Historical Geology Contents 0.1 Introduction .............................................. 1 0.1.1 What is historical geology? .................................. 1 0.1.2 Pre-requisites for reading this book .............................. 1 0.1.3 The purpose of this book ................................... 1 0.1.4 The introductory nature of this book ............................. 2 0.1.5 Selection of material ..................................... 2 0.1.6 Arrangement of material ................................... 2 0.1.7 Vocabulary in this book .................................... 2 0.1.8 Note on references ...................................... 2 0.1.9 Note to potential editors ................................... 3 0.1.10 Acknowledgements ...................................... 3 1 Minerals and rocks 4 1.1 Minerals ................................................ 4 1.1.1 Minerals ............................................ 4 1.1.2 Mineraloids .......................................... 4 1.1.3 Rocks ............................................. 5 1.2 Silicate minerals ............................................ 5 1.2.1 Silicate structures ....................................... 5 1.2.2 Aluminosilicates ....................................... 6 1.2.3 Felsic and mafic silicates ................................... 6 1.2.4 Note on vocabulary ...................................... 6 1.3 Rocks ................................................. 6 1.3.1 Igneous, sedimentary, and metamorphic rocks ........................ 6 1.3.2 The rock cycle ........................................ 7 1.3.3 How do we know? ...................................... 7 1.4 Igneous rocks ............................................. 7 1.4.1 Intrusive and extrusive igneous rocks ............................. 7 1.4.2 Texture ............................................ 7 1.4.3 Chemistry ........................................... 8 1.4.4 Igneous structures ....................................... 8 1.4.5 How do we know? ...................................... 9 1.4.6 Note on vocabulary ...................................... 9 i ii CONTENTS 1.5 Sedimentary rocks ........................................... 9 1.5.1 Types of sedimentary rocks .................................. 10 1.5.2 Clastic sedimentary rocks ................................... 10 1.5.3 Chemical sedimentary rocks ................................. 11 1.5.4 Biochemical sedimentary rocks ................................ 11 1.5.5 Modes of deposition ..................................... 11 1.5.6 Bedding ............................................ 11 1.5.7 How do we know? ...................................... 11 1.5.8 Note on vocabulary ...................................... 12 1.6 Metamorphic rocks .......................................... 12 1.6.1 Types of metamorphism ................................... 12 1.6.2 Chemical changes ....................................... 12 1.6.3 Metasomatism ........................................ 13 1.6.4 Textural changes ....................................... 13 1.6.5 How do we know? ...................................... 14 2 Erosion and deposition 15 2.1 Mechanical weathering and erosion .................................. 15 2.1.1 Definitions .......................................... 15 2.1.2 Mechanical weathering .................................... 15 2.1.3 Mechanical erosion ...................................... 15 2.1.4 Modes of erosion ....................................... 15 2.1.5 Transport of sediment ..................................... 16 2.1.6 How do we know? ...................................... 16 2.2 Chemical weathering ......................................... 16 2.2.1 Agents of chemical weathering ................................ 16 2.2.2 Chemical weathering of common minerals .......................... 16 2.2.3 Summary ........................................... 17 2.2.4 How do we know? ...................................... 18 2.3 Glaciers ................................................ 18 2.3.1 Formation and motion of glaciers ............................... 18 2.3.2 Types of glacier ........................................ 19 2.3.3 Erosion associated with glaciers ................................ 19 2.3.4 Deposition associated with glaciers .............................. 20 2.3.5 Former glaciers: how do we know? .............................. 21 2.4 Deserts ................................................. 22 2.4.1 Definition of a desert ..................................... 22 2.4.2 Causes of deserts ....................................... 22 2.4.3 Deserts and water ....................................... 22 2.4.4 Deserts and wind ....................................... 23 2.4.5 Lithified deserts: how do we know? .............................. 24 2.5 Volcanic ash .............................................. 24 CONTENTS iii 2.5.1 Origin and dispersal of volcanic ash ............................. 24 2.5.2 Tuff .............................................. 24 2.5.3 Volcanic ash: the igneous sediment .............................. 25 2.5.4 Volcanic ash and tuff: how do we know? ........................... 25 2.6 Soils and paleosols ........................................... 26 2.6.1 Soil: what is it? ........................................ 26 2.6.2 Paleosols: definition ...................................... 27 2.6.3 Paleosols: how do we know? ................................. 27 2.7 Rivers ................................................. 27 2.7.1 Braided and meandering rivers ................................ 28 2.7.2 Sedimentary structures .................................... 28 2.7.3 Vanished rivers: how do we know? .............................. 29 2.7.4 Note on superposed and antecedent rivers .......................... 29 2.8 Deltas ................................................. 30 2.8.1 The dynamics of a delta .................................... 30 2.8.2 Types of delta ......................................... 30 2.8.3 Former deltas: how do we know? ............................... 31 2.9 Lakes ................................................. 31 2.9.1 Lakes ............................................. 31 2.9.2 Lacustrine sedimentary rocks: how do we know? ....................... 31 2.9.3 Note on identifying freshwater organisms ........................... 32 2.10 Peat and coal ............................................. 32 2.10.1 Some definitions ....................................... 32 2.10.2 Deposition of peat ...................................... 32 2.10.3 Peatification and coalification ................................. 33 2.10.4 Coal from swamps: how do we know? ............................ 34 2.11 Nearshore sediments .......................................... 35 2.11.1 Waves and the nearshore ................................... 35 2.11.2 A note on terminology .................................... 35 2.11.3 Varieties of nearshore environment .............................. 35 2.11.4 Some nearshore sedimentary structures ............................ 35 2.11.5 Lithified nearshore sediment: how do we know? ....................... 36 2.12 Marine sediments ........................................... 37 2.12.1 The sea in profile ....................................... 37 2.12.2 Distribution of marine sediments ............................... 38 2.12.3 Types of marine sediment .................................. 38 2.12.4 Marine sediments and plate tectonics ............................. 38 2.13 Turbidites ............................................... 39 2.13.1 Turbidity currents ....................................... 39 2.13.2 Turbidity sediments and turbidites .............................. 39 2.13.3 Turbidites: how do we know? ................................. 40 iv CONTENTS 2.14 Reefs ................................................. 41 2.14.1 What is a reef? ........................................ 41 2.14.2 Reef-forming organisms ................................... 41 2.14.3 Ancient reefs: how do we know? ............................... 41 2.14.4 A puzzle and a solution .................................... 42 2.15 Ooids and oolite ............................................ 42 2.15.1 Ooids and oolite ........................................ 42 2.15.2 Oolite: how do we know? ................................... 43 2.16 Calcareous ooze ............................................ 43 2.16.1 Calcareous ooze: what is it? .................................. 43 2.16.2 The CCD ........................................... 44 2.16.3 Rocks from calcareous ooze: how do we know? ....................... 45 2.17 Siliceous ooze ............................................. 45 2.17.1 Siliceous ooze ......................................... 45 2.17.2 The opal compensation depth ................................. 46 2.17.3 Rocks from siliceous ooze: how do we know? ........................ 46 2.18 Pelagic clay .............................................. 47 2.18.1 Origin and distribution of pelagic clay ............................ 47 2.18.2 Appearance .......................................... 47 2.18.3 Lithified pelagic clay: how do we know? ........................... 48 2.19 Deposition rates ............................................ 48 2.19.1 How do we know? ...................................... 48 2.20 Glacial marine sediment ........................................ 49 2.20.1 Deposition of glacial marine sediment ............................ 49 2.20.2 Glacial marine sedimentary rocks: how do we know? .................... 49