The Microfacies Of The Cap Carbonate From The Sinian Doushantuo Formation At The Jiulongwan Section, Yichang, Hubei

Cap carbonates are macrocrystalline carbonate sequences overlying the Neoproterozoic glacial rock, which are represented, in South China, by the basal carbonates of the Doushantuo Formation, Ediacaran. Based on the microfacies studies of the cap carbonates from the Sinian Doushantuo Formation at Jiulongwan section of Yichang, Hubei, we consider the cap carbonates are stable mud peloidal limestone and recrystallized in varying degrees after the deposition.Its primary grain type is the mud peloids. The sedimentary structures are dominated by open-space structures,e.g. birdseyes and stromatactis, which are very common in various carbonates with different origins. No convincing evidence for cold-seep carbonates which includes a chaotic fabric produced by bioturbation,concretionary carbonate formation,early in-situ brecciation and late fracturing has been found in field work and microscopy. The precipitation of Doushantuo cap carbonates was deposited in warm, brackish water, and between the intertidal-subtidal inner ramp and shallow basin. Microfacies data indicate that the cap carbonates in Yichang may have been deposited in the inner ramp comprising protected shallow-marine environments with moderate water circulation.