The Drakensberg Group is a geological group named after the Drakensberg mountain range where in its uppermost sections the rocks are found. The Drakensberg Group lies over most 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 ...

and localities in 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 ...

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 ...

, and Free State provinces of South Africa. It forms part of the greater Karoo Igneous Province, which occurs over an extensive area of southern Africa. Platberg, basalt op sandsteen

Background

The Drakensberg Group was formed approximately 182 million years ago during the early Jurassic period. Rifting tectonics in response to the breakup of the supercontinent

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 ...

are believed to have been the cause for the formation of the Drakensberg Group. Networks of hyperbyssal (shallow intrusives)

dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes, ...

and sills represent the conduits through the crust that brought basaltic and andesitic lava to the surface, and caused the formation of the extrusive flood basalts of the Drakensberg Group. The

and sills are preserved throughout the

Karoo Basin The Karoo Supergroup is the most widespread stratigraphy, stratigraphic unit in Africa south of the Kalahari Desert. The group (stratigraphy), supergroup consists of a sequence of units, mostly of nonmarine origin, deposited between the Pennsylvan ...

, and have served as a weathering barrier for much of the

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

rocks. The Drakensberg Group comprises minor sedimentary (ie. sandstones,

lapilli Lapilli is a size classification of tephra, which is material that falls out of the air during a volcanic eruption or during some meteorite impacts. ''Lapilli'' (singular: ''lapillus'') is Latin for "little stones". By definition lapilli range f ...

deposits,

pyroclastic Pyroclastic rocks (derived from the el, πῦρ, links=no, meaning fire; and , meaning broken) are clastic rocks composed of rock fragments produced and ejected by explosive volcanic eruptions. The individual rock fragments are known as pyroc ...

deposits, and igneous (ie. continental flood basalt/ andesite sequences, shallow intrusive

and sills, and diatremes) and is part of the greater volcanic

extrusive rock Extrusive rock refers to the mode of igneous volcanic rock formation in which hot magma from inside the Earth flows out (extrudes) onto the surface as lava or explodes violently into the Earth's atmosphere, atmosphere to fall back as Pyroclastic ...

sequences of the Karoo Igneous Province. In its entirety, the Karoo Igneous Province represents a vast suite of sedimentary, extrusive and

intrusive rock Intrusive rock is formed when magma penetrates existing rock, crystallizes, and solidifies underground to form ''Igneous intrusion, intrusions'', such as batholiths, dike (geology), dikes, Sill (geology), sills, laccoliths, and volcanic necks.I ...

s ranging from 200 - 130 million years in age. Past studies have shown that there are major

geochemical Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...

changes in the provinces from the north and the south. The provinces of the central to southern areas are composed of Titanium - Zirconium low (Ti-Zr) tholeiitic basalt, and andesitic compositions also occur. The Drakensberg Group has been subdivided into two recognized geological formations. While both formations are composed of tholeiitic basalt, they have minor

differences. The two formations are listed below (from oldest to youngest): *Barkly East Formation: This

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondar ...

is the only formation of the Drakensberg Group to contain sedimentary units. These sedimentary units are composed of sandstones,

deposits, and

deposits. They are only found in the lower sections and are interbedded with basalts. *Lesotho Formation: Composed entirely of tholeiitic basalts. However, in some parts of

pillow lava basalts are found which means these basalts had extruded out as lava underwater ( subaqueous extrusion) into large lakes.

Geographic extent

The Drakensberg Group lavas compose the upper levels of the entire Drakensberg mountain range. The lavas stretch out over most of

and into the northeastern

, the southern Free State, and eastern

provinces of South Africa. Basalt provinces of the same low Ti-Zr chemical composition as the Drakensberg lavas are found in the Springbok Flats province in Limpopo, and other basalt sub-outcrops are found in eastern Botswana and central Namibia. These occurrences suggest that the Drakensberg Group lavas once covered a vast area over southern Africa. In addition, basalt xenoliths of the same chemical structure as the Drakensberg lavas have been found in the

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 ...

within Cretaceous-aged

kimberlite pipes Volcanic pipes or volcanic conduits are subterranean geological structures formed by the violent, supersonic eruption of deep-origin volcanoes. They are considered to be a type of ''diatreme''. Volcanic pipes are composed of a deep, narrow cone o ...

(~ 90 Ma) that intruded older rocks of the

. In the Lesotho highlands and the highest sections of the Drakensberg mountain range, only erosional remnants of the Drakensberg lavas remain.

Correlation

The Drakensberg Group is part of the greater Mesozoic-aged Karoo Igneous Province of southern Africa and the Ferrar Large Igneous Province of Antarctica ( Karoo-Ferrar). The Kirwan basalts of Antarctica particularly resemble the Drakensberg Group, because Antarctica was close to the southern Lebombo province before the break up of

. The Drakensberg basalts are

geochemically Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing th ...

identical to the Springbok Flats

volcanics Volcanic rock (often shortened to volcanics in scientific contexts) is a rock formed from lava erupted from a volcano. In other words, it differs from other igneous rock by being of volcanic origin. Like all rock types, the concept of volcanic ...

. It was thought for some time that the Drakensberg volcanics were associated with the Parana Igneous Province of Brazil and the Etendeka Province in northern Namibia. However, these provinces have since been dated some 50 million years younger than the Karoo-Ferrar provinces.

References

{{Geology of South Africa, formations Geologic groups of Africa Geologic formations of Lesotho Geologic formations of South Africa Jurassic System of Africa Jurassic South Africa Jurassic volcanism