PALEOGEOGRAPHY, SEDIMENTOLOGY, AND GEOCHEMISTRY OF PLEISTOCENE PALEOLAKES IN DAKHLEH OASIS, WESTERN DESERT, EGYPT

Lacustrine marls in Dakhleh Oasis, in the currently hyper-arid Western Desert of Egypt, provide evidence for a more humid Pleistocene climate in comparison with the present. The deposits occur as remnant caps up to eight meters thick on yardangs along the southern and eastern margins of the Kellis, Balat, and Tineida basins to the south of the Libyan Plateau escarpment. Differential GPS measurements of the bedrock-lacustrine facies contact allow for a partial reconstruction of the paleolake bed topography, as at least eight meters of surface deflation has occurred since the lakes were present. These measurements also provide an estimate of minimum lake, ~60 km², as defined by the spatial extent of residual deposits, though topographic relationships imply that it could have been an order of magnitude larger. The influence of topography is also evident in lateral sedimentary facies changes. Marginal deposits in the Tineida basin contain abundant evaporite minerals including halite and thenardite, whereas deposits towards the interior of Balat and Kellis basins are dominated by low-magnesium carbonates. Root traces, red-green mottling, and carbonate nodules are present in the basal portions of the sections, indicating subaerial environments early in the history of the lake. These facies tend to grade into fine-grained carbonate silts, indicating rising water levels. Water sources for the lake would have included overland flow, groundwater flow, and meteoric precipitation. Overland flow is indicated by the presence of integrated drainage patterns on the Libyan Plateau and tufa deposits along the escarpment. Groundwater input to the Dakhleh paleolakes from the Nubian aquifer is indicated by the presence of iron-rich spring deposits at a similar topographic base level to the lake deposits, as well as recent artesian flow in the modern oasis. These lakes were likely exploited by early human groups, as demonstrated by the association of Early and Middle Stone age artifacts with the spring and lake deposits. The geochemistry of these sediments will be utilized to address questions regarding water balance of the lakes, which will in turn enhance current understanding of the Pleistocene paleoclimate of the Sahara.