# Tesuque Formation

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The **Tesuque Formation** is a [geologic formation](/source/Formation_(geology)) in north-central [New Mexico](/source/New_Mexico), United States. The formation provides an unusually complete record of the [evolution](/source/Evolution) of [mammals](/source/Mammals) during the [Miocene](/source/Miocene) [epoch](/source/Epoch_(geology)).

## Description

The formation is primarily [siltstone](/source/Siltstone) and fine [sandstone](/source/Sandstone), with some boulder [conglomerate](/source/Conglomerate_(geology)) beds in its eastern exposures close to the [Sangre de Cristo Mountains](/source/Sangre_de_Cristo_Mountains). It is interpreted as coalesced [alluvial fans](/source/Alluvial_fan) with highly variable [lithology](/source/Lithology). There is significant [crossbedding](/source/Crossbedding) and lenticular bedding, and some sandstone beds are well [cemented](/source/Cementation_(geology)) with [calcite](/source/Calcite). The formation [dips](/source/Dip_(geology)) 10 degrees to the west. [Faulting](/source/Fault_(geology)) makes an accurate estimate of its thickness uncertain, and it was originally estimated to be over 2,000 metres (6,600 feet) thick.[1] However, a careful reconstruction taking into account faults gives a thickness of 1,370–1,460 metres (4,490–4,790 feet).[2]

The *Nambe [Member](/source/Member_(stratigraphy))* is pinkish to reddish coarse-grained alluvial fan deposits resting on [basement rock](/source/Basement_rock) of the [Sangre de Cristo Mountains](/source/Sangre_de_Cristo_Mountains). The member is named for [Nambé Pueblo](/source/Namb%C3%A9_Pueblo,_New_Mexico) and has a total thickness of about 125 metres (410 feet).[3] An [ash](/source/Volcanic_ash) bed within the member has an aged based on [Ar-Ar](/source/Argon%E2%80%93argon_dating) dating of 25.52 ± 0.07 million years ([Ma](/source/Ma_(unit))). Its age range is estimated to be from 25.6 to 16.1 Ma.[4]

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](/source/Erosion). The member is up to 230 metres (750 feet) 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.[5] An ash bed in the Skull Ridge Member has an Ar-Ar age of 15.45±0.06 Ma.[6]

The *Pojoaque Member* is separated from the Skull Ridge Member by a greenish-gray [conglomerate](/source/Conglomerate_(geology)) 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](/source/Pojoaque,_New_Mexico). The formation disappears into the subsurface under the [Rio Grande River](/source/Rio_Grande_River) [floodplain](/source/Floodplain) but is at least 550 metres (1,800 feet) thick.[7] Its age range is estimated to be from 14.9 to 12.5 Ma.[8]

The *Chama-El Rito Member* is found only in the northwestern portion of the Espanola Basin. It [correlates](/source/Correlation_(geology)) with the Skull Ridge and Pojoaque Members, but contains conglomerate lenses with distinctive volcanic [clasts](/source/Clasts) (rock fragments) likely derived from the [San Juan volcanic field](/source/San_Juan_volcanic_field).[9]

The **Ojo Caliente Member** is 140 metres (460 feet) of soft [eolian](/source/Aeolian_processes) sandstone overlying the Chama-El Rito member. It is named for the village of [Ojo Caliente](/source/Ojo_Caliente,_New_Mexico).[10] [Radiometric dating](/source/Radiometric_dating) of ash beds suggests the base of the member has a maximum age of 13.5 to 13.3 Ma.[11]

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.[12]

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.[13]

In addition to the traditional [lithostratigraphic](/source/Lithostratigraphic) units, the Tesuque Formation is divided into two [lithosomes](/source/Lithosome). Lithosome A is [granitic](/source/Granitic) material deposited by a network of westward-flowing streams off the [Sangre de Cristo Mountains](/source/Sangre_de_Cristo_Mountains). Lithosome B is richer in [clay](/source/Clay) and [Paleozoic](/source/Paleozoic) clasts and was deposited by south- to southwest-flowing rivers coming from the [Penasco](/source/Penasco,_New_Mexico) 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.[14]

## Fossils

[G.K. Gilbert](/source/G.K._Gilbert) visited [San Ildefonso Pueblo](/source/San_Ildefonso_Pueblo,_New_Mexico) with the [Hayden Survey](/source/Hayden_Survey) in 1873 and found fossil mammal bones characteristic of the [Pliocene](/source/Pliocene). Some of these were sent to [Othniel Marsh](/source/Othniel_Marsh). Marsh's bitter rival, [Edward Drinker Cope](/source/Edward_Drinker_Cope), arrived at San Ildefonso the next year and collected a number of [Miocene](/source/Miocene) reptile, bird, and mammal fossils.[15]

[Childs Frick](/source/Childs_Frick) sent an expedition into the [Tesuque](/source/Tesuque) area in 1924, and immediately recognized the [paleontological](/source/Paleontological) potential of the Santa Fe beds. The Fricks Laboratory (merged with the Department of Vertebrate Paleontology of the [American Museum of Natural History](/source/American_Museum_of_Natural_History) 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.[16] 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](/source/Claystone) to fine-grained siltstone beds of lithosome B. These are interpreted as small [lacustrine](/source/Lacustrine) deposits.[17]

Fossils found in the Tesuque Formation include the [canids](/source/Canid) *[Hemicyon](/source/Hemicyon)* and *[Carpocyon](/source/Carpocyon) webbi*, the [antilocaprids](/source/Antilocapridae) *[Cosoryx](/source/Cosoryx)*, *[Merycodus](/source/Merycodus)*, and *[Ramoceros](/source/Ramoceros)*, [chiroptera](/source/Chiroptera) from the [Vespertilionidae](/source/Vespertilionidae) and [Antrozoinae](/source/Antrozoinae), the [turtles](/source/Emydidae) *Glyptemys valentinensis* and *[Kinosternon pojoaque](/source/Kinosternon_pojoaque)*,[18] and [mastodonts](/source/Mastodont).[19][20] The formation provides an unusually complete record of the evolution of mammals through the Miocene.[21]

## 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](/source/Santa_Fe_Group_(geology)).[22] 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](/source/Tesuque,_New_Mexico).[23]

In 1971, Galusha and Blick removed the uppermost beds from the Tesuque Formation as the [Chamita Formation](/source/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.[19] Manley added the Cejita Member in 1977.[13] Koning and Aby added the Cuarteles Member in 2005.[12]

## Footnotes

1. Baldwin 1956, pp. 118–119.

1. Galusha & Blick 1971, p. 8.

1. Galusha & Blick 1971, pp. 45–53.

1. Koning 2002, p. 51.

1. Galusha & Blick 1971, pp. 53–59.

1. McIntosh & Quade 1995.

1. Galusha & Blick 1971, pp. 59–64.

1. Koning 2002, p. 31.

1. Galusha & Blick 1971, pp. 64–67.

1. Galusha & Blick 1971, pp. 67–70.

1. Slate et al. 2013.

1. Koning & Aby 2005.

1. Manley 1977.

1. Koning 2002.

1. Kues, Lewis & Lueth 2014.

1. Galusha & Blick 1971, p. 14.

1. Williamson 2016, p. iv.

1. Bourque 2012.

1. Galusha & Blick 1971, p. 19.

1. Williamson 2016.

1. Tedford & Barghoorn 1997.

1. Bryan & McCann 1937.

1. Baldwin 1956, pp. 115–116.

## See also

- [List of fossiliferous stratigraphic units in New Mexico](/source/List_of_fossiliferous_stratigraphic_units_in_New_Mexico)
- [Paleontology in New Mexico](/source/Paleontology_in_New_Mexico)

## References

- Baldwin, Brewster (1956). ["The Santa Fe Group of north-central New Mexico"](https://nmgs.nmt.edu/publications/guidebooks/downloads/7/7_p0115_p0121.pdf). *New Mexico Geologic Society Field Conference Series*. **7**: 115–121. Retrieved 13 May 2020.
- Bryan, Kirk & McCann, Franklin T. (November 1937). "The Ceja Del Rio Puerco: A Border Feature of the Basin and Range Province in New Mexico: I. Stratigraphy and Structure". *The Journal of Geology*. **45** (8): 801–828. [Bibcode:1937JG.....45..801B](https://ui.adsabs.harvard.edu/abs/1937JG.....45..801B). [doi:10.1086/624608](https://doi.org/10.1086/624608). [S2CID 128563355](https://api.semanticscholar.org/CorpusID:128563355)
- Bourque, Jason R. (January 2012). "An extinct mud turtle of the Kinosternon flavescens group (Testudines, Kinosternidae) from the middle Miocene (late Barstovian) of New Mexico". *Journal of Vertebrate Paleontology*. **32** (1): 68–81. [doi:10.1080/02724634.2012.626824](https://doi.org/10.1080/02724634.2012.626824). [S2CID 84889382](https://api.semanticscholar.org/CorpusID:84889382)
- Galusha, Ted & Blick, John C. (1971). ["Stratigraphy of the Santa Fe Group, New Mexico"](https://digitallibrary.amnh.org/bitstream/handle/2246/1633/B144a01.pdf?sequence=1&isAllowed=y). *Bulletin of the American Museum of Natural History*. **144** (1). Retrieved 13 May 2020.
- Koning, Daniel J. (May 2002). ["Geologic Map of the Española Quadrangle, Rio Arriba and Santa Fe Counties, New Mexico"](https://geoinfo.nmt.edu/publications/maps/geologic/ofgm/details.cfml?volume=54). *New Mexico Bureau of Geology & Mineral Resources Open Map Series*. **54**. Retrieved 13 May 2020.
- Koning, D.J. & Aby, S.B. (2005). ["Proposed Members of the Chamita Formation, north-central New Mexico"](https://nmgs.nmt.edu/publications/guidebooks/downloads/56/56_p0258_p0278.pdf). *New Mexico Geological Society Guidebook Series*. **56**: 258–278. Retrieved 11 July 2022.
- Kues, Barry S.; Lewis, Claudia J.; Lueth, Virgil W. (2014). *A brief history of geological studies in New Mexico : with biographical profiles of notable New Mexico geologists*. First ed. New Mexico Geological Society. ISBN 978-1-58546-011-3.
- Manley, K.A. (1977). "Geologic map of the northeastern part of the Espanola Basin, New Mexico showing the Cejia Member (new name) of the Tesuque Formation". *U.S. Geological Survey Miscellaneous Field Studies Map*. **MF-877**. [doi:10.3133/mf877](https://doi.org/10.3133/mf877)
- McIntosh, William C. & Quade, Jay (1995). ["40Ar/39Ar geochronology of tephra layers in the Santa Fe Group, Espanola Basin, New Mexico"](https://nmgs.nmt.edu/publications/guidebooks/downloads/46/46_p0279_p0287.pdf). *New Mexico Geological Society Guidebook*. **46**: 279–287. Retrieved 10 August 2020.
- Slate, J.L.; Sarna-Wojcicki, A.M.; Koning, D.J.; Wan, E.; Wahl, D.B.; Connell, S.D.; Perkins, M.E. (2013). ["Upper Neogene tephrochronologic correlations of the Espanola Basin and Jemez Mountains volcanic field, northern Rio Grande rift, north-central New Mexico"](https://books.google.com/books?id=YMUzJmFqlgUC&dq=%22tesuque+formation%22+tephrochronology&pg=PA303). *Geological Society of America Special Paper*. **494**: 303–322. ISBN 9780813724942. Retrieved 7 July 2021.
- Tedford, R.H. & Barghoorn, S.T.E.V.E.N. (1997). ["Miocene mammals of the Espanola and Albuquerque basins. North-central New Mexico"](https://books.google.com/books?id=YWcdCgAAQBAJ&dq=%22tesuque+formation%22++%22north+american+faunal%22&pg=PA77). *New Mexico's Fossil Record*. Vol. 1. Lucas, SG; Estep, JW; Williamson, TE; Morgan, GS (eds.). pp. 77–96. Retrieved 7 July 2021.
- Williamson, Garrett R. (2016). ["The stratigraphic position of fossil vertebrates from the Pojoaque Member of the Tesuque Formation (middle Miocene, late Barstovian) near Española, New Mexico"](https://scholarworks.sfasu.edu/cgi/viewcontent.cgi?article=1041&context=etds). *Electronic Theses and Dissertations*. **41**

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Adapted from the Wikipedia article [Tesuque Formation](https://en.wikipedia.org/wiki/Tesuque_Formation) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Tesuque_Formation?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.