# 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.
The fluvial and aeolian siltstones, sandstones and tuffs of the formation contain many mammals, such as Thylacosmilus and Huayqueriana, reptiles, amphibians and fossils of terror birds as well as Argentavis, 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. The formation overlies crystalline basement or the Arroyo Chasicó Formation. The mammal assemblage of the Cerro Azul-Epecuén unit is the most diverse for the Huayquerian Late Miocene age, possibly ranging into the Pliocene. The formation is considered contemporaneous with the Río Negro Formation of the Colorado Basin.
The unit is characterized by a monotonous succession of loess containing moderately developed paleosols. In particular, the formation is considered as representing the interval between 10 and 5.7 Ma. The maximum exposed thickness in outcrop is 54 metres (177 ft), although the unit reaches about 180 metres (590 ft) in the subsurface.
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.
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.
Large cylindrical sediment-filled structures, 115 of which interpreted as mammal burrows occur within the loess-paleosol sequence of the formation.

## 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

| Taxa | Species | Presence | Abundance | Description | Images | Notes |
| Ceratophrynidae | C. sp. | Quehué | | | | |
| Lepidobatrachus | L. sp. | Quehué | | | | |

### Birds
#### Cathartid

| Taxa | Species | Presence | Abundance | Description | Images | Notes |
| Argentavis | A. magnificens | Carhué | | | | |

#### Phorusrhacids

| Taxa | Species | Presence |
| Devincenzia | D. pozzi | Carhué |
| Procariama | P. simplex | Salinas de Hidalgo |
| Phorusrhacidae | indet. | |

#### Tinamou

| Taxa | Species | Presence | Abundance | Description | Images | Notes |
| Eudromia | E. sp. | Salinas de Hidalgo | | | | |
| Nothura | N. sp. | Bajo Giuliani El Guanaco Salinas de Hidalgo | | | | |

#### Rheidae

| Taxa | Species | Presence | Abundance | Description | Images | Notes |
| Rhea | R. sp. | Salinas de Hidalgo | | | | |

### Mammals
#### Carnivora

| Taxa | Species | Presence | Description |
| Cyonasua | C. brevirostris | Salinas de Hidalgo | A procyonid mammal. |
| Cyonasua | C. prebrevirostris | Salinas de Hidalgo | A procyonid mammal. |
| Cyonasua | C.sp. | Telén | A procyonid mammal. |

#### Sparassodonts

| Taxa | Species | Presence |
| Borhyaenidium | B. musteloides | Salinas de Hidalgo |
| Dimartinia | D. pristina | Arroyo Chasicó |
| Thylacosmilus | T. atrox | El Guanaco Quehué Salinas de Hidalgo |
| Borhyaenidae | indeterminate. | Telén |

#### Didelphimorphs

| Taxa | Species | Presence |
| Didelphinae | indet. | Telén |
| Hyperdidelphys | H. pattersoni | El Guanaco Telén |
| Hyperdidelphys | H. sp. | Salinas Grandes de Hidalgo |
| Lutreolina | L. sp. | Salinas de Hidalgo |
| Sparassocynidae | indet. | Telen |
| Thylamys | T. pinei | Laguna Chillhué |
| Thylamys | T. zetti | Estancia Ré Arroyo Guaminí |
| Thylatheridium | T. dolgopolae | El Guanaco Quehué Telén |
| Thylatheridium | T. hudsoni | Bajo Giuliani Telén |
| Thylatheridium | T. sp. | Estancia Ré Telén |
| Zygolestes | Z. tatei | Bajo Giuliani |

#### Polydolopimorphia

| Taxa | Species | Presence |
| Argyrolagus | A. rusconii | Bajo Giuliani El Guanaco Barrancas Coloradas |
| Argyrolagidae | indet. | Telén |
| Pliolestes | P. venetus | Bajo Giuliani Laguna Chillhué |

#### Rodents

| Taxa | Species | Presence |
| Abrocoma | A. antiqua | Estancia Ré |
| Cardiatherium | C. aff. orientalis | Laguna Chillhué Laguna Guatraché |
| Cardiomys | C. sp. | Salinas de Hidalgo |
| Chasichimys | C. bonaerense | Cerro Patagua |
| Chasichimys | C. scagliai | Laguna Chillhué |
| Chasichimys | C. sp. | Bajo Giuliani |
| Caviidae | indet. | Barrancas de Sarmiento |
| Clyomys | C. aff. sp. | Barrancas Coloradas |
| Ctenomyidae | indet. | Telén |
| Dolicavia | D. sp. | Grünbein Cantera Seminario |
| Echimyidae | indet. | Telén |
| Hydrochoeridae | indet. | Salinas de Hidalgo |
| Neocavia | N. pampeana | Estancia El Recado |
| Lagostomus | L. pretrichodactyla | Salinas de Hidalgo |
| Lagostomus | L. (Lagostomopsis) sp. | Grünbein Cantera Seminario Barrancas de Sarmiento Estancia Ré Salinas de Hidalgo |
| Neocavia | N. sp. | Grünbein Cantera Seminario |
| Neophanomys | N. pristinus | Estancia Don Mariano Quehué |
| Neophanomys | N. sp. | Estancia Ré |
| Palaeocavia | P. sp. | Grünbein Cantera Seminario Barrancas de Sarmiento Estancia Ré |
| Palaeoctodon | P. aff. simplicidens | Bajo Giuliani |
| Pampamys | P. emmonsae | Laguna Chillhué Bajo Giuliani Estancia Ré |
| Phtoramys | P. hidalguense | Barrancas Coloradas Salinas de Hidalgo |
| Phtoramys | P. cf. hidalguense | Grünbein Cantera Seminario |
| Phtoramys | P. sp. | Estancia Ré |
| Proctenomys | P. simpsoni | El Guanaco Barrancas Coloradas |
| Protabrocoma | P. sp. | Telén |
| Octodontoidea | indet. | Estancia Ré |
| Orthomyctera | O. sp. | Grünbein Cantera Seminario Salinas de Hidalgo |
| Reigechimys | R. octodontiformis | Bajo Giuliani Estancia Ré |
| Reigechimys | R. plesiodon | Laguna Chillhué |
| Reigechimys | R. simplex | Bajo Giuliani |
| Tetrastylus | T. araucanus | Salinas de Hidalgo |
| Tetrastylus | Tetrastylus sp. | Telén |
| Theridomysops | T. parvulus | Telén |
| Xenodontomys | X. ellipticus | Grünbein Cantera Seminario Barrancas de Sarmiento |

#### Xenarthrans
##### Cingulata

| Taxa | Species | Presence | Notes |
| Aspidocalyptus | A. castroi | Robilote Field Salinas de Hidalgo | |
| Aspidocalyptus | A. sp. | Telén | |
| Aspidocalyptus | A. cf. sp. | Grünbein Cantera Relleno Sanitario Level 2 | |
| Chasicotatus | C. ameghinoi | Laguna Chillhué Estancia Don Mariano Cerro Patagua Cerro El Chancho Cerro de los Guanacos Puesto Colorado Estancia Quiñi-Malal Bajo Giuliani El Guanaco Telen El Recado Laguna Guatraché Loventué Quehué Barrancas Coloradas Estancia Ré Salinas de Hidalgo | [16][37] [38][39] |
| Chasicotatus | C. cf. peiranoi | Grünbein Cantera Relleno Sanitario Level 2 | |
| Chasicotatus | C. sp. | El Recado | |
| Chorobates | C. villosissimus | Laguna Chillhué Estancia Don Mariano Grünbein Cantera Relleno Sanitario Level 2 Puesto Colorado Ruta 14 Estancia Quiñi-Malal El Guanaco Telen El Recado Loventué Quehué Estancia Ré Salinas de Hidalgo | [13][26][37] [38][39] |
| Chorobates | Chorobates sp. | Grünbein Cantera Seminario | |
| Coscinocercus | C. brachyurus | Robilote Field Salinas de Hidalgo | |
| Coscinocercus | C. marcalaini | Robilote Field Salinas de Hidalgo | |
| Coscinocercus | C. sp. | Telén | |
| Doellotatus | D. chapadmalensis | El Recado Salinas de Hidalgo | |
| Doellotatus | D. inornatus | Laguna Chillhué Estancia Don Mariano Grünbein Cantera Seminario Puesto Colorado Ruta 14 El Guanaco El Recado Laguna Guatraché Loventué Quehué Barrancas Coloradas Estancia Ré Telén Salinas de Hidalgo | [13][26] [37][38] [39][16] |
| Doellotatus | D. cf. praecursor | Grünbein Cantera Seminario | |
| Doellotatus | D. sp. | Laguna La Paraguaya | |
| Eosclerocalyptus | E. sp. | Laguna La Paraguaya | |
| Eumysops | E. sp. | Laguna Chillhué | |
| Glyptodontidae | indet. | Laguna La Paraguaya Salinas Grandes de Hidalgo | |
| Hoplophorus | H. sp. | Telén | |
| Hoplophractus | H. tapinocefalus | Laguna de los Paraguayos Salinas de Hidalgo | |
| Hoplophractus | H. sp. | Telén | |
| Macrochorobates | M. chapalmalensis | El Guanaco Barrancas Coloradas | |
| Macrochorobates | M. scalabrinii | Laguna Chillhué Estancia Don Mariano Telen Loventué Quehué Salinas de Hidalgo | [13][37] [38][16] |
| Macroeuphractus | M. morenoi | Grünbein Cantera Relleno Sanitario Level 2 Puesto Colorado Laguna Chillhué Telen El Recado Laguna Guatraché Loventué Quehué Barrancas Coloradas Estancia Ré Salinas de Hidalgo | [13][26] [37][38] [39][16] |
| Macroeuphractus | M. retusus | Salinas de Hidalgo | |
| Macroeuphractus | M. sp. | Grünbein Cantera Relleno Sanitario Level 2 El Recado | |
| Paleuphractus | P. sp. | Salinas de Hidalgo | |
| Plohophorus | P. araucanus | Salinas de Hidalgo | |
| Proeuphractus | P. limpidus | Laguna Chillhué Telén | |
| Proeuphractus | P. sp. | Laguna Chillhué Cerro Patagua Telen El Recado Laguna Guatraché Quehué Salinas de Hidalgo | [13][37] [38][39] [16] |
| Pseudoplohophorus | P. cf. sp. | Grünbein Cantera Relleno Sanitario Level 2 | |
| Vetelia | V. perforata | Cerro Patagua Cerro de los Guanacos Telén | |
| Zaedyus | Z. pichiy | Laguna Chillhué Telen Quehué | |

##### Pilosans

| Taxa | Species | Presence | Notes |
| Mylodontidae | indet. | Telén | |
| Plesiomegatherium | P. sp. | Salinas de Hidalgo | |
| Proscelidodon | P. gracillimus | Estancia Don Mariano Huayquerías de San Carlos Laguna Epecuén Bajo Giuliani Laguna Chillhué Loventué Salinas Grandes de Hidalgo Quehué Barrancas Coloradas Estancia Ré Arroyo Guaminí Laguna de los Paraguayos Carhué | [42][43] [22][44] |

#### Litopterns

| Taxa | Species | Presence | Description |
| Brachytherium | B. cf. cuspidatum | Telén Salinas de Hidalgo | |
| Diplasiotherium | D. pampa | Bajo Giuliani Laguna Chillhué Salinas de Hidalgo | A litoptern. |
| Eoauchenia | E. cingulata | Robilote Field Salinas de Hidalgo | |
| Eoauchenia | E. primitiva | El Guanaco | |
| Epecuenia | E. thoatherioides | Robilote Field Salinas de Hidalgo | |
| Huayqueriana | H. cristata | Robilote Field Salinas de Hidalgo | Previously called as Macrauchenia latidens. |
| Litopterna | indet. | Telén | |
| Neobrachytherium | N. sp. | Bajo Giuliani Salinas de Hidalgo | |
| Promacrauchenia | P. sp. | Grünbein Cantera Relleno Sanitario Level 2 Salinas de Hidalgo | |
| Proterotheriidae | indet. | Bajo Giuliani Telén | |

#### Notoungulate

| Taxa | Species | Presence | Description | Notes |
| Hemihegetotherium | H. achataleptum | Cerro Patagua Eduardo Castex Cerro de los Guanacos Puesto Colorado Bajo Giuliani Laguna Chillhué Loventué Salinas de Hidalgo | A hegetotheriidae notoungulate. | [47][38] [37][48] |
| Hemihegetotherium | H. lazai | Salinas de Hidalgo | A hegetotheriidae notoungulate. | |
| Mesotheriinae | indet. | Laguna La Paraguaya Telén | | |
| Paedotherium | P. bonaerense | Barrancas de Sarmiento | A notoungulate. | |
| Paedotherium | P. minor | Laguna La Paraguaya Estancia Ré Salinas de Hidalgo | A notoungulate. | |
| Paedotherium | P. cf. minor | Grünbein Cantera Seminario | A notoungulate. | |
| Paedotherium | P. sp. | Bajo Giuliani Laguna Chillhué Estancia Ré | A notoungulate. | |
| Pisanodon | P. nazari | Salinas de Hidalgo | A toxodont. | |
| Pseudotypotherium | P. carhuense | Robilote Field Salinas de Hidalgo | A mesotheriidae notoungulate. | |
| Tremacyllus | T. impressus | Grünbein Cantera Seminario Bajo Giuliani Laguna Chillhué Salinas Grandes de Hidalgo Quehué Barrancas Coloradas | A hegetotheriidae notoungulate. | |
| Typotheriodon | T. grandis | Robilote Field | | |
| Typotheriopsis | T. minimus | Robilote Field | A Mesotheriidae notoungulate. | |

### Reptiles

| Taxa | Species | Presence |
| Tupinambis | T. sp. | Telén |
| Chelidae | indet. | Telén |
| Testudinidae | indet. | Salinas de Hidalgo |

## SALMA correlations

Huayquerian correlations in South America :
| Formation | Cerro Azul | Ituzaingó | Paraná | Camacho | Raigón | Andalhuala | Chiquimil | Las Flores | Maimará | Palo | Pebas | Muyu | Rosa | Saldungaray | Salicas | Urumaco | Map |
| Basin | Colorado | Paraná | Paraná | Paraná | Paraná | Hualfín | Hualfín | Tontal | Andes | Salta | Amazon | Huasi | Altiplano | BA | Velasco | Falcón | Cerro Azul Formation (South America) |
| Country | Argentina | Argentina | Argentina | Uruguay | Uruguay | Argentina | Argentina | Argentina | Argentina | Argentina | Brazil Peru | Bolivia | Bolivia | Argentina | Argentina | Venezuela | Cerro Azul Formation (South America) |
| Cardiatherium | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Lagostomus | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Macroeuphractus | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Proeuphractus | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Pronothrotherium | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Pseudotypotherium | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Thylacosmilus | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Xotodon | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Macraucheniidae | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Primates | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Rodents | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Reptiles | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Birds | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Terror birds | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Flora | | | | | | | | | | | | | | | | | Cerro Azul Formation (South America) |
| Environments | Aeolian-fluvial | Fluvio-deltaic | Fluvio-deltaic | Fluvio-deltaic | Fluvial | Fluvial | Fluvial | Fluvial | Fluvial | Fluvial | Fluvio-lacustrine | Fluvial | Fluvial | Fluvial | Fluvio-lacustrine | Fluvio-deltaic | Huayquerian volcanoclastics Huayquerian fauna Huayquerian flora |
| Volcanic | | | | | | Yes | | | | | | | | | | | | Huayquerian volcanoclastics Huayquerian fauna Huayquerian flora |