Mineralogy and geochemistry of alluvial sediments from the Kadey plain, eastern Cameroon: Implications for provenance, weathering, and tectonic setting

Abstract

Mineralogical analyses by X-ray diffraction and geochemical analyses by X-ray fluorescence and inductively coupled plasma-mass spectrometry were performed on the Kadey Plain clastic sediments in order to determine their provenance and weathering. The Kadey Plain has four types of clastic sediments, shales, wackes, litharenites, and Fe-sands. The shales and wackes consist of kaolinite, quartz, muscovite, gibbsite, illite, anatase, and goethite. In the litharenites, minerals found are quartz, illite, kaolinite, gibbsite, muscovite, and goethite. Fe-sands consist of quartz, muscovite, and kaolinite, whereas gibbsite, illite, iron oxyhydroxides and anatase occur as traces. The U/Th (0.11–0.37) and V/Cr (0.99–1.73) ratios indicate an oxidising deposition environment. The behavior of trace elements is the same in these sediments, except for U content which is depleted in Fe-sands. Rare earth elements (REE) normalized with chondrite for the studied clastic sediments, demonstrate a slightly light REE enrichment (3.74 < (La/Sm)n < 5.80) and comparatively flat heavy REE patterns (1.12 < (Gd/Yb)n < 1.78) associated to negative Eu anomaly (0.51 < Eu/Eu* < 0.67). These materials disclose less fractionation of REE [7.10 ≤ (La/Yb)n ≤ 18.41]. These ratios are higher than that of Post-Archean Australian Average Shale [(La/Yb)n = 9.15], except for wackes. Al2O3/TiO2 vs. (SiO2)adj diagram, Eu/Eu*, La/Sc, Th/Sc, La/Co, Th/Co, and Th/Cr ratios suggest that the studied clastic sediments were derived from felsic sources. The REE patterns for sediments from the Kadey Plain disclosed closer resemblance to those of granites, quartzites, migmatites, and chlorite schists found relatively near to the study area. The tectonic discrimination diagrams indicate chiefly passive margin setting for these alluvial sediments.