FAROUK EL-BAZ AWARD FOR DESERT RESEARCH: HOW OLD IS THE NEGEV LOESS AND CAUSES FOR ITS SUDDEN APPEARANCE IN THE LATE MIDDLE PLEISTOCENE

Synchronicity of the Negev loess with the last glacial and its Holocene erosion were used in favor of deposition-erosion (glacial-interglacial, respectively) cycles of regional loess during the entire Quaternary. Erosion explained the absence of loess older than stage 6. An alternative that the conditions necessary for loess formation are relatively recent in the eastern Mediterranean is raised here. We analyzed soils continuously developed on abandoned stable surfaces. Potentially, these soils accumulated dust since surface abandonment ~2 My, however, field and chronological data indicate that dust started to accumulate only after ~170 ka. This is synchronous with the age of the Negev primary loess initial deposition (~180 ka). The sudden appearance of the loess indicates its relationships with nearby sources, rather than with the long-term available distant dust sources such as the Sahara and Arabia. Furthermore, the major constituent of the loess in the Negev is angular coarse silt (modes 40-70 µm) quartz that cannot be derived from the regional carbonate terrain or from distant source; only from quartz-rich proximal sources. Such local source is the sand dunes of the northern Sinai-Negev erg and these sands, in turn, sourced probably during low sea level in the Nile delta, an early middle Pleistocene feature. Analyses of Quaternary sand sequences in the northern Negev show that until ~200 ka, most of the coastal sands were stabilized by vegetation as evident by successions of buried calcic soils. Evidence for active dunes that can abrade quartz sand into silt appears only since the late middle Pleistocene (~200 ka). Therefore, we suggest that the Negev loess is one of the newest responses to the accretion of the Nile delta and the formation of the Sinai erg from delta sands.