Trace and rare earth elements (REE) distribution in Ngaye alluvial sediments of Mbere-Djerem Basin, North Cameroon: implications for origin, depositional conditions and paleoclimate reconstitution

Abstract

Ten (10) bulk samples of four sequences were collected at the left and the right banks of Ngaye River (North Cameroon), to assess their origin, depositional conditions and paleoclimate. For this purpose, granulometric, mineralogical and geochemical analysis were performed. The sediments are sandy-clayey, silty-clayey to clayey which are exclusively made up of kaolinite, quartz, illite, accessory muscovite, feldspars, anatase and goethite. La/Sc, Th/Sc, Th/Co, Th/Cr concentration ratios suggested that these sediments were derived from UCC. The bivariate plots diagrams of Hf versus La/Th and La/Sc versus Co/Th show that Ngaye alluvial sediment is mainly composed with acidic source rock and old sedimentary rock. Additionally, the diagram of ΣREE versus La/Yb suggested that these sediments derived from alkali basalts, sedimentary and granites rocks. The correlation matrix implies that the distribution of trace elements in the analysed sequence samples shows a good correlation in the majority of the samples. Correlation coefficients between trace elements and total REE of the studied sequences indicate that REEs of the Ngaye alluvial sediments are mainly from the terrigenous formations. Discriminant diagrams, consisting of La-Th-Sc and Th-Co-Zr/10, suggest that the Ngaye alluvial sediment was deposited in continental island arc tectonic setting. Redox proxies (V/Ni, V/(V + Ni) suggested that anoxic depositional condition was prevailed during deposition of the Ngaye alluvial deposit. The Ga/Rb ratio values range from 0.19 to 1.47 whereas those of Sr/Cu ratio range from 2.81 to 29.34, suggested that Ngaye area was characterized by dry and humid climate condition during the depositional period.