The Diatom Genus Actinocyclus in the 

Western United States

A, Aciinocyclm Species from Lacustrine Miocene Deposits pf the 

Western United States

B, Geologic Ranges of Lacustrine Species, Western SnltS States

0 ; SU G E Q L Q G S U PR O F E,S g- 1 PA P: :B - B
AVAILABILITY OF BOOKS AND MAPS OF THE U.S. GEOLOGICAL SURVEY

Instructions on ordering publications of the U.S. Geological Survey, along with prices of the last offerings, are given in the current-year 

issues of the monthly catalog "New Publications of the U.S. Geological Survey." Prices of available U.S. Geological Survey publications released prior to the current year are listed in the most recent annual "Price and Availability List." Publications that may be listed in various U.S. 

Geological Survey catalogs (see back inside cover) but not listed in the most recent annual "Price and Availability List" may no longer be 

available.

Reports released through the NTIS may be obtained by writing to the National Technical Information Service, U.S. Department of 

Commerce, Springfield, VA 22161; please include NTIS report number with inquiry.

Order U.S. Geological Survey publications by mail or over the counter from the offices listed below.

BY MAIL

Books

Professional Papers, Bulletins, Water-Supply Papers, Techniques of Water-Resources Investigations, Circulars, publications of 

general interest (such as leaflets, pamphlets, booklets), single copies 

of Earthquakes & Volcanoes, Preliminary Determination of Epicenters, and some miscellaneous reports, including some of the foregoing series that have gone out of print at the Superintendent of 

Documents, are obtainable by mail from

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Subscriptions to periodicals (Earthquakes & Volcanoes and 

Preliminary Determination of Epicenters) can be obtained ONLY 

from the

Superintendent of Documents

Government Printing Office

Washington, DC 20402

(Check or money order must be payable to Superintendent of 

Documents.)

Maps

For maps, address mail orders to

U.S. Geological Survey, Information Services

Box 25286, Federal Center

Denver, CO 80225

Residents of Alaska may order maps from

US. Geological Survey, Earth Science Information Center

101 Twelfth Ave., Box 12

Fairbanks, AK 99701

OVER THE COUNTER

Books and Maps

Books and maps of the U.S. Geological Survey are available 

over the counter at the following U.S. Geological Survey offices, all 

of which are authorized agents of the Superintendent of Documents.

• ANCHORAGE, Alaska-Rm. 101, 4230 University Dr.

• LAKEWOOD, Colorado-Federal Center, Bldg. 810

• MENLO PARK, California-Bldg. 3, Rm. 3128, 

345 Middlefield Rd.

• RESTON, Virginia-USGS National Center, Rm. 1C402, 

12201 Sunrise Valley Dr.

• SALT LAKE CITY, Utah-Federal Bldg., Rm. 8105, 

125 South State St.

• SPOKANE, Washington-U.S. Post Office Bldg., Rm. 135, 

West 904 Riverside Ave.

• WASHINGTON, D.C.-Main Interior Bldg., Rm. 2650, 

18th and CSts.,NW

Maps Only

Maps may be purchased over the counter at the following 

U.S. Geological Survey offices:

• FAIRBANKS, Alaska-New Federal Bldg, 101 Twelfth Ave.

• ROLLA, Missouri-1 400 Independence Rd.

• STENNIS SPACE CENTER, Mississippi-Bldg .3101
The Diatom Genus Actinocyclus in the 

Western United States

J. Platt Bradbury and William N. Krebs, Editors

A. Actinocyclus (Bacillariophyta) Species from Lacustrine Miocene Deposits of the 

Western United States

By J. Platt Bradbury and William N. Krebs

B. Geologic Ranges of Lacustrine Actinocyclus Species, Western United States 

By William N. Krebs and J. Platt Bradbury

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543A-B

UNITED STATES GOVERNMENT PRINTING OFFICE : 1995
U.S. DEPARTMENT OF THE INTERIOR 

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY 

Robert M. Hirsch, Acting Director

For sale by U.S. Geological Survey, Map Distribution

Box 25286, MS 306, 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

Library of Congress Cataloging-in-Publication Data

The Diatom genus Actinocyclus in the Western United States / J. Platt Bradbury and 

William N. Krebs, editors.

p. cm.—(U.S. Geological Survey professional paper ; 1543) 

Includes bibliographical references

Contents: A. Actinocyclus (Bacillariophyta) species from lacustrine Miocene 

deposits of the Western United States / by J. Platt Bradbury and William N. Krebs— 

B. Geologic ranges of lacustrine Actinocyclus species, Western United States / by 

William N. Krebs and J. Platt Bradbury. 

Supt. of Docs, no.: I19.16:P1543A&B.

1. Actinocyclus, Fossil—West (U.S.) 2. Paleobotany—Miocene. 

II. Krebs, William N. III. Series. 

QE955.D53 1993

561'.93—dc20 93-35637

CIP
CONTENTS

[Letters designate the chapters]

(A) Actinocyclus (Bacillariophyta) species from lacustrine Miocene deposits of the Western United States, by J. Platt Bradbury and William N. Krebs

(B) Geologic ranges of lacustrine Actinocyclus species, Western United States, 

by William N. Krebs and J. Platt Bradbury
Actinocyclus (Bacillariophyta) Species from 

Lacustrine Miocene Deposits of the 

Western United States

By J. Platt Bradbury and William N. Krebs

THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543-A

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
CONTENTS

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

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

Acknowledgments.......................................................................................................... 1

Materials and methods ................................................................................................... 2

Choice of generic epithet................................................................................................ 2

Key for separation of some nonmarine species of Actinocyclus.................................... 3

Systematic descriptions.................................................................................................. 4

Paleoecology of Miocene lacustrine Actinocyclus......................................................... 13

References...................................................................................................................... 14

Index............................................................................................................................... 68

	PLATES

	[Plates follow references]

1. Actinocyclus acanthus .................................................................................................................../............................. 21

2. Actinocyclus cedrus......... ............................................................................................................................................ 23

3. Actinocyclus cedrus........... .......................................................................................................................................... 25

4. Actinocyclus cedrus and Actinocyclus c/av/o/M5.......................................................................................................... 27

5. Actinocyclus claviolus and Actinocyclus CM/?reMs......................................................................................................~ 29

6. Actinocyclus sp. cf. A cupreus and Actinocyclus «/jr«n^r,gj7..................................................................................... 31

7. Actinocyclus ehrenbergii and Actinocyclus grobunovii .............................................................................................. 33

8. Actinocyclus kanitzii, Actinocyclus krasskei, and Actinocyclus tubulosus.................................................................. 35

9. Actinocyclus krosskei and Actinocyclus mon'/w........................................................................................................... 37

10. Actinocyclus motilis............................ ......................................................................................................................... 39

11. Actinocyclus motilis and Actinocyclus nebulosus................... ..................................................................................... 41

12. Actinocyclus nebulosus, Actinocyclus normanii f. subsalsa, and Actinocyclus pinnulus........ .................................... 43

13. Actinocyclus pinnulus, Actinocyclus sp. cf. A. pinnulus, and Actinocyclus theleus........ ............................................ 45

14. Actinocyclus theleus, Coscinodiscus (^Actinocyclus) variabilis, and Actinocyclus venenosus.................................. 47

15. Actinocyclus venenosus ............................................................................................................................................... 49

VII
ACTINOCYCLUS (BACILLARIOPHYTA) SPECIES FROM

LACUSTRINE MIOCENE DEPOSITS OF THE

WESTERN UNITED STATES

By J. PLATT BRADBURY and WILLIAM N. KREBS

ABSTRACT

Species of the diatom genus Actinocyclus Ehrenberg 

were important constituents of lacustrine phytoplankton in 

the Western United States during much of the early and 

middle Miocene (19-10 Ma). Similar and (or) identical fossil Actinocyclus species are found elsewhere in the world, 

particularly in Eurasia, in Neogene lacustrine diatomaceous 

rocks. Ten new species of fossil lacustrine Actinocyclus 

(A acanthus, A. cedrus, A. claviolus, A. cupreus, A. motilis, 

A. nebulosus, A. pinnulus, A. theleus, A. venenosus, and 

Actinocyclus gorbunovii var. fossa) are described and a 

new name (A. krasskei) is proposed based on the study of 

samples from 115 localities in the Western United States 

that range in age from the early Miocene to Pleistocene. 

Seventy of these localities contain Actinocyclus. Diagnostic 

characteristics include degree and nature of fasciculation, 

size of pseudonodule, areolae density, disposition and 

shape of hyaline stripes on the valve disk and mantle, 

degree of undulation, diameter, presence and nature of marginal tubular processes and spines, size and shape of 

areolae, and character of labiate processes.

INTRODUCTION

The diatom genus Actinocyclus characterized openwater lacustrine environments in the Western United States 

during much of the early and middle Miocene (19-10 Ma). 

Fossil localities containing Actinocyclus are found in diatomites and diatomaceous shales deposited in paleolake systems of Nevada, Idaho, California, Oregon, and Washington 

(Krebs and others, 1987). The forms of Actinocyclus found 

in these deposits resemble those from other parts of the 

world (for example, Bradbury and Krebs, 1982; Bradbury, 

1984; Bradbury and others, 1985), particularly from Eurasia, 

where a number of distinct taxa have been described. Radiometric dates associated with Actinocyclus occurrences in the

United States suggest that some of the forms have biochronologic value. Preliminary information about the geologic 

distribution of related taxa in other parts of the world indicates that this group may have potential for use in a worldwide lacustrine diatom biochronology.

This report describes and presents light and scanning 

electron microscope photographs of several distinctive 

Actinocyclus species from the Western United States. An 

artificial key based on characters observable in the light 

microscope assists separation of these morphologically variable taxa. The key includes a few European taxa, some of 

which also appear in the United States, and two modern 

nearshore marine species that can live in limnic environments. One of these species, Actinocyclus normanii f. subsalsa (pi. 12, figs. 2-5), lives today in the Great Lakes and 

has been recovered from late Holocene sediments of Lake 

Ontario (Stoermer and others, 1985).

The appropriate morphological characters for taxonomic separation of Actinocyclus are still largely unknown. 

The variability of surface areolae patterns (for example, fasciculation), degree of undulation, and mantle characteristics 

is great in these centric diatoms, and may be environmentally 

controlled to some degree (Theriot and Stoermer, 1984). 

Study of smaller structures, such as labiate processes, external processes and pseudonodules, and their morphometric 

relationships may be required to understand the natural classification of these diatoms. We do not resolve these questions, but we do present guidelines for the consistent 

description and identification of Actinocyclus species applicable to biostratigraphy and paleoecology.

ACKNOWLEDGMENTS

We particularly acknowledge the efforts of Kathryn 

Dieterich-Rurup in securing scanning electron microscope 

photographs of the Actinocyclus species illustrated in the 

accompanying plates. Horst Lange-Bertalot photographed
THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

Krasske's type material of Coscinodiscus (Actinocyclus) 

miocenicus and C. (=A.) variabilis. E.G. Theriot, Reimer 

Simonsen, Simone Servant-Vildary, and O.K. Khursevich 

have all provided many helpful discussions and insights into 

the morphological variations and taxonomic-descriptive 

problems with Actinocyclus. Simone Servant-Vildary, 

Rainer Gersonde, S.W. Starratt, L.H. Burckle, and Fumio 

Akiba kindly supplied comparative material. J.A. Barron 

and Elisabeth Fourtanier reviewed the manuscript and 

provided many useful suggestions. We thank all these individuals for their interest in this study.

MATERIALS AND METHODS

Diatomites, diatomaceous tuffs, and lacustrine shales 

have been sampled from outcrops and wells in the Western 

United States. The locality numbers referred to in the text 

refer to these sites whose age (if known) and locations are 

given in Appendix 1 and figure 2 of Krebs and Bradbury 

(Chapter B).

To minimize contamination by water and airborne 

diatoms (Sovereign, 1963), outcrops were cleaned in the 

field to a depth of about 5 cm during sampling, and material 

representing 1-5 cm of stratigraphic thickness was removed 

and placed in air-tight plastic bags. About 1 cc of diatomaceous sediment, with all surfaces cleaned a second time, was 

disaggregated in distilled water and boiled in concentrated 

nitric acid. The samples, once rinsed of all traces of acid, 

were mounted in Hyrax (n=1.60). Observations for species 

descriptions were made with a compound microscope (LM) 

at appropriate magnifications.

An aliquot of the diatom preparation was settled on a 

scanning electron microscope (SEM) stub and sputtercoated with gold/palladium. SEM photographs of selected 

specimens were taken with a JEOL 35 C scanning electron 

microscope. In general, internal surfaces of diatoms are better preserved than external surfaces (Bradbury, 1984), but 

where appropriate, SEM documentation of both sides of the 

diatom was made to illustrate external characteristics necessary for identification. Type and LM-figured specimens are 

located on designated 2.54x7.62 cm microscope slides by 

England Finder (E.F.) coordinates.

CHOICE OF GENERIC EPITHET

Coscinodiscus, Cestodiscus, Stephanodiscus, Pontodiscus, and Actinocyclus have all been used as generic epithets 

for fossil lacustrine centric diatoms that possess a marginal 

ring of laterally expanded (fan-shaped) labiate processes and 

radial-fasciculate areolation (for example, Krasske, 1934; 

Lohman, 1957; Haj6s, 1970; Temniskova-Topalova and

others, 1981; Bradbury, 1984). The very close similarity of 

Pontodiscus and Cestodiscus (Radionova, 1987) suggests 

that some of these names might be synonymous.

Bradbury (1984) confirmed the presence of a pseudonodule on Neogene lacustrine centric diatoms from Idaho 

and China supporting their inclusion in the genus Actinocyclus (see also, Simonsen, 1975). Nevertheless, in some 

marine species of Actinocyclus, the pseudonodule is tiny and 

difficult to distinguish from a normal areola (Watkins and 

Fryxell, 1986), and Radionova (1987) maintained that Cestodiscus may or may not have a pseudonodule. She 

distinguished this genus from Actinocyclus by the form of 

the labiate process (mushroom-shaped in Cestodiscus and 

nozzle-shaped in Actinocyclus) and by the character of the 

velum covering the areolae (star-shaped perforations in 

Cestodiscus and sieve-like openings in Actinocyclus) (Radionova, 1987). Marginal hyaline stripes of unadorned silica, 

positioned above and around the openings of the labiate processes characterize many Cestodiscus species (Radionova,

1987), but these structures are also present on diatoms 

referred to Actinocyclus (Simonsen, 1982).

The choice of the generic epithet for these centric diatoms clearly depends upon whether expanded or restricted 

generic definitions are employed. SEM examination of representatives of type species may suggest the synonymy of 

some genera. Labiate process morphology in nonmarine 

diatoms of the family Hemidiscaceae is variable and easily 

altered by corrosion in fossil forms. Pseudonodules may be 

obscured by debris or overgrowths of silica and clay minerals, further complicating the use of these structures for 

generic classification. At this time, there is no compelling 

reason to use the name Cestodiscus for these otherwise 

clearly Actinocyclus-like diatoms, and the latter name is 

retained for this study. Coscinodiscus appears to be genuinely different (as shown by Radionova, 1987), although it 

is still not properly typified, and at least some Pontodiscus 

species have been incorporated into Actinocyclus (Khursevich and others, 1990).

The species of Actinocyclus described in this report 

have been separated by more or less obvious, if variable, 

morphological differences. It can be argued (compare Mann,

1988) that each paleolake contained its own Actinocyclus 

species, particularly when such paleolake systems were temporally separated by hundreds of thousands or millions of 

years. Such great temporal and geographic separation with 

concomitant differences in climate, geology, hydrology, and 

ecology reduce the likelihood of potential biological interaction between individuals of Actinocyclus despite their 

morphological similarity. Nevertheless, the morphological 

units described here are moderately consistent and at least 

imply similar environmental controls on Actinocyclus that 

can be meaningful for biostratigraphic and paleoecologic 

ends.
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES

KEY FOR SEPARATION OF SOME

NONMARINE SPECIES OF

ACTINOCYCLUS

The following key organizes the characters of the nonmarine species of Actinocyclus described in this report and a 

few others described elsewhere to facilitate their separation 

and identification. The species of Actinocyclus are quite 

variable, yet morphologically similar, and examination of a 

moderately large series of specimens is required to obtain an 

appreciation of the variation and a general sense of their 

structural characteristics. Even so, intermediate forms often 

occur that defy simple classification. Specimens at the very 

large and very small ends of the size spectrum may be difficult to sort out with this key.

A. Fasciculate: clearly defined sectors of areolae rows. 

B. Fascicles marked off only by radial rows of areolae. 

C. Pseudonodule large, conspicuous; areolae on 

marginal "/3 of disk in more or less regular tangential rows; often in brackish water. Actinocyclus ehrenbergii Ralfs, (pi. 6, fig. 3). 

C. Pseudonodule tiny, difficult or impossible to see 

in LM, especially in heavily silicified individuals; areolae on marginal Va of disk in undulating, disorganized rows. Areolae within fascicles parallel. Actinocyclus nebulosus, (pi. 11, 

figs. 3,4).

C. Pseudonodule small, but generally visible in LM. 

Marginal areolae not in widely spaced undulating rows. Areolae within fascicles subparallel/ 

subradial. Actinocyclus cupreus, (pi. 5, figs. 6,7)

B. Fascicles marked off by a combination of radial rows 

of areolae and (or) comparatively long, hyaline 

stripes originating at labiate process exit pore near 

disk/mantle juncture.

C. Hyaline stripes extending about f/3 the distance 

toward the valve center and continuing in a 

radial row of areolae (see Frenguelli, 1928; 

Krasske, 1934). Coscinodiscus (=Actinocyclus) 

variabilis (sensu Krasske, 1934), (pi. 14, figs. 

5,6).

C. Fascicles marked off only by long hyaline stripes 

that extend nearly to the valve center (see 

Schauderna, 1983). Actinocyclus kanitzii (Pant, 

and Grun.) Schauderna, (pi. 8, fig. 1).

C. Fascicles marked off by pyriform or cloveshaped hyaline stripes with narrow, pointed ends 

that extend a short distance towards the valve 

center; the remaining fascicle boundary composed of a radial row of areolae. Actinocyclus 

claviolus, (pi. 5, figs. 1, 2).

B. Fascicles marked off only by directional incongruity 

between adjacent sets of subparallel areolae rows. 

Hyaline stripes absent (see Hasle, 1977). Actinocyclus normanii (Juhl.-Dannf.) Hustedt, (pi. 12, 

figs. 2, 3).

A. Nonfasciculate: no clear sectors or fascicles of areolae, 

or fascicles irregularly formed, difficult to define or 

highly variable on specimens of different size. Hyaline stripes mark location of labiate processes. 

B. >12 areolae/10 Jim (usually 14-18).

C. Marginal processes present, located on the exit 

pore of labiate process. 

D. Marginal processes conspicuous.

E. Marginal processes narrow tubes with 

lateral, fin-like projections. Actinocyclus 

pinnulus, (pi. 13, fig. 1). 

E. Marginal processes are broad, irregularly 

forked tubes 1-2 Jim long. Actinocyclus 

nordlingen.sis Schauderna, (not figured). 

E. Marginal process usually angled, unforked 

rather broad tubes, occasionally adorned 

with lateral spines. Actinocyclus acanthus, 

(pi. 1, fig. 3). 

D. Marginal processes inconspicuous.

E. Marginal process is a low, small, shieldlike bump or nipple; often difficult to 

observe, fine areolation, 13-18 areolae/ 

10 Jim, diameter typically <30 |am. Actinocyclus theleus, (pi. 14, fig. 1). 

E. Marginal processes slender, unornamented tubes on hyaline stripes. Actinocyclus tubulosus (pi. 8, fig.7) Khursevich 

(Khursevich and others, 1990). 

C. Marginal processes at labiate process exit pore 

absent.

D. Diameter 20-70 |jm, valve conspicuously 

undulate, weakly undulate, or flat, areolae 

generally 12-13/10 Jim. Actinocyclus 

krasskei (Krasske), (pi. 8, figs. 2-8). 

E. Valve conspicuously undulate, often >50 

jim in diameter. Actinocyclus krasskei 

(undulate form), (pi. 8, fig. 5). 

E. Valve flat or weakly undulate, diameter 

typically <50 jam. Actinocyclus krasskei 

(pi. 8, fig. 2).

D. Diameter 30-70 \\m, valve conspicuously 

undulate, areolae 14-18/10 ^m. A "moat" 

surrounds the pseudonodule. Actinocyclus 

gorbunovii var. fossa, (pi. 7, fig. 3). 

B. <12 areolae/10 |nm

C. Areolae large (1+ |im), closely packed, typically 

7-10/10 |am, polygonal in outline.
THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

D. Conspicuous, generally pointed hyaline 

stripes enclosing exit pore and extending 

onto the valve disk. Actinocyclus venenosus, 

(pi. 15, fig. 1).

D. Generally inconspicuous hyaline stripes that 

end near the valve/mantle juncture. Spines 

may or may not be present at disk/mantle 

junction. Actinocyclus cedrus (pi. 2, fig. 1) 

and A. cedrus spinose form (pi. 4, fig. 4). 

C. Areolae smaller, circular in outline and typically

loosely packed. Marginal areolae rows sinuous

and interdigitating. Actinocyclus motilis, (pi. 9,

figs. 4-6).

SYSTEMATIC DESCRIPTIONS

ACTINOCYCLUS ACANTHUS 

Bradbury & Krebs sp. nov.

Plate 1, figures 1-9

Description.—Valve circular, shallowly concave 

with slightly raised margin. Diameter typically ranging 

from 30 to 100 jam. Disk with round areolae arranged in 

non-fasciculate, radial rows; 9-14 areolae/10 jam. Valve 

center of larger specimens sometimes hyaline, containing 

only scattered areolae. Small, often obscure, radial, marginal hyaline stripes at disk-mantle juncture mark positions 

of labiate processes and are adorned with stout, hollow 

tubules up to 2 jam in length that may bear terminal lateral 

spines. Tubule stems either rounded or angled (often triangular) in cross-section (pi. 1, fig. 7). Because of breakage, 

morphological characteristics of tubule ends seldom visible. Valve mantle finely areolate (20/10 jam) and steeply 

sloping away from disk margin. Labiate processes short, 

narrow-stemmed, with broad, spade-shaped labiae. Pseudonodule small, about 1 urn in diameter, and variably 

located between labiate processes near valve margin.

Variability.—The length of hyaline stripes appears to 

vary among individuals both within and between localities. 

In an unnamed unit at New Pass, Lander County, Nevada 

(loc. 42) and in the Esmeralda Formation (Miocene) at Cedar 

Mountain, Nye County, Nevada (loc. 74), the hyaline stripes 

are often very small and obscure (pi. 1, fig. 6). Specimens 

from the Bully Creek Formation (Miocene), Malheur 

County, Oregon (loc. 7) have longer hyaline stripes (2-3 jam 

or longer), as do occasional specimens from the Cedar 

Mountain section (Lohman, 1957).

The hyaline central area is largest and best developed in 

specimens from the Cedar Mountain section, while in material from New Pass it is smaller or absent. Pseudonodule 

position also seems to vary. In New Pass and Cedar Mountain (Esmeralda Formation) specimens, it is small and 

closely adjacent to a labiate process, while in the Bully 

Creek Formation material, it is located about >/3 the distance 

between two labiate processes.

Because of their susceptibility to abrasion and

corrosion, the external tubules of this species are often 

poorly preserved or incomplete. In material from New Pass, 

some appear to bifurcate or are adorned with short lateral 

spines or flanges, suggesting that the typically short, blunt 

tubes often seen in LM may be artifacts of preservation. 

Tubules vary in cross section, being either round, triangular, 

or elliptical, but it is not known how constant tubules are on 

a single specimen from our available material.

The apiculate species of Actinocyclus from other localities are close to the type in appearance, but not identical. 

Detailed study, including morphometric analysis, may 

require splitting this apiculate Actinocyclus group into several species.

Diagnosis.—Actinocyclus acanthus can be distinguished from other lacustrine members of the genus by the 

presence of robust, often angled, hollow thorn-like tubes on 

the hyaline stripes that mark the exit pores of labiate processes. A. gorbunovii is more finely areolate, and external 

tubules are absent. Actinocyclus nordlingensis Schauderna 

has forked tubes and is more finely areolate (14-20/10 jam). 

Its labiate processes are narrow-stemmed but comparatively 

long (>2 jam). The pseudonodule location in A. nordlingensis is located about lh the distance between adjacent labiate 

processes (Schauderna, 1983). Carina-like spines may be 

present on Actinocyclus cedrus, but they are irregularly 

placed, apparently solid, and not necessarily located on the 

hyaline stripes. Actinocyclus tubulosus Khursevich is 

smaller (16-34 jam diameter), has more densely packed 

areolae (16-22/10 jam), and external tubes with a rounded 

cross section. A. cedrus has coarse, polygonal areolae. Actinocyclus pinnulus is similar to A. acanthus, but has distinctly 

finned tubules, is clearly fasciculate, and has long, narrow 

hyaline stripes.

Types.—Holotype: Strew slide United States National 

Museum (USNM) #465534. specimen located at E.F. 

(England Finder) H46.

Isotypes: Strew slides in the following institutions: 

Academy of Natural Sciences of Philadelphia (ANSP) 

A-G.C. #64465; U.S. Geological Survey, Denver 

(USGS-D) #14 VII 85^; California Academy of Sciences (C AS) #216051.

Type Locality.—Because the diatom is best preserved 

and most abundant in unnamed deposits near New Pass, 

Lander County, Nevada (loc. 42 = USGS Denver 14 VII 

85-4), this site has been selected as the type locality.

Remarks.—The specific epithet "acanthus" (L. thorn) 

refers to the presence of hollow, thorn-like tubes at the 

labiate process exit pores.

Actinocyclus acanthus has also been found in the Bully 

Creek Formation, Harper Basin, Malheur County, Oregon, 

and in the Esmeralda Formation near Cedar Mountain, Nye 

County, Nevada (loc. 74). Here the taxon was originally 

described by Lohman (1957) as Cestodiscus apiculatus 

nomen nudum. At the Cedar Mountain section, Actinocyclus 

acanthus is associated with species of Surirella, Anomoeoneis, and Pinnularia (Lohman, 1957), whose modern
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES

relatives suggest deposition in moderately saline, alkaline 

water. At some levels in the New Pass locality, it is associated with Chaetoceros, also suggesting saline water, but 

elsewhere at New Pass, and at Bully Creek, freshwater species ofAulacoseira dominate the samples. At Silvies Valley, 

Grant County, Oregon (loc. 75), Actinocyclus acanthus is 

associated with large numbers of Fragilaria sp. cf. F. virescens. Other diatoms present include Aulacoseira, Tetracyclus, Tabellaria, Eunotia, and Achnanthes. Perhaps the 

morphological differences seen in Actinocyclus acanthus 

reflect salinity or other environmental characteristics.

ACTINOCYCLUS CEDRUS Bradbury & Krebs sp. nov.

Plate 2, figures 1-7; plate 3, figures 1-8; plate 4, figures 1-6

Description.—Valve circular, with slightly raised margin. Diameter typically 50-100 jam, but ranging from 20 to 

>150 jam. Valve face shallowly concave to weakly concentrically undulate with radial rows of large (1 jam diameter), 

polygonal-shaped areolae, ranging from 6-10/10 jam. Vague 

fasciculation of valve disk caused by bundles of mutually 

parallel areolae rows that extend variable distances towards 

the valve center progressively truncating one another (pi. 3, 

fig. 2). Valve center typically densely packed with areolae. 

Small, generally short, hyaline stripes at valve mantle junction barely extend over mantle to enclose large (1 |jm diameter) exit pores of labiate processes. Labiate processes 3-5 

|im tall, with narrow, round or oval stems and relatively 

broad, spade-shaped labiae. Disk/mantle margin often hyaline and irregularly areolate and (or) variably ornamented 

with solid, granule-, keel-, or spine-like protuberances. Mantle variably high (10-15 jam), and nearly perpendicular to 

valve face plane, with vertical areolae rows, 16 areolae/10 

|im. Pseudonodule small and variably located between labiate processes, generally closer to one.

Variability.—The disk/mantle juncture may or may 

not be hyaline and irregularly areolate, or ornamented with 

spine- or granule-like protuberances. Such ornamentation is 

more typical in specimens from the Turner Creek (Pit 

River) locality in Modoc County, California (loc. 17) (pi. 4, 

figs. 4-6), and less common at the type locality in Stewart 

Valley, Mineral County, Nevada (loc. 20). Areolae near the 

valve disk center are sometimes sparse and surrounded by 

hyaline silica. Fasciculation is more apparent in some specimens than others. For example, specimens from the 

Virginia Range, 16 km north of Virginia City, Storey 

County, Nevada (loc. 68), are not clearly fasciculate, 

although they conform to the species in other features. Size 

of the hyaline stripes varies to some degree among specimens from different sites and may represent temporal or 

environmental gradations within this species. Forms of this 

species from deposits correlated to the Aldrich Station Formation (Miocene), Lyon County, Nevada (loc. 1), and from 

deposits near Drewsey, Harney County, Oregon (loc. 63),

tend to be less fasciculate than the type and are typically 

spinose. The labiate processes are taller and thinner in specimens from Goose Creek, Baker County, Oregon (loc. 27).

Diagnosis.—Actinocyclus cedrus is very similar to A. 

venenosus, another nonmarine, fossil Actinocyclus species 

with coarse, polygonal areolation on the valve face. Actinocyclus venenosus is characterized by generally longer and 

more prominent hyaline stripes that extend well onto the 

valve disk. A. cedrus tends to be more obviously, if irregularly, fasciculate than A. venenosus, and concentric undulation is usually poorly developed in A. cedrus.

Types.—Holotype: Strew slide USNM #465535, specimen located at E.F. L38/1.

Isotypes: Strew slides ANSP A-G.C. #64466; CAS 

#216052; USGS-D #31:1:88-1 (65).

Type Locality.—"Diatomite Ridge" in Stewart Valley, 

northwest of Cedar Mountain, Mineral County, Nevada 

(loc. 20 = USGS Denver 31 I 88-1 [651) has been selected 

as the type locality for Actinocyclus cedrus. The collection 

site is located at 38.62° N., 117.94° W., about 8 m below the 

top of a 40-m section of buff, thin-bedded to laminated diatomaceous shales, and about 28 m above a volcanic ash dated 

at 15.1 Ma (S.W. Starratt, written commun., 1986). The section has been assigned to the Esmeralda Formation.

Remarks.—The specific epithet "cedrus" (L. cedar) 

refers to the type locality of this species near Cedar Mountain. The type material was collected by S.W. Starratt and 

represents his sample DR-65. Lohman (1957) identified this 

diatom by the name Cestodiscus cedarensis nomen nudum at 

a nearby locality on the southeast flank of Cedar Mountain. 

The same (or very similar) species is reported from the Otis 

Basin, Harney County, Oregon (VanLandingham, 1967) 

under the name Coscinodiscus subtilis.

Associated diatoms at the type locality include freshwater, benthic Fragilaria species, Ellerbeckia arenaria v. 

teres, Tetracyclus sp., and a dominance of planktonic Aulacoseira spp.

ACTINOCYCLUS CLAVIOLUS 

Bradbury & Krebs sp. nov.

Plate 4, figure 7; plate 5, figures 1-5

Description.—Valve circular, nearly flat with a 

slightly raised or depressed center. Diameter ranging 

between 17 and about 60 jam, typically about 27-30 ujn. 

Areolae about 13-14/10 jam, small, round and in subparallel to radial rows. Areolae rows grouped into fascicles set 

off by continuous rows of areolae originating from hyaline 

stripe of each labiate process and running to valve center. 

Valve center sometimes a small, irregular hyaline area. 

Hyaline stripes marking locations of labiate processes comparatively long (3-7 jam), narrowed, or pointed proximally 

and expanded distally to form irregular, somewhat triangular-, cross- or clove-shaped areas (pi. 5, figs. 1-3). External
THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

expression of labiate process is a short, blunt, rather thickwalled tube with a narrow opening rising 1-2 Jim above 

disk/mantle junction (pi. 5, fig. 3). Valve mantle steeply 

sloping away from disk, finely areolate (about 26/10 |im) 

and fairly short. Labiate processes not observed, but presumably with narrow, round stems. Pseudonodule of 

medium size (1-2 ^m in diameter) and often easily visible 

between hyaline stripes (pi. 5, figs. 2, 4, 5).

Variability.—Actinocyclus claviolus is known only 

from Jungle Point, Idaho County, Idaho (loc. 33). At this 

locality, large specimens have fascicles with radial areolae 

rows. Consequently, the radial row associated with the hyaline stripe is less distinctive. Small specimens have fascicles 

in which the areolae rows are parallel to the central areolae 

row or in irregular groups of subparallel rows. The hyaline 

stripes are irregular but always somewhat pyriform or crossshaped. Larger specimens have proportionally longer 

stripes. The central hyaline area is typically irregular, but 

always small.

Diagnosis.—Actinocyclus claviolus is morphologically 

similar to A. cupreus, but it can be distinguished by its thick, 

prominent hyaline stripes, generally smaller size, and the 

presence of thick external tubes over the labiate process 

pore. Like A. cupreus, A. claviolus is also morphologically 

close to Coscinodiscus (-Actinocyclus) variabilis (sensu 

Krasske 1934) (pi. 14, figs. 5, 6), but that species does not 

have laterally expanded hyaline stripes and is more coarsely 

areolate than A. claviolus. In addition, the hyaline stripes of 

Coscinodiscus variabilis (sensu Krasske) are typically 

longer, extending to about lh of the disk radius.

Types.—Holotype: Strew slide USNM #465536, specimen at E.F. R28/2.

Isotypes: Strew slides ANSP A-G.C. #64467; 

USGS-D #5 XII 80-7; CAS #216053.

Type Locality.—The type locality of Actinocyclus claviolus is an unnamed lacustrine deposit at Jungle Point, 

northwest of the town of Lowell, Idaho County, Idaho; 

SEto, SEi/4 sec. 15, T. 33 N., R. 6 E. (loc. 33 = USGS 

Denver 5 XII 80-7). The diatoms at this locality show 

some corrosion and breakage.

Remarks.—The specific epithet "claviolus" (L. diminutive for nail or clove) refers to the small clove-like shape of 

the hyaline stripes of this species. Aulacoseira sp. cf. A. 

praeislandica is the dominant diatom associated with Actinocyclus claviolus.

ACTINOCYCLUS CUPREUS 

Bradbury & Krebs sp. nov.

Plate 5, figures 6-9

Description.—Valve circular, shallowly concave with 

a broadly raised margin. Diameter typically around 50 |am 

and ranging between 20 and 76 jam. Areolae roundpolygonal, in roughly radial to parallel rows. Areolae rows

grouped in broad fascicles set off by continuous rows of 

areolae originating from hyaline stripe of each labiate process and running to valve center. Areolae about 13/10 |im, 

generally loosely packed near valve center. Comparatively 

long (2-5 jam), prominent hyaline stripes extend from exit 

pore of labiate processes over disk/mantle junction and onto 

disk. Valve mantle finely areolate (about 20/10 |im) and 

gently sloping away from valve disk. Labiate processes 

with narrow, round stems and rather broad, spade-like 

labiae. Pseudonodule small, but usually clearly visible; 

located at a variable distance between labiate processes on 

disk-mantle junction.

Variability.—To date, Actinocyclus cupreus has been 

found at four localities in the Western United States. At 

Copper Kettle Canyon, Churchill County, Nevada (loc. 16), 

evident variability has been found in the degree of fasciculation. Small specimens, probably referable to this species, 

tend to be more coarsely areolate and do not clearly show 

the radial areolae rows running between the hyaline stripes 

and the valve center that separate the areolae fascicles. In 

large specimens, strong valve undulation may obscure the 

radial areolae rows that border fascicles. Between labiate 

processes, areolae rows become more radial than mutually 

parallel in small individuals. Hyaline stripes show some 

variation in length, with relatively longer stripes on larger 

specimens. At Juliaetta, Nez Perce County, Idaho (loc. 32), 

and at Jungle Point, Idaho County, Idaho (loc. 33), diatoms 

referable to A. cupreus are comparatively small and resemble A. claviolus and A. krasskei, respectively, although the 

distinctive fasciculation is evident. In the Miocene Humboldt Formation, Eureka County, Nevada (loc. 30), comparatively large forms are present that closely resemble the 

Copper Kettle Canyon material.

Diagnosis.—Actinocyclus cupreus is distinguished 

from A. ehrenbergii (which also has single, radial areolae 

rows between hyaline stripes and the valve center) by its 

inconspicuous small pseudonodule, finer areolation, and 

generally smaller size. See also diagnosis under A. nebulosus 

and A. claviolus.

Actinocyclus cupreus is also similar to an Actinocyclus 

species identified as Coscinodiscus variabilis Frenguelli by 

Krasske (1934) from Miocene freshwater deposits near the 

town of Ruckers on the southeast margin of the Vogelsberg 

Range at the northern end of the Rhine graben in central 

Germany. The Ruckers material tends to have slightly 

coarser areolation (9-12 areolae/10 jam) than do specimens 

from Copper Kettle Canyon, and the hyaline stripes are 

longer, often extending to one half the valve radius. Also, C. 

variabilis appears to have an external extension associated 

with each pore of the labiate process, unlike A. cupreus. 

Pseudonodules are visible on well-preserved valves of the 

Ruckers material indicating their probable affiliation with 

Actinocyclus.

Types.—Holotype: Strew slide USNM #465537, E.F. 

F46/4.
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES

Isotypes: Strew slides ANSP A-G.C. #64468; 

USGS-D #15 XII 88-1F; CAS #216054.

Type Locality.—The type locality of Actinocyclus 

cupreus is an unnamed formation at Copper Kettle Canyon 

in the northern Stillwater Mountains, sec. 26, T. 24 N., 

R. 34 E., Churchill County, Nevada (loc. 16 = USGS 

Denver 15 XII 88-1F). Specimens of A. cupreus are 

uncommon and poorly preserved.

Remarks.—The specific epithet "cupreus" (L. of 

copper) refers to the type locality in Copper Kettle Canyon. 

A similar, perhaps closely related species of Actinocyclus 

has been found in Miocene freshwater sediments now 

covered by the Sea of Japan in the region of Yamato Bank 

(pi. 6, figs. 1,2) (Burckle and Akiba, 1978; Tsoy and others, 

1985), and from Japan (Koizumi, 1988). Specimens from 

Yamato Bank have hyaline stripes that can be very long, in 

some cases extending more than halfway towards the valve 

center in large individuals. The valve disk of this diatom is 

flatter than in A. cupreus, and the parallel-rowed fasciculation pattern is more regular and distinct. Further studies may 

confirm that all these diatoms are closely related.

Freshwater, planktonic species of Aulacoseira dominate the type material containing Actinocyclus cupreus; 

Pinnularia, Tetracyclus, and Fragilaria are present in 

smaller numbers.

ACTINOCYCLUS EHRENBERGII 

Ralfs in Pritchard (1861)

Plate 6, figures 3-9; plate 7, figures. 1, 2

Description.—Descriptions, figures, and diagnoses of 

Actinocyclus ehrenbergii from nearshore marine localities 

(such as in Hustedt, 1930) suffice to identify and separate 

this distinctive diatom from nonmarine species of Actinocyclus. The chief characteristic is the large, well defined, 

annulate-operculate pseudonodule of A. ehrenbergii. In 

addition, marine examples of this species have numerous, 

close-spaced, short-stemmed labiate processes. In contrast, 

nonmarine Actinocyclus species appear to have small, nonannulate (but perhaps also operculate?) pseudonodules and 

typically few and wide-spaced labiate processes with relatively longer stems.

Remarks.—Actinocyclus ehrenbergii (pi. 6, figs. 3-5) 

is present in upper Miocene continental deposits of the 

Quiburis Formation, Edgar Canyon, Pima County, Arizona 

(loc. 92), where it is associated with brackish-water diatoms, 

such as Hyalodiscus sp. cf. H. laevis, Melosira moniliformis, 

Diploneis interrupta, D. ovalis, Mastogloia braunii, M. 

elliptica, Frustulia interposita, species of Amphora, 

Nitzschia, Achnanthes, Navicula, and many others. Benthic 

alkaline-water diatoms, such as Fragilaria brevistriata, 

Denticula elegans, and Caloneis silicula, are also abundant 

and indicate a transitional brackish, perhaps estuarine 

(Blake, 1902), to freshwater environment. A. ehrenbergii is

also present in the uppermost Miocene to lowermost 

Pliocene Furnace Creek Formation of Death Valley, Inyo 

County, California (loc. 113).

ACTINOCYCLUS GORBUNOVII var. FOSSA 

Bradbury & Krebs var. nov.

Plate 7, figures 3-8

Description.—Valve face characterized by comparatively small, round areolae (14-18/10 Jim) arranged in a 

radial, generally non-fasciculate pattern. Valve diameter 

averages about 30 Jim but varies between 15 and 48 Jim. 

Valve disks typically strongly undulate. Labiate processes 

with narrow, long stems and circular cross sections. Short 

(4 |im) hyaline stripes extend from external opening of 

labiate process at valve margin towards valve center. 

Pseudonodule comparatively distinct, located between labiate processes, and usually closer to one. A tiny, moat-like 

structure surrounds external opening of pseudonodule 

(pi. 7, figs. 5-6). In favorable cases, this structure can be 

seen by LM as a small ring of hyaline silica around pseudonodule pore.

Variability.—Actinocyclus gorbunovii var. fossa is 

known from only one locality. Some variation in the degree 

of areolation is present in the center of the valve disk. In 

large individuals, areolae may be loosely scattered about the 

valve center. Large valves tend to be more conspicuously 

undulate than small valves. Not enough SEM observations 

have been made to determine the constancy of the moat-like 

structure surrounding the external opening of the pseudonodule. From light microscope observations, it appears to be 

better developed in some valves than in others.

Diagnosis.—Actinocyclus gorbunovii var. fossa is 

distinguished from A. gorbunovii by the presence of a small 

moat-like structure of hyaline silica that surrounds the external 

opening of the pseudonodule. This structure is not present in 

type material of Actinocyclus gorbunovii (G.K. Khursevich, 

written commun., 1990). The closely spaced areolae (14-18/ 

10|i m) and the strongly undulate valve disk, however, suggest 

a varietal affinity with Actinocyclus gorbunovii.

Actinocyclus krasskei is generally more coarsely 

areolate (12-13/10 jam, although finer forms are reported), 

smaller, and flatter than A. gorbunovii var. fossa. 

Nevertheless, considerable variation exists, and some overlap is found in all these characters. Separation of these 

species is not likely to be consistent in mixed assemblages, 

and it may turn out that they all belong to the same variable 

taxon.

Types.—Holotype: Strew slide USNM #465538, E.F. 

N33/L

Isotypes: Strew slides ANSP A-G.C. #64775; 

USGS-D #2 IX 87—3B; CAS #216081.

Type Locality.—Actinocyclus gorbunovii var. fossa is 

common in the early middle Miocene leaf-bearing
THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

diatomites at Forty-nine Camp, Washoe County, Nevada 

(loc. 69). Preservation is variable, and valves are often 

broken.

Remarks.—The varietal epithet "fossa" (L. "ditch") 

refers to the small ditch or moat surrounding the pseudonodule of this taxon. In the upper Cedarville Formation at Fortynine Camp, Washoe County, Nevada, Actinocyclus gorbunovii var. fossa is associated with abundant Aulacoseira 

sp. cf. A. islandica. Tetracyclus ellipticus, Ellerbeckia 

arenaria v. teres, and several other freshwater diatoms are 

present in smaller numbers.

Bradbury (1984) suggested that Coscinodiscus gorbunovii (Sheshukova-Poretzkaja and Moissejeva, 1964), 

belonged in the genus Actinocyclus according to its general 

morphology and the presence of a pseudonodule in a related 

species from the Poison Creek Formation (Miocene) in the 

Snake River Plain, Idaho. Khursevich and others (1990) 

formally transferred C. gorbunovii to Actinocyclus. The 

Poison Creek Formation taxon is now regarded as distinct 

from A. gorbunovii and has herein been described as Actinocyclus venenosus. In view of the biostratigraphic importance of A. gorbunovii in Eurasia and of closely related taxa 

in the Western United States, it is appropriate to evaluate 

the original description of Coscinodiscus gorbunovii Shesh. 

and its varieties.

The following description of Coscinodiscus gorbunovii 

represents an approximate translation from Russian 

(Sheshukova-Poretzkaja and Moissejeva, 1964). The original description includes two varieties, Coscinodiscus 

gorbunovii \. gorbunovii Shesh. and C. gorbunovii v. ethmodiscoidus Moiss.

COSCINODISCUS GORBUNOVII SHESHUKOVA 

In Sheshukova-Poretzkaja & Moissejeva 1964,

P. 94, pi. 2, figs. 1-5.

Description.—Cells of yellow-brown color, short 

cylindrical or disk-shaped, with or without intercalary 

bands, 30-70 |im in diameter, 2-20 [am tall. Valves concentrically undulate with a single concave zone and concave center. Valve structure of small, dense areolae in 

radial rows, 12-18/10 [am, not forming fascicles. Central 

area small, round or of irregular shape with one or several 

isolated areolae, or occasionally absent. Distinct undulating rows of areolae occur at the valve margin, and a ring 

of 7-14 short, blunt spines (=tubules) from which short, 

radial, hyaline rays emanate towards the valve center. 

Valve mantle edge narrow, delicately crosshatched (23-24 

striae/10 |im or not visible). Short-cylindrical cells have 

valves with clearly expressed mantles of moderate height 

(3-4 |im) and with small areolae in radial and obliquely 

intersecting rows, 23-24/10 |im.

COSCINODISCUS GORBUNOVII v. GORBUNOVII SHESHUKOVA 

In Sheshukova-Poretzkaja & Moissejeva 1964,

P. 96, pi. 2, figs. 1-5.

Description.—Frustules disk-shaped, height 2-3 |im, 

without intercalary bands. Diameter of the valves 35-70 |im. 

On the frustule, 13-18 rows of areolae/10 |im, central zone 

present, marginal zone narrow, delicately crosshatched. 

Mantle not developed.

COSCINODISCUS GORBUNOVII v. ETHMODISCOIDUS 

MOISSEJEVA in Sheshukova-Poretzkaja & Moissejeva 1964,

P. 96, pi. 3, figs. 1-7.

Description.—Frustules short-cylindrical with small 

collar-shaped, structureless intercalary bands, 30-50 \im 

diameter, and up to 20 |0m high. 12 areolae rows/10 jam on 

the frustule, central zone absent, marginal zone inconspicuous. Mantle of the frustule 3-4 [am high with small areolae 

in radial and obliquely intersecting rows, 23-24/10 |im.

Variability and Comments on the Descriptions.—For 

the most part, the description of Coscinodiscus gorbunovii 

and varieties is straight forward. Some points however, 

require discussion and revision.

1. It is not quite clear what is meant by the undulating 

areolae rows on the valve margin. In direct translation this 

passage reads, "In the area by the edge are distinct 

concentric-undulating rows of the same kind of areolae 

and * * *". Published figures of this species (SheshukovaPoretzkaja and Moissejeva, 1964; Cheremisinova, 1968; 

Moissejeva, 1971; and Temniskova-Topalova and others, 

1981) do not clearly illustrate what might be meant by this 

remark. It is possible that it refers to a wavy pattern of 

short, interdigitated, and truncated radial areolae rows 

sometimes visible near the margin of this diatom. Alternatively, it could refer to a looser and somewhat undulate 

pattern of areolae distributed tangentially along the valve 

margin and visible in some specimens. The revised 

description of A. gorbunovii (Khursevich and others, 1990) 

does not mention this feature. Such patterns are evident on 

other freshwater Actinocyclus species, however, and are 

of unknown taxonomic significance. 

2. The description of valve disk undulation sounds equivalent to the "shallowly concave" terminology used in this 

report. Both light and SEM photographs of Coscinodiscus 

gorbunovii from the literature show individuals that have 

raised central areas (truly "concentrically undulate") (for 

example, Temniskova-Topalova and others, 1981 pi. 3, 

fig. 3) among specimens that are shallowly (or deeply) concave. This probably represents normal variation within the 

species. It appears that undulation consisting of a raised 

margin and center (for example, in Khursevich and others, 

1990) characterizes larger individuals of this species.
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES

3. The reference to the yellow-brown color of Coscinodiscus gorbunovii is taken to be taxonomically important 

by Moissejeva (1971). The color of Coscinodiscus gorbunovii or any other diatom for that matter, partly relates to 

the density of its structural elements, but also to its magnification, the refractive index of the mounting medium, and 

related optical properties that have nothing to do with the 

biological characters required for taxonomic separation 

(Bradbury, 1984).

4. The comment about the presence or absence of "intercalary bands" probably reflects preservation and also seems 

irrelevant to the description of Coscinodiscus gorbunovii.

5. The "lack of mantle development" suggested for Coscinodiscus gorbunovii v. gorbunovii presumably means 

that the mantle of this species is short in comparison to that 

of Coscinodiscus gorbunovii v. ethmodiscoidus.

6. The presence of short, blunt spines associated with the 

hyaline rays is difficult to confirm by most illustrations of 

Coscinodiscus gorbunovii. Typically, no spines of any kind 

are shown, and the only figure that clearly illustrates spines 

(Temniskova-Topalova and others, 1981, pi. 3, fig. 3), 

shows a number of irregular, spine-like protrusions along 

the disk/mantle junction and without clear relation to the 

hyaline rays. The description of the spines in this case 

states that they are between the hyaline rays (TemniskovaTopalova and others, 1981). Such spine-like projections 

(see also Khursevich and others, 1990) may represent an 

ecotypical variant of this species.

The description of the synonym, Pontodiscus gorbunovii (Shesh.) Shesh. et Moiss. (Temniskova-Topalova 

and others, 1981), also indicates the presence of external 

tubules at the openings of the labiate processes, although 

these are not illustrated. Furthermore, Moissejeva in an oral 

communication to G.K. Khursevich (written commun., 

1989) stated that the labiate processes of Coscinodiscus 

gorbunovii were mistaken as short spines in the original 

description of this species.

7. Khursevich and others (1990) gave 16-18 areolae 

rows/10 m and 14-18 areolae/10 m (presumably along a 

radial row) for A. gorbunovii. According to Khursevich 

and others (1990), the coarser Coscinodiscus gorbunovii v. 

ethmodiscoidus is no longer considered a variety of A. 

gorbunovii. In this report, we follow the revised description with regard to areolar density of A. gorbunovii.

ACTINOCYCLUS KRASSKEI (KRASSKE) 

Bradbury & Krebs nom. nov.

Plate 8, figures 2-6, 8-11; plate 9, figures 1-3

Syn. Coscinodiscus miocenicus Krasske 1934, p. 23, 

figs. 5-7.

A nomenclatural problem exists with Coscinodiscus 

miocenicus Krasske. Unmounted type material of this taxon 

has not been found, precluding SEM investigations to

precisely document micromorphological characters of this 

species. Nevertheless, pseudonodules can be seen by light 

microscopy in well-preserved specimens of type material 

(pi. 8, fig. 3). By this and other criteria (see Simonsen, 1982), 

Coscinodiscus miocenicus can be confidently transferred to 

Actinocyclus. Because the name Actinocyclus miocenicus 

Jous6 (Jous6,1973) has preempted the logical new combination, we propose that Actinocyclus krasskei be used to designate this taxon.

Description (From Krasske, 1934).—Valve circular, 

rather flat, 11-47 Jim in diameter. Large areolae in radial 

rows, at the margin about 13/10 |im, organized in unclear 

fascicles. Secondary rows in clear spirals. Mantle ornamented with delicate areolae organized in three self-crossing 

linear systems (quincunx), about 20 striae in 10 Jim. Central 

area lacking. Small individuals show irregular areolation.

Observations of the type material [Beuern (Vogelsberg) Hessen Kieselgur O. Miocene No. 3004 and 3005, 

No. 24/25] by LM indicate the presence of a comparatively 

distinct pseudonodule, located between short to mediumlength, hyaline stripes that mark the position of narrow, 

long-stemmed labiate processes. In addition, concentrically 

undulate valve disks are common in the material. Areolae 

along radial rows are about 12-13/10 Jim in type material, 

although densities of 15-22/10 Jim had been stated for this 

species (Moissejeva, 1971; Temniskova-Topalova and 

others, 1981). No external tubes are visible at the labiate 

process exit pores.

Variability.—As stated by Krasske (1934), small individuals have irregular areolation. The shape of the valve disk 

varies from flat to concentrically undulate. In the Western 

United States, diatoms that otherwise conform to Actinocyclus krasskei have somewhat undulate disks and diameters 

as large as 70 nm. The large, undulate forms of A. krasskei 

may actually be synonymous with Coscinodiscus gorbunovii, although they tend to be coarser than most Asian 

examples of A. gorbunovii.

Diagnosis.—Moissejeva (1971) stated that the marginal zone of Coscinodiscus gorbunovii is similar to that of 

Coscinodiscus miocenicus Krasske, but that C. gorbunovii 

is larger, yellow-brown, and concentrically undulate. Type 

material of Coscinodiscus miocenicus (light yellow or 

colorless) includes undulate valves whose diameter (11- 

47 nm; Krasske, 1934) overlaps with the lower end of the 

size range reported for Actinocyclus gorbunovii. The color 

of these diatoms is not taxonomically relevant, and in most 

other respects A. gorbunovii and A. krasskei are quite similar. In the type material and in examples of A. krasskei 

from the Western United States, areolae density does not 

exceed 13/10 ^im along radial areolae rows.

Remarks.—The specific epithet of Actinocyclus 

krasskei acknowledges the original author of this taxon 

(Krasske, 1934).

Krasske (1934) reported large quantities of freshwater 

Aulacoseira and Fragilaria species in association with
10 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

Coscinodiscus miocenicus. The identification of Stephanodiscus astraea (Krasske, 1934) could not be confirmed by 

close re-inspection of the type material (Reimer Simonsen, 

written commun., 1984).

Actinocyclus krasskei has been reported as Coscinodiscus miocenicus from the Harper Basin, Malheur County, 

Oregon (Abbott and VanLandingham, 1972), and from the 

Squaw Creek Member of the Ellensburg Formation 

(Miocene) in Yakima County, Washington (VanLandingham, 1964). At both localities, fresh water Aulacoseira 

species are dominant. At Vinegar Creek, in the Mascall Formation in Grant County, Oregon (loc. 88), and at Juliaetta, 

Nez Perce County, Idaho (loc. 32), undulate A. krasskei 

occur with coarsely structured Aulacoseira sp., possibly 

related to A. islandica or A. granulata. Flat forms of Actinocyclus krasskei are present in the Latah Formation 

(Miocene), Spokane County, Washington (loc. 77), and in 

unnamed Miocene units at Oviatt Creek, Clearwater County, 

Idaho (loc. 43), and Arrow Junction, Nez Perce County, 

Idaho (loc. 72). At these localities, Aulacoseira species 

related to A. distans and A. praeislandica dominate along 

with Ellerbeckia arenaria v. teres, Melosira undulata, and 

species ofEunotia, Tetracyclus, and Tabellaria.

Some diatoms from Siberia, identified as Pontodiscus 

(=Coscinodiscus) miocenicus, have SEM illustrations of 

external tubules placed at the hyaline stripes (for example, 

Temniskova-Topalova and others, 1981, pi. 4, figs. 2,3, and 

8). Khursevich and others (1990) have renamed such 

diatoms Actinocyclus tubulosus, but this name probably 

should not be applied to Krasske's (1934) material nor to 

forms in the Western United States without tubules. Nevertheless, A. tubulosus is also present in the Squaw Creek 

Member (loc. 49). When the tubules of this diatom are missing because of breakage or corrosion, it cannot be effectively 

separated from A. krasskei by light microscopy (like that of 

pl. 8, fig. 7).

ACTINOCYCLUS MOTILIS Bradbury and Krebs 

sp. nov.

Plate 9, figures 4-6; plate 10, figures. 1-12; plate 11, figure 1

Description.—Valve circular, disk slightly concave to 

weakly concentrically undulate with broadly raised margin. 

Diameter 20-90 [im. Disk with spaced, round areolae in 

slightly sinuous radial rows (especially near margin). 

Areolae rows of variable length, interdigitating with one 

another near margin of disk. Areolae density of type material 

11-13/10 Jim. Areolae near disk margin noticeably smaller 

and more crowded (to 16/10 \im) than those closer to valve 

center (10/10 |im). Fasciculation not apparent. Valve center 

small and irregularly hyaline with loosely packed areolae. 

Hyaline rays at disk/mantle junction short, radial, and distinct. Valve/mantle junction typically abrupt, with a steeply 

sloping mantle. Mantle finely areolate (about 18/10 |Jm)

with vertical-quincunx arrangement. Pseudonodule very 

small (often not visible in LM), located between labiate processes, usually closer to one. Externally, pseudonodule 

appears on a slightly elevated platform or mound (pl. 11, 

fig. 1 ). Internally, it is represented by a small field of several 

irregular areolae or pores (pl. 10, figs. 4 and 6). Internal 

expression of pseudonodule on specimens of Actinocyclus 

motilis from Ellensburg Formation (Squaw Creek Member) 

is very difficult to differentiate from normal areolation 

pattern. Labiate processes have long, narrow, circular stems 

with narrow, flanged labiae.

Variability. — Some variability can be seen in the character of the disk/mantle junction. Typically it is abrupt, but 

in some specimens it tends to become more gradual and gently sloping. A stellate pattern, caused by the termination of 

areolae rows, is distinctive in large specimens of this species 

but absent in smaller ones. As with most species of Actinocyclus, the hyaline central area is quite variable and sometimes absent. Specimens from some localities have hyaline 

rays that are very small and obscure. Large specimens of 

Actinocyclus motilis appear to grade into A. cedrus at Goose 

Creek, Baker County, Oregon (loc. 27), and at the Ellensburg Formation localities in Washington (Iocs. 49, 59). 

These forms have coarser, crowded, and somewhat polygonal areolation, especially near the valve center.

Diagnosis. — Actinocyclus motilis is best distinguished 

by its sinuous, interdigitating rows of round, spaced areolae. 

This pattern is also visible in A. cedrus and A. venenosus, but 

the areolae in these species tend to be larger, uniformly 

crowded and polygonal. Labiate process labiae are also 

narrower in A. motilis. Nevertheless, large forms of A. motilis can be confused with the former taxa. The coarseness of 

areolation separates A. motilis from large forms of A. 

gorbunovii and A. krasskei.

7Y/x?s.— Holotype: Strew slide USNM #465539, E.F.

Isotopes: Strew slides ANSP A.-G.C. #64469; 

USGS-D #23 I 81-10; CAS #216055.

Type locality. — Actinocyclus motilis is abundant and 

well preserved in deposits of the Esmeralda Formation at the 

southeast end of Cedar Mountain, Mineral County, Nevada 

(loc. 22). This deposit (USGS Denver 23 1 81-10) is chosen 

as the type locality.

Remarks. — The specific epithet "motilis" (L. motion) 

refers to an apparent rotational movement of the valve when 

focusing through it in the light microscope, apparently 

caused by the sinuous nature of the marginal areolae rows. 

This species, called Cestodiscus mobilis Lohman (nomen 

nudum), was first recognized by Lohman (1957) from the 

Esmeralda Formation near Cedar Mountain, Nye County, 

Nevada, but here the species is rare, poorly preserved, and 

mixed with other forms of Actinocyclus. Similar but somewhat coarser forms are extensively figured in VanLandingham (1964) under the name Coscinodiscus subtilis from the
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 11

Squaw Creek Member of the Ellensburg Formation in 

Yakima County, Washington.

At the type locality, Actinocyclus motilis dominates the 

assemblage. Associated taxa include freshwater species of 

Aulacoseira, Tetracyclus, Fragilaria, and occasional fragments of Actinocyclus cedrus.

ACTINOCYCLUS NEBULOSUS 

Bradbury & Krebs sp. nov.

Plate 11, figures 2-8; plate 12, figure 1

Description.—Valve circular, diameter 35-100 Jim. 

Disk shallowly concave to slightly concentrically undulate 

and ornamented with fascicles of areolae. Areolae rows 

parallel to middle row of each fascicle. Fascicles separated 

by hyaline, costa-like rays enclosing a single row of widespaced areolae that run from disk margin to center. Areolae 

in fascicles irregularly spaced on distal third of valve and 

forming irregularly undulating rows tangential to valve circumference. Areolae small and widely separated (9-12/10 

Jim), and apparently with large and irregularly shaped internal loculae, especially on distal third of disk. Central area of 

disk variable. Marginal hyaline stripes comparatively long 

(about 10 urn) and with irregular edges. Stripes merge proximally into hyaline rays and corresponding radial rows of 

areolae marking fascicle. Disk/mantle junction sharp and 

mantle steep, finely areolate (16-20/10 ^m) with vertical, 

slightly quincunx pattern. Labiate processes with broad, 

recurved flanges and comparatively narrow, circular stems. 

Pseudonodule small, generally close to labiate process.

Variability.—On some valves, the labiate process 

stems appear to be shorter and broader than the typical condition. The areolae, especially what are presumed to be their 

locules, are highly irregular in shape and apparently 

expanded internally so that the integrity of the areola disappears when focusing through the comparatively thin disk 

wall. This may be a partial artifact of preservation. The hyaline central area of the valve is highly variable, sometimes 

discrete and large, other times irregular or absent. Hyaline 

stripes, because of the irregularity of surrounding areolae, 

are also variable in shape, length, and clarity.

Diagnosis.—Actinocyclus nebulosus is close to A. 

ehrenbergii in character of fasciculation, but it can be separated from that species by its small, obscure pseudonodule 

and the irregular, disorganized arrangement of areolae 

around the disk margin. A. cupreus is also similar but does 

not have disorganized areolae on the disk margin, and 

areolae rows within fascicles are not clearly parallel to the 

central areolae row.

Types.—Holotype: Strew slide USNM #465540, E.F. 

K41.

Isotypes: Strew slides ANSP A.-G.C. #64479; 

USGS-D #26 XII 86-2A; CAS #216056.

Type Locality.—We designate outcrops of the Esmeralda Formation near Black Spring, Nye County, Nevada 

(loc. 93 = USGS Denver 26 XII 86-2A), as the type locality 

of this species.

Remarks.—The specific epithet "nebulosus" (L. cloudy 

or obscure) refers to the poorly defined marginal region of 

the valve apparently caused by irregular loculae beneath 

areoles.

Smedman (1969) described and illustrated this species 

as Coscinodiscus nevadensis (nomen nudum) from an 

unnamed formation in Buffalo Canyon, southeast of Eastgate, Churchill County, Nevada (loc. 6), but she failed to 

designate a type specimen, slide, or a repository. The species 

is also common near the base of the Cedar Mountain section 

in Nye County, Nevada (loc. 74), and was described and figured (Lohman, 1957) as Cestodiscus fasciculatus Lohman 

(nomen nudum).

Aulacoseira sp. cf. A. distans dominates in a sample 

containing abundant Actinocyclus nebulosus from near 

Buffalo Canyon, Nevada. Smedman (1969) listed several 

species of Melosira (Aulacoseira), Cymbella, Pinnularia, 

Navicula, and Gomphonema in the type assemblage. A. 

nebulosus is also present in the Mascall Formation near 

Aldrich Mountain, Grant County, Oregon (loc. 85), where it 

associates with freshwater Aulacoseira species related to A. 

distans, A. agassizii, and A. islandica. At the type locality, 

Actinocyclus nebulosus codominates with Aulacoseira spp.

ACTINOCYCLUS PINNULUS 

Bradbury & Krebs sp. nov.

Plate 12, figures 6,7; plate 13, figures 1-5

Description.—Valve circular, with raised rim and shallowly concave center. Diameter ranging between 47 and 76 

|nm, typically between 65 and 70 Jim. Disk with small, 

round areolae, about 13/10 |um. Near center of disk, areolae 

smaller and somewhat loosely packed. On disk margin, 

areolae larger, closely packed and slightly polygonal in 

shape. Areolae pattern obscurely fasciculate with two 

wedge-shaped fascicles of subparallel areolae rows between 

each pair of labiate processes. Intersection of adjacent sets 

of subparallel areolae rows evident near the disk margin and 

less so towards valve center. Valve center generally, but not 

necessarily, with loosely packed areolae forming irregular 

hyaline space. Disk/mantle juncture sharp, with mantle perpendicular to disk plane. Mantle 8-10 Jim high with tiny 

areolae in a quincunx pattern, about 18/10 Jim. Marginal, 

hyaline stripes narrow, about 5 Jim long and extending from 

disk-mantle juncture onto valve disk. External tubules of 

labiate processes with a narrow stem, ornamented with two 

or more fin-like projections resembling pinnae or small leaflets attached parallel to tubule axis. Labiate processes long 

stemmed, with comparatively small, recurved and flexed
12 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

labiae. Pseudonodule small to medium, often obscurely visible between two labiate processes.

Variability.—Actinocyclus pinnulus is known only 

from three localities in the Western United States (Iocs. 81, 

90, 91). Different collections of A. pinnulus from the Holein-the-Wall diatomite quarry (Miocene), Gooding County, 

Idaho (Iocs. 90,91), show variations in the degree of central 

area development; in some populations the central areas are 

mostly absent or very small, while in others they are typically large and irregular. The pseudonodule is larger and 

more visible in some specimens than others, and the fins on 

the external tubules of the labiate processes exhibit some 

variation apart from differences in preservation. Generally, 

each tubule has two opposite fins that lie in a plane tangential 

to the valve circumference. Rarely, individual tubules will 

have three or even four fins irregularly placed along the 

tubule axis. Fasciculation and diameter of A. pinnulus appear 

comparatively uniform.

At 986 m depth in the AMOCO Becharof No. 1 well, 

Alaska (loc. 112), a nonmarine species of Actinocyclus 

related to A. pinnulus is rare (pi. 13, fig. 6). It resembles A. 

pinnulus by the presence of flanged marginal apiculae and 

general pattern of fasciculation, although the areolae are 

smaller and less polygonal than in the species. It also differs 

from the species in having a sloping mantle with vertical (not 

a quincunx pattern) areolae rows.

Diagnosis.—Actinocyclus pinnulus is closest to A. 

acanthus. A. acanthus does not, however, have tubules with 

fins, is non-fasciculate, and has only tiny, obscure hyaline 

stripes in contrast to A. pinnulus. A. nordlingensis has 

forked, not finned tubules, and Coscinodiscus (= Actinocyclus) gorbunovii apparently lacks tubules.

Types.—Holotype: Strew slide USNM #465541, E.F. 

L34/2.

Isotypes: Strew slides ANSP A-G.C. #64471; 

USGS-D #21 VI 88-1; CAS #216057.

Type Locality.—The type locality for Actinocyclus pinnulus is the Hole-in-the-Wall diatomite quarry, NW 1/* sec. 

12, T. 4 S., R. 13 E., Gooding County, Idaho (loc. 90), along 

the drainage of Clover Creek.

Remarks.—The specific epithet "pinnulus" (L. small 

fin or pinna) refers to the fin-like projections on the external 

tubes of the labiate processes of this diatom.

The species has also been collected from the same unit 

exposed in the NE>/4 of sec. 19, T. 3 S., R. 13 E. (loc. 91 = 

USGS Denver 21 VI 88-1). Aulacoseira sp. cf. A. praeislandica is the dominant associate of Actinocyclus pinnulus, 

and a species of Mesodictyon Theriot and Bradbury (Thalassiosiraceae) is present in smaller numbers. Mesodictyon also 

occurs with A. pinnulus in the unnamed lacustrine beds at 

Durkee, Baker County, Oregon (loc. 81).

ACTINOCYCLUS THELEUS 

Bradbury & Krebs sp. nov.

Plate 13, figure 7; plate 14, figures 1-4

Description.—Valve circular, concentrically undulate 

with broadly raised margin and shallowly raised or 

depressed center. Diameter 11-35 urn, typically around 

20 nm. Areolae small, round, loosely packed, about 13- 

18/10 Jim and not forming clear fascicles. Areolae in valve 

center often scattered, but not always. Hyaline stripes 

inconspicuous, narrow, and extending onto disk edge. Exit 

pores of labiate processes with a low, shield-shaped or 

nipple-like protrusion rising about 1 {im above valve surface. Valve mantle perpendicular, with vertical rows of 

fine areolae, about 25/10 ^irn. Labiate processes with narrow, round stems and spade-shaped labiae with curved, 

slit-like openings. Pseudonodule generally small but prominent and variably located between labiate processes at 

valve-disk margin.

Variability.—The nipple-like protrusions at the exit 

pores of the labiate processes and associated hyaline stripes 

may be more or less prominent, perhaps as a result of preservation. At Emerald Creek, Benewah County, Idaho (loc. 21), 

degree of undulation and density of areolae vary considerably. Generally poor preservation of the species at Oviatt 

Creek, Clearwater County, Idaho (loc. 43), complicates 

comparison of these forms, but in general they appear flatter 

than the Emerald Creek forms, and with reduced shield-like 

processes. At Juliaetta, Nez Perce County, Idaho (loc. 32), 

and at the White Hills (Mascall Formation), Grant County, 

Oregon (loc. 87), A. thelelus tends to be coarser and more 

heavily silicified than at Emerald Creek. Perhaps the larger 

and coarser members of this complex merit separation.

Diagnosis.—Actinocyclus theleus is characterized by 

the presence of nipple-like tubules external to the labiate 

processes and by its typically undulate shape and fine areolation. It can be distinguished from small forms of A. gorbunovii and A. krasskei by the presence of the shield-like 

platforms that subtend the small external processes. The 

external processes of Actinocyclus acanthus are heavier, 

larger, and longer than those of A. theleus.

7^5 _Holotype: Strew slide USNM #465542, E.F. 

M34/4.

Isotypes: Strew slides ANSP A-G.C. #64472; 

USGS-D #5 XII 80^; CAS #216058.

Type Locality.—Finely laminated lacustrine siltstone 

from the "Clarkia Lake deposits" of Miocene age from 

Emerald Creek, near Clarkia, Idaho (loc. 21 = USGS Denver 

5 XII 80-4) represents the type locality of Actinocyclus 

theleus. The sample location is in the NWA, NE>/4, sec. 33, 

T. 43 N., R. 1 E., Benewah County, Idaho (= locality UIMM 

P-37, Smiley and Rember, 1985, at Emerald Creek; loc. 21).
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 13

Remarks.—The specific epithet "theleus" (G. nipple) 

refers to the character of the external tubes of the labiate 

processes.

The species is figured as Actinocydus sp. in Bradbury 

and others (1985), and at both Emerald Creek and at Oviatt 

Creek, Clearwater County, Idaho (loc. 43), it co-occurs 

with abundant Aulacoseira species related to A. lirata and 

A. distans, and a large variety of benthic diatoms indicative 

of soft, fresh, humic-rich, slightly acid water. Actinocydus 

theleus is not widely distributed, and it may be that this 

form is characteristic of softwater, slightly acid environments. The coarser and larger forms at Juliaetta (loc. 32) 

and the White Hills (Mascall Formation), Grant County, 

Oregon (loc. 87) are associated with heavily silicified Aulacoseira sp. (cf. A. praeislandica) that may indicate more 

silicon-rich, eutrophic environments.

ACTINOCYCLUS TUBULOSUS Khursevich 

(Khursevich and others, 1990)

Plate 8, figure 7

Remarks.—This small, fine Actinocydus species with 

short external tubules of circular cross section occurs rarely 

in the Squaw Creek Member of the Ellensburg Formation in 

central Washington. Poorly preserved specimens (lacking 

external tubules) may be misidentified as Actinocydus 

krasskei that is otherwise similar (for example, TemniskovaTopalova and others, 1981). The specimen figured (pi. 8, 

fig. 7), has external tubules that appear above the focal plane 

in light microscopy. The type locality is in western Siberia 

along the Tim River (Khursevich and others, 1990).

ACTINOCYCLUS VENENOSUS 

Bradbury & Krebs sp. nov.

Plate 14, figures 7, 8; plate 15, figures 1-6

Description.—Valve circular, with broadly raised rim 

and shallowly concave to concentrically undulate valve disk. 

Diameter 35 to > 160 |Lim, but typically around 70 to 100 Jim 

in type material. Disk with coarse (about 1 Jim diameter) 

polygonal areolae arranged in approximately radial rows, 6- 

10 in 10 Jim. Areolae pattern non-fasciculate or vaguely fasciculate. In medium to large specimens, shorter areolae rows 

interspersed between longer rows terminate in narrow triangles of hyaline silica at variable distances from valve margin. 

Valve center either tightly or loosely packed with areolae. 

Disk/mantle juncture often loosely and irregularly areolate 

and typically unornamented. Occasionally, closely spaced, 

keel-like spines present along the disk/mantle junction. Marginal hyaline stripes prominent (often 2-3 Jim in length) and 

proximally pointed or tapered. Stripes usually extend across 

valve mantle and onto valve disk. On mantle, marginal hyaline stripes enclose comparatively large and often elliptical

exit pores of labiate processes. Labiate processes typically 

short, broad-stemmed, and with broad, recurved, crescentic, 

spade-like labium. Pseudonodule small, at disk/mantle junction, and typically closer to one labiate process.

Variability.—Like other species of Actinocydus, A. 

venenosus varies morphologically. The hyaline stripes are 

usually rather long and prominent but may be comparatively 

small; some variation is seen on single valves. They are 

generally easily seen at low magnifications. Typically, the 

disk/mantle junction is broad, and the mantle gently slopes 

away from the plane of the disk. In some specimens, however, the junction is sharper and the mantle more steeply 

sloping. Labiate processes usually have short, elliptical 

stems and broad, recurved, crescent-shaped labiae, but occasionally, relatively taller, more circular-stemmed labiate 

processes occur. Fasciculation is occasionally evident. It is 

not certain whether these variations, which tend to co-occur 

(fasciculation, steep, sharp mantles, and sometimes longer 

labiate processes), represent intraspecific variation or characters of Actinocydus cedrus. More fasciculate forms of this 

species occur in the Coal Valley Formation (Miocene), Lyon 

County, Nevada (loc. 15).

Diagnosis.—Actinocydus venenosus is best recognized 

by its prominent hyaline stripes, broad disk/mantle junction, 

gradually sloping mantle, radial, non-fasciculate areolation, 

and concentric undulation of the valve disk. It is closest to A. 

cedrus, and type material can usually be separated from this 

species that typically has a sharp disk/mantle junction, a 

steep, tall mantle, more evident and consistent fasciculation, 

and minute, blunt hyaline stripes. Nevertheless, intergradations occur at other sites that frustrate simple separation, and 

broken valves may be impossible to identify.

Actinocydus cupreus is distinguished from A. venenosus by the presence in the former of continuous radial 

areolae rows that extend from each labiate process to the 

valve center. Actinocydus cupreus is also somewhat more 

finely structured (13 rounded-polygonal areolae/10 |Um) and 

has labiate processes with comparatively long stems.

Types.—Holotype: Strew slide USNM #465543, E.F. 

E39.

Isotypes: Strew slides ANSP A-G.C. #64473; 

USGS-D #11 VI78-1 A; CAS #216059.

Type Locality.—The type locality is at Reynolds Creek, 

Owyhee County, Idaho (NW1/4 sec. 2, T. 2 S., R. 3 W.) (loc. 

44 = USGS Denver 11 VI 78-1 A).

Remarks.—The specific epithet "venenosus" (L. very 

poisonous) refers to its abundance in the Poison Creek Formation of the Idaho Group, western Snake River Plain, 

Idaho.

This species, labeled Actinocydus sp. cf. A. gorbunovii 

from the Poison Creek Formation and from diatomaceous 

deposits in the Xian Feng Basin near Kunming, China is figured in Bradbury (1984). Actinocydus sp. (Khursevich and 

others, 1990) from the Primor region of western Siberia 

appears to be closely related to A. venenosus. Associated
14 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

diatoms at the type locality are dominated by Aulacoseira 

species. Navicula, Diploneis, Tetracyclus, Cymbella, Stauroneis, and several other genera are present in smaller 

numbers.

PALEOECOLOGY OF MIOCENE 

LACUSTRINE ACTINOCYCLUS

Between 20 and 10 Ma, species of Actinocyclus were 

the dominant planktonic discoid diatoms of temperate lake 

systems in the Northern Hemisphere. With the clear exception of Actinocyclus ehrenbergii, and possibly of A. acanthus, the Actinocyclus species from Miocene lacustrine 

deposits in the Western United States are freshwater planktonic diatoms. Actinocyclus krasskei and A. theleus seem to 

have dominated in smaller, neutral to slightly acidic lake systems (for example, Bradbury and others, 1985), while the 

larger and more coarsely structured forms, A. motilis, A. 

cedrus, and A. venenosus, appear to have been characteristic 

of larger, more eutrophic, slightly alkaline environments.

Little is known about the limnology of the lakes inhabited by Actinocyclus. It is reasonable to assume that large 

Miocene lakes in the Western United States were warm 

monomictic; that is, circulating in the winter at temperatures 

above 4°C because Miocene climates were less seasonal and 

winters milder. By analogy to modern lake systems, Aulacoseira species would dominate the diatom plankton during 

times of circulation where turbulence could suspend the 

heavy cells and supply nutrients to the photic zone. Actinocyclus normanii f. subsalsa is the only known extant Actinocyclus species living in freshwater. Its ecology is not well 

known, although in Lake Ontario it prefers nutrient-enriched 

water and reaches maximum populations in late summer 

(Stoermer and others, 1974). In contrast, Aulacoseira islandica blooms in late spring and early summer in Lake Ontario 

(Stoermer and others, 1974), during or shortly following 

spring circulation in less contaminated parts of the lake.

The common association of Actinocyclus and Aulacoseira species in Miocene lakes suggests that perhaps the 

two diatoms occupied limnological niches similar to their 

counterparts in Laurentian Great Lakes. Nonetheless, 

extrapolation from the modern distribution of Actinocyclus 

normanii f. subsalsa may be compromised by the fact that 

this species has significant morphological differences compared to Miocene Actinocyclus species (for example, lack of 

hyaline stripes and apparently a structurally more complicated pseudonodule).

REFERENCES

Abbott, Jr., W.H., and VanLandingham, S.L., 1972, Micropaleontology and paleoecology of Miocene non-marine diatoms from 

the Harper District, Malheur County, Oregon: Nova Hedwigia, 

v. 13, p. 847-906.

Blake, W.P., 1902, Arizona diatomites: Transactions of the Wisconsin Academy of Sciences, Arts, and Letters, v. XIV, pt. 1, 

p. 107-111.

Bradbury, J.P., 1984, Fossil Actinocyclus species from freshwater 

Miocene deposits in China and the United States, in Mann, D. 

G. (ed.), Proceedings of the 7th International Diatom Symposium, Philadelphia, 22-27 August, 1982: Koenigstein, 

Germany, Koeltz, p. 157-171.

Bradbury, J.P., Dieterich, K.V., and Williams, J.L., 1985, Diatom 

flora of the Miocene lake beds near Clarkia in northern Idaho, 

in Smiley, C. J. (ed.), Late Cenozoic history of the Pacific 

Northwest: San Francisco, California, Pacific Division of the 

American Association for the Advancement of Science, 

p. 33-59.

Bradbury, J.P., and Krebs, W.N., 1982, Neogene and Quaternary lacustrine diatoms of the western Snake River Basin, 

Idaho-Oregon, USA: Acta Geologica Academiae Scientiarum Hungaricae, v. 25, no. 1-2, p. 97-122.

Burckle, L.H., and Akiba, Fumio, 1978, Implications of late Neogene fresh-water sediment in the Sea of Japan: Geology, v. 6, 

p. 123-127.

Cheremisinova, E.A., 1968, New data about the diatoms of the 

Neogene deposits of the Baikal area, in Fossil Diatoms of the 

USSR: Moscow, USSR, Academy of Science, Siberian Division, Institute of Geology and Geophysics, p. 71-74.

Frenguelli, Joaquin, 1928, Diatomeas del Ocdano Atldntico frente 

a Mar del Plata (Republica Argentina): Anales del Museo National de Historia Natural, Tomo XXXIV, p. 497-572.

Haj6s, Marta, 1970, Kieselgurvorkommen im Tertiarbecken von 

Aflenz (Steiermark): Mitteilungen der Geologischen Gesellschaft in Wien, v. 63, p. 149-159.

Hasle, G.R., 1977, Morphology and taxonomy of Actinocyclus normanii f. subsalsa (Bacillariophyceae): Phycologia, v. 16, no. 3, 

p. 321-328.

Hustedt, Friedrich, 1930, Die Kieselalgen Deutschlands, Osterreichs und der Schweiz unter Beriicksichtigung der iibrigen 

La'nder Europas sowie der angrenzenden Meeresgebiete, in Rabenhorst, L., Kryptogamen-Flora von Deutschland, Osterreich 

und der Schweiz: Leipzig, Akademische Verlagsgesellschaft 

m.b.H., Band VII, 920 p.

Jouse", A.P., 1973, Diatoms in the Oligocene-Miocene biostratigraphic zones of the tropical areas of the Pacific Ocean, in 

Simonsen, Reimer (ed.), Second symposium on recent and fossil marine diatoms: Beihefte zur Nova Hedwigia, Heft 45, 

p. 333-363.

Khursevich, O.K., Moisseeva, A.I., Kozirenko, T.F., and Rubina, 

N.V., 1990, New taxa of the genus Actinocyclus (Bacillariophyta) from the Neogene freshwater deposits of the USSR: 

Botanicheski Zhurnal v. 75, no. 10, p. 1439-1442.

Koizumi, Itaru, 1988, Early Miocene Proto-Japan sea: Journal of 

the Paleontological Society of Korea, v. 4, p. 6-20.

Krasske, Georg, 1934, Die Diatomeenflora der hessischen Kieselgurlager: Sitzungsberichte der Heidelberger Akademie der 

Wissenschaften, Abhandlung 5, 26 p.

Krebs, W.N., Bradbury, J.P., and Theriot, B.C., 1987, Neogene and 

Quaternary lacustrine diatom biochronology, western USA: 

Palaios, v. 2, p. 505-513.

Lohman, K.E., 1957, Cenozoic non-marine diatoms from the Great 

Basin: Pasadena, California Institute of Technology, Ph.D. dissertation, 190 p.
ACTINOCYCLUS SPECIES FROM LACUSTRINE MIOCENE DEPOSITS OF THE WESTERN UNITED STATES 15

Mann, D.G., 1988, The nature of diatom species: analysis of sympatric populations, in Round, F. E., Proceedings of the 9th 

International Diatom Symposium: Bristol, Biopress Ltd., 

p. 317-327.

Moissejeva, A.I., 1971, Atlas of the Neogene diatom algae of the 

Primor region: Moscow, USSR, All Union Lenin Order of 

Scientific Investigation, Geological Institute, new series, 

v. 171,152 p.

Pritchard, A., 1861, A history of infusoira including the Desmidiaceae and Diatomaceae British and foreign: London, 4th 

Edition, Whittaker and Co., 968 p.

Radionova, E.P., 1987, Diatom morphology of the genus Cestodiscus from lower middle Miocene deposits of the tropical zone 

of the Pacific Ocean: Academy of Sciences, USSR, Institute of 

Geology, Micropaleontology Edition, Issue 29, p. 141-154.

Schauderna, Hedwig, 1983, Die Diatomeenflora aus den Miozanen 

Seeablagerungen im Nordlinger Ries: Paleontographica, 

Abteilung B, Band 188, p. 83-193.

Sheshukova-Poretzkaja, V.S., and Moissejeva, A.I., 1964, New and 

curious diatoms from the Neogene of western Siberia and the 

Far East: New Systematics of Lower Plants. Academy of 

Science, USSR, Botanical Institute, M-L, p. 92-103.

Simonsen, R., 1975, On the pseudonodulus of the centric diatoms, 

or Hemidiscaceae reconsidered: Beihefte zur Nova Hedwigia, 

Heft 53, p. 83-94.

————1982, Notes on the diatom genus Charcotia M. Peragallo: 

Bacillaria, v. 5, p. 101-116.

Smedman, Gunilla, 1969, An investigation of the diatoms from 

four Tertiary lake bed deposits in western Nevada: PaleoBios 

(Contributions from the University of California Museum of 

Paleontology, Berkeley) no. 9, 16 p.

Smiley, C.J., and Rember, W.C., 1985, Physical setting of the 

Miocene Clarkia fossil beds, northern Idaho, in Smiley, C.J. 

(ed.), Late Cenozoic history of the Pacific Northwest: San 

Francisco, California, Pacific Division of the American Association for the Advancement of Science, p. 11-31.

Sovereign, H.E., 1963, New and rare diatoms from Oregon and 

Washington: Proceedings of the California Academy of 

Sciences. 4th Series v. 31, no. 14 p. 349-368.

Stoermer, E.F., Bowman, M.M., Kingston, J.C., and Schadel, A.L., 

1974, Phytoplankton composition and abundance in Lake 

Ontario during IFYGL: Special report no. 53 of the Great 

Lakes Research Division, University of Michigan, 373 p.

Stoermer, E.F., Wolin, J.A., Schelske, C.L., and Conley, D.J., 1985, 

Assessment of ecological changes during the recent history of 

Lake Ontario based on siliceous algal microfossils preserved in 

lake sediments: Journal of Phycology, v. 21, p. 257-276.

Temniskova-Topalova, D.N., Kozyrenko, T.F., Moisseeva, A.I., 

and Sheshukova-Poretzkaya, V.S., 1981. A new genus Pontodiscus (Bacillariophyta): Botaniska Zhurnal (Leningrad), 

v. 66, p. 1308-1311.

Theriot, E.G., and Stoermer, E.F., 1984, Principal component 

analysis of character variation in Stephanodiscus niagarae 

Ehercnb.: Morphological variation related to lake trophic 

status, in Mann, D.G., (ed.), Proceedings of the 7th International Diatom Symposium, Philadelphia, 1982: Koenigstein, 

Germany, Koeltz, p. 97-111.

Tsoy, I.B., Vashchenkova, N.G., Gorovaya, M.T., and Terekhov, 

Ye.P., 1985, The finding of continental deposits on Yamato 

Rise, Sea of Japan: Tikhookeanskaya Geologiya (Pacific 

Geology), no. 3, p. 50-55.

VanLandingham, S.L., 1964, Miocene non-marine diatoms from 

the Yakima region in south-central Washington: Beihefte zur 

Nova Hedwigia, Heft 14,78 p.

————1967, Paleoecology and microfloristics of Miocene 

diatomites from the Otis Basin-Juntura region of Harney and 

Malheur Counties, Oregon: Beihefte zur Nova Hedwigia, Heft 

26,77 p.

Watkins, T.P., and Fryxell, G.A., 1986, Generic consideration of 

Actinocyclus: consideration in light of three new species: 

Diatom Research, v. 1, p. 291-312.
PLATES 1-15

Contact photographs of the plates in this report are available, at cost, from the U.S. Geological Survey Photographic Library

Federal Center, Denver, Colorado 80225
PLATE 1

Figures 1-9. Actinocyclus acanthus Bradbury & Krebs, sp. nov. (p. 4). Scale bars in Jim.

1. Unnamed Miocene unit, New Pass, Lander County, Nevada (loc. 42). 

Arrows mark marginal tubular processes at disk/mantle junction and 

concentric undulation of valve. Diameter 65 Jim. Slide USGS-D 14 VII 

85-4(2),E.F.G32/l.

2. New Pass, Lander County, Nevada (loc. 42). Internal view showing 

pseudonodule (arrow). Diameter 55 ^m. Slide USGS-D 14 VII85-4 (2), 

E.F. L45/3.

3. Bully Creek Formation, Harper Basin, Malheur County, Oregon (loc. 

7). Valve view of exterior surface showing obscure pseudonodule 

(arrow). Diameter 69 ^m. Slide AMOCO: OM-29-l(+), E.F. K4/4. 

4-6. New Pass, Lander County, Nevada (loc. 42). Internal views showing

pseudonodule (arrows in figs. 4, 5) and labiate process (fig. 6). 

7, 8. New Pass, Lander County, Nevada (loc. 42). Detail of marginal tubular

processes.

9. New Pass, Lander County, Nevada (loc. 42). Base of broken marginal 

tubular process.

(18)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 1

ACTINOCYCLUS ACANTHUS
PLATE2

Figures 1-7. Actinocyclus cedrus Bradbury & Krebs, sp. nov. (p. 5).

1. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada

(loc. 20). Note short, blunt hyaline stripe at the disk/mantle junction (arrow) 

and polygonal areolae. Diameter 53 |im. Slide USGS-D 

31I88-1(65),E.F.P41/1.

2. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada 

(loc. 20). Valve with hyaline rim. Diameter 56 |im. Slide USGS-D 

31I88-l(65),E.F.L41/4.

3. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada

(loc. 20). Arrow marks pseudonodule. Diameter 45 |im. Slide USGS-D 

31I88-1(65),E.F.M32.

4. Poison Creek Formation, Reynolds Creek, Owyhec County, Idaho 

(loc. 44). Detail of valve surface showing pseudonodule (arrow). 

Diameter 85 ^m. Slide AMOCO: IO-24-5(+), E.F. O9/2.

5. Unnamed Miocene unit, southern Stillwater Mountains, Churchill County, 

Nevada (loc. 48). Detail of disk and mantle under different focus (a, mantle; 

b, disk center). Diameter is 67 ^m. Slide USGS-D 29181-3B, E.F. N38

6. Juntura (?) Formation, Otis Creek, Harney County, Oregon (loc. 34). 

Diameter 68 ^m. Slide USGS-D 14 VI 78-4B (3), E.F. O34/4.

7. Juntura (?) Formation, Otis Creek, Harney County. Oregon (loc. 34). Large 

valve with triangular hyaline patches between rows of areolae producing 

stellate pattern. Diameter 157 Jim. Slide USGS-D 14 VI78-4B (3), 

E.F. O32/1.

(20)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 2

5b

ACTINOCYCLUS CEDRUS
PLATE 3

Figures 1-8. Actinocyclus cedrus Bradbury & Krebs, sp. nov. (p. 5). Scale bars in \im.

1. Unnamed Miocene unit, southern Stillwater Mountains, Churchill County,

Nevada (loc. 48). Valve with hyaline rim. Diameter 49 pirn. Slide

AMOCO: S.E. Carson Sink-low (-), E.F. Q4/3. 

2, 3. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada

(loc. 20). Valve exterior with hyaline rim and exit pores of labiate

processes (arrows). 

4, 5. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada

(loc. 20). Exit pores of labiate processes indicated by arrows. 

6. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada

(loc. 20). Detail of valve margin and mantle. The arrow pinpoints an exit

pore. 

7, 8. Esmeralda Formation, Diatomite Ridge, Mineral County, Nevada

(loc. 20). Overview of valve interior (fig. 7) and detail of disk/mantle

junction showing labiate process and position of pseudonodule (arrow)

(fig. 8).

(22)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 3

ACTINOCYCLUS CEDRUS
PLATE 4

Figures 1-3. Actlnocyclus cedrus Bradbury & Krebs, sp. nov. (p. 5). Esmeralda Formation, 

Diatomite Ridge, Mineral County, Nevada (loc. 20). Scale bars in jam.

1. Overview of valve interior showing ring of labiate processes. Arrow marks 

location of pseudonodule.

2. Closeup of labiate processes. 

3. Internal view of pseudonodule (arrow).

4-6. Actinocyclus cedrus (spinose form) (p. 5). Unnamed Miocene unit, Turner Creek, 

Modoc County, California (loc. 17). Scale bars in Jim.

4. Valve view; arrows highlight marginal spines. Diameter is 91 Jim. Slide

AMOCO: Pit River (+30), E.F. T72. 

5, 6. Views of marginal spines.

7. Actinocyclus claviolus Bradbury & Krebs, sp. nov. (p. 5). Unnamed middle Miocene 

unit, Jungle Point, Idaho County, Idaho (loc. 33). Note clove-shaped hyaline stripes on 

disk/mantle junction. Diameter 21 Jim. Slide USGS-D 5 XII 80-7 (1), E.F. S37/1.

(24)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 4

ACT/NOCYCLL/S CEDRL/S AND AC77NOCYCLL/S CLAU/OLc/S
PLATE 5

Figures 1-5. Actinocyclus claviolus Bradbury & Krebs, sp nov. (p. 5). Unnamed middle Miocene 

unit, Jungle Point, Idaho County, Idaho (loc. 33). Scale bars in Jim.

1. Valve view. Diameter 30 urn. Slide USGS-D 5 XII80-7 (3), E.F. J33/2.

2. Valve view. Arrow marks probable pseudonodulc.

3. Detail of marginal clove-shaped hyaline stripe.

4. Valve interior showing position of pseudonodulc (arrow).

5. Internal view of pseudonodule (arrow). 

6-9. Actinocyclus cupreus Bradbury & Krebs, sp. nov. (p. 6).

6. Unnamed lower Miocene unit. Copper Kettle Canyon, Churchill County, 

Nevada (loc. 16). Note the pattern of fasciculation and the simple hyaline 

marginal stripes that delimit each fascicle. Diameter 37 (im. Slide AMOCO: 

NSD-6(-), E.F.U9/1.

7. Humboldt Formation, Eureka County, Nevada (loc. 30). Valve view. 

Diameter 43 urn. Slide AMOCO: PC-3-79 (+), E.F. H15/4.

8. Unnamed middle Miocene unit, Juliaetta, Nez Percc County, Idaho (loc. 32). 

Valve view. Diameter 29 |im. Slide USGS-D 5 XII 80-3 (2), E.F. K30/4.

9. Juliaetta, Nez Perce County, Idaho (loc. 32). Valve view. Scale bar in (im.

(26)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 5

• k »^l ^T?*^^^^^ 

&"' V:::: ^~^V* * % i */ * * *•** •***•*•

«I'»**;.'. •,•'•'••• **' ^^^K A ^. ^ .^_TM W ^ ^. *.*»;Tv.'.- .-.•.*:•. ••;'.;•

'«,•,.•••«••.•

• . •

ACTINOCYCLUS CLAVIOLUS AND ACTINOCYCLUS CUPREUS
PLATE 6

Figures 1,2. Actinocyclus cf. A. cupreus (p. 7). Freshwater Miocene deposits, Yamato Bank, Sea of 

Japan. Valve views. Note the flat disk and long marginal hyaline stripes.

1 . Core RC 12-394 (600 cm). Diameter 62 |im. Slide AMOCO: RC12-394 

600cm(+),E.F. E33/4.

2. Core RC 12-394 (600 cm). Diameter 54 |im. Slide AMOCO: RC12-394

600 cm (+), E.F. V10/2. 

3-9. Actinocyclus ehrenbergii Ralfs in Pritchard (p. 7).

3-5. Quiburis Formation, Edgar Canyon, Pima County, Arizona (loc. 92). Scale 

bars in (im.

3. Valve view showing large pseudonodule (arrow). Diameter 

146 ^im. Slide USGS-D 19 IV 80-3A (2), E.F. H36/3.

4. Internal detail of disk/mantle junction showing the closely spaced 

pores of labiate processes. Labiate processes are missing.

5. Closeup of labiate process.

6-9. Actinocyclus ehrenbergii Ralfs in Pritchard. Holocene marine sediment, Walvis Bay, 

Namibia. Scale bars in (im.

6. Overview of valve interior showing marginal ring of labiate processes. 

7, 8. Closeup of labiate processes.

9. Internal view of pseudonodule (arrow).

(28)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 6

ACTINOCYCLUS sp.cf. A. CUPREUS AND ACTINOCYCLUS EHRENBERGII
PLATE 7

Figures 1,2. Actinocyclus ehrenbergii Ralfs in Pritchard (p. 7). Holocene marine sediment, Walvis 

Bay, Namibia. Scale bars in (irn.

1. Internal view of corroded pseudonodule (arrow).

2. External view of annulate pseudonodule (arrow) and exit pores of labiate

processes. 

3-8. Actinocyclus gorbunovii (Sheshukova) var. fossa Bradbury & Krebs, van nov.

(p. 7). Cedarville Formation, Forty-nine Camp, Washoe County, Nevada (loc. 69). 

Scale bars in (im.

3. Valve view; note the pseudonodule (arrow), the lack of marginal tubular 

processes, and the concentric undulation of valve. Diameter 35 (irn. Slide 

USGS-D 2IX 87-3B (1). E.F. P35.

4. Overview of frustule showing steep mantle, concentric undulation, and 

position of pseudonodule (arrow).

5. Detail of pseudonodule (arrow).

6. View of disk/mantle junction and pseudonodule (arrow). Note the circular 

moat-like structure that surrounds the pseudonodule.

7. Overview of valve interior showing labiate processes and pseudonodule 

(arrow).

8. Interior closeup of disk/mantle junction with labiate process and 

pseudonodule (arrow).

(30)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 7

ACTINOCYCLUS EHRENBERGII AND ACTINOCYCLUS GROBUNOVII
PLATE 8

Figure 1. Actinocyclus kanitzii (Pant. & Grun.) Schauderna (p. 3). Middle Miocene lacustrine and 

brackish water deposits, Szurdokpuspoki, Matra Mountains, Hungary. The fascicles 

are separated by hyaline stripes that run from the disk/mantle junction to the center of 

the disk. Diameter 74 |am. Slide USGS-D 3 IX 80-1B, E.F. F43/3. 

2-6, 8-11. Actinocyclus krasskei (Krasske) Bradbury & Krebs, nom. nov. (p. 9).

2. "Kieselgur" (diatomile) deposits of Miocene? age in Vogelsberg

Range, Beuern, Germany. Different focus showing detail of slightly 

undulate valve center (a) and margin (b). Diameter 31 Jim. Slide Krasske 

Collection, Natural History Museum, Kassel, Germany, Beuern #3004.

3. Beuern, Germany. Valve view showing hyaline stripes and pseudonodule 

(arrow). Diameter 21 |am. Slide Krasske Collection, Natural History 

Museum, Kassel, Germany, Beuern #3004.

4. Beuern, Germany. View of undulate valve showing disk/mantle junction 

and areolae on mantle arranged in quincunx pattern. Diameter 40 fj.m. 

Slide Krasske Collection, Natural History Museum, Kassel, Germany, 

Beuern #3004.

5. Unnamed middle Miocene unit, Juliaetta, Nez Perce County, Idaho (loc. 

32). Valve view. Diameter 29 \im. Slide USGS-D 5 XII 80-3 (2), E.F. 

D32/1.

6. Unnamed Miocene? unit. Arrow Junction, Nez Perce County, Idaho 

(loc. 72). Valve view. Diameter 27 jam. Slide AMOCO: 

USGS-DC#2289, E.F. H30/1. 

8. Juliaetta, Nez Perce County, Idaho (loc. 32). View of undulate valve.

Diameter 40 \im. Slide USGS-D 5 XII 80-3 (2), E.F. Q38. 

9, 10. Squaw Creek Member, Ellcnsburg Formation, Yakima County,

Washington (loc. 49). Interior of valve showing long-stemmed labiate 

processes and pseudonodule (arrow). Scale bars in |am. 

11. Mascall Formation, Vinegar Creek, Grant County, Oregon (loc. 88). 

Interior of valve showing ring of long-stemmed labiate processes. Scale 

bars in |am. 

7. Actinocyclus tubulosus Khursevich. (p. 13). Squaw Creek Member, Ellcnsburg

Formation, Yakima County, Washington (loc. 49). Valve view. Diameter 27 (im. Slide 

USGS-D 26II79-2A (3), E.F. N47/4.

(32)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 8

1-U "

ACTINOCYCLUS KAMTZII, ACTINOCYCLUS KRASSKEI, AND ACTINOCYCLUS TUBULOSUS
PLATE 9

Figure 1. Flat forms of Actinocydus krasskel (Krasske) Bradbury & Krebs, nom. nov. (p. 9).

Mascall Formation, Vinegar Creek, Grant County, Oregon (loc. 88). Closeup of labiate 

process. Scale bars in pirn.

2, 3. Undulate forms of Actinocydus krasskei (Krasske) Bradbury & Krebs, nom. nov. (p. 9). 

Squaw Creek Member, Ellensburg Formation, Yakima County, Washington (loc. 49). 

Scale bars in pim.

2. Closeup of labiate process.

3. Valve interior showing position of pseudonodule (arrow). 

4-6. Actinocydus motilis Bradbury & Krebs, sp. nov. (p. 10).

4. Esmeralda Formation, Cedar Mountain, Mineral County, Nevada (loc. 22). Note 

the truncation of sinuous rows of areolae by other rows. Diameter 23 (im. Slide 

USGS-D 231 81-10 (1), E.F. L34/2.

5. Unnamed middle Miocene unit, Augusta Mountains, Churchill County, Nevada 

(loc. 4). Focus on valve margin (a) and center (b). Diameter 42 pim. Slide 

AMOCO: AMS-l-l(-), E.F. M34/2.

6. Unnamed middle Miocene unit. Goose Creek, Baker County, Oregon (loc. 27). 

Focus on valve margin (a) and center (b). Diameter 46 pim. Slide USGS-D 10 

VI 78-2B (3), E.F. L24/4.

(34)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 9

ACTINOCYCLUS KRASSKEI AND ACTINOCYCLUS MOTILIS
PLATE 10

Figure 1-12. Actinocyclus motilis Bradbury & Krebs, sp. nov. (p. 10). Scale bars in Jim.

1. Squaw Creek Member, Ellensburg Formation, Yakima County, Washington

(loc. 49). Diameter 34 urn. Slide USGS-D 27 II79-1, E.F. R31/4. 

2-8. Esmeralda Formation, Cedar Mountain, Mineral County, Nevada (loc. 22).

2. Valve view showing separation of valve from intercalary bands. Arrow 

marks probable pseudonodule.

3. Valve interior showing position of pseudonodule (arrow).

4. Detail of pseudonodule (arrow) showing pore structure. 

5,6. Broken stumps of labiate processes. Arrow marks location of probable

pseudonodule in figure 6.

7, 8. Closeups of long-stemmed labiate processes. 

9-12. Squaw Creek Member, Ellensburg Formalion, Yakima County, Washington (loc. 49).

9. Exterior of valve showing concentric undulation and interdigitation of rows 

of areolae at the valve margin. Arrow marks probable pseudonodule.

10. Girdle view of frustule.

11. View of valve interior showing a marginal ring of long-stemmed labiate 

processes.

12. Closeup of labiate processes.

(36)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 10

ACTINOCYCLUS MOTILIS
PLATE 11

Figure I. Actinocyclus motilis Bradbury & Krebs, sp. nov. (p. 10). Squaw Creek Member,

Ellensburg Formation, Yakima County, Washington (loc. 49). Detail of valve disk/ 

mantle junction showing pseudonodule (arrow) and hyaline stripe with exit pore. Scale 

bar in |im.

2-8. Actinocyclus nebulosus Bradbury & Krebs. (p. 11). Scale bars in |im.

2. Esmeralda Formation, Black Spring, Nye County, Nevada (loc. 93). Valve 

view. Diameter 67 urn. Slide USGS-D 26 XII86-2A (1), E.F. H38/1.

3. Esmeralda Formation, Black Spring, Nye County, Nevada (loc. 93). Valve 

view. Diameter 77 |im. Slide USGS-D 26 XII86-2A (1), E.F. G36/3.

4. Buffalo Canyon Formation, Buffalo Canyon, Churchill County, Nevada 

(loc. 6). Valve view. Diameter 83 |im. Slide AMOCO: Buffalo Canyon, 

E.F. E6/4.

5. Esmeralda Formation, Cedar Mountain, Nye County, Nevada (loc. 74). 

Arrow marks probable pseudonodule. Diameter 67 |im. AMOCO: 

USGS-DC #3394 (3). E.F. M42/2.

6-8. Esmeralda Formation, Black Spring, Nye County, Nevada (loc. 93). Views 

of valve interior; arrow indicates position of pseudonodule.

(38)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 11

»i*:*m

V/% *< »*»•!•* * • • *

ACTINOCYCLUS MOTILIS AND ACTINOCYCLUS NEBULOSUS
PLATE 12

Figure 1. Actinocyclus nebulosus Bradbury & Krebs, sp. nov. (p. 11). Esmeralda Formation, Black 

Spring, Nye County, Nevada (loc. 93). Interior detail of mantle/disk junction showing 

short-stemmed broad labiate process and position of pseudonodule (arrow). Scale bar in 

|im.

2-5. Actinocyclus normanii f. subsalsa (Juhl.-Dannf.) Hustedt. (p. 3). Holocene lake 

sediment, Saginaw Bay, Lake Huron, Michigan. Scale bars in |im.

2. Valve view. Diameter 33 |im. Slide USGS-D 24II82-1 (1), E.F. P31/1.

3. Valve view. Diameter 37 jam. Slide USGS-D 24II82-1 (1), E.F. N39/1-2. 

4, 5. Valve views. Arrows indicate position of pseudonodule.

6,7. Actinocyclus pinnulus Bradbury & Krcbs, sp. nov. (p. 11). Hole-in-the-Wall Diatomite, 

Gooding County, Idaho (loc. 90).

6. Valve view. Arrows indicate positions of marginal flanged tubular 

processes. Diameter 61 ^m. Slide USGS-D 21 VI 88-1 (1), E.F. N29.

7. Valve view. Arrows highlight marginal hyaline stripes. Diameter 66 |im. 

Slide USGS-D 21 VI88-1 (1), E.F. P43.

(40)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 12

6

ACTINOCYCLUS NEBULOSUS, ACTINOCYCLUS NORMANII f. SUBSALSA, 

AND ACTINOCYCLUS PINNULUS
PLATE 13

Figures 1-5. Actinocyclus pinnulus Bradbury & Krebs, sp. nov. (p. 11). Hole-in-the-Wall 

Diatomite, quarry, Gooding County, Idaho (loc. 90). Scale bars in jam.

1. Valve view. Arrows highlight marginal flanged tubular processes.

Diameter 66 \im. Slide USGS-D 21 VI88-1 (1), E.F. P43. 

2,3. Valve view. Arrows indicate the position of a marginal flanged tubular 

process

4. Overview of valve interior showing a ring of marginal short-stemmed labiate processes and the pseudonodule (arrow).

5. Closeup of labiate processes and the pseudonodule (arrow).

6. Actinocyclus sp.cf. A. pinnulus (p. 12). AmocoBecharofNo. 1 well, depth 3220-3250 

feet, Alaska Peninsula, Alaska (loc. 112). Focus on valve margin (a) and center (b). 

Arrow indicates the position of the pseudonodule. Diameter 40 (im. Slide AMOCO: 

Becharof 3220-3250 ft. (-), E.F. V22/3.

7. Actinocyclus theleus Bradbury & Krebs, sp. nov. (p. 12). "Clarkia Lake deposits," 

Emerald Creek, Benewah County, Idaho (loc. 21). Valve view; pseudonodule 

indicated by arrow. Diameter 25 [im. Slide USGS-D 5 XII 80-4 (2), E.F. P28/2.

(42)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 13

ACTINOCYCLUS PINNULUS, ACTINOCYCLUS sp.cf. A. PINNULUS, 

AND ACTINOCYCLUS THELEUS
PLATE 14

Figures 1-4. Actinocyclus theleus Bradbury & Krebs, sp. nov. (p. 12). Scale bars in (im.

1. Unnamed middle Miocene unit, Oviatt Creek, Clearwater County, Idaho 

(loc. 43). Valve view. Note arrow to the nipple-like marginal processes) 

(mp). Pseudonodule is indicated by other arrow (pn). Diameter 34 (im. Slide 

USGS D 5 XII 80-1 (1), E.F. V39/1.

2. "Clarkia Lake deposits," Emerald Creek, Benewah County, Idaho GOC. 21). 

Valve view of exterior surface showing the pseudonodule (pn) and marginal 

processes) (mp).

3. Emerald Creek, Benewah County, Idaho (loc. 21). Closeup of disk/mantle 

junction showing marginal process (mp) and pseudonodule (pn).

4. Emerald Creek, Benewah County, Idaho GOC. 21). Interior view with two

labiate processes, and the pseudonodule (arrow).

5, 6. Coscinodiscus (= Actinocyclus) variabilis sensu Krasske. (p. 3). Unnamed Miocene? 

unit in the Vogelsberg Range, Ruckers, Germany.

5. Valve view. Diameter 37 Jim. Slide Krasske Collection, Natural History 

Museum, Kassel, Germany, Ruckers #2996.

6. Focus on the valve disk (a) and mantle (b). Diameter 52 (im. Slide Krasske

Collection, Natural History Museum, Kassel, Germany, Ruckers #2996. 

7, 8. Actinocyclus venenosus Bradbury & Krebs, sp. nov. (p. 13). Poison Creek Formation, 

Reynolds Creek, Owyhee County, Idaho (loc. 44).

7. Valve view showing long, pointed hyaline stripes. Diameter 71 p,m. Slide 

AMOCO: IQ-23-2(+), E.F. Q22/4.

8. Valve view of large specimen. Note the dash-like hyaline stripes. Diameter 

125 ^im. Slide AMOCO: IQ-23-6(+), E.F. F35/4.

(44)
U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543 PLATE 14

ACTINOCYCLUS THELEUS, COSCINODISCUS (=ACTINOCYCLUS) VARIABILIS, 

AND ACTINOCYCLUS VENENOSUS
PLATE 15

Figures 1-6. Actinocydus venenosus Bradbury & Krebs, sp. nov. (p. 13). Scale bars in jam. 

1. Poison Creek Formation, Reynolds Creek, Owyhee County, Idaho

(loc. 44). Valve view showing polygonal areolae, concentric undulation of 

the valve face, and pointed marginal hyaline stripes. Diameter 66 fim. 

Slide USGS-D 11 VI 78-1A (2), E.F. G35.

2, 3. Idaho Group, Washington County, Idaho (loc. 31). View of exterior valve 

surface showing the exit pores of the labiate processes and marginal 

hyaline stripes.

4. Idaho Group, Washington County, Idaho (loc. 31). Detail of valve disk/ 

mantle junction showing exit pores, hyaline stripes, and hyaline rim.

5. Idaho Group, Washington County, Idaho (loc. 31). View of interior surface. 

Note the ring of marginal short-stemmed, broadly flanged labiate 

processes.

6. Poison Creek Formation, Reynolds Creek, Owyhee County, Idaho 

(loc. 44). Closeup of labiate process. Arrow indicates the position of 

pseudonodule.

(46)
U.S. GEOLOGICAL SURVEY

r

PROFESSIONAL PAPER 1543 PLATE 15

ACTINOCYCWS VENENOSUS
Geologic Ranges of Lacustrine Actinocyclus 

Species, Western United States

By William N. Krebs and J. Platt Bradbury

THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

U.S. GEOLOGICAL SURVEY PROFESSIONAL PAPER 1543-B

Preliminary geologic ranges of lacustrine species of the 

Western United States determined from radiometrically 

dated outcrops ofdiatomites and diatomaceous sediments 

from Nevada, California, Washington, Oregon, and Idaho

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1995
CONTENTS

Abstract.......................................................................................................................... 53

Introduction.................................................................................................................... 53

Materials and Methods................................................................................................... 53

Results............................................................................................................................ 54

Discussion...................................................................................................................... 58

References...................................................................................................................... 59

Appendix........................................................................................................................ 63

Index............................................................................................................................... 68

ILLUSTRATIONS

Figure 1. Biochronology and general relative diversities of six lacustrine diatom genera, Western United States.......... 54

2. Location of sample sites .................................................................................................................................... 54

3. Preliminary range chart of obligate lacustrine Actinocyclus species, Western United States........................... 56

51
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLUS 

SPECIES, WESTERN UNITED STATES

By William N. Krebs 1 and J. Platt Bradbury2

ABSTRACT

In the Western United States, twelve obligate freshwater species of Actinocydus Ehrenberg are restricted to the 

early and middle Miocene. Maximum diversity (11 species) 

was attained during the early middle Miocene, before the 

appearance of obligate lacustrine genera of the family 

Thalassiosiraceae. Three, possibly five, species of Actinocydus are restricted to the early middle Miocene; A. pinnulus 

is restricted to the late middle Miocene. Actinocydus ehrenbergii Ralfs, a coastal marine species, has been found in 

latest Miocene to earliest Pliocene lake sediments, but 

because of its long geologic range in marine sediments and 

rarity in lacustrine rocks, it is probably not a useful biostratigraphic indicator in continental deposits. Fossil lacustrine 

Actinocydus spp. are found elsewhere in the world and may 

have geologic ranges that differ in detail, but which are generally similar to those in the Western United States.

INTRODUCTION

Interest in lacustrine diatom biochronology has greatly 

increased in recent years (Servant-Vildary, 1978; Gasse, 

1980; Rehakova, 1980; Bradbury and Krebs, 1982; 

Khursevich, 1982; Loginova, 1982; Loginova and others, 

1984; Bradbury, 1984, 1986; Bradbury and others, 1985; 

VanLandingham, 1985; Fourtanier, 1987; Krebs and others, 1987; Theriot and Bradbury, 1987; Fourtanier and 

Gasse, 1988; Serieyssol, 1988). In the Western United 

States, lacustrine diatomaceous sediments are often interbedded with volcanic rock and are thus well suited for 

radiometric dating. Fossil microfloras can therefore be 

arranged geochronologically and key diatoms can be traced 

through time. In this manner, Krebs and others (1987) have 

documented the succession of several lacustrine diatom 

genera through the Neogene and Quaternary of the Western

'William N. Krebs, Amoco Production Co., 501 Westlake Park Blvd., 

Houston, Texas 77079

2J. Platt Bradbury, U.S. Geological Survey, MS 919 Box 25046, 

Denver Federal Center, Lakewood, Colorado 80225

United States (fig. 1). The purpose of this study is to 

present the geologic ranges of species belonging to one of 

these genera, Actinocydus. These ranges will, of course, 

change as additional data accumulate and as lacustrine 

diatomaceous sediments become better dated. We present 

this information as our knowledge to date and hope that it 

will stimulate comparative studies in the Western United 

States and in other regions worldwide.

MATERIALS AND METHODS

Our data are derived from 115 localities in the Western 

United States, including Alaska, mostly from the Great 

Basin (fig. 2 and "Appendix"). From these localities, several 

hundred samples were collected and analyzed for their lacustrine diatom content. Forty-nine of these sites have radiometric dates or have age estimates based on stratigraphic 

relationships with other dated units. Of these 49 dated localities, 28 have obligate lacustrine species of Actinocydus— 

that is, they are found only in continental (lake) deposits and 

only in association with other nonmarine diatom taxa (see 

chapter A). Unfortunately, the exact stratigraphic and depositional relationships of diatomaceous samples to the dated 

volcanic rock(s) are often obscure or poorly documented. In 

addition, radiometric dates may be inaccurate and conflicting. We are confident, however, that the general pattern of 

lacustrine diatom biochronology in the Western United 

States presented in figure 1 is accurate and that the species 

ranges of Actinocydus (fig. 3) reflect evolutionary and (or) 

environmental changes during the Miocene.

Natural reworking and the rare occurrence of whole 

specimens or fragments poses problems of interpretation 

(Krebs and others, 1987). Excluding contamination during 

collecting and processing, rare occurrences of poorly preserved specimens older than the oldest known occurrence are 

regarded as significant and merit range extension. Rare 

(occasionally common) occurrences and fragments younger 

than the youngest true occurrence may be the result of natural reworking. Clearly, large upward range extensions based 

on rare occurrences evoke suspicion. Also, poor preservation 

(abrasion and (or) corrosion) of frustules relative to those of

53
54 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

Figure 1. Biochronology and general relative diversities of six lacustrine diatom genera. Western United States. The numbers represent 

localities with radiometric ages (see "Appendix" and fig. 2). Diversity patterns are qualitative and not comparable between genera. Time 

scale is from Berggren and others (1985) and Haq and others (1987).

other diatoms in a sample may indicate reworking. In any 

case, we have queried occurrences and dashed lines where 

there is sufficient doubt about absolute age and (or) rare 

occurrences. Additional localities and closer examination of 

questionable occurrences may resolve these uncertainties.

RESULTS

The geologic ranges of lacustrine Actinocydus species 

will be discussed in alphabetical order rather than by oldest 

first occurrence, which may change with additional information. Figure 3 is a range chart of these species.

Actinocydus acanthus Bradbury & Krcbs

Actinocydus acanthus was originally described as Cestodiscus apiculatus by Lohman (1957) from the Esmeralda

Formation (Miocene) at Cedar Mountain, Nye County, 

Nevada (loc. 74). Evernden and others (1964) obtained two 

radiometric dates from this formation in the Cedar Mountain 

area whose corrected average is 11.4 Ma. These two dates 

were taken 61m and 76 m, respectively, above early Clarendonian (=12 Ma) vertebrates. J. H. Stewart (oral commun., 

1988), however, reported that the lower (diatomaceous) half 

of the Esmeralda Formation dates from about 14 to 12 Ma 

(Barstovian). Furthermore, recent field work in this area has 

demonstrated that there is an unconformity between the 

lower half of the "Esmeralda Formation" and the upper-half 

that yielded Clarendonian vertebrates and the dates of Evernden and others (1964) (H. E. Schorn, oral commun., 1989). 

Barstovian vertebrates have been found in the lower diatomaceous portion beneath the unconformity, and a radiometric date of 15.1 Ma obtained from this unit nearby (loc. 20) 

confirms this age. We, therefore, assign a Barstovian age to 

the diatomites collected by Lohman at Cedar Mountain
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLUS SPECIES, WESTERN UNITED STATES 55

45°

Figure 2. Location of sample sites (see "Appendix").
56 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

Ma 

0-

2 ~

4 -

6-

8-

10-

12-

14-

16-

18-

2U90-

1

CO

n

LU

Z

O

g

Q_

LU

Z

8

LU

\gf

~*

z

LJJ

8

_i

Q

111

Z

0

o

cc

111

European 

Staqes

Calabrian

Piacenzian

Zanclean

Messinian

Tortonian

Serravallian

Langhian

Burdigalian

N. Amer. 

Mammal Aqes

Rancholabrean

Irvingtonian

Hemphillian

Clare ndonian

Barstovian

Hemingfordian

Arikareean

Geologic Ranges

14

5

23 25

46

3105

92 113

115

1211 (, ^ S 

52 £ ^i "^ 3 ^^ ""^ * & ^ §ff*

2104 C g 53

ft ^ ^^ ^5

1Q7 ^j ?j SO"

• • g> ^

-^ -^ rv . "

l *> inj -a \ ' '"• ^ ^ rt

4464 <J >

75 66 (1 -S *> o

-s J

20333674 * ; • <> • 

13 21 32 Sa • H ^< 

65=0 •

16 ,,

« S d. >

^ "^ "^ a "^

S ^ II

»-> f> -5 i <(o ! • • .§ ^ § < •?

^ •S

• ^

k • I n • *

Figure 3. Preliminary range chart of obligate lacustrine Actinocyclus species, Western United States. The numbers represent localities 

with radiometric ages (see "Appendix" and fig. 2). The species ranges have been established by localities with radiometric ages.

(loc. 74), and estimate their absolute age at about 15.1 Ma. 

We do not know if A. acanthus occurs above the unconformity in this section.

The only other occurrences of A. acanthus are at the 

type locality, New Pass, Lander County, Nevada (loc. 42; 

undated), in Silvies Valley, Grant County, Oregon (loc. 75; 

about 12.5 Ma), possibly in the Latah Formation (Miocene) 

near Mead, Spokane County, Washington (loc. 106), and in 

the Bully Creek Formation (Miocene), Malheur County, 

Oregon (loc. 7), which has an estimated age of 12 Ma (S.L. 

VanLandingham, written commun., 1983). This estimate 

appears loosely constrained, so the Bully Creek Formation 

may in fact be considerably older. Actinocyclus acanthus 

occurs in the lower middle Miocene (15.1 Ma) and may 

range into the mid middle Miocene (about 12 Ma).

Actinocyclus cedrus Bradbury & Krebs

Lohman (1957) originally described this species as 

Cestodiscus cedarensis from the Esmeralda Formation at 

Cedar Mountain, Nye County, Nevada (loc. 74, about 

15.1 Ma). Actinocyclus cedrus is common in many 

Miocene lacustrine formations of the Great Basin and can

constitute nearly the entire mass of a diatomite, for 

example, in the southern Stillwater Mountains, Churchill 

County, Nevada (loc. 48). Among our sample localities, its 

oldest first occurrence is at the type locality at Diatomite 

Ridge, Stewart Valley, Mineral County, Nevada (loc. 20; 

15.1 Ma). VanLandingham (1988), however, reported the 

presence of this species at New Pass Summit, Nevada (E>/2 

sec. 32, T. 20 N., R. 40 E., Churchill County) in rocks that 

date from about 22 Ma (Hudson and Geissman, 1988). 

Inasmuch as VanLandingham did not figure this species 

and was unclear how his sample relates stratigraphically to 

the dated tuff, we cannot confirm his assertion.

In addition to the above mentioned localities, A. cedrus 

has been found in the Squaw Creek Member of the Ellensburg Formation, Yakima County, Washington (loc. 49; 

15.5-14.5 Ma), the Ellensburg Formation at Vantage, Grant 

County, Washington (loc. 59; 15.5-14.5 Ma), in the Beaverdam Formation at Trapper Creek, Cassia County, Idaho 

(loc. 53, estimated 12.0-11.5 Ma), in the Virginia Range 

north of Virginia City, Storey County, Nevada (loc. 68; 

undated), at Drewsey, Harney County, Oregon (loc. 63; 

undated), Turner Creek, Modoc County, California (loc. 17; 

late Barstovian-Clarendonian), Otis Creek, Harney County,
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLUS SPECIES, WESTERN UNITED STATES 57

Oregon (loc. 34; undated), Esmeralda Formation, Black 

Spring, Nye County, Nevada (loc. 93; undated) and in the 

Milford Federal No. 1 Well, Lemhi County, Idaho (loc. 40; 

undated). In the middle member of the Truckee Formation 

(Miocene) at Browns Hill, Churchill County, Nevada 

(loc. 55; 9.8 Ma), fragments and a few whole specimens of 

A. cedrus have been noted. Redeposited A. cedrus occurs in 

the middle member of the Truckee Formation near Fernley, 

Churchill County, Nevada (loc. 41; 9.8 Ma), and in the 

basal Truckee Formation in the Hot Springs Mountains, 

Churchill County, Nevada (loc. 56). It has also been 

reworked into the diatomite of the Kate Peak Formation at 

the Eagle-Picher diatomite quarry near Clark Siding, Storey 

County, Nevada (loc. 84; 11.210.3 Ma). Deposits with 

abundant A. cedrus have been found to the southeast (for 

example, loc. 48) and southwest (for example, loc. 68) of 

Browns Hill (loc. 55). Therefore, we consider the occurrence at Browns Hill as possible reworked contamination. 

Actinocyclus cedrus, thus, has a known geologic range from 

15 to about 12 Ma (middle Miocene) in the Western United 

States, and it also occurs in Miocene lacustrine diatomite of 

the Moon-To Basin near Kunming in southwestern China.

Actinocyclus claviolus Bradbury & Krebs

Actinocyclus claviolus has only been found at its type 

locality at Jungle Point, Idaho County, Idaho (loc. 33, 

15.4—14.5 Ma). A few specimens and fragments occur in the 

Latah Formation (Miocene) near Mead, Spokane County, 

Washington Uoc. 106; undated). Thus far, it is restricted to 

the lower middle Miocene.

Actinocyclus cupreus Bradbury & Krebs

This species has been found at only four localities in the 

Western United States—the type locality at Copper Kettle 

Canyon, Churchill County, Nevada (loc. 16; 18.9±1.2 Ma), 

at Juliaetta, Nez Perce County, Idaho (loc. 32; 15.3 Ma), at 

Jungle Point, Idaho County, Idaho (loc. 33, 15.4-14.5 Ma), 

and in the Humboldt Formation, Eureka County, Nevada 

(loc. 30; undated). Fields (1983) assigned a middle Miocene 

age to the Humboldt Formation. In the United States, A. 

cupreus ranges from the lower to middle Miocene >19 to 

<15.3 Ma). A similar species of Actinocyclus has been found 

in lower Miocene freshwater deposits beneath the Sea of 

Japan and on the Japanese mainland (Koizumi, 1988).

Actinocyclus gorbunovii var. fossa Bradbury & Krebs

We have found this taxon only at Forty-nine Camp, 

Washoe County, Nevada (loc. 69; 16 Ma). In the Western 

United States, its geologic age is approximately 16 

Ma—earliest middle Miocene.

Actinocyclus krasskei (Krasske) Bradbury & Krebs

Actinocyclus krasskei appears to be restricted to the 

lower middle and mid middle Miocene (15.3 to 12.5 or 12 

Ma), although VanLandingham (1988) reported it from 

New Pass Summit, Nevada (about 22 Ma). As previously 

noted with Actinocyclus cedrus, we cannot confirm this 

occurrence.

Although small and variable in form, A. krasskei occurs 

abundantly, particularly in the lower middle Miocene of 

Idaho. Its youngest occurrence may be in the Bully Creek 

Formation, Malheur County, Oregon (loc. 7; estimated at 12 

Ma). The absolute age of this formation, however, is very 

uncertain and may well prove to be older. In addition, we 

have found A. krasskei at the following localities: Juliaetta, 

Nez Perce County, Idaho (loc. 32; 15.3 Ma), Latah(?) Formation, Hangman Valley, Spokane County, Washington 

(loc. 36; 14.9 Ma), Squaw Creek Member, Ellensburg Formation, Yakima County, Washington (loc. 49; 15.5-14.5 

Ma), Oviatt Creek, Clearwater County, Idaho (loc. 43; 12.8 

Ma), Arrow Junction, Nez Perce County, Idaho (loc. 72; 

undated), near Weiser, Washington County, and Whitebird, 

Idaho County, Idaho (Iocs. 70, 71, respectively; undated), 

North Fork Fitsum Creek, Valley County, Idaho (loc. 94; 

undated), Silvies Valley, Grant County, Oregon (loc. 75; 

about 12.5 Ma), the Columbia River Basalt Group 

(Miocene), Seven Mile Creek, Umatilla County, Oregon 

(loc. 38; undated), in the Humboldt Formation, Eureka 

County, Nevada (loc. 30; undated), and in the Mascall Formation (Miocene) at Vinegar Creek, Grant County, Oregon 

(loc. 88; undated). In the Latah Formation, Spokane County, 

Oregon (Iocs. 76, 106; undated), rare (reworked?) Actinocyclus, possibly A. krasskei, has been observed.

Actinocyclus motilis Bradbury & Krebs

Lohman (1957) first described this species as Cestodiscus mobilis (mobllensis) in his unpublished dissertation, and 

reported it from the Esmeralda Formation at Cedar Mountain, Nye County, Nevada (loc. 74; about 15.1 Ma). Actinocyclus motilis is widely distributed and often abundant in 

the Western United States. The type specimens come from 

locality 22 (Esmeralda Formation, Cedar Mountain, Mineral 

County, Nevada). This species also occurs in the Squaw 

Creek Member, Ellensburg Formation, Yakima County, 

Washington (loc. 49; 15.5-14.5 Ma), at Vantage, Grant 

County, Washington in the Ellensburg Formation (loc. 59; 

15.5-14.5 Ma), Augusta Mountains, Churchill County, 

Nevada (loc. 4; 14.6 Ma), in the Juntura(?) Formation, Harney County, Oregon (loc. 86; 12.4 Ma), in the Bully Creek 

Formation, Harper Basin, Malheur County, Oregon (loc. 7; 

estimated 12 Ma), in the Esmeralda Formation, Black 

Spring, Nye County, Nevada (loc. 93; undated), in the Mascall Formation, White Hills, Grant County, Oregon (loc. 87; 

undated), and at Goose Creek, Baker County, Oregon
58 THE DIATOM GENUS ACTINOCYCLVS IN THE WESTERN UNITED STATES

(loc. 27; 14.5 Ma). These dated localities indicate a geologic 

range for A. motilis of about 15 Ma to possibly 12 Ma 

(middle Miocene) within the Western United States.

Actinocyclus nebulosus Bradbury And Krebs

Actinocyclus nebulosus, although very distinctive and 

locally abundant, has been found at only a few localities. 

Lohman (1957) originally described it in his unpublished 

dissertation as Cestodiscus fasciculatus from the Esmeralda Formation of Cedar Mountain, Nye County, Nevada 

(loc. 74; about 15.1 Ma). Smedman (1969) named it Coscinodiscus nevadensis, and reported its occurrence at Buffalo Canyon, Churchill County, Nevada (loc. 6; 14.6 Ma). 

Actinocyclus nebulosus also occurs in the Mascall Formation at Aldrich Mountain, Grant County, Oregon (loc. 85; 

about 15.8 Ma), in the Latah Formation near Mead, 

Spokane County, Washington (loc. 106), and in the Esmeralda Formation at Black Spring (loc. 93) and Cedar Spring 

(loc. 95), Nye County, Nevada. It is thus far restricted to 

the lower middle Miocene (15.8-14.6 Ma).

Actinocyclus pinnulus Bradbuiy & Krebs

The type locality for A. pinnulus is the Hole-in-theWall diatomite (Iocs. 90, 91; 10.3 Ma) in Gooding County, 

Idaho, where it occurs in association with Mesodictyon 

Theriot & Bradbury. It is also found with Mesodictyon at 

Durkee, Baker County, Oregon (loc. 81; undated). A form of 

Actinocyclus very similar to A. pinnulus is present near 

-985 m in the AMOCO Becharof No. 1 well, Alaska 

(loc. 112) in deposits of unknown age. A. pinnulus is thus far 

restricted to the uppermost middle Miocene.

Actinocyclus theleus Bradbury & Krebs

Actinocyclus theleus has been found at only a few sites 

in the Pacific Northwest: Emerald Creek, Benewah County 

(loc. 21; 15.3 Ma), Juliaetta, Nez Perce County (loc. 32; 

15.3 Ma), Oviatt Creek, Clearwater County (loc. 43; 12.8 

Ma), Idaho, in the Mascall Formation, White Hills, Grant 

County, Oregon (loc. 87), and possibly reworked in the 

Latah Formation, Spokane County, Washington (Iocs. 76, 

106). Its known range is, therefore, from the lower middle 

to mid middle Miocene (15.3-12.8 Ma).

Actinocyclus tubulosus Khursevich

Galina Khursevich (written commun., 1992) has 

confirmed the presence of Actinocyclus tubulosus in the 

Squaw Creek Member of the Ellensburg Formation, Yakima 

County, Washington (loc. 49, -15 Ma). It has not been found 

elsewhere in the United States and is thus far restricted to the 

early middle Miocene. Its similarity to and possible

misidentification with Actinocyclus krasskei may partly 

account for its restricted range.

Actinocyclus venenosus Bradbury & Krebs

Actinocyclus venenosus is found abundantly and well 

preserved at the type locality (loc. 44, Poison Creek Formation, Reynolds Creek, Owyhee County, Idaho, 8.9 Ma). This 

radiometric date is from the Banbury(?) basalt stratigraphically well above the last occurrence of A. venenosus in that 

section, and probably represents the uppermost age limit of 

the Poison Creek Formation. Armstrong and others (1975) 

reported that the formation is Clarendonian in age and estimated its age at 11 Ma from dates on enclosing volcanic 

rocks. Fields (1983), after a thorough literature review, also 

centered the formation at 11 Ma. For the purposes of this 

study, we accept this estimate as the most accurate.

Actinocyclus venenosus also occurs in the Esmeralda 

Formation, Cedar Mountain, Nye County, Nevada (loc. 74; 

about 15.1 Ma), the Coal Valley Formation, Pine Grove 

Hills, Lyon County, Nevada (loc. 15, 11.1-9.5 Ma), the 

Beaverdam Formation at Trapper Creek, Cassia County, 

Idaho (loc. 53, estimated 12.0-11.5 Ma), an unnamed unit 

at Turner Creek, Modoc County, California (loc. 17), and 

at sites within the Poison Creek Formation (Iocs. 108, 109) 

and Idaho Group (Iocs. 31, 111), Washington County, 

Idaho. Poorly preserved, possibly reworked specimens of 

A. venenosus (?) have been observed within the Sucker 

Creek Formation (Miocene) at Leslie Gulch, Malheur 

County, Oregon (loc. 50; estimated 12 Ma). Its geologic 

range in the United States appears to span most of the 

middle Miocene (15 to about 11 Ma). Actinocyclus aff. A. 

venenosus has been found in Miocene lacustrine diatomites 

of the Xian Feng Basin of southwest China (Bradbury, 

1984; chapter A).

DISCUSSION

In the Western United States, obligate freshwater 

species of Actinocyclus range from the lower Miocene to 

upper middle Miocene (about 19 to 10 Ma). We have examined Oligocene and lowest Miocene lacustrine diatomaceous 

sediments from southwestern Montana, Eocene material 

from British Columbia, Idaho, and Montana, and Oligocene 

material from Colorado and Nevada, but we have not found 

Actinocyclus. An upper Eocene diatom assemblage from 

Wyoming does not contain Actinocyclus (Lohman and 

Andrews, 1968). Similarly, our extensive collection of upper 

Miocene and younger material has failed to produce fossil 

obligate lacustrine Actinocyclus species that are not probable 

contaminants reworked from older sediments. We have confirmed however, the presence of A. ehrenbergii in lacustrine 

sediments of the Quiburis Formation at Edgar Canyon near 

Tucson, Pima County, Arizona (loc. 92) and in the Furnace
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLUS SPECIES, WESTERN UNITED STATES 59

Creek Formation of Death Valley, Inyo County, California 

(loc. 113). The Quiburis Formation is latest Miocene in age 

(6.6-5.4 Ma; Shenk, 1990) and apparently formed in a moderately saline (sodium chloride) lake. The age of the Furnace 

Creek Formation (7.35-5.18 Ma) (Marvin and Dobson, 

1979) is late Miocene to earliest Pliocene. Actinocyclus 

ehrenbergii is a coastal marine species that can live in 

lagoons and saline lakes (Yezdani, 1970; Foged, 1978). 

Although of ecological interest, it is probably not biostratigraphically important because (1) its age range in marine 

rocks extends from at least the early Oligocene (Fenner, 

1977) to the Holocene, and (2) it is rare in lacustrine diatomaceous sediments.

Elsewhere in the world, freshwater species of Actinocyclus appear to have a longer geologic range. In the former 

Soviet Union, for example, the genus may range from the 

early Miocene, or even the late Oligocene (Moisseeva and 

others, 1974), to early Pliocene, although its maximum 

diversity occurred during the middle Miocene (Khursevich, 

1982). Similarly, Actinocyclus occurs in early Pliocene 

deposits in Bulgaria (Temniskova-Toplova and OgnjanovaRumenova, 1990). Although these reported ranges are without radiometric age control, the associations of diatom 

genera within samples do indicate significant differences in 

the geologic ranges of some lacustrine diatom genera 

between western North America and Eurasia. Late Miocene 

samples from Macedonia in northern Greece (Gersonde and 

Velitzelos, 1977) confirms this conclusion. In these samples, 

Stephanodiscus Ehrenberg and obligate freshwater Actinocyclus are common and co-occur, an association never 

seen in the Western United States except for isolated (probably contaminated) examples (for examples, see VanLandingham, 1964, 1967). Nevertheless, Fourtanier (1987) and 

Serieyssol (1988) have demonstrated that there is a remarkable synchroneity of events in the evolution of lacustrine diatoms between continents—that is, the decline of Actinocyclus during the late Miocene, the late Miocene species 

diversification of Mesodictyon Theriot and Bradbury, and 

the appearance of Stephanodiscus and Cyclostephanos 

Round near the Miocene-Pliocene boundary.

In conclusion, we note that the appearance of freshwater Actinocyclus in the Western United States coincides with 

the early Miocene species radiation of marine Actinocyclus 

(Radionova, 1987), high stand in sea level (Haq and others, 

1987), and the initiation of extensional basin-and-range tectonics (Stewart and Carlson, 1976). Furthermore, the worldwide decline in freshwater Actinocyclus during the late 

Miocene corresponds with the origin and (or) species radiations of Mesodictyon and Cyclotella (Kiitzing) Brebisson, 

and the appearance of Stephanodiscus and Cyclostephanos. 

The ways in which paleoenvironmental changes and species 

competition influenced the course of lacustrine diatom evolution remain unknown but are worthy of study.

REFERENCES

Armstrong, R.L., Leeman, W.P., and Malde, H.E., 1975, K-Ar 

dating, Quaternary and Neogene volcanic rocks of the Snake 

River Plain, Idaho: American Journal of Science, v. 275(3), 

p. 225-251.

Axelrod, D.I., 1958, The Pliocene Verdi flora of western Nevada: 

University of California Publications in the Geological Sciences, v. 34, p. 91-159.

————1966, Potassium-argon ages of some western Tertiary 

floras: American Journal of Science, v. 264, no. 7, p. 497-506.

Beeson, M.H., Fecht, K.R., Reidel, S.P., and Toland, T.L., 1985, 

Regional correlations within the Frenchman Springs Member 

of the Columbia River Basalt Group: new insight into the 

middle Miocene tectonics of northwestern Oregon: Oregon 

Geology, v. 47, p. 87-96.

Berggren, W.A., Kent, D.V., Flynn, J.J., and Van Couvering, 

J.A., 1985, Cenozoic geochronology: Geological Society of 

America Bulletin, v. 96, p. 1407-1418.

Bradbury, J.P., 1984, Fossil Actinocyclus species from freshwater 

Miocene deposits in China and the United States: in Mann, 

D.G. (ed.), Proceedings of the 7th International Diatom Symposium, Philadelphia, 22-27 August, 1982: Koenigstein, Germany, Koeltz, p. 157-171.

————1986, Continental diatom biostratigraphy and paleolimnology: a review and evaluation of research directions and 

applications: in Ricard, Michel (ed.), Proceedings 8th International Diatoms Symposium, Paris: Koenigstein, Germany, 

Koeltz, p. 667-686.

Bradbury, J.P., Dieterich, K.V., and Williams, J.L., 1985, Diatom 

flora of the Miocene lake beds near Clarkia in northern Idaho: 

in Smiley, C. J. (ed.), Late Cenozoic history of the Pacific 

Northwest: San Francisco, California, Pacific Division of the 

American Association for the Advancement of Science, 

p. 33-59.

Bradbury, J.P., and Krebs, W.N., 1982, Neogene and Quaternary 

lacustrine diatoms of the western Snake River Basin, IdahoOregon, USA: Acta Geologica Academiae Scientiarum 

Hungaricae, v. 25, no. 1-2, p. 97-122.

Dalrymple, G.B., 1979, Critical tables for conversion of K-Ar ages 

from old to new constants: Geology, v. 7, p. 558-560.

Evernden, J.F., and James, G.T., 1964, Potassium-argon dates and 

the Tertiary floras of North America: American Journal of 

Science, v. 262, p. 945-974.

Evernden, J.F., Savage, D.E., Curtis, G.H., and James, G.T., 1964, 

Potassium-argon dates and the Cenozoic mammalian chronology of North America: American Journal of Science, v. 262, 

p. 145-198.

Fenner, Juliane, 1977, Cenozoic diatom biostratigraphy of the 

equatorial and southern Atlantic Ocean: in Supko, P. R., and 

others (eds), Initial Reports of the Deep Sea Drilling Project: 

National Science Foundation, v. 39, p. 491-624.

Fiebelkorn, R.B., Walker, G.W., MacLeod, N.S., McKee, G.H., 

and Smith, J.G., 1983, Index to K-Ar determinations for the 

state of Oregon: Isochron/West, v. 37, p. 3-60.

Fields, P.P., 1983, A review of the Miocene stratigraphy of southwestern Idaho, with emphasis on the Payette Formation and 

associated floras: Berkeley, University of California, M.S. 

Thesis, 363 p.
60 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

Foged, Niels, 1978, Diatoms in eastern Australia: Bibliotheca 

Phycologia, v. 41,242 p.

Fourtanier, Elisabeth, 1987, Diatome'es Ne"ogenes d'Afrique: 

Approche biostratigraphique en milieux marin (sud-ouest 

africain) et continental: Paris, These de Doctoral de 1'Universit6 P. et M. Curie, Me"moires des Sciences de la Terre, Universit6 Paris, no. 87-44, 365 pp.

Fourtanier, Elisabeth, and Gasse, Franchise, 1988, Premiers jalons 

d'une biostratigraphie et Evolution des diatome'es lacustres 

d'Afrique depuis 11 Ma: Comptes Rendus de 1'Academic des 

Sciences de Paris, 306, series II, p. 1401-1408.

Gasse, Franchise, 1980, Les diatome'es lacustres plio-ple"istocenes 

du Gadeb (Ethiopie): syste"matique, pale'oe'cologie, biostratigraphie: Revue Algologique, v. 3 p. 1-249.

Gersonde, Rainer, and Velitzelos, Evagelos, 1977, Diatomeenpalaookologie im Neogen-Becken von Vegora N-W Mazedonien (Vorlaufige Mitteilung): Annales Ge"ologiques des Pays 

Helteniques, v. 29, p. 373-382.

Gilbert, C.M., and Reynolds, M.W., 1973, Character and chronology of basin development, western margin of the Basin 

and Range province: Geological Society of America Bulletin, v. 84, no. 8, p. 2489-2510.

Golia, R.T., and Stewart, J.H., 1984, Depositional environments 

and paleogeography of the Upper Miocene Wassuk Group, 

west-central Nevada: Sedimentary Geology, v. 38, p. 159-180.

Haq, B.U., Hardenbol, Jan, and Vail, P.R., 1987, Chronology of 

fluctuating sea levels since the Triassic: Science, v. 235, 

no. 4793, p. 1156-1167.

Hudson, M.R., and Geissman, J.W., 1988, Reply on "Paleomagnetic and structural evidence for middle Tertiary counterclockwise block rotation in the Dixie Valley region, westcentral Nevada": Geology, v. 16, no. 8, p. 757.

Khursevich, O.K., 1982, Neogene diatom assemblages from 

Byelorussia and their stratigraphic significance: Acta Geologica Academiae Scientiarum Hungaricae, v. 25, nos. 1-2, 

p. 123-134.

Kimmel, P.O., 1979, Stratigraphy and paleoenvironments of the 

Miocene Chalk Hills Formation and Pliocene Glenns Ferry 

Formation in the western Snake River Plain, Idaho: Ann Arbor, 

University of Michigan, Ph.D. dissertation, 331 p.

Koizumi, Itaru, 1988, Early Miocene Proto-Japan sea: Journal of 

the Paleontological Society of Korea, v. 4, p. 6-20.

Krebs, W.N., Bradbury, J.P., and Theriot, E.G., 1987, Neogene and 

Quaternary lacustrine diatom biochronology, Western USA: 

Palaios, v. 2, p. 505-513.

Loginova, L.P., 1982, The Likhvin diatom flora from the central 

part of the East European Plain, its paleogeographical and 

stratigraphical significance: Acta Geologica Academiae Scientiarum Hungaricae, v. 25, nos. 1-2, p. 149-160.

Loginova, L. P., Lupikina, E. G., and Khursevich, G. K., 1984, 0 

novom predstavitele roda Cyclostephanos Round i ego stratigraficheskom znachenii: Dokladi Akademii Nauk BSSR, 

Botanika v. 28, no. 2, p. 170-173.

Lohman, K. E., 1957, Cenozoic non-marine diatoms from the Great 

Basin: Pasadena, California Institute of Technology, Ph.D. dissertation, 190 p.

Lohman, K.E., and Andrews, G.W., 1968, Late Eocene nonmarine 

diatoms from the Beaver Divide area, Fremont County, Wyoming: U.S. Geological Survey Professional Paper 593-E, 26 p.

Malde, H.E., 1972, Stratigraphy of the Glenns Ferry Formation 

from Hammett to Hagerman, Idaho: U.S. Geological Survey 

Bulletin 1331-D, 19 p.

Manley, Kirn, and Mehnert, H.H., 1981, New K-Ar ages for 

Miocene and Pliocene volcanic rocks in the northwestern 

Espanola Basin and their relationships to the history of the Rio 

Grande Rift: Isochron/West, no. 30, p. 5-8.

Marvin, R.F., and Dobson, S.W., 1979, Radiometric ages: compilation B, U.S. Geological Survey: Isochron/West, no. 26, 

p. 3-32.

Moisseeva, A.I., Rubina, N.V., Cheremisinova, E.A., 1974, 

Miocene diatoms (Chapter 11, Neogene freshwater diatom 

algae) in Gleser, S.I., Jouse, A.P., Marakova, I.V., ProschinkaLavrenko, A.I., and Sheshukova-Poretzkaja, V.S., (eds), 

Diatom algae of the USSR. vol. 1, NAUK A, Leningrad: 

Koenigstein, Germany, Koeltz, p. 190-204. [Reprint 1979]

Neville, Coleen, Opdyke, N.D., Lindsay, E.H., and Johnson, N.M., 

1979, Magnetic stratigraphy of Pliocene deposits of the Glenns 

Ferry Formation, Idaho, and its implications for North American mammalian biostratigraphy: American Journal of Science, 

v. 279, no. 5, p. 503-526.

Radionova, E.P., 1987, Diatom morphology of the genus Cestodiscus from lower middle Miocene deposits of the tropical zone 

of the Pacific Ocean: Academy of Sciences, USSR, Institute of 

Geology, Micropaleontology Edition, Issue 29, p. 141-154.

Rehakova, Zadenka, 1980, Siisswasserdiatomeenflora des oberen 

Miozans in der Tschechoslowakei: Journal of Geological Sciences, v. 23, p. 83-184.

Repenning, C.A., 1987, Biochronology of the microtine rodents of 

the United States: in Woodburne, M.O., (ed.), Cenozoic mammals of North America, Geochronology and Biostratigraphy: 

Berkeley, University of California Press, p. 236-268.

Rymer, M.J., 1981, Stratigraphic revision of the Cache Formation 

(Pliocene and Pleistocene), Lake County, California: U.S. 

Geological Survey Bulletin 1502-C, p. 1-35.

Serieyssol, K.K., 1988, Biostratigraphy and taxonomic interpretations based on the survey of fossil freshwater centric genera 

[abs]: Huhmari, Joensuu, Finland, 10th International Diatom 

Symposium, Aug. 28-Sept. 2, 1988, p. 114.

Servant-Vildary, Simone, 1978, Etude des diatome'es et pale"olimnologie du bassin Tchadien au Ce"nozoique superieur: Travaux et documents de ORSTOM, v. 84, 346 p. [2 volumes]

Shenk, J.D., 1990, Economic geology of the White Cliffs diatomite 

deposit, Mammoth, Arizona: Tucson, University of Arizona, 

M.S. Thesis, 156 p.

Smedman, Gunilla, 1969, An investigation of the diatoms from four 

Tertiary lake bed deposits in western Nevada: PaleoBios 

[Contributions from the University of California Museum of 

Paleontology, Berkeley] no. 9, 16 p.

Smiley, C.J., and Rember, W.C., 1985, Physical setting of the 

Miocene Clarkia fossil beds, northern Idaho: in Smiley, C.J., 

(ed.), Late Cenozoic history of the Pacific Northwest: San 

Francisco, California, Pacific Division of the American Association for the Advancement of Science, p. 11-31.

Smith, G.A., 1988, Neogene synvolcanic and syntectonic sedimentation in central Washington: Geological Society of America 

Bulletin, v. 100, p. 1479-1492.

Stewart, J.H., and Carlson, J.E., 1976, Cenozoic rocks of 

Nevada—Four maps and brief description of distribution,
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLUS SPECIES, WESTERN UNITED STATES 61

lithology, age, and centers of volcanism: Nevada Bureau of 

Mines and Geology, Map 52, p. 1-5.

Temniskova-Topalova, Dobrinka, and Ognjanova-Rumenova, 

Nadja, 1990, Non-marine diatoms from Neogene sediments of 

Bulgaria: in Simola, Heikki, (ed.), Proceedings, 10th International Diatom Symposium, Joensuu, Finland (1988): Koenigstein, Germany, Koeltz, p. 357-363.

Theriot, E.G., and Bradbury, J.P., 1987, Mesodictyon, a new fossil 

genus of the centric diatom family Thalassiosiraceae from the 

Miocene Chalk Hills Formation, western Snake River Plain, 

Idaho: Micropaleontology, v. 33, no. 4, p. 356-367.

VanLandingham, S.L., 1964, Miocene non-marine diatoms from 

the Yakima region in south central Washington: Beihefte zur 

Nova Hedwigia, Heft 14,78 p.

————1967, Paleoecology and microfloristics of Miocene diatomites from the Otis Basin—Juntura region of Harney and 

Malheur Counties, Oregon: Beihefte zur Nova Hedwigia, Heft 

26, 77 p.

——1985, Potential Neogene diagnostic diatoms from the western Snake River Basin, Idaho and Oregon: Micropaleontology, 

v. 31, no. 2, p. 167-174.

1988, Comment on "Paleomagnetic and structural evidence for middle Tertiary counterclockwise block rotation in 

the Dixie Valley region, west-central Nevada": Geology, 

v. 16, no. 8, p. 756.

Wolfe, J.A., 1971, Tertiary climate fluctuations and methods of 

analysis of Tertiary floras: Palaeogeography, Palaeoclimatology, Palaeoecology, v. 9, no. 1, p. 27-59.

Wood, H.E., Chancy, R.W., Clarke, John, Colbert, E.H., Jepsen, 

G.L., Reeside, Jr., J.B., and Stock, Chester, 1941, Nomenclature and correlation of the North American continental Tertiary: Geological Society of America Bulletin,, v. 52, p. 1-48.

Yezdani, G.H., 1970, A study of the Quaternary vegetation history 

in the volcanic lakes region of western Victoria: Clayton, 

Victoria, Australia, Monash University, Ph.D. dissertation, 

522 p.

Published in the Central Region

Manuscript approved for publication July 19,1993

Graphics by J. Platt Bradbury and William N. Krebs

Edited by Thomas Kohnen

Photocomposition by Marie Melone
APPENDIX

List of Diatom Sample Localities
64 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

LIST OF DIATOM SAMPLE 

LOCALITIES

Localities with absolute ages are marked with an asterisk (*); + identifies localities wthActinocyclus. The location 

of each sample site is shown in figure 2. Locality information includes the name of the formation (if known), geographic coordinates, the name of the collector and sampling 

year, and age (if known), and where the information has been 

published. Radiometric ages have been corrected according 

to Dalrymple (1979). Formation names in quotes indicate 

that the assigned name is of dubious validity. (?) indicates 

that the deposit is not assignable to the formation with certainty. "UCMP" = University of California Museum of Paleontology; "P####" = plant locality number.

1+ Aldrich Station(?) Formation, east Walker River, 

38.84°N., 119.06°W., Lyon Co., Nevada, J. H. Stewart, 1980; Miocene.

2* Alturas Formation, Howards Gulch, sec. 27, T. 42 N., 

R. 15 E., Modoc Co., California, R. A. Laws, 1981; 

8.1 Ma (Evernden and James, 1964), 8.3 Ma 

corrected.

3* Alturas Formation, 3.5 miles west of Alturas, California Academy of Sciences locality 36805, Modoc Co., 

California, G. D. Hanna; 4.8 Ma (Repenning, 1987).

4*+ Augusta Mountains, unnamed unit, sec. 31, T. 24 N., R. 

39 E., Churchill Co., Nevada, W. N. Krebs, 1982; 

14.6 Ma (Krebs and others, 1987).

5* Bruneau Formation, W. Snake River Plain, sec. 27, 

T. 5 S., R. 4 E., Elmore Co., Idaho, J. P. Bradbury, 

1978; 1.36 Ma (Evernden and others, 1964), 1.4 Ma 

(Armstrong and others, 1975).

6*+ Buffalo Canyon Formation, Buffalo Canyon, sec. 2, T. 

15 N., R. 37 E., southeast of Eastgate, Churchill Co., 

Nevada, D. I. Axelrod, (Smedman, 1969); 14.6±0.4 

Ma (AMOCO, unpublished data, 1982), 14.5-15.0 

Ma (H. E. Schorn, written commun., 1989).

7*+ Bully Creek Formation, type section, Harper Basin, 

sec. 11, T. 19 S., R. 41 E., Malheur Co., Oregon, 

W. N. Krebs, 1980; middle Miocene (estimated 12 

Ma) VanLandingham, written commun., 1983).

8* Chalk Hills Formation, base of formation, West 

Browns Creek, sec. 2, T. 5 S., R. 1 W., Owyhee Co., 

Idaho, W. N. Krebs, 1980; about 9 Ma (Kimmel, 

1979).

9* Chalk Hills Formation, Castle Creek, sec. 9, T. 6 S., 

R. 1 E., Owyhee Co., Idaho, W. N. Krebs, 1980; 7-9 

Ma (Kimmel, 1979).

10* Chalk Hills Formation, Chalk Hills, sec. 20, T. 7 S., R. 

4 E., Owyhee Co., Idaho, W. N. Krebs, 1980; 7-9 Ma 

(Kimmel, 1979).

11* Chalk Hills Formation, Shoofly Creek, lower Horse 

Hill ash, sec. 9, T. 7 S., R. 3 E., Owyhee Co., Idaho, 

M. J. Evens, 1979; 7 Ma (Kimmel, 1979).

12* Chalk Hills Formation, type section, lower Horse Hill 

ash, sec. 25, T. 7 S., R. 4 E., Owyhee Co., Idaho, M. 

J. Evens, 1979; 7 Ma (Kimmel, 1979).

13*+Clarkia Basin, unnamed unit, sec. 13, T. 42 N., R. 1 E., 

Shoshone Co., Idaho, C. J. Smiley; 15.3 Ma (Bradbury and others, 1985).

14* Kelseyville Formation, Clear Lake, sec. 27, T. 13 N., 

R. 9 W., Lake Co., California, M. J. Rymer, 1978; 0.4 

Ma(Rymer, 1981).

15*+Coal Valley Formation, Pine Grove Hills, sec. 2, T. 9 

N., R. 26 E., Lyon Co., Nevada, J. H. Stewart, 1983; 

9.3-10.8 Ma (Gilbert and Reynolds, 1973), 9.5-11.1 

Ma corrected.

16*+Copper Kettle Canyon, unnamed unit, sec. 26, T. 24 N., 

R. 34 E., Churchill Co., Nevada, W. N. Krebs, 1982; 

18.9±1.2 Ma (AMOCO, unpublished data, 1982).

17+ Turner Creek, unnamed unit, sec. 1, T. 41 N., R. 8 E., 

Modoc Co., California, J. P. Bradbury, 1985; late 

Barstovian-Clarendonian (J. A. Wolfe, oral commun., 1985).

18 Dead Camel Mountains, unnamed unit, sec. 24, T. 18 

N., R. 26 E., Churchill Co., Nevada, W. N. Krebs, 

1981; Miocene.

19 AMOCO Delta Stephan Szot No. 1 well, sec. 19, T. 14

N., R. 1 E., Cache Co., Utah, W. N. Krebs, 1983. 

20*+Esmeralda Formation, Diatomite Ridge, Stewart Valley, 38°37'02"N., 117°56 /35// W., Mineral Co.,

Nevada, S. W. Starratt, 1986, 15.1 Ma (S. W. Starratt, written commun., 1986). 

21*+Clarkia Basin, Emerald Creek, unnamed unit, sec. 33,

T. 43 N., R. 1 E., Benewah Co., Idaho, C. J. Smiley,

1978; 15.3 Ma (Bradbury and others, 1985). 

22+ Esmeralda Formation, Cedar Mountain, 38.5°N.,

44.75° W., Mineral Co., Nevada, J. H. Stewart, 1980;

Miocene. 

23* Glenns Ferry Formation, Hagerman Horse quarry,

sec. 16, T. 7 S., R. 13 E., Twin Falls Co., Idaho, J. P.

Bradbury, 1979; about 3.2 Ma (Neville and others,

1979). 

24 Glenns Ferry Formation, Malde's (1972) section

no. 55, sec. 1, T. 6 S., R. 8 E., Owyhee Co., Idaho, M.

J. Evens, 1979; Pliocene. 

25* Glenns Ferry Formation, Shoofly Creek, sec. 6, T. 7 S.,

R. 3 E., Owyhee Co., Idaho, M. J. Evetts, 1979;

3.0-3.3 Ma (M. L. Porter, oral commun., 1985). 

26 Glenns Ferry (?) Formation, Weiser, sec. 35, T. 15 S.,

R. 46 E., Washington Co., Idaho, M. J. Evetts, 1979;

Pliocene(?). 

27*+Goose Creek, unnamed unit, sec. 29, T. 8 S., R. 43 E.,

Baker Co., Oregon, J. P. Bradbury, 1978, 14.5 Ma

(Fiebelkorn and others, 1983).
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLUS SPECIES, WESTERN UNITED STATES 65

28 Michel T. Halbouty Federal No. 1 well, sec. 14, T. 17 

N., R. 28 E., Churchill Co., Nevada, W. N. Krebs, 

1982.

29 Alturas Formation, Howards Gulch, sec. 22, T. 42 N.,

R. 9 E., Modoc Co., California, J. P. Bradbury, 1985;

Miocene. 

30+ Humboldt Formation, sec. 31, T. 31 N., R. 52 E.,

Eureka Co., Nevada, Susan Laule, 1979; Miocene. 

31+ IW-24, IW-26, Idaho Group, sec. 34, T. 12 N., R. 4

W., Washington Co., Idaho, M. J. Evetts, 1979;

Neogene. 

32*+Juliaetta, unnamed unit, sec. 20, T. 37 N., R. 3 W., Nez

Perce Co., Idaho, C. J. Smiley; 15.3 Ma (Bradbury

and others, 1985). 

33*+Jungle Point, unnamed unit, sec. 15, T. 33 N., R. 6 E.,

Idaho Co., Idaho; 14.5-15.4 Ma (Smiley and

Rember, 1979). 

34+ Juntura(?) Formation, Otis Creek, sec. 32, T. 19 S.,

R. 36 E., Harney Co., Oregon, J. P. Bradbury, 1978;

Miocene. 

35 Lake Britton, unnamed unit, sec. 29, T. 37 N., R. 3 E.,

Shasta Co., California, R. A. Laws, 1981. 

36*+Latah(?) Formation, Hangman Valley, sec. 6, T. 24 N.,

R. 43 E., Spokane Co., Washington, J. P. Bradbury,

1979; 14.5 Ma (Evernden and James, 1964; 14.9 Ma

corrected). 

37 Raft River Formation, Burley, sec. 35, T. 10 S., R. 27

E., Cassia Co., Idaho, J. P. Bradbury, 1979;

Pleistocene. 

38+ Lower(?) part of the Columbia River Basalt Group,

Seven Mile Creek, sec. 19, T. 2 S., R. 33 E., Umatilla

Co., Oregon, M. J. Evetts, 1979; Miocene. 

39 AMOCO Lynn Reese No. 1 well, sec. 17, T. 12 N., R. 1

E., Cache Co., Utah, W. N. Krebs, 1983. 

40+ AMOCO Milford Federal No. 1 well, sec. 19, T. 15 N.,

R. 27 E., Lemhi Co., Idaho, W. N. Krebs, 1983. 

41*+Truckee Formation (middle member), Fernley, sec. 8,

T. 19 N., R. 26 E., Churchill Co., Nevada, W. N.

Krebs, 1981; 9.8 Ma (F. H. Brown, unpublished data,

1986). 

42+ New Pass, unnamed unit, unsurveyed T. 19 N., R. 40

E., Lander Co., Nevada, J. P. Bradbury, 1985;

Miocene. 

43*+Oviatt Creek, unnamed unit, sec. 12, T. 39 N., R. 1 E.,

Clearwater Co., Idaho, C. J. Smiley; 12.8 Ma (Smiley

and Rember, 1979). 

44*+Poison Creek Formation, Reynolds Creek, NW/4

sec. 2, T. 2 S., R. 3 W., Owyhee Co., Idaho, W. N.

Krebs, 1980; minimum age 8.9 Ma (Krebs and others, 1987), estimated 11 Ma (Armstrong and others,

1975). 

45+ Poison Creek Formation, sec. 17, T. 11 N., R. 6 W.,

Washington Co., Idaho, M. J. Evetts, 1979; Miocene.

46* Ringold Formation, White Cliffs, Columbia River, 

sec. 1, T. 10 N., R. 28 E., Franklin Co., Washington, 

J. P. Bradbury, 1978; 4.3 Ma (Repenning, 1987).

47 Big Smokey Valley, unnamed unit, unsurveyed T. 2 

N., R. 38 E., Esmeralda Co., Nevada, J. P. Bradbury, 

1984; Miocene.

48 + Southern Stillwater Mountains, unnamed unit, sec.22, 

T. 18 N., R. 31 E., Churchill Co., Nevada; Miocene.

49*+Squaw Creek Member, Ellensburg Formation, sec. 9, 

T. 14 N., R. 19 E., Yakima Co., Washington, J. P. 

Bradbury, 1979; 14.5-15.5 Ma (Beeson and others, 

1985),-15 Ma (Smith, 1988).

50*+Sucker Creek Formation, Leslie Gulch, sec. 28, T. 24 

S., R. 46 E., Malheur Co., Oregon, M. J. Evetts, 

1979; estimated 12 Ma (Fields, 1983).

51 Swayze Creek, unnamed unit, sec. 6, T. 12 S., R. 44 E., 

Baker Co., Oregon, J. P. Bradbury, 1978.

52* Thousand Creek Formation, unsurveyed T. 46 N., R. 

25 E., Humboldt Co., Nevada, J. P. Bradbury, 1985; 

Hemphillian (Wood and others, 1941), estimated 7.8 

Ma (VanLandingham, written commun., 1983).

53*+Beaverdam Formation, Trapper Creek, sec. 2, T. 15 S., 

R. 20 E., Cassia Co., Idaho, C. J. Smiley; estimated 

11.5-12.0 Ma (Wolfe, 1971).

54+ Truckee Formation (middle member), Bradys Hot 

Spring, sec. 21, T. 23 N., R. 27 E., Churchill Co., 

Nevada, W. N. Krebs, 1981; Miocene.

55*+Truckee Formation (middle member), Browns Hill, 

sec. 33, T. 23 N., R. 27 E., Churchill Co., Nevada, 

W. N. Krebs, 1981; 9.8 Ma (Krebs and others, 1987).

56+ Truckee Formation (lower member), Hot Springs 

Mountains, sec. 36, T. 22 N., R. 27 E., Churchill Co., 

Nevada, W. N. Krebs, 1981; Miocene.

57+ Truckee Formation (middle member), Nightingale, 

sec. 18, T. 24 N., R. 26 E., Churchill Co., Nevada, 

W. N. Krebs, 1981; Miocene.

58 Tulare Formation, La Ceja Ridge, Kettleman Hills, 

sees. 26 and 35, T. 21 S., R. 17 E., Kings Co., California; Pliocene to Pleistocene.

59*+Ellensburg Formation, Vantage, sec. 17, T. 18 N., 

R. 23 E., Grant Co., Washington, 14.5-15.5 Ma 

(Beeson and others, 1985).

60 "Yonna" Formation, Dorris, sec. 11, T. 47 N., R. 1 E., 

Siskiyou Co., California, J. P. Bradbury, 1978; 

Pliocene.

61 "Yonna" Formation, Klamath Falls, sec. 23, T. 38 S., 

R. 8 E., Klamath Co., Oregon, Maura O'Brian, 

1980; Pliocene.

62 "Yonna" Formation, Yonna Valley, sec. 23, T. 38 S.,

R. 11 ft E., Klamath Co., Oregon, J. P. Bradbury,

1978; Pliocene. 

63+ Unnamed unit, USGS 1019, 1020, Drewsey, sec. 14,

T. 20 S., R. 36 E., Harney Co., Oregon, B. N. Moore,

1931.
66 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

64+ Bully Creek Formation, USGS 1022, Westfall, Harper

Basin, sec. 15, T. 18 S., R. 41 E., Malheur Co.,

Oregon, B. N. Moore, 1931; Miocene. 

65+ Bully Creek Formation, USGS 1023, Harper Basin,

sec. 34, T. 19 S., R. 42 E., Malheur Co., Oregon, B.

N. Moore, 1931; Miocene. 

66+ Bully Creek Formation, USGS 1024, Harper Basin,

sec. 34, T. 18 S., R. 41 E., Malheur Co., Oregon, B.

N. Moore, 1931; Miocene. 

67 Lake beds of Burnt River, USGS 1030, Swayze Creek,

sec. 11, T. 11 S., R. 43 E., Baker Co., Oregon, B. N.

Moore, 1931.

68+ "Truckee" lake beds, USGS 1187, 10 miles N. of Virginia City, Virginia Range, Storey Co., Nevada, V. P.

Gianella, 1932. 

69*+USGS 1690, upper part of the Cedarville Formation,

Forty-nine Camp, Washoe Co., Nevada, 17 miles E.

of N. of Cedarville, California, R. S. LaMotte, 1933;

15.6Ma(Axelrod, 1966), 16.0 Ma corrected. 

70+ Unnamed unit, USGS 2280, 15 miles NE. of Weiser,

Washington Co., Idaho, R. W. Brown, 1934. 

71+ Unnamed unit, USGS 2281, 2.5 miles NE. of Whitebird, Idaho Co., Idaho, on road to Grangeville, R. W.

Brown, 1934. 

72+ Unnamed unit, USGS 2289, about 2.5 miles NE. of

Arrow Junction, Nez Perce Co., Idaho, on road to

Juliaetta, R. W. Brown, 1934. 

73+ Unnamed unit, USGS 3707, Goose Creek, sec. 35,

T. 14 S., R. 20 E., Cassia Co., Idaho, J. R. Gill, 1951. 

74*+Esmeralda Formation, USGS 3394, Cedar Mountain,

T. 8 N., R. 38 E., Nye Co., Nevada, K. E. Lohman,

1938, about 15.1 Ma (H. E. Schorn, oral commun.,

1989). 

75*+Unnamed unit, USGS 4213, Silvies Valley, sec. 36,

T. 17 S., R. 31 E., Grant Co., Oregon, R. E. Wallace,

1955; about 12.5 Ma (Fiebelkorn and others, 1983). 

76+ Latah Formation, USGS 5678, Shelly Lake, sec. 24,

T. 25 N., R. 44 E., Spokane Co., Washington, J. W.

Hosterman, 1963; Miocene. 

77+ Latah Formation, USGS 5679, sec. 15, T. 24 N., R. 43

E., Spokane Co., Washington, J. W. Hosterman,

1963; Miocene. 

78+ Latah(?) Formation, USGS 5681, Peone, sec. 27, T. 26

N., R. 44 E., Spokane Co., Washington, J. W.

Hosterman, 1963. 

79+ Unnamed unit, USGS 6007, sec. 20, T. 24 N., R. 26 E.,

Churchill Co., Nevada, Ronald Willden, 1966. 

80 Unnamed unit, USGS 6035, N. Santiam River, T. 11

S., R. 7 E., Linn Co., Oregon, Harry Wheeler, 1967. 

81+ Unnamed unit, USGS 6364, 6371, 6373, Durkee, sec.

23, T. 11 S., R. 43 E., Baker Co., Oregon, R. A.

Sheppard, 1970. 

82 Unnamed unit, USGS 6368, Durkee, sec. 20, T. 11 S.,

R. 43 E., Baker Co., Oregon, R. A. Sheppard, 1970.

83* Aldrich Station Formation, type section, 38°29'30"N., 

118° 53'21" W., Mineral Co., Nevada, J. H. Stewart, 

1980; 13.0-11.4 Ma (Golia and Stewart, 1984) 

(13.4-1.7 Ma corrected).

84*+Kate Peak Formation, Eagle-Picher diatomite quarry, 

Clark Siding, Nevada, T. 20 N., R. 23 E., Storey Co., 

Nevada; (11.2±0.3 Ma, AMOCO, unpublished data, 

1980).

85*+Mascall Formation, Aldrich Mountain, "meadow locality," Grant Co., Oregon (UCMP loc. P4123); SE</» 

sec. 14, T. 13 S., R. 28 E.; N. side of east fork of John 

Day River, Carlton Condit, 1941; (15.4 Ma, Evernden and others, 1964; corrected 15.8 Ma.).

86*+Juntura(?) Formation, Harney Co., Oregon, Stinking 

Water flora (UCMP loc. P4121); NWto sec. 17, 

T. 21 S., R. 35 E.; Carlton Condit, 1941; (12.1 Ma, 

Evernden and James, 1964; corrected 12.4 Ma).

87+ Mascall Formation, White Hills, Belshaw Ranch locality, Grant Co., Oregon (UCMP loc. P3735); center 

N£2 sec. 13, T. 13 S., R. 28 E., Carlton Condit.

88+ Mascall Formation, Blue Mountains, Vinegar Creek, 

Grant Co., Oregon (UCMP loc. P5404); sec. 17, 

T. 10 S., R. 35 E; 1 mile NW. of Bates on road to Susanville, R. W. Chancy, 1954.

89+ Unnamed unit, Thorn Creek, Boise Co., Idaho (UCMP 

loc. P4600); sec. 28, T. 5 N., R. 5 E., H.V. Smith, 

1941.

90*+Hole-in-the-Wall diatomite quarry, Gooding Co., 

Idaho, along the drainage of Clover Creek; NW 1/* 

sec. 12, T. 4 S., R. 13 E., J. P. Bradbury, 1988; (10.0 

Ma, Evernden and others, 1964; corrected 10.3 Ma).

91*+Hole-in-the-Wall diatomite quarry, Gooding Co., 

Idaho; NE "A sec. 19, T. 3 S., R. 13 E., J. P. Bradbury, 

1988; (10.0 Ma, Evernden and others, 1964; corrected 10.3 Ma).

92*+Quiburis Formation, Edgar Canyon, San Pedro Valley, 

Pima Co., Arizona, 900 m E. and 200 m N. of SW. 

corner, sec. 21, T. 11 S., R. 18 E.; J. P. Bradbury, 

1980, (5.4-6.6 Ma, Shenk, 1990).

93+ Esmeralda Formation, Black Spring, Nye Co., Nevada; 

sec. 19, T. 8 N., R. 38 E., Douglas Bergstrom, 1986.

94+ Unnamed unit, N. Fork Fitsum Creek, Valley Co., 

Idaho; sec. 6, T. 19 N., R. 6 E., B. F. Leonard, 1986.

95+ Esmeralda Formation, Cedar Spring, Nye Co., Nevada; 

unsurveyed T. 8 N., R. 38 E., Douglas Bergstrom, 

1986.

96 Unnamed unit, USGS 642, Baker Co., Oregon; sec. 8, 

T. 8 S., R. 42 E., B. N. Moore, 1930.

97 Unnamed unit, USGS 1013, Clover Creek District, 

Baker Co., Oregon; sec. 11, T. 8 S., R. 42 E., B. N. 

Moore, 1931.

98 Unnamed unit, USGS 1031, Malheur Co., Oregon; sec. 

2, T. 15 S., R. 42 E., B. N. Moore, 1931.
GEOLOGIC RANGES OF LACUSTRINE ACTINOCYCLVS SPECIES, WESTERN UNITED STATES 67

99 Unnamed unit, USGS 1037, Grant Co., Washington; 

T. 28 N., R. 30 E., (Grand Coulee flora), T. H. Bonser, 1927.

100 Unnamed unit, USGS 1133, 4 miles E. of Basalt, 

Esmeralda Co., Nevada; T. 2 N., R. 34 E., H. G. Ferguson, 1923.

101 "Truckee" lake beds, USGS 1186, Chalk Bluff, 3 miles 

W. of Reno, Washoe Co., Nevada; T. 19 N., R. 19 E., 

V. P. Gianella, 1932.

102 Unnamed unit, USGS 2268, Wikiup Damsite, 

Deschutes River, Deschutes Co., Oregon; T. 22 S., 

R. 9 E., A. C. Spencer, 1934.

103 Thousand Creek Formation, USGS 3544, Humboldt 

Co., Nevada; unsurveyed T. 45 N., R. 26 E., K. E. 

Lohman, 1938.

104* Santa Fe Formation, USGS 4671, Rio Arriba Co., New 

Mexico; T. 21 N., R. 7 E., R. L. Smith, 1948; (~8 Ma; 

Manley and Mehnert, 1981).

105*Alturas Formation, USGS 4690, Modoc Co., 

California; sec. 7, T. 42 N., R. 12 E., lan Campbell, 

1958; (-4.8 Ma, see loc. 3).

106+Latah Formation, USGS 5682, Mead, Spokane Co., 

Washington; sec. 14, T. 26 N., R. 43 E., J. W. 

Hosterman, 1963.

107*Teewinot Formation, USGS 5935, Teton Co., Wyoming; sec. 36, T. 42 N., R. 116 W., G. W. Andrews, 

1966; (9.2 Ma, Evemden and others, 1964; 9.4 Ma 

corrected).

108+Poison Creek Formation, IW-7, Washington Co., 

Idaho; SWV4, SWV4 sec. 29, T. 12 N., R. 6 W., M. J. 

Evetts, 1979.

109+Poison Creek Formation, IW-8, Washington Co., 

Idaho; SWV4 , SWV4 sec. 32, T. 12 N., R. 6 W., M. J. 

Evetts, 1979.

110 IW-9, Poison Creek Formation, Washington Co., 

Idaho; SEV4, SE'A sec. 19, T. 12 N., R. 6 W., M. J. 

Evetts, 1979.

111+Idaho Group, IW-13, Washington Co., Idaho; NEVfc, 

NEV4 sec. 19, T. 12 N., R. 4 W., M. J. Evetts, 1979.

112+AMOCO Becharof No. 1 well, depth -985 m, 

57.78°N., 157.11°W., Alaska Peninsula, Alaska, W. 

N. Krebs, 1985.

113*+Furnace Creek Formation, USGS 4070, Inyo Co., California; 1.15 miles N. 77°W. of Travertine Point, 

road cut on south side of Highway 190. Hard gray 

limestone 3 ft below base of travertine, K. E. 

Lohman, 1954; (5.18±0.15 Ma, 6.05±0.18 Ma, 

7.35±0.22 Ma, Marvin and Dobson, 1979).

114* Coal Valley Formation sensu Axelrod, 1958, Washoe 

Co., Nevada; roadcut along Highway 40 W. of Reno, 

sec. 18, T. 19 N., R. 19 E.; (<5.7 Ma, Evernden and 

James, 1964; <5.9 Ma corrected).

115* Coal Valley Formation sensu Axelrod, 1958, Washoe 

Co., Nevada; Verdi flora locality, sec. 16, T. 19 N., 

R. 18 E.; (5.7 Ma, Evernden and James, 1964; 5.9 Ma 

corrected).
INDEX

[Boldface page numbers indicate major references]

acanthus, Actinocyclus 3, 4; pi. 1

Achnanthes 5,1

Actinocyclus 1, 2

Actinocyclus acanthus 3, 4, 12, 14, 54, 56;

pi. 1 

cedrus 4, 5, 10, 11, 13, 14, 56; pis. 2, 3,

4

claviolus 3, 5, 6, 57; pis. 4, 5 

cupreus 3, 6, 6,11,13, 57; pi. 5 

ehrenbergii 3, 6, 7, 11, 14, 58, 59; pis.

6,7 

gorbunovii 4, 7,8,12

\ar.fossa 3, 7, 57; pi. 7 

kanitzii 3; pi. 8 

krasshei 3, 6, 7, 9, 12, 13, 14, 57; pis.

8,9

matttts 4,10, 14, 57; pis. 9, 10, 11 

nebulosus 3, 6,11, 58; pis. 11, 12 

nordlingensis 3, 4, 12 

normanii 3

normanii f. subsalsa 1, 14; pi. 12 

pinnulus 3,4,11, 58; pis. 12,13 

sp. 13

sp. cf. A. gorbunovii 13 

sp. cf. A. pinnulus pi. 13 

theleus 3,12, 14, 58; pis. 13, 14 

tubulosus 3, 4, 10, 13, 58; pi. 8 

venenosus 4, 5, 8, 10, 13, 14, 58; pis.

14, 15

Alaska, AMOCO Becharof No. 1 well, (loc.

112)12,58,67; pi. 13 

Aldrich Mountain, Grant Co., Ore. (loc. 85)

11,58,66 

Aldrich Station Formation type sec., Mineral

Co., Nev. (loc. 83) 5, 64, 66 

Alturus, Modoc Co., Calif, (loc. 3) 64 

Alturas Formation 64, 65, 67 

AMOCO Becharof No. 1 well, Alaska

(loc. 112) 12, 58, 67; pi. 13 

AMOCO Delta Stephan Szot No. 1 well,

Cache Co., Utah (loc. 19) 64 

AMOCO Lynn Reese No. 1 well, Cache Co.,

Utah (loc. 39) 65 

AMOCO Milford Federal No. 1 Well, Lemhi

Co. (loc. 40) 57, 65 

Amphora 1 

Anomoeoneis 4 

apiculatus, Cestodiscus 4 

areolae patterns 1

Arizona,

Edgar Canyon, Pima Co. (loc. 92) 7,

58, 66; pi. 6 

Arrow Junction, Nez Perce Co., Idaho (loc.

72) 10, 57, 66; pi. 8 

Augusta Mountains, Churchill Co., Nev. (loc.

4) 57; pi. 9 

Aulacoseira 5, 7,11,14

See also Melosira.

agassizii 11

distans 10, 11, 13

granulata 10

islandica 10, 11,14

lirata 13

praeislandica 10,

sp. cf. A. islandica 8

sp. cf. A. distans 11

sp. cf. A. praeislandica 6, 12, 13

spp. 5, 9,10

B

Baker County, sec. 8, Ore. (loc. 96) 66

B anbury basalt 58

Barstovian age 54

Basalt, Esmeralda Co., Nev. (loc. 100) 67

Beaverdam Formation 56, 65

Belshaw Ranch, White Hills, Grant Co., Ore.

(loc. 86) 66 

See also White Hills.

Beuern, Vogelsberg Range, Germany 9; pi. 8 

Big Smokey Valley, Esmeralda Co., Nev.

(loc. 47) 65 

Black Spring, Nye Co., Nev. (loc. 93) 11, 57,

58, 66; pis. 11,12 

Blue Mountains, Vinegar Creek, Grant Co.,

Ore. (loc. 88) 66 

See also Vinegar Creek. 

Bradys Hot Spring, Churchill Co., Nev. (loc.

54)65 

Browns Hill, Churchill Co., Nev. (loc. 55)

57,65

Bruneau Formation 64 

Buffalo Canyon, Churchill Co., Nev. (loc. 6)

11, 58; pi. 11

Buffalo Canyon Formation pi. 11 

Bulgaria 59 

Bully Creek Formation 4, 56, 57, 58, 64, 66;

pi. 1 

Burley, sec. 35, Cassia Co., Idaho (loc. 37)

65 

Burnt River, lake beds, Swayze Creek, Baker

Co., Ore. (loc. 67)66

California 1

Alturas, Modoc Co. (loc. 3) 64 

Clear Lake, Lake Co. (loc. 14) 64 

Death Valley, Inyo Co. (loc. 113) 7, 59 

Dorris, Siskiyou Co. (loc. 60) 65 

Howards Gulch, sec. 22, Modoc Co.

(loc. 29) 65 

Howards Gulch, sec. 27, Modoc Co.

(loc. 2) 64

Kettleman Hills, Kings Co. (loc. 58) 65 

La Ceja Ridge, Kettleman Hills, Kings

Co. (loc. 58) 65

Lake Britton, Shasta Co. (loc. 35) 65 

Modoc Co., sec. 7 (loc. 105) 67 

Pit River, Modoc Co. (loc. 17) 5; pi. 4 

Travertine Point, Inyo Co. (loc. 113) 67 

Turner Creek, Modoc Co. (loc. 17) 5,

56, 58, 64; pi. 4

Caloneis silicula 1

Castle Creek, Owyhee Co., Idaho (loc. 9) 64

Cedar Mountain, Mineral Co., Nev. (loc. 22)

5, 10, 57, 64; pis. 9, 10 

Cedar Mountain, Nye Co., Nev. (loc. 74) 4,

11,54, 56, 57, 58, 66; pi. 11 

Cedar Spring, Nye Co., Nev. (loc. 95) 58, 66 

Cedarville Formation 8, 66; pi. 7 

cedrus, Actinocyclus 4, 5, 10, 11, 13, 14, 56;

pis. 2, 3, 4 

Cestodiscus 2

apiculatus 4, 54 

cedarensis 5, 56 

fasciculatus 11, 58 

mobilensis 57 

mobilislb, 57 

Chaetoceros 5 

Chalk Bluff, Reno, Washoe Co., Nev. (loc.

101) 67

Chalk Hills, Owyhee Co., Idaho (loc. 10) 64 

Chalk Hills Formation 64 

China, Kunming, Xian Feng Basin 13, 58 

China, Kunming, Moon-To basin 57 

Churchill Co., Nev. (loc. 4) 57; pi. 9 

Churchill Co., sec. 20, Nev. (loc. 79) 66 

Clarendonian vertebrates 54, 58 

Clarkia Basin, Shoshone Co., Idaho (loc. 13)

64 

Clarkia Basin, Emerald Creek, Benewah Co.,

Idaho (loc. 21) 12, 13, 58, 64; pis.

13, 14

Clarkia Lake deposits 12; pis. 13,14 

claviolus, Actinocyclus 3, 5, 6, 57; pis. 4, 5 

Clear Lake, Lake Co., Calif, (loc. 14) 64

68
INDEX 69

Clover Creek District, Baker Co., Ore. (loc.

97)66

Coal Valley Formation 13, 58, 64, 67 

Columbia River Basalt Group 57, 65 

Copper Kettle Canyon, Churchill Co., Nev.

(loc. 16) 6, 57, 64; pi. 5 

Coscinodiscus 2

(Actinocyclus) miocenicus 2

(= Actinocyclus) gorbunovii 12

(=Actinocyclus) variabilis 2, 3, 6, 6

gorbunovii 8, 9

v. ethmodiscoidus 8, 9

v. gorbunovii 8

miocenicus 9

nevadensis 11, 58

subtilis 5, 10

cupreus, Actinocyclus 3, 6,11, 13, 57; pi. 5 

Cyclotella 59 

Cyclosteplianos 59

D

Dead Camel Mountains, Churchill Co., Nev.

(loc. 18) 64 

Death Valley, Inyo County, Calif, (loc. 113)

7,59

Denticula elegans 7 

Diatomite Ridge, Stewart Valley, Mineral

Co., Nev. (loc. 20) 5, 56, 64; pis.

2,3,4

Diploneis interrupta 7 

ovalis 7 

sp. 14

Dorris, Siskiyou Co., Calif, (loc. 60) 65 

Drewsey, Harney County, Ore. (loc. 63) 5,

56,65 

Durkee, sec. 23, Baker Co., Oregon (loc. 81)

12, 58, 66 

Durkee, sec. 20, Baker Co., Oregon (loc. 82)

66

Eagle-Picher diatomite quarry, Clark siding,

Storey Co., Nev. (loc. 84) 57, 66 

Eastgate, Churchill Co., Nev. (loc. 6) 11 

Ecology 14 

Edgar Canyon, Pima Co., Ariz. (loc. 92) 7,

58, 66; pi. 6 

ehrenbergii, Actinocyclus 3, 6, 7,11, 14, 58,

59; pis. 6, 7 

Ellensburg Formation, Squaw Creek Member

10,11,13,56,57, 58, 65; pis. 8,

9, 10, 11

Ellerbeckia arenaria v. teres 5, 8,10 

Emerald Creek, Benewah Co., Idaho (loc.

21) 12, 13, 58, 64; pis. 13, 14 

Esmeralda Formation 4, 5, 10, 11, 54, 56,

57, 58, 64, 66; pis. 2, 3, 4, 9, 10,

11,12

Eunotia 5, 10 

Eureka County, sec. 31, Nev. (loc. 30) 6, 57,

65; pi. 5

Femley, Churchill Co., Nev. (loc. 41) 57, 65 

Formations, (and other units)

Aldrich Station Formation 5, 64, 66

Alturas Formation 64, 65, 67

Banbury basalt 58

Beaverdam Formation 56, 65

Bruneau Formation 64

Buffalo Canyon Formation pi. 11

Bully Creek Formation 4, 56, 57, 58,

64, 66; pi. 1

Cedarville Formation 8, 66; pi. 7 

Chalk Hills Formation 64 

Clarkia Lake deposits 12; pis. 13,14 

Coal Valley Formation 13, 58, 64, 67 

Columbia River Basalt Group 57, 65 

Ellensburg Formation, Squaw Creek

Member 10, 11, 13, 56, 57, 58,

65; pis. 8, 9,10, 11 

Esmeralda Formation 4, 5, 10, 11, 54,

56, 57, 58, 64, 66; pis. 2, 3, 4, 9,

10,11, 12

Furnace Creek Formation 7, 58, 67 

Glenns Ferry Formation 64 

Horse Hill ash (loc. 11)64 

Humboldt Formation 6, 57, 65; pi. 5 

Idaho Group 65; pi. 15 

Juntura Formation 57, 65, 66; pi. 2 

Kate Peak Formation 57, 66 

Kelseyville Formation 64 

Latah Formation 10, 56, 57, 58, 65, 66,

67 

Mascall Formation 10, 11, 12, 57, 58,

66; pis. 8, 9 

Poison Creek Formation 8, 13, 58, 65,

67; pis. 2,14, 15 

Quiburis Formation 7, 58, 66; pi. 6 

Raft River Formation 65 

Ringold Formation 65 

Santa Fe Formation 67 

Sucker Creek Formation 58, 65 

Teewinot Formation 67 

Thousand Creek Formation 65, 67 

Truckee Formation 57, 65, 66, 67 

Tulare Formation 65 

Yonna Formation 65

Forty-nine Camp, Washoe Co., Nev. (loc. 69)

8, 57, 66; pi. 7 

Fragilaria brevistriata 7 

Fragilaria species 5, 7, 9,11 

Fragilaria sp. cf. F. virescens 5 

Frustulia interposita 7 

Furnace Creek Formation 7, 58, 67

Germany, Vogelsberg Range, Beuem 9; pi. 8

Vogelsberg Range, Ruckers 6; pi. 14 

Glenns Ferry Formation 64 

Gomphonema 11 

Goose Creek, Baker Co., Oregon (loc. 27) 5,

10, 57, 64; pi. 9 

Goose Creek, sec. 35, Cassia Co., Idaho (loc.

73)66

gorbunovii, Actinocyclus 4, 7,12 

Coscinodiscus 8

v. ethmodiscoidus, Coscinodiscus 8 

v. gorbunovii, Coscinodiscus 8 

var. fossa, Actinocyclus 3, 7, 57; pi. 7

Grand Coulee flora (loc. 99) 67

Grant Co., Wash. (loc. 99) 67

Great Lakes 1

Greece, Macedonia 59

H

Hagerman horse quarry, Twin Falls Co.,

Idaho (loc. 23) 64 

Halbouty, Michael T. Halbouty Federal No.

1 well, Churchill Co., Nev. (loc.

28)64 

Hangman Valley, Spokane Co., Wash. (loc.

36) 57, 65

Harney Co., sec. 17, Ore. (loc. 86) 57, 66 

Harper Basin, Malheur Co., Oregon (loc. 7)

10, 56, 57; pi. 1 

Harper Basin, sec. 15, Malheur Co., Oregon

66 

Harper Basin, sec. 34, Malheur Co., Ore.

(loc. 65) 66 

Harper Basin, sec. 34, Malheur Co., Ore.

(loc. 66) 66 

Hemidiscaceae 2 

Hole-in-the-Wall diatomite quarry, Gooding

Co., Idaho (Iocs. 90, 91) 12, 58,

66; pis. 12,13

Holocene sediment pis. 6, 7,12 

Horse Hill ash (loc. 11)64 

Howards Gulch, sec. 22, Modoc Co., Calif.

(loc. 29) 65 

Howards Gulch, sec. 27, Modoc Co., Calif.

(loc. 2) 64 

Hot Springs Mountains, Churchill Co., Nev.

(loc. 56) 57, 65

Humboldt Co., Nev. (loc. 52) 65 

Humboldt Co., Nev. (loc. 103) 67 

Humboldt Formation 6, 57, 65; pi. 5 

Hungary, Szurdokpuspoki, Matra Mountains

pi. 8 

Hyalodiscus sp. cf. H. laevis 7

Idaho 1

AMOCO Milford Federal No. 1 Well, 

Lemhi Co. (loc. 40) 57, 65

Arrow Junction, Nez Perce Co. (loc. 

72) 10, 57, 66; pi. 8

Bruneau Formation 64

Burley, sec. 35, Cassia Co. (loc. 37) 65

Castle Creek, Owyhee Co. (loc. 9) 64

Chalk Hills, Owyhee Co. (loc. 10) 64

Clarkia 12

Clarkia Basin, Shoshone Co. (loc. 13) 

64

Clarkia Basin, Emerald Creek, Benewah Co. (loc. 21) 12, 13, 58, 64; 

pis. 13,14

Emerald Creek, Benewah Co., (loc. 21) 

12, 13, 58, 64; pis. 13, 14
70 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

Idaho—Continued

Goose Creek, sec. 35, Cassia Co. (loc.

73)66 

Hagerman horse quarry, Twin Falls Co.

(loc. 23) 64 

Hole-in-the-Wall diatomke quarry,

Gooding Co. (Iocs. 90, 91) 12, 58,

66; pis. 12,13 

Juliaetta, Nez Perce Co. (loc. 32) 6, 10,

13, 57, 58, 65; pis. 5, 8 

Jungle Point, Idaho Co. (loc. 33) 6, 57,

65; pis. 4, 5

Lowell, Idaho Co. (loc. 33) 6 

Malde's (1972) section no. 55, Owyhee

Co. (loc. 24) 64 

North Fork Fitsum Creek, Valley Co.

(loc. 94) 57, 66 

Oviatt Creek, Clearwater Co. (loc. 43)

10, 12, 13, 57, 58, 65; pi. 14 

Owyhee Co. GOC. 12) 64 

Reynolds Creek, Owyhee Co. (loc. 44)

13, 58, 65; pis. 2,14, 15 

Shoofly Creek, Owyhee Co. (loc. 11)

64 

Shoofly Creek, sec. 6, Owyhee Co.

(loc. 25) 64 

Snake River Plain 8, 13

western, Elmore Co. (loc. 5) 64 

Thorn Creek, Boise Co. (loc. 89) 66 

Trapper Creek, Cassia Co. (loc. 53) 56,

58,65 

Washington Co., Idaho Group (loc.

111)58

Washington Co., sec. 17 (loc. 45) 65 

Washington Co., sec. 19, Poison Creek

Formation (Iocs. 110,111)67 

Washington Co., sec. 29, Poison Creek

Formation (loc. 108) 58, 67 

Washington Co., sec. 32, Poison Creek

Formation (loc. 109) 58, 67 

Washington Co., sec. 34 (loc. 31) 65;

pi. 15 

Weiser, sec. 35, Washington Co. (loc.

26)64

Weiser, Washington Co. (loc. 70) 57, 66 

West Browns Creek, Owyhee Co. (loc.

8)64 

Whitebird, Idaho Co. (loc. 71) 57, 66

Idaho Group 65; pi. 15

Japan, Sea of, Yamato Bank 7, 57; pi. 6 

John Day River, Grant Co., Ore. (loc. 85) 66 

Juliaetta, Nez Perce Co., Idaho (loc. 32) 6,

10, 12,13, 57, 58, 65; pis. 5, 8 

Jungle Point, Idaho Co., Idaho (loc. 33) 6,

57, 65; pis. 4, 5 

Juntura Formation 57, 65, 66; pi. 2

K

kanitzii, Actinocyclus 3; pi. 8 

Kate Peak Formation 57, 66 

Kelseyville Formation 64

Kettleman Hills, Kings Co., Calif, (loc. 58)

65

Key of Actinocyclus species 3 

Klamath Falls, Klamath Co., Ore. (loc. 61)

65 

krasskei, Actinocyclus 3, 6, 7, 9, 12, 13, 14,

57; pis. 8,9

La Ceja Ridge, Kettleman Hills, Kings Co.,

Calif, (loc. 58) 65

Lake Britton, Shasta Co., Calif, (loc. 35) 65 

Lake Huron, Michigan pi. 12 

Lake Ontario 1, 14 

Lander County, New Pass 4 

Latah Formation 10, 56, 57, 58, 65, 66, 67 

Leslie Gulch, Malheur Co., Ore. (loc. 50) 58,

65

Limnology 14 

Localities

Aldrich Mountain, Grant Co., Ore. (loc.

85)11,58,66 

Aldrich Station Formation, type sec.,

Mineral Co., Nev. (loc. 83) 66 

Alturas, Modoc Co., Calif, (loc. 3) 64 

AMOCO Becharof No. 1 well, Alaska

(loc. 112) 12, 58, 67; pi. 13 

AMOCO Delta Stephan Szot No. 1 

well, Cache Co., Utah (loc. 19) 64 

AMOCO Lynn Reese No. 1 well,

Cache Co., Utah (loc. 39) 65 

AMOCO Milford Federal No. 1 Well,

Lemhi Co. (loc. 40) 57, 65 

Arrow Junction, Nez Perce Co., Idaho

(loc. 72) 10, 57, 66; pi. 8 

Augusta Mountains, Churchill Co.,

Wash. (loc. 4) 66

Baker County, sec. 8, Ore. (loc. 96) 66 

Basalt, Esmeralda Co., Nev. (loc. 100)

67 

Beuem, Vogelsberg Range, Germany 9;

pi. 8 

Belshaw Ranch, White Hills, Grant Co.,

Ore. (loc. 86) 66 

See also White Hills. 

Big Smokey Valley, Esmeralda Co.,

Nev. (loc. 47) 65 

Black Spring, Nye Co., Nev. (loc. 93)

11,57,58, 66; pis. 11, 12 

Blue Mountains, Vinegar Creek, Grant

Co., Ore. (loc. 88) 66 

See also Vinegar Creek. 

Bradys Hot Spring, Churchill Co., Nev.

(loc. 54) 65 

Browns Hill, Churchill Co., Nev. (loc.

55) 57, 65 

Bruneau Formation, Elmore Co., Idaho

(loc. 5) 64 

Buffalo Canyon, Churchill Co., Nev.

(loc. 6) 11, 58; pi. 11 

Bulgaria 59

Burley, sec. 35, Cassia Co., Idaho (loc. 

37)65

Localities—Continued

Burnt River, lake beds, Swayze Creek,

Baker Co., Ore. (loc. 67) 66 

Castle Creek, Owyhee Co., Idaho (loc.

9)64 

Cedar Mountain, Mineral Co., Nev.

(loc. 22) 5, 10, 57, 64; pis. 9, 10 

Cedar Mountain, Nye Co., Nev. (loc.

74) 4, 11, 54, 56, 57, 58, 66; pi.

11 

Cedar Spring, Nye Co., Nev. (loc. 95)

58,66 

Chalk Bluff, Reno, Washoe Co., Nev.

(loc. 101) 67 

Chalk Hills, Owyhee Co., Idaho (loc.

10)64

Churchill Co., Nev. (loc. 4) 57; pi. 9 

Churchill Co., sec. 20, Nev. (loc. 79) 66 

Clarkia Basin, Shoshone Co., Idaho

(loc. 13)64 

Clear Lake, Lake Co., Calif, (loc. 14)

64 

Clover Creek District, Baker Co., Ore.

(loc. 97) 66 

Copper Kettle Canyon, Churchill Co.,

Nev. (loc. 16) 6, 57, 64; pi. 5 

Dead Camel Mountains, Churchill Co.,

Nev. (loc. 18) 64 

Death Valley, Inyo Co., Calif, (loc. 113)

7,59

Diatomite Ridge, Stewart Valley, Mineral Co., Nev. (loc. 20) 5, 56, 64;

pis. 2, 3, 4

Dorris, Siskiyou Co., Calif, (loc. 60) 65 

Drewsey, Harney Co., Ore. (loc. 63) 5,

56,65 

Durkee, sec. 20, Baker Co., Oregon

(loc. 82) 66 

Durkee, sec. 23, Baker Co., Oregon

(loc. 81)12, 58, 66 

Eagle-Picher diatomite quarry, Clark

siding, Storey Co., Nev. (loc. 84)

57,66

Eastgate, Churchill Co., Nev. (loc. 6) 11 

Edgar Canyon, Pima Co., Ariz. (loc.

92) 7, 58, 66; pi. 6 

Emerald Creek, Benewah Co., Idaho

(loc. 21) 12, 13, 58, 64; pis. 13,14 

Eureka Co., sec. 31, Nev. (loc. 30) 6,

57, 65; pi. 5 

Femley, Churchill Co., Nev. (loc. 41)

57,65 

Forty-nine Camp, Washoe Co., Nev.

(loc. 69) 8, 57, 66; pi. 7 

Goose Creek, Baker Co., Ore. (loc. 27)

5, 10, 57, 64; pi. 9 

Goose Creek, sec. 35, Cassia Co., Idaho

(loc. 73) 66

Grant Co., Wash. (loc. 99) 67 

Hagerman horse quarry, Twin Falls Co.,

Idaho (loc. 23) 64 

Hangman Valley, Spokane Co., Wash.

(loc. 36) 57, 65 

Hamey Co., sec. 17, Ore. (loc. 86) 57,

66
INDEX 71

Localities—Continued

Harper Basin, Malheur Co., Ore. (loc.

7) 4,10, 56, 57; pi. 1 

Harper Basin, sec 15 Malheur Co.,

Oregon 66 

Harper Basin, sec. 34, Malheur Co.,

Ore. (loc. 65) 66 

Harper Basin, sec. 34, Malheur Co.,

Ore. (loc. 66) 66 

Hole-in-the-Wall diatomite quarry,

Gooding Co., Idaho (Iocs. 90, 91)

12, 58, 66; pis. 12,13 

Hot Springs Mountains, Churchill Co.,

Nev. (loc. 56) 57, 65 

Howards Gulch, sec. 27, Modoc Co.,

Calif, (loc. 2) 64 

Howards Gulch, sec. 22, Modoc Co.,

Calif, (loc. 29) 65 

Humboldt Co., Nev. (loc. 52) 65 

Humboldt Co., Nev. (loc. 103) 67 

John Day River, Grant Co., Ore. (loc.

85)66 

Juliaetta, Nez Perce Co., Idaho (loc. 32)

6,10, 12, 13, 57, 58, 65; pis. 5, 8 

Jungle Point, Idaho Co., Idaho (loc. 33)

6, 57, 65; pis. 4, 5 

Klamath Falls, Klamath Co., Ore. (loc.

61 65 

La Ceja Ridge, Kettleman Hills, Kings

Co., Calif, (loc. 58) 65 

Lake Britton, Shasta Co., Calif, (loc.

35) 65 

Latah Formation, Spokane Co., Wash.

(Iocs. 77, 78) 66 

Leslie Gulch, Malheur Co., Ore. (loc.

50) 58, 65

Lowell, Idaho Co., Idaho (loc. 33) 6 

Lyon Co., Nev. (loc. 1) 5 

Lyon Co., Nev. (loc. 15) 13 

Macedonia, Greece 59 

Malde's (1972) section no. 55, Owyhee

Co., Idaho (loc. 24) 64 

Malheur Co., sec. 2, Ore. (loc. 98) 66 

Mead, Spokane Co., Wash. (loc. 106)

56, 57, 58, 67 

Michael T. Halbouty Federal No. 1

well, Churchill Co., Nev. (loc. 28)

65

Modoc Co., sec. 7, Calif, (loc. 105) 67 

Moon-To Basin, China 57 

New Pass, Lander Co., Nev. (loc. 42) 4,

56, 65; pi. 1 

New Pass Summit, Churchill Co., Nev.

56,57 

Nightingale, Churchill Co., Nev. (loc.

57)65 

North Fork Fitsum Creek, Valley Co.,

Idaho (loc. 94) 57, 66 

North Santiam River, Linn Co., Ore.

(loc. 80) 66

Otis Basin, Harney Co., Ore. 5 

Otis Creek, Harney Co., Ore. (loc. 34)

56, 65; pi. 2 

Oviatt Creek, Clearwater Co., Idaho

(loc. 43) 10, 12, 13, 57, 65; pi. 14 

Owyhee Co., Idaho (loc. 12) 64 

Peone, Spokane Co., Wash. (loc. 78) 66

Localities—Continued

Pine Grove Hill, Lyon Co., Nev. (loc.

15) 58, 64

Pit River, Modoc Co., Calif, (loc. 17) 5 

Reno, Washoe Co., Nev. (loc. 101) 67 

Reynolds Creek, Owyhee Co., Idaho

(loc. 44) 13, 58, 65; pis. 2,14,15 

Rio Arriba Co., N. Mex. (loc. 104) 67 

Ruckers, Vogelsberg Range, Germany

6; pi. 14 

Saginaw Bay, Lake Huron, Michigan

pi. 12 

Seven Mile Creek, Umatilla Co., Ore.

(loc. 38) 57, 65 

Shelly Lake, Spokane Co., Wash. (loc.

76)66 

Shoofly Creek, Owyhee Co., Idaho (loc.

11)64 

Shoofly Creek, sec. 6, Owyhee Co.,

Idaho (loc. 25) 64 

Silvies Valley, Grant Co., Ore. (loc. 75)

5, 56, 57, 66

Snake River Plain, Idaho 8 

Snake River Plain, western, Elmore

Co., Idaho (loc. 5) 64 

Soviet Union. See Russia 

Spokane Co., Wash. (loc. 76) 57, 58, 66 

Spokane Co., Wash. (loc. 77) 10, 66 

Stewart Valley, Mineral Co., Nev. (loc.

20)5 

Stillwater Mountains, Churchill Co.,

Nev. (loc. 16)7

Stillwater Mountains, southern, Churchill Co., Nev. (loc. 48) 56, 57, 65;

pis. 2, 3 

Swayze Creek, Baker Co., Ore. (loc.

51)65 

Szurdokpuspoki, Matra Mountains,

Hungary pi. 8 

Teton Co., sec. 36, Wyoming (loc. 107)

67 

Thorn Creek, Boise Co., Idaho (loc. 89)

66 

Trapper Creek, Cassia Co., Idaho (loc.

53) 56, 58, 65 

Travertine Point, Inyo Co., Calif, (loc.

113) 67

Tucson, Pima Co., Ariz. (loc. 92) 58 

Turner Creek, Modoc Co., Calif, (loc.

17) 5, 56, 58, 64; pi. 4 

Vantage, Grant Co., Wash. (loc. 59) 10,

56, 57, 65 

Vinegar Creek, Grant Co., Oregon (loc.

88) 10, 57, 66; pis. 8, 9 

Virginia City, Storey Co., Nev. (loc. 68)

5, 56, 57, 66 

Virginia Range, Storey Co., Nev. (loc.

68) 5, 56, 57, 66 

Vogelsberg Range, Beuem, Germany 9;

pi. 8 

Vogelsberg Range, Ruckers, Germany

6; pi. 14 

Walker River, Lyon Co., Nev. (loc. 1)

64

Washington Co., Idaho, Idaho Group

(Iocs. 111)58 

Localities—Continued

Washington Co., sec. 17, Idaho (loc.

45)65 

Washington Co., sec. 19, Idaho, Poison

Creek Formation (Iocs. 110, 111)

67 

Washington Co., sec. 29, Idaho, Poison

Creek Formation (loc. 108) 58, 67 

Washington Co., sec. 32 Idaho, Poison

Creek Formation (loc. 109) 58, 67 

Washington Co., sec. 34, Idaho (loc.

31) 65; pi. 15

Washoe Co., Nev. (Iocs. 114,115) 67 

Weiser, sec. 35, Washington Co., Idaho

(loc. 26) 64 

Weiser, Washington Co., Idaho (loc. 70)

57,66 

West Browns Creek, Owyhee Co.,

Idaho (loc. 8) 64 

Westfall, Harper Basin, Malheur Co.,

Ore. (loc. 64) 66 

White Cliffs, Franklin Co., Wash. (loc.

46)65 

White Hills, Grant Co., Oregon (loc.

87) 12, 13,57,58,66 

Whitebird, Idaho Co., Idaho (loc. 71)

57,66 

Wikiup Damsite, Deschutes River, Deschutes Co., Ore. (loc. 102) 67 

Xian Feng Basin, China 13, 58 

Yakima Co., Washington (loc. 49) 10,

11,56, 57, 58, 65; pis. 8, 9, 10,11 

Yamato Bank, Sea of Japan 7, 57; pi. 6 

Yonna Valley, Klamath Co., Ore. (loc.

62)65

Lowell, Idaho Co., Idaho 6 

Lyon Co., Nev. (loc. 1)5 

Lyon Co., Nev. (loc. 15) 13

M

Macedonia, Greece 59

Malde's (1972) section no. 55, Owyhee Co.,

Idaho (loc. 24) 64

Malheur Co., sec. 2, Ore. (loc. 98) 66 

Mascall Formation 10, 11, 12, 57, 58, 66;

pis. 8, 9

Mastogloia braunii 1 

Mastogloia elliptica 1 

Mead, Spokane Co., Wash. (loc. 106) 56, 57,

58,67

Melosira moniliformis 1 

Melosira undulata 10 

Mesodictyon 12, 58 

Michael T. Halbouty Federal No. 1 well,

Churchill Co., Nev. (loc. 28) 65 

Michigan

Saginaw Bay, Lake Huron pi. 12 

miocenicus, Coscinodiscus (Actinocyclus) 2 

Modoc Co., sec. 7, Calif, (loc. 105) 67 

Moon-To Basin, China 57 

motilis, Actinocyclus 4, 10, 14, 57; pis. 9,

10, 11
72 THE DIATOM GENUS ACTINOCYCLUS IN THE WESTERN UNITED STATES

N

Namibia, Walvis Bay pis. 6, 7

Navicula 7,11, 14

nebulosus, Actinocyclus 3, 6,11, 58; pis. 11,

12 

Nevada 1

Aldrich Station Formation, type sec.,

Mineral Co. (loc. 83) 67 

Augusta Mountains, Churchill Co. (loc.

4) 57; pi. 9

Basalt, Esmeralda Co. (loc. 100) 67 

Big Smokey Valley, Esmeralda Co.

(loc. 47) 65 

Black Spring, Nye Co. (loc. 93) 11, 57,

58, 66; pis. 11,12 

Bradys Hot Spring, Churchill Co. (loc.

54)65 

Browns Hill, Churchill Co. (loc. 55) 57,

65 

Buffalo Canyon, Churchill Co. (loc. 6)

11, 58; pi. 11 

Cedar Mountain, Mineral Co. (loc. 22)

5, 10, 57, 64; pis. 9, 10 

Cedar Mountain, Nye Co. (loc. 74) 4,

11,54,56, 57, 58, 66; pi. 11 

Cedar Spring, Nye Co. (loc. 95) 58, 66 

Chalk Bluff, Reno, Washoe Co. (loc.

101) 67

Churchill Co., sec. 20 (loc. 79) 66 

Churchill Co., sec. 31 (loc. 4) 57; pi. 9 

Copper Kettle Canyon, Churchill Co.

(loc. 16) 6, 57, 64; pi. 5 

Dead Camel Mountains, Churchill Co.

(loc. 18) 64

Diatomite Ridge, Stewart Valley, Mineral Co. (loc. 20) 5, 56, 64; pis. 2,

3,4 

Eagle-Picher diatomite quarry, Clark

siding, Storey Co. (loc. 84) 57, 66 

Eastgate, Churchill Co. (loc. 6) 11 

Eureka Co. sec. 31 (loc. 30) 6, 57, 65;

pi. 5

Femley, Churchill Co. (loc. 41) 57, 65 

Forty-nine Camp, Washoe Co. (loc. 69)

8, 57, 66; pi. 7 

Hot Springs Mountains, Churchill Co.

(loc. 56) 57, 65 

Humboldt Co. (loc. 52) 65 

Humboldt Co. (loc. 103) 67 

Lyon Co. (loc. 1) 5 

LyonCo. (loc. 15) 13 

Michael T. Halbouty Federal No. 1

well, Churchill Co. (loc. 28) 65 

New Pass, Lander Co. (loc. 42) 4, 56,

65; pi. 1

New Pass Summit, Churchill Co. 56, 57 

Nightingale, Churchill Co. (loc. 57) 65 

Pine Grove Hills, Lyon Co. (loc. 15)

58,64

Reno, Washoe Co., (loc. 101) 67 

Stewart Valley, Mineral Co. (loc. 20) 5 

Stillwater Mountains, Churchill Co.

(loc. 16) 7

Stillwater Mountains, southern, Churchill Co. (loc. 48) 56, 57, 65; pis. 2, 

3

Virginia City, Storey Co. (loc. 68) 5, 

57,66

Walker River, Lyon Co. (loc. 1) 64

Washoe Co. (Iocs. 114,115) 67

New Mexico,

Rio Arriba Co. (loc. 104) 67

New Pass, Lander County, Nev. (loc. 42) 4,

56, 65; pi. 1 

New Pass Summit, Churchill Co., Nev. 56,

57

Nightingale, Churchill Co., Nev. (loc. 57) 65 

Nitzschia 7

nordlingensis, Actinocyclus 3,4,12 

normanii, Actinocyclus 3 

normanii f. subsalsa, Actinocyclus 1, 14; pi.

12 

North Fork Fitsum Creek, Valley Co., Idaho

(loc. 94) 57, 66 

North Santiam River, Linn Co., Ore. (loc.

80)66

O

Ontario, Lake 1 

Oregon 1

Aldrich Mountain, Grant Co. (loc. 85)

11,58,66

Baker County, sec. 8 (loc. 96) 66 

Belshaw Ranch, White Hills, Grant Co.

(loc. 86) 66 

Burnt River, lake beds, Swayze Creek,

Baker Co. (loc. 67) 66 

Clover Creek District, Baker Co. (loc.

97)66

Drewsey, Harney Co. (loc. 63) 5, 56, 65 

Durkee, sec. 20, Baker Co. (loc. 82) 66 

Durkee, sec. 23, Baker Co. (loc. 81) 12,

58,66 

Goose Creek, Baker Co. (loc. 27) 5, 10,

57, 64; pi. 9

Harney Co., sec. 17 (loc. 86) 57, 66 

Harper Basin, Malheur Co. (loc. 7) 4,

10, 56, 57; pi. 1 

Harper Basin, sec. 34, Malheur Co.

(loc. 65) 66 

Harper Basin, sec. 34, Malheur Co.

(loc. 66) 66 

John Day River, Carlton condit, Grant

Co. (loc. 85) 66 

Klamath Falls, Klamath Co. (loc. 61)

65 

Leslie Gulch, Malheur Co. (loc. 50) 58,

65

Malheur Co., sec. 2 (loc. 98) 66 

North Santiam River, Linn Co. (loc. 80)

66

Otis Basin, Harney Co. 5 

Otis Creek, Harney Co. (loc. 34) 56,

65; pi. 2 

Seven Mile Creek, Umatilla Co. (loc.

38) 57, 65

Silvies Valley, Grant Co. (loc. 75) 5,

56. 57, 66

Swayze Creek, Baker Co. (loc. 51) 65 

Vinegar Creek, Grant Co. (loc. 88) 10,

57. 66; pis. 8, 9 

Westfall, Harper Basin, Malheur Co.

(loc. 64) 66 

White Hills, Grant Co.(loc. 87) 12, 13,

57, 58, 66 

Wikiup Damsite, Deschutes River, Deschutes Co. (loc. 102) 67 

Yonna Valley, Klamath Co. (loc. 62) 65

Otis Basin, Harney Co., Ore. 5

Otis Creek, Harney Co., Ore. (loc. 34) 56,

65; pi. 2 

Oviatt Creek, Clearwater Co., Idaho (loc. 43)

10, 12, 13, 57, 65; pi. 14 

Owyhee Co., Idaho (loc. 12) 64

Paleoecology 14

Paleolakes 1

Peone, Spokane Co., Wash. (loc. 78) 66

Pine Grove Hills, Lyon Co., Nev. (loc. 15)

58,64

Pinnularia 4,7,11 

pinnulus, Actinocyclus 3, 4, 11, 58; pis. 12,

13

Pit River, Modoc Co., Calif, (loc. 17) 5 

Poison Creek Formation 8, 13, 58, 65, 67;

pis. 2, 14, 15 

Pontodiscus 2 

Pontodiscus gorbunovii 9 

Pontodiscus (=Coscinodiscus) miocenicus 10 

Preparation 2 

Preservation (diatom) 53

Quiburis Formation 7, 58, 66; pi. 6

Radiometric dating 53

Raft River Formation 65

References 14, 59

Reno, Washoe Co., Nev. (loc. 101) 67

Reworking of diatoms 53

Reynolds Creek, Owyhee Co., Idaho (loc.

44) 13, 58, 65; pis. 2, 14, 15 

Rhine graben, Germany 

Ringold Formation 65 

Rio Arriba Co., N. Mex. (loc. 104) 67 

Ruckers, Vogelsberg Range, Germany 6; pi.

14 

Russia, Siberia 10

Primor region, Siberia 13

Tim River, Siberia 13

Saginaw Bay, Lake Huron, Michigan pi. 12 

San Pedro Valley, Ariz. See Edgar Canyon. 

Santa Fe Formation 67
INDEX 73

Seven Mile Creek, Umatilla Co., Ore. (loc.

38) 57, 65 

Shelly Lake, Spokane Co., Wash. (loc. 76)

66 

Shoofly Creek, sec. 6, Owyhee Co., Idaho

(loc. 25) 64 

Shoofly Creek, sec. 9, Owyhee Co., Idaho

(loc. 11)64 

Siberia, Russia 10 

Silvies Valley, Grant Co., Ore. (loc. 75) 5,

56, 57, 66

Snake River Plain, Idaho 8, 13 

Snake River Plain, western, Elmore Co.,

Idaho (loc. 5) 64 

Soviet Union 59

See also Russia.

Spokane Co., Wash. (loc. 76) 57, 58, 66 

Spokane Co., Wash. (Iocs. 77, 78) 10, 66 

Squaw Creek Member, Ellensburg Formation

10, 11, 13, 56, 57, 58, 65; pis. 8,

9, 10, 11 

Stauroneis 14 

Stephanodiscus 2, 59 

Steplianodiscus astraea 10 

Stewart Valley, Mineral Co., Nev. (loc. 20) 5 

Stillwater Mountains, Churchill Co., Nev.

(loc. 16) 7 

Stillwater Mountains, southern, Churchill

Co., Nev. (loc. 48) 56, 57, 65; pis.

2,3

Stinking Water flora (loc. 86) 66 

Sucker Creek Formation 58, 65 

Surirella 4

Swayze Creek, Baker Co., Ore. (loc. 51) 65 

Szurdokpuspoki, Matra Mountains, Hungary

pi. 8

Tabellaria 5,10

Techniques, collection and preparation 2

Teewinot Formation 67

Teton Co., sec. 36, Wyoming (loc. 107) 67

Tetracyclus 5, 7, 10, 11, 14

ellipticus 8

sp. 5,14 

theleus, Aainocyclus 3, 12, 14, 58; pis. 13,

14

Thorn Creek, Boise Co., Idaho (loc. 89) 66 

Thousand Creek Formation 65, 67 

Tim River, Siberia, Russia 13 

Time range 58

Trapper Creek, Cassia Co., Idaho (loc. 53) 

56, 58, 65

Travertine Point, Inyo Co., Calif, (loc. 113)

67

Truckee Formation 57, 65, 66 

tubulosus, Aainocyclus 3, 4, 10,13, 58; pi. 8 

Tucson, Pima Co., Ariz. (loc. 92) 58 

Tulare Formation 65 

Turner Creek, Modoc Co., Calif, (loc. 17) 5,

56, 58, 64; pi. 4

u,v

Utah,

AMOCO Delta Stephan Szot No. 1 

well, Cache Co. (loc. 19) 64

AMOCO Lynn Reese No. 1 well, 

Cache Co. (loc. 39) 65

Vantage, Grant Co., Wash. (loc. 59) 10, 56,

57,65 

variabiHs, Coscinodiscus (=Actinocyclus) 2,

3,6 

venenosus, Actinocyclus 4, 5, 8, 10, 13, 14,

58; pis. 14, 15 

Vinegar Creek, Grant Co., Oregon (loc. 88)

10, 57, 66; pis. 8, 9 

Virginia City, Storey Co., Nev. (loc. 68) 5,

56, 57, 66 

Virginia Range, Storey Co., Nev. (loc. 68) 5,

56, 57, 66

Vogelsberg Range, Beuem, Germany 6; pi. 8 

Vogelsberg Range, Ruckers, Germany 9; pi.

14

W

Walker River, Lyon Co., Nev. (loc. 1) 64 

Walvis Bay, Namibia pis. 6, 7 

Washington 1

Grant Co. (loc. 99) 67

Hangman Valley, Spokane Co. (loc. 36)

57,65 

Mead, Spokane Co. (loc. 106) 56, 57,

58,67

Peone, Spokane Co. (loc. 78) 66 

Shelly Lake, Spokane Co. (loc. 76) 66 

Spokane Co. (loc. 76) 57, 58, 66 

Spokane Co. (loc. 77) 10 

Vantage, Grant Co. (loc. 59) 10, 56, 57,

65

White Cliffs, Frankiin Co. (loc. 46) 65 

Yakima Co. (loc. 49) 10, 11, 56, 57, 58,

65; pis. 8, 9, 10, 11

Washoe Co., Nev. (Iocs. 114, 115) 67

Washington Co., sec. 17, Idaho (loc. 45) 65 

Washington Co., sec. 19, Idaho, Poison

Creek Formation (Iocs. 110, 111)

67 

Washington Co., sec. 29, Idaho, Poison

Creek Formation (loc. 108) 58, 67 

Washington Co., sec. 32, Idaho, Poison

Creek Formation (loc. 109) 58, 67 

Washington Co., sec. 34, Idaho (loc. 31) 65;

pi. 15 

Washington Co., Idaho, Idaho Group (loc.

111)58 

Weiser, sec. 35, Washington Co., Idaho (loc.

2664 

Weiser, Washington Co., Idaho (loc. 70) 57,

66 

Wells

AMOCO Becharof No. 1 well, Alaska

(loc. 112) 12, 58, 67; pi. 13 

AMOCO Delta Stephan Szot No. 1

well, Cache Co., Utah (loc. 19) 64 

AMOCO Lynn Reese No. 1 well,

Cache Co., Utah (loc. 39) 65 

AMOCO Milford Federal No. 1 Well,

Lemhi Co. (loc. 40) 57 

Michael T. Halbouty Federal No. 1

well, Churchill Co., Nev. (loc. 28)

65

West Browns Creek, Owyhee Co., Idaho

(loc. 8) 64 

Westfall, Harper Basin, Malheur Co., Ore.

(loc. 64) 66

White Cliffs Franklin Co., Wash. (loc. 46) 65 

White Hills, Grant Co., Oregon (loc. 87) 12,

13, 57, 58, 66

Whitebird, Idaho Co., Idaho (loc. 71) 57, 66 

Wikiup Damsite, Deschutes River, Deschutes

Co., Ore. (loc. 102) 67 

Wyoming,

Teton Co., sec. 36 (loc. 107) 67

X,Y

Xian Feng Basin, Kunming, China 13, 58

Yakima Co., Washington (loc. 49) 10, 11,

56, 57, 58, 65; pis. 8, 9, 10, 11 

Yamato Bank, Sea of Japan 7, 57; pi. 6 

Yonna Formation 65 

Yonna Valley, Klamath Co., Ore. (loc. 62) 65

<rU.S. QOVERNMHir PRINTING OFFICE: 1994-673-046/86068
SELECTED SERIES OF U.S. GEOLOGICAL SURVEY PUBLICATIONS

Periodicals

Earthquakes & Volcanoes (issued bimonthly). 

Preliminary Determination of Epicenters (issued monthly).

Technical Books and Reports

Professional Papers are mainly comprehensive scientific reports 

of wide and lasting interest and importance to professional scientists and 

engineers. Included are reports on the results of resource studies and of 

topographic, hydrologic, and geologic investigations. They also include 

collections of related papers addressing different aspects of a single scientific topic.

Bulletins contain significant data and interpretations that are of 

lasting scientific interest but are generally more limited in scope or geographic coverage than Professional Papers. They include the results of resource studies and of geologic and topographic investigations; as well as 

collections of short papers related to a specific topic.

Water-Supply Papers are comprehensive reports that present significant interpretive results of hydrologic investigations of wide interest 

to professional geologists, hydrologists, and engineers. The series covers 

investigations in all phases of hydrology, including hydrology, availability of water, quality of water, and use of water.

Circulars present administrative information or important scientific information of wide popular interest in a format designed for distribution at no cost to the public. Information is usually of short-term interest.

Water-Resources Investigations Reports are papers of an interpretive nature made available to the public outside the formal USGS publications series. Copies are reproduced on request unlike formal USGS 

publications, and they are also available for public inspection at depositories indicated in USGS catalogs.

Open-File Reports include unpublished manuscript reports, maps, 

and other material that are made available for public consultation at depositories. They are a nonpermanent form of publication that may be cited in other publications as sources of information.

Maps

Geologic Quadrangle Maps are multicolor geologic maps on topographic bases in 7 1/2- or 15-minute quadrangle formats (scales mainly 1:24,000 or 1:62,500) showing bedrock, surficial, or engineering 

geology. Maps generally include brief texts; some maps include structure 

and columnar sections only.

Geophysical Investigations Maps are on topographic or planimetric bases at various scales, they show results of surveys using geophysical 

techniques, such as gravity, magnetic, seismic, or radioactivity, which reflect subsurface structures that are of economic or geologic significance. 

Many maps include correlations with the geology.

Miscellaneous Investigations Series Maps are on planimetric or 

topographic bases of regular and irregular areas at various scales; they 

present a wide variety of format and subject matter. The series also includes 7 1/2-minute quadrangle photogeologic maps on planimetric 

bases which show geology as interpreted from aerial photographs. The 

series also includes maps of Mars and the Moon.

Coal Investigations Maps are geologic maps on topographic or 

planimetric bases at various scales showing bedrock or surficial geology, 

stratigraphy, and structural relations in certain coal-resource areas.

Oil and Gas Investigations Charts show stratigraphic information for certain oil and gas fields and other areas having petroleum potential.

Miscellaneous Field Studies Maps are multicolor or black-andwhite maps on topographic or planimetric bases on quadrangle or irregular areas at various scales. Pre-1971 maps show bedrock geology in relation to specific mining or mineral-deposit problems; post-1971 maps 

are primarily black-and-white maps on various subjects such as environmental studies or wilderness mineral investigations.

Hydrologic Investigations Atlases are multicolored or black-andwhite maps on topographic or planimetric bases presenting a wide range 

of geohydrologic data of both regular and irregular areas; the principal 

scale is 1:24,000, and regional studies are at 1:250,000 scale or smaller.

Catalogs

Permanent catalogs, as well as some others, giving comprehensive 

listings of U.S. Geological Survey publications are available under the 

conditions indicated below from USGS Map Distribution, Box 25286, 

Building 810, Denver Federal Center, Denver, CO 80225. (See latest 

Price and Availability List.)

"Publications of the Geological Survey, 1879-1961"may be purchased by mail and over the counter in paperback book form and as a set 

microfiche.

"Publications of the Geological Survey, 1962-1970" may be purchased by mail and over the counter in paperback book form and as a set 

of microfiche.

"Publications of the US. Geological Survey, 1971-1981" may be 

purchased by mail and over the counter in paperback book form (two volumes, publications listing and index) and as a set of microfiche.

Supplements for 1982, 1983, 1984, 1985, 1986, and for subsequent years since the last permanent catalog may be purchased by mail 

and over the counter in paperback book form.

State catalogs, "List of U.S. Geological Survey Geologic and Water-Supply Reports and Maps For (State)," may be purchased by mail and 

over the counter in paperback booklet form only.

"Price and Availability List of U.S. Geological Survey Publications," issued annually, is available free of charge in paperback booklet 

form only.

Selected copies of a monthly catalog "New Publications of the 

U.S. Geological Survey" is available free of charge by mail or may be obtained over the counter in paperback booklet form only. Those wishing a 

free subscription to the monthly catalog "New Publications of the U.S. 

Geological Survey" should write to the U.S. Geological Survey, 582 National Center, Reston, VA 22092.

Note.-Prices of Government publications listed in older catalogs, 

announcements, and publications may be incorrect. Therefore, the prices 

charged may differ from the prices in catalogs, announcements, and publications.