INVESTIGATION OF FOLDS AND FAULTS IN EOCENE CARBONATES OF THE SERAI FORMATION USING SATELLITE IMAGERY, WESTERN DESERT, EGYPT

High-resolution (~1 m/pixel or less) satellite imagery enables detailed mapping of structures in Early Cenozoic carbonate bedrock of the Western Desert of Egypt. Folds in limestone of the Serai Formation occur as broad (~500-1000 m wide) elongate domes separated by a network of narrow (~100-200 m wide) synclines with shallowly dipping limbs, very shallow plunges, and multiple basin closures. Hundreds of minor dip slip faults oriented NS, NNW/SSE, and NW/SE cut the folds. The narrow synclines form a network with a dominant NW/SE trend and a less prominent but clear EW to ENE/WSW trend. The synclines branch, bend, and merge in a way that suggests simultaneous development, rather than subsequent cross folding. Elsewhere in the area, graben mapped by others as associated with Red Sea rifting clearly cut these fold structures, constraining the timing of fold development in the study area to between Early Eocene deposition of the Serai Formation and Oligocene/Miocene rifting of the Red Sea.

In the western section of the study area, several prominent sets of paired NW/SE and WNW-ESE faults define narrow (~200 m wide) graben with no topographic relief. Folds at the same scale as the basin closures in the network of narrow synclines occur within these graben and are truncated by the graben-bounding faults. West of the study area, these graben are collinear with narrow synclines with basin closures, and the bounding faults cut pre-existing fold structures that extend beyond the width of the graben. These small graben are clearly distinct both in scale and in lack of topographic relief from graben with widths of several kilometers and topographic relief of many tens of meters that have been mapped by others as associated with Red Sea rifting.

The branching geometry of networks of very narrow synclines is unusual and not typical of folds in regional contractional settings. We suggest that mobility in the underlying Esna Shale may have developed new layer-confined faults or deformed an existing polygonal fault network in the Esna, causing deformation in the overlying Serai. Lack of topographic relief of the narrow graben plus collinearity with narrow synclines suggests that the narrow graben are distinct from larger, younger Red Sea Rift-related graben, perhaps representing a late phase of the process that formed the network of narrow synclines