| 华南李家沱剖面寒武纪纽芬兰世海水氧化还原性质演化及其驱动因素 |
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| 引用本文： | 向雷,蔡春芳,贺训云,姜磊,袁余洋,汪天凯,贾连奇.华南李家沱剖面寒武纪纽芬兰世海水氧化还原性质演化及其驱动因素[J].地球科学,2015,40(7):1197-1214. |
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| 作者姓名： | 向雷 蔡春芳 贺训云 姜磊 袁余洋 汪天凯 贾连奇 |
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| 作者单位： | 1.中国科学院地质与地球物理研究所, 北京 100029 |
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| 基金项目： | 国家重点基础研究发展计划“973“项目，国家基金委重大项目，国家杰出青年基金项目 |
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| 摘 要： | 大气-海洋含氧量的演化对埃迪卡拉纪-寒武纪转折期的后生动物大爆发事件具有重要影响.为探讨寒武纪纽芬兰世中国南方海洋氧化还原性质的演化及其初级生产力、海水硫酸盐浓度等演化驱动因素, 分析了李家沱剖面纽芬兰世留茶坡组和小烟溪组微量元素、有机碳含量、有机碳同位素、总硫含量、黄铁矿硫同位素等.该剖面沉积于斜坡-盆地环境且出露齐全.该剖面上V/Sc、Th/U及Mo、U、V、Ni、Cu等元素的富集系数呈现出5个变化旋回, 其中留茶坡组中上部和小烟溪组中部各存在一氧化环境段, 其余层段处于缺氧环境, 而Re/Mo则显示仅在小烟溪组中部水体出现过短暂的氧化环境和含有游离H2S的硫化环境, 其余层段处于没有游离H2S的缺氧非硫化环境.Ba、Ni、Cu、Zn、Cd等微量元素的富集系数及TOC表明: 留茶坡组的有机质沉降量和埋藏量都明显小于上覆小烟溪组; 而在小烟溪组中, 其中部有机质的沉降量和埋藏量最低, 下部最高, 上部次之.TOC/TS、TS以及黄铁矿硫同位素的垂向演化趋势等都显示李家沱剖面纽芬兰世大都处于低海水硫酸盐浓度环境.低海水硫酸盐浓度是造成李家沱剖面纽芬兰世缺氧水体未富集游离H2S的主要原因.大气含氧量的升高是导致李家沱剖面小烟溪组中部出现短暂氧化环境以及近硫化环境的主要原因.
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| 关 键 词： | 微量元素 黄铁矿硫同位素 氧化还原性质 海水硫酸盐浓度 纽芬兰世 李家沱剖面 地球化学 |
| 收稿时间： | 2014-12-30 |
Ocean Redox State Evolution and Its Controlling Factors during Cambrian Terreneuvian Epoch:Evidence from Lijiatuo Section,South China |
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| Xiang Lei,Cai Chunfang,He Xunyun,Jiang Lei,Yuan Yuyang,Wang Tiankai,Jia Lianqi.Ocean Redox State Evolution and Its Controlling Factors during Cambrian Terreneuvian Epoch:Evidence from Lijiatuo Section,South China[J].Earth Science-Journal of China University of Geosciences,2015,40(7):1197-1214. |
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| Authors: | Xiang Lei Cai Chunfang He Xunyun Jiang Lei Yuan Yuyang Wang Tiankai Jia Lianqi |
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| Abstract: | The evolution of atmospheric and oceanic oxygen content played an important role in the metazoans' radiation around Ediacaran-Cambrian transition. To explore the vertical stratigraphic evolution and controls of the redox ocean state, primary productivity and seawater sulfate levels during the Terreneuvian epoch, South China, Lijiatuo section, a well-exposed one that is located in the slope and basin environment and consists of mudstones of Xiaoyanxi Formation and cherts of Liuchapo Formation, is selected as the study area for an in-depth analysis of the trace elements, total organic carbon(TOC), organic carbon isotopes, total sulfur(TS) and the sulfur isotope of the pyrite. Based on the ratios of V/Sc, Th/U and the enrichment factors of Mo, U, V, Ni and Cu in the Lijiatuo section, five oxic-anoxic cycles are identified across the Terreneuvian epoch. Except for the middle-upper Liuchapo Formation and the middle Xiaoyanxi Formation, the rest parts of the Lijiatuo section are under anoxic conditions. The Re/Mo ratios demonstrate that the oxic environment of the middle Xiaoyanxi Formation is accompanied by transient sulfidic conditions, and the rest parts of the section are under anoxic and non-sulfidic conditions. All the TOC and the enrichment factors of Ba, Ni, Cu, Zn and Cd demonstrate that both the sink and burial flux of organic matter of Liuchapo Formation are lower than those of the overlying Xiaoyanxi Formation. The highest sink and burial fluxes of organic matter in the Xiaoyanxi Formation appeare in its lower parts, however, whereas the lowest sink and burial fluxes of organic matter in the Xiaoyanxi Formation appeare in its middle parts. The proxies of TOC/TS, TS and the vertical trend of sulfur isotope of pyrite show that the majority of the Lijiatuo section is under low seawater sulfate levels. The low seawater sulfate level was the dominating control for the depletion of free H2S in the majority of the anoxic depositional environment of Lijiatuo section during Terreneuvian epoch. The rise of the atmospheric oxygen content was the principal driver for the coupled, transient oxic and near sulfidic environment in the middle Xiaoyanxi Formation. |
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| Keywords: | trace element sulfur isotope of pyrite redox state seawater sulfate level Terreneuvian epoch Lijiatuo section geochemisty |
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