Mid-Late Quaternary loess-paleosol sequence in Lantian's Yushan,China:An environmental magnetism approach and its paleoclimatic significance  

作　　者：WU Yi ZHU ZhaoYu RAO ZhiGuo QIU ShiFan YANG Tian 

机构地区：[1]Key Laboratory of Marginal Sea Geology, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China [2]Key Laboratory of Western China's Environment Systems (Ministry of Education), Lanzhou University, Lanzhou 730000, China [3]School of Geography and Planning, Sun Yat-sen University, Guangzhou 510275, China [4]Graduate University of Chinese Academy ofScienees, Beijing 100049, China

出　　处：《Chinese Science Bulletin》2010年第26期2989-3000,共12页

基　　金：supported by the National Basic Research Program of China (2004CB720200 and 2010CB833405);the Knowledge Innovation Program of Chinese Academy of Sciences (KZCX2-SW-133);the National Natu-ral Science Foundation of China (40872111)

摘　　要：The application of rock magnetism methods to investigating the variations of magnetic minerals in the sediments is an important approach to the reestablishment of paleoclimate evolution. Thus we performed fine magnetic measurements on the loess-paleosol sequence (from L15 upwards to S5, in which L is short for Loess, S is short for Paleosol, the same hereinafter) of Yushan strati-graphic section, which is on the southeastern margin of Chinese Loess Plateau, in Lantian County of China's Shaanxi Province, and the thickness of which is ca. 40 m. Our study shows that the primary magnetic carriers of loess and paleosol in this section are magnetite, maghemite, hematite and goethite. Thermomagnetic analyses on the samples of representative horizons show that the higher pedogenesis degree of the sediments, the smaller variations of magnetization there will be before and after heating, probably related to the pedogenic alteration of loess sediments. Analyses of several magnetic parameters show a significant discrepancy between the paleoclimatic conditions recorded in the strata from the loess unit L15 upward to the paleosol unit S5 in the study area and those recorded in the relative strata of other sections on the Chinese Loess Plateau, and those recorded in marine sediments, indicating the great impact of regional geological background. Similarly, the rapid and intensive change recorded in the segment from L15 to S9-1, and the significant difference between the paleoclimate evolutions of the two periods before and after the change (from L15 to S9-1, and from L9 to the base of S6) indicate the strong alteration of magnetic carriers in the study area as a result of the alternations of summer and winter monsoons in East Asia.The application of rock magnetism methods to investigating the variations of magnetic minerals in the sediments is an important approach to the reestablishment of paleoclimate evolution. Thus we performed fine magnetic measurements on the loess-paleosol sequence （from L15 upwards to $5, in which L is short for Loess, S is short for Paleosol, the same hereinafter） of Yushan stratigraphic section, which is on the southeastern margin of Chinese Loess Plateau, in Lantian County of China＇s Shaanxi Province, and the thickness of which is ca. 40 m. Our study shows that the primary magnetic carriers of loess and paleosol in this section are magnetite, maghemite, hematite and goethite. Thermomagnetic analyses on the samples of representative horizons show that the higher pedogenesis degree of the sediments, the smaller variations of magnetization there will be before and after heating, probably related to the pedogenic alteration of loess sediments. Analyses of several magnetic parameters show a significant discrepancy between the paleoclimatic conditions recorded in the strata from the loess unit L15 upward to the paleosol unit S5 in the study area and those recorded in the relative strata of other sections on the Chinese Loess Plateau, and those recorded in marine sediments, indicating the great impact of regional geological background. Similarly, the rapid and intensive change recorded in the segment from L15 to S9-1, and the significant difference between the paleoclimate evolutions of the two periods before and after the change （from L15 to S9-1, and from L9 to the base of S6） indicate the strong alteration of magnetic carriers in the study area as a result of the alternations of summer and winter monsoons in East Asia.

关 键 词：古土壤序列 黄土高原 古气候意义 环境磁学 晚第四纪 中国 玉山 黄土沉积物 

分 类 号：P531[天文地球—古生物学与地层学] S157[天文地球—地质学]