PRELIMINARY INVESTIGATION OF THE EL KASER STRUCTURE OF THE WESTERN DESERT OF EGYPT – IMPLICATIONS FOR THE ORIGIN OF “DESERT EYES”

High resolution satellite imagery of the Sinn el-Kaddab Plateau and surrounding Nubian Plain in the Western Desert of Egypt reveals numerous elongate domes and basins, informally referred to as “Desert Eyes” (Tewksbury et al., 2009) that range from several hundred meters to several kilometers in long dimension. Desert Eyes are typically closely associated with dominantly E-W fault zones (e.g., Seiyal, Kalabsha Fault Zones) and less common N-S fault zones and are likely related to propagation of basement faults into sedimentary cover and slip along those faults. The El Kaser Structure, located in the Nubian Plain ~50 km SW of Aswan, is a well-exposed and readily accessible example of one of these Desert Eyes. The structure is an elongate ring of low-relief hogbacks approximately 6 km by 2 km in resistant Cretaceous to Eocene carbonate units. The structure is a shallowly plunging double basin with low limb dips (10-25°). The basin is elongate NNW-SSE, in contrast to the more typical Desert Eyes that are elongate EW. The structure is also unique in that it stands in isolation in the otherwise horizontal sedimentary rock of the Nubian Plain, with no other Desert Eyes in vicinity. The western edge of El Kaser is partially buried by younger sands and gravels transported in wadis originating along the retreating edge of the Sinn el-Kaddab Plateau. Resistant ridges along the southwestern edge of the structure are truncated by faults striking 325 and 335 that display well developed calcite veins and cataclasites, with slickenlines indicating dip-slip motion. Sand and gravel cover contains ground cracks oriented parallel to the strike of the faults and suggest modern motion on these faults. Along the southeastern edge of the structure, red-brown sandstones define zones of steeply dipping (30-70^o), thinly layered beds that are rotated and offset from the main trend of the structure, suggesting localized displacement along fault splays. The El Kaser Structure is likely to have formed as the result of reactivation of a pair of intersecting Precambrian basement faults, with the basin initially developing on the downthrown blocks near the fault intersection and subsequently being cut by subsidiary faults as they propagated through the cover.