Gradual onset of anoxia across the Permian-Triassic Boundary in Svalbard, Norway

► We examine onset of marine anoxia and extinction at the Permian-Triassic Boundary. ► Pyrite framboid size distribution indicates a gradual onset of oxygen restriction. ► Carbon isotope record shows an abrupt negative excursion to − 31.3‰. ► Transgressive lag deposits and glauconite facies indicate major sea level rise. ► Significant marine ecosystem changes occur before the final anoxia onset.