The Yampa Bed — A regionally extensive tonstein in the Williams Fork Formation, northwestern Piceance Creek and southern Sand Wash Basins, Colorado
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Abstract
A regionally persistent and distinctive unit of Upper Cretaceous age is here formally named the Yampa Bed of the Williams Fork Formation for exposures in the Yampa, Danforth Hills, and Grand Hogback coal fields, Moffat and Routt Counties, northwest Colorado; the name is derived from the Yampa River valley. The type section was measured in the NE¼ SW¼ sec. 6, T. 5 N., R. 91 W., about 8 miles south of Craig, Colo., where the bed is 38 inches thick and lies within the C-D coal bed in the lower part of the Williams Fork Formation, about 165 feet above the Trout Creek Sandstone Member of the Iles Formation. The Yampa Bed is dated at 72.2 ± .1 mega-annum using the K-Ar method. Regionally, the Yampa Bed is a 0.5- to 5-ft-thick, regionally persistent tonstein that can be readily identified in several different lithofacies in the lower part of the Williams Fork Formation. The unit is useful as a regional datum in the correlation of facies within the Williams Fork, and it is easily recognized on geophysical logs by its low resistivity response. Evidence suggests that it is a diagenetically altered airfall ash.
Study Area
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | The Yampa Bed — A regionally extensive tonstein in the Williams Fork Formation, northwestern Piceance Creek and southern Sand Wash Basins, Colorado |
| Series title | Scientific Investigations Report |
| Series number | 2008-5033 |
| DOI | 10.3133/sir20085033 |
| Edition | Version 1.0 |
| Year Published | 2008 |
| Language | English |
| Publisher | Geological Survey (U.S.) |
| Contributing office(s) | U.S. Geological Survey |
| Description | Report: vi, 32 p.; 2 Plates: 40 x 40 inches and 34 x 36 inches |
| Country | United States |
| State | Colorado |
| Other Geospatial | Williams Fork Formation |
| Online Only (Y/N) | Y |
| Additional Online Files (Y/N) | Y |
| Google Analytic Metrics | Metrics page |