An integrated bio- and chemostratigraphic framework for the Triassic–Jurassic boundary interval and its potential for global correlations

The Triassic/Jurassic boundary (TJB) interval records one of the major Phanerozoic mass extinctions, commonly linked to the effects of volcanism of the Central Atlantic Magmatic Province. However, uncertainties persist regarding the age, duration and synchroneity of events across the boundary, largely because of ambiguities in stratigraphic correlations, even among reference TJB sections. Stratigraphic correlations across the TJB have traditionally been based on the δ 13 C record of the sedimentary organic carbon (δ 13 C org ), while the carbonate carbon-isotope record (δ 13 C carb ) has been long considered unreliable. Here, we reassess inorganic carbon-isotope stratigraphy across the TJB using well-preserved skeletal and bulk carbonate δ 13 C records from reference sections of the Northern Calcareous Alps (Austria) and the Laurasian Seaway (UK). These records are used to build a new δ 13 C carb framework that is anchored to ammonite biostratigraphy and complemented with the sequence of negative δ 13 C org excursions adopted in previous studies. We document reproducible δ 13 C carb patterns consisting of: (1) a prominent negative excursion, corresponding to the initial carbon-isotope excursion of the δ 13 C org record in the topmost Marshi Chronozone and characterised by the minimum point “a”, (2) a positive excursion encompassing the TJB herein named “Triassic/Jurassic Boundary Event” and culminating in the positive peak “b” in the top Tilmanni Chronozone, (3) a negative trend to pre-excursion values with the minimum point “c” documented in the Angulata Chronozone and (4) a second positive excursion encompassing the Hettangian/Sinemurian Boundary and culminating in the positive peak “d” in the Semicostatum Chronozone. These δ 13 C carb patterns appear globally reproducible across deep-sea to shallow-water sections and are potentially extended to the δ 13 C carb signature of pedogenic carbonates in continental records, offering a powerful new tool for global basin-to-land correlations and for understanding carbon-cycle perturbations associated with CAMP volcanism.