Gravity flows in steep-slope zones of lacustrine rift basins interact with deep-water shales to form heterogeneous mixed sedimentation zones, yet their sedimentary evolution and hydrocarbon occurrence characteristics remain poorly understood. In this study, core and thin section observations, X-ray diffraction, scanning electron microscopy, mercury intrusion porosimetry, low-pressure nitrogen physisorption, total organic carbon testing, step-by-step Rock-Eval pyrolysis, and time series analysis, were conducted to decode sedimentology and hydrocarbon occurrence characteristics based on lithofacies combinations controlled by astronomical cycles. Results reveal five microfacies (calcareous/felsic semi-deep lake, outer fan, channel front, braided channel) and six lithofacies combinations (LC1–LC6) shaped by debris flows, turbidity currents, and felsic mixed floating currents. The 406-kyr long eccentricity cycle governs sediment supply and reservoir heterogeneity. During high eccentricity phases, increased monsoon-driven terrigenous input enhances sandstone deposition, developing braided channel (LC5) and channel front (LC6) microfacies. These intervals exhibit elevated terrigenous quartz/feldspar content and reduced organic carbon in fine-grained sedimentary rocks, with hydrocarbons occurring as quasi-continuous to discontinuous accumulations. Conversely, during low eccentricity phases, felsic mineral layers or isolated sandstone interlayers dominate, forming outer fan (LC3), channel front (LC4), and semi-deep lake (LC1–LC2) microfacies. These intervals show lower terrigenous content and higher TOC in fine-grained sedimentary rocks, with hydrocarbons occurring as continuous to quasi-continuous accumulations. A novel sedimentary evolution and hydrocarbon occurrence model demonstrates the ordered coexistence of conventional and unconventional reservoirs, driven by astronomically forced climate fluctuations. This framework advances theoretical understanding and optimizes exploration strategies for steep-slope lacustrine basins with mixed sedimentation.

An integration of core observation, casting thin section identification, scanning electron microscopy (SEM) observation, porosity-permeability test of samples and mercury intrusion porosimetry (MIP), in combination with the local burial and hydrocarbon charging history, is applied to the study on the diagenesis, differential lithofacies-based diagenesis mechanism and reservoir pore structure of the Sangonghe Formation in Moxizhuang area, Junggar Basin. The results show that the Sangonghe Formation mainly experienced mechanical compaction, cementation and dissolution during the diagenetic evolution. Reservoirs of diverse lithofacies are significantly different in diagenetic mechanism: the calcareous sandstone facies, argillaceous carbonaceous sandstone facies and volcanic tuffaceous matrix sandstone facies tend to get tight in the early diagenetic stage, while featuring weak diagenesis intensity in the middle stage; the pores of the massive sandstone facies are well preserved in the early diagenetic stage with smooth fluid migration in the middle stage, and there are multi-stage cementation and dissolution occurring in between; and the conglomeratic sandstone and conglomerate facies feature high gravel content, resulting in poor fluid migration, and weak compaction in the early diagenetic stage, while characterized by weak cementation and weak dissolution in the middle stage. The different diagenetic mechanisms for the lithofacies serve to determine the pore structure. The calcareous sandstone facies and argillaceous carbonaceous sandstone facies of lamination texture have poor pore connectivity, complex structure and poor overall physical properties, which are not conducive to oil and gas enrichment; the pore throat of the massive sandstone facies is well sorted, and the pores of the facies are the most developed with strong connectivity, resulting in good overall physical properties, conducive to oil and gas enrichment; the particles of conglomeratic sandstone and conglomerate facies are poorly sorted and in close contact, limiting the pore connectivity to some extent, but the destructive diagenesis intensity is weak, and the overall physical properties are good, conducive to forming effective oil and gas reservoirs.