SAHARAN DUST IN PALEOSOLS OF NORTHWEST
COASTAL RIDGES, EGYPT, AND ITS PALEOCLIMATIC IMPLICATIONS:
GEOCHEMICAL AND ISOTOPIC EVIDENCES
HESHAM M. ELASMAR
Dept. Geology, Damietta Fac. Sciences, Damietta, 34517, Egypt.
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Geochemical analyses of Al2O3, TiO2, Y, Zr, and Sr, and the isotopic ratio of
87Sr/ 86Sr are made to test the aeolian materials in the Quaternary paleosols developed along the lime-stone coastal ridges, NW of Egypt.
ð13C, ð18O and the % of C4 plants have been also used to signify the paleoclimate and paleovegetation history dominated during the development of the paleosols.
The detection of ratios of Al2O3 /TiO2, Ti/Y, Ti/Zr, Sr content and
87Sr/86Sr isotopic ratios all prove that the studied paleosols are of two end member sources. The Saharan dust represents 64% to 90% of the parent materials forming the paleosols, with additionally subordinate source from the Nile sediments of 10% to 33%.
Theð13C values suggest that most carbon was derived from soil organic lighter
12C with little atmospheric CO2. A decrease in the % of C4 plants (arid grasses, herbs and shrubs) is noticed, accompanied with a decrease in the seasonal growing temp., being
26oC and 17oC from Late Holocene to Middle Pleistocene respectively.
ð18O, on the other hand, shows an increase in the -ve values in the same trend, indicating a tendency of the climate to change from dry to wet, with higher contribution of fresh water enriched
16O, and a decrease in salinity by ab. 6‰.
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