The Cub Mountain 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 ...

in southern

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe, New Mexico, Santa Fe , LargestCity = Albuquerque, New Mexico, Albuquerque , LargestMetro = Albuquerque metropolitan area, Tiguex , Offi ...

. It preserves

fossils 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 ...

dating back to the

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'', " ...

epoch In chronology and periodization, an epoch or reference epoch is an instant in time chosen as the origin of a particular calendar era. The "epoch" serves as a reference point from which time is measured. The moment of epoch is usually decided by ...

. The formation also records the progressive unroofing of nearby mountainous uplifts during the

Laramide orogeny The Laramide orogeny was a time period of mountain building in western North America, which started in the Late Cretaceous, 70 to 80 million years ago, and ended 35 to 55 million years ago. The exact duration and ages of beginning and end of the o ...

Description

The formation consists of interbedded gray to red

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 ...

and mudstone with minor

conglomerate Conglomerate or conglomeration may refer to: * Conglomerate (company) * Conglomerate (geology) * Conglomerate (mathematics) In popular culture: * The Conglomerate (American group), a production crew and musical group founded by Busta Rhymes ** C ...

with a total thickness of . This is the greatest exposed interval of Eocene

basin Basin may refer to: Geography and geology * Depression (geology) ** Back-arc basin, a submarine feature associated with island arcs and subduction zones ** Debris basin, designed to prevent damage from debris flow ** Drainage basin (hydrology), ...

sediments 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, sand a ...

found in New Mexico. Sandstone dominates the lower part of the formation, but the fraction of mudstone increases further up in the formation. The formation disconformably rests on the

Crevasse Canyon Formation The Crevasse Canyon Formation is a coal-bearing Cretaceous geologic formation in New Mexico and Arizona. Description The formation is divided into three members, in ascending stratigraphic order: ''Dilco Coal Member'', ''Dalton Sandstone Memb ...

of the

Mesaverde Group The Mesaverde Group is a Late Cretaceous stratigraphic group found in areas of Colorado, New Mexico, Utah, and Wyoming, in the Western United States. History The Mesaverde Formation was first described by W.H.Holmes in 1877 during the ...

and conformably underlies the

Sanders Canyon Formation The Sanders Canyon Formation is a geologic formation exposed north and west of the Sierra Blanca of southern New Mexico. It preserves fossils dating back to the Eocene epoch. Description The formation consists of volcaniclastic mudstone (70%) ...

. In the vicinity of Sierra Blanca, the formation is intruded by

dikes Dyke (UK) or dike (US) may refer to: General uses * Dyke (slang), a slang word meaning "lesbian" * Dike (geology), a subvertical sheet-like intrusion of magma or sediment * Dike (mythology), ''Dikē'', the Greek goddess of moral justice * Dikes, ...

with K-Ar ages of 47.7 +/-2.9 Ma (million years ago). The formation is interpreted as deposited in a

braided stream A braided river, or braided channel, consists of a network of river channels separated by small, often temporary, islands called braid bars or, in English usage, '' aits'' or ''eyots''. Braided streams tend to occur in rivers with high sediment ...

environment. The lowermost beds contain pebbles similar to those of the underlying Crevasse Canyon Formation, suggesting these beds include reworked sediments from the underlying formation. The composition of the upper beds records progressive unroofing of nearby mountainous uplifts during the

, with decreasing amounts of sandstone fragments and increasing amounts of

basement rock In geology, basement and crystalline basement are crystalline rocks lying above the mantle and beneath all other rocks and sediments. They are sometimes exposed at the surface, but often they are buried under miles of rock and sediment. The baseme ...

fragments.

Fossils

Fossil turtles have been found towards the base of the formation. These are characteristic of the

Wasatchian The Wasatchian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 55,400,000 to 50,300,000 years BP lasting . It is usually c ...

Bridgerian The Bridgerian North American Stage on the geologic timescale is the North American faunal stage according to the North American Land Mammal Ages chronology (NALMA), typically set from 50,300,000 to 46,200,000 years BP lasting . It is usually c ...

boundary at about 50 Ma.

History of investigation

The first definition of the formation was credited to H.R. Weber in a publication by M.W. Bodine, Jr., in 1956, but Weber did not publish a type section until 1964. The formation is named after an isolated peak in southern New Mexico. Kenneth Segerstrom and his coinvestigators argued in 1979 that the beds of the Cub Mountain Formation properly belong to the

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

McRae Formation The McRae Formation is a geological formation exposed in southern New Mexico whose strata date back to the Late Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation. Description The formation consist ...

Spencer G. Lucas Spencer George Lucas is an American paleontologist and stratigrapher, and curator of paleontology at the New Mexico Museum of Natural History and Science. His main areas of study are late Paleozoic, Mesozoic and early Cenozoic vertebrate fo ...

and his coinvestigators disagreed on the basis of fossil evidence, placing the formation in the Eocene. Steven M. Cather removed the uppermost fine-grained

volcaniclastic Volcaniclastics are geologic materials composed of broken fragments (clasts) of volcanic rock. These encompass all clastic volcanic materials, regardless of what process fragmented the rock, how it was subsequently transported, what environment it ...

beds in the formation as originally defined into their own formation, the Sanders Canyon Formation, in 1991.

Footnotes

References

* * * * {{cite journal , last1=Segerstrom , first1=Kenneth , last2=Stotelmeyer , first2=R.B. , last3=Williams , first3=F.E. , date=1979 , title=Mineral resources of the White Mountain Wilderness and adjacent areas, Lincoln County, New Mexico , journal=U.S. Geological Survey Bulletin , number=1453 , url=https://ngmdb.usgs.gov/Prodesc/proddesc_21553.htm , accessdate=2 August 2020 Paleogene formations of New Mexico

Description

Fossils

History of investigation

See also

Footnotes

References