Age constraints for the northernmost outcrops of the Triassic Cuyana Basin, Argentina

摘要

Age constraints on the Cerro Puntudo Formation at the northernmost exposures of the continental Triassic Cuyana Basin are presented based on palynological data and U-Pb zircon dating. The lacustrine facies of the upper part of the Cerro Puntudo Formation contains a palynological assemblage with low diversity that is dominated by spores of ferns and lycopsids with subordinated inaperturated forms of uncertain affinity. The U-Pb SHRIMP zircon age of 243.8 ± 1.9 Ma (Anisian), obtained from juvenile magmatic zircons in a tuff interbedded in the same beds, provides the first chronostratigraphic date of the Cuyana Basin infilling at its northernmost exposures. According to additional dates already known from the southern part of the basin, a new stratigraphic correlation is proposed thus restricting the first tectono-sedimentary sequence (Synrift I depositional event of Kokogian et al. (1993)) to the Anisian. This depositional event has already been recorded in the Cacheuta and Rincon Blanco sub-basins, but it is for the first time now constrained across the whole basin.