Style and sequence of deformation during extensional fault-propagation folding: examples from the Hammam Faraun and El-Qaa fault blocks, Suez Rift, Egypt

Abstract

Kilometre-scale fault-parallel folds are identified adjacent to normal faults in the Oligo-Miocene Suez Rift, Egypt and are interpreted to have formed in response to fault-propagation folding above upward propagating blind faults. The geometry, scale and distribution of secondary structures within the folds and their cross-cutting relationships with the master faults allow the style and sequence of deformation during fault-propagation folding to be established and suggest that during the initial stages of folding, the proto-footwall underwent extension which was accommodated by layer-parallel slip in encasing mudstone horizons and linked normal faulting and block rotation in carbonate and sandstone units. The proto-hanging wall also contains dominantly extensional normal faults although locally, where the master fault had a convex-into-the-footwall map-view trace, reverse faulting and fracturing occurred. Secondary structures adjacent to the master fault were not all active simultaneously, but initiated and died at different stages during the evolution of the fault-propagation fold. The results of this study confirm many key predictions of numerical and physical analogue models but also highlight several important controls on the evolution of fault propagation folds in extensional settings which existing models cannot capture, such as the influence of the map-view trace of the propagating fault and lateral variations in cover stratigraphy lithology and strength on the style and magnitude of secondary deformation.