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TOPIC: Dakhleh Oasis Impact


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Dakhleh Oasis Impact
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Title: Potential consequences of a Mid-Pleistocene impact event for the Middle Stone Age occupants of Dakhleh Oasis, Western Desert, Egypt
Authors: Jennifer R. Smith, Maxine R. Kleindienst, Henry P. Schwarcz, Charles S. Churcher, Johanna M. Kieniewicz, Gordon R. Osinski, and Albert F.C. Haldemann

While it is expected that prehistoric populations experienced the effects of impacts by extraterrestrial objects, there is little record of such events in occupied regions. We discuss the ramifications of an impact between 100 and 200 ka into Dakhleh Oasis, at that time experiencing humid phase conditions and inhabited by Middle Stone Age people. Based on modelling of impact processes using estimated impact parameters, the impact blast would likely have felled or dismembered most trees over 280-2400 km²  of the oasis, and inhabitants would have been injured over much of the region, although severely only near the blast location. The impact would not have vaporized much of the Dakhleh paleolake(s), although some water was probably lost through boiling and through waves initiated by the impact blast. Water quality would have decreased as lake turbidity increased, and soot from regional fires fell into the lake. A relatively small event would not have immediately ignited much of the oasis vegetation, but sedimentary evidence suggests that impact-generated fires did spread to significantly affect the landscape. The impact and resulting fires may have triggered mass wasting events as well as significant changes in erosion rates and have substantially affected human uses of the area.

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-- Edited by Blobrana at 22:57, 2009-01-31

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Strange specimens of natural glass found in the Egyptian desert are products of a meteorite slamming into Earth between 100,000 and 200,000 years ago, scientists have concluded.
The glass—known locally as Dakhla glass—represents the first clear evidence of a meteorite striking an area populated by humans.
At the time of the impact, the Dakhla Oasis, located in the western part of modern-day Egypt, resembled the African savannah and was inhabited by early humans, according to archaeological evidence.

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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 (>500 km²). Furthermore, the sedimentology of the deposits is taken into account-- do the deposits record a deep water, shallow water, or palustrine environment?

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29.14291E_25.57641N
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Latitude: 25.57886 N; Longitude; 29.03890 E

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Mapping Impact Modified Sediments: Subtle Remote-Sensing Signatures of the Dakhleh Oasis Catastrophic Event, Western Desert, Egypt

A.F.C. Haldemann (JPL, Caltech), M.R. Kleindienst (U. Toronto at Mississauga), C.S. Churcher (U. Toronto), J.R. Smith (Washington University in St. Louis), H.P. Schwarcz, K. Markham (McMaster University), G. Osinski (Agence Spatiale Canadienne/Canadian Space Agency)

Over the past decade members of the Dakhleh Oasis Project have studied enigmatic signatures in the Pleistocene geologic record of portions of the Dakhleh oasis and palaeo-oasis.
In particular, Ca-Al rich glass (Dakhleh Glass) points to a catastrophic event between c. 100,000 - 200,000 years ago in this well-studied African savannah and freshwater lake, Middle Stone Age environment. The known glass deposits occur at locations separated by tens of kilometres. Here we report on mapping of remote sensing data (visible, infrared and radar) that is being used to guide wider reconnaissance of the Dakhleh Glass deposits. The remote sensing is anchored on the best-studied feature, the Dakhleh Bow Wave Structure (DBWS), where structural elements of a ~ 400 m putative crater are preserved. These structures are highly degraded, and only subtly apparent in the remote sensing data.
The Dakhleh Glass (DG), while chemically unique as a natural glass, is nowhere very extensive, and is thus only a minor constituent in each remote sensing pixel; a full mapping of DG and inferences about the initiating catastrophic event will require detailed field work. The subtle remote-sensing signatures of this relatively recent impact(s) into a sedimentary target at Dakhleh, where the erosion rate is estimated at 0.1 mm/yr, underscore the difficulty in accumulating a clear characterization of the range of sedimentary target modifications associated with smaller (100 m - 1 km) terrestrial craters.

Source


"Bracketing by archaeological remains confirms the chronometric date obtained on the glass of 122,000 ± 40,000 years for the heating event--during the Middle Stone Age occupations of the oasis area"

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The Dakhleh Oasis lies some 800 km SSE of Cairo, surrounded by the wastes of the eastern Sahara, centred at 25o 30'N and 29o 07'E. The oasis is some 80-km west to east and 25-km maximum wide.

The capital is at Mut, which has been the main town since at least the eighteenth dynasty, about 1,500 BCE. Before then, the site of 'Ain Asil at Balat in eastern Dakhleh had been the seat of the government, since 2,500 BCE , and before that the less settled Neolithic and earlier populations inhabited the area. The Dakhleh Oasis has had a continuity of settlement for about the last 8,000 years but only since 2,500 BCE has it been politically tied to the Nile region. Climatic trends and events that can be discerned in most of the eastern Sahara are also seen at Dakhleh.

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