A large-scale marine regression occurred during the depositional period of the Middle Jurassic Xiali Formation in the North Qiangtang Depression,accompanied by the widespread deposition of gypsum-bearing clastic sediments. Based on integrated petrological characteristics and elemental geochemical analyses of clastic rocks from the Xiali Formation in the Shenglihexi section and Well QK-1,we systematically analyzed the intensity of chemical weathering,provenance characteristics,and tectonic setting of these sediments,which is critical for understanding the evolutionary history and evaporite response of the Jurassic basin system. The results indicate that the Chemical Index of Alteration(CIA)values of these clastic rocks are significantly influenced by grain size and sediment sorting,but minimally affected by sedimentary recycling;thus,the CIA values of mudstone samples reflect the intensity of chemical weathering in the source region. Mudstones from the Xiali Formation in Well QK-1 exhibit considerable variation in CIA values(60-77),with negligible influence from potassium metasomatism,indicating that the source area underwent generally moderate to weak chemical weathering. In contrast,mudstones from the Shenglihexi section show significant effects of potassium metasomatism;after correction for this influence(CIAcorr),their values range from 80 to 85,suggesting intense chemical weathering in the corresponding source region. Discriminant diagrams based on La/Th vs. Hf,Co/Th vs. La/Sc,La/Yb vs. 􀰐REE,and A-CN-K plots,along with pronounced negative Eu anomalies,collectively indicate a predominantly felsic rock provenance for these clastic deposits. Clastic sediments from the western and central segments of the North Qiangtang Depression were deposited in a continental collision setting,whereas those from the eastern segment were formed in an arc-related tectonic environment. This interpretation aligns well with the established tectonic framework of the North Qiangtang Depression during the Middle Jurassic. During this period,the central and western regions functioned as a weakly magmatic intracontinental foreland basin,while the eastern region likely developed as a back-arc foreland basin,induced by southward subduction of the Bangonghu-Nujiang Tethys Ocean. Multiple transgressive-regressive cycles,combined with a relatively arid palaeoclimate and restricted paleogeographic conditions in the North Qiangtang Depression during the Early to Middle Jurassic,may have created favorable conditions for the formation of extensive gypsum-rich evaporites within the Xiali Formation.