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]

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	35.7°S 64.7°W / -35.7; -64.7
Approximate paleocoordinates	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 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

Sedimentary logs of the Cerro Azul Formation

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.^[3] The formation overlies crystalline basement or the Arroyo Chasicó Formation.^[4] The mammal assemblage of the Cerro Azul-Epecuén unit is the most diverse for the Huayquerian Late Miocene age, possibly ranging into the Pliocene.^[5] The formation is considered contemporaneous with the Río Negro Formation of the Colorado Basin.^[6][7]

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.^[8]

The Cerro Azul Formation deposits were described by Linares et al. in 1980.^[3] 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.^[9]

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.^[10]

Large cylindrical sediment-filled structures, 115 of which interpreted as mammal burrows occur within the loess-paleosol sequence of the formation.^[11]

Fossil content

The following fossils have been recovered from the formation:^[1]

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				[12]
Lepidobatrachus	L. sp.

Birds

Cathartid

Taxa	Species	Presence	Abundance	Description	Images	Notes
Argentavis	A. magnificens	Carhué				[13]

Phorusrhacids

Taxa	Species	Presence	Abundance	Description	Images	Notes
Devincenzia	D. pozzi	Carhué				[14]
Procariama	P. simplex	Salinas de Hidalgo				[15]
Phorusrhacidae	indet.					[14]

Tinamou

Taxa	Species	Presence	Abundance	Description	Images	Notes
Eudromia	E. sp.	Salinas de Hidalgo				[14]
Nothura	N. sp.	Bajo Giuliani El Guanaco Salinas de Hidalgo				[14]

Rheidae

Taxa	Species	Presence	Abundance	Description	Images	Notes
Rhea	R. sp.	Salinas de Hidalgo				[14]

Mammals

Carnivora

Taxa	Species	Presence	Abundance	Description	Images	Notes
Cyonasua	C. brevirostris	Salinas de Hidalgo		A procyonid mammal.		[13]
	C. prebrevirostris	Salinas de Hidalgo
	C.sp.	Telén				[16]

Sparassodonts

Taxa	Species	Presence	Abundance	Description	Images	Notes
Borhyaenidium	B. musteloides	Salinas de Hidalgo				[13]
Dimartinia	D. pristina	Arroyo Chasicó	A left dentary and its associated teeth	A thylacosmiliform		[17]
Thylacosmilus	T. atrox	El Guanaco Quehué Salinas de Hidalgo		A saber-toothed thylacosmilid		[13][18]
Borhyaenidae	indeterminate.	Telén				[16]

Didelphimorphs

Taxa	Species	Presence	Abundance	Description	Images	Notes
Didelphinae	indet.	Telén				[16]
Hyperdidelphys	H. pattersoni	El Guanaco Telén				[18][16]
	H. sp.	Salinas Grandes de Hidalgo				[19]
Lutreolina	L. sp.	Salinas de Hidalgo				[13]
Sparassocynidae	indet.	Telen				[18][16]
Thylamys	T. pinei	Laguna Chillhué				[20]
	T. zetti	Estancia Ré Arroyo Guaminí				[21][22]
Thylatheridium	T. dolgopolae	El Guanaco Quehué Telén				[23][16]
	T. hudsoni	Bajo Giuliani Telén				[18][16]
	T. sp.	Estancia Ré Telén				[21][16]
Zygolestes	Z. tatei	Bajo Giuliani				[18][20]

Polydolopimorphia

Taxa	Species	Presence	Abundance	Description	Images	Notes
Argyrolagus	A. rusconii	Bajo Giuliani El Guanaco Barrancas Coloradas				[18]
Argyrolagidae	indet.	Telén				[16]
Pliolestes	P. venetus	Bajo Giuliani Laguna Chillhué				[18]

Rodents

Taxa	Species	Presence	Abundance	Description	Images	Notes
Abrocoma	A. antiqua	Estancia Ré				[21]
Cardiatherium	C. aff. orientalis	Laguna Chillhué Laguna Guatraché				[24]
Cardiomys	C. sp.	Salinas de Hidalgo				[13]
Chasichimys	C. bonaerense	Cerro Patagua				[25]
	C. scagliai	Laguna Chillhué
	C. sp.	Bajo Giuliani
Caviidae	indet.	Barrancas de Sarmiento				[26]
Clyomys	C. aff. sp.	Barrancas Coloradas				[20]
Ctenomyidae	indet.	Telén				[16]
Dolicavia	D. sp.	Grünbein Cantera Seminario				[26]
Echimyidae	indet.	Telén				[16]
Hydrochoeridae	indet.	Salinas de Hidalgo				[18]
Neocavia	N. pampeana	Estancia El Recado				[27]
Lagostomus	L. pretrichodactyla	Salinas de Hidalgo				[13]
	L. (Lagostomopsis) sp.	Grünbein Cantera Seminario Barrancas de Sarmiento Estancia Ré Salinas de Hidalgo				[13][21][26]
Neocavia	N. sp.	Grünbein Cantera Seminario				[26]
Neophanomys	N. pristinus	Estancia Don Mariano Quehué				[28]
	N. sp.	Estancia Ré				[29]
Palaeocavia	P. sp.	Grünbein Cantera Seminario Barrancas de Sarmiento Estancia Ré				[13][21][26]
Palaeoctodon	P. aff. simplicidens	Bajo Giuliani				[30][20]
Pampamys	P. emmonsae	Laguna Chillhué Bajo Giuliani Estancia Ré				[20][31]
Phtoramys	P. hidalguense	Barrancas Coloradas Salinas de Hidalgo				[20][32]
	P. cf. hidalguense	Grünbein Cantera Seminario				[26]
	P. sp.	Estancia Ré				[21]
Proctenomys	P. simpsoni	El Guanaco Barrancas Coloradas				[33]
Protabrocoma	P. chasicoensis	Telén				[16][34]
Octodontoidea	indet.	Estancia Ré				[29]
Orthomyctera	O. sp.	Grünbein Cantera Seminario Salinas de Hidalgo				[26][13]
Reigechimys	R. octodontiformis	Bajo Giuliani Estancia Ré				[35]
	R. plesiodon	Laguna Chillhué				[36]
	R. simplex	Bajo Giuliani				[35]
Tetrastylus	T. araucanus	Salinas de Hidalgo				[13]
	Tetrastylus sp.	Telén				[16]
Theridomysops	T. parvulus	Telén				[16]
Xenodontomys	X. ellipticus	Grünbein Cantera Seminario Barrancas de Sarmiento				[26]

Xenarthrans

Cingulata

Taxa	Species	Presence	Abundance	Description	Images	Notes
Aspidocalyptus	A. castroi	Robilote Field Salinas de Hidalgo				[13][37]
	A. sp.	Telén				[16]
	A. cf. sp.	Grünbein Cantera Relleno Sanitario Level 2				[26]
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][38] [39][40]
	C. cf. peiranoi	Grünbein Cantera Relleno Sanitario Level 2				[26]
	C. sp.	El Recado				[26][40]
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][38] [39][40]
	Chorobates sp.	Grünbein Cantera Seminario				[26]
Coscinocercus	C. brachyurus	Robilote Field Salinas de Hidalgo				[13][37]
	C. marcalaini	Robilote Field Salinas de Hidalgo				[13][37]
	C. sp.	Telén				[16]
Doellotatus	D. chapadmalensis	El Recado Salinas de Hidalgo				[13][40]
	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] [38][39] [40][16]
	D. cf. praecursor	Grünbein Cantera Seminario				[26]
	D. sp.	Laguna La Paraguaya				[40]
Eosclerocalyptus	E. sp.	Laguna La Paraguaya				[41]
Eumysops	E. sp.	Laguna Chillhué				[20]
Glyptodontidae	indet.	Laguna La Paraguaya Salinas Grandes de Hidalgo				[41]
Hoplophorus	H. sp.	Telén				[16]
Hoplophractus	H. tapinocefalus	Laguna de los Paraguayos Salinas de Hidalgo				[13][42]
	H. sp.	Telén				[16]
Macrochorobates	M. chapalmalensis	El Guanaco Barrancas Coloradas				[38]
	M. scalabrinii	Laguna Chillhué Estancia Don Mariano Telen Loventué Quehué Salinas de Hidalgo				[13][38] [39][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] [38][39] [40][16]
	M. retusus	Salinas de Hidalgo				[13]
	M. sp.	Grünbein Cantera Relleno Sanitario Level 2 El Recado				[26][40]
Paleuphractus	P. sp.	Salinas de Hidalgo				[13]
Plohophorus	P. araucanus	Salinas de Hidalgo				[13]
Proeuphractus	P. limpidus	Laguna Chillhué Telén				[38][16]
	P. sp.	Laguna Chillhué Cerro Patagua Telen El Recado Laguna Guatraché Quehué Salinas de Hidalgo				[13][38] [39][40] [16]
Pseudoplohophorus	P. cf. sp.	Grünbein Cantera Relleno Sanitario Level 2				[26]
Vetelia	V. perforata	Cerro Patagua Cerro de los Guanacos Telén				[38][39][16]
Zaedyus	Z. pichiy	Laguna Chillhué Telen Quehué				[39]

Pilosans

Taxa	Species	Presence	Abundance	Description	Images	Notes
Mylodontidae	indet.	Telén				[16]
Plesiomegatherium	P. sp.	Salinas de Hidalgo				[13]
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				[43][44] [22][45]

Litopterns

Taxa	Species	Presence	Abundance	Description	Images	Notes
Brachytherium	B. cf. cuspidatum	Telén Salinas de Hidalgo				[13][16]
Diplasiotherium	D. pampa	Bajo Giuliani Laguna Chillhué Salinas de Hidalgo		A litoptern.		[13][46]
Eoauchenia	E. cingulata	Robilote Field Salinas de Hidalgo				[13][37]
	E. primitiva	El Guanaco				[46]
Epecuenia	E. thoatherioides	Robilote Field Salinas de Hidalgo				[13][37]
Huayqueriana	H. cristata	Robilote Field Salinas de Hidalgo		Previously called as Macrauchenia latidens.		[37][13][47]
Litopterna	indet.	Telén				[16]
Neobrachytherium	N. sp.	Bajo Giuliani Salinas de Hidalgo				[13][46]
Promacrauchenia	P. sp.	Grünbein Cantera Relleno Sanitario Level 2 Salinas de Hidalgo				[13][26]
Proterotheriidae	indet.	Bajo Giuliani Telén				[46][16]

Notoungulate

Taxa	Species	Presence	Abundance	Description	Images	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.		[48][39] [38][49]
	H. lazai	Salinas de Hidalgo				[13]
Mesotheriinae	indet.	Laguna La Paraguaya Telén				[16][41]
Paedotherium	P. bonaerense	Barrancas de Sarmiento		A notoungulate.		[26]
	P. minor	Laguna La Paraguaya Estancia Ré Salinas de Hidalgo				[13][41]
	P. cf. minor	Grünbein Cantera Seminario				[26]
	P. sp.	Bajo Giuliani Laguna Chillhué Estancia Ré				[29]
Pisanodon	P. nazari	Salinas de Hidalgo		A toxodont.		[13]
Pseudotypotherium	P. carhuense	Robilote Field Salinas de Hidalgo		A mesotheriidae notoungulate.		[13][37]
Tremacyllus	T. impressus	Grünbein Cantera Seminario Bajo Giuliani Laguna Chillhué Salinas Grandes de Hidalgo Quehué Barrancas Coloradas		A hegetotheriidae notoungulate.		[26][49]
Typotheriodon	T. grandis	Robilote Field				[37]
Typotheriopsis	T. minimus	Robilote Field		A Mesotheriidae notoungulate.		[37]

Reptiles

Taxa	Species	Presence	Abundance	Description	Images	Notes
Tupinambis	T. sp.	Telén				[16]
Chelidae	indet.	Telén				[16]
Testudinidae	indet.	Salinas de Hidalgo				[50]

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				Hualfín		Tontal	Andes	Salta	Amazon	Huasi	Altiplano	BA	Velasco	Falcón	Cerro Azul Formation (South America)
Country	Argentina			Uruguay		Argentina					Brazil  Peru	Bolivia		Argentina		Venezuela
Cardiatherium
Lagostomus
Macroeuphractus
Proeuphractus
Pronothrotherium
Pseudotypotherium
Thylacosmilus
Xotodon
Macraucheniidae
Primates
Rodents
Reptiles
Birds
Terror birds
Flora
Environments	Aeolian-fluvial	Fluvio-deltaic			Fluvial						Fluvio-lacustrine	Fluvial			Fluvio-lacustrine	Fluvio-deltaic	Huayquerian volcanoclastics Huayquerian fauna Huayquerian flora
Volcanic						Yes

See also

• South American land mammal ages
• Honda Group
• Ituzaingó Formation
• Pebas Formation
• Urumaco