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 ».