Loeme Super Gr

The Nyanga-Niari Basin in the northern part of the West Congo Belt on the western margin of the Congo Shield comprises two distinct geologic domains from west to east, i.e. the metasedimentary hinterland domain and the unmetamorphosed internal domain, i.e. the Nyanga syncline. The Mayumba basin is exposed on the Mabouine´ and Mayumba complexes. All rocks of Palaeoproterozoic (Eburnean orogeny) age are now combined into the Loeme Super Gr (Loémé Supergroup); the unit is further subdivided into the autochthonous Loukoula Fm (Group) intruded by the calc-alkaline Bilinga Suite Gr, and the allochthonous Bikossi Fm (Group).

Synonym: Loémé Supergroup; Loeme Supergroup

References: Fullgraf et al., 2024.

[Fig 1. Lithostratigraphic synthesis for the Neoproterozoic to Early Paleozoic period. Compiled after various authors (see text).Dotted lines between Banalia, Alolo and Galamboge formations: stratigraphic transition by recurrences.]

[Fig 2. Lithostratigraphic columns for the Congo Basin established using data from the 4 wells in the central part of the basin and outcrops on its NE margin (Lindi-Ubangi and Kisangani-Kindu region), compared with the West-Congo and Katanga stratigraphy.]

[Fig 3. Simplified geological map of Sub-Saharan Africa showing the Neoproterozoic basins on and around the Congo Shield (modified after De Waele et al. 2008). (LC) Lower Congo Basin, (Co) Comba Basin, (Sa) Sangha Basin, (Ny) Nyanga-Niari Basin, (An) Angola Basin, (SO) Semb-Ouesso Basin, (Ba) Ubangui Basin, (LiB) Likki-Bembe´ Basin, (Bk) Bakouma Basin, (Fou) Fouroumbala Basin, (Li) Lindi Basin, It Itombwe Basin, (Ma)Malagarazi-Bukoban Basin, (Mb) Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin, (Lu) Luamba Group, (Kat) Katanga Basin, (RB) Ruwenzorian Belt, KaB) Karagwe-Ankole Belt, (RuB) Ruzisian Belt, (KiB) Kibaran Belt,(UB) Ubendian Belt, IB Irumide Belt]

[Fig. 4. Stratigraphic correlation between the Neoproterozoic sedimentary basins in Central Africa. Correlations based on Sr isotopic data, radiometric age constraints and revised lithological relationships]

Ca. 75% up in Rhyacian to 28% up in Orosirian (2110 to 1980 Ma) on Fig. 21 of Fullgraf et al. (2024). The maximum age of sedimentation and high-grade metamorphism of the migmatitic paragneiss is constrained by U-Pb SHRIMP analyses of detrital zircons to 2111-2064 Ma. Late Eburnean U-Pb zircon SHRIMP ages between 2028 and 2060 Ma have been determined on orthogneisses of tonalitic to granitic composition from the Bilala, Bilinga and Les Saras quarries which, together with similar geochemistry and Neo-Archaean NdTDM model ages, constrains their common origin in the late stage of the Eburnean orogeny. These intrusions are now combined into the Bilinga Suite. Deposition of the Bikossi Gr post-dates Eburnean plutonism and pre-dates Tonian magmatism. U-Pb SHRIMP and LA-ICP-MS analysis of detrital zircons from basal quartzite constrains maximum deposition ages of 2043 ± 13 Ma and 1971 ± 40 Ma, respectively being indicative for the erosion of Eburnean middle crust and the interpretation as a molasse (Fullgraf et al., 2024).