The Upper Triassic Xujiahe Formation in the Longmen Mountain area, Sichuan

The N-S-elongated Upper Triassic Xujiahe Formation strata cover an area of 150 km² and a thickness of more than 2851 m in the Dayi-Chongzhou-Dujiangyan-Wenchuan zone, Sichuan. After the surveying of the 1:50000 Sanjiang Sheet and Wanjiaping Sheet from 1997 to 1999, the author subdivided the Formation into three members, with particular emphasis on lithology, stratigraphic boundary and correlation, biostratigraphy and chronostratigraphy. Two types of sedimentary environmerts are also discriminated:delta facies and fluvial facies.