Paper No. 4
Presentation Time: 8:00 AM-6:00 PM
DEFORMATION BANDS AND THE EXPRESSION IN SILICICLASTIC COVER ROCKS OF SLIP ON BASEMENT FAULTS IN SOUTHERN EGYPT
TEWKSBURY, Barbara J.1, HOGAN, John P.
2, KEMP, Stephen M.
1, KEREN, Tucker T.
1, TEWKSBURY-CHRISTLE, Carolyn M.
3, SCHULTZ, Richard A.
4 and MEHRTENS, Charlotte
5, (1)Dept. of Geosciences, Hamilton College, 198 College Hill Rd, Clinton, NY 13323, (2)Geological Sciences and Engineering, University of Missouri-Rolla, 127 McNutt Hall, Rolla, MO 65401, (3)1101 Chamisoso Ct. SE, Albuquerque, NM 87116, (4)ConocoPhillips, 600 N Dairy Ashford, PR-2010, Houston, TX 77079, (5)Geology, University of Vermont, 180 Colchester Avenue, Burlington, VT 05401, btewksbu@hamilton.edu
In southern Egypt, basement faults of Precambrian age have been repeatedly reactivated and cut Cretaceous to Eocene rocks in a wide region west of the Nile River. Faults in Cretaceous siliciclastic rocks of the Nubian Plain and Kharga Valley display a different range of structures from those in the overlying Early Tertiary carbonates that cap the Sinn el-Kaddab Plateau. In the carbonates capping the Plateau, faults have little topographic expression but are characterized by spectacular eye-shaped domes and basins aligned along fault strike. In the Cretaceous siliciclastic rocks of the Nubian Plain and Kharga Valley, faults are commonly more resistant than surrounding rocks and are characterized by sets of discontinuous ridges several meters wide and rising a few meters above the surrounding countryside. “Eyes” are present along these faults as well but are much less common than along faults in the overlying carbonates.
Southwest of Aswan, the E-W-striking Seiyal Fault cuts a sequence of siliciclastic rocks containing friable, porous quartz sandstone. The discontinuous resistant fins marking the surface expression of the fault consist of a core zone of deformation bands overprinted by joints and sheared joints cemented by calcite, with poikilotopic calcite extending from the veins into cement halos adjacent to the veins. Damage zones containing deformation bands lie adjacent to the fault core. The deformation bands, veins, and related cement halos combine to make the fault zones more resistant than the surrounding country rock.
E-W and NNE-SSW faults cut siliciclastic rocks of the Six Hills area of the Kharga Valley over a distance of at least 200 km west of the Sinn el-Kaddab Plateau. High resolution satellite imagery reveals that the faults are characterized by en echelon major ridges and intersecting subsidiary ridges in ladder-like linking band and conjugate geometries. Geometries are consistent with predominantly strike-slip movement, dextral on EW faults and sinistral on NNE-SSW faults, with a compression axis oriented NW-SE. Based on our field work along the Seiyal Fault, we infer that slip along basement faults in the Six Hills area was likely accommodated in the overlying siliclastic units by formation of deformation band arrays and that basement faults focused fluid flow in the overlying siliciclastic cover.
