Structural geometry and tectonic evolution of an Early Cretaceous rift crossing the Nile Valley in Upper Egypt

Abstract

Two-dimensional (2D) seismic reflection data tied to well logs are used to present new insights on the structural geometry and tectonic evolution of an Early Cretaceous rift crossing the Nile Valley in Upper Egypt. This rift extends to ∼260 km long in a NW-SE direction, and 80–100 km wide, and was previously unstudied due to a lack of subsurface data. It is named here as the Upper Egypt Rift. It is divided into three depocentres, or segments, from southeast to northwest: The Kharit, Nuqra, and Komombo basins, filled with thick (ca. 3700 m) continental to open marine Lower Cretaceous-Campanian/Maastrichtian strata. The Kharit and Komombo basins are NW-striking fault-bounded half-grabens associated with NE-dipping syn-rift rocks. They are linked by a major N–S oriented normal fault bounding the eastern side of the Nuqra basin and terminate in two overlapping synthetic transfer zones. This rift geometry is controlled by the reactivation of a Precambrian Najd-parallel (N125°E) shear zone during rift initiation. Seismic cross-section restoration indicates a multiphase extensional history for the Upper Egypt Rift. The first rift episode occurred during the Berriasian-Valanginian and the early Aptian as a result of the opening of the South Atlantic, and was influenced by the tectonic evolution of the Neotethys Ocean as well. The second rift locally developed in the area during the Cenomanian-Turonian and was characterized by extrusive alkaline volcanics and intrusive rocks. Rift-related Natash volcanics and trachyte plugs of Cenomanian/Turonian age are exposed at the eastern side of the Nuqra basin but not recorded in the Komombo and Kharit basins. Soon after that, the whole basin experienced mild tectonic inversion synchronously with the Syrian Arc compressional events. Rotated fault blocks and slightly inverted anticlines thus comprise the main hydrocarbon trapping structures in the Komombo basin. Further work is required to define the time-dependent relationship between oil migration and trap development in the Upper Egypt Rift.