This is believed to be a meteorite impact structure because of its high degree of circularity, however one thought is that it is a symmetrical uplift (circular anticline or dome) that has been laid bare by erosion. Paleozoic quartzites form the resistant beds outlining the structure."
Sunday, 3 January 2010
"The Richat Structure is a prominent circular feature in the Sahara desert of Mauritania near Ouadane. It has attracted attention since the earliest space missions because it forms a conspicuous bull's-eye in the otherwise rather featureless expanse of the desert. The structure, which has a diameter of almost 50 kilometres (30 miles), has become a landmark for space shuttle crews.