Molecular and stable carbon isotopic compositions of saturated fatty acids within one sedimentary profile in the Shenhu,northern South China Sea: Source implications |
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| Institution: | 1. Géosciences et Environnement Cergy, Université de Cergy-Pontoise, Bâtiment E, 5, mail Gay-Lussac, Neuville-sur-Oise, F-95031 Cergy-Pontoise, France;2. Department of Geology, University of Johannesburg, PO Box 524, Auckland Park 2006, Johannesburg, South Africa;3. Shell International Exploration and Production, 3333 Hwy 6, South Houston, TX 77079, USA;1. Laboratoire de Géologie de l''Ecole Normale Supérieure, CNRS UMR 8538, 24 rue Lhomond, 75005 Paris, France;2. Sorbonne Universités, UPMC Univ Paris 06, UMR 7193, ISTeP, F-75005, Paris, France;3. iSTeP, UMR 7193, CNRS, F-75005 Paris, France;4. Département Géosciences Environnement, Université de Cergy-Pontoise, 5 mail Gay-Lussac, Neuville/Oise, 95031 Cergy-Pontoise, France;5. EPOC Université de Bordeaux, UMR 5805, avenue des facultés, 33405 Talence, France;6. Beicip-Franlab, 232 Avenue Napoléon Bonaparte, 92500 Rueil-Malmaison, France |
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| Abstract: | This study examined the distributions and stable carbon isotopic compositions of saturated fatty acids (SaFAs) in one 300 cm long sedimentary profile, which was named as Site4B in Shenhu, northern South China Sea. The concentrations of total SaFAs in sediments ranged from 1.80 to 10.16 μg/g (μg FA/g dry sediment) and showed an even-over-odd predominance in the carbon chain of C12 to C32, mostly with n-C16 and n-C18 being the two major components. The short-chain fatty acids (ScFAs; n-C12 to n-C18) mainly from marine microorganisms had average δ13C values of ?26.7‰ to ?28.2‰, whereas some terrigenous-sourced long-chain fatty acids (LcFAs; n-C21 to n-C32) had average δ13C values of ?29.6‰ to ?34.1‰. The other LcFAs (n-C24 & n-C26 ～ n-C28; average δ13C values are ?26.1‰ to ?28.0‰) as well as n-C19 and n-C20 SaFAs (average δ13C values are ?29.1‰ and ?29.3‰, respectively) showed a mixed signal of carbon isotope compositions.The relative bioproductivity calculation (marine vs. terrigenous) demonstrated that most of organic carbon accumulation throughout the sedimentary profile was contributed by marine organism. The high marine productivity in Shenhu, South China Sea may be related to the hydrocarbon seepage which evidenced by diapiric structures. Interestingly, there is a sever fluctuation of terrigenous inputs around the depth of 97 cm below the seafloor (bsf), probably resulting from the influence of the Dansgaard–Oeschger events and the Younger Dryas event as revealed by 14C age measurements. |
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| Keywords: | Saturated fatty acids Molecular distribution Carbon isotope Marine productivity Shenhu area South China Sea |
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