Keywords: 
• provenance and depositional system /
• Upper Jurassic Penglaizhen Formation /
• Western Sichuan /
• petrographical and geochemical approaches

Abstract: The Upper Jurassic Penglaizhen Formation constitutes important gas reservoir in western Sichuan and the study of provenance of the Penglaizhen sandstones is of great importance in determining the spatial distribution of depositional systems and reservoirs. Owing to the absence of systematic studies, the provenance and lateral distribution of Penglaizhen Formation in the middle part of Western Sichuan have long been speculated upon. Based on detrital mineral analysis, trace element geochemistry, and paleogeomorphology, this study reveals that the sediments of the Penglaizhen Formation were derived from the middle and northern segments of Longmen Shan orogenic belt and Micang Shan orogenic belt. The sediments in the western region of depression are mostly coarse-grained, poor-sorted sandstones with low compositional maturity and porosity, and were sourced from the middle segment of Longmen Shan, indicating southeastward delta depositions close to the source area. The deposits in the middle and eastern parts are generally fine-grained, well-sorted sandstones with high feldspar content, compositional maturity, and porosity, and were supplied from the northern segment of Longmen Shan and Micang Shan, suggesting northeast-to-southwest delta depositions far from their sources. Additionally, it is shown that there existed different provenances during different periods and the dominant provenance transferred from the middle to the northern segment of Longmen Shan from J₃p¹ to J₃p⁴.