Rio de la Plata inner estuary (Argentina). Main sedimentary forms and Holocene evolution

COLOMBO F.; SERRA F; BEDMAR, J. M.; ISLA, F.

Córdoba

Congreso; XIX Congreso Geologico Argentino; 2014

AGA

The Parana River, which in South America is surpassed only by the Amazon in terms of length and water discharge, generates a large delta in the Rio de La Plata Estuary. This estuary contains a variety of coastal systems with a dynamic complexity marked by fluvial and flooding processes of high magnitude, tides and prevailing southeasterlies that produce an upcurrent surge effect owing to estuary narrowing to the northwest. The distribution, chronology and shape of some of the features of the differentiated sand bodies such as beach and coastal ridges, cheniers, dunes, bars provide fresh insights into the physical and conceptual evolution of the sedimentary infill of the inner part of the Rio de La Plata Estuary. This estuary was generated between the last transgressive period?s maximum, and the progradational present stage during which the Parana delta attains a rate of about 28 m/a. The Ibicuy Delta underwent a combination of waves, surges and flooding events of the Parana River under high sea-level conditions. Parallel beach distribution coeval with the development of the beach ridge reflects different episodes of sea-level fall to its current position. This distribution was due to the northwest influence of water dynamics and the resulting sedimentary estuarine infill processes. Low sand bodies internal structure display progradational internal features as in the Ibicuy Delta front and Beach Barriers. Progradation rates can be deduced from the geochronology and the correlation of the main sedimentary structures. This is the case of the circa 250km long sequence of beach ridges on the northern side of the Parana River estuary. The present study of the inner part of the Río de la Plata Estuary throws new light on the morphogenetic control of sandy bodies and on their evolution during the last sea-level highstand and lowering. The preservation of these sedimentary features has been facilitated by the recent rapid fall in sea-level.