OKAVANGO OASIS, KALAHARI DESERT - A CONTEMPORARY ANALOG FOR THE LATE CRETACEOUS VERTEBRATE HABITAT OF THE GOBI BASIN, MONGOLIA

There are conspicuous similarities between the late Cretaceous Gobi an d the present-day Okavango vertebrate habitats. Both habitats combine conditions of a life-supporting haven with a life-threatening desert. Both the Gobi and the Okavango environments developed in continental, extensional settings (tectonic grabens), and both accommodate eolian a nd fluvio-lacustrine facies. There are also striking sedimentological similarities between the Upper Cretaceous Gobi succession of Mongolia and the modern Okavango Delta of Botswana. The most important of these similarities is an alternation of wind-blown dunes and water-laid lac ustrine and fluvial deposits. Changes from arid conditions (wind-blown sand and dust) to sub-humid conditions (water-laid mud or sheet-flood sandstone) may have been gradual or instantaneous. It is inferred tha t tectonically induced climatic changes of various magnitudes and recu rrence intervals governed the dinosaur-supporting or dinosaur-threaten ing habitats of the Gobi Basin in Late Cretaceous time. Recurrent cond itions of extreme aridity contributed to the extermination of many lat e Cretaceous dinosaurs (e.g., Protoceratops) in much the same way that antelopes and other animals are being killed by cataclysmic droughts in the Okavango oasis at the present time.