The Morokweng impact structure is an
impact structure buried beneath 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 d ...
near the town of
Morokweng in
South Africa
South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...
's
North West province
North West is a province of South Africa. Its capital is Mahikeng. The province is located to the west of the major population centre of Gauteng and south of Botswana.
History
North West was incorporated after the end of Apartheid in 1994, an ...
, close to the border with
Botswana
Botswana (, ), officially the Republic of Botswana ( tn, Lefatshe la Botswana, label= Setswana, ), is a landlocked country in Southern Africa. Botswana is topographically flat, with approximately 70 percent of its territory being the Kalaha ...
.
Description
The impact structure is at least about in diameter and the age is estimated to be 146.06 ± 0.16 million years, placing it within the
Tithonian stage of the
Late Jurassic
The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987.
In European lithostratigraphy, the name ...
, several million years before the
Jurassic
The Jurassic ( ) is a geologic period and 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 Jurassic constitutes the middle period of ...
–
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 ...
boundary.
[Kenny, G.G., Harrigan, C.O., Schmitz, M.D., Crowley, J.L., Wall, C.J., Andreoli, M.A., Gibson, R.L. and Maier, W.D., 2021. ''Timescales of impact melt sheet crystallization and the precise age of the Morokweng impact structure, South Africa''. ''Earth and Planetary Science Letters'', 567, no. 117013, 13 p.][Schmieder, M. and Kring, D.A., 2020. ''Earth's impact events through geologic time: a list of recommended ages for terrestrial impact structures and deposits''. ''Astrobiology'', 20(1), pp.91-141.] Discovered in 1994, it is not exposed at the surface, but has been mapped by magnetic and
gravimetric
Gravimetry is the measurement of the strength of a gravitational field. Gravimetry may be used when either the magnitude of a gravitational field or the properties of matter responsible for its creation are of interest.
Units of measurement
G ...
surveys. Core samples have shown it to have been formed by the impact of an
L chondrite
The L type ordinary chondrites are the second most common group of meteorites, accounting for approximately 35% of all those catalogued, and 40% of the ordinary chondrites. The ordinary chondrites are thought to have originated from three parent a ...
asteroid estimated to have been in diameter.
[Mcdonald, I., Andreoli, M.A.G., Hart, R.J. and Tredoux, M., 2001. ''Platinum-group elements in the Morokweng impact structure, South Africa: Evidence for the impact of a large ordinary chondrite projectile at the Jurassic-Cretaceous boundary''. ''Geochimica et Cosmochimica Acta'', 65(2), pp.299-309.]
In May, 2006, a group of scientists drilling into the site announced the discovery of a -diameter fragment of the original asteroid at a depth of below the surface, along with several much smaller pieces a few millimetres across at other depths. This discovery was unexpected, since previous drillings on large impact structures had not produced such fragments, and it was thought that the asteroid had been almost entirely vaporised.
Some of the fragments can be seen in the Antenna Wing of
London's Science Museum.
References
Further reading
*
*
External links
Fossil Meteorite Unearthed From Crater
Impact craters of South Africa
Cretaceous impact craters
Jurassic impact craters
Late Jurassic Africa
Early Cretaceous Africa
Cretaceous South Africa
Jurassic South Africa
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