Abstract:The Upper Permian Changxing Formation at Panlongdong, Xuanhan, Sichuan Province is a platform marginal facies sequence consisting of 4 lithologic parts in ascending order: the Lower Bioclastic Member, the Reef Member, the Upper Bioclastic Member, and the Microbialite Member. The Lower Bioclastic Member consists of the lower dark lime mudstone with small foraminifers below 1mm and the upper bioclastic packstone with abundant brachiopod and crinoidal bioclasts. The Reef Member is about 108m thick, consisting of framestone and bafflestone. The Upper Bioclastic Memberis 45.3m thick, composed of fine dolostone. Previous researchers interpreted it as evaporate facies. This study, however, determined it is open platform facies, consisting of bioclastic packstone and wackestone. The Microbialite Member is 8.7m thick, and contains microbial fossils. The Changxing Formation sequences of Panlongdong, Well Puguang-6, and Lichuan, Hubei Province have similar facies sequence: the lower deep water limestone, the middle reef rocks, and the upper open platform limestone. This sequence is typical of the platform marginal deposits in the Sichuan Basin, and is significant to understanding the platform marginal facies reservoirs. Previous researchers did not recognize the Microbialite Member, and the P-T boundary was not correctly determined. We propose in this paper to place the P-T boundary at the medium of the Microbialite Member.