The Chainman Shale was named for fissile shales exposed near the Chainman Mine about 2 miles northwest of Ely Nevada in the northern Egan Range (Spencer, 1917). The term White Pine Shale applied by Hague (1883) for the general Chainman stratigraphic interval, was dropped by Nolan and others (1956) because this usage included rocks now designated as the Pilot Shale, Joana Limestone, and Diamond Peak Formation as well as the Chainman Formation. The lithologic variability within the formation prompts us to prefer the term Chainman Formation; the shale facies of the Chainman is limited areally.

The Chainman Formation is Late Mississippian (Meramecian and locally Chesterian) in age. The Chainman commonly sharply overlies the Joana Limestone and is either overlain by the Diamond Peak Formation, or as a result of deposition or low-angle faulting, by the Pennsylvanian Ely Limestone (Brew, 1971; Hose and Blake, 1976; Nolan and others, 1974). The Chainman in the Eureka District is older than the type Chainman Shale and may actually be a temporal equivalent of the Joana Limestone according to Mackenzie Gordon (Tschanz and Pampeyan, 1970). The upper part of the Eleana Formation in Nye County is correlated with the Chainman Shale (Tschanz and Pampeyan, 1970).

Regionally, the Chainman Formation is lithologically variable, consisting mainly of dark-gray to black variably silicified shale and olive-gray platy siltstone or silty shale which locally contains thin beds of dark-gray bituminous fine-grained limestone, and light gray organic detrital limestone beds in the lowermost and uppermost portions of the unit (Hose and Blake, 1976). Where it is overlain by the Ely Limestone, the upper half of the formation often contains a few beds of reddish-brown to olive quartzite and quartzitic siltstone. In many cases, interfingering of Chainman and Diamond Peak Formations siltstones, sandstones, conglomerates and shale make separation of the two formations impossible and they are combined as a map unit. Where combined as one unit they are described under an appropriate designation which represents the dominant formation.

It is important for the reader to realize that the Chainman and Diamond Peak Formations are really part of the same major gradational depositional sequence. The Diamond Peak grades laterally into, as well as overlies the Chainman Formation. Because many workers have only seen the formation in the immediate area of their mapping, the designations of Chainman and Diamond Peak have been used inconsistently on a regional scale; essentially one mappers' "Chainman" is another mappers' "Diamond Peak" is another mappers' "Chainman/Diamond Peak Undifferentiated". This inconsistency has been removed where possible but still exists in certain areas within this evaluation. Many workers have followed a scheme similar to Smith and Ketner (1975) who reserved Chainman Formation for sequences dominated by shale and siltstone, Diamond Peak for those dominated by conglomerate and sandstone, and Chainman and Diamond Peak Formations undivided for sequences where sandstone and siltstone, shale and conglomerate were subequal.

In most cases, the Chainman is poorly exposed, often only as a soft spongey soil or in low swales and valleys because of its softness and position in the stratigraphic sequence, as well as structural contortion and faulting. In many cases the basal or upper contacts of the formation are low-angle faults of either extensional or compressional origin. This makes contact relationships, sequence, and thickness difficult to determine within the Chainman. Several of the areas which reveal aspects of sequence and lithology are described below.

In the Eureka district, the Chainman Formation is mainly composed of black shales, claystones and siltstones, interbedded with thin sandstones which are more abundant in the upper portion of the formation, and minor chert pebble conglomerates in beds and lenses (Roberts and others, 1967; Nolan and others, 1971, 1974). In the Devils Gate, area the lower portion of the Chainman-Diamond Peak interval is a black silty carbonaceous shale, with an upper portion composed of intercalated poorly sorted dark grey, brown-weathering sandstones, fine-grained conglomerate with angular green and black chert fragments, and shale. Alaskite sills up to 50 feet in thickness are common in the Chainman and Diamond Peak south of Devils Gate (Merriam, 1963).

In the southern Diamond Mountains, juxtaposition of differing Chainman facies has occured along the Bold Bluff thrust fault (Brew, 1961b). The upper plate Chainman varies lithologically along strike, but on average is composed of 39 percent olive-gray and brown-weathering gray siltstone, 35 percent dark-gray to black, pencil-weathering siltstone and claystone, 24 percent brown and gray, fine to medium-grained sandstone, and 2 percent chert and quartzite pebble and cobble conglomerate, and 2 percent chert and quartzite pebble conglomerate in local lenses. The lower plate Chainman Formation consists of 90 percent pyritiferous claystone and lesser clayey siltstone, which are dark-gray to grayish black and weather to angular brownish pencil-like fragments as much as 8 inches long and an inch in diameter (Brew, 1961b). Mapping in the Diamond Springs Quadrangle (Larson and Riva, 1963) showed the Chainman and Diamond Peak to be exceedingly difficult to separate regionally. In general, the Chainman was described as containing medium to dark-gray, brittle siltstone in the lower portion of the formation and successively higher beds of subgraywacke, pebbly mudstone, a thick conglomerate, yellowish and greenish quartz arenite and greenish-gray shale.

In the Buck Mountain-Bald Mountain area Rigby (1960) divided a thick section of Chainman Formation into three members. The lower member is about 155 feet of tan to yellow-gray silty shale, overlain by the middle 100 feet of medium to dark-gray fine- grained limestone, and an upper member of about 700 feet of dark-green to greenish-black carbonaceous sandstone and clay shale.

In the Carlin-Pinon Range the Chainman Formation is mainly gray, fine to medium-grained sandstone or quartzite composed of quartz and chert grains, and soft gray to almost black shale, and minor interbedded lenses of chert-pebble conglomerate, pebbly mudstone, and thin limestone and calcareous sandstone beds (Smith and Ketner, 1975). The micaceous shales are lenticular and poorly exposed and contain variable amounts of silt. Locally the shales have been metamorphosed to a siliceous argillite. Thin lenses of solid bitumen are locally present in the shales as along Smith Creek indicating the former presence of liquid hydrocarbons (Smith and Ketner, 1975). The sandstones are poorly to moderately sorted, angular to subrounded, lenticular, and locally grade into pebbly layers or conglomerates. The sandstones often preserve plant fragments along bedding surfaces (Smith and Ketner, 1975). Gray to tan limestone, sandy limestone and calcareous sandstone up to 1 foot in thickness form less than 1 percent of the Chainman and are concentrated in the lower portion of the formation. The pebbly mudstones contain fragments of various lithologies, are sometimes scoured, and contain flute markings (Smith and Ketner, 1975). The conglomerates are also lenticular with angular to well rounded quartzite, sandstone and chert pebbles, or rarely limestone pebbles and cobbles in a sandy matrix.

Farther north in the northern Adobe Range, Ketner and Ross (1983) describe the Chainman Formation as a para-autochthonous sequence of shale and sandstone with local basal olistostromes containing cobbles derived from the Ordovician Valmy and other units, and thin greenstone sills and flows. Much of the unit is actually composed of siliceous black thin-bedded brittle argillites and brown siltstone.

In the southern Adobe Range, Sillitonga (1974) broke out a 440 foot thick conglomerate member and a 260 to 880 foot thick sandstone and shale member within the Chainman in the Kittridge Springs Quadrangle area. The conglomerate member is gray to olive or reddish-brown conglomerate in layers 4 inches to 3 feet thick. Pebbles of rounded gray quartzite and siltstone, and angular green and gray chert are set in a matrix of silicified sandstone and mudstone. The pebbles are commonly 0.5 to 2 inches and as large as 4 inches across. The sandstone in the sandstone and shale member is light gray to olive, fine to coarse-grained, subangular to rounded, and poorly to moderately sorted (Sillitonga, 1974). Quartz forms about 10 to 50 percent, chert about 20 to 35 percent and rock fragments of shale, siltstone and sandstone compose 10 to 40 percent of the rock. The sandstone locally grades into pebbly sandstone, conglomeratic sandstone and siltstone, and is interbedded with minor amounts of shale and 3 to 6 foot thick, lenticular chert and quartzite pebble and cobble conglomerate. The siltstones are gray to red-brown, are faintly cross-laminated and locally rippled, with casts of brachiopods (Sillitonga, 1974). The shale in the sandstone and shale member occurs as thick lenses, up to 360 feet, of dark greenish-gray shale which grades into cross-laminated siltstone and sandstone. The sequence is essentially dominated by conglomerate at the base overlain by sandstone, a middle unit of shale and an upper unit of sandstone and interbedded shale and siltstone.

Near Wheeler Mountain in the central Independence Mountains, Kerr (1962) mapped several hundred feet of Mississippian clastics which he assigned to the Waterpipe Canyon Formation and are considered unifferenttiated Diamond Peak and Chainman Formations by Coats (1985). Most, if not all of this unit, appears to represent the Chainman Formation. It is dominantly composed of platy, black, argillaceous quartz siltite which is interbedded with fine to medium-grained sandstone (Kerr, 1962). The base of the formation is composed of medium-grained sandstone with occasional black shale and chert pebbles.

In the Pancake and White Pine Ranges, the Chainman is composed of black fissile carbonaceous shale and gray argillaceous shale and siltstone, with a few thin, 1 to 2 inch thick interbeds, of sandstone and dense, blue-black, thin-bedded and fine-grained limestones. The upper portion of the unit becomes increasingly sandy and is dominantly composed of reddish-brown, fine to medium-grained quartz sandstone interbedded with gray to black shale and black fossiliferous lithographic limestones (Gaal, 1958).

In the Egan Range near Ely, Brokaw and Shawe (1965) describe the Chainman as a dark olive gray to black fissile shale containing interbeds of thin, olive-gray, platy organic detrital limestones and limestone nodules in the lower portion. About 250 feet below the top of the unit yellow and brown lenticular quartzitic sandstones, about 150 feet in total thickness, are overlain by dark-gray calcareous shale (Brokaw, 1967). Near Lund, Playford (1961) divided the formation into upper and lower members. The lower member is soft black shale with a few lenticular dark-gray and brown calcilutite beds and concretions and the upper member is composed of interbedded black shale, and interbedded orthoquartzite, quartz sandstone, and thin limestone beds.

Farther north in the Egan and Cherry Creek Ranges (Woodward, 1962; Fritz, 1960), the Chainman is very poorly exposed and is often inferred from the position of swales and valleys and light brown soil horizons. Where exposed it is a black fissile shale to siltstone, with minor 6 inch to 1 foot thick interbeds of light-tan and olive-green, fine to medium-grained sandstone concentrated near the middle of the unit, and calcareous siltstones near the base. Both coal and abundant pelecypods were found in several sections in the Cherry Creek Range during the course of this evaluation.

In the southern Butte Mountains, the Chainman is over 1,200 feet of non-calcareous, platy and brittle black to olive-gray shale (Douglass, 1960).

In the southern Snake Range, the Chainman Formation is composed of dark-gray to pale-yellowish brown shale and minor siltstone with interbedded sandy dark-gray organic detrital limestone and calcareous sandstone (Whitebread, 1969). The upper portion of the formation is alternating shale and sandstone which is mainly very fine-grained and well sorted but is locally medium grained and crossbedded. About 60 to 70 percent of the unit is shale with the remainder composed of about 25 to 35 percent sandstone and 5 to 15 percent siltstone and limestone.

In the Schell Creek Range, various Chainman exposures are composed entirely of fine-grained, rippled and cross-bedded white to gray or green quartzite or of black to olive soft shale with thin interbeds of calcareous sandstone and silty limestone. In the central Schell Creek Range, Conway (1965) reported a basal unit of dark brownish-black, platy to fissile, silty shale with interbedded platy gray siltstone and, a few dark limonitic fossiliferous limestones up section. Much of the upper portion of the unit is composed of yellowish to reddish, medium-grained quartzite. Dechert (1967) noted that a dark brown to black soil with small thin chips of brown siltstone and shale is the only indications of Chainman in outcrops without quartzite. Lenticular brownish, yellowish, and greenish fine-grained quartzite forms most outcrops in the northern portion of the range.

In the western Red Hills west of the Kern Mountains, the Chainman Formation is structurally complicated. The lower portion is composed of poorly exposed, dark gray, carbonaceous and occasionally calcareous shale with brown siltstone, and platy argillaceous dark gray limestone interbeds (Bartel, 1968). The upper part of the formation contains about 300 feet of reddish-brown, planar cross-stratified, lenticular, quartzitic, well-sorted and rounded sandstone with forset attitudes indicating flow directions of North 8-59 West (Bartel, 1968). Quartz composes about 75 to 90 percent of the sand with some chert, orthoclase, rutile, apatite, tourmaline, and muscovite. Overlying the quartzite is about 150 feet of olive to black, thin-bedded and fissile shale with thin interbeds of gray argillaceous limestone, and gray siltstone (Bartel, 1968).

In the northwestern Kern Mountains, the Chainman is poorly exposed olive to dark brown fissile shale with thin interbeds of gray, locally cherty limestone and lenses of brownish-weathering, gray quartzite and fine-grained sandstone which is locally pebbly. The sandstones are commonly cross-bedded on a small scale and locally show climbing ripple cross-laminations.

In the Golden Gate and Fairview Ranges and on Dutch John and Grassy Mountains, the Chainman Formation can be divided into three informal members. The lower member is resistant black calcareous siltstone or silty limestone which weathers brown. It is about 140 feet thick on Grassy Mountain and 300 feet thick in the southern Egan Range (Tschanz and Pampeyan, 1970). Bedded black, red and green chert, about 60 feet in thickness and in layers as much as 15 feet in thickness, are present at Grassy Mountain. Thin limestones or quartzite beds are at the base of the lower member in other sections (Tschanz and Pampeyan, 1970). Overlying the lower siltstone member is black shale which contains disk-like rust-weathering concretions near the base of the unit. This shale unit is commonly 250 to 450 feet thick. The upper member is a poorly exposed silty gray shale with several interbeds 10 to 20 feet thick of olive-gray fossiliferous limestone, and locally thin quartzite or olive-gray shale. The upper unit is 460 feet thick on Grassy Mountain (Tschanz and Pampeyan, 1970).

In the Wood Hills and Pequop Mountains, the Chainman Formation is present in several complexly faulted Meramaceian to Chesterian age sections (Thorman, 1962, 1970); the northern Pequop section is mainly black shale, and the southern Pequop and Wood Hills sections are dominantly siltstone (Thorman, 1970; Coats, 1985). Various sections of the Chainman are composed of interbedded brown siltstone and quartzite generally in beds 2 to 3 feet thick, very poorly exposed fissile, black and greenish shale with minor interbedded thin gray limestones, and thin beds of chert-pebble conglomerate with an overall increase in grain size towards the top of the unit. In the most complete and unfaulted section in the Pequop Mountains, the Chainman can be divided into 4 informal members which lie over the faulted upper contact of the Joana Limestone. The basal member is about 250 feet of fissile, non-calcareous, dark gray, olive green weathering silty shale with a few thin gray limestone lenses. Above this is about 910 feet of dark gray, brown weathering siltstone with light brown to gray, fine-grained, laminated and cross-bedded quartzite concentrated in the lower 475 feet. Interbedded within this member are 1 to 5 foot thick beds of chert-pebble conglomerate and lithic sandstone, as well as plant fragments (Thorman, 1962). The third member is about 730 feet of gray siltstone and silty shale with nematode impressions and cephalopod fragments. The upper member is about 1080 feet thick with quartzite and conglomerate in the lower 530 feet and interbedded siltstone and ripple marked and cross-bedded quartzite in the upper 550 feet (Thorman, 1970).

In the HD Range, the Chainman Formation is poorly exposed, intensely deformed, light gray weathering, black, brittle and siliceous shale or mudstone (Riva, 1970). In the Windermere Hills, the Chainman was only locally differentiated from the Diamond Peak Formation. It consists of several hundred feet of gray to black and olive-green fissile shale and interbedded light gray to brown siltstone and sandstone which locally have sole marks such as flutes and grooves (Oversby, 1969).

In the Ferguson Mountain area of the southeastern Goshute Mountains, the Chainman is light brown, fine to medium-grained quartzite, light brown sandstone, and silty cherty limestone of Meramecian age (Berge, 1960). In the White Horse Mountain area of the Goshute Range, Messin (1973) described the Chainman as light blue-gray to dark-gray fissile shale which is conformably overlain by the Ely Limestone.

In the Leppy Range, Schaeffer and Anderson (1960) mapped Undifferentiated Chainman and Diamond Peak Formations where they felt the lenticularity of units prohibited distinct designations. The formation can be broken into 5 units (Coats, 1985), of which only the upper conglomerate unit is here considered to be Diamond Peak Formation with the underlying units representing the Chainman Formation. The lower unit is dominantly dark-gray quartzite which weathers to orange tan colors. This is overlain by grayish and brownish limestones and calcareous siltstones which contain abundant gastropod fauna. The calcareous unit is predominantly overlain by fissile black claystone which weathers purple, black, maroon, and tan, and a brown-gray, orange-brown weathering siltstone. The overlying conglomerate is discussed with the Diamond Peak Formation. The Chainman here overlies the Guilmette and Pilot Formations and Joana Limestone along an angular unconformity (Coats, 1985).

In the Pilot Range, the Chainman Formation consists of alternating medium-gray thin-bedded argillaceous limestone and thin-bedded light brown sandstone (O'Neill, 1968).

Because of the difficulties with structural complication and poor exposure, thicknesses vary considerably within the Chainman Formation and represent structural rather than depositional thicknesses in nearly all cases. Thicknesses of over 1,000 feet of Chainman can be seen to thin to only a few feet within perhaps 200 feet laterally. Intertonguing of the Chainman with the Diamond Peak Formation also introduces variability in thickness measurements both within and between ranges.

In the Eureka area, about 4,000 feet of Chainman is present at Diamond Peak, 2,500 feet at Newark Summit and a fault repeated 5,000 feet at Secret Canyon (Nolan and others, 1956; Larson and Riva, 1963). In the Carlin-Pinon Range the Chainman varies from 1,600 to 2,500 feet in thickness (Smith and Ketner, 1978), Sillitonga (1974) measured about 1,320 feet in the southern portion of the Adobe Range, and 7,000 feet of undifferentiated Chainman and Diamond Peak Formations are present in the central Independence Mountains (Kerr, 1962). In the Buck Mountain-Bald Mountain area it varies from 940 to 1,280 feet (Rigby, 1960), and reaches a thickness of 1,600 feet in the northern Cherry Creek Range (Hose and Blake, 1976). It is about 1,015 feet thick in the northern Egan Range (Fritz, 1960) and 1,500 feet in the southern Egan Range (Playford, 1961), although much of the unit has been tectonically eliminated and a thickness of only 200 feet was measured by Woodward (1962) in the north central Egan Range.

In the Schell Creek Range the Chainman Formation is 1,000 to 1,100 feet thick (Drewes, 1967, Dechert, (1967) and varies from about 300 to 1,200 feet in the central portion of the range as a result of structural thinning (Conway, 1965), and from 650 feet to about 2,000 feet of Chainman are exposed in the southern White Pine-Grant Range area (Moores and others, 1968; Hyde and Huttrer, 1970), and Gaal (1958) reported about 1,500 feet in the western White Pine Range although the unit is locally absent due to tectonic thinning. In the southern Butte Mountains, 1,200 to 1,500 feet of Chainman Formation are present (Douglass, 1960) and it is estimated at 2,000 feet in the Windermere Hills (Oversby, 1969). In northern Lincoln County, the Chainman Formation is about 1,000 feet thick on Dutch John and Grassy Mountains as well as in the northern Fairview Range (Tschanz and Pampeyan, 1970). In the southern Snake Range the Chainman is 1,000 to 2,000 feet thick (Whitebread, 1969), about 1,500 feet in the northwestern Kern Mountains (Nelson, 1959), 2,790 feet in the Pequop Mountains (Thorman, 1970), about 350 feet in the southern Goshute Mountains (Berge, 1960), 180 feet thick in the Pilot Range (Oneill, 1968), and undifferentiated Chainman-Diamond Peak is 1,141 feet thick in the southern Silver Island Range (Blue, 1960; 1963).

The Chainman Formation is widely exposed in the Mahogany and Peko Hills, Buck Mountains-Bald Mountain area, Diamond and Ruby Mountains, Pinon, Adobe, Sulphur Spring, Pancake, Grant, White Pine, Egan, Cherry Creek, and Schell Creek Ranges, Dutch John and Grassy Mountains, Fairview, Snake, southern Silver Island, Pilot and Leppy Ranges, Independence, Butte, Pequop, Kern, and Goshute Mountains, Wood and Windermere Hills, and HD Range.

The Chainman Formation represents the initial major clastic pulse into the Antler foreland basin. The details of depositional setting for the Chainman are still somewhat poorly understood and disagreed upon. Poole and Sandberg (1977) for instance, suggest that the Chainman represents "proximal and distal turbidites" and debris flows in a deep-marine setting. Organic-rich and phosphatic mudstones and shales are interpreted as deep-marine starved basin facies. Thin turbidites have been reported in several outcrop localities which permit detailed examination of Chainman lithologies. Smith and Ketner (1975) describe pebbly mudstones and sandstone as turbidites with graded beds, and flute markings which indicate southeast directed currents in the Carlin-Pinon Range.

Harbaugh and Dickinson (1981) suggest that the Chainman Formation represents a sequence of fan-delta slope, front, and plain sediments deposited with subsidence greater than sedimentation, in water depths of about 1,000 meters. Wilson and Laule (1979) felt that the Chainman dominantly represented shallow marine fan delta deposition. They point to the abundance of shallow water fauna such as brachiopods, corals, pelmatazoans, pelecypods, bryozoans, gastropods, and crinoids. The presence of rippled silts, mudcracked and burrowed muds as well as land plant fragments, also prompted Wilson and Laule (1979) to suggest a shallow-water environment for the Chainman.

Wilson and Laule (1979) suggested that an instantaneous dropping of the foreland basin floor from shallow marine Pilot-Joana deposition to deep-marine abyssal deposition of the Chainman is implausible. Sadlick (1965) suggested that the Camp Canyon and Donner Members, the basal members of the Chainman were deposited in water depths of about 200 feet and that the overlying Willow Gap and Jensen Members, the upper two members of the Chainman, were deposited in near shore deltaic environments. Others argue that shallow-water sediments were later carried into deep water environments via turbidites (Poole, 1974).

The exploration significance of the Chainman is paramount. Geochemical work during the course of this evaluation has shown that the Trap Spring, Grant Canyon and Blackburn oil fields in Railroad and Pine Valley were most likely sourced by the Chainman Formation. The gas chromatography analysis of oils from these fields, and potential source rocks for these oils, including the Chainman, are displayed and discussed within the Geochemistry and Geothermal Data Volume of this evaluation.

One hundred two (102) surface geochemical samples were taken within the Chainman Formation throughout the evaluation area. Maturity, organic richness, and kerogen type all vary significantly within the Chainman Formation. A discussion of the geochemical results is provided within the Geochemical and Geothermal Data volume of this evaluation. The maturity and TOC data are contoured on Overlays VII and VIII. Several samples of shales from the Diamond Peak Formation are included on these overlays. The surface geochemistry has shown that the Chainman Formation provides one of the best source opportunities within northeastern Nevada. It also points out that only local areas contain organic-rich and thermally favorable facies of the Chainman capable of hydrocarbon generation.