Encyclopedia of Geology (V_05)

ENCYCLOPEDIA OF

GEOLOGY

ENCYCLOPEDIA OF

GEOLOGYEDITED BY

RICHARD C. SELLEY L. ROBIN M. COCKS IAN R. PLIMER

ELSEVIERACADEMIC PRESS Amsterdam Boston Heidelberg London New York Oxford Paris San Diego San Francisco Singapore Sydney Tokyo

Elsevier Ltd., The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK 2005 Elsevier Ltd. The following articles are 2005, The Natural History Museum, London, UK: FOSSIL VERTEBRATES/Hominids Palaeontology PALAEOZOIC/Silurian PRECAMBRIAN/Overview Terranes, Overview Conservation of Geological Specimens MINERALS/Olivines MINERALS/Sulphates TERTIARY TO PRESENT/Pleistocene and The Ice Age Environmental Geochemistry Biological Radiations and Speciation PALAEOZOIC/Ordovician TERTIARY TO PRESENT/Eocene TERTIARY TO PRESENT/Paleocene FOSSIL PLANTS/Angiosperms FOSSIL PLANTS/Gymnosperms Biozones MESOZOIC/Cretaceous MESOZOIC/End Cretaceous Extinctions Stratigraphical Principles FOSSIL INVERTEBRATES/Molluscs Overview FOSSIL INVERTEBRATES/Trilobites FOSSIL INVERTEBRATES/Echinoderms (Other Than Echinoids) FOSSIL INVERTEBRATES/Echinoids TERTIARY TO PRESENT/Pliocene FOSSIL INVERTEBRATES/Bryozoans MINERALS/Feldspathoids Russia The following article is a US Government work in the public domain and not subject to copyright: NORTH AMERICA/Atlantic Margin "Earth from Space" endpaper figure reproduced with permission from Reto Stockli, Nazmi El Saleous, and Marit Jentoft-Nilsen and NASA GSFC All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopy, recording, or any information storage and retrieval system, without permission in writing from the publishers. Permissions may be sought directly from Elsevier's Rights Department in Oxford, UK: phone (+44) 1865 843830, fax (+44) 1865 853333, [email protected]. Requests may also be completed on-line via the homepage (http://www.elsevier.com/locate/permissions). First edition 2005 Library of Congress Control Number: 2004104445 A catalogue record for this book is available from the British Library ISBN 0-12-636380-3 (set) This book is printed on acid-free paper Printed and bound in Spain

EDITORS v

Editors

EDITORSRichard C. Selley

Imperial College London, UKL. Robin M. Cocks

Natural History Museum London, UKIan R. Plimer

University of Melbourne Melbourne, VA Australia

CONSULTANT EDITORJoe McCall

Cirencester Gloucestershire, UK

vi EDITORIAL ADVISORY BOARD

Editorial Advisory BoardJaroslav Aichler Georg Hoinkes

Czech Geological Survey Jesen k, Czech RepublicAndrew R Armour

t Graz Universita tplatz 2 Universita Graz, AustriaR A Howie

Revus Energy A/S NorwayJohn Collinson

Royal Holloway, London University London, UKShunsho Ishihara

Delos, Beech Staffordshire, UKAlexander M Davis

Geological Survey of Japan Tsukuba, JapanGilbert Kelling

Infoscape Solutions Ltd. Guildford, UKPeter Doyle

Keele University Keele, UKKen Macdonald

University College London London, UKWolfgang Franke

University of California Santa Barbara Santa Barbara, CA, USANorman MacLeod

Institut fu r Geowissenschaften Giessen, GermanyYves Fuchs

The Natural History Museum London, UKStuart Marsh

Marne la Valle Universite FrancePaul Garrard

British Geological Survey Nottingham, UKJoe McCall

Cirencester, Gloucestershire, UKDavid R Oldroyd

Formerly Imperial College London, UKR O Greiling

University of New South Wales Sydney, NSW, AustraliaRong Jia-yu

t Heidelberg Universita Heidelberg, GermanyGwendy Hall

Nanjing Institute of Geology and Palaeontology Nanjing, ChinaMike Rosenbaum

Natural Resources Canada Ottawa, ON, CanadaRobert D Hatcher, Jr.

Twickenham, UKPeter Styles

University of Tennessee Knoxville, TN, USA

Keele University Keele, UK

EDITORIAL ADVISORY BOARD vii

Hans D Sues

S H White

Carnegie Museum of Natural History Pittsburgh, PA, USAJohn Veevers

Universiteit Utrecht Utrecht, The Netherlands

Macquarie University Sydney, NSW, Australia

FOREWORD ix

ForewordFew areas of science can have changed as fast as geology has in the past forty years. In the first half of the last century geologists were divided, often bitterly, between the drifters and those who believed that the Earth and its continents were static. Neither side of this debate foresaw that the application of methods from physics, chemistry and mathematics to these speculations would revolutionize the study of all aspects of the Earth Sciences, and would lead to accurate and detailed reconstructions of world geography at former times, as well as to an understanding of the origin of the forces that maintain the continental movements. This change in world-view is no longer controversial, and is now embedded in every aspect of the Earth Sciences. It is a real pleasure to see this change, which has revitalized so many classic areas of research, reflected in the articles of this encyclopedia. Particularly affected are the articles on large-scale Earth processes, which discuss many of the new geological ideas that have come from geophysics and geochemistry. Forty years ago we had no understanding of these topics, which are fundamental to so many aspects of the Earth Sciences. The editors have decided, and in my view quite rightly, not to include detailed discussion of the present technology that is used to make geophysical and geochemical measurements. Such instrumental aspects are changing rapidly and become dated very quickly. They can easily be found in more technical publications. Instead the editors have concentrated on the influence such studies have had on our understanding of the Earth and its evolution, and in so doing have produced an excellent and accessible account of what is now known. Any encyclopedia has to satisfy a wide variety of users, and in particular those who know that some subject like sedimentation or mineral exploration is part of geology, and go to an encyclopedia of geology to find out more. The editors have made a very thorough attempt to satisfy such users, and have included sections on such unexpected geological topics as the evolution of the Earths atmosphere, the geology of Jupiter, Saturn, and their moons, aggregates, and creationism. I congratulate the editors and authors for producing such a fine summary of our present knowledge, and am particularly pleased that they intend to produce an online version of the encyclopedia. Though I have become addicted to using the Internet as my general encyclopedia, I will be delighted to be able to access something concerned with my own field that is as organized and scholarly as are these volumes.Dan McKenzie Royal Society Professor of Earth Sciences Cambridge University, UK

INTRODUCTION xi

IntroductionCivilization occurs by geological consent subject to change without notice.... Will Durant (1885 1981)

Richard de Bury, Bishop of Durham from 1333 to 1345, divided all knowledge into Geologia, earthly knowledge, and Theologia, heavenly knowledge. By the beginning of the last century, however, Geology was generally understood to be restricted to the study of rocks: according to the old dictum of the Geological Survey of Great Britain If you can hit it with a hammer, then its geology. Subsequently geology has been subsumed into Earth Science. This includes not only the study of rocks (the lithosphere), but also the atmosphere and hydrosphere and their relationship with the biosphere. Presently these relationships now form a nexus in Earth System Science. The Encyclopedia of Geology is what it says on the cover. What appealed to us when first approached to edit this work by Academic Press was a request that the encyclopedia should be rock-based. Readers are referred to the companion volumes, Encyclopedia of Atmospheric Sciences, Encyclopedia of the Solar System, Encyclopedia of Soils in the Environment and Encyclopedia of Ocean Sciences for knowledge on the other branches of Earth Science. Nonetheless we have extended our brief to include articles on the other planets and rocky detritus of our solar system, leaving others to argue, as no doubt Bishop Richard would have done, where the boundaries of earthly and heavenly knowledge might be. (His Grace would probably have charged the editors of the Encyclopedia of the Solar System with heresy.) One of the first, and most difficult, tasks of editing this encyclopedia was to decide, not only which topics merited articles, but also how these articles should be grouped to facilitate the reader. This is easy for some branches of geology, but difficult for others. It is relatively easy to logically arrange articles on mineralogy and palaeontology, since they are defined by their chemistry and evolutionary biology. Articles that describe Earth history may be conveniently arranged in a chronological order, and articles on regional geology may be presented geographically. Other topics present problems, particularly in the area of sedimentology. There is, for example, a range of inter-related topics associated with deserts. This area could be described geomorphologically, and in terms of the aeolian and aqueous processes of deserts, aeolian sedimentary structures, and aeolian deposits. All of these aspects of deserts deserve mention, but there is no obvious logical way of arranging the discrete topics into articles. To help us in this task we relied heavily on our editorial board, whose individual members had more specialized knowledge of their field than we. To the Editorial Board Members, authors and anonymous referees of each article we give heartfelt thanks. We were also, of course, constrained by the willingness of expert authorities to contribute articles. To some degree therefore, the shape of the encylopedia owes as much to the enthusiasm of experts to write for us, as for our wish list of articles. To facilitate readers finding their way around the Encyclopedia of Geology great care has been taken in crossreferencing within and between articles, in providing See Also lists at the end of articles, and in the index. No doubt it will be easier for readers to navigate around the online version of the work, than to manipulate the several hard copy volumes. As geological knowledge expands there is always more to learn and understand. While preparing the Encyclopedia of Geology we have ourselves learned a great deal about geology, both within and beyond our own specialties. We invite you to read this encyclopedia and join us in the field trip of a lifetime. Richard C. Selley L. Robin M. Cocks Ian R. Plimer 1 August 2004 References to related encyclopedia published by Elsevier, Academic Press: Encyclopedia of the Solar System, 1998 Encyclopedia of Ocean Sciences, 2001 Encyclopedia of Atmospheric Sciences, 2002 Encyclopedia of Soils in the Environment, 2005

GUIDE TO USE OF THE ENCYCLOPEDIA xiii

Guide to Use of the EncyclopediaStructure of the EncyclopediaThe material in the Encyclopedia is arranged as a series of entries in alphabetical order. Most entries consist of several articles that deal with various aspects of a topic and are arranged in a logical sequence within an entry. Some entries comprise a single article. To help you realize the full potential of the material in the Encyclopedia we have provided three features to help you find the topic of your choice: a Contents List, Cross-References and an Index.

1. Contents ListYour first point of reference will probably be the contents list. The complete contents lists, which appears at the front of each volume will provide you with both the volume number and the page number of the entry. On the opening page of an entry a contents list is provided so that the full details of the articles within the entry are immediately available. Alternatively you may choose to browse through a volume using the alphabetical order of the entries as your guide. To assist you in identifying your location within the Encyclopedia a running headline indicates the current entry and the current article within that entry. You will find 'dummy entries' where obvious synonyms exist for entries or where we have grouped together related topics. Dummy entries appear in both the contents lists and the body of the text. Example If you were attempting to locate material on erosional sedimentary structures via the contents list: EROSION see SEDIMENTARY PROCESSES: Fluxes and Budgets; Aeolian Processes; Erosional Sedimentary Structures. The dummy entry directs you to the Erosional Sedimentary Structures article, in the SEDIMENTARY PROCESSES entry. At the appropriate location in the contents list, the page numbers for articles under Sedimentary Processes are given. If you were trying to locate the material by browsing through the text and you looked up Erosion then the following information would be provided in the dummy entry:

EROSIONSee SEDIMENTARY PROCESSES: Erosional Sedimentary Structures; Aeolian Processes; Fluxes and Budgets

xiv

GUIDE TO USE OF THE ENCYCLOPEDIA

Alternatively, if you were looking up Sedimentary Processes the following information would be provided:

SEDIMENTARY PROCESSESContents Erosional Sedimentary Structures Depositional Sedimentary Structures Post-Depositional Sedimentary Structures Aeolian Processes Catastrophic Floods Deep Water Processes and Deposits Fluvial Geomorphology Glaciers Karst and Palaeokarst Landslides Particle-Driven Subaqueous Gravity Processes Deposition from Suspension Fluxes and Budgets

2. Cross-ReferencesAll of the articles in the Encyclopedia have been extensively cross-referenced. The cross-references, which appear at the end of an article, serve three different functions. For example, at the end of the PRECAM BRIAN: Overview article, cross-references are used: i. To indicate if a topic is discussed in greater detail elsewhere. Africa: Pan-African Orogeny. Antarctic Asia: Central. Australia: Proterozoic Biosediments and Biofilms Earth Structure and Origins. Earth System Science.Europe: East European Craton; Timanides of Northern Russia. Gondwanaland and Gondwana. Grenvillian Orogeny. Indian Subcontinent. North America:Precambrian Continental Nucleus; Continental Interior. Precambrian: Eukaryote Fossils; Prokaryote Fossils; Vendian and Ediacaran, Russia, Sedimentary Rocks: Banded Iron Formations. Shields. Terranes, Overview.ii. To draw the reader's attention to parrallel discussions in other articles.

Africa: Pan-African Orogeny. Antarctic. Asia: Central. Australia: Proterozoic. Biosediments and Biofilms. Earth Structure and Origins. Earth System Science. Europe: East European Craton; Timanides of Northern Russia. Gondwanaland and Gondwana. Grenvillian Orogeny Indian Subcontinent. North America: Precambrian Continental Nucleus; Continental Interior. Precambrian: Eukaryote Fossils; Prokaryote Fossils; Vendian and Ediacdran. Russia. Sedimentary Rocks: Banded Iron Formations. Shields. Terranes, Overview.

GUIDE TO USE OF THE ENCYCLOPEDIA xv

iii. To indicate material that broadens the discussion. Africa: Pan-African Orogeny. Antarctic. Asia: Central. Australia: Proterozoic. Biosediments and Biofilms. Earth Structure and Origins. Earth Syatem Science. Europe: East European Graton; Timanides of Northern Russia. Gondwantand and Gendwana. Grenvillian Orogeny. Indian Subcontinent. North America: Precambrian Continental Nucleus; Continental Interior. Precambrian: Eukaryote Fossils; Prokaryote Fossils; Vendian and Ediacaran. Russia. Sedimentary Rocks: Banded Iron Formations. Shields. Terranes, Overview.

3. IndexThe index will provide you with the page number where the material is located, and the index entries differentiate between material that is a whole article, is part of an article or is data presented in a figure or table. Detailed notes are provided on the opening page of the index.

4. ContributorsA full list of contributors appears at the beginning of each volume.

CONTRIBUTORS xvii

ContributorsAbart, R University of Basel, Basel, Switzerland Aldridge, R J University of Leicester, Leicester, UK Al-Jallal, I A Sandroses Est. for Geological, Geophysical Petroleum Engineering Consultancy and Petroleum Services, Khobar, Saudi Arabia Alkmim, F F Universidade Federal de Ouro Preto, Ouro Preto, Brazil Allen, P M Bingham, Nottingham, UK Allwood, A C Macquarie University, Sydney, NSW, Australia Al-Sharhan, A S United Arab Emirates University, AI-Ain, United Arab Emirates Anderson, L I National Museums of Scotland, Edinburgh, UK Arndt, N T LCEA, Grenoble, France Arnott, R Oxford Institute for Energy Studies, Oxford, UK Asimow, P D California Institute of Technology, Pasadena, CA, USA Atkinson, J City University, London, UK Bacon, M Petro-Canada, London, UK Bailey, J Anglo-Australian Observatory and Australian Centre for Astrobiology, Sydney, Australia Bani, P Institut de la Recherche pour le Dveloppement, Noumea, New Caledonia Bell, F G British Geological Survey, Keyworth, UK Bell, K Carleton University, Ottawa, ON, Canada Best, J University of Leeds, Leeds, UK Birch, W D Museum Victoria, Melbourne, VIC, Australia Bird, J F Imperial College London, London, UK Black, P Auckland University, Auckland, New Zealand Bleeker, W Geological Survey of Canada, Ottawa, ON, Canada Bogdanova, S V Lund University, Lund, Sweden Bommer, J J Imperial College London, London, UK Boore, D M United States Geological Survey, Menlo Park, CA, USA Bosence, D W J Royal Holloway, University of London, Egham, UK Boulanger, R W University of California, Davis, CA, USA Braga, J C University of Granada, Granada, Spain Branagan, D F University of Sydney, Sydney, NSW, Australia Brasier, M D University of Oxford, Oxford, UK Brewer, P A University of Wales, Aberystwyth, UK Bridge, M University College London, London, UK Brown, D Institute de Ciencias de la Tierra 'Jaume Almera' CSIC, Barcelona, Spain Brown, A J Macquarie University, Sydney, NSW, Australia Brown, R J University of Bristol, Bristol, UK

xviii CONTRIBUTORS Bucher, K University of Freiburg, Freiburg, Germany Burns, S F Portland State University, Portland, OR, USA Byford, E Broken Hill, NSW, Australia Calder, E S Open University, Milton Keynes, UK Cameron, E M Eion Cameron Geochemical Inc., Ottawa, ON, Canada Carbotte, S M Columbia University, New York, NY, USA Carminati, E Universita La Sapienza, Rome, Italy Chamberlain, S A Macquarie University, Sydney, NSW, Australia Charles, J A Formerly Building Research Establishment Hertfordshire, UK Chiappe, L M Natural History Museum of Los Angeles County Los Angeles, CA, USA Clack, J A University of Cambridge, Cambridge, UK Clayton, C Eardiston, Tenbury Wells, UK Clayton, G Trinity College, Dublin, Ireland Cocks, L R M The Natural History Museum, London, UK Coffin, M F University of Tokyo, Tokyo, Japan Collinson, J John Collinson Consulting, Beech, UK Comerford, G The Natural History Museum, London, UK Condie, K C New Mexico Tech, Socorro, NM, USA Cornford, C Integrated Geochemical Interpretation Ltd, Bideford, UK Cornish, L The Natural History Museum, London, UK

Cosgrove, J W Imperial College London, London, UK Coxon, P Trinity College, Dublin, Ireland Cressey, G The Natural History Museum, London, UK Cribb, S J Carraig Associates, Inverness, UK Cronan, D S Imperial College London, London, UK Currant, A The Natural History Museum, London, UK Davies, H University of Papua New Guinea, Port Moresby Papua New Guinea Davis, G R Imperial College London, London, UK DeCarli, P S SRI International, Menlo Park, CA, USA Dewey, J F University of California Davis Davis, CA, USA, and University of Oxford, Oxford, UK Doglioni, C Universita La Sapienza, Rome, Italy Doming, K J University of Sheffield, Sheffield, UK Dott, Jr R H University of Wisconsin, Madison, Wl, USA Doyle, P University College London, London, UK Dubbin, W E The Natural History Museum, London, UK Dyke, G J University College Dublin, Dublin, Ireland Echtler, H GeoForschungsZentrum Potsdam, Potsdam, Germany Eden, M A Geomaterials Research Services Ltd, Basildon, UK Eide, E A Geological Survey of Norway, Trondheim, Norway Eldholm, O University of Bergen, Bergen, Norway

CONTRIBUTORS xix

Elliott, D K Northern Arizona University, Flagstaff, AZ, USA Elliott, T University of Liverpool, Liverpool, UK Eriksen, A S Zetica, Witney, UK Payers, S R University of Aberdeen, Aberdeen, UK Feenstra, A GeoForschungsZentrum Potsdam, Potsdam, Germany Felix, M University of Leeds, Leeds, UK Figueras, D BFI, Houston, TX, USA Fookes, P G Winchester, UK Forey, P L The Natural History Museum, London, UK Fortey, R A The Natural History Museum, London, UK Foster, D A University of Florida, Gainesville, FL, USA Frda, J Czech Geological Survey, Prague, Czech Republic Franke, W Johann Wolfgang Goethe-Universitat Frankfurt am Main, Germany Franz, G Technische Universitat Berlin, Berlin, Germany French, W J Geomaterials Research Services Ltd, Basildon, UK Fritscher, B Munich University, Munich, Germany Frostick, L University of Hull, Hull, UK Fuchs, Y Universit Marne la Valle, Marne la Valle, France Gabbott, S E University of Leicester, Leicester, UK Garaebiti, E Department of Geology and Mines, Port Vila, Vanuatu

Garetsky, R G Institute of Geological Sciences, Minsk, Belarus Garrard, P Imperial College London, London, UK Gascoyne, J K Zetica, Witney, UK

Gee, D G University of Uppsala, Uppsala, SwedenGeshi, N Geological Survey of Japan, Ibaraki, Japan Giese, P Freie Universitat Berlin, Berlin, Germany Giles, D P University of Portsmouth, Portsmouth, UK Glasser, N F University of Wales, Aberystwyth, UK Gluyas, J Acorn Oil and Gas Ltd., Staines, UK Gorbatschev, R Lund University, Lund, Sweden Gordon, J E Scottish Natural Heritage, Edinburgh, UK Gradstein, F M University of Oslo, Oslo, Norway Gray, D R University of Melbourne, Melbourne, VIC, Australia Greenwood, J R Nottingham Trent University, Nottingham, UK Grieve, RAF Natural Resources Canada, Ottawa, ON, Canada Griffiths, J S University of Plymouth, Plymouth, UK Hambrey, M J University of Wales, Aberystwyth, UK Hancock, J M Formerly Imperial College London, London, UK Hansen, J M Danish Research Agency, Copenhagen, Denmark Harff, J Baltic Sea Research Institute Warnemunde, Rostock, Germany

Deceased

xx

CONTRIBUTORS

Harper, DAT Geologisk Museum, Copenhagen, Denmark Harper, E M University of Cambridge, Cambridge, UK Harrison, JP Imperial College London, London, UK Hatcher, Jr RD University of Tennessee, Knoxville, TN, USA Hatheway, A W Rolla, MO and Big Arm, MT, USA Hauzenberger, C A University of Graz, Graz, Austria Hawkins, A B Charlotte House, Bristol, UK Haymon, R M University of California-Santa Barbara Santa Barbara, CA, USA He Guoqi Peking University, Beijing, China Head, J W Brown University, Providence, Rl, USA Heim, N A University of Georgia, Athens, GA, USA Helvaci, C Dokuz Eyll niversitesi, Izmir, Turkey Hendriks, B W H Geological Survey of Norway, Trondheim, Norway Henk, A Universitt Freiburg, Freiburg, Germany Herries Davies, G L University of Dublin, Dublin, IrelandHey, R N University of Hawaii at Manoa, Honolulu, HI, USA

Howell, J University of Bergen, Bergen, Norway Howie, R A Royal Holloway, University of London, London, UK Hudson-Edwards, K University of London, London, UK Huggett, J M Petroclays, Ashtead, UK and The Natural History Museum, London, UK Hughes, N C University of California, Riverside, CA, USA Hutchinson, D R US Geological Survey, Woods Hole, MA, USA Idriss, I M University of California, Davis, CA, USA Ineson, J R Geological Survey of Denmark and Greenland Geocenter Copenhagen, Copenhagen, Denmark Ivanov, M A Russian Academy of Sciences, Moscow, Russia Jger, K D Martin Luther University, Halle, Germany Jarzembowski, E A University of Reading, Reading, UK and Maidstone Museum and Bentlif Art Gallery, Maidstone, UK Jones, B University of Alberta, Edmonton, AB, Canada Jones, G L Conodate Geology, Dublin, Ireland Joyner, L Cardiff University, Cardiff, UK Kaminski, M A University College London, London, UK

Hoinkes, G University of Graz, Graz, Austria Hooker, J J The Natural History Museum, London, UK Home, D J University of London, London, UK Hovland, M Statoil, Stavanger, Norway

Kay, S MCornell University, Ithaca, NY, USA Kemp, A I S University of Bristol, Bristol, UK Kendall, A C University of East Anglia, Norwich, UK Kenrick, P The Natural History Museum, London, UK

CONTRIBUTORS xxi

Kogiso, T Japan Marine Science and Technology Center, Yokosuka, Japan Krings, M Bayerische Staatssammlung fr Palontologie und Geologic, Geo-Bio Center, Munich, Germany Lancaster, N Desert Research Institute, Reno, NV, and United States Geological Survey, Reston, VA, USA Lang,K R Tufts University, Medford, MA, USA Laurent, G Brest, France

MacLeod, N The Natural History Museum, London, UK Maltman, A University of Wales, Aberystwyth, UK Martill, D M University of Portsmouth, Portsmouth, UK Martins-Neto, M A Universidade Federal de Ouro Preto, Ouro Preto, Brazil Marvin, U B Harvard-Smithsonian Center for Astrophysics Cambridge, MA, USA Mason, P J HME Partnership, Romford, UK Massonne, H-J Universitt Stuttgart, Stuttgart, Germany Matte, P University of Montpellier II, Montpellier, France Mayor, A Princeton, USA McCaffrey, W University of Leeds, Leeds, UK McCall, G J H Cirencester, Gloucester, UK McCave, I N University of Cambridge, Cambridge, UK McGhee, G R Rutgers University, New Brunswick, NJ, USA McKibben, M A University of California, CA, USA McLaughlin, Jr P P Delaware Geological Society, Newark, DE, USA McManus, J University of St. Andrews, St. Andrews, UK McMenamin, MAS Mount Holyoke College, South Hadley, MA, USA Merriam, D F University of Kansas, Lawrence, KS, USA Metcalfe, I University of New England, Armidale, NSW, Australia Milke, R University of Basel, Basel, Switzerland

Lee, E M York, UKLemke, W Baltic Sea Research Institute Warnemnde, Rostock Germany Lesher, C M Laurentian University, ON, Canada Lewin, J University of Wales, Aberystwyth, UKLiu, J G Imperial College London, London, UK

Long,J A The Western Australian Museum, Perth WA, Australia Loock, J C University of the Free State Bloemfontein, South Africa Lowell, R P Georgia Institute of Technology, Atlanta, GA, USA Lucas, S G New Mexico Museum of Natural History Albuquerque, NM, USA Liming, S University of Bremen, Bremen, GermanyLuo, Z-X Carnegie Museum of Natural History Pittsburgh, PA, USA

Macdonald, K C University of California-Santa Barbara Santa Barbara, CA, USA Machel, H G University of Alberta, Edmonton, Alberta, Canada

xxii CONTRIBUTORS

Milner, A R Birkbeck College, London, UK Mojzsis, S J University of Colorado, Boulder, CO, USA Monger, J W H Geological Survey of Canada, Vancouver, BC, Canada and Simon Fraser University Burnaby, BC, Canada Moore, P Selsey, UK

Oneacre, J W BFI, Houston, TX, USA Orchard, M J Geological Survey of Canada Vancouver, BC, Canada

Orr, P JUniversity College Dublin, Dublin, Ireland Owen, A W University of Glasgow, Glasgow, UK Plike, H Stockholm University, Stockholm, Sweden Page, K N University of Plymouth, Plymouth, UK Paris, F University of Rennes 1, Rennes, France Parker, J R Formerly Shell EP International, London, UK Pfiffner, O A University of Bern, Bern, Switzerland Piper, D J W Geological Survey of Canada, Dartmouth, NS, Canada Price, R A Queens University Kingston, ON, Canada Prothero, D R Occidental College, Los Angeles, CA, USA Puche-Riart, O Polytechnic University of Madrid, Madrid, Spain

Morris, N JThe Natural History Museum, London, UK Mortimer, N Institute of Geological and Nuclear Sciences, Dunedin New Zealand Mountney, N P Keele University, Keele, UK Mpodozis, C SIPETROL SA, Santiago, Chile Mungall, J E University of Toronto, Toronto, ON, Canada Myrow, P Colorado College, Colorado Springs, CO, USA Naish, D University of Portsmouth, Portsmouth, UK Nickel, E H CSIRO Exploration and Mining, Wembley, WA, Australia Nielsen, K C The University of Texas at Dallas, Richardson, TX, USA Nikishin, A M Lomonosov Moscow State University, Moscow, Russia Nokleberg, W J United States Geological Survey, Menlo Park, CA, USA Norbury, D CL Associates, Wokingham, UK O'Brien, P J Universitt Potsdam, Potsdam, GermanyOgg, J G Purdue University, West Lafayette, IN, USA

Pye, KRoyal Holloway, University of London, Egham, UK Rahn, P H South Dakota School of Mines and Technology Rapid City, SD, USA Ramos, V A Universidad de Buenos Aires, Buenos Aires, Argentina Rankin, A H Kingston University, Kingston-upon-Thames, UK Rebesco, M Istituto Nazionale di Oceanografia e di Geofisica Sperimentale (OGS), Italy Reedman, A J Mapperley, UK

Oldershaw, C St. Albans, UK Oldroyd, D R University of New South Wales, Sydney, Australia

CONTRIBUTORS xxiii

Reisz, R R University of Toronto at Mississauga Mississauga, ON, Canada Retallack, G J University of Oregon, Eugene, OR, USA Rickards, R B University of Cambridge, Cambridge, UK Riding, R Cardiff University, Cardiff, UK Rigby, J K Brigham Young University, Provo, UT, USA Rigby, S University of Edinburgh, Edinburgh, UK Rodda, P Mineral Resources Department, Suva, Fiji Rona, P A Rutgers University, New Brunswick, NJ, USA Rose, E P F Royal Holloway, University of London, Egham, UK Rosenbaum, M S Twickenham, UK Rothwell, R G Southampton Oceanography Centre, Southampton, UKRoy, A B Presidency College, Kolkata, India

Searle, R C University of Durham, Durham, UK Seibold, I University Library, Freiburg, Germany Selley, R C Imperial College London, London, UK Sellwood, B W University of Reading, Reading, UK Shields, G A James Cook University, Townsville, OLD, Australia Simms, M J Ulster Museum, Belfast, UK Slipper, I J University of Greenwich, Chatham Maritime, UK Smallwood, J R Amerada Hess pic, London, UK Smith, A B The Natural History Museum, London, UK Smith, I Auckland University, Auckland, New Zealand Snoke, A W University of Wyoming, Laramie, WY, USA Soligo, C The Natural History Museum, London, UK Stein, S Northwestern University, Evanston, IL, USA Steinberger, B Japan Marine Science and Technology Center Yokosuka, Japan Stemmerik, L Geological Survey of Denmark and Greenland, Geocenter Copenhagen, Copenhagen, Denmark Stern, R J The University of Texas at Dallas, Richardson, TX, USA Stewart, I University of Plymouth, Plymouth, UK Storey, B C University of Canterbury, Christchurch, New Zealand Storrs, G W Cincinnati Museum Center, Museum of Natural History and Science, Cincinnati, OH, USA

Rushton, A W A The Natural History Museum, London, UK Russell, A J University of Newcastle upon Tyne, Newcastle upon Tyne, UK Schmid, R ETH-centre, Zurich, Switzerland Scott, E National Center for Science Education Berkeley, CA, USA Scon, A C Royal Holloway, University of London, Egham, UK Scrutton, C T Formerly University of Durham, Durham, UK Searle, M University of Oxford, Oxford, UK

xxiv

CONTRIBUTORS

Strachan, R A University of Portsmouth, Portsmouth, UK Suetsugu, D Japan Marine Science and Technology Center, Yokosuka Japan Surlyk, F University of Copenhagen, Geocenter Copenhagen, Copenhagen, Denmark Tait, J Ludwig-Maximilians-Universitt, Mnchen, Germany Talbot, M R University of Bergen, Bergen, Norway Taylor, P D The Natural History Museum, London, UK Taylor, T N University of Kansas, Lawrence, KS, USA Taylor, W E G University of Lancaster, Lancaster, UK Tazawa, J Niigata University, Niigata, Japan Theodor, J M Illinois State Museum, Springfield, IL, USA Timmerman, M J Universitt Potsdam, Potsdam, Germany Tollo, R P George Washington University, Washington, DC, USA Torsvik, T H Geological Survey of Norway, Trondheim, Norway Trendall, A Curtin University of Technology, Perth, Australia Trewin, N H University of Aberdeen, Aberdeen, UK Turner, A K Colorado School of Mines, Colorado, USA Twitchett, R J University of Plymouth, Plymouth, UK Tyler, I M Geological Survey of Western Australia East Perth, WA, Australia Valdes, P J University of Bristol, Bristol, UK

van Geuns, L C Clingendael International Energy Programme The Hague, The Netherlands van Staal, C R Geological Survey of Canada, Ottawa, ON, Canada Vanecek, M Charles University Prague, Prague, Czech Republic Vaughan,D J University of Manchester, Manchester, UK Veevers, J J Macquarie University, Sydney, NSW, Australia Verniers, J University of Ghent, Ghent, Belgium Wadge, G University of Reading, Reading, UK Walter, M R Macquarie University, Sydney, NSW, Australia Wang, H China University of Geosciences, Beijing, China Ware, N G Australian National University, Canberra, ACT, Australia Warke, P A Queen's University Belfast, Belfast, UK Weber, K J Technical University, Delft, The Netherlands Welch, M D The Natural History Museum, London, UK Westbrook, G K University of Birmingham, Birmingham, UK Westermann, G E G McMaster University, Hamilton, ON, Canada Whalley, W B Queen's University Belfast, Belfast, UK White, N C Brisbane, OLD, Australia White, S M University of South Carolina, Columbia, SC, USA Wignall, P B University of Leeds, Leeds, UK Williams, P A University of Western Sydney, Parramata, Australia

CONTRIBUTORS xxv

Wise, W S University of California-Santa Barbara Santa Barbara, CA, USA Worden, R H University of Liverpool, Liverpool, UK Wyatt, A R Sidmouth, UK Xiao, S Virginia Polytechnic Institute and State University Blacksburg, VA, USA

Yakubchuk, A S The Natural History Museum, London, UK Yates, A M University of the Witwatersrand, Johannesburg South Africa Zhang Shihong China University of Geosciences, Beijing, China Ziegler, P A University of Basel, Basel, Switzerland

CONTENTS xxvii

ContentsVolume 1AAFRICA Pan-African Orogeny A Krner, R J Stern North African Phanerozoic S Lning Rift Valley L Frostick AGGREGATES M A Eden, W J French ALPS See EUROPE: The Alps ANALYTICAL METHODS Fission Track Analysis B W H Hendriks Geochemical Analysis (Including X-ray) R H Warden Geochronological Techniques E A Eide Gravity / R Smallwood Mineral Analysis N G Ware ANDES S M Kay, C Mpodozis, V A Ramos B C Storey / A Al-Jallal, A S Al-Sharhan VA Ramos ANTARCTIC ARGENTINA43 54 77 92 107 118 132 140 153 164 169

1 12 2634

ARABIA AND THE GULF ASIA Central S G Lucas South-East / Metcalfe

ASTEROIDS See SOLAR SYSTEM: Asteroids, Comets and Space Dust ATMOSPHERE EVOLUTION S J Mojzsis197 208 222 237

AUSTRALIA Proterozoic / M Tyler Phanerozoic J J Veevers Tasman Orogenic Belt D R Gray, D A Foster

BBIBLICAL GEOLOGY BIODIVERSITY E Byford P L Forey253 259 266 279 294 306 328

A W Owen M R Walter, A C Allwood

BIOLOGICAL RADIATIONS AND SPECIATION BIOSEDIMENTS AND BIOFILMS BIOZONES BRAZIL N MacLeod F F Alkmim, M A Martins-Neto A W Hatheway

BUILDING STONE

xxviii

CONTENTS

cCALEDONIDE OROGENY See EUROPE: Caledonides Britain and Ireland; Scandinavian Caledonides (with Greenland) CARBON CYCLE CLAY MINERALS G A Shields H Wang, Shihong Zhang, Guoqi He Y Fuchs / M Huggett 335 345 358 366 370 L Cornish, G Comerford 373 381 CHINA AND MONGOLIA CLAYS, ECONOMIC USES COLONIAL SURVEYS

COCCOLITHS See CALCAREOUS ALGAE A J Reedman COMETS See SOLAR SYSTEM: Asteroids, Comets and Space Dust CONSERVATION OF GEOLOGICAL SPECIMENS CREATIONISM E Scott

DDELTAS See SEDIMENTARY ENVIRONMENTS: Deltas DENDROCHRONOLOGY DIAGENESIS, OVERVIEW M Bridge R C Selley 387 393 DESERTS See SEDIMENTARY ENVIRONMENTS: Deserts DINOSAURS See FOSSIL VERTEBRATES: Dinosaurs

EEARTH Mantle GJH McCall 397

Crust

GJHMcCallH Palike GJH McCall

403410 421 430

Orbital Variation (Including Milankovitch Cycles) EARTH STRUCTURE AND ORIGINS EARTH SYSTEM SCIENCE R C Selley

EARTHQUAKES See ENGINEERING GEOLOGY: Aspects of Earthquakes; TECTONICS: Earthquakes ECONOMIC GEOLOGY G R Davis 434 444 448 456 463 474 482 499 515 525 535

ENGINEERING GEOLOGY Overview M S Rosenbaum Codes of Practice D Nor bury Aspects of Earthquakes A W Hatheway Geological Maps / S Griffiths Geomorphology M Lee, J S Griffiths, P G Fookes Geophysics / K Gascoyne, A S Eriksen Seismology J J Bommer, D M Boore Natural and Anthropogenic Geohazards G J H McCall Liquefaction / F Bird, R W Boulanger, IM Idriss Made Ground / A Charles

CONTENTS xxix

Problematic Rocks F G Bell Problematic Soils F G Bell Rock Properties and Their Assessment F G Bell Site and Ground Investigation / R Greenwood

543 554 566 580

Volume 2ENGINEERING GEOLOGY Site Classification A W Hatheway Subsidence A B Hawkins Ground Water Monitoring at Solid Waste Landfills ENVIRONMENTAL GEOCHEMISTRY ENVIRONMENTAL GEOLOGY W E Dubbin

/ W Oneacre, D Figueras

1 9 14 21 25

P Doyle

EROSION See SEDIMENTARY PROCESSES: Erosional Sedimentary Structures; Aeolian Processes; Fluxes and Budgets EUROPE East European Craton R G Garetsky, S V Bogdanova, R Gorbatschev Timanides of Northern Russia D G Gee Caledonides of Britain and Ireland R A Strachan , J F Dewey Scandinavian Caledonides (with Greenland) D G Gee Variscan Orogeny W Franke, P Matte, J Tait The Urals D Brown, H Echtler Permian Basins A Henk, M J Timmerman Permian to Recent Evolution PA Ziegler The Alps O AP fiffner Mediterranean Tectonics Carminati, C Doglioni Holocent W Lemke, J HarffA EVOLUTION S Rigby, E MEharper 34 49 56 64 75 86 95 102 125 135 147 160

FFAKEFOSSILS D I Martill 169 174 179 184 188

FAMOUS GEOLOGISTS Agassiz D R Oldroyd Cuvier G Laurent Darwin D R Oldroyd Du Toit / C Loock, D F Branagan

Hall R H Dott, JrHutton D R Oldroyd Lyell D R Oldroyd Murchison D R Oldroyd Sedgwick D R Oldroyd Smith D R Oldroyd Steno / M Hansen Suess B Fritscher Walther I Seibold Wegener B Fritscher FLUID INCLUSIONS A H Rankin

194200 206 210 216 221 226 233 242 246 253

xxx

CONTENTS

FORENSIC GEOLOGY

K Pye

261 274 281 295 301 310 321 334 342 350 357 367 369 378 389 396 408 418 428 436 443 454 462 468 479 490 497 502 508 516 523 527 535 541

FOSSIL INVERTEBRATES Arthropods LI Anderson Trilobites A WA Rushton Insects E A Jarzembowski Brachiopods D AT Harper Bryozoans P D Taylor Corals and Other Cnidaria C T Scrutton Echinoderms (Other Than Echinoids) A B Smith Crinoids M / Simms Echinoids A B Smith Graptolites R B Richards Molluscs Overview N J Morris Bivalves E M Harper Gastropods / Fry da Cephalopods (Other Than Ammonites) P Doyle Ammonites G E G Westermann Porifera / K Rigby FOSSIL PLANTS Angiosperms P Kenrick Calcareous Algae / C Braga, R Riding Fungi and Lichens T N Taylor, M Krings Gymnosperms P Kenrick FOSSIL VERTEBRATES Jawless Fish-Like Vertebrates D K Elliott Fish / A Long Palaeozoic Non-Amniote Tetrapods / A Clack Reptiles Other Than Dinosaurs R R Reisz Dinosaurs A M Yates Birds G / Dyke, L M Chiappe Swimming Reptiles G W Storrs Flying Reptiles D Naish, D M Martill Mesozoic Amphibians and Other Non-Amniote Tetrapods Cenozoic Amphibians A R Milner Mesozoic Mammals Z-X Luo Placental Mammals D R Prothero Hominids L R M Cocks

A R Milner

Volume 3

GGAIA GJHMcCallC Oldershaw L Joyner M Cameron / E Gordon A K Turner

16 14 21 29 35

GEMSTONES

GEOARCHAEOLOGY

GEOCHEMICAL EXPLORATION GEOLOGICAL CONSERVATION GEOLOGICAL ENGINEERING

CONTENTS xxxi

GEOLOGICAL FIELD MAPPING GEOLOGICAL SOCIETIES GEOLOGICAL SURVEYS GEOLOGY OF BEER GEOLOGY OF WHISKY GEOMORPHOLOGY GEOMYTHOLOGY

P Canard A Maltman

43 53 60 65 73 78 82 85 90 96

GEOLOGICAL MAPS AND THEIR INTERPRETATION G L Merries Davies P M Allen G L Jones

GEOLOGY, THE PROFESSION S J Cribb

S J Cribb P H Rahn

GEOLOGY OF WINE / M Hancock 85 A Mayor

GEOPHYSICS See EARTH: Orbital Variation (Including Milankovitch Cycles); EARTH SYSTEM SCIENCE; ENGINEERING GEOLOGY: Seismology; MAGNETOSTRATIGRAPHY; MOHO DISCONTINUITY; PALAEOMAGNETISM; PETROLEUM GEOLOGY: Exploration; REMOTE SENSING: Active Sensors; CIS; Passive Sensors; SEISMIC SURVEYS; TECTONICS: Seismic Structure at Mid-Ocean Ridges GEOTECHNICAL ENGINEERING GEYSERS AND HOT SPRINGS GOLD MAMcKibben J J Veevers D P Giles G J H McCall 100 105 118 128 155

GLACIERS See SEDIMENTARY PROCESSES: Glaciers GONDWANALAND AND GONDWANA GRANITE See IGNEOUS ROCKS: Granite GRENVILLIAN OROGENY R P Tollo

HHERCYNIAN OROGENY See EUROPE: Variscan Orogeny HIMALAYAS See INDIAN SUBCONTINENT HISTORY OF GEOLOGY UP TO 1780 O Puche-Riart D R Oldroyd D R Oldroyd D F Branagan 167 173 179 185 197 HISTORY OF GEOLOGY FROM 1780 TO 1835 HISTORY OF GEOLOGY FROM 1835 TO 1900 HISTORY OF GEOLOGY FROM 1900 TO 1962 HISTORY OF GEOLOGY SINCE 1962I

U B Marvin

IGNEOUS PROCESSES IGNEOUS ROCKS Carbonatites K Bell Granite AIS KempDeceased

P D Asimow

209 217 233

xxxii

CONTENTS

Kimberlite Komatiite Obsidian

GJH McCall N TArndt, C M Lesher G / H McCall RAF Grieve A B Roy

247 260 267 277 285

IMPACT STRUCTURES INDIAN SUBCONTINENT

JJAPAN / Tazawa 297 JUPITER See SOLAR SYSTEM: Jupiter, Saturn and Their Moons

LLAGERSTTTEN S E Gabbott M F Coffin, O Eldholm 307 315 323

LARGE IGNEOUS PROVINCES LAVA N Geshi

MMAGNETOSTRATIGRAPHY S G Lucas D Suetsugu, T Kogiso, B Steinberger 331 335

MANTLE PLUMES AND HOT SPOTS MARS See SOLAR SYSTEM: Mars MERCURY See SOLAR SYSTEM: Mercury

MESOZOIC Triassic S G Lucas, M J Orchard Jurassic K N Page Cretaceous N MacLeod End Cretaceous Extinctions N MacLeod METAMORPHIC ROCKS Classification, Nomenclature and Formation Facies and Zones K Bucher PTt-Paths PJ O'Brien METEORITES See SOLAR SYSTEM: Meteorites MICROFOSSILS Acritarchs K J Doming Chitinozoa F Paris, J Verniers Conodonts R J Aldridge Foraminifera M A Kaminski Ostracoda D / Home Palynology P Coxon, G Clayton MICROPALAEONTOLOGICAL TECHNIQUES I J Slipper 470 MILANKOVITCH CYCLES See EARTH: Orbital Variation (Including Milankovitch Cycles) MILITARY GEOLOGY EPF Rose G R Davis G Hoinkes, C A Hauzenberger, R Schmid

344 352 360 372 386 402 409

418 428 440 448 453 464 470

475 488

MINERAL DEPOSITS AND THEIR GENESIS

CONTENTS xxxiii

MINERALS Definition and Classification E H Nickel 498 Amphiboles R A Howie Arsenates K Hudson-Edwards 506 Borates C Helvaci Carbonates B Jones Chromates PA Williams Feldspars R A Howie Feldspathoids M D Welch Glauconites J M Huggett 542 Micas R A Howie Molybdates P A Williams Native Elements P A Williams Nitrates PA Williams Olivines G Cressey, R A Howie Other Silicates R A Howie Phosphates See SEDIMENTARY ROCKS: Phosphates Pyroxenes R A Howie Quartz R A Howie Sulphates G Cressey Sulphides D J Vaughan Tungstates P A Williams Vanadates P A Williams Zeolites W S Wise Zircons G J H McCall MINING GEOLOGY Exploration Boreholes M Vanecek Exploration N C White Mineral Reserves M Vanecek Hydrothermal Ores M A McKibben Magmatic Ores / Mungall MOHO DISCONTINUITY P Giese

498 503 506 510 522 532 534 539542

548 551 553 555 557 561 567 569 572 574 586 588 591 601 609 613 623 628 637 645

MOON See SOLAR SYSTEM: Moon

Volume 4

NNEW ZEALAND N Mortimer NORTH AMERICA Precambrian Continental Nucleus W Bleeker Continental Interior D F Merriam Northern Cordillera J W H Monger, R A Price, W J Nokleberg 36 Southern Cordillera AWSnoke Ouachitas K C Nielsen Southern and Central Appalachians R D Hatcher, Jr Northern Appalachians C R van Staal Atlantic Margin D R Hutchinson1

8 21 36 48 61 72 81 92

xxxiv CONTENTS

oOCEANIA (INCLUDING FIJI, PNG AND SOLOMONS) I Smith, E Garaebiti, P Rodda ORIGIN OF LIFE / Bailey H Davies, P Bani, P Black, 109 123

pPALAEOCLIMATES PALAEOMAGNETISM PALAEONTOLOGY PALAEOPATHOLOGY B W Sellwood, P J Valdes T H Torsvik L R M Cocks S G Lucas 131 140 147 156 160 163 175 184 194 200 214 219 225 229 248 261268

PALAEOECOLOGY E M Harper, S Rigby

PALAEOZOIC Cambrian N C Hughes, N A Heim Ordovician R A Fortey Silurian L R M Cocks Devonian G R McGhee Carboniferous A C Scott Permian P B Wignall End Permian Extinctions RJ Twitchett PANGAEA S G Lucas PETROLEUM GEOLOGY Overview / Gluyas Chemical and Physical Properties C Clayton Gas Hydrates M Hovland The Petroleum System C Cornford 268 Exploration / R Parker Production KJ Weber, L C van Geuns Reserves R Arnott PLATE TECTONICS R C Searle PRECAMBRIAN Overview L R M Cocks Eukaryote Fossils S Xiao Prokaryote Fossils M D Brasier Vendian and Ediacaran MAS McMenamin 371 PSEUDOFOSSILS PYROCLASTICS D M Martill R J Brown, E S Calder

295 308 331 340 350 354 363371

382 386

QQUARRYING A W Hatheway 399

RREEFS See SEDIMENTARY ENVIRONMENTS: Reefs ("Build-Ups") REGIONAL METAMORPHISM A Feenstra, G Franz 407

CONTENTS xxxv

REMOTE SENSING Active Sensors G Wadge CIS P J Mason Passive Sensors / G Liu RIFT VALLEYS See AFRICA: Rift Valley ROCK MECHANICS JP Harrison R C Selley

414 420 431 440 452 456

ROCKS AND THEIR CLASSIFICATION RUSSIA A S Yakubchuk, A M Nikishin

sSATURN See SOLAR SYSTEM: Jupiter, Saturn and Their Moons SEAMOUNTS S M White 475 485 492 495 501 513 528 539 550 562 570 580 587 593 602 612 628 641 650 663 678 687

SEDIMENTARY ENVIRONMENTS Depositional Systems and Fades J Collinson Alluvial Fans, Alluvial Sediments and Settings K D Jger Anoxic Environments P B Wignall Carbonate Shorelines and Shelves D W J Bosence Contourites M Rebesco Deltas T Elliott Deserts N P Mountney Lake Processes and Deposits M R Talbot Reefs ('Build-Ups') B W Sellwood Shoreline and Shoreface Deposits J How ell Storms and Storm Deposits P Myrow SEDIMENTARY PROCESSES Erosional Sedimentary Structures J Collinson Depositional Sedimentary Structures / Collinson Post-Depositional Sedimentary Structures / Collinson Aeolian Processes N Lancaster Catastrophic Floods A J Russell Deep Water Processes and Deposits D J W Piper Fluvial Geomorphology / Lewin, P A Brewer Glaciers M / Hambrey, N F Glasser Karst and Palaeokarst M J Simms Landslides S F Burns

Volume 5SEDIMENTARY PROCESSES Particle-Driven Subaqueous Gravity Processes M Felix, W McCaffrey 1 Deposition from Suspension IN McCave Fluxes and Budgets L Frostick SEDIMENTARY ROCKS Mineralogy and Classification R C Selley Banded Iron Formations A Trendall Chalk / R Ineson, L Stemmerik, F Surlyk Chert N H Trewin, S R Payers

1 8 17 25 37 42 51

xxxvi CONTENTS

Clays and Their Diagenesis / M Huggett Deep Ocean Pelagic Oozes R G Rothwell Dolomites H G Machel Evaporites A C Kendall Ironstones W E G Taylor Limestones R C Selley Oceanic Manganese Deposits D S Cronan Phosphates W D Birch Rudaceous Rocks / McManus Sandstones, Diagenesis and Porosity Evolution SEISMIC SURVEYS M Bacon

J

Gluyas

62 70 79 94 97 107 113 120 129 141151

SEQUENCE STRATIGRAPHY SHIELDS K C Condie

P P Mclaughlin, Jr

159 173 179 184 194 203 209 220 228 238 244 264 272 282 289 295

SHOCK METAMORPHISM P S DeCarli SOIL MECHANICS / Atkinson SOILS Modern Palaeosols G J Retallack G J Retallack

SOLAR SYSTEM The Sun K R Lang Asteroids, Comets and Space Dust P Moore Meteorites G J H McCall Mercury G J H McCall Venus M A Ivanov, J W Head Moon P Moore Mars M R Walter, A J Brown, S A Chamberlain Jupiter, Saturn and Their Moons P Moore Neptune, Pluto and Uranus P Moore SPACE DUST See SOLAR SYSTEM: Asteroids, Comets and Space Dust STRATIGRAPHICAL PRINCIPLES N MacLeod

STROMATOLITES See BIOSEDIMENTS AND BIOFILMS SUN See SOLAR SYSTEM: The Sun

TTECTONICS Convergent Plate Boundaries and Accretionary Wedges G K Westbrook Earthquakes G J H McCall Faults S Stein Folding / W Cosgrove Fractures (Including Joints) / W Cosgrove Hydrothermal Activity R P Lowell, P A Rona Mid-Ocean Ridges K C Macdonald Hydrothermal Vents At Mid-Ocean Ridges R M Haymon Propagating Rifts and Microplates At Mid-Ocean Ridges R N Hey Seismic Structure At Mid-Ocean Ridges S M Carbotte Mountain Building and Orogeny M Searle Neotectonics I Stewart 307 318 330 339 352 362 372 388 396 405 417 425

CONTENTS xxxvii

Ocean Trenches R J Stern Rift Valleys L Frostick TEKTITES G J H McCall L R M Cocks TERRANES OVERVIEW

428 437 443 455459

TERTIARY TO PRESENT Paleocene J J Hooker 459 Eocene / / Hooker Oligocene D R Prothero Miocene J M Theodor 478 Pliocene C Soligo Pleistocene and The Ice Age THERMAL METAMORPHISM TIME SCALE TRACE FOSSILS

466 472478

A Currant R Abart, R Milke

486 493 499 503 520

F M Gradstein, J G Ogg P J Orr

uULTRA HIGH PRESSURE METAMORPHISM H-J Massonne 533 UNCONFORMITIES A R Wyatt / Best 533 541 548 557

UNIDIRECTIONAL AQUEOUS FLOW URALS See EUROPE: The Urals URBAN GEOLOGY A W Hatheway 557

VVENUS See SOLAR SYSTEM: Venus VOLCANOES G J H McCall 565

WWEATHERING W B Whalley, P A Warke 5 81

Index

591

SEDIMENTARY PROCESSES/Particle-Driven Subaqueous Gravity Processes 1

Particle-Driven Subaqueous Gravity ProcessesM Felix and W McCaffrey, University of Leeds, Leeds, UK 2005, Elsevier Ltd. All Rights Reserved.

IntroductionParticulate subaqueous gravity flows are sedimentwater mixtures that move as a result of gravity acting on the sediment-induced density excess compared with the ambient water. The mixtures can range from densely-packed sediment flows, that are essentially submarine landslides, to very dilute flows carrying only a few kg m3 of sediment. Gravity flow can take place in lakes and oceans, but some dense flows also occur in rivers. Sediment volumes transported by individual events can range up to thousands of cubic kilometres, although most events are of much smaller magnitude. Due to their infrequent occurrence and destructive nature, much information about subaqueous gravity processes comes from the study of their deposits and from laboratory experiments. Flow initiation mechanisms, sediment transport mechanisms, and flow types are described here separately, to emphasise the sense of process continuum needed to appreciate the development of most natural subaqueous gravity flows. This is followed by a description of internal and external influences on flow behaviour. Finally, the influence of flow regime on individual deposits is outlined.

river outflow is less than that of the ocean, and turbid surface plumes are generated. Nevertheless, particulate gravity flows can also form from surface plumes if material settling out collects near the bed at high enough concentrations to begin moving. A similar effect results from flow generated by glacial plumes where the sediment is slowly released into the water body. Where the interstitial fluid in a hyperpycnal plume is of lower density than that of the ambient fluid, as is the case when freshwater rivers flow into brackish or fully saline bodies of water, ongoing sedimentation may induce buoyancy reversal. Thus, the gravity current will loft, in a manner similar to some subaerial pyroclastic density flows, and the flow will essentially cease to travel forwards, resulting in the development of abrupt deposit margins.Sediment Resuspension

Loose sediment on the seafloor can be resuspended if bed shear stress is high enough. This can occur during storms or during passage of flows caused by density differences as a result of temperature or salinity. The resulting suspended sediment concentrations can be high enough to allow the mixtures to flow under the influence of gravity. As in the case of river-derived flows, resuspension usually generates initially dilute currents.Slope Failure

Flow Initiation MechanismsA variety of processes can generate subaqueous gravity currents, with varying initial concentrations.Direct Formation From Rivers

Currents can be formed when turbid river water flows into bodies of standing water such as lakes or oceans. If the bulk density of the turbid river water (sediment plus interstitial fluid) is higher than that of the receiving body of water, the river outflow will plunge, travelling along the bed as a hyperpycnal flow (or plume) beneath the ambient water. Such sediment-laden underflows may mix with the ambient water and transport sediment oceanward as particulate gravity currents. Although sometimes these river-derived flows are of high concentration (e.g., the Yellow River hyperpycnal plume), mostly they are dilute. Direct formation of subaqueous gravity currents in this way is, however, the exception rather than the rule. More commonly, the bulk density of the turbid

Flows of much higher concentration may form as a result of slope failure. Sediment on submarine slopes can become unstable as a result of slope oversteepening during ongoing sedimentation, and during sealevel falls, as a result of high inherited pore fluid pressures and gas hydrate exsolution. Slope failure can alternatively be triggered by externally applied stresses, due to earthquakes, or as a result of loading induced by internal waves in the water column above (which chiefly occur in oceans). Initially, the failing mass becomes unstable along a plane of instability and a whole segment of the slope starts moving. Retrogressive failure and/or breaching can continue, adding material following the initial loss of stability. The concentration of this mass is at packing density but can become more dilute as flow continues.Terrestrial Input

Not all subaqueous gravity flows need originate under water. Landslides, pyroclastic flows, and aeolian sediment transport originating on land can enter

2 SEDIMENTARY PROCESSES/Particle-Driven Subaqueous Gravity Processes

lakes or oceans and continue flowing underwater if the rates of mass flux are sufficiently high.

Flow TypesBroadly speaking, flows can be divided into three main types, depending on density:Dense, Relatively Undeformed Flows, Creeps, Slides and Slumps

Grain Transport MechanismsMatrix Strength and Particle-Particle Interactions

Within dense flows, grains can be prevented from settling as a result of matrix strength (Figure 1). This strength may arise if some or all of the particles are cohesive. The resulting cohesive matrix prevents both cohesive and non-cohesive particles from settling out. In addition, particles can be supported by matrix strength within flows of non-cohesive grains if the particles are in semi-permanent contact, as is the case for flows whose densities are close to that of static, loose-packed sediment. For slightly lower concentrations, inter-particle collisions will help keep particles in suspension.Hindered Settling and Buoyancy

Settling of particles can be slowed down by water displaced upwards by other settling particles (Figure 1). Such hindered settling is especially effective in dense mixtures with a range of grain sizes so that the smaller particles are slowed down by settling of the larger particles. The presence of smaller particles also increases the effective density of the fluid that the particles are settling in and thus enhances the buoyancy of the suspended particles and reduces settling rates.Turbulence

Flows of this type essentially have the same density as the pre-failure material. In each case the sediment moves as one large coherent mass, but with varying amounts of internal deformation. Grains remain in contact during flow and thus matrix strength is the main sediment transport mechanism. Such flows will stop moving or shear stress becomes too low to overcome friction, at which point the entire mass comes to rest. Flow thickness and deposit thickness are essentially the same, although flows may thicken via internal thrusting or ductile deformation as they decelerate prior to arrest. Slope creep caused by gravity moves beds slowly downslope with gentle internal deformation of the original depositional structure. Slides undergo little or no pervasive internal deformation, while slumps undergo partial deformation but the original internal structure is still recognisable in separate blocks. Thicknesses of slides and slumps range from several tens of metres to 12 km and travel distances can be up to about 100 km, with displaced volumes of up to 1012 m3, although most flows are considerably smaller.Dense, Deformed Flows: Rockfalls, Grain flows, Debris Flows and Mudflows

The motion of sediment-laden flows can generate turbulence through shear at the bed, internally in the flow or at the top of a dense layer. The turbulent bursts generated at the bed tend to have an asymmetrical vertical velocity structure, with slower downward sweeps and more rapid upward bursts. This turbulence pattern counteracts the downwards settling of particles, moving them higher up in the flow (Figure 1). Turbulence generation is hindered and dissipation increased, however, if the particle concentration is high, or if the flow is very cohesive or highly stratified.

In flows of this type, sediment still moves as one coherent mass, but concentrations can be lower and the mass is generally well mixed, with little or no preservation of remnant structure from the original failed material. Sediment support mechanisms are matrix strength, buoyancy, hindered settling, and grain-grain collisions. Rheologically such flows are plastic (i.e., they have a yield strength). Clast types generally range from purely cohesive in mudflows, to cohesive and/or non-cohesive in debris flows (Figure 2) and purely non-cohesive for grain flows and rockfalls (where movement is by freefall on very steep slopes). These types of flow are formed as a

Figure 1 Schematic illustration of the principal grain transport mechanisms, shown in decreasing order of concentration from left to right.


Figure 2 A laboratory debris flow from right to left. Note: a dilute turbidity current has been generated on the upper surface of the debris flow due to erosion of material by fluid shear. (After Mohrig et al. (1998) GSA Bulletin 110: 387 394.)

Figure 3 A laboratory turbidity current flow from right to left. Field of view is 55 cm wide. (After McCaffrey et al. (2003) Marine and Petroleum Geology 20: 851 860, with permission from Elsevier.)

result of rapid internal deformation following slope failure, from high concentration river input or from reconcentration of dilute flows (described below). Flow and deposit thicknesses can be up to several tens of metres with travel distances of several hundreds of kilometres. Erosion can add material to the flow and thus extend both travel distances and size of deposit neither of which, therefore, necessarily relate to the initial flow mass. Motion will stop once friction is too high and flows will generally deposit en masse. Debris flows may develop a rigid plug of material at the top of the flow, where the applied stress falls below the yield strength. Such flows move along a basal zone of deformation, and may progressively freeze from the top downwards, ultimately coming to rest when the freezing interface reaches the substrate.(Partly) Dilute Flows: Turbidity Currents

to turbulent entrainment of ambient water. Velocities can be up to tens of m s, but more commonly are around 1 m s or less. Larger flows, such as the welldocumented Grand Banks event of 1929, may travel distances of a few thousand kilometres, even on nearly flat slopes, although distances of tens to hundreds of kilometres are more common. Sediment eroded during flow can add to the driving force and will increase flow duration and travel distance. Flows will gradually slow down as sediment settles out, with coarse material being deposited proximally and fine material distally. Deposit thicknesses generally are significantly smaller than flow thickness and are on the order of cm to dm, but can be up to multi-metre scale for large flows. However, ongoing sedimentation from flows of long duration can result in deposits whose thickness relates principally to flow longevity rather than flow thickness. Consequently, it is generally more difficult to interpret flow properties from analysis of turbidity current deposits (turbidites) than it is for the denser flow types.Flow Transformations

In flows of this type, the sediment does not move as one coherent mass (Figure 3). These flows are generally dilute although parts of these flows can be of high concentration, especially near the bed. In the dilute parts of these flows, sediment is transported in either laminar or turbulent suspension. In higher concentration areas additional sediment transport mechanisms, such as grain-grain interactions, hindered settling, and buoyancy effects may also play a role. Rheologically, the dense parts of such flows can behave plastically, but the dilute parts are Newtonian. Concentrations in turbidity currents range from only a few kg m3 to concentrations approaching those of static, loose-packed sediment. The dilute parts of these flows are commonly strongly vertically densitystratified. Turbidity currents can be formed via dilution of debris flows (see below), directly from river input or from resuspension of sediment. Turbidity current thicknesses can be up to several hundreds of metres and can increase during flow due

Transformations of one flow type into another are common. Initially-dense slide masses may be disrupted due to internal shear, liquefaction, and disaggregation on various scales. If this deformation is sufficiently vigorous all the original structure of the failed material will be lost and the slides transformed into debris flows. In turn, these can transform into turbidity currents by erosion of sediment from the front and top of the dense mass due to ambient fluid shear (Figure 2), by disaggregation and dilution, and by deposition of sediment, diluting the flow. Turbidity currents can be transformed into debris flows if they reconcentrate, for example when mud-rich flows slow down. Further transformation into slides is not possible once the original internal structure is broken up. The extent of transformation depends on flow size, velocity, and sediment content. Variable degrees of


transformation can lead to the development of different flow types within one current, both vertically and from front to back. This co-occurrence of different flow types is especially common in flows with a dense basal layer and more dilute upper part. Thus, classification schemes which subdivide flows on the basis of discrete flow types do not recognise the diversity of natural flows, in which different types of flow may occur simultaneously and vary in relative importance in time and space as the flows evolve.

flow to keep sediment in suspension, known as the flow efficiency, directly affects flow run-out lengths. Flow efficiency depends on flow magnitude, with larger flows being more efficient, and on grain size, as finer grains settle out more slowly than coarser grains. The presence of fine sediment in the flow also increases the ability to carry coarse sediment so both types of sediment will be carried further and both flow duration and run-out length will be increased.Spatial and Temporal Changes to Flow

Internal and External Influences on Flow BehaviourFlow behaviour is influenced both by internal factors such as concentration and grain size distribution and external factors such as input conditions and topography.Flow Velocity

The driving force, and hence velocity of subaqueous gravity currents increases with both concentration and flow size. However, resistance to internal shear will increase with increasing viscosity due to increasing particle concentrations, and with increasing yield strength caused by cohesive particles. This will inhibit the increase of flow velocities. However, because concentration-induced resistance to shear does not scale with flow size, it can more readily be overcome by the higher gravitational driving forces of larger flows, which are, therefore, faster than smaller flows.Flow Duration and Run-Out Length

Slope failure-induced slumps and slides that do not transform into debris flows and/or turbidity currents will generally be of short duration and have run-out lengths on the order of the initial failure size. If the failed sediment mass does transform into a debris flow, the duration and run-out length depend on the mobility as described above, with larger flows travelling further. However, because debris flows stretch out as they are flowing and because they may incorporate material by erosion, their run-out length may not be directly related to the initial failure size. The duration and run-out length of turbidity currents depend on their size and sediment content, and hence also on their formation mechanism. Sustained input from rivers or glacial plumes can result in long duration flows, even if the input concentration is low. Turbidity currents that are generated from slope failures can have a short duration input, but tend to stretch considerably due to turbulent mixing and will thus increase in flow duration provided the transported sediment is kept in suspension. The ability of a

Flows are influenced both by the input conditions and by the terrain over which flow takes place. Flow behaviour therefore varies both temporally and spatially, causing local areas of erosion and deposition that lead to a deviation from a simple decelerating depositing flow and complicate the depositional pattern. Both spatial and temporal changes in flow behaviour can be caused by changes in sediment content of the flow: erosion adds driving force to the flow and increases velocity, while deposition slows flows down. Temporal changes to flow can also be caused by changing input conditions. River input from floods leads to flows that initially have a progressive increase in velocity followed by a long period of decreasing velocity. In retrogressive failure ongoing detachment of discrete sediment masses will result in pulsed sediment input; the rate of input generally tends to peak rapidly, and then diminish as successive slope failures reduce in size. Local spatial changes in flow are caused by changes in the topography (Figure 4). The angle of the slope on which flow takes place is obviously important for gravity driven flows; when slope angle increases, the flow will go faster although the velocity increase will be diminished by the increase of friction with the ambient water. Nevertheless, small changes in slope angle can change flow behaviour. If the slope angle decreases, very dense flows can be stopped as the basal friction becomes too high. More dilute flows may undergo hydraulic jumps, in which they abruptly thicken and decelerate. This deceleration can cause coarser sediment to be deposited. Local changes to flow can also be caused by changes in the constriction of the flow path. When a flow goes into a constriction, velocity will increase. Where a flow can expand, as at the end of submarine canyons, velocity will decrease.Momentum Loss

The evolution of flow behaviour can be different along flow-parallel and flow-transverse directions. Momentum will be greater in the direction of flow


than in the transverse direction. For coarse sediment in dilute flows, this means transport is principally in the main flow direction as rapid transverse momentum loss results in rapid deposition. This is less the case for fine-grained sediment, which will stay in suspension more easily and will thus generate momentum for flow in the transverse direction. These differences are not so important in restricted parts of the flow path, such as in canyons, but are important in less confined settings.Channelised flow

Figure 4 Schematic illustration of the interaction of turbidity currents with (A) high amplitude and (B) low amplitude bathym etry. Flows are uniform if the velocity does not change with distance and are non uniform if the velocity does change. Accu mulative flows have spatially increasing velocity while depletive flows have decreasing velocity. (After Kneller and McCaffrey (1995) SEPM, Gulf Coast Section, 137 145.) Published with the permission of the GCSSEPM Foundation; Further copying re quires permission of the GCSSEPM Foundation.

If flows are erosive they can create conduits (incisional channels) both for themselves and for later flows. In aggradational systems, dense flows such as debris flows will start to form levees at their edges where flow becomes too thin to overcome the matrix strength. Sideway expansion of coarser-grained turbidity currents may lead to loss of momentum in the transverse direction, and thus greater rates of offaxis than on-axis deposition. This incipient levee formation may lead to the development of aggradational channels (Figure 5). These channels, which are generally sinuous, and often meandering, partly confine flow and can carry sediment downstream for long distances. Dilute parts of the flow can overtop the levee crests resulting in overspill and deposition of thin sheets of relatively fine-grained sediment that decrease in thickness away from the channel. This winnowing process causes the flows progressively to become relatively depleted in fine grained material, resulting in the development of sandy lobe deposits at the end of relatively muddy channel-levee systems. Levee height decreases downstream and flows become less confined. Like subaerial channels,

Figure 5 GLORIA image of sinuous submarine channels on the Indus fan. (From Kenyon et al. (1995). In: Pickering et al. Atlas of Deepwater Environments: architectural style in turbidite systems: London: Chapman and Hall, 89 93.)


aggradational submarine channels may undergo avulsion, resulting in the formation of internally-complex sedimentary fan deposits. Although channels are largely formed by the flows themselves, they can be influenced by pre-existing topography.Flow in Unconfined Basins

Flow Regime Recorded in Depositional SequencesErosion and Bypass

When the basin size is very large compared to the flow, the flows are effectively unconfined. Flows that are not strong enough to erode and that are not captured by antecedent channels can start to spread out. Fine-grained, efficient turbidity currents spread out more evenly in all directions than their coarsergrained counterparts as a result of differing rates of momentum loss. Such unconfined flows can be influenced by Coriolis forces, being deflected to the right in the northern hemisphere, and to the left in the southern hemisphere. Unconfined flows deposit sediment in lobes, with deposit thicknesses decreasing in all directions away from the depocentre. Development of depositional topography may cause subsequent flows to be steered away from depocentres of previous flows and to deposit relatively more of their sediment load in offset positions in a process of autocyclic compensation. Deep-sea fan systems can form in unconfined basins settings through this process.Flow in Confined Basins

If flow power is large enough, erosion can take place, which can remove significant volumes of sediment. This material adds to the driving force of the flow and can lead to acceleration (a process called ignition), and increased flow duration and travel distance. Smaller-scale erosion can form structures that indicate palaeoflow direction, including grooves, where an object is dragged along the bed, and flutes, where turbulent motions erode a characteristic shape that is deeper upstream, and both flares and shallows downstream. Erosion can take place beneath both debris flows and turbidity currents, although flutes require turbulence for their formation, a condition more likely to be met in turbidity currents. Not all flows are capable of erosion, but this does not necessarily mean they deposit their transported load. Bypass of sediment is common in upstream areas and may leave no record in the deposit. This behaviour is closely related to the process of autosuspension, in which sediment is transported by turbulence generated by flow caused by the density difference due to the sediment itself. Strictly speaking, such flows neither erode nor deposit.Deposition

When the basin size is smaller than or of the same size as the flow, the basin margins will prevent flow from expanding and the basin is said to be confined. Processes of topographic interaction induce spatial changes to flow, as detailed above. Flows can overcome small topographic obstacles, but as obstacle height increases relative to the flow height, part or all of the flow will be diverted. Flows in confined basins can be reflected back and forth between different basin margins if enough energy is available, which can result in reworking of the part of the deposit laid down during a previous pass of the flow. If the basin walls are sufficiently high to prevent any of the flow escaping, the basin is said to be ponded. In this case all the sediment is retained in the basin, and any mud present in the flow will be distributed in suspension evenly across the basin and will slowly settle out. The spatial restriction created by confined or ponded basins will hinder flow expansion. Thus, although autocyclic processes can play a role in dictating sedimentary architecture, in general basin fill patterns will be dominated by the confinement. Successive deposits can gradually fill up a basin completely. This can result in flows being able to partially bypass the basin, and enter the next basin downstream, in a process known as fill-and-spill.

Eventually all flows, whether they start out as dense or as dilute flows, will lose their momentum and deposit their sediment. Dense flows such as slumps and debris flows will leave deposits whose structure more or less corresponds to that of the flows themselves. This is not the case for turbidity currents, which generally deposit their sediment progressively. Whether deposition takes place at all in turbidity currents depends on local flow competence and capacity. Flow competence indicates which grain sizes can be transported by a flow of a given velocity and flow capacity indicates how much sediment can be carried by a flow of a given velocity. The depositional structures of turbidity current deposits (turbidites) are influenced by the grain sizes carried in the flow, the velocity of the flow, and the sediment fallout rate. High sediment fall-out rates cause suppression of primary sedimentary structures and lead to the formation of massive (structureless) deposits. The grains in these deposits tend not to be packed at maximum density and commonly re-organise themselves post-depositionally, expelling pore water in the process. This process commonly produces structures that overprint any primary depositional fabric. If fallout rate is low enough, structures such as ripples and


laminations can be formed, depending on grain size and flow regime. Deposit thickness is influenced both by flow size, with larger flows resulting in thicker deposits, and also by flow duration, with sustained flows being able to deposit thick beds, even if the flows themselves are not particularly large. Various models have been proposed to describe the vertical succession of features in an idealised turbidite. The most widely applied is the model of Bouma, which describes a sequence deposited by a gradually decelerating turbidity current. Because all flows must eventually wane, full or (more commonly) partial Bouma sequences are developed quite frequently, particularly in relatively distal locations. However, the assumption that flows gradually decelerate over the entire flowpath is unlikely to be met, and many deposits will not look like this or other standard sequences. The influence of temporal changes and spatial changes on deposits will be reflected in terms of bed thickness and grain size distribution (grading). These are schematically presented in the diagram of Kneller for turbidity current deposits (Figure 6). This scheme is strictly valid only for flow where

concentration does not change, which limits the applicability of the approach, but it illustrates the idea well. Finally, it should be borne in mind that depositional sequences may be reworked by surface currents, dewatering, and/or bioturbation. These processes may obscure any evidence of flow character that was originally recorded in the deposit.

SummarySubaqueous particulate gravity currents may exhibit a wide range of concentrations, magnitudes, grain size, and type and flow velocities, all of which may change as flow develops. Flow behaviour is dictated both by input conditions (affecting flow magnitude, grain size distribution, and duration), and by the flow pathway (including its bathymetry, and the erodibility of the substrate). Thus, subaqueous particulate gravity currents form a complex and variable range of flow types, which together constitute the principal means by which coarser-grained clastic material is transported into the deep ocean.

Further ReadingAllen PA (1997) Earth surface processes. Blackwell Science, Oxford. Hampton MA, Lee HJ, and Locat J (1996) Submarine landslides. Reviews of Geophysics 34(1): 33 59. Kneller BC (1995) Characters of Deep Marine Clastic Systems. Geological Society Special Publication 94. Kuenen Ph H (1950) Turbidity currents of high density. 8th International Geological Congress, London 8: 44 52. Kuenen Ph H (1952) Estimated size of the Grand Banks turbidity current. American Journal of Science 250(12): 874 884. McCaffrey WD, Kneller BC, and Peakall J (eds.) (2001) Particulate Gravity Currents IAS Special Publication 31: 302. Schwarz HU (1982) Subaqueous slope failures experi ments and modern occurrences. Contributions to Sedimentology 11: 116. Simpson JE (1997) Gravity currents in the environment and the laboratory, 2nd edn. Cambridge: Cambridge Univer sity Press. Stow DAV, Reading HG, and Collinson JD (1996) Deep seas. In: Reading HE (ed.) Sedimentary environments: processes, facies and stratigraphy, 3rd ed., chapter 10, pp. 395 453. Blackwell Science, Oxford. Walker RG (1992) Turbidites and Deep Sea Fans. In: Walker RG and James NP (eds.) Facies Models, 3rd edition, ch.13, pp. 239 263, Geol. Soc. Canada, St Johns Canada.

Figure 6 Schematic representation of vertical and lateral grain size variation within single beds as a function of the combined effects of flow steadiness and uniformity. The two logs in each field represent relatively proximal and distal configurations, re spectively (arrow indicates flow direction). Flows are steady if velocity does not change with time and are unsteady if the vel ocity does change with time. Waxing flows have temporally in creasing velocity while waning flows have decreasing velocity. Non uniformity definitions are given in Figure 4. (After Kneller and McCaffrey (1995) SEPM, Gulf Coast Section, 137 145.) Pub lished with the permission of the GCSSEPM Foundation; Further copying requires permission of the GCSSEPM Foundation.

8 SEDIMENTARY PROCESSES/Deposition from Suspension

Deposition from SuspensionI N McCave, University of Cambridge, Cambridge, UK 2005, Elsevier Ltd. All Rights Reserved.

IntroductionGeological treatments of sediment dynamics generally lose sight of the fact that the last event of dynamic importance that happened to the sediment was that it was deposited. Instead, most accounts concentrate on the process of transport. Of course, a fair amount of work deals with the creation of bedforms, many of which are depositional, but occur in the transport regime of steady flow, as well as in the unsteady regime of flow deceleration which leads to deposition. It is not possible to deal sensibly with the topic of deposition from suspension without some mention of how material is transported, and so this article deals briefly with this aspect after giving an outline of the controlling factors and before describing the processes of deposition. Almost any material, even boulders, can be transported in an aqueous turbulent suspension if the flow is large and sufficiently rapid. Even gravels were in suspension in the flood following the bursting of the glacial Lake Missoula in western Washington State (USA). However, most material deposited from suspension is mud and fine sand. Indeed, most (>50%) of the sedimentary geological record is of silt and finer sizes (200 m per day, which means that they reach the bottom quickly, resulting in significant clearing of the water in a 10 m deep estuary in a slack-tide period of 2 h.Boundary Layer Turbulence

Figure 2 Flocculation factor F (ratio of floc settling velocity to settling velocity of the primary particles from which it is made) vs. diameter of the primary particles. It should be noted that F is negligible in flowing water for d50 > 10 mm. Data from Migniot C (1968) Etude des proprietes physiques de differents sediments tres fins et de leur comportement sous des actions hydrodynamiques. La Houille Blanche 7: 591 620 and Dixit JG (1982) Resuspension Potential of Deposited Kaolinite Beds, MS thesis, U. of Florida, Gainesville.

frontier of research in cohesive sediment dynamics. The importance of aggregation is shown in Figure 2, where the flocculation factor, the ratio of the settling velocity of an aggregate to the settling velocity of the primary particles from which it is made, can be up to 105. Aggregates are not stable entities. The organic membrane covering faecal pellets decays and the mucus that holds aggregates together also degrades, and so particles fall apart whilst sinking. Aggregates assembled by moderate levels of turbulence in the outer part of the boundary layer may be broken up by more energetic turbulent eddies close to the boundary. The relationship between aggregate size and boundary shear stress is very poorly known and, if the floc diameter df / t n, then n ranges from 0.25 to 1 (t is the shear stress in the fluid). The larger aggregates, which can be up to 5 mm in diameter, are thus found in the moderately turbulent, highconcentration environment of the estuarine turbidity maximum above the region within a metre of the bed. Closer to the bed, high shear breaks these

A fluid flowing over a surface exerts a drag force on it. The drag at the boundary slows the fluid down, but some distance out, known as the boundary layer thickness, the average flow speed no longer changes much with distance. Most rivers are completely boundary layer as are shallow marine tidal flows. In the atmosphere and deep sea, the boundary layer extends several tens of metres above the surface. Boundary layers are intensely turbulent, and the drag force t0 exerted on the bed is related to that intensity because the stress is transmitted by eddies. In the vertical plane, t0 ruw, where u is the turbulent component in the flow direction and w is the up and down component (actually perpendicular to stream lines which may not be quite vertical). This expression is very important because u and w are related, so that t0 / w2. This vertical turbulent velocity is responsible for keeping particles in suspension, and the turbulent stress uw either causes aggregation or, at higher values, disaggregates fine particles. The term (t0/r) has the dimensions of a velocity squared and that velocity is called the shear or friction velocity: U* (t0/r)1/2. From the above, it can be seen that U* / w.Regions of the Boundary Layer

Flows may be distinguished as laminar or turbulent on the basis of their Reynolds number, Ul/n, where l is some relevant length scale (e.g., depth of a river, diameter of a particle) (see Unidirectional Aqueous Flow). Low Reynolds number flows are laminar, high Reynolds number flows are turbulent. In a turbulent flow, the speed decreases towards the bed because of the drag, so that very close to the bed the flow becomes laminar, or at least dominated by viscosity, in a layer known as the viscous sublayer of the turbulent boundary layer. This is very thin. In water, for a flow that just moves very fine sand (U* 0.01 m s 1, n 10 6 m2 s 1), dv 10n/U* is just 1 mm thick. (In

SEDIMENTARY PROCESSES/Deposition from Suspension 11

Figure 3 Regions of the turbulent boundary layer for a flow 1 10 m deep. In the centre, the linear representation of flow speed vs. height cannot resolve the viscous sublayer, but the speed vs. log height (z, expressed as a Reynolds number) shows it very well.

air, for the same stress, its thickness is similar, about 0.5 mm.) However, this is ten times the diameter of very fine sand. The shear across this layer is very large; for U* 0.01 m s 1, the speed goes from 0 to 0.1 m s 1 in just 1 mm. Weak aggregates cannot survive this shear and break up. Above this sublayer, there is a transition (buffer layer) to a region in which the flow speed varies as the logarithm of height above the bed (Figure 3). As the flow speed decreases, U* decreases and dv increases, so that, in deposition, most particles that are going to become part of the geological record have to get through the viscousdominated layer. Although viscous dominated, this layer is actually not laminar. Spatially, it has a structure of high- and low-speed streaks, and temporally very high-speed bursts of fluid out of the layer and sweeps of fluid into it from outside. These are associated with stresses typically up to 10 times the average (and extremes of 30 times), and so the mean shear example given above is a minimum, and even strongly bound particles may find themselves ripped apart just as they were getting within sight of the bed and posterity. Above the viscous sublayer, the buffer layer is overlain by a zone in which the flow speed varies as the logarithm of distance from the bed (the log layer). This zone is fully turbulent with eddies becoming longer with height above the bed and turbulence intensity becoming smaller. The roughness of the bed positively influences the drag and turbulence, but also provides quiet regions in between large grains where fine particles can settle. Fine sediment can thus be deposited in the interstices of gravel, affecting several processes, e.g., the spawning of salmon.

turbulent intensity can hold particles up, and so suspension depends on whether the particles are ejected from the viscous sublayer; and (2) sublayer ejections are fast, and so suspension depends on whether the vertical turbulent velocity can hold the particles up after injection into the flow. The second view was held by many, but recent work suggests that the first view may be correct. This view is based on high-speed video observations of particles close to the bed, which show that there is a threshold level of shear stress for the particles to respond to turbulent ejections of fluid from the viscous sublayer. The second view would mean that fine to very fine sand would immediately go into suspension as soon as it moved. For example, for 100 mm sand, the critical erosion shear velocity U* is 0.012 m s 1, and the settling velocity of this very fine sand is 0.008 m s 1, and so it is capable of being held up by the flow, but video data show that it is not suspended. This means that there is a region of bedload transport for all particles of settling velocity, at least down to $30 mm silt. This is shown on a conventional nondimensional erosion diagram in Figure 4. The significance of this is that, in a decelerating flow, below the suspension threshold, material may continue to move, but not in suspension. Experimentally it has usually been found easier to determine the critical suspension condition with increasing flow, rather than failure of suspension on decreasing flow. It is generally assumed that the two views are equivalent.

Transport in SuspensionOnce material is moved out of the near-bed region, it is held in suspension by the action of fluid turbulence. For this, because the vertical turbulent component of velocity is about the same as the shear velocity U*, the normal suspension criterion is that ws/U* 1.

Critical Conditions for SuspensionTwo views of the critical suspension condition are as follows: (1) at critical movement conditions, the

12 SEDIMENTARY PROCESSES/Deposition from Suspension

Figure 4 A critical erosion diagram on non dimensional axes with a critical suspension line added. This divides the diagram into regions of suspension, bedload, and no movement. Below the suspension threshold, material falls out and, as the capacity of a flow to carry bedload is limited, deposition will ensue. Two suspension lines are shown, suspension threshold results from view (1), while Bagnold expresses view (2); see text y t0/Drsgd, X Drsgd 3/rn2.

Particles in steady transport diffuse up from the source at the bed and sink back down under gravity with a balance in steady state. This is expressed as Cws es dC=dz 0 where the first term is gravity settling and the second is upward diffusion (es is the sediment diffusivity). The result of this is that, for a given value of U*, the faster settling grains are found closer to the bed and the finer slower settling particles are more uniformly distributed over the flow depth (Figure 5). In the bottom of a deep flow, the concentration at height z in the flow is Cz Ca(a/z)z, where Ca is the concentration at height a (the point n

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