1.  College of Earth Sciences, Jilin University, Changchun 130061, China

2. Key-Lab for Oil Shale and Paragenetic Energy Minerals, Jilin Province, Changchun 130061, China

3. College of Earth Science, China University of Petroleum, Beijing 102249, China

4. The Third Oil Production Plant of PetroChina Changqing Oilfield Company，Yinchuan 750006,China

5. Liaohe Oilfield Exploration and Development Research Institute,Panjin 124010,Liaoning，China

Abstract： Based on the analysis of oil content, total organic carbon(TOC), rock pyrolysis and biomarker, the authors studied the organic geochemical characteristics, hydrocarbon generation potential, the origin of organic matter, and depositional environment of Eocene Dalianhe Formation oil shale in Yilan basin. The results show that there are two types of oil shales, the independent oil shale of semi-deep lake facies and the coal-bearing oil shale of limno-telmatic facies in the study area. The oil content of independent oil shale is between 3.55%-4.18%, w(TOC) is between 9.00%-10.55%, and the kerogen is type Ⅱ1. The oil content of coal-bearing oil shale is between 3.85%-18.57%, w(TOC) is 8.90%-30.10%, and the kerogen is type Ⅰ-Ⅱ1, which has better hydrocarbon generation potential. Low Tmax (425-440 ℃), High CPI (1.32-1.68), low C2920S/(20S+20R), low C29ββ/(αα+ββ) and low Ts/Tm indicate that the organic matter of the two types of oil shale is in the immature stage. The main peak of n-alkanes is C27 or C29, the average value of CPI is 1.50, which shows that odd carbon number of single and back peak is dominant, and Pr/Ph (average value: 3.16) indicates that pristane is dominant. The carbon number distribution of n-alkanes and the relative content of C27-29 regular steranes indicate that oil shale is a mixed source of higher plants and algae, and algae contribute more to the organic matter of coal-bearing oil shale. The contents of Pr/Ph and rearranged steranes in the coal-bearing oil shale are significantly higher, in contrast, the gamma paraffin index of the two types of oil shale is very low, which reveals that the independent oil shale is deposited in the oxygen-limited freshwater environment, and the coal-bearing oil shale is deposited in the weakly oxidized freshwater environment. The independent oil shale is affected by frequent gravity flows, and its quality decreases. Based on the above research, it is considered that the origin of organic matter and the gravity flows are the critical factors for the differential enrichment of organic matter between the two types of oil shale in the study area.