Dakhleh Oasis, Egypt

Extensive lacustrine marls in Dakhleh Oasis, Egypt, attest to a significantly more humid climate in comparison with the present (e.g. Churcher et al., 1999).  Shown in the picture above, these deposits occur as remnant caps atop the Cretaceous bedrock, due to the intense aeolian erosion that has occurred since the evaporation of the lake.  Because the deposits have been largely deflated by >10 m in areas, reconstructing the size and extent of the paleolake becomes a challenge.  By mapping the deposits with differential GPS (vertical accuracy ~0.3 m) and extrapolating onto the modern topography in GIS, constraints are placed upon its possible extent (>1000 km²).  Furthermore, the sedimentology of the deposits is taken into account-- do the deposits record a deep water, shallow water, or palustrine environment? 

I am also interested in considering the climatic and hydrologic conditions necessary to form and maintain the Dakhleh palaeolake.  Spring mounds record the influx of iron-rich Nubian aquifer water to the basin, probably in the earliest stages of the lake, and this water likely helped to maintain the lake throughout the year.  However, tufa deposits along the escarpment, and drainage networks atop the escarpment indicate that local meteoric precipitation and input from local aquifers were also important components to the water balance.  Using isotope and energy balance methods for reconstructing the palaeohydrology of the Dakhleh palaeolake, I have found that rainfall as high as 500 mm/year may have been necessary to sustain that body of water.

Aside from two U-series dates on tufa blocks from the escarpment (which do not actually date the lake itself), the only chronological constraint (122± 40 ka; Schwarcz et al., in press) for the lacustrine sediments comes from an Ar/Ar on Dakhleh Glass (below), a Ca-Al-silicate glass, which has been found as a surface lag atop the lake sediments, as well as in situ within the sediments in some areas.  At this time, the leading hypothesis for the formation of this glass is an impact, though a crater has yet to be identified (Osinski et al., 2007).  I am involved with the palaeolandscape reconstruction of this event, and my contribution to this research comes in the form of the sedimentology, stratigraphy, and geochemistry of the sediments surrounding the in situ occurrences of the Dakhleh Glass.

This work is conducted in association with our colleagues at the Dakhleh Oasis Project, an international archaeological project focused on human-environment interactions dating from the prehistoric to the present day in Dakhleh Oasis.  Late Early Stone Age and Middle Stone Age artifacts have been found in situ and associated with the lacustrine sediments and ironstone spring mounds in Dakhleh Oasis (e.g. Kleindienst, 2003).  Ultimately, placing constraints upon the size of the Dakhleh lake, its water balance, and the setting of a potentially catastrophic event are important for understanding the environment that these early humans/hominids inhabited. More humid conditions in the currently hyper-arid Sahara would have been favorable for human migration out of Africa into the Mediterranean and Levant.

References/Further Information:

Brookes, I. A. (1993). Geomorphology and Quaternary geology of the Dakhla Oasis region, Egypt. Quaternary Science Reviews 12, 529-552

Churcher, C. S., Kleindienst, M. R., and Schwarcz, H. P. (1999). Faunal remains from a middle Pleistocene lacustrine marl in Dakhleh Oasis, Egypt; palaeoenvironmental reconstructions. Palaeogeography, Palaeoclimatology, Palaeoecology 154, 301-312.

Kieniewicz, J. M., and Smith, J. R. (2005). Paleogeography, Sedimentology, and Geochemistry of Pleistocene Paleolakes in Dakhleh Oasis, Western Desert, Egypt. GSA Abstracts with Programs 37, 210-7  Click here to read.

Kleindienst, M. R. (2003). Strategies for studying Pleistocene archaeology based upon surface evidence: first characterization of an older Middle Stone Age unit, Dakhleh Oasis, Western Desert, Egypt. In "The Oasis Papers III." (C. A. Hope, Ed.). Oxbow Books, Oxford.

Osinski, G. R., Schwarcz, H. P., Smith, J. R., Kleindienst, M. R., Haldemann, A. F. C., and Churcher, C. S., 2007, Evidence for a ~200–100 ka meteorite impact in the Western Desert of Egypt: Earth and Planetary Science Letters, v. 253, p. 378-388.

Schwarcz, H. P., Szkudlarek, R., Kleindienst, M. R., and Evensen, N. (in press). Fire in the Desert: The Occurrence of a high-Ca Silicate Glass near the Dakhleh Oasis, Egypt. In "The Oasis Papers 4." (A. J. Mills, Ed.). Oxbow Books, Oxford.