A biomarker study of depositional paleoenvironments and source inputs for the massive formation of Upper Cretaceous lacustrine source rocks in the Songliao Basin, China

► The occurrences of biomarker in the Cretaceous lacustrine sediments are investigated. ► The source rocks were formed under salinity and anoxic stratified water column. ► The type and quality of OM are largely controlled by palaeodepositional conditions. ► An unusual heavier δ13C composition pattern of n-C30 and n-C32 alkanes is identified.