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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]

The Babouri-Figuil Basin (BFB) is a frontier basin for petroleum in Cameroon. It belongs to the series of Cretaceous rift basins of the West and Central Rift System (WCARS), the origin of which is related to the opening of the South Atlantic. Within the same rift system, commercial hydrocarbon accumulations have been discovered in Chad, Sudan, Niger and, more recently, in Nigeria (Gongola Basin). The study of the geology of the BFB just recently received considerable attention, mainly because of its presumed hydrocarbon potential. In the pursuit of researching possible petroleum systems in the BFB, the current study provides a first look into the characterization of source and reservoir rock and its integration into a 2D lithostratigraphic model. The study was solely based on outcrop samples. Black shale and massive claystone are good to excellent hydrocarbon source rocks [e.g., up to 38 wt% total organic carbon (TOC), up to 943 mg/g hydrogen index, up to 85 m thickness, up to 20–30 km lateral extension], with moderate to high values of extractable organic matter (e.g., >10,000 ppm). Calcareous claystone, on the other hand, are poor source rocks [e.g., <0.20 wt% TOC]. The samples are thermally immature, except for those located close to volcanic intrusion at Golombe that have reached the threshold for oil generation (Tmax >435 °C, production index >0.1). The petrographic analysis of sandstone revealed that they are fine-grained to coarse-grained, poorly to moderately sorted, texturally and compositionally immature to submature, subarkosic to arkosic arenites. The main diagenetic processes that affected sandstones are as follows: moderate to intense compaction characterized by the development of long, concavo-convex, and sutured contacts between grains; cementation through calcite, iron oxide, and quartz cements; alteration of mica and feldspar grains; partial to complete dissolution of feldspar, mica, amphibole grains, and calcite cement; and the replacement of feldspar and mica grains by clay minerals. Alteration and dissolution increase the porosity of sandstone through the creation of secondary pores. However, mechanical compaction through the development of a pseudomatrix and cementation as pore-filling materials have significantly reduced the quality of sandstone beds as conventional petroleum reservoirs. Hence, the best reservoir-quality sandstones in the basin are generally located in the upper portion of the basin in terms of its lithostratigraphic model. They are the cleanest sandstones with the smallest amount of cement and the lowest ductile grain content (pseudomatrix), with a thickness that varies from 3 m to 120 m and a lateral extension of 20 km. The lithostratigraphic model of the basin is characterized by an extensive lacustrine environment that provided a thick sequence of organic-rich formations; sand deposited as extensive reservoirs sandwiched between shale/claystone beds; the development of stratigraphic traps through lateral facies change; and the widespread deposition of lacustrine and floodplain claystone that provide regional seals. The similarities between the Babouri-Figuil Basin and proven petroleum systems in other WCARS rift basins suggest that the basin may host at least one petroleum system where actively generating source rocks are present. [ABSTRACT FROM AUTHOR]