Discovering of Continental Infra? Middle Triassic in the South of the Piedmont Area of Mendoza

Abstract

The discovering of fossils of reptiles (Therapsids of the Dicynodontia and Cynodontia groups) in the low hills of San Rafael (west and southwest zones), permits extending the Triassic System to the south of the province of Mendoza.

The continental deposits are intercalated with vulcanites of basic (basalts) and acid (ignimbrites) composition.

The portion of the Triassic column considered in this paper is included in the Middle Triassic in general. Its upper part is placed in the Anisian (according to Bonaparte) or ??preladinian inclusive?? (according to Casamiquela), The age of the basal portion of the Puesto Viejo Formation is uncertain and may be considered as the highest part of the Lower Triassic (Upper Scythian).

An extensive profile was surveyed between the mouth of Puesto Agua de los Burros and the Seco de la Frazada river, across the Atuel river?s arch.

The unconformable position of this formation in relation to the underlying vulcanic masses (Choiyoilitense), which have been considered to be of Upper Triassic age, makes it necessary to modify the position of this last eruptive cycle in the chronological seale. As a result it is now considered as Upper Permian age sensu lato, being difficult to place exactly its upper limit, which may be situated below the Upper Scythian.