Composition and geochemistry of clay sediments offshore the northeastern Sicilian coast (Southeastern Tyrrhenian Sea, Italy)

Abstract

Grain-size, mineralogical and chemical analyses were carried out on fine fraction of sediments collected in the Gulfs of Patti and Milazzo, two borderland basins in the Southern Tyrrhenian extending offshore the northeastern Sicilian coast. Results of granulometric analyses on size fractions smaller than 63 μm showed that the investigated samples can be classified mainly as clayey silts. The coarse fractions (>63 μm), examined by optical microscopy, consist of a terrigenous component, representing in some samples about 98–99% of the total sediment, and by a biogenic component. This latter is mainly made up of benthic Foraminifera. The mineralogical composition of the fine fraction, determined by X-Ray diffractometry, is represented by muscovite, quartz, clay minerals, carbonates (calcite) and, in some samples, by calcium and sodium-rich plagioclases. The method of saturation with K and Mg, followed by ethylene glycol solvation and heating, are used for a qualitative determination of the clay minerals. Clay mineralogical composition is characterized by the dominance of clinochlore and illite, with minor amounts of smectite (especially montmorillonite) and vermiculite. The chemical data reflect the main mineralogical composition showing a uniform quantitative composition, with high Al 2O 3 and SiO 2 values and very few variations in the relative abundance of the other components. The Cr/Th, Th/Sc, Th/Co and La/Sc ratios suggest a felsic nature of the source rocks. Finally the geochemical parameters such as V/Cr, U/Th, Ni/Co and Cu/Zn ratios indicate that examined sediments were deposited under oxic environments.