A REMOTE SENSING AND FIELD INVESTIGATION OF THE EL KASR DESERT EYE IN THE WESTERN DESERT OF EGYPT

The “desert eyes” of the Western Desert SW of Aswan, Egypt (Tewksbury et al., 2009) consist of numerous elongate structural basins and domes, several hundred meters to several kilometers in length that exhibit dominantly E-W orientations and are typically closely associated with E-W fault zones. El Kasr (N23.857, E32.491) is unique among these structures in that it: 1) occurs in isolation in otherwise horizontal sedimentary rock with no other desert eyes in the vicinity, 2) the long dimension of the basin is oriented NNW, and 3) it is associated with the less common NNW fault zones.

El Kasr was investigated using high resolution satellite images (GeoEye) and field mapping. The structure is an elongate composite basin with shallow limb dips (10-25°) and is readily visible due to prominent ridges. The basin is approximately 6 km by 2 km and occurs in resistant Cretaceous to Eocene carbonate units. Lower Eocene Garra Fm crops out in the center of the basin and forms a prominent white ridge. Tan ridges to the east and south are underlain by Paleocene Kurkur Fm. The structure can be seen fading out as gently dipping Dakhla Fm (cropping out as resistant ridges) transition to horizontal beds. The northern and larger basin has an interlimb angle of ~152^°, fold axes of 162/06 and 346/08 (N and S respectively). The smaller basin to the SE has interlimb angles of ~156° with trend and plunge of one of the hinge lines being 321/03 the other indeterminate. The basin is truncated along the southwest by a prominent normal fault zone that show indications of normal dip-slip motion (325-310/75). Evidence of an eastern fault system includes, in the NE, truncation of layers of Dakhla Fm that strike at a high angle to basin strata and terminate along possible drag folds and, in the SE, layers of Dakhla Fm that are locally steeply dipping (30-70^o), offset by numerous small faults (i.e., fault splays), and rotated from the strike of basin strata.

El Kasr occurs in the hanging wall(s) between two fault systems, that merge S of the structure, as an elongated basin sub-parallel to the trace of these faults. Reactivation of Precambrian basement faults, with the basin developing on the downthrown blocks (e.g., Schlische 1995), and subsequently being cut by subsidiary faults as they propagated through the cover rocks might be one explanation for the formation of this structure.