Master Thesis Submitted to Department of Earth Sciences, University of Benghazi in Partial Fulfillment of the Requirements

Abstract

The present work aims to characterize the mineralogy, geochemistry and environmental geochemistry of the beach sands along the Mediterranean Coast from Al Kuwifia to Tolmeita, NE Libya. The microscopic examination and SEM-EDX indicate abundance of carbonates, quartz, feldspars, glauconite and evaporites. Carbonate grains are mainly represented by biogenic grains made of aragonite and/or calcite. Quartz is mostly monocrystalline with uniform and undulatory extinction. It occurs either in the form of angular grains or as rounded grains. The former type is the more abundant. The detected evaporites are gypsum and halite. Feldspars, glauconite and heavy minerals are controlled by terra rossa and only detected in the eastern side of the studied beach, while they are lacking in the western side. The recorded heavy minerals are zircon, augite, tourmaline, rutile, biotite, garnet, monazite, titanite, hornblende, pistachite, magnetite, ilmenite, hematite, goethite, limonite and pyrite. Based on the mineral composition, two distinct types or groups of sediments were extracted. The major oxides CaO and MgO are the main constituents of the carbonate minerals; calcite and aragonite. SiO2 is mainly in the form of quartz. Sometimes a high quotient of SiO2 together with the oxides; Al2O3, K2O and partly of Na2O, TiO2 and Fe2O3 are essentially allocated within the structure of the feldspars. Part of Na2O and the content of Cl belong mainly to halite. Part of Fe2O3 and TiO2 may be accommodated as iron oxyhydroxides. Part of CaO and the content of SO3 are allotted within the gypsum structure. Ba, Sr, Th, U and REE are basically controlled by the carbonate fraction, while Cu, Zn, V and Cr are strongly correlated with Al2O3. The prevailing well oxidizing coastal environments are well expresses by the low authigenic uranium and low U/Th, V/Cr and Cu/Zn ratios. ΔCe values are not correlated with U and CaO contents, which suggest that the ΔCe values are not related to the paleoredox conditions. Metals analyzed in this study, except Cr and V in some locations, have EF > 2 suggesting that they are mainly of anthropogenic origin and that natural activities exert little influence on their abundances. The Igeo values suggest that the studied samples are unpolluted with Cu, Zn, V, Cr, Pb and Th, very lightly polluted to lightly polluted with As and lightly polluted with U.