Río Frías Formation ( es, Formación Río Frías) is a

Middle Miocene The Middle Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene. The sub-epoch lasted from 15.97 ± 0.05 Ma to 11.608 ± 0.005 Ma (million y ...

geologic 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 exp ...

made up

sedimentary rock Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...

located in Aysén Region, western Patagonia. The formation crops out along the upper couse of

Cisnes River The Cisnes River (Spanish for ''swan'') is a river located in the Aysén del General Carlos Ibáñez del Campo Region of the Chilean Patagonia. It runs in east-west direction from the mountains near the border to Argentina and empties into the Pa ...

( es, Río Cisnes).Marshall & Salinas, 1990

Marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a po ...

fossils have been found in the formation.Marshall, 1990 The

Friasian The Friasian age is a period of geologic time (16.3–15.5 Ma) within the Early Miocene epoch of the Neogene, used more specifically within the SALMA classification of South America. It follows the Santacrucian and precedes the Colloncuran age. ...

period in the

South American Land Mammal Ages The South American land mammal ages (SALMA) establish a geologic timescale for prehistoric South American fauna beginning 64.5 Ma during the Paleocene and continuing through to the Late Pleistocene (0.011 Ma). These periods are referred to as age ...

is named after the formation.Paleo Database: Friasian
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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 The 1902 Arbitral award of the Andes between Argentina and Chile ( es, Laudo limítrofe entre Argentina y Chile de 1902) was a British arbitration in 1902 that established the present-day boundaries between Argentina and Chile. In northern and ce ...

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 Florentino Ameghino (born Giovanni Battista Fiorino Giuseppe Ameghino September 19, 1853 – August 6, 1911) was an Argentine naturalist, paleontologist, anthropologist and zoologist, whose fossil discoveries on the Argentine Pampas, especially ...

who was active at La Plata. It was with this fossils Ameghino established the

period. Later research on ⁴⁰Ar/³⁹Ar data revealed the base of the formation dating to 16.5 Ma, which means a slight overlap with the

Santacrucian The Santacrucian age is a period of geologic time (17.5 – 16.3 Ma) within the Early Miocene epoch of the Neogene, used more specifically with SALMA classification in South America. It follows the Colhuehuapian and precedes the Friasian age. ...

land mammal age (ending at 16.3 Ma).Bostelmann et al., 2012, p.44 The formation was deposited in a

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluviog ...

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

, characterized by an intermontane valley flanked by

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...

basement A basement or cellar is one or more floors of a building that are completely or partly below the ground floor. It generally is used as a utility space for a building, where such items as the furnace, water heater, breaker panel or fuse box, ...

rocks.Bellosi et al., 2014, p.40

Fossil content

The following fossils have been found in the formation:

References

Bibliography

* * * * * {{Geology of Chile, state=expanded Geologic formations of Chile Miocene Series of South America Neogene Chile Tuff formations Siltstone formations Conglomerate formations Fluvial deposits Formations Geology of Aysén Region