Artículo

Aspectos geomorfológicos del sector medio e inferior de la Pampa Deprimida, provincia de Buenos Aires

Geomorphological aspects of the middle and lower sectors of La Pampa Deprimida, Buenos Aires province
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Resumen

The Llanura Pampeana (Pampean Plains) is a geomorphological realm which is currently dominated by warm and humid climatic conditions, which promote almost exclusively, chemical weathering and fluvio-lacustrine processes. These are very contrasting with those processes developed in previous periods in which arid and semiarid conditions left the most conspicuous records. In the western sector of the Buenos Aires province, the Pampa Arenosa (Sandy Pampa) is developed, where longitudinal, parabolic and blowout, currently stabilized dunes, can be recognized. These features reflect extremely arid conditions. On the Coastal Plain, the littoral area of the Río de la Plata and the Atlantic Ocean, the topography is flat with wide flooded areas formed by lagoons, non-functional tidal channels, littoral barriers and dunes, associated with the post-glacial marine ingression of the Oxygen Isotopic Stage (MSI) 1. In this area, older records of high sea level can be also recognized. Between both areas, the Pampa Deprimida (Depressed Pampa) is developed. This is an elongate NW-SE depression with the Salado river as main collector and a large number of lagoons, some of which are silted. These lagoons are developed in deflation basins generated or re-activated at different times when climatic conditions were more arid. Lunettes are developed mostly on the NE sector. Stratigraphic survey at different sites of the Salado River showed fluvial deposits that ranged from the end of the late Pleistocene to the Holocene, with numerical ages from 13.400 ± 200 14C years BP to 680 ± 60 14C years BP. The origin of the depression of the Salado River is related to a combination of processes, in which physical-chemical weathering and deflation produced the gradual excavation of the landscape. Weathering was localized in some cases, producing deflation basins associated with lunettes. These processes where inhibited when warm-temperate conditions prevailed, triggering the fluvial processes which gradually silted the whole depression. The lagoons developed on the Salado River valley are in process of silting, while those located away from the main valley show minor changes in their shaping because of lesser sedimentary supply.

La llanura pampeana constituye un ámbito geomorfológico dominado actualmente por condiciones climáticas cálido húmedas, que promueven casi exclusivamente procesos de meteorización química y fluvio-lacustres, en un ambiente caracterizado por morfologías generadas en períodos áridos a semiáridos. El objetivo de este trabajo es describir los rasgos geomorfológicos más destacados del sector pampeano en la provincia de Buenos Aires, haciendo hincapié en las formas y procesos intervinientes en la Pampa Deprimida. En la Pampa Arenosa, sector Oeste de la provincia de Buenos Aires, se diferencian dunas longitudinales, parabólicas y hoyos de deflacción en la actualidad estabilizados. En la Planicie Costera se destacan extensos sectores inundables con lagunas, canales de marea afuncionales, cordones litorales y cadenas de dunas, asociadas a la ingresión marina postglacial (MIS 1). La Pampa Deprimida con el río Salado como colector principal presenta, cuencas de deflacción, lunettes y lagunas, algunas de ellas parcial o totalmente colmatadas. Relevamientos estratigráficos realizados en diferentes localidades del río Salado, permiten observar depósitos fluviales que abarcan la parte final del Pleistoceno y todo el Holoceno, con edades que fluctúan entre 13.400 ± 200 años 14C AP y 680 ± 60 años 14C AP, indicando que la acción fluvial para la depresión del Salado se habría desarrollado a partir del último máximo glacial.

Palabras clave
Quaternary
Pampa Deprimida
fluvial deposits
loess
Cuaternario
Pampa Deprimida
depósitos fluviales
lagunas
loess
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