【摘要】 中国黄土高原粉尘堆积以往注重从物源区携带粉尘的古风向,对粉尘沉积→固结期的古风向缺乏研究。本文评述了近年来应用黄土高原黄土、红粘土磁化率各向异性研究古季风风向变迁所取得的一些重要进展并指出磁化率各向异性最大轴和最小轴的方位和倾伏均与沉积→固结期风向变化密切相关。黄土磁组构结果与利用各种统计方法计算出的古风向在多个剖面与现代夏季风方向相似,由此推论黄土是冬季风带来的沙尘在经历夏季风携带的降雨洗礼后才固结而成。而在黄土之下的红粘土地层中的初步研究发现磁组构显示明显的西风带沉积特征,指出这一现象将在今后研究中继续深入探讨。更多还原

【Abstract】 The eolian loess-paleosol sequences and underlying red-clay formation ranging in age from Miocene to Holocene have been widely accepted as a unique geologic archive for understanding the history and variability of the East Asian palaeomonsoon climate(eg’.Ding et al.,1998;Liu et al.,1998;An et al.,2000;Guo et al.,2002). While there is still no a straight evidence,for example,a proxy tool to identify which direction of the paleowind (westly jet,northerly winter monsoon,southeastly Asian summer monsoon and southwestly Indian summer monsoon) played a major role for the formation and fabric in the eolian sediments. The measured anisotropy of magnetic susceptibility(AMS) was compared to theoretically derived magnetic fabrics occuring in airflow conditions from Baicaoyuan,Xifeng,Yichuan,Lingtai and Shilou profiles.The major and minor ellipsoid axis orientations were used to evaluate the paleowind direction in the Chinese Loess Plateau.In the new interpretation,the stronger southeasterly monsoon is able to reorient particles which are on the ground until they are immobilized by the summer rain and vegetation,the stronger summer monsoon were responsible for the magnetic fabric formation of loess-paleosol sequence.The westerly and northerly only brought the eolian material to the area while the sedimentary particles including magnetite were rearranged,settled,and fixed during the windy and rainy summer time. While for the underlying red clay,the measured AMS apparently reveals that the maximum susceptibilities group in the NW quadrant and the minimum susceptibilities are clustered in the SE quadrant.It evidently shows that westerly jet still played a major role for the formation of the AMS ellipsoid orientation before the Pleistocene.更多还原