Guercif Basin, Northeast Morocco: A Seismic Interpretation Case History

Niels C. Arveschoug

The Guercif basin is a Miocene molasse depocenter lying at the northeastern end of the Middle Atlas mountains and bordered to the southeast by the High Plateau. To the northwest lie the Prerif thrust sheets of the Rif Alpine thrust zone.

Geophysical investigations over the basin include extensive regional gravity and magnetic surveys. The Guercif basin has several interesting features, including salt diapirs, basalt intrusions, and complex Jurassic-Miocene tectonic activity giving rise to several gravity and magnetic anomalies that correspond with mapped seismic features. Nearly 850 km of Vibroseis data acquired in 1984 and 1985 were interpreted using gravity and magnetic profiles. Two recently drilled wells proved some 10,000 ft (3,000 m) of Jurassic-age sediments beneath the Miocene basin.

Evidence for regional wrench faulting was also observed on the basal Miocene unconformity time structure map. Dislocation of fold axes, low-angle faulting, and flower structures confirmed the basin had undergone reverse movement, probably originating from reactivated listric normal extensional faults and possibly as major detachments in a linked normal fault system.

The structural considerations are important because seismic interpretation in the Guercif area should place more emphasis on reverse and wrench faulting than on only conventional horst and graben block tectonics with exclusively normal faults.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.