GEOLOGY LIBRARY 

OCT * " *'s

Revision of the

Type Mankomen Formation

(Pennsylvanian and Permian),

Eagle Creek Area,

Eastern Alaska Range, Alaska

GEOLOGICAL SURVEY BULLETIN 1395-B

f

Revision of the

Type Mankomen Formation 

(Pennsylvanian and Permian), 

Eagle Creek Area, 

Eastern Alaska Range, Alaska

By D. H. RICHTER and J. T. DUTRO, JR.

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 1395-B

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON: 1975
: . . . ; ;,. - 

UNITED STATES DEPARTMENT OF THE INTERIOR

ROGERS C. B. MORTON, Secretary

GEOLOGICAL SURVEY 

V. E. McKelvey, Director

Library of Congress Cataloging in Publication Data

Richter, Donald H.

Revision of the type Mankomen Formation (Pennsylvanian and Permian), Eagle

Creek area, eastern Alaska Range, Alaska.

(Contributions to Stratigraphy) (Geological Survey Bulletin 1395-B) 

Bibliography: p. 20-21. 

Supt. of Docs. No.: I 19.3:1395-6 

1. Geology, Stratigraphic-Permian. 2. Geology, Stratigraphic-Pennsylvanian.

3. Geology-Alaska-Alaska Range. I. Dutro, J. Thomas, joint author.

II. Title. III. Series: United States Geological Survey. Bulletin 1395-B. 

QE75.B9 No. 1395-B [QE674] 557.3'08s 74-31194

[551.7'52'097983]

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

Washington, D. C. 20402

i . ' ... ; ' '..'- '. /.:' '-' -..!.' !.'''.' 

Stock Number 024-001-02600
CONTENTS

	Page

Abstract ._________._______________-_______________ Bl

Introduction ___________ ____ __ 1

Physical stratigraphy of the Mankomen Group __ -__ -_ 3

Slana Spur Formation____ __ _ __ _ 4

Eagle Creek Formation __________ __ - -_ 10

Lower limestone member _________________________ 10

Lower argillite member __________ __ 13

Upper limestone member ________ ________ _ 17

Upper argillite member _________________-___________ 18

Biostratigraphy of the Mankomen Group ________________ ._ 19

Age and correlation _______________ ________ 20

Tectonic significance ______________________________ - - 24

References ______________________________________ 24

ILLUSTRATIONS

FIGURE 1. Map of part of south-central Alaska showing the Eagle Creek area 

and other localities where Pennsylvanian and Permian rocks are 

exposed ____________________________________ B2

2. Geologic map of the Eagle Creek area, eastern Alaska Range ___ 4

3. Stratigraphic columnar sections, with fossil assemblages, of the Slana

Spur Formation (Mankomen Group), Eagle Creek area _____ 6

4. Photographs showing lithologic features of the calcareous volcaniclastic member of the Slana Spur Formation ________________ 8

5. Photograph showing the four members of the Eagle Creek Formation

along part of the west wall and upper basin of Eagle Creek ____ 11

6. Photograph showing lower limestone member and overlying lower argillite member of the Eagle Creek Formation along the west wall of 

Eagle Creek valley ____________________________ 12

7. Stratigraphic columnar sections, with fossil assemblages, of the Eagle

Creek Formation (Mankomen Group), Eagle Creek area_____ 14

8. Generalized Stratigraphic columnar sections of Pennsylvanian and 

Permian sequences in the eastern and east-central Alaska Range 

showing zonation of fusulinids and corals, suggested lithologic correlation of the Mankomen Group, and some inferred time boundaries- 22

in

CONTRIBUTIONS TO STRATIGRAPHY

REVISION OF THE TYPE 

MANKOMEN FORMATION

(PENNSYLVANIAN AND PERMIAN),

EAGLE CREEK AREA, 

EASTERN ALASKA RANGE, ALASKA

By D. H. RICHTER and J. T. DUTRO, JR.

ABSTRACT

The Mankomen Formation is raised to group rank in its type area. Two new formations are recognized: the Slana Spur Formation, about 4,550 feet thick, consisting chiefly 

of volcaniclastic and calcareous volcaniclastic rocks and the overlying Eagle Creek 

Formation, about 2,940 feet thick, consisting of nonvolcanogenic marine argillite and 

limestone.

The Mankomen Group is underlain conformably by the Tetelna Volcanics, consisting 

of massive volcanic flows and volcaniclastic rocks of Pennsylvanian(?) age. The Nikolai 

Greenstone, of Middle and (or) Late Triassic age, and locally a thin sequence of chert and 

limestone, of probably Triassic age, rest unconformably on the Mankomen.

Fusulinids in the volcaniclastic member of the Slana Spur Formation are Middle 

Pennsylvanian (Atokan) in age. Fossils in the upper part of the Slana Spur Formation 

and the lower part of the Eagle Creek Formation are of Wolfcampian (Sakmarian) age. 

The upper limestone and upper argillite members of the Eagle Creek yield younger 

faunas of Leonardian (Artinskian) and, possibly, early Guadalupian (Ufimian?) age.

The Tetelna Volcanics reflect the development of a late Paleozoic volcanic island arc 

whose waning stages are represented by the volcaniclastic rocks of the Slana Spur 

Formation. Lithologies of the Tetelna-Mankomen strata, and the new age data, suggest 

that this arc had become virtually inactive by Early Permian time.

INTRODUCTION

The Mankomen Formation was named by Mendenhall (1905, p. 

40-47) for the predominantly sedimentary sequence in the mountains 

north of Mankomen Valley between the Middle Fork of the Chistochina River and the valley of the Slana River (fig. 1). Eagle Creek 

valley and an adjacent mountain spur just west of the Slana River were 

designated the type area for the formation, and a composite section of 

6,700 feet was presented. Mendenhall (1905, p. 45) assigned a Permian 

age to the Mankomen on the basis of fossil identifications by Charles 

Schuchert. Later history of study of Permian strata in the eastern 

Alaska Range is summarized by Moffit (1954, p. 103-118).

Bl
B2 CONTRIBUTIONS TO STRATIGRAPHY

30 40 KILOMETRES

FIGURE 1. Eagle Creek area and other localities (numbered) where Pennsylvanian 

and Permian rocks are exposed.

Although no other recent stratigraphic work has been done in the 

type area, a number of investigations have been carried out on the 

Permian rocks and faunas from elsewhere in the eastern and eastcentral Alaska Range. Corals and fusulinids from the Permian in the 

Delta River area (localities 1 and 2, fig. 1), 45-50 miles northwest of 

Mankomen Lake, were described by Rowett (1968) and Petocz (1970), 

respectively, and the volcanic stratigraphy and biostratigraphy in the 

Gulkana Glacier area (locality 3, fig. 1), 40 miles northwest of Mankomen Lake, were studied by Bond (1969) and Gilbertson (1969), respectively. Permian corals near Slana (locality 4, fig. 1), southeast of 

Mankomen Lake, were described by Rowett (1971), who suggested a 

correlation with strata in the Delta River area.

During the period July 3-9, 1972, the writers refined the 1967
REVISION OF THE MANKOMEN FORMATION, ALASKA B3

reconnaissance mapping of Richter (unpub. data) north of Mankomen 

Lake and measured most of the stratigraphic sequence in detail. Two 

different lithologic suites are recognized in Mendenhall's original 

Mankomen Formation: a lower marine volcaniclastic sequence containing both Pennsylvanian and Permian faunal assemblages and a 

conformable upper nonvolcanogenic marine sequence containing only 

Permian fauna. We therefore raise the Mankomen Formation to group 

rank and, on the basis of lithologic homogeneity, propose two new 

formations, the Slana Spur Formation and the Eagle Creek Formation, to define the two distinct marine sequences within the group.

We wish to thank our U.S. Geological Survey colleagues R. C. Douglass and Mackenzie Gordon, Jr., for identifying the fusulinids and 

ammonoids, respectively. R. E. Grant and G. A. Cooper of the U.S. 

National Museum have provided valuable suggestions concerning the 

significance of the brachiopods in correlation with Permian strata in 

other parts of the world.

The redefined Mankomen Group is approximately 7,500 feet thick. 

It includes the Slana Spur Formation, consisting predominantly of 

calcareous and noncalcareous volcaniclastic rocks about 4,550 feet 

thick, and the Eagle Creek Formation, consisting predominantly of 

argillite and limestone about 2,940 feet thick. The Mankomen Group 

overlies with apparent conformity massive volcanic rocks of the 

Tetelna Volcanics (Mendenhall, 1905, p. 36-38).

Both new formations of the Mankomen Group are intruded by locally abundant dikes, sills, and small stocks of gabbro, a variety of 

hornblende-plagioclase porphyries mostly andesite in composition, 

and dark fine-grained mafic rocks. Gabbro sills, as much as 85 feet 

thick, are especially conspicuous in the lower limestone member of the 

Eagle Creek Formation.

Because a large number of high-angle faults cut the Mankomen 

Group, the measured sections presented here are composites based on 

detailed mapping and correlation of units largely within the drainage 

of Eagle Creek. The locations of the individual sections used in compiling the composite sections are shown on the geologic map in figure 2. 

Only about 700 feet of the Slana Spur Formation, including the uppermost 500 feet of section, were measured in detail. Although data on 

the remainder of the formation are taken from less-detailed traverses 

(sections F and G, fig. 2), they are sufficient to describe the major 

lithologic features of the rocks. Most of our attention has been focused 

on the Eagle Creek Formation, whose two distinctive limestone members and two predominantly argillite members have yielded 

significant collections of marine fossils.
B4 CONTRIBUTIONS TO STRATIGRAPHY

144'30'

Base from U.S. Geological Survey 

Mt. Hayel A-l. 1:63.360, 1955. 

Minor reyUions 1965

Geology by D. H. Richtei. 1967 and 

1972; and J. T. Dutro, Jr.. 1972

FIGURE 2. Eagle Creek area, eastern Alaska Range. 

SLANA SPUR FORMATION

The type locality for the new Slana Spur Formation is designated as 

Eagle Creek valley and adjacent Slana Spur, a north-trending mountain ridge separating the Eagle Creek and Slana River drainages (fig. 

2). This locality is within sees. 1 and 12, T. 14 N., R. 5 E.; sec. 6, T. 14 N., 

R. 6 E.; sees. 26 and 34, T. 15 N., R. 5 E.; and sec. 31, T. 15 N., R. 6 E., in 

the Mt. Hayes A-l quadrangle (scale 1:63,360).

The Slana Spur Formation, about 4,550 feet thick, is divided into 

two lithologic members: a lower or volcaniclastic member, approximately 3,100 feet thick, and an upper or calcareous volcaniclastic 

member, approximately 1,450 feet thick. The base of the formation, 

placed at the top of the first massive volcanic flow unit from the top of
REVISION OF THE MANKOMEN FORMATION, ALASKA

EXPLANATION

B5

Surficial deposits 

Includes alluvial, glacial, fluvioglacial, rock glacier, and 

colluvtal deposits

Intrusive rocks 

Only larger bodies shown 

Mzq,gabbro 

Mzd, diorite and undifferentiated

intermediate to basic Intmsivt

rocks

Nikolai Greenstone 

DISCONFORMITY

Chert and limestone 

DISCONFORMITY /?)

Eagle Creek Form 

Peua. upper argillite i 

Peul, upper limcstont 

Vein, lower argillltem 

Pell, lower limestone

Tetelna Volcunics

Fault, know 

Dotted wl 

U, upthr

and inferred 

e concealed, 

<n side: D,

d Horlzor 

and dip of beds

®

APPROXIMATE MEAN 

DECLINATION, 1974

0 1 2 KILOMETRES 

CONTOUR INTERVAL 100 FEET

FIGURE 2. Continued.

the section, is consistent with Mendenhall's (1905, p. 40) original 

designation of the base of the Mankomen Formation. This flow unit 

and the underlying 500 feet of section exposed on the south side of the 

Slana Spur (fig. 2; section G, fig. 3) are considered to belong to the 

Tetelna Volcanics. The Tetelna consists predominantly of dark-graygreen massive fragmental volcanic rocks, apparently submarine 

lahars and flow breccias, and massive dark-green porphyritic and,
B6 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 3. Sections, with fossil assemblages, of the Slana Spur 

Formation (Mankomen Group), Eagle Creek area. Location 

of section shown in figure 2.
REVISION OF THE MANKOMEN FORMATION, ALASKA B7

locally, amygdaloidal flows. Dark thin-bedded volcaniclastic rocks in 

places separate the massive volcanic units. No fossils were observed in 

the Tetelna.

Rocks of the volcaniclastic member of the Slana Spur Formation are 

predominantly dark-gray, dark-green, and maroon volcaniclastics 

with interbedded tuff, fragmental volcanic rock, and limestone. Carbonate debris in the clastic rocks is generally negligible. The volcaniclastic rocks range from massive conglomerate and sandstone to thinbedded sandstones, grit, and siltstone that commonly show graded 

bedding. Most strata contain variable amounts of dark argillaceous 

matrix and could be classified as volcanic graywackes and volcanilutites. One conspicuous lens of medium-bedded limestone, as much as 

80 feet thick, and a much thinner lens of siliceous limestone occur in 

the lower half of the member. Foraminifers and nondiagnostic 

brachiopod shell fragments occur in these limestone lenses, but in 

general, the rocks are only sparsely fossiliferous.

Section of Slana Spur Formation, volcaniclastic member

[Numbered lithologic units correspond to units shown in fig. 3] 

. Thickness Section G: (ft) 

Calcareous volcaniclastic member (overlying unit). 

9. Not measured in detail. Interbedded gray, maroon, and darkgreen volcanic sandstone and grit with subordinate volcanic 

conglomerate, lapilli tuff, and lahar(?) deposits; beds 2 in. to 

more than 3 ft thick; locally graded _____________ 1,800 (approx)

8. Limestone, gray, fine- to medium-grained; beds 1-3 ft thick __ 45 

7. Limestone, light-gray, siliceous, buff-weathering; beds M>-2 ft

thick; base contains abundant volcanic debris_______ 35

6. Sandstone, volcanic, green-buff, calcareous ____---____-__ 20

5. Limestone, dark-gray; contains volcanic debris ________ 3 

4. Fragmental volcanic rocks, green-gray, massive; contains

pumice (altered to chlorite) and angular volcanic fragments- 90 

3. Not measured in detail. Interbedded green and maroon volcanic 

conglomerate, grit, and coarse- to fine-grained sandstone. 

Massive in coarser beds, thin bedded and graded in finer beds. 

Cut by a number of dark-gray mafic sills and dikes ________ 400 (approx)

2. Limestone, gray, siliceous, hackly fracture _________ 7

1. Not measured in detail. Chiefly coarse-grained volcaniclastic 

rocks with subordinate lapilli tuff and lahar(?) deposits. Gray, 

green, and maroon; graded beds common ______________ 700 (approx)

Tetelna Volcanics (underlying unit).

The calcareous volcaniclastic member is gradational with the underlying volcaniclastic member. It consists of a variety of volcanic-rich 

clastic limestone and both calcareous and noncalcareous volcaniclastic 

.rocks with minor interbedded massive and bioclastic limestone, tuff, 

and volcanic breccia. The predominant rocks are grayish-green cross-
B8 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 4. Lithologic features of the calcareous volcaniclastic member of the Slana 

Spur Formation. A, Thin crossbedded volcanic-rich clastic limestone interbedded with 

thin calcareous sandstone. B, Analcite-bearing mottled calcareous sandstone.
REVISION OF THE MANKOMEN FORMATION, ALASKA B9

bedded coarse clastic limestones (fig. 4A), ranging in thickness from a 

few inches to 80 feet, and grayish-green calcareous coarse-grained 

sandstones that locally exhibit a pronounced mottled texture (fig. 4B). 

Noncarbonate grains in these rocks consist chiefly of red and green 

jasper, gray chert, epidote- and chlorite-bearing volcanic rock, and 

feldspar. The ratio of limestone to nonlimestone detritus ranges from 

1:1 to 1:4 in the clastic limestone and is generally less than 1:4 in the 

calcareous sandstone. The mottled texture in some of the calcareous 

sandstone is due to replacement and cementation of the grains by 

authigenic analcite. Brachiopods and echinoderm debris are scattered 

throughout the member; the upper part contains a few poorly preserved horn corals.

Section of Slana Spur Formation, calcareous volcaniclastic member

[Numbered lithologic units correspond to units shown in fig. 3]

Thickness 

(ft)

Section A:

Lower limestone member, Eagle Creek Formation (overlying unit). 

13. Sandstone, volcanic, dark-gray, coarse-grained, mottled; minor

clastic limestone; locally graded _____________________ 54

12. Limestone, gray, volcanic-rich, clastic; interlayered with 

green-gray volcanic sandstone; beds Vfe-6 in. thick. Locally 

crossbedded __________________________________ 85

11. Sandstone, volcanic, green-gray, massive to thin-bedded, locally calcareous _______________________ 45

10. Sandstone, dark-green-gray, friable-_______________ 5

9. Siltstone and sandstone, volcanic, green-gray, mottled, thinbedded in graded sets 4-8 in. thick; locally crossbedded __ 40 

8. Sandstone, volcanic, green-gray, massive to thin-bedded,

calcareous __________________________________ 25

7. Sandstone, volcanic, and volcanic-rich clastic limestone, gray,

crossbedded; sandstone locally mottled ______________ 100

Talus. 

Section F:

7. Sandstone and limestone similar to, and assumed equivalent 

with, unit 7 in section A. Also contains minor thin volcanicrich bioclastic limestone. Intruded by a number of hornblendefeldspar dikes and sills _____________________ --- 100

Covered ________________________________ 35

6. Limestone, dark-gray, massive, crinoidal; contains abundant

volcanic detritus _______________________ 20

Covered ___________________________1 _________ 20

5. Argillite, dark-gray, brecciated______________ 15

4. Sandstone and siltstone, volcanic, buff, calcareous _______ 15

3. Lapilli tuff, light-green-gray, massive; contains chlorite clasts 40 

2. Sandstone and grit, volcanic, light-green, buff, calcareous;

granules of red and green chert common; some graded beds- 45 

Alluvium.
BIO CONTRIBUTIONS TO STRATIGRAPHY

Section of Slana Spur Formation, calcareous volcaniclastic member-Continued

Thickness

(ft)

Section G:

1. Not measured in detail. Consists chiefly of gray massive crossbedded clastic limestone and volcanic sandstone, thin-bedded 

volcanic-rich limestone, graded volcanic sandstone and siltstone and minor calcareous volcanic grit, green chert, and 

massive lapilli tuff and volcanic agglomerate ________ 900 

Volcaniclastic member (underlying unit).

EAGLE CREEK FORMATION

The type locality for the new Eagle Creek Formation is designated 

as the west side of Eagle Creek valley in sees. 22, 23, 27, and 34, T. 15 

N., R. 5 E., Mt. Hayes A-l quadrangle (scale 1:63,360). Four informally named members are recognized in the Eagle Creek Formation at 

the type locality (fig. 5). These four members and their lithologic 

subunits, together with approximate thicknesses, are as follows from 

the top downward:

Approximate thickness 

(ft)

4. Upper argillite member _________________ 410

3. Upper limestone member _____________________ 266

2. Lower argillite member:

c. Limestone and siltstone "ribbon bed" unit __________ 340

b. Bryozoan biostrome unit ______________________ 120

a. Argillite and siltstone unit __________________ 880

Total ______________________________ 1,340

Lower limestone member: 

c. Upper limestone marker______________________ 249

b. Calcareous volcanic sandstone unit__________________ 498

a. Basal limestone marker ________________________ 175

Total ________________________________ 922

Total thickness ____________________________________ 2,938

LOWER LIMESTONE MEMBER

The lower limestone member forms prominent outcrops and conspicuous light-gray cliffs along the west and upper east walls of Eagle 

Creek valley (fig. 6). Total thickness of the member is about 922 feet. 

Three lithologic units are recognized: a basal limestone marker, a 

calcareous volcanic sandstone unit, and an upper limestone marker. 

The base of the lower limestone member is placed at the base of the 

lowest distinctive sequence of limestone beds (basal limestone marker) 

in the marine section. These limestones conformably overlie volcanicrich calcareous clastic rocks with interbedded tuff, volcanic breccia, 

and bioclastic limestone. We consider this change in lithology, which 

reflects a significant change in depositional conditions and in the
REVISION OF THE MANKOMEN FORMATION. ALASKA Bll

FIGURE 5. The four members of the Eagle Creek Formation along part of west wall and 

upper basin of Eagle Creek. Pell, lower limestone member; Pela, lower argillite 

member; Peul, upper limestone member; Peua, upper argillite member; PFscv, calcareous volcaniclastic member of the Slana Spur Formation.

nature of the source materials, to mark the contact between the Slana 

Spur Formation and Eagle Creek Formation.

The basal limestone marker consists of 175 feet of thin-bedded to 

massive gray limestone with interbeds of graded volcaniclastic rock 

and minor gray chert lenses. The limestones are fine grained with 

locally abundant coarse clastic volcanic debris.

The basal limestone marker is separated from the upper limestone 

marker by about 500 feet of interbedded calcareous volcanic sandstone, siltstone, and grit, volcanic-rich clastic limestone, and minor 

dark-gray bioclastic limestone. Graded bedding is common in the 

calcareous volcaniclastic rocks, and crossbedding is locally pronounced in the volcanic-rich limestones.

The upper limestone marker, about 250 feet thick, consists principally from bottom to top of medium- to thin-bedded gray limestone 

with abundant dark-gray buff-weather ing siliceous layers, massive 

light-gray limestone in beds as much as 12 feet thick, and mediumbedded gray limestone. Most of the limestone is fine grained with local 

bioclastic zones containing abundant crinoidal debris. Nodules and
B12 CONTRIBUTIONS TO STRATIGRAPHY

FIGURE 6. Lower limestone member and overlying lower argillite member of the Eagle 

Creek Formation along the west wall of Eagle Creek valley. The approximate contacts 

of the three lithologic units in the lower limestone member are shown.

lenses of black to light-gray chert constitute as much as 25 percent of 

the strata in the upper 40 feet of the unit, and beds of gray chert as 

much as 2 feet thick are common near the base of the massive limestone.

Section of Eagle. Creek Formation, lower limestone member

[Numbered lithologic units correspond to units in fig. 7]

Thickness Section A: Ift}

Lower argillite member (overlying unit).

Upper limestone marker:

20. Limestone, gray, fine-grained; beds 1-2 ft thick; abundant nodules and

lenses of black to light-gray chert ____________________ 40

19. Limestone, light-gray, massive; beds 2-12 ft thick; gray chert lenses in

lower part; locally crinoidal; several thin dark-gray fine-grained mafic

sills ______________________________ __________ 86

18. Sandstone, v^icanic, dark-green-gray, coarse-grained ______________ 8

17. Limestone, gray to dark-gray, fine-grained; beds 1-2 ft thick; dark-gray

siliceous layers; crinoidal at base ___ ___ -___ __ 115 

Gabbrosill _________________________- - - 17

Calcareous volcanic sandstone unit: 

: ' 16. Sandstone, volcanic, dark-gray-green, coarse-grained, calcareous;

gravelly clastic limestone _______ _____ 15
REVISION OF THE MANKOMEN FORMATION, ALASKA B13

Section of Eagle Creek Formation, lower limestone member-Continued

Thickness

(ft)

Section A Continued

15. Limestone, bioclastic, gray, thin-bedded; siliceous mudstone and chert 39 

14. Mudstone, siliceous, dark-gray to brown; minor sandstone; contains

abundant bryozoans _______________-____________ 55

13. Limestone, gray, massive_________________________________ 5

12. Mudstone, siliceous, brown-gray, thin-bedded; graded coarse-grained

volcanic sandstone and grit __________________________ 25

11. Limestone, gray, massive to thin-bedded; dark chert lenses in middle;

crinoidal at base ___________________________________. 47

10. Argillite, dark-gray, calcareous; minor calcareous sandstone containing abundant crinoidal debris. Two hornblende-feldspar porphyry sills 46 

Covered _____________________________________ 30 

9. Sandstone and grit, gray-green; calcareous siltstone and gray

volcanic-rich limestone; locally graded ___________________ 30

Covered _____________________________________ 20 

8. Sandstone, volcanic, gray-green, calcareous, crossbedded, friable._ 27 

7. Sandstone, volcanic, green; interbedded friable calcareous sandstone, 

light-gray calcareous siltstone, and minor volcanic grit, pebble conglomerate, and chert; locally graded _________________________ 102

6. Limestone, clastic, brown-gray, thin-bedded __-_____---_______ 2

5. Sandstone, volcanic, calcareous, crossbedded __________________ 10

4. Limestone, thin, volcanic-rich; interbedded green-gray volcanic sandstone, thin creamy chert, and dark argillite ________________ 45

Gabbro sill ____________________________________ 85 

Basal limestone marker:

3. Limestone, gray and dark-gray, massive to thin-bedded, fine- to 

medium-grained; minor sandstone, argillite, grit and chert; cut by 

mafic sill ____________________________________ 68

2. Argillite, dark-gray-green; maroon volcanic sandstone and dark-green

grit______________________________________________ 21

1. Limestone, gray, massive, fine-grained; abundant laminae of siliceous 

argillite and minor volcanic sandstone and chert. Grades downward 

into thin-bedded gray limestone with subordinate interbeds of argillite and sandstone ________________________ 86

Calcareous volcaniclastic member, Slana Spur Formation 

(underlying unit).

LOWER ARGILLITE MEMBER

The lower argillite member, 1,340 feet thick, is divided into three 

lithologic units: an argillite and siltstone unit, a bryozoan biostrome 

unit, and a limestone and siltstone "ribbon bed" unit. In measured 

section B (fig. 7), the base of the lower argillite member is marked by a 

1-foot-thick bed of green medium-grained calcareous sandstone. This 

sandy bed appears to fill small erosional(?) irregularities at the top of 

the lower limestone member, suggesting a local unconformity between 

the two members.

The argillite and siltstone unit, 880 feet thick, forms rather subdued 

talus-covered slopes (figs. 5, 6) and hence is relatively poorly exposed.
B14 CONTRIBUTIONS TO STRATIGRAPHY

GENERALIZED 

ITHOLOGY AND FIELD 

NUMBERS OF FOSSIL

COLLECTIONS 

Numbered unit! ere

described in text

LIT

GENERALIZED

NUMBERS OF FOSSIL

COLLECTIONS 

Numbered uniti ire 

described In text

 £. . 72 ARh 64- 

Daublchttes 1 

Megousia

ncrlnella 

' Waagenoconc 

Neoiplrtfer 

Wtlktngla t

Floet from upper ergillita 

member (72 ARh 58) 

Chonetina 

Megousia 

Waagenoconcha 

Rhynchopora

Pscudofiuullnella sp. 

Schwagerlna aff. S. 

hyperborea (Sailer) 

Schwagerina ip. 

Ramose bryozoans

Bathymyonia

Horridonia

Kochlproductut ?

Spiriferella

delothyriaina

SpiriferelHna

Horridonia 

' Rettculatia ? 

Splrtferella

Ramose bryozoanj 

- Anemonarla 

Neoiptrlfer

Elevetio

6900'

 72 ARh 64

Reticulatta ? 

Neosptrtfer

Rettculatia 

Penicularts 1 

Neosptrtfer

Rettculatia 

Penlcularlt 1 

Neoiplrtfer 

Pteudomorttrtia

72 ARh 48

-- r--~.-J i __... '_ Elevatipi -v^ -*, **C3( Section B ^ R00nr

Yakolevla

Spiriferella

Neosptrtfer

5920' bryo

y-^^J 72ARh46 Reticulatta 

\ Anemonarla 1 

\-Spirtferella 1 

Neosplrtfer 

6 (perhaps

Septosptrtfer)

. 72ARH44 Ramose

L bryozoans 

Rettculatia 

Anemonarla 

Bathymyonia 

Penicularis 7

72ARM40 Artiraklal

72ARh39- Artimkta t 

Elevation 5220'

FIGURE 7. Sections, with fossil assemblages, of the Eagle Creek Formation (Mankomen Group), Eagle Creek area. Location of sections shown in figure 2.
REVISION OF THE MANKOMEN FORMATION, ALASKA B15

FIGURE 7. Continued.
B16 CONTRIBUTIONS TO STRATIGRAPHY

Predominant are thin-bedded dark-gray shaly argillite and graygreen to gray locally calcareous siltstone with minor dark-gray bioclastic limestone. Dense siliceous mudstone concretions, as much as 6 

inches in diameter, generally with a nucleus of marcasite, are locally 

concentrated near the base and toward the top of the unit. Dark 

mud-filled trace fossils are scattered throughout.

The bryozoan biostrome unit consists of 120 feet of interbedded 

dark-gray argillite, gray calcareous siltstone, and minor dark dirty 

bioclastic limestone. Bedding ranges from less than 1 inch to as much 

as 1 foot in thickness. Bryozoans and brachiopods are common 

throughout the unit but are especially abundant in the siltstone beds.

The limestone and siltstone "ribbon bed" unit consists of 340 feet of 

gray, dirty limestone, in beds as much as 3 feet thick, alternating with 

dark-gray argillite and siltstone interbeds as much as 2 feet thick. 

Limestone increases in abundance upwards in the unit, generally 

resulting in a gradational contact with the overlying upper limestone 

member.

Section of Eagle Creek Formation, lower argillite member

[Numbered lithologic units correspond to units in fig. 7] 

Section C: Thickness

Upper limestone member (overlying unit).

Gabbro.

Limestone and siltstone "ribbon bed" unit:

8. Limestone, gray, dirty; dark-gray argillite and siltstone imparting a ribbon effect to the unit. Beds 1 in. to 3 ft thick. Limestone 

increases in abundance upward in section __________ 340

Hornblende-feldspar porphyry intrusive______________ 11

Bryozoan biostrome unit:

7. Argillite, dark-gray; interbedded gray calcareous siltstone and 

dark dirty limestone; beds 1-12 in. thick. Limestone and siltstone contain extremely abundant bryozoan and brachiopod 

fragments ________________________ 120

Argillite and siltstone unit:

6. Siltstone, gray, thin-bedded, shaly; locally calcareous with wispy 

laminae of dark-gray argillite; worm burrows common and 

mudstone concretions abundant in upper 30 ft. Unit intruded 

by several porphyritic dikes and sills. Base terminated by fault 145 (approx) 

Section B:

7. Argillite, dark-gray; interbedded calcareous siltstone and dark

bioclastic limestone. Equivalent to unit 7, section C. 

6. Siltstone; equivalent to unit 6, section C ____________ 175

Feldspar porphyry_______________________ 5

5. Siltstone, light-gray, thin-bedded; abundant worm burrows,

common dark-gray mudstone concretions _ _ _ _ _ _ _ _ _ _ 50

4. Argillite, black, shaly; contains interbeds of calcareous gray

siltstone; occasional worm burrows____________ _ 335

Hornblende-feldspar porphyry ______________ _ _ 15

3. Argillite, dark-gray; minor dirty, black limestone, dense hornfels at base__________________________ 60
REVISION OF THE MANKOMEN FORMATION, ALASKA B17 

Section of Eagle Creek Formation, lower argillite member-Continued

Thickness

(ft)

Section B Continued

Gabbro ___.____ ______________________.________.__-______.__ 30

2. Argillite, dark; siliceous green-gray siltstone and iron 

carbonate-bearing siltstone; dense mudstone concretions and 

worm burrows locally common___________________ 200

Hornblende porphyry _____________________________ 10

1. Argillite, dark-gray, shaly; 2-ft-thick gray bioclastic limestone

and 1-ft-thick basal green calcareous sandstone ________ 50

Lower limestone member (underlying unit).

UPPER LIMESTONE MEMBER

The upper limestone member, 266 feet thick, consists predominantly of gray limestone containing irregular patches of ocherous silica. 

The lower contact is generally gradational and is arbitrarily placed 

within the series of alternating limestone and siltstone beds in the 

lower argillite member where limestone becomes the principal lithology (sec. C, fig. 7). In section D, figure 7, the lower contact is sharper 

with thick limestone beds containing minor interbedded siltstone and 

argillite overlying a thin-bedded limestone and siltstone sequence in 

the lower argillite member. The lower 190 feet of the member is 

composed of relatively massive limestone in beds as much as 3 feet 

thick that exhibits an increase in siliceous material upward. The 

remainder of the member is predominantly thin-bedded (2-12 in. 

thick) limestone that, owing to an abundance of ocherous silica, 

weathers a conspicuous yellow orange. One thin-bedded dark-gray 

bioclastic limestone unit approximately 6 feet thick, containing abundant bryozoans and fusulinids, occurs about 70 feet above the base of 

the member. The contact between the upper limestone and upper 

argillite members is sharp.

Section of Eagle Creek Formation, upper limestone member

[Numbered lithologic units correspond to units in fig. 7]

Section E: Thickness 

Upper argillite member (overlying unit). 

4. Limestone, gray, thin-bedded, siliceous; weathers conspicuous

yellow orange _____________________._____ 75

3. Limestone, gray, thick-bedded, fine- to coarse-grained; contains

abundant siliceous patchworks; beds 1-3 ft thick; hackly

fracture _________________________________ 115

2. Limestone, bioclastic, gray, thin-bedded; weathers ochre ____ 6

Section D: 

Gabbro.

2. Limestone; equivalent to unit 2, section E. 

1. Limestone, gray, thick-bedded; minor interbedded gray siltstone

and argillite; siliceous patchworks common near top ____ 70 

Lower argillite member (underlying unit).
B18 CONTRIBUTIONS TO STRATIGRAPHY 

UPPER ARGILLITE MEMBER

The 410-foot-thick upper argillite member consists predominantly 

of thin-bedded dark-gray argillite with thin lenses and laminae of gray 

siltstone. A dark-gray bioclastic limestone and calcareous siltstone 

unit about 35 feet thick occurs 300 feet above the base, and about 30 

feet of coarser clastic beds, consisting of pyritic sandstone and interbedded sandstone and siltstone, occur at the top of the member.

In the vicinity of section E (fig. 2), the upper argillite member is 

overlain by 120 feet of interbedded light-colored chert with light-gray 

crystalline limestone and minor siltstone. These strata are apparently 

of only local extent, as both east and west of section E the upper 

argillite member is overlain unconformably by amygdaloidal basalt 

flows of the Nikolai Greenstone of Middle and (or) Late Triassic age. 

Although only nondiagnostic crinoid fragments were found in the 

chert and limestone beds, we suspect that these rocks are equivalent to 

Daonella-bearing chert, limestone, and shale beds of Middle Triassic 

age recently found west of Eagle Creek in the headwaters of Canyon 

Creek (Richter and Dutro, unpub. data). The Eagle Creek strata are 

also similar to Daonella -bearing beds that discontinuously overlie 

Permian argillite to the southeast in the eastern Alaska Range (Richter and Jones, 1973) and the southern Wrangell Mountains (Mac 

Kevett, 1970). The contact between the upper argillite member and 

the chert and limestone is sharp and structurally conformable, but on 

the basis of the assumed age difference of the two sequences, it represents an erosion interval of long duration. The Nikolai Greenstone 

locally includes a basal conglomerate containing clasts of chiefly argillite and chert set in a poorly sorted argillaceous to sandy matrix.

Section of Eagle Creek Formation, upper argillite member

[Numbered lithologic units correspond to units in fig. 7] 

Section E: Thickness

Nikolai Greenstone. ^n

Hornblende diorite.

Chert and limestone of Middle Triassic(?) age (overlying unit).

5. Siltstone, dark-gray, shaly; contains fine-grained gray sandstone interbeds ___________________-_____ 15

4. Sandstone, fine-grained, gray, thin-bedded; contains pyrite

crystals _____________________ 15

3. Argillite, dark-gray; gray siltstone with argillite clasts; minor

dirty limestone; dikes of hornblende-feldspar porphyry 50

2. Limestone, bioclastic, dark-gray, thin-bedded; gray calcareous

siltstone __________________________-- 35

1. Argillite, dark-gray, silty; minor bioclastic limestone and graygreen cherty argillite _______________ _ _-__ 295

Upper limestone member (underlying unit).
REVISION OF THE MANKOMEN FORMATION, ALASKA B19 

BIOSTRATIGRAPHY OF THE MANKOMEN GROUP

Marine fossils, present throughout the Mankomen Group, are especially abundant in the Eagle Creek Formation. Vertical distribution is 

generally erratic, and preservation is not always adequate to permit 

generic identification. Nevertheless, fossils were collected from many 

levels in the group. The more abundant forms are brachiopods and 

bryozoans. Fusulinids abound in a few layers; corals and mollusks are 

rare. Identified fossils are listed at their respective locations in the 

stratigraphic columnar sections in figures 3 and 7.

ShortFusulinella sp. are abundant in the two limestone lenses in the 

volcaniclastic member of the Slana Spur Formation. In the overlying 

Eagle Creek Formation, larger fusulinids are found in a number of 

beds. Long, thin forms, includingEoparafusulina mendenhalli Petocz, 

E. waddelli Petocz, E. aff.E. alaskensis (Duribar),Schwagerina rowetti 

Petocz, andSchwagerina sp. occur in the lower limestone member, and 

stouter forms, such as Schwagerina aff. S. hyperborea (Salter) and 

Pseudofusulinella sp., occur in the lower part of the upper limestone 

member. No fusulinids were recovered from the calcareous volcaniclastic member of the Slana Spur Formation or from either of the 

argillite members of the Eagle Creek Formation.

Brachiopods, the commonest marine megafossils, are widely 

distributed throughout most of both formations. The thicker bedded 

crinoidal limestones may contain many brachiopods to the exclusion of 

nearly all other fossils. Most brachiopod shells are scattered and isolated, although some form coquinoid layers, especially in the upper 

part of the lower argillite member of the Eagle Creek Formation. The 

small, readily recognizable brachiopod Anemonaria is especially 

abundant in the lower argillite and upper limestone members of the 

Eagle Creek Formation, and where stratigraphic control is lacking, its 

presence may serve as a field criterion for distinguishing between the 

two limestone members.

Both ramose and fenestrate bryozoans are common throughout the 

Eagle Creek Formation and the calcareous volcaniclastic member of 

the Slana Spur Formation. They are particularly abundant in the 

bryozoan biostrome unit of the lower argillite member of the Eagle 

Creek Formation where they occur in association with spiriferoid and 

productoid brachiopods.

Corals are rare except in a few strata in the lower limestone member 

of the Eagle Creek Formation, where they occur in profusion, and in 

the calcareous volcaniclastic member of the Slana Spur Formation. 

Those in the Slana Spur Formation are poorly preserved. In the Eagle 

Creek Formation the corals include Caninia and the syringoporoid
B20 CONTRIBUTIONS TO STRATIGRAPHY

Sinopora and are found associated with abundant Eoparafusulina. 

These coral-fusulinid beds are probably equivalent to Assemblage 

Zone C of Petocz (1970, p. 19).

Mollusks are very rare and are represented by a few poorly preserved pelecypods and gastropods found only in the Eagle Creek Formation. Cephalopods were collected at two horizons in the Eagle Creek 

Formation and are important in corroborating other evidence as to 

age. One form, Artinskia? orSynartinskia?, occurs in the lower 200 feet 

of the lower argillite member. A second form, resembling Daubichites, 

was collected from high in the upper argillite member.

AGE AND CORRELATION

The Slana Spur Formation is Middle Pennsylvanian to Early Permian in age. Fossils collected from the two limestone lenses in the 

volcaniclastic member, approximately 700 and 1,200 feet above the top 

of the Tetelna Volcanics, include abundant Fusulinella sp. associated 

with other smaller foraminifers including Bradyina sp. and 

Climacammina sp. A Middle Pennsylvanian (probable Atokan) age is 

indicated. This age is within the limits given by Rowett (1969, p. 15, 

18) for lithologically similar volcanogenic rocks exposed on Rainbow 

Mountain in the Delta River area (locality 2, fig. 1). Brachiopods from 

the calcareous volcaniclastic member are similar to the Early Permian 

(Sakmarian) forms from the lower part of the overlying Eagle Creek 

Formation.

The Eagle Creek Formation is entirely of Early Permian age. The 

lower limestone member contains Early Permian brachiopods, associated with fusulinids which Petocz (1970) described from his Assemblage Zone C (fig. 8). Petocz assigned a late middle to late(?) 

Sakmarian age to this zone. This level is also probably equivalent to 

fusulinids found in beds near the top of Zone E of Waterhouse (in 

Bamber and Waterhouse, 1971), the uppermost of his E Zone faunas. 

Brachiopods from the lower argillite member are not too different from 

those in the underlying lower limestone member. The cephalopod 

Artinskia?, or possibly Synartinskia, was collected from low in the 

lower argillite member, but the material is not well enough preserved 

for positive generic identification. The age of the lower argillite 

member is either late Sakmarian or early Artinskian. The lower two 

members are, in part, correlatives of the Jungle Creek Formation of 

the Yukon Territory (Bamber and Waterhouse, 1971).

The upper limestone member contains brachiopods like those in 

Waterhouse's Zone F, together with Schwagerina aff. S. hyperborea 

(Salter), which is also characteristic of this level in the Yukon Territory. Schwagerina hyperborea is found in Petocz's Assemblage Zone F,
REVISION OF THE MANKOMEN FORMATION, ALASKA B21

which he considered of early to middle Artinskian age. The age of the 

upper limestone member is, therefore, most likely middle or late Artinskian (upper Leonardian). Finally, the few brachiopods from the 

upper argillite, together with the occurrence ofDaubichitest, indicate 

a correlation with the upper part of Waterhouse's brachiopod Zone F. 

This suggests a post-Artinskian, possibly Ufimian, equivalence. The 

upper limestone and upper argillite members of the Eagle Creek 

Formation are thus approximate correlatives of the type Tahkandit 

Limestone (Brabb and Grant, 1971).

Probable correlations of Mankomen Group strata in the eastern and 

east-central Alaska Range are shown in figure 8. The lithology of the 

Slana Spur Formation and observed fusulinid zonation suggests affinity with the upper part of Bond's (1969) informal Phelan Creek formation in the Gulkana Glacier area and with the lower sequence of 

Rowett's (1971) and Petocz' (1970) Mankomen Formation in the Rainbow Mountain and upper Delta River areas. The nonvolcanogenic 

sequences of limestone and argillite in these same areas are, without 

much question, correlative with the Eagle Creek Formation. Less 

certain is correlation to the southeast in the Slana area, where Permian limestones, overlying a thick sequence of volcaniclastic rocks, 

contain abundant volcanic debris. Eagle Creek affinity is indicated, 

however, because of the similarity in coral zonation between the Slana 

and Rainbow Mountain areas (Rowett, 1971).

In the upper Delta River and Rainbow Mountains areas, both Petocz 

(1970) and Rowett (1971) placed the Wolfcampian-Leonardian boundary near the base of the limestone and argillite sequence (fig. 8). At 

Eagle Creek however, fusulinids in apparently correlative rocks indicate that the boundary is higher, probably near the base of the upper 

limestone member of the Eagle Creek Formation. This interpretation 

agrees with the middle Wolfcampian age assigned to the lower units of 

limestone and argillite in the Gulkana Glacier area (informal Gulkana Glacier formation) by Bond (1969) and Gilbertson (1969).

The Pennsylvanian-Permian boundary at Eagle Creek lies somewhere within the Slana Spur Formation, probably near the base of the 

calcareous volcaniclastic member. Northwest in the east-central 

Alaska Range, a similar change in lithology from predominantly 

volcanic-noncalcareous volcaniclastic rock to calcareous volcaniclastic 

rock also appears to span the Pennsylvanian-Permian boundary (fig. 

8). Southeast of the area shown in figure 8, the thick sequences of 

andesitic volcanic, and interbedded volcaniclastic rocks mapped by 

Moffit (1954) and Richter (197la, b) are now considered equivalent to 

the Tetelna Volcanics and hence presumably are of Pennsylvanian 

age. These sequences were originally thought to be Permian in age 

chiefly because of their association with conformably overlying Per-
B22 CONTRIBUTIONS TO STRATIGRAPHY

Locality 1 Locality 2 Locality 3

UPPE

(P

c

1

c

-1 .

Z

E

]

1 DELTA RIVER DELTA RIVER- GULK

Btocz 1970) RAINBOW MOUNTAIN (

(Rowett, 1969, 1971; Gil

Hanson, 1963) Not

measured

to top

i 

5

^ :

 c

1

c

8

i

FEET

2000

1000

0

:

a,

s~~~~. ^*

lgH-C:-^ rr ~i'

5v5 H&£?:

:?£?:.' . u°.?.!?.

..?.?.-

S*.?..

c

Assemblage S

"I Schwagerina . . - o

vScfiwagtfn'na p w

-.

^ Schwagerina 6

Eoparafusulina

Schwagerina B

Pwudo/bju//n-

-'"" A 

IS Fault

.1 "

i ' s

-,-

c

.2

CD fiii-. . §

\ ::flf!~. * " 

Bas.no, \ '!§:, | c

"POMd \ '%, s 1 i

\ "%

\ %,

\ '%

\ "«

\

\ 

\

METRES '

 10OO \

\

1 |

1 =i

'"' %; /;:.

'S

Fault ?'

\

\

 BOO < \

> \

Z \

Z x

S! \

 o

\

731*1

E «

j*j»?

n:5

?.J?.°

00^0

s

VVVx'v

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0000

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sag

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'ooVo

n?i°'°V

|

vvSS

Jo'OQ

P

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0000

JS

vvvv

?.?.?.?.

0000

ft!

0=?

0 

Durhamtna g

Sinopora £

Timania o

Auloclisia -

Ca nlnia

c 

Timania «j

c E

2 .S 0

< 0. u, 

S

IE J J>

" 5: s

Q.

T Botnropnyllum .^ li

< Pseudobradyphyllum _.:;; : ;:H!.--:

1 Bradyphyllum .:; :' ]IH.;: ' /

f Bothrophyllum ..: «;»::!'" 

< Stringopora .-ijlHllj:''' '

[ Timania .: ;:i!lf' /

f Heritschiodes ' 

:.l Bolhrophyllum /

Fusulinella >

WedektndeUlna /

/

 « / 10 miles 

/

/

/ Cryptophyllum

/ Cladochonus

Michelinla

AN A GLACIER

Bond 1969;

her ton, 1969)

Tertary

rocks

-I-V

«: r£oparo/l<»«mi 

7J7:y1 { Schwagerina 

 JVi'~ \_Pseudoftisulinella "°°-

s°tt

o'Vo'o Thompsonella 

.?.?. ?:: Pseudoflaullnella

VxxX'

g3ffi Pseudoflisullnella

°iii "' vis

£-!4iV. Pseudofusullnella

^sf ,.,.,^s?^P^s''v

: ^M^PS^'

°o°o° ^ \

HI ^N

Fault

\

FIGURE 8. Generalized sections of Pennsylvanian and Permian sequences in 

the eastern and east-central Alaska Range showing zonation of fusulinids 

and corals, suggested lithologic correlation of the Mankomen Group, and 

some inferred time boundaries. Ages at left side of each column are those 

assigned by author(s) cited at top of column. The time lines that extend 

across the diagram are based on faunal evidence from the Eagle Creek area.
REVISION OF THE MANKOMEN FORMATION, ALASKA B23

EAGLE CREEK 

(Thij report)

Locality 4

SLANA 

(Rowett, 197t)

5 .3 

£ I

argllllta

< c 

S I

Lowar

.. isssd

Pseudofusulinella | p.tocj' 

Sch wagerina 

hyperborea

g Top not 

-1 expotad

I/I

/I!

Timania 

Auloclltta

EXPLANATION

PRINCIPAL ROCK TYPES

Calcareous volcaniclastic

Top and bottom ofSlana Spur

Limestone; stippling Volcnniclastic rocks, luff, 

indicates volcanic detritus and minor limestone

Volcanic Hows, 

fragmental volcanic rocks.

FIGURE 8. Continued.
B24 CONTRIBUTIONS TO STRATIGRAPHY

mian marine strata (the upper parts of our Mankomen Group). Similar 

volcanic and volcaniclastic rocks in the Station Creek Formation in 

the northern Wrangell Mountains described by Smith and MacKevett 

(1970), and assigned a Permian(?) age by them, also suggest affinity 

with the Tetelna Volumes.

TECTONIC SIGNIFICANCE

The available lithologic and paleontologic data from Eagle Creek 

and elsewhere in the eastern part of the Alaska Range suggest that the 

beginning of marine carbonate deposition and the end of persistent 

volcanism occurred near the end of Pennsylvanian time. Recognition 

of a Pennsylvanian age for the bulk of the volcanogenic rocks, conformably underlying Permian marine deposits, shifts the timing of 

volcano-tectonic events in this part of Alaska. On the basis of the 

earlier assumed Permian age of most of the volcanic rocks in the 

eastern Alaska Range, Richter and Jones (1973) and Berg, Jones, and 

Richter (1972) postulated that a late Paleozoic volcanic island arc from 

which these rocks were derived was also mostly Permian in age. The 

new data presented in this paper suggest that the arc developed in the 

Pennsylvanian and may have been virtually inactive by the Early 

Permian.

REFERENCES

Bamber, E. W., and Waterhouse, J. B., 1971, Carboniferous and Permian stratigraphy

and paleontology, northern Yukon Territory, Canada: Bull. Canadian Petroleum

Geology, v. 19, no. 1, p. 29-250. 

Berg, H. C., Jones, D. L., and Richter, D. H., 1972, Gravina-Nutzotin belt tectonic

significance of an upper Mesozoic sedimentary and volcanic sequence in southern

and southeastern Alaska, in Geological Survey research 1972: U.S. Geol. Survey

Prof. Paper 800-D, p. D1-D24. 

Bond, G. C., 1969, Permian volcanics, volcaniclastics, and limestones in the Cordilleran

eugeosyncline, east-central Alaska Range, Alaska: Ph.D. thesis, Univ. Wisconsin,

Madison, 144 p. 

Brabb, E. E., and Grant, R. E., 1971, Stratigraphy and paleontology of the revised type

section for the Tahkandit Limestone (Permian) in east-central Alaska: U.S. Geol.

Survey Prof. Paper 703, 26 p. 

Gilbertson, R. L., 1969, Biostratigraphy of the upper Paleozoic rocks in the Gulkana

Glacier area, Alaska: M.S. thesis, Univ. Wisconsin, Madison, 43 p. 

Hanson, L. G., 1963, Bedrock geology of the Rainbow Mountain area, Alaska Range,

Alaska: Alaska Div. Mines and Minerals Geol. Rept. 2, 82 p. 

MacKevett, E. M., Jr., 1970, Geologic map of the McCarthy C-4 quadrangle, Alaska:

U.S. Geol. Survey Geol. Quad. Map GQ-844, scale 1:63,360. 

Mendenhall, W. C., 1905, Geology of the central Copper River region, Alaska: U.S. Geol.

Survey Prof. Paper 41, 133 p. 

Moffit, F. H., 1954, Geology of the eastern part of the Alaska Range and adjacent areas:

U.S. Geol. Survey Bull. 989-D, p. 65-218. 

Petocz, R. G., 1970, Biostratigraphy and Lower Permian Fusulinidae of the upper Delta

River area, east-central Alaska Range: Geol. Soc. America Spec. Paper 130, 94 p.
REVISION OF THE MANKOMEN FORMATION, ALASKA B25

Richter, D. H., 1971a, Reconnaissance geologic map and section of the Nabesna A-3 

quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 1-655, scale 1:63,360.

 1971b, Reconnaissance geologic map and section of the Nabesna B-4 quadrangle,

Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map t-656, scale 1:63,360. 

Richter, D. H., and Jones, D. L., 1973, Structure and stratigraphy of eastern Alaska

Range, Alaska, in Arctic Geology: Am. Assoc. Petroleum Geologists, Memoir 19, p.

408-420. 

Rowett, C. L., 1969, Upper Paleozoic stratigraphy and corals from the east-central

Alaska Range, Alaska: Arctic Inst. North America, Tech. Paper 23, 120 p.

 1971, Reconnaissance biostratigraphy of the Lower Permian in the Slana area, 

eastern Alaska Range, Alaska: Pacific Geology, v. 3 , p. 31-44.

Smith, J. G., and MacKevett, E. M., Jr., 1970, The Skolai Group in the McCarthy B-4, 

C-4, and C-5 quadrangles, Wrangell Mountains, Alaska: U.S. Geol. Survey Bull. 

1274-Q, 26 p.