Cañadón Asfalto Formation
The Cañadón Asfalto Formation is a Middle Jurassic to Late Jurassic geologic formation, from the Jurassic period of the Mesozoic Era. Its age is controversial, uranium-lead dating of the volcanic tuff beds having given various different ages. Recent work suggests that the base of the formation was formed around 171 Ma, during the upper Aalenian, while the main age for the Lower Las Chacritas Member being around 168 Ma, during the Bajocian, Bathonian and Callovian While the overlying Puesto Almada Member seems to be around 158 ma, or Oxfordian age.
It is located in the Cañadón Asfalto Basin, a rift basin in Chubut Province of northwestern Patagonia, in southern Argentina. The basin started forming in the earliest Jurassic.
It is composed of fluvial-lacustrine deposits, typically sandstones and shales with a saline paleolake carbonate evaporitic sequence of limestone in its lowest Las Chacritas Member. Interbedded with these are volcanic tuffites. It is divided into two members, the Las Chacritas Member, and the overlying Puesto Almada member, but the latter has also been assigned to the overlying Cañadón Calcáreo Formation by other authors.
According to a palynological study the dominant pollen was produced by the conifer families Cheirolepidiaceae and Araucariaceae, suggesting that warm-temperate and relatively humid conditions under highly seasonal climate prevailed during the depositional times of the unit. The abundance of Botryococcus supports the presence of a shallow lake with probably saline conditions.Vertebrate fauna
Amphibians
Turtles
Lepidosaurs
Pterosaurs
Crocodyliformes
Dinosaurs
Mammals
