Río Frías Formation, Geological formation in Aysén Region, Chile
The Río Frías Formation is a geological formation in the Aysén Region of western Patagonia that extends along the upper course of the Cisnes River. It is composed of sedimentary rocks and volcanic deposits laid down in this remote area over time.
Santiago Roth first documented the formation in 1897-98 while conducting surveys under the direction of Francisco Moreno from the La Plata Museum. This discovery helped identify an important geological time period recognized in South American science.
The formation established the Friasian period in South American Land Mammal Ages, marking a significant milestone in regional geological classification systems.
Access to the formation requires specialized equipment and official permits due to its location in rugged mountain terrain in southern Chile. Extreme weather conditions and lack of infrastructure mean careful planning is essential for any visit.
The rock layers contain fossils of marsupials such as Astrapotherium hesperinum and Prothylacinus patagonicus from the Miocene epoch. These remains represent animals that lived in this region roughly 16.5 million years ago.
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