Abnormal Sedimentary Events and Gas Hydrate Dissociation in Dongsha Area of the South China Sea during Last Glacial Period
Author(s): Chen Fang, Zhuang Chang, Zhang Guangxue, Lu Hongfeng, Duan Xiao, Zhou Yang, Su Xin, Wu Cong, Liu Guanghu, Key Laboratory of Marine Mineral Resources, Ministry of Land and Resources, Guangzhou Marine Geological Survey, School of Ocean Sciences, China University of Geosciences
Pages: 1517-1526
Year: 2014 Issue: 11
Journal: Earth Science-Journal of China University of Geosciences
Keyword: gas hydrate dissociation; depleted δ13 C; carbonate dissolution; last glacial period; Dongsha slope; marine geology.;
Abstract: Core 973-3 is located at the potential gas hydrate area on the slope within Dongsha area of the South China Sea,with the water depth of 1026 m.According to the sedimentology,chronology,isotope and B/Ca ratio of the foraminiferal tests,carbonate and pyrite content,the light δ13 C values of planktonic Globigerinoides ruber and benthic Uvigerina peregrine are found in several core layers with the most negative value of-2.03‰.In the δ13 C distinctly depleted layers,the concentration of environmental[CO32-]is relatively low,and the pyrites are abundant up to 17%,which indicates abnormal seepage of methane.Below the δ13 C depleted layers,the carbonate intensely dissolves,and its content decreases to the bottom.It suggests that it has probably been caused by the gas hydrate dissociation.The seepage and anaerobic oxidation of methane resulted from the dissociation and release of gas hydrates is the primary reason of the depleted δ13 C values of foraminiferal tests,carbonate dissolution and the deposits of enormous pyrites.Methane release events occurred in the last glacial period,which implies that the descending sea level induced the gas hydrate dissociation.According to the δ13 C depleted record of foraminiferas,it is concluded that there were at least four times release events of methane,and their intensities were almost at the same level.
Pages: 1517-1526
Year: 2014 Issue: 11
Journal: Earth Science-Journal of China University of Geosciences
Keyword: gas hydrate dissociation; depleted δ13 C; carbonate dissolution; last glacial period; Dongsha slope; marine geology.;
Abstract: Core 973-3 is located at the potential gas hydrate area on the slope within Dongsha area of the South China Sea,with the water depth of 1026 m.According to the sedimentology,chronology,isotope and B/Ca ratio of the foraminiferal tests,carbonate and pyrite content,the light δ13 C values of planktonic Globigerinoides ruber and benthic Uvigerina peregrine are found in several core layers with the most negative value of-2.03‰.In the δ13 C distinctly depleted layers,the concentration of environmental[CO32-]is relatively low,and the pyrites are abundant up to 17%,which indicates abnormal seepage of methane.Below the δ13 C depleted layers,the carbonate intensely dissolves,and its content decreases to the bottom.It suggests that it has probably been caused by the gas hydrate dissociation.The seepage and anaerobic oxidation of methane resulted from the dissociation and release of gas hydrates is the primary reason of the depleted δ13 C values of foraminiferal tests,carbonate dissolution and the deposits of enormous pyrites.Methane release events occurred in the last glacial period,which implies that the descending sea level induced the gas hydrate dissociation.According to the δ13 C depleted record of foraminiferas,it is concluded that there were at least four times release events of methane,and their intensities were almost at the same level.
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