Palaeomagnetism

1 Introduction.- 1.1 Scope of the book.- 1.2 Historical perspective.- 1.3 Data presentation, magnetic units and geological ages.- 1.3.1 Data presentation.- 1.3.2 Magnetic units.- 1.3.3 Geological ages.- 2 The physical basis.- 2.1 Magnetization on an atomic scale.- 2.2 Magnetic domains and anisotropy.- 2.3 Temperature, grain size and time.- 2.3.1 Thermoremanent magnetization (TRM).- 2.3.2 Chemical remanent magnetization (CRM).- 2.3.3 Viscous remanent magnetization (VRM) and partial thermal demagnetization.- 2.3.4 Coercivity, alternating magnetic fields and laboratory remanences.- 3 Magnetic mineralogy and magnetic identification of minerals.- 3.1 Introduction.- 3.2 Magnetic minerals.- 3.2.1 Titanomagnetites.- 3.2.2 Ilmenohaematites.- 3.2.3 Iron hydroxides and carbonates, etc..- 3.2.4 Pyrrhotite.- 3.2.5 Iron and nickel.- 3.2.6 General comments.- 3.3 Identification of magnetic minerals.- 3.3.1 Isothermal remanence.- 3.3.2 Magnetic hysteresis and coercivity spectra.- 3.3.3 Low-temperature transitions.- 3.3.4 Curie temperature.- 3.3.5 Chemical analyses.- 3.3.6 Magnetic study of chemical changes during heating.- 4 The magnetization of natural materials.- 4.1 Introduction.- 4.2 Igneous rocks.- 4.3 Unconsolidated sediments and sedimentary rocks.- 4.3.1 Physical orientation processes and unconsolidated sediments.- 4.3.2 Chemical processes and consolidated sediments.- 4.4 Metamorphic rocks.- 4.5 Archaeological materials.- 4.5.1 Heated materials.- 4.5.2 Deposited materials.- 4.5.3 Chemically changed materials.- 4.6 Secondary magnetizations.- 4.7 Magnetic inhomogeneity and anisotropy.- 4.7.1 Inhomogeneity.- 4.7.2 Anisotropy.- 4.8 Summary.- 5 Sampling, measurement and procedures.- 5.1 Introduction.- 5.2 Sampling and orientation.- 5.2.1 Sampling consolidated materials.- 5.2.2 Sampling unconsolidated materials.- 5.2.3 Orientation of samples.- 5.2.4 Tectonic corrections.- 5.3 Measurements of remanence, low-field susceptibility and anisotropy.- 5.3.1 Magnetometers.- 5.3.2 Low-field susceptibility meters.- 5.3.3 Magnetic anisotropy meters.- 5.4 The stability of remanence.- 5.4.1 Thermal demagnetization.- 5.4.2 Alternating magnetic field demagnetization.- 5.4.3 Direct current demagnetization.- 5.4.4 Other stability indicators.- 5.5 The age of the remanence.- 5.5.1 Viscous remanence.- 5.5.2 Consistency.- 5.5.3 Folds, tilts and great circles.- 5.5.4 Identification of the carriers of remanence.- 5.6 Palaeointensities.- 5.7 Summary.- 6 Statistical and mathematical analyses.- 6.1 Introduction.- 6.2 Intensity of remanence and susceptibility.- 6.3 Directional analyses.- 6.3.1 Mean directions and poles.- 6.3.2 Precision.- 6.3.3 Scatter estimates.- 6.3.4 Combining and comparing groups of vectors.- 6.3.5 Fischer and non-Fischer distributions and error estimates.- 6.4 Analyses of vector components and their stability.- 6.5 Levels of direction analyses and sampling numbers.- 6.6 Magnetic fabric.- 7 Archaeological applications.- 7.1 Introduction.- 7.2 Archaeomagnetic dating.- 7.2.1 Intensity.- 7.2.2 Directions.- 7.2.3 Master curves and assessment of standard methods.- 7.2.4 Viscous remanence and ‘alignment’ dating.- 7.3 Other applications.- 7.3.1 Sourcing (provenance) of archaeological materials.- 7.3.2 Technological and other potential applications.- 8 Geomagnetic applications.- 8.1 Introduction.- 8.2 The present geomagnetic field and historical observations.- 8.3 Secular variations and the drift of the non-dipole field.- 8.4 Polarity reversals, transitions and excursions.- 8.4.1 Polarity reversals.- 8.4.2 Transitions of polarity.- 8.4.3 Geomagnetic excursions.- 8.5 The general nature of the geomagnetic field.- 9 Geological applications.- 9.1 Introduction.- 9.2 Magnetic dating.- 9.2.1 Secular variations.- 9.2.2 Reversals and excursions.- 9.2.3 Palaeomagnetic poles.- 9.3 Magnetic fabric.- 9.3.1 Sediments and sedimentary rocks.- 9.3.2 Igneous rocks.- 9.3.3 Metamorphic rocks.- 9.4 Sedimentological applications.- 9.4.1 Sandstones and siltstones.- 9.4.2 Carbonates.- 9.4.3 Coal.- 9.4.4 Evaporites.- 9.4.5 ‘Sedimentary’ ores.- 9.5 Igneous and metamorphic rocks.- 9.5.1 Composition, redox conditions and oceanic rocks.- 9.5.2 Emplacement temperatures.- 9.5.3 Metamorphic aureoles, thermal contacts and depth of burial.- 9.6 Structural applications.- 9.6.1 Introduction.- 9.6.2 Intracontinental movements.- 9.6.3 Large-scale intracontinental tectonics.- 9.6.4 Small-scale tectonic applications.- 9.6.5 Very large-scale applications.- 9.7 Biological, weather, climatic, palaeontological and palaeogeographic aspects.- 9.7.1 Biological aspects.- 9.7.2 Weather and climatic aspects.- 9.7.3 Palaeontology, palaeolatitudes and palaeogeography.- 9.8 Extraterrestrial studies.