Negative sea level oscillation in Bahía Blanca Estuary related to a Global Climatic Change around 2,650 yr B.P

Abstract

Bathymetric and side scan sonar surveys, sedimentological analyses and boreholes carried out in the external zone of Bahía Blanca Estuary, determined the regional presence of cohesive fine-stratified layers cropping out at depths of up to 17 m below the present mean sea level. Sedimentological and micropalaeontological studies carried out on the most representative core give evidence of an alternating environmental energy during deposition as it currently occurs in muddy tidal plains. The lower core section consists of sediments which are deposited in a restricted intertidal environment. The middle section represents an intertidal environment which is more strongly influenced by the action of tidal currents as it currently occurs in tidal flats in close relation with a channel system. The upper section shows the gradual passage to present conditions (strong tidal currents). The core lower section (¹⁴ C 6350 yr B.P.) could have been deposited before the maximum Holocene transgression while its middle section (¹⁴ C 2460 yr B.P.) indicates the occurrence of an important negative mean sea-level oscillation that is correlated with evidence emerging from the coasts of southern Argentina and central-southern Brazil. The magnitude of this negative oscillation below the current sea level may be correlated with the worldwide climatic change that occurred around 2650 yr B.P. This suggests that the consequences resulting from relatively short perturbations in the global climate are more important than heretofore believed.