Source of Groundwater Recharge over the Nubian Sandstone Aquifer, Sinai Peninsula, Egypt: Geochemical and Geochronological Constraints
Abstract
Two main hypotheses have been advocated to address the origin of the fossil water of the Nubian Aquifer: (1) intensification of paleowesterlies during glacial periods and (2) intensification of paleomonsoons during interglacial periods. Seven groundwater samples were collected from deep (>300 m <800 m) productive wells tapping the Lower Cretaceous Nubian Sandstone Aquifer in Sinai and were analyzed for their isotopic compositions (δ18O and δD), ages (C-14), and recharge temperatures (dissolved noble gas concentrations). Analyses yielded two groups of samples: group I: (age: 26k yrs to 31k yrs; δ18O: -8.9% to -7.2%, δD: -63.1% to -49.3%, and recharge T: 17.5°C to 22.03°C), and group II: (age: 1740 yrs to 6180 yrs; δ18O: -5.9% to -4.9%, δD: -33.3% to -25.1%, and recharge T: 20.6°C to 26.2°C). The following observations could be made from the data: (1) C-14 ages indicate that Group I waters were recharged during the Last Glacial Maximum (LGM), whereas Group II waters were recharged during relatively dry interglacial periods; and (2) the depleted nature of Group I isotopic compositions compared to Group II (average δ18O: Group I: -8%; Group II: -5.4%; average δD: Group I: -56%; Group II: -29.2%) and their lower recharge temperatures (Group I average T: 19.9°C; Group II average T: 23.4°C) are consistent with recharge of Group I waters during cooler time periods and Group II waters during warmer periods. We interpret these results to indicate that the Nubian Aquifer was largely recharged through the intensification of paleowesterlies during glacial periods (represented by Group I waters) but is still receiving modest contributions during relatively dry interglacial periods (represented by Group II waters).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFMPP21A1767A
- Keywords:
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- 1041 GEOCHEMISTRY / Stable isotope geochemistry;
- 1626 GLOBAL CHANGE / Global climate models;
- 4914 PALEOCEANOGRAPHY / Continental climate records