Stratigraphy of the Quebrada de los Colorados Formation: a complex unit of the basal foreland basin in northern Valle Calchaquí

CECILIA EUGENIA DEL PAPA; F, H.; PETRINOVIC,I,; J, P.; R, M.

Bariloche

Congreso; . IV Congreso Latinoamericano de Sedimentología y XI Reunión Argentina de Sedimentología; 2006

The Los Colorados Formation is the basal unit of the Payogastilla Group and was originally defined in the Valle Calchaquí (Diaz et al., 1987). This unit is quite variable in thickness, color and lithology being the brink-color siltstones strata the most characteristic.  The Valle Calchaquí is a north-south bivergent tectonic depression delineating the Puna Plateau-Cordillera Oriental boundary. In the northern Valle Calchaquí, the Los Colorados Formation is characterized by a red coarsening up-ward succession of continental strata of 1.500 m of mean thickness, which represents the foreland sedimentation. This deposit overlies unconformably the postrift sediments of Salta Group (del Papa et al., 2004), moreover syntectonic unconformities have been described in this unit (Hongn et al., in press). In order to gain insight into the knowledge of the complex paleogeography of this basin, we present new sedimentological data and stratigraphic analysis from three stratigraphic logs at El Saladillo, Esquina Azul and Cerro Bayo, located in the northern Valle Calchaquí. Based on distinct unconformity surfaces and on the characteristics of the vertical facies succession, paleocurrents and provenance, five sedimentary sequences were recognized. The basal sequences I and II are integrated by fine-grained sediments, sheet-like sandstones and paleosols. The sequences III and IV are constituted by conglomeratic sandstones and conglomerates channel-fill and mudflow deposits. The sequence V consists of intermediate participation of fine-grained sediments and sandy to gravely channel-fill facies. The recognition of sedimentary sequences limited by unconformity surfaces remarks the active tectonics coeval with Los Colorados basin and highlights the early stage in foreland evolution.