This study investigates Lower Cretaceous Bayingebi Formation sediments in the Yin'e Basin, integrating petrological, mineralogical, organic/elemental geochemical, and biomarker analyses. During the OAE1a event (similar to 120 Ma), the regional climate shifted from warm-semiarid to warm-humid, which intensified terrestrial chemical weathering; fluvial erosion subsequently transported large amounts of nutrients into the lake, thereby enhancing lacustrine primary productivity. Increased terrestrial detrital input elevated lake salinity, stabilizing salinity stratification, while stagnant anoxic bottom waters facilitated organic carbon enrichment and preservation. Mechanistically, weathering intensity, biological pump efficiency, and salinity stratification jointly disrupted the lacustrine carbon cycle via a positive feedback loop: climate change -> intensified chemical weathering -> enhanced nutrient input/productivity -> strengthened stratification/anoxia -> promoted organic carbon sequestration. This study fills a gap in northern China's continental OAE1a response records, provides key geochemical constraints for Early Cretaceous global carbon cycle dynamics and lacustrine paleoenvironmental evolution, and integrates atmospheric-terrestrial-aquatic perspectives-deepening understanding of paleoclimate-carbon cycle regulation across spheres in land-lake systems.