干旱区生态环境知识资源中心

More than 25 years of geoarchaeological investigations in the hyperarid regions of southwestern Egypt and northwestern Sudan, the Darb el Arba’in desert, demonstrate that Holocene pluvial conditions began about 9800 yr B.P., essentially at the end of Younger Dryas cooling. The eastern Sahara changed from a hyperarid, lifeless desert dominated by eolian activity and deflation to an and to semiarid savanna that attracted Sudano-Sahelian fauna and Neolithic pastoralists to the region until about 5000 yr B.P., when the current episode of hyperaridity ensued. In the lake and playa basins of the eastern Sahara, Younger Dryas time, about 10,800-9700 yr B.P., is represented by an erosional hiatus, during which deflation of basins occurred. The only deposition that may have occurred during this hyperarid period is sand sheet aggradation and dune formation consistent with the Sahara being hyperarid during the glacial periods. Younger Dryas-age eolian deposits have yet to be identified by optically stimulated luminescence (OSL). The current hyperaridity would imply that glacial conditions exist in the northern hemisphere, yet the opposite is the case. Perhaps global glaciation lags the onset of Saharan hyperaridity by several millennia, and the area is in a transitional phase much like the Bolling and Allerod periods. (C) 2001 John Wiley & Sons, Inc.