Basic Geological Mapping

The Geological Field Guide Series

The Field Description of Metamorphic Rocks, Norman Fry

The Mapping of Geological Structures, Ken McClay

Field Geophysics, Fourth edition John Milsom

The Field Description of Igneous Rocks, Second edition Dougal Jerram and NickPetford

Sedimentary Rocks in the Field, Fourth edition Maurice Tucker

Basic Geological MappingFIFTH EDITION

Richard J. LisleSchool of Earth and Ocean Sciences, Cardiff University

Peter J. BrabhamSchool of Earth and Ocean Sciences, Cardiff University

and

John W. Barnes

A John Wiley & Sons, Ltd., Publication

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

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Library of Congress Cataloging-in-Publication Data

Lisle, Richard J.Basic geological mapping. – 5th ed. / Richard J. Lisle, Peter J. Brabham, and John W. Barnes.

p. cm.Rev. ed. of: Basic geological mapping / John W. Barnes, with Richard J. Lisle. 4th ed.Includes index.

ISBN 978-0-470-68634-8 (pbk.)1. Geological mapping. I. Brabham, Peter. II. Barnes, J. W. (John Wykeham), 1921- III. Barnes, J. W.(John Wykeham), 1921- Basic geological mapping. IV. Title.

QE36.B33 2011550.22′3–dc23

2011022844

ISBN: 978-0-470-68634-8

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

This book is published in the following electronic format: ePDF 978-1-119-97402-4;ePub 978-1-119-97751-3; MOBI 978-1-119-97752-0

Typeset in 8.5/10.5pt Times by Laserwords Private Limited, Chennai, India.

First Impression 2011

CONTENTS

Preface to the Fourth Edition ixPreface to the Fifth Edition xi

1 Introduction 11.1 Outline and Approach 11.2 Safety 21.3 Field Behaviour 41.4 A Few Words of Comfort 5

2 Field Equipment 62.1 Hammers and Chisels 62.2 Compasses and Clinometers 82.3 Hand Lenses 132.4 Tapes 142.5 Map Cases 142.6 Field Notebooks 152.7 Scales 162.8 Protractors 162.9 Pencils, Erasers and Mapping Pens 172.10 Acid Bottles 182.11 Global Positioning System (GPS) and Mobile Phones 192.12 Other Instruments 232.13 Field Clothing 26

3 Topographic Base Maps 273.1 Types of Geological Map 273.2 Topographic Base Maps 293.3 Geographic Coordinates and Metric Grids 303.4 Grid Magnetic Angle 333.5 Position Finding on Maps 343.6 Use of Air Photography as a Mapping Tool 433.7 Suitability of Images for Geological Mapping 48

4 Methods of Geological Mapping 504.1 Strategy for the Mapping Programme 504.2 Mapping by Following Contacts 51

v

CONTENTS

4.3 Traversing 524.4 Exposure Mapping 554.5 Mapping in Poorly Exposed Regions 574.6 Superficial Deposits 624.7 Drilling 664.8 Geophysical Aids to Mapping 674.9 Large-Scale Maps of Limited Areas 714.10 Underground Mapping 744.11 Photogeology 76

5 Technological Aids to Mapping 805.1 Digital Terrain Models 805.2 Topographic Surveying Techniques 86

6 Field Measurements and Techniques 956.1 Measuring Strike and Dip of Planar Structures 956.2 Plotting Strike and Dip 1016.3 Recording Strike and Dip 1016.4 Measuring Linear Features 1026.5 Folds 1056.6 Faults 1106.7 Thrusts 1126.8 Joints 1126.9 Unconformities 1146.10 Map Symbols 1146.11 Specimen Collecting 1166.12 Field Photography 1186.13 Panning 124

7 Mappable Rock Units and Lithology 1267.1 Lithostratigraphy and Sedimentary Rocks 1267.2 Sedimentary Formations 1277.3 Rock Descriptions 1287.4 Identifying and Naming Rocks in

the Field 1297.5 Fossils 1337.6 Phaneritic Igneous Rocks 1347.7 Aphanitic Igneous Rocks 1357.8 Veins and Pegmatites 1357.9 Igneous Rocks in General 136

vi

CONTENTS

7.10 Pyroclastic Rocks 1387.11 Metamorphic Rocks 1387.12 Economic Geology 140

8 Field Maps and Field Notebooks 1468.1 Field Maps 1468.2 Field Notebooks 154

9 Fair Copy Maps and Other Illustrations 1629.1 Fair Copy Maps 1629.2 Transferring Topography 1639.3 Transferring Geology 1639.4 Lettering and Symbols 1649.5 Formation Letters 1659.6 Layout 1659.7 Colouring 1679.8 Stratigraphic Column 1679.9 Overlays 1689.10 Computer Drafting of the Fair Copy Map 169

10 Cross-Sections and 3D Illustrations 17110.1 Cross-Sections 17110.2 Method of Apparent Dips 17510.3 Down-Plunge Projection Method 17710.4 Balanced Cross-Sections 17910.5 Columnar Sections 17910.6 Block Diagrams 18010.7 Models 183

11 Geological Reports 18511.1 Preparation 18611.2 Revising and Editing 18611.3 Layout 18611.4 The ‘Introduction’ 18811.5 Main Body of the Report 18811.6 The ‘Conclusions’ Section 19111.7 Text Illustrations 19111.8 References 19211.9 Appendices 19311.10 Some Final Thoughts 193

vii

CONTENTS

Appendix A: Adjustment of a Closed Compass Traverse 195

Appendix B: Field Equipment Checklist 197

Appendix C: Indicators of Stratigraphical Way-Up 202

Appendix D: Useful Chart and Tables 203

References 205

Index 209

viii

PREFACE TO THE FOURTH EDITION

This book is a basic guide to field techniques used in geological mapping. It ismeant to be kept in camp with you and even carried in your rucksack in thefield. In addition, because no piece of geological mapping can be consideredcomplete until the geology has been interpreted and explained, chapters areprovided on drawing cross-sections, on preparing and presenting ‘fair copy’maps, and on presenting geological diagrams from your fieldwork suitable forinclusion in your report. A report explaining the geology is an essential part ofany field project, and a brief chapter on the essentials for writing and illustratingit concludes this book. Some emphasis, too, is given to field sketch-mappingbecause many reports lack those large-scale detailed maps of small areas thatcan often explain complex aspects of the geology that cannot be shown on thescale of the field map being used, and that are difficult to describe in words.Attention is also given to field notebooks, which are, in many cases, deplorable.

It is assumed that readers of this book have already had at least one year ofuniversity or equivalent geology, and have already been told what to look forin the field. Geological mapping cannot, however, be taught in lectures and thelaboratory: it must be learnt in the field. Unfortunately, only too often, traineegeologists are left largely to their own devices, to sink or swim, and to learn tomap for themselves with a minimum of supervision on ‘independent’ mappingprojects. It is hoped that this book will help in that task.

John W. Barnes and Richard J. Lisle2003

ix

PREFACE TO THE FIFTH EDITION

This fifth edition of Basic Geological Mapping was revised without the helpof John Wakeham Barnes who sadly passed away in 2007. On the suggestionof referees we have updated the text by including mention of modern tech-nological aids and data that are used in modern geological mapping, such asapplied geophysics, digital terrain models, and optical and GPS-based surveying.There has also been more emphasis given to structural geology and cross-section construction. Whilst making these additions we have been consciousof the need to maintain John’s successful formula; to offer a practical guide forthe student undertaking a mapping project with a minimum of resources andacademic supervision.

We are grateful for the advice of Jim Hendry and Rob Strachan (Universityof Portsmouth), Chris Berry and Alun Rodgers (Cardiff University) and thebook’s reviewers.

Richard J. Lisle and Peter J. BrabhamJanuary 2011

xi

1INTRODUCTION

Most geological maps record the regional distribution of rocks belonging todifferent formations. However, such maps reveal far more than where we couldfind rocks belonging to a given formation. The geometrical shape of the differ-ent formations on the geological map can also be interpreted in terms of thegeological structure and geological history of the region concerned. As an earthscientist you must remember that accurate geological maps form the basis ofmost geological work, even laboratory work. They are used to solve problems inearth resource exploration (minerals and hydrocarbons), civil engineering (roads,dams, tunnels, etc.), environmental geoscience (pollution, landfill) and hazards(landslides, earthquakes, etc.). Making a geological map is therefore a funda-mental skill for any professional geologist. As Wallace (1975) states, ‘There isno substitute for the geological map and section – absolutely none. There neverwas and there never will be. The basic geology still must come first – and if itis wrong, everything that follows will probably be wrong.’

There are many kinds of geological map, from small-scale reconnaissancesurveys to large-scale detailed underground maps and engineering site plans,and each is made using different techniques. In this textbook, however, we areconcerned only with the rudiments of geological mapping. The intention is toprovide basic methods and good field practice on which you can further build,and adapt, to deal with a wide range of types of geological mapping.

1.1 Outline and ApproachThis book is arranged in what is hoped is a logical order for those about to go intothe field on their first independent mapping project. This first chapter includesthe important issue of fieldwork safety and appropriate conduct during fieldwork,which should always be considered before anything else. The equipment youwill need for mapping is described in Chapter 2, which is followed by a chapterdevoted to the many types of geological map you may have to deal with sometime during your professional career. A description follows of the differentkinds of topographic base maps that may be available on which to plot yourgeological observations in the field. Methods to locate yourself on a map are

Basic Geological Mapping , Fifth Edition.Richard J. Lisle, Peter J. Brabham and John W. Barnes. 2011 John Wiley & Sons, Ltd. Published 2011 by John Wiley & Sons, Ltd.

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