Mechanical response of the stratigraphic succession to rifting in the Gulf of Suez, Egypt, varies depending on the degree of competence of the rock units. This "mechanical stratigraphy" has been documented by observational evidence from field surveys in the northern Esh el Mallaha and in the Ras Issaran area, in conjunction with seismic reflection data. Complex response patterns to basement-rooted block faulting is seen on several scales in both the prerift and synrift rocks. The prerift section is divided into three major units based on mechanical response: Precambrian basement, pre-Cenomanian "Nubian sandstone," and Cenomanian-through-Eocene stable platform marine rocks. Brittle faulting in the basement propagates into the Nubian sandstone by densely fracturing the latter parallel to the fault planes. The overlying inhomogeneous Cenomanian-Eocene section drapes and folds over underlying structural elements. These rocks contain complicated structures due to the interlayering of thin brittle and ductile beds. The incompetent units allow bedding-parallel detachment and also flow into voids created during faulting or folding of the competent units. The synrift section comprises three major stratigraphic units, each of which reacts differently to block faulting. These are the early Miocene carbonate/clastic section, the middle-late Miocene evaporite section, and the onshore Pliocene-Recent clastic passive-cover sequence. In general, the lower synrift rocks respond to deformation much like the Cenomanian-Eocene units, draping and folding due to interlayered brittle and ductile beds. Seismic reflection data indicate that the evaporite section is a major detachment zone, with faults in underlying units dying out upwards, as the ductile salts or anhydrites drape and flow. Structural response in this section is varied and complex. The deformation of the evaporites breaks the overlying passive-cover rocks, with faults in the latter soling into the underlying ductile strate. On gravel plains flanking the Gulf of Suez, the neotectonic fault pattern and resulting topographic and drainage changes reflect underlying structures. The faults breaking the passive cover sequence at the surface initially form en echelon traces; with continued movement these coalesce into straight or curved, often splaying, fault traces. Where the evaporite section reaches a significant thickness, the structures seen at the surface may be entirely decoupled from those of the prerift and early synrift sequences. © 1990.
