Jurassic sedimentary transformation event recorded by detrital components in the middle part of western Sichuan

Abstract：Sandstone is the direct record of mountain uplift in the basin, and its detrital components have a good effect in analyzing orogenic belts and tectonic setting of sedimentary provenances. Jurassic sediments were systematically investigated with four main methods, i.e., features comparison in detrital components, vertical evolution characteristics of detrital components in single well, Dickinson chart and evolution characteristics between Q/（F+L） and F/L of component maturity. Some conclusions have been reached： (1) On the basis of spatial distribution features of the detrital components of sandstones, the authors believe that the middle Jurassic Shaximiao Formation in the study area was effected by the western Longmenshan orogenic belt and the northern Micang-Daba orogenic belt simultaneously. (2) According to the vertical correlation of the detrital components and the analysis of compositional maturity of sandstones in a single well, the authors have found that near the boundary between Qianfoya Formation and Shaximiao Formation, the provenance had a significant change, suggesting that there existed an important sedimentary transformation event in western Sichuan area at that time, which was closely connected with the tectonic evolution of Micang-Daba Mountain. (3) The detrital components of sandstones reflect the activity of the orogenic belts around the basin. With relatively stable structures, sandstones had a high compositional maturity from the early Jurassic to the middle Jurassic. In middle and late Middle Jurassic, due to the influence of the thrusting of the Micang-Daba Mountian, sandstones showed a low compositional maturity, and volcanic detritus increased. In the early Late Jurassic, the structures got relatively stable, and the compositional maturity of sandstones increased. Towards the late Late Jurassic, due to the influence of the Longmenshan orogenic belt in western Sichuan, the feature of sandstones became similar to that of the front sandstones in Longmenshan area.