Karoo System
The main Karoo Basin ( in older literature also Karoo system) forms a significant part of the geological structure in southern Africa and consists mainly of sediments. His landscapes are highly differentiated today. The Karoo main pool is a very large structure unit within the Karoo Supergroup.
- 4.1 coal
- 4.2 Natural stones
Definition
The word " Karoo " (originally Kuru ) comes from the language of the Khoi Khoi and means " dry". The same term also applies to the National Park and the surrounding landscape space application.
Derived from the South African Karoo landscape, the concept has found its way into the geosciences. He called sedimentary sequences that have been explored first in the South African Karoo landscape. A key role took this one in the 19th and 20th century geologists of Rhodes University. Spectacular fossils near Grahamstown, starting with the work of Andrew Geddes Bain, global focused attention on this region. In 1867, the British geologist and paleontologist Thomas Rupert Jones published an article entitled Synopsis of the Karoo Beds, which appeared in the Journal of the Geological Society of London. This paper is one of the earliest overviews of the field. A well-known fossil collectors in the Karoo was James Kitching.
Expansion
The main Karoo basin is in its extension far beyond the landscape Karoo and southern Africa covers an area of about 1.56 million square kilometers. Primarily, these are the territories of South Africa, Lesotho and Swaziland. More foothills of the system extend to the border of Mozambique and the Limpopo River in the north of South Africa. From Botswana, and from the eastern and central Namibia grab some parts of neighboring Karoo structures on the territory of South Africa.
Its maximum length expansion in South Africa is 1300 km, and its maximum width is reached between Kimberley and East London with about 590 kilometers. At landforms the Karoo main pool is extraordinarily diverse. There are flat plains, rolling hills, mid- mountain country with distinct height levels and high mountain structures. Rivers form shallow meandering valleys and deeply incised canyons.
For the full understanding it is important to point out that the Karoo sediments already extend from the African equatorial region over a large area in a southerly direction and individual sequences of these geological unit are also north of the Equator in Gabon and Sudan recognizable. In the continental context, the totality of these sediments is named Karoo Supergroup ( Karoo Supergroup ). The following discussion is limited to the geographic area of southern Africa, ie the States of South Africa, Lesotho and Swaziland, called the Karoo main pool, on the edge on Namibia and Botswana.
Development, geological structure
The Karoo Supergroup is composed mainly of sedimentary sequences together that formed in the Carboniferous, Permian and the Triassic. Your degree is the Karoo - time in the Mesozoic sediments of the Jura. At this time there came again to the formation of extensive and thick Lavaaustritten that shape the face of the Karoo main basin in South Africa. Overall, the sedimentation lasted well over 100 million years, and in some cases produced a layered structure with a thickness of about 10 kilometers.
At its outer edges the Karoo main basin is bounded by multiple older rocks. Examples are the greenstone complex in the Barberton district and the Bushveld Complex northwest of Johannesburg.
The origin of the Karoo main basin, as well as the Karoo Supergroup is based on mutually -acting tectonic and climatic processes. In the Upper Devonian to the Upper Carboniferous, the southern continent of Gondwana with the northern continent Laurussia and the Asia continent joined to the geologically recent supercontinent Pangaea. Along the edges of the then Panthalassa and the Tethysozeans originated off the coast of Gondwana subduction, and alluvial deposits, and mountain building the foundations for the later Karoo structures, such as the Cape Supergroup between Cape Town and Port Elizabeth.
The onset of sedimentation in the Karoo Supergroup is located in the following uppermost Carboniferous, before about 300 million years ago, when a strong continental glaciation existed on the continent of Pangaea, the considerable scree deposits generated ( Dwyka Group). This was followed by addition tectonic influences climatic fluctuations of cold and semi-arid to warm and hot periods with changing precipitation phases. In this period existed on the continent large inland lakes that left extensive sediments in their pool. The climatic amplitudes had a direct effect on the amount of debris in Pangaea, and there was a temporary contact to the open ocean.
Breaking Pangaea and thus also of the former Gondwana led at the end of the Jurassic and early Cretaceous to strong tectonic activity with concomitant volcanism. In its course he created in the area of today's Eastern Cape Province extensive penetrations of the Karoo sediments with basaltic masses, primarily as dolerite. In this way arose dome-shaped Magmenaustritte, horizontal intrusions between individual sediment layers and intersecting exit slits ( Dykes ), as they are easily observed in the Amathole Mountains. In the Drakensberg basalt masses of the Karoo main basin reached its greatest extent and form its youngest lithostratigraphic unit. The totality of the basalt mass is classified because of their sheer size and geologically relatively rapid emergence in the group of Igneous United Provinces.
The layers of the Karoo main basin in South Africa have a very low slope, the dip of the layering is directed to the northwest, north and east. At its edge in the southwest and southern part of the layer structure is graded and folded. There they interact with the folding zone of the Cape fold belt (Cape Fold Belt ) in contact.
With the exploration of the Karoo main basin was divided it into the following groups described. The group names are derived from the places and regions which played an important role in their discovery and geological exploration. The order of the following individual representation goes from young to old.
Drakensberg Group ( Drakensberg Group)
This latest and thus final part of the Karoo Supergroup is strongly influenced by basalt rocks and has only a few, small mighty sandstone layers. This igneous event lasted only a few million years and therefore accounts for only a relatively short period of time in the history of the main Karoo Basin. The Drakensberg basalts have been dated at about 180 million years, and thus fall into the chronostratigraphic Jurassic period.
The lava flows of this era are among the largest volcanic events of earth's history. The continuation of these basalts are found due to the continental drift today in Patagonia and the Falkland Islands as well as in Tasmania and parts of Antarctica .. As the lava flows clearly erosion -resistant than the older sedimentary rocks, which they store, they now form the peaks of the Drakensberg.
In older literature geoscientific the Drakensberg basalts are still considered as subgroup of Stormberg Group. According to recent views, they represent a distinct lithostratigraphic unit
Stormberg Group ( Stormberg Group)
This group is dominated by sandstones and is also one of the youngest sections in the main Karoo Basin. It got its name from Storm Mountain massif south of the town of Aliwal North. Their formation extends from the Middle Triassic to the Jurassic ( 230-183 million years). It occurs mainly in the Vorgebirgszonen of Lesotho and the South African province of KwaZulu -Natal. In the Elliot Formation was found 12 meters long dinosaur skeletons ( Melanorosaurus ). The name derives from the town of Elliot. To Stormberg Group remains one of the Molteno and Clarens formation. Molteno is a town in the Storm Mountain and Clarens a settlement on the northern edge of the Drakensberg.
Beaufort Group ( Beaufort Group)
The first description of the group goes to the British geologist Thomas Rupert Jones (* 1819 in Cheapside, † 1911 in Chesham ), who examined the sediment layers at Beaufort West to 1867. Their emergence time between the Late Permian and the Middle Triassic ( 255-237 million years).
Typical rocks of this group are sandstones and pelites (English mudstone ) on. In the landscape of their layered structure is often good to watch, and in this way they shape the relief of the respective regions. Particularly striking are the Doleritintrusionen and crests in Amatholegebirge between Alice, King William's Town and Cathcart. Another striking landform of the Beaufort Group are widely stretched levels with only slight pronounced ripple.
The sedimentary sequences of the Beaufort Group have a particular susceptibility weather. Under these circumstances, they break easily and form only small powerful soils of sands and silts. An intensive land use in rural areas specifically reinforces this trend. As a result of those processes, it is used in many areas for so-called gully formation. Due to soil erosion valuable ecosystems and agricultural land will be destroyed. In addition, the flushed away by surface water soil pollutes the river with large quantities of mineral Schwebstoffeinträgen, can make the dams and other water management facilities inoperable.
Important discovered fossil reptile species in this group are Cistecephalus ( Dicynodontia ) Cynognathus, Eodicynodon, Lystrosaurus, Pristerognathus, Procolophon, Tapinocephalus and Tropidostoma.
Ecca Group ( Ecca Group)
The Ecca Group is the second oldest unit of the Karoo Supergroup. It took its name from the Ecca Pass near Grahamstown, where they have their type profile. The period of their deposition falls mainly within the lower Permian (about 290-260 million years ago). Your outcrop lines the entire Karoo core area with the sediments of the Beaufort and Stormberg Group. Along the southern margin of the Karoo Basin, the Ecca sediments have direct contact with the adjacent folding zone in the Cape (Cape Fold Belt ).
The main rocks are bluish to greenish mudstones and fine-grained conglomerates. Chance of sandstones are turned on. South of Aberdeen, the Ecca strata are rather sandy mudstones and siltstones and are rather subordinate ago. In addition, there are lenticular limestone on. In this southern area the sandstones are tough, trained by dark, blotchy color and medium-to fine-grained and contain feldspars. In the north of the main Karoo Basin, in the Highveld to find coal seams in the middle layers (there: Vryheid Formation) of the Ecca Group.
In this group are more common plant fossils ( Gangamopteris, Glossopteris, Phyllotheca ).
Dwyka Group ( Dwyka Group)
The Dwyka Group is the oldest section of the main Karoo Basin and formed in the upper Carboniferous (ca. 300-290 million years). It occurs as a contiguous part, especially in the northwest, west and south. Addition, there are narrow zones in KwaZulu- Natal, island-shaped units east of Pretoria and in the eastern part of Namibia and the South African Kalahari. The name is derived from the Dwyka River and the settlement in the southern Karoo Dwyka from. South of the scattered settlement cuts through the canyon several times these sediments.
The most striking rocks of the Dwyka Group (also called Dwykakonglomerat ), a thick blue-gray mudstone with grained sediment and smaller boulders of various rocks of the Dwyka - origin Tillit. He emerged from the glacial boulders during permokarbonischen continental glaciation on the Gondwana continent. In addition to the tillites themselves siltstones and quartzites find.
Likely to be encountered here important fossils include fish ( Palaeoniscus ), crustaceans ( Pygocephalus, Anthrapalaemon ) and plants ( Lepidodendron ). In Namibia, they found echinoderms and marine mollusks. Only occasionally occur silicified tree trunks that were swept away by large masses of water in the glaciers melt and deposited elsewhere.
Useful resources
The main Karoo Basin provides relatively little exploitable commodities. Especially it lacks significant mineral deposits.
Coal
South Africa is the world 's sixth largest producer of coal and has various grades of coal. There are lignite and hard coal are available. Add small amounts of anthracite is available. Coal deposits are in the region east of Johannesburg ( Mpumalanga Province ) to a great extent available, which make up 83 percent of the coal reserves in South Africa. In the northern sectors of the coal is mined. Other deposits are in the provinces of Free State, Limpopo, KwaZulu -Natal and the Eastern Cape. However, they are only partially funded industrially.
The discovery of coal deposits by European immigrants dates back to the early 18th century, and came to Franschhoek, a mining extraction, however, is first detected in 1864 in Molteno. However, the local population is said to have won even before colonization by Europeans, coal to a small extent.
Natural stones
The most derived for construction and decoration purposes natural stones from the main Karoo Basin are sandstones with varied rock formations. Particularly influential architecture they are represented, for example, in the cities of Aliwal North, Queenstown, Cradock, Graaff -Reinet and Grahamstown. Intrusive rocks, such as dolerite in the Eastern Cape, one uses only subordinate to rubble in rural house construction, for the garden or in road construction (heavy masonry). Their high strength makes their processing.
From an isolated lying sedimentary sequence of the Clarens Formation ( Stormberg Group) in the Northern Province is the internationally renowned sandstone Naboomspruit. Also worth mentioning are numerous sandstone mining sites in the western parts of Lesotho, which provide low-cost bricks for the inner country and South African markets.
On the northern edge of the system, west and east of Pretoria, you win igneous rocks, such as gabbros and granites. Of these mining locations known worldwide as the commercial varieties Belfast Black and Nero Impala and African originate Red