Mesozoic–Cenozoic history of the Congo Basin

Abstract

Geophysical surveys and drilling of deep wells have recently led to the recognition of underlying Precambrian basement, and to an interpretation of the structural evolution of the Congo Basin. Deformation estimated as Late Cambrian to Early Ordovician corresponds to the late Pan-African event more accurately dated as end-early Cambrian in West Africa. Subsequently, Paleozoic deformation led to widespread erosion and the development of a marked regional unconformity. The 1000-m-thick mostly continental deposition during the Cretaceous and Tertiary did not involve a noticeable subsidence process. There was no volcanism during this deposition, except at the Early Cretaceous, with the advent of kimberlites that are distributed over the border of the Cuvette. As a consequence most of the diamonds were transported northward or southward from upstream sources. The Mesozoic sediments of the Congo Basin were formed in lacustrine or lagoonal basins close to the sea level as demonstrated by some intercalations with marine fossils. In the eastern part of the basin, a limited marine connection during the Kimmeridgian was only possible with a gulf belonging to the young Indian Ocean. In southern Kasai, the same Kimmeridgian transgression is observed. In the northern part of the basin, a probable Cenomanian marine connection was suggested between the Tethys and the South Atlantic, and the marine deposition at Kipala suggests a connection with the Trans-Saharan corridor during the Late Cretaceous. The geometry of the continental Mesozoic and Cenozoic deposits begins with beds overlying a widespread planation level unconformity and/or the presence of gravel or conglomerate in the lower portion. The Sables Ocres Series and the Grès Polymorphes Series rest on the planation levels of Late Cretaceous and mid-Tertiary ages respectively. Mechanical composition and morphoscopic characters argue for a dominant eolian transport for the Grès Polymorphes and for a fluvial deposition for the Sables Ocres. The silicification process achieves its maximum extent during the Paleogene interval characterised by a micaceous mineral rich clay fraction in the Congo basin sediments. This process stopped at the beginning of the Neogene interval when the kaolinitic component increased significantly.