The first definitive Albian ammonites from the Kribi-Campo sub-basin in Cameroon and biostratigraphic implications for the opening of the South Atlantic

Abstract

The timing of the opening of the Equatorial South Atlantic Ocean during the Cretaceous is poorly constrained. Despite previous research carried out along the West African continental margin , the biostratigraphic attribution of the Kribi-Campo sedimentary deposits in Cameroon remain poorly known leading to uncertainties in the ages of the formation and thus leading to incorrect interpretations and correlations of stratigraphic sequences. To date, the deposits are known to correspond to alluvial fan facies from the Lower Mundeck Formation and the assigned age is Barremian?-Aptian. We carried out a prospection in the sedimentary outcrops along the shoreline in the Kribi-Campo sub-Basin where poorly preserved but identifiable ammonite specimens were discovered and collected for analysis in order to determine the age of the formation. The marker bed containing the ammonite fossils consists of thin carbonaceous sandy shale. Our determinations revealed the following ammonites: Douvilleiceras sp. and Uhligellinae that characterize the basal Lower Albian ( Douvilleiceras leightonense Zone) interval. This result allows us to suggest a reconsideration of the Kribi-Campo sub-basin deposits to be part of the upper Mundeck Formation. Our results confirm a diachronic separation of South America and Africa and a full connection between the North and South Atlantic Ocean during the Lower Albian.