Les bivalves du Crétacé Supérieur (Turonien) de la Formation de l'Azilé dans le bassin côtier gabonais : la Coupe de Nouvelle Cité

Upper Cretaceous (Turonian) bivalves of Azilé Formation within Gabonese coastal basin : 'Nouvelle Cité' section.- A study of Gabonese coastal basin Turonian bivalves has been carried out based on 186 specimens collected from Nouvelle Cité section in Libreville region. Fourteen species are recognised : Arca? sp., Cucullaea (Idonearca) thevestensis (Coquand, 1862), Exogyra (Costagyra) olisiponensis Sharpe, 1850, Exogyra delettrei (Coquand, 1862), Pycnodonte (Phygraea) vesiculosa (Sowerby, 1823), Camptonectes virgatus (Nilsson, 1827), Neithea (Neithea) cf. regularis (von Schlotheim, 1813), Plicatula fourneli Coquand, 1862, Plicatula ventilabrum Coquand, 1880, Unicardium matheroni Coquand, 1862, Protocardia cf. pauli (Coquand, 1862), Granocardium mermeti Coquand, 1862, Granocardium sp., and Liopistha (Sergipemya) alta (Roemer, 1852). Among those, Arca? sp., C. (Idonearca) thevestensis, P. (Phygraea) vesiculosa, N. (Neithea) cf. regularis, P. ventilabrum, U. matheroni, G. mermeti and L. (Sergipemya) alta are found here for the first time in the Gabonese coastal basin. The geographic range of C. (Idonearca) thevestensis, P. (Phygraea) vesiculosa, N. (Neithea) cf. regularis, U. matheroni, G. mermeti and L. (Sergipemya) alta is extended up to the Gabon. The stratigraphic distribution of U. matheroni is extended to the Turonian. In the Gabonese coastal basin, the stratigraphic and geographic ranges of P. cf. pauli (Coquand, 1862) and C. virgatus (Nilsson, 1827) are extended to the Turonian and to the Libreville region, respectively. The bivalves assemblage of the Nouvelle Cité section is dominated by the specimens of E. (Costagyra) olisiponensis and L. (Sergipemya) alta. Its composition suggests a marine environement with strong water energy that kept organic matter in suspension and a soft to rocky substrate. The assembly is looked at here as being parautochtone.