The Tesuque 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 north-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 ...

, United States. The formation provides an unusually complete record of the

evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...

of mammals during 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 ...

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 formation is primarily

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.Blatt ''et al.'' 1980, p ...

and fine

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) ...

, with some boulder

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 ...

beds in its eastern exposures close to the

Sangre de Cristo Mountains ) , country= United States , subdivision1_type= States , subdivision1= , parent= Rocky Mountains , geology= , orogeny= , area_mi2= 17193 , range_coordinates= , length_mi= 242 , length_orientation= north-south , width_mi= 120 , w ...

. It is interpreted as coalesced alluvial fans with highly variable

lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...

. There is significant crossbedding and lenticular bedding, and some sandstone beds are well cemented with

calcite Calcite is a Carbonate minerals, carbonate mineral and the most stable Polymorphism (materials science), polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on ...

. The formation dips 10 degrees to the west. Faulting makes an accurate estimate of its thickness uncertain, and it was originally estimated to be over thick. However, a careful reconstruction taking into account faults gives a thickness of . The ''Nambe

Member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

'' is pinkish to reddish coarse-grained alluvial fan deposits resting on

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 ...

of the

. The member is named for Nambé Pueblo and has a total thickness of about . An

ash Ash or ashes are the solid remnants of fires. Specifically, ''ash'' refers to all non-aqueous, non- gaseous residues that remain after something burns. In analytical chemistry, to analyse the mineral and metal content of chemical samples, ash ...

bed within the member has an aged based on Ar-Ar dating of 25.52 ± 0.07 million years ( Ma). Its age range is estimated to be from 25.6 to 16.1 Ma. The ''Skull Ridge Member'' is separated from the Nambe Member by a distinctive ash bed. The member has numerous other ash beds, which result in relatively strong cementing that makes this a cliff-forming member. The upper portion is much less resistant to

erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...

. The member is up to thick. Galusha and Blick did not identify the geographical location for which the member was named, and the place name "Skull Ridge" is unknown in New Mexico. An ash bed in the Skull Ridge Member has an Ar-Ar age of 15.45±0.06 Ma. The ''Pojoaque Member'' is separated from the Skull Ridge Member by a greenish-gray

bed interpreted as lag gravel on an erosional surface. It is named for the Pojoaque Bluffs, also known as Los Barrancos, near the town of Pojoaque, New Mexico. The formation disappears into the subsurface under the

Rio Grande River The Rio Grande ( and ), known in Mexico as the Río Bravo del Norte or simply the Río Bravo, is one of the principal rivers (along with the Colorado River) in the southwestern United States and in northern Mexico. The length of the Rio G ...

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

but is at least thick. Its age range is estimated to be from 14.9 to 12.5 Ma. File:Los Barrancos Pojoaque.jpg, Pojoaque Member at Los Barrancos The ''Chama-El Rito Member'' is found only in the northwestern portion of the Espanola Basin. It correlates with the Skull Ridge and Pojoaque Members, but contains conglomerate lenses with distinctive volcanic clasts (rock fragments) likely derived from the

San Juan volcanic field The San Juan volcanic field is part of the San Juan Mountains in southwestern Colorado. It consists mainly of volcanic rocks that form the largest remnant of a major composite volcanic field that covered most of the southern Rocky Mountains in t ...

. File:Chama-El Rito Member at Mesa Vista.jpg, Chama-El Rito Member north of Mesa Vista School The Ojo Caliente Member is of soft eolian sandstone overlying the Chama-El Rito member. It is named for the village of Ojo Caliente.

Radiometric dating Radiometric dating, radioactive dating or radioisotope dating is a technique which is used to date materials such as rocks or carbon, in which trace radioactive impurities were selectively incorporated when they were formed. The method compares t ...

of ash beds suggests the base of the member has a maximum age of 13.5 to 13.3 Ma. The ''Cuarteles Member'' is found in the northeastern part of the Espanola Basin. It was originally defined in the Chamita Formation west of the Rio Grande, but is assigned to the Tesuque Formation east of the Rio Grande. The ''Cejita Member'' is found in the northeastern part of the Espanola Basin, where it overlies the Cuarteles member. It is interbedded conglomerate and sandstone. It is probably similar in age to the Skull Ridge and Pojoaque Members. In addition to the traditional lithostratigraphic units, the Tesuque Formation is divided into two

lithosome Lithostratigraphy is a sub-discipline of stratigraphy, the geological science associated with the study of strata or rock layers. Major focuses include geochronology, comparative geology, and petrology. In general, strata are primarily igne ...

s. Lithosome A is granitic material deposited by a network of westward-flowing streams off the

. Lithosome B is richer in

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay par ...

and

Paleozoic The Paleozoic (or Palaeozoic) Era is the earliest of three geologic eras of the Phanerozoic Eon. The name ''Paleozoic'' ( ;) was coined by the British geologist Adam Sedgwick in 1838 by combining the Greek words ''palaiós'' (, "old") and ' ...

clasts and was deposited by south- to southwest-flowing rivers coming from the Penasco area. The two can be distinguished in the field by the redder coloration of Lithosome A compared with the tan to gray color of Lithosome B. File:Ojo Caliente Member.jpg, Ojo Caliente Member of the Tesuque Formation at Embudo Station File:Ojo Caliente concretions.jpg, Concretions in an outcrop of the Ojo Caliente Member on the Lemitas Trail

Fossils

G.K. Gilbert visited San Ildefonso Pueblo with the

Hayden Survey Ferdinand Vandeveer Hayden (September 7, 1829 – December 22, 1887) was an American geologist noted for his pioneering surveying expeditions of the Rocky Mountains in the late 19th century. He was also a physician who served with the Union Ar ...

in 1873 and found fossil mammal bones characteristic of the

Pliocene The Pliocene ( ; also Pleiocene) is the epoch in the geologic time scale that extends from 5.333 million to 2.58Othniel Marsh. Marsh's bitter rival,

Edward Drinker Cope Edward Drinker Cope (July 28, 1840 – April 12, 1897) was an American zoologist, paleontologist, comparative anatomist, herpetologist, and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested ...

, arrived at San Ildefonso the next year and collected a number of

reptile, bird, and mammal fossils.

Childs Frick Childs Frick (March 12, 1883 - May 8, 1965) was an American vertebrate paleontologist. He was a trustee of the American Museum of Natural History and a major benefactor of its Department of Paleontology, which in 1916 began a long partnership wi ...

sent an expedition into the Tesuque area in 1924, and immediately recognized the paleontological potential of the Santa Fe beds. The Fricks Laboratory (merged with the Department of Vertebrate Paleontology of the

American Museum of Natural History The American Museum of Natural History (abbreviated as AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. In Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 26 inter ...

in 1968) carried out field work through 1972. Work prior to 1940 was careless about identifying exact source strata, though greater care was taken thereafter. Most of the fossils came from the Pojoaque Member of the Tesuque Formation and were almost entirely found within thin (0.5–3 m) maroon-red to pale green

claystone Mudrocks are a class of fine-grained siliciclastic sedimentary rocks. The varying types of mudrocks include siltstone, claystone, mudstone, slate, and shale. Most of the particles of which the stone is composed are less than and are too sm ...

to fine-grained siltstone beds of lithosome B. These are interpreted as small lacustrine deposits. Fossils found in the Tesuque Formation include the canids ''

Hemicyon ''Hemicyon'', also known as the "dog-bear" (literally "half dog", from Greek (half) + (dog)), is an extinct genus of hemicyonine bear, which probably originated in Eurasia but was found in Europe, Asia and North America during the Miocen ...

'' and ''

Carpocyon ''Carpocyon'' is an extinct genus of the Borophaginae subfamily of canids native to North America. It lived from the Middle to the Late Miocene, 13.6 to 5.3 Ma Mya, existing for approximately . The four species in the genus varied in size, with t ...

webbi'', the antilocaprids ''

Cosoryx ''Cosoryx'' is an extinct genus of antilocaprid that lived in the Miocene of Nevada. Fossils of this genus have also been found in the Santa Fe Group in New Mexico. ''Cosoryx'' has sometimes been considered synonymous with ''Merycodus ' ...

'', ''

Merycodus ''Merycodus'' is an extinct genus of the artiodactyl family Antilocapridae. Fossils of this genus have been found in the Santa Fe Group of New Mexico. Taxonomy ''Merycodus'' has had a confusing taxonomic history. The closely related ''Meryceros ...

'', and ''

Ramoceros ''Ramoceros'' is an extinct genus of the artiodactyl family Antilocapridae endemic to Middle Miocene (Clarendonian) North America.Blount, Kitty and Crowley, Maggie. ''Encyclopedia of Dinosaurs & Prehistoric Life'', p. 271 (Penguin, 2008). Tax ...

'', chiroptera from the

Vespertilionidae Vespertilionidae is a family of microbats, of the order Chiroptera, flying, insect-eating mammals variously described as the common, vesper, or simple nosed bats. The vespertilionid family is the most diverse and widely distributed of bat familie ...

and

Antrozoinae Antrozoini is a tribe of bats in the subfamily Vespertilioninae of the family Vespertilionidae. It contains the pallid bat (''Antrozous pallidus''), Van Gelder's bat (''Bauerus dubiaquercus''), the genus ''Rhogeessa'', and the fossil '' Anzanyct ...

, the

turtle Turtles are an order of reptiles known as Testudines, characterized by a special shell developed mainly from their ribs. Modern turtles are divided into two major groups, the Pleurodira (side necked turtles) and Cryptodira (hidden necked tu ...

s ''Glyptemys valentinensis'' and '' Kinosternon pojoaque'', and

mastodont Mammutidae is an extinct family of proboscideans that appeared during the Oligocene epoch and survived until the start of the Holocene. The family was first described in 1922, classifying fossil specimens of the type genus ''Mammut'' (mastodon ...

s. The formation provides an unusually complete record of the evolution of mammals through the Miocene.

History of investigation

The beds making up the unit were originally described by Bryan and McCann in 1937 as the Middle Red member of the

Santa Fe Formation The Santa Fe Group is a group of geologic formations in New Mexico and Colorado. It contains fossils characteristic of the Oligocene through Pleistocene epochs. The group consists of basin-filling sedimentary and volcanic rocks of the Rio Gr ...

. The formation was named by Baldwin in 1956 at the same time that the Santa Fe Formation was raised to group rank. The formation is named after exposures around the town of

Tesuque, New Mexico Tesuque (Tewa: Tetsʼúgéh Ówîngeh / Tetsugé Oweengé ) is a census-designated place (CDP) in Santa Fe County, New Mexico, United States. It is part of the Santa Fe, New Mexico, Metropolitan Statistical Area. The population was 909 at the 2 ...

. In 1971, Galusha and Blick removed the uppermost beds from the Tesuque Formation as the Chamita Formation and divided the Tesuque Formation into members. These were, in ascending stratigraphic order, the Skull Ridge Member, the Nambe Member, Pojoaque Member, the Chama-El Rito Member, and the Ojo Caliente Member. Manley added the Cejita Member in 1977. Koning and Aby added the Cuarteles Member in 2005.

Footnotes

References

* * * * * * * * * * * * {{cite journal , last1=Williamson , first1=Garrett R. , url=https://scholarworks.sfasu.edu/cgi/viewcontent.cgi?article=1041&context=etds , title=The stratigraphic position of fossil vertebrates from the Pojoaque Member of the Tesuque Formation (middle Miocene, late Barstovian) near Española, New Mexico , year=2016 , journal=Electronic Theses and Dissertations , volume=41 Neogene formations of New Mexico

Description

Fossils

History of investigation

Footnotes

See also

References