Textural characteristics and geochemical composition of a tropical coastal marine sediment: a case study of transgressive mud beach, Bight of Benin, Nigeria.

Abstract

The study determines the textural characteristics and geochemical composition of the transgressive mud coastal marine sediments of the Bight of Benin, Nigeria. The sediment samples were collected using a VanVeen grab sampler from three onshore and three offshore locations. The particle size analysis was conducted with a combination of the pipette sampling and wet sieving of the fraction > 62-µm method, while the concentrations of major oxides were determined by employing X-ray fluorescence technique. The onshore and offshore sediment samples were composed of 54% silt and 30% sand (sandy silt) and 45% sand and 31% clay (clayey sand), respectively. The sequence of concentrations of major oxides was SiO2 > CaO > Al2O3 > Fe2O3 > Na2O > MgO > K2O > TiO2 > P2O5 > MnO. Chemical classification scheme of the sediment sampled was Fe-shale. The range of SiO2/Al2O3 and K2O/Na2O ratios of the onshore sites was 5.59-6.74 and 0.31-0.32, respectively, while of the offshore site was 6.19-6.99 and 0.32-0.46, respectively, indicating a low-to-moderate sediment recycling. K2O/Al2O3 ratios were low across the sampling sites suggesting abundance of aluminosilicates. The values of weathering indices consisting of Plagioclase Index of Alteration (PIA), Index of Composition Variations (ICV), Chemical Index of Weathering (CIW), and Chemical Index of Alteration (CIA) were similar and varying from low to moderate. Principal component factor analysis (PCFA) extracted three factors for onshore and offshore data with factor loading of clay with MnO, K2O, and Fe2O3 contents in the offshore sediments while onshore were loaded with CaO, MnO, Al2O3, and Fe2O3 with sand. Geochemical characteristic signified a mixed nature of provenance of both terrigenous and lithogenous sources for onshore and offshore sites respectively.