Schists of the 

Central Alaska Range

GEOLOGICAL SURVEY BULLETIN 1254-E

Schists of the 

Central Alaska Range

By CLYDE WAHRHAFTIG

CONTRIBUTIONS TO STRATIGRAPHY

GEOLOGICAL SURVEY BULLETIN 125 4-E

Distribution of schists within 

Fairbanks A-2, A-3, and A-4 

quadrangles and Healy D-2, 

D-3, and D-4 quadrangles

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

STEWART L. UDALL, Secretary

GEOLOGICAL SURVEY 

William T. Pecora, Director

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

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

Page

Abstract__. ___________________________________.____-___-___-___--_ El

Introduction. _____________________________________________________ 2

General structural and areal relations. ___________--_-_-_-________--_- 8

Birch Creek Schist_________..___________________ ___________--__-___.. 10

Keevy Peak Formation_____..________________________________-___-__ 11

Totatlanika Schist._________________________________________________ 13

Moose Creek Member___-._-__--_____-_______-_-_-______-___---- 13

California Creek Member____ __-_-.__________-____-_______-_----- 14

Chute Creek, Mystic Creek, and Sheep Creek Members.___________ 16

Age and origin of the Totatlanika Schist______-___________________ 18

Metavolcanic schists and associated rocks south of the Birch Creek Schist. 20

References cited.__________________________________________________ 21

ILLUSTRATIONS

Page 

FIGURE 1. Index map of Alaska__________________----___-_-__-_----- E3

2. Generalized geologic map of part of the central Alaska Range 

Fairbanks A-2, A-3, and A-4 quadrangles and Healy D-2, 

D-3, and D-4 quadrangles. ___-_----------------------- 4

3. Geologic map of the northeastern part of Healy D-2 quadrangle. _______________________________________________ 7

4. Sections showing structural relations of the schist formations-- 11

5. Diagrammatic stratigraphic panel of the schist formations in 

the northern part of Healy D-2 and D-3 quadrangles and 

southwestern part of Fairbanks A-3 quadrangle._._____-__ 15

in

CONTRIBUTIONS TO STRATIGRAPHY

SCHISTS OF THE CENTRAL ALASKA RANGE

By CLYDE WAHRHAFTIG

ABSTRACT

The schist formations of the central Alaska Range lie in belts that trend 

east-west. The formations are deformed into a broad arch having steep limbs, 

and there is a belt of gentle dips in foliation along the north side of the arch. 

The Birch Creek Schist underlies a belt fr-10 miles wide along the axis of the 

arch and is flanked on the north by the Keevy Peak Formation, beyond which is 

the Totatlanika Schist. South of the Birch Creek Schist are metavolcanic rocks.

The most conspicuous structure is an axial-plane cleavage in the Birch Creek 

Schist and Keevy Peak Formation and a mineral foliation in the Totatlanika 

Schist. These are generally parallel to contacts between the formations and 

are deformed into the broad arch. The mineral foliation in the Birch Creek 

Schist and Keevy Peak Formation, as defined by oriented mica flakes and 

thin segregation laminae of quartz and sericite, is deformed into tight minor 

folds whose axial planes are parallel to the conspicuous cleavage and whose 

axes trend east and are nearly horizontal. The schists have been intensely 

deformed, and most formational contacts are thought to be thrusts whose original 

nature has been obscured by metamorphism.

The Birch Creek Schist is restricted to quartz-sericite schist and interbedded 

quartzite, black schist, and marble along the crest of the arch; it lacks original 

sedimentary structures. The Keevy Peak Formation is a newly named formation, 

between 2,500 and 4,000 feet thick, and is thought to be unconformable on the 

Birch Creek Schist. It consists of quartz-sericite schist, black schist and quartzite, 

purple and green slate, and thick lenticular bodies of stretched conglomerate.

The Totatlanika Schist is here divided into five new members, as follows: 

(1) At the base is the Moose Creek Member, 0-5,000 feet thick, which consists 

of three strongly contrasting lithologies black schist, green chloritic schist, and 

yellow quartz-orthoclase gneiss and schist, (2) overlying this is the California 

Creek Member, at least 3,000 feet thick, which consists of white- to buff-weathering gray quartz-orthoclase gneiss and schist, one facies of which contains abundant megacrysts of orthoclase up to 2.5 centimeters long, (3) overlying and interfingering with the California Creek Member is the Chute Creek Member 

1,300-1,500 feet of dark-green chloritic schist, (4) this in turn is overlain by 

the Mystic Creek Member 2,000-3,000 feet of predominantly fine grained purple, 

green, and yellow schist of rhyolitic origin, and (5) at the top is the Sheep Creek 

Member 400-1,000 feet of black schist, overlain by 2,000 feet of purple and

El
E2 CONTRIBUTIONS TO STRATIGRAPHY

green slate (probably metamorphosed tuff) overlain by 2,000 feet of epiclastic 

quartz-feldspar-sericite schist.

The Totatlanika Schist is predominantly of volcanic origin, and interbedded 

black schist and a fossiliferous limestone lens indicate a submarine origin. The 

chloritic schist may originally have been basaltic flows or basic intrusions, and 

the feldspathic schists may have originally been related to underwater pyroclastic eruptions.

The metavolcanic schists south of the Birch Creek Schist include a lower unit 

800-2,000 feet thick of interbedded green chloritic schist and black schist, tentatively correlated with the Ohute Creek Member of the Totatlanika Schist, and 

an upper unit at least 1,000 feet thick of quartz-feldspar-sericite schist of 

rhyolitic origin, tentatively correlated with the Mystic Creek Member.

The only fossil evidence on the age of the schists comes from a fossiliferous 

limestone lens in the Mystic Creek Member, which yielded Syringopora of Mississippian(?) age. The Totatlanika Schist is therefore assigned a Mississippian(?) 

age. The Birch Creek Schist and Keevy Peak Formation are considered to be 

Precambrian or Paleozoic.

INTRODUCTION

Schists and gneisses have been known from the central part of the 

Alaska Range ever since the pioneering explorations of Brooks and 

Prindle in 1902. In their reports (Prindle, 1907, p. 206-207; Brooks, 

1911, p. 56-60,149-150), they described two formations: (1) A belt of 

quartz-sericite schist, which they correlated with the Birch Creek 

Schist of the Yukon-Tanana Upland (Spurr, 1897), and (2) to the 

north of the quartz-sericite schist, a belt of quartz-orthoclase-sericite 

gneiss, which they regarded as metamorphosed rhyolite and assigned 

to the Silurian or Lower Devonian.

The Birch Creek Schist of the Mount McKinley area (fig. 1) was 

traced eastward to the Delta River by Capps (1912, pi. 2) and eastward 

from the Delta River by Moffit (1954, pi. 7) to a point that was near 

the Tanana River and only 3 miles distant along the strike from schist 

in the Yukon-Tanana Upland correlated by Mertie (1937) with the 

Birch Creek Schist of the type locality. These tracings confirm Brooks' 

and Prindle's long-range correlation. Mertie concluded that the Birch 

Creek Schist of the Yukon-Tanana Upland was Precambrian, probably early Precambrian, in age (Mertie, 1937, p. 55-59).

Strontium-87-rubidium-87 ages ranging from 120 m.y. (million 

years) to 1,170 m.y. were reported for biotite, muscovite, and wholerock samples of the Birch Creek Schist by Wasserburg, Eberlein, and 

Lanphere (1963). However, Lanphere later wrote that all the isotopic 

data are compatible with a period of Mesozoic metamorphism if interpreted in the light of recent work on the redistribution of strontium 

during metamorphism. Thus, to date, no proof of a Precambrian age 

for the Birch Creek Schist has been found by isotopic methods, and the 

late age of the metamorphism suggested by the isotopic data renders 

Mertie's argument for a Precambrian age invalid. The uncertainties
SCHISTS OF THE CENTRAL ALASKA RANGE E3

introduced by the new data have led to the assignment of the Birch 

Creek Schist to the Precambrian or early Paleozoic (Pewe, 

Wahrhaftig, and Weber, 1966).

Capps (1912, p. 22-26) mapped the distribution of the quartz - 

orthoclase-sericite schist and gneiss and named these feldspathic rocks 

the Totatlanika Schist, from their exposures in the lower canyon of 

the Totatlanika Eiver (fig. 2). In the Totatlanika Schist, Capps included bodies of schistose conglomerate and quartz-sericite schist in 

the basin of the Wood River. He found no evidence regarding the age 

of the formation. In 1954 fossils were found in fragments of limestone weathering from a hill of Totatlanika Schist about three-fourths 

of a mile southwest of the junction of Rogers and Sheep Creeks in 

Healy D-2 quadrangle (fig. 3). These fossils included a Syringopora 

identified by Helen Duncan as being similar to a Syringopora in limestones of the Lisburne Group, and consequently the Totatlanika Schist 

was assigned a Mississippian( ?) age (Wahrhaftig, 1958, p. 12).

An area of eight 15-minute quadrangles in the northern part of the 

central Alaska Range (fig. 1), including the type locality of the Totatlanika Schist and the area where the Birch Creek Schist was first seen 

in the Alaska Range, was studied by the author and his associates between the years 1944 and 1958, in conjunction with coal investigations 

in the Nenana coal field. The geo] ogic mapping for a publication scale 

of 1: 63,360 has made it possible in the Wood River basin to separate

146 C

142°

FIGURE 1. Index map of Alaska showing location of area (crosshatched) 

of figure 2.
E4 CONTRIBUTIONS TO STRATIGRAPHY

149°00' 148-30'

64° 00

63°45

Contact Fault

Dotted where 

concealed

Thrust fault

Sawteeth on upper 

plate

FIGUEE 2. Generalized geologic map of part of the central Alaska Range showing distribution of the schist formations in the Fairbanks A-2, A-3, and A-4 

quadrangles and the Healy D-2, D-3, and D-4 quadrangles.
SCHISTS OF THE CENTRAL ALASKA RANGE

148-00' 147°30'

EXPLANATION

QTs

Sedimentary deposits

Ti

Intrusive rocks

Includes Mesozoic 

intrusive rocks

Kc

Cantwell Formation

Sheep Creek Member

Mystic Creek Member

Chute Creek Member

Locally includes tongues 

of Mystic Creek Member

Mtc 

California Creek Member

Moose Creek Member

' I < D ?

. UJ<

H

Fossil locality Outline of text 

figure

Green metavolcanic schist and

Birch Creek Schist

FIGURE 2. Continued..
E6 CONTRIBUTIONS TO STRATIGRAPHY
EXPLANATION

Intrusive rhyolite schist

 : : : wstsb

Sheep Creek Member 

Mtse, epiclastic quartz-feldsparsericite schist 

Mtst, tuffaceous slate 

Mtsb, black carbonaceous schist

Mystic Creek Member

ct

H >-LJ <

H

u

California Creek Member

Mtb, black carbonaceous schist

Moose Creek Member

Mtb, black carbonaceous schist

Keevy Peak Formation

kpb, black carbonaceous schist 

kpc, stretched conglomerate

Birch Schist

Z~ <0 CC N 

CD O

CC CC 0-0

Contact

Fault

Fossil locality

FIGURE 3. Geologic map of the northeastern part of Healy D-2 quadrangle, showing the distribution of members 

of the Totatlanika Schist. Outline of area is shown in figure 2.
PJ8 CONTRIBUTIONS TO STRATIGRAPHY

the Totatlanika Schist from the quartz-sericite schist and stretched 

conglomerate, although Capps (1912) originally included them in the 

formation. This quartz-sericite schist and stretched conglomerate are 

here named the Keevy Peak Formation. The Totatlanika Schist overlying the Keevy Peak is divided into five named members: Moose 

Creek, California Creek, Chute Creek, Mystic Creek, and Sheep Creek 

Members. Schists of volcanic origin, lying south of the Birch Creek 

Schist, have also been separated from the Birch Creek Schist as 

mapped by Capps (1940, pi. 2). These schists are not formally named, 

although they probably correlate with the Totatlanika Schist. The distribution of the schist formations in six of the quadrangles (Fairbanks 

A-2, A-3, A-4; Healy D-2, D-3, D-4) is shown in figure 2.

GENERAL STRUCTURAL AND AREAL RELATIONS

The schist formations lie in belts that trend east and west, parallel to 

the trend of the range. The Totatlanika Schist lies to the north; it is 

probably the basement rock in the southern part of the area shown on 

Fairbanks quadrangle map (scale, 1: 250,000) (Pewe, Wahrhaftig, and 

Weber, 1966) and extends south into the northern parts of Healey D-2 

and Healy D-3 quadrangles (fig. 2). Its exposures are limited, however, 

for over most of this area it is buried beneath Cenozoic deposits. South 

of the Totatlanika Schist, the Keevy Peak Formation crops out in a 

belt 3,500-7,000 feet wide in northern Healy D-2 and Healy D-3 quadrangles. Its extension to the west is largely buried beneath Tertiary 

rocks. The Birch Creek Schist lies south of the Keevy Peak Formation 

and makes up the rugged mountains of the northern part of the Alaska 

Eange, including the ridge through which the Nenana Eiver has cut 

its gorge between McKinley Park Station (south of fig. 2) and Healy. 

South of the Birch Creek Schist, in southern Healy D-2, D-3, and D-4 

quadrangles, is a belt of metavolcanic and associated metasedimentary 

schists. This belt is cut off on the south by an immense zone of faulting. 

South of this fault the Paleozoic and Mesozoic rocks are relatively unmetamorphosed and undef ormed as compared with the schists.

Within the schists, the most conspicuous structures are an axial-plane 

cleavage in the Birch Creek Schist and Keevy Peak Formation and a 

mineral foliation in the Totatlanika Schist. These structures appear to 

be roughly parallel to the contacts between the formations.

The planar structures and the contacts between the formations are 

folded into a broad east-trending arch whose core is the Birch Creek 

Schist. To the north of the arch is an area of rather gentle dips in the 

foliation of the Totatlanika Schist, in which at least one prominent 

syncline can be recognized. The flanks of the arch are steep, dipping 

from 45° to vertical. The steep north flank includes all the area of the
SCHISTS OF THE CENTRAL ALASKA RANGE E9

Keevy Peak Formation plus a considerable amount of Birch Creek 

Schist and Totatlanika Schist. The south, flank includes part of the 

Birch Creek Schist and the metavolcanic schists south of the Birch 

Creek Schist. This simple structural pattern becomes even more pronounced if the overlying Tertiary rocks are "unfolded," for the 

moderately dipping foliation in the Totatlanika Schist of the northern 

foothills is generally nearly parallel to the dip of the overlying coalbearing rocks.

These simple structures conceal much structural complexity within 

the schist formations, however. Original sedimentary structures are 

completely destroyed within the Birch Creek Schist, and the foliation 

within the formation is due to planar parallelism of sericite flakes and 

to segregation of quartz and sericite into sheets a millimeter or so thick. 

The rocks are tightly folded into minor folds with amplitudes and 

wavelengths of several inches to 20 feet. The axial-plane cleavage of 

these minor folds causes the conspicuous schistosity visible on canyon 

walls and distant outcrops. Lithologic layering in the Birch Creek 

Schist, as between quartzite layers and sericite schist, is generally 

parallel to the mineral foliation and the tight folds. Axes of the minor 

folds plunge gently or are horizontal and generally trend east or northeast, as does the mineral elongation and streaking in the Totatlanika 

Schist. Lineations that bend around the axes of the minor folds suggest a still earlier period of deformation, whose evidence has been all 

but destroyed.

Original sedimentary features, such as pebbles, graded bedding, and 

crossbedding, are locally preserved within the Keevy Peak Formation, 

but this formation, too, had undergone intense minor folding during 

more than one period of deformation. Both sedimentary schist formations are tectonites, and the pervasive minor folding probably developed in the manner described by Paterson and Weiss (1966).

Several features suggest that the schist formations of the central 

Alaska Range have been cut by numerous unmapped thrusts and that 

many of the mapped lithologic contacts between schists of different 

units are in fact tectonic contacts whose original nature has been 

obscured by subsequent metamorphism. These supposed thrust-fault 

contacts are parallel to the axial planes of the minor folds in the Birch 

Creek Schist and Keevy Peak Formation and to the mineral foliation 

of the Totatlanika Schist.

Slices of rocks characteristic of some members of the Totatlanika 

Schist lie above or below their normal stratigraphic position in the 

Totatlanika Schist or lie within the Keevy Peak Formation or the 

Birch Creek Schist (fig. 2). These are thought to be thrust slices. 

Although a tectonic origin for these bodies seems most likely, the

283-147 O 68 2
E10 CONTRIBUTIONS TO STRATIGRAPHY

ppssibility that they are metamorphosed intrusions cannot be ruled 

out.

Complicated stratigraphy of interbedded green metavolcanic schist 

and black schist characterizes one of the schist units south of the Birch 

Creek Schist and is repeated in at least two lenticular bodies separated 

by quartz-sericite schist continuous with the Birch Creek Schist (fig. 4, 

lower). This repetition is best explained as the result of thrusting, as 

is the increasingly complex pattern of rhyolite schist and basic metavolcanic schist as one proceeds eastward across the south part of Healy 

D-3 and D-2 quadrangles.

Although most of the unmapped thrusts suggested only by stratigraphic dislocation appear to have predated or to have been contemporaneous with the metamorphism, one mapped thrust in the 

north part of Healy D-3 and south part of Fairbanks A-3 quadrangles, 

between two members of the Totatlanika Schist, cuts the foliation and 

lithologic boundaries at a considerable angle and apparently postdates 

the metamorphism. It predates the deposition of the Tertiary rocks in 

the area.

The structural complexities of the schist formations make meaningful stratigraphic thicknesses impossible to obtain in most cases. Even 

the stratigraphic sequence between some of the formations is doubtful. 

The thicknesses given herein are present measured thicknesses of 

representative bodies perpendicular to their contacts or to the latest 

foliation. They may or may not be equivalent to the true stratigraphic 

thickness.

BIRCH CREEK SCHIST

The Birch Creek Schist in the central Alaska Range is restricted 

to the terrane that is predominantly quartz-sericite schist, quartzite, 

sericite schist, and quartz-sericite-calcite schist, with minor amounts 

of carbonaceous schist and marble. It is of sedimentary origin, probably as marine shales and sandstones. Typical schist consists of 60-80 

percent quartz, 10-25 percent sericite, 5-10 percent calcite, and 5-15 

percent albite and microcline. Pyrite is the most common opaque 

mineral. Tourmaline and zircon are rarely present and are probably 

detrital. A few bodies and layers of chloritic schist, chlorite-epidote, 

chlorite-actinolite, tremolite, and epidote-chlorite-albite schist that 

occur in the area mapped as Birch Creek Schist were probably sills or 

volcanic layers. They establish the metamorphic grade of the schist 

as that of the greenschist facies. Typical Birch Creek Schist is light 

gray to greenish gray in fresh exposures but weathers to buff or light 

brown. Its thickness measured perpendicular to the axial-plane cleavage of the minor folds (not a true stratigraphic thickness) is at least 

10,000 feet.
SCHISTS OF THE CENTRAL ALASKA RANGE

A

10,000' ,

Ell 

B

SEA LEVEL I

Mtcc Mtm

Mts

be

Mtcc Mtb

0 1 2 MILES 

I_______I_______I

D

be

be KKc

ftr-3

FIGUKE 4. Sections showing structural relations of the schist formations. Upper: 

Section through the Sheep Creek syncline showing structural relations in the 

Keevy Peak Formation and Totatlanika Schist. See figure 3 for explanation 

and location of section. Lower: Section through tihe metavolcanic schists in 

southern Healy D-3 quadrangle. See figure 2 for explanation and location of 

section.

KEEVY PEAK FORMATION

A belt of quartz-sericite schist, black carbonaceous schist, gray and 

green and purple slate, black quartzite, and stretched conglomerate, 

originally mapped by Capps (1912) with the Totatlanika Schist and 

earlier mapped by Wahrhaftig (1958, pi. 1) with the Birch Creek 

Schist, is here named the Keevy Peak Formation. Although the Keevy 

Peak resembles the Birch Creek Schist in lithology and structural 

complexity, it is thought to be unconformable upon it. Lenticular 

bodies of stretched conglomerate as much as 5 miles long and 1,200 

feet thick, containing pebbles of quartz, chert, and phyllite, occur 

along its contact with the Birch Creek Schist, and are thought to be a 

basal conglomerate of the Keevy Peak derived in part from the Birch 

Creek Schist. Sedimentary structures, such as graded bedding, crossbedding, and pebble beds, are present in places in the Keevy Peak For-
El<2 CONTRIBUTIONS TO STRATIGRAPHY

mation despite the intense deformation it has undergone. They have 

not been observed in the Birch Creek Schist.

Because of the deformation undergone by the Keevy Peak Formation, a type section is difficult to define. The type locality for the formation is in the Healy D-3 quadrangle on the northwest shoulder of 

Keevy Peak (fig. 2), from a point on the ridge crest 5,700 feet N. 40° 

W. of the summit, where mixed stretched conglomerate and black 

schist overlie quartz-sericite schist of the Birch Creek Schist, to the 

north side of a saddle on the same ridge about 10,000 feet N. 36° W. 

of the summit, where black schist of the Keevy Peak Formation is 

overlain by quartz-orthoclase gneiss of the Totatlanika Schist. The 

thickness of the Keevy Peak in this section is 2,500-3,000 feet, and the 

formation appears to dip 50°-65° N. The formation in this section consists of green and purplish slates, greenish-gray quartz-sericite schist, 

black schist, black quartzite, brownish-weathering calcareous schist, 

and a schist consisting of large bluish grains of quartz and feldspar 

embedded in a fine-grained matrix of quartz and sericite. This last 

schist is known in the field as grit. Stretched conglomerate occurs near 

the base.

Another typical section, designated a reference section, occurs at 

the headwaters of Rogers Creek in the Healy D-2 quadrangle (fig. 3) : 

At the base, 1,200-2,000 feet of stretched conglomerate, overlain by 

200-800 feet of black schist; about 1,000 feet of quartz-sericite schist 

and sericite schist; about 500 feet of black quartzite; 500 feet of 

quartz-sericite schist and stretched conglomerate; and, at the top, 

about 800 feet of interbedded black schist and quartzite. The section 

dips 35°-65° N.

Under the microscope, typical quartz-sericite schist from the Keevy 

Peak Formation is seen to consist of 60-90 percent quartz, 5-20 percent sericite, 5-30 percent calcite, and a few percent feldspar. Carbonaceous matter, chlorite, and rarely stilpnomelane may be present. Textures are cataclastic to crystalloblastic, and grain size ranges from 

0.02 mm (millimeter) for the fine-grained matrix to 1 mm for the 

large bluish quartz grains whose presence gave rise to the term "grit" 

for describing the schist.

The Keevy Peak Formation is overlain by the Totatlanika Schist. 

If the stratigraphic relations reflect a depositional sequence, the Keevy 

Peak Formation might be Mississippian or older in age. However, 

until the field relations are better understood, the Keevy Peak is assigned to the Precambrian or Paleozoic.
SCHISTS OF THE CENTRAL ALASKA RANGE E13 

TOTATLANIKA SCHIST

The Totatlanika Schist is the quartz-orthoclase-sericite schist and 

gneiss of the Northern Foothills of the Alaska Range (Wahrhaftig, 

1965, p. 35) and is interpreted by Capps (1912, p. 22) to be metamorphosed rhyolite. Geologic mapping in the period 1954 57 showed 

that the typical gray to pale-buff quartz-orthoclase-sericite schist and 

gneiss of the type locality in the canyon of the Totatlanika River 

interfingered eastward in the Wood River valley with several stratigraphic units of great lithologic variety, although volcanic rocks predominate. In order to clarify the stratigraphic relationships, these 

stratigraphic and lithologic units are here grouped together into five 

members, whose relationships are shown in the panel diagram in 

figure 5.

MOOSE CREEK MEMBER

The lowest unit of the Totatlanika Schist, here named the Moose 

Creek Member, is made up of rock bodies of three sharply contrasted 

lithologies black schist, green chloritic schist, and yellow quartzorthoclase schist and gneiss. These rock bodies are generally lenticular 

and are tectonically disturbed, for in much of the area of exposure, this 

member underlies a thrust fault, The type locality is designated as a 

small canyon tributary to Moose Creek from the north (148°06' W., 

63°59' N.), where all three lithologic types are exposed, but in obscure 

relationships. A reference section, also within the Healy D-3 quadrangle, is designated as the exposures along the ridge crest between 

the headwaters of Sheep Creek and Last Chance Creek, about 4 to 

5 miles southwest of the type locality. In this section, 100-500 feet of 

black schist is overlain by a lens of dark-green chloritic schist about 2^ 

miles long and as much as 1,700 feet thick. This is overlain in turn by 

about 700 feet of black carbonaceous schist, 2,300 feet of pale-yellow 

quartz-orthoclase schist and gneiss, and about 300 feet of black schist 

to the base of the overlying California Creek Member. This is the 

thickest section of the Moose Creek Member but may be tectonically 

thickened (see fig. 5). It is not known whether the dark-green chloriteschist bodies were originally thick basic extrusive piles or were diabasic 

sills. The Moose Creek Member pinches out eastward but is sporadically present beneath the California Creek Member east of Rogers 

Creek. It pinches out to the west at Sheep Creek (tributary of Tatlanika Creek) along the south border of the Totatlanika Schist but 

is present in the lower plate of a thrust fault along the north border 

of Healy D-3 quadrangle and in southernmost Fairbanks A-3 and A-4 

quadrangles, as far west as the head of Bonanza Creek (fig. 2). Yellow 

slate present on Slate Creek near Ferry and quartz-orthoclase gneiss
E14 CONTRIBUTIONS TO STRATIGRAPHY

and yellow schist near the lower Teklanika Kiver, both areas in Healy 

D-5 quadrangle west of the area shown in figure 2, may be part of the 

Moose Creek Member. The contact with the underlying Keevy Peak 

Formation is probably considerably faulted although it may have 

originally been an unconformity.

CALIFORNIA CREEK MEMBER

The California Creek Member is here named for rocks exposed at 

its type locality, California Creek, in the Fairbanks A-4 quadrangle 

(see fig. 2). The member comprises all the schist exposed at the type 

locality of the Totatlanika Schist in the lower canyon of the Totatlanika River. It consists of white- to buff-weathering gray quartzorthoclase-sericite schist and gneiss which occurs in a coarse-grained 

and in a medium-grained facies; the two facies are commonly in 

sharp contact parallel to the foliation and are intimately mixed. The 

California Creek Member, the most widespread member of the Totatlanika Schist, is exposed from the mountains around Windy Creek 

in Fairbanks A-5 quadrangle (just west of the area shown in fig. 2) 

eastward and southward to the headwaters of the Totatlanika River 

and thence east across the Wood River at least as far as the east edge 

of Healy D-2 quadrangle. The Totatlanika Schist exposed in the 

Japan Hills in Fairbanks A-2 quadrangle is correlated with this 

member.

The coarse facies contains large augen of potassium feldspar, 2.5 

to 25 mm in average diameter, and smaller augen of quartz, one-half 

to one-tenth the size of the feldspar, in a gray to greenish-gray matrix 

consisting of sericite, chlorite, quartz, feldspar, and calcite. Most of 

the feldspar is perthitic microcline, but albite crystals are also present. 

In some places the feldspar augen are well-formed megacrysts with 

sharp crystal faces against which the foliation in the groundmass 

ends abruptly; these megacrysts are oriented with the long axes at 

broad angles to the foliation; some may even be perpendicular to it. 

The best formed crystals were observed in the canyon of Last Chance 

Creek in Healy D-3 quadrangle. All gradations were found from wellformed megacrysts to crystals broken by lines of shearing and rounded 

or lenticular parallel to the foliation. In the vicinity of Rex Dome the 

megacrysts take the form of flat spindles several inches long.

The medium-grained facies consists of flattened to sharply angular 

grains of quartz and feldspar (feldspar predominating), 0.5 to 2 mm 

across, in a strongly schistose groundmass of sericite, orthoclase, and 

quartz. Texture is typically cataclastic. Other minerals present are 

stilpnomelane, zoisite, chlorite, and calcite. Feldspar is about equally 

albite (anorthite, less than 5 percent) and orthoclase.
50 00

HORIZONTAL SCALE 

VERTICAL EXAGGERATION APPROXIMATELY X 10

FIGUBE 5. Diagrammatic stratigraphic panel of the schist formatio

D-2 and D-S quadrangles and southwestern part of Fairbanks 

geologic map and sections to eliminate some structural complexit

relationships along Sheep Creek. Mtmg, dark-green metavoloanic s

of the Totatlanika Schist. For explanation of other formation sy
E16 CONTRIBUTIONS TO STRATIGRAPHY

A fine-grained facies on California Creek about 6 miles above its 

mouth contains well-formed phenocrysts of feldspar and quartz, 

making up 2-5 percent of the rock, in an aphanitic yellow schistose 

groundmass.

Thin layers of black carbonaceous schist and slate, probably of 

sedimentary origin, are interbedded with the quartz-feldspar-sericite 

schist and gneiss of the California Creek Member.

The total thickness of the California Creek Member is unknown. 

Sections exposed in the walls of the canyon of Last Chance Creek 

measure 2,000-3,000 feet, and the lower and middle canyons of the 

Totatlanika Kiver, each 2,000 feet deep, are cut entirely in this member. 

In these areas the top has been eroded. East of the Wood Kiver, the 

California Creek Member interfingers with the overlying Chute Creek 

Member, and its thickness in the eastern part of Healy D-2 quadrangle 

is 1,000-1,500 feet. (See figs. 4 and 5.)

CHUTE CHEEK, MYSTIC CHEEK, AND SHEEP CHEEK MEMBERS

The three uppermost members of the Totatlanika Schist are well 

exposed in a large syncline that makes up the mountains around Sheep 

Creek and Kogers Creek in the northeast quarter of the Healy D-2 

quadrangle (fig. 3). The type sections of two of these, the Chute 

Creek and Mystic Creek Members, are on Rogers Creek, a tributary of 

Sheep Creek, on the south limb of this syncline. The type section of 

the uppermost member, the Sheep Creek Member, is on Sheep Creek 

above the mouth of Rogers Creek, on the north limb and axis of the 

syncline.

In addition to these three members, lenticular bodies of rhyolite 

schist, which apparently originated as shallow sill-like intrusions, 

are found in the Mystic Creek Member and basal part of the Sheep 

Creek Member, shown separately on figure 3. These bodies are probably close in age to the units which they intrude.

CHUTE CREEK MEMBER

The Chute Creek Member, here named after exposures on Chute 

Creek, consists largely of dark-green schist; under the microscope, 

typical specimens are seen to consist of chlorite, zoisite (or epidote), 

actinolite, albite, and biotite. One specimen showed relict pyroxene 

and plagioclase (the latter altered to albite). The Chute Creek Member 

is a metamorphosed basic volcanic rock in the greenschist facies of 

metamorphism and may have originated as basaltic flows. Its type 

section is along Rogers Creek from 8,500 feet to 10,700 feet south of 

the mouth. It is 1,300-1,500 feet thick on the limbs of the Sheep Creek 

syncline and interfingers to the west with both the underlying Call-
SCHISTS OF THE CENTRAL ALASKA RANGE El 7

fornia Creek Member and the overlying Mystic Creek Member. Its 

westernmost exposure is on the north side of the Mystic Creek coal 

basin, in northwestern Healy D-2 quadrangle.

MYSTIC CREEK MEMBER

The Mystic Creek Member, as here named, consists of fine-grained 

purple, green, and yellow schist exhibiting conspicuous linear streaking on the foliation surfaces and containing abundant grains of a 

few millimeters in diameter that in hand specimen appear to be relict 

phenocrysts of quartz and feldspar. Under the microscope the schist 

is confirmed to be a metarhyolite containing 10-20 percent relict 

phenocrysts of beta-quartz, albite, and orthoclase in a fine-grained 

schistose groundmass of intergrown quartz, feldspar, sericite, chlorite, 

hematite, and stilpnonielane. Layers of fine-grained purple and palegreen schist of this member have euhedral megacrysts of feldspar 

(that appear to be phenocrysts) as large as one-fourth to one-half inch 

in diameter, which resemble the feldspar megacrysts of the California 

Creek Member. Float from one thin fossiliferous limestone bed was 

found in the area of the formation near the top of the hill west of 

the mouth of Rogers Creek (fig. 3) .

The type section of the Mystic Creek Member is on Rogers Creek, 

from 5,000 feet to 8,500 feet upstream from its mouth (fig. 3). It is 

about 2,000 feet thick along Rogers Creek and is as much as 3,000 feet 

thick at the eastern end of the Sheep Creek syncline. In fault blocks 

on the south limb of the syncline between Chute Creek and the Wood 

River, it appears to interfinger westward with the underlying Chute 

Creek Member. Just north of the mouth of Mystic Creek, schist 

lithologically similar to the Mystic Creek Member, and mapped as 

part of that member (fig. 3), lies between dark chloritic schist of the 

Chute Creek Member and the underlying California Creek Member. 

A stratigraphic interpretation of these relationships is shown in figure 

5. The Mystic Creek Member is exposed as far west as the upper part 

of Mystic Creek, in the Healy D-2 quadrangle, and is named for 

this stream.

SHEEP CREEK MEMBER

The uppermost member of the Totatlanika Schist, here named the 

Sheep Creek Member, underlies the axial part of the Sheep Creek 

syncline. The type section is defined as the section along Sheep Creek 

above the mouth of Rogers Creek, as far as the highest exposed beds 

in the trough of the syncline.

Four lithologic units are grouped in the Sheep Creek Member. At 

the base is a layer 400-1,000 feet thick of fine-grained black schist, 

which under the microscope is seen to consist of 60 percent quartz and -

MAY1S4S68
E18 CONTRIBUTIONS TO STRATIGRAPHY

40 percent black carbonaceous material. This is overlain by about 2,000 

feet of purple and pale-green slates thought to be metamorphosed tuffs. 

One thin section examined consisted of chlorite, sericite, epidote, and 

a little quartz. The slate unit interfingers upward with quartz-f eldsparsericite schist in which are preserved graded bedding and crossbedding. 

Thin sections of this rock reveal about 80 percent subangular grains 

of quartz, orthoclase, and plagioclase, in the ratio of about 3:1:1, 

averaging 0.5-2 mm in diameter, in a fine-grained matrix of sericite 

and crushed and recrystallized quartz. This rock was probably originally arkose. As much as 2,000 feet of this epiclastic schist lies above 

the purple and green slates. The top of the formation, in the center 

of the syncline, has been removed by erosion.

A fourth lithologic unit placed tentatively in the Sheep Creek Member is a body of thinly bedded dark-gray and light-gray slate, the 

color beds being only a few inches thick. This body lies in the center 

of the Mystic Creek coal basin and is surrounded on all sides by coalbearing Cenozoic sedimentary deposits. Its relations to the other units 

of the Totatlanika Schist are unknown.

AGE AND ORIGIN OF THE TOTATLANIKA SCHIST

In the summer of 1954, the writer found fossils in float from a limestone ledge in the upper part of the Mystic Creek Member of this 

report. The fossiliferous fragments were found at an altitude of 4,100 

feet, at the southeast end of the mountain west of the junction of 

Rogers and Sheep Creeks, at a point about 3,500 feet S. 65° W. of the 

junction (fig. 3). The report of Helen Duncan, who identified the 

fossils and assigned an age to the formation, is quoted below (from 

Wahrhaftig, 1958, p. 12): 

I examined all the pieces of rock in this collection and sawed and polished 

several. The only things I could find that I am sure are organic are crinoid 

columnals, a small gastropod in section, and several pieces of Syringopora that 

is closely similar to if not identical with a form that occurs in the Wachsnmth 

limestone of the Lisiburne group. The specimens of Syringopora are a little distorted, but the internal structures are well preserved * * *.

The presence of Syringopora (sensu stricto) indicates that the rock is postOrdovician, and the chances are that it is not Silurian at least I have not seen 

any good evidence that Syringopora in the strict sense occurs in the Silurian 

of Alaska. However, Silurian species of the genus have been described from the 

Arctic regions of the U.S.S.R. and might occur in Alaska. I have seen a few 

specimens from the Devonian of Alaska that I would refer to Syringopora, but 

they did not closely resemble the species In this collection. We do not have enough 

information on stratigraphic occurrences, however, to rule out the possibility of 

Devonian age in this case. Possibly because I am more familiar with the Mississippian Syringoporas of Alaska and -because the species in this collection looks 

very much like a form that I know is common in the Mississippian, I favor a 

Mississippian assignment. Verification of that assignment will depend on getting 

other kinds of fossils.
SCHISTS OF THE CENTRAL ALASKA RANGE E19

On the basis of Helen Dimcan's report, the Totatlanika Schist was 

assigned to the Mississippian (?).

The mineralogy and chemistry of the Totatlanika Schist point 

clearly to an igneous origin for the bulk of the formation. The interbedded layers of black carbonaceous schist and the occurrence of fossiliferous limestone in the Mystic Creek Member suggest that it originated as a series of submarine eruptions. The lateral persistence and 

thinness of the members and individual units make a flow origin unlikely for a rock as siliceous as the bulk of the Totatlanika Schist. An 

origin related to a series of submarine pyroclastic eruptions or ash 

flows seems most likely.

The origin of the feldspar megacrysts that characterize the 

Totatlanika Schist presents a special problem. The euhedral outline of 

many of the megacrysts, sharply crosscutting the foliation, suggests 

growth during metamorphism; in particular, the elongated spindleshaped crystals showing strong parallel alinement in the plane of 

foliation, such as are found around Rex Dome, must have developed 

during metamorphism. The large size of the megacrysts, 2.5 cm or 

more in diameter, is also strong evidence for a metamorphic origin.

Yet, in the Sheep Creek syncline, in both the California Creek and 

Mystic Creek Members, layers of schist with large megacrysts are 

interbedded with layers of fine-grained schist with 1-mm-long phenocrysts of feldspar and quartz grains pseudomorphous after embayed 

beta-quartz. The factors that influenced crystal growth during the 

metamorphism must have been selective along certain beds, if megacrysts with these field relations are porphyroblasts.

Although large phenocrysts in volcanic rocks are rare, they are not 

unknown. They have been reported from the Galapagos Islands (McBirney and Aoki, 1966), Steens Mountain, Oregon, and JSTunivak 

Island (Allan Cox, oral commun., Dec. 30, 1966), and the San Juan 

Mountains, Colo. (Larsen and others, 1938). It is not impossible, therefore, that some of the megacrysts did originate as phenocrysts; others 

are certainly porphyroblasts, but probably had phenocrysts as nuclei.

The medium-grained facies of the California Creek Member, likewise, has two possible origins. There is a strong suggestion of a 

cataclastic origin for the angular fragments of quartz and feldspar 

in many thin sections in that they appear to be tectonically broken 

fragments of much larger crystals. If so, the medium-grained facies 

originated through shearing of the coarse-grained facies along zones 

of intense deformation. On the other hand, the medium grain size may 

be an original feature, of at least part of this facies, and could represent medium-grained pyroclastic accumulations.
E20 CONTRIBUTIONS TO STRATIGRAPHY

METAVOLCANIC SCHISTS AND ASSOCIATED ROCKS 

SOUTH OF THE BIRCH CREEK SCHIST

The metavolcanic schists south of the Birch Creek Schist form a 

belt 1/2 to 4 miles wide along- the south border of Healy D-2, D-3, 

and D-4 quadrangles (fig. 2). In Healy D-4 quadrangle and in the 

western two-thirds of Healy D-3 quadrangle, where their structure 

is fairly simple, these schists dip 35°-50° to the south. They can be 

divided into two units a lower unit of interbedded green metavolcanic schist and black carbonaceous schist and an upper unit of 

quartz-sericite-felds>par schist.

The lower metavolcanic unit, 800-2,000 feet thick, consists of interbedded green metavolcanic schist and black carbonaceous schist. The 

black schist beds, best developed in Healy D-3 quadrangle, are about 

5-20 feet thick, make up about 5 percent of the section, and are spaced 

50-200 feet apart. They consist of quartz, sericite, and carbonaceous 

matter, having a grain size of about 0.02 mm. Much of the green schist 

in Healy D-4 quadrangle shows well-preserved agglomerate textures 

on weathered or stream-polished surfaces. At one locality in Healy 

D-4 quadrangle, relict pillow structure was observed. In many thin 

sections of the green schist, the original igneous minerals such as 

hornblende, amphibole, and plagioclase are still partly preserved 

(probably as phenocrysts) but are sheared or drawn apart and are 

more or less replaced by chlorite, calcite, sericite, quartz, leucoxene, 

and albite. In some thin sections, tremolite and actinolite have also 

formed at the expense of the original igneous minerals.

The upper metavolcanic unit is a quartz-sericite-f eldspar schist of 

rhyolitic origin. Its thickness is at least 1,000 feet, but it is overlain 

unconformably by the Cantwell Formation and its total thickness is 

unknown. There are no interbedded black schists in this unit. In outcrop at the west end of the belt, this schist also shows evidence of a 

pyroclastic origin. Farther east, recrystallization has been more extensive, and textures related to the origin, other than preserved phenocrysts, are lacking.

The metarhyolite schist is characterized by beta-quartz pseudomorphs with well-preserved phenocrystic form, including resorption 

embayments, and by phenocrysts of feldspar, generally orthoclase, 

having more or less completely preserved crystal form. The phenocrysts are 0.5 to 2 mm across and make up 15-25 percent of the rock. 

The beta-quartz pseudomorphs show strong strain shadows. The 

groundmass consists of quartz, sericite, and, generally, orthoclase and 

albite. It is strongly foliated, and the foliation, marked by sericite 

flakes and stringers, tends to bend around phenocrysts. Phenocrysts 

whose long axes are parallel to the foliation are well preserved, but
SCHISTS OF THE CENTRAL ALASKA RANGE E,21

many phenocrysts whose long axes were nearly perpendicular to the 

foliation have been nearly destroyed by shearing.

Inter bedded with these two schist formations are bodies of schist of 

sedimentary origin, including gray marble and black carbonaceous 

schist. A fossil from a marble lens at the base of the green metavolcanic 

schist in southern Healy D-4 quadrangle was reported by Ralph Imlay 

(oral coinmun., 1958) as a badly deformed and unidentifiable gastropod. On the basis of this fossil find, these rocks are assigned to the 

Paleozoic.

Large, crudely equidimensional bodies of dark-green rock consisting 

of epidote, chlorite, quartz, sericite, calcite, and albite(?) are associated with the green metavolcanic schist or intrude the Birch Creek 

Schist. These bodies tend to be resistant to erosion and to form high 

peaks. They are interpreted as metagabbro.

Although no formal correlation of these schists is made in this 

paper, the most reasonable correlation is of the green metavolcanic 

schist with the Chute Creek Member of the Totatlanika Schist and 

the metarhyolite with the Mystic Creek Member. If this correlation 

is valid, the Keevy Peak Formation and part of the Totatlanika 

Schist are missing in the south flank of the Birch Creek Schist, either 

through unconformity or thrusting. The body of epiclastic schist 

near the head of the Wood River in Healy D-2 quadrangle may be 

part of the Birch Creek Schist, exposed on the south limb of a 

syncline.

REFERENCES CITED

Brooks, A. H.. 1911, The Mount McKinley region, Alaska, with descriptions of the

igneous rocks and of the Bonnifield and Kantishna districts, by L. M. Prindle :

U.S. Geol. Survey Prof. Paper 70, 234 p. 

Capps, S. R., 1912, The Bonnifield region, Alaska: U.S. Geol. Survey Bull. 501,

64 p. 

 1940, Geology of the Alaska Railroad region: U.S. Geol. Survey Bull. 907,

201 p. 

Larsen, E. S., Irving, John, Gonyer, F. A., and Larsen, E. S., 3d, 1938, Petrologic

results of a study of the minerals from the Tertiary volcanic rocks of the

San Juan region, Colorado: Am. Mineralogist, v. 23, no. 4, p. 227-257; no. 7,

417-429. 

McBirney, A. R., and Aoki, Kenichiro, 1966, Petrology of the Galapagos Islands,

in Bowman, R. I., ed.. The Galapagos proceedings of the symposia of the

Galapagos International Scientific Project: Berkeley, California Univ. Press,

p. 71-77. 

Mertie, J. B., Jr., 1937, The Yukon-Tanana region, Alaska: U.S. Geol. Survey

Bull. 872, 276 p. 

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

area : U.S. Geol. Survey Bull. 989-D, p. 63-218. 

Paterson, M. S.. and Weiss, L. E., 1966, Experimental deformation and folding

in phyllite: Geol. Soc. America Bull., v. 77, no. 4, p. 343-374.
E22 CONTRIBUTIONS TO STRATIGRAPHY

Pewe T. L., Wahrhaftig, Clyde, and Weber, Florence, 1966, Geologic map of the 

Fairbanks quadrangle, Alaska: U.S. Geol. Survey Misc. Geol. Inv. Map 

1-455, scale 1: 250,000.

Prindle, L. M., 1907, The Bonnifleld and Kantishna regions: U.S. Geol. Survey 

Bull. 314, p. 205-226.

Spurr, J. E., 1897, Geology of the Yukon gold district, Alaska, with an introductory chapter on the history and condition of the district to 1897, ~by 

H. B. Goodrich: U.S. Geol. Survey 18th Ann. Rept., pt. 3, p. 87-392.

Wahrhaftig, Clyde, 1958, Quaternary geology of the Nenana River valley and 

adjacent parts of the Alaska Range: U.S. Geol. Survey Prof. Paper 293-A, 

p. 1-68.

 1965, Physiographic divisions of Alaska: U.S. Geol. Survey Prof. Paper 

482, 52 p.

Wasserburg, G. J., Eberlein, G. D., and Lanphere, M. A., 1963, Age of the Birch 

Creek Schist and some batholithic intrusions in Alaska [abs.] : Geol. Soc. 

America Spec. Paper 73, p. 258.

U.S. GOVERNMENT PRINTING OFFICE: 1968 O 283-147