AN ABSTRACT OF THE THESIS OF
Robert Vincent Visconti for the degree of Master of Science in Geology presented on December 9, 1982
Title: PALEOZOIC STRATIGRAPHY AND STRUCTURE OF THE DRY CREEK AREA,
ELKO AND EUREKA COUNTIES, NEVADA.
Abstract approved: Redacted for Privacy C) Dr. J.Gljohnson
The purpose of this investigation was to test two hypotheses.
The first hypothesis interprets allochthonous rocks in the southern
Pinyon Range to lie on the Devonian Nevada Group. The second hypothesis interprets allochthonous rocks to lie on the Mississippian
Dale Canyon Formation. Evidence presented here supports the second hypothesis.
During Late Silurian to Middle Devonian time, deposition in the southern Pinyon Range occurred in a miogeoclinal shallow shelf environment characterized by the Lone Mountain Dolomite and Nevada
Group.
Deposition of the Pilot Shale in an incipient basin developed within the shelf, beginning no later,than marginifera-Lower velifer
Zone time, marked the onset of the Antler orogeny. A westward- dipping subduction zone formed to the west, developing an accretionary wedge which later became the Roberts Mountains allochthon. Incipient subduction of continental crust resulted in obduction of the allochthon onto the continential crust. The Antler foreland basin formed east of the advancing allochthon where deposition of the Dale Canyon Formation unconformably on the Pilot Shale formed a submarine fan complex consisting of siliciclastic sediments shed from the rising allochthon.
The Roberts Mountains allochthon in the southern Pinyon Range consists of the Devonian Woodruff Formation forming the base, the
Ordovician Vinini Formation thrust over the Woodruff, with slices of the Devonian Roberts Mountains Formation occurring in between at places. The allochthon was emplaced in the southern Pinyon Range, over the Dale Canyon Formation during or after late isosticha-Upper crenulata Zone time. Paleozoic Stratigraphy and Structure
of the Dry Creek Area, Elko and
Eureka Counties, Nevada
by
Robert Vincent Visconti
A THESIS
submitted to
Oregon State University
in partial fulfillment of the requirements for the degree of Master of Science
Completed December 9, 1982
Commencement June 1983 APPROVED: Redacted for Privacy
Professor in charge of major Redacted for Privacy
Chairman of Department of7blogy
Redacted for Privacy
Dean of Grad e School d
Date thesis is presented December 9, 1982
Typed by Heidi W. Pearson for Robert Vincent Visconti ACKNOWLEDGEMENTS
I am grateful to many people for their help in this project.
The guidance and encouragement given by Dr. J.G. Johnson was deeply appreciated. I thank Dr. E. Julius Dasch and Dr. Harold Demarest
for their critical review of the manuscript. Claudia Regier prepared
the conodont samples, which were identified by Dr. Gilbert Klapper
of the University of Iowa. A coral was identified by Dr. William
Oliver of the U.S. Geological Survey. Graptolites were identified
by Dr. W.B.N. Berry of the University of California at Berkeley.
Dr. Keith B. Ketner of the U.S. Geological Survey provided an
interesting field trip and discussion. Dr. Donald Carlisle and Dr.
C.A. Nelson of the University of California at Los Angeles provided a
copy of their unpublished map of the Mineral Hill quadrangle and
unpublished fossil data.
I thank John Whitaker for many helpful discussions and car
pooling into town during the field season.
I thank my parents for their support and patience.
A National Science Foundation grant to Dr. J.G. Johnson provided much of the financial support. TABLE OF CONTENTS
Page
INTRODUCTION 1
Purpose 1 Location and Accessibility 1 Previous Work 2 Methods and Terminology 5
GEOLOGIC SETTING 7
VININI FORMATION (ALLOCHTHONOUS) 9
ROBERTS MOUNTAINS FORMATION (ALLOCHTHONOUS) 12
WOODRUFF FORMATION (ALLOCHTHONOUS) 13
General Statement 13 Age 13 Lithology 14 Laminated quartz-silty dolomite and bioturbated dolomitic siltstone 14 Chert 14 Partially dolomitized biomicrite 16 Siliceous mudstone 16 Depositional Environment and Regional Significance 16
LONE MOUNTAIN DOLOMITE (AUTOCHTHONOUS) 19
NEVADA GROUP (AUTOCHTHONOUS) 20
Beacon Peak Dolomite 20 Oxyoke Canyon Sandstone 21 Telegraph Canyon Formation 21 Lithology 22 Silicification 23
PILOT SHALE (AUTOCHTHONOUS) 25
General Statement 25 Thickness and Contact Relations 25 Age 26 Lithology 26 Page
Lower member 26 Upper member 28 Silicified shale 28 Depositional Environment 32 Regional Significance 32
DALE CANYON FORMATION (AUTOCHTHONOUS) 34
General Statement 34 Age 35 Contact Relations and Thickness 35 Facies Interpretation 36 Basin slope facies 36 Inner fan facies 38 Lithology 38 Chert-arenite 33 Pebbly chert-wacke 41 Fine grained rocks 41 Coarse-grained debris flow deposits 46 Regional Significance 46
INTRUSIVE ROCKS 48
LANDSLIDE DEPOSITS 49
STRUCTURE 50
GEOLOGIC HISTORY 53
SUMMARY 55
REFERENCES CITED 58
APPENDIX 62 LIST OF FIGURES
Figure Page
1. Index map of the Pinyon Range. 3
2. Summary Paleozoic stratigraphic section of the mapped area. 4
3. Photomicrograph of bedded chert (Ordovician). 11
4. Photomicrograph of laminated quartz-silty dolomite 15 (Devonian).
5. Photomicrograph of partially dolomitized biomicrite 17 (Devonian).
6. Photomicrograph of jasperoid in the Telegraph Canyon 24 Formation.
7. Photomicrograph of laminated quartz-silty dolomite 27 (Devonian).
8. Photomicrograph of laminated carbonaceous shaly 29 dolomite (Devonian).
9. Silicified Pilot Shale. 30
10. Photomicrograph of silicified shale (Devonian). 31
11. Channel filled with coarse sandstone, basin slope facies 37 of the Dale Canyon Formation.
12. Amalgamated massive sandstone beds (Mississippian). 39
13. Unconformable contact between the Pilot Shale and 40 Dale Canyon Formation.
14. Photomicrograph of chert-arenite (Mississippian). 42
15. Photomicrograph of pebbly chert-wacke (Mississippian). 43
16. Photomicrograph of carbonaceous spicular biomicrite 44 (Mississippian).
17. Photomicrograph of coarse-grained debris flow 45 conglomerate (Mississippian). Figure Page
18. Comparative geologic cross sections along Dry Creek 56 LIST OF PLATES
Plate Page
I. Geologic map of the Dry Creek Area, Elko and pocket Eureka Counties, Nevada.
2. Geologic cross sections. pocket PALEOZOIC STRATIGRAPHY AND STRUCTURE OF THE DRY CREEK AREA, ELKO AND EUREKA COUNTIES, NEVADA
INTRODUCTION
Purpose
The Paleozoic rocks in the vicinity of Dry Creek, Sulphur Spring and Pinyon Ranges, are in several elongate fault blocks across and subparallel to the toe of the Roberts Mountains thrust. Published and unpublished geologic maps (Smith and Ketner, 1978; Carlisle and Nelson, ms) interpret allochthonous rocks to lie below the Chainman Shale or
Chainman-Diamond Peak Formation, undivided. However, Johnson and
Pendergast (1981) interpret the same maps to show the allochthon over- lying the Chainman Shale. Remapping of the critical area was done to test the two hypotheses.
The Dry Creek area also includes the "Dry Creek fault", recently proposed (Thorman and Ketner, 1979) as an important left-lateral strike- slip fault zone. Johnson (oral commun., 1981) suggests that there is no strike-slip fault zone and that it also is a misinterpretation.
These two hypotheses are also tested.
Location and Accessibility
The area mapped is located approximately 33 miles south of the town 2
of Carlin, lying along the boundary of Elko and Eureka Counties, Nevada.
It includes the southwestern edge of the Pinyon Range and the northern tip of the Sulphur Spring Range (Fig. 1). The area mapped occupies
roughly 13 square miles (34 square kilometers). Access may be gained from the west on three unimproved dirt roads leading east from Union
Summit Road.
Previous Work
Carlisle and Nelson (ms) mapped the southern one third of the thesis area as part of an unpublishedgeologic map of the MineralHill quadrangle.
They mapped the allochthonous units as Ordovician Vinini Group (western facies), Devonian Bruffey Formation (transitionalfacies), and an.unnamed
Devonian shale, all thrust over the autochthonous Silurian-Devonian Lone
Mountain Dolomite, Devonian Nevada Group, and Devils Gate Limestone.
The Mississippian Diamond Peak Formation-Chainman Shale undivided was mapped as overlapping the autochthonous and allochthonous units. Carlisle and Nelson (1955) did not assign an age to the Roberts Mountains thrust.
Carlisle and others (1957) described Devonian stratigraphy of the Pinyon and Sulphur Spring Ranges with emphasis on the autochthonous carbonate units. Reconnaissance mapping of Elko County (Granger and others, 1958) included approximately the eastern three fourths of the thesis area.
Smith and Ketner (1975, 1977) describe the Paleozoic stratigraphy and interpret the tectonic history of the Pinyon Range. The northern two thirds of the study area was mapped by Smith and Ketner (1978) as part of a U.S. Geological Survey map of the Pinyon Range. Smith and
Ketner's mapping shows the same basic stratigraphic sequence as 3
CARLIN 1166 0
40°30'
Map Area NEVADA
DRY CREEK AREA
0 5 10 15 miles
1
Figure I. Index map of the Pinyon andSulphur Spring Ranges, showing the location of theDry-Creek Area. 4
AGE ROCK UNIT THICKNESS
Ordovician Vinini Formation 1500 ft. A A A Roberts Mts. Fm 200 A A A Devonian Woodruff Formation 1200 A A
Mississippian Dale Canyon Formation 1000
Pilot Shale . 200
Telegraph Canyon 2065 Formation
Devonian Oxyoke Canyon Ss. 400
Beacon Peak Dolomite 675
Lone Mt. Dolomite 1400 Silurian
Figure 2. Summary Paleozoic stratigraphic section of themapped area. 5 mapped by Carlisle and Nelson. The allochthonous units were mapped as
Ordovician Vinini and Valmy Formations, Devonian Woodruff Formation, and unnamed Devonian limestone and chert of the transitional facies.
The overlap facies were mapped as the Mississippian Chainman Shale and
Diamond Peak FormationChainman Shale undivided. Thorman and Ketner
(1979) propose the Dry Creek fault, a north-west-trending, left-lateral strike-slip fault separating the Pinyon and Sulphur Spring Ranges.
Displacement of sedimentary facies and structural features are cited as evidence in support of the hypothesis. Johnson and Pendergast (1981) interpret the toe of the allochthon to be overlying the Mississippian
Chainman Shale.
Methods and Terminology
Field work was carried out mainly during the 1981 field season, with one week of follow-up work during the summer of 1982. Paleozoic units were mapped to a scale of 1:15,840 using enlarged 15 minute quadrangles. Samples were collected for lithologic and paleontological analysis. Aerial photographs were used as an aid in determining structures. Thirty thin sections were analyzed. Fourteen samples were processed for conodonts. Claudia Regier did the heavy liquid separation and hand picked the conodonts from the heavy fractions. Dr. Gilbert
Klapper of the University of Iowa identified and assigned ages to the conodont collections.
The carbonate classifications of Folk (1952, 1980) have been used in this report where applicable. Classification of siliciclastic rocks follows that of Folk (1980). Stratification and splitting properties 6 are described using the terminology of McKee and Weir (1953). 7
GEOLOGIC SETTING
Early to Middle Paleozoic rocks in Nevada and western Utah were
deposited in the Cordilleran geosyncline, a north-south-trending
continental margin structure. Two models of the Cordilleran geosyncline have been proposed (Stewart and Poole, 1974). In the first model, deposition is envisaged as occurring in a marginal basin bounded on the west by an island arc system. In the second model deposition is envisaged as occurring along a stable continental margin.
Deposition of Cordilleran Lower and Middle Paleozoic rocks occurred
in three lithofacies assemblages which reflect geographic subdivision of the geosyncline into three depositional and tectonic regimes: 1) the eastern shallow shelf assemblage, consisting mostly of limestone, dolomite, and minor quartz arenite; 2) the transitional assemblage, characterized by limestone, shale, and chert; 3) the western siliceous assemblage, deep basinal deposits composed mainly of siliceous mudstone, chert, and shale (Roberts and others, 1958; Smith and Ketner, 1968;
Stewart and Poole, 1974; Matti et al., 1975).
Large scale thrusting of the eastern shallow shelf facies under the western siliceous facies occurred during the Late Devonian -Early
Mississippian Antler orogeny, resulting in the Roberts Mountains thrust
(Merriam and Anderson, 1942; Roberts and others, 1958; Smith and Ketner,
1968). Development of a flysch trough (Poole, 1974), east of the toe of the advancing allochthon, occurred during late stages of emplacement. 8
The allochthon formed the Antler orogenic highland, which shed detritus eastward into the adjacent flysch trough. Kinderhookian siliciclastic sediments derived from the allochthon were deposited in the flysch trough as submarine fans (Poole, 1974) and then were thrust under the allochthon during the final phase of emplacement (Johnson and Pendergast,
1981). The area was affected by Tertiary faulting, folding, and instrusion. Autochthonous and allochthonous units are exposed in the thesis area as several elongate north-northwest-trending fault blocks resulting from Tertiary normal faulting which produced the typical
Basin and Range topography. 9
VININI FORMATION
The Ordovician Vinini Formation belongs to the deep-water western
assemblage of Roberts et al., (1958). In the area studied it forms, along with the Woodruff Formation and imbricate slices of the Roberts
Mountains Formation, the Roberts Mountains allochthon. The Vinini lies
structurally above the Woodruff as an imbricate thrust sheet within
the allochthon.
The Vinini Formation was named by Merriam and Anderson (1942) for exposures along Vinini Creek in the eastern Roberts Mountains. They recognized two units. The lower Vinini consists of quartzite, arenaceous limestone and "fine laminated sandy and brownish-gray and greenish-brown silty sediments" (Merriam and Anderson, 1942, p. 1694).
The upper Vinini consists of mainly black bedded chert with thin argillaceous partings and black organic shale. Merriam and Anderson
(1942) dated the Vinini Formation as Early to Middle Ordovician based on graptolites. Murphy et al. (1982) show that the upper Vinini is
Lower Ordovician and that the lower Vinini is Middle-Upper Ordovician and that the two units are probably separated by a thrust fault.
Black bedded chert with minor amounts of black organic shale in the mapped area resembles the upper unit of Merriam and Anderson (1942).
It was assigned to the Devonian Woodruff Formation by Smith and Ketner
(1978). This unit resembles the Vinini found in the Willow Creek area three miles north of the mapped area where Smith and Ketner (1975) have collected Ordovician 'age graptolites. In the Willow Creek area, 10
Smith and Ketner (1978) interpreted Woodruff thrust over Vinini with thrust slices of the Roberts Mountains Formation between the Woodruff and Vinini. The reverse structural sequence is observed along Pony
Creek. South of Pony Creek, bedded chert of the Vinini structurally overlies Woodruff dated by conodonts as Late Devonian (Famennian). The
Vinini Formation is poorly exposed and is folded and faulted on a small scale so that estimated thickness is approximately 1500 feet (460 m).
In the mapped area, the Vinini consists mainly of black bedded chert which weathers brown and gray. Most beds are 5 to 15 cm thick, separated by thin argillaceous partings. Fine laminations are visible on weathered surfaces. In thin section the chert is very dark due to abundant carbonaceous material; radiolarian molds are abundant as are quartz filled microfractures. Black organic shale makes up a minor portion of the Vinini and is poorly exposed, it weathers to form a dark gray soil composed of small shale chips.
It is generally accepted that the Vinini Formation was deposited in a deep-water oceanic environment based on the association of bedded cherts, shales, graptolite faunas, and trace fossils. Chamberlain
(in Stanley et al., 1977) reports a bathyal Nerietes trace fossil assemblage in the Vinini Formation in the Roberts Mountains. 11
Figure 3.
Photomicrograph of bedded chert. Note abundant radiolarian molds and dark color due to abundant carbonaceous material. Ordovician. NE4 NE4 section 30, T. 28 N., R. 53 E. Plane light. 12
ROBERTS MOUNTAINS FORMATION
The Roberts Mountains Formation was assigned by Smith and Ketner
(1975) to the transitional assemblage of Roberts et al. (1958), but
Johnson (oral commun.) regards it as comprising rocks deposited in an outer shelf basin. It was named by Merriam (194) for exposures on the east side of Roberts Creek Mountain. In the mapped area, the Roberts
Mountains Formation occurs in a thrust slice between the Vinini and
Woodruff Formations and is exposed only along Pony Creek.
Smith and Ketner (1975, 1978) describe a similar occurrence of the
Roberts Mountains Formation along Willow Creek in the Pinyon Range, about two miles north of the mapped area. They assign an age of earliest Devonian basedongraptolites of the Monograptus uniformis Zone.
Along Pony Creek, the Roberts Mountains Formation consits of dark gray shaly and platy carbonaceous laminated silty dolomite, .which weathers to a yellowish brown. The unit is coarser-grained than the
Woodruff and is distinguished from rocks of similar lithology of the
Woodruff Formation by the occurrence of abundant but poorly preserved graptolites identified by W.B.N. Berry (written commun., 1982) as
Monograptus birchensis Berry and Murphy and Linograptus? sp. Thin section study reveals that the rock consists of quartz silt (10 to 20%) set in a matrix of finely crystalline dolomite with abundant carbonaceous and argillaceous material.
The age range of M. birchensis is latest Silurian to early Early
Devonian (Berry and Murphy, 1975, e.g. Fig. 15). 13
WOODRUFF FORMATION
General Statement
The allochthonous Devonian Woodruff Formation was named by Smith
and Ketner (1968) for exposures along Woodruff Creek in the Pinyon
Range. In the mapped area the Woodruff consists of silty dolomite,
dolomitic siltstone, chert, and siliceous mudstone. Although Smith
and Ketner (1968) assign the Woodruff to the siliceous western assem-
blage, it should be considered to belong to the transitional assemblage
due to abundant carbonate rocks.
In the mapped area the Woodruff has been emplaced at the base of the Roberts Mountains allochthon, it structurally overlies the
Mississippian Dale Canyon Formation. The Vinini Formation structurally overlies the Woodruff as an imbricate thrust sheet. Thickness of the
Woodruff in the mapped area is estimated at about 1200 feet (365 m).
Age
Conodont collections from two localities yielded faunas assigned to the crepida and-Upper styriacus Zones of the Famennian (Late
Devonian). In the type locality, Smith and Ketner (1975) report a
Famennian age based on goniatites of the genus Platyclymenia. 14
Lithology
Laminated quartz-silty dolomite and bioturbated dolomitic siltstone
Laminated quartz-silty dolomite is the dominant lithology of the
Woodruff exposed in the mapped area. These shaly rocks are dark gray
to black and weather grayish orange. Thin section study shows that
they consist of subrounded to angular quartz silt (5 to 15%) set ina
finely crystalline dolomite matrix, with abundant carbonaceous material.
Radiolarian molds are rare. Pyrite and argillaceous material are also
present. Laminae are defined by concentrations of carbonaceous material and concentrations of coarser dolomite rhombs. The dolomite is
considered to be replacement in origin. The cloudy and dirty appearance of the dolomite suggests that it may have been deposited originally as
an argillaceous lime mud. This lithology is similar to some of the
Pilot Shale.
Dolomitic siltstone is similar to the quartz-silty dolomite; however, quartz silt composes up to 50% of the rock. These rocks show evidence of bioturbation as they are mottled and contain small burrows. The dolomitic siltstone is gray to light brown and contains less carbonaceous material than the quartz-silty dolomites.
Chert
Black chert which weathers to brown and gray is interbedded with silty dolomite and siliceous mudstone. The chert is poorly exposed, with few outcrops. It is usually found as blocky pieces up to 15 cm 15
Figure 4.
Photomicrograph of laminated carbonaceous quartz- silty dolomite. Note that laminae are defined by carbonaceous material. Devonian. NE1/4 SE4 section 13, T. 28 N., R. 52 E. Plane light. 16
together with chips of silty dolomite littering gentle slopes. Thin
section study of the chert shows that although it is similar to chert
of the Vinini Formation it differs in that it is generallycoarser and
contains less carbonaceous material and radiolarian molds.
Partially dolomitized biomicrite
Partially dolomitized biomicrite makesup a small but significant
part of the Woodruff and has yielded good conodont faunas. The rock is
dark gray with light gray laminations.Thin section study reveals
abundant calcispheres in a matrix of carbonaceous and argillaceous
lime mud. Laminae are defined by dolomite rhombs and quartz silt.
Dolomite rhombs are scattered throughout the rock. Calcispheres are
problematic fossils generally assumed to be marine plahkton (Horowitz
and Potter, 1971).
Siliceous mudstone
Dark gray to black carbonaceous siliceous mudstone makesup a
minor portion of the Woodruff Formation exposed in the mappedarea. It
breaks into tabular chips 0.5-10 cm thick. Faint laminae are visible
on weathered surfaces. Chert forms thin beds and nodules within the mudstone.
Depositional Environment and Regional Significance
The Woodruff Formation appears to have been deposited inan outer Figure 5.
Photomicrograph of partially'dolomitized biomicrite. Note abundant calcispheres and that laminae are defined by dolomite rhombs and quartz silt. Devonian. NW; NW;section 5, T. 27 N., R. 53 E. Plane light. 18 shelf or slope environment. No diagnostic trace fossils were found.
Conodont faunas correspond to the Palmatolepid-Polygnathid biofacies of
Sandberg (1976) indicating shallow to moderately deep water. Presence of fine laminations, carbonaceous material, authigenic pyrite along with minor bioturbation indicates an aerobic-to dysaerobic bottom conditions.
The Woodruff is reported by Smith and Ketner (1975) to span most of Devonian time. However, the term should be restricted to Famennian age rocks (J.G. Johnson, oral commun.) based on evidence presented by
Murphy et al. (1982), that rocks correlative with the Woodruff in the
Roberts Mountains appear to have overlapped the allochthon during the
Famennian after an earlier phase of emplacement. In the mapped area, the Woodruff does not show the intense deformation characteristic of the Vinini Formation. This indicates that the Woodruff has not been displaced a great distance compared to displacement of the Vinini, which is consistent with the hypothesis of Murphy et al. (1982).
Autochthonous Famennian age rocks in the Cortez Mountains mapped by Gilluly and Masursky (1965) as Pilot Shale resemble the type
Woodruff (Sandberg in Johnson and Pendergast, 1981). If the Woodruff
Formation was deposited in the vicinity of the Cortez Mountains, then displacement of the Woodruff in the mapped area can be estimated to be about 15 miles (24 km), compared to a minimum estimate of 50 miles
(80 km) of displacement for the Vinini Formation in the Roberts
Mountains by Murphy (1968). 19
LONE MOUNTAIN DOLOMITE
The Lone Mountain Dolomite of the eastern shallow shelf assemblage was named by Hague (1883) and was redefined by Merriam (1940). Nolan,
Merriam, and Williams (1956) present a description and history of the nomenclature for the formation. Detailed facies mapping in the Roberts
Mountains by Winterer and Murphy (1960) demonstrated that the Lone
Mountain Dolomite is primarily composed of the reef rocks of a shelf- edge reef complex in facies relationship with basinal and reef flank rocks of the Roberts Mountains Formation.
The Lone Mountain Dolomite is exposed along a fault on the eastern margin of the mapped area, where the thickness of the unit cannot be determined. Smith and Ketner (1975) estimate thickness of the Lone
Mountain to be about 1400 feet (430 m) in the Pinyon Range.
Lone Mountain Dolomite exposed in the mapped area consists of thick bedded, very light gray finely crystalline dolomite. Fossils are sparse in the Lone Mountain Dolomite and none were found in the area mapped. Smith and Ketner (1975) report poorly preserved corals and brachiopods which indicated a Late Silurian age, they consider the Lone
Mountain Dolomite in the Pinyon Range to span from Late Silurian to
Early Devonian. Klapper and Murphy (1980) report conodonts assigned to the delta Zone (Early Devonian) from the Lone Mountain Dolomite in the
Sulphur Spring Range. The contact with the overlying Beacon Peak
Dolomite is conformable and gradational in the Pinyon and Sulphur Spring
Ranges (Smith and Ketner, 1975; Carlisle and others, 1956). 20
NEVADA GROUP
The Nevada Group belongs to the eastern shallow shelf assemblage.
It was named by King (1878) and was redefined by Merriam (1940). In the
Eureka area the Nevada was divided into five members by Nolan, Merriam,
and Williams (1956). These were raised to formation rank by Hose et al.
(1982). In the Sulphur Spring and Pinyon Ranges, Carlisle et al. (1957)
divided the Nevada into three members. In the Pinyon Range, Smith and
Ketner (1975) divided the Nevada into three members, but employed the
nomenclature. of Nolan et al. (1956). In this report, the Nevada Group
is divided into three formations, the Beacon Peak Dolomite and Oxyoke
Canyon Sandstone of Nolan et al. (1956), and the Telegraph Canyon
Formation (as "member ") of Carlisle et al. (1957). Thickness of the
group is estimated at about 3,200 feet (975 m) by Smith and Ketner
(1975).
The Nevada Group is poorly dated due to scarcity of fossils; its
age range is Early Devonian to Late Devonian (Frasnian) based on sparse
brachiopods in the Beacon Peak Dolomite (Smith and Ketner, 1975)and a
coral in the Telegraph Canyon Formation.
Beacon Peak Dolomite
The Beacon Peak Dolomite is exposed along the northeast edge of the mapped area. The lower contact is a fault so thickness cannot be determined. Smith and Ketner (1975) report a thickness of 675 feet 21
(205 m) in the Pinyon Range. The upper contact with the Oxyoke Canyon
Sandstone is gradational, the contact is placed at the change from quartz sandy dolomite to quartz arenite or sedimentary quartzite.
The Beacon Peak consists mainly of thin to thick-bedded light gray medium crystalline dolomite. Dark red stylolites are common and very abundant locally. No fossils were recognized.
Oxyoke Canyon Sandstone
The Oxyoke Canyon Sandstone forms prominent ledges and cliffs in the mapped area. Thickness averages about 400 feet (120 m), although thickness is less than 50 feet (15 m) on the south slope of hill 7072 in section 18, T. 28 N., R. 53 E. (Kendall, 1975; Smith and Ketner,
1978). The upper contact with the Telegraph Canyon Formation is gradational.
Oxyoke Canyon Sandstone consists of white, pink, and gray dolomitic quartz arenite and sedimentary quartzite. It is thin to thick bedded and crossbedded on a small scale.
Telegraph Canyon Formation
The Telegraph Canyon Formation is composed mainly of dolomite.
Smith and Ketner (1975) report a thickness of 2,065 feet (625 m).
Fossils are scarce in the Telegraph Canyon Formation. Corals collected near Dry Creek, near the top of the formation were identified by W.A.
Oliver (written commun., 1982) and belong to the genus Smithiphyllum and closely resemble S. kindlei Pedder, 1965. The genus is only known 22 from the Frasnian (Oliver, written commun., 1982).
Regionally, the Telegraph Canyon Formation is overlain by the
Devils Gate Limestone, which is overlain by the Pilot Shale. In the mapped area and adjacent area immediately to the south the Pilot Shale lies directly on the Telegraph Canyon Formation and the Devils Gate
Limestone is not recognized. This problematic stratigraphic relation- ship is open to speculation. One possible solution is that the Devils
Gate Limestone has been subject to secondary dolomitization, which would have destroyed primary features such as fossils and sedimentary structures, leaving it indistinguishable from the Telegraph Canyon
Formation. Another possibility is that of an intertongueing facies relationship between the Devils Gate Limestone and Telegraph Canyon
Formation such that the Devils Gate was not deposited in the mapped area (Johnson and Pendergast, 1981). The actual contact with the overlying Pilot Shale is masked by silicification and appears to be depositional.
Lithology
This formation consists of gray to brown medium crystalline dolo- mite. Laminations are visible on weathered surfaces in some locations.
The dolomite is mottled in places. Thin section study reveals that most of the primary features have been obliterated by dolomitization. The dolomite forms a mosaic texture of anhedral dolomite with large rhombs very common. Small amounts of detrital quartz are present. 23
Silicification
Jasperoid occurs in the Telegraph Canyon Formation as small irregu- lar bodies, it is especially common along the contact with the overlying
Pilot Shale. The jasperoid is dark red to brown, fine grained chert- like rock. Veins of barite occur in and around the jasperoid bodies.
In thin section (Fig. 6) finely crystalline quartz has replaced dolomite.
Detrital quartz grains have developed large irregular syntaxial over- growths. Veins of barite consist of large bladed crystals up to 7 mm.
Lovering (1972) describes jasperoid as an epigenetic replacement of limestone and dolomite by cryptocrystalline quartz, a product of hydrothermal alteration. In the Taylor mining district near Ely,
Nevada Drewes (1962) observed that silicification occurred in the
Guilmette Formation along the contact with the overlying Pilot Shale.
He noted that silicification was primarily restricted to stratigraphic contacts where impermeable shaly rocks cap permeable carbonate rocks and along normal faults.
The Pilot Shale probably formed an impermeable cap rock which trapped silica-rich hydrothermal fluids, resulting in the development of jasperoid along much of the upper contact of the Telegraph Canyon
Formation. This silicified zone has been misinterpreted as a thrust fault by Carlisle and Nelson (unpub. map) and Smith and Ketner (1978). Figure 6.
Photomicrograph of jasperoid from below theupper contact with the Pilot Shale. Note fine-grained quartz replacing dolomite. NE4 NW1/4 section 24, T. 27 N., R. 52 E. Crossed nicols. 25
PILOT SHALE
General Statement
The Pilot Shale was named by Spencer (1917) for exposures in the
Ely region of eastern Nevada. Nolan et al. (1956) recognized two members in the Eureka area, a lower member consisting of calcareous shale and shaly limestone and an upper member consisting of carbonaceous calcareous shale. According to Poole (1974) the Pilot Shale was deposited in an incipient flysch basin developed in late Frasnian to Famennian time due to initial pulses of the Antler orogeny.
Smith and Ketner (1968, 1978) and Carlisle and Nelson (ms) interpreted this unit in the mapped area as part of the allochthonous Woodruff
Formation and allochthonous unnamed Devonian shale respectively. Field evidence presented in this report shows that this unit is autochthonous and should be assigned to the Pilot Shale on the basis of lithology and stratigraphic position. In the mapped area, two members can be distin- guished in the Pilot where exposures are good. The lower member consists of grayish orange to pink shaly quartz-silty dolomite. The upper member consists of black carbonaceous shaly dolomite. Large areas of the Pilot
Shale have been silicified.
Thickness and Contact Relations
The Pilot Shale is about 200 feet (60 m) thick in the southern part 26 of the mapped area and thins toward the west and north where it is absent due to erosion and non-deposition. The lower contact with under- lying Nevada Group rocks is poorly exposed and is obscured by silicifi- cation in many places. There is no evidence of deformation near the contact. Bedding plane attitudes between the underlying Nevada Group and-Pilot are concordant everywhere they were mapped. On the basis of these observations the contact is interpreted as depositional and not a thrust fault. The upper contact with the overlying Dale Canyon Formation is unconformable.
Age
The Pilot Shale is poorly dated in the mapped area. Three conodont collections (see appendix) from the lower member yielded faunas assigned to the marginifera-Lower velifer Zones of the Famennian (Late
Devonian). No conodonts were recovered from the upper member.
Sandberg (1979) reports an age span of late Frasnian to Kinderhookian time for three members of the Pilot Shale in the Great Basin region.
Lithology
Lower member
The lower member of the Pilot Shale consists of grayish orange to reddish purple, laminated quartz-silty dolomite. Thin section analysis shows that this member consists of sub-rounded to angular quartz silt Figure 7.
Photomicrograph of laminated quartz-silty dolomite. Note dolomite rhombs and angular quartz silt.
Lower member, Pilot Shale. Devonian. NI414 NE1/4 section 6, T. 27 N., R. 53 E. Plane light. 28
(5 to 15%) set in a finely crystalline dolomite matrix. Dolomite grains
range in size from 0.02 to 0.004 mm and are mostly anhedral with rhombs common. Carbonaceous and argillaceous material along with authigenic pyrite make up a minor portion of the rock. Laminae are defined by concentrations of coarser dolomite and quartz silt. The dolomite is replacement in origin; its cloudy and dirty texture suggests that it
was originally deposited as an argillaceous lime mud.
Upper member
The upper member of the Pilot Shale consists of laminated black carbonaceous shaly dolomite. In thin section, this rock is seen to be a finely crystalline dolomite with abundant argillaceous and carbonaceous material. Minor constituents include quartz silt, radiolarian molds, and authigenic pyrite. The dolomite is finer than that of the lower member, ranging in size from 0.01 to 0.002 mm and is mostly anhedral with some rhombs. Laminae are defined by concentrations of coarser dolomite. The origin of the dolomite is similar to that in the lower member.
Silicified Shale
Silicification is widespread in the Pilot Shale. The silicified shale is a hard chert-like rock, commonly light gray to white with dark red, lavender, and pink liesegang rings and bands. The rock has lost its original shaly fissility and fractures irregularly along bedding planes. In thin section, the dolomite has been completely replaced by 29
Figure 8.
Photomicrograph of laminated carbonaceous shaly dolomite. Note that laminae are defined by concentration of coarser dolomite and quartz silt. Upper member, Pilot Shale. Devonian. NW1/4 SE; section 6, T. 27 N., R. 53 E. Plane light. 30
Figure 9.
Silicified Pilot Shale (Devonian), near lower contact. Note bedding and lack of small scale deformation. NE4 NW1/4 section 24, T. 27 N., R. 52 E. 31
... a , .eui.v. .. . . 'i.- ... ' %,',. Oh . :, -r-., -wed, - 17-,.. e-, ..L. t".. .
,... ,s. --. 4.-' 1.,,,- $ ,I! *Si , -41P14,:-1,-,:a .Y...... - .0)::...... 10.--, . , - . 4*-3). i.,,, .., ..'....:1::-'--. , ... N,.: ;,.;:. ,' % ...... a .. ,-0...$.Pft ;." .. . fir*IP .- .... to:
WA, '0..'4.. APAKI., . il::.: V., , .1. - 16. %. ';', ..' ,I, 4:. 4 -..t.,-.. tAt..-.. -1.... *:i.o..., 111. 4tslit IV"' . e : ..- .. "----"ft'''' --. P-.,,,,-truk!. or ...i. Iv.- t 7.6 4...:...t. ...,,. .. -. .-. . '.44'' *44 . '; 20'--,:1401 ,".. '4:".. 4.de .-p was..;;417. ir, ...j."" .1. . :Zrit... .,..V1 alt 4- -.: $ : ,t.,,,,.. .:...st ohi`t 7... : . , , e ,,,..
ONE,
Figure 10.
Photomicrograph of silicified shale. Note that clay minerals have been altered to mica, cryptocrystalline silica has replaced carbonates. Quartz silt has not been affected. Devonian. SE1/4 N1414 section 16, T. 27 N., R. 53 E. Crossed nicols. 32
cryptocrystalline silica. Clay minerals have been altered to sericite.
Original quartz silt has not been affected by the silicification.
Depositional Environment
The Pilot Shale was deposited in an incipient flysch basin on the
continental shelf (Poole, 1974); actual depths of deposition cannot be
determined. No trace fossils or macrofauna where found. Conodont
faunas correspond to the Palmatolepid- Polygnathid biofacies of
Sandberg (1976) which indicates shallow to moderately deep-water. Lack
of bioturbation along with abundant carbonaceous material and authigenic
pyrite indicate anaerobic bottom conditions. Although most of the Pilot
is now dolomite, it was probably originally deposited as an argillaceous micritic sediment settling out of suspension from a turbid layer
introduced by distant turbidity currents.
Regional Significance
Deposition in the Pilot protoflysch basin marked the beginning of the Antler orogeny (Poole, 1974). Deposition began during the A. triangularis Zone(mid Frasnian)near thecenter of thebasin and spread outward (Sandberg and Poole, 1977). At Devils Gate, west of Eureka,
Sandberg and Poole (1977) recognize evidence of deepening along the western rim of the Pilot basin. Here, the Devils Gate Limestone grades upward from shallow water biohermal and biostromal limestones into deeper water slope deposits consisting of debris flow and turbiditic limestones that intertongue with the Pilot Shale. This facies 33 relationship is not observed in the mapped area; if it exists it is
probably obscured by dolomitization.
Conodont collections from a measured section of Pilot Shale in the adjacent Diamond Mountains by Sandberg and Poole (1977) indicate a starved interval between the A. triangularis Zone at the top of the
Devils Gate Limestone and Middle crepida Zone in the Pilot Shale. A similar relationship probably exists in the mapped area where beds of the marginifera-Lower velifer Zonesare found approximately 6-10 m above the base of the Pilot. 34
DALE CANYON FORMATION
General Statement
The Dale Canyon Formation was named by Nolan et al. (1974) for exposures of interbedded shale, sandstone, and conglomerate of early
Mississippian age in the Eureka region. In the area mapped, rocks of
the Dale Canyon Formation were formerly assigned to the Chainman Shale by Smith and Ketner (1978) and Chainman Shale - Diamond Peak Formation undivided by Carlisle and Nelson (ms). The Dale Canyon Formation in the mapped area is correlated with the type Dale Canyon by stratigraphic position, paleogeographic position, lithologic similarity, andage.
Conodont collections from the type locality (Sandberg in Johnson and
Pendergast, 1981) and the mapped area indicate an age of late
Kinderhookian to early Osagean.
The Dale Canyon Formation in the Pinyon Range is interpreted here as basin slope and submarine fan facies deposited in the Antler foreland basin (Poole, 1974). This interpretation follows that of Harbaugh and
Dickinson (1981) for essentially the same unit in the adjacent Diamond
Mountains.
The Mississippian palinspastic correlation chart compiled by
Poole and Sandberg (Fig. 2, 1977) shows clearly that "true" Chainman
Shale represents a younger (Late Osagean to Chesterian age) and more distal facies generally deposited farther east in the foreland basin than the older, proximal Dale Canyon Formation. 35
Age
Four conodont collections from the Dale Canyon Formation (twoare
from Carlisle and Nelson, unpub. data) appear to belong to the
isosticha-Upper crenulata Zone (Sandberg, 1979) which is interpreted
as latest Kinderhookian, but may range into the Osagean (G. Klapper in
Johnson and Pendergast, 1981). This zonal assignment is valid only if
Siphonodella spp. are not reworked. If Siphonodella spp. are reworked,
then the age determination would be based on the range of G. punctatus,
which is late Kinderhookian to early Osagean (G. Klapper in Johnson
and Pendergast, 1981). Famennian Palmatolepis spp. present in the
collections have been reworked.
Contact Relations and Thickness
The lower contact with the Pilot Shale and Telegraph Canyon
Formation is disconformable. Along Dry Creek, a large channel has been
cut into the Pilot Shale and infilled with coarse Dale Canyon debris
flow deposits (Fig.11). Large clasts eroded from the Pilot Shale have
been included in the debris flow deposits. Bedding plane attitudes observed in the Pilot Shale and Dale Canyon Formation along Dry Creek vary less than 5 degrees.
Thickness of the Dale Canyon Formation cannot be determined
because the upper contact is a thrust or normal fault everywhere in the mapped area. Minimum thickness is estimated at about 1,000 feet (305 m).
Rocks near the thrust contact with the overlying Woodruff Formation have been brecciated. 36
Facies Interpretation
Poole (1974) showed that early Mississippian orogenic clastics
deposited in the Antler flysch trough were emplaced by various types
of sediment gravity flows, mainly turbidity currents forming submarine
fan complexes. Harbaugh and Dickinson (1981) recognize and map in
detail basin slope and submarine fan facies in the lower part of their
"Chainman-Diamond Peak sequence" in the Diamond Mountains, which is
essentially the same unit as the Dale Canyon Formation. They recognize
a retrogradational (transgressive) sequence of basin slope facies
overlain by inner-fan facies which is overlain by middle-fan facies.
A similar relationship is observed in the mappedarea where basin slope
facies are overlain by inner-fan facies. Nerietes trace fossil
assemblages are reported by Poole (1974) and Harbaugh and Dickinson
(1981) and indicate bathyal depths.
Facies analyses presented here follow the interpretative scheme
of Mutti and Ricci-Lucchi (1972) and Walker and Mutti (1973).
Basin Slope Facies
Basin slope facies form the base of the Dale Canyon Formation.
This unit consists mainly of black carbonaceous shale with interbeds
of fine-rained sandstone, 2-4 cm thick, which belong to facies G and E
of Walker and Mutti (1973). Large channels, 100to 150 m wide, cut
through the shale and are filled with pebbly sandstone, massivecoarse
sandstone, and conglomerate consisting of angular chert cobbles and boulders in a coarse sand matrix. A large block of Telegraph Canyon 37
Figure 11.
Channel filled with coarse sandstone scoured into shale. Basin slope facies of the Dale Canyon Formation. NW1/4 SE1/4 section 6, T. 27 N., R. 53 E. 38
Formation dolomite which yielded a Frasnian age conodont fauna (sample RV-
158; appendix) was found in a channel fill deposit encased in a matrix of coarse sand. The channel fill units represent facies Ai, A3 and B2 of
Walker and Mutti (1973). These units were probably emplaced by debris flow and grain flow mechanisms described by Middleton and Hampton (1973).
Inner Fan Facies
The inner fan facies consists of rythmically bedded sandstone and shale with some lenticular beds of pebbly sandstone. The contact with the basin slope facies is gradational and interfingering. Sandstone beds are 30 to 50 cm thick and commonly massive to poorly laminated.
Graded bedding is uncommon and poorly developed. Lower contacts are scoured with abundant flute and groove casts. Upper contacts are sharp and planar. Bouma sequences are rarely seen. Sand td shale ratios range from 1:1 to 1:3. Sandstone beds up to 3 m thick are clearly amalgamated and are composed of several individual flows.
The sandstones represent facies B2 of Walker and Mutti (1973). The interpreted mode of emplacement is by grain flow.
Lithology
Chert-arenite
Most of the sandstones of the Dale Canyon Formationare chert arenites. They are medium to coarse grained gray to greenish-gray with surfaces stained yellowish-brown by iron hydroxides. Most of these 39
Figure 12.
Amalgamated massive sandstone beds. Note sharp contacts with interbeds of shale. Facies B2 of Walker and Mutti (1973). Scale is 40 cm. NE4 NW4 section 6, T. 27 N., R. 53 E. 40
Figure 13.
Unconformable contact between the Pilot Shale and Dale Canyon Formation. A channel scoured into the Pilot Shale has been infilled by a coarse debris flow deposit which includes clasts of chert and Pilot Shale. NW; SE; section 6, T. 27 N., R. 53 E. 41 sandstones are massive with laminations common; graded bedding is occasionally observed. Modal analysis of six chert-arenites shows that framework composition ranges from 29 to 76% for quartz, 18 to 60% for chert, and 3 to 11% for fine-grained argillaceous rock fragments. The rocks are texturally submature with moderate sorting and grains are subangular to rounded. A bimodal texture is often seen with chert generally coarser and more angular than quartz which is generally finer and more rounded. This relationship is probably caused by the quartz being multicycle and chert grains are first cycle. The cement is mostly silica with syntaxial overgrowths on quartz grains common.
Calcite cement is occasionally found in finer grained sandstones.
Pebbly chert-wacke
Pebbly chert-wacke forms a minor part of the formation and occurs as lenticular channel fill complexes. The rock is dark olive gray with pebbles of green, gray, and black chert and gray quartzite in a matrix of sand, silt, and clay. Thin section study shows that the rock consists of about 30% chert pebbles, 50% sand consisting of chert and quartz and 20% fine silt and clay. The rock is texturally immature, very poorly sorted, grains are angular to rounded. The pebbly chert-wacke was probably emplaced by debris flow.
Fine-grained rocks
Dark gray shale and siltstone form interbeds between sandstone beds.
Fissility varies from shaly to papery. Quartz silt is abundant along Figure 14.
Photomicrograph of chert-arenite. Note the bimodal grain size distribution between the large angular chert clast and smaller rounded quartz grains. Mississippian. NW' NW1/4 section 30, T. 28 N., R. 53 E. Crossed nicols. 43
Figure 15.
Photomicrograph of pebbly chert-wacke. Note large angular to subrounded chert grains (brownish-yellow) and smaller quartz grains (white) in a fine argillaceous matrix. Mississippian. NE; NWk section 6, T. 27 N., R. 53 E. Plane light. 44
Figure 16.
Photomicrograph of carbonaceous spicular biomicrite. Note abundant sponge spicules and calcispheres. Mississippian. NE1/4 NE1/4 section 7, T. 27 N., R. 53 E. Plane light. 45
Figure 17.
Photomicrograph of coarse-grained debris flow conglomerate. Note chert grains cemented by crystalline quartz. Mississippian. NV& SE4 section 6, T. 27 N., R. 53 E. Crossed nicols. 46 with carbonaceous material. Rarely seen are thin beds of hemipelagic lime mudstone. These rocks are significant because they yield conodont faunas. Thin section analysis shows that these rocks consist of abundant sponge spicules and calcispheres in an argillaceous and carbonaceous micritic matrix. They are classified as spicular biomicrites using Folk's classification (1962, 1980).
Coarse-grained debris flow deposits
Coarse-grained debris flow deposits form channel fill complexes near the base of the formation. This unit differs from the pebbly chert-wackes in that it consists of cobble-and boulder-size clasts of angular chert in a matrix of coarse sand. Thin section study reveals that fine matrix material is nearly absent. The coarse sand matrix is mainly chert and is cemented by finely crystalline quartz.
Regional Significance
The Dale Canyon Formation was deposited in the flysch trough that developed adjacent to the Antler orogenic highlands during late
Kinderhookian time (Poole, 1974). Composition of the Dale Canyon indicates a provenance entirely within the allochthon (Poole, 1974;
Harbaugh and Dickinson, 1981). Paleocurrent data in the Pinyon Range and Diamond Mountains indicate a northwest to southeast transport direction (Smith and Ketner, 1975; Harbaugh and Dickinson, 1981). The
Dale Canyon Formation represents the earliest detritus shed eastward into the flysch trough.of the Pinyon Range from the rising Antler orogenic 47 highland. However, paleogeographic data provided by Johnson and
Pendergast (1981) show that the earliest deposition in the flysch trough occurred west of the mapped area and consisted of hemipelagic
Webb Formation and carbonate detritus shed from a shallow water environment that developed on the rising allochthon (Johnson, oral commun.). 48
INTRUSIVE ROCKS
Two small dikes consisting of rhyolite porphyry occur in the mapped area. The rock is light-colored with large phenocrysts of quartz, sanidine, plagioclase, and hornblende in a felsitic groundmass.
Smith and Ketner (1976) report similar dikes in the Pinyon Range.
They believe such dikes are relateded to a rhyolite porphry stock intruded near Bullion, on the east side of the Pinyon Range, as they are of identical lithology and composition. Armstrong (1970) reports a radiometric age of 36 ± 1.3 m.y. (Oligocene) for the rhyolite porphyry stock at Bullion.
Oligocene intrusive activity is a probable source for hydrothermal solutions that resulted in silicification and mineralization of some of the Paleozoic units. Mabey (in Smith and Ketner, 1976) interprets magnetic anomalies to indicate buried intrusive rocks in the Pinyon
Range. An anomaly east of the southern part of the mapped area corresponds to a large zone of silicification in the Pilot Shale. 49
LANDSLIDE DEPOSITS
Normal faulting during the Tertiary produced steep unstable fault line scarps resulting in downslope movement of large coherent landslide' blocks. Landslide blocks in the mapped area consist mainly of Oxyoke
Canyon Sandstone and Beacon Peak Dolomite. Landslide blocks resting on the allochthonous Woodruff Formation have been misinterpreted as structural windows by Smith and Ketner (1978) and Carlisle and Nelson
(ms). A landslide block north of Pony Creek lies partially on the
Quaternary alluvium and thus indicates a similar age for the downslope movement. 50
STRUCTURE
Thrust faulting
The Woodruff, Vinini, and Roberts Mountains Formations were emplaced as part of the Roberts Mountains allochthon during the Antler orogeny. The Woodruff Formation forms the base of the allochthon and structurally overlies the autochthonous Dale Canyon Formation. The
Vinini overlies the Woodruff in thrust contact with slices of the
Roberts Mountains Formation occurring in between at plaCes (Smith and
Ketner, 1978). Conodont collections from the autochthonous Dale Canyon
Formation indicate that the allochthon was emplaced during or after late isosticha-Upper crenulata Zone time (late Kinderhookian or possibly early Osagean time).
Minimum displacement of the Vinini Formation in the Roberts
Mountains has been estimated at 50 miles (80 km) by Murphy (1968).
Displacement of the Woodruff as described in a previous section in this report is estimated at up to 15 miles (24 km).
The Dry Creek Fault
Thorman and Ketner (1979) propose the Dry Creek fault, northwest-trending left-slip fault, one of three strike-slip faults they propose for northeastern Nevada. The proposed Dry Creek fault projects through the mapped area in the vicinity of Dry Creek. The 51
evidence they cite in support of their hypothesis is apparent offset of Paleozoic sedimentary facies belts. Stevens (1981) argues against such strike-slip faults, citing large differences in the amount of offset of Paleozoic sedimentary facies of different ages.
Ketner (written commun. to J.G. Johnson, 1981) explains that the expression of the Dry Creek fault between the Pinyon and Sulphur Spring
Ranges is a plexus of faults trending north-northwest each with a small amount of strike-slip movement. In the mapped area there are no significant data supporting the presence of a Dry Creek fault. The autochthonous sequence shows no such offset of facies along the entire length of the area. Aerial photographs and Landsat imagery do not reveal any lineations that can be attributed to the Dry Creek Fault.
High angle faults appear to be normal faults with no evidence for the strike-slip displacement suggested by Ketner. It is concluded here that there is no availableevidence to support the proposed Dry Creek fault.
Normal Faulting
Field evidence indicates two phases of high angle normal faulting in the mapped area. The first episode developed north to northwest- trending normal faults of major displacement which produced the basin and range topography of the region. A younger episode of normal faulting produced northeast-trending normal faults of generally less displacement which offset the major north and northwest-trending faults. Interpre- tation of some of the normal faults in the mapped area differs from that of Smith and Ketner (1968, 1978). Observed dip of fault planesand drag indicate that two normal faults mapped by Smith and Ketner (1968, 1978) 52
are actually opposite in terms of dip and displacement (Fig. 18, p. 56;
P1. 2). A Tertiary age for normal faulting is generally accepted in the Great Basin region.
Folding
A large north-northwest-trending syncline which plunges north is located near the center of the mapped area. The extent of the syncline is unclear because it is truncated by Tertiary age normal faults. Field relations in the Pinyon Range as mapped by Smith and
Ketner (1978) indicated the period of folding occurred after emplacement of the allochthon and before Tertiary age normal faulting. 53
GEOLOGIC HISTORY
During latest Precambrian to Middle Devonian time, deposition in the
southern Pinyon Range occurred in a miogeoclinal shallow shelf environ-
ment. The area immediately to the west was characterized by deep-water
outer shelf and oceanic continential slope sediments.
Stable continental margin conditions came to a close with the onset of the Antler orogeny during the Late Devonian (Johnson and
Pendergast, 1981). The Pilot protoflysch basin developed within the shelf, the result of initial pulses of the Antler orogeny (Poole, 1974;
Poole and Sandberg, 1977). A westward-dipping subduction zone formed to the west, developing an accretionary wedge which later became the allochthon. Incipient subduction of continental crust during late
Kinderhookian and Osagean time resulted in the obduction of the allochthon composed of telescoped oceanic sediments onto the continental crust (Johnson and Pendergast, 1981; Speed and Sleep, 1982).
Down-warping of the continental crust during incipient subduction probably formed the flysch trough (Johnson and Pendergast, 1981).
Initial sediments deposited in the flysch trough west of the mapped area were chert and micritic and argillaceous sedimentoverlain by limestone turbidites derived from the top of the rising allochthon to the west
(Johnson, oral commun.). In the mapped area, deposition in the flysch trough formed a submarine fan complex consisting of siliciclastic sediments shed from the uplifted allochthon.
During the final stages of the Antler orogeny the allochthon was 54 emplaced over flysch trough deposits in the Pinyon Range by the end of isosticha-Upper crenulata Zone time. 55
SUMMARY
A purpose of this investigation was the testing of hypotheses.
Smith and Ketner (1978) and Carl isle and. Nelson (ms) mapped al lochthonous rocks as overlying the Devonian Nevada Group and overlapped by the
Chainman Shale or Chainman-Diamond Peak Formation undivided. However, evidence presented in this report shows that the Nevada Group is overlain depositionally by the Pilot Shale and Dale Canyon Formation
("Chainman and Chainman-Diamond Peak"). The allochthon structurally overlies the Dale Canyon Formation. This observation is consistent with the interpretation of Johnson and Pendergast (1981). Figure 18 illustrates the two contrasting interpretations. Quaternary and
Tertiary features such as hydrothermal alteration along impermeable contacts and landsliding have been previously misinterpreted as evidence for major thrust faulting.
Smith and Ketner (1968) provided evidence for dating the final emplacement of the allochthon in the Pinyon Range. They reported that the Early Mississippian Webb Formation overlapped the toe of the allochthon and rested unconformably on both the autochthonous Devils
Gate Limestone and the allochthon. However, the same authors have recently questioned their previous conclusions and believe that a post-Paleozoic age for emplacement of the allochthon should not be ruled out (Ketner and Smith, 1982). Large angular clasts of chert which resemble the Vinini Formation in debris flow deposits of the
Dale Canyon Formation, exposed in the mapped area strongly suggest 56
6000 ft
4000 EXPLANATION
2000 WOODRUFF FM.
Smith and Ketner (1968)
DALE CANYON FM.
PILOT SHALE
Dn
NEVADA GROUP
DSI
LONE MT. DOLOMITE
ThisReport
0 0.5 1 MILE
I I 1
Figure 18. Cross sections showing the interpretationof Smith and Ketner (1968) and the interpretationof this report. (Location corresponds approximately to sectionB-B' on Plates 1 and 2.) 57 that the allochthon was emplaced adjacent to the flysch trough no later than Early Mississippian time.
No evidence was found to support the existence of the Dry Creek fault, a left-lateral strike-slip fault proposed by Thorman and
Ketner (1979). 58
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CONODONT COLLECTIONS AND LOCALITIES
The following nine conodont collections were identified by
Gilbert Klapper, 1982. Two collections are from unpublished data of
Carlisle and Nelson and were identified by W.H. Hass and J.W. Huddle.
Conodont localities are plotted on Plate 1.
Nevada Group Telegraph Canyon Formation
Sample: RV-158
Location: Approx. 1500 ft. S, 600 ft. W of NE cor. of sec. 6, T. 27 N.,
R. 53 E., This sample was collected from a large block of
Telegraph Canyon Formation dolomite, in a channel fill
complex in the Dale Canyon Formation
Icriodus subterminus Youngquist Polygnathus angustidiscus Youngquist indet. ramiform elements
Age: Frasnian
Woodruff Formation
Sample: RV-122
Location: Approx. 1200 ft. S, 600 ft. E of NW cor. of sec. 5, T. 27
N., R. 53 E. 63
Palmatolepis subperlobata Branson & Mehl Pa. cf. Pa. regularis Cooper Pa. minuta minuta B. & M. Pa. minuta ?Pa. termini Sannemann [according to W. Ziegler (May 19, '82)] Pa. n. sp. A of Helms (1963, text-fig. 2, fig. 40) Pa. n. sp. Pa. tenuipunctata Sannemann Pa. subgracilis Bischoff Pa. wolskajae Ovnatanova [see Catalogue, v. III, p. 413] Pa. sp. indet. Polygnathus glaber glaber Ulrich & Bassler P. sp. indet. Pelekysgnathus sp. "Spathognathodus" sp. indet. ramiform elements
Age: crepida Zone, probably Upper crepida Zone
Sample: RV-154
Location: Approx. 250 ft. N, 160 ft. W of SE cor. of sec. 6, T. 27 N.,
R. 53 E.
Palmatolepis gracilis gracilis Branson & Mehl Pa. gracilis sigmoidalis Ziegler Pa. rugosa rugosa Branson & Mehl Pa. sp. indet. Pa. perlobata schindewolfi Muller P. sp. [possibly a small P. styriacus, according to Willi Ziegler (May 19, '82)]. P. sp. indet. "Spathognathodus" bohlenanus Helms "S." sp. indet. indet. ramiform elements
Age: Upper styriacus Zone (according to ranges in Ziegler, in
Klapper & Ziegler, 1979, fig. 6).
Pilot Shale
Sample: RV-1
Location: Approx. 1300 ft. S, 2000 ft. W of NE cor. of Sec. 24, T. 27
N., R. 52 E., southwest of mapped area near Union Summit Road. 64
Palmatolepis glabra Ulrich & Bassler Pa. marginifera Helms Pa. sp. indet. indet. ramiform elements
Age: marginifera-Lower velifer Zone.
Pa. glabra ranges higher than shown by Ziegler (in Klapper and
Ziegler, 1979, Fig. 6).
Sample: RV-103
Location: Approx. 2000 ft. S, 1600 ft. W of NE cor. of sec. 8, T. 27
N., R. 53 E.
Palmatolepis alabra Pa. marginifera Pa. minuta Branson & Mehl Pa. sp. indet. Polygnathus sp. indet.
Age: marginifera-Lower velifer Zone.
Sample: RV-113
Location: Approx. 700 ft. S, 1500 ft. W of NW cor. of sec. 30, T.
28 N., R. 53 E.
Palmatolepis sp. indet indet. ramiform elements indet. platform elements
Age: Zonally indeterminate, Upper Devonian
Sample: RV-162
Location: Approx. 160 ft. S, 3100 ft. N. of NW cor. of sec. 5, T. 27
N., R. 53 E.
Palmatolepis marginifera Pa. glabra group Polygnathus sp. indet. indet. ramiform elements indet. simple cone 65
Age: marginifera-Lower velifer Zone.
Dale Canyon Formation
Sample: RV-12
Location: Approx. 1400 ft. S, 1600 ft. E of NW cor. of sec. 17, T.
27 N., R. 53 E.
Gnathodus punctatus (Cooper) G. sp. indet. Siphonodella obsoleta Hass S. quadruplicata Branson & Mehl S. sp. indet. Polygnathus symmetricus Branson P. inornatus Branson P. sp. P. communis communis .Branson & Mehl Pseudopolypathus primus Branson & Mehl Pa. glabra Pa. marginifera Pa. sp. indet. indet. ramiform elements
Age: The fauna of RV-12 appears to belong to the isosticha-Upper
crenulata Zone (Sandberg, 1979) which is interpreted as
latest Kinderhookian, but may range into the Osagean (G. Klapper
in Johnson and Pendergast, 1981). This zonal assignment is
valid only if Siphonodella spp. are not reworked. If
Siphonodella spp. are reworked, then the age determination would
be based on the range of G. punctatus, which is upper Kinderhookian
to lower Osagean (G. Klapper in Johnson and Pendergast, 1981).
Famennian Palmatolepis spp. present in the collection have been
reworked. 66
Sample: RV-118
Location: Approx. 500 ft. S, 1000 ft. W of NE cor. of sec. 7, T.
27 N., R. 53 E.
Gnathodus punctatus G. sp. Siphonodella obsoleta S. sp. indet Polygnathus communis communis
Age: As RV-12
Sample: 7
Location: Approx. 500 ft. NNW of BM 6060, sec. 8, T. 27 N., R. 53 E.
This collection is from unpublished data of Carlisle and
Nelson and was identified by J.W. Huddle, 1963.
Bryantodus sp. Gnathodus punctatus Hindeodella sp. Palmatolepis distorta Branson & Mehl Pa. perlobataUTFTEF& Bassler Polygnathus communis P. sp. Pseudopolygnathus sp. Siphonodella n. sp. A S. n. sp. B S n. sp. C S. sp.
Age: The age of this fauna is Early Mississippian. Note reworked
Famennian Palmatolepis.
Sample: 13
Location: Approx. 150 ft. S, 300 ft. E of NW cor. of sec. 17, T. 21
N., R. 53 E.
This collection is from unpublished data of Carlisle and
Nelson and was identified by W.H. Hass, 1955. 67
Siphonodella duplicata Branson & Mehl Polygnathus communis Branson & Mehl Pseudopolygnathus cf. kr:Lna Branson & Mehl Neoprioniodus sp. Palmatolepis cf. ?labra Gnathodus cf. delicatus Branson & Mehl G. sp. Spathognathus sp. Trichonodella sp. Hibbardella sp. Hindeodella sp.
Age: As 7