Sedimentology and chemostratigraphy of the late Neoproterozoic carbonate ramp sequences of the Huttenbeg Formation (northwestern Namibia) and the C5 Formation (western central Democratic Republic of Congo): Record of the late post-Marinoan marine transgression on the margin of the Congo Craton

The Neoproterozoic Marinoan climatic event corresponded to the Snowball Earth-type glaciation, and is commonly marked by the deposition of diamictites and by a negative carbon isotope anomaly. This event was followed by a sudden return to a greenhouse climate and a rapid post-glacial transgression with deposition of cap carbonates. Although the cap carbonates and marine carbonate sediments at the base of the post-glacial period are well known in the literature, few studies focused on the end of the marine transgression, which is a prelude to the Pan African Orogeny in Central Africa. In this paper, we present new descriptions of these carbonate rocks and a sedimentological study from key cores and outcrops in the Otavi Mountainland (Namibia) and West Congo belt (DRC) of the Huttenberg Formation and the C5 Formation, respectively. Both successions show five main facies: (i) microbial 'mounds' and pinnacles; (ii) ooid-shoal barrier; (iii) evaporitic brackish lagoon; (iv) beach and (v) coastal sabkha. The Huttenberg Formation consists of an open-marine mid-inner carbonate ramp setting including microbial mounds and pinnacles, and oolitic shoal-barrier islands. The C5 Formation exhibits a hypersaline inner carbonate ramp including an ooid shoal barrier, an evaporitic brackish lagoon, a beach and a coastal sabkha plain. Sedimentological, chemostratigraphical and biostratigraphical comparisons between the C5 and Huttenberg formations suggest these are coeval carbonate shelf deposits on the margins of the Congo Craton, with a depositional age between 580 Ma and 540 Ma for both formations.