CONICET | Buscador de Institutos y Recursos Humanos

Expressions of the landscape that appear on the large smooth surface of the central pampean plain in Argentina, point out the presence of neotectonic activity. The studied area is covered by deposits of fluvial belts and fans, lacustrine sediments and an extensive loess blanket, all of them belonging to the Quaternary. These deposits constitute the upper stratigraphic column at the distal part of the foreland basin, located to the east of the Sierras Pampeanas Orientales. Neogene strains from the flat subduction of the Nazca plate underneath the South American plate are widely distributed in the Andean foreland, beneath central western Argentina (28º-33º latitud S). Therefore, geotectonic conditions of this portion of the active continental margin are in correspondence with the particular behaviour of the intraplate region, evidenced by presence of regional N- S tectonic lineaments that caused the appearance of the laguna Mar Chiquita and large shallow lagoons aligned in the distal area of the Río Dulce alluvial fan. Structural analyses of lineaments and the identification of geomorphologic units and topographic features, starting from the interpretation of satellite images and field observations, have allowed indicating limits of the blocks that shape the region and define morphostructural domains. Furthermore, the surface information was correlated with that obtained by means the interpretation of data from drill holes, as well as the electric resistivity record of the ground. This correlation allowed establishing the neotectonic character of the deformation and deducing the existence of relative movements in structural blocks. As a consequence, at least two activity episodes have been established. The first one, of more hierarchy, affected to the sediments of transition and continental environments overlaying marine-shallow deposits of the Formation Paraná (Upper Miocene). On the other hand, lateral variations of wetlands facies affecting typical aeolian deposits of the Tezanos Pinto Formation, mark discontinuities wich are correlated with the linear features observed in surface. Existence of deformation can be inferred for Upper Quaternary from disruptions in the superficial drainage. Key words: neotectonics, structural units and Pampa plain.