南海东北部陆坡天然气水合物多期次分解的沉积地球化学响应  

Sedimentary Geochemical Response to Gas Hydrate Episodic Release on the Northeastern Slope of the South China Sea

作　　者：陈芳[1] 陆红锋[1] 刘坚[1] 庄畅[1] 吴聪[1] 曹珺[1] 周洋[1] 刘广虎[1] 

机构地区：[1]广州海洋地质调查局国土资源部海底矿产资源重点实验室,广东广州510075

出　　处：《地球科学（中国地质大学学报）》2016年第10期1619-1629,共11页Earth Science-Journal of China University of Geosciences

基　　金：国家自然科学基金面上项目(No.41372012);国家专项项目课题(No.GZH2011003050602)

摘　　要：南海地区天然气水合物资源丰富,针对其分解方式的研究有助于资源的开采.对南海东北部天然气水合物钻探区GMGS08站位岩心沉积物开展沉积学、地球化学分析研究.结果表明:该站位自上而下分布11层含自生碳酸盐岩和双壳碎屑层(其中6层呈粥状沉积)以及2层自生碳酸盐岩灰岩层;各层自生碳酸盐岩除一个样品δ13 C值稍高(-38.85×10-3)外,其他的δ13 C值介于-41.36×10-3^-56.74×10-3,均低于-40.00×10-3,δ18 O值介于2.94×10-3~5.37×10-3,明显偏重,表明其为天然气水合物分解的产物,形成于微生物对甲烷的缺氧氧化作用,甲烷主要源自生物成因;各层自生碳酸盐岩层中的有机质碳同位素负偏明显,最低达-82.44×10-3,可能与微生物活动有关;根据自生碳酸盐岩的分布推断该站位至少发生过6次天然气水合物分解释放,每期次自生碳酸盐岩的差异说明其甲烷通量强弱不同.The resource of gas hydrate in South China Sea is plentiful. It redound to resource development by investigating how the gas hydrate decompose. A sedimentology and geochemistry study has been done in gas-hydrate-bearing borehole sediment collected at site GMGS08 within the gas hydrate drilling area in the northeastern South China Sea. Results show that 11 layers of authigenic carbonate and bivalve bioclast, and 2 layers of carbonate limestone are distributed from top to bottom in hole GMGS08. Authigenic carbonate and bivalve bioclast primarily occurred in soupy structure sediments with high water content. The δ13 C values of authigenic carbonate ranged from -41.36×10 a to -56.74× 10-3 except one sample with a higher δ13C value of -38.85×10-3 , and the δ18O values were apparently heavy ranging from 2.94 ×10-3 to 5.37 × 10 -3, suggesting they were attributed to gas hydrate dissociation via microbial anaerobic oxidation of methane, which was predominantly biogenic gas. The δ13 C values of organic carbon varied from - 21.33 × 10-3 to -82.44 × 10-3 , in which the δ13Cnegative excursion intervals corresponded to authigenic carbonate layers. According to the distribution of anthigenic carbonate, it is concluded that at least 6 episodes of gas hydrate release existed in geologic record, and the varying si- zes of authigenic carbonate among the layers indicated the intensity of methane flux in each episode was different.

关 键 词：粥状沉积 自生碳酸盐岩 碳同位素 天然气水合物多期次分解 海洋地质 

分 类 号：P736[天文地球—海洋地质]