Roberts Mountains Thrust Relationships in a Critical Area, Northern Sulphur Spring Range, Nevada

Home , Roberts Mountains, Vinini Formation

Roberts Mountains thrust relationships in a critical area, northern Sulphur Spring Range, Nevada

J. G. JOHNSON | Department of Geosciences, Oregon State University, Corvallis, Oregon 97331-5506 ROBERT VISCONTI*

ABSTRACT (oceanic) Ordovician rocks on top of eastern two units were recognized. The lower Vinini assemblage (shelf) Devonian carbonate rocks in consists of quartzite, arenaceous limestone, and At the orogenic front of the Antler orog- the Roberts Creek Mountain quadrangle (Fig. "fine laminated sandy and brownish-gray and eny, the Roberts Mountains allochthon lies 1). Roberts and others (1958) developed the greenish-brown silty sediments" (Merriam and on Lower Mississippian Dale Canyon Forma- concept that the Roberts Mountains thrust was Anderson, 1942, p. 1694). The upper Vinini tion and consists of Middle and Upper Devo- the principal structure of the Antler orogeny and consists of mainly black, bedded chert with thin nian Woodruff Formation, slivers of Silurian accepted the earlier postulate of Kay (1952) that argillaceous partings and black organic shale. to Lower Devonian Roberts Mountains For- thrusting had occurred as a middle Paleozoic Merriam and Anderson (1942) dated the Vinini mation, and Ordovician Vinini Formation, in event. Smith and Ketner (1968), mapping in the as Early to Middle Ordovician based on grapto- structural succession. Devonian Pilot Shale, Pinyon Range (Pine Valley and adjacent quad- lites. Murphy and others (1984) showed that the mapped unconformably below Dale Canyon rangles to the north), interpreted the Lower Mis- upper Vinini is Lower Ordovician, and that the flysch, was mapped previously as allochtho- sissippian Webb Formation to postdate thrust- lower Vinini is Middle to Upper Ordovician, nous Woodruff Formation. The Vinini recog- ing, but the Webb was not shown by mapping and that the two units are separated by a thrust nized here was also mapped previously as to be continuous across the thrust. Smith and fault. Woodruff. The Dale Canyon was mapped Ketner's (1977, 1978) structural analysis and In the northern Sulphur Spring Range, the previously as Chainman Shale. published maps postulated a complex history of Vinini Formation consists mainly of black, Recognition of Pilot Shale here necessi- events for rocks related to the Roberts Moun- bedded chert which weathers brown and gray. tates the elimination of a previously postu- tains allochthon (RMA). Later, a significantly Most beds are 5 to 15 cm thick, separated by lated thrust plate in which Woodruff was different interpretation of the structure and its thin argillaceous partings. Fine laminations are shown thrust upon Devonian carbonate age was published by Johnson and Pendergast visible on weathered surfaces. In thin section, rocks; it also makes more consistent the struc- (1981). the chert is very dark due to carbonaceous mate- tural sequence within the Roberts Mountains The present report summarizes results and rial; radiolarian molds are common. Black or- allochthon along its frontal margin. conclusions based on remapping an area that ganic shale composes a minor part of the Vinini Assignment of fine-grained siliciclastic tur- crosses the boundary between the Pine Valley and is poorly exposed. bidites in the flysch trough of the Antler fore- (Smith and Ketner, 1968, 1978) and Mineral Bedded chert was mapped as part of the land to the Dale Canyon Formation elimi- Hill (Carlisle and Nelson, 1990) 15-minute Devonian Woodruff Formation by Smith and nates anomalous use of Chainman Shale as a quadrangles (Fig. 1). This area proves critical to Ketner (1978), but it resembles the Vinini stratigraphic term and allows its useful reten- the solution of problems left unsolved by pre- Formation found in the Willow Creek area, tion for delta-slope deposits distal to the Di- vious mapping, and our results differ in some three miles north, where Smith and Ketner amond Peak molasse. fundamental aspects. (1975) collected Ordovician graptolites. South The so-called Dry Creek fault, previously of Pony Creek, bedded chert of the Vinini struc- interpreted to cross the mapped area, cannot ALLOCHTHONOUS ROCKS: turally overlies Woodruff dated by conodonts as be recognized. Some outcrops of Devonian VININI FORMATION Late Devonian (Smith and Ketner, 1975). carbonate rocks, previously mapped as in In the northern Sulphur Spring Range, the structural windows below Woodruff Forma- The Ordovician Vinini Formation belongs to Vinini Formation, along with the Woodruff tion, are actually Quaternary landslide the western assemblage of Roberts and others Formation and fault slices of the Roberts Moun- blocks. (1958), deposited in an oceanic (eugeosynclinal) tains Formation, forms the Roberts Mountains lithotope. Deposition in a deep-water, oceanic allochthon (RMA). The Vinini lies structurally INTRODUCTION environment is based on the association of above the Devonian Woodruff within the RMA bedded chert, shale, graptolite faunas, and trace (Figs. 2, 3). The Roberts Mountains thrust (Merrian and fossils. Chamberlain (in Stanley and others, Anderson, 1942) was first characterized as a re- 1977) reported a Nereites trace-fossil assem- ALLOCHTHONOUS ROCKS: gional structure that placed western assemblage blage in the Vinini of the Roberts Mountains. ROBERTS MOUNTAINS FORMATION The Vinini Formation was named by Mer- •Present address: 4904 S. Broadway, no. 227, St. riam and Anderson (1942) for exposures along The Roberts Mountains Formation (Mer- Louis, Missouri 63111. Vinini Creek in the eastern Roberts Mountains; riam, 1940) was assigned by Smith and Ketner

Geological Society of America Bulletin, v. 104, p. 1208-1220, 7 figs., September 1992.

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(1975) to the transitional assemblage of Roberts 117° 116° 115° and others (1958), but we regard it as compris- ing rocks deposited in an outer shelf basin (Johnson and others, 1991). In the northern Sulphur Spring Range, along Pony Creek, the Roberts Mountains Formation is present in a thrust slice between the Vinini and Woodruff Formations, as it is in the Willow Creek area to the north (Smith and Ketner, 1978; Whitaker, 1985). Smith and Ketner (1975, 1978) assigned an age of earliest Devonian based on graptolites of the Monograptus uniformis Zone. Along Pony Creek, the Roberts Mountains Formation consists of dark gray shaley and platy carbonaceous, laminated, silty dolomite that weathers to a yellowish brown. Thin sections reveal that the rock consists of quartz silt (10% to 20%) set in a matrix of finely crystalline dolomite with abundant carbonaceous and argillaceous materials. The unit is coarser grained than the Woodruff and is distinguished from rocks of similar lithology in the Woodruff For- mation by the presence of graptolites, identified by W.B.N. Berry (1982, written commun.) as Monograptus birchensis Berry and Murphy and Linograptusl sp. The age range of M. birchensis is latest Silurian to early Early Devonian (Berry and Murphy, 1975, see their Fig. 15).

AUTOCHTHONOUS ROCKS: WOODRUFF FORMATION

Lithology

The Devonian Woodruff Formation was named by Smith and Ketner (1968) for exposures along Woodruff Creek in the Pinyon Range. In the northern Sulphur Spring Range, the Woodruff consists of silty dolomite, dolomitic siltstone, chert, and siliceous mudstone. Although Smith and Ketner (1968) assigned the Figure 1. Index map of east-central Nevada and its counties. The frontal margin of the Woodruff to the siliceous western assemblage, Roberts Mountains thrust is shown as a dashed barbed line. Its position, but not its continuity we assign it to the transitional assemblage be- to the south, is questioned. The two lS-minute topographic quadrangles that encompass the cause of the presence of carbonate rocks. mapped area are Pine Valley (PV) and Mineral Hill (MH); nearby locations referred to are Laminated quartz-silty dolomite (Fig. 4A) is Cortez quadrangle (CZ) and Roberts Creek Mountain quadrangle (RCM). The mapped area is the dominant lithology of the Woodruff in the shown in Figure 2. northern Sulphur Spring Range. These rocks are dark gray to black and weather grayish orange. Thin sections show quartz silt (5% to 15%) set in a finely crystalline dolomite matrix, with abun- quartz silt composes as much as 50% of the rock, makes up a small but significant part of the dant carbonaceous material and minor pyrite and it contains less carbonaceous material. Mot- Woodruff and has yielded good conodont fau- and argillaceous materials. Radiolarian molds tling and small burrows are evidence of nas (see Appendix). The rock is dark gray with are rare. Laminae are defined by concentrations bioturbation. light gray laminations. Thin sections reveal of carbonaceous material and coarser dolomite Black chert that weathers to brown and gray abundant calcispheres in a matrix of carbona- rhombs. The dolomite, replacement in origin, is is interbedded with silty dolomite and siliceous ceous and argillaceous lime mud. Laminae are cloudy and dirty, suggesting original deposition mudstone. Thin sections of the chert show that it defined by dolomite rhombs and quartz silt. as an argillaceous lime mud, similar to some of differs from chert of the Vinini Formation in Dark gray to black, carbonaceous, siliceous the Pilot Shale. that it is generally coarser and contains less car- mudstone makes up a minor part of the Wood- Dolomitic siltstone is gray to light brown and bonaceous material and radiolarian molds. ruff Formation that we mapped. Chert forms similar to the quartz-silty dolomite; however, Partially dolomitized biomicrite (Fig. 4B) thin beds and nodules within the mudstone.

Geological Society of America Bulletin, September 1992

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GEOLOGY OF THE DRY CREEK AREA, ELKO AND EUREKA COUNTIES, NEVADA

GEOLOGY BY ROBERT 198VISCONT1 I

0.5 1 Mile vi?

2000 Feet

SURFICIAL DEPOSITS Landslides O Quaternary

Alluvium Qa Quaternary

ALLOCHTHONOUS ROCKS

Vinini Group Ordovician

Roberts Mts. Fm. Lower Devonian

Woodruff Formation Upper Devonian

AUTOCHTHONOUS ROCKS

Dale Canyon Formation Lower Mississippian

Pilot Shale Upper Devonian

/ . / Carbonate platform rocks V / Lower, Middle, & Upper Devonian

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Faint laminae are visible on weathered surfaces. EXPLANATION Thickness of the Woodruff mapped here is esti- Figure 2. Geologic map of the Dry Creek mated at about 1,200 ft (365 m). area plotted on a section grid. Dry Creek is in Fault the alluvium-covered drainage south of cross Zonal Range and Age section B-B'. The mouth of Pony Creek is in - Thrust fault section 13, near cross section A-A'. Dry Conodont collections from two localities Creek extends northwestward from sections (Appendix, samples RV-122, RV-154) yielded Contact 8 and 9 in the southeast part of the map area faunas assigned to the crepida and Lower ex- (dashed where opproximote, to section 36 along its west-central margin. panse Zones of the Famennian (Late Devo- dotted where concealed) Cross sections are shown in Figure 3. Arrows nian). At the type locality, Smith and Ketner labeled "DC" on either side of the map indi- (1975) reported a Famennian age based on Strike and dip cate the position of the so-called Dry Creek goniatities of the genus Platyclymenia. fault, not recognized here. The locations of rock units and their boundaries on this map Syncline Depositional Environment and are similar enough to locations on the maps of Regional Significance t (showing direction Smith and Ketner (1978) and Carlisle and of plunge) Nelson (1990) so that direct comparisons of The Woodruff Formation appears to have differing interpretations can be made. ,12 Conodont locality been deposited in an outer-shelf or slope environment. Presence of fine laminations, carbonaceous material, and authigenic pyrite, along with minor bioturbation, indicate aerobic to dysaer- obic bottom conditions. Conodont faunas (see Appendix) correspond to the Palmatolepid- Polygnathid biofacies of Sandberg (1976), indi- cating shallow to moderately deep water. No diagnostic trace fossils were found.

6000 ft -

5000 ft-

4000 ft

6000 ft-

5000 ft -

4000 ft

Figure 3. Geologic cross sections of the Dry Creek area. Positions of cross sections are shown in Figure 2. The Devonian-Mississippian unconformity is shown with a wavy line. Thrust faults are shown with a heavy barbed line; the lowest thrust, below the Woodruff Formation, is at the base of the Roberts Mountains allochthon. Symbols are as follows: DS1, Lone Mountain Dolomite; Db, Beacon Peak Dolomite; Do, Oxyoke Canyon Sandstone; Dt, Telegraph Canyon Formation (shown arbitarily divided by two dashed lines parallel to bedding); Dp, Pilot Shale; Md, Dale Canyon Formation; Dw, Woodruff Formation; Dr, Roberts Mountains Formation; Ov, Vinini Formation. Section B-B' is in approximately the same position as section B-B' of Smith and Ketner (1968, Fig. 4).

Geological Society of America Bulletin, September 1992

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/9/1208/3381627/i0016-7606-104-9-1208.pdf by guest on 28 September 2021 Figure 4. Photomicrographs of Devonian rocks. A: Woodruff Formation, plane light, xlOO, of laminated carbonaceous quartz-silty dolomite. Note laminae defined by carbonaceous material. Sample RV-41; NE%, SE'/i, sec. 13, T. 28 N., R. 52 E. B: Woodruff Formation, plane light, x40, of partially dolomitized biomicrite. Note calcispheres and laminae that are defined by dolomite rhombs and quartz silt. Sample RV-122; NW'/i, NW

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In the northern Sulphur Spring Range, the two members in the Eureka area, a lower everywhere they were mapped. On the basis of Woodruff does not show the intense deforma- member consisting of calcareous shale and these observations, the contact is intepreted as tion characteristic of the Vinini Formation. Au- shaley limestone and an upper member consist- depositional and not a thrust fault. The upper tochthonous Famennian age rocks in the Cortez ing of carbonaceous calcareous shale. contact with the overlying Dale Canyon Forma- quadrangle (Fig. 1) mapped by Gilluly and Ma- In the area mapped, these two members can tion is unconformable. sursky (1965) as Pilot Shale resemble the type be distinguished in the Pilot where exposures are Woodruff (Sandberg, in Johnson and Pender- good. The lower member consists of grayish- Zonal Range and Age gast, 1981). If the Woodruff Formation were orange to pink, shaley quartz-silty dolomite. The deposited in the vicinity of the Cortez Moun- upper member consists of black carbonaceous Three conodont collections from the lower tains, then displacement of the Woodruff in the shaley dolomite. Large areas of the Pilot Shale member of the Pilot Shale (see Appendix) northern Sulphur Spring Range would have have been silicified. yielded faunas assigned to the marginifera Zones been considerably less than for the Vinini For- of the Famennian (Late Devonian). No cono- mation in the Roberts Mountains, as estimated Lithology donts were recovered from the upper member. by Murphy and others (1984). Sandberg (1979) reported an age span of late The lower member of the Pilot Shale consists Frasnian to Kinderhookian for the Pilot Shale in AUTOCHTHONOUS ROCKS: of grayish-orange to reddish-purple, laminated the Great Basin region. CARBONATE SHELF SEQUENCE quartz-silty dolomite (Fig. 4C). Thin-section analysis shows sub-rounded to angular quartz Depositional Environment The carbonate shelf sequence comprises Lone silt (5% to 15%) set in a fine-crystalline dolomitic Mountain Dolomite (Silurian-Lower Devo- matrix. Dolomite grains range in size from 0.02 The Pilot Shale was deposited in a shelf basin nian), Beacon Peak Dolomite (Lower Devo- to 0.004 mm, with rhombs common. Carbona- (Sandberg and others, 1989); actual depths of nian), Oxyoke Canyon Sandstone (Lower to ceous and argillaceous materials, along with deposition cannot be determined. Trace fossils Middle Devonian), and Telegraph Canyon authigenic pyrite, are a minor constituent. Lam- or macrofauna were not found. Conodont fau- Formation (Middle to Upper Devonian). Stra- inae are defined by concentrations of coarser nas correspond to the Palmatolepid-Polygnathid tigraphy of the Devonian carbonate units has dolomite and quartz silt. The cloudy and dirty biofacies of Sandberg (1976), which indicates an been described by several workers (Nolan and appearance of the dolomite suggests that it re- offshore environment. Lack of bioturbation, others, 1956; Carlisle and others, 1957; Smith places argillaceous lime mud. along with abundant carbonaceous material and and Ketner, 1975; Kendall and others, 1983). The upper member of the Pilot Shale consists authigenic pyrite, indicates anaerobic bottom Silicification in the Telegraph Canyon For- of laminated, black, carbonaceous, shaley do- conditions. Although most of the Pilot Shale is mation is present as small irregular bodies of lomite (Fig. 4D). Thin-section analysis shows a now dolomite, it was probably originally depos- jasperoid, which are especially common along finely crystalline dolomite with abundant argil- ited as an argillaceous micritic sediment, settling the contact with the overlying Pilot Shale. The laceous and carbonaceous material. Minor con- out of suspension from a turbid layer introduced jasperoid is dark red to brown, fine-grained, stituents include quartz silt, radiolarian molds, by distant turbidity currents. chert-like rock. Veins of barite are in and around and authigenic pyrite. The dolomite is finer than the jasperoid bodies. In the Taylor mining dis- that of the lower member, ranging in size from Regional Significance trict near Ely, Nevada, Drewes (1962) observed 0.01 to 0.002 mm, and is mostly anhedral with that silicification occurred in the Guilmette some rhombs. Laminae are defined by concen- Smith and Ketner (1968, 1978) and Carlisle Formation along the contact with the overlying trations of coarser dolomite. The origin of the and Nelson (1990) interpreted this unit in the Pilot Shale. He noted that silicification was re- dolomite is similar to that in the lower member. northern Sulphur Spring Range as part of the stricted primarily to stratigraphic contacts where Silicification is widespread in the Pilot Shale allochthonous Woodruff Formation. Field evi- impermeable shaley rocks cap permeable car- (Fig. 5A). The silicified shale is a hard, chert-like dence presented here shows that this unit is au- bonate rocks, and along normal faults. rock, commonly light gray to white with dark tochthonous and should be assigned to the Pilot The Pilot Shale probably formed an imper- red, lavender, and pink Liesegang rings and Shale on the basis of lithology and stratigraphic meable cap rock which trapped silica-rich hy- bands. The rock has lost its original shaley fissil- and geographic position. drothermal fluids, resulting in the development ity, and it fractures irregularly along bedding Formation of the Pilot basin on the Late of jasperoid along much of the upper contact of planes. In thin section, the dolomite appears to Devonian carbonate platform has been inter- the Telegraph Canyon Formation. This silicified be completely replaced by cryptocrystalline sil- preted to mark the beginning of the Antler orog- zone has been misinterpreted as a thrust fault by ica. Clay minerals have been altered to sericite. eny (Poole, 1974). Goebel (1991) has recently Carlisle and Nelson (1990) and by Smith and The Pilot Shale is about 200 ft (60 m) thick in clarified this interpretation by identifying the Ketner (1978). the southern part of the mapped area and thins Pilot basin as a back-bulge basin associated with toward the west and north, where it is absent. the approach of the Roberts Mountains alloch- AUTOCHTHONOUS ROCKS: The lower contact with underlying Devonian thon. Deposition began during the A. triangula- PILOT SHALE carbonate rocks is poorly exposed and is ob- ris Zone (mid-Frasnian) near the center of the scured by silicification in many places. There is basin and spread outward (Sandberg and others, The Pilot Shale was named by Spencer no evidence of deformation near the contact. 1989; Johnson and others, 1991). At Devils (1917) for exposures in the Ely region of eastern Bedding-plane attitudes between the underlying Gate, about 7 mi northwest of Eureka, Sandberg Nevada. Nolan and others (1956) recognized carbonate rocks and the Pilot are concordant and Poole (1977) recognized evidence of deep-

Geological Society of America Bulletin, September 1992

Downloaded from http://pubs.geoscienceworld.org/gsa/gsabulletin/article-pdf/104/9/1208/3381627/i0016-7606-104-9-1208.pdf by guest on 28 September 2021 Figure 5. Photomicrographs of Devonian and Mississippian rocks. A: Pilot Shale, crossed nichols, xlOO, of silicified shale. Clay minerals have been altered to mica, cryptocrystalline silica has replaced carbonates. Quartz silt has not been affected. Sample RV-60; SEVi, NW'i, sec. 16, T. 27 N., R. 53 E. B: Dale Canyon Formation, crossed nichols, x40, of cherty quartz-arenite. Note the bimodal grain-size distribution between the large angular chert clast and smaller rounded quartz grains. Sample RV-21; NW'A, NWH, sec. 30, T. 28 N., R. 53 E. C: Dale Canyon Formation, plane light, x40, of chert-pebble-wacke. Note large angular to subrounded chert grains and smaller quartz grains in fine argillaceous matrix. Sample RV-56; NE'A, NWS, sec. 6, T. 27 N., R. 53 E. D: Dale Canyon Formation, plane light, x40, of carbonaceous spicular biomicrite. Note sponge spicules and calcispheres. Sample RV-118; NE%, NE'/i, sec. 7, T. 27 N., R. 53 E.

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ening along the western rim of the Pilot basin. basin-slope facies is gradational and interfinger- channel-fill complexes near the base of the for- Here, the Devils Gate Limestone grades upward ing. Sandstone beds are 30 to 50 cm thick and mation. These deposits differ from the pebbly from shallow-water biohermal and biostromal commonly massive to poorly laminated. Graded chert-wackes in that they consist of cobble- and limestone into east-facing, deeper-water, slope bedding is uncommon and poorly developed. boulder-sized clasts of angular chert in a matrix deposits, consisting of debris-flow and turbiditic Lower contacts are scoured, with abundant flute of coarse sand. Fine matrix is nearly absent. The limestone that intertongues with the Pilot Shale. and groove casts. Upper contacts are sharp and coarse-sand matrix is mainly chert and is ce- This facies relationship was not observed in the planar. Bouma sequences are rarely seen. Sand- mented by finely crystalline quartz. area mapped. to-shale ratios range from 1:1 to 1:3. Sandstone The lower contact with the Pilot Shale and beds up to 3 m thick are clearly amalgamated Telegraph Canyon Formation is disconform- AUTOCHTHONOUS ROCKS: and are composed of several individual flows. able. Along Dry Creek, a large channel has DALE CANYON FORMATION The sandstone beds represent facies B2 of been cut into the Pilot Shale and infilled by the Walker and Mutti (1973). The interpreted mode coarse Dale Canyon debris-flow deposits. Large The Dale Canyon Formation was named by of emplacement is by grain flow. clasts eroded from the Pilot Shale have been Nolan and others (1974) for exposures of inter- Chert arenite (Fig. 5B) composes most sand- included in the debris flow. Bedding-plane atti- bedded shale, sandstone, and conglomerate of stone of the Dale Canyon Formation. It is me- tudes observed in the Pilot Shale and Dale Can- Early Mississippian age described by Stewart dium to coarse grained, gray to greenish gray, yon Formation along Dry Creek differ less (1962) in the vicinity of Eureka. In the northern with surfaces stained yellowish brown by iron than 5 degrees. Sulphur Spring Range, all rocks of the Dale Can- hydroxides. Most of the sandstone is massive, Thickness of the Dale Canyon Formation yon Formation were previously assigned to the with laminations common; graded bedding is cannot be determined because the upper contact Chainman Shale by Smith and Ketner (1978). observed in some beds. Modal analysis of six is a thrust or normal fault everywhere it was The Dale Canyon Formation in the area chert-arenites shows that framework composi- mapped. Minimum thickness is estimated at mapped is correlated with the type Dale Canyon tion ranges from 29% to 76% for quartz, 18% to about 1,000 ft (305 m). Rocks near the thrust by stratigraphic and paleogeographic position, 60% for chert, and 3% to 11% for fine-grained contact with the overlying Woodruff Formation lithologic similarity, and age. Conodont collec- argillaceous rock fragments. The rocks are tex- have been brecciated. tions from the type locality (Sandberg, in John- turally submature, with moderate sorting, and son and Pendergast, 1981) and from the area grains are subangular to rounded. A bimodal Zonal Range and Age mapped indicate an age of late Kinderhookian texture is common, with chert generally coarser to early Osagean. The Mississippian palinspastic and more angular than quartz, which is gener- Four conodont collections from the Dale correlation chart compiled by Poole and Sand- ally finer and more rounded. This relationship is Canyon Formation (two from Carlisle and berg (1977, Fig. 2) shows that "true" Chainman probably caused by the quartz being multicycle Nelson's unpub. data) appear to belong to the Shale represents a younger (late Osagean to and chert grains being first cycle. The cement is interval isosticha-Upper crenulata to the Lower Chesterian age), shallower, and more distal fa- mostly silica, with syntaxial overgrowths on typicus Zone. See Appendix for a fuller discus- cies generally deposited farther east in the Antler quartz grains common. Calcite cement is found sion. Famennian Palmatolepis spp. present in the foreland basin than the older, proximal Dale in some fine-grained sandstone. collections have been reworked. Canyon Formation. Chert-pebble-wacke (Fig. 5C) forms a minor Basin-slope facies form the base of the Dale part of the formation and occurs as lenticular Regional Significance Canyon Formation. This unit consists mainly of channel-fill complexes. The rock is dark olive black carbonaceous shale with interbeds of fine- gray with pebbles of green, gray, and black chert Poole (1974) demonstrated that early Missis- grained sandstone, 2-4 cm thick, which belong and gray quartzite in a matrix of sand, silt, and sippian orogenic clastics deposited in the Antler to facies G and E of Walker and Mutti (1973). clay. Thin-section analysis shows about 30% flysch trough were emplaced by various types of Large channels, 100 to 150 m wide, cut through chert pebbles; 50% sand, consisting of chert and sediment gravity flows, mainly turbidity currents the shale and are filled with pebbly sandstone, quartz; and 20% fine silt and clay. The rock is forming submarine-fan complexes. Composition massive coarse sandstone, and conglomerate texturally immature, with very poorly sorted an- of the Dale Canyon, with the exception of lime consisting of angular chert cobbles and boulders gular to rounded grains. The chert-pebble- mudstone beds, indicates a provenance within in a coarse sand matrix. A large block of Tele- wacke was probably emplaced by debris flow. the RMA (Poole, 1974; Harbaugh and Dickin- graph Canyon Formation dolomite, which Dark gray shale and siltstone form interbeds son, 1981; Johnson and Pendergast, 1981, Fig. yielded a Frasnian conodont fauna (sample RV- between sandstone beds. Fissility varies from 4). The Dale Canyon Formation in the Pinyon 158, Appendix), was found in a channel-fill shaley to papery. Quartz silt is abundant along Range is interpreted here (Fig. 6) as basin-slope deposit encased in a matrix of coarse sand. The with carbonaceous material. Thin beds of hemi- and submarine-fan facies, deposited in the channel-fill units represent facies Aj, A3, and B2 pelagic lime mudstone are rare. These rocks are Antler foreland basin (Poole, 1974). This inter- of Walker and Mutti (1973). These units were significant because they yield conodont faunas pretation follows that of Harbaugh and Dickin- probably emplaced by debris-flow and grain- (see Appendix). Abundant sponge spicules and son (1981) for approximately the same unit in flow mechanisms as described by Middleton and calcispheres in an argillaceous and carbonaceous the adjacent Diamond Mountains. In the Dia- Hampton (1973). micritic matrix were found in thin section (Fig. mond Mountains, Harbaugh and Dickinson The inner-fan facies consists of rhythmically 5D). They are classified as spicular biomicrite, (1981) recognized basin-slope and submarine- bedded sandstone and shale with some lenticular using Folk's classification (1962, 1980). fan facies in the lower part of their "Chainman- beds of pebbly sandstone. The contact with the Coarse-grained debris-flow deposits form Diamond Peak sequence." We assign that lower

Geological Society of America Bulletin, September 1992

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Figure 6. Cross section of the Antler foreland trough in Late Mississip- pian time. Horizontal di- mensions are not to scale. The western end is at the longitude of the Roberts Mountains; the eastern end is at the longitude of Ely. RMA is the Roberts Mountains allochthon. Mississippian Webb For- mation is regarded as pre- flysch. Tripon Pass Lime- stone (Oversby, 1973) is a limestone turbidite unit derived by erosion from the eastern carbonate shelf. The Pilot Shale is combined here with the Devonian carbonate platform. Depiction of the Antler flysch-molasse sequence is modified from Harbaugh and Dickinson (1981, Fig. 8).

part to the Dale Canyon Formation. A similar Roberts Mountains allochthon (RMA) during and Pendergast, 1981, p. 653) described a north- relationship is observed in the mapped area the Antler orogeny. The Woodruff Formation northwest-plunging anticline with an over- where basin-slope facies are overlain by inner- forms the base of the allochthon and structurally turned western limb. fan facies. Nereites trace-fossil assemblages have overlies the autochthonous Dale Canyon For- Field relations in the Pinyon Range, as been reported by Poole (1974) and Harbaugh mation (Fig. 7). The Vinini structurally overlies mapped by Smith and Ketner (1978), indicate and Dickinson (1981) and indicate quiet water. the Woodruff, with slices of the Roberts Moun- that the period of folding occurred after em- Thin beds of lime mudstone with Mississip- tains Formation in between at Pony Creek. The placement of the RMA and before Tertiary pian conodonts and reworked Devonian cono- same structural sequence was mapped by Smith normal faulting. donts are interpreted as being derived from the and Ketner (1978) in the Willow Creek area, a east (Johnson and Pendergast, 1981, Fig. 4B) few miles to the north. Conodont collections NORMAL FAULTING and as tongues of the Tripon Pass Limestone from the autochthonous Dale Canyon Forma- (Oversby, 1973). The Tripon Pass Limestone tion indicate that the RMA was emplaced dur- Field evidence indicates two phases of high- (Fig. 6) has been identified by Poole and Clay- ing or after late isosticha-X)pper crenulata Zone angle normal faulting in the study area. The first pool (1984, p. 184) in the Diamond Mountains time (late Kinderhookian or possibly early Osa- episode developed north-northwest-trending and is present all along the Antler foreland gean time). Whitaker (1985) mapped beds low normal faults of major displacement, which trough from near Wells, in Elko County, to in the Diamond Peak Formation, dated by co- produced the Basin-and-Range topography of Warm Springs, in northern Nye County. We nodonts as typicus Zone, as depositionally over- the region. Larger displacements on the system regard the Tripon Pass limestone turbidite beds, lying the RMA in the Willow Creek area. of north-northwest-trending faults are all down- with reworked conodonts, as basin-fill deposits to-the-west, defining four narrow, elongate fault that formed by reciprocal sedimentation during FOLDING blocks with relatively simple internal structure times of emergence and exposure of the carbon- (Figs. 2 and 3). A younger episode of faulting ate platform. Goebel (1991, p. 414) reported an A large north-northwest-trending syncline produced northeast-trending normal faults of inverted clast stratigraphy in the Tripon Pass, that plunges north is located near the center of generally less displacement, which offset the which is consistent with our interpretation. the mapped area. The extent of the syncline is major north-northwest-trending fault system. unclear because it is truncated by Tertiary nor- THRUST FAULTING mal faults. The same pattern of folding is exhib- DRY CREEK FAULT ited in the Willow Creek area (Smith and The Woodruff, Vinini, and Roberts Moun- Ketner, 1978; Whitaker, 1985), a few miles Thorman and Ketner (1979) proposed the tains Formations were emplaced as part of the north of the area of our map, where Johnson Dry Creek fault as a northwest-trending, left-slip

Geological Society of America Bulletin, September 1992

LOCS. DEVILS DRY LEE WOODRUFF CK. GATE CREEK CANYON EMIGRANT SPR. ZONES

Cavusgnathus QL LÜ texanus © (- varions) NOT Diamond Peak < anchora/is • NOT EXPOSED NOT LU Fm. latus EXPOSED EXPOSED cn O Webb ty pi eus Woodruff _A Ù-

o L. crenuiata Phosphatic bed Webb Fm. o X en sandbergi Ul o duplicata FORE LAND I F T sulcata

Figure 7. Correlation of Lower Mississippian rocks along the Antler flysch trough from south (left) to north (right). Allochthonous units are indicated by sawteeth and are plotted according to their time of emplacement. Revised and modified from Johnson and Pendergast (1981, Fig. 3). Conodont collections diagnostic of the zone shown opposite on the left are indicated by heavy dots. "A" indicates an occurrence of Protocanites lyoni, and "F" indicates an occurrence of the Ferdelford fossil beds (Smith and Ketner, 1975, p. 47-50).

fault. The so-called Dry Creek fault projects LANDSLIDE DEPOSITS and outcrops mapped by Carlisle and Nelson through the area mapped in the vicinity of Dry (1990) as Woodruff in the same structural Creek. The evidence cited by Thorman and Normal faulting during the Tertiary produced belt south of Dry Creek, are identified by us Ketner in support of their hypothesis is apparent steep, unstable, fault-line scarps, resulting in as Pilot Shale in normal stratigraphie position offset of Paleozoic sedimentary fades belts. downslope movement of large coherent land- (Figs. 2-3). This interpretation was postulated Stevens (1981) argued against any such strike- slide blocks. Landslide blocks in the area by Johnson and Pendergast (1981, p. 655) for slip faults in the region, citing large differences in mapped consist mainly of Oxyoke Canyon rocks in the range-front belt north of Dry the amount of offset of Paleozoic sedimentary Sandstone and Beacon Peak Dolomite. Land- Creek. It agrees with the observation of Smith facies of different ages. slide blocks resting on the allochthonous Wood- and Ketner (1975, p. 29) that these rocks K. B. Ketner (1981, written commun.) ex- ruff Formation have been misinterpreted as resemble Pilot Shale. Remapping both north plained that the expression of the Dry Creek structural windows by Smith and Ketner (1978). and south of Dry Creek shows that the rock fault between the Pinyon and Sulphur Spring A landslide block north of Pony Creek lies par- unit we identify as Pilot Shale is everywhere Ranges is a plexus of faults trending north- tially on the Quaternary alluvium and thus indi- found in normal stratigraphie position between northwest, each with a small amount of strike- cates an age that young for the downslope Devonian carbonate and Mississippian clastic slip movement. The autochthonous sequence movement. If this were not convincing, by itself, rocks, has bedding attitudes parallel with bed- shows no such offset of facies along the entire there is a trail of smaller, unmapped carbonate ding in those units, and displays a two-member north-south extent of the area. Aerial photo- boulders upslope from the larger blocks, indica- stratigraphy typical of the Pilot Shale else- graphs and Landsat imagery do not reveal any tive of their source. where. Furthermore, these Pilot Shale out- lineations in the northern Sulphur Spring Range crops are at the margin of the known Pilot that can be attributed to the Dry Creek fault. DISCUSSION AND CONCLUSIONS basin (Sandberg and others, 1989, p. 204) High-angle faults appear to be normal faults and thus are not anomalous. with no evidence of the strike-slip displacement 1. The string of outcrops mapped by Smith The interpretation by Carlisle and Nelson suggested by Ketner. We conclude that there is and Ketner (1978) as Woodruff mantling struc- (1990) of rocks we identify as Pilot Shale as no Dry Creek fault. tural windows between Pony and Dry Creeks, belonging to the allochthonous Woodruff For-

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mation would require a thrust fault between the 3. The long belt of allochthonous rocks be- Ketner, 1978; Johnson and Pendergast, 1981, shale and the carbonate rocks below. Carlisle tween Pony and Dry Creeks mapped as Wood- Fig. 3) should be assigned to the Dale Canyon and Nelson (1988, written commun.) cited ruff Formation by Smith and Ketner (1978) Formation. Carlisle and Nelson (1990) have fol- crenulation, fracturing, and silicification up to includes Ordovician Vinini Formation at higher lowed our interpretation (1988, written com- 30 ft thick at the base of the shale as evidence of structural levels, as mapped by us (Fig. 2). This mun.) to the extent that they have labeled their faulting. Silicification can occur in shale units belt extends from section 13, north of Pony Mississippian clastic unit as Dale Canyon-Dia- that overlie carbonate rocks where faulting is Creek, to Dry Creek, along the boundary be- mond Peak undivided. not in evidence and where the shale acts as a tween sections 5 and 6, and was mapped by 5. Devonian carbonate rocks mapped by permeability barrier to ascending fluids. We Smith and Ketner as Woodruff only. We iden- Smith and Ketner (1978) as occurring in struc- suggest that crenulation and fracturing of the tify the eastern, structurally higher, part of this tural windows beneath Woodruff Formation are shales can have resulted from Mesozoic folding belt as Vinini Formation, based on lithologic identified by us as Quaternary landslide blocks of the rocks in question. Such folding is in evi- differences from known Woodruff Formation (Fig. 2). These carbonate blocks form topo- dence in sections 7 and 8, south of Dry Creek and similarities with known Vinini, but it is as graphic prominences along the west slope of the (Fig. 2), and in the Willow Creek drainage yet unconfirmed by fossils. Our interpretation range, north of Pony Creek. They are clearly on north of the mapped area (Smith and Ketner, agrees with the recognition of a structural sliver top of outcrops of the Woodruff Formation and 1978). of Roberts Mountains Formation, identified by one is atop Quaternary alluvium. Because our For rocks we identify as Pilot Shale to be lithology and fossils, at a position along the mapping and the mapping of Smith and Ketner interpreted as allochthonous Woodruff Forma- Woodruff-Vinini structural contact (Figs. 2, 3, (1978) agree on the identification of Woodruff tion would require the identification of Wood- section A-A'). Thus, the structural sequence we Formation in section 13 (Fig. 2), our finding ruff both below and above the Mississippian identify across this belt is Ordovician Vinini on that the associated carbonate rocks are not in clastic succession. The Smith and Ketner (1968, Siluro-Devonian Roberts Mountains Forma- structural windows eliminates one basis for their Fig. 4) interpretation of Woodruff Formation tion, on Upper Devonian Woodruff, and on structural interpretation. Mississippian clastic rocks; this same sequence is below Mississippian rocks would require a thin, 6. The Dry Creek fault, proposed by Thor- present a few miles to the north, in the Willow tabular plate of Woodruff to have been in place man and Ketner (1979), is not in evidence, al- Creek drainage (Smith and Ketner, 1978; John- in time to be depositionally overlapped by Mis- though it was postulated to cross the Sulphur son and Pendergast, 1981, p. 653; Whitaker, sissippian clastics (as pointed out by Drowley, Spring Range in the area of our map (Fig. 2). 1985). 1983). The Carlisle and Nelson (1990) interpre- The Dry Creek fault was regarded as a strike- tation of rocks in the same position is that the 4. Mississippian clastic rocks mapped as slip fault having left-lateral separation of north- Mississippian rocks arrived piggyback atop the Chainman Shale by Smith and Ketner (1978) south linear trends in central Nevada and to allochthonous Woodruff. Their interpretation is are identified by us as Dale Canyon Formation. cross the Sulphur Spring Range at about Dry untenable because the type Woodruff and the It has been customary in central Nevada to as- Creek, that is, across the central part of our map Woodruff in the Willow Creek drainage every- sign relatively fine-grained Mississippian clastic area. Although this finding has no relation to an where lie above, not below, Mississippian clastic rocks to the Chainman Shale and the overlying interpretation of the Roberts Mountains thrust, rocks (Smith and Ketner, 1978; Johnson and relatively coarser-grained clastic rocks to the it is a significant result of our mapping. Pendergast, 1981, p. 653). Diamond Peak Formation. The term "Chain- 2. Johnson and Pendergast's (1981, p. 653) man," however, has been applied to rocks of ACKNOWLEDGMENTS review of published mapping at the toe of the diverse lithotopes and ages, obscuring significant RMA, along a 115-km span in central Nevada, facies considerations. The type Chainman crops Research was supported by National Science concluded that the RMA everywhere rests on out far to the east of the Sulphur Spring Range, Foundation Grants EAR-7926094 and EAR- Kinderhookian rocks, but there were interpre- at the longitude of Ely, Nevada, as an Upper 9003703. We thank C. A. Nelson and Donald tive exceptions. Testing of the 1981 hypothesis Mississippian, shallow-water, delta-slope unit Carlisle of the University of California, Los An- by M. A. Murphy and his students resulted in above the Joana Limestone (Poole and Sand- geles for making available a pre-publication the discovery of Kinderhookian rocks below the berg, 1977, Fig. 2). We restrict the term copy of their geologic map of the Mineral Hill Roberts Mountains thrust in the Roberts Moun- "Chainman Shale" to rocks like those of the quadrangle. M. A. Murphy and Walter S. tains (Murphy and others, 1984) and along the type area, in the Ely District (Spencer, 1917, Snyder provided useful reviews. W.B.N. Berry western slope of the Sulphur Spring Range p. 26-27). The Chainman is a distal facies of the and Gilbert Klapper identified graptolites and (Thomas, 1985). Carlisle and Nelson (1990) in- Diamond Peak molasse (Fig. 6). conodonts, respectively. corporated Thomas' results in their map. The Dale Canyon Formation is interpreted The interpretations of Smith and Ketner here as basin-slope and submarine-fan facies APPENDIX OF CONODONT (1978) and Carlisle and Nelson (1990) that the deposited in the Antler foreland basin—that is, COLLECTIONS AND LOCALITIES RMA lies on Devonian carbonate rocks at ex- flysch. This interpretation agrees with that of posures closest to the toe would require that the Harbaugh and Dickinson (1981) for approxi- The following nine conodont collections were iden- Roberts Mountains thrust cut downsection mately the same unit in the adjacent Diamond tified by Gilbert Klapper, 1982, and updated in 1991. Two collections are from unpublished data of Carlisle along its eastern extremity, a situation that we Mountains. All of the Mississippian rocks below and Nelson and were identified by W. H. Hass and consider anomalous. Our remapping of this crit- the Roberts Mountains allochthon and which J. W. Huddle. Conodont localities are plotted in ical strip removes this anomaly. have been labeled Chainman (Smith and Figure 2.

Geological Society of America Bulletin, September 1992

TELEGRAPH CANYON FORMATION Pa. marginifera marginifera Helms Kinderhookian species of Siphonodella terminate at Pa. sp. indet. the level of the top of the Kinderhookian, but without Sample: RV-158 indet. ramiform elements definitive evidence that the lowermost Osagean occur- Location: approx. 1,500 ft S, 600 ft W of NE cor. of Zonal range: Lower-uppermost marginifera Zones rences are reworked. sec. 6, T. 27 N., R. 53 E. This sample was collected (Ziegler and Sandberg, 1984, p. 182-183). from a large block of Telegraph Canyon Formation Sample: RV-118 dolomite, in a channel-fill complex in the Dale Can- Sample: RV-103 Location: approx. 500 ft S, 1,000 ft W of NE cor. of yon Formation. Location: approx. 2,000 ft S, 1,600 ft W of NE cor. of sec. 7, T. 27 N., R. 53 E. About 30 ft above formation lcriodus subterminus Youngquist sec. 8, T. 27 N., R. 53 E. Far NE corner of Mineral base. Polygnathus angustidiscus Youngquist Hill quadrangle. Gnathodus punctatus indet. ramiform elements Palmatolepis glabra pectinata Ziegler G. sp. Zonal range: the range of the two identified species is Pa. marginifera marginifera Helms Siphonodella obsoleta from the disparilis Zone (upper Givetian) through the Pa. minuta Branson & Mehl S. sp. indet. Frasnian. Pa. sp. indet.. Polygnathus communis communis Polygnathus sp. indet. Zonal range: as RV-12 WOODRUFF FORMATION Zonal range: Lower-uppermost marginifera Zones (Ziegler and Sandberg, 1984, p. 182-183). Sample: 7 Sample: RV-122 Location: approx. 500 ft NN W of BM 6060, sec. 8, T. Location: approx. 1,200 ft S, 600 ft E of NW cor. of Sample: RV-113 27 N., R. 53 E. This collection is from unpublished sec. 5, T. 27 N„ R. 53 E. (Pine Valley quadrangle; Location: approx. 700 ft S, 1,500 ft W of NW cor. of data of Carlisle and Nelson and was identified by Smith and Ketner's Woodruff). sec. 30, T. 28 N., R. 53 E. Pilot Shale outcrop too J. W. Huddle, 1963. Palmatolepis subperlobaia Branson & Mehl small to map. Bryantodus sp. [including specimen of Helms, 1963, PI. 1, Fig. 10] Palmatolepis sp. indet. Gnathodus punctatus Pa. cf. Pa. regularis Cooper indet. platform and ramiform elements Hindeodella sp. Pa. minuta minuta Branson & Mehl Zonal range: zonally indeterminate, Upper Devonian Palmatolepis distorta Branson & Mehl Pa. minuta minuta — IPa. termini Sannemann Pa. perlobata Ulrich & Bassler [according to W. Ziegler, May 19,1982] Sample: RV-162 Polygnathus communis and P. sp. Pa. minuta subtilis Khalymbadzha and Chernysheva Location: approx. 160 ft S, 3,100 ft N of NW cor. of Pseudopolygnathus sp. Pa n. sp. sec. 5, T. 27 N., R. 53 E. Far NE comer of Mineral Siphonodella spp. Pa. tenuipunctata Sannemann Hill quadrangle. Age: the age of this fauna is Early Mississippian. Note Pa. subgracilis Bischoff Pa. marginifera marginifera Helms reworked Famennian Palmatolepis. Pa. wolskajae Ovnatanova [see Catalogue, v. Ill, Pa. glabra group p. 413] Polygnathus sp. indet. Sample: 13 Pa. sp. indet. indet. ramiform elements Location: approx. 150 ft S, 300 ft E of NW cor. of sec. Polygnathus glaber glaber Ulrich & Bassler indet. simple cone 17, T. 21 N., R. 53 E. This collection is from unpub- P. sp. indet. lished data of Carlisle and Nelson and was identified Pelekysgnathus sp. Zonal range: Lower-uppermost marginifera Zone. by W. H. Hass, 1955. "Spathognathodus" sp. Siphonodella duplicata Branson & Mehl indet. ramiform elements DALE CANYON FORMATION Polygnathus communis Branson & Mehl Zonal range: crepida Zone, probably Upper crepida Pseudopolygnathus cf. prima Branson & Mehl Zone Sample: RV-12 Neoprioniodus sp. Location: approx. 1,400 ft S, 1,600 ft E of NW cor. of Palmatolepis cf. glabra Sample: RV-154 sec. 17, T. 27 N., R. 53 E. Gnathodus cf. delicatus Branson & Mehl Location: approx. 250 ft N, 160 ft W of SE cor. of sec. Gnathodus punctatus (Cooper) G. sp. 6, T. 27 N., R. 53 E. (Pine Valley quadrangle; Smith G. sp. indet. Spathognathus sp. and Ketner's Woodruff). Siphonodella obsoleta Hass Trichonodella sp. Palmatolepis gracilis gracilis Branson & Mehl S. quadruplicata (Branson & Mehl) Hibbardella sp. Pa. gracilis sigmoidalis Ziegler S. sp. indet. Hindeodella sp. Pa. rugosa rugosa Branson & Mehl Polygnathus symmetricus Branson Age: same as sample 7 Pa sp. indet P. inomatus Branson Pa perlobata schindewolfi Miiller P. sp. P. sp. [possibly a small P. styriacus, according to P. communis communis Branson & Mehl REFERENCES CITED W. Ziegler (May 18,1982)]. Pseudopolygnathus primus Branson & Mehl Berry, W.B.N., and Murphy, M. A., 1975, Silurian and Devonian graptolitcs of P. sp. indet. Palmatolepis glabra central Nevada: University of California Publications in Geological Sciences, v. 110, 109 p., 15pls. Branmehla bohlenana (Helms). Pa. marginifera Carlisle, D„ and Nelson, C. A., 1990, Geologic map of the Mineral Hill "S." sp. indet. Pa. sp. indet. quadrangle, Nevada: Nevada Bureau of Mines and Geology, Map 97. Carlisle, D„ Murphy, M. A., Nelson, C. A., and Winterer, E. L„ 1957, Devo- indet. ramiform elements indet. ramiform elements nian stratigraphy of Sulphur Spring and Pin yon Ranges, Nevada: Amer- Zonal range: Lower expansa Zone, on the overlap of Zonal range: possible correlation for this fauna is up- ican Association of Petroleum Geologists Bulletin, v. 41, p. 2175-2191 Pa. rugosa rugosa and B. bohlenana (Ziegler and permost Kinderhookian to lowermost Osagean (from Drewes, H., 1962, Structural and stratigraphic controls of mineralization in the Taylor mining district near Ely, Nevada: U.S. Geological Survey Profes- Sandberg, 1984, p. 184). the isosticha-Vpper crenulata to the Lower typicus sional Paper 450-B, p. 1-3. Zone). The two species that are critical for this deter- Drowley, D., 1983, Comment on "Mid-Paleozoic age of the Roberts thrust mination are Gnathodus punctatus and Siphonodella unsettled by new data from northern Nevada": Geology, v. 11, PILOT SHALE p. 617-618. obsoleta. The first definitely ranges through the cited Folk, R. L., 1962, Spectral subdivision of limestone types: American Associa- Sample: RV-1 zone span. The second species also apparently ranges tion of Petroleum Geologists Memoir 1, p. 62-84. as high as equivalents of the Lower typicus Zone, both 1980, Petrology of sedimentary rocks: Austin, Texas, Hemphill, 183 p Location: approx. 1,300 ft S, 2,000 ft W of NE cor. of Gilluly, J., and Masursky, H., 1965, Geology of the Cortez quadrangle, Nevada: sec. 24, T. 27 N., R. 52 E., southwest of mapped area in Nevada (for example, Whitaker's 1985 collection U.S. Geological Survey Bulletin 1175,117 p. JW-73, which has Gnathodus cuneiformis) and in Ok- Goebet,K. A., 1991, Paleogeogniphic setting of Late Devonian to Early Missis- near Union Summit Road. sippian transition from passive to coltisional margin. Antler foreland, Palmatolepis glabra pectinata Ziegler lahoma (Thompson and Fellows, 1970). Of course, eastern Nevada and western Utah, in Cooper, J. D., and Stevens, C. H-, published papers indicate that all of the uppermost

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Nevada: Journal of Sedimentary Petrology, v. 51, p. 1223-1234. p. 58-82. Stanley, K. O., Chamberlain, C. K., and Stewart, J. H., 1977, Depositional Johnson, J. G., and Pendergast, A., 1981, Timing and mode of emplacement of Poole, F. G., and Claypool, G. E., 1984, Petroleum source-rock potential and setting of some eugeosynclinal Ordovician rocks and structurally inter- the Roberts Mountains allochthon. Antler orogeny: Geological Society crude-oil correlation in the Great Basin, in Woodward, J., Meissner, leaved Devonian rocks in the Cordilleran mobile belt, Nevada, in of America Bulletin, v. 92, p. 648-658. F. F., and Clayton, J. L., eds., Hydrocarbon source rocks of the Greater Stewart, J. H., Stevens, C. H„ and Fritsche, A. E., eds., Paleozoic Johnson, J. G., Sandberg, C. A., and Poole, F. G., 1991, Devonian lithofacies Rocky Mountain region: Denver, Colorado, Rocky Mountain Associa- paleogeography of the western United States: Society of Economic of western United States, in Cooper, J. D., and Stevens, C. H., eds., tion of Geologists, p. 179-229. Paleontologists and Mineralogists, Pacific Section, Pacific Coast Paleo- Paleozoic paleogeography of the western United States, II: Society of Poole, F. G., and Sandberg, C. A., 1977, Mississippian paleogeography and geography Symposium 1, p. 259-274. Economic Paleontologists and Mineralogists, Pacific Section, v. 67, tectonics of the western United States, in Stewart, J. H., Stevens, C. H., Stevens, C. H., 1981, Evaluation of the Wells fault, northeastern Nevada and p. 83-105. and Fritsche, A. E., eds., Paleozoic paleogeography of the western northwestern Utah: Geology, v. 9, p. 534-537. Kay, Marshal], 1952, Late Paleozoic orogeny in central Nevada: Geological United States: Society of Economic Paleontologists and Mineralogists, Stewart, J. H., 1962, Variable facies of the Chainman and Diamond Peak Society of America Bulletin, v. 63, p. 1269-1270. Pacific Section, Pacific Coast Paleogeography Symposium 1, p. 67-85. formations in western White Pine County, Nevada: U.S. Geological Kendall, G. W., Johnson, J. G., Brown, J. O., and Klapper, G., 1983, Stratig- Roberts, R. J., Hotz, P., Gilluly, J., and Ferguson, H. G., 1958, Paleozoic rocks Survey Professional Paper 450-C, p. 57-60. raphy and facies across Lower Devonian-Middle Devonian boundary, of north-central Nevada: American Association of Petroleum Geologists Thomas, K. K., 1985, Paleozoic stratigraphy and structure of a part of the central Nevada: American Association of Petroleum Geologists Bulletin, Bulletin, v. 42, p. 2813-2857. northwestern Sulphur Spring Range, Eureka County, Nevada [M.S. v. 67, p. 2199-2207. Sandberg, C. A., 1976, Conodont biofacies of Late Devonian Polygnathus thesis]: Riverside, California, University of California, Riverside, 79 p., Merriam, C. W., 1940, Devonian stratigraphy and paleontology of the Roberts styriacus Zone in western United States: Geological Association of Can- 4 pis. Mountains region, Nevada: Geological Society of America Special ada Special Paper 15, p. 171-186. Thorman, C. H., and Ketner, K. B., 1979, West-northwest strike-slip faults and Paper 25,114 p. 1979, Devonian and Lower Mississippian conodont zortation of the other structures in alhchthonous rocks in central and eastern Nevada Merriam, C. W., and Anderson, C. A., 1942, Reconnaissance survey of the Great Basin and Rocky Mountains: Brigham Young University, Geol- and western Utah: Rocky Mountain Association of Geologists, Basin Roberts Mountains, Nevada: Geological Society of America Bulletin, ogy Studies, v. 26, pt. 3, p. 87-106. and Range Symposium, p. 122-133. v. 53, p. 1675-1728. 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