The Cerro Fortaleza Formation, in older literature described as Pari Aike Formation, is a Late Cretaceous geologic formation of Campanian to Maastrichtian age (although it has formerly been reported to be Cenomanian to Santonian) of the Austral Basin in southern Patagonia, Argentina.

The sandstones of the formation were deposited in a fluvial environment. The formation has an estimated thickness of 460 metres (1,510 ft) and overlies the Anita Formation, while it is overlain by the La Irene Formation. These formations are considered Campanian and Maastrichtian in age, respectively, making the Cerro Fortaleza Formation aged between them.

The giant titanosaurs Puertasaurus and Dreadnoughtus, the megaraptoran Orkoraptor, the berthasaurid Austrocheirus isasii, and the ornithopod Talenkauen have been recovered from the formation alongside turtles and crocodiles.

Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon		Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited.

Sauropods of the Cerro Fortaleza Formation
Taxa	Species	Locality	Stratigraphic unit	Material	Notes	Images
Ankylosauria	indet.			Small-sized isolated osteoderms.
Iguanodontoidea	indet.			One incomplete maxillary tooth crown.
Ornithopoda	indet.			Two isolated caudal centra.
Talenkauen	T. santacrucensis	Corro Los Hornos near Lake Viedma.	Upper	A partial articulated skeleton with exception of the rear part of the skull, the tail, and the hands.	An elasmarian ornithopod.

Sauropods of the Cerro Fortaleza Formation
Taxa	Species	Locality	Stratigraphic unit	Material	Notes	Images
Clasmodosaurus	C. spatula	Lago Viedma		Two incomplete teeth.	A titanosaur
Dreadnoughtus	D. schrani	Rio La Leona Valley,	Upper	Four incomplete proximal caudals and incomplete left astragalus.	A titanosaur.
Puertasaurus	P. reuili	Cerros Los Hornos, La Leona.	Upper	A holotype based on four disarticulated vertebrae, specifically one cervical, one dorsal, and two caudal vertebrae.	A titanosaur.

Theropods of the Cerro Fortaleza Formation
Taxa	Species	Locality	Stratigraphic unit	Material	Notes	Images
Abelisauridae	indet.			An incomplete ziphodont tooth.
Austrocheirus	A. isasii	Hoyada Arroyo Seco.		An incomplete right ulna	An ceratosaurian theropod.
Orkoraptor	O. burkei	Cerro Los Hornos.	Upper	Several isolated teeth, including two anteriormost, probably premaxillary teeth, left manual phalanx I-1, right, nearly complete fibula, and right ungual.	A megaraptoran

Sauropods of the Cerro Fortaleza Formation
Taxa	Species	Locality	Stratigraphic unit	Material	Notes	Images
Atlantoceratodus	A. iheringi	Cerro Los Hornos and Hoyada Arroyo Seco.		Four lower tooth plates, one lower tooth plate attached to a partial mandibular bone and four upper tooth plates.	A lungfish.

• List of dinosaur-bearing rock formations

• Marenssi, Sergio A.; Casadio, Silvio; Santillana, Sergio N. (30 September 2003). "Estratigrafía y sedimentología de las unidades del Cretácico superior-Paleógeno aflorantes en la margen sureste del lago Viedma, provincia de Santa Cruz, Argentina" [Stratigraphy and sedimentology of the Upper Cretaceous-Paleogene units outcropping on the southeastern margin of Lake Viedma, Santa Cruz Province, Argentina]. Revista de la Asociación Geológica Argentina (in Spanish). 58 (3): 403–416.
• Varela, Augusto N.; Poiré, Daniel G.; Martin, Thomas; Gerdes, Axel; Goin, Francisco J.; Gelfo, Javier N.; Hoffmann, Simone (27 September 2012). "U-Pb zircon constraints on the age of the Cretaceous Mata Amarilla Formation, Southern Patagonia, Argentina: its relationship with the evolution of the Austral Basin". Andean Geology. 39 (3). doi:10.5027/andgeoV39n3-a01.