Factors controlling the burial of organic carbon in laminated and bioturbated sediments off NW Mexico: implications for hydrocarbon preservation |
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| Institution: | 1. Library of Marine Samples, Korea Institute of Ocean Science & Technology, Geoje 656-830, Republic of Korea;2. Biological Resource Center/Korean Collection for Type Cultures (KCTC), Korea Research Institute of Bioscience and Biotechnology, Jeonbuk 56212, Republic of Korea;3. Pukyong National University, Yongso-ro, Busan 48513, Republic of Korea;4. Marine Ecosystem Research Center, Korea Institute of Ocean Science & Technology, Busan 49111, Republic of Korea;5. Marine Biotechnology Research Center, Korea Institute of Ocean Science & Technology, Busan 49111, Republic of Korea;6. National Institute of Fisheries Science, Tongyeong 53085, Korea;7. Marine Ecology Research Center, Yeosu 59697, Republic of Korea;8. Biological Daegu Center, Korea Basic Science Institute (KBSI), Daegu, Republic of Korea;9. National Institute of Fisheries Science, Busan, 619-705, Republic of Korea;10. Marine observation team, Korea Institute of Ocean Science & Technology, Geoje 656-830, Republic of Korea;11. Ballast Water Research Center, Korea Institute of Ocean Science & Technology, Geoje 53201, Republic of Korea;1. School of Earth Sciences and Engineering, Xi''an Shiyou University, Xi''an, Shaanxi 710065, China;2. Shaanxi Key Laboratory of Petroleum Accumulation Geology, Xi''an Shiyou University, Xi''an, Shaanxi 710065, China;3. College of Geosciences, China University of Petroleum (Beijing), Beijing 102249, China;4. State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China;5. No.6 Oil Production Plant of PetroChina Changqing Oilfield Company, Xi''an 710299, China;6. No. 1 Gas Production Plant of Changqing Oilfield Company, PetroChina, Xi''an 750001, China;7. Development and Research Center, National Geological Archives of China, China Geological Survey, Beijing 100037, China;1. Department of Geology, University of Tartu, Ravila 14A, 50411 Tartu, Estonia;2. Department of Earth and Atmospheric Sciences, University of Alberta, Edmonton T6G 2E3, Canada;3. Department of Earth Sciences, University of Minnesota–Twin Cities, Minneapolis 55455, USA;4. CAGE – Centre for Arctic Gas Hydrate, Environment and Climate, Department of Geosciences, UiT The Arctic University of Norway, 9037 Tromsø, Norway;5. Geological Survey of Norway, 7491 Trondheim, Norway |
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| Abstract: | Factors controlling the burial of organic carbon (OC) in Late Quaternary sediments on the NW Mexican continental margin are assessed using a suite of box and piston cores strategically located on the shelf-slope rise with respect to the intense oxygen minimum in this region. An OC concentration maximum occurs on the mid-slope, below the core of an intense water-column O2 minimum, due to current winnowing on the outer shelf, the preferential accumulation of organic matter in fine-grained deposits, and the offshore decrease in the settling flux of organic detritus. The organic matter at all water depths is overwhelmingly marine. Hydrogen indices (HI) are higher on the slope (>300 mg HC/g TOC) than on the shelf (<300 mg HC/g TOC), where current winnowing has promoted organic matter degradation, but there is no difference in HI in slope sediments accumulating under well oxygenated and O2-deficient conditions. The degree of winnowing appears to be the primary factor affecting the preservational quality of organic matter deposited on this margin.Rates of accumulation of OC and opal are all higher in the interglacial intervals when compared with the glacial deposits over the last 140,000 yr. However, matrix-corrected HI values in the mid- and lower-slope cores are invariant and are similar to values in the laminated intervals from the oxygen-minimum site. Thus, cyclic changes in organic carbon accumulation on this margin have been controlled by production variations rather than differential preservation. HI values in Late Quaternary sediments from several continental margins, including NW Mexico, and euxinic basins correspond to type II kerogen, irrespective of bottom water O2 concentrations. Therefore, the preservation of oil-prone kerogen in productive margin settings does not appear to be restricted to sediments deposited under conditions of low bottom water O2 concentrations as envisioned in models of petroleum source-rock deposition. |
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