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Río Frías Formation
Stratigraphic range: Middle Miocene (Friasian) ~16.5–15.5 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Geological formation
Overlies	Ñirehuao Formation
Lithology
Primary	Tuff, tuffite, siltstone, unconsolidated sand, conglomerate
Location
Coordinates	44°36′S 71°12′W / 44.6°S 71.2°W / -44.6; -71.2
Approximate paleocoordinates	45°12′S 66°18′W / 45.2°S 66.3°W / -45.2; -66.3
Region	Aysén Region
Country	Chile
Extent	Aysén Basin
Type section
Named for	Río Frías
Named by	Santiago Roth
Year defined	1898
Río Frías Formation (Chile)

Río Frías Formation (Spanish: Formación Río Frías) is a Middle Miocene geologic formation made up sedimentary rock located in Aysén Region, western Patagonia. The formation crops out along the upper course of Cisnes River (Spanish: Río Cisnes). Marsupial fossils have been found in the formation. The Friasian period in the South American Land Mammal Ages is named after the formation.

Description

Río Frías Formation was discovered by Santiago Roth in the summer of 1897–98. Roth was a Swiss immigrant who had been sent to survey the area by Francisco Moreno. Moreno was director of La Plata Museum and was involved in the Cordillera of the Andes Boundary Case between Chile and Argentina, thus there was both a political and scientific motivation behind the exploration of Patagonia. Santiago Roth called the upper course of Río Cisnes for Río Frías being unaware that it was the same river. Further he thought this unexplored area to be in Argentina and not in Chile. This led the formation to acquire its name. Roth sent fossils he collected from the formation to Florentino Ameghino who was active at La Plata. It was with this fossils Ameghino established the Friasian period. Later research on Ar/Ar data revealed the base of the formation dating to 16.5 Ma, which means a slight overlap with the Santacrucian land mammal age (ending at 16.3 Ma). The formation was deposited in a fluvial environment, characterized by an intermontane valley flanked by Cretaceous basement rocks.

Fossil content

The following fossils have been found in the formation:

Group	Fossils	Image	Notes
Mammals	Astrapotherium hesperinum
	Prothylacinus patagonicus
	Adinotherium sp.
	Nesodon sp.
	Protypotherium sp.
	Borhyaena tuberata
	Theosodon sp.
	Cladosictis patagonica
	Pachyrukhos sp.
	Homalodotherium sp.
	Abderites meridionalis, Alloiomys friasensis, Megathericulus friasensis, Microbiotherium tehuelchum, Parabderites bicrispatus, Palaeothentes intermedius, P. lemoinei, P. minutus, Pichipilus halleuxi, Pitheculites rothi, Prototrigodon rothi, Sipalocyon gracilis, Neonematherium sp., Phoenixauchenia sp., ?Propalaehoplophorus sp., Prozaedyus sp., Trachytypotherium sp., Platyrrhini indet.

References

1. ^ Marshall & Salinas, 1990
2. Marshall, 1990
3. Paleo Database: Friasian
4. Bostelmann et al., 2012, p.44
5. Bellosi et al., 2014, p.40
6. Río Frías at Fossilworks.org
7. Alto Río Cisnes at Fossilworks.org

Bibliography

• Abello, María Alejandra; Rubilar Rogers, David (2012), "Revisión del género Abderites Ameghino, 1887 (Marsupialia, Paucituberculata)", Ameghiniana, 49 (2): 164–184, doi:10.5710/AMGH.v49i2(408), retrieved 2019-02-15
• Bellosi, Eduardo S. (2014), Ambientes asociados a la fauna Friasense (Mioceno Medio) en Alto río Cisnes (Aysén, Chile), XIV Reuñión Argentina de Sedimentología, pp. 40–41, retrieved 2018-09-10
• Bostelmann, J.E. (2012), The Alto Río Cisnes Fossil Fauna (Río Frías Formation, Early-Middle Miocene, Friasian SALMA): A keystone and paradigmatic vertebrate assemblage of the South American Fossil Record, III Simposio Paleontología en Chile, pp. 44–45, retrieved 2018-09-10
• Marshall, Larry G (1990), "Fossil Marsupialia from the type Friasian land mammal age (Miocene), Alto Río Cisnes, Aisén, Chile", Revista Geológica de Chile, 17: 19–55, retrieved 2017-10-21
• Marshall, Larry G.; Salinas, Patricia (1990), "Stratigraphy of the Río Frías Formation (Miocene) along the Alto Río Cisnes, Aisén, Chile", Revista Geológica de Chile, 17: 57–87, retrieved 2017-10-21

v t e South American land mammal ages
Ages	Lujanian Ensenadan Uquian Chapadmalalan Montehermosan Huayquerian Chasicoan Mayoan Laventan Colloncuran Friasian Santacrucian Colhuehuapian Deseadan Tinguirirican Divisaderan Mustersan Casamayoran Itaboraian Riochican Peligran Tiupampan
Defining formations and sites	Quaternary Luján Formation Ensenada Formation Uquía Formation Neogene Chapadmalal Formation Monte Hermoso Formation Huayquerías Formation Arroyo Chasicó Formation Río Mayo Formation Honda Group La Venta fauna Collón Curá Formation Río Frías Formation Santa Cruz Formation Colhué Huapí Member Paleogene Deseado Formation Abanico Formation Tinguiririca fauna Divisadero Largo Formation Sarmiento Formation Lake Musters Casamayor Formation Itaboraí Formation Río Chico Group Salamanca Formation Punta Peligro Santa Lucía Formation Tiupampa fauna
Sources	Bibliography
Category • Images

v t e Geology of Chile
Terranes	Arequipa-Antofalla Chaitenia Chilenia Chiloé Cuyania Fitz Roy Madre de Dios Mejillonia Patagonia
Sedimentary formations and groups	Cenozoic Neogene Abanico Fm. Angostura Fm. Ayacara Fm. Bahía Inglesa Fm. Caldera Beds Caleta Godoy Fm. Caleta Herradura Fm. Campanario Fm. Chaicayán Gp. Cheuquemó Fm. Cholchol Fm. Chucal Fm. Cola de Zorro Fm. Coquimbo Fm. Cura-Mallín Gp. Farellones Fm. La Cascada Fm. Lacui Fm. La Montaña Fm. La Portada Fm. Lauca Fm. Malleco Fm. Mininco Fm. Navidad Fm. Oxaya Fm. Parga Fm. Puduhuapi Fm. Pupunahue Beds Quebrada Macusa Fm. Ranquil Fm. Río Frías Fm. San Pedro Beds Santo Domingo Fm. Temuco Fm. Traiguén Fm. Trapa-Trapa Fm. Tubul Fm. Vargas Fm. Paleogene Abanico Fm. Azapa Fm. Caleta Chonos Fm. Cheuquemó Fm. Cura-Mallín Gp. La Cascada Fm. Lebu Gp. Loreto Fm. Lupica Fm. Oxaya Fm. Parga Fm. Purilactis Gp. Pupunahue Beds Temuco Fm. Vargas Fm. Mesozoic Cretaceous Baños del Flaco Fm. Cerro Colorado Fm. Chacarilla Fm. Chañarcillo Gp. Coihaique Gp. Divisadero Gp. Dorotea Fm. Hornitos Fm. La Liga Fm. Ñirehuao Fm. Punta del Cobre Fm. Purilactis Gp. Quiriquina Fm. Viñita Fm. Way Gp. Zapata Fm. Jurassic Chacarilla Fm. Coihaique Gp. Ibáñez Fm. La Liga Fm. La Negra Fm. Nacientes del Biobío Fm. Nacientes del Teno Fm. Pan de Azúcar Fm. Tobífera Fm. Triassic Canto del Agua Fm. Choiyoi Gp. Panguipulli Fm. Santa Juana Fm. Tralcán Fm. Paleozoic Llano de Chocolate Beds
Batholiths	Coastal central Chile Elqui-Limarí Futrono-Riñihue North Patagonian Panguipulli South Patagonian Vicuña Mackenna
Metamorphic complexes	Bahía Mansa Belén Chañaral Choapa Chonos Cordillera Darwin Eastern Andes Mejillones Puerto Edén Punta de Choros Quebrada del Carrizo Trafún Tierra del Fuego
Faults	Atacama Fault Biobío-Aluminé Fault Cachet Fault Domeyko Fault El Arrayán Fault Futrono Fault Gastre Fault Lanalhue Fault Liquiñe-Ofqui Fault Magallanes-Fagnano Fault Mocha-Villarrica Fault Pichilemu Fault Reigolil-Pirihueico Fault San Ramón Fault Valeriano Fault
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• Geologic formations of Chile
• Miocene Series of South America
• Neogene Chile
• Friasian
• Tuff formations
• Siltstone formations
• Conglomerate formations
• Fluvial deposits
• Austral or Magallanes Basin
• Geology of Aysén Region