Environmental Magnetism

1 Introduction.- 2 Magnetic properties of solids.- 2.1 Introduction.- 2.2 Basic magnetic properties.- 2.2.1 Diamagnetism.- 2.2.2 Paramagnetism.- 2.2.3 Ferromagnetism.- 2.2.4 Ferrimagnetism and antiferromagnetism.- 2.3 Hysteresis.- 2.4 Effects of crystal size, shape and structure.- 2.4.1 Anisotropy.- 2.4.2 Domains and domain walls.- 2.4.3 Multidomain behaviour.- 2.4.4 Single-domain behaviour.- 2.4.5 Superparamagnetism.- 2.4.6 Critical grain sizes.- 2.5 Time dependence of magnetisation.- 2.6 Grain interactions.- 2.7 Summary.- Further reading.- 3 Natural magnetic minerals.- 3.1 Iron and its abundance.- 3.2 Iron oxides.- 3.2.1 The spinel group.- 3.2.2 The corundum group.- 3.3 Pyrrhotite and the iron sulphides.- 3.4 Iron hydroxides and oxyhydroxides.- 3.5 Other magnetic minerals.- 3.6 Formation of natural magnetic minerals.- 3.6.1 Igneous rocks.- 3.6.2 Metamorphic rocks.- 3.6.3 Sediments.- 3.7 Summary.- Further reading.- 4 Magnetic properties of natural materials.- 4.1 Introduction.- 4.2 Units.- 4.3 Magnetic remanence.- 4.3.1 Natural magnetic remanences.- 4.3.2 Laboratory-imparted remanences.- 4.4 Magnetic susceptibility.- 4.5 Anisotropy of susceptibility.- 4.6 Magnetic hysteresis.- 4.7 General magnetic properties of natural materials.- 4.8 Temperature dependence of magnetic properties.- 4.9 Summary.- Further reading.- 5 The Earth'1 Introduction.- 2 Magnetic properties of solids.- 2.1 Introduction.- 2.2 Basic magnetic properties.- 2.2.1 Diamagnetism.- 2.2.2 Paramagnetism.- 2.2.3 Ferromagnetism.- 2.2.4 Ferrimagnetism and antiferromagnetism.- 2.3 Hysteresis.- 2.4 Effects of crystal size, shape and structure.- 2.4.1 Anisotropy.- 2.4.2 Domains and domain walls.- 2.4.3 Multidomain behaviour.- 2.4.4 Single-domain behaviour.- 2.4.5 Superparamagnetism.- 2.4.6 Critical grain sizes.- 2.5 Time dependence of magnetisation.- 2.6 Grain interactions.- 2.7 Summary.- Further reading.- 3 Natural magnetic minerals.- 3.1 Iron and its abundance.- 3.2 Iron oxides.- 3.2.1 The spinel group.- 3.2.2 The corundum group.- 3.3 Pyrrhotite and the iron sulphides.- 3.4 Iron hydroxides and oxyhydroxides.- 3.5 Other magnetic minerals.- 3.6 Formation of natural magnetic minerals.- 3.6.1 Igneous rocks.- 3.6.2 Metamorphic rocks.- 3.6.3 Sediments.- 3.7 Summary.- Further reading.- 4 Magnetic properties of natural materials.- 4.1 Introduction.- 4.2 Units.- 4.3 Magnetic remanence.- 4.3.1 Natural magnetic remanences.- 4.3.2 Laboratory-imparted remanences.- 4.4 Magnetic susceptibility.- 4.5 Anisotropy of susceptibility.- 4.6 Magnetic hysteresis.- 4.7 General magnetic properties of natural materials.- 4.8 Temperature dependence of magnetic properties.- 4.9 Summary.- Further reading.- 5 The Earth's magnetic field.- 5.1 Geomagnetism.- 5.1.1 Description of the geomagnetic field.- 5.1.2 Secular variation.- 5.1.3 Origin of the geomagnetic field.- 5.2 Palaeomagnetism.- 5.2.1 Archaeomagnetism.- 5.2.2 Palaeosecular variation.- 5.2.3 Polarity timescale.- 5.2.4 Apparent polar wandering.- 5.3 Summary.- Further reading.- 6 Techniques of magnetic measurements.- 6.1 Introduction.- 6.2 Measurement of remanent magnetisation.- 6.2.1 Generator magnetometer.- 6.2.2 Astatic and parastatic magnetometers.- 6.2.3 Fluxgate magnetometer.- 6.2.4 Superconducting magnetometer.- 6.3 Measurement of initial susceptibility.- 6.3.1 The a.c. method.- 6.3.2 The direct method.- 6.3.3 Anisotropy of initial susceptibility.- 6.3.4 Quadrature and frequency-dependent susceptibility.- 6.4 Measurement of induced magnetisation.- 6.4.1 The force method.- 6.4.2 Ballistic magnetometer.- 6.4.3 Vibrating sample magnetometer.- 6.4.4 Alternating field method.- 6.5 Magnetic cleaning techniques.- 6.5.1 Alternating field demagnetisation.- 6.5.2 Thermal demagnetisation.- 6.6 Magnetic fields.- 6.6.1 Measurement.- 6.6.2 Generation.- 6.6.3 Shielding.- 6.7 Portable instruments.- 6.7.1 Magnetometers.- 6.7.2 Gradiometers.- 6.7.3 Pulsed induction.- 6.7.4 Induction balance.- 6.8 A basic environmental magnetic kit.- 6.9 Summary.- Further reading.- 7 Magnetic minerals and environmental systems.- 7.1 Surface processes and magnetic minerals.- 7.2 Primary and secondary magnetic minerals.- 7.3 Magnetic minerals and material flux.- 7.4 Natural remanence and mineral magnetic properties.- 7.5 Sampling and measurement.- 7.6 Summary.- 8 Soil magnetism.- 8.1 Introduction.- 8.2 Magnetic properties of soil minerals.- 8.3 Weathering and magnetic properties.- 8.4 The magnetic enhancement of surface soils.- 8.5 Particle size relationships.- 8.6 Some representative soil profiles.- 8.7 The effects of gleying on magnetic properties.- 8.8 Soil magnetism and slope processes.- 8.9 The persistence of magnetic oxides in the soil.- 8.10 Soil magnetism and archaeology.- 8.11 Conclusions.- 9 Magnetic minerals and fluvial processes.- 9.1 Introduction.- 9.2 Suspended sediment sources.- 9.2.1 Suspended sediments in the Jackmoor Brook.- 9.2.2 Other studies of suspended sediment sources.- 9.2.3 Prospects and problems.- 9.3 Magnetic tagging and tracing of stream bedload.- 9.3.1 The Plynlimon case study.- 9.3.2 The prospects for magnetic tracing.- 9.4 Magnetic measurements of stormwatersuspended solids.- 9.5 Conclusions.- 10 Mineral magnetic studies of lake sediments.- 10.1 Lake sediments and environmental reconstruction.- 10.2 The origin of magnetic minerals in lake sediments.- 10.3 Sampling and measurement.- 10.4 Prospecting, core correlation and sediment accumulation rates.- 10.5 Sediment resuspension and focusing.- 10.6 Sediment sources and ecological change.- 10.7 Magnetic measurements and fire.- 10.8 Lake sediment magnetism and climatic change.- 10.9 Summary and conclusions.- 11 Magnetic minerals in the atmosphere.- 11.1 Introduction.- 11.2 Sources of magnetic minerals in the atmosphere.- 11.3 Magnetic properties and aerosol modes.- 11.4 Magnetic-heavy metal linkages.- 11.5 Peat magnetism and the history of atmospheric particulate deposition.- 11.6 Contemporary particulate pollution monitoring.- 11.7 Magnetic particulates in ice and snow.- 11.8 Global dust studies.- 11.9 Summary and conclusions.- 12 Mineral magnetism in marine sediments.- 12.1 Introduction.- 12.2 The origin and flux of marine magnetic minerals.- 12.3 Core correlation in marine sediments.- 12.4 Mineral magnetism and palaeoclimate in deep-sea sediments.- 12.5 Particulate pollution monitoring in coastal waters.- 12.6 Summary and conclusions.- 13 Reversal magnetostratigraphy.- 13.1 Introduction.- 13.2 Geomagnetic signatures.- 13.2.1 Origin of remanent magnetisation in igneous rocks.- 13.2.2 Origin of magnetisation in sediments.- 13.3 The geomagnetic polarity timescale.- 13.4 Polarity transitions.- 13.5 Summary.- 14 Secular variation magnetostratigraphy.- 14.1 Introduction.- 14.2 Experimental methods.- 14.3 Magnetic dating and magnetostratigraphy.- 14.4 Origin of palaeolimnomagnetic secular variation.- 14.5 Palaeomagnetic pitfalls.- 14.6 Excursions and the reinforcement syndrome.- 14.7 Summary.- 15 Biomagnetism.- 15.1 Introduction.- 15.2 Magnetic navigation.- 15.3 Pneumomagnetism.- 15.4 Cardiomagnetism.- 15.5 Neuromagnetism.- 15.6 Summary.- 16 The Rhode River, Chesapeake Bay, an integrated catchment study.- 16.1 Physical setting.- 16.2 Sediment sources.- 16.3 Study aims.- 16.4 Methods.- 16.5 The magnetic mineralogy of the Rhode River catchment.- 16.6 Suspended sediment samples.- 16.7 Estuarine sediment cores: mineral magnetic characteristics.- 16.8 Chronology and links with land-use change.- 16.9 Summary and implications.- 17 Prospects.- 17.1 Palaeomagnetism of recent sediments.- 17.2 The mineral magnetic approach.- Glossary of magnetic terms.- References.