A SURVEY OF METEORITE IMPACT STRUCTURES IN AFRICA

Impact craters on Earth are difficult to recognize because of the active geological processes that constantly reshape the Earth's surface. Depending on the age of the crust, the intensity of local geological processes, and other factors, such as accessibility or vegetation cover, known impact craters show a rather irregular distribution on the Earth's surface; in contrast to their formation, which is evenly distributed. Currently, about 185 impact structures have been recognized on Earth, based on the commonly accepted impact characteristics, i.e., (1) finding meteorites or admixture of meteoritic debris in impactites, (2) detection of chemical traces of the projectile in crater rocks or ejecta, and/or (3) detection of shock metamorphic effects. The African impact record has recently been reviewed [1], and so far, only 19 structures have been confirmed on that continent to be of impact origin – a very low number in relation to Africa’s proportion of global landmass and in comparison with other, much smaller regions, such as Scandinavia. In addition, one location with abundant shatter cones at Agoudal, Morocco, has been identified; an impact structure has, however, not yet been identified. As proposed and not yet confirmed impact structures in Africa are concerned, 49 of those have been listed, with some seemingly excellent targets for ground-truthing amongst them. As a result of detailed studies, 28 previously proposed structures have been determined as not being of impact origin. This overall record indicates strongly that impact cratering research has successfully been promoted in Africa, but that further ground-truthing ought to be seriously pursued – not an easy task in the face of wide-spread unrest on this continent. The study of impact craters in Africa is clearly only at the beginning, as many geoscientists in Africa have not had sufficient training in the rather specific aspects of mineralogy, petrography, or geochemistry that are necessary to identify impact structures, and also due to lack of specialized equipment. However, given the importance of impact cratering also as a natural hazard, and the potential economic benefits of impact structures, it is hoped that in the future more researchers will start to be interested in this topic.

[1] Reimold, W. U. and Koeberl, C. 2014. J. African Earth Sci. 93:57-175.