Río Frías Formation () is a

Middle Miocene The Middle Miocene is a sub-epoch of the Miocene epoch (geology), epoch made up of two Stage (stratigraphy), stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene. The sub-epoch lasted from 15.97 ± 0. ...

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 (geology), rock formed by the cementation (geology), cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or de ...

located in

Aysén Region The Aysén del General Carlos Ibáñez del Campo Region (, , '), often shortened to Aysén Region or Aisén,Examples of name usage1, official regional government site refers to the region as "Región de Aysén"., Chile's official meteorological ...

, western Patagonia. The formation crops out along the upper course of Cisnes River ().Marshall & Salinas, 1990

Marsupial Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a r ...

fossils have been found in the formation.Marshall, 1990 The Friasian 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
/ref>

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 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, especial ...

who was active at La Plata. It was with this fossils Ameghino established the Friasian 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 Mya (unit), Ma) within the Early Miocene epoch of the Neogene, used more specifically with South American land mammal age, SALMA classification in South America. It follows the Colhue ...

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

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

environment, characterized by an intermontane valley flanked by

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

basement A basement is any Storey, floor of a building that is not above the grade plane. Especially in residential buildings, it often is used as a utility space for a building, where such items as the Furnace (house heating), furnace, water heating, ...

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 of Chile Siltstone formations Conglomerate formations Fluvial deposits Formations Geology of Aysén Region