Cañadón Asfalto Formation
The Cañadón Asfalto Formation is a geological formation from the Lower Jurassic, with doubtful layers of Late Jurassic age previously referred to it. The Cañadón Asfalto Formation is located in the Cañadón Asfalto Basin, a rift basin in the Chubut Province of northwestern Patagonia, southern Argentina. The basin started forming in the earliest Jurassic.
| Cañadón Asfalto Formation | |
|---|---|
| Stratigraphic range: Middle-Late Toarcian ~ Dubious assigantion of the Puesto Almada Member of likely Callovian-Oxfordian age, that can be part of the Cañadón Calcáreo Formation or the Sierra de la Manea Formation instead | |
Cañadón Asfalto Formation near Cerro Cóndor, Chubut, Argentina | |
| Type | Geological formation |
| Unit of | Sierra de Olte Group |
| Sub-units |
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| Underlies |
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| Overlies | Lonco Trapial Formation |
| Thickness | 600 m (2,000 ft) |
| Lithology | |
| Primary | Sandstone |
| Other | Limestone, shale, conglomerate, tuffite |
| Location | |
| Coordinates | 43.4°S 69.2°W |
| Approximate paleocoordinates | 40.5°S 29.3°W |
| Region | Chubut Province, Patagonia |
| Country | Argentina |
| Extent | Cañadón Asfalto Basin |
| Type section | |
| Named for | The Cañadón Asfalto in Chubut River region |
| Named by | Stipanicic, P.N., Rodrigo, F.O.L., & Martínez, C.G |
| Year defined | 1968 |
Formation map and location, shaded horizontally | |
The formation 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.
The exact age of the formation has been controversial, with uranium-lead dating of the volcanic tuff beds having given various different ages. Recent work has suggested that the base of the formation was formed around 171 Ma, during the upper Aalenian, with 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 in age. But that changed thanks to the discovery of zircons near the location of the discovery of Bagualia, allowing a precise dating of the Las Charcitas Member as Middle-Late Toarcian, 178-179 million years. And a more advanced dating constrained the age of the formation as Middle-Late Toarcian, contemporaneous to the Chon Aike volcanic activity, making it a local equivalent to Antarctica's Mawson Formation (Ferrar Volcanic Province) and the South African Drakensberg Group (Karoo Volcanic Province). The Volcanic-Lacustrine Ellsworth Land Volcanic Group of the Antarctic Peninsula are not only coeval with, but also continuations of the biozone seen in the Chacritas member.