Paleoclimate record in the Nubian Sandstone Aquifer, Sinai Peninsula, Egypt

摘要

Sixteen groundwater samples collected from production wells tapping Lower Cretaceous Nubian Sandstone and fractured basement aquifers in Sinai were analyzed for their stable isotopic compositions, dissolved noble gas concentrations (recharge temperatures), tritium activities, and ~(14)C abundances. Results define two groups of samples: Group I has older ages, lower recharge temperatures, and depleted isotopic compositions (adjusted ~(14)Cmodel age: 24,000-31,000 yr BP; δ~(18)O:-9.59‰to-6.53‰; δ~2H:-72.9‰to-42.9‰; b1 TU; and recharge T: 17.5-22.0℃) compared to Group II (adjusted ~(14)C model age: 700-4700 yr BP; δ~(18)O: -5.89‰ to -4.84‰; δ~2H: -34.5‰ to - 24.1‰; b1 to 2.78 TU; and recharge T: 20.6-26.2℃). Group II samples have isotopic compositions similar to those of average modern rainfall, with larger d-excess values than Group I waters, and locally measurable tritium activity (up to 2.8 TU). These observations are consistent with (1) the Nubian Aquifer being largely recharged prior to and/or during the Last Glacial Maximum (represented by Group I), possibly through the intensification of paleowesterlies; and (2) continued sporadic recharge during the relatively dry and warmer interglacial period (represented by Group II) under conditions similar to those of the present.