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What Physical Correlation, Geochronology, Magnetic Polarity Stratigraphy, and Palynology Reveal About the End-Permian Terrestrial Extinction Paradigm in South Africa

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What Physical Correlation, Geochronology, Magnetic Polarity Stratigraphy, and Palynology Reveal About the End-Permian Terrestrial Extinction Paradigm in South Africa A tale of two Tweefonteins: What physical correlation, geochronology, magnetic polarity stratigraphy, and palynology reveal about the end-Permian terrestrial extinction paradigm in South Africa Robert A. Gastaldo1,†, Johann Neveling2, John W. Geissman3,4, Sandra L. Kamo5, and Cindy V. Looy6 1 Department of Geology, Colby College, Waterville, Maine 04901, USA 2 Council for Geosciences, Private Bag x112, Silverton, Pretoria, 0001, South Africa 3 Department of Geosciences, The University of Texas at Dallas, Richardson, Texas 75080-3021, USA 4 Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-0001, USA 5 Jack Satterly Geochronology Laboratory, Department of Earth Sciences, University of Toronto, Toronto, M5S 3B1, Canada 6 Department of Integrative Biology, Museum of Paleontology, University and Jepson Herbaria, University of California at Berkeley, 3060 Valley Life Sciences Building, #3140, Berkeley, California 94720-3140, USA ABSTRACT of diagnostic pre- and post-extinction verte- The Karoo Basin preserves an extensive ver- brate taxa demonstrates that the L. declivis tebrate record that has been used for more than a The contact between the Daptocephalus AZ did not replace the Daptocephalus AZ century to subdivide a repetitious sandstone-and- to Lystrosaurus declivis (previously Lystro- stratigraphically, that a biotic crisis and turn- siltstone succession several kilometers thick into saurus) Assemblage Zones (AZs) described over likely is absent, and a reevaluation is biostratigraphic assemblage zones (Fig. 2). Ver- from continental deposits of the Karoo required for the utilization of these biozones tebrate assemblage zones were assigned either to Basin was commonly interpreted to repre- here and globally. Based on our data set, we the Permian or Triassic based on early-twentieth sent an extinction crisis associated with the propose a multidisciplinary approach to cor- century interpretations of Broom (1906, 1911). end-Permian mass-extinction event at ca. relate the classic Upper Permian localities These assemblage zones were used by numerous 251.901 ± 0.024 Ma. This terrestrial extinc- of the Eastern Cape Province with the Free workers (e.g., Keyser and Smith, 1978; Rubidge, tion model is based on several sections in State Province localities, which demonstrates 1995) during a time when no numerical age the Eastern Cape and Free State Provinces their time-transgressive nature. information existed for the rocks in the basin. of South Africa. Here, new stratigraphic That condition has changed in the past decade, and paleontologic data are presented for the INTRODUCTION and the ages of several biozones are now bet- Eastern Cape Province, in geochronologic ter defined by high-resolution, U-Pb chemical and magnetostratigraphic context, wherein Fully continental deposits in the Karoo abrasion-isotope dilution-thermal ionization lithologic and biologic changes are assessed Basin, South Africa, have been used in the past mass spectrometry (CA-ID-TIMS) zircon ages over a physically correlated stratigraphy to record the transition from the latest Permian (Rubidge et al., 2013; Day et al., 2015; Gastaldo exceeding 4.5 km in distance. Spatial varia- (Changhsingian) to the earliest Triassic (Induan) et al., 2015, 2020a). Several of these ages also tion in lithofacies demonstrates the grada- ecosystems documenting the fate of the terres- are placed into magnetostratigraphic context tional nature of lithostratigraphic boundar- trial Gondwanan biota during the end-Permian and correlated with southern hemisphere paly- ies and depositional trends. This pattern is extinction event (Ward et al., 2005; Smith nozones established for this critical interval in mimicked by the distribution of vertebrates and Botha-Brink, 2014; Rubidge et al., 2016; Earth history (Gastaldo et al., 2015, 2018, assigned to the Daptocephalus and L. declivis Viglietti et al., 2018; Botha et al., 2020; Botha 2019a, 2020a). Geochronometric and magneto- AZs where diagnostic taxa of each co-occur and Smith, 2020). And, until recently, a 70% stratigraphic constraints, in conjunction with the as lateral equivalents in landscapes domi- estimate in terrestrial biodiversity loss, largely development of lithostratigraphic frameworks at nated by a Glossopteris flora. High-precision based on the vertebrate record of the Karoo, was key localities, now allow for a more thorough U-Pb zircon (chemical abrasion-isotope dilu- interpreted to have occurred across the Dapto- evaluation of the vertebrate fossil record that has tion-thermal ionization mass spectrometry) cephalus to Lystrosaurus declivis Assemblage been the basis of a reported turnover event in age results indicate maximum Changhsin- Zone boundary (AZ; Fig. 1). This biodiversity the basin. gian depositional dates that can be used as crisis has been interpreted as coeval with extinc- Here, we focus on the lithostratigraphy, approximate tie points in our stratigraphic tion events in the oceans (e.g., Benton and New- geochronology, magnetic polarity stratigraphy framework, which is supported by a mag- ell, 2014; Benton, 2018). The Karoo model was (and related rock magnetic properties), and netic polarity stratigraphy. The coeval nature extrapolated to other southern (South America: palynology, with previously published verte- Langer, 2000; Antarctica: Collinson et al., 2006; brate paleontology (Smith and Botha-Brink, Robert Gastaldo https://orcid.org/0000-0002- India: Gupta and Das, 2011; Laos: Battail, 2009) 2014; Gastaldo et al., 2017) and paleobotany 7452-8081 and northern hemisphere continents (Angara: (Gastaldo et al., 2017, 2018) of a stratigraphic †[email protected]. Battail, 1997; and Cathaysia: Tong et al., 2019). succession with a lateral, traceable extent of GSA Bulletin; Month/Month 2021; 0; p. 1–31; https://doi.org/10.1130/B35830.1; 21 figures; 2 tables; 1 supplemental file. published online 23 June 2021 1 © 2021 The Authors. Gold Open Access: This paper is published under the terms of the CC-BY license. Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/doi/10.1130/B35830.1/5399991/b35830.pdf by guest on 26 September 2021 Gastaldo et al. Figure 1. In this diagram, the International Chronostrati- graphic Chart (v. 2020/03) is coordinated with magnetic po- larity time scales for central Europe (Szurlies, 2013) and the global composites of Ogg (2012), Henderson et al. (2012), and Hounslow and Balabanov (2016) with the Permian– Triassic boundary identified at 251.901 ± 0.024 Ma (Shen et al., 2011). Changhsingian palynological and vertebrate assemblage zones for the Ka- roo Basin, South Africa, are shown constrained by both magnetostratigraphy and geo- chronometry (Gastaldo et al., 2018, 2020a). The boundary between the Daptocephalus and Lystrosaurus declivis As- semblage Zones has been used by other workers to define the end-Permian extinction event and considered equivalent to the Permian–Triassic boundary in the marine realm. ∼4.5 km that constitutes what has been known context, indicates that vertebrate taxa used to Formation in the former and the Katberg Forma- in the literature as the locality Tweefontein (see delimit the pre-extinction Permian Daptocepha- tion in the latter are considered to span the inter- below). We present observations and data from lus AZ and reportedly post-extinction Lower val from the Upper Permian to the Lower Trias- five Tweefontein stratigraphic sections, which Triassic L. declivis AZ are coeval and of early sic (SACS, 1980; Johnson et al., 2006; Fig. 2). have been correlated physically across the Changhsingian age. Both represent vertebrate The succession culminates in the Drakensberg area, encompassing >850 m of measured sec- communities that coexisted in a Glossopteris- Group basalts of Early Jurassic age, which are tion in strata that previously were inferred to be dominated landscape. genetically related to the intrusions of the Karoo uppermost Changhsingian to lowermost Induan Large Igneous Province (LIP) dolerite suite. in age (Fig. 1; Smith and Botha-Brink, 2014; Karoo Basin Lithostratigraphy, Vertebrate As is the case for much of the Beaufort Group, Botha et al., 2020). These Tweefontein sections Biostratigraphy, and Chronostratigraphy Balfour and Katberg Formation rocks in the are physically correlated with measured strati- study area can be described by six basic litholo- graphic sections at Old Lootsberg Pass on the The Karoo Basin, a foreland basin that devel- gies that are vertically and laterally arranged in Blaauwater Farm (Gastaldo et al., 2018), extend- oped inboard of the rising Cape Fold Belt (Lind- a seemingly monotonous succession (Gastaldo ing the correlation to 7 km along the strike of eque et al., 2011; Viglietti et al., 2017), filled et al., 2018). These are: (1) intraformational the major NW-SE–oriented escarpment ∼40 km with a turbidite to fully continental succession conglomerate, (2) fine to very fine feldspathic southwest of Middelburg (Fig. 3). Both plant and in response to continental deglaciation beginning or lithic wacke, (3) rare medium feldspathic or vertebrate fossils confirm that these successions in the late Carboniferous (Johnson et al., 2006). lithic wacke, (4) coarse to fine siltstone of vari- are in the uppermost Daptocephalus and low- The Karoo Supergroup contains five lithostrati- ous hues, (5) silicified siltstone, and (6) devitri- ermost L. declivis AZs (Gastaldo et al., 2017) graphic groups. The basal Dwyka (upper Car- fied claystone. Intraformational conglomerate
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