The Xiaochaka Group and Riganpeicuo Group stratigraphic sequence and correlation in the Qiangtang area, Tibet-question the validity of the boundary between Qiangnan and Qiangbei strata

In the study area, the late Trassic strata were divided to Qiangnan-Baoshan strata division, Duoma subdivision, Riganpeicuo Group and Qiangbei-Changdu-Simao strata division, Chibuzhangcuo subdivision, Xiaochaka Group by the formers. Through the study in the study area, according to the rock association characteristics, the primary Riganpeicuo Group was divided to Luzongnai Formation, Quruiqianai Formation and kuimotaque Formation, the primary Xiaochaka Group was divided to Jielari Formation, Duoyong Formation, Zhana Formation and Saigongyao Formation, among which, Duoyong Formation is contrast with Luzongnai Formation and Zhana Formation and Saigongyao Formation is contrast with Quruiqianai Formation. Through the correlation, it is considered that the late Triassic sedimentary environment is the same on the whole in the study area, therefore, it is considered that there is no boundary between Qiangnan and Qiangbei strata.[