New Integrated Chemoand Biostratigraphy of CPE Deposits (carnian Pluvial Episode, Late Triassic) from the Transdanubian Range, Hungary (western Tethys)

The Late Triassic Carnian Pluvial Episode (CPE) is among the most extensively studied Mesozoic hyperthermal events characterized by the perturbation of the global carbon cycle, climate change (global warming, wetter climate, enhanced hydrological cycle) and biotic turnovers. Chemostratigraphy is a key tool in the global correlation of the biotic events across the CPE yet the lack of proper calibration of isotope curves can lead to erroneous correlation of negative carbon isotope excursions (NCIE). We provide new bulk organic carbon isotope, conodont, microfacies, and foraminifer data from five successions in the Transdanubian Range (TR, Western Hungary) representing key CPE locations within the Western Tethys realm spanning the early Julian to early Tuvalian interval. Previous carbon isotope data suggested the onset of the CPE to be coeval with a pronounced shift from carbonate-dominated to mixed clastic-carbonate sediments represented by the Veszprém Marl Formation, yet palynological and clay mineral data did not show a clear shift to a humid climate. Similarly, new microfacies and foraminifer data suggested that shallow water microbial carbonate factories were still active after the presumed onset of the CPE. Our new conodont findings and reinterpreted biostratigraphical data thus recquired the recalibration of the onset of the CPE in the TR marked by the first NCIE and the correlation of Carnian strata of Hungary within the Western Tethys realm. Elevated terrestrial influx and ecosystem disturbances were present already during the early Julian represented by a Julian 1 NCIE (Pre-CPE NCIE), so far not extensively studied in the Western Tethys albeit this “event” had a much smaller biotic impact. The onset of the CPE is placed in a higher stratigraphic position than before associated with a marked NCIE (originally NCIE-2 of the CPE in previous works) in multiple successions and large-scale ecological reorganization among foraminifers, ostracods, and phytoplankton. Proliferation of pelagic calcifiers, calcipsheres in the TR shortly after the onset of the CPE can be linked to a calficiation overshoot after carbonate production crisis. Climax of the environmental perturbation represented by the predominanty hygrophyte terrestrial floral elements and temporal demise of marine microbiota is recorded in the upper part of the Veszprém Formation in the late Julian 2. Carbon cycle instability continued in the latest Julian to early Tuvalian represented by further NCIEs yet the return of rich shallow water biota and oscillations in the terrestrial influx do not unequivocally indicate humid climate in the early Tuvalian. Our work provides new timelines and scenarios for CPE-related biotic events in the Western Tethys and points to a longer interval of environmental instability in the Carnian that was punctuated by more severe events linked to the CPE carbon cycle perturbation. This research was supported by the National Research, Development and Innovation Office of Hungary (NKFIH FK 134229 grant). The research was conducted within the internal research project “WEGETA” at the Croatian Geological Survey, funded by the National Recovery and Resilience Plan 2021–2026 of the European Union – NextGenerationEU, monitored by the Ministry of Science and Education of the Republic of Croatia.