TRACING SOURCES OF PLEISTOCENE NEGEV DESERT LOESS AND ITS EFFECTS ON EASTERN MEDITERRANEAN CONTINENTAL ENVIRONMENT

The Pleistocene loess of the Negev desert is a unique archive of dust in the eastern Mediterranean and potentially can trace synoptic-scale atmospheric circulation patterns. It records distinct temporal variations in dust sources in the distal deserts of North Africa, Arabia and the proximal Sinai-Negev deserts. Therefore, detailed analyses of the Negev loess are used here to reconstruct Quaternary paleoenvironments and paleoclimates. These analyses assist in identifying coeval dust in soils, lacustrine and marine environments around the Mediterranean that are also fed by dust from these deserts.

The Negev loess is reflected by its bi-modal particle-size distribution of fine (4-10 µm) and coarse (30-60 µm) silts. These two modes are mainly derived, respectively, from entrainment in the distal Arabia-Sahara and by aeolian abrasion in the nearby Sinai-Negev dune field (Crouvi et al., 2008, Quaternary Research, 70: 275-282).

The provenance and the transport routes of the loess were also detected by using the isotopic fingerprinting of Sr and Nd. Results of the isotopic composition of the two grain size modes of the Negev loess fall on a mixing line between two proto-sources: Phanerozoic and paleo-Phanerozoic rocks of the African craton and Tertiary basalts of eastern Africa, similar to other fine sediments sampled in the nearby region. Weathering products of these source rocks might also serve as end members with Saharan dust eroded mainly from the African granitoids on one side of the Sr-Nd plot and Nile River sediments carried by the Nile from the Ethiopian highlands on the other side. The Nile delta exhibits isotopic values similar to these of the Negev loess as well as of sediments from the eastern Mediterranean Sea. This confirms that this massive sediment reservoir is not merely a sink but also acts as a source, supplying aeolian dust to the region (Amit et al., 2011, Geological Society of America Bulletin, 123(5-6): 873-889). However, while the Negev loess is composed of a mixture of sediments, its fine fraction has both higher Mg/Al ratios and slightly higher ⁸⁷Sr/⁸⁶Sr ratios along with more positive εNd than the coarse fraction, indicating a contribution of dust from Arabia in addition to Saharan dust, highlighting the advantage in studying the loess in the Negev.