Abnormal Sedimentary Events and Gas Hydrate Dissociation in Dongsga Area of tge Soutg Cgina Sea during Last Glacial Period
Chen Fang
Zhuang Chang
Zhang Guangxue
Lu Hongfeng
Duan Xiao
Zhou Yang
Su Xin
Wu Cong
Liu Guanghu
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 1 026 m.According to the sedimentology,chronology,isotope and B/Ca ratio of the foraminiferal tests,car-bonate and pyrite content,the lightδ13 C values of planktonic Globigerinoidesruber and benthicUvigerina peregrine are found in several core layers with the most negative value of-2.03‰.In theδ13 C distinctly depleted layers,the concentration of envi-ronmental [CO3 2-]is relatively low,and the pyrites are abundant up to 1 7%,which indicates abnormal seepage of methane. Below theδ13 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 depletedδ13 C values of foraminiferal tests,carbonate disso-lution 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 theδ13 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.
Keywords：gas hydrate dissociationdepletedδ13 Ccarbonate dissolutionlast glacial periodDongsha slopemarine geology
Publication Date：2014-01-01
Online Publishing Date：2025-08-15(First online date of this platform, not the publication date of the document)
Pages：10( 1517-1526 )