Sr, Nd and Li isotopes in carbonates of the Yangtze Platform and from Kazakhstan as tracers for the Ediacaran and Cambrian weathering history

要了解前寒武纪-寒武纪边界生命的快速演化，需要对其快速变化的环境有很好的了解。大气层含氧量的增加和海水成分的变化通常被认为是演化的可能驱动因素；然而，详细的原因、过程和与生物圈的反馈仍然受到很少的限制，反映了埃迪卡拉纪和寒武纪沉积物的地球化学示踪数据的不完整记录。在FOR736的这个项目和其他一些项目中，我们打算用多代理方法研究中国南部和哈萨克斯坦的几个特征良好的地层剖面。在本子项目中，将研究埃迪卡拉纪和寒武纪海相碳酸盐的微量元素丰度、锶、钕和锂同位素组成。这些数据将被用来评估碳酸盐的成岩改造作用，并恢复关于这段时间间隔内海水成分变化的信息。我们还将检验假设，如风化速率增加可能是锶同位素组成波动的原因，并评估浅水和深水替代记录之间的异同。

Understanding the rapid evolution of life at the Precambrian-Cambrian boundary requires a good understanding of its rapidly changing environment. The increase in oxygen content of the atmosphere and changes in seawater composition at around this time are often implicated as possible drivers of evolution; however, detailed causes, processes and feedbacks with the biosphere remain poorly constrained and reflects the incomplete record of geochemical tracer data of Ediacaran and Cambrian sediments. In this and some other projects of FOR 736, we intend to study several well-characterized stratigraphic sections from South China and Kazakhstan using a multi-proxy approach. In the present subproject, trace element abundances, strontium, neodymium and lithium isotopic compositions of Ediacaran and Cambrian marine carbonates will be studied. The data will be used to assess the diagenetic modification of the carbonates and to retrieve information on changes of seawater composition during this time interval. We will also test hypotheses, such as increased weathering rates as a possible cause of fluctuations in Sr isotopic composition, and evaluate similarities and differences between shallow- and deep-water proxy records.