Sedimentología y arquitectura de las dunas costeras de la Formación Allen, Grupo Malargüe, cuenca Neuquina - Río Negro, Argentina

Abstract

A detailed sedimentary analysis of Upper Cretaceous deposits, based on the description of lithofacies and architectural elements, allowed the reconstruction of the paleoenvironment and the stratigraphic evolution of the Allen Formation that outcrops south of the area of Paso Córdoba, in the Río Negro province, Argentina. The facies association gave the criteria for the identification of eolian and fluvial architectural elements: crescent dunes with straight crests, complex dunes with sinuous crests, wet interdune, dry interdune, sand sheets and ephemeral currents. The spatial distribution of these architectural elements and the analysis of unconformities allowed to interpret two eolian systems for the Allen Formation. The Eolian System I (ES I) is defined by sand sheets associated with ephemeral channels, interdune deposits and complex dunes. This dune type shows differences in the paleocurrents data and in the thickness of the sets, suggesting that smaller superimposed dunes have migrated on top of the main dune, which is interpreted as a draas. The Eolian System II (SE II) is characterized by transverse dunes and wet interdunes. The main wind direction was SW for the ES I and SSE/S for the ES II, as indicated by the paleocurrents data. Both systems are in contact through an extinction surface, interpreted as supersurface, which suggests low availability of sand due to an increase in the flooded areas located north of the studied area, associated to the atlantic ingression.