PETROGRAPHY AND GEOCHEMICAL APPRAISAL OF AFOWO SANDSTONE FACIES, DAHOMEY BASIN, SOUTHWESTERN NIGERIA

Abstract

Sandstones are sedimentary rocks formed by the cementation of sediment by material cements and they show a great deal of variation in mineral composition, degree of sorting and roundness.

A petrographic and geochemical study of sandstones in the Afowo Formation of Dahomey basin southwestern Nigeria was carried out to infer the various elemental compositions, mineralogical composition, degree of sorting and degree of roundness of the sandstones in order to classify them.

Seven (7) samples were collected and subjected to standard laboratory preparation and analytical method which include geochemical x-ray fluorescence for (trace and major elements analysis), and thin section petrography. The result of the geochemical analysis revealed the presence of some major elements (SiO₂,Al₂O_3,Fe₂O₃,CaO,Br,and TiO₂) and trace elements (V₂O₅,SO₃,P₂O₅,CuO,MnO,Rb₂O, and AS₂O₃) respectively. The mineral compositions obtained from the petrographical analysis are Quartz, Aluminum oxides, and high percentage of Iron oxides acting as the cementing material. The high percentage of Fe₂O₃ indicates that the sandstone is ferruginous while high concentration of Bromine ( Br) suggest a shallow marine environment of deposition of the sandstone.

Key words: Petrography, Sand stone, Aluminum, Bromine, Marine, Quartz,