Chitinozoaires ordoviciens du Sahara algérien: biostratigraphie et affinités paléogéographiques

Abstract

Biostratigraphic investigations have been carried out on Ordovician chitinozoans from three boreholes (Gd.1bis, N1.2 and Clr.1) of the Algerian Sahara. Almost all the chitinozoan biozones recently proposed for the Ordovician of northern Gondwana regions have been identified. This allows an accurate age assignment of the investigated formations and also documents large stratigraphic gaps. The most important stratigraphic hiatus is related to the Ashgill glaciation whereas the other ones resulted from Arenig and Llanvirn local readjustments of the Panafrican basement. The great majority of the recovered chitinozoan assemblages are identical, even at specific level, with the contemporaneous ones from southwestern Europe. This implies easy marine communications as well as a close palaeogeographic location and similar climatic constraints for northern Gondwana regions during the Ordovician.