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

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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.