Spatiotemporal evolution of transfer structures and linked fault systems in an extensional setting: Southwest Gebel Akheider, Cairo-Suez District, Egypt

Abstract

Detailed geological field mapping of the area located to the southwest of Gebel Akheider, south-central part of the Cairo-Suez District (Egypt), was carried out to identify the geometry, structural style, and evolution of the normal fault systems in the study area. The present structural geometry of the study area is of Miocene age and is the result of the propagation, kinematic interaction, and eventual linkage of extensional fault segments. Eight mapped relay ramps formed between synthetic non-overlapping and overlapping normal faults. Fault displacement profiles showing variation in displacement along strike revealed steep displacement gradients and local displacement minima at the locations of these relay ramps. Conjugate normal faults in the area also showed signs of kinematic interaction. Fault displacement profiles revealed complimentary displacement distribution between interacting overlapping conjugate faults. In competent rock units (Middle Eocene limestone), this interaction resulted in the formation of horsts and grabens relay zones, while in incompetent rock units (Middle Miocene soft marl and sandy limestone), this interaction resulted in a series of en echelon plunging anticlines and synclines (accommodation folds). Several transfer faults marked by points of local displacement minima were also identified, forming a distinctive zigzag pattern in map view that is characteristic of the Cairo-Suez District. Curved fault traces represent another form of fault linkage in the study area. Fault displacement profiles indicated two different growth mechanisms, either as the result of bilateral growth of two along-strike faults, or the intersection of previously isolated and differently oriented fault segments.