Stratigraphy, Sedimentology, and Palaeontology of the Permian–Triassic Boundary Interval, Karoo Basin, South Africa
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The End Permian Mass Extinction, dated at 252.25 ± 0.06 Ma in a
marine sequence, is reported as a synchronous event in the marine and terrestrial realms
playing out over a 200 ka interval. Marine biodiversity loss is estimated at about 85%, with
different extinction rates in various clades over variable time scales. Terrestrial vertebrate
extinction is reported to be near 63% of families in which 89% of tetrapod genera associated with ecological instability and pre- or coincident collapse of plant communities with the crisis. This "Mother of Mass Extinctions" is a model for ecosystem response to
severe perturbation and is considered a possible scenario for how Earth Systems may react
to current rapid global warming and climate extremes.
The Karoo Basin in South Africa serves as one of a small number of continental
sequences in which the affects to, and the response of, the terrestrial ecosystem are
preserved. The current model of phased end-Permian vertebrate biodiversity loss is interpreted to be accompanied by catastrophic vegetational perturbation and followed by
the rapid recovery of vertebrate faunas in the earliest Triassic. The stratigraphic framework
in which these events occurred is interpreted to represent continuous sedimentation across
this critical interval in Earth’s history that reflects a global response to changing climate and
a turnover in fluvial environment. Ten reportedly well-exposed Permian–Triassic boundary
(PTB) sections in South Africa comprise the focus of all published studies, to date, and are:
Bethulie, Caledon, and Nooitgedacht in the Free State; and Carlton Heights,
Commandodrift, Wapadsberg Pass, (East) Lootsberg Pass, Tweefontein, Old (West) Lootsberg Pass, and Ripplemead in the Eastern Cape. Key to interpretations resulting from
these investigations is the assumption that a datum exists between localities upon which to
correlate the PT transitional interval.
We previously have demonstrated that no specific physical datum exists on which the PTB can be identified, and the event is recognized strictly on a turnover in vertebrate biostratigraphic zones, from the Permian Dicynodon Assemblage Zone (DAZ) to the Triassic Lystrosaurus Assemblage Zone. Hence, each reported PT boundary locale must be evaluated
individually to understand the extent of the stratigraphic record preserved therein. The
transitional stratigraphy of the boundary interval is reported to comprise uppermost Permian, pre-extinction, and lowermost Triassic, post-extinction, fluvial and floodplain strata. Permian landscapes are represented by strata placed in the Elandsberg Member and the informal lower Palingkloof Member of the Balfour Formation, whereas Triassic
landscapes are assigned to the informal upper Palingkloof Member of the Balfour Formation and Katberg Formation, both considered to be of Induan age on the basis of associated vertebrate elements. The symposium will focus on currently published models of the response of terrestrial ecosystems to the crisis, and recently acquired stratigraphic, sedimentologic, geochronometric,
palaeomagnetic, and palaeontological data used to test hypotheses about this critical time in Earth history.
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Johann Neveling and Robert Gastaldo
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