Geochemistry of the Late Cretaceous to Paleogene sedimentary deposits of the SW Anambra Basin (Nigeria): Implications for provenance, tectonic conditions, and hydrothermal influence

Abstract

The Anambra Basin in southwestern Nigeria is part of the West and Central Africa Rift System (WCARS), with sedimentary successions comprising freshwater, deltaic, and marginal marine deposits. In the present study, we provide new mineralogical and geochemical data from mudrocks of the Campano-Maastrichtian Nkporo and Mamu formations and the Paleocene Imo Formation, intersected by the Owan-1 and Ubiaja wells. The analyses aim to identify source composition, sedimentary grain sorting, hydrothermal influence, and depositional environment, focusing on the understudied southwestern margin of the basin. Additionally, the data provide insights into the tectonic evolution of the Anambra Basin and its genetic link to the Benue Trough and other WCARS basins. The studied mudrocks contain detrital grains 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 that correlate with the high clay mineral contents. The few coarse-grained deposits suggest periods of direct sediment input into the basin and less recycling. There is no evidence of hydrothermal influence in the basin. Therefore, a significant pelagic influence is proposed for the analysed sequence. 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 the identified detrital contributions to the Paleocene Imo Formation and Cretaceous Mamu and Nkporo formations, the studied siliciclastic rocks are interpreted to be derived primarily from proximal felsic plutonic rocks that were uplifted to the surface by tectonic processes. Distinction diagrams from discriminant functions show that the sediments of the Anambra Basin were deposited in a rift setting, which is consistent with the other WCARS basins.