Geochemistry of sediments from the Mugheb River, Bamenda, Cameroon Volcanic Line: implications for provenance, paleoweathering and tectonic setting

Abstract

Sediment samples from the Mugheb River in Bamenda were analyzed by inductively coupled plasma-optical emission spectrometry to determine their major, trace, and rare earth element contents, so as to ascertain their provenance, paleoweathering, and tectonic setting. The enrichment of Fe₂O₃ suggests these are derived from hematization of basaltic rocks. Significant SiO₂ content recalculated to an anhydrous basis and adjusted to 100% (SiO_2(adj)) indicates the abundance of quartz and kaolinite in sediment samples. Enrichment of transition elements relative to the reference values indicates mafic source rocks. The rare earth element patterns indicate negative Eu (Eu/Eu* = 0.54–0.82) and positive Ce (Ce/Ce* ~ = 1.04–1.67) anomalies, suggesting that they were derived by fractionated mafic rocks and, to a little extent, by fractionated felsic rocks. The chemical index of alteration (CIA) and plagioclase index of alteration (PIA) indicate intense weathering in the source area in a hot humid climate reflected by the removal of labile cations relative to stable residual constituents, which corroborate with the climate of the Cameroon. The ratios of SiO_2(adj)/Al₂O₃, K₂O/Al₂O₃, and K₂O/Na₂O and the index of compositional variability (ICVn) indicate compositionally mature sediments in which sediment samples experienced recycling and noticeable effect of sorting and reworking. The river sediments are deposited in oxic conditions within the riverine environment. The sediments were sourced dominantly from mafic and little contributions from felsic sources, and represent mature recycled detritus. Tectonic discrimination diagrams suggest that Mugheb River sediments were derived from rock types, which represent a passive continental margin, which is consistent with several tectonic history models of the Cameroon Volcanic Line and the Pan-African fold belt.