GRAVITY AND MAGNETIC ANALYSIS OF THE BORNU BASIN, NORTHEAST NIGERIA

The Bornu Basin which is the Nigerian sector of the broader Chad Basin is a structural depression that occupies northeastern Nigeria. The Bornu Basin is one of several Cretaceous and younger basins in central and western Africa that formed as a series of extensional basins. The basin formed along northeast-trending structures during the Pan African orogeny with these structures being reactivated during the initial breakup of Gondwana in the Early Cretaceous. Additional basin formation and deformation of the basin occurred in the Late Cretaceous-Tertiary with the deformation of the basement involving normal faults. During the formation of the basin, four main sedimentary formations (Birma sandstone, Gongila shales, carbonates and sandstones, Fika shale, Gombe sandstone) were deposited in continental and shallow marine environments. The available gravity and magnetic data are used to determine the structural configuration of the Bornu Basin, which is currently unknown. Using land and satellite gravity data, and satellite magnetic models, a variety of enhancement techniques including band-pass filtering, Euler deconvolution and tilt derivatives were used to delineate structural trends within the basin. These methods showed that the basin has a complex basement structure with a series of basement blocks separating the deeper portions of the basin. Most basement structures trend toward the northeast along Pan African structures. 2D power spectral analysis, 3D Euler deconvolution and 3D inverse modeling were used to determine the thickness variations within the basin which varies between 1.5 and 4.0 km in depth.