Evolución paleoambiental del Grupo Payogastilla (Cenozoico) en el valle Calchaquí-Tonco, provincia de Salta, Argentina

GALLI, C.I.; REYNOLDS, J.

Relatorio de la XIII Reunión Argentina de Sedimentología

SCS Publisher

Lugar: Salta; Año: 2012; p. 67 - 80

Paleoenvironmental evolution of the Payogastilla Group (Cenozoic) in the Calchaquí - Tonco valley, Salta province, Argentina. Sedimentological characteristics of the Payogastilla Group (Cenozoic) were analyzed in the southern sector of the Calchaquí - Tonco Valley basin, in the Salta province. The deposits are composed of Los Colorados, Angastaco formations in both valleys; Palo Pintado and San Felipe formations are also present in the Calchaquí Valley. In order to establish the distribution and evolution of sedimentary paleoenvironments, it was necessary tostudy the lithofacies present. Fourteen lithofacies were identified, which were grouped into seventeen associations based on architectural elements. These architectural elements, according to their sequence, are characterized by different fluvial styles. It is possible to identify five evolutionary stages, from a paleoenvironmental standpoint, in the Payogastilla Group deposits.The Eocene Los Colorados Formation, at the base of the unit, represents the first stage of basin filling and in the paleoenvironmental evolution. It presents ephemeral fluvial system facies association with aeolian deposits, represents a period of maximum aridity. The second stage began with the sudden appearance of coarse arenaceous facies and/or conglomeratic aeolian deposits and corresponds to the basal middle Miocene Angastaco Formation. This unit has typical facies associations of shallow gravel-bed, braided fluvial system, that gradually, in the third stage, developeds deeper channels associated with gravity-flow deposits. The fourth stage, from 10 Ma to 5 Ma, is represented by the Palo Pintado Formation. This period had some significant climate changes, to warm and humid conditions, and the paleoenvironment evolved into a meandering river system with development of impressive sandy lagoons and marshes on the floodplain. The last stage of development, consisting of the San Felipe Formation, is characterized byconglomeratic facies with imbricate clasts in low-sinuosity channels, which form a braided fluvial fan, that gradually changes to a shallow braided gravel-bed.