Basic Geological Mapping
FOURTH EDITION
John W. Barnes
formerly of the Department of Earth Sciences,
University of Wales Swansea
with
Richard J. Lisle
Department of Earth, Ocean and Planetary Sciences Cardiff University
CONTENTS
Preface ix
Acknowledgments xi
1 Introduction 1
1.1 Outline and Approach 1
1.2 Field Behaviour 2
1.3 Safety 2
1.4 Ancillary Skills 3
1.5 A Few Words of Comfort 3
2 Field Equipment 5
2.1 Hammers and Chisels 5
2.2 Compasses and Clinometers 7
2.3 Handlenses 13
2.4 Tapes 13
2.5 Map Cases 13
2.6 Field Notebooks 13
2.7 Scales 14
2.8 Protractors 15
2.9 Pencils and Erasers 16
2.10 Acid Bottles 16
2.11 Global Positioning System (GPS) 16
2.12 Other Instruments 18
2.13 Field Clothing 19
3 Geological Maps and Base Maps 21
3.1 Types of Geological Map 21
3.2 Topographic Base Maps 23
3.3 Geographic Coordinates and Metric Grids 25
3.4 Position Finding on Maps 27
3.5 Magnetic Declination 33
3.6 Planetable Mapping 33
3.7 Aerial Photographs 34
3.8 Satellite Imagery 42
4 Methods of Geological Mapping 43
4.1 Traversing 43
4.2 Following Contacts 47
4.3 Exposure or Green Line Mapping 47
4.4 Mapping in Poorly Exposed Regions 50
4.5 Superficial Deposits 53
4.6 Drilling 58
4.7 Geophysical Aids to Mapping 59
4.8 Large-scale Maps of Limited Areas 59
4.9 Underground Mapping 63
4.10 Photogeology 64
5 Field Measurements and Techniques 69
5.1 Measuring Strike and Dip 69
5.2 Plotting Strike and Dip 73
5.3 Recording Strike and Dip 74
5.4 Measuring Linear Features 75
5.5 Folds 79
5.6 Faults 82
5.7 Thrusts and Unconformities 84
5.8 Joints 85
5.9 Map Symbols 86
5.10 Specimen Collecting 86
5.11 Field Photography 89
5.12 Panning 90
6 Rocks, Fossils and Ores 93
6.1 Rock Descriptions 93
6.2 Identifying and Naming Rocks in the Field 94
6.3 Litho-stratigraphy and Sedimentary Rocks 94
6.4 Fossils 99
6.5 Phaneritic Igneous Rocks 100
6.6 Aphanitic Igneous Rocks 101
6.7 Veins and Pegmatites 101
6.8 Igneous Rocks in General 103
6.9 Pyroclastic Rocks 103
6.10 Metamorphic Rocks 104
6.11 Economic Geology 105
7 Field Maps and Field Notebooks 113
7.1 Field Maps 113
7.2 Field Notebooks 120
8 Fair Copy Maps and Other Illustrations 125
8.1 Fair Copy Maps 125
8.2 Transferring Topography 126
8.3 Transferring Geology 126
8.4 Lettering and Symbols 127
8.5 Formation Letters 128
8.6 Layout 128
8.7 Colouring 128
8.8 Cross-sections 130
8.9 Overlays 131
8.10 Computer Drafting of the Fair Copy Map 131
8.11 Text Illustrations 132
9 Cross-sections and Three-dimensional Illustrations 133
9.1 Cross-sections 133
9.2 Plotting and Drawing Cross-sections 134
9.3 Three-dimensional Illustrations 139
9.4 Models 140
10 Geological Reports 143
10.1 Preparation 143
10.2 Revision and Editing 144
10.3 Layout 145
10.4 Introduction 146
10.5 Main Body of the Report 147
10.6 Conclusions 148
10.7 References 148
10.8 Appendices 150
Appendix I: Safety in the Field 151
I.1 Emergency Kit 152
I.2 Distress Signals 152
I.3 Exposure 152
I.4 Lightning 153
I.5 Health in Warm Climates 153
I.6 Students in the Field 154
Appendix II: Adjustment of a Closed Compass Traverse 157
Appendix III: Geological Planetabling 159
Appendix IV: Field Equipment Checklist 163
Mapping equipment 163
Sampling equipment 164
Rucksack kit 164
Rucksack emergency kit 164
Field clothing (temperate and cold climates) 165
Field clothing (warm climates) 165
Drawing, plotting, ‘office’ equipment 165
Items for camp use 166
Paperwork 167
Also! 167
Appendix V: Useful Charts and Tables 169
Table AV.1 Spacing for bedding and jointing 169
Table AV.2 Abridged grain-size scales 169
Chart AV.1 Percentage area chart 170
References and further reading 171
Index 175
PREFACE
This book is a basic guide to field techniques used in geological mapping. It is meant to be kept in camp with you and even carried in your rucksack in the field. In addition, because no piece of geological mapping can be considered complete until the geology has been interpreted and explained, chapters are provided on drawing cross-sections; on preparing and presenting ‘fair copy’ maps; and on presenting geological diagrams from your fieldwork suitable for inclusion in your report. A report explaining the geology is an essential part of any field project and a brief chapter on the essentials for writing and illustrating it concludes this book. Some emphasis, too, is given to field sketch-mapping because many reports lack those large-scale detailed maps of small areas which can often explain complex aspects of the geology that cannot be shown on the scale of the field map being used, and which 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 of university or equivalent geology, and have already been told what to look for in the field. Geological mapping cannot, however, be taught in lectures and the laboratory: it must be learnt in the field. Unfortunately, only too often, trainee geologists are left largely to their own devices, to sink or swim, and to learn to map for themselves with a minimum of supervision on ‘independent’ mapping projects. It is hoped that this book will help them in that task.
John W. Barnes, Richard J. Lisle, 2003
INTRODUCTION
There are many kinds of geological map, from small-scale reconnaissance surveys to large-scale detailed underground mine maps and engineering site plans, and each needs a different technique to make. Here, however, we are concerned only with the rudiments of geological mapping. The intention is to provide basic knowledge which can be built upon. We cannot tell you everything you need to know but we hope we can stimulate your imagination so that you can adapt your methods to most prevailing field conditions and to the scale and quality of your topographic base maps and, where necessary, to develop and devise new methods of your own. As a geologist, you must also remember that accurate geological maps are the basis of all geological work, even laboratory work, for it is pointless to make a detailed investigation of a specimen whose provenance is uncertain. As Wallace said in a 1975 Jacklin lecture: ‘There is no substitute for the geological map and section – absolutely none. There never was and there never will be. The basic geology still must come first – and if it is wrong, everything that follows will probably be wrong.’
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