Germanium/silica ratio and trace element composition of Early Cambrian siliceous rocks in Keping:implications for the siliceous rocks'formation and paleoenvironment interpretations  

作　　者：Zixuan Guan Shibiao Deng Peixian Liu Yiqiu Jin Xingchun Cao 

机构地区：[1]MOE Key Laboratory od Orogenic Belts and Crustal Evolution,School of Earth and Space Science,Peking University,Beijing 100871,China [2]Research Institute of Petroleum Exploration and Development,CNPC,Beijing 100083,China

出　　处：《Acta Geochimica》2020年第6期797-810,共14页地球化学学报（英文）

基　　金：National Key Basic Research Program of China(973 Program,No.2012CB214801).We also thank Prof.Dong Lin at Peking University for the help in the ICP-OES analyses.

摘　　要：This study used the germanium/silica(Ge/Si)ratios,together with rare earth elements and other trace elements to infer the siliceous source and sedimentary environment of the siliceous rocks located at the bottom of Yuertusi Formation in Northwestern Tarim Basin,Keping,China.Previous studies have shown that this siliceous rock stratum formed at the edge of the carbonate platform on the continental shelf.Researchers suggest that these siliceous rocks were formed by hydrothermal activity,but some still draw different conclusions.Understanding the silicon source and depositional environment of these siliceous rocks would help us learn the processes of environmental changes and the causes of biological explosions during this period.The value of germanium/silica ratios of these siliceous rocks is from 0.15 to 0.37 pmol/mol and much lower than above 10|imol/mol values in siliceous rocks that are known formed by hydrothermal activity.All samples are rich in HREE,which differ from hydrothermal siliceous rocks that are rich in LREE.Most samples lack hydrothermal related elements.All these features show that the source of these siliceous rocks'siliceous is not hydrothermal flu ids.The samples'Ce/Ce*range from 0.88 to 1,and Th/U ratios range from 0.01 to 0.36.These features suggest these siliceous rocks were formed in an anoxic environment.Considering all the evidence,we conclude that the siliceous rock stratum at the bottom of the Lower Cambrian Yuertusi Formation in northwest Tarim Basin.Keping,was formed in anoxic seawater at the edge of the carbonate platform on the continental shelf.Its silicon source is seawater instead of hydrothermal fluid.

关 键 词：Siliceous rocks Trace elements Ge/Si ratio Tarim Basin 

分 类 号：P534.41[天文地球—古生物学与地层学] P588.2[天文地球—地质学]