Structural analysis and tectonic evolution of the Komombo basin, south Egypt; an example of interior Cretaceous rift

Abstract

Structural geometry of the Komombo basin was demonstrated using 2D seismic data. Komombo basin appears as two, left-stepping, en-echelon half grabens separated by a NNE oriented broad anticline dissected by NNE oriented oblique-slip faults. The developed fault pattern in the Komombo basin is a typical, non-collinear fault system which encompasses several segments of NW, N–S and WNW orientations. Komombo basin shows along strike variation in the fault pattern. Its southern part is further subdivided into several intrabasinal troughs and highs bounded by synthetic down-dip and antithetic up-dip fault systems, while the northern part is characterized by a synthetic SW dipping step fault pattern producing small eastward rotated half-grabens. The two fault patterns are separated by N–S shear zone.The architecture of the Komombo basin is developed through two extensional phases. The first phase occurred during the Barressian- Hautervian (a NE-SW directed extension), producing predominantly NNW-SSE to NW oriented normal faults. The first phase was followed by a tectonically quiescent period during Barremian-Early Aptian. The rifting resumed during Late Aptian-Late Albian (phase II) under similar stress condition. A group of small NW oriented faults were developed during the second phase as indicated by Late Aptian-Late Albian growth in their hanging walls.The seismic reflection data and D-z graph display dip-linkage between the NW oriented faults that developed during the two rift phases. The Late Aptian-Late Aptian fault system nucleated in a vertical isolation from the Barressian-Hautervian fault system as indicated by the displacement minima observed at the Late Barremian-Early Aptian thick shale.