Constraints on Pleistocene pluvial climates through stable-isotope analysis of fossil-spring tufas and associated gastropods, Kharga Oasis, Egypt

摘要: Abstract Stable-isotope analyses of fossil-spring carbonates (tufas) and freshwater gastropods (Melanoides tuberculata) from the currently hyperarid Western Desert Egypt indicate that this region received enough precipitation to support a small perennial lake during height oxygen-isotope stage 6/5e pluvial event, substantial volume spring discharge prior phases. Tufa gastropod ratios are generally low relative modern in region, confirming majority Pleistocene came an Atlantic source, as determined by previous workers. Mean tufa δ13C (−2‰ PDB) suggests significant proportion C4 vegetation recharge area tufa-depositing springs, while paucity tufas with greater than 0‰ equilibrium between water atmospheric CO2 represented endpoint for evolution carbon. Though carbonate deposition requires increase humidity central conditions, high variation δ18O (up 4‰ within individual stratigraphic units), well positive covariance carbon- ratios, reflect effects evaporation on formation. Similarity values different units indicates climatic conditions did not vary significantly among phases recorded spring-carbonate deposition. The lack formation at localities Holocene phase, however, represents substantially wetter have existed time.