Crustal Structure of the Nile Delta: Interpretation of Seismic-Constrained Satellite-Based Gravity Data

Soha Hassan,Abdelaziz Abdeldayem,Elsayed Issawy,Mohamed Sobh,Mohamed S Elhebiry,Khaled Zahran,Mohamed Sultan,Samir Kamh

doi:10.3390/rs13101934

Abstract

Interpretations of the tectonic setting of the Nile Delta of Egypt and its offshore extension are challenged by the thick sedimentary cover that conceals the underlying structures and by the paucity of deep seismic data and boreholes. A crustal thickness model, constrained by available seismic and geological data, was constructed for the Nile Delta by inversion of satellite gravity data (GOCO06s), and a two-dimensional (2D) forward density model was generated along the Delta’s entire length. Modelling results reveal the following: (1) the Nile Delta is formed of two distinctive crustal units: the Southern Delta Block (SDB) and the Northern Delta Basin (NDB) separated by a hinge zone, a feature widely reported from passive margin settings; (2) the SDB is characterized by an east–west-trending low-gravity (~−40 mGal) anomaly indicative of continental crust characteristics (depth to Moho (DTM): 36–38 km); (3) the NDB and its offshore extension are characterized by high gravity anomalies (hinge zone: ~10 mGal; Delta shore line: >40 mGal; south Herodotus Basin: ~140 mGal) that are here attributed to crustal thinning and stretching and decrease in DTM, which is ~35 km at the hinge zone, 30–32 km at the shoreline, and 22–20 km south of the Herodotus Basin; and (4) an apparent continuation of the east-northeast–west-southwest transitional crust of the Nile Delta towards the north-northeast–south-southwest-trending Levant margin in the east. These observations together with the reported extensional tectonics along the hinge zone, NDB and its offshore, the low to moderate seismic activity, and the absence of volcanic eruptions in the Nile Delta are all consistent with the NDB being a non-volcanic passive margin transition zone between the North African continental crust (SDB) and the Mediterranean oceanic crust (Herodotus Basin), with the NDB representing a westward extension of the Levant margin extensional transition zone.

Highlights

We explored the use of numerical modelling the best geophysical tools for demarcating transitional zones within passive margin settings
They can provide evidence for lateral thickness variations associated with the thinning of continental crust within transition zones that separate continental from oceanic crust [24,130,131]
Bouguer gravity anomaly maps remain one of the best geophysical tools for demarcating transitional zones within passive margin settings

Summary

Introduction

The Nile fan comprises the largest sedimentary clastic accumulation within the eastern Mediterranean Sea [4,5] and exhibits a classical. Clastic accumulation within the eastern Mediterranean Sea [4,5] and exhibits a classical morphology for a mud-rich turbidite system [6]. The Delta is fed by sediments carried by morphology for a mud-rich turbidite system [6]. The Delta is fed by sediments carried by the Nile River, the longest and one of the oldest river systems; it has apparently been acthe Nile River, the longest and one of the oldest river systems; it has apparently been active tive for 30 million years or more [7,8,9,10]. The size and longevity of the Nile drainage system for 30 million years or more [7,8,9,10]. The size and longevity of the Nile drainage system introduced extensive extensive sedimentary sedimentary fluxes fluxesto tothe theDelta

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Discussion

Conclusion