Palynologie comparée du Permien nigérien (Afrique occidentale) et Péritéthysien. Implications stratigraphiques et phytogéographiques

Abstract

A microflora with undoubtedly Permian characters has been reconstructed in the upper sequence of the Tarat Formation (Arlit region, Northern Nigeria). This formation as a whole used to be considered as Carboniferous in age. Subsequently, however, as a result of sedimentological, paleobotanical and palynological studies, a Permian age has been assigned to this sequence. This noticeably well preserved microflora shows particular association of Gondwanian elements and taxa typical of Euramerican realm. Although older (Carboniferous) floristic associations known in this area are clearly Gondwanian, Euramerican affinities express definitely during the Permian. This change is all the more important that the associated macroflora is dominated by Euramerican elements ( Autunia, Callipteris conferta, Walchia spp.) well-known to be characteristic in the Lower Permian (Autunian) of Western Europe. It is now established that in the Triassic of the Mediterranean area northern and southern floras are mixed together. The discovery in Nigeria of a Permian microflora without any global equivalent neither in the Northern nor in the Southern Hemisphere, and the comparison of this microflora with associations from other areas e.g., South Africa, Zaïre, Gabon, Pakistan, South Spain, Western Europe), imply that floristic exchanges between Gondwana and Laurasia in the Tethysian realm as soon as Lower Permian. These new data allow to propose an interpretation of the processes that have determined the settlement of post-Carboniferous floras in the Tethysian realm in relation to paleogeographical modifications.