Structural characteristics of the Qena Bend of the Egyptian Nile River, using remote-sensing and geophysics

Abstract

The Qena Bend of the Nile River, named after Qena town in Upper Egypt, is considered a remarkable geomorphological feature in southern Egypt. It is unique and its geodynamic formation is still not fully understood. This study addresses the relationship between the bend geometry and the structural setting of the underlying basement complex using remotely sensed and aeromagnetic data. The hillshade and drainage extraction algorithms were applied to the digital elevation model (DEM) of the Shuttle Radar Topography Mission (SRTM) to define the lineaments dissecting the limestone plateaus and control the Nile Valley cliffs. Moreover, the Interferometry Synthetic Aperture Radar (InSAR) coherence image was derived from two Sentinel-1 images to delineate and/or confirm the structures, which underlie and control the sand dunes movement. In addition, various edge-detection derivatives were applied on the reduced-to-pole (RTP) aeromagnetic anomaly to define the basement structures. The results showed the derived surface and subsurface structures are controlled by the NW–SE and NE–SW trends of the Suez–Red Sea, Aqaba–Dead Sea, and Qena–Safaga Shear Zone. The RTP anomaly reveals a strong NE–SW positive anomaly zone coinciding with the bend. The magnetic 2D forward modelling and 3D depth inversion suggest the basement consists of granitic rocks (0.02 – 0.033 cgs) and the positive anomaly below the bend probably attributes to a major uplift at a depth of 750 m. This uplift broke the plateau forming NE–SW-oriented weak structural zones along which the bend was developed.