PALAEOENVIRONMENTAL RECONSTRUCTION OF A MID-PLEISTOCENE PLUVIAL ENVIRONMENT, DAKHLEH OASIS, WESTERN DESERT EGYPT

Mid-Pleistocene lacustrine marls exposed as erosional remnants in Dakhleh Oasis in the Western Desert of Egypt attest to a considerably more humid climate than that present today.  Terminal Earlier Stone Age and Middle Stone Age artifacts are found in association with these sediments and ironstone spring deposits, indicating the utilization of these water resources by human/hominid groups.  The lake was likely in part supported by groundwater discharged from underlying Nubian aquifer beds, indicated by fossil artesian spring vents associated with the marls.  However, the high carbonate content of the sediments requires input of local runoff from the limestone-capped Libyan Plateau, indicated by tufa deposits along the escarpment.  d¹⁸O values of the authigenic low-Mg calcite in the sediments are consistent with equilibrium precipitation from water 3-7‰ heavier than modern Nubian aquifer water, suggesting that the water was susceptible to evaporation and/or that the locally-derived precipitation had a considerably heavier d¹⁸O than the groundwater inflow.   Water balance modeling that includes postulated Nubian aquifer pluvial phase discharge, rainfall and runoff over the Dakhleh watershed, evaporation, and stable isotopes analyses of modern Nubian aquifer water and the lacustrine marls suggests that a lake as large as ~800 km²  could be maintained at hydrologic and isotopic steady state.  This is considerably smaller than the largest lake area estimate of 1,735 km² derived from extrapolation of the maximum elevations of the deposits onto the modern (deflation-corrected) topography.   These results are consistent with the presence of shoreline facies indicative of shallow lacustrine to palustrine conditions, such as mottling, root traces, and reed casts.  However, the presence of freshwater gastropods, an African savanna fauna requiring permanent fresh water, and carbonate d¹⁸O values inconsistent with a highly evaporative environment, suggest that relatively fresh water was available perennially.  The presence of habitable environments in the Eastern Sahara would have facilitated mid-Pleistocene human migration out of Africa into the Mediterranean and Levant along routes independent of the ‘Nile Corridor' pathway.