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

摘要

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-Permocalculus, 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 depositional features, 23 habitat types, mainly occurring from inner to outer shelves, were recognized at the Shangsi Section in order to reconstruct the depositional 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.