AN INTEGRATED PETROLEUM EVALUATION OF NORTHEASTERN NEVADA
Type Section Information
The Joana Limestone was named for exposures at the Joana Mine on the south side of Robinson Canyon, 2 miles north of Ely (Spencer, 1917).
The Joana Limestone is Early Mississippian (Osagean to Kinderhookian) in age. It overlies the Pilot Formation and underlies the Chainman Formation, which have together been called the White Pine Group (Spencer, 1917; Misch, 1960).
In general, the Joana Limestone is mainly a massive, medium to light gray, organic-detrital limestone composed of fragments of echinoderms, bryozoans, foraminifers, algae and indurated calcareous mud which forms both rounded ledges, slopes and cliffs (Hose and Blake, 1976). In areas of structural disturbance, the upper part of the formation may be altered and silicified to form a reddish or brownish jasperoid. In various Nye County localities, Kleinhampl and Ziony (1985) found the Joana Limestone to be composed of a lower thick-bedded to massive, coarse-grained, gray crinoidal cliff-forming limestone, and an upper unit of fine to medium-grained, thin-bedded to platy, dark-gray limestone and silty limestone which form a ledge-and-slope topography.
In the Diamond Mountains-Pancake Range area, the Joana Limestone is made up of varying sequences of dense bluish-grey porcelaneous limestone; fine to coarse grained, light grey to black, sandy crinoidal limestone which locally contains shale, chert, and quartzite pebbles; nodular cherty limestone; interbedded platy dark-grey to black calcareous shales; and thin sandstones beds similar to those in the Pilot Formation, which gradationally underlies the Joana (Nolan and others, 1956; Roberts and others, 1967). The contact with the overlying Chainman Formation is sharp and locally an erosional surface which causes significant variations in Joana thickness, and in fact causes the Joana to wedge out over short distances in both the Diamond Mountains and Pancake Ranges (Nolan and others, 1956). The Pancake Range section probably contains some limestone which grades laterally into rocks mapped elsewhere as Pilot Formation (Hose and Blake, 1976). The Pancake Range section of Joana Limestone is unique in that it contains rocks uncharacteristic of the Joana in other ranges, including about 90 feet of light brown platy quartzitic siltstone near the base, a thick layer of fine-grained dark platy limestone near the middle of the formation and an upper 150 feet which contains beds of crinoidal limestone, and large pebbles of chert and limestone (Hose and Blake, 1976). In the northern Pancake Range, near Big Louie Spring, the lower 75 feet of the formation are platy to sandy, fossiliferous limestone overlain by a massive conglomerate with pebbles, cobbles, and boulders of limestone in a limestone matrix. This conglomeratic facies contains jasperoid near Portuguese Mountain in the Pancake Range, and is also present in the Morey Peak area of the Hot Creek Range with chert and quartz sand and silt in a calcareous matrix (Kleinhampl and Ziony, 1985). The Joana in general, thickens gradually eastward from the Pancake Range (Kleinhampl and Ziony, 1985).
In the Ruby Mountains, the Joana Limestone is present in several blocks in the central and southern portions of the range (Willden and Kistler, 1979; Sharp, 1942; Coats, 1985). It is a cliff-forming unit of medium to dark gray limestone in beds 3 to 8 inches thick, with locally interbedded dark gray to nearly black nodular chert layers 1 to 2 inches in thickness. In the Buck Mountain-Bald Mountain area, the Joana is composed of very fine-grained pinkish-brown to brown-gray limestone overlain by medium to coarsely crystalline, medium to dark-gray, encrinal limestone (Rigby, 1960).
In the northern Reveille Range, the Joana is a dark-gray to yellowish weathering, aphanitic to laminated and thin-bedded limestone which is considered Kinderhookian on the basis of conodonts (Ekren, Rogers, and Dixon, 1973).
In the Grant and White Pine Ranges, the Joana is a very massive, fine-grained, tan to bluish-gray, crinoidal limestone with irregular lenses of chert concentrated in the lower part, grading upward into thinner-bedded, dark to medium gray limestone with a top bed of reddish-brown chert. As in many sections of the Joana, there is a noticeable increase in crinoid debris towards the top of the unit which is a crinoid hash in places (Moores and others, 1968; Hyde and Huttrer, 1970; Lumsden, 1964; Gaal, 1958).
In the southern Cherry Creek and northern Egan Ranges the Joana is a tan to gray, medium-grained, crinoidal limestone. Bedding varies from 1 to 4 feet in the lower half of the formation to 4 to 6 inches in the upper half with scattered light brown, reddish, and black chert nodules up to 2 inches thick throughout (Woodward, 1962; Fritz, 1960). This writer has observed graded beds and possible sole markings in the upper tens of feet of the formation, and cross-bedding has been noted in the upper portion of the Joana in the central Egan Range by Brokaw and Shawe (1965). In the northern Cherry Creek Range, the Joana gradationally overlies the Pilot Formation and is a medium to dark gray, fine to medium-grained, bioclastic limestone with horn corals, brachiopods, crinoids and snails.
In the northeastern Dolly Varden Mountains about 20 to 30 feet of brecciated blocks of Joana Limestone have been mapped by Snow (1964). The Joana is medium-crystalline, dark gray to black fetid limestone cemented by light gray calcite, and cut by jasperoid dikes and veins.
In the northern Schell Creek Range, the Joana Limestone is present in several fault slices (Dechert, 1967). The lower 100 feet are massive cliff-forming, very dark gray, light-gray weathering crystalline limestone with light to dark brown chert in several nodular layers. The upper 50 feet of the Joana is dark gray, coarse-grained highly fossiliferous limestone with corals, brachiopods, and gastropods (Dechert, 1967). Young (1960) reports about 100 feet of Joana in the central Schell Creek Range with about 80 feet of massive crinoidal limestone overlain by about 20 feet of thin-bedded dark-gray limestone. In the central Schell Creek Range, Conway (1965) reported about 400 feet of Joana. The lower 250 feet are dark gray to brown-gray micritic limestone with up to 20 percent dark gray to black chert nodules, and are overlain by about 200 feet of alternating thick-bedded to massive, dark gray and brown-gray, medium to coarse-grained limestone, and medium-bedded, dark gray to black, fine to coarse-grained limestone with gastropods, brachiopods, crinoids and corals.
In the southern Schell Creek and Snake Ranges, the Joana Limestone is medium to dark-gray, organic detrital, crinoidal limestone which is mainly massive, but is thinner bedded in the upper portion. Nodules and stringers of chert up to a foot in thickness are locally abundant, and a 3 to 10 foot thick quartzite marks the base of the formation (Young, 1960; Whitebread, 1969).
In the western Red Hills west of the Kern Mountains, the Joana is divided into three informal members (Bartel, 1968). The lower massive member is composed of about 200 feet of massive to thick-bedded light and medium gray crinoidal limestone with abundant dark brown and purplish-black chert bands and nodules. The middle member is composed of about 40 feet of silty, medium-gray, platy and locally nodular limestone in beds from .5 to 6 inches thick. The middle member is locally missing due to faulting (Bartel, 1968). The upper member is about 35 feet of massive to thick-bedded crinoidal limestone without chert nodules or stringers. Corals, gastropods, fenestrate bryozoans, and crinoids are present in the limestone (Bartel, 1968).
In the Kern Mountains, the Joana Limestone is often highly folded. In relatively undeformed sections it is divided into an upper and lower member (Nelson, 1959). The lower member is composed of massive and brecciated, dark gray to purplish-gray, coralline limestone. The upper member is thick-bedded, dark purplish-gray, crystalline limestone with abundant beds and nodules of black-weathering chert (Nelson, 1959).
In the Pequop Mountains-Wood Hills area, the Joana disconformably overlies the Devonian Guilmette in several tectonic slices which Thorman (1970) divided into an eastern and western succession. The eastern succession is fine to coarse-grained crinoidal limestone which is considered Kinderhookian in age and is truncated at its top by a fault. The thicker and more complete western succession is divided into three informal members. The basal member is 65 feet of medium to coarse-grained encrinite. The middle member is about 280 feet of interbedded platy brown siltstone, black chert, and platy fine-grained gray limestone. It is overlain by the upper member of platy thin-bedded, fine-grained, argillaceous limestone which is about 1,400 feet thick and is considered equivalent to the Tripon Pass Limestone of Oversby (1973) by Coats (1985).
In the Spruce Mountain area, the Joana Limestone is a thick-bedded, medium-gray, fine-grained, bioclastic limestone with abundant crinoid stems (Coats, 1985). The upper portion of the section is thin-bedded limestone with dark gray to black chert stringers. The upper contact of the Joana along the western flank of Spruce Mountain is a low angle fault contact (Coats, 1985).
In the Ferguson Mountain area along the eastern flank of the Goshute Mountains, the Joana was mapped by Berge (1960) as a 15 to 20 foot thickness of crystalline dark to medium-gray lithographic limestone. This section has been tectonically thinned along low angle normal faults.
In the northern Pahroc, Golden Gate, and Seaman Ranges and on Dutch John Mountain, the Joana is composed of a lower portion of massive, blue-gray, dense to coarsely crystalline, crinoidal and cherty, cliff forming limestone about 50 to 260 feet thick. The lower part is overlain by 200 to 700 feet of less resistant, thin to medium-bedded, dark-gray limestone with shale partings and abundant cherty beds. It often contains horn corals up to 9 inches in length (Tschanz and Pampeyan, 1970).
The Joana Limestone has a variable thickness ranging from 85 to 135 feet where present in the Eureka district (Nolan and others, 1956), and is commonly 90 to 225 feet thick north of the latitude of Ely in White Pine County (Hose and Blake, 1976). In the Pancake Range Hose and Blake (1976) report 500 feet of Joana and Kleinhampl and Ziony (1985) note 75 feet of Joana north of Portuguese Mountain, and about 180 feet a few miles to the south in the range.
The Joana is as much as 230 feet thick in the northern Reveille Range (Ekren, Rogers and Dixon, 1973), 250 to 300 feet in the Ruby Mountains (Willden and Kistler, 1979; Sharp, 1942) and about 100 feet thick to the south in the Buck Mountain - Bald Mountain area (Rigby, 1960). About 150 to 175 feet of Joana are present in the White Pine Range (Moores and others, 1968; Lumsden, 1964; Hose and Blake, 1976), 410 to 445 feet in the Horse Range (Wire, 1961; Ptacek, 1962), 100 to 200 feet in the White Pine Range (Lumsden, 1964), 115 feet in the southern Cherry Creek and Northern Egan Ranges (Woodward, 1962; Fritz, 1968), 590 feet in the central Egan Range (Playford, 1961) and 705 to 1,000 feet in the southern Egan Range (Kellogg, 1963; Tschanz and Pampeyan, 1970).
150 feet of Joana Limestone are exposed in the northern Schell Creek Range (Dechert, 1963) and 100 to 400 feet in the central Schell Creek Range (Young, 1960; Conway, 1965). 306 feet of Joana are present in the western Red Hills (Bartel, 1968), about 160 feet in the western Kern Mountains (Nelson, 1959), about 400 feet in the southern Butte Mountains (Douglass, 1960) and Snake Range (Whitebread, 1969), 650 feet at Dutch John Mountain (Tschanz and Pampeyan, 1970), and 268 feet in the southern Silver Island Mountains (Blue, 1960). Nearly 100 feet of Joana Limestone has been meaured in the Spruce Mountain area (Coats, 1985), about 30 feet are present in a brecciated section in the Dolly Varden Mountains (Snow, 1964), and 15 to 20 feet are exposed in the Ferguson Mountain area of the Goshute Mountains (Berge, 1960).
The Joana is found in the Reveille, Hot Creek, Monitor, Pancake, White Pine, Horse, Grant, Egan, Cherry Creek, Schell Creek, Snake, northern Pahroc, Golden Gate and Seaman, southern Silver Island, and Leppy Ranges, Dutch John Mountain, Wood, Windermere and Red Hills, Ruby, Diamond, southern Butte, Pequop, Dolly Varden, Kern and Goshute Mountains, and Spruce Mountain Ridge.
The Joana Limestone is generally considered a shallow subtidal bank-type limestone as a result of its abundant shelly fauna and corals, gastropods, and crinoids. The Joana appears to have formed a low lying carbonate-bank or barrier to clastic influx along the eastern edge of the Antler foreland basin. It may have been deposited in water as much as 300 meters deep (Poole and Sandberg, 1977).
The Joana Limestone often has good surface porosity and permeability (Douglass, 1960) and is often the host of jasperoids. Its position between two formations which contain substantial amounts of organic-rich shale, the Pilot and Chainman, places it in a favorable depositional position to be charged as a reservoir. Since much of the structural strain is taken up by thinning of these units, the Joana is also in a favorable position for secondary permeability related to fracturing.
The top of the Joana Limestone is an erosional unconformity and the entire formation has locally been removed during Mississippian erosion. Significant sections of Joana have also been removed along low-angle normal faults.
The Joana Limestone is laterally equivalent to the Tripon Pass Limestone and Camp Creek Sequence which contain porous carbonate sands. The Joana Limestone in northeastern Nevada is the temporal equivalent of the Lodgepole and Madison Limestones which produce in the thrust belt and various Rocky Mountain oil fields.