LARGE SCALE PLEISTOCENE LAKES OF EGYPT'S WESTERN DESERT

At present, the hyperarid Egyptian Sahara retains little surface evidence for the former pluvial periods that have been documented by archaeological sites, radar detected fluvial channels, and numerous radiometric dates. Processing of the Shuttle Radar Topography Mission (SRTM) data at the available 90 m (spatial) resolution reveals details that tie together several disparate lines of evidence for large-scale, mid-Pleistocene lakes. At Bir Tarfawi, 400 km west of the Nile, fossil fish of the last interglacial occur at the same elevation as the termination of shallow surface runoff channels north of Selima Oasis in Sudan. Stepwise infilling of the present topography suggests an extensive lake at an elevation of ~240 m that accounts for both features. This lake extended more than 300 km south to north from the Sudan border to Kharga Oasis in central Egypt, and covered an area of 68,000 km². A lower lake level at ~190 m coincides with the elevation of the connection with the Nile through Wadi Tushka, and with the transition from topographically higher Paleolithic sites to lower Neolithic sites in the Kiseiba Oasis region. The timing of these mid- to late-Pleistocene lakes coincides with the change in drainage direction of southern Egypt. From late Tertiary to mid Pleistocene, drainage from the Eastern Desert was to the south through Wadi Qena and west across the Kiseiba-Tushka depression. In addition to the Shuttle radar-detected channels, an isolated meander bend on the south edge of the limestone plateau west of the Nile may be a relict of this drainage. We believe that the African connection and northward drainage of the Nile began in mid Pleistocene, perhaps aided by overflow of extensive lakes in Sudan across the Nubian swell. Although local precipitation was greater in the mid Pleistocene (~500 mm/yr), the overflow from annual Nile flooding following establishment of northward Nile drainage seems a more likely source for the Egyptian lakes.