## 5 Discussion  
Organic Matter Preservation Patterns Controlled by Astronomical Cycles  
The trace elements, organic matter abundance, and mineral composition of lacustrine sediments undergo periodic changes in response to variations in paleoclimate, paleo-water depth, and sediment supply [50,51], leading to differences in organic matter accumulation patterns at different stages. Earth's orbital parameters to some extent regulate the patterns of Earth's climate changes. When eccentricity approaches its maximum, Earth's orbital trajectory becomes more elliptical, increasing the difference between perihelion and aphelion. This enhances the precession amplitude regulated by eccentricity, leading to greater seasonal variations, with shorter winters and prolonged summers. As a result, Earth's surface receives more solar radiation, leading to a warmer climate. At the same time, surface evaporation increases, precipitation becomes more abundant, and surface runoff intensifies, transporting a large number of nutrients into the lake basin, which benefits algae and plankton growth, significantly enhancing lake productivity. Laminated and bedded structures are more likely to develop under strong seasonal variations (Figure 7). During this period, some Fe(II) remains in deep water, undergoing rapid deposition without immediate oxidation, leading to its rapid accumulation in the deeper parts of the lake basin. When encountering hydrogen sulfide retained at the lake bottom, Fe(II) reacts to form pyrite precipitates, resulting in higher pyrite concentrations. Additionally, an abundant sediment supply provides a solid material foundation for organic matter accumulation. A higher lake level provides ample space for organic matter accumulation. The weakly reducing conditions of the bottom water in the lake basin create favorable conditions for the burial and preservation of organic matter. The thin sections of mudstone samples near the eccentricity maximum primarily show dark mudstone with well-developed organic-rich laminae (Figure 8a-d). Therefore, fine-grained strata deposited under warm humid climatic conditions exhibit high organic matter abundance and significant hydrocarbon generation potential. Figure 7: Organic matter enrichment model of lacustrine fine-grained sedimentary rocks in warm and wet climate. When eccentricity approaches its minimum, Earth's orbital trajectory becomes nearly circular, reducing the difference between perihelion and aphelion. The precession amplitude, regulated by eccentricity, also decreases, resulting in weaker seasonal contrasts characterized by prolonged and colder winters and shorter summers. As a result, Earth's surface receives relatively less solar radiation, leading to a drier and colder climate. Laminated or platy structures tend to develop under weak seasonal variations (Figure 9). At this stage, surface evaporation decreases, precipitation diminishes, surface runoff declines, and river transport capacity weakens, leading to reduced sediment supply. The paleo-water body becomes shallower, algae and plankton populations decline, and lake productivity decreases. Meanwhile, in relatively shallow water zones, Fe(II) is rapidly oxidized to Fe(III) due to the oxidizing environment, reducing the reaction between Fe(II) and sulfur ions and thereby decreasing pyrite precipitation. Additionally, the reduced sediment supply limits organic carbon input, and the arid climate inhibits algae and plankton growth, resulting in relatively low TOC content in the corresponding sedimentary strata, which are characterized by laminated silty mudstone and massive calcareous mudstone. The thin sections of mudstone samples near the eccentricity minimum primarily show sandy mudstone with poorly developed organic-rich laminae (Figure 8e-h). Figure 8: Microscopic photos of typical rock core from Well N10. (**a**) Microscopic image of moderately organic-rich laminated mudstone at 2050.1 m in Well Nai-10, showing silt-sized clastic particles.