New U–Pb zircon age for the Pennsylvanian in Argentina: Implications in palynostratigraphy and regional stratigraphy

Abstract

A continuous Pennsylvanian succession belonging to the Agua Colorada and De La Cuesta formations is exposed in the Las Angosturas area (Catamarca Province) of the Paganzo Basin. Glacial, postglacial, fluvial and shallow marine deposits are identified and referred to seven stratigraphic stages. The Agua Colorada Formation provides a persistent record of palynological assemblages in the first five stages, which are assigned to the Subzones A and B of the Raistrickia densa/Convolutispora muriornata Biozone. These palynofloras span the late Serpukhovian-Bashkirian interval. The first isotopic age for the basal section of the De La Cuesta Formation was obtained from shallow marine deposits. Zircons from a tuff intercalated with mudstones and sandstones in the marine interval were analyzed by the CA-TIMS technique providing an age of 311.89 ± 0.21 Ma, based on the weighted average of 206 Pb/ 238 U dates. This new age is compared with previous isotopic ages obtained from different successions in the Paganzo Basin, resulting in the youngest known radiometric date, for the Moscovian transgression. Indeed, a late Moscovian age is already known by isotopic dating of the reddish fluvial deposits of the lower section of the Patquía Formation, which overlies the marine transgression in the Huaco area (San Juan Province). The record of this marine flooding surface in reddish strata at Las Angosturas area provides a cautionary note on considering the appearance of red beds as indicators of the onset of continental conditions in the Paganzo Basin.