摘要
///Mid-deep lacustrine organic-rich shales in Member 2 of the Liushagang Formation(LS2) are the most important high-quality source rock in the Beibuwan Basin.These dark-grey or-brown shales with developed lamellation contain abundant non-marine dinoflagellate,rugasphaera and leiosphaeridia fossils,they are rich in organic matter. Analysis indicated that the organic matter in those shales was mainly of algal origin.In this area, the sedimentation rate for Member 2 of the Liushagang Formation(LS2) was relatively low and the lake remained as a starved basin,meanwhile the bloom and death of algae near surface supplied a great deal of organic matter to lacustrine sediments,and the oxygen-depleted bottom water of palaeo-lakes,due to the water-column stratification,favored the accumulation and preservation of sedimentary organic matter,resulting in the formation of organic-rich shales,a high-quality source rock.