Submarine evidence of Holocene sea-level fluctuations in the Bahيa Blanca estuary, Argentina

Sedimentological and micropaleontological studies were carried out on a core representative of regional submarine outcrops located in the external area of the Bahيa Blanca estuary. Three different zones were characterized within the core. The lower core section is composed of sediments deposited in a restricted intertidal environment, such as a coastal lagoon or the upper part of extensive and vegetated tidal flats, whereas sedimentation in the middle section was influenced more by the action of tidal currents, as presently occurs in tidal flats closely related to a channel system. The upper section of the core shows the gradual passage toward modern conditions, in which sand is transported as bedload by strong tidal currents. The characteristics of both the lower and middle sections of the core indicate a relative mean sea level located below that of the present. The lower section probably was deposited before the maximum Holocene transgression, and the age of the core middle section indicates an important negative mean sea-level oscillation that could be correlated with a worldwide climatic change around 2700 yr BP. This finding indicates that relatively short perturbations in global climate could have more important consequences than heretofore has been believed.