Quaternary environmental change in the Western Desert of Egypt: Evidence from cave speleothems, spring tufas, and playa sediments

U-series ages for speleothems in Djara Cave, and spring tufas along the eastern scarp of the Kharga Oasis, suggest humid intervals during marine isotope stages (MIS) 5, 7, 9 and 13 and possibly also during warm interstadials of MIS 6 and 8, when sapropels formed in the eastern Mediterranean. Based on TL analysis, eroded playa sediments in the Farafra, Kharga and Dakhla Oasis are Holocene. The absence of speleothem and tufa of MIS 1 age indicates drier conditions than during earlier interglacials. If meteoric water with the same δ ¹⁸O as deep Nubian aquifer groundwater deposited the Djara Cave speleothems, and if they were deposited in isotopic equilibrium with these waters, then mean annual temperatures in the Western Desert at times of speleothem deposition were at least as warm as today. Published δ ¹³C of bicarbonate in Nubian aquifer groundwaters in the Kharga, Dakhla, Farafra and Bahariya oases indicates recharge in an area of C ₃ vegetation probably in southwest Egypt and northwest Sudan with subsequent artesian flow to the northeast. δ ¹³C of cave speleothem and tufa resulted from local recharge through a vegetation cover with at least 50% C ₄ plants. This suggests a north-to-south increase in rainfall at the time of speleothem and tufa deposition. Greater rainfall during pre-Holocene interglacials may be a response to higher summer solar radiation and increased monsoonal activity, and to lower winter radiation and a more southerly position for the winter westerlies.