AAPG Middle East Region Geoscience Technology Workshop, Rift Basin Evolution and Exploration

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Structural Provinces and Potential Trap Types in Extensional Margins: Red Sea Case Study

Abstract

One of the main problematics in passive margins is to have a coherent structural interpretation to explain the transition from a 35-45km thick continental crust to a 6-8km thin oceanic crust. Several structural models have been suggested since the early 1970’s and have been evolving thanks to the improvement in seismic imaging, regional 2D seismic lines, ODP’s and HC well results (McKenzie, 1978; Wernicke, 1985; Manatschal, 1999; Huismans, 2011; Callot, 2002). A simple way of understanding a passive margin is by capturing the inherited structures and defining structural provinces: continental crust domain, necking zone, thin continental crust and oceanic crust area. Moreover, understanding the magmatic nature of the margin (magma rich or magma poor) will significantly help the explorationists with the structural interpretation and trap definitions. The Red Sea area has been under extension from about 27MA until the present day and represents one of the best analogues for understanding extensional processes. Based on gravimetric and magnetic data analysis, it is broadly accepted that drifting and formation of oceanic crust is occurring in the southern Red Sea; the central Red Sea is known to be transitional whereas the northern Red Sea is characterized by thinned continental crust (Almalki et al. 2015). A regional study aiming to understand the transition from thick to thin continental crust that allows the identification of potential traps was conducted on the Egyptian Red Sea. The study integrates outcrop data, hydrocarbon well results, gravi and magnetic data, refraction profiles and available 2D seismic data. We propose a structural framework along the entire Egyptian offshore in which three main fault trends are identified: NNW/SSE (orthogonal opening between 24-14myr); NWW/SEE inherited Najd trend (oblique opening between 24-14myr), and NNE-SSW transform fault pattern, probably also inherited from Proterozoic structuration. Moreover, two main structural provinces are identified, the necking zone, with predominantly high angle faults extending from north to south and about 40 to 50km from the coast vs. thinned continental crust domain with low angle faults couple and rooted in the Moho towards the distal area. The necking zone includes potential stratigraphic traps against the margin as well as structural 3 to 4-way dip closures. The thin continental crust domain is mainly dominated by salt-related structures (subsalt structures, dome related traps, turtle back etc.).