Holocene beach ridge evolution at Río de la Plata estuary, Argentina: Former answers for future questions?

LEANDRO D´ELIA; AUGUSTO N. VARELA; MARINA L. AGUIRRE; DR. SEBASTIAN RICHIANO; ANDRES BILMES

Workshop; 2nd NEPTUNE INTERNATIONAL WORKSHOP; 2021

The Holocene shows rapid climatic changes associated with alternating intervals of glacier advances and retreats. The coastal regions, where beach ridges constitute common preserved landforms, are highly sensitive to register such changes and bring light into past littoral environments. Excellent marine Argentinean Holocene deposits associated with the last climate optimum are preserved at the Río de la Plata estuary (Argentina). In this beach ridge a palaeoenvironmental model was performed, including the analysis of major hierarchy surfaces (clinoforms) that subdivide it into eleven clinothems (two siliciclastic; nine carbonatic). Selected clinothems were dated between 5,240±110 and 3,900±90 calBP, while stable isotope analyses allowed to infer that the temperature during the evolution of the ridge has two maximum values of 22.5 ºC. The sudden change from sandy to carbonate sediments in the ridge, could be interpreted as a combined result of an increase of carbonate productivity along with a decrease of siliciclastic supply at the coast. This stage would have been developed approximately around 5ka B.P., when propitious climatic conditions may have led to the proliferation of large communities of warm-temperate benthic organisms. We stress that, the strong activity of the Brazilian current during the Mid-Holocene enabled excellent conditions for the development of a carbonate warm beaches similar to that occurring at tropical and subtropical areas nowadays. This study provides an example of the strong changes occurred in coastal environments as a result of climate change, particularly in the context of global warming episodes which characterized interglacial periods of the Late Quaternary in eastern South America.