Sedimentation in the African GEOLOGICAL SOCIETY SPECIAL PUBLICATION NO 25

Sedimentation in the African Rifts

EDITED BY L.E. FROSTICK R.W. RENAUT Department of Geology Department of Royal Holloway and Geological Sciences Bedford New College University of Saskatchewan University of London Saskatoon

I.REID Department of Geography Birkbeck College University of London

J.J. TIERCELIN GIS Oc6anologie et G6odynamique Universit6 de Bretagne Occidentale Brest

1986

Published for The Geological Society by Blackwell Scientific Publications

OXFORD LONDON EDINBURGH BOSTON PALO ALTO MELBOURNE Published by DISTRIBUTORS Blackwell Scientific Publications USA and Canada Osney Mead, Oxford OX2 0EL Blackwell Scientific Publications Inc. 8 John Street, London WCIN 2ES PO Box 50009, Palo Alto 23 Ainslie Place, Edinburgh EH3 6AJ California 94303 52 Beacon Street, Boston, Massachusetts 02108, USA 667 Lytton Avenue, Palo Alto, California 94301, USA Australia 107 Barry Street, Carlton, Victoria 3053, Australia Blackwell Scientific Publications (Australia) Pty Ltd First published 1986 107 Barry Street Carlton, Victoria 3053 © 1986 The Geological Society. Authorization to photocopy items for internal or personal use, or the British Library Cataloguing in Publication Data internal or personal use of specific clients, is granted Sedimentation in the African rifts.-- by The Geological Society for libraries and other (Geological Society special publication, users registered with the Copyright Clearance Center ISSN 0305-8719; no. 25) (CCC) Transactional Reporting Service, provided that a base fee of $02.00 per copy is paid directly to 1. Geology--Africa, Eastern.... Valley CCC, 27 Congress Street, Salem, MA 01970, USA. I. Frostick, L.E. II. Geological Society of London 0305-8719/86 $02.00 Ill. Series 556.76 QE326 Printed in Great Britain by ISBN 0-632-01534-9 the Alden Press Ltd, Oxford Contents

List of contributors ..... vii

Preface ...... ix

Obituary ...... xiii

Continental Rift Basins

READING, H.G. African Rift tectonics and sedimentation: an introduction ...... GROVE, A.T. Geomorphology of the African Rift System ......

African Rift Basin Development

FAIRHEAD, J.D. Geophysical controls on sedimentation within the African Rift Systems . 19 ROSENDAHL, B.R., REYNOLDS, D.J., LORBER, P.M., BURGESS, C.F., McGmL, J., SCOTT, "D., LAMBIASE,J.J. 8/; DERKSEN, S.J. Structural expressions of rifting: lessons from Lake Tanganyika, Africa ...... 29 BAKER, B.H. Tectonics and volcanism of the southern Rift Valley and its influence on rift sedimentation ...... 45 WILLIAMS, L.A.J. & CHAPMAN, G.R. Relationships between major structures, salic volcanism and sedimentation in the Kenya Rift from the equator northwards to . 59 SWAIN, C.J., SKINNER,N.J. & KHAN, M.A. Depth to metamorphic basement in the region from seismic and gravity data ...... 75 WATK~NS, R.T. Volcano-tectonic control on sedimentation in the Koobi Fora , Lake Turkana ...... 85

Siliciclastic, Chemical, Pedogenic and Organic Sediments in Contemporary Rift Environments

REID, I. & FROSTICK, L.E. Slope processes, sediment derivation and landform evolution in a rift valley basin, northern Kenya ...... 99 FROSTICK, L.E. & REID, I. Evolution and sedimentary character of lake deltas fed by ephemeral rivers in the Turkana basin, northern Kenya ...... 113 COHEN, A.S., FERGUSON, D.S., GRAM, P.M., HUBLER, S.L. & SIMS, K.W. The distribution of coarse-grained sediments in modern Lake Turkana, Kenya: implications for clastic sedimen- tation models of rift lakes ...... 127 YURETICH, R.F. Controls on the composition of modern sediments, Lake Turkana, Kenya . 141 ABELL, P.I. & MCCLORY, J.P Sedimentary carbonates as isotopic marker horizons at Lake Turkana, Kenya ...... 153 RENAUT, R.W., TIERCELIN, J.J. & OWEN, R.B. Mineral precipitation and diagenesis in the sediments of the Lake Bogoria basin, Kenya Rift Valley ...... 159 EUGSTER, H.P. Lake Magadi, Kenya: a model for rift valley hydrochemistry and sedimentation? 177 CROSSLEY, R. Sedimentation by termites in the Malawi Rift Valley ...... 191 CASANOVA,J. stromatolites ...... 201 HAMILTON, A. 8~; TAYLOR, D. Mire sediments in ...... 211

Sedimentary History of African Rift Basins

TIERCELIN, J.J. The Hadar Formation, Afar depression of ...... 221 WILLIAMS, M.A.J., GETANEH ASSEFA • ADAMSON, D.A. Depositional context of Ptio-Pleistocene hominid-bearing formations in the Middle Awash valley, southern Afar Rift, Ethiopia . . 241 vi Contents

BONNEFILLE, R., ROBERT, C., DELIBRIAS, G., ELENGA, C., HERBIN, J.P., LEZINE, A.M., PERINET, G. • TIERCELIN,J.J. Palaeoenvironment of Lake Abijata, Ethiopia, during the past 2000 years. 253 WILEIAMSON, P.G. & SAVAGE, R.J.G. Early rift sedimentation in the Turkana basin, northern Kenya ...... 267 HILL, A., CURTIS, G. & DRAKE, R. Sedimentary stratigraphy of the Tugen Hills, Baringo, Kenya 285 NYAMWERU, C.K. environments of the Chalbi basin, Kenya: sedimentary and geomorphological evidence ...... 297 OWEN, R.B. & RENAUT, R.W. Sedimentology, stratigraphy and palaeoenvironments of the Holocene Galana Boi Formation, NE Lake Turkana, Kenya ...... 311 VINCENS, A., CASANOVA,J. 8z TIERCELIN,J.J. Palaeolimnology of Lake Bogoria (Kenya) during the 4500 BP high lacustrine phase ...... 323 THOUVENY, N. & TAIEB, M. Preliminary magnetostratigraphic record of Pleistocene deposits, Lake Natron basin, Tanzania ...... 331

Sedimentation and the Preservation of Faunas

HAY, R.L. Role of tephra in the preservation of in Cenozoic deposits of East Africa 339 PICKFORD, M. Sedimentation and fossil preservation in the Nyanza Rift System, Kenya . . 345 DENYS, C., CHOROWICZ, J. & TIERCELIN, J.J. Tectonic and environmental control on rodent diversity in the Plio-Pleistocene sediments of the African Rift System ...... 363

Index ...... 373 List of contributors

P.I. Abell Dept of Chemistry, University of Rhode C. Elenga, Ecole Normale Supbrieure, 5 rue Island, Kingston, Rhode Island 02881, USA Boucicaut, 92260 Fontenay-aux-Roses, France

D.A. Adamson School of Biological Sciences & H.P. Eugster Dept of Earth & Planetary Sciences, Quaternary Research Unit, Macquarie University, Johns Hopkins University, Baltimore, Maryland 21218, North Ryde, New South Wales 2113, Australia USA

Getaneh Assefa Faculty of Sciences, Addis Ababa J.D. Fairhead Dept of Earth Sciences, The University, PO Box 1176, Addis Ababa, Ethiopia University, Leeds LS2 9JT, UK

B.H. Baker Center for Volcanology, University of D.S. Ferguson Dept of Geology, The Colorado Oregon, Eugene, Oregon 97403, USA College, Colorado Springs, Colorado 80903, USA

R. Bonnefille Laboratoire de Gbologie du L.E. Frostick Dept of Geology, Royal Holloway & Quaternaire, CNRS--Case 907 Luminy, 13288 Bedford New College, Egham Hill, Egham, Surrey Marseille, Cedex 9, France TW20 OEX, UK

C.F. Burgess Dept of Geology, Duke University, P.M. Gram Dept of Geology, The Colorado Durham, North Carolina 27706, USA College, Colorado Springs, Colorado 80903, USA

J. Casanova Laboratoire de Gbologie du A.T. Grove Dept of Geography, The University, Quaternaire, CNRS--Case 907 Luminy, 13288 Cambridge CB2 3EN, UK Marseille, Cedex 9, France A. Hamilton Dept of Environmental Sciences, G.R. Chapman British Geological Survey, 154 University of Ulster, Coleraine, Co. Londonderry, Clerkenwell Road, London EC1R 5D U, UK Northern Ireland

J. Chorowicz Dept de Gbotectonique, Universitb de R.L. Hay Dept of Geology, 245 Natural History P. et M. Curie, 4 place Jussieu, 75252 Paris, Cedex Building, 1301 W. Green Street, University of Illinois, 05, France Urbana, Illinois 61801, USA

A.S. Cohen Dept of Geology, The Colorado J.P. Herbin Institut Francais du Pbtrole, BP18, College, Colorado Springs, Colorado 80903, USA 92502 Rueil Malmaison, Cedex, France

R. Crossley Dept of Geography & Earth Science, A. Hill Dept of Anthropology, Yale University, New Chancellor College, University of Malawi, PO Box Haven, Connecticut 06520, USA 280, Zomba, Malawi S.L. Hubler Dept of Geology, The Colorado G. Curtis Dept of Geology & Geophysics, University College, Colorado Springs, Colorado 80903, USA of California, Berkeley, California 94720, USA M.A. Khan Dept of Geology, University of G. Delibrias Centre Faibles Radioactivitbs-- Leicester, Leicester LE1 7RH, UK CNRS, 91/90 Gif-sur-Yvette, France J.J. Lambiase Marathon Oil Co., PO Box 269, Littleton, Colorado 80160, USA C. Denys Laboratoire de Palbontologie des Vertbbrbs et de Palbontologie Humaine, Universitb de A.M. Lezine Laboratoire de Gbologie du P. et M. Curie, 4 place Jussieu, 75252 Paris, Cedex Quaternaire, CNRS--Case 907 Luminy, 13288 05, France Marseille, Cedex 9, France

S.J. Derksen Marathon Oil Co., PO Box 269, P.M. Lorber Dept of Geology, Duke University, Littleton, Colorado 80160, USA Durham, North Carolina 27706, USA

R. Drake Dept of Geology & Geophysics, University J.P. McClory Dept of Chemistry, University of of California, Berkeley, California 94720, USA Rhode Island, Kingston, Rhode Island 02881, USA vii viii List of contributors

J. McGill Dept of Geology, Duke University, N.J. Skinner Dept of Physics, Unirersity of Durham, North Carolina 27706, USA Botswana, Private Bag 0022, Gaborone, Botswana

C.K. Nyamweru Dept oJ" Geography, Kenyatta C.J. Swain Dept of Physics, University of University, PO Box 43844, Nairobi, Kenya Zimbabwe, PO Box MP 167, Harare, Zimbabwe

R.B. Owen Dept of Geography & Earth Science, M. Taieb Laboratoire de G~ologie du Quaternaire, Chancellor College, University of Malawi, PO Box CNRS--Case 907 Luminy, 13288 Marseille, Cedex 9, 280, Zomba, Malawi France

G. Perinet Laboratoire de GOologie du Quaternaire, D. Taylor Dept of Environmental Sciences, CNRS--Case 907 Luminy, 13288 Marseille. Cedex 9, University of Ulster, Coleraine, Co. Londonderry, France Northern Ireland

M. Pickford Institut de Palkontologie, 8 rue Buffon, N. Thouveny Laboratoire de Gkologie du 75005 Paris, France Quaternaire, CNRS--Case 907 Luminy, 13288 Marseille, Cedex 9, France H.G. Reading Dept of Earth Sciences, The University, Parks Road, Oxford OX1 3PR, UK J.J. Tiercelin GIS OcOanologie et G~odynamique, Universit~ de Bretagne Occidentale, 29287 Brest, I. Reid Dept of Geography, Birkbeck College, Cedex, France London WC1E 7HX, UK A. Vincens Laboratoire de G~ologie du Quaternaire, R.W. Renaut Dept of Geological Sciences, CNRS--Case 907 Luminy, 13288 Marseille, Cedex 9, University of Saskatchewan, Saskatoon. Saskatchewan France S7N 0 WO, Canada R.T. Watkins Dept of Geology, University of Cape D.J. Reynolds Dept of Geology, Duke University, Town, Rondebosch, Cape Town, South Africa Durham, North Carolina 27706, USA L.A.J. Williams Dept of Environmental Sciences & C. Robert Laboratoire de G~ologie du Quaternaire, Museum o/" Comparative Zoology, University of CNRS--Case 907 Luminy, 13288 Marseille, Cedex 9, Lancaster, Lancaster LA 1 4 YQ, UK France M.A.J. Williams Dept of Geography, Monash B.R. Rosendahl Dept of Geology, Duke University, Clayton, Victoria 3168, Australia University, Durham, North Carolina 27706, USA P.G. Williamson Dept of Geological Sciences & R.J.G. Savage Dept of Geology, University of Museum of Comparative Zoology, Harvard University, Bristol, Bristol BS8 ISS, UK Cambridge, Massachusetts, USA

O. Scott Dept of Geology, Duke University, R.F. Yuretich Dept of Geology & Geography, Durham, North Carolina 27706, USA University qf Massachusetts, Massachusetts 01003, USA K.W. Sims Dept of Geology, The Colorado College, Colorado Springs, Colorado 80903, USA Preface

This book arises out of an international meeting and quality of clastic reservoirs are largely con- held at the apartments of the Geological Society trolled by the rate and nature of tectonic adjust- of London in September 1984. The meeting ment. Fault movements govern the size, location attracted considerable interest from academics and subsidence of sedimentary basins, as well as working on both African Rift geology in particu- the pathways of sediment transport and the lar, and fault-controlled sedimentation in thickness, orientation and interdigitation of the general. In addition, a large group ofoil company facies belts. Saline lakes are a common feature of representatives attended, reflecting the general rift basins and are often sites of high organic increase in exploration interest in non-marine productivity. Much of the kerogen that evolves is basins and the recent recognition of the impor- sapropelic. This, combined with rapid burial and tance of non-marine sediments as sources of oil high thermal gradients, favours rapid maturation and gas. of hydrocarbons which can then migrate into The main aim of the meeting and of this book is flanking coarse elastic alluvial fan and deltaic to provide an opportunity for the presentation of deposits. In closed lake basins the rapid fluctua- recent results and ideas that have been produced tion of water level results in an interdigitation of by many individuals working on various aspects coarse and fine lithofacies near the shoreline, and of African Rift sedimentation. The research has this provides the excellent stratigraphic traps for been carried out in universities and other estab- oil and gas. lishments in more than ten countries spread The volume opens with an introduction by throughout four different continents. Fieldwork Reading which places the African Rifts in a global associated with this research has been conducted context. Grove follows with a broad view of the in eight different African countries--Chad, Eth- present landforms and the relationship between iopia, Kenya, Malawi, Nigeria, Sudan, Tanzania the rift basins. These set the scene for later more and . Geographical representation is very local analyses of these important sediment sinks. wide, but it is not comprehensive. This is partly As tectonic adjustment is paramount in con- explained by the difficulties of access that have trolling rift basin sedimentation, the next section arisen because of political unrest. Some sectors of of the book focuses on the structural evolution of the rift have been effectively closed to research in both the western (Fairhead) and the eastern recent years. There has been a concentration of (Rosendahl et al.; Baker; Williams & Chapman; effort in the Kenyan, Ethiopian and Tanzanian Swain et al.; Watkins) branches of the African sectors of the African Rift in the last two decades. Rift. Baker, Williams & Chapman, and Watkins This has arisen as geologists have adopted the concentrate on surface expressions of faulting role of camp followers to the exciting fossil and volcanism, relating these to basin location hominid discoveries of Louis, Mary and Richard and size, as well as to controls on sediment Leakey, and of Don Johanson and others. provenance. In contrast, Fairhead and Rosen- However, in the last few years there have been dahl et al. use geophysical data to elucidate both southward and westward trends in interest subsurface rift basin structure and the thickness and more research has been conducted in the of sedimentary fills. Lake Tanganyika and Lake Malawi sectors of The third section is concerned with contempor- East Africa and in the and its ary patterns of sedimentation. The first three extensions (see Fig. 1). papers (Reid & Frostick; Frostick & Reid; Cohen Another aim of both the meeting and this et al.) consider various aspects of elastic sediment volume is to provide a clearer picture of the sources, transport and deposition in the Turkana interrelationship of structure and patterns of basin, following the debris train from source right sedimentation during the early and middle phases through to present sink. Then follow papers of continental rift development. The models dealing with chemical processes and diagenesis in developed here for the African Rift will undoub- modern rift lakes (Yuretich; Renaut et al.; Eugs- tedly find application in the interpretation of ter), and Abell & McClory discuss the application ancient rift sediments worldwide. This is not only of isotopic analyses of sedimentary carbonates to of academic importance. There are significant stratigraphic and palaeoenvironmental interpre- economic implications attached to the current tation. The section closes with a consideration of interpretation of non-marine petroleum source organic controls of sediment deposition. Crossley and reservoir rocks. examines the effect of a pedogenic subaerial In rifts, as in all sedimentary basins, the nature process, Casanova investigates the lacustrine

ix x Preface biosediments, and Hamilton & Taylor review the parts of the rift, ranging in age from late Meso- accumulation of plant material in marginal wet- zoic to Holocene. These case studies focus atten- lands. tion on the Ethiopian (Tiercelin; Williams et al.; The modern patterns discussed in the third Bonnefille et al.), the Kenyan (Williamson & section are analogues that assist interpretation of Savage; Hill et al.; Nyamweru; Owen & Renaut; older preserved equivalents and are a natural Vincens et al.) and the Tanzanian (Thouveny & precursor for the fourth section. This consists of a Taieb) Rifts. Each paper provides an important series of case studies of sediments from various insight into the ways in which long-term lake level

• i

I l I / / i

Location of StudiesKey ~~i,

FIG. 1. Location of studies. Preface xi fluctuations, responding to tectonic and climatic This book provides an overview of sedimen- controls, influence patterns of sedimentation. tation in a single, extensive continental rift sys- One important aspect of the sediments of the tem. However, the wider implications of the work African Rifts which has drawn them particularly that has been, and continues to be, carried out in to world attention, is the prolific and well- Africa are considerable. There are strong similari- preserved vertebrate faunas, especially the early ties in both structure and sediment character hominid remains. The volume would be incom- between the African Rifts and others which are plete if they were not mentioned. As a result, the proven sources of oil and gas (e.g. the North Sea final section deals with some of the volcanic and basins, the Ta Chung basin of China, and the sedimentary factors that lead to good fossil of Libya). Models developed for the preservation (Hay; Pickford; Denys et al.). Rift African Rifts may find wider applications in the basins provide sites in which rapid burial and exploration of new, as yet untapped, sources of early mineralization preserves a fine record of the hydrocarbons in little-known rift basins. Besides evolution of species, including our own. Bill this, the research in Africa clearly enhances our Bishop, late friend and colleague of many of the understanding of already productive basins, and contributors to this volume, often lectured under thereby helps industry optimize exploration dur- a favourite title: 'Rift basins are a good place to ing further development. die!' This is a good summary of the value of the Saskatoon L.E. Frostick deposits to palaeontologists in general, but to August 1985 R.W. Renaut palaeoanthropologists in particular. I. Reid J.J. Tiercelin Obituary

In the period that has elapsed between the King, Emeritus Professor of the University of meeting at the Geological Society and the final London died at his retirement home in his stages in the preparation of this Special Publica- beloved Isle of Arran, Scotland. Glynn Isaacs, tion three eminent professors of the African Rift Professor of Archaeology, University of Califor- System have passed away. A glance through the nia, Berkeley, and more recently of Harvard acknowledgements of the papers that follow will University, was a victim of sudden illness. Brian reveal how much we are indebted to the enthu- Baker, Professor of Geology at the University of siasm, the insight and the support that each of Oregon, died in Nairobi close by the rift he loved these men gave to succeeding generations. Basil so much. We shall miss all three.

xiii