Multi-proxy records of seawater chemistry and environmental change from Precambrian-Cambrian carbonate-phosphorite and chert-phosphorite assemblages: Implications for enhanced bioproductivity and phosphorgenesis

前寒武纪到寒武纪早期的过渡期包括一个重大的环境变化，被认为与地球历史上最突出的生物辐射有关：从藻类和微生物是主要生命形式的海洋到一个重要的生物进化的海洋。伴随着这些全球性的变化是生物矿化和广泛的磷酸钙沉积的开始，后者往往是与沉积丰富的层状燧石在盆地设置。上一个项目的重点是重建总沉积物磷（TSP）曲线，以及沉积和地球化学参数。它记录了三次重要的磷化事件，并提供了覆盖扬子地台的前寒武纪-寒武纪海洋中存在过量磷的证据。然而，到目前为止，无论是块状磷块岩的磷酸盐来源，还是微生物在磷酸化作用中的重要性和作用，都没有得到确切的认识。伴生硅质岩的成因和形成也是如此。基于这些结果，我们的目标有两个方面：（1）我们的目标是探索原生沉积（无机和/或生物介导）与成岩过程的相关性，导致形成块状磷块岩，（2）调查如何显着的回收和溶解的P和Si的浓度可以实现，以及风化，热液活动和/或生物生产力如何影响海洋系统和生物矿化。这将通过与其他地球化学子项目密切合作，并在多代理方法内研究华南地区暴露和记录良好的埃迪卡拉纪至早寒武纪剖面来实现。为了识别区域与全球的地球化学现象，将整合来自中国西北部塔里木地块、哈萨克斯坦和印度的使用相同替代物的其他样品。特别是，使用沉积学和古生物学数据和地球化学代用指标，已知以高灵敏度指示生物体对海洋元素循环的影响，可能会提供新的见解，哪些因素触发了前寒武纪-寒武纪生物辐射。

The Precambrian to early Cambrian transition comprises an episode of major environmental changes which are believed to be relevant for the most prominent bioradiation in Earth’s history: from an ocean in which algae and microbes were the dominant form of life to one in which significant skeletonforming higher life spread. Concomitant with these global changes is the onset of biomineralization and widespread calcium phosphate deposition, the latter which is often associated with the deposition of abundant bedded chert in basinal settings. The previous project has focused to reconstruct Total Sediment Phosphorus (TSP) curves, together with sedimentary and geochemical parameters. It documented three important phosphogentic events, with evidence for excess phosphorus in the Precambrian-Cambrian ocean covering the Yangtze Platform. However, so far, neither the source of phosphate for massive phosphorite nor the importance and function of micro-organisms in phosphogenesis are known with certainty. The same holds true for the origin and formation of associated cherts. Based on these results, our aims are twofold: (1) we aim to explore the relevance of primary depositional (anorganic and/or biomediated) versus diagenetic processes leading to the formation of massive phosphorites, and (2) investigate how the remarkable retrieval and concentration of dissolved P and Si can be achieved, and how weathering, hydrothermal activity and/or bioproductivity influenced the oceanic system and biomineralization. This will be achieved by studying well-exposed and welldocumented Ediacaran to Early Cambrian sections in South China in close collaboration with the other geochemical subprojects and within a multi-proxy approach. To identify regional versus global biogeochemical phenomena, additional samples using the same proxies from the Tarim block of NW China, from Kazachstan and India will be integrated. Particularly, the use of sedimentological and palaeontological data and geochemical proxies that are known to indicate the effect of skeletonforming organisms on element cycling in the oceans with high sensitivity may provide new insights which factors triggered the Precambrian-Cambrian bioradiation.