Variations des lignes de rivage du plateau continental du Cameroun a la fin du Pleistocene (40 ka a 10 ka B.P.); chronologie et environnements sedimentaires

Abstract

Some 80 Kullenberg core samplings associated with high- resolution seismic reflection surveys allowed the analysis of the main sedimentary bodies of the Cameroon shelf as a result of the last glacio-eustatic movements. In some 16 core sections, it was possible to date the last oscillations of the shoreline--before or after the last glacial low-stand emersion--using 14 C. The high-stand of the isotopic stage 3 may not have reached -50 m. The last glacial low-stand was very near -130 m and for the first time on the West-African margin, the steps of the regressive process were analyzed and compared to the author9s eustatic graphs. On the outer shelf, a metric veneer of bioclastic gravels of the reef type was deposited between 14 and 12 ka B.P., during the very active eustatism phase at the beginning of the transgression. A pause in the transgression between 12 and 11 ka B.P. as a result of the Younger Dryas temporary cooling was often observed in the inherited morphostructural depressions which allowed the record. The bioclastic debris were extensively spread and reworked during this 12-11 ka B.P. relative stability of the shoreline. Some of these successions were considered at the wide scale of the Guinea Gulf shelves which show the same pattern. Hiatuses were observed as a result of the last low-stand, but the recorded stratigraphical lacunae do not seem closely related to the depth and to the emergence episode. A better conservation is probably associated with the subsiding property of narrow basins of aggrading sedimentation: inversely, the roofs of the shoals have been frequently planed off.