Conodont diversity, biostratigraphy, and environmental dynamics: Unravelling the Smithian-Spathian transition at Guryul Ravine, Kashmir

The late Smithian and Smithian-Spathian boundary (SSB) witnessed significant conodont extinction approximately 2.7 million years after the major Permian-Triassic boundary extinction. This study offers a detailed examination of the Smithian-Spathian transition at the Guryul Ravine section in the Srinagar district, Kashmir, focusing on conodonts and δ13Ccarb values. The section features an unprecedented conodont taxonomic richness, with 53 species from 17 genera, including three newly formalized species: Neospathodus aristatus n. sp., Neospathodus guryulensis n. sp. and Borinella? prima n. sp. Additionally, Borinella ex gr. buurensis and Scythogondolella ex gr. milleri are subdivided into multiple morphotypes, facilitating a refined biochronological scheme. A high-resolution δ13Ccarb record spanning the Early Triassic captures global carbon isotope excursions. The integration of δ13Ccarb with conodont biostratigraphy enhances global correlation of the Smithian-Spathian transition. The late Smithian conodont extinction aligns with a globally observed positive δ13Ccarb excursion, reaching an exceptional value of + 12 ‰, likely of diagenetic origin. This study proposes a new conodont biochronological framework based on the Unitary Association Method (UAM). Placing the SSB between the extinction climax and re-diversification onset, the framework relies on a rich conodont collection from Guryul Ravine, Kashmir, and a comprehensive reassessment of conodont data from 19 other sections along the northern Gondwana margin. The resulting 16 Unitary Association Zones (UAZs) are cross-referenced with lithological, chemostratigraphical (δ13Ccarb), and ammonoid markers, establishing an unprecedentedly robust basis for defining the SSB. The proposed boundary is within UAZ8 but allows for future refinements.