ATTEMPTS ON CONSTRAINING THE OCEANIC AND ATMOSPHERIC CHANGES DURING THE PROTEROZOIC: INSIGHTS FROM LITHIUM ISOTOPES IN JIXIAN SECTION, NORTH CHINA

The evolution of lithium isotopic composition of seawater throughout the Earth’s history is a key issue for the geochemical study of lithium isotopes. It is commonly recognized that Li isotopic composition of seawater plays a substantial role in reconstructing the partial pressure of atmospheric carbon dioxide, as well as in understanding the relationships among silicate weathering rate and tectonic and climatic changes, and thus in maintaining global surface climatic stability over the geologic timescale. Planktonic foraminifer has been successfully applied to investigate lithium isotopic evolution history of seawater and the partial pressure of atmospheric carbon dioxide in the Cenozoic. During the aggregation and breakup of the supercontinents in Precambrian, such as Rodinia during Mesoproterozoic to early Neoproterozoic and Columbia during Paleoproterozoic to Mesoproterozoic, lithium isotopic compositions of the seawater must have great changes in contrast to the modern ocean. However, it is poorly understood and previous studies focusing on the Li isotopic composition of the ancient ocean are rare, which limits the development of Li isotope geochemistry. In this study we explored well preserved strata of the marine carbonate-dominated Jixian section in north China, which spanned from Mesoproterozoic to early Neoproterozoic with relatively continuous deposition, few major interruptions, and well preserved sedimentary features. We will measure Li isotopic composition of Jixian section, and explore the evolution of oceanic Li isotopic composition and changes in oceanic environment during Proterozoic, in combined with oxygen, carbon, boron isotopic compositions, and major and trace element geochemistry, as well as a compilation of data all over the world. This study will provide basic information for the reconstruction of the evolution history of the Earth’s environment, especially the oceanic and atmospheric evolution under a geological background of open–close of supercontinent.