La lithostratigraphie des grandes zones structurales des Mauritanides, entre le 14e et le 16e parallèles nord (Sénégal oriental et Rép. Isl. de Mauritanie). Essai d'interpretation geodynamique

Abstract

In eastern Senegal and southern Mauritania, the thrusted and more or less metamorphosed units of the Mauritanides belt involve similar lithostratigraphical sequences including, from the bottom to the top, a green volcano-sedimentary series (Nagara and Bouly groups) then a detrital red series (Ndouméli group) and a quartzitic series (Ndiéo group). In the more external part of the belt these sequences are completed with coarse sandstones which are thought to be the equivalent of upper Ordovician sediments of glacial origin (Sakha group) and, at the top, red fossiliferous sandstones of Devonian age. All of these sequences can be correlated with the upper Proterozoic-Devonian sedimentary sequence of the West African craton. The facies variations as well as the volcanic features allow one to define four main structural zones that are, from east to west: an Autochthonous, which includes the western margin of the Taoudeni basin, a Parautochthonous, displaced but not metamorphosed, an External Zone which comprises basic and ultrabasic rocks, and an Internal Zone marked by acid and andesitic metavolcanism. These zones are more or less linked with palaeogeographic domains which were created during an upper Precambrian distensive phase occurring prior to the Mauritanides orogeny. The detrital sedimentation is regarded as the result of the erosion of structures which arose during different stages of a compressive taconic-hercynian event.