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Tectono-Stratigraphic Evolution of the Bornu Basin, Nigeria: Linking Plate Boundary and Plate Interior Geodynamics and Implications for the Opening of the South Atlantic Ocean


Recent studies of the South Atlantic oceanic fracture zones indicate that the timing of changes in their azimuth during continental breakup can be linked to the timing of the regional unconformities in the circum-South Atlantic continental blocks. However, it is not yet clear if and how the timing of other geologic events, such as tectonic inversion and igneous activity, are linked to changes in the oceanic fracture azimuthal geometry. Here, we attempt to link plate boundary and plate interior geodynamics associated with South Atlantic opening by focusing on the tectono-stratigraphic evolution of the Bornu Basin, NE Nigeria, one of several continental rifts located in the West African Rift System. More specifically, we use 2D and 3D time-migrated seismic reflection, borehole, field and geochemical data to determine how plate margin processes impact normal fault growth, inversion, stratigraphic patterns, igneous activity and petroleum systems development within interior basins. We demonstrate that key tectonic events in the basin were broadly time equivalent to changes in the azimuth of the major oceanic fracture zones. For example, the timing of rift initiation in Bornu Basin during the Early Aptian correlates with the early change in azimuth observed in Kane Oceanic Fracture Zone (KFZ). The subsequent change in azimuth of the KFZ during the Turonian was coeval with the onset of basin shortening and inversion, with the formation of a major regional unconformity corresponding to another major change in azimuth of the KFZ in the Late Maastrichtian. Furthermore, the three main phases of igneous activity in the basin in the Early Cretaceous, Late Cretaceous and Tertiary correlate with the timing of the major azimuth changes observed in the Kane, Fifteen Twenty and St. Paul Oceanic fracture zones. Our study highlights that the geodynamics of the South Atlantic Ocean opening during continental break up was not only expressed by changes in the azimuth of the oceanic fracture zones, but was also recorded in the surrounding, intra-plate continental rift basins. Furthermore, understanding of the timing of the normal fault inversion and igneous activity can help to minimize exploration risks associated with trap charging, reservoir quality and source rock hydrocarbon potential.