AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
Type Section Information
The Grandeur Formation was originally defined as the Grandeur Member of the Park City Formation by Cheney and others (in McKelvey and others, 1959), and was raised to formational status by Hose and Repenning (1959). The type section, for both the member and formation, is near the mouth of Mill Creek Canyon in Sec. 36, T. 1 S., R 1 E, near Salt Lake City, Utah (McKelvey and others, 1959).
In western Utah, the Grandeur Formation is considered the lowest formation of the Park City Group. It is laterally equivalent to the Kaibab Limestone which is considered the basal portion of the Park City Group over most of eastern Nevada. The Grandeur Formation is considered Lower Permian (lower Guadalupian) in age.
At the type section along Mill Creek Canyon in Utah, the Grandeur Formation is composed of dark gray, massive phosphorite and argillaceous, silty gray to brown limestone that is overlain by silty, sandy, and cherty, dense, thin-bedded to massive, gray to brown dolomite that is locally phosphatic.
In the Leach Mountains, the Grandeur Formation overlies the Pequop conformably or along a low-angle fault, and underlies the Mead Peak Tongue of the Phosphoria Formation (Martindale, 1981). Martindale (1981) recognizes that these rocks were originally designated as the Loray by Steele (1960) and concludes after a review of the highly faulted Loray type section that a reexamination and redefinition of the Loray is in order.
Nearly 70 percent of the Grandeur Formation consists of very fine-grained, medium to thick-bedded, white weathering, light to dark-gray dolomite and sandy dolomite with bryozoa, algae, crinoid and brachiopod fragments in the lower beds (LeCompte, 1978; Martindale, 1981). Interbedded dark gray chert nodules, and nodular gray organic and locally silty limestone beds with brachiopods, echinoderms, gastropods, crinoids, and pelecypods are abundant in some horizons near the top of the unit. Chert forms about 20 percent, and limestone about 15 percent of the formation (LeCompte, 1978). A few beds of chert-granule conglomerate and glauconitic cherty sand are present in a few bioclastic limestones near the base of the formation (Coats, 1985). Martindale (1981) reports small to medium-scale planar and trough cross-laminae, ripples, and desiccation cracks in the unit.
In the Leach Range, the Grandeur Formation is about 2,300 feet thick (LeCompte, 1978; Martindale, 1981).
In the evaluation area, the Grandeur Formation has only been differentiated within the Leach and Delano Mountains.
The Grandeur Formation represents shallow marine restricted intertidal shelf and lagoonal deposition (LeCompte, 1978).