--> Structural Embayments and Straits Control on Early Syn-Rift Shallow Marine Deposition: Nezzazat Fault System, Suez Rift, Egypt

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Structural Embayments and Straits Control on Early Syn-Rift Shallow Marine Deposition: Nezzazat Fault System, Suez Rift, Egypt

Abstract

The inherent deformation due to the growth of normal faults in an extensional basin results in mechanisms such as rotation and subsidence of the hangingwall and syncline growth that constitute first order modifiers of the substrate gradients. Their interaction with the marine environment can result in an intricate development of straits and embayments affecting the circulation of marine currents. The impact of these structural induced features is studied by a combination of traditional field methods and digital outcrop techniques (LIDAR and photogrammetry) from very well preserved Miocene early syn-rift exposures at the Nezzazat Fault System, Suez Rift, Sinai Peninsula, Egypt. The early syn-rift succession is composed of shallow marine carbonates and siliciclastics of early Miocene age (Aquitanian) found in a series of synclines developed in a terrace zone along the El Qaa half-graben's western border (Nezzazat Fault System). They are constituted by bioclastic rudstones and conglomerates forming 2 to 8 m thick cross-bedded sets, intercalated by 1.5 to 9 m mudstone-rich intervals containing some millimetric silty horizons and a few floating pebbles. Rudstones appear in 20 to 50 cm thick tabular beds with sharp planar bases and tops. The conglomerates are well sorted 30 cm thick beds, made of rounded to subrounded equant and prolate coarse pebbles to cobbles with fine to medium boulders derived from the pre-rift lithologies. The cross-bedded sets resulted from the migration of 3D dunes. Detailed analysis of their geometries and palaeotransport directions show a preferred orientation aligned parallel to the syncline axes and the main normal faults. The deposition of the dunes was synchronous with the formation of the synclines and growth of the normal faults in the area. The deposits in the area consistently thin towards the syncline limbs while they thicken towards their axes. Thickness variations also occur consistently along strike the syncline axes, following its dip direction. Reconstruction of the 3D geometry of the syn-rift units preserved in the area together with the main extensional structures suggests that the dunes were deposited along a shallow structural strait with local embayments, less than 1.5 km wide than prolonged for at least 5 km parallel to a depocentre's border fault system.