Paleoenvironments in Meso–Neoproterozoic carbonates of the Mbuji-Mayi Supergroup (Democratic Republic of Congo) – Microfacies analysis combined with C–O–Sr isotopes, major-trace elements and REE + Y distributions

Abstract

The Meso- and Neoproterozoic Mbuji-Mayi Supergroup (1155 Ma to ca. 800 Ma) was deposited in the SE–NW trending siliciclastic-carbonate failed-rift in the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. Drillcore- and outcrop-derived microfacies, isotope (C, O and Sr) compositions of carbonates and REE + Y distributions are integrated to unravel the paleoenvironmental and chemical conditions prevailing during deposition and alteration (or contamination) of the Mbuji-Mayi carbonates. The carbonate succession (BIe subgroup and BIIa to BIIe subgroups), composed of 11 microfacies (MF), records the evolution of a marine ramp submitted to evaporation, with basinal and low-energy outer-ramp environments (MF1–MF5), biohermal mid-ramp (MF6) and restricted tide-dominated lagoon inner-ramp (MF7–MF9) settings, overlain by lacustrine (MF10) and sabkha (MF11) environments. The ramp margin is characterized by thick stacks of stromatolitic bioherms. d13C and d18O relationships in the Mbuji-Mayi carbonates...