Provenance and depositional history of Mesozoic sediments from the Mamfe basin and Douala sub-basin (SW Cameroon) unraveled by geochemical analysis

Abstract

Mineralogical and geochemical analytical methods were employed to characterize sediment samples from the Mamfe basin (MB) and Douala sub-basin (DSB) in order to constrain the provenance, weathering, paleoclimate, and depositional history of rocks from both basins. Sediments under study are classified as shales, wackes, and arkoses and are essentially derived from felsic rocks which likely correspond to nearby extensive Neoproterozoic migmatitic and gneissic basement rocks. The A-CN-K plot indicates that the K-metasomatism may have affected the bulk composition of most of the studied rocks. The Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA), and (A-K)-C-N plots suggest that the intensity of weathering was higher for DSB relative to MB samples. This differentiation can be related to active tectonism during the deposition of the MB sediments. The SiO2/Al2O3, Al2O3/Na2O, and K2O/Na2O ratios, and the Index of Chemical Variability (ICV), indicate a low compositional maturity for MB compared with DSB samples. The values of U/Th, V/Cr, Ni/Co, and authigenic U suggest an oxic depositional condition for all studied samples. The average Sr/Ba ratios for the MB (0.31 ± 0.12 and 0.59 ± 0.25, for the Okoyong and Nfaitok-Yawo areas, respectively) and DSB sediments (0.31 ± 0.08 and 0.20 ± 0.09, for southern Kumba and western Mbanga areas, respectively), suggest a depositional paleoenvironment with low salinity. The average Rb/Sr ratios for the MB (0.62 ± 0.36 and 0.17 ± 0.06, for the Okoyong and Nfaitok-Yawo areas, respectively) and DSB sediments (0.53 ± 0.11 and 0.73 ± 0.29, for southern Kumba and western Mbanga areas, respectively) are low, suggesting warm and humid condition during the deposition of MB and DSB sediments. Multi-element tectonic diagrams indicate passive and rift settings, which are consistent with the local geology, but also a collisional setting, which is probably linked to the tectonic evolution of the Neoproterozoic metamorphic source rocks.