Présence d’un microplancton du Ludlovien supérieur dans les argilites, d’âge discuté, de Tomboya (Guinée)

Graptolites attributed to Praguian (Lower Devonian) in association with a microplancton from upper Ludlovian were found in the layer of Tomboya considered so far as lower Wenlockian. These results pose the problem of the layer’s, since the data provided by different organisms are apparently contradictory.