Variations of geochemical compositions and the paleoclimatic significance of a loess-soil sequence from Garzê County of western Sichuan Province,China  

作　　者：QIAO YanSong ZHAO ZhiZhong WANG Yan FU JianLi WANG ShuBing JIANG FuChu 

机构地区：[1]Institute of Geomechanics, Chinese Academy of Geological Sciences, Beijing 100081, China [2]Key Laboratory of Neotectonic Movement & Geohazard, Beijing 100081, China

出　　处：《Chinese Science Bulletin》2009年第24期4697-4703,共7页

基　　金：Supported by the Geological Survey Program (Grant Nos. 1212010741403 and 1212010541401);National Natural Science Foundation of China (Grant No. 404720 88);Basic Research Foundation of Institute of Geomechanics (Grant No. DZL- XJK200711)

摘　　要：The West Sichuan Plateau is located in the southeast margin of the Tibetan Plateau, where the climate is mainly influenced by the Indian southwest summer monsoon and the Tibetan Plateau monsoon. In this study, detailed geochemical analysis has been carried out on Ganzisi loess-paleosol sequence in Ganzê County of western Sichuan Province. The results indicate that Ganzê loess and paleosol have experienced the incipient stage of chemical weathering in dust source regions, characterized by the decomposition of plagioclase which caused the depletion of mobile elements Na and Ca. The post-depositional chemical weathering is characterized by carbonate dissolution and oxidation of Fe2+. The variations of some geochemical indexes (such as CIA values, Na/K and Fe2+/ Fe3+ ratios) in Ganzisi loess-paleosol sequence indicate a gradually decreased chemical weathering intensity in the dust source regions and deposition areas since 1.15 Ma BP consistent with the general increase of global ice volume, reflecting that the arid trend since 1.15 Ma BP in the southeast Tibetan Plateau is a regional response to the global climate change. The geochemical indexes in this section also reveal an obvious drying step occurred at about 250 ka BP in this region. We interpret this drying step as a result of decreased influence of the Indian southwest summer monsoon. This decrease in monsoon moisture is probably attributable to the uplift of the southeast margin of the Tibetan Plateau at about 250 ka BP.The West Sichuan Plateau is located in the southeast margin of the Tibetan Plateau, where the climate is mainly influenced by the Indian southwest summer monsoon and the Tibetan Plateau monsoon. In this study, detailed geochemical analysis has been carried out on Ganzisi loess-paleosol sequence in Ganzê County of western Sichuan Province. The results indicate that Ganzê loess and paleosol have experienced the incipient stage of chemical weathering in dust source regions, characterized by the decomposition of plagioclase which caused the depletion of mobile elements Na and Ca. The post-depositional chemical weathering is characterized by carbonate dissolution and oxidation of Fe2＋. The variations of some geochemical indexes （such as CIA values, Na/K and Fe2＋/ Fe3＋ ratios） in Ganzisi loess-paleosol sequence indicate a gradually decreased chemical weathering intensity in the dust source regions and deposition areas since 1.15 Ma BP consistent with the general increase of global ice volume, reflecting that the arid trend since 1.15 Ma BP in the southeast Tibetan Plateau is a regional response to the global climate change. The geochemical indexes in this section also reveal an obvious drying step occurred at about 250 ka BP in this region. We interpret this drying step as a result of decreased influence of the Indian southwest summer monsoon. This decrease in monsoon moisture is probably attributable to the uplift of the southeast margin of the Tibetan Plateau at about 250 ka BP.

关 键 词：古土壤序列 地球化学分析 甘孜黄土 化学成分 四川省 古气候 青藏高原东南部 西部 

分 类 号：P531[天文地球—古生物学与地层学] P632[天文地球—地质学]