The role of the Nile in initiating a massive dust influx to the Negev late in the middle Pleistocene

The late middle Pleistocene initiation of loess accretion in the Negev Desert, Israel, resulted from a chain of events starting with the exposure of shallow offshore Nile delta sands beginning ∼180 ka, during a period of glacially lowered eustatic sea level. This exposure allowed the formation of the dunes of the Sinai-Negev erg and the eastward movement of the dunes under the gusty glacial-time winds in northern Sinai. This eastward dune advance occurred by eolian saltation that generated the coarse silts that accumulated downwind as loess. We postulate that the absence of earlier Negev loess is not a result of interglacial erosion as previously proposed but is due to the relatively recent convergence of the above conditions necessary for loess formation. We based our interpretation on analyses of two long-term natural dust traps and the association of coarse quartz silt production with the advancing quartz-rich dunes over this carbonate terrain. Although the Nile delta is considered an early to middle Pleistocene feature, and therefore could have been the source of sand throughout the Quaternary, it attained the shallow depth range of glacial-interglacial sea-level changes only during late marine oxygen isotope stage 7 to early stage 6, allowing its wide exposure. In Quaternary times prior to erg formation, Negev dust was finer, composed of silt and clays derived from distal sources in the Sahara and Arabian deserts.