CECOAL   02625
CENTRO DE ECOLOGIA APLICADA DEL LITORAL
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
The megafan of the Paraná River from the Pleistocene to the Present
Autor/es:
ORFEO, O.; IRIONDO, M.
Lugar:
Mendoza
Reunión:
Congreso; 18th International Sedimentological Congress; 2010
Institución organizadora:
International Association of Sedimentologists
Resumen:
Downstream of the basaltic plateau located at the south of Brazil and northeastern of Argentina, the Parana River flows in the extensive Argentine plain. In the first stretch, the river generates a large alluvial fan (or Megafan), which covers the northwestern portion of the Corrientes Province in Argentina and the southern part of eastern Paraguay. The megafan is 260 km long and 500 km wide in the distal part, and has been stable for most of the Upper Quaternary. Inside it, the river channel built relatively stable belts occupied during some hundreds or thousands of years, eventually abandoned by the main stream and replaced by large swamps. A sequence of such intervals formed the present megafan. A few extensive deposits produced by spill outs during dry climatic phases in the Upper Quaternary are intercalated among the abandoned belts. Also during dry phases, important deflation of sand occurred in the abandoned belts, generating up to 80-km-long and 5-km-wide dune fields. Most of these fluvial deposits are named Ituzaingo Formation in Argentina, and represents the typical sedimentation of the Parana River all along its evolution. The present river belt crosses the fan in an east–west direction; the channel design there is braided, with frequent elliptical islands and sand bars. The youngest abandoned belt in the megafan is Holocene in age and runs along the eastern limit of the system and includes some present lakes of the Ibera wetland. Paleocurrent directions measured in the Ituzaingo Formation at Corrientes Province suggest alternative expansion and downstream migration of the Parana River. A comparison between these old and present fluvial deposits revealed that both are homologous, but the first ones seems to be smaller than those belong to the main channel of the present river, and would be related with the sedimentation of lateral and central channel-bars. In change, the present deposits showed sedimentological features linked with higher energy conditions compared with the paleodeposits.