Sarmiento Formation
| Sarmiento Formation | |
|---|---|
| Stratigraphic range: Bartonian-Burdigalian (Casamayoran-Colhuehuapian) ~ | |
 | |
| Sub-units | Colhué Huapí Member, Gran Barranca Member, Puesto Almendra Member, Rosado Member, Trelew Member, and Vera Member |
| Underlies | Chenque Formation Gaiman Formation |
| Overlies | Koluel Kaike Formation (Río Chico Group) |
| Thickness | 319 metres |
| Lithology | |
| Primary | Sandstone, mudstone |
| Other | Limestone |
| Location | |
| Country | Argentina |
| Extent | Golfo San Jorge Basin |
| Type section | |
| Named for | Sarmiento, Chubut |
| Region | Chubut Province |
| Country | Argentina |
| Thickness at type section | 319 metres (1,047 ft) (tuffs) |
 Location of the Sarmiento Formation within Argentina | |
The Sarmiento Formation (Spanish: Formación Sarmiento), in older literature described as the Casamayor Formation, is a geological formation in Chubut Province, Argentina, in central Patagonia, which spans around 30 million years from the mid-Eocene to the early Miocene. It predominantly consists of pyroclastic deposits, which were deposited in a semi-arid environment. It is divided up into a number of members. The diverse fauna of the Sarmiento Formation, including a variety of birds, crocodilians, turtles and snakes, also includes many mammals such as South American native ungulates (notoungulates, litopterns, astrapotheres) as well as armadillos, and caviomorph rodents. Some trace fossils have also been found, such as Teisseirei.