Depositional Environment and Geochemical Classification of Ilaro Sandstone, Dahomey Basin, Southwestern Nigeria

Abstract

Sandstones are sedimentary rocks formed from cemented sand-sized clasts. The cement that binds the clasts can vary from clay minerals to ca, silica or iron oxides. Sandstone can be further divided according to: Clast size – fine (0.06-0.2mm), medium (0.2-0.6mm), coarse (0.6-2mm); Sorting - poorly sorted, moderately well sorted and well sorted.  Sandstones could also be discussed in terms of little or significant amount of silt and / or clay as arenaceous or argillaceous (wacke). Nine (9) samples were collected from the Ilaro sandstone and subjected to granulometric, petrographic and geochemical analysis precisely ICP-MS (Inductively coupled plasma mass spectrometry) for the major elements and their oxides. Granulometric analysis reveals that the texture of the sediments ranged from medium to coarse through to very coarse, they are symmetrically skewed and dominantly mesokurtic. Bivariate plot however depicts the Ilaro sandstone to be fluviatile in their depo-setting. All the samples also showed strong inclination towards sub-greywacke in terms of their geochemical classification.