Geochemistry and mineralogy of the shallow subsurface Red Sea coastal sediments, Rabigh, Saudi Arabia: provenance and paleoenvironmental implications

Abstract

Mineralogical and geochemical characteristics of the shallow subsurface sediments retrieved from a short sediment core (2.05m long) collected from the tidal flat south of Al-Kharrar Lagoon, Rabigh area, Saudi Arabia, are presented to determine the impact oftemporal change of depositional environment and distinguish the principal control(s) on their chemical composition. The sedimentsare dominantly siliciclastic, consisting of two vertically stacked sedimentary facies: lagoonal (LG) gray silt-rich mud to argillaceousvery fine sand at the base and intertidal flat (TF) brown mud and argillaceous very fine-grained sands at the top. The sediments of thetwo facies are similar in their mineralogical and chemical composition except for slight vertical variations in the relative abundanceof minerals and concentrations of major oxides and trace elements. The mineralogical composition is dominated by quartz, feldspars,and plagioclase with less abundant clay minerals and hornblende, all of detrital origin. In addition, traces of high and low Mg-calcite,dolomite, and gypsum were recognized. Geochemically, the sediments are first-cycle and compositionally immature. The Al2O3/TiO2 ratios range from 9.4 to 17 and from 13 to 15.4 for the sediments of the LG and TF facies, respectively. These values suggest anintermediate igneous source rock of the Birak group that belongs to the oceanic island arc of the Hijaz Terrane, western Arabian Shield.The average values of paleoweathering indices CIA, CIW, and PIA are