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Is the Vertebrate-Defined Permian-Triassic Boundary in the Karoo Basin, South Africa, the Terrestrial Expression of the End-Permian Marine Event?

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Is the Vertebrate-Defined Permian-Triassic Boundary in the Karoo Basin, South Africa, the Terrestrial Expression of the End-Permian Marine Event? Is the vertebrate-defined Permian-Triassic boundary in the Karoo Basin, South Africa, the terrestrial expression of the end-Permian marine event? Robert A. Gastaldo1, Sandra L. Kamo2, Johann Neveling3, John W. Geissman4, Marion Bamford5, and Cindy V. Looy6 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 horsetails (e.g., Trizygia), which grew on immature olive-green paleosols The end-Permian extinction records the greatest ecological catastro- with poorly developed soil horizons (Gastaldo et al., 2014). Landscape phe in Earth history. The vertebrate fossil record in the Karoo Basin, devegetation (Smith and Ward, 2001) is thought to be the consequence of South Africa, has been used for more than a century as the standard increasing drought that took a toll on the food chain, ultimately leading for understanding turnover in terrestrial ecosystems, recently claimed to vertebrate extinction. The first appearance of paleosol color mottling to be in synchrony with the marine crisis. Workers assumed that sys- associated with a shift in siltstone color to grayish-red (Smith and Ward, tematic turnover at the Dicynodon assemblage zone boundary, followed 2001), found below the vertebrate-defined PTB, is interpreted to reflect a by the appearance of new taxa directly above the base of the Lystrosau- rapid change in seasonality (Smith and Botha-Brink, 2014) that affected rus assemblage zone, is the continental expression of the end-Permian the Glossopteris flora. An increasing proportion of massive, grayish-red event and recovery. To test this hypothesis, we present the first high- siltstone above the vertebrate-defined PTB is believed to be of earliest precision age on strata close to the inferred Permian-Triassic boundary. Triassic age, reflecting an overall drying trend, a view supported by the ap- A U-Pb isotope dilution–thermal ionization mass spectrometry zircon pearance of intraformational pedogenic conglomeratic facies concentrated age of 253.48 ± 0.15 Ma (early Changhsingian) is from a silicified ash in channel-lag deposits (Ward et al., 2005; Smith and Botha-Brink, 2014). layer ~60 m below the current vertebrate-defined boundary at Old We present new paleontologic, geochronometric, and magnetostrati- Lootsberg Pass (southern South Africa). This section yields newly dis- graphic data and observations from Old Lootsberg Pass (southern South covered plants and vertebrates, and is dominated by a normal polarity Africa, ~31.5°S, 24.5°E; Fig. 1), a critical South African locality on which signature. Our collective data suggest that the Dicynodon-Lystrosaurus the current continental extinction model is based (Ward et al., 2005; Smith assemblage zone boundary is stratigraphically higher than currently and Botha-Brink, 2014). These data and observations are used in conjunc- reported, and older than the marine extinction event. Therefore, the tion with the original biostratigraphic database of Smith and Botha-Brink turnover in vertebrate taxa at this biozone boundary probably does not (2014) and their global positioning system (GPS) specimen coordinates represent the biological expression of the terrestrial end-Permian mass to extend the stratigraphic range of both Permian plants and vertebrates extinction. The actual Permian-Triassic boundary in the Karoo Basin in the basin. From beds above the vertebrate-defined PTB, we have dis- is either higher in the Katberg Formation or is not preserved. The cur- covered Glossopteris-dominated megafloral assemblages and a typical rently accepted model of the terrestrial ecosystem response to the crisis, Permian palynoflora in olive-gray siltstone; and a dicynodontoid skull of both in this basin and its extension globally, requires reevaluation. characteristically Permian aspect and woody trunk segments of Agath- oxylon africanum from the stratigraphically lowest intraformational con- INTRODUCTION glomerate facies (Fig. 2), currently considered as indicative of the lower The Permian vertebrate biostratigraphy of the Karoo Basin, South Af- Triassic in the Karoo Basin (Botha and Smith, 2006). The stratigraphy rica, forms the basis of a global model to explain the terrestrial ecosys- at Old Lootsberg Pass is dominated by normal magnetic polarity, with a tem response to the end-Permian crisis as recognized in the marine record short reverse polarity magnetozone in sandstone and siltstone exposed ~3 (Ward et al., 2005; Smith and Botha-Brink, 2014). Here (and elsewhere; m above a silicified volcaniclastic bed (Figs. 1B and 2) located beneath Lucas, 2010) the terrestrial Permian-Triassic boundary (PTB) currently is the vertebrate-defined PTB. This silicified volcaniclastic unit has a U-Pb associated with the Last Appearance Datum of the therapsid Dicynodon, isotope dilution–thermal ionization mass spectrometry (ID-TIMS) age of and three other taxa of the Dicynodon assemblage zone (AZ), and their re- 253.48 ± 0.15 Ma, determined from single, chemically abraded zircon placement by an array of taxa with their first appearance in theLystrosau - grains, that places our studied section in the early Changhsingian. rus AZ (Smith and Botha-Brink, 2014). Estimates of as much as 89% of tetrapod generic biodiversity loss (Benton and Newell, 2014) are reported GEOLOGIC SETTING across this boundary. Vertebrate turnover is interpreted as coincident with Karoo Supergroup deposition began in the late Carboniferous and the marine mass extinction event (Ward et al., 2005), which was dated as ended in the Jurassic, filling a basin fronting the Cape Fold Belt (Johnson 251.9 Ma (Burgess et al., 2014). et al., 2006). Rocks of the Beaufort Group record fully continental depos- The extinction of Dicynodon AZ taxa is interpreted as a consequence its. Meandering fluvial architectures, typical of the Elandsberg Member of of dramatic climate change affecting the Karoo Basin (Ward et al., 2005), the uppermost Permian Balfour Formation, incised into widespread olive- although others (e.g., Gastaldo et al., 2014; Gastaldo and Neveling, 2014) gray paleosols. These were replaced by fluvial architectures interpreted have demonstrated inconsistencies in the lithologic and chemostrati- to represent low-sinuosity regimes, and grayish-red mottled siltstone as- graphic data on which this model was based. Latest Permian floodplains sociated with the Palingkloof Member (Smith and Botha-Brink, 2014), were colonized by the gymnosperm Glossopteris and ground-creeping in which the vertebrate-defined PTB is placed (Fig. 2). A transition to GEOLOGY, October 2015; v. 43; no. 10; p. 939–942 | Data Repository item 2015313 | doi:10.1130/G37040.1 | Published online 28 August 2015 GEOLOGY© 2015 Geological | Volume Society 43 | ofNumber America. 10 Gold | www.gsapubs.org Open Access: This paper is published under the terms of the CC-BY license. 939 Downloaded from http://pubs.geoscienceworld.org/gsa/geology/article-pdf/43/10/939/3548836/939.pdf by guest on 29 September 2021 RR RR 150 E024° 47.774’ Middelburg A 102 S 31 47.594' 98-101 102 E024 47.719' ± 3 m 53 54 97 97-98 Old 140 94-96 55Lootsberg Lootsberg N 10 94-96 92-93 Pass Pass ’ 87-89 85-86 82-84 Wapadsberg R61 130 92-93 50-52 Pass N 9 81 80 49 Cradock 48 90-91 50 km 9 BUa 46/47 Graaf-Reinet 120 44/45 S31° 47.777 43 42 84-8 40/41 39 Assemblage Zone 110 N RS 20 82-84 38 Katberg Formation 36 37 35 -52 30 Agathoxylon africanum 34 RS 18 100 50 100.90 m dicynodontoid skull RR 32/33 29 RS 19 31 49 48 BUa Glossopteris RS 80 ystrosaurus 90 47 Paleomag sample site 27/28 L & Permian palynoflora 26 Smith & Botha-Brink (2014) vertebrate 24 25 43- 23 Smith & Botha-Brink Current vertebrate-defined PTB 22 80 (2014) PTB 19-21 -42 Porcellanite (253.48 ± 0.15 Ma) 18 17 15 38 PNC-bearing, fossiliferous sandstone 16 Porcellanite 12 70 RS 20 O. baini 13-14 11 10 35-37 Glossopteris 9 8 N 4 femur (-13 m) 7 5 4 n Glossopteris & Permian palynoflora Palingkloof Mbr 6 3 60 31-3 Agathoxylon & Dicynodontoid skull 2 B RS 18 ?Dicynodon 56.35M 1 Ward et al. (2000) section GPS 0 175 350 29-30 lacerticeps (-26 m); meters 50 RS 19 ?Rubidgea sp. (-27 m) Figure 1. A: Old Lootsberg Pass in South Africa. B: Measured-sec- tion transect showing paleomagnetic (Paleomag) sample sites and 40 r RS 80 Dicynodon 3-28 porcellanite location on the Blaauwater 87 farm, Eastern Cape Prov- 2 lacerticeps skull 33.15m Balfour Formatio ince. Global positioning system (GPS) located positions and Smith Assemblage Zone (-50 m) and Botha-Brink (2014) vertebrate samples and the vertebrate-defined 30 17-22 15-16 Permian-Triassic boundary (PTB) (dotted line) relative to our section 13-14 are shown. New paleontological collections are marked. Drill sites 9-12 253.48±0.15 Ma for magnetostratigraphy are shown by closed circles. RR—railroad; 20 7-8 S31° 48.159” PNC—pedogenic nodule conglomerate. All GPS coordinates are 6 3- Elandsberg Mb E024° 48.304”± 3 m World Geodetic System 1984 (WGS 84) standard; base map is 3124DD Dicynodon 11.30m 2 Lootsberg 1:50,000 South Africa, Council for Geoscience, Pretoria. 10 1 S3148.296' 0 E024 48.396' ± 5 m s SS c braidplain architectures and maroon paleosols is reported in the overlying sandstone-dominated Katberg Formation (Ward et al., 2005). Pedogenic nodule Olive gray siltstone (S) Mottled siltstone (S) conglomerate (c) V.F. gray-yellow Light olive gray PALEONTOLOGY Grayish red siltstone (S) wacke (ss) siltstone (S) Smith and Botha-Brink (2014) reported four Dicynodon AZ verte- brate sites below their PTB at Old Lootsberg Pass, all of which are above Figure 2.
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