Sedimentary Rocksin the Field

FOURTH EDITION

The Geological Field Guide Series

Barnes, J.W. and Lisle, R.J. (2004) Basic Geological Mapping ,4th edn. ISBN: 978-0-470-84986-6, 5th edn publishing (2011).ISBN: 978-0-470-68634-8

Fry, N. (1991) The Field Description of Metamorphic Rocks .ISBN: 978-0-471-93221-5

McClay, K.R. (1991) The Mapping of Geological Structures .ISBN: 978-0-471-93243-7

Milsom, J. and Eriksen, A. (2010) Field Geophysics , 4th edn.ISBN: 978-0-470-74984-5

Tucker, M.E. (2011) Sedimentary Rocks in the Field , 4th edn.ISBN: 978-0-470-68916-5

Sedimentary Rocksin the Field:

A Practical GuideFOURTH EDITION

Maurice E. TuckerDepartment of Earth Sciences

Durham University

Durham DH1 3LE

England

A John Wiley & Sons, Ltd., Publication

This edition first published 2011 2011 by John Wiley & Sons, Ltd.

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Library of Congress Cataloguing-in-Publication DataTucker, Maurice E.

Sedimentary rocks in the field : a practical guide / Maurice E. Tucker. – 4th ed.p. cm.

Includes bibliographical references and index.ISBN 978-0-470-68916-5 (paper)

1. Sedimentary rocks. 2. Petrology–Fieldwork. I. Title.QE471.T84 2011552′.5–dc22

2010033307

A catalogue record for this book is available from the British Library.

This book is published in the following electronic formats:ePDF: 978-0-470-97368-4

Typeset in 9.5/11.5pt Times by Laserwords Private Limited, Chennai, India.

Impression 2011

CONTENTS

Preface ixAcknowledgements xi

1 Introduction 11.1 Tools of the Trade 11.2 Other Tools for the Field 31.3 Use of GPS (Global Positioning System)

in Sedimentary Studies 41.4 Safety in the Field and General Guidance

for Fieldwork 5

2 Field Techniques 92.1 What to Look For 92.2 The Approach 112.3 Field Notes 122.4 Graphic Logs 132.5 The Logging of Cores 192.6 Lithofacies Codes 202.7 Collecting Specimens 222.8 Presentation of Results 222.9 The Way-Up of Sedimentary Strata 242.10 Stratigraphic Practice 26

3 Sedimentary Rock Types 353.1 Principal Lithological Groups 353.2 Sandstones 383.3 Conglomerates and Breccias 443.4 Mudrocks 463.5 Limestones 473.6 Evaporites 593.7 Ironstones 633.8 Cherts 653.9 Phosphate Deposits (Phosphorites) 67

v

CONTENTS

3.10 Organic-Rich Deposits 683.11 Volcaniclastic Deposits 70

4 Sedimentary Rock Texture 854.1 Introduction 854.2 Sediment Grain-Size and Sorting 854.3 Grain Morphology 894.4 Sediment Fabric 914.5 Textural Maturity 944.6 Texture of Conglomerates and Breccias 954.7 Induration and Degree of Weathering 974.8 Colour of Sedimentary Rocks 99

5 Sedimentary Structures and Geometry of SedimentaryDeposits 1055.1 Introduction 1055.2 Erosional Structures 1055.3 Depositional Structures 1115.4 Depositional Structures of Limestones

(Including Dolomites) 1455.5 Post-Depositional Sedimentary Structures 1575.6 Biogenic Sedimentary Structures 1725.7 The Geometry of Sedimentary Deposits and

Lateral Facies Changes 187

6 Fossils in the Field 1936.1 Introduction 1936.2 Fossil Distribution and Occurrence 1976.3 Fossil Associations and Diversity 2026.4 Skeletal Preservation (Taphonomy) and Diagenesis 206

7 Palaeocurrent Analysis 2117.1 Introduction 2117.2 Palaeocurrent Measurements 2117.3 Structures for Palaeocurrent Measurement 2177.4 Presentation of Results and Calculation

of Vector Means 2207.5 Interpretation of the Palaeocurrent Pattern 222

vi

CONTENTS

8 What Next? Facies Identification and Sequence Analysis 2258.1 Introduction 2258.2 Facies Analysis 2258.3 Facies, Facies Models and Depositional

Environments 2278.4 Cycle Stratigraphy and Sequence Stratigraphy 228

Recommended Reading 263

Index 270

vii

PREFACE

The study of sedimentary rocks is often an exciting, challenging,rewarding and enjoyable occupation. However, to get the most out ofthese rocks, it is necessary to undertake precise and accurate fieldwork.The secret of successful fieldwork is a keen eye for detail and anenquiring mind; knowing what to expect and what to look for areimportant, although you do need to remain open-minded. Be observant,see everything in the outcrop, then think about the features seen andlook again. This book is intended to show how sedimentary rocks aretackled in the field, and has been written for those with a geologicalbackground of at least first-year university or equivalent.

At the outset, this book describes how the features of sedimentaryrocks can be recorded in the field, particularly through the constructionof graphic logs. The latter technique is widely used since it provides ameans of recording all details in a handy form; further, from the data,trends through a succession and differences between horizons readilybecome apparent. In succeeding chapters, the various sedimentary rock-types, textures and structures are discussed as they can be describedand measured in the field. A short chapter deals with fossils since theseare an important component of sedimentary rocks and much usefulinformation can be derived from them for palaeoenvironmental analysis;they are also important in stratigraphic correlation and palaeontologicalstudies. Having collected the field information, there is the problem ofknowing what to do with it. A concluding section deals briefly withfacies identification and points the way towards facies interpretations,and the identification of sequences and cycles.

Maurice E. Tucker

ix

ACKNOWLEDGEMENTS

I should like to thank the friends and colleagues who have willinglyread drafts of this handbook, suggested changes for this fourth edi-tion, and kindly provided photographs, in particular Jenny Bevan, TelmBover-Arnal, Jim Gallagher, Annette George, Dougal Jerram, Juan-Carlos Laya, Mike Mawson, Zahra Seyedmehdi and Paul Wright. Zoetook the picture on the front cover. I am indebted to Vivienne for pro-viding support, encouragement, assistance and patience in ways thatonly a wife can.

xi

Bed number

Sedimentarystructures

Lithology

Bed/unit thickness

metres above base

cm

fvf

Mud

GP

WR

F

CarbonatesFormation:

Date:

Location:

vc

Palaeocurrents

Fossils

Bioturbationindex

43

21

56

Colour

Cycles

Samples

SheetNo.

Sand

Grainsize

Mud

GB