Puerta de Las Angosturas Formation (Permian, Catamarca province): definition, age, and stratigraphic meaning

Abstract

A new Permian lithostratigraphic unit denominated Puerta de Las Angosturas Formation is defined for the Paganzo Basin. The new formation is mainly composed of variegated mudstones and sandstone beds, among which several levels of chert, limestone, and tuff are interstratified. The area of Las Angosturas (Sierra de Narváez, Catamarca province) is set as its type section, in which six stratigraphic intervals were distinguished and described. Stratigraphic interval 1, formed by massive or laminated red and purple sandstones (23 m thick), overlies eolian deposits belonging to the De La Cuesta Formation through a low-relief erosive unconformity. Interval 2 comprises 55 meters of purple to grayish-brown mudstones and fine-grained sandstones that transitionally cover interval 1 or overlap on the red beds of the De La Cuesta Formation. Interval 3 is made of interbedded sandstone and limestone beds with millimeter levels of chert; the whole interval reaches 110 m of thickness. Interval 4 (70 m) shows similar lithological characteristics to 3 but differs in the predominance of mudstones over sandstone and the presence of thin and recurrent tuff levels. Interval 5 is very thin, 35 m thick, and shows marked lithological changes concerning those previously described intervals since it is formed by medium- to coarse-grained cross-bedded sandstones. Finally, interval 6 (76 m) corresponds to a fine-grained sequence in which mudstones, very fine-grained sandstones, limestone, and a few tuff beds alternate. The Puerta de Las Angosturas Formation is covered in unconformity by the red beds of the Talampaya Formation. Intervals 2, 3, and 4 of the Puerta de Las Angosturas Formation have provided palynological assemblages corresponding to the Lueckisporites/Weylandites biozone that suggests a Kungurian age, at least for the lower half of the unit.