Thickness variation of the sedimentary cover in the south Western Desert of Egypt as deduced from Bouguer gravity and drill-hole data

Abstract

Bouguer gravity anomaly mapped at a scale of 1:500,000 and the lithological logs of about 120 deep wells were used to determine the thickness of the sedimentary sequence containing the main sandstone water formation in important area of Egypt. The area is located in the southern part of the Western Desert bounded by the latitudes 22°00′–26°30′ N, and longitudes 28°30′–33°00′ E. The predominant structures affecting the basement rocks and the sedimentary cover were also studied. The gravity stripping approach was applied to eliminate the gravity effects caused by sedimentary sequence and to separate density anomalies within the sedimentary fill from the influence of rocks at deeper levels in the crystalline crust.The present study indicated that the surface of the basement rocks is highly rugged and mostly controlled by structures which have a direct effect on thickness variation of the sedimentary cover all over the area. Regionally the area is characterized by two major intracratonic basins (the Dahkla Basin and the Nile valley Basin) separated by a NE–SW trending swell of the Kharga uplift and bounded at the south by the Oweinat–Bir Safsaf–Aswan uplift. These major tectonic units are controlled by fault structures trending in N–S, E–W, NE–SW, NW–SE, which cut the basement rocks and extend upward in the sedimentary cover. The maximum thickness of sandstone formations is recorded at west Oweinat, west Kurkur, southwest of Aswan, Gramashin, Dakhla oasis and some localities west of Sohag and Qena towns. At these localities the thickness ranges between 600 and 900m. As this formation is the main water aquifer in the study area, therefore these localities are characterized by the presence of big amount of groundwater. Accordingly, these areas must take the priority in the sustainable development programs of southern Egypt.