Stratigraphie isotopique du strontium et datation des formations carbonatées et glaciogéniques néoprotérozoiques du Nord et de l’Ouest du craton du Congo

Numerous occurrences of Neoproterozoic carbonate platforms and glacigenic lithofacies are present around the Congo craton. They are especially well developed on its western and northern borders, i.e. in the forelands of the West Congo and Oubanguides belts. Sr isotopic stratigraphy enables us to characterize the deposition age of some carbonate units from these two domains. The ⁸⁷Sr/⁸⁶Sr isotopic ratios of limestones from the late ‘Haut Shiloango’ (0.7068) and the ‘Schisto-calcaire’ (0.7075) of the West-Congo domain are of post-Sturtian and post-Marinoan ages, respectively. The Lenda carbonates (0.7066) from the Northeast of the Democratic Republic of Congo and the limestones (0.7076) from the Bangui Basin, both in the Oubanguides foreland, are of pre-Sturtian and post-Marinoan ages, respectively. These data associated with lithostratigraphic correlations allow us to ascribe the ‘Bas Congo’ lower mixtite (tillite) and the Akwokwo tillite (Lindian) to the Sturtian ice age. In the same way, the ‘Bas Congo’ upper mixtite (tillite) and the Bondo tillite (Bakouma Basin) are likely Marinoan in age. A new synthetic stratigraphy for these Neoproterozoic domains is developed.