THE DESERT EYES PROJECT PART II: STRUCTURES ALONG EAST-WEST AND NORTH-SOUTH FAULTS OF THE WESTERN DESERT, EGYPT
The SFZ & GFZ, visible in GeoEye imagery as EW and NS lineaments, consist of multiple fault segments that extend for 100s of kms across the Western Desert. Domes and basins are common along the SFZ and are cross-cut by the SFZ with visible dip-slip displacement. Field investigations confirm the presence of a structural basin on the north side with down to the north displacement along one strand of the SFZ in Eocene carbonates. Detailed mapping of a structural dome along the SFZ in Late Cretaceous sandstones reveals both soft sedimentation deformation features (likely seismites) and later conjugate structures and deformation bands that crosscut the dome. Conjugate structures are consistent with a significant dextral strike slip component, and mapping suggests a component of down-to-the-south dip slip as well.
The El Kasr structure occurs at a left stepover between two segments of the GBZ. El Kasr is an elongate NNW-SSE 6 x 2 km composite basin. Folded Cretaceous to Eocene sedimentary layers dip 10 - 25° in the limbs of folds. Folds are open, upright, with subhorizontal to gently plunging hinges (<20o). The western and eastern limbs are both truncated by normal fault zones. The El Kasr structure formed in the hanging wall of normal faults related to slip along the GBZ.
The SFZ and GFZ are likely reactivated basement faults with long-lived slip histories. Seismites along the Seiyal may have formed in thin, weakly consolidated sediments during Cretaceous faulting, with cross-cutting brittle structures forming later, after deposition of Early Tertiary sediments. Open sand-filled fractures along the trace of both the SFZ & GFZ reflect active modern slip. Dextral strike-slip focal mechanism solutions along the EW Kalabsha Fault suggest that modern motion along the similarly oriented SFZ has a large component of dextral slip.