Multiphase Phanerozoic Subsidence and Uplift History Recorded in the Congo Basin: A Complex Successor Basin
Résumé
The Congo Basin of central Africa is a large iconic Phanerozoic sedimentary basin whose origin and tectonic evolution are poorly understood, mostly because of a lack of modern stratigraphic data, reflecting a long hiatus in field investigations during the past five decades. It is usually assumed that the Congo Basin experienced a long and continuous history of slow subsidence since the late Precambrian (e.g. 2–4 m/Ma), linked to steady-state mantle processes. Here, we used revised sedimentological and stratigraphic data of the four historic deep boreholes drilled in the center of the basin to calculate a new first-order model for its subsidence and uplift history. Because the sedimentary sequences of this basin are largely terrestrial, we apply a new backstripping method especially designed for continental domain. The results reveal two main episodes of subsidence: initially rapid subsidence during the Carboniferous-Triassic (10–20 m/Ma), and then slower subsidence during the Jurassic-Cretaceous (5–10 m/Ma), punctuated by several uplifts at 160–180 Ma (e.g. ‘Karoo’), 120–140 Ma (e.g. ‘Paraná-Etendeka’), and again in the Cenozoic, ca. 30–50 Ma (e.g. ‘Ethiopian’). This complex, multiphase subsidence and uplift history of the Congo Basin can be linked to evolving far-field geodynamic processes that first led the formation of Pangea (large-scale compression) during the late Paleozoic, and then to its break-up associated with successive outpourings of Large Igneous Provinces (or hotspot plumes) and the opening of the Indian and South Atlantic Oceans around Africa.