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The Karoo Supergroup of South Africa, internationally renowned for its almost continuous Carboniferous to Jurassic record of deposition in a foreland basin setting, hosts an unparalleled record of fossil tetrapods that provides unique insight into terrestrial biodiversity change over this extended period. Understanding of the litho-, bio- and chronostratigraphy of the Karoo Basin has greatly improved in recent years but most work has focused on the thicker and better-exposed rocks in the basinal foredeep. A core issue that has remained ambiguous is the stratigraphic placement of the diachronous Ecca-Beaufort contact, for which different criteria have been used during mapping in different parts of the main Karoo Basin. Comparison of biostratigraphy and contrasting lithological facies changes with those in the better-studied foredeep enabled us to revise the lithostratigraphy of the Ecca and Beaufort groups in the distal part of the main Karoo Basin. The presence of proximal marine facies associations in the distal sector conform with the definition of the Waterford Formation of the Ecca Group, so far recognised only in the southern foredeep. The upper contact of the Waterford Formation represents a change from a subaqueous to a subaerial delta plain depositional environment and marks the boundary between the Ecca and Beaufort groups, as in the south. This has consequences for Beaufort Group stratigraphic subdivision in the distal sector of the Karoo foreland basin.

The relationship between the tetrapod assemblage zones of the South African Karoo Basin and the lithostratigraphic divisions of the Beaufort Group is well-established, and provides an independent means of dating fossil occurrences. However, this relationship may not be consistent across the basin; a discrepancy exists between the historical tetrapod assemblages in the vicinity of Victoria West, Northern Cape Province, and the expected tetrapod assemblage zones based on mapped geology. In order to examine this disconnect, we collected fossils at two localities close to Biesiespoort railway station, a locality that was visited on a number of occasions by Robert Broom. Our fossil samples support the biostratigraphic determinations of Broom and thus confirm that the stratigraphic extent of the biozones at these localities differs from their type areas further south. The reasons for this are unclear but could be related to the northward younging of the lithological units, implying complex depositional processes, or result from difficulties in mapping. Nevertheless, caution should be exercised when using mapped geology near Victoria West as a guide to the age of fossils found there., Palaeontologia africana 2019. ©2019 Michael O. Day and Bruce S. Rubidge. This is an open-access article published under the Creative Commons Attribution 4.0 Unported License (CC BY4.0). To view a copy of the license, please visit http://creativecommons.org/licenses/by/4.0/. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited., NHM Repository

The relationship between the tetrapod assemblage zones of the South African Karoo Basin and the lithostratigraphic divisions of the Beaufort Group is well-established, and provides an independent means of dating fossil occurrences. However, this relationship may not be consistent across the basin; a discrepancy exists between the historical tetrapod assemblages in the vicinity of Victoria West, Northern Cape Province, and the expected tetrapod assemblage zones based on mapped geology. In order to examine this disconnect, we collected fossils at two localities close to Biesiespoort railway station, a locality that was visited on a number of occasions by Robert Broom. Our fossil samples support the biostratigraphic determinations of Broom and thus confirm that the stratigraphic extent of the biozones at these localities differs from their type areas further south. The reasons for this are unclear but could be related to the northward younging of the lithological units, implying complex depositional processes, or result from difficulties in mapping. Nevertheless, caution should be exercised when using mapped geology near Victoria West as a guide to the age of fossils found there., Palaeontologia africana 2019. ©2019 Michael O. Day and Bruce S. Rubidge. This is an open-access article published under the Creative Commons Attribution 4.0 Unported License (CC BY4.0). To view a copy of the license, please visit http://creativecommons.org/licenses/by/4.0/. This license permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Both the supplement and the article are permanently archived at: https://hdl.handle.net/10539/26240. The attached file is the published version of the article., NHM Repository

A basin analysis of the lower Beaufort Group in the Karoo Basin (Carboniferous-Jurassic) west of 24°E, cover an area of nearly 70000 km2. The Karoo Sequence reaches a composite thickness greater than 7500 m, comprising diamictites, sandstones, shales and mudstones. Along the southern margin of the Basin the entire succession is intensely folded, becoming flat or gently undulating in the north. Minor displacements along dolerite dykes and small-scale thrusting are the only evidence of faulting in the Basin. The transition from the uppermost Ecca to the lower Beaufort Group reflects a change from deltaic to fluvial depositional environments. The contact is taken above the uppermost deltaic sandstones, where the succession becomes distinctly argillaceous, and where therapsid fossils appear in the succession. The lower Beaufort succession consists of alternating sandstones, and red and green mudstones forming cyclical, upwards-fining, fluvial sequences. Channel sandstones (greywackes and arkosic wackes) and intraformational conglomerates are overlain by red and green overbank mudstones with intercalated crevasse splay sandstone sheets and lenses. The mudstone facies (Fg, Fl, Fr and Fv) are commonly bioturbated and contain a variety of therapsid fossils, calcareous nodules, and palaeosols. Tuff beds are sparsely preserved. Freshwater molluscans, fish imprints and plant fossils occur at certain horizons. The lower Beaufort comprises four upwards-fining megasequences, the uppermost incompletely preserved. The basal megasequence (A) overlies and grades diachronously into the Ecca Group from south to north across the Basin, thinning from more than 2500 m in the south to where it pinches out on surface, just south of Carnarvon in the north. In the unit which consists of a basal Combrinkskraal sandstone member overlain by the Leeu Gamka member, green and subordinate red mudstones are interbedded with thick, tabular sandstones. Megasequence B contains thick, tabular sandstones

The regional sediment transport directions, the controlling tectonic framework of sedimentation and the palaeogeography within the Karoo Basin during Ecca and Lowermost Beaufort times are indicated. Reconstructions of this magnitude have a direct bearing on the hypothesis of continental drift, and can be useful in regional exploration programmes for coal, uranium and fossil heavy mineral beach sands., The regional sediment transport directions, the controlling tectonic framework of sedimentation and the palaeogeography within the Karoo Basin during Ecca and Lowermost Beaufort times are indicated. Reconstructions of this magnitude have a direct bearing on the hypothesis of continental drift, and can be useful in regional exploration programmes for coal, uranium and fossil heavy mineral beach sands.

The sandstone beds are interlayered with mudstone and siltstone, with the thickest sandstone sequences being 15 m thick. Uranium mineralisation occurs within the thicker units, with 90% of the mineralisation occurring in the bottom 8 m of the sequences. Mineralisation decreases upwards, related to an abundance of carbonaceous debris derived from plants., The sandstone beds are interlayered with mudstone and siltstone, with the thickest sandstone sequences being 15 m thick. Uranium mineralisation occurs within the thicker units, with 90% of the mineralisation occurring in the bottom 8 m of the sequences. Mineralisation decreases upwards, related to an abundance of carbonaceous debris derived from plants.

Molybdenum occurs in specific fine-grained fluvial sandstone packages up to 350 m thick in the SW part of the basin, deposited by sheet floods in straight to braided channels and by perennial rivers in meandering channels. Two types of mineralisation are recognised: laminated sandstone and carbonate-cemented sandstone, both containing around 1 400 ppm uranium. Molybdenum was sourced from intermittently exposed granites to the SW, SSE and WNW, and precipitated when slightly oxidised, metal-rich solutions encountered carbonaceous matter. Reducing conditions were most intense at the base of the sand bodies, where laminated-sandstone-type mineralisation contains around 1 000 ppm Mo and carbonate-cemented mineralisation 500 ppm Mo; higher up, carbonate-cemented mineralisation grades around 100 ppm Mo. In the semi-arid climate, the palaeowater-table preserved reductant and ore only at the base of the thicker sandstones. The Poortjie Member has the best Mo-U potential, but development would not be economic at current prices and costs., Molybdenum occurs in specific fine-grained fluvial sandstone packages up to 350 m thick in the SW part of the basin, deposited by sheet floods in straight to braided channels and by perennial rivers in meandering channels. Two types of mineralisation are recognised: laminated sandstone and carbonate-cemented sandstone, both containing around 1 400 ppm uranium. Molybdenum was sourced from intermittently exposed granites to the SW, SSE and WNW, and precipitated when slightly oxidised, metal-rich solutions encountered carbonaceous matter. Reducing conditions were most intense at the base of the sand bodies, where laminated-sandstone-type mineralisation contains around 1 000 ppm Mo and carbonate-cemented mineralisation 500 ppm Mo; higher up, carbonate-cemented mineralisation grades around 100 ppm Mo. In the semi-arid climate, the palaeowater-table preserved reductant and ore only at the base of the thicker sandstones. The Poortjie Member has the best Mo-U potential, but development would not be economic at current prices and costs.

U in the Beaufort Group may have been derived partly from the leaching of heavy minerals in the host sandstones. To establish the basic hydrodynamic controls on the distribution and concentration of heavy minerals under different flow regime conditions, three flume runs were conducted using natural sand similar to that of the Beaufort sandstones. Sinuous dunes showed the highest concentration of ilmenite, followed by linguiod ripples and upper flow regime plane beds. Relative bed roughness played a major role in determining the amount of heavy minerals left behind in the sediments. The results of the flume studies showed that trough cross-laminated sandstones may have the best potential for hosting U, which agrees with preliminary field observations in the Beaufort Group., U in the Beaufort Group may have been derived partly from the leaching of heavy minerals in the host sandstones. To establish the basic hydrodynamic controls on the distribution and concentration of heavy minerals under different flow regime conditions, three flume runs were conducted using natural sand similar to that of the Beaufort sandstones. Sinuous dunes showed the highest concentration of ilmenite, followed by linguiod ripples and upper flow regime plane beds. Relative bed roughness played a major role in determining the amount of heavy minerals left behind in the sediments. The results of the flume studies showed that trough cross-laminated sandstones may have the best potential for hosting U, which agrees with preliminary field observations in the Beaufort Group.