Resumen de Migración de campos de dunas en cañadones costeros de patagonia. Geomorfología e implicaciones paleoclimáticas
Alejandro Montes, Silvana Soledad Rodríguez, Cristina Natalia San Martín, José Oscar Allard
- español
Este trabajo presenta una caracterización de geoformas eólicas erosivas y deposicionales, vinculadas a la migración de campos de dunas en la Patagonia extraandina, en torno a la latitud de 46° S. Estos campos de dunas migran a través de una zona de cañadones labrados en rocas sedimentarias de edad Oligoceno-Mioceno y orientados oeste-este, en coincidencia con la dirección predominante del viento. Estos, están constituidos por dunas transversales barjanoides y en el frente por mantos arenosos. En los sectores interdunares hay microyardangs, pavimentos desérticos, raíces y estructuras pedogenéticas exhumadas. A barlovento y orientadas según la dirección predominante del viento, quedan preservadas crestas arenosas entre las que se identifican rasgos erosivos que permiten reconocer el recorrido sinuoso e irregular realizado por los campos de dunas. Mediante la utilización de imágenes de satélite obtenidas entre los años 2003 y 2013, se realizaron medidas de la velocidad de avance de dos campos de dunas activos, con valores promedio de 29,6 y 70,0 m/año. Teniendo en cuenta estas velocidades y la longitud de los rastros que dejaron a su paso, se estima que dichas dunas estarían migrando desde mediados a fines del siglo XIX d.C. En el presente trabajo se describe el modelo de migración de estos campos y las interpretaciones paleoclimáticas que se desprenden del análisis geomorfológico de su entorno.
- English
Erosional and depositional aeolian landforms related to dunefield migration in Patagonia (Argentina) was characterized using satellite images around 46° south latitude. In this semi-arid region, dunefields moved in west-east direction oriented canyons carved in Oligocene-Miocene sedimentary rocks, parallel to prevailing wind direction. The continuous movement of the dunefields is associated to a self-feeding mechanism based on interdunar and windward erosion. Shrub vegetation is covered by wind deposits, leaving a windward vulnerable area to wind erosion. This process provides sediments to dunes and contributes to their movement. Dunefields margins, parallel to the prevailing wind direction, often remain preserved as longitudinal sandy ridges, because their deposits did not cover entirely the vegetation which trapps the sediments. An erosive trace is preserved between the sandy ridges. Both landforms (sandy ridges and erosive traces) allow us to recognize where dunes movement began and to know which their path was. Actives dunefields consist of barjanoid transverse dunes, 1 to 4 m high, and thin sandy sheets at their front (up to 1,2 m) with topographic irregularities generated by accumulations behind bushes (nebkas). Microyardangs, desert pavements, exhumed roots and palaeosoil structures was recognized in interdune areas. Satellite images of 2003-2013 were used to measure the advance of dunefields speeds and their speeds of the advancing front of two actives dunefields were 29,6 and 70,0 m/years. Taking into account these advance speeds and the length of their erosive traces, the dunes are migrating since 169 and 128 years from today. Study area have not sediment generator environments like occurs in other dunefields of Patagonia, where sediment availability is related to lakes or sea gulf beaches. Therefore, the origin of the studied dunefields would be associated with drier weather conditions in mid to late 19th century A.D. (end of Little Ice Age). The fluvial canyons that characterized the relief have evidence of superimposed wind erosion, even acquiring yardangs morphology in some cases, suggesting that drier weather conditions have been recurrent at least during the Quaternary in Patagonia and even associated with greater aridity.
