Ojo Alamo Formation

The Ojo Alamo Formation is a geologic formation in New Mexico spanning the Mesozoic/Cenozoic boundary.

Ojo Alamo Formation Stratigraphic range: Maastrichtian-Danian ~69–64 Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Ojo Alamo Formation in the Bisti/De-Na-Zin Wilderness
Type	Geological formation
Sub-units	Naashoibito Member, Kimbeto Member
Underlies	Nacimiento Formation
Overlies	Kirtland Formation
Lithology
Primary	Conglomerate, sandstone, shale
Location
Coordinates	36.3305764°N 108.0350723°W
Region	San Juan Basin, New Mexico
Country	USA
Type section
Named for	Ojo Alamo Spring
Named by	B. Brown
Year defined	1910

Description

The Ojo Alamo Formation is divided into two subunits separated by a large unconformity—a gap in the geologic record. The lower Naashoibito member (sometimes considered part of the Kirtland Formation) was deposited during the Maastrichtian age of the Cretaceous period, specifically between about 69-68 million years ago. It overlies the De-na-zin member of the Kirtland formation, though the two are separated by another large unconformity that spans a period of geologic time equivalent to 73-69 million years ago.[1] All dinosaur fossils probably come from this unit.[2]

The upper unit of the Ojo Alamo Formation is the Kimbeto Member, which was deposited mainly during the earliest Cenozoic (Danian age of the Paleogene period), between 66 and 64 million years ago.[1]

Fossils

A restoration of the environment, featuring Dineobellator (center front), Ojoceratops (right), a tyrannosaurid (far left), and Alamosaurus (center back), taxa all known from the formation.

Ojo Alamo Formation showing conglomerate lens with petrified wood, De-Na-Zin Wilderness

Dinosaur remains are among the fossils that have been recovered from the formation, though all dinosaur remains come from the lowest part of the formation, the Naashoibito member (sometimes considered part of the Kirtland Formation, which dates to the late Maastrichtian stage of the Cretaceous period.[3]

Some researchers have claimed to find isolated non-avian dinosaur remains in the younger Kimbeto Member. If this is the case, it would represent the only known instance of a non-avian dinosaur population persisting after the Cretaceous–Paleogene extinction event. However, most scientists consider these to have been stratigraphically misinterpreted or reworked from the older Naashoibito member.[2]

Alamo Wash fauna

The following species are known to be present in the Naashoibito Member "Alamo Wash Fauna".[4]

• Lizards
  • Peneteius
• Fish
  • Myledaphus sp.
  • Squatirhina sp.
  • cf. Lepisosteus sp.
  • ?Osteichthyes indet.
• Amphibians
  • Caudata indet.
• Turtles
  • Aspideretoides
  • Compsemys
  • cf. Hoplochelys sp.
  • Neurankylus
  • Plastomenus
  • Adocus?
  • Basilemys?
• Theropods
  • Dineobellator notohesperus[5]
  • Ojoraptorsaurus boerei[6]
  • Caenagnathidae indet.
  • Ornithomimidae indet.
  • Richardoestesia sp.
  • Troodontidae indet.
  • Tyrannosauridae indet. similar to Tyrannosaurus
• Sauropods
  • Alamosaurus sanjuanensis[7]
• Ankylosaurs
  • Glyptodontopelta mimus[8]
  • Ankylosauridae indet. similar to Euoplocephalus and Ankylosaurus
  • Ankylosauria indet.
• Hadrosaurids
  • Hadrosauridae indet.
  • Lambeosaurini indet. similar to Corythosaurus and Hypacrosaurus altispinus[9]
• Ceratopsians
  • Ceratopsidae indet.
  • Ojoceratops fowleri[10]
• Pterosaurs
  • Quetzalcoatlus northropi
• Mammals
  • cf. Alphadon marshi
  • Alphadontinae indet.
  • Essonodon browni[11]
  • cf. Glasbius sp.
  • Mesodoma formosa
  • cf. Meniscoessus sp.
  • Multituberculata indet.
  • cf. Pediomyidae indet.

History of investigation

The formation was named by Barnum Brown in 1910 for exposures near Ojo Alamo springs in the San Juan Basin.[12] Baltz et al. reassigned the lower beds to the Kirtland Formation in 1966, but this has not been generally accepted.[13]

See also

• List of dinosaur-bearing rock formations

References

1. Sullivan, R.M., and Lucas, S.G. 2006. "The Kirtlandian land-vertebrate "age" – faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America." New Mexico Museum of Natural History and Science, Bulletin 35:7-29.
2. Sullivan, RM (2003). "No Paleocene dinosaurs in the San Juan Basin, New Mexico". Geological Society of America Abstracts with Programs. 35 (5): 15. Retrieved 2007-07-02.
3. Williamson, T.E. and Weil, A. (2008). "Metatherian mammals from the Naashoibito Member, Kirtland Formation, San Juan Basin, New Mexico and their biochronologic and paleobiogeographic significance. Journal of Vertebrate Paleontology, 28: 803-815.
4. Jasinski, S. E., Sullivan, R. M., & Lucas, S. G. (2011). Taxonomic composition of the Alamo Wash local fauna from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member) San Juan Basin, New Mexico. Bulletin, 53, 216-271.
5. Jasinski, Steven E.; Sullivan, Robert M.; Dodson, Peter (2020-03-26). "New Dromaeosaurid Dinosaur (Theropoda, Dromaeosauridae) from New Mexico and Biodiversity of Dromaeosaurids at the end of the Cretaceous". Scientific Reports. 10 (5105). doi:10.1038/s41598-020-61480-7.
6. Robert M. Sullivan, Steven E. Jasinski and Mark P.A. Van Tomme (2011). "A new caenagnathid Ojoraptorsaurus boerei, n. gen., n. sp. (Dinosauria, Oviraptorosauria), from the Upper Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico" (PDF). Fossil Record 3. New Mexico Museum of Natural History and Science Bulletin. 53: 418–428.
7. Gilmore, Charles W. (1922). "A new sauropod dinosaur from the Ojo Alamo formation of New Mexico (with two plates)" (PDF). Smithsonian Miscellaneous Collections. 72 (14): 1–9. Retrieved 23 October 2020.
8. T.L. Ford. (2000). "A review of ankylosaur osteoderms from New Mexico and a preliminary review of ankylosaur armor", In: S. G. Lucas and A. B. Heckert (eds.), Dinosaurs of New Mexico. New Mexico Museum of Natural History and Science Bulletin 17: 157-176
9. Jasinski, Steven E.; Sullivan, Robert M.; Lucas, Spencer G.; Spielmann, Justin A. "The first "lambeosaurin" (Dinosauria, Hadrosauridae, Lambeosaurinae) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico: further implications for the age of the Alamo Wash local fauna". www.researchgate.com. Retrieved 21 August 2016.
10. Robert M. Sullivan and Spencer G. Lucas, 2010, "A New Chasmosaurine (Ceratopsidae, Dinosauria) from the Upper Cretaceous Ojo Alamo Formation (Naashoibito Member), San Juan Basin, New Mexico", In: Ryan, M.J., Chinnery-Allgeier, B.J., and Eberth, D.A. (eds.) New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, Bloomington, Indiana University Press, 656 pp.
11. Willamson, Thomas M.; Weil, Anne (12 September 2008). "Metatherian Mammals from the Naashoibito Member, Kirtland Formation, San Juan Basin, New Mexico and Their Biochronologic and Paleobiogeographic Significance". Journal of Vertebrate Paleontology. Taylor & Francis, Ltd. 28 (3): 803–815. Retrieved 19 November 2020.
12. Brown, Barnum, 1910, The Cretaceous Ojo Alamo beds of New Mexico with description of the new dinosaur genus Kritosaurus: American Museum of Natural History Bulletin, v. 28, art. 24, p. 267-274.
13. Baltz, E.H., Ash, S.R., and Anderson, R.Y., 1966, History of nomenclature and stratigraphy of rocks adjacent to the Cretaceous-Tertiary boundary, western San Juan basin, New Mexico, IN Shorter contributions to general geology, 1965: U.S. Geological Survey Professional Paper, 524-D, p. D1-D23.

Further reading

• Burns, Michael E. (2008). "Taxonomic utility of ankylosaur (Dinosauria, Ornithischia) osteoderms: Glyptodontopelta mimus Ford, 2000: a test case". Journal of Vertebrate Paleontology. 28 (4): 1102–1109. doi:10.1671/0272-4634-28.4.1102. S2CID 140672072.