“Laminated marlstone”，which is an important part of the self-sourced tight reservoir system of Shulu sag，is defined simply as fine-grained carbonate rock with the single-layer thickness less than 1 cm and without any reference to the distinction in microscopic geometry and compositions of laminations. Based on the observation of cores and thin sections of the studied area，this paper focuses on studying the sedimentary characteristics and reservoir significance of laminations with the aid of X-ray diffraction，electron probe and stable isotope analysis. The carbonate-rich fine-grained laminations were grouped into two types：the seasonal rhythm laminae combination and the turbidity current graded laminae combination. The former constitute the laminated marlstone which consisted of lacustrine sediments formed by the physical，chemical and biological processes controlled by seasonal hydrology variations. The latter constitute the turbidity laminated marlstones and laminated calcisiltites which are turbidity current sediments deposited from a series of events. Laminae combination can influence reservoir property. Abundant interlayer fractures develop in seasonal rhythm laminae combinations，and the organic matter within the clastic lamina can improve reservoir quality through thermal maturation and hydrocarbon expulsion. Thus，the reservoir property of seasonal laminated marlstones are better than that of the turbidity laminated marlstone and laminated calcisiltites.