The Lower Jurassic Da'anzhai Member in the Sichuan Basin preserves a rare continental archive of the Toarcian Oceanic Anoxic Event (T-OAE). However, the mechanisms governing differential organic matter (OM) enrichment in its lacustrine shale successions remain debated. This study presents an integrated organic geochemical, biomarker, and paleoenvironmental investigation of the Da1 3 and Da1 submembers from the central Sichuan Basin, aiming to elucidate their contrasting OM accumulation processes and link them to global climatic forcing. The results demonstrate that the Da1 3 submember, deposited during the T-OAE climatic optimum, is dominated by aquatic (algal) OM, reflecting high primary productivity under warm-humid conditions and stable thermal stratification in an open lacustrine system. In contrast, the Da1 submember exhibits greater terrestrial input and elevated salinity under a hot-arid climate, where OM preservation was largely confined to deep, stratified settings due to frequent fluvial disruption in a closed basin. Integrating these findings with regional T-OAE records from the marine Qiangtang and lacustrine Ordos basins, we establish a unified open-lake (warm-humid) versus closed-lake (hot-arid) enrichment model that links global climatic perturbation, basin evolution, and sediment supply to differential lacustrine OM accumulation. Importantly, the interpreted lake evolution from a warm-humid, open system to a hot-arid, closed system finds a strong parallel in lacustrine records of the Early Cretaceous OAE1a from the Jiaolai Basin, eastern China. This consistency suggests that our proposed framework captures a recurring pattern of lacustrine response to extreme climate perturbations, thereby reinforcing its reliability and potential transferability to other basins and geological periods characterized by similar climatic forcing. This study advances the understanding of continental paleoenvironmental responses to global anoxic events and provides a predictive framework for shale oil exploration in analogous lacustrine settings worldwide.