RECONNAISSANCE STUDY OF DOMES AND BASINS IN TERTIARY SEDIMENTARY ROCKS IN THE WESTERN DESERT OF EGYPT USING HIGH RESOLUTION SATELLITE IMAGERY

High resolution satellite imagery of the remote Western Desert of Egypt reveals spectacular small scale dome and basin structures in Early Tertiary limestone, marl, shale, and chalk. Although domes and basins occur from the southern end of the Sinn El Kaddab Plateau at least as far as 27.75N (over 500 km), the character of structures changes from south to north.

On Sinn el Kaddab, elongate domes and basins ranging from <250 m to >1.5 km in length occur as prominent “eyes” both along major E-W faults and along minor faults and linear zones of other orientations. Many aspects of these domes and basins are consistent with the geometry produced by extensional fault-propagation folding, and offsets of fold layering on many of the faults require dip slip. This is consistent with normal slip mapped in the field by others. Focal mechanisms along the Kalabsha Fault at the southern end of Sinn el Kaddab indicate modern right-lateral strike slip movement. Because the Kalabsha has structures similar to those along the other E-W faults of the Plateau, however, strike slip may represent modern reactivation.

In contrast to the linear alignment of domes and basins on the Sinn el Kaddab Plateau, these features between the latitude of Asyut and 27.75N cluster in roughly equidimensional fields approximately 1-2 km across. Dome fields are dominated by clusters of 100-500 m diameter domes characterized by very low dip angles. Adjacent dome fields are separated from one another by narrow zones (100-200 m wide) that typically contain doubly-plunging, dominantly synclinal structures.

Between southern Sinn el Kaddab and the area in the north, structures are a hybrid. Folds (primarily narrow, doubly plunging synclines) occur along prominent structural trends, with only minor evidence of faulting and minor occurrences of domes and basins in the tracts in between.

The presence of dome fields in the north and domes and basins away from the main faults on the Sinn El Kaddab suggests a model that is more complex than localized folding associated with fault propagation. We are exploring whether subsurface sediment mobilization may have been responsible for the dome fields, which are strikingly similar to structures related to polygonal faulting in the North Sea, and whether such processes may have played a role in formation of structures along the major faults.