Paleoceanographic Indicators for Early Cambrian Black Shales from the Yangtze Platform, South China: Evidence from Biomarkers and Carbon Isotopes

查看全文 作　　者：CHEN [1,2,3]Lan;ZHONG [4]Hong;HU [4]Ruizhong;XIAO [4]Jiafei;TSAI Louis Loung-[2]Yie;LIN Andrew Tien-[4]Shun;ZOU [5]Yanrong

机构地区：[1]College of Petroleum Engineering,Chongqing University of Science and Technology,Chongqing 401331,China;[2]Institute of Applied Geology,National Central University,Jhongli 32001;[3]Institute of Geophysics,National Central University,Jhongli 32001;[4]State key Laboratory of Ore Deposit Geochemistry,Institute of Geochemistry,Chinese Academy of Sciences,Guiyang,Guizhou 550002,China;[5]State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou,Guangdong 510640,China

出　　处：《Acta Geologica Sinica(English Edition)》索引2012年第86卷第5期,共11页

基　　金：supported by the 'CAS Hundred Talents'Foundation of the Chinese Academy of Sciences to H.Z.,National Natural Science Foundation of China (Grant No.41102066, 40972084);Natural Science Foundation Project of CQ CSTC (Grant No. 2009BB7383);Opening Foundation of the State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences 摘　　要：The lower Cambrian Niutitang Formation, a widespread black shale deposition, is of geological interest because of its polymetallic beds, Cambrian explosion, depositional ages, dramatic environmental changes and so on. Previous study focused mainly on inorganic geochemistry and few studies have investigated the organic fractions of upper Neoproterozoic-lower Cambrian strata in South China. Here we report a study of biomarkers plus organic carbon isotopes for black shales from Ganziping, Hunan Province (China). All the saturated hydrocarbon fractions have a unimodal distribution of n-alkanes, a high content of short-chain alkanes and maximize at C 19 or C 20 (C 23 for sample Gzh00-1). The C 27 /C 29 sterane ratio ranges from 0.77 to 1.20 and 4-methylsteranes are in low abundance. These parameters indicate that algae and bacteria are the important primary producers. Furthermore, biomarker maturity proxies show the samples to be higher maturity. The low Pr/Ph values (<0.7) suggest that the samples were deposited under anoxic conditions and, likely, under stratified water columns. In addition, 25-norhopanes and gammacerane are present as diagnostic indicators of normal marine salinity and dysoxic to anoxic conditions. During the Early Tommotian, known to coincide with a transgression event, small shelly fossils increased in abundance and diversity. Moreover, positive δ 13 C org excursions close to 1.4‰ occur at the base of the Tommotian stage. In summary, the Early Cambrian black shales were deposited under dramatic paleoenvironmental changes, including oceanic anoxia, higher primary productivity and sea-level rise. 关键词：有机碳同位素生物标志物黑色页岩古海洋学中国南方早寒武世扬子地台成熟度指标

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Paleoceanographic Indicators for Early Cambrian Black Shales from the Yangtze Platform, South China: Evidence from Biomarkers and Carbon Isotopes

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