QUATERNARY GEOLOGY AND GEOMORPHOLOGY IN SOUTHERN EGYPT: SEDIMENTARY AND STRATIGRAPHIC EVIDENCE FOR ENVIRONMENTAL CHANGE AND LANDSCAPE EVOLUTION AT BIR TARFAWI, BIR SAHARA, AND GEBEL RAMLAH

The Egyptian Sahara west of the Nile and east of the Gilf el Kebir contains several localities where sedimentary sequences provide evidence for changing environmental conditions during the Pleistocene and Holocene. At Bir Tarfawi and Bir Sahara, for example, Paleolithic artifacts are associated with Middle and Late Pleistocene deposits, but Holocene playa deposits are very limited. East of these localities, early and middle Holocene sedimentary remnants, some of which are directly associated with Neolithic artifacts and fossils (vertebrates and invertebrates), are preserved in the drainage basin south of Gebel Ramah. Playa-paludal deposits composed of fine-grained clastics (sandy silts, silts, and muds) cover the area. The surface sediments exhibit a prominent network of desiccation cracks. Along the north side of the playa, sedimentary features interpreted as high-energy slope wash indicate episodes of torrential rains, while wadi channels and alluvial deposits are prominent along the edges of the basin. A stratigraphic sequence of alternating beds of silts and sands with shells and charcoal lenses is exposed along the banks of wadi channels on the southeast side of the basin. The playa basin contains fields of yardangs. The yardangs are sometimes several meters high, and are composed mostly of silts and sands with interbedded trace fossil layers and several species of gastropods (e.g., Zootecus insularis). The traces fossils appear to be chiefly rhizoliths (root casts) formed in marsh-like settings within the basin. Besides the prominent Holocene deposits, stratigraphic trenches and bore-holes document Pleistocene sediments within Ramlah basin. Based on coring conducted in 2018, a >7 m thick stratigraphic sequence is present. Sediments interpreted as representing alluvial, paludal-lacustrine, and eolian depositional facies overlie the bedrock and appear to be similar to basin edge Pleistocene sedimentary facies at Bir Tarfawi. When compared and correlated with other stratigraphic localities, the Quaternary stratigraphic sequence in the Ramlah basin provides evidence of spatial and temporal variation in sedimentary depositional environments that may reflect regional differences in climate and hydrologic conditions in southern Egypt during the Quaternary.