Depositional mechanism of deep-lacustrine mudstones controlled by the coupling of sediment provenance and orbital-paced environmental evolution

Unraveling the sedimentary process and spatiotemporal distribution of deep-lacustrine mudstones is critical for clarifying the origin and distribution of shale-oil reservoirs in the Chang 7 3 sub-member (Ordos Basin). In this study, comprehensive analyses of petrology and cyclostratigraphy were conducted to decode the lithofacies and their provenance within a high-resolution astronomical framework. Subsequently, analysis of the paleoenvironmental evolution and its driving mechanism reveals the sedimentary genesis and depositional models of deeplacustrine mudstones under the dual control of provenance supply and lakelevel fluctuation. Within the Chang 7 3 sub-member, three primary lithofacies have been identified. Massive mudstones, derived from the Alxa Terrane, are generally deposited in the northern part of the basin. In contrast, the other two types of binary laminated shales (“silt-sized felsic (SSFL) [Formula: see text] organic-rich (ORL)” and “tuff-rich (TRL) [Formula: see text] organic-rich (ORL)”), sourced from the volcaniclastics within the Qinling orogenic belts, are mainly deposited in the central and southern parts of the basin. Under the control of paleogeomorphology characterized by “steep-south and gentle-north”, hyperpycnal flows are prone to occur within the southern part of the basin and carried volcaniclastics into the lake basin. Periodic lake-level fluctuations driven by obliquity cycle further controlled the transport distance of silt-sized particles to the center of the lake basin, inducing the alternate deposition of “SSFL [Formula: see text] ORL” laminated shales (lowstand) and “TRL [Formula: see text] ORL” laminated shales (highstand). Within the central part of the basin, the hyperpycnal flows were only able to transport volcaniclastics into this area during the period of low lake-level (low obliquity). High lake-level (high obliquity) led to the retreat of volcaniclastics, and the fine-grained sediments derived from the Alxa Terrane mainly occurred as suspension settling, forming massive mudstones. Conversely, within the northern part of the basin, isolated from southern volcaniclastic inputs, the fine-grained sediments derived from the Alxa Terrane continuously occurred in suspension, settling to form massive mudstones.