Earth:Aorounga crater

Short description: Prehistoric impact crater

Aorounga crater

Synthetic Aperture Radar image of the Aorounga crater
Impact crater/structure
Confidence	Confirmed
Diameter	12.6 km (7.8 mi)
Age	<345 Ma <Early Carboniferous
Exposed	Yes
Drilled	No
Location
Location	Sahara
Coordinates
Country	Chad
State	Borkou
Location of the crater in Chad

Astronaut photo of Aorounga crater

Aorounga is an eroded meteorite impact crater in Chad, Africa. The exposed remnant of the crater is 12.6 km (7.8 mi) in diameter and its age is estimated to be less than 345 million years (Carboniferous or younger).

Description

An outer and an inner ring (11 and 7 kilometres [6.8 and 4.3 mi], respectively) rise about 100 metres (330 ft) 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 kilometres (0.93 mi) is almost centrally located in the depression.

The crater is accompanied by two nearby circular features revealed by Space Shuttle SIR-C radar. These may be related impact craters, and if correct, Aorounga may be part of a crater chain. 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 yardangs by geomorphologists. Yardangs form by wind erosion of exposed rock layers in a unidirectional wind field. The wind blows from the northeast at Aorounga, and sand dunes formed between the yardangs are actively migrating to the southwest.

Topographic map of the Aorounga crater

See also

• List of impact craters in Africa
  • Gweni-Fada crater

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. 1994

External links

• Description and exclusive pictures in the field by Alain Beauvilain