Willwood Formation
| Willwood Formation | |
|---|---|
| Stratigraphic range: Thanetian-Ypresian (Clarkforkian-Bridgerian) ~ | |
| Type | Geological formation |
| Sub-units | Gray Bull beds, Sand Coulee beds, Sand Creek Facies, Wa-1 Zone |
| Lithology | |
| Primary | Mudstone, shale |
| Other | Sandstone, conglomerate |
| Location | |
| Coordinates | 44°30′N 108°00′W / 44.5°N 108.0°W |
| Approximate paleocoordinates | 49°12′N 90°48′W / 49.2°N 90.8°W |
| Region |  Wyoming |
| Country |  USA |
| Extent | Bighorn Basin |
| Type section | |
| Named for | Shale, mudstone, limestone |
  Willwood Formation (the United States)  Willwood Formation (Wyoming) | |
The Willwood Formation is a sedimentary sequence deposited during the late Paleocene to early Eocene, or Clarkforkian, Wasatchian and Bridgerian in the NALMA classification.[1][2]
Description
It consists of fine grained clastic rocks (mudstone and shale) interbedded with medium grained clastic rocks (sandstone) and sporadic conglomerates. The formation underlies portions of the Bighorn Basin of Big Horn, Hot Springs, Park and Washakie counties of Wyoming.[3]
Dating
Radiometric dating of volcanic tuffs, combined with comparisons with other formations using magnetostratigraphy, using numerous samples from various levels of the formation suggest an age range of 55 - 52 million years ago, placing the Paleocene-Eocene boundary near the base of the formation.[4]
Fossil content
Trace fossils have been found in the Willwood Formation.[5] Fossil birds include Gastornis, Neocathartes and Paracathartes. A fossil alligatorid, namely Orthogenysuchus, was also found in this formation.
Wasatchian correlations
See also
References
- ^ Willwood Formation at Fossilworks.org
- ^ Neasham & Vondra, 1972
- ^ "Willwood Formation". USGS.
- ^ Tauxe et al., 1994
- ^ Bown & Kraus, 1982
Bibliography
- Template:Cite LSA
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- Template:Cite LSA doi:10.1130/0016-7606(1972)83[267:SAPOTL2.0.CO;2]
- Geologic formations of the United States
- Paleocene Series of North America
- Eocene Series of North America
- Paleogene geology of Wyoming
- Thanetian Stage
- Ypresian Stage
- Bridgerian
- Clarkforkian
- Wasatchian
- Limestone formations
- Mudstone formations
- Shale formations of the United States
- Sandstone formations of the United States
- Conglomerate formations
- Fluvial deposits
- Lacustrine deposits
- Ichnofossiliferous formations
- Fossiliferous stratigraphic units of North America
- Paleontology in Wyoming