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Vertebrates at Permian-Triassic boundary in Karoo Basin (free pdf)



Ben Creisler
bcreisler@gmail.com


A new online paper in open access:

Robert A. Gastaldo, Sandra L. Kamo, Johann Neveling, John W. Geissman,
Marion Bamford and Cindy V. Looy (2015)
Is the vertebrate-defined Permian-Triassic boundary in the Karoo
Basin, South Africa, the terrestrial expression of the end-Permian
marine event?
Geology (advance online publication)
doi: 10.1130/G37040.1
http://geology.gsapubs.org/content/early/2015/08/28/G37040.1.abstract

Free pdf:
http://geology.gsapubs.org/content/early/2015/08/28/G37040.1.full.pdf+html


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.