PALEOENVIRONMENTAL RECONSTRUCTION OF THE AFTERMATH OF A MID-PLEISTOCENE METEORITE IMPACT EVENT, DAKHLEH OASIS, EGYPT

The Dakhleh Glass, a Ca-Al-silicate glass believed to have been produced by a meteorite impact, is distributed across 40 km within Dakhleh Oasis in the Western Desert of Egypt. Although the glass primarily occurs as a surface lag in association with Mid-Pleistocene paleolake sediments, it is also found in situ within them in a substantial sedimentary stratigraphy. Paleolandscape reconstruction using differential GPS measurements of glass elevations suggests that the impact event probably occurred at a relative lowstand of the lake. This is supported by the frequent presence of plant casts on the undersides of Dakhleh Glass found as surface lags, as well as evidence for ponding and cooling of molten glass at the surface. The sediments associated with the in situ Dakhleh Glass provide a record of intense burning, indicated by the reddening of the sediments underlying the in situ glass, the formation of maghemite, the silicification of silica-rich monocot leaves, and the presence of charcoal. The sediments overlying the lower Dakhleh Glass layer are likely reworked and redeposited from elsewhere in the basin, and contain soft sediment deformation consistent with rapid deposition of sediment. Comparison of the chemical composition of the glass to that of the underlying lacustrine sediment supports the hypothesis that the glass did not form in place. The distribution and chemistry of the glass, as well as evidence for rapid deposition of sediment in the aftermath of the impact event, suggests that an impact into a lacustrine environment may be a possibility, although a crater has not yet been conclusively identified. It is probable that the aftermath of the Dakhleh impact event was highly detrimental to the Middle Stone Age occupants of the oasis, due to adverse effects on the local ecosystems, and the degredation of a major water source as a result of the partial vaporization of the lake, waves generated by the impact blast, and increased turbidity and soot content of lake waters.