Cerro Azul Formation

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]

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

Locations:

La Pampa

Buenos Aires

Group	Clade	Taxa	Location	Images	Notes
Mammals	Carnivora	Cyonasua brevirostris	Salinas de Hidalgo		[12]
		C. prebrevirostris	Salinas de Hidalgo		[12]
		Cyonasua sp.	Telén		[13]
	Sparassodonta	Borhyaenidium musteloides	Salinas de Hidalgo		[12]
		Thylacosmilus atrox	El Guanaco Quehué Salinas de Hidalgo		[12][14]
		Borhyaenidae indet.	Telén		[13]
	Rodents	Abrocoma antiqua	Estancia Ré		[15]
		Cardiatherium aff. orientalis	Laguna Chillhué Laguna Guatraché		[16]
		Chasichimys bonaerense	Cerro Patagua		[17]
		C. scagliai	Laguna Chillhué		[17]
		Neocavia pampeana	Estancia El Recado		[18]
		Lagostomus pretrichodactyla	Salinas de Hidalgo		[12]
		Neophanomys pristinus	Estancia Don Mariano Quehué		[19]
		Palaeoctodon aff. simplicidens	Bajo Giuliani		[20][21]
		Pampamys emmonsae	Laguna Chillhué Bajo Giuliani Estancia Ré		[21][22]
		Phtoramys hidalguense	Barrancas Coloradas Salinas de Hidalgo		[21][23]
		Proctenomys simpsoni	El Guanaco Barrancas Coloradas		[24]
		Reigechimys octodontiformis	Bajo Giuliani Estancia Ré		[25]
		R. plesiodon	Laguna Chillhué		[26]
		R. simplex	Bajo Giuliani		[25]
		Tetrastylus araucanus	Salinas de Hidalgo		[12]
		Theridomysops parvulus	Telén		[13]
		Xenodontomys ellipticus	Grünbein Cantera Seminario Barrancas de Sarmiento		[27]
		Phtoramys cf. hidalguense	Grünbein Cantera Seminario		[27]
		Cardiomys sp.	Salinas de Hidalgo		[12]
		Chasichimys sp.	Bajo Giuliani		[17]
		Dolicavia sp.	Grünbein Cantera Seminario		[27]
		Lagostomus (Lagostomopsis) sp.	Grünbein Cantera Seminario Barrancas de Sarmiento Estancia Ré Salinas de Hidalgo		[12][15][27]
		Neocavia sp.	Grünbein Cantera Seminario		[27]
		Neophanomys sp.	Estancia Ré		[28]
		Orthomyctera sp.	Grünbein Cantera Seminario Salinas de Hidalgo		[27][12]
		Palaeocavia sp.	Grünbein Cantera Seminario Barrancas de Sarmiento Estancia Ré		[12][15][27]
		Phtoramys sp.	Estancia Ré		[15]
		Protabrocoma sp.	Telén		[13]
		Tetrastylus sp.	Telén		[13]
		aff. Clyomys sp.	Barrancas Coloradas		[21]
		Caviidae indet.	Barrancas de Sarmiento		[27]
		Ctenomyidae indet.	Telén		[13]
		Echimyidae indet.	Telén		[13]
		Hydrochoeridae indet.	Salinas de Hidalgo		[14]
		Octodontoidea indet.	Estancia Ré		[28]
	Xenarthra	Aspidocalyptus castroi	Robilote Field Salinas de Hidalgo		[12][29]
		Coscinocercus brachyurus	Robilote Field Salinas de Hidalgo		[12][29]
		C. marcalaini	Robilote Field Salinas de Hidalgo		[12][29]
		Hoplophractus tapinocefalus	Laguna de los Paraguayos Salinas de Hidalgo		[12][30]
		Plohophorus araucanus	Salinas de Hidalgo		[12]
		Proscelidodon 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		[31][32] [33][34]
		Aspidocalyptus sp.	Telén		[13]
		Coscinocercus sp.	Telén		[13]
		Eosclerocalyptus sp.	Laguna La Paraguaya		[35]
		Eumysops sp.	Laguna Chillhué		[21]
		Hoplophorus sp.	Telén		[13]
		Hoplophractus sp.	Telén		[13]
		Plesiomegatherium sp.	Salinas de Hidalgo		[12]
		cf. Aspidocalyptus sp.	Grünbein Cantera Relleno Sanitario Level 2		[27]
		cf. Pseudoplohophorus sp.	Grünbein Cantera Relleno Sanitario Level 2		[27]
		Glyptodontidae indet.	Laguna La Paraguaya Salinas Grandes de Hidalgo		[35]
		Mylodontidae indet.	Telén		[13]
	Cingulata	Chasicotatus 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		[13][36] [37][38]
		Chasicotatus cf. peiranoi	Grünbein Cantera Relleno Sanitario Level 2		[27]
		Chorobates 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		[12][27][36] [37][38]
		Doellotatus chapadmalensis	El Recado Salinas de Hidalgo		[12][38]
		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		[12][27] [36][37] [38][13]
		D. cf. praecursor	Grünbein Cantera Seminario		[27]
Macrochorobates chapalmalensis		El Guanaco Barrancas Coloradas		[36]
M. scalabrinii		Laguna Chillhué Estancia Don Mariano Telen Loventué Quehué Salinas de Hidalgo		[12][36] [37][13]
Macroeuphractus 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		[12][27] [36][37] [38][13]
M. retusus		Salinas de Hidalgo		[12]
Proeuphractus limpidus		Laguna Chillhué Telén		[36][13]
Vetelia perforata		Cerro Patagua Cerro de los Guanacos Telén		[36][37][13]
Zaedyus pichiy		Laguna Chillhué Telen Quehué		[37]
Chasicotatus sp.		El Recado		[27][38]
Chorobates sp.		Grünbein Cantera Seminario		[27]
Doellotatus sp.		Laguna La Paraguaya		[38]
Macrochorobates sp.		Grünbein Cantera Relleno Sanitario Level 2 El Recado		[27][38]
Paleuphractus sp.		Salinas de Hidalgo		[12]
Proeuphractus sp.		Laguna Chillhué Cerro Patagua Telen El Recado Laguna Guatraché Quehué Salinas de Hidalgo		[12][36] [37][38] [13]
Didelphimorphia	Hyperdidelphys pattersoni	El Guanaco Telén		[14][13]
	Thylamys pinei	Laguna Chillhué		[21]
	T. zetti	Estancia Ré Arroyo Guaminí		[15][33]
	Thylatheridium dolgopolae	El Guanaco Quehué Telén		[39][13]
	T. hudsoni	Bajo Giuliani Telén		[14][13]
	Zygolestes tatei	Bajo Giuliani		[14][21]
	Hyperdidelphys sp.	Salinas Grandes de Hidalgo		[40]
	Thylatheridium sp.	Estancia Ré Telén		[15][13]
	Didelphinae indet.	Telén		[13]
	Lutreolina sp.	Salinas de Hidalgo		[12]
	Sparassocynidae indet.	Telen		[14][13]
Ungulates	Diplasiotherium pampa	Bajo Giuliani Laguna Chillhué Salinas de Hidalgo		[12][41]
	Eoauchenia cingulata	Robilote Field Salinas de Hidalgo		[12][29]
	E. primitiva	El Guanaco		[41]
	Epecuenia thoatherioides	Robilote Field Salinas de Hidalgo		[12][29]
	Huayqueriana cristata	Robilote Field		[29]
	Macrauchenia latidens	Salinas de Hidalgo		[12]
	cf. Brachytherium cuspidatum	Telén Salinas de Hidalgo		[12][13]
	Neobrachytherium sp.	Bajo Giuliani Salinas de Hidalgo		[12][41]
	Promacrauchenia sp.	Grünbein Cantera Relleno Sanitario Level 2 Salinas de Hidalgo		[12][27]
	Proterotheriidae indet.	Bajo Giuliani Telén		[41][13]
	Litopterna indet.	Telén		[13]
Notoungulata	Hemihegetotherium achataleptum	Cerro Patagua Eduardo Castex Cerro de los Guanacos Puesto Colorado Bajo Giuliani Laguna Chillhué Loventué Salinas de Hidalgo		[42][37] [36][43]
	H. lazai	Salinas de Hidalgo		[12]
	Paedotherium bonaerense	Barrancas de Sarmiento		[27]
	Paedotherium minor	Laguna La Paraguaya Estancia Ré Salinas de Hidalgo		[12][35]
	Paedotherium cf. minor	Grünbein Cantera Seminario		[27]
	Pisanodon nazari	Salinas de Hidalgo		[12]
	Pseudotypotherium carhuense	Robilote Field Salinas de Hidalgo		[12][29]
	Tremacyllus impressus	Grünbein Cantera Seminario Bajo Giuliani Laguna Chillhué Salinas Grandes de Hidalgo Quehué Barrancas Coloradas		[27][43]
	Typotheriodon grandis	Robilote Field		[29]
	Typotheriopsis minimus	Robilote Field		[29]
	Paedotherium sp.	Bajo Giuliani Laguna Chillhué Estancia Ré		[44]
	Mesotheriinae indet.	Laguna La Paraguaya Telén		[13][35]
Polydolopimorphia	Argyrolagus rusconii	Bajo Giuliani El Guanaco Barrancas Coloradas		[14]
	Argyrolagidae indet.	Telén		[13]
Paucituberculata	Pliolestes venetus	Bajo Giuliani Laguna Chillhué		[14]
Birds	Phorusrhacidae	Devincenzia pozzi	Carhué		[45]
		Procariama simplex	Salinas de Hidalgo		[46]
		Phorusrhacidae indet.	Laguna Guatraché Carhué		[45]
	Cathartidae	Argentavis magnificens	Carhué		[12]
	Tinamiformes	Eudromia sp.	Salinas de Hidalgo		[45]
		Nothura sp.	Bajo Giuliani El Guanaco Salinas de Hidalgo		[45]
	Rheidae	Rhea sp.	Salinas de Hidalgo		[45]
Reptiles	Squamata	Tupinambis sp.	Telén		[13]
	Testudines	Chelidae indet.	Telén		[13]
		Testudinidae indet.	Salinas de Hidalgo		[47]
Amphibians	Ceratophrynidae	Lepidobatrachus sp.	Quehué		[48]