Trace element characteristics of carbonate rocks from the Ediacaran Doushantuo Formation of Xikou section, Cili County, Hunan Province and its palaeoenvironmental significance

Trace element and rare earth element (REE) of 64 carbonate rock samples from the Ediacaran Doushantuo Formation of Xikou section, Cili County, Hunan Province are analyzed. Palaeoredox indicated by the combination of U/Th, Ce anomalies and Ca/Mg is in accordance with that by sequence stratigraphic studies, suggesting that the three proxies in carbonates are applicable in reconstructing palaeoredox environment of the Ediacaran. In the bottom and middle of Doushantuo Formation, the REE distributional pattern changes from typical fresh water to typical sea water, probably indicating the injecting of deglacial meltwater and thus being replaced by normal sea water during the post-Marinoan and post-Gaskier period. The strong Eu anomalies, relatively higher Eu value as well as the seismites discovered in Xikou section by previous research may suggest that the hydrothermal activity probably occurs during the whole Doushantuo Age, being strong in the early and then weakened in the late stage. The hydrothermal activity