Palaeomagnetism: Principles and Applications in Geology, Geophysics and Archaeology

ISBN-13: 9789400959576 / Angielski / Miękka / 2011 / 380 str.

Donald H. Tarling

Opis

Palaeomagnetism and archaeomagnetism are fascinating specialized studies because they are applicable to such a wide range of problems in geology, archaeology and geophysics. They can also be undertaken cheaply, when compared with most other geophysical techniques, and, at first sight, simply. In fact, real comprehension of the magnetic processes that have occurred in rocks and other types of material over several thousands or many millions of years is still extremely difficult to assess and measure. On this basis, this book cannot explain all such features, nor can it attempt to cover all the actual and potential applications of the method. All that can be attempted is to give an impression of the ways in which such techniques can be used in a wide variety of fields, and how these techniques are usually applied. The magnetization of rocks is, in fact, one of the earliest of the true sciences, but we are still not in a position to answer many of the problems posed. Consequently some of the examples given of applications are, essentially, state-of-the-art comments, rather than being a review as such. The changing position of the geomagnetic poles with time is still not adequately defined, for example, and some of the more recent conventional views are given, although the emphasis is placed on more subjective, probably more controversial, evaluations.

Spis treści

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.