Geological significance of late Mid-Permian stratigraphy in northern and eastern Sichuan Basin, SW China

Abstract

The Mid-Permian Maokou Formation in the Sichuan Basin shows good petroleum prospectivity. However, knowledge of the stratigraphy in the northern and eastern Sichuan Basin during the late Maokou period are still unclear. The interface between the Maokou and Wujiaping formations was re-identified, and the sedimentary pattern in the study area during the late Maokou period was clarified based on the logging data from 120 wells combined with the measured data of three field profiles. The results suggest the following. (1) Natural gamma-ray spectral logging can effectively identify the siliceous sediments at the top of Maokou Formation and the mud shale at the bottom of Wujiaping Formation. According to a new stratigraphic division, the erosional edge on LHST2 section of Maokou Formation moved eastward to the Kaixian area. (2) Tectonic subsidence controlled the eastward thinning and the sedimentary evolution in the late Maokou period. (3) The sedimentary evolution in the late Maokou period was from the homoclinal carbonate ramp facies to the distal steepening ramp facies, and then to the weak rimmed platform facies. Distal steepening ramp facies controlled the formation of dolomite and siliceous sediments, while the weak rimmed platform facies controlled the formation of the platform margin.

Keywords

• natural gamma-ray spectral logging
• siliceous sediment
• tectonic subsidence
• sedimentary evolution
• wujiaping formation
• maokou formation
• northern and eastern sichuan basin