BORON, BERYLLIUM AND SULFUR IN HOLOCENE SEDIMENTS AND PEATS OF THE NILE DELTA, EGYPT - THEIR USE AS INDICATORS OF SALINITY AND CLIMATE

The concentrations of 14 major and trace elements (B, Ba, Be, Co, Cr, Cu, Fe, Mn, Ni, P, S, V, Zn and organic C) in bulk sediment samples of Holocene age from bore holes in the Nile delta, Egypt, are considered in terms of sediment grain size and depositional setting. Using this background information, an attempt is made to evaluate paleosalinity and paleoclimatic change by geochemical analyses of peats. In every sediment facies examined, we find that grain size is a major controlling factor of geochemical composition, but the B/Be ratio is helpful in paleoenvironmental interpretations. Organic-matter content is the major factor affecting element concentrations in peats. Zn, Cr, Fe, Be, Cu, Mn concentrations on an organic-matter-free basis are lower in these organic-rich layers than in other Nile delta sediment facies. The sulfur content of the peats indicates a decreased importance of freshwater input to Holocene lagoons from about 8000 to 3400 years BP. High boron/beryllium ratios and the presence of gypsum in peats deposited between 6300 and 4900 years BP record the most evaporitic phase affecting this region. This geochemical finding is in close agreement with results of other independent paleoclimatic studies which indicate the onset of arid conditions in northeast Africa at about 5000 years BP.