Trace element and rare earth element of cap carbonate in Ediacaran Doushantuo Formation in Yangtze Gorges  

作　　者：HUANG Jing1,2,3, CHU XueLei1,2, CHANG HuaJin1,2,3 & FENG LianJun1,2 1 Institute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, China 2 State Key Laboratory of Lithospheric Evolution, Beijing 100029, China 3 Graduate University of the Chinese Academy of Sciences, Beijing 100049, China 

出　　处：《Chinese Science Bulletin》2009年第18期3295-3302,共8页

基　　金：Supported by the National Natural Science Foundation of China (Grant Nos. 40532012, 40873007 and 40603021);Chinese Academy of Sciences (Grant No. KZCX3-SW-141)

摘　　要：For the Doushantuo cap carbonate at the Jiulongwan section in the Yangtze Gorges, its concentrations of redox sensitive elements suggest two distinct enrichments in stratigraphy. These enrichments occur at about 0.8 m and 3.3 m above the bottom of cap carbonate, respectively. They are interpreted as the temporary anoxic depositional conditions due to the oxidation of seeped methane. REE+Y patterns of the cap carbonate are classified into three types with different styles: (1) from the bottom to 2.45 m, representing the behaviors of freshwater and suggesting that massive meltwater swarmed into surface oceans during the deglaciation; (2) from 2.45 m to 3.3 m, indicating the pattern of ancient seawater possibly due to upwelling of deep water; and (3) from 3.3 m to the top, showing "MREE bulge" pattern with HREE-depletion as a result of diagenesis. The three-stage REE+Y patterns represent the transformations of shallow water in the wake of the Marinoan glaciation in this region: the fresh meltwater was dominant first, and then it interfused into the oceanic basin by the transgression and upwelling. Bloom of plankton further introduced anoxia near the water-sediment interface.For the Doushantuo cap carbonate at the Jiulongwan section in the Yangtze Gorges, its concentrations of redox sensitive elements suggest two distinct enrichments in stratigraphy. These enrichments occur at about 0.8 m and 3.3 m above the bottom of cap carbonate, respectively. They are interpreted as the temporary anoxic depositional conditions due to the oxidation of seeped methane. REE＋Y patterns of the cap carbonate are classified into three types with different styles： （1） from the bottom to 2.45 m, representing the behaviors of freshwater and suggesting that massive meltwater swarmed into surface oceans during the deglaciation; （2） from 2.45 m to 3.3 m, indicating the pattern of ancient seawater possibly due to upwelling of deep water; and （3） from 3.3 m to the top, showing ＂MREE bulge＂ pattern with HREE-depletion as a result of diagenesis. The three-stage REE＋Y patterns represent the transformations of shallow water in the wake of the Marinoan glaciation in this region： the fresh meltwater was dominant first, and then it interfused into the oceanic basin by the transgression and upwelling. Bloom of plankton further introduced anoxia near the water-sediment interface.

关 键 词：碳酸盐岩帽 稀土元素 长江三峡 微量元素 迪卡 氧化还原 冰川融水 陡山沱组 

分 类 号：P595[天文地球—地球化学]