INTEGRATED GEOPHYSICAL INVESTIGATION OF IJEBU-IMERI ARCHEOLOGICAL SITE, SOUTH WESTERN NIGERIA

Abstract

Integrated geophysical investigations involving ground magnetic and electrical resistivity methods were conducted at Ijebu-Imeri archeological site, Ogun state, Southwestern Nigeria. The site served as a location for fabrication of tools used for construction of Sungbo Eredo for defensive purpose 600 years ago. The surveys were aimed at locating, determining the spatial distribution and depth of burial of artifacts, thereby reducing wild-cats excavation. Magnetic data were acquired using proton precession magnetometer while resistivity data were acquired using the Campus Ohmega resistivity meter. The magnetic survey comprises thirty-one profiles in N-S and E-W directions with station interval of 5 m and inter-profile spacing of 5 m while the electrical survey comprises five parallel and four perpendicular profiles selected based on result of magnetic data. Wenner configuration with electrode spacing ranging from 1.0 – 6.0 m was employed for 2D electrical resistivity tomography. Profile length ranges from 1.0 100 m in the E-W direction and 0 – 68 m in the N-S direction for both methods. The magnetic data were processed and analyzed using Oasis Montaj Geosoft software while the resistivity data were processed and analyze using DIPRO for Windows software. Results of processed data were integrated and it revealed a distribution of the buried archaeological features within the study area. From the magnetic maps, regions of magnetic highs correspond to those of high resistivity on the 2D subsurface structure models. It was concluded that the areas with high magnetic and resistivity anomalies are possible areas that has buried artifacts with depths ranging 0 2 m. Trial pits located at regions of high total magnetic intensity and model resistivity yielded burnt pipes (TUYERE), iron slag; pottery fragments (POTSHERDS) and charcoal occurring at 0 – 0.6 m. The geophysical results therefore provided reliable and useful guide in pre-excavation of archaeology materials.