Towards a Model for Predicting Magnetic Susceptibility of BedrockRegolith and Soils

摘要

One of the Department of Defense's most pressing environmental problems is the efficient detection and identificationof unexploded ordnance (UXO). In regions of highly magnetic soils, magnetic and electromagnetic sensors often detectanomalies that are of geologic origin, adding significantly to remediation costs. In order to develop predictive models formagnetic susceptibility, it is crucial to understand modes of formation and the spatial distribution of different ironoxides. Most rock types contain iron and their magnetic susceptibility is determined by the amount and form of ironoxides present. When rocks weather, the amount and form of the oxides change, producing concomitant changes inmagnetic susceptibility. The type of iron oxide found in the weathered rock or regolith is a function of the duration andintensity of weathering, as well as the original content of iron in the parent material. The rate of weathering is controlledby rainfall and temperature; thus knowing the climate zone, the amount of iron in the lithology and the age of the surfacewill help predict the amount and forms of iron oxide. We have compiled analyses of the types, amounts, and magneticproperties of iron oxides from soils over a wide climate range, from semi arid grasslands, to temperate regions, andtropical forests. We find there is a predictable range of iron oxide type and magnetic susceptibility according to theclimate zone, the age of the soil and the amount of iron in the unweathered regolith.