Pyrite framboid study of marine Permian–Triassic boundary sections: A complex anoxic event and its relationship to contemporaneous mass extinction

Abstract

Size analysis of pyrite framboids has been undertaken on epicontinental Permian- Triassic boundary sections throughout the world in order to evaluate the intensity and duration of anoxia. Mid-paleolatitude sections from the margins of the Boreal (Spitsbergen, Greenland) and Neotethyan oceans (Western Australia) reveal intense anoxia throughout the Permian-Triassic boundary interval with euxinic conditions frequently developing, and dysoxia encountered even in relatively shallow-water settings above storm wave base. At equatorial paleolatitudes, weakly oxygenated (dysoxic) conditions are widely developed in a broad range of water depths including those shallow enough to produce oolite deposition, although euxinia was rare. Western and eastern Tethyan locations re- veal a complex and unstable redox history: anoxia in the Hindeodus praeparvus Zone was replaced by oxygenated facies in the Permian- Triassic boundary interval (H. changxingensis to H. parvus zones). Oxygen-poor deposition returned during the succeeding Isarcicella isarcica Zone. The more persistent and intense development of oxygen restriction in cooler water, mid-paleolatitude sections argues against warming and dissolved oxygen decline as the key cause of Permian-Triassic bound- ary anoxia. In higher paleolatitudes the ben- thic invertebrate extinctions occurred during a prolonged phase of oxygen-poor deposition, while in equatorial Tethyan locations benthic losses occurred at the end of the fi rst anoxic phase (in the late H. praeparvus Zone).