Sedimentary Rocks in the Field

Preface ix

Acknowledgements xi

1 Introduction 1

1.1 Tools of the Trade 1

1.2 Other Tools for the Field 3

1.3 Use of GPS (Global Positioning System) in Sedimentary Studies 4

1.4 Safety in the Field and General Guidance for Fieldwork 5

2 Field Techniques 9

2.1 What to Look For 9

2.2 The Approach 11

2.3 Field Notes 12

2.4 Graphic Logs 13

2.5 The Logging of Cores 19

2.6 Lithofacies Codes 20

2.7 Collecting Specimens 22

2.8 Presentation of Results 22

2.9 The Way-Up of Sedimentary Strata 24

2.10 Stratigraphic Practice 26

3 Sedimentary Rock Types 35

3.1 Principal Lithological Groups 35

3.2 Sandstones 38

3.3 Conglomerates and Breccias 44

3.4 Mudrocks 46

3.5 Limestones 47

3.6 Evaporites 59

3.7 Ironstones 63

3.8 Cherts 65

3.9 Phosphate Deposits (Phosphorites) 67

3.10 Organic-Rich Deposits 68

3.11 Volcaniclastic Deposits 70

4 Sedimentary Rock Texture 85

4.1 Introduction 85

4.2 Sediment Grain-Size and Sorting 85

4.3 Grain Morphology 89

4.4 Sediment Fabric 91

4.5 Textural Maturity 94

4.6 Texture of Conglomerates and Breccias 95

4.7 Induration and Degree of Weathering 97

4.8 Colour of Sedimentary Rocks 99

5 Sedimentary Structures and Geometry of Sedimentary Deposits 105

5.1 Introduction 105

5.2 Erosional Structures 105

5.3 Depositional Structures 111

5.4 Depositional Structures of Limestones (Including Dolomites) 145

5.5 Post-Depositional Sedimentary Structures 157

5.6 Biogenic Sedimentary Structures 172

5.7 The Geometry of Sedimentary Deposits and Lateral Facies Changes 187

6 Fossils in the Field 193

6.1 Introduction 193

6.2 Fossil Distribution and Occurrence 197

6.3 Fossil Associations and Diversity 202

6.4 Skeletal Preservation (Taphonomy) and Diagenesis 206

7 Palaeocurrent Analysis 211

7.1 Introduction 211

7.2 Palaeocurrent Measurements 211

7.3 Structures for Palaeocurrent Measurement 217

7.4 Presentation of Results and Calculation of Vector Means 220

7.5 Interpretation of the Palaeocurrent Pattern 222

8 What Next? Facies Identification and Sequence Analysis 225

8.1 Introduction 225

8.2 Facies Analysis 225

8.3 Facies, Facies Models and Depositional Environments 227

8.4 Cycle Stratigraphy and Sequence Stratigraphy 228

Recommended Reading 263

Index 270