Abstract:
The redefinition and correlation of Upper Triassic lithostratigraphic framework in Qiangtang Basin are key to understand their sedimentary-tectonic evolution and evaluate the oil-gas resources. The Late Triassic strata are widely distributed in Qiangtang Basin, but the researches on stratigraphic division and correlation are poor, which have hindered the regional geological understanding on the Qiangtang Basin. In this study, we systematically summarized all the Upper Triassic lithostratigraphic units on rock associations, sedimentary sequences, depositional environment, contact relation of strata, fossil, and chronostratigraphy based on the previous research and latest drilling data, and then redefined the Upper Triassic lithostratigraphic framework in the South and North Qiangtang, and finally proposed the new scheme of stratigraphic correlation. The data shows that the contact relation exists in both contemporaneous heterophase and top-bottom of the Upper Triassic strata in the Qiangtang Basin. In order to further understand the Upper Triassic lithostratigraphic framework of the Qiangtang Basin, we suggested using the Jiapila, Bolila, and Bagong formations to represent the lower part of the Upper Triassic in the depression upward, while using the Xiaoqiebao, Jiaomuchaka, and Zana formations in the central uplift area, which may be attributed to the Carnian-Norian age. In addition, the Nadi Kangri Formation is uniformly used to represent the Late Triassic Norian-Rhaetian volcanic-sedimentary sequence, which is parallel or angular unconformity with the lower strata. In addition, the Juhuashan Formation, Rigan Peico Formation and Suobucha Formations are still remained because these lithostratigraphic units have special significance on indicating sedimentary environment.