Sedimentology and geochemistry of Cretaceous source rocks from the Tiancao Sag, Yin'e Basin, North China: Implications for the enrichment mechanism of organic matters in small lacustrine rift basins

•Mudstones in small rift basins may have good potentials of hydrocarbon accumulation.•Anoxic, brackish-saline environments are favorable for deposition of effective source rocks.•Moderate sedimentation rates (60–70 m/Myr) are important for organic matter enrichment.•A “supply-preservation-dilution” model for the formation of source rock is proposed.