Geochemical evidence of paleo-depositional environment of Triassic Adula Formation source rocks of eastern Qiangtang Basin

The mudstone within the Upper Triassic Adula Formation constitutes a crucial hydrocarbon source rock reservoir in the Qiangtang Basin, yet there is considerable debate regarding its paleo-depositional environment. Through systematic studies, including petrology, organic geochemistry, and elemental geochemistry analyses of the Adula Formation at the Eertuolongba section in the Quemocuo area of the eastern Qiangtang Basin, this study investigated the paleo-depositional environment of the Adula Formation source rocks and its impact on hydrocarbonsource rock development. The total organic carbon (TOC) content of the Adula Formation mudstone ranges from 0.27% to 3.46%, with an average of 1.60%, indicating overall favorable source rocks with locally deve-loped high-quality source rocks. The shelf facies mudstone in the lower section of the Adula Formation was formed during a phase of sea-level rise, characterized by deeper, oxygen-poor water, a semi-arid to semi-humid paleoclimate, moderate chemical weathering, min