Biostratigraphic of the Middle Jurassic Sêwa, Shaqiaomu and Bi Qu formations in the Quruiqianai area, south Qiangtang basin, northern Tibet, China

Late Triassic-Jurassic strata were studied in the Quruiqianai area, south Qiangtang basin, northern Tibet. The strata may be divided in ascending order into the Late Triassic Rigain Pünco Group, Late Triassic-Early Jurassic Suobucha Formation, Early Jurassic Qusi Formation, Middle Jurassic Sêwa, Shaqiaomu, Bi Qu and Xali formations and Late Jurassic Suowa Formation. In the paper the authors focus the discussion on the Middle Jurassic biostratigraphic of the Sêwa, Shaqiaomu and Bi Qu formations. The study provides an important basis for the establishment of the stratigraphic sequence and detailed correlation of the Middle Jurassic in the area.