Geochemistry of vein and wallrock carbonates from the Ediacaran system in South China: Insights into the origins of depositional and post-depositional fluids

For the lower unit (LU), veins exhibit different C-O isotope compositions and REE + Y patterns from wallrock carbonate, indicating that post-depositional fluids have different geochemical compositions from depositional fluids and thus are of external origin. The simultaneous changes in δ18O and δ13C values with different laminations in the wallrock carbonates suggest the preservation of the primary geochemical compositions. The δ18O values and REE + Y patterns for the LU veins indicate that the post-depositional fluids were probably the mixtures of continental and marine glacial meltwaters. Therefore, the Lantian carbonates record the incorporation of continental glacial meltwater into the marginal sea of Ediacaran age. Nevertheless, the geochemical screening can provide constraints on the preservation of primary signatures and thus on the origins of depositional and post-depositional fluids in the Neoproterozoic marine carbonates.