Geochemical characteristics of hydrocarbon source rocks of the Lower Cretaceous in the Chagan Sag

Lacustrine dark mudstones of the lower Cretaceous Bayinggebi Formation and Suhongtu Formation are the main hydrocarbon source rocks in the Chagan Sag.This paper revealed the geochemical characteristics of the source rocks on the basis of the abundance,types and maturity of organic matter and biomarker analysis.The results show that hydrocarbon source rocks have high abundance of organic matter and belong to good hydrocarbon source rocks,and the type of organic matter belongs to transition type.The organic matter type of Bayinggebi Formation is superior to that of Suhongtu Formation.The former is mainly ofⅡ 1-Ⅱ 2,while the latter is mainly ofⅡ 2-Ⅲ.The organic matter of the hydrocarbon source rocks has a high degree of thermal evolution and is at maturity stage,even a high-post maturity stage.The hydrocarbon source rocks occurred in the weak oxidation-weak reducing environment,and the organic source material is mainly lower aquatic plants mixed with some higher plants.