Sedimentology and sequence stratigraphy of the late Precambrian carbonates of the Mbuji-Mayi supergroup in the Sankuru-Mbuji-Mayi-Lomami-Lovoy basin (Democratic Republic of the Congo)

Abstract

The late Mesoproterozoic-middle Neoproterozoic carbonate succession (1155 Ma-800 Ma) of the Mbuji-Mayi Supergroup (Democratic Republic of Congo) represents a classic late Precambrian carbonate sequence whose architecture is poorly known. Here we present new data and synthesis of microfacies analysis, sequence stratigraphy, Fischer plots coupled with C and O isotopes, to evaluate the paleoecology and sea level variations of the carbonate series of the Mbuji-Mayi Supergroup, and to establish hierarchical approach stratigraphic framework from which to resolve the evolution of the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. Our microfacies and sequence stratigraphy analyses show that the carbonate succession consists of strata accumulated on a ramp, during cyclic sedimentation across the inner ramp. Here plurimetric ‘thin’ peritidal cycles (±4 m-thick on average) record a relative maximum sea level of ca. 4 m, with fluctuations in the range around 1-4 m. This shallow-water depth and the abundance of cyanobacteria suggest that water column was oxygenated. By contrast the subtidal cyclic facies at the outer/middle ramp, preserve ‘thick’ subtidal sequences characterized by an average thickness of ±17 m. Accurate relative sea level fluctuations are difficult to assess in this ‘deeper’ environment since the facies could have been deposited in a wide range of shallow water that did not completely fill the accomodation space or available space. A probable magnitude for sea-level fluctuations here is around 10-20 m. These data are the first to place a quantitative constraint on the late Mesoproterozoic to middle Neoproterozoic carbonate deposits that have lively covered much of the Congo Shield at the end of the Precambrian, and is therefore an important type section for Central Africa.