Occurrence of upper Burdigalian silexite beds within the Beni Ider Flysch Fm. in the Ksar-es-Seghir area (Maghrebian Flysch Basin, Northern Rif, Morocco): stratigraphic correlations and geodynamic implications.

In the Maghrebian Chain, pelagic and turbiditic successions deposited on the oceanic crust of the Flysch Basin crop out from Gibraltar to Sicily, tectonically juxtaposed between the External and Internal Nappes. In the Rifian Maghrebids, the Mauretanian successions, deposited on the northern side of the basin and supplied by a << Mesomediterranean Microplate >>, are represented by the Tisirene and Beni Ider Nappes, the latter including at the top the turbiditic Beni Ider Flysch Formation. The age of the Beni Ider Flysch, important to constrain both the evolution to foredeep of the basin and the onset of the compressional deformation, is still highly debated because ages ranging from early Oligocene to early Burdigalian have been proposed. In the Dchar Foual area, some sections, characterized at the top by silexite beds, have been sampled. The lowermost beds furnished nannoplankton associations not older than Chattian (Zone CP19b), whereas the highest ones gave results not older than late Burdigalian (Zone CN3). The latter age fully agrees with ages found in the Betic Algeciras Flysch and in the Sicilian Troina-Tusa Flysch, as well as in the Sicilide successions of Southern Apennines. This late Burdigalian age represents a constraint that cannot be neglected in the reconstructions of the tectonic evolution of the Alpine Chains of the Western Mediterranean, from the Betic Cordillera to the Apennines.