Is the vertebrate-defined Permian-Triassic boundary in the Karoo Basin, South Africa, the terrestrial expression of the end-Permian marine event?
Robert A. Gastaldo 1, Sandra L. Kamo 2, Johann Neveling 3, John W. Geissman 4, Marion Bamford 5 and Cindy V. Looy 6
1Department of Geology, Colby College, Waterville, Maine 04901, USA
2Jack Satterly Geochronology Laboratory, Department of Geology, University of Toronto Toronto, Ontario M5S 3B1, Canada
3Council for Geosciences, Private Bag x112, Silverton, Pretoria 0001, South Africa
4Department of Geosciences, University of Texas at Dallas, Richardson, Texas 75080-3021, USA
5Evolutionary Studies Institute, University of Witwatersrand, Johannesburg 2050, South Africa
6Department of Integrated Biology and Museum of Paleontology, 2033 Valley Life Sciences Building #3140, University of California–Berkeley, Berkeley, California 94720, USA
Abstract
The end-Permian extinction records the greatest ecological catastrophe in Earth history. The vertebrate fossil record in the Karoo Basin, South Africa, has been used for more than a century as the standard for understanding turnover in terrestrial ecosystems, recently claimed to be in synchrony with the marine crisis. Workers assumed that systematic turnover at the Dicynodon assemblage zone boundary, followed by the appearance of new taxa directly above the base of the Lystrosaurus assemblage zone, is the continental expression of the end-Permian event and recovery. To test this hypothesis, we present the first high-precision age on strata close to the inferred Permian-Triassic boundary. A U-Pb isotope dilution–thermal ionization mass spectrometry zircon age of 253.48 ± 0.15 Ma (early Changhsingian) is from a silicified ash layer ∼60 m below the current vertebrate-defined boundary at Old Lootsberg Pass (southern South Africa). This section yields newly discovered plants and vertebrates, and is dominated by a normal polarity signature. Our collective data suggest that the Dicynodon-Lystrosaurus assemblage zone boundary is stratigraphically higher than currently reported, and older than the marine extinction event. Therefore, the turnover in vertebrate taxa at this biozone boundary probably does not represent the biological expression of the terrestrial end-Permian mass extinction. The actual Permian-Triassic boundary in the Karoo Basin is either higher in the Katberg Formation or is not preserved. The currently accepted model of the terrestrial ecosystem response to the crisis, both in this basin and its extension globally, requires reevaluation.
Received 4 June 2015.
Revision received 19 August 2015.
Accepted 20 August 2015.
© 2015 Geological Society of America
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