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Curtis Formation
Curtis Formation
Stratigraphic range: Callovian PreꞒ Ꞓ O S D C P T J K Pg N ↓
	Curtis Formation type
Type	Formation
Unit of	San Rafael Group
Underlies	Summerville Formation
Overlies	Entrada Sandstone
Lithology
Primary	Sandstone
Other	Mudstone, limestone
Location
Coordinates	39°07′36″N 110°26′51″W / 39.126665°N 110.447615°W
Region	Utah
Country	United States
Type section
Named for	Curtis Point, Emery County, Utah
Named by	Gilluly and Reeside
Year defined	1928

The Curtis Formation is a geologic formation in Utah. It preserves fossils dating back to the Callovian age of the Jurassic period.

Description

The Curtis Formation is composed of shallow marine sandstone, with thin beds of mudstone and minor limestone and gypsum. The sandstone is grayish-green in color and flat bedded or cross bedded. The presence of glauconite and marine invertebrate fossils indicates it was laid down in a shallow marine environment that became hypersaline towards the end of deposition. It represents a high stand of the Sundance Sea in the Callovian.^[1]

History of investigation

The formation was first described by Gilluly and Reeside in 1928 and named for exposures in the northeast San Rafael Reef at Curtis Point (39°07′36″N 110°26′51″W / 39.126665°N 110.447615°W / 39.126665; -110.447615). Pipiringos and Imlay reassigned the Curtis as a member of the Stump Formation in 1979,^[2] but this was rejected by Peterson in 1988.^[3]

Footnotes

^ Lucas and Anderson 1992
^ Pipiringos and Imlay 1979
^ Peterson 1988

References

Gilluly, James; Reeside, J.B. Jr. (1928). "Sedimentary rocks of the San Rafael Swell and some adjacent areas in eastern Utah". Shorter Contributions to General Geology, 1927: U.S. Geological Survey Professional Paper. 150-D: D61–D110.
Lucas, Spencer G.; Anderson, O.J. (November 1992). "The Middle Jurassic Summerville Formation, northern New Mexico" (PDF). New Mexico Geology. 14 (4). Retrieved 4 June 2020.
Peterson, Fred (1988). "Stratigraphy and nomenclature of Middle and Upper Jurassic rocks, western Colorado Plateau, Utah and Arizona". Revisions to Stratigraphic Nomenclature of Jurassic and Cretaceous Rocks of the Colorado Plateau: U.S. Geological Survey Bulletin. 1633-B: B13-56.
Pipiringos, G.N.; Imlay, R.W. (1979). "Lithology and subdivisions of the Jurassic Stump Formation in southeastern Idaho and adjoining areas". Unconformities, Correlations, and Nomenclature of Some Triassic and Jurassic Rocks, Western Interior United States: U.S. Geological Survey Professional Paper. 1035-C: C1–C25.
Entrada (orange) and Curtis formations exposed in a road cut, Green River Cutoff Road. They are separated by the J3 unconformity.
Lower and middle members of the Curtis Formation, Green River Cutoff Road, Emery County, Utah.