The Rock Point Formation is a geologic formation in New Mexico, Arizona, and Utah. It preserves fossils dating back to the late Triassic.
| Rock Point Formation | |
|---|---|
| Stratigraphic range: | |
 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 |
| 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)  Rock Point Formation (Arizona) | |
Description
editThe 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
editThe 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
editThe 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]
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Bed of concretions in the Rock Point Formation near Youngsville, New Mexico -
Fossil from Rock Point Formation
See also
edit
Footnotes
editReferences
edit- 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.