SEDIMENTARY GEOLOGY AND GEOCHRONOLOGY OF QUATERNARY STRATIGRAPHIC SEQUENCES IN THE SOUTHERN EGYPTIAN SAHARA

The Sahara Desert of North Africa is today one of the driest areas in the world. Interdisciplinary studies conducted by the Combined Prehistoric Expedition (CPE) in southern Egypt provide evidence for paleoclimate and paleohydrologic models of landscape evolution and environmental change, and are important for understanding the spread of prehistoric humans across the African continent and into Eurasia. During the Quaternary, erosional basins in southern Egypt were filled with Pleistocene and Holocene lacustrine, alluvial, and eolian sediments. The sedimentary sequences provide evidence for alternating wet and dry periods during the Middle/Late Pleistocene and Holocene. For example, stratigraphic exposures at Wadi Eagle and yardangs within the Gebel Ramlah (GR) paleo-lake basin containing eolian, alluvial, and playa deposits. The sediments are interpreted as reflecting paleoenvironmental changes during the Early and Middle Holocene, while archaeological evidence indicates the presence of humans from ca. 9500 cal BP to ca. 6250/6150 cal BP. Lithostratigraphic and geochronologic (14C, OSL) evidence in the GR basin document the presence of Middle/Late Pleistocene deposits, while artifact assemblages typologically assigned to the Middle Paleolithic/Middle Stone Age (MP/MSA) document the presence of Pleistocene human populations. The deposits at GR and from other localities studied by the CPE can be used to develop and test regional-scale chrono-climatic and paleohydrologic models. For instance, in contrast to the Quaternary strata at GR dominated by clastic sediments, Middle and Late Pleistocene sedimentary sequences at Bir Tarfawi-Bir Sahara (BT-BS) contain lacustrine and palustrine carbonate deposits directly associated with Acheulian and MP/MSA artifacts. The 5-6 meters of playa sands and silts underlying early Holocene sediments at El Adam Playa and at El Gebel El Beid can can also be correlated with the Middle/Late Pleistocene sedimentary sequences at GR and BT-BS. The Holocene strata at GR also provide the opportunity to test the chrono-climate model developed at nearby Nabta Playa where the CPE documented Early to Final Neolithic archaeology associated with wet periods and the deposition of alluvial and playa clastic sediments, separated by dry periods of erosion and eolian sedimentation.