Calcareous Nannofossils from the Cretaceous of the Deep Ivorian Basin

Micropaleontological investigation of four sites drilled by Ocean Drilling Program Leg 159 on the Côte d’Ivoire-Ghana Margin indicates that the initial invasion of oceanic surface waters into the Deep Ivorian Basin, as indicated by the presence of calcareous nannofossils, occurred during the late Albian. The nature of these assemblages suggests that these first Cretaceous oceanic surface waters were warm and relatively high in nutrients. These upper Albian sediments were deposited prior to significant tectonism at some of the sites, as indicated by their structurally deformed nature. The likely age of this tectonism is Cenomanian. The Upper Cretaceous consists of condensed sequences of hemipelagic carbonates and phosphatic hardgrounds with very low sediment accumulation rates overlain, at Site 959, by non-calcareous claystones. These Turonian through Santonian hemipelagic carbonates contain nannofossil assemblages that suggest low surface water nutrient content, resulting in starved basin conditions