New evidence for a long Rhaetian from a Panthalassan succession (Wrangell Mountains, Alaska) and regional differences in carbon cycle perturbations at the Triassic-Jurassic transition

• New Triassic-Jurassic section, paleontological-geochemical data, open Panthalassa. Complete record, new δ 13 C org curve across the transition. Norian-Rhaetian and boundaries constrained by paleontological data. Four U–Pb dates Boundary support a long Rhaetian (∼8 Ma). global interpretation: variable carbon cycle dynamics, Panthalassa vs. Tethys. The end-Triassic mass extinction is one of big five events in Phanerozoic Earth history. It linked with emplacement Central Atlantic Magmatic Province host interconnected environmental climatic responses that caused profound deterioration terrestrial marine biospheres. Current understanding, however, hampered (i) geographically limited set localities data; (ii) incomplete stratigraphic records low relative sea-level European sections during Late Triassic earliest Jurassic; (iii) major discrepancies estimated duration latest limit spatiotemporal evaluation biotic locally globally. Here, we investigate Triassic–Early Jurassic time interval from stratigraphically well-preserved sedimentary succession deposited tropical oceanic We present diverse data lower McCarthy Formation exposed at Grotto Creek (Wrangell Mountains, southern Alaska), including ammonoid, bivalve, hydrozoan, conodont biostratigraphy; organic isotope ( ) stratigraphy; CA-ID TIMS zircon dates. These are consistent (NRB) ∼209 Ma, providing evidence to Rhaetian. They also constrain boundary (TJB) ∼6 m section. Our TJB record Creek, conjunction previous demonstrates features not only appear correlative on scale but shows local heterogeneities compared some Tethyan records. Notably, smaller excursions within large negative excursion [NCIE] known absent Panthalassan This comparative isotopic becomes useful for distinguishing regional overprinting signal; raising questions about ubiquity smaller-scale NCIEs TJB; highlighting largely unresolved presumed perturbations. geochemical establish section as an important Upper Lower due its paleogeographic position complete record. represents best documentation NRB intervals Wrangellia, likely entire North American Cordillera.