Pleistocene pluvial lakes of the western desert of Egypt: Paleoclimate, paleohydrology, and paleolandscape reconstruction

Paleolake sediments from Dakhleh and Kharga Oases in the Western Desert of Egypt indicate a considerably wetter Mid-Pleistocene climate than the modern hyper-arid conditions. Authigenic calcite silts at Wadi Midauwara in Kharga Oasis attest to a ∼4 km2, primarily groundwater-supported lake at ∼125 ka. Sequential stable isotope and minor element analyses of aragonite gastropod shells from the lake sediments are consistent with water temperature changes and modest evaporation. Thus, the lake did not experience intense seasonal evaporation, suggesting that it was likely fed by perennial spring flow. Stable isotope and minor element trends for the silts indicate that the lake water may have been isotopically heaviest when it experienced the least evaporation and/or the shortest residence time in local aquifers. The observed geochemical trends may be explained by the addition of Indian Ocean-sourced moisture to that derived from the Atlantic Ocean, associated with an enhanced monsoon. Mid-Pleistocene paleolake deposits in Dakhleh Oasis provide evidence for a lake that may have been as large as 1735 km 2. The sediments primarily comprise shallow water to palustrine facies, with carbonate stable isotope compositions consistent with formation in a poorly-mixed, mildly evaporative environment. The Dakhleh paleolake was likely fed by a combination of Nubian aquifer groundwater, and surface runoff. Water balance modeling for the lake at a range of sizes indicates that between 410 and 860 mm/yr of rainfall would have been necessary to sustain the lake. The Dakhleh paleolake was also likely the site of a meteorite impact, attested to by the Dakhleh Glass, a Ca-Al-silicate glass that occurs in situ within the lake sediments. Although a crater has not yet been conclusively identified, the sediments associated with the glass support the impact hypothesis in their chemistry, which indicates that the glass could not have formed in-place, and in their sedimentology, which suggests that rapid deposition of sediment and intense burning occurred in the aftermath of the probable impact event. A highly turbid lake and widespread fires would have been highly detrimental to the Middle Stone Age occupants and savanna fauna of Dakhleh Oasis.