Frequent Magnetic Susceptibility Characteristics of the Wushan Loess and Its Paleoclimatic, Paleoenvironmental Significance in Wushan Area

摘要

In order to explore and reveal the paleoclimatic and paleoenvironmental evolution of the Yangtze River in Three Gorges area since the late Pleistocene,we test the samples collected from “Wushan loess” on their frequency magnetic susceptibility.The result showed that:①The frequency magnetic susceptibility of “Wushan loess” is between 0.39％ and 7.25％ and an average of 2.72％.Lower SP grain content in “Wushan loess” describe that the sediment pedogenesis is weak,and indicate that when “Wushan loess” has been accumulating,the climate is cold and dry,mainly winter monsoon.②The frequency magnetic susceptibility values of “Wushan loess” in the area of paleoclimate indicates that the law for the high-frequency magnetic susceptibility value reflects the summer monsoon climate of warm and humid rainy conditions,while the low value reflects the winter monsoon dry and cold-dry climatic conditions.③According to the characteristics of cyclic fluctuations of the frequency magnetic susceptibility curve,we could divide the area of the paleoclimate and paleoenvironment into five different stages of evolution: partial warm and wet period under cold and dry background→partial warm and humid period of the dry background→climate gets colder period →colder and drier period→dry and cold period.