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Marius Ramirez-Cardona, State University of Hidalgo (UAEH) (Mexico)
Ahmed El-Barkooky, University of El Cairo (Egypt)
Mohamed Hamdan, University of El Cairo (Egypt)
Kinardo Flores-Castro, State University of Hidalgo (UAEH) (Mexico)
Nancy I. Jimenez-Martinez, State University of Hidalgo (UAEH) (Mexico)
Milton Mendoza-Espinosa, State University of Hidalgo (UAEH) (Mexico)
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LDSG has been described as a melt product from an impact event and has been dated at 28.5 m.y. (Oligocene). Fragments of this glass are mostly scattered upon the exposed bedrock of Nubia group (cretaceous sandstone), on a large surface area along wide corridors between dunes of the Great Sand Sea (SW of Egypt). This distribution is somewhat the result of the tektite fluvial transport occurring throughout the Oligocene-Miocene boundary. This assessment is based on the present knowledge of the drainage system that dominated all this part of the Western Desert of Egypt from the Oligocene to the Late Miocene. Both the uplift of the southwestern land of Egypt and the intense precipitations originated a complex fluvial system called the Gilf River (Oligocene-late Miocene). The water running off from the highlands in the southwestern of Egypt (Gilf Kebir and Gebel Uweinat) flowed north through the slightly north-dipping Eocene strata and reached the receded shoreline of the Tethys Sea, situated by that time near Siwa or Qattara. The intense weathering of flowing water removed hundreds of meters of the Cretaceous sandstones, limestones and shales, and the Eocene limestones. The key factor that remains to be solved is the identification of a nearby source impact structure. The association between some impact craters of the region (i.e., BP and Oasis craters) and the current emplacement of silica glass has not been still well-established. However, a recently identified circular geomorphological feature has been selected in this study as the source area that supplied impact melted material to the Oligocene fluvial system. This geoform (Kebira crater) is a 32-km-diameter double-ringed structure located at northwestern side of the Gilf Kebir plateau (24.40°N 24.58°E, 100 km southwest from the southern limit of the LDSG area). Its impact origin is ambiguous since the structure identification was only performed by remote sensing techniques without further analysis of the affected geological material. Nevertheless, the hydrographic patterns inside and surrounding the structure can be interpreted as a tributary subsystem of the central Gilf River fluvial system.
This study presents a preliminary model of LDSG transport/deposition taking into account the Oligocene-Miocene Gilf River system and including the Kebira crater as the source area of the impact glass. Although the impact origin of this structure is not definite, the suitability of the model is showed by combining field information with topography, hydrographic data and tectonic evolution. The methodology is based on the analysis of a digital model of terrain, deducing hydrological and erosion patterns, setting a slope-distribution map and mapping LDSG localities. Some of the field information has been derived from in situ observations during the "Gilf Kebir 2007" mexican-egyptian scientific expedition to the Gilf Kebir plateau and the Great Sand Sea region (03/27/2007-04/05/2007).
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