Devonian and Mississippian 

Rocks and the Date of the 

Roberts Mountains Thrust 

In the Carlin-Pinon Range 

Area, Nevada

GEOLOGICAL SURVEY BULLETIN 1251-1

Prepared in cooperation with the 

Nevada Bureau of Mines

Devonian and Mississippian 

Rocks and the Date of the 

Roberts Mountains Thrust 

In the Carlin-Pinon Range 

Area, Nevada

By J. FRED SMITH, JR., and KEITH B. KETNER

CONTRIBUTIONS TO GENERAL GEOLOGY

GEOLOGICAL SURVEY BULLETIN 1251-1

Prepared in cooperation with the 

Nevada Bureau of Mines

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1968
UNITED STATES DEPARTMENT OF THE INTERIOR 

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

For sale by the Superintendent of Documents, U.S. Government Printing Office 

Washington, D.C. 20402 - Price 15 cents (paper cover)
CONTENTS

Page

Abstract__________________________________________ ____________ I 1

Introduction.._-----_-____--__-_______-_---__-----_----___----_--- 1

Devonian System__________________________________________________ 3

Carbonate (eastern) assemblage rocks__________-_______-_______-_ 3

Nevada Formation and Devils Gate Limestone________________ 3

Siliceous (western) assemblage rocks.___________ ___________ 4

Woodruff Formation__-_________--_--_---_--_-___-_------_- 4

Transitional-assemblage rocks._________-_________-_______---__-- 7

Mississippian System._____________________________________________ 8

Overlap assemblage.______________ ___________________________ 8

Webb Formation____-_______--__-_----_---_-_---_------___ 8

Chainman Shale and Diamond Peak Formation._____ _____ 12

Argillite unit of Lee Canyon.___________-______-__-_--_---__ 14

Present relative positions of the depositional units _____________________ 15

Date of the Roberts Mountains thrust in the Carlin-Pinon Range area___ 15

References.--.-__-___-_______-_______-___---------_----_--_------_ 17

ILLUSTRATIONS

Page 

FIGURE 1. Index map of part of northeastern Nevada.________________ 12

2. Chart showing Devonian and Mississippian rocks__________ 3

3. Map showing generalized outcrop areas of Paleozoic rocks____ 4

4. Generalized structure sections showing evidence for dating

the Roberts Mountains thrust___________ ___________ 16

TABLES

Page 

TABLE 1. Chemical analyses of samples of siliceous mudstone from the

Webb Formation, Carlin-Pinon Range area, Nevada------ 19

2. Conodonts from the Webb Formation...___________________ 11

in

CONTRIBUTIONS TO GENERAL GEOLOGY

DEVONIAN AND MISSISSIPPIAN ROCKS AND THE DATE

OF THE ROBERTS MOUNTAINS THRUST IN THE

CARLIN-PINON RANGE AREA, NEVADA

By J. FRED SMITH, JR., and KEITH B. KETNER

ABSTRACT

Devonian and Mississippian rocks of the Oarlin-Pinon Range area are separated 

into eight principal units. Two Devonian units make up the carbonate (eastern) 

assemblage, one the siliceous (western) assemblage and one the transitional 

assemblage. Mississippian units compose an overlap assemblage that is unconf ormable on the lower Paleozoic rocks.

Mississippian rocks overlie unconformably Devonian and older rocks of both 

siliceous and carbonate assemblages, and this relation serves to date the Roberts 

Mountains thrust in this area. The youngest strata involved in the thrusting 

are of late Late Devonian age. The oldest strata that rest tmconformably on both 

lower and upper plate rocks of the thrust are at least as old as late Kinderhook 

or Early Mississippian age. Movement of upper plate rocks of the Roberts Mountains thrust into the Carlin-Pinon Range area, then, probably started in late 

Late Devonian time and must have been concluded no later than late Kinderhook 

time of the Early Mississippian.

INTRODUCTION

Lower Paleozoic rocks in north-central Nevada are separable into 

three broad groupings: a carbonate (eastern) assemblage deposited 

in the Cordilleran miogeosyncline; a siliceous (western) assemblage 

deposited in a eugeosyncline to the west; and a transitional assemblage 

that contains lithologic types found in both of the other two. These 

assemblages of sedimentary rocks were brought together by movement 

along the Roberts Mountains thrust (Merriam and Anderson, 1942) 

during the Antler orogeny, and then covered unconformably by younger Paleozoic sedimentary rocks which make up an overlap assemblage. 

(For discussion of the general relations see Roberts and others, 1958.)

In the Carlin-Pinon Range area in northeastern Nevada (fig. 1) the 

Devonian and Mississippian rocks of the general stratigraphic section

II
12 CONTRIBUTIONS TO GENERAL GEOLOGY

are classified into eight units (fig. 2). Four of the units are recognized 

as established formations in the region, two are given new formation 

names, one will be named by others as a result of studies in an adjoining area to the south, and one is unnamed because it is not yet recognized over a large enough area to warrant formation status.

The youngest beds involved in movement along the Roberts Mountains thrust are of late Late Devonian age, and the oldest beds of 

the overlap assemblage are of early Early Mississippian age, so that 

beds moved along the Eoberts Mountains thrust probably reached this 

area in latest Devonian or earliest Mississippian time.

117 C 

42" 

116° 115°

4.1

40°

"NEVADA" IDAHO

ELKO

Wells o

Elko

1 WHITE

I Eurekao ) PINE

Ely

NYE

0 20 

I , i i I

40 

I

60 MILES 

_J

FIGURE 1. Location of the Carlin-Pinon Range area.
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS. THRUST 13

Overlap assemblage

c to /- Diamond Peak Formation c'E

« ft I Chainman Shale

Webb Formation Siliceous 

(New name) argillite

UNCONFORMITY

' Siliceous

(western)

assemblage

Woodruff

Formation

(New name)

v

Transitional

assemblage

Limestone

and chert

Carbonate

(eastern)

assemblage

Devils Gate

Limestone

Nevada

Formation

FIGTTEE 2. Devonian and Mississippian rocks in the Carlin-Pinon Range area.

DEVONIAN SYSTEM

CARBONATE (EASTERN) ASSEMBLAGE BOCKS 

NEVADA FORMATION AND DEVILS OATH LIMESTONE

Carbonate-assemblage rocks of Devonian age comprise the Nevada 

Formation and the Devils Gate Limestone. (See Nolan and others, 

1956, p. 40-52, for general descriptions and regional relations.) These 

units form the core of the Pinon Range in the southern quarter of the 

range and for about 5 miles in the center of the range (fig. 3).

The Nevada Formation in the Pinon Range consists of three members; dolomite makes up most of the lower and upper members, and 

sandy and quartzitic rocks make up the middle member (Carlisle and 

others, 1957). No complete section of the Nevada Formation is exposed in any one part of the report area, but the composite total thickness of several partial sections indicates a maximum thickness of about 

3,200 feet.

The Early and Middle Devonian age of the Nevada was established 

by studies south of the report area (Merriam, 1940, p. 50-59; Nolan 

and others, 1956, p. 46-47; Carlisle and others, 1957, p. 2185-2188; 

Johnson, 1962). Fossils are scarce and poorly preserved in the formation in the Carlin-Pinon Range area.

The Devils Gate Limestone is composed mostly of medium- to thickbedded light- and dark-gray fine-textured limestone which weathers 

gray and bluish gray. The maximum measured thickness is 940 feet, 

which can be taken as a minimum figure for the original thickness.
14 CONTRIBUTIONS TO GENERAL GEOLOGY

116'15' 116° 115*45'

FIGURE 3. Generalized outcrop areas (stippled) of Paleozoic rocks in the CarlinPinon Range area. Type section of the Webb Formation is indicated by W. 

Fossil localities mentioned in the text are identified by numbers. A-A' and 

B-B' are locations of sections shown in figure 4 (p. 116).

SILICEOUS (WESTERN) ASSEMBLAGE ROCKS 

WOODRUFF FORMATION

A thick unit of siliceous-assemblage rocks of Devonian age differs 

from previously recognized formations in the region and is named 

the Woodruff Formation in this report. The type area is along and 

near the upper part of Woodruff Creek (fig. 3), principally in sees. 

24 and 25, T. 32 N., R. 52 E., and sec. 30, T. 32 N., R. 53 E. The Woodruff is also exposed elsewhere in the Pinon Range and forms about a 

4-mile-long band of outcrop along the west side of the range at the 

south end of the area.

Contacts between the Woodruff and other formations are either 

faults or unconformities. In the southern part of the area the lowest
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS. THRUST 15

exposed beds of the Woodruff are at the Roberts Mountains thrust. 

Elsewhere the lowest exposed beds are at thrust faults of lesser magnitude. The Woodruff is overlain unconformably by beds of Early 

Mississippian age.

The Woodruff consist principally of siliceous mudstone and chert; it 

contains lesser amounts of shale, siltstone, dolomitic siltstone, and 

dolomite and a few lenses of limestone and very few beds of sandy limestone and calcareous sandstone. The siliceous mudstone, chert, and 

shale are mostly dark gray to black and weather the same, so that 

slopes covered by weathered fragments commonly are dark. Other 

lithologic types are mostly tan and, locally, light gray and weather 

the same colors. Lack of marker beds and irregular bedding attitudes 

preclude accurate thickness measurements of the Woodruff. The thickness must be 3,000 feet in the southern part of the area and may be 

several thousand feet more than that in the entire area.

The oldest part of the formation, as established by fossils, consists 

of black to pale-brown siltstone in beds about 1-6 inches thick. Some 

of these beds are calcareous; others are carbonaceous and sooty. Oval 

to round nodules, which have high calcium and phosphate contents and 

are as much as 1% inches across, are prominent in these beds locally.

In its type area, the Woodruff consists of siliceous mudstone and 

chert, and lesser amounts of shale and dolomite. The mudstone is carbonaceous and is brown to gray on fresh surfaces and light gray on 

weathered ones, and it breaks into tabular nonfissile chips about ^-4 

inches across; in places a soft soil has been developed on slopes underlain by the mudstone. The chert, which forms prominent exposures 

locally, is mainly black and weathers gray to brown. Bedding in the 

chert generally is 1-4 inches thick, but laminae a few millimeters thick 

are visible on weathered surfaces of some layers. Argillaceous partings are common. Abundant spheres and elongate pods of white chert 

one-fourth inch across and up to 4 inches long contrast with the dark 

chert. The chert is very brittle and breaks with an uneven to conchoidal 

fracture. Examination of thin sections indicates that the chert contains 

argillaceous material, commonly abundant organic material, and many 

spheres of radiolarian tests and molds. Detrital grains of quartz form 

as much as 1 percent of some thin sections. Bound nodules mostly 1/^-1 

inch in diameter and commonly gray to black occur locally in the chert 

and in the mudstone. Shale, which makes up a minor amount of the 

formation in the type area, is dark gray, siliceous, and poorly fissile.

Gray to brown dolomite that weathers yellow to brown forms a small 

but conspicuous part of the formation. Dolomite beds are %-G inches 

thick, and some have prominent laminae about 1 mm thick. In thin 

section the dolomite is seen to consist mostly of dolomite rhombohe278-816 68 2
I 6 CONTRIBUTIONS TO GENERAL GEOLOGY

drons, which range in length from 0.005 to 0.03 mm. Some rhombs have 

rounded edges, and others do not; evidently some are clastic grains 

and others are diagenetic or primary grains or secondary crystals. One 

thin section contains 95 percent dolomite grains between 0.01 and 0.03 

mm in diameter that appear to be mostly clastic fragments and 5 percent rounded quartz grains of the same size; all grains are set in a 

dolomite cement. Quartz grains compose as much as 50 percent of some 

thin sections; they range from 0.01 to 0.04 mm in diameter and are 

subangular to rounded. Clastic grains of barite or possibly of carbonate minerals replaced by barite occur in a few places.

Woodruff units exposed away from the type area include characteristic gray to tan dolomitic siltstone and claystone, which weather tan and 

buff and break into platy pieces and into irregularly shaped fragments 

mostly 1-2 inches across. These rocks are in beds mainly one-half inch 

thick or less and, at many places, composed of laminae 0.1-0.2 mm 

thick. In thin sections these rocks are seen to consist of dolomite grains 

that range mostly from 0.005 to 0.05 mm across. Quartz grains form 

less than 5 percent of most sections and less than 1 percent of some. 

Light-colored calcareous shale and shaly dolomite with pink and lavender tints and black shale that weathers to form splintery fragments 

up to about 3 inches long are distinctive lithologic types in the southern 

part of the report area. Very carbonaceous black to brown siltstone, 

Tentaculites-b&^ring gray limestone in a few thin lenses, and coarsegrained sandy limestone and calcareous sandstone make up a very 

small part of the formation.

The beds that are considered youngest, on the basis of fossil evidence, 

consist of dark-gray to black siliceous shale; they are exposed near the 

central part of the type area. Because of structural complexities, the 

exact stratigraphic position of these beds in the formation is not 

determinable.

The Devonian age of the Woodruff Formation is based on conodonts, 

goniatites, and graptolites. Conodonts were found in several localities, 

goniatites in one, graptolites in one, and clawlike rami of Angustidontus in many.

The oldest dated beds in the Woodruff cover a small area in the 

eastern part of sec. 33 and the western part of sec. 34, T. 32 N., K. 52 E. 

Conodonts collected there by David L. Clark of the University of Wisconsin and Kaymond L. Ethington of the University of Missouri are of 

Early Devonian age (D. L. Clark, written commun., 1963). The graptolite Monograptus hercynicus from beds near those containing the 

conodonts is also of Devonian age (Berry, 1967, p. B27). Other beds 

from this same locality contain abundant Tasmanites (J. M. Schopf, 

written commun., 1957).
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS, THRUST I 7

Clawlike or jawlike rami of the fish Angustidontus (Jean M. Berdan, written comnxun., 1964) are so widespread in the formation that 

with diligent search one can find them almost anywhere in the gray 

shale or mudstone, the tan-weathering dolomitic siltstone, and the 

black splintery shale. Two collections (USGS 4981-SD and 4982-SD) 

containing Angustidontus also contain goniatites of the genus Platyclymenia (Pleuroclymenia) , according to Mackenzie Gordon, Jr. 

(written commun., 1958), who stated that this fossil is found in rocks 

about equivalent to the middle Famennian of Europe. The ages of 

two conodont collections were reported by the late W. H. Hass (written 

commun., 1959) to be Middle or early Late Devonian chiefly on the 

basis of the forms Polygnatfius linguifornus and PolygnatJius pennata. D. L. Clark (written commun., 1961) considered two of the three 

conodont collections he studied to be medial Late Devonian in age and 

one to be early Late Devonian.

The Woodruff Formation, then, seems to be an age equivalent of the 

Nevada Formation, the Devils Gate Limestone, and the lower part of 

the Pilot Shale. The youngest dated beds are in the Platydymenia 

zone, about the middle of the Famennian of Europe, or late Late 

Devonian. This age is of critical importance in dating the Eoberts 

Mountains thrust, as these are the youngest siliceous-assemblage 

rocks involved in the thrusting.

The Slaven Chert, which consists of gray to black chert, less dark 

shale and sandstone, and a small amount of limestone, crops out in the 

Shoshone Range (Gilluly and Gates, 1965, p. 37-42) and in the 

southern part of the Cortez Mountains (Gilluly and Masursky, 1965, 

p. 59-61) west of the Carlin-Pinon Range area. The Slaven, like the 

Woodruff, is a siliceous-assemblage unit in the upper plate of the 

Roberts Mountains thrust, but the Woodruff differs from it chiefly 

in containing relatively much less chert and much more very fine 

grained clastic siliceous rock and fine-grained dolomite. The Slaven 

Chert is of Middle Devonian and possibly of Late Devonian age 

(Gilluly and Gates, 1965, p. 41), and the Woodruff Formation is of 

Early to Late Devonian age; so the two formations are in part 

equivalent.

TRANSITIONAL-ASSEMBLAGE BOCKS

Devonian rocks placed in the transitional assemblage in the CarlinPinon Range area consist of limestone, sandy limestone, and chert, 

and thus have lithologic types common to both the carbonate and 

siliceous assemblages. This transitional unit has been studied in the 

Sulphur Springs Range south of this report area by Donald Carlisle 

and others, who plan to give the unit a formal name.
I 8 CONTRIBUTIONS TO GENERAL GEOLOGY

The Devonian age of this unit in the Carlin-Pinon Range area is 

based on four conodont collections from sandy limestones which also 

contain Tentaculiies in places. These collections probably are Middle 

Devonian and possibly early Late Devonian (W. H. Hass, written 

commun., 1958). This unnamed unit and the Woodruff Formation are 

at least in part age equivalents. The unit also is equivalent to the 

Devils Gate Limestone and may be equivalent to the upper part of 

the Nevada Formation. Contacts between this unnamed formation and 

other Paleozoic formations probably are faults.

MISSISSIPPIAN SYSTEM

OVERLAP ASSEMBLAGE

WEBB FORMATION

Mississippian and younger rocks that are unconformable on 

siliceous- and carbonate-assemblage units brought together by the 

Roberts Mountains thrust have been called the overlap assemblage 

(Roberts and Lehner, 1955; Roberts and others, 1958, p. 2838-2839). 

The oldest Mississippian rocks in the Carlin-Pinon Range area are 

mostly siliceous mudstone and claystone; sandstone and limestone 

occur in much smaller amounts. This sequence is here named the Webb 

Formation for exposures near Webb Creek. The designated type section is near the north edge of sec. 19, T. 31 N., R. 53 E., and in the 

SE14 sec. 13, T. 31 N., R. 52 E., where only the mudstone is well 

exposed in many places.

The following type section of the Webb Formation was measured by 

use of an Abney level mounted on a Jacob's staff. Location of section is 

shown in figure 3. 

Mississippian System: 

Ohainman Shale.

Gradational contact. Thickness 

Webb Formation: (ft) 

3. Mudstone, very dark gray; weathers gray and brown; siliceous; 

contains minute hollow spheres having septa; some beds 

near top are finer grained than most and ark black and 

argillitic; barite nodules at top.___ 385 

2. Mudstone, gray ; weathers light gray to tan; siliceous; coarser 

grained than units above and below, some beds are sandy; 

breaks into larger pieces than units above and below, some 

pieces about 6 in. across_ ___ _ 250 

1. Mudstone, gray; weathers brown; siliceous; breaks into chips

about 2 in. across; many minute spheres with septa 100

Total thickness__________________________ 735 

Contact uncomformable; poorly exposed. 

Woodruff Formation.
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS. THRUST I 9

In the north half of the area the Webb Formation occurs as a wedgeshaped mass that is thickest at the north and pinches out between the 

type section and the head of Webb Creek. To the south it crops out in 

lenticular bodies. It is 735 feet thick at the type section and at least 

800 feet thick to the north. Lenticular bodies east and north of the 

upper part of Trout Creek may be 300 feet thick in places; these 

bodies consist of limestone, less shale, and a very small amount of 

chert. The most southerly exposure of the Webb is limestone.

The siliceous mudstone and claystone of the Webb Formation are 

mostly gray and weather gray to brown; a few beds have a pink 

cast. Some strata, particularly near the top of the formation, are black 

and weather black; they are argillitic and finer grained than most 

beds in the formation. All these rocks are thin bedded, a few are 

faintly laminated, and some are shaly. They break into chips and 

chunky fragments, mostly about 2 inches across. Spicules are abundant 

locally in the mudstone. In thin section the mudstone is seen to consist of angular grains of quartz and chert, each forming about 10 

percent of the section, set in a submicroscopic matrix. The grains 

have diameters of about 0.05 mm. Some of the chert appears to be in 

small chalcedonic nodules that probably are recrystallized radiolarians. Hematite is abundant. Composition of Webb Formation 

siliceous mudstone is shown by chemical analyses of three samples 

(table 1).

TABLE 1. Chemical analyses (in weight percent) of samples of siliceous mudstone 

from the Webb Formation, Carlin-Pinon Range area, Nevada

[Analysts, Paul Elmore, Samuel Botts, and GiUison Chloe, 1962; rapid rock analyses by methods similar 

to those described by Shapiro and Brannock (1962)]

Lab No ...... _ _ _

Field No ........ . _ .......

SiOj... 

AliOj . ...

FesOs - ... _ ..... ... ..... .... ....

FeO.. ... . .

MgO._ 

CaO 

NajO.. -_ .. .

K2O 

TiO»-._ .

Pj06 .. . .._____ _ .

MnO ............... ........

Loss on Ignition (1,050°).-.- __ ._ _ .

TotalCi- ...............

HjO- .

HsO+ _ . _ __ _ ...............

COj ___ __ .

Acid insoluble- .. . . ... __ _ .. __ .

 159697

.---.-.-...----.....- 525

...... . 84.0

 . 4.0

 ... .38

 . .56

 .74

....... ... . .67

.12

 .89

 .22

.13

 . .01

7.0

. . - - - _ ----- 3.54

.52

. .. . 2.5

. .06

159698

823-B

84.2

6.6

.72

.15

.43

.04

.14

1.6

.33

.12

.00

4.7

.16

.76

2.5

<-05

159699

872

86.4

4.8

.36

.22

.40

.02

.12

1.2

.29

.08

.00

3.5

.43

.74

2.2

<.05

22.7

1 Determined by I. C. Frost, 1962,

2 Chiefly barite.
I 10 CONTRIBUTIONS TO GENERAL GEOLOGY

In places, thin layers of sandstone made of many grains as large 

as medium-sand size and sparse grains of very coarse sand size are 

interbedded with the mudstone. A thin section of the sandstone shows 

well-rounded chert and quartz grains. The chert grains are 0.1-0.5 mm 

in diameter and make up 85 percent of the grains; the quartz grains 

are 0.1-1.5 mm in diameter. Chert forms the cement. Hematite and 

limonite stains are prominent.

Limestone in the Webb Formation occurs in lenses mostly 1-30 

feet thick and up to about iy2 miles long. One lens is almost 200 

feet thick. The lenses are in the upper part of the formation and at 

the very top in some places. The rock is black to gray, generally 

weathers tan, is thin bedded, and commonly breaks down into platy 

fragments that litter a slope. Thin sections of the limestone from 

separated localities reveal that calcite grains from 0.003 to 0.03 mm 

across are its chief constituent. Quartz is less abundant and occurs as 

silt-size clastic grains; some of the quartz is partly replaced by a carbonate mineral. Chemical analyses of five samples of this rock by 

James A. Thomas of the U.S. Geological Survey show that it contains more noncarbonate material than is recognized in thin sections 

because of its fine grain size. Total calculated carbonate is only about 

47-65 percent. All the thin sections contain sparse to abundant vague 

spherical microfossils, probably radiolarians, which are mostly 0.03- 

0.1 mm in diameter and are largely recrystallized. Vague irregularly 

shaped microfossils are also present but are much less common than 

the spherical ones.

Claystone nodules, many of which contain barite, and barite nodules 

occur at the top of the formation in many places and also in the lower 

beds of the overlying Chainman Shale. Beds of gray to black chert, 

generally 1 inch thick or less, crop out at a very few places in the 

Webb Formation.

The basal contact of the Webb is an unconformity along which the 

formation lies on Devils Gate Limestone of the carbonate assemblage 

and on the Ordovician Vinini Formation and the Devonian Woodruff 

Formation of the siliceous assemblage. Where the Webb rests on Devils 

Gate, bedding attitudes in the two formations are so nearly the same 

that the units appear to be conformable. Fossil ages, however, indicate a hiatus, and lateral relations across the area demonstrate the 

unconformity.

The conformable contact between the Webb Formation and the 

overlying Chainman Shale is gradational at some places and abrupt 

at others. The upper beds of the Webb generally are hard siliceous 

mudstone or shale and dark limestone in a few places, whereas the
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS. THRUST I 11

basal beds of the Chainman generally are soft gray shale. Barite 

nodules commonly occur at or very near this contact.

The Early Mississippian age of the Webb Formation is established 

on the basis of conodonts (table 2) studied by the late W. H. Hass, 

John W. Huddle of the U.S. Geological Survey, and David L. Clark 

of the University of Wisconsin.

TABLE 2. Conodonts from the Webb Formation

[Fossil-collection localities shown in fig. 3]

TTSGSfossilcoUn. No -------- 17304-PC 17306-PC 17303-PC 22839-PC

Field coUn. No--..-..-----.--- 5251 5401 544 a 800» SF-251 SF-250

SF-252 4 SF-253 *

Bryantodus sp._-___-____ X X _____ __.._- .._-_-_. __-.___ 

jDi7iod«s/ra0os«s(E.R.Brausou)_ X ____ _..___ X _____ _____ 

Elictognathus lacerata (Brauson X _____ _____ _____ _____ . _ ___

and Mehl).

Elictognathus sp . -_. -___-. ___-_ _. X - .- 

Gnathodus punctatus (Cooper) ___ X -__.__ _--.- - _ _. .___ 

Gnathodus aff. G. punctatus _______ _____ ____ X __...._- _.__-----

(Cooper). 

Hibbardellasp ----------_--- _-__-_ _-__- _---_- X -._-_-.-.- _ 

Hindeodellasv-.-- ------ ---- ------ - --___- _-- -- X . . 

Hindeodella spp . X ______-_ ..-__-____ ..-. _ 

Icriodussp. (regarded as reworked)- __.____ ____ __._..- X .-_--_-.-- . 

Ligonodina sp_________.. .____ ...-__. _____ X _...__ _-_ -....

Lonchodina sp .____-_-_.__-- ... __ _._..... .._.__..._ X 

Neoprioniodus sp ____-__- _------- ..___. _..._. X -..-.--._- . 

Ozarkodinasp___________ X .____ _____ X --...-_. ------ 

Pinacognathusl sp________- __ ... ____- _..._- X .__ .... 

Polygnathus communis Branson .._ -... _-.-.._--_ X ... . . 

and Mehl. 

Polygnathus inoinata E. R. _____ X _____ X __----- ... 

Bransou. 

Polygnathus sp....___.___- X X _..._. ..__.-. ... . 

Polygnathus spy-. ___.___-. __.__ X _....... .._.. _ 

Siphonodella cooperiHass....._-- _____ X _____ __ _ ._ 

Siphonodella obsoleta Hass_._. ___ _ X _..._. X ..- . 

Siphonodella ct. S. obsolete Hass-- __ ___ ..___ X ____. _._-_. . 

Siphonodella duplka (Branson ---------- ....___. .._ _. -..-_ X

and Mehl). 

SiphonodeUa quadruplicate (Bran- X ..____ _____ ___ X 

son and Mehl). 

Siphonodettasp-.- ________ __.__ X _____ ____. ... ..-. X

Siphonodella spp____.___. X _____. _____ .._ . 

Spathognathodus sp________ X _____ _____ ..__ _ . 

Spathognathodus 2 species-__... __.__ _____ _____ X _--------

Synprioniodina sp__.__ X ____. __.__ ..__ . 

1 Collections from mudstone. argillitic in places, from near top of formation. Identifications by the late 

W. H. Hass.

2 Collection from limestone near top of formation. Identifications by W. H. Hass.

3 Collection from limestoneat top of formation. Identifications by John W. Huddle, U.S. Geological Survey.

4 Collections from sandstone in a mostly mudstone sequence near base of formation. Identifications by 

David L. Clark, University of Wisconsin.
I 12 CONTRIBUTIONS TO GENERAL GEOLOGY

According to Hass, collections 525, 540, and 544 are all of Early 

Mississippian age (equivalent to the Kinderhook Series). Eegarding 

the age of collection 540 Hass wrote (1959):

This collection comes from rocks of Early Mississippian age. In the Llano 

region of Texas, the specifically identified conodonts in the list are present in a 

faunal zone of the Ohappel limestone; which zone is considered to be of late 

Kinderhook (Chouteau) age on the basis of megafossils. These same conodont 

species are present in other late Kinderhook rocks, including the Welden 

limestone of Oklahoma.

Huddle reported (written commun., 1962), concerning collection 

800, that Siphonodella obsolete Hass makes up about 80 percent of the 

specimens recovered and Gnathodus aff. G. punctatus (Cooper) about 

10 percent. He stated that the presence of these species "suggests a 

correlation of the rock containing them with the Chappel Limestone 

of Texas and the Chouteau Limestone of the Mississippi Valley * * *. 

The rock containing this conodont fauna is probably Early Mississippian in age."

As reported by Clark (written commun., 1963), the four collections 

he studied are Early Mississippian in age, and probably early, although 

not the earliest, Kinderhook.

The Early Mississippian age of the Webb Formation makes it 

probably equivalent to at least part of the Joana Limestone (Nolan 

and others, 1956, p. 54^-56; Langenheim, 1960, p. 75) of eastern Nevada. 

The siliceous mudstone in the Webb is similar to some mudstone of the 

Pilot Shale in the type locality in the Ely district (Spencer, 1917, p. 

26), and the Pilot and Webb probably are equivalent in part also. These 

two formations differ markedly in their lower contacts, however; the 

Pilot near Eureka is conformable on carbonate-assemblage Devils 

Gate Limestone (JSTolan and others, 1956, p. 52), whereas the Webb is 

unconformable on both carbonate- and siliceous-assemblage formations. The lower part of the Chainman Shale and Diamond Peak 

Formation undivided in the south half of the Carlin-Pinon Kange area 

is also of Early Mississippian age, as based on megafossils. The Webb 

Formation in the south half is mostly limestone like that farther north 

in the uppermost part of the formation. The Webb and the undivided 

Chainman and Diamond Peak, then, may be equivalent in part at 

least, and the southward wedge-out of the Webb may be partly by 

gradation into the Chainman and Diamond Peak, although no actual 

gradation between the two units was observed.

CHAINMAN SHALE AND DIAMOND PEAK FORMATION

The Chainman Shale and Diamond Peak Formation compose one 

sequence of clastic rocks which records the depositional history of
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS. THRUST I 13

material derived from the region of continuing uplift in the Antler 

orogenic belt. In general, the texture of these rocks becomes coarser 

upward, but beds of coarse clastic material occur low in the sequence 

as well as high. Lateral changes from fine- to coarse-grained rocks are 

abrupt at places, and coarse- and fine-grained units also interfinger, 

This intimate, and in places seemingly haphazard, association of clastic 

rocks of different size grades makes the two formations virtually one 

unit (Man and others, 1956, p. 56-59; Sadlick, 1960, p. 82-83; 

Stewart, 1962). The development of the nomenclature of beds of Mississippian age in the region was reviewed by Nolan, Merriam, and 

Williams (1956, p. 56-59).

In our mapping we separated these chiefly Mississippian rocks into 

three units: Chainman Shale, where the rocks are mainly shale and 

sandstone; Diamond Peak Formation, where the rocks are mainly 

conglomerate and sandstone; and Chainman Shale and Diamond Peak 

Formation undivided, where conglomerate, sandstone, and shale seem 

to be about equally prominent. The Tonka Formation of Dott (1955) 

is included in the Diamond Peak. In general, the percentage of finegrained rocks (shale and sandstone) relative to coarse-grained rocks 

(sandstone and conglomerate) increases southward across the CarlinPinon Kange area; it also increases southward on a more regional 

scale. The upper 3,500-4,500 feet of this sequence in the report area 

contains 40-60 percent conglomerate, whereas the Diamond Peak 

Formation about 75 miles to the south, at the type locality in the 

Diamond Mountains, contains only 12 percent conglomerate (Brew, 

1961, p. Clll). About 12 miles still farther south, the top of the sequence is eroded, but conglomerate makes up less than 2 percent of 

the total section of 4,700 feet and only 7 percent of the highest 860 

feet (Stewart, 1962, p. C58-C59).

The Chainman and Diamond Peak sequence is 6,000-7,000 feet thick 

in the Carlin-Pinon Range area.

In the northern part of the Carlin-Pinon Eange area the Chainman 

and Diamond Peak rock sequence is conformable on the Webb Formation of the overlap assemblage. In the southern part of the area this 

rock sequence is unconformable on Devonian units of the carbonate 

assemblage and on the Woodruff Formation of the siliceous assemblage.

The age of beds composing the Chainman Shale and the Diamond 

Peak Formation in the Carlin-Pinon Kange area spans Early Mississippian to Early Pennsykanian time. Dating is based on many fossil 

collections studied mostly by MacKenzie Gordon, Jr., and Helen Duncan. This sequence of beds is somewhat older in the report area than it 

is elsewhere in most of eastern Nevada, but because no lithologic basis is 

evident for subdivision of these shales in the Carlin area, they are all
I 14 CONTRIBUTIONS TO GENERAL GEOLOGY

included in the Chainman and Diamond Peak sequence. Good collections are from rocks of Early Mississippian age and from the tan and 

yellow silty beds of late Early and possibly early Late Mississippian 

age (Osage and possibly early Meramec). After making a preliminary 

report (1961) on the early Mississippian faunas, MacKenzie Gordon, 

Jr., and Helen Duncan have been continuing their studies of collections 

from this area. Other good collections are from beds of late Late Mississippian and early Early Pennsylvanian ages. Only poorly preserved 

fossils were found in much of the sequence between those rocks containing Early Mississippian fossils and those containing late Late Mississippian ones, but a late Meramec age is indicated by one collection 

(MacKenzie Gordon, Jr., written commun., 1967), and the lack of 

other well-dated fossil collections does not indicate a break in this 

continuous rock sequence.

ARGIULITE UNIT OF LKB CANYON

Black siliceous argillite and some black chert are exposed in a band 

centered in Lee Canyon (Ketner and Smith, 1963, p. BIO). The unit 

crops out on bare black slopes and ridges. Beds are mostly an inch 

to several inches thick, and the entire unit is about a mile thick. In 

thin section this dense rock is seen to consist mainly of quartz grains 

about 0.10 mm in diameter making a mosaic texture. Carbonaceous 

material is so abundant in much of the argillite that thin sections are 

cloudy or opaque. A few beds of conglomerate and quartzite occur 

in the upper part of the unit.

The only fossil found in the argillite unit of Lee Canyon is a poorly 

preserved plant stem from near the top of the unit. The siliceous argillite is similar to black siliceous argillitic mudstone near the top of the 

Webb Formation, and the coarser grained beds in the upper part of the 

argillite are similar to beds in the Chainman Shale and the Diamond 

Peak Formation.

A thrust contact with the Chainman Shale, the Webb Formation, and 

the Woodruff Formation marks the base of the argillite unit. A normal 

fault along most of the length and a conformable contact beneath 

probable Chainman Shale for a short distance mark the upper contact. 

We interpret the argillite unit of Lee Canyon to be allochthonous in the 

Carlin-Pinon Range area; it probably was moved into the area from 

somewhere to the east on a thrust fault younger than the Roberts 

Mountains thrust. An anticline in the lower plate of this younger 

thrust is sharply overturned to the west in places (Ketner and Smith, 

1963, p. B14).
DEVONIAN, MISSISSIPPIAN ROCKS, ROBERTS MTS. THRUST I 15

PRESENT RELATIVE POSITIONS OF THE DEPOSITIONAL

UNITS

The unite of the carbonate, siliceous, and transitional assemblages, 

although probably deposited many miles apart, were juxtaposed 

by movement along the Eoberts Mountains thrust. Those rocks of the 

carbonate assemblage now appear in the lower plate of the thrust, and 

those of the siliceous and transitional assemblages in the upper plate. 

Devonian units in the lower plate are the Kevada Formation and the 

Devils Gate Limestone, and those in the upper plate are the Woodruff 

Formation and the transitional-assemblage limestone and chert unit.

Sedimentary units of Ordovician and Silurian ages also were 

brought together by the thrusting and occur in both the upper and 

lower plates in the area. Carbonate-assemblage units of Ordovician 

age in the lower plate include the uppermost part of the Pogonip 

Group, the Eureka Quartzite, and the Hanson Creek Formation. Siliceous-assemblage units of Ordovician age in the upper plate are the 

Valmy and Vinini formations. Silurian age rocks include the carbonate 

assemblage in the Lone Mountain Dolomite in the lower plate and a 

siliceous-assemblage unnamed unit in the upper plate.

Mississippian unite that make up the overlap assemblage unconf ormable on the older rocks comprise the Webb Formation, the Chainman Shale, and the Diamond Peak Formation. The youngest beds in 

the Diamond Peak are of Early Pennsylvanian age.

DATE OF THE ROBERTS MOUNTAINS THRUST IN THE 

CARLIN-PINON RANGE AREA

The overlap relations which cause the Mississippian rocks to rest 

unconformably on Devonian and older rocks of both siliceous and 

carbonate assemblages serve to date the Antler orogeny and the Roberts 

Mountains thrust in this area. Previously the principal deformation in 

the Carlin-Pinon Range area could not be dated more precisely than 

pre-Meramec (Dott, 1955, fig. 11), but closer control on the time of 

principal deformation is afforded from evidence farther south. The 

general unconformable relations are clearly shown a few miles south 

of the Humboldt River, where the Webb Formation rests unconformably on the Ordovician Vinini Formation of the siliceous assemblage 

and on the Devonian Devils Gate Limestone of the carbonate assemblage (fig. 4, section A-A'). The unconformable relations also are 

clearly seen in the southern part of the area, where the Nevada Formation of the carbonate assemblage is exposed in a window in the Roberts 

Mountains thrust. Upper plate rocks surrounding this window are in 

the Woodruff Formation of the siliceous assemblage, which is overlain
116 CONTRIBUTIONS TO GENERAL GEOLOGY

ROBERTS MOUNTAINS 

THRUST^

LEVEL

6000'-i

4000'-

ROBERTS MOUNTAINS THRUST 

Die / ROBERTS MOUNTAINS THRUST

B'

LEVEL

FIGUEE 4. Generalized structure sections showing evidence for dating the 

Roberts Mountains thrust. Note that in section B-B' the transitional facies 

(Die) is in thrust contact with the siliceous facies (Ov) and the siliceous 

facies (Dw) is in thrust contact with the carbonate facies (Dn). Location of 

sections is shown in figure 3 (p. 14). Explanation on facing page.

unconformably by the Chainman Shale and Diamond Peak Formation 

undivided of the overlap assemblage (fig. 4, section B-B'}.

The overlapping relations of the Webb Formation, which lies with 

sedimentary contacts on both the allochthonous and autochthonous 

sequences in the northern part of the area, effectively dates the Eoberts 

Mountains thrust as post-late Late Devonian, and pre-early Early 

Mississippian. In the southern part of the area, the Chainman Shale 

rests unconformably on both allochthonous and autochthonous formations. The youngest allochthonous siliceous-assemblage rocks are 

dated as late Late Devonian. This date was established by Mackenzie 

Gordon, Jr., who identified fossils that belong in the Platyclymenia 

ammonoid zone of late Late Devonian age. Thrust transport of these 

rocks was certainly concluded by Early Mississippian time, as the 

Webb Formation of late Kinderhook age rests unconformably on both 

allochthonous and autochthonous units of the Eoberts Mountains 

thrust.

Confirmation of uplift of nearby siliceous-assemblage rocks by 

Mississippian time is found in the sediments deposited in the CarlinPinon Eange area. These sediments consist largely of both fine and 

coarse detritus derived from upper plate rocks of the Eoberts Mountains thrust.
DEVONIAN, MJSSISSJPPIAN ROCKS, ROBERTS MTS, THRUST I 17

EXPLANATION

Webb Formation

ROBERTS MOUNTAINS THRUST

SILICEOUS 

FACIES

TRANSITIONAL 

FACIES

CARBONATE 

FACIES

Woodruff 

Formation

Valmy and

Vinini 

Formations

REFERENCES

Berry, W. B. N., 1967, Monoffraptus hercynicus nevadensis n. subsp., from the 

Devonian in Nevada, in Geological Survey research 1967: U.S. Geol. Survey 

Prof. Paper 575-B, p. B26-B31.

Brew, D. A., 1961, Lithologic character of the Diamond Peak Formation (Mississippian) at the type locality, Eureka and White Pine Counties, Nevada, in 

Short papers in the geologic and hydrologic sciences: U.S. Geol. Survey Prof. 

Paper 424-C, p. C11G-C112.
I 18 CONTRIBUTIONS TO GENERAL GEOLOGY

Carlisle, Donald, Murphy, M. A., Nelson, C. A., and Winterer, E. L., 1957, Devonian stratigraphy of Sulphur Springs and Pinon Ranges, Nevada : Am. Assoc. 

Petroleum Geologists Bull. v. 41, p. 2175-2191.

Dott, R. H., Jr., 1955, Pennsylvanian stratigraphy of Elko and northern Diamond 

Ranges, northeastern Nevada: Am. Assoc. Petroleum Geologists Bull., v. 39, 

p. 2211-2305.

Gilluly, James, and Gates, Olcott, 1965, Tectonic and igneous geology of the 

northern Shoshone Range, Nevada: U.S. Geol. Survey Prof. Paper 465,153 p.

Gilluly, James, and Masursky, Harold, 1965, Geology of the Cortez quadrangle, 

Nevada: U.S. Geol. Survey Bull. 1175,117 p.

Gordon, Mackenzie, Jr., and Duncan Helen, 1961, Early Mississippian faunas in 

southwestern Elko County, Nevada, in Short papers in the geologic and 

hydro-logic sciences: U.S. Geol. Survey Prof. Paper 424-C, p. C233-C234.

Johnson, J. G., 1962, Lower Devonian-Middle Devonian boundary in central 

Nevada: Am. Assoc. Petroleum Geologists Bull., v. 46, p. 542-546.

Ketner, K. B., and Smith, J. F., Jr., 1963, Geology of the Railroad mining district, 

Elko County, Nevada : U.S. Geol. Survey Bull. 1162-B, 27 p.

Langenheim, R. L., Jr., 1960, Early and Middle Mississippian stratigraphy of 

the Ely area, in Intermountain Assoc. Petroleum Geologists Guidebook llth 

Ann. Field Conf., Geology of east-central Nevada, 1960: p. 72-80.

Merriam, C. W., 1940, Devonian stratigraphy and paleontology of the Roberts 

Mountains region, Nevada: Geol. Soc. America Spec. Paper 25.

Merriam, C. W., and Anderson, C. A., 1942, Reconnaissance survey of the Roberts 

Mountains, Nevada: Geol. Soc. America Bull., v. 53, p. 1675-1726.

Nolan, T. B., Merriam, C. W., and Williams, J. S., 1956, The stratigraphic section 

in the vicinity of Eureka, Nevada: U.S. Geol. Survey Prof. Paper 276, 77 p.

Roberts, R. J., and Lehner, R. E., 1955, Additional data on the age and extent of 

the Roberts Mountains thrust fault, north-central Nevada tabs.] : Geol. Soc. 

America Bull., v. 66, p. 1661.

Roberts, R. J., Hotz, P. E., Gilluly, James, and Ferguson, H. G., 1958, Paleozoic 

rocks of north-central Nevada: Am. Assoc. Petroleum Geologists Bull., v. 42, 

p. 2813-2857.

Sadlick, Walter, 1960, Some preliminary aspects of Chainman stratigraphy, in 

Intermountain Assoc. Petroleum Geologists, Guidebook llth Ann. Field Conf., 

Geology of east-central Nevada, 1960: p. 81-90.

Shapiro, Leonard, and Brannock, W. W., 1962, Rapid analyses of silicate, carbonate, and phosphate rocks: U.S. Geol. Survey Bull. 1144-A, 56 p.

Spencer, A. C., 1917, The Geology and ore deposits of Ely, Nevada: U.S. Geol. 

Survey Prof. Paper 96,189 p.

Stewart, J. H., 1962, Variable facies of the Chainman and Diamond Peak Formations in western White Pine County, Nevada in Short papers in geology and 

hydrology : U.S. Geol. Survey Prof. Paper 450-C, p. C57-C60.

U.S. GOVERNMENT PRINTING OFFICE: 1938