High-resolution integrated conodont and radiolarian biostratigraphy with δ13Corg record across the Norian/Rhaetian boundary in the Sasso di Castalda section, Lagonegro Basin, southern Italy

The Norian/Rhaetian boundary (NRB) is marked by faunal turnover and global carbon cycle perturbation. Several possible causes of the environmental perturbation across the NRB have been proposed, including the volcanic activity from the Angayucham Terrane and an impact event related to the Rochechouart crater. Evaluating these proposed causes requires high-resolution biostratigraphy and accurate interregional correlation of carbon isotope curves. However, such comparisons remain challenging due to the limited resolution and inconsistent calibration of radiolarian and conodont biostratigraphic frameworks. Here, we present integrated, high-resolution radiolarian and conodont biostratigraphy and organic carbon isotope (δ13Corg) data from an Upper Triassic pelagic sequence in the Sasso di Castalda section of the Lagonegro Basin, southern Italy. Our biostratigraphic analyses reveal two radiolarian assemblages, the Betraccium deweveri and Proparvicingula moniliformis zones, indicating an age from uppermost Norian to lowermost Rhaetian. The first occurrence of the conodont Misikella posthernsteini s.s. (sensu stricto) constrains the base of the Rhaetian. The δ13Corg profile in the latest Norian exhibits an overall negative shift characterized by positive and negative fluctuations that correspond to the globally recognized carbon isotope excursion at this boundary. Furthermore, based on our conodont biostratigraphic data, the deposition of the platinum group elements-enriched layer reported in the studied section is constrained to the latest Norian, suggesting a correlation with the Rochechouart impact. Since this layer corresponds to the onset of the negative δ13Corg shift, our new δ13Corg record, integrated with highresolution biostratigraphy, could contribute to understanding the cause of extinction across the NRB.