MARINE INFLUENCES IN THE SO-CALLED CONTINENTAL SEDIMENTS OF THE PALEOZOIC-MESOZOIC KANDI BASIN (NORTHERN BENIN - WEST AFRICA)

The continental Sende Formation of northeastern Benin dated by means of silicified wood as Lower Cretaceous overlies the Kandi Formation unconformably. Trace fossils (Arthrophycus and Cruziana) place the Kandi Formation in the Lower Paleozoic. These traces indicate two marine transgressions, one during the middle to Late Ordovician, the other during Lower Silurian, supported by fluvial-marine sandstones from deltaic, marginal-littoral and epicontinental environments. This proposed stratigraphic and paleogeographic model contradicts the former idea of the "Kandi basin" as being a Mesozoic, continental deposit. The Ordovician transgression previously, described in northern Niger, thus extended 1000 km further south, thereby implying a new interpretation of the geological history of West Africa. Close ichnofaunistic relationships are found between the study area and the North African domain, thus supporting the proposal of an Ordovician transgression across the Sahara. These results should be seen in the context of a circumgondwanan province along this northeastern margin.