Enrique J. Schnack

Correlation and dating of Quaternary littoral zones along the Patagonian coast, Argentina

Six areas of the Patagonian coast, Argentina, were investigated in order to determine the number, characteristics, geomorphology and development of Quaternary littoral zones. It became apparent that utilizing dl ratios of aspartic acid and leucine of various molluscan species would be the most useful in correlation, relative age dating and estimating the ages of these zones. The oldest littoral zone is found at elevations between 24 and 41 m above mean sea level and is judged to be older than Oxygen Isotope Substage 5e in age based on relatively high amino acid ratios and extrapolated from non-linear kinetic models. An intermediate aged littoral zone may be present at some locations based upon beach ridges or platforms varying in elevation between 16 and 28 m above mean sea level. dl ratios are generally lower than those for the oldest zone but show a greater variation. This zone may represent the Substage 5e sea level stand. Well defined young beach ridges 8–12 m above mean sea level are found in most locations and have been 14C dated, and verified by amino acid ratios, as being Holocene. The presence of Quaternary aged emerged littoral zones at roughly the same elevation suggest that the glacio-eustatic contribution is the primary cause of the high sea level stands whereas secondary variations are attributed to other factors.

Pleistocene and holocene beaches and estuaries along the Southern Barrier of Buenos Aires, Argentina

Abstract The Buenos Aires aggradation plain has a good record of Quaternary sea-level fluctuations. To the east of the Tandilia Range, the elevations of the Pleistocene beaches respond to the tectonic behaviour of the Salado Basin. Holocene beaches indicate a maximum transgression higher than 2 m. The low relief permitted an extended horizontal record of beach/chenier plains interfingered with estuarine environments (coastal lagoons, marshes) covered by a sandy (Eastern) barrier. Between the Tandilia and Ventania ranges, the location of Pleistocene and Holocene beaches are related to a former higher relief; i.e. they are attached to low-altitude cliffs and underneath cliff-top dunes composing the Southern Barrier. At Claromeco, Pleistocene gravel beaches, mostly composed of caliche pebbles, occur at heights between 4 and 7 m, and are overlying estuarine Pleistocene environments. Beaches of the same age are at a level of 10 m at Mar del Plata Harbour and Arroyo Sotelo (west of Mar Chiquita Lagoon). Holocene beaches found at Punta Mogotes and Costa Bonita are at higher altitudes than on the Eastern Barrier (ca. 2–4 m). The Holocene estuarine sequences are related laterally to present operating inlets (Las Brusquitas, La Ballenera, Quequen Grande, Claromeco, Quequen Salado). They are seldon thicker than 2.4 m, and comprise basal layers of black muds; towards the top, the layers are thinner, of coarser grain size and white colours. Grain-size analyses were performed comparatively on Pleistocene, mid-Holocene and present beaches. Sangamonian beaches aregravelly or coarser than medium sand (mean). Holocene beaches are usually coarser than medium sand, but dominantly shelly to the north of Mar del Plata, and composed of volcanic clasts to the south of this city. Modern beaches are dominated by fine sand, except at some erosive beaches between the Mar del Plata capes. They have a lesser content of shells than those of mid-Holocene.

Sea Level Changes During Marine Isotopic Stage 3 (MIS 3) in Argentina

Marine Isotopic Stage 3 (MIS 3) was a period of rapid climatic changes and sea level fluctuations. Regarding these fluctuations some doubts were based on the limit of the radiocarbon dating method (about 50,000 years B.P.). However, the modelling of the isotopic oxygen ratios is also indicating sea level fluctuations. In this sense, only at certain depths it is possible to accept these ages at stable coasts, and taking note about the taphonomic conditions within the sequence. Shells located at depths higher than 60 m on stable and wide continental shelves as that of the Northern Patagonia have been analyzed here in that sense.

The Changing Coastlines of South America

South American coasts are subject to many different natural hazards. In general terms, the Pacific coast is tectonic, and therefore, earthquakes and tsunamis are likely to occur in this area. The Caribbean coast is constantly subject to trade winds and episodically to hurricanes and tsunami-triggered waves. The Atlantic coasts of Brazil, Uruguay, and Argentina suffer the action of storm surges coming from the south (southeasterlies). At the same time, the South American coast is particularly exposed to El Nino-Southern Oscillation (ENSO)-triggered effects. These effects are different in different regions. In Colombia the seasonal increase of the mean sea level alters the dynamics of barrier islands. In Peru, ENSOs are responsible for sudden inputs of sediments to the coast; similar processes impact the estuarine complexes of Lagoa dos Patos (southern Brazil) or Parana-Rio de la Plata floods (Argentina–Uruguay). In northern Brazil, on the other hand, dry conditions induce the migration of dunes landward. In several countries of South America, population is concentrated at or near the coast, and therefore some natural coastal processes increase their impacts. In recent years, erosion effects have been more severe due to the action of humanity.

Sea foam as a sediment transport agent

Abstract Some aspects of sea foam as a sediment transport agent are discussed. Sediment-loaded foam in large amounts can occasionally occur at the shore. This situation was observed by the authors on May 1, 1980, at Mar de Cobo beach. Here wind action removed foam fragments from the 0.50 m thick foam layer, and initiated their movement by rolling and saltation up the backshore and the dune system. A similar but much less intense phenomenon was observed on September 30, 1980, at Mar Chiquita lagoon inlet. Foam samples were obtained and their sediment content was analysed. Finer sediments were found to belong to the initial foam content, while coarser ones (sand and shell fragments) were seen to have been incorporated by the “foam rolls” during transportation. This phenomenon is significant in relation to: sediment contamination of perimarine environments, anomalous grain-size distributions in sand dunes and salt concentrations in soils.