Geochemistry of pore waters from the Xisha Trough, northern South China Sea and their implications for gas hydrates |
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| Authors: | Shao-Yong Jiang Tao Yang Lu Ge Jing-Hong Yang Hong-Fei Ling Neng-You Wu Jian Liu Dao-Hua Chen |
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| Institution: | (1) State Key Laboratory for Mineral Deposits Research, Department of Earth Sciences, Nanjing University, Nanjing, 210093, China;(2) Research Center for Marine Geochemistry, Nanjing University, Nanjing, 210093, China;(3) Guangzhou Marine Geological Survey, China Geological Survey, Guangzhou, 510760, China |
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| Abstract: | This paper reports all available geochemical data on sediments and pore waters from the Xisha Trough on the northern continental
margin of the South China Sea. The methane concentrations in marine sediments display a downhole increasing trend and their
carbon isotopic compositions (δ
13C = −25 to −51‰) indicate a thermogenic origin. Pore water Cl− concentrations show a range from 537 to 730 mM, and the high Cl− samples also have higher concentrations of Br−, Na+, K+, and Mg2+, implying mixing between normal seawater and brine in the basin. The SO4
2− concentrations of pore waters vary from 19.9 to 36.8 mM, and show a downhole decreasing trend. Calculated SMI (sulfate-methane
interfaces) depths and sulfate gradients are between 21 and 47 mbsf, and between −0.7 and −1.7 mM/m, respectively, which are
similar to values in gas hydrate locations worldwide and suggest a high methane flux in the basin. Overall, the geochemical
data, together with geological and geophysical evidence, such as the high sedimentation rates, high organic carbon contents,
thick sediment piles, salt and mud diapirs, active faulting, abundant thermogenic gases, and occurrence of huge bottom simulating
reflector (BSR), are suggestive of a favorable condition for occurrence of gas hydrates in this region. |
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| Keywords: | Gas hydrate geochemical anomaly Xisha Trough South China Sea |
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