Stable carbon isotope compositions of isoprenoid chromans in Cenozoic saline lacustrine source rocks from the Western Qaidam Basin,NW China:Source implications  

作　　者：ZHANG YongDong JIANG AiZhu SUN YongGe XIE LiuJuan CHAI PingXia 

机构地区：[1]State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China [2]Department of Earth Science, Zhejiang University, Hangzhou 310027, China [3]Graduate University, Chinese Academy of Sciences, Beijing 100049, China

出　　处：《Chinese Science Bulletin》2012年第9期1013-1023,共11页

基　　金：supported by the National Natural Science Foundation of China (40972093);the National Special Program of Oil and Gas in China (2011ZX05008-002);the Natural Science Foundation of Zhejiang Province (R5080124);the Fundamental Research Funds for the Central Universities

摘　　要：Although the distribution of mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans(MTTCs) is well understood as an indicator of water salinity,their origin and formation mechanism are still ambiguous and under debate.In this paper,abnormally high levels of MTTCs were detected in Cenozoic saline lacustrine source rocks from the Western Qaidam Basin.Using a two-step column chromatography method,the MTTCs and naphthalenes were separated from other aromatic compounds and concentrated in one fraction,so that the stable carbon isotope compositions of these compounds could be accurately measured.Similar carbon isotope ratios for the mono-,di-and trimethylated 2-methyl-2-(4,8,12-Trimethyltrideeyl) chromans in a given sample suggest the MTTCs may share the same biological source(s).The MTTCs from the Western Qaidam Basin have similar carbon isotope compositions to primary producer-derived pristane and phytane.However,the ? 13C values for the MTTCs showed significant differences with other primary producers-derived biomarkers(e.g.C27 and C29 steranes),probably indicating a distinct microalgae source from specific niches for the MTTC compounds.We speculate that the MTTCs distribution patterns may be controlled by the water chemistry dynamics in niches,which,in turn,is affected by hypersaline bottom water.Although the distribution of mono-, di- and trimethylated 2-rnethyl-2-（4,8,12-Trimethyltrideeyl） chromans （MTTCs） is well un- derstood as an indicator of water salinity, their origin and formation mechanism are still ambiguous and under debate. In this pa- per, abnormally high levels of MTTCs were detected in Cenozoic saline lacustrine source rocks from the Western Qaidam Basin. Using a two-step column chromatography method, the MTTCs and naphthalenes were separated from other aromatic compounds and concentrated in one fraction, so that the stable carbon isotope compositions of these compounds could be accurately measured. Similar carbon isotope ratios for the mono-, di- and trimethylated 2-methyl-2-（4,8,12-Trimethyltrideeyl） chromans in a given sample suggest the MTTCs may share the same biological source（s）. The MTTCs from the Western Qaidam Basin have similar carbon isotope compositions to primary producer-derived pristane and phytane. However, the δ13C values for the MTTCs showed significant differences with other primary producers-derived biomarkers （e.g. C27 and C29 steranes）, probably indicating a distinct microalgae source from specific niches for the MTTC compounds. We speculate that the MTTCs distribution patterns may be controlled by the water chemistry dynamics in niches, which, in turn, is affected by hypersaline bottom water.

关 键 词：稳定碳同位素组成 柴达木盆地西部 烃源岩 新生代 异戊二烯 盐湖 芳香族化合物 中国 

分 类 号：P618.130.2[天文地球—矿床学] S791[天文地球—地质学]