Los Bastos Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

of the

Neuquén Basin Neuquén Basin () 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 basin bounds to the wes ...

in the northern

Patagonia Patagonia () is a geographical region that includes parts of Argentina and Chile at the southern end of South America. The region includes the southern section of the Andes mountain chain with lakes, fjords, temperate rainforests, and glaciers ...

n provinces of Mendoza and

Neuquén Neuquén (; ) is the capital city of the Argentine province of Neuquén and of the Confluencia Department, located in the east of the province. It occupies a strip of land west of the confluence of the Limay and Neuquén rivers which form t ...

. The formation dates to the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cre ...

, early to middle Coniacian, and belongs to the

Río Neuquén Subgroup The Río Neuquén Subgroup is a geological subgroup in the Neuquén Basin, Neuquén Province, Argentina, whose strata date back to the Late Cretaceous. The subgroup, formerly defined as a formation, is the middle unit of the Neuquén Group and co ...

of the

Neuquén Group The Neuquén Group is a geologic unit, group of geologic formations found in Argentina. Rocks in the Neuquén Group fall within the Cenomanian to early Campanian stages of the Late Cretaceous Period. It overlies the older Lohan Cura Formation and ...

. The formation overlies the

Portezuelo Formation The Portezuelo Formation is a geologic formation of Late Cretaceous (Turonian, Late Turonian to Coniacian, Early Coniacian) age, outcropping in the Mendoza Province, Mendoza, Río Negro Province, Río Negro and Neuquén Province, Neuquén provinc ...

, in which it was formerly included and is overlain by the

Sierra Barrosa Formation The Sierra Barrosa Formation is a geologic formation of the Neuquén Basin in the northern Patagonian provinces of Mendoza Province, Mendoza and Neuquén Province, Neuquén. The formation dates to the Late Cretaceous, Coniacian, middle to late Con ...

. Los Bastos Formation comprises

mudstone Mudstone, a type of mudrock, is a fine-grained sedimentary rock whose original constituents were clays or muds. Mudstone is distinguished from ''shale'' by its lack of fissility.Blatt, H., and R.J. Tracy, 1996, ''Petrology.'' New York, New York, ...

s and

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

s deposited in a

fluvial A river is a natural stream of fresh water that flows on land or inside caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of its course if it ru ...

environment. A

meridiolestid Meridiolestida is an extinct clade of mammals known from the Cretaceous and Cenozoic of South America and possibly Antarctica. They represented the dominant group of mammals in South America during the Late Cretaceous. Meridiolestidans were morph ...

mammal were recovered from the formation.

Description

The formation was named by Garrido in 2010 as shaly unit conformably and transitionally overlying the

, to which the layers were formerly defined and in the same manner underlying the

, all belonging to the

of the

in the

. The unit now known as Los Bastos Formation was included in the original definition by Herrero Ducloux (1938, 1939) as "Portezuelo Medio", as part of the "Portezuelo Beds" he described.Garrido, 2011, p.236 The type locality of the formation is located at the foot of the

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

of the eponymous Los Bastos Field, between the localities of Sierra Barrosa and Cerro Senillosa. The formation at its type section reaches a thickness of . The formation comprises red

s intercalated by thin levels of

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

s and fine well-sorted yellowish to greenish grey

s. The formation has similar lithological characteristics as the

Lisandro Formation __NOTOC__ The Lisandro Formation, alternatively known as the Cerro Lisandro Formation, is a Late Cretaceous ( Late Cenomanian to Early Turonian) geologic formation with outcrops in the Neuquén, Río Negro and Mendoza Provinces of Argentina. It ...

and was deposited in a

environment characterized by sinuous channels. Based on the stratigraphic relations with the overlying and underlying units, the age has been estimated to be early to middle

Coniacian The Coniacian is an age or stage in the geologic timescale. It is a subdivision of the Late Cretaceous Epoch or Upper Cretaceous Series and spans the time between 89.8 ± 1 Ma and 86.3 ± 0.7 Ma (million years ago). The Coniacian is preceded by ...

.Garrido, 2011, p.237

Fossil content

The formation has provided fossils of:Los Bastos Formation
at

Fossilworks Fossilworks was 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 cr ...

.org *

Mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s ** Meridiolestida indet.Forasiepi et al., 2012

References

Bibliography

* * {{citation , last=Garrido , first=Alberto C , year=2011 , title=El Grupo Neuquén (Cretácico Tardío) en la Cuenca Neuquina , url=https://www.researchgate.net/publication/268688238 , publisher=XVIII Congreso Geológico Argentino , pages=231–244 , accessdate=2020-07-07 Geologic formations of Argentina Neuquén Group Upper Cretaceous Series of South America Cretaceous Argentina Coniacian Stage Mudstone formations of Argentina Sandstone formations Fluvial deposits Fossiliferous stratigraphic units of South America Paleontology in Argentina Geology of Mendoza Province Geology of Neuquén Province Geology of Patagonia

Description

Fossil content

See also

References

Bibliography