埃迪卡拉纪-寒武纪沉积黄铁矿的多硫同位素组成及其对古环境的指示意义

Neoproterozoic Oxygenation Event (NOE) is the second great oxygenation event in Earth's history. At about 575Ma, Edicaran biota appeared and then disappeared at 542Ma, when Cambrian Explosion took place. Due to enhanced organic carbon burial, δ13C of carbonate has high positive values through out the Neoproterozoic, only punctuated by negative δ13C excursions, mostly associated with glaciations. Sulfur isotope fractionation between seawater sulfate and sedimentary pyrite Δ34S shows an increase to 40-70‰ at NOE and was suggested to be due to baterial sulfur disproportionation (BSD). However, whether this increase in Δ34S is local or global is still under debate. And whether sea water sulfate concentration increased at Ediacaran-Cambrian (Ed-C) boundary and whether deep sea oxygenation was widespread at this period are also under debate. In this proposal, we will carry out the first study of multiple sulfur isotopic compositions of sedimentary pyrite at multiple Ed-C sections at Yangtz platform with the aim to answer those important questions and to recover the paleoenvronment. Our initial data of Xiaotan section from Yongshan County, Yunnan Province, demonstrates high positive δ34S of pyrite, implying low seawater sulfate concentration.However, our model for the sulfur cycle shows that this may not be the case. Further discussion is still necessary.

新元古代大氧化事件（NOE）是地质历史上第二次大气中氧气浓度有显著增高的事件。在生物演化上表现为埃迪卡拉生物群的出现和灭绝及其后寒武纪生物的大爆发；在地球化学上表现为沉积碳酸岩的δ13C值的增高和海水硫酸根离子和沉积黄铁矿之间的硫同位素分馏(Δ34S)的增高等。本项目将在国内外学者对埃迪卡拉纪-寒武纪（Ed-C）界线沉积黄铁矿和碳酸岩中的微量硫酸盐（CAS）的δ34S值的研究的基础上，通过测量华南扬子地台Ed-C界线的多个剖面的沉积黄铁矿的多硫同位素组成，结合硫循环模型计算，系统的对扬子地台古海洋海水硫酸根离子浓度（指示大气的氧浓度）和深海氧化程度进行进一步的探讨，最终建立模型恢复古环境。目前初步测得的云南永善县肖滩的黄铁矿的多硫同位素组成数据显示该剖面具有高正的δ34Spy值，指示Ed-C界线海水的硫酸根离子浓度仍然比较低，然而硫循环模型的结果却有分歧，有待进一步的探讨。

新元古代大氧化事件（NOE）是地质历史上第二次大气中氧气浓度有显著增高的事件。在生物演化上表现为埃迪卡拉生物群的出现和灭绝及其后寒武纪生物的大爆发；在地球化学上表现为沉积碳酸岩的δ13C值的增高和海水硫酸根离子和沉积黄铁矿之间的硫同位素分馏( 34S)的增高等。本项目将对埃迪卡拉纪-寒武纪（Ed-C）界线华南扬子板块肖滩剖面的沉积碳酸盐岩中提取的黄铁矿的δ34S值进行测量，通过与扬子板块Ed-C界线的多个剖面的沉积黄铁矿的多硫同位素组成的对比，结合硫循环模型计算，系统的对扬子地台古海洋海水硫酸根离子浓度（指示大气的氧浓度）和深海氧化程度进行探讨，最终建立模型恢复古环境。扬子板块沉积黄铁矿的多硫同位素组成数据显示该剖面具有高正的δ34Spy值，指示华南在Ed-C界线海水的硫酸根离子浓度仍然比较低，深海并未完全氧化。