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Contents

Preface xi

Chapter 1 Geomagnetism and Paleomagnetism

1.1 Geomagnetism 1

1.1.1 Historical 1

1.1.2 Main Features of the Geomagnetic Field 3

1.1.3 Origin of the Main Field 7

1.1.4 Variations of the Dipole Field with Time 12

1.2 Paleomagnetism 14

1.2.1 Early Work in Paleomagnetism 14

1.2.2 Magnetism in Rocks 16

1.2.3 Geocentric Axial Dipole Hypothesis 18

1.2.4 Archeomagnetism 22

1.2.5 Paleointensity over Geological Times 25

1.2.6 Paleosecular Variation 26

Chapter 2 Rock Magnetism

2.1 Basic Principles of Magnetism 31

2.1.1 Magnetic Fields, Remanent and Induced Magnetism 31

2.1.2 Diamagnetism and Paramagnetism 34

2.1.3 Ferro-, Antiferro-, and Ferrimagnetism 35

2.1.4 Hysteresis 37

2.2 Magnetic Minerals in Rocks 38

2.2.1 Mineralogy 38

2.2.2 Titanomagnetites 40

2.2.3 Titanohematites 45

2.2.4 Iron Sulfides and Oxyhydroxides 46

2.3 Physical Theory of Rock Magnetism 48

2.3.1 Magnetic Domains 48

2.3.2 Theory for Single-Domain Grains 51

2.3.3 Magnetic Viscosity 54

2.3.4 Critical Size for Single-Domain Grains 56

2.3.5 Thermoremanent Magnetization 60

2.3.6 Crystallization (or Chemical) Remanent Magnetization 64

2.3.7 Detrital and Post-Depositional Remanent Magnetization 68

2.3.8 Viscous and Thermoviscous Remanent Magnetization 71

2.3.9 Stress Effects and Anisotropy 74

Chapter 3 Methods and Techniques

3.1 Sampling and Measurement 79

3.1.1 Sample Collection in the Field 79

3.1.2 Sample Measurement 82

3.2 Statistical Methods 84

3.2.1 Some Statistical Concepts 84

3.2.2 The Fisher Distribution 87

3.2.3 Statistical Tests 91

3.2.4 Calculating Paleomagnetic Poles and Their Errors 98

3.2.5 Other Statistical Distributions 99

3.3 Field Tests for Stability 100

3.3.1 Constraining the Age of Magnetization 100

3.3.2 The Fold Test 101

3.3.3 Conglomerate Test 108

3.3.4 Baked Contact Test 109

3.3.5 Unconformity Test 111

3.3.6 Consistency and Reversals Tests 112

3.4 Laboratory Methods and Applications 114

3.4.1 Progressive Stepwise Demagnetization 114

3.4.2 Presentation of Demagnetization Data 119

3.4.3 Principal Component Analysis 124

3.4.4 Analysis of Remagnetization Circles 125

3.5 Identification of Magnetic Minerals and Grain Sizes 127

3.5.1 Curie Temperatures 127

3.5.2 Isothermal Remanent Magnetization 128

3.5.3 The Lowrie-Fuller Test 131

3.5.4 Hysteresis and Magnetic Grain Sizes 133

3.5.5 Low-Temperature Measurements

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