Print this pageGrowth Faulting/Folding from the Gulf of Suez Rift: Structural Style and Sedimentary Response
SHARP, IAN R., ROB L. GAWTHORPE, JOHN R. UNDERHILL, and SANJEEV GUPTA
Growth folds in the Suez rift are related to steep dipping (60+ degrees) normal faults which propagated upwards from a Pre-Cambrian basement resulting in the development of broad upward-widening monoclines within overlying pre-rift strata. Folding during fault propagation was accommodated by both normal and reverse upward steepening secondary faults which propagated away from the master fault, as well as conspicuous layer-parallel slip and detachment along shale and clay horizons within the pre-rift strata. Ultimately, the upward steepening secondary normal and reverse faults propagate through to the surface, followed by the master normal fault, leaving the steep limb of the monocline and most of the secondary faults in the hangingwall. Where fault propagation was minimal or where fault displacement gradients decrease towards tip-points (e.g. transfer zones) unbroken growth folds are preserved.
This evolving structural style excerpted a marked control on the geometry and stacking patterns of coeval syn-rift sediments. Towards the growth folds syn-rift sediments display on lap and intraformational unconformities, whilst they diverge into broadly synclinal expanded sections away from the growth fold. Continued movement on buried faults resulted in the progressive rotation of folds and associated syn-rift sediments, such that each successively younger sequence dips basinwards at a shallower angle than the previous one. This results in an upward-widening growth syncline and complex onlap-offlap relationships. Along strike variations in stacking patterns are also marked, often being associated with a decrease in displacement on individual faults/folds towards transfer zones.