新视角下的埃迪卡拉纪海洋环境―基于岩芯样品黄铁矿的矿物学和原位微区SIMS同位素分析

埃迪卡拉纪是早期多细胞生命辐射的关键时期，探讨该时期海洋环境变化对认识早期生命演化的环境影响机制具有重要意义。硫同位素是重建该时期海洋环境演化过程的重要指标，但以往研究大多使用全岩黄铁矿硫同位素指标，忽略了沉积地层中黄铁矿本身形成环境及成岩过程的复杂性。本研究以华南不同沉积相区埃迪卡拉纪岩芯为研究对象，在掌握区域岩相变化和综合地化特征基础上，以新鲜岩芯样品的岩石学、黄铁矿的矿物学和微区硫同位素组成特征为突破口，探讨引起全岩黄铁矿硫同位素变化的原因，综合评估其在恢复古环境中的可靠程度。研究也将对比不同沉积相区黄铁矿的矿物学和同位素组成特征，推导其所反映的古海洋环境在深水和浅水区的差异；尝试从黄铁矿形成过程及其所反映的环境信息角度，探寻该时期“蓝田生物群”和最大碳同位素负漂事件（EN3/DOUNCE）的发生原因。分析结果将为探讨该时期海洋环境的演化过程及其与早期生命演化的关系提供新证据。

Lying between the termination of the Neoproterozoic global glaciation and the onset of Cambrian explosion, the Ediacaran represents a key transitional period in the Earth history and witnesses the emergence and diversification of metazoans in the late Neoproterozoic. Ediacaran oceanic environment plays important role in understanding the evolution mechanism of early life. Thereinto, sulfur isotope is a critical geochemical index in the reconstruction of Ediacaran ocean redox conditions. Previous studies mostly applied bulk-rock pyrite sulfur isotope as oceanic redox index, however, the inherent complexity of sedimentary pyrites and their various post-depositional diagenetic processes have often been neglected. In this context, mechanisms causing variations of bulk-rock pyrite sulfur isotope and its fidelity on reconstructing ocean redox state are still open to debate. In this project, on the basis of previous high-resolution lithostratigraphic study and comprehensive bulk-rock geochemical index analysis, we will carry out detailed petrological observation, as well as mineralogical and in-situ SIMS sulfur isotopic measurements on different types of sedimentary pyrites collected from both Ediacaran deep- and shallow-water facies drill-cores of South China. Our goal is to explore the cause of various bulk-rock pyrite sulfur isotopes, and estimate the reliability of bulk-rock pyrite sulfur isotopic index on reconstructing the palaeoenvironment. The study also aims to compare the petrological, mineralogical and in-situ SIMS sulfur isotopic patterns of sedimentary pyrites in different depositional facies in order to infer the oceanic environment. Based on the integrated studies of sedimentary pyrites, our study would try to seek the possible cause and mechanism of occurrence of key Ediacaran geological events, such as the occurrence of the Lantian biota and EN3/DOUNCE. The proposed research will provide important clues for understanding the evolution process of the Ediacaran ocean, as well as its coevolutionary relationship with the evolution of early life.