Nemba Complex Fm

Period:

Neoproterozoic

Age Interval:

Middle Tonian

Province:
West Congo Margin Basins

Type Locality and Naming

Lower volcanic formation in the Sounda 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. The Mayumba basin is exposed on the Mabouine´ and Mayumba complexes (de Wit et al., 2015; Fullgraf et al., 2024).

Synonym:

References: de Wit et al., 2015; Fullgraf et al., 2024

[Fig 1. Simplified geological map of the Congo Basin, compiled from various published map. The stratigraphic units have been assembled into major sequences (Late Neoproterozoic, Paleozoic and Cenozoic)]

[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

Meta-basalt and gabbro, green schist, epiclastics (de Wit et al., 2015; Fullgraf et al., 2024).

Lithology Pattern:

Volcanics

Relationships and Distribution

Lower contact

Major unconformity of nearly 1 billion years below. Unconformable on the coarse-clastics of the Bikossi Fm of upper Loeme Super Gr.

Upper contact

Overlain by the Kakamoek Fm of quartzite.

Regional extent

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

GeoJSON

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Fossils

Age

Dated at ca. 915 Ma => ca. 30% up in Tonian. The overlying Kakamoek Fm is dated at 903 and 915 Ma => used 910 = 32% 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:

0.30

Ending date (Ma):

916.00

Depositional setting

Initiation of continental rift.

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.