Climax in Wrangellia LIP activity coincident with major Middle Carnian (Late Triassic) climate and biotic changes: Mercury isotope evidence from the Panthalassa pelagic domain

The Carnian Pluvial Episode (CPE, -233 Ma) was characterized by multiple negative carbon-isotope excursions, turnovers in marine and terrestrial biota, and a Tethys-wide humid climate accompanied by abundant terrigenous sediment and freshwater input into sedimentary basins. A general temporal coincidence between the CPE and the emplacement of the Wrangellia Large Igneous Province (Wrangellia LIP) has been well documented, however, it remains unclear whether fluctuations in the intensity of the LIP's activity could be linked to the biotic and climate changes at the CPE. We here present mercury (Hg) concentration and isotope ratio records from a pelagic deep-water succession (Section N-O, Inuyama, Japan) that encompasses the CPE interval. Data reveal concurrent peaks in the Hg concentrations and ratios of Hg to TOC and enrichment factors ThEF, AlEF, ZnEF, and NiEF implying that excess Hg loading in the sediments occurred, likely due to volcanic activity, prior to the CPE siliciclastic input. Furthermore, A199Hg values show a negative shift across the boundary between the Julian 1 and Julian 2, followed by a positive shift up to near-zero values at the Julian/Tuvalian transition. The near-zero A199Hg values at the Julian/Tuvalian boundary are associated with an increase in Hg and Cu loading, suggesting a peak of volcanogenic Hg and Cu input that may indicate a climax in the Wrangellia LIP activity. Most notably, the Julian/Tuvalian transition is where evidence of the most pronounced changes in carbonate platform evolution, biological turnover and climate change associated with the event has been highlighted. Our results therefore suggest that variations in the intensity of LIP volcanism may have played a major role in driving biotic and climate changes during the CPE. Our results provide a model for other mass extinction events associated with LIPs (e.g., the end-Permian) where low-intensity background volcanism was punctuated by high-intensity pulses, these latter being the real killers.