The Karoo Supergroup is the most widespread
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: lithostrati ...
unit in
Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
south of the
Kalahari Desert
The Kalahari Desert is a large semi-arid sandy savanna in Southern Africa extending for , covering much of Botswana, and parts of Namibia and South Africa.
It is not to be confused with the Angolan, Namibian, and South African Namib coastal de ...
. The
supergroup Supergroup or super group may refer to:
* Supergroup (music), a music group formed by artists who are already notable or respected in their fields
* Supergroup (physics), a generalization of groups, used in the study of supersymmetry
* Supergroup ...
consists of a sequence of units, mostly of nonmarine origin, deposited between the
Late Carboniferous
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
and
Early Jurassic
The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
, a period of about 120 million years.
In southern Africa, rocks of the Karoo Supergroup cover almost two thirds of the present land surface, including all of
Lesotho
Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked country, landlocked as an Enclave and exclave, enclave in South Africa. It is situated in the Maloti Mountains and contains the Thabana Ntlenyana, highest mountains in Sou ...
, almost the whole of
Free State, and large parts of the
Eastern Cape
The Eastern Cape is one of the provinces of South Africa. Its capital is Bhisho, but its two largest cities are East London and Gqeberha.
The second largest province in the country (at 168,966 km2) after Northern Cape, it was formed in ...
,
Northern Cape
The Northern Cape is the largest and most sparsely populated province of South Africa. It was created in 1994 when the Cape Province was split up. Its capital is Kimberley. It includes the Kalahari Gemsbok National Park, part of the Kgalagadi T ...
,
Mpumalanga
Mpumalanga () is a province of South Africa. The name means "East", or literally "The Place Where the Sun Rises" in the Swazi, Xhosa, Ndebele and Zulu languages. Mpumalanga lies in eastern South Africa, bordering Eswatini and Mozambique. It ...
and
KwaZulu-Natal Province
KwaZulu-Natal (, also referred to as KZN and known as "the garden province") is a province of South Africa that was created in 1994 when the Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu) and Natal Province were merged. It is locat ...
s of
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 countri ...
. Karoo supergroup
outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.
Features
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficial ...
s are also found in
Namibia
Namibia (, ), officially the Republic of Namibia, is a country in Southern Africa. Its western border is the Atlantic Ocean. It shares land borders with Zambia and Angola to the north, Botswana to the east and South Africa to the south and ea ...
,
Eswatini
Eswatini ( ; ss, eSwatini ), officially the Kingdom of Eswatini and formerly named Swaziland ( ; officially renamed in 2018), is a landlocked country in Southern Africa. It is bordered by Mozambique to its northeast and South Africa to its no ...
,
Zambia
Zambia (), officially the Republic of Zambia, is a landlocked country at the crossroads of Central Africa, Central, Southern Africa, Southern and East Africa, although it is typically referred to as being in Southern Africa at its most cent ...
,
Zimbabwe
Zimbabwe (), officially the Republic of Zimbabwe, is a landlocked country located in Southeast Africa, between the Zambezi and Limpopo Rivers, bordered by South Africa to the south, Botswana to the south-west, Zambia to the north, and Mozam ...
and
Malawi
Malawi (; or aláwi Tumbuka: ''Malaŵi''), officially the Republic of Malawi, is a landlocked country in Southeastern Africa that was formerly known as Nyasaland. It is bordered by Zambia to the west, Tanzania to the north and northeast ...
, as well as on other continents that were part of
Gondwana
Gondwana () was a large landmass, often referred to as a supercontinent, that formed during the late Neoproterozoic (about 550 million years ago) and began to break up during the Jurassic period (about 180 million years ago). The final stages ...
. The basins in which it was deposited formed during the formation and breakup of
Pangea
Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...
.
[McCarthy, T., Rubridge, B. (2005). ''The Story of Earth and Life.'' pp. 161, 187–241. Struik Publishers, Cape Town] The
type area of the Karoo Supergroup is the Great
Karoo
The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi-desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its ext ...
in
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 countri ...
, where the most extensive outcrops of the sequence are exposed.
[Geological map of South Africa, Lesotho and Swaziland (1970). Council for Geoscience, Geological Survey of South Africa.] Its strata, which consist mostly of shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
s and 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 silicates) ...
s, record an almost continuous sequence of marine glacial
A glacial period (alternatively glacial or glaciation) is an interval of time (thousands of years) within an ice age that is marked by colder temperatures and glacier advances. Interglacials, on the other hand, are periods of warmer climate betw ...
to terrestrial deposition from the Late Carboniferous
Late may refer to:
* LATE, an acronym which could stand for:
** Limbic-predominant age-related TDP-43 encephalopathy, a proposed form of dementia
** Local-authority trading enterprise, a New Zealand business law
** Local average treatment effect, ...
to the Early Jurassic
The Early Jurassic Epoch (geology), Epoch (in chronostratigraphy corresponding to the Lower Jurassic series (stratigraphy), Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-J ...
. These accumulated in a retroarc 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 ...
called the "main Karoo
The Karoo ( ; from the Afrikaans borrowing of the South Khoekhoe !Orakobab or Khoemana word ''ǃ’Aukarob'' "Hardveld") is a semi-desert natural region of South Africa. No exact definition of what constitutes the Karoo is available, so its ext ...
" Basin. This basin was formed by 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, the ...
and orogenesis
Orogeny is a mountain building process. An orogeny is an event that takes place at a convergent plate margin when plate motion compresses the margin. An ''orogenic belt'' or ''orogen'' develops as the compressed plate crumples and is uplifted t ...
along the southern border of what eventually became Southern Africa, in southern Gondwana. Its sediments attain a maximum cumulative thickness of 12 km, with the overlying basaltic lavas (the Drakensberg
The Drakensberg (Afrikaans: Drakensberge, Zulu: uKhahlambha, Sotho: Maluti) is the eastern portion of the Great Escarpment, which encloses the central Southern African plateau. The Great Escarpment reaches its greatest elevation – within th ...
Group) at least 1.4 km thick.
Fossils include 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 exclud ...
s (both macro-fossils and pollen
Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametophyt ...
), rare 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 pairs ...
s and fish
Fish are aquatic, craniate, gill-bearing animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Approximately 95% of li ...
, common and diverse tetrapod
Tetrapods (; ) are four-limbed vertebrate animals constituting the superclass Tetrapoda (). It includes extant and extinct amphibians, sauropsids ( reptiles, including dinosaurs and therefore birds) and synapsids (pelycosaurs, extinct theraps ...
s (mostly therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
reptiles, temnospondyl
Temnospondyli (from Greek language, Greek τέμνειν, ''temnein'' 'to cut' and σπόνδυλος, ''spondylos'' 'vertebra') is a diverse order (biology), order of small to giant tetrapods—often considered Labyrinthodontia, primitive amphi ...
amphibians, and in the upper strata dinosaur
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
s), and ichnofossils. Their biostratigraphy
Biostratigraphy is the branch of stratigraphy which focuses on correlating and assigning relative ages of rock Stratum, strata by using the fossil assemblages contained within them.Hine, Robert. “Biostratigraphy.” ''Oxford Reference: Dictiona ...
has been used as the international standard for global correlation of 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 Paleoz ...
to Jurassic
The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...
nonmarine strata.
Geological origin
Origins of sediment deposition
About 510 million years ago a rift valley
A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear dep ...
developed across Southern Gondwana just south of Southern Africa, but extending westward into South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
, and eastward into Eastern 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 contine ...
and possible even into Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
. An 8 km thick layer of sediment, known as the Cape Supergroup, accumulated on the floor of this rift valley. Closure of the rift valley, starting 330 million years ago, resulted from the development of a 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, the ...
zone along the southern margin of Gondwana, and the consequent drift of the Falkland Plateau back towards Africa, during the Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
and Early Permian 01 or '01 may refer to:
* The year 2001, or any year ending with 01
* The month of January
* 1 (number)
Music
* '01 (Richard Müller album), 01'' (Richard Müller album), 2001
* 01 (Son of Dave album), ''01'' (Son of Dave album), 2000
* 01 (Urban ...
periods. After closure of the rift valley, and compression of the Cape Supergroup into a series of parallel folds, running mainly east-west, the continued subduction of the paleo-Pacific Plate beneath the Falkland Plateau and the resulting collision of the latter with Southern Africa, raised a mountain range of immense proportions to the south of the former rift valley. The folded Cape Supergroup formed the northern foothills of this mountain range.
The weight of the Falkland-Cape Supergroup mountains caused the continental crust of Southern Africa to sag, forming a retroarc foreland system, which became flooded to form the Karoo Sea. Sedimentation, beginning with glacial deposits from the north, but later from the Falkland Mountains to the south, into this depression formed the Karoo Supergroup.
The Dwyka group
About 330 million years ago Gondwana had drifted over the South Pole
The South Pole, also known as the Geographic South Pole, Terrestrial South Pole or 90th Parallel South, is one of the two points where Earth's axis of rotation intersects its surface. It is the southernmost point on Earth and lies antipod ...
,[Norman, N., Whitfield, G. (2006). ''Geological Journeys''. pp. 28, 122. Struik Publishers, Cape Town.] with the result that an ice sheet several kilometers thick covered much of Africa, and other parts of Gondwana. The glacial deposits from this ice sheet were the first of the sediments to be deposited to the north of the Cape Fold Mountains (and partially over these incipient mountains). The basin into which these sediments settled was deepest immediately north of the Cape Fold Mountain ranges. The ice sheet therefore floated on an inland lake, termed the Karoo inland sea, into which icebergs
An iceberg is a piece of freshwater ice more than 15 m long that has broken off a glacier or an ice shelf and is floating freely in open (salt) water. Smaller chunks of floating glacially-derived ice are called "growlers" or "bergy bits". The ...
which had calved off the glaciers
A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
and ice sheet to the north deposited vast quantities of mud and rocks of various sizes and origins. Such deposits are known as tillite
image:Geschiebemergel.JPG, Closeup of glacial till. Note that the larger grains (pebbles and gravel) in the till are completely surrounded by the matrix of finer material (silt and sand), and this characteristic, known as ''matrix support'', is d ...
.
Further north, the ice sheet was grounded also leaving diamictite
Diamictite (; from Ancient Greek ''δια'' (dia-): ''through'' and ''µεικτός'' (meiktós): ''mixed'') is a type of lithified sedimentary rock that consists of nonsorted to poorly sorted terrigenous sediment containing particles that ra ...
deposits whenever it partially melted, but, in addition, it scoured the bedrock, leaving behind striations (scratch marks) which can be seen near Barkly West
Barkly West is a town in the Northern Cape province of South Africa, situated on the north bank of the Vaal River west of Kimberley, Northern Cape, Kimberley.
Establishment and naming
Barkly West was the site of the first major diamond rush, in 18 ...
in the Northern Cape, and in the grounds of the University of KwaZulu-Natal
The University of KwaZulu-Natal (UKZN) is a university with five campuses in the province of KwaZulu-Natal in South Africa. It was formed on 1 January 2004 after the merger between the University of Natal and the University of Durban-Westville. ...
. This layer of tillite, traces of which can be found over a wide area of Southern Africa, India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, and South America provided crucial early evidence in support of the Theory of Continental Drift. In South Africa the layer is known as the Dwyka Group. It is the earliest and lowermost of the Karoo Supergroup of sedimentary deposits.
The Ecca group
As Gondwana drifted away from the South Pole, the glaciers melted, leaving a vast inland sea, extending across South Africa, and neighboring regions of Gondwana. It might have had an opening to the ocean (similar to the Black Sea
The Black Sea is a marginal mediterranean sea of the Atlantic Ocean lying between Europe and Asia, east of the Balkans, south of the East European Plain, west of the Caucasus, and north of Anatolia. It is bounded by Bulgaria, Georgia, Roma ...
) but tidal effects were small. Rivers draining mountains to the north of the Karoo Sea formed large swampy deltas
A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...
in which plants belonging to the ''Glossopteris
''Glossopteris'' tymology: from Ancient Greek γλῶσσα (glôssa, " tongue ") + πτερίς (pterís, " fern ")is the largest and best-known genus of the extinct Permian order of seed ferns known as Glossopteridales (also known as Arberia ...
'' flora flourished. This dense vegetation accumulated as peat, which eventually turned into coal. The coal deposits are confined to the northern shores of the early 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 Paleoz ...
Karoo Sea, and is mined today in the Highveld
The Highveld (Afrikaans: ''Hoëveld'', where ''veld'' means "field") is the portion of the South African inland plateau which has an altitude above roughly 1500 m, but below 2100 m, thus excluding the Lesotho mountain regions to the south-east of ...
and KwaZulu-Natal.
These sedimentary deposits are termed 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 ...
of the Karoo Supergroup. They consist largely of shales
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especiall ...
and 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 silicates) ...
s, and extend over the entire former Karoo Sea, but the southerly deposits do not contain coal, even though rivers from the Cape Fold Mountains formed small deltas. Although the vegetation in the south was not as dense as on the northern shores of the inland sea, several early reptiles such as ''Mesosaurus
''Mesosaurus'' (meaning "middle lizard") is an extinct genus of reptile from the Early Permian of southern Africa and South America. Along with it, the genera '' Brazilosaurus'' and ''Stereosternum'', it is a member of the family Mesosauridae a ...
'' are found in these Ecca deposits. This is a fossil reptile found only in Southern Africa and Brazil
Brazil ( pt, Brasil; ), officially the Federative Republic of Brazil (Portuguese: ), is the largest country in both South America and Latin America. At and with over 217 million people, Brazil is the world's fifth-largest country by area ...
providing important paleontological evidence of the existence of the Gondwana supercontinent.
The northern shores contain mainly fossil plants, pollens and spores. Fossils of a cephalopod
A cephalopod is any member of the molluscan class Cephalopoda (Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...
and some echinoids
Sea urchins () are spine (zoology), spiny, globular echinoderms in the class Echinoidea. About 950 species of sea urchin live on the seabed of every ocean and inhabit every depth zone from the intertidal seashore down to . The spherical, hard s ...
are also found in the north.
During the Ecca period the Falklands Plateau collided and then fused with Southern Africa, forming a vast range of mountains to the south of the Cape Fold Belt. This new mountain range was comparable in size to the Himalayas
The Himalayas, or Himalaya (; ; ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the planet's highest peaks, including the very highest, Mount Everest. Over 100 ...
. The northern slopes of these mountains generally dipped steeply into the Karoo Sea which was at its deepest at this point. The earthquakes that accompanied the formation of the Cape Mountains therefore initiated frequent underwater mud- and rock-slides, forming fan-shaped accumulations of turbidite
A turbidite is the geologic deposit of a turbidity current, which is a type of amalgamation of fluidal and sediment gravity flow responsible for distributing vast amounts of clastic sediment into the deep ocean.
Sequencing
Turbidites were ...
s, which can be seen in the south west corner of the Karoo today (see photograph lower down on the right). Turbidites have for some time been recognized as petroleum producing rocks, because the underwater avalanches that cause these deposits often carry organic matter from close to the coastline, especially near river estuaries and deltas, into the anoxic depths of adjoining troughs. Here it is buried in the turbidite and turns into hydrocarbons
In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons are generally colourless and hydrophobic, and their odors are usually weak or ex ...
, particularly petroleum
Petroleum, also known as crude oil, or simply oil, is a naturally occurring yellowish-black liquid mixture of mainly hydrocarbons, and is found in geological formations. The name ''petroleum'' covers both naturally occurring unprocessed crud ...
and gas. The turbidites in the Ecca formation of the Tanqua and Laingsburg Karoo regions have thus, recently, come under scrutiny by the petroleum industry and geologists, who have found them to have rich and readily accessible deposits of oil and gas. Thus the north-eastern Ecca basin is rich in coal, while its south-western corner is becoming renowned for its oils reserves.
Beaufort Group
With the formation of the Falkland Plateau and Cape Fold Mountain ranges, rivers from the south began to dominate the sedimentation in the Karoo Sea, which began to silt up. (The highlands to the north of the Karoo Sea had, by this time, been leveled by erosion and begun to be buried under newer sediments.) Several Mississippi-like rivers flowed over the silted up Karoo Basin from the south, creating rich new habitats for a variety of flora and fauna. The terrestrial (as opposed to lacunar or marine) deposits created by these rivers gave rise to 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 underlie ...
. It is composed of a monotonous sequence of shale
Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...
s and 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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...
s, with some interbedded lenticular sandstones
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 silicates) b ...
. The Beaufort Group is rich in reptilian, and to a lesser extent, amphibian remains. There is a plethora of both herbivorous and carnivorous reptile fossils. The Beaufort rocks are internationally famous for its rich record of therapsid
Therapsida is a major group of eupelycosaurian synapsids that includes mammals, their ancestors and relatives. Many of the traits today seen as unique to mammals had their origin within early therapsids, including limbs that were oriented more ...
synapsids
Synapsids + (, 'arch') > () "having a fused arch"; synonymous with ''theropsids'' (Greek, "beast-face") are one of the two major groups of animals that evolved from basal amniotes, the other being the Sauropsida, sauropsids, the group that inc ...
(mammal-like reptiles), which mark an intermediary stage in the evolution of the mammals from reptiles. The most abundant herbivores were the anomodonts
Anomodontia is an extinct group of non-mammalian therapsids from the Permian and Triassic periods. By far the most speciose group are the dicynodonts, a clade of beaked, tusked herbivores.Chinsamy-Turan, A. (2011) ''Forerunners of Mammals: R ...
, whose most primitive forms are also known from the Beaufort rocks. The dinocephalians
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. Dinocephal ...
(terrible head) are so named because of their extraordinary thick boned skulls, which were probably used for head butting during territorial fights. With their 3-meter body length, they were the first large animals to live on land.
During the course of the laying down of the 6 km thick Beaufort deposits, the massive end-Permian mass extinction, 251 million years ago, extinguished about 96% of all species alive at that time. The global event can clearly be seen in the Beaufort rocks. A few members of the genus Lystrosaurus
''Lystrosaurus'' (; 'shovel lizard'; proper Greek is λίστρον ''lístron'' ‘tool for leveling or smoothing, shovel, spade, hoe’) is an extinct genus of herbivorous dicynodont therapsids from the late Permian and Early Triassic epochs (a ...
were the only mammal-like reptiles that survived this event. The Beaufort sediments that were laid down after this event tend to be coarser than the ones that preceded them, probably because of a massive die-off of vegetation, which had protected the surface against erosion. These early Triassic sandstone-dominated strata are known as the Katberg formation (within the Beaufort Group), which accumulated to a thickness of 1 km. With time the Beaufort deposits became more fine-grained once again, probably indicating a recovery of the vegetation in the Karoo, and with it the appearance of a wide range of new species, including the dinosaurs
Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...
, and true mammals
Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...
during the late Triassic – early Jurassic.
Stormberg group
As Gondwana drifted north, conditions in the portion that was to become Southern Africa became increasingly hot and arid. Sandstones were the predominant rocks that formed. However, in some areas there was sufficient water to form swamps with consequent coal formation, but the quality is poor. The landscape probably resembled the Kalahari desert of today, with rivers like the present-day Orange River
The Orange River (from Afrikaans/Dutch: ''Oranjerivier'') is a river in Southern Africa. It is the longest river in South Africa. With a total length of , the Orange River Basin extends from Lesotho into South Africa and Namibia to the north ...
or the Nile
The Nile, , Bohairic , lg, Kiira , Nobiin language, Nobiin: Áman Dawū is a major north-flowing river in northeastern Africa. It flows into the Mediterranean Sea. The Nile is the longest river in Africa and has historically been considered ...
running through it, sustaining localized areas of Triassic flora and fauna.
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 ...
contains South Africa's earliest dinosaur fossils. It also contains the fossil remains of the shrew-sized Megazostrodon
''Megazostrodon'' is an extinct genus of basal mammaliaforms belonging to the order Morganucodonta. It is approximately 200 million years old. , the oldest mammal in Africa. A remarkable array of insect and plant fossils are found in some of the strata.
The uppermost strata of the Stormberg group were probably laid down under true sand desert conditions, similar to the Namib Desert
The Namib ( ; pt, Namibe) is a coastal desert in Southern Africa. The name is of Khoekhoegowab origin and means "vast place". According to the broadest definition, the Namib stretches for more than along the Atlantic coasts of Angola, Namib ...
in Namibia. It was probably as large as the Sahara Desert
, photo = Sahara real color.jpg
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today, extending from the Cape Fold Mountains many thousands of kilometers northwards over large parts of Gondwana. Only a small remnant of this massive formation can be found in and around Lesotho
Lesotho ( ), officially the Kingdom of Lesotho, is a country landlocked country, landlocked as an Enclave and exclave, enclave in South Africa. It is situated in the Maloti Mountains and contains the Thabana Ntlenyana, highest mountains in Sou ...
today. This formation was formerly known as “Cave Sandstone” as wind-eroded shallow caves often developed in cliffs made up of these rocks. These caves were later used by the San people
The San peoples (also Saan), or Bushmen, are members of various Khoe, Tuu, or Kxʼa-speaking indigenous hunter-gatherer cultures that are the first cultures of Southern Africa, and whose territories span Botswana, Namibia, Angola, Zambia, ...
who frequently decorated the walls with their paintings
Painting is the practice of applying paint, pigment, color or other medium to a solid surface (called the "matrix" or "support"). The medium is commonly applied to the base with a brush, but other implements, such as knives, sponges, and ai ...
. Today the Cave Sandstones are called the Clarens Formation
The Clarens Formation is a geological formation found in several localities in Lesotho and in the Free State, KwaZulu-Natal, and Eastern Cape provinces in South Africa. It is the uppermost of the three formations found in the Stormberg Group of ...
.
The oldest dinosaur embryo
An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male spe ...
s ever discovered were found in the Clarens Formation in 1978. The eggs were from the Triassic Period
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 period ...
(220 to 195 million years ago) and had fossilised foetal skeletons of ''Massospondylus
''Massospondylus'' ( ; from Greek, (massōn, "longer") and (spondylos, "vertebra")) is a genus of sauropodomorph dinosaur from the Early Jurassic. (Hettangian to Pliensbachian ages, ca. 200–183 million years ago). It was described by S ...
'', a prosauropod
Sauropodomorpha ( ; from Greek, meaning "lizard-footed forms") is an extinct clade of long-necked, herbivorous, saurischian dinosaurs that includes the sauropods and their ancestral relatives. Sauropods generally grew to very large sizes, had lon ...
dinosaur. More examples of these eggs have since been found in the Golden Gate Highlands National Park
Golden Gate Highlands National Park is located in Free State, South Africa, near the Lesotho border. It covers an area of . The park's most notable features are its golden, ochre, and orange-hued, deeply eroded sandstone cliffs and outcrops, es ...
, situated on the Clarens Formation rocks. Other fossils found in the park include those of advanced cynodont
The cynodonts () (clade Cynodontia) are a clade of eutheriodont therapsids that first appeared in the Late Permian (approximately 260 mya), and extensively diversified after the Permian–Triassic extinction event. Cynodonts had a wide variety ...
ia (canine toothed animals), small thecodontia
Thecodontia (meaning 'socket-teeth'), now considered an obsolete taxonomic grouping, was formerly used to describe a diverse "order" of early archosaurian reptiles that first appeared in the latest Permian period and flourished until the end of t ...
(animals with teeth set firmly in the jaw), bird-like and crocodile-like dinosaurs.[Weishampel, David B; et al (2004). "Dinosaur distribution (Early Jurassic, Africa)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 535–536. .]
Drakensberg and Lebombo groups
About 182 million years ago the southern African portion of Gondwana passed over the Bouvet hotspot
causing the crust under the Karoo Supergroup to rupture, releasing huge volumes of basaltic lava over the Clarens desert, covering nearly the whole of Southern Africa and other portions of Gondwana.The pile of lava that accumulated over the course of several eruptions was more than 1600 m thick, especially in the east (in present-day Lesotho). This massive lava outpouring brought the Karoo sedimentation to an abrupt end.
The name ''Drakensberg Group'' is derived from the fact that this layer forms the uppermost 1400 m of the Great Escarpment
The Great Escarpment is a major topographical feature in Africa that consists of steep slopes from the high central Southern African plateauAtlas of Southern Africa. (1984). p. 13. Reader's Digest Association, Cape Town downward in the directio ...
on the international border between Lesotho and KwaZulu-Natal, often referred to as ''the'' Drakensberg
The Drakensberg (Afrikaans: Drakensberge, Zulu: uKhahlambha, Sotho: Maluti) is the eastern portion of the Great Escarpment, which encloses the central Southern African plateau. The Great Escarpment reaches its greatest elevation – within th ...
(although technically the "Drakensberg" refers to the entire 1000 km long eastern portion of the Great Escarpment, only about a third of which is capped by the Drakensberg lavas).
The magma welled up through long crack-like fissures, with occasional spatter cones, but typical volcanoes were rare. Each surface lava flow was between 10 and 20 meters thick. These flows piled up in rapid succession over 2 million years, to form a single continuous 1 to 1.6 km thick lava layer. However, not all of the magma reached the surface, but extruded under high pressure between the horizontal strata of the Ecca and Beaufort rocks. When this magma solidified it formed multiple dolerite
Diabase (), also called dolerite () or microgabbro,
is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...
sills at various depths throughout the southern and south-western Karoo sediments. These sills vary in thickness from a few centimeters to hundreds of meters.
This outpouring of lava coincided with uplifting of the Southern African portion of Gondwana, and the formation of rift valley
A rift valley is a linear shaped lowland between several highlands or mountain ranges created by the action of a geologic rift. Rifts are formed as a result of the pulling apart of the lithosphere due to extensional tectonics. The linear dep ...
s along what were to become the sea borders of the subcontinent. As these rift valleys widened they became flooded to form the proto-Indian and Southern Atlantic Oceans, as Gondwana fragmented into today's separate continents of South America
South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the southe ...
, Africa
Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...
, 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 contine ...
, Australia
Australia, officially the Commonwealth of Australia, is a Sovereign state, sovereign country comprising the mainland of the Australia (continent), Australian continent, the island of Tasmania, and numerous List of islands of Australia, sma ...
, India
India, officially the Republic of India (Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the so ...
, 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 Africa ...
and Arabia
The Arabian Peninsula, (; ar, شِبْهُ الْجَزِيرَةِ الْعَرَبِيَّة, , "Arabian Peninsula" or , , "Island of the Arabs") or Arabia, is a peninsula of Western Asia, situated northeast of Africa on the Arabian Plate. ...
.
In close association with this rifting, a second episode of basalt eruption occurred along the border with Mozambique
Mozambique (), officially the Republic of Mozambique ( pt, Moçambique or , ; ny, Mozambiki; sw, Msumbiji; ts, Muzambhiki), is a country located in southeastern Africa bordered by the Indian Ocean to the east, Tanzania to the north, Malawi ...
to form the Lebombo Mountains
The Lebombo Mountains, also called Lubombo Mountains ( pt, Montes Libombos), are an , narrow range of mountains in Southern Africa. They stretch from Hluhluwe in KwaZulu-Natal in the south to Punda Maria in the Limpopo Province in South Africa in ...
. A layer of lava more than 4800 m thick was violently extruded at this time. While the Drakensberg lavas form nearly horizontal layers, the Lebombo lavas dip to the east, so it is difficult to gauge how far the lava spread laterally.
The uplifting of Southern Africa heralded a phase of massive erosion, removing a layer several kilometers thick from the African Surface
The African Surface or African Erosion Surface is a land surface formed by erosion covering large swathes of Africa.Burke & Gunnell 2008, pp. 6–7. The type area of the surface lies in South Africa where the surface was first identified as such ...
. Nearly all of the Drakensberg lavas were eroded away, leaving a remnant in Lesotho, several small patches on the Springbok Flats
The Springbok Flats is an extensive plain situated in Limpopo, South Africa. The southern boundary is the Pienaars River which intersects the N1 main road between Pretoria and Polokwane. To the west it includes the towns of Bela-Bela, Modimolle, ...
in the north of the country, and in the Lebombo mountains along the Mozambique border. Once the layer of hard lava was eroded away, the softer Karoo sediments over the rest of the basin eroded even faster. However, the dolerite sills resisted erosion, protecting the softer Beaufort and Ecca shales beneath them. This created numerous and widespread flat topped hills, known as Karoo Koppies ("koppie" being the Afrikaans
Afrikaans (, ) is a West Germanic language that evolved in the Dutch Cape Colony from the Dutch vernacular of Holland proper (i.e., the Hollandic dialect) used by Dutch, French, and German settlers and their enslaved people. Afrikaans gra ...
term for hill), which are iconic of the Karoo, and, by extension, the South African landscape. The dykes, or vertical fissures which brought the lava to the surface stand out today as linear ridges extending across large stretches of the Karoo.
Post Karoo period
The continued erosion of Southern Africa over the past 180 million years has meant that rocks younger than The Drakensberg Group are almost non-existent over most of the interior. Some of the eroded material from the interior was trapped between the Cape Fold Mountains to the south during the Cretaceous
The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
Period to form the Enon Formation and similar deposits near the coast of KwaZulu-Natal
KwaZulu-Natal (, also referred to as KZN and known as "the garden province") is a province of South Africa that was created in 1994 when the Zulu bantustan of KwaZulu ("Place of the Zulu" in Zulu) and Natal Province were merged. It is locate ...
, north of Richards Bay
Richards Bay ( af, Richardsbaai) is a town in KwaZulu-Natal, South Africa. It is situated on a 30 square kilometre lagoon of the Mhlatuze River, which makes it one of the country's largest harbours. Richards Bay also has the deepest natural ha ...
. Apart from that, only very minor patches of very recent, mainly sandy deposits occur in South Africa.
The Karoo supergroup elsewhere in Africa
In Zambia, Zimbabwe and Mozambique the Karoo Supergroup is divided into (from oldest to youngest):
* Lower Karoo Group, comprising the Dwyka, Hwange (Zimbabwe) / Siankondobo (Zambia) and Madumabisa formations.
* Upper Karoo Group
The Upper Karoo Group is a sequence of Triassic to Early Jurassic sedimentary and volcanic rocks found in Botswana, Zambia, and Zimbabwe.
It comprises the Escarpment Grit (in the Mid-Zambezi and Limpopo basins) and the Angwa Sandstone (in the M ...
, comprising the Escarpment Grit formation (in the Mid-Zambezi and Limpopo basins) and the Angwa Sandstone Formation
The Angwa Sandstone is a geological formation of the mid-Triassic Cabora Bassa Basin and Mana Pools Basin of southern Africa, consisting mainly of sandstone.
Description Stratigraphy
The Angwa Sandstone is the lowest formation in the Upper Karoo ...
(in the Mana Pools and Cabora Bassa Basins), overlain by the Pebbly Arkose Formation
The Pebbly Arkose Formation is a Late Triassic geologic formation found in southern Africa.
Geology Description
The formation comprises mainly coarse, arkosic sandstones.
Extent
The Pebbly Arkose Formation is found in Botswana, Zambia and ...
and the Forest Sandstone Formation
The Forest Sandstone is a geological formation in southern Africa, dating to roughly between 200 and 190 million years ago and covering the Hettangian to Sinemurian stages of the Jurassic Period in the Mesozoic Era. As its name suggests, it cons ...
, capped by Batoka basalts.
See also
*
*
References
Further reading
*
* Sukatsheva I.D., Beattie R. & Mostovski M.B. 2007
''Permomerope natalensis'' sp. n. from the Lopingian of South Africa, and a redescription of the type species of ''Permomerope'' (Insecta: Trichoptera).
''African Invertebrates
''African Invertebrates'' is a peer-reviewed open access scientific journal that covers the taxonomy, systematics, biogeography, ecology, conservation, and palaeontology of Afrotropical invertebrates, whether terrestrial, freshwater, or marine. I ...
'' 48 (2): 245–251.
*
{{Geology of South Africa, formations
Karoo
Mesozoic Erathem of Africa
Paleozoic Erathem of Africa
Paleontological sites of Africa
Geologic formations of Africa
Stratigraphy of Africa
Geologic formations of Botswana
Geologic formations of the Democratic Republic of the Congo
Geologic formations of Kenya
Geologic formations of Lesotho
Geologic formations of Madagascar
Geologic formations of Mozambique
Geologic formations of Namibia
Geology of Eswatini
Geologic formations of South Africa
Geologic formations of Tanzania
Geologic formations of Zambia
Geologic formations of Zimbabwe