Rock Point Formation

Rock Point Formation
Stratigraphic range: late Triassic PreꞒ Ꞓ O S D C P T J K Pg N
Rock Point Formation capped by Entrada Formation, near Youngsville, New Mexico
Type	Formation
Unit of	Chinle Group
Underlies	Wingate Sandstone
Overlies	Petrified Forest Formation
Thickness	70 m
Lithology
Primary	Siltstone
Other	Fine sandstone
Location
Coordinates	36°31′29″N 109°33′22″W / 36.5247221°N 109.5560845°W / 36.5247221; -109.5560845
Region	Utah, Arizona, New Mexico
Country	United States
Type section
Named for	Rock Point School, Apache County, Arizona
Named by	Harshbarger, J.W., Repenning, C.A., and Irwin, J.H., 1957
Rock Point Formation (the United States) Show map of the United States Rock Point Formation (Arizona) Show map of Arizona

The Rock Point Formation is a geologic formation in New Mexico, Arizona, and Utah. It preserves fossils dating back to the late Triassic.

Description

The formation is up to 70 m thick and is mostly reddish-brown and grayish-red massive siltstone and fine sandstone beds. It is the uppermost portion of the Chinle Group wherever it is exposed. In the Chama basin, its base is placed at the first persistent sandstone bed above the mudstones of the Petrified Forest Formation. Its contact with the overlying Entrada Sandstone is sharp.^[1]

Fossils

The Whitaker quarry of Ghost Ranch, New Mexico is believed to be located in the Rock Point Formation, although these beds have also controversially been assigned to the Owl Rock Formation.^[1] This quarry has also been referred to as the Coelophysis quarry due to preserving a large number of specimens of the early theropod dinosaur Coelophysis bauri.^[2]

History of investigation

The unit was first named by J.W. Harshbarger, C.A. Repenning, and J.H. Irwin in 1957, who assigned Herbert E. Gregory's (1917) "A" division of the Chinle Formation to the Wingate Formation as the Rock Point Member. It was named for Rock Point School, located near the type exposures at Little Round Rock.^[3] J.H. Stewart and coinvestigators argued in 1972 that the unit has more affinity with the Chinle,^[4] and R.F. Dubiel assigned the Rock Point to the Chinle in 1989.^[5] The unit has created an unusual amount of controversy, but Spencer G. Lucas and coinvestigators raised it to formation rank within the Chinle Group in 2005.^[1]

• 
  Bed of concretions in the Rock Point Formation near Youngsville, New Mexico
• 
  Fossil from Rock Point Formation

See also

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

Footnotes

References

• Dubiel, R.F. (1989). "Sedimentology and revised nomenclature of the Upper Triassic Chinle Formation and the Lower Jurassic Wingate Sandstone, northwestern New Mexico and northeastern Arizona" (PDF). New Mexico Geological Society Field Conference Series. 40: 213–223. Retrieved 25 May 2020.
• Harshbarger, J.W.; Repenning, C.A.; Irwin, J.H. (1957). "Stratigraphy of the uppermost Triassic and the Jurassic rocks of the Navajo country". U.S. Geological Survey Professional Paper. 291. Retrieved 25 May 2020.
• Lucas, Spencer G.; Zeigler, Kate E.; Heckert, Andrew B.; Hunt, Adrian P. (2005). "Review of Upper Triassic stratigraphy and biostratigraphy in the Chama Basin, northern New Mexico" (PDF). New Mexico Geological Society Field Conference Series. 56: 170–181. Retrieved 29 April 2020.
• Rinehart, L.F.; Lucas, S.G.; Heckert, A.B.; Spielmann, J.A.; Celesky, M.D. (2009). "The paleobiology of Coelophysis bauri (Cope) from the Upper Triassic (Apachean) Whitaker quarry, New Mexico, with detailed analysis of a single quarry block". New Mexico Museum of Natural History & Science, A Division of the Department of Cultural Affairs Bulletin. 45: 260.
• Stewart, J.H.; Poole, F.G.; Wilson, R.F. (1972). "Stratigraphy and origin of the Chinle Formation and related Upper Triassic strata in the Colorado Plateau region, with sections on sedimentary petrology by R.A. Cadigan and conglomerate studies by William Thordarson and H.F. Albee". U.S. Geological Survey Professional Paper. 690. doi:10.3133/pp690.

This page was last edited on 28 March 2024, at 22:42