According to local nomenclature, there are four sub lagoons that represent the lagoon system of Grand-Lahou. The Tagba lagoon is the most important one because it is in contact with the sea through the mouth of Bandama river. The Morphology and the bathymetry constitute a challenge for local residents whose main activity is fishing. The present study aimed to update the bathymetry of the lagoon. The depths obtained are low, 3 m on average with maximum of 6 meters. The action of river currents and tidal current is responsible of the morphology of channels.

The petrography of Miocene ferruginous muddy sandstones of Bingerville permitted to understand the transformation of muddy sands to muddy sandstones. The muddy sands lithification starts during the rainy seasons which distribute the iron hydroxides in the kaolin of muddy sands. During the evaporation of pore waters during the arid seasons, the iron hydroxides lose their water. These hydroxides are transformed into iron oxides supporting the transformation of muddy sands to muddy sandstones thanks to ferruginous cement. This cement derives from the total oxidation of the ochreous matrix. This matrix is a mixture of kaolinite and iron oxides. These muddy sandstones are quartz wackes with ferruginous cement. There are always nano-vacuums between the grains of quartz and ferruginous cement which surrounds them. These nano-vacuums are the spaces left after the evaporation of pore waters which surrounded the grains of quartz. Quartz of quartz wackes are transformed into iron oxides through their weakness zones. That is supported by the lot of iron oxides in the sedimentation environment. The muddy sands lithification of Miocene took place at Holocene thanks to their exposure in subaerial environment and/or aerial.