Conodont Biostratigraphy of the Guadalupian–Lopingian (Middle–Upper Permian) Succession at the Daxi Village Section, Hefeng, Western Hubei, South China

Well-developed Late Permian intraplatform rift basins are exposed in western Hubei, part of the Middle Yangtze Block. The Dalong Formation, which is dominated by siliceous sediments, is considered a prospective shale gas reservoir and an excellent succession for studying the co-evolution of deep-water biota and paleoenvironment during the Late Permian. This work studied the Daxi section in Hefeng, Western Hubei Province, which reveals a continuous stratigraphic succession comprising the Middle Permian Maokou and Gufeng formations, the Upper Permian Longtan, Xiayao, and Dalong formations, and the overlying Lower Triassic Daye Formation. The Maokou Formation consists of thick-bedded limestones deposited on a shallow-water carbonate platform. The Gufeng Formation is characterized by black, laminated, pyrite-bearing siliceous rocks and carbonaceous shales, indicating deposition in a deep-shelf setting. The Longtan Formation is dominated by carbonaceous mudstones, reflecting a marine-terrestrial transitional environment. The Xiayao Formation shows an upward transition from bioclastic limestones to interbedded calcareous mudstones and limestones, corresponding to a slope to shallow-shelf setting. The lower member of the Dalong Formation comprises siliceous rocks with interbeds of siliceous and micritic limestones, indicative of a basinal-slope environment, whereas the upper member gradually shifts to interbedded limestones and calcareous mudstones. The overlying Daye Formation consists of argillaceous limestones interbedded with mudstones, representing a shallow marine carbonate platform. A high-resolution biostratigraphic framework spanning the Capitanian to Changhsingian has been established. Nine Permian conodont zones are recognized in ascending order: the Jinogondolella prexuanhanensis Zone (upper Maokou to Gufeng formations), the Clarkina asymmetrica Zone (Xiayao Formation), and within the Dalong Formation, the Clarkina leveni, C. liangshanensis, C. orientalis, C. longicuspidata, C. wangi, C. changxinensis, and C. yini zones. This conodont succession documents a relatively complete evolutionary transition from Jinogondolella to Clarkina and correlates well with equivalent zones in South China and globally. The high-resolution biostratigraphic framework defines the age and distribution of shale-gas targets in the Dalong Formation of Western Hubei. It provides a reliable basis for reservoir analysis and resource assessment, thereby refining the regional stratigraphy and supporting exploration efforts.