Exeter Sandstone

Exeter Sandstone
Stratigraphic range: middle Jurassic PreꞒ Ꞓ O S D C P T J K Pg N
Exeter Formation capping Steamboat Butte, New Mexico, US
Type	Formation
Unit of	Dockum Group
Underlies	Bell Ranch Formation
Overlies	Sheep Pen Sandstone
Thickness	24 meters (79 ft)
Lithology
Primary	Sandstone
Location
Coordinates	36°58′32″N103°12′22″W / 36.9756°N 103.2060°W / 36.9756; -103.2060
Region	Colorado New Mexico
Country	United States
Type section
Named for	Exter Post Office
Named by	W.T. Lee
Year defined	1902
Exeter Sandstone (the United States) Show map of the United States Exeter Sandstone (New Mexico) Show map of New Mexico

The Exeter Sandstone is a geologic formation exposed in northeastern New Mexico. ^[1] Its age is poorly controlled, but it is thought to have been deposited during the middle Jurassic. ^[2]

Description

The formation consists of up to 24 meters (79 ft) of white to pale pink crossbedded quartz sandstone. It unconformably overlies the Sheep Pen Sandstone and is in turn overlain by the Bell Ranch Formation. ^[1] The Exeter Formation varies greatly in thickness, with the maximum thickness in synclinal valleys of the underlying Dockum Group and the formation being absent on some anticlinal crests of the Dockum Group. ^[2]

The formation has long been thought to have formed in the eastern part of the Entrada Formation dune sea and thus to be correlative with the Entrada Formation, ^{[3] [4]} and Spencer G. Lucas and coinvestigators recommended demoting the Exeter Sandstone to member rank within the Entrada Formation. ^[5] However, age control is poor on the Exeter Sandstone, ^[2] and other investigators have retained the Exeter Sandstone at formation rank until the correlation becomes clearer. ^{[6] [2]}

History of investigation

The formation was first named by W.T. Lee in 1902 for exposures near the Exter Post Office. ^{[7] [8]}

See also

• Earth sciences portal
• Colorado portal
• Paleontology portal

• List of fossiliferous stratigraphic units in Colorado
• Paleontology in Colorado

Footnotes

1. Baldwin & Muehlberger 1959.
2. Ziegler, Ramos & Zimmerer 2019.
3. Johnson 1959.
4. Conrad, Lockley & Prince 1987.
5. Lucas, Kietzke & Hunt 1985.
6. Scott 1986.
7. Lee 1902.
8. GEOLEX: "Exeter" notes that "Exter" is the correct spelling of the town name.

References

• Baldwin, Brewster; Muehlberger, W.R. (1959). "Geologic studies of Union County, New Mexico" (PDF). New Mexico Bureau of Mines and Mineral Resources Bulletin. 63 (2). Archived from the original (PDF) on 30 August 2017. Retrieved 1 September 2020.
• Conrad, Kelly; Lockley, Martin G.; Prince, Nancy K. (1987). "Triassic and Jurassic vertebrate-dominated trace fossil assemblages of the Cimarron Valley region--Implications for paleoecology and biostratigraphy" (PDF). New Mexico Geological Society Field Conference Series. 38: 127–138. Retrieved 1 September 2020.
• Johnson, R.B. (1959). "Geology of the Huerfano Park area, Huerfano and Custer Counties, Colorado" (PDF). U.S. Geological Survey Bulletin. 1071-D: D87 –D119. Retrieved 2 September 2020.
• Lee, W.T. (1902). "The Morrison shales of southern Colorado and northern New Mexico". Journal of Geology. 10: 36–58. Retrieved 2 September 2020.
• Lucas, S.G.; Kietzke, K.K.; Hunt, A.P. (1985). "The Jurassic System in east-central New Mexico" (PDF). New Mexico Geological Society Field Conference Guidebook. 36: 213–242. Retrieved 2 September 2020.
• Scott, G.R. (1986). "Geologic and structure contour map of the Springer 30' x 60' quadrangle, Colfax, Harding, Mora, and Union Counties, New Mexico". U.S. Geological Survey Miscellaneous Investigations Series Map. I-1705. Retrieved 2 September 2020.
• Ziegler, Kate E.; Ramos, Frank C.; Zimmerer, Matthew J. (2019). "Geology of Northeastern New Mexico, union and Colfax Counties, New Mexico: A Geologic Summary" (PDF). New Mexico Geological Society Field Conference Series. 70 (4): 47–54. Retrieved 1 September 2020.