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Geologic Unit: Roberts Mountains

Publication:
Merriam, C.W., 1940, Devonian stratigraphy and paleontology of 
   the Roberts Mountains region, Nevada: Geological Society of 
   America Special Paper, 25, 114 p., (incl. geologic map, scale 
   1:211,200)
Usage in Publication:
Roberts Mountains formation

Modifications: Geologic Province: Dominant Lithology:
 Named
 Biostratigraphic dating
 Great Basin province
 Limestone

Summary:
Roberts Mountains formation [probably] named for the Roberts Mountains, NV. Type section lies on west side of Roberts Creek Mountain [Roberts Creek Mountain 7.5' quad, Eureka Co]. Partial equivalent [lower part] at Lone Mountain; included by Hague (1883) in "Lone Mountain limestone". Consists of well-bedded, frequently slabby, dark slate gray limestone. Bedding becomes more massive in upper 800 ft; dolomitic 220 ft from top of unit. Much of lower and middle part of section consists of crystalline limestone beds (in part crinoidal). Moderately coarse-grained crinoidal beds from 6 in to about 2 ft in thickness are sometimes separated by thin-bedded, shaly limestone layers. Thickness at type section is 1900 ft; at Lone Mountain 741 ft. Overlies [conformably] the Hanson Creek formation (new) and conformably underlies the Lone Mountain formation (redefined). Lower boundary is drawn at base of a laterally persistent belt of bluish-black chert. Age is Silurian on the basis of fossils (brachiopods, corals, graptolites).
Source: GNU records (USGS DDS-6; Menlo GNULEX).


Publication:
Nolan, T.B., Merriam, C.W., and Williams, J.S., 1956, The 
   stratigraphic section in the vicinity of Eureka, Nevada: U.S. 
   Geological Survey Professional Paper, 276, 77 p., (incl. 
   geologic map, scale 1:21,200) [Available online from the USGS 
   PubsWarehouse:  http://pubs.er.usgs.gov/pubs/pp/pp276]
Usage in Publication:
Roberts Mountains formation*

Modifications: Geologic Province: Dominant Lithology:
 Adopted
 Redescribed
 Great Basin province
 

Summary:
Roberts Mountains formation is adopted as defined by Merriam (1940). Type section is informally divided into lower (1100 ft) and upper (800 ft) units. Lower unit composed of medium gray to medium dark and dark slate gray, flaggy, platy, and shaly limestone; upper unit contains more massive and dolomitic beds. Age is Silurian (Niagara) on the basis of fossils (corals, brachiopods, graptolites).
Source: GNU records (USGS DDS-6; Menlo GNULEX).


Publication:
Skipp, Betty, and Sandberg, C.A., 1975, Silurian and Devonian 
   miogeosynclinal and transitional rocks of the Fish Creek 
   Reservoir window, central Idaho: U.S. Geological Survey 
   Journal of Research, v. 3, no. 6, p. 691-706.
Usage in Publication:
Roberts Mountains Formation*

Modifications: Geologic Province: Dominant Lithology:
 Areal limits
 Overview
 Idaho Mountains province
 

Summary:
A sequence of Upper Silurian (Pridolian) and Lower Devonian (Lochkovian) fossiliferous reef limestone, platy calcareous and dolomitic siltstone, and limestone phenoplast conglomerate assigned to Roberts Mountains Formation on the basis of age, lithologic character, and paleontologic setting. Is at least 656 ft thick. The lower unit is predominantly medium-gray, medium- to coarse-grained coralline patch-reef limestone with coral FAVOSITES and conodonts. The middle unit has lenticular reef limestone beds at base overlain by coarser encrinite, and has abundant reef talus. The upper unit is dominantly a fossiliferous phenoplast conglomerate or intraformational sedimentary limestone breccia. Fossils (corals, gastropods, forams, tentaculids, trilobites, brachiopods, calcareous algae, conodonts) in all three units. Geologic map, columnar section. Is a transitional facies thrust over the shelf sequence.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Dover, J.H., 1983, Geologic map and sections of the central 
   Pioneer Mountains, Blaine and Custer Counties, central Idaho: 
   U.S. Geological Survey Miscellaneous Investigations Series 
   Map, I-1319, 1 sheet, scale 1:48,000
Usage in Publication:
Roberts Mountains Formation*

Modifications: Geologic Province: Dominant Lithology:
 Age modified
 Overview
 Idaho Mountains province
 

Summary:
Mapped within Wildhorse window in northeast part of study area, Custer Co, ID, Idaho Mountains province. Divided into lower limestone and upper siltstone units. Limestone unit consists of light-gray, platy-bedded to massive, silty limestone and dolomitic limestone containing prominent 11 m thick bed of interlayered black dolomite and black chert at base; contains Monograptid graptolites of Wenlockian (Middle Silurian) age; lower part unfossiliferous but may be Early Silurian age; minimum measured thickness is 40 m; minimum thickness on cross section is 120 m. Siltstone unit consists of buff, tan- to orange-weathering, thin- to medium-bedded, slabby to block, slightly calcareous to dolomitic siltstone with graded bedding, small-scale cross-bedding, and convolute structure; dense and silicified in places; base not exposed though generally concordant with underlying limestone unit; contains unidentified brachiopod molds and crinoid debris, and Silurian corals; thickness about 600 m. Roberts Mountains underlies unnamed dolomite (Silurian and Devonian) with sharp concordant contact; overlies, probably disconformably, Hanson Creek Formation. Assigned Middle and (or) Late Silurian age.
Source: GNU records (USGS DDS-6; Denver GNULEX).


Publication:
Radtke, A.S., 1985, Geology of the Carlin gold deposit, Nevada: 
   U.S. Geological Survey Professional Paper, 1267, 124 p., 
   (incl. geologic map, scale 1:12,000)
Usage in Publication:
Roberts Mountains Formation*

Modifications: Geologic Province: Dominant Lithology:
 Age modified
 Great Basin province
 

Summary:
Age of the Roberts Mountains Formation in the Lynn window, Tuscarora Mountains [Rodeo Creek NE 7.5' quad, Eureka Co], NV is Early Silurian (late Llandoverian) to Early Devonian on the basis of fossils (graptolites) identified by W.B.N. Berry.
Source: GNU records (USGS DDS-6; Menlo GNULEX).