Tectonic and Sedimentological Significance of Miocene Brackish Water and Lacustrine Deposition in the Suez Rift

W. A. Wescott, W. N. Krebs, P. A. Bentham, D. T. Pocknall, G. Azazi, and S. A. Karamat

From its inception during the early Miocene, the Suez Rift has been dominated by marine sedimentation. New high-resolution biostratigraphic and sedimentological analyses of synrift deposits have resulted in the recognition of late Burdigalian-early Langhian brackish water and lacustrine deposits in the Wadi Abu Gaada-Gebel Gushia area, Sinai Peninsula. Previously, these deposits were interpreted as unfossiliferous, bathyal marine shales; however, recent studies have resulted in the recovery and recognition of abundant freshwater and shallow marine algae. Those present include the nonmarine diatoms Aulacoseira spp., Fragilaria construens, Synedra ulna, and Surrirella spp. as well as the freshwater algae Botryococcus sp. and Pediastrum sp. Shallow marine diatoms are represented by Actinoptychus spp., Actinocyclus ehrenbergii, Paralia sulcata, Rhaphoneis spp., and Hyalodiscus sp. This lacustrine-brackish water deposition has interesting implications concerning the tectonic and sedimentologic evolution of the basin.

The late Burdigalian-early Langhian Wadi Abu Gaada section is approximately 400 m thick. The lower 145 m of the section comprises interbedded lower shoreface sandstones and neritic shales which fine upward into inner neritic shales that yield the benthic foraminifer Nonion boueanum. This grades upward into a 170 m algal-bearing brackish water and lacustrine shale section which is capped by evaporites (Marka Anhydrite). A shallow marine section, including sub-tidal rhodolitic limestones, overlies the evaporites.

Correlations with other coeval stratigraphic sequences in the Sinai Peninsula indicate that brackish water and lacustrine deposition occurred only in the Wadi Abu Gaada-Gebel Gushia area. This can be explained by uplift and tilting of the bounding faults separating the Wadi Abu Gaada-Gebel Gushia block from adjacent rift blocks where normal marine conditions prevailed.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California