A simplified geological map of the outcrops of Karoo Supergroup rocks in Southern Africa. The Beaufort Group is represented by the yellow key on the map.
During the period whensedimentation of the Beaufort Group rocks took place, the Ecca sea had retreated to the northeasternKaroo Basin. Allsedimentdeposition at this time took place in a terrestrial, although in a predominantlyfluvial oralluvial environment that was seasonallyarid. This environment covered a vast area and deposition was influenced by aretroarcforeland basin. This foreland system was caused bycrustal uplift (orogenesis) that had previously begun to take course due to thesubduction of the Palaeo-pacific plate beneath the Gondwanan Plate. This resulted in the rise of the Gondwanide mountain range in what is known as theGondwanide orogeny. The continuation of mountain-building and erosion from the growing Gondwanide mountain chain and associated subduction created accommodation space for sediment deposition in the Karoo Basin. Orogenic loading was the initial subsidence mechanism acting on the Karoo Basin and flexural tectonics partitioned the Karoo Basin into theforedeep,forebulge, and backbulge flexural provinces. Orogenic loading and unloading caused changes in position of the forebulge and foredeep. This resulted in the deposition zones shifting from the proximal or distal regions of the Karoo Basin.[6]
The Beaufort Group rocks are predominantly mudstone-dominated up until the upper sections in the lower Tarkastad Subgroup. Tuffs are also found due to concurrent volcanic activity that took place with the foreland tectonics.[7][8][9][10]
Hill in siliciclastic strata (mud or siltstones capped by solid sandstone) of Teekloof or Abrahamskraal formation (Beaufort Group) of the Main Karoo Basin. Karoo National Park near Beaufort West, Western Cape Province, South Africa.
The geological formations of the Beaufort Group are outcrop over approximately 145 000 km2, attaining a total thickness of around 6000 m thick at its thickest outcrops. In the west, the lowermost Beaufort Group rocks are found east of Laingsburg and remain continuous eastward to East London. Deposits are also found in the central Karoo and continue north-north-eastwards to Gariep Dam, Colesberg, and up to Bloemfontein. In the extreme north and north-east, the Beaufort Group outcrops in Harrismith and northeastern KwaZulu-Natal.
The Adelaide Subgroup is the lower subgroup of the Beaufort Group and contains all Middle toLate Permian-aged rocks. This subgroup contains sixgeological formations in total, however, these formations arelatitude specific. These formations are theAbrahaamskraal and Teekloof Formations, west of 24°E, Middleton andBalfour Formations east of 24°E, and the Normandien and Emakwezini Formations in the northernFree-State andKwa-Zulu Natal provinces. Composing the lower Beaufort succession, the rocks are mudstone-dominated. Themudstones in the lower Beaufort Group are mainly greenish-grey to blueish-grey and gradually change to greyish-red, reddish-brown or purple in color. The dominant presence of mudstones in the lower Beaufort Group represent tranquil depositional settings such asoverbank orfloodplainfacies associations. The formations here are listed below (from oldest to youngest):
West of 24 degrees
Abrahamskraal Formation: The Abrahamskraal Formation is found in both its western and easterndeposits. Previously, east of 24 degrees deposits of the Abrahaamskraal Formation were known as the Koonap Formation.[11] Recently these were amalgamated into the Abrahaamskraal Formation due to recentstratigraphic andbiostratigraphic research.[12][13][14][15][16]
Teekloof Formation:Floodplain facies association comprising some greenish-grey mudstones. However, redder mudstones are dominant.[17]
Normadien Formation (northeastern region only): Mudstone-rich, but these are interbedded with diagnostic layers of very coarse-grainedsandstones that exhibit coarsening upward cycles.
Emakwezini Formation (northeasternKwaZulu-Natal only): An extremely understudiedgeological formation that outcrops in a thin,faulted, andmeridional belt in centralEswatini and the southern Lebombo Basin of northeasternKwaZulu-Natal. It is actively mined for itscoal seams which are found intercalated with fine, greenish-grey to brown mudstones andcarbonaceousshales. The mudstones contain layers of fining upward successions of coarse-grained, yellow-white sandstones. Rarelimestonelenses are sometimes also found. The mudstones have yielded diverse fossils, mainly of plants such asPhyllotheca,Glossopteris and associatedDictyopteridium.Insectfossils are also found, such as ofNeoliomopterum picturatum, variousmollusc fossils, fish scales ofCoelacanthus dendrites and unidentifiedganoid fish scales and teeth. Being upperPermian in age, it correlates with the Normandien andBalfour Formations, but is differentiated from these two formations due to its uniquesedimentaryfacies structure. Unlike the rest of the Beaufort Group sequence, the Emakwezini Formation was deposited in a permanently wet,fluvial-lacustrine environment wherepeatswamps were present.[21][22][23][24]
Tarkastad Subgroup
There are no equivalentdeposits of the Tarkastad Subgroup west of 24°E. This is either due toerosion of the lowlands west of 24°E orsedimentdeposition in the western section of theKaroo Basin ceased at the end of thePermian. In the lower sections sandstones dominate, especially in theKatberg Formation. In the upper units the sandstone to mudstone ratio steadily evens out.[25] The Tarkastad Subgroup is composed of the following formations (from oldest to youngest):
Upper-side 3D rendering of the content inside the burrow cast BP/1/5558 in semi-transparency.Thrinaxodon liorhinus (in brown; BP/1/7199) is lying on its ventral side;Broomistega putterilli (in grey; BP/1/7200) deposited upside down on the right side of theThrinaxodon. Source: Abdala et al. 2013)
^Keyser, A. W., & Smith, R. M. H. (1978). Vertebrate biozonation of the Beaufort Group with special reference to the western Karoo Basin. Geological Survey, Department of Mineral And Energy Affairs, Republic of South Africa.
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