First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet,China

查看全文 作　　者：TONG [1,2]HongPeng;CHEN [1]DuoFu

机构地区：[1]CAS Key Laboratory of Marginal Sea Geology,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,China;[2]Graduate University of Chinese Academy of Sciences,Beijing 100049,China

出　　处：《Chinese Science Bulletin》索引2012年第57卷第33期,共10页

基　　金：supported by the National Natural Science Foundation of China (41273041);No. IS-1542 from GIGCAS 摘　　要：Hydrocarbon seeps,widely occurring in continental margins,have become increasingly focused owing to their close relationships with gas hydrates,strong greenhouse gas methane,and biological resources in extreme environments.Ancient hydrocarbon seeps have already been recognized from Devonian to Quaternary strata worldwide based on seep carbonates or seep-related fossil chemosynthetic assemblages.However,seep-related deposits are rarely found from ancient strata in the China's Mainland.Here,we report the first discovery of an ancient seep deposit,specifically late Cretaceous seep carbonates from Xigaze in Tibet,China.Xigaze seep carbonates,occurring as nodules,are enclosed in upper Cretaceous turbidite strata in Xigaze forearc basin.These carbonates are composed of authigenic carbonate(56.2% on average),clastic quartz and feldspar(27.3% on average),and clay minerals(chlorite,illite and smectite,16.5% on average).Clotted micrites,peloids and framboid pyrites are frequently observed,all of which are common in modern seep carbonates.The carbonates have negative δ13 C values varying from 27.7‰ to 4.0‰(V-PDB),suggesting that thermogenic methane is the primary carbon source.Ce/Ce* values revised by eliminating La effects show no real Ce anomaly,indicating the carbonates were primarily precipitated in a weak reducing environment.Overall,these features provide unequivocal evidences that the seafloor of Xigaze forearc basin developed hydrocarbon seeps in late Cretaceous. 关键词：冷泉碳酸盐岩日喀则地区晚白垩世中国大陆西藏天然气水合物碳氢化合物第四纪地层

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First discovery and characterizations of late Cretaceous seep carbonates from Xigaze in Tibet,China

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