THE ORIGIN OF MINOR FOLDS ASSOCIATED WITH A STRUCTURAL DOME ALONG THE SEIYAL FAULT IN THE WESTERN DESERT OF EGYPT

The Sinn el-Kaddab Plateau and surrounding Nubian Plain of the Western Desert of Egypt is characterized by the presence of numerous elongate domes and basins or “Desert Eyes” (Tewksbury et al., 2009) that range from several hundred meters to several kilometers in length. These Desert Eyes are commonly associated with dominantly E-W fault zones (e.g., Kalabsha Fault Zones). One such Desert Eye occurs as a structural dome cross-cut by fault splays associated with the trace of the Seiyal Fault Zone. Reconnaissance field studies of this dome suggested the presence of localized minor folding within a sandstone unit near the trace of one of the splays of the Seiyal Fault. Two models were proposed for the origin of these folds: 1) the folds were the result of localized soft-sediment deformation (soft-sediment folding was locally observed), and 2) the folds were tectonic in origin produced during formation of the dome and/or motion along the Seiyal Fault Zone. To test these models a detailed 10’s of meter scale geologic map of the sandstone units was constructed using a handheld GPS. Structural orientation data and locations of minor folds, joints, fractures, and deformation bands were also collected. Outcrop geologic mapping immediately revealed that one set of possible folds was only “apparent” (a result of the outcrop distribution pattern) as primary bedding within the individual outcrops of sandstone all had consistent orientations of 112, 35-45^o. However several minor folds within sandstone layers were observed and measured. These minor folds all exhibited similar orientations: axial planes striking 177-200^o, dipping 33-51° and hinge lines trending 87-111^o. These folds are asymmetrical with reclined axial planes and are moderate to steeply plunging (40-60^o) with interlimb angles of 20-60^o. The consistent orientation data for the five minor folds suggest a tectonic origin for these minor folds, possibly related to motion along the Seiyal fault, is likely.