Path-Dependent Diagenesis and Facies-Controlled Reservoir Quality in Lower Cretaceous Fan-Delta Sandstones, North Yellow Sea Basin: A Model for Superimposed Rift Basins

The Lower Cretaceous fan-delta sandstones in the North Yellow Sea Basin underwent a distinctive polyphase burial trajectory, offering a natural laboratory to investigate path-dependent diagenesis and its impact on reservoir quality evolution in superimposed rift basins. Integrating petrographic, cathodoluminescence, SEM, and quantitative diagenetic analysis, this study reveals an anomalously compaction-dominated diagenetic regime wherein mechanical compaction accounted for 32.1% porosity loss (ICOMPACT ~0.8) compared to only 7.4% by cementation. This anomaly is attributed to a path-dependent mechanism as follows: a >60 Ma erosional hiatus arrested early calcite cementation, leaving sandstones mechanically metastable and vulnerable to intensified anomalous re-compaction triggered by rapid reburial since ~37 Ma during the Himalayan tectonic phase (since 66 Ma). The paragenetic sequence progresses from early poikilotopic calcite precipitation to late-stage microquartz, ferroan carbonates, and illitization, with intermediate feldspar dissolution generating secondary porosity. Critically, reservoir quality exhibits strong facies-dependent heterogeneity driven by divergent diagenetic pathways. Proximal matrix-supported gravels (Gcm/Gmm) are destroyed by pseudomatrix formation, whereas channelized sandstones (St/Sp) with localized early cement frameworks are buffered against compaction and preserve enhanced porosity (12%–18%) through subsequent dissolution. Consequently, this polyphase burial history fundamentally decouples reservoir quality from maximum burial depth. Effective reservoir prediction requires a paradigm shift from conventional depth-porosity transforms to integrated diagenetic facies analysis, validated by static petrophysical and well-log signatures (e.g., elevated Th/K ratios). These findings establish a transferable genetic model for evaluating porosity preservation in analogous Mesozoic polyphase-reactivated rift basins.