AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
Type Section Information
Walcot (1908) proposed the name "Dunderberg" for the shale unit originally defined as the Hamburg Shale by Hague (1883) for exposures in the vicinity of the Hamburg and Dunderberg mines near Eureka.
The Dunderberg is middle Late Cambrian (late Dresbachian and early Franconian) in age. The Dunderberg is equivalent to the Corset Spring Shale in the Snake Range (Whitebread, 1969). It is equivalent to the Johns Wash Limestone and Corset Spring Shale interval in the southern Snake Range (Drewes and Palmer, 1957) and is probably partially equivalent with the Mendha Formation (Tschanz and Pampeyan, 1970). East of Railroad Valley, the Dunderberg is in laterally gradational with the Lincoln Peak Formation, forming an intertonguing shale/limestone sequence (Kleinhampl and Ziony, 1985).
The Dunderberg Shale is conformably overlain by the Windfall Formation or equivalent units such as the Notch Peak Formation or Whipple Cave Formation (Hose and Blake, 1976; Adair, 1961; Kellogg, 1963). It conformably overlies the Highland Peak Formation in many sections in Lincoln County (Tschanz and Pampeyan, 1970). In the Hot Creek Range, the Dunderberg appears to gradationally overlie the Cambrian Swarbrick Formation along a tectonically disturbed contact, and also grades into the overlying Ordovician Goodwin Limestone (Quinlivan and Rogers, 1974).
In the Eureka area, the Dunderberg is composed of roughly equal thicknesses of olive-gray to blue-gray, silty shale and interbedded shale with thin, nodular and lenticular, blue-gray, medium-grained, trilobite-rich limestones up to 6 inches in thickness (Roberts and others, 1967; Hose and Blake, 1976). The contact with the underlying Hamburg Dolomite is sharp and often shows evidence of shearing (Nolan and others, 1956). The upper contact with the Windfall Formation is sharp and conformable.
In the Hot Creek Range, the Dunderberg is typically an olive-gray fissile shale with minor interbedded calcareous shale and limestone beds and lenses about 3 to 6 inches thick. Limestone and chert interbeds are more common in exposures of the formation east of Railroad Valley where the shales are a brown color, and commonly show phyllitic textures as a result of weak metamorphism (Kleinhampl and Ziony, 1985; Hyde and Huttrer, 1970). Fossils collected from the Dunderberg in the Hot Creek Range near Tybo often show evidence of deformation. The entire unit is strongly crumpled and sheared.
In the Ruby Mountains, the Dunderberg is a brown limestone and dark-gray hornfels which grades into phyllites. It overlies metamorphosed equivalents of the Hamburg and underlies the Windfall Formation in the Jiggs Quadrangle according to Wilden and Kistler (1979). In the southern Ruby Mountains within the Sherman Mountain Quadrangle, the Dunderberg is dark green, shaly, sparitic brachiopod and trilobite-bearing limestone and calcareous shale which is distinctly more argillaceous in the upper part of the formation (Millikin, 1978). To the south in the Buck Mountain-Bald Mountain area, the Dunderberg is soft, dark green-gray or black shale with minor thin, black, finely crystalline limestone in two to six inch beds (Rigby, 1960). The Dunderberg is mainly unaltered, but has been metamorphosed to a hornfels near intrusives.
In the Cherry Creek Range, as elsewhere in White Pine County, the Dunderberg is a greenish brown, silty shale which often weathers to small chips. Medium to dark gray, medium to coarse-grained, thin-bedded limestones composes about 10 percent of the Dunderberg (Fritz, 1968).
In the White Pine Range, the Dunderberg has been deformed and slightly metamorphosed. It is composed of interbedded dark brown to green shale or phyllite, and thin-bedded, bluish-gray limestone in varying percentages (Lumsden, 1964; Moores and others, 1968). In the Horse Range, the Dunderberg is a cherty, dark-gray, medium-grained, thick-bedded limestone with tan to red argillaceous parting.
In the Egan and northern Schell Creek Ranges, the Dunderberg is composed of a lower portion of olive to gray shale with minor interbedded, thin, nodular limestone, overlain by thin to medium-bedded, fine to coarse-grained, nodular limestone with brachiopod and trilobite fragments (Young, 1960; Kellogg, 1960; Dechert, 1967).
In the the Highland and Bristol Ranges, the Dunderberg Shale has been described as alternating layers of gray-brown weathering limestone, clastic limestone and oolitic limestone, which alternate with green or brownish, platy, fissile shale in partings and beds as much as 3 feet thick (Tschanz and Pampeyan, 1970). The Dunderberg forms a prominent swale on top of the underlying massive and resistant Highland Peak Formation.
In the Kingsley Range on the White Pine-Elko County boundary, the Dunderberg forms low brown hills of dark gray to brown argillaceous shale with 5 to 10 foot thick beds of dark-gray limestone in the lower and uppermost beds (Buckley, 1967; Coats, 1985). In the Pilot Range, the Dunderberg is about 200 feet of brown to greenish fissile shale (O'Neill, 1968).
In the Elk Mountains (Mathias, 1959), the Dunderberg is a yellow-brown fissile shale with the upper 15 feet composed of gray limestone in beds up to 1 inch thick interlaminated with the shale. The Dunderberg conformably overlies the Hamburg Dolomite.
The shale beds within the Dunderberg are often crumpled and sheared. A section 265 feet thick is present where structurally undisturbed in the Eureka area. Thicknesses range from 500 to 1,600 feet in the Tybo Canyon and Hot Creek Canyon areas of the Hot Creek Range (Ferguson, 1933; Quinlivan and Rogers, 1974; Kleinhampl and Ziony, 1985), 1,200 to 1,400 locally to 500 feet in the Ruby Mountains (Hose and Blake, 1976; Willden and Kistler, 1979), 340 feet in the Sherman Mountain Quadrangle in the southern Ruby Mountains (Millikan, 1978), and are about 400 feet to the south in the Bald Mountain area (Rigby, 1960).
1,100 feet of deformed and metamorphosed Dunderberg is present in the White Pine Range (Moores and others, 1968), 430 feet in the Horse Range (Wire, 1961), 485 to 685 in the southern Cherry Creek Range (Adair, 1961; Young, 1960), 290 to 480 feet in the northern Egan and Schell Creek Ranges (Young, 1960; Kellogg, 1963), 480 to 600 feet in the northern Egan Range (Young, 1960), 720 feet locally in the northern Schell Creek Range (Dechert, 1967), 430 feet in the central Grant Range (Moores and others, 1968), greater than 500 feet in the Kingsley Range (Coats, 1985), 215 feet thick in the Elk Mountains (Mathias, 1959), and 200 feet in the Pilot Range (O'Neill, 1968).
The Dunderberg Shale is found within the Eureka district, and Ruby Mountains, the Hot Creek, Ruby, Egan, Grant, Horse, southern White Pine, Cherry Creek, Schell Creek, Highland and Bristol, Kinsley, and Pilot Ranges, and the Elk Mountains.
The depositional setting for the Dunderberg is not well understood. Brachiopods and trilobites within oolitic limestone beds suggest that the Dunderberg represents shallow marine shelf deposition.