Structure of the Western Rif (Morocco): Possible Hydrocarbon Plays: ABSTRACT

Abstract

Seismic data offshore and onshore northwestern Morocco (i.e. Atlantic margin, Rharb Basin, Rif foothills) provided a detailed picture of the Western Rif Cordillera. The most external units of the folded-belt consist of allochthonous Cretaceous and Neogene strongly deformed sediments that constitute a westward-directed accretionary wedge. The structure of the accretionary wedge consist of a complex set of thrust and normal faults. The inner part of the study area consist of NW-SE trending thrust faults, partially exposed in the foothills of the Western Rif. Proceeding towards the foreland, thrust faults are offset by low-angle extensional detachments characterized by anastomosing extensional horses. Widespread extension overlying the accretionary wedge defines a Late Neogene episode of extensional collapse. Extension is not characterized by localized conventional half-grabens but consists of a complex extensional system with variable orientation. Locally shale ridges and toe-thrusts characterized by rear extension and frontal compression define a set of mixed extensional-compressional satellite basins that significantly differ from conventional thrust-related piggy-back basins. Satellite basins are filled with Upper Tortonian to Pliocene sediments. Shallow fields of biogenic gas are present in this Upper Neogene succession of the satellite basins. The frontalmost part of the wedge consist of WNW-ESE trending thrust imbricates. A flexuralmore » basin (foredeep) developed as a result of the accretionary prism loading. The foredeep basin discordantly overlies thinn Cretaceous and Lower-Middle Miocene shallow-water sediments that indistinctly cover Plaeozoic basement rocks and Triassic half-grabens. Pre-foredeep units are related to rifting and passive margin development of the Atlantic Ocean. East from the Rharb Basin the Rif Cordillera is essentially unexplored. Few scattered seismic sections display subsurface ramp anticlines similar to those exposed in the mountain belt.« less