Sedimentary Deposits and Paleoenvironmental Changes in the Cenomanian–Turonian and Coniacian–Santonian Formations of the Ivorian Offshore Basin (Southeastern Abidjan Offshore Margin): The Case of the C1 Borehole

This geological study, conducted on a borehole located in the southeastern part of the offshore margin of Abidjan, Côte d'Ivoire, aims to reconstruct the sedimentary history and past environmental conditions of this area. This work. Following a lithological description, the 6 samples analyzed were washed, dried, sorted, and examined under a binocular microscope. The lithological analysis identified two major sedimentary units between depths of 3,420 m and 3,750 m: Unit I (Base): An alternation of clay and glauconite-rich sandstone beds (p. 3). Unit II (Top): A strong clay dominance with some intercalations of sandstone, containing pyrite and glauconite. The micropaleontological analysis revealed a microfauna dominated 82.77% by agglutinated benthic foraminifera (living on the seafloor), while planktonic foraminifera account for only 17.23%. Calcareous benthic foraminifera are completely absent. Biostratigraphy identified two age intervals based on Cenomanian–Turonian fossils (3,755 m–3,700 m), characterized by the species Caudammina ovuloides and Caudammina ovulum which are exclusively agglutinated benthic formaminifera. The Coniacian–Santonian (3,700 m–3,420 m) is identified by species such as Dicarinella hagni and Archaeoglobigerina bosquensis. The paleoenvironmental reconstruction concludes that the depositional environment evolved within a deep marine setting: Outer shelf near the slope: For the earliest period (Cenomanian–Turonian). Middle to outer shelf: For the more recent period (Coniacian-Santonian), with evidence of a low-oxygen (anoxic) environment explaining the rarity of calcareous forms.