ABSTRACT
The Selima Sand Sheet, the hyperarid core of the eastern Sahara first described by Bagnold, is a relatively flat, sand-covered surface of ca. 40,000 sq. km. extending 1.5° of latitude either side of the Egyptian-Sudanese border between 26°W and 29°W longitude. Unit C, calcareous alluvial sands (CAS) and calcified pebble gravel (CPG), underlie the sand sheet deposits and fill the valleys of ancient rivers revealed by radar carried in earth orbit by NASA's shuttle missions SIR-A and SIR-B. Alluvial sands and gravels within the radar-revealed valleys show considerably less pedogenesis than in adjacent low uplands, but some portions are cemented by ground water deposited calcium carbonate to form CPG ranging from light coatings on grains to dense impermeable kunker. Under the hyperarid climate, the Selima Sand Sheet is active and few places have seen significant rainfall since the 1950s.
