Particle-size fractionation of eolian sand along the Sinai-Negev erg of Egypt and Israel

Abstract

Eolian sand fractions along the west-east transport system of the northern Sinai Peninsula–northwestern Negev erg of Egypt and Israel were analyzed in this study with regard to source, dune geomorphology, eolian transport, and paleoclimate. The studied erg is composed of active linear (seif) dunes in northern Sinai (western part), and stabilized vegetated linear dunes in the NW Negev dune field (eastern part). Linear seif dunes differ from vegetated linear dunes in their vegetation cover, linearity, internal structure, and dynamics. Sand samples were analyzed for sand-grain morphology and particle-size distribution. Although both dune types are continuous landforms with similar orientations and sand-grain roundness values, the linear dunes of Sinai are coarser grained than the Negev vegetated linear dunes. The vegetated linear dunes have a variable but higher proportion of very fine sand (50–125 μm) content and a varying but lower sand fining ratio (defined as the ratio of fine sand percentage to very fine sand percentage). From these observations, we infer that fractionation of sand occurred along the studied eolian transport path during periods of enhanced windiness. Very fine sands are suggested to have been transported by saltation and low suspension from source deposits and sand sheets. We suggest that a significant proportion of the very fine sand fraction of Nile Delta sands has been transported downwind through northern Sinai during the late Pleistocene, especially when linear dunes reached the NW Negev due to last-glacial period windiness and probably larger sediment supply. Generally decreasing wind velocities and increasing precipitation along the west-east dune transport path enhanced vegetative cover in the northern Negev and enabled deposition of the very fine sand component within the dunes and probably further downwind. Our results suggest that particle-size distribution can elucidate much about erg history over time scales of a glacial-interglacial cycle, especially in cases where the sand provenance is of a single dominant source.