Carbonate carbon isotope evolution of seawater across the Ediacaran-Cambrian transition: evidence from the Keping area, Tarim Basin, NW China

Sedimentary rocks from the Ediacaran-Cambrian boundary record important biological, climatic and geotectonic changes during this time. To date, only few geochemical investigations on the upper Ediacaran - upper Cambrian rocks in the Tarim Basin have been carried out. Here, we report high-resolution delta C-13(carb) records from the Penglaiba, the Wushi phosphorite and the Dongergou sections from Ediacaran-Cambrian Series 3 in the Keping area of the Tarim Basin. The sections display several obvious delta C-13(carb) shifts; delta C-13(carb) values increased from 3 parts per thousand to 6.7 parts per thousand across the Qigebulage Formation. Moreover, a negative delta C-13(carb) shift across the Ediacaran-Cambrian boundary is apparent; delta C-13(carb) values decreased to a minimum of -9.8 parts per thousand in the Wushi phosphorite section (-7.7 parts per thousand in Dongergou section and -5.4 parts per thousand in Penglaiba section), followed by a positive carbonate carbon isotopic excursion across the Yuertusi Formation into the middle of the overlying Xiaoerbulak Formation. Furthermore, more or less invariable positive delta C-13(carb) values characterize the middle and upper Xiaoerbulak Formation. The most negative delta C-13(carb) value (-14.3 parts per thousand) occurred near the base of the Shayilik Formation, which is the absolute minimum value among the studied sections of the Cambrian Series 2 to Cambrian Series 3 transition in the world. The delta C-13 data from Keping, Tarim Basin are in good agreement with carbon isotope profiles recorded in South China, and these events may reflect the perturbation of the carbon cycle in the Tarim Basin during the Ediacaran-Cambrian and the Cambrian Series 2 - Cambrian Series 3 transitions.