Sedimentary Facies And Paleogeographic Evolution Of The Upper Triassic Xujiahe Formation In West Sichuan Foreland Basin

West Sichuan Foreland Basin and Longmenshan thrust belt have been studied in a long time. Many progresses have been achieved in these areas, but there are three major problems remained, which include the division and correlation of the Xujiahe Formation of upper Triassic, the deficit in systematically studying the provenance of Xujiahe Formation and the ambiguity in confirming the time when the sedimentary environment changes from marine to continental of the late Triassic in West Sichuan Foreland Basin.On the basis of the theories of sedimentology, tectonics and the principle of basin analysis. The author try to solve above problems by stratigraphy relationship of studied area, analysis of provenance, types of sedimentary facies and the spreading characteristic of facies zone, the characteristic of tectonic evolution and paleogeographic evolution in West Sichuan foreland Basin. And the author studies in detail sedimentary facies, paleogeographic characteristics and evolution of the Xujiahe Formation of upper Triassic in studied area. The thesis has gained the following achievements:1. Merging and dividing the stratigraphy of late Triassic, and name unitedly Xujiahe Formation which is divided five sections.2. The provenance areas of studying area mainly lain on the Songpan-Ganzi Fold Belt and western island which have uplifted in the first and second stages of the Xujiahe sedimentary period (T₃x¹²). Clastic material came from the Longmenshan thrust belt in the third to fifth stages of the Xujiahe sedimentary period (T₃x³⁵). At the same time, with the Longmenshan Thrust belt taking place strongly tectonic movement in the north sector of the Longmenshan, there were a large of carbonate clastic debris came from the Paleozoic-the middle Triassic carbonate strata depositing in the north sector of the Foreland Basin. On the contrary, there were a large of siltstone and mudstone or shale debris which came from T₃x¹² strata depositing in the south sector of the south sector of the Foreland Basin, because the movement of the Longmenshan Thrust belt was weaker in the south sector than in the north sector.