Continental Sedimentation in the Protorift of the Northwest Red Sea and Gulf of Suez: ABSTRACT

Abstract

Late Oligocene-early Miocene tectonics associated with lateral and vertical displacements resulted in a series of elongate half-grabens and tilted horsts whose multidirectional orientations are oblique or parallel to the axis of the rift. The morphological-structural depressions were areas of fluviatile sedimentation whose textures and bedding clearly express early rift morphology. Prerift Eocene sediments are generally preserved, indicating the protorift in the northwest Red Sea was not associated with major doming but with the creation of blocks of moderate relief. Basal rift sediments include conglomerates and sands whose nonerosional base and inclined bedding indicate proximal slope deposition. Mudstones deposited on alluvial plains confirm moderate relief and subhorizontal morphologies in the depressions. Erosional channels and playa deposits are best developed toward the top of the continental series, suggesting increasing relief. Finally, the protorift continental beds are strongly tilted and deformed along the edges of grabens by the strike-slip and vertical movements prior to the succeeding early Miocene marine transgression. This 200 to 300 m-thick continental series exhibits many synsedimentary deformational structures deposited on sub-horizontal substrates. These structures which express repeated earthquake activity, are typical of both the continental and marine sediments and are important sedimentary expressions of early rift tectonics.