The Tanos Formation is a geologic formation in central

New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...

. It is estimated to be about 25 million years in age, corresponding to the

Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...

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 ...

Description

The Tanos Formation consists of a very pale brown basal

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 ** Co ...

overlain by reddish-yellow to reddish-brown

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 reddish-brown and olive-gray

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 (parallel layering).Blatt, H., and R.J. Tracy, 1996, ''Petrology. ...

. It is exposed in a small belt along the east flank of Espinaso Ridge in the

Hagan Hagan may refer to: __NOTOC__ Places Iran * Hagan, Iran, a village in Hamadan Province Norway * Hagan, a village in Harstad * Hagan, a village in Akershus United States * Hagan, Georgia, a city * Hagan, Minnesota, an unincorporated community * Hag ...

basin of central New Mexico, where it is truncated to the northwest by the San Francisco Fault and disappears to the southeast in the subsurface. The formation is thick at the type section on Arroyo de la Vega de los Tanos east of Espinaso Ridge. The age is constrained by an interbedded

basalt Basalt (; ) is an aphanite, aphanitic (fine-grained) extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic lava) exposed at or very near the planetary surface, surface of a terrestrial ...

flow Flow may refer to: Science and technology * Fluid flow, the motion of a gas or liquid * Flow (geomorphology), a type of mass wasting or slope movement in geomorphology * Flow (mathematics), a group action of the real numbers on a set * Flow (psych ...

at the bottom of the formation that has a radiometric age of 25.41 ± 0.32 million years ( Ma). The upper age range is poorly controlled but may extend into the

Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...

. The formation lies disconformably on the

Espinaso Formation The Espinaso Formation is a geologic formation in New Mexico. It has a radiometric age of 34.6 to 26.9 million years, corresponding to the late Eocene through Oligocene epochs. Description The Espinaso Formation is principally debris flows a ...

and interfingers with the overlying Blackshare Formation, with the boundary placed at the highest thickly bedded tabular sandstone below the lenticular conglomerate of the Blackshare Formation. The Tanos Formation dips 20 to 32 degrees to the northeast. It is interpreted as

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 ...

deposited in a closed basin during early rifting along the Rio Grande rift, and is the oldest exposed Santa Fe Group formation near the

Albuquerque Basin The Albuquerque Basin (or Middle Rio Grande Basin) is a structural basin and ecoregion within the Rio Grande rift in central New Mexico. It contains the city of Albuquerque. Geologically, the Albuquerque Basin is a half-graben that slopes down to ...

History

The beds were first studied in detail by Charles E. Stearns in 1953, who tentatively assigned them to the

Abiquiu Formation The Abiquiu Formation is a geologic formation found in northern New Mexico. Radiometric dating constrains its age to between 18 million and 27 million years, corresponding to the late Oligocene to Miocene epochs. The formation is composed mos ...

. However, no clasts of Amalia Tuff, pervasive in the Abiquiu Formation further north, are present. The beds were reassigned to the Zia Formation by V.C. Kelley in 1977 and finally designated as the Tanos Formation by S.D. Connell, S.M. Cather, N.W. Dunbar, and W.C. McIntosh in 2002.

References

Bibliography

* * * {{cite journal , last1=Stearns , first1=Charles E. , title=Tertiary geology of the Galisteo-Tonque area, New Mexico , journal=Geological Society of America Bulletin , date=1953 , volume=64 , issue=4 , pages=459 , doi=10.1130/0016-7606(1953)64 59:TGOTGA.0.CO;2, bibcode=1953GSAB...64..459S Paleogene formations of New Mexico