Integration of gravity, magnetic, and seismic data for subsalt modeling in the Northern Red Sea

Abstract

Rifts and rifted passive margins are often associated with thick evaporite layers which challenge seismic reflection imaging in the sub-salt domain. This makes understanding the basin evolution and crustal architecture difficult. An integrative, multidisciplinary workflow has been developed using the exploration well, gravity and magnetics data together with seismic reflection and refraction datasets in order to build a comprehensive 3D subsurface model of the Egyptian Red Sea.Using a 2D iterative workflow first, we constructed cross-sections using the available well penetrations and seismic refraction data as preliminary constraints. The 2D forward model uses regional gravity and magnetic data to investigate the regional crustal structure. The final models are refined using enhanced gravity and magnetic data and geological interpretations. This process reduces uncertainties in basement interpretation and magmatic body identification. Euler depth estimates are used to point out the edges of high susceptibility bodies. We achieved further refinement by initiating a 3D gravity inversion. The resultant 3D gravity model increases precision in crustal geometries and lateral density variations within the crust and the pre-salt sediments. Along the Egyptian margin, where data inputs are more robust, basement lows are observed and interpreted as basins. Basement lows correspond with thin crust (lt;12 km), indicating that the evolution of these basins is closely related to the thinning or necking process. In fact, the Egyptian Northern Red Sea is typified by dramatic crustal thinning or necking that is occurring over very short distances ~30 km, and very proximal to the present day coastline. The integrated 2D and 3D modelling reveals the presence of high density, magnetic bodies which are located along the margin. The location of the present day Zabargad Transform fault zone (ZTFZ) is very well delineated in the computed crustal thickness maps, suggesting it is associated with thin crust, and shallow mantle.

Red Sea rifting in central Egypt: constraints from the offshore Quseir province

“…Based on seismic refraction data, the seismic velocities below the NRS axial trough range from 5.53 to 6.38 km/s (Gaulier et al 1988) suggesting the presence of continental crust at the rift axis, although small areas with higher density and seismic velocity have been observed, probably due to mafic intrusions. A view in line with a NRS rift model suggested by several authors (Cochran 1983(Cochran , 2005Bonatti 1985;Mahsoub et al 2012;Mitchell and Park 2014;Almalki et al 2015;Ligi et al 2018;Le Magoarou et al 2021).…”

“…M A N U S C R I P T seismic reflection data, coupled with limited well data, means that the geological evolution of the Red Sea remains obscure. Furthermore, the seismic image of the Red Sea is hampered due to the presence of shallow carbonates and allochthonous evaporite sequences, which leads to difficulties in determine the stratigraphy (Masini et al 2020) and in understanding the structure and nature of the crust in the distal margin regions (Ball et al 2018a, b;Le Magoarou et al 2021).…”

“…Towards the north, where a proper ridge-like morphology is lacking and linear magmatic anomalies are absent, determining the nature of the crust is problematic. The crust under the NRS has been reported to be either oceanic crust (e.g., Girdler and Underwood 1985;Gaulier et al 1988;Augustin et al 2021;El Khrepy et al 2021), or as a region of hyperextended continental crust punctuated by volcanic deeps, sometimes interpreted as nascent ridges (Bonatti 1985;Cochran 2005;Cochran and Karner 2007;Ligi et al 2012Ligi et al , 2018Mahsoub et al 2012;Mitchell and Park 2014;Almalki et al 2015;Sinadinovski et al 2017;Keller et al 2018;Stockli and Bosworth 2019;Le Magoarou et al 2021).…”

Magmatism at an ultra-slow spreading rift: high-resolution geomorphological studies of a Red Sea Rift segment in Hadarba Deep

“…Indeed, several studies argue for a continuous spreading and formation of an oceanic crust since 13 to 15 Ma along the entire rift (e.g., Izzeldin, 1987;Sultan et al, 1993;Augustin et al, 2021;Delaunay et al, 2023;Mitchell et al, 2023). Others postulate that the oceanization is of much younger age (5 Ma;Issachar et al, 2023) and that the basement north of 19.5°N consists of a hyperextended continental crust punctuated by volcanic deeps (e.g., Bonatti, 1985;Ligi et al, 2011;Ligi et al, 2018;Le Magoarou et al, 2021;Saleh et al, 2021;Afifi et al, 2023;Sang et al, 2023). However, while the nature of the crust under the Miocene evaporites is up to debate, it is generally agreed that the uncovered crust, consisting of isolated bathymetric troughs and basins, the so-called "Deeps" in the central RSR consists of oceanic crust (e.g., Tramontini and Davies, 1969;Pautot, 1983;Bonatti, 1985;Haase et al, 2000;Augustin et al, 2014;van der Zwan et al, 2015;Ligi et al, 2018;Augustin et al, 2021;Mitchell et al, 2023;Sang et al, 2023).…”

Geophysical Evidence for Magmatism Southwest of the Brothers Islands, Northern Red Sea (Offshore Quseir, Egypt)

“…Only 14 exploratory wells have been drilled in the Egyptian Red Sea margin for hydrocarbon prospecting in the last 50 years, and little associated data are in the public domain. In addition, offshore seismic interpretation is severely limited by a thick layer of syn‐rift evaporites (e.g., Cochran, 1983; Le Magoarou et al., 2021; Rowan, 2014). As a result, the structure and the nature of the crust that floors the NRS is still a matter of debate (e.g., Augustin et al., 2021).…”