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 δ¹³C_carb 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 δ¹³C_carb record spanning the Early Triassic captures global carbon isotope excursions. The integration of δ¹³C_carb with conodont biostratigraphy enhances global correlation of the Smithian-Spathian transition. The late Smithian conodont extinction aligns with a globally observed positive δ¹³C_carb 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 (δ¹³C_carb), and ammonoid markers, establishing an unprecedentedly robust basis for defining the SSB. The proposed boundary is within UAZ₈ but allows for future refinements.