Neogene palaeoenvironmental evolution in the Atlantic side of the Rifian Corridor (Morocco)

Outcrops of Upper Miocene to Upper Pliocene deposits in the Atlantic side of the Rifian Corridor, northwest Morocco, provide data that allow an assessment of the palaeoenvironmental evolution of the main seaway that connected the Mediterranean to the Atlantic Ocean, until its final closure at the end of the Miocene. A reconstruction of the sedimentary regimes and palaeobathymetries in the Gharb and Saiss Basins has been carried out from the physical and microfaunal (benthic foraminifera) characteristics of sediments and three sedimentary sequences are distinguished, fi om the oldest rocks deposited at the opening of the corridor (more than 8 Ma) to the Upper Pliocene sediments (younger than 4 Ma) that ended the marine sedimentation. The maximum palaeodepth recognised (about 500 m) occurs in marry sediments of the coastal area (Bou Regreg composite section) between 8 and 5.9 Ma. This is followed by a tectonically controlled, shallowing phase leading to the establishment of neritic conditions and corresponding to a relative sea-level lowering of about 300 m, that we suggest relates to closure of the passageway and consequent onset of the Meditcrranenn evaporite deposition. The persistence in the Saiss Basin of middle neritic palaeodepths since the upper. Tortonian (about 7.8 Ma) suggests, for this internal basin, a sill physiography. Evidence from the present and previously documented palaeobathymetric reconstructions indicates that the tectonic activity in the Atlantic corridor started from the eastern side and moved to the west. (C) 2000 Elsevier Science B.V. All rights reserved.