A PREVIOUSLY UNRECOGNIZED SYSTEM OF FOLDS AND RELATED FAULTS IN STABLE PLATFORM LIMESTONES OF THE EL RUFUF AND DRUNKA FORMATIONS, WESTERN DESERT, EGYPT
TEWKSBURY, Barbara1, DOKMAK, Asmaa A.2, TARABEES, Elhamy3, MANSOUR, Ahmed Sadek M.2, FATTAH, Tharwat Abdel2 and RASHED, Mohamed A.2, (1)Dept. of Geosciences, Hamilton College, 198 College Hill Rd, Clinton, NY 13323, (2)Geology Department, Faculty of Science, Alexandria University, Moharam Beih, Alexandria, 21511, Egypt, (3)Geology Department, Faculty of Science, Damanhour University, 22 Galal Street, Damanhour, 22516, Egypt, btewksbu@hamilton.edu
Landsat images of the Western Desert of Egypt show a pervasive and systematic patterning. Our study of recent high resolution satellite imagery in Google Earth, combined with targeted field work, reveals that although some of the patterning results from aeolian erosion and deposition, a remarkable proportion is fundamentally structural over an area of at least 20,000 km2. Eocene carbonates display hundreds of narrow synclinal structures that are typically several 100 meters wide and separated by much broader anticlinal structures. Synclinal structures are generally gentle to open, with shallow but variable plunges and multiple basin closures along their lengths. Although these narrow synclinal structures define many of the lineaments previously shown on regional bedrock maps, they are only rarely accompanied by major faults. Anticlinal structures are generally very different in both geometry and scale from the synclines. They are broad, flat-topped, and up to 10 times wider than the immediately adjacent synclines. In some areas, intersecting sets of WNW-ESE and N-S synclines separate broad, blocky domical structures. In other areas, the WNW-ESE synclines have a sigmoidal pattern, changing trend along their lengths from WNW-ESE to NW-SE.
In contrast to the synclines described above, a small number of narrow N-S synclinal structures spaced 6-10 km apart in the El Rufuf and the Drunka Formations are clearly associated with major faults. The two most prominent of these extend to the south, defining the shape of the Kharga Valley as well as the oasis trends.
As far as we are aware, these fold structures have not been previously recognized. The combination of low dip angles, scale of the structures, and only slight differences in erosional resistance of massively bedded limestones results in structures that are too subtle and too big to be readily noticeable from the ground and too small to be identifiable except in satellite images with resolutions of a few m/pixel. Detection from the ground is also confounded by yardangs, which obscure bedding and structures in many areas.
Furthermore, analysis of high resolution visible light, ASTER SWIR, and ASTER TIR images offers compelling evidence that the El Rufuf-Drunka contact west of the Asyut-Kharga Road is incorrectly mapped on existing regional bedrock maps.
