Dynamic ocean redox conditions during the end-Triassic mass extinction: Evidence from pyrite framboids

The end-Triassic (∼201 Mya) records one of the five largest mass extinction events of the Phanerozoic. Extinction losses were coincident with large igneous province volcanism in the form of the Central Atlantic Magmatic Province (CAMP) and major carbon isotope excursions (CIEs), suggesting a link between these phenomena. Marine anoxia has been implicated as a causal factor in the crisis, but there remains some uncertainty regarding the role of marine redox changes in marine extinction phases because both intensity and duration of marine anoxia are poorly constrained. We employ high resolution pyrite framboid size-frequency analysis at two Triassic-Jurassic (Tr-J) boundary sections: Kuhjoch in Austria (the Tr-J Global Boundary Stratotype Section and Point; GSSP) and St. Audrie's Bay in England (former GSSP candidate) in order to further evaluate the role of marine anoxia in the end-Triassic mass extinction (ETME). The St. Audrie's Bay section records predominantly anoxic conditions punctuated by weakly oxygenated (dysoxic) conditions through the Tr-J transition, even during shallow-water intervals. Kuhjoch experienced both anoxic and dysoxic conditions during the ETME but became better oxygenated near the Tr-J boundary. Marine anoxia is therefore implicated in the extinction at both locations. A similar redox history is known from the Central European Basin, Western Tethys and Panthalassa, where marine anoxia developed in the lead up to the ETME prior to reoxygenation around the Tr-J boundary.