Sedimentary system and main controlling factors of the Upper Triassic Xujiahe Formation in Tongnanba area

Exploration and research show that the Upper Triassic Xujiahe Formation has good prospect for exploration in Tongnanba area. Based on observation of outcrops and core, combining with comprehensive analysis of well logging and analysis data, as well as facies marks, the paper concludes that Xujiahe Formation has a composite sedimentary system consisting of alluvial fans, fluvial, lacustrine deltas, lacustrine (affected by seawater), marine deltas facies. The main sedimentary system models are marine-continental transition delta and alluvial fans-braided river delta-lacustrine. It is also revealed that the paleoclimate, tectonic movement and provenance had controlled the sedimentary system. The paleoclimate controlled the especial sedimentary structure formed by alternating layers of mudstone-sandstone and source-reservoir-cap assemblage of Xujiahe Formation. Tectonic movement controlled sedimentary system types and sand-body distribution during every sedimentary period. The property of parent rock in different provenances have controlled the composition and the texture of sediments.