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The structure of igneous plumbing systems in circum-South Atlantic, intra-continental rift basins, e.g., the West and Central African Rift Systems (WCARS), remains enigmatic due to poor subsurface data coverage and quality. How magmatism in these basins related to the opening of the South Atlantic is thus poorly understood. We 14 integrate 2D and 3D seismic reflection data (c. 27600 km 2), data from 23 boreholes, 15 and field observations from the Bornu Basin and Upper Benue Trough, onshore NE 16 Nigeria to examine the timing and development of igneous bodies possibly related to 17 opening of the South Atlantic. We identify numerous sills, which typically have saucer-18 shaped and en-echelon morphologies, and extrusive volcanic cones. The igneous rocks 19 are alkali basalts and dolerites. Seismic-stratigraphic relationships indicate that 20 emplacement occurred in the Early Cretaceous (Albian-to-Cenomanian; ca. 120 Ma), 21 Late Cretaceous (Santonian-to-early Campanian; ca. 83 Ma), and Cenozoic (Miocene; 22 ca. 22 Ma). Magmatism was broadly coeval with major plate boundary interactions, 23 characterized by major azimuthal changes in fracture zones in the developing South 24 Article text Click here to download Article text Adamu Paper Manuscript_CM_II.docx Atlantic Ocean. The broad temporal correlation between intra-continental rift basin 25 magmatism and plate boundary interactions suggests that periods of magma 26 emplacement may have, in some way, been instigated by stress dissipation into intra-27 continental rift basins. 28

Several soft sediment deformational structures were identified during fieldwork survey carried out on exposures of Gombe Formation in the Gongola sub-basin of the Northern Benue Trough at Gombe and environs. These soft sediment deformational structures includes: simple internal cusps, which occur wide spread across a single bed or intermittently across several beds, and slump structures that are represented by complex recumbent folds and concave upwards structures. These structures are proxy to syn-depositional energy operating within the depositional environment and this current research aims to evaluate their trigger mechanism. These deformational structures are commonly hosted in the mouth-bar deltaic sequences of the Gombe Formation. The deltaic setting is usually a locus for high sediment influx and accumulation. This may have generated high quantum of depositional energy which was probably responsible for the development of the syn-depositional soft sediment depositional structures in the Gombe Formation during Campano-Maastrichtian times.

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