PALYNOFACIES AND CALCAREOUS NANNOFOSSILS OF THE ARAROMI FORMATION (MAASTRICHTIAN-EOCENE), SOUTHERN DAHOMEY BASIN, NIGERIA

The Dahomey Basin is an extensive sedimentary basin located in the Gulf of Guinea, spreading over the Central West African margin from Ghana to Togo and Benin to the west, and eastwards along southern Nigeria. This work presents the results of integrated palynofacies and calcareous nannofossil biostratigraphy studies carried out in the Araromi cored well section, drilled onshore in southern Nigeria. The interval investigated corresponds to Cretaceous - Paleogene marine strata of the Araromi Formation, comprising fine- to coarse-grained sandstones with shales, mudstones and subordinate limestone intercalations. The palynofacies analysis allowed to characterize the nature and vertical distribution of the organic matter, which in the study section is dominated by palynomorphs, mainly dinoflagellates, and amorphous organic matter of algal origin, indicating open marine settings. The palynofacies distribution patterns suggest a depositional variation from a very proximal oxic shelf to a distal dysoxic-anoxic deep-water environment. The calcareous nannofossil biostratigraphy indicates a Late Cretaceous (Maastrichtian) to early Eocene age span, with variable nannofossil abundance, diversity and preservation throughout the section. The integrated study improves the understanding of the environmental evolution of the sedimentary succession, and demonstrates the control exerted by the changing paleoceanographic conditions on the varying distribution patterns of palynofacies types and nannofossil assemblages. The project is jointly coordinated and carried out by PETROBRAS-CENPES, Rio de Janeiro, the Technische Universität Berlin (TUB), Germany, and the University of Ilorin, Nigeria. The financial support by the Volkswagen-Stiftung Program of Partnerships is gratefully acknowledged.