干旱区生态环境知识资源中心

Mid-Pleistocene lacustrine sediments exposed as erosional remnants in Dakhleh Oasis in the Western Desert of Egypt provide evidence for a more humid climate than that which persists today. The sediments range in facies from palustrine to fully lacustrine and generally reflect an increase in water depth upward through the strata. Ironstone spring deposits associated with the lacustrine sediments and modern artesian discharge in the oasis indicate that Nubian aquifer water was probably an important component of the water balance, but the high carbonate content of the lake sediments requires the input of surface drainage derived from the nearby limestone-capped Libyan Plateau. Although definitive shorelines have not been observed, a maximum lake size of 1735 km(2) is derived from extrapolation of the elevations of the deposits onto the modern deflated topography. Theoretical water balance modeling suggests that in addition to the discharge derived from the Nubian aquifer, similar to 410-860 mm/yr of rainfall would be required over the Dakhleh Oasis drainage basin in order to maintain the lake at hydrologic steady state. The persistence of climatic and hydrologic conditions amenable to maintaining a shallow freshwater lake would have allowed the region to be inhabited by a savanna fauna, as well as early human groups.