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Ngandu Formation
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Ngandu Fm base reconstruction

Ngandu Fm

Period: 
Ediacaran

Age Interval: 
571–575 Ma


Province: 
West Congo Basin / Bas-Congo region, DRC

Type Locality and Naming

Lukala area, Bas-Congo, DRC. The Schisto-Calcaire Subgroup is subdivided into C1–C5 formations (Delhaye & Sluys, 1923; Cahen, 1954).

Synonym:

Includes CIV unit. Occurs only in the Luozi region.

Reference section:


Lithology and Thickness

greyish to greenish clayey limestones, sometimes dolomitic, with lenticular intraformational breccia and dark cherty levels, reddish to pinkish limestone beds and red calcareous claystone interbeds, grey-greenish claystones with cherts, and reddish calcareous claystones with very thin greenish clayey limestones and pinkish limestones, evolving to reddish sandy claystones and fine-grained feldspathic quartzites Thickness: ~ 90 m.


Lithology Pattern: 
Clayey limestone


Relationships and Distribution

Lower contact

Underlain by the Bangu Fm.

Upper contact

Overlain by the Bangu and Niari Conglomerate (local) Fm.

Regional extent

West Congo Belt (DRC, Republic of Congo, Gabon, NW Angola).


GeoJSON

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Fossils

Stromatolites, cyanobacterial mats (Siphonophycus septatum), oolites, oncolites.


Age 

Anchor age "ca. 550 Ma" — BUT top of Mpioka is also assigned as 550 Ma (= onset of tectonic event) → perhaps 575 Ma is more realistic? "ca. 575 Ma upper limit used here to allow for karst erosion before deposition of overlying late-Ediacaran(?) Mpioka Gr"

Age Span: 

    Beginning stage: 
Ediacaran

    Fraction up in beginning stage: 
0.66

    Beginning date (Ma): 
571.51

    Ending stage: 
Ediacaran

    Fraction up in the ending stage: 
0.62

    Ending date (Ma):  
575.36

Depositional setting

Ramp composed of deep-marine outer ramp to shallow-marine inner ramp with oolitic shoal barrier, stromatolitic bioherms, lagoon- and sabkha-type environments (Cahen, 1954; Alvarez, 1995; Delpomdor et al., 2015).


Depositional pattern:  


Additional Information


Compiler:  

Cailteux, J.L.H., Delpomdor, F.R.A., & Ngoie Ndobani, J.-P. (2015). The Neoproterozoic West-Congo 'Schisto-Calcaire' sedimentary succession from the Bas-Congo region (Democratic Republic of the Congo) in the frame of regional tentative correlations. Geologica Belgica, 18/2-4, 126–146.