Redox history of the Three Gorges region during the Ediacaran and Early Cambrian as indica

Redox history of the Three Gorges region during the Ediacaran and Early Cambrian as indicated by

the Fe isotope

Yusuke Sawaki;Miyuki Tahata;Tsuyoshi Komiya;Takafumi Hirata;Jian Han;Degan Shu

【期刊名称】《地学前缘(英文版)》 【年(卷),期】2018(009)001

【摘要】The Ediacaran-Cambrian transition is characterized by numerous events such as the emergence of large multi-cellular metazoans and surface environmental disturbances. Based on geological evidence, it has been proposed that this transition coincided with the increase in the atmospheric oxygen level that was key to the evolution of life.Even though ancient redox conditions can be inferred from the composition of sedimentary iron mineral species, this method is not necessarily applicable to all rocks. In the Earth system, the cycling of iron is of considerable interest owing to its sensitivity to redox conditions. In-formation regarding the paleo-oceanic iron cycle is revealed in the iron isotopic composition of iron-bearing minerals. Unfortunately, only limited iron isotopic data exists for Ediacaran- to Cambrian-period oceans. To circumvent this deficiency, we drilled a fossiliferous Ediacaran to Early Cambrian sedimentary succession in the Three Gorges region, South China. We analyzed the iron isotope ratios (δ56/54Fe) of pyrite grains in the drill cores using laser ablation multi

collector inductively coupled plasma mass spectrometry.The results demonstrate large variations in δ56/54Fe,from-1.6 to 1.6‰,and positive iron isotope ratios are observed in many successions.The presence of positive δ56/54Fe in pyrite indicates that the ferrous iron in the seawater was partially oxidized, suggesting that seawater at Three Gorges was ferruginous during the Ediacaran and Early Cambrian periods. However, aggregated pyrite grains in organic carbon-rich black shales at Member 4 of the Doushantuo Formation and the base of the Shui-jingtuo Formation yield near-zero δ56/54Fe values;this suggests that the ocean was transiently dominated by sulfidic conditions during these periods. Notably negative δ56/54Fe values, lower than -1‰, can be interpreted as a signature of DIR.The DIR also might contribute in part to the re-mineralization of organic matter during the largest negative carbon isotope anomaly in the Ediacaran. 【总页数】18页(155-172) 【关键词】

【作者】Yusuke Sawaki;Miyuki Tahata;Tsuyoshi Komiya;Takafumi Hirata;Jian Han;Degan Shu

【作者单位】Department of Earth and Planetary Sciences, Tokyo Institute of Technology,2-12-1 O-okayama,Meguro-ku,Tokyo 152-8551, Japan;Department of Earth and Planetary Sciences, Tokyo Institute of Technology,2-12-1

O-okayama,Meguro-ku,Tokyo

152-8551,

Japan;Department of Earth Science and Astronomy Graduate School of Arts and Sciences,The University of Tokyo,3-8-1 Komaba,Meguro-ku,Tokyo 153-8902, Japan;Geochemistry Research Center,The University of Tokyo,Hongo 7-3-1,Bunkyo-ku,Tokyo 113-0033,Japan;Department of Geology and Key Laboratory for Continental Dynamics,Northwest University, Xi'an 710069,China;Department of Geology and Key Laboratory for Continental Dynamics,Northwest University, Xi'an 710069,China 【正文语种】英文 【中图分类】 【文献来源】

https://www.zhangqiaokeyan.com/academic-journal-cn_geoscience-frontiers_thesis/0201253165951.html 【相关文献】

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