Structural Control on Stratigraphic Architecture of Rift-Initiation Fluvial and Tidal Deposits: Modelling the Nukhul Half-Graben, Suez Rift, Egypt

Wilson, Paul¹, Franklin Rarity¹, David Hodgetts¹, Rob L. Gawthorpe¹ (1) University of Manchester, Manchester, England

Exceptional exposures of normal faults and rift-initiation strata in the Suez rift provide an opportunity to study the 4D evolution of a normal fault array and the consequent stratigraphic response. We integrate data from terrestrial LIDAR, DGPS, digital imagery, traditional field sedimentology and structural analysis to model structural geology and subtle variations in thickness of rift-initiation strata. This facilitates the creation of improved tectono-stratigraphic models for rift initiation.

The Nukhul half-graben consists of rift-initiation deposits, comprising the continental Abu Zenima and tidally-influenced Nukhul Formations, bounded by the northwest-striking Nukhul fault (displacement 0-1 km). Along the length of the Nukhul fault (~11 km), syn-rift strata are folded around a fault-parallel syncline representing a fault-propagation fold. Subtle fault-perpendicular folds (wavelength <1 km, amplitude 20-100 m) have also been identified. The axes of fault-perpendicular anticlines coincide with bends in the Nukhul fault that are interpreted as sites of linkage of precursor fault segments; the fault is made up of at least three such segments. Thickness variations in early units are controlled by active normal faults and infill of antecedent palaeovalleys. Thickness variations in later units are controlled by syn-depositional folds, but are not consistent across all stratigraphic units. Units with erosional bases thicken over synclines and thin over anticlines, while eroded units thin over synclines and thicken over anticlines. This may be because the rate of subsidence during rift initiation is low, such that thickness changes due to erosion exceed thickness changes resulting from variations in accommodation space around syn-depositional folds.