Point Lookout Sandstone

The Point Lookout Sandstone is a Cretaceous bedrock formation occurring in New Mexico and Colorado.

Point Lookout Sandstone Stratigraphic range: Upper Cretaceous
Point Lookout, Mesa Verde National Park
Type	Formation
Unit of	Mesaverde Group
Sub-units	Hosta Tongue
Underlies	Menefee Formation
Overlies	Crevasse Canyon Formation
Thickness	300 ft (91 m)
Lithology
Primary	Sandstone
Other	Shale
Location
Coordinates	37.3158126°N 108.4188265°W
Region	Paradox Basin, San Juan Basin
Country	United States
Type section
Named for	Point Lookout
Named by	A. J. Collier
Year defined	1919

Stratigraphic section of formations exposed at the surface, Mesa Verde National Park, Colorado (USGS).

San Juan Basin Upper Cretaceous stratigraphy

Description

The formation consists of two informal members. The lower is a sequence of thinly bedded sandstone and shale,[1] while the upper is a massive medium- to fine-grained cross-bedded sandstone, light gray to buff in color, that is a conspicuous cliff-forming unit.[1][2] Maximum thickness is 131 meters (430 feet).[1]

The lower contact is placed at the first thin sandstone bed above the shale of the Mancos Shale. The formation is overlain by the Menefee Formation.[1]

The Point Lookout Sandstone was deposited in the Cretaceous Interior Seaway, as part of a regressive sequence as the seaway was receding. It is transitional between the marine environment of the underlying Mancos and the coastal plain environment of the overlying Menefee Formation.

Fossils

Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.[3]

The ammonite Clioscaphites vermiformis was identified in the formation.[4]

History of investigation

The sandstone was first described by A. J. Collier for exposures in cliffs at Point Lookout, in Mesa Verde National Park, Montezuma County, Colorado, in the Paradox Basin,[5] and later described by Allen and Balk in 1954 as part of the Mesaverde Group in the San Juan Basin in New Mexico.[6]

See also

• List of dinosaur-bearing rock formations
  • List of stratigraphic units with indeterminate dinosaur fossils

Footnotes

1. Lucas and Heckert 2005
2. Cather 2010
3. Weishampel et al. 2004
4. Tschudy 1976
5. Collier 1919
6. Allen and Balk 1954

References

• Allen, J.E.; Balk, Robert (1954). "Mineral Resources of Fort Defiance and Tohatchi quadrangles, Arizona and New Mexico". New Mexico Bureau of Mines and Mineral Resources Bulletin. 36.
• Cather, Steven (2010). "Preliminary geologic map of the San Lucas Dam quadrangle, McKinley County, New Mexico". New Mexico Bureau of Geology and Mineral Resources, Open-File Geologic Map. OF-GM 212. Retrieved 4 June 2020.
• Collier, A.J. (1919). "Coal south of Mancos, Montezuma County, Colorado". Contributions to economic geology, 1918; Part 2, Mineral fuels: U.S. Geological Survey Bulletin. 691-K: K293–K310.
• Lucas, Spencer G.; Heckert, Andrew B. (2005). "Mesozoic stratigraphy at Durango, Colorado" (PDF). New Mexico Geological Society Field Conference Series. 56. Retrieved 8 June 2020.
• Tschudy, R.H. (1976). "Palynology of Crevasse Canyon and Menefee Formation of San Juan basin, New Mexico". In Beaumont, E.C.; Shomaker, J.W.; Stone, W.J. (eds.). Guidebook to coal geology of northwest New Mexico: New Mexico Bureau of Mines and Mineral Resources Circular. 154. pp. 48–55.
• Weishampel, David B.; Dodson, Peter; Osmólska, Halszka. The Dinosauria (2nd ed.). Berkeley: University of California Press. ISBN 0-520-24209-2.