Оңтүстік Африка Кару тобының Бофорт тобы

Third of the main subdivisions of the Karoo Supergroup in South Africa

The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup in South Africa. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and unconformably underlies the Stormberg Group. Based on stratigraphic position, lithostratigraphic and biostratigraphic correlations, palynological analyses, and other means of geological dating, the Beaufort Group rocks are considered to range between Middle Permian (Wordian) to Early Triassic (Anisian) in age.

During the period when sedimentation of the Beaufort Group rocks took place, the Ecca sea had retreated to the northeastern Karoo Basin. All sediment deposition at this time took place in a terrestrial, although in a predominantly fluvial or alluvial environment that was seasonally arid. This environment covered a vast area and deposition was influenced by a retroarc foreland basin. This foreland system was caused by crustal uplift (orogenesis) that had previously begun to take course due to the subduction of the Palaeo pacific plate beneath the Gondwanan Plate. This resulted in the rise of the Gondwanide mountain range in what is known as the Gondwanide 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 the foredeep, 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. 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.

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 Beaufort Group rocks correlate chronologically with numerous other geological formations and groups within southern Africa and abroad. Most notably from numerous localities in Russia, China, South America, Antarctica, Madagascar, India, and Australia.