SUDDEN LATE QUATERNARY LOWERING OF THE SO UTHERN GUINEAN CONTINENTAL-MARGIN - SEDIMENTARY EVIDENCE

During the EQUAMARGE II cruise (1988) along the Guinean continental ma rgin (central Equatorial Atlantic) a 2.17 m long core has been sampled at 840 m water depth on the top of one of the volcanic seamounts crop ping out in this area. Planktonic foraminiferal assemblages observed w ithin the 2.13 m unconsolidated sediments indicate an age of 0.20 to 0 .15 Ma, corresponding to the transition from interglacial to glacial e vents. Depth of deposition of the calcareous sand ranges between 150-2 00 m and progressively decreased during the glacial stage onset. Detai led sedimentological and micropaleontological studies, carried out on the 4 cm thick indurated core cap, indicate a deposition depth of 50-1 00 m, or even less. Taking into account the Pleistocene sea level fluc tuations, these data suggest a rapid subsidence of the magmatic seamou nt since the upper most Pleistocene.