HR: 0830h
AN: GP41B-0049    [PDF]
TI: COERCIVITY DISTRIBUTIONS OF SOFT-MAGNETIC COMPONENTS AND THEIR OCCURRENCE IN SEDIMENTS ANS SEDIMENTARY ROCKS
AU: * Egli, R
EM: egli@mag.ig.erdw.ethz.ch
AF: Institute of Geodesy and Photogrammetry, ETH Honggerberg, Zurich, 8093 Switzerland
AU: Spassov, S
EM: simo@spassov.ch
AF: Department of Geophysics, School of Geology Aristotle University of Thessaloniki, Thessaloniki, 54124 Greece
AU: Heller, F
EM: heller@mag.ig.erdw.ethz.ch
AF: Institute of Geophysics, ETH Honggerberg, Zurich, 8093 Switzerland
AB: The analysis of magnetization curves with model functions is a valuable tool for identifying magnetic mineral sources in sediments and sedimentary rocks. The method is limited by two main factors: the ability of the model function in reproducing appropriately the magnetic properties of an individual component, and its extreme sensitivity to measurement errors. Both factors influence the number of components, which are needed to fit a magnetization curve within the measurement error. Recent investigations on the shape of coercivity distributions (Heslop, 2003; Egli 2003) support the use of model functions introduced by Egli (2003). Extremely detailed measurements of alternating field (AF) demagnetisation curves of isothermal (IRM) and anhysteretic (ARM) remanent magnetizations have been performed on a wide variety of sediments and sedimentary rocks including sediments from rivers, lakes and oceans, recent soils, paleosols, loesses, red clays, limestones and also on atmospheric dusts, urban pollution and magnetotactic bacteria. The component analysis allowed the identification of several magnetic components with specific properties, which reflect different magnetic mineral sources: extracellular, bacterial and pedogenic magnetite, lithogenic minerals transported by water or in air, and magnetic minerals associated to anthropogenic pollution sources. Each magnetic component is described by nine parameters: four for the shape of the IRM, four for the shape of the ARM coercivity distribution, and one for the ratio of the ARM to the IRM. By comparing similar components occurring in different samples, empirical relations can be established between different parameters, which reflect fundamental physical processes that control the shape of coercivity distributions. As a consequence, only four parameters, so-called magnetic fingerprints, are necessary to characterise a magnetic component. The effect of environmental changes on the magnetic properties of specific magnetic components has been investigated in detail for sediments from lakes and oceans, highlighting the complex and non-linear behaviour of such natural systems. Heslop, D. and G. McIntosh, The influence of initial state, interaction and thermal relaxation on the isothermal remanent magnetisation curves, IUGG 2003 (GAI.03/03A/A14-007). Egli, R., The analysis of demagnetisation curves with skewed generalized functions (SGG): a novel method for the identification of magnetic sources in sediments, IUGG 2003 (GAI.03/03A/A14-008).
DE: 1512 Environmental magnetism
DE: 1519 Magnetic mineralogy and petrology
DE: 1540 Rock and mineral magnetism
DE: 1594 Instruments and techniques
SC: Geomagnetism and Paleomagnetism [GP]
MN: 2003 Fall Meeting