L’histoire de la subsidence et de l’évolution thermique du sous-tasse de Kribi-Campo situé dans le Golfe de Guinée ont été contraintes à l’aide de dix puits offshore en utilisant la technique de délestage après décompaction.
Quatre principales phases de subsidence ont été discriminées : la première, du Barrémien à l’Aptien (130-112 Ma); la deuxième, de l’Albien au Sénonien (112-65 Ma), la troisième, s'étendant du Paléocène au Miocène (65-5 Ma), et la quatrième du Pliocène au Pléistocène (5-2 Ma). Les cartes de quantité et de vitesse de subsidence et de sédimentation montrent une grande zone subsidente dans la partie ouest du bassin autour de Kribi. Le facteur d’extension β pour le modèle d’extension uniforme correspond à des valeurs allant de 1,04 à 1,06. Graphiquement, les courbes de subsidence tectonique apparaissent encadrées par les courbes correspondant à β =1,03 et β =1,09. Les pentes des courbes linéaires de la subsidence tectonique par rapport à la racine carrée du temps t, ont permis d’avoir des paléotempératures des sédiments ainsi que des gradients géothermiques en parfait accord avec les valeurs observées dans les puits. Par exemple, un gradient de température de 35, 316 OC/km a été calculé avec les températures maximales tandis que celui obtenu à partir des puits est de 35,554 OC/km. La comparaison des valeurs calculées de la réflectance de la vitrinite Ro avec les valeurs mesurées montre une bonne correspondance. Ces valeurs de la vitrinite indiquent que les roches-mères d’âge Crétacé et Tertiaire inférieur ont probablement atteint la maturité thermique.
In this study, a seismic reflection dataset and well-log data were integrated to investigate the geometry and internal configuration of a turbidite channel system within the Late Cretaceous interval of the deep-water Kribi-Campo sub-basin, offshore Cameroon. This interval is characterized by a well-developed submarine channel system consisting of an early and a late-stage channel. Morphologically, the submarine channel system has a northeast-southwest trend and is U-shaped in cross-section with a length of 56 km within the study area. The early-stage channel has a relatively straight morphology and varies in width and depth from 3 to 5 km and 89 to 197 m, respectively. However, the late stage of the channel is characterized by a narrower (1 to 3 km) and shallower (41 to 103 m) incision, with sinuous morphology carved into the early channel infill. The changing interaction of differential tectonic subsidence, relative sea level, source sediment supply and slope gradient change are considered to be the major control on the geometry and internal characteristics of the submarine channel system. Sag subsidence during the Campanian led to basin deepening and the widespread development of basinal sediments as submarine fans and promotion of submarine channel system development. The filling of the channel system occurred during a long-term Maastrichtian relative sea level rise, punctuated by falls in relative sea level. Sand appears to have been fed to the channel system by the palaeo-Sanaga and palaeo-Nyong Rivers, with sand rich aprons developed were these rivers debouched into the study area. The early stage of the submarine channel is dominated by coarse-grained sediments in the southwest and fine-grained sediments in the northeast, while the late-stage channel is mainly filled with fine-grained sediments. The presence of coarse-grained sediments occur within the submarine channel axis downstream represents a potential for hydrocarbon reservoirs with enhanced petrophysical qualities due to a low depositional gradient. The geomorphological analysis of this ancient submarine channel system along the western African margin, as presented in this study, has broad implications in the understanding of the distribution of deep-water sediments with potential for hydrocarbon exploration in the region.
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