**6. The study area**

The area is underlain by rock and younger sediments of the Chad formation. The Chad Basin lies within a vast area of Central and West Africa at an elevation between 200 and 500 m above sea level and covers 230,000 km<sup>2</sup> . The basin is referred to as an interior sag basin, due to a sagging episode that has affected it before the onset of continental separation during which a rift system junction was formed providing an appropriate site for sedimentation. Therefore, it lies at the junction of basins, (comprising the West African rift), which becomes active in the early Cretaceous when Gondwana started to split up into component plates. Sediments are mainly continental, sparsely fossiliferous, poorly sorted, and medium-tocoarse grained, feldspathic sandstones called the Bima Sandstone. Both geophysical

**Figure 1.** *Nigerian map showing Chad basin area.*

and geological interpretations of data suggest a complex series of Cretaceous grabens extending from the Benue Trough to the southwest (**Figure 1**) [12].
