| Dockum Group | |
|---|---|
| Stratigraphic range: late Carnian-Rhaetian ~ | |
 Steamboat Butte, showing Dockum Group red beds at its base | |
| Type | Group |
| Sub-units | See text |
| Underlies | Exeter Sandstone |
| Overlies | Anton Chico Formation |
| Lithology | |
| Primary | Sandstone |
| Other | Siltstone, Mudstone |
| Location | |
| Coordinates | 35°21′22″N 102°54′36″W / 35.356°N 102.910°W |
| Country |  United States |
| Type section | |
| Named for | Town of Dockum, Texas |
| Named by | William Fletcher Cummins |
| Year defined | 1890 |
The Dockum is a Late Triassic (approximately late Carnian through Rhaetian, or 223–200 Ma) geologic group found primarily on the Llano Estacado of western Texas and eastern New Mexico with minor exposures in southwestern Kansas, eastern Colorado, and Oklahoma panhandle.[1] The Dockum reaches a maximum thickness of slightly over 650 m but is usually much thinner. The Dockum rests on an unconformity over the Anisian (242–234 Ma) aged Anton Chico Formation.
The Dockum and Chinle Formation were deposited roughly at the same time and share many of the same vertebrates and plant fossils. They appear to have very similar paleoenvironments.[2] The two units are approximately separated by the Rio Grande in central New Mexico. This has led to controversy over the stratigraphic nomenclature for the Chinle and Dockum.[3]
- ^ Dunay, R.E.; Fisher, M.J. (June 1979). "Palynology of the Dockum group (Upper Triassic), Texas, U.S.A.". Review of Palaeobotany and Palynology. 28 (1): 61–92. doi:10.1016/0034-6667(79)90025-3.
- ^ Cornet, B. (1993). "Applications and limitations of palynology in age, climatic, and paleoenviromental analyses of Triassic sequences in North America". New Mexico Museum of Natural History Bulletin. 3: 75–93. Retrieved 1 September 2020.
- ^ Lehman, T.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. Retrieved 1 September 2020.