Recurring photic zone euxinia in the northwest Tethys impinged end-Triassic extinction recovery

The end-Triassic extinction (ETE) is associated with rapid atmospheric CO2-driven warming amplified by positive feedbacks involving weathering, nutrient oversupply, water column anoxia and sul.fate reduction. These conditions culminated in photic zone euxinia (PZE) at least locally in the Western Tethys, but its broader extent across northwest Europe has yet to be identified. Here we present new biomarker and bulk 613Corg isotopic data that document redox and palaeoecological changes from two end-Triassic sites in the Western Tethys: Felixkirk, in the Cleveland Basin, northeast England, and Lavernock Point, in the Bristol Channel Basin, S Wales. The presence of aryl isoprenoids and Chlorobi-derived isorenieratane indicates shoaling of anoxia and toxic H2S to the photic zone caused by flooding in restricted or semi-enclosed basins. Oscillating redox conditions and severe PZE prevented a swift recovery of at least the benthic ecosystem across several British basins. Additionally, in concert with recent discoveries in the Bristol Channel Basin, in the Cleveland Basin we find that the 'initial' negative carbon isotope excursion (CIE) is related to a localized change in organic matter sources. PZE in British and other European basins points towards H2S toxicity as an extinction driver for the Western Tethys, highlighting the need for a global characterization of redox changes across the end-Triassic and other extinction events.