Late cretaceous organic-walled dinoflagellate cysts from the Alta Vista Formation, Austral Basin, Argentina

GONZÁLEZ ESTEBENET, MARÍA; GULER, MARÍA; CERECEDA, ABRIL

AMEGHINIANA

ASOCIACION PALEONTOLOGICA ARGENTINA

Lugar: Buenos Aires; Año: 2017 vol. 54 p. 688 - 699

0002-7014

The Alta Vista Formation represents one of the first Late Cretaceous marine deposits accumulated during the foreland stage of the Austral Basin, Patagonia. All the analyzed samples contain dinoflagellate cysts, denoting marine conditions throughout the unit, and despite the extremely poor preservation of the assemblages diagnostic species were identified. The age of the Alta Vista Formation was assigned between the late Santonian and the late Campanian on the base of the invertebrate remains. Nevertheless, the age is still debatable and a detailed biostratigraphy have not been proposed for the unit so far. As in other Late Cretaceous Southern Hemisphere middle to high latitudes successions, the dinoflagellate cysts from the Alta Vista Formation are useful for biostratigraphic interpretations. The co-occurrence of Odontochitina porifera, Palaeohystrichophora infusorioides, Nelsoniella aceras, Nelsoniella tuberculata and Xenikoon australis is consistent with a Campanian age, in agreement with the age indicated by the invertebrates recorded in other localities where the unit crop-outs. In particular, the occurrence of Xenikoon australis and Nelsoniella tuberculata constrains the age to the early?middle Campanian. Since the basal levels of the Alta Vista Formation were not identified in the studied sections, the age suggested herein corresponds to the upper part of the unit.