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Occurrences and distributions of branched alkylbenzenes in the Dongsheng sedimentary uranium ore deposits,China
Institution:1. Key Laboratory of Petroleum Resources Research, Institute of Geology and Geophysics, Chinese Academy of Sciences, Lanzhou, 730000 Gansu, PR China;2. Graduate University of the Chinese Academy of Sciences, Beijing 100039, PR China;1. Department of Earth Sciences Indian Institute of Technology Bombay Powai, Mumbai, India, 400076;2. Institute of Earth Sciences, Academia Sinica P.O. Box 1-55, Nankang Taipei, 11529 Taiwan;1. Chinese Academy of Geological Sciences, Beijing 100037, China;2. MNR Laboratory of Deep Geosciences and Exploration Technology, Chinese Academy of Geological Sciences, Beijing 100037, China;3. College of Earth Science, Chengdu University of Technology, Chengdu 610059, Sichuan, China;4. Tibet Bureau of Geological Exploration, Lhasa Tibet 850000, China;5. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Beijing 100083, China
Abstract:A series of branched alkylbenzene ranging from C15 to C19 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 C15 to C19 homologues, in which the C17 or C18 dominated. On the other hand, the C19 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.
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