Alfonsina Tripaldi
2 013
Anales de la Academia Nacional de Ciencias Exactas, Físicas y Naturales 64: 55–71.
Las cuencas de antepaís andinas del Cenozoico, del noroeste de Argentina, presentan un relleno sedimentario esencialmente fluvial con intercalaciones de sucesiones eólicas. En este trabajo se analiza una de estas unidades eólicas, la Formación Vallecito, dominada por sets entrecruzados de areniscas finas, que afloran en la Precordillera y las Sierras Pampeanas. El análisis de facies y arquitectural, en tres localidades de las provincias de La Rioja y San Juan, permitió diferenciar ocho elementos arquitecturales y cinco asociaciones de facies que caracterizan distintos tipos de depósitos eólicos y estadios en la evolución del sistema eólico, respectivamente. Se interpretaron depósitos de manto eólico, interduna, draas con dunas crecientes sobreimpuestas, dunas crecientes de crestas sinuosas, dunas crecientes de crestas rectas y morfología variable, y de interacción eólica-fluvial. En función del similar arreglo de facies, composición petrográfica de las areniscas y patrones de paleocorrientes se propone una correlación litoestratigráfica de las sucesiones estudiadas. La información cronológica disponible en la bibliografía indica que la sedimentación eólica habría ocurrido durante el Mioceno temprano. Estas espesas sucesiones eólicas estarían indicando una interacción positiva entre factores climáticos (condiciones áridas) y tectónicos (alta tasa de subsidencia) que posibilitaron la formación de extensos mares de arena y la acumulación y preservación de las arenas eólicas. A nivel regional diversas cuencas del sur de América del Sur indican semejantes condiciones climáticas áridas durante el Mioceno temprano, en tanto a escala global una tendencia de calentamiento y reducción de la extensión del hielo antártico fue interpretada para el intervalo ca. 27-15 Ma.
The Vallecito Formation, an example of Cenozoic aeolian sedimentation in the Andean basins of northwestern Argentina: paleoenvironments, stratigraphic and paleoclimatic inferences.
The Andean foreland basins, developed during the Cenozoic in northwestern Argentina, comprise a dominantly fluvial sedimentary record with several aeolian intervals along their geologic history. In this work one of these aeolian units is studied, the Vallecito Formation mainly formed by cross-bedded, fine to very fine sandstones outcropping at several places of the Precordillera and the Pampean Ranges. The facies and architectural analysis allowed recognizing eight architectural elements of aeolian origin. Based on these elements five facies associations were defined depicting different stages in the evolution of the aeolian system of the Vallecito Formation, interpreted as deposits of: aeolian sand sheets, interdune, draas with superimposed crescentic dunes, crescentic dunes of sinuous crests, crescentic dunes of right crests and variable morphology, and fluvial-aeolian interaction. The similar facies arrangement, petrographic sandstone composition and paleocurrent patterns suggest a lithostratigraphic correlation among the successions at the three surveyed locations. The available chronologic information indicates the deposition of the very thick (between 200 and 1200 meters) and laterally extended (hundreds to thousands of meters) aeolian succession likely took placed during the lower Miocene. Regionally, several sedimentary basins of southern South America also illustrate arid conditions during this time interval, while at a global scale a warming trend and reduction of the extent of Antarctic ice were inferred during ca. 27-15 Ma.
The Andean foreland basins, developed during the Cenozoic in northwestern Argentina, comprise a dominantly fluvial sedimentary record with several aeolian intervals along their geologic history. In this work one of these aeolian units is studied, the Vallecito Formation mainly formed by cross-bedded, fine to very fine sandstones outcropping at several places of the Precordillera and the Pampean Ranges. The facies and architectural analysis allowed recognizing eight architectural elements of aeolian origin. Based on these elements five facies associations were defined depicting different stages in the evolution of the aeolian system of the Vallecito Formation, interpreted as deposits of: aeolian sand sheets, interdune, draas with superimposed crescentic dunes, crescentic dunes of sinuous crests, crescentic dunes of right crests and variable morphology, and fluvial-aeolian interaction. The similar facies arrangement, petrographic sandstone composition and paleocurrent patterns suggest a lithostratigraphic correlation among the successions at the three surveyed locations. The available chronologic information indicates the deposition of the very thick (between 200 and 1200 meters) and laterally extended (hundreds to thousands of meters) aeolian succession likely took placed during the lower Miocene. Regionally, several sedimentary basins of southern South America also illustrate arid conditions during this time interval, while at a global scale a warming trend and reduction of the extent of Antarctic ice were inferred during ca. 27-15 Ma.
