Structural Styles of the High Atlas Mountains, Morocco: Potential Hydrocarbon Traps in the Footwall of Thrusts Developed from the Reactivation of Syn-Rift Normal Faults

Weldon Beauchamp, Richard W. Allmendinger, Muawia Barazangi, Ahmed Demnati, and Mohamed El Alji

Large asymmetrical folds and box folds created by fault bend and fault propagation folding characterize the style of deformation in the High Atlas mountains. Several compressional phases of faulting and folding from the Lower Jurassic through Cenozoic indicate a long and varied tectonic origin for the High Atlas intracontinental mountain belt. Footwall shortcut faults are formed with the inversion of syn-rift Iistric normal faults, and progress into low angle thrust faults with fault bend fold geometries. This style of deformation is illustrated on reprocessed seismic reflection data and confirmed by field mapping.

Geological field mapping, air photographs, and Thematic Mapper imagery provide important constraints for the interpretation of seismic reflection profiles along the margins of the High Atlas mountains. Balanced cross sections across the High Atlas suggest large horizontal displacements along low angle thrust faults. These thrusts place massive Lower Jurassic carbonates above post-rift Upper Cretaceous and Tertiary rocks. Refolding of thrusts and large scale regional folds indicate oblique slip deformation during and after the inversion of syn-rift normal faults. Low angle thrusts propagate along detachments in shales and marls of the Lower Jurassic. Lower Jurassic shales provide an excellent seal for potential sandstone reservoirs in the Middle Jurassic and Triassic sandstones in the ootwall of thrusts.

AAPG Search and Discover Article #91019©1996 AAPG Convention and Exhibition 19-22 May 1996, San Diego, California