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Comparison and Primarily Interpretation of Magnetic Susceptibilities in Different Sediments

JI Yunping1) XIA Zhengkai2) 1) Institute of Hydrogeology and Environmental Geology, CAGS, Shijiazhuang, Hebei, 050061; 2) College of Urban and Environmental Science, Peking University, Beijing, 100871  
Magnetic susceptibility has been widely used in Quaternary paleoclimate studies in recent years, with good results obtained. Nevertheless, some scientists have pointed out that, due to the complexity of its mechanism, the magnetic susceptibility interpretations for different types of sediments show obvious diversity. Five types of sediments, i.e., loess, river sediments, lake sediments, aeolian sediments and red earth, were chosen from South China for magnetic susceptibility measurement, grain-size measurement and pollen analysis. Based on a comparison between the magnetic susceptibility and other related paleoenvironment indicators, the authors tried to study the factors affecting magnetic susceptibilities in different types of sediments so as to provide scientific evidence for the correct interpretation of magnetic susceptibilities. It is held that, as the factors affecting the magnetic susceptibility are diverse in different types of sediments, we should use different means to interpret different magnetic susceptibilities. Magnetic susceptibility can be used to indicate the paleoclimate changes in loess and lake sediments, for it is affected mainly by climatic changes. Magnetic susceptibility in river sediments is mainly affected by grain sizes which have close relationship with the dynamical condition and physiographic position of the river, and hence it can serve as evidence of dynamical environment, but cannot respond to the climatic changes. In aeolian sediments, magnetic susceptibility is also mainly influenced by grain sizes which are closely related to the power and direction of the wind. The factors affecting the magnetic susceptibility in red earth are very complicated: not only the original characteristics but also the subsequent strong eluviation and weathering can affect the magnetic susceptibility. So the interpretation of magnetic susceptibility of red earth is controversial and needs further study. It is thus concluded that, as magnetic susceptibilities in different types of sediments are obviously affected by many different factors, the interpretation of magnetic susceptibilities has to be conducted with great care.
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