Inorganic geochemistry of Paleogene strata in the N’kapa Formation of the western Douala Basin, Cameroon: implications for provenance and tectonic settings

Abstract

The geochemistry of Paleogene strata (sandstones and shales) of the N’kapa Formation in part of the western Douala Basin has been studied through major, trace, and rare earth elements (REEs) in order to understand their provenance and tectonic settings. The NF sandstones and shale are clustered around granodiorite with minor contributions from granitic source. The samples show high and fairly constant Th/Sc ratios 0.64–6.9 for sandstone and 1.01–8.7 for shale that strongly indicate provenance from a relatively evolved igneous source (mafic) also different geochemical signatures of Eu/Eu*, La/Sc, La/Co, Th/Sc, Th/Co, Zr/Sc, Cr/V, and Y/Ni ratios, and their plots suggest a mafic igneous provenance with substantial sediment recycling. Geochemical signatures from plots of The La/Th–Hf diagram, La/Sc vs Ti/Zr, and Fe2O3 + MgO vs TiO2 tectonic discrimination diagrams show that the studied rocks were deposited mainly in a passive continental margin setting. The large quantities of alkalis classify the rocks as wackes, Fe-sand, shale, and Fe-shale. The studied lithofacies have been classified based on Al–Fe-Mn enrichment as follows: terrigenous and metalliferous rocks.