Cub Mountain Formation

Cub Mountain Formation
Stratigraphic range: Eocene 50–47.7  Ma PreꞒ Ꞓ O S D C P T J K Pg N ↓
Type	Formation
Underlies	Sanders Canyon Formation
Overlies	Crevasse Canyon Formation
Lithology
Primary	Sandstone, mudstone
Other	Conglomerate
Location
Coordinates	33°31′15″N105°54′52″W / 33.520700°N 105.914505°W / 33.520700; -105.914505
Region	New Mexico
Country	United States
Type section
Named for	Cub Mountain
Named by	H.R. Weber
Year defined	1964
Cub Mountain Formation (the United States) Show map of the United States Cub Mountain Formation (New Mexico) Show map of New Mexico

The Cub Mountain Formation is a geologic formation in southern New Mexico. It preserves fossils dating back to the Eocene epoch. ^[1] The formation also records the progressive unroofing of nearby mountainous uplifts during the Laramide orogeny.

Description

The formation consists of interbedded gray to red sandstone and mudstone with minor conglomerate with a total thickness of 730 meters (2,400 ft). ^[1] This is the greatest exposed interval of Eocene basin sediments found in New Mexico. Sandstone dominates the lower part of the formation, but the fraction of mudstone increases further up in the formation. The formation disconformably rests on the Crevasse Canyon Formation of the Mesaverde Group and conformably underlies the Sanders Canyon Formation. ^[2] In the vicinity of Sierra Blanca, the formation is intruded by dikes with K-Ar ages of 47.7 +/-2.9 Ma (million years ago). ^[1]

The formation is interpreted as deposited in a braided stream environment. ^[1] The lowermost beds contain pebbles similar to those of the underlying Crevasse Canyon Formation, suggesting these beds include reworked sediments from the underlying formation. The composition of the upper beds records progressive unroofing of nearby mountainous uplifts during the Laramide orogeny, with decreasing amounts of sandstone fragments and increasing amounts of basement rock fragments. ^[2]

Fossils

Fossil turtles have been found towards the base of the formation. These are characteristic of the Wasatchian-Bridgerian boundary at about 50 Ma. ^[1]

History of investigation

The first definition of the formation was credited to H.R. Weber in a publication by M.W. Bodine, Jr., in 1956, ^[3] but Weber did not publish a type section until 1964. The formation is named after an isolated peak in southern New Mexico. ^[1]

Kenneth Segerstrom and his coinvestigators argued in 1979 that the beds of the Cub Mountain Formation properly belong to the Cretaceous McRae Formation. ^[4] Spencer G. Lucas and his coinvestigators disagreed on the basis of fossil evidence, placing the formation in the Eocene. ^[1] Steven M. Cather removed the uppermost fine-grained volcaniclastic beds in the formation as originally defined into their own formation, the Sanders Canyon Formation, in 1991. ^[2]

See also

• Earth sciences portal
• Paleontology portal

• List of fossiliferous stratigraphic units in New Mexico
• Paleontology in New Mexico

Footnotes

1. Lucas et al. 1989.
2. & Cather 1991.
3. Bodine 1956.
4. Segerstrom, Stotelmeyer & Williams 1979.

References

• Bodine, M.W. Jr. (1956). "Geology of the Capitan coal field, Lincoln County, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Circular. 35. Retrieved 2 August 2020.
• Cather, Steven M. (1991). "Stratigraphy and provenance of upper Cretaceous and Paleogene strata of the western Sierra Blanca Basin, New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 42: 265–275. Retrieved 13 July 2021.
• Lucas, S.G.; Cather, S.M.; Sealey, Paul; Hutchison, H.C. (1989). "Stratigraphy, paleontology, and depositional systems of the Eocene Cub Mountain Formation, Lincoln County, New Mexico; a preliminary report" (PDF). New Mexico Geology. 11 (1): 11–17. Retrieved 2 August 2020.
• Segerstrom, Kenneth; Stotelmeyer, R.B.; Williams, F.E. (1979). "Mineral resources of the White Mountain Wilderness and adjacent areas, Lincoln County, New Mexico". U.S. Geological Survey Bulletin (1453). Retrieved 2 August 2020.