Sedimentation and inversion history of three molasse basins of the western Central Eastern Desert of Egypt: Implications for the tectonic significance of Hammamat basins

The initiation, deformation and tectonic significance of the Zeidun and Arak basins in the Central Eastern Desert (CED) of Egypt are the topics of this study. The basins probably formed in a N-S regional extensional regime, with basin subsidence structurally controlled by marginal normal faults. In these basins red, grey and green coloured conglomerates, litharenites and mudstones accumulated in an alluvial fan-braided stream environment. A two-stage basin subsidence history included early modest basin relief during Arak sedimentation followed by rapid increase in basin margins during Zeidun deposition. Forced folding in the basin sediments may have occurred during the basin sedimentation stage or in the earliest stages of deformation. A regional subhorizontal foliation with NW-SE stretching lineation is found in the Arak and Meesar basins and is correlated with foliations farther north in the Wadi Hammamat, El Qash and Um Esh-Um Seleimat basins. Two substages of post-foliation are identified based on different orientations of regional σ₁ (NNE to NE-oriented in the early substage and E to ENE-oriented in the second substage). Early substage basin and basement structures are E- to ENE-oriented steep reverse faults that are inverted normal faults, and N-S dextral strike-slip shears. Basin and basement structures of the later substage are folds, and NE- and NW-trending conjugate strike-slip faults. The post-foliation deformation has reversed the normal displacements on basin marginal faults. This is an example of basin inversion. Tectonic settings for the study area basins are discussed. The role of the regional subhorizontal foliation and CED major extension ductile shear zones (the EDSZ, forming a carapace over the Meatiq complex; and the SNSZ, along the northern boundary of the Hafafit complex) in the ductile thinning of the Neoproterozoic crust is also considered in the light of recent tectonic extension models that explore the possibility of lithospheric delamination.