Nacimiento Formation

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.

Nacimiento Formation
Stratigraphic range: Paleocene
~65.7–61 Ma
↓
The badlands below Angel Peak are made up of Nacimiento Formation rocks
TypeFormation
UnderliesSan Jose Formation
OverliesOjo Alamo Formation
Thickness254 m (833 ft)
Lithology
PrimaryShale
OtherSiltstone, sandstone
Location
Coordinates36.0126977°N 106.9855481°W / 36.0126977; -106.9855481
RegionNew Mexico
CountryUnited States
Type section
Named forNacimiento (now Cuba, New Mexico)
Named byJ.H. Gardner
Year defined1910
Nacimiento Formation (the United States)
Nacimiento Formation (New Mexico)

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] 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 formations are indistinguishable, and are called the "main body".[5] Above them are two more informal members. These preserve a younger, Tiffanian fauna.[7] 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.[8] Fossils belonging to a number of different organisms have been found here, including: plants (mostly dicotyledonous angiosperms),[6][9] gastropods, freshwater bivalves,[10] cartilaginous fish and bony fish, salamanders, turtles, champsosaurs, amphisbaenians, lizards, snakes, crocodilians,[11] birds,[12] and a variety of archaic mammals. Mammalian groups represented include multituberculates, didelphid marsupials, insectivorans, plesiadapiforms, carnivorans, taeniodonts, mesonychids, condylarths, and cimolestans.[1]

History of investigation

Workers in the early 1900s divided the rocks of the Nacimiento Formation into two formations, the lower Puerco Formation and the upper Torrejon Formation.[12] 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.[8] 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.[13]

Footnotes
  1. Williamson and Lucas 1992
  2. Schoch 1981
  3. Lucas and Ingersoll 1981
  4. Lucas 1984
  5. Williamson 1996
  6. Tidwell et al. 1981
  7. Libed 2005
  8. Simpson 1959
  9. Anderson 1960
  10. Hartman 1981
  11. Sullivan and Lucas 1986
  12. Gardner 1910
  13. Fassett 1992

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.
  • 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. 25. Socorro, New Mexico: New Mexico Geological Society. pp. 225–230. Retrieved 8 June 2020.
  • 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.
  • 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. 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.
  • 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, 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. New Mexico Geological Society Guidebook. 43. Socorro, New Mexico: New Mexico Geological Society. pp. 265–296. ISBN 99922-2-673-0.
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