Abstract

ISLA, Federico Ignacio  and  BUJALESKY, Gustavo Gabriel. Tendencias evolutivas y disponibilidad de sedimento en la interpretación de formas costeras: casos de estudio de la costa Argentina. Rev. Asoc. Argent. Sedimentol. [online]. 1995, vol.2, n.1-2, pp.75-89. ISSN 1853-6360.

Classical descriptions and evolutive models on coastal environments have been formulated from Northern Hemisphere studies; in other words, in relation to a Holocene sea-level rise. These models should not be extrapolated to other places (emergent coasts or with isostasy), neither regardlessly to the geological record. The argentine coast -more than 3,500 km long-, has a microtidal regime at Buenos Aires Province. Towards Patagonia, tidal ranges increase up to 10 m at Southern Santa Cruz and Northern Tierra del Fuego. It also increases into bays and gulfs and in relation to the width of the platform shelf. To the Beagle Channel, tidal range becomes again less than 1 m. Wave height varies along the coastline, also in response to the width of the platform shelf. Higher waves are generated by storms coming from the South Atlantic Ocean while waves coming from the north are smaller. The present paper analyzes critically models proposed globally that fail to represent eases from the Argentine coast, and particularly from Patagonia and Tierra del Fuego, i.e. a sea level dropping glacioeustatically for the last 5,000 years in a coast uplifting at a lower rate. The relationship between the tidal prism and the minimum flow area for argentine tidal inlets (coastal lagoons, bays and macrotidal estuaries) are statistically different. Sea-level stability is thought to be responsible of this trend. Minimum flow area are smaller in relation to the predicted tidal prisms of the model of O´Brien/Jarrett; exceptions are explained by a lack of sediment availability. Sand-consumption and cannibalism processes were also caused by the relative stability of the sea level during the last 5,000 years. The Eastern and Southern barriers of Buenos Aires evolved in response to different sand availability and due to the timing of sand exhaustion. Littoral drift reversals during this period indicate changes in the wind circulation patterns and are possibly paleoclimate indicators. The morphology at the beach-foredune boundary and the gravel-ridge overlapping at spits are the record of these cannibalism phenomena. Morphodynamic models proposed for macrotidal beaches are not applicable for those composed of gravel in the sense they have a reflective behaviour during high tide and dissipative at low tide. In gravel beaches, other processes as water-table, armouring and overtopping effects should be considered.

Keywords : Tidal inlets; Barriers; Classification of beaches and splits; Morphodinamic models; Coastal regime; Sea level changes; Sediment availability; Cannibalism.

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