Diagenesis of organic matter in a 400 m organic rich sediment core from offshore Namibia using solid state 13C NMR and FTIR |
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| Affiliation: | 1. Department of Chemistry and Biochemistry, Old Dominion University, Norfolk, VA 23529, USA;2. UPMC – Univ. Paris 06 et CNRS-UMR 7193 ISTeP, Equipe Evolution et Modélisation des Bassins Sédimentaires, Case 117, 4 Place Jussieu, 75252 Paris Cedex 05, France;3. Total Exploration and Production, Paris La Défense F.92078, France;1. Schlumberger Information Solutions, Mill Valley, CA 94941, USA;2. Department of Geological & Environmental Sciences, Stanford University, Palo Alto, CA 94305, USA;3. Biomarker Technologies, Inc., Rohnert Park, CA 94928, USA;4. Department of Geosciences and The Earth & Environmental Systems Institute, The Pennsylvania State University, University Park, PA 16802, USA;1. NIOZ Royal Netherlands Institute for Sea Research, NL-1790 AB Den Burg, The Netherlands;2. CEFREM-UMR CNRS 5110, University of Perpignan, 52 avenue Paul Alduy, F-66860 Perpignan, France;3. Institut de Radioprotection et de Sûreté Nucléaire (IRSN), PRP-Env/SESURE/LERCM, BP3, Saint Paul Lez Durance F-13115, France;4. Ifremer, Géosciences Marines, BP 70, 29280 Plouzané, France;1. State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences (Wuhan), Hubei Province, Wuhan 430074, China;2. Institute of Oceanology, Chinese Academy of Sciences, Shandong Province, Qingdao 266071, China;3. Heisenberg Group on Marine Kerogen, Center for Marine Environmental Sciences (MARUM), Bremen University, D-28359 Bremen, Germany;4. Bureau of Economic Geology, The University of Texas at Austin, TX 78712, USA;1. State Key Laboratory for Mineral Deposits Research (Nanjing University), School of Earth Sciences and Engineering, Nanjing University, 22 Hankou Road, Nanjing 210093, China;2. Université Pierre et Marie Curie, BioEMco, CNRS UMR 7618, 4 Place Jussieu, Paris F-75252, France;3. University of Washington, School of Oceanography, Seattle, WA 98195, USA;1. WA Organic and Isotope Geochemistry Centre, Department of Chemistry, Curtin University, GPO Box U1987, Perth, WA 6845, Australia;2. CSIRO Land and Water, Glen Osmond, SA 5064, Australia;3. Centre for Exploration Targeting and West Australian Biogeochemistry Centre, The University of Western Australia, 35 Stirling Highway, Crawley, WA 6009, Australia;4. CSIRO Marine and Atmospheric Research, GPO Box 1538, Hobart 7001, Tasmania, Australia |
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| Abstract: | Although rates and mechanisms of early diagenesis have been well studied, the effects of microbial metabolism on the molecular composition of the sedimentary organic matter (SOM) over long periods of time need more investigation. In this study, we characterize the early diagenesis of marine SOM from organic rich sediments of the Ocean Drilling Program site 1082 located off Namibia, in the vicinity of the Benguela coastal upwelling system. We used both Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance spectroscopy (13C NMR) to assess the quantitative partitioning of the organic carbon into major compound classes (aliphatic, aromatic, ester, carboxylic, amide and carbons from carbohydrates). Then, we calculate the SOM composition in the main biomolecules (proteins, carbohydrates, lipids and lignin) on the basis of previous 13C NMR based estimates of the molecular composition of the organic mixtures. Results show that the SOM is still labile at 7 m below the seafloor (mbsf) and composed of about 25% proteins and 15% carbohydrates. With increasing depth, the protein content exponentially decreases to 13% at 367 mbsf, whereas the carbohydrate content decreases linearly to 11%. The lignin and lipid content consistently represent around 10% and 40% of the SOM, respectively, and show an increase with depth, due mostly to selective enrichment as the more labile components are lost by degradation. Thus, these components of the SOM are considered refractory at the depth scale considered. The calculated remineralization rates are extremely slow ranging from 5.6 mol C m−3 ky−1 at the top of the core to 0.2 mol C m−3 ky−1 according to the organic carbon flux to the seafloor. Knowing the labile carbon losses, we propose a method to calculate the initial TOC before the diagenesis took place. |
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| Keywords: | Early diagenesis Sedimentary organic matter Marine sediments Nuclear magnetic resonance Diagenesis rates TOC |
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