Occurrences and distributions of branched alkylbenzenes in the Dongsheng sedimentary uranium ore deposits, China

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• 责任者：Tuo Jincai ; Chen Ru ; Zhang Mingfeng ; Wang Xianbin
• 年：2010
• 作者单位：Chinese Academy of Sciences, Institute of Geology and Geophysics, Lanzhou, China
• 刊：Journal of Asian Earth Sciences
• 期：6

摘要

A series of branched alkylbenzene ranging from C (sub 15) to C (sub 19) with several isomers (2-5) at each carbon number were identified in sediments from the Dongsheng sedimentary uranium ore deposits, Ordos Basin, China. The distribution patterns of the branched alkylbenzenes show significant differences in the sample extracts. The branched alkylbenzenes from organic-rich argillites and coals range from C (sub 15) to C (sub 19) homologues, in which the C (sub 17) or C (sub 18) dominated. On the other hand, the C (sub 19) branched alkylbenzenes dominated in the sandstone/siltstone extracts. The obvious differences of the branched alkylbenzene distributions between the uranium-host sandstones/siltstones and the interbedded barren organic-rich mudstones/coals probably indicate their potential use as biological markers associated with particular depositional environments and/or maturity diagenetic processes. Possible origins for these branched alkylbenzenes include interaction of simple aromatic compounds with, or cyclization and aromatization reactions of, these linear lipid precursors such as fatty acids, methyl alkanoates, wax esters or alkanes/alkenes that occur naturally in carbonaceous sediments. The possible simple aromatic compounds may include substituted benzenes, functionalized compounds such as phenols that are bound to kerogen at the benzyl position, and phenols that are decomposition products derived from aquatic and terrestrial sources. The distributions of methyl alkanoates and n-alkanes were found to be different between organic-rich mudstone/coal and sandstone/siltstone. From this result, it can be concluded that such differences of the alkylbenzene distributions were mainly resulting from the differences of organic precursors, although maturity effect and radiolytic alteration cannot be completely excluded.