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Middle-Late Permian mass extinction on land

Gregory J. Retallack^,1, Christine A. Metzger¹, Tara Greaver², A. Hope Jahren², Roger M.H. Smith³ and Nathan D. Sheldon⁴

¹ Department of Geological Sciences, University of Oregon, Eugene, Oregon 97403-1272, USA
² Department of Earth and Planetary Sciences, Johns Hopkins University, Baltimore, Maryland 21218, USA
³ Department of Karoo Palaeontology, Iziko South African Museum, P.O. Box 61, Cape Town 8000, South Africa
⁴ Department of Geology, Royal Holloway University of London, Egham, Surrey TW20 OEX, England

The end-Permian mass extinction has been envisaged as the nadir of biodiversity decline due to increasing volcanic gas emissions over some 9 million years. We propose a different tempo and mechanism of extinction because we recognize two separate but geologically abrupt mass extinctions on land, one terminating the Middle Permian (Guadalupian) at 260.4 Ma and a later one ending the Permian Period at 251 Ma. Our evidence comes from new paleobotanical, paleopedological, and carbon isotopic studies of Portal Mountain, Antarctica, and comparable studies in the Karoo Basin, South Africa. Extinctions have long been apparent among marine invertebrates at both the end of the Guadalupian and end of the Permian, which were also times of warm-wet greenhouse climatic transients, marked soil erosion, transition from high- to low-sinuosity and braided streams, soil stagnation in wetlands, and profound negative carbon isotope anomalies. Both mass extinctions may have resulted from catastrophic methane outbursts to the atmosphere from coal intruded by feeder dikes to flood basalts, such as the end-Guadalupian Emeishan Basalt and end-Permian Siberian Traps.

Key Words: Permian • Triassic • extinction • paleosol • palynology • vertebrates