Sedimentary Structures

Preface vii
Acknowledgements ix

1 Introduction 1
1.1 The nature of this book 1
1.2 The wider geological context 3
1.3 Sedimentary structures and science 3
Study techniques 5

2 Bedding 7
2.1 The nature of bedding 7
2.2 The significance of bedding 15
Study techniques 20

3 Basic properties of fluids, flows and sediment 21
3.1 Introduction 21
3.2 Properties of low-viscosity fluids and flows 21
3.3 Waves 27
3.4 Properties of sediments moved by flows 29
3.5 Erosion 31
3.6 Modes of sediment transport 33
3.7 Sediment gravity flows 34
3.8 Pyroclastic density currents 42
Study techniques 43

4 Erosional structures 45
4.1 Introduction 45
4.2 Sole marks 45
4.3 Small-scale structures on modern and ancient upper surfaces 56
4.4 Erosional features in vertical section 59
Study techniques 65

5 Depositional structures in muds, mudstones and shales 67
5.1 Introduction 67
5.2 Structures and lamination 69
Study techniques 73

6 Depositional structures of sands and sandstones 74
6.1 Ripples and cross lamination 74
6.2 Aqueous dunes, sandwaves, bars and cross bedding 92
6.3 Aeolian dunes and cross bedding 111
6.4 Flat beds and parallel lamination 128
6.5 Undulating smooth surfaces and lamination 130
6.6 Hummocky and swaley cross stratification 131
6.7 Massive sand and sandstone beds 132
6.8 Normally graded beds, inverse grading and the Bouma sequence 133
Study techniques 136

7 Depositional structures in gravels, conglomerates and breccias 138
7.1 Introduction 138
7.2 Problems of classification 138
7.3 Morphology and general settings of gravel deposition 140
7.4 Structures and other descriptive features: mode of formation 142
7.5 Processes of formation of mass properties and structures 156
7.6 Uses of structures 161
Study techniques 162

8 Depositional structures of chemical and biological origin 163
8.1 Introduction 163
8.2 Chemical precipitation 163
8.3 Precipitation and binding of sediment by organisms 168
8.4 Early cementation 177
8.5 Other bedding phenomena in limestones 180
Study techniques 180

9 Structures created by deformation and disturbance 182
9.1 Introduction 182
9.2 Physically induced soft-sediment deformation 182
9.3 Chemically induced disturbance 204
9.4 Biogenic sedimentary structures: trace fossils 216
Study techniques 242

10 Assemblages of structures and environmental interpretation 243
10.1 Introduction 243
10.2 Mapping of modern environments 243
10.3 Measurement of sections in rock sequences 244
10.4 Interpretation of vertical sequences in rocks 246
10.5 Key stratigraphical surfaces 252
10.6 Interpretation of lateral relationships in sedimentary rocks 253
Study techniques 253

Appendix 1 Directional data: collection, display, analysis and interpretation 257

Appendix 2 Sampling and preserving unconsolidated sediments 262

Appendix 3 Methods for studying present-day environments 263

Appendix 4 Techniques for the study of trace fossils 265

Appendix 5 Techniques for sedimentary logging 266

Appendix 6 Key to common sedimentary lithologies and structures 269

Bibliography 271

Index 281