Stormberg Group
Encyclopedia
The Stormberg Group is the name given to the sedimentary
geological formations found in Karoo
Basin region of Southern Africa
, immediately above the Beaufort Group
. It consists mainly of sandstone
s and mudstone
s and preserves a record of gradual desertification.
The Stormberg Group is subdivided into three formations:
Sedimentary rock
Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....
geological formations found in Karoo
Karoo
The Karoo is a semi-desert region of South Africa. It has two main sub-regions - the Great Karoo in the north and the Little Karoo in the south. The 'High' Karoo is one of the distinct physiographic provinces of the larger South African Platform division.-Great Karoo:The Great Karoo has an area of...
Basin region of Southern Africa
Africa
Africa is the world's second largest and second most populous continent, after Asia. At about 30.2 million km² including adjacent islands, it covers 6% of the Earth's total surface area and 20.4% of the total land area...
, immediately above the Beaufort Group
Beaufort Group
The Beaufort Group is the third of the main subdivisions of the Karoo Supergroup of geological strata in Southern Africa. It follows conformably after the Ecca Group and consists essentially of sandstones and shales, deposited in the Karoo Basin from the Middle Permian to the early part of the...
. It consists mainly of sandstone
Sandstone
Sandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
s and mudstone
Mudstone
Mudstone is a fine grained sedimentary rock whose original constituents were clays or muds. Grain size is up to 0.0625 mm with individual grains too small to be distinguished without a microscope. With increased pressure over time the platey clay minerals may become aligned, with the...
s and preserves a record of gradual desertification.
The Stormberg Group is subdivided into three formations:
- Sandstone of the oldest, the Molteno FormationMolteno FormationThe Molteno Formation is a palaeontological formation of the Stormberg Group, located in the main Karoo Basin, South Africa. It dates to the Upper Triassic period and is rich in fossils....
, was formed from river sands in the Upper TriassicTriassicThe Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
. This is now exposed as cliffs in the Drakensberg and can be easily recognised by its sparkling appearance. This is due to minute quartz crystals that coat and bind together the sand grains.
- The Molteno Formation consists of two major coarsening-upward sequences, the basal sequence is made up by the Bamboesberg and Indwe Sandstone and the upper sequence by the Transitional Member. Tabular sheets of horizontally and cross stratified medium- to coarse grained sandstone dominate the formation. The sandstones were deposited by braided streams on a vast braidplain.
- The Molteno Formation is in turn overlain by red mudstone of the Elliot FormationElliot FormationThe Elliot Formation is a geological formation dating to roughly 210 to 190 million years ago and covering the Norian to Sinemurian stages. The Elliot Formation is found in South Africa and Lesotho and is a member of the Stormberg Group. It consists mainly of limestone, sandstone, and mudstone...
which contains dinosaurDinosaurDinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
fossils such as the 12 metre long MelanorosaurusMelanorosaurusMelanorosaurus , is a genus of basal sauropodomorph dinosaur that lived during the Late Triassic period. A herbivore from South Africa, it had a large body and sturdy limbs, suggesting it moved about on all fours...
.
- The Elliot Formation is dominated by red floodplain mudstones with subordinate channel and crevasse splay deposits. These were interpreted as a mixed load dominated meandering system in an increasingly arid setting. Towards the top of the formation aeolian sediments occur as metre-scale intercalations in the fluvial deposits of the Elliot Formation.
- The white cliffs of the middle DrakensbergDrakensbergThe Drakensberg is the highest mountain range in Southern Africa, rising to in height. In Zulu, it is referred to as uKhahlamba , and in Sesotho as Maluti...
are composed of Clarens FormationClarens FormationThe Clarens Formation is a prominent fossil site in the Tuli Basin, in the KwaZulu-Natal region of South Africa.-Fauna of the Clarens Formation:Unidentified dinosaur eggs have been recovered from the formation.-Bony fish:-Dinosaurs:-Synapsids:...
sandstoneSandstoneSandstone is a sedimentary rock composed mainly of sand-sized minerals or rock grains.Most sandstone is composed of quartz and/or feldspar because these are the most common minerals in the Earth's crust. Like sand, sandstone may be any colour, but the most common colours are tan, brown, yellow,...
. These sandstones were deposited as large dunes in a desert environment. Worm burrows and dinosaurDinosaurDinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...
footprints can also be found in these rocks.
- The Clarens Formation consists of yellow fine-grained sandstones, sandy siltstones and mudstones. This indicates strong aridification of the climate. Wind blown dunes suggest deposition in a desert environment with shallow playa lake and river deposits in the wetter parts of the basin , producing a complex interaction of aeolian and aqueous sedimentation.
See also
- Karoo SupergroupKaroo SupergroupThe Karoo Supergroup is the largest stratigraphic unit in Southern Africa, covering almost two thirds of the present land surface, including central Cape Province, almost all of Orange Free State, western Natal, much of south-east Transvaal, Zambia, Zimbabwe and Malawi...
- Molteno FormationMolteno FormationThe Molteno Formation is a palaeontological formation of the Stormberg Group, located in the main Karoo Basin, South Africa. It dates to the Upper Triassic period and is rich in fossils....
- Elliot FormationElliot FormationThe Elliot Formation is a geological formation dating to roughly 210 to 190 million years ago and covering the Norian to Sinemurian stages. The Elliot Formation is found in South Africa and Lesotho and is a member of the Stormberg Group. It consists mainly of limestone, sandstone, and mudstone...
- Clarens FormationClarens FormationThe Clarens Formation is a prominent fossil site in the Tuli Basin, in the KwaZulu-Natal region of South Africa.-Fauna of the Clarens Formation:Unidentified dinosaur eggs have been recovered from the formation.-Bony fish:-Dinosaurs:-Synapsids:...
- Stormberg MountainsStormberg MountainsThe Stormberg Mountains are a range of mountains situated in the Eastern Cape province of South Africa and are a subsection of the greater Drakensberg mountain range. They form part of the 'Amatola and Stormberg' region which includes major towns like Grahamstown, East London and Port Alfred.Towns...