Anatomy of a Half Graben: Structural Style and Stratigraphic Fill -- A Case Study from the Sinai Margin of the Suez Rift, Egypt

By

Ian Sharp¹, Rob Gawthorpe², Ian Carr³, John Underhill⁴

(1) Norsk Hydro Research Center, Bergen, Norway (2) University of Manchester, Manchester, United Kingdom (3) The University of Manchester, Manchester, United Kingdom (4) Grant Institute, Edinburgh, United Kingdom

 The past decade has seen increasing research on the interaction between fault growth and stratigraphic architecture in extensional basins. In particular, variations in accommodation development associated with the vertical and lateral propagation and linkage of originally isolated normal fault segments have been investigated as a primary control on sediment dispersal and stratigraphic architecture. The aim of this contribution is to document the structural style and stratigraphic fill of a well exposed half graben from the Suez Rift, with emphasis on understanding the dynamic interaction.

The Wadi Nukhul half graben is a well exposed example of a “rift initiation” depocenter. The segmented border fault system to the half graben is exposed over 6 km, and comprises distinct NW-SE and N-S striking elements. Displacement is at a maximum in the south and decreases northwards towards a well defined tip point and fault-tip monoclinal fold. Folds are evident parallel and perpendicular to the border fault. Fault perpendicular folds are associated with distinct fault segments, while folding parallel to the boarder fault is associated with a faulted monocline configuration.

Contemporaneous syn-rift sediments show marked thickness and facies variations about the structural elements. The non-marine Abu Zenima Fm is thickest in hangingwall depocenters adjacent to NW-SE striking segments of the border fault, and is thinnest over transverse anticlines associated with N-S striking segments. In contrast, the estuarinal Nukhul Formation is thickest and more “marine” in nature at the southern tip of the Nukhul Fault, and shows progressive northwards thinning, onlap and overstep parallel to decreasing fault displacement.