铁、硒同位素重建晚新元古代海洋氧化还原分层结构

The Late Neoproterozoic era marked a turning point in the development of the modern earth system. The global strongly tectonic upheavals drove chain reactions between the oceans, atmosphere, climate, and life. In this study, iron and selenium isotopic composition of Late Neoproterozoic sedimentary rocks(the band of iron formation, chert, phosphorite, carbonate and black shale) from South China will be analyzed, which lead us to understand iron and selenium isotopic fractionation mechanism and reconstruct the redox chemostratigraphy of Late Neoproterozoic Ocean，combined with other geochemical proxies, such as mineralogy and the distribution of iron and selenium speciation. This study will not only provide lines of evidence for widely applying of iron and selenium isotope in paleoceanographic environment evolution. It is more important that iron and selenium isotopic composition of Late Neoproterozoic typical sections will help us to elucidate the origin and available scope of ferruginous anoxic condition and euxinic condition in Late Neoproterozoic Ocean of South China, reconstruct the redox chemostratigraphy, and constrain the oxygenation model of Late Neoproterozoic Ocean. The horizontal contrast study of different regions at the same time and the vertical contrast study of same region at large time scale will produce more available geochemical information for exploring the relation between marine environment and life evolution and enrichment of elements (sedimentary deposits) in global Late Neoproterozoic Ocean.

晚新元古代是地球历史上关键的转折时期，当时全球构造活动诱发了海洋和大气环境、气候、生物演化的重要变化。本项目拟选取华南晚新元古代典型沉积岩作为研究对象，以铁、硒稳定同位素为主要研究手段，以同位素分馏机制和海洋氧化还原演化为研究核心，结合其它地质地球化学指标，揭示晚新元古代特殊沉积体系(含铁建造、硅质岩、磷块岩、碳酸盐、黑色页岩)中铁、硒稳定同位素的分馏机制，为铁、硒同位素作为新的地球化学示踪剂提供基础的研究资料。更重要的是，基于华南晚新元古代典型地质剖面的铁、硒同位素研究，探讨富铁缺氧环境和硫化静海环境的成因及存在范围，重建华南晚新元古代海洋的氧化还原分层结构，进而约束华南晚新元古代海洋的氧化模式。通过大时间尺度的纵向和同一时间不同区域的横向对比研究，为探索全球晚新元古代海洋环境与生物演化、元素富集(沉积矿床)之间的联系提供更丰富的地球化学信息。

在项目的支持下完成了项目设计的目标。本项目完成了晚新元古代特殊沉积体系(含铁建造-硅质岩-磷块岩-碳酸盐-黑色页岩)中Fe，Se稳定同位素的测试，确定这一时期铁、硒同位素的组成主要受氧化还原环境控制，而硒同位素的组成还收到沉积水深的控制，即海洋或盆地中存在深度梯度变化。同时，基于华南晚新元古代典型地质剖面的铁、硒同位素研究，我们发下含铁缺氧环境主要是由于陆架氧化物被重新还原释放出溶解二价铁导致，而硫化静海环境的成因主要归因于大陆风华输入的溶解硫酸盐和海洋中溶解有机质/生物有机质反应生成多余的硫化氢导致。我们的研究结果发现含铁缺氧环境的存在广泛存在，而硫化环境间断出现，但在陆架、斜坡、盆地均有出现。重建了华南晚新元古代海洋的氧化还原分层结构，进而约束华南晚新元古代海洋的动态的演化模式。