Stratigraphic Distribution and Zonation 

of Jurassic (Callovian) Ammonites in 

Southern Alaska

GEOLOGICAL SURVEY PROFESSIONAL PAPER 836
Stratigraphic Distribution and Zonation 

of Jurassic (Callovian) Ammonites in 

Southern Alaska

By RALPH W. IMLAY

GEOLOGICAL SURVEY PROFESSIONAL PAPER 836

Studies of Callovian ammonites from southern 

Alaska provide correlations with lower and 

middle Callovian ammonite zones of Europe

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1975
UNITED STATES DEPARTMENT OF THE INTERIOR 

STANLEY K. HATHAWAY, Secretary

GEOLOGICAL SURVEY 

V. E. McKdvey, Director

Library of Congress Cataloging In Publication Data

Imlay, Ralph Willard, 1908-

Stratigraphic distribution and zonation of Jurassic (Callovian) ammonites in southern Alaska.

(Geological Survey professional paper; 836)

Bibliography: p.

Includes index.

Supt. of Docs, no.: I 19.16:836

1. Geology, Stratigraphic-Jurassic. 2. Ammonoidea. 3. Geology-Alaska. I. Title. II. Series: United States.

Geological Survey. Professional paper; 836. 

QE683.I44 564'.5 75-619185

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

Washington, D.C. 20402 

Stock Number 024-001-02650-3
CONTENTS

Page

Abstract ___ _ 1

Introduction ____ 1

Stratigraphic summary _ 1

Callovian ammonite succession 2

West of Cook Inlet ____________________ __ ____ 2

Talkeetna Mountains _ _ 3

Alaska Peninsula __________ _ _ _ _ 3

Ammonite zonation _ _ 7

Cadoceras (Stenocadoceras) stenoloboide Zone ________ _ ___- 7

Cadoceras catostoma Zone _-__ _______-__-_-___ __ 7

Iniskinites intermedius Subzone __________________________ 7

Ages and correlations __________________________ _ ___ 7

Ammonite faunal setting _ _ _ _ ______ _ _ 15

Geographic distribution ________________________________ 15

Systematic descriptions _ _ __________________________ 15

References cited _____________________________________ 25

Index ______,______________________________________ 27

ILLUSTRATIONS

[Plates 1-6 follow index]

PLATE 1. Kepplerites.

2. Chinitnites.

3. Chinites and Iniskinites.

4. Iniskinites.

5. Iniskinites and Kepplerites.

6. Parareineckeia and Kepplerites.

Page

FIGURE 1. Correlation chart showing stratigraphic positions of some ammonite localities in the Chinitna Formation west of Cook Inlet _______________________________________________ 4

2. Diagram showing stratigraphic ranges of ammonites in the Chinitna Formation west of Cook Inlet _ 6

3. Correlation chart showing stratigraphic positions of ammonite localities in the Chinitna Formation in

the southeastern part of Talkeetna Mountains __________________ _ _ _ 8

4-7. Diagrams showing 

4. Stratigraphic ranges of ammonites in the Chinitna Formation northwest of Limestone Hills

in the Talkeetna Mountains _______________________________________ 10

5. Stratigraphic ranges of ammonites in the Chinitna Formation between Limestone Hills and

Horn Mountains in the Talkeetna Mountains ___________________________ 11

6. Stratigraphic ranges of ammonites in the Shelikof Formation between Puale Bay and Wide

Bay, Alaska Peninsula __________________________________________ 12

7. European and East Greenland ranges of certain ammonites present, or possibly present, in

Alaska ____________________________________________________ 13

8. Chart showing correlation of Callovian formations and faunas in southern Alaska _____________ 14

9. Index map of listed fossil localities in the Chinitna Formation in the Talkeetna Mountains ________ 18

TABLES

Page

TABLE 1. Some Callovian ammonite genera and species described herein, showing biological relationships and relative numbers available for study ___________________________________________ 2

2. Geographic distribution of ammonites in the Chinitna Formation in the Talkeetna Mountains, Alaska _ 16

3. Descriptions of Jurassic ammonite localities in the Chinitna Formation in the Talkeetna Mountains,

Alaska ___________________________________________________________ 19

in
STRATIGRAPHIC DISTRIBUTION AND ZONATION

OF JURASSIC (CALLOVIAN) AMMONITES

IN SOUTHERN ALASKA

By RALPH IMLAY

ABSTRACT

Jurassic ammonites of early and middle Callovian Age 

occur in southern Alaska in the Chinitna and Shelikof 

Formations. Ranges of the ammonite genera and subgenera 

present, on the basis of the stratigraphic distribution of these 

fossils in Eurasia and East Greenland, show that these 

formations should be equivalent te at least the European 

zones of Sigaloceras calloviense, Kosmoceras jason, and 

Erymnoceras coronatum. Whether the basal few hundred 

feet of these formations is equivalent to the earliest Callovian or to the highest Bathonian, or both, cannot be demonstrated for certain.

Two ammonite zones are recognizable. The upper zone, 

named after Cadoceras (Stenocadoceras) stenoloboide (Pompeckj), is characterized by an abundance of the subgenus 

Stenocadoceras. It has been recognized west of Cook Inlet in 

the Paveloff Siltstone Member of the Chinitna Formation 

and in the upper one-sixth of the underlying Tonnie Siltstone Member. In the Talkeetna Mountains it is represented 

locally near the top of the Chinitna Formation. In the Alaska 

Peninsula it occurs in the middle member of the Shelikof 

Formation and in the upper fifth of the lower member.

The lower ammonite zone, named after Cadoceras catostoma 

Pompeckj, is characterized also by the presence of C. glabrum Imlay, all species of C. (Paracadoceras), and all 

species of Lilloettia except L. stantoni Imlay. These ammonites range through the entire lower part of the Chinitna 

Formation below the beds characterized by C. (Stenocadoceras) stenoloboide (Pompeckj) and C. (S.) multicostatum 

Imlay.

The lower part of the C. catostoma Zone is herein recognized as a subzone and is named after the most common 

species, Iniskinites intermedius (Imlay). This subzone marks 

the top of the range of Parareineckeia, of the new genus 

Iniskinites, and also of Xenocephalites, except for one spscimen. Its lower part includes also all known specimens of 

evolute Kepplerites. Characteristic ammonites of the subzone 

occur in the lower 500 feet of the Chinitna Formation west 

of Cook Inlet and in the lower half of the lower member of 

the Shelikof Formation on the Alaska Peninsula.

The Callovian ammonites of southern Alaska include some 

genera characteristic of the Boreal realm, such as Kepplerites, Cadoceras, and Pseudocadoceras, and other genera 

characteristic of the Pacific realm, such as Xenocephalites, 

Lilloettia, and Parareineckeia. On the specific level, however, 

nearly all relationships are southward with Callovian ammonites in British Columbia, Oregon, and northern California. Evidently, southern Alaska during Callovian time 

was part of a Pacific Coast faunal province.

INTRODUCTION

The Callovian ammonites of southern Alaska described by the writer in 1953 have been restudied 

in order to revaluate the stratigraphic distribution 

of the genera and species, to establish ammonite 

zones for regional and continental correlations, and 

to date the formations and zones more precisely in 

terms of the standard Jurassic zones of western 

Europe. This study is based on biostratigraphic data 

compiled by Detterman and Hartsock (1966, p. 38, 

39, 44-46, 48) for the Chinitna Formation west of 

Cook Inlet and by Arthur Grantz (written commun., 

Apr. 1972) for the Chinitna Formation in the Talkeetna Mountains. These data are much more accurate than those available to the writer in 1950. 

Likewise, study of the many fossil collections made 

by Arthur Grantz and associates in the Talkeetna 

Mountains between 1952 and 1963 has provided a 

check on conclusions based on data from other areas 

concerning ammonite associations, generic and specific variations, and stratigraphic distribution.

The study includes descriptions of two new genera, 

Iniskinites and Chinitnites, that succeed and are 

closely related to Cranocephalites, a genus of late 

Bajocian(?) to early or middle Bathonian Age. Also, 

two specimens of Parareineckeia are illustrated to 

show the characteristics of the small septate whorls 

and of the body chamber of a genus hitherto represented only by four specimens (Imlay, 1953b, p. 101, 

pi. 55, fig. 1, 2, 5-8; 1962, p. C25, C26, pi. 7, figs. 

1-7). The biological distribution of the described 

species is shown in table 1.

STRATIGRAPHIC SUMMARY

On the west side of Cook Inlet between Iniskin 

Bay and Tuxedni Bay the Callovian is represented 

by the Chinitna Formation which, as described by 

Detterman and Hartsock, 1966, p. 40-47), consists 

of two siltstone members separated by a sandstone 

unit 30-200 feet thick. The lower member, named
JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

TABLE 1. Some Callovian ammonite genera and species described herein, showing biological relationships and relative 

numbers available for study.

Famiy Genus and species

Number of 

specimens

Kosmoceratidae -Kepplerites chisikensis Imlay, n. sp _ 2 

Cardioceratidae -Chinitnites chinitnaensis Imlay, n.

gen., n. sp 102

parviformis (Imlay) __ _ 22

Iniskinites magniformis (Imlay) 7

abruptus (Imlay) ________ 9

martini (Imlay) _________ 3

intermedius (Imlay) ______ 12

Reineckeiidae _Parareineckeia shelikofana (Imlay) _ 2

the Tonnie Siltstone Member, is roughly equivalent 

to the lower two-thirds of the Chinitna Formation, 

as classified by Imlay (1953b, p. 51). It thins northward from 1,300 to 800 feet, rests sharply on the 

Bowser Formation, and north of Chinitna Bay is 

marked basally by pebbles or by channel conglomerates that locally cut as much as 200 feet into the 

Bowser Formation. The upper member, named the 

Paveloff Siltstone Member, ranges in thickness from 

900 to 1,350 feet, is thickest in the central part of 

the area, is generally marked basally by a sandstone 

unit, and is overlain unconformably by the Naknek 

Formation. This unconformity is most conspicuous 

where the Paveloff Siltstone Member is thinnest.

The Shelikof Formation on the Alaska Peninsula 

between Wide Bay and Puale Bay consists of three 

members, as originally described by Capps (1923, 

p. 97-101) and later summarized by Martin (1926, 

p. 192-199), Imlay (1953b, p. 48, 49), and Burk 

(1965, p. 27). The lower member consists of 800 to 

1,800 feet of siltstone and sandy siltstone, contains 

limestone concretions throughout, and in its lower 

part has many thin beds of volcanic ash. These ash 

beds, plus associated fossils, serve to differentiate 

the basal beds of the lower member from similar 

siltstone beds in the underlying Kialagvik Formation. The middle member consists of 1,000 to 3,500 

feet of massive gray sandstone interbedded with 

some siltstone and conglomerate. Its upper part 

grades laterally and vertically into the adjoining 

siltstone members. The upper member consists of 

900 to 1,500 feet of siltstone, contains some beds oi 

sandstone and limestone, and is overlain unconformably by conglomerate at the base of the Naknek 

Formation.

The Chinitna Formation in the Nelchina area is 

overlain by the Naknek Formation with a marked 

unconformity that becomes angular to the north. At 

some places the Chinitna Formation rests concordantly but disconformably on Cranocephalitesbearing beds which are older than Callovian and 

which correlate faunally with the lower part of the 

Bowser Formation west of Cook Inlet (Imlay, 1962, 

p. C2; Detterman and Hartsock, 1966, p. 35-40). At 

many other places in the Talkeetna Mountains, the 

Chinitna Formation rests directly and unconformably on beds of middle to late Bajocian Age (Grantz, 

written commun., 1959).

The Chinitna Formation crops out extensively in 

the southern Talkeetna Mountains but has been 

mapped in detail only in the southeasternmost part 

of those mountains, known as the Nelchina area 

(Grantz, 1960a, b; 1965). North of Horn Mountains 

in the Nelchina area the formation has been divided 

into two unnamed members, whereas south of the 

mountains it has been mapped as a single undivided 

unit of siltstone and shale that contains limestone 

concretions and thin sandstone beds. The lower member north of the mountains comprises two facies: 

(1) a northern facies that consists of cobble conglomerate and conglomeratic sand siltstone, contains 

many fossil wood and coal fragments, attains a 

thickness of 100 feet, and lies in channels cut in 

the underlying rocks and (2) a southern facies that 

consists of sandstone and siltstone, contains marine 

mollusks, and attains a thickness of as much as 1,500 

feet. The upper member north of Horn Mountains 

consists of siltstone and shale, contains limestone 

concretions and thin sandstone beds, thickens southward from 0 to 800 feet or more, and is similar in 

appearance to the entire Chinitna Formation south 

of Horn Mountains (Grantz, 1965; written commun., 

1972).

CALLOVIAN AMMONITE SUCCESSION 

WEST OF COOK INLET

Most of the fossil collections from the Chinitna 

Formation between Iniskin Bay and Tuxedni Bay 

(Imlay, 1953b, p, 65-71) have been described stratigraphically with respect to member boundaries by 

Detterman and Hartsock (1966, p. 44-46, 48) and 

are depicted herein on columnar sections (fig. 1) 

modified from those authors (1966, pi. 5). This information permits fairly accurate determinations of 

the stratigraphic ranges of many ammonite species 

(fig. 2) and necessitates revision of interpretations 

previously published (Imlay, 1953b, p. 50) which 

were based on much less accurate stratigraphic data. 

These ranges show clearly that the ammonites of the 

formation occur as two assemblages or zones. Of 

these, the upper assemblage is dominated by Cadoceras (Stenocadoceras) stenoloboide (Pompeckj)
CALLOVIAN AMMONITE SUCCESSION

and by C. (5.) multicostatum Imlay and ranges 

from the upper sixth of the Tonnie Siltstone Member to the top of the formation. The lower assemblage is characterized by Cadoceras catostoma Pompeckj, Lilloettia buckmani (Crickmay), and by species of the subgenus Cadoceras (Paracadoceras) 

and ranges through most of the Tonnie Siltstone 

Member. These ammonites in the lower assemblage 

are likewise associated in the lower two-fifths of the 

Tonnie Siltstone Member with Iniskinites, n. gen., 

and Xenocephalites.

TALKEETNA MOUNTAINS

The stratigraphic position of most of the fossil 

collections from the Chinitna Formation in the Nelchina area of the Talkeetna Mountains has been 

located fairly accurately by Arthur Grantz (written 

commun., 1972) and is depicted herein on generalized columnar sections (fig. 3). His information permits determinations of the stratigraphic ranges of 

ammonite taxa within the Chintna Formation in 

the Talkeetna Mountains (fig. 4 and 5) These ranges 

show that both the upper member northwest of 

Limestone Hills and the lower member east of those 

hills correlate very well with the Tonnie Siltstone 

Member below the lowest occurrences of Cadoceras 

(Stenocadoceras) multicostatum Imlay and C. (S.) 

stenoloboide (Pompeckj). This correlation is based 

on the presence of Lilloettia buckmani (Crickmay), 

Cadoceras catostoma Pompeckj, C. glabrum Imlay, 

Chinitnites, Iniskinites, Kepplerites (evolute forms), 

certain species of Paracadoceras and Xenocephalites, 

and on the absence of Stenocadoceras. The presence 

of Chinitnites chinitnaensis Imlay, n. sp., directly 

above Iniskinites in the upper member northwest of 

Limestone Hills corresponds to the stratigraphic 

position of these taxa within the Tonnie Siltstone 

Member west of Cook Inlet (fig. 2). It seems, therefore, that Chinitnites ranges higher than Iniskinites 

and that the species C. chinitnaensis marks the middle part of the range of Cadoceras catostoma.

The upper member of the Chinitna Formation 

between Limestone Hills and Horn Mountains has 

yielded ammonites only in its lower two-thirds, and 

these are also identical with species in the Tonnie 

Siltstone Member west of Cook Inlet. The basal part 

of the upper member is probably about the same 

age as the underlying lower member, as shown by 

the presence of Iniskinites. The middle third correlates with the highest part of the Tonnie Siltstone 

Member, as shown by an occurrence of Cadoceras 

(Stenocadoceras) multicostatum Imlay (USGS

Mesozoic loc. 25308) at a position slightly lower than 

the highest occurrence of the subgenus Paracadoceras (USGS Mesozoic loc. 24224), which ranges 

through the lower two-thirds of the upper member. 

This relationship is of age significance because 

Paracadoceras west of Cook Inlet does not range 

above the very base of the Paveloff Siltstone Member (see USGS Mesozoic loc. 22524 in Detterman 

and Hartsock, 1966, p. 48), and Stenocadoceras multicostatum is not known below the upper sixth of the 

underlying Tonnie Siltstone Member.

ALASKA PENINSULA

The stratigraphic distribution of ammonite species within the members of the Shelikof Formation 

between Wide Bay and Puale Bay (fig. 6) is based 

on 35 fossil collections for which fairly accurate 

stratigraphic data are available. These collections 

include 18 from the lower member, 16 from the middle member, and 1 that is possibly from the basal 

part of the upper member. The biostratigraphic data 

(Imlay, 1953b, p. 69-71) as not nearly so accurate 

as data available for the members of the Chinitna 

Formation west of Cook Inlet (figs. 1 and 2) because 

fewer collections are involved, lateral changes are 

much greater within the members of the Shelikof 

Formation, and many of the fossil collections made 

before 1944 could not be so precisely located on the 

available maps as on aerial photographs. Nonetheless, the ranges of ammonite species within the 

lower and middle members of the Shelikof Formation correspond approximately to their ranges within 

the members of the Chinitna Formation. It follows, 

therefore, that the same ammonite assemblages are 

recognizable.

Recent reexamination of ammonite collections 

from the Shelikof Formation of the Alaska Peninsula, previously reported by Imlay (1953b, table 6 

opposite p. 72), shows that Paracadoceras is lacking; Xenocephalites is known only from Chignik 

Bay (USGS Mesozoic loc. 29342); Kepplerites and 

Iniskinites are known only from one place about 

500 feet above the base of the formation at Wide 

Bay (USGS Mesozoic loc. 19793); Parareineckeia 

is represented only by one specimen obtained about 

200 feet lower at Wide Bay (USGS Mesozoic loc. 

21355); and the only common taxa present are 

Lilloettia, Cadoceras, C. (Stenocadoceras), and 

Pseudocadoceras. The lower member is characterized 

by Lilloettia buckmani (Crickmay) in association 

with Cadoceras catostoma Pompeckj and C. glabrum 

Imlay. The middle member is characterized by C. 

(Stenocadoceras) stenoloboide Pompeckj and C.(S.)
JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

NORTH

TUXEDNI BAY AREA 

ON CHISIK ISLAND

LAKE HICKERSON AREA 

ALONG LAKE SHORE

NAKNEK FORMATION

CHINITNA

FORMATION

PAVELOFF

SILTSTONE

MEMBER

TONNIE

SILTSTONE

MEMBER

BOWSER FORMATION

805 feet

Siitstone, 

massive

Some thin 

beds of 

sandstone

Some limestone 

lentils and 

concretions

95 feet 

Sandstone, 

massive

155 feet

Siitstone, sandy, 

massive to 

thin-bedded

135 feet 

Shale, silty, 

thin-bedded

270 feet

Covered

-2990

-22670,22554

\2991 

f21290

155 feet 

Siitstone, massive

Sandstone units

215 feet 

Conglomerate 

in channels 

and massive 

sandy siltstone

12-13 MILES

22677 

} 21291

- 22679

- 22680 

22681,21344

- 22543

- 22683, 22684 

> 22*00 

ft-21287 

, 3015, 21273 U-->?686

21272,3014

900 feet

Siitstone, 

massive

Some thin 

beds of 

graywacke

Some limestone 

concretions

} 22704

} 22702 

- 22703

100 feet 

Sandstone

300 feet 

Siitstone, 

massive

Thin beds of 

graywacke

Some limestone 

concretions

490 feet

Siitstone, 

massive

Large limestone 

concretions

100 feet 

Pebbly graywacke

18-19

FIGURE 1. Stratigraphic positions of some ammonite localities in the Chinitna
CALLOVIAN AMMONITE SUCCESSION

SOUTH

CHI

MILES

-

NITNA BAY AREA BOWSER AND TONNIE 

SOUTH SIDE CREEKS AREA

680 feet

Siltstone, massive

Some beds of 

graywacke

220 feet 

Siltstone, 

massive

Some limestone 

concretions

210 feet

Sandstone, 

medium-bedded 

to massive

100 feet 

Pebbly sandstone

360 feet 

Siltstone, 

massive

Many limestone 

concretions

380 feet 

Siltstone 

as above

Limestone 

lentils and 

concretions

/ 80 feet \ 

Sandstone,

4 MILES

. 26590 --21 342

"21346

21776 

-21347

-21778. 

-21777,21339

> 22556 

- 21340^^ 

-21774 ^"^^ 

 21338,21781, -^^ 

. 27097 ^^ 

 21337

} 21348,22348 

1 22421

} 21277 

. 22437

-21341 

x 22438

700 feet

Siltstone, 

massive

Some beds of 

sandstone

640 feet

Siltstone 

as above

Some limestone 

lentils and 

concretions

/ 30 feet \ 

/ Sandstone \

580 feet

Siltstone, 

massive, 

sandy 

toward top

Some limestone 

concretions

/ 25 feet \ 

/ Sandstone \

135 feet Siltstone, 

massive

/ 40 feet \ 

f Sandstone \

220 feet 

Siltstone, 

massive

/ , 20 feet \ 

/ Pebblv sandstoneN

4-5 MILES

^22430,22451,20159

"22429,22452,20757 

- 22541 

- 20762

\ 22425 

^ 21323

- 21322

-21331 

-21324

\ 20761 

f 21321,21325 

} 21349

-21329,21332

} 21328, 20760 

-21326

£tL J £t 1 $ £* L<J <J\J

INISKIN BAY 

ON EAST SIDE

Siltstone, 

massive, 

sandy

280 feet

Siltstone, 

massive

Limestone 

lentils and 

concretions

270 feet 

Siltstone, 

thin-bedded

Beds of sandstone 

and limestone 

lentils

110 feet 

Sandstone

200 feet 

Siltstone, 

medium-bedded 

Some limestone 

lentils

960 feet

Siltstone, 

massive

Some silty shale 

and limestone 

concretions

150 feet 

Sandstone and 

siltstone 

Pebbly at base

-11060

-3030 

} 22435

} 22415, 22417

} 22434 

- 20763

_ 22433 

} 22411

- 22419

- 22422 

22432

. 22413 

_ 22412, 22431 

> 22428

2920, 3027, 

\ 20755, and 

J 22448 

^ 22446

s 22559, 20753

Formation west of Cook Inlet (data from Detterman and Hartsock, 1966, p. 44-48, pi. 5).
JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

Unit

Genus and species

Chinitna Formation

Tonnie Siltstone Member Pavetoff Siltstone Member

Phylloceras (Phylloceras) bakeri Imlay -

(Calliphylloceras) freibrocki Imlay -

(Partschiceras) subobtusiforme Pompeckj

grantzi Imlay - __-

(Macrophylloceras) grossicostatum Imlay 

Oppelia (Oxycerites) sp - __ - 

(O.) chinitnana Imlay 

Lilloettia buckmani (Crickmay) _______

milleri Imlay - ________.

mertonyarwoodi Crickmay - ____-

lilloetensis Crickmay ________

stantoni Imlay ____________

Xenocephalites hebetus Imlay ________

vicarius Imlay ___ ____.

hartsocki Imlay ___________

Iniskinites magniformus (Imlay) _______

martini (Imlay) ____________

abruptus (Imlay) ___________

varicostatus (Imlay) __________

intermedius (Imlay)__________

Chinitnites parviformus (Imlay) _______

chinitnaensis Imlay, n. sp _______

Cadoceras catostoma Pompeckj _______

comma Imlay ____________

glabrum Imlay ____________

tenuicostatum Imlay _________

doroschini (Eichwald)_ _ _______

wosnessenskii (Grewingk) _______

kialagvikense Imlay __________

(Paracadoceras) moffiti Imlay_ _ _ _ _ _

multiforme Imlay ________

tonniense Imlay_ _________

chisikense Imlay ________

SP ______________

(Stenocadoceras) multicostatum Imlay_. 

striatum Imlay _________

iniskinense Imlay ________

bowserense Imlay_ _______

stenoloboide (Pompeckj) _ _ ___.

(Longaevicerasl) pomeroyense Imlay -

Pseudocadoceras grewingki (Pompeckj) -

chinitnense Imlay __________

crassicostatum Imlay _________

Kepplerites (Seymourites) alticostatus Imlay _ _ 

(5.) multus McLearn _ _______

chisikensis Imlay, n. sp _ _ _ _ _

ingrahami (McLearn) ______

mcevoyi (McLearn) _______

abruptus (McLearn) _______

spinosus (Imlay) ________

snugharboremis (Imlay) ________

alaskanus (Imlay)___________

Procerites sp _______________

Grossouvria sp ______________

Choffatia irreguiaris (Imlay) _________

FIGURE 2. Stratigraphic ranges of ammonites in the Chinitna Formation west of Cook Inlet.
AMMONITE ZONATION

multicostatum Imlay in association with several 

species of Pseudocadoceras and with Cadoceras 

tenuicostatum Imlay. C. (S.) stenoloboide and C. 

tenuicostatum are also recorded from the upper 

part of the lower member at positions that seem 

to be lower than the highest occurrences of Lilloettia. They have not been found, however, at the 

same localities as Lilloettia or even in the same 

stratigraphic sequences. The upper member has not 

furnished ammonites except possibly one occurrence 

of Pseudocadoceras grewingki (Pompeckj) (USGS 

Mesozoicloc. 10813).

AMMONITE ZONATION 

CADOCERAS (.STENOCADOCERAS) STENOLOBOIDE ZONE

This zone is characterized by an abundance of the 

subgenus Stenocadoceras and particularly by the 

species Cadoceras (Stenocadoceras) stenoloboide 

Pompeckj and C. (S.) multicostatum Imlay. Most 

of the associated species of other genera (fig. 2) 

either range upward from the C. catostoma Zone or 

are represented by so few occurrences that their 

total ranges are unknown. Some species, however, 

seem to be restricted to the C. (S.) stenoloboide 

Zone, including C. (Longaevicerasl) pomeroyense 

Imlay, Pseudocadoceras chinitnense Imlay, and P. 

crassicostatum Imlay. Stenocadoceras itself has not 

been found in association with C. catostoma Pompeckj in any collection made since 1921. Older records of such an association at USGS Mesozoic 

localities 2921, 3028, 3029, and 11052a (Imlay, 

1953b, table 6) are questioned because the collection at USGS Mesozoic locality 2921 was made 

from about 1,200 feet of beds, that at USGS Mesozoic locality 3028 does not now contain any specimen of Stenocadoceras, and the collections from 

USGS Mesozoic localities 3029 and 11052a contain 

single small immature specimens whose identification with C. catostoma Pompeckj (Imlay, 1953b, 

p. 83) is doubtful.

The characteristic ammonites of the Cadoceras 

(Stenocadoceras) stenoloboide Zone west of Cook 

Inlet range through the upper part of the Chinitna 

Formation (fig. 2), including the upper one-sixth 

of the Tonnie Siltstone Member. In the Talkeetna 

Mountains they are represented by only two occurrences (fig. 5), of which at least one is in the upper 

fifth of the Chinitna Formation (USGS Mesozoic 

loc. 25308). In the Alaska Peninsula they occur 

mainly in the middle member of the Shelikof Formation (fig. 6), but the zonal species occurs also in 

the upper fifth of the lower member, apparently a 

little higher than Lilloettia and C. catostoma Pompeckj. This relationship is essentially identical with

that in the upper part of the Tonnie Siltstone Member of the Chinitna Formation west of Cook Inlet.

CADOCERAS CATOSTOMA ZONE

This zone is characterized by a fair abundance 

of Cadoceras catostoma Pompeckj and Lilloettia 

buckmani (Crickmay). Associated but less common 

ammonites include C. glabrum Imlay, all species of 

C. (Paracadoceras) , and all species of Lilloettia except L. stantoni Imlay. These ammonites range 

through all or most of the lower five-sixths of the 

Tonnie Siltstone Member of the Chinitna Formation 

west of Cook Inlet (fig. 2), apparently range through 

most of the Chinitna Formation in the Talkeetna 

Mountains (figs. 4 and 5), and all except Paracadoceras occur in the lower member of the Shelikof 

Formation on the Alaska Peninsula (fig. 6).

INISKINITES INTERMEDWS SUBZONE

The lower part of the Cadoceras catostoma Zone 

is herein recognized as a subzone characterized by 

Iniskinites intermedium (Imlay). This subzone marks 

the top of the ranges of Parareineckeia and of the 

new genus Iniskinites. It also marks the top of the 

range of Xenocephalites, except for one specimen 

(USGS Mesozoic loc. 22434) from near the middle 

of the Paveloff Siltstone Member of the Chinitna 

Formation. Characteristic species other than those 

described under Iniskinites probably include Kepplerites (Seymourites) alticostatus Imlay, K. (S.) 

chisikensis Imlay, K. (S.) abruptus (McLearn), K. 

snugharborense (Imlay), Choffatia irregularis (Imlay), and Parareineckeia shelikofana (Imlay). Most 

of these species occur in the lower part of the Tonnie Siltstone Member of the Chinitna Formation 

west of Cook Inlet (fig. 2). Two of the species occur 

in the lower half of the lower member of the Shelikof Formation on the Alaska Peninsula (fig. 6). 

Iniskinites in the Talkeetna Mountains occurs a little below the middle of the upper member of the 

Chinitna Formation exposed northwest of Limestone 

Hills and ranges through the lower member into 

the basal part of the upper member of the formation exposed between Limestone Hills and Horn 

Mountains.

AGES AND CORRELATIONS

The only ammonites from the Chinitna and Shelikof Formations that are useful for dating and correlating with faunal sequences in Europe and East 

Greenland are Cadoceras, C. (Paracadoceras), C. 

(Stenocadoceras), Kepplerites, and Pseudocadoceras. 

Their ranges in those areas, as shown in figure 7, 

are based partly on the studies of Callomon (1955,
JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

NORTH LITTLE OSHETNA RIVER

ON SOUTH SIDE WEST OF

CONGLOMERATE CREEK

NORTHWEST OF LIMESTONE HILLS

IN HEADWATERS OF 

LITTLE NELCHINA RIVER

NAKNEK FORMATION

CHINITNA

FORMATION

UPPER

MEMBER

LOWER 

MEMBER

UNNAMED BEDS 

TUXEDNI GROUP

UPPER PART

(CRANOCEPHALITES BEDS)

TALKEETNA

FORMATION

0-800 feet

Siltstone,

thick-bedded;

limestone 

concretions

Some thin

beds of

sandstone

near base

0-100 feet 

Conglomerate, 

sandstone^and

s wtstooe / 

650 feet

Sandstone, 

thick-bedded; 

some

conglomerate

Lower part

has coaly

beds, fossil

plants,

siltstone, and

claystone

Volcanic

rocks

/V\A

3-4 MILES

} 24796

- 26727, 24795

\ 

\

750 feet

Siltstone

and shale;

limestone 

concretions

 lODfeet Conglomerate 

and sandy 

v siltstone /

1200 feet

or more

Sandstone 

and siltstone, 

medium- to

thick-bedded

Upper part 

has some

conglomerate

8-10

^24*04,24139, 

^ 24797, 24798

24140

/ 30285, 24 141, 

^24142

V 30284 

L 24805, 24144, 

f 24800, 24799 

>- 24146

^ 30283

- 24145

 24801

- 30282 

-24818

?

\

\

TUXEDNI GROUP 

LOWER PART

FIGURE 3. Stratigraphic positions of ammonite localities in the Chinitna Formation of the Nelchina area in the southeastern

many localities are estimations
FLAT CREEK AND SHEEP

CREEK AREAS 

NORTH OF CARIBOU FAULT

AGES AND CORRELATIONS

WEST END OF

HORN MOUNTAINS

NORTH OF CARIBOU FAULT

9 

SOUTH

MILES

1000 feet

Siltstone 

and shale; 

limestone 

concretions 

and thin 

beds of 

sandstone

1500 feet 

or less

Sandstone 

and siltstone

Sandstone

8 MILES

--24224,24816

25354 

+ 25308

24806

"I 25310, 24809 

24151 

25356 

25341,25338,25348. 25585

 25337

-h 25355

25584,25340, 25357, 

24811, and 24815

1300 feet 

or more

Siltstone 

and shale; 

limestone 

concretions 

and thin 

beds of 

sandstone

Base poorly 

exposed 

and possibly 

faulted

Mostly 

sandstone

AAA

 24135,28757

TUXEDNI GROUP 

LOWER PART

--24793

part of the Talkeetna Mountains. Data furnished by Arthur Grantz (written commun., 1972); stratigraphic positions of 

because of poor or faulted exposures.
10 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

Unit

Genus and species

Chinitna Formation

Lower 

member

Upper member

Phylloceras (Cattiphyttoceras) freibrocki Imlay _____

(Partschiceras)grantzi Imlay _______

cf. P. (P. ) grantzi Imlay _______

Oppelia (Oxycerites)chinitnana Imlay ________

Littoettia buckmani (Crickmay) __________

Iniskinitesintermedtus (Imlay)___________

sp ________ _ ______

Chinitnites chinitnaensis Imlay, n. sp _ _ ______

Cadocerascatostoma Pompeckj___________

comma Imlay_______________

glabrum Imlay ______________

tenuicostatum Imlay_____ _______

wosnessenskii (Grewingk) _________

kialagvikense Imlay ____________

(Paracadoceras) multiforme Imlay ______

tonniense Imlay___________

Pseudocadoceras grewingki (Pompeckj) _ _ _ _ _

Kepplerites (Seymourites) cf. K. (S. ) alticostatus Imlay

FIGURE 4. Stratigraphic ranges of ammonites in the Chinitna Formation northwest of Limestone Hills in the Talkeetna

Mountains.

p. 255. 1964, p. 274-281). The ranges of the subgenera Stenocadoceras and Paracadoceras are 

based, however, on the ranges of species that have 

been assigned to those subgenera by the writer (Imlay, 1953b, p. 44, 46).

Thus, under C. (Paracadoceras), C. (P.) elatmae 

(Nikitin) (1881b, p. 116, pi. 11, figs. 20, 21, 23) in 

the U.S.S.R. is associated with Chamoussetia, which 

is characteristic of the lower part of the calloviense 

zone (Sazanov, 1964, p. 797). C. (P.) breve Blake 

(1905-07, p. 48, pi. 5, fig. 1) in England occurs in 

the macrocephalus zone (Callomon, 1964, p. 273; 

Arkell, 1956, p. 27). C. (P.) ammon (Spath) 

(1932, p. 78, pi. 21, figs. 5a, b) in East Greenland 

is recorded with other ammonites (Spath, 1932, p. 

126) that Callomon (1959, p. 507-511) placed partly

in the highest Bathonian and partly in the lowest 

Callovian.

Callomon's Bathonian assignment of such ammonites as Cadoceras (P.) variabile Spath and C. calyx 

Spath is based entirely on their stratigraphic position below beds that he correlated faunally with the 

basal Callovian of Europe. This assignment seems 

reasonable but needs to be substantiated by descriptions and illustrations of the GreenLmd ammonites 

that represent the basal Callovian.

Under the subgenus C. (Stenocadoceras), C. (S.) 

milaschevici (Nikitin) (1881a, p. 66, pi. 3, fig. 25) 

in Siberia occurs in beds of middle Callovian Age 

(Sachs, 1964, p. 770) ; in the Russian Platform it 

occurs in beds that are correlated with the jason 

zone (Sazonov, 1964, p, 793) ; and in western Europe
AGES AND CORRELATIONS 11

Unit

Genus and species

Chinitna Formation

Lower member Upper member

Phylloceras (Calliphylloceras) freibrocki Imlay _.

(Macrophylloceras) grossicostatum Imlay . 

Oppelia (Oxycerites) sp ___________

Lilloettia buckmani (Crickmay) ________

Xenocephalites cf. X. hebetus Imlay ______

vicarius Imlay ____________

Iniskinitesabruptus (Imlay) _________.

cf./. abruptus (Imlay) _________

intermedius (Imlay) __________

cf. /. intermedius (Imlay) ________

sp _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _.

Cadoceras catostoma Pompeckj ________

(Paracadoceras) moffiti Imlay _ _ _ __. _.

(Stenocadoceras) multicostatum Imlay _. 

Pseudocadoceras grewingki (Pompeckj) _____ 

Kepplerites (Seymourites) ingrahami (McLearn) .

(S. ) cf. K. (S.) ingrahami McLearn _ _ _. 

mcevoyi (McLearn) _______

sp ___ ____ 

cf. K. lindgreni (Hyatt) ________.

sp ______ ______ _.

FIGURE 5. Stratigraphic ranges of ammonites in the Chinitna Formation between Limestone Hills and Horn Mountains in

the Talkeetna Mountains.

it occurs in the coronatum zone (Callomon, 1964, p. 

279). A similar or possibly identical species was 

reported from the upper part of the calloviense zone 

in Yorkshire (Arkell, 1956, p. 26). In addition, C. 

(S.) stenolobum (Keyserling) (1846, p. 329, pi. 20, 

fig. 7, pi. 22, figs. 13, 14) in the Russian Platform 

occurs in beds that are correlated with the athleta 

zone of western Europe (Sazonov, 1964, p. 793).

Cadoceras (Cadoceras) in western Europe ranges 

from at least the base of the calloviense zone through 

tine jason zone (Callomon, 1955, p. 255; 1964, p. 273, 

275, 278). It is probably represented also in the 

Russian Platform by C. tchefkini (d'Orbigny) 

(1845, p. 439, pi. 35, figs. 10-15) in association with 

Erymnoceras coronatum and other ammonites of the 

coronatum zone (Sazonov, 1964, p. 797). In Greenland, C. (Cadoceras) occurs partly in beds that correlate faunally with the basal Callovian of Europe 

and partly in underlying beds that are tentatively 

assigned by CaJlomon (1959, p. 508, 509) to the 

highest Bathonian on the basis of stratigraphic position.

The genus Pseudocadoceras in western Europe is 

most common in the calloviense zone but ranges upward through the remainder of the Callovian (Callomon, 1964, p. 275-281). In the Russian Platform 

it is reported from beds of early to middle Callovian 

Age, including the macrocephalus zone (Sazanov, 

1964, p. 797).

The genus Kepplerites in western Europe ranges 

through the macrocephalus and calloviense zones 

(Callomon, 1964, p. 274, 275). In East Greenland
12 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

Unit

Genus and species

Shelikof Formation

Lower member Middle member Upper member

Phyttoceras (Calliphylloceras) freibrocki Imlay _

Oppelia (Oxycerites) sp __________

Ulloettia buckmani (Crickmay) _____ _

mertonyanvoodi Crickmay __ _ _ _ _

Moetensis Crickmay _ _._ _ __ _ _..

stantoni Imlay ___________

Iniskinitesabruptus (Imlay) _________

intermedtus (Imlay) -

Cadoceres catostoma Pompeckj _______

cf. C catostoma Pompeckj _ _ _ . 

comma Imlay _ _ _ _ __ ______

giebrum Imlay ___________

batttompholum Imiay ________

tenuicoitatum Imlay __________

doroschini (Eichwald) ________

wosnessenskii (Grewingk) _______

toalagvikense Imlay _________

(Stenocadocerss) multicostatum Imlay _. 

.(5.) iniskinense Imlay ________

stenoloboide (Pompeckj) _ _ _.

Pstudocadoceres petelini (Pompeckj) _ _ _ _.

erewingki (Pompeckj) ________

crasacostatum Imlay _________

schmidti f Pompeckj) ________.

Keppterites (Seymourites) ingrahami (McLearn).

(5.) plenus (McLearn) ________.

chisikensii Imlay, n. sp _ _ __.

Parareineckeia shetikofana (Imlay) _ _ _ .

 (Reworked concretions)

FIGURE 6. Stratigraphic ranges of ammonites in the Shelikof Formation between Puale Bay and Wide Bay,

Alaska Peninsula.

it is recorded from beds that contain ammonites 

typical of those zones, but it occurs also in underlying beds that are assigned to the upper Bathonian 

on the basis of stratigraphic position (Callomon, 

1959, p. 507-509). The lowest occurrence of Kepplerites in East Greenland is in the upper part of

the range of Arcticoceras, just below the lowest 

occurrence of Cadoceras (J. H. Callomon, oral 

commun., 1972).

If the ranges of these ammonites in Europe and 

East Greenland (fig. 7) are approximately the same 

as in Alaska (figs. 2, 4-6), then the Chinitna and
AGES AND CORRELATIONS 13

Genera and subgenera

CadoTfrwt

(foracodoctrm)

(Stenocadocena) _

PsfttdocodocfMS

Kepplerites

Bathonian

7-

7 .

Callovian

Lower

g 

8 

|

§ 

1 

j

calloviense Sigaloceras zone

Middle

jason Kosmoceras zone

Erymnoceras coronatum zone

Upper

Peltoceras athleta zone

Quenstedtoceras lamberti zone

FIGURE 7. European and East Greenland ranges of certain Jurassic ammonites present, or possibly present, in Alaska.

Shelikof Formations should be equivalent to at least 

the middle Callovian as well as the upper part of 

the lower Callovian (fig. 8). The athleta zone of 

the basal upper Callovian might also be represented 

by the upper 150-200 feet of the Chinitna Formation above the range of Cadoceras proper (fig. 2), 

although positive fossil evidence is lacking. In descending order, the coronatum and jason zones of 

the middle Callovian would then be represented by 

most of the upper half of the Paveloff Siltstone 

Member of the Chinitna Formation above the range

of Kepplerites and below the highest occurrence of 

Cadoceras. Likewise, the upper part of the calloviense zone would be represented by the lower half 

of the Paveloff Siltstone Member and by the upper 

fourth of the Tonnie Siltstone Member above the 

highest occurrence of C. (Paracadoceras). Finally, 

the lower part of the calloviense zone would be represented by all or only part of the remainder of the 

Tonnie Siltstone Member.

Evidently, the exact age of the basal few hundred feet of the Chinitna Formation is not now
14 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

Stages

Alaska Peninsula 

(Puale Bay to 

Wide Bay)

Iniskin Bay

to 

Tuxedni Bay

Talkeetna 

Mountains

Characteristic ammonites

in 

southern Alaska

o.

D

C Shelikof 

Formation

1 

o.

D

B

Upper 

member

Middle 

member Chinitna 

Formation

Lower 

member

Paveloff 

Siltstone 

Member

Not identified

Cadoceras (Stenocadoceras) stenoloboide

Tonnie 

Siltstone 

Member

Chinitna 

Formation

Cadoceras catostoma

Bowser 

Formation

Unnamed 

beds

Iniskinites intermedms 

 ? 

Kepplerites sp.

Not identified 

 ? 

Arctocephalites cf. A. elegans 

________ 7 

Cranocephalites sp. 

 7 _____

Cranocephalites costidensus

FIGURE 8. Correlation of Callovian formations and faunas in southern Alaska.

determinable by the fossils found therein. In particular, the specimens formerly assigned to the subgenus Kepplerites (Gowericeras) by Imlay (1953b, 

p. 99, 100, pi. 53, figs. 6-11) are of little age significance because they do not show certain features 

characteristic of that subgenus (Donovan, 1953, p. 

132; 1957, p. 135). Nonetheless, the basal beds could 

be older than the calloviense zone and even as old 

as the latest Bathonian provided that the earliest 

occurrences of Cadoceras and Paracadoceras in East 

Greenland are actually latest Bathonian as proposed 

by Callomon (1959, p. 507-509).

The basal part of the Chinitna Formation, regardless of its exact age, is probably equivalent to beds 

in East Greenland that contain the lowest occurrences of Cadoceras and Paracadoceras because in 

both areas the underlying beds in the Bowser Formation contain Kepplerites without Cadoceras. 

Furthermore, these beds are underlain in turn by 

Arctocephalites and then by Cranocephalites. The

main difference is the absence to date of any specimens of Arcticoceras between Arctocephalites and 

Cadoceras in southern Alaska. The Arcticoceras beds 

could, however, be represented in the Red Glacier 

area west of Cook Inlet by 360-380 feet of beds 

above an occurrence of Arctocephalites (USGS 

Mesozoic loc. 22699). They could also be represented 

in part by an erosional unconformity between the 

Bowser and Chinitna Formations in that area (Detterman and Hartsock, 1966, p. 40, 42, pi. 5).

None of the age assignments made in the preceding discussion is based on the presence of Cosmoceras. For example, the specimen formerly described 

as C. (C.) cf. C. (C.) spinosum (Sowerby) (Imlay, 

1953b, p. 100, pi. 53, figs. 4, 5), obtained as float 

near the middle of the Paveloff Siltstone Member, 

probably represents an immature form of Kepplerites gitinsi McLearn. Donovan (1957, p. 136) assigned it to Torricelliceras, which Callomon (1955, 

p. 235, 238) considered to be a microconch of Kep-
AMMONITE FAUNAL SETTING 15

plerites. Similarly, the type specimens of C. (Gulielmiceras) alaskanum Imlay (1953b, p. 100, pi. 49, 

figs. 13-19) are identical in shape and ribbing with 

the inner whorls of K. ingraha/mi (McLearn), and 

the holotype is evidently a microconch of that 

species.

AMMONITE FAUNAL SETTING

The Callovian ammonites of southern Alaska 

(Imlay, 1953b, p. 54-57; 1965, p. 1031) are dominated by genera characteristic of the Boreal realm, 

such as Kepplerites, Cadoceras, and Pseudocadoceras, but include several genera characteristic of 

the Pacific realm, such as Xenocephalites, Lilloettia, 

and Parareineckia. They also include two new genera, Iniskinites and Chinitnites, which to date are 

known only from southern Alaska. On the specific 

level, the Callovian ammonites of southern Alaska 

have a great deal in common with ammonites of 

that age in British Columbia (McLearn, 1929, p. 

4-12), Oregon (Imlay, 1964, p. D10-D15), and 

northern California (Imlay, 1961, p. D9-D11, D19- 

D21), and nothing in common specifically with the 

western interior of North America (Imlay, 1953a; 

Frebold, 1957, p. 19, 56-65) and Arctic Canada 

(Frebold, 1961, p. 17-22, 28-29; 1964, p. 6-18, 22- 

24). In contrast, some of the Callovian species of 

Cadoceras from Arctic Canada are closely similar 

to, or possibly identical with species in East Greenland (Frebold, 1964, p. 24). Evidently, southern 

Alaska during Callovian time was part of a Pacific 

Coast faunal province, and that province had some 

marine connections with Canada and northern 

Alaska through Yukon Territory and British Columbia, as discussed by Imlay and Detterman (1937, p. 

18, fig. 5).

GEOGRAPHIC DISTRIBUTION

Nearly all the ammonite localities described or 

mentioned herein from the Chinitna Formation west 

of Cook Inlet and from the Shelikof Formation on 

the Alaska Peninsula have been previously published 

in three U.S. Geological Survey professional papers 

(Imlay, 1953b, p. 65-71, figs. 4-9; 1962, p. C3, C16, 

C17; Detterman and Hartsock, 1966, p. 44-46, pi. 

3). The exception is USGS Mesozoic locality 3027, 

which is at the same spot as USGS Mesozoic localities 2920 and 20755 (Imlay, 1953b, p. 68, fig. 7). 

The species occurrences from the Chinitna Formation in the Talkeetna Mountains are listed in table 

2. The position of the fossil localities are shown in 

figure 9 and are described in detail in table 3.

SYSTEMATIC DESCRIPTIONS

Family Kosmoceratidae

Genus KEPPLERITES Neumayr and UUig, 1892 

Subgenus SEYMOURITES Kilian and Reboul, 1909

Kepplerites (Seymourites) chisikensis Imlay, n. sp.

Plate 1, figures 1-5

Kepplerites (Seymourites) tycjionis (Ravn.) Imlay, 1953b, 

U.S. Geol. Survey Prof. Paper 249-B, p. 96, pi. 48, figs. 

14, 17.

This species is represented in available collections by two specimens which show the body whorl 

and parts of the outer two septate whorls. The 

largest specimen has been crushed laterally on its 

right side.

Shell moderately compressed. Whorls subquadrate, 

higher than wide, widest at about one-third of 

height. Flanks flattened below, converging gently 

above to a moderately rounded venter, rounding 

rather abruptly into umbilicus on septate whorls. 

Umbilicus very small on septate whorls, but enlarging markedly on body chamber. Umbilical wall vertical on septate whorls, becoming gently inclined 

adorally on adult whorl. Body chamber occupies 

slightly more than half a whorl and becomes contracted adorally. Aperture marked on internal mold 

by a forwardly inclined constriction that is followed 

by a low swelling.

The ribs on the next-to-the-largest septate whorl, 

partially exposed on the broken right-hand side of 

the holotype (pi. 1, fig. 1), are fine, closely spaced, 

and incline gently forward on the flanks. Secondary 

ribs outnumber primary ribs about three to one and 

arise mostly from the swollen to weakly tuberculate 

ventral ends of the primary ribs.

The ribs on the outermost septate whorl remain 

fine and closely spaced but become higher and 

sharper adorally. They incline forward rather 

strongly on the flanks and cross the venter transversely. Primary ribs are slightly swollen ventrally 

but do not bear tubercles. On the outermost septate 

whorl, secondary ribs outnumber the primary ribs 

nearly four to one.

Similar ribbing persists adorally on the body 

chamber except near the aperture, where secondary 

ribs outnumber primary ribs only about three to 

one. On the holotype, the ribbing does not appear to 

be so sharp on the body chamber as on the septate 

whorls owing to corrosion of shell material. On the 

paratype, by contrast, the few fragments of body 

whorl that are preserved bear sharp primary ribs.

The suture line is not well preserved.

The paratype near the adoral end of its outer
16 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

TABLE 2. Geographic distribution of ammonites in the

[Numbers 1-40 are keyed to locality numbers in figure 9.

Species

Imlay.

Imlay.

Xt sp - 

(Paraeadoceras) moffiti Imlay ______

(Stenocadoceraa) multicoatatum Imlay.

alticostatus Imlay.

cf. K. (S.) ingrahami ( McLearn )_

spinosua (Imlay) _ _________ _

snuaharborensis (Imlay) _ _

cf. K. lindgreni (Hyatt) ____ _______

Parareineckeia ahelikofana (Imlay)

1

StS

v

2

10 te> N t- t- <* <o

IN N

X V

3

"* IO N CO « * IO 

O O 00 00 00 00 

OO OO N N N N

 ** ** o o o o

N N CO CO CO CO

X V

v

v

X V V V

4

 <* <*

T-t S

v

v

6

§

i

v

6

CO <* 

 <*

N

7

00 

00 <*

N

v

v

8

0 0

o o

t- 00

CO * 

N

v

9

ia to 1-1 ** ** o

T-t T-t OO * «* *

N N N

v

10

O T-I <N **** * 

t-) r-l rH 

"* -* -* 

N N N

 X X

11

§ § 00 00 -* -*

N N

X -

12

c» 

c»t- <*

N

X

13

t- 00

e» c» t- t- rf -* 

<N IN

 X

X 

septate whorl has a diameter of 96 mm (millimeters), a whorl height of 51 mm, a whorl thickness of 43 mm, and an umbilical width of 12 mm. 

Adorally, the umbilicus widens rapidly and is 14 

mm in width at a diameter of only 100 mm.

This species is characterized by a moderately compressed shell, by an umbilicus that is small on the 

septate whorls but enlarges markedly on the body 

chamber, by fine dense ribbing, and by the ventral 

ends of its primary ribs being swollen to weakly 

tuberculate on its inner whorls and only swollen on 

its outer whorls.

Kepplerites chisikensis Imlay, n. sp., was previously identified (Imlay, 1953b, p. 96) with K. 

tychonis Ravn (1911, p. 490, pi. 37, figs, la, b) from 

East Greenland because of resemblances in form, 

coiling, and ribbing. The holotype of K. tychonis 

Ravn (see pi. 5f fig. 4 and pi. 6, fig. 6, of this report) 

differs, however, by having a wider umbilicus on its 

septate whorls, a less eccentric body chamber, a 

stouter whorl section, and shorter primary ribs that

become weaker instead of stronger on the adult body 

chamber. Another specimen from Greenland, described as K. tychonis Ravn var. fasciculata Spath 

(1932, p. 86, pi. 26, fig. 6), resembles the Alaskan 

species more closely in coiling and whorl shape but 

differs by having shorter and weaker primary ribs 

that bear weak but distinct tubercles on the body 

chamber.

The Alaskan species does not include a small specimen from USGS Mesozoic loc. 20755, as previously 

suggested (Imlay, 1953b, p. 96). That specimen has 

sparser primary ribs that terminate in weak tubercles and shows considerable resemblance to the inner 

whorls of K. ingrahami (McLearn). It also resembles Cosmoceras (Gulielmiceras) alaskanum Imlay 

(1953b, p. 100, pi. 49, figs. 13-16), which is probably 

the microconch of K. ingrahami (McLearn).

Types. Holotype, USNM 180717; paratype, 

USNM 108125.

Occurrences. Shelikof Formation at USGS Mesozoic loc. 19793 northwest of Wide Bay on the Alaska
SYSTEMATIC DESCRIPTIONS 17

Chinitna Formation of the Talkeetna Mountains, Alaska

Higher numbers are USGS Mesozoic locality numbers]

14

s

 **

N

X

15

iHto

iH 

^* 

<N

X

16

* s >°

eo £ to 

eo «5 eo

10 ^ to 

N N N

 X 

17

iH

3to

N

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Peninsula; Chinitna Formation at USGS Mesozoic 

loc. 21287 on Chisik Island in Cook Inlet region.

The holotype from the Wide Bay area was collected 

500 feet above the base and 2,400 feet below the top 

of the Shelikof Formation in association with K. 

ingrahami (McLearn), K. plenum (McLearn), 7mskinites abruptm (Imlay), /. intermedium (Imlay), 

and Cadoceras glabrum Imlay.

The paratype from Chisik Island was collected 

about 80 feet above the base and 850 feet below the 

top of the Tonnie Siltstone Member of the Chinitna 

Formation. This occurrence is a little above the 

middle of the range of Iniskinites intermedius (Imlay) and 100 feet or less, stratigraphically, above 

K. snugharborensis (Imlay), Xenocephalites hebetus 

Imlay, and Choffatia irregularis (Imlay) at USGS 

Mesozoic loc. 3015. Its occurrence in or near the 

lower part of the range of K. ingrahami (McLearn) 

is shown by the presence of that species (USGS 

Mesozoic loc. 12074) in the lower third of the Chinitna Formation on Chisik Island. It is shown, also,

by some small ammonites (USGS Mesozoic Iocs. 

2920 and 20755), probably representing the inner 

whorls of K. ingrahami (McLearn), which were 

obtained 50 to 100 feet above the base of the formation on the east shore of Iniskin Bay.

Family CARDIOCERATIDAE Siemiradzki, 1891 

Subfamily CADOCERATINAE Hyatt, 1900

Genus CHINITNITES Imlay, n. gen.

Chinitnites is characterized by small compressed 

to stout shells; a very small umbilicus on septate 

whorls; a contracted adult body chamber that occupies about half a whorl; an apertural constriction 

that is conspicuous only low on the flanks; and sharp 

flexous ribs that arch gently forward on the venter. 

Some ribs fork fairly low on the flanks, and others 

remain simple or alternate with short ribs All ribs 

become stronger and more widely spaced centrally 

and adorally except for one or two ribs next to the 

adult aperture. The suture line bears lobes and saddles of nearly equal width and a fairly long first
18 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

148°30' 148-00 147-30' 147"00'

62" 15'

62"00'

61 45'

FIGURE 9. Index map of listed fossil localities in the Chinitna Formation in the Talkeetna Mountains. Detailed descriptions of localities are given in table 3.

lateral lobe that is nearly as long as the ventral lobe. 

Its overall plan is similar to that on some specimens 

of Cranocephalites (Spath, 1932, pi. 3, fig. 5, pi. 5, 

fig. 8) but shows no simplification such as occurs 

in adults of that genus (Spath, 1932, pi. 1, fig. 6, 

pi. 4, fig. 8). The suture line is likewise similar to 

but less complicated that that of Arctocephalites 

(Spath, 1932, pi. 11, fig. 7b). Chinitnites chinitnaensis (Imlay), described herein, is designated as the 

type species.

Chinitnites differs from Xenocephalites by having 

a wider umbilicus on its septate whorls, an apertural 

constriction, lower and less widely spaced ribs on 

its body chamber, and a smaller adult size. It shows 

much more resemblance to Cranocephalites (Spath, 

1932, p. 14-16; Donovan, 1953, p. 78, 130, 133) but

differs by being much smaller, by its apertural constriction being more conspicuous low on the flanks, 

and by its ribs on the venter of the adult body whorl 

becoming high and sharp instead of low or slightly 

reduced in strength along the midline of the venter. 

Arctocephalites'! alticostatus Imlay (1962, p. C22, pi. 

2, figs. 1-8) is not assigned to Chinitnites because 

the ribs on its inner septate whorls are higher and 

sharper, and its adult body chamber does not contract from the inner whorls.

Chinitnites occurs north of Cook Inlet in the upper 

part of the Bowser Formation and in the lower part 

of the Chinitna Formation. Its highest occurrences 

are of early Callovian Age. Its lowest occurrences 

could be of late Bathonian Age.
SYSTEMATIC DESCRIPTIONS 19

TABLE 3. Descriptions of Jurassic ammonite localities in the Chinitna Formation in the Talkeetna Mountains, Alaska

uses

Loc. No. Mesozoic Collector's 

(fig. 9) loc. No. field No.

Collector, year of collection, description of locality, and stratigraphic assignment 

(VABM indicates vertical angle elevation bench mark)

1 24796 53AGz217 ____ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. Lat

62°10'23" N., long 147°43'15" W. Chinitna Formation, in siltstone near top of 

upper member.

2 24795 53AGz209 ______ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. Lat

62°10'00" N., long 147°40' W. Chinitina Formation, float from near top of 

upper member which is about 800 ft thick.

2 26727 57AGzllW _____ Arthur Grantz, 1957. Talkeetna Mountains (A-2) quad. Bedrock at same place as

USGS Mesozoic loc. 24795. Chinitna Formation, in siltstone 650 ft above base 

of upper member which is about 800 ft thick.

3 24804 53AGz262 ______ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. Lat

62°07'43" N., long 147°41'56" W. Chinitna Formation, near top of upper 

member.

3 24805 53AGz263 Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. From lat

62°07'33" N., long 147°42'03" W. to a point 550 ft upstream. Probably equivalent to USGS Mesozoic Iocs. 30283-30285. Chinitna Formation, upper third of 

upper member.

3 30282 72ADtl4*l R. W. Imlay and R. L. Detterman, 1972. Talkeetna Mountains (A-2) quad. In same

gulch as USGS Mesozoic loc. 24805, but probably lower; 2.3 miles N. 47° W. of 

junction of Cadoceras Creek and Little Nelchina River. Lat 62°07'45" N., long 

147°42' W. SW% sec. 31, T. 24 N., R. 10 E. Chinitna Formation, upper member, about 500 ft stratigraphically below faulted top in interbedded sandstone 

and siltstone.

3 30283 72ADtl4*2 R. W. Imlay and R. L. Detterman, 1972. Talkeetna Mountains (A-2) quad. In same

gulch as USGS Mesozoic loc. 30282. Chinitna Formation, upper member about 

325 ft stratigraphically below top.

3 30284 72ADtl4*3 R. W. Imlay and R. L. Detterman, 1972. Talkeetna Mountains (A-2) quad. In same

gulch as USGS Mesozoic loc. 30282. Chinitna Formation, upper member, about 

250 ft stratigraphically below top.

3 30285 72ADtl4*4 R. W. Imlay and R. L. Detterman, 1972. Talkeetna Mountains (A-2) quad. In same

gulch as USGS Mesozoic loc. 30282. Chinitna Formation, upper member about 

200 ft below top.

4 24144 52AGzl64 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. North Branch of Little Nelchina River, 3.96 miles west of main headwater fork. Chinitna Formation, upper third of upper member.

5 24139 52AGzl57 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. North branch Little Nelchina River, 2.53 miles west of main headwater 

fork. Chinitna Formation, near top of upper member.

6 24143 52AGzl61 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. North branch of Little Nelchina River, 2.74 miles west of main headwater fork. Chinitna Formation, upper half or perhaps middle third of upper 

member.

7 24818 53AGz260A Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. Lat

62°07'15" N., long 147°40'00" W. Chinitna Formation, 325 ft above base of 

upper member which is here about 750 ft thick.

8 3700 6AK156 Adolf Knopf, 1906. Talkeetna Mountains (A-2) quad. Near headwaters of Little

Nelchina River, about 10 miles N. 10° E. of mouth of Billy Creek at altitude 

of 5,000 ft. Float from Chinitna Formation.

8 24800 53AGz255 Arthur Grantz, 1953. Talkeetna Mountains (A-2). quad. Lat 62°06'32" N., long

147°40'01" W. Chinitna Formation, upper third of upper member.

9 24145 52AGzl66 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. On small tributary of Little Nelchina River, 0.99 mile S. 65y2 0 W. of main 

headwater fork. Chinitna Formation, 380 ft above base of upper member which 

is about 750 ft thick.

9 24146 52AGzl67 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. On small tributary of Little Nelchina River, 0.93 mile S. 62%° W. of 

main headwater fork. Chinitna Formation, 450 ft above base of upper member 

which is about 750 ft thick.
20 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

TABLE 3. Description of Jurassic ammonite localities in the Chinitna Formation in the Talkeetna Mountains,

A laska Continued

uses

Loc. No. Mesozoic Collector's 

(fig. 9) loc. No. field No.

Collector, year of collection, description of locality, and stratigraphic assignment

9 24801 53AGz256 ____ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. Lat

62°06'32" N., long 147°40'01" W. Chinitna Formation, 325 ft above base of 

upper member which is about 750 ft thick.

10 24140 52AGzl58 ___ Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. On small tributary of Little Nelchina River, 0.74 mile S. 53° W. of main 

headwater fork. Chinitna Formation, 700 ft above base of upper member which 

is about 750 ft thick.

10 24141 52AGzl59 ____ Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. On small tributary of Little Nelchina River, 0.83 mile S. 58^° W. of 

main headwater fork. Chinitna Formation, 550 ft above base of upper member 

which is about 750 ft thick.

10 24142 52AGzl60 ___ Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-2)

quad. On small tributary of Little Nelchina River, 0.81 mile S. 56° W. of main 

headwater fork. Chinitna Formation, 550 ft above base of upper member which 

is about 750 ft thick.

11 24802 53AGz257 Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. On small

tributary of Little Nelchina River. Lat 62°06'13" N., long 147°41'39^" W. 

Chinitna Formation, middle or upper third of upper member.

11 24803 53AGz258 ___ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. On small

tributary of Little Nelchina River. Lat 62°06'15" N., long 147°42'10" W. 

Chinitna Formation, upper half of upper member.

12 24799 53AGz251 ___ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2). About % mile

south of Little Nelchina River and 2 miles east of main headwater fork. Lat 

62°07'23%" N., long 147°34'24" W. Chinitna Formation, upper member.

13 24797 53AGz248 __ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. On south

side of Little Nelchina River. Lat 62°07'24}&" N., long 147°33'22"y2 W. 

Chinitna Formation, near top of upper member.

13 24798 53AGz249 ___ Arthur Grantz and L. F. Fay, 1952. Talkeetna Mountains (A-2) quad. On south

side of Little Nelchina River. Lat 62°07'261/4" N., long 147°33'16" W. Chinitna 

Formation, near top of upper member.

14 24184 52AGzl05 ____ Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Talkeetna Mountains (A-l)

quad. On north tributary that enters Little Nelchina River 1 mile west of 

mouth of Flat Creek, 1.08 miles S. 10° E. of VABM 1 Wal (4,610 ft). From 

reworked concretions in basal part of Cretaceous shales overlying the Nelchina 

Limestone. Concretions derived partly from the Chinitna Formation and partly 

from the Naknek Formation.

15 24151 52AHr22 R. D. Hoare, 1952. Talkeetna Mountains (A-l) quad. North bank of Little Nelchina

River, 2.47 miles S. 27° W. of VABM Wal (4,610 ft). Chinitna Formation, near 

base of upper member.

16 25337 54AGzl56 Arthur Grantz,, 1954, Talkeetna Mountains (A-l) quad. On small tributary about

0.75 mile south of Little Nelchina River. Lat 62°05/37// N., long !47°26/57 1/^ // 

W. Chinitna Formation, 1,300 ft above base of lower member which is here 

about 1,500 ft thick.

16 25354 54AFy87 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. About 1/5 mile southwest of

USGS Mesozoic loc. 25337. Lat 62°05'35" N., long 147°27'20^" W. Chinitna 

Formation, middle third of upper member.

16 25355 54AFy88 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. Near USGS Mesozoic loc. 25337.

Lat 62°05'35" N., long 147°27'03%" W. Chinitna Formation, top of middle 

third of lower member.

17 25341 54Fy22 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. Lat 62°05/04" N., long

147°27'41" W. Chinitna Formation, near top of lower member.

18 25310 54AGz34 Arthur Grantz, 1954. Talkeetna Mountains (A-l) quad. About 2% miles west of

Flat Creek on southeast-flowing tributary. Lat 62°04/39// N., long 147°28'42" 

W. Chinitna Formation, in lower 70 ft of upper member, which is here about 

1,000 ft thick.

19 24806 53AGz275 Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. On Bubb

Creek about 3.25 miles west of junction with Flat Creek. Lat 62°03'59" N., 

long 147°30'24" W. Chinitna Formation, 300 ft above base of upper member, 

which is here about 1,000 ft thick.
SYSTEMATIC DESCRIPTIONS 21

TABLE 3. Description of Jurassic ammonite localities in the Chinitna Formation in the Talkeetna Mountains,

A laska Continued

TJSGS

Loc. No. Mesozoic Collector's 

(fig. 9) loc. No. field No.

Collector, year of collection, description of locality, and stratigraphic assignment

19 24809 53AGz283 ____ Arthur Grantz and L. F. Fay, 1953. Talkeetna Mountains (A-2) quad. About 900

ft southwest of USGS Mesozoic loe. 24806. Lat 62°03'54V2 " N., long 147°30'12" 

W. Chinitna Formation, 0 to 70 ft above base of upper member, which is here 

about 1,000 ft thick.

19 25308 54AGz25 ___ Arthur Grantz, 1954. Talkeetna Mountains (A-2) quad. About 700 ft northwest of

USGS Mesozoic loc. 24806. Lat 62°04'02" N., long 147°30'37" W. Chinitna 

Formation, 450 to 500 ft above base of upper member, which is here about 

1,000 ft thick.

20 25309 54AGz31 ____ Arthur Grantz, 1954. Talkeetna Mountains (A-l) quad. Lat 62°03'31%" N., long

147°29'54" W. Chinitna Formation, 400 ft above base of lower member, which 

is here about 1,500 ft thick.

21 25338 54AGzl57 ____ Arthur Grantz, 1954. Talkeetna Mountains (A-l) quad. About 2 miles west of Flat

Creek near head of southeast-flowing tributary. Lat 62°05'08" N., long 

1470 24/29%// W. Chinitna Formation, near top of lower member.

22 25356 54AFyl22 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. On west side of Flat Creek.

Lat 62°04'04" N., long 147°24'49" W. Chinitna Formation, from top of lower 

member.

23 25584 54AFy89A L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. On west side of Flat Creek

about 2.75 miles above junction with Little Nelchina River. Lat 62°04'22%" N., 

long 147°23'06" W. Chinitna Formation, middle third of lower member.

24 25340 54AFy21 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. On Flat Creek about 4.5 miles

above its mouth. Lat 62°03'22%" N., long 147°25'53" W. Chinitna Formation, 

middle third of lower member.

25 25348 54AFy37 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. About % mile south of Flat

Creek on north-flowing Shovel Creek. Lat 62°03'09" N., long 147°24'54%" W. 

Chinitna Formation, near top of lower member.

26 25357 54AFyl23 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. About 1.5 miles south of Flat

Creek on unnamed north-flowing tributary. Lat 62°03'05" N., long 147°23'08%" 

W. Chinitna Formation, middle third of lower member.

27 25358 54AFyl27 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. About 1.25 miles south of Flat

Creek on north-flowing Placer Creek. Lat 62°03'20" N., long 147°21'25" W. 

Chinitna Formation, probably from top of lower third of lower member.

28 25585 54AFyl06 L. F. Fay, 1954. Talkeetna Mountains (A-l) quad. About 1.20 miles from Flat

Creek on northwest-flowing Meyer Creek. Lat 62°03'43%" N., long 147°19'49" 

W. Chinitna Formation, near top of lower member.

29 25339 54AGz200 Arthur Grantz, 1954. Talkeetna Mountains (A-l) quad. About 2 miles south of Flat

Creek and 0.75 mile south of USGS Mesozoic loc. 25358. Lat 62°02'49" N., 

long 147°22'Q9ty". Chinitna Formation, lower third of lower member.

30 24811 53AFy2 L. F. Fay, 1953. Anchorage (D-2) quad. About 0.4 mile due north of VABM Sheep

(5,462 ft) lat 61°58'34%" N., long 147°42'05" W. Chinitna Formation, middle 

third of lower member.

31 24793 53AGzl56 Arthur Grantz, 1953. Anchorage (D-2) quad. On a northeast-trending fork of

Sheep Creek, 0.4 mile above junction. Lat 61°58'35%" N., long 147°40'15" W. 

Chinitna Formation, near base of lower member.

31 24815 53AGzl58 Arthur Grantz and L. F. Fay, 1953. Anchorage (D-2) quad. About 0.2 mile southsouthwest of USGS Mesozoic loc. 24793. Lat 61°58'27" N., long 147°40'25" W. 

Chinitna Formation, middle third of lower member.

32 8584 35 G. C. Martin, 1913. Anchorage (D-3) quad. North bank of Caribou Creek., 0.1

mile west of east boundary of quadrangle. Chinitna Formation, undivided, 

probably from lower third.

32 24147 52AGzl97 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Anchorage (D-3) quad. North

side of Caribou Creek from 200 to 600 yds east of mouth of Billy Creek. 

Chinitna Formation undivided, probably from lower third.

33 24224 52AGz224 Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Anchorage (D-2) quad. On

ridge between Billy Creek and Sheep Creek, 1,500 ft N. 72° W. of VABM Sheep 

(5,462 ft). Chinitna Formation, probably upper part of middle third of upper 

member.
22 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

TABLE 3. Description of Jurassic ammonite localities in the Chinitna Formation in the Talkeetna Mountains,

Alaska Continued

uses

Loc. No. Mesozoic Collector's 

(fig. 9) loc. No. field No.

Collector, year of collection, description of locality, and stratigraphic assignment

33 24816 53AGz224 ___ Arthur Grantz and L. F. Fay, 1953. Anchorage (D-2) quad. From same spot as

USGS Mesozoic loc. 24224. Chinitna Formation, probably upper part of middle 

third of upper member.

34 24119 52AGzl85 ___ Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Anchorage (D-2) quad. On

Caribou Creek about 2.5 miles west of mouth of Sheep Creek. Chinitna Formation, about 200 ft above base of upper member, which is locally more than 

450 ft thick.

35 24789 53AGz58 ____ Arthur Grantz and L. R. Fay, 1953. Anchorage (D-2) quad. On south side of Caribou

Creek 1.75 miles west of mouth of Sheep Creek. Lat 61°56'44" N., long 

147°43'28" W. Chinitna Formation, undivided lower half south of Caribou fault.

36 24135 52AGz276 ___ Arthur Grantz, R. D. Hoare, and R. W. Imlay, 1952. Anchorage (D-2) quad. 2.56

miles N. 49° E. of mouth of Sheep Creek. Chinitna Formation, about 750 ft 

above base where formation is 1,300 ft thick and where lower 800 ft may 

represent a distal facies of the lower member.

36 28757 63AGzl27 ____ Arthur Grantz, 1963. Anchorage (D-2) quad. About 800 ft northwest of USGS

Mesozoic loc. 24135. Lat 61°57.7' N., long 147°37' W. Chinitna Formation, same 

stratigraphic data as USGS Mesozoic loc. 24135.

37 26951 9-17-OB2 ____ E. R. Orwig, 1957. Anchorage (D-3) quad. 15,700 ft north and 3,100 ft east of

VABM Boulder (6,318 ft). Coordinates 2.63, 13.94 in. Chinitna Formation.

38 8576 25 ________R. M. Overbeck, 1913. Anchorage (D-3) quad. 3,000 ft up creek which enters Boulder

Creek from north at point 5.5 miles above junction of Boulder Creek with East 

Fork, about 3,000 ft upcreek and at altitude of 3,300 ft. Chinitna Formation.

39 8571 20 ___ G. C. Martin, 1913. Anchorage (D-4) quad. Tributary to Boulder Creek from

north, 3 miles above junction of Boulder Creek with East Fork. Float from 

Chinitna Formation.

40 26950 9-17-OB1 ____ E. R. Orwig, 1957. Anchorage (D-3) quad 1,830 ft north and 1,500 ft west of

VABM Boulder (6,318 ft). Coordinates 1.76, 11.3 in. Chinitna Formation.

Chinitnites chinitnaensis Imlay, n. sp.

Plate 2, figures 1-31

This species is represented by 102 specimens of 

which 10 have complete body chambers. Shell small, 

moderately compressed. Whorls depressed ovate, 

much wider than high, widest a little below the 

middle of the flanks, embracing about two-thirds 

of previous whorls except for the body chamber 

which adorally becomes slightly less involute. Flanks 

evenly convex, merging gradually into broadly 

rounded venter. Umbilicus very small but enlarging 

somewhat on body chamber; wall fairly low, vertical at base, rounding evenly into flanks. Body chamber represented by slightly more than half a whorl. 

Aperture marked by a forwardly inclined constriction that is fairly pronounced on the lower part of 

the flanks and disappears on the venter.

Ribs are flexuous, vary considerably in density 

and coarseness, are highest and sharpest on the 

flanks, and adorally gradually become stronger and 

more widely spaced. They curve forward on the 

umbilical wall and on the lower part of the flanks, 

recurve slightly on the upper part of the flanks, and

are transverse or arch gently forward on the venter. 

Some primary ribs remain simple. Others bifurcate 

or are indistinctly connected with secondary ribs at 

about two-fifths of the height of the flanks. In places, 

alternation of simple and short intercalary ribs occurs along the zone of furcation. Secondary ribs outnumber the primary ribs about 2 to 1. Among the 

specimens in hand, 17 represent a finely ribbed 

variant, 14 a coarsely ribbed variant, and the other 

specimens are of intermediate coarseness.

The suture line has a moderately slender first lateral lobe that is essentially as long as the ventral 

lobe. The second lateral lobe is much shorter.

Specimens 

(Pi. 2)

Diameter

Whorl 

height

Whorl Umbilical 

thickness width

Paratype (figs. 19-21)

Paratype (figs. 10-12)

Paratype (figs

Paratype (figs.

13,14) 

5-7) .

Paratype (figs. 2, 3) __ 

Holotype (figs. 27, 29-31)

24

20

16.3

16.4

13

30

9 (0.37) 

9.5 ( .47) 

7 ( .43) 

6.5 ( .40) 

5.5 ( .42) 

12 ( .40)

12.5(0.52)

12.2 ( .61)

10 ( .61)

9 ( .55)

7.8( .60)

17 ( .57)

6.7(0.27) 

5 ( .25) 

4.2 ( .26) 

4 ( .24) 

3.2 ( .25) 

8 ( .27)

This species differs from Chinitnites parviformus 

(Imlay) by having a depressed ovate instead of a 

subquadrate whorl section, fewer secondary ribs
SYSTEMATIC DESCRIPTIONS 23

per primary rib, and slightly to much coarser ribbing.

Types. Holotype, USNM 180725; paratypes, 

USNM 180718-180724 and 180726-180729.

Occurrences. Chinitna Formation at USGS 

Mesozoic Iocs. 21348, 22432, 24139, 24143, 24803, 

24805, and 30283-30285. The fossils at USGS 

Mesozoic Iocs. 21348 and 22432 are from 450-500 

feet above the base of the Tonnie Siltstone Member 

on the Iniskin Peninsula (Detterman and Hartsock, 

1966, p. 45). The other localities are in the upper 

half of the upper member of the Chinitna Formation in the Talkeetna Mountains northwest of Limestone Hills. Associated fossils show that the species 

occurs in the middle part of the range of Cadoceras 

catostoma Pompeckj and C. (Paracadoceras) tonniense Imlay. The occurrences on the Iniskin Peninsula are 150-200 feet higher than the highest occurrences of Chinitnites parviformus (Imlay, 1953b, 

p. 82, pi. 33, figs. 3, 6, 8-10, 12) and are above the 

range of Iniskinites.

Chinitnites parviformus (Imlay)

Plate 3, figures 1, 2, 5-7

Kheraicerasl parviforme Imlay, 1953b, U.S. Geol. Survey 

Prof. Paper 249-B, p. 82, pi. 33, figs. 3, 6, 8-10, 12.

This species is characterized by a subquadrate 

whorl section that is nearly as high as wide; a very 

small umbilicus that enlarges appreciably on the 

adoral part of the adult body chamber; an apertural 

constriction; and sharp flexuous ribs, of which some 

bifurcate fairly low on the flanks and others remain 

simple but may alternate with short ribs along the 

zone of furcation. Body chamber occupies about half 

a whorl instead of five-sixths as stated in the original 

description. Minor variations in coarseness and 

density of ribbing occur among specimens from the 

same locality.

The suture line, partly exposed on one specimen, 

is similar to that on Cranocephalites vulgaris Spath 

(1932, pi. 3, fig. 5).

In addition to the occurrences previously recorded, 

the species is represented by five specimens from 

the upper part of the Bowser Formation. One of 

these (pi. 3, figs, 1, 2), bears ribbing that is a little 

finer than on the holotype but is comparable with 

that on one paratype (Imlay, 1953b, pi. 33, fig. 6). 

The species does not include one small ammonite 

illustrated by Imlay (1962, pi. 1, fig. 7) as Arctocephalites (Cranocephalites) pompeckj (Madsen). 

That ammonite has a somewhat wider umbilicus 

that does not enlarge on the body whorl, and its

primary ribs, as exposed in the umbilicus, are considerably stronger.

Types. Holotype, USNM 108052; paratypes 

USNM 108053a-c; hypotypes, USNM 180734 and 

180735.

Occurrences. Chinitna Formation, west of Cook 

Inlet near Oil Bay, at USGS Mesozoic Iocs. 21334 

and 22427; Bowser Formation at USGS Mesozoic 

Iocs. 11038 and 11042. The species ranges upward 

from about 750 feet below the top of the Bowser 

Formation to 300 feet above the base of the Chinitna 

Formation.

Genus INISKINITES Imlay, n. gen.

Iniskinites is characterized by medium to large, 

fairly stout to globose shells; an extremely small 

umbilicus on septate whorls; an eccentric to hookshaped body chamber that occupies about threefourths of a whorl and becomes depressed near the 

aperture; a deep apertural constriction that becomes shallower ventrally; and low to high, sharp 

to rounded, nearly radial to gently flexuous ribs that 

cross the venter transversely. During growth, the 

ribs become stronger ventrally and adorally, on some 

species become markedly stronger on the adult body 

chamber, and on most species persist to the aperture 

without any reduction in strength. Most primary 

ribs branch into two to four slightly weaker secondary ribs at about the top of the lower third of 

the flanks, but some remain simple or are indistinctly connected with secondary ribs. Short ribs 

occur commonly between pairs or bundles of 

branched ribs. The suture line has very broad saddles and moderately stocky lobes.

Iniskinites ma,gniformus (Imlay) (1953b, p. 79, 

pi. 31, figs. 5-8) is designated as the type species.

Iniskinites differs from the genotypes of Kheraiceras (Arkell, 1952, p. 89; Arkell and others, 1957, 

p. L292, L293) by its inner whorls being less depressed and less spindle shaped, by its body whorl 

being less eccentric or contracted, by its aperture 

being marked by a constriction, by its ribs remaining 

strong or becoming stronger adorally on the adult 

body chamber instead of fading, and by its second 

lateral lobe being stocky and trifid instead of broad 

and bifid.

It differs from Cranocephalites Spath by having 

a smaller umbilicus on its septate whorls, by the 

adult body chamber becoming depressed near the 

aperture, by the ribs on the venter of the body 

whorl tending to become stronger adorally instead 

of weaker, and by its suture line being more complex.
24 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

Iniskinites magniformus (Imlay)

Plate 3, figures 8, 9; plate 4, figures 2, 7, 8

Kheraiceras magniforme Imlay, 1953b, U.S. Geol. Survey 

Prof. Paper 249-B, p. 79, 80, pi. 31, figs. 5-8.

This species has stout inner whorls, globose 

penultimate and body whorls, an extremely small 

umbilicus, a hook-shaped adult body chamber that 

becomes depressed toward the aperture, and a constricted inclined aperture. Its ribs are very fine, 

sharp, and closely spaced on the adapical part of the 

outermost septate whorl (pi. 4, fig. 7). Adorally on 

that whorl and on the body chamber, the ribs gradually become broa.der, more widely spaced, indistinct 

near the umbilicus, and stronger on the venter except near the aperture. The suture line has broad 

saddles, fairly broad lobes, and is finely subdivided, 

The first and second lateral lobes are nearly the same 

length as the ventral lobe.

Types. Holotype, USNM 108047; hypotypes, 

USNM 180736 and 180737.

Occurrences. Chinitna Formation. The holotype 

is from an unknown locality on the east shore of 

Iniskin Bay. The hypotypes, herein figured, are from 

USGS Mesozoic loc. 22431 near Iniskin Bay west of 

Cook Inlet and from USGS Mesozoic loc. 24147 in 

the Talkeetna Mountains. Near Iniskin Bay, the 

species occurs about 400 feet above the base of the 

Chinitna Formation. Associated ammonites show 

that Iniskinites magniformus (Imlay) occurs in the 

middle part of the range of Cadoceras catastoma 

Pompeckj. Some previous records of the species 

(Imlay, 1953b, p. 80) from USGS Mesozoic Iocs. 

22427 and 22448, based on small individuals, are 

probably erroneous.

Iniskinites abruptus (Imlay) 

Plate 5, figures 1-3

Kheraiceras abruptum Imlay, 1953b, U.S. Geol. Survey Prof. 

Paper 249-B, p. 80, 81, pi. 33, figs. 1, 7, 11, 13.

This species has fine dense ribbing on its inner 

whorls as on Iniskinites magniformus (Imlay). It 

differs by having a stout instead of a globose shell, 

by the ribs on the body chamber being much coarser, 

and by the ribbing changing abruptly from fine to 

coarse near the beginning of the body chamber.

Types. Holotype, USNM 108049; hypotypes, 

USNM 180738 and 180739.

Occurrences. Chinitna Formation on the Iniskin 

Peninsula west of Cook Inlet at USGS Mesozoic Iocs. 

22412, 22428, 22431, and 22433 (holotype). Chinitna 

Formation in Talkeetna Mountains at USGS Mesozoic Iocs. 24119, 24135, 24147, and 25310. Shelikof 

Formation near Wide Bay, Alaska Peninsula, at 

USGS Mesozoic loc. 19793. On the Iniskin Peninsula, 

the species occurs 350-475 feet above the base of 

the Chinitna Formation.

Iniskinites martini (Imlay)

Plate 4, figures 1, 3-6

Kheraiceras martini Imlay, 1953B, U.S. Geol. Survey Prof. 

Paper 249-B, p. 80, pi. 32, figs. 1, 4, 6.

Several ammonites closely resemble I. martini 

(Imlay) in whorl shape and ribbing, occur at least 

in part at the same stratigraphic position, and are 

considered to be immature forms of that species. At 

a comparable size, I. intermedius Imlay (1953b, p. 

81, pi. 31, figs. 1-4, pi. 32, figs. 2, 3, 5, 7, 8) is much 

more compressed.

Types. Holotype, USNM 108048; hyptoypes, 

USNM 180740 and 180741.

Occurrences. Chinitna Formation in basal 50- 

100 feet at USGS Mesozoic Iocs. 3027 and 22448 

near Iniskin Bay. These localities are near USGS 

Mesozoic loc. 22446 from which the holotype of 7. 

martini (Imlay) was obtained.

Iniskinites intermedius (Imlay)

Plate 3, figures 3, 4

Kheraiceras intermedium Imlay, 1953b, U.S. Geol. Survey 

Prof. Paper 249-B, p. 81, pi. 31, figs. 1-4, pi. 32, figs. 2, 

3, 5, 7, 8.

This species is most similar to 7. martini (Imlay) 

(1953b, p. 80, pi. 32, figs. 1, 4, 6) but differs by being appreciably smaller and more compressed and by 

its ribbing being higher and sparser, particularly oh 

the adult body whorl.

Types. Holotype, USNM 108223; paratypes, 

USNM 108051, 108224, and 108225; hypotype, 

USNM 180742.

Occurrences. Chinitna Formation in Talkeetna 

Mountains at USGS Mesozoic Iocs. 24151, 24184, 

24793, 24818, 25341, and 30282; west of Cook Inlet 

at USGS Mesozoic Iocs. 21273, 21334, 22427, and 

22690. Topmost foot of the Bowser Formation USGS 

at Mesozoic loc. 21272 ( = 3014). On Chisik Island 

the species ranges from the very top of the Bowser 

Formation (USGS Mesozoic loc. 21272) to 125 feet 

above the base of the Chinitna Formation (USGS 

Mesozoic loc. 22690). Assignment of the lowest occurrence to the Bowser Formation is based on its 

position 1 foot below a channel conglomerate which 

is mapped as the basal unit of the Chinitna Formation.
REFERENCES CITED 25

Family REINECKEIIDAE Hyatt, 1900 

Genus PARAREINECKEIA Imlay, 1962

Tarareineckeia shelikofana (Imlay)

Plate 6, figures 1-5, 7

Reineckeia (Kellawaysites) shelikofana Imlay, 1953b, U.S.

Geol. Survey Prof. Paper 249-B, p. 101, pi. 55, figs. 1,

2, 5-8. 

Parareineckeia shelikofana (Imlay), 1962, U.S. Geol. Survey

Prof. Paper 374-C, p. 25, 26.

This species is represented by two specimens in 

addition to the holotype. One of these shows the 

smallest septate whorls. The other shows most of 

the remainder of the shell, including the adoral part 

of the adult body chamber, a feature not preserved 

on the holotype.

The small specimen, which is slightly depressed, 

at a diameter of 35 mm, has a whorl height of 13.5 

mm, a whorl thickness of 19.2 mm, and an umbilical 

width of 12.8 mm. It differs from the inner whorls 

of the holotype by having somewhat finer and denser 

ribbing.

On the large specimen the septate whorls are 

identical in shape and ribbing with comparable 

septate whorls on the holotype. On the body chamber the ribs become much stronger, broader, and 

more widely spaced adorally than on the septate 

whorls. Primary ribs become fairly prominent, incline adorally on the flanks, and pass into two or 

three lower and broader secondary ribs along an 

irregular zone below the middle of the flanks. A 

few secondary ribs arise freely or are indistinctly 

connected with the primary ribs. All secondary ribs 

arch gently forward on the venter. The aperture 

terminates simply.

Types. Holotype, USNM 108143; hypotypes, 

USNM 180744 and 180745.

Occurrences. Shelikof Formation, 350 feet above 

base on north side of Wide Bay, Alaska Peninsula, 

at USGS Mesozoic loc. 21355 (holotype). Hypotypes 

from USGS Mesozoic loc. 24184 in the Talkeetna 

Mountains were obtained from reworked concretions 

in basal part of Cretaceous shales. The holotype 

should be from slightly older beds than those containing Kepplerites chisikensis Imlay, n. sp., at 

USGS Mesozoic loc. 19793 (Imlay, 1953b, p. 70).

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pis., 83 figs.

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Blake, J. F., 1905-07, A monograph of the fauna of the 

Cornbrash: London, Palaeontographical Soc., 106 p., 9 

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London Philos. Trans., ser. B, v. 239, no. 664, p. 215- 

263, 2 pis., 5 figs.

 1959, The ammonite zones of the Middle Jurassic 

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Detterman, R. L., and Hartsock, J. K., 1966, Geology of the 

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Greenland: Medd. Gr0nland, v. 155, no. 4, 214 p., 4 pis., 

25 figs.

Frebold, H. W. L., 1957, The Jurassic Fernie group in the 

Canadian Rocky Mountains and foothills: Canada Geol. 

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 1961, The Jurassic faunas of the Canadian Arctic 

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Survey Bull. 74, 43 p., 21. pis., 3 figs.

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pis., 1 fig.

Grantz, Arthur, 1960A, Geologic map of Talkeetna Mountains (A-2) quadrangle, Alaska, and the contiguous 

area to the north and northwest: U.S. Geol. Survey 

Misc. Geol. Inv. Map 1-313.

 1960b, Geologic map of Talkeetna Mountains (A-l) 

quadrangle, and the south third of Talkeetna Mountains 

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open-file report, 4 sheets, scale 1:63,360. 

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the United States and Alaska Part 1. Western interior 

United States: U.S. Geol. Survey Prof. Paper 249-A, p. 

1-39, pis. 1-24, figs. 1, 2.
26 JURASSIC AMMONITE DISTRIBUTION AND ZONATION, SOUTHERN ALASKA

 1953b, Callovian (Jurassic) ammonites from the 

United States and Alaska Part 2. Alaska Peninsula 

and Cook Inlet regions: U.S. Geol. Survey Prof. Paper 

249-B, p. 41-108, pis. 25-55, figs. 3-9.

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Sierra Nevada, California: U.S. Geol. Survey Prof. 

Paper 374-D, 30 p., 6 pis., 3 figs.

 1962, Jurassic (Bathonian or early Callovian) ammonites from Alaska and Montana: U.S. Geol. Survey 

Prof. Paper 374-C, 32 p., 8 pis., 7 figs.

 1964, Upper Jurassic mollusks from eastern Oregon 

and western Idaho: U.S. Geol. Survey Prof. Paper 483- 

D, 21 p., 4 pis., 3 figs.

1965, Jurassic marine faunal differentiation in North

America: Jour. Paleontology, v. 39, no. 5, p. 1023-1038,

6 figs. 

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801, 34 p., 15 figs. 

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INDEX

[Italic page numbers indicate major references and descriptions]

Page

abruptum, Kheraiceras ...______ - 24 

abruptus, Iniskinites ... 17, 24; pi. S

Kepplerites (Seymourites) ... 7 

Alaska Peninsula 3

ammonite succession 5 

alaskanum, Cosmoceras (Gulielmiceras) 15,16 

alticostatus, Arctocephalites ..._____ 18

Kepplerites (Seymourites) ........ 7

ammon, Cadoceras (Paracadoceras) .... 10

Ammonite faunal setting -- - IS 

Ammonite zonation _____-_.____... 7

Aretocephalites ..._____.______._ 14,18

alticostatus ._____.________ 18

(Cranocephalites) pompeekj ...._ 23

Artieoceras ...........___.______ 12,14

athleta zone ________________ 13

Biological distribution ___________ 1

Bowser Formation _____________ 2

breve, Cadoceras (Paracadoceras) ..._ 10

buckmani. LUloettia _______________ 3, 7

Cadoceras .................. 3, 7,12, 13, 14,15

athleta zone, Western Europe ____ 11

calloviense zone, U.S.S.R. _____ 10

zone, Yorkshire -___.______ 11

calyx ...... ______________ 10

catostoma ....._______________ 3,7,23,24

zone _________________ 7

coronatum zone, Western Europe _ 11 

glabrum .__________________ 3, 7, 17

jason zone, Russian Platform ___-_ 10 

macrocephalus zone, England ____ 10 

tchefkini ...________________ 11

tenuicostatum _____________ 7

(Cadoceras) ...................... 11

(Longaeviceras) pomeroyense ____ 7

(Paracadoceras) .................. 7, 10

ammon ...._____________ 10

breve ......................... 10

elatmae ....................... 10

mttaschevici .................. 10

tonniense ..................... 23

variabile .___________ 10

(Stenocadoceras) ................ 3,7,10

multicostatum ................. 3, 7

stenoloboide .................. 2,3,7

Stenoloboide Zone ________ 7 

stenolobum .................... 11

(Cadoceras), Cadoceras ............... 11

Callovian ammonite succession ______ 2

Callovian ammonites ________...___ 1

calloviense zone _________.___ 10,13,14

calyx, Cadoceras ._____________ 10

catostoma, Cadoceras ....._ 3,7,23,24

Chamoussetia ......................... 10

Chignik Bay __________________ 3

Chinitna Formation ________ 3,12,13,15

Nelchina area _ ... 2

Talkeetna Mountains 1

west of Cook Inlet __----___ 1

ehinitnaensis, Chinitnites ...._ 3,18, 22; pi. 2

ehinitnense, Pseudoeadoeeras ........._ 7

Chinitnites .................... 1, 3, 15 ,17, 18

ehinitnaensis .........__ 3, 18, 22; pi. 2

parviformus ................. 22, 28; pi. S

Page

chisikensis, Kepplerites ....___,___ 25 

Kepplerites (Seymourites) ... 7, 15; pi. 1

Choffatia irregularis ... __________ 7,17

Cook Inlet 7 

ammonite succession #

coronatum, Erymnoceras ... 11 

zone __-. 13

Cosmoceras ............... . - 14

(Cosmoceras) spinosum ........... 14

(Gulielmiceras) alaskanum ........ 15,16

'(Cosmoceras) spinosum, Cosmoceras ... 14

Cranocephalites ............... 1, 2, 14,18, 23

vidgaris .______ - --__ _ -- 23

( Cranocephalites) pompeekj,

Arctocephalites ............ 23

crassicostatum, Pseudocadoceras ........ 1

elatmae, Cadoceras (Paracadoceras) ... 10 

Erymnoceras coronatum ... 11

fasciculata, Kepplerites ....__ . 

Formations, ages and correlation

16

7

Geographic distribution IS

gitinsi, Kepplerites .................... 14

glabriim, Cadoceras .................. 3,7,17

(Gowericeras) Kepplerites ............ 14

Greenland _________ 10

grewingki, Pseudocadoceras ........... 7

(Gulielmiceras) alaskanum, Cosmoceras 15,16

hebetus, Xenocephalites .........____ 17

Horn Mountains 2 

ingrahami, Kepplerites ............ 15, 16,17

Iniskin Bay ____________ ____ 2

Iniskinites ..................... 1,3,7,15,2*

abruptus .................... \1,24;pl.S

intermedius -..._____ --. 7, 17,24; pi. 3

subzone ___ _.___ 7

magniformus ........... 23, 24; pi. S, pi. 4

martini ......................... 24; pi. 4

intermedius, Iniskinites ........ 7,17, 24; pi. S

irregularis, Choffatia .................. 7, 17

jason zone _____ .._____ 13

Jurassic zones of western Europe __ 1

(Kella way sites) shelikofana, Reineckeia 25 

Kepplerites ............. 3, 7, 11,12, 13, 14,15

chisikensis ...............-____ 25

fasciculata ........................ 16

gitinsi ............................ 14

ingrahami ..................... 15,16,17

plenus ............................ 17

snugharborensis ................... 7, 17

tychonis ................... 16; pi. 5, pi. 6

(Gowericeras) .................... 14

(Seymourites) abruptus .......... 7

alticostatus .. _.___-_________ 7

chisikensis ............... 7, 15; pi. 1

Kheraiceras ........................... 23

abruptum ......................... 24

magniforme .........._______ 24

martini ........................... 24

parviforme ....................... 23

Kialagvik Formation ____ -__._.__ 2

Page 

LUloettia .........-____ - 3,7,15

buckmani ......................___ 3, 7

stantoni ........................__ 7

Limestone Hills 3

(Longaeviceras) pomeroyense,

Cadoceras ......-.-- 7

macrocephalus zone _ 10 

magniforme, Kheraiceras 24 

magniformus, Iniskinites ... 23, 24; pi. S, pi. 4 

martini, Iniskinites ................. 24; pi. 4

Kheraiceras ............... --.... 24

mttaschevici, Cadoceras (Paracadoceras) 10 

multicostatum, Cadoceras

(Stenocadoceras) ......... 3, 7

Stenocadoceras .................... 3

Naknek Formation __________

Nelchina area of the Talkeetna 

Mountains _______

Paracadoceras ......................... 3, 14

(Paracadoceras) ammon, Cadoceras ... 10 

breve, Cadoceras _____ _ __ 10

Cadoceras ........................ 7, 10

elatmae, Cadoceras .......... .... 10

milaschevici, Cadoceras ............ 10

tonniense, Cadoceras .............. 23

variabile, Cadoceras ....._ _ 10

Parareineckeia ................. 1, 3, 7,15, 25

shelikofana ........______ 7,25;pl.6

parviforme, Kheraiceras .............. 23

parviformus, Chinitnites .____ 22, 28; pi. S

Paveloff Siltstone Member _________ 2,13 

plenus, Kepplerites ................... 17

pomeroyense, Cadoceras (Longaeviceras) 7 

pompeekj, Arctocephalites

(Cranocephalites) ......... 23

Pseudocadoceras .................. 3,7,11,15

ehinitnense ....................... 1

crassicostatum .................. __ 7

grewingki ........................ 7

Puale Bay 2

Red Glacier area ..__ 14 

Reineckeia (Kettawaysites) shelikofana.. 25 

Russian Platform 10,11

(Seymourites) abruptus, Kepplerites ... 7 

(Seymourites) alticostatus, Kepplerites. 1

chisikensis, Kepplerites ........ 7, 15; pi. 1

Shelikof Formation ________ 2, 3,13, 15

Alaska Peninsula _ -..- 7 

shelikofana, Parareineckeia ....... 7, 25; pi. 6

Reineckeia (Kettawaysites) ........ 25

Siberia ____ _ 10 

snugharborensis, Kepplerites .......... 7,17

spinosum, Cosmoceras (Cosmoceras).... 14

stantoni, LUloettia .................... 7

Stenocadoceras ....................... 3, 7

multicostatum ..................... 3

(Stenocadoceras), Cadoceras ......... 3,7,10

multicostatum, Cadoceras .......... 3, 7

stenoloboide, Cadoceras ........... 2, 3, 7

stenolobum, Cadoceras ............ 11

27
28 INDEX

Page 

stenoloboide, Cadoceraa

(Stenocadoceraa) ......... 2,3,7

atenolobum, Codoceraa (Stenocadoceraa) 11 

Stratigraphic summary _____ __ 1

Talkeetna Mountains .....____ 1, 3

ammonite succession _________ *

tchefkini, Cadoceras .................. 11

tenuicostatum, Cadoceraa .............. 1

Page

tonniense, Cadoceraa (Paracadoceros) 23 

Tonnie Siltstone Member 2,5,13 

Torrieelliceraa ............ _ . - 14

Tuxedni Bay ______ 2 

tychonis, Kepplerites __..... 16; pi. 5, pi. 8

U.S.S.R. ______... 10 

variabile, Cadoceraa (Paracodoceroa) 10

Page 

vulgaris, Cranocephalitea .............. 23

Wide Bay __-____ _ 2, 3 

Xenocephalitea ................... 3, 7,15,18

hebetus ........................... 17

zones, ammonite 2, 7

*U.S. GOVERNMENT PRINTING OFFICE: 1975 O SSS 476/11O
PLATES 1-6

[Contact photographs of the plates in this report are available, at cost, from U.S. 

Geological Survey Library, Federal Center, Denver, Colorado 80225.]
PLATE 1

[All figures are natural size]

FIGURES 1-5. Kepplerites (Seymourites) chisikensis Imlay, n. sp. (p. 15).

1,5. Holotype, USNM 108717, from USGS Mesozoic loc. 19793. 

Figure 1 shows fine ribs and weak tubercles exposed on 

inner whorls of broken right-hand side. Figure 5 shows 

nearly complete body chamber.

2-4. Septate paratype, USNM 108125, from USGS Mesozoic loc. 

21287. Note imprint of contracted body chamber. For 

other views, see Imlay (1953b, pi. 48, figs. 14, 17).
GEOLOGICAL SURVEY PROFESSIONAL PAPER 836 PLATE 1

KEPPLERITES
PLATE 2

[Figures 1, 19, and 27 are X 1- Figure 4 is X 3. All others are X 2]

FIGURES 1-31. Chinitnites chinitnaensis Imlay, n. sp. (p. 22).

1,8, 9. Paratype, USNM 180723, from USGS Mesozoic loc. 24803. 

2-4. Paratype, USNM 180722, from USGS Mesozoic loc. 24803.

Suture line drawn at whorl height of 6 mm. 

5-7. Paratype, USNM 180721, from USGS Mesozoic loc. 24143. 

10-12. Paratype, USNM 180719, from USGS Mesozoic loc. 24803. 

13,14. Paratype, USNM 180720, from USGS Mesozoic loc. 24803. 

15,16. Paratype, USNM 180729, from USGS Mesozoic loc. 24139. 

17, 18. Paratype, USNM 180724, from USGS Mesozoic loc. 24139. 

19-21. Paratype, USNM 180718, from USGS Mesozoic loc. 21348. 

22, 28. Paratype, USNM 180727, from USGS Mesozoic loc. 22432. 

23, 24. Paratype, USNM 180728, from USGS Mesozoic loc. 24143. 

25, 26. Paratype, USNM 180726, from USGS Mesozoic loc. 24805. 

27,29-31. Holotype, USNM 180725, from USGS Mesozodc loc. 24805. 

Specimens shown in figures 1-14 represent a coarsely ribbed variant; in figures 

15-21, a moderately ribbed variant; and in figures 22-26 and 28, a finely ribbed variant. The holotype shown in figures 27 and 29-31 has fairly fine ribbing on its outermost septate whorl and moderate ribbing on its body chamber.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 836 PLATE 

2

* I/'/.
PLATE 3

[All figures natural size unless otherwise indicated]

FIGURES 1,2, 5-7. Chinitnites parviformus (Imlay) (p. 23).

1,2. Hypotype, USNM 180735 (X 2), from USGS Mesozoic

loc. 11042.

5-7. Apertural and lateral views (X 2) and suture line (X 3) 

of hypotype, USNM 180734, from USGS Mesozoic loc. 

21334. 

3,4. Iniskinites intermediiis (Imlay) (p. 24).

Hypotype, USNM 180742, from USGS Mesozoic loc. 25341.

Shows adult body whorl and apertural construction. 

8,9. Iniskinites magniformus (Imlay) (p. 24).

Hypotype, USNM 180736, from USGS Mesozoic loc. 24147. In 

figure 9 the adoral third of the body chamber has been removed along crack shown in figure 8.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 836 PLATE 3

CHINITNITES AND INISKINITES
PLATE 4

[All figures are natural size]

FIGURES 1,3-6. Iniskinites martini (Imlay) (p. 24).

1, 3. Laterally compressed specimen, USNM 180740, from USGS

Mesozoic loc. 3027. 

4,5. Slightly distorted specimen, USNM 180741, from USGS

Mesozoic loc. 22448.

6. Partly diagrammatic suture line from adapical end of 

adult body chamber at whorl height of 50 mm. Holotype, USNM 108048, from USGS Mesozoic loc. 22446. 

2,7,8. Iniskinites magniformus (Imlay) (p. 24).

Inner septate whorls and nearly complete body whorl of hypotype, 

USNM 180737, from USGS Mesozoic loc. 22431. Position of 

cross-sectional view shown in figure 2 corresponds to crack 

in figure 7.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 836 PLATE 4
PLATE 5

[All figures are natural size]

FIGURES 1-3. Iniskinites abruptus (Imlay) (p. 24).

1. Laterally crushed hypotype, USNM 180739, from USGS 

Mesozoic loc. 24147. Note that ribs are much coarser on 

body chamber than on septate whorl.

2,3. Outermost septate whorl (fig. 2) and nearly complete body 

chamber of hypotype, USNM 180738, from USGS Mesozoic loc. 25310. 

4. Kepplerites tychonis Ravn (p. 16).

Ventral view of plaster cast of holotype from East Greenland, 

University of Copenhagen collection, for comparison with Kepplerites chisikensis Imlay, n. sp. See pi. 6, fig. 6, for lateral view.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 836 PLATE 5

INISKINITES AND KEPPLERITES
PLATE 6

[All figures are natural size]

FIGURES 1-5, 7. Parareineckeia shelikofana (Imlay) (p. 25).

1, 2, 7. Ventral and lateral views of adoral part of body chamber

(figs. 1, 2) and lateral view of rubber imprint of

external mold (fig. 7) of hypotype, USNM 180744,

from USGS Mesozoic loc. 24184.

3-5. Small septate whorl of hypotype, USNM 187045, from

USGS Mesozoic loc. 24184. 

6. Kepplerites tychonis Ravn (p. 16).

Lateral view of plaster cast of holotype from East Greenland, 

University of Copenhagen collection, for comparison with Kepplerites chisikensis Imlay, n. sp. See pi. 5, fig. 4, for ventral 

view.
GEOLOGICAL SURVEY PROFESSIONAL PAPER 836 PLATE 6

PARAREINECKEIA AND KEPPLERITES