Geological Field Techniques

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 field 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 Classification and colour charts 28

2.7 Hammer, chisels and other hardware 31

2.8 The hardcopy field 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, field safety and field 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 Defining the fieldwork objectives 42

3.1.2 Deciding where to do the fieldwork 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

4 The Field Notebook 53

4.1 Introduction: The purpose of field 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

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 fieldwork 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 Classification 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

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 field map 216

10.4.1 Information to record on field 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 field 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 scientific report writing 260

References 261

Appendix A1: General 263

Appendix A5: Fossils 265

Appendix A6: Sedimentary 273

Appendix A7: Igneous 293

Appendix A8: Structural 296

Appendix A9: Metamorphic 302

Appendix A10: Mapping 306

Index 310