Tralcán Formation ( es, Formación Tralcán) is a

sediment Sediment is a naturally occurring material that is broken down by processes of weathering and erosion, and is subsequently transported by the action of wind, water, or ice or by the force of gravity acting on the particles. For example, sa ...

ary

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

age in

Los Ríos Region The Los Ríos Region (Spanish: ''Región de Los Ríos'', , ''Region of the Rivers'') is one of Chile's 16 regions, the country's first-order administrative divisions. Its capital is Valdivia. It began to operate as a region on October 2, 200 ...

in south–central Chile. It overlies

unconformably An unconformity is a buried erosional or non-depositional surface separating two rock masses or strata of different ages, indicating that sediment deposition was not continuous. In general, the older layer was exposed to erosion for an interval o ...

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 The Riñihue Lake ( es, Lago Riñihue ) is a lake of glacial origin in eastern Valdivia Province, southern Chile. It is surrounded by several mountains. The eastern side receives the waters of the Panguipulli Lake by the Enco River, its main con ...

.Herbst et al., 2005

Description

The Tralcán Formation was first defined by Aguirre and Levi in 1964, based on the

outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...

at Tralcán. The more than thick formation comprises reddish-grey conglomerates with a

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a soil texture, textur ...

y matrix and intercalated reddish

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especia ...

s. The shales of the formation contain abundant

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

flora Flora (: floras or florae) is all the plant life present in a particular region or time, generally the naturally occurring (indigenous (ecology), indigenous) native plant, native plants. The corresponding term for animals is ''fauna'', and for f ...

. Fossils of '' Cladophlebistenia oeshi'' have helped to redefine the age of the formation, that was formerly considered

Late Jurassic The Late Jurassic is the third epoch of the Jurassic Period, and it spans the geologic time from 163.5 ± 1.0 to 145.0 ± 0.8 million years ago (Ma), which is preserved in Upper Jurassic strata.Owen 1987. In European lithostratigraphy, the ...

(

Kimmeridgian In the geologic timescale, the Kimmeridgian is an age in the Late Jurassic Epoch and a stage in the Upper Jurassic Series. It spans the time between 157.3 ± 1.0 Ma and 152.1 ± 0.9 Ma (million years ago). The Kimmeridgian follows the Oxford ...

Tithonian In the geological timescale, the Tithonian is the latest age of the Late Jurassic Epoch and the uppermost stage of the Upper Jurassic Series. It spans the time between 152.1 ± 4 Ma and 145.0 ± 4 Ma (million years ago). It is preceded by t ...

), to the

Rhaetian The Rhaetian is the latest age of the Triassic Period (in geochronology) or the uppermost stage of the Triassic System (in chronostratigraphy). It was preceded by the Norian and succeeded by the Hettangian (the lowermost stage or earliest ...

of the Triassic.Di Biase & Lillo, 1973, p.12

Fossil content

The following

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial ...

of fossil flora have been identified in the formation: * ''

Asterotheca ''Asterotheca'' is a genus of seedless, spore-bearing, vascularized ferns dating from the Carboniferous of the Paleozoic to the Triassic of the Mesozoic. Description ''Asterotheca sp.'' is a vascularized, seedless fern that reproduces vi ...

'' * ''

Cladophlebis ''Cladophlebis'' is an extinct form genus of fern, used to refer to Paleozoic and Mesozoic fern leaves that have "fern fronds with pinnules that are attached to the rachis, and have a median vein that runs to the apex of the pinnule, and veins ...

'' * ''

Dicroidium ''Dicroidium'' is an extinct genus of fork-leaved seed ferns that were widely distributed over Gondwana during the Triassic (). Their fossils are known from South Africa, the Arabian Peninsula, Australia, New Zealand, South America, Madagascar, t ...

'' * ''

Ginkgoites ''Ginkgoites'' is a genus that refers to extinct plants belonging to Ginkgoaceae. Fossils of these plants have been found around the globe during the Triassic, Jurassic, Cretaceous, with fossils also known from the Paleogene. The name was create ...

'' * '' Gleichenites'' * '' Heidiphyllum'' * '' Johnstonia'' * ''

Lepidopteris ''Lepidopteris'' ("scaly fern") is a form genus for leaves of Late Permian to Late Triassic Period Pteridospermatophyta, or seed ferns, which lived from around 260 to 200 million years ago in what is now Australia, Antarctica, India, South ...

'' * '' Linguifolium'' * ''

Neocalamites ''Neocalamites'' is an extinct genus of Equisetales, equisetalean plant. ''Neocalamites'' thrived during the Permian and Triassic, and occurs worldwide. Description According to Elgorriaga et al. 2018, characteristics of ''Neocalamites'' include ...

'' * '' Phoenicopsis'' * ''

Pseudoctenis ''Pseudoctenis'' is a genus of fossil foliage attributable to the Cycadales. It is one of the most common genera of cycad fossil foliage in the Mesozoic. Taxonomy The genus was erected by Albert Seward based on material from the Jurassic of Suth ...

'' * ''

Pterophyllum ''Pterophyllum'' is a small genus of freshwater fish from the family Cichlidae known to most aquarists as angelfish. All ''Pterophyllum'' species originate from the Amazon Basin, Orinoco Basin and various rivers in the Guiana Shield in tropica ...

'' * '' Rissikia'' * ''

Sphenobaiera ''Sphenobaiera'' is a form genus for plant leaves found in rocks from Triassic to Cretaceous periods. The genus ''Sphenobaiera'' is used for plants with wedge-shaped leaves that can be distinguished from ''Ginkgo'', ''Ginkgoites'' and '' Baiera' ...

'' * ''

Taeniopteris ''Taeniopteris'' is an extinct form genus of Mesozoic vascular plant leaves, perhaps representing those of cycads, bennettitaleans, or marattialean ferns. The form genus is almost certainly a polyphyletic category for unfertile leaves of a cert ...

References

Bibliography

* * {{Geology of Chile Geologic formations of Chile Triassic Chile Rhaetian Stage Conglomerate formations Shale formations Lacustrine deposits Fluvial deposits Fossiliferous stratigraphic units of South America Paleontology in Chile Geology of Los Ríos Region