Cenozoic

Mesozoic

Paleozoic

Neoproterozoic

Paleoproterozoic

Alolo Formation

Alolo Fm

Period:

Cambrian

Age Interval:

earliest Cambrian

Province:
Northern Congo Margin

Type Locality and Naming

Upper unit of the Aruwimi Gr. 200m thick middle grey zone of the Alolo shales is exposed along the lower course of the Aruwimi River near Yambuya (Sechse et al., 2011).

Synonym: Alolo Subgroup

Reference: De Wit et al., 2015; Kadima et al., 2011; Trompette,1994;Sechse 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, 1974) and the 1: 4M map Geology 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. 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. Northern margin of the Congo Shield. (A) Geological sketch map of the Lindi Basin (modified after Verbeek 1970; Poidevin 1985)]

[Fig 7. Stratigraphic logs of the Lindi Supergoup in the DRC (modified after Verbeek 1970). (C and D) Stratigraphic logs of the Lindi Supergoup in CAR (modified after Poidevin 1985). cc cap carbonates, SG Sturtian Glaciation, MG Marinoan Glaciation]

[Fig 8. 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 Alolo Fm is made up of 100m red dark shales and sandstones with limestone intercalations (de Wit et al., 2015).

Lithology Pattern:

Continental marl

Relationships and Distribution

Lower contact

Lies on Galamboge Fm below

Upper contact

Overlain by the Banalia Gr

Regional extent

Extend in the Lindi Basin of the northeastern DRC. Trompette (1994) considered this basin and Fouroumbala-Bakouma basins of the south-western CAR, and to be part of the Lindi Basin

GeoJSON

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Fossils

Age

Arbitrarily put as the Cambrian portion of the Aruwirri Gr for graphic purposes

Age Span:

Beginning stage:

Fortunian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

538.80

Ending stage:

Cambrian Stage 2

Fraction up in the ending stage:

1.0

Ending date (Ma):

521.00

Depositional setting

Lacustrine to lagoonal depositional environment (Kadima et al., 2011)

Depositional pattern:

The shales of the Alolo Subgroup contain types III – IV Kerogen, which disqualifies the subgroup as a potential oil source rock (Sechse et al., 2011).

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

Kadima, E., Delvaux, D., Sebagenzi, S.N., Tack, L., Kabeyaz (2011). Structure and geological history of the Congo Basin: an integrated interpretation of gravity, magnetic and reflection seismic data Basin Research (2011) 23, 499–527, doi: 10.1111/j.1365-2117.2011.00500.x