WRANGELLIA LIP VOLCANISM AND CARBON CYCLE PERTURBATION IN THE CARNIAN (EARLY LATE TRIASSIC)

In the Late Triassic (~230 Ma) a climate change from arid to more humid conditions, called the Carnian Pluvial Event (CPE), was marked by the sudden input of siliciclastic material, anoxia and a crisis of carbonate production into marine sedimentary basins. In continental environments, palaeosols typical of tropical humid environments developed, the floral associations shifted towards more hygrophytic elements and massive resin production occurred. The CPE is also closely associated with biological turnover among some marine groups and could be linked to major evolutionary innovations. A 4‰ negative C-isotope excursion (CIE) in higher plant n-alkanes coincides with the onset of the CPE. This C-cycle disturbance has been linked to the coeval eruption of the Wrangellia oceanic plateau (western North America), a Large Igneous Province (LIP) that is thought to have outpoured up to 1 million cubic kilometres of basalts.

Here we present organic carbon isotope analyses from stratigraphic sections in Italy, Austria and Hungary, regions that were part of north-western Tethys during the Carnian. In all the studied sections the onset of a 2–4‰ negative CIE occurs ca. at the boundary between the Trachyceras aonoides and Austrotrachyceras austriacum ammonoid zones (Concentricisporites bianulatus – Aulisporites astigmosus sporomorph assemblages) and is coincident with a sudden change of sedimentation that marks the CPE in the studied stratigraphic sections, indicative of massive terrigenous input and oxygen depletion.

We propose that intensification of Pangea megamonsoon activity linked to the injection of large amount of ¹³C-depleted carbon into the atmosphere–ocean system caused a sudden increase of the continental runoff in the Carnian. CO₂ injection from Wrangellia LIP activity could have caused an increase in frequency and intensity of rainfall events.