Carbonate rocks micro-characteristics and paleoenvironment significance in Baomoshan formation of early Permian of Shuicheng area,Guizhou Province，China

Baomoshan formation of the Early Permian widely distributes in Shuicheng area; its lithology is a layer of carbonate rock with an intercalated thin clastic rocks. The composition of the carbonate rocks greatly changes in horizontal direction. In this study, 9 strip plane sections and more than 300 pieces of rock thin sections were measured and analyzed, from which 6 microfacies were summarized. These microfacies include abundant foraminiferal grainstone/ bioclastic lime-argillaceous limestone (SMF18), bioclastic lime-argillaceous limestone with skeletal fragment/grain lime-argillaceous limestone (SMF10), oncolite rudstone/ grained limestone (SMF13), sea lily enriched limestone (SMF12-CRIN), the shells of skeletal fragment(SMF11) and biological boundstone (SMF7). Through the comparison of different sections of rock structure, biological assemblage and hydrodynamic energy feature, the results show that the sedimentary environment of the Baomoshan formation was betweenopen sea platform and sea platform margin, with at least three times of the sea regression events from the northwest to the southeast in Shuicheng area, which coincide with the trough basin shrinking period deposition effect of this area.