water interface, of fine-grained mud or organic matter. Both groups construct burrows to an appreciable depth, but whereas many fossil and recent crustaceans' burrows extend to a metre or more, and may be regarded as deep-tier structures, echinoid burrows are relatively shallow-tier. This is an aspect that relates to the relative preservation of the tiers, especially, under conditions of more or less continuous sediment aggradation. It is to be expected that spatangoid traces would be readily overprinted by other deeper traces, and possibly eliminated from the fossil record. Indeed, observations by JMdeG and RG on the Miocene shelfal sandy biosparites of Alicante (Spain) (below) show that this is indeed the case. But only in the Miocene of the Maltese Islands have echinoid burrows been strongly overprinted to apparent obscurity by deeper-tier crustacean activity (below). Preservation of shallow tiers may be favoured by several situations (Taylor et al. 2003; Mcllroy 2004), in which event beds are particularly involved (we do not refer to tier preservation associated with geochemical changes, such as oxygenation, e.g. Wignall 1994):


density are not readily assessed for ancient body or trace fossils, but are relevant factors in respect of shallow as well as deep marine environments. It follows from the above discussion that turbidites with Ophiomorpha, owing to their being relocated animals, might have originated in tropical or subtropical waters. However, we reserve judgement on endemic populations, except that, following Dworschak (2000), it is unlikely that water depth would be greater than 2000m. Further, Tchoumatchenco & Uchman (2001) pointed out that the environmental range of trace fossils is considered mainly at the ichnogenus level, but the ichnospecies of Ophiomorpha in deepwater facies differ from the common O. nodosa of shallow water, in being mostly hypichnia with long, smooth segments. Uchman (1999) attributed this to substrate conditions, but barrier prospecting (Jensen & Atkinson 2001) may also be an explanation. Off the Georgia coast (Dorjes 1972), where Callichirus major is common in the beach environments, the echinoid Moira bioturbates medium- to coarse-grained relict sand, which may be too clean for thalassinidean burrowing. In contrast, in the southern North Sea Callianassa subterranea occupies silty mud, whereas Echinocardium cordatum occupies fine- to medium-grained sand. In the Gulf of Gaeta (Mediterranean) (Dorjes 1971) recorded Echinocardium cordatum but no extensive activity by thalassinideans. The spatial separation of modern echinoids and thalassinideans seems to be related to substrate preference, but it might be expected that pellet-lined burrows would be formed in sandy substrates in the North Sea if higher temperatures were present! The thalassinidean present in the North Sea forms Thalassinoides-type burrows, but not Ophiomorpha. We have few data from modern coastal waters, and there are probably many more records available from the Pacific and Indian oceans. We can tentatively recognize three latitudinal zones in modern coasts and shoreface settings: in the tropics and sub tropics, where pelletforming thalassinideans and burrowing echinoids are present, though in different facies; in temperate latitudes, where spatangoid echinoids are present with Thalassinoides producers (in different facies), but not Ophiomorpha producers; in arctic latitudes, where neither group is present, and the principal bioturbators are annelids and bivalves (Aitken et al. 1988). We can apply this model to Pleistocene and Cenozoic occurrences with a certain degree of confidence, depending on the data available,

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but with caution to Cretaceous and older settings in respect of the distribution of Ophiomorpha producers. Ophiomorpha and spatangoid trace fossils With infaunal echinoid trace fossils not being recorded prior to the Tithonian (Tchoumatchenco & Uchman 2001) (and mostly later), their usefulness as climatic indicators is stratigraphically limited. Echinoid burrows have been extensively described from the Pleistocene of the Mediterranean, though less frequently from Cenozoic strata. Ophiomorpha is commonly recorded from older Mesozoic sediments and onwards. Tropical and subtropical associations (Table 1) Eocene of southern England Pollard et al. (1993) described several ichnofabrics containing Ophiomorpha from units of the Eocene in southern England where the ichnotaxon is prominent (Fig. 2 right), and made comparisons with other occurrences, especially from the southeast coast of the USA (Frey et al. 1978). Muddier units contain abundant spatangoid echinoids (Lewis 1989). Echinoid burrows were tentatively recognized in the highly bioturbated mudstones (Pollard et al. 1993). The climate of the Eocene is generally recognized as subtropical (Purton & Brasier 1997), with a flora that is compared to that of southeast Asia today (e.g. Collinson 1983). Oligocene of New Zealand Ward & Lewis (1975) recognized well-preserved spatangoid burrows in the Arno Limestone, a bioturbated calcarenite with associated largescale cross-beds, and scour channels. Ophiomorpha nodosa is uncommon, and Ward & Lewis (1975) noted the somewhat disparate occurrence of echinoid burrows (Scolicid) and Ophiomorpha, though with extensive overlap. Scolicia is also recorded in association with Cardioichnus from the Upper Miocene to Lower Pliocene (Gregory 1985). Miocene of Austria, Denmark and Poland Radwanski et al. (1975) and Radwanski (1977) described echinoid burrows, which can be assigned to Bichordites, in shallow marine heterolithic sands and muds from Denmark, in association with a diverse ichnofauna, including Ophiomorpha nodosa. O. nodosa is not, however, present in the same lithology as Bichordites.

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Table 1. Occurrences of Bichordites/Scolicia and Ophiomorpha in tropical/ subtropical, temperate and arctic climatic zones in the Cenozoic. For most, the palaeoclimate can be corroborated from associated body fossils Arctic

? Pliocene, Alaska

Temperate

Eocene/Oligocene, South Australia Pliocene, Washington State, USA ?Pleistocene, Washington State, USA Pleistocene, Mediterranean ?Pleistocene, Korea

Tropical/subtropical

Eocene, southern England Oligocene, New Zealand Miocene, Amazonia, Brazil Miocene, Austria, Denmark and Poland Miocene, Mediterranean Miocene, Patagonia, Argentina Pliocene, northwestern Mediterranean Pleistocene (Tyrrhenian), Tunisia Pleistocene, Jamaica

Radwanski et al. (1975) noted that the depositional environment was similar to that described from the modern southeastern North Sea coast, though recognizing the warmer climatic conditions from the presence of warm water molluscs, and burrows that they attributed to warm water holothurians and amphipods. Uchman & Krenmayr (1995) described occurrences of Ophiomorpha and Bichordites from shoreface sands and muds (molasse facies) of the Lower Miocene of Austria. This represents the oldest record of Bichordites. IScolicia and Ophiomorpha were also recorded from transgressive siliciclastics in SE Poland (Rajchel & Uchman 1999). Miocene and Pliocene of the Mediterranean area The molluscs and corals show that the climate of the Mediterranean area during the Middle to late Miocene was warm to subtropical. Ophiomorpha nodosa has been described from a number of sites (Table 1). In Alicante (Spain) Bichordites dominates the sandy biosparites of the Middle to late Miocene in the Bateig Hill area of Novelda, where the Miocene sediments occupy one of the small foreland Eastern Prebetic Basins (Sanz de Galdeano & Vera 1992). Bateig Hill is extensively quarried for architectural stone (Bland et al. 2001), and the variety Bateig Fantasia displays Bichordites ichnofabric (Fig. 3) in 5-20 cm thick, planar event beds, occasionally associated with Maretia sp. O. nodosa is occasionally present, and is more prominent in stratigraphically adjacent facies, where it may be the dominant ichnotaxon. In the Maltese Islands, in contrast to Alicante, shallow, pelagic wackestones of the Globigerina

Limestone Formation of the Maltese Islands, neither echinoid burrows nor O. nodosa are common. This is in spite of the high frequency and diversity of infaunal echinoids (especially Schizaster), which are in or close to life position (Rose 1974; Rose et al. 1992). Echinoid burrows have been observed (Goldring et al. 2002) at a few specific levels associated with event beds, where the shallow tiers have not been overprinted by deep-tier, bow-form burrows in Cylindrichnus-mode preservation (Goldring et al. 2002). The Pliocene marginal marine basins of the northwestern Mediterranean were described by Gibert & Martinell (1998, 1999). Echinoid burrows are present in the Roussillon Basin in

Fig. 3. Bateig Fantasia, Miocene, Alicante. Slab cut parallel to stratification with Bichordites isp. cut by other traces.


sandy blue clays in the Planolites—TeichichnusThalassinoides association. In the contemporaneous Baix Llobreget Basin, Scolicia is present in the more distal deposits whereas Ophiomorpha is present in more proximal and coarser sandy channel sediments, associated with Macaronichnus isp. and Skolithos linearis. The bioturbation index does not exceed BI2. The Lower Pliocene sediments are regarded as having been deposited under warm water conditions (Martinell et al. 1984). Miocene of Patagonia In the Lower Miocene of Patagonia (Argentina), Ophiomorpha nodosa is prominent in shoreface silty sandstones of Chubut Province (Buatois et al. 2003; Carmona & Buatois 2003), and a diverse suite of trace fossils is present in associated lower shoreface sediments. Scolicia is recorded. The authors suggested that the climatic signature was cold-temperate due to polar currents, based on independent analysis of microfossil elements, and cetacean and penguin skeletal remains. This would appear to question our model. However, the palaeoclimatic model for the Middle Miocene of the area (Valdes et al. 2000) predicts warmer conditions, not dissimilar from those of the Miocene of the Mediterranean area (above). Also, evidence from insect trace fossils in palaeosols, fossil plants and mammals in the contemporary Punturas Formation in inland Patagonia at the same latitude indicates a tropical to subtropical climate (Bown & Laza 1990). Miocene of Brazil Gingras et al. (2002) described inclined heterolithic stratification (tidally influenced point bar sediments) from the Miocene of Amazonia, deposited in an environment of fluctuating salinity, with the co-occurrence of Ophiomorpha and Scolicia, the latter indicating colonization during saline incursions. Pleistocene of Jamaica and Tunisia Bichordites is also recorded from the Pleistocene of Jamaica (Pickerill et al. 1993), in stormdominated, medium- to coarse-grained, commonly amalgamated sandstones. Most examples are seen only on upper surfaces, but in association with Ophiomorpha, Thalassinoides, Skolithos and rare Chondrites. The occurrence probably represents warm conditions and thus a mixed association. In the late Pleistocene (Tyrrhenian) of Khunis (Tunisia), Plaziat & Mahmoudi (1988) and Mahmoudi (1988) drew their examples of Bichordites from a Skolithos ichnofacies association with

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Ophiomorpha, Monocraterion, Skolithos and small, curved burrows, with the only mollusc being Loripes lacteus (a lucinoid bivalve). The Tyrrhenian of the Mediterranean represents warm-water conditions (Amore et al. 2000).

Temperate associations The Lower Tertiary of South Australia Ophiomorpha is not observed in the well-known and extensive Tertiary deposits of southeastern Australia, probably a reflection of the high to mid-latitudinal placement of this region, lending support to James's (1997) and James et al.'s (1997, 2001) recognition of many marine calcarenites of this province as 'cool-water carbonates'. Most of these carbonates are principally made of current transported bryozoan remains, and distinctive trace fossils are rare in the more offshore shelf settings. However, distinctive and exquisitely preserved crustacean remains, generally of characteristic Indo-West-Pacific aspect, are common (Jenkins 1977, 1985). Despite the abundance of echinoids in Australian basinal calcarenites, examples of their traces are rare. A spectacular bed of Scolicia with straight and closely meandering backfilled burrows 8-10 cm wide forms the upper threequarters of a 1 m thick cross-bedded shoreface, sand-rich calcarenite above the major flooding surface, marking the base of the transgressive Early Oligocene Aldinga Member of the Port Willunga Formation at Port Willunga (Fig. 4). A likely echinoid producer is occasionally found in association with the traces, the bigger examples of which can be attributed to Meoma

Fig. 4. Scolicia at the base of the transgressive Early Oligocene Aldinga Formation at Port Willunga. Hammer graduated in 5 cm intervals.

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tuberculata (McNamara et al. 1986), but fragments of another unidentified smaller spatangoid are also present. Thalassinoides appears with the transgression at the beginning of the Late Eocene, and at Port Noarlunga, south of Adelaide, metre-deep examples penetrate into cracks in the pre-lithified Tortachilla Limestone before ramifying the soft, decalcified underlying sands. Subpolygonal developments of the ichnotaxon are silicified in the overlying lower parts of the Gull Rock Member of the Blanch Point Formation. However, it is in the Late Oligocene to older Miocene of the Port Phillip basin, Victoria, where common phosphatized examples of Thalassinoides include associated remains of producers such as Ctenocheles (Callianassidae). Paired claws of Callianassa that died in their burrows are seen in the shoreface Pliocene at Port Willunga, south of Adelaide. The fully articulated, stalk-eyed crab Ommatocarcinus, clearly indicative of a warm-water influence during the late Early and Middle Miocene, apparently died in sloping burrows which show a stacked septation (Jenkins 1975). The abundant foraminiferal, faunal and floral indications of warm climatic episodes in southern Australia during the Cenozoic are well documented (Wright et al. 2000).

Swinbanks & Murray (1981) noted that the former lines its burrow with mud and mucus, whereas the latter does not line its burrow. Only the Pleistocene deposits contain Ophiomorpha associated with bay sediments. Although the authors do not explain whether the Pleistocene deposits represent glacial or interglacial sedimentation, we suggest that they may represent interglacial sedimentation, warmer than at present.

Pleistocene of Mediterranean The Pleistocene of the Mediterranean offers a number of examples of shallow water, shoreface facies, several of which show abundant traces due to burrowing echinoids. D'Alessandro & Massari (1997), in a comprehensive and integrated study of the Pliocene and Pleistocene deposits in southern Italy, showed that the Middle Pleistocene (Calcarenite della Casarana) contains a cool-water (foramol) fauna including Arctica islandica (Raffi 1986). Facies 1 includes metre-scale cross-stratification with laminatedto-bioturbated calcarenitic event beds. The bioturbated intervals are 5-10 cm thick, with Bichordites isp., whereas the laminated part can be much thicker. In some intervals the bioturbated beds are complex and up to a metre thick. The laminated-to-bioturbated units represent grain flow avalanche deposits, subsequently burrowed. Pliocene of Washington State, USA Ophiomorpha is recorded as very rare. The clinoCampbell & Nesbitt (2000) and Nesbitt & Camp- form stratification is truncated by a unit (up to bell (2002) have provided a convincing account 2 m thick) of fine-grained calcarenites, intensely of an active margin, storm-flood influenced bioturbated by Thalassinoides boxworks. The Pliocene estuary fill, grading to shelfal (basinal) Calcarenite della Casarana as a whole represents muddy sediments. Whereas the shelfal sediments coarse sediments deposited at relatively lower contain echinoid burrows, more proximal sandy, sea-level during forced regression. estuarine sediments contain Psilonichnus latimurThe succeeding Middle Pleistocene (preatus. Campbell & Nesbitt (2000) recorded only Tyrrhenian) Sabbie della Serrazza is a more rare Ophiomorpha. Psilonichnus appears to have heterogeneous unit that coarsens upwards from a wider latitudinal distribution than Ophiomor- micaceous sandy muds to coarse-grained pha, and, as Campbell & Nesbitt (2000) note, calcarenites. It is associated with a relatively its producers appear to have a tolerance to cool-water (D'Alessandro & Massari 1997) lower salinity. (cooler than present-day) shelly fauna with numerous Pseudamussium septemradiatum and Pleistocene of Washington State, USA A. islandica. Thalassinoides networks and Gingras et al. (1999, 2000) compared the modern boxworks are present, which in some instances trace-forming biota from Willapa Bay with the are of Spongeliomorpha type when piped into trace fossils in closely similar Pleistocene Early Pleistocene marls. Similar large-scale cross-stratification in grainestuarinent nized as of common occurrence in several stones to packstones was described by Bromley Pleistocene facies. This appears to refute our & Asgaard (1975), and Hanken et al. (1996) model, as it is unlikely that subtropical condi- from the Pleistocene Cape Arkhangelos calcartions reached to 47°N, even during warmer inter- enite facies of the Rhodes Formation of glacials. Thalassinoides and 'Ophiomorpha-\ike' Rhodes. The unit represents a spectacular, and burrows were recognized from the modern unusual, example of such stratification, which sediments at Willapa Bay and linked to Upogebia forms large asymptotic clinoforms in beds with pugettensis and Callianassa californiensis, though dips up to 30°. The facies is composed of event


beds, from less than 10 cm to over 1 m thick, each fining upwards. As in Italy, the beds appear to represent grain-flow avalanches on clinoforms constructed at the outer margin of a shallowwater, carbonate sand body that was prograding into deeper water. The beds are intensely bioturbated by Echinocardium, which forms winding traces of Bichordites. Ophiomorpha nodosa is absent, but is recorded from lower units of the Rhodes Formation, as are large corals, which are of late Pliocene age, representing warmwater sedimentation. Ophiomorpha is well known from ancient cross-stratified siliciclastic and carbonate sands, though often relatively sparse (Pollard et al. 1993). There are several possible explanations for the absence of crustacean activity crosscutting echinoid burrows in the clinoform stratification of Rhodes: (a) temporal exclusion as in the deep sea (above); (b) the short duration of the colonization window between successive avalanches, though this does not seem to have prevented the formation of Ophiomorpha in Cretaceous and Cenozoic cross-stratified strata (Pollard et al. 1993); (c) climatic control. The association with foramol facies in Italy suggests that a climatic control is the most likely explanation. In these examples from Italy and Rhodes Ophiomorpha appears to be virtually absent, but Thalassinoides is present in the same stratigraphic units associated with echinoid activity, thus corresponding to present-day occurrences. Hanken et al. (1996, figs 8, 14) interpreted the Cape Arkhangelos as representing highstand sedimentation, but this is somewhat inimical for a cool-water (glacial) interval, and may be better attributed to local tectonic activity. Confirmation of the climatic control is seen in the Novoli Graben (Salento Peninsula, Puglia, southern Italy), where 9m-scale sequences have been described by D'Alessandro et al. (in press). The sediments predominantly comprise bioclastic packstones and grainstones to rudstones, and represent foramol-type calcarenites. Biogenic mottling is ubiquitous, and discrete trace fossils include Thalassinoides, Bichordites, and (restricted to certain horizons) Ophiomorpha, Cylindrichnus, Gyrolithes and Tasselia. The vertical changes in the body and trace fossils within the sequences indicate water depth changes corresponding to known sixthorder glacio-eustatic climate fluctuations, with Ophiomorpha entering the stratigraphy with

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rising sea-levels. Most of the sequences are bounded by subaerial, karstic unconformities. A different association is recorded in another sequence with O. nodosa associated with Arctica islandica, a bivalve that today is found only in waters where the February temperature are equal or lower than 5-6 °C, i.e. cool to cooltemperate (Raffi 1986). However, O. nodosa is atypical, being less than 1 cm in diameter with a lining of numerous small pellets, and a different overall morphology, with scarcely branched long shafts. Pleistocene of Korea Kim & Heo (1997) described marginal marine and shelfal siliciclastics from the Early Pleistocene Seogwipo Formation of Jeju Island (Cheju-do) (latitude 33°N), Korea. Probable Bichordites or Scolicia (recorded as Laminites) are present in association with a Cruziana ichnofacies assemblage. Thalassinoides is recorded, but not Ophiomorpha. The palaeoenvironment and molluscan assemblage were described by Kang (1995), who recognized the influence of coldwater currents, and a southward migration of boreal species.

Arctic associations Eyles et al. (1992) described Pliocene? glacially influenced continental shelf and slope trace fossils from the Yakataga Formation of Alaska. We are not convinced by their identification of Ophiomorpha (Eyles et al. 1992, fig. 10), or that the backfilled burrow (op. cit. fig. 11) is attributable to echinoid activity. Thus their trace fossil assemblages may be better interpreted as attributable to annelid and molluscan activity in an arctic setting. Conclusions Our analysis of a number of Cenozoic and Pleistocene occurrences of echinoid and crustacean burrows, together with modern examples, suggests a general model of climate control for this geological interval. We tentatively recognize three latitudinal zones in modern coastal and shoreface settings: Tropical and Subtropical Zone, where pellet-forming thalassinideans and burrowing echinoids are present, though in discrete facies; Temperate Zone, where spatangoid echinoids are present with facially separated Thalassinoides producers, but not Ophiomorpha producers;

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Although we have referred to relatively few examples, and with differing degrees of confidence, our model for climatic distribution of shallow marine trace fossils appears to be robust. There are two anomalous examples from the Pliocene and Pleistocene. The Pliocene example we regard as probable misidentification of both the crustacean and echinoids traces, though we must reserve judgement on the Pleistocene example from Washington State. The occurrence in Italy of O. nodosa in association with Arctica islandica is also anomalous, but the size and overall morphology of the trace fossil are quite atypical. The association of Ophiomorpha in apparently cold-temperate sediments in the Miocene of Patagonia is anomalous, but the palaeoclimate model suggests much warmer conditions than those suggested by the micropalaeontological data. We also tentatively suggest that these assessments may be applied to deep water (turbiditic) occurrences. We recognize the problem of extending this zonation further back in the geological record to Mesozoic occurrences of Ophiomorpha because of the problems in knowing what the constructor(s) were, and whether they were capable of forming a pellet lining to the burrow. We also raise some of the questions that need to be addressed by ichnology: the types and methods of construction of burrow linings, turbiditic distributions of Ophiomorpha and related crustacean traces, and ecological tolerances of spatangoid echinoids. The distribution of other ichnotaxa should be investigated for possible latitudinal distributions. We also emphasize the necessity for careful identification of ichnotaxa, and the identification of the sedimentary surface actually colonized. We are grateful to the management and quarrymen of Bateig Laboral SA (Alicante) for access to the quarries of Bateig Hill, Novelda. E. Stamhuis (Groningen) generously provided a copy of his thesis, and L. Buatois (Tucuman), P. Dworschak (Vienna) and J.-Y. Kim (Chungbuk, Korea) kindly provided relevant literature. B. Sellwood (Reading) discussed and provided a CDROM for Miocene climates. A. Curran (Smith College, Massachusetts), K. Campbell and M. Gregory (Auckland), Shaoping Fu (Bochum) and L. Nesbitt (Washington) are acknowledged for generous discussion. L. Buatois and J. Genise constructively reviewed the paper. Participation of JMdG forms part of the activities of the consolidated research group 2001SGR-00077 of the University of Barcelona, and research project BTE 2000-0584 of the Ministerio de Ciencia y Technologia of Spain.

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HAYWARD, P. J. & RYLAND, J. S. (eds) 1990. The Marine Fauna of the British Isles and North- West Europe. Vol. 1: Introduction and Protozoans to Arthropods. Clarendon Press, Oxford HERTWECK, G. 1972. Georgia coastal region, Sapelo Island, USA: sedimentology and biology. V, Distribution and environmental significance of lebensspuren and in-situ skeletal remains. Senckenbergiana Maritima, 4, 125-166. INSALACO, E. 1996. The use of Late Jurassic coral growth bands as palaeoenvironmental indicators. Palaeontology, 39, 413^431. JAMES, N. P. 1997. The cool-water carbonate depositional realm. In: JAMES, N. P. & CLARKE, J. A. D. (eds) Cool-Water Carbonates. Society for Sedimentary Geology, Special Publications, Tulsa, Oklahoma, 56, 185-203. JAMES, N. P., BONE, Y., HAGEMAN, S., GOSTIN, V. A. & FEARY, D. A. 1997. Cool-water carbonate sedimentation during the terminal Quaternary, high-amplitude sea-level cycle: Lincoln Shelf, southern Australia. In: JAMES, N. P. & CLARKE, J. A. D. (eds) Cool-Water Carbonates. Society for Sedimentary Geology, Special Publications, Tulsa, Oklahoma, 56, 53-76. JAMES, N. P., BONE, Y., COLLINS, L. B. & KYSER, K. 2001. Surficial sediments of the Great Australian Bight: facies dynamics and oceanography on a vast cool-water carbonate shelf. Journal of Sedimentary Research, 71, 549-567. JENKINS, R. J. F. 1975. The fossil crab Ommatocarcinus corioensis (Cresswell) and a review of the related Australasian species. Memoirs of the National Museum of Victoria, 36, 33—62. JENKINS, R. J. F. 1977 A new fossil homolid crab (Decapoda, Brachura), middle Tertiary, southeastern Australia. Transactions of the Royal Society of South Australia, 101, 1-10. JENKINS, R. J. F. 1985. Fossil spider crabs from Australia. In: MURRAY LINDSAY (ed.) Stratigraphy, Palaeontology, Malacology Papers in Honour of Dr Nell Ludbrook. Department of Mines and Energy South Australia, Special Publications, 5, 145-165. JENSEN, S. & ATKINSON, R. J. A. 2001. Experimental production of animal trace fossils, with a discussion of allochthonous trace fossil producers. Neues Jahrbuch fur Geologic und Palaontologie, Monatshefte, 2001, 594-606. KANAZAWA, K. 1992. Adaptation of test shape for burrowing and locomotion in spatangoid echinoids. Palaeontology, 35, 733-750. KANAZAWA, K. 1995. How spatangoids produce their traces: relationship between burrowing mechanism and trace structure. Lethaia, 28, 211—219. KANG, S. S. 1995. Reconstruction of the paleoenvironment and molluscan assemblage of the Lower Pleistocene Sogwipo Formation, Cheju Island, Korea. PhD thesis, Niigata University, Japan. KIM, J.-Y. & HEO, W.-H. 1997. Shell beds and trace fossils of the Seogwipo Formation (Early Pleistocene), Jeju Island, Korea. Ichnos, 5, 89-99. KOTAKE, N. 1989. Paleoecology of the Zoophycos producers. Lethaia, 22, 327-341.

CLIMATIC CONTROLS ON MARINE ICHNOLOGY LEES, A. 1975. Possible influence of salinity and temperature on modern shelf carbonate sedimentation. Marine Geology, 19, 159-198. LEES, A. & DULLER, A. T. 1972. Modern temperatewater and warm-water shelf carbonate sediments contrasted. Marine Geology, 13, M67-M73. LEWIS, D. N. 1989. Fossil Echinoidea from the Barton Beds (Eocene, Bartonian) of the type locality at Barton-on-Sea in the Hampshire Basin, England. Tertiary Research, 11, 1-47. MclLROY, D. 2004. A review of some ichnological concepts, methodologies, applications and frontiers. In: MclLROY, D. (ed.) The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 3-27. MCNAMARA, K. J., PHILLIP, G. M. & KRUSE, P. O. 1986. Tertiary brissid echinoids of southern Australia. Alcheringa, 10, 55-86. MAHMOUDI, M. 1988. Nouvelle proposition de subdivisions stratigraphiques des depots attribues au Tyrrhenien en Tunisie (region de Monastir). Bulletin Societe geologique de France, 1988 (8), IV, 431-435. MARTINELL, J., DOMENECH, R. & MARQUINA, M. J. 1984. Molluscan assemblages in the north-east Spanish Pliocene. Annales Geologiques des Pays Helleniques, 32, 35-56. NESBITT, E. A. & CAMPBELL, K. A. 2002. A new Psilonichnus ichnospecies attributed to mud-shrimp Upogebia in estuarine settings. Journal of Paleontology, 76, 892-961. ORR, P. J. 1994. Trace fossil tiering within event beds and preservation of frozen profiles: an example from the Lower Carboniferous of Menorca. Palaios, 9, 202-210. PEMBERTON, S. G., MACEACHERN, J. A. & FREY, R. W. 1992. Trace fossil facies models: environmental and allostratigraphic significance. In: WALKER, R. G. & JAMES, N. P. (eds) Facies Models. Geological Association of Canada, 47-72. PERRY, C. T. 1998. Grain susceptibility to the effects of microboring: implications for the preservation of skeletal carbonates. Sedimentology, 45, 39-51. PICKERILL, R. K., DONOVAN, S. K., DIXON, H. L. & DOYLE, E. N. 1993. Bichordites monastirensis from the Pleistocene of southeast Jamaica. Ichnos, 2, 225-230. PLAZIAT, J.-C. & MAHMOUDI, M. 1988. Trace fossils attributed to burrowing echinoids: a revision including new ichnogenus and ichnospecies. Geobios, 21, 209-233. POLLARD, J. E., COLORING, R. & BUCK, S. G. 1993. Ichnofabrics containing Ophiomorpha: significance in shallow-water facies interpretation. Journal of the Geological Society, London, 150, 149-164. PURTON, L. & BRASIER, M. 1997. Gastropod carbonate 618O and 813C values record strong seasonal productivity and stratification shifts during the late Eocene in England. Geology, 25, 871-874. RADWANSKI, A. 1977. Present-day types of trace in the Neogene sequence; their problems of nomenclature and preservation. In: CRIMES, T. P. & HARPER, J. C. (eds) Trace Fossils 2, Geological Journal, Special Issue, 9, 227-264.

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A new approach to the analysis and interpretation of tracks: examples from the dinosauria PHILLIP L. MANNING

The Manchester Museum, University of Manchester, Oxford Road, Manchester, M13 9PL, UK Abstract: Tracks can potentially offer unique sources of information, providing insight into the environments, gait and posture, locomotion and behaviour. Track preservation can yield important information on substrate consistency and enable the recognition of transmitted subsurface tracks. The ability to recognize transmitted tracks has broad implications for the understanding of palaeoenvironments and interpretation of ichnological assemblages. In order to gain an understanding of how tracks are formed in three dimensions, and of their variability of expression in different substrates, controlled laboratory simulations were undertaken. Experiments were designed to recover subsurface track layers, yielding for the first time detailed information on subsurface morphology that could be related to 'true' surface track features. It was found that subsurface track relief can be correlated with the magnitude and distribution (across a foot) of load acting on the surface sediment. This pressure is transmitted through the sediment, and deforms successive layers at depth, producing an undertrack. The most significant factor controlling track morphology, whether surface or subsurface, was found to be the moisture/density relationship within the substrate at the time of track formation. Variability in the dimensions of simulated tracks, relative to the 'true' surface track, indicates that caution should be exercised when using fossil tracks to calculate hip height, speed, age, and population dynamics. In addition, comparison of experimental tracks with dinosaur tracks from the Yorkshire coast suggests that many morphological differences between vertebrate ichnotaxa reflect sediment rheology and taphonomy rather than taxonomy of the track-maker.

Fossil tracks have the potential to reveal information on the size, gait and speed of individuals, as well as clues to their behaviour and the environments in which the animals lived. However, the interpretation of tracks is often difficult, in that what is available for study is, in many cases, not an original track surface. If fossil tracks are to be a useful tool for interpreting behaviour and environments, it is essential that preservational types are recognized and can be related to a realistic surface trace. Improved understanding of track formation and preservation could also assist in diagnosing the properties and behaviour of sediment at the time of track formation. This study provides some insight into, and interpretation and understanding of, the complex, threedimensional processes occurring beneath the surface of a track (subsurface deformation) at the time of track formation. Guidelines are also provided for the interpretation of fossil tracks and their use. Experimental equipment was designed and built to optimize repeatability of experiments, to control rheological conditions, and to enable recovery of subsurface track layers. Foot templates used were designed to be comparable to dinosaur feet, though a similar methodology could be used for any foot morphology or gait.

Field study of Middle Jurassic dinosaur tracks was undertaken on the Yorkshire Coast and compared with experimental tracks. Recent work has highlighted the importance of understanding and interpreting the formation and preservation of dinosaur tracks in the field (Romano & Whyte 2003 and references therein). The diverse dinosaur track morphologies found within the Middle Jurassic track assemblages of the Yorkshire coast were studied with a view to improving their interpretation through comparison with laboratory track simulations. History of experimental vertebrate palaeoichnology The study of vertebrate tracks and traces - vertebrate palaeoichnology - has concentrated on describing the trace, with little or no interpretation of track formation/preservation. The first laboratory investigations into vertebrate track formation and preservation were carried out in December 1827 at Oxford University by William Buckland (Sarjeant 1974). Buckland persuaded a crocodile and then a tortoise to walk across a soft pie-crust (presumably of dough) and also over wet sand and soft clay

From'. MclLROY, D. (ed.) 2004. The Application of Ichnology to Palaeoenvironmental and Stratigraphic Analysis. Geological Society, London, Special Publications, 228, 93-123. 0305-8719/04/S 15.00 © The Geological Society of London.

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Fig. 1. Stacked tracks as recognized by Hitchcock (redrawn from Hitchcock 1858).

(Buckland 1828). Later work by Hitchcock (1858) on fossil tracks from the Lower Jurassic of Connecticut, USA, astutely recognized transmitted tracks (Fig. 1). It took over 100 years for ichnologists to rediscover this phenomenon through experimental work by Lingen & Andrews (1969) on horse tracks. Subsequent work has refined our understanding of tracks and track formation through a variety of approaches.

Preservation of skin/scale impressions (Lockley 1991). Presence of 'messy tracks' in which clay adhering to the foot distorts the foot outline (Bird 1944). Detached mud clasts (presumed to have been once adherent to the foot) within the track (Whyte & Romano 1993a, 1994a; Allen 1997). Collapse/flow features in which the track margin overlies the sole of the track (e.g. Lockley et al 1989; Allen 1997). The presence of a raised displacement rim or bourrelet, which is a direct reflection of the sediment's consistency at the time of track formation. Cohesive sediments tend to bulge into an unbroken, smooth rim, but more friable sands tend to bulge into a radially cracked displacement rim, and spill onto the track surface (Thulborn 1990; Allen 1997). A scenario that clouds this issue of surface track recognition is created when a limb punctures into underlying laminated strata, causing the presence of an underprint in which only the deeper portion of the limb is impressed into the sediment (e.g. Thulborn 1990). These underprints are distinct from transmitted tracks (Fig. 1), which are the primary focus of this paper.

Experimental neoichnology Detailed study of vertebrate trace fossils A number of authors have studied deposits with abundant well-preserved tracks from which a variety of broad-scale observations about sediment conditions and track preservation have been made. It is generally considered that firmground conditions produce the best preservational conditions for surface tracks (e.g. Tucker & Burchette 1977) and that soft/soupground conditions resulted in poor surface track preservation (e.g. Whyte & Romano 1981) (terminology for sediment consistency from Dodd & Stanton 1990). Detailed study of Neogene avian and mammalian ichnofaunas by Scrivner & Bottjer (1986) documented wide morphological diversity in artiodactyl tracks. They attributed the difference in morphology to variations in sediment water content at the time of formation. It was also noted by Scrivner & Bottjer (1986) that surface track preservation was improved by rapid casting by sand.

A second approach to understanding trace fossil preservation has come through observations of known organisms in identifiable sedimentological/rheological conditions. As mentioned above, experimentation has been a fundamental tool in vertebrate ichnology since the early experiments of Buckland (1828). Recent advances in reptilian, avian and mammalian neoichnology have come through careful consideration of foot anatomy and the kinematics of locomotion. Of particular importance to this study is the work on a variety of dinosaur-like modern taxa, from komodo dragons to ostrich (e.g. Padian & Olsen 1984; Demathieu 1987; Farlow 1989; Gatesy et al, 1999). Preservation of surface tracks is improved by microbial mat growth on the track surface (Thulborn 1990) and, in desert environments, by moistening by dew before casting by sand (McKee 1947).

Application ofindenter theory Determination of surf ace tracks The recognition of surface tracks is facilitated by:

Experimentation using artificial indenters in order to understand track formation and morphology was first undertaken by Allen (1989).

CONTROLS ON PRESERVED TRACK MORPHOLOGY

He suggested that mechanical theory offered a number of insights into the likely character of animal tracks in the field. In particular, it suggests that: the track shaft is surrounded by a substantial deformed zone; the deformed zone is likely to include faulted as well as folded layers; and the character of the track is likely to vary with the stratigraphy of the affected sediment. Allen (1989) found that the use of an indented plastic material in laboratory tests qualitatively reproduced all the essential features of real tracks. In the laboratory experiments the limb and foot cut a shaft into the sediment, creating an extensive zone of deformed sediment around and below the shaft; the degree of deformation increased with increased depth of penetration. The deformed zone comprised an axial downfold, in which downward-decaying undertraces were preserved, and a marginal upfold, with associated shear and fracture zones. Allen (1989) found that, where the sole of the foot was complex in shape, anatomical details - in the form of cross-folds (sensu Allen 1989) were preserved in the undertrack.

Extrapolation of biomechanics from tracks An initial contribution to the understanding of tracks in relation to biomechanics was the suggestion that the greater the force borne by a limb, the deeper will be its underprint impression (Demathieu 1987). Hence 'relative foot [track] depth' (relative to the surface on which the animal walked) was proposed as a crucial parameter for understanding the mechanics of track formation, and for estimating the centre of gravity of track-makers. This statement predicts that deeper underprint impressions will represent the dominant weight-bearing limbs, such as the manus or even particular parts of the limb (e.g. distal portion of digits). Through study of a rich dinosaur track deposit in Australia, Thulborn & Wade (1989) distinguished three distinct phases of track creation during footfall, termed: touch down (T-phase); weight bearing (W-phase); and kick-off (K-phase). Some of the morphological variability was attributed to sediment consistency, but Thulborn & Wade (1989) also related some differences between tracks to variability in the footfall cycle. Variation in the track shape with depth

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was noted as a common phenomenon, with underprints often differing greatly from the surface tracks. They noted that digit III was probably the thickest in the track-maker's foot, and normally produced a correspondingly broad impression. However, sometimes this principal load-bearing digit generated a thixotropic reaction in the underlying sediment, where on withdrawal of the foot the walls of digit III were sucked inwards, generating a narrow middle digit (cf. Figs 6c, 19). In addition the authors found that the foot did not sink into the substrate during their T-phase or the Wphase, leading to gaps in the trackways. The first attempt at interpreting complex three-dimensional surface failure in association with dinosaur tracks was undertaken by Gatesy et al (1999). Theropod tracks from the Fleming Fjord Formation (Norian-Rhaetian), East Greenland, were compared with tracks produced by a modern avian theropod, a helmeted guineafowl (Numida meleagris). The Triassic tracks indicated that the animals had walked over substrates in quite variable conditions (dry to saturated), producing a diverse assemblage. The serial sectioning of tracks confirmed that Triassic theropod feet sank, moved forward and were extracted with convergent toes, in a similar fashion to guinea-fowl (Gatesy et al. 1999). Although great inroads have been made into understanding vertebrate tracks, a thorough study of variability of tracks in three dimensions in relation to transmitted features is lacking. Presented herein is a first attempt to link surface features described from dinosaur tracks Thulborn & Wade (1989), modern tracks (Allen 1997; Gatesy et al. 1999) and the experimental indenter approach (Allen 1989) to the subsurface. A continuous trackway from dry to saturated sediment is easy to follow on a modern beach; however, the interpretation of fossil tracks in various stages of water cover is not always obvious, especially with less complete track material. The depth of the water may have affected a dinosaur's method of locomotion and the resultant track morphology. The tracks of wading dinosaurs would be quite different from those of 'swimming' dinosaurs. The 'swimming' (actually punting of a partially buoyant individual off the bed of a water body) animals may take longer strides, because they tended to be buoyed up between one footfall and the next, and their tracks may show only the tips of the toes (Coombs 1980; Thulborn 1990; Whyte & Romano 1994b; Romano & Whyte 1996). Current strength would also affect stride length.

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Experimental tracks The methodology used herein is designed to recover data from transmitted tracks generated by experimentation. The transmitted tracks can then be studied and compared with respect to the sediment conditions under which they were formed. The analysis of the distribution of ground reaction forces on indenter templates was undertaken to assist interpretation of load and pressure distribution during track formation and its bearing on final track morphology. The equipment used, an optical pedobaragraph, also allowed determination of the centre of pressure during footfall. This provided a dynamic insight into the distribution of pressure across the indenter foot for comparison with track morphology. Laboratory equipment included indenter templates, indenter assembly, Newton compression meter, and various sediment-testing boxes in which sediments could be constructed and moisture content could be varied. Indenting a substrate to record the formational and preservational history of a track appeared a simple task at the outset. However, the surface features were analogous to icebergs, with most of the information locked beneath the surface of the track as a complex, three-dimensional structure. The indenter templates varied a great deal in form and functional ability, allowing a study of the relationship between form, function and substrate. The grain size and moisture content were varied between individual track simulations, as Scrivner & Bottjer (1986) recognized these as important variables affecting track preservation. Experimental equipment

Construction of indenter templates Both simple and complex shape templates were cut from 50mm thick, rigid plastic. The shapes were chosen to represent a variety of dinosaur pes morphologies in plan view. The surface area of the seven (templates T1-T7) rigid, plastic templates (Fig. 2) was calculated using a planimeter. This study primarily concerns a semi-rigid T8 that consists of three converging steel bars threaded into an aluminium heel with a moulded silicone rubber outer. Silicone rubber was applied to the frame when held within a plaster mould. The two-part mould had been formed around a sculpted foot, of generic tridactyl type

Fig. 2. Templates used in creation of surface tracks. Surface areas for the templates were: Tl, 750.6mm2; T2, 764mm2; T3, 624.2mm2; T4, 1294mm2; T5, 1257mm2; T6, 757mm2; T7, 1005mm2.

similar to the tridactyl tracks of the Yorkshire Coast. Porous plate box Previous studies have only allowed the introduction of fluids to a sediment from above, often disrupting or destroying any constructed laminae. A better approach is to introduce water in a controlled fashion from underneath via a porous plate. A large plastic box (with reinforced struts to prevent deformation of the box under load) had a porous plate inserted 40mm above the floor of the box. The porous plate was constructed from a piece of 5mm thick plastic, drilled with a close, regular array of 3 mm diameter holes and covered in a fine (105 um) polyester monofilament mesh before its insertion into the box. Separate inlet and outlet valves were inserted into the box, beneath the level of the porous plate. The outlet valve allowed the water level to be monitored, and hence the saturation of the sediment could be controlled. When the sediment had reached the desired saturation point, flooding of the sample could be stopped immediately. When it was required to expel water from the sample, the hydrostatic head tube was removed and the water could drain away freely (Fig. 3). The porous-plate testing box had to withstand temperatures of at least 100°C during oven drying. The temperature was incrementally


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allowing the template to be indented by hand to a given force. The freedom of the NCM allowed more natural movements of the templates to be mimicked, at the price of some experimental control. The NCM was invaluable with the porous plate generated tracks, as the indenter assembly would have proved difficult to apply within the confines of the testing box. This method was employed for most of the experiments discussed below. Experimental methods Fig. 3. The porous-plate testing box as used for subsurface track simulations.

increased from 30 °C to 100 °C over 8-10 days in an oven. Indenter assembly An indenter assembly was constructed, and initially used in track simulations, so that the templates were driven into the sediments in the same way and at a controlled rate (Fig. 4). The indenter assembly allowed a template to be attached and pulled against a counterbalance by means of a spring balance, so that the template indented the sediment below. The disadvantage of this assembly was that it gave the template a forward shunt on initial contact with a sediment surface, and very unnatural reverse motion on retraction of the template. It was also difficult to generate large forces through the template without the apparatus moving or lifting with the template as the pivot. Owing to the natural rolling motion observed in almost all bipedal vertebrates when walking, a second indenting device was adapted to mimic this motion. A Newton force compression meter (NCM) was adapted so that a template could be threaded onto the end of the device,

Fig. 4. Indenter assembly used for surface track simulations.

The optical pedobaragraph (OPB) The OPB experiments were either dynamic or static loaded tests. In some experiments additional load was exerted on a specific digit or digits to record possible effects of an uneven gait. The OPB recorded the dynamically loaded tests at a frame capture rate of either 25 frames per second (25 Hz) or 16.7 frames per second (16.7 Hz). The apparatus consists of a glass plate illuminated at two opposing edges by strip lights and covered by a thin sheet of white deformable film, which is the surface on which a force can be applied (Fig. 5). Light rays are totally internally reflected within the glass plate, except at points where the white film touches the glass. At these points the light rays are refracted out of the glass plate and scatter back from the white film. The film surface is undulating in appearance on the microscopic scale, and an increase in pressure on the film results in these undulations being deformed into intimate contact with the glass plate. The greater the pressure applied to the film, the greater the area of contact with the film and glass, and the greater the quantity of light that escapes from the glass.

Fig. 5. The optical pedobaragraph.

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The result is a continuous grey-scale image of the indenter, in which intensity is proportional to the applied pressure (Betts et al. 1991). A colour image is generated from the digitized data, with the colour of the image being related to the intensity and distribution of pressure at a given time. From such images it is possible to see where high pressures occur, and to assess the general pressure-distribution changes from

the initial strike of an indenter to its toe-off. Pressure is expressed in kgcm~ 2 , which can be converted to the official SI unit of pressure, the pascal (Pa). The conversion factor is: lkgcnT 2 = 98.1kPa. It is also possible to calculate the progression of the centre of pressure throughout the sequence of frames, enabling assessment of the loadbearing properties of any indenter, as well as to

Fig. 6. (a) Tridactyl dinosaur track (F00813) sectioned parallel to digit III. Scalby Formation, Scalby Bay, Yorkshire, (b) Foot template 8 (T8) used in laboratory track simulations (scale 10cm). (c) Track simulation T8/F13 layer 3, top surface of plaster track layer 3T, from a depth of 1.3cm below the surface track layer (scale bar increments 1 cm), (d) Track simulation T8/D1.7b using T8, indented into sediment D with a force of TON when dry (moisture content 0.3%). (e) Track simulation T8/D2.7 using T8 indented into sediment D with a force of 49 N when moist (moisture content 7.3%).


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produce a combined frames image. The combined frames image is a useful indicator of pressure distribution over an indenter throughout a complete dynamic cycle, which can then be compared with static loading of the same indenter. Template 8 was tested in both static and dynamic runs on the OPB. Sediment was also placed on top of the transducer material to measure the transmission of forces. Templates 1-7 were found to be too rigid for the OPB transducer material, and gave no usable data. The results generated by the OPB provided useful data on the relationship between the distribution of load over the sole of a foot in both static and dynamic load situations. Such information is applied to the interpretation of preservation features observed in both fossil and laboratory-simulated tracks below.

Recovery of surface track features The initial indenter tests were undertaken to record surface features relating to the formation and preservation of tracks, using characterized, homogeneous sediments. The sediment was placed in a large tray 1 m long by 500 mm wide and 150mm deep. The sediment was at first indented dry, and then moisture content was increased incrementally. Moisture content was calculated at the beginning and end of each indenter test. For the surface tests the static indenter assembly was used. Templates 1-8 were indented into the substrate, with the sediment mixed and levelled before each experiment. A 300mm x 300mm wire grid of 10mm squares was lightly impressed on the surface of the sediment before indentation, to emphasize the surface displacement features (e.g. Fig. 6d, e below). The indenter force applied and the depth, width and length of each resultant track were recorded, as was the slope angle of the track wall and other distinct characteristics. Any transient features observed at the time of track formation were also noted, such as dewatering of sediment around a track, or suction of the floor of a track above true track surface. The main surface features relating directly to the foot are as shown in Figure 7.

Recovery of subsurface track features A prerequisite for retrieving subsurface deformed track layers is that separable laminae be present. Homogeneous sediments were not suitable for recording subsurface deformation, and so laminated sediments had to be

Fig. 7. Generic tridactyl track showing position of surface features recorded that relate to track morphology: digit length and interdigital angle (IDA).

constructed for each track simulation. Kaffir D™ plaster of Paris (British Gypsum™) was the material used to inter-laminate with the characterized sand and clay samples. Kaffir D™ plaster has suitable properties, including a setting time of 8 min, a high compressive strength (once dry), minimal effect on the behaviour of surrounding sediments, and a very low linear expansion on drying (around 0.25%). Other materials were tried, including cement, various muds and even flour, but none of them fulfilled all the above criteria. Laminated sediments were constructed when dry, as this enabled up to 16 layers of sand and plaster to be constructed (sometimes including laminae of damp clay sandwiched between dry sand), without affecting the dry plaster. The alternating layers of sand and plaster were individually sieved into the porous-plate testing box, with the uppermost and lowermost layers always consisting of sand. Equal volumes of sediment were used in all layers (approximately 900 ml per layer) and equal volumes of plaster (approximately 200ml per layer). Plaster was not sieved right up to the edges of the porousplate testing box, so that water would pass freely through the sand, around and between the plaster layers. Once the laminated sediment had been constructed, it could be indented either dry or moist (by introducing water via the porous plate). There was a time interval of approximately

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4min (with Kaffir D™ Plaster of Paris) before the plaster began to harden. In this time water had to be introduced via the porous plate, and the sediment had to be indented. As soon as a sample had been indented (using template 8 for this set of experiments), four 3 mm thick copper rods were inserted vertically through the sediment, puncturing each plaster layer immediately around the track to leave reference points. A further thin layer of sand was added to the surface track feature to act as a release agent, enabling an additional layer of wet plaster to be poured into the surface track to record its morphology (relative to the copper reference rods). When the top layer of plaster was dry, the copper rods were removed from the sample. The porous-plate testing box, sediment and track were placed in an oven at 30 °C for 24 h. The temperature was then increased every daily by 10 °C until the oven reached 100 °C. After 8—10 days the porous-plate testing box was removed from the oven, and the sample was removed. The sample then had to be returned to the oven for a period of 5 days to expel any remaining moisture. The sediment had to be completely dry because of the delicate plaster layers, which are easily destroyed when damp. In addition, cohesive sands hamper recovery of plaster layers. When removed from the oven, the sides of the sample were brushed clear of sand until the layers of plaster appeared as relief ledges. The depth of each layer, relative to the surface-track layer, was measured. The lowermost sand layer was first brushed away, revealing a cast of the upper surface of the lowermost horizon. Any feature that was associated with transmitted or underprint features was mapped onto an acetate sheet and photographed. The reference points made by the copper rods were also mapped onto the acetate sheet, and a track layer reference number was assigned. A spatula was then used to gently lift the plaster layer, so that the lower surface could be brushed clean, mapped onto an acetate sheet and photographed. The process of acetate sheet mapping and photographing was repeated for each successive track layer.

defined as those that have not been transmitted from overlying sediments. In the laboratorysimulated tracks this category encompasses tracks from the top sand layer, infilled by the uppermost plaster layer and best seen as a cast. The nomenclature used here is for laboratorygenerated tracks, where the unique situation exists of knowing the exact dimensions and morphology of the track-maker's pes. Nomenclature is used in this study to include the track dimensions and angles recorded from track morphology (Figs 7, 8a). Many of these terms have been used to describe fossil tracks (Haubold 1984; Leonardi 1987; Gillette & Lockley 1989; Thulborn 1990). It is difficult, if not impossible, to associate some features of fossil tracks with the morphology of a track-maker's pes or manus, owing to the vagaries of preservation. Descriptive terminology for subsurface track morphology This terminology relates to transmitted track features from the recovered subsurface layers and puncture features associated with undertracks (Fig. 8b). It is important that, if a term is used, the layer from which the feature is described is made clear, i.e. Aw, Bw, C" etc., where n is the layer number and surface type (upper or lower). Subsurface tracks were all produced using template 8 (T8). As discussed earlier, the template was very basic in form, representing the simplified morphology of a theropod or very gracile ornithopod dinosaur pes. The proximal convergence of the digits produced an unnatural intersection of the median lines for each digit. The median lines of dinosaur's digits do not usually, if ever, converge in any example of a dinosaur's skeletal pes. However, it was convenient in the current study that the position of the heel and digits of the template made measurements of track dimensions much easier, as well as being able to relate track morphologies between layers more easily. Data recording

Track description Descriptive terminology for surface track features Surface track features are taken to include the upper surface of the base of shafts of undertracks (sensu stricto Thulborn 1990). Surface tracks are

Experiments were recorded using the abbreviation for the template followed by the experiment number: for example, T8/F2 was the second experiment carried out using template 8 (T8). Six types of data were recorded from the recovered plaster track layers. The maximum zone of deformation (MZD) (Fig. 8b) was recorded for the top (T) and base

Fig. 8. (a) Track dimensions recorded for surface tracks; (b) features recorded from recovered subsurface layers. Data were used for subsequent ichnometric analysis and measured relative to known points described by puncture holes made by copper rods.

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(B) of each plaster track layer (except for T8/F2, where only one of the basal track surfaces could be recorded). The coordinates were plotted for each track simulation on a standard grid (300 mm x 300 mm), to allow comparison between layers within an individual track and their relationship with other track simulation experiments. Individual track surface tracings were generated and placed in successive order, for ease of interpretation. The direction of travel was marked on the first plot of each track data series. The position of the 'heel' was recorded in all successive layers, as was the most anterior point attributable to the distal end of each digit (Fig. 8b). The coordinates were recorded and plotted in the same way as for the MZD. Track length was recorded for the top and base surfaces of each plaster track layer. The track length was taken as the length of the MZD (Fig. 8b), as this was the most persistent track length parameter to be recorded at any depth. Track width was recorded for the top and base surfaces of each plaster track layer. The width of the track was taken as MZD track width, as shown on Figure 8b. The width of the MZD was taken as the maximum width of the track as measured perpendicular to the track axis (axis of digit III) (as shown on Fig. 8b). Digit length was also studied, taking the length measured from the most anterior point attributable to the distal end of each digit to the posterior margin of the 'heel' from each track layer (Fig. 8b). The IDA was measured as the angle of divarication at the point of intersection of the median axis of the digits about the 'heel' (Fig. 8b). Interpretation of results

Indenter theory The force exerted on T8 (Fig. 6b) during each of the subsurface track experiments was considerably smaller than those expected for a dinosaur with a similar-sized foot. A load of 5 kg (49 N) was applied over the surface area of template 8 (470mm2), producing a force of 1.06kN/m2 (1.06kPa). When different-sized structures retain the same shape, they are considered to scale with isometry or to be geometrically similar (Swartz & Biewener 1992). The surface area (S) increases in proportion to the square of its linear dimensions (/):

However, the volume (V) increases even faster, in proportion to the cube of its linear dimensions (/): Each time the dimensions of T8 are doubled, the surface area of the foot increases by a factor of 4 (FL2) FL (Footlength) and the volume increases by a factor of 8 (FL ). This means that, if the dimensions of the template 8 are doubled, the surface area increases from 470mm (125mm long foot) to 1880mm2 (250mm long foot) and the weight of the animal (load) increases from 5kg to 40kg. This means that eight times the load is exerted over four times the area, so that the pressure under the bigger foot is twice that of the smaller foot. The application of a 40 kg load was not possible in the existing experimental testing frame, so the scaled load of 5kg was applied. The larger foot would be dynamically similar to the smaller one, but twice the load would be transmitted through the sediment, affecting the resulting scale but not the morphology of a resultant track. It is impossible to achieve a quantitative test for all fossil dinosaur tracks as there are too many variables to account for. These variables include the moisture content at the time of track formation, the weight of the dinosaur, the true morphology of the dinosaur's foot, and the exact gait of the dinosaur at the time of track formation. Although these variables are controlled in the current laboratory track simulations, it is impossible to know them from a fossil track. This means that the quantitative data produced in this study can be used only as a qualitative guide to the conditions prevailing, and the foot morphology of the track-maker, at the time of track formation. The magnitude of the maximum zone of deformation (MZD) (e.g. Fig. 6d) and related features was in proportion to the load applied to the isotropic sediment. The MZD marked the distribution of vertical pressure at the point of failure at the surface and within the sediment. In transverse cross-section the deformation has an onion-shaped force bulb, as reflected in the width of the MZD with depth (Fig. 9). In longitudinal section the force bulb is found to be distorted, owing to the dynamic nature of track formation (Fig. 10). These results are in line with the predictions of Boussinesq (1883), who solved the problem of stresses reproduced at any point in a homogeneous, elastic and isotropic medium as the result of a point load applied on the surface of an infinitely large half-space. Boussinesq's elastic analysis is represented by the following


Fig. 9. MZD length/depth plot for track simulation T8/F8 showing a characteristic onion-shape force bulb.

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at a horizontal distance r from the line of action. Application of Boussinesq's equation to a hypothetical homogeneous sediment with a bearing capacity of approximately 0.4 N m"2 loaded with a 49 N force produces a failure zone (force bulb) (Fig. 11) that is remarkably similar to that seen during experimentation (Fig. 9). Boussinesq's theory relates the distribution of a static load at depth, but the current study applied dynamic loading, and therefore the application of Boussinesq's theory was qualitative rather than quantitative. Variations from the expected onion-shaped bulb were produced by the experiments, owing to the dynamic (forward-directed) loading (Fig. 10). One of the longitudinally cross-sectioned fossil tracks studied (F00813) also displayed a distorted force bulb (Fig. 6a). Experiments T8/F6 and T8/F7 were the only interlaminated clays and sands (non-homogeneous sediments) tested, and it was observed that they also generated a distorted force bulb consistent with possible failure predictions using Boussinesq's theory.

Fig. 10. MZD length/depth plot for simulation T8/F8 displaying an anteriorly displaced force bulb.

Kinematics

where P is the point load (P), and

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