When and how did the terrestrial mid-Permian mass extinction occur? Evidence from the tetrapod record of the Karoo Basin, South Africa
Authors:
Day et al
Abstract:
A mid-Permian (Guadalupian epoch) extinction event at approximately 260 Ma has been mooted for two decades. This is based primarily on invertebrate biostratigraphy of Guadalupian–Lopingian marine carbonate platforms in southern China, which are temporally constrained by correlation to the associated Emeishan Large Igneous Province (LIP). Despite attempts to identify a similar biodiversity crisis in the terrestrial realm, the low resolution of mid-Permian tetrapod biostratigraphy and a lack of robust geochronological constraints have until now hampered both the correlation and quantification of terrestrial extinctions. Here we present an extensive compilation of tetrapod-stratigraphic data analysed by the constrained optimization (CONOP) algorithm that reveals a significant extinction event among tetrapods within the lower Beaufort Group of the Karoo Basin, South Africa, in the latest Capitanian. Our fossil dataset reveals a 74–80% loss of generic richness between the upper Tapinocephalus Assemblage Zone (AZ) and the mid-Pristerognathus AZ that is temporally constrained by a U–Pb zircon date (CA-TIMS method) of 260.259 ± 0.081 Ma from a tuff near the top of the Tapinocephalus AZ. This strengthens the biochronology of the Permian Beaufort Group and supports the existence of a mid-Permian mass extinction event on land near the end of the Guadalupian. Our results permit a temporal association between the extinction of dinocephalian therapsids and the LIP volcanism at Emeishan, as well as the marine end-Guadalupian extinctions.
Anatomy of a mass extinction: Sedimentological and taphonomic evidence for drought-induced die-offs at the Permo-Triassic boundary in the main Karoo Basin, South Africa
Authors:
Smith et al
Abstract:
The southern part of the Karoo Basin of South Africa contains a near complete stratigraphic record of the Permo-Triassic boundary (PTB). Isotope- and magneto-stratigraphy confirm that these predominantly fluvial strata are approximately the same age as zircon-dated marine PTB sections (252 million years ago). By August 2013, our team had found 579 in situ vertebrate fossils, mostly of the clade Therapsida, in PTB exposures at three widely separated locations in the southern Karoo Basin. Biostratigraphic ranges of the various taxa found in each of the sections reveal three separate phases of die-off within the same roughly 75 metre-thick stratigraphic interval displaying the same sequence of sedimentary facies interpreted as indicative of climatic drying, increased seasonality and the onset of an unpredictable monsoon-type rainfall regime. The three phases of an inferred ecologically-stepped mass extinction are: Phase 1 (45m-30m below PTB datum) brought on by lowered watertables, which led to loss of shallow rooting groundcover in the more elevated proximal floodplain areas and the disappearance of the smaller groundcover-grazing herbivorous dicynodonts and their attendant small carnivores. Phase 2 (20-0 m below PTB datum), is the main extinction that occurs in massive maroon/grey mudrock culminating in an event bed of laminated reddish-brown siltstone/mudstone couplets. This facies reflects progressively unreliable rainfall leading to vegetation loss in proximal and distal floodplain areas. The larger tree-browsing herbivores and their attendant carnivores are confined to watercourses before finally disappearing. Phase 3 (25-30 m above PTB datum) occurs in massive maroon siltstone facies with evidence of climatic aridity including the accumulation of mummified carcasses buried by windblown dust. All of the surviving Permian taxa disappear within 30 metres of the PTB.
Temporal resolution based on accretion rates and pedogenic maturity of each stratigraphic section reveals that Phase 1 and Phase 2 die-offs lasted 21 000 and 33 000 years separated by a short period of 7000 years where no disappearences are recorded and this was followed by 50 000 years of stasis for the final extinction phase, lasting only 8000 years, that removed all the Permian survivor taxa,. We propose that the recorded disappearances are real (rather than preferential preservation failure) and that they represent drought-induced die-offs moving progressively up the food chain as the terrestrial ecosystem collapsed; the latter mostly likely caused by volcanogenic greenhouse gas emissions and rapid global warming.
High-precision temporal calibration of Late Permian vertebrate biostratigraphy: U-Pb zircon constraints from the Karoo Supergroup, South Africa
Authors:
1. Bruce S. Rubidge (a)
2. Douglas H. Erwin (b,c)
3. Jahandar Ramezani (d)
4. Samuel A. Bowring (d)
5. William J. de Klerk (e)
Affiliations:
a. Bernard Price Institute for Palaeontological Research, School of Geosciences, University of the Witwatersrand, PO Wits, Johannesburg 2050, South Africa
b. Department of Paleobiology, National Museum of Natural History, Washington, D.C. 20560, USA
c. Santa Fe Institute, 1399 Hyde Park Road, Santa Fe, New Mexico 87501, USA
d. Department of Earth, Atmospheric and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
e. Department of Geology and the Albany Museum, Rhodes University, Grahamstown 6140, South Africa
Abstract:
Therapsid and other tetrapod fossils from the South African Karoo Supergroup provide the most detailed and best studied terrestrial vertebrate record of the Middle and Late Permian. The resulting biostratigraphic scheme has global applicability. Establishing a temporal framework for these faunas has proven difficult: magnetostratigraphy has been hampered by a Jurassic overprint, and intercorrelation with Permian marine sequences has been equivocal. Here we report U-Pb zircon isotope dilution–thermal ionization mass spectrometry (ID-TIMS) dates for five volcanic ashes interbedded with fossils from the Pristerognathus, Tropidostoma, and Cistecephalus vertebrate biozones of the Beaufort Group. This temporal framework allows correlation to marine zonations and improves understanding of rates of faunal evolution and patterns of basin evolution. Our results identify no correlative vertebrate extinctions in the Karoo Supergroup to the marine end-Guadalupian mass extinction and raise the question of whether there is any record of a terrestrial extinction related to the Emeishan large igneous province.
