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Aorounga is an eroded
Description and exclusive pictures in the field by Alain Beauvilain
{{Impact cratering on Earth Impact craters of Chad Carboniferous impact craters Carboniferous Africa Borkou Region
Aorounga is an eroded meteorite
A meteorite is a solid piece of debris from an object, such as a comet, asteroid, or meteoroid, that originates in outer space and survives its passage through the atmosphere to reach the surface of a planet or Natural satellite, moon. When the ...
impact crater
An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
in Chad
Chad (; ar, تشاد , ; french: Tchad, ), officially the Republic of Chad, '; ) is a landlocked country at the crossroads of North and Central Africa. It is bordered by Libya to the north, Sudan to the east, the Central African Republic ...
, Africa. The exposed remnant of the crater is in diameter
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can also be defined as the longest chord of the circle. Both definitions are also valid for ...
and its age is estimated to be less than 345 million years (Carboniferous
The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
or younger).VINCENT P.M., BEAUVILAIN A., 1996. Découverte d'un nouveau cratère d'impact météoritique en Afrique : l'astroblème de Gweni-Fada (Ennedi, Sahara du Tchad). C. R. Acad. Sci. Paris, t. 323, série II a, pp. 987-997Description
An outer and an inner ring (11 and 7 km, respectively) rise about 100 m above the mean level of the surrounding plain (see topographic map). Both aforementioned rings are separated by a relatively flat depression of uniform width. A possible central hill, maybe an uplift structure, of 1.5 km is almost centrally located in the depression. The crater is accompanied by two nearby circular features revealed bySpace Shuttle
The Space Shuttle is a retired, partially reusable low Earth orbital spacecraft system operated from 1981 to 2011 by the U.S. National Aeronautics and Space Administration (NASA) as part of the Space Shuttle program. Its official program na ...
SIR-C radar. These may be related impact craters, and if correct, Aorounga may be part of a crater chain
A crater chain is a line of craters along the surface of an astronomical body. The descriptor term for crater chains is catena , plural catenae (Latin for "chain"), as specified by the International Astronomical Union's rules on planetary nome ...
. On the assumption that this hypothesis is correct, the exposed Aorounga crater is sometimes referred to as Aorounga South. The central highland, or peak, of the crater is surrounded by a small sand-filled trough; this in turn is surrounded by a larger circular trough. Linear rock ridges alternating with light orange sand deposits cross the image from upper left to lower right; these are called yardang
A yardang is a streamlined protuberance carved from bedrock or any consolidated or semiconsolidated material by the dual action of wind abrasion by dust and sand and deflation (the removal of loose material by wind turbulence.) Yardangs become e ...
s by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the north-east at Aorounga, and sand dunes formed between the yardangs are actively migrating to the south-west.
See also
* List of impact craters in Africa ** Gweni-Fada craterReferences
Further reading
* Becq-Giraudon, J. -F., Rouzeau, O., Goachet, E. and Solages,S., Meteoritic impact origin of the annular depression of Aorounga, Chad (Africa). C. R. Acad. Sci. Paris, t. 315, série II, p. 83-88. 1992 * Koeberl, C., African meteorite impact craters: Characteristics and geological importance. Journal of African Earth Sciences, v. 18, pp. 263–295. 1994 * Koeberl, C., Reimold, W. U. , Cooper, G. , Cowan, D. and Vincent, P. M., Aorounga and Gweni Fada impact structures, Chad: Remote sensing, petrography, and geochemistry of target rocks, Meteoritics & Planetary Science, 40, No 9/10 P. 1455 - 1471. 2005 * Koeberl, C., Reimold, W.U., Vincent, P. M., Brandt,D., Aorounga and Gweni Fada Impact Structures, Chad, Central Afr.: Petrology and Geochemistry of Target Rocks, LPSC XXIX, Lunar and Planetary Institute, Houston, TX, (CD-ROM). 1998 * McHone J.F., Greeley, R., More impact and impact-like structures on the SIR-C radar; Europe, Africa, and Arabian Peninsula (abstract). Lunar and Planetary Science XXVIII, pp. 915–916. 1997 * Miallier, D., Sanzelle, S., Falgueres, C., Fain, J., Pilleyre, Th. And Vincent,P.M., TL and ESR of quartz from the astrobleme of Aorounga (Sahara of Chad), Quaternary Science Reviews, Vol 16 (3-5), pp. 265–274. 1997 * Ocampo, A. C., Pope, K. O., Shuttle Imaging Radar (SIR-C) Images Reveal Multiple Impact Craters at Aorounga, Northern Chad, 27th Lunar and Planetary Science Conference. 1996 * Vincent, P. M., Beauvilain, A., Boudeulle, M. and Moutaye,A.H., The astrobleme of Aorounga (Sahara of Tchad): Preliminary structural data (abstract). European Science Foundation, Third International Workshop. Shock Wave Behaviour of Solids in Nature and Experiments, Limoges, France. 1994External links
Description and exclusive pictures in the field by Alain Beauvilain
{{Impact cratering on Earth Impact craters of Chad Carboniferous impact craters Carboniferous Africa Borkou Region