Characteristics of Mid-Upper Jurassic carbonate rocks in the Yichangma area, Qiangtang Basin, Tibet：Implications for the sedimentary environment

Abstract：The macroscopic characteristics, mineral and clastic compositions, textures, carbon and oxygen stable isotopes and paleontological and paleoecological characteristics of Mid-Upper Jurassic carbonates in the Qiangtang basin, northern Tibet, have been studied systematically based on detailed field section surveys. Study shows that the carbonate rocks mainly include micrite, grainstone and packstone. The δ13C and δ18O values show two cyclic variations from low→high→low→high→low from the Quemo Co Formation→the Buqu Formation→Xiali Formation→Suowa Formation→Xueshan Formation. The Quemo Co and Xueshan formations are dominated by fluvial-dominated deltaic deposits, the Buqu Formation by carbonate ramp deposits, the Xiali Formation by tidal flat-deltaic deposits and the Suowa Formation by tidal flat-lagoonal deposits. The water table in the Mid-Late Jurassic Qiangtang basin showed the rising and falling cycles from shallow→deep→shallow→deep→shallow in the general trend of water table lowering. Meanwhile, the depocenter of the basin migrated from east to west and the Jurassic sedimentary environment of the Qiangtang basin is controlled by the combined regional tectonic evolution and global sea level change.