Exeter Sandstone Explained
The Exeter Sandstone is a geologic formation exposed in northeastern New Mexico. Its age is poorly controlled, but it is thought to have been deposited during the middle Jurassic.
Description
The formation consists of up to 24meters 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. 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.
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, and Spencer G. Lucas and coinvestigators recommended demoting the Exeter Sandstone to member rank within the Entrada Formation. However, age control is poor on the Exeter Sandstone, and other investigators have retained the Exeter Sandstone at formation rank until the correlation becomes clearer.
History of investigation
The formation was first named by W.T. Lee in 1902 for exposures near the Exter Post Office.[1]
See also
References
- Baldwin . Brewster . Muehlberger . W.R. . 1959 . Geologic studies of Union County, New Mexico . New Mexico Bureau of Mines and Mineral Resources Bulletin . 63 . 2 . 1 September 2020 . 30 August 2017 . https://web.archive.org/web/20170830172016/http://geoinfo.nmt.edu/publications/monographs/bulletins/downloads/63/Bulletin63.pdf . dead .
- Conrad . Kelly . Lockley . Martin G. . Prince . Nancy K. . 1987 . 127–138 . Triassic and Jurassic vertebrate-dominated trace fossil assemblages of the Cimarron Valley region--Implications for paleoecology and biostratigraphy . New Mexico Geological Society Field Conference Series . 38 . 1 September 2020.
- Johnson . R.B. . 1959 . Geology of the Huerfano Park area, Huerfano and Custer Counties, Colorado . U.S. Geological Survey Bulletin . 1071-D . D87-D119 . 2 September 2020.
- Lee . W.T. . 1902 . The Morrison shales of southern Colorado and northern New Mexico . Journal of Geology . 10 . 36–58 . 2 September 2020.
- Lucas . S.G. . Spencer G. Lucas . Kietzke . K.K. . Hunt . A.P. . 1985 . The Jurassic System in east-central New Mexico . New Mexico Geological Society Field Conference Guidebook . 36 . 213–242 . 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 . 2 September 2020.
- Ziegler . Kate E. . Ramos . Frank C. . Zimmerer . Matthew J. . Geology of Northeastern New Mexico, union and Colfax Counties, New Mexico: A Geologic Summary . New Mexico Geological Society Field Conference Series . 2019 . 70 . 4 . 47–54 . 1 September 2020.
Notes and References
- https://ngmdb.usgs.gov/Geolex/Units/Exeter_8058.html GEOLEX: "Exeter"
