A seismic refraction study of the boundary between Bida basin and adjoining Zaria basement complex, Nigeria.

The area under study spans a suspected boundary between the Bida Basin and the Zaria Basement complex, Nigeria. The study involves eleven profiles covering an area of about 0.3km2. The result indicates that the depth to the refractor varies from 2.3m to 17.4m with an average of 7.7m. This variation indicates the degree of weathering and erosion of the bedrock whose irregular planar subsurface was subsequently filled with large deposits of alluvium forming a thickness as much as 16m. The average velocity of the first layer is 1700 ms-1, representing a higher presence of dry alluvium, clay and sand in the overburden. The average velocity of the second layer is 6100 ms-1, which indicates that the basement in the survey area consists of rocks mostly of granite schists, with other volcanic (meta-igneous or igneous) rock. The velocity values ranging from 717.7 ms-1 to 2000 ms-1 found on the eastern and western part of the area indicates the presence of thick alluvium deposits (meta-sedimentary) of the Bida basin to the west. This implies that considerable erosion had taken place during oregin event of the Pan-African era. Towards the Zungeru (eastern) part, the thickness reduced to 2.3m indicating that the survey area lies over the boundary between the Zaria basement complex and the Bida sedimentary basin.Keywords: Basement Complex, Sedimentary Basin, Geologic Boundary, Weathering and Erosion, In-line Refraction profiling