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, 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.

The Paraná Basin is a large cratonic sedimentary basin situated in the central-eastern part of South America. About 75% of its areal distribution occurs in Brazil, from Mato Grosso to Rio Grande do Sul states. The remainder area is distributed in eastern Paraguay, northeastern Argentina and northern Uruguay. The shape of the depression is roughly elliptical and covers an area of about 1,500,000 km2 (580,000 sq mi).