Rattlesnake Formation
| Rattlesnake Formation | |
|---|---|
| Stratigraphic range: Miocene-Late Pliocene | |
| File:Rattlesnake Formation near Picture Gorge.jpg The caprock in this photo (near Picture Gorge) is the ignimbrite layer | |
| Type | Sedimentary and igneous |
| Overlies | Mascall Formation, Columbia River Basalt Group |
| Area | John Day Valley |
| Thickness | 700 feet (210 m) |
| Lithology | |
| Primary | Fanglomerate, siltstone |
| Other | Tuff (ignimbrite) |
| Location | |
| Coordinates | Lua error in Module:Coordinates at line 489: attempt to index field 'wikibase' (a nil value). |
| Approximate paleocoordinates | Lua error: callParserFunction: function "#coordinates" was not found. |
| Region | Oregon |
| Country | United States |
| Extent | eastern Oregon |
| Type section | |
| Named for | Rattlesnake Creek |
| Named by | J. C. Merriam |
| Year defined | 1901[1] |
Rattlesnake Formation (the United States) Rattlesnake Formation (Oregon) | |
The Rattlesnake Formation is a Miocene to late Pliocene geologic formation found along the John Day River Valley of Oregon, in the Western United States.
Description
[edit | edit source]The formation is described in Geologic Formations of Eastern Oregon (1972) as follows:
The unit is composed of up to 700 feet of fanglomerate and finer terrestrial sediments and a 40-foot thick ignimbrite unit which crops out in the middle of the section. The gravel is well rounded and consists of pebbles of basalt, chert, siltstone, diorite, rhyolite, and chert set in a medium-grained matrix of poorly indurated volcanic sandstone. The ignimbrite displays zonation typical of welded ashflow tuffs and is a prominent ridge former.[2]
Age
[edit | edit source]The ignimbrite was radiometrically dated by the Potassium–argon method at 6.4 million years by Evernden and James (1964).[3]
Fossil content
[edit | edit source]
Middle and late Pliocene mammals have been recovered from beneath the ignimbrite. Fossils found here include Amebelodon sp., the extinct peccary Mylohyus longirostris, the extinct North American rhino Teleoceras fossiger, Indarctos oregonensis, Pliohippus spectans, Machairodus sp., Hemiauchenia vera, an extinct species of fox known as Vulpes stenognathus and the earliest record of modern-day beavers.[4][5][6]
In the lower fanglomerate member of the Rattlesnake Formation, remains of Pekania occulta were found.[7][8]
References
[edit | edit source]- ^ Merriam, J. C., 1901. A contribution to the geology of the John Day Basin, Oregon: Univ. Calif., Dept. Geol. Sci. Bull., v. 2, p. 269-314
- ^ Geologic Formations of Eastern Oregon (East of longitude 121°30'), 1972. John D. Beaulieu. Bulletin 73. Oregon Department of Geology and Mineral Industries.
- ^ Evernden, J. F., and James, G. T., 1964. Potassium-argon dates of the Tertiary floras of North America: Am. Jour. Sci., v. 262, p. 945-974.
- ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
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- ^ Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
- ^ Samuels & Cavin 2013
- ^ Pekania occulta type locality at Fossilworks.org
Bibliography
[edit | edit source]- Lua error in Module:Citation/CS1/Configuration at line 2172: attempt to index field '?' (a nil value).
- Geologic formations of Oregon
- Miocene Series of North America
- Pliocene Series of North America
- Neogene geology of Oregon
- Hemphillian
- Sandstone formations of the United States
- Siltstone formations of the United States
- Tuff formations of the United States
- Miocene volcanism
- Alluvial deposits
- Paleontology in Oregon
- Grant County, Oregon