GEOLEX

Summary of Citation: Muddy

Publication:
Waage, K.M., 1955, Dakota group in northern Front Range foothills,
   Colorado, IN Shorter contributions to general geology, 1955-57:
   U.S. Geological Survey Professional Paper, 274-B, p. B15-B51

Usage in Publication:
Muddy sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Overview

Summary:
Correlation with other Cretaceous units in Powder River basin of northeast WY, Wind River basin of central WY and Denver basin in southeast WY, northeast and south-central CO shown on fig 19.

Summary of Citation: Muddy

Publication:
MacKenzie, D.B., 1965, Depositional environments of Muddy
   Sandstone, western Denver basin, Colorado: American Association
   of Petroleum Geologists Bulletin, v. 49, no. 2, p. 186-206

Usage in Publication:
Muddy Sandstone

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits Revised	Denver basin

Summary:
Geographically extended as a formation in Lower Cretaceous Dakota Group to the northern Front Range foothills, between Loveland and Boxelder Creek (sec 9, T10N, R69W), Larimer Co, CO, Denver basin from central WY. Name applied to rocks formerly called first sandstone of South Platte Formation of Dakota Group and "J" sandstone. Divided into Fort Collins (base) and Horsetooth (top) Members, both newly named. Overlies Skull Creek Shale (extended from Black Hills). Underlies Mowry Shale (replacement term for lower part, Benton Formation). Correlates with and has same trace fossils in basal part as Newcastle Sandstone of Bighorn basin has in its basal part. Decreases from 72 ft thick near Boulder to a feather edge west of Berthoud. Ranges from 10-150 ft thick. Fort Collins Member is a shallow-water marine deposit. Horsetooth Member is a shoal-water delta or alluvial-plain deposit. Correlation chart.

Summary of Citation: Muddy

Publication:
Harshman, E.N., 1972, Geology and uranium deposits, Shirley
   basin area, Wyoming: U.S. Geological Survey Professional
   Paper, 745, 82 p.

Usage in Publication:
Muddy Sandstone Member*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Denver basin Greater Green River basin

Summary:
Thermopolis and Mowry Shales mapped as a single unit in the southeast part of the Shirley basin western Albany Co (Denver basin) and eastern Carbon Co (Greater Green River basin), WY. Basal Thermopolis lies conformably above the Cloverly Formation. The upper Mowry underlies the Frontier Formation. Rocks of the Thermopolis consist of: 1.) basal gray to black carbonaceous shale about 60 ft thick of marine origin, 2.) the Muddy Sandstone Member about 14 ft thick, 3.) a brown-gray, thin-bedded, fine grained, silty sandstone interbedded with thin bedded siltstone and shale 50 ft thick, that has a 2 ft thick lignite bed at top, and 4.) a 60 ft thick interval of sandy siltstone and shale interbedded with "typical" Mowry siliceous shale. Unit 4 is arbitrarily considered to be upper Thermopolis. Unit 3 is poorly indurated and makes poor outcrops; it is of paladal origin. Some of the buff to gray thin-bedded sandstone beds of the Muddy are ripple marked. The 110 ft of gray, dense or siliceous, laminated shale with fish scales and interbedded 2-3 ft thick bentonite beds are the Mowry, this sequence very resistant to erosion forms long narrow ridges. Stratigraphic chart. Cretaceous age.

Summary of Citation: Muddy

Publication:
Rice, D.D., 1976, Revision of Cretaceous nomenclature of the
   northern Great Plains in Montana, North Dakota, and South
   Dakota, IN Cohee, G.V., and Wright, W.B., Changes in
   stratigraphic nomenclature by the U.S. Geological Survey,
   1975: U.S. Geological Survey Bulletin, 1422-A, p. A66-A67

Usage in Publication:
Muddy Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Revised	Williston basin

Summary:
Raised to formation rank in MT in Williston basin area. Is widely used in subsurface. Interpreted to be of marine origin. Correlates with the Vaughn Member of Blackleaf Formation of Sweetgrass arch. Correlates with the Newcastle Sandstone of the Black Hills uplift.

Summary of Citation: Muddy

Publication:
Tysdal, R.G., Dyman, T.S. and Nichols, D.J., 1989, Lower Cretaceous
   bentonitic strata in southwestern Montana assigned to Vaughn
   Member of Mowry Shale (east) and of Blackleaf Formation
   (west): The Mountain Geologist, v. 26, no. 2, p. 53-61

Usage in Publication:
Muddy Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Revised Areal limits	Montana folded belt province

Summary:
Revised in that Muddy Sandstone unconformably underlies the Vaughn Member which is newly assigned to the Mowry Shale in the Greenhorn, Madison, Gallatin, and Gravelly Ranges, Beartooth and Centennial Mountains of southwest MT in Montana folded belt province. Use of Muddy in these mountain ranges represents the western limit of the use of the name. The axis of the Ruby River valley which separates the Snowcrest Range from the Greenhorn and Gravelly Range is the arbitrary location of the nomenclature change. The rocks equivalent to the Muddy to the west are in the upper part of the Flood Member and, to the northwest, the Taft Hill Member of the Blackleaf Formation. Conformably overlies Thermopolis Shale. Nomenclature chart. Of Albian, Early Cretaceous age.

Summary of Citation: Muddy

Publication:
Tysdal, R.G., Dyman, T.S. and Nichols, D.J., 1989, Correlation
   chart of Lower Cretaceous rocks, Madison Range to Lima Peaks
   area, southwestern Montana: U.S. Geological Survey Miscellaneous
   Field Studies Map, MF-2067, 15 p., 1 sheet

Usage in Publication:
Muddy Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Overview	Montana folded belt province

Summary:
Name applied to two yellowish-green, cross-bedded, thin-bedded sandstones separated by mudstone that lie above the shale member of the Thermopolis Shale and beneath the Vaughn Member of the Mowry Shale. Is part of the nomenclature used east of the Ruby River, Beaverhead Co, MT in the Montana folded belt province. Ranges from 50 to 115 ft thick. Is equivalent to rocks assigned to the upper part of the Flood Member of the Blackleaf Formation on the west of the Ruby River. Rocks assigned to Muddy in this report have been variously assigned to the Aspen? Formation, Muddy? Sandstone Member of the Thermopolis Shale, Colorado Formation. Muddy is of Albian, Early Cretaceous age. Columnar section.

Summary of Citation: Muddy

Publication:
Fox, J.E., 1993, Stratigraphic cross sections showing electric
   logs of Upper Cretaceous and older rocks, Powder River basin,
   southeastern Montana and northeastern Wyoming: U.S. Geological
   Survey Oil and Gas Investigations Chart, OC-135 to OC-138,
   4 sheets, sections A-A' trhough F-F'; G-G' through L-L'; M-M'
   through R-R'; S-S' through V-V'

Usage in Publication:
Muddy Sandstone*

Modifications:	Geologic Province:	Dominant Lithology:
Areal limits	Powder River basin

Summary:
Identified throughout the subsurface of the Powder River basin in MT and WY where it overlies Skull Creek Shale unconformably and underlies Mowry Shale. Of Early Cretaceous age. [This nomenclature shown on 22 cross sections in this OC series.]