Holocene coastal evolution in Buenos Aires...

ISLA, F

Quaternary of South America and Antarctic Peninsula

Balkema

Lugar: Rotterdam; Año: 1998 p. 297 - 321

The coast of Buenos Aires Province evolved under condi- tions that changed during the last 6000 years. The sea level raised until that age and has been dropping since then. Some authors believe that some radiocarbon dates from beach ridges mean short-term sea-level rises in- stead of the simple topographic expression of a storm deposit. In some ar- eas, topographic differences have been explained by tectonic behaviour or different tidal ranges or wave set-up. In low-gradient areas, there was a progradation of beach-ridge plains interfingered with former tidal flats and coastal lagoons. In these areas lo- cal vegetational changes took place, when marshes developed and barriers helped to expand the psammophytic assemblages. In high-gradient regions, the Holocene coastal record is presented as beach ridges attached to palaeocliffs or infilled estuaries carved into Pleistocene continental deposits. These estuaries recorded the evolution of salinity indicators towards fresh-water assemblages. Sea-surface temperature changes have been proposed to explain dis- placements of mollusk taxa bearing on beach ridges. Several reasons were suggested to explain mass-mortalities of infaunal mollusks in former tidal flats. Changes in the composition of littoral deposits have also been re- corded. Present barrier dunes (Eastern and Southern) were the consequence of sand availability, dominant wind directions and heavy littoral drifts. How- ever, many beaches are today under critic erosive balances: some are the consequence of a very-modern sand scarcity or southeastern storm recur- rence; other erosion problems are induced by improper beach managements or to the anachronistic policy in coastal defense.