The Cerro Azul Formation (), also described as Epecuén Formation, is a

geological formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics (lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock expo ...

Late Miocene The Late Miocene (also known as Upper Miocene) is a sub-epoch of the Miocene epoch (geology), Epoch made up of two faunal stage, stages. The Tortonian and Messinian stages comprise the Late Miocene sub-epoch, which lasted from 11.63 Ma (million ye ...

(

Tortonian The Tortonian is in the geologic time scale an age or stage of the late Miocene that spans the time between 11.608 ± 0.005 Ma and 7.246 ± 0.005 Ma (million years ago). It follows the Serravallian and is followed by the Messinian. The Tort ...

, or

Huayquerian The Huayquerian () age is a period of geologic time (9.0–6.8 Ma) within the Late Miocene epoch of the Neogene, used more specifically within the SALMA classification. It follows the Chasicoan and precedes the Montehermosan age. Etymology T ...

in the SALMA classification) age in the Colorado Basin of the

Buenos Aires Buenos Aires, controlled by the government of the Autonomous City of Buenos Aires, is the Capital city, capital and largest city of Argentina. It is located on the southwest of the Río de la Plata. Buenos Aires is classified as an Alpha− glob ...

and

La Pampa Province La Pampa () is a sparsely populated province of Argentina, located in the Pampas in the center of the country. Neighboring provinces are from the north clockwise San Luis, Córdoba, Buenos Aires, Río Negro, Neuquén and Mendoza. History In ...

s in northeastern

Argentina Argentina, officially the Argentine Republic, is a country in the southern half of South America. It covers an area of , making it the List of South American countries by area, second-largest country in South America after Brazil, the fourt ...

.Cerro Azul Formation
in the

Paleobiology Database The Paleobiology Database (PBDB) is an online resource for information on the distribution and classification of fossil animals, plants, and microorganisms. History The Paleobiology Database originated in the NCEAS-funded Phanerozoic Marine Pale ...

Epecuén Formation
in the

The

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

and aeolian

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s and

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock co ...

s of the formation contain many mammals, such as ''

Thylacosmilus ''Thylacosmilus'' is an extinct genus of saber-toothed metatherian mammals that inhabited South America from the Late Miocene to Pliocene epochs. Though ''Thylacosmilus'' looks similar to the "saber-toothed cats", it was not a felid, like the we ...

'' and ''

Huayqueriana ''Huayqueriana'' is an extinct genus of South American litoptern, related to ''Macrauchenia'', and belonging to the same family, Macraucheniidae. It was formerly known as ''Macrauchenidia latidens'', described in 1939 by Cabrera, but redefined as ...

'', reptiles, amphibians and fossils of

terror bird Phorusrhacids, colloquially known as terror birds, are an extinct family of large carnivorous, mostly flightless birds that were among the largest apex predators in South America during the Cenozoic era. Their definitive fossil records range from ...

s as well as ''

Argentavis ''Argentavis'' is an extinct genus of teratornithid known from three sites in the Epecuén and Andalhualá Formations in central and northwestern Argentina dating to the Late Miocene (Huayquerian). The type species, ''A. magnificens'', is some ...

'', the largest flying bird ever discovered.

Description

The Cerro Azul Formation crops out in patches in the southwestern Buenos Aires Province and southeastern Pampa Province. The Epecuén Formation has been correlated to the Cerro Azul Formation in the early 2000s. The Cerro Azul and Epecuén Formations were named after the Cerro Azul ("Blue Hill") and Epecuén Lake where the formation crops out.Visconti et al., 2010, p.259 The formation overlies crystalline

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

or the

Arroyo Chasicó Formation Arroyo often refers to: * Arroyo (watercourse), an intermittently dry creek Arroyo may also refer to: Places United States * Arroyo, Pennsylvania * Arroyo, Puerto Rico, a municipality * Arroyo, West Virginia Spain * Arroyo (Santillana del Mar), ...

.Visconti et al., 2010, p.262 The mammal assemblage of the Cerro Azul-Epecuén unit is the most diverse for the

age, possibly ranging into the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch (geology), epoch in the geologic time scale that extends from 5.33 to 2.58Río Negro Formation of the Colorado Basin.Pérez, 2012, p.11Visconti et al., 2010, p.258 The unit is characterized by a monotonous succession of loess containing moderately developed

paleosol In Earth science, geoscience, paleosol (''palaeosol'' in Great Britain and Australia) is an ancient soil that formed in the past. The definition of the term in geology and paleontology is slightly different from its use in soil science. In geo ...

s. In particular, the formation is considered as representing the interval between 10 and 5.7 Ma. The maximum exposed thickness in outcrop is , although the unit reaches about in the subsurface.Cardonatto & Melchor, 2018, p.2 The Cerro Azul Formation deposits were described by Linares et al. in 1980. They are discontinuous along the whole occupied area in the provinces of La Pampa and Buenos Aires. They are composed of silts, sandy silts and very thin silty sands, reddish and brown colored, with a homogeneous and compact general aspect, and frequent carbonate nodules and evidences of pedogenic processes. Visconti et al. (2010) interpreted them as eolian deposits characterized by loessic materials, with a high percentage of lithic fragments and volcaniclastic sediments.Caleufú
at

Fossilworks Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org The sediments and their fauna belong to a sedimentary and faunal cycle, which followed the withdrawal (around 10 Ma) of a widespread marine transgression that extended from central Argentina, to western Uruguay and southern Paraguay and Brazil, the "Paraná Sea" or ''mar paranense'' in Spanish.Verzi & Montalvo, 2008, p.285 Large cylindrical sediment-filled structures, 115 of which interpreted as mammal burrows occur within the loess-paleosol sequence of the formation.Cardonatto & Melchor, 2018, p.1

Fossil content

The following fossils have been recovered from the formation: Locations: ;La Pampa * Barrancas Coloradas - Cerro Azul Formation - La Pampa * Caleufú - Cerro Azul Formation - La Pampa * Cerro El Chancho - Cerro Azul Formation - La Pampa * Cerro Patagua - Cerro Azul Formation - La Pampa * Estancia Don Mariano - Cerro Azul Formation - La Pampa * Estancia El Recado - Cerro Azul Formation - La Pampa * Estancia Ré - Cerro Azul Formation - La Pampa * El Guanaco - Cerro Azul Formation - La Pampa * Huayquerías de San Carlos - Cerro Azul Formation - La Pampa * Laguna Chillhué - Cerro Azul Formation - La Pampa * Laguna Guatraché - Cerro Azul Formation - La Pampa * Quehué - Cerro Azul Formation - La Pampa * Salinas Grandes de Hidalgo - Cerro Azul Formation - La Pampa * Telen - Cerro Azul Formation - La Pampa ;Buenos Aires * Bajo Giuliani - Cerro Azul Formation - Buenos Aires * Barrancas de Sarmiento - Cerro Azul Formation - Buenos Aires * Eduardo Castex - Cerro Azul Formation - Buenos Aires * Estancia los Médanos - Cerro Azul Formation - Buenos Aires * Estancia Quiñi-Malal - Cerro Azul Formation - Buenos Aires * Grünbein Cantera Seminario - Cerro Azul Formation - Buenos Aires * Grünbein Cantera Seminario Level 2 - Cerro Azul Formation - Buenos Aires * Laguna Epecuén - Cerro Azul Formation - Buenos Aires * Laguna La Paraguaya - Cerro Azul Formation - Buenos Aires * Puesto Colorado - Cerro Azul Formation - Buenos Aires * Ruta 14 - Cerro Azul Formation - Buenos Aires * Arroyo Guaminí - Epecuén Formation - Buenos Aires * Carhué - Epecuén Formation - Buenos Aires * Laguna de los Paraguayos - Epecuén Formation - Buenos Aires * Robilote Field - SE of Epecuén lagoon & E of Laguna de Epecuén - Epecuén Formation - Buenos Aires * Salinas Grandes de Hidalgo - Epecuén Formation - Buenos Aires

Amphibians

Birds

Cathartid

Phorusrhacids

Tinamou

Rheidae

Mammals

Carnivora

Sparassodonts

Didelphimorphs

Polydolopimorphia

Rodents

Xenarthrans

= Cingulata

= Pilosans

Litopterns

Notoungulate

Reptiles

SALMA correlations

References

Bibliography

;Geology * * ;Paleontology * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * {{citation , last=Rovereto , first=C , year=1914 , title=Los Estratos Araucanos y sus fósiles , journal= Anales del Museo de Historia Natural de Buenos Aires , volume=25 , pages=1–24 Geologic formations of Argentina Miocene Series of South America Tortonian Huayquerian Neogene Argentina Sandstone formations Siltstone formations of Argentina Conglomerate formations Aeolian deposits Fluvial deposits Lacustrine deposits Fossiliferous stratigraphic units of South America Paleontology in Argentina Formations Formations