INTEGRATED GEOPHYSICAL INVESTIGATION OF YEMOO GROVE ARCHAEOLOGICAL SITE IN ILE-IFE, OSUN STATE, SOUTHWEST NIGERIA

Abstract

Integrated geophysical investigation involving the electrical resistivity and magnetic methods was carried out at Yemoo Grove archaeological site at Ile-Ife in Osun State, Southwest Nigeria. The resistivity survey involved 1-D Vertical Electrical Sounding (VES) with the Schlumberger array and 2-D Dipole-Dipole resistivity imaging (profiling) technique. The VES data were interpreted quantitatively by partial curve matching and computer assisted 1-D forward modelling with the W-GeoSoft/WinSev 5.1 software. The 2-D Dipole-Dipole data were inverted to 2-D subsurface structure with the DIPRO for Windows software. The VES delineated a stratigraphic sequence composed of the topsoil, lateritic clay and weathered basement within the upper 14.0 m. The topsoil, which is the most archaeologically relevant horizon, had thicknesses of up to 2.0 m. The 2-D structures identified four priority zones with relatively thick topsoil (up to 2.0 m) along the existing trench and at the shoulders of the flanking ridges. Three of these zones were excavated plus one random location. Archaeological artefacts ranging from ceramics, potsherd pavement, charcoal and stone concretion were identified within the excavated priority zones while nothing was found at the randomly located site. The 2-D structure along one of the traverses identified a terraced surface on the underlying lateritic layer. This was corroborated by excavation. No metallic artefact was identified. The geophysical results provided a reliable guide to archaeological prospection at the Yemoo Grove Site.