Río Frías Formation

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 couse of Cisnes River (Spanish: Río Cisnes).[1] Marsupial fossils have been found in the formation.[2] The Friasian period in the South American Land Mammal Ages is named after the formation.[3]

Río Frías Formation
Stratigraphic range: Middle Miocene
(Friasian)
~
TypeGeological formation
OverliesÑirehuao Formation
Lithology
PrimaryTuff, tuffite, siltstone, unconsolidated sand, conglomerate
Location
Coordinates44.6°S 71.2°W / -44.6; -71.2
Approximate paleocoordinates45.2°S 66.3°W / -45.2; -66.3
RegionAysén Region
Country Chile
ExtentAysén Basin
Type section
Named forRío Frías
Named bySantiago Roth
Year defined1898
Río Frías Formation is located in Chile
Río Frías Formation
Río Frías Formation (Chile)

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.[1] 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.[1] 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 land mammal age (ending at 16.3 Ma).[4] The formation was deposited in a fluvial environment, characterized by an intermontane valley flanked by Cretaceous basement rocks.[5]

Fossil content

The following fossils have been found in the formation:

Group Fossils Image Notes
MammalsAstrapotherium 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

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