In order to further elucidate the petrographic classification and genetic mechanisms of lacustrine fine-grained rocks, the Qingshankou Formation in Gulong Depression was systematically investigated through integrated analytical approaches. Comprehensive methodologies including well log interpretation, core characterization, thin-section petrography, scanning electron microscopy(SEM), X-ray diffraction(XRD), and major/trace element geochemistry were employed to evaluate the terrigenous-endogenic binary coupling processes controlling material composition and sedimentary dynamics of organic-rich fine-grained deposits. The Qingshankou Formation fine-grained rocks exhibited dual provenance characteristics, comprising both terrestrial-derived components and lacustrine authigenic materials. Nine distinct petrographic types were identified based on material provenance, sedimentary structures, and organic matter content. Low-organic laminated felsic mud shale(LF1), medium-organic laminated felsic shale(LF2), low-organic massive felsic mud shale(LF3), medium-high organic laminated claystone(LF4), low-organic massive oolitic limestone(LF5), low-organic massive coquina(LF6), medium-high organic massive mud-microcrystalline dolomite(LF7), high-organic laminated biosiliceous shale(LF8), and low-organic shell-silt mixed fine-grained rock (LF9). The results indicate that spatial distribution patterns of these lithofacies are jointly controlled by paleohydrological dynamics including lake-level fluctuations, paleoclimatic variations, and salinity gradients. Vertical evolution characteristics demonstrate upward-decreasing paleosalinity, shallowing water depth, weakening redox conditions, and enhanced terrigenous input from the formation base to top. The most favorable shale oil exploration targets are identified in the Qing1 Member to lower Qing2-1 Submember, exhibiting predominant LF2, LF4, and LF6 lithofacies with high organic matter abundance (average TOC 2.8%), well-developed authigenic carbonates, and biogenic silica accumulations. It is concluded that the Qing2-1 Sub-member represents a critical paleo-environmental transition surface, marked by abrupt shifts to terrigenous-dominated sedimentation and significant organic matter depletion. The Qing 2-1 Sub-member is identified as a critical paleo-environmental transition surface, characterized by abrupt shifts to terrigenous mineral-dominated composition and significant reduction in organic matter content.