Tectonic setting, paleoweathering, and maturity of beach sediments along the West Atlantic Coast of Cameroon

Abstract

Grain size parameters and major, trace, and rare earth elements of beach sands along the west Atlantic coast of Cameroon between the coastal basins and the Cameroon Volcanic Line were evaluated to decipher their source, weathering, depositional conditions, textural maturity, and tectonic settings with the application of new formulae. Grain size analysis shows that most of the sediments are fine to medium-grained, moderately sorted to well sorted, and deposited in moderate to low energy environments with clear fluvial and beach signatures. Log(Fe₂O₃/K₂O) vs log (SiO₂/Al₂O₃) indicates that most of the sediments are iron sands while trace element plots such as 10*Th/Co, Cr/Th, 100*Th/Sc, Th/Yb, and 10*La/Co indicate mafic to intermediate sources for most of the sediments. This is further confirmed by rare earth elements (REE) normalized patterns revealing enriched light rare earth elements (LREEs) over heavy rare earth elements (HREEs) by moderate amounts, positive Eu anomalies from Post Archean Australian Shale (PAAS), and upper continental crust (UCC) normalized plots. Newly developed indices CIX and PIX, from elimination of CaO, suggest moderate to high weathering intensity which conforms with the climatic conditions of Cameroon. La/Yb chondrite normalized vs Zr plots positioned a significant portion of the sediments in a mantle environment, with minimal zircon enrichment. The volcaniclastic sands were identified as first cycle, non-recycled sediments. High ICV values (ICV > 1) indicate that most of the sands are immature, but the newly introduced ICV_new, whereby oxides of Fe and Ca are eliminated, shows that some of the sediments are mature and recycled, confirmed also by SiO₂/Al₂O₃ ratios especially at the tail ends of the study area. DF(A-P)M and DF (A-P)MT plots indicate that the sediments are of the passive margin setting.