The Beaufort Group is the third of the main subdivisions of the

Karoo Supergroup The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a peri ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the southernmost country in Africa. It is bounded to the south by of coastline that stretch along the South Atlantic and Indian Oceans; to the north by the neighbouring coun ...

. It is composed of a lower Adelaide Subgroup and an upper Tarkastad Subgroup. It follows conformably after the Ecca Group and

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval ...

underlies the

Stormberg Group The Stormberg Group is one of the four geological groups that comprises the Karoo Supergroup in South Africa. It is the uppermost geological group representing the final phase of preserved sedimentation of the Karoo Basin. The Stormberg Group roc ...

. Based on stratigraphic position, lithostratigraphic and biostratigraphic correlations, palynological analyses, and other means of

geological dating Geochronology is the science of determining the age of rocks, fossils, and sediments using signatures inherent in the rocks themselves. Absolute geochronology can be accomplished through radioactive isotopes, whereas relative geochronology is pr ...

, the Beaufort Group rocks are considered to range between Middle

Permian The Permian ( ) is a geologic period and stratigraphic system which spans 47 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 251.9 Mya. It is the last period of the Paleo ...

( Wordian) to Early

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest per ...

(

Anisian In the geologic timescale, the Anisian is the lower stage or earliest age of the Middle Triassic series or epoch and lasted from million years ago until million years ago. The Anisian Age succeeds the Olenekian Age (part of the Lower Triassic ...

) in age.

Background

During the period when sedimentation of the Beaufort Group rocks took place, the Ecca sea had retreated to the northeastern

Karoo Basin The Karoo Supergroup is the most widespread stratigraphic unit in Africa south of the Kalahari Desert. The supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Late Carboniferous and Early Jurassic, a perio ...

. All

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sand ...

deposition Deposition may refer to: * Deposition (law), taking testimony outside of court * Deposition (politics), the removal of a person of authority from political power * Deposition (university), a widespread initiation ritual for new students practiced f ...

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 The back-arc region is the area behind a volcanic arc. In island volcanic arcs, it consists of back-arc basins of oceanic crust with abyssal depths, which may be separated by remnant arcs, similar to island arcs. In continental arcs, the back-ar ...

foreland basin. This foreland system was caused by crustal uplift ( orogenesis) that had previously begun to take course due to the

subduction Subduction is a geological process in which the oceanic lithosphere is recycled into the Earth's mantle at convergent boundaries. Where the oceanic lithosphere of a tectonic plate converges with the less dense lithosphere of a second plate, ...

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 Gondwanide orogeny was an orogeny active in the Permian that affected parts of Gondwana that are by current geography now located in southern South America, South Africa, Antarctica, Australia and New Guinea. The zone of deformation in ...

. The continuation of mountain-building and erosion from the growing Gondwanide mountain chain and associated

created accommodation space for

in the

. Orogenic loading was the initial subsidence mechanism acting on the

and flexural tectonics partitioned the

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

. 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.

Geographic extent

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.

Stratigraphic units

Adelaide Subgroup The Adelaide Subgroup is the lower subgroup of the Beaufort Group and contains all Middle to Late Permian-aged rocks. This subgroup contains six geological formations in total, however, these formations are

latitude In geography, latitude is a coordinate that specifies the north– south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from –90° at the south pole to 90° at the north ...

specific. These formations are the Abrahaamskraal and Teekloof Formations, west of 24°E, Middleton and Balfour Formations east of 24°E, and the Normandien and Emakwezini Formations in the northern Free-State and Kwa-Zulu Natal provinces. Composing the lower Beaufort succession, the rocks are mudstone-dominated. The mudstones 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 as overbank or floodplain facies associations. The formations here are listed below (from oldest to youngest): West of 24 degrees *

Abrahamskraal Formation The Abrahamskraal Formation is a geological formation and is found in numerous localities in the Northern Cape, Western Cape, and the Eastern Cape of South Africa. It is the lowermost formation of the Adelaide Subgroup of the Beaufort Group, a ma ...

: The Abrahamskraal Formation is found in both its western and eastern deposits. Previously, east of 24 degrees deposits of the Abrahaamskraal Formation were known as the Koonap Formation. Recently these were amalgamated into the Abrahaamskraal Formation due to recent stratigraphic and biostratigraphic research. *Teekloof Formation: Floodplain facies association comprising some greenish-grey mudstones. However, redder mudstones are dominant. East of 24 degrees *Middleton Formation: Lies conformably over the Abrahamskraal Formation in the east. Semi-arid climate supported a lush

flora Flora is all the plant life present in a particular region or time, generally the naturally occurring ( indigenous) native plants. Sometimes bacteria and fungi are also referred to as flora, as in the terms '' gut flora'' or '' skin flora''. ...

and

fauna Fauna is all of the animal life present in a particular region or time. The corresponding term for plants is '' flora'', and for fungi, it is '' funga''. Flora, fauna, funga and other forms of life are collectively referred to as '' biota''. ...

that thrived along meander belts and semi-permanent lakes. The formation contains lenses of red mudstone which are likely to have been deposited in a

sub-aerial In natural science, subaerial (literally "under the air"), has been used since 1833,Subaerial
in the Merriam ...

fluvial environment. * Balfour Formation: Low-energy, fluvial environmental facies, most likely one that had

meandering rivers A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank (cut bank) and deposits sediments on an inner, convex ba ...

. Mudstone-rich. *Normadien Formation (northeastern region only): Mudstone-rich, but these are interbedded with diagnostic layers of very coarse-grained

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...

s that exhibit coarsening upward cycles. *Emakwezini Formation (northeastern KwaZulu-Natal only): An extremely understudied geological formation that outcrops in a thin, faulted, and meridional belt in central Eswatini and the southern Lebombo Basin of northeastern KwaZulu-Natal. It is actively mined for its

coal Coal is a combustible black or brownish-black sedimentary rock, formed as rock strata called coal seams. Coal is mostly carbon with variable amounts of other elements, chiefly hydrogen, sulfur, oxygen, and nitrogen. Coal is formed when ...

seams which are found intercalated with fine, greenish-grey to brown mudstones and

carbon Carbon () is a chemical element with the symbol C and atomic number 6. It is nonmetallic and tetravalent—its atom making four electrons available to form covalent chemical bonds. It belongs to group 14 of the periodic table. Carbon ma ...

aceous shales. The mudstones contain layers of fining upward successions of coarse-grained, yellow-white

s. Rare

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms w ...

lenses are sometimes also found. The mudstones have yielded diverse fossils, mainly of plants such as '' Phyllotheca'', '' Glossopteris'' and associated '' Dictyopteridium''.

Insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

s are also found, such as of ''Neoliomopterum picturatum'', various mollusc fossils, fish scales of '' Coelacanthus dendrites'' and unidentified ganoid fish scales and teeth. Being upper

in age, it correlates with the Normandien and Balfour Formations, but is differentiated from these two formations due to its unique sedimentary facies structure. Unlike the rest of the Beaufort Group sequence, the Emakwezini Formation was deposited in a permanently wet, fluvial- lacustrine environment where

peat Peat (), also known as turf (), is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. The peatland ecosystem covers and ...

swamp A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...

s were present. Tarkastad Subgroup There are no equivalent deposits of the Tarkastad Subgroup west of 24°E. This is either due to

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...

of the lowlands west of 24°E or

in the western section of the

ceased at the end of the

. In the lower sections

s dominate, especially in the Katberg Formation. In the upper units the

to mudstone ratio steadily evens out. The Tarkastad Subgroup is composed of the following formations (from oldest to youngest): * Katberg Formation: Dominated by fine to medium-grained

s. Alluvial fan and braided river environmental facies. *Burgersdorp Formation: Very mudstone-rich which are reddish or purple in color. *Verkykerskop Formation (extreme northeast only): Composed entirely of fine-grained

interbedded with very coarse

s. *Driekoppen Formation (extreme northeast only): Nearly entirely composed of mudstone.

Paleontology

The Beaufort Group is internationally renowned for its diverse

, in particular for its therapsid

s. The entire expanse of this geological group has been categorized into eight fossil biozones or assemblage zones. These assemblage zones are listed below: * ''Cynognathus'' Assemblage Zone (Youngest) * ''Lystrosaurus'' Assemblage Zone * ''Daptocephalus'' Assemblage Zone * ''Cistecephalus'' Assemblage Zone * ''Tropidostoma'' Assemblage Zone * ''Pristerognathus'' Assemblage Zone * ''Tapinocephalus'' Assemblage Zone * ''Eodicynodon'' Assemblage Zone (Oldest) The Beaufort Group deposits also yield numerous

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

plant Plants are predominantly photosynthetic eukaryotes of the kingdom Plantae. Historically, the plant kingdom encompassed all living things that were not animals, and included algae and fungi; however, all current definitions of Plantae excl ...

, and trace fossils.

Correlation

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 Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-ei ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's List of countries and dependencies by population, most populous country, with a Population of China, population exceeding 1.4 billion, slig ...

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Antarctica Antarctica () is Earth's southernmost and least-populated continent. Situated almost entirely south of the Antarctic Circle and surrounded by the Southern Ocean, it contains the geographic South Pole. Antarctica is the fifth-largest cont ...

Madagascar Madagascar (; mg, Madagasikara, ), officially the Republic of Madagascar ( mg, Repoblikan'i Madagasikara, links=no, ; french: République de Madagascar), is an island country in the Indian Ocean, approximately off the coast of East Afric ...

India India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area, the List of countries and dependencies by population, second-most populous ...

, and

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

References