Formation and evolution of West and Central African superimposed rift basins.

West and Central African superimposed rift basins are Meso-Cenozoic multicycle intra-continental rift basins developed on the Precambrian crystalline basement. Previous studies mainly focused on the formation and superimposition process of several prototype basins developed in a single superimposed basin, but it is rarely documented that research on the different contemporaneous complex superimposed rift basins in the same tectonic region as well as those superimposed rift basins with different prototypes basins in vertical through time has been carried out. Based on the geological, geophysical, and geochemical data obtained during the oil and gas exploration activities in the West and Central African superimposed rift basins recently, combined with the previous research results, this paper focuses on the basin evolution, formation and superimposition process of prototype basins through time of the West and Central African superimposed rift basins. Results show that since the breakup of Gondwana, affected by the relative movements among the Northwest African block, the Northeast African block, and the Central and South African block of the African continent and the tectonic events of the surrounding plates, the West and Central African superimposed rift basins have roughly experienced three phases of tectonic evolution, namely, Early Cretaceous, Late Cretaceous and Paleogene-Neogene. Early Cretaceous evolution phase is the key period of the formation and evolution of the rift basins, during which the boundary faults of these rift basins develop and act intensively. Three types of prototype basins are developed, including rift basin, strike-slip pull-apart basin and aulagu basin. Basement subsidence of these rift basins is the largest with the fastest subsidence rate among the total subsidence. Lower Cretaceous sedimentary filling has the largest percent in the total filling, and sedimentary systems in whole rifts system are non-marine elastic deposition. During Late Cretaceous evolution phase, these early prototype basins were inherited. However, the difference in rifting and the sedimentary filling among those rift prototype basins become larger. The Early Cretaceous sedimentary system also evolved into a marine-continental sedimentary system. During Paleogene-Neogene, the evolution of West and Central African superimposed rift basins became more complex, and the difference was further intensified. The rifting, strike-slip and compression-reversion occurred simultaneously in different basins, during which the rift prototype basins or inversion deformation developed. According to the differences in prototype basin type, sedimentary filling and vertical superimposition of the prototype basins in these three phases, these superimposed rifts in Central and Western Africa are divided into two types, inherited superimposed basins and reversed superimposed basins. They are further divided into eight subtypes, namely, early-developed superimposed basins, successive superimposed basins, dynamic superimposed basins, late-developed type I superimposed basins, late-developed type II superimposed basins, and rift-inverted superimposed basins, aurora-inverted superimposed basins, and strike-slip-inverted superimposed basins. The characteristics of different types of superimposed basins are discussed. These results are of great significance for deepening the understanding of the geological evolution of superimposed rift basins and guiding the search for favorable oil and gas enrichment areas and exploration activities in such basins worldwide.