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The aim of this study was to map the transpressional and transtensional relay zones of the Central Cameroon Shear Zone in the Mbere Administrative Division of the Adamawa Region of Cameroon using, geological and geophysical data analysis. The central Cameroon Shear Zone (CCSZ) is characterised by several large strike-slip faults oriented between N030E and N070E. The geological and structural field data analysis revealed two deformation regimes (strike-slip and tensile) that exhibit characteristic deformation markers identified in the field. The dextral movements on the strike-slip faults of the CCSZ were associated with these markers, the two regimes were found to be associated with the D3 deformation along the CCSZ. The tensile regime generated transtensional structures and led to the formation of the Cretaceous Mbere and Djerem basins, whereas the transcurrent regime caused the transpressional tectonics. Structural analysis of the joints and veins of the D4 deformation shows that their directions describe those of the major axes of the CCSZ. As the D4 deformation is controlled by transcurrent tectonics, to show that the vein intrusions constitute transpressional relay zones and to derive different models, processing, and interpretation methods (spectral analysis, shaded relief analysis, magnetic signal filtering, upward continuation, horizontal gradient magnitude, analytical signal, and 2.5D inversion) have been applied to the geophysical data. Magnetic residual analysis shows that the transpressional relay zones are characterised by high-frequency rectilinear magnetic anomalies (207.12–305.809 nT) and interference along the strike-slip faults. Through the superimposition of the geophysical interpretations, a structural model integrating the two deformation regimes with relay and Cretaceous basin models was developed. [Display omitted] • The two interpreted deformation regimes are associated with transtensional and transpressional tectonics, respectively. • The first favored the development of cretaceous basins and the second the formation of transpressional relays. • Transpressional relays, rectilinear with high frequencies are associated with strike-slip faults. [ABSTRACT FROM AUTHOR]

The Babouri-Figuil Basin (BFB) is a frontier basin for petroleum exploration in northern Cameroon that belongs to the series of Cretaceous rift basins of the West and Central Rift System (WCARS), and contiguous related WCARS rift basins in Niger, Chad, Sudan, and Nigeria have yielded commercial deposits. The recent discovery of Precambrian basement reservoirs in Chad (Bongor basin) highlights the existence of a new play for petroleum exploration in the region. A network of interconnected magmatic intrusions directly related to basement faults cross-cuts the BFB stratigraphy. This study aims to evaluate the interactions between magmatic intrusions and potential source rocks in the BFB and make comparisons with similar basins in the WCARS context. The results showed that magmatic intrusions are made up of dolerite and basalt, characterized by onion peel (ball-shape) or columnar joint structures, respectively, and a fine-grained microlithic-porphyritic texture. The analyzed samples are thermally immature except for the samples located close to magmatic intrusions, which are thermally mature. The SEM images revealed that organic matter was subrounded with a regular shape in the samples that are located away from magmatic intrusions, while it presented a characteristic pattern of thermally evolved organic matter in sample located closer to magmatic intrusions, characterized by a cloudy visual aspect that is filling small fractures and being disseminated over mineral grains. Contact metamorphism and hydrothermal processes led to the neoformation of mixed-layered illite/chlorite and illite/micas. This study shows that the interactions between sedimentary formations and magmatic intrusions are stronger when the distance toward magmatic intrusions decreases. The source rock maturation of outcrop samples was predominantly triggered by magmatic intrusions, so that the overall area would be immature without intrusions. The formation of secondary organic matter (solid bitumen) in source rocks provides a perspective into a working petroleum system in the BFB. The presence of magmatic intrusions in the Babouri-Figuil Basin may positively affect the thermal maturation history of source rocks and can activate petroleum generation at a shallow burial depth. Thus, the Babouri-Figuil Basin may host an atypical petroleum system. • The magmatic intrusions in the Babouri-Figuil Basin are made up of dolerite and basalt. • Contact metamorphism and hydrothermal processes led to the disappearance of detrital clay minerals and the neoformation of mixed-layered illite/chlorite and illite/micas. • The thermal maturity proxies of the analyzed samples revealed a systematic increase in thermal maturity indexes as the distance with magmatic intrusions decreases. • The formation of solid bitumen in source rocks provides a perspective on an atypical petroleum system in the Babouri-Figuil Basin. [ABSTRACT FROM AUTHOR]