Irati Formation is the name of a geological formation of the Paraná Basin in Brazil. It has previously been dated as Late Permian using palynomorphs, but is now dated as Early Permian using zircon ages obtained from bentonite layers. The base of the formation has been dated at 278.4 ± 2.2 Ma. Exposures of the Irati Formation are to be found in the South (Geopark of Paleorrota), southeastern Brazil and in the states of Goiás, Mato Grosso, São Paulo, Paraná, Santa Catarina, Rio Grande do Sul and Mato Grosso do Sul. The formation is part of the Passa Dios Group, underlying the Serra Alta Formation and overlying the Palermo Formation. The formation has been deposited in a restricted marine environment. The Irati Formation, with a maximum thickness of 80 metres (260 ft), was defined and named by White in 1908.

Fossil content

The formation is particularly famous for the occurrences of the mesosaurs Mesosaurus tenuidiens, and Stereosternum tumidum. Other fossils found in the formation are Myelontordoxylon camposii, and crustaceans of the genera Paulocaris, Pygaspis, Liocaris, and Clarkecaris. It is considered time equivalent to the Whitehill Formation of the Ecca Group of the Karoo Supergroup of southern Africa and the Mangrullo Formation of Uruguay.

See also

• Geology of Brazil
• Paleontological sites of Brazil
• Ganigobis Formation