Morphology of the Atlantic coast between Punta Ninfas and Cabo Dos Bahías, Chubut, Argentina.

Abstract

A description and genetic analysis of themorphological units present in the northwestern coastal area of Chubut province, betweenPunta Ninfas and Cabo Dos Bahías, along 300 km approximately, were carried out. Thiswork aims to define the processes that have acted to shape the different geomorphologicalfeatures of the area. Also, based on the morphological traits evaluate changes in sea level thattook place during the Quaternary. In a semiarid environment, with temporary water courseswith the exception of the Chubut River, several morphological units were developed. Morphological and geological maps, aerial photographs (1:20.000 scale) and in situ detailedsurveys data were used to determine the units present in the area. Topographical profilesbetween tide levels using the Emery method adapted to large beaches were performed andmorphological examinations into the continent were made up to about 10 km from the coast.Tectonically, are classified as Trailing edge coasts. According to its structure are ruggedcoastlines. Correspond to coasts under the action of storm waves caused by winds reach 10m/s. Among the morphological units continental and marine types were recognized. Thecontinental forms are integrated by terraces, depressions, valleys and gullys. Among themarine units active and inactive units were found. The active marine units determined were:cliffs, beach ridges, beaches, wave-cut platforms, coastal dunes and tombolos. The inactivemarine units determined were: palaeo cliffs, coastal lagoons and raised beaches. In themorphological modeling area have involved reactivation tectonic processes in conjunctionwith changes in sea level. The structures of positive and negative relief would be linked totectonic reactivation occurred during the Pleistocene. The Holocene initiate with atransgressive cycle; towards the middle Holocene around 6000 yr BP began a regressivecycle leaving raised beaches, boulder beds and coastal lagoons in sedimentary silting process.One last ingressive cycle between 4000 and 2000 BP have modeled some bays, beach ridges,wave-cut platforms and notches originated at the foot of the cliffs. The presence of a step inthe abrasion wave-cut platforms may be an index of sea level fall and a current period ofstabilization. At present, marine erosion is favored in jointed wave-cut platforms.Sedimentary material generated by marine erosion (sand and pebbles) are transported by theaction of longshore drift. To the northern sector of the study area the beaches are open typewhile southward pocked beaches are dominant. Cliff top dunes occur in bays closed by cliffs.