ABSTRACT

Desert sedimentary sequences of Late Quaternary age, mainly subrecent, were studied in several stream segments of Wadi El Arish (northern Sinai, Egypt). Morphologically, these stream systems can be divided into three types: confined, open, and terminal floodplains. The confined and open floodplain sequences consist of repeated flood-originated sedimentation units, each around 50 cm thick. An idealized sequence begins with mud clasts or either sand or pebble-bearing plane beds reflecting the upper-flow regime during peak flow stage of the flood. These are overlain by cross-bedded sands and climbing ripples. Lower intensities of the flow result in sequences beginning with cross-stratified sands. Cracked mud layers represent the final desiccation stage of the flood. In comparison with th confined floodplain units, the open (up to thousands of meters wide) floodplain units are thinner (20-50 cm), the horizontal strata are less developed, and the mud layers are thicker. The terminal floodplain, which in the modern examples is a flat a few kilometers wide, is the area where the remaining flood energy dissipates and, therefore, the resultant sedimentation units axe very thin, usually less than 20 cm, and consist of either finely laminated, massive mud, or cross-laminated fine sand. The wadi systems studied are in close geographic relationship with eolian dune fields. Nevertheless, the wadi sequences consist of waterlaid units only.