Tectonic and sedimentary evidence for synchronous and out-of-sequence thrusting, Larache-Acilah area, Western Moroccan Rif

Abstract

Syn-tectonic turbidites were analysed using measured sections, structural relationships and bio-and litho-correlations of sedimentary units to determine the tectonic evolution of the alpine thrust belt of the Northwestern Moroccan Rif. The external zones of the northwestern Moroccan Rif contain two Tertiary turbidite sequences which can be sub-divided into type I, II and III turbidite packages sensu Mutti 1984. One turbidite sequence, the Acilah sandstone (Oligocene–earliest Miocene), is found at the leading edge of the Tangier thrust sheet while a second, the Sidi-Mrait flysch, is seen in the underlying Prerif thrust sheet. The Lower Sidi-Mrait flysch was probably deposited in a foredeep basin. At the end of the Eocene-early Oligocene the advancing thrust front incorporated the foredeep basin deposits into the thrust belt. Subsequent turbidite deposition occurred in piggyback basins. Palaeocurrent directions indicate sediment transport from SSE to NNW, along troughs elongated parallel to the tectonic strike. Creation of piggyback basins, turbidite onlap relationship, unconformities and structural relationships indicate that complex synchronous and out-of-sequence thrusting accompanied the overall foreland-progressing deformation sequence.