Cerro Azul Formation

Cerro Azul Formation
Stratigraphic range: Tortonian (Huayquerian) ~10–5.7 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Fossil burrow fills in the Cerro Azul Formation
Type	Geological formation
Underlies	alluvium
Overlies	Arroyo Chasicó Formation or Crystalline basement
Thickness	54 m (177 ft) (outcrop) 180 m (590 ft) (subsurface)
Lithology
Primary	Siltstone, sandstone
Other	Conglomerate
Location
Coordinates	35°42′S 64°42′W / 35.7°S 64.7°W / -35.7; -64.7
Approximate paleocoordinates	35°54′S 62°42′W / 35.9°S 62.7°W / -35.9; -62.7
Region	Buenos Aires & La Pampa Provinces
Country	Argentina
Extent	Colorado Basin
Type section
Named for	Cerro Azul, Epecuén Lake
Named by	Linares et al.
Year defined	1980
Outcrop map of the Cerro Azul Formation

The Cerro Azul Formation (Spanish: Formación Cerro Azul), also described as Epecuén Formation, is a geological formation of Late Miocene (Tortonian, or Huayquerian in the SALMA classification) age in the Colorado Basin of the Buenos Aires and La Pampa Provinces in northeastern Argentina.^[1][2]

The fluvial and aeolian siltstones, sandstones and tuffs of the formation contain many mammals, such as Thylacosmilus and Macrauchenia, reptiles, amphibians and fossils of terror birds as well as Argentavis, the largest flying bird ever discovered.