Geochemical insights into contribution of petroleum hydrocarbons to the formation of hydrates in the Taixinan Basin, the South China Sea  

作　　者：Yan Li Yun-Xin Fang Qian-Zhi Zhou Xiang-Po Xu Jin-Zhong Liu Guo-Yi Zhou Jiang-Hai Wang 

机构地区：[1]Guangdong Provincial Key Laboratory of Marine Resources and Coastal Engineering,School of Marine Sciences,Sun Yat-Sen University,Guangzhou,510006,China [2]Guangzhou Marine Geological Survey,Guangzhou,510760,China [3]State Key Laboratory of Organic Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou,510640,China [4]Southern Marine Science and Engineering Guangdong Laboratory(Zhuhai),Zhuhai,519000,China

出　　处：《Geoscience Frontiers》2021年第6期394-403,共10页地学前缘（英文版）

基　　金：This study was jointly supported by the National Natural Science Foundation of China(Grant Nos.41703043 and 41673066);the Guangzhou Marine Geological Survey(Grant Nos.DD20189310,DD20190230,and 42000–41090063);the Fundamental Research Funds for the Central Universities(Grant No.19lgpy91);the State Key Laboratory of Organic Geochemistry,GIG-CAS(Grant Nos.SKLOG201903)。

摘　　要：Methane hydrate in the South China Sea (SCS) has extensively been considered to be biogenic on the basis of its δ13C andδD values.Although previous efforts have greatly been made,the contribution of thermogenic oil/gas has still been underestimated.In this study,biomarkers and porewater geochemical parameters in hydrate-free and hydrate-bearing sediments in the Taixinan Basin,the SCS have been measured for evaluating the contribution of petroleum hydrocarbons to the formation of hydrate deposits via a comparative study of their source inputs of organic matters,environmental conditions,and microbial activities.The results reveal the occurrence of C_(14)–C_(16) branched saturated fatty acids (bSFAs) with relatively high concentrations from sulfate-reducing bacteria(SRBs) in hydrate-bearing sediments in comparison with hydrate-free sediments,which is in accord with the positive δ^(13)C values of dissolved inorganic carbon (DIC),increasing methane concentrations,decreasing alkalinity,and concentration fluctuation of ions (Cl^(-),Br^(-),SO_(4)^(2-),Ca^(2+),and Mg^(2+)).These data indicate the relatively active microbial activities in hydrate-bearing sediments and coincident variations of environmental conditions.Carbon isotope compositions of b SFAs (-34.0‰to -21.2‰),n-alkanes (-34.5‰to-29.3‰),and methane(-70.7‰to -69.9‰) jointly demonstrate that SRBs might thrive on a different type of organic carbon rather than methane.Combining with numerous gas/oil reservoirs and hydrocarbon migration channels in the SCS,the occurrence of unresolved complex mixtures (UCMs),odd-even predominance (OEP) values (about 1.0),and biomarker patterns suggest that petroleum hydrocarbons from deep oil/gas reservoirs are the most probable carbon source.Our new results provide significant evidence that the deep oil/gas reservoirs may make a contribution to the formation of methane hydrate deposits in the SCS.

关 键 词：Petroleum hydrocarbons Sulfate-reducing bacteria(SRBs) Biomarkers Porewater geochemistry Gas hydrates The South China Sea(SCS) 

分 类 号：P618.13[天文地球—矿床学]