Subdivision of Permian Fossil Communities and Habitat Types in Northeast Sichuan,South China

Recent achievement in hydrocarbon exploration in Northeast Sichuan （四川） demonstrated that Permian calcareous and argillaceous deposits are the major contributing source rocks. Reevaluation on the hydrocarbon potential of the Permian strata over the whole Yangtze region is thus to be desired. A comprehensive corroboration was carried out at the Shangsi （上寺） Section, Guangyuan （广元）, Northeast Sichuan, which is believed to be another promising area in South China. This article deals with the ecological and depositional conditions of the Permian strata in the section, including the Chihsia, Maokou （茅口）, Wujiaping （吴家坪）, and Dalong （大隆） formations, which share some similarities with those occurring in the broad Yangtze carbonate platforms. Five fossil communities of Mizzia-Permocaiculus, Hayasakaia, Inozoan, Ostracod, and Crinoid were identified in the Yangtze region and described in detail including their components and occurrence. On the basis of the fossil communities and depositionai features, 23 habitat types, mainly occurring from inner to outer shelves, were recognized at the Shangsi Section in order to reconstruct the depositionai conditions and accordingly to evaluate the paleoproductivity. In addition, the subdivision of Chihsia Formation in the section was revised, which would be of significance for the reconstruction of the Chihsian paleogeography in the study area.

Evolution of sedimentary facies and fossil communities in the Middle Permian Maokou Formation in Zigui County, Hubei Province,South China

A geological event that happened at the end of the Middle Permian resulted in different levels of erosion in a shallow-water platform of South China, which led to diverse geological records in different sections. The Lianziya section in western Hubei Province of South China has a well-exposed stratigraphic sequence of the late Middle Permian rocks with abundant fossils and sedimentary facies types, providing new evidences for understanding the evolution of marine biota and environment in the late Middle Permian. Our study shows that four fossil communities can be recognized with the change of sedimentary facies in the late Middle Permian: Foraminiferal-algal community, phylloid algal community, bryozoan community and Ungdarella community. The foraminiferal-algal community is dominated by fusulinids and calcareous algae, but was soon replaced by the phylloid algal community. With an increase of terrestrial input, the phylloid algal community was again replaced by the bryozoan community. Near the end of the Middle Permian, with a decrease of terrestrial input, the bryozoan fossil community disappeared while the Ungdarella community became dominant. A 10 cm-thick weathered crust occurred at the top of the Middle Permian limestone, marking a large amplitude fall in sea-level and the beginning of a terrestrial erosion stage. The sedimentary facies and fossil community changes in the Lianziya section indicates that the Middle Permian crisis was a gradual process while the sea-level fall mainly occurred in the latest Middle Permian.