Abstract: Dayangshu basin is a Late Mesozoic residual basin with a low degree of exploration and research. It shows a good exploration prospect with the industrial oil flows obtained from several wells in recent years in the southern depression. A systematic understanding of the source rocks and the hydrocarbon origin of Jiufengshan Formation is still uncertain. Based on the geochemical analysis data of source rocks and crude oils, including TOC、Rock-Eval、GC-MS, and carbon isotope, the hydrocarbon generation potential of source rocks of Jiufengshan formation are evaluated, the properties of crude oils and oil source are studied. The results show that medium-good source rocks are developed in the first member (K1j1) and the third member(K1j3) of Jiufengshan Formation, with w（TOC） of 1.76% and 2.59%, w（ S1 + S2） of 4.44 mg/g and 7.36 mg/g, bitumen of 0.21% and 0.09% respectively. The organic matter type of the K1j1 is mainly type Ⅱ1 including some typeⅠ, K1j3 is mainly type Ⅱ1 including some typeⅡ2, and the vitrinite reflectance (Ro) of the source rocks in K1j1 is mainly 0.70% to 1.60%, at the mature to high mature evolution stage. Ro in K1j3 is mainly from 0.50% to 1.10% and at the mature evolution stage. The hydrocarbon generation threshold of the source rock is about 1 300 m, and the hydrocarbon generation peak is about 1 750 m. The source rock has the characteristics of early hydrocarbon generation. The crude oils are light to medium, characterized by high viscosity, high wax, low sulfur, and high saturated hydrocarbon. The crude oil enriches light carbon isotope with δ13Coil from -30.40‰ to -29.38‰, δ13C sat from -30.78‰ to -29.07‰, and δ13Caro from -29.73‰ to -27.91‰, which indicates the source of lacustrine algae. The main peaks of alkane in oil are nC19 and nC21, OEP is 1.07 to 1.08, and Pr / Ph is 0.83 to 1.10. The crude oil can be divided into two groups based on terpenoid steroid marker. Group one includes the crude oil of Wells YC1 and Y3, with relatively high tricyclic terpane, C30D, Ts/Tm, C29Ts/C29 hopane, sterane C27R/C29R, regular sterane / hopane, rearranged sterane / regular sterane, C2920S / 20 (S+R), C29ββ/(ββ++αα) and low β-carotene. Group two includes the crude oil of Well YX4 and Well Y6, with high β-carotene and relatively low sterane terpane ratios, indicating that the maturity of Well YC1 and Well Y3 oil is higher than that of Well YX4 and Well Y6, and there are slight differences in sedimentary environment and parent material source. The oil and rock correlation of biomarkers shows that the crude oil of Wells YC1 and Y3 mainly comes from the source rock of K1j1, and the crude oil of YX4 and Y6 wells mainly comes from the source rock of K1j3. The potential hydrocarbon accumulations in this area are source-reservoir integrated accumulations and lower source rocks generation-upward migration accumulations.

Key words: Dayangshu basin；Southern depression；Jiufengshan Formation；source rocks；geochemical, oil source