The Onverwacht Group or Onverwacht Series is a series of
greenstone belt
Greenstone belts are zones of variably metamorphosed mafic to ultramafic volcanic sequences with associated sedimentary rocks that occur within Archaean and Proterozoic cratons between granite and gneiss bodies.
The name comes from the green ...
s and
volcanic rock
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 r ...
formations from the
Archean
The Archean Eon ( , also spelled Archaean or Archæan) is the second of four geologic eons of Earth's history, representing the time from . The Archean was preceded by the Hadean Eon and followed by the Proterozoic.
The Earth
Earth ...
Eon in the
Kaapvaal Craton
The Kaapvaal Craton (centred on Limpopo Province in South Africa), along with the Pilbara Craton of Western Australia, are the only remaining areas of pristine 3.6–2.5 Ga (billion years ago) crust on Earth. Similarities of rock records fro ...
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 ...
and
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 ...
.
A well known part of the Onverwacht Series is visible in the
Komati valley, located in the east of the
Transvaal Transvaal is a historical geographic term associated with land north of (''i.e.'', beyond) the Vaal River in South Africa. A number of states and administrative divisions have carried the name Transvaal.
* South African Republic (1856–1902; af, ...
region.
Subdivision
The Onverwacht Group can be divided into two subgroups with six formations:
*
Geluk Subgroup
**
Swartkoppie Formation –
**
Kromberg Formation –
**
Hooggenoeg Formation –
*
Tjakastad Subgroup
**
Komatii Formation
The Komati Formation, also named as Komatii Formation, is a 3.475 billion year old Paleoarchean rock formation, named after the nearby Komati River in South Africa. It is the type locality for komatiite, a high temperature, magnesium-rich volcanic ...
–
**
Theespruit Formation –
**
Sandspruit Formation –
The
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 preserved ...
s found in the Onverwacht Series are among the oldest found on Earth.
[Engel et al., 1968]
See also
*
Archean life in the Barberton Greenstone Belt
The Barberton Greenstone Belt of eastern South Africa contains some of the most widely accepted fossil evidence for Archean life. These cell-sized prokaryote fossils are seen in the Barberton fossil record in rocks as old as 3.5 billion years. T ...
*
Warrawoona Group
The Warrawoona Group is a geological unit in Western Australia containing putative fossils of cyanobacteria cells. Dated 3.465 Ga, these microstructures, found in Archean chert, are considered to be the oldest known geological record of life on E ...
References
Bibliography
*
External links
*
Der Barberton Greenstone Belt und Komatiite
Geologic groups of Africa
Geologic formations of South Africa
Geology of Eswatini
Archean Africa
Fossiliferous stratigraphic units of Africa
Paleontology in South Africa
Origin of life
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