Early Paleozoic Biochronology of the Great Basin, 

Western United States

Michael E. Taylor, Scientific Editor

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1579

Chapter titles are listed on volume contents page

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1997
CONTENTS I

CONTENTS

[Letters designate chapters]

A. The Ibexian, Lowermost Series in the North American Ordovician

 By Reuben J. Ross Jr., Lehi F. Hintze, Raymond L. Ethington, James F. Miller, 

Michael E. Taylor, and John E. Repetski

With a section on Echinoderm Biostratigraphy 

 By James Sprinkle and Thomas E. Guensburg

B. An Ibexian (Lower Ordovician) Reference Section in the Southern Egan Range,

Nevada, for a Conodont-based Chronostratigraphy

By Walter C. Sweet and Celeste M. Tolbert

C. Upper Ordovician–Silurian Macrofossil Biostratigraphy of the Eastern Great Basin,

Utah and Nevada

 By Peter M. Sheehan and Mark T. Harris

III
The Ibexian, Lowermost Series in the

North American Ordovician

By Reuben J. Ross Jr., Lehi F. Hintze, Raymond L. Ethington, James F. Miller,

Michael E. Taylor, and John E. Repetski

With a section on ECHINODERM BIOSTRATIGRAPHY by James Sprinkle and Thomas E. Guensburg

EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN, WESTERN UNITED STATES

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1579–A

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1997
For sale by U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Any use of trade, product, or firm names in this publication is for descriptive purposes only and

does not imply endorsement by the U.S. Government

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Gordon P. Eaton, Director
VI

CONTENTS

Abstract.................................................................................................................................. 1

Introduction ........................................................................................................................... 1

Ibexian Series Type Area and Sections ......................................................................... 2

Acknowledgments ......................................................................................................... 3

Definition of the Ibexian Series............................................................................................. 3

Lithostratigraphy ................................................................................................................... 5

Construction of the Composite Stratotype .................................................................... 6

Notch Peak Formation........................................................................................... 7

Hellnmaria and Red Tops Members.............................................................. 7

Lava Dam Member........................................................................................ 7

House Limestone ................................................................................................... 8

Fillmore Formation................................................................................................ 8

Basal Ledge-forming Limestone Member (1)............................................... 8

Slope-forming Shaly Siltstone Member (2) .................................................. 9

Light-gray Ledge-forming Member (3)......................................................... 10

Brown Slope and Ledge Member (4) ............................................................ 10

Calcarenite Member (5)................................................................................. 10

Calathium Calcisiltite Member (6)................................................................ 11

Wah Wah Limestone ............................................................................................. 11

Ibexian Biostratigraphy ......................................................................................................... 11

Introductory Statement .................................................................................................. 11

Pre-Ibexian Faunal Zones.............................................................................................. 13

Ibexian Faunal Zones and Chronostratigraphy.............................................................. 14

Ibexian Stages and Trilobite Zones ....................................................................................... 14

Skullrockian Stage (New).............................................................................................. 14

Eurekia apopsis Zone ............................................................................................ 14

Missisquoia Zone................................................................................................... 14

Symphysurina Zone (=Zones A and B, Revised) .................................................. 15

Bellefontia-Xenostegium Zone (=Zone B in Part) ................................................. 16

Paraplethopeltis Zone (=Zone C) ......................................................................... 16

Stairsian Stage (New) .................................................................................................... 17

Leiostegium-Kainella Zone (=Zone D) ................................................................. 17

Tesselacauda Zone (=Zone E)............................................................................... 17

Rossaspis superciliosa Zone (=Zone F) ................................................................ 18

Tulean Stage (New) ....................................................................................................... 18

Hintzeia celsaora Zone (=Zone G-1) .................................................................... 18

Protopliomerella contracta Zone (=Zone G-2)..................................................... 19

Blackhillsian Stage (New)............................................................................................. 19

Trigonocerca typica Zone (=Zone H) ................................................................... 19

Presbynileus ibexensis Zone (=Zone I) ................................................................. 20

Pseudocybele nasuta Zone (=Zone J).................................................................... 20

Hesperonomiella minor Zone (=“Zone K” of Hintze, 1953) ................................ 20

Whiterockian Series............................................................................................................... 21

Rangerian Stage (New).................................................................................................. 21

Paralenorthis-Orthidiella Zone (=Zone L) ........................................................... 21

Conodont Zones..................................................................................................................... 22

Introductory Statement .................................................................................................. 22

Pre-Ibexian Conodont Zones......................................................................................... 22

Ibexian Conodont Zones................................................................................................ 23

VI
CONTENTS VII

Cordylodus proavus Zone (=Fauna A, Lower Part).............................................. 23

Cordylodus intermedius Zone (=Fauna A, Upper Part)........................................ 23

Cordylodus lindstromi Zone (=Fauna B, Lower Part) .......................................... 23

Iapetognathus Zone (New) (=Fauna B, Middle Part) ........................................... 23

Cordylodus angulatus Zone (=Fauna B, Upper Part) ........................................... 24

Rossodus manitouensis Zone (=Fauna C)............................................................. 24

Low Diversity Interval (=Fauna D, Lower Part)................................................... 24

Macerodus dianae Zone (New) (=Fauna D, Middle Part).................................... 25

Acodus deltatus/Oneotodus costatus Zone (New) (=Fauna D, Upper Part) ......... 25

Oepikodus communis Zone (=Fauna E, Lower Part) ............................................ 25

Reutterodus andinus Zone (New) (=Fauna E, Middle Part) ................................. 26

Whiterockian Conodont Zones ..................................................................................... 26

Tripodus laevis Zone (New) (=Fauna E, Upper Part) ........................................... 26

Graptolite Correlations.......................................................................................................... 27

Ibexian Graptolites........................................................................................................ 27

Anomalies and Correlations.......................................................................................... 28

Historical Perspective............................................................................................................ 28

Background and Appeals for Tradition......................................................................... 28

Alternative Viewpoints ................................................................................................. 29

Geographic Perspective......................................................................................................... 29

North America............................................................................................................... 29

Utah and Southeastern Idaho ................................................................................ 29

Canadian Rocky Mountains .................................................................................. 30

Eastern Canada...................................................................................................... 30

Eastern United States ............................................................................................ 30

Southern Midcontinental United States ................................................................ 31

Mexico................................................................................................................... 31

Outside North America ................................................................................................. 32

South America....................................................................................................... 32

Spitsbergen............................................................................................................ 32

Wales..................................................................................................................... 32

Australia ................................................................................................................ 32

Tasmania ....................................................................................................... 32

Queensland.................................................................................................... 33

Republic of Kazakhstan ........................................................................................ 33

Jilin Province, People’s Republic of China........................................................... 33

Cambrian-Ordovician Boundary........................................................................................... 34

Summary ............................................................................................................................... 34

Selected References .............................................................................................................. 34

Appendixes 1–3. Taxonomic Notes ...................................................................................... 43

Appendix 1. Trilobita .................................................................................................... 43

Appendix 2. Conodonta ................................................................................................ 45

Appendix 3. Brachiopoda.............................................................................................. 48

Appendix 4. Echinoderm Biostratigraphy, by James Sprinkle and

Thomas E. Guensburg....................................................................................................... 49

PLATE

[Separate document]

1. Observed ranges of trilobites, conodonts, and echinoderms, molluscs, and brachiopods 

in the Ibexian Series composite stratotype section and adjacent rocks, House-Confusion 

Range area, west-central Utah.
VIII CONTENTS

FIGURES

1. Index map of Ibex area, western Utah, showing locations of detailed maps in figures 2–7....................................... 4

2–7. Geologic maps showing:

2. Location of the A Section of Hintze (1951, 1973) ......................................................................................... 5

 3. Location of the Sneakover Pass measured section of Hintze and others (1988) ........................................... 5

4. Location of the Square Top measured section of Hintze (1973) .................................................................... 6

5. Location of the Mesa and 1965-C measured sections of Hintze (1973)......................................................... 7

6. Location of the B Section of Hintze (1951) and the Lava Dam North and Lava Dam Five measured

sections of Hintze (1973) and Hintze and others (1988) ................................................................................ 9

7. Location of the G, H, and J measured sections of Hintze (1951, 1973)......................................................... 10

8. Detailed range chart for selected trilobites and conodonts at the lower boundary stratotype of the

Ibexian Series in the Lava Dam Five segment of the Steamboat Pass–Lava Dam section of

Hintze and others (1988) ............................................................................................................................................ 11

9. Photographs of the Lava Dam Five section, southern House Range, Utah ................................................................ 12

10. Diagram of new stages of the Ibexian Series showing shelly fossil and conodont zones by which

they are characterized, and correlations with previous fossil zones and faunas......................................................... 15

TABLE

1. Universal Transverse Mercator Coordinates of component sections of the Ibexian composite stratotype section.... 8
1

The Ibexian, Lowermost Series in the

North American Ordovician 

By Reuben J. Ross Jr.,1

 Lehi F. Hintze,2 Raymond L. Ethington,3 James F. Miller,4

 Michael E. Taylor,5 and John E. Repetski6

With a section on ECHINODERM BIOSTRATIGRAPHY by James Sprinkle7 and Thomas E. Guensburg8

ABSTRACT

The Ibexian Series, first proposed by Hintze (1982), is

the accepted chronostratigraphic unit for the Lower Ordovician of North American usage. The lower boundary stratotype of the Ibexian Series is defined at a point in rock 39.1

meters (128.3 feet) above the base of the Lava Dam Member

of the Notch Peak Formation in the Lava Dam Five section of

the Steamboat Pass–Lava Dam composite section of Hintze

and others (1988). The lower boundary of the Ibexian Series

coincides with the lowest observed occurrence of Cordylodus ?andresi Viira and Sergeeva in Viira and others, 1987,

which also defines the base of the Hirsutodontus hirsutus

Subzone of the Cordylodus proavus Zone. This horizon is

about 0.1 meter (4 inches) below the lowest trilobite sample

assigned to the Eurekia apopsis Zone. The top of the Ibexian

Series is defined as the base of the Whiterockian Series,

which, at its stratotype, is drawn at the base of the Tripodus

laevis Conodont Zone and coincidentally with the base of the

Paralenorthis-Orthidiella Brachiopod Zone (=Zone L of

Ross, 1951). In the type area of the Ibexian, the base of the

Tripodus laevis Zone is 6.3 meters below the top of the Wah

Wah Limestone.

1Department of Geology, Colorado School of Mines, Golden, CO

80401. 2Department of Geology, Brigham Young University, Provo, UT

84602-4646. 3Department of Geological Sciences, University of Missouri, Columbia, MO 65211. 4Department of Geography, Geology and Planning, Southwest Missouri State University, Springfield, MO 65904-0089. 5U.S. Geological Survey (retired), Box 25046, MS 913, Denver

Federal Center, Denver, CO 80225-0046. Current address: Institute for

Cambrian Studies, P.O. Box 8, Springer, NM 87747-0008. 6U.S. Geological Survey, National Center 970, Reston, VA 20192. 

7Department of Geological Sciences, University of Texas, Austin, TX

78712. 8Physical Science Division, Rock Valley College, Rockford, IL 61114.

The Ibexian Series is characterized by more than 150

conodont species and more than 150 trilobite and articulate

brachiopod species from a composite stratotype of 11 measured sections in the type area, located in the southern House

Range and southern Confusion Range in the USGS Notch

Peak and The Barn 15-minute quadrangles, Millard County,

Utah. The composite stratotype section involves the Lava

Dam Member of the Notch Peak Formation, House

Limestone, Fillmore Formation, and part of the Wah Wah

Limestone. The composite section aggregates 801 meters

(2,628 feet) of abundantly fossiliferous limestone and subordinate calcareous siliciclastic rocks that formed in a miogeoclinal, shallow-water carbonate-platform environment.

The Ibexian Series is here divided, in ascending order,

into the Skullrockian, Stairsian, Tulean, and Blackhillsian

Stages and into 11 conodont zones and 14 shelly fossil zones

that augment and refine the original 10 Ross (1951) and

Hintze (1953) shelly fossil zones, which have been widely

used in correlation within the North American Faunal Province for 40 years. In addition nautiloid cephalopods, gastropods, sponges, echinoderms, ostracodes, and graptolites

occur in the composite section.

Recent work shows that the base of the Ibexian Series

can be recognized in low paleolatitude sites in both carbonate shelf and slope facies in the Western United States, Appalachian Mountains, eastern and western Canada, Mexico,

Greenland, Kazakhstan, Australia, southeastern Asia, People’s Republic of China, and elsewhere. In deeper water carbonate facies the Ibexian Series is underlain in many places

by rocks bearing the geographically widespread trilobite

Lotagnostus hedini (Troedsson). 

INTRODUCTION

Here we reiterate Hintze’s (1982) proposal that the

Ibexian Series is superior to the fractionated and confusing

Canadian Series, which to many stratigraphers has been the

lowest Ordovician Series for the United States. We designate
2 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

a stratotype for the lower boundary of the Series and tabulate

its characteristic shelly fossil and conodont zones (figs. 8,

10; pl. 1, charts A–C). The fossils make remarkable biostratigraphic control available for the series in the type area. Four

new stages (in ascending order Skullrockian, Stairsian,

Tulean, and Blackhillsian) were tentatively proposed (Ross

and others, 1993) to supplant current stratigraphically inexact, geographically confusing terms, and to construct a biochronologic reference section to be used for correlation

throughout North America and other applicable areas. Our

primary purpose here is to focus attention on the superb

lithostratigraphic column in the Ibex area, to demonstrate the

biostratigraphic excellence of the consolidated Ibexian

stratigraphic succession, and to formally describe the new

stages. In the opinion of the senior author, the continuity of

the composite-stratotype section and its biostratigraphic documentation are currently unsurpassed by any other Lower

Ordovician section in the world.

At the outset we note that the Pogonip Group (Hintze,

1951, p. 11–12; Nolan, Merriam, and Williams, 1956, p.

23–25; Merriam, 1963) includes the Lower Ordovician and

lower Middle Ordovician formations of the Basin Ranges.

Therefore the group includes but is not limited to the Ibexian

units of this report.

After 30 years of fostering cooperative work on sections in the Ibex area, Hintze (1979) assembled an important

summary of the biostratigraphic occurrences of trilobites,

brachiopods, graptolites, conodonts, nautiloid cephalopods,

and other fossils, by leading paleontological authorities and

by graduate students. Detailed conodont studies were published by Miller (1969, 1988), Ethington and Clark (1971,

1981), Ethington and others (1987), and Miller in Hintze

and others (1988).

The composite stratotype of the Ibexian Series has been

and continues to be used increasingly as the reference section for the Lower Ordovician in North America with few

exceptions (Ross and others, 1992). Perhaps the exceptions

can be explained by poor distribution of its first publication

(Hintze in Ross and others, 1982) in the United States or perhaps by the inertia of regional tolerance of habitual, if less

exact, terminology. The Ibexian Series has been used outside

the United States with increasing frequency.

Acceptance of the Ibexian Series stems from the ease

with which its correlatives are recognized in the cratonic,

carbonate-platform, and upper slope facies throughout the

continent. The applicability of the Ibexian biostratigraphic

zonation has been enhanced by the studies of Taylor and Halley (1974) in New York State, Stitt (1977, 1983) and Derby

and others (1991) in Oklahoma, and Westrop (1986) and

Loch and others (1993) in Alberta, Canada. Ji and Barnes

(1996) have made a valuable contribution to Ibexian conodont biostratigraphy in Jasper National Park, Canada; their

interpretation of the position of the Cambrian-Ordovician

boundary differs slightly from ours.

Although no volcanic ash beds satisfactory for isotopic

dating of the series have been found in North America to

early 1997, based on correlation against controlled isotopic

dating elsewhere, we estimate that the duration of the Ibexian

Epoch probably exceeded 20 million years. 

Field measurements were taken in feet and in many critical places the footages were painted on the rock. For purposes of publication feet have been converted to meters. So

that geologists can identify stratigraphic levels, both meters

and feet are given in this report to help them coordinate text

with painted footages on the outcrops of specific units and

horizons in the field.

IBEXIAN SERIES TYPE AREA

AND SECTIONS

The Ibexian Series is superbly exposed in the southern

House and Confusion Ranges of west-central Utah (figs.

1–7). Outcrops are readily accessible both north and south of

combined U.S. Highway 6 and 50 in the southern Notch

Peak 15-minute quadrangle (Hintze, 1974b) and from there

southward for 19 km (12 mi) in the Black Hills on the east

side of Tule Valley in The Barn quadrangle (Hintze, 1974a).

The upper contact with beds assigned to the younger Whiterock Series is exposed 8–9.7 km (5–6 mi) to the west of Tule

Valley at the south end of Blind Valley. The geologic map of

The Barn quadrangle was partly modified by Hintze and others (1988, figs. 8, 9) to show formation and member boundaries in improved detail. New 1:24,000-scale topographic

quadrangle maps became available in 1991 and are utilized

in explanations of figures 1–7.

Following recommendations of the North American

Stratigraphic Code (NACSN, 1983) and guidelines of the

International Commission on Stratigraphy of the International Union of Geological Sciences (Cowie and others,

1986), the lower boundary stratotype of the Ibexian Series is

defined as a point in rock in a measured section. The top of

the Ibexian Series is defined as the base of the overlying

Whiterockian Series.

Descriptions of the physical and many of the paleontological attributes of the Ibexian Series presented here graphically (pl. 1, chart A and part of chart C) are updated from data

previously published by Hintze (1951, 1953, 1973, 1979) and

Hintze and others (1988). Hintze and others (1972) called

attention to this same series of sections at the 23rd International Geological Congress in Prague in 1968. Figure 1 indicates the locations of maps (figs. 2–7) showing measured

traverses along which features of lithologic units are most

easily observed and from which fossils were collected. 

The type sections of the formations constituting the

composite stratotype of the Ibexian Series lie in an area

whose detailed geology was first mapped by Hintze (1974a,

1974b). The few fault displacements of Ibexian strata in the
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 3

type area are small and easily taken into account in measuring and compiling a composite-stratotype section. Dips are

low. Exposures are excellent and key beds can be traced over

distances measured in kilometers. Fossils are abundant

throughout the section. 

Although the Ibexian Series was formally proposed by

Hintze in Ross and others (1982), precise designation of a

base was deferred pending recommendation of a CambrianOrdovician boundary level by the Cambrian-Ordovician

Boundary Working Group of the International Commission

on Stratigraphy, International Union of Geological Sciences

(for example, Henningsmoen, 1973; Bassett and Dean, 1982;

Norford, 1988; Chen, 1986). An expected international

agreement failed to materialize in 1982. In 1985, Rolf Ludvigsen and S.R. Westrop, tired of waiting for a decision, designated the biostratigraphic level of the base of the Ibexian

Series at the base of the Eurekia apopsis Zone in the published Lava Dam Five section of Miller and others (1982,

text-fig. 8; also see Hintze and others, 1988, p. 23–24, pl. 1).

The formal definition of the Ibexian Series as proposed here

coincides with the observed base of the Cordylodus proavus

Zone which for all practical purposes coincides with the base

of the Eurekia apopsis Zone in the typical reference section

(fig. 9). In the definition of the Ibexian lower-boundary stratotype, we place slight emphasis on conodonts rather than

trilobites because conodonts are more easily extracted from

the rock at closely spaced intervals, and many conodont taxa

are geographically widespread.

The base of the Ibexian Series coincides with abrupt

faunal change, sea-level change, and geochemical anomalies

that are recognized over a broad geographic area (for example, Erdtmann and Miller, 1981; Miller, 1984, 1992; Miller

and others, 1989; Wright and others, 1987; Nicoll and Shergold, 1991; Ripperdan and others, 1992; Shergold and

Nicoll, 1992; and Ripperdan and others, 1993). The boundary is thought to coincide with an isochronous event that was

global in scale (Miller and others, 1993).

ACKNOWLEDGMENTS

Dr. Peter Guth, Oceanography Department, U.S. Naval

Academy, Annapolis, Md., provided us with a version of his

STRATCOL computer program, specially modified to produce the biostratigraphic range charts shown on plate 1.

Over a period of 4 years he has spent many hours working

cheerfully with Ross to tailor STRATCOL for changes to

computer programs and to a variety of printers. In fact it was

the ease and accuracy of detail achieved by using STRATCOL that led to realization that the assembled Ibexian composite stratotype was unique in several ways. We thank

James Reed of RockWare Earth Science Software, Wheat

Ridge, Colo., and Cynthia Scheiner, Department of Geology,

Colorado School of Mines, Golden, Colo., for advice on

computer applications.

J.F. Miller’s research was supported by National Science Foundation Grants EAR-8108621, EAR-8407281,

and EAR-8804352, and by Faculty Research Grants and

other funds from Southwest Missouri State University,

Springfield, Mo.

James Sprinkle and T.E. Guensburg thank Fred Siewers, Ronald Johns, Anita Brosius, Colin Sumrall, Mike Slattery, Mark Wilson, J.F. Miller, J.D. Loch, and David Sprinkle

for assistance in the field. Ronald Johns reviewed the manuscript section on Echinoderm Biostratigraphy. This work

was supported by the National Science Foundation under

Grant BSR-8906568 and by the Geology Foundation, University of Texas at Austin (Sprinkle), and by an American

Chemical Society–Petroleum Research Fund Grant to Mark

Wilson, College of Wooster (Guensburg).

J.T. Dutro, G.S. Nowlan, A.R. Palmer, and W.C.

Sweet are thanked for helpful reviews of an early draft of

the report, although the reviewers do not necessarily agree

with all the conclusions. Lorna Carter and Carol A.

Quesenberry are thanked for outstanding editing and final

preparation of illustrations.

DEFINITION OF THE IBEXIAN SERIES

The lower-boundary stratotype of the Ibexian Series is

here formally defined as a point in rock 39.1 m (128.3 ft)

above the base of the Lava Dam Member of the Notch Peak

Formation in the Lava Dam Five segment of the Steamboat

Pass–Lava Dam section of Hintze and others (1988, p.

23–24, fig. 9; this report, figs. 8, 10). This measurement

takes into account a 0.9 m (3 ft) offset by a minor normal

fault in the lower part of the Lava Dam Member. The boundary stratotype point coincides with the lowest observed

occurrence of Cordylodus ?andresi Viira and Sergeeva, in

Viira and others, 1987, which locally defines the base of the

Hirsutodontus hirsutus Subzone of the Cordylodus proavus

Zone (fig. 8). This boundary stratotype point is approximately 0.1 m (4 in.) below the lowest observed occurrence of

trilobites assigned to the Eurekia apopsis Zone (fig. 8). The

highest observed occurrence of trilobites diagnostic of the

underlying Saukiella serotina Subzone of the Saukia Zone is

about 10 cm (4 in.) below the base of the Cordylodus proavus

Zone. This near coincidence of boundaries of conodont and

trilobite zones also occurs in Texas and Oklahoma (Miller

and others, 1982).

The top of the Ibexian Series is recognized as the base of

the Whiterockian Series, which was defined in the Monitor

Range of central Nevada by Ross and Ethington (1991) as the

base of the Tripodus laevis conodont Zone and the coincident

base of the Paralenorthis-Orthidiella brachiopod Zone

(=Zone L of Ross, 1951) (fig. 10). That level is 11 m (36 ft)

below the top of the Wah Wah Limestone (see p. 11, 26–27).

Herein, we follow recommendations outlined in the

North American Stratigraphic Code (NACSN, 1983) and

the International Commission on Stratigraphy (Cowie and
4 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

39 ̊

00'

38 ̊

52'

30"

113 ̊ 113 22'30"  ̊30'

UTAH

Figure 1

Figure 3

Figure 2

Figure 4

Figure 7 Figure 6

Figure 5
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 5

10 11

15 14

N 4,327,000

E 292,000 E 293,000

Oh

Oh

Oh

Oh

Oh

Qa

Qa

Oh

Oenl

Oenl

Oh

Oh

Oh

Of

Of

Of

Of

Of

Of

Oenl

>>> >>>>>

A

s

s

s

Oenl

Oenl

Oenl

Oenl

Oh

Oh

Oh Oh

Qa

>>>>>

enr

enr

enr

enr

enr

enh enh

enh enh

SnP

N 4,330,000

N 4,329,000

E 298,000 E 299,000

5 4

8 9

others, 1986) for definition of biostratigraphic and

chronostratigraphic units. In addition, a distinction is made

between definition of units by selection and description of a

lower-boundary stratotype point in a measured section, and

characterization which deals with the faunal content of

units in the type area and the principal faunal data upon

which correlations are interpreted (Murphy, 1977). Only the

base of a unit is defined; tops are determined by the definition of the next overlying unit.

In order to help relocate the lower-boundary stratotype

point of the Ibexian Series, J.F. Miller in the summer of 1992

drove a steel bolt marked with a brass plate (fig. 9A, B), into

the upper part of the Lava Dam Member of the Notch Peak

Formation at the Lava Dam Five section (fig. 6). The bolt is

39.1 m (128.3 ft) above the contact between the Red Tops

Member and overlying Lava Dam Member of the Notch Peak

Formation. The marker is approximately 59 m (194 ft) stratigraphically above the alluvial fill of the valley floor; the lower

20.1 m (66 ft) is the thickness of the exposed part of the Red

Tops Member, and the upper 39 m (128.3 ft) is the thickness

of part of the Lava Dam Member up to the boundary. 

Definitions and faunal characterizations of the new

Skullrockian, Stairsian, Tulean, and Blackhillsian Stages are

given under appropriate headings herein.

We summarize, in ascending order, the lithostratigraphy, biostratigraphy, and chronostratigraphy of the Ibexian

Series and adjacent rocks in the type area, which is located in

the southern House Range–Ibex area of western Utah.

LITHOSTRATIGRAPHY

The stratotype section of the Ibexian Series is a composite section consisting of part of the Lava Dam Member

of the Notch Peak Formation, all of the House Limestone

and Fillmore Formation, and part of the Wah Wah Limestone. The House, Fillmore, and Wah Wah formations,

which are the lower part of the Pogonip Group, were initially defined in this area by Hintze (1951) and redescribed

by Hintze (1973). The locations of measured stratigraphic

sections that include typical examples of these lithostratigraphic units are shown in figures 1–7, and geographic

coordinates are tabulated in table 1.

Figure 1 (facing page). Index map of Ibex area, western Utah,

showing locations of detailed maps in figures 2–7. Base from U.S.

Geological Survey 100,000 Tule Valley (1981) and Wah Wah

Mountains North (1980). The small squares on the map base are

about 1 mi2 in area.

Figure 2. Geologic map showing location of the A Section of

Hintze (1951, 1973). Oenl, Lava Dam Member of the Notch

Peak Formation; Oh, House Limestone, the middle sandy zone

of which is shown by a dashed line labeled s; Of, Fillmore Formation; Qa, surficial deposits. Heavy line, fault; bar and ball on

downthrown side. Tielines indicate equivalent beds across

faults. Line of section indicated by inverted “V’s.” Base from

U.S. Geological Survey 1:24,000 Hell’n Moriah Canyon provisional quadrangle (1991). Geology from Hintze (1974b).

Figure 3. Geologic map showing location of the Sneakover

Pass (SnP) measured section of Hintze and others (1988). enh,

Hellnmaria Member of the Notch Peak Formation; enr, Red Tops

Member of the Notch Peak Formation; Oenl, Lava Dam Member

of the Notch Peak Formation; Oh, House Limestone; Qa, surficial

deposits. Heavy line, fault; dotted where concealed; bar and ball

on downthrown side. Tieline indicates equivalent beds across

fault. Line of section indicated by inverted “V’s.” Base from U.S.

Geological Survey 1:24,000 Skull Rock Pass provisional quadrangle (1978). Geology from Hintze (1974b).
6 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

CONSTRUCTION OF THE

COMPOSITE STRATOTYPE

The composite stratotype is based on lithostratigraphic

units exposed in eight of the sections measured by Hintze

(1951, 1953, and 1973) and by Hintze and others (1988)

(figs. 2, 5, 6, and 7 herein). In order to establish a firm Cambrian foundation and to facilitate correlation with a section in

the Southern Egan Range, being studied by W.C. Sweet, the

Red Tops Member of the Notch Peak Formation at the

Steamboat Pass–Lava Dam section is designated as the basal

unit (fig. 6). It is 40 m (131 ft) thick. The Lava Dam Member

(77.4 m (254 ft) thick) is the next higher unit and includes the

base of the Ibexian Series 39.1 m (128.3 ft) above the base of

the member, or 79 m (259.3 ft) above the base of the composite section (pl. 1). The lithostratigraphic description used to

construct this lowest part of the composite stratotype is

found on pages 23–25 of USGS Professional Paper 1393

(Hintze and others, 1988), including the exposed beds of the

House Limestone through Unit 41. This inclusion provided a

natural continuum for ranges of trilobites through the lower

26.2 m (86 ft) of the House strata. 

The thickness of the House Limestone at Section A, its

type section, was corrected from 475 ft to 515 ft by Hintze

(1973, p. 8, table 1). However, J.F. Miller found during the

1994 field season that the thickness should be 558 ft (170 m),

and we have adjusted the total thickness of the House Limestone accordingly. The House Limestone at the Lava Dam

section is integrated with Section A by using only the upper

472 ft (143.8 m) (558 minus 86 ft) for the composite.

Because of the change from the original 475 ft to 558 ft, the

spacing of the trilobite collections reported by Hintze (1951,

p. 30–33; 1953, p. 24–25) was revised proportionally. The

spacing of conodonts is that reported by Ethington and Clark

for Section A (1981, table 1). 

The top of the House Limestone at the Lava Dam North

section is marked by a resistant thoroughly burrowed limestone bed, 3 m (10 ft) thick, that is traced northward to the B

Section (Hintze, 1951, p. 33–37; 1953, p. 25–26), as verified

by Ethington and Ross in June 1994. This permits integration

of the ranges of trilobites in the top 104.6 m (343 ft) of the B

Section with those in the A Section.

The Fillmore Formation was separated into six members by Hintze (1973, p. 9–11, table 2) (numbered 1 to 6 on

p. 8–11 herein). In assembling the composite we have used

the two lowest members from the C Section, respectively

485 ft and 320 ft thick. The third and fourth members, 180

ft and 324 ft thick, were taken from the Mesa Section.

However, in order to assemble the greatest available thickness, the fourth member in the H Section is integrated by

aligning “Marker ledge 1” in unit 6 (Hintze, 1973, p. 27)

with the same “Marker ledge 1” in unit 2 in the Mesa Section (Hintze, 1973, p. 20). The resulting aggregate thickness of the Fillmore Formation at the top of the fourth

member is 1,322 ft. By aligning the “Marker ledge 1” in

unit 4 in the G Section (Hintze, 1973, p. 24), the ranges of

trilobites in the three sections have been integrated. Both

the fifth and sixth members of the Fillmore are taken from

>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>> >

Oe

Oes

Qa

Qa

Of

Ow

Ow

Qs

Tsr

Ow

Of

Oes

Oes

Oes Oes

Square Top

N 4,313,000

N 4,312,000

E 295,000 E 296,000 E 297,000

Figure 4. Geologic map showing location of the Square Top measured section of Hintze (1973). Of, Fillmore Formation; Ow, Wah Wah Limestone; Oe, Eureka Quartzite; Oes, Ely Springs Dolomite; Qa, surficial

deposits; Qs, sand. Line of section indicated by inverted “V’s.” Base from U.S. Geological Survey 1:24,000

Burnout Canyon provisional quadrangle (1991). Geology from Hintze (1974a).
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 7

the H Section. The total thickness of the Fillmore aggregates 558 m (1,803 ft). The thickness of the composite

section at the top of the Fillmore is 836 m (2,744 ft). 

The Wah Wah Limestone, Juab Limestone, and Kanosh

Shale and their trilobite and brachiopod faunas are taken

from the J Section (Hintze, 1973, p. 28–30; 1951, p. 57–63;

1953, p. 36–40). 

Conodonts of the Fillmore Formation are taken from

the same pertinent sections as published by Ethington and

Clark (1981), but collections made by Ethington in 1994 supplement earlier collections in the J Section.

NOTCH PEAK FORMATION

The Notch Peak Formation of Walcott (1908a, b) was

redescribed and divided in ascending order into the Hellnmaria, Red Tops, and Lava Dam Members by Hintze and others (1988). The lithostratigraphy and biostratigraphy of the

Notch Peak Formation in the Steamboat Pass–Lava Dam

area were described by Hintze and others (1988, p. 23-26).

Emendations to biostratigraphic ranges of conodonts and trilobites were given by Miller and others (1982) and Miller

and Taylor (1989). 

HELLNMARIA AND RED TOPS MEMBERS

The Hellnmaria and Red Tops Members are mentioned

here only for completeness, because neither member is

involved in the Ibexian Series. The Red Tops is the lowest

unit exposed in the lower part of the Lava Dam Five segment of the Steamboat Pass–Lava Dam section (Hintze and

others, 1988, p. 23–26).

The Lava Dam Five segment of the Steamboat

Pass–Lava Dam section begins in a minor gully near the

south end of the “Lava Dam,” a channel eroded into the

Notch Peak Formation and filled with Oligocene volcanic

rocks, and Tule Valley fill (Hintze, 1988, figs. 8, 9; this

report, figs. 1, 6). The base of the section is within the Red

Tops Member, 20.1 m (66 ft) below the contact between the

Red Tops and Lava Dam Members of the Notch Peak Formation. The stratigraphically lowest point in the measured section is marked by “0” with yellow paint. The exposed part of

the Red Tops Member consists of current-rippled oolitic,

skeletal, and intraclastic lime grainstone and lime packstone

that contains trilobites representative of the Saukiella junia

Subzone of the Saukia Zone (Taylor, 1971; Taylor in Hintze

and others, 1988, pl. 1). In constructing the composite stratigraphic section shown on plate 1 the full thickness of the Red

Tops Member, 39.9 m (=131 ft) has been used (Hintze and

others, 1988, p. 25).

LAVA DAM MEMBER

The type locality of the Lava Dam Member is at Sneakover Pass (fig. 3) in the central House Range (Hintze and

others, 1988, p. 21, fig. 5, table 1) where it is 110.9 m (364 ft)

thick. As a result of facies changes, the Lava Dam Member is

76.0 m (249.5 ft) thick in the Steamboat Pass–Lava Dam

composite section (Hintze and others, 1988, p. 25).

> >>> > >>

>>>

>>

>

>>>>>>

> >>> >>>>>

>>>>

>>>>> >>>>>>>>>>

Qa

Qa

Of

Of

Of

Of

Of

Qa

Tsr

Tsr

Tsr

Qa

Oh

Qa

N 4,309,000

N 4,308,000

N 4,307,000

N 4,306,000

E 296,000 E 297,000

Mesa

1965–C

Figure 5. Geologic map showing location of the Mesa and 1965-

C measured sections of Hintze (1973). In the 1965-C Section, the

lower boundary stratotype of the Tulean Stage is marked by the lowest observed occurrence of Menoparia genalunata located at 11.6

m (38 ft) above the base of unit 2 of the informal slope-forming

shaly siltstone member of the Fillmore Formation. Oh, House Limestone; Of, Fillmore Formation (dashed line indicates a key bed); Tsr,

Skull Rock Pass Conglomerate (Hintze and Davis, 1992); Qa, surficial deposits. Lines of sections indicated by inverted “V’s.” Base

from U.S. Geological Survey 1:24,000 Burnout Canyon provisional

quadrangle (1991). Geology from Hintze (1974a).
8 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

The Lava Dam Member consists of skeletal, oolitic, and

intraclastic lime grainstone and of cherty lime mud-supported limestone. Massive stromatolitic limestone forms the

upper half of the Lava Dam Member in sections farther

north, but stromatolites are restricted to a thin interval in the

middle part of the member at the Lava Dam. In most of its

exposures the member forms conspicuous cliffs and ledges

below the low ledges and rounded slopes of the conformably

overlying House Limestone.

HOUSE LIMESTONE

The type locality of the House Limestone is the A Section of Hintze (1973, p. 8–9; 1951, p. 30–33), where the formation was considered to be 156.9 m (515 ft) thick.

Subsequent inspection in 1993 led J.F. Miller to conclude

that a unit 13.1 m (43 ft) thick had been left out of this measurement. The thickness of the House Limestone used in the

composite section is therefore 170.1 m (558 ft) on plate 1.

Supplementary sections are the Lava Dam North (LDN) section of Hintze (1973, p. 15–16) and Lava Dam Five (LD5)

section. Figures 2 and 6 show locations of sections.

Only the lower 27.6 m (90.5 ft) of the House Limestone

is present at the Lava Dam Five section. The composite section is offset and continues on the north side of the Lava Dam

where outcrops are continuous from the upper part of the

Lava Dam Member of the Notch Peak Formation through the

House Limestone and into the Fillmore Formation.

The House Limestone consists of thinly to thickly bedded, dark-gray limestone containing abundant brown to

black chert, grading from irregular masses to well-bedded

continuous layers. The base is marked by arenaceous limestone in the Lava Dam Five section. Detailed descriptions

of the Lava Dam Five section and other sections of the

Notch Peak Formation and the lower part of the House

Limestone are given by Hintze and others (1988), and by

Hintze (1951, 1973).

FILLMORE FORMATION

Although Hintze (1951, p. 14) designated his sections

D, G, and H as the composite type section of the Fillmore

Limestone, his subsequent (1973, p. 16–19) redescription of

the Fillmore Formation and its five informal lithostratigraphic members has effectively supplanted that definition.

These members aggregate 549.5 m (1,803 ft) in thickness.

The informal members and their best representative sections

are discussed here in ascending order. Because of a change

in his original C Section, it is essential that reference be

made to the modifications in location of the measured section that is designated 1965-C Section by Hintze (1973, p.

16; and fig. 5 herein).

BASAL LEDGE-FORMING LIMESTONE MEMBER (1)

The typical reference section of the informal ledgeforming limestone member (1) is in the 1965-C Section of

Hintze (1973, p. 18–19) where the informal member is 147.8

m (485 ft) thick. The lowermost 22.5 m (71.5 ft) form the

ledgy part of the member, which rests directly on the uppermost massive ledge of the House Limestone at this locality.

A supplementary section is in the G Section of Hintze (1973,

p. 25). See figures 5 and 7 for locations.

Table 1. Universal Transverse Mercator 1,000 m grid coordinates, Zone 12, for bottoms and tops of constituent segments of the Ibexian

Series composite stratotype section. 

[Map locations are shown in figures 1–7. Segments are listed in the order they should be visited to demonstrate the continuity of the section]

SEGMENT BOTTOM TOP

Lava Dam Five E 295,950 m; N 4,300,980 m E 295,910 m; N 4,300,770 m

Lava Dam North E 296,230 m; N 4,302,000 m E 296,560 m; N 4,302,120 m

A (1951) E 292,320 m; N 4,326,980 m E 292,570 m; N 4,326,910 m

B (1951) E 296,060 m; N 4,304,150 m E 296,330 m; N 4,304,400 m

Sneakover Pass E 298,440 m; N 4,329,580 m E 298,250 m; N 4,329,450 m

Square Top E 295,600 m; N 4,312,230 m E 295,870 m; N 4,312,540 m

Mesa (lower) E 296,600 m; N 4,307,850 m E 296,860 m; N 4,308,100 m

Mesa (upper) E 297,100 m; N 4,308,320 m E 297,040 m; N 4,308,600 m

1965-C (lower) E 296,160 m; N 4,305,800 m E 296,760 m; N 4,305,800 m

1965-C (upper) E 296,880 m; N 4,306,500 m E 296,950 m; N 4,307,000 m

G E 287,400 m; N 4,300,720 m E 287,680 m; N 4,301,080 m

H (lower) E 287,200 m; N 4,301,800 m E 286,900 m; N 4,301,830 m

H (middle) E 286,960 m; N 4,302,220 m E 286,600 m; N 4,302,130 m

H (upper) E 286,590 m; N 4,302,130 m E 286,400 m; N 4,302,150 m

J E 286,640 m; N 4,303,670 m E 285,700 m; N 4,304,060 m
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 9

SLOPE-FORMING SHALY SILTSTONE MEMBER (2)

The typical reference section of the informal slopeforming shaly siltstone member (2) is in the 1965-C Section of Hintze (1973, p. 17–18), where the informal member is 97.5 m (320 ft) thick. It should be noted that only the

uppermost 9.4 m (30 ft) are exposed above the underlying

informal basal ledge-forming limestone member and that

the section is offset approximately 0.8 km (0.5 mi) to the

north (see fig. 5). In the Mesa supplementary section, the

member is 98 m (312 ft) thick; its base is traced northward

from the 1965-C Section. A second supplementary section

is the G Section of Hintze (1973, p. 21–22 and 25). See figures 5 and 7 for locations.

>>>>>>>> >>>>>> >>>>

>>>>>>>>>>

N 4,304,000

N 4,303,000

N 4,302,000

N 4,301,000

E 295,000 E 296,000

Of

Of

Qs

Qa

Qa

Qa

Tv

Tv

Tv

LAVA

DAM

Of

Of

Of

Of

Of

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

Oh

LDN

B

LD5

Oenl

Oenl

Oenl Oenl

Oenl

Oenl

Oenl

enr

enr

enr

enr

Oenl

Figure 6. Geologic map showing location of the B Section

of Hintze (1951) and the Lava Dam North (LDN) and Lava

Dam Five (LD5) measured sections of Hintze (1973) and

Hintze and others (1988). enr, Red Tops Member of the

Notch Peak Formation; Oenl, Lava Dam Member of the

Notch Peak Formation; Oh, House Limestone (dashed line

indicates a key bed); Of, Fillmore Formation; Tv, Tertiary

volcanic rocks; Qa, surficial deposits; Qs, sand. Heavy line,

fault; dashed where inferred; dotted where concealed; bar

and ball on downthrown side. Tielines indicate equivalent

beds across faults. Lines of sections are indicated by inverted “V’s.” Lower boundary stratotypes of the Ibexian Series

and Skullrockian Stage are coincident and located in the

LD5 Section (see text). Base from U.S. Geological Survey

1:24,000 Red Tops provisional quadrangle (1991). Geology

from Hintze (1974a) and Hintze and others (1988).
10 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

LIGHT-GRAY LEDGE-FORMING MEMBER (3)

The typical reference section of the informal light-gray

ledge-forming member (3) is in the Mesa Section of Hintze

(1973, p. 20–21) where the informal member is 54.9 m

(180.0 ft) thick. The position of the base of the member is

established by tracing the base of the underlying informal

member (2) northward from the 1965-C Section. Only 48.8

m (160 ft) of this member (3) is present in the supplementary

1965-C Section and 59.1 m (194 ft) in the G Section of

Hintze (1973, p. 17 and 24). See figures 5 and 7 for locations.

BROWN SLOPE AND LEDGE MEMBER (4)

The typical reference section of the informal brown

slope and ledge member (4) is in the Mesa Section of Hintze

(1973, p. 20) where the informal member is 98.8 m (324 ft)

thick. A conspicuous 1.5-m-thick (5 ft) ledge located

51.8–53.3 m (170–175 ft) above the base of the informal

member is used as a marker to offset 0.3 km (0.2 mi) to the

northwest and to correlate with the highest of four marker

ledges in the G supplementary section of Hintze (1973, p.

23–24) and in the H Section (Hintze, 1973, p. 27). See

figures 5 and 7 for locations.

CALCARENITE MEMBER (5)

The typical reference section of the informal calcarenite

member (4) is in the H Section of Hintze (1973, p. 26–27)

where the member is 94.5 m (310 ft) thick. A supplementary

section is in the Square Top section of Hintze (1973, p. 22).

See figures 4 and 7 for locations.

D

D

D

D

D

>>

>>

>>

>>>> > >>>>>> >> >>> >>

>> >>

>>

>>

>>

>>

>>

>>

>>

>>>> >> >>

>> >> >> >> >

Tv

Tv

Tv

Tv

Tv

Tv

Tv

Ou

Ou

Ou Qa

Qa

Qa

Qa

Qs

Ou

Ok

Ok

Ok

Ok

Ow

Ow

Ow

Ow

Ow

Of

Of

Of

Of

Of

Of

Of

Of

Of

Of

Of

Of

Of

Of

Ok

Oj

Oj

Oj

Oj

H

G

J

N 4,301,000

N 4,302,000

N 4,303,000

N 4,304,000

E 286,000 E 287,000

Figure 7. Geologic map showing location of

the G, H, and J measured sections of Hintze

(1951, 1973). The lower boundary of the Tulean

Stage is located 1.8 m (6 ft) above the base of unit

2 of the informal slope-forming shaly siltstone

member of Hintze (1973, p. 25) in the G Section.

The lower boundary stratotype of the Blackhillsian Stage is 5.8 m (19 ft) above the base of unit

2 of the informal calcarenite member of Hintze

(1973, p. 26) in the H Section. Of, Fillmore Formation (dashed lines indicate key beds); Ow,

Wah Wah Limestone; Oj, Juab Limestone; Ok,

Kanosh Shale; Ou, undivided Middle and Upper

Ordovician rocks, considerably faulted; Tv, Tertiary volcanic rocks; Qa, surficial deposits; Qs,

sand. Heavy line, fault, dotted where covered; bar

and ball on downthrown side; sawteeth on upthrown block. Tie lines indicate equivalent beds

across faults. Lines of section are indicated by inverted “V’s.” Base from U.S. Geological Survey

1:24,000 Warm Point provisional quadrangle

(1991). Geology from Hintze (1974a).
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 11

Eurekia eos

Euptychaspis kirki

Macronoda cf. prima

Stenopilus bacca

Bowmania ulrichi

Rasettia wichitaensis

Idiomesus intermedius

Stenopilus latus

Rotundoconus sp.

Cordylodus andresi

Cambrian Ordovician System

Croixian Ibexian

Skullrockian (part)

Series

Stage

Fm./Mbr.

Trilobite Zones

Conodont and Trilobite Ranges

Trempealeauan (part)

Ss

?

Sj Md

Notch Peak Formation ( Lava Dam Mbr.) House Ls.

Ea Mt

0 30 meters

feet

Triarthropsis nitida

Hirsutodontus hirsutus

Missisquoia depressa

Plethometopus armatus

Cordylodus proavus

Fryxellodontus inornatus 

Fryxellodontus lineatus

Missisquoia typicalis

Hirsutodontus rarus 

Clavohamulus elongatus

Clavohamulus bulbousus

Semiacontiodus nogamii 

Symphysurina brevispicata 

Highgatella cordilleri 

Hystricurus 

Monocostodus sevierensis

Hirsutodontus simplex 

Utahconus utahensis

Albiconus postcostatus

sp.

Missisquoia inflata

Symphysurina bubops

Symphysurina sp.

Teridontus nakamurai

Eurekia apopsis

Acheilops masonensis

Larifugula leonensis

Cordylodus drucei

Cordylodus intermedius

Semiacontiodus lavadamensis

Clavohamulus hintzei

Utahconus tenuis

0 100

Symphysurina

Ch Conodont Subzones

Cordylodus proavus Eoconodontus

Missisquoia

Conodont Zones Cordylodus intermedius

Hs Ce Fi

Proconodontus muelleri 

Cambrooistodus cambricus

Cambrooistodus minutus 

Proconodontus serratus

Heterocaryon tuberculatum

Leiocoryphe platycephala

Hh

CALATHIUM CALCISILTITE MEMBER (6)

The typical reference section of the informal Calathium

calcisiltite member (5) is in the H Section of Hintze (1973, p.

26), where the informal member is 51.8 m (170 ft) thick. A

supplementary section is in the Square Top section of Hintze

(1973, p. 22). See figures 4 and 7 for locations.

WAH WAH LIMESTONE

The type section of the Wah Wah Limestone is in the J

Section of Hintze (1951, p. 16–17). The formation is well

exposed in the mountain front between sections H and J of

Hintze (1951; 1973, p. 29–30). The Wah Wah is 78.6 m (258

ft) thick, but only the lower 67.6 m (222 ft) is Ibexian in age.

The upper 11 m (36 ft) of the formation is correlated with the

lowermost beds of the type Whiterockian Series (Ross and

Ethington, 1991). See figure 7 for location. 

IBEXIAN BIOSTRATIGRAPHY

INTRODUCTORY STATEMENT

As applied to lower Paleozoic rocks of the Western

United States and elsewhere, trilobite zones and subzones

traditionally have been contiguous assemblage zones and

subzones (Taylor, 1987, p. 55, fig. 7.3). They are defined and

characterized by associations of taxa that occur in a consistent homotaxial arrangement. (Compare NACSN, 1983, p.

862–863, fig. 4.) Correlation of trilobite assemblage zones

Figure 8. Detailed range chart for selected trilobites and conodonts at the lower boundary-stratotype of the Ibexian Series in the Lava Dam

Five segment of the Steamboat Pass–Lava Dam section of Hintze and others (1988). Lowest observed occurrence of Cordylodus andresi

coincides with the stratigraphic level of a steel bolt marking the base of the Ibexian Series at 39.1 m (128.3 ft) above the base of the Lava

Dam Member of the Notch Peak Formation. Open rectangles are error bars that provide a semiquantitative (nonprobabilistic) estimate of

how well established are lowest and highest occurrences of a species as suggested by occurrence/absence in subjacent and superjacent fossilbearing samples. Sj, Saukiella junia Subzone and Ss, Saukiella serotina Subzone of Saukia Zone; Ea, Eurekia apopsis Zone; Md, Missisquoia depressa Subzone and Mt, Missisquoia typicalis Subzone of Missisquoia Zone; Hh, Hirsutodontus hirsutus Subzone, Fi, Fryxellodontus inornatus Subzone, and Ce, Clavohamulus hintzei Subzone of the Cordylodus proavus Zone; Hs, Hirsutodontus simplex Subzone and

Ch, Clavohamulus hintzei Subzone of Cordylodus intermedius Zone.
12 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

emphasizes comparison of faunal content of the zone, rather

than zonal boundaries. In contrast, conodont zones and subzones are customarily interval zones in the nomenclature of

the North American Stratigraphic Code (NACSN, 1983, p.

862, fig. 5; also compare Taylor, 1987, p. 55, fig. 7.3) and

normally are defined by the lowest observed occurrence of a

specified taxon in a typical reference section. Correlation by

conodont interval zones may be accomplished by recognizing the lowest occurrence of the defining taxon in rocks away

from the typical reference section and by assuming that the

two points are isochronous. In this practice, emphasis is

placed on boundaries rather than content of conodont

interval zones. Used alone the interval-zone method of

correlation risks error because of ecological (facies) differences in sections away from the boundary stratotype.

In this report, we have integrated conodont, brachiopod,

and trilobite biostratigraphic data (fig. 10). The result is a

biostratigraphic classification scheme that includes zones

that are (1) defined by the lowest observed occurrence of a

particular taxon; and (2) characterized by faunal assemblages with species that lived under different ecologic

requirements and whose remains exhibit widely divergent

patterns of paleobiogeographic distribution. Thus, the Ibexian high-resolution zonal scheme enhances the probability of

overcoming local facies differences and improving precision

in long-range biochronologic correlations.

9

8

4

7 6

5 6

3

2

1

A

Figure 9 (above and facing page). Lava Dam Five section (LD5), southern House Range, Utah. A, Areal view, looking south. Numbers

on photograph identify the following: 1, east end of dirt track connecting to Tule Valley Road; 2, base of Lava Dam Five traverse within the

Red Tops Member of the Notch Peak Formation; 3, base of Lava Dam Member, from which all vertical measurements on plate 1 are taken;

4, normal fault that repeats 3 ft (0.9 m) of strata in lower part of Lava Dam Member (left side is uplifted); 5, boundary stratotype point at

base of the Ibexian Series; 6, base of massive cliff-forming limestone unit in upper part of Lava Dam Member; 7, vertical fault with 12.2 m

(40 ft) displacement (strata to right uplifted); 8, base of House Limestone; 9, top of LD5 part of measured section. See figure 6 for location

of traverse. B, Closeup of lower boundary stratotype point of Ibexian Series, viewed from the east. Metal plaque near tip of arrow, attached

to outcrop by an iron bolt, is engraved, “Base of Ibexian Series J.F. Miller 1992.” Paint numbers 130 and 135 indicate footage above base of

Lava Dam Member without correction for 3-ft-displacement fault shown in view A (position 4). Photographs by J.F. Miller.
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 13

PRE-IBEXIAN FAUNAL ZONES

The lithostratigraphy and biostratigraphy of rocks

underlying the lower boundary of the Ibexian Series are

briefly summarized here to provide a context for definition

of the lower-boundary stratotype in the Lava Dam Five segment of the Steamboat Pass–Lava Dam section of Hintze and

others (1988, fig. 8; this report, figs. 6, 8).

Although the Notch Peak Formation of the Ibex area

has yielded trilobites that are as old as the Upper Cambrian

Taenicephalus Zone (Taylor, 1971; M.E. Taylor in Miller and

others, 1982), for practical reasons discussion here begins in

the Lava Dam Member of the Notch Peak Formation with trilobites of the Upper Cambrian Saukiella serotina Subzone of

the Saukia Zone.

The Saukiella serotina Subzone of the Saukia Zone was

named by Longacre (1970, p. 12) as a replacement name for

the Saukiella norwalkensis Subzone of Winston and Nicholls

(1967, p. 69), which was based on an association of trilobites

underlying the Corbinia apopsis Subzone of the Saukia Zone

(=Eurekia apopsis Zone of this report) in the Wilberns Formation of central Texas. 

The Saukiella serotina Subzone is recognized in the

Lava Dam Five section by the occurrence of Euptychaspis

kirki Kobayashi, Macronoda sp., Heterocaryon tuberculatum Rasetti, and Leiocoryphe platycephala Kobayashi.

Based on present knowledge, no indicator of the Saukiella

serotina Subzone occurs above the lower-boundary stratotype point at the base of the Ibexian Series.

Pre-Ibexian conodonts in the Lava Dam Member of the

Notch Peak Formation in the Lava Dam Five section are

assigned to the Cambrooistodus minutus Subzone of the

Eoconodontus Zone (Miller, 1988) (figs. 8, 10). Conodont

species present include Cambrooistodus cambricus, Cambrooistodus minutus, Eoconodontus notchpeakensis, Phakelodus elongatus, Proconodontus muelleri, Proconodontus

serratus, and Prosagittodontus eureka, all but one of whose

ranges terminate abruptly in the Ibex area at the lower

boundary of the Ibexian Series. Other conodonts that range

across the lower boundary of the Ibexian include Eoconodontus notchpeakensis, Furnishina sp., Problematoconites

perforatus, Prooneotodus gallatini, and Prooneotodus rotundatus. Rare specimens assigned to Rotundoconus sp. occur at

the top of the Cambrooistodus minutus Subzone.

B
14 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

IBEXIAN FAUNAL ZONES AND

CHRONOSTRATIGRAPHY

Silicified trilobites of the type Ibexian were first

described in a classic monograph by Hintze (1953). Jensen

(1967) documented the stratigraphic occurrences of brachiopods, although most of the species he described were from

younger Whiterockian strata. Demeter (1973), Terrell

(1973), and Young (1973) augmented taxonomic knowledge

of Ibexian trilobites as well as information on their stratigraphic ranges. Conodont occurrences for these sections

were documented by Miller (1969), Ethington and Clark

(1971, 1981), Ethington and others (1987), Miller and others

(1982, p. 168–169), Miller in Hintze and others (1988, pl. 1),

and Miller (1988). Hook and Flower (1977) described

numerous nautiloid cephalopods from the Ibexian part of the

Wah Wah Limestone. Braithwaite (1976) described graptolites from the Ibexian sections, but their ranges have not been

precisely determined. The ranges of genera and species of

echinoderms are discussed in Appendix 4 by James Sprinkle

and T.E. Guensburg, and are shown on plate 1, chart C.

IBEXIAN STAGES AND

TRILOBITE ZONES

Ross (1951) and Hintze (1953) subdivided the Lower

Ordovician into a succession of trilobite and brachiopod

assemblage zones, which have been widely applied in biostratigraphic correlation of North American rocks here

assigned to the Ibexian Series. Ethington and Clark (1981),

Miller and others (1982), and Ethington and others (1987)

provided detailed conodont zonal ranges in the Ibexian type

area, but the conodont zone boundaries do not precisely

coincide with the trilobite zone boundaries. As a matter of

convenience and for general communication, we divide the

Ibexian Series into four new stages with stage boundaries

primarily defined on trilobite ranges in the composite stratotype section of the series. The stages take their names from

geographic features in the general vicinity of the Ibexian

composite stratotype in the southern House and Confusion

Ranges. However, rocks exposed at those geographic features are not representative of the chronostratigraphic units.

The new stage names and their component shelly fossil and

conodont zones are listed in figure 10. The inadequacies of

former Lower Ordovician stages are discussed in a section

entitled “Historical Perspective.”

The utility of the trilobite zones of the type Ibexian is

exceptionally well illustrated by Dean’s (1989) monograph

on the trilobites of the Survey Peak, Outram, and Skoki Formations at Wilcox Pass, Jasper National Park, Alberta.

SKULLROCKIAN STAGE (NEW)

The lower-boundary stratotype of the Skullrockian

Stage coincides with the lower-boundary stratotype of the

Ibexian Series, 39.1 m (128.3 ft) above the base of the Lava

Dam Five section of the Steamboat Pass–Lava Dam composite section. This point coincides with the base of the Hirsutodontus hirsutus Subzone of the Cordylodus proavus Zone.

The name “Skullrockian Stage” is taken from Skull Rock

Pass (UTM Coord., Zone 12: E 297,380 m; N 4,322,800 m),

although the rocks exposed in the pass are actually younger

than the Skullrockian Stage. 

The Skullrockian Stage is characterized by the Eurekia

apopsis Zone, Missisquoia, Symphysurina, BellefontiaXenostegium, and Paraplethopeltis trilobite Zones, and the

Cordylodus proavus, Cordylodus intermedius, Cordylodus

lindstromi, Iapetognathus, Cordylodus angulatus, and all

except the uppermost part of the Rossodus manitouensis conodont Zones. The upper limit of the stage is the base of the

Stairsian Stage, which is drawn at the base of the Leiostegium-Kainella Zone. 

EUREKIA APOPSIS ZONE

Nomenclatural history of divisions of the Saukia Zone

has been recently summarized by Loch and others (1993).

Herein we follow Ludvigsen and Westrop (1985, p.

139–140, fig. 1) by including the Eurekia apopsis Subzone

of the Saukia Zone in the overlying Ibexian Series, rather

than in the underlying Croixian Series as recommended by

Loch and others (1993, fig. 3). The Eurekia apopsis Subzone can be recognized widely in North American platform

sites; therefore, we recognize the subzone as an independent zone in this report.

The Eurekia apopsis Zone is recognized in the Lava

Dam Member in the Lava Dam Five section by the occurrence of Eurekia apopsis (Winston and Nicholls), Acheilops

masonensis Winston and Nicholls, Larifugula leonensis

(Winston and Nicholls), and Triarthropsis nitida Ulrich (pl.

1; fig. 8). Lowest trilobite collections assigned to the Eurekia

apopsis Zone were collected 39.2 m (128.6 ft) above the base

of the Lava Dam Member, whereas the highest collections

are from 40.9 m (134.1 ft) above the base of the member. In

the composite column (pl. 1) the zone ranges from 80.46 m

(264 ft) to 83.2 m (273 ft) above the base.

MISSISQUOIA ZONE

The Missisquoia Zone was named by Winston and

Nicholls (1967) for a characteristic trilobite assemblage in

the upper part of the Wilberns Formation in central Texas.

Derby and others (1972) redefined the Missisquoia Zone to

include those faunas above the “Saukia Zone” (that is, above
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 15

the Eurekia apopsis Zone of this report) and below the lowest

occurrence of Symphysurina in the Survey Peak Formation,

southern Alberta, Canada. This restricted the lower part of

the zone in order to exclude the lower range of Symphysurina, which had been included in the original zone by Winston and Nicholls (1967). Taylor and Halley (1974)

recognized the Missisquoia Zone in eastern New York State.

Stitt (1977, pl. 12) refined and divided the Missisquoia

Zone into a lower Missisquoia depressa Subzone and an

upper Missisquoia typicalis Subzone in the Signal Mountain Limestone in Oklahoma. Both subzones can be recognized in the Lava Dam Member of the Notch Peak

Formation in the Lava Dam Five section. The Missisquoia

depressa Subzone is indicated by trilobites collected from

41.5 m (136.1 ft) above the base of the Lava Dam Member

in the Lava Dam Five section. The assemblage contains

Missisquoia depressa Stitt, Plethometopus armatus (Billings), and a single olenid? free cheek.

The Missisquoia typicalis Subzone is recognized in the

Lava Dam Five section by the occurrence of Missisquoia typicalis Shaw. The subzone extends from 43.0 to 72.6 m (141.0

to 238.1 ft) above the base of the Lava Dam Member. This

translates to an interval 83.2 m (273 ft) to 114.3 m (375 ft)

above the base of the composite section (pl. 1, charts A–C).

The top of the Missisquoia Zone coincides with the

lower boundary of the Symphysurina Zone which is recognized locally by the lowest occurrence of Symphysurina

brevispicata.

SYMPHYSURINA ZONE (=ZONES A AND B, REVISED)

Lower and Middle Ordovician rocks in the Western

United States were initially divided by Ross (1949, 1951,

1953, 1968) into a scheme of trilobite and brachiopod assemblage zones lettered from A to M in the Garden City and

Swan Peak formations of southeastern Idaho and northeastern Utah. Hintze (1951, 1953, 1954) applied Ross’s zonal

scheme, with some emendations, to the Pogonip Group in

the House Range–Ibex area of western Utah, the area of the

present report. Hintze (1953, p. 5) did not recognize Zone A

System

Series

Stage

Formation

Shelly Fossil Zones

(this report)

Conodont Zones

(this report)

W. Utah

Hintze

(1953)

W. Utah

Ethington &

Clark (1971)

N. Utah - 

SE. Idaho

Ross (1951,

1968)

Shelly Fossil Zones Conodont 

Faunas

Whiterockian

Series Lower Ordovician Ibexian Series

PO ParalenorthisOrthidiella

Hm Hesperonomiella minor

Pn Pseudocybele nasuta

Pi Presbynileus ibexensis

Tt Trigonocerca typica

Pc Protopliomerella contracta

Hc Hintzeia celsaora

Rs Rossaspis superciliosa

Te Tesselacauda

LK Leiostegium-Kainella

Pa Paraplethopeltis

BX Bellefontia-Xenostegium

Sy Symphysurina

Mi Missisquoia

Ea Eurekia apopsis

Ss Saukiella serotina

Sj Saukiella junia

Rangerian

Wah Wah

Fm. Fillmore Formation

Tl Tripodus laevis

Ra Reutterodus andinus

Oc Oepikodus communis

AO Acodus deltatus -

Oneotodus costatus

Md Macerodus dianae 

LD "Low diversity interval"

Rm Rossodus manitouensis

Ca Cordylodus angulatus

Ia Iapetognathus n. sp.

Cl Cordylodus lindstromi

Cp Cordylodus proavus

Eo Eoconodontus

Blackhillsian Tulean Skullrockian Tremp.

Ci Cordylodus intermedius

Stairsian

St.Charles Dol. Garden City Formation

Not

Studied

Not

Studied

Not

Studied

E

D

C

B

A

L

K

L

"K"

J J

I I

H H

G-2 G-2

G-1 G-1

F F

E E

D D

House

Ls.

Notch Peak

Formation

Up. C

Croixian

Series

C C

B

A + B

Figure 10. New stages of the Ibexian Series showing the shelly fossil and conodont zones by which they are characterized with recommended abbreviations for zones. Also shown are correlations with previous lettered shelly fossil zones of Ross (1951) for northern Utah and

southeastern Idaho, Hintze (1953) for the Ibex area of western Utah, and lettered conodont faunas of Ethington and Clark (1971). Line pattern, rocks missing at unconformity.
16 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

of Ross; instead he assigned his lowest Ordovician trilobite

assemblage to Zone B, which he called the Symphysurina

Zone. Hintze’s (1953, p. 7) Symphysurina Zone consists of a

lower part characterized by Hystricurus millardensis Hintze

and Symphysurina brevispicata Hintze, and an upper part

that contains different species of Hystricurus and Symphysurina in association with species of Clelandia, Xenostegium,

and Bellefontia.

Stitt (1977) studied detailed trilobite ranges in the Signal Mountain Limestone of the Wichita Mountains, Oklahoma, and divided the Symphysurina Zone into a lower

Symphysurina brevispicata Subzone, a middle Symphysurina bulbosa Subzone, and an upper Symphysurina woosteri Subzone. Stitt (1977, p. 32–36, pl. 7) defined the base of

the Symphysurina brevispicata Subzone as the lowest

observed occurrence of Symphysurina brevispicata Hintze

and Highgatella cordilleri (Lochman). The overlying Symphysurina bulbosa Subzone is defined by the lowest

observed occurrence of Symphysurina bulbosa Lochman. As

so defined, the Symphysurina brevispicata Subzone can be

recognized in the Steamboat Pass–Lava Dam composite section beginning 73.5 m (241 ft) above the base of the Lava

Dam Member (equals 1.6 m (5.4 ft) below the top of Notch

Peak Formation). In the composite section (pl. 1, charts

A–C) the Symphysurina Zone ranges from 114.3 m (375 ft)

to 216 m (708.6 ft) above the base.

Taylor and Landing (1982) studied new trilobite and

conodont collections from the lowermost part of the Garden

City Formation in northeastern Utah and southeastern Idaho

and showed that an unconformity exists between the Garden City and the underlying St. Charles Formation. They

concluded that the hiatus corresponds to most of the Symphysurina brevispicata Subzone, whereas trilobite Zones A

and B of Ross (1949, 1951) are equivalent to the upper part

of the Symphysurina Zone B of Hintze (1951, 1953) (see

further, Stitt, 1977, p. 35–36; and Taylor and Landing,

1982, p. 184–185).

Stitt’s (1977) three-fold division of the Symphysurina

Zone currently cannot be recognized in the type area of the

Ibexian Series. The possible reason for this is the presence of

a massive cliff-forming layer, composed of lime mudstone

from which few fossils can be broken out, within the stratigraphic interval of the Symphysurina Zone.

The top of the Symphysurina Zone in the type area of

the Ibexian Series is here recognized at the lower boundary

of the overlying Bellefontia-Xenostegium Zone (pl. 1, chart

A), which corresponds to assemblages assigned to the upper

part of the Symphysurina Zone B by Hintze (1953, p. 6–8).

The following trilobite species characterize the Symphysurina Zone, as revised herein, in the typical reference

section of the Skullrockian Stage:

Trilobites:

Hystricurus millardensis Hintze

Pseudokainella? sp. 

Symphysurina brevispicata Hintze

Highgatella cordilleri (Lochman)

Missisquoia inflata Winston and Nicholls

Symphysurina bubops Winston and Nicholls

BELLEFONTIA-XENOSTEGIUM ZONE

(=ZONE B IN PART)

The Bellefontia-Xenostegium Zone was named by Aitken and Norford (1967, p. 180) in Alberta. Stitt (1983, p.

13–15) restricted the Bellefontia-Xenostegium Zone to trilobite assemblages that occur above the Symphysurina Zone

and below the Paraplethopeltis Zone in the McKenzie Hill

Formation of Oklahoma. The zone is correlated with the

upper part of Symphysurina Zone B of Hintze (1953) and is

here recognized as a separate zone in western Utah. The

Bellefontia-Xenostegium Zone occurs in a stratigraphic

interval 71 m (233 ft) to 5.5 m (18 ft) below the top of the

House Limestone in the B Section of Hintze (1951). That is

equivalent to 216 m (708.6 ft) to 281 m (923 ft) in the composite section.

The following trilobite and brachiopod species characterize the Bellefontia-Xenostegium Zone in the typical reference section of the Skullrockian Stage:

Trilobites:

Bellefontia chamberlaini Clark

Bellefontia ibexensis Hintze

Clelandia utahensis Ross

Hystricurus genalatus Ross

Hystricurus politus Ross

Parabellefontia concinna Hintze

Symphysurina globocapitella Hintze

Symphysurina cf. S. cleora (Walcott)

Symphysurina cf. S. spicata Walcott

Symphysurina uncaspicata Hintze

Symphysurina cf. S. woosteri Walcott

Xenostegium franklinense Ross

Xenostegium cf. X. acuminiferentis (Ross)

Brachiopods:

Apheoorthis cf. A. melita (Hall and Whitfield)

Lingulella cf. L. pogonipensis Walcott

PARAPLETHOPELTIS ZONE (=ZONE C)

In northeastern Utah, Ross (1951, p. 16, 19, 29) found

an interval 30 ft thick in the Garden City Formation that was

poorly fossiliferous and lacked markedly distinctive trilobites or brachiopods. Hintze (1953, p. 8) discovered forms by

which this thin interval might be correlated. However, his

assemblage included Hystricurus genalatus Ross, a species

thought to be characteristic of the underlying XenostegiumBellefontia association of Ross’s (1951) Zone B. The distinguishing taxa are two species assigned to Paraplethopeltis.
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 17

The zone occurs in a bed approximately 2.5 m (8 ft) thick

located 3.05 to 6.4 m (10 to 18 ft) below the top of the House

Limestone in the B Section of Hintze (1951, p. 34). This

horizon is approximately 281.5 m (923.6 ft) above the base

of the composite section (pl. 1).

Trilobite and brachiopod species recorded from the

Paraplethopeltis Zone in the Ibex area include:

Trilobites:

Hystricurus genalatus Ross

Paraplethopeltis genacurvus Hintze

Paraplethopeltis genarectus Hintze

Brachiopod:

Syntrophina cf. S. campbelli (Walcott)

STAIRSIAN STAGE (NEW)

The lower boundary stratotype for the Stairsian Stage is

in a thick-bedded, fine-grained ledge-forming limestone,

2.9–3.0 m (9.5–10.0 ft) thick that forms the prominent

uppermost part of the House Limestone in the B Section of

Hintze (1951, p. 33–34). This limestone marker bed is traced

northward in outcrop to the base of the 1965-C Section of

Hintze (1973, p. 16–25). The base of the stage coincides with

the lowest observed occurrence of Leiostegium and Kainella,

which coincides with the base of the Leiostegium-Kainella

Zone (=Zone D of Hintze, 1953, p. 9). In addition to the

Leiostegium-Kainella Zone, the Stairsian Stage is characterized by the Tesselacauda, Rossaspis superciliosa, uppermost

part of Rossodus manitouensis, Low Diversity Interval, Macerodus dianae, and lower part of the Acodus deltatus–Oneotodus costatus Zones.

The Stairsian Stage takes its name from “The Stairs,” a

narrow valley along U.S. Highway 6 and 50 that descends

from Skull Rock Pass westward into Tule Valley (UTM

Coord., Zone 12: E 297,000 m; N 4,322,200 m). Alternating

layers of resistant limestone and nonresistant shale of the

Fillmore Formation inspired the name.

The top of the Stairsian Stage is the base of the Tulean

Stage, which is defined by the lowest observed occurrence of

faunas assigned to the Hintzeia celsaora Zone.

LEIOSTEGIUM-KAINELLA ZONE (=ZONE D)

As noted, the base of the Leiostegium-Kainella Zone is

in a thick limestone unit, 2.9–3.0 m (9.5–10.0 ft) thick,

which forms the uppermost part of the House Limestone in

the B Section of Hintze (1951, p. 34). The base of the zone

lies at least 0.76 m (2.5 ft) below the top of the House Limestone. Therefore, the boundary is no higher than 286 m (938

ft) above the base of the composite section (pl. 1, charts

A–C). Ethington and Ross revisited Hintze’s (1951) B Section on June 17, 1994, to verify the observations of K.M.

Engel (1984) concerning the positioning of this boundary.

The base of the Leiostegium-Kainella Zone is defined

under “Stairsian Stage.” On plate 1, the LeiostegiumKainella Zone is indicated by the letters LK. In the typical

reference section of the Stairsian Stage, the zone is characterized by the following shelly fossils:

Trilobites:

Apatokephalus finalis (Walcott)

Hystricurus sp.

Kainella sp.

Leiostegium manitouensis Walcott

Pseudoclelandia sp.

Rossaspis pliomeris Demeter

Brachiopods:

Apheoorthis cf. A. meeki Ulrich and Cooper

Nanorthis cf. N. hamburgensis (Walcott)

Syntrophina sp.

As noted by Hintze (1953, p. 9), the LeiostegiumKainella Zone has proven to be one of the most useful

assemblages for correlation throughout North America, as

well as in Colombia and Argentina. It occurs in a variety of

depositional facies, from the shallow-shelf deposits of the

Manitou Formation of Colorado, to the Roberts Creek

Mountains and Antelope Range of central Nevada, and in

volcaniclastic breccias (Ross, 1958) of the Valmy Formation

in western Nevada. Both Kainella and Leiostegium are

present in the Survey Peak Formation in Alberta (Dean,

1978). Pratt (1988) reported Leiostegium and Kainella

eleutherolfi Pratt from the Rabbitkettle Formation in the

MacKenzie Mountains, N.W.T. Kainella and Leiostegium

are illustrated by Pribyl and Vanek (1980, pl. 12) from

Bolivia. Although Kainella seems to be the cosmopolitan

form, often associated with the olenid Hypermecaspis,

Leiostegium is reported as far away as the Digger Island

Fauna from Warata Bay, Victoria (Jell, 1985). Also, Qian in

Chen and Gong (1986, p. 257–260) reported species of

Leiostegium in the Dayangcha section, northeastern China.

Demeter (1973) described Rossaspis pliomeris as a stem species for pliomerids found in younger assemblages. 

TESSELACAUDA ZONE (=ZONE E)

The base of the Tesselacauda Zone occurs in unit 23 of

the informal ledge-forming limestone member (member 1)

of the Fillmore Formation in the 1965-C Section of Hintze

(1973, p. 18). This level is approximately 112 m (368 ft)

above the base of the Fillmore Formation. Although that

level appears to be approximately 399 m (1,309.6 ft) above

the base of the composite section, Demeter (1973, p. 42;

text-fig. 2) and Terrell (1973, p. 71) showed that the lowest

indicator of the zone is from 349 m (1,145 ft) of the composite section (pl. 1).

This assemblage zone has been recognized in the subsurface of the Williston Basin by Lochman (1966) despite

the lack of silicified preservation. It is also present in the
18 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

upper part of the middle member and upper member of the

Survey Peak Formation in Alberta (Dean, 1978), where it is

indicated by Leiostegium (Evansaspis), Tesselacauda, and

Paenebeltella. Terrell (1973) made additional collections

from the Ibex area and noted four species characteristic of

Zone F that occurred in the upper part of the range of a Zone

E assemblage. Demeter (1973) confirmed the presence of

Tesselacauda depressa and added Pilekia? loella to the

assemblage. He also indicated that Pilekia? trio Hintze

ranges into Zone F. 

Trilobites:

Amblycranium variabile Ross

Amechilus palaora Ross

Hillyardina sp.

Hystricurus robustus Ross

Hystricurus sp. C of Ross (1951)

Leiostegium (Evansaspis) formosa Hintze (=L. (E.)

ceratopygoides Raymond)

Paenebeltella vultulata Ross

Parahystricurus carinatus Ross

Pseudoclelandia lenisora Ross

Pseudoclelandia aff. P. fluxafissura Ross

Tesselacauda aff. T. depressa Ross

Tesselacauda depressa Ross

Pilekia? trio Hintze

Pilekia? loella Demeter

Brachiopod:

Syntrophina? sp.

ROSSASPIS SUPERCILIOSA ZONE (=ZONE F)

Hintze (1953, p. 11) applied the name Protopliomerops

superciliosa Zone to a trilobite assemblage in the Fillmore

Formation with a high percentage of taxa in common with

Zone F of Ross (1951) in northeastern Utah. Harrington

(1957, p. 812) placed Protopliomerops in junior synonymy

with Rossaspis.

From the Tarutao Formation of Southern Thailand,

Stait and others (1984) reported Rossaspis bunopasi, a species almost indistinguishable from Rossaspis superciliosa.

It and associated trilobites suggest correlation with this part

of the Ibexian Series. There is an increasing variety of pliomerid trilobites, possibly derived from Rossaspis, in

younger assemblages in the Tarutao Formation. Hystricurus

and Hystricurus-like forms seem to reach a maximum

diversity in this zone.

The base of the Rossaspis superciliosa Zone is in unit 4

of the informal basal ledge-forming limestone member

(member 1) of the Fillmore Formation in G Section of Hintze

(1973, p. 25). This level is 53 m (174 ft) above the lowest

exposure of the Fillmore Formation in that section. The level

is 124 m (406 ft) above the base of the Fillmore Formation in

the 1965-C Section of Hintze (1973) and approximately 408

m (1,340 ft) above the base of the composite section (pl. 1).

Trilobites:

Amblycranium cornutum Ross

Goniophrys prima Ross

Hillyardina semicylindrica Ross

Hyperbolochilus marginauctum Ross

Hystricurus contractus Ross

Hystricurus flectimembrus Ross

Hystricurus oculilunatus Ross

Parahystricurus fraudator Ross

Parahystricurus bispicatus Hintze

Pseudoclelandia cornupsittaca Ross

Pseudoclelandia fluxafissura Ross

Pseudohystricurus obesus Ross

Rossaspis superciliosa (Ross)

TULEAN STAGE (NEW)

The Tulean Stage takes its name from Tule Valley,

which bounds the west side of the House Range. Lower Paleozoic strata, including those of the Ibexian Series, are extensively exposed along both sides of the valley.

The base of the Tulean Stage coincides with the base

of the Hintzeia celsaora Zone. In some sections that level

may be indicated by the lowest occurrence of Menoparia

genalunata and Psalikilus spinosum. In other sections the

earliest appearance of Hintzeia celsaora, name bearer of

zone G-1 of Hintze (1953, p. 12) may be the better indicator. Although Aulacoparina quadrata is present in either

case, the difference stratigraphically may be as much as

11.6 m (38 ft). Currently the lowest occurrence of

Menoparia genalunata is the pragmatic choice because of

its recognition outside the Ibex area.

The stratotype for the base of the Tulean Stage is located

in unit 2 of the informal slope-forming shaly siltstone member (member 2) of the Fillmore Formation. In the 1965-C

Section of Hintze (1973, p. 17), unit 2 is 28 m (92 ft) thick,

and underlain by 3.4 m (11 ft) of the informal slope-forming

shaly siltstone member. The lowest reported occurrence of

Menoparia genalunata is 11.6 m (38 ft) above the base of unit

2. In the G Section of Hintze (1973, p. 25), unit 2 is 9.1 m (30

ft) thick, but underlain by a 24.7 m (81 ft) covered interval

from which no distinctive fossils have been reported. Here

the lowest reported occurrence of Menoparia genalunata is

1.8 m (6 ft) above the base of unit 2, where it is joined by

Hintzeia celsaora. That occurrence is approximately 448 m

(1,472 ft) above the base of the composite section.

We expect that additional attempts to collect fossils from

the poorly exposed shaly beds below unit 2 of member 2 will

require that the base of the stage be redefined downward. 

HINTZEIA CELSAORA ZONE (=ZONE G-1)

The lowest part of the Outram Formation (Dean, 1978)

in Alberta contains species characteristic of this zone, particularly Menoparia genalunata. Lochman (1966, p. 524–526)
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 19

recognized the zone in the subsurface of the Williston Basin,

but preferred to combine it with the next higher zone

(=Zones G-1 and G-2). Benthamaspis obreptus (Lochman)

was reported by Lochman (1966, p. 541–542) from the

Deadwood Formation in the Williston Basin, Montana. A

similar species was reported by Ross (1958) from a volcaniclastic flow breccia in central Nevada.

Trilobites:

Aulacoparina quadrata (Hintze) 

Hintzeia celsaora (Ross)

Hintzeia firmimarginis (Hintze)

Menoparia genalunata Ross

Peltabellia sp. B of Hintze (1953)

Psalikilus spinosum Hintze

Graptolite:

Rhabdinopora sp.

PROTOPLIOMERELLA CONTRACTA ZONE (=ZONE G-2)

The lower contact of the Protopliomerella contracta

Zone is located at the bottom of unit 2 of the informal lightgray ledge-forming member (member 3) of the Fillmore

Formation in the G Section of Hintze (1973, p. 25). In the

G and H Sections the zone ranges upward for 183 m (600

ft) through most of the overlying informal brown slope and

ledge member (member 4). The base of the zone is approximately 518 m (1,700 ft) above the base of the composite

section (pl. 1).

The Protopliomerella contracta Zone of Hintze (1953,

p. 13) is equivalent to Zone G-2 of Ross (1951). In addition

to the lists of Ross (1951, p. 28) and Hintze (1953, p. 14),

note should be made of the study of pliomerids by Demeter

(1973). Fortey and Peel (1990) found both Peltabellia and

Licnocephala in the Poulsen Cliff Formation in northern

Greenland and gave an excellent account of the wide geographic occurrence of Peltabellia.

Trilobites:

Aulacoparia venta (Hintze)

Aulacoparina impressa Lochman

Hintzeia celsaora (Ross)

Licnocephala bicornuta Ross

Licnocephala? cavigladius Hintze

Macropyge gladiator Ross

Menoparia genalunata Ross

Peltabellia peltabella (Ross)

Peltabellia sp. A of Hintze (1953)

Protopliomerella contracta (Ross)

Protopliomerella pauca Demeter

Protopliomerops quattuor Hintze

Psalikilus paraspinosum Hintze

Psalikilus typicum Ross

Protopresbynileus willdeni (Hintze)

Ptyocephalus fillmorensis (Hintze)

Scinocephalus solitecti Ross

Brachiopods, cephalopods, and graptolites:

Nanorthis sp.

Syntrophina? sp.

Endoceras sp.

Rhabdinopora sp.

Didymograptus? sp.

BLACKHILLSIAN STAGE (NEW)

The Blackhillsian Stage takes its name from the low

hills at the south end of the House Range that extend southward from Skull Rock Pass for more than 32 km (20 mi). The

dark color of the lower Paleozoic carbonate rocks exposed

there lends itself to the name. Many of the exposures of the

Ibexian Series are arrayed along the west flank of these

Black Hills. The base of the stage and of its lowest faunal

zone, the Trigonocerca typica Zone, is marked by the lowest

observed occurrence of Trigonocerca typica. The lower

boundary stratotype is located in the H Section of Hintze

(1973, p. 26), 5.8 m (19 ft) above the base of unit 2 of the

informal calcarenite member (member 5) of the Fillmore

Formation. This level is 708 m (2,327 ft) above the bottom of

the composite section (pl. 1).

TRIGONOCERCA TYPICA ZONE (=ZONE H)

As just mentioned, the base of the Trigonocerca typica

Zone of Hintze occurs 5.8 m (19 ft) above the base of unit 2

of the informal calcarenite member (member 5) of the Fillmore Formation in the H Section of Hintze (1973, p. 26). It is

equivalent to Zone H of Ross (1951, p. 28). To the lists of taxa

published by Ross (1951, p. 28) and by Hintze (1953, p. 16)

the faunal list of Young (1973) must be added. The earliest

appearance of cosmopolitan Carolinites, Ischyrotoma, and

Pseudocybele, and the arrival of bathyurinids, such as Goniotelina, set the stage for the closing of the Ibexian Epoch. Trigonocerca typica can be recovered in many outcrops from

bioclastic limestones with relative ease. Fortey (1979) in a

well-illustrated paper interpreted the Catoche Formation of

western Newfoundland to be correlative with this zone.

Ischyrotoma blanda Hintze normally is considered a

member of this assemblage, but in the H Section it occurs 8.8

m (29 ft) lower in the section.

Trilobites:

Amblycranium? linearus Young

Carolinites genacinaca nevadensis Hintze

Carolinites killaryensis utahensis Hintze

Diacanthaspis? trispineus Young

Goniotelina? plicolabeonus Young

Goniotelina? unicornis Young

Ischyrotoma blanda (Hintze)

Ischyrotoma ovata (Hintze)

Kanoshia? depressa Young
20 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Peltabellia? sp.

Presbynileus elongatus (Hintze) 

Protopliomerops? quattuor brevis Young

Psalikilopsis alticapitalis Young

Pseudocybele lemurei Hintze

Pseudocybele altinasuta Hintze

Ptyocephalus accliva Hintze

Opipeuter angularis (Young)

Shumardia exopthalmus Ross

Trigonocerca typica Ross

Trigonocerca typica piochensis Hintze

Graptolites:

Didymograptus cf. D. nitidus

Rhabdinopora? 2 spp.

Brachiopods:

Diparelasma sp.

Trematorthis? sp.

Molluscs:

Euomphalus? sp.

Catoraphiceras sp.

Endoceras sp.

PRESBYNILEUS IBEXENSIS ZONE (=ZONE I)

The Presbynileus ibexensis Zone as recognized by

Hintze (1953, p. 15) is equivalent to Zone I of Ross (1951).

The base of the zone is 3.3 m (10 ft) above the bottom of unit

7, which forms the uppermost 35 ft of the informal calcarenite

member (member 5) of the Fillmore Formation in the H Section of Hintze (1973, p. 25). The level is approximately 777

m (2,549 ft) above the base of the composite section (pl. 1).

Trilobites:

Carolinites genacinaca Ross

Isoteloides flexus Hintze

Ptyocephalus yersini (Hintze)

Ptyocephalus accliva (Hintze)

Presbynileus ibexensis (Hintze)

Pseudocybele altinasuta (Hintze)

Pseudocybele lemurei Hintze

Goniotelus? sp.

Brachiopods:

Hesperonomia sp.

Diparelasma sp.

Graptolites:

Phyllograptus sp.

Retiograptus sp.

PSEUDOCYBELE NASUTA ZONE (=ZONE J)

The Pseudocybele nasuta Zone was recognized by

Hintze (1953, p. 15–18) in the uppermost Fillmore Formation and lower Wah Wah Limestone. It is equivalent to Zone

J of Ross (1951). The base of the zone is 8.8 m (29 ft) above

the base of unit 9 of the informal Calathium siltstone member (member 6) of the Fillmore Formation in the H Section of

Hintze (1973, p. 26). The lower boundary of the zone is

defined by the lowest observed occurrence of Pseudocybele

nasuta, which is approximately 830 m (2,723 ft) above the

bottom of the composite section.

The Pseudocybele nasuta Zone has yielded one of the

most diverse and abundant faunas in the Ibexian Series. The

following list is supplemented by Diparelasma rowelli Ross

and Tritoechia loganensis Ross from the Garden City Formation (Ross, 1951, p. 27–28; 1968, p. H2–H4). Because of

the great diversity of trilobites and burst of orthid brachiopods, this zone has been recognized widely. Dean (1988)

noted the zone’s occurrence in the upper McKay Group in

British Columbia and (1978) in the top of the Outram Formation in Alberta. The zone is also represented in the Dounans

Limestone in the Highland Border Complex, Scotland (Ingham and others, 1985).

Trilobites:

Benthamaspis diminutiva Hintze

Carolinites genacinaca Ross

Cybelopsis cf. C. speciosa Poulsen

Goniotelina williamsi (Ross)

Goniotelina brighti (Hintze)

Goniotelina brevus (Hintze)

Goniotelina wahwahensis (Hintze)

Ischyrotoma caudanodosa (Ross)

Isoteloides polaris Poulsen

Kanoshia cf. K. insolita (Poulsen)

Kawina sexapugia Ross

Kawina webbi Hintze

Lachnostoma latucelsum Ross

Presbynileus utahensis (Hintze)

Pseudocybele nasuta Ross

Ptyocephalus declivita (Ross)

Ptyocephalus cf. P. vigilans Whittington

Stenorhachis genalticurvatus (Hintze)

Trigonocercella acuta Hintze

Brachiopods:

Diparelasma cf. D. transversa Ulrich and Cooper

Hesperonomia fontinalis (White)

Hesperonomia cf. H. dinorthoides Ulrich and Cooper

Syntrophopsis cf. S. polita Ulrich and Cooper

Tritoechia sinuata Ulrich and Cooper

Cephalopods:

Campbelloceras sp.

Catoraphiceras sp.

Endoceras sp.

HESPERONOMIELLA MINOR ZONE

(=“ZONE K” OF HINTZE, 1953)

The Hesperonomiella minor Zone of Hintze (1953, p.

19) is based on a remarkable 0.3-m (1 ft) thick shell bed of

white-weathering brachiopods. It occurs in unit 20 of the
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 21

Wah Wah Limestone, at 65.5 m (215 – 217 ft) above the base

of the J Section of Hintze (1973, p. 29). The level is 902 m

(2,959 ft) above the bottom of the composite section. The faunal assemblage occurs below a thin calcareous siltstone bearing a variety of runzel marks. Scattered valves occur higher

through a thickness of 6 m (20 ft) in the stratigraphic section.

On the basis of stratigraphic position alone, the Hesperonomiella minor Zonal assemblage has been referred, probably incorrectly, to Zone K of Ross (1951, p. 27, 30). In

addition to the Ibex area, it occurs as far east as Kanosh,

Utah. In Utah the species may be associated with discontinuous facies-controlled carbonate sand bars.

The critical features of the interior of the brachial valve

of Hesperonomiella minor were poorly known (Ulrich and

Cooper, 1938, p. 124) until Hintze made specimens available

to Cooper (1956, p. 337, pl. 121H, figs. 20–22). Jensen

(1967) also published a description of the interior.

The genus Hesperonomiella is represented by Hesperonomiella porcias (Walcott) in the Sarbach Formation of

the Canadian Rockies (Ulrich and Cooper, 1938, p.

124–125) and by Hesperonomiella quebecensis in boulders

of the Mystic Conglomerate in southern Quebec (Cooper,

1956, p. 337–338). It has also been reported by Laurie

(1980) from Tasmania. 

The Zone K of Ross (1951, p. 27, 30) contains a transitional assemblage in northeastern Utah. Diparelasma sp. and

Hesperonomia sp. suggest affinities with Zone J, while the

appearance of Blastoidocrinus suggests a markedly younger

“Chazyan” age. Sprinkle (1971, particularly figure 2, column C) subsequently confirmed that this echinoderm is an

indicator of upper Zone L. Ross listed Notorthis from his

Zone K, but it was a single valve identified with trepidation.

The close interrelation of Zones K and L was further discussed by Ross (1968, p. H2–H4).

The seeming absence of Zone K from some sections

cannot be taken seriously as an indicator of hiatus, because it

was never established as a distinct zone in the first place.

WHITEROCKIAN SERIES

The Whiterockian, originally proposed as a Stage by

Cooper (1956), was redefined as a Series in Ross and others

(1982). Ross and Ethington (1991) provided a precise definition of the basal stratotype in the Monitor Range, central

Nevada, supported by graptolite zonation by Mitchell

(1991). The base of the Whiterockian Series marks the top of

the Ibexian Series in the Ibexian type area.

RANGERIAN STAGE (NEW)

The Rangerian Stage is proposed here for the interval

represented by a Zone L fauna (Ross and Ethington, 1991,

fig. 6; Ross and Ethington, 1992, fig. 4A) in the upper Paiute

Ridge and Ranger Mountains Members of the Antelope Valley Limestone in the northern Ranger Mountains, Nevada,

from which the stage takes its name. This is the lowest stage

of the Whiterockian Series. In the Ibex area Zone L is present

in the highest 8.5 m (28 ft) of the Wah Wah Limestone,

throughout the Juab Limestone, and in the lowermost limestone beds of the Kanosh Shale. In the composite-stratotype

section the base of zone L is 902 m (2,966 ft) above the base.

The upper limit of the Rangerian is not a subject for this

report. Under consideration is a proposed Kanoshian Stage,

to include brachiopod zones M and N , probably with a type

section in the Ibex area. Prior to a formal proposal its relationship to the Chazyan must be precisely determined. The

base of the Kanoshian in the Ibex section is 974 m (3,194 ft)

above the bottom of the composite section.

PARALENORTHIS-ORTHIDIELLA ZONE (=ZONE L)

The Paralenorthis-Orthidiella Zone is equivalent to the

Zone L of Ross (1951) and the Orthis subalata Zone of

Hintze (1953, p. 19). At Ibex the brachiopod fauna is not as

fully developed as in sections to the west. Here Anomalorthis

juabensis and species of Orthidiella appear in the upper part

of the zone. The full faunal complement of the zone is listed

by Ross and Ethington (1992, table 1).

Subsequent to the writing of the original manuscript of

this report (Ross and others, 1993), Fortey and Droser (1996,

particularly table 1) made an important addition to trilobite

biostratigraphy of the Rangerian Stage and of Zone L at the

Ibex section. With the exception of cursory treatment by

Hintze (1953, p. 19), by Ross (1970, pl. 21), and in a master’s

thesis by Valusek (1984, p. 133–138), the trilobites of this

interval had received little attention. The trilobites described

by Fortey and Droser (1996) have been included on plate 1,

chart A of this publication. 

It should be noted that the base of the Tripodus laevis

conodont Zone essentially coincides with the base of the

Paralenorthis-Orthidiella Zone. 

Brachiopods:

Paralenorthis marshalli (Wilson)

Anomalorthis juabensis Jensen

Anomalorthis lambda Ross

Orthidiella spp.

Syntrophopsis transversa Ulrich and Cooper

Trilobites:

Eleutherocentrus sp.

Parapilekia? sp.

Pseudomera sp.

The trilobites added by Fortey and Droser are Carolinites ekphymosus Fortey, Ectenonotus progenitor Fortey and

Droser, E. whittingtoni Ross, Goniotellina ensifer Fortey and

Droser, Ischyrotoma stubblefieldi Ingham, Kanoshia reticulata Fortey and Droser, Kawina wilsoni Ross, Madaraspis

magnifica Fortey and Droser, Petigurus inexpectans Fortey
22 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

and Droser, Psephothenaspis glabrior Fortey and Droser, P.

microspina Fortey and Droser, P. pseudobathyurus (Ross),

Pseudomera arachnopyge Fortey and Droser, Pseudoolenoides aspinosus Fortey and Droser, Punka cf. P. nitida (Billings), and Uromystrom cf. U. validum (Billings).

Echinodermata:

Blastoidocrinus? sp.

CONODONT ZONES

INTRODUCTORY STATEMENT

Miller (1969) was the first to describe conodonts from

the type Ibexian strata. Ethington and Clark (1971) summarized the then current knowledge of the Lower Ordovician

conodonts of North America, a study that was followed by an

overview of the distribution of these fossils in the Ibexian

type area and other parts of the Great Basin by Ethington

(1978, 1979). A detailed taxonomic and biostratigraphic

study of conodonts in the Ibex area of western Utah was presented by Ethington and Clark (1981), whose collecting horizons were keyed into the detailed descriptions of

stratigraphic sections of Hintze (1951, 1973). J.F. Miller

(1988) has studied the lowest Ibexian conodonts in multiple

sections in the type area, and his range charts have been used

widely in international and intracontinental correlations.

These several reports demonstrated that conodonts are virtually ubiquitous throughout carbonate rocks of the type area

of the Ibexian Series.

In Ibexian Series rocks, a sample of no more than several hundred grams usually contains conodonts in sufficient abundance and diversity to allow evaluation of the

collection and biostratigraphic placement. Preservation of

the specimens ranges from adequate to good. Conodont

Alteration Index (CAI) values of about 3.0 are typical for

the Ibex area. A composite range chart prepared by Ethington and Clark (1981) shows a near continuum of species

introduced in the Ibex sections. Although this sequence of

species offered promise of a high-resolution biostratigraphic zonation of the Ibexian strata, Ethington and Clark

chose not to establish biozones that might be only of local

significance and instead recognized discrete segments

within the Ibexian sequence as “intervals” that are characterized by loosely defined faunal associations. Subsequent

work in other parts of North America has demonstrated that

many conodonts among those known at Ibex occur in consistent sequential order elsewhere, and conodont biozones

have been recognized in some parts of the Lower Ordovician. Additional zones for previously unzoned parts of the

succession are offered herein. Figure 10 summarizes the

older and new biostratigraphic nomenclature.

This discussion for the most part utilizes the taxonomic

nomenclature of Ethington and Clark (1981) with some

generic reassignments and species synonymies based on

later reports. Ranges of conodonts shown on plate 1, chart B

are taken from the work of Miller (1969, 1984) on lower

Ibexian faunas and on that of Ethington and Clark (1981) for

the House, Fillmore, and Kanosh Formations. Ranges of the

Wah Wah and Juab conodonts are based on unpublished data

from Ethington’s recollection of the entire span of these two

units in Section J of Hintze (1973). Several major studies of

Lower Ordovician conodonts are in press or in progress, and

further revisions of nomenclature can be expected. However,

the purpose of this report is to demonstrate the general lithic

and fossil successions of the type Ibexian, and discussion of

taxonomic nuances will detract from that objective.

Conodonts from the lowest part of the Ibexian Series

(lower part of the Skullrockian Stage) are cosmopolitan in

their distribution, and intercontinental correlation of these

strata is not difficult (Miller, 1984). Rocks from the upper

part of the Skullrockian Stage (Rossodus manitouensis

Zone) contain species that are more provincial in their distribution. Strata of the succeeding Stairsian, Tulean, and Blackhillsian Stages contain conodont species of the North

American Midcontinent Conodont Province. This faunal

province generally is associated with epicratonal and miogeoclinal environments, and intercontinental correlations

based on these younger faunas are more difficult. Some species in these younger strata do occur elsewhere so that such

correlations are possible at some biostratigraphic levels.

The relationships between conodont and trilobite zones

in the Ibexian composite stratotype section is indicated on

plate 1, charts A and B, and in figure 10. 

PRE-IBEXIAN CONODONT ZONES

The conodont biostratigraphy of pre-Ibexian strata was

discussed by Miller (1969), Miller and others (1982), Miller

in Hintze and others (1988), and Miller (1988). Conodonts in

pre-Ibexian strata in Utah are represented wholly by coniform elements. Uppermost strata of the Trempeleauan Stage

(upper part of the Red Tops Member and lower half of the

Lava Dam Member of the Notch Peak Formation) are

assigned to the Eoconodontus Zone, which consists of two

subzones. The lower, the Eoconodontus notchpeakensis Subzone, is characterized by Eoconodontus notchpeakensis and

Proconodontus muelleri, species that continue to the top of

the overlying subzone, which is characterized by the presence of Cambrooistodus minutus. The top of the Cambrooistodus minutus Subzone is marked by an abrupt termination

of the ranges of conodonts and trilobites. Of the abundant

conodonts, only Eoconodontus notchpeakensis occurs in

younger strata in the Ibex sections. The complete thickness

of the Eoconodontus notchpeakensis Subzone is not shown

on plate 1, but the thickness of the Cambrooistodus Subzone

is 44.8 m (147 ft).
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 23

IBEXIAN CONODONT ZONES

CORDYLODUS PROAVUS ZONE

(=FAUNA A, LOWER PART)

Cordylodus is the oldest ramiform conodont genus, the

oldest whose elements display secondary denticles, in North

America. Most of the conodont zones of the Skullrockian are

named for species of Cordylodus, although species whose

elements are all coniform are used to recognize several subzones. The lowest observed occurrence of Cordylodus Pander is immediately above the bolt and plaque that mark the

base of the Ibexian Series and Skullrockian Stage (fig. 9B).

The base of the Cordylodus proavus Zone is 39.1 m (128.3

ft) above the base of the Lava Dam Member in the Lava Dam

Five section. The lowest observed occurrence of Cordylodus

andresi marks the base of the Cordylodus proavus Zone. The

lowest observed occurrence of Cordylodus proavus is 3.7 m

(12 ft) higher, and it ranges into younger zones.

The Cordylodus proavus Zone occurs in the upper half

of the Lava Dam Member of the Notch Peak Formation, and

the top of the zone apparently coincides with the top of the

member in several sections in the Ibex area. The Zone is

divided into three subzones all of which are defined in the

Lava Dam Five section. From oldest to youngest, the subzones are (1) the Hirsutodontus hirsutus Subzone, defined at

39.1 m (128.3 ft) above the base of the Lava Dam Member

and characterized by Cordylodus andresi, Cordylodus proavus, and Hirsutodontus hirsutus; (2) the Fryxellodontus inornatus Subzone, defined at 43.9 m (144 ft) above the base of

the Lava Dam Member and characterized by Cordylodus

proavus, Fryxellodontus spp., Hirsutodontus hirsutus, and

Hirsutodontus rarus; and (3) the Clavohamulus elongatus

Subzone, defined at 67.4 m (221 ft) above the base of the

Lava Dam Member and characterized by Clavohamulus bulbousus, Clavohamulus elongatus, Cordylodus proavus,

Fryxellodontus spp., and Semiacontiodus nogami.

The Cordylodus proavus Zone can be recognized in

many parts of North America and elsewhere in the world

(Miller and others, 1982; Miller, 1988, 1992).

CORDYLODUS INTERMEDIUS ZONE

(=FAUNA A, UPPER PART)

Advanced cordylodontiform species are introduced in

the overlying Cordylodus intermedius Zone in which they

are associated with a diverse fauna of species with coniform elements, many of which continue into overlying

strata. This zone occurs in the lower part of the House

Limestone and includes two subzones. The lower, the Hirsutodontus simplex Subzone, begins at the base of the

House Limestone in the Lava Dam North section. This

horizon is equal to the “50 ft” paint mark above the base of

the Lava Dam North traverse. The Hirsutodontus simplex

Subzone is characterized by an influx of new species with

coniform elements, including Albiconus postcostatus, Hirsutodontus simplex, Monocostodus sevierensis, Semiacontiodus lavadamensis, and Utahconus utahensis. The upper

subzone, that of Clavohamulus hintzei, begins 20.7 m (68

ft) above the base of the House Limestone in the Lava Dam

North section. It is characterized by advanced species of

Cordylodus, including Cordylodus drucei and Cordylodus

intermedius, that occur most commonly in the upper part of

the subzone and continue into overlying strata. The

Clavohamulus hintzei Subzone varies in thickness within

the Ibex area but typically is about 15.2 m (50 ft) thick. In

addition to nearly all of the species of the underlying subzone, the Clavohamulus hintzei Subzone is characterized by

Clavohamulus hintzei and Utahconus tenuis.

CORDYLODUS LINDSTROMI ZONE

(=FAUNA B, LOWER PART)

Other advanced cordylodontiform and coniform conodonts are introduced in the succeeding Cordylodus lindstromi Zone. The taxonomy of Cordylodus lindstromi is

controversial, and we use the name in the loose sense, including in it elements that Nicoll (1991) described as Cordylodus

prolindstromi. Thus the base of our Cordylodus lindstromi

Zone correlates with the Cordylodus lindstromi Zone of

Nicoll (1991) and with the base of the Cordylodus prolindstromi Zone of Shergold and Nicoll (1992) in Australia. In

the Ibex area, the Cordylodus lindstromi Zone begins 29.9 m

(98 ft) above the base of the House Limestone in the Lava

Dam North section. It is 11.9 m (39 ft) thick and is characterized by Cordylodus lindstromi. Several species with coniform elements continue into this zone from the underlying

Cordylodus intermedius Zone.

IAPETOGNATHUS ZONE (NEW)

(=FAUNA B, MIDDLE PART)

The Iapetognathus Zone begins at 42.7 m (140 ft)

above the base of the House Limestone in the Lava Dam

North section. It is characterized by elements of Iapetognathus n. sp., a complex species that has worldwide distribution. The base of the zone in the Ibexian type area is at

the lowest observed occurrence of Iapetognathus. The top

is at the base of the overlying Cordylodus angulatus Zone.

The Iapetognathus Zone also contains several species with

coniform elements that are assigned to “Acontiodus,”

“Scolopodus,” and Utahconus. The Iapetognathus Zone is

7.9 m (26 ft) thick and occurs in the middle part of the

House Limestone. This zone contains several taxa that also

occur in the underlying zone, including Cordylodus lindstromi. Previously, strata assigned to this new zone were

included in the Cordylodus lindstromi Zone or the lower

part of conodont Fauna B of some previous authors.
24 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Iapetognathus n. sp. is associated with the Tremadocian

olenid trilobite Jujuyaspis borealis (see Acenolaza and

Acenolaza, 1992) in the Drum Mountains, Utah, and in central Texas (Stitt and Miller, 1987), and in the House Limestone north of Skull Rock Pass, central House Range (Miller

and others, 1990). A probable association of Jujuyaspis and

Iapetognathus has been reported for the Rocky Mountains of

Canada (Westrop and others, 1981). At the time of publication of that report, Iapetognathus had not been named, and

Ed Landing discussed as New Genus B specimens whose

description suggests that they represent what he later named

Iapetognathus. Iapetognathus occurs with earliest Tremadocian graptolites and Jujuyaspis at Naersnes near Oslo, Norway (Bruton and others, 1988) and with earliest

Tremadocian graptolites in Estonia (Kaljo and others, 1988)

and in western Newfoundland (Landing, 1988). These occurrences support a correlation of the base of the Tremadocian

Series of the Acado-Baltic faunal province with the base of

the Iapetognathus Zone in the type area of the Ibexian Series.

CORDYLODUS ANGULATUS ZONE

(=FAUNA B, UPPER PART)

The Cordylodus angulatus Zone begins 50.3 m (165 ft)

above the base of the House Limestone in the Lava Dam

North section. It is 18.3 m (60 ft) thick and includes the most

advanced species of Cordylodus that occur in the Ibexian as

well as a great variety of species with only coniform elements. This zone is characterized by Cordylodus angulatus

Pander and many species that continue into this zone from

underlying strata, for example, Cordylodus lindstromi (see

further, pl. 1).

ROSSODUS MANITOUENSIS ZONE (=FAUNA C)

The Rossodus manitouensis Zone begins 84.4 m (277 ft)

above the base of the House Limestone in the Lava Dam

North section. It contains a much more diverse conodont

assemblage than is present in earlier zones. The base of the

zone is marked by the lowest observed occurrence of Rossodus manitouensis. Cordylodus is represented by occasional

specimens of Cordylodus angulatus Pander, but many of the

taxa that Furnish (1938) reported from the Oneota Formation

of the American Midcontinent dominate the conodont faunas

of the upper half of the House Limestone. These include

“Acanthodus” lineatus, “Oistodus” triangularis, Variabiloconus bassleri, and Scolopodus? sulcatus. Less common faunal elements are Clavohamulus densus Furnish, “Paltodus”

spurius Ethington and Clark, and Loxodus bransoni Furnish.

Ethington and Clark (1971) identified this assemblage of

conodonts Fauna C, and they (1981) subsequently discussed

the upper House strata in which it occurs as the Loxodus

bransoni Interval. Landing (in Landing and others, 1986)

noted that, although Loxodus bransoni is persistent through

the range of this fauna and widespread geographically, only

a few specimens are found in most occurrences and many

samples lack the species. He recommended that this biostratigraphic interval be identified as the Rossodus manitouensis

(= New Genus 3 of Ethington and Clark, 1981) Zone.

Ethington and Clark (1981) observed that the conodonts of the Rossodus manitouensis Zone, which flourished

during deposition of the upper half of the House Limestone,

disappear abruptly at the top of that formation. They are

replaced in the lower part of the Fillmore Formation by an

almost wholly new population that has low diversity and

abundance. They noted that this same succession is seen at

many places on and adjacent to the North American craton

and inferred that this faunal replacement event might be the

most persistent biostratigraphic event for correlation within

the Lower Ordovician conodont succession of North America. Ethington and others (1987) further documented this

event by comparing its expression in the type Ibexian with

the conodont succession in the coeval lower Arbuckle Group

in Oklahoma. They suggested that this seeming continentwide abrupt replacement of a well-established conodont

fauna by an impoverished population mimics the trilobite

biomeres that have been recognized in the Cambrian of

North America. They also reported that significant changes

in the invertebrate faunas in the same sections occur at different horizons than the conodont event, so that mutual

response to environmental change seems not to be indicated.

Additional evidence for this event is provided by Ji and Barnes (1993), who recorded a similar abrupt termination at the

top of the range of the conodonts of the R. manitouensis

Zone in the St. George Group of the Port au Port Peninsula in

western Newfoundland. 

The horizon of this event is just above the top of the trilobite Paraplethopeltis Zone and the boundary between the

House Limestone and Fillmore Formation (see Ethington

and others, 1987, for details). It lies within the basal part of

the Leiostegium-Kainella Zone and of the Stairsian Stage.

LOW DIVERSITY INTERVAL (=FAUNA D, LOWER PART)

The conodonts in the lowermost 100 m (318 ft) of the

Fillmore Formation occur in very sparse numbers and have

low diversity. Principal components of the fauna are

Drepanoistodus basiovalis (Sergeeva) and a species very

similar to and perhaps conspecific with Scolopodus rex

Lindstrom. This part of the section also has sporadic occurrences of Colaptoconus quadraplicatus (Branson and Mehl)

and Eucharodus parallelus (Branson and Mehl), two species that Ethington and Clark (1971) considered to be fundamental to the assemblage that they identified as conodont

Fauna D. These latter species are long ranging in the type

Ibexian and elsewhere in Lower Ordovician successions.

Frequently they are found to the exclusion of any other
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 25

conodonts, and, by themselves, are insufficient to characterize a zone. We therefore follow the lead of Ethington and

Clark (1981) in not defining a conodont zone for the lower

part of the Stairsian Stage; as a result, the stage depends

upon the trilobites and brachiopods of the LeiostegiumKainella Zone for definition of its lower boundary and characterization of its lowermost zone. The informal conodont

Low Diversity Interval encompasses all but the lowest 6 m

(20 ft) of Stairsian Stage (all but the basal LeiostegiumKainella Zone and most of the Tesselacauda Zone).

MACERODUS DIANAE ZONE (NEW)

(=FAUNA D, MIDDLE PART)

The Macerodus dianae Zone comprises the upper part

of the basal informal ledge-forming member of the Fillmore

Formation (upper part of the Tesselacauda Zone through

almost all of the Rossaspis superciliosa Zone). Its stratigraphic expression corresponds to the range of Macerodus

dianae Fahraeus and Nowlan beginning at 110 m (350 ft)

above the base of the Fillmore and continuing upward to 145

m (460 ft) in the formation. Macerodus dianae is associated

with Scolopodus floweri Repetski (identified as “aff. Paltodus sexplicatus” by Ethington and Clark, 1981) in the type

area of the Ibexian Series, as well as with long-ranging components of the former conodont Fauna D. This assemblage is

present in the Manitou Formation in Colorado and in the Cool

Creek Formation in southern Oklahoma (R.L. Ethington,

unpub. data) as well as in the El Paso Group of West Texas

(Repetski, 1982). Ji and Barnes (1994) found this association

of species in the Boat Harbour Formation (St. George Group)

on the Port au Port Peninsula in western Newfoundland.

Macerodus was described initially by Fahraeus and Nowlan

(1978) from Bed 8 of the Cow Head Group in western Newfoundland, and Nowlan (1976) recorded its presence in the

Baumann Fiord Formation of Devon Island in the Arctic

Archipelago of Canada. Williams and others (1994) referred

to a Macerodus dianae Zone in a report on the biostratigraphic significance of the type Cow Head Group of Newfoundland but did not discuss its stratigraphic limits or

characterize its fauna. These widely separated geographic

occurrences with consistent biostratigraphic position relative

to faunas above and beneath justify recognition of a Macerodus dianae Zone, although additional collecting in all of these

localities is needed to document its range completely.

ACODUS DELTATUS/ONEOTODUS COSTATUS ZONE 

(NEW) (=FAUNA D, UPPER PART)

The lowest occurrence in the type Ibexian of the characteristic P elements of Acodus deltatus Lindstrom is at 151

m (480 ft) in the Fillmore Formation (425 m above the base

of the composite section). Acodus deltatus is associated

through its range with two species that make their appearance

slightly lower in the Fillmore Formation, aff. Acodus emanuelensis McTavish (138.7 m; 455 ft) and Oneotodus costatus

Ethington and Brand (129.5 m; 425 ft) (417 m and 408 m

respectively above the base of the composite section). These

species, together with Walliserodus ethingtoni, aff. Drepanodus forceps (Lindstrom), Oistodus bransoni Ethington and

Clark, and the ubiquitous long-ranging components of conodont Fauna D dominate the conodonts in the lower middle

part of the Fillmore Formation. This assemblage of conodont

species is a distinct one among the succession of faunas in the

Ibexian, and we identify the interval between the lowest

observed occurrence of Acodus deltatus and the lowest

observed occurrence of Oepikodus communis (Ethington and

Clark) as the Acodus deltatus/Oneotodus costatus Zone. It

includes almost all of the Hintzeia celsaora Zone and much

of the Protopliomerella contracta Zone, thus encompassing

the slope-forming siltstone member, the light-gray ledgeforming member, and the lower 55 m (175 ft) of the informal

brown slope and ledge member of the Fillmore Formation.

Recognition of this zone can be made in other regions at

the craton margin where Acodus deltatus is present, but that

species is not widely distributed in the continental interior.

Correlation with sections in the shallow-water carbonates of

the interior may be possible using Oneotodus costatus,

which is introduced in the Arbuckle Group in Oklahoma near

the base of the Kindblade Formation. O. costatus also

appears above a thick interval in the middle and upper part of

the Cool Creek Formation with faunas of the Macerodus

dianae Zone (R.L. Ethington, unpub. data). Repetski (1982)

reported similar distributions of these species in the type El

Paso Group of West Texas. Acodus deltatus is present in

lower Arenigian strata in Sweden, and its occurrence in this

part of the Ibexian provides a tie point with the Lower

Ordovician succession of northern Europe.

OEPIKODUS COMMUNIS ZONE

(=FAUNA E, LOWER PART)

In a review of paleogeography of conodonts of the

Lower Ordovician of North America, Repetski and Ethington (1983) established the Oepikodus communis Zone for

the rocks containing conodont Fauna E of Ethington and

Clark (1971). They suggested the top of this zone be recognized at or near the base of the Tripodus laevis/Microzarkodina flabellum Interval of Ethington and Clark (1981)

thereby excluding from it the top of the range of Fauna E in

the Ibex region as originally envisioned by Ethington and

Clark. We herein further restrict the top of the Oepikodus

communis Zone.

Oepikodus communis was described initially by Ethington and Clark (1964) from the El Paso Group in the Franklin

Mountains, West Texas. Subsequently this species has been

recognized widely in North America. Its range in the type
26 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Ibexian is from 56.4 m (185 ft) below the top of the informal

brown slope and ledge member of the Fillmore Formation

through the lower 66.1 m (217 ft) of the Wah Wah Limestone, an interval of 268.9 m (882 ft) of strata; this interval is

equivalent to 635–904 m (2,084.6–2966.6 ft) above the base

of the composite section. In 1981, Ethington and Clark

reported that a diversity of conodont species is introduced

into the section within the range of Oepikodus communis,

and therefore they divided the stratigraphic range of that species into three “Intervals” based upon these other species. We

here are restricting the Oepikodus communis Zone to the

lowest of these (the Oepikodus communis/Fahraeusodus

marathonensis Interval). The conodonts of the zone include

Oepikodus communis and Fahraeusodus marathonensis

(Bradshaw) (formerly “Microzarkodina” marathonensis)

and long-ranging species that continue upward from the

underlying zones. The Oepikodus communis Zone extends

from the lowest occurrence in the section of the named species to the lowest occurrence of ?Reutterodus andinus Serpagli at 439 m (1,440 ft) above the base of the Fillmore

Formation (718 m (2,354.6 ft) above the base of the composite section). This interval encompasses the upper 56.4 m (185

ft) of the informal brown slope and ledge-forming member

of the Fillmore and the lower 25.9 m (85 ft) of the informal

calcarenite member. The boundary between shelly fossil

zones Protopliomerella contracta and Trigonocerca typica

(the boundary between the Tulean and Blackhillsian Stages)

is within this conodont zone in the type Ibexian. 

REUTTERODUS ANDINUS ZONE (NEW)

(=FAUNA E, MIDDLE PART)

?Reutterodus andinus was reported by Serpagli (1974)

from the San Juan Limestone in Precordilleran Argentina.

Ethington and Clark (1981) described and illustrated distinctive coniform elements from the Fillmore and Wah Wah Formations whose morphology is closely similar to that of

specimens that Serpagli interpreted as “cone-like elements”

of the apparatus of R. andinus. Ethington and Clark did not

find the other elements (unibranched, bibranched) of that

reconstructed apparatus and therefore assigned their coniform elements to R. andinus with query. The holotype of R.

andinus Serpagli is what was described in the initial report as

a “unibranched element.” Repetski (1982) illustrated specimens from the El Paso Group of Texas that are identical to the

coniform elements from the type Ibexian and also reported a

few specimens that he identified as unibranched elements.

His illustrations of the latter specimens do not show marked

differences from the coniform elements, however. This is the

only report of these specimens in association with the coniform elements other than in Serpagli’s initial definition of the

species. Identical coniform elements have been recovered

from many samples from numerous localities in the Great

Basin west of the Ibex area (R.L. Ethington, unpub. data), and

it is unlikely that the absence of bibranched and unibranched

elements from the Ibexian collections is unique to that area.

Stouge and Bagnoli (1988) found only the coniform elements

in Bed 11 of the Cow Head Group in western Newfoundland,

although their collection consisted of only nine specimens

from a single sample. As a result we retain the query in the

designation of these forms as representatives of R. andinus.

Should subsequent research demonstrate that R. andinus does

not contain coniform elements or that the elements reported

by Ethington and Clark are not properly assigned to Reutterodus, a new generic and specific name will be required for

these coniform elements because Serpagli designated

another element as the holotype of R. andinus. 

?Reutterodus andinus is a significant part of an association of conodonts in the highest Fillmore Formation

through most of the Wah Wah Limestone in the type Ibexian.

These species include Jumudontus gananda Cooper, Protoprioniodus aranda Cooper, and Juanognathus variabilis Serpagli, as well as Oepikodus communis and Fahraeusodus

marathonensis, which continue upward from the Oepikodus

communis Zone beneath. This assemblage is that for which

Ethington and Clark proposed the designation conodont

Fauna E. The subsequent use of that term by numerous

authors to report conodont faunas from elsewhere documents

the potential of this faunal association for biostratigraphy.

We establish the ?Reutterodus andinus Zone to formalize biostratigraphic correlations using these species. The base

of the zone in the type Ibexian is at the lowest occurrence of

?Reutterodus andinus at 439 m (1,440 ft) above the base of

the Fillmore Formation (718 m or 2,354.6 ft above the base of

the composite section). The zone comprises all strata from

that horizon through the lower 67.3 m (221 ft) of the overlying Wah Wah Limestone. It includes the upper part of the calcarenite member of the Fillmore, all of the overlying

Calathium calcisiltite member, and the Wah Wah Limestone

through 1.2 m (4 ft) above the distinctive brachiopod coquina

of the Hesperonomiella minor Zone of Hintze (1953, p. 19).

As now understood, the ?Reutterodus andinus Zone

encompasses the upper two-thirds of the Trigonocerca typica

Zone and all of the Presbynileus ibexensis, Pseudocybele

nasuta, and Hesperonomiella Zones. It includes all but the

lowest part of the Blackhillsian Stage.

Jumudontus and Protoprioniodus are abundant in

coeval Australian faunas from the Horn Valley Siltstone

(Cooper, 1981), and a few specimens representing these genera are known from the Baltic region in Europe. Juanognathus and ?Reutterodus provide ties with South America. 

WHITEROCKIAN CONODONT ZONES

TRIPODUS LAEVIS ZONE (NEW)

(=FAUNA E, UPPER PART)

Ethington and Clark (1981) assumed the base of the

Middle Ordovician to be indicated by the appearance near the

bottom of the Kanosh Shale of a distinctive assemblage of

conodonts dominated by Histiodella altifrons and a variety of
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 27

species with hyaline elements. This association of species is

found at the bottom of the Middle Ordovician sequence in

southern Oklahoma and is present in the lower part of the

Middle Ordovician Whiterockian Series in central Nevada.

These occurrences led them to assign the upper part of the

Wah Wah and the Juab Limestones at Ibex to the Lower

Ordovician, although Ross (1970) earlier had considered

these units to be Whiterockian on the basis of their brachiopod faunas. Recent work in the Roberts Mountains (Finney

and Ethington, 1992) and on the type lower Whiterockian in

the Monitor Range in central Nevada (Ross and Ethington,

1991, 1992) showed that the lowest occurrences of Histiodella altifrons and the associated hyaline conodonts may

be diachronous in the Great Basin. These results essentially

substantiated Ross’s earlier correlation of the highest Wah

Wah and Juab with the lower part of the Whiterockian Series.

In the type area of the Ibexian Series, Tripodus laevis

Bradshaw is present and abundant in the upper 11.3 m (37 ft)

of the Wah Wah Limestone and through the overlying Juab

Limestone. It is associated through this range with Protoprioniodus aranda, Fahraeusodus marathonensis, Juanognathus variabilis, and occasionally with Jumudontus

gananda. Microzarkodina flabellum (Lindstrom) and a species probably conspecific with Oepikodus minutus (McTavish) occur with these species through much of their collective

ranges. The same association is present at the base of the

type Whiterockian in the Roberts Mountains (Finney and

Ethington, 1992) in association with abundant Histiodella

altifrons. These latter occurrences provide positive evidence

for defining the top of the Ibexian in its type area at the base

of the Tripodus laevis Zone 11.3 m (37 ft) below the top of

the Wah Wah Limestone, and 1.2 m (4 ft) above the Hesperonomiella minor shell bed.

GRAPTOLITE CORRELATIONS

IBEXIAN GRAPTOLITES

Although graptolites are not abundant in the Ibexian

stratotype section, they do occur at several levels. Braithwaite (1976) made extensive collections from the Fillmore

Formation, Wah Wah Limestone, Juab Limestone, and overlying Kanosh Shale. He arranged these collections into seven

biostratigraphic zones, of which the lower five are Ibexian in

age. The possibility of effective correlation with graptolites

elsewhere at first seems difficult. However, the graptolites in

the Ibexian stratotype occur interbedded with trilobite, brachiopod and conodont assemblages, an advantage lacking in

most graptolite-bearing sections. 

A comparison with the Cow Head Group of western

Newfoundland (James and Stevens, 1986) is helpful in dealing with the upper Ibexian in particular. The sedimentology

of the Cow Head with its breccia flows contrasts with the

platform-to-ramp facies of the typical Ibexian. 

The superb interpretation and exposition of the physical

stratigraphy of the Cow Head Group authored by James and

Stevens (1986) provided the concrete foundation for work on

the graptolites by Williams and Stevens (1988). A convention was established whereby the coarse flow breccias, composed of carbonate clasts, were given even bed numbers and

the intervening graptolite-bearing shales were given odd bed

numbers. A minimum age for each breccia is established by

the youngest trilobite or brachiopod found in a clast. On that

basis Bed 12 is known to be of earliest Whiterockian age and

Bed 10 is correlative with uppermost Zone G2 and all of

Zone H at Ibex. Bed 11 therefore must be older than basal

Whiterockian and no older than Bed 10. Bed 11 correlates

with Braithwaite’s Zone 4; similarly Bed 9 correlates with

trilobite Zone G2, establishing the Tulean age of the Tetragraptus approximatus graptolite Zone. 

Graptolite zones as designated by Braithwaite (1976,

fig. 10) are listed in ascending order, as follows:

ZONE 1. Dendrograptidae. Based on long-ranging Callograptus spp. and Dictyonema spp. (s.l.), this zone extends

from the Bellefontia-Xenostegium Zone (Zone B) almost

through the Hintzeia celsaora Zone (Zone G1). Cactograptus pogonipensis Braithwaite occurs at the level of Zone D

and Mastigograptus sp. at the top of Zone F. Unfortunately,

there is no cosmopolitan species with which to subdivide or

even to characterize this zone as originally defined. A partial

solution to this misfortune lies in a collection made on July

28, 1977, by David Skevington and B.D. Erdtmann on an

excursion led by Ross up the north tributary canyon of Ninemile Canyon, Antelope Range, central Nevada.

From the resulting collection Erdtmann and Comeau

(1980) identified Anisograptus richardsoni Bulman. It was

collected from the lower part of the Goodwin Formation

above the bed crowded with abundant obelloid brachiopods, which in turn overlies the Caryocaris beds of the

uppermost part of the Windfall Formation. (The coordinates of the locality are UTM 1,000 m grid, Zone 11: E

564,200 m; N 4,339,600 m, Horse Heaven Mtn. 15-minute

quadrangle, Nevada.)

Repetski has identified conodonts of the Rossodus manitouensis Zone in the uppermost part of the Windfall Formation in the Antelope Range. Ross has identified Kainella

flagricauda and Hypermecaspis sp. in the lower part of the

Goodwin immediately above the graptolite locality and considers those beds to belong to trilobite Zone D. Although the

locality is well to the west of the Ibex area, it provides a

definitive graptolitic fix on this level in the Antelope Range,

well above the base of the Ibexian Series. This same level is

represented in the southern Rocky Mountains of Canada

where Dean (1989, fig. 10) has equated the Anisograptus

richardsoni Zone with the Bellefontia-Xenostegium Zone

(trilobite zone B). Therefore the zone is late Skullrockian to

Stairsian in age. Based on the work of VandenBerg and Cooper (1992), we conclude that this level correlates with
28 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Australian Lancefield La1b and that it is an interval with

wide geographic recognition, as shown by Cooper and Lindholm (1990, p. 506–507, fig. 1, parts I–III; figs. 4, 5).

ZONE 2. Adelograptus. This zone is limited to the topmost part of trilobite Zone G1 and all but the topmost part of

G2 and is Tulean in age. It includes the appearances of Dendrograptus spp. and of Desmograptus spp., and the continuation of Callograptus spp. and Dictyonema spp. Dictyonema

cordillerensis Braithwaite, D. fillmorensis Braithwaite, Adelograptus novus (Berry), Clonograptus cf. C. sarmentosus

Moberg, Cactograptus utahensis Braithwaite, and Temnograptus utahensis Braithwaite are the designated species,

and their occurrences are limited to the lower part of Zone

G2. Only two of these species have outside distribution.

ZONE 3. Clonograptus flexilis (Hall) and Phyllograptus

archaios Braithwaite are the only two species in this zone;

they occur in uppermost trilobite Zone G2. The latter species

has no outside distribution and the former has a long range. 

In western Newfoundland Fortey (1979) has presented a thorough and beautifully illustrated analysis of the

trilobite fauna of the Catoche Formation. He concluded that

the age of the formation ranges from highest Zone G2

through Zone H of the type Ibexian or late Tulean to early

Blackhillsian. He suggested the possible correlation of the

lower Catoche with Berry’s (1960) graptolite Zone 4 (Zone

of Tetragraptus (now=Pendeograptus) fruticosus 4-

branched). On that basis we might conclude that Braithwaite’s Zone 3 could be equivalent to the Zone of P.

fruticosus 4-branched (or Bendigonian 1–2).

ZONE 4. Didymograptus fillmorensis Braithwaite–Didymograptus millardensis Braithwaite. In addition

to the two named species, this zone includes the continuation

of Dendrograptus sp., and Dictyonema sp., as well as the

appearance of Phyllograptus ilicifolius major and Phyllograptus griggsi. The zone is found in the uppermost Fillmore Formation, equivalent to upper trilobite Zone H and all

of Zone I or middle Blackhillsian. The two species with outside distribution suggest the Didymograptus protobifidus

Zone (in the Australian scheme equal to Chewtonian).

ZONE 5. Tetragraptus. The zone characterizes the entire

Wah Wah Limestone. It includes the continuation of Dendrograptus spp., the termination of Desmograptus spp.,

Dichograptus octobrachiatus, Tetragraptus pogonipensis

Braithwaite, T. ibexensis Braithwaite, T. bigsbyi (Hall), T.

agilis Braithwaite, Tetragraptus sp., Phyllograptus loringi

White, P. ilicifolius major, P. griggsi, P. anna longus, P. anna,

and Didymograptus extensus (Hall). The age of this zone

clearly falls within the range of the Australian Bendigonian

Be2 to lower Castlemainian.

ZONE 6. Didymograptis nitidus (Hall)–Didymograptus

patulus (Hall). Both species of this zone occur in the upper

part of the Juab Limestone in the basal Whiterock Series.

ANOMALIES AND CORRELATIONS

The stratigraphic range of Tetragraptus approximatus

in the Australian scheme (VandenBerg and Cooper, 1992,

range chart) is La3–Be1. In western Newfoundland Williams

and Stevens (1988), in their study of Lower Ordovician graptolites of the Cow Head Group, indicated that T. approximatus occurs in Bed 9 of the Ledge section (text-fig. 4) and in

Bed 9 of the Jim’s Cove section (text-fig. 6) on the Cow Head

peninsula. In the Western Brook Pond section (text-fig. 5) T.

approximatus occurs in Beds 9 and 10, and the base of 11. At

Martin Point North (text-fig. 8), it is in Bed 9, and at Martin

Point South (text-fig. 9) it was found near the top of Bed 9.

At St. Paul’s inlet, North Tickle section (text-fig. 10), T.

approximatus is present through much of Bed 9 and possibly

as high as the base of Bed 11. In fact Tetragraptus approximatus is an important component of both the T. approximatus and T. akzharensis Zones, underlying the Pendeograptus

fruticosus Zone. Nor should one overlook the possibility that

the Pendeograptus fruticosus and Tetragraptus approximatus Zones are partly correlative, as indicated in text-figure 6

of Williams and Stevens (1988).

A close examination of figures 4–10 of Williams and

Stevens (1988) reveals not only that (1) T. approximatus

belongs to Bed 9, and (2) a new Zone of T. akzharensis

belongs in either the very top of Bed 9 or the bottom of Bed

11, but also that (3) the Zone of P. fruticosus is disturbingly

fickle because it is in lower Bed 11 (text-fig. 6), or in upper

Bed 11 (text-fig. 5), or it may be designated in an interval

without any graptolites at all (see their fig. 10) in a section

wherein P. fruticosus itself occurs in the higher? Zone of D.

bifidus. We conclude that the graptolites of Cow Head Bed

11 are correlative with upper Zone 3 and Zone 4 of Braithwaite, or very high Ibexian.

Our attention goes to Fortey (1979), who showed that

the Catoche Formation, St. George Group, is equivalent to

Zones G2 and H at Ibex. James and Stevens (1986) indicated

that the youngest trilobites from clasts in Bed 9 also matched

G2, that trilobites from Bed 10 (a flow breccia) matched

Zones H and possibly I from Ibex, and that brachiopods from

Bed 12 are Whiterockian. In other words the key to dating

the Cow Head slope facies and the St. George platform facies

lies in matching the faunas of the carbonates against the type

Ibexian! The odd-numbered beds are the graptolite bearers

and they are locked in between the carbonate breccias.

Therefore, the position of graptolite zones in the deeper

facies is also locked into the Ibexian stratotype. 

HISTORICAL PERSPECTIVE

BACKGROUND AND APPEALS

FOR TRADITION

Some traditionalists may not favor the introduction of

the Ibexian or of these new stage names because they do not

realize the inadequacies of the old familiar ones. In support
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 29

of the correlation chart of Ordovician strata in the United

States, Ross and others (1982, p. 5–7) provided a detailed

account of the origin, evolution, dislocation, and physical

inadequacies of the components of the original Canadian

Period of Dana (1874). For the sake of clarity, a synopsis of

the material covered by Ross and others is expanded herein.

Teichert and Flower (1983) thought that the term

“Canadian” could be applied to rocks of part of the Pogonip

Group in western Utah to preserve tradition, and Fortey

(1988, p. 43–44) recognized that the base of the “Canadian”

is best defined in the Ibexian section. The opinions of these

authors reflect their rejection of the inadequacies of the

“Canadian” relative to requirements of the International

Commission on Stratigraphy (Cowie and others, 1986),

which emphasizes biostratigraphy over pure tradition. 

ALTERNATIVE VIEWPOINTS

From the 1930’s into the 1950’s, the stratigraphic section in the Ozark region of Missouri and Arkansas served as

the reference section for the Lower Ordovician. Although

better than the New York composite sections, even here the

units are not all in stratigraphic succession one above another

in a single section. In fact, all of the formations are not present

in outcrop in any single area. There is no widely held agreement about the identification of formations or stratigraphic

equivalents in various outcrop belts (Thompson, 1991).

The formations assigned to the Lower Ordovician in the

Ozark region are the following:

Smithville Dolomite (and its Black Rock Limestone

Member)

Powell Dolomite

Cotter Dolomite

Jefferson City Dolomite

Roubidoux Formation

Gasconade Dolomite

The Lower Ordovician Series was based on these formations in the 1940’s. Cullison (1944) described trilobites

from the Roubidoux, Jefferson City, Cotter, and Powell Formations. Each formation was supposed to include a characteristic fauna, largely molluscan, but no range charts other

than Cullison’s were available. Subsequently there has been

no suitable documentation or synthesis of either the physical

stratigraphy or biostratigraphy of the Lower Ordovician

Ozark succession that could be used as the basis for intraregional correlation, let alone as an interregional standard.

In a paper on ellesmeroceratid cephalopods, Flower

(1964) recommended that the Canadian Series be a system,

divided into the Gasconadian, Demingian, Jeffersonian, and

Cassinian Series. The Gasconadian and Jeffersonian were

derived from the Ozark region. The Cassinian came from

eastern New York (Fort Cassin Formation and its fauna).

Although the Demingian was named for a section south of

Deming, New Mexico, it was based largely on the Fort Ann

Limestone plus “300 feet of Cutting dolomite.” Subsequently, Fisher and Mazzullo (1976) correlated this part of

the Cutting Dolomite with the Smith Basin Limestone of

Flower (1964). (Compare their figure 8 with Flower’s (1964)

figure 53.) Flower (1964, and thereafter) included the Smith

Basin Limestone in his Gasconadian Series. This inconsistent correlation among authors has tainted the use of the

Demingian. In any case, to determine where one of those

stages ended and the next began was and is impossible

because of the combination of disjunct geographic distribution and poor biostratigraphic control in the reference areas.

Conodonts have the strongest potential for delimiting

Ibexian correlatives in the shallow-water sandstone and

dolostone facies of southern Missouri and northern Arkansas

(Kurtz, 1981, p. 115–117). R.L. Ethington and J.E. Repetski

have undertaken systematic stratigraphic collecting of conodonts from the six formations in the Ozark Mountains of

Missouri (Repetski and others, 1993). Such work may lead to

a better understanding of Lower Ordovician biostratigraphy

in the Ozark area.

Wright and others (1987) and Miller (1988) expressed

concern that previous usage of the term “Ibex” might disqualify its further application. Widespread use of the Ibexian

Series by stratigraphers in North America and abroad indicates that most have been unconcerned about this nomenclatural problem. Previous usages included the little-used Ibex

Member of the Ely Springs Dolostone of Budge and Sheehan

(1980). Sheehan (written commun. to RJR, March 7, 1989)

saw no reason for confusing this Upper Ordovician member

with the Lower Ordovician Ibexian Series. The “Ibex Substage of the Cassinian Stage” of LeMone (1975, p. 176–179)

was proposed to be equivalent to the single Ross/Hintze trilobite Zone H (=Trigonocerca typica Zone of this report) in

a stratigraphic classification that has not been used by other

stratigraphers. The Permian Ibex Limestone of Texas

(Cheney, 1948) is less than one meter thick and is now considered to be a member of the Moran Formation, Wichita

Group (Price, 1978).

GEOGRAPHIC PERSPECTIVE

NORTH AMERICA

UTAH AND SOUTHEASTERN IDAHO

In 1951 Ross assumed that the base of the Ordovician

was at the base of the Garden City Formation of northern

Utah and southeastern Idaho. In the Bear River Range of Utah

and Idaho, Landing (1981), Taylor and Landing (1982), and

Taylor, Landing, and Gillette (1981) demonstrated that a hiatus representing the lower part of the Symphysurina Zone is

present between the Garden City Formation and underlying

dolostones of the St. Charles Formation. Additionally, they

showed that the Cordylodus proavus Zone, which is equivalent to the Missisquoia Zone and Eurekia apopsis Zone, is

present in the upper part of the St. Charles Formation.
30 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

In 1985 M.E. Taylor and J.E. Repetski reviewed the

trilobite and conodont evidence in the Bear River Range

and carried it southwestward, through the southern Lakeside Mountains, Stansbury Island, the northern end of the

Stansbury Range, to the southern House Range and the type

area of the Ibexian Series where deposition is considered to

have been more or less continuous. A similar trilobite-conodont succession is present in the Egan Range, east-central

Nevada (Taylor, Repetski, and Sprinkle, 1981, fig. 20; Taylor and others, 1989, figs. 6-2, 6-3). The correlations can be

extended to mixed carbonate-siliciclastic platform margin,

slope, and basin facies in south-central Nevada (Taylor,

1976; Taylor and Cook, 1976; Cook and Taylor, 1977;

Miller, 1992; Cook, Taylor, and Miller, 1989; Repetski and

Taylor, 1983).

Miller (1984, p. 48–55, fig. 1) presented evidence for a

eustatic lowering of sea level, termed the Lange Ranch

Eustatic Event (LREE), coinciding with the base of Hirsutodontus hirsutus Subzone of the Cordylodus proavus Zone.

This event has been recognized widely, and Miller (1992)

discussed the evidence for it in detail in several depositional

settings. In some sections at the level at which evidence for

the LREE might be expected, generally shallow water sedimentary characteristics occur, as in central and western

North Greenland (Bryant and Smith, 1990). 

CANADIAN ROCKY MOUNTAINS

The base of the Ibexian Series is a biostratigraphically

correlated level in the Canadian Rockies and other western

areas (Derby and others, 1972, faunal unit 2, fig. 2). Dean

(1978, p. 4, figs. 3, 4) noted the presence of Eurekia apopsis

in the basal Silty Member of the Survey Peak Formation in

the Canadian Rockies of Alberta. In a stratigraphically controlled and well-illustrated monograph, Dean (1989) demonstrated that virtually every assemblage zone of the Ibexian

Series is represented at Wilcox Pass in the Rocky Mountains

of Alberta. Westrop and others (1981) and Westrop (1986)

provided the documentation of trilobite and conodont distribution in the upper Mistaya and lower Survey Peak Formations from their measured section at Wilcox Pass, near

Dean’s area of investigation.

Loch and others (1993) discussed details of uppermost

Cambrian and lowermost Ordovician biostratigraphy of the

Survey Peak Formation in the Mount Wilson and Wilcox

Pass sections in Alberta. They provided new data and reinterpreted some earlier published work. Loch and others (1993,

fig. 3) recognized the lower part of the Ibexian Series and

placed the base of the Ibexian at the base of the Missisquoia

depressa Subzone of the Missisquoia Zone. The underlying

Eurekia apopsis Subzone of the Saukia Zone of Loch and

others (1993) correlates with the Eurekia apopsis Zone of

this report. Our different placement of the base of the Ibexian

Series is a difference in definition, not in correlation.

In their detailed study of the upper Rabbitkettle Formation, District of MacKenzie, Canada, Landing and others

(1980) correlated their lowest Missisquoia-bearing interval

and the base of their Cordylodus proavus Zone (identified as

Cordylodus oklahomensis and corrected in erratum) with the

Corbinia apopsis Subzone (=Eurekia apopsis Zone of this

report) in Texas and Oklahoma. This correlation confirmed

the earlier observation of Tipnis and others (1979).

EASTERN CANADA

At Navy Island, New Brunswick, Canada, Landing and

others (1978, p. 75–78) demonstrated that Cordylodus proavus occurs below Dictyonema flabelliforme (now Rhabdinopora flabelliformis) and with trilobites of the AcadoBaltic Westergaardia Subzone of the Acerocare Zone,

thereby providing a tie with the Acado-Baltic faunal province.

In western Newfoundland Cordylodus proavus Zone

conodonts and Eurekia apopsis Zone trilobites were

reported in both in-place rocks and transported limestone

blocks of the Cow Head Group by Fortey and others (1982,

p. 95–129) along with a graptolite assigned to Radiograptus

rosieranus flexibilis Fortey. Deferring to a coincident paper

by Rushton (1982), these authors sought to move the Cambrian-Ordovician boundary stratigraphically upward to the

lowest occurrence of long-ranging Dictyonema flabelliformis. Barnes (1988) corroborated that the Cordylodus proavus Zone has been recognized from the slope-facies

carbonate deposits of the Cow Head.

Detailed work in the coeval autochthonous platform

carbonate sequence of western Newfoundland (upper Port au

Port and St. George Groups) clarified Ibexian relationships

there (Stouge, 1982; Stouge and Boyce, 1983). From clasts

in the debris flow conglomerate of Bed 19 at Green Point,

Newfoundland, J.F. Taylor (written commun., April 15,

1997) reported that he has found Symphysurina cf. S. cleora

and other trilobites diagnostic of the basal Ibexian zones in

Utah. Bed 19 is below the level of a proposed CambrianOrdovician boundary stratotype, on which no final decision

has been reached as of April 17, 1997.

EASTERN UNITED STATES

M.E. Taylor and Halley (1974) identified trilobites

indicative of both the Saukiella serotina Subzone of the

Saukia Zone and the Missisquoia Zone in samples from the

upper part of the Whitehall Formation in the Champlain Valley of eastern New York. Repetski (1977) identified the

Cordylodus proavus Zone in the same unit in that region, as

well as North American Midcontinent conodont faunas C

(=Rossodus manitouensis of this report), D (=Low Diversity

Interval, Macerodus dianae, and Acodus deltatus–Oneotodus

costatus Zones of this report), and E (=Oepikodus communis
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 31

Zone of this report) in overlying formations. These studies

show that the Skullrockian and Stairsian Stages can be recognized in platform rocks of the Champlain Valley.

In an important contrast with the carbonate-platform

and platform margin faunas of Utah and Alberta, J.F. Taylor

and others (1991, particularly fig. 4) found the base of the

Hirsutodontus hirsutus Subzone of the Cordylodus proavus

Zone to be equivalent to the Elkanaspis corrugata trilobite

Zone and to be immediately underlain by strata with geographically widespread Lotagnostus hedini in the deepwater, slope facies at Highgate Gorge, Vermont. They called

attention to the identical relationship in Kazakhstan (Apollonov and others, 1988, figs. 2 and 3), in southwestern P.R.C.

(People’s Republic of China; Lu and Lin, 1980, 1984), and

northwestern P.R.C. (Wang and others, 1985). Both Apollonov (1991, p. 34–43) and Dubinina (1991, p. 117, 121)

have supported these observations in Kazakhstan.

J.F. Taylor and others (1991) demonstrated that Landing’s (1983, p. 1149–1167) earlier interpretation that Cordylodus proavus appeared earlier in slope settings than on the

shelf in Vermont was based on a miscorrelation of a key

debris-flow marker bed. Landing (1993) has continued to

support his 1983 correlation.

Cordylodus proavus Zone conodonts from low in the

Stonehenge Formation of northern New Jersey and eastern

and central Pennsylvania (Tipnis and Goodwin, 1972; Karklins and Repetski, 1989; J.E. Repetski, unpub. data) show

that the base of the Ibexian locally falls near or at the base of

that unit. Most or all of the younger Ibexian conodont zones

can be recognized in overlying formations of the Beekmantown Group in this region.

In the central Appalachian region J.F. Taylor and others (1992, p. 414) found that “the most tightly constrained

and easily recognized of the three potential CambrianOrdovician boundary stratotype levels is the base of the

Cordylodus proavus Zone.” They found evidence of a rapid

marine transgression in the lower Stonehenge Limestone in

the younger Cordylodus angulatus Zone. The Cordylodus

proavus Zone lies 80 m (262 ft) lower in the stromatoliterich peritidal beds of the Conococheague Formation, but no

distinct signature of the Lange Ranch Eustatic Event is evident. However, they concluded that evidence of shallowing

followed by transgression closely paralleled the stratigraphic sequence from St. Charles Formation to Garden

City Formation in central and northern Utah and southeastern Idaho (Taylor, Landing, and Gillette, 1981; Taylor and

Landing, 1982; Taylor and Repetski, 1985).

Repetski (1985, p. 28) called attention to possible evidence for the Lange Ranch Eustatic Event at the base of the

Chepultepec Dolomite at Thorn Hill in eastern Tennessee,

but the currently available biostratigraphic evidence is only

suggestive. In the southern Appalachians lower Ibexian and

underlying Cambrian rocks are in mainly dolomitized carbonate-platform/ramp facies. As a result of unfavorable

facies and lack of detailed study in this region, conodont

evidence is sparse and macrofossils are almost nonexistent.

Thus far, only a few conodont collections (Repetski, 1992, p.

39–46) are available to show the general position of these

rocks within the lower part of the Ibexian Series.

J.F. Taylor and others (1996) have demonstrated the

usefulness of the Ibexian and its stages in the Frederick

Valley of Maryland.

SOUTHERN MIDCONTINENTAL UNITED STATES

Stitt (1971, 1977, 1983) and Derby and others (1991,

figs. 5, 6) have assembled a thorough review of the Cambrian

and Ordovician of Oklahoma. The position of key basal

Ibexian trilobite and conodont species approximately 122 m

(400 ft) above the base of the Signal Mountain Limestone is

clearly demonstrated at Chandler Creek, Wichita Mountains.

Miller (1992) discussed how the Lange Ranch Eustatic Event

is manifested in these strata.

Flower (1957, p. 18) named the Jeffersonian Stage of

the Canadian Series for dolomitic rocks and chert-mold fossils in the Jefferson City Formation of Missouri. Loch (1995)

redefined the Jeffersonian Stage on trilobite faunas in the

Kindblade Formation of southern Oklahoma. Loch’s redefined Jeffersonian Stage correlates with shelly fossil Zones

G-1 and G-2 (Hintzeia celsaora and Protopliomerella contracta Zones of this report). The Hintzeia celsaora and Protopliomerella contracta Zones characterize the Tulean Stage

of the Ibexian Series in the type area. Loch’s data (1995) are

further evidence that the Ibexian Series and its stage divisions are recognizable in different facies of Laurentia and the

North American Faunal Province. Repetski (1982, 1988)

described Ibexian conodonts from West Texas.

Repetski and others (1997) have demonstrated the close

applicability of the Ibexian Series and its stages and zones to

the stratigraphy of the Ozarks region in southern Missouri.

In the continental-slope deposits of the Ouachita Mountains, west-central Arkansas and eastern Oklahoma, Cordylodus proavus Zone conodont faunas have been recovered by

Ethington and Repetski and will be instrumental in understanding the stratigraphy of this structurally complex region.

MEXICO

The Lower Ordovician platform succession of mixed

carbonate and minor siliciclastic rocks in northeastern and

north-central Sonora, Mexico, has little biostratigraphic documentation. Preliminary studies show that it can be correlated readily with platform successions in the central and

western United States, including the Ibexian type area

(Repetski and others, 1985). To the west, in northern Mexico, Ibexian strata comprise mainly deeper water siliciclastic

deposits with sparsely documented graptolites and conodonts from isolated and structurally poorly constrained
32 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

localities (Gastil and Miller, 1983; Bartolini and others,

1989). In Oaxaca, southern Mexico, the deeper water Tinu

Formation contains Upper Cambrian and Lower Ordovician

fossil assemblages (Robison and Pantoja-Alor, 1968; Sour

and Buitron, 1987). The lowermost Ibexian at Oaxaca contains cosmopolitan trilobites and conodonts assigned to the

Cordylodus proavus to Cordylodus angulatus Zones (Clark

in Robison and Pantoja-Alor, 1968). The Oaxaca shelly fossils have affinities with the Acado-Baltic faunal province.

OUTSIDE NORTH AMERICA

SOUTH AMERICA

The thick Upper Cambrian to Middle Ordovician succession in northwestern Argentina correlates well with the

type Ibexian where its fauna has been documented. For

example, Rao (1988, in Sarmiento and Garcia-Lopez, 1993)

reported conodonts of the Cordylodus proavus and Cordylodus intermedius Zones in Jujuy Province. F.G. Acenolaza

(1983) and Acenolaza and Acenolaza (1992) summarized

the distribution of trilobites, graptolites, and conodonts in

Latin America critical to choosing the lower boundary of the

Ordovician System and recommended that the Cordylodus

proavus Zone be included in the Ordovician.

Lower Ordovician conodonts were summarized by Serpagli (1974), Sarmiento and Garcia-Lopez (1993), and Lehnert (1993) for middle and upper parts of the Ibexian Series

in Argentina. Many of the middle Ibexian conodonts

reported in Argentina show affinities with the Acado-Baltic

faunal province. These faunas are similar to those in outer

platform facies in the central and western parts of the Basin

and Range province, Western United States. In the upper part

of the Ibexian Series, however, numerous species in the San

Juan Limestone also occur through the upper part of the Fillmore Formation and Wah Wah Limestone.

SPITSBERGEN

In his classic study of the Ordovician trilobites of Spitsbergen, Fortey (1980, p. 8–17, fig. 3) presented his presumed

evidence for the erection of a distinct Valhallan Stage, older

than the Whiterockian and younger than the Ibexian Series.

Perusal of his figure 3 reveals the flaw in this proposal. It is

now known that the Isograptus victoriae Zone is overlapped

by the Didymograptus bifidus Zone. It is also known now

that the base of the Whiterockian (Orthidiella Zone) coincides with the base of the Isograptus victoriae Zone (Finney

and Ethington, 1992). Ross and Ethington (1992, p. 146)

noted the close parallelism, both faunal and sedimentological, between the upper Valhallan of Spitsbergen and the

Whiterockian of Utah and Nevada. The lower Valhallan is

clearly of late Ibexian age. The Valhallan fauna is present in

the deeper water facies of Ikes Canyon in the Toquima

Range, central Nevada. Fortey and Droser (1996, p. 80, table

1) have compared trilobites of the uppermost Ibexian and

lower Whiterockian with those of Spitsbergen, particularly

those of the upper Olenidsletta Member and Profilbekken

Member of the Valhallfona Formation (Fortey, 1980, fig. 1 in

pocket (not figure 3)).

WALES

Rushton (1982) reported on the lithologies, trilobites

and graptolites within the traditional interpretation of the

Tremadoc Series, and (p. 46) noted that Cordylodus proavus

is associated with Shumardia alata within the Acerocare

Zone at Bryn-llin-fawr. There Dictyonema (=Rhabdinopora)

flabelliformis was about 20 m higher (Rushton’s fig. 3).

These are the same relative positions that are present in Oslo

Fjord, where Boekaspis hirsuta occurs less than 1.0 m below

Rhabdinopora flabelliformis (Bruton and others, 1988). 

AUSTRALIA

TASMANIA

Laurie (1980, 1991) described an array of brachiopods

from Tasmania that are so similar to Ibexian forms from the

Basin Ranges that one can hardly avoid the correlation and

the environmental similarity of the two areas. Leptella and

Archaeorthis in the lower Karmberg Formation suggest a link

with the Ninemile Formation of central Nevada. Hesperonomiella in siltstones near Caroline Quarry, Railton area, suggest the Wah Wah Limestone of western Utah. Laurie’s

discussion (1991, p. 19–21) of brachiopod zonal assemblages

from the Florentine Valley Formation leaves little doubt that

the formation closely parallels the typical Ibexian Series,

from Apheoorthis near the base, through Nanorthis, Tritoechia, and Leptella. This succession includes many of the

same graptolite, trilobite, and conodont genera and species.

Above them is Hesperonomiella, which we interpreted (p.

21) as uppermost Ibexian, not necessarily Whiterockian. 

Webby and Nicoll (1989) published a new correlation

chart for the Ordovician of Australia. This chart indicated the

trend in Australian thinking concerning the base of the system. The authors called attention (1989, p. 4) to the ease with

which North American terms could be applied to Australian

units, and indicated (p. 20–21) their preference for the base

of the Hirsutodontus simplex Subzone of the Cordylodus

proavus Zone for the level of the Cambrian-Ordovician

boundary. This level is only slightly above the base of the

Symphysurina Zone in North America. Their chart correctly

showed the base of the North American Ibexian Series as

being older than the base of the “British” Tremadoc Series. 

In his taxonomic revision of Cordylodus, Nicoll (1990)

recognized the validity of the Cordylodus proavus Zone,

consisting of three subzones, that of Hirsutodontus hirsutus
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 33

being the oldest. He dispensed with the Cordylodus intermedius Zone for taxonomic reasons, replacing it with two zones

that were formerly the two constituent subzones of the

Cordylodus intermedius Zone of Miller (1988), the Hirsutodontus simplex Subzone below and the Clavohamulus

hintzei Subzone above. 

QUEENSLAND

Nicoll and Shergold (1991, p. 95–98) discussed conodont biostratigraphy at Black Mountain in western

Queensland, Australia, and clarified ranges of key taxa.

They noted that the lower boundary of the Hirsutodontus

hirsutus Subzone of the Cordylodus proavus Zone is well

below the top of the Ninmaroo Formation and indicative of

the base of the Datsonian Series. Their figure 2 shows the

stratigraphic position of Cordylodus primitivus (=Cordylodus andresi of this report), Fryxellodontus inornatus, Hirsutodontus hirsutus, Teridontus sp. B, Cordylodus proavus,

and Clavohamulus spp. between 582 and 632 m

(1,852–2,011 ft) above the base of the section. This assemblage clearly correlates with the Hirsutodontus hirsutus

Subzone of Miller, and is earliest Ibexian in age. Ripperdan and Magaritz, joined by these same two authors (Ripperdan and others, 1992, figs. 1 and 3), showed that the

components of this assemblage at Black Mountain appear

first at approximately 540 m (1,718 ft), coinciding with a

paleomagnetic polarity reversal, believed to be coincident

with the eustatic sea level change of the Lange Ranch

Eustatic Event. The plotting of first appearance of Cordylodus proavus some 40 m (127 ft) higher is peculiar because

it seems to be related to an interval that lacks conodonts. In

any case, for those seeking physical as well as biostratigraphic confirmation of the importance of the base of the

Ibexian Series, this and a corroborating paper by Ripperdan and Kirschvink (1992, fig. 6) are noteworthy. Shergold and Nicoll (1992, p. 86–87) repeated and emphasized

the importance of this “event in Cambrian-Ordovician conodont evolution.”

Shergold and Nicoll (1992) showed that the lowest

occurrences of Cordylodus and Fryxellodontus inornatus are

coincident, and additional collections from the Black Mountain section confirm this relationship (J.F. Miller, unpub.

data, 1991). A relatively thin interval of strata beneath these

faunas contains molds of anhydrite, and is barren of conodonts. We suggest that the base of the Datsonian Stage in

Australia correlates within the Fryxellodontus inornatus

Subzone of this report and that the base is slightly younger

than the base of the Ibexian Series.

REPUBLIC OF KAZAKHSTAN

Apollonov (1991) reviewed the reasons for the Soviet

decision to use the base of the Cordylodus proavus Zone,

locally underlain by Lotagnostus hedini, to mark the base of

the Ordovician System in southern Kazakhstan. He also

emphasized the inadequacies of the first appearance of

Rhabdinopora flabelliformis as a boundary indicator. Dubinina (1991) compared Ordovician sections in two different

paleoenvironments, the Sarykum section in central Kazakhstan and the Batyrbai section in southern Kazakhstan. In both

she reported that Cordylodus proavus is underlain by Lotagnostus hedini and marked the base of the Ordovician System.

The conodont succession is strikingly similar to that at the

base of the Ibexian in the type area and in a deep-water succession reported by J.F. Taylor and others (1991) in Vermont.

Subsequent collecting at Batyrbai, southern Kazakhstan, by J.F. Miller (unpub. data, 1990) suggests a slight

overlap of ranges of Lotagnostus hedini and Cordylodus

primitivus (=Cordylodus andresi, this report) as reported

by Apollonov and others (1988). However, specimens are

rare and the interval is thin, occurring in thinly bedded

lime mudstone, so the slight overlap may be merely an

artifact of sampling.

JILIN PROVINCE, PEOPLE’S REPUBLIC OF CHINA

Chen and others (1985, 1988) and Chen (1986) documented ranges of conodonts and other fossils from a section

near Dayangcha in northeast P.R.C. Their figure 6 (1988)

shows ranges of conodonts in one part of the Xiaoyangqiao

composite section. This section was under consideration for

a global stratotype for the base of the Ordovician System, but

it was not approved in 1992 by a postal ballot of the Cambrian-Ordovician Boundary Working Group of the International Union of Geological Sciences. Approximately the

lower 10 m of the Xiaoyangqiao composite section is referred

to the Cambrooistodus Zone, which correlates directly with

the Cambrooistodus minutus Subzone of this report. Therefore, these strata are pre-Ibexian in age. Younger strata in the

Xiaoyangqiao composite section are referred to the Cordylodus proavus, Cordylodus intermedius, Cordylodus lindstromi, and Cordylodus angulatus–Chosonodina herfurthi

Zones, which correlate with the Skullrockian Stage.

Chen and others (1988) referred the interval from about

10.0 to 28.5 m to the Cordylodus proavus Zone and divided

it into lower, middle, and upper parts. The lower part correlates with the Hirsutodontus hirsutus Subzone of the Cordylodus proavus Zone of this report. The middle part correlates

with the Fryxellodontus inornatus Subzone of this report.

The upper part of the Cordylodus proavus Zone at Dayangcha correlates, in part, with the Clavohamulus elongatus

Subzone of this report, but the upper portion of this subzone

at Dayangcha has few conodonts that are biostratigraphically

diagnostic. Conodont collections from the Dayangcha section contain Hirsutodontus simplex from the stratigraphic

interval from which Chen and others (1988, fig. 6) collected

samples 10 A(1–6) (J.F. Miller, unpub. data). Chen and others (1988) referred this stratigraphic interval to the upper part

of the Cordylodus proavus Zone, but the presence of
34 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Hirsutodontus simplex indicates that the interval correlates

with the Cordylodus intermedius Zone of this report. Iapetognathus also occurs at higher stratigraphic levels in the

Dayangcha section (J.F. Miller, unpub. data).

Ripperdan and others (1993) reported results of carbon

isotope and magnetostratigraphic studies of the Dayangcha

section and concluded that several hiatuses (or highly condensed intervals) exist. One hiatus was interpreted to occur at

the base of the Cordylodus proavus Zone and a second

slightly higher hiatus at the base of the second division of the

Cordylodus proavus Zone (=base of Fryxellodontus inornatus Subzone of this report). They (Ripperdan and others,

1993, fig. 5) related the two hiatuses to the two stages of the

Lange Ranch Eustatic Event of Miller (1992).

CAMBRIAN-ORDOVICIAN 

BOUNDARY

Selection of the international boundary stratotype for

the Cambrian-Ordovician boundary is under consideration

by the Cambrian-Ordovician Boundary Working Group of

the International Commission on Stratigraphy, International

Union of Geological Sciences. Important summaries of the

Working Group’s studies are found in Henningsmoen

(1973), Bassett and Dean (1982), Lu (1984), Chen (1986),

and nine articles in a special issue of Geological Magazine

(1988, v. 125, no. 4, p. 323–473). Herein, we have purposely

refrained from discussion of the relative merits of boundary

stratotype proposals and let the biostratigraphic data of the

Ibexian Series speak for themselves.

SUMMARY

The North American Ibexian Series, as represented in

the Ibex area by its abundantly fossiliferous and exceptionally well exposed strata in laterally contiguous or closely

neighboring typical sections in the southern House and Confusion Ranges of west-central Utah, provides an unrivalled

composite stratotype, a standard for biostratigraphic subdivision of and correlation within the interval between the end of

the North American Cambrian Croixian Series and the

beginning of the lower Middle Ordovician Whiterockian

Series.

The composite stratotype of the Ibexian Series is a reference section for precise biochronologic correlation over

the entire span of Early Ordovician time. It contains a highresolution biostratigraphy comprising concurrent ranges of

trilobites, conodonts, brachiopods, echinoderms, and other

fossils. Although graptolites are not present throughout the

section they do occur in some of the shaly intervals and add

to the utility of the stratotype.

The base of the Ibexian Series is characterized by a distinctive faunal turnover among conodonts from the Eoconodontus Zone to the Hirsutodontus hirsutus Subzone of the

Cordylodus proavus Zone and trilobites from the Saukiella

serotina Subzone of the Saukia Zone to the Eurekia apopsis

Zone. The boundary meets the rigid requirements of the

North American Stratigraphic Code (NACSN, 1983) and the

International Commission on Stratigraphy (Cowie and others, 1986) for definition of chronostratigraphic units. The

sharp biostratigraphic boundary is also marked by several

geochemical anomalies that make the boundary one of the

more useful lower Paleozoic horizons for global correlation

(Miller and others, 1993).

The upper limit of the Ibexian Series is the base of the

Rangerian Stage of the Whiterockian Series, recently shown

to be marked by conodonts of the Tripodus laevis Zone, trilobites and brachiopods of the Paralenorthis-Orthidiella

Zone (=Zone L of Ross, 1951) (Ross and Ethington, 1991,

1992), and by graptolites of the Isograptus victoriae Zone

(Finney and Ethington, 1992).

The type Ibexian is a continuous chronostratigraphic

reference section for the Lower Ordovician of North America and of Laurentia. No stratigraphic section in North America surpasses the Ibexian composite-stratotype section in

excellence of exposure, abundance of fossils, quality of fossil preservation, and accessibility. A brief perusal of figures

1–7 demonstrates that although the stratotype is not a single

vertically stacked sequence of layers, the fortuitous array of

incremental sections, either contiguous or in close proximity,

contributes to the superlative accessibility of the whole.

SELECTED REFERENCES

Acenolaza, F.G., 1983, The Tremadocian beds and the CambrianOrdovician boundary problem in Latin America in Papers for

the Cambrian-Ordovician and Ordovician-Silurian boundaries

symposium, Nanjing, China, p. 88–93.

Acenolaza, F.G., and Acenolaza, G.F., 1992, The genus Jujuyaspis

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IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 43

APPENDIXES 1–3.

TAXONOMIC NOTES

Trilobite, conodont, and brachiopod taxa reported from

the Ibexian stratotype section are listed here with reference

to original description and illustration. Echinoderms are

listed in Appendix 4.

APPENDIX 1. TRILOBITA

Acheilops masonensis Winston and Nicholls, 1967, p.

77–78, pl. 11, figs. 23–25.

Amblycranium cornutum Ross, 1951, p. 67, pl. 13, figs. 1–9.

Amblycranium? linearus Young, 1973, p. 96–97, pl. 4, figs.

9–15.

Amblycranium variabile Ross, 1951, p. 64–66, pl. 13, figs.

10–18.

Aulacoparia venta (Hintze, 1953), p. 134, pl. XVI, figs. 6–11.

Aulacoparina impressa Lochman, 1966, p. 537, pl. 61, figs.

1–11.

Aulacoparina quadrata (Hintze, 1953), p. 133, pl. XVI, figs.

1–4.

Bellefontia chamberlaini Clark, 1935. Ross, 1951, p. 98–99,

pl. 24, figs. 1–7; pl. 25, figs. 10–15; pl. 22, figs.

1–2; pl. 23, fig. 4. Hintze, 1953, p. 142, pl. IV, figs.

9–13.

Bellefontia ibexensis Hintze, 1953, p. 141, pl. IV, figs. 1–8.

Benthamaspis diminutiva Hintze, 1953, p. 142, pl. XIII, figs.

9–13.

Benthamaspis obreptus (Lochman, 1966), p. 541–542, pl.

62, figs. 1–7; Ross, 1951, p. 120, pl. 29, figs. 20, 21,

24. Fortey, 1979.

Bolbocephalus sp., Hintze, 1953, p. 143–144, pl. IX, fig. 17.

Carolinites ekphymosus Fortey and Droser, 1996, p.97–98,

figs. 14.6, 14.7, 14.17.

Carolinites genacinaca Ross, 1951, p. 84, pl. 18, figs. 25, 26,

28–36. Hintze, 1953, pl. XX, figs. 7–9.

Carolinites genacinaca nevadensis Hintze, 1953, pl. XX,

figs. 3–6.

Clelandia utahensis Ross, 1951, p. 117, pl. 29, figs. 1–4,

6–9; Hintze, 1953, p. 147, pl. 4, figs. 15–17.

Corbinia apopsis (Winston and Nicholls, 1967). Westrop

and Ludvigsen, 1986; Westrop, 1986. (See Eurekia

apopsis below.)

Cybelopsis cf. C. speciosa Poulsen. Hintze, 1953, p.

152–153, pl. XXV, figs. 5, 6, 8–12.

Diacanthaspis? trispineus Young, 1973, p. 98–99, pl. 5, figs.

1–14.

Ectenonotus progenitor Fortey and Droser, 1996, p. 93–94,

figs. 16.3, 16.7.

Ectenonotus whittingtoni Ross, 1967. Fortey and Droser,

1996, p. 94, figs. 16.1, 16.2.

Euptychaspis kirki Kobayashi, 1935. Winston and Nicholls,

1967, p. 79, pl. 9, fig. 18.

Euptychaspis typicalis Ulrich in Bridge, 1931. Winston and

Nicholls, 1967, p. 78, pl. 9, fig. 17.

Eurekia apopsis (Winston and Nicholls, 1967), p. 86, pl. 11,

figs. 13, 14, 27, 22. Westrop, 1986, p. 77.

Eurekia longifrons Westrop, 1986, p. 78–79, pl. 6, figs. 1–5.

Goniophrys prima Ross, 1951, p. 81–82, pl. 18, figs. 9, 15,

17–20, 22, and 27.

Goniotelina Whittington and Ross, in Whittington, 1953, p.

663–667.

Goniotelina brevus (Hintze, 1953), p. 159–160, pl. XXVI,

figs. 7–10.

Goniotelina brighti (Hintze, 1953), p. 158–159, pl. XXVI,

figs. 1–6.

Goniotelina ensifer Fortey and Droser, 1996, p.81, fig. 6.

Goniotelina wahwahensis (Hintze, 1953), p. 160–161, pl.

XXVI, figs. 11–13.

Goniotelina williamsi (Ross, 1951), p. 69–71, pl. 14, figs.

16–22, 25.

Goniotelina? plicolabeonus Young, 1973, p. 99–100, pl. 5,

figs. 15–22.

Goniotelus? unicornis Young, 1973, p. 100, pl. 4, figs.

21–24.

Heterocaryon tuberculatum Rasetti, 1944, p. 241, pl. 36, fig.

55.

Highgatella cordilleri (Lochman, 1964). Winston and

Nicholls, 1967, p. 73, pl. 13, figs. 8, 11, 13.

Hillyardina semicylindrica Ross, 1951, p. 71–72, pl. 16,

figs. 1–9.

Hintzeia Harrington, 1957, p. 811.

Hintzeia celsaora (Ross, 1951), p. 135, pl. 35, figs. 1–15; pl.

34, figs. 9–12, 20; pl. 35, fig. 29.

Hintzeia firmimarginis (Hintze, 1953), p. 208, pl. XXII, figs.

1–8.

Hyperbolochilus marginauctum Ross, 1951, p. 77–78, pl.

17, figs. 24–27, 30–31, 34–35.

Hystricurus contractus Ross, 1951, p. 48, pl. 10, figs. 4, 6, 7,

10.

Hystricurus flectimembrus Ross, 1951, p. 48–50, pl. 10, figs.

25, 26, 29–33; pl. 11, figs. 16–18, 20–33.

Hystricurus genalatus Ross, 1951, p. 40–42, pl. 8, figs.

1–13; pl. 9, figs. 1–13, 17–19.

Hystricurus lepidus Hintze, 1953, p. 166–167, pl. VII, figs.

10–12.

Hystricurus millardensis Hintze, 1953, p. 168, pl. VI, figs.

17–21.

Hystricurus oculilunatus Ross, 1951, p. 47–48, pl. 10, figs.

1–3, 5, 8, 9, 12.

Hystricurus paragenalatus Ross, 1951, p. 42–45, pl. 8, figs.

14–26; pl. 9, figs. 1–13, 17–19.

Hystricurus politus Ross, 1951, p. 45–47, pl. 9, figs. 23–24,

27, 28, 32–33; pl. 15, figs. 1–6.

Hystricurus robustus Ross, 1951, p. 51–53, pl. 10, figs. 11,

13–16; pl. 14, fig. 27.

Ischyrotoma blanda (Hintze, 1953), p. 155–156, pl. XIX,

figs. 6–8.

Ischyrotoma caudanodosa (Ross, 1951), p. 123–125, pl. 35,

figs. 18, 22–28; Hintze, 1953, p. 154, pl. XIX, figs.

5, 10.

Ischyrotoma ovata (Hintze, 1953), p. 155, pl. XIX, figs. 1–4. 
44 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Ischyrotoma stubblefieldi Ingham, Curry, and Williams,

1985, p. 494–498, figs. 7–9. Fortey and Droser,

1996, p. 91, fig. 15.

Isoteloides flexus Hintze, 1953, p. 172–173, pl. XVII, figs.

2c, 3–8.

Isoteloides polaris Poulsen, 1927. Hintze, 1953, p. 171–172,

pl. XVII, figs. 9–15.

Kanoshia Harrington, 1957, p. 811.

Kanoshia? cf. K. insolita (Poulsen, 1927). Hintze, 1953, p.

222, pl. 23, figs. 5–13.

Kanoshia? depressus Young, 1973, p. 102, 104, pl. 3, figs.

21–27.

Kanoshia reticulata Fortey and Droser, 1996, p. 94–96, fig.

17.

Kawina sexapugia Ross, 1951, p. 127–129, pl. 35, figs. 6, 7,

11, 17, 19–21. Kawina? sexapugia Ross, Hintze,

1953, p. 178, pl. XXI, fig. 18.

Kawina unicornica Hintze, 1953, p. 179–180, pl. XXVIII,

figs. 1–5.

Kawina vulcanus Billings, 1865. (=Nieskowskia? sp. of

Hintze, 1953, p. 193, pl. XXVIII, figs. 6, 7).

Kawina webbi Hintze, 1953, p. 178–179, pl. XXI, figs.

15–17.

Kawina wilsoni Ross, 1972. Fortey and Droser, 1996, p.97,

figs. 14.15, 14.16.

Lachnostoma latucelsum Ross, 1951, p. 95–97, pl. 21, figs.

13–25; pl. 22, figs. 3, 6–8; pl. 23, figs. 5, 6. Hintze,

1953, p. 187, pl. XVIII, figs. 4–16.

Larifugula leonensis (Winston and Nicholls, 1967), p. 75, pl.

11, figs. 16, 20, 21. Generic reassignment Ludvigsen, 1982, p. 79.

Leiocoryphe platycephala Kobayashi, 1935, p. 49, pl. 8, fig.

2.

Leiostegium (Evansaspis) ceratopygoides (Raymond, 1925)

Dean, 1989, p. 30–31, pl. 21, figs. 1–3,5, 6, 8, 9, 11,

12; pl. 22, figs. 1, 2, 4, 6; pl. 42, figs. 1, 5. (also Norford in Aitken and Norford, 1967, p. 181, 183).

Leiostegium formosum Hintze, 1953, p. 189–190, pl. VIII,

figs. 8–10. (=L. (E.) ceratopygoides)

Leiostegium manitouensis Walcott, 1925. Ross, 1951, p.

105–106, pl. 27, fig. 1.

Licnocephala bicornuta Ross, 1951, p. 109–111, pl. 28, figs.

12–14.

Licnocephala? cavigladius Hintze, 1953, p. 190, pl. X, figs.

1–5.

Macronoda cf. M. prima Lochman, 1964. Westrop, 1986, p.

40, pl. 11, figs. 6–8.

Macropyge gladiator Ross, 1951, p. 122–123, pl. 30, figs.

14, 22; pl. 27, figs. 8–10.

Madaraspis magnifica Fortey and Droser, 1996, p. 88–89,

fig. 13.

Menoparia genalunata Ross, 1951, p. 88–89, pl. 20, figs.

13–24, 28, 29, 34–35.

Missisquoia depressa Stitt, 1971, p. 25, pl. 8, figs. 5–8.

Missisquoia typicalis Shaw, 1951. Winston and Nicholls,

1967, p. 88–89, pl. 13, figs. 2, 5–6, 10, 12, 15, 18.

Opipeuter angularis (Young, 1973), p. 112–114, pl. 1, figs.

21–22, 25–27. Fortey, 1979, p. 68.

Pachycranium? sp. of Ross, 1951, p. 73, pl. 17, figs. 4–6,

9–11, 14, 15.

Paenebeltella vultulata Ross, 1951, p. 79, pl. 18, figs. 1, 2,

5, 6; pl. 19, fig. 10.

Parabellefontia concinna Hintze, 1953, p. 194–195, pl. III,

figs. 1–8.

Parahystricurus bispicatus Hintze, 1953, p. 195–196, pl.

VIII, figs. 3–4.

Parahystricurus carinatus Ross, 1951, p. 60, figs. 23–27,

30–32, 35–37.

Parahystricurus fraudator Ross, 1951, p. 58–59, pl. 12, figs.

1–16.

Paraplethopeltis genarectus Hintze, 1953, p. 204, pl. VII,

figs. 6–9.

Paraplethopeltis? genacurvus Hintze, 1953, p. 202–204, pl.

VII, figs. 1–5.

Peltabellia peltabella (Ross, 1951), p. 76–77, pl. 17, figs. 7,

8, 12, 13, 16–22. Whittington, 1953, p. 662.

Peltabellia sp. A of Hintze, 1953, p. 174, 175, pl. X, figs.

7–10.

Petigurus inexpectatus Fortey and Droser, 1996, p. 82, fig.

7.1–7.7.

Plethometopus armatus (Billings, 1860). Rasetti, 1959, p.

383, pl. 53, figs. 1–8; pl. 52, fig. 14.

Presbynileus elongatus (Hintze, 1953), p. 199, pl. XII, figs.

2–5. Hintze, 1954, p. 119.

Presbynileus Hintze, 1954, p. 119.

Presbynileus ibexensis (Hintze, 1953), p. 199, pl. XII, fig.

6–ff. Hintze, 1954, p. 119.

Presbynileus utahensis (Hintze, 1953), p. 200–201, pl. XIII,

figs. 1–4. Hintze, 1954, p. 119.

Protopliomerella Harrington, 1957, p. 811–812.

Protopliomerella contracta (Ross, 1951), p. 136–137, pl. 33,

figs. 15–19, 22–32. Demeter, 1973, p. 59.

Protopliomerella pauca Demeter, 1973, p. 59–60, pl. 4, figs.

3, 13, 14.

Protopliomerops? quattuor brevis Young, 1973, p. 106, pl.

3, figs. 1, 5–7, 9–10.

Protopliomerops? quattuor Hintze, 1953, p. 209, pl. XXI,

figs. 9–14.

Protopresbynileus Hintze, 1954, p. 119.

Protopresbynileus willdeni (Hintze, 1953), p. 224–225, pl.

XV, figs. 14–17; Hintze, 1954, p. 119.

Psalikilopsis cuspidicauda Ross, 1953, p. 639–640, pl. 63,

figs. 2–9, 12.

Psalikilopsis Ross, 1953, p. 638.

Psalikilopsis? alticapitalis Young, 1973, p. 106–108, pl. 4,

figs. 1–8.

Psalikilus paraspinosum Hintze, 1953, p. 213, pl. IX, figs. 4,

5.

Psalikilus pikum Hintze, 1953, p. 214, pl. IX, fig. 1. 

Psalikilus spinosum Hintze, 1953, p. 212–213, pl. IX, figs. 3,

6, 7.

Psalikilus typicum Ross, 1951, p. 62–63, pl. 11, figs. 1–5, 8,

9, 13, 14, 19.

Psephothenaspis glabrior Fortey and Droser, 1996, p. 87,

fig. 11.
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 45

Psephothenaspis microspina Fortey and Droser, 1996, p.

85–86, fig. 10.

Psephothenaspis pseudobathyurus (Ross), 1967, p. D20, pl.

6, figs. 16–23. Fortey and Droser, 1996, figs. 8.2,

8.5, 9.1–9.9.

Pseudoclelandia cornupsittaca Ross, 1951, p. 119, pl. 29,

figs. 11, 12, 13, 16, 19.

Pseudoclelandia fluxafissura Ross, 1951, p. 119–120, pl. 29,

figs. 14, 17, 18.

Pseudoclelandia lenisora Ross, 1951, pl. 29, figs. 5, 10, 15.

Pseudocybele altinasuta Hintze, 1953, p. 216, pl. XXIV,

figs. 1, 2.

Pseudocybele lemurei Hintze, 1953, p. 217, pl. XXIV, figs

3–7.

Pseudocybele nasuta Ross, 1951, p. 137–140, pls. 33, 34;

Hintze, 1953, p. 215, pl. XXIV, figs. 8–11.

Pseudohystricurus obesus Ross, 1951, p. 74, pl. 16, figs. 25,

30, 34.

Pseudokainella? armatus Hintze, 1953, p. 218, pl. V, figs.

1–5.

Pseudomera arachnopyge Fortey and Droser, 1996, p.

96–97, fig.18.

Pseudoolinoides aspinosus Fortey and Droser, 1996, p.

87–88, fig. 12.

Ptyocephalus Whittington, 1948, p. 567–572.

Ptyocephalus accliva (Hintze, 1953), p. 185–186, pl. XIV,

figs. 6, 16, 17; pl. XV, figs. 1, 2. Whittington, 1948,

p. 567–572.

Ptyocephalus declivita (Ross, 1951), p. 91–94, pl. 21, figs.

1–12. Hintze, 1953, p. 183, pl. XV, figs. 3, 4, 9–12.

Whittington, 1948, p. 567–572.

Ptyocephalus fillmorensis (Hintze, 1953), p. 186. pl. XIV,

figs. 1–5. 

Ptyocephalus yersini (Hintze, 1953), p. 184–185, pl. XIV,

figs. 7–15.

Punka cf. P. nitida (Billings), Fortey and Droser, 1996, p. 91,

figs. 14.5, 14.7, 14.8–14.10, 14.14.

Remopleuridiella caudalimbata Ross, 1951, p. 86–87, pl. 20,

figs. 1–12.

Rossaspis Harrington, 1957, p. 812.

Rossaspis superciliosa (Ross, 1951), p. 133–135, pl. 31, figs.

16–26; pl. 34, figs. 5–8, 19.

Saukiella pepinensis (Owen, 1852). Longacre, 1970, p. 51,

pl. 5, figs. 9–11.

Scinocephalus solitecti Ross, 1951, p. 89–91, pl. 20, figs. 25,

26, 27, 30–33, 36–38.

Shumardia exopthalmus Ross, 1967, p. 9–10, pl. 10, figs.

23–33.

Stenorhachis genalticurvatus (Hintze, 1953), p. 173, pl.

XVII, figs. 1, 2a, 2b; pl. XVIII, figs. 1–3.

Symphysurina brevispicata Hintze, 1953, p. 236–237, pl. III,

figs. 9–17.

Symphysurina bulbosa Lochman, 1964. Stitt, 1977, p. 37, pl.

5, figs. 1–6.

Symphysurina globocapitella Hintze, 1953, p. 232–233, pl.

I, figs. 1–9.

Symphysurina sp. B of Ross, 1951, p. 116, pl. 28, figs. 19,

23, 24, 30.

Symphysurina uncaspicata Hintze, 1953, p. 233–234, pl. II,

figs. 1–7.

Symphysurina woosteri Walcott, 1925. Ross, 1951, pl. 23,

figs. 7–12.

Symphysurina cf. S. cleora (Walcott, 1925). Hintze, 1953, p.

234–236, pl. II, figs. 8–11.

Tesselacauda depressa Ross, 1951, p. 130–131, pl. 31, fig.

27–31; pl. 34, figs. 1–4, 18.

Triarthropsis nitida Ulrich in Bridge, 1931. Winston and

Nicholls, 1967, p. 78, pl. 11, figs. 27–28.

Trigonocerca typica Ross, 1951, p. 104, pl. 26, figs. 5–13.

Hintze, 1953, pl. XI, figs. 6–11.

Trigonocerca typica piochensis Hintze, 1953, p. 238, pl. XI,

figs. 12–18.

Trigonocercella acuta Hintze, 1953, p. 239–240, pl. XI, figs.

1–5.

Uromystrum cf. U. validum (Billings), Fortey and Droser,

1996, p. 91, figs. 14.1–14.4.

Xenostegium cf. X. acuminiferentis (Ross, 1951), p. 99–100,

pl. 24, figs. 15–18; pl. 25, figs. 6–9. Hintze, 1953,

p. 241, pl. V, figs. 19–24.

Xenostegium franklinense Ross, 1951, p. 102, pl. 24, figs.

8–14; pl. 25, figs. 1–6. Hintze, 1953, p. 240, pl. 5,

figs. 13–18.

APPENDIX 2. CONODONTA

Acanthodus lineatus (Furnish, 1938), p. 328 p. 41, figs. 33,

34. Ethington and Clark, 1981, p. 17, pl. 1, fig. 7.

Acodus deltatus Lindström, 1955, p. 544, pl. 3, fig. 30. Ethington and Clark, 1981, p. 18–19, pl. 1, text–figs.

1–6.

Acodus emanuelensis McTavish, 1973, p. 40–41, pl. 2, figs.

16–21, text-fig. 3e–i. Ethington and Clark, 1981, p.

19–20, pl. 1, figs. 9–13, text-fig. 5. 

aff. Acodus gladiatus Lindström, 1955, p. 544–545, pl. 3,

figs. 10, 11 (non fig. 12). Ethington and Clark,

1981, p. 20, pl. 1, fig. 14.

Acodus oneotensis Furnish, 1938, p. 325, pl. 42, figs. 26–29.

Ethington and Clark, 1981, p. 20–21, pl. 1, fig. 16.

Acodus sp. 1 s.f. Ethington and Clark, 1981, p. 21, pl. 1, fig.

17, text-fig. 6.

Acodus sp. 2 Ethington and Clark, 1981, p. 21, pl. 1, figs. 19,

20.

Acodus sp. 3 Ethington and Clark, 1981, p. 22, pl. 1, figs. 22,

23, text-fig. 8.

Acodus sp. 4 Ethington and Clark, 1981, p. 22–23, pl. 1, fig.

25.

aff. Acontiodus latus Pander, 1856. Ethington and Clark,

1981, p. 23–24, pl. 1, fig. 18, text-fig. 9.

?Acontiodus sp. Ethington and Clark, 1981, p. 24–25, pl. 1,

fig. 21.

Albiconus postcostatus Miller, 1980, p. 8, fig. 2.

Aloxoconus iowensis (Furnish, 1938), p. 325–326, pl. 42,

figs. 16–17, text-fig. 1L. Ethington and Clark,

1981, p. 23, pl. 1, fig. 15.
46 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Aloxoconus propinquus (Furnish, 1938), p. 326, pl. 42, figs.

13–15. Ethington and Clark, 1981, p. 24, pl. 1, fig.

26.

Aloxoconus staufferi (Furnish, 1938), p. 326, text-fig. 1K, pl.

42, fig. 11 (only). Ethington and Clark, 1981, p. 24,

pl. 1, fig. 24.

Cambrooistodus cambricus (Miller, 1969), p. 431, pl. 66,

figs. 8–12. Miller, 1980, p. 9–11, pl. 1, fig. 9, textfigs. 3A, 4E.

Cambrooistodus minutus (Miller, 1969), p. 433, pl. 66, figs.

1–4. Miller, 1980, p. 11, pl. 1, fig. 8, text-fig. 4F.

Chionoconus robustus (Serpagli, 1974), p. 69, pl. 18, figs.

31–4d, pl. 28, figs. 12, 13. Ethington and Clark,

1981, p. 94, pl. 10, figs. 25–27.

Clavohamulus bulbousus (Miller, 1969), p. 435, pl. 64, figs.

1–5.

Clavohamulus densus Furnish, 1938. Ethington and Clark,

1981, p. 30, pl. 2, fig. 21.

Clavohamulus elongatus Miller, 1969, p. 422, pl. 64, figs.

17–18.

Clavohamulus hintzei Miller, 1969, p. 422–423, pl. 64, figs.

19–24.

Clavohamulus sp. Ethington and Clark, 1981, p. 31, pl. 2,

fig. 22.

Colaptoconus quadraplicatus (Branson and Mehl, 1933), p.

63, pl. 4, figs. 14, 15. Ethington and Clark, 1981, p.

103–104, pl. 11, figs. 24, 30.

Cordylodus andresi Viira and Sergeeva, 1987, p. 147–148,

pl. I, figs. 1–8, pl. II, figs. 1, 2, 4, text-figs. 2-18, 2-

33, 2-36, 2-42 to 2-59, 4-28.

Cordylodus angulatus Pander, 1856. Ethington and Clark,

1981, p. 34, pl. 2, fig. 24.

Cordylodus caseyi Druce and Jones, 1971, p. 67–68, pl. 2,

figs. 9a–12c, text-figs. 23d, 23e. Ethington and

Clark, 1981, p. 31–32, pl. 2, fig. 25.

Cordylodus drucei Miller, 1980, p. 16, pl. 1, figs. 20, 21, 25.

Cordylodus intermedius Furnish, 1938, p. 338, pl. 42, fig.

31. Miller, 1980, p. 17, pl. 1, fig. 16, text-fig. 4L.

Ethington and Clark, 1981, p. 32, pl. 2, fig. 17.

Cordylodus lindstromi Druce and Jones, 1971, p. 68–69, pl.

1, figs. 7a–9b, pl. 2, figs. 8a–c, text-fig. 23h. Miller,

1980, p. 18, pl. 1, figs. 18, 19, text-figs 4I, J.

Cordylodus prion Lindström, 1955, p. 552–553, pl. 5, figs.

14–16. Ethington and Clark, 1981, p. 33, pl. 2, figs.

13, 14.

Cordylodus proavus Müller, 1959, p. 448–449, pl. 15, figs.

11, 12, 18, text-fig. 3B. Miller, 1969, p. 424, pl. 65,

figs. 37–46. Miller, 1980, p. 19–20, pl. 1, figs. 14,

15. Ethington and Clark, 1981, p. 33–34, pl. 2, figs.

18, 19.

Cordylodus sp. A Ethington and Clark, 1981, p. 35, pl. 2, fig.

26.

Cornuodus longibasis (Lindström, 1955), p. 564, pl. 3, fig.

31. Serpagli, 1974, p. 43, pl. 7, figs. 2a, b, pl. 20,

fig. 12.

Cristodus ethingtoni Ji and Barnes, 1994 (=New Genus 2 of

Ethington and Clark, 1981), Ethington and Clark,

1981, p. 117, pl. 13, figs. 18–20, 24. Ji and Barnes,

1994, p. 33, pl. 6, figs. 1–4.

Drepanodiform 1 Ethington and Clark, 1981, p. 41, pl. 3,

figs. 10, 15.

Drepanodus arcuatus Pander. Ethington and Clark, 1981, p.

43, pl. 3, figs. 22–24, text-fig. 13.

Drepanodus gracilis (Branson and Mehl) sensu Lindström,

1955, p. 562–563, pl. 4, fig. 44, pl. 5, figs. 6, 7. Ethington and Clark, 1981, p. 37–38, p. 3, fig. 7, textfig. 10.

Drepanodus sp. 1 Ethington and Clark, 1981, p. 40, pl. 3, fig.

13, text-fig. 11.

Drepanodus sp. 2 Ethington and Clark, 1981, p. 40, pl. 3, fig.

14, text-fig. 12.

aff. Drepanoistodus basiovalis (Sergeeva). Ethington and

Clark, 1981, p. 42–43, pl. 3, figs. 25–27, text-fig.

13.

aff. Drepanoistodus forceps (Lindström). Ethington and

Clark, 1981, p. 43, pl. 3, figs. 22–24, text-fig. 13.

Eoconodontus notchpeakensis (Miller, 1969), p. 438, pl. 66,

figs. 13–29. Miller, 1980, p. 22, pl. 1, figs. 10–12,

text-figs. 3D, E.

Eucharodus parallelus (Branson and Mehl, 1933), p. 59, pl.

4, fig. 17, Ethington and Clark, 1981, p. 38–39, pl.

3, fig. 8.

Eucharodus simplex (Branson and Mehl) sensu Druce and

Jones, 1971, p. 74, pl. 13 figs. 1a–4b, text-fig. 24b.

Ethington and Clark, 1981, p. 39, pl. 3, fig. 9.

Eucharodus toomeyi (Ethington and Clark, 1964), p. 690, pl.

113, fig. 17, pl. 114, fig. 22, text-fig. 2H. Ethington

and Clark, 1981, p. 39–40, pl. 3, fig. 11.

Fahraeusodus marathonensis (Bradshaw, 1969), p. 1151, pl.

137, figs. 13–15, text-figs. 3S, T, U. Ethington and

Clark, 1981, p. 55–56, pl. 5, figs. 14, 19, 20, 23, 24,

27.

Fryxellodontus inornatus Miller, 1969, p. 426, pl. 65, figs.

1–10, 12–16, 23–25.

Fryxellodontus lineatus Miller, 1969, p. 429, pl. 65, figs.

17–22, 26–29.

Furnishina Müller, 1959, p. 451. 

Hirsutodontus hirsutus Miller, 1969, p. 431, pl. 64, figs. 25,

26, 29–31.

Hirsutodontus rarus Miller, 1969, p. 431, pl. 64, figs. 36–42.

Hirsutodontus simplex (Druce and Jones, 1971), p. 98–99,

pl. 6, figs. 1a–5b, text-fig. 31. Miller, 1969, pl. 64,

figs. 27, 28, 32–35.

Histiodella altifrons Harris, 1962, p. 208–209, pl. 1, figs.

4a–c. Ethington and Clark, 1981, p. 447, pl. 4, figs.

5–12.

Histiodella donnae Repetski, 1982, p. 25, pl. 8, figs. 6, 7.

Ethington and Clark, 1981, p. 50, pl. 5, fig. 18.

Histiodella minutiserrata Mound, 1965, p. 21–22, pl. 3, figs.

1–3. Ethington and Clark, 1981, p. 48–49, pl. 5, fig.

11.

Iapetognathus Landing, 1982, in Fortey and others, 1982 p.

124–126, text-figs. 6, 8.

Iapetognathus sprakersi Landing, Westrop, and Knox, 1996,

p. 672–673, figs. 5.1–5.3.

Juanognathus jaanussoni Serpagli, 1974, p. 50–51, pl. 11,

figs. 1–12, pl. 23, figs. 1–5, text-fig. 9. Ethington

and Clark, 1981, p. 50, pl. 5, figs. 12, 13. 
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 47

Juanognathus variabilis Serpagli, 1974, p. 49–50, pl. 11,

figs. 1–7, pl. 22, figs. 6–17, text-fig. 8. Ethington

and Clark, 1981, p. 50–51, pl. 5, figs. 8–10, 17.

Jumudontus gananda Cooper, 1981, p. 170–172, pl. 31, fig.

13. Ethington and Clark, 1981, p. 51–52, pl. 2, figs.

9, 10.

Laurentoscandodus triangularis (Furnish, 1938), p.

330–331, pl. 42, fig. 22, text-fig. 1P. Ethington and

Clark, 1981, p. 70–71, pl. 7, figs. 15, 18, 22, 23.

Landing, Westrop, and Knox, 1996, p. 673–674,

figs. 8.12–8.29, 9.14, 9.18–9.21.

Loxodus bransoni Furnish, 1938, p. 339, pl. 42, figs. 33–34,

text-fig. 2A. Ethington and Clark, 1981, p. 52, pl. 5,

fig. 15.

Macerodus dianae Fåhraeus and Nowlan, 1978, p. 461, pl. 1,

figs. 26, 27. Ethington and Clark, 1981, p. 53–54,

pl. 5, fig. 16.

Microzarkodina flabellum (Lindström, 1955), p. 587, pl. 6,

figs, 23–25. Ethington and Clark, 1981, p. 54–55,

pl. 4, fig. 2, pl. 5, figs. 21, 22, 25, 26.

Monocostodus sevierensis (Miller, 1969), p. 418, pl. 63, figs.

25–31, pl. 64, figs. 49–54. Miller, 1980, p. 26–27,

pl. 2, figs. 8, 9; text-fig. 4U. 

Oepikodus communis (Ethington and Clark, 1964), p. 690,

692, pl. 6, figs. 18, 22, 25. Ethington and Clark,

1981, p. 61–62, pl. 6, figs. 18, 22, 25. 

aff. Oepikodus minutus (McTavish, 1973), p. 42–43, pl. 3,

figs. 3, 14, 17. Ethington and Clark, 1981, p. 62–65,

pl. 6, figs. 19, 23, 24, 26–28.

Oistodus bransoni Ethington and Clark, 1981, p. 65–66, pl.

7, figs. 1–3, 5, 6, text-fig. 17.

Oistodus ectyphus Smith, 1991, p. 46, text-fig. 27a; (=Oistodus sp. 2 of Ethington and Clark, 1981, p, 71, pl. 8,

fig. 1, text-fig. 18). 

Oistodus hunickeni Serpagli, 1974, p. 54–55, pl. 13, figs.

1a–3b, pl. 23, figs. 6, 7. Ethington and Clark, 1981,

p. 67, pl. 7, fig. 8.

Oistodus inaequalis Pander, 1856. Ethington and Clark,

1981, p. 67–68, pl. 7, text-fig. 7.

aff. Oistodus inaequalis Pander. Ethington and Clark, 1981,

p. 68, pl. 7, fig. 8, text-fig. 16.

Oistodus sp. 1 Ethington and Clark, 1981, p. 71, pl. 7, figs.

16, 19–21, text-fig. 17.

Oistodus sp. 4 Ethington and Clark, 1981, p. 72, pl. 8, fig. 3.

Oneotodus costatus Ethington and Brand, 1981, p. 242–245,

text-figs. 1B. D, G, H, 2A, D–M; (=aff. Oneotodus

simplex (Furnish) of Ethington and Clark, 1981, p.

73–74, pl. 8, fig. 7).

aff. Paltodus? jemtlandicus Löfgren, 1978, p. 65, pl. 4, figs.

1–3, 8. Ethington and Clark, 1981, p. 75, pl. 8, fig.

10, text-fig. 19.

Paltodus spurius Ethington and Clark, 1964, p. 695, pl. 114,

figs. 3, 10, text-fig. 28. Ethington and Clark, 1981,

p. 76, pl. 8, figs. 9, 13.

Parapanderodus asymmetricus (Barnes and Poplawski,

1973), p. 781–782, pl. 21, figs. 12, 12a, 14, 16, textfig. 2A. Ethington and Clark, 1981, p. 83–84, pl. 9,

figs. 11, 12, 14, 19 (also includes Scolopodus paracornuformis Ethington and Clark, 1981, p. 102, pl.

11, fig. 21, text-fig. 25).

Parapanderodus emarginatus (Barnes and Tuke, 1970). Ethington and Clark, 1981, p. 99–100, pl. 11, figs. 15,

16.

Parapanderodus filosus (Ethington and Clark, 1964), p. 699,

pl. 114, figs. 12, 17–19. Ethington and Clark, 1981,

p. 100, pl. 11, fig. 22.

Parapanderodus striatus (Graves and Ellison), 1941, p. 11,

pl. 1, figs. 3, 12 (=“Scolopodus” gracilis Ethington

and Clark, 1981, p. 100–101, pl. 11, figs. 27, 28).

Paroistodus parallelus (Pander, 1856). Ethington and Clark,

1981, p. 100–101, pl. 11, figs. 27, 28.

Phakelodus elongatus (An, 1983 in An and others), p. 125,

pl. 5, figs. 4, 5. Müller and Hinz, 1991, p. 32, pl. 1,

figs. 1–5, 14, 15, 18–20, 22.

Problematoconites perforatus Müller, 1959, p. 471, pl. 15,

fig. 17. Müller and Hinz, 1991, p. 36, pl. 23, figs.

1–10, 14, 15, 18–20, 22.

Proconodontus muelleri Miller, 1969, p. 437, pl. 66, figs.

30–40.

Proconodontus serratus Miller, 1969, p. 438, pl. 66, figs.

41–44.

Prooneotodus gallatini (Müller, 1959), p. 457, pl. 13, figs.

5–10, 18. Müller and Hinz, 1991, p. 37, pl. 24, figs.

1–28.

Prooneotodus rotundatus (Druce and Jones, 1971), p.

62–63, pl. 9, figs. 10a–13b, text-figs. 22c, d.

Prosaggitodontus eureka (Müller, 1959), p. 461, pl. 14, fig.

6. Miller, 1969, p, 438, pl. 65, figs. 30–36, text-fig.

5J.

aff. Protopanderodus arcuatus (Lindström, 1955), p. 547,

pl. 2, figs. 1–4. Ethington and Clark, 1981, p. 83, pl.

9, fig. 10.

Protopanderodus elongatus Serpagli, 1974, p. 73–75, pl. 16,

figs. 8–11, pl. 25, figs. 13–16, pl. 30, fig. 4, text-fig.

16. Ethington and Clark, 1981, p. 84, pl. 9, fig. 15.

Protopanderodus gradatus Serpagli, 1974, p. 75–77, pl. 15,

figs. 5a–8b, pl. 26, figs. 11–15, pl. 30, figs. 1a, b,

text-fig. 17. Ethington and Clark, 1981, p. 84–85,

pl. 9, figs. 16, 17, 20, 21. 

Protopanderodus leonardii Serpagli, 1974, p. 77–79, pl. 16,

figs. 1–4, pl. 27, figs. 12–16. Ethington and Clark,

1981, p. 85, pl. 9, figs. 18, 22, 23.

Protoprioniodus aranda Cooper, 1981, p. 175–176, pl. 30,

figs. 1, 6, 7, 10, 12. Ethington and Clark, 1981, p.

86–87, pl. 90, figs. 24–30.

Protoprioniodus papiliosus (van Wamel, 1974), p. 76–77,

pl. 1, figs. 18–20. Ethington and Clark, 1981, p.

87–88, pl. 10, fig. 5.

?Reutterodus andinus Serpagli, 1974, p. 79–81, pl. 17, figs.

7a, b, 8a–d, pl. 28, figs. 4, 8. Ethington and Clark,

1981, p. 412–423, pl. 19, figs. 4–7.

Reutterodus borealis Repetski, 1982, p. 41–42, pl. 19, figs.

4–7 (=Reutterodus sp. Ethington and Clark, 1981,

p. 91–92, pl. 10, figs. 14–16, 19).

Rossodus manitouensis Repetski and Ethington, 1983, p.

289–301, figs. 1–4 (=New Genus 3 Ethington and

Clark, 1981, p. 118–119, pl. 13, figs. 21–23, 25–27).

Rotundoconus An and Zhang in An and others, 1983, p.

135–137.
48 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Scalpellodus striatus Ethington and Clark, 1981, p. 92–93,

pl. 10, figs. 23, 24.

Scandodus americanus Serpagli, 1974, p. 291–292, pl. 16,

figs. 6a–7b, pl. 26, figs. 16–17, pl. 30, fig. 10, textfig. 22.

aff. Scandodus flexuosus Barnes and Poplawski, 1973, p.

785–786, pl. 2, figs. 1–4, text-fig. 2L. Ethington

and Clark, 1981, p. 93–94, pl. 10, figs. 20–22, textfig. 21.

Scandodus sp. 1 Ethington and Clark, 1981, p. 96–97, pl. 11,

figs. 6, 7, text-fig. 22.

Scandodus sp. 2 Ethington and Clark, 1981, p. 97, pl. 11,

figs. 8, 9, text-fig. 23.

Scandodus sp. 3 Ethington and Clark, 1981, p. 97–98, pl. 11,

fig. 10, text-fig. 24.

Scandodus sp. 4 Ethington and Clark, 1981, pl. 11, fig. 11.

Scandodus sp. 6 Ethington and Clark, 1981, p. 98, pl. 11,

figs. 17, 18.

Scolopodus floweri Repetski, 1982, p. 47–48, pl. 24, figs. 7,

9, 10, pl. 25, figs. 1, 4 (reported by Ethington and

Clark, 1981, p. 75–76, pl. 8, figs. 5,6, text-fig. 20,

as aff. Paltodus sexplicatus (Jones) sensu Abaimova). 

Scolopodus multicostatus Barnes and Tuke, 1970, p. 92–93,

pl. 18, figs. 5, 9, 15, 16, text-fig. 6D. Ethington and

Clark, 1981, p. 101–102, pl. 11, figs. 19, 20.

aff. Scolopodus rex Lindström, 1955, p. 595–596, pl. 3, fig.

32. Ethington and Clark, 1981, p. 104–105, pl. 12,

figs. 1, 2.

?Scolopodus sexplicatus Jones, 1971, p. 65–67, pl. 5, figs.

4a–c, 7a–c, 8a–c, pl. 9, figs. 4a–c, text-figs. 16a–c.

Ethington and Clark, 1981, p. 105, pl. 12, figs. 3,4.

aff. Scolopodus striatus Pander, 1856. Ethington and Clark,

1981, p. 105, pl. 12, figs. 5, 6.

Scolopodus sulcatus Furnish, 1938, p. 325–334, pl. 41, figs.

14, 15, pl. 42, figs. 26–29. Ethington and Clark,

1981, p. 105–106, pl. 12, figs. 7, 8. Repetski, 1982,

p. 126, text-fig. 2B–E.

?Scolopodus sp. Ethington and Clark, 1981, p. 106, pl. 12,

figs. 9–11.

Scolopodiform A Ethington and Clark, 1981, p. 106, pl. 12,

fig. 27.

Scolopodiform B Ethington and Clark, 1981, p. 106–107, pl.

12, fig. 13, text-fig. 28.

Scolopodiform C Ethington and Clark, 1981, p. 107, pl. 12,

fig. 4, text-fig. 29.

Scolopodiform D Ethington and Clark, 1981, p. 107, pl. 12,

figs. 15–17, 23, text-fig. 30.

Scolopodiform E Ethington and Clark, 1981, p. 107–108, pl.

12, fig. 18, text-fig. 31.

Semiacontiodus lavadamensis (Miller, 1969), p. 420, pl. 64,

figs. 55–61. Miller, 1980, p. 33, pl. 2, fig. 4.

Semiacontiodus nogamii Miller, 1969, p. 421, pl. 63, figs.

11–20, 41–50. Miller, 1980, p. 32, pl. 2, figs.

10–12, text-figs. 4V, W.

Teridontus nakamurai (Nogami, 1967), p. 216–217, pl. 1,

figs. 9–13, text-figs. 3A–E. Miller, 1980, p. 34, pl.

2, figs. 15, 16, text-fig. 4O.

Toxotodus amphigyus Smith, 1991, p. 64–65, text-figs.

37a–d.

Tripodus laevis Bradshaw, 1969, p. 1164, pl. 135, figs. 9, 10.

Ethington and Clark, 1981, p. 110–112, pl. 122,

figs. 24, 25, 27–29, text-fig. 112. 

Tropodus comptus (Branson and Mehl, 1933), p. 61, pl. 4,

fig. 9. Ethington and Clark, 1981, p. 114–116, pl.

13, figs. 6, 7, 11–13, text-fig. 34.

Ulrichodina abnormalis (Branson and Mehl, 1933), p. 57,

pl. 4, figs. 24, 25. Ethington and Clark, 1981, p.

112, pl. 12, fig. 31.

Ulrichodina cristata Harris and Harris, 1965, p. 40–41, pl. 1,

figs. 5a–d. Ethington and Clark, 1981, p. 112–113,

pl. 12, figs. 22, 30.

Ulrichodina deflexa Furnish, 1938, p. 335–336, pl. 41, figs.

23–24. Ethington and Clark, 1981, p. 113, pl. 13,

figs. 1, 2.

Ulrichodina? simplex Ethington and Clark, 1981, p. 113, pl.

13, figs. 3, 4, 9.

?Ulrichodina wisconsinensis Furnish, 1938, p. 335, pl. 41,

figs. 19, 20. Ethington and Clark, 1981, p. 113–114,

pl. 13, fig. 15.

?Ulrichodina sp. Ethington and Clark, 1981, p. 114, pl. 13,

fig. 8.

Utahconus tenuis Miller, 1980, p. 36, pl. 2, figs. 5–7.

Utahconus utahensis (Miller, 1969), p. 436, pl. 63, figs.

21–24, 33–40, pl. 64, figs. 46–48. Miller, 1980, p.

35, pl. 2, figs. 1, 2, text-figs. 3B, F, G. 

Variabiloconus bassleri (Furnish, 1938), p. 331, pl. 42, fig.

1. Ethington and Clark, 1981, p. 116–117, pl. 8,

figs. 11–12. 

?Walliserodus ethingtoni (Fåhraeus) sensu Löfgren, 1978, p.

114–116, pl. 4, figs. 27–35, text-fig. 33. Ethington

and Clark, 1981, p. 116–117, pl. 13, figs. 10, 14–16,

text-fig. 35. 

Westergaardodina Müller, 1959, p. 465–467.

 ? New Genus 1 Ethington and Clark, 1981, p. 117, pl. 13,

fig. 17. 

APPENDIX 3. BRACHIOPODA

Diparelasma rowelli Ross, 1968, p. H7, pl. 2, figs. 3–10, 13.

Diparelasma cf. D. transversa Ulrich and Cooper, 1938.

Ross, 1968, p. H8, pl. 1, figs. 14–17; pl. 2, figs. 1, 2.

Hesperonomia fontinalis (White). Ross, 1968, p. H5, pl. 1,

figs. 1–9.

Hesperonomia cf. H. dinorthoides Ulrich and Cooper, 1938.

Ross, 1968, p. H5–H6, pl. 1, figs. 10–13.

Syntrophopsis cf. S. polita Ulrich and Cooper, 1938, p.

237–238, pl. 51C, figs. 23, 24, 27, 30, 31.

Tritoechia loganensis Ross, 1968, p. H8–H9, pl. 3, figs.

8–18.

Hesperonomiella minor (Walcott). Ulrich and Cooper, 1938,

p. 124, pl. 21, fig. 28. Cooper, 1956, p. 337, pl.

121H, figs. 20, 22). Jensen, 1967, p. 84–85, pl. 2,

figs. 16–19.
IBEXIAN SERIES, NORTH AMERICAN ORDOVICIAN 49

APPENDIX 4. ECHINODERM 

BIOSTRATIGRAPHY

BY JAMES SPRINKLE1 AND THOMAS E. GUENSBURG2

INTRODUCTION

In this section, we plot stratigraphic ranges of echinoderms from the Lower and Middle Ordovician Fillmore Formation, Wah Wah Limestone, Kanosh Shale, and Lehman

Formation in the Ibex area of western Utah (pl. 1, chart C).

Relatively few echinoderms previously have been reported or

described from these units. (See Lane, 1970; Paul, 1972;

Kelly and Ausich, 1978, 1979; Hintze, 1979; Guensburg and

Sprinkle, 1990, 1992a; Blake and Guensburg, 1993.) We

have also included comments on the stratigraphy and physical correlations of Lower Ordovician stratigraphic sections in

western Utah based on findings made during our recent field

work (James Sprinkle and T.E. Guensburg, unpub. data,

1989–91).

IBEX AREA, WESTERN UTAH

Our field work in western Utah during the summers of

1989–1991 concentrated on the Fillmore Formation and the

base of the overlying Wah Wah Limestone. A total of 140

partial or complete echinoderms were collected from these

units at 25 localities, nearly half of which were along or

near measured sections described by Hintze (1973). Other

echinoderm localities where tied to nearby measured sections and Hintze’s composite section by using distinctive

mound or reef horizons, measurements from key features in

his informal members (1973, p. 10–11), and by direct tracing of beds along strike.

The Fillmore Formation is a thick shallow-water unit

containing a wide variety of lithologies (Hintze, 1973; Dattilo, 1988, 1993), including flat-pebble conglomerates, limy

siltstones, mega-ripplemarked grainstones, sponge-algal

mounds, and interbedded micrites or shales. Although echinoderm debris is common, especially in coarser lithofacies

throughout the formation, complete echinoderm specimens

are rare, widely scattered, and sometimes difficult to collect. We collected complete echinoderms at specific horizons throughout the Fillmore (pl. 1, chart C). Gaps between

productive horizons are characterized by poor exposure and

1

Department of Geological Sciences, University of Texas, Austin, TX

78712. 2

Physical Science Division, Rock Valley College, Rockford, IL

61114.

(or) unfavorable lithofacies. Two distinct echinoderm

assemblages were found in different lithologies of the

Fillmore, implying that substrate was an important factor in

the diversification of echinoderms during the Ordovician

radiation (Sprinkle and Guensburg, 1991; Guensburg and

Sprinkle, 1992a, 1992b). Seventy-eight specimens of

crinoids make that group dominant in the Fillmore echinoderm fauna (Guensburg and Sprinkle, 1990, 1992a). The

crinoids are found almost exclusively on hardgrounds

developed on sponge-algal mounds, flat-pebble conglomerates, and grainstones, along with less common edrioasteroids and eocrinoids. This association was noted previously

by Dattilo (1988). In contrast, other common echinoderm

groups, such as mitrate stylophorans and rhombiferans, are

found primarily in micrites, shales, and limy siltstones that

originated as soft substrates.

Most of the echinoderms from the Fillmore Formation

and Wah Wah Limestone are undescribed and are currently

being studied. At least 25 genera are present (pl. 1), along

with several other distinctive but still unidentified plates,

stems, attachment holdfasts, and arm fragments. Another

medium-sized echinoderm fauna containing at least 10 genera has been collected from the Middle Ordovician Kanosh

Shale (see Wilson and others, 1992, table 2), and two additional echinoderms have been found in the overlying Lehman Formation and are currently being described in

separate papers (Blake and Guensburg, 1993; Guensburg

and Sprinkle, 1994).

While attempting to correlate different parts of the

Fillmore section during our recent field work, we discovered a long-standing problem in one of the correlations

originally made by Braithwaite (1969, 1976) and adopted

by Church (1974, 1991) and Dattilo (1988). Braithwaite

(1976, p. 57–58) had several inconsistencies in the usage of

“fossil localities” (his fig. 3) and “collection sites” (his pl.

20) vs. “collection localities” and in the location of the base

of graptolite Zones 2 and 3 (his fig. 10) vs. measurements

above the base of the Fillmore for collection localities 4

and 11. More importantly, Braithwaite’s correlations from

the U.S. Highway 6–50 first roadcut at Skull Rock Pass

(collection locality 4) west to the Pyramid and Amphitheater Sections (collection localities 9 and 10) are too low by

about 42 m (138 ft) according to our measurements. We

suggest that Church’s (1974, 1991) mound horizon at the

Pyramid Section is about 240 m (787 ft) above the base of

the Fillmore Formation near the top of the slope-forming

shaly siltstone member in the lower part of trilobite Zone

G-2 (see Hintze, 1973). This change has also affected the

stratigraphic occurrence of Pogonipocrinus, which was

found on the mound horizon at this locality (Kelly and

Ausich, 1978). The age of this crinoid therefore becomes

Early Arenig rather than Tremadoc by British usage.
50 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

TAXONOMIC NOTES ON ECHINODERMATA

Archaetaxocrinus lanei Lewis, 1981, p. 236–237, pl. 1, fig.

9 (=Cupulocrinus sp. A Lane, 1970).

Atopocrinus priscus Lane, 1970, p. 15, pl. 1, figs. 4–6, textfig. 2F–J.

Blastoidocrinus? sp. A of Billings, 1859. See Sprinkle,

1973a, p. 144–155; Wilson and others, 1992, p. 26,

table 2.

Blastoidocrinus? sp. B of Billings, 1859. See Sprinkle,

1973a, p. 144–155; Wilson and others, 1992, p. 26,

table 2.

Bockia n. sp. Hecker, 1938. See Bockelie, 1981, p. 127–138,

figs. 2–9.

Cheirocystella antiqua Paul, 1972, p. 33–37, pl. 1, figs. 1–4,

text-figs. 7–9.

Hoplocrinus sp. A of Lane, 1970, p. 12, pl. 1, figs. 2, 3.

Hybocrinus sp. of Billings, 1857. See Brower and Veinus,

1974, p. 30–37.

Hybocrinus sp. A of Lane, 1970, p. 9–12, pl. 1, fig. 8, textfig. 2E. Plotted as “large conical disparid” on plate

1, chart C, herein.

Ibexocrinus lepton Lane, 1970, p. 12–14, pl. 1, fig. 1, textfig. 2B–C.

Mandalacystis n. sp. See Lewis and others, 1987, p.

1233–1235, figs. 1–7; Wilson and others, 1992, p.

26, table 2.

Pogonipocrinus antiquus (Kelly and Ausich, 1978), p.

916–919, figs. 1A–D. Kelly and Ausich, 1979, p.

1433.

Protopalaeaster starfish. See Wilson and others, 1992, p. 26,

table 2; Blake and Guensburg, 1993, p. 112, fig.

1.6.
An Ibexian (Lower Ordovician) Reference Section 

in the Southern Egan Range, Nevada,

for a Conodont-Based Chronostratigraphy

By Walter C. Sweet and Celeste M. Tolbert

EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN, WESTERN UNITED STATES

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1579–B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1997
I

CONTENTS

Abstract................................................................................................................................. 53

Introduction........................................................................................................................... 53

Acknowledgments......................................................................................................... 53

Stratigraphy........................................................................................................................... 54

The Ibexian Series......................................................................................................... 54

Lithostratigraphy........................................................................................................... 55

Conodont Biostratigraphy............................................................................................. 55

Correlation with Ibexian Sections Elsewhere....................................................................... 56

Correlation with the Composite-Stratotype Section in the Ibexian Type Area ............ 56

Correlation with the El Paso Group, Texas .................................................................. 63

Summary............................................................................................................................... 63

References Cited ................................................................................................................... 64

Appendix 1. Shingle Pass Section ........................................................................................ 67

Appendix 2. Ranges of Conodont Species in Ibexian Sections

at Eight Localities ......................................................................................................... 71

Appendix 3. Composite Standard-equivalent Ranges of Conodont Species

Listed in Appendix 2..................................................................................................... 76

Appendix 4. Taxonomic Notes ............................................................................................. 80

FIGURES

1. Index map showing location of the three subsections that compose the Shingle Pass section.................................. 54

2. Graphic correlation of Ibex-area sections STP, LD5, A, E, B, C, M, H, ST, J, KA, KB, and CP

with Shingle Pass and Scenic Drive sections............................................................................................................. 57

3–9. Graphic correlations of various Ibex-area sections with composite standards (CS) composed of

maximized range data:

3. Lower 170 m of Ibex-area composite section B-KA with a CS comprising Ibex-area sections

STP, LD5, A, and E; the Scenic Drive section in El Paso, Texas; and the Shingle Pass section,

the standard reference section............................................................................................................................. 58

4. Upper 593 m of Ibex-area composite section B-KA with a CS comprising the Scenic Drive

 section and the Shingle Pass section.................................................................................................................. 59

5. Ibex-area section A with a CS comprising the Shingle Pass and Scenic Drive sections and

Ibex-area sections STP, LD5, E, and lower B-KA.............................................................................................. 60

6. Ibex-area section E with a CS comprising the Shingle Pass and Scenic Drive sections,

and Ibex-area sections STP, LD5, A, and lower B-KA ...................................................................................... 61

7. Ibex-area Steamboat Pass section with a CS comprising Ibex-area sections LD5, A, and E,

and the Shingle Pass and Scenic Drive sections ................................................................................................. 62

8. Ibex-area Lava Dam 5 section with a CS comprising the Shingle Pass and Scenic Drive sections

and Ibex-area sections STP, A, E, and lower B-KA ........................................................................................... 62

9. Ibex-area sections K and CP with a CS comprising the Shingle Pass section and the uppermost

part of Ibex-area section B-KA........................................................................................................................... 63

10. Graphic correlation of the Scenic Drive section, El Paso, Texas, with a composite standard composed

of maximized range data from the Shingle Pass and Ibex-area sections ................................................................... 64
53

An Ibexian (Lower Ordovician) Reference Section

in the Southern Egan Range, Nevada,

for a Conodont-Based Chronostratigraphy

By Walter C. Sweet1 and Celeste M. Tolbert2

ABSTRACT

A long section of Pogonip Group strata, just south of

Shingle Pass in the southern Egan Range, Nevada, is established as the reference section for the Ibexian Series (Lower

Ordovician) in a graphically assembled, conodont-based

chronostratigraphy for the North American Ordovician. The

2,924 feet (892 meters) of dominantly carbonate strata in this

section, between the base of the House Limestone and a level

64 feet (19.5 meters) above the base of the Kanosh Shale,

were sampled in 1985 at approximately 7-meter intervals,

and conodont elements representing 121 species of 59 genera have been collected from acid-insoluble residues of these

samples. All samples were productive of conodonts, which

have a color-alteration index (CAI) between 3.5 and 4. The

distribution of conodont species is used graphically to demonstrate correlation between the Shingle Pass section, sections in the Ibex district of western Utah, and a section of the

El Paso Group in the southern Franklin Mountains, Texas. 

INTRODUCTION

A long, continuous surface section through the

Pogonip Group in the southern Egan Range, Lincoln

County, Nevada, is established here as the reference section for the Ibexian (Lower Ordovician) segment of a

graphically compiled, conodont-based chronostratigraphic

framework for the Ordovician of North America. This section (fig. 1) is situated about 3.5 mi (5.6 km) east of

Nevada Highway 318 and about 1 mi (1.6 km) south of the

unpaved, unnumbered road that extends through Shingle

Pass and connects Highway 318 with U.S. Highway 93,

some 20 mi (32 km) to the east. The section, herein identified as the Shingle Pass section, is exposed in, and on the

flanks of, a broad northwest-projecting salient of the south1Department of Geological Sciences, The Ohio State University,

Columbus, OH 43210. 25243 Connemara Court, S.E., Grand Rapids, MI 49546.

ern Egan Range, in sections 25 and 36, T. 8 N., R. 62 E.,

and section 30, T. 8 N., R. 63 E., northwestern Lincoln

County, Nevada (Shingle Pass, Nevada, 7.5-minute quadrangle).

In the Shingle Pass section, the Pogonip Group is

directly and conformably underlain by the stratotype of the

Whipple Cave Formation (Kellogg, 1963), a sequence of

thick-bedded, stromatolitic, lime grainstones and wackestones primarily of Late Cambrian age, but including nearly

70 m of Early Ordovician strata at the top. The distribution of

conodonts in the upper part of the Whipple Cave and lowermost part of the Pogonip in Sawmill Canyon, in the central

Egan Range, about 25 mi north of Shingle Pass, is reliably

documented in a recent report (Taylor and others, 1989), and

this has made duplication of that work in this study unnecessary. Also, the Pogonip Group in the Shingle Pass section

was not sampled above a level in the lower part of the

Kanosh Formation because that part of the Pogonip is difficult of access and Whiterockian in age.

In this report we summarize the lithic stratigraphy of

the Shingle Pass section, document the distribution of conodonts in it, and demonstrate its utility as an Ibexian reference section by plotting on biaxial graphs the ranges of

conodonts common to the Shingle Pass section and important sections in the Ibex district of western Millard County,

Utah, and in the southern Franklin Mountains of Texas. A

detailed description of that part of the Shingle Pass section

studied in detail is provided in Appendix 1. Appendix 2 lists

ranges of 210 conodont species in the Shingle Pass section

and in the other Ibexian sections we compare with it. Appendix 3 gives the composite standard-equivalent ranges of

those species, and Appendix 4 includes notes on taxonomy

of the conodont species represented.

ACKNOWLEDGMENTS

Joseph R. Wilson, then of Ohio Wesleyan University

(Delaware, Ohio), assisted the junior author in the field in

August 1985, when the Shingle Pass section was measured
54 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

NEVADA

38 ̊

30'

40 ̊

42 ̊

38 ̊

36 ̊

T

8

N

T

7

N

115 ̊00'

120 ̊ 114 ̊

R62E R63E

Shingle Peak

Whipple

Cave

X

Whipple

Peak

Whipple

Ranch

Sunnyside WHITE RIVER VALLEY 

EGAN RANGE

CAVE VALLEY

X

Lund

o318

Shingle Pass EGAN RANGE

85WA 85WB

85WC

Nye County

Lincoln County

0 3 KILOMETERS

and sampled. Y.B. Kim processed many of our carbonate

samples in acid and helped concentrate the acid-insoluble residues. John E. Repetski, of the U.S. Geological Survey,

Reston, Virginia, discussed identification of many conodont

species and allowed extended access to his bulk collections

from the El Paso Group, Texas. Professor Raymond L.

Ethington, University of Missouri-Columbia, made conodont

collections from the Ibex district, Utah, available for study

and kindly discussed many of the problems associated with

the identification of species represented in them. The help and

assistance of all these persons are gratefully acknowledged.

The illustrations were enhanced by the graphic skills of Carol

Quesenberry, USGS.

STRATIGRAPHY

THE IBEXIAN SERIES

The Ibexian Series was proposed (Ross and others,

1982) as a substitute for Canadian Series, the lowest major

division of the North American Ordovician, because the

Canadian was deemed to have been poorly defined originally and inconsistently used subsequently. However, as

Hintze’s (in Ross and others, 1982) description of the type

section indicates, the Ibexian includes much less of the

North American Lower Ordovician than do most usages of

Canadian, which embrace substantial parts of units now

included in the younger Whiterockian Series. In brief, the

Ibexian is not a one-for-one substitute for the Canadian, but

a more precisely defined chronostratigraphic unit, with a

well-known succession of fossils and a designated and

well-described type section in the Ibex district of Millard

County, western Utah.

In the type area of the Ibexian Series, Hintze (in Ross

and others, 1982) placed the base of the Ibexian in the uppermost beds of the Notch Peak Formation, at the base of the

Missisquoia trilobite Zone, which, following then-current

North American practice, also marked the base of the Ordovician System. The top of the Ibexian is the base of the overlying Whiterockian Series, which Hintze (in Ross and others,

1982) and Ethington and Clark (1982) both placed at the

base of the Kanosh Shale in the Ibexian type area. Ross (in

Ross and others, 1982) and others, however, have argued that

the Whiterockian base be sited in the Ibex district at the level

in the Wah Wah Limestone (Hintze, 1988) at which Orthambonites subalata Ulrich and Cooper first occurs, for that brachiopod is regarded as the lowest representative of Cooper’s

(1956) Orthidiella Zone, the basal biozone of the typical

Whiterockian Series. In the type area of the Ibexian, this

level is also very close to the base of Ethington and Clark’s

(1982) Tripodus laevis conodont Zone, and the same relation

holds in the type section of the Whiterockian Series (Ross

and Ethington, 1991, 1992).

Data on the distribution of trilobites and conodonts in

the upper part of the Whipple Cave Formation and lowermost part of the House Limestone in a section in Sawmill

Canyon, some 25 mi (40 km) northwest of Shingle Pass

Figure 1. Index map showing location of the three subsections (85WA, 85WB, 85WB) that compose the

Shingle Pass section of this report.
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 55

(Taylor and others, 1989) suggest that the base of the Ibexian

there is about 70 m below the base of the House Limestone,

and this is almost certainly the situation in the Shingle Pass

section. Because of the currency and evident thoroughness of

the sequence established in Sawmill Canyon, we have not

attempted to duplicate that part of the succession in the Shingle Pass section, although it may someday be desirable to do

so. Hence the base of the Ibexian cannot at present be located

precisely in the Shingle Pass section. We note that although

Hintze (in Ross and others, 1982) drew the base of the type

Ibexian at the base of the Missisquoia trilobite Zone, he did

so obviously to make the Ibexian base coincident with the

base of the Ordovician System. No formal international definition of the Ordovician base has yet been recommended or

approved, however, although it seems likely from reports of

recent deliberations that in making such a recommendation

the distribution of conodonts, not trilobites or other fossils,

will be the guiding criterion.

In the Shingle Pass section, the conodont species Tripodus laevis appears abruptly and in abundance in the

upper third of the Shingle Limestone, 134 m below the base

of the Kanosh Shale. We use this level to mark the base of

the Whiterockian Series, and thus the top of the Ibexian.

We note also that Kellogg (1963) reported Orthambonites

subalata Ulrich and Cooper from near the top of the Shingle Limestone at a locality 0.4 mi (0.6 km) northeast of the

main ridge, Shingle Pass.

Thus, in the Shingle Pass section, the Ibexian Series

includes the House Limestone, the Parker Spring Formation,

the lower two-thirds of the Shingle Limestone, and probably,

depending on the level at which the Ordovician base is ultimately sited, the uppermost 70 m or so of the subjacent

Whipple Cave Formation.

LITHOSTRATIGRAPHY

For more than 40 years, Great Basin stratigraphers have

included Ordovician rocks below the widespread Eureka

Quartzite in the Pogonip Group, which was revised, subdivided into formations, and stabilized in content by Hintze

(1951). In the Ibex district of western Utah, Hintze divided

the Pogonip, in ascending order, into House Limestone, Fillmore Limestone, Wah Wah Limestone, Juab Limestone,

Kanosh Shale, and Lehman Formation; and in 1952, he recognized the same succession in the Shingle Pass section of

eastern Nevada (his Sunnyside section). Later, however, in

the southern Egan Range, Kellogg (1963) divided Pogonip

strata between the House Limestone and Kanosh Shale into

just two lithic units, a lower, poorly exposed, slope-forming

succession of thin-bedded carbonates and shales, the Parker

Spring Formation; and an upper, cliff-forming unit of more

thickly bedded carbonates, the Shingle Limestone. In his

1963 report, Kellogg also defined and described the Whipple

Cave Formation, a thick succession of mostly Upper

Cambrian carbonate rocks immediately below the Pogonip

Group, and with a stratotype just below the House Limestone

in the Shingle Pass section. Kellogg’s lithic subdivisions are

the ones recognized in this report, which focuses primarily

on the distribution of conodonts and not on lithostratigraphic

details. However, in order to locate our bulk samples in

appropriate lithostratigraphic context, we include a detailed

distribution of the Shingle Pass section in Appendix 1.

It should be noted that Hintze (1952, p. 60–76) measured, described, and reported on the identity of trilobites

and other megafossils in some 21 samples collected at

widely spaced stratigraphic intervals from the Whipple Cave

Formation and Pogonip Group in the Shingle Pass (his Sunnyside) section. Also, in a recent guidebook contribution,

Droser and Sheehan (p. 83–85 in Cooper, ed., 1995) included

additional information about Ibexian strata at Shingle Pass,

but focused primarily on the Shingle Limestone and its

sponge mounds.

In his report, Hintze (1952) was able to recognize in

the Shingle Pass section the equivalents of all the Pogonip

formations he defined in the Ibex district of western Utah.

However, we suspect that, in doing so, he may have relied

somewhat more on the distribution of trilobites and other

guide fossils than on details of the lithic succession. Droser

and Sheehan, and the junior author of this report, on the

other hand, paid principal attention to the succession of

rock types in the Shingle Pass section. Hence, unit thicknesses given in these previous reports differ considerably

from one another, and that makes it difficult to integrate

into a single scheme all the information they contain. Here,

we comment only that, compared with the typical Ibexian,

the Shingle Pass section appears to be complete and not

interrupted by the erosional gap at the level of the Juab Formation shown by Droser and Sheehan. The Juab Formation

was recognized at Shingle Pass by Hintze (1952), and our

collections from the upper part of the Shingle Limestone

include conodonts typical of that unit. Further, no discontinuity is indicated graphically in the upper part of the

Shingle Limestone, as we recognize it in this report. 

CONODONT BIOSTRATIGRAPHY

In August 1985, the junior author (Wilson, 1988) measured and described the Shingle Pass section, between the

base of the House Limestone and a point 19.5 m above the

base of the Kanosh Shale, which was recognized in the field

as the level at which receptaculitids appear in fine-grained,

dominantly calcareous beds. As the section was measured,

bulk limestone samples were also collected at 20-ft (6.1-m)

intervals. These samples, 119 in number, were returned to

our laboratory in Columbus, Ohio, where they were crushed,

and 1 kg of each was processed in a 10 percent solution of

acetic acid. Every one of the samples yielded well-preserved

conodont elements, and it is on these specimens that we base
56 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

the following discussion of conodont biostratigraphy. Bulk

collections are kept in the micropaleontological collections

of the Department of Geological Sciences, The Ohio State

University, where they are identified by the prefixes 85WA,

85WB, and 85WC.

Ibexian rocks in the type area of western Utah are

divided into a succession of 11 conodont-defined biozones,

which are named and characterized in a report by Ross and

others (1993; this volume, chapter A). Although equivalents

of at least nine of these zones are recognizable in the Shingle

Pass section, we have not used them as the principal tool in

correlating the two successions. Instead, we have followed a

correlation strategy that was devised by Shaw (1964) and

which is demonstrated in a variety of different situations by

contributors to a recent volume (Mann and Lane, 1995) on

graphic correlation.

Use of the graphic procedure in assembling a network

of closely correlated sections requires data on the measured

distributions of fossils in all the sections that are potential

contributors to the network. One long section in which fossil

ranges are well controlled is selected as standard reference

section (SRS), and additional sections are compared with it

by plotting the first and last occurrences of common species

as points in a biaxial graph. On such a graph, the equation of

a line of correlation (LOC) fit to the array of points on or

closely adjacent to the interface between first- and lastoccurrence sectors of the graph helps determine the most

reasonable relationship between the SRS and another data

set being considered, and provides the means of translating

ranges in the second section into terms of the SRS. Following comparison of the second section with the SRS, a composite standard (CS) is created by selecting from the two

range-data sets the lowest and highest ranges for each species. The resultant data set, or CS, which is composed of the

best information from the two initial data sets, is then used as

the basis for comparing a third section and creating a new CS

after that graphic episode. Customarily all the sections considered in the initial round of graphic correlation are recorrelated with CS’s composed of the best data from all the other

sections of the network for as many rounds as it takes to

reach a stable CS.

In this report we are concerned primarily with demonstrating the relationship between the Shingle Pass section

and sections in the type area of the Ibexian Series. However,

because the Shingle Pass and Ibexian type sections are

closely spaced geographically and developed in similar

litho- and biofacies, we consider it desirable to compare the

results of the graphic assembly of those sections with one in

a more distant location that is known to be of generally comparable age but developed in somewhat different facies. For

such a comparison, we selected the section of El Paso Group

strata exposed along Scenic Drive, in El Paso, Texas. Conodonts from the Scenic Drive section were described and

illustrated by Repetski (1982), who provided scaled data in

his report on the ranges of all the species represented.

CORRELATION WITH

IBEXIAN SECTIONS ELSEWHERE

Our objective in this report is to establish the Shingle

Pass section as the reference section for the Ibexian Series in

a graphically assembled framework of carefully sampled

sections that is the basis for a conodont-based Ordovician

chronostratigraphy (Sweet, 1984; 1995a, 1995b). Thus it is

important first to show how rocks in the Shingle Pass section

correlate with those in sections in the Ibex area of western

Millard County, Utah, that make up the composite Ibexian

stratotype (Ross and others, 1993). 

CORRELATION WITH THE

COMPOSITE-STRATOTYPE SECTION

IN THE IBEXIAN TYPE AREA

Data on the measured ranges of conodonts in the Ibex

area are from three sources, Ethington and Clark (1982),

Ethington and others (1987), and Hintze and others (1988).

We take information from these three sources at face value,

with modification only of the names used for several taxa.3

Ethington and Clark (1982) based their monographic

study of conodonts from the Ibex area on nearly 27,000 discrete elements recovered from acid residues of 758 carbonate samples collected at 4- to 24-ft intervals from sections at

11 localities in western Millard County, Utah. Sections sampled by Ethington and Clark include Hintze’s (1951, 1973)

A, B, C, E, H, M, ST, J, K, and CP Sections, which were

assembled, following information in Hintze’s reports, to

form a continuous sequence from just below the base of the

House Limestone to the top of the Crystal Peak Dolomite.

Ethington and Clark evidently used this assembly as the

basis for the composite range chart included as figure 3 in

their 1982 report, and Sweet (1995b) used it with minor

modification in a preliminary graphic correlation of Ibex

area and Shingle Pass sections. In this report, however, we

follow a somewhat more conservative procedure, which is

explained in the following paragraphs.

3The variation in measurement units in this report is attributable to the

use by various workers in the area of feet or of meters and the present authors’ concern for precise reporting of previous studies. One foot=0.3048 m.
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 57

1300

csu

SP

1200

Not sampled

for conodonts

in this study

Crystal Peak Dol.

Watson Ranch Qtzt.

Lehman Fm.

1168

728

912

735

437

240

I A L

682

667

652

625

577

479

Juab

Phragmodus

polystrophos

Zone

Histiodella

holodentata

Zone

Histiodella

sinuosa

Zone

Histiodella

altifrons

Zone

Tripodus

laevis

Zone

Reutterodus

andinus

Zone

Oepikodus

communis

Zone

Diaphorodus

deltatus/

Oneotodus

costatus

Zone

Macerodus

dianae

Zone

Cordylodus angulatus Zone

Iapetognathus Zone

Cordylodus lindstromi Zone

Low Diversity

Interval

Rossodus

manitouensis

Zone

Cordylodus

proavus Zone

Cordylodus

intermedius

Zone

Wah Wah

1332

1301

1227

1168

995

1100

1000

900

800

700

600

500

400

300

200

100

0

Whipple Cave Fm. House Ls. Shingle Ls.

Fillmore Formation*

Padre Fm. McKelligon Fm.

El Paso Group

Hitt Canyon Fm.

Lehman Formation Kanosh Sh.

Juab

Ls.

Lava Dam

Mbr.

Lava Dam

Mbr.

Wah Wah

Ls.

Kanosh Sh.

Kanosh Sh.

Parker Spring Formation

SKULLROCKIAN STAGE STAIRSIAN STAGE TULEAN STAGE Stages not formally established

WHITEROCKIAN SERIES IBEXIAN SERIES

BLACKHILLSIAN

STAGE

CP

1174

1003

876

991

955

933

743

878 874

826

747

826

732

MB4=680

MB2=666

MB1=652

619

593

629

574

479

331 331 331

J

KA

KB

168

196

313 318

190 196

165

78

55

74

29

House Ls.

House Ls.

House Ls.

STP

LD5

A E

B

EL PASO

C

M

H ST

6 6 6

5 5

4

3

5

4

3

2

1 1 1

2 2

3 3

4

5

Red Tops Mbr.

Red Tops Mbr.

House Ls.

Notch Peak Fm.

*1 basal ledge-forming mbr.

 2 slope-forming shaly siltstone mbr.

 3 light-gray ledge-forming mbr.

 4 brown slope and ledge mbr.

 5 calcarenite mbr.

 6 Calathium calcisiltite mbr.

Figure 2. Correlation of Ibex-area sections STP, LD5, A, E, B, C, M, H, ST, J, KA, KB, and CP with Shingle Pass (SP) and Scenic

Drive (El Paso) sections. Vertical scale is in composite standard units (csu), each equivalent to 1 m in the SP section. Thicknesses of lithic

and biostratigraphic units are those determined by graphic correlation with SP, which is SRS for this compilation. Numbers at contacts are

SP-equivalent levels (for example, the Fillmore Formation base in Ibex-area sections B, C, and M is at 331 csu in the CS, or projects to a

level 331 m above the base of SP). In effecting correlations between Ibex-area sections M and H, Hintze (1973) used marker beds here labeled MB1, MB2, and MB4.
58 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

0

50

200 250 300 350 400csu

100

150

m

IBEX—B-KA SECTION (LOWER PART)

COMPOSITE STANDARD

+

+

+ +

+ ++

+

+

+ +

+

+

+

+

+

+

177

43

167

119

158 43

107

158

28

84

167

177

CS = (B-KA) + 226

In figure 2, we follow Hintze (1951, 1973) in linking his

B, C, M, H, ST, J, and KA Sections into a single sequence,

948 m thick, which ranges upward to the top of the Kanosh

Shale from a point 105 m below the top of the House Limestone. Ranges of conodonts in this segment of the Ibex composite section, which we designate B-KA, have been

assembled from Ethington and Clark (1982) and Ethington

and others (1987) and are given in Appendix 2, in which we

also include ranges of the same conodont species in the Shingle Pass section and in a section along Scenic Drive in the

southern Franklin Mountains, in El Paso, Texas.

In figures 3 and 4 we plot the first and last occurrences

of conodont species common to Ibex-area composite section

B-KA and a CS composed of range data from Ibex-area sections STP, LD5, A, and E, the Shingle Pass section, and the

Scenic Drive section in El Paso, Texas. Although the arrays

of points plotted in these two graphs exhibit modest dispersion, a majority of the first occurrences plot above and to the

left of a line with the equation SP=(B-KA)+226, and most

last occurrences plot below and to the right of that line. The

array to which we have fit the line in figures 3 and 4 is composed of the 31 points that plot on or very close to the interface between first-occurrence and last-occurrence sectors of

the graph. The array is clearly rectilinear, which suggests

that composite section B-KA very closely approximates a

single, unbroken sequence. This may also be taken as

Figure 3. Graphic correlation of the lower 170 m of Ibex-area composite section B-KA with a composite standard (CS) composed of maximized range data from Ibex-area sections STP, LD5, A, and E; the Scenic Drive section in El Paso, Texas; and the Shingle Pass section,

which is the standard reference section (SRS). Dots are range bases; crosses are range tops. Numbers by dots and crosses refer to the conodont

species listed in Appendixes 2 and 3 and identify only those points composing the array to which the line of correlation (LOC) has been fit.
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 59

400

300

200

170

500

600

700

800m

500 600 700 800 900 1000 1100 csu 340 400

IBEX—B-KA SECTION (UPPER PART)

COMPOSITE STANDARD

+ + + ++

+

+

+

+ +

+ +

+ +

+

+

+ + +

+

+ + +

+

+ +

87

97

149

3

34

106

156

145

95

157

174

33

196

47

3

51

146

173

201

87

95

CS = (B-KA) + 226

support for our decision to treat seven of the Ibex-area sections as a single succession for the purpose of establishing

correlation with Ibexian rocks elsewhere.

In the graph of figure 3, it should be noted that crosses

marking the upper range limits of four conodont species plot

above and well to the left of the LOC, in a sector of the graph

otherwise dominated by first occurrences (dots). At first we

interpreted the anomalous position of these upper range limits as indicative of a discontinuity in the section, at about the

level of the House Limestone/Fillmore Limestone contact.

However, neither we nor Ethington and others (1987) have

been able to detect any physical evidence in the field of such

a discontinuity. Consequently, it seems reasonable to

conclude that these surprisingly high “tops” merely record

upper range limits in section B-KA that are higher than in

any other section we have thus far considered. They might,

of course, be the results of reworking; but we discount this

possibility because other ranges, established from the same

samples, appear to be congruent with a LOC based on many

other range limits established and closely controlled in either

the Shingle Pass or Scenic Drive sections. 

Initially, we included Hintze’s A Section, the stratotype

of the House Limestone, in the assembly just described, by

assuming that rock accumulated at an essentially uniform

rate throughout the Ibex area and that the top of section A

equated with the base of section C, which Hintze (1973)

Figure 4. Graphic correlation of the upper 593 m of Ibex-area composite section B-KA with a composite standard (CS) composed of maximized range data from the Scenic Drive section, El Paso, Texas, and the Shingle Pass section, which is SRS. Dots are range bases; crosses

are range tops. Numbers by dots and crosses refer to the conodont species listed in Appendixes 2 and 3 and identify only those points composing the array to which the line of correlation (LOC) has been fit.
60 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

250

150

200

m

100

50

0

300 350 csu 150 200

IBEX—SECTION A

COMPOSITE STANDARD

+

+

+

+

+

+

+

+

+

+ +

+

+ +

++++

+ +++

54

119

40

113

4

177

43

9

159

167

119

35

5

205

14

179

158

84

168

107

65

16 54

43 41 40

29

38

13

36

1

29

4

1

158

107

13

14

5

159

84

177

167

35 9

16

36 38

CS = 0.7 A + 190

determined to be coeval with the top of the House Limestone

in section B. However, inclusion in the Ibex-area composite

of conodont range data from section A introduced a puzzling

amount of dispersion into the lower part of the graphic array,

and this suggested that section A should be correlated independently with a composite section that included information from the Shingle Pass section, an Ibex-area assembly

composed of data from sections B, C, M, H, ST, J, and KA,

and a section of El Paso Group strata along Scenic Drive, in

El Paso, Texas (Repetski, 1982).

Figure 5, a graph that relates Ibex-area section A to a

composite standard that includes information from all the

sections mentioned in a preceding paragraph, suggests that

the rate of rock accumulation may have been somewhat

greater in the vicinity of section A than to the south in section B-KA. Thus, in figure 2 we show the position of

Hintze’s A Section as indicated graphically in figure 5.

Note that the top of the House Limestone in Ibex-area section A is at a level some 18 m lower in the framework that

controls the CS than the top of the House Limestone in

Ibex-area sections B, C, and M.

Figure 5. Graphic correlation of Ibex-area section A with a composite standard composed of maximized range data from the Shingle Pass

and Scenic Drive sections and Ibex-area sections STP, LD5, E, and lower B-KA. Dots are range bases; crosses are range tops. Numbers by

dots and crosses refer to conodont species identified in Appendixes 2 and 3.
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 61

50

100

150

m

0

IBEX—SECTION E

150 200 250 300 350csu

COMPOSITE STANDARD

+

+

+

+ +

+

+ +

+

+

+

+

+ + +

+

+ +

13 107 191

158

167

9

16

177 5

84

2

38 113 113

159

35 36

40

119

2

177

9 119

84

167

158

159

1

5 35 16

205

13

107

35 29

40

41

29

38

CS = 0.92 E + 196

Hintze’s (1951) E Section, in the Wilden Hills, is also

isolated from the body of composite section B-KA, and we

show its relationship to the graphically compiled composite

standard in figure 6. Note that the rate of rock accumulation

in the vicinity of Ibex-area section E was also apparently

somewhat greater than elsewhere in the Ibex area, or in the

Shingle Pass section, which is the standard reference section

for the composite standard. In figure 2 we show section E in

the position indicated graphically in figure 6.

In their study of the Notch Peak Formation, Hintze and

others (1988) reported the distribution of conodonts in sections at three localities in the Ibex area. Range data for two of

these, the Steamboat Pass and Lava Dam 5 sections, are summarized in Appendix 2 and are used graphically in figures 7

and 8 to illustrate the relations of these two sections to a

composite section that includes information from the

Shingle Pass and Sawmill Canyon sections, the Ibex-area

sections mentioned in preceding paragraphs, and an El Paso

Group section in the southern Franklin Mountains, Texas.

The positions of these sections indicated by graphic correlation are shown in figure 2.

In figure 2 the Ibex-area sections just discussed are

assembled in a chart, the vertical scale of which is that of the

Shingle Pass–Sawmill Canyon succession, which is the SRS

for the CS with which we have compared Ibex-area sections

graphically. Sections in this assembly include the stratotype

of the Ibexian Series base (39.1 m above the base of the Lava

Dam Member in Ibex-area section LD5), as well as the basal

stratotypes of all Ibexian stages and conodont biozones. The

top of the Ibexian Series, defined as the base of the

Whiterockian Stage, is not included objectively in the sections assembled in figure 2. It is drawn in that figure at the

level of first occurrence of the conodont Tripodus laevis in

the Shingle Pass-based CS.

Figure 6. Graphic correlation of Ibex-area section E with a composite standard composed of maximized range data from the Shingle Pass

and Scenic Drive sections, and from Ibex-area sections STP, LD5, A, and lower B-KA. Dots are range bases; crosses are range tops. Numbers

by dots and crosses refer to conodont species identified in Appendixes 2 and 3.
62 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

50

100

m

0

IBEX—STEAMBOAT PASS SECTION

100 150 200 250csu 0 50

COMPOSITE STANDARD

+

+

+

+

+

+

++

+69 61

71

140

139

41

21

22 137

72

69

71 41

132

22

21 139 140

61

137

191

CS = 1.13 SP + 29

100

50

0

150m

IBEX—LAVA DAM 5 SECTION

100 150 200 250

csu

0 50

COMPOSITE STANDARD

+ + +++

+

+

+

+ ++ +

+

+ +

++

+

+

72 71 140

27 30 37

61,189

88

41 204 37

139 30

38, 73

188

73

88

70 29

29 27,189

69

21

22

138

137 140 61,139,141

191 141

138

69

71

41

72 70

137

21 22

CS = 1.13 LD5 + 55

Figure 7. Graphic correlation of the Ibex-area Steamboat Pass (STP) section with a composite standard composed of maximized range

data from Ibex-area sections LD5, A, and E, and from the Shingle Pass and Scenic Drive sections. Dots are range bases; crosses are range

tops. Numbers by dots and crosses refer to conodont species listed in Appendixes 2 and 3.

Figure 8. Graphic correlation of the Ibex-area Lava Dam 5 section with a composite standard composed of maximized range data from the

Shingle Pass and Scenic Drive sections and from Ibex-area sections STP, A, E, and lower B-KA. Dots are range bases; crosses are range

tops. Numbers by dots and crosses refer to conodont species listed in Appendixes 2 and 3.
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 63

100

200

m

0

IBEX—K + CP SECTION

1050 1100 csu 950 1000

COMPOSITE STANDARD

+

+

+ +

+

+

+

+

+

+

+

+

57

126

106

78

154

93

60

78

74

77

81

147

77 97

93

154

74

57

CS = 1.15KCP + 995

Ethington and Clark’s (1982) monograph on Ibex-area

conodonts also includes information on the nature and

ranges of some 45 conodont species in Whiterockian strata

in Hintze’s (1973) sections J, K, and CP. Although our studies have focused primarily on biostratigraphic characterization and correlation of Ibexian strata, we include a graph (fig.

9) that shows the relations between rocks in Ibex-area sections K and CP and those in the upper 150 m or so of the

Shingle Pass-based CS. This graph is included largely to provide a biostratigraphic cap for the Ibexian Series and to

enable its subsequent incorporation into a composite standard that will include the entire Ordovician System (Sweet,

1995a, 1995b). In figure 2, Hintze’s Ibex-area sections K

(our KB) and CP are shown in relation to other Ibex-area sections.

CORRELATION WITH THE

EL PASO GROUP, TEXAS

Collections from Pogonip Group strata in the Shingle

Pass and Ibex-area sections contain representatives of at least

two-thirds of the conodont species described by Repetski

(1982) from the El Paso Group exposed along Scenic Drive,

in the southern Franklin Mountains, in El Paso, Texas.

Ranges of those species are included in Appendix 2 of this

report and are used graphically in figure 10 to effect a correlation between the El Paso Group and a CS that includes

information from the Shingle Pass and Ibex-area sections

described in preceding sections of this report.

In the graph of figure 10, a line of correlation (LOC) is

fit to the rectilinear array of 27 points that defines the interface between the first-occurrence and last-occurrence sectors

of the graph. With only two exceptions, these points are the

range limits of well-known, widely distributed species about

whose physical attributes there is little question. Thus, we

regard the correlation indicated in figure 10 to be the one best

supported by the evidence presently available.

In figure 10, last occurrences of only three species and

first occurrences of only five plot at significant distances

away from the LOC. For the most part, these points represent

the first or last occurrences of species that are either rare or

absent in one or another of the sections contributing to the

composite standard, or they are the range limits of species

about which there is still a considerable taxonomic question.

Slope of the LOC indicates that El Paso Group strata accumulated at a slower rate than did those in the Ibex or Shingle

Pass areas, and sedimentologic data (Hayes and Cone, 1975)

suggest deposition was probably in much shallower water.

Thus faunal differences in the Early Ordovician likely were

appreciable between the two regions compared in this report,

and reliable correlations between them will have to depend

on the distribution of the more or less cosmopolitan species

we have utilized in figure 10.

SUMMARY

Graphic analysis demonstrates that the Shingle Pass section (augmented by information from a well-controlled section in Sawmill Canyon), in the southern Egan Range,

Nevada, provides an excellent template for assembly of information from sections in the Ibex area of western Millard

County, Utah, and along Scenic Drive in El Paso, Texas. That

the Shingle Pass succession can be used as a template for

relating post-Ibexian rocks in the Ibex area to older strata also

appears possible, thereby enabling establishment of a wellcontrolled local composite standard that extends from a level

well below the base of the Ordovician System to a point well

above the base of the Whiterockian Series. Such a local composite standard will be of great utility in building the panOrdovician CS outlined recently by Sweet (1995a, 1995b).

Figure 9. Graphic correlation of Ibex-area sections K and CP

with a composite standard composed of maximized range data

from the Shingle Pass section and the uppermost part of Ibex-area

section B-KA. Dots are range bases; crosses are range tops. Numbers by dots and crosses refer to conodont species listed in

Appendixes 2 and 3.
64 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

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400

m

300

200

100

0

SCENIC DRIVE - EL PASO, TEXAS

700 800 900 csu 200 300 400 500 600

COMPOSITE STANDARD

+

+ +

+ +

+

+

+

+ + + +

+++

+ + +

+

+

+ +++

++ + +

149

34

106

128 94

47

48 95 94

67

128

201 199

146

170

75

148

144

1 126

5 176

105

2 177

84 39

28

CS = 1.64 SD + 240

Figure 10. Graphic correlation of the Scenic Drive section, in El Paso, Texas, with a composite standard composed of maximized range

data from the Shingle Pass and Ibex-area sections. Dots are range bases; crosses are range tops. Numbers by dots and crosses refer to conodont species listed in Appendixes 2 and 3, but only points in the array to which the LOC is fit are identified by number.
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 65

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———1992, North American Whiterock Series suited for global

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66 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

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IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 67

APPENDIX 1. SHINGLE PASS SECTION

Section measured perpendicular to strike, in stratigraphically continuous

traverses at three different sites on northwest-trending ridge immediately south of Shingle Pass road, in the southern Egan Range, Nevada. Subsections are designated 85WA,

85WB, and 85WC, but sample designations are given in terms of footage above base of

subsection 85WA, which is also the local base of the House Limestone. Sample

85WB-751, for example, is from a limestone bed 751 feet above the base of the House

Limestone, in subsection 85WB.

SUBSECTION 85WC

Section of upper part of Shingle Limestone and lowermost Kanosh

Shale in NEcSEc sec. 36, T. 8 N., R. 62 E. (Shingle Pass, Nevada 7.5-

minute quadrangle). 

Thickness Cumulative

(feet) thickness 

(feet)

Kanosh Shale (lower 64 ft measured; overlying part

covered).

Limestone, medium-dark-gray, medium-bedded;

receptaculitids, cephalopods; thin covered

intervals (85WC-2924; 85WC-2893).........................39 2924

Limestone, medium-dark-gray, medium-bedded;

receptaculitids; few burrows; thin covered

intervals (85WC-2873) ...............................................25 2885

Shingle Limestone (1,539 ft; 26 percent covered).

Limestone, medium-dark-gray; weathers yellowish

orange; medium bedded, poorly developed beds;

brachiopods, trilobites; thin covered intervals

(85WC-2848; 85WC-2820)........................................55 2860

Covered .............................................................................4 2805

Limestone, medium-dark-gray; weathers yellowish

orange; very thin bedded to thin bedded; mottled;

few clasts (85WC-2801)...............................................2 2801

Covered .........................................................................124 2799

Limestone, medium-gray; weathers grayish orange

and pale yellowish orange; very thin bedded to

thin bedded; mottled; sponges, silicified burrows; 

thin covered intervals (85WC-2674; 85WC-2653; 

85WC-2638) ...............................................................42 2675

Limestone, medium-gray; weathers yellowish

orange; very thin bedded to thin bedded; mottled;

sponges, gastropods, brachiopods, cephalopods

(85WC-2620; 85WC-2602)........................................34 2633

Limestone, medium-gray to medium-dark-gray,

thin-bedded; mottled; brachiopods, gastropods .........12 2599

Limestone, medium-gray to medium-dark-gray,

thin-bedded; few fossils (85WC-2569;

85WC-2542; 85WC-2520) .........................................82 2587

Limestone, medium-gray to medium-dark-gray,

thin-bedded; gastropods, cephalopods, brachiopods, crinoids, trilobites, sponges; burrows

(85WC-2500; 85WC-2480)........................................35 2505

Limestone, medium-gray to medium-dark-gray,

very thin bedded to medium-bedded; fossiliferous

(85WC-2460)..............................................................30 2470

Limestone, medium-gray to medium-dark-gray;

weathers grayish orange; very thin bedded to

thin bedded (85WC-2440; 85WC-2420 with

first occurrence of Tripodus laevis)............................30 2440

Limestone, medium-dark-gray, very thin bedded to

medium-bedded; bioclastic layers (85WC-2404) ......28 2410

Limestone, medium-gray, weakly developed beds;

massive appearance; fossiliferous (85WC-2380).......12 2382

Thickness Cumulative

(feet) thickness 

(feet)

Shingle Limestone—Continued

Limestone, medium-gray, thin- to medium-bedded;

contorted beds; bioclastic layers; trilobites,

sponges, crinoids...........................................................9 2370

Limestone, light- to medium-gray, thin- to

medium-bedded; contorted beds; bioclastic

layers, trilobites; silicified burrows (85WC-2360;

85WC-2333; 85WC-2316; 85WC-2298) ...................76 2361

Limestone, medium-dark-gray, very thin bedded;

irregular bedding; trilobites; silicified burrows

(85WC-2278) ..............................................................20 2285

Limestone, medium-gray; weathers pale yellowish

orange; thickly laminated to very thin bedded;

mottled; bioclastic layers; trilobites; silicified

burrows (85WC-2260)................................................11 2265

Limestone, medium-gray, very thin bedded to

thin-bedded; irregular bedding planes;

light-brownish-gray clasts; bioclastic layers;

trilobites; silicified burrows (85WC-2238) ................20 2254

Limestone, brownish-gray to medium-gray, thin- to

medium-bedded; irregular bedding planes; mottled;

tabular to spherical clasts; very fossiliferous:

gastropods, cephalopods, trilobites, brachiopods,

abundant sponges; silicified burrows (85WC-2220)..19 2234

Limestone, light- to medium-gray, thin- to

medium-bedded; mottled; thin bioclastic layers 

(85WC-2198) ..............................................................17 2215

Covered ...........................................................................25 2198

Limestone, medium-gray; weathers pale orange;

very thin bedded to medium bedded; mottled;

sparry; bioclastic layers; gastropods, cephalopods,

trilobites (85WC-2173).................................................1 2173

Covered .........................................................................145 2172

Limestone, olive-black to medium-dark-gray,

medium-bedded to thick-bedded (85WC-2020).........10 2027 

Limestone, medium-gray, medium-bedded; sparry;

bioclastic layers; abundant sponges; thin covered

intervals.......................................................................17 2017

Limestone, light- to medium-light-gray; weathers

moderate red; medium bedded; intraclast and

bioclastic layers (85WC-2000).....................................1 2000

Covered .............................................................................6 1999

Limestone, medium-dark-gray and grayish-orange,

thin-bedded; trilobites, cephalopods, crinoids..............1 1993

Limestone, medium-dark-gray and grayish-orange,

thin- to medium-bedded; mottled; gastropods,

brachiopods, silicified burrows.....................................5 1992 

Covered .............................................................................4 1987

Limestone, medium-light- to medium-gray,

thin-bedded; intraclasts.................................................1 1983

SUBSECTION 85WB

Section of Parker Spring Formation and lower part of Shingle

Limestone in SWcNWc sec. 30, T. 8 N., R. 63 E. (Shingle Pass, Nevada,

7.5-minute quadrangle). Although offset below 85WC, section is

continuous with 85WC. 

Thickness Cumulative

(feet) thickness 

(feet)

Shingle Limestone

Covered .............................................................................2 1982 

Limestone, interbedded medium-light-gray and

medium-gray to medium-dark-gray, thinly laminated

to medium-bedded; intraclast and bioclastic layers;

chert lenses; very fossiliferous: gastropods,

brachiopods, cephalopods, crinoids, trilobites;

thin covered intervals (85WB-1980; 85WB-1957;

5WB-1940) .................................................................42 1980
68 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Thickness Cumulative

(feet) thickness 

(feet)

Shingle Limestone—Continued

Covered ...........................................................................26 1938

Limestone, medium-light-gray; weathers very light

to light brownish gray; thin to medium bedded; 

rounded clasts, weathers light brown to moderate

red; tabular clasts oriented parallel to bedding; very

fossiliferous, gastropods, crinoids, trilobites; thin

covered intervals (85WB-1912; 85WB-1896; 

85WB-1874; 85WB-1860) .........................................52 1912

Covered .............................................................................2 1860

Limestone, medium-light-gray; weathers moderate

red; thickly laminated to medium bedded; tabular

clasts; bioclastic layers; silicified burrows; 

stromatolites? (85WB-1840).......................................23 1858

Limestone, medium-light-gray; weathers moderate

red; very thin bedded to medium bedded; few 

chert and bioclastic layers; cephalopods, gastropods,

silicified burrows (85WB-1820; 85WB-1800;

85WB-1780) ..............................................................74 1835

Limestone, medium-light-gray, medium-bedded;

burrowed (85WB-1760)................................................6 1761

Limestone, medium-light-gray; weathers grayish

orange to moderate red; medium bedded; 

burrowed, some silicified burrows................................2 1755

Limestone, medium-light-gray, medium-bedded; 

some intraclasts; burrowed ...........................................3 1753

Limestone, medium-light-gray; weathers grayish 

orange to moderate red; medium bedded; 

heavily burrowed; some silicified burrows.................10 1750

Limestone, medium-gray, thickly laminated to 

medium-bedded, burrowed; gastropods

(85WB-1740; 85WB-1721) ........................................25 1740

Limestone, medium-gray; weathers grayish orange 

to moderate red; thickly laminated to medium 

bedded; chert layers; gastropods, brachiopods;

silicified burrows (85WB-1700; 85WB-1680; 

85WB-1661)................................................................68 1715

Limestone, medium-dark-gray, thickly laminated to

medium-bedded; chert layers; silicified burrows

(85WB-1640) ..............................................................26 1647

Limestone, medium-gray; weathers moderate red 

and grayish yellow; very thin bedded to medium 

bedded; wavy bedding planes; silicified burrows

(85WB-1621; 85WB-1602) ........................................36 1621

Limestone, medium-gray, thin- to medium-bedded;

chert layers; silicified burrows (85WB-1580; 

85WB-1559; 85WB-1540) .........................................48 1585

Limestone, medium-dark-gray; weathers yellowish 

gray to dark brown; thickly laminated; brachiopods, gastropods; burrowed (85B-1521) ....................18 1537

Limestone, medium-dark-gray; weathers yellowish 

gray to dark brown; thickly laminated to medium 

bedded; gastropods (85WB-1503)..............................34 1519

Limestone, medium-gray, medium-bedded, burrowed.....1 1485

Limestone, medium-dark-gray; weathers yellowish

gray to dark brown; thickly laminated; burrowed

(85WB-1483) ................................................................9 1484

Limestone, medium-dark-gray, very thin bedded; 

bioturbated; gastropods, brachiopods; base of

high cliff........................................................................3 1475

Covered .............................................................................2 1472

Limestone, medium-gray, thin- to thick-bedded; 

mottled ..........................................................................2 1470

Thickness Cumulative

(feet) thickness 

(feet)

Shingle Limestone—Continued

Limestone, medium-gray, thinly laminated; base

of low cliff (85WB-1467 at base)................................ 1 1468

Covered........................................................................... 34 1467

Limestone, medium-gray, thin-bedded; mottled;

bioclastic (85WB-1432 at base)................................... 1 1433

Covered........................................................................... 30 1432

Limestone, medium-gray, thin- to thick-bedded; 

mottled (85WB-1402; 85WB-1385).......................... 35 1402

Limestone, medium-gray; weathers grayish orange;

thinly to thickly laminated; laminations destroyed 

by burrows in places; silicified laminae and 

burrows (85WB-1361) ............................................... 15 1367

Limestone, medium-gray; weathers grayish orange 

gray; thin to thick bedded; mottled; few intraclasts;

localized chert layers; brachiopods; burrowed

(85WB-1343).............................................................. 22 1352

Limestone, medium-gray, thinly laminated to

thick-bedded; chert; weathers orangish brown; 

burrows; gastropods; stromatolites; laminae 

continuous through stromatolites and chert................. 9 1330

Parker Spring Formation (851 ft; 81 percent covered).

Limestone, medium-gray, thin- to medium-bedded; 

mottled; bioturbated; burrowed (85WB-1320) ........... 1 1321

Limestone, medium-gray, very thin bedded to

thin-bedded; intraclast layers with tabular clasts

parallel to bedding........................................................ 2 1320

Covered. Probably shale; forms slope .......................... 10 1318

Limestone, medium-gray, medium-bedded; intraclast 

layers with bioclastic matrix (85WB-1306) ................ 3 1308

Covered. Probably shale; forms slope .......................... 20 1305

Limestone, medium- to dark-gray, thickly laminated...... 1 1285

Covered. Probably shale; forms slope ............................ 5 1284

Limestone, medium-gray, medium-bedded; intraclast

layers with clasts parallel to bedding, bioclastic

matrix (85WB-1277 at base) ....................................... 2 1279

Covered. Probably shale; forms slope .......................... 12 1277

Limestone, medium-gray, thickly laminated; 

crossbeds; intraclast layers with rounded clasts .......... 2 1265

Covered. Probably shale; forms slope ............................ 8 1263

Limestone, medium-gray, very thin bedded to

thin-bedded; intraclast layers ....................................... 1 1255

Covered. Probably shale; forms slope ............................ 1 1254

Limestone, medium-gray, very thin bedded to

thin-bedded; intraclast layers; minor bioclastic

material (85WB-1253) ................................................. 1 1253

Covered. Probably shale; forms slope ............................ 4 1252

 Limestone, medium-gray to dark-gray, thickly

laminated to medium-bedded; intraclast layers; 

bioturbated.................................................................... 2 1248

Covered. Probably shale; forms slope .......................... 29 1246

Limestone, medium-gray, medium-bedded; intraclast layers with clasts in random orientation 

(85WB-1217)................................................................ 2 1217 

Covered. Probably shale; forms slope ............................ 8 1215

Limestone and chert interlayered; limestone

medium-gray, thickly laminated to very thin 

bedded; bioturbated; few intraclasts ............................ 2 1207

Covered. Probably shale; forms slope ........................... 3 1205
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 69

Thickness Cumulative

(feet) thickness 

(feet)

Parker Springs Formation—Continued

Limestone, medium-gray, thin- to medium-bedded;

intraclast layers with rounded and tabular clasts 

in random orientation, bioclastic matrix; 

minor chert (85WB-1200 at base)................................2 1202

Covered. Probably shale; forms slope...........................24 1200

Limestone, medium-gray, thin- to medium-bedded;

intraclast layers with tabular clasts oriented 

subparallel to bedding (85WB-1175)...........................2 1176

Covered. Probably shale; forms slope...........................48 1174

Limestone, medium-light-gray to medium-gray,

medium-bedded; intraclast layers with clasts

subparallel to bedding (85WB-1126)...........................1 1126

Covered. Probably shale; forms slope...........................21 1125

Limestone, medium-light-gray to medium-gray, 

thin- to medium-bedded; intraclast layers with

tabular and rounded clasts oriented subparallel

with bedding in bioclastic matrix; pelecypods 

(85WB-1103)................................................................2 1104

Covered. Probably shale; forms slope...........................53 1102

Limestone, medium-gray, medium-bedded; intraclast 

layers with randomly oriented tabular and 

rounded clasts ...............................................................1 1049

Covered. Probably shale; forms slope.............................3 1048

Limestone, medium-gray, medium-bedded; intraclast 

layers with randomly oriented tabular and rounded

clasts; thin covered intervals ........................................2 1045

Limestone, medium-gray, medium-bedded; intraclast 

layers with randomly oriented tabular and 

rounded clasts; pelecypods (85WB-1042 at base).......1 1043

Covered. Probably shale; forms slope.............................2 1042

Limestone, medium-gray, medium-bedded; intraclast 

layers with randomly oriented tabular and rounded

clasts..............................................................................1 1040

Covered. Probably shale; forms slope...........................16 1039

Limestone, medium-gray, medium-bedded; intraclast 

layers with tabular and rounded clasts (85WB-1022 

at base)..........................................................................1 1023

Covered. Probably shale; forms slope.............................9 1022

Limestone, medium-gray to medium-dark-gray,

medium-bedded; intraclast layers with bioclastic

matrix; gastropods (85WB-1012 at base) ....................1 1013

Covered. Probably shale; forms slope...........................20 1012

Limestone, medium-gray, thin-bedded, intraclast layers 

(85WB-991 at base)......................................................1 992

Covered. Probably shale; forms slope...........................22 991

Limestone, medium-gray, medium-bedded; intraclast 

layers with clasts parallel to bedding (85WB-968

at base)..........................................................................1 969

Covered. Probably shale; forms slope...........................13 968

Limestone, medium-gray to medium-dark-gray, 

medium-bedded; intraclast layers with clasts 

parallel to bedding ........................................................1 955

Covered. Probably shale; forms slope.............................3 954

Limestone, medium-gray to medium-dark-gray, 

medium-bedded ............................................................1 951

Covered. Probably shale; forms slope.............................9 950

Limestone, medium-gray to medium-dark-gray,

medium-bedded; intraclast layers with bioclastic

matrix; cephalopods, pelecypods (85WB-941)............3 941

Covered. Probably shale; forms slope.............................6 938

Thickness Cumulative

(feet) thickness 

(feet)

Parker Springs Formation—Continued

Limestone, medium to medium-dark-gray, thin- to

medium-bedded; intraclast layers with bioclastic 

matrix and clasts parallel to bedding ...........................1 932

Covered. Probably shale; forms slope.............................9 931

Limestone, medium-gray to dark-olive-gray, thin- to

medium-bedded; intraclast layers with tabular clasts

parallel to bedding; bioclastic layers (85WB-921) ......2 922

Covered. Probably shale; forms slope...........................14 920

Limestone, medium-light-gray to medium-gray, 

thin- to medium-bedded; intraclast layers with 

tabular clasts subparallel to bedding; minor 

bioclastic material (85WB-906) ...................................5 906

Covered. Probably shale; forms slope...........................32 901

Limestone, medium-light-gray to medium-gray,

medium-bedded; intraclast layers (85WB-868) ...........2 869

Covered. Probably shale; forms slope...........................30 867

Limestone, medium-gray, medium-bedded; bioclastic; 

trilobites ........................................................................1 837

Limestone, medium-gray, very thin bedded to

thin-bedded; some bioclastic layers (85WB-836)........3 836

Limestone, medium-light-gray to medium-gray, 

thin- to medium-bedded; intraclast layers with 

tabular clasts oriented primarily parallel to bedding ...3 833

Covered. Probably shale; forms slope...........................19 830

Limestone, medium-light-gray to medium-gray, 

thin- to medium-bedded; intraclast layers with 

rounded and a few tabular clasts ..................................1 811

Limestone, medium-light-gray to medium-gray, 

thin- to medium-bedded; intraclast layers with 

tabular clasts oriented subparallel to bedding..............1 810

Covered. Probably mostly shale; forms slope; single

thin limestone bed exposed 19 ft above base 

(85WB-799)................................................................29 809

Limestone, medium-light-gray to medium-gray,

thin-bedded; sparry in places; intraclast layers 

with clasts parallel to bedding; bioclastic layers,

pelecypods.....................................................................1 780

Covered. Probably shale; forms slope...........................19 779

Limestone, medium-light-gray to medium-gray,

thin- to medium-bedded; intraclast layers with 

tabular clasts parallel to bedding; bioclastic 

layers with pelecypods, gastropods, cephalopods 

(85WB-751) ...............................................................10 760

Covered. Probably shale; forms slope............................ 9 750

Limestone, medium-gray, thin- to medium-bedded; 

intraclast layers with tabular clasts; bioclastic 

layers (85WB-739 at base).......................................... 2 741

Covered. Probably mostly shale; forms slope ..............11 739

Limestone, gray, medium-bedded; intraclast layers ........ 1 728

Covered. Probably shale; forms slope ............................ 6 727

Limestone, gray, medium-bedded; intraclast layers ........ 1 721

Covered. Probably shale; forms slope.............................8 720

Limestone, medium-light-gray, thin-bedded; intraclast

layers; minor bioclastic layers; limestone beds

draped over chert cores (85WB-712)...........................2 712

Limestone, medium-light-gray to medium-gray, 

thickly laminated to thin-bedded; intraclast layers

with sparry matrix; discontinuous chert layers 

(85WB-683 at base)....................................................27 710

Covered. Probably shale; forms slope...........................39 683 
70 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Thickness Cumulative

(feet) thickness 

(feet)

Parker Springs Formation—Continued

Limestone, medium-light-gray to medium-gray,

thickly laminated to thin-bedded; intraclast 

layers with bioclastic and sparry matrix and 

clasts subparallel to bedding; minor chert 

nodules and stringers (85WB-640) .............................5 644

Covered. Probably shale; forms slope.............................8 639

Limestone, medium-light-gray to medium-gray, 

very thin bedded; sparry; intraclast layers

(85WB-630) .................................................................1 631

Covered. Probably shale; forms slope ..........................56 630

Limestone, medium-light-gray; intraclast layers

with clasts parallel to bedding and surrounded 

by sparry calcite (85WB-573 at base) .........................1 574

Covered. Probably shale; forms slope 8......................573

Limestone, medium-light-gray, medium-bedded;

sparry; intraclast layers ................................................1 565

Covered. Probably shale; forms slope...........................26 564

Limestone, medium-gray, medium-bedded; interbedded intraclast and bioclastic layers

(85WB-538) .................................................................1 538

Covered. Probably shale; forms slope ..........................10 537

Limestone, medium-light-gray to medium-gray; 

laminated; interbedded intraclast and bioclastic

layers; trilobites (85WB-518).....................................10 527

Limestone, medium-gray, thinly laminated to 

medium-bedded; sparry; intraclast layers; chert 

stringers and layers .....................................................11 517

Covered. Probably shale; forms slope ............................4 506

Limestone, medium-gray, thick-bedded; intraclast

layers up to 8 in. thick with clasts subparallel to

bedding and chert coating some clasts; chert 

nodules and stringers; thin bioclastic layers 

(85WB-501) .................................................................3 502 

Limestone, medium-gray, thin-bedded; intraclast

layers ...........................................................................10 499

Shale, light-brownish-gray, thinly laminated....................1 489

Limestone, medium-light-gray to medium-gray;

laminated; intraclast layers with randomly 

oriented clasts; few thin covered intervals ...................6 488

Limestone, light-gray to light-brownish-gray; intraclast

layers with clasts subparallel to bedding in bioclastic

and sparry matrix..........................................................2 482

Limestone, light-gray to light-brownish-gray, very thin

bedded to medium-bedded; bedding uniform, with 

sparry matrix; chert nodules and stringers

(85WB-480) ...............................................................10 480

SUBSECTION 85WA

Section of House Limestone in center of sec. 25, T. 8 N., R. 62 E.

(Shingle Pass, Nevada 7.5-minute quadrangle).

Thickness Cumulative

(feet) thickness 

(feet)

House Limestone (470 ft; completely exposed).

Limestone, gray, thin- to medium-bedded; forms

ledge; chert stringers.....................................................6 470

Limestone, gray, thin- to medium-bedded; bioclastic

layers up to 5 in. thick; intraclast layers with

bioclastic matrix (85WA-455) ....................................10 464

Limestone, gray, red-stained; intraclast layers with

rotated clasts in bioclastic matrix (85WA-435)..........20 454

Thickness Cumulative

(feet) thickness 

(feet)

House Limestone—Continued

Limestone, gray, red-stained; thin- to 

medium-bedded; a few intraclast layers interbedded with bioclastic layers; minor contortion ....... 10 434

Limestone, light-gray to brownish-gray, thin- to

medium-bedded; sparry matrix; bioclastic layers........ 4 424

Limestone, medium-gray to medium-dark-gray, 

very thin bedded to medium-bedded; intraclastic

and bioclastic layers; gastropods abundant

(85WA-420; 85WA-401)............................................ 20 420

Limestone, medium-gray; few intraclast layers;

bioclastic layers;?worm trails (85WA-379; 

85WA-363) ................................................................. 40 400

Limestone, light-gray to medium-light-gray, very 

thin bedded to medium-bedded; sparry; some

bioclastic layers............................................................ 4 360

Limestone, gray; sparry; fractured and brecciated; 

some intraclast layers with rounded clasts;

gastropods (85WA-342; 85WA-320) ......................... 42 356

Limestone, medium-gray, very thin bedded to

medium-bedded; sparry calcite filling joints and

fractures; gastropods (85WA-300)............................. 19 314

Limestone, light-gray to medium-light-gray, thinly 

laminated to medium-bedded; bioclastic layers ........ 15 295

Limestone, medium-gray, thickly laminated to

medium-bedded; sparry; intraclasts in some

layers; some bioclastic layers; less chert than 

below (85WA-280; 85WA-263; 85WA-240) ............. 52 280

Limestone, medium-gray, thin- to medium-bedded; 

sparry; chert in discrete units; brecciated;

burrowed....................................................................... 8 228

Limestone, gray; thin to medium beds with randomly

oriented intraclasts; chert content approximately 

60 percent; forms ridge; brecciated, includes rotated 

limestone blocks; some chert nodules and ribbony

chert layers; chert decreases rapidly away from 

ridge crest (85WA-220; 85WA-200).......................... 37 220

Limestone, gray; possibly crossbedded; tabular

intraclasts in some layers parallel to bedding; 

chert content 50 percent (85WA-180) ....................... 10 183

Limestone and chert, as below, with ribbony chert 

layers and some intraclasts ........................................ 13 173

Limestone, gray; bedding variable, bedding planes 

wavy; sparry; chert more than 50 percent but 

localized, in layers; brecciated intervals of chert 

and limestone (85WA-159)........................................ 20 160

Limestone, light-gray; tabular and rounded interclasts;

some bedding planes wavy; 25 percent chert; chert

localized and in layers; some layers brecciated ........ 18 140

Limestone, light-gray, thickly laminated to very thin

bedded; 10 percent chert (85WA-120)......................... 4 122

Limestone, light-gray, thickly laminated to

thin-bedded; sparry calcite filling joints ...................... 8 118

Limestone, light-gray, thickly laminated to very thin

bedded; chert layers and nodules; numerous

bioclastic layers; burrowed ........................................ 10 110

Limestone, light-gray; wavy bedding; chert stringers

and nodules; less chert than in units below 

(85WA-99).................................................................. 18 100

Limestone, light-gray; finely laminated; bioclastic

layer 8 in. thick; laminae discontinuous, contorted 

(85WA-82) ................................................................... 2 82
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 71

Thickness Cumulative

(feet) thickness 

(feet)

House Limestone—Continued

Limestone, light-gray; thinly laminated; wavy 

bedding planes; less chert than below, 

bioclastic layers more numerous; brachiopods,

crinoid stem fragments (85WA-60) ...........................24 80

Limestone, light-gray; thinly laminated; chert beds

up to 4 in. thick ..........................................................16 56

Limestone, light-gray; beds thinly laminated;

bedding planes wavy; sparry; chert layers; 

rippled (85WA-40)........................................................2 40

Thickness Cumulative

(feet) thickness 

(feet)

House Limestone—Continued

Limestone, medium-light-gray to medium-gray;

thin- to medium-bedded; some bedding planes 

wavy; chert stringers, nodules and beds; bioclastic

beds up to 4 in. thick; poorly preserved

brachiopods, crinoid stem fragments; burrowed

(85WA-23; 85WA-00) ................................................38 38

Whipple Cave Formation (not measured).

Contact between Whipple Cave Formation and House Limestone well 

exposed. Whipple Cave is dolomite below contact.

APPENDIX 2. RANGES (IN METERS) OF CONODONT SPECIES IN

IBEXIAN SECTIONS AT EIGHT LOCALITIES

Localities identified in column headings are:

 SHINGLE: Shingle Pass, Nevada (data new in this report)

STP: Steamboat Pass, Nevada (data from Hintze and others, 1988)

LD5: Lava Dam 5 (data from Hintze and others, 1988)

A: Hintze’s (1951) Ibex-area section A (data from Ethington and Clark, 1982)

E: Hintze’s (1951) Ibex-area section E (data from Ethington and Clark, 1982)

B-KA: Composite of Hintze’s (1951, 1973) Ibex-area sections B, C, M, H, ST, J, and K as indicated in figure

2 of this report (data from Ethington and Clark, 1982)

K-CP: Composite of Hintze’s (1973) Ibex-area K and CP Sections as indicated in figure 2 of this report (data

from Ethington and Clark, 1982)

“Ref” refers to places in which the reader may find descriptions and (or) illustrations of the named conodont species. 

E&C82 = Ethington and Clark, 1982

Rep 82 = Repetski, 1982

App4 = Appendix 4, this report
72 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

# Species Ref SHINGLE STP LD5 A E B-KA K-CP ElPaso

[m] [m] [m] [m] [m] [m] [m] [m]

1 Acanthodus lineatus E&C82 202-364 27-176 70-133 9-109 0-79

2 A. uncinatus E&C82 270-288 94 ?95-109 24

3 Acodus? aff A. emanuelensis E&C82 455-923 244-696

4 aff. A. gladiatus E&C82 270-353 114-163

5 "A." oneotensis E&C82 215-336 91-173 52-114 7-105 0-55

6 A. sp. 1 E&C82 142-190

7 ?A. sp. 2 E&C82 195-204

8 ?A. sp. 3 E&C82 248-395

9 A. sp. 4 E&C82 101-176 70-129

10 "Acontiodus" aff "A" latus E&C82 216-248

11 "A." sp. E&C82 43-304

12 Albiconus postcostatus App4 99-122

13 Aloxoconus? iowensis App4 202-306 40-173 45-133 12-106 6.-24

14 A.? propinquus App4 215-318 84-170 12-106 6.-37

15 A. staufferi App4 485-492

16 ?A. staufferi App4 67-176 52-133 0-86

17 Bergstroemognathus sp. App4 715-768

18 Belodella robusta E&C82 195-284

19 ?aff Belodina sp. E&C82 280

20 ?Bryantodina sp. E&C82 267-270

21 Cambrooistodus cambricus App4 69-123 33 0-60

22 C. minutus App4 71-123 37-83 14-60

23 Chionoconus robustus App4 928-1082 690-718

24 Chirognathus sp. E&C82 270-288

25 Chosonodina herfurthi E&C82 301-312

26 C. rigsbyi E&C82 166-213

27 Clavohamulus bulbousus App4 180-187 90-118

28 C. densus E&C82 275-329 91-104 18-31

29 C. elongatus E&C82 158-186 88-96 15-23 12.0-13

30 C. hintzei App4 196-198 115-125

31 C. lemonei Rep82 397 171-305

32 C. primitus E&C82 23

33 C. n. sp. E&C82 499 279-285

34 Colaptoconus quadraplicatus App4 336-853 120-653 55-390

35 Cordylodus angulatus E&C82 220-312 102-173 52 34 0-31

36 C. caseyi E&C82 208 35-171 13-52 0-91

37 C. drucei App4 202-245 121-122

38 C. intermedius E&C82 188-312 112-125 34-171 9.0-89 0-97 0-18

39 C. lindstromi Rep82 202-270 12.-18

40 C. prion E&C82 57-171 17-45 0-32

41 C. proavus E&C82 87-94 61-125 0-57 5.0-9

42 C. rotundatus Rep82 207-312 0-31

43 C. sp. A E&C82 56-96 3.0-32

44 Cornuodus longibasis App4 318-648 443-477 92-384

45 Cristodus loxoides Rep82 397-751 214-293

46 Dapsilodus? nevadensis E&C82 288-292

47 Diaphorodus deltatus App4 471-665 251-648 189-263

48 D. delicatus App4 654-873 250-407

49 D. russoi App4 1059 171-201

50 Dischidognathus primus E&C82 186-198

51 ?Drepanodus arcuatus E&C82 434-999 212-690 110-409
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 73

52 D. gracilis E&C82 265-642 122-406

53 D. cf. D. planus Rep82 896-974

54 "D." simplex E&C82 70-109 12-102

55 D. sp. 1 E&C82 107-677

56 D.? sp. 2 E&C82 160-724

57 Drepanoistodus angulensis E&C82 999-1082 2-213

58 ?D. angulensis E&C82 267-293

59 D. cf. basiovalis E&C82 381-999 107-250

60 D. aff. forceps E&C82 381-1006 238-763 2.-84 98-409

61 Eoconodontus notchpeakensis App4 20-202 21-94 0-125

62 Erismodus asymmetricus E&C82 267-293

63 Erraticodon aff balticus E&C82 154-293

64 ?Erraticodon sp. E&C82 154-170

65 Eucharodus parallelus App4 220-984 70-109 12-741 0-390

66 E, toomeyi App4 485-757 556-650 110-406

67 Fahraeusodus marathonensis App4 618-1072 416-758 226-390

68 Falodus sp. E&C82 151-172

69 Fryxellodontus inornatus App4 140-158 92-94 65-92

70 F. lineatus App4 158-174 65-93

71 Hirsutodontus hirsutus App4 174-190 89 61-125

72 H. rarus App4 134-184 89 63-125

73 H. simplex App4 190-192 98-112

74 Histiodella altifrons E&C82 1006-1082 12.-59

75 H. donnae Rep82 384-414 267 85-98

76 H. holodentata E&C82 192-213

77 H. minutiserrata E&C82 1050-1082 36

78 H. sinuosa E&C82 1072 69-192

79 Iapetognathus preaengensis App4 202-215

80 Juanognathus hayesi Rep82 397-401

81 J. jaanussoni E&C82 896-1082 653-763 2.-12 401-409

82 J. variabilis E&C82 684-1006 577-718 256-409

83 Jumudontus gananda E&C82 773-1006 527-741 348-406

84 Loxodus bransoni E&C82 257-323 91-171 74-107 9.0-96 0-31

85 ?aff Loxodus sp. E&C82 186-202

86 Macerodus dianae E&C82 212-245 92-134

87 Microzarkodina flabellum E&C82 953-974 724-743

88 Monocostodus sevierensis App4 188-220 96-125

89 Multioistodus auritus E&C82 15-150

90 ?M. auritus E&C82 195

91 M. subdentatus E&C82 172-204

92 M. sp. E&C82 195

93 Neomultioistodus compresus App4 984-1082 15-150

94 Oelandodus sp. cf. O. costatus Rep82 629-745 244-305

95 Oepikodus communis E&C82 672-959 440-726 256-409

96 O. sp. cf. O. evae App4 995

97 aff. O.? minutus E&C82 896-1006 665-763 2.-38

98 Oistodus bransoni E&C82 556-782? 419-648

99 O. cristatus E&C82 84-129

100 "O." hunickeni E&C82 650-724

101 "O." inaequalis E&C82 253-684

102 aff. "O." inaequalis E&C82 206-565 98-401

103 O. cf. O. lanceolatus Rep82 360-409

104 O.? lecheguillensis Rep82 116-134
74 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

105 "O." mehli Rep82 202-306 0-43

106 O. multicorrugatus App4 853-1082 622-733 0-189 372-401

107 "O." triangularis E&C82 202-329 66-176 35-133 0-105

108 O. sp. 1 E&C82 650-757

109 "O." sp. 2 E&C82 523-550

110 "O." sp. 3 E&C82 577

111 "O." sp. 4 E&C82 38-127

112 "O." sp. 5 E&C82 3.-32

113 "O." sp. 6 E&C82 151-174 89

114 Oneotodus costatus App4 492-715 288-648 177-406

115 O. simplex App4 336-466 235-247 0-98

116 Paltodus sp. cf. P. deltifer App4 318-353

117 P. sp. cf. P. subaequalis App4 397-533

118 aff. P. jemtlandicus E&C82 151-244

119 "P." spurius E&C82 238-257 101-139 70-114 9.-56 6.-12

120 Panderodus spp. E&C82 281-293

121 ?P. sp. E&C82 195

122 Paracordylodus gracilis Rep82 381-672 98-134

123 Parapanderodus asymmetricus A pp4 739-1082 608-763 348-401

124 P. emarginatus App4 618-1082 398-650 220-406

125 P. paracornuformis App4 653-768 20

126 P. striatus App4 353-1082 166-763 9-198 73-409

127 Paraprioniodus costatus E&C82 63-119

128 Paraserratognathus abruptus App4 526-768 182-323

129 Paroistodus numarcuatus? App4 323-406

130 P. originalis? App4 896-1044

131 P. parallelus E&C82 485-974 267-650 92-409

132 Phakelodus tenuis App4 66 65

133 ?Phragmodus flexuosus E&C82 267-293

134 ?Plectodina sp. E&C82 267

135 Polonodus corbatoi App4 612-618

136 Prioniodus sp. App4 648-660

137 Proconodontus muelleri App4 0-125 2.0-83 0-60

138 P. serratus App4 37-123 17-23

139 Prooneotodus gallatini App4 20-215 31-87 0-118

140 P. rotundatus App4 15-196 32-63 0-125

141 Prosagittodontus eureka App4 20 0-60

142 Protopanderodus aff arcuatus E&C82 565-584

143 P. elongatus E&C82 794-891 596-653

144 P. elongatus of Repetski 82 Rep82 381-434 85-110

145 P. gradatus E&C82 739-1082 521-758 2-195 360-409

146 P.? leei Rep82 336-444 153-241 73-134

147 P. leonardii E&C82 660-1059 521-763 4.-52 244-406

148 P.? n.spp.1+2 of Repetski 82 Rep82 397-556 98-183

149 Protoprioniodus aranda E&C82 896-999 658-758 397-409

150 P. nyinti App4 896-1006

151 P. papiliosus E&C82 677

152 P. simplicissimus? App4 502-853

153 P.? n. sp. App4 984

154 Pteracontiodus cryptodens E&C82 965-1044 0-144

155 P. gracilis E&C82 170-192

156 ?Reutterodus andinus E&C82 773-923 532-718 360-409

157 R.? borealis Rep82 648-660 431-471 263-372
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 75

158 Rossodus manitouensis App4 227-336 84-183 70-133 3-109 0-31

159 ?R. manitouensis App4 104-176 60-74 9.-91

160 R.? n. sp. App4 245-251

161 Scalpellodus striatus E&C82 230-646

162 aff "Scandodus" flexuosus E&C82 111-632 0-189

163 S. sinuosus E&C82 4-219

164 "S." sp. 1 E&C82 448-648

165 "S." sp. 3 E&C82 229-648

166 "S." sp. 4 E&C82 28-52

167 "S." sp. 5 E&C82 91-181 60-123 25-91

168 "S." sp. 6 E&C82 87-176 17-193

169 "Scolopodus" acontiodiformis Rep82 245-251 55-406

170 "S." bolites Rep82 406-419 92-104

171 S. cornutiformis E&C82 107-110 214-336

172 "S." filosus E&C82 329-853 119-606 73-409

173 S. floweri Rep82 434-477 233-244 31-134

174 S. multicostatus E&C82 593-618 373-487

175 "S." peselephantis E&C82 431-648

176 aff S. rex E&C82 318-654 131-427 55-275

177 ?"S." sexplicatus E&C82 101-176 74-114 35-87 18-31

178 S. sp. aff. S. striatus E&C82 547-600

179 "S." sulcatus E&C82 220-556 84-170 86-92 210-328 12.-79

180 "S." triangularis App4 336-1082

181 ?S. sp. E&C82 547-649

182 Scolopodiform A of E&C82 E&C82 177-236

183 Scolopodiform B of E&C82 E&C82 794-891 443-601

184 Scolopodiform C of E&C82 E&C82 697-928 204-547

185 Scolopodiform D of E&C82 E&C82 275-653

186 Scolopodiform E of E&C82 E&C82 268-637

187 Scolopodiform F of E&C82 E&C82 161-754

188 Semiacontiodus lavadamensis App4 188 112-121

189 S. nogamii App4 180-202 90-125

190 Stolodus stola E&C82 635-653

191 Teridontus nakamurai App4 0-318 92-94 63-125 7-176 3-133 0-102

192 Toxotodus amphigyus App4 ?715

193 T. carlae App4 220-409

194 "Trichonodella" ? sp. Mound App4 301

195 Tripodus laevis E&C82 928-1082 717-760

196 Tropodus comptus App4 485-891 265-690 189-397

197 Ulrichodina abnormalis E&C82 263-623 232-409

198 U. cristata E&C82 768 321-638

199 U. deflexa E&C82 247-288 146-207

200 U.? simplex E&C82 373-638

201 ?U. wisconsinensis E&C82 485-709 265-471 153-305

202 ?U. sp. E&C82 222

203 Utahconus tenuis App4 116-125

204 U. utahensis App4 188-238 96-125

205 Variabiloconus bassleri App4 208-364 87-176 45-133 0-109 0-79

206 ?Walliserodus ethingtoni E&C82 548-800 298-620

207 N. genus 1 E&C82 118-190

208 N. genus 2 E&C82 443-605

209 N. genus 4 E&C82 160

210 N. genus 5 E&C82 ?292
76 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

# Species SHINGLE STP LD5 A E B-KA K-CP ElPaso CS

[csu] [csu] [csu] [csu] [csu] [csu] [csu] [csu] [csu]

1 Acanthodus lineatus 202-364 209-314 260-318 235-335 240-370 202-370

2 A. uncinatus 270-288 282 321-335 279 270-335

3 Acodus? aff A. emanuelensis 455-923 470-922 455-922

4 aff A. gladiatus 270-353 270-305 270-353

5 "A." oneotensis 215-336 254-312 244-301 233-331 240-330 215-336

6 A. sp. 1 368-416 368-416

7 ?A. sp. 2 421-430 421-430

8 ?A. sp. 3 474-621 474-621

9 A. sp. 4 261-314 260-315 260-315

10 "Acontiodus" aff. A. latus 442-474 442-474

11 "A. " sp. 1044-1345 1044-1345

12 Albiconus postcostatus 167-193 167-193

13 Aloxoconus? iowensis 202-306 218-312 237-318 238-332 250-279 202-332

14 A.? propinquus 215-318 249-309 238-332 250-301 215-332

15 A. staufferi 485-492 485-492

16 ?A. staufferi 237-314 244-318 226-312 226-318

17 Bergstroemognathus sp. 715-768 715-768

18 Belodella robusta 1219-1322 1219-1322

19 ?aff Belodina sp. 1317 1317

20 ?Bryantodina sp. 1302-1306 1302-1306

21 Cambrooistodus cambricus 69-123 66 55-123 55-123

22 C. minutus 71-123 71-123 71-123 71-123

23 Chionoconus robustus 928-1082 916-944 916-1082

24 Chirognathus sp. 1306-1326 1306-1326

25 Chosonodina herfurthi 301-312 301-312

26 C. rigbyi 1186-1240 1186-1240

27 Clavohamulus bulbousus 180-187 157-188 157-188

28 C. densus 275-329 317-330 270-291 270-330

29 C.elongatus 158-186 154-163 201-207 207-208 154-208

30 C. hintzei 196-198 185-196 185-198

31 C. lemonei 397 520-740 397-740

32 C. primitus 207 207

33 C. n. sp. 499 505-511 499-511

34 Colaptoconus quadraplicatus 336-853 346-879 330-880 330-880

35 Cordylodus angulatus 220-312 262-312 244 260 240-291 220-312

36 C. caseyi 208 215-309 208-244 226-317 208-317

37 C. drucei 202-245 192-193 192-245

38 C. intermedius 188-312 170-196 214-309 204-278 226-323 240-270 170-323

39 C. lindstromi 202-270 260-270 202-270

40 C. prion 230-309 212-237 226-258 212-309

41 C. proavus 127-135 118-196 190-230 201-204 118-230

42 C. rotundatus 207-312 240-291 207-312

43 C. sp. A 230-258 229-258 229-258

44 Cornuodus longibasis 318-648 669-703 391-870 318-870

45 Cristodus loxoides 397-751 591-721 397-751

46 Dapsilodus? nevadensis 1326-1331 1326-1331

47 Diaphorodus deltatus 471-665 477-874 550-671 471-874

48 D. delicatus 654-873 650-907 650-907

49 D. russoi 1059 520-568 520-1059

50 Dischidognathus primus 1209-1223 1209-1223

51 ?Drepanodus arcuatus 434-999 438-916 420-911 420-999

APPENDIX 3. COMPOSITE STANDARD-EQUIVALENT RANGES OF

CONODONT SPECIES LISTED IN APPENDIX 2

Sections identified in Appendix 2. The column headed CS lists composite-standard ranges as determined in this report. 
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 77

52 D. gracilis 491-868 440-906 440-906

53 D.planus 896-974 896-974

54 "D." simplex 230-267 238-328 238-328

55 D. sp. 1 333-903 333-903

56 D.? sp. 2 386-950 386-950

57 Drepanoistodus angulensis 999-1082 997-1240 997-1240

58 ?D. angulensis 1275-1332 1275-1332

59 D. cf. basiovalis 381-999 333-476 334-999

60 D. aff. forceps 381-1006 464-989 997-1092 401-911 381-1092

61 Eoconodontus notchpeakensis 20-202 53-135 55-196 20-202

62 Erismodus asymmetricus 1275-1332 1275-1332

63 Erraticodon aff balticus 1172-1332 1172-1332

64 ?Erraticodon sp. 1172-1191 1172-1191

65 Eucharodus parallelus 220-984 239-267 238-967 240-880 220-984

66 E. toomeyi 485-757 782-876 420-906 420-906

67 Fahraeusodus marathonensis 618-1072 642-984 611-880 611-1072

68 Falodus sp. 1169-1193 1169-1193

69 Fryxellodontus inornatus 140-158 133-135 128-159 128-159

70 F. lineatus 158-174 128-160 128-174

71 Hirsutodontus hirsutus 174-190 130 124-196 124-196

72 H. rarus 134-184 130 126-196 126-196

73 H. simplex 190-192 166-184 166-192

74 Histiodella altifrons 1006-1082 1009-1063 1006-1082

75 H. donnae 384-414 493 379-401 379-493

76 H. holodentata 1216-1240 1216-1240

77 H. minutiserrata 1050-1082 1036 1036-1082

78 H. sinuosa 1072 1074-1216 1072-1216

79 Iapetognathus preaengensis 202-215 202-215

80 Juanognathus hayesi 891-898 891-896

81 J. jaanussoni 896-1082 879-989 997-1009 898-911 879-1082

82 J. variabilis 684-1006 803-944 660-911 660-1006

83 Jumudontus gananda 773-1006 753-967 811-906 753-1006

84 Loxodus bransoni 257-323 254-309 264-294 235-322 240-291 235-323

85 ?aff Loxodus sp. 1209-1227 1209-1227

86 Macerodus dianae 438-471 391-460 391-471

87 Microzarkodina flabellum 953-974 950-968 950-974

88 Monocostodus sevierensis 188-220 163-196 163-220

89 Multioistodus auritus 1012-1168 1012-1168

90 ?M. auritus 1219 1209

91 M. subdentatus 1193-1230 1193-1230

92 M. sp. 1219 1209

93 Neomultioistodus compressus 984-1082 1012-1168 984-1168

94 Oelandodus sp. cf. O. costatus 629-745 640-740 629-745

95 Oepikodus communis 672-959 666-952 660-911 660-959

96 O. sp. cf. O. evae 995 995

97 aff. O.? minutus 896-1006 891-989 997-1039 891-1039

98 Oistodus bransoni 556-782? 645-874 556-874

99 O. cristatus 1092-1143 1092-1143

100 "O." hunickeni 876-950 876-950

101 "O." inaequalis 479-910 479-910

102 aff. "O." inaequalis 432-791 401-898 401-898

103 O. cf. O. lanceolatus 830-911 830-911

104 O.? lecheguillensis 430-460 430-460
78 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

105 "O." mehli 202-306 240-311 202-311

106 O. multicorrugatus 853-1082 848-959 995-1212 850-898 848-1212

107 "O." triangularis 202-329 237-314 228-318 226-331 202-331

108 O. sp. 1 876-983 876-983

109 "O." sp. 2 749-776 749-776

110 "O." sp. 3 803 804

111 "O." sp. 4 1039-1141 1039-1141

112 "O." sp. 5 229-258 229-258

113 "O." sp. 6 296-312 278 278-312

114 Oneotodus costatus 492-715 514-874 530-906 492-906

115 O. simplex 336-466 461-473 240-401 240-473

116 Paltodus sp. cf. P. deltifer 318-353 318-353

117 P. sp. cf. P. subaequalis 397-533 397-533

118 aff. P. jemtlandicus 378-470 378-470

119 "P." spurius 238-257 261-288 260-301 235-282 250-260 235-301

120 Panderodus spp. 1318-1332 1318-1332

121 ?P. sp. 1219 1219

122 Paracordylodus gracilis 381-672 401-460 381-672

123 Parapanderodus asymmetricus 739-1082 834-989 811-898 739-1082

124 P. emarginatus 618-1082 624-876 601-906 601-1082

125 P. paracornuformis 879-994 1018 879-1018

126 P. striatus 353-1082 392-989 1005-1223 360-911 353-1223

127 Paraprioniodus costatus 1067-1132 1067-1132

128 Paraserratognathus abruptus 526-768 538-770 526-770

129 Paroistodus numarcuatus? 323-406 323-406

130 P. originalis? 896-1044 896-1044

131 P. parallelus 485-974 493-876 391-911 391-974

132 Phakelodus tenuis 66 102 66-102

133 ?Phragmodus flexuosus 1302-1332 1302-1332

134 ?Plectodina sp. 1302 1302

135 Polonodus corbatoi 612-618 612-618

136 Prioniodus sp. 648-660 648-660

137 Proconodontus muelleri 0-125 31-123 55-123 0-125

138 P. serratus 37-123 74-81 37-123

139 Prooneotodus gallatini 20-215 64-127 55-188 20-215

140 P. rotundatus 15-196 65-100 55-196 15-196

141 Prosagittodontus eureka 20 55-123 20-123

142 Protopanderodus aff. arcuatus 791-810 792-810

143 P. elongatus 794-891 822-879 794-891

144 P. elongatus of Repetski 82 381-434 379-420 379-434

145 P. gradatus 739-1082 747-984 997-1219 830-911 739-1219

146 P.? leei 336-444 379-467 360-460 336-467

147 P. leonardii 660-1059 747-989 1000-1055 640-906 640-1059

148 P.? n.spp.1+2 of Repetski 82 397-556 401-540 397-556

149 Protoprioniodus aranda 896-999 884-984 891-911 884-999

150 P. nyinti 896-1006 896-1006

151 P. papiliosus 903 903

152 P. simplicissimus? 502-853 502-853

153 P.? n. sp. 984 984

154 Pteracontiodus cryptodens 965-1044 995-1161 965-1161

155 P. gracilis 1191-1216 1181-1216

156 ?Reutterodus andinus 773-923 758-944 830-911 758-944

157 R.? borealis 648-660 657-697 671-850 648-850
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 79

158 Rossodus manitouensis 227-336 249-319 260-318 229-335 240-291 227-336

159 ?R. manitouensis 263-314 251-264 235-317 235-317

160 R.? n. sp. 245-251 245-251

161 Scalpellodus striatus 456-872 456-872

162 aff "Scandodus" flexuosus 337-858 240-550 240-858

163 S. sinuosus 1000-1247 1000-1247

164 "S." sp. 1 674-874 674-874

165 "S." sp. 3 455-874 455-874

166 "S." sp. 4 1027-1055 1027-1055

167 "S." sp. 5 254-317 251-309 251-317 251-317

168 "S." sp. 6 251-314 243-419 243-419

169 "Scolopodus" acontiodiformis 245-251 330-906 245-906

170 "S." bolites 406-419 391-411 391-419

171 S. cornutiformis 333-336 591-791 333-791

172 "S." filosus 329-853 345-832 360-911 329-911

173 S. floweri 434-477 459-470 291-460 291-477

174 S. multicostatus 593-618 599-713 593-713

175 "S." peselephantis 657-874 657-874

176 aff S. rex 318-654 357-653 330-691 318-691

177 ?"S." sexplicatus 261-314 264-301 261-313 270-291 261-314

178 S. sp. aff. S. striatus 773-826 773-826

179 "S." sulcatus 220-556 249-309 275-281 436-554 260-370 220-554

180 "S." triangularis 336-1082 336-1082

181 ?S. sp. 773-875 773-875

182 Scolopodiform A of E&C82 403-462 403-472

183 Scolopodiform B of E&C82 794-891 669-827 669-827

184 Scolopodiform C of E&C82 697-928 430-773 430-928

185 Scolopodiform D of E&C82 501-879 501-879

186 Scolopodiform E of E&C82 494-863 494-863

187 Scolopodiform F of E&C82 387-980 387-980

188 Semiacontiodus lavadamensis 188 182-192 182-192

189 S. nogamii 180-202 157-196 157-202

190 Stolodus stola 861-879 861-879

191 Teridontus nakamurai 0-318 133-135 126-196 195-314 197-318 226-328 0-328

192 Toxotodus amphigyus ?941 ?941

193 T. carlae 601-911 601-911

194 "Trichonodella" ? sp. Mound 301 301

195 Tripodus laevis 928-1082 943-986 928-1082

196 Tropodus comptus 485-891 491-916 550-891 485-916

197 Ulrichodina abnormalis 489-849 620-911 489-911

198 U. cristata 768 547-864 547-864

199 U. deflexa 473-514 479-579 473-579

200 U.? simplex 599-864 599-864

201 ?U. wisconsinensis 485-709 491-697 491-740 485-740

202 ?U. sp. 448 448

203 Utahconus tenuis 186-196 186-196

204 U. utahensis 188-238 163-196 163-238

205 Variabiloconus bassleri 208-364 251-314 237-318 226-335 240-370 208-370

206 ?Walliserodus ethingtoni 548-800 524-846 524-846

207 N. genus 1 344-416 344-416

208 N. genus 2 669-831 669-831

209 N. genus 4 1179 1179

210 N. genus 5 ?1331 ?1331
80 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

APPENDIX 4. TAXONOMIC NOTES

A majority of the conodonts considered in this report

are identified and named according to the schemes described

in monographs by Ethington and Clark (1982) and Repetski

(1982), which include illustrations of typical forms. In

Appendix 2, the notations “E&C82” and “Rep82,” which

follow the names in the column headed “Species”, indicate

that the species are described and illustrated in either Ethington and Clark (1982) or Repetski (1982). Names in Appendix 2 followed by the notation “App4” are those of conodont

species that either were not described and illustrated in Ethington and Clark or Repetski, or were included under different names in one or both of those reports. References to

illustrations and descriptions of those forms follow in this

appendix.

We do not consider taxonomic questions in detail, propose many revisions, or make any major changes. On the

contrary, we have been concerned primarily that the names

we use refer to the same entities subsumed under those

names in reports on the stratigraphic sections with which we

compare the Shingle Pass section.

Acanthodus lineatus (Furnish, 1938). Typical forms are illustrated by Ethington and Clark (1982, pl. 1, fig. 7)

and Repetski (1982, pl. 1, figs. 1, 3).

Acanthodus uncinatus Furnish, 1938. See Ethington and

Clark (1982, pl. 1, fig. 8) and Repetski (1982, pl. 1,

fig. 4). 

Albiconus postcostatus Miller, 1980, p. 8, figure 2.

Aloxoconus? iowensis (Furnish, 1938) and Aloxoconus? propinquus (Furnish, 1938). Albid coniform representatives of these common Lower Ordovician species

were originally referred to Acontiodus, a practice

that has been followed by most subsequent authors.

Smith (1991) based Aloxoconus on Acontiodus

staufferi Furnish (1938), whose distinctive coniform elements are hyaline, not albid, but also included Acontiodus iowensi Furnish and Acontiodus

propinquus Furnish, both with elements that are solidly albid above the base. Numerous specimens

from the House Limestone in the Shingle Pass section are clearly conspecific with Furnish’s species.

Although it is unlikely that either species is referable to Acontiodus Pander, 1856, we question reference to Aloxoconus because it has been customary

to assign considerable taxonomic weight to the

presence or absence of white matter in conodont elements and it has not been possible to verify Smith’s

(1991, p. 19) assertion that A.? iowensis evolved

into A. staufferi, and that this development involved, among other things, a loss of white matter.

Bergstroemognathus sp. Single specimens in two samples

from the mid-portion of the Shingle Limestone are

components of the apparatus of an indeterminate

species of Bergstroemognathus, which was established by Serpagli (1974, p. 39–40) for B. extensus

(Graves and Ellison, 1941). 

Cambrooistodus cambricus (Miller, 1969), p. 431, pl. 66,

figs. 8–12 (as Oistodus cambricus). Miller, 1980, p.

9–11, text-figure 3A, 4E; pl. 1, figure 9.

Cambrooistodus minutus (Miller, 1969), p. 433, pl. 66, figs.

1–4 (as Oistodus minutus). Miller, 1980, p. 11, textfigure 4F; pl. 1, figure 8.

Chionoconus robustus (Serpagli, 1974), p. 85, pl. 18, figs. 3,

4; pl. 28, figs. 12, 13 (as “Scandodus” robustus).

Ethington and Clark, 1982, p. 94, pl. 10, figs. 25–27

(as “Scandodus” robustus).

Clavohamulus bulbousus (Miller, 1969), p. 435, pl. 64, figs.

1–5 (as Oneotodus bulbousus).

Clavohamulus hintzei Miller, 1969, p. 422–423, pl. 64, figs.

19–24.

Colaptoconus quadraplicatus (Branson and Mehl, 1933).

Coniform elements typical of this widely distributed Lower Ordovician species were originally

referred to Scolopodus, later to Glyptoconus

Kennedy, 1980, and most recently to Colaptoconus

Kennedy, 1994, a new name for Glyptoconus

Kennedy, 1980, non Moellendorff, 1894.

Kennedy’s (1980) concept of the species is followed here. Typical representatives are illustrated

by Kennedy (1980, pl. 1, figs. 39–45). 

Cordylodus. Every sample, from the base to 122 m above the

base of the House Limestone, contains dolabrate

ramiform elements that represent species of Cordylodus. We have assigned these elements to seven

species, at least three of which appear first in the

upper Whipple Cave Formation (Miller, in Taylor

and others, 1989). Although the stratigraphic distribution of Cordylodus is considered critical to definition of the base of the Ordovician System and

Ibexian Series, species-level taxonomy is in a state

of flux (for example, Nicoll, 1990, 1991, 1992a).

Species are identified here in terms of the concepts

discussed by Miller (1980), Ethington and Clark

(1982), and Repetski (1982), whose reports include

synonymies and illustrations of typical specimens. 

Cordylodus drucei Miller, 1980, p. 16, 17, text-figure 4K,

M; pl. 1, figs. 17?, 20, 21, 25.

Cornuodus longibasis (Lindström, 1955), p. 564, pl. 3, fig.

31. Ethington and Clark, 1982, p. 100, pl. 11, figs.

23, 25, 29 (as ?“Scolopodus” aff. “S.” filosus).

Repetski, 1982, p. 40, pl. 17, figs. 11, 12 (as Protopanderodus longibasis).

Diaphorodus. Kennedy (1980) established Diaphorodus for

multielement species previously referred to Acodus

Pander, 1856, a genus whose place in a modern taxonomy for conodonts may always be obscure.

Sweet (1988) concluded that Diaphorodus and Tripodus Bradshaw, 1969 (as reconstructed by Ethington and Clark, 1982) “*** are based on different,

but probably congeneric species***” and thus regarded Diaphorodus as a junior synonym of Tripodus. This is not the place to explore that conclusion,

or for further revision of the generic concepts involved; hence the only change we advocate is reference to Diaphorodus of the species described by

Ethington and Clark (1982) and Repetski (1982) as

Acodus deltatus and A. delicatus, and the species

described by Serpagli (1974) as A.? russoi. 
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 81

Diaphorodus delicatus (Branson and Mehl, 1933). In Shingle

Pass collections this species is represented by only

a few elements, the most distinctive a geniculate coniform element that probably occupied the M position in the apparatus and has a very short posterior

extension of the base. Kennedy (1980) assembled

form species originally described by Branson and

Mehl (1933) and provided an extensive synonymy,

but his illustrations of type material and associated

forms from the Jefferson City Formation of Missouri leave much to be desired. Better illustrations are

provided by McTavish (1973, pl. 1, figs. 1–9,

12–14), who was the first to reconstruct D. delicatus

but referred it to Acodus deltatus deltatus Lindström. Repetski (1982) recognized D. delicatus (as

Acodus delicatus) in his collections from the El Paso

Group of Texas, where the species has essentially

the same range as in the Shingle Pass section. Ibex

district ranges suggest that Ethington and Clark

(1982) may have included representatives of D. delicatus in the upper part of the range of a species for

which they used the name Acodus deltatus. The Ibex

district specimens illustrated, however, are referable to D. deltatus, not D. delicatus.

Diaphorodus deltatus (Lindström, 1955). A recurrent group

of elements similar or identical to those assembled

by Ethington and Clark (1982, p. 18–19, text-fig.

4; pl. 1, figs. 1–6) in Acodus deltatus Lindström,

1955, characterizes Shingle Pass collections from

138 m above the base of the Parker Spring Formation to 72 m above the base of the Shingle Limestone. Above the latter level, elements of

Diaphorodus are less abundant and for a few

meters appear to represent both D. delicatus and

D. deltatus, in which the base of the geniculate coniform M element extends somewhat farther posteriorly than is apparently the case with

comparable structures in the apparatus of D. delicatus. In collections from an interval in the Parker

Spring Formation 31 m to 112 m above its base

are single specimens that clearly represent a species of Diaphorodus with elements closely related

morphologically to those of D. deltatus but probably not conspecific. This may be the same species

that is represented in the Ibex area of Utah, in the

lower part of the Fillmore Formation below the

one that yields clear representatives of D. deltatus.

Diaphorodus russoi (Serpagli, 1974), p. 35-37, text-figure

5; pl. 8, figs. 1–5; pl. 20, figs. 7, 8 (as Acodus?russoi). Repetski, 1982, p. 13, pl. 3, figs. 1–5 (as

Acodus? russoi). 

Eoconodontus notchpeakensis (Miller, 1969), p. 438, pl. 66,

figs. 13–29 (as Proconodontus notchpeakensis).

Miller, 1980, p. 22, text-figs. 3D, E; pl. 1, figs.

10–12.

Eucharodus parallelus (Branson and Mehl, 1933), p. 59, pl.

4a, figure 17. Ethington and Clark, 1982, p. 38, 39,

pl. 3, figure 8 (as “Drepanodus” parallelus).

Kennedy, 1980, p. 58–60, pl. 1, figs. 35–38.

Eucharodus toomeyi (Ethington and Clark, 1964). Ethington

and Clark, 1982, p. 39–40, pl. 3, figure 11 (as

“Drepanodus” toomeyi).

Fahraeusodus marathonensis (Bradshaw, 1969). Ethington

and Clark, 1982, p. 55–56, pl. 5, figs. 14, 19, 20, 23,

24, 27 (as “Microzarkodina” marathonensis).

Fryxellodontus inornatus Miller, 1969, p. 426, pl. 65, figs.

1–10, 12, 16, 23–25.

Fryxellodontus lineatus Miller, 1969, p. 429, pl. 65, figs.

17–22, 26–29.

Glyptoconus Kennedy, 1980. See Colaptoconus Kennedy,

1994.

Hirsutodontus hirsutus Miller, 1969, p. 431, pl. 64, figs. 25,

26, 29–31.

Hirsutodontus rarus Miller, 1969, p. 431, pl. 64, figs. 36–42.

Hirsutodontus simplex (Druce and Jones, 1971). Miller,

1969, pl. 64, figs. 27, 28, 32–35 (as Hirsutodontus

hirsutus).

Iapetognathus preaengensis Landing, in Fortey and others,

1982, p. 124, 126, figs. 6B, C, 8B, C, H. 

Jumudontus gananda Cooper, 1981, pl. 31, figure 13. Ethington and Clark, 1982, pl. 2, figs. 9, 10. Nicoll,

1992b, figs. 7, 8. This species is represented by its

distinctive Pa elements in just 10 Shingle Pass samples, and in a majority of these by just one or two

specimens. Nicoll (1992b) has reconstructed the

complete septimembrate apparatus of Jumudontus

gananda, but only a few of the ramiform types he

included are represented in our samples from Shingle Pass. Although all of the ramiform elements we

refer to J. gananda are similar to those Nicoll includes in the species’ apparatus, there are also differences that are difficult to evaluate. The latter

may indicate considerable variability in various elements of the apparatus, or they may indicate that

the Shingle Pass specimens represent an undescribed species or subspecies.

Monocostodus sevierensis (Miller, 1969), p. 418, pl. 63,

figs. 25–31; pl. 64, figs. 49–54 (as Acodus sevierensis). Miller, 1980, p. 26–27, text-figure 4U; pl.

2, figs. 8,9.

Neomultioistodus compressus Harris and Harris, 1965, p.

43–44, pl. 1, figs. 7a–c. Ethington and Clark, 1982,

p. 58–59, pl. 6, figs. 8–11, 16 (as Multioistodus

compressus). 

Oepikodus sp. cf. O. evae (Lindström, 1955). Elements typical of the apparatus of O. evae are assembled by

Lindström and illustrated in Ziegler, ed., 1977, p.

253–255, Oepikodus-Plate 1, figs. 6–11. Specimens

from Shingle Pass samples are closely comparable,

but process sides of P elements lack the ledges characteristic of typical representatives of the species.

The significance of this feature is uncertain, hence

our identification is tentative.

Oistodus multicorrugatus Harris, 1962. Ethington and Clark,

1982, p. 68–70, text-figure 17; pl. 7, figs. 9, 10,

12–14. Single specimens reported by Ethington and

Clark (1982) from samples 250 and 340 ft above the

base of Ibex-area section H, but the first full apparatus is in a sample 330 ft above the base of Ibexarea section ST, and we take this as the level of first

appearance of the species in the Ibex area.
82 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Oneotodus costatus Ethington and Brand, 1981, p. 242–245,

figs. 2B,D,G,H; 2A, D–M. O. costatus had evidently not been determined to be distinct from O. simplex when Ethington and Clark prepared their report

on Ibex-area conodonts. Hence, we initially assumed that the specimens they logged in their tables

as aff. Oneotodus simplex were like the one they illustrated, which is from a sample 260 ft above the

base of Hintze’s Square Top section and would now

be referred to Oneotodus costatus. In their discussion of the Acodus deltatus/Oneotodus costatus

Zone, however, Ross and others (1993) noted that

O. costatus appears first 600 ft (183 m) above the

base of the Fillmore Formation, whereas Ethington

and Clark (1982) identified as “aff. O. simplex”

specimens from as low as 425 ft (130 m) and 559 ft

(or 170 m) above the base of the Fillmore in

Hintze’s C and M Sections. We have not seen these

specimens, but we suspect that they should now be

referred to Oneotodus simplex, or to an unnamed

species intermediate between O. simplex and O.

costatus. In the faunal lists of Appendixes 2 and 3,

we log these specimens as O. simplex. Ji and Barnes

(1994) established O. costatus as type species of a

new genus, Stultodontus, which also includes species with apparatuses composed of elements like

those we refer to Paraserratognathus abruptus. 

Oneotodus simplex (Furnish, 1938). Ethington and Brand,

1981, p. 239–242, text-figure 1A, C, E, F, I; textfigure 2B, C.

Paltodus sp. cf. P. deltifer (Lindström, 1955). A few Shingle

Pass specimens are similar morphologically to the

types of multielement P. deltifer. They may represent P. deltifer or an unnamed, closely related species. Typical P. deltifer is diagnosed and illustrated

by Lindström in Ziegler, ed., 1977, p. 421–423,

Paltodus-Plate 1, figs. 1–4.

Paltodus sp. cf. P. subaequalis Pander, 1856. Specimens in

three Shingle Pass samples resemble the elements

of multielement P. subaequalis as reconstructed by

Lindström in Ziegler, ed., 1977, p. 427–428, Paltodus-Plate 1, figs. 7–9, but cannot be assigned to that

species with certainty. The elements may represent

an undescribed, unnamed species.

Parapanderodus emarginatus (Barnes and Tuke, 1970). Ethington and Clark, 1982, p. 99, 100, pl. 11, figs.

15,16 (as “Scolopodus” emarginatus).

Parapanderodus paracornuformis (Ethington and Clark

1982), p. 102, figure 25, pl. 22, figure 21 (as Scolopodus paracornuformis).

Parapanderodus striatus (Graves and Ellison, 1941). Ethington and Clark, 1982, p. 100, 101, pl. 11, figs. 27,

28 (as “Scolopodus” gracilis).

Paraserratognathus abruptus (Repetski, 1982). Repetski

(1982 p. 45–46, pl. 21, figs. 1, 3) provided good

views of the type specimen of this distinctive species, which he referred to Scolopodus. One year later, An (1983) established Paraserratognathus for

the species P. obesus Yang, which was diagnosed

for the first time in the same report and is based on

elements that are closely similar morphologically to

the types of Scolopodus abruptus. Elements typical

of Scolopodus species are hyaline, however, whereas those of Paraserratognathus have albid cusps.

Thus we have transferred Repetski’s Scolopodus

abruptus to Paraserratognathus in the faunal lists

of Appendixes 2 and 3. Nomenclature of this taxon

was further complicated, however, by Smith (1991)

and Ji and Barnes (1994). Smith erected Wandelia

for species with elements closely related or identical morphologically to those of Scolopodus abruptus and regarded Paraserratognathus as a probable

junior subjective synonym of Oneotodus. He did

not mention S. abruptus, which may be the senior

synonym of Wandelia guyi, the type species of

Wandelia. Ji and Barnes established Stultodontus

for Oneotodus costatus Ethington and Brand, 1981

and noted that Scolopodus abruptus may be a senior

synonym of their species S. pygmaeus. They do not

mention Paraserratognathus in connection with

their discussion of Stultodontus. In collections from

the Shingle Pass section, we have only a few specimens referable to Paraserratognathus abruptus,

which makes its debut 55 m above the base of the

deltatus /costatus Zone and ranges upward to a level a few meters above the base of the andinus Zone.

Specimens in the upper two-thirds of the deltatus/

costatus Zone intergrade morphologically with

those of Oneotodus costatus, which is thus a credible ancestor and should perhaps be included in the

same genus. Should that revision ultimately be

made, we suggest that the appropriate genus is

Paraserratognathus, not Wandelia or Stultodontus. 

Paroistodus numarcuatus (Lindström, 1955)? Nine samples

from the lower part of the Parker Spring Formation

contain a few elements that may represent P. numarcuatus but cannot be referred to that species

with certainty. Elements of P. numarcuatus have

most recently been described and illustrated by

Stouge and Bagnoli (1988, p. 127–128, pl. 8, figs.

8–11), who included a synonymy.

Paroistodus originalis (Sergeeva, 1963)? Nine samples from

late Ibexian and early Whiterockian strata in the upper Shingle Limestone have yielded elements that

may represent this species but cannot be assigned to

it with confidence. Typical P. originalis was described and illustrated by Löfgren (1978, p. 69–71,

pl. 1, figs. 22–25; text-fig. 28), who demonstrated

in a later report (Löfgren, 1995) that an early population of P. originalis was probably ancestral to

species like “Cordylodus” horridus Barnes and

Poplawski, 1973, which has been reported by Harris and others (1979) from the Whiterockian Antelope Valley Limestone at two localities in the

Toquima Range of central Nevada.

Phakelodus tenuis (Müller, 1959), p. 457–458, pl. 13, figs.

11, 13, 14, 20c (as Oneotodus tenuis).

Polonodus corbatoi (Serpagli, 1974), p. a47–48, pl. 10,

figs. 1a–6c; pl. 22, figs. 1–5 (as Fryxellodontus?

corbatoi).
IBEXIAN REFERENCE SECTION, EGAN RANGE, NEVADA 83

Prioniodus sp. Three samples from the lower part of the

Shingle Limestone contain very small, inconspicuously denticulated elements that compare favorably

in many (but not all) respects with the ones from

beds 9 and 11 of the Cow Head Group in Newfoundland identified as Prioniodus elegans Pander

by Stouge and Bagnoli (1988). Specific assignment

of these specimens will require further study.

Proconodontus muelleri Miller, 1969, p. 437, pl. 66, figs.

30–40.

Proconodontus serratus Miller, 1969, p. 438, pl. 66, figs.

41–44.

Prooneotodus gallatini (Müller, 1959), p. 457, pl. 13, figs.

5–10, 18. Müller and Hinz, 1991, p. 37, pl. 24, figs.

1–28.

Prooneotodus rotundatus (Druce and Jones, 1971), p. 62, 63,

text-figure 22c, d; pl. 9, figs. 10a–13b.

Prosagittodontus eureka (Müller, 1959), p. 461, pl. 14, figure 6 (as Sagittodontus eureka). Miller, 1969, pl.

65, figs. 32, 33 (as Sagittodontus eureka).

Protopanderodus elongatus Serpagli, 1974. The few Shingle

Pass specimens referred to this species are closely

similar to typical forms illustrated and described by

Serpagli (1974, pl. 16, figs. 8a–11c; pl. 25, figs.

13–16; pl. 30, figure 4; text-fig. 16) and to the single specimen illustrated by Ethington and Clark

(1982, pl. 9, figure l5).

Protopanderodus elongatus Serpagli, 1974 of Repetski,

1982. El Paso specimens included in P. elongatus

by Repetski (1982, pl. 16, figs. 4, 5, 7, 9, 11, 12) exhibit a similar range of morphologic variation, but

differ from the types in being hyaline, rather than

albid. Morphologically identical specimens from

Shingle Pass samples group with “scandodontiform” elements to form a distinctive multielement

assembly, which probably represents a species for

which there are currently no appropriate generic or

specific names. This species has a range in the

Shingle Pass section comparable to that in

Repetski’s (1982) El Paso section. 

Protopanderodus gradatus Serpagli, 1974, pl. 15, figs.

5a–8b; pl. 26, figs. 11–15; pl. 30, figs. 1a,b; text-fig.

17. 

Protopanderodus leonardii Serpagli, 1974, pl. 16, figs.

1a–4c; pl. 27, figs. 12–16; text-fig. 18.

Protoprioniodus nyinti Cooper, 1981, p. 176, 178, pl. 29,

figs. 1–8, 11, 12.

Protoprioniodus simplicissimus McTavish, 1973, p. 48–49,

pl. 2, figs. 6, 8, 9.

Protoprioniodus? n. sp. One denticulate element from the

Shingle Limestone occurs with others that clearly

represent a species of Protoprioniodus. Characteristically, however, elements of Protoprioniodus

species are adenticulate and that makes assignment

of these forms uncertain. They may indicate transition to Fahraeusodus, which is similar morphologically and of which Protoprioniodus is a likely

ancestor. However, the specimens in question are

younger than the earliest Fahraeusodus, so they

may indicate iterative development of species of

that genus from Protoprioniodus. Further study is

obviously needed. 

Rossodus manitouensis Repetski and Ethington, 1983, p.

289–301, figs. 1–4. Ethington and Clark, 1982, p.

118, pl. 13, figs. 21, 23, 25–27 (as New genus 3). 

?Rossodus manitouensis Repetski and Ethington, 1983. Ethington and Clark, 1982, p. 119, pl. 3, figure 26 (as

?New genus 3).

“Scolopodus” triangularis Ethington and Clark, 1964, p.

699, pl. 115, figs. 2–4, 8, 9. Ethington and Clark,

1982, included this species in the apparatus on

which they based their concept of “Scolopodus”

gracilis. We regard S. gracilis as a junior synonym

of Drepanodus striatus Graves and Ellison, 1941,

and have elsewhere included it in Parapanderodus.

Although “S.” triangularis has essentially the same

range as P. striatus in the Shingle Pass section,

some elements are albid and thus rather different

than the typically hyaline components of the P. striatus apparatus. For this reason, we report the range

of this species separate from that of P. striatus.

Semiacontiodus lavadamensis (Miller, 1969), p. 420, pl. 64,

figs. 55–61 (as Acontiodus lavadamensis). Miller,

1980, p. 33, pl. 2, figure 4.

Semiacontiodus nogamii (Miller, 1969), p. 421, pl. 63, figs.

11–20, 41–50 (as Acontiodus (Semiacontiodus)

nogamii). Miller, 1980, p. 32, figure 4V, W; pl. 2,

figs. 10–12.

Teridontus nakamurai (Nogami, 1967). Miller, 1969, p. 435,

pl. 63, figs. 1–10 (as Oneotodus nakamurai). Miller, 1980, p. 34, figure 40, pl. 2, figs. 15,16.

Toxotodus amphigyus Smith, 1991, p. 64–65, figure 37a–d.

Toxotodus carlae (Repetski, 1982), p. 49–50, pl. 23, figs. 1,

2 (as Scolopodus carlae) Smith, 1991, p. 65,

figure 37e, f.

“Trichonodella”? sp. Mound, 1968, p. 420–421, pl. 6, figure

73. Ethington and Clark, 1971, pl. 1, figure 9 (as

Clavohamulus? sp.). The albid elements of this taxon are rare, but widespread geographically. They

are certainly not referable to Trichonodella, a junior

synonym of Plectodina, and probably not to

Clavohamulus, whose elements show some similarity but are hyaline.

Tropodus comptus (Branson and Mehl, 1933). Ethington and

Clark, 1982, p. 114–116, text-fig. 34; pl. 13, figs. 6,

7, 11–13 (as Walliserodus comptus). Kennedy,

1980, p. 65–66, pl. 2, figs. 20–27.

Utahconus tenuis Miller, 1980, p. 36, text-fig. 4T; pl. 2,

figs. 5–7.

Utahconus utahensis (Miller, 1969), p. 436, pl. 63, figs.

21–24, 33–40; pl. 64, figs. 46–48 (as Paltodus utahensis). Miller, 1980, p. 35, text-figs. 3B, F, G; pl.

2, figs. 1, 2.
84 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Variabiloconus bassleri (Furnish, 1938) p. 33l, pl. 42, figure 1. Ethington and Clark,1982, p. 74, pl. 8, figs.

11, 12 (as “Paltodus” bassleri). Druce and Jones

(1971) regarded Paltodus bassleri and P. variabilis of Furnish (1938) as components of Scolopodus

bassleri. Sweet and Bergström (1972) added Furnish’s Acodus oneotensis and Oistodus? triangularis to this multielement assembly, for which no

generic name was then available. Subsequently,

Ethington and Clark (1982) noted that Furnish had

not documented the full range of morphologic

variation within each of his form species and concluded that neither A. oneotensis nor O.? triangularis were components of the assembly. Their

conclusion was followed by Repetski (1982).

Landing and others (1986), however, regarded not

only A. oneotensis and P. bassleri (including P.

variabilis), but also Scolopodus sulcatus Furnish,

1938, and several other named form species as apparatus components of a species they named Variabiloconus bassleri (Furnish). In the Shingle Pass

section, A. oneotensis, S. sulcatus, and P. bassleri

(including P. variabilis) all appear first within a

few meters of one another in the House Formation. However, the three species have different upper range limits and, as noted by Ethington and

Clark (1982), typical A. oneotensis is part of a

symmetry-transition series that suggests it represents a species different from the others grouped

by Landing and others in V. bassleri. Smith (1991)

tentatively accepted the reconstruction of Landing

and others but noted that his Greenland collections

were too small to serve as an adequate test of that

reconstruction. Because much obviously remains

to be learned about the architecture and distribution of this species, we refer Shingle Pass specimens conservatively to V. bassleri, “Acodus”

oneotensis, and Scolopodus sulcatus. “Oistodus”?

triangularis of Furnish (1938), regarded as part of

this apparatus by Sweet and Bergström (1972) and

several subsequent authors, is quite rare in our

Shingle Pass collections and is logged separately.
Upper Ordovician–Silurian Macrofossil 

Biostratigraphy of the Eastern Great Basin,

Utah and Nevada

By Peter M. Sheehan and Mark T. Harris

EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN, WESTERN UNITED STATES

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1579–C

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1997
I

CONTENTS

Abstract ................................................................................................................................. 89

Introduction .......................................................................................................................... 89

The Late Ordovician Glaciation and Mass Extinction ................................................. 90

Depositional Framework ............................................................................................... 90

Acknowledgments ........................................................................................................ 91

Upper Ordovician Biostratigraphy ........................................................................................ 92

The Carbonate Platform ............................................................................................... 92

Upper Ordovician Corals ..................................................................................................... 92

Carbonate Platform Corals ........................................................................................... 92

Carbonate Ramp Corals ............................................................................................... 94

Upper Ordovician Brachiopods ............................................................................................ 94

Carbonate Platform Brachiopods ................................................................................. 95

Carbonate Ramp Brachiopods ...................................................................................... 96

Carbonate Ramp Trilobites .................................................................................................. 96

Upper Ordovician Trace Fossils ........................................................................................... 97

Hirnantian–Late Ordovician Eustatic Sea-level Lowstand .................................................. 97

Silurian Biostratigraphy ....................................................................................................... 97

The Carbonate Platform ............................................................................................... 98

The Carbonate Ramp .................................................................................................... 99

Conversion of the Carbonate Ramp to a Carbonate Slope............................................ 99

The Carbonate Slope .................................................................................................... 99

Silurian Brachiopod Biostratigraphy .................................................................................... 100

Lower and Middle Llandoverian Carbonate Platform Brachiopods ............................. 100

Lower Upper Llandoverian (C1-3) Carbonate Platform Brachiopods........................... 100

Upper Llandoverian (C4-5) Carbonate Platform Brachiopods ...................................... 101

C6–Lower Wenlockian Carbonate Platform Brachiopods ............................................ 101

Middle Wenlockian and Younger Carbonate Platform Brachiopods............................ 102

Carbonate Slope Brachiopods ....................................................................................... 103

Wenlockian Brachiopods from Roberts Creek Mountain Region ............................... 103

Ludlovian Brachiopods from Roberts Creek Mountain Region ................................... 103

Pridolian Brachiopods from Roberts Creek Mountain Region ..................................... 104

Silurian Brachiopods from Other Regions on the Slope ............................................... 104

Summary of Silurian Brachiopod Biostratigraphy................................................................ 105

Silurian Corals....................................................................................................................... 105

Silurian Ostracodes ............................................................................................................... 107

Silurian Algae........................................................................................................................ 107

Sequence Stratigraphy and Biostratigraphic Boundaries...................................................... 107

Conclusions ........................................................................................................................... 108

References Cited ................................................................................................................... 108

Appendix. Species Listed in Text ........................................................................................ 112
CONTENTS II

FIGURES

1. Correlation chart for the principal Upper Ordovician, Llandoverian, and Wenlockian formations

and members from the carbonate shelf, carbonate ramp, and carbonate slope in the eastern Great Basin................... 91

2. Index map of localities discussed in text ....................................................................................................................... 92

3. Diagram of Ordovician faunal intervals ........................................................................................................................ 93

4. Diagram of Silurian faunal intervals.............................................................................................................................. 98

TABLES

1. Colonial corals from the Ely Springs Dolomite described by Pandolfi (1985)............................................................. 94

2. Brachiopods reported by Sheehan (1969) from the Ely Springs Dolomite in Nevada and Utah .................................. 95
89

Upper Ordovician–Silurian Macrofossil Biostratigraphy

of the Eastern Great Basin, Utah and Nevada

By Peter M. Sheehan1 and Mark T. Harris2

ABSTRACT

In the eastern Great Basin during the Late Ordovician,

a carbonate platform developed on the broad shelf region

and received marine deposits. Along its western margin lay

a westward-facing carbonate ramp. Near the end of the

Ordovician, the carbonate platform was exposed in a

regression, and the ramp shallowed to within wave base. In

Early Silurian, transgression reflooded the shelf. In late

Early Silurian, the continental margin stepped backward

toward the craton, and the gently inclined carbonate ramp

changed to an abrupt carbonate slope, with an accompanying shift in depositional style. Massive, fine-grained carbonates typify the upper slope deposits; turbidites and

slumps (uncommon on the carbonate ramp) appear on the

lower slope along with debris flows, gravity flows, and

other features consistent with an active slope.

The macrofossil biostratigraphy of the Upper Ordovician and Silurian deposits of the Great Basin has been studied

for more than 100 years, and a synthesis of the macrofossil

forms and their stratigraphic distribution is appropriate to this

volume. The most abundant and well-studied macrofossils

are brachiopods, corals, and trilobites, but the level of knowledge of these groups varies widely. On both the carbonate

platform and carbonate slope, the biostratigraphic distribution of Silurian brachiopods (a group of low diversity) is well

established; that of Upper Ordovician brachiopods, however,

is not, though they are abundant, well preserved, and diverse.

Upper Ordovician corals on the carbonate platform have been

placed into two faunizones and are more clearly understood

than those on the carbonate ramp. The biostratigraphy of Silurian corals is well documented for the Middle and Upper Silurian but not for the lower part of the Silurian. Upper

Ordovician trilobites are rare on the carbonate platform but

common in carbonate ramp deposits; they have been studied

primarily on the carbonate ramp.

1 Department of Geology, Milwaukee Public Museum, 800 West Wells

St., Milwaukee, WI 53233. 2Department of Geosciences, University of Wisconsin–Milwaukee,

Milwaukee, WI 53201.

Sequence stratigraphic study of Silurian rocks on the

carbonate platform has revealed strong correlation of

sequences with macrofaunal biostratigraphy. Ordovician

biostratigraphic intervals are not adequately documented to

determine whether sequence boundaries match biostratigraphic boundaries.

INTRODUCTION

The biostratigraphic distribution of Late Ordovician

and Silurian fossils in the eastern Great Basin has been studied since Hayden (1872) first reported tabulate corals in

northern Utah. An extensive literature on macrofossils has

been developed, but this literature is in such a diverse variety

of publications that it is difficult to access. This investigation

is a synthesis of the current understanding of the biostratigraphic distribution of macrofossils in Utah and Nevada.

The most abundant and well-studied macrofossils are

brachiopods, corals, and trilobites, but knowledge of these

groups is incomplete. On both the carbonate platform and

carbonate slope, the biostratigraphic distribution of Silurian

brachiopods is well established; Upper Ordovician brachiopods, however, are virtually unstudied. Upper Ordovician

corals have been studied on the carbonate platform but not on

the carbonate ramp. The biostratigraphy of Silurian corals is

well documented for the Middle and Upper Silurian but not

for the lower part of the Silurian. Upper Ordovician trilobites

have been studied primarily on the carbonate ramp. 

Graptolite and conodont biostratigraphy is not treated

in this report, but macrofossil distributions are consistent

with graptolite and conodont biostratigraphy. Graptolites

have been widely studied in the ramp and slope settings.

Conodonts have been studied from both platform and slope

environments. 

Upper Ordovician and Silurian stratigraphy and lithofacies patterns have been extensively studied. Summaries and

an introduction to the literature are available for the Ordovician in Ross (1977) and Sheehan (1989) and for the Silurian

in Poole and others (1977), Johnson and Murphy (1984),

Sheehan (1989), and Sheehan and Boucot (1991). The primary stratigraphic units are shown in figure 1. Localities

referred to in the text are shown in figure 2.
90 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

THE LATE ORDOVICIAN GLACIATION

AND MASS EXTINCTION

The most notable biostratigraphic change during this

time interval is a clearly defined mass extinction that affected

the record of all fossil groups at the end of the Ordovician.

The mass extinction was caused by glaciation centered in

Africa, which produced glacio-eustatic excursions in sea

level and climatic change (Sheehan, 1973, 1975, 1988;

Brenchley, 1989). Glaciation probably lasted less than a million years, but the duration is still poorly constrained.

Numerous small eustatic sea-level changes probably accompanied an overall decline in sea level. Post-glacial sea-level

rise was rapid. (See discussion and additional references in

Brenchley, 1989.) This worldwide extinction event decimated virtually all groups of organisms. (See Sheehan, 1973,

1988; Berry and Boucot, 1973; Brenchley, 1989.) 

As a result of the extinction event, the endemic epicontinental-sea brachiopod fauna of North America was eliminated (Sheehan and Coorough, 1990). Graptolite

(Skevington, 1978; Berry, 1979) and conodont (Barnes and

others, 1979; Sweet and Bergström, 1984; Barnes and Bergström, 1988) faunas were devastated. 

Two effects of the extinction are important for biostratigraphy. First, because of the extinction, earliest Silurian faunas are of low diversity, and refined correlation in

the Early Silurian is difficult compared to the Late Ordovician. Early Silurian conodont zones, for example, are long

ranging and have low diversity. Second, Late Ordovician

faunas were endemic, and correlation between North America and other tectonic plates is difficult. This pattern is the

basis of the need to establish a separate sequence of stages

and series for the Late Ordovician in North America. The

Cincinnatian Series and the Edenian, Maysvillian, and

Richmondian stages are used only in areas containing

endemic North American faunas.

The extinction event selectively eliminated endemic

taxa (Sheehan and Coorough, 1990). As a result the Silurian

fauna was cosmopolitan, and long-distance correlation is relatively easy. The Llandoverian and Wenlockian series and

their subdivisions can be recognized worldwide (Berry and

Boucot, 1970). Because of the distinct dichotomy of faunas,

most biostratigraphers have focused on either the Ordovician

or the Silurian-Devonian interval.

DEPOSITIONAL FRAMEWORK

Following late Precambrian rifting (Stewart, 1976,

1980; Bond and others, 1985), a passive continental margin

was established in western North America. Thermal subsidence of thinned and stretched continental basement to the

east of the rift produced a broad shelf region between the

margin and a hingeline in central Utah (Bond and others,

1985). The passive margin evolved normally through the

interval of time considered in this report. During the early

Paleozoic, the edge of the shelf retreated toward the craton in

a series of back steps along probable growth faults. During

the Late Ordovician and Silurian, a broad carbonate platform

developed on the shelf (fig. 1). In the late Middle Ordovician,

regression was accompanied by widespread deposition of

quartz sand (Eureka and Swan Peak quartzites). In the Late

Ordovician (probably during the latest Edenian, Leatham,

1985), a transgression initiated marine deposition across a

broad carbonate platform in eastern Nevada and western

Utah. Along the western margin of the carbonate platform, a

westward-facing carbonate ramp led to deep water west of

the continental margin, which was located in what is now

central Nevada (Carpenter and others, 1986). Carbonate

ramp facies become progressively finer grained down the

ramp. The ramp was stable, and few gravity-emplaced

deposits originated on the ramp.

Near the end of the Ordovician, a glacio-eustatic regression of 70 m or more drained epicontinental seas around the

world (Sheehan, 1973, 1988; Berry and Boucot, 1973;

Brenchley, 1989). In the Great Basin the shallow carbonate

platform was exposed (Sheehan and Boucot, 1991). Along

the platform margin, proximal ramp facies shallowed to

within wave base. Distal ramp environments must have

remained below wave base, but direct sedimentologic evidence for this is lacking. The ramp profile was reestablished

when the Early Silurian transgression reflooded the shelf.

During the latter part of the Early Silurian, the margin

stepped backward toward the craton once more, and the

gently inclined carbonate ramp was converted to an abrupt

carbonate platform margin (Johnson and Potter, 1975; Hurst

and Sheehan, 1985; Hurst and others, 1985; Sheehan, 1986,

1989). The change from a gently inclined carbonate ramp to

a steep carbonate slope was accompanied by a shift in depositional style. During the carbonate ramp phase, gradational

facies changes reflect gradual change from shallow shelf to

distal ramp settings. Turbidites and slumps were uncommon

on the carbonate ramp. The depositional pattern on the steep

slope was clearly different: Upper slope deposits are massive,

fine-grained carbonates. Lower slope deposits are marked by

carbonate turbidites, slumps, and debris flows. Stratigraphic

sections on the carbonate slope reveal intermittent sedimentation, consistent with an active slope, characterized by sedimentary bypassing, erosion, slumping, and gravity flows.

The abrupt platform margin prograded slowly westward

throughout the Silurian and into the Early Devonian until the

passive continental margin changed to a compressive margin

during the Antler orogeny. 

Two distinct basins developed on the platform margin

(fig. 2), separated by the east-west-trending Tooele arch

(Sheehan and Boucot, 1991). Hintze (1982) named them

the Ibex and the North Utah basins. Open-marine sedimentation in the North Utah basin continued through the Llandoverian, but in the early Wenlockian the basin shallowed to

near sea level. During the remainder of the Silurian, nondeposition or restricted marine deposition dominated in the

North Utah basin.
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 91

Faunal Assemblages

Slope

slope

faunas

open marine

mollusc fauna

?

(unknown)

open marine

soft substrate

fauna

Shelf

Series

&

Stages

Lithostratigraphy

Sequences

Slope Shelf

Wenlock Llandovery Ashgill

Hirnantian

Cardoc Telychian Aeronian Rhuddanian

Brachyprion

open marine

shelly fauna

Roberts

Mountains

Formation

upper part,

Hanson Creek

Formation

lower part,

Hanson

Creek

Formation

Lone

Mountain

Dolomite

Jacks

Valley

Member

Portage

Canyon

Member

Gettel

Member

Decathon Member

High Lake Member

Tony Grove

Lake Member

Floride

Member

Lost

Canyon

Member

Barn Hills Mbr

Ibex Mbr

Bloomington

Lake

Member

Deep Lake

Member

Paris Peak Mbr

Laketown Dolomite

Ely Springs Dolomite

Fish Haven Dolomite

S6

S5

S4

S3

S2

S1

O5

O4

O3

O2

O1

Virgiana

open marine

shelly fauna

Thalassinoides

open marine

shelly fauna

Pentameroides

open marine

shelly fauna

Pentamerus

open marine

shelly fauna

open marine

shelly fauna

?

Hiatus

In the Ibex basin open-marine deposition continued

well into the Wenlockian, after which nondeposition or

restricted-marine deposition dominated throughout the Silurian. Along the carbonate platform margin to the west and

on the southern part of the platform in southern Nevada and

adjacent California, shallow, open-marine deposition continued throughout the Silurian (Sheehan and Boucot, 1991).

ACKNOWLEDGMENTS

The authors thank Walter C. Sweet and Michael E. Taylor for extensive and constructive reviews of the manuscript.

The work was supported by U.S. National Science Foundation grants to Peter Sheehan (EAR-9317719) and Mark

Harris (EAR-9303966).

Figure 1. Correlation chart for the principal Upper Ordovician, Llandoverian, and Wenlockian formations and members from the carbonate shelf, carbonate ramp, and carbonate slope in the eastern Great Basin. Faunal assemblages and

stages are discussed in the text. Stratigraphic sequences from Harris and Sheehan (1992, 1996).
92 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

0 100 KILOMETERS

37 ̊

114 ̊

NORTH UTAH

BASIN

IBEX BASIN

carbonate

platform

margin

1

3

5

9

4

6

8

7

10

11

12 13

14 15

16

20

21 22

23

24

25

26

17

18

19

28

29

30 31

34

32

33

35

36

27

2

TOOELE ARCH

IDAHO

NEVADA

UTAH

UPPER ORDOVICIAN 

BIOSTRATIGRAPHY

THE CARBONATE PLATFORM

Upper Ordovician platform dolomites are assigned to

the Fish Haven Dolomite in northern Utah and to the Ely

Springs Dolomite in central and western Utah and eastern

Nevada (Budge and Sheehan, 1980a). A wide variety of

facies occurs, ranging from restricted-marine laminites (tidal

flats) to open-marine sediments deposited within and below

storm wave base.

Subtidal dolomites and dolomitic limestones with

storm beds mark the upper ramp west of the platform. In

more distal ramp settings progressively more argillaceous

limestones predominate, and deposition was below storm

wave base.

UPPER ORDOVICIAN CORALS

CARBONATE PLATFORM CORALS

Budge (1972, 1977) described Upper Ordovician and

Lower Silurian corals from many localities on the carbonate

platform. He recognized two faunizones based on corals from

the Ely Springs and Fish Haven Dolomites. (Figure 3 outlines

Ordovician faunal intervals for macrofossils of this area.)

Budge (1972) recognized a “Streptelasma” haysii

Faunizone (now the Grewingkia haysii Faunizone based on

reassignment of the species by Elias, 1981) at the base of the

Ely Springs Dolomite. This faunizone is present in the Ibex

and Barn Hills Members of the Ely Springs Dolomite. Corals

restricted to the faunizone include Lobocorallium goniophylloides, which is the same as Grewingkia haysii according to

Elias (1981, p. 17), and Grewingkia robusta var. amplum,

which may include a species of Deiracorallium (see Elias,

IDAHO:

1. Paris Peak

UTAH:

2. Tony Grove Lake, Bear River Range

3. Portage Canyon, West Hills

Figure 2. Index map of localities discussed in text.

4. Silver Island Mountains

5. Lakeside Mountains

6. Sheeprock Range

7. East Tintic Mountains

8. Thomas Range

9. Deep Creek Mountains

10. Confusion Range

11. Barn Hills

NEVADA:

12. Independence Mountains

13. Antelope Peak

14. Pequop Range

15. Toano Range

16. Shoshone Range

17. Ruby Mountains

18. Cherry Creek Range

19. Northern Egan Range

20. Roberts Creek Mountain

21. Lone Mountain

22. Mountain Boy Range

23. Wood Cone Peak

24. Fish Creek Range

25. Copenhagen Canyon, Monitor Range

26. Ikes Canyon and June Canyon, Toquima Range

27. Pancake Range

28. Southern Egan Range

29. Fossil Mountain

30. Pahranagat Range

31. Delamar Range

32. Ranger Mountain

33. Spotted Range

34. Arrow Canyon Range

CALIFORNIA:

35. Funeral Mountains

36. Panamint Range 
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 93

STAGE CARBONATE RAMP

HIRNANTIAN

RICHMONDIAN

MAYSVILLIAN

UPPER EDENIAN

CARBONATE PLATFORM

BRACHIOPODS CORALS

North American

Province

brachiopods

Arctic

colonial

coral

fauna

Grewingkia

haysii

Faunizone

Bighornia

Faunizone

Exposure / no fauna Molluscan fauna

Richmondian

trilobites

(increasing

diversity

down ramp)

Thalassinoides common

1981, p. 22). Corals found in the faunizone but which extend

into the overlying faunizone include Favistina sp., Manipora

sp., Palaeophyllum sp., Calapoecia sp., Catenipora sp., and

Paleofavosites sp.

Above (what is now) the Grewingkia haysii Faunizone,

Budge (1972) recognized a much more widespread Bighornia Faunizone, which he subdivided into three zones. These

three zones are not considered further here, because their

recognition is dependent on the unpublished systematic

descriptions in Budge (1972).

The Bighornia Faunizone contains the rugose corals

Bighornia n. spp., Bighornia solearis, Bodophyllum n.sp.,

Cyathophylloides n.sp., Deiracorallium n.sp., Favistina sp.,

Grewingkia sp., Lobocorallium sp., Streptelasma spp.,

Astrocerium sp., Tryplasma n.sp., Palaeophyllum sp.,

Palaeophyllum cateniforme?, and the tabulates Agetolites

spp., aff. Aulocystis sp., Calapoecia sp., Catenipora sp.,

Paleofavosites sp., Favosites sp., Manipora sp., and Foerstephyllum sp. The genera Tryplasma, Palaeophyllum, Cyathophylloides, Favosites, Paleofavosites, and Catenipora range

upward into Silurian strata. 

The most extensive published study of Upper Ordovician colonial corals is by Pandolfi (1985), who described 20

species of colonial corals from the Ely Springs Dolomite in

the northern Egan Range and the Silver Island Mountains

(table 1). Greatest diversity was found in the open marine

Lost Canyon Member, which contained 18 species. The

Ibex Member contained only two species, both of which

were also found in the overlying members. The Floride

Member had nine species, only one of which was not found

in the underlying members.

The fauna found by Pandolfi (1985) in the Lost Canyon

and Floride Members is so similar that the members cannot

be distinguished on the basis of faunal content. The fauna is

part of the “Arctic Ordovician” fauna, which ranges from the

upper Middle Ordovician through the Late Ordovician.

Associated dasycladacean algae described by Johnson and

Sheehan (1985) are Vermiporella sp., Rhabdoporella sp., and

Cyclocrinites spp.

Most of the colonial corals in these two members are

consistent with the Maysvillian-Richmondian age of the

Ely Springs Formation that is indicated by other fossil

groups discussed in this report. One exception is ?Billingsaria parvituba, which is a species previously known only

from Canada in the Middle Ordovician Bad Cache Rapids

Formation on the Melville Peninsula and the Blackriverian

age Lourdes Formation in western Newfoundland. The species is considerably younger in the Great Basin than in

Canada (Pandolfi, 1985).

Duncan (1956) illustrated corals from several localities

on the platform. Many of the illustrations and much of the

discussion are based on material for which no locality data

are available. Illustrated species include Catenipora gracilis

from the Bluebell Dolomite in the Tintic District, Utah, and

Palaeophyllum sp., from an unrecorded area in Utah. She

also recorded but did not illustrate Tetradium tubifer from

the Tintic District, Utah. W.A. Oliver in Kleinhampl and

Ziony (1985) reported Palaeophyllum sp. and Nyctopora?

Figure 3. Ordovician faunal intervals. The Bighornia and Grewingkia haysii faunizones are from

Budge (1972). The Arctic colonial coral fauna was described by Pandolfi (1985). Richmondian trilobites have been described by Ross and others (1979). During the latest Ordovician the carbonate platform was exposed by a glacio-eustatic regression.
94 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

sp. from the Floride Member of the Ely Springs Dolomite

in the Pancake Range. Langenheim and others (1962)

reported an 8- to 9-ft-thick3 Favistella biostrome about

two-thirds of the way through the Ely Springs Dolomite in

the Arrow Canyon Range.

CARBONATE RAMP CORALS

A Richmondian assemblage of corals was reported

from the upper carbonate ramp in the Mountain Boy Range

in the Hanson Creek Formation by Ross and others (1979;

see corresponding discussion of brachiopods). Included

were Bighornia sp., Lobocorallium trilobatum major (which

Elias (1981) assigned to Grewingkia haysii), Catenipora sp.,

Paleofavosites sp., Saffordophyllum sp., and Nictopora? sp.

Duncan (1956) illustrated Cyathophylloides sp. from an

unnamed location in the Hanson Creek Formation.

3Measurements in feet are those of previous workers and are used here

to maintain the precision of their studies; 1 ft=0.305 m.

C.W. Merriam in Evans (1980) identified Catenipora

sp., Palaeofavosites sp., Palaeophyllum sp. cf. P. thomi, and

Streptelasma sp. associated with eight species of brachiopods (listed in “Carbonate Ramp Brachiopods”) from the

Hanson Creek Formation in the Tuscarora Mountains. J.M.

Berdan in Radtke (1985) reported Catenipora sp., Favosites

sp., Palaeophyllum sp., and Lobocorallium trilobatum from

a nearby locality in the Hanson Creek Formation.

UPPER ORDOVICIAN BRACHIOPODS

Upper Ordovician brachiopods are abundant, well preserved, and diverse in the Ely Springs Dolomite, Fish Haven

Dolomite, and Hanson Creek Formation; however, they have

received little study. Brachiopods have been reported in

numerous studies of regional geology, and a sample of such

mention is provided here, to indicate the diversity of brachiopods in the area. However, because the brachiopods have not

been systematically studied, biostratigraphic assemblages

cannot be identified. The brachiopods are part of the highly

endemic Upper Ordovician North American Brachiopod

Province (Sheehan and Coorough, 1990; this report, fig. 3).

Table 1. Colonial corals from the Ely Springs Dolomite described by

Pandolfi (1985).

[x, occurrence; blank, not found]

______________________________________________________

Coral Ibex Lost Canyon Floride 

 taxa Member Member Member 

______________________________________________________

Calapoecia anticostiensis x x x 

Calapoecia sp. cf. C. coxi x x 

Paleofavosites poulseni x x 

Paleofavosites mccullochae x x 

Paleofavosites okulitchi x x 

Paleofavosites sp. cf. 

 P. transiens x 

Paleofavosites sp. cf. 

 P. capax x x 

?Billingsaria parvituba x x 

Nyctopora sp. x x 

Agetolites budgei x 

Saffordophyllum crenulatum x 

Catenipora workmanae x 

Catenipora sheehani x 

Catenipora sp. cf. C. foerstei x 

Tollina sp. x 

Palaeophyllum humei x 

Palaeophyllum gracile x 

Palaeophyllum sp. cf. 

 P. raduguini x 

Cyathophylloides sp. A x 

Cyathophylloides sp. B x 
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 95

CARBONATE PLATFORM BRACHIOPODS

The only systematic study of Upper Ordovician brachiopods in Nevada and Utah is by Howe and Reso (1967), who

described a collection from near the top of the Floride

Member of the Ely Springs Dolomite at Fossil Mountain and

in the Pahranagat Range, south-central Nevada. The brachiopods include Diceromyonia ignota, Hypsiptycha sp. cf. H.

anticostiensis, and Hiscobeccus capax. Associated corals

include Bighornia sp. and Catenipora sp. cf. C. gracilis. A

Richmondian age is indicated. Reso (1963) reported Hiscobeccus capax? and Zygospira? sp. from the lower Ely

Springs Dolomite in the Pahranagat Range. Sheehan (1969)

recorded brachiopods from the Floride Member and from

lower Ely Springs Dolomite at several sections on the carbonate platform (table 2).

There are several other reports of brachiopods from the

Ibex basin. Staatz and Osterwald (1959) reported Catazyga?

sp., Hesperorthis sp., and Fardenia sp. from the Thomas

Range, Utah, in strata now considered lower Ely Springs

Dolomite. Morris and Lovering (1961) reported Lepidocyclus

perlamellosus and Strophomena sp. from a similar position in

the lower Ely Springs Dolomite in the East Tintic Mountains,

Utah. Kellogg (1963) reported Hesperorthis sp., Paucicrura

sp. cf. P. meeki, and Paucicrura sp. cf. P. multisecta (the latter

two species are assigned to Onniella) from the Ely Springs

Dolomite in the southern Egan Range, Nevada.

Chamberlain and Langenheim (1971) found Hypsiptycha anticostiensis? and Diceromyonia ignota in the upper

Ely Springs Dolomite in the Arrow Canyon Range. They

were associated with rugose and tabulate corals.

On Ranger Mountain Byers and others (1961) recorded

Austinella sp., Holtedahlina sp., Thaerodonta sp., Sowerbyella? sp., Leptaena sp., Zygospira? sp., and Favosites sp.

from between 105 and 185 ft above the base of the Ely

Springs Dolomite, and Dinorthis sp. from 150 ft below the

top of the formation.

North of the Tooele arch in the northwest Silver Island

Range, Utah, R.H. Waite (in Schaeffer and Anderson, 1960,

p. 52) identified Hiscobeccus capax?, Platystrophia sp.,

Hebertella? sp., and Hesperorthis? sp. in beds now assigned

to the Ibex Member of the Ely Springs Dolomite. (See Carpenter, and others, 1986.) In the same publication Waite

recorded Plaesiomys sp., Austinella sp., and Rhynchotrema

sp. from strata now assigned to the Lost Canyon Member of

the Ely Springs Dolomite.

In northern Utah Williams (1948) reported Strophomena sp. cf. S. planumbona and Dinorthis sp. associated with

the corals Halysites sp., Calapoecia sp. cf. C. canadensis,

Favistina? sp. (identified as Columnaria sp. cf. C. alveolata,

but see Flower, 1961, p. 76–79), and Streptelasma sp. from

the Fish Haven Dolomite. Richardson (1913) reported Hiscobeccus capax from the same unit.

Lower part of Floride Member 

Ely Springs Dolomite

Localities 1 2 3 4 5 6 7 

Hesperorthis sp. x ?

Glyptorthis sp. x x x

Plaesiomys (Plaesiomys) sp. x x

Platystrophia sp. x

Paucicrura? sp. x

Diceromyonia tersa x

Thaerodonta sp. x x x

Lepidocyclus sp. x x x x x

Rhynchotrema sp. ?

Zygospira sp. ? x

Austinella sp. x x x

Diceromyonia sp. x x

Spinorthis sp. x

Streptis? sp. x

Leptaena sp. x

Hypsiptycha sp. x x

Table 2. Brachiopods reported by Sheehan (1969) from the Ely Springs Dolomite in Nevada and Utah. 

[Localities: 1, Pequop Range; 2, Cherry Creek Range; 3, Southern Egan Range; 4, Northern Silver Island Range; 5, Pancake Range; 6, Spotted Range; 7, Ranger Mountain. Queried where uncertain; x,

occurrence; blank, not found]
96 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

CARBONATE RAMP BRACHIOPODS

Ross and others (1979) reported a diverse assemblage

of brachiopods, trilobites, bryozoans, corals, and conodonts

from the upper part of the carbonate ramp in eastern exposures of the Hanson Creek Formation at Wood Cone Peak

and the Mountain Boy Range. Only the trilobites and conodonts were illustrated. The fossils are from nodular limestone, wackestone, and dolomitic limestone in the middle of

the formation. The two areas contain distinct assemblages.

The Mountain Boy Range assemblage has more diverse corals, bryozoans, and brachiopods than the Wood Cone Peak

collections, which have a more diverse trilobite assemblage

and lack corals. 

Brachiopods from the Mountain Boy locality are Plaesiomys (Dinorthis) occidentalis, Hesperorthis sp., Glyptorthis sp., Lepidocyclus gigas, cf. Anoptambonites sp.,

Rafinesquina sp., Oepikina? sp., and Thaerodonta sp. Associated bryozoans are Astreptodictya sp., Diplotrypa sp.,

Goniotrypa sp., Homotrypa sp., and Trematopora sp. Six

coral species and three species of trilobites were also associated. (See “Carbonate Ramp Corals” and “Carbonate Ramp

Trilobites.”) An indeterminate rhynchonellid, Thaerodonta

sp., Thaerodonta or Sowerbyella sp., Glyptorthis sp., Hesperorthis sp., and Plaesiomys (Dinorthis) occidentalis were

found higher in the section with no other associated fauna.

Brachiopods from eight closely spaced collections near

Wood Cone Peak include Plaesiomys (Dinorthis) occidentalis, Lepidocyclus gigas, Thaerodonta sp., and Thaerodonta

or Sowerbyella sp., which were also found in the Mountain

Boy Range. In addition, Lepidocyclus sp., Skenidioides sp.,

Strophomena sp., and Diceromyonia sp. A, and a single bryozoan, Sceptropora sp., occur near Wood Cone Peak but

were not found in the Mountain Boy Range. No corals and

20 species of trilobites were also found (see “Carbonate

Ramp Trilobites”). The macrofossils and diverse collections

of conodonts from these localities indicate a Richmondian

age (Ross and others, 1979). 

Although collections from Wood Cone Peak and the

Mountain Boy Range are from the Hanson Creek Formation

and only 15 km apart, the Mountain Boy collections are from

farther east (much farther updip) on the ramp. The nature of

the fauna indicates that the Wood Cone Peak assemblage was

positioned lower on the ramp because of the much greater

diversity of trilobites and the absence of corals and near

absence of bryozoans. Among the brachiopods, Skenidioides, present only at Wood Cone Peak, is commonly found

in relatively deep water settings.

The upper Llandoverian–Early Wenlockian Diana

Limestone in Ikes Canyon in the Toquima Range contains

Upper Ordovician, brachiopod-bearing carbonate clasts that

could be as young as Richmondian. The clasts of older rock

were emplaced during the downdropping of the margin in the

late Llandoverian (Leatham, 1988). Brachiopods reported by

Ross (1970) include (combining two collections) Paucicrura

sp., Oxoplecia? sp., Leptaena sp., Zygospira? sp., and an

indeterminate brachiopod (illustrated on pl. 9, fig. 26). Seven

species of ostracodes were reported, and four species of trilobites are listed herein.

Evans (1980) reported Glyptorthis sp., Lepidocyclus?

sp., Leptellina sp., Paucicrura sp., Plaesiomys? sp., Rhynchotrema sp., Thaerodonta sp., and Zygospira sp. cf. Z.

recurvirostrus in association with four species of corals

(listed previously in “Carbonate Ramp Corals”) from 105 m

below the top of the Hanson Creek Formation in the Lynn

Window in the Tuscarora Mountains, northern Nevada.

Associated conodonts are of late Middle or Late Ordovician

age. Evans (1980) noted that Leptellina was probably no

younger than Trentonian age, but the genus is now known to

occur in Ashgillian age rocks in Ireland, People’s Republic

of China, and Kazakhstan. A small collection from near the

top of the formation included Chaulistomella? sp. and an

unidentified trilobite.

Kerr (1962) reported a diverse fauna from the Hanson

Creek Formation in the Independence Mountains. Hiscobeccus capax is associated with three species of trilobites,

Streptelasma sp., Echinosphaerites sp., echinoderm columnals, Michelinoceras beltrami?, and Climacograptus sp. The

fossils are from thin-bedded calcisiltites and thin-bedded

calcisiltites interbedded with shaly layers. Geographically,

the area is well beyond the platform margin (see Sheehan,

1989). The trilobite-dominated fauna, geographic position,

and lithofacies are indicative of deposition below normal

storm wave base, well down on the carbonate ramp.

CARBONATE RAMP TRILOBITES

Trilobites are rare in carbonate platform strata, but are

common in the carbonate ramp deposits of the Hanson Creek

Formation, especially in distal settings (fig. 3). Many trilobites have been reported in regional geologic investigations,

and only a few of these are mentioned here. The best known

assemblage of trilobites was illustrated by Ross and others

(1979) from the middle of the Hanson Creek Formation in

the Mountain Boy Range and from near Wood Cone Peak,

Nevada. The Mountain Boy Range collection contains 20

species dominated by brachiopods, and includes three species of trilobites, Anataphrus sp., a calymenid, and Calyptaulax sp. In deeper ramp setting from nearby Wood Cone

Peak, these three species also occur and are associated with

Isotelus sp., a proetid, Stygina? sp., Otarion sp., Cryptolithoides sp., Ceraurinus icarus, three species of Ceraurus,

an acanthoparyphinid, Sphaerocorphe sp., Encrinurus sp.,

Cybeloides sp., a lichid, possibly Hemiagres sp., and an

odontopleurid, possibly Ceratocephala sp.

The increasing abundance of trilobites down the ramp

can also be documented in a transect in north-central

Nevada. At Lone Mountain, on the upper part of the ramp,

where the Hanson Creek Formation grades into the Ely
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 97

Springs Dolomite, trilobites are relatively uncommon. To the

west, in the type section at Roberts Creek Mountain, trilobites are much more common; and farther west, in the Shoshone Range, Gilluly and Gates (1965, p. 17) described the

Hanson Creek Formation as, “***abundantly fossiliferous,

with many trilobites and some gastropod fragments.”

Ross (1970) listed Astroproetus sp., Brongniartella sp.,

Whittingtonia? sp., and Encrinuroides sp. from the late

Llandovery to early Wenlock Diana Limestone below the

Roberts Mountain Formation in Ikes Canyon. Associated

brachiopods were listed previously.

In the Tuscarora Mountains, Ross, in Evans (1980),

recorded Anataphrus or Bumastoides sp. associated with the

brachiopod Chaulistomella? sp. high in the Hanson Creek

Formation. Kerr (1962) reported Cryptolithoides sp., Isotelus

sp., and Ceraurus sp. associated with brachiopods and other

fossils in the Hanson Creek Formation in the Independence

Mountains. These areas were well down the carbonate ramp.

UPPER ORDOVICIAN TRACE FOSSILS

Chamberlain (1977, 1979) and Miller (1977) described

various trace fossils, primarily from the carbonate platform.

However, regional distributions of trace fossils are still little

known. The gallery-forming genus Thalassinoides is

encountered in places throughout the carbonate platform

wherever open-marine conditions prevailed during the Late

Ordovician and Early Silurian (fig. 3). However, Thalassinoides is most abundant in the Floride Member of the Ely

Springs Dolomite and the Bloomington Lakes Member of

the Fish Haven Dolomite (Sheehan and Schiefelbein, 1984).

Galleries composed of 2- to 3-cm diameter burrows of

Thalassinoides dominate the lithology, forming a burrowgenerated fabric that replaces depositional fabrics (Tedesco

and Wanless, 1991). Thalassinoides galleries are characteristic of members at the top of the Ordovician sequences

throughout the carbonate platform and upper ramp.

Bioturbation in the Ely Springs Dolomite is much more

intense than on the carbonate platform from the Cambrian to

the Middle Ordovician (Droser and Bottjer, 1989). Droser

and Bottjer found that bioturbation intensity was comparable

to that of post-Ordovician Paleozoic carbonate platform

environments.

HIRNANTIAN–LATE ORDOVICIAN

EUSTATIC SEA-LEVEL LOWSTAND

During the glacial maximum the carbonate platform was

exposed during the glacio-eustatic sea-level lowstand. The

most proximal ramp facies (for example, at Lone Mountain)

shallowed to exposure as evidenced by soil formation (Ross,

1970; Dunham and Olson, 1980; Carpenter and others, 1986).

Slightly downdip, carbonate ramp sedimentation shallowed

from below to within normal storm wave base, for example at

Roberts Creek Mountain and Antelope Peak, Nevada (Carpenter and others, 1986) and Copenhagen Canyon (Berry,

1986). Distal ramp environments shallowed, but not sufficiently to bring the deep-ramp within storm wave base.

Within-wave-base carbonate grainstones in the Mountain Boy Range contain Zone 13 age conodonts (Harris and

others, 1979). This unit caps a glacio-eustatic, shallowingupward sequence that began well below wave base on the

carbonate ramp (Sheehan and Boucot, 1991). Undescribed

macrofossils occur, primarily poorly preserved bivalves and

gastropods. This shallow-water grainstone unit is present

immediately below the Silurian in many proximal ramp sections in Nevada.

SILURIAN BIOSTRATIGRAPHY

The biostratigraphic distribution of macrofossils is well

enough known in this region to permit recognition of the

major subdivisions of the Silurian System. Silurian brachiopod faunas are more thoroughly described than are those of

the Late Ordovician. Coral faunas have been described in the

Wenlockian, Ludlovian, and Pridolian, but Llandoverian corals are relatively unstudied. Brachiopods permit recognition

of subdivisions of the Llandoverian and Wenlockian series

on the carbonate platform. Shallow marine sedimentation

continued throughout the Silurian in southern Nevada and

along the platform margin in central and northern Nevada,

and extensive brachiopod and coral faunas have been

described from these areas. Figure 4 outlines Silurian faunal

intervals for brachiopod and coral faunas.

Following the Ordovician extinction, brachiopods

became cosmopolitan, and the British Silurian series are recognizable over most of the world (Berry and Boucot, 1970).

Brachiopod workers use the traditional lower, middle, and

upper subdivisions of the Llandoverian Series, which have

been designated A, B, and C, respectively. These stage-level

subdivisions have been further subdivided in the type areas

by a sequence of numbers (A1-4, B1-3, C1-6). Brachiopod

workers cannot carry the individual numbered intervals out

of the type regions, but they have established ranges of brachiopods that allow recognition of the following stage-level

intervals of the Llandoverian (Berry and Boucot, 1970): A2-

4, B1-3, C1-3, C4-5, and C6–Lower Wenlockian. By definition

of the Ordovician-Silurian boundary, A1 is now placed at the

top of the Ordovician. 

Work in the British Isles has resulted in selection of a

sequence of stages based on graptolite zones. The new stages

and the original units are Rhuddanian (A2-4), Aeronian (B to

mid-C4), and Telychian (mid-C4 through C6). However,

these intervals are difficult to recognize with brachiopods, so

in this report the subdivisions outlined in Berry and Boucot

(1970) are used. 
98 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

SERIES BRACHIOPODS CORALS

Pridolian

Ludlovian

Wenlockian

E Fauna

D Fauna

C Fauna Atrypella

Fauna

B Fauna

Zone C

EntelophyllumHowellella

Zone 3

Zone B / Zone 2

Zone A / Zone 1

A Fauna

C6–Lower Wenlockian fauna

C4–5 Pentameroides interval

C1–3 Pentamerus interval

A–B

Virgiana interval

Upper

C6

Telychian

Aeronian

Rhuddanian

Middle

Lower

Llandoverian

THE CARBONATE PLATFORM

Following the Late Ordovician glaciation, a rapid Early

Silurian global sea-level rise flooded the platform. Brachiopods in these early to middle Llandoverian deposits have no

relationship with the brachiopods of the underlying Ely

Springs and Fish Haven Dolomites. The extinction event had

decimated the Late Ordovician North American Province

brachiopods. The new Silurian faunas originated from openmarine areas and parts of Siberia, Baltica, and Kazakhstan

(Sheehan and Coorough, 1990).

Early and Middle Llandoverian strata on the carbonate

platform, the Tony Grove Lake Member of the Laketown

Dolomite, are dominated by open-marine sediments with

intervals of shallow, restricted cryptalgal-laminites. These

facies locally continued into the C1-3 interval. The dominant

C1-3 facies is the coarsely recrystallized, very light colored,

massive, poorly bedded, high-energy High Lake Member of

the Laketown Dolomite (Sheehan and Boucot, 1991). The

Verticillopora dasycladacean algal community was common

in protected, shallow-water settings.

A broad range of depositional environments developed

during the C4-5 interval. Water depths at times exceeded

storm wave base, especially in the center of the Ibex basin.

Stromatolites and cryptalgal communities were common in

restricted areas, particularly along the Tooele arch, in the

east-central part of Utah, and near the western carbonate

platform margin. The Verticillopora community was present

but much less common than during the preceding interval.

Diverse brachiopods and corals dominated open-marine settings. Distinct brachiopod guilds characterize communities

from different substrates and water-energy conditions.

Open-marine sedimentation ended in the North Utah

basin early in the C6–Lower Wenlockian. Laketown Dolomite sections are capped by exposure surfaces or cryptalgal

laminites of the Water Canyon Formation in the North Utah

Figure 4. Silurian faunal intervals. The Llandoverian and C6–lower Wenlockian intervals for brachiopods are from Berry and Boucot (1970) and Sheehan (1980b). The lettered brachiopod faunas

A–E are from Johnson and others (1973, 1976). The Atrypella fauna is from Johnson and Reso

(1964). Coral Zones 1–3 are the Rhabdocyclus zones from Budge (1972), and the other coral zones

are from Merriam (1973b).
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 99

basin (Williams and Taylor, 1964). The age of the basal part

of the Card Member of the Water Canyon Formation cannot

be determined because of a lack of fossils, but it could range

from Wenlockian to Devonian. The overlying Grassy Flat

Member of the Water Canyon Formation has an Early Devonian fish fauna.

Ibex basin deposition continued well into the C6–Lower

Wenlockian interval. The center of the Ibex basin contains

sediments deposited near and below storm wave base (Sheehan and Boucot, 1991). Around the margin of the basin, shallower water sediments were deposited within storm wave

base. A variety of brachiopod-dominated communities are

commonly restricted to particular depositional environments. The most abundant and diverse brachiopod and coral

faunas of the Laketown Dolomite flourished during this time

interval in the Ibex basin. Deposition of open-marine sediments ended in the Ibex basin in the Wenlockian. The

restricted marine Sevy Dolomite overlies the Laketown, but

a lack of fossils makes correlation difficult. 

Open-marine sedimentation continued throughout the

Silurian in southern Nevada and along the carbonate platform

margin in central Nevada. The upper Decathon Member of

the Laketown thickens to more than 1,000 ft in southern

Nevada (Sheehan and Boucot, 1991). In central Nevada this

unit is given the name Lone Mountain Dolomite. Tongues of

dark dolomite in the Lone Mountain Dolomite resemble the

Portage Canyon Formation but are much younger. 

THE CARBONATE RAMP

Lower Silurian macrofaunas on the carbonate ramp

were scarce, and little can be done with them biostratigraphically. Following conversion of the carbonate ramp to a relatively steep carbonate slope, macrofossils are abundant from

the Wenlockian through the Pridolian, during which time

they are useful for correlation.

The Llandoverian part of the Hanson Creek Formation

is laterally equivalent to the Tony Grove Lake Member and is

a ramp deposit that in a few places produces a macrofauna.

On the upper carbonate ramp, near the platform margin,

scarce brachiopods occur. Virgiana sp. has been found by the

authors just below the Roberts Mountains Formation in the

Toano Range north of Interstate 80. 

Above the Ordovician part of the Hanson Creek Formation near the platform margin in the Mountain Boy Range,

Virgiana sp. occurs in storm-generated coquinas that resemble the Tony Grove Lake Member of the Laketown Dolomite. This area was very close to the ramp-platform margin

because it was not downdropped, and late Llandoverian units

belong to the Lone Mountain Dolomite of the platform margin rather than being slope deposits of the Roberts Mountains Formation. 

Farther down the ramp at Pete Hanson Creek on Roberts

Creek Mountain, for example, the upper Hanson Creek Formation has few storm beds such as those that dominate the

member on the platform. Macrofossils are very scarce, possibly because the fauna was eliminated by the Late Ordovician extinction event (Sheehan and Boucot, 1991).

CONVERSION OF THE CARBONATE RAMP 

TO A CARBONATE SLOPE

Timing of the late Llandoverian conversion of the gently inclined carbonate ramp to a more steeply inclined carbonate slope with an abrupt shelf margin (Johnson and

Potter, 1975; Hurst and Sheehan, 1985; Hurst and others,

1985) is not well constrained. Tectonic downdropping,

which established this new margin, probably is associated

with the progressive retreat of the platform margin along the

lower Paleozoic passive margin of Cordilleran North America (Sheehan and Boucot, 1991).

The Hanson Creek Formation, underlying the subsidence-event horizon, includes rocks of late Llandoverian age.

The base of the overlying Roberts Mountains Formation

probably contains a condensed interval. Condensed and even

missing graptolite zones are reported, and a cherty interval

and local phosphatic lenses indicate slow deposition (Hurst

and Sheehan, 1985). The earliest macrofossils on the slope

are late Llandovery corals.

Conodont evidence dates the subsidence event as late

Llandoverian. Rocks below are from the Distomodus kentuckyensis conodont zone, and rocks above belong in the

younger Pterospathodus celloni conodont zone (Poole and

others, 1977; Murphy and others, 1979). The change

occurred during or prior to the Monograptus spiralis Zone,

but not earlier than the Rastrites maximus Subzone of the

Monograptus turriculatus Zone (Berry, 1986). In arctic

Canada the Monograptus spiralis Zone ranges down to the

top of the Monograptus turriculatus Zone (Lenz, 1988), a

position near the C3–C4 boundary in the United Kingdom.

At Roberts Creek Mountain and adjacent regions, Berry and

Murphy (1975) showed that the first occurrence of M. spiralis is in the basal Roberts Mountains Formation, and it is

beneath the first occurrence of Cyrtograptus lapworthi wherever the two species occur in the same section. Thus, in the

biostratigraphic scheme adopted for this study, the downdropping event could have occurred as early as the C3–C4

boundary or as late as C6. 

THE CARBONATE SLOPE

The carbonate slope and shelf margin following the

downdropping event have been extensively studied (Matti

and others, 1975; Matti and McKee, 1977; Nichols and Silberling, 1977; Hurst and Sheehan, 1985; Hurst and others,

1985; Sheehan, 1979, 1986, 1989; Sheehan and Boucot,

1991). The Lone Mountain Dolomite was deposited along

the carbonate shelf margin. Most carbonate slope deposits
100 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

are assigned to the Roberts Mountains Formation. The lateral

facies within the Roberts Mountain Formation are complex.

Berry and Boucot (1970) recognized a platy-limestone facies

low on the carbonate slope and a thick-bedded facies closer

to the platform margin. 

The platy-limestone facies is thin-bedded, argillaceous,

red-tinged to buff dolomitic limestone with alternating light

and dark laminae. Silt layers occur as low-amplitude climbing ripples, irregular laminae, and faded ripples. Deposition

was probably from distal, dilute turbidity currents on the

deep slope. (See summary in Sheehan and Boucot, 1991; and

Hurst and Sheehan, 1985.) Macrofossils are rare, possibly

because of low oxygen conditions. An abundant graptolite

fauna makes accurate correlation possible (Berry and Boucot, 1970; Berry and Murphy, 1975; Berry, 1986). Conodonts have also been extensively studied (Murphy and

others, 1979; Klapper and Murphy, 1975).

The thick-bedded facies of Berry and Boucot (1970) is

composed of several distinct subfacies with two distinct origins (Hurst and Sheehan, 1985; Sheehan and Boucot, 1991).

A coarsening-upward, thick-bedded facies (CUF) found at

the top of the formation in eastern sections (Sheehan and

Boucot, 1991) is composed of sands and conglomerates

associated with the prograding Lone Mountain Dolomite.

These beds were gravity emplaced, and some contain a

mixed fauna derived from higher on the slope.

A second thick-bedded facies, composed of finegrained, laminated carbonates (LTBF) illustrated by Sheehan

(1989) occurs along the eastern margin of the Roberts Mountains Formation (Hurst and Sheehan, 1985; Sheehan and

Boucot, 1991). These upper-slope finely laminated or bioturbated argillaceous limestones may have been derived from

shelf sediments placed in suspension by storms and tidal currents and swept over the margin (Hurst and Sheehan, 1985).

Slumps are common in the LTBF (Hurst and Sheehan, 1985;

Sheehan, 1989). The substrate was soft, and many corals and

brachiopods from this facies have “snow-shoe” adaptations

to prevent their sinking into the mud (Sheehan, 1989).

SILURIAN BRACHIOPOD 

BIOSTRATIGRAPHY

LOWER AND MIDDLE LLANDOVERIAN

CARBONATE PLATFORM BRACHIOPODS

Lower and middle Llandoverian brachiopods (fig. 4)

lived in ecologically widespread, low-diversity communities. The brachiopods occur in a wide variety of facies, permitting correlation with other regions of the world. 

The brachiopod Virgiana was one of the geographically most widespread genera of brachiopods that ever

lived (Boucot, 1975). Sheehan and Coorough (1990)

recorded it in Laurentia, the margins of Laurentia, Baltica,

Kazakhstan, Siberia, and South China (People’s Republic

of China). It was distributed in virtually all shallow carbonate platforms of the world.

Virgiana occurs in great abundance in the Tony Grove

Lake Member of the Laketown Dolomite in more than 50

sections from the carbonate platform (Sheehan, 1980a). The

most common species is Virgiana utahensis, although

another species may also be present. Associated brachiopods

are low in diversity and are rare. They include Platystrophia

sp., both coarsely and finely ribbed orthids, a dalmanellid,

two rhynchonellids, Plectatrypa sp., Hyattidina? sp., and an

atrypid. Sheehan (1980a) recovered more than 1,500 silicified specimens of Virgiana from 33 separate localities. Only

two collections had as many as four other species of brachiopods associated with Virgiana utahensis. Since 1980 the

Virgiana Community has been observed at hundreds of horizons, so the relative proportions of species in the community

and the environmental distribution of the community are

well established.

A second brachiopod-dominated community occurs as

monospecific coquina beds of an indeterminate rhynchonellid in the Tony Grove Lake Member of the Laketown Dolomite in the Cherry Creek Range (Sheehan, 1980b). The

presence of only two brachiopod-dominated communities

(one of them uncommon) on the carbonate platform during

the early and middle Llandoverian is remarkable and is part

of a worldwide pattern.

Sheehan (1975, 1980b, 1992) attributed the broad ecologic distribution and low diversity of the Virgiana Community to a recovery of the fauna following the Ordovician

extinction event. The extinction had reduced species diversity, and surviving species became widely distributed ecologically in a variety of habitats marked by little

competition. Subsequently, communities became progressively more diverse and confined to progressively narrower

environmental ranges.

LOWER UPPER LLANDOVERIAN (C1-3)

CARBONATE PLATFORM BRACHIOPODS

The pentamerid brachiopod Virgiana was replaced at

the beginning of the upper Llandoverian by Pentamerus sp.

in the Great Basin (Sheehan, 1980a, 1980b). The transition

was not an evolutionary event, because Pentamerus did not

evolve from Virgiana. Pentamerus is a well-established biostratigraphic marker for the beginning of the upper Llandoverian (Berry and Boucot, 1970). Pentamerus sp.

commonly occurs in shell-lag deposits associated with storm

beds and locally as densely packed, in-place shell assemblages. Growth of many specimens is asymmetric because

adjacent individuals interfered with each other during

growth in the densely packed colonies. Contemporary communities include the Verticillopora Community, dominated

by dasycladacean algae interpreted to have lived in shallow,
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 101

relatively protected environments (Rezak, 1959; Sheehan,

1980b). Pelmatozoan columnals are also commonly associated with the Pentamerus Community, and pelmatozoan

communities were common in the High Lake Member.

Restricted conditions are reflected by the presence of stromatolites and cryptalgal laminites, especially as caps to shallowing-upward sequences.

Pentamerus sp. commonly occurs in great abundance

and in places is associated with specimens of a fine-ribbed

orthid, ?Brachyprion sp., Microcardinalia sp. A, Atrypa

sp., Atrypa (Gotatrypa) sp. cf. A. gibbosa, and ?Pentlandella sp. Over most of the North Utah and Ibex basins,

water depths were not deep enough for deeper water communities such as those dominated by stricklandids in other

regions of the world. 

UPPER LLANDOVERIAN (C4-5) CARBONATE 

PLATFORM BRACHIOPODS

The brachiopod Pentameroides sp. A of Sheehan (1982)

dominated the Pentameroides Community, which occupied

an ecologic setting similar to that of the earlier Pentamerus

Community. Pentameroides sp. A was derived from Pentamerus, and many of the associated species probably had ancestors in the Pentamerus Community. Pentameroides sp. A, a

form transitional between the genera (see Sheehan, 1982), is

of late Llandoverian (C4-5) age. 

The Pentameroides Community is strongly dominated

by Pentameroides, but associated species are more diverse

and more common than they were in the Pentamerus Community. Associated species include Flabellitesia flabellites,

Dolerorthis? sp., Isorthis sp., fine- and coarse-ribbed orthids,

Microcardinalia sp., a rhynchonellid, Atrypa (Gotatrypa) sp.

cf. A. gibbosa, Meristina? sp., Pentlandella merriami, and

Cyrtia sp. (Sheehan, 1982).

The Microcardinalia Community also occurs in slightly

deeper water platform settings than the Pentamerus Community, near or slightly below storm wave base in the Portage

Canyon Section, Utah (Sheehan, 1980b, 1982). Tabulate corals of Zone 1 of Budge (1972) dominate this assemblage.

Associated brachiopods include Isorthis sp., coarse- and

fine-ribbed orthids, ?Spirinella pauciplicata, and rare Pentameroides sp. A.

Muddy platform facies of the lower Gettel Member

contain two additional communities, which probably had to

make do with very soft substrates. In the southern Egan

Range the Pentlandella Community occurs stratigraphically

between the Verticillopora Community and the Pentameroides sp. B Community (of C6–early Wenlockian age). The

Pentlandella Community is probably of C4-5 age, but could

be younger. Species include Pentlandella merriami (abundant), and much less common Atrypina erugata, Spirigerina

sp., a plectambonitid, a fine-ribbed orthid, an atrypid, and the

coral Asthenophyllum sp. It is interpreted to be a quiet-water

equivalent of the Pentameroides Community. Tabulate and

solitary rugose corals are present but not common.

The Cyrtia Community occupies a similar position

stratigraphically above the Verticillopora Community in bioturbated, silty dolomites with occasional storm deposits in

the Gettel Member in the Barn Hills, Utah. Species include

Flabellitesia flabellites, Atrypa (Gotatrypa) hedei americensis, Cyrtia sp., and Spirinella pauciplicata. Corals are

uncommon. A similar C4-5 age is inferred.

Boucot and Johnson, in Wilden and Kistler (1979,

p. 237) identified an upper Llandoverian horizon (from two

localities) in the Lone Mountain Dolomite in the Ruby Mountains that contains “Dolerorthis” sp., Dicoelosia sp., Salopina

sp. aff. S. conservatrix, Gypidula sp., Leptaena sp., “Chonetes” sp., Hebetoechia? sp., “Ancestrorhyncha” sp., Atrypa

sp., Howellella (Acanthospirifer) sp., Howellella? sp., and

Spirinella sp. aff. S. pauciplicata. It is underlain by a collection of Virgiana? sp. of early to middle Llandoverian age.

C6–LOWER WENLOCKIAN CARBONATE 

PLATFORM BRACHIOPODS

A brachiopod biostratigraphic interval encompasses the

very latest Llandoverian (C6) and the early Wenlockian

(Berry and Boucot, 1970). In the North Utah basin only a few

meters of section at the top of the Laketown Dolomite belong

in this interval. In the Tony Grove Lake and Portage Canyon

sections, a few meters of strata contain the Spirinella Community. It occurs in dark dolomite deposited below storm

wave base (Sheehan, 1980b). Brachiopods include abundant

Spirinella pauciplicata, common Ancillotoechia sp., and

rare Brachyprion (Eomegastrophia) geniculata. Six species

of Rhabdocyclus Zone 2 corals of Budge (1972; see section,

“Silurian Corals”) are associated with these brachiopods.

Restricted cryptalgal laminites were deposited along

the margin of the Ibex basin. The Verticillopora algal community was also present in more open marine settings (Sheehan, 1980b). Pentameroides sp. B of Sheehan (1982)

dominates a community from the Gettel Member of the

Laketown on the east side of the southern Egan Range. Associated brachiopods include Atrypa (Gotatrypa) sp. cf. A. gibbosa, Flabellitesia flabellites, and Cyrtia sp. Associated

fossils include dasycladacean algae, echinoderm columnals

and calyxes, rare tabulate corals, and stromatoporoids. Pentameroides sp. B has a more derived morphology than Pentameroides sp. A, and is characteristic of C6–early

Wenlockian species of the genus (Sheehan, 1982).

On the west side of the southern Egan Range, five localities from the Gettel Member of the Laketown Dolomite

(from Unit 4 of Budge and Sheehan, 1980b, which was

assigned to the High Lake Member) contain Pentameroides

sp. B. Sheehan (1980b) noted that these collections are not
102 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

dominated by Pentameroides as is common in the

Pentameroides Community and that many associated brachiopods are common in deeper water communities. The Gettel

Member was deposited below normal storm wave base,

strengthening this conclusion. Associated taxa include Flabellitesia flabellites, Isorthis sp., Dicoelosia biloba, Eoplectodonta sp., Microcardinalia sp., Atrypina erugata, Cyrtia

sp., and Spirinella pauciplicata. Collections from the upper

part of the Laketown Dolomite that overlie strata with Pentameroides sp. B are also probably of C6–early Wenlockian

age, but could range higher into the Wenlockian.

The Spirinella Community is the deepest community

in platform sections in the Jack Valley Member of the

Laketown Dolomite in the Ibex basin in the Barn Hills,

Confusion Range, and Sheeprock Range, Utah. Species

include Brachyprion (Eomegastrophia) geniculata, Hercotrema pahranagatensis, Hercotrema perryi, an athyridacid, and Spirinella pauciplicata (Waite, 1956; Sheehan,

1982). A diverse, undescribed tabulate and rugose coral

fauna is present, including corals assigned to zones 2 and 3

of Budge (1972), discussed in “Silurian Corals.” Rare

bivalves, common trochoid and high-spired gastropods, and

a few bryozoans occur. 

The Atrypina Community, from the Jack Valley Member of the Laketown Dolomite in the southern Egan Range,

has the greatest brachiopod diversity and abundance of any

community in the Laketown Dolomite. Corals are also very

diverse and include many assigned to Zone 2 of Budge. Rare

planispiral and trochoid gastropods and bivalves also occur.

Brachiopods, which are evenly distributed, include Flabellitesia flabellites, Isorthis sp., Dicoelosia biloba, Dicoelosia

sp., Dalejina sp., Eoplectodonta sp., Leptaena sp., Protochonetes elyensis, Camerella? sp., Pentameroides sp. B, Microcardinalia sp., Stegerhynchus estonicus (=Ferganella

borealis of Sheehan, 1982), Hercotrema perryi, Plectatrypa

sp. cf. P. imbricata, Atrypa (Gotatrypa) sp. cf. A. gibbosa,

Atrypina erugata, Cyrtia sp., Hedeina? sp., Howellella sp.,

and Spirinella pauciplicata eganensis. Corals and brachiopods described by Merriam (1973a) from the Mountain Boy

Range probably are part of the Atrypina Community.

Boucot and Johnson, in Wilden and Kistler (1979, p.

237) identified a fauna from the Lone Mountain Dolomite in

the Ruby Mountains that includes Skenidioides sp., Dicoelosia sp., Anastrophia sp., Antirhynchonella? sp., Leptaena

sp., Stegerhynchus sp. aff. S. estonicus, Lingulopugnoides?

sp., Atrypa sp., Zygatrypa sp. aff. Z. paupera, Hedeina sp.,

and the rugose coral Palaeocyclas sp. They assigned a

C6–early Wenlockian age. Skenidioides, which normally

occurs in relatively deep water, is found here in the shallowwater Lone Mountain Dolomite.

MIDDLE WENLOCKIAN AND YOUNGER CARBONATE PLATFORM BRACHIOPODS

Several faunas have been described from the middle

Wenlockian and younger platform strata in southern Nevada

and from the Lone Mountain Dolomite along the platform

margin in central and northern Nevada. In the Pahranagat

Range Johnson and Reso (1964) identified probable Wenlockian brachiopods and corals from these dark beds. Similar

faunas in similar strata occur in the Delamar and Pancake

ranges (Budge and Sheehan, 1980b; Sheehan, 1980b).

Johnson and Reso (1964) recorded the brachiopods Atrypa

spp., Howellella sp. cf. H. nucula, Howellella sp., Hyatidina

hesperalis, Hercotrema pahranagatensis, and indeterminate

dalmanellids and rhynchonellids. Waite (1956) also recorded

Howellella smithi from near this horizon. Associated corals

include Halysites sp., Favosites sp., Breviphyllum? sp., Disphyllum? sp., Clavidictyon sp., and “Cladopora” sp.

At the base of the Decathon Member of the Laketown

Dolomite in strata originally assigned to the Sevy Dolomite,

Johnson and Reso (1964) identified a late Wenlockian or

Ludlovian Atrypella carinata fauna of brachiopods associated with a single species of high-spired gastropod. Brachiopods include Gypidula? biloba, Stegerhynchus? lincolnensis,

Camarotoechia? reesidei, Atrypa sp., Atrypella carinata,

Atrypella sp., Macropleura? sp., Spirinella pauciplicata,

Howellella sp. cf. H. nucula, Howellella? sp. cf. H.? arctica,

Hyattidina hesperalis, and Nucleospira hecetensis.

Merriam (1973a) described an Entelophyllum-Howellella assemblage from dark tongues of dolomite in the

upper part of the Lone Mountain Dolomite in the Fish Creek

Range and the Mountain Boy Range that is very similar to

that in the Pahranagat Range. Johnson and Oliver (1977)

reviewed these fossils and concluded they were of late Wenlockian or early Ludlovian age. Brachiopods from the Mountain Boy Range include Camarotoechia sp.,?Hyattidina sp.,

and Spirinella pauciplicata. The latter species resembles the

plicate subspecies Spirinella pauciplicata eganensis from

the Jack Valley Member of the Laketown Dolomite in the

Egan Range. Corals are listed in the section, “Silurian Corals.” A different assemblage is recorded by Merriam (1973a)

from the upper Lone Mountain Dolomite in the Fish Creek

Range. Brachiopods include Salopina sp., Hercotrema pahranagatensis, Camarotoechia sp. b and sp. f, Atrypa

sp.,?Hyattidina sp., a species incorrectly assigned to Hindella, and Howellella smithi. Three species from the latter

assemblage are present in the probable Wenlockian assemblage from the Portage Canyon Member in the Pahranagat

Range. None of the species from the Mountain Boy Range

occur in the Pahranagat Range assemblage, but the occurrence of Spirinella pauciplicata eganensis suggests correlation with the early to middle Wenlockian assemblages in the

Jack Valley Member of the Laketown Dolomite.
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 103

CARBONATE SLOPE BRACHIOPODS

Brachiopod biostratigraphy of the Roberts Mountains

Formation has been intensely studied. Brachiopod biostratigraphy can be integrated with graptolite (Berry and Murphy,

1975), conodont (Klapper and Murphy, 1975), and ostracode

(McClellan, 1973; Stone and Berdan, 1984) biostratigraphy

in well-studied sections on Roberts Creek Mountain.

Five brachiopod faunas ranging in age from middle

Wenlockian through Pridolian have been described by

Johnson and others (1973, 1976). The faunas, designated by

the letters A to E, are listed in the next section. Many of the

faunas are composed of collections made from several different facies; thus they are biostratigraphic units, not communities. Many of the shelly horizons in the Roberts Mountains

Formation are from gravity-emplaced sediments, and so the

collections may contain individuals that lived in different

environments. In addition to the five lettered faunas, several

other collections are discussed.

WENLOCKIAN BRACHIOPODS FROM

ROBERTS CREEK MOUNTAIN REGION 

The A Fauna of Johnson and others (1976) comes from

the lower few hundred feet (approximately 100 m) of the

Roberts Mountains Formation and is composed of species

from several communities. The brachiopods are of middle to

late Wenlockian age, which is consistent with associated

graptolites of the Cyrtograptus rigidus through Monograptus

testus zones (Berry and Murphy, 1975). One assemblage of

very small, thin-shelled brachiopods including Chonetoidea

sp. cf. C. andersoni, Dicoelosia parvifrons, and Epitomyonia

clausula, was recognized as a community representing the

outermost shelly-fauna community developed adjacent to

platy limestones containing only pelagic fossils. 

Species restricted to the A Fauna are Skenidioides sp.,

Ptychopleurella sp., Dolerorthis sp., Salopina? sp., Isorthis

sp., Isorthis microscapha, Resserella canalis celtica, Dalejina? sp., Dicoelosia parvifrons, Epitomyonia clausula, Conchidium brevimura, Conchidium sp., Vosmiverstum

wenlockum, Cymbidium sp., “Cymbidium” sp. (smooth),

Spondylostrophia? sp., Kirkidium? sp., Pentameroides? sp.,

Brooksina? sp., Morinorhynchus sp., Eoplectodonta sp. cf.

E. transversalis, Chonetoidea sp. cf. C. andersoni, Stegerhynchus estonicus, “Ancillotoechia” sp. cf. “A.” minerva,

Rhynchotreta sp., Atrypa sp., Atrypa sp. A, Reticulatrypa sp.

A, Spirigerina sp., Plectatrypa sp. cf. P. rugosa, Gracianella

praecrista, Gracianella sp., Eospirifer sp., Janius sp., Cyrtia

sp., Plicocyrtia sp., Howellella sp., and Spirinella sp.

At most five species extend upward into the B Fauna.

The A Fauna shares Gypidula sp. and Nucleospira sp. with

the B Fauna. Atrypella sp. is found in the A Fauna and has

questionably been identified in B Fauna. Two species from

the B Fauna, Kozlowskiellina deltidialis and Meristina sp.,

have questionably been found in the A Fauna.

B Fauna overlies the A Fauna and is of latest Wenlockian age based on the brachiopods and associated graptolites of Pristograptus dubius frequens and Pristograptus

ludensis zones (Berry and Murphy, 1975). Five species

associated with A Fauna are listed previously. Only two

species, “Schuchertella” sp. and Nucleospira sp., extend

upward into the C Fauna. Species restricted to B Fauna are

Ptychopleurella micula, Salopina sp. cf. S. conservatrix,

Anastrophia sp., Leptaena sp., Placotriplesia sp., Leangella

sp., Ancillotoechia sp., Plagirhyncha sp., Rhynchotreta

cuneata, Spinatrypa sp., Cryptatrypa triangularis, Atrypina erugata, Lissatrypa sp., Protozeuga sp., Homeospira

evax, and Spirinella sp. B.

The B Fauna occurs in a narrow stratigraphic interval of

the Roberts Mountains Formation and is characterized by the

small size of the species and lack of pentamerids. It is very

distinct from both older and younger faunas.

LUDLOVIAN BRACHIOPODS FROM

ROBERTS CREEK MOUNTAIN REGION

The C Fauna of Johnson and others (1976) comes from

lower but not lowest and middle Ludlovian strata. Associated

graptolites include the upper part of the Colonograptus colonus and the Saetograptus chimaera Zones of Berry and Murphy (1975). Brachiopods were not found in the lower and

middle part of the C. colonus Zone in the Roberts Creek

Mountain area.

C Fauna is characterized by large species, especially

pentamerids, and high diversity. It shares 2 species with the

underlying B Fauna, and 31 species are confined to it. Eight

species are shared with D Fauna, and five other species probably occur in both faunas. Species restricted to C Fauna

include Dolerorthis birchensis trisecta, Dolerorthis sp., Isorthis sp., Dalejina sp., Dicoelosia sp., Conchidium synclastica, Conchidium sp., Lamelliconchidium micropleura,

Cymbidium sp., “Cymbidium” lissa, Vadimia nevadensis,

Severella spiriferoides, Kirkidium vogulicum, Brooksina sp.

cf. B. alaskensis, Pentamerifera sp., Gypidula sp. c, Morinorhynchus sp., “Schuchertella” sp., Chonetoidea andersoni,

Reticulatrypa savagei, Spirigerina marginalis, “Spirigerina”

sp., Gracianella crista, Protathyris sp., Nucleospira sp.,

Hedeina? sp., Cyrtia sp., Howellella? sp., Spirinella spp.,

Delthyris? sp., and Eoplicoplasia tumeoventer.

The following species and subspecies occur in both the

C and D Faunas: Ptychopleurella cymbella, Dolerorthis

birchensis birchensis, Severella munda, Antirhynchonella

minuta, Atrypella spp., Dubaria sp., Gracianella lissumbra

lissumbra, Chnaurocoelia transversa. Species found in C

fauna but only questionably identified in D Fauna are Aenigmastrophia cooperi and Cryptatrypa sp. Species found in D

Fauna which are questionably identified in C Fauna are

Salopina delta, Stegerhynchus? sp. cf. S. lincolnensis, Gracianella lissumbra costata, and Gracianella plicumbra.
104 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Johnson and others (1976) recognized three communities in the D Fauna. However, because many gravityemplaced deposits are present in the Roberts Mountains Formation, it will be necessary to reevaluate the facies in which

each community was found.

D Fauna comes from middle Ludlovian strata of the

Polygnathoides siluricus conodont zone. D Fauna is less

diverse than C Fauna and has smaller pentamerid species.

Species that also occur in the C Fauna are listed previously.

The 17 species restricted to D Fauna are Skenidioides operosa, Isorthis microscapha, Dicoelosia diversifrons, Conchidium microlocularis, Cymbidium imitor, Spondylopyxis

ignotus, Pentamerifera sp. cf. P. oblongiformis, Carygyps

plicata, Gypidula sp. cf. G. orbitatus, Leptaena sp., Morinorhynchus subcarinatus, Areostrophia rara, Aesopomum? sp.,

Reticulatrypa variabilis, Meristina sp., Hedeina ananias,

and Delthyris fulgens.

Few brachiopods have been found in upper Ludlovian

strata, but one collection from the upper (but not uppermost)

Ludlovian Pedavis latialata conodont zone was described by

Johnson and others (1976). This collection contains Dolerorthis? sp., Skenidioides sp., Isorthis sp., Dicoelosia sp.,

Kirkidium sp., Anastrophia sp., Gypidula sp., Morinorhynchus? sp., Sphaerirhynchia? sp., Spirigerina sp., Reticulatrypa sp. cf. R. savagei, Atrypella sp., Cryptatrypa

triangularis, Gracianella plicumbra, Coelospira planorostra, Nucleospira sp., Meristina? sp., and Delthyris sp. cf. D.

elevata. Johnson and others (1976) also described Conchidium ultima and Kirkidium? sp. cf. K.? hospes from Ludlovian

collections from Roberts Creek Mountain.

PRIDOLIAN BRACHIOPODS FROM

ROBERTS CREEK MOUNTAIN REGION

A single distinctive collection from near the base of

the Pridolian was recorded by Johnson and others (1973).

Only three species occur in the overlying E Fauna. Species

include “Dolerorthis” sp., Ptychopleurella sp., Anastrophia

sp., Gypidula sp., Mesopholidostrophia? sp., Reticulatrypa

neutra, Atrypella sp., Gracianella cryptumbra, Nucleospira

sp., Meristina? sp., Howellella sp., Delthyris sp., and Alaskospira? sp.

E Fauna of Johnson and others (1973) is of Pridolian

age and is from collections immediately below an occurrence of Monograptus angustidens and the Ozarkodina remschenidensis eosteinhornensis conodont zone. Species

include “Dolerorthis” sp., Salopina sp., Gypidula sp., Leptaena sp., Morinorhynchus punctorostra, Aesopomum? sp.,

Mesodouvillina (Protocymostrophia) costatuloides, Lanceomyonia sp. cf. L. confinis, Eoglossinotoechia? sp., Reticulatrypa? sp., Atrypella? sp., Gracianella reflexa,

Gracianella sp. cf. G. cryptumbra, Protathyris sp., Delthyris

sp., Tenellodermis matrix, and Cyrtina sp. which may be

present because of contamination during preparation.

Finally, three collections from the uppermost 10 m of

the Silurian part of the Roberts Mountains Formation contain

a fauna that is transitional to the Devonian fauna. Dicoelosia

nitida, Salopina submurifer, and Ptychopleurella sp. F,

which are common in overlying Devonian collections, make

their first appearance in this fauna. Species with strong Silurian affinity include Atrypella sp., Gracianella sp. cf. G.

cryptumbra, Gracianella sp. cf. G. lissumbra, Reticulatrypa

neutra, Tenellodermis matrix, and Dubaria megaeroides.

Other species are: Tyersella? sp., Salopina sp., Gypidula sp.,

Plectodonta? sp., Atrypa “reticularis,” Reticulatrypa sp. aff.

R. granulifera, Meristina? sp., and Howellella sp.

SILURIAN BRACHIOPODS FROM

OTHER REGIONS ON THE SLOPE

Outside the Roberts Creek Mountain region, Silurian

brachiopod faunas on the carbonate slope are less well

known. Virtually all upper slope sections (“Thick-Bedded

Facies” of Berry and Boucot, 1970) have abundant brachiopods at some horizons. Sheehan (1976) described an early

Wenlockian brachiopod fauna collected from bioturbated,

fine-grained upper slope carbonates of the Thick-Bedded

Facies of the Roberts Mountains Formation in the Silver

Island Mountains, Utah. This assemblage was in a position

high on the carbonate slope, close to the platform margin

(Sheehan, 1986). The prograding shelf margin facies (Lone

Mountain Dolomite) is found about 35 m above these collections. Sheehan (1976) assigned the collection to the Dicoelosia-Skenidioides Community, which is commonly found in

fine-grained sediments near or below storm wave base in

“Benthic Assemblages 4 or 5” of Boucot (1975). Brachiopods recovered are Skenidioides sp. cf. S. pyramidalis,

Resserella brownsportensis, Isorthis (Tyersella?) amplificata, Isorthis (Arcualla) sp., Dicoelosia johnsoni, Salopina

boucoti, Mesounia sp., Eoplectodonta budgei, Leptagonia

sp., “Leptostrophia” sp., Conchidium sp., Cymbidium? sp.,

Stegerhynchus estonicus, Hercotrema berryi, Reticulatrypa

sp., Atrypina disparilis, Atrypina erugata, Plectatrypa sp.,

and Janius sp. Rugose corals are common in these beds; tabulate corals are also locally common. Small gastropods and a

few bryozoans also occur. A late Wenlockian or possibly earliest Ludlovian age was assigned, based on the brachiopods.

More recent work (Boucot and others, 1988) suggests that

Janius does not occur above the lower Wenlockian. This

assemblage and also the B Fauna are characterized by the

presence of few pentamerid brachiopods. Of these species

only Atrypina erugata from the B Fauna of Johnson and others (1976) and Rhynchotrema estonicus from the A Fauna

have been recorded from collections in the Roberts Creek

Mountain. No conodonts or graptolites have been recorded

in this section. The recovery of a distinct fauna in the Silver

Island Range is an indication that many assemblages remain

to be found in the Roberts Mountains Formation.
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 105

In the Roberts Mountains Formation in the Hot Creek

Range, Boucot in Kleinhampl and Ziony (1985) identified

the following brachiopods: Dolerorthis sp., Dicoelosia sp.,

Isorthis sp., Conchidium? sp., Cymbidium sp., Gypidula sp.,

Coolinia? sp., Plectodonta sp., Atrypa “reticularis,” Spirigerina sp., Lissatrypa sp., Nucleospira? sp., and Spirinella sp.

aff. S. pauciplicata. The fauna is Ludlovian because of the

presence of Cymbidium.

A diverse collection of brachiopods has been described

by Boucot and others (1988) from unit h3 of the Hidden Valley Dolomite in southeastern California north of the Death

Valley–Furnace Creek fault in the Funeral Mountains. The

relationship between the Hidden Valley and Laketown dolomites is poorly understood. Descriptions of the Hidden Valley Dolomite by McAllister (1974) are consistent with the

interpretation that this part of the Hidden Valley Dolomite is

a carbonate slope deposit. Suggestions by Boucot and others

(1988) that the collection might include shallow-water species brought into a deeper water setting are consistent with

this suggestion. The brachiopod fauna has similarities with

both slope and carbonate platform faunas in central Nevada

and northwestern Utah. 

Thirty-two species of brachiopods are present in the

Hidden Valley locality, which is about 60 m above Coral

Zone B locality described by Merriam (1973b; see section,

“Silurian Corals”). Species are Hesperorthis kessei, Skenidioides sp. cf. S. operosa, Resserella canalis erecta, Dicoelosia sp. cf. Dicoelosia alticavata, Eoplectodonta california,

“Eoplectodonta” sp., Aegiria sp., Leptaena sp. cf. L.

depressa, Coolinia sulcata, Vosmiverstum wenlockum, Rhipidium (Pararhipidium) filicostatum, Kirkidium (Pinguaella)

mcallisteri, Apopentamerus? sp., Gypidula sp. cf. G.?

biloba, Stegerhynchus estonicus, Rhynchotreta sp. aff. R.

americana, Hercotrema berryi, Hercotrema perryi, Zygatrypa stenoparva, Spirigerina sp., Reticulatrypa ryanensis,

Eospinatrypa sagana, Atrypa (Gotatrypa) altera, Dubaria?

sp., Lissatrypa sp., Merista sp., Nucleospira sp., Janius occidentalis, Cyrtia sp., and Spirinella sp. cf. S. pauciplicata.

Some of the species have been found elsewhere in both slope

and platform regions of Nevada and Utah. Skenidioides operosa occurs in the D Fauna and Vosmiverstum wenlockum

and Stegerhynchus estonicus occur in the A Fauna at Roberts

Creek Mountain. Hercotrema berryi and Stegerhynchus

estonicus occur in the Roberts Mountains Formation in the

Silver Island Range. Gypidula? biloba occurs in the base of

the Decathon Member in the Pahranagat Range. Stegerhynchus estonicus, Hercotrema perryi, and Spirinella pauciplicata occur in the Jack Valley Member of the Laketown

Dolomite in eastern Nevada and Utah.

SUMMARY OF SILURIAN 

BRACHIOPOD BIOSTRATIGRAPHY

The biostratigraphy and facies distribution of carbonate

platform brachiopods (fig. 4) have been well documented in

many sections. Understanding facies distributions of brachiopods is essential if new faunas are to be correlated. Llandoverian brachiopod diversity is higher on the platform than

on the carbonate ramp. Conversely, carbonate platform brachiopod diversity was much lower than on the carbonate

slope during the Middle and Late Silurian. The carbonate

slope environment apparently had more favorable habitats

for brachiopods than the carbonate ramp.

The faunas from the Roberts Creek Mountain section

provide the best biostratigraphic control for ranges of Wenlockian, Ludlovian, and Pridolian brachiopods in the Great

Basin. They occur in sections in which superpositional relationships have been established and the conodont and graptolite zonations have been carefully documented.

Thirty-eight new species were described by Johnson

and others (1973, 1976) from the Roberts Creek Mountain

area. Most of these species have not been reported elsewhere

in the Great Basin. A great potential clearly exists for developing a refined brachiopod biostratigraphy of the slope

deposits of the Roberts Mountains Formation. As faunas

from other parts of central Nevada are described, the new

species will be reencountered. In addition, the facies distribution of slope brachiopod communities needs to be determined. Very distinctive facies are known to occur along the

profile of the carbonate slope, but little information is yet

available about the faunas present in many of the facies.

Most of the Roberts Mountains Formation brachiopods

that have been described were collected in the late 1960’s

and early 1970’s before modern concepts of carbonate facies

had been developed. Particularly for slope settings, much of

our understanding of depositional facies has been developed

since the faunas were collected. Future progress will require

the integration of the biostratigraphic and systematic studies

with a facies evaluation of faunas. Fortunately, the locations

of most collections in the Roberts Creek Mountain region are

very accurately known and a return to these sites will be possible. Of particular significance is the potential for tying brachiopod faunas to stratigraphic sequences extending across

the platform and slope settings.

SILURIAN CORALS

Corals of the lower and middle Llandoverian Tony

Grove Lake Member of the Laketown Dolomite are essentially unstudied. Small solitary rugose corals are commonly

associated with the Virgiana Community, both in the same
106 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

beds and interbedded with that community. Tabulate corals

including halysitid, favositid, and heliolitid colonies are also

common in the Tony Grove Lake Member, though they are

less commonly associated with Virgiana than are the rugose

corals. In addition, large colonial rugose corals commonly

occur; they are in need of study. Corals from the early part of

the late Llandoverian (C3-4) have also received little or no

attention: tabulate corals are common and diverse, and rugose corals are locally abundant. (See fig. 4 for coral zones.)

Merriam (1973a, b) proposed a coral zonation for the

Silurian of the Great Basin. The correlation of these zones

was revised by Johnson and Oliver (1977), and their revision

is accepted here. Merriam’s (1973b) “Coral Zone A” is based

on collections from the lower Hidden Valley Dolomite in the

Panamint Range of southeastern California. Johnson and

Oliver (1977) accepted the late Llandoverian date because

Miller (1976) had found conodonts at this level belonging to

the Pterospathodus celloni Zone. Corals include Arachnophyllum kayi, Dalmanophyllum sp., Palaeocyclus porpita

mcallisteri, “Rhegmaphyllum” sp., and Tryplasma? sp. Merriam (1973b) assigned collections from the Confusion Range

(probably the Jack Valley Member of the Laketown) to Coral

Zone A, but Johnson and Oliver (1977) assigned them a

Wenlockian age.

On the carbonate slope in central Nevada, Merriam

(1973b) recorded a latest Llandoverian assemblage from the

base of the Roberts Mountains Formation at Ikes Canyon in

the Toquima Range. Species are Arachnophyllum kayi, Cyathophylloides fergusoni, and “Neophyma” crawfordi. Only

Arachnophyllum kayi occurs in the Hidden Valley Dolomite.

Budge (1972) recognized three carbonate platform

coral zones in a Rhabdocyclus Faunizone at the top of the

Laketown Dolomite. The lower zone, here informally called

“Zone 1,” is of Late Llandoverian age, based on associated

brachiopods. Zone 1 was found only in the North Utah basin

in the Portage Canyon Member of the Laketown Dolomite in

sections at Portage Canyon in the West Hills, Utah, and at

Paris Peak, in the Bear River Range in Idaho. The associated

brachiopods Pentameroides sp. A and Microcardinalia sp. B

indicate a C4-5 late Llandoverian age, approximately equivalent to Coral Zone A of Merriam (1973b) as revised by

Johnson and Oliver (1977). Zone 1 includes the rugose corals

Rhabdocyclus sp. A, Aphyllostylus sp. aff. gracilis, Palaeocyclus sp., Ptychophyllum? sp., Rhizophyllum n.sp., Tryplasma radicula, Rhegmaphyllum sp. aff. R. conulus,

Astenophyllum patula, and the tabulate corals Astrocerium

sp., Catenipora sp., Cladopora sp., Coenites sp., Cystihalysites spp., Emmonsia sp., Favosites sp., Planalveolites sp.,

Romingeria sp., Striatopora sp., Syringopora sp., Alveolites

sp., Aulopora sp., and Heliolites sp.

Collections from the Ruby Mountains, Nevada (Palaeocyclus and Halysites), and the Confusion Range, Utah

(Palaeocyclus sp. cf. P. porpita, Brachyelasma sp., Tryplasma sp. cf. T. hedstromi, Alviolites sp., Heliolites sp.,

and Halysites sp.), assigned by Merriam (1973b) to Coral

Zone A have been reassigned a Wenlockian age by Johnson

and Oliver (1977). The Confusion Range collections are

probably from the Jack Valley Member and possibly the

Gettel Member of the Laketown. All are part of Coral Zone

2 of Budge (1972).

Corals of Zone 2 of Budge (1972) were found widely in

the Ibex basin in rocks of C4-5 and C6-early Wenlockian age

in the Jack Valley, Portage Canyon, and Gettel Members of

the Laketown (see discussion of brachiopod biostratigraphy

and Johnson and Oliver, 1977). The zone was recognized at

only one locality in the North Utah basin, from the Jack Valley

Member at the very top of the Tony Grove Lake section. 

Zone 2 of Budge (1972) includes the rugose corals

Amplexoides n. sp., Asthenophyllum sp. (of Norford), Palaeocyclus n. sp., Ptychophyllum? sp., Rhabdocyclus n.sp. A,

Rhizophyllum n.sp., Tryplasma radicula, Asthenophyllum sp.

cf. orthoseptatum, Rhegmaphyllum? sp. aff. R. conulus, and

the tabulate corals Cystihalysites spp., Halysites sp., Romingeria sp., Syringopora sp., Alveolites sp., Aulopora sp., and

Heliolites sp. An associated fauna of abundant brachiopods

is discussed in the section, “C6–Lower Wenlockian Carbonate Platform Brachiopods.” Rigby (1967) described sponge

spicules from this unit.

The uppermost Coral Zone 3 of Budge (1972) was

found only at the top of the Jack Valley Member in the Confusion Range. Zone 3 includes the rugose corals Asthenophyllum sp. (of Norford), Rhabdocyclus n. sp. B,

Asthenophyllum sp. cf. A. orthoseptatum, and the tabulate

corals Syringopora sp., Cystihalysites sp., and Heliolites sp.

Merriam (1973b) characterized his Coral Zone B by a

fauna from 325 ft above the base of the Hidden Valley Dolomite in the Panamint Range and 110 ft above the base of the

Hidden Valley Dolomite in the Funeral Mountains. Merriam

(1973b) assigned Zone B to the lower to middle Wenlockian.

Johnson and Oliver (1977) agreed with this assignment, noting that the horizon in the Funeral Mountains is about 200 ft

below beds containing Rhipidium sp. cf. R. tenuistriatum

illustrated by Amsden and others (1967). Thus, at least the

lower part of Zone B corresponds to the platform Zones 2

and 3 of Budge (1972). 

Zone B corals from the Hidden Valley Dolomite include

the rugose corals Ryderophyllum ubehebensis, Brachyelasma sp., Pycnactis sp., Petrozium mcallisteri, and the tabulate corals Cystihalysites sp. aff. C. magnitubus, Heliolites

sp., and Syringopora sp.

An additional assemblage, the Entelophyllum-Howellella Assemblage of Merriam (1973b), occurs between

Coral zones B and C. Merriam originally included the

assemblage in his Coral Zone D, but Johnson and Oliver

(1977) pointed out the close similarity of the brachiopods

with those in the Decathon Member of the Laketown Dolomite in the Pahranagat Range described by Johnson and Reso

(1964). They suggested a late Wenlockian or early Ludlovian

age, which is younger than Coral Fauna B but older than

Coral Fauna C. 
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 107

The Entelophyllum-Howellella Assemblage was found

in the upper part of the Lone Mountain Dolomite in the

Mountain Boy Range and the Fish Creek Range, Nevada.

In the Mountain Boy Range, corals include ?Thamnopora

sp. and Entelophyllum engelmanni. In the Fish Creek

Range, corals include small, massive favositids, thinwalled, ramose favositids, ?Thamnopora sp., Entelophyllum

engelmanni subsp. b, Entelophyllum eurekaensis, Alveolites

sp., and Tryplasma sp. Associated brachiopods are discussed in the section on brachiopods. Entelophyllum engelmanni was also recognized questionably in association with

brachiopods described by Johnson and Reso (1964) in the

Pahranagat Range.

Coral Zone C of Merriam (1973b) is known only from

the Roberts Mountains Formation at Roberts Creek Mountain. Johnson and Oliver (1977) showed that conodonts, brachiopods, and graptolites described in these sections by

Klapper and Murphy (1975), Johnson and others (1976), and

Berry and Murphy (1975) establish a Pridolian age for Coral

Zone C. Rugose corals include Denayphyllum denayensis,

Tryplasma newfarmeri, and Entolophylloides (Prohexagonaria) occidentalis. Two other species (Tryplasma sp. and

Microplasma? sp.) also occur in this section in beds assigned

to this zone by Merriam. 

Merriam (1973b) established Coral Zones D and E,

which he believed were Late Silurian in age. Johnson and

Oliver conclusively demonstrated that brachiopods and conodonts from the sections in which Zones D and E were

described are Early Devonian in age.

Several isolated coral collections from the Great Basin

have been reported in the literature. Buehler (1955)

described and illustrated Halysites magnitubus from the

Laketown Dolomite near Gold Hill, Utah, but the position

within the Laketown is unknown. He noted the occurrence of

Halysites labyrinthica, but again the position in the Laketown is unknown.

In the lower 200 m of the type section of the Roberts

Mountains Formation, Merriam and McKee (1976) found

Cladopora sp., Heliolites sp., Halysites sp., Orthophyllum

sp., and pycnostylid rugosa. These are probably of early to

middle Wenlockian age based on their position in the section.

In the June Canyon Sequence in the Toquima Range,

Nevada, D.R. Budge and W.A. Oliver (in McKee, 1976, p.

17) identified corals from the basal dolomite unit of the

Gatecliff Formation. Included were Cladopora? sp.,

Favosites spp., Halysites or Cystihalysites sp., “Cystiphyllum” sp., and an amplexoid coral. An Early Silurian age was

proposed by McKee based on nearby graptolites from an

overlying chert. 

SILURIAN OSTRACODES

Only two studies have been made of ostracodes. Stone

and Berdan (1984) described a single well-preserved collection of Pridolian age from the Willow Creek area of Roberts

Creek Mountain. Thirty-three species were found at the one

horizon in a carbonate gravity-flow bed. The fauna included

3 new genera and 18 new species. The closest similarities

were with ostracodes from northwestern Canada and Alaska.

McClellan (1973) identified several poorly preserved

ostracodes from the Roberts Mountains Formation. He found

2 Ludlovian species at Ikes Canyon in the Toquima Range, 3

Wenlockian species at Wood Cone Peak, and 14 Ludlovian

species at Willow Creek. None of the species recorded by

McClellan was found by Stone and Berdan (1984).

SILURIAN ALGAE

The Verticillopora Community is present throughout

the Silurian in the Great Basin. Species of the community

were originally described by Rezak (1959) from Wenlockian

strata in the Great Basin. Verticillopora occurs widely on the

carbonate platform in the early late Llandoverian (Sheehan,

1980b). Verticillopora was recorded in Coral Zone B in the

Hidden Valley Dolomite in the Panamint Range and Funeral

Mountains, California, by Merriam (1973b). He noted that

Silurian specimens have thin shafts compared with those

from the Devonian, but he illustrated Lower Devonian specimens of Verticillopora, which he assigned to the Wenlockian species of Rezak. Devonian specimens of Verticillopora

have been described and illustrated from the middle part of

the Devonian Vaughn Gulch Limestone in the Inyo Mountains, California, and the Roberts Mountains Formation in

the Toquima Range and Roberts Creek Mountain by Merriam and McKee (1976). Until they are more carefully documented, dasycladacean algae will have limited

biostratigraphic value.

SEQUENCE STRATIGRAPHY AND 

BIOSTRATIGRAPHIC BOUNDARIES

A sequence stratigraphic study of Silurian rocks on the

carbonate platform (Harris and Sheehan, 1992, 1996) has

revealed strong correlation of sequences with macrofaunal

biostratigraphy. From the early Llandoverian through the

C6–early Wenlockian, five stratigraphic sequences (S1 to S5

in fig. 1) have been identified by Harris and Sheehan (1992,

1996). The sequences are stratigraphic packages that shallow

upward and are capped by very shallow water facies or exposure surfaces. Each of the four Llandoverian through middle

Wenlockian carbonate platform biostratigraphic intervals

based on brachiopods (fig. 1) is bounded above and below by

regressions that mark sequence boundaries. During the early

and middle Llandoverian (a single biostratigraphic interval),

there are two stratigraphic sequences (S1 and S2). The other

three biostratigraphic intervals each correspond to a single

stratigraphic sequence.
108 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

The sequence stratigraphy has been carefully documented in only two sections, but the same intervals and

boundaries have been found in a reconnaissance of several

other sections. Ordovician biostratigraphic intervals are not

adequately documented to determine whether or not

sequence boundaries match biostratigraphic boundaries.

The correspondence of regressive sequence boundaries

with biostratigraphic boundaries in the Silurian could have a

number of causes. Because each of the lower five biostratigraphic boundaries in the Silurian corresponds with a

sequence boundary, a spurious correlation seems unlikely,

and some direct causal connection is likely. A regression

marks each boundary, which raises two obvious possibilities.

The first is simply a passive effect: sufficient time elapsed

during the regression that when open-marine environments

returned to the platform in the next stratigraphic sequence, the

faunas had changed through evolution. The second possibility is that the regression caused the faunal change by physically disrupting communities and stimulating enough faunal

turnover to allow recognition of a new biostratigraphic interval.

The first possibility seems unlikely, because the faunal change during the intervals of deposition is far less than

that found across sequence boundaries. Therefore, some

disruption of faunas by the regression seems to be the likely

cause of the change.

The biostratigraphic boundaries are of two types. The

first type involves nonevolutionary replacement of faunas

across the boundary. This occurred at the end of the Ordovician and at the transition between the middle and upper

Llandoverian. The Ordovician-Silurian boundary corresponds with a worldwide glacio-eustatic regression and a

global mass extinction. The boundary between the middle

(B) and upper (C) Llandoverian corresponds to a nonevolutionary replacement of many brachiopod groups on the platform. For example, Virgiana was replaced by Pentamerus,

which was derived from a genus not found in the Great Basin

(Sheehan, 1980b). The extinction was followed by invasion

of brachiopods from other regions. 

The other biostratigraphic boundaries involve evolutionary changes that occurred during the regressive intervals.

An example is the evolutionary replacement of Pentamerus

by Pentameroides at the boundary between C1-3 and C4-5.

The preliminary finding that stratigraphic sequences

and biostratigraphic intervals correspond could become a

powerful new tool for correlation. However, further study is

clearly needed. The detailed investigation of sequence

stratigraphy needs to be conducted in more sections on the

platform. Examination of sequences downdip will be essential, because during the regressive interval between platform

sequences, deposition should have been continuous on the

ramp and slope. Platform species may have retreated to the

ramp and slope environments during regressions. 

Understanding the nature of the interaction of regressions and biostratigraphic units must await further study of

both platform and ramp-slope environments. Fortunately, as

has been shown, macrofossils are both abundant and diverse

on the carbonate slope.

CONCLUSIONS

The distribution of macrofossils in the Upper Ordovician and Silurian strata of the Great Basin is well documented for certain intervals, but much work remains to be

done. Brachiopods and corals are the most diverse and best

preserved macrofossils. 

The diverse and locally abundant Upper Ordovician

brachiopods have received very little study. There is considerable potential for developing a useful biostratigraphic

framework if systematic studies are undertaken. 

Silurian brachiopods on the carbonate platform have

received considerable study. The Llandoverian and early

Wenlockian faunas allow recognition of four biostratigraphic

intervals. Upper Wenlockian and Ludlovian brachiopods

have also been described. Carbonate slope brachiopods have

been extensively studied in the Roberts Creek Mountain

region, where five biostratigraphic intervals from Wenlockian to Pridolian have been recognized. However, the presence of many new species in slope settings from other areas

of the Great Basin indicates that much descriptive work

remains to be done.

The potential for Ordovician and Silurian coral biostratigraphy on the carbonate platform was well demonstrated in Budge’s (1972) dissertation. Unfortunately,

because the work has not been published elsewhere, the

names of new taxa are not widely available. Corals from

slope settings have been studied, but, as with the brachiopods, many slope faunas need taxonomic work. Corals are

best known from Late Ordovician, Wenlockian, and Ludlovian strata. Llandoverian corals are essentially unstudied.

Late Ordovician trilobites are abundant on the carbonate ramp, but few trilobites are described. Additional studies are needed.

Early Silurian sequence and biostratigraphic boundaries appear to correspond. This pattern needs to be carefully documented in carbonate-platform, shelf-margin, and

carbonate-slope settings. The combination of sequence

stratigraphy and biostratigraphy may become an important

tool for correlation.

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112 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

APPENDIX. SPECIES LISTED IN TEXT

ORDOVICIAN CORALS

Agetolites budgei Pandolfi, 1985, p. 30–31, pl. 9, fig. 2; pl.

11, fig. 2; pl. 12, fig. 1; pl. 13, figs. 1, 2; pl. 18, fig.

2.

?Billingsaria parvituba (Troedsson, 1928). Pandolfi, 1985,

p. 20–21, pl. 4, figs. 1, 2. 

Bighornia solearis (Ladd, 1929), p. 397–399, p. 4, figs.

6–12. Elias, 1981, p. 24.

Calapoecia anticostiesis Billings, 1865. Pandolfi, 1985, p.

18–19, pl. 1, figs. 1, 2; pl. 2, fig. 1; pl. 18, fig. 1

Calapoecia sp. cf. C. canadensis Billings, 1865, p. 426, pl.

20, fig. 12. Bassler, 1950, p. 275.

Calapoecia sp. cf. C. coxi Bassler, 1950. Pandolfi, 1985, pp.

19–20, pl. 1, fig. 3; pl. 2, fig. 2.

Catenipora sp. cf. C. foerstei Nelson, 1963. Pandolfi, 1985,

p. 33–34, pl. 7, fig. 4; pl. 10, fig. 2.

Catenipora gracilis Hall, 1852. Duncan, 1956, pl. 27, figs.

1a, 1c.

Catenipora sheehani Pandolfi, 1985, p. 34–35, pl. 20, figs.

1, 2.

Catenipora workmanae Flower, 1961. Pandolfi, 1985, p. 32,

pl. 13, fig. 3; pl. 21, figs. 1, 2.

Favistina? sp. (= Favistella sp. cf. F. alveolata (Goldfuss,

1826). Bassler, 1950, p. 271, pl. 16, fig. 3. Flower,

1961, p. 76–79.)

Grewingkia haysii (Meek, 1865). Elias, 1981, p. 17, pl. 5,

figs. 1–15; pl. 6, figs. 1–12.

Grewingkia robusta var. amplum (Troedsson), 1928 p. 108,

pl. 26, figs. 1–4.

Lobocorallium goniophylloides (Teichert, 1937). Duncan,

1956, pl. 22, figs. 3a, 3b. = Grewingkia haysii

(Meek, 1865). Elias, 1981, p. 17.

Palaeophyllum cateniforme? Flower, 1961, p.91, pl. 49, figs.

1–6. pl. 5, figs. 1–5.

Palaeophyllum gracile Flower, 1961. Pandolfi, 1985, p. 37,

pl. 15, fig. 1; pl. 23, figs. 1, 2.

Palaeophyllum humei Sinclair, 1961. Pandolfi, 1985, p.

35–36, pl. 14, figs. 1, 2; pl. 24, figs. 1, 2.

Palaeophyllum sp. cf. P. raduguini Nelson, 1963. Pandolfi,

1985, p. 38, pl. 15, fig. 2; pl. 16, figs. 1, 2.

Palaeophyllum sp. cf. P. thomi (Hall, 1857). Flower, 1961,

p. 91–92, pl. 47, fig. 9; pl. 51, figs. 1–8; pl. 52, figs.

1–7.

Paleofavosites sp. cf. P. capax (Billings, 1865). Bolton,

1980, p. 22–25, pl. 2.7, figs. 1, 4–6.

Paleofavosites mccullochae Flower, 1961. Pandolfi, 1985, p.

25–26, pl. 8, fig. 2; pl. 9, figs. 1, 3; pl. 10, fig.1

Paleofavosites okulitchi Stearn, 1956. Pandolfi, 1985, p.

24–25, pl. 7, fig. 2.

Paleofavosites poulseni Teichert, 1937. Pandolfi, 1985, p.

23–24, pl. 5, figs. 1–3; pl. 6, figs. 1, 2; pl. 7 figs. 1,

3, 5.

Paleofavosites sp. cf. P. transiens Stearn, 1956. Pandolfi,

1985, p. 27, pl. 11, fig. 3; pl. 16, fig. 3.

Saffordophyllum crenulatum (Bassler, 1932). Pandolfi,

1985, p. 22, pl. 4, fig. 3.

Tetradium tubifer Troedson, 1928, p. 137–138, pl. 46, figs.

3a, 3b; pl. 47, pl. 1a–1h.

LATE ORDOVICIAN BRACHIOPODS

Diceromyonia ignota (Sardeson, 1897). Howe and Reso,

1967, p. 354–358, pl. 40, figs. 1–16.

Diceromyonia tersa (Sardeson, 1892). Wang, 1949, p. 36, pl.

12B, figs. 1–8; Howe, 1965, pl. 36, figs. 16–25.

Hypsiptycha sp. cf. H. anticostiensis (Billings, 1865). Howe

and Reso, 1967, p. 358–361, pl. 40, figs. 17–20.

Hiscobeccus capax (Conrad, 1842). Howe and Reso, 1967,

p. 362, pl. 40, figs. 21–25.

Lepidocyclus gigas Wang, 1949. Macomber, 1970, p. 447,

pl. 80, figs. 1–17.

Lepidocyclus perlamellosus (Whitfield, 1877). Wang, 1949,

p. 14, pl. 6A, figs. 1–5.

Onniella sp. cf. O. meeki (Miller, 1875). Hall, 1962, p.

145–148, pl. 19, figs. 1–24; pl. 20, figs. 1–10.

Onniella sp. cf. O. multisecta (Meek, 1873). Hall, 1962, p.

148–150, pl. 20, figs 11–31.

Plaesiomys (Dinorthis) occidentalis (Okulitch, 1943). Macomber, 1970, p. 430–433, pl. 75, figs. 12–15; pl.

76, figs. 1–27.

Strophomena sp. cf. S. planumbona (Hall, 1847). Wang,

1949, p. 23–24, pl. 6D, figs. 1–7.

Zygospira sp. cf. Z. recurvirostrus Hall, 1847. Ross, 1959, p,

457, pl. 54, figs. 3, 7, 12, 18. 

LATE ORDOVICIAN CEPHALOPODS

Michelinoceras beltrami? (Clarke, 1897). Foerste, 1932, p.

77, pl. 35, fig. 6.

LATE ORDOVICIAN TRILOBITES

Ceraurinus icarus (Billings, 1865). Ross, Nolan, and Harris,

1979, fig. 4, s, z.

SILURIAN BRACHIOPODS

Aenigmastrophia cooperi Boucot, 1971. Johnson, Boucot,

and Murphy, 1976, p. 56–57, pl. 21, figs. 1–11.

“Ancillotoechia” sp. cf. “A.” minerva (Barrande, 1847).

Johnson, Boucot, and Murphy, 1976, p. 66–67, pl.

5, figs 14–27.

Antirhynchonella minuta Johnson, Boucot, and Murphy,

1976, p. 53, pl. 41, figs. 1–16; pl. 42, figs. 1, 2.

Areostrophia rara Johnson, Boucot, and Murphy, 1976, p.

61–62, pl. 44, figs. 12–19.

Atrypa (Gotatrypa) altera Boucot, Johnson, and Zhang,

1988, p. 118–119, pl. 7, figs. 18–30.

Atrypa (Gotatrypa) sp. cf. A. gibbosa Hall, 1852. Copper,

1982, p. 698–700, pl. 3, figs. 1–13; =Atrypa sp. cf.

A. parva of Sheehan, 1982, p. 37–39, pl. 10, figs.

1–14.

Atrypa (Gotatrypa) hedei (Struve, 1966) americensis Sheehan, 1982, p. 39–40, pl. 10, figs. 15–23.
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 113

Atrypella carinata Johnson in Johnson and Reso, 1964, p.

81, pl. 20, figs. 9, 18–26. Brachyprion (Eomegastrophia) geniculata (Waite, 1956). Sheehan, 1982,

p. 16–21, pl. 4, figs. 24, 25; pl. 5, figs. 1–19; pl. 6,

figs. 1–8.

Atrypina disparilis (Hall, 1852). Sheehan, 1976, p. 731, pl.

2, figs. 8–14.

Brooksina sp. cf. B. alaskensis Kirk, 1922. Johnson, Boucot,

and Murphy, 1976, p. 51–52, pl. 19, figs. 3–15.

Camarotoechia? reesidei Kirk and Amsden, 1952. Johnson

and Reso, p. 80, pl. 19, figs. 13–19.

Carygyps plicata Johnson, Boucot, and Murphy, 1976, p.

54–55, pl. 42, figs. 3–15; pl. 43, figs. 1–11.

Chnaurocoelia transversa Johnson, Boucot, and Murphy,

1976, p. 95–96, pl. 55, figs. 1–19. 

Chonetoidea sp. cf. C. andersoni Johnson, Boucot, and Murphy, 1976, p. 58–59, pl. 20, figs. 3–25.

Coelospira planorostra Johnson, Boucot, and Murphy,

1976, p. 83, pl. 26, figs. 5–16.

Conchidium brevimura Johnson, Boucot, and Murphy, 1976,

p. 35–36, pl. 2, figs. 21–28; pl. 3, figs. 1–13.

Conchidium microlocularis Johnson, Boucot, and Murphy,

1976, p. 37–38, pl. 35, figs. 1–26; pl. 36, figs. 1–3.

Conchidium synclastica Johnson, Boucot, and Murphy,

1976, p. 36–37, pl. 15, figs. 11–24; pl. 16, figs. 1–7.

Conchidium ultima Johnson, Boucot, and Murphy, 1976, p.

38–39, pl. 27, figs. 1–20. 

Coolinia sulcata Boucot, Johnson, and Zhang, 1988, p.

111–112, pl. 2, figs. 44–45; pl. 3, figs. 1–5.

Cryptatrypa triangularis Johnson, Boucot, and Murphy,

1976, p. 75–76, pl. 25, figs. 22–30; pl. 26, figs. 1–4.

Cymbidium imitor Johnson, Boucot, and Murphy, 1976, p.

42–43, pl. 36, figs. 4–23; pl. 37, figs. 1–11.

“Cymbidium” lissa Johnson, Boucot, and Murphy, 1976, p.

43, pl. 16, figs. 8–14.

Delthyris sp. cf. D. elevata Dalman, 1828. Johnson, Boucot,

and Murphy, 1976, p. 89, pl. 26, figs. 17–24.

Delthyris fulgens Johnson, Boucot, and Murphy, 1976, p.

89–90, pl. 53, figs. 11–16.

Dicoelosia sp. cf. Dicoelosia alticavata (Whittard & Barker,

1950). Boucot, Johnson, and Zhang, 1988, p.

109–110, pl. 1, figs. 25–43.

Dicoelosia biloba (Linnaeus, 1758). Sheehan, 1982, p.

9–10, pl. 3, figs. 18–26; pl. 4, figs. 1–3.

Dicoelosia diversifrons Johnson, Boucot, and Murphy,

1976, p. 27–28, pl. 33, figs. 3–20.

Dicoelosia johnsoni Sheehan, 1976, p. 720–721, pl. 4, figs.

1–11.

Dicoelosia nitida Johnson, Boucot and Murphy, 1973, p.

22–24, pl. 16, figs. 16–24; pl. 17, figs. 1–7.

Dicoelosia parvifrons Johnson, Boucot, and Murphy, 1976,

p. 27, pl. 1, figs. 15–28.

Dolerorthis birchensis birchensis Boucot, Johnson, and

Murphy, 1976, p. 22–23, pl. 29, figs. 16–18; pl. 30,

figs. 1–31.

Dolerorthis birchensis trisecta Boucot, Johnson, and Murphy, 1976, pl. 31, figs. 1–19.

Dubaria megaeroides Johnson and Boucot, 1970, p. 267, pl.

54, figs. 10–25. Johnson, Boucot and Murphy,

1973, p. 51, pl. 27, figs. 13–15.

Eoplectodonta budgei Sheehan, 1976, p. 726–727, pl. 4, figs.

12–17.

Eoplectodonta california Boucot, Johnson, and Zhang,

1988, p. 110, pl. 3, figs. 6–13.

Eoplectodonta sp. cf. E. transversalis (Dalman, 1828).

Johnson, Boucot, and Murphy, 1976, p. 58, pl. 4,

figs. 17–20.

Eoplicoplasia tumeoventer Johnson and Lenz, 1992.

Johnson, Boucot, and Murphy, 1976, p. 94–95, pl.

25, figs. 1–12.

Eospinatrypa sagana Boucot, Johnson, and Zhang, 1988, p.

118, pl. 7, figs. 31–47.

Epitomyonia clausula Johnson, Boucot, and Murphy, 1976,

p. 29, pl. 1, figs. 29–36; pl. 2, figs. 1–20. 

Flabellitesia flabellites (Foerste, 1889). Sheehan, 1982, p. 3,

pl. 1, figs. 13, 14, 17–20; pl. 2, figs. 1–14. Zhang,

1989, p. 56.

Gracianella crista Johnson and Boucot, 1967. Johnson,

Boucot, and Murphy, 1976, p. 81, pl. 24, figs.

11–28.

Gracianella cryptumbra Johnson, Boucot and Murphy,

1973, p. 56–57, pl. 3, figs. 1–20.

Gracianella lissumbra costata Johnson, Boucot, and Murphy, 1976, p. 81, pl. 48, figs. 19–25.

Gracianella lissumbra lissumbra Johnson and Boucot, 1967.

Johnson, Boucot, and Murphy, 1976, p. 80, pl. 50,

figs. 1–19.

Gracianella plicumbra Johnson and Boucot, 1967. Johnson,

Boucot, and Murphy, 1976, p. 81, pl. 49, figs. 1–24.

Gracianella praecrista Johnson, Boucot, and Murphy, 1976,

p. 79–80, pl. 7, figs. 1–15.

Gracianella reflexa Johnson, Boucot and Murphy, 1973, p.

54–56, pl. 7, figs. 1–18; pl. 8, figs. 1–10.

Gypidula sp. cf. G. orbitatus (Barrande, 1879). Johnson,

Boucot, and Murphy, 1976, p. 56, pl. 43, figs.

12–18.

Gypidula? biloba Johnson in Johnson and Reso, 1964, p.

79–80, pl. 19, figs. 1–4.

Hedeina ananias Johnson, Boucot, and Murphy, 1976, p.

86–87, pl. 51, figs. 11–20; pl. 52, figs. 1–14.

Hercotrema berryi (Sheehan, 1976), pl. 5, figs. 6–14. Boucot, Johnson, and Zhang, 1988, p. 116, pl. 6, figs.

34–40. Jin, 1989, p. 88.

Hercotrema pahranagatensis (Waite, 1956), pl. 3, figs. 1–5.

Sheehan, 1982, p. 33–34, pl. 8, figs. 11–19. Jin,

1989, p. 88.

Hercotrema perryi (Sheehan, 1982), p. 32–33, pl. 9, figs.

1–15. Boucot, Johnson, and Zhang, 1988, p. 116,

pl. 6, figs. 1–8. Jin, 1989, p. 88.

Hesperorthis kessei Boucot, Johnson, and Zhang, 1988, p.

107–108, pl. 1, figs. 1–16.
114 EARLY PALEOZOIC BIOCHRONOLOGY OF THE GREAT BASIN

Homeospira evax (Hall, 1863). Johnson, Boucot, and Murphy, 1976, p. 85, pl. 11, figs. 28–31; pl. 12, figs.

1–7.

Howellella sp. cf. H. nucula (Barrande, 1879). Johnson and

Reso, p. 83, pl. 20, figs. 14–17.

Howellella smithi Waite, 1956, pl. 3, figs. 16–19.

Howellella? sp. cf. H.? arctica (Poulsen, 1943), pl. 6, figs.

9–12. Johnson and Reso, 1964, p. 83.

Hyatidina hesperalis (Waite, 1956), pl. 4, figs. 11–15.

Johnson and Reso, 1964, p. 83, pl. 19, figs. 22, 23,

25–28.

Isorthis (Tyersella?) sp. cf. I. (T.) amplificata Walmsley,

1965. Sheehan, 1976, p. 716–718, pl. 3, figs. 9–16.

Isorthis microscapha Johnson, Boucot, and Murphy, 1976,

p. 25–26, pl. 1, figs 13, 14; pl. 32, figs. 13–23; pl.

33, figs. 1, 2.

Janius occidentalis Boucot, Johnson, and Zhang, 1988, p.

120–121, pl. 9, figs. 1–22.

Kirkidium (Pinguaella) mcallisteri Boucot, Johnson, and

Zhang, 1988, p. 113–114, pl. 4, figs. 17–32.

Kirkidium vogulicum (Verneuil, 1845), Johnson, Boucot,

and Murphy, 1976, p. 50–51, pl. 18, figs. 2–14; pl.

19, figs. 1, 2.

Kirkidium? sp. cf. K.? hospes (Barrande, 1879). Johnson,

Boucot, and Murphy, 1976, p. 51, pl. 17, figs. 11,

12; pl. 18, fig. 1.

Kozlowskiellina deltidialis (Hedstroem, 1923). Johnson,

Boucot, and Murphy, 1976, p. 90–91, pl. 12, figs.

8–21. 

Lamelliconchidium micropleura Johnson, Boucot, and Murphy, 1976, p. 40–41, pl. 13, figs. 23–30; pl. 14, figs.

1–19; pl. 15, figs. 1–10.

Lanceomyonia sp. cf. L. confinis (Barrande, 1848). Havlicek, 1961, p. 116, pl. 13, figs. 4, 5.

Leptaena sp. cf. L. depressa (J. de C. Sowerby 1824). Boucot, Johnson, and Zhang, 1988, p. 111, pl. 2, figs.

42, 43.

Mesodouvillina (Protocymostrophia) costatuloides Johnson,

Boucot and Murphy, 1973, p. 41, pl. 6, figs. 1–18.

Morinorhynchus punctorostra Johnson, Boucot and Murphy, 1973, p. 36–38, pl. 4, figs. 1–20; pl. 5, figs.

1–17.

Morinorhynchus subcarinatus Johnson, Boucot, and Murphy, 1976, p. 60–61, pl. 45, figs. 1–16; pl. 46, figs.

1–8.

Nucleospira hecetensis Kirk and Amsden, 1952. Johnson

and Reso, 1964, p. 83–84, pl. 19, figs. 24, 29.

Pentamerifera sp. cf. P. oblongiformis (Nikiforova, 1937).

Johnson, Boucot, and Murphy, 1976, p. 49–50, pl.

40, figs. 1–17.

Pentlandella merriami Sheehan, 1982, p. 35–37, pl. 9, figs.

16–30. Atrypina erugata Amsden, 1968. Johnson,

Boucot, and Murphy, 1976, p. 78–79, pl. 11, 8–20;

Sheehan, 1982, p. 42, pl. 13, figs. 1–13.

Plectatrypa sp. cf. P. imbricata (J. de C. Sowerby, 1839).

Sheehan, 1982, p. 41, pl. 10, figs. 26, 27.

Plectatrypa sp. cf. P. rugosa (Hall, 1852). Johnson, Boucot,

and Murphy, 1976, p. 68–69, pl. 6, figs. 20–27.

Protochonetes elyensis Sheehan, 1982, p. 22–24, pl. 6, figs.

5–9.

Ptychopleurella cymbella Johnson, Boucot, and Murphy,

1976, p. 20–21, pl.31, figs. 20–25; pl. 32, figs.

1–12.

Ptychopleurella micula Johnson, Boucot, and Murphy,

1976, p. 19–20, pl. 8, figs. 1–24.

Resserella brownsportensis (Amsden, 1949). Sheehan,

1976, p. 715–716, pl. 3, figs. 1–8.

Resserella canalis celtica Bassett, 1972. Johnson, Boucot,

and Murphy, 1976, p. 26, pl. 1, figs. 1–12.

Resserella canalis erecta Boucot, Johnson, and Zhang,

1988, p. 108–109, pl. 2, figs. 21–41.

Reticulatrypa sp. aff. R. granulifera (Barrande). Johnson,

Boucot and Murphy, 1973, p. 49–50, pl. 2, figs.

19–24.

Reticulatrypa neutra Johnson, Boucot and Murphy, 1973, p.

49, pl. 2, figs. 1–18.

Reticulatrypa ryanensis Boucot, Johnson, and Zhang, 1988,

p. 117–118, pl. 7, figs. 1–17.

Reticulatrypa savagei Johnson, Boucot, and Murphy, 1976,

p. 72–73, pl. 21, figs. 14–25; pl. 22, figs. 1–13.

Reticulatrypa variabilis Johnson, Boucot, and Murphy,

1976, p. 73–74, pl. 47, figs. 13–26.

Rhipidium sp. cf. R. tenuistriatum (Lindstrom, 1880). Amsden, Boucot, and Johnson, 1967, p. 866, pl. 108,

figs. 1–11.

Rhipidium (Pararhipidium) filicostatum Boucot, Johnson,

and Zhang, 1988, p. 113, pl. 5, figs. 1–19.

Rhynchotreta sp. aff. R. americana (Hall, 1879). Boucot,

Johnson, and Zhang, 1988, p. 115–116, pl. 6, figs.

41–49.

Rhynchotreta cuneata (Dalman, 1828). Johnson, Boucot,

and Murphy, 1976, p. 65–66, pl. 9, figs. 17–32.

Salopina boucoti Sheehan, 1976, p. 721–722, pl. 1, figs.

13–23; pl. 2, figs. 1–6.

Salopina sp. cf. S. conservatrix (McLearn, 1924). Johnson,

Boucot, and Murphy, 1976, p. 30–31, pl. 8, figs.

25–32.

Salopina delta Johnson, Boucot, and Murphy, 1976, p.

31–32, pl. 34, figs. 1–16.

Salopina submurifer Johnson, Boucot and Murphy, 1973, p.

26–28, pl. 11, figs. 15–23; pl. 12, figs. 1–19.

Severella munda Johnson, Boucot, and Murphy, 1976, p.

46–47, pl. 38, figs. 1–30; pl. 39, figs. 1–23.

Severella spiriferoides Johnson, Boucot, and Murphy, 1976,

p. 45–46, pl. 16, figs. 15–28.

Skenidioides operosa Boucot, Johnson, and Murphy, 1976,

p. 23–24, pl. 29, figs. 1–15.

Skenidioides sp. cf. S. pyramidalis (Hall, 1852). Sheehan,

1976, p. 714–715, pl. 1, figs. 1–12.

Spirigerina marginalis (Dalman, 1828). Johnson, Boucot,

and Murphy, 1976, p. 69–70, pl. 22, figs. 14–28; pl.

23, figs. 1, 2.
MACROFOSSIL BIOSTRATIGRAPHY OF THE EASTERN GREAT BASIN 115

Spirinella pauciplicata (Waite, 1956), p. 17, pl. 3, figs. 6–10.

Sheehan, 1982, p. 50, pl. 11, figs. 29–31; pl. 12,

figs. 1–18.

Spirinella pauciplicata (Waite, 1956) eganensis Sheehan,

1982, p. 50, pl. 12, figs. 15–18. 

Spondylopyxis ignotus Johnson, Boucot, and Murphy, 1976,

p. 48, pl. 37, figs. 12–24.

Stegerhynchus estonicus Rubel, 1977. =Ferganella borealis

of Sheehan, 1982, pl. 8, figs. 1–10. Boucot,

Johnson, and Zhang, 1988, p. 115, pl. 6, figs. 9–33.

Stegerhynchus? lincolnensis (Johnson, in Johnson and Reso,

1964), pl. 19, figs. 5–12. Jin, 1989, p. 55. Johnson,

Boucot, and Murphy, 1976, p. 64–65, p. 47, figs.

1–12.

Tenellodermis matrix Johnson, Boucot and Murphy, 1973, p.

65–66, pl. 9, figs. 1–19.

Vadimia nevadensis Boucot and Rong, 1994, p. 407;

Johnson, Boucot, and Murphy, 1976, p. 44, pl. 17,

figs. 1–10.

Virgiana utahensis Sheehan, 1980, p. 3–7, pl. 1, figs. 15–17;

pl. 2, figs. 1–10. 

Vosmiverstum wenlockum Boucot, Johnson, and Zhang,

1988, p. 112–113, pl. 4, figs. 1–16. Johnson, Boucot, and Murphy, 1976, p. 41, pl. 3, figs. 14–18.

Zygatrypa paupera (Billings, 1866). Copper, 1977, p.

310–311, pl. 37, figs. 21–19.

Zygatrypa stenoparva Boucot, Johnson, and Zhang, 1988, p.

117, pl. 8, figs. 11–28.

SILURIAN CORALS

Aphyllostylus gracilis Whiteaves, 1904. Stearn, 1956 p. 91,

pl. 6, figs. 1, 8.

Arachnophyllum kayi Merriam, 1974, p. 43, pl. 5, figs. 7, 8.

Astenophyllum patula (Rominger, 1876). Ehlers, 1973, p.

44, pl. 1, figs. 9–12; pl. 19, fig. 11.

Asthenophyllum sp. cf. A. orthoseptatum Grubbs, 1939, p.

546–547, pl. 61, figs. 14–18.

Cyathophylloides fergusoni Merriam, 1974, p. 33, pl. 5, figs.

9, 10.

Cystihalysites magnitubus (Buehler, 1955), 68, pl. 11, figs.

1–3. Merriam, 1974, p. 15.

Denayphyllum denayensis Merriam, 1974, p. 57, pl. 7, figs.

15–18.

Entelophyllum engelmanni Merriam, 1973, p. 38–39, pl. 10,

figs. 5–11; Merriam, 1974, p. 49, pl. 10, figs. 5–13.

Entelophyllum engelmanni subsp. b Merriam, 1973, p. 39,

pl. 10, figs. 12–13; pl. 11, figs. 26–17.

Entelophyllum eurekaensis Merriam, 1973, p. 39–40, pl. 10,

figs. 1–4. Merriam, 1974, p. 49, pl. 10, figs. 1, 2, 14,

15.

Entolophylloides (Prohexagonaria) occidentalis Merriam,

1974, p. 50–51, pl. 9, figs. 1–4. 

Halysites labyrinthica (Goldfuss, 1826). Buehler, 1955, p.

29–30, pl. 3, figs. 1–5. Ehlers, 1974, p. 50, pl. 3,

fig. 7. 

Neophyma crawfordi Merriam, 1974, p. 51, pl. 13, figs. 5–8.

Palaeocyclus porpita mcallisteri Merriam, 1974, p. 39–40,

pl. 1, figs. 12–15, 17.

Petrozium mcallisteri Merriam, 1974, p. 48, pl. 9, figs. 6–10.

Rhegmaphyllum sp. aff. R. conulus (Lindstrom, 1868, p. 428,

pl. 6, fig. 8). Ehlers, 1973, p. 53, pl. 4, figs. 3–5,

Merriam, 1974, p. 31.

Ryderophyllum ubehebensis Merriam, 1974, p. 44–45, pl. 6,

figs. 1–7.

Tryplasma sp. cf. T. hedstromi Wedekind, 1927, pl. 29, figs.

1, 2.

Tryplasma newfarmeri Merriam, 1974, p. 37–38, pl. 2, figs.

1–4.

Tryplasma radicula (Rominger, 1876). Ehlers, 1973, p. 53,

pl. 4, figs. 13–14.

Manuscript approved for publication May 12, 1997

Published in the Central Region, Denver, Colorado

Graphics and photocomposition by Carol A. Quesenberry

Edited by Lorna Carter PLATE 1