The source and paleoclimatic implication of hydrogen isotopic composition of n-alkanes in sediments from the Yixian Formation,western Liaoning Province,NE China |
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| Institution: | 1. Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering/South China Sea Bioresource Exploitation and Utilization Collaborative Innovation Center, School of Marine Sciences, Sun Yat-Sen University, Guangzhou 510006, China;2. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;3. Guangdong Ocean University, Zhanjiang 524088, China;1. SE Asia Research Group, Department of Earth Sciences, Royal Holloway University of London, Egham TW20 0EX, United Kingdom;2. Research School of Earth Sciences, Australian National University, Canberra, ACT 2601, Australia;1. Institute for Marine and Antarctic Studies, University of Tasmania, Private Bag 129, Hobart, Tasmania 7001, Australia;2. ARC Centre of Excellence for Core to Crust Fluid Systems (CCFS)/GEMOC, Department of Earth and Planetary Sciences, Macquarie University, NSW 2109, Australia;1. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, 3, Koptyug ave., Novosibirsk 630090, Russia;2. Novosibirsk State University, 2, Pirogova str., Novosibirsk 630090, Russia;3. Trofimuk Institute of Petroleum Geology and Geophysics, Siberian Branch of the Russian Academy of Sciences, 3, Koptyug ave., Novosibirsk 630090, Russia;4. Vinogradov Institute of Geochemistry, Siberian Branch of the Russian Academy of Sciences, 1А Favorsky str., Irkutsk 664033, Russia;1. Hebei GEO University, Shijiazhuang, Hebei 050031, China;2. Tianjin Institute of Geology and Mineral Resources, Tianjin 300170, China;3. School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, China;4. Department of Earth Science, University of Adelaide, Adelaide 5005, Australia;1. School of Geography, Geology & Environment, Kingston University, Penrhyn Road, Kingston upon Thames KT1 2EE, UK;2. Camborne School of Mines, University of Exeter, Cornwall Campus, Penryn, Cornwall TR10 9FE, UK;3. Department of Mineralogy, Natural History Museum, Cromwell Road, London SW7 5BD, UK;4. Department of Earth and Planetary Sciences, Birkbeck College, Gower Street, London WC1E 7HX, UK;1. Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville, FL 32611, USA;2. School of Earth Sciences and Resources, China University of Geosciences Beijing, Beijing 100083, PR China;3. Department of Earth Sciences, The University of Adelaide, Adelaide, SA 5005, Australia;4. Department of Earth System Sciences, Yonsei University, Seoul 03722, Republic of Korea |
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| Abstract: | Hydrogen isotopic composition of n-alkanes was measured in sediments from an excavated profile of the Early Cretaceous Yixian Formation in Liaoning Province, NE China, aiming to assess the significance of the δD value of n-alkanes in ancient lacustrine sediments as the indicator for determining the source inputs of organic matters and paleoclimatic conditions. The δD values of n-alkanes are in the range of ? 250‰ to ? 85‰ and display an obvious three-stage variation pattern through the profile, which is consistent with the distribution of the dominated n-alkanes and the profile of their δ13C values. The δD and δ13C values of n-alkanes suggest that short-chain n-alkanes are primarily derived from photosynthetic bacteria and algae; n-C29 and n-C31 are mainly originated from terrestrial higher plants; n-C28 and n-C30 may be derived from the same precursor but via the different biological mechanism of hydrogen isotopic fractionation; while the source inputs of medium-chain n-alkanes are more complicated, with n-C23 being derived from some specific algae or biosynthesized by various aquatic organisms. The paleoclimatic conditions are reconstructed via two approaches. The reconstructed hydrogen isotopic values of lake water and meteoric water (expressed as δDLW and δDMW, respectively) were at the intervals of ? 51.8‰ to 17.0‰ and ? 118.1‰ to ? 43.5‰, respectively, indicating a general climate transition from semi-arid to arid. The calculated ΔδDLW-MW values vary from 37.0‰ to 89.1‰ and display a similar but a significant large-scale variation trend with the ΔδDC23 ‐ long (? 28.8‰ to 85.0‰; long represents long-chain n-alkanes) and ΔδDmid-long (? 15.4‰ to 43.4‰; mid represents medium-chain n-alkanes) values. The discrepancy may be attributed to the source input overlap for n-alkanes and the uncertainties of εwater/lipid values. The coupling of ΔδDC23 ‐ long, ΔδDmid-long and ΔδDLW-MW values with the paleoclimatic evidence indicates that the δD values of n-alkanes could be more sensitive to the change of paleoclimatic conditions. |
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