A two-stage model is proposed: Member 1 records a sediment-starved, strongly anoxic setting; Member 2 records increasing terrigenous flux and improving bottom-water oxygenation following Late Changhsingian sea-level fall

The Late Permian Dalong Formation in the Western Hubei Trough (Middle Yangtze Block, South China) records critical paleoenvironmental information during a period of profound global change. Based on high-resolution geochemical analyses of core samples from Well EY3, this study uses rare earth element (REE) systematics to reconstruct the provenance and tectono-sedimentary evolution of this deep-water sequence. The shales are depleted in total REEs (average ΣREE = 108.06 ppm) relative to NASC, with LREE-enriched patterns, weak negative Ce anomalies (average Ce/Ce* = 0.94), negative Eu anomalies (average Eu/Eu* = 0.75), and a pronounced positive Gd anomaly. Diagenetic evaluation confirms that these REE systematics reliably reflect primary depositional signals. Provenance analysis indicates a dominant upper continental crust source with negligible hydrothermal influence. Based on these characteristics, a two-stage tectono-sedimentary evolution model is proposed. Stage I (Member 1) records persistently strongly reducing to anoxic conditions (average U/Th = 3.97) and low REE fractionation (average (La/Yb) N = 5.62), reflecting a sediment-starved, strongly anoxic regime that favored the accumulation of organic-rich black siliceous shales. Stage II (Member 2) records a transition to suboxic–weakly conditions (average U/Th = 1.49), accompanied by an upward increase in (La/Yb) N (to an average of 6.94) and ∑LREE/∑HREE (from 3.07 to 3.22), indicating enhanced terrigenous influx and a relative increase in sedimentation rate driven by the Late Changhsingian regression. The vertical heterogeneity of the Dalong Formation thus reflects a transition from a preservation-dominated, sediment-starved system in Member 1 to a system characterized by increasing terrigenous flux and progressively improving bottom-water ventilation in Member 2, providing a high-resolution geochemical archive of the late-stage depositional evolution of the Western Hubei Trough prior to the Permian–Triassic boundary.