THE STRATIGRAPHIC RECORD OF IMPACT EVENTS

All bodies in our solar system that have solid surfaces are covered by impact craters. Only on the Earth is it difficult to recognize meteorite impact structures because of active geological and atmospheric processes on our planet that obscure or erase the impact record in geologically short times. Apart from studying meteorite impact craters per se, large amounts of information can also be gained from the study of impact ejecta. Impact ejecta are commonly divided into two groups - proximal ejecta (those that are deposited closer than 5 crater radii from the crater rim), and distal ejecta. In some cases, impact events have been identified solely from the discovery and study of regionally extensive or globally distributed impact ejecta. A well known case in point is the Cretaceous-Tertiary boundary, where the discovery of an extraterrestrial signature, together with the presence of shocked minerals, led not only to the identification of an impact event as the cause of the end-Cretaceous mass extinction, but also to the discovery of a large buried impact structure about 200 km in diameter, the Chicxulub structure. Tektites are another form of distal impact ejecta, the source craters of which have long remained elusive. To date only three of the four known Cenozoic tektite strewn fields have been connected to source craters. In this paper a review of distal impact ejecta will be presented.