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Sounda Gr

Sounda Gr

Period: 
Neoproterozoic

Age Interval: 
Middle Tonian


Province: 
West Congo Margin Basins

Type Locality and Naming

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. The Mayumba basin is exposed on the Mabouine´ and Mayumba complexes.

Synonym:

References: de Wit et al., 2015; 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]


Lithology and Thickness

The 1000–850 Ma Sounda Gr consists of basal volcanics (Nemba Complex Fm), lower quartzites (Katamoek Fm), granitic intrusions (Mt. Kanda – Mfoubo Fm), terminating in sandstone (Mvouti Fm). The hinterland domain comprises the Loukoula Gr, fluvio-glacial sedimentary M’beia Fm and metasedimentary 713 ± 49 Ma Louila Fm (de Wit et al., 2015; Fullgraf et al., 2024).


Lithology Pattern: 
Sandstone


Relationships and Distribution

Lower contact

Major unconformity (ca. 1 billion years). Below is the Bikossi Fm of the Loeme Super Gr.

Upper contact

Overlain by the clayey sandstone of the Mssouva Fm at the base of the Mayombe Gr.

Regional extent

Niari Basin (Gabon) and Mayombe Chain (RC and Gabon)


GeoJSON

null

Fossils


Age 

Ca. 915 Ma date on basal Nemba Complex Fm volcanics until beginning of basin fill at 870 Ma (base of Mossouva Fm) = 30% to 45% up in Tonian

Age Span: 

    Beginning stage: 
Tonian

    Fraction up in beginning stage: 
0.30

    Beginning date (Ma): 
916.00

    Ending stage: 
Tonian

    Fraction up in the ending stage: 
0.45

    Ending date (Ma):  
874.00

Depositional setting

Neoproterozoic continental rift (ca. 1000 – 870 Ma)


Depositional pattern:  


Additional Information


Compiler:  

Enam O. Obiosio, Solomon Joshua Avong and Henry Nasir Suleiman (2024) - Stratigraphic Lexicon compiled from the following books:

Geology and Resource Potential of the Congo Basin by Maarten J. de Wit, François Guillocheau and Michiel C.J. de Wit , Published Springer-Verlag Berlin Heidelberg 2015; DOI 10.1007/978-3-642-29482-2

Fullgraf, T., Callec, Y., et al. (2024) Structural architecture and metamorphism of the Mayombe Chain and Niari Basin (West Congo Belt) in Congo Brazzaville. Jour. Afr. Earth Sci., 220: article 105369.