Geological Field Techniques

337 Pages·2010·32.6 MB·English

by  Angela L. Coe

GEOLOGICAL FIELD TECHNIQUES
Cartoons by Ian Wightman
Front cover image: Carboniferous age (Namurian) rocks exposed at Sugar Sands Bay, near
Alnwick, Northumberland, UK. These are part of a succession of rocks interpreted as infi ll of an
interdistributary bay or lagoon along the shore of a delta. Superimposed on the photograph is
part of a graphic log of the succession summarizing the thickness of the units, lithology,
sedimentary structures and cycles. (Angela L. Coe, The Open University, UK.)
Back cover images (in descending order):
1. Walcott Quarry, Canadian Rockies during 1998 showing the exposure of the Burgess Shale
(Cambrian) that is famous for the exceptional soft body preservation of some of the oldest
fossils on Earth. (Angela L. Coe, The Open University, UK.)
2. Geologists working on the organic-rich mudrocks of the Monterey Formation (Miocene),
Naples Beach, California, USA. (Anthony S. Cohen, The Open University, UK.)
3. Asymmetric folds in Proterozoic strata, Harvey’s Return, Kangaroo Island, Australia. Lens
cap is 5.5 cm across. (Tom W. Argles, The Open University, UK.)
4. A Silva compass-clinometer being used to measure the dip of a fault plane, Whitesands Bay,
St David’s, Wales, UK. (Tom W. Argles, The Open University, UK.)
5. The ammonite Psiloceras planorbis (J. de C. Sowerby) from the Lias Group, UK.
This species defi nes the lowermost ammonite zone of the Jurassic. Ammonite is c. 4 cm
across. (Peter R. Sheldon, The Open University, UK.)
Companion Website: A companion resources site for this book is available at
www.wiley.com/go/coe/geology
With:
• All fi gures and tables from the book
• Additional excercises and answers
• Useful websites, selected by the authors
GEOLOGICAL FIELD TECHNIQUES
Edited by Angela L. Coe
Authors:
Angela L. Coe
Tom W. Argles
David A. Rothery
Robert A. Spicer
Department of Earth and Environmental Sciences,
The Open University, Walton Hall, Milton Keynes, UK
A John Wiley & Sons, Ltd., Publication
Published by Blackwell Publishing Ltd
in association with
The Open University
Walton Hall, Milton Keynes
MK7 6AA
United Kingdom
First published 2010
Copyright © 2010, The Open University
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Library of Congress Cataloging-in-Publication Data
Geological fi eld techniques / edited by Angela L. Coe.
p. cm.
Includes bibliographical references and index.
ISBN 978-1-4443-3061-8 (hardback)
ISBN 978-1-4443-3062-5 (paperback)
1. Geology–Fieldwork. I. Coe, Angela L.
QE45.G46 2010
550.072'3–dc22
2010016419
v
Contents
Preface x
Acknowledgements xi
1 INTRODUCTION 1
1.1 A selection of general books and reference material on geology 2
1.2 Books on geological fi eld techniques 3
2 FIELD EQUIPMENT AND SAFETY 4
2.1 Introduction 4
2.2 The hand lens and binoculars 5
2.3 The compass-clinometer 6
2.3.1 Orientation of a dipping plane 11
2.3.2 Orientation of a linear feature 16
2.3.3 Triangulation: Determining location using a compass 20
2.4 Global positioning systems and altimeters 25
2.5 Measuring distance and thickness 26
2.5.1 Standard thickness and distance measurements 26
2.5.2 Use of the Jacob staff to measure the thickness of
inclined strata 27
2.6 Classifi cation and colour charts 28
2.7 Hammer, chisels and other hardware 31
2.8 The hardcopy fi eld notebook 33
2.9 The laptop, netbook or PDA as a notebook 34
2.10 Writing equipment, maps and relevant literature 35
2.10.1 Writing equipment 35
2.10.2 Maps and relevant literature 35
2.11 Comfort, fi eld safety and fi eld safety equipment 36
2.11.1 Clothes, backpack/rucksack and personal provisions 36
2.11.2 Field safety 36
2.11.3 Field safety equipment 39
2.12 Conservation, respect and obtaining permission 40
2.13 Further reading 41
3 INTRODUCTION TO FIELD OBSERVATIONS AT DIFFERENT SCALES 42
3.1 Introduction: What, where and how? 42
3.1.1 Defi ning the fi eldwork objectives 42
3.1.2 Deciding where to do the fi eldwork 43
3.1.3 Locating your position 45
3.2 Scale of observation, where to start and basic measurements 45
3.2.1 Regional context 45
3.2.2 Whole exposure 46
3.2.3 Hand specimens 49
3.3 Overview of possible data formats 51
vi Contents
4 THE FIELD NOTEBOOK 53
4.1 Introduction: The purpose of fi eld notes 53
4.2 Field notebook layout 54
4.2.1 Preliminary pages 54
4.2.2 Daily entries 54
4.2.3 General tips 56
4.3 Field sketches: A picture is worth a thousand words 57
4.3.1 General principles: Aims, space and tools 59
4.3.2 Sketches of exposures 63
4.3.3 Sketching metre- and centimetre-scale features 67
4.3.4 Sketch maps 68
4.4 Written notes: Recording data, ideas and interpretation 72
4.4.1 Notes recording data and observations 72
4.4.2 Notes recording interpretation, discussion and ideas 72
4.5 Correlation with other data sets and interpretations 77
5 RECORDING PALAEONTOLOGICAL INFORMATION 79
5.1 Introduction: Fossils are smart particles 79
5.1.1 Why are fossils important? 79
5.1.2 Collecting fossil data 80
5.2 Fossil types and preservation 82
5.2.1 Body fossil classifi cation 82
5.2.2 Body fossil preservation 82
5.2.3 Trace fossils 85
5.2.4 Molecular fossils 87
5.3 Fossil distribution and where to fi nd them 87
5.3.1 Transported or life position? 88
5.4 Sampling strategies 90
5.4.1 Sampling for biostratigraphic or evolutionary studies 90
5.4.2 Sampling of bedding surfaces and palaeoecology 92
5.5 Estimating abundance 95
5.5.1 Presence/absence and qualitative abundance estimates 96
5.5.2 Quantitative measures of abundance 96
5.5.3 How many samples are required? 99
5.6 Summary 100
5.7 Further reading 101
6 RECORDING FEATURES OF SEDIMENTARY ROCKS AND
CONSTRUCTING GRAPHIC LOGS 102
6.1 Introduction 102
6.2 Description, recognition and recording of sedimentary deposits
and sedimentary structures 104
6.2.1 Recording sedimentary lithology 104
6.2.2 Recording sedimentary structures 109
6.3 Graphic logs 117
6.3.1 Conventions for graphic logs 119
6.3.2 Constructing a graphic log 121
6.4 Rocks in space: Reconstructing sedimentary environments and
their diagnostic features 127
Contents vii
6.5 Using sedimentary rocks to interpret climate change and sea-level change 133
6.5.1 Climate change 134
6.5.2 Sequence stratigraphy and relative sea-level change 134
6.6 Further reading 137
7 RECORDING FEATURES OF IGNEOUS ROCKS 139
7.1 Equipment, basic tips and safety 139
7.2 Field relationships of igneous rocks 140
7.2.1 Relationships with surrounding rocks 140
7.2.2 Internal architecture: Joints and veins 144
7.2.3 Internal architecture: Other exposure-scale fabrics 146
7.3 Mineralogy and small-scale textures of igneous rocks 154
7.3.1 Petrologic type 155
7.3.2 Mineral texture and fabric 155
7.4 Recent and active volcanoes 159
7.4.1 Equipment and safety 159
7.4.2 Access 160
7.4.3 Observations 160
7.5 Further reading 161
8 RECORDING STRUCTURAL INFORMATION 163
8.1 Equipment and measurement 164
8.1.1 Structural measurements and notations 164
8.2 Brittle structures: Faults, joints and veins 165
8.2.1 Planar brittle features – orientation 165
8.2.2 Determining past motion on brittle structures 170
8.3 Ductile structures: Shear zones, foliations and folds 176
8.3.1 Orientation of ductile planar features 176
8.3.2 Direction of shear/stretching: Stretching lineations 180
8.3.3 Sense of shear: Kinematic indicators 182
8.3.4 Magnitude of shear strain 185
8.3.5 Fold analysis 185
8.4 Further reading 191
9 RECORDING FEATURES OF METAMORPHIC ROCKS 192
9.1 Basic skills and equipment for metamorphic fi eldwork 192
9.1.1 Field relations and context 192
9.2 Textures 194
9.2.1 Banding 194
9.2.2 Grain textures 196
9.2.3 Reaction textures 197
9.3 Mineralogy 198
9.3.1 Identifying common metamorphic minerals 198
9.3.2 Using mineral assemblages 198
9.3.3 Classifi cation of metamorphic rocks 200
9.4 Unravelling metamorphism and deformation 201
9.4.1 Pre-kinematic features 202
9.4.2 Syn-kinematic features 202
9.4.3 Post-kinematic features 203
9.5 Further reading 205
viii Contents
10 MAKING A GEOLOGICAL MAP 206
10.1 Principles and aims 206
10.2 Preparation and materials 207
10.2.1 Base maps and other aids 207
10.2.2 Equipment for mapping 212
10.3 Location, location, location 214
10.3.1 Equipment 214
10.3.2 Using base maps 214
10.4 Making a fi eld map 216
10.4.1 Information to record on fi eld maps 216
10.4.2 The evolving map 218
10.4.3 Sketch cross-sections 221
10.5 Mapping techniques 222
10.5.1 Traverse mapping 223
10.5.2 Contact mapping 225
10.5.3 Exposure mapping 226
10.5.4 Using other evidence 228
10.6 The geological map 233
10.6.1 Inking in the fi eld map 233
10.6.2 Cross-sections 235
10.6.3 Fair copy maps 235
10.6.4 Digital maps and GIS 239
10.7 Further reading 240
11 RECORDING NUMERICAL DATA AND USE OF INSTRUMENTS IN THE FIELD 241
11.1 Data collection 241
11.1.1 Instrument calibration and base stations 244
11.1.2 Survey grids 244
11.2 Transport and protection of the instruments 245
11.3 Correlation with other data sets 245
11.4 Further reading 246
12 PHOTOGRAPHY 247
13 SAMPLING 250
13.1 Selecting and labelling samples 250
13.1.1 Samples for thin-sections 251
13.1.2 Orientated samples 251
13.1.3 Samples for geochemical analysis 253
13.1.4 Samples for mineral extraction 253
13.1.5 Samples for fossils 253
13.1.6 Sampling for regional studies 254
13.1.7 High-resolution sample sets 254
13.1.8 Labelling samples and their packaging 255
13.2 Practical advice 256
13.2.1 Packing and marking materials 256
13.2.2 Extraction of samples 257
14 CONCLUDING REMARKS 259
14.1 Further reading on scientifi c report writing 260