In the Lower Sangha through, apart from the glacial deposit of lower and upper Diamictites, detrital sedimentation is represented by the shales and sandstones of Sansikwa and Petite Bembezi formations as well as by conglomerates, shales and sandstones of the Mpioka Subgroup related respectively to the Tonian, the Cryogenian and the Cambro-Ordovician. The carbonate precipitation of Sekelolo and Schisto-Calcaire in the saline waters from the Adamastor paleo-ocean in the Araçuai basin in Brazil are responsible for the interruption of this detrital sedimentation in the entire West Congo basin. In the latter, the erosion of the stepped limestone plateaus, vector of the clasts of the Bangu-Niari conglomerate at the base of the Mpioka Subgroup, sufficiently proves that the releases from the faults of the substratum reactivated in the underlying limestones before the pan-African orogenic thrust had caused the total withdrawal of the sea in the Mayumbe North, Mayumbe South and Lower Sangha throughs. In this aulacogen of the Lower Sangha, the weak accommodation of the Mpioka lake submerging the collapsed median compartment, hardly exceeding the rejection of the border faults, justifies the restriction of the Mpioka deposit only to the Bangu plateau, a collapsed compartment at the both normal and reverse conjugate faults.

In the Western Congo Basin, The C4a Member of the Lufu-Toto region is characterized by the combination of mixed silico-clastic carbonate facies and purely carbonate facies divided into four zones of the facies. The first area of facies (ZF1) is characterized by the gray-green marls with lenticular bedding of maritime marshes, the purple marls with planar bedding of muddy flat and the dolomitic shales of salt pond. The second zone of facies (ZF2) is characterized by mixed flat sandstone marls. The combination of these two areas with the tidal channels (ZF4) translated by the purple marls with oblique bedding is typical of a macrotidal coast, adjacent to the restricted lagoon (ZF3) with laminar limestone, mudstone limestone and gray dolomite otherwise called « coastal-lagoon complex ».