The Huitrera Formation is a geological

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 ...

in the

Neuquén Basin Neuquén Basin ( es, Cuenca Neuquina) is a sedimentary basin covering most of Neuquén Province in Argentina. The basin originated in the Jurassic and developed through alternating continental and marine conditions well into the Tertiary. The ba ...

in northern

Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and ...

Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, t ...

whose strata date back to the

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

of the

Paleogene The Paleogene ( ; also spelled Palaeogene or Palæogene; informally Lower Tertiary or Early Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago (Mya) to the beginning of ...

, or Casamayoran in the

South American land mammal age 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 ...

classification.

Description

The Huitrera Formation was first defined by Ravazzoli and Sesana in 1977. The name has been used to identify various volcaniclastic sequences, among others in the Ñirihuau fold-and-thrust belt.Escosteguy & Franchi, 2010, p.420 The up to thick formation comprises mudstones and

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s deposited in a

crater lake Crater Lake (Klamath: ''Giiwas'') is a volcanic crater lake in south-central Oregon in the western United States. It is the main feature of Crater Lake National Park and is famous for its deep blue color and water clarity. The lake partly fills ...

environment Environment most often refers to: __NOTOC__ * Natural environment, all living and non-living things occurring naturally * Biophysical environment, the physical and biological factors along with their chemical interactions that affect an organism or ...

. Part of the formation comprises

andesite Andesite () is a volcanic rock of intermediate composition. In a general sense, it is the intermediate type between silica-poor basalt and silica-rich rhyolite. It is fine-grained (aphanitic) to porphyritic in texture, and is composed predomina ...

s, dacitic and

rhyolitic Rhyolite ( ) is the most silica-rich of volcanic rocks. It is generally glassy or fine-grained ( aphanitic) in texture, but may be porphyritic, containing larger mineral crystals ( phenocrysts) in an otherwise fine-grained groundmass. The miner ...

ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...

s, volcanic

breccia Breccia () is a rock composed of large angular broken fragments of minerals or rocks cemented together by a fine-grained matrix. The word has its origins in the Italian language, in which it means "rubble". A breccia may have a variety of d ...

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

s and trachybasalts.Prez & Massafero, 2013, p.228 The formation was initially described as

Late Eocene The Eocene ( ) Epoch is a geological epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''ēṓs'', "d ...

Early Oligocene The Rupelian is, in the geologic timescale, the older of two ages or the lower of two stages of the Oligocene Epoch/ Series. It spans the time between . It is preceded by the Priabonian Stage (part of the Eocene) and is followed by the Chattia ...

, but was later dated to 54.24 ± 0.45 Ma, meaning the Huitrera Formation is

Ypresian In the geologic timescale the Ypresian is the oldest age or lowest stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by the Eocene Lutetian Age. The Ypresian i ...

, or in the SALMA classification, Casamayoran in age.

Fossil content

The following macrofossils were reported from the formation:Huitrera Formation
at

Fossilworks Fossilworks is a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cre ...

.org *

Bird Birds are a group of warm-blooded vertebrates constituting the class Aves (), characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a strong yet lightweig ...

s ** ''

Ueekenkcoracias ''Ueekenkcoracias'' is an extinct genus of primobucconid bird in the order Coraciiformes from the Huitrera Formation of Patagonia. A relatively large member of the stem-Coracii, ''Ueekenkcoracias'' possessed a robust femur and stout tibiotarsu ...

'' * Amphibians ** '' Llankibatrachus truebae''Báez & Pugener, 2003 ** '' Patagopipa corsolinii''Aranciaga et al., 2019 *

Insects Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs ...

Odonata Odonata is an order of flying insects that includes the dragonflies and damselflies. Members of the group first appeared during the Triassic, though members of their total group, Odonatoptera, first appeared in Late Carboniferous. The two co ...

*** '' Inacayalestes aikunhuapi'' **

Beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s *** '' Thesaurus punctatus''Jin et al., 2020 (originally ''

Catogenus ''Catogenus'' is a genus of beetles in the family Passandridae Passandridae, the "parasitic flat bark beetles," are a family of beetles notable for being one of the very few beetle families with larvae that are, as far as known, exclusively ect ...

'')Ramírez et al., 2016 *

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 ...

** '' Menispermites calderensis''Jud et al., 2018 ** '' Raiguenrayun cura''Barrera et al., 2012 ** Cupressaceae indet. ** Podocarpaceae indet. ** Lauraceae indet. The formation has also provided many

pollen Pollen is a powdery substance produced by seed plants. It consists of pollen grains (highly reduced microgametophytes), which produce male gametes (sperm cells). Pollen grains have a hard coat made of sporopollenin that protects the gametop ...

, analyzed in 2003 by Melendi et al.Melendi et al., 2003

References

Bibliography

* * * * * * * * * {{cite LSA , last=Melendi , first=D.L. , first2=L.H. , last2=Scafati , first3=W. , last3=Volkheimer , year=2003 , title=Palynostratigraphy of the Paleogene Huitrera Formation in N-W Patagonia, Argentina , journal= Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen , volume=228 , pages=205-273 Geologic formations of Argentina Eocene Series of South America Paleogene Argentina Ypresian Stage Casamayoran Mudstone formations Sandstone formations Tuff formations Lacustrine deposits Formations Fossiliferous stratigraphic units of South America Paleontology in Argentina Geology of Neuquén Province Geology of Río Negro Province

Description

Fossil content

See also

References

Bibliography