ELEMENTAL GEOCHEMISTRY OF THE LATE CRETACEOUS - EARLY PALEOGENE DEPOSITS OF THE SW ANAMBRA BASIN (NIGERIA): IMPLICATIONS FOR PROVENANCE, TECTONIC CONDITIONS, AND HYDROTHERMAL INFLUENCE

The Anambra Basin, located in southwestern Nigeria, is part of the West and Central Africa Rift System (WCARS) basins, with sedimentary successions ranging from freshwater to deltaic and marginal marine deposits. So far, surface and subsurface research on the nature of the Anambra Basin and its genetic relationship to other WCARS basins is poorly documented. In this study, we used mineralogical and geochemical data from the Paleogene Imo Shale, and the Cretaceous Mamu and Nkporo Formations to analyse sediment grain sorting, provenance, hydrothermal influence, and the depositional setting. Furthermore, these data contribute to reconstruct the tectonic evolution of the Cretaceous Anambra Basin and its paleotectonic link with other WCARS basins as well as the primary controlling factors during deposition. The major oxides and mineral data of the Imo, Mamu, and Nkporo formations demonstrate that the detrital grains are predominantly composed of quartz and clay minerals, with little feldspar. Major and trace element proxies used to evaluate sediment grain sorting reveal primarily fine-grained clastics, indicating long transport distances (which correlate with high clay mineral contents). A few samples are more coarse-grained, suggesting periods of direct sediment input and less recycling. There is no evidence of hydrothermal influence in the basin; a significant pelagic input was hypothesised. This hypothesis is corroborated by the presence of gypsum, which is typically precipitated from seawater. Based on provenance- sensitive inorganic geochemical proxies (i.e., Cr/Th vs. Sc/Th, La/Th vs. Hf, Th/Co vs. La/Sc, Th/Sc vs. La/Sc, Th/U vs. Th/Sc, TiO₂ vs. Zr, and discriminant functions DF1 vs. DF2) and detrital and pelagic contributions to the Paleogene Imo Shale and Cretaceous Mamu and Nkporo formations, it is concluded that the siliciclastic rocks are primarily derived from proximal felsic plutonic rocks that have been uplifted to the surface by tectonic processes. Arc-Rift-Collision tectonic settings distinction diagrams from discriminant functions reveal that the sediments of the Anambra Basin were deposited in a rift paleotectonic environment, which is consistent with the other WCARS basins.