RECONSTRUCTING QUATERNARY GROUNDWATER AVAILABILITY IN DAKHLEH OASIS, EGYPT

Quaternary humid periods in North Africa led to the development of large freshwater lakes in many areas that are now hyper-arid desert. In Dakhleh Oasis, the remnants of Pleistocene pluvial sediments consist of carbonate lake deposits from surface runoff as well as iron-rich groundwater deposits from the Nubian Aquifer. These groundwater deposits are preserved as resistant mounds of iron-cemented sands, known as spring mounds, and unlike carbonate lacustrine sediments their formation would not have been limited to pluvial periods as long as artesian groundwater flow was present in the oasis. However, groundwater spring deposits are difficult to date, due to the erosive nature of modern North Africa as well as the lack of datable materials, such as carbonates or organic matter, in most groundwater deposits. In the past, the infrequent recovery of in situ archaeological materials suggested that the majority of the groundwater availability in Dakhleh occurred during the Pleistocene. More recent observational evidence as well as the recovery of limited ceramic materials from spring contexts suggests ongoing or reactivated groundwater availability at a number of sites in Dakhleh, indicating that poor preservation of Holocene sediments is a significant barrier to accurate paleoenvironmental reconstructions and the lack of Holocene evidence for groundwater deposition does not reflect a true picture of water resource availability over time.