LANDSCAPE DYNAMICS IN THE EASTERN SAHARA: SEDIMENTARY GEOLOGY, STRATIGRAPHY, AND GEOMORPHOLOGY IN THE GEBEL RAMLAH REGION, SOUTHWEST EGYPT

The geologic record of the presently hyperarid Eastern Sahara in North Africa provides evidence for significant late Quaternary environmental change. In the Gebel Ramla region, south of the Sin El Kaddab scarp and west of the Nile valley in southwest Egypt, sedimentary sequences and geomorphic landforms appear to document wet-land and playa environments as well as intervals of increased wadi activity. Episodes of aridity are associated with aeolian erosion and deposition. Coring has revealed the presence of Pleistocene deposits that appear to reflect alluvial and playa-basin depositional processes. Gravelly sands overlie bedrock and are overlain by a sequence of clastic deposits interpreted as reflecting sand sheets, sheet-wash, paludal-playa settings, aeolian sands, and alluvium. Stratigraphic trenches and mapping of the surficial geomorphic features provide evidence of changing depositional environments during the Holocene. Early Holocene stratigraphic sequences include sand- and silt-dominated deposits that contain trace-fossils and molluscs, as well as archaeological evidence (Neolithic artifacts and features). The molluscs include land-snails that currently inhabit marsh settings, and the trace-fossils are interpreted as root-casts or rhizholiths associated with vegetation within a Holocene palustrine wetland basin. Sedimentary deposits and land features interpreted as reflecting alluvial, slope wash, and debris flow activity indicate intermittent but significant erosional and depositional processes associated with localized rain events during the late Holocene, including the present-day. These processes have eroded the older Holocene aggradational sequences, resulting in the present-day wadi drainage pattern. Sief and barchan dunes are currently active in the region, and eolian processes also actively erode the older sedimentary deposits. The sediments and landforms of the Gebel Ramlah region appear to reflect changing environments that influenced biogeographic patterns and landscape processes during the late Quaternary in Saharan North Africa.