| Gaiman Formation | |
|---|---|
| Stratigraphic range: Burdigalian (Colhuehuapian) ~ | |
 Gaiman Formation stratigraphy at Cerro Castillo | |
| Type | Geological formation |
| Underlies | Puerto Madryn Formation |
| Overlies | Sarmiento Formation |
| Thickness | 70 m (230 ft) |
| Lithology | |
| Primary | Mudstone, sandstone |
| Other | Tuff, phosphate |
| Location | |
| Coordinates | 43°18′S 65°18′W / 43.3°S 65.3°W |
| Approximate paleocoordinates | 44°00′S 59°12′W / 44.0°S 59.2°W |
| Region | Chubut Province |
| Country | Argentina |
| Extent | Peninsula Valdés Basin |
| Type section | |
| Named for | Gaiman |
| Named by | Mendía & Bayarsky |
| Year defined | 1981 |
  Gaiman Formation (Argentina) | |
The Gaiman Formation (Spanish: Formación Gaiman), in older literature also referred to as Patagonian Marine Formation (Spanish: Formación Patagonia Marino, Patagoniense), is a fossiliferous geologic formation of the Peninsula Valdés Basin in the eastern Chubut Province of northwestern Patagonia, eastern Argentina.
The 70 metres (230 ft) thick formation overlies the Sarmiento Formation and is overlain by the Puerto Madryn Formation and comprises grey and white tuffaceous mudstones and sandstones, deposited in a shallow marine environment.
The Gaiman Formation has provided fossils of many extinct penguins, among which five species in the genus Palaeospheniscus, as well as whales and dolphins, most notably Aondelphis talen, Prosqualodon australis, Idiorophus patagonicus and Argyrocetus patagonicus, indeterminate seal and turtle fossils, shark and other fossils. The richness of the formation, and the other formations in the area, such as the underlying Sarmiento Formation, led to the establishment of the Bryn Gwyn Paleontological Park, with a Welsh name, reflecting the number of Welsh settlers in the region.