Absence of hexavalent chromium in marine carbonates:implications for chromium isotopes as paleoenvironment proxy

作     者：Ziyao Fang Liping Qin Wei Liu Tao Yao Xiaoyan Chen Shiqiang Wei Ziyao Fang;Liping Qin;Wei Liu;Tao Yao;Xiaoyan Chen;Shiqiang Wei

作者机构：CAS Key Laboratory of Crust-Mantle Materials and EnvironmentsUniversity of Science and Technology of China CAS Center for Excellence in Comparative Planetology National Synchrotron Radiation LaboratoryUniversity of Science and Technology of China 

出 版 物：《National Science Review》 (国家科学评论(英文版))

年 卷 期：2021年第8卷第3期

页      面：151-158页

核心收录：

学科分类：081702[工学-化学工艺] 070902[理学-地球化学] 0709[理学-地质学] 07[理学] 08[工学] 0817[工学-化学工程与技术] 

基　　金：supported by the Strategic Priority Research Program (B) of Chinese Academy of Sciences (XDB41000000) the National Natural Science Foundation of China (41625013,41721002, 41888101) the Pre-research Project on Civil Aerospace Technologies (D020202) of Chinese National Space Administration the Fundamental Research Funds for the Central Universities of China (WK2080000102) 

主　　题：Cr isotopes XANES speciation atmospheric oxygen level 

摘      要：The oxygenation of Earth’s atmosphere is widely regarded to have played an important role in early-life ***(Cr) isotopes recorded in sedimentary rocks have been used to constrain the atmospheric oxygen level(AOL) over geological times based on the fact that a positive Cr isotopic signature is linked to the presence of Cr(Ⅵ) as a result of oxidative continental ***,there is no direct evidence of the presence of Cr(Ⅵ) in sedimentary rocks *** are most widely distributed over geological times and were thought to have incorporated Cr(Ⅵ) directly from ***,we present results of Cr valence states in carbonates which show Cr(Ⅲ) is the dominant species in all samples spanning a wide range of geological *** findings indicate that Cr(Ⅵ) in seawater was reduced either before or after carbonate precipitation,which might have caused Cr isotopic fractionation between seawater and carbonates,or marine carbonates preferentially uptake Cr(Ⅲ) from *** Cr(Ⅲ) can come from non-redox Cr cycling,which also can cause isotopic fractionation,we suggest that positively fractionated Cr isotopic values do not necessarily correspond to the rise in AOL.