Aridification of the Egyptian Sahara 5000–4000 cal BP revealed from x-ray fluorescence analysis of Nile Delta sediments at Kom al-Ahmer/Kom Wasit

Elemental XRF analysis carried out on an 8 m long core from the Nile Delta reveals a gradual increase in the Ca/Ti ratio between 5000 and 4000 cal BP which is linked to the progressive development of hyper-aridity in this region. The increase results from elevated flux of aeolian material entering the Nile river system from calcareous source rock geologies in the dryer Egyptian Sahara. The most major increase in hyper-aridity occurs around 4000 cal BP. Such a perspective suggests a locally abrupt, regionally time-transgressive inception of hyper-aridity in this region at the end of the African Humid Period. After this time, reorganisation of wind circulation meant that less Saharan-derived aeolian material entered the Nile Valley, and the contribution of aeolian material in the Nile's sedimentary signal was also dwarfed by an increase in Blue Nile sedimentary flux. Chronological control is provided by two radiocarbon dates and the top and bottom of a well-constrained pottery horizon that dates from the period of occupation of two nearby archaeological sites: Kom al-Ahmer and Kom Wasit.