AN  INTEGRATED PETROLEUM  EVALUATION OF NORTHEASTERN  NEVADA


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MURDOCK MOUNTAIN FORMATION

Type Section Information

The Murdock Mountain Formation is named for exposures along the eastern flank of Murdock Mountain, in Sec. 36, T. 39 N., R. 67 E., in the Loray Quadrangle portion of the Leach Mountains (Wardlaw and others, 1979).

Geologic Age

The Murdock Mountain Formation is considered Upper Permian (Guadalupian) in age. The Murdock Mountain Formation is equivalent to the Plympton Formation and to the Rex Chert Member of the Phosphoria Formation (Wardlaw and others, 1979).

General Lithology

In the Leach Mountains, the Murdock Mountain Formation is an interbedded sequence of slope-forming, thin-bedded, yellowish-brown to dark gray, dolomitic and locally phosphatic siltstone, light gray medium-bedded dolomite, and black, thin-bedded or nodular cherts which grade laterally into gray cherty and sandy limestone, and pebbly cherty fine-grained sandstone (Wardlaw and others, 1979; Martindale, 1981). Fossils include brachiopods, bryozoans, crinoids, pelecypods. Fecal pellets and horizontal burrows are also preserved (Martindale, 1981).

The formation grades laterally into the Plympton Formation in the southern Pequop Mountains and is not described to the south of the Leach Mountains in the evaluation area. Coats (1985) suggests that the Murdock Mountain Formation may have been lumped with the Gerster Formation and locally with the Phosphoria Formation in several sections mapped in northeastern Elko County. As discussed above, the Murdock Mountain represents at least some of the rocks originally described as Loray Formation as well.

Average Thickness

The Murdock Mountain Formation is 1,260 feet thick at the type section in the Leach Mountains and is about 1,500 feet thick in the southern portion of the range (Martindale, 1981).

Areal Distribution

The Murdock Mountain Formation is currently only known and mapped within the Leach Mountains in the evaluation area.

Depositional Setting

The Murdock Mountain Formation is a lateral equivalent of the Plympton Formation and the Rex Chert Member of the Phosphoria Formation. It represents very shallow marine near shelf sedimentation, possibly with small isolated islands providing clastic debris (Wardlaw and others, 1979). Martindale (1981) felt that the Murdock Mountain in the Leach Mountains represents shallow supratidal to intertidal deposition in normal marine waters.


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Last modified: 09/12/06