阿拉伯海北部马克兰增生楔G16站位地球化学特征及其对天然气水合物的指示  

Geochemical characteristics of the sediments at site G16 of the Makran accretionary wedge,the northern Arabian Sea,and their implications for gas hydrates

作　　者：李强[1,2] 杨天邦 庄畅 邓希光[1,2] 王海峰 于淼[1,2] LI Qiang;YANG Tianbang;ZHUANG Chang;DENG Xiguang;WANG Haifeng;YU Miao(Guangzhou Marine Geological Survey,Guangzhou 510760,China;Key Laboratory of Marine Mineral Resources,Ministry of Natural Resources,Guangzhou 510760,China)

机构地区：[1]中国地质调查局广州海洋地质调查局,广州510760 [2]自然资源部海底矿产资源重点实验室,广州510760

出　　处：《海洋地质与第四纪地质》2021年第3期161-169,共9页Marine Geology & Quaternary Geology

基　　金：中国地质调查局工作项目(DD20190582)。

摘　　要：阿拉伯海马克兰海域是具有天然气水合物勘查潜力的重要区域之一。对该海域G16站位沉积物样品的碎屑矿物、钼、有机碳和顶空气甲烷含量以及孔隙水总碱度和阴阳离子等地球化学特征进行综合分析。结果表明:Mg^(2+)和Ca^(2+)的浓度随深度明显降低,总碱度、Mg^(2+)/Ca^(2+)随深度显著增加;在硫酸盐-甲烷界面(SMI),SO4^(2−)的浓度线性降低至0.31 mmol/L,甲烷含量急剧增加至784μmol/L,黄铁矿含量达到最大值并形成一个Mo峰。研究区硫酸根浓度线性降低和强烈亏损梯度以及Mg^(2+)、Ca^(2+)、总碱度和有机碳含量的变化特征,指示研究区存在强烈的甲烷厌氧氧化反应(AOM),并形成浅的SMI(估算深度4.62 mbsf)。孔隙水样品的地球化学异常与沉积物自生黄铁矿和Mo含量存在耦合现象,表明本站位深部沉积物中可能赋存有天然气水合物藏。The Makran accretionary wedge in the northern Arabian Sea is one of the important areas with large gas hydrate potential.Sediment,headspace gas and pore water samples were collected from the sediment core at site G16 PC of the area.Comprehensive studies are conducted on organic carbon,molybdenum,methane concentrations in headspace gas,and total alkalinity,anions and cations in pore water and detrital sediments.It is revealed that concentrations of Mg^(2+)and Ca^(2+)decrease clearly with the increasing in depth,while the total alkalinity and the Mg^(2+)/Ca^(2+)ratio increases sharply.Around the sulfate methane interface(SMI),the concentration of dissolved sulfate(SO4^(2−))decreases linearly to 0.31 mmol/L,with a sharp increase in methane to 784μmol/L.At the same time,the content of pyrite in sediments reaches its maximum together with a Mo peak.Combined with changing characteristics of total alkalinity and concentrations of Mg^(2+),Ca^(2+)and organic carbon,the concentration of sulfate decreased linearly and the high sulfate gradients suggest that there is strong anaerobic methane oxidation(AOM)occurred at the SMI,which is estimated in a depth of 4.62 mbsf.A coupling phenomenon exists between geochemical anomaly characteristics of sediment samples and pore water samples from the sediment core and the content of authigenic pyrite,which strongly indicate that gas hydrate reservoirs may occur in the deeper layer of the study area.

关 键 词：地球化学 天然气水合物 马克兰增生楔 阿拉伯海北部 

分 类 号：P736.4[天文地球—海洋地质]