BII Gr

Cenozoic

Mesozoic

Paleozoic

Neoproterozoic

Paleoproterozoic

BII Gr

Period:

Tonian

Age Interval:

Tonian

Province:
Southern Congo Margin

Type Locality and Naming

BII Group (Delpomdor et al. 2013) is in the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin, which is located between the Archean-Paleoproterozoic Kasai Craton to the north and west, and along the Mesoproterozoic Kibaran Belt to the south and east.

Synonym:

References: Bertrand-Sarfati 1972; Cahen and Mortelmans 1947; Delpomdor et al. 2013; Fernandez-Alonso et al., 2012; Kadima et al. 2011

[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 2. Tectonic setting of the Neoproterozoic basins of present-day Central Africa, compiled from the 1: 2M geological map of the Zaire (Lepersonne, 1974a) and the 1: 4MmapGeology and Major Ore Deposits of Africa (Milesi et al., 2006)]

[Fig 3. 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 4. 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 5. 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. 6. Southern margin of the Congo Shield. (A) Sketched geological map of the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin (modified after Raucq 1957, 1970). (B) Synthetic stratigraphic log combined with C and Sr isotopic curves of the Mbuji-Mayi Supergroup in the DRC (Modified after Raucq 1957, 1970)]

[Fig 7. Stratigraphic correlation between the Neoproterozoic sedimentary basins in Central Africa. Correlations based on Sr isotopic data, radiometric age constraints and revised lithological relationships]

[Fig. 8. Chrono- and lithostratigraphic section of the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin. This study focuses on the BIe to BIIe carbonates and black shales which were deposited in marine and lacustrine environments. Chronostratigraphy is from Cahen (1954), Holmes and Cahen (1955), Delhal et al. (1966), Cahen et al. (1974, 1984), Maheshwari et al. (1977), Delpomdor et al. (2013b) and François et al. (2017); depositional environments are from Raucq (1957, 1970), Delpomdor et al. (2015) and this paper (see text).]

[Fig. 9. (A) Simplified geological map of the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin in the Democratic Republic of Congo (see Fig 1), showing the location of the five studied boreholes and the two outcrops intersecting the BIe-BIIe subgroups. (B) Cross-sections of the Mbuji-Mayi succession which rests on Archean crystalline basement or on the Kibaran Supergroup in the SMLL Basin (profile lines are shown in Fig. 3A). Cross-sections A-A’ and B-B’ show a tabular Mbuji-Mayi succession resting on Archean basement; well Kafuku #15 in the Luembe area penetrates the BIe subgroup. Cross-section C-C’ shows that the Mbuji-Mayi succession in the Kiankodi area is folded, with dips of up to 60° (Cahen and Mortelmans, 1947). Cross-section D-D’ shows that the succession in the Makukulu area is folded with dips of 10-40°, and that it rests unconformably on the Kibaran Supergroup (Cahen and Mortelmans, 1947). Raucq (1970) suggested that the basin succession in general deepens to the south.]

[Fig. 10. Simplified geological map of the Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin (Democratic Republic of Congo) with location of (i) studied drillholes (S70 Tshinyama, B13 Kanshi, Bena Kalenda, Bena Tshovu, Kaf.15) stored at the Royal Museum for Central Africa (RMCA); (ii) studied drillhole of de Beers stored at the Société Minière de Bakwanga (MIBA); and (iii) samples retrieved from outcrops (226, 243, 628, Forminière) kept at the Royal Museum for Central Africa (RMCA). (from Delpomdor et al., 2013)]

Lithology and Thickness

1,000 m-thick carbonate, including stromatolitic bioherms (Bertrand-Sarfati 1972) with local shales.

Lithology Pattern:

Reef limestone

Relationships and Distribution

Lower contact

Overlies the BI Gr, with dolerite intrusions of ages apparently close to that facies change.

Upper contact

Unconformably overlain by the Kabale-Kabanga Fm glacial deposits of basal Cryogenian, considered as coeval with the Grand Conglomerate Formation (Cahen and Mortelmans 1947), may be correlated with the Sturtian-equivalent Tshibangu Formation and the Bandjia Tillitic Complex. Correlation figure in Dolpmodor and Preat (in de Wit et al., 2015) indicates a volcanic episode (timing of intrusions) during this hiatus interval.

Regional extent

The Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin

GeoJSON

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Fossils

Age:

Age

Age: The BII Gr is suggested (e.g., Dolpmodor and Preat (in de Wit et al., 2015)) to be is coeval with the Sansikwa Gr (ca. 880 to 720 Ma) in the West Congo Margin basins), and the top of the BII Gr is indicated on the correlation diagram of Dolpmodor and Preat (in de Wit et al., 2015) as extending nearly to the onset of the Cryogenian glacial. However, in the Sankuru-Mbuji-Mayi type area, five nearly concordant K-Ar whole-rock ages (Cahen et al., 1974) on amygdaloidal basalts overlying the Mbuji-Mayi Supergroup range from 870 ± 20 Ma to 953 ± 20 Ma. Those ages would conflict with being coeval with the Sansikwa Gr (ca. 880 to 720 Ma).

Age Span:

Beginning stage:

Tonian

Fraction up in beginning stage:

0.4

Beginning date (Ma):

888.00

Ending stage:

Tonian

Fraction up in the ending stage:

0.9

Ending date (Ma):

748.00

Depositional setting

Deposition occurs in a failed rift intracratonic basin (Kadima et al. 2011; Delpomdor et al. 2013). These successions are interpreted as deposits related to a tectonic reactivation of the Kibaran and/or Karangwe-Ankole mountains (Fernandez-Alonso et al. 2012), or as rift deposits during the first phases of Rodinia break-up.

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