Un modèle de lagune d'âge protérozoïque supérieur: le schisto-calcaire du Congo

Abstract

The Upper Proterozoic lagoon of the Schisto-calcaire Cycle (West Congolian Supergroup) of the Nyanga-Niari basin (Congo, Gaboon) and the western end of the Comba basin (Congo), corresponds to internal shelf deposits isolated from the open marine environment by an oolitic and locally stromatolitic continuous barrier. In the East, this confined environment communicates with the open marine environment by a high followed by shelf deepening to the North East, towards the Congolian basin.

The interpretation of the outcrops in the basin from drilling data leads to interpret very peculiar mixed facies of dolomites and limestones as lagoon of deposits with evaporites. Sequence of the internal lagoon show calcareous or marly, detritic, bioclastic or stromatolitic basal unit bearing copper mineralizations.

The proliferation of algal mats, dolomite and evaporite deposits must be compared with the present limestone sedimentation in confined lagoons.