Nacimiento Formation

Nacimiento Formation
Stratigraphic range: Paleocene ~65.7–61 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
The badlands below Angel Peak are made up of Nacimiento Formation rocks
Type	Formation
Underlies	San Jose Formation
Overlies	Ojo Alamo Formation
Thickness	254 m (833 ft)
Lithology
Primary	Shale
Other	Siltstone, sandstone
Location
Coordinates	Nacimiento Formation (the United States) Show map of the United States Nacimiento Formation (New Mexico) Show map of New Mexico

The Nacimiento Formation is a sedimentary rock formation found in the San Juan Basin of western New Mexico (United States).^[1] It has an age of 61 to 65.7 million years, corresponding to the early and middle Paleocene. The formation has yielded an abundance of fossils from shortly after the Cretaceous-Paleogene extinction event that provide clues to the recovery and diversification of mammals following the extinction event.

Description

The Nacimiento Formation is a heterogeneous nonmarine formation composed of shale, siltstone, and sandstone,^[2] deposited in floodplain, fluvial and lacustrine settings,^[3] and made up of sediment shed from the San Juan uplift to the north and the Brazos-Sangre de Cristo uplift to the east.^[4] It was deposited mostly between ~65.7 and ~61 million years ago, during the early and middle Paleocene.^[5] The climate was humid and warm to hot^[6] and stable, but with a distinct dry season.^[7] This unit interbeds with the underlying Ojo Alamo Formation but is separated by an unconformity from the overlying San Jose Formation.^[3]

The Nacimiento Formation is divided into several subunits known as members. In outcrops in southern areas of the formation, the Puercan fauna is found in the Arroyo Chijuillita Member, the Torrejonian fauna is found in the Ojo Encino Member, and the uppermost Escavada Member lacks age-diagnostic fossils.^[1] In northern outcrops, the two lower members are indistinguishable, and are called the "main body".^[5] Above them are two more informal members. These preserve a younger, Tiffanian fauna.^[8] The Puercan and Torrejonian faunas are further subdivided into several biostratigraphic zones.^[5]

Fossils

Many fossils are known from the Nacimiento Formation, although bone is often altered into phosphatic concretions.^[9] Fossils belonging to a number of different organisms have been found here, including: plants (mostly dicotyledonous angiosperms),^[6][10] gastropods, freshwater bivalves,^[11] cartilaginous fish and bony fish, salamanders, turtles, champsosaurs, amphisbaenians, lizards, snakes, crocodilians,^[12] birds,^[13] and a variety of archaic mammals. Mammalian groups represented include multituberculates,^[14] plesiadapiforms,^[15] didelphid marsupials, insectivorans, carnivorans, taeniodonts, mesonychians, condylarths, and cimolestans.^[1] Fossil remains found in the formation support the validity of the genus Thylacodon and the species T. montanensis.^[16]

These fossils provide important clues to the impact of the Cretaceous–Paleogene extinction event on mammals^[16] and to the recovery, evolution, and turnover of mammals shortly after the event. The formation and its fossils provide a particularly clear record of the To2-To3 turnover event, allowing the timing of the event to be constrained to between 62.59 and 62.47 million years ago. The event may have been associated with climate change or with the rapid development of a river system across the San Juan basin, which caused a temporary pause in sediment deposition that separates the Nacimiento Formation from the San Jose Formation.^[17]

History of investigation

Edward Drinker Cope described the fossils during the Wheeler Survey.^[18]

Workers in the early 1900s divided the rocks of the Nacimiento Formation into two formations, the lower Puerco Formation and the upper Torrejon Formation.^[13] This was rejected on the grounds that there were no lithological differences between the two, only differences in fossil faunas, making determination of which formation was present in a given area impossible if fossils could not be found.^[9] The Puerco and Torrejon were retained as zones within the Nacimiento Formation, and their faunas became the basis of the Puercan and Torrejonian North American Land Mammal Ages.^[19]

Footnotes

References

• Anderson, R.Y. (1960). Cretaceous-Tertiary palynology, eastern side of the San Juan Basin, New Mexico (PDF). Memoir 6. Socorro, New Mexico: New Mexico Bureau of Mines and Mineral Resources. Retrieved 8 June 2020.
• Davis, Adam J.; Peppe, Daniel J.; Atchley, Stacy C.; Williamson, Thomas E.; Flynn, Andrew G. (December 2016). "Climate and landscape reconstruction of the Arroyo Chijuillita Member of the Nacimiento Formation, San Juan Basin, New Mexico: Providing environmental context to early Paleocene mammal evolution". Palaeogeography, Palaeoclimatology, Palaeoecology. 463: 27–44. Bibcode:2016PPP...463...27D. doi:10.1016/j.palaeo.2016.09.011.
• Fassett, J.E. (1992). "Cretaceous and Tertiary rocks of the eastern San Juan Basin, New Mexico and Colorado". In Siemers, C.T.; Woodward, L.A.; Callender, J.F. (eds.). Ghost Ranch. New Mexico Geological Society Guidebook. Vol. 25. Socorro, New Mexico: New Mexico Geological Society. pp. 225–230. CiteSeerX 10.1.1.527.6438.
• Gardner, J.H. (1910). "The Puerco and Torrejon formations of the Nacimiento Group". Journal of Geology. 18 (8): 702–741. Bibcode:1910JG.....18..702G. doi:10.1086/621799.
• Hartman, J.H. (1981). "Early Tertiary nonmarine Mollusca of New Mexico: a review". Geological Society of America Bulletin. 92 (12): I 942–I 950. Bibcode:1981GSAB...92..942H. doi:10.1130/0016-7606(1981)92<942:ETNMON>2.0.CO;2.
• Leslie, Caitlin; Peppe, Daniel; Williamson, Thomas; Bilardello, Dario; Heizler, Matthew; Secord, Ross; Leggett, Tyler (March 2018). "High-resolution magnetostratigraphy of the Upper Nacimiento Formation, San Juan Basin, New Mexico, USA: Implications for basin evolution and mammalian turnover". American Journal of Science. 318 (3): 300–334. Bibcode:2018AmJS..318..300L. doi:10.2475/03.2018.02. S2CID 135327595.
• Libed, S.A. (2005). Lithostratigraphy and mammalian biostratigraphy of the Torrejonian-Tiffanian transition in the Nacimiento Formation, northwestern San Juan Basin, New Mexico. M.A. thesis. Albuquerque, New Mexico: University of New Mexico.
• Lucas, S.G. (1984). "Correlation of Eocene rocks of the northern Rio Grande Rift and adjacent areas: implications for Laramide tectonics". In Baldridge, W.S.; Dickerson, P.W.; Riecker, R.E.; Zidek, J. (eds.). Rio Grande Rift: northern New Mexico (PDF). New Mexico Geological Society Guidebook. Vol. 35. Socorro, New Mexico: New Mexico Geological Society. pp. 123–128. Retrieved 8 June 2020.
• Lucas, S.G.; Ingersoll, R.V. (1981). "Cenozoic continental deposits of New Mexico: an overview". Geological Society of America Bulletin. 92 (12): I 917–I 932, II 1807–II 1981. Bibcode:1981GSAB...92..917L. doi:10.1130/0016-7606(1981)92<917:CCDONM>2.0.CO;2.
• Schoch, R.M. (1981). "Taxonomy and biostratigraphy of the early Tertiary Taeniodonta (Mammalia: Eutheria)". Geological Society of America Bulletin. 92 (12): I 933-I 941, II 1982-II 2267. Bibcode:1981GSAB...92.1982S. doi:10.1130/gsab-p2-92-1982.
• Silcox, Mary T.; Williamson, Thomas E. (December 2012). "New discoveries of early Paleocene (Torrejonian) primates from the Nacimiento Formation, San Juan Basin, New Mexico". Journal of Human Evolution. 63 (6): 805–833. doi:10.1016/j.jhevol.2012.09.002. PMID 23084622.
• Simpson, G.G. (1959). "Fossil mammals from the type area of the Puerco and Nacimiento strata, Paleocene of New Mexico" (PDF). American Museum Novitates (1957). Retrieved 8 June 2020.
• Sullivan, R.M.; Lucas, S.G. (1986). "Annotated list of fossil vertebrates from the Paleocene Nacimiento Formation (Puercan-Torrejonian), San Juan Basin, New Mexico". Journal of Herpetology. 20 (2): 202–209. doi:10.2307/1563945. JSTOR 1563945.
• Tidwell, W.D.; Ash, S.R.; Parker, L.R. (1981). "Cretaceous and Tertiary floras of the San Juan Basin". In Lucas, S.G.; Rigby Jr., J.K.; Kues, B.S. (eds.). Advances in San Juan Basin paleontology. Albuquerque, New Mexico: University of New Mexico Press. pp. 307–332. ISBN 0-8263-0554-7.
• Williamson, T.E. (1996). The beginning of the age of mammals in the San Juan Basin, New Mexico: biostratigraphy and evolution of Paleocene mammals of the Nacimiento Formation. New Mexico Museum of Natural History and Science Bulletin, 8. Albuquerque, New Mexico: New Mexico Museum of Natural History and Science. Retrieved 8 June 2020.
• Williamson, Thomas E.; Brusatte, Stephen L.; Carr, Thomas D.; Weil, Anne; Standhardt, Barbara R. (1 December 2012). "The phylogeny and evolution of Cretaceous–Palaeogene metatherians: cladistic analysis and description of new early Palaeocene specimens from the Nacimiento Formation, New Mexico". Journal of Systematic Palaeontology. 10 (4): 625–651. doi:10.1080/14772019.2011.631592. S2CID 83996185.
• Williamson, Thomas E.; Brusatte, Stephen L.; Secord, Ross; Shelley, Sarah (May 2016). "A new taeniolabidoid multituberculate (Mammalia) from the middle Puercan of the Nacimiento Formation, New Mexico, and a revision of taeniolabidoid systematics and phylogeny: Revision of Taeniolabidoidea". Zoological Journal of the Linnean Society. 177 (1): 183–208. doi:10.1111/zoj.12336.
• Williamson, T.E.; Lucas, S.G. (1992). "Stratigraphy and mammalian biostratigraphy of the Paleocene Nacimiento Formation, southern San Juan basin, New Mexico". In Lucas, S.G.; Kues, B.S.; Williamson, T.E.; Hunt, A.P. (eds.). San Juan Basin IV (PDF). New Mexico Geological Society Guidebook. Vol. 43. Socorro, New Mexico: New Mexico Geological Society. pp. 265–296. ISBN 99922-2-673-0. Retrieved 26 August 2020.