The Holocene maximum transgression in South America: Comparative progradation of coastal plains.

ISLA, F.I. & ESPINOSA, M.A.

Vigo, España

Simposio; II Simposio Internacional de Ciencias del Mar; 2009

Universidade de Vigo

Sea level has reached about 3 m in the last 6000 years in mid-latitudes of South America. This means that present coastline is the product of sediment supply in relation to tectonism, glacioeustatism and the previous slope of the coastal plain. Radiocarbon datings of coastal sequences from Argentina, Brazil, Chile and Uruguay have been stored into a GIS environment in order to analyze not only regional sea-level curves, but also the landward limit of the Holocene transgression. Sea level indicators were discriminated into beaches, estuarine deposits, tidal flats and peats. Shell middens were avoided in regard to their low precission in relation to the sea level. Maximum excursion of the transgression has been estimated for some bays and estuaries: Paraná delta (150 km), Negro estuary (42 km), Santos Bay (37 km), Samborombón  Bay (18 km), Mar Chiquita coastal lagoon (16 km), Deseado estuary (9 km), Bahía Blanca complex estuary (7 km), Quequén Grande estuary (7 km) and San Sebastián Bay (6 km). In terms of  progadation, it is hard to compare the product of Patagonian macrotidal regime with microtidal regimes of Northern Argentina and Southern Brazil. Atlantic coastal plains are more extended than those of the Pacific coast. In coastal lagoons, deltas prograde alongshore while fluvial deltas progrades across-shore. Within bays, beaches characterized distal portions while chenier plains are scattered on more recent supratidal flats. Estuaries occupying incised valleys have been usually obstructed by spits. The aggradation of coastal dunes was analyzed in relation to sand availability and wind regimes, in different stages of the Holocene sea-level fluctuation.