Fine-grained sedimentology is crucial to understanding paleoclimatology and unconventional oil and gas sedimentology. However, the controlling factors and evolutionary patterns of sedimentary structures in shale—the most fundamental and widespread features of fine-grained sediments—remain enigmatic. In this study, five types of organic-rich lacustrine shale sedimentary structures were identified in the lower Qingshankou Formation in Well C41-70 in the Songliao Basin: massive structures, layered structures, weakly laminated structures, laminated structures, and event sediment structures. Furthermore, Milankovitch cycles were identified using the gamma-ray logging curve of Well C41-70, and an astronomical time scale (ATS) was established. The frequency and combination patterns of different types of sedimentary structures, referred to as “sedimentary structure evolution sets (SSESs)”, exhibit covariations at multiple scales with changes in lake levels, short eccentricity, and precession. This suggests that lake levels and orbital cycles are the multi-order controls on SSESs variations. Cross-well correlations of geochemical proxies based on the ATSs further indicate that shifts in SSESs coincide with changes in the lacustrine sedimentary environment. Notably, marine incursion events appear to have induced significant variations in both the sedimentary environment and the SSESs. These findings imply that SSESs may preserve more information on paleoclimatic–paleoenvironmental changes and geological events, which challenges the conventional wisdom of strong heterogeneity and weak distribution patterns in sedimentary structures within shale reservoirs. Furthermore, SSESs not only provide critical references for optimizing fracturing process parameters in lacustrine shale development, but also help reveal the dilution of organic matter during deposition and elucidate the genesis of TOC heterogeneity. This demonstrates the significant value of depiction and analysis of sedimentary structures for shale oil and gas exploration and development.

Although the Late Cretaceous marine incursion events (MI) significantly boosted organic carbon (OC) accumulation in the Songliao Basin, their net effects and accumulation mechanisms have long been debated. By integrating high-resolution geological data, multi-proxy paleoenvironmental analysis, and a machine learning-based approach for TOC prediction in Member 1 of the Qingshankou Formation, we reveal that total OC sediment accumulation rates (OCSAR) during high-intensity MI (HMI) increased by 28.8% compared to low-intensity MI (LMI) intervals, with the areal OCSAR of the study area rising from 0.43 × 10⁻² to 0.55 × 10⁻² GtC/(Myr·km²). The OC accumulation models during HMI and LMI are established: driven by the interplay of seawater influxes, basin morphology, and terrigenous inputs, which collectively modulated the bacterial sulfate reduction, redox conditions, and nutrient availability in the water column, the growth rate of areal OCSAR exhibited pronounced spatial heterogeneity, defining four distinct zones (I–IV). The validation case from the Nenjiang Formation demonstrates the robustness of the models. These findings establish MI as a global amplifier of OC burial in mega-paleolake systems and redefine resource development frameworks for lacustrine shales within MI sequences.