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The Yampa Bed - A Regionally Extensive Tonstein in the Williams Fork Formation, Northwestern Piceance Creek and Southern Sand Wash Basins, Colorado

Scientific Investigations Report 2008-5033

By:
and

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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 NE? SW? 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.

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Additional Publication Details

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
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: Plate 1 - 40 x 40 inches and Plate 2 - 34 x 36 inches
Online Only (Y/N):
Y
Additional Online Files(Y/N):
Y