| Colorado City Formation | |
|---|---|
| Stratigraphic range: Late Triassic | |
| Type | Formation |
| Unit of | Dockum Group |
| Underlies | possibly Cooper Canyon Formation |
| Overlies | Camp Springs Formation |
| Lithology | |
| Primary | siltstone, sandstone |
| Location | |
| Region | Texas |
| Country | United States |
The Colorado City Formation is a Late Triassic geologic formation in the Dockum Group of Texas, United States. It has previously been known as the Iatan Member,[1] Colorado City Member[2][3] or 'Pre-Tecovas Horizon'[4] (as it is assumed to be older than the Tecovas Formation).
The Colorado City Formation is mostly restricted to Howard and Borden counties. The formation hosts the Otis Chalk fossil sites, named after a ghost town in Howard County. Despite their importance, the Otis Chalk localities have been difficult to resolve in the stratigraphy of Triassic Texas.[5] They occupy a narrow band of sediments between the slightly older Camp Springs Formation and much younger Cretaceous deposits.
The first major excavations near Otis Chalk were led by UMMP paleontologists starting in 1927. Several new phytosaur species were discovered during these digs. University of Oklahoma paleontologists followed with their own expedition in 1931. The vast majority of fossils collected from the formation were recovered during a 1939–1941 state-sponsored Works Progress Administration paleontological survey. Several sites southeast of Big Spring were particularly productive. Fossils collected by these efforts were stored at the newly opened Texas Memorial Museum in Austin. Since the 1940s, collection from the Otis Chalk area has been more limited. One notable find is a pond deposit, the Schaeffer Fish Quarry, discovered in 1967 by AMNH paleontologist Bobb Schaeffer.[4]
- ^ Lucas, Spencer G.; Hunt, Adrian P.; Kahle, Robert (1993). "LATE TRIASSIC VERTEBRATES FROM THE DOCKUM FORMATION NEAR OTIS CHALK, HOWARD COUNTY, TEXAS". New Mexico Geological Society Guidebook, 44th Field Conference, Carlsbad Region: 237–244.
- ^ Lucas, Spencer G.; Anderson, Orin J.; Hunt, Adrian P. (1994). "Triassic stratigraphy and correlations, southern High Plains of New Mexico—Texas" (PDF). New Mexico Bureau of Mines & Mineral Resources Bulletin. 150: 105–126.
- ^ Heckert, Andrew B.; Lucas, Spencer G. (1999-03-15). "A new aetosaur (Reptilia: Archosauria) from the Upper Triassic of Texas and the phylogeny of aetosaurs". Journal of Vertebrate Paleontology. 19 (1): 50–68. doi:10.1080/02724634.1999.10011122. ISSN 0272-4634.
- ^ a b Long, Robert A.; Murry, Phillip A. (1995). "Late Triassic (Carnian and Norian) Tetrapods from the Southwestern United States". New Mexico Museum of Natural History and Science Bulletin. 4.
- ^ Lehman, Thomas M. (1994). "The saga of the Dockum Group and the case of the Texas/New Mexico boundary fault" (PDF). New Mexico Bureau of Mines & Mineral Resources Bulletin. 150: 37–51.