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A tale of two Tweefonteins: What physical correlation, geochronology, magnetic polarity stratigraphy, and palynology reveal about the end- terrestrial extinction paradigm in South Africa

Robert A. Gastaldo1,†, Johann Neveling2, John W. Geissman3,4, Sandra L. Kamo5, and Cindy V. Looy6 1Department of Geology, Colby College, Waterville, Maine 04901, USA 2Council for Geosciences, Private Bag x112, Silverton, Pretoria, 0001, South Africa 3Department of Geosciences, The University of Texas at Dallas, Richardson, Texas 75080-3021, USA 4Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, New Mexico 87131-0001, USA 5Jack Satterly Geochronology Laboratory, Department of Earth Sciences, University of Toronto, Toronto, M5S 3B1, Canada 6Department 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 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 -and- to declivis (previously Lystro- stratigraphically, that a biotic crisis and turn- 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 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.

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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 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 , 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 (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 as currently defined (Viglietti, 2020; Botha and boniferous) and Ecca (Lower–middle Permian) consists of calcite-cemented pedogenic glaeb- Smith, 2020). The Tweefontein sections com- groups are generally represented by diamictite ules/nodules, disarticulated vertebrate remains prise both greenish-gray and reddish-gray - and turbidite deposits, respectively, that filled a (skull and bone or fragments thereof), and mud- stone (Li et al., 2017), both laterally and verti- deep basin that was open to marine influence. As clast aggregates as framework grains in either cally separated, that are dominated by normal open waters regressed, the basin began to fill with a fine/very fine sand, sandy silt, or coarse silt magnetic polarity, thus defining a normal polar- fully continental that are assigned to matrix (Pace et al., 2009; Gastaldo et al., 2013). ity magnetozone. We report two new U-Pb CA- the Beaufort (middle Permian–Middle Triassic) Intraformational conglomerate was considered ID-TIMS zircon age constraints from these sec- and Stormberg (Upper Triassic–Lower Jurassic; to be diagnostic of the Katberg Formation and tions that provide maximum depositional ages. Catuneanu et al., 2005) groups. The Beaufort the L. declivis AZ (Ward et al., 2005; Smith Correlation across our stratigraphic framework, Group is subdivided into the lower Adelaide and and Botha, 2005; Smith and Botha-Brink, in geochronometric and magnetostratigraphic upper Tarkastad subgroups, of which the Balfour 2014). This lithofacies has been shown to be a

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in the (Fig. 2). A perceived increase in the ratio of sandstone to siltstone is used to delineate a transitional contact of up to 100 m between the Balfour and Katberg Forma- tions, which is placed where a marked increase in sandstone abundance can be observed (John- son, 1976; Groenewald, 1996). The monotonous nature in, and limited variation of, Beaufort Group required a means by which to subdivide the succession into quasi-chro- nostratigraphic units. The dearth of macro- and microfossil plants (Gastaldo et al., 2005, 2019a; Barbolini et al., 2018) and the abundance of ver- tebrate skeletons and skeletal elements (van der Walt et al., 2010, 2015) allowed for coarse age assignments to be placed on the strata following the early interpretations of Broom (1906, 1911). These were later augmented by inter-basinal cor- relations based on the vertebrate biostratigraphy (e.g., Rubidge, 2005). Broom (1906) established a six-part bio- stratigraphic subdivision of Karoo Basin rocks using fossil-vertebrate assemblages by plac- ing specimens of Lystrosaurus into the Trias- sic and all underlying biozones, including the interval now encompassing the Daptocephalus AZ (Viglietti et al., 2016), into the Late Perm- ian. A recent vertebrate biostratigraphy incor- porates geochronological data (Smith et al., 2020; Viglietti, 2020; Botha and Smith, 2020). A Permian (Wuchiapingian) age for the base of the Daptocephalus AZ was reported by Rubidge et al. (2013; 255.24 ± 0.16 Ma; U-Pb ID-TIMS zircon) for the lower part of the Balfour Forma- tion (Fig. 2). Day et al. (2015) presented a mid- dle Permian (Capitanian) age estimate for the base of the underlying Middleton Formation Figure 2. Generalized stratigraphy of the terrestrial Beaufort Group and lithostratigraphic (260.25 ± 0.081 Ma; U-Pb ID-TIMS zircon). subdivision east of 24 longitude as recognized by the South African Committee on Stra- ° Subsequently, the first high-precision U-Pb tigraphy is shown (Johnson et al., 2006; Cole et al., 2016). The upper part of the Dapto- CA-ID-TIMS ages of zircon grains from two cephalus Assemblage Zone (AZ) is defined by the range of Lystrosaurus maccaigi, while the horizons in the upper part of the Balfour For- first appearance datum ofL. murrayi marks the base of the Lystrosaurus declivis AZ, the mation were reported by Gastaldo et al. (2015, boundary between which is purported to represent the terrestrial expression of the end- 2018). A porcellanite bed, in the Elandsberg Permian extinction event (Viglietti et al., 2016). Vertebrate ranges are modified following Member, has a maximum early Changhsingian results presented herein. Age assignments are based on Day et al. (2015) for the boundary age (253.48 ± 0.15 Ma; Gastaldo et al., 2015). of the Tapinocephalus biozone; Rubidge et al. (2013) for the age constraints associated with The second horizon, located higher in the the Pristerognathus, Tropidostoma, Cistecephalus, and lower Daptocephalus biozones; and Elandsberg Member or possibly in the lower Gastaldo et al. (2015, 2020a) for the age assignments in the upper Daptocephalus and lower Palingkloof Member, but in the Daptocepha- Lystrosaurus declivis Assemblage Zones. The placement of the Permian–Triassic boundary lus AZ, yielded a detrital zircon population of in the Katberg Formation follows our conclusions. Wuchiapingian age (256.8 ± 0.6 Ma; Gastaldo et al., 2018). This older (maximum deposi- ­component of sandstone bodies in the underly- variants; Li et al., 2017; Gastaldo et al., 2019a, tional) age in strata some 20 m above the por- ing Elandsberg Member of the Balfour Forma- 2019b) along with very light gray to white when cellanite indicates reworking of an older ashfall tion (Fig. 2; Viglietti et al., 2016, 2017; Gastaldo silicified (porcellanite). Rare light gray to olive- deposit in response to landscape degradation et al., 2018). Fluvial bedload deposits are fine- gray devitrified claystone occurs (Gastaldo et al., (Gastaldo and Demko, 2011) and redeposi- to very fine-grained, yellowish-gray feldspathic 2018). Traditionally, siltstone color has been tion into a younger landform. More recently, wacke that rarely exhibits a medium grain size, used to distinguish predominantly reddish-gray a late Changhsingian age (252.24 ± 0.11 Ma) enveloped in coarse-to-fine siltstone. Siltstone siltstone (and or mottling with greenish gray) of was reported from a pristine volcanic ash varies in color from greenish, olive, or light the Palingkloof Member from the greenish-gray deposit in the basal part of the L. declivis AZ at olive gray (and variants) to reddish gray (and siltstone of the underlying Elandsberg Member Farm Nooitgedacht in the Free State Province

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A

B

Figure 3. (A) Locality map shows the position of the Tweefontein sections (star) in southern Africa. (B) Topographic map shows the area between Old (West) Lootsberg Pass and Lootsberg Pass and the Tweefontein localities discussed herein. Published coordinates for Ward et al.’s (2000) Tweefontein section are shown in a black cross in relation to: surrounding farms (dotted lines indicate farm boundaries and farm names), Old Lootsberg Pass on the Blaauwater 67 Farm, and Lootsberg Pass on the Lucerne 70 Farm. Measured stratigraphic sec- tions forming the basis of the current study at Tweefontein1, Tweefontein1.5, and Tweefontein2 are solid lines with arrows (see text for naming convention); the positions of new devitrified claystone beds (asterisk) from which zircon grains have been recovered are shown. All GPS coordinates are WGS 84 standard; scale is in kilometers and miles; base map is 3124DD Lootsberg 1:50,000 South Africa.

(Gastaldo et al., 2020a). This date demonstrates scribed (Botha and Smith, 2007, 2020; Fig. 1), was based. It is used as one of three localities that the L. declivis AZ begins in the latest Perm- is unique in space and time. in the Lootsberg Pass area that is reported to ian rather than being solely restricted to the Tri- contain the Permian–Triassic boundary (Ward assic. Whether a ­biodiversity crisis is recorded MATERIAL AND METHODS et al., 2000, 2005). Tweefontein is positioned in the Balfour Formation or not depends on the between Lootsberg Pass, along the N9 High- temporal and spatial relationships of taxa con- Geologic and Sedimentologic Setting way, and Old Lootsberg Pass on the Blaauwater sidered to be diagnostic of pre- and post-extinc- 67 Farm (Fig. 3). Unfortunately, no GPS coor- tion landscapes (Gastaldo et al., 2017, 2019a). Tweefontein is one of seven principal sections dinates or other data regarding the location of Hence, the question remains as to whether the in the Karoo Basin around which the model for either the base or top of any measured section base of the L. declivis AZ, as currently circum- the terrestrial response to the end-Permian crisis have been provided in the literature (Smith,

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1995; Ward et al., 2000, 2005; Viglietti et al., the escarpment in 2017. Two shorter sections a well-exposed donga section ∼600 m to the 2018), which would have facilitated duplicative are documented in adjacent gullies and corre- northwest of Tweefontein2 where another mea- efforts to resolve the reported turnover event. lated (Fig. 3). All sections were measured and sured section, totaling ∼205 m in thickness, was Only a single locality coordinate set is avail- described as previously reported (e.g., Gastaldo completed. This section is referred to, herein, as able. The GPS coordinates of Ward et al. (2000, et al., 2017, 2019a, 2020a). We have referred to Tweefontein1.5 (Fig. 3). 2005; S31° 49.334′, E(W)024° 48.565′, origi- this complex of stratigraphic sections as Twee- The GPS locations of vertebrate fossils col- nally reported as W longitude; WGS84 standard) fontein1 (Gastaldo et al., 2017). lected in these areas, which were used by Ward place the Tweefontein section in an open field GPS coordinates of vertebrates collected in et al. (2005), Botha and Smith (2006), and Smith with no nearby exposure. Beginning in 2010 these areas, and reported by Smith and Botha- and Botha-Brink (2014), were incorporated into and until 2019, we examined all erosional gul- Brink (2014) from their Tweefontein locality, Viglietti et al.’s (2016) database. Each collection lies (dongas) below the main escarpment that place these specimens on the Lucerne 70 Farm site was placed into our measured sections using expose outcrops across a ∼5 km transect from beneath the resistant Katberg Formation sand- standard field methods. A Garmin Map62S with southeast of the reported GPS coordinates north- stones of Lootsberg Pass. The site is >4 km to barometric altimeter served to assist physical west to Old Lootsberg Pass. Strata in the area are the southeast of the coordinates published by correlation by verifying elevational relationships nearly horizontal, dipping at a low, ∼1° angle Ward et al. (2000, 2005). Here, we have mea- (see supplemental information in Gastaldo et al., to the northwest, and each of our stratigraphic sured and correlated two long stratigraphic sec- 2019a, for a discussion and test of South Afri- sections intersects one or more traceable sand- tions, totaling >240 m, adjacent to where Smith can coordinate systems). These data augment the stone bodies. The bounding surfaces of these and Botha-Brink’s (2014) vertebrate specimens supplemental information published by Smith sandstone bodies can be physically walked over were collected. Herein, we refer to these sections and Botha-Brink (2014) and Daptocephalus distances of several kilometers depending on as Tweefontein2 (Fig. 3). AZ specimens discovered and published by our stratigraphic position and cover (Gastaldo et al., To construct our stratigraphic framework for group (Gastaldo et al., 2015, 2017). 2018), demonstrating the absence of fault dis- exposures along the northwest to southeast face placement along strike. In addition, they allow of the Lootsberg Pass escarpment, we physi- U-Pb CA-ID-TIMS Sampling Methods for an understanding of lateral and coeval litho- cally traced the upper bounding surface of thick facies relationships (Fig. 4). fluvial sandstone bodies with a waypoint taken Thin (10 cm) beds of white claystone The outcrop closest to the published Tweefon- every 40 m to 80 m (Fig. 4). Gastaldo et al. exposed at both localities (lower Tw1: tein coordinates is ∼400 m to the northeast of (2017) presented the results of one such way- S31.81260°, E024.81520°; upper Tw1: the reported location of Ward et al. (2000, 2005; pointed sandstone body that can be followed S31.811733°, E024.817450°; Tw2 S31.839417°, Fig. 3). Three correlative sections provide the along strike for a distance of more than 4 km E024.850317° ± 3 m) were sampled for U-Pb most exposure in the area (Gastaldo et al., 2017) in, likely, the Elandsberg Member. This basal- geochronology. Zircon grains were extracted with the most extensive one being >126 m thick most sandstone body is used, herein, as one of from silicified or devitrified claystone from the on Blaauwater 65 Farm. Sections were measured several inter-locality correlation datums (Fig. 4; upper Tw1 bed and lower Tw2 beds. U-Pb zircon in 2012 and 2013 and extended higher onto Gastaldo et al., 2017). In 2017, we encountered CA-ID-TIMS geochronological methods were

Figure 4. Waypoints plotted on GoogleEarth digital elevation model show traceable upper contacts of laterally continuous sandstone bodies (yellow balloons) used as datums into which stratigraphic sections (green balloons) were measured. A white dot is the position of specimen AM 4757 cf. leontocephalus (Gastaldo et al., 2017, their fig. 12). A white arrow shows the position of the vertebrate-defined Perm- ian–Triassic boundary in the area as reported by Ward et al. (2000) and Retallack et al. (2003, their fig. 3A), but see Gastaldo et al. (2009) and text for an alternative interpretation.

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employed in the Jack Satterly Geochronology these strata in the Eastern Cape are not well barforms of various geometries and thicknesses, Laboratory, Department of Earth Sciences, at documented. More recent work in the general consist of fine- to very fine-grained lithic wacke the University of Toronto as previously reported study area, as well as in the Free State Prov- and are organized into trough cross-bedded bed- (Gastaldo et al., 2015, 2018, 2020a). Method- ince (Gastaldo et al., 2019a, 2020a), has dem- sets that fine upwards to very thin, low angle ological details are provided in the Supplemental onstrated evidence of reverse polarity magne- cross beds (Fig. 6A). Ripple structures or small- Information1. tozones, which are defined by well-behaved, scale trough cross beds (Fig. 6B) characterize stable endpoint magnetizations of relatively bed contacts. Paleocurrent data, based on trough Magnetic Polarity Stratigraphy high laboratory unblocking temperatures. cross bed axial directions, indicate a northwest Evidence of reverse polarity magnetozones is orientation (azimuth = 307°; Fig. 6C). Isolated Thirty-nine sufficiently competent beds were limited, in a stratigraphic context, due to the and scattered euhedral pyrite crystals may occur sampled at Tweefontein1 and 29 at Tweefon- impact of Late Permian erosion and landscape along bedding contacts (Fig. 6D) in sandstone tein2 including sandstone, siltstone, and con- degradation (Gastaldo et al., 2018). bodies with the highest proportion commonly cretions in siltstone. Sampling for these beds Core samples were prepared into standard encountered in Tweefontein1.5, Tweefontein2, (each an independent site) was done by drilling 2.2-cm-high specimens for remanence (pro- and eastward toward Old Wapadsberg Pass seven to 12, and occasionally more, indepen- gressive demagnetization) and rock magnetic (Gastaldo et al., 2020b). Fining up sequences of dently oriented cores using a portable field drill measurements. Rock magnetic measurements sandy siltstone and siltstone, interbedded with with a non-magnetic diamond drill bit (Table include acquisition of isothermal remanence thin, decameter-scale lenticular wacke, are com- SI1; see footnote 1). In addition, three horizons magnetization to saturation (IRMS), measure- mon as channel fill successions. Fine-grained in hematitic siltstone/ within 1 m of ment of bulk susceptibility as a function of tem- rock types range from sandy coarse to fine the zircon-bearing bed at Tweefontein2 were perature, and anisotropy of magnetic suscepti- siltstone, in which fossil floral and faunal ele- sampled by extracting small flakes of rock, bility (AMS). Methods follow those previously ments may be preserved, and devitrified or silici- oriented with respect to the vertical and geo- published for these rocks (e.g., Gastaldo et al., fied claystone Figs. 7B( –7D; see Supplemental graphic north, placing them into non-magnetic 2018, 2020a) and are available in the Supple- Information; see footnote 1). ceramic boxes packed tightly with either cotton mental Information (see footnote 1). Fossil occurrences are limited primarily to or glass wool, and firmly taping them shut. All intervals. Thin, laminated siltstone beds sampled at the two localities are exposed Palynological Methods beds infrequently preserve megafloral and in the principal gully in which the longest microfloral elements Fig. 7A( ; Gastaldo et al., stratigraphic section is described. Our sam- Plant-bearing lithologies at Tweefontein1 were 2015, 2017, 2018). In contrast, thick siltstone pling areas are as low as absolutely possible processed for palynomorphs by Global Geolab intervals may preserve vertebrate skeletal ele- in the two deeply eroded gullies; we avoided Ltd., Alberta, Canada, using standard methods. ments whereas vertebrate remains are rarely sampling any prominent feature susceptible to Palynological residues were mounted in polyes- encountered in intraformational conglomerate lightning strikes. The number of independently ter casting resin. The Tweefontein assemblage lag deposits (e.g., Gastaldo et al., 2017, 2020c). oriented samples obtained is relatively high for had a very poor yield and was slightly less Ichnofossils are the most common fossil and magnetic polarity stratigraphy investigations. mature than the one reported from Blaauwater found in coarse siltstone, regardless of color, This is: (1) because of the implicit need to fully Farm (Gastaldo et al., 2017). Images were taken and very fine wacke.Katbergia carltonichnus characterize the magnetization in these rocks with a Nikon DS-Fi1 digital camera mounted burrows (Fig. 8A; Gastaldo and Rolerson, 2008) and (2) to convincingly assess the homogene- on a Leica DM2500 microscope. Sample resi- are ubiquitous across the escarpment and found ity, or lack thereof, of the remanence at each dues and slides are housed in the Paleobotani- throughout all measured sections. These ichno- stratigraphic level. This is done because of the cal Collections of the University of California fossils often are associated with concretionary potential thermal, or thermochemical, effects Museum of Paleontology, Berkeley, California, intervals. A unique interval of reddish-gray mas- of the emplacement of widespread mafic (dia- USA, curated with the numbers UCMP 398697– sive siltstone in Tweefontein1.5 contains large base) intrusions of the Early Jurassic Karoo 398704 (see figure captions). (50-cm-wide × 30-cm-high) burrows, circular LIP throughout the Eastern Cape. In this to elliptical in section, filled with greenish- area, most intrusions are of normal polarity RESULTS gray siltstone piped down from overlying strata (Gastaldo et al., 2018) and, therefore, it is not (Fig. 8B). Here, isolated bone fragments are scat- a straightforward exercise to separate an early The rocks exposed in the Tweefontein sec- tered infrequently in both the massive siltstone acquired, normal polarity remanence in upper tions do not differ significantly from those we and burrow fills. Reported vertebrate elements Paleozoic and lower Mesozoic strata from have reported upon previously to the north- include articulated skeletons, skeletons with a normal polarity Early Jurassic “overprint” west at Old Lootsberg Pass on Blaauwater isolated limb bones, and isolated skulls (Smith secondary magnetization, as recognized by De Farm (Gastaldo et al., 2014, 2015, 2018). The and Botha-Brink, 2014, their supplemental table; Kock and Kirschvink (2004). The few initial exception is the presence of white claystone Gastaldo et al., 2017). publications on paleomagnetic results from at several levels. The coarsest is a calcite-cemented, intraformational, clast- or Tweefontein1 Lithostratigraphy and matrix-supported conglomerate (Pace et al., Paleobotany 1Supplemental Material. (1) U-Pb CA-ID-TIMS 2009) that includes mudchip rip-up clasts, frag- Analytical Methods and Analyses, (2) Magnetic mented bone, and pedogenic nodule conglom- Three measured sections are physically cor- Polarity Methods and Stratigraphic Results, and (3) erate (PNC; Figs. 5A–5B). These lenticular, related and form the basis of this locality. The Descriptions of Fine-grained Lithofacies. Please visit https://doi​.org/10.1130/GSAB.S.14495223 to access cross-bedded intervals generally appear as basal principal section, consisting of 127 m of rela- the supplemental material, and contact editing@ channel lag deposits and may be >1 m in thick- tively well exposed rock, is supplemented with geosociety.org with any questions. ness. Sandstone bedload deposits, representing two shorter measured sections (Fig. 3), one of

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Figure 5. General character- istics of coarse-grained, in- traformational conglomerate lithologies in the Tweefontein sections and concretionary nodules are shown. (A) Thick pedogenic nodule conglomer- ate (PNC) lag deposit in a sand- stone body at Tweefontein1.5 shows sigmoidal cross beds (yellow arrow) in contact with an underlying light olive, sandy A B coarse siltstone (S31.83258°, E024.84473°). Basal bed is 0.5 m thick. (B) PNC constitu- ents include spherical to el- liptical, carbonate-cemented nodules, bone fragments, and millimeter- and centimeter- scale olive-gray and reddish- gray mudchips enveloped in a fine silty sandstone matrix. (C) Example of large, in situ car- bonate-cemented, moderate- brown nodules at Tweefontein1 (S31.81967°, E024.81520°; yel- C D low arrows) and elsewhere. In some instances, vertebrate re- mains may serve as the nucleating agent that facilitates skeletal preservation. (D) Image of basal carbonate-cemented concretions identified above exhibiting a greenish-gray color with surficial reddish-gray texture and a septarian-nodule appearance. Scale in decimeters.

which is detailed in Figure 9. A short 10 m sec- and mixed preservation was exhibited (Fig. 10). At least four localities to the southeast (Gastaldo tion, from which a vertebrate skull was recov- Identifiable specimens includeColumnisporites et al., 2018, their figs. 4 and 5; 2020c) expose ered and described (Gastaldo et al., 2017, their (trizygiod sphenophytes) and simple trilete basal, PNC channel lag deposits that contain fig. 12) and correlated into the main section, is spores (Granulatisporites and Lophotriletes). pebble- and cobble-sized clasts. The complex located in Figure 3. The lowest beds crop out Granulatisporites is known from very differ- is overlain by a ∼15-m-thick interval of fining in shallow, <1-m-deep gulleys at the main sec- ent plant groups, whereas Lophotriletes spores up siltstone successions with mudstone rip-up tion’s base (S31.82050°, E024.81363°). These have been described from several herbaceous clasts in coarser lithologies and a few nodular consist of fining up sequences of coarse (or ferns (see Balme, 1995). Pollen include alete horizons in olive-gray siltstone. A thin (30 cm), sandy coarse) to fine, olive gray, well to poorly and taeniate bisaccates (cf. Lunatisporites and finely laminated, silica-cemented porcellanite cemented siltstone. Several intervals contain Protohaploxypinus), similar to those reported and overlying devitrified claystone (lower Tw1) pale to moderate to dark brown large carbonate- from other assemblages (Prevec are correlative with an interval of coarse siltstone cemented nodules (Figs. 5C–5D), the exteriors et al., 2009, 2010; Gastaldo et al., 2014, 2015, in the primary gully that is truncated by an ero- of which are either smooth or exhibit amalga- 2020a; Fig. 10). A centimeter-thick, light gray sional contact of a thin overlying lithic wacke mation features. Septarian concretions, slicken- devitrified claystone caps this interval; no zircon body (Fig. 9). sides, and subvertical to subhorizontal burrows grains were recovered. The siltstone interval is The major upper sandstone body ranges from are rare. Limited reddish-gray color mottling in sharp erosional contact with a basal channel a thickness of 8 m in the main section to >11 m occasionally is found in olive , and Kat- form sandstone body (Fig. 9). to the northwest (Fig. 9). It also is a fine- to bergia burrows (Gastaldo and Rolerson, 2008) The basal channel system varies in thick- very fine-grained lithic wacke, although with are present (Fig. 9). ness from a maximum of ∼11 m to less than a slightly higher content, organized An increasing proportion of coarse olive-gray a meter of lithic wacke exposed in correlative into trough cross bed sets that attain a thickness siltstone and very fine, and very thin, pale olive sections to the southeast. This sandstone body of >1 m. Neither basal PNC lag deposits nor to gray-yellow lithic wacke is encountered in can be traced laterally along strike for several mud-pebble conglomerates were observed in the overlying succession, culminating in a fos- kilometers (Gastaldo et al., 2018) before it these locations. Basal, low-angle trough cross siliferous, laminated siltstone (Figs. 7A and 9) thins to the southeast and is obscured by cover. beds, of centimeter- to millimeter-scale, are in which a Glossopteris (Glossopteridales) and Clasts of fine- to very fine-grained sandstone are organized into 5 cm bedsets near the top. Paleo- Trizygia (sphenopsid) megaflora and palyno- organized into trough cross bed sets ranging in current data, based on trough cross bed axial logical assemblage is preserved (Gastaldo et al., thickness to >1.5 m and consist of millimeter- directions, indicate a unimodal flow direction 2017). Here, palynomorph recovery was low, to centimeter- scale, low angle beds (Fig. 6A). to the northwest (azimuth = 327°; Fig. 6C).

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conglomerate displaying random orientations. Katbergia burrows are preserved in both the olistoliths and siltstone matrix, and bone frag- ments are a component of all PNCs. The interval coarsens upwards to lenticular beds of intrafor- mational PNC and bluish-gray (5B 6/1), sandy coarse siltstone. This, in turn, is overlain by a fossiliferous 20 cm interval in which small- diameter unidentifiable plant axes,Katbergia , and slickensides are preserved. Katbergia-bur- rowed intervals continue upsection in which both grayish-red (10R 4/2), pale olive (10Y 6/2), and mottled olive and grayish-red siltstone are found. Grayish-red siltstone dominates, grad- A B ing up section to mottled and pale olive litholo- gies. Katbergia burrows may exceed 25 cm in length along exposed surfaces, and successive lithologies appear to have been independently burrowed, including low-angle, cross bedded lenticular sand bodies. There is a distinct change in sandstone color upsection to yellow-gray (Fig. 11), where euhedral pyrite crystals become common on bedding planes (Fig. 6D). Sandstone bodies dominate the measured sec- tion, each of which exhibits an erosional lower contact with underlying fine-grained litholo- gies. Intraformational PNC lag deposits are more common in this region of the escarpment and are exposed at the base of nearly all thick C D sandstone intervals. One particularly thick PNC exhibits sigmoidal cross stratification Fig. 5A( ). Figure 6. General characteristics of sandstone lithologies in the Tweefontein sections are range from thin, lenticular bodies shown. (A) Centimeter-scale bedded, trough cross beds characteristic of all sandstone bod- of <0.5 m in thickness to greater than 15 m ies in the measured sections (S31.81618° E024.82018°); scale in decimeters. (B) Plan view of (Fig. 11) where low-angle trough cross bed sets small-scale trough cross beds characteristic of upper trough infill structures (S31.819666° are organized on the scale of 60 cm or more near E024.81520°); scale in centimeters and decimeters. (C) Rose diagram of paleocurrent di- the channel base to 15 cm or less near its top. rection measured on trough axes of small-scale cross beds (N = 13) exposed in Tweefon- Lenticular beds are en echelon stacked. Due to tein1 exhibiting a northwest orientation. (D) Plan view of bedset contacts on which small, the prevalence of cover outside of the erosional euhedral pyrite crystals (yellow circles) are distributed (S31.83307°, E024.84096°); scale in donga, it is not possible to determine if fining centimeters. up intervals of thick sandstone to sandy coarse siltstone represent individual channels or if these intervals represent multi-storied bodies. These bedload-channel deposits are overlain by ter occurs in the upper 20 m of section with an Internal bed thickness of a typical bedset ranges interbeds of olive-gray coarse and fine siltstone increasing proportion of reddish-gray coloration from centimeters overlying an erosional contact and thin, very fine wacke. A 10-cm-thick, thinly (Fig. 9). As one ascends the slope of the escarp- to millimeter-scale at the top of the trough fill bedded, zircon-bearing claystone (upper Tw1), ment, exposure becomes limited to resistant (Fig. 6B). exposed in the shorter section to the northwest, sandstone benches with a few meters of under- In contrast to siltstone intervals in Tweefon- is part of the overlying channel fill complex lying fine lithologies, and the remaining intervals tein1, reddish-gray (brownish-gray) siltstone pre- (Figs. 7B and 9 at asterisk). are covered by colluvium, talus, and vegetation dominates over olive-gray siltstone. Mudchips, Olive-gray siltstone, with few concretionary/ at higher elevations. ranging from 1 mm to roughly 1 cm in size, are nodular horizons, predominates in the over- intermixed with these lithologies and also may lying stratigraphic section. An isolated skull Lithostratigraphy Tweefontein1.5 be found in Katbergia burrow fills. Millimeter- (AM4757), identified as eitherDaptocephalus to centimeter-sized, carbonate-cemented nod- leoniceps or a large Dicynodon sp. (Kammerer The base of the section is exposed as pave- ules are uncommon in rubified intervals. The et al., 2011; C.F. Kammerer, 2016, personal ment in this donga (S31.83327°, E024.84056°). first reddened mudrock intervals are terminated commun.; Gastaldo et al., 2017, their fig. 12) The lowest 1.5 m interval is unique and consists upsection by greenish-gray to olive-gray silt- was recovered from a nodule-bearing, olive- of mottled greenish- (5G 6/1) and brownish- stone over which lies a sandstone body with a gray siltstone exposed in the short section to gray (5YR 4/1) sandy coarse siltstone in which basal erosional contact. Large presumably ver- the southeast (S31.8175833°, E024.825233°; centimeter-scale mudchips are abundant. This tebrate burrows are preserved in a reddish-gray, Fig. 4). Thereafter, a change in siltstone charac- matrix envelopes olistoliths of intraformational 4 m interval near the top of the section (Figs. 8B

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Figure 7. General characteris- tics of fine-grained lithologies in the Tweefontein sections are shown. (A) Fossiliferous olive- gray siltstone interval beneath erosional contact with the lowermost fluvial sandstone in Tweefontein1 (S31.81930°, E024.81685°); arrow shows position of Glossopteris-dom- inated impression flora and palynological sampling site. A B (B) Silicified claystone, sam- ple site SK12–04 (S31.81175°, E024.80676°), in a channel fill sequence correlative with the uppermost fluvial sand- stone body in Tweefontein1 yielding a U-Pb CA-ID-TIMS maximum depositional age of 254.73 ± 0.24 Ma (Fig. 12A); hammer for scale. (C) Zir- con-bearing, devitrified - stone in reddish-gray siltstone (white arrow) at Tweefontein2 (S31.83943°, E024.85032°), CDsample 260319, yielding a U-Pb CA-ID-TIMS maximum depo- sitional age of 252.43 ± 0.19 Ma (Fig. 12B). (D) Field image of zircon-bearing bed in (C) in which primary structures include fine lamination.

and 11). These elliptical to amorphous-shaped large (decimeter-scale), carbonate-cemented The channel complex in the middle of the structures are the first to be encountered on concretions and Katbergia burrows. Thin len- main section (starting at ∼105 m; Fig. 11) may any Blaauwater, Lucerne, or Tweefontein Farm ticular or sheet sandstone bodies are intercalated be multistoried. Meter-scale lenticular bodies exposure (Fig. 3). Burrow casts consist of light in these basal deposits. A light olive, devitrified overlie an erosional contact with reddish-gray bluish gray (5B 7/1) or light olive gray (5Y 6/1) claystone overlain by centimeter-scale, fining up siltstone. These are in erosional contact with sandy coarse siltstone, in which mudchips and cycles of sandy coarse to coarse siltstone and a overlying PNC and may represent a second dispersed mica flakes are prominent and sur- lenticular, trough-fill claystone crop out in the phase of channel organization. Exposure in the rounded by brownish-gray coarse siltstone. Bur- lower part of the section. Both were sampled for shorter section to the northwest shows a thick set row fills occasionally show brownish-gray mot- zircons (see below). There is an increasing sand of fining up successions of light olive siltstone tling or cross-cutting burrow casts of Katbergia component upsection to the base of the first thick between thick lithic wacke bedsets, which are and an unidentified 0.5-cm-diameter cylindri- lithic wacke (Fig. 11). interpreted as channel fill deposits. These fine- cal burrow. Grain size and sedimentologic features of the grained rocks are overlain by an erosional con- basalmost sandstone body are no different here tact (at ∼110 m) and another interval of meter- Tweefontein2 Lithostratigraphy than elsewhere. It attains a thickness of <12 m, scale wacke bedsets, which may represent a third and there is no evidence for intraformational phase of bedload deposition. Fining up cycles of Our two measured sections, ∼0.3 km apart, pedogenic nodule conglomerate lags in the gully reddish-gray, coarse- to fine-grained siltstone, in are dominated by the same coarse clastic frac- exposures of this unit. The first exposure of PNC which decimeter-scale carbonate-cemented con- tion as in other measured sections, with a higher is found higher in the stratigraphy. It is exposed cretions and Katbergia burrows are preserved, proportion of sandstone than mudrock intervals in the complementary section to the northwest, continue and are interrupted by thin beds of (Fig. 11). There is no variation in the characteris- where it occurs as a lens enveloped by reddish lithic wacke. tics of channel bodies upsection, although there is gray siltstone and is unassociated with any sand- Resistant sandstone bodies become more notable variation in the character of fine-grained stone body (at ∼88 m; Fig. 11). Above it are fin- prominent at higher elevations of the main sec- sedimentary rocks. The base of our longest sec- ing up cycles of coarse to fine light olive-gray tion, where fine-grained intervals are covered tion begins in a pavement exposure located in and reddish-gray siltstone, in which both Katber- by talus and vegetation. The measured section is a shallow gully in an open field (S31.84307°, gia burrows and vertebrate bone are preserved. capped by a >15-m-thick channel succession in E024.84777°) where light olive-gray and olive- These units overlie lenticular and planar sand- erosional contact with underlying reddish-gray gray siltstone occurs. Reddish-gray siltstone first stone bodies. There is an increasing proportion siltstone. The predominance of reddish-gray appears within 10 m of the base and increases in of sandstone upsection, where a second channel siltstone in this part of the escarpment contrasts abundance vertically with the presence of both complex is encountered. markedly with the greenish-gray, fine-grained

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Figure 9. Two measured strati- graphic sections at Tweefon- tein1 (Figs. 3 and 4), correlative position of interval in which zircon-bearing silicified clay- A stone occurs, and interpreted normal polarity magnetozone, including a plot of rotated vir- tual geomagnetic pole (rVGP) latitudes for sites with a suf- ficient number of samples de- magnetized (Table 2). The extension of the longer section onto the escarpment is shown in Figure 19. U-Pb CA-ID-TIMS age results for zircon grains B indicate a maximum Wuchiap- ingian (254.73 ± 0.24 Ma) dep- Figure 8. Ichnological components of mea- ositional age, which conforms sured Tweefontein sections are shown. (A) in its stratigraphic position Inclined portion of ichnotaxon Katbergia with another reworked tuffite carltonichnus (Gastaldo and Rolerson, 2008) of Wuchiapingian age north- in an olive-gray silstone interpreted as an im- west at Old Lootsberg Pass mature inceptisol (S31.81988°, E024.81448°) (Gastaldo et al., 2018). in Tweefontein1. Scale in decimeters. (B) Olive-gray, large filled burrows envel- oped in reddish-gray coarse siltstone posi- tioned at several horizons at Tweefontein1.5 (S31.83246°, E024.84532°). Sandstone body with sigmoidal pedogenic nodule conglomer- ate lag deposit in Figure 5A directly overlies this paleosol interval. Scale in decimeters. to 254.51 ± 0.33 Ma (Fig. 12A, Table 1). The to represent a maximum age for deposition of youngest five results form a cluster (z10–14, the claystone horizon. intervals exposed to the northwest at Tweefon- Fig. 12A) that has a weighted mean 206Pb/238U tein1 (Figs. 3, 4, and 9). age of 254.73 ± 0.24 Ma (2σ, MSWD = 1.9; Magnetic Polarity Stratigraphy and Rock Fig. 12A inset; Fig. 9 for stratigraphic context), Magnetism U-Pb Geochronology which is interpreted as a maximum age for the time of deposition. Intensities of the natural remanent magne- Zircon grains were recovered from two Abundant zircon grains recovered from tization in the rocks sampled at Tweefontein1 horizons sampled, one exposed at Tweefon- a lenticular claystone trough fill at Twee- (Tw1; N = 39 sites) and Tweefontein2 (Tw2; tein1 (Tw1; S31.81173°, E024.81745°) and fontein2 range from euhedral to subhedral, N = 32 sites) typically range from ∼5 mA/m the other at Tweefontein2 (Tw2; S31.83942°, long prismatic to equant multi-faceted grains to 0.5 mA/m. Specimens from all samples from E024.85032°). The upper claystone at Tweefon- (Fig. 12B, inset; Figs. SI1–SI2; see footnote both Tweefontein sites studied, to date, yield a tein1 contains abundant zircon, which includes 1). A selection of the freshest, least rounded first removed well-defined northwest to north- both euhedral elongate crystals, equant multi- grains gave a range of dates typical of a detri- northwest, moderate to steep negative inclination faceted grains, and many mechanically rounded, tal population (Fig. 12B; Table 1). Results magnetization. At higher laboratory unblocking frosted, detrital grains (Fig. 12A). Rounded of four of the five youngest grains (Z11–14) temperatures or peak alternating field (AF) val- detrital grains of both rutile and titanite are overlap and have a weighted mean 206Pb/238U ues, a similar, well-defined component of mag- present in trace amounts. Sharply faceted zir- age of 252.432 ± 0.19 Ma (MSWD = 0.5). netization usually is isolated, and the remanence con grains that showed no surface abrasion and, The youngest date obtained (Z15) plots to the is interpreted to be of normal polarity (Fig. 13; thus, a greater likelihood of derivation directly right of the concordia curve, which may indi- Table 2; Fig. SI3 and Table SI1; see footnote 1). from a volcanic source were analyzed. Con- cate minor Pb loss in the grain and, therefore, a We refer to this remanence as the characteristic cordant U-Pb results for 14 zircon grains have 206Pb/238U that is younger than its crystallization remanent magnetization (ChRM) in these rocks. 206Pb/238U dates that range from 277.8 ± 0.9 Ma age. Therefore, we consider 252.43 ± 0.19 Ma As above, this ChRM component is notably

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demagnetization (Fig. 16). This is supported A B D by continuous susceptibility versus temperature measurements. (Fig. SI6; see footnote 1). In total, the paleomagnetic data obtained, to date, from both Tweefontein sections show that these sequences are dominated by a ChRM of E normal polarity (Fig. 17; Figs. SI7–SI8, see footnote 1; Table 2). At the site level, the dis- persion of individual sample directions is at the

acceptable level (estimated α95 values typically less than ∼15°; Table 2; Table SI1). However, in some cases, the dispersion is higher, and this F is partially interpreted to be a function of the C limited number of samples presently demag- netized and the relatively low natural remanent magnetization (NRM) intensities in some of the beds sampled. The ensemble of estimated site- G mean directions from a total of 45 sites (out of 57 reported at present, Table 2) from both Twee- fontein sections, which we accept on the basis of having a 95% confidence limit of less than 16.5°, yields a grand-mean direction of Decl. = 331.2°, Incl. = −55.0° (N = 45 sites, α = 3.7°, H 95 k = 34.0). This grand-mean direction, admit- tedly uncorrected for possible inclination shal- lowing (see Fig. SI17 and discussion in caption; see footnote 1), provides a southern hemisphere pole position of 66.3° S, 95.7° E (K = 17.0,

A95 = 5.3 (Table 2). If we can assume that this paleomagnetic result represents a suitably time- averaged record of the geomagnetic field in the 1 Figure 10. Selected pollen and spores from Tweefontein horizon with Glossopteris flora latest Permian, then the resulting pole can be are shown; University of California Museum of Paleontology (UCMP) collection locality compared with paleomagnetic data placed into number code PA1379. Taxonomic names or descriptions are followed by the UCMP speci- southern African coordinates (e.g., Torsvik et al., men number and England Finder graticule coordinates. (A) Lophotriletes novices (UCMP 2012; Fig. 17I). It also can be compared with 398697, U15-3). (B) Taeniate pollen grain (UCMP 398698, S41-3). (C) Alete bisaccate in- results from other continents by first placing det. (UCMP 398699, N13-4). (D) Trilete spore (UCMP 398700, S35-1). (E) Granulatisporites Southern African coordinates into West African (UCMP 398701, Z24-1). (F) Columnisporites sp. cf. C. peppersii (UCMP 398702, G41-1). coordinates using a −7.8° rotation about a Euler (G) cf. Protohaploxypinus limpidus (UCMP 398703, U17-1). (H) cf. Lunatsporites (UCMP pole located at 9.3°N and 5.7°E (Torsvik et al., 398704, M24-2). 2012). This results in a southern hemisphere pole location of 57.8°S, 106.2°E (Fig. 17J). We note comparable to the present day field direction of are interpreted to indicate that magnetite is that if a correction for inclination shallowing was the Eastern Cape as well as the ChRM direc- the principal carrier of the remanence in these applied (SI7; see footnote 1), then any result- tion of mafic intrusions of the Early Jurassic (ca. rocks. This interpretation is supported by results ing pole location will lie closer to the sampling 184 Ma) Karoo LIP (e.g., Hargraves et al., 1997; of IRM acquisition and backfield demagnetiza- locality in the Eastern Cape Province. Geissman and Ferre, 2013; Gastaldo et al., 2018, tion (Fig. SI4; see footnote 1) and continuous Samples from two sites (Tw1_19 and Tw1_20) 2019a), which are predominantly of normal measurements of bulk magnetic susceptibility provide, to varying degrees in progressive ther- polarity in this part of the basin (e.g., Gastaldo as a function of heating and cooling (Figs. SI5– mal demagnetization, subtle evidence for the et al., 2018). In most sites at both Tweefontein SI6; see footnote 1). However, several sites that preservation of a remanence of southeast to sections, this principal magnetization component are located high in the stratigraphic sequence at south-southeast declination and moderate posi- is unblocked over a range of laboratory unblock- Tw2 (e.g., sites Tw2_68 and Tw2_69) yield well- tive inclination. Admittedly, this was not well- ing temperatures to ∼580 °C and randomized in defined magnetizations of normal polarity but of isolated at a high level of confidence (Fig. 18 and AF demagnetization by 80–100 mT. At the site laboratory unblocking temperatures that range Fig. SI9; see footnote 1). We tentatively interpret (= bed) level, the within site (between sample) well above 600 °C (Figs. 13 and 15). These these magnetizations to represent the possibility consistency in magnetization character is typi- characteristics indicate that hematite is the prin- of a reverse polarity magnetozone preserved in cally high (Figs. 14–15) with estimated precision cipal remanence carrier at these horizons. Hema- the Tweefontein1 section. parameters (k; Fisher, 1953) typically greater titic sampled (sites Tw2_2019_1–3) Bulk magnetic susceptibility (MS) values for than 30 (Table 2). For most sites, the maximum above and below the zircon-bearing claystone sites in both of the Tweefontein sections typically laboratory unblocking temperatures of ∼580 at ­Tweefontein2 contain a mixture of both mag- range from ∼7 × 10−4 to 3 × 10−5 SI volume °C and median destructive fields of 20–40 mT netite and hematite, as shown in progressive units and are usually very consistent at the site

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Figure 11. Closely spaced stratigraphic Tweefontein1.5 and Tweefontein2 sections (Figs. 3 and 4) are correlated on upper contacts of the highest sandstone bodies traceable across the escarpment face (see Fig. 19). The youngest concordant U-Pb CA-ID-TIMS zircon dates are early Changhsingian (252.43 ± 0.19 Ma) from a devitrified claystone Figs. 7C( –7D). Sample location is marked with a cross (S31.83943°, E024.85032°) and is shown with our interpreted magnetic polarity for the Tweefontein2 section; a plot of rotated virtual geomagnetic pole (rVGP) latitudes is included for sites with a sufficient number of demagnetized samples (Table 2).

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of an unpredictable monsoonal climate (Retal- A lack et al., 2003; Smith and Botha, 2005; Smith and Botha-Brink, 2014). This pattern has been extrapolated to other parts of the globe (e.g., Benton and Newell, 2014). In the Karoo model, taxa of the Daptocepha- lus (formerly Dicynodon AZ; Viglietti et al., Figure 12. Concordia diagrams 2016; Viglietti, 2020) AZ are assigned a Permian for U-Pb CA-ID-TIMS results age and reported from the Elandsberg and lower are shown. (A) Results from a si- Palingkloof Members of the Balfour Formation licified claystone (tuffite) sample (Figs. 1–2). Olive-gray siltstone is reported to SK 12-04A (Fig. 7B) in which predominate in these pre-extinction landscapes, data for the five youngest con- although an upwards change in siltstone color cordant and overlapping data also is noted (associated with the Palingkloof have a weighted mean 206Pb/238U Member), which includes an increased fre- age of 254.73 ± 0.24 Ma (2σ). (B) quency of mottling and alteration to reddish gray Results from devitrified clay- color. Together with sandstone geometry, the B stone sample 260319 (Figs. 7C– presence of PNC, and other features, this change 7D) in which the 4 youngest has been associated with climate drying across concordant zircon grains have the basin (Ward et al., 2000, 2005; Smith and a mean age of 252.43 ± 0.19 Botha-Brink, 2014; Viglietti et al., 2018). A drier Ma (MSWD = 0.59; 2σ). The climate is interpreted to have pushed ecosystems claystone samples represent past physiological thresholds, which resulted in maximum ages for the time of ecological collapse associated with facies C deposition of the unit. (Ward et al., 2000; Smith and Ward, 2001; Huey and Ward, 2005; MacLeod et al., 2017; but see Retallack et al. [2003] and Gastaldo et al. [2014, 2020b, 2020c] for a different interpretation of climatic conditions during the same interval). This horizon marks the top of the Daptocepha- lus AZ and the culmination point of extinctions reported over the uppermost ∼20 m of this biozone. The bulk of the vertebrate turnover from the Daptocephalus to L. declivis AZs is level (Fig. SI10; see footnote 1). Anisotropy of model proposes a succession of five lithofacies, reportedly restricted to a narrow stratigraphic magnetic susceptibility (AMS) data from these distributed over ∼60 m of stratigraphy, in which interval of ∼20–30 m straddling either side of rocks reveal magnetic fabrics that are consistent an aridification trend is interpreted. Massive, the biozone boundary (Smith and Botha-Brink, with the preservation of primary depositional greenish-gray siltstone characterized by mean- 2014, their fig. 12; Botha et al., 2020, their

textures (Fig. SI10) with Kmin axes oriented close dering fluvial channels (Facies A; Smith and fig. 9). These extinctions equated to the end- to vertical. Kmax and Kint axes either are relatively Botha-Brink, 2014) is overlain by an interval of Permian event (Phase 2; Smith and Botha-Brink, well grouped with sub-horizontal orientations massive maroon and gray mudrock, with some 2014; but see Gastaldo et al., 2019a, 2020a) (triaxial distribution) or more uniformly distrib- attendant mottling (Facies B), culminating in a reportedly are succeeded by a rapid recupera- uted within a sub-horizontal plane, in which case thin, interlaminated heterolithic and, reportedly, tion of vertebrate taxa (Recovery Phase 1; Botha the T parameter approaches 1.0. The degree of unique “event bed” (Smith and Ward, 2001) and Smith, 2006, 2007; Smith and Botha-Brink, anisotropy (P) ranges from 1.004 to 1.114 and is that is interpreted as a basin-wide isochronous 2014) in the overlying L. declivis AZ (Botha and typically very consistent at the site level; this is playa deposit (Facies C). This horizon is consid- Smith, 2020). This pattern is in sharp contrast to especially true for those sites with a small varia- ered to be coeval with the end-Permian marine a diversification lag in the marine realm, where tion in bulk susceptibility among specimens. extinction event of similar duration (Smith and the extinction of major invertebrate lineages, Botha-Brink, 2014) and marks the maximum ocean anoxia, and a shallow oxygen-minimum DISCUSSION extent of aridification, vegetational collapse, and zone retarded recovery (Lau et al., 2016). Evi- vertebrate extinction (Ward et al., 2000, 2005). dence used to propose an arid setting for the The current terrestrial end-Permian biodi- Predominantly massive maroon siltstone that rapid recovery in the lower/basal L. declivis AZ versity crisis and vertebrate-extinction model immediately overlies the heterolithic interval is under arid conditions includes: the proposed (e.g., Erwin, 2006; Ward et al., 2005; Smith and interpreted to be indicative of harsh, semi-arid predominance of loess (Smith and Botha-Brink, Botha-Brink, 2014; Roopnarine and Angielczyk, conditions in which vertebrate assemblages 2014; Both and Smith, 2020; Viglietti et al., 2015; Rubidge et al., 2016; Botha et al., 2020; rapidly recover. Fluvial channels of the overly- 2018), vertic structures and iron content reported and others, but see: Lucas, 2017, 2018, 2020; ing Katberg Formation have been interpreted to from paleosols (Smith and Ward, 2001; Smith Schneider et al., 2019) is based, largely, on represent anabranching regimes that formed in and Botha-Brink, 2014; Botha et al., 2020), the lithostratigraphic and vertebrate biostratigraphic response to increased load as a conse- presence of PNC beds (Smith and Botha-Brink, patterns reported from the Karoo Basin. The quence of landscape denudation and the onset 2014, Botha et al., 2020), architectural elements

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TABLE 1. U-Pb ISOTOPIC DATA FOR SINGLE, CHEMICALLY ABRADED ZIRCON GRAINS FROM TWO TUFFITE LAYERS, TWEEFONTEIN SECTION, KAROO BASIN, EASTERN CAPE PROVINCE, SOUTH AFRICA

a b 206 c 207 d 206 d e g No. Weight U Th/U PbC Pb Pb 2σ pb 2σ Error Age (Ma) % (μg) (ppm) (pg) 204 235 238 corr. Disc Pb Pb U 206pbf 2σ 207pbf 2σ 207Pbf 2σ measured 238U 235U 206Pb Claystone (tuffite) layer (S31.81173°, E024.81745°): Tweefontaine1 section Z1 4.9 121 1. 10 0.4 4488 0.3147 0.0022 0.044034 0.000149 0.598 277.79 0.92 277.8 1. 7 278 12.9 0.2 Z2 5.5 111 1. 13 0.7 2455 0.3040 0.0017 0.042602 0.000061 0.536 268.94 0.38 269.5 1. 3 274 11. 2 2.0 Z3 6.9 99 0.73 0.6 3347 0.3027 0.0013 0.042391 0.000041 0.597 267.64 0.25 268.5 1. 0 276 8.9 3.3 Z4 6.0 183 0.69 1. 0 2878 0.3011 0.0014 0.042312 0.000052 0.564 267.15 0.32 267.2 1. 1 268 9.6 0.3 Z5 7. 9 32 1.39 0.8 925 0.2968 0.0043 0.041787 0.000061 0.701 263.90 0.38 263.9 3.4 264 31.4 –0.1 Z6 7. 3 46 0.96 0.4 2438 0.2899 0.0018 0.040864 0.000062 0.524 258.18 0.38 258.5 1. 4 261 12.9 1. 0 Z7 5.5 103 1.26 0.7 2127 0.2894 0.0020 0.040860 0.000101 0.527 258.16 0.62 258.1 1. 6 258 14.1 –0.3 Z8 7. 2 60 0.72 0.2 5751 0.2889 0.0011 0.040679 0.000052 0.593 257.04 0.32 257.7 0.8 264 7. 0 2.7 Z9 4.6 136 0.81 2.7 616 0.2875 0.0062 0.040642 0.000086 0.685 256.81 0.53 256.6 4.9 255 46.6 –0.8 Z10 6.2 127 1.45 3.0 699 0.2889 0.0051 0.040403 0.000083 0.632 255.33 0.51 257.7 4.0 279 38.1 8.7 Z11 6.5 146 1.63 0.5 5357 0.2861 0.0019 0.040338 0.000240 0.913 254.93 1.49 255.5 1. 5 261 6.3 2.2 Z12 2.8 175 1.44 0.6 1994 0.2851 0.0023 0.040332 0.000184 0.643 254.89 1. 14 254.7 1. 8 253 14.4 –0.7 Z13 9.0 93 1.46 0.8 2734 0.2850 0.0018 0.040288 0.000083 0.517 254.62 0.51 254.6 1. 4 255 12.9 0.0 Z14 2.8 60 1.04 0.6 3001 0.2848 0.0017 0.040270 0.000053 0.504 254.51 0.33 254.5 1. 3 254 12.4 –0.2 Claystone (tuffite) layer (S31.83943°, E024.85032°): Tweefontaine2 section Z1 3.2 45 0.91 0.2 2470 0.5575 0.0015 0.056412 0.000066 0.516 353.77 0.40 449.9 1. 0 977 4.7 65.5 Z2 1. 0 170 0.81 0.3 2026 0.4142 0.0013 0.054490 0.000097 0.397 342.03 0.59 351.9 0.9 418 6.5 18.6 Z3 2.3 152 1. 14 0.2 4561 0.3056 0.0015 0.042875 0.000083 0.467 270.63 0.51 270.8 1. 2 272 9.9 0.5 Z4 1. 5 64 0.92 0.7 391 0.2964 0.0035 0.041026 0.000123 0.019 259.19 0.76 263.6 2.8 303 28.0 14.7 Z5 3.9 64 0.69 0.3 2324 0.2894 0.0017 0.040813 0.000042 0.498 257.87 0.26 258.1 1. 3 260 12.4 0.7 Z6 1. 4 104 1. 01 2.6 163 0.2879 0.0088 0.040637 0.000121 0.363 256.78 0.75 256.9 6.9 258 68.2 0.4 Z7 1. 0 117 3.12 0.2 1314 0.2860 0.0013 0.040281 0.000069 0.339 254.57 0.43 255.4 1. 0 263 9.9 3.3 Z8 1. 0 108 1. 14 0.6 479 0.2835 0.0035 0.040111 0.000070 0.346 253.52 0.44 253.4 2.8 253 27.4 –0.3 Z9 2.7 72 1. 10 0.3 1667 0.2824 0.0053 0.040047 0.000074 0.654 253.12 0.46 252.5 4.2 247 40.0 –2.5 Z10 1. 6 137 0.87 0.4 1356 0.2909 0.0035 0.040032 0.000061 0.452 253.03 0.38 259.3 2.7 316 25.8 20.4 Z11 1. 0 156 1.02 0.3 1439 0.2837 0.0030 0.039971 0.000067 0.475 252.66 0.42 253.6 2.4 263 22.5 3.9 Z12 4.4 63 1.23 0.2 3587 0.2833 0.0008 0.039929 0.000039 0.574 252.39 0.24 253.3 0.6 262 5.5 3.7 Z13 1. 0 154 1.00 0.2 1608 0.2825 0.0029 0.039914 0.000089 0.424 252.30 0.55 252.7 2.3 256 21.8 1. 5 Z14 1. 0 118 0.94 0.3 1214 0.2818 0.0047 0.039894 0.000159 0.453 252.17 0.99 252.0 3.7 251 34.8 –0.5 Z15 1. 4 119 1. 17 0.7 659 0.2839 0.0031 0.039714 0.000061 0.450 251.06 0.38 253.7 2.4 278 23.5 10.0 Notes: Zircon grains pretreated prior to analysis by thermal annealing and HF etching (Mattinson, 2005). Decay constants are those of Jaffey et al. (1971): 238U and 235U are 1.55125 × 10–10/yr and 9.8485 × 10–10/yr. aTh/U calculated from radiogenic 208Pb/206Pb ratio and 207Pb/206Pb age assuming concordance. b PbC is total common Pb assuming the isotopic composition of laboratory blank. c206Pb/204Pb corrected for fractionation and common Pb in the spike. dPb/U ratios corrected for fractionation, common Pb in the spike, and blank. eError Corr is correlation coefficients of X–Y errors on the concordia plot. fCorrection for 230Th disequilibrium in 206Pb/238U and 207Pb/206Pb assuming Th/U of 4.2 in the magma. gDisc is percent discordance for the given 207Pb/206Pb age.

associated with low sinuosity fluvial regimes in Formation. To date, we have been unable to reveals some similarities along with major dif- the upper Palingkloof Member and anabranch- locate any physical evidence of conventional ferences in their overall character. Single-storied ing regimes for the Katberg Formation (Smith (drill hole) sampling in rocks at Old (West) sandstone bodies are reported to be enveloped and Ward, 2001; Smith and Botha-Brink, 2014; Lootsberg Pass that could be resampled at the in olive-colored siltstone of the uppermost Dap- Viglietti et al., 2018; Botha and Smith, 2020), as identical locations to replicate the reported pat- tocephalus AZ, where occasional reddish-gray well as isotope geochemistry (Rey et al., 2016). tern. In addition, we have been unable to repli- mottling may be found (Smith, 1995; Ward et al., Yet, detailed analyses of the transition interval cate the previously reported polarity pattern at 2000, 2005) that increases in abundance upsec- over which the turnover is interpreted to have Old (West) Lootsberg Pass (Gastaldo et al., 2015, occurred yields no physical or geochemical evi- 2018). We have identified two very thin reverse dence of loess deposition (Gastaldo and Nevel- polarity magnetozones in the section (Fig. 19), Figure 13. Orthogonal progressive demag- ing, 2016; Gastaldo et al., 2019b) or other evi- one of which is constrained by a U-Pb CA-ID- netization diagrams (Zijderveld, 1967) show dence for aridity (Li et al., 2017; Gastaldo et al., TIMS maximum depositional Changhsingian the end point of the magnetization vector 2019b, 2020b, 2020c). age (253.48 ± 0.15 Ma; Gastaldo et al., 2015). plotted onto the horizontal (filled symbols) Ward et al. (2005) presented magnetostrati- Magnetic polarity and geochronometric data and vertical (open symbols) planes (NS- graphic information for sections, reportedly from our Tweefontein1 and Tweefontein2 sec- EW, EW-up/down) for individual specimens sampled across the boundary, at West (Old) tions, which are in an intermediate geographic from samples from selected sites sampled at Lootsberg and (East) Lootsberg Pass (Fig. 3). position between Old Lootsberg Pass and Loots- the Tweefontein1 and Tweefontein2 sections The magnetic polarity stratigraphy that they berg Pass (Figs. 3 and 4), in conjunction with that have been subjected to either progres- present begins with a normal polarity zone (in new and previously published paleontologic sive alternating field (AF) or thermal de- Old Lootsberg Pass) and then a short reverse data, allow us to test the Karoo Basin paradigm magnetization. Selected demagnetization polarity interval, which is succeeded by a nor- previously used by other workers. steps are shown for data points in the ver- mal polarity zone that commences a few meters tical position. Also shown are normalized above their vertebrate-defined boundary. This Lithostratigraphic Patterns intensity decay plots showing response to normal polarity magnetozone is at least 120 m progressive AF or thermal demagnetization thick and is followed by a reverse magnetozone A comparison of our stratigraphic sections and stereographic projections of the mag- that begins ∼100 m above the reported biozone (Figs. 9 and 11) with those previously presented netization vector measured at each step. boundary and extends higher into the Katberg for Tweefontein (Ward et al., 2000, their fig. 1) NRM—natural remanent magnetization.

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TABLE 2. SUMMARY OF PALEOMAGNETIC DATA; ESTIMATED SITE MEAN DIRECTIONS FROM THE TWEEFONTEIN 1 AND TWEEFONTEIN 2 SECTIONS FOR SITES WITH A SUFFICIENT NUMBER OF SPECIMENS FROM INDEPENDENT SAMPLES SUITABLY DEMAGNETIZED AS WELL AS THE GRAND MEAN DIRECTION AND RESULTING POLE POSITION AND ASSOCIATED STATISTICS. Site Rock typea n/nob Decl.c Incl.d α95e kf Typical Int.g VGPh rVGPj demag. (dp/dmi) latitude TW 1_1 12/12 344.0 –50.1 4.4 97.5 422–565 –76.3 114.5 (5.9/3.9) 51.5 TW 1_2 12/13 336.1 –52.0 5.0 76.9 466–595 –69.8 106.1 (6.8/4.7) 56.3 TW 1_3 concr in grn/gry slt 16/16 331.6 –55.8 5.5 46.7 388–555 –66.1 96.0 (7.9/5.6) 61.4 TW 1_4 concr in grn/gry slt 15/15 326.9 –57.5 3.1 154.1 366–538 –62.3 92.4 (4.5/3.30) 64.7 TW 1_5 concr in grn/gry slt 16/16 353.8 –62.7 5.5 33.0 388–566 –76.8 44.6 (8.6/6.7) 57.2 TW 1_6 5/5 354.9 –59.4 15.2 26.4 377–555 –80.6 49.5 (22.8/17.1) 53.9 TW 1_7 5/5 327.7 –63.2 10.1 58.5 411–560 –61.8 78.3 (15.9/12.1) 70.1 TW 1_8 5/5 353.7 –59.9 22.0 13.0 411–560 –79.7 52.5 (33.4/25.2) 54.9 TW 1_9 6/6 336.1 –61.9 10.2 43.8 435–570 –68.0 77.0 (15.8/12.2) 65.2 TW 1_10 4/4 323.1 –57.8 7. 4 154.8 377–555 –59.3 91.9 (10.9/8.0) 66.2 TW 1_11 concr in grn/gry slt 6/6 329.9 –58.3 3.2 427.6 435–588 –64.6 90.0 (4.7/3.5) 64.3 TW 1_12 concr in grn/gry slt 4/4 299.7 –44.3 21.8 18.8 510–580 –37.6 104.8 (27.4/17.2) 55.0 TW 1_13 9/9 335.8 –54.4 5.2 100.2 477–584 –69.6 99.4 (7.3/5.2) 58.5 TW 1_14 10/10 330.2 –58.7 7. 1 47.4 411–560 –64.7 88.9 (10.6/7.8) 64.6 TW 1_15 7/7 342.1 –59.7 6.3 93.0 477–584 –73.2 78.5 (9.5/7.1) 60.3 TW 1_16 7/7 339.1 –56.7 1. 7 1335.1 444–573 –72.0 91.4 (2.5/1.8) 59.1 TW 1_17 6/6 348.2 –53.6 4.5 220.7 444–576 –79.8 98.3 (6.3/4.4) 52.3 TW 1_18 concr in grn/gry slt 8/8 333.2 –57.4 4.4 158.0 365–553 –67.2 91.5 (6.4/4.7) 62.3 TW 1_19k 10/10 335.9 –56.0 4.4 119.5 411–533 –69.6 94.8 (6.3/4.5) 59.8 TW 1_20k 11/11 336.7 –56.6 3.0 227.3 400–540 –70.1 92.7 (4.3/3.1) 60.0 TW 1_22 concr in grn/gry slt 6/7 333.3 –67.7 10.4 42.2 320–440 –62.7 63.3 (17.4/14.5) 71.9 TW 1_23A tan wckst 5/5 16.1 –77.6 17.6 19.8 400–569 –54.2 13.8 (33.0/30.9) 58.7 TW 1_23B 4/4 355.5 –54.1 30.0 10.3 366–525 –85.3 76.6 (42.1/29.5) 49.2 TW 1_24 grn/gry slt 6/6 335.4 –63.7 8.8 58.3 400–555 –66.6 72.4 (14.1/11.1) 67.2 TW 1_25 7/7 355.8 –61.1 14.9 1 7. 3 368–568 –79.1 41.5 (22.9/17.5) 54.8 TW 1_27 6/6 356.8 –49.6 15.0 20.9 411–555 –86.9 140.5 (20.0/13.3) 45.1 TW 1_28 6/6 339.9 –60.4 14.8 21.5 444–544 –71.3 78.4 (22.5/17.1) 62.0 TW 1_29 4/4 340.9 –56.0 6.3 213.1 422–556 –73.5 92.8 (9.1/6.5) 57.7 TW 1_30 concr in grn/gry slt 6/6 329.1 –56.1 17.0 16.5 440–569 –64.1 95.5 (24.5/17.6) 62.6 TW 1_31 3/3 345.1 –60.1 7. 3 286.3 422–556 –74.9 73.0 (11.1/8.4) 59.3 TW 1_33 7/7 334.3 –47.5 5.9 107.2 422–556 –67.6 116.3 (7.7/5.0) 53.4 TW 1_34 4/4 336.5 –49.0 16.5 32.1 400–555 –69.8 114.0 (21.8/14.4) 53.8 TW 1_35 5/5 332.9 –62.9 22.9 12.1 466–556 –65.4 76.4 (36.0/28.2) 67.6 TW 1_36 4/4 333.5 –50.5 23.6 16.2 477–565 –67.5 109.2 (31.7/21.3) 56.1 TW 1_38 hem ss 5/5 334.2 –58.6 19.1 17.1 466–555 –67.8 87.8 (28.4/21.2) 62.9 TW2_40 5/5 300.5 –54.7 7. 6 102.2 400–565 –40.6 93.6(10.7/7.6) 65.6 TW 2_41 dk grn/gry slt 6/6 325.2 –64.5 8.0 73.5 289–507 –59.7 76.0 (12.8/10.3) 72.4 TW 2_42 12/12 321.7 –61.9 5.1 72.2 289–528 –57.9 83.1 (7.9/6.1) 70.9 TW 2_43 9/9 324.2 –59.1 3.0 304.3 289–528 –60.1 89.0 (4.5/3.3) 67.2 TW 2_44 5/5 306.7 –43.6 20.2 8.5 300–568 –43.2 108.4 (25.2/15.7) 56.1 TW 2_45 4/4 319.8 –52.7 15.2 37.3 391–557 –56.3 101.3 (21.0/14.5) 62.2 TW2_46 5/5 299.6 –20.8 11. 9 42.6 350–565 –18.3 140.7 (12.5/6.6) 19.7 TW 2_47 8/8 293.8 –49.2 13.2 18.4 343–528 –34.1 97.8 (17.5/11.5) 59.7 TW2_50 5/6 287.3 –46.6 20.4 15.0 350–565 –29.0 97.8 (26.2/16.9) 56.8 TW 2_56 grn/gry slt 5/5 318.1 –54.5 8.0 92.5 391–557 –55.1 97.9 (11.3/8.0) 64.3 TW 2_58 grn/gry hem slt 4/4 336.4 –60.6 7. 6 146.7 391–557 –68.8 80.7 (11.6/8.8) 63.8 TW2_59 5/6 316.8 –10.0 7. 1 14.3 350–573 –34.8 148.6 (7.2/3.6) 25.0 TW2_62 4/5 335.1 –27.1 9.8 88.9 350–573 –38.0 173.6 (10.7/5.8) 12.4 TW2_63 3/3 314.4 –49.8 52.8 6.5 350–565 –51.3 104.2 (70.4/46.9) 60.6 TW2_64 7/8 310.6 –36.1 15.1 1 7. 0 350–573 –44.4 117.3 (17.6/10.2) 50.5 TW 2_65 grn/gry fn slt 10/10 337.7 –49.6 8.9 30.2 333–528 –70.9 113.0 (11.8/7.9) 53.8 TW 2_67 lt grn med wacke 8/8 328.3 –55.4 2.7 407.3 530–675 –63.5 97.1 (3.8/2.7) 62.2 W 2_68 hem crs slt 5/5 319.2 –55.0 13.2 34.5 550–670 –56.1 97.1 (18.7/13.3) 64.5 TW 2_69 hem crs slt 12/12 325.3 –60.7 1. 8 591.4 570–675 –60.7 85.2 (2.7/2.1) 68.4 TW 2_2019_Cube1hem mdst 5/5 0.3 –59.1 22.0 13.1 497–671 –81.9 23.2 (32.9/24.6) 50.9 TW 2_2019_Cube2hem mdst 4/4 0.1 –53.2 14.3 42.3 448–638 –88.0 22.4 (19.8/13.8) 46.3 TW 2_2019_Cube3hem mdst 4/4 336.8 –56.1 23.5 16.2 497–678 –70.3 94.2 (33.8/24.3) 59.5 “Grand” Mean1: Nl = 45/57 331.2 –55.0 3.70 34.0 (R m = 43.7) Pole: –66.3 (S), 95.7 (E), A95 = 5.3°, K = 17.0, S = 19.9° “Grand” Mean2: Nl = 57/57 330.5 –55.6 3.42 31.3 (R m = 55.2) Notes: Farm Tweefontein, Lootsberg Pass area, Eastern Cape Province, South Africa. All data expressed in geographic coordinates. With an average site location of –31.83°S and 24.82°E, the estimated Grand Mean direction, which has not been corrected for any magnitude of inclination shallowing (see Supplemental Information; text footnote 1) yields a southern hemisphere pole position at 66.3°S and 95.7°E) (K n = 16.9, A95° = 5.3°). This pole, if it does represent a suitably time averaged representation of the geomagnetic field in the latest Permian, can be compared to paleomagnetic poles case in southern Africa coordinates (e.g., Torsvik et al., 2012) (Fig. 17I). In addition, this pole can be rotated from Southern Africa coordinates to West African coordinates by –7.8° about a Euler pole located at 9.3°N and 5.7°E (Torsvik et al., 2012). This results in a southern hemisphere pole location of 57.8°S, 106.2°E) (Fig. 17J). Lines that are in italics refer to site data that were not used in the calculation of the Grand Mean 1 overall mean direction for the sections. Those site data in italics are associated with unacceptable levels of sample dispersion. aBrief description of rock sampled; hem—hematitic; crs—coarse; slt—siltstone; mdst—mudstone; fn—fine; ss—sandstone; concr—carbonate concretion; lt—light; grn/gry—greenish-gray. bRatio of the number of specimens fully demagnetized and accepted for statistical analysis to the total number of specimens analyzed (typically one to two specimens analyzed per independent sample). cDeclination, in degrees east of north, of the estimated site mean direction. dInclination, in degrees positive downwards and negative upwards, of the estimated site mean direction. eSemi-angle of the cone of 95% confidence about the estimated site mean direction, within which at 95% confidence the true mean direction lies. fBest estimate of Fisher’s (1953) directional precision parameter. gLaboratory unblocking temperature interval (in °C) over which the characteristic remanent magnetization for that site is commonly removed. hEstimated virtual geomagnetic pole position (VGP) based on the estimated site mean direction and the location of the sampling locality. iSemi-angles of the elliptical cone of confidence at the 95% confidence level about the estimated virtual geomagnetic pole. jrVGP “rotated” VGP relative to the ca. 250 Ma southern Africa, inclination-corrected paleomagnetic pole position of Torsvik et al. (2012) located at –44.7°S latitude and 60.7°E longitude (from their table 10). kNorth–northwest-directed, moderate to steep negative inclination magnetization removed over a range of moderate to high laboratory unblocking temperatures with suspicion of a remaining remanence of opposite polarity (see text for details). lNumber of estimated site mean directions used to estimate a grand mean direction. mVector resultant vector of N unit vectors. nEstimate of Fisher’s (1953) precision parameter based on the distribution of virtual geomagnetic poles (VGPs) generated by the N estimated site mean directions. oSemi-angle of the cone of 95% confidence about the estimated pole position based on the distribution of virtual geomagnetic poles (VGPs) generated by the N estimated site mean directions

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Figure 14. Orthogonal progressive demagnetization diagrams (Zijderveld, 1967) show the end point of the magnetization vector plotted onto the horizontal (filled symbols) and vertical (open symbols) planes (NS-EW, EW-up/down) for individual specimens from independent samples from site Tw1_14 (Tweefontein1 section) that have been subjected to progressive thermal demagnetization. Selected demagnetization steps are shown for data points in the vertical projection. Also shown are normalized intensity decay plots showing response to progressive demagnetization and stereographic projections of the magnetization vector measured at each step. NRM—natural remanent magnetization.

tion (Botha and Smith, 2006; Viglietti, 2020). ciation with single-story channels situated tens of Triassic (Gastaldo et al., 2020a), this particular Single-storied channel deposits incised into meters below the base of the Katberg Formation feature ascribed to the global continental extinc- olive-gray siltstone with occasional mottling are (Gastaldo et al., 2018; also see Viglietti et al., tion model (Benton and Newell, 2014) should be consistent with our observations at Tweefontein1 2017). Rather, we find evidence in support of sim- reconsidered. but not at Tweefontein2, where basal erosional ilar channel architectures continuing into the L. Color differences in mudrock deposits surfaces of channel architectures are in contact declivis AZ as it is currently defined (Figs. 9, 11, continue to be used as one of a suite of diag- with reddish-gray siltstone (Fig. 19). At Twee- and 19). All sandstone channels display: (1) basal, nostic criteria to identify lithofacies in the fontein1, greenish-gray siltstone predominates in intraformational PNC lag deposits; (2) similar ­Daptocephalus and the L. declivis AZs (Smith the first∼ 100 m of stratigraphy rather than being maximum thicknesses; (3) trough cross bed sets and Botha-Brink, 2014; Viglietti et al., 2018; restricted to the lowest 25 m of section, as illus- of similar thickness and stacking patterns; (4) the Botha et al., 2020). Kitching (1968) described trated by Ward et al. (2000), which is more con- same set of primary structures; (5) identical grain mudrock color as generally greenish-gray at sistent with the pattern at Tweefontein2. Key sedi- size distributions and mineralogical features; and the base of his Lystrosaurus AZ with a change mentary successions interpreted to represent the (6) similar architectural organization in exposures to overlying bright reddish maroon and purple post-extinction facies of the L. declivis AZ (Ward along strike. The reported differences in previous mudrock upsection. The Palingkloof Member, et al., 2000) consist of multistoried sandstone channel architecture interpretations may be due, characterized by the predominant reddish color bodies that are frequently bounded at the base by in part, to the location at which each section was exhibited by the mudstones, was subsequently isolated PNC lag deposits. This change in fluvial measured or how the composite stratigraphic established for the uppermost interval of the architecture reportedly is preceded by a change in section was constructed. We note that there Balfour Formation (Johnson, 1976; S.A.C.S., siltstone color to reddish gray ∼20–30 m above appears to be no evidence in the Sydney Basin, 1980). Smith (1995, p. 87) placed the last the base of the Lootsberg and Tweefontein sec- Australia, to support a change in fluvial style occurrence of Dicynodon (= Daptocephalus) tions of Ward et al. (2000). In contrast, we find across the Permian–Triassic boundary sections coincident with the first rubified of no evidence in any ­Tweefontein section for a there (Fielding et al., 2019). Also, given that the the Palingkloof Member. Subsequently, Ward change in fluvial architecture and, previously, basal Lystrosaurus AZ, as currently defined, is et al. (2000, p. 1741) described the interfluvial PNC lenticular lag deposits were reported in asso- ­apparently latest Permian in age rather than Early silt-and-mudstone facies of the L. declivis AZ

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Figure 15. Orthogonal progressive demagnetization diagrams (Zijderveld, 1967) show the end point of the magnetization vector plotted onto the horizontal (filled symbols) and vertical (open symbols) planes (NS-EW, EW-Up/Dn) for individual specimens from independent samples from site Tw2_68 (Tweefontein2 section) that have been subjected to progressive thermal demagnetization. Selected demagnetization steps are shown for data points in the vertical projection. Also shown are normalized intensity decay plots showing response to progressive de- magnetization and stereographic projections of the magnetization vector measured at each step. NRM—natural remanent magnetization.

as being predominantly maroon in color when and Tweefontein2 sections show this gradi- demonstrates the gradational and spatially vari- compared to the olive colors of the Permian ent over a distance of more than 4.5 km. If we able nature of the lithostratigraphic boundaries (then equated with the Daptocephalus AZ). The expand the stratigraphic framework to include in the study interval. position of the biostratigraphic boundary was our measured sections at Old Lootsberg Pass on reassigned to the lower strata of the Palingk- Blaauwater Farm (Fig. 19; Gastaldo et al., 2015, U-Pb Geochronology loof Member (Smith and Botha, 2005; Botha 2018), the lateral (7 km distance) and vertical et al., 2020; Viglietti, 2020). But, in general, (250 m) gradient pattern becomes more pro- Beds of whitish to light gray silicified or siltstones of the Daptocephalus AZ have been nounced. The greater part of the stratigraphy in devitrified claystone, from which euhedral considered to be dominated by color variants of the ­northwestern part of the escarpment is domi- zircon grains are recovered, are exposed in olive-gray hues, albeit with “patchy rubification nated by olive-gray siltstone variants. In contrast, the stratigraphic sections at both Tweefontein of the mudrocks” at the very top of the biozone siltstones to the southeast are dominated by red- localities and elsewhere (Gastaldo et al., 2015, (Smith and Botha-Brink, 2014, p.103). In con- dish-gray siltstone variants at stratigraphically 2018, 2020a; unpublished data). Zircon grains trast, the fine-grained rocks of theL. declivis correlative horizons (Figs. 19–20). A parallel recovered from a reworked, devitrified claystone AZ are reported to be dominated by variants pattern is observed in the upsection increase of at Tweefontein1 (Figs. 9 and 19) yield a maxi- of maroon, grayish-red, or brownish-gray color. channel fill sandstone complexes, which is used mum depositional age of 254.73 ± 0.24 Ma Spatial variation in color and mottling of these to delineate the base of the Katberg Formation (Fig. 12A). This Wuchiapingian (259.1– end-member hues has been documented verti- (Johnson et al., 2006; Groenewald, 1996). The 254.14 Ma) age conforms to a reworked cally and laterally throughout both assemblage highest sandstone-to-siltstone ratios commonly (youngest zircon at 256.8 ± 0.6 Ma; Gastaldo zone intervals (Gastaldo et al., 2017, 2018, are encountered where roadcuts (preferentially et al., 2018) that was recovered from the same 2019b). The Tweefontein transect along the exploited by many researchers) expose resistant­ relative stratigraphic interval reported ∼1.3 km escarpment demonstrates this pattern on a wider sandstone ledges. Laterally, though, these chan- to the northwest in the Old Lootsberg Pass sec- spatial scale. Color variation and mottling are a nel deposits pinch out and are replaced by tion (Fig. 19). These zircon dates are interpreted function of the localized effects of diagenetic siltstone-dominated lithologies, which supports as maxima for the time of deposition of each bed processes associated with changes in the posi- observations by Groenewald (1996, p. 20) that and assume that all dated grains in the Tweefon- tion of the water table (Li et al., 2017). Coeval the Katberg Formation exposures at Lootsberg tein1 sample are detrital or re-worked to some siltstones in the Tweefontein1, Tweefontein1.5, Pass exhibit a high siltstone content. This clearly extent. These two horizons act as one additional

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A D

E

B C

I G H

F J

Figure 16. Cube specimens and demagnetization diagrams are shown. (A–B) Images show open ceramic cubes with oriented (up and north-facing) fragments of hematitic mudstone before and after filling with non-magnetic alumina cement. (C–H) Orthogonal progressive demagnetization diagrams (Zijderveld, 1967) show the end point of the magnetization vector plotted onto the horizontal (filled symbols) and vertical (open symbols) planes (NS-EW, EW-up/down) for individual ceramic cube specimens collected at sites Tw2_2019_1,2,3 (Twee- fontein2 section) within 20 cm above and below the volcanic component rich claystone sampled for U-Pb zircon geochronology. The cube specimens have been subjected to progressive thermal demagnetization. Selected demagnetization steps are shown for data points in the vertical projection. Also shown are normalized intensity decay plots showing response to progressive thermal demagnetization and stereo- graphic projections of the magnetization vector measured at each step. (I–J) Equal area projection shows the directions of components of magnetization resolved (first-removed in I; second removed in J) in principal components analysis of the specimen data.

tie-point in the stratigraphic framework. Another of deposition, especially when they are used to consistent hint, albeit very poorly defined, of the tie point in the stratigraphic framework is in the estimate the age of the Permian–Triassic bound- presence of a south-directed magnetization of main Tweefontein2 section. Here, we report on ary (e.g., Marchetti et al., 2019; Botha et al., moderate positive inclination. This inferred pos- a maximum depositional age based on results 2020). Herein, we use such dates only to guide sible reverse polarity remanence is a small per- from four of the youngest zircon crystals, at and approximate our stratigraphic correlation. centage of the NRM and, again, not well defined 252.43 ± 0.19 Ma (Changhsingian; Fig. 12B), (Fig. 18; Fig. SI9; see footnote 1), in particular from a tuffaceous deposit. This horizon is at a Magnetic Polarity Stratigraphy when compared to data from horizons reported similar relative position as the horizon yield- from Old (West) Lootsberg Pass (Gastaldo et al., ing a Changhsingian age at Old Lootsberg Pass Our interpreted magnetic polarity stratigraphy 2018). To date, all demagnetization data from the (Gastaldo et al., 2015; Fig. 19). These circum- for the Tweefontein area (summarized in Figs. 9 Tweefontein2 section have yielded exclusively stances further support the importance of acquir- and 11) differs from that reported by Ward et al. normal polarity results, including those hori- ing dates for multiple beds in a given section to (2005), which is reportedly based on data from zons immediately below and above the claystone demonstrate adherence to stratigraphic superpo- two nearby Lootsberg Pass sections as noted horizon that has yielded U-Pb zircon age data sition (Bowring and Schmitz, 2003; Eberth and above. Demagnetization data from most beds (Fig. 16). Results from other localities sampled Kamo, 2019; Rasmussen et al., 2021). We cau- (specific sites) at the Tweefontein1 section show (e.g., a resampling of Old Lootsberg Pass: tion against the use of maximum depositional them to be dominated by normal polarity. Only Gastaldo et al., 2015, 2018; Bethulie: Gastaldo dates from single zircon grains as the true time two beds (Tw1_19 and Tw1_20) exhibit a semi- et al., 2019a; Nooitgedacht: Gastaldo et al.,

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Figure 17. Equal area pro- jections show estimated site mean directions for those sites (N = 45) from the Tweefontein1 and Tweefontein2 (TWFTN) sections where specimens from a sufficient number of inde- pendent samples have been subjected to progressive de- magnetization and have yielded interpretable demagnetization A B C results and are accepted on the basis of within-site directional dispersion (see Table 2). (A) Projection shows just estimated site mean directions and overall “grand” mean direction (larger gray circle); (B) same but with projected cones of 95% confi- D E F G H dence (a95 – radii) about each estimated site mean direction and the “grand” mean direc- tion (larger gray circle). (C) I Distribution of virtual geo- magnetic poles (VGPs) about a centered mean pole position J with the cone of 95% confi- dence level, the Deenen et al. (2011) criteria cone, and the cutoff cone. (D–H) Examples of sample directions from se- lected individual sites with es- timated mean directions and cones of 95% confidence. In all of these projections, open (filled) symbols represent up- per (lower) hemisphere projec- tions. (I) Southern hemisphere projection shows the position of the paleomagnetic pole (and associated confidence ellipse) obtained in this study (green square with A95 oval in green) based on the estimated grand mean direction from VGPs for a total of 45 accepted sites from the Tweefontein sections (Ta- ble 2). This estimated pole is in southern Africa coordinates and is compared with the Southern Africa coordinates global apparent polar wander path (GAPWaP; solid dark gray line with selected running mean poles, with A95 ovals, at 10 Ma intervals) corrected for inclina- tion shallowing of results from sedimentary rocks, by Torsvik et al. (2012) (see text and Table 2; modified from Torsvik et al., 2012, their fig. 13C). Dashed line is the global spline path from Torsvik et al. (2012; their fig. 13C). (J) Same; southern hemisphere projection shows the position of the paleomagnetic pole obtained in this study based on the data from the Tweefontein sections, assuming the preservation of primary or near-primary magnetizations; pole is rotated into West Africa coordinates to compare with the apparent polar wander path shown by Sciscio et al. (2017) along with paleomagnetic data from Upper Triassic to Lower Jurassic sedimentary rocks from the Karoo Basin, as reported by Sciscio et al. (2017) (see text and Table 2; modified from Sciscio et al., 2017).

2020a) are interpreted to indicate that the normal tion of the remanence, the ChRM persists up to magnetization associated with Early Jurassic polarity ChRM typically persists up to ∼580 °C ∼680 °C. The principal component of the NRM Karoo magmatism (and possibly even younger in thermal demagnetization and, for some hori- in these rocks is likely a composite of a lower events), and an earlier acquired remanence. At zons where hematite carries a substantial frac- laboratory unblocking temperature, secondary some Old Lootsberg Pass sites, as well as several

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sites at the Bethel Farm (Free State Province) stratigraphic framework for the area, geochro- (2012) are also based on composites from a locality, this normal polarity overprint magneti- nometric constraints, and an even more rigorous number of sources. Gastaldo et al. (2018), in zation is demonstrated to be fully unblocked by sampling program for magnetic polarity strati- conjunction with temporal constraints from laboratory unblocking temperatures of ∼450 °C graphic information in that context, one could a U-Pb CA-ID-TIMS age from a porcellanite or less, and a south-directed, moderate positive arrive at two very different interpretations of (253.48 ± 0.15 Ma, 2σ error; MSWD = 0.47), inclination remanence (interpreted as reverse how much time is represented in the succession. as discussed above, placed deposition of these polarity) is sufficiently well-isolated at higher Strata sampled at Tweefontein2 yield normal Karoo Basin rocks in the earliest quarter of the temperatures (Gastaldo et al., 2015, 2018). We polarity magnetizations that persist well above Changhsingian stage (254.14–251.902 Ma), interpret the reverse polarity magnetizations as 450 °C in demagnetization and indicate, at least a time interval dominated by normal polarity. early acquired, likely primary magnetizations, based on our sampling strategy and currently New U-Pb CA-ID-TIMS zircon dates recovered and show that they can be isolated at tempera- available data, the presence of one long, and from other beds in the stratigraphic framework tures above ∼450 °C depending on the char- likely uninterrupted, normal polarity magne- (Figs. 19–20) help to support a maximum age acter of the rocks containing this remanence. tozone. Applying the traditional model for the limit for these rocks. This observation is consistent with the results end-Permian crisis to this terrestrial pattern, in reported and interpreted by Tohver et al. (2015) the absence of geochronometric constraints, Palynostratigraphy and Lanci et al. (2013) from lower Beaufort would easily allow for an interpretation that the Group strata in the westernmost Cape Province, stratigraphic record was continuous (e.g., Ward Two palynological biozone schemes are which were sampled in an area that is largely et al., 2005; Smith and Botha-Brink, 2014; proposed for the Karoo Basin and surrounding removed from any major exposures of Early Botha et al., 2020). In addition, any paleonto- basins over the past 25 years. Aitken (1998) Jurassic Karoo LIP intrusions. Thus, based on logical change could be equated to the marine described 10 zones based on palynological the available demagnetization data, we interpret extinction, which, based on magnetic polarity assemblages from the northeastern part of the that the Tweefontein1 section possibly contains a data from the Meishan section in SW China, Karoo Basin, specifically from the Vryheid, thin reverse-polarity magnetozone, sandwiched is thought to have occurred within a normal Volksrust (), and Normandien For- between underlying and overlying normal polar- polarity chron of ca. 700 ka duration (Li and mations (Beaufort Group). Aitkin’s upper five ity magnetozones, but its presence is poorly Wang, 1989; Yin et al., 2001, Zhao et al., 2007; biozones (VI–X) were largely based on samples defined. Such a reverse polarity magnetozone Szurlies, 2013). In contrast, the identification of from the borehole PA106, Lindley, Free State may exist within the Tweefontein2 section, but it two reverse polarity magnetozones of unknown Province. These zones were characterized by either has yet to be identified in laboratory analy- duration, as a consequence of landscape degra- concurrent range zones of two taxa and were sis, may simply not have been sampled, or may dation, situated between three normal polarity not always defined by the presence of certain be missing from the sedimentary record as a con- intervals in the Old Lootsberg Pass section and taxa with a last appearance datum (LAD) or first sequence of erosion. Regardless, successions in the possible presence of a short reverse polarity appearance datum (FAD). Rather, zones were both sections represent a time interval dominated interval at Tweefontein1, provides a plausible characterized by overlap and relative abundance by normal polarity chrons. This differs from our means to correlate these sections to proposed of the particular taxa. Aitken (1998) counted his data at Old Lootsberg Pass, more than 1.5 km to global magnetic polarity time scales for this samples quantitatively and, although the changes the northwest, where we have presented a refined interval of time (Hounslow and Muttoni, 2010; in relative abundance of major pollen-and-spore magnetostratigraphy for the area. Ogg, 2012; Henderson et al., 2012; Szurlies, categories show a clear change in dominance Two very short siltstone intervals yielding 2013; Hounslow and Balabanov, 2016). We from striate to trilete and disacciatriletes, two results that are interpreted to define magne- note, though, that the magnetic polarity time thick intervals in the core were unproductive tozones of reverse polarity have been identified scales referenced here differ in their place- (between biozones VII–VIII and IX–X). Unfor- at Old Lootsberg Pass (Gastaldo et al., 2015, ment of the Permian–Triassic boundary in the tunately, the three sources of information in Ait- 2018; Fig. 19). Both intervals are less than a few chron record and in their approach to develop ken’s (1998) thesis—biozone taxa, range charts, meters thick and directly underlie an erosional each polarity time scale. Hounslow and Mut- and zone presence accompanying the taxon contact with a thick sandstone channel body, in toni (2010) and Hounslow and Balabanov description—sometimes produce contradictory which intraformational PNC lag deposits occur. (2016) place the Permian–Triassic boundary information. Range charts indicate a termination This lithostratigraphic relationship indicates the at the very base of a ca. 700 ka duration chron of five out of sevenProtohaploxypinus and Stri- scale of missing section represented by a signifi- of entirely or almost entirely normal polarity. atopodocarpites (Glossopteris-associated) taxa cant diastem of possibly 1 Ma duration based on These two estimates of the magnetic polarity going from biozone VII to VIII but, at the same the physical relationships of our age constraints time scale represent a composite of a number time, the number of taxa recorded in the higher (Fig. 20). The diastem is in close association of magnetic polarity stratigraphic sections from biozones also declines. For example, there are with landscape degradation where fluvial and numerous localities, some of which have more declines of 38, 18, and nine taxa, respectively, interfluvial deposits were eroded in response to a robust age control than others. In contrast, Ogg for biozones VIII, IX, and X, while more than change in fluvial gradient (Gastaldo and Demko, (2012), Henderson et al. (2012), and Szurlies 10 samples were counted per biozone. This sug- 2011). During the latter, fine-grained detritus (2013) place the Permian–Induan boundary, and gests that the preservation in these rocks is much was transported farther into the basin, whereas the span of marine extinction events, within a poorer than that in the richer lower biozones. the coarsest fraction (mudclast aggregates comparable ca. 700 ka duration normal polar- The most recently published palynological [Gastaldo et al., 2013], pedogenic nodules [Pace ity chron. The magnetic polarity time scale of biozone scheme for the Karoo Basin is by Bar- et al., 2009; Gastaldo et al., 2020b], and bone Szurlies (2013) is based on data from the largely bolini et al. (2018). They combined data from [Gastaldo et al., 2017]) were retained locally non-marine Germanic Basin and has complete previous studies from the western, southern, and as a function of fluvial competence rather than stratigraphic superposition. The period-level northeastern part of the Karoo Basin with new capacity. Hence, without the development of a time scales of Ogg (2012) and Henderson et al. data from roadcuts and outcrops. These authors

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Figure 18. Examples of paleomagnetic data from sites Tw1_19 and Tw1_20 are shown, which tisporites noviaulensis and Protohaploxypinus provide a suggestion of the preservation of a reverse polarity (southeast-seeking, moderate microcorpus) and both simple and cavate spores, positive inclination) magnetization. Orthogonal progressive demagnetization diagrams (A–D; respectively, represent increased dominance of Zijderveld, 1967) show the end point of the magnetization vector plotted onto the horizon- other gymnosperm taxa, ferns, and lycopods. tal (filled symbols) and vertical (open symbols) planes (NS-EW, EW-up/down) for individual More recently, and based on well-dated mate- specimens from independent samples from site Tw1_19 (Tweefontein1 section) that have been rial from the Sydney Basin, the start of a major subjected to progressive thermal demagnetization. Selected demagnetization steps are shown compositional floral change was demonstrated for data points in the vertical projection. Also illustrated are normalized intensity decay plots to have occurred at the transition between the showing response to progressive treatment and stereographic projections of the magnetization Australian Dulhuntyispora parvithola and the vector measured at each step. (E–F) Equal area projections of paleomagnetic data from Site Playfordiaspora crenulata zones (Fielding et al., Tw1_19; (E) show first-removed vectors; (F) show higher laboratory unblocking temperature 2019; Vajda et al., 2020; Mays et al., 2020). magnetizations along with projected maximum angular deviation (MAD values) for each speci- These data contrast with a previous interpreta- men result. (G) Same as (A–D) but for specimens from independent samples from site Tw1_20 tion that indicated a floral turnover from the P. (Tweefontein1 section). (J–L) Equal area projections summarize demagnetization results. (J) crenulata zone to the overlying P. microcorpus Directions of linear segments and projected maximum angular deviations for each specimen zone (or, if the indicator taxon P. crenulata is result with large circle as the estimated mean direction of the population; open (closed) sym- missing, in the basal part of the P. microcorpus bols represent projections on the upper (lower) hemisphere. (K) Great circles (dashed on up- zone). Hence, the palynological assemblage per hemisphere) defined by demagnetization trajectories for some of the specimens from site recovered from Tweefontein1 (Fig. 10) and the Tw1_20 show estimated mean normal to the great circles and confidence limit. (L) Combination assemblage reported from Old Lootsberg Pass of linear segments and great circles show locations of end points along great circle trajectories. (Gastaldo et al., 2017) now are assigned to the Further details in Figure SI9 (see footnote 1). NRM—natural remanent magnetization. Dulhuntyispora parvithola zone. And a conse- quence of these new findings is that the paly- nological assemblages that we described from describe 11 biozones that cover the same strati- the uppermost Daptocephalus AZ or in the basal the Wapadsberg section (Prevec et al., 2010), graphic interval as Aitken’s. Barbolini et al. part of the overlying assemblage zone (Gastaldo also in the Eastern Cape Province and ∼13 km (2018) established a latest Permian palynozona- et al., 2020a). Hence, we have not incorporated to the southeast, would now more appropriately tion using indicator taxa to separate the Dapto- this palynostratigraphic nomenclature into our be correlated to the D. parvithola zone of lat- cephalus AZ of the Palingkloof Member from interpretations. Both studies confirm what we est Permian age. That assemblage originally underlying Elandsberg and Barberskrans (now have experienced over the years. First, it is dif- was correlated to the basal part of the Australian Ripplemead) members. This uppermost paly- ficult to find productive samples from strata that P. microcorpus zone. nozone (then considered to be latest Permian) are presumed to be of latest Permian age; as a was based on only two productive sample sites result, it is not feasible to produce a high-resolu- Vertebrates and Correlative Stratigraphic (Barbolini, 2014, table 3.1) and data from Ait- tion record of the Late Permian floral turnover. Patterns ken’s (1998) PA106 core. These data were used Second, few of the sections in the Karoo Basin to establish the Dictyophyllidites mortonii Inter- provide numerical age data. Because of these The ability to physically trace bounding val Zone (Barbolini et al., 2018). The authors limitations, we continue to rely on correlation surfaces of major sandstone bodies across the indicate that both localities originate from the of our palynological assemblages to the revised escarpment from Old Lootsberg Pass to Loots- transition from the Daptocephalus to the L. Australian palynozonation using overall species berg Pass, along the valley floor exposures of declivis AZs and equate this turnover to the end- associations and the relative abundance of major the Elandsberg Member and to the flanks of Permian extinction event. Gastaldo et al. (2019a, pollen-and-spore groups. the mountainside where the Katberg Formation their supplemental information) detail efforts to The Australian Basins are one of the few crops out (Fig. 4; Gastaldo et al., 2018), pro- recover palynomorphs from these sediments, regions in Gondwana where Lopingian to Early vides the opportunity to correlate the Tweefon- only one of which was found to be productive. Triassic age palynostratigraphic biozones have tein stratigraphic sections and place the reported The one productive palynological assemblage been calibrated against both marine invertebrate vertebrate records into chronostratigraphic, comes from a thin heterolithic interval on Don- zones and U–Pb zircon dates. These pollen- magnetostratigraphic, and palynostratigraphic ald 207 (Fairydale) Farm (Gastaldo et al., 2019a; and-spore biozones are mostly based on first, or context (Fig. 19). The stratigraphic position of GPS coordinates are S30° 24.416ˊ, E026° consistent, occurrence of indicator taxa in the vertebrates, based on GPS coordinates of col- 14.261ˊ in Barbolini, 2014, p. 103, table 3.1). western and eastern Australian basins (Metcalfe lection sites documented by Smith and Botha- Barbolini et al. (2018) indicate that the locality et al., 2015; Laurie et al., 2016). Palynological Brink (2014) and incorporated by Viglietti represents the transition across the Permian– records in both regions show a floral transition et al. (2016) into their Daptocephalus AZ, are Triassic boundary. All vertebrates reported from from diverse assemblages characterized by mul- reported to be of high resolution when compared Donald 207 (Fairydale) Farm are assigned to the titaeniate bisaccate pollen to those dominated to collections made prior to 1976. These older L. declivis AZ by Smith and Botha-Brink (2014; by algal remains with low amounts of other collections appear in catalogues only as farm their supplemental table) and are not coincident multitaeniate bisaccate and alete non-taeniate names or, at best, as estimated coordinates, at with the reported vertebrate boundary on the bisaccate pollen as well as cavate spores. This which specimens were recovered and identified adjacent Bethel Farm locality, which is >50 m suggests the decline in diversity and abundance as “farm centroids” (van der Walt et al., 2010, lower in the section. There was no question of glossopterids that produced multitaeniate 2015). Such records have been omitted in recent that the palynomorph assemblage reported by bisaccates Protohaploxypinus and Striatopodo- analyses due to the inherent vagaries (Viglietti Gastaldo et al. (2019a) originates from high in carpites was stepwise, while non-glossopterid et al., 2016). Biostratigraphic patterns and con- the L. declivis AZ and did not originate either in taeniate forms (e.g., Lueckisporites, Luna- clusions about extinction and diversification

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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. ). Fig. 4 AZ in olive- in AZ Daptocephalus ) at Old Lootsberg Pass (Gastaldo et Pass ) at Old Lootsberg al., 2018) to ) their assemblage zone boundary (and equated by these ) their assemblage zone boundary (and equated by these + Fig. 3 AZ in reddish-gray siltstone (right). Taxa of both assemblages of both assemblages Taxa (right). siltstone reddish-gray AZ in using laterally continuous and traceable sandstone bodies as datums ( 2 Lystrosaurus declivis Lystrosaurus and Tweefontein 1.5 (Gastaldo et al., 2017) and further southeast to Tweefontein 2017) and further southeast to (Gastaldo et al., 1 Figure 19. Stratigraphic framework of measured sections beginning in the northwest of the escarpment ( sections beginning in the northwest of escarpment of measured 19. Stratigraphic framework Figure Tweefontein taxa used by Smith and Botha-Brink adjacent to sampled sections. Collection sites of vertebrate for shown are results Magnetostratigraphic and chronostratigraphic ( (–) or above stratigraphic position in meters below et al. (2016) along with their reported Viglietti (2014) and upper the of diagnostic and characteristic Vertebrates boxes. in shown are boundary) Permian–Triassic terrestrial the to others, and authors, the contemporaneous with taxa deemed characteristic of were gray siltstone (left) defined. See as currently the biozone boundary, position for lower This necessitates a new, zones coexisted in an early Changhsingian, glossopterid-dominated landscape. details and discussion. text for

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Figure 20. Simplified illustra- Botha et al., 2020) near Tweefontein1 (AM4757; tion shows the relationship be- Gastaldo et al., 2017). The Daptocephalus AZ tween Daptocephalus AZ (DAZ) fauna extends even higher at Tweefontein1, and Lystrosaurus declivis AZ where a skull cf. Dicynodon leontocephalus (LAZ) diagnostic taxa, siltstone (Gastaldo et al., 2017) occurs at nearly the same color, magnetostratigraphic stratigraphic horizon as L. declivis (SAM-K- and chronostratigraphic con- 10583) and L. murrayi (RS90) from Tweefon- text, and palynozone from tein2 where both taxa are diagnostic of the L. northwest (Blaauwater Farm) declivis AZ (Botha and Smith, 2007; Botha and to southeast (Tweefontein2). Smith, 2020). Extending the correlation north- Note that we have found no evi- west to Old Lootsberg Pass (Gastaldo et al., dence for either reverse polarity 2017, 2018) does not change the relationships chron identified at Old Loots- between these vertebrate taxa; if anything, the berg Pass (Gastaldo et al., 2018) degree of biozone overlap increases. We reiter- toward the southeast, which is ate that there is no evidence of faulting along the the result of landscape degrada- escarpment that could have resulted in displaced tion through erosion (Gastaldo strata (Fig. 4). and Demko, 2011) and rework- Together with the degree of biostratigraphic ing and transport of these sediments to another part of the basin. See text for implications. overlap, which has also been reported at Bethel (Gastaldo et al., 2019a) and Wapadsberg Pass drawn by workers since rely on more accurate measured section at Tweefontein1. Five speci- (Neveling et al., 2016a; Gastaldo et al., 2020b), locality data with GPS coordinates that allow mens were collected from exposures in, or in these spatial relationships of vertebrate taxa placement of vertebrate fossils into measured very close proximity to, our measured sections along the Lootsberg Pass escarpment represent stratigraphic sections (Viglietti et al., 2016). It at Tweefontein2 assigned to the upper Palingkloof strong evidence of faunal co-occurrence. The is on this data set that a three-phased extinction Member and overlying Katberg Formation. All only difference between these collection sites pattern, based on a narrow interval displaying these vertebrate records have been correlated is siltstone color; olive gray dominates the sec- a sharp turnover from the Daptocephalus to physically into our stratigraphic framework. One tions at Tweefontein1 (colors commonly asso- the L. declivis AZ faunas (Smith and Botha- specimen, RS17 (Tweefontein1; Fig. 19), was ciated with the Daptocephalus AZ; e.g., Smith Brink, 2014, their fig. 12; Botha et al., 2020, used by Viglietti et al. (2016, their supplemental and Botha-Brink, 2014) and reddish gray domi- their fig. 9), was proposed. It is this pattern that data) as part of the data set on which the Upper nates the lithostratigraphy at Tweefontein2 (col- has been widely accepted as the end-Permian Daptocephalus AZ was established. The FAD of ors associated with the L. declivis AZ). These event across the vertebrate-biozone boundary two taxa, Lystrosaurus murrayi and L. declivis, relationships are depicted in a simplified panel (e.g., Ward et al., 2005; Smith and Botha-Brink, are used to define the base of the overlyingLys - diagram (Fig. 20), which illustrates that diag- 2014; Botha et al., 2020; Smith et al., 2020). trosaurus AZ and are considered to be recovery nostic taxa of the upper Daptocephalus AZ taxa And, although ∼86% of the database on which faunal elements (Smith and Botha, 2005; Botha (Viglietti, 2020) were coeval with diagnostic taxa Smith and Botha-Brink (2014) developed their and Smith, 2007, 2020; Smith and Botha-Brink, of the L. declivis AZ (Botha and Smith, 2020). extinction model was collected only on three 2014; Botha et al., 2020). Therefore, we con- Both assemblage zones are of early Changhsin- adjacent farms—Bethel, Heldemoed, and Don- sider the stratigraphic positions of these 10 gian age and both assemblages existed in a glos- ald 207 (Fairydale; Gastaldo et al., 2019a)—and specimens relative to each other as accurate in sopterid landscape (see above). Our data indicate the Tussen-Die-Riviere game reserve in the Free the following analysis, with some acknowledged that the proposed assemblage zone boundary at State Province, the distribution of taxa assigned variance (±5 m stratigraphically) due to poten- Lootsberg Pass (Fig. 4, white arrow; Retallack to either the Daptocephalus or L. declivis AZs tial problems associated with GPS replication et al., 2003), considered by many to represent along the escarpment in the Eastern Cape Prov- (see Gastaldo et al., 2019a, their supplemental the terrestrial expression of the Permian–Trias- ince can be used to further test the extinction ­information for a thorough discussion of South sic boundary and used as a correlation datum model (see Gastaldo et al., 2019a, for a similar African coordinate system usage). across the basin (e.g., Ward et al., 2005; Smith test on the Free State Province records). When the reported sites of Daptocephalus and Botha-Brink, 2014; Botha et al., 2020), lies Keyser and Smith (1978, p. 30) designated and L. declivis AZ taxa are placed into our strati- significantly below the position reported by the succession at Lootsberg Pass as the strato- graphic framework, discordant and inexplicable Ward et al. (2000, 2005), as field checked and type for their Lystrosaurus AZ (now L. declivis relationships appear (Fig. 19). For example, the documented by Gastaldo et al. (2009, 2018), at AZ) which, in turn, is the basis for the Lootsber- remains at Tweefontein2 of a Moschorhinus Old Lootsberg Pass. The stratigraphic position gian land-vertebrate faunachron (Lucas, 2010). (SAM-K-K10698), a therocephalian of this reported “event bed” (Smith and Ward, Thirty-one vertebrates are reported from the gen- that is one of only four genera considered to 2001; Retallack et al., 2003) is early Changhs- eral area (Old Lootsberg Pass [N = 14], Twee- span the biozone boundary (Smith et al., 2020), ingian and, applying this criterion in association fontein [N = 8], and Lootsberg Pass [N = 9]; previously was assigned by Smith and Botha- with the reported vertebrate biostratigraphic Smith and Botha-Brink, 2014, their supplemen- Brink (2014) to the L. declivis AZ (Fig. 20). Yet, boundary at each classic locality, demonstrates tal data; Fig. 19). Five specimens were collected it overlaps specimens of Dicynodon lacerticeps that the vertebrate-defined PTB occurs in differ- from pavement exposures and assigned (based (=Daptocephalus leoniceps RS16) and Lystro- ent magnetozones in different stratigraphic posi- on current criteria) to the Elandsberg and Pal- saurus maccaigi (RS81), and both taxa are diag- tions in the D. parvithola palynozone (Fig. 21). ingkloof Members (Balfour Formation) in the nostic of the upper Daptocephalus AZ (Smith In summary, when vertebrate collections low relief fields< 0.9 km from our primary and Botha-Brink, 2014; Viglietti et al., 2016; in the area of Lootsberg Pass are placed into

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Figure 21. Proposed correlation of Eastern Cape Province (Tweefontein, Blaauwater) and Free State (Bethel, Nooitgedacht) localities through extrapolation of the magnetostratigraphic, chronostratigraphic, and palynostratigraphic data following Gastaldo et al. (2019a, 2020a). We use current vertebrate assemblage zone terminology as applied at these localities and note that these concepts require reevaluation and redefinition based on our current and previous findings. Diagnostic taxa of both the DAZ and LAZ were parts of a glossopterid-dominated landscape (Dulhuntyispora parvithola palynozone) beginning in the early Changhsingian (253.48 Ma) and continuing into the latest Changhs- ingian (Gastaldo et al., 2019a, 2020a). The effect of the floral change on vertebrate biodiversity to the Playfordiaspora crenulata palynozone in the latest Changhsingian remains unknown due to a paucity of accurate collection site records placed into high-resolution stratigraphies con- strained by either magnetic polarity or reliable geochronometric data. The distance from Old Lootsberg Pass to Bethel/Donald 207 is 200 km to the northeast; the distance from Bethel/Donald 207 to Nooitgedacht is ∼33 km to the west-northwest. The Australian palynozones in their geochronometric contexts are shown (Dulhuntyspora parvithola in green; Playfordiaspora crenulata in yellow; Protohaploxypinus microcorpus in pink) and used as the biostratigraphic basis for correlation with Karoo palynological assemblages reported herein.

a lithostratigraphic framework constrained by Gastaldo et al., 2015, 2017). These findings model is the presence of a “unique” heterolithic­ chrono- and magnetostratigraphy (Figs. 19– also highlight the risks and limitations of using interval that has been used as the criterion to sep- 20), there appears to be no criterion on which lithostratigraphic data to constrain a biostrati- arate the underlying Daptocephalus AZ from the to distinctly separate either the Daptocephalus graphic horizon (Smith and Botha, 2005; Smith overlying L. declivis AZ (Smith and Ward, 2001; (Viglietti, 2020) or L. declivis (Botha and Smith, and Botha-Brink, 2014; Botha et al., 2020) in Retallack et al., 2003; Ward et al., 2005; Smith 2020) AZ. Vertebrates that have been assigned a basinal setting that is characterized by grada- and Botha-Brink, 2014; Botha et al., 2020). This to a latest “Permian” age at Tweefontein1 come tional lithostratigraphic boundaries. interlaminated bed of olive-gray and reddish- from a stratigraphic section dominated by gray sandstone/siltstone, of a few meters in thick- ­olive-gray mudrock whereas those taxa collected Changhsingian Karoo Assemblage Zones in ness, is reportedly isochronous. It is interpreted at Tweefontein2 localities, assigned an earliest Space and Time as a playa-lake deposit and used for correlation “Triassic” age, come from equivalent strati- purposes across the Karoo Basin (Ward et al., graphic horizons dominated by reddish-gray To date, two different approaches have been 2000; Smith and Botha-Brink, 2014). In con- siltstone and sandstone. The ­overlap between employed to recognize the boundary between trast, physical and geochemical evidence indi- assemblage zone taxa is amplified when con- the Daptocephalus and L. declivis AZs as it is cates that the bed is neither a playa-lake deposit sidering their occurrence in Old Lootsberg Pass. currently defined (Rubidge, 1995; Botha and nor does it occur at a single stratigraphic horizon There is no definitive level at which one assem- Smith, 2007, 2020; Smith and Botha-Brink, in the Bethel Farm section where it is typified blage replaces another and results in a biostrati- 2014; Botha et al., 2020; Viglietti, 2020). These and to which other Karoo sections are correlated graphic pastiche. It is not our intention, here, to approaches control how stratigraphic sections (Neveling et al., 2016b; Gastaldo et al., 2009, redefine either the vertebrate assemblage zone are interpreted and related in space and time. The 2019b). The heterolithic facies is neither unique or the biozone boundary (Fig. 21), which would first is based solely on a lithofacies approach. nor does it occur as a singleton at one specific necessarily require a thorough re-evaluation The second utilizes a multidisciplinary approach stratigraphic horizon in the basin. Although these of the vertebrate fossil record, with accurate, combining lithostratigraphic frameworks, geo- facts are acknowledged by Ward et al. (2012), the high-precision collection sites placed into a chronology, magnetostratigraphy, and paly- “event bed” concept continues to be applied as a stratigraphic framework developed at each col- nostratigraphy. correlation datum from sections in the Free State lection locality and correlated using a multidis- In the lithofacies approach, the stratigraphy Province to those in the Eastern Cape Province, ciplinary approach (see below). We note that the spanning the biozone boundary is presumed a distance of >200 km (Smith and Botha-Brink, recent published biostratigraphic nomenclature to exhibit a characteristic facies sequence (i.e., 2014; Botha et al., 2020). And, given that this (Botha and Smith, 2020) necessitates a lower facies A–E; Smith and Botha-Brink, 2014; Botha “unique” lithofacies at Lootsberg Pass (e.g., position for the biozone contact than previously et al., 2020) that reportedly corresponds with Retallack et al., 2003, their fig. 3A) is located at was assumed (Smith and Botha-Brink, 2014; biostratigraphic trends. A key component of this an elevation below our stratigraphic framework

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(Fig. 4, white arrow) and is likely early Chang- cranial material assignable to either a Dicyn- dacht lies in a normal polarity magnetozone hsingian (Fig. 19) rather than latest Permian, odon, Daptocephalus, or L. maccaigi skull) into (Gastaldo et al., 2020a). Botha et al. (2020) its usefulness as a correlation datum should be an intraformational conglomerate lag deposit at report the presence of Glossopteris and sphenop- abandoned. Old Lootsberg Pass (datum sandstone; Fig. 19). sid megafloral elements, similar to those reported Botha et al. (2020) presented results of LA- This position overlies the higher, short reverse by Prevec et al. (2010) and Gastaldo et al. (2014, ICP-MS analyses on suites of detrital zircon polarity chron on Blaauwater Farm (Gastaldo 2017), in rocks ∼17–20 m below the pristine grains from two measured sections on Farm et al., 2017). We note, however, that Botha et al. volcanic ash deposit in the upper Daptocephalus Nooitgedacht in the Free State Province. Here, (2020, their table 1) recently extended upwards AZ. We identify a palynoflora assignable to the four major Paleozoic modal ages, three of the stratigraphic range of L. maccaigi, a diag- D. parvithola biozone from a heterolithic unit which are Cambro- and one that is nostic taxon of the Daptocephalus AZ (Viglietti, immediately overlying the thin ash bed. Both the late Paleozoic to earliest Mesozoic, were identi- 2020), overlapping the basal elements of the L. ash and palynological assemblage occur ∼16 m fied. The largest modal peak appears to be latest declivis AZ at Nooitgedacht. This upsection above the biozone contact as defined in previ- Permian with all dates reported with uncertain- shift of the taxon’s range removes one criterion ous work at Farm Nooitgedacht (Botha-Brink ties of several million years. A U-Pb TIMS age that is used to constrain the purportedly sharp et al., 2014; for reasons of uncertainty about the of 251.7 ± 0.3 Ma, based on five detrital zir- terrestrial extinction of Smith and Botha-Brink biozone position, see Gastaldo et al., 2020a). cons, also is reported (Botha et al., 2020, their (2014). Glossopteris megafossils and palyno- This relationship demonstrates the continued table 2), but no U-Pb data are presented either in logic assemblages assigned to the D. parvithola presence of glossopterid vegetation in the over- the text or supplemental data. Therefore, we only biozone of middle to Late Permian age are pre- lying normal polarity magnetozone and extend- can note that their earliest Triassic detrital zircon served in coeval deposits at Old Lootsberg Pass. ing into the basal L. declivis AZ at Nooitgedacht, maximum age for the upper Daptocephalus AZ Here, megafloral elements extend into the over- similar to what has been reported on Blaauwater potentially postdates the end-Permian event in lying normal polarity chron that has been con- Farm (Gastaldo et al., 2015, 2017, 2018). A paly- the oceans (251.941–250.880 Ma; Burgess et al., sidered to be in the basal part of the L. declivis nological assemblage assigned to the Playfordia- 2014) and may indicate little effect on the ter- AZ, as currently defined (Gastaldo et al., 2015, pora crenulata biozone occurs ∼10 m higher at restrial biota if true. In contrast, a latest Chang- 2017, 2020c). A similar magnetostratigraphic Nooitgedacht above an erosional contact with an hsingian U-Pb age of 252.24 ± 0.15 (2σ) Ma, and vertebrate relationship has been reported intraformational, conglomerate-bearing sand- based on 13 overlapping zircon results obtained from Bethel Farm, which is some 200 km away stone body (Fig. 21). This palynological pattern, by CA-ID-TIMS methods for the base of the L. to the north-northeast in the Free State Province. constrained by geochronology and magneto- declivis AZ, as currently recognized (see above), The presence of a reverse polarity magne- stratigraphy, parallels that reported in Australia, has been documented from a pristine volcanic tozone of undetermined thickness on the Bethel albeit the turnover in vegetation may be slightly ash deposit at the same Nooitgedacht locality in Farm, which is considered to be the golden spike younger in South Africa. lithostratigraphic and magnetostratigraphic con- for the end-Permian vertebrate record (Smith and In summary, vertebrate taxa currently assigned text (Gastaldo et al., 2020a). This discrepancy Botha-Brink, 2014), was first reported by Nevel- to either the Daptocephalus or L. declivis AZs between age estimates from a pristine volcanic ing et al. (2016a). Subsequently, further analy- were coeval on early Changhsingian landscapes ash deposit and a detrital and, ses refined the stratigraphic extent of the reverse possibly as early as 252.43 Ma (Figs. 19–21). hence, a maximum depositional age, reinforces polarity magnetozone and indicated that the There is no evidence that the L. declivis AZ the problem identified by numerous work- magnetozone could be traced across three mea- replaced the upper Daptocephalus AZ strati- ers with using the latter approach to constrain sured sections that encompass more than 20 m graphically. Second, these landscapes were vege- time (e.g., Ibañez-Mejia et al., 2018; Andersen of stratigraphy in the interval reported to transi- tated, at times, by glossopterid-dominated forests et al., 2019; Rasmussen et al., 2021). Our age tion from the currently definedDaptocephalus to (Gastaldo et al., 2014, 2019a) and, during cooler constraint at Nooitgedacht, in conjunction with L. declivis AZ (Fig. 21; Gastaldo et al., 2019a). and drier times when calcic Vertisols developed data presented herein, provides a means for cor- Leaves of Glossopteris are preserved in these (Gastaldo et al., 2020b), other gymnosperm relation in the Karoo Basin using the second transitional rocks (Gastaldo et al., 2005), above groups previously considered characteristic of approach (Fig. 21). which a normal polarity chron characterizes the the Early Triassic were more common (Gastaldo Our maximum depositional age of 253.48 Ma basal part of the L. declivis AZ at this locality et al., 2018). Third, these coeval taxa persisted for from a porcellanite at Old Lootsberg Pass in the (Gastaldo et al., 2019a, 2019b). One palynologic a time interval of likely 100 k.y. or more before Daptocephalus AZ is located in a normal polar- assemblage assigned to the Protohaploxypinus the stratigraphic disappearance of Daptocepha- ity magnetozone, the base of which is undefined microcorpus zone of latest Permian age, which lus and other genera currently considered as (the section continues downwards for at least postdates the disappearance of Glossopteris in restricted to the Daptocephalus AZ (e.g., Smith 50 m, all of which is of normal polarity, into the Australia (Mays et al., 2020; Vajda et al., 2020), and Botha-Brink, 2014; Viglietti et al., 2016; subsurface). This normal polarity magnetozone is preserved higher in the L. declivis AZ on the Botha et al., 2020). If the absence of Daptoceph- is overlain by a reverse polarity magnetozone of Donald 207 (Fairydale) Farm (Gastaldo et al., alus AZ taxa higher in the stratigraphy is not unknowable original thickness and, thus, dura- 2019a, 2019b). To date, we have been unable to due to either sampling bias (Marshall, 2005) or tion (see above for reasons; Gastaldo et al., 2015, locate any volcanic deposit or reworked tuffite in misinterpretation of their original collection sites 2018). This geochronometric and magnetostrati- the sections in this area. However, a latest Perm- (see Gastaldo et al., 2019a; Gastaldo and Nevel- graphic relationship is consistent with the global ian U-Pb date from a thin volcanic ash deposit in ing, 2020), the timing of their last occurrence is geomagnetic polarity time scales proposed by magnetostratigraphic and palynological context somewhere high in the D. parvithola or possibly Ogg (2012), Henderson et al. (2012), Szurlies that lies ∼33 km to the northwest on Farm Nooit- P. crenulata palynozone. Nonetheless, there is no (2013), and Hounslow and Balabanov (2016; gedacht forms the basis for further correlation. evidence for the evolutionary first appearance of Fig. 21). The LAD of Daptocephalus AZ taxa The stratigraphic interval yielding a latest the diagnostic taxa identified as part of a terres- could be extended (based on the occurrence of Permian date of 252.24 ± 0.15 Ma at Nooitge- trial “recovery” (Botha and Smith, 2006) higher

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in the section. Rather, at least several “recovery” both of which are interpreted as reworked. These Province (Old Lootsberg Pass, Tweefontein, taxa were present in the early Changhsingian two detrital ages in reworked channel deposits Lootsberg Pass) and the Free State Province and persisted into the latest Permian, and the serve as one tie point in our stratigraphic frame- (Bethel, Heldenmoed, Donald 207 [Fairydale], narrow lithofacies interval over which there was work. The second horizon, which is lower in the Nooitgedacht) using this multidisciplinary a reported vertebrate turnover occurs at several section and in a stratigraphic position similar approach. The vertical extent of our measured stratigraphic horizons in different magnetozones to our previously published silicified siltstone, sections and lithostratigraphic framework of the across the basin. Lastly, the proposal that a single, yields a Changhsingian age (252.43 ± 0.19 Ma). Eastern Cape Province encompass the early to isochronous lithofacies can be used to correlate This horizon serves as a second chronometric late Changhsingian, where three normal polar- vertebrate assemblages across the Karoo Basin is tie point in the stratigraphic framework and is ity chrons are separated by at least two reverse demonstrated to be unrealistic when evaluated in located in an area where all vertebrate fossils polarity chrons. Stratigraphic frameworks and a multidisciplinary context (Fig. 21). have been assigned a Triassic age in the L. dec- measured sections in the Free State Province are livis AZ. Hence, we conclude that diagnostic correlated with the youngest reverse and normal CONCLUSIONS taxa assigned to the Daptocephalus AZ and L. polarity chrons at Old Lootsberg Pass and are declivis AZ in the Lootsberg Pass area, which constrained to the latest Changhsingian with a A stratigraphic framework correlated across demonstrate coeval stratigraphic relationships, U-Pb CA-ID-TIMS zircon age from a pristine the escarpment from Old Lootsberg Pass to New were contemporaries beginning sometime in the volcanic ash in the basal part of the L. declivis Lootsberg Pass, South Africa, demonstrates that early Changhsingian. This temporal relation- AZ at the Farm Nooitgedacht section. The cur- lateral facies relationships account for, and help ship likely continued for at least one hundred rent correlation model differs markedly from one elucidate, interpretations about the latest Perm- thousand years if not longer. Palynologic and based solely on a lithofacies approach and should ian terrestrial extinction paradigm in the Karoo macropaleobotanic evidence indicates that these aid in our future understanding and interpretation Basin. Greenish-gray mudrock coloration, previ- vertebrate communities occupied glossopterid- of the end-Permian crisis and preceding events. ously used as a criterion for recognizing Upper dominated landscapes during wet intervals and, Permian deposits, and reddish-gray mudrock likely, landscapes dominated by other Permian ACKNOWLEDGMENTS color, previously used as a criterion to recognize gymnosperm groups during cooler and drier lowermost Triassic deposits, are laterally equiva- intervals. But, again, there appears to be little The authors appreciate the hospitality of J. and L. Kingwill, Blaauwater Farm, and J.P. and H. Steynberg, lent over at least 100 m of vertical stratigraphic evidence in the Lootsberg Pass area for a strati- Ganora Farm; field assistance by S. Makubalo and V. section and do not represent a time-transgressive graphic replacement or turnover of vertebrate Nxumalo, Council for Geoscience; and T. Chizinski phenomenon. Rather, color variation is a func- assemblages over time. ‘14, M. Langwenya ‘14, K. Spencer ‘14, J. Li ‘16, tion of early diagenetic processes associated with Results of magnetic polarity stratigraphic K. Lipshultz ‘16, T. Sasajima ‘16, S. Sinkler ‘18, and K. Kus ‘18, Department of Geology, Colby College; individual landscape changes in the water table investigations, at the current level of sampling, laboratory assistance with magnetic susceptibility/an- over space and time. When vertebrate fossils used demonstrate the presence of normal polarity mag- isotropy of magnetic susceptibility measurements by by previous workers to circumscribe two verte- netozones in the eastern half of the escarpment. B.J. Lycka; laboratory assistance with thermal demag- brate assemblage zones—the upper Daptoceph- In contrast, two thin magnetozones of reverse netization measurements during the COVID-19 pan- alus and Lystrosaurus declivis—are placed into polarity have been documented in the western demic by S. Akatakpo; assistance with data reduction by Z. Haque and assistance with scanning electron mi- their respective collection sites in stratigraphic part of the area, both of which underlie a basal croscope and petrographic microscope inspection by context along the escarpment, taxa diagnostic of channel erosional contact indicative of landscape Z. Haque and L. Roberts, University of Texas at Dal- each are shown to be coeval rather than strati- degradation and loss of a part of the stratigraphic las; curatorial assistance by Diane Erwin at the Uni- graphically replacive. Hence, the coexistence of record. Hence, whether one interprets a single versity of California Museum of Paleontology; and R.H.M. Smith for the vertebrate database on which vertebrate taxa previously considered diagnostic long, normal polarity magnetozone interval of the end-Permian extinction model was based. We of pre-extinction and post-extinction ecosystems more than 100 m or several oscillations in mag- appreciate comments by the editor, associate editor, in glossopterid-dominated landscapes precludes netic polarity over the same stratigraphic thick- and two anonymous reviewers that strengthened the the interpretation of a sudden extinction and bio- ness, either interpretation is a function­ of both final manuscript. Student participation was supported diversity crisis as a consequence of the loss of sampling and the inherent processes that operated­ by the Selover Family Student Research Endowment and Barrett T. Dixon Geology Research and Intern- this vegetation. And the interpretation of a rapid in the area and resulted in the available rock ship Fund for undergraduate experiences in the De- recovery of a Lystrosaurus-dominated com- record. In combination with constraining U-Pb partment of Geology, Colby College. R.A. ­Gastaldo’s munity appearing above the biozone boundary, CA-ID-TIMS zircon ages, it appears that a time research was supported by the Council for Geosci- which occurs in different magnetozones in differ- interval of up to 1 Ma may be missing in the east- ence; National Science Foundation EAR 0749895, 0934077, 1123570, and 1624302; a Fulbright Award ent parts of the basin, now is questionable. These ern part of the escarpment within the documented to R.A. Gastaldo at the Geology Department, Rhodes observations are placed into geochronometric, single long, normal polarity magnetozone, which University; and faculty start-up funding to J.W. Geiss- magnetostratigraphic, and palynologic contexts, would suggest a record of inconsistent sediment man from the University of Texas at Dallas. all of which indicate that these assemblages are preservation at Old Lootsberg Pass. Without a early to late Changhsingian. multidisciplinary approach, in which high-res- REFERENCES CITED We present two new U-Pb zircon maximum olution stratigraphic frameworks are combined depositional ages for devitrified claystone depos- with geochronologic, palynostratigraphic, and Aitken, G., 1998, A palynological and palaeoenvironmental analysis of Permian and Early Triassic sediments of the its with maximum depositional ages, which aug- magnetostratigraphic data, the generalities inher- Ecca and the Beaufort Groups, Northern Karoo Basin, ment our previously published age constraints for ent in composite or coarse stratigraphic trends South Africa [Ph.D. thesis]: University of the Witwa- tersrand, Johannesburg, South Africa. the area. 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