AGE AND ISOTOPIC CONSTRAINTS ON PLEISTOCENE PLUVIAL EPISODES IN THE WESTERN DESERT, EGYPT

North Africa has undergone drastic climatic changes over the past seve ral hundred thousand years, The timing of humid intervals called pluvi als was investigated by uranium-series disequilibrium dating of traver tines from the Kurkur Oasis. Western Desert. Egypt. The youngest and b est dated travertines (70-160 ka) are found in Wadi Kurkur and include spring and lacustrine units exposed as 2 to 3 m high terraces. Traver tines having an age of approximately 191-220 ka are exposed by differe ntial erosion as linear mounds produced by spring systems over fractur e zones in ancient wadis. The oldest travertines, having ages >260 ka, are extensive, cap limestone units above the oasis, and were deposite d in paludal and lacustrine environments. Oxygen isotope ratios were m easured for the wadi travertines (delta(18)O values ranging from 16.7 to 19.1 parts per thousand SMOW) and for spring mound travertines (18. 5-20.5 parts per thousand). Equilibrium oxygen isotope fractionation c alculations indicate that the Kurkur travertines were deposited from w aters having delta(18)O values similar to ancient Western Desert groun dwaters (similar to -11 parts per thousand, Sonntag er al., 1978a.b: T horweithe, 1990: Sultan et al., 1996). The ages of the travertines cor respond to times of monosonal maxima, eustatic sea level high stands a nd interglacial maxima. Rainfall producing these groundwaters (and tra vertines) was significantly fractionated during atmospheric transport, in contrast to modern meteoric waters (-2.09 parts per thousand, Jose ph et al., 1992), implying a distant source for the pluvial waters. In creased precipitation, recharge of Western Desert groundwaters, and re sultant travertine deposition are interpreted to be consequences of Mi lankovitch insolation cycle forcing, through enhanced Atlantic and Ind ian Ocean monsoons during interglacial time periods. (C) Elsevier Scie nce B.V.