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

前寒武纪到早寒武世的过渡包括一段重大的环境变化，据信这与地球历史上最突出的生物辐射有关：从以藻类和微生物为主要生命形式的海洋转变为形成更高生命的重要骨骼。伴随着这些全球变化的是生物矿化的开始和广泛的钙磷沉积，后者往往与盆地环境中丰富的层状硅质岩的沉积有关。前一个项目的重点是重建沉积物总磷(TSP)曲线，以及沉积和地球化学参数。它记录了三个重要的成磷事件，证据表明覆盖扬子地台的前寒武纪-寒武纪海洋中存在过剩的磷。然而，到目前为止，无论是块状磷矿的磷酸盐来源还是微生物在磷形成中的重要性和作用都不是很确定。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：(1)我们的目标是探索原生沉积(无机物和/或生物变质)与导致块状磷矿形成的成岩过程的相关性，以及(2)如何实现显著的溶解P和Si的回收和浓缩，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成矿作用。这将通过与其他地球化学子项目密切合作，通过多代理方法研究中国南部早寒武世埃迪卡拉纪至早寒武世剖面，实现这一目标。为了确定区域和全球生物地球化学现象，将整合来自哈萨克斯坦和印度的使用来自哈萨克斯坦和印度的中国西北塔里木区块的相同代用品的额外样品。特别是，利用沉积学和古生物学数据以及已知的指示骨骼形成生物对海洋中元素循环的影响的高灵敏度地球化学指标，可能提供新的洞察，哪些因素触发了前寒武纪-寒武纪的生物辐射。

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.