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The Early Cretaceous Yingcheng Formation shale gas in the Lishu Fault Depression of the Songliao Basin presents immense prospects for exploration and development. Concurrently, the division of high-frequency sequences within shale intervals has gradually become a research focus. However, traditional sequence stratigraphy faces challenges in the precise delineation of sequences within the shale series, while the understanding of organic matter enrichment patterns within the shale series remains unclear, hindering the exploration and development of shale oil and gas. The utilization of cyclostratigraphy methods allows for the subdivision of high-frequency sequences within the shale series, and further, it provides a beneficial means to explore the enrichment patterns of organic matter in shale based on Milankovitch cycles, aiding in the prediction of "sweet spots" within the layers. Through astronomical cycle analysis of natural gamma-ray data from the research area in the Yingcheng Formation, the following conclusions have been drawn: (1) Well SN65 effectively preserves the signals of Milankovitch cycles within the Yingcheng Formation. Long and short eccentricities serve as reference curves for the fourth and fifth-order sequences, respectively, delineating 14 fourth-order sequences and 51 fifth-order sequences, thus establishing a high-precision isochronous stratigraphic framework for the study area. (2) The organic matter enrichment of the shale within the Yingcheng Formation on the northern slope of the Lishu Fault Depression is controlled by astronomical cycles, exhibiting an antiphase relationship. During periods of high long eccentricity, the climate was warm and humid, corresponding to low Total Organic Carbon (TOC) values; conversely, during periods of low long eccentricity, the climate was cold and dry, corresponding to high TOC values. (3) Two shale sedimentation models have been established: warm-humid and cold-dry. Through the introduction of the concept of the metalimnetic oxygen minimum (MOM) , it has been demonstrated that cold-dry environments are conducive to the enrichment of organic matter in shale. (4) The data were divided into 4 organic-rich shale intervals and 3 organic matter-bearing shale intervals based on the half-amplitude points of the long eccentricity cycle curve. High-quality shale intervals develop at the tops and bottoms of various sequences rather than at the maximum flooding surface. Shallow water environments are conducive to the development of organic-rich shale. These research findings not only provide theoretical support for predicting "sweet spots" of shale gas within the Yingcheng Formation in the Lishu Fault Depression of the Songliao Basin but also serve as a reference for the organic matter enrichment patterns in other lacustrine basins, holding significant implications for the evaluation of shale oil and gas exploration selection.