The Abrahamskraal Formation is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

and is found in numerous localities in the

Northern Cape The Northern Cape ( ; ; ) is the largest and most sparsely populated Provinces of South Africa, province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley, South Africa, Kimberley. It includes ...

Western Cape The Western Cape ( ; , ) is a provinces of South Africa, province of South Africa, situated on the south-western coast of the country. It is the List of South African provinces by area, fourth largest of the nine provinces with an area of , an ...

, and the

Eastern Cape The Eastern Cape ( ; ) is one of the nine provinces of South Africa. Its capital is Bhisho, and its largest city is Gqeberha (Port Elizabeth). Due to its climate and nineteenth-century towns, it is a common location for tourists. It is also kno ...

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. It is the lowermost formation of the Adelaide Subgroup of the

Beaufort Group 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 under ...

, a major geological group that forms part of the greater

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 per ...

. It represents the first fully terrestrial geological deposits of the

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 per ...

Outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth and other terrestrial planets. Features Outcrops do not cover the majority of the Earth's land surface because in most p ...

s of the Abrahamskraal Formation are found from the small town Middelpos in its westernmost localities, then around

Sutherland Sutherland () is a Counties of Scotland, historic county, registration county and lieutenancy areas of Scotland, lieutenancy area in the Scottish Highlands, Highlands of Scotland. The name dates from the Scandinavian Scotland, Viking era when t ...

, the Moordenaarskaroo north of Laingsburg, Williston,

Fraserburg Fraserburg is a town in the Karoo region of South Africa's Northern Cape province. It is located in the Karoo Hoogland Local Municipality. The town has some of the coldest winters in South Africa. The nearest towns are Williston, Northern Cape, W ...

Leeu-Gamka Leeu-Gamka is a small town in the Western Cape province of South Africa, located north-east of Cape Town in the Karoo. History The town of Leeu-Gamka owes its existence to the route chosen by Prime Minister John Molteno for the Cape Government Ra ...

, Loxton, and

Victoria West Victoria West is a town in the central Karoo region of South Africa's Northern Cape province. It is situated on the main N12 route, at an elevation of . It is the seat of the Ubuntu Local Municipality within the Pixley ka Seme District Municip ...

in the

and

. In the

outcrops are known from

Rietbron Rietbron is a town in Sarah Baartman District Municipality in the Eastern Cape province of South Africa. It is on the R306 road. Village 85 km south-east of Beaufort West and 64 km north-west of Willowmore Willowmore is a town in Sarah Baar ...

, north of

Klipplaat Klipplaat is a town in Sarah Baartman District Municipality in the Eastern Cape province of South Africa. The town is some 185 km north-west of Port Elizabeth and 75 km south-east of Aberdeen. It takes its name from large slabs of rock on the su ...

and

Grahamstown Makhanda, formerly known as Grahamstown, is a town of about 75,000 people in the Eastern Cape province of South Africa. It is situated about northeast of Gqeberha and southwest of East London. It is the largest town in the Makana Local Mun ...

, and also southwest of

East London East London is the part of London, England, east of the ancient City of London and north of the River Thames as it begins to widen. East London developed as London Docklands, London's docklands and the primary industrial centre. The expansion of ...

Geology

The Abrahamskraal Formation comprises the majority of the Middle

Permian The Permian ( ) is a geologic period and System (stratigraphy), 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 251.902 Mya. It is the s ...

Beaufort sequence, and are thought to range between 268 - 259 million years in age. The lowermost deposits of the Abrahamskraal Formation found in the

until recently were named the Koonap Formation, but these outcrops have been amalgamated into the Abrahamskraal Formation due to recent

stratigraphic Stratigraphy is a branch of geology concerned with the study of rock layers (strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

and

biostratigraphic Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock strata by using the fossil assemblages contained within them.Hine, Robert. "Biostratigraphy." ''Oxford Reference: Dictionary of Biology ...

research. The Abrahamskraal Formation incorporates the entire ''Tapinocephalus'' Assemblage Zone in its upper sections and the entire ''Eodicynodon'' Assemblage Zone its lowermost southern deposits. In the west and northerly deposits the Abrahamskraal Formation overlies the Waterford Formation and the Middleton Formation in the south, both formations containing the uppermost deposits of the

Ecca Group The Ecca Group is the second of the main subdivisions of the Karoo Supergroup of geological strata in southern Africa. It mainly follows conformably after the Dwyka Group in some sections, but in some localities overlying unconformably over much ...

. The rocks of the Abrahamskraal Formation comprise mainly greenish-grey to blueish-grey

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

coupled with rarer instances of greyish-red, reddish-brown or purple

s. These include subordinate greenish-grey, fine-grained

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s which are normally observed in fining upward cycles. The

s vary in thickness from several metres to several tens of metres in some localities.

Siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

s are also found

interbedded In geology, interbedding occurs when beds (layers of rock) of a particular lithology lie between or alternate with beds of a different lithology. For example, sedimentary rocks may be interbedded if there were sea level variations in their sedimen ...

with the

beds. The presence of these rocks reveal much about the past environment that they were deposited in. They were formed by

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

ary material being deposited in the

- a retro-arc

foreland basin A foreland basin is a structural basin that develops adjacent and parallel to a mountain belt. Foreland basins form because the immense mass created by crustal thickening associated with the evolution of a mountain belt causes the lithospher ...

- by vast, low-energy

alluvial plain An alluvial plain is a plain (an essentially flat landform) created by the deposition of sediment over a long period by one or more rivers coming from highland regions, from which alluvial soil forms. A ''floodplain'' is part of the process, bei ...

s flowing northwards from the south. The lowermost deposits are considered to be

deltaic A river delta is a landform, archetypically triangular, created by the deposition of the sediments that are carried by the waters of a river, where the river merges with a body of slow-moving water or with a body of stagnant water. The creati ...

and grade laterally into the underlying

deposits in its southern localities. Deposits grade steadily younger in the northeast where the

sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...

facies In geology, a facies ( , ; same pronunciation and spelling in the plural) is a body of rock with distinctive characteristics. The characteristics can be any observable attribute of rocks (such as their overall appearance, composition, or con ...

turn fully terrestrial. The greenish-grey

s are usually associated with the

while the redder mudstones with the terrestrial. All

sedimentary rock Sedimentary rocks are types of rock (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

s of the

were transported downhill from the south in the shadow of the rising Gondwanide mountain range. The Gondwanides were the result of

tectonic uplift Tectonic uplift is the orogeny, geologic uplift of Earth#Surface, Earth's surface that is attributed to plate tectonics. While Isostasy, isostatic response is important, an increase in the mean elevation of a region can only occur in response to ...

that had previously begun to take course due to

subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...

of the Palaeo-pacific plate beneath the Gondwanan Plate.

Orogenic Orogeny () is a mountain-building process that takes place at a convergent plate margin when plate motion compresses the margin. An or develops as the compressed plate crumples and is uplifted to form one or more mountain ranges. This involv ...

pulses from the growing Gondwanides mountain chain and associated

created accommodation space for

sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...

in the

where the deposits of the Abrahamskraal Formation and all succeeding deposits of the Karoo Basin were deposited over millions of years.

Paleontological significance

The Abrahamskraal Formation is highly

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 preserve ...

iferous and well known for its

biozone In biostratigraphy, biostratigraphic units or biozones are intervals of geological strata that are defined on the basis of their characteristic fossil taxon, taxa, as opposed to a Lithostratigraphy, lithostratigraphic unit which is defined by the ...

assemblages of therapsid

s. The ''

Eodicynodon ''Eodicynodon'' (''eo-,'' early or primitive, dicynodont) is an extinct genus of Dicynodontia, dicynodont therapsids, a highly diverse group of herbivorous synapsids that were widespread during the middle-late Permian and early Triassic. As its ...

'' and ''Tapinocephalus'' Assemblage Zones to which this

incorporates preserve the first appearance of the earliest

dicynodont Dicynodontia is an extinct clade of anomodonts, an extinct type of non-mammalian therapsid. Dicynodonts were herbivores that typically bore a pair of tusks, hence their name, which means 'two dog tooth'. Members of the group possessed a horny, t ...

dinocephalia Dinocephalians (terrible heads) are a clade of large-bodied early therapsids that flourished in the Early and Middle Permian between 279.5 and 260 million years ago (Ma), but became extinct during the Capitanian mass extinction event. ...

ns,

biarmosuchia Biarmosuchia is an extinct clade of non-mammalian synapsids from the Permian. Biarmosuchians are the most basal group of the therapsids. They were moderately-sized, lightly built carnivores, intermediate in form between basal sphenacodont " pel ...

ns,

therocephalia Therocephalia is an extinct clade of therapsids (mammals and their close extinct relatives) from the Permian and Triassic periods. The therocephalians ("beast-heads") are named after their large skulls, which, along with the structure of their te ...

ns,

gorgonopsia Gorgonopsia (from the Greek Gorgon, a mythological beast, and 'aspect') is an extinct clade of Saber-toothed predator, sabre-toothed therapsids from the Middle Permian, Middle to the Upper Permian, roughly between 270 and 252 million years ago. ...

ns, and

pareiasaur Pareiasaurs (meaning "cheek lizards") are an extinct clade of large, herbivorous parareptiles. Members of the group were armoured with osteoderms which covered large areas of the body. They first appeared in southern Pangea during the Middle Per ...

ian

parareptiles Parareptilia ("near-reptiles") is an extinct group of basal sauropsids ("reptiles"), traditionally considered the sister taxon to Eureptilia (the group that likely contains all living reptiles and birds). Parareptiles first arose near the end ...

. The upper sections of this formation document the rise of and diversification of the

ns. The

ns subsequently went extinct at the contact of the Abrahamskraal Formation with the overlying Teekloof Formation. The basal

pelycosaur Pelycosaur ( ) is an older term for basal or primitive Late Paleozoic synapsids, excluding the therapsids and their descendants. Previously, the term mammal-like reptile was used, and Pelycosauria was considered an order, but this is now thoug ...

synapsid Synapsida is a diverse group of tetrapod vertebrates that includes all mammals and their extinct relatives. It is one of the two major clades of the group Amniota, the other being the more diverse group Sauropsida (which includes all extant rept ...

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

, '' Elliotsmithia longiceps'', has also been found in the deposits of this formation. The presence of this basal

is indicative of this geological formations significance. For decades,

paleontologists Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

have puzzled over what has been termed Olsen’s Gap, which is used to describe the

evolution Evolution is the change in the heritable Phenotypic trait, characteristics of biological populations over successive generations. It occurs when evolutionary processes such as natural selection and genetic drift act on genetic variation, re ...

ary gap in the

tetrapod A tetrapod (; from Ancient Greek :wiktionary:τετρα-#Ancient Greek, τετρα- ''(tetra-)'' 'four' and :wiktionary:πούς#Ancient Greek, πούς ''(poús)'' 'foot') is any four-Limb (anatomy), limbed vertebrate animal of the clade Tetr ...

fossil record 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 ...

between the appearance of the more derived therapsids and their ancestors, the

s. The rocks of the Abrahamskraal Formation and its geological correlates abroad hold the promise of that fossil gap being bridged through future research endeavors in the years to come. More notable fossil species include the

'' Diictodon feliceps'' which first appears in the upper sections of this formation, remaining ubiquitous until the Permian-Triassic boundary. Finally, fossils of

temnospondyl Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') or temnospondyls is a diverse ancient order (biology), order of small to giant tetrapods—often considered Labyrinth ...

amphibian Amphibians are ectothermic, anamniote, anamniotic, tetrapod, four-limbed vertebrate animals that constitute the class (biology), class Amphibia. In its broadest sense, it is a paraphyletic group encompassing all Tetrapod, tetrapods, but excl ...

s such as of ''

Rhinesuchus ''Rhinesuchus'' (meaning "rasp crocodile" for the ridged surface texture on its skull bones) is a large temnospondyl. Remains of the genus are known from the Permian of the South African Karoo Basin's ''Tapinocephalus'' and ''Cistecephalus'' as ...

'', the fish ''Namaichthys'',

invertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordata, chordate s ...

s of

molluscs Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...

, invertebrate trackways and burrows,

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

footprints Footprints are the impressions or images left behind by a person walking or running. Hoofprints and pawprints are those left by animals with hoof, hooves or paws rather than foot, feet, while "shoeprints" is the specific term for prints made by ...

of therapsids, and a variety of plant fossils such as '' Dadoxylon'', '' Equisetum modderdriftensis'', ''Schizoneura africana'', and several different species of ''

Glossopteris ''Glossopteris'' (etymology: from Ancient Greek γλῶσσα (glôssa, " tongue ") + πτερίς (pterís, " fern ")) is the largest and best-known genus of the extinct Permian order of seed plants known as Glossopteridales (also known as Ar ...

'' have been recovered. Among the species found in the Abrahamskraal Formation is Moschops Capensis

Paleobiota

Amphibians

Fish

; Actinopterygian

Reptiles

Sauropsida

Synapsids

Therapsids

= Anomodonts

Chainosauria

Dicynodontia

= Biarmosuchia

= Dinocephalian

Anteosauridae

Styracocephalidae

Tapinocephalidae

Titanosuchidae

= Gorgonopsia

= Therocephalia

Varanopidae

Correlation

The Abrahamskraal Formation corresponds with numerous localities abroad. Currently it is considered to correlate chronostratigraphically with the

Rio do Rasto Formation The Rio do Rasto Formation is a Late Permian sedimentary geological formation in the South Region, Brazil, South Region of Brazil. The official name is Rio do Rasto, although in some publications it appears as ''Rio do Rastro''. The strata were d ...

from the

Paraná Basin The Paraná Basin (, ) is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande do Sul states. The remainder area is distribu ...

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, the Madumabisa Mudstone Formation of

Zambia Zambia, officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa. It is typically referred to being in South-Central Africa or Southern Africa. It is bor ...

, the Ocher and Isheevo faunas of

Russia Russia, or the Russian Federation, is a country spanning Eastern Europe and North Asia. It is the list of countries and dependencies by area, largest country in the world, and extends across Time in Russia, eleven time zones, sharing Borders ...

, and to the Dashankou fauna from the Xidagou Formation of

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

. However, correlative dating between the Xidagou Formation and the Abrahamskraal Formation remains inconsistent and needs further study.

References

{{Geology of South Africa, formations Geologic formations of South Africa Permian System of Africa Permian South Africa Guadalupian Sandstone formations Shale formations Deltaic deposits Permian southern paleotemperate deposits Beaufort Group Formations Formations Formations