Stable Isotope Geochemistry Of Neoproterozoic Tumen Group In Western Shandong Area

The Neoproterozoic strata in Shandong area are well exposed,have not experienced extensive metamorphism,and preserved many types of fossils.They are areas with great potential for the study of the biological origin and early evolution of multicellular macro bodies.In recent years,chronostratigraphy and biostratigraphy have made some progress,but there is a lack of geochemical research.This paper intends to use stable isotope stratigraphic contrast to constrain the sedimentary age of the Tumen Group and discuss the sedimentary environment of the Tumen Group.The analysis and comparison of the ?¹³C_carb(The distribution range is -2.1 ‰?4.0 ‰,the average value is 1.2 ‰ ± 0.05 ‰)curve of the Tumen Group shows that the negative movement at the top of the Shiwangzhuang Formation(with shift magnitude of 4.5 ‰) is similar to the negative movement at the top of the Huaibei section in Anhui(with shift magnitude of 4.8 ‰) and the Jixian section in Tianjin(with shift magnitude of 4.5 ‰).The 17 ?¹³C_carb points at the top of the Tongjiazhuang Formation of the Tumen Group were found,and the trend formed may be considered as a part of the potential negative drift of the bitter spring.It can indicate that the Tumen Group existed before the Tonian ice age in the Neoproterozoic.Analysis of the ?³⁴S_Pyr(The distribution range is-10.5 ‰ 36.7 ‰,the average value is 13.1 ‰±1.4 ‰)curve can infer that most of the sediments of the Tumen Group are deposited under non-oxygen-rich shallow water marine conditions.In the age of the Shiwangzhuang Formation sedimentation,a negative direction shift of 37.1‰ occurred,Its location is comparable to the location of ?¹³C_carb float drift at the top of the Shiwangzhuang Formation,which may indicate changes in its sedimentary environment.In summary,this study was the first to obtain stable isotope geochemical data for the Tumen Group,filling the gap in geochemical research in this area.