%0 Journal Article
%T A SEVEN MILLION GEOCHEMICAL RECORD FROM CHINESE REd-CLAY AND LOESS-PALEOSOL SEQUENCE:WEATHERING AND EROSION IN NORTHWESTERN CHINA
灵台红粘土和黄土-古土壤序列的地球化学演化
%A Gu Zhaoyan
%A Ding Zhongli
%A Xiong Shangfa
%A Liu Tungsheng
%A
顾兆炎
%A 丁仲礼
%A 熊尚发
%A 刘东生
%J 第四纪研究
%D 1999
%I
%X The surface of the earth is continuously undergoing changes as a result of weathering-erosion, plate tectonics and volcanic processes. Contiental weatheringerosion with its complex rock-water interactions is the central process of globalbiochemical cycling of elements. Rates of the weathering-erosion depend on a varietyof factors, in particular rock properties and chemical composition, climate(especiallyrainfall), structure, and elevation. They are quite variable on a regional scale.Chemical composition of debris sediment must be related to the rate of weatheringerosion in its source region. Thus history of weathering-erosion on the earth surfacewould be revealed by studies of geochemistry of sediments.It is believed that a material volume as 3-5 times as the present QinghaiXizang Plateau has been removed from the plateau and its adjacent regions byweathering and erosion since the beginning of itS uplifting. The wind blown dustdeposits in the Chinese Loess Plateau is derived from the arid and semiarid regions innorthwestern China, in turn, where the deposits have been derived from TibetanPlateau and the high mountains around. Therefore, geochemistry of the wind blownloess-paleosol and red-clay sequences in the Loess Plateau may provide insight to thehistory of uplihng and weathering-erosion on the QinghaiXizang Plateau.Chemical analyses were carried out on the samples from the seven million-yearred-clay/loess-paleosol sequence in Lingals, Chinese Loess Plateau. The weight ratiosof Na/Al and Fe2+ /Fe3+ in the samples have been employed as indices in degrees ofchemical weathering (or alteration) and oxidation of the dust deposits respectively.The lower the ratios are, the higher the degrees indicate. The ratios tend to increasestepwisely since about 5.6Ma B. P., which is believed as a result of globalpaleoclimatic changes indicated by both δ18O and aeolian dust flux records from thePacific rather than the degree of Pedogenic strength of the sequence obtained from ourfieldwork. Furthermore,the Fe/Al ratios show a decreasing trend toward the top of thesequence.These facts induced us to make the conclusions as following :(1) The chemical composition of the dust deposited in the Loess Plateau hasbeen changed step by step since about 7Ma B. P., which may be relaied to theuplifting of the Qinghai-Xizang Plateau and/or glaciation in the Northern Hemisphere.Uplifting and glaciation would increase the rate of erosion in the dust source regions,degrade chemical weathering of parent dust. The dry and windy climate alsostrengthens mechanical erosion in the dust source regions.(2) Variations in the ratios of Na/Al and Fe2+ /Fe3+in the red-clay-loess-paleosol sequence resulted mainly from changes in chemical composition of the dustin source regions, and were modified by in situ weathering.(3) The Na/Al and Fe2+ /Fe3+ ratios may be used as the indices of weatheringerosion history in the dust source regions, so much as the rates of denudation of theQinghai-Xizang
%K red-clay
%K loess-paleosol
%K weathering
红粘土
%K 黄土－古土壤
%K 风化作用
%K 地球化学
%U http://www.alljournals.cn/get_abstract_url.aspx?pcid=E62459D214FD64A3C8082E4ED1ABABED5711027BBBDDD35B&cid=621CF755B1A341E5&jid=EA07051745CDC8D89D5F01A3A4CFE6A9&aid=7747E9E4F817F963A099385335F94823&yid=B914830F5B1D1078&vid=2A8D03AD8076A2E3&iid=E158A972A605785F&sid=FA88DCCE84EA0A56&eid=683005D16807E4FE&journal_id=1001-7410&journal_name=第四纪研究&referenced_num=34&reference_num=32