ABSTRACT
The present Sahara region has undergone dramatic changes in its environment which can be correlated with the palaeogeographic position of the African continent and the continuous variations in world climate. Mainly micropalaeontological studies have shown that the humid tropical climate of the Late Cretaceous became progressively drier. Savanna and woodlands replaced the tropical forest in Early Tertiary times. This process is the consequence of the northward shift of the continent, the diminishing of the oceanic influence and the cooling of the Earth since the Early Tertiary.
So far no well dated close correlations are available between the lowering in temperature in the Antarctic and the gradual desiccation of North Africa but the parallel trend of these events cannot be denied. The abrupt cooling which has been described from the Southern Ocean at the Eocene–Oligocene bundary must have affected the climate of the southern continents and even aggravated the aridification of the North African region. When in the late-Miocene the Nothofagus flora died out in Antarctica as a consequence of the severe polar climate, desert conditions developed in the Sahara. The complete desiccation of the Mediterranean Sea between 6.2 and 5.3 MY ago was probably closely correlated with the glacial evolution of Antarctica. This geological catastrophe intensified the arid conditions in the whole of Northern Africa.
Little is known about the Pliocene environments of the Sahara region, but an impressive accumulation of data has in recent times become available on the climatic changes of the desert region during the Quaternary. It is not yet possible to correlate these changes with events in the Antarctic region. The alternation of more humid and hyperarid periods inferred from geomorphological and palaeontological studies is strongly influenced by the glacial history of the Northern Nemisphere.
