International audienc

Using 2D seismic data and well logs from the Kribi-Campo subbasin in the south Cameroon margin, we have analyzed the postrift succession with the aim of deriving a chronostratigraphic chart and identifying stratigraphic traps. The Kribi-Campo subbasin related to the rifting between Africa and South America could be divided into a structurally complex eastern depocenter and a relatively less disturbed western depocenter in which a break-up unconformity approximately 107.5 Ma underlined the beginning of postrift history. We have used the modern concepts of sequence stratigraphy to identify and characterize seven second-order (SS1, SS2, SS3, SS4, SS5, SS6, and SS7) sequences and one third-order (SS8) sequences grouped into three megasequences (A, B, and C) from Albian to Recent. Sequence 1 (Albian-Cenomanian) was characterized by a retrogradation overlying a lowstand progradational pattern. The SS2 (Campanian-Maastrichtian) and SS3 (Maastrichtian) sequences were deposited during a highstand normal regression. From Paleocene to Eocene, the deposition of sequences SS4–SS5 was controlled by the development of submarine fan turbiditic system related to a forced regression of coastline. From the Middle Miocene to Recent age, the SS6, SS7, and SS8 sequences have been characterized by the development of sigmoidal-oblique clinoforms of a deltaic system well observed in the northern part of the study area. We have studied a new undocumented phase of forced regression of Mio-Pliocene in age within the postrift sequence SS7. The forced regression phases are associated with the Paleogene and Neogene uplift. Relative sea-level curves were constructed and compared with the existing published curves. The processes involved in the formation of these sequences were interpreted as a combination of tectonics, sediment supply, and sea-level changes. Potential reservoirs embedded within the sequences include channel fill, shingled turbidites, slope fan, and basin-floor fan complex.

Intracontinental elevated plateaus remain geomorphologic features which are poorly studied. Their genesis requires a coupling between climate and deformation. The Fish River canyon (southern Namibia), the second largest canyon of the Earth, carved the South-African plateau on 550 m along 65 km. This study reveals that the upper and the lower segments are shaped by NE-SW and north-south grabens, respectively. These deformations increased the meandering and the vertical incision mainly in the lower canyon. However the river main trend was not drastically modified attesting that the river was ancient and that the rate of the vertical displacement was slow compared to the erosion rate. The main incision occurred during a NW-SE stretching of Plio-Pleistocene. These stretching episodes belong to two deformation phases previously poorly described in the South-African plateau. These widespread stretching phases are interpreted as a result of deep mantle dynamics affecting the inner African continent.ß 2011 Published by Elsevier Masson SAS on behalf of Acade ´mie des sciences. R E ´S U M E Ĺesplateaux intracontinentaux e ´leve ´s sont des objets ge ´omorphologiques peu e ´tudie ´s. Leur formation re ´sulte d'un couplage subtil entre climat et de ´formation. Le canyon de la rivie `re Fish (Sud Namibie) a creuse ´le plateau sur 550 m le long de 65 km. Cette e ´tude re ´ve `le que les parties supe ´rieure et infe ´rieure du canyon sont structure ´es par des grabens respectivement NE-SW et nord-sud. Ces de ´formations ont permis le de ´veloppement de me ´andres et d'une incision verticale, notamment dans la partie infe ´rieure du canyon. Cependant, le cours principal de la rivie `re n'a pas e ´te ´modifie ´attestant que la rivie `re est ancienne et que le taux du de ´placement vertical a e ´te ´lent par rapport au taux de l'e ´rosion. L'incision principale s'est produite au cours d'un e ´tirement NW-SE du Plio-Ple ´istoce `ne. Ces e ´pisodes appartiennent a `deux phases de de ´formation mal de ´crites sur le plateau sudafricain et sont interpre ´te ´s comme un re ´sultat de la dynamique du manteau profond.ß 2011 Publie ´par Elsevier Masson SAS pour l'Acade ´mie des sciences.