Phosphorites on the Sea Floor: Origin, Composition and Distribution (Developments in Sedimentology)

DEVELOPMENTS IN SEDIMENTOLOGY 33

PHOSPHORITES ON THE SEA FLOOR Origin, Composition and Distribution

FURTHER TITLES IN THlS SERIES VOLUMES 1, 2, 3, 5 , 8 and 9 are out of print

.

4 F.G. T I C K E L L T H E TECHNIQUES O F SEDIMENTARY MINERALOGY 6 L. V A N D E R P L A S THE IDENTIFICATION O F DETRITAL FELDSPARS 7 S. D Z U L Y N S K I and E.K. W A L T O N SEDIMENTARY FEATURES O F FLYSCH AND GREYWACKES 10 P.McL.D. DUFF. A . H A L L A M and E.K. W A L T O N CYCLIC SEDIMENTATION 11 C.C. R E E V E S Jr. INTRODUCTION T O PALEOLIMNOLOGY 12 R.G.C. B A T H U R S T CARBONATE SEDIMENTS AND THEIR DIAGENESIS 13 A.A. MANTEN SILURIAN REEFS O F GOTLAND 14 K . W. G L E N N I E DESERT SEDIMENTARY ENVIRONMENTS 15 C.E. W E A V E R and L.D. P O L L A R D THE CHEMISTRY O F CLAY MINERALS 16 H.H. R I E K E 111 and G . V . C H I L I N G A R I A N COMPACTION O F ARGILLACEOUS SEDIMENTS 17 M.D. PICARD and L . R . HIGH Jr. SEDIMENTARY STRUCTURES OF EPHEMERAL STREAMS 18 G.V. C H I L I N G A R I A N and K.H. W O L F COMPACTION O F COARSE-GRAINED SEDIMENTS 19 W. S C H W A R Z A C H E R SEDIMENTATION MODELS AND QUANTITATIVE STRATIGRAPHY 20 M.H. W A L T E R , Editor STROMATOLITES 21 B. V E L D E CLAYS AND CLAY MINERALS IN NATURAL AND SYNTHETIC SYSTEMS 22 C.E. W E A V E R and K.C. BECK MIOCENE O F THE SOUTHEASTERN UNITED STATES 23 B.C. HEEZEN. Editor INFLUENCE O F ABYSSAL CIRCULATION ON SEDIMENTARY ACCUMULATIONS IN SPACE AND TIME 24 R.E. GRIM and N . G U V E N BENTONITES 25A G. L A R S E N and G.V C H I L I N G A R I A N . Editors DIAGENESIS IN SEDIMENTS AND SEDIMENTARY ROCKS 26 T. SUDO and S. SHIMODA, Editors CLAYS AND CLAY MINERALS O F JAPAN 27 M.M. M O R T L A N D and V.C. F A R M E R INTERNATIONAL CLAY CONFERENCE 1978 A . NISSENBAUM. Editor 28 HYPERSALINE BRINES AND EVAPORITIC ENVIRONMENTS 29 P TURNER CONTINENTAL RED BEDS 30 J.R.L. A L L E N SEDIMENTARY STRUCTURES I AND I1 31 T . SUDO. S. SHIMODA, H. Y O T S U M O T O and S . AITA ELECTRON MICROGRAPHS O F CLAY MINERALS 32 C.A. N I T T R O U E R , Editor SEDIMENTARY DYNAMICS O F CONTINENTAL SHELVES

DEVELOPMENTS IN SEDIMENTOLOGY 33

PHOSPHORITES ON THE SEA FLOOR Origin, Composition and Distribution G.N. BATURIN The P.P. Shirshou Institute o f Oceanology, Academy o f Sciences o f the U.S.S.R., Moscow, U.S.S.R.

(Translated by Dorothy B. Vitaliano, U.S.Geological Survey)

ELSEVIER SCIENTIFIC PUBLISHING COMPANY AMSTERDAM - OXFORD - NEW YORK 1982

ELSEVIER SCIENTIFIC PUBLISHING COMPANY 1, Molenwerf P.O. Box 211, 1000 AE Amsterdam, The Netherlands Distributors for the United States and Canada: ELSEVIER SCIENCE PUBLISHING COMPANY, INC. 52,Vanderbilt Avenue New York, N.Y. 10017

L i h r a r \ or ('onyrr** ('alaloyinL: i n I'ublivalion D a t a

B a t u r i n , G . N. (Gleb N i k o l a e v i c h ) P h o s p h o r i t e on t h e s e a f l o o r - o r i g i i : . (Developments i n s e dirne ntoloc y : v . 33) T r a n s l a t i o n of F : ) s f o r i t y n a dne okeanov. I n c l u d e s b i b l i o g r a p h y and i n d e x . 1. Phos phat e rock. 2 . Marine m i n e r a l res?lirces. I. T i t l e . 11. Series. QE471.15.Pk8B3713 553.6'4 81-Ult71 IifiCR?

ISBN 0-444-41990-X (Vol. 33) ISBN 0-444-41238-7 (Series) 0 Elsevier Scientific Publishing Company, 1981

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, without the prior written permission of the publisher, Elsevier Scientific Publishing Company, P.O. Box 330, 1000 AH Amsterdam, The Netherlands Printed in The Netherlands

FOREWORD Baturin’s book is a summary of recent data on the distribution, conditions of occurrence, composition, geochemistry, and origin of phosphorites on the ocean floor. In it main attention is paid to shelf phosphorites, includingvery young ones - Late Quaternary and Holocene; information also is given on phosphorite on seamounts, which has been studied in less detail. The most voluminous and most important part of the factual data given by Baturin were obtained by him and other investigators in working up material collected in recent years by numerous Soviet oceanographic expeditions (on the ships “Vityaz’ ”, “Academician Kurchatov”, “Dmitriy Mendeleyev”, “Mikhail Lomonosov”, and others) in the Atlantic, Pacific and Indian Oceans. This material - samples of bottom sediments, phosphorite, phosphatized rocks, and also interstitial waters pressed out of the sediments -was investigated by a number of chemical and physical methods, and as a result several thousand determinations of individual components and parameters were obtained. In addition the author used numerous data pertaining to problems of oceanic phosphorite formation published in the foreign literature. The work contains a review of the principal material on the specific group of oceanological factors governing the facies environment of oceanic phosphorite formation. Such a review is timely. Since the time when phosphorite was found on the ocean floor by the British “Challenger” expedition (1873-1876), it has commanded the attention of geologists as a possible key to an understanding of the origin of phosphorite deposits. As is known, current hypotheses of phosphorite formation are based on the use of oceanographic as well as geologic data; they are the biolithic hypothesis of J. Murray (Murray and Renard, 1891), the chemogenic hypothesis of Kazakov (1937), and the biochemical hypothesis of Bushinskiy (1963). But none of these hypotheses was based on direct observations on the actual processes of recent oceanic phosphoritization, the existence of which remained problematic. This gap was not filled until after 1969, when on the third cruise of the scientific research vessel “Academician Kurchatov” Baturin succeeded in finding numerous and diverse definitely Recent phosphorite concretions on the shelf of southwest Africa, and in following in detail the processes and conditions of their generation and formation. Subsequently Baturin participated in the finding and investigation of phosphorite formed in similar conditions on the shelf of Peru and Chile. In analyzing these data, which are new in principle, Baturin essentially has made more precise and more specific a number of earlier ideas on the for-

VI mation of phosphorite which depend on the interaction of hydrological, biological, and geological processes. It has turned out that oceanic phosphorite formation actually is caused by upwelling, as Kazakov believed. But it is not accomplished as a result of chemogenic deposition of dissolved phosphate from the ocean waters, but rather, in a complex way with other processes participating. These are: consumption of dissolved phosphate by organisms, deposition of biogenic phosphate-containing detritus on the bottom, diagenetic concentration of phosphate in the form of concretions in sediments, and subsequent reworking of the sediments. The importance of these factors for the formation of phosphorite beds was also stressed earlier (Murray and Renard, Bushinskiy), but was largely unrecognized. Now their role has been demonstrated with the help of direct oceanological observations in zones of recent upwelling, and this undoubtedly is a convincing argument in favor of the concept of phosphorite formation on the ocean shelves developed by Baturin. Therefore Baturin’s book, devoted to one of the pressing problems of the geology of the oceans, is a t the same time a contribution to an understanding of the origin of phosphorite in marine sedimentary rocks on land. P.L.BEZRUKOV

FOREWORD TO THE ENGLISH EDITION The publication of this book in the English language apparently is evidence of the increasing interest of the world’s scientific community in problems of the mineral resources of the ocean and in such quite specific questions as the origin of marine phosphorites and the role of upwelling in geology. The discovery of Recent and Upper Quaternary phosphorites on the ocean shelves was the incentive for writing this book, as it made it possible t o ascertain for the first time the actual rather than the presumed facies setting of their formation. The author, being a geologist by training, began his scientific activity with the investigation of Tertiary marine deposits of the southern U.S.S.R. and was more than once a witness of and a participant in flaming and fruitless scientific debates over the conditions of formation of the deposits related t o these formations, inasmuch as there never were any unambiguously interpretable geological facts available t o the disputants. This aroused his interest in Recent processes of sedimentation, especially those going on in zones of upwelling, the existence of which he first learned of from sources of such different character as the works of A.V. Kazakov (1937) and M. BrongersmaSanders (1957). The author’s practical acquaintance with a zone of upwelling came about in 1968 on the shelf of Namibia, which he visited on the research vessel “Academician Kurchatov”. The first samples of diatomaceous oozes brought on board there, which were unlike any other marine or oceanic sediments, filled him with the presentiment that unusual geochemical processes must be connected with them. Therefore the phosphate concretions of various forms and consistency that were found when these oozes were washed away immediately suggested Recent phosphorite formation, which was confirmed by subsequent investigations. It is natural that in describing these results the author tried t o throw light on the question of the composition and distribution of all other phosphorites known on the ocean floor and on the marine geochemistry of phosphorus as a whole. A number of additions to the Russian edition of 1978 have been introduced in the English edition, but it was impossible to encompass all the new literature pertaining t o the subject, and the author begs the reader’s indulgence in advance. The basic idea of the book is that upwelling, in conjunction with biological, diagenetic, and hydrodynamic factors, is the driving force not only of Recent but also of pre-Quaternary marine phosphoritization. Many d o not

VIII agree with this, considering it intolerable interference by oceanology in geology and an excess of the possibilities of the method of actualism. But these disagreements and controversies are in no position to overshadow the fact that the advances in the field of oceanology and the impressive discoveries of a number of geological processes on the ocean floor, including ore processes, that have been made in recent years also are having an undoubted effect on the development of modern geological science as a whole. G.N. BATURIN

CONTENTS Foreword

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

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

VII

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

1

Foreword to the English edition INTRODUCTION

V

CHAPTER 1 . PRINCIPAL FEATURES O F THE MARINE GEOCHEMISTRY OF DISSEMINATED PHOSPHORUS . . . . . . . . . . . . . . . . . . . . . . . .

5

Sources of phosphorus . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus in waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus in suspension . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Phosphorus in organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Recycling of phosphorus in water . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deposition of phosphorus from waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Disseminated phosphorus in sea and ocean sediments . . . . . . . . . . . . . . . . . . . . Phosphorus in interstitial water of marine and oceanic sediments . . . . . . . . . . . . . Release of phosphorus from sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

5 17 23 24 27 30 36 45 50

CHAPTER 2. PHOSPHORITE ON THE OCEAN SHELVES . . . . . . . . . . . . . . . .

55

East Atlantic province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . West Atlantic province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . California province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Peruvian-Chilean province . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Local accumulations and isolated finds of phosphorite on the ocean shelves . . . . . .

55 107 115 125 153

.

CHAPTER 3 PHOSPHORITE ON SEAMOUNTS. . . . . . . . . . . . . . . . . . . . . . .

163

Pacific Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Atlantic Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Indian Ocean . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . On the origin of phosphorite on seamounts . . . . . . . . . . . . . . . . . . . . . . . . . . .

163 177 181 181

CHAPTER 4 . FACIES SETTING OF RECENT OCEANIC PHOSPHORITE F O R M A T I O N * . * - - .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185

Winds . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Waves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Currents and water masses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Upwelling . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Hydrochemistry of the waters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Primary productivity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Biota . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Mass mortality of fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

185 188 188 191 195 196 201 201 206 207

X CHAPTER 5. STAGES OF LATE QUATERNARY PHOSPHORITE FORMATION 219 ON THE OCEAN SHELVES. . . . . . . . . . . . . . . . . . . . . . . . . . . Supply of phosphorus to the shelf by ocean waters . . . . . . . . . . . . . . . . . . . . . . Consumption of phosphorus by organisms . . . . . . . . . . . . . . . . . . . . . . . . . . . . Deposition of phosphorus on the bottom . . . . . . . . . . . . . . . . . . . . . . . . . . . . Diagenetic redistribution and concentration of phosphorus . . . . . . . . . . . . . . . Reworking of phosphatic sediments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 6. SOME FEATURES O F THE BEHAVIOR OF ELEMENTS ASSOCIATED WITH PHOSPHORUS IN THE COURSE O F OCEANIC PHOSPHORITE FORMATION. . . . . . . . . . . .

..

......

Organic matter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Carbon and oxygen isotopes of COz and PO4 . . . . . . . . . . . . . . . . . . . . . . . . . Amorphous silica . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Fluorine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iodine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Uranium isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Thorium isotopes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare earth elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Iron . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Rare and disseminated elements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . CHAPTER 7. ON THE SIMILARITY O F THE PROCESSES OF RECENT AND PRE-QUATERNARY PHOSPHORITE FORMATION . . . . . . . .

231 231 235 240 242 244 245 255 256 265 266

..

279

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

293

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

297

CHAPTER 8. CONCLUSIONS References

219 219 220 221. 223

Subject Index

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

329

INTRODUCTION The purpose of this work is to clarify the voluminous factual data accumulated recently on the marine geochemistry of phosphorus and on all the oceanic phosphorites now known, their composition, age, combination of concomitant facies conditions, and genesis. Main attention has been paid to phosphorite on the submerged margins of the continents (mainly on the shelves) as being the most widespread, best studied, and closest to concretionary phosphorite on land. The phosphorite discovered relatively recently on seamounts and differing essentially from shelf phosphorite has been less studied so far and is described only in general features. Phosphorite was discovered on the ocean floor more than a hundred years ago, at the time of the first joint oceanographic expedition on the “Challenger” (1873-1876). On the basis of what was known of their composition and conditions of occurrence, J. Murray (Murray and Renard, 1891) suggested one of the first versions of the biogenic-diagenetic hypothesis of the origin of phosphorite on the ocean floor and of the concretionary phosphorites from marine sedimentary rocks on land, which are similar to them in morphological features. Recent achievements in the field of oceanography have been used repeatedly to substantiate other hypotheses of the origin of phosphorites, both similar to Murray’s scheme (the biochemical hypothesis of Bushinskiy, 1963) and different in principle (the chemogenic hypothesis of Kazakov, 1937). In recent years marine geology and chemical oceanography have developed a t especially rapid tempos in connection with the overall intensification of the mastering of the oceans. As a result there has been a considerable expansion and renewal of the whole arsenal of data, which on the one hand concern the behaviour of disseminated phosphorus in marine and oceanic sedimentation, and on the other the distribution, composition, age, and conditions of occurrence of phosphorite on the ocean floor. Especially noteworthy are the results of determination of the age of oceanic phosphorites, which have made it possible to dispel the long-standing fallacy of identifying any oceanic phosphorites as Recent. As had been ascertained, phosphorite formation in the ocean occurred in a wide time interval from Cretaceous to Holocene, but its recent manifestations are limited mainly to the areas of the shelves of southwest Africa (Namibia and the northern part of the South African Republic) and Peru-Chile. The undeniable evidence of recent phosphorite formation occurring in

2 the ocean, obtained with the help of mutually consistent geological, geochemical, and geochronological data, permits a new approach to the problem of the origin of phosphorite from the standpoint of the method of actualism, the importance of which in geology has been recognised since the time of Lyell. To accomplish this purpose it was necessary to examine a wide circle of phenomena and trace the Recent paths and forms of migration of phosphorus from its sources of supply to the ocean to the phosphorite occurrences being generated on the ocean floor. Previously such attempts could not be crowned with success as only the initial (phosphorus in the ocean water) and final (phosphorite deposits) links in the chain were open to the eyes of investigators. Its main central part - the transition from Clarke contents of phosphorus t o ore concentrations was left to the fate of hypotheses, formulated on the basis of ambiguously interpretable indirect data. Now that this gap has been filled it has become possible not merely to reconstruct, but also to observe the whole complicated combination of phenomena making up the process of oceanic phosphorite formation. The main source of phosphorus in the present ocean is run-off from the continents; the contribution of a volcanic source is of minor and local significance. The greater part of the total mass of phosphorus arriving in the ocean in the composition of suspended detrital matter is geochemically inert and settles relatively rapidly without taking part in the process of phosphorite formation. The relatively smaller geochemically active part of the phosphorus reaches the ocean in dissolved form. The fate of dissolved phosphorus is decided by its role as one of the most important biogenic elements. Its movement toward the bottom is complicated by repeated use in food chains, beginning from phytoplankton and ending with fish and marine mammals. The main path of extraction of dissolved phosphorus from sea water is biogenic. Being deposited on the bottom in biogenic detritus together with other sedimentary material, geochemically mobile phosphorus is usually disseminated in bottom sediments where its bulk composition fluctuates within the Clarke range usual for sedimentary rocks as a whole. But in those cases where phosphorus-rich biologic detritus accumulates on the floor, relative concentration of phosphorus also occurs. The active process of deposition of geochemically mobile phosphorus is typical only of the near-shore biologically productive zones where upwelling of phosphorus-rich waters occurs; the largest of these zones are located off the coast of southwest Africa and off Peru-Chile. The next stage in the concentration of geochemically active phosphorus - the diagenetic - is related to redistribution of the elements in the upper layer of sediments rich in organic matter and leads to the formation of phos-

3

phate grains, nodules, concretions, phosphate cement, and phosphatization of carbonate detritus, bones, and coprolites. But all these formations, scattered in the sediments, are only the formal elements of a potential phosphorite deposit, which can be produced only by way of concentration of the phosphatic material. For this the final stage of phosphorite formation is necessary - mechanical sorting or redeposition of sediment, which occurs periodically in the zone of the ocean shelves throughout their whole geologic history due to the action of waves and currents. That seems to be the general trend of Cenozoic phosphorite formation on the shelves of the oceans in the light of recent oceanological, geochemical, and geological data, summarized in this book and indicating the multistage nature of this process and biogenic-diagenetic essence of its main links.

This Page Intentionally Left Blank

Chapter 1 PRINCIPAL FEATURES OF THE MARINE GEOCHEMISTRY OF DISSEMINATED PHOSPHORUS

SOURCES OF PHOSPHORUS

Phosphorus is supplied to the ocean from several sources: from the continents in the composition of atmospheric precipitation and dust, and from river, underground, and glacial run-off; by abrasion of the shores; from the depths of the earth in volcanic and hydrothermal activity; and in the composition of cosmic material. Let us consider the data characterizing the share of each of the enumerated sources in the introduction of phosphorus into the World Ocean.

Atmospheric precipitation and dust Every year 1~324,000km3 of water fall on the ocean surface in the form 0 on land (Table 1-1). of atmospheric precipitation, and ~ 9 9 , 0 0 km3 Every year about 38,000 km3 of water are supplied from the ocean to the land in the form of atmospheric precipitation, and from the land t o the ocean, not more than 8000 km3 (Defant, 1961; Horn, 1972). The content of dissolved phosphorus in pure atmospheric precipitation (rain, snow, hoarfrost) over the continents ranges between 0.0003 and 0.006 mg/l. In contaminated rain water the phosphorus content may rise to 0.02-0.06mg/l due to the water-soluble part of dust (Bashmakova et al., 1969). In fresh snow contaminated by dust, in particular in the snowfields of Kazakhstan and the Altay, the content of dissolved inorganic phosphorus is still higher - in isolated cases up to 0.8 mg/l (Table 1-2).

TABLE 1-1 Water balance of the earth (Defant, 1961) Surface

Atmospheric precipitation ( km3/ur)

Evaporation (km3/ur)

Oceans Continents

324,000 99,000

361,000 62,000

Earth as a whole

423,000

423,000

TABLE 1-2 Phosphorus content of atmospheric precipitation Reference

Object of investigation

Time of observation

Baikal area

rain water

Aug. 1951 Jul. 1953 Sep. 1951 Feb. 1952 Jan. 1953

7.8-8.7

tr.4.008

Votintsev, 1954

7.6-8.7

0.00 5-0 .O1 0

Votintsev, 1954

Nov. 1957 Mar. 1958

0.9-5.4

0.003-0.006

Voronkov, 1963a

Nov. 1957 Mar. 1958 Jan. 1958 Mar., Apr. 1958

1.1-15.2

0.009-0.135

Voronkov, 1963a

5-8 11.4-53.2

0.003-0.005 0.0003-0.786

Voronkov, 1963a Voronkov, 1963a

snow water hoarfrost Lowland Altay

new-fallen uncontaminated snow new-fallen snow rime packed snow at end of winter

Mineralization (mg/l)

P( mg/l)

Area

5.4

tr.

Votintsev, 1954

Northern Kazakhstan

packed snow at end of winter

Mar., Apr. 1955-1957

4.0-1 11.3

0.0003-0.786

Voronkov, 1963a

Left bank of Ishim River

packed snow at end of winter

Mar. 1955

4.6-11.5

0.003

Voronkov, 1963b

Various areas

rain and snow waters rain water

1965,1966

-

0.010-0. 120

Semenov et al., 1967

0.0 1 0 4 . 0 30

Bashmakova et al., 1969

of U.S.S.R.

Stavropol’ area Antarctica

snow

Jun.-Nov. 1966

18.09-50.92

Oct. 1961 Jan. 1962

40

n.d

Angino et al., 1964

7 To calculate the balance of dissolved phosphorus in atmospheric precipitation it can be assumed that its average content in the moisture evaporated from the ocean surface is 0.003 mg/l, and in the moisture evaporated from the land surface (taking into account contamination by dust) is 0.010-0.015 mg/l. In that case, 3 t/km3 x 38,000 km3 = 114,000 t is supplied annually by the ocean to the land, and 10-15 t/km3 x 8000 km3 = 80-120 x l o 3 t P from the land to the ocean, which indicates that the role of atmospheric precipitation is relatively small in the exchange of dissolved phosphorus between the ocean and the continents. In addition to moisture, solid particles of dust are present in the atmosphere over the oceans, in concentrations ranging from 0.003 to 10 pg/m in various areas, and f r o m < 2 to 20pm, rarely up to 4 0 p m , in size. The predominant components of the mineralogic composition of the dust usually are illite, chlorite, kaolinite, less often plagioclases and quartz. With strong winds dust is carried for hundreds and thousands of kilometers over the oceans, in particular from the Sahara to the West Atlantic (Barbados island). The results of investigation of the dust collected over the oceans have been described in many works (Aston et al., 1973; Chester, 1972). The total amount of atmospheric dust supplied to the ocean from the land is estimated at 1.6 x lo9 t/yr (Lisitsyn, 1974). In some areas it plays an appreciable role in the total balance of sedimentation, which is confirmed by the presence of minerals of eolian origin in deep-sea bottom sediments (Arrhenius, 1966; Griffin et al., 1968; Rex et al., 1969). Atmospheric dust collected over the tropical part of the Pacific Ocean (Prosper0 and Bonatti, 1969) is similar in composition of the main chemical components to the average composition of the rocks of the earth’s crust (Vinogradov, 1956, 1962; Turekian and Wedepohl, 1961). Apparently this also pertains t o the phosphorus content; thus, in atmospheric dust from the northern Caspian area the phosphorus content ranges from 0.04 to 0.10% (Bruyevich, 1949; Bruyevich and Gudkov, 1953) and averages ~ 0 . 0 7 %Thus . the amount of phosphorus reaching the ocean in the composition of atmospheric dust approaches 1.6 x l o 9 (7 x ) N 1.1x l o 6 t.

River discharge The rivers of the earth which flow into the World Ocean drain an area of about 100 X lo6 km2 (Chebotarev, 1953). Their total annual discharge is 36 x l o 3 km3 of water, 3.3 x lo9 t of dissolved and 13-18 x lo9 t of suspended matter (Alekin, 1966; Lisitsyn, 1974; Lopatin, 1950). The intensity and composition of river discharge depend on the climate, relief, and composition of the rocks and soils in the catchment area (Strakhov. 1960).

8

Phosphorus occurs in the river waters in solution and in suspension, in inorganic and organic forms.

Dissolved inorganic phosphorus. The first data on the content of dissolved inorganic phosphorus in rivers were summarized by Clarke (1924), but as was ascertained later, they were much too high (0.11-0.66 mg/l). Usually the dissolved inorganic phosphorus content in river waters is 0.001-0.08 mg/l (Table 1-3) and only in rare cases 0.1-0.2 mg/l (Almazov, 1955; Yeremenko, 1948; Golterman, 1973). In a natural regime of discharge the maximum phosphorus content in the rivers of the European part of the U.S.S.R. is observed at the time of freezeup, due t o regeneration from dead aquatic organisms, and also at the time of the spring floods due to washing out from the soils. During the growing season the phosphorus content drops t o minimal values (Konenko, 1952). The soils of many areas are substantially depleted in phosphorus compared to argillaceous sedimentary rocks. In the podzol loams of the European part of the U.S.S.R. the phosphorus content averages 0.024%, in podzol sandy loams 0.01% (Zonn, 1967), which dictates the extensive use of inorganic phosphate fertilizers. It is because of this that a local high concentration of dissolved inorganic phosphorus in river waters may occur, particularly at the time of spring floods and after rain (Butkute, 1966; Veselovskiy e t al., 1966). The sharpest fluctuations in concentration of dissolved inorganic phosphorus are characteristic of streams and brooks draining the surface soil layer of tilled fields. At the very beginning of the spring thaw the phosphorus concentration in the streams of northern Kazakhstan and the lowland Altay can reach 0 . 1 4 . 2 m g / l , which is related to enrichment in dissolved phosphates of the uppermost soil layer ( t o 3-5cm), which is characterised by low pH values (‘~5.5-6.5). A few days after the beginning of the thaw the content of phosphorus, and also of nitrates, in the streams decreases t o the background values; at the same time the pH increases t o 7-8 (Voronkov, 1963b; Voronkov and Zubareva, 1963). The phosphorus content of river and brook waters varies with fluctuations in the total mineralization. In the dry inorganic residue of river waters the phosphorus content is within 0.002-0.11% (Table 1-3), averagmg 0.023%. The coefficient of aqueous migration of phosphorus, i.e. the ratio of its content in the inorganic residue of river waters and in rocks of the catchment area (Perel’man, 1961), is 0.2-0.3 on the average, which is an indication of the relatively slight geochemical mobility of phosphorus in the supergene zone. On the basis of degree of mobility in river waters, Strakhov (1960) puts phosphorus, iron, and manganese in the same subgroup. On the basis of the data given in Table 1-3, the average content of dis-

9 solved inorganic phosphorus in rivers, calculated taking into account the annual discharge of the rivers*, is 0.015 mg/l. According to other estimates it ranges from 0.010 (Vinogradov,l967) to 0.100mg/l (Clarke, 1924); in particular, for the rivers of the Black Sea basin the phosphorus content is 0.019 mg/l (Volkov, 1975). Dissolved organic phosphorus. The content of dissolved organic phosphorus in the waters of Kuban’, Don, and Volga ranges within 0.005-0.280 mg/l and in most cases is 1.5-3 times greater than the content of dissolved inorganic phosphorus (Barsukova, 1971; Datsko and Guseynov, 1959,1960; Yeremenko et al., 1953). Obviously this is due t o the fact that river waters are often rich in dissolved organic matter, including organophosphorus compounds. The organic matter content in the dry residue of the waters of the Dnieper, Pripyat’, Ob’, and Ket’ is 7-24% (Glagoleva, 1959; Nesterova, 1960), and in the dry residue of the waters of tropical rivers (La Plata, Rio Negro, Uruguay), up to 50-6096 (Clarke, 1924). On this basis it can be presumed that the average content of dissolved organic phosphorus in river waters is -0.030 mg/l. Suspended phosphorus. The phosphorus content in suspended matter in rivers is within 0.02-0.296. In the subcolloidal fraction of suspended matter it is higher - 0.09-0.37% (see Table 1-3). The ratio of inorganic and organic forms in the composition of suspended phosphorus is very variable and depends mainly on the season and drainage condition of the soils. In the waters of the Don the content of suspended inorganic phosphorus varies from 0.06 t o 0.330 mg/l, of suspended organic phosphorus from 0.000 t o 0.212 mg/l, with mean annual values fluctuating within 0.045-0.142 and 0.030-0.063 mg/l, respectively. In the waters of the Kuban’ the average content of suspended inorganic phosphorus in 1949--1950 was 0.438 mg/l, and of suspended organic phosphorus 0.265 mg/l (Datsko and Guseynov, 1959,1960; Yeremenko et al., 1953). The total amount of suspended phosphorus in river waters is usually much higher than that of dissolved - from a ratio of 9 9 : l t o 1:l.Sharp predominance of suspended phosphorus is characteristic of turbid river waters (Table 1-3). According to most available data, the average phosphorus content in river suspensions is 0.06-0.07% (Bruyevich and Solov’yeva, 1957; Glagoleva, 1959; Gorshkova, 1961; Lubchenko and Belova, 1973; Nesterova, 1960; Pakhomova, 1959). For a turbidity of 360-500 mg/l the content of sus-

* According

t o the data of Alekin (1948,1949,1953), Lopatin (1949,1950,1952),and L’vovich (1945,1953).

F

0

TABLE 1.3 Dissolved and suspended phosphorus in river waters River. point

Water NnOff (km’lyr)

Mineralization (mg/l)

Turbidity (mgll)

Phosphorus dissolved (mK/l)

P ratio suspended (mg/l)

in inorg. residue

in suspension

Reference

(%)

imclll

coarse

tine

SUSP.

diss.

0.06

0.23’

45

55

Glagoleva, 1959

-

-

-

Glagoleva. 1959 Almazov, 1955

-

-

-

Glagoleva. 1959

0.370 0.240

67.1 61.6 69.3

32.3 38.4 30.7

0.011-0).192 (av. 0.073) 0.038 0.120 0.036 0.090

94.2

5.8

Yeremenko e t al., 1953

92.7 97.1

7.3 2.9

Glagoleva, 1959 Glagoleva. 1959

Europe

Dnieper Kherson. 1956 Verkhnedneprovsk. 1956 Kakhovka. 1951

53 180 180 184-357

Ripyat’

13.4

Don Aksay. 1940 Aksny. 1956 Donskaya, 1956

28

Ku ban’ Krasnodar, 1950

11

Danube Reni, 1949

113-350 154 176 201

Izmail. 1956

0.027

-

0.018

0.025-0.116 0.051 0.037

0.0254.330 0.082 0.083

0.005-0.059 0.016 0.021

0.008-0.084

0.008-1.175

0.002-0.072

0.026 0.018

0.330 0.630

0.017 0.011

179

0.021

0.066

132 122 182b

25 1 65 102=

0.017 0.017 0.034

0.088 0.029 0.10

0.013 0.014 0.019

-

431

26347

52.7

-

0.023 0.006-0.045

233

-

RhBne

31-1347 970 1626

-

0.006 0.068 0.009

Rivers of Baltic basin

-

78 155

0.018

0.043 0.020-0.105

0.015-0.180

Kuma

Loire Blois Nantes

-

-

-

13 8.6 255

7.9

5

0.032

257-349

Rioni, 1956 Chorokh, 1956 Volga

Seine Corbeil Pont d e Sevres

24 -

149 184-647 322 177

Krasnodar, 1956 Temryuk, 1956

27

2415‘ -

-

-

-

-

0.0014.074 0.006-0.060

-

-

0.002-0.044

-

0.072 0.052

0.033

-

0.040 0.120 0.045 0.110 0.06-0.28 0.02-0.04d -

-

-

-

-

Yeremenko, 1948 Glagoleva, 1959 Glagoleva, 1959

Almazov, 1955

75

25

Glagoleva, 1959

83.8 63.0 75

16.2 37.0 25

Gkgoleva. 1959 Glagoleva, 1959 Strakhov, 1948,1954

-

-

-

Veselovskiy e t al., 1966 Matisone, 1961

0.025 0.115

0.019 0.107

-

-

-

43 48

57 52

Demolon and Marquis, 1961 Demolon and Marquis, 1961

-

-

-

89 14.5

11 85.5

Demolon and Marquis, 1961 Demolon and Marquis, 1961

-

65

35

Demolon and Marquis, 1961

95.2 90.9 72.8 64.0

4.8 9.1 27.2 36.0

Nesterova. Nesterova. Nesterova, Nestcrova,

-

-

-

-

0.006 0.130

0.049 0.022

-

-

0.024

0.039

97.31 96.48 88.20 83.18

512 259 63 44

0.020 0.023 0.025 0.027

0.397 0.231 0.067 0.048

Ash Ob’, 1958 Barnaul Kolpashevo Sugut

Salekhard

394 0.021 0.024 0.028 0.032

0.075 0.085 0.111 0.114

0.111 0.143 -

-

1960 1960 1960 1960

Ket'. 1958 Syr-Dar'ya Amu-Dar'ya Yenisey Chu

-

65.87 432b 421b 140'

14 42 548 1.5

500a

47 1160' 2510E 19c 65gE

70

168'

1250

590 3187

146' 53

1200

-

0.087 0.757 3.750 0.034 0.340

-

0.476

-

0.750

0.031 0.008e 0.010=

-

0.047 0.002 0.002

-

0.200 0.13.0.07e 0.21.0 . 0 P -

73.7 99 99.8 -

26.3 1 0.2

-

Nesterova. 1960 Strakhov. 1948,1954 Strakhov. 1948,1954 Strakhov, 1948.1954 Straknov. 1948.1954

Apia

Nile

Shakhov. 1948,1954

America MisJissippi Amazon

-

0.0034.08 (av. 0.013)

-

-

0.008-0.11 (av. 0.024)

'

'Strakhov, 1948. Alekm, 1953. Lopatm, 1948. Pakhomova, 1959, Bruyevlch and Solov'yeva, 1957. Clarke, 1924

Strakhov, 1948,1954 Gihbs, 1972

12 pended inorganic phosphorus in river ‘waters is 0.200-0.350 mg/l or 8090% of the total phosphorus in rivers. On the basis of these estimates it can be concluded that ~ 0 . million 5 tons of dissolved inorganic and ~1million tons of dissolved organic phosphorus and 10 million tons of suspended, chiefly inorganic, phosphorus reach the ocean every year in river discharge. Other authors have estimated the total amount of dissolved phosphorus brought t o the ocean each year by rivers in figures from 0.7 to 1.9 million tons (Holland, 1971; Riley and Chester, 1971; Stumm, 1972).

Underground discharge A substantial part of the waters draining the continents goes through a stage of underground discharge and then reaches river arteries and becomes part of the river run-off (Makarenko and Zverev, 1970). In addition t o this, there are centers of discharge of ground water in the seas and oceans, sometimes at a considerable distance from the shore (Buachidze and Meliva, 1967). The mineralization of ground waters from different areas ranges from 1 or 2 to 100-200 g/l, and the phosphorus content from traces to a few milligrams per litre (Clarke, 1924). In Caucasus mineral waters the phosphorus content is from 0.003 mg/l (Smirnovskiy spring, Zheleznovodsk) t o 0.053 mg/l (Yekaterina spring, Borzhomi); in the waters of the Polyustrov and Rakhmanov springs i t is 0.13 and 0.4 mg/l, respectively (Alekin, 1953). In the reservoir drainage and ground waters of the Rostov district the phosphorus content ranges within 0.055-0.071 mg/l, and in well waters there, within 0.001-0.014 mg/l (Alekin e t al., 1969). The usual phosphorus content in the inorganic residue of ground waters is thousandths and hundredths of a percent, in isolated cases tenths of a percent . The phosphorus content in ground waters does not depend on their total mineralization or hydrochemical type. Apparently i t is determined primarily by the overall composition of the rocks being drained and by the aggressiveness of the waters with respect to inorganic phosphate compounds, i.e. it is ultimately related to the whole complicated geochemical evolution of ground waters. At present it is impossible t o suggest any criteria for estimating the average phosphorus content in ground waters. Determination of the volume of underground discharge into the seas and oceans is a very complicated matter. A typical example is the underground discharge into the Caspian Sea, which has been investigated for many years using hydrogeological methods. In the opinion of Kudelin

13 (1948), ' ~ km3 3 of water, or 1%of the total volume of river discharge, reaches the Caspian Sea annually from underground discharge. Other estimates give from 0.3 to 49.3 km3 /yr, i.e. the data diverge 160-fold (Apollov, 1935; Zektser et al., 1967; Ulanov, 1965). From the example of several seas of the U.S.S.R. it has been ascertained that some ions (Ca2+,Mg2+,SO,"-, HCOj ) reach them chiefly in the composition of river discharge, others (Na+, Cl-, I-, B-, Br-) in the composition of underground discharge (Glazovskiy , 1976). Phosphate ion apparently belongs to the first group. Glacier discharge At the present time, continental and sea ice occupies about 20%of the area of the earth; its load of sediment reaches 1%,and the total amount of this material reaching the ocean is about 1.5 x lo9 t/yr (Lisitsyn, 1974). For an average phosphorus content of -0.07% in the composition of the detrital material of glacier discharge, about 1 million tons of phosphorus is deposited on the ocean floor annually.

Coastal a brasion The coasts of the World Ocean, the length of which amounts to about 400,000 km, are subject to wave and ice action which is most intensive in the humid zones. The amount of abraded material is estimated at 0.3 X lo9 t/yr (Leont'yev, 1963), and the amount of phosphorus in it, ' ~ 0 . 2million tons.

Volcanism The role of volcanism in the formation of the water mass and salt content of the ocean is tremendous. The ultimate source of all the main anions of ocean water is acid fumes of volcanic eruptions, liberated in degassing of the mantle (Vinogradov, 1959, 1964, 1967). In present conditions, -66 km3 of volcanogenic hot springs (Rubey, 1951) and 2-3 x lo9 t of volcanics (Lisitsyn, 1974) reach the surface from the depths of the earth annually. The phosphorus content in thermal waters (Table 1-4) fluctuates exceedingly widely - from traces t o 111 mg/l. I t is not related to the total mineralization of the hot springs, but shows a slight positive correlation with iron. In the dry residue the phosphorus content ranges from 0.001 t o 0.63% and in the deposits precipitated from thermal waters, from analytical zero in siliceous material from the flank of Mendeleyev volcano (Kunashir Island) to 12.6%in the iron phosphate from Tjiater spring (Central Java) (Zelenov,

TABLE 1-4 Phosphorus in thermal waters and geysers Sampling site

Uzon caldera, Kamchatka Lower Mendelevev spring, Kunashir Island Upper Doctor spring, Kunashir Island Biryuzovoye Lake, Simushir Island, 1933 1958 Crater lake of Kawah IdjenNolcano. East Java Tjiater spring, Central Java Cameron spring, Rotorua, New Zealand Hot Lake, White Island. New Zealand Yellow Crater lake, Taal volcano, Philippines Green Crater lake, Taal volcano, Philippines Yellowstone geysers, U.S.A. Teterata geyser, New Zealand Caldera of Santorin volcano. Aeaean Sea Atlantis I1 basin. Red Sea, metalliferous brine interstitial brine a

2.124.35

674-3778

0-85.2

0-152

0-2.0

0-0.026

04.026

Lebedev, 1975

1.70-2.06

2747-4027

0.7-1.8

60-95

7.8-1 1.6

1.1-1.9

0.044.07

Lebedev. 1975

5.03-12.58

0.7-1.5

0.03-0.04

Lebedev, 1975

0.05

-

0.28 0.884.91

0.007 0.023

Zelenov, 1972 Zelenov, 1972

-

9

0.009

Zelenov, 1972

0.43-0.97

0.007

Van Bemmelen. 1949

tr.

1.8-2.1

1890-4330

0.5-7.5

6.8 3.30

3768 3616-4008

0.05 4.99-6.56

0.02

106.336

2.32-2.81

361.42

850-1018 1862

-

158,051

9448

-

26,989

1444

6-8

60,023 1336-1388 2064 ca. 37,000

5.61'

256,840b

6.1-6.5'.'

250,000

-

-

1496.54

1.4-2.0

4.00-16.65'

-

-

15.7-89.0

5.94

3330

-

-

-

tr.

210 618 tr.-2.0=

0.001

Clarke, 1924

987

0.63

Clarke, 1924

-

111

0.42

Clarke, 1924

-

143

0.14 0.002

Clarke, 1924 Clarke, 1924

0.001

Clarke, 1924

tr.

tr.

2.9=

-

tr.

0.36-2.0

0.05-2.05

0.004-0.04

60-95 b'e (total) 4(t174"' (total)

70-98b'e

5.89d

60-274'.'

0.03-8.48'

'

t o 0.0001

0.002 to 0.003

Hartmann. 1969; Brewer et al.. 1969;' Brewer and Spenser, 1969; Dietrich and Krause. 1969;' Brooks et al.. 1969; Hendricks et al.. 1969

Pushkina, 1967

TABLE 1-5 Distribution of absolute amounts of elements (in geograms, or lo2' g) in sediments, waters, and igneous rocks weathered during the geologic history of the earth (Horn and Adams, 1966) Element

Sediments continental

1

c1 S B Br I Mo Mn Na K Ca Fe P U

38.7 3.17 0.130 0.00571 0.00444 0.00192 0.573 38.3 44.6 159 69.3 1.50 0.00774

Connate water

Ocean water

oceanic shelf

2 116 8.96 0.429 0.0108 0.0149 0.00594 1.44 104 151 208 228 4.85 0.0235

hemipelagic 3

74.5 9.20 0.346 0.200 0.000186 0.0223 27.2 170 203 210 355 10.1 0.0153

Weathered igneous rocks

Difference (1i2 3 i4 + 5+6)-7

pelagic

4 45.6 5.52 0.206 0.124 0.000114 0.0137 16.1 102 120 155 210 5.99 0.00912

5 27.8 1.32 0.00703 0.0953 73.3 X 14.7 X 22.93 X 15.4 0.557 0.586 14.7 X 103 X 44 X

6 267 12.6 0.0673 0.912 0.000701 0.00014 28.1 X 147 5.33 5.61 0.00014 0.000982 0.000421

7 9.79 10.6 0.245 0.0639 0.0102 0.0306 22.4 572 524 739 862 22.4 0.0561

559 30.2 0.940 1.28 0.00102 0.0134 22.9 0 0 0 0 0 0

16 1972). The phosphorus content in iron ore precipitates from the Atlantis I1 basin in the Red Sea is 0.3--0.4% (Hendricks et al., 1969; James, 1969),from the caldera of Santorin volcano in the Mediterranean Sea 0.25-1.6495 (Butuzova, 1968), and in the ore precipitates of steam vents in New Zealand, up to 3%(Weissberg, 1969). There is no correlation between phosphorus and iron in these precipitates. Evidently phosphorus and iron can migrate either together or separately at different stages of the hydrothermal process. High, although not very much so, phosphorus contents related t o submarine eruptions have been observed in the waters off the shores of Japan (0.05-4.06 mg/l) (Okada, 1936) and in the Tyrrhenian Sea (0.013 mg/l; buljan, 1954, 1955). The dissolved hydrothermal phosphorus coming into the ocean is in part disseminated in the water layer, in part deposited along with the accompanying iron. It has been established that the sediments of the Red Sea, Pacific and Atlantic Oceans that are rich in hydrothermal and volcanogenic iron are also rich in phosphorus, but its source may not be hot springs so much as sea water with a background content of phosphorus sorbed by iron hydroxides*. The origin of the elements in the ocean can be judged from their absolute amounts liberated in the weathering of igneous rocks during the geologic history of the earth and entering into sedimentary rocks, ocean sediments, and water. The results of such calculation suggest that the main anions of sea water are undoubtedly volcanogenic, but on the whole volcanogenic sources play a secondary role in the balance of phosphorus, and also of iron and several other cations (Table 1-5).

Cosmogenic material The amount of cosmic dust falling on the earth’s surface amounts t o -10 x l o 6 t/yr (Lisitsyn, 1974). The phosphorus content in cosmic material can be judged from the composition of meteorites. Stony meteorites contain 0.04-0.38% P, stony-iron meteorites 0.006-0.2% P, iron meteorites 0.02-0.94% P, and the samples of lunar rocks collected by “Apollo 11” 0.04-0.32% P (Moore, 1973). For an average content of 0.2-0.3%, the total amount of phosphorus reaching the ocean from cosmogenic material is not more than 30,000 t/yr. On the basis of the data given it can be concluded that 15-20 million tons of phosphorus reach the World Ocean annually in the solid phases and more than 1.5 million tons in solution (Table 1-6).

* See sections below dealing with deposition of phosphorus from waters and phosphorus in sediments.

17 TABLE 1-6 Introduction of suspended and dissolved phosphorus into the World Ocean Source

Phosphorus in solid phases Eolian River suspensions Glacial discharge Coastal abrasion Volcaniclastic Cosmic dust

Dissolved phosphorus River discharge Volcanic exhalations Underground discharge*

Amount of material ( l o 9 t)

Average P content

(%I

Absolute mass of P(106 t )

1.6 13-18 1.5 0.3 2-3 0.01

0.07 0.07 0.07 0.07 0.1 0.3 ( ? )

1.1 9-1 4 1 0.2 2-3 0.03

36 X l o 3 km3 66 km3 -

0.045 mg/l 1 mg/l -

1.5 0.066

-

* Volume of underground discharge and its phosphorus content not established. PHOSPHORUS IN WATERS

Phosphorus dissolved and suspended in sea and ocean waters occurs in inorganic and organic forms. The ratio between them varies considerably depending on the season, depth, and local conditions in the basin.

Dissolved inorganic phosphorus In the surface waters of the seas the content of dissolved inorganic phosphorus ranges from 0.1 to 40pg/l (Table 1-7). At a time of intensive proliferation of phytoplankton it drops to analytical zero, and before the growing season it reaches a maximum. In the deep waters of the seas the phosphorus content as a rule is considerably higher and relatively constant. In aerated basins the maximum phosphorus content in deep waters reaches 100-130pg/l (Sea of Okhotsk and Bering Sea), in the waters of stagnant basins 300 pg/l (Black and Baltic Seas, Norwegian fjords). In the surface layer of the waters of the open ocean the phosphorus content varies widely, from analytical zero to tens of micrograms per liter (Table 1-8). In a period of proliferation of phytoplankton it is minimal, as in the seas, but after the growing season it rises to 3 - 6 p g / l in the tropics and 60-68 pg/l in polar regions. In intermediate layers of water the content of dissolved inorganic phosphorus reaches a maximum, and in different parts of the

18 TABLE 1-7 Content of dissolved inorganic phosphorus (pg/l) in sea waters Sea

Surface waters

Deep waters

Aral

0.7-3.1

0.0-17

Blinov, 1956; Bruyevich and Solov’yeva, 1957

Caspian North Central South

0.0-35 0.1-15 0.1-17

8-7 5 7-78

Bruyevich, 1937 Bruyevich, 1937 Bruyevich, 1937

Black

7-40

107-299

Azov

0.0-22

4-200

Mediterranean

0.0-6.5

2.2-13

Bernard, 1939; McGill, 1961; Thompson, 1 9 3 1

Adriatic

0.2-20

-

White Baltic Gotland basin Landsort basin h a n d basin Barents Bering Okhotsk Japan Norwegian fjords

Reference

Bruyevich, 1953; Datsko, 1959; Dobrzhanskaya, 1960; Skopintsev, 1975; Fonselius, 1974 Bronfman, 1972; Datsko, 1959

.2-30

to 46

5.5-14 7 .l-7.8 9-10

28-309 13-8 5 10-20

ErcegoviE, 1934; Scaccini-Cicatelli, 1972 Bruyevich, 1960, Trofimov and Golubchik, 1947 Chernovskaya et al., 1965 Chernovskaya e t al., 1965 Chernovskaya e t al., 1965

20

Bruyevich, 1948

20-87

80-130

Ivanenkov, 1964; Mokiyevskaya, 1959; Wardani, 1960

0.0-20

60-100

Bruyevich e t al., 1960; Mokiyevskaya, 1958

5-20 -

5 0-6 0

Bruyevich e t al., 1960

6

to 300

Strom, 1936

ocean this maximum occurs at different depths (Fig. 1-1).In the northeastern part of the Pacific Ocean the maximum phosphorus content (105 pg/l) is characteristic of depths of about 400 m, and in the southwestern part in the Coral Sea region, it is -60pgll and is observed at a depth of about 2200 m. Below the layer of the maximum the phosphorus content decreases somewhat, and in deep waters it again reaches about the same values as in the intermediate layer. The average weighted concentration of dissolved inorganic phosphorus is: in the Atlantic Ocean 55pg/l, in the Indian 68, in the Pacific 77, and the average of the waters of the World Ocean 72. Dissolved inorganic phosphorus

19 TABLE 1-8 Average content of phosphorus (pg/l) in the meridional strip 150-160' hemisphere, summer, Pacific Ocean (Chemistry of the Pacific Ocean, 1966) Depth (m)

50-40'

0 25

37 46

N

E, northern

4C+3Oo N

30-20'N

20-10'N

10-O'N

0-10's

7 5

1.5 1.5

2 2

1 1

3 5

constitutes %90%of the total content in the ocean (Chemistry of the Pacific Ocean, 1966). The proportions of the forms of dissolved inorganic phosphorus depend on the salinity, temperature, and pH of the water (Fig. 1-2). In ocean water of normal salinity (35Yo0)at 20°C and pH of 8 the proportions of the forms are as follows: H,POi = 1%,HPOi- = 87%;and PO:- = 12%;99.6%of the phosphate ions form single-charge complexes with Ca2+and Mg2+ (Kester and Pytkowicz, 1967). The complete spectrum of the forms of phosphorus in sea water has the following aspect (5%) (Atlas et al., 1976): MgHPOi

HP0:-

NaHPO:

Cap040 CaHP0:

MgPO;

H2P04 NaH2P0i

41.4

28.7

15.0

7.6

1.5

0.9

4.7

0.1

MgH2PO; PO:-

NaPO:.

CaH2POr

0.1

0.01

0.01

0.01

The average residence time of dissolved phosphorus in the waters of the World Ocean is estimated as 160,000 (Ronov and Korzina, 1960) t o 270,000 years (Vinogradov, 1967). Starting from an amount of water in the World Ocean of 2/14 x lo" t (Vinogradov, 1967; Poldervaart, 1955), an average % P in it, and an average content of dissolved inorganic content of 7.2 x phosphorus in river discharge of 1 . 5 x %, we obtained a figure close to those given above -200,000 years. If the organic phosphorus in river discharge is taken into account, this figure is halved. However, it cannot be taken as the average value, inasmuch as the present epoch is characterized by maximum development of land areas with relatively high relief and correspondingly high rates of erosion (Ronov and Korzina, 1960). In addition, the anthropogenic factor, which causes an acceleration of erosion of soils and contamination of rivers by organic phosphorus from industrial and agricultural waste, must be taken into account.

Dissolved organic phosphorus The content of dissolved organic phosphorus in the surface waters of the seas ranges from 6 to 60 pg/l; at depth it gradually decreases. In most cases the maximum content is observed in shallow-water areas, especially near the shore (Datsko, 1959; Mokiyevskaya, 1958).

20

6C

63

4c

40

20

20

I


1%P2O5) on the shelf of northwest Africa is estimated as 3300 km2,the thickness as 5 m, and the P205 reserves as 430 million tons (Summerhayes et al., 1972). But the existence of vast reserves and high quality of the phosphorite on the adjacent land makes the practical utilization of the phosphorite of the shelf of northwest Africa very remote.

74 Shelf of southwest Africa The shelf of southwest Africa includes the Namibia shelf (from the mouth of the Cunene River, 16'S, to the mouth of the Orange River, 28'30's) and the northwestern part of the shelf of the South African Republic to the Cape of Good Hope (34's). In the northern part of this zone the shelf is narrow and steep, and south of 20's it is relatively wide (100-200 km) and flat; the slope of the bottom in the Walvis Bay area (23's) is 0'14'. On the whole the shelf of southwest Africa is asymmetrical and includes a flat inner shelf, a relatively clearly expressed scarp at a depth of 140-160m, a steeper, often concave outer shelf, and a bend marking the boundary of the shelf and continental slope (at depths of 270-400 m). Here the rocks of the Precambrian/Paleozoic crystalline basement lie at great depth; in the Capetown area they dip toward the ocean at an angle of 2-3". The basement is overlain by presumably Cretaceous rocks, on which lie Tertiary rocks consisting of four members of the same type separated by erosional surfaces. The total thickness of the sedimentary cover in the zone of the shelf and continental slope reaches 3-4 km, and the thickness of Tertiary rocks on the shelf reaches 0.8-1.3 km (Bryan and Simpson, 1971; DuPlessis et al., 1972;Van Andel and Calvert, 1971). On top of the shelf floor and upper part of the continental slope of southwest Africa there occur siliceous (diatomaceous), calcareous, clastic, and glauconitic sediments (Fig. 2-12).The sediments of each of these types are locally enriched in phosphorus due to the presence of phosphate grains, fragments of phosphate rocks, and biogenic detritus. An investigation of 900 samples (Summerhayes et al., 1973) has established that the most extensive zone of high phosphorus contents in the sediments (up to 23% P,O,) occupies the shelf and upper part of the continental slope north of 26's to Walvis Bay. Farther south, phosphatic sediments containing up to 9% P,05 occur in the form of isolated patches (Fig. 2-13). The phosphorites on the shelf and upper part of the continental slope of southwest Africa consist of phosphate sands, sheets, blocks, and large concretions of dense phosphate rock, unconsolidated and compacted phosphate nodules in diatomaceous oozes, phosphatized coprolites, bones of fish and marine mammals. Phosphatic medium and fine sands, containing 6-23s P, 0, , occur among the clastic slightly calcareous and biogenic calcareous sediments (Table 2-5). According to the data of an investigation of eight samples of the sands, their median diameter lies between 0.15 and 0.31mm, the coefficient of sorting between 1.52 and 2.86,and the content of phosphate grains between 29.5 and 74%.

75

Fig. 2-12.Types of sediments on the shelf of southwest Africa (Yemelyanov and Senin, 1969). (a) Granulometry of the sediments: 1 = stations; 2 = sands and coarse silts; 3 = fine-grained sediments; 4 = mud-sand interface; 5 = 200- and 4000-m isobaths; 6 = boundary of humid and arid zones. (b) Sediments: 7 = clastic; 8 = calcareous; 9 = siliceous; 10 = glauconitic; 11 = chamositic. (c) Distribution of fecal, chamositic, and glauconitic pellets; percent by weight of sediments: 12 = 1; 13 = 1-10; 14 = 10.




34"

32"

33O

31'

30'

29"

28"

27'

26'

25'

24'

U1

17' Q0

[14 2

B3

10O

4

130

R '41

34O

33 O

32'

31'

30'

28O

27'

26'

25'

Fig. 2-13. Distribution of phosphorus in the sediments on the shelf and continental slope of southwest Africa (Summerhayes et al., 1973): I = 0 - 0 . 5 ; 2 = 0.5-1.0; 3 = 1.0-2.5; 4 = 2.5-5.0; 5 = 5-15; 6 = 15%P205.

>

24'

5 6

77 TABLE 2-5 Phosphorus content in the sediments of the outer shelf of southwest Africa (Senin, 1970) Sediment

Depth (m)

CaC03 (%)

N

p 2 0 5 (%)

range of values

average

-

6.84 4.38 6.79 3.75

range of values

average

-

0.60 0.29 1.26 0.28

1 2 11 1

19.02 8.44 0.74

1 7 7

5.27 0.46 0.39

6 1 1

0.46 2.29 2.53

1 11 4

Clastic medium sands fine sands silts fine silty muds

151 113-124 99-3 12 360

Clastic slightly calcareous medium sands fine sands silts

172 110-2 12 12.40-2 5.74 118-380 10.26-25.1 3

28.28 19.90 20.03

Biogenic slightly calcareous fine sands silts fine silty muds

150-285 370 310

41.37 32.30 48.49

Biogenic calcareous medium sands fine sands silts

130 160-305 305-470

51.42-6 8.69 57.21-69.40

68.20 63.29 64.20

Biogenic highly calcareous fine sands silts fine silty muds

150-3 52 71.66-8 4.81 295-382 70.99-7 4.25 420

76.54 73.00 74.20

0.14-2.60 0.25-3.45

0.80 1.85 0.51

10 4 1

Glauconitic fine sands silts

142-3 10 230

4.48 12.88

0.36-4.18 1.77-2.13

1.65 1.95

5 2

3.50-5.2 7 2.16-8.83 -

36.05-48.33 -

0.32-7.5 1 8.47-1 7.30

0.25-0.31 0.25-6.62 -

-

0.21-2 2.9 0.32-2.14

0.39-15.00 -

0.23-6.46 0.37-6.3 5

-

N = number of samples.

The size of the phosphate grains in these sediments usually is 0.05-0.25 mm, the shape round or slightly oval, the color black, the surface shiny or rough (Fig. 2-14), the specific gravity usually 2.50-2.89 (sometimes somewhat more or somewhat less), and the average P , 0 5 content about 32.3%. The grains consist of yellowish-brown amorphous or cryptocrystalline phosphate with abundant black flocs of organic matter. Under the microscope in transmitted light they are opaque or transparent only at the edges. Semi-

78

Fig. 2-14. Phosphatic sand from the outer shelf of southwest Africa (grains of phosphate, quartz, and foraminifera tests); X 30 (Baturin, 1971b).

transparent and transparent phosphate usually is isotropic, with a refractive index of 1.579-1.610. In some grains the phosphate is crystalline and characterized by anisotropy with weak birefringence (0.002-0.005) and its refractive index is higher than that of the isotropic phosphate (1.610-1.630), but there are no clean-cut boundaries between these two modifications of the phosphate. Judging from the results of X-ray analysis, the phosphate of the grains is fluorcarbonate-apatite with unit cell parameters of a = 9.32, c = 6 . 8 7 a (Senin, 1970; Yemel'yanov, 1973a). Grains of this type occur in foraminifera tests, phosphate nodules, and coprolites, as well as in phosphatic sands. Sheets, blocks, and large concretions of dense phosphorite occur in the northern (18-26"S, depths of 115-335 m) and southern parts (30-33'S, depths of 250-1000 m) of the region in question in reworked clasticcalcareous sediments and consist chiefly of fine-grained, to a lesser extent of brecciform and conglomeratic, varieties (Fig. 2-15), The last two varieties are similar in composition to the phosphorites of Agulhas Bank and the Morocco shelf. Phosphatized limestones and sandstones containing more than 10% P, O5 belong to the fine-grained phosphorites. Rocks of similar composition but with a lower P, O5 content are also known.

79

Fig. 2-15. Conglomeratic concretions from the outer shelf of southwest Africa (Walvis Bay area); X 0.5.

The fine-grained phosphorites consist of various grains, chiefly of sand-silt dimensions, and a cementing matrix. The phosphate grains are round, oval, or irregular in shape. The phosphate of the grains is slightly anisotropic and differs from the phosphate cement in the more intense yellow color. Often the grains are surrounded by a thin (0.01mm) rim of crystalline phosphate and are pyritized, sometimes to complete replacement of the phosphate by pyrite. In some grains tiny bone fragments are observed. Inclusions of elongated and angular bone fragments are also observed in the cementing matrix; usually they are surrounded by a rim (0.3mm) of finely crystalline phosphate and are pyritized. Microglobules of pyrite and clusters of them are concentrated on the periphery of the bone fragments, but sometimes also inside them and in the Haversian canals. Glauconite occurs in the form of angular and semi-rounded grains, sometimes fractured and in part broken. The glauconite is often pyritized. Micro-

00 0

TABLE 2-6 Chemical composition (9%) of phosphorites from reworked sediments o n shelf o f southwest Africa (Kharin and Soldatov, 1975) Coordinates

Depth (m)

Sample*

P,O,

CaO

17"25'S, 11'29'E 25'31'5, 14'02'E 31°53'S, 16'16'E 3lo15'S, 16'08'E 32'45'S, 16'55'E 3Zo45'S, 16'55'E 33'21's. 17'39'E 33'28'S, 17'38'E 33"28'S, 17'38'E 33'33'S, 18°21'E 18'35'S, 11'45'E 18'35'S, 11'45'E 18'35'S, 11'45'E 18'35'S, 11'45'E 30'35'5, 15'06'E

150 215 465 490 430 430 245 238 238 318 185 185 185 185 470

a** b b b

21.77 10.67 13.70 10.58 15.10 19.95 11.97 11.79 15.22 16.68 19.23 24.37 23.90 28.99 25.40

34.27 33.64 41.10 36.05 26.37 40.54 24.81 22.25 25.36 30.08 37.71 46.59 36.32 49.37 53.90

b b b b

b b*** c c d d d

1.80 13.22

-

1.51 1.68 1.14 3.74 2.61 1.75 2.22 4.71 0.90 12.04 0.80 -

SiO,

TiO,

Al,O,

19.13 1.53

0.34 0.07 0.05 0.12 0.22 0.10 0.11 0.27 0.05

1.92 0.63

-

7.16 10.06 10.61 30.07 39.97 38.79 26.70 2.65 2.30 0.56 0.17 -

-

0.15 0.08 0.06 0.03 0.05

-

0.95 1.17 2.16 2.10 1.47 2.33 7.51 0.42 1.16 tr. 0.78 -

MnO 4.60 2.03 10.40 2.49 2.47 2.73 12.32 5.23 4.81 5.34 1.74 2.04 0.99 0.78 2.50

0.013 0.01 0.06 0.01 tr.

0.76 1.23

-

-

-

0.59 0.63 -

0.01 0.03

2.40

0.52 0.45

-

-

1.75 -

0.01 -

0.01

= dense uniform concretion; b = fine-grained phosphorite; c = brecciform phosphorite; d = conglomeratic *** aAfter Baturin et al. (1970). *** After Murray and Philippi (1908).

-

0.66

-

phosphorite.

27.97 13.15 15.90 8.82 5.19

-

-

1.11

0.112

-

-

-

0.01

7.61 30.54

-

2.40 -

2.62 -

12.33 14.89 11.33 11.69 -

-

0.088 -

0.098

-

0.090 -

81 globules of pyrite are situated on the periphery, in the center, and in fractures in the glauconite grains. Clastic material consists of angular grains of quartz, sometimes with mosaic extinction, and to a lesser extent of grains of feldspar, rarely of monoclinic pyroxene, zircon, and ore minerals. Other components are the following: finely dispersed calcite, foraminifera tests with brown phosphate cores, fragments of mollusk shells, dolomite, flocculent inclusions of organic matter. All in all, the amount of inclusions contained in the cement ranges from 5 to 50%in different places. The cement of the rock is clayey-calcareous-phosphatic, sometimes with an admixture of iron hydroxides. The phosphate of the cement is grayish yellow, mainly amorphous, with a refractive index of 1.592-1.600 (Baturin et al., 1970; Kharin and Soldatov, 1975). According to the data of chemical analyses (Table 2-6), the P, O5 content in the slabs and blocks of phosphorite on the shelf of southwest Africa ranges from 10 to 22% in the fine-grained and from 19 to 29% in the brecciform and conglomeratic varieties. The extent of ferruginization of the phosphorites varies widely (0.8--12.3% Fe, O3 ). The fine-grained phosphorites from the southern part of the area (31-33”s) are the most ferruginized. Phosphate concretions in diatomaceous oozes consist of a number of varieties representing a gradual transition from unconsolidated to lithified formations. The main types of these concretions are the following: (1)Phosphatized soft clots of diatomaceous ooze from fractions of a millimeter to 1-4 mm in size. They occur in the form of round, lenticular, tabular, and also incrusting and shapeless formations. They differ from the enclosing dark green semi-liquid diatomaceous oozes in the yellowish-white color and somewhat denser consistency (Fig. 2-16). Wet clots are easily smeared, and dry ones crumble with slight pressure. (2) Unconsolidated phosphatic concretions, white, light yellow, or yellowish-gray in color, round or flattened in shape, and from fractions of a millimeter to 1-4 cm in size (Fig. 2-17). In thin-section and under the scanning microscope it is seen that concretions of this kind are of phosphatized diatomaceous ooze (Fig. 2-18). The diatom valves are 0.05-0.25 mm in size and in many cases are covered with a blue coating of iron sulfide. In some of them small pyrite globules are observed. Fusiform segregations of phosphate (probably microcrystals), mainly 1-3 pm in size, are formed on the surface of the valves (Fig. 2-19). In some of the valves the opal wall is replaced by slightly polarizing phosphate. The mineral grains are fragments of feldspars, quartz, pyroxenes, hornblende, and ore minerals. They are angular, within 0.01-0.25 mm in size. The matrix consists of light yellow microgranular phosphate, in some places cryptocrystalline (non-polarizing), but mainly

82

Fig. 2-16. Phosphatized areas (white) in cores of diatomaceous oozes on the shelf of southwestern Africa (Veeh et al., 1974).

microcrystalline (faintly polarizing) and contaminated by pelite, tiny fragments of valves and spines of diatoms. In the phosphate there occasionally are encountered microglobules of pyrite, both solitary and in intergrowths of several individuals. The maximum size of the globules is 0.02 mm. (3) Granular (globular, up to 0.1-0.3 mm in size of globules) nodules of

83

Fig. 2-17 . Unconsolidated phosphatic concretions from diatomaceous oozes of the shelf of southwest Africa; natural size.

Fig. 2-18. Microstructures of unconsolidated phosphatic concretions. (a) Structure of diatomaceous ooze; scanning microscope, x 130. ( b ) Phosphate filling pores in diatom valve; scanning microscope, X 4000.

84

Fig. 2-19. Fusiform segregations of phosphate on the surface of diatom valve in uncon. solidated phosphate concretion; scanning microscope, X 12,000.

yellowish-gray color, with a hardness of 3 on Mohs’ scale, brittle, chiefly round or lozenge-shaped, up to 3-4 cm in size (Fig. 2-20). Nodules of this type are of three varieties: highly phosphatized diatomaceous ooze, chiefly amorphous concretions, and concretions mainly of finely crystalline phosphate. In the phosphatized diatomaceous ooze 40-6076 of the field of view in thin-sections is occupied by diatom valves, leaving rectangular cavities in transverse section (Fig. 2-21). Most of the valves are covered with a blue coating of iron sulfide which, as is seen in transverse sections, in some cases forms an easily discernible layer on the walls. In some valves intergrowths of pyrite microglobules are observed. The opal valves are replaced by slightly polarizing phosphate, the crystalline elements of which are oriented perpendicular t o the surface of the

85

Fig. 2-20. Dense granular phosphate nodules from diatomaceous oozes on the shelf of southwest Africa; natural size.

valve. The cavities of the valve sometimes are partially filled with pure yellowish phosphate. Angular grains of quartz, feldspars, pyroxenes, hornblende, biotite, and saussurite, and also acicular and columnar grains of calcite up to 0.10 mm in size, occupy 1-5% of the field of view. The diatom valves and mineral grains are embedded in a matrix (35-6096) of grayishyellow microglobular finely crystalline phosphate, contaminated by clayey and in part by carbonate pelite. The structure of the phosphate is fairly unconsolidated, as it consists of an aggregate of round clots of different size, the centers of which are more contaminated by pelite than the periphery. The phosphate microcrystals are mainly randomly oriented, but at the edges of some clots they are radially arranged. Microglobules of pyrite occur in places in the phosphate mass. Phosphate nodules of the second kind consist of microglobular isotropic phosphate (Fig. 2-22) with rare diatom valves (or cavities from them), an admixture of clayey pelite and angular grains of feldspars and calcite 0.010.05 mm in size (2-4% altogether). Intergrowths of pyrite microglobules tend to be associated with some diatom valves. In the phosphate mass rare and tiny irregular cavities and a large number of inclusions of nearly pure light yellow and yellow phosphate (up to 30%) are observed. Some of the

86

Fig. 2-21. Granular phosphatic concretion with cavities from diatom valves; thin-section, X 30, I( nicols.

inclusions are round or oval and consist of isotropic phosphate. They apparently are the filling of various cavities, including the cavities of diatom valves, produced in the formation of the phosphate concretions. In some cases the phosphate fills only part of these cavities. Intergrowths of pyrite globules are sometimes seen at the edges of the filling. Some other inclusions also are round or nearly oval in shape, but they consist of finely crystalline phosphate. These inclusions apparently were present in the sediment before formation of the nodules, in the form of isolated phosphate grains of an early generation. Phosphate nodules of the third variety consist of grayish-yellow microgranular, in part finely crystalline and in part (locally) isotropic phosphate with rare irregular cavities and fragments of bones (up t o a few millimeters in size) and with a small number of pyrite microglobules restricted mainly to the walls of the cavities. The cavities and bone fragments sometimes constitute 10-2096 of the thin-section area. In addition to these there occur isolated grains of clastic material, 0.01-0.10 mm in size. They are a deeper yellow color, sometimes striated (fibrous) and contaminated with a white opaque substance concentrated mainly in the middle of the inclusions, forming indistinct clots. The inclusions are phosphatized coprolites (see below).

87

Fig. 2-22. Globular microstructure of phosphate in granular phosphate nodule; scanning microscope, X 6000.

(4)Dense massive tannish-brown nodules, round, lozenge-shaped, elongated, and irregular in shape (Fig. 2-23).Their size varies from fractions of a millimeter t o 5-6 cm. Their color is due to the presence of a matte film on their surface which disappears on calcination. Beneath the brown film the material of the nodules is yellowish-gray in color; its hardness on the Mohs scale is 4-5. The nodules consist of fairly pure light yellow phosphate, chiefly microgranular and finely crystalline, in the mass of which rather many (5--15%) diatom valves are observed, sometimes coated with blue iron sulfides. The opal of the walls of the valves is replaced by finely crystalline phosphate. Pyrite in the form of solitary or clustered microglobules (up to 5%) is usually present in the phosphate and diatom valves. In addition, iso-

88

Fig. 2-23. Dense massive phosphate nodules from diatomaceous oozes on the shelf of rn southwest Africa, natural size.

lated angular grains of quartz, feldspars, and pyroxenes of silt size are encountered. Sometimes round and oblong opaque cavities (up to 2-3 mm long) are encountered. Rare radial aggregates of highly elongated flat colorless phosphate crystals with wedge-shaped, sometimes asymmetrical terrninations, 10-30 pm in size, with parallel extinction and positive elongation, are observed in the large cavities (Baturin et al., 1970). In electron microscope investigations of this type of concretion, several forms of secretion of the phosphate were established: fusiform crystals -1 pm long, aggregates of microglobules -0.1 pm in diameter with faint signs of crystallization, and also globules from one to several microns in diameter. The large globules are crystalline only on the periphery (Fig. 2-24a, lower left), but some small globules are completely crystalline (center of lower half). A t a magnification of x 20,000 it is seen that the crystallites constituting them are aggregates of relatively ordered st.acked filiform crystallites of second order, which in turn consist of still tinier crystalline elements (Fig. 2-24b). At the time of detailed sampling of the sediments of the shelf of Namibia during the 26th cruise of the research vessel “Mikhail Lomonosov” (1972), about 10 kg of phosphate concretions were washed out of the diatomaceous oozes, which made it possible to classify them in more detail lithologically and increase the number of varieties from 3 t o 6: soft, unconsolidated, compacted granular, compacted massive, dense gray, and dense brown (Baturin, 1974b).

89

Fig. 2-24. Globular microstructure of dense phosphate concretion. (a) Aggregates of phosphate microglobules; electron microscope, x 7000 (photo by V.T. Dubinchuk). ( b ) Crystallization of microglobules; electron microscope, x 20,000 (photo by V.T. Dubinchuk).

(5) A t the lower boundary of the zone of distribution of diatomaceous oozes, in diatom-shell sediments, there are no phosphate concretions of the varieties described above, but dense black phosphate grains of irregular shape with glazed surface and phosphate casts of gastropod shells (Fig. 2-25) are encountered. Some of the grains are fragments of completely phosphatized bones. Coprolites are diverse in morphology and composition and occur in sediments of various types. In the clastic and calcareous sediments of the shelf of southwest Africa both soft and lithified coprolites are encountered; they consist of elongated oval grains from 0.05 to 1-3 mm long, gray, greenish, or yellowish in color, opaque, fine-granular, with rough surface. In individual samples coprolites constitute up to 50-70% of the weight of the sediment. Coprolites of this type consist of fine-grained carbonate shell detritus and a yellow-brown flocculent mass of organic matter with inclusions of grains of clastic material and diatom valves. A high phosphorus content (up to 2%) is characteristic of

90

Fig. 2-25. Dense phosphate grains and phosphate cast of a gastropod from carbonate sediments near the lower boundary zone of diatomaceous oozes (depth 148 m); x 6.

the sediments rich in coprolites. Round phosphate grains 0.03-0.13 mm in diameter have been found in some coprolites (Senin, 1970). Beyond the shelf of southwest Africa, in the Niger delta area, coprolites of similar morphology consisting of clay material and glauconite are known in clastic sediments (Allen, 1965; Porrenga, 1967). Phosphatized coprolites from 1-2 mm to 5-6 cm in size, from fish and marine animals, are encountered in the diatomaceous oozes of the shelf of southwest Africa. Unlithified and lithified varieties are distinguished among the coprolites. White and gray unconsolidated coprolites (Fig. 2-26a) consist of isotropic phosphate of irregularly patchy color. The color of the spots is from pale yellowish gray to deep brownish yellow. In the phosphate mass there are many irregular elongated, sometimes branching cavities (up to 50% of the field of view), relatively rare inclusions of fragments of bones, scales, and teeth of fish (not more than 2-3% altogether), and also single and coalescing pyrite globules (not more than 1%). A typical feature of the structure of the material is the clearly manifested fibrous nature of many parts of it. Aggregates of fibers of different thickness sometimes bend in different directions. Also typical is contamination of the

91

Fig. 2-26. Phosphatized coprolites from diatomaceous oozes on the shelf of southwest Africa, natural size: (a) unconsolidated; (b) dense.

phosphate by a nearly opaque or opaque white substance, accumulations of which are situated in large indistinct areas of irregular shape, sometimes elongated in the direction of the fibers. The nearly opaque parts of this substance have a dark brown color in strong transmitted light.

92 No microgranular structure is detected in the phosphate; it resembles a glassy mass, the cracks in which have pink edges and often are curved as is typical of conchoidal fracture. Brown compacted and dense coprolites (Fig. 2-26b) consist of light grayish-yellow or yellow irregularly colored finely crystalline phosphate, with a multitude of round and highly elongated, sometimes branching cavities (up to 50%of the field of view). In places the phosphate is pure, in places contaminated to different degrees by an opaque brown or white finely dispersed substance. The latter is irregularly distributed, forming indistinct clusters of curved bands and spots, bounded by veinlets of purer phosphate (reticular structure). In many cavities radial aggregates of flat colorless crystals of phosphate and single or coalescing microglobules of pyrite are observed. In the phosphate mass, fragments of fish bones and pyrite microglobules are encountered. The phosphate is not microgranular but solid, with sharp edges where there are cracks. Bones of fish and marine mammals are encountered everywhere on the shelf of southwest Africa, but mostly in the northern part of the area (1723'S), where in places they form substantial accumulations (Baturin, 1974a).

Fig. 2-27. Bones of recent fish from diatomaceous oozes on the shelf of southwest Africa, natural size.

93 In diatomaceous oozes there are present relatively fresh white bones of recent fish - sardines, mackerel, hake (Fig. 2-27);on some of them phosphorite concretions are growing (Fig. 2-28).In calcareous and clastic sediments the bones usually are fossilized (brown or black, dense, brittle). Dense bones are phosphatized to some extent or other. The phosphatization is manifested in the filling of cavities in the bone tissue with phosphate, and in the crystallization of fibrous amorphous bone phosphate and its conversion to microgranular finely crystalline phosphate, with simultaneous transformation of hydroxylapatite into fluorcarbonate-apatite. The refractive index of the phosphate increases as the extent of crystallization increases, from 1.56-1.57 t o 1.600-1.630. In the outer layer of fossilized bones from the outer shelf iron hydroxides are often observed, in the form of dendritic segregations up to a few centimeters in size. The tiny cavities in the structure of the bone tissue are filled with microglobular pyrite (globules up t o 0.015 mm in size). The large cavities of porous bones are filled with diverse clastic-carbonate materials of sand and silt size, from the enclosing sediments (from 3-5 to 25% of the field of view in thin-section). Biogenic calcareous detritus, tests of foraminifera, angular grains of quartz and less often of plagioclases, monoclinic pyroxenes, and epidote predominate in this material; sometimes grains of glauconite are encountered, and also round or oval phosphate grains 0.10.25mm in size, consisting of relatively pure yellow finely crystalline phosphate.

Fig. 2-28. Phosphate concretions growing on fish bones; X 2.

94 Chemical composition of the phosphorites. Chemical X-ray structural and thermogravimetric methods were used in addition to optical in investigating the composition of the phosphate concretions, phosphatized coprolites and bones described above and also phosphate fractions isolated from them. According to the results of chemical analyses, the P,Os content in the soft lumps of phosphatized diatomaceous ooze ranges from 3 to 11%, averaging 5%(Table 2-7A,B). In morphologically shaped unconsolidated concretions the P , 0 5 content rises to 20-25%, and in compacted ones to 3133%. Thus lithification and phosphatization of the concretions in question take place simultaneously. The content of CaO, COZYand F increases in that order in parallel with P , 0 5 , while the content of H,O, Corg, SiO,, Al,03, TiO2, and S decreases. A similar picture is observed when the results of analyses of phosphatized coprolites are examined (Table 2-7). In tiny soft coprolites, apparently from fish, the P 2 0 5 content is 1-2% (Senin, 1970), and in natural coprolites of marine animals and birds feeding on fish, 4-1696 (Hutchinson, 1950) ; in phosphatized unconsolidated coprolites from shelf sediments, 25.8% on the average; in compacted coprolites 28.7%, and in dense coprolites 32.4%. By means of X-ray structural investigations on natural samples of phosphatic concretions and phosphatized coprolites it has been established that the phosphate mineral constituting them belongs t o the apatite group (Table 2-8). The isotropic phosphate of the unconsolidated concretions and coprolites is X-ray-amorphous. In samples of granular concretions with intermixed areas of isotropic and cryptocrystalline phosphate, the structural features of apatite are slightly manifested. In dense massive concretions and coprolites these features are quite clearly manifested. The unit cell parameters of the phosphate ranges in these limits: a. = 9.304-9.314, co = 6.868-6.876 8. The chemical composition of bones depends on their mineralization and contamination by non-phosphatic material from the surrounding sediments. Relatively fresh bones contain up to 10-20% of organic matter impregnating the bone tissue and several percent of water. Mineralization of bones is manifested in removal of water, decay of organic matter, phosphatization, and pyritization. The P,Os content in unmineralized porous bones of cetaceans is 18-24%, in bones of living fish 26-28%, and in mineralized bones 29-3276. To investigate the phosphatic material in concretions, phosphatized coprolites, and bones the raw material was ground to 0.075-0.15mm and centrifuged in heavy liquids. The specific gravity of the phosphate fraction

TABLE 2 - I A Average chemical composition (%) of Holocene phosphate concretions, coprolites, and bones from diatomaceous oozes on the shelf of southwest Africa (Baturin, 1970; Baturin et al., 1970) Sample Phosphatized diatomaceLOUS ooze Unconsolidated concretions Compacted concretions Dense concretions Unconsolidated coprolites Compacted coprolites Dense coprolites Unidentified fish bones Lithified bones*

P,O,

CaO

MgO

SiO,

TiO,

A1103

Fe2O3

MnO

C02

Corn

S,,

F

LO1

1R

F/P,O,

5.10

6.96

2.50

49.18

0.08

2.00

1.24

0.001

2.16

3.40

1.46

0.46

19.44

50.09

0.090

23.85 28.66 32.74

35.92 43.12 46.42

1.70 1.47 1.70

14.82 6.06 0.17

0.005 0.005 0.005

0.45

0.80 1.23 0.20

0.001

tr. n.d.

0.001 0.002

5.52 5.54 6.33

1.80 1.03 0.92

0.83 0.90 0.73

2.25 2.87 3.02

14.00 12.41 12.20

15.23 6.32 0.15

0.094 0.100 0.094

25 85 28.72 32.40

35.67 42.11 46.13

2.90 2.55 2.12

1.56 0.20 0.16

0.003 0.016 0.003

0.02 0.10 0.02

0.14 0.52 0.10

0.003 0.004 0.001

5.90 5.34 6.37

2.86 0.88 0.60

1.06

1.50 5.01

-

2.59

0.058 0.168 -

27.88 31.07

37.85 43.68

1.10 0.2

0.93 0.66

0.14

0.50 1.59

n.d. n.d.

4.51 4.92

7.20 1.10

1.28

~~

~

LO1 = loss o n ignition; IR = insoluble residue; n.d. = not detected. * Bones from elastic sediments of outer shelf.

tr.

-

-

-

-

11.35

-

2.16 2.80

23.20 9.36

0.93 0.66

0.077 0.090

TABLE 2-7B Results of partial chemical analysis southwest Africa (Baturin, 1974b)

(a)of

a complete series of phosphate concretions and coprolites from the diatomaceous oozes of the shelf

co2

PlO5 2046* Diatomaceous ooze Phosphatized ooze Concretions soft unconsolidated compacted granular compacted massive dense gray dense brown Phosphatized coprolites unconsolidated compacted dense gray dense brown *

Station locations

- 2046:

2047

cow

2046

2047

2048

2046

2047

2048

2046

2047

2048

2.62 2.86

5.31 3.97

4.37 3.10

5.54 4.02

59.32 38.00

57.00 41.32

58.90 27.26

-

2.25 1.28

1.41 1.13

14.24 0.21

7.70 4.00

1.21 4.16

0.82 11.28

1.28 1.07

1.66

19.51 29.53

25.81 27.24

4.32 5.90

4.94 5.01

5.29 5.92 9.19 6.14

29.60 30.31 31.94

30.36 30.36 30.62

20.68 25.69 30.24 30.23 31.56 32.41

29.50 29.60 30.61 30.00

26.79 30.49 31.13 30.87

27.66 29.91 30.87 31.19

-

Amorphous SO:!

2048

1.33 3.56

-

Of

-

6.21 6.39

-

5.16 5.78 6.10

5.28 5.94 5.76 6.34 6.36

4.33 5.47

-

5.66

6.36 6.21

-

-

-

1.05 0.97 0.98

1.06 1.01 0.88

2.10 1.18 1.21 1.03 1.02 0.87

1.51 1.18 0.88 1.08

1.35 0.90 0.91 0.91

1.56 1.00 0.79 0.71

-

-

0.11 tr. tr.

0.04 tr. 0.03

10.00 5.02 2.08 0.10 0.10 tr.

0.17 tr. tr. 0.04

0.10 0.07 0.17 0.08

0.15 0.15 0.35 0.12

22O40’S, 14O15.6’E, depth 8 7 m ; 2047: 22’27’s. 14’10.5’E. depth 7 8 m ; 2048: 22OO8‘S, 13’58.4’E, depth 85 m .

97 'TABLE 2-8 Results of X-ray structural analysis of phosphate concretions and coprolites from the inner shelf of southwest Africa (Baturin e t al.. 1970) Station Coordinates

Depth (m)

Sample* PzO, (%)

Unit cell parameters

Clarity of lines

(A) Qo

209 161 152 152 152 152 152 160 144

22'59'5, 14'11'E 21'49'S, 13'45'E 22'41'S, 14'20'E 22'41'S, 14'20'E 22'41'S, 14'20'E 22'41'5, 14'20'E 22'41'S, 14'20'E 21'59'S, 13'51'E 22'56'5,13'48'E

120 97 76 76 76 76 76 91 148

a b c b b d e e f

27.53 3 1.08 27.88 30.18 29.62 31.64 32.74 31.16 -

9.314 9.314 9.309 9.309 9.314 9.314 9.304

co

6.868 6.876 6.872 6.874 6.872 6.868 6.876

very weak weak well expressed well expressed well expressed well expressed well expressed well expressed well expressed

* a = unconsolidated coprolite; b = granular phosphate nodule; c = unconsolidated phosphate nodule; d = dense lithified coprolite; e = dense brown concretion; f =phosphatized gastropod mold. ranges from 2.2-2.5 (bone) t o 2.7-2.8 (phosphate concretions). There are no free grains of non-phosphate minerals in the material of this fraction. An insignificant amount of quartz, glauconite, and iron hydroxides is observed only in the form of films and inclusions in the phosphate grains and aggregates (Bliskovskiy et al., 1975a). The data of chemical and thermogravimetric analyses show that the phosphate mineral of the concretions and coprolites is fluorcarbonate-apatite with a P , 0 5 content of -32%, 3% F, and 4% C 0 2 (Table 2-9). In thermogravimetric investigations it was established that the phosphatic substance of the compacted granular nodules from diatomaceous oozes on the shelf of southwest Africa contains an unusually large amount of adsorbed water (3.77%), which is given off in the temperature range of 80-300°C. In the phosphate of commercial phosphorite deposits the content of adsorbed water is much less, of the order of 0.6% (Bliskovskiy et al., 197513). The exothermal peak of the phosphate of the granular nodules, with a maximum at 377°C and the kink in the DTG curve corresponding t o it (Fig. 2-29a) are related to oxidation of organic matter, the content of which is determined from the TG curve in the 300-499°C range and is 1.48%. The loss of bound water is localized in a very narrow range. Beginning at 500°C it takes place mainly in the 650-750°C range, which is manifested in the sharp kink in the DTG curve. The process of dehydration is accompanied by a small but dis-

TABLE 2-9 Chemical composition of phosphatic material of concretions, coprolites, and hones from diatomaceous oozes on the shelf of southwest Africa (Bliskovskly e t al.. 1 9 7 5 a ) Material

Thermogravimetric analysis

Chemical analysis (%) PlOS (total)

p10:

CaO

MgO

AI1O,

Fe20:*

K I O Na,O

CO,

F

SO3

IR

C,

H20 adsorbed

(maximum dissolved

Hi0 hound

PI

O=F

911

organlc matter

Dense phosphatic concretion

31.70

12.60

47.32

0.50

2.68

0.20

046

1.97

4.26 (4.04)

2.85

1.30

0.41

0.92

377

2.R3

1.48

101.73

108

100.65

Phosphatized coprolite

3 1 70

13.16

45.92

1.20

n.d.

0.19

0.10

1.44

4.22 (3.51)

3.22

154

0.15

0.71

4.48

3.36

102

99.25

1.22

98.03

Unlithified whale hone

24.10

14.35

36.68

1.10

-

0.40

0.60

1.44

3.64 (3.50)

1.40

1.08

0.37

8.67

8 80

3.20

15.60

9 8 38

0.53

97.85

Figures in parentheses indicate CO, content determined thermogravimctrically Not included in total. *** Total Fe.

99

!a)

!b)

!C)

Fig. 2-29. Thermograms of phosphorites from the shelf of southwest Africa (Bliskovskiy et al., 1975a). (a) Dense massive nodule: rn = 670 mg; DTG = 1/3; DTA = 1/3; TG = 100 mg; atmosphere - air. (b) Dense phosphatized coprolite: rn = 670 mg; DTG = 1/3; DTA = 1/3; TG = 100 mg: atmosphere - air. (c) Slightly fossilized whale vertebra: rn = 500 mg; DTG = 1/5; DTA = 1/5; TG = 200 mg; atmosphere -air.

tinct exoeffect. The exothermic effect of recrystallization of fluorcarbonateapatite into fluorapatite practically coincides with the end of dehydration. Most of the C02 is removed right after it (kink in the DTG curve with a maximum at 820°C). A small amount of C 0 2 is given off in a highertemperature region (beginning at 946°C); this process is not finished even at 1035°C. The thermogram of the phosphatic substance of phosphatized coprolite (Fig. 2-2913) is similar to that described above and differs from it only in details - the temperatures of all the reactions here are 10-40" lower. Removal of C 0 2 ends at 1005°C. Thus a characteristic feature of the phosphatic material of phosphate concretions and coprolites is a high content of water in adsorbed and structurally bound forms. Nearly all apatite-like calcium phosphates contain more bound water than expected from the stoichometry in the case of isomorphism of PO:- 5 C 0 3 0 H , i.e. CO, : H 2 0 = 5 : l (Bliskovskiy et al., 1975b). This difference is especially large for two of the samples examined. The behavior of these minerals when dehydrated (accompanying exoeffects and final recrystallization to fluorapatite) suggests possible differences in the structural positions of the hydroxyl ions in these oceanic phos-

100 TABLE 2-10 Optical and X-ray structural characteristics of phosphatic material (Bliskovskiy et al. 1975a) Samples

Refractive index

Unit cell parameters (A)

(k0.002) a0

Phosphate concretion Phosphatized coprolite Whale vertebra

1.586 1.591 1.568

CO

9.334 6.89 9.330 6.89 X-ray amorphous

phates compared to the phosphatic material of economic phosphorite ores on land. The phosphate fraction of bone includes more organic matter and adsorbed water and less fluorine than other phosphates; the most characteristic features of its thermic behavior are the narrow localization of the regions of liberation of bound water and coincidence of the exothermic reaction of reorganization of the phosphate lattice with the end of the dehydration state. Decarbonation is finished at 87OoC (Fig. 2-29c). An excess of sodium, which is present in greater amount than needed to compensate for the substitution of P5++ S6+by the substitution CaZ++. Na', is characteristic of the chemical composition of the phosphatic material of all the samples investigated. Apparently, the Na' ions are in firmly sorbed form inasmuch as all the easily soluble sodium salts were removed in the course of preliminary treatment of the material, by repeated washing with distilled water. The refractive index of the phosphates investigated is 1.568-1.591, and the unit cell parameters are a. = 9.33, co = 6.89 (Table 2-10). The refractive index and a. parameter of the unit cell of the phosphate depends on the extent of isomorphic substitution of carbon for phosphorus (Maslennikov and Kavitskaya, 1956; McClellan and Lehr, 1969). In the samples examined the CO2/PZO5ratio is 0.13-0.15. Usually with such a C02/P2 O5 ratio the refractive index of the phosphate of economic ores is much higher than 1.591. The discrepancy established between these characteristics in oceanic phosphates is related to their high water content. The specific gravity of oceanic phosphate is relatively low for the same reason (2.7-2.8). Age of the phosphorites. The diversity of morphology, composition, and

10:. conditions of occurrence of the phosphorites of the shelf of southwest Africa suggests that they are of different ages, which is confirmed by a number of direct and indirect data. Judging from their structural and textural features, the sheets and blocks of phosphorite from the coarse-grained sediments of the outer shelf (brecciform, conglomeratic, and fine-grained varieties) were formed in several stages and eroded from pre-Quaternary deposits. The equilibrium relationship of the activities of the uranium isotopes contained in such phosphorites shows that their absolute age is greater than 1Ma (Baturin et al., 1974). The foraminiferal microfauna contained in phosphorites of this type belongs to the Middle Miocene, according t o identifications by V.A. Krasheninnikov (Kharin and Soldatov, 1975). The dense glazed phosphate grains, accumulations of which locally form phosphate sands in the clastic and clastic-calcareous sandy-silty sediments of the outer shelf, likewise are not Recent (pre-Holocene). The good sorting of these sands and similar median diameters of the phosphate and quartz grains indicate that the sands were formed by reworking and concentration of the grains at a time when sea level was lower, at the expense of pre-Holocene deposits no longer preserved. The equilibrium of uranium isotopic activities = 1.00 kO.01, sample from 225m in the phosphate grains (234U/23gU depth) shows that the age of the sands is more than 1Ma (Veeh et al., 1974). The youngest of all phosphate concretions known on the ocean floor It was shown occur on the inner shelf of sourthwest Africa (20-23's). above that these concretions are genetically related to the enclosing diatomaceous oozes. The latter could have been deposited on the inner shelf, at depths of 60--120m, only in the Holocene, when sea level rose by about 100 m after the end of the last glaciation. Any pre-Holocene fine-grained sediments accumulated in this zone inevitably would have been eroded when the sea level was low. All the diatoms constituting the diatomaceous oozes in question are exclusively Recent species (Mukhina, 1974). The same pertains to most of the fish bones which occur in abundance in the diatomaceous oozes (V.M. Makushok, personal communication). The absolute age of the diatomaceous oozes (samples from layers from 0-10 to 160-203cm), determined by radiocarbon, fall within contemporary to 6600 years old (Table 2-11). The following facts indicate the Recent and Holocene age of the phosphate concretions themselves, in the diatomaceous oozes. The gel-like and unconsolidated phosphate clots are nothing but phosphatized diatomaceous ooze, analogous in all characteristics (except phosphate content) t o the enclosing diatomaceous oozes. The gel-like phosphate fills the cavities in the valves of Recent diatoms and coats relatively fresh bones of Recent species of fish. In turn, the gel-like and unconsolidated phosphate

102 TABLE 2-11 Absolute age (from 14C) of diatomaceous oozes on the shelf of southwest Africa (Veeh et al., 1974) Station (core) CIR 175

CIR 177B CIR 179B CIR 189B

K 153* K 160*

Horizon (em)

Dated material

Age (years)

Sedimentation rate (cm/103 yr) (g/cm2

0-10 0-1 0 70-75 70-75

CO, CaC03 CO, CaC03

730 f60 Recent

-

43

34

15

-

0-3 0 100-1 30 0-30 80-1 10 0-30 0-3 0 60-84 60-84

CO, CO,

340 f150 1470 f310

-

CO, CO,

410 f 140 1470 fllO

-

CO, CaC03

1770 f70 2750 f150 3770 f100 6610 f80

-

-

95-135 160-203

COX

1790 f360 1400f420

53 114

CO,

CaC03 CO,

-

103

1380 f80 1980 f 130

88 65 29 15

lo3 yr)

-

-

38 -

32 -

12 6

-

22 47.5

* According

to determination by I.V. Grakova and V.A. Andriyevskiy (Institute of Oceanology of the Academy of Sciences of the U.S.S.R., personal communication).

concretions grade gradually into dense phosphate grains and nodules; both usually occur together in dredge and core samples. The number of diatoms in the phosphate concretions ranges from 0.4 million valves per gram (compacted varieties) to 120 million valves per gram (unconsolidated varieties). The composition of the diatoms on the whole is the same as in the diatomaceous oozes. The species Actinocyclus ehrenbergii Ralfs, Hercotheca peruviana f. nervosa Mertz, Thalassiosira decipiens Jorg. are encountered most frequently (Table 2-12). The uranium disequilibrium method, described in detail in the works of Cherdyntsev (1969) and Chalov (1968), was used in determining the absolute age of the phosphate concretions. To use this method, a combination of the following conditions is necessary: (a) the isotopic composition of uranium in sea water remained constant during the last million years; (b) the source of the uranium in the phosphorite was sea water; (c) the time of accumulation of uranium in the phosphorite was short compared to their age; (d) after they were formed, the phosphorite concretions were a closed system with respect to uranium.

103 TABLE 2-12 Relative abundance (9i of total number) of the main species of Recent diatoms in phosphate concretions from the diatomaceous oozes of the shelf of southwest Africa (according to identification by Mukhina, 1974) Diatom species

Phosphate concretions unconsolidated

Actinocyclus ehrenbergii Ralfs A . divisus Kiss. Actinothychus undulatus (Bail.) Ralfs Biddulphia alternans (Bail.) Van Heurck Chaetoceros lorenzianus Grun. Ch. subsecundus Hust. Chaetoceros spp. (spores) Coscinodiscus asteromphalus Ehr. C. curvatulus Grun. C. gigus Ehr. C. janischii A. S . C. perforatus Ehr. C. radiatus Ehr. C. stellaris Roper Coscinodiscus sp. Hercotheca? peruviana f. nervosa Mertz Melosira sulcata (Ehr.) Ktz. M. italic0 Ktz. Planctoniella sol (Wall.) Schutt Pleurosigma normanii Ralfs Rhaphoneis simonseni Mertz Rh. wetzeli Mertz Rhizosolenia styliformis Brightw. Stephanopyxis nipponica Gran and Jendo Thalassio ne m a n itzsch io ides Grun . Thalassiosira decipiens Jorg. Th. lineata Jouse Dictyocha fibula - silicoflagellate Sticholoncha zonea - radiolarian spines

5.04 3.4 0.3

-

-

0.8 3.6

-

3.6 0.3

-

3.1

-

2.2

-

34.4 1.2 -

0.3 0.3 0.8 8.1 0.3 0.3 3.6 9.6 17.4

+ +

slightly cemented

compacted

43.20 -

1.4 1.4

-

1.4 6.5 0.7 7.2 13.7 10.1 2.2 2.2 0.7 1.4 -

0.7 0.7

-

0.7

-

5.8

-

+ = present Data on the marine geochemistry of uranium as a whole and on its behavior during phosphorite formation on the shelf of southwest Africa show that in this case all these conditions are fulfilled (Baturin et al., 1974). The content and isotopic composition of uranium in sea water are fairly stable. Uranium is introduced into the phosphate concretions from surrounding sediments rich in this element, and into the latter from sea water, with a

TABLE 2-13 Uranium isotopes in phosphate concretions from diatomaceous oozes on the shelf of southwest Africa Station (core)

152 CIR 175,117B 179B, 189B 152 CIR 186A, 188A 157 152 2048 152 2048

Coordinates

20°48'S, 14'19'E

Depth (m)

76 119-1 34

2Oo48'S, 14'19'E 22'28'5, 14'14'E 2Oo48'S, 14'19'E 22'08'5, 13'58'E 2Oo48'S, 14'1 9% 22'08'S, 13'58'E

76 75-93 75 76 89 76 89

Sample* a* *

***

b* * b*** C**

d* * d* * e* * e* *

p2

O5

(%I

U

Activity ratio %)

1.38

16

0.09-0.6 8

10-30

234u/238u 1.171 f0.009

8.52

6

1.13 f0.02 1.16 f0.02 1.169 f0.013

-

78 29 62 52 86 30

1.16 f0.02 1.160 fO.O1O 1.165 f0.009 1.148 kO.009 1.163 kO.009 1.145 f O . O 1 l

23.85 29.62 31.56 32.74 32.41

from to

CIR 175P (40-50 cm)

134

f***

-

158

0.87 f O . O 1

CIR 175P (90-1 00 cm)

134

f***

-

117

0.96 f O . O 1

* a = enclosing diatomaceous ooze; b = phosphatized diatomaceous ooze; c = unconsolidated concretion; d = compacted granular concretion; e = dense brown concretion; f = dense gray concretion. ** After Baturin e t al. (1972b,c; 1974). *** After Veeh et al. (1974).

105

very insignificant portion of terrigenous uranium in the concretions (not more than 1%). The uranium is accumulated in the concretions at the same time as the phosphorus, and the process of formation of the concretions usually ended in several hundred or a very few thousand years. Compaction and dehydration of the concretions, crystallization of the phosphate and its residence in a reducing environment promoted the closure of the system after formation of the phosphate concretions. The uranium isotopic activity ratio 234U/238Uin the diatomaceous oozes containing the concretions ranges from 1.13 k0.02 to 1.171 k0.009, in the phosphatized diatomaceous oozes from 1.16 k0.02 to 1.169 k0.013, and in morphologically shaped unconsolidated and dense concretions from the upper layer of oozes from 1.145 kO.011 to 1.164 kO.009 (Table 2-13). The uranium isotopic activities in the waters of the World Ocean range within the same limits (Cherdyntsev, 1969). Inasmuch as the difference between the 234U/238Uratios in the diatomaceous oozes (or sea water) and in the concretions falls within the limits of error of determination, the results obtained make it possible to calculate tentatively only the possible upper age limit of the concretions. For this we use the formula of one-time introduction of uranium into the concretion (Chalov, 1968):

where yo is the initial 234U/238Uratio in the concretions, y t is the 234U/ l s a U ratio at the present time, h is the 234U decay constant, and t is the absolute age. Taking the maximum value of 234U/23EUin the diatomaceous oozes (1.171 kO.009) as yo and the average 234U/23*Uratio in the concretions as y t , we find that the maximum age of the concretions from stations 152 and 157 (Table 2-13) is 45,000 years (17,000 k28,OOO years), and from station 2048, 88,000 years (54,000 k34,OOO years). Taking into account all the determinations of 234U/23*Uwe find that the average value of yo in the diatomaceous oozes (1.15 kO.01) is identical to yt in the concretions from the upper layer of oozes (1.155 k0.008), which indicates that they are of the same age. In the deeper layer of diatomaceous oozes, old phosphorite concretions were also found in which the 2MU/238Uactivity ratio was in equilibrium from 0.87 kO.01 to 0.96 kO.01 (Table 2-13). Their age is more than 1Ma. Apparently these concretions are redeposited, and formed in now-eroded sediments (probably diatomaceous oozes) deposited on the shelf earlier.

TABLE 2-14 Chemical composition (%) of phosphate rocks from the western shelf of central Africa Sample

Coordinates

Ferruginized conglomerate* 06'56'S, 12'01'E Fine-grained limestone**

13'43"

17°02'W

Depth (m) 160

20

* After Baturin (1975a). ** After Kharin and Soldatov (1975).

P20,

8.98

10.0

CaO

MgOz SiO,

Ti02

1 4 . 4 9 2.60

19.25 0.02

35.60 4.79

1.33 0.06

LO1

IR

A1,03

F e 2 0 3 FeO

MnO

CO2 C,

F

3.69

37.01

0.57

0.01

2.27 0.57

0.75 10.61 20.2

-

0.02

tr.

1.32

-

1.90

-

27.17

-

107 Western shelf of central Africa Phosphorite and phosphate rocks are found at several points on the western shelf of central Africa - on the shelves of Guinea, Ghana, Gabon, the Congo, and Angola (Baturin, 1975a;Kharin and Soldatov, 1975;Cornen et al., 1973;Giresse and Cornen, 1976). The phosphorites are mainly phosphatized limestones and sandstones, less often phosphatized coprolites. Among the phosphate rocks on the Gabon and Congo shelves there are distinguished: (a) calcareous ochers with carbonate-phosphate cement, containing 20-40% phosphate grains and 510% glauconite; (b) brown sandstones with clay or calcareous cement, containing less phosphate but more quartz; (c) ferruginous organogenic sandstones with abundant quartz grains. Cylindrical coprolites occurring in this same area consist of fluorapatite (Cornen et al., 1973). A phosphatized fermginous conglomerate from the Angola shelf consists of rounded and angular quartz grains up to 3-5 mm in size, usually fractured, with mosaic extinction. The quartz grains are cemented by reddish brown hydrogoethite, including hydrogoethite ovoids 0.1-0.8mm in diameter with concentric-shell structure. The phosphatic part of the rock is the light yellow, microgranular, finely crystalline cement filling the numerous cracks in the mass of hydrogoethite and quartz grains. In the phosphate there are encountered grains of quartz up to 0.5 mm in size, angular fragments of the hydrogoethite cement, and isolated rounded grains of light green glauconite 0.1-0.2 mm in size. Judging from the results of the few analyses, the P,O, content in the phosphatized limestones, sandstones, and conglomerates is low, 9-13%. The fermginized rock varieties contain up to 37% Fe203 (Table 2-14). According to the conclusions of French investigators, the age of the phosphorites from the Gabon and Congo shelves is Neogene (Cornen et al., 1973). Probably the phosphatized conglomerate from the Angola shelf also is Neogene; its absolute age, according to the uranium isotope ratio, is more than 1 Ma (Baturin et al., 1974).

-

WEST ATLANTIC PROVINCE

The West Atlantic phosphate province extends from the southern tip of Florida on the south to Georges Bank on the north, for a distance of more than 1400 km, and includes several areas where phosphate sands, phosphorite concretions, sheets, and various phosphatized rocks have been found (Emery, 1965, 1968; Emery and Uchupi, 1972). Phosphorite was first found in this region (Straits of Florida) by expeditions of the American

108 research vessel “Blake” (1877-1880) and was described by Murray (1885) and Agassiz (1888).

Blake Plateau The Blake Plateau is a vast, relatively flat part of the continental slope east of Florida, situated at a depth of 300--800m. There are practically no unconsolidated sediments on the plateau. The phosphorite occurs on the shallower northern and western parts of the plateau. Farther east there is a zone where the phosphorite is covered by manganese crusts which sometimes coalesce into a continuous sheet. Ferromanganese nodules without phosphorite occur on the deep-water southeastern periphery of the plateau (Fig. 2-30). Phosphorite and manganese nodules occur on the cemented globigerina sand (calcarenite), sometimes are buried in it. In the northern and northwestern parts of the plateau the phosphate material consists of grains, concretions (Fig. 2-31), and blocks weighing up to 56 kg and in the center of the plateau, also of bands of phosphate in iron-manganese crusts (Hathaway, 1971; Hawkins, 1969; Manheim, 1965; Milliman et al., 1967; Pratt, 1963, 1968; Pratt and Manheim, 1967; Pratt and McFarlin, 1966; Sheridan et al., 1969; Stetson et al., 1962). In an investigation of samples obtained in the northern part of the plateau on the seventh cruise of the scientific research vessel “Mikhail Lomonosov” (1960) it was established that the phosphorites are phosphatized limestones. The carbonate material (40-50% of the field of view in thin-section) consists mainly of tests of planktonic foraminifera. Glauconite grains 0.1-0.45 mm in size are present in substantial amounts (5-10%). Pyrite is occasionally encountered; it is partially oxidized, with the formation of brown iron hydroxides. Clastic material (-5%) consists mainly of angular grains of quartz, less often of K-feldspars and plagioclases. The carbonate detritus, glauconite grains, and clastic material are cemented by finely crystalline phosphate, which also fills chambers in foraminifera tests (Fig. 2-32). Pelitomorphic calcite is disseminated in the phosphate. According to the data of chemical analyses (Table 2-15), the P , 0 5 content in the concretions ranges from 20.26 t o 23.53%,CaO from 33.32 to 52.15%,and insoluble residue from 0.52 to 15.37%,which is due both to the extent of phosphatization of the original limestones and t o the variable amount of clastic material included in the concretions. Judging from the eroded surface of the bottom, the phosphorites on the Blake Plateau originated by way of residual concentration when phosphate deposits on the coastal plain were eroded (Pratt and Manheim, 1967). This idea is confirmed by data on the composition of the microflora of

109 79OOO'

78OOO W

3'00' N

2aoo'

f00'

0"00' N 79'06

78OOO'W

Fig. 2-30. Bathymetxy and rocks on the Blake Plateau (Pratt and McFarlin, 1966): 1 = zone of iron-manganese crusts; 2 = zone of phosphorite concretions; 3 = zone of ironmanganese concretions; 4 = submarine photography stations; 5 = dredging stations.

coccolithophorids included in the phosphorites; according to the identification by S.I. Shumenko, these belong to the Late Cretaceous ( Watznaueria deflandrei No&l;Ahmuelerella mirabilis Perch-Nielsen) and Oligocene (Chiasmolithus sp. cf. oamarnensis, Fig. 2-33;Sphenolithus sp.). Submerged Pourtales Terrace The Pourtales Terrace is a levelled erosional bench of the continental shelf at the southern tip of the Florida peninsula. The terrace is 115 nautical miles

110

Fig. 2-31. Phosphorite concretions from the Blake Plateau; reduced to half size.

long and up t o 17 nautical miles wide, and consists of dense Miocene limestones (Jordan, 1954; Jordan and Stewart, 1961; Jordan et al., 1964). Phosphorite has been found at seven stations (Table 2-16) in a zone 70 x 5 miles in area. It consists of concretions, conglomerates, fragments of phosphatized limestone with concentrically layered and dendritic structure, and phosphatized bones of marine mammals. The phosphorite conglomerate consists of dark gray rounded fragments of phosphatized foraminiferal limestone, held together by a lighter-colored cement in which there is no microfauna, which indicates that there were at least two stages of phosphatization. The concentrically layered structure of some concretions apparently reflects rhythmic accumulation of phosphate, taking place over a long period of time. The phosphate of these rocks is francolite; using the X-ray fluorescence method, 1-10s iron and up t o 1%manganese were found in them. Correlation of the geology of the Pourtales submerged erosional terrace with the land part of Florida shows that the phosphorites on the terrace are

111

Fig. 2-32. Structure of phosphorite concretion from the Blake Plateau. Foraminifera tests, grains of clastic material and glauconite with phosphate cement. Thin-section, X 80, I1 nicok.

analogs of the Miocene phosphorites of the Bone Valley Formation. The evidence for this is the Miocene foraminifera microfauna included in the phosphorites (Gorsline and Milligan, 1963).

Shelf of Georgia and North Carolina The phosphorites off the coast of Georgia and North Carolina have been studied by numerous investigators (Gorsline, 1963; Hersey et al., 1959, Lutenauer and Pilkey, 1967;Milliman et al., 1967,1968;Mooreand Gorsline, 1960;Pevear and Pilkey, 1966; Pilkey and Lutenauer, 1967; Pratt, 1969; Pratt and Thompson, 1962;Weinstein, 1973). Chiefly slightly phosphatic quartz-calcareous sands occur on the shelf (Table 2-17);according to all signs they are relict. The phosphatic material consists of hard black and brown nodules, up to 8 cm in size, and well-sorted rounded grains. The size of the phosphate grains is the same as that of the quartz grains in the enclosing sediments. In places the concentration of phosphate grains reaches 14-40%. The phosphorite sands usually lie at depths up t o 30-40 m and are concentrated in individual

112 TABLE 2-15 Chemical composition (%) of phosphorite concretions from the Blake Plateau ~~

~

~

~~

~~

Component

Station 317: 31'57" 78'13'W depth 607 m (Murray, 1885)

Average, 18 samples (Hathaway, 1971)

Station 540: 32'10" 77'52'W, depth 590 m (Baturin, 1975a)

Sample without precise tie-in (Burnett, 1974)

p205

23.53 52.15 1.01 tr.

22.7 46.4

20.26 33.32 1.10 15.37 0.10 7.29 7.06 0.27 0.11

25.80 51.33 1.02 0.20

CaO MgO Si02 Ti02 A12 O3

tr.

Fez 0 3 FeO MnO Na2 0

tr.

-

-

4.0

}

5.5

-

tr.

F CI

so3 CO,

LO1

IR

-

0.58 0.45

K2 0

CO2

0.51 2.80

15.56 2.28 0.16 2.29 -

3.15 0.52

13.2 3.1

6.39 2.00

-

3.25 1.52

0.41 8.86 15.37

-

15.20

* Organic matter. places (Fig. 2-34), from which they are carried by wave action into the neighboring zones. According to the results of the drilling of two exploratory boreholes on the shelf of Georgia southeast of the mouth of the Savannah River, it has been established that the Upper Miocene phosphorite sands are 7.3m thick and overlain by a layer of non-phosphatic sands 1.2 m thick. The reserves of phosphorite sands on the shelf apparently are greater than in the deposits of the same age on the adjacent land (Furlow, 1969). Phosphate grains have been found in drill cores in Miocene rocks and at many points on the Atlantic shelf of the U.S.A. (Bunce et al., 1965; Hathaway e t al., 1970; Nesteroff, 1966). In the opinion of American investigators, the origin of the phosphorite sands is related to transportation of phosphate grains from the shore by rivers in the Pliocene, and to erosion and secondary enrichment of Miocene deposits exposed on the bottom (Pevear and Pilkey, 1966; Lutenauer and Pilkey, 1967).

i13

Fig. 2-33. Oligocene coccolith Chiasmolithus sp. cf. oamarnensis in phosphorite concretion from the Blake Plateau; electron microscope, X 15,000 (identification by S.I. Shumenko).

TABLE 2-16 Points where phosphorite has been found on the Pourtales Terrace (Gorsline and Milligan, 1963) Station

Research vessel

Coordinates

6 9 10 19 6 7

“Gerda” “Gerda” “Gerda” “Gerda” “Explorer” “Explorer” “Blake”

24’17‘N, 24’15‘N, 24’13’N, 24’18‘N, 24’15‘N, 24’15’N, 24’20’N,

-

81’11‘W 81’19’W 81’24%’ 82’21‘W 82”OO’W 82’00’W 82’0O’W

295 327 513 237 491-510 73-437 227

114 TABLE 2-17 Phosphorus content (%) in phosphate-bearing sediments on the Atlantic shelf of the U.S.A. (Goodell, 1967) ~~

PzO5 content

Sediment

N

range of values Sorted foraminiferal sand Foraminiferal and bryozoan sand with grit Foraminiferal muddy sand Glauconitic foraminiferal sand Foraminiferal-quartz muddy sand Quartz sand Quartz sand with shells (15%) Quartz sand with shells (25%) Muddy fine-grained quartz sand Quartz sand with shells and phosphate grains Quartz gravel with shells

average

3.27-6.20

4.61

7

3.28-6.57 3.71-6.47 3.62-3.95 3.18-6.34 0.76-5.93 < 0.01-5.94 < 0.01-5.64 < 0.01-5.81

4.41 4.37 3.79 4.55 3.95 1.43 2.39 2.23

12 8 2 5 22 19 20 18

7.37 5.69

20 14

3.58-4 2.60 3.58-10.81 ~~

N = number of samples

34

I

. _...*. ..

/

5

70

Fig. 2-34.Distribution of phosphatic sands on the Carolina shelf (Lutenauer and Pilkey, 1967): 1 = 0-1;2 = 1-3; 3 = 3-7; 4 = 7-14; 5 = 14% P ~ 0 5 .

>

115 Georges Bank On the northern periphery of the phosphate zone, on Georges Bank, diagenetic concretions with phosphate grains (2-19s) and glauconite (14%) have been found in relict sediments. The microcrystalline calcite, phosphate grains, and fragments of fauna in these concretions are embedded in a ferruginous clay cement (Stanley e t al., 1967). CALIFORNIA PROVINCE

The California phosphate province extends along the west coast of the U.S.A. and Mexico from Point Reyes (north of San Francisco) to the southern tip of Baja California, a distance of more than 2000 km. Accumulations of phosphorite were first found off the coast of California during geological work by the research vessel “Scripps”. Later the phosphorites were traced south along the Mexican part of the California peninsula (D’Anglejan, 1967; Emery and Dietz, 1950;Uchupi and Emery,

1963). Shelf and continental slope o f California (U.S.A.) The phosphorites off the coast of California have been studied in most detail in the area of Los Angeles and San Diego (Dietz e t al., 1942;Emery, 1952, 1960, Emery and Dietz, 1950; Emery and Shepard, 1945; Hanna, 1952;Mero, 1961;Uchupi and Emery, 1963). The submarine relief in the region of southern California is very complex. Beyond the narrow shelf belt, in the upper part of the zone of the continental slope, there is a series of trenches 1500-2200 m deep separated by rises which in places emerge as small islands (Fig. 2-35). Phosphorites occur on the outer part of the continental shelf, on the island shelves, on the summits and slopes of submarine banks and hills, and on the flanks of the trenches and submarine canyons. As a rule the accumulations of phosphorite occur on parts of the bottom where sedimentation is slow or zero and are absent on the bottom of the trenches. The depths at which phosphorites have been found range from 80 to 2800 m, but in 95% of the cases they do not exceed 330 m. The enclosing sediments usually are quartz-mica and glauconite sands and silts, less often silty muds, in which phosphate grains and oolites 0.1-0.3 mm in size are often present. The.P, O5 content in these sediments usually is not more than 0.3-0.5%. The phosphorites consist of grains, sheets, and concretions of various

116 120"

119O

118O

0

10

20

30

40

50

34

33

32

Fig. 2-35. Map of the sea floor in the Southern California area: 1 = stations where phosphorite concretions have been found; 2 = possible occurrences of phosphorite. M, P = samples containing Miocene and Pliocene foraminifera, respectively (Emery, 1960).

shapes (Figs. 2-36, 2-37), usually with a flat bottom side and convex upper side. The maximum dimensions of the phosphorite concretions are 60 x 50 x 20 cm, the average size 5 cm in diameter. At some stations the dragnets brought up hundreds of concretions. Judging from individual estimates and underwater photographs, the concentration of phosphorite ranges from a few kilograms to 100 kg/m2. The phosphorites are hard compact rocks; in color they are tan, brown or black. Their specific gravity is 2.62, the hardness on the Mohs scale -5. The surface is smooth and polished. Concretions from greater depths are coated on top with a film of manganese oxide, which indicates that phosphate

117

Fig. 2-36. External view of phosphorites from the California basin: (a) concretion; ( b ) phosphorite breccia; ( c ) phosphatized sea-lion bone; ( d ) layered phosphorite nodule (Dietz et al., 1942).

deposition has ceased. In places phosphorite conglomerates and breccias consisting of fragments of phosphorite and other rocks bonded by phosphate cement, and also bones of marine mammals and fish, are encountered. Often corals, bryozoa, brachiopods, sponges, and serpulids are attached to the upper surface of the phosphorites. The presence of fauna growing on the concretions indicates that they occur on the bottom in a fixed state. In some concretions tracks of burrowing organisms are observed, filled with calcium carbonate or phosphate. Thin-section investigations have shown that the phosphorites contain phosphate oolites with nuclei of foraminifer tests, glauconite grains, or clastic material. In addition, angular and semirounded fragments of various sedimentary, volcanic, and metamorphic rocks, and grains of quartz, feldspars, pyroxenes, micas, and other minerals are present in the phosphorite sheets and concretions. Abundant glauconite forms round grains and fills chambers in foraminifer tests. The insoluble residue obtained by treating the concretions with hydrochloric acid amounts to 6-30%. Besides clastic

118

Fig. 2-37. Structures of phosphorites from the California basin (Dietz et al., 1942). (a) Phosphate oolites with nuclei in the form of foraminifer tests and mineral grains; thinsection, X 28, 11 nicols. ( b ) Holes bored by pholads, filled with phosphatized ooze (indicated by arrows); polished surface, X 3.5.

material, it contains amorphous silica, remains of diatoms, radiolaria, and sponge spicules (Dietz et al., 1942). According to the results of semiquantitative X-ray-structural mineralogic analysis, the phosphorite concretions contain 72% apatite, 18%potassium feldspar, 5%quartz, 3%kaolinite, and 2%pyrite (Burnett, 1974). Petrographic investigations of the phosphorites have shown that the phosphatic material consists of an isotropic phosphate - collophane - and an anisotropic one - francolite; the latter forms the fibrous concentric layers of the oolites, and replaces foraminifera tests and other calcareous particles. The data of X-ray structural and chemical analyses indicate that the phosphate of the California phosphorites, like that of most phosphorite deposits of old sedimentary formations, is similar in composition to fluorapatite or fluorcarbonate-apatite. The phosphorite concretions contain 20-30% P2 0 5 ,37-47% CaO, 0.34%R2 0 3 ,up to 10%SiO, ,4-5.5% C 0 2 , 2.47-3.9876 F, up to 21%insoluble residue. The F/P20, ratio ranges from 0.096 to 0.130, C 0 2 / P 2 0 5 from 0.1373 to 0.2060 (Table 2-18). When the California phosphorites were investigated, it was originally suggested that they are Recent or Upper Quaternary (Dietz et al., 1942), although the foraminiferal microfauna in them is chiefly Middle Miocene (Table 2-19). Later, after new data on the marine geology of the area and on

TABLE 2-18 Chemical composition (7%) of phosphorites off the coast of California ~

Station

P,Os

CaO

69' 106' 127* 158* 162* 183* 14415** 14002**

29.56 20.19 28.96 29.09 22.43 29.66 30.61 30.65 30.0

47.35 45.43 45.52 46.58 37.19 47.41 44.78 44.18 47.8

Unnumbered***

*** Dietz et al. (1942).

MgO

R2O3

AI203

Fe203 Si02

N a 2 0 KzO

-

0.43 0.30 2.03 0.70 3.93 1.40

-

-

-

-

-

0.64 0.78

-

1.06 1.71

1.00 0.99

8.17 9.70 9.5

0.80 0.87

0.64 0.56

~

-

3.3

(1974). *** Burnett Inderhitzen e t al.. (1970;average of 20 samples).

-

-

-

-

-

CO,

,C ,

F

3.91 4.01 4.30 4.54 4.63 4.87

0.10 1.90 2.25 0.44 0.35 1.50

3.31 3.12 3.07 3.15 2.47 3.36 2.95 3.98 3.4

~-

5.5

-

-

SO3

LO1

-

-

0.85 0.90 2.1

9.34

~-

IR

C

F/P2 0,

C 0 2 /P, 0,

2.59 3.57 4.45 3.57 20.99 2.12 -

100.2

0.1120 0.1069 0.1060 0.1082 0.1099 0.1133 0.096 0.130 0.113

0.1323 0.1373 0.1486 0.1560 0.2060 0.164

-

87.25 87.52 90.58 88.07 91.99 90.32 100.33 -

-

0.183

120 TABLE 2-19 Main foraminifera1 species in the phosphorites off the coast of California (Dietz et al., 1942) Foraminifera species

Age

Anomalina salinasensis Kleinpell Siphogenerina branneri Bagg Biggina robusta Kleinpell Valvulineria californica Cushman Bolivina advena Cushman Bolivina girardensis Rankin Nonion costifera Cushman Nodogenerina advena Cushman a. Laiming

Middle Miocene

Buggina californica Cushman Bolivina imbricata Cushman B. sinnata Galloway a. Wissler Cassidulina crassa d’Orbigny Plum bina ornata d’Orbigny Pullenia miocenica Kleinpell Uvigerinella cf. obesa Cushman

Middle-Lower Miocene

Bolivina californica Cushman Bulimina uvigerinaformis Cushman a. Kleinpell B. ovula d’Orbigny Cassidulina monicana Cushman a. Kleinpell C. modeloensis Rankin Eponides healdi Stewart a. Stewart Cassidulina su bglo bosa Cushman a. Hughes C. californica Cushman a. Hughes Cassidulina spp.

I

Lower Miocene

Pliocene-Recen t

the Miocene/Pliocene phosphorites on the adjacent land had been obtained, that idea had to be rejected. According to Emery’s (1960) data, there were two stages of phosphorite formation in the basin. The first stage went on from the Middle Miocene to the beginning of Late Miocene, the second from Late Pliocene to the beginning of the Pleistocene. In the time interval between these stages (end of Late Miocene/Middle Pliocene), no phosphate sediments were deposited. A t the time of the second stage the Miocene phosphorites were recemented by phosphate. Beginning from the Late Pleistocene, the process of phosphorite formation ceased. The last conclusion is confirmed by data on the isotopic composition of uranium in the California phosphorites. In the 22 samples investigated, from different zones in the basin, the 234U/23*Uactivity ratio is between 0.95 k0.05 and 1.02 k0.05, i.e. close to equilibrium, which indicates an age of more than 1Ma (Kolodny, 1969a, b; Kolodny and Kaplan, 1970a).

121 Western shelf o f Baja California (Mexico) According to D'Anglejan's (1967) data, phosphorites occur on the western shelf of the California peninsula in a belt up to 80 km wide, between 24' and 26'N latitude (Fig. 2-38).The area occupied by phosphorite-bearing sediments is about 13,000 km2. The shelf, which in its origin is an erosional 30" 20" .

115'

I

f

\

/

2c

21

Ilt

.. ..

:... , /

.:I

110'

Fig. 2-38. Area of occurrence of phosphate (hatched) off the coast of Baja California (D'Anglejan, 1967).

122 platform developed on the west flank of the California syncline, is characterized by relatively gentle relief. It is separated from the continental slope by a narrow basin and a series of banks at depths of 50-100 m. The phosphorites occur mainly at depths up to 100 m, often on beaches and in lagoons, and consist of well sorted grains of sand size, the amount of which reaches 15-4076 by weight of the sediment in places. The thickness of the phosphate sediments, penetrated by sediment samplers, is 125 cm. Two types of phosphate grains are distinguished: (1) black ovoid grains predominate in the 0.125- to 0.250-mm fractions, (2) biogenic detritus predominates in the larger fractions; the biogenic particles are flat or platy in shape and are fragments of the valves of phosphatic brachiopods (Disciniscus cumingii Broderip). The surface of the phosphate grains usually is uneven, bumpy (Fig. 2-39). In thin-section it is seen that they are unstructured; sometimes concentric coats are observed, due to contamination of the phosphate by organic matter. The phosphate grains that occur in the reducing zone (middle part of the shelf) are black in color; grains from the oxidizing beach zone are brownish.

123

Fig. 2-39. Phosphate grains from the western shelf of Baja California (D’Anglejan, 1967). (a) Uneven surface of grains; 0.125- to 0.250-mm fraction. (b) Opal coatings of phosphate grains, left after dissolving the phosphate in hydrochloric acid; X 250. (c) Microstructure of phosphate grain. Areas of crystalline and amorphous phosphate alternate with black inclusions of organic matter; thin-section, X 1500, nicok.

+

One of the components of the phosphorites is amorphous silica, which fills cavities in the grains or coats them with a thin film (Fig. 2-3913). About 90% of the field of view in thin-section is occupied by phosphate and -10% by amorphous silica. In some phosphate grains, diatoms are found. Opal, pyrite, inclusions of organic matter, and finely dispersed calcite also are present. The phosphate of the grains corresponds in composition to carbonate fluorapatite and is represented by two varieties: anhedral crystals a few microns in size and a cryptocrystalline amorphous groundmass in which these crystals are embedded (Fig. 2-39c). The crystals often are grouped around inclusions of organic matter. Isolated grains of clastic material scattered in the phosphate mass represent the same mineral assemblage as in

124 the surrounding sediments - quartz, feldspar, less often hornblende, magnetite, epidote, hypersthene, zircon, sphene, and garnet. The P,05 content of the phosphate grains averages 30.2%, the F content 2.8%, and COZ 1.25--1.75%. The concentration of phosphate grains in the sediments is controlled by their granulometry. In fine muds and in coarse-grained carbonate sediments the content of phosphatic material is less than 5% (up to 2% in the < 0.062 mm fraction). Closer’ to the shore, phosphate grains are encountered in dune sands, both Recent and old, that are buried in lagoonal mangrove swamps. Here the content of phosphatic material reaches 10-20% by weight of the sediments. The phosphate grains are very similar in granulometry to the enclosing sediments, which suggests that they were transported and eroded by the same processes. The coefficient of sorting of the grains, both of phosphate and of sediment, is less than 0.5 (i.e. the sorting is good). The origin of the phosphate sands apparently is related to a substantial extent to erosion of pre-Holocene deposits. In particular, this is indicated by the sharp boundary of the phosphorus-rich sediments, which corresponds approximately to the 100-misobath, i.e. to sea level at the time of the last glaciation. Thus the phosphate sands may be remnants of completely eroded Pliocene and Pleistocene deposits. Sands of that type occur on land and lie unconformably on eroded Miocene rocks. In D’Anglejan’s opinion, the unordered structure of the grains indicates that the phosphate did not accumulate around any centers of crystallization, but rather in pore space. The clustering of apatite crystals around shapeless opaque organic segregations indicates that the source of the phosphorus is organic matter. In this respect a typical feature also is the close association of phosphate with amorphous silica, inasmuch as both components could have reached the bottom with remains of phytoplankton, intensively developed in connection with upwelling. And finally, the presence of silica coatings on the phosphate grains suggests that the material apparently was deposited in the course of diagenesis. Besides the phosphate grains described, phosphatic material of other types occurs in the near-shore zone of the southern part of Baja California. Phosphate nodules have been found on the flat tops of underwater banks, at depths of 100-200 m. Thin-section study indicates that they were formed by replacement of carbonate rocks by phosphate. Among unaltered fragments of dolomite, some are found which have phosphate developed on the periphery or along cleavage planes. N o apatite is associated with fragments of non-carbonate rocks (phyllites, basalts). In other parts of the same banks a large number of fragments of phosphatized foraminiferal limestone with a Miocene microfauna were obtained

125 by dredging. Fragments of phosphate rock also were found in dredging the bottom near the cliffs of Bahia San Juanico. Probably some of this material reached the floor as a result of erosion of Tertiary deposits. No aggregates of phosphate grains have been found in phosphorites of this type. Partially phosphatized foraminifera, including Recent benthic and planktonic forms, have been found on the upper part of the continental slope at depths of -750 m. In one core the phosphate content increased from 5% at the top to 12% in the 6 0 c m horizon, while the CaC03 content decreased. In thinsection it is seen that phosphate replaces both the calcite of the tests and the clay-carbonate material in them; glauconite, which often fills the chambers of the tests, is associated with the apatite. Silt grains covered with a fragile apatite crust also are found in the sediments of the phosphorite zone. Apparently in this case the apatite is secondary and was produced due to redistribution and redeposition of phosphorus, inasmuch as that phenomenon is not observed outside the phosphorite zone. In an attempt to determine the absolute age of the phosphate grains from the upper part of the shelf of the area in question by the radiocarbon method, from CO, , values within 9860 +200 to 26,640 +600 years were obtained. However, the possibility of using this method to date phosphorites is doubtful inasmuch as there is no guarantee that all the C 0 2 given off was originally part of the fluorcarbonate-apatite molecules, and is not a secondary younger biogenic or chemogenic impurity. In the dating of phosphatic brachiopod shells which occur along with the phosphate grains, it was ascertained that their age falls beyond the limits of resolution of this method, i.e. it is more than 50,000 years. In ionium dating of two fractions from the same sample of phosphate grains, an age of 230,000 years was obtained. However, the reliability of this result is inadequate in connection with the lack of data on the total ratio of all the uranium and thorium isotopes in the samples. Evidently the age of the phosphorites off the coast of Baja California on the whole is Miocene-Pliocene, except for isolated cases of phosphatization of the tests of Recent species of foraminifera. The area of occurrence of phosphatic sediments with a content of more than 5% apatite is estimated as 1800 km2 ; according to the data of exploratory drilling the thickness of these sediments is about 20 m, and the total reserves of P, 0, are from 1.5 to 4 billion tons (D’Anglejan, 1967,1968). PERUVIAN-CHILEAN PROVINCE

Phosphorite occurs off the coasts of Peru and Chile on the shelf and upper

126 part of the continental slope, chiefly at depths of 100-450m, in a belt -1000 miles long, from 5' to 21"s latitude. The geology of this zone is determined by the conjunction of the structures of the Andes mountain system and the Atacama deep-sea trench, with the greatest amplitude of heighbto-depth drop on Earth (up to 14,700 m). The west flank of the Andes, closely approaching the coast, consists of rocks of various compositions, mainly granitoids of different age and Tertiary sedimentary and volcanogenic rocks. Some peaks of the Andes are active volcanoes, the lavas of which have an andesitic, andesitic-dacitic, and andesitic-basaltic composition. In the Cenozoic there were intensive block movements accompanied by accumulation of substantial thicknesses of clastic deposits in graben-like depressions (Gerth, 1959; Jenks, 1959; Khain, 1971; Lomnitz, 1962). The Pacific shelf of South America is a terrace from 3-5 (off Antofagasta) to 10-20 miles wide (south of Valparaiso). The knee of the shelf is clearly expressed, at depths of the order of 150 m. Below that begins the near-continental slope of the Atacama trench, which is one of the steepest and narrowest in the ocean. The average steepness of the slope is 5-6'; individual scarps of it (for instance, in the region of 21's) are up to 700 m high and up to 45' in slope (Fisher and Raitt, 1962). The surface of the near-continental slope of the trench is complicated by benches, scarps, ridges, and furrows. Along the axis of the slope and at an angle of -30" to its strike there are short low ridges; the depressions between them usually are not closed, but open on the ocean side (Udintsev, 1972). Transverse to the slope submarine valleys and canyons have been cut, most numerous off the coast of Peru in the region of 15-16's. The largest of these is incised 800 m deep and its channel is 1.5 miles wide. On the basis of the character of the bottom relief, thickness of unconsolidated sediments, and geophysical characteristics, main (8-32's) and marginal (north and south) provinces are distinguished (Agapova, 1972). Depths of -6000 m, V-shaped transverse profiles, a narrow and in places flat floor, and maximum values of gravity (up to -259mgal) and magnetic anomalies are typical of the main province. The south marginal province is in the form of a depression up to 4000 m deep, filled with unconsolidated sediments up to 2000m thick. In the northern province the depths do not exceed 3500 m, and the thickness of the unconsolidated sediments is 5001000 m (Ewing, 1963; Ewing et al., 1969). In the main province the thickness of the sedimentary cover is minimal at depths up to 8100 m (a very few hundred meters). On the surface of the floor of the shelf and upper part of the continental slope of the Peruvian-Chilean region, chiefly clastic and to a lesser extent biogenic (slightly siliceous and carbonate) and glauconitic sediments occur

127

Fig. 2-40. Principal types of Recent sediments on the shelf and upper part of the con(Gershanovich and Konyukhov, 1975): 1 = tinental slope of Peru and Chile, 4-18's sands; 2 = fine silty muds; 3 = clayey muds; 4 = foraminifera1 sands; 5 = diatomaceous oozes; 6 = glauconite sands; 7 = outcrops of old deposits.

128

Fig. 2-41. Distribution of phosphorus in the surface layer of sediments of the shelf and in the upper part of the continental slope of Peru and Chile, 4-18's (Gershanovich and Konyukhov, 1975): 1 = 0 . 1 ; 2 = 0.1-0.3; 3 = 0 . 3 - 0 . 5 ; 4 = 0.5-0.7; 5 = 0.7% P.




129 (Fig. 2-40). Most of these sediments are characterized by a high content of disseminated phosphorus compared to the Clarke (0.1-0.5%). In slightly phosphatic and phosphatic sediments which occur in the form of relatively small areas, the phosphorus content reaches 2-18% (Fig. 2-41, Table 2-20). The phosphorite occurs mainly in clastic-diatomaceous and foraminiferal sediments of diverse granulometric composition - from silty pelites to sands. Samples of phosphorite were first obtained in this region at the time of the “Challenger” expedition (Murray, 1898), and in later years by a number of Soviet and American expeditions (Baturin et al., 1975; Baturin and Petelin, 1972, Gershanovich and Konyukhov, 1975; Logvinenko et al., 1973; Logvinenko and Romankevich, 1973; Saidova, 1971; Bumett, 1974, 1977; Manheim et al., 1975; Niino and Chamberlain, 1961). Lithology and mineralogy of the phosphorites

The phosphorites on the submerged margin of Peru and Chile are represented on the whole by the same complex of formations as on the shelf of southwest Africa - soft, unconsolidated, compacted, and dense phosphate grains and concretions, phosphatized coprolites, bones of fish and marine mammals (Fig. 2-42). The size of the grains and concretions varies from 0.3-0.5 to 5-10 cm. Their shape is diverse - isometric, flattened, irregular; some platy concretions have been perforated by boring organisms. The color of the concretions is from whitish to dark gray and black, sometimes greenish; the surface is rough, less often smooth, but not glazed. Usually there is no internal zoning or structure in the concretions. In every area of occurrence the unconsolidated and dense concretions are similar to each other in mineralogic composition and differ chiefly in the proportions of the major components - phosphatic, biogenic, and clastic. Most of the concretions are phosphatized clastic-diatomaceous sediments similar in composition to the non-phosphatic material from the surrounding sediments. The soft pellet-like phosphate concretions found in diatomaceous and diatom-foraminiferal sediments of the upper part of the continental slope of Peru are of the order of a few millimeters in size. Judging from the results of semiquantitative X-ray mineralogic determinations, the main components of their crystalline fraction are phosphate (20-40%), quartz (5-30%), carbonates (up to 38%),plagioclases (up to 22%),and less often dolomite, Kfeldspar, and augite (Burnett, 1974). Unconsolidated, compacted, and dense concretions are found at several points off the coast of Peru (phosphatized diatomaceous and clastic-diatom-

CI

TABLE 2-20

w

0

Phosphorus content (%) in sediments of the submerged margin of Peru and Chile (Manheim et al., 1975) ~~

~

~~~

~

Station

Depth (m)

Type of sediment

22a 22b 23

2400 1400 1400

clay pellets

28

197

37 38 39 40

144 315 500 1000

206 207 208 209 210

203 700 1660 135 160

211 212 215 216 217 218

350 300 300 1025 2200 100

220

510

clay pellets medium- and coarse-grained glauconite sands with admixture of mud, quartz grains, and diatom remains silt with admixture of diatom and carbonate detritus as above, with admixture of glauconite grains limestone with inclusions of phosphate grains, shell detritus, sand, and diatoms silt with diatom detritus and sand grains (about 5%) diatomaceous silt diatomaceous clayey-silty ooze with soft greenish aggregates and compacted pellets silty sand with diatom and carbonate detritus and phosphate grains silty sand with diatom and carbonate detritus and phosphate grains clayey silt with admixture of diatom detritus silty sand with diatom detritus and phosphate grains sand with shell fragments, admixed silty-pelitic material, and partially phosphatized foraminifera sandy-silty-clayey sediment with diatoms and phosphate grains (up to 5%) sand with foraminifera and phosphate grains of the same size calcareous silt with admixture of diatom detritus silt with shell fragments silt without diatoms and foraminifera diatomaceous silt well-sorted, slightly diatomaceous silt

p205

H2°

0.05 0.03

56.0 64.6

0.04 0.17 0.32 1.10 0.17 0.05

48.0 82.6 93 4.2 84.4 88.1

0.42 0.75 0.82 0.05 0.71

65.1 59.0 56.6 72.3 27.4

0.85 4.80 18.50 0.04 0.08 0.09 0.18

41.0 71.5 37.4 88.1 76.1 79.6 78.2

1.91

61.8

221 223

1000 3350

224

85

225

750

226

1450

pebbles of schist and phosphorite well-sorted silt with slight amount of diatom and carbonate detritus

23.7 0.09 0.05

20.1 82.5 71.7

slightly sandy silt with glauconite, foraminifer tests, and isolated phosphate grains

0.43

59.6

glauconitic silt with rare diatom valves

0.32

49.8

silt with diatom detritus and mica flakes

132

Fig. 2-42. Phosphorites from the Peru-Chile shelf. (a) Unconsolidated concretions (Chile shelf), reduced by 1.5 times. ( b ) Dense concretion perforated by burrowing organisms (Peru shelf), reduced to half size. ( c ) Unconsolidated concretion (light) developed on a dense one (gray) (Chile shelf), X 3. (d) Dense phosphatized sea-lion coprolites (Chile shelf), natural size.

133 aceous sediments) and Chile (phosphatized clastic-diatomaceous and clastic sediments). Concretions off the coast of Peru usually contain 4 W O % clastic material of sand-silt size; represented mainly by grains of quartz, basic and intermediate plagioclases, and subalkalic pyroxenes (Fig. 2-43).The feldspars are highly chloritized and sericitized. The non-phosphatic component second in its relative importance is biogenic silica, the amount of which reaches 20-30’36. In most samples, especially unconsolidated ones, the organogenic structure of diatomaceous ooze is observed. Carbonate material occurs in subordinate amount and consists of dolomite (rhombohedra) and calcite (grains and aggregates of irregular shape). Pyrite also is present, in the form of spherules (about 0.01 mm in diameter) and accumulations of spherules. The phosphatic part of the rock consists of a homogeneous cement which fills the interstices between grains of clastic minerals and the cavities of diatom valves. The phosphate, which has a refractive index of 1.585, is for

Fig. 2-43. Microstructures of phosphorite from the Peru shelf (Burnett, 1974). (a) Angular grains of quartz and other clastic minerals in dark collophane cement; sample PD-15-13, thin-section, 11 nicols. (b) Phosphate-rich area (in center); sample KK-71-161, thin-section, 11 nicols.

134 the most part amorphous. Partial crystallization of the phosphate is observed only in dense concretions. The unit cell parameters of the phosphate are: a. = 9.329, co = 6.889 (Baturin et al., 1975). Fig. 2-44 gives an X-ray diagram of the phosphate. White unconsolidated concretions off the coast of Chile are phosphatized fine silty mud and consist mainly of angular particles of clastic and volcanogenic material bonded by phosphate cement (Fig. 2-45a). These particles, which are 0.01-0.05 mm in size (rarely 0.05-0.5 mm) occupy 50-60% of the field of view of thin-section and consist of plagioclases (71%), quartz (ll%), colorless volcanic glass (6%), magnetite and titanomagnetite (6%), monoclinic pyroxenes (3%), basaltic hornblende (2%) and blue-green hornblende (1%). Organogenic components consist of diatom valves, fragments of skeletons of calcareous organisms, and fish bones up to 1.2 mm in size. About 4% of the field of view is pyrite and phosphate of early generations. Pyrite occurs in the form of microglobules up to 0.01 mm in size, rarely 0.02mm. In places the microglobules are concrescent or clustered around diatom valves. The cement consists of light-yellow isotropic glassy phosphate. In some places cementation is not complete, and round (0.1-0.5 mm in size) or ramifying cavities are left, irregularly distributed and occupying up to 5%of the field of view. On the whole, the lightrgray compacted concretions are analogous in composition to concretions of the first type, but they are unevenly phosphatized. The amount of clastic and volcanogenic material amounts to 2035% to 80% in different places. The cavities (up to 2.5 mm in diameter) are

400

5

-

Eb

-

26

g

-

v1

:

0-

-C I

1

I

I

I

I

I

I

1

I

I

Fig. 2-44. X-ray diagram of phosphorite from the Peru shelf; sample PD-15-13 (Burnett, 1974).

135

Fig. 2-45. Microstructures of phosphorite from the Chile shelf (Baturin and Petelin, 1972). (a) Grains of clastic minerals in phosphate cement; thin-section, X 200, I ( nicols. (b) Cavity filled with isotropic phosphate, thin-section, X 80, (1 nicols.

often filled with yellow isotropic phosphate (Fig. 2-45b), in which in turn smaller round and irregular cavities (0.05-0.2 mm) are observed. The light-gray and gray dense concretions also are phosphatized clastic ooze, in places with amorphous and in other places with microcrystalline phosphate cement. The composition of the non-phosphatic components in them is the same as in the first two varieties. Cavities partially or completely filled with phosphate occur in the concretions, occupying 2-10% of the field of view. In some of the cavities coalescing coatings consisting of finely crystalline phosphate are observed. The phosphate microcrystals are arranged perpendicular to the surface of the coatings. The interstices between the coatings are either empty, due to which a spongy texture is created, or filled with isotropic phosphate, in places contaminated with pelitic material. The inner walls of some cavities are coated with a thin layer (0.005mm) of finely crystalline phosphate. In other cavities there is no crystalline phosphate, but pure yellow glassy isotropic phosphate is present, with occasional cavities (up to 0.12 mm) and small cracks.

136 The refractive index of the phosphate is 1.584 k0.003 in the unconsolidated concretions, 1.587 k0.003 in the compacted ones, and 1.593 k0.003 in the dense ones. According t o the data of X-ray-structural analysis, the unit cell parameters are as follows: u0 = 9.330, co = 6.880 (unconsolidated concretion); uo = 9.335, co = 6.880 A (dense concretion). On the Chilean shelf solid black concretions in sheet form also occur; they consist of phosphatized finegrained arkosic sandstone, partially coated with a layer of finely crystalline phosphate. The boundary between the sandy and finely crystalline phosphate is clear everywhere. The phosphatized sandstone consists 60% of angular particles 0.01-0.6 mm in size. Plagioclases predominate among them (up to 78%); quartz (-lo%), K-feldspar (6%), monoclinic pyroxenes (5%), epidote (l%), and isolated grains of blue-green hornblende are also present. The particles of clastic minerals are cemented by light-yellow isotropic phosphate, in places contaminated by fine fragmental clastic material. Microglobules of pyrite up to 0.07 mm in size are often encountered in the cementing mass. The finely crystalline phosphate is mottled in color, due t o the alternation of dark- and light-yellow areas. The light parts occur in the form of spots or bands intersecting at various angles, and are more strongly polarizing. Valves and fragments of spines of diatoms are occasionally encountered in the phosphate, and also microglobules of pyrite up to 0.01 mm in size. There is noticeably less pyrite here than ir. the phosphate cementing the sandstone. Up to 3-4% of the field of view in thin-sections of the finely crystalline phosphate is occupied by round and irregular cavities (up to 0.3 mm; Baturin and Petelin, 1972). Tests of foraminifera, some of them completely replaced by phosphate, are often encountered in the phosphorite concretions (Fig. 2-46). Probably they were phosphatized before the formation of the concretions, in which phosphatized and unphosphatized foraminifera were included along with grains of clastic material (Bumett, 1974). Phosphate grains (round, oval, and irregular in shape) up to 0.7 mm in size and fragments of phosphorite are constant components of the phosphorite concretions of all types. The grains consist of yellow, dark-yellow, yellowishgray, or brown phosphate, usually isotropic, less often slightly anisotropic, in some cases pure and in others contaminated by pelitic material. The grains have no internal structure. Some of the grains are uniform in composition (Fig. 2-47), others have nuclei in the form of particles of feldspar, quartz, or glauconite (Fig. 2-48). On some particles the phosphate coating is not fully developed, and only thin (ab0v.t 0.02mm) phosphate crusts are formed, coating individual parts of their surface (Fig. 2-48a). Some of the phosphate grains apparently were formed by cavity-filling, secretion or accretion of

a

13’7

Fig. 2-46. Tests of foraminifera in phosphorite from the Chile shelf (Burnett, 1974). (a) Calcitic, with n o signs o f phosphatization; (b) completely phosphatized ; thin-section, 11 nicols.

Fig. 2-47. Homogeneous phosphate grains in concretions from the shelf of Chile: (a) in phosphatized silty-pelitic ooze; thin-section, x 200, II nicols; (b) in phosphatized sandstone; thin-section, X 80, 11 nicols.

138

Fig. 2-48. Phosphate grains with nuclei in concretions from the shelf of Chile (Burnett, 1974). Composition of nuclei: (a) feldspar, (b) quartz, (c) glauconite. Thin-section, 11 nicols.

139 phosphate on the surface of non-phosphatic particles in the concretions themselves before they were completely lithified, others are phosphate of previous generations which was present in the enclosing sediments before the concretions began t o form. In addition to phosphate concretions and bones, phosphatized coprolites have been found in trawl samples from the Chile shelf. They consist either of yellowish-brown microgranular isotropic phosphate, or of light-yellow, glassy, finely crystalline phosphate. There are many voids in the phosphate (from 5 to 25% of the field of view), usually in the form of cracks from 0.1 to 4-5 mm long. In samples of both types there are a large number of fragments of fish bones from 0.1 to 2-4 mm in size (Fig. 2-49). Accumulations of microglobules and individual microglobules of pyrite up to 0.01 mm in size are often encountered in the phosphate and also in the crack-like voids. In some coprolites consisting of isotropic phosphate, numerous phosphatized remains of unidentified organisms, usually elongate and angular, are observed in addition to fish bones. They consist of non-polarizing isotropic phosphate and are either colorless or in part (and sometimes completely)

Fig. 2-49. Fragments of fish bones in phosphatized coprolite from the shelf of Chile; thinsection, X 80, 11 nicols.

140

141 yellowish-brown or reddish. In many cases they are coated with thin films (0.001 mm) of polarizing phosphate consisting of elongated microcrystals arranged perpendicular to the surface of the coating. In most cases the coprolites are structureless; locally, areas of phosphate contaminated by pelitic material, alternating with elongated cavities, are arranged in bands. Using the electron and scanning microscopes, amorphous, globular, and crystalline phosphate with several mutual transitions have been clearly identified in the phosphorites from the shelves of Peru and Chile (Figs. 2-50, 2-51). The amorphous phosphate consists of a homogeneous mass with no signs of granulation or crystallization (Fig. 2-50a). The globular phosphate consists of microglobules up t o 2-5 pm in size and aggregates of them (Fig. 2-50b), or of relatively larger globules (10-30 pm) with a bumpy surface in which radial crystallization of phosphate has occurred locally (Fig. 2-5Oc). The crystalline phosphate consists of hexagonal flakes and prismatic crystallites from fractions of a micron to 1-2 pm in size, which occur in the form of discrete segregations against a background of an amorphous groundmass (Fig. 2-51a, unconsolidated concretion) or form relatively compact accumulations (Fig. 2-51c, dense concretion). In many unconsolidated and dense concretions, elongated fusiform particles with rounded or splintery tips, up to 1-2pm in size, are encountered (Figs. 2-50b7 2-51b). The results of microdiffraction investigations of these particles indicate that they belong to the group of apatite-like minerals in their make-up. In some of those particles signs of crystal form are detected. The fusiform particles usually form pockets or stellate (rosette) accumulations and intergrowths on the surface of diatom valves, in association with mineral grains or in the interpore space (Figs. 2-50d, 2-51c, d). Probably these particles are an intermediate stage between amorphous and crystalline phosphate. Semiquantitative X-ray-structural mineralogic analysis, with subsequent computer processing of the results, also was used to investigate the overall composition of the phosphorites of the Peru-Chile region. The main components of the crystalline phase of the phosphorites are: apatite (8-76%), quartz (4-25544, plagioclases (11-25%), micas, including glauconite (017%),and pyrite (0-7%) (Table 2-21).

Fig. 2-50. Ultramicrostructures of phosphorite from the shelf of Peru. (a) Amorphous phosphate; sample PD-15-13, scanning microscope, x 1100 (Burnett, 1974). ( b ) Aggregates of microglobules and fusiform segregations of phosphate, sample 553-20, electron microscope, x 10,000 (photo by V.T. Dwbinchuk). ( c ) Radial crystallization of phosphate globules, sample 546, electron microscope, X 10,000 (photo by V.T. Dubinchuk). (d) Microcrystals of apatite on the surface of a diatom valve, sample PD-12-05, scanning microscope, X 14,450 (Burnett, 1974).

142 Chemical composition of the phosphorites

The chemical composition of the phosphorites was investigated using classic wet chemistry and the X-ray emission method (Tables 2-22, 2-23). All the investigated samples of concretions except the first (Table 2-23) are phosphate rocks with a P z 0 5 content between 12.7 and 29.0%. In the bones of fish and marine mammals from the sediments on the Chile shelf the P, 0, content is 27.3-29.5%, in phosphatized coprolites 30.7%(amorphous phosphate) and 32.3%(finely crystalline phosphate) (see Table 2-22). To a substantial degree the chemical composition of the concretions correlates with the extent of their lithification. On passing from unconsolidated to dense varieties their P z 0 5 content increases (from 13-24 to 1929%),likewise CaO (from 15-30 to 31-42%), COz (from 2-3 to 3-3.5%), and F (from 1.3-2.1 to 2.0-2.6%). At the same time the content of nonphosphatic components, related to clastic and biogenic siliceous material, decreases: SiOz from 19-44 to 10-3076, AlZO3 from 4.4-9.0 to 2.0-5.7%. N o clear-cut tendencies are observed in the behavior of manganese, iron, sodium, potassium, and sulfur.

143

Fig. 2-51. Ultramicrostructures of phosphorite from the shelf of Chile. (a) Crystallization of apatite in amorphous mass in unconsolidated concretion; sample 250-1 ; electron microscope, x 10,000 (Baturin and Dubinchuk, 1974a). (b) Fusiform segregations of phosphate in unconsolidated concretion: sample 250-1; electron microscope, X 16,500 (photo by V.T. Dubinchuk). (c) Microcrystalline phosphate in dense concretion; sample 250-3; scanning microscope, x 7500. (d) Rosette aggregate of microcrystalline phosphate; sample PD-19-37; scanning microscope, x 11,000 (Burnett, 1974).

TABLE 2-21 Composition of crystalline fraction of phosphorite concretions from the submerged margin of Peru and Chile, according to data of semiquantitative X-raystructural mineralogical analysis (Burnett. 1974) Station

Coordinates

Depth (m)

Mineralogic composition (96) apatite

micas kaolinite

quartz

K-feldspar

plagioclase

10

25 23 12 12 19 11

0 10

Peru shelf KK-7 1- 161 553 A-183 PD-12-05 PD-15-13 PD-15-17

5"09'S, 9'13's. 12'26's. 1Z05'S, 15'13'5, 15' 17's.

81O25'W 79'39'W 77'32'W 77'46'W 75O22'W 75'23'W

299-257 260-340 446 330-360 117-123 350-389

8 33 81 54 43 67

4 12 0 17 3

0 4 0 4 2

0

2

25 24 7 13 16 13

Chile shelf PD-18-30 PD-19-30 PD-19-33 PD-19-37 PD-21-25

18'30'S, 19O3O'S, 19'33'S, 19'37's. 2lo25'S,

70'36'W 70'19'W 70'23'W 70'26'W 70'22'W

346-423 127-132 341-370 430 100

63 67 76 66 61

0 0 0 12 0

0 0 0 3 0

10 5 4 4 8

0

0 0

15 0

0

0 8

23 14 15 12 20

tremolite

calcite

dolomite 28 2

0 0 0 0

pyrite

TABLE 2-22 Chemical composition (90)o f phosphorites from the submerged margin of Peru and Chile, from the data of chemical analyses Sample'

P205

CaO

MgO

Si02

AI,O,

FelOl

FeO

17.70 21.10 21.80 17.28 22.26

30.52 34.02 34.72 34.60 41.50

2.00 2.60 2.20 2.23 2.67

24.91 20.33 19.42 26.62 12.22

6.50 5.48 4.01 3.59 3.59

2.79** 1.89** 2.09** 2.30 0.30

15.73

24.90

1.8

22.23

6.11

20.64 25.62

24.92 38.64

1.2 1.6

31.60 12.30

6.00 3.31

26.45 29.51 27.36

35.01 39.55 41.38

LO1

IR

K20

CO,

COm

SO3

F

-

-

-

3.15 3.57 4.04

-

0.98 0.99

0.70 2.59

0.70 0.35

-

-

2.79

0.48

-

2.31

0.65

-

1.00

7.26

27.01

0.102

2.98 1.79

0.36 0.40

-

3.02 3.01

-

-

0.60

-

2.06 2.55

7.20 8.65

39.17 14.95

0.100 0.100

0.55 0.29

3.56 3.41 4.00

-

-

-

1.62 5.27

-

2.45 2.80

9.11 14.02

13.90 0.79

0.097 0.095

-

-

-

-

-

MnO

Na20

FtP2Os

Peru shelf

Unconsolidated concretions Compacted concretions Dense concretions Dense phosphatized rock Dense phosphatized rock Chile shelf Unconsolidated white concretions Compacted light gray concretions Dense gray concretions Dense black platy concretions Fish bones Whale vertebra Phosphatized coprolite. black Phosphatized coprolite. gray

30.67

-

32.33

-

0.8 0.5 0.69

10.80 0.79 2.98

2.55 n.d. ~

-

2.39 1.59 -

-

-

1.70 2.02 2.30

-

2.49 4.95

-

-

-

9.87 9.89

-

6.00 6.76

32.71 26.27 23.62 -

-

-

5.63

1.39

-

-

-

-

4.51

0.92

-

-

-

-

0.096 0.096 0.106 -

-

-

* Peru shelf: all samples are from Baturin e t al. (1975). except for the frrst o f the dense phosphatized rock samples which is from Gershanovich and Konyukhov (1975). Chile shelf: all samples are from Baturin and Petelin (1972). ** Total iron.

TABLE 2-23

Chemical composition (5%) of phosphorite concretions from the submerged margin of.Peru and Chile, according to the data of X-ray emission analyses (Burnett, 19741 P,Os

CaO

MgO

SiOl

A1203

Fe203 (total)

Na10

K20

S

F

LOI**

ZI

-0

Peru shelf KK-71-161 546 553 A-183 PD-12-05 (a) PD-12-05 (b) PD-15-13 (a) PD-15-13 (b) PD-15-17 (a) PD-15-17 (b)

5.95 21.96 19.80 29.00 24.54 28.82 12.76 18.96 19.03 22.14

19.10 34.60 30.34 42.35 36.32 41.45 21.37 31.17 29.00 33.94

4.87 1.48 1.13 0.88 1.09 1.02 0.68 0.86 1.05 1.36

41.40 22.62 27.89 10.17 18.86 12.41 44.48 30.37 25.77 21.21

8.20 5.11 6.75 1.99 4.82 3.27 9.08 5.76 4.43 4.80

3.68 1.69 1.71 1.42 1.39 1.26 2.09 1.53 6.05 3.27

0.75 0.77 0.91 0.70 0.85 0.80 1.00 0.90 0.88 0.83

1.65 1.12 1.47 0.78 1.11 0.85 2.01 1.48 1.11 1.22

0.05 0.15 0.15 0.09 0.04 0.12 0.27 0.16 0.32 0.14

0.59 2.46 2.18 2.61 2.36 2.63 1.35 1.95 2.09 2.36

15.60 9.77 8.20 10.28 10.24 7.80 4.73 7.52 11.73 11.06

101.84 101.73 100.53 100.27 101.62 100.43 99.82 100.66 101.46 102.33

Chile shelf PD-18-30 (a) PD-16-30 (b) PD-19-30 PD-19-33 PD-19-37 PD-21-25

16.02 22.30 25.06 28.71 22.43 27.67

25.09 32.97 36.02 40.01 33.79 40.51

1.34 1.24 0.85 1.11 1.23 0.74

33.89 23.59 17.99 12.86 16.67 13.31

9.82 6.15 5.07 3.10 3.74 3.39

2.68 2.84 2.69 1.75 6.34 2.39

0.98 0.86 0.86 0.76 0.75 0.90

2.11 1.56 1.27 0.76 1.78 0.81

0.06 0.01 0.39 0.12 0.09 0.23

1.62 2.22 2.25 2.57 2.24 2.49

6.12 8.60 7.43 9.27 10.21 8.69

Average***

22.61

33.93

1.07

22.13

5.15

2.85

0.85

1.30

0.16

2.22

8.78

Station (sample)*

* Samples: a = light-gray concretions; b = dark-gray concretions. ** At 1000°C. *** Not counting first sample.

XI1

CaO/P2Os

F/PzOs

0.25 101.59 1.03 100.70 0.92 99.61 1.10 99.17 0.99 100.63 1.11 99.32 0.57 99.25 0.82 99.84 0.88 100.58 0.99 101.34

3.21 1.57 1.53 1.46 1.48 1.44 1.67 1.64 1.52 1.53

0.099 0.112 0.110 0.090 0.096 0.091 0.106 0.103 0.110 0.106

99.73 102.34 99.88 100.84 99.27 101.13

0.68 0.93 0.95 1.08 0.94 1.05

99.05 101.41 98.93 99.76 98.33 100.08

1.57 1.48 1.44 1.39 1.51 1.46

0.101 0.099 0.090 0.089 0.100 0.090

101.05

0.93

100.12

1.50

0.098

147 The scanning microprobe, by means of which particles of relatively pure material 10-30 pm in diameter were analyzed, was used to determine the composition of the phosphatic and non-phosphatic fractions of the phosphorites. The composition of the phosphatic fraction (Table 2-24) is considerably different from the bulk composition of the concretions (Table 2-23); the contents of P,O, (24-30%), CaO (35-40%), and F (2.4-3.396) are higher. At the same time the contents of Na and Mg in the phosphatic fraction remain about the same as in the bulk samples, which apparently indicates that these elements substitute for calcium in the apatite lattice. The CaO/P, O5 and F/P, O5 ratios in the phosphatic fraction also are practically unchanged compared t o the bulk samples (Burnett, 1974). The P,O, content in the cement of the concretions ranges from 20 to 3096, in the phosphate coatings on glauconite grains from 26 to 2796, and within glauconite grains from 0.2 to 1.6%(Table 2-25, Fig. 2-52). Using the same method, schemes of distribution of the elements were plotted by area of thin-section; the relative concentration of elements on these schemes corresponds t o the density of white dots. The area illustrated in Fig. 2-53 consists of grains of quartz, alkali feldspar, and plagioclase in phosphate cement. On the scheme it is seen that the zone of occurrence of calcium is somewhat broader than that of phosphorus, which is related to the presence of plagioclase and tiny rhombohedra of dolomite in the thinsection. A thin-section area of another concretion (Fig. 2-54) consists of a plagioclase grain in phosphate cement. The concentration of calcium and phosphorus on the surface of the plagioclase grain is somewhat greater than that of the rest of the area of phosphate cement. Possibly this phenomenon represents the initial stage of formation of phosphate pellets around grains of clastic material, which act as centers of accumulation of phosphorus (Burnett, 1974). Age o f the phosphorite The phosphorite from the submerged margins of Peru and Chile has been dated by micropaleontological and radiometric methods. According to the determinations by A.P. Zhuze and V.V. Mukhina (Institute of Oceanology of the Academy of Sciences of the U.S.S.R.), the diatoms in the phosphorite of this region are Recent species. Among them there have been identified: Coscinodiscus perforatus Ehr., C. asteromphalus var. centralis Grun, C. gigas Ehr., Actinoptichus undulatus Bail, A . splendens Ralfs, Rhaphoneis wetzeli Mertz (Fig. 2-55a), Cyclotella striata (Ktz.) Grun, Thalassiosira decipiens (Fig. 2-55b) - Peru shelf, station 553, 9'13'S, 79'39'W, depth 260-340m; Chaetoceros sp., Grammatophora angulosa Ehr., Thalassiosira decipiens

TABLE 2-24

CL

Chemical composition ('70)of areas of pure phosphate in thin-sections of phosphorites from the submerged margin of Peru and Chile according to data of scanning microprobe analysis (Burnett. 1974) N

PzO, CaO

MgO

SiO:

A1203

FeO (total)

Na20

F

CI

KK-71-161 PD-12-05( a ) PD-13-15 (b) PD-15-17( a ) (b) PD-18-30 PD-19-30 PD-19-33 PD.19.37 PD-21-24 PD.21.25

2 3 2 2 3 4 3 3 2 9

23.82 26.10 29.83 27.64 29.76 30.23 27.65 25.74 29.28 30.45

1.40 0.94 1.03 1.73 1.45 0.89 1.33 1.04 1.07 1.10

15.07 3.53 7.16 7.06 6.18 6.84 3.17 16.03 4.51 2.86

4.69 1.44 1.23 1.62 1.73 3.01 0.83 3.82 0.68 1.05

2.99 0.44 0.80 1.30 2.24 0.82 0.77 1.10 1.22 0.71

1.03 1.01 1.02 0.83 0.93 1.20 0.79 1.11 0.78 1.27

2.41 2.56 3.08 2.75 3.05 2.81 2.64 2.57 3.14 3.36

0.31 0.02 0.83 0.02 0.17 0.01 0.39 0.01 0.20 0.01 0.48 0.03 0.15 0.02 0.10 0.01 0.11 0.01 0.26 0.02

35.41 39.05 43.38 42.09 44.26 44.65 44.63 38.85 46.41 46.46

La203

Ce203 Nd203

?:

CaO/PzOj F / P z O j

0.02 0.01 0.32 0.03 0.01

0.01 0.01 0.01 0.11 0.06 0.27 0.06 0.10 0.10 0.03

87.25 74.95 88.27 85.57 89.92 91.33 82.08 90.59 87.33 87.62

1.49 1.50 1.45 1.52 1.49 1.48 1.61 1.51 1.58 1.52

Y20,

Station (sample)*

0.08

0.01 0.01 0.01 0.02

0.07 0.01 0.23 0.01 0.04 0.02 0.03 0.11 0.01 0.03

0.103 0.098 0.103 0.099 0.102 0.093 0.095 0.100 0.107 0.110

N = number of determinations. * Samples: a = light parts of concretions; b = dark parts of concretions.

TABLE 2-25 Chemical composition (70)of the phosphate cement, phosphate coatings, and glauconite and plagioclase grains in thin-sections of phosphorites from the shelf Chile. according t o the data ofscanning microprobe analysis (Burnett 1974)

Y203

Of

2

AreaNo.

Materialanalyzed

P20,

CaO

MgO

SiO,

FeO*

Na20

K20 F

CI

La203

Ce203

Nd203

1** 2** 3** 4** 5** 1*** 2*** 3*** 4*** 5***

cement glauconite phosphate coating glauconite cement

19.75 1.65 27.58 0.20 28.01

28.65 0.24 43.27 0.17 41.31

0.51 2.14 1.41 3.24 1.27

29.25 14.84 7.65 49.52 14.56

7.81 3.13 2.65 3.83 2.66

0.67 50.85 2.78 28.37 1.33

1.75 0.56 0.99 0.31 0.95

1.73 1.75 0.01 3.18 7.70 0.02 2.67

0.10 0.01 0.32 0.01 0.14 0.02 0.19 0.03 0.09 0.01

0.01 0.01 0.01 0.01 0.01

0.08

0.01 0.06

0.14 0.09 0.01 0.02 0.19

90.28 85.61 89.77 93.62 93.12

glauconite plagioclase cement glauconite phosphate coating

0.79 10.70 30.38 46.33 0.22 0.24 26.48 40.02

3.59 50.61 0.10 55.96 1.01 5.65 3.17 49.97 6.60 1.28

6.52 28.15 0.81 6.79 1.69

25.12

0.34 5.19 0.91 0.53 1.13

8.10 0.07 0.38 3.53 7.48 0.02 2.32

0.59

0.06

0.01

96.38 101.36 90.00 95.93 82.77

0.56

-

* ** Total Fe. of analyzed areas is shown in Fig. 2-52a,b. *** Location Location of analyzed areas is shown in Fig. 2-52c.d.

AI,03

0.88

1.19 27.12 2.66

-

0.01 0.08

0.01

-

0.01

-

-

-

0.13 0.22 0.36

0.01 0.01 0.01

0.01 0.01 0.01

0.03 0.02 0.11

-

0.01 0.13 0.12

&

149

Fig. 2-52. Thin-sections of phosphorite from the shelf of Chile, investigated by means of the microprobe (for area numbers see Table 2-25; Burnett, 1974). (a), (b) Sample PD-1937. (c), (d) Sample PD-21-24.

(Grun.) Jorg, Trachyneis aspera (Ehr.) Cl., Coscinodiscus radiatus Ehr., Melosira sulcata (Ehr.) Ktz., Rhopalodia musculus (Ktz.) 0 .Mull., Epithemia sorex Ktz., Actinoptichus undulatus (Bail) Ralfs, Cyclotella kuetzingiana Thw., Dictiocha fibula Ehr. - Chile shelf, station 250, 2lo07'S, 7Oo21'W, depth 150 m. The absolute age of the concretions was determined radiometrically from the 234U/238Uactivity ratio as a whole and from tetravalent uranium, and

150

Fig. 2-53. Distribution of elements by area in a thin-section of a phosphorite concretion from the shelf of Peru; sample KK-71-161(Bumett, 1974).

Fig. 2-54. Distribution of elements by area in a thin-section of a phosphorite concretion from the shelf of Chile: sample PD-21-24 (Burnett, 1974).

152 from z30Th/z34U(Baturin e t al., 1972c, 1974; Burnett, 1974; Burnett and Veeh, 1977; Veeh e t al., 1973). In the phosphorites considered, the uranium content ranges within 26219 x %, thorium within 1.1-9.0 x %. Tetravalent uranium constitutes 40-7176 of the total uranium. Uranium in equilibrium was found in only one sample (from station 544, Table 2-26) from the continental slope of Peru. In the rest of the samples the 234U/238U activity ranges from 1.04 k0.03 to 1.16 kO.01 in total uranium and from 0.84 k0.03 to 1.19 k0.04 in tetravalent uranium, and the z30Th/234Uratio from 0.010 kO.001 t o 0.74 k 0.03. If it is assumed that all the ionium contained in these phosphorites was produced by decay of 234U,their maximum age, calculated from the 230Th/ 234U activity ratio, is from 1000 to 140,000 years. The age of the phosphorites calculated from the z 3 4 U / 2 3 8 Uactivity ratio of total uranium ranges from Recent to > 800,000 years, and from the activity ratio of these isotopes in tetravdent uranium, from Recent to > 150,000 years (Table 2-26).

153

Fig. 2-55. Recent diatoms in phosphorite from the Peru shelf (identified by A.P. Zhuze). (a) Rhaphoneis wetzeli Mertz; scanning microscope, x 4400. ( b ) Thalassiosira decipiens; scanning microscope x 1500.

In the latter case the age was calculated on the basis of a theoretical model according to which, as a result of radioactive decay and subsequent oxidation of 238U(IV)and 2MU(IV)in the concretions, fractionation of urkium isotopes between U(1V) and U(V1) takes place (Kolodny, 1969a; Kolodny and Kaplan, 1970a). Thus on the submerged margin of Peru and Chile, as on the shelf of southwest Africa, there occur Recent, Upper Quaternary, and apparently preQuaternary phosphorites.

LOCAL ACCUMULATIONS AND ISOLATED FINDS OF PHOSPHORITE ON THE OCEAN SHELVES

In addition to the vast phosphorite provinces, there are small phosphate outcrops and local accumulations of phosphorite on the ocean shelves, some of which have been investigated in sufficient detail.

T.\Bl.E 2.26 .\IIsoIute are

d phosphorite from the rubmereed marein

of Peru and Chile. from the aelivitv ratios of uranium and thorium isotows

total)

I'V"

Sl,Cl/

KK-71-161

5'00's. 81'25'W

eonei~tion

106(110)"

5.9

KK-71-161

5 ' 0 0 ' 5 . LI1'25'W 299-257

299-257

concretion, upper layer

103

6.7

1.09f0.01 (1.1OtO.02) 1.09t0.01

KK.71.161

5'OO'S. LIl-25'W 299-257

concretion.

10

61

1.10'0.01

77

2.0 4.7 2.2

1.16

1.07'0.01

1.16

0.40f002

l8Of45

55

-

-

0.46+0.02

180t45

66

0.62+0.03

14Of40

102

-

""&W

-

553

9 1 3 S. i9'39.W 260-340 9"46'S . ( 9= 2 3 ' W 360

i46

-

2.1

65

1.1

1.14t0.01

-

0.040f0.002

fish hone light concretion

101

n.d.

27

2.4

1.15f0.01 1.17f0.03

-

0.02OfO.001 Recent 0.050t0.002 Recent

6

dark

1021hll

3.2

concretlo" rish bone light

101

0.4

382(219)

5.5

721531

2.3

RI 150) l o o ( 103)

3.7 3.0

372(1561 IO?(i6)

9.0 3.1

544 KK-71-96 4.183 PD.12-05

67 16 118

9G 168

5.7 5 1

CO"C
m 7

I

8

m 9

Fig. 5-4.Scheme of the process of Quaternary phosphorite formation on the ocean shelves: A = supply of phosphorus to the shelf zone by upwelling waters; B = consumption of phosphorus by organisms; C = deposition of phosphorus on the bottom in biogenic detritus and its burial in sediments; D = formation of phosphate concretions in biogenic sediments; E = reworking of sediments and concentration of phosphate concretions when sea level is low. Zones: I = zone of shallow-water clastic deposits; I Z = zone of biogenic sediments with high content of organic matter and disseminated biogenic phosphorus; I I Z = zone of reworked sediments rich in phosphate concretions; ZV = zone of carbonate sediments, locally with phosphate concretions. Legend: 1 = paths of movement of phosphorus in sea and interstitial waters; 2 = plankton; 3 = clastic sediments; 4 = biogenic siliceous, siliceous-clastic, and siliceous-carbonate sediments; 5 = carbonate sediments; 6 = unconsolidated phosphate concretions; 7 = dense phosphate concretions; 8 = glauconite; 9 = erosional surface.

Changes in sea level, which in the Pleistocene fluctuated from -200 to 4-120 m (Menard, 1966), were still more important for reworking of the shelf sediments. Due to these a substantial part of shelf sediments bear traces of reworking (Zenkovich, 1946; Leont'yev, 1963; Curray, 1964; Emery, 1969a), which in particular is true of the phosphate sands on the shelves of southern California, Georgia, the Carolinas, Morocco, and southwest Africa, described above (see Chapter 2). In the sediment wedge on the submerged margin of southwest Africa, five erosional surfaces have been established, formed when sea level stood lower. On the surface of the bottom of the shelf, seven erosion terraces 5-20 m high have been distinguished, and in the coastal belt four wave-cut terraces at heights of 2, 3, 7, and 23 m above present sea level; the lowest and youngest of these is dated as 24,000-48,000 years (Hoyt et al., 1969; Van Andel and Calvert, 1971). In many other shelf regions erosional terraces are buried beneath a layer of younger unconsolidated sediments, or are masked by the slope of the bottom (Emery, 1968). As the dating of phosphate concretions from the shelf of Peru and Chile

228 TABLE 5-3 Rough calculation of the balance of mobile phosphorus in the present ocean Index

Ocean as a whole

Phosphate-bearing and potentially phosphate-bearing shelves

Area ( lo6 km2 )

361

up t o 1-3*

Supply of dissolved phosphorus ( l o 6 t/yr)

1.5 (with river discharge)

more than 10 (due to upwelling)

Phosphorus involved in primary production (mg/m2 day) (l o 6 t / v ) Deposited phosphorus ( lo6 tlyr)

2.5-17 3 00-2 000

50-150 30-100

up to 4

up to 0.6-2

Phosphorus buried in sediments ( l o 6 t/yr)

1.5

up to 1

Phosphorus involved in formation of phosphorite concretions ( lo6 tlyr)

up to 0 . 0 1

up to 0.01

~~

~

~

* The total area of the ocean shelves is 27.5 X lo6 km2 (Poldevaart, 1957). has shown, during the last 150,000 years they were formed only when sea level was high (Fig. 5-2),which could have been a result of warming of the climate, heating of shelf waters and of the upper layer of sediments, and also of the expansion of the shelf area favorable for phosphorite formation or intensification of upwelling, biological productivity, and biogenic sedimentation. When sea level was low, owing to cooling of the climate and glaciation, only erosion of phosphatic sediments, residual concentration and accumulation of phosphorites occurred. In each cycle of phosphorite formation this process was repeated, due to migration of the surf zone twice: when sea level dropped and then when it rose (Fig. 5-3).This apparently explains the well known fact that many platform phosphorites are related to transgressive series. Thus the complete cycle of phosphorite formation on the ocean shelves includes five stages: (1)supply of phosphorus t o the shelf zone in upwelling ocean waters; (2) consumption of phosphorus by phytoplankton and other organisms; (3) deposition of phosphorus on the bottom in biogenic detritus and accumulation of sediments with a high content of mobile biogenic phosphorus; (4)formation of gel-like, gradually hardening phosphate concretions in the sediments; (5)reworking of the sediments and residual concentration of the concretions. The scheme of this cycle is depicted in Fig. 5-4. Intensive phosphorite formation on the ocean shelves is possible only with

229

an optimal combination of biogenic sedimentation and brief reworkings of the sediments, i.e. in the case of multiple repetitions of the multistage cycle described above. One of the conditions necessary for the concentration of phosphatic material in well-sorted phosphorite deposits is the “purest” possible composition of the original sediments with respect to the material not being removed, inasmuch as any coarse-grained elastic and biogenic nonphosphatic components of the sediments would be residually concentrated along with the phosphate concretions. Obviously the concretions concentrated in the deposits are far less in amount than those left scattered in the sediments. The potential rate of Recent and Late Quaternary phosphorite formation on the ocean shelves is about 10,000 t P/yr or, taking into account the area of the zones of active upwelling (300,000 km2),tenths of a millimeter per thousand years (Table 5-3). Thus if the present regime of sedimentation on the shelves of southwest Africa and Peru-Chile were maintained for one million years, phosphorite deposits a few tens of centimeters thick with total reserves of 10 billion tons of phosphorus would accumulate; this is close to the rate of formation of some pre-Quaternary phosphorite deposits.

-

This Page Intentionally Left Blank

Chapter 6 SOME FEATURES O F THE BEHAVIOR O F ELEMENTS ASSOCIATED WITH PHOSPHORUS IN THE COURSE O F OCEANIC PHOSPHORITE FORMATION Phosphorites are characterized by the presence of certain components which are constant or frequent associates of phosphorus in the biogenic and sedimentary cycles - organic matter, amorphous silica, fluorine, and several trace elements. Their behavior in the course of phosphorite formation is a component part of the geochemistry of phosphorites which is important for understanding the regularities of their composition.

ORGANIC MATTER

The functions of organic matter in the course of phosphorite formation are diverse. The main one is the fact that organic matter is a direct supplier of organic phosphorus which when mineralized forms concretions. Organic matter also plays the part of the main factor determining the pH and Eh of the environment of phosphorite formation, which correspondingly controls the deposition of calcium phosphate. Possibly the organic matter included in gel-like phosphate clots is the source of the energy used in the formation of the concretions. And finally, carbon dioxide produced in the decay of organic matter apparently is included in the composition of the molecules of carbonate-fluorapatite. Sulfate-reducing bacteria take part in the decay of organic matter in phosphatic sediments; primarily they consume the most labile compounds - proteins, carbohydrates, and organic acids, which are used as hydrogen donors in the reduction of sulfates to hydrogen sulfide (Schlegel, 1972). During phosphatization of Recent diatomaceous ooze and transformation of its phosphatized parts into concretions, the Corg content decreases 4-t o 6-fold. At the same time there is a decrease in the content of nitrogen, carbohydrates, and free lipids, calculated both as dry substance and in the composition of organic matter (Table 6-1). As relatively unstable compounds, carbohydrates are highly reactive in the course of lithification and phosphatization; their content in dry substance (in the series: ooze-unconsolidated concretions-dense concretions) decreases from 9667 to 421 pg/g, i.e. 22-fold, and recalculated to organic carbon, from 8.5 to 2.2%. Compared t o carbohydrates, the free lipids, the nitrogenous part of organic matter, and especially the bound lipids are much more conservative

to

w

to

TABLE 6-1 Composition (%) of organic matter of phosphorite concretions from the shelf of southwest Africa (Romankevich and Baturin, 1972) Components and their ratios

Enclosing diatomaceous ooze station 152

pz 0 5 SiOZ arnorph COZ Corg Norg

PZ0 5 K o r g SiOZ amorph/Corg Norg/Corg ( X 100) Cinorg K o r g Composition of organic matter (%; % of Co, in parentheses) carbohydrates free lipids bound lipids humic acids

Phosphatized diatomaceous ooze

Concretions from diatomaceous oozes unconsolidated

compacted

dense

Concretions from reworked sediments of outer shelf

station 157

1.40 38.9 1.63 4.25 0.399

1.15 53.8 1.50 5.20 0.604

8.52 30.00 2.16 3.40 0.363

23.85 7.80 5.52 1.80 0.178

29.62 4.05 5.34 1.03 0.097

32.74 0.90 6.33 0.92 0.081

21.27 0.84 3.65 0.76 0.053

0.33 9.2 9.4 0.10

0.22 10.35 11.6 0.08

2.51 8.82 10.68 0.17

13.25 4.33 9.89 0.84

28.76 3.93 9.42 1.41

35.58 0.98 8.80 1.88

27.99 1.11 6.97 1.31

0.3111 (6.91)

0.1342 (5.21) 0.1100 (8.01) 0.1250 (7.28)

0.0710 (3.09) 0.0575 (4.69) 0.0875 (5.71)

0.0421 (2.21)

0.9667 (9.10) 0.6796 (12.0) 0.1888 (2.7) 3.99 (51.6)

1.1100 (8.54) -

-

-

0.7556 (8.89) 0.4840 (10.68) 0.2600 (4.59) 3.39 (54.80)

-

-

-

-

-

Composition of carbohydrates (% of total) oligosaccharides water-soluble polysaccharides water-insoluble polysaccharides

Loss of corg* Increase of cinorg* Acinorz/Acorz

(X

100)

-

-

3.3

-

5.0

-

9.6

-

-

7.3

-

12.5

-

22.2

-

-

89.4

-

82.5

-

68.2

-

-

-

0.85 0.15 17.6

3.13 1.10 32.9

3.22 1.02 31.6

3.33 1.29 38.7

-

-

*Loss and increase compared to enclosing sediments in absolute percentage.

N

w w

234 components. In the series under consideration their content decreases from 4840 to 575pg/g (free lipids), from 0.363 to 0.08--0.053% (nitrogen), and from 2600 to 875 pg/g (fixed lipids), i.e. by about 8.5, 7, and 3 times, respectively. The amount of free lipids in the composition of organic matter decreases (from 12.8 to 5.0%), but the content of bound lipids increases (from 2.2 to 4.8-6.1%), which apparently is related to conversion of part of the free lipids t o an insoluble state. On the whole the content of lipids decreases in the series under consideration (from 1 5 to 10%of organic carbon). Thus on the basis of increasing conservatism, these classes of compounds constitute the following series: carbohydrates-free lipids-nitrogenous part of organic matter-fixed lipids. The correctness of distinguishing such a series is governed by the autochthonous syngenetic type of initial organic matter in all the substances studied. Its autochthonous nature is suggested by the systematic character of the change in composition of organic matter, in particular by the gradual decrease in ratio of free t o fixed lipids on passing from diatomaceous oozes to lithified phosphorite concretions. It should be mentioned that the nitrogenous part of organic matter in diatomaceous oozes and phosphorite concretions is much more resistant to oxidation than the analogous component of the original organic matter of the diatomaceous plankton and suspended matter. In these oozes and concretions nitrogen is part of humic acids which constitute up t o 50% of all the organic matter, while in diatomaceous plankton 70% or more of the total amount of nitrogen is included in proteins and peptides (Krey, 1958; Parsons et al., 1961). The relatively rapid decay of the most oxygen-rich organic compounds (carbohydrates) and also the substantial predominance of water-insoluble polysaccharides in the composition of the carbohydrate complex indicate the biogenic nature of the processes of oxidation of organic matter under both aerobic and anaerobic conditions (Rodionova, 1951 ; Uspenskiy, 1970). As the phosphorite concretions become lithified the content of waterinsoluble polysaccharides in the carbohydrates decreases and the content of oligosaccharides and water-soluble polysaccharides increases. These results are additional evidence that the phosphorite concretions under consideration represent one genetic series in which the content and composition of organic matter changes systematically in correspondence with the extent of lithification and age of the concretions. The most sensitive indicators in this respect are carbohydrates, to a lesser extent lipids and Norg.The proportional decrease in the concentration of carbohydrates, free lipids, and also in the total amount of organic matter and the increase in the content of phosphorus (Fig. 6-1) shows that the initial stages of the process of formation of phosphorite concretions went on continuously at a relatively constant rate (Romankevich and Baturin, 1972).

23 5

Fig. 6-1. Evolution of the composition of organic matter in Holocene phosphorite concretions (shelf of southwest Africa) as they lithify (Romankevich and Baturin, 1972). Samples: I = diatomaceous ooze; II = phosphatized ooze; III = unconsolidated concretion; I V = compacted concretion; V = dense concretion. Components: I = Corg; 2 = Cinorg; 3 = Ptotd; 4 = Si02amorph; 5 = carbohydrates; 6 = free lipids; 7 = fixed lipids; 8 = Norg.

Data on the carbon isotopic composition of lipids extracted from the phosphorites are evidence of this. In the formation and subsequent lithification of phosphorite concretions, the carbon of A lipids becomes isotopically lighter, from -20.7 to -24.2yoO, and the carbon of C lipids becomes heavier, from -24.0 to -23.0~00.This leads to an inversion of the carbon isotopic composition of the A and C lipids in the concretions relative to the enclosing sediments, where the carbon isotopes are distributed in the lipids in a directly opposite way. Apparently the observed picture is produced by the rapid biological oxidation of phospholipids, phosphorus and C 0 2 , which enter into the composition of calcium phosphate as they are liberated (Shadskiy et al., 1980).

CARBON AND OXYGEN ISOTOPES OF C02 AND PO4

Carbon and oxygen isotopes in oceanic phosphorites were investigated in

236 order to clarify the question whether C 0 2 enters into the composition of the apatite molecule. Phosphorites from the California basin, the submerged Chatham Rise, and isolated samples from other regions, including a Recent phosphatic Lingula shell, and also synthetic apatite obtained by replacement of calcite were involved in the investigations (Kolodny, 1969a; Kolodny and Kaplan, 1970b). Two parallel batches were taken from each sample, one of which was analyzed for total C 0 2 and the other for C02 fixed in apatite; for this purpose the second batch was first treated with ammonium citrate, which dissolves calcium carbonate but hardly affects apatite (Silverman et al., 1952). The C 0 2 given off was made to react with a 95% solution of phosphoric acid in a mass spectrometer with a calcite standard, taking into account a correction for the background, mixing and impurities of 1 7 0 (Craig, 1957). All the analyses were run twice. The standard deviation of the results was k0.4yoOat the 95% confidence level. The results obtained (Table 6-2) are expressed in per mil:

~ ( T O O=)

(

Rsample

standard

1

-1 x

1000, where R is the 13C/12Cor 180/170 ratio.

Carbon isotopes. In the California phosphorites no significant difference is observed in the composition of the carbon isotopes of the apatite and calcite phases. The only exception is the phosphate sand from the Baja California region (sample KP 62). In it, and also in the phosphorites of the Chatham Rise, the seamount “NI5”, Agulhas Bank, and the sample of synthetic apatite containing about 7% CaC03 unreplaced by phosphate (sample SI-6), the calcite carbon is appreciably heavier than the apatite carbon. The opposite picture is observed in the phosphatic Lingula shell and the practically pure synthetic apatite (sample SI-1). When the A13C values that are definitely different from zero and the calcite content in the investigated phosphorite samples are compared, an inverse relationship between these values is noted. Probably fractionation of carbon isotopes between the calcite and apatite phases increases as phosphatization of the carbonates progresses, due to preferential removal of the light isotopes from them in the form of HCO;. Oxygen isotopes. A similar but less clearly manifested tendency toward fractionation in proportion to phosphatization is observed in the oxygen isotope ratio. In the California phosphorites this tendency is weakly manifested. In the dark cores of samples KP 33 and KP 51, rich in organic matter, no fractionation of oxygen isotopes is observed, whereas in the light outer parts of these samples where there is little organic matter the calcite phase is markedly

TABLE 6-2 Carbon and oxygen isotopes (%,) Sample No.

Sampling site

in CO2 isolated from phosphorites (Kolodny, 1969a; Kolodny and Kaplan, 1970b) Original material

Calcite content (%)

C 0 2 in apatite

Carbon isotopes

(%)

total 6%

California region KP 1 Coronado Bank KP 2 Forty Mile Bank KP 3 Catalina Bank Catalina Bank KP 4 KP 5 Off San Clemente Is. KP 6 Off San Nicolas Is. KP 1 5 Pioneer Seamount Forty Mile Bank KP 33

KP 51

Thirty Mile Bank

KP 62

Baja California

Submerged Chathom Rise KP 9 43°20’S, 179’31’E KP 6 3 43O27‘S, 179’19’E KP 64 43O26’S 178°00’W KP 6 5 43O30‘5, 179’06‘E Other samples KP 54 Seamount NT5 26”42’S, 159O17’E (521-322m) KP 55 Agulhas Bank LH Hawaii, Kaeoha Bay ( 2 m ) SI-1

SI-6 SI-2

-

a atite 6%

Oxygen isotopes calcite 6°C

oolitic phosphorite oolitic phosphorite oolitic phosphorite oolitic phosphorite oolitic phosphorite

1.3 1.5 2.2 1.9 1.1

87 86 77 80 20

-2.2 -1.3 -1.9 -1.8 -1.4

-2.6 -1.6 -1.7 -1.8 -1.2

-1.3f5.9 -0.7f4.5 -2.5f 2.4 -1.8t2.9 -3.226.5

oolitic phosphorite oolitic phosphorite ( a ) outer part of nodule (b) core of nodule (a) outer part of nodule ( b ) core o f nodule phosphate sand

1.3 3.5 1.5

90 59 87

-2.5 -2.0 -1.3

-2.2 -2.0 -1.5

-5.Of8.2 -2.Of1.2 0.3f4.6

1.9 2.0

82 78

-1.1 -1.2

-1.5 -1.3

0.7 f 3.1 -0.6f 2.4

2.3 9.3

78 16

-1.6 -2.4

-2.1 -8.4

-0.lf 2.6 -1.3f1.3

limestone limestone limestone limestone

23.9 24.8 20.9 42.4

30 31 33 20

1.1 1.1 0.7 1.3

-0.3 -0.5 -1.4 -0.9

phosphatized limestone

41.0

23

1.9

pellet phosphorite Lingula shell

15.1 2.0

32 63.5

phosphatized phosphatized phosphatized phosphatized

synthetic apatite, replacing calcite synthetic apatite, not completely reacted original calcite

1.0 -4.4

0.3 -0.8

-2.0

1.3

89

-22.3

-20.0

6.9

58

-19.8

-22.0

100

-

-24.0

-

A~”C

-

total

a atite

calcite

6180

8 8 0

6180

-0.3

A6”O

-

-0.3 -1.7 0.3 1.3

0.2 0.1 -0.3 0.4 1.1

-3.6f4.1 -2.8f3.8 -6.1f2.3 0.122.6 2.8f6.4

-0.8 -0.2 0.9

0.2 -0.2 -0.2

-9.4f5.5 -0.2 t 1.1 8.3 f 4.2

-0.3 0.5

-0.3 -0.4

-0.3f 2.1 3.6f2.3

4.0f2.3

7.1f1.4

-0.3 -0.4

-0.5 -3.1

0.4f2.4 0.2 f 0.7

3.3f0.8

1.7f0.6 1.9t0.6 1.7f0.7 1.8t0.5

2.0f0.7 2.3f0.7 3.1f0.8 2.7f0.7

1.7 0.4 1.1 -0.2

0.8 -0.1 0.2 0.1

2.3f0.5

2.0f0.7

0.7

1.820.6 -8.6f1.5

2.6f0.7 -6.6f1.6

1.1

-40.3f47 -16.8f3.9 -24.02 0.4

-

-

-

-

5.2f3.9 -

-5.8f2.3 -

-9.6f5.5 -

8.5f4.2 -

-

2.0f0.6 0.6f0.6 1.5f0.6 -0.2?0.5

1.2f0.7 0.7f0.6 1.3f0.8

-0.5

1.1f0.5

1.6f0.7

-0.4 -5.8

1.8f0.6 -6.9f1.9

2.3? 0.7

-6.2 -12.0

-9.0

-8.4

-10.0

-12.5

-

-

-35.5f24

-6.2f 2.0 -12.5

-

-

-26.5t 24 3.8f2.0 -

N

w

238 enriched in the isotope. Possibly this was caused by secondary isotopic exchange between the phosphorite and the cold "0-enriched bottom water after the phosphatization process had ended. In the other phosphorite samples investigated, the calcite C 0 2 also is substantially enriched in the l80 isotope compared to apatite C 0 2 . There is an inverse relationship between the CaCO, content and oxygen isotope fractionation ( A 1 8 0 ) in the calcite and apatite phases. As for the Lingula shell, the 6I8O value of its apatite phase is about -6O/'&, whereas for calcite a t a corresponding water temperature (26.5'C) 6I8O would be about -2To0. Probably this indicates a difference in the isotopic composition of the COz of apatite and calcite in biogenic material, on the one hand, and the ability of Lingula to fractionate the isotopes in building its shell, on the other. The data on carbon and oxygen isotopes in oceanic phosphorites and similar results of an investigation of marine phosphorites from the Upper Cretaceous of the Near East indicate that there is a fairly clear linear correlation between 6"O and 613C values in the apatite phase of phosphorites. In general the apatite COz is enriched in the light isotopes compared t o calcite COz . The average coefficient of isotopic fractionation between the calcite and apatite phases (1+ A / l O O O ) in phosphorite samples is: 1.0031 for carbon, 1.0008 for oxygen, and together with the Near Eastern samples mentioned above, 1.0028 and 1.0021 respectively, which is confirmation of the idea that C 0 2 enters the apatite lattice (Kolodny, 1969a; Kolodny and Kaplan, 1970b).

PO4 A considerable volume of work has been done by Longinelli and his coauthors on the oxygen isotopes of phosphates in various objects in the marine environment, in the remains of organisms in sedimentary deposits and in phosphorites (Table 6-3). Through these investigations it has been established that in many organisms isotopic equilibrium is established between the phosphate oxygen of their tissues and sea water oxygen, on the basis of which several paleotemperature and paleoisotopic reconstructions are possible. At the same time the oxygen isotopic composition of phosphate in fossil biogenic carbonate formations varies unsystematically, but in phosphorites and fossil bones there is observed a tendency for the oxygen isotopic composition of the phosphate to become lighter as the age of the material increases. Apparently this indicates a change in the original oxygen isotopic composition under the influence of secondary processes, for instance coming in contact with ground water, rather than a higher temperature of the waters of the ancient oceans.

TABLE 6-3 Oxygen isotopic composition of phosphates from the marine environment ~

~~~~

Object

6' 8 0

Region

relative t o SMOW (Yo0

Number of samples

Reference

20 10

Longinelli et al., 1976 Longinelli et al., 1976

)

Sea water

Atlantic Pacific Ocean

Recent Recent

Flesh of mollusks

Tyrrhenian Sea

Recent

17.0-2 3.1

9

Longinelli et al., 1976

Flesh of fish

Atlantic and Mediterranean Sea

Recent

21.3-24.3

19

Longinelli et al., 1976

Mollusk shells

Atlantic, Tyrrhenian Sea Europe, North America*

Recent Mesozoic, Cenozoic Paleozoic

17.0-20.6 13.4-24.2 12.1-13.4

18 55 6

Longinelli, 1965, 1966 Longinelli, 1965, 1966 Longinelli, 1965, 1966

Belemnites

Europe, North America*

Jurassic/Cretaceous

16.1-24.8

33

Longinelli, 1966; Longinelli and Nuti, 1968a

Fish teeth and bones

Pacific Ocean and Atlantic

Recent Recent Recent Cenozoic

19.5-24.9 15.3-1 8.7 18.2-19.9 16.1-20.5

24 3 3 11

Cretaceous

12.8-20.1

8

England*

Paleozoic

11.6

1

Longinelli and Nuti, 1973 Gromova et al., 1976 Baturin et al., 1980a Longinelli, 1966; Longinelli and Nuti, 1968a Longinelli, 1966; Longinelli and Nuti, 1968a Longinelli, 1966; Longinelli and Nuti, 1968a

Bones of cetaceans

Pacific Ocean

Pleistocene

18.3-19.7

Phosphorites

shelves of Namibia and Chile Atlantic shelves Pacific seamounts deposits of Europe and America*

Holocene, Pleistocene Neogene Cretaceous/Pleistocene Mesozoic/Cenozoic Precambrian/Paleozoic

20.0-21 .o 17.4-24.5 14.5-22.5 15.6-23.2 8.6-1 5.5

Europe and North America*

* Data from marine sedimentary deposits on the continents.

19.4-20.0 20.1-21.2

2 3 2 10 33 16

Baturin et al., 1980a, b Baturin et al., 1980a Baturin et al., 1980a Strizhov et al., 1980 Longinelli and Nuti, 1968b Longinelli and Nuti, 1968b

240 A number of determinations of the oxygen isotopic composition of phosphate in phosphorites and bones have also been made by Soviet investigators (Gromova et al., 1976; Baturin et al., 1980a, b; Strizhov et al., 1980). According to these determinations, the range of variation of the oxygen isotopic composition of phosphate in mammal bones from the ocean floor is about the same as in the bones of Recent fish, and in phosphorites from the ocean floor the same as in phosphorites from marine sedimentary rocks on land. But in the Holocene phosphorites from the shelves of Namibia and Chile this range falls within 20-21%,, in Neogene phosphorites (from Agulhas Bank and the shelf of Namibia) within 17':4-24.5?,,, and in Cretaceous/Pleistocene phosphorites from Pacific seamounts within 14.5-22.5yoO (Table 6-3). In the brown varieties of phosphorite from seamounts, 6l8O is 18.120.9yoO, in the white varieties 22.5?,, and in quartz associated with the phosphate 19.5YoO.An attempt to interpret these data as an indication of the temperature of formation of the phosphates gave a temperature range of 18-29" to 40-50°C for the phosphates and of 110--130°C for the quartz (Strizhov et al., 1980). The complexity of the geologic environment on seamounts allows the possibility of such an interpretation, but it is hardly applicable to Recent phosphorites and bones inasmuch as the environment of their formation and deposition is characterized by a narrow temperature range. Therefore to ascertain the cause of the fluctuations in the 6 l 8 0 of phosphates in shelf phosphorites and bones from the present ocean bottom, it apparently is necessary to trace its variation in the full cycle of migration of phosphate on the paths: sea waterphytoplankton-planktonophagi-sediments-phosphorites.

AMORPHOUS SILICA

The behavior of amorphous silica in the course of phosphorite formation is of interest in connection with the fact that present phosphorite concretions are forming in siliceous diatomaceous oozes (Baturin, 1969; Burnett, 1974), and many old phosphorites are related to siliceous formations (Bushinskiy, 1966b). In zones of recent phosphorite formation amorphous silica reaches the bottom as part of diatom detritus, containing up to 77% s i o 2amo& (average 43%) (Vinogradov, 1953). The amorphous silica content of the diatomaceous oozes on the shelf of southwest Africa reaches 50-70%. In phosphatized ooze it constitutes 30-4576, in unconsolidated phosphate concretions 7-1596, in compacted and dense ones, one or two or fractions of a percent (see Chapter 2).

241 TABLE 6-4 Variation in average sioz amorph/Corgand sioz amor,,h/P ratios in the course of phosphorite formation on the shelf of southwest Africa* Material

SiOZ amorph lCorg

SiOZ amorph Ip

Diatomaceous plankton Diatomaceous ooze Phosphatized ooze Unconsolidated phosphate concretions Compacted phosphate concretions Dense phosphorite concretions Interstitial waters from diatomaceous oozes

2.5 7 13 15 4 1 1

53 150 12.5 1.3 0.3 0.06 10

* According to data of Artem’yev and Baturin, 1969; Baturin, 1969, 1972; Baturin et al., 1970; Shishkina and Baturin, 1973; Vinogradov, 1953. Thus whereas amorphous silica, organic carbon, and phosphorus migrate together in the biogenic cycle and during sedimentation in the productive shelf zones, in the diagenetic process of formation of phosphorite concretions their paths of migration may diverge, as is demonstrated by comparison of the average Si02amorph /Corgand Si02amorph /P ratios in diatomaceous plankton, diatomaceous oozes, interstitial waters, and Recent phosphorite concretions (Table 6-4). In diatomaceous plankton the Si02amorph /Corg ratio averages 2.5. When biogenic detritus is deposited the decay of organic matter goes on at a much faster rate than solution of amorphous silica, therefore the Si02amorph /Corg ratio in diatomaceous oozes is about three times greater than in diatomaceous plankton (7, on the average). During phosphatization of the oozes and formation of unconsolidated phosphate concretions this tendency is maintained, and the Si02amorph /Corg ratio doubles again (to 13-15). Subsequently, when the concretions are lithified, the most stable part of organic matter is preserved in the dense concretions, but silica is easily removed from them in the /Corg ratio gradually self-purging of phosphate, due t o which the Si02 decreases to unity. That same ratio of these components is also typical, on the whole, of interstitial waters from diatomaceous oozes (Artem’yev and Baturin, 1969; Shishkina and Baturin, 1973). The SiOzamorph /P ratio changes with much greater amplitude during phosphorite formation. In diatomaceous plankton it averages 53, in diatomaceous oozes, due t o loss of phosphorus in the deposition of biogenic detritus, it averages 150. Thus, when biogenic detritus is deposited the Si02amorph /P ratio, like the Si02amorph /Corg ratio, increases threefold. Subsequently, when the oozes are phosphatized and the phosphorite concretions are formed,

242 amorphous silica and phosphorus behave as antagonistic elements and the SiO,.,,/P ratio drops sharply - on the average to 12.5 in phosphatized ooze, to 1.3 in unconsolidated concretions, to 0.3 in compacted ones and to 0.06 in dense. In the interstitial waters the average ratio of these components is about the same as in phosphatized ooze - 10. During the formation of phosphorite concretions in diatomaceous oozes the phosphate originally adheres to the surface of diatom valves and fills pores in them (see Chapter 2). In parallel with lithification of the concretions, amorphous silica is replaced by phosphate; in dense Holocene concretions from the shelves of southwest Africa, Chile and Peru, in contrast to unconsolidated varieties, only isolated diatoms unreplaced by phosphate are observed (Baturin, 197413; Baturin and Petelin, 1972; Baturin et al., 1970). In pre-Quaternary phosphorites, in particular the Paleogene and Upper Cretaceous ones of the Nile syneclise, only rare relicts of diatoms are preserved, represented by aggregates of opal (Mikhaylov et al., 1972).

FLUORINE

In the diatomaceous oozes of the shelf of southwest Africa the fluorine content averages -0.0596, in the phosphatized ooze 0.3-0.4%. As the phosphorite concretions form and lithify, the fluorine content increases to 2-3%. Fluorine also accumulates in biogenic phosphatic material subjected to diagenetic phosphatization, the content increasing from 0.7-1.2 to 3.03.4% in scales and bones and from 1.50 to 3.82-5.48% in phosphatized coprolites (Table 6-5). In the course of phosphorite formation the fluorine content in the concretions increases by 4 orders of magnitude compared to surface waters, the phosphorus content by 6-7 orders, and the F / P 2 0 , ratio decreases by 2 orders, but rises somewhat on passing from diatomaceous ooze to lithified phosphorite concretions (Fig. 6-2). Thus the F/P,05 ratio indicates that the enclosing sediments are the immediate source of the fluorine and phosphorus concentrated in the phosphorite concretions, phosphatized bones and coprolites. The F/P, O5 ratio in interstitial waters of the sediments of the productive zones of the ocean is intermediate with respect t o the values typical of sea waters and sediments. The increase in F/P, O5 ratio in the order sediments-phosphatized sediments-unconsolidated phosphate concretions-lithified phosphorite concretions shows that accumulation of fluorine in the concretions takes place somewhat in advance of phosphorus. This apparently is caused by partial conversion of phosphate from the amorphous to the cryptocrystalline form and more intensive introduction of fluorine into the crystal lattice of apatite (Baturin and Shishkina, 1973).

243 TABLE 6-5 Content of fluorine, iodine, phosphorus and organic carbon (%) in phosphorites from the shelves of southwest Africa and Peru-Chile* Material

F

I

P

Corg

Phosphorite concretions: unconsolidated compacted dense

1.54-2.05 1.98-2.87 2.42-3.00

134-209 X 84-90 X 66 X

6.8-10.4 9.0-12.9 11.0-14.2

0.65-1.93 0.62-1.20 0.604.90

Dense phosphatized co pr olit es

3.22-5.48

13.74-14.24

0.60-0.88

82

X

Fish and mammal bones : unfossilized slightly fossilized fossilized

1.19-1.68

136-512

X

8.1-12.1

6.10-7.20

2.50-2.56 3.03-3.44

88-126 144--220

X X

12.8 12.7-16.5

4.20-4.80 1.10-1.62

Fish scales

0.70

10.0

9.17-10.12

Enclosing diatomaceous oozes**

0.02-0.28

4.3-31.9

Interstitial waters (mg/kg)

6-1 1

0.12-0.2 1

47 x 1 0 - ~ X

0.10-0.60 0.1-8.7

4 2-1 5.6 -

* According to Baturin and Shishkina, 1973; Shishkina and Pavlova, 1973; Shishkina e t al., 1972. ** Iodine c o n t e n t in diatomaceous oozes from t h e shelf of southwest Africa, rid o f salt, is (Price and Calvert, 1973). 10.9-48.3 X The F/P2O5 ratio in lithified Holocene phosphorite concretions is somewhat higher than the theoretical ratio in fluorapatite (0.089). The same thing has been observed in pre-Quaternary phosphorite concretions from the ocean floor (Dietz et al., 1942; Parker and Siesser, 1972), in phosphorite deposits on land (Bushinskiy, 1966b; Gimmel’farb, 1965) and in fossil bones (Blokh and Kochenov, 1964). This is due to the formation of ultramicroscopic secretions, grains, and veinlets of secondary fluorite (Blokh and Kochenov, 1964; Bushinskiy, 1966b; Krasil’nikova, 1963; D’Anglejan, 1967; Dietz et al., 1942). Experimental investigations of the process of take-up of fluorine from aqueous solutions by calcium phosphate showed that the final value of F/P2O5 does not exceed the theoretical value for fluorapatite; after this limit is reached, take-up of fluorine by calcium phosphate ceases (Adler and Klein, 1938). In biogenic phosphatic material - scales, bones, coprolites - the amplitude of variation in the F/P2O5 ratio as phosphatization progresses is much

244 106-

105 -

lo4lo3 ~

102 -

10

.

1

-

/‘4

Id’-

‘2O5

1

2

3

4

5

6

7

8 9

1 0 11

12 13 14 15

16 17 18

Fig. 6-2. Fluorine in the course of Recent phosphorite formation (according to Shishkina et al., 1972; Baturin and Shishkina, 1973). Open ocean: 1 = surface waters; 2 = bottom waters; 3 = interstitial waters; 4 = sediments. Productive inshore zones of the ocean: 5 = surface waters; 6 = bottom waters; 7 = interstitial waters; 8 = sediments (diatomaceous oozes); 9 = phosphatized diatomaceous ooze; 10 = unconsolidated phosphorite concretions; 1 1 = dense phosphorite concretions; 12 = fish scales; 13 = unfossilized fish bones; 1 4 = slightly fossilized fish bones; 15 = fossilized fish bones; 16 = unconsolidated coprolites; 1 7 = compacted coprolites; 18 = dense coprolites.

wider than in concretions. A very low fluorine content, 0.43% on the average (Klement, 1935), and also a very low F / P 2 0 5 ratio (-O.Ol), are typical of the bones of living marine fish. In relatively fresh fish scales from the diatomaceous oozes of the shelf of southwest Africa the F / P 2 0 5 ratio rises to 0.03, in unfossilized bones t o 0.04, in fossilized bones to 0.08-0.09, and in phosphatized coprolites to 0.16-0.18. In Holocene phosphorite concretions the F/P, 0, ratio is more stable than in bones and coprolites. Evidently this is due to the fact that the phosphorite concretions formed in diagenesis of sediments take up fluorine from the interstitial water simultaneously with phosphorus as they form, and there is relatively little subsequent enrichment in fluorine. In contrast, bone material and coprolites are originally poor in fluorine and it accumulates with greater intensity in biogenic phosphates which reach the bottom than it does in the concretions.

IODINE

The iodine content of the sediments enclosing Recent and Late Quaternary phosphorite ranges within 4.3-31.9 x (Table 6-5), which is at least 2 orders of magnitude higher than the Clarke of the earth’s crust - 4 x

245 (Vinogradov, 1959). Apparently such enrichment of the sediments in iodine is related to their high content of organic matter - up t o 10-20%. As the phosphorite concretions form and become depleted in organic matter the iodine content also decreases, averaging 172 x lo-’% in unconsolidated concretions, 87 x lo-’% in compacted concretions, 66 x lo-’% in dense concretions, and 82 x lo-’ % in dense phosphatized coprolite. In the course of fossilization of bone material iodine behaves differently: unfossilized bones of fish and marine mammals contain an average of iodine, slightly fossilized ones 107 x lo-’%, fossilized ones 383 x 167 x and relatively fresh fish scales 47 x lo-’%. In this case the ratio between I and C,, is disturbed: the scales are enriched in organic matter and poor in iodine, while the fossilized bones, which are poor in organic matter, contain more iodine than bones in the intermediate stage of fossilization. Possibly, in fossilized bones iodine is again concentrated in late diagenesis due to its extraction by the phosphatic material from interstitial waters containing 0.1-0.2 mg/kg of iodine. On the whole, during Late Quaternary phosphorite formation iodine and fluorine - the two end members of the halogen group - became separated (Shishkina and Pavlova, 1973). Among old phosphorites there are known both iodine-rich (up to 9 x - the Devonian phosphorites of Nassau, West Germany) and iodine-poor varieties (to 8 x - the Permian phosphorites of the Rocky Mountains in the U.S.A.), with no correlation of I and Corg(Bliskovskiy and Parfenskaya, 1971; Hill and Jacob, 1932).

URANIUM ISOTOPES

The uranium content in oceanic phosphorites ranges from 1t o 524 x i.e. within the same limits as in phosphorites on land (Baturin, 197513;Baturin and Kochenov, 1974). Uranium occurs in oceanic phosphorites chiefly in a dispersed state and is fixed in phosphatic material, which is demonstrated by radiographic investigation of thin sections (Burnett, 1974). In isolated cases uranium forms an independent phase in the form of ultramicroscopic segregations of uraninite crystals, discovered by V.T. Dubinchuk, in particular in the Recent phosphorite concretions from the shelf of southwest Africa. Previously a similar phenomenon was reported in pre-Quaternary phosphorites and bone detritus from marine sedimentary rocks on the continents (Kochenov e t al., 1973; Levina et al., 1976). Usually tetra- and hexavalent uranium are present in oceanic phosphorites. In Late Quaternary phosphorite concretions from the shelves of Peru and Chile

246 the relative content of tetravalent uranium is 40-7196, in the Miocene phosphorites from the California basin 38-7996, and in the Miocene phosphorites from the submerged Chatham Rise 60-8996; only hexavalent uranium has been found in the phosphorites from the Blake Plateau (Burnett, 1974; Kolodny, 1969a, b). The phosphorites from the Chatham Rise are enriched in both total (up to and tetravalent uranium (Kolodny, 1969a), but on the whole 534 x there is no correlation between U(1V) and Utotal in oceanic phosphorites (Burnett, 1974). The 234U/238Uisotope activity ratio in oceanic phosphorites ranges from 0.95k0.05 t o 1.169k0.013 in total uranium, from 0.5120.04 t o 1.19k0.04 in tetravalent uranium, and from 1.11t o 2.61 in hexavalent uranium. In Recent and Late Quaternary phosphorites these ratios are the same as in sea water on the whole - 1.14-1.16 (Tables 2-13, 2-26; Baturin e t al., 1972a,b,c, 1974; Burnett, 1974). Concerning the mechanism of accumulation of uranium in phosphorites, several hypotheses have been suggested: (a) reduction of uranium t o the tetravalent state and its replacement of calcium in the apatite structure (Altschuler et al., 1958); (b) sorption of hexavalent uranium compounds by phosphate in an oxidizing environment (Rozhkova et al., 1959); (c) introduction of hexavalent uranium into the structure of calcium phosphate during metasomatic phosphatization of carbonate rocks (Ames, 1960). Data on recent phosphorite formation show that the immediate source of g/l U), but uranium in phosphorites is not sea water (which contains 3 x the enclosing sediments, which contain up to 60 x and the interstitial waters, which contain up t o 650 x g/1 U. Despite the reducing environment in these sediments (Eh about -200 mV), uranium has a certain mobility in them and apparently occurs in the composition of metallo-organic complexes in the tetra- and hexavalent state (Baturin, 1975b). As the Recent phosphorites on the shelf of southwest Africa form, their uranium content gradually increases from unconsolidated to dense phosphatic concretions, from 3-8 t o 17-86 x A similar picture is observed in the phosphorites from the Chile shelf (Table 6-6, Fig. 6-3). Apparently when phosphate gels form in the sediments they sorb uranium-organic complexes from the interstitial waters. Subsequently, when the organic matter decays, the uranium enters into calcium phosphate both in form of an isomorphous substitution and sorptionally, inheriting the tetra- or hexavalent state from the stage of its occurrence in the interstitial waters. During formation of Recent phosphorite concretions the U/P, O5 ratio on the whole changes little in them, which indicates the syngenetic nature of concentration of uranium. Despite the fact that on the scale of the whole ocean the uranium content in phosphorites varies greatly and there is no U-P205

TABLE 6-6 Content of uranium and P2 O5 in Recent oceanic phosphorites (Baturin and Kochenov, 1974) Sample

Southwest Africa shelf Lenses of phosphatized diatomaceous ooze Unconsolidated concretions Compacted concretions Dense concretions Unconsolidated coprolites Compacted coprolite Dense coprolite Chile shelf Unconsolidated concretions Compacted concretions Dense concretions Dense black coprolite Dense gray coprolite

p2°5

u

(%)

U/P~O ( x~

range of values

average

range of values

average

range of values

average

5.10-11.54 23.85-26.53 27.88-3 1.09 31.16-32.7 7 23.69-2 7.53

8.32 25.20 29.37 32.09 25.85 31.64 32.06

3-8 9-1 9 9-80 17-86 3-52

5 14 35 53 28 68 77

0.3-0.8 0.5-0.8 0.3-3.1 0.6-2.5 0.1-1.9

0.5 0.6 1.4 1.6 1.0 2.2 2.4

15.32 20.21 25.72 30.67 32.38

7-4 5 8-4 5 9-54

28 29 34 30 40

0.5-3.0 0.4-2.2 0.4-2.2

1.8 1.5 1.5 1.0 1.3

-

14.92-1 5.73 19.78-20.64 25.10-26.45

-

-

Number of samples

,@"& /*-..*

3010-

i

1-

@/.--.--.

P*O, %

P2% %

-.

i

10.'-

2

1

2

3

4

5

6

7

8

9

1 0 1 1

12

13

-

1415

u

16

Fig. 6-3.Uranium in the course of Recent phosphorite formation (after Baturin and Kochenov, 1974, with additions). 1 = sea waters;2 = interstitial waters; 3 = diatomaceous sediments in which phosphorite concretions are forming; 4 = phosphatized diatomaceous ooze; 5 to 7 = phosphorite concretions (5 = unconsolidated; 6 = compacted; 7 = dense); 8 to 11 = coprolites ( 8 = living marine organisms; 9 = unconsolidated, from the bottom; 10, 11 = compacted and dense, from sediments); 12 to 15 = bones of fish and marine mammals ( 12 = fresh; 13 = unfossilized, from sediments; 1 4 = slightly fossilized; 15 = fossilized).

correlation, the average uranium contents in phosphorites of various shelf zones and the average U/P2 O5 ratios are relatively stable: U = 52 f25 x U / P 2 0 5 = 2.3f0.8 x (Baturin and Kochenov, 1974). The same thing has been noted in marine phosphorites from sedimentary rocks on land (Levina et al., 1976). In particular, in the phosphorites of the Russian (Baturin and Kochenov, platform the average U/P205 ratio is 3.2 x 1974), and in the phosphorites of the Phosphoria Formation it is 3.0 x (Gulbrandsen, 1966). Probably these facts indicate a similarity in the geochemical environment of phosphorite formation and in the mechanism of accumulation of uranium in them. Lithified phosphorites from the ocean floor differ from unlithified ones in greater density, lower porosity and water content, partial crystallization of the phosphate, and also formation of a dense coating on the surface

249 consisting of condensed organic matter and finely crystalline phosphate, which inhibits the process of further concentration of uranium in them. In phosphorites washed out of the enclosing sediments and in contact with oxygen-bearing bottom water for a long time, partial oxidation and loss of uranium occur. This is demonstrated by data on the content and valency of uranium in the outer and inner parts of concretions from the California basin (Kolodny and Kaplan, 1970a). In the light outer parts of the conin the dark inner part cretions the total uranium content is 6 2 - 6 7 x 71-72 x The relative content of tetravalent uranium is falling on passing from inner to outer zones from 64-70 to 44-58%. The outer zone of these concretions is depleted in the 234U isotope. The 2MU/238Uratio in tetravalent uranium is as follows: in one sample, 0.81 in the core and 0.78 in the shell of the concretion, in another 0.71 and 0.65, respectively. On the whole the data on the isotopic composition of tetra- and hexavalent uranium in pre-Quaternary oceanic phosphorites show that in an oxidizing environment, -30% of the 2 M U formed by decay of 238U(IV) is oxidized and acquires migrational mobility (Kolodny, 1969a), as in pelagic sediments (Ku, 1965). In biogenic phosphates (scales, bones of fish and mammals) occurring in the sediments of zones of Recent phosphorite formation, concentration of uranium goes on more intensively than in the concretions. Coprolites and uranium bones of living marine organisms contain no more than n x (Aten et al., 1961; Pertsov, 1964; Risik, 1973). Relatively fresh bones and %, slightly phosscales from the top layer of sediments contain 2-28 x phatized bones and scales up to 1 x and highly phosphatized bones and scales up to 7 x 5% uranium. The ability of bone material to accumulate uranium actively is due to the porous structure of bone tissue, the low degree of crystallization of bone phosphate, and the high content of organic matter in bones (Baturin et al., 1971; Baturin and Kochenov, 1974). New detailed data on the distribution and forms of uranium in oceanic phosphorites have been obtained in investigations of their ultramicroscopic structure and composition, using a combination of the methods of scanning and transmission electron microscopy, microradiography, microdiffraction and microanalysis (Baturin and Dubinchuk, 1978,1979). It has been established that the greater part of the uranium in oceanic phosphorites occurring in a reducing environment (the Recent and Upper Quaternary phosphorites on the shelves of Namibia and Peru-Chile) is present in a highly dispersed form, forming round and flocculent ultramicroscopic inclusions hundredths of a micron in a size. The relative concentration of these inclusions varies from sparse t o dense, and their distribution from even to uneven. In places the microinclusions merge into a solid field, forming aggregates of various shapes (Fig. 6-4). The microinclusions tend mainly to be

250

Fig. 6-4. Ultramicroscopic secretions of uranium, round and flocculent in shape, in phosphate with collomorphic-block structure (Baturin and Dubinchuk, 1978). Slightly cemented concretion from the shelf of Namibia, station 2048; X 32,000. In upper corner, microdiffraction pattern of the uranium secretions.

associated with amorphous phosphate, but they also are encountered in the phosphatized remains of diatoms, where they encrust the cavities of the valves, and on the surface of mineral grains, forming films on their boundaries. Another form of secretion of uranium is oval (acorn-like) and crystallomorphic isometric formations of larger size, up t o 0.3-0.5 pm. They also are restricted mainly t o amorphous phosphate and phosphatized diatom remains. In the latter case they usually fill the cavities of the valves and take on the corresponding shape (Fig. 6-5). In addition, they occur in the peripheral parts, less often in the center, of slightly crystallized phosphate globules. The largest secretions of uranium are euhedral crystals of cubic habit from fractions of a micron to 1 or 2 p m in size (Figs. 6-6, 6-7).In isolated cases the crystals have indistinct, poorly developed faces. Both isolated crystals and colonies of crystals of the same or different size are encountered. In some concretions the crystals are limited just to the microcrystalline phosphate and are absent in the amorphous, in others they also form in the

251

Fig. 6-5. Oval and crystallomorphic secretions of uranium (below) on a fragment of a valve of a diatomaceous alga included in a m a s of colloform phosphate (Baturin and Dubinchuk, 1978). Compacted concretion from the shelf of Namibia, station 2048; X 35,000. At the right, microdiffraction pattern of the uranium secretions.

amorphous phosphate. Occasionally crystals are observed on the surface of grains of clastic minerals, in particular quartz. Large crystals are sometimes associated with small ones; usually ultramicroscopic secretions of uranium, irregular in shape, are scattered on the surface of the large crystals (Fig. 6-6). In some places it is seen that small crystals or accumulations of finely dispersed uranium secretions are engulfed by a large crystal (Fig. 6-7). Each of the types of uranium secretions described is morphologically distinct, but there is no clear-cut boundary between them inasmuch as intermediate varieties are observed. The microdiffraction patterns representing areas of dense concentration of ultramicroscopic inclusions and the oval or isometric secretions and cubic crystals were similar - ring-like and corresponding to uraninite (Figs. 6-4, 6-5). On some preparates microdiffraction patterns of metallic lead, probably radiogenic, were also obtained. In pre-Quaternary phosphorites occurring in an oxidizing environment (from Agulhas Bank, the Blake Plateau and Pacific seamounts), as in the young shelf phosphorites, uranium is associated with various components in which phosphate does not always remain of foremost importance.

252

253

Fig. 6-8.Ultramicroscopic secretions of uranium in crystalline phosphate (Baturin and Dubinchuk, 1978). Phosphatized limestone from Pacific seamounts, station 6364; X 15,600.

In gel-like and collomorphic-granular phosphate the uranium is dispersed and forms round, oval or irregular secretions 0.01-0.1pm in size, rarely larger. The uranium secretions are scattered irregularly in the phosphate mass and sometimes form clumps. Ultramicroscopic secretions of uranium are similarly distributed in crystalline phosphate also, some crystals being full of them while in others they are absent (Fig. 6-8). In phosphate with block structure the ultramicroscopic secretions of uranium are concentrated mainly along the block boundaries. In those cases where the phosphate blocks are in contact with a collomorphic mass, uranium also apparently is expelled from the crystallized phosphate into the contact zone. Occasionally ultramicroscopic uranium secretions in phosphate form a semblance of crystallomorphic forms about 0.2 pm in size, and in one prepFig. 6-6(top). Crystals of uraninite in collomorphic phosphate in unconsolidated concretion from the shelf of Namibia, station 2048;X 22,500 (Baturin and Dubinchuk, 1978). Fig. 6-7(bottom). Large crystal of uraninite on fragment of the valve of a diatom, absorbing small crystals (Baturin and Dubinchuk, 1978). Compacted concretion from the shelf of Chile, station 250;X 30,000.

2 54

Fig. 6-9. Ultramicroscopic secretions of uranium on a fragment of a coccolithophore plate (Baturin and Dubinchuk, 1979). Phosphatized limestone from Pacific seamounts, station 6348; X 42,500.

arate an oval grain of uraninite, 0.3 x 0.6 pm in size, was found. Carbonate material is much poorer in uranium than the phosphate. In coccolithophore platelets only isolated, sparsely disseminated ultramicroscopic secretions of uranium were found, 0.01-0.1pm in size (Fig. 6-9); in carbonate with block structure they are as tiny, but are disseminated more evenly and somewhat more thickly. Uranium is distributed very unevenly in feldspar grains. Its usual form is sparse round or flocculent ultramicroscopic secretions, but sometimes an independent oxide mineral phase of it is encountered, in the form of irregular formations fractions of a micron in size. In quartz and flaky layered silicates, uranium usually forms a sparse irregular ultramicroscopic dissemination, sometimes with local clumps. Needle-like layer silicates are more active uranium concentrators. In cases where they come up against apatite crystals the uranium is secreted to about the same extent in both minerals. But if a carbonate mass contains flaky or needle-like silicates, the uranium is concentrated on those.

255 TABLE 6-7 Thorium isotopes in oceanic phosphorites Material

Content ( lo4

"/.I

U

Th

Southwest Africa shelf* Diatomaceous ooze 10.2-54.6 Phosphatized ooze 78.6 Pre-Quaternary concretions 1.7-158 Pre-Quaternary fish bones and teeth 139 Peru-Chile shelf ** Upper Quaternary concretions Fish bones

51-182 101 Submerged Chatham Rise** Miocene concretions 124-241 Blake Plateau** Oligocene concretions 50 California Basin** * Miocene concretions 37-73

1.1-8.1 4 1-1 8 22

Number of samples

Weight ratio U/Th

Activity ratio 230Th/234 U

7-21 78.6

0.04-0.40 0.01

7 1

7-117

1.00-1.09

3

6.6

1.04

1

1.1-9.0 11-70 0.0-0.4 252-300

0.020-0.7 1 0.010-0.020

17 2

1.1-1.3

95-219

1.01

2

4.6

11

0.99

1

4.5-43

1.7-101

0.99-1.25

10

* Veeh et al., 1974. ** Burnett, 1974. *** Kolodny and Kaplan, 1970a. When phosphate, carbonate and silicates occur together in one preparate the form and distribution of the ultramicroscopic uranium secretions may be complex in character. Therefore the relative importance of these components as concentrators of uranium (in cases where its contents are low) may vary considerably in different parts of the rock, but carbonate usually is in last place in this respect (Baturin and Dubinchuk, 1979). THORIUM ISOTOPES

The thorium content of ocean waters is n x lo-"% (Vinogradov, 1967), in pelagic sediments 5-28 x in diatomaceous oozes of the shelf of southwest Africa 1.1-8.1 x and in Recent phosphatized diatomaceous ooze 1 x (Veeh et al., 1974). The Recent and Late Quaternary phosphorites from the shelves of Peru and Chile contain 1.9-9.0 x thorium, pre-Quaternary concretions

256 from various areas 1-43 x and ,fish bones from 0.0 t o 22 x depending on the extent of fossilization (Table 6-7). The U/Th ratio in ocean water is >300, in pelagic sediments 0.1-0.5, in Recent diatomaceous oozes of the shelf of southwest Africa 7-21, in Recent and Late Quaternary phosphorites 11-78, in the Miocene phosphorites of the California basin 1.7-101, in the Miocene phosphorites from the Chatham Rise 95-219, and in fish bones from 6.6 to 300. On the whole the thorium content of oceanic phosphorites is of the same order of magnitude as in the enclosing sediments, but the U/Th ratio is higher than in the sediments but lower than in the ocean water. This indicates that the predominant part of the thorium contained in phosphorites is fixed in inclusions of clastic material. Ionium accumulates in phosphorites mainly due to decay 0f 234U contained in them. In young phosphorites the 230Th/234Uratio is much lower than the equilibrium value (0.020-0.71), in old ones it is at the equilibrium value or higher. Excess ionium can get into pre-Quaternary phosphorite concretions exposed on the eroded bottom surface both from the ionium-rich surface layer of sediments and directly from sea water, due to which the 230Th/234Uratio in some samples of Miocene phosphorites off the coast of California is increased to 1.04-1.25 (Kolodny and Kaplan, 1970a). RARE EARTH ELEMENTS

The content of rare earth elements (REE) in the waters of the World in suspended matter it is 0.001Ocean ranges from n x lo-’ to n x 0.035%,in oceanic biogenic sediments 0.007-0.014%, in red deep-sea clays up to 0.050% (Balashov and Lisitsyn, 1968; Balashov and Khitrov, 1961; Volkov and Fomina, 1967; Goldberg et al., 1963; Piper, 1974; Wildeman and Haskin, 1965). The Recent and Late Quaternary phosphorites from the shelves of southwest Africa and Peru-Chile contain 0.005-0.010% REE , pre-Quaternary phosphorites from various regions 0.010-0.098%, bones of fish and mammals from shelf sediments 0.019-0.021% and from pelagic sediments 0.2220.721%(Baturin et al., 1972a; Blokh and Kochenov, 1964). The composition of REE has been determined in pre-Quaternary oceanic phosphorites which contain at least 0.030%REE, and also in bone phosphate (Table 6-8, Fig. 6-10). The shelf phosphorites are relatively rich in elements of the cerium group and similar in REE composition t o the nodular phosphorites of the Russian platform and t o sedimentary rocks as a whole. The phosphorites from the Mid-Pacific Mountains, on the other hand, are similar to sea water in REE composition. Bone phosphate occupies an intermediate po-

TABLE 6-8 Composition of lanthanoids in phosphorites and the marine environment ZTRIO,

Content (5% of Z T R , 0 3 )

(%)

La

1. Sea water

10-8

2. Mediterranean Sea suspended matter 3. Ocean sediments

0.009

Material

4. California shelf phosphorites 5. Phosphorites of t h e southwest Africa shelf 6 . Blake Plateau phosphoritrs 7. Agulhas Bank phosphorites 8. Phosphorites of Pacific seamounts 9. Bone phosphate from ocean floor 10. Karatau bedded phosphorites 11. Nodular phosphorites, Russian platform 12. Coquina phosphorites of t h e U.S.S.R. 13. Average in sedimentary rocks

Reference

Ce

Pr

Nd

S(La-Nd)

27.4

12.2

6.0

21.6

67.2

4.1

1.0

13.5

33.7

6.7

14.8

68.7

10.0

-

0.0173

18.5

39.2

5.3

21.3

84.3

4.0

1.1

0.0435

19.8

35.8

5.0

19.4

80.0

3.6

0.066

19.3

46.4

3.9

18.2

87.8

3.5

0.040

29.1

25.0

3.5

18.0

75.6

4.6

23

0.030

36.7

38.0

-

18.8

93.5

-

2.6

0.098

28.9

9.1

5.0

23.1

66.1

5.3

1.9

0.356

15.7

28.1

2.6

27.4

73.8

13.4

-

0.080

23.7

21.4

5.2

21.3

77.6

5.0

0.06

19.7

44.7

3.9

20.9

89.2

0.100

15.0

37.1

5.0

16.7

0.024

23.4

36.8

5.8

19.0

Sm

Z(Sm-Ho)

Er

2.0

19.8

5.8

0.7

28.4

1.9

0.7

11.0

2.2

0.3

2.2

-

4.7

3.7

1.0

14.4

2.8

0.4

2.0

0.4

5.6

-

2.4

-

10.8

0.8

-

0.6

-

1.4

5.8

-

3.5

1.2

17.4

3.5

-

3.5

-

7.0

2.6

-

-

-

5.2

1.3

-

-

-

1.3

6.9

0.8

6.2

1.7

22.8

4.1

0.9

5.2

0.9

11.1

3.0

-

5.2

-

21.6

13

0.1

3.2

-

4.6

0.6

6.2

0.6

4.3

0.7

17.4

2.5

0.3

1.7

0.5

5.0

2.8

0.3

2.9

0.3

2.1

0.3

8.7

1.0

09

0.1

0.1

2.1

Baturin e t al., 1972a Baturin e t al.. 1972a Baturin e t al., 1972a Blokh and Kochenov, 1964 Bliskovskiy et al., 1969 eBliskovskiy t al.. 1969

73.8

7.7

0.5

1.5

0.8

4.1

0.5

21.1

2.1

0.3

22

0.5

5.1

Loog, 1968

85.0

4.0

1.0

3.9

0.6

-

0.8

10.3

2.1

0.3

2.0

0.3

4.7

Vinogradov,

Eu

Gd

Tb

Dy

5.8

-

6.9

10.7

-

7.0

4.5

0.7

-

0.8

4.7

0.6

1.2

3.7

Ho

Yb

Lu

X(Et-Lu)

1.2

4.9

1.1

13.0

03

0.8

-

3.0

Tu

Goldherg e t al., 1963 Balashov and Lisitsyn. 1968 Wildeman and Haskin, 1965 Goldberg e t al., 1963 Baturin e t al., 1972a

1 q5fi

258

A

3

8

Fig. 6-10. Relationship of lanthanoids in oceanic phosphorites (Baturin et al., 1972a):

Z = field of phosphorites of the Russian platform; ZZ = field of Karatau phosphorites. For numbers see Table 6-8.

sition and is similar in REE composition to the shell-limestone phosphorites of the northwestern part of the U.S.S.R. This difference apparently is caused by the fact that the composition of the REE in shelf phosphorites is controlled by the composition of the enclosing sediments, which are the direct source of the phosphorus and other elements that take part in the formation of the phosphorite concretions. The low REE content in Recent and Late Quaternary phosphorites can be explained first by their youth, and second by the composition of the enclosing diatomaceous oozes, which are poor in REE. The phosphorites from seamounts, which often are porous phosphatized limestones, have been in contact with sea water for a long geologic time, and this probably has determined the concentration and composition of the REE they contain. The high REE concentration in bones from the pelagic zone of the ocean is explained on the one hand by the spongy structure of bone tissue, and on the other by the duration of their exposure (Miocene/Pliocene) on the bottom surface (Blokh and Kochenov, 1964). In that case the source of the REE, judging from their composition, also is sea water and the en-

259

LO

Sm ELI

Tb

Yb

Lu

Fig. 6-11. Composition of REE in Recent diatomaceous oozes and phosphate concretions from the shelf of Namibia (Tambiyev et al., 1979). Normalized to average composition of REE of platform clays. 1 = diatomaceous ooze; 2 = phosphate concretions; 3 = phosphatized coprolites.

closing red deep-sea clays, rich in REE compared t o other types of ocean sediments. To ascertain the behavior of the REE in the initial and early stages of the process of phosphorite formation, a special investigation was made of a series of 30 samples of Recent and Upper Quaternary phosphorite concretions from the shelves of Namibia and Pem-Chile (Tambiyev et al., 1979). The general chemical composition of these samples is given in Tables 2-7B and 2-22. The total REE content of all the samples studied was less than 0.005% (Table 6-9). In the course of formation of the phosphate concretions on the shelf of Namibia, the concentrations of all the REE are reduced, and only slightly higher in the dense than in the compacted concretions. In phosphatized coprolites the REE content also is much lower than in the enclosing diatomaceous oozes. When the results obtained are normalized to the composition of the REE of platform clays (Balashov, 1976), it is seen that diatomaceous oozes are characterized by a relatively monotonous REE composition with slight enrichment in the light lanthanoids (Fig. 6-11). A t the same time depletion in Eu and La or an excess of Ce is observed in the phosphorites. A typical feature of the behavior of the REE during the formation of phosphate concretions is the preferential removal of the light and intermediate lanthanoids, while the heavy ones are retained in them (Fig. 6-12). The maximum rate of

to r n

0

TABLE 6-9 REE content

in Recent and Late Quaternary shelf phosphorites and in the enclosing sediments (Tamhiyev et al., 1979)

Sample

P 2 0 , (%)

La

Ce

Sm

Eu

Tb

Tm

Yb

Lu

Shelf o f Namibia (stations 2048, 2046) Diatomaceous ooze Phosphatized ooze Concretions: soft unconsolidated compacted granular compacted massive dense gray dense brown Coproli tes : unconsolidated compacted dense gray dense brown insoluble residue

1.33, 0.82 3.7, 4.16 19.0, 29.5, 28.6 29.2, 30.3, 31.9,

23.3 25.7 30.2 31.6 33.9

29.5, 26.8 29.9 30.6, 30.9 31.9, 32.4

10.5, 8.0 6.2, 3.3

23.2,16.0 9.8,10.6

1.4 n.d.

0.27, 0.21 0.03, 0.17

0.13, 0.10 0.03, 0.082

0.48 0.57,0.80

0.056 0.16, 0.059

2.1, 3.0 2.1, 2.6 2.3 2.0, 1.1 0.77,1.9 2.0, 2.2

15.5 9.8 12.2 3.3 4.1 4.1, 5.7

0.65 n.d.

0.048,0.039 0.023,0.013 n.d. 0.017 0.030,0.015 0.034,0.017

0.036 n.d. n.d. 0.053 0.030,0.082 0.027,0.091

0.32,0.23 0.22 0.49 0.18 0.21 0.18,0.25

0.038 0.087 0.059 0.033 0.047,0.039 0.044,0.039

0.051 0.038 0.053 0.026 2.21

0.15 n.d. 0.37 0.32 14

1.4 1.1 1.7, 1.5 1.0, 1.1 162

-

-

n.d. n.d. n.d.

0.053 0.054 0.040 0.065,0.037 1.9

-

0.010 n.d. 0.021 0.035 2.6

Concretions (average)

-

2.1

9.1

0.6

0.026

0.053

0.26

0.043

Coprolites (average)

-

1.3

4.9

0.23

0.022

0.042

0.28

0.050

17.1

35.8

4.0

0.91

0.29

1.6

0.37

12.8 11.1 9.4 21.3

27.7 22.0 19.5 39.1

2.4 n.d. 1.6 3.4

0.66 0.52 0.42 0.95

0.21 0.23 0.18 0.33

0.42 0.83 0.78 1.7

0.16 0.18 0.21 0.40

-

-

4.1 5.7 269

0.26 0.10 n.d. 0.34

S h e l f o f Chile (station 250) Terrigenousdiatomaceous oozes Concretions: unconsolidated compacted dense insoluble residue

0.72 16.9 21.7 28.4 -

Shelf o f P e r u (stations 546,553) Concretions : unconsolidated compacted dense

11.1 18.0 19.4

Average of Chile-Peru shelf phosphorites Andesite basalts of southern Peru* Platform clays** ~~

* Dostal et al., 1977.

** Balashov, 1976.

-

14.5 13.6 14.5

21.2 29.3 21.2

2.7 1.8 2.3

0.48 0.49 0.74

0.22 0.20 0.29

0.14 0.37 0.19

0.66 0.61 1.30

0.14 0.19 0.24

12.7

23.5

2.2

0.55

0.22

0.17

0.77

0.19

35 35.5

72 67

6.0 6.7

1.46 1.24

0.68 1.0

-

2.30 2.95

0.34 0.45

0.45

262 2 /

/

,

/

,,*'4+5

*

., 0.05Ll I La Ce

I

Eu

Tb

I

)

Yb Lu

Fig. 6-12. Behavior of REE during lithification of phosphate concretions on the shelf of Namibia (average of two stations; Tambiyev et al., 1979). Normalized to average composition of REE in enclosing diatomaceous ooze. 1 = diatomaceous ooze; 2 = phosphatized ooze; 3 to 8 = concretions ( 3 = soft, 4 = unconsolidated, 5 = compacted granular, 6 = compacted massive, 7 = dense gray, 8 = dense brown).

removal is observed for Eu and probably for La. In the initial stage of formation of phosphate concretions there is a brief increase in the contents of heavy REE as compared t o the diatomaceous oozes (Fig. 6-12). The lanthanoids behave similarly in the phosphatization of coprolites. * The REE content in Late Quaternary phosphorites from the shelves of Chile and Peru also is lower than in the enclosing sediments (Table 6-9), but substantially higher than in Holocene phosphorite concretions from the shelf of Namibia. The spectra of distribution of REE in the phosphorites from the shelves of Chile and Peru are identical (Fig. 6-13)and are characterized by a Eu maximum. When these concretions are lithified the concentrations of the light and intermediate REE decrease and simultaneously the contents of the heavy REE increase. The process of formation of Recent phosphorite concretions is accompanied by self-purification of the phosphate, which is manifested in a decrease in the concentration of biogenic (organic matter, amorphous silica) and clastic impurities in them (Baturin, 1969, 1974b). Therefore the observed decrease in REE contents can be explained by the fact that it is to those components, i.e. diatom remains and detrital minerals, that they are mainly related. In

263

i

0.5

0.3

\\

5

M I

0.2

_J

La

Ce

Sm Eu

Tb

Tm

Yb

Lu

Fig. 6-13. Composition of REE in andesites and andesite basalts of southern Peru (Dostal et al., 1977), Recent sediments of the Chile-Peru shelf (average of two stations) and phosphorite concretions from the shelf of Chile (station 250; Tambiyev et al., 1979). Normalized t o the REE composition of platform clays. I = andesites and andesite basalts; 2 = sediments, 3 = unconsolidated concretions; 4 = compacted concretions; 5 = dense concretions.

fact, the calcined insoluble (in 1.7%HC1) residue of a dense coprolite consisting of clastic material and ash of organic matter, is sharply enriched in the lanthanoids (Table 6-9). Constituting only 0.5% by weight of the original sample, it contains from 22 t o 75%of the total amount of REE. The clastic impurities in the phosphorites from the shelf of Namibia are quartz, feldspars, pyroxenes and hornblendes (Baturin e t al., 1970), i.e. minerals which do not accumulate REE (Balashov, 1976). The opal of diatom valves likewise does not concentrate trace elements (Arrhenius e t al., 1957). Therefore i t is logical to assume that most of the REE in these phosphorites is related to organic matter, which is capable of concentrating a wide range of rare and disseminated elements. It is possible that this concentration begins during the lifetime of diatomaceous phytoplankton (Volkov and Fomina, 1967), inasmuch as diatomaceous ooze is enriched in the light lanthanoids [the La/Yb ratio in rocks is 5.3, in soils 6.0, and in algae 29 (Cowgill, 1973)l. The organic matter of diatoms decomposing in the sediments additionally extracts REE from the interstitial waters, which continues during the formation of phosphate gels. Their organic matter content is almost the same as that of the enclosing oozes, but the extent of its mineralization, and the sorption capacity related to that, are appreciably higher (Romankevich and Baturin, 1972). Apparently this circumstance explains the relative increase

264 in the contents of the heavy REE in the concretions being formed, as those are stronger complex-formers than the light REE and have a greater tendency toward sorption. Upon further lithification of the concretions, the organic matter included in them undergoes more thorough decay and loss, removing the REE. In conjunction with this, the composition of the REE additionally becomes relatively heavy and there is preferential removal of Eu and La (with inhibited removal of Ce). In the highly reducing environment (Eh up to -330mV) typical of the environment of formation of the Recent phosphate concretions on the shelf of Namibia, reduction of Eu to the divalent state, its conversion t o the soluble cation group and its removal from the concretions are possible, t o which its depletion might be related. After the phosphate concretions are transformed into dense nodules the redistribution and removal of matter from them cease and apparently the process of sorption of trace elements from the interstitial waters begins to predominate, which marks a new stage in the geochemical fate of the REE not already bound in organic matter. As a result there is an increase in the content of all the REE in dense concretions compared to compacted ones. In the Late Quaternary phosphorites of the shelf of Chile-Peru the geochemistry of the REE is essentially different. Here identical spectra of the REE in the phosphorites and in the enclosing sediments are observed, which is related to the higher content of clastic impurities in the former (up to 40-60%). With Eh values up t o -100 mV, which are insufficient for the reduction of Eu3+,that element is not separated from the other REE. The observed maximum apparently is related to the fact that andesitic volcanism, the products of which are characterized by a high Eu content (Dostal e t al., 1977), is developed in this region (Gerth, 1959). During the lithification of the Late Quaternary phosphorites from the shelves of Chile and Peru the removal of light and intermediate lanthanoids is accompanied by an accumulation of the heavy ones (Fig. 6-13), the same as on the shelf of Namibia. The content of intermediate T b hardly changes. The intensity of removal of the light and intermediate REE is the same; likewise the character of the distribution of the REE in the enclosing sediments and phosphorites is the same. This is evidence of the clastic nature of the main part of the light and intermediate REE in these phosphorites, as is confirmed by analysis of the calcined residue (insoluble in 1.7% HCl) of unconsolidated and compacted concretions (Table 6-9). Amounting to 23% by weight in the original sample, the residue contains 40-6076 of the total amount of REE in them. A comparison of the balances of the distribution of REE in the Recent phosphorites on the shelf of Namibia and of the Late Quaternary phosphorites on the shelves of Chile and Peru shows that the specific concentration of

26 5 lanthanoids in the phosphate of the latter is several times higher than in the former. Thus Recent phosphorites as a whole, and especially their phosphatic matter, are depleted in REE compared to the enclosing sediments due to the strong competition of the organic matter of these sediments. In the Late Quaternary phosphorites the Clarke contents of the REE are regenerated, phosphate taking an active part. But in fact high REE contents are typical only of old phosphorites (Bliskovskiy et al., 1969). Consequently the geochemical history of the REE in phosphorites consists of several stages, and their effective concentration does not begin until the stage of late diagenesis and continues mainly in epigenesis.

IRON

The iron oxide content of oceanic phosphorites ranges from 0.1-0.6% in Recent phosphorite concretions from the shelf of southwest Africa to 50% in the ferruginous phosphatized limestones from Agulhas Bank. Most of the iron oxide is fixed in goethite, less in glauconite. Ferrous iron is present in oceanic phosphorites in amounts of 0.05-1.43%, and is fixed chiefly in pyrite. The paragenetic association of phosphate with pyrite and less often with glauconite, which forms under less reducing conditions, is characteristic of the diagenetic reducing stage of Recent phosphorite formation. The abundance of ferrous iron in some pre-Quaternary oceanic phosphorites is due to secondary ferruginization (formation of iron-manganese crusts, impregnation of phosphate with iron hydroxides from the periphery of the concretions toward the center; Bezrukov et al., 1969; Heezen et al., 1973; Pratt and Manheim, 1967; Tooms et al., 1969). But when a phosphate-goethite cement is present in phosphorites (Parker, 1971, 1975; Parker and Siesser, 1972) its formation evidently is related to joint diagenetic migration of iron and phosphorus and their subsequent deposition when reducing conditions are succeeded by oxidizing, as has repeatedly been observed in Recent sediments (Volkov and Sevast’yanov, 1968; Bonatti et al., 1971). Thus the initial stage of phosphorite formation is always accompanied by disseminated pyritization. In ocean shelf phosphorites pyrite is found practically universally. In Holocene phosphorite concretions it impregnates diatom valves, clumps into microglobules, and forms irregular secretions. Under the electron and scanning microscope it is seen that as a rule the pyrite is crystallized. The crystals are mainly octahedral and cuboctahedral but sometimes, when diatom valves are pyritized, they may take on a hexagonal habit corresponding t o the shape of the alveoli perforating the valves.

266 Usually the crystals are grouped into globular aggregates (Fig. 6-14), less often they form random accumulations. In cases where a reducing environment of initial phosphorite formation is succeeded by an oxidizing environment, the pyrite decomposes and is dissolved, which is expressed in disintegration of globules, blurring and loss of crystal form. In the lithification of Recent phosphorite concretions pyrite, along with detrital material, is expelled from them in the course of self-purging of the phosphate, which is manifested in a decrease in the concentration of total iron (see Table 6-11). RARE AND DISSEMINATED ELEMENTS

Many rare and disseminated elements have been found in oceanic phos-

26 7

Fig. 6-14. Globular aggregate of pyrite in Holocene (a) and Miocene (b) concretions from the shelf of Namibia; x 40,000 (a) and X 27,000 (b) (Baturin and Dubinchuk, 1979).

phorites. In shelf phosphorites the content of most of them often is at the limit of sensitivity of the spectral methods of determination that are used. In this connection, a t the present time only far-from-complete data can be given on the behavior of Sr, Cr, V, Ni, Co, Mo, Pb, Zn, Cu, and As in the process of phosphorite formation (Table 6-10). When data on the shelf of southwest Africa are examined it is ascertained that during their formation the Holocene phosphorite concretions are substantially depleted, compared to the enclosing sediments, in all these disseminated metals, except strontium - in chromium (from 60-140 to 3-14 x vanadium (from 30-360 t o 20 x loT4%),nickel (from 5-150 t o 2-14 x cobalt (from 10-14 to 5 x molybdenum (from 1 0 - 6 0 t o 1-3 x lead (from 1 - 6 t o 1 x zinc (from 2-70 t o 1-2 x and copper (from 5-38 t o 2-5 x lo4%). The behaviour of As is variable: in unconsolidated concretions its content is lower than in the

TABLE 6-10 Rare and disseminated elements in oceanic phosphorites* (in

Shelf o f southwest Africa Recent diatomaceous oozes Phosphatized diatomaceous ooze

Unconsolidated concretion Compacted concretion Dense concretion Phosphorite block (pre-Quaternary) Unconsolidated coprolite Dense coprolite

Chile shelf Unconsolidated concretion Compacted concretion Dense concretion Platy dense concretion Dense phosphatized coprolite

0.2-1

unless otherwise indicated)

4.5-9.3

0.002FO.01

60-140

8.52 23.85 27.70 32.74 21.27

3.59 1.27 1.03 0.92 0.75

0.08

47 16 14 3 30

100 34 20 20 21

24 16 14 2

15 15 5

1

1 1 1

15

10

18

1

25.85 29.72

3.72 0.88

3

30

12 33

2 6

5 14

2 2

1 1

15.7 20.64 25.62 26.45

0.65 0.60 -

30 30 40 200

40 40 50 30

20 30 20 30

1 1

100 20 30 20

1

0.20 0.24 0.24 0.16 0.13

0.18 0.1

0.3 0.4 0.4

30-360

5-150

10-14

1040

31 15 3

11

-

5 4

2-70

4-6 21

5-38

1

9 8

2 2

5

-

tr. v

6-14 3 6 3 10 26 9 11

6

1

4

9

20

60

50 40 40 50

-

1

200

40

-

10

10

30.67

1.39

0.5

100

10

20

Blake Plateau Concretion

20.26

0.41

0.11

100

42

30

20

4

11

3

3

15

Morocco shelf Phosphorite conglomerate

18.88

0.52

0.12

46

37

6

15

1

8

6

1

15

19.11

0.38

0.12

49

58

100

50

10

66

3

10

29

31.12

5.41-10.12

0.02-0.18

1

1

1

1

1

18-34

upto 1

4-10

18.51-27.29

3.92-6.54

0.17FO.20

1

1

1

1-3

4-10

4-10

28.61-31.64

0.44-3 03

0 . 1 3 4 22

1-19

1-9

1-48

1-36

4-43

3-120

4-79

10-40

9-15

Agulhos Bonk Phosphorite nodule Bone phosphate: bones and teeth of living fish. whales unfossilized bonen from shelves fossilized bones from shelves bones from pelagic sediments

* According to Baturin and

19.50-34.58