The Gaiman Formation (Spanish: Formación Gaiman), in older literature also referred to as Patagonian Marine Formation (Spanish: Formación Patagonia Marino, Patagoniense), is a geologic formation of the 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 and comprises grey and white tuffaceous mudstones and sandstones, deposited in a shallow marine environment.