Loia Gr

Cenozoic

Mesozoic

Paleozoic

Neoproterozoic

Paleoproterozoic

Loia Gr

Period:

Cretaceous

Age Interval:

Albian

Province:
Northern Congo Margin, Southern Congo Margin, Central Congo region

Type Locality and Naming

The Loia Fm (Gr) was first recognized in the Dekese well by 254 m of aeolian sand dunes (Cahen et al. 1960; Linol 2013) and in the Samba well, by 280 m of shallow lacustrine sandstones and mudstones with a few thin black shale levels (Cahen et al. 1959, 1960).

Synonym: Loia Fm; Unit S4 of the Samba Well section (de Wit et al., 2015).

Reference: Cahen et al. 1960, 1960; Linol et al., 2015; Kadima et al., 2011; Linol 2013; 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

Made up of sandstones-mudstones (Kadima et al., 2011). Loia Group (Unit S4) is 280 m thick, and comprises green and analcime-rich, poorly sorted, sandstones and mudstones with black shale intercalations (Cahen 1983); or to southeast, lacustrine argillaceous and calcareous sandstones, argillites and marls including thin conglomerates and black shales (Maheshwari et al., 1977; Delhal and Ladmirant, 1979; Linol et al., 2015) where the top of this sequence is a distinct silicified layer (de Wit et al., 2015).

Lithology Pattern:

Relationships and Distribution

Lower contact

Lies conformably on upper Jurassic of the Kisangani Gr (Linde basin), or unconformably on Permian of the Lukuga Gr (Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin of SE DRC).

Upper contact

Overlain conformably or unconformably by Bokungu Gr

Regional extent

Located in the northeastern DRC (Lindi Basin) and southeastern DRC (Sankuru-Mbuji-Mayi-Lomami-Lovoy Basin).

GeoJSON

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Fossils

fossil fish (Casier, 1961) and pollen (Boulouard and Calandara,1963), non-marine phyllopods (Bairdestheria kasaiensis, Pseudoasmussia banduensis, P. dekeseensis, Asmussia dekeseensis, A. ubangiensis and Euestheria sambaensis; Marlie`re 1950; Defretin- Lefranc 1967) and ostracods (Cypridea elisabethaensis, C. maringaensis, C. yakokoensis, Ilyocypris lomamiensis, I. minor, Metacypris polita, M. pustulosa and Pattersoncypris rotunda; Grekoff 1957; Colin 1994), pollen

Age

Albian (Linol et al., 2015, Fig. 11.4)

Age Span:

Beginning stage:

Albian

Fraction up in beginning stage:

0.0

Beginning date (Ma):

113.20

Ending stage:

Albian

Fraction up in the ending stage:

1.0

Ending date (Ma):

100.50

Depositional setting

Continental – shallow lacustrine (Kadima et al., 2011, Delpomdor et al., 2018)

Depositional pattern:

Additional Information

The Loia Group is considered an excellent petroleum source rock and could be part of a petroleum system, where sufficient burial and maturation occurred (Sechse et al., 2011).

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

Linol, B., de Wit, M.J., Guillocheau, F., Robin, C., Dauteuil, O., (2015). Multiphase Phanerozoic subsidence and uplift history recorded in the Congo Basin: A complex successor basin. In: M.J. de Wit et al. (eds.), Geology and Resource Potential of the Congo Basin, Regional Geology Reviews, DOI 10.1007/978-3-642-29482-2_11, # Springer-Verlag Berlin Heidelberg 2015

Giresse, P. (2005). Mesozoic-Cenozoic history of the Congo Basin. Jour. African Earth Sciences, 43: 301-315. doi:10.1016/j.jafrearsci.2005.07.009

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