New constraints on the evolution of ⁸⁷Sr/⁸⁶Sr of seawater during the Upper Triassic

The Late Triassic time interval witnessed several important biological turnovers, extinctions and onset of new life forms. Therefore, it is crucial to better constrain the tectonic, climatic and oceanographic framework at this time. The radiogenic strontium isotopic composition (⁸⁷Sr/⁸⁶Sr) of seawater, recorded in marine carbonates is sensitive to variations in continental weathering and oceanic spreading rates. This makes it a powerful proxy for palaeo-environmental reconstructions and an excellent global stratigraphic correlation tool of marine sediment records. In this study, we present a new and extended ⁸⁷Sr/⁸⁶Sr dataset across the late Norian - Hettangian interval, established from carbonate successions in Austria and Turkey. The well-established biostratigraphy and high sampling resolution allow evaluating changes in the ⁸⁷Sr/⁸⁶Sr record with a better time constraint than in previous studies. An exceptionally sharp trend towards unradiogenic values has been observed in the latest Norian and in the early Rhaetian from 0.70800 to 0.70779. Considering Late Triassic climate change, updated tectonic models and actual dating of magmatic events, possible explanations for the observed trend in the ⁸⁷Sr/⁸⁶Sr record are: (i) enhanced dissolution of pre-Norian carbonates, (ii) dissolution of widespread Late Triassic evaporites and (iii) tectonic reorganization of sedimentary basins due to the break-up of the supercontinent Pangea. At the very end of the Choristoceras marshi Zone, in the late Rhaetian, the unradiogenic ⁸⁷Sr/⁸⁶Sr trend is reversed. This is likely related to environmental changes due to the continental emplacement of the Central Atlantic Magmatic Province.