The integration of mineralogical and geochemical data of a sedimentary rock can reveal the nature of source regions, the tectonic settings of the sedimentary basins and the paleoclimatic conditions. The aim of this research is to determine the dominant minerals in sandstone sample from part of the Eastern Dahomey Basin in order to infer the origin and its environmental effect. Eight (8) rock samples collected from the study area were subjected to geochemical analysis in order to determine their chemical composition using X ray fluorescence; thin sectioning of the sample were also done for petrographic description of the mineral compositions. Quartz, Iron Oxide and Microcline are the dominant minerals identified from the petrographic studies. Result of the geochemical analysis revealed sixteen (16) elements and oxides which include SiO2, Al2O3, Fe2O3, CaO, V2O5, ZrO2, SO3, K2O, Br, P2O5, CuO, TiO2, MnO, Rb2O, As2O3, Cr2O3 while Quartz, Iron Oxide, Microcline with some Accessory minerals were dominantly observed under the microscope. The presence of element and oxides such as Br, V2O5, ZrO2, CuO, Rb2O, As2O3 and MnO (especially Br of 12%-27%) suggests the depositional environment to be shallow marine or near marine environment, however abundance of SiO2 and Fe2O3, especially Fe2O3 suggests the incorporation of the sediments into the environment from a metamorphic source. The CIW´ and CIA’ value of the Sandstone samples vary from 69 to 95 (mean ~86, s=9; median ~88), and 58 to 87 (mean ~80, s=12; median ~83) respectively, both implying a high degree of weathering and alteration of the alkali minerals. The parent rock is a metamorphic rock which was recycled and deposited in shallow to near marine environment with Iron Oxide acting as the dominant cementing material.
