Tralcán Formation (Spanish: Formación Tralcán) is a sedimentary formation of Triassic age in Los Ríos Region in south–central Chile. It overlies unconformably the Trafún Metamorphic Complex. Tralcán Formation and nearby Panguipulli Formation form possibly the remnants of an ancient lake and river system. The formation is named after Mount Tralcán on the western edge of Riñihue Lake.^[1]

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Tralcán Formation
Stratigraphic range: Rhaetian
Type	Geological formation
Underlies	Quaternary glacial deposits
Overlies	Trafún Metamorphic Complex
Thickness	>800 m (2,600 ft)
Lithology
Primary	Conglomerate, sandstone, mudstone
Other	Shale
Location
Coordinates	39.8°S 72.5°W / -39.8; -72.5
Region	Los Ríos Region
Country	Chile
Type section
Named for	Tralcán
Named by	Aguirre & Levi
Year defined	1964
Tralcán Formation (Chile)

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The Tralcán Formation was first defined by Aguirre and Levi in 1964, based on the outcrop at Tralcán. The more than 800 metres (2,600 ft)^[1] thick formation comprises reddish-grey conglomerates with a sandy matrix and intercalated reddish shales. The shales of the formation contain abundant fossil flora. Fossils of Cladophlebistenia oeshi have helped to redefine the age of the formation, that was formerly considered Late Jurassic (Kimmeridgian to Tithonian), to the Rhaetian of the Triassic.^[2]

The following genera of fossil flora have been identified in the formation:^[1]