Age of the Dakhleh impact event and implications for Middle Stone Age archeology in the Western Desert of Egypt

Dakhleh Glass comprises a suite of chemically distinctive and heterogeneous glassy rocks that occur over an area of ca. 400km2 in and around the Dakhleh Oasis in central western Egypt. Previous studies establish a meteorite impact origin for the Dakhleh Glass. No impact crater has yet been found, suggesting an airburst origin. The Dakhleh Glass-forming impact event occurred during the Middle Stone Age time of occupation, but the timing of this event has not been well established. 40Ar/39Ar incremental heating of three aliquots from a sample of Dakhleh Glass yield data that can be ascribed to quenched glass which efficiently purged radiogenic 40Ar inherited from the target rocks. One of the aliquots yielded data suggestive of an undegassed clast of target material, but these are easily resolved. The age of the impact event is determined from a compositionally filtered subset of the data that yield an isochron age of 145±19ka.