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ABSTRACT The Triassic Katberg Formation has played a central role in interpreting the end-Permian ecosystem crisis, as part of a hypothesis of aridification, vegetation loss, and sediment release in continental settings. We use drone images of an inaccessible cliff near Bethulie to investigate the Swartberg member, a braided-fluvial body 45 m thick, describing remote outcrop facies to identify geomorphic units and using spatial analysis to estimate their proportions in 2-D sections. Here the Swartberg member comprises three channel belts within shallow valleys, the lowermost of which is ∼500 m wide and incised into lacustrine deposits. The component channel bodies consist mainly of trough cross-bedded sand sheets (48%) and channel-scour fills (28%). Recognizable bars (15%) comprise unit bars with high-angle slipfaces and mounded bar cores (components of mid-channel compound bars), bars built around vegetation, and bank-attached bars in discrete, probably low-sinuosity conduits. Abandoned channels constitute 8% and 16% of flow-parallel and -transverse sections, respectively. When corrected for compaction, the average thalweg depth of the larger channels is 3.9 m, with an average bankfull width of 84 m, scaling broadly with the relief of the bars and comparable in scale to the Platte and South Saskatchewan rivers of North America. The fluvial style implies perennial but seasonably variable flow in a vegetated landscape with a humid paleoclimate. The northward paleoflow accords with regional paleoflow patterns and deposition on a megafan sourced in the Cape Fold Belt, where the Swartberg member represents the avulsion of a major transverse-flowing river. U-Pb dating of in situ and reworked pedogenic carbonate nodules from below the base of the Swartberg member yielded Anisian to Ladinian ages (Middle Triassic), younger than the previously assumed Early Triassic age and implying that considerable gaps in time exist in the succession. An assessment of the interval spanning the lower to mid Katberg Formation is needed to reevaluate the inferred unidirectional trend in fluvial style, aridification, and fossil distributions in this condensed, disjunct succession. 

We report U-Pb age determinations of carbonate nodules from an in situ paleosol horizon in the Upper Permian Balfour Formation and from several horizons of pedogenic nodule conglomerate (PNC) in the Triassic Katberg Formation, Karoo Basin, South Africa, using laser ablation−inductively coupled plasma−mass spectrometry (LA-ICP-MS). The paleosol sample yields an age of 252 ± 3 Ma, which overlaps with a previous high-precision U-Pb zircon date from a volcanic ash deposit 2 m above the paleosol. This relationship demonstrates the reliability of using LA-ICP-MS dating techniques on terrestrial pedogenic calcite. Two PNC samples collected at the base of the Katberg Formation within the same sandstone unit yield ages of 255 ± 3 Ma and 251 ± 3 Ma. The age of 251 ± 3 Ma overlaps with the high-precision U-Pb zircon date below the PNC and is a maximum age estimate of deposition for the base of the Katberg Formation. Our results show that reworked nodules in the same concentrated conglomerate lag can be of different ages, but that similarly aged nodules are spatially associated. In addition, two PNC samples collected higher in the section yield ages of 249 ± 3 Ma and 241 ± 3 Ma, providing maximum depositional ages for the lower to middle Katberg Formation for the first time. We demonstrate that pedogenic carbonate nodules can be dated with meaningful precision, providing another mechanism for constraining the age of sedimentary sequences and studying events associated with the Permian−Triassic transition in the central Karoo Basin, even though the extinction boundary may not be preserved in this area. 

ABSTRACT The fully continental succession of the Beaufort Group, Karoo Basin, South Africa, has been used in the development of environmental models proposed for the interval that spans the contact between the Daptocephalus to Lystrosaurus Assemblage Zones, associated by some workers with the end-Permian extinction event. An aridification trend is widely accepted, yet geochemical data indicate that the majority of in situ paleosols encountered in this interval developed in waterlogged environments. To date, the presence of calcic paleosols in the latest Permian can be inferred only from the presence of calcite-cemented pedogenic nodules concentrated in fluvial channel-lag deposits. Here, we report on the first empirical evidence of in situ calcic Vertisols found in the upper Daptocephalus Assemblage Zone near Old Wapadsberg Pass, one of eight classic localities in which the vertebrate turnover is reported in the Karoo Basin. Seven discrete intervals of calcic Vertisols, exposed over a very limited lateral extent, occur in an ∼ 25 m stratigraphic interval. Estimates of mean annual temperature and mean annual precipitation are calculated from geochemical measurements of one paleosol, and these estimates indicate that the prevailing climate at the time of pedogenesis was seasonally cold and humid. Correlation with adjacent stratigraphic sections indicates that the late Permian landscape experienced poorly drained and better-drained phases, interpreted to reflect a climate that varied between episodically dry and episodically wet. In contrast to a paleoenvironmental reconstruction of unidirectional aridification from strata in the Wapadsberg Pass region, this study provides new evidence for a wetting trend towards the Daptocephalus–Lystrosaurus Assemblage-Zone boundary.