Reconnaissance study of 

Upper Cretaceous to Miocene 

Stratigraphic units and Sedimentary facies, 

Kodiak and adjacent ^f islands, X Alaska

Reconnaissance study of 

Upper Cretaceous to Miocene 

Stratigraphic units and Sedimentary facies, 

Kodiak and adjacent islands, Alaska

By TOR H. NILSEN and GEORGE W. MOORE

With a section on SEDIMENTARY PETROGRAPHY

BY GARY R. wINKIER

GEOLOGICAL SURVEY PROFESSIONAL PAPER 1093

UNITED STATES GOVERNMENT PRINTING OFFIGE, WASHINGTON: 1979
UNITED STATES DEPARTMENT OF THE INTERIOR 

CECIL D. ANDRUS, Secretary

GEOLOGICAL SURVEY 

H. William Menard, Director

Library of Congress Catalog-card Number 79-600035

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

Washington, D.C. 20402

Stock Number 024-001-03195-7
CONTENTS

Page

Abstract..........................................................

Introduction ... ... ..........................................

Turbidite facies and facies associations. 

Kodiak Formation .........................................

Background.............................................

Basin-plain facies association ...........

Slope facies association .......................

Paleocurrent pattern .........................

Ghost Rocks Formation ..............................

Background ..............................................

Sedimentary facies............................ ....

Paleocurrent pattern .............................

Sitkalidak Formation ...................................

Background ....

Narrow Cape ...........................................

Sitkalidak Island .......... ......................

Page

1 Sitkalidak Formation Continued

1 Sitkalidak Island Continued

3 Partition Cove ................................................................. 11

6 Tanginak Anchorage..................................................... 13

6 Sitkinak Island.......................................................................... 15

6 Sitkinak Formation ........................................................................ 17

6 Background............................................................................... 17

7 Sitkalidak Island ...................................................................... 17

7 Sitkinak Island...................................................................... 19

7 Narrow Cape Formation ............................................................. 23

7 Background............................................................................. 23

9 Narrow Cape ....._._..............._....... ........ ... -. 23

11 Sitkinak Island......................................................................... 23

11 Sedimentary petrography, by G. R. Winkler........................... 23

11 Summary and conclusions ...................._........... .............. . .... 26

11 References cited............................................................................... 32

ILLUSTRATIONS

Page

FIGURE 1. Map showing distribution of major geologic terranes and faults along the margin of the Gulf of Alaska-....... 2

2. Simplified geologic map of Kodiak and adjacent islands, Alaska.............................................................................................. 4

3. Sections showing characteristic vertical cycles or megasequences of various deep-sea turbidite facies associations 5

4. Photographs showing sedimentary facies, Kodiak Formation.................................................................... -. ...- ............. 8

5. Paleocurrent map for the Kodiak and Ghost Rocks Formations ................................................................................................ 10

6. Photographs showing sedimentary facies, Ghost Rocks Formation....................................................................... . - - 12

7. Photographs showing sedimentary facies, Sitkalidak Formation ....................................................................................... - 14

8. Paleocurrent map for the Sitkalidak Formation .................................................................................................................... ......... 16

9. Photographs showing sedimentary facies, Sitkinak Formation.................................................................. . ................. 18

10. Measured section of part of the Sitkinak Formation near Tanginak Anchorage, Sitkalidak Island.. ...................... 20

11. Paleocurrent map for the Sitkinak Formation ............................................................................................................................. 21

12. Measured section of part of the Sitkinak Formation at quarry west of landing strip, Sitkinak Island ....................... 22

13. Photographs showing sedimentary facies, Narrow Cape Formation.................................................. -... ................ ......... 24

14. Approximate section at contact of Narrow Cape and Sitkinak Formations, south coast of Sitkinak Island .............. 26

15. Ternary diagrams showing sedimentary petrography of Upper Cretaceous to Miocene stratigraphic units, Kodiak

	and adjacent islands...... .. ........................................................................... ......................... ......................................... -............. 27

16. Selected photomicrographs of sandstone samples from the Kodiak, Ghost Rocks, Sitkalidak, Sitkinak, and

	Narrow Cape Formations........................ ... ............... ..................................................................................................... 28

17. Block diagram showing inferred paleogeography and depositional setting of the Kodiak Formation ......................... 29

18. Block diagram showing inferred paleogeography and depositional setting of the Sitkalidak and Sitkinak

	Formations ... ... ............................ ........................ ................... ............. ............... ........................... ... 31

RECONNAISSANCE STUDY OF UPPER CRETACEOUS TO MIOCENE

STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES,

KODIAK AND ADJACENT ISLANDS, ALASKA

By TOR H. NILSEN and GEORGE W. MOORE

ABSTRACT

The sedimentary structures and facies, paleocurrents, and 

stratigraphic relations of five formations exposed on Kodiak and 

adjacent islands were studied in reconnaissance fashion at 

several localities during the summer of 1976. The Upper Cretaceous 

Kodiak Formation, in fault contact with both younger and older 

formations, consists of turbidites deposited primarily in slope 

and basin-plain environments; paleocurrents indicate sediment 

transport to the southwest. The Paleocene and Eocene Ghost 

Rocks Formation, in fault contact with both younger and older 

formations, consists of at least in part syndepositionally deformed 

hemipelagic argillite and turbidites interbedded with pillow 

basalt; paleocurrents have an irregular orientation, possibly as a 

result of extensive post-depositional deformation that has disrupted the sedimentary characteristics of the formation.

The Eocene and Oligocene Sitkalidak Formation consists of 

middle- and outer-fan turbidites that locally include some basinplain deposits; paleocurrents indicate general transport of sediments toward the south-southeast, although directions are variable, 

suggesting prominent southwestward transport southwest of 

Sitkalidak Island and northeastward transport northeast of 

Sitkalidak Island. The Oligocene Sitkinak Formation, where 

examined, consists of two distinctive facies: (1) on Sitkalidak 

Island, where it rests conformably on and interfingers in part 

with the Sitkalidak Formation, southward-transported turbidites 

deposited in inner-fan channel and slope environments; and 

(2) at its type locality on Sitkinak Island, where it essentially 

conformably underlies the Narrow Cape Formation and is in fault 

contact with the Sitkalidak Formation, eastward-transported 

marginal-marine strata deposited in fan-delta and lagoonal 

environments. The upper Oligocene? and Miocene Narrow Cape 

Formation consists of mollusk-rich, bioturbated siltstone and 

silty fine-grained sandstone deposited in shelf environments, 

probably derived from source areas to the northwest.

The Upper Cretaceous through Miocene sandstones on Kodiak 

and adjacent islands, which are primarily feldspatholithic, indicate a predominantly volcanic provenance. About 95-percent of 

the Kodiak and Ghost Rocks lithic detritus is composed of volcanic 

and plutonic rock fragments; in younger formations, the composition of rock fragments is more diverse. The sandstone modes 

indicate a general increase through geologic time in the total 

amount of quartzose grains (especially chert) and a decrease in 

the total amount of feldspar grains.

The Kodiak Formation forms part of the extensive Chugach 

terrane, thick Upper Cretaceous flyschlike strata in southern 

Alaska, apparently deposited in a major southwest-trending 

linear basin, possibly a southwest-sloping trench floor developed 

adjacent to the Alaskan continental margin. The highly deformed

Ghost Rocks Formation, though possibly a distantly derived 

fragment rafted into southern Alaska along a convergent margin 

by sea-floor spreading processes, was most likely also deposited 

at the continental margin and derived from a southern Alaskan 

provenance, as indicated by its sedimentary petrography.

The Eocene to Miocene sequence Sitkalidak, Sitkinak, and 

Narrow Cape Formations represents a major first-order progradational cycle of shelf, slope, and deep-sea fan deposits that 

filled a northeast-trending sedimentary basin. These deposits 

filled either an inactive trench or major trench-slope basin 

developed during episodes of plate convergence.

INTRODUCTION

During the summer of 1976, we examined in reconnaissance fashion outcrops of the Kodiak, Ghost 

Rocks, Sitkalidak, Sitkinak, and Narrow Cape Formations of Kodiak and adjacent islands, which had 

earlier been mapped and named by Moore (1967, 

1969). Moore had described the lithologies, type 

localities, approximate thicknesses, fossils, stratigraphic relations, and distribution of seven newly 

named Mesozoic and Cenozoic formations on Kodiak 

and adjacent islands. Earlier studies of the geology 

of Kodiak Island had been published by Martin 

(1912) and Capps (1937). In this report, we describe 

the outcrops, facies, sedimentology, petrography, 

and inferred paleogeography and depositional environments of the five formations, which range in 

age from Late Cretaceous to Miocene.

Strata on Kodiak Island are part of a widespread 

sequence of similar Mesozoic and Cenozoic rocks 

that form an arclike outcrop belt in southern Alaska 

extending from near Sitka in the southeast to the 

Shumagin and Sanak Islands in the southwest 

(fig. 1). This belt consists of five different terranes, 

separated by faults or unconformities. The interior 

terrane consists of metamorphic rocks of possible 

Paleozoic and Mesozoic age that crop out north of 

the Border Ranges fault (MacKevett and Plafker, 

1974); these unnamed schists are present in northeastern Kodiak Island, from which they extend
cr

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TURBIDITE FACIES AND FACIES ASSOCIATIONS

northeastward to the Kenai Peninsula, where similar 

schists crop out near Seldovia (fig. 1). The second 

terrane consists of melange that crops out between 

the Border Ranges fault and the Eagle River fault; 

this melange on Kodiak Island has been named the 

Uyak Formation by Moore (1969) and on the Kenai 

Peninsula to the northeast the McHugh Complex 

by Clark (1972, 1973). The third terrane, named the 

Chugach terrane by Berg, Jones, and Richter (1972), 

consists of Upper Cretaceous flyschlike strata that 

crop out between the Eagle River fault and the 

Contact fault (Plafker and others, 1977a, b). On 

Kodiak Island, this terrane is represented by the 

Kodiak Formation (fig. 2); on the Shumagin and 

Sanak Islands, by the Shumagin Formation (Moore, 

1974b, c); on the Kenai Peninsula, by the Valdez 

Group (Clark, 1972, 1973); near Yakutat, by part of 

the Yakutat Group (Plafker and others, 1976); and 

near Sitka, by the Sitka Graywacke (Loney and 

others, 1975). The fourth terrane crops out south of 

the Contact fault and consists of folded and faulted 

Paleogene turbidites and related mafic volcanic 

rocks; on Kodiak and adjacent islands it consists of 

the Ghost Rocks, Sitkalidak, and Sitkinak Formations, which resemble in part the Orca Group of the 

Prince William Sound area (Winkler, 1976). The fifth 

and most ocean ward terrane consists of less-deformed 

upper Paleogene and Neogene shallow-marine deposits, which on Kodiak and adjacent islands consist 

of the Narrow Cape and Tugidak Formations.

Kodiak Island lies in the western Gulf of Alaska 

and is about 100 km wide by 160 km long. Northeasttrending folded and faulted rocks underlie Kodiak 

and adjacent islands and extend southwestward 

from similarly trending rocks of the Kenai Peninsula 

(fig. 2). Metamorphic rocks that include quartz-mica 

schist, greenschist, blueschist, and epidote amphibolite form a northwesterly and older terrane on 

Kodiak Island (Garden and Forbes, 1976; Connelly 

and Moore, 1977). Potassium-argon dates from 

crossite and white mica in the schists yield ages of 

approximately 140-190 m.y. (Garden and others, 

1977), the ages of metamorphism and possibly emplacement of the schist terrane. An age of 190 m.y. 

was determined from similar schist near Seldovia 

(Forbes and Lanphere, 1973). Less metamorphosed 

Upper Triassic volcaniclastic rocks crop out in small 

areas northwest of the schist along the coasts of 

Kodiak, Afognak, and Shuyak Islands (Connelly 

and Moore, 1977).

The Uyak Formation to the southeast of the schist 

terrane is at least in part a complexly deformed 

melange thought to be thrust southeastward over 

the Upper Cretaceous Kodiak Formation. It contains 

blocks or knockers of layered gabbro, clinopyroxenite, 

dunite, greenstone, chert, argillite, and wacke (Connelly and others, 1976,1977). Various blocks contain 

Late Triassic fossils, and a distinctive unit of red 

chert underlain by pillow basalt contains radiolarians 

dated by E. A. Pessagno (written commun., 1976) as 

Early Cretaceous (Valanginian or Hauterivian). The 

Uyak Formation is thought to have been formed as 

part of a subduction complex of Mesozoic age 

(Connelly and Moore, 1975; Moore and Wheeler, 

1975; Connelly and others, 1976, 1977; Connelly, 

1976; Moore and Connelly, 1976,1977). A subductionslip vector of N. 38° W. ±11° was determined for this 

complex by Moore and Connelly (1976).

Granitic batholiths intrude the Upper Cretaceous 

Kodiak Formation and Paleocene and Eocene Ghost 

Rocks Formations at many localities on Kodiak and 

adjacent islands (Moore, 1967; fig. 2). The batholithic 

rocks on Kodiak Island have been dated by the potassium-argon method in part as 58 ±2.5 m.y. old 

(Karlstrom, 1969, p. 28); they form part of a belt of 

granitic intrusions in Cretaceous and Paleogene 

turbidites along the Gulf of Alaska margin (Kienle 

and Turner, 1976). The batholiths to the northeast 

in the Chugach Mountains have been dated by the 

potassium-argon method at 47-52 m.y. (Hudson and 

others 1977), to the southwest in the Shumagin 

Islands, at 56 to 64 m.y. (Burk, 1965; Moore, 1973b; 

Kienle and Turner, 1976), and in the Sanak Islands 

at 59.9 m.y. (Moore, 1973b; Kienle and Turner, 1976).

The Pliocene and Pleistocene Tugidak Formation 

consists of shallow-marine siltstone and sandstone 

containing ice-rafted dropstones. It crops out only 

on Tugidak Island, which is southwest of Kodiak 

Island (fig. 2), and at the north end of Chirikof Island 

(fig. 1). The schists, Uyak Formation, batholiths, 

and Tugidak Formation will not be further discussed 

herein.

The physical characteristics of all the Tertiary 

formations, in particular their porosity and permeability, are summarized by Lyle and others (1978). 

Additional fieldwork by us and other workers during 

the summer of 1977 focused in detail on the sedimentology of the Sitkalidak and Sitkinak Formations 

(Bouma and others, 1977); the results of this study 

will be reported in other publications.

TURBIDITE FACIES AND FACIES ASSOCIATIONS

The turbidite facies and fades associations described 

here in general follow the classification systems 

presented by Mutti and Ricci Lucchi (1972, 1975) 

and Nelson and Nilsen (1974), as summarized by 

Nilsen (1977). According to these systems, marine 

turbidites generally can be referred to three distinctive facies associations: slope, fan, and basin-plain 

(fig. 3).

The slope facies association is characterized by 

deposition of hemipelagic argillaceous mud and
4 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

155° 154° 153° 152°

57'

Ugak Island 

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Tanginak 

Anchorage

Partition Cove 

Sitkalidak Island

EXPLANATION

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Tugidak Formation

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QUATERNARY

Pleistocene! QUATERNARY

AND 

TERTIARY

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Tgrr

Tugidak Island

Geese Islands

Sitkinak Island

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and 

Dligocene(?)

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Sitkinak Formation J

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Sitkalidak Formation J

Intrusive 

granitic 

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Oligocene

and 

Eocene

Eocene 

and

- TERTIARY

Paleo- Ghost Rocks Formation I Paleocene

Kodiak Formation

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Older rocks, undivided

- CRETACEOUS

- MESOZOIC(?)

Contact

"Fau'l'f 

Dotted where concealed

0 5 10 15 20 25 KILOMETERS 

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FIGURE 2.—Simplified geologic map of Kodiak and adjacent islands, Alaska. Geology modified from Moore (1967).

thinly interstratifled fine-grained turbidites, cut in 

places by coarser grained submarine-canyon deposits.

Upper-slope deposits typically slump and slide downslope, resulting in accumulation of imbricated slices
SLOPE

TURBIDITE FACIES AND FACIES ASSOCIATIONS

INNER-FAN MIDDLE-FAN OUTER-FAN BASIN-PLAIN

EXPLANATION

Conglomeratic layers

Sandstone turbidites

Hemipelagic mudstones

Slumped intervals

FIGURE 3.—Characteristic vertical cycles or megasequences of various deep-sea turbidite facies associations (modified from Mutti 

and Ricci Lucchi, 1972, fig. 14, and Nilsen, 1977, fig. 3-7). Larger cycles shown by bars to right of column.

of this material on the lower slope and base-of-slope. 

The deep-sea fan facies association can be divided 

into: (1) inner-fan facies association, generally 

characterized by deposition of argillaceous channelmargin and interchannel mudstone and thick, 

noncyclically arranged beds of conglomerate and 

sandstone in one or several major channels; (2) 

middle-fan facies association, generally characterized 

by channelized, cyclically arranged thinning-upward 

and fining-upward megasequences of sandstone beds 

deposited in numerous distributary channels and 

channel-margin and interchannel mudstones with 

associated thinly bedded and fine-grained turbidites; 

and (3) outer-fan facies association, generally characterized by cyclically arranged thickening-upward 

and coarsening-upward megasequences of sandstone 

beds deposited as nonchannelized depositional lobes 

of considerable lateral extent downfan from the 

middle-fan distributaries. The thinning-upward

middle-fan cycles generally result from gradual 

abandonment of channels, whereas the thickeningupward outer-fan cycles generally result from progradation, including progradation of feeding channel 

systems over depositional lobes.

The basin-plain facies association is generally 

characterized by noncyclically arranged, nonchannelized beds of sandstone and shale of wide lateral extent. This facies association in general has a lower 

sandstone:shale ratio than the deep-sea fan facies 

association and contains abundant hemipelagic 

shale. Bed thickness is nonsystematic because 

individual turbidites are derived randomly from 

numerous distributaries and multiple sources.

The classification of Mutti and Ricci Lucchi (1972, 

1975) introduces a set of seven facies designated by 

letters—facies A to G—to refer to individual 

bedding types in turbidite sequences. Assemblages 

of beds of these lettered facies are characteristic of
6 CRETACEOUS TO MIOCENE STRATI-GRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

and comprise the slope, fan, and basin-plain fades 

associations. This system, ideally suited to reconnaissance study of turbidite sequences, will be used 

throughout this report. The facies, in brief, are: facies 

A—thick to massive, lenticular, graded and nongraded beds of conglomerate or sandstone generally 

lacking conspicuous sedimentary structures; facies 

B—thick to massively bedded, medium- to coarsegrained sandstone characterized by irregular planeparallel, wavy, or inclined laminae and fluid-escape 

structures; facies C—graded beds of sandstone organized into Bouma (1962) sequences that start with 

the basal a division; facies D—thinner bedded and 

finer grained graded sandstone beds organized into 

Bouma sequences that lack the basal a division; 

facies E—thin- to medium-bedded, coarse- to fine 

grained sandstone characterized by dune-shaped 

tops, wedging of adjacent beds, and cross-stratification; facies F—chaotic deposits retransported byslumping and sliding; and facies G—hemipelagic 

pelites.

KODIAK FORMATION 

BACKGROUND

The Kodiak Formation, of Late Cretaceous (Maestrichtian) age (Moore, 1969; Jones and Clark, 

1973), crops out in a broad, general northwestdipping faulted and folded tract over most of the 

central part of Kodiak Island. It is in fault contact 

with the probably older Uyak Formation to the 

northwest and the younger Ghost Rocks Formation 

to the southeast (Moore, 1967, 1969). The Kodiak 

Formation was examined in roadcuts and coastal 

outcrops along Ugak Bay and Uyak Bay (fig. 2). 

Originally considered to be about 30,000 m thick 

(Moore, 1969, 1975), the Kodiak Formation is now 

thought to be of the order of 5,000 m thick and to be 

repeated structurally by numerous folds and faults. 

Stratigraphic correlation is extremely difficult 

because of structural repetition of beds and recurrence of similar facies.

BASIN-PLAIN FACIES ASSOCIATION

Almost all the Kodiak Formation is of the basinplain or slope facies associations. Deep-sea fan facies 

are only locally developed, probably where they fill 

relatively small intraslope basins.

The basin-plain facies association, structurally the 

lowest part of the formation, is characteristic of most 

of the Kodiak Formation on the southeast side of 

Kodiak Island. Here the basin-plain facies association 

consists of repetitively interstratified graded sandstone beds and hemipelagic shales, typically 30 cm

thick, without any ordering or development of megasequences (fig. 4A, B). Some calcite-cemented turbidites are present. Sandstone:shale ratios range 

in general from 1:1 to 1:5. The interstratified hemipelagic shale is generally bioturbated; trace fossils 

typically are those of the surface-grazing deep-marine 

Nereites facies and include Helminthoida and Helminthopsis as well as larger trace fossils possibly 

formed by moving gastropods. The sandstone beds 

are plane-parallel, extend over long distances with 

out noticeable changes in thickness or grain size, 

are not channelized, and generally range in thickness from 1 to 35 cm, although single thicker beds 

are present in some areas. The beds are most commonly fine- to medium-grained facies D sandstone 

turbidites probably deposited by low-density turbidity currents of variable volume that have traveled 

long distances from source areas. Sedimentary 

structures include sole markings, parallel and wavy 

lamination, convolute lamination, current-ripple 

markings, and, rarely, ripple-drift lamination.

Thicker, coarser grained beds with rip-up clasts 

of siltstone or mudstone are occasionally found 

within the basin-plain facies association, generally 

along the northwest edge or stratigraphically upper 

part of the outcrops of the basin-plain facies association. These isolated beds, in places groups of beds 

that may possibly be locally tuffaceous, represent 

slumps or debris flows that traveled from marginal 

slopes out onto the basin-plain floor, forming thick, 

contorted wildflysch-like strata. Beds of this type 

were observed along the southeast shore of Hidden 

Basin in Ugak Bay (fig. 2).

Locally within the basin-plain facies, as at Mill 

Bay, Anton Larsen Bay and in quarries south of the 

city of Kodiak, thin lobelike outer-fan sequences are 

developed (fig. 4C). These occurrences are isolated, 

however; the preserved lobes are thin, generally only 

about 5 m thick. The strata consist primarily of facies 

C and D turbidites.

SLOPE FACIES ASSOCIATION

The slope facies association of the Kodiak Formation crops out on the northwest side of Kodiak Island; 

there it consists primarily of thick mudstone sequences 

that may form imbricate slices juxtaposed during 

multiple phases of synsedimentary slumping (fig. 4D). 

These rocks, which are primarily facies G and F 

deposits, contain chaotically oriented blocks, slabs, 

and disordered fragments of hemipelagic mudstone 

that probably slid from upper slope depositional 

sites to the lower slope or base of slope under the 

influence of gravity. The blocks are composed mainly 

of mudstone with thin interbeds of noncyclically
GHOST ROCKS FORMATION

arranged fine-grained sandstone, siltstone, and 

mudstone characterized by Bouma Tc-e, Td-e, and Te 

sequences. Sandstone:shale ratios are typically 

very low, ranging from 1:30 to 1:10. Large slump 

blocks containing complexly folded thicker beds of 

sandstone and shale are present within the finer 

grained slope deposits (fig. 4£), possibly representing downslope-transported blocks of outer-shelf 

facies. Some disrupted parts of the sequence consist 

of completely broken beds that contain isolated 

blocks of contorted and folded sandstone; locally 

only fold noses suspended in a fine-grained matrix 

of mudstone are preserved (fig. 4£).

Channelized thick beds of conglomerate and sandstone associated with thin beds of channel-margin 

turbidites crop out locally within the slope facies 

association, as in the Uyak Bay area (fig. 4F). These 

conglomerates, which have sandy matrices, represent the fill of canyons or channels cut into the slope 

that may have supplied some sediment to the more 

distal basin-plain depositional areas. The conglomeratic sequences exposed along the shores of Uyak 

Bay are of the order of 50 m thick; they consist of 

poorly developed thinning- and fining-upward cycles 

with channelized bases. Intermixed with the conglomerates are large fragments of slumped mudstone 

as long as several meters in longest dimension, 

derived from the channel or canyon walls, and some 

beds of pebbly mudstone (fig. 4G). Stratigraphically 

above and below the conglomeratic sequences are 

thin-bedded channel-margin overbank deposits composed of facies D turbidites (fig. 4H). These overbank 

turbidites form Bouma Tb-e and Tc-e sequences that 

most characteristically contain ripple-drift lamination thought to have been deposited by turbidity 

currents that overspilled channel margins and 

transported sediment away from the channel axes. 

Individual beds within the overbank turbidites thin 

and pitch out laterally and locally are arranged 

en echelon.

Present locally within the slope facies of the Kodiak 

Formation are thin fan facies apparently developed 

in depressions on the lower slope. Some of these 

small basins probably formed behind major slump 

blocks and slump masses. Alternatively, they may 

have developed tectonically as a result of slope 

deformation. Two sequences of fan facies of this type 

are exposed at Uyak Bay, where thickening-upward 

lobes are developed in sequences bounded above 

and below by slumped and imbricated hemipelagic 

slope facies. In the first sequence, one lobe is developed, in the second, four lobes; the lobes are 5-10 m 

thick and consist of facies C and D turbidites characterized by well-developed Bouma (1962) sequences.

Sandstone:shale ratios are approximately 3:1 

to 1.5:1.

PALEOCURRENT PATTERN

Paleocurrents obtained from the Kodiak Formation 

are relatively uniform in orientation, generally 

indicating southwestward transport of sediment 

by turbidity currents in both slope and basin-plain 

facies associations (fig. 5), although paleocurrents 

at the northwest end of Uyak Bay in the slope facies 

association indicate a more southerly direction of 

sediment transport. A total of 52 paleocurrents 

were measured, almost all from flute casts and 

groove casts; measurements were corrected by twotilt stereonet rotation. The range of paleocurrent 

directions is 110° and 265°, that is, east-southeast 

to west-southwest, with a vector mean of 212° and a 

standard deviation of 34°. These data indicate that 

during deposition of the Kodiak Formation, turbidity 

currents mainly flowed toward the southwest.

GHOST ROCKS FORMATION

BACKGROUND

The Ghost Rocks Formation crops out in a long 

continuous belt southeast of the Kodiak Formation 

and appears to be separated from younger strata 

to the southeast by faults (fig. 2). It is isoclinally 

folded, faulted, and sheared; it may be as thick as 

5,000 m, but structural complications preclude an 

accurate measurement of its thickness. Moore (1969) 

considered the Ghost Rocks Formation to be Paleocene and Eocene in age and recognizable by pillow 

basalt or greenstone, hard black clay stone, thin 

limestone beds, and locally prominent zeolite-bearing 

tuffaceous sandstone beds. A limestone layer directly 

overlying pillow lava at 57°23.0'N., 152°36.1'W., 

contains planktonic foraminifers tentatively idenfied in thin section as "Globigerina"pseudobulloides, 

Planorotalites sp., and Subbotina triangularis or 

S. triloculinoides, a Paleocene assemblage (R. Z. 

Poore, written commun., 1976).

SEDIMENTARY FACIES

Because of the structural complications and because 

it was examined at only a few localities, understanding of the Ghost Rocks Formation in terms of turbidite facies and facies associations is uncertain. 

Most of the unit consists of sheared and highly 

deformed shale, argillite, and mudstone. Isolated 

and thin Tc-e and Td-e sandy and silty facies D turbidites are present; they are characteristically
CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

FIGURE 4.—Sedimentary facies, Kodiak Formation. A, Thinly 

bedded facies C and D basin-plain turbidites, Mill Bay; stratigraphic top to right. B, Thinly bedded facies D basin-plain to 

lobe-fringe turbidites, Uyak Bay; stratigraphic top to right.

D

C, Basin-plain turbidites, Mill Bay, with irregular thinningupward outer-fan sequence (center of photo); stratigraphic top 

to right. D. Synsedimentary recumbent fold in facies F slope 

turbidites, Uyak Bay; beds overturned.

folded and deformed such that only noses of folds 

are preserved and fold limbs are sheared out (figs. 

6A, B, and C).

Some thicker facies C and D graded beds of turbiditic character are less deformed. These beds, 

characterized by convolute laminae, flame and load 

structures, and sandstone dikes and sills, are commonly contorted; they are typically greenish and 

tuffaceous and may form either thinning-upward 

or thickening-upward vertical megasequences (figs. 

6D, E, and F). Very well developed thinning- and 

fining-upward middle-fan channel and interchannel

megasequences are exposed east of Eagle Harbor 

on the south side of Ugak Bay (fig. 2). Levee deposits, 

locally slumped, are preserved at the tops of some 

of the channelized megasequences. The interval 

of megasequences is approximately 70 m thick and 

is bounded on the top and bottom by more sheared 

and deformed argillitic facies of the Ghost Rocks 

Formation. The relation of this preserved interval 

to other facies or facies associations within the 

Ghost Rocks is unclear.

Veins, fractures, minor faults, and melangelike 

features are characteristic of the Ghost Rocks For-
GHOST ROCKS FORMATION

FIGURE 4.—Continued. E, Probable channel-margin facies F beds 

of slump-folded conglomerate, sandstone, and shale, UyakBay. 

F, Channelized facies A conglomerate and sandstone, Uyak 

Bay; stratigraphic top to left. G, Shale rip-up fragments in

H

channel-fill facies A sandstone, Uyak Bay. H, Ripple-driftlaminated facies D levee and overbank deposits, Uyak Bay; 

sequence overturned, stratigraphic top to lower right.

mation. How many, if any, of the various structural 

complications are synsedimentary rather than tectonic in origin is difficult to determine on the basis 

of our brief reconnaissance.

PALEOCURRENT PATTERN

The few paleocurrents measured in the Ghost 

Rocks Formation are variable in orientation. Eleven 

measurements of cross-strata, flute casts, and groove 

casts along Ugak Bay yielded northwesterly, northeasterly, and southerly directions (fig. 5). Near 

Narrow Cape, three crossbed measurements yielded

westerly paleocurrents. G. R. Winkler (written 

commun., July 1976) obtained southeasterly to 

southerly directions from two flute-cast measurements near Cape Chiniak.

The Ghost Rocks Formation may represent basinplain or slope deposits that were severely deformed 

in a subduction zone. The direction of sedimentary 

transport for the elastics is not certain; the major 

facies associations are unclear because of extensive 

deformation; and the sedimentary and tectonic relations of the Ghost Rocks to younger and older 

formations are not well understood.
10 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

155 154 152

Tnc

Narrow Cape KODIAK ISLAND

.' Dangerous Cape

Tanginak ^ 

Anchorage

Partition Cove 

Sitkalidak island

EXPLANATION

See figure 2 for explanation 

of geologic symbols

OBSERVATIONS 

12

Twoheaded 

island

Kodiak Formation — Vector 

mean, standard deviation, 

and number of observations at a single locality

Kodiak Formation — Single 

paleocurrent direction

Ghost Rocks Formation — 

Single paleocurrent direction

SUMMARY OF OBSERVATIONS 

52

Tnc 

Sitklnak Lagoon

Kodiak Formation — Vector 

mean, standard deviation, 

and total number of observations

16

Ghost Rocks Formation — 

Paleocurrent direction and 

total number of observations

0 5 10 15 20 25 KILOMETERS

i i I 1 i i

FIGURE 5.—Paleocurrent map for the Kodiak and Ghost Rocks Formations, Kodiak Island.
SITKALIDAK FORMATION 11

SITKALIDAK FORMATION

BACKGROUND

The Sitkalidak Formation, of Eocene and Oligocene 

age, crops out in separate areas along the southeastern parts of Kodiak, Sitkalidak, and Sitkinak 

Islands (Moore, 1967; fig. 2). It is separated from the 

older Ghost Rocks Formation to the northwest by 

faults; on Sitkalidak Island, it is conformably overlain by the Sitkinak Formation, whereas on Sitkinak 

Island it is separated from the Sitkinak Formation 

by faults (Moore, 1969). At Narrow Cape, it is overlain 

unconformably by the Narrow Cape Formation. 

Outcrops of the Sitkalidak Formation were examined 

at Narrow Cape and on Sitkalidak and Sitkinak 

Islands. On Sitkalidak Island, it was examined along 

the southeastern coast west of Partition Cove and 

along the northeastern coast east of Tanginak 

Anchorage (fig. 2). The formation everywhere consists of interbedded sandstone and shale that forms 

a thick series of turbidites, estimated by Moore 

(1969) to be about 3,000 m thick at the type section 

in eastern Sitkalidak Island.

NARROW CAPE

The Sitkalidak Formation at Narrow Cape is overturned toward the north and consists of coarseningand thickening-upward megasequences formed 

primarily of facies C and D turbidites. The strata 

and megasequences are typical of outer-fan lobes. 

Three megasequences, about 10-40 m thick, are well 

exposed along the shoreline.

In the lower part of one megasequence, a prominent 90-cm-thick slurried bed contains scattered 

fragments of argillite in a sandstone matrix in the 

middle of the bed at the top of the Bouma b division 

and below the Bouma c division. Slurried beds of this 

type described from interlobe and lobe-fringe sequences by Mutti, Nilsen, and Ricci Lucchi (1978) 

and van Vliet (1978) seem to indicate erosion of the 

flanks or tops of lobes by turbidity currents.

At the tops of the megasequences are facies B beds 

as thick as 3 m. These beds are partly channelized 

into underlying strata (fig. 7A), probably a result of 

progradation in which the channel that fed the lobe 

eventually eroded part of the lobe constructed at its 

mouth. Alternatively, the erosive basal surfaces of 

these beds may simply represent erosion of the tops 

of lobes by turbidity currents, the same process that 

apparently yields slurried beds.

Nine paleocurrents from each of the three cycles 

were measured from flute casts, groove casts, and

cross-strata. These paleocurrents indicate sediment 

transport toward the south with a vector mean of 

171° and a standard deviation of 26° (fig. 8).

SITKALIDAK ISLAND

PARTITION COVE

On the west side of Partition Cove, the Sitkalidak 

Formation consists of a thick turbidite sequence that 

contains, in ascending order, lobe-fringe and distallobe deposits of the outer-fan facies association, some 

lobe deposits of the outer-fan facies association, 

channel and interchannel deposits of the middle-fan 

facies association, and possibly deposits of the innerfan facies association. The sequence clearly indicates 

a prograding or outbuilding deep-sea fan sequence, 

presumably with inner-fan, slope, and shelf deposits 

present still higher stratigraphically in the formation, and basin-plain deposits lower in the formation.

The formation here consists almost entirely of 

sandstone and shale with no conglomerate present 

except for some granule-size detritus filling large 

flute casts at the bases of some thicker sandstone 

beds. Calcite-cemented turbidites and concretions 

are present locally, particularly in the lower part of 

the section. Coalified plant debris is abundant in 

most beds of sandstone, commonly concentrated in 

the Bouma b division or at the tops of thicker beds. 

Because of its low density, the plant debris probably 

was one of the last constituents to settle out of the 

depositing turbidity currents. Plant fragments are 

common in channel-margin and levee deposits, where 

they were deposited by overbank spilling of channelized larger turbidity currents. The abundant plant 

material may indicate the presence of a delta in more 

proximal marginal-marine areas.

The sequence shows no major development of 

outer-fan lobes; instead it is dominated by a large 

number of channelized thinning- and fining-upward 

megasequences in the upper two-thirds of the observed section. Possibly thick sequences of outer-fan 

lobes may be located either below the observed section 

or laterally to the northeast or southwest. The lobefringe sequences characteristically contain five or 

six laterally continuous beds of fine-grained facies D 

sandstone (fig. IB) and some slurried beds 5-15 cm in 

thickness (fig. 1C). Sandstone:shale ratios are of 

the order of 1:1 to 1:2.

Only two outer-fan lobe megasequences were 

observed stratigraphically above the lobe-fringe 

deposits. These lobes are approximately 10 m thick 

and consist of 10-15 beds of facies B, C, and D sand-
12 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

c

FIGURE 6.—Sedimentary fades, Ghost Rocks Formation. A, Broken 

beds of sandstone and shale, south shore of Ugak Bay; stratigraphic top not clear. B, Broken beds of sandstone and shale, 

west of Narrow Cape; stratigraphic top to left. C, Deformed

D

greenstone and argillite, west of Narrow Cape; stratigraphic 

top uncertain. D, Massive facies A tuffaceous sandstone with 

interval of thin-bedded facies D sandstone and shale, south 

shore of Ugak Bay; stratigraphic top to left.

stone that have a sandstone: shale ratio of about 

1:0.75. The thickest bed of sandstone is about 1.5 m 

thick. The stratigraphically highest lobe thins 

upward in its upper part and appears to contain an 

erosional surface in its middle part. A thick sequence 

of thinning-upward channel-fill cycles overlies this 

composite lobe; this relationship indicates relatively 

rapid progradation of the fan. Several slurried beds 

as thick as 150 cm are present in the lobe megasequences. Thin calcareous turbidites above the 

thickest lobe beds may represent sediment supply 

from a different source terrane.

The channelized middle-fan megasequences generally consist of thick beds of facies A sandstone 

and conglomerate at the base, thinner beds of facies 

A and B turbidites in the middle, and thinner facies 

C turbidites at the top (fig. ID). The megasequences 

characteristically thin and fine upward and are 

separated from one another by shaly intervals. Dish 

structures are locally present, and minor channeling 

is very common. The megasequences, which range in 

thickness from 15 to 60 m, generally have sandstone: shale ratios of 2:1 to 5:1. The lower contact 

of the megasequence is generally channelized,
SITKALIDAK FORMATION 13

FIGURE 6.—Continued. E, Ripple-laminated facies D turbidites, south shore of Ugak Bay; stratigraphic top to'left. F, Ripple-marked

facies D turbidites, south shore of Ugak Bay; stratigraphic top to left.

cutting into underlying fine-grained interchannel 

and levee deposits that are locally as thick as 8 m. 

Ungraded debris-flow deposits that consist of sandstone and mudstone containing scattered and chaotically oriented rip-up clasts are present in some of 

the channelized megasequences.

The overbank and levee deposits consist of thin 

ripple-marked beds of siltstone, fine-grained sandstone, and mudstone. The siltstone and sandstone 

beds are discontinuous and characteristically vary 

in thickness laterally (fig. IE and F). They typically 

consist of ripple-topped facies D turbidites that 

locally form thin, thinning-upward megasequences 

that presumably mimic the thinning-upward channelfill cycles. Facies E beds present locally may represent 

reworking of channel-margin deposits by succeeding 

turbidity currents or overbanking of very large 

coarse-grained turbidity currents. Slump folds and 

synsedimentary faults in these overbank deposits 

are indicated by filling of topographic lows by turbidites of variable thickness (fig. 7G). In some 

deposits, outward migration of slumping away from 

the channel margin or growth slumping from prograding levee deposition is demonstrable.

Nonleveed interchannel deposits were seen at only 

one locality in this sequence, situated above slumped 

overbank deposits. Here they may be inner-fan interchannel deposits. These deposits consist of thinly 

interstratified siltstone and shale with numerous 

calcareous turbidite layers. The sandstone:shale 

ratio is about 1:3 to 1:6. Turbidite beds are about 3-7 

cm thick; no cyclicity in bed thickness was noted 

within the sequence.

The uppermost part of the section west of Partition 

Cove contains very thick and almost continuous 

beds of amalgamated sandstone that may represent 

inner-fan channel deposits. Megasequences formed 

by variations in bedding thickness are not clearly 

defined. The sandstone:shale ratio in this part of 

the section is 10:1 or greater, and interbedded 

deposits of shale or mudstone are thin to nonexistent.

Nineteen paleocurrents from the Partition Cove 

sequence indicate sediment transport toward the 

southeast in the lower part of the sequence (lobefringe, outer-fan lobe, and lower part of the middlefan channel deposits); the vector mean is 142°, 

standard deviation 36° (fig. 8). In the upper part of 

the sequence, paleocurrents are more variable and 

indicate flow in channels toward the northeast 

(vector mean of 48° from six measurements) and 

toward the southwest (vector mean of 226° from four 

measurements). Part of this variability in transport 

direction results from measurement of directions 

of both channel-axis flow and overbank spilling. 

The data in general suggest a source area to the 

north or northwest.

TANGINAK ANCHORAGE

East of Tanginak Anchorage on northeastern 

Sitkalidak Island, extensive thinning- and finingupward channelized middle-fan megasequences— 

alternating channel, channel-margin and interchannel deposits—crop out stratigraphically below 

channelized inner-fan conglomerates of the Sitkinak 

Formation. The channel-fill sequence consists mainly
14 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

c

ffi n^PT &S**^^^ :^^^m&* "Hi i i'i r ' mi j£

D

FIGURE 7.—Sedimentary fades, Sitkalidak Formation: A, Thickly 

bedded facies B turbidites at top of outer-fan lobe sequence, 

Narrow Cape; stratigraphic top to left. B, Thinly bedded facies 

D lobe-fringe turbidites, Partition Cove, Sitkalidak Island; 

stratigraphic top to left. C, Slurried bed of lobe-fringe turbidites.

Partition Cove, Sitkalidak Island; stratigraphic top to left. 

D, Thinning-upward middle-fan channel deposit bounded by 

thin-bedded interchannel deposits, Partition Cove, Sitkalidak 

Island. Base of overlying thinning-upward cycle at left; stratigraphic top to left.

of facies B sandstone beds that are wedge-shaped, 

amalgamated, and commonly channeled into underlying beds. The sandstone beds form discrete thinning 

upward cycles 5-70 m thick. The upper parts of the 

cycles commonly contain more shale, thinner beds, 

and thin dune-shaped beds of facies E sandstone.

The channel-margin facies consists of thin- to 

medium-bedded, cross-stratified, and ripple-marked 

facies E sandstone and thin, isolated, and starvedripple beds similar to those described by Nelson, 

Mutti, and Ricci Luchi (1975) for proximal thin-bedded

turbidites. These beds wedge out abruptly away 

from the channels and have a relatively high 

sandstone: shale ratio.

The interchannel deposits consist primarily of 

bioturbated mudstone with thin facies D siltstone 

and fine-grained sandstone turbidites. These deposits 

form sequences 10-50 m thick between channel and 

channel-margin deposits. Moderately channelized 

facies B and C sandstone beds scattered within the 

fine-grained interchannel deposits probably are 

produced by random channel avulsions or channel
SITKALIDAK FORMATION 15

E G

FIGURE 7.—Continued. £, Ripple-marked interchannel fades D 

turbidites, Partition Cove, Sitkalidak Island; stratigraphic top 

to right. F, Ripple-marked interchannel facies D turbidites, 

Partition Cove, Sitkalidak Island; stratigraphic top to right. G,

H

Slumped channel-margin turbidites, Partition Cove, Sitkalidak 

Island; stratigraphic top to left. H, Flute and groove casts at 

base of facies C lobe-fringe turbidites, near Sitkinak Dome, 

Sitkinak Island; paleocurrents toward lower left.

overspilling by very large turbidity currents.

Paleocurrents in this channelized sequence have a 

bimodal distribution (fig. 8). About half are oriented 

toward the north (vector mean of 354° from seven 

measurements), half toward the south (vector mean 

of 191° from five measurements).

SITKINAK ISLAND

The Sitkalidak Formation crops out extensively 

in the eastern and western parts of Sitkinak Island 

peripheral to a central belt of younger rocks (fig. 2).

It was examined in the Sitkinak Dome area and 

near Sitkinak Lagoon (fig. 2).

Near Sitkinak Dome, roadcuts expose facies C 

and D turbidites of the basin-plain, lobe-fringe, and 

outer-fan facies associations. Relative to the Sitkalidak Formation at Narrow Cape, the outer-fan 

lobe megasequences here are thinner, sandstone 

grain size is generally finer, beds are generally 

thinner, and more shale is present. Partially developed thickening- and coarsening-upward cycles are 

most prominent here and are more characteristic of 

lobe-fringe deposits than fully developed outer-fan
16 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

155" 154"

153 152

Twoheaded EXPLANATION

See figure 2 for explanation of geologic symbols 

OBSERVATIONS

Vector mean, standard deviation, and number of observations at a single locality

SUMMARY OF ALL OBSERVATIONS

Sitkinak Lagoon

Vector mean, standard deviation, and total number of 

observations

0 5 10 15 20 25 KILOMETERS

I I I I I I

FIGURE 8.—Paleocurrent map for the Sitkalidak Formation, Kodiak Island and adjacent islands.

lobe deposits. No channels were observed in the 

upper parts of the megasequences. Sole markings

are locally spectacularly developed, and thick and 

well-developed convolute laminae are common.
SITKINAK FORMATION 17

Seven paleocurrents measured near Sitkinak Dome 

yield a direction of sediment transport toward the 

west, with a vector mean of 280° and a standard 

deviation of 25° (fig. 8).

Basin-plain and lobe-fringe deposits are exposed 

along the northwest shore of the northern part of 

Sitkinak Lagoon. The sequence here consists typically 

of laterally extensive beds of facies C and D sandstone and siltstone interlayered with mudstone. 

Only a few thickening- and coarsening-upward cycles 

are present. Seven paleocurrents measured at this 

locality indicate sediment transport toward the 

north; a vector mean of 355° and a standard deviation of 15° are based on flute casts, groove casts, and 

single occurrences of small-scale cross-strata, prod 

marks, and primary current lineation (fig. 8). This 

direction of transport is opposite that of most 

paleocurrents measured in the Sitkalidak Formation, 

including directions measured near Sitkinak Dome.

SITKINAK FORMATION 

BACKGROUND

The Sitkinak Formation crops out in small areas 

of southeastern Kodiak Island and adjacent islands 

from near Dangerous Cape to Chirikof Island, located 

southwest of Kodiak Island (figs. 1 and 2; Moore, 

1967), a lateral distance of about 250 km. Its type 

section is along the south shore of Sitkinak Island, 

where it is 1,500 m thick; plant fossils indicate a 

middle or late Oligocene age (Moore, 1969). In this 

study, outcrops were examined both at the type section on Sitkinak Island and on Sitkalidak Island, 

where a different sedimentary facies is present. On 

Sitkalidak Island, it rests conformably on the Sitkalidak Formation and is in fault contact with the 

Ghost Rocks Formation. On Sitkinak Island, it is in 

fault contact with the Sitkalidak Formation and is 

overlain without angular discordance by the Narrow 

Cape Formation.

SITKALIDAK ISLAND

Coastal outcrops of conglomerate, sandstone, and 

shale of the Sitkinak Formation were examined at 

northeastern Sitkalidak Island about 3 km northeast 

of Tanginak Anchorage (fig. 2). Here the sequence 

rests on thinning- and fining-upward middle-fan 

megasequences of the Sitkalidak Formation.

Conglomerate that contains rounded clasts of 

volcanic rocks, graywacke, chert, and carbonate 

rocks as long as 50 cm forms most of the basal part 

of the sequence. The upper part of the sequence consists of turbidite sandstone and interbedded shale

(fig. 9A). Above this part of the sequence is poorly 

exposed shale that underlies gently sloping, grasscovered areas inland from the coast and forms the 

core of a southwest-plunging syncline. In the part of 

the exposed sequence measured (fig. 10), the overall 

fining- and thinning-upward nature of the sequence 

is apparent, although cyclicity is not particularly 

well developed within the measured part of the 

sequence. The sequence represents a channel or 

canyon fill in an inner-fan or lower-slope environment. The overlying shale probably represents a 

slope facies, although it was not examined in detail.

The lower part of the sequence (lower 60 m of 

measured section, fig. 10) contains numerous erosional 

surfaces, typically at the base of graded beds of conglomerate. Such surfaces indicate channelization 

and erosion of underlying beds. Blocks of canyon- or 

channel-margin deposits as long as 1.5 m are irregularly distributed in the lower part of the conglomerate 

section. Consisting mostly of thinly interstratified 

ripple-marked sandstone and shale, probably originally deposited on levees or other areas adjacent to 

the main channel, these blocks slumped or slid into 

the channel and became incorporated in the channel 

conglomerates; many are folded and deformed, 

probably by the slumping.

Facies A, consisting here of organized and graded 

beds of conglomerate locally containing lenses of 

coarse-grained sandstone, makes up most of this 

sequence (fig. 9B). The beds of conglomerate are 

separated at some horizons by very thin shale partings that commonly pinch out laterally as a result 

of erosion or channelization, producing amalgamated 

beds of conglomerate. These shale partings probably 

represent facies G hemipelagic sediments deposited 

during intervals when coarser elastics were not in 

transit down the postulated canyon or inner-fan 

valley. Interbedded with the shale in some places 

are crossbedded, medium- to coarse-grained beds 

of facies E sandstone with ungraded and wavy or 

dune-shaped tops (fig. 9C). These facies E beds may 

represent either reworking of bed load in channels 

by subsequent turbidity currents or channel-margin 

levee deposits formed by overspilling either from the 

main channel or canyon or from subchannels within 

the larger channel. Other interbedded thinly laminated siltstone strata contain abundant mica and 

plant fragments indicative of overbank-spilling 

processes. Strata higher than 55 m above the base 

of the measured section contain slumped and contorted layers, discontinuous and en echelon thin 

strata of siltstone, and alternating facies E and 

D beds.

Finer grained, parallel-laminated, graded, and
18 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

A C

FIGURE 9.—Sedimentary fades, Sitkinak Formation. A, Outcrop 

of inner-fan channel facies near Tanginak Anchorage, Sitkalidak Island; stratigraphic top to left. See figure 10 for 

measured section. B, Graded facies A conglomerate and sandstone beds, Tanginak Anchorage, Sitkalidak Island; stratigraphic 

top to left. C, Wavy-topped, cross-stratified, coarse-grained

D

facies E sandstone bed above fine conglomerate and below 

shale interval, Tanginak Anchorage, Sitkalidak Island; stratigraphic top to left. D, Thinly interbedded facies D sandstone 

turbidites and shale above coarse-grained facies E sandstone 

bed, Tanginak Anchorage, Sitkalidak Island; stratigraphic 

top to left.

locally ripple-marked sandstone beds are interbedded 

with shale at the top of the sequence (fig. 9D). These 

beds of sandstone are primarily facies B, but they 

include some facies D beds. At this level, the canyon 

or channel may have been nearly filled with sediment 

(to a depth of at least 80 m) and no longer very active, 

thus permitting some deposition of facies D turbidites 

that normally are more typical of outer-fan and 

basin-plain deposits.

In vertical sequence, an overall upward-fining 

and thinning can be observed within the 80-m-thick

measured section. An attempt to subdivide this 

larger cycle into smaller thinning- and fining-upward 

cycles is shown on the measured section (fig. 10); 

the smaller cycles are not clearly developed and are 

marked more by the abrupt occurrence at 10- to 15-m 

intervals of thin shale partings with associated 

facies E turbidites than by sequences that gradually 

fine and thin upward. This relation suggests that 

the sequence represents an inner-fan channel or 

lower-slope canyon fill. The partly developed smaller 

cycles may represent deposition in subchannels
SITKINAK FORMATION 19

E G

FIGURE 9.—Continued. E, Cross-stratified lens of sandstone in 

conglomerate, south coast of Sitkinak Island. F, Outcrop of 

thickly bedded, imbricated conglomerate containing thin, 

generally parallel-stratified lenses of sandstone, south coast 

of Sitkinak Island. G, Alternating darker colored siltstone and

H

coal intervals and lighter colored conglomerate and sandstone 

intervals, south coast of Sitkinak Island. H, Coalified piece of 

log oriented parallel to bedding in siltstone interval, south coast 

of Sitkinak Island.

10-15 m deep that formed within a much larger 

channel.

Ten paleocurrents measured near Tanginak 

Anchorage from flute casts, groove casts, pebble 

imbrications, preferred orientations of plant fragments, and facies-E cross-strata indicate transport 

of sediment toward the east-northeast, with a vector 

mean of 81° and a standard deviation of 20° (fig. 11). 

In summary, the formation in this locality probably 

represents an eastward-trending inner-fan to lowerslope valley fill, grading stratigraphically upward

to upper-slope shale facies and downward to middlefan sandstone facies.

SITKINAK ISLAND

Outcrops of the Sitkinak Formation were examined 

at several quarries and excavations in the central 

part of Sitkinak Island and along the southern coast 

of the island (fig. 2). The formation consists of alternating conglomerate-sandstone units and fine-grained 

sandstone and siltstone units with some coal and
20 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

FIGURE 9.—Continued. /, Cross-stratified sandstone tongue below 

and within siltstone-coal interval, south coast of Sitkinak 

Island. J, Interbedded coal (dark layers), siltstone (gray layers), 

and conglomerate at quarry adjacent to landing strip, Sitkinak 

Island.

carbonaceous shale strata. The alternating units 

are as thick as several hundred meters. The conglomerate-sandstone units make up about 70 percent 

of the formation, although the siltstone-coal intervals 

became relatively more numerous upward.

The conglomerate-sandstone units average 10-75 m 

in thickness and have a conglomerate: sandstone 

ratio greater than 5:2. Thin lenses of sandstone containing flat-stratification or very low angle crossstratification and, at some localities, medium- to 

large-scale cross-stratification (fig. 9E), separate thick 

accumulations of well-imbricated conglomerate (fig. 

9F). The conglomerate-sandstone units are typical of

THICKNESS, 

IN METERS

75 -

70 -

65 -

60 -

55

50 -

45 -

40 -

35 -

20 -

15 -

10 -

5 -

DEPOSITIONAL 

CYCLES

TURBIDITE FACIES OF

MUTTI AND RICCI LUCCHI

(1972, 1975)

EXPLANATION

Cross-strata

Thinning-and f i ning-upward 

mega sequence

Covered interval

FIGURE 10.—Measured section of part of the Sitkinak Formation 

near Tanginak Anchorage, Sitkalidak Island. Larger cycles in 

bedding thickness shown to right of columnar section. Lettered 

symbols to right indicate type of turbidite facies for adjacent 

beds according to scheme of Mutti and Ricci Lucchi (1972, 

1975), described in text in section on "Turbidite Facies and 

Facies Associations."
SITKINAK FORMATION 21

155

nton

Larsen ^ Mill Bay 

Bay 

Kodiak

Tgr y t.> Dangerous Cape ^

Anchorage 

Partition Cove

Sitkalidak Island

EXPLANATION

See figure 2 for explanation of geologic symbols 

OBSERVATIONS 

10

Vector mean, standard deviation, and number of observations at a single locality

SUMMARY OF OBSERVATIONS

Vector mean, standard deviation, and total number of 

observations

0 5 10 15 20 25 KILOMETERS 

i i i i i i

FIGURE 11.—Paleocurrent map for the Sitkinak Formation, Sitkalidak and Sitkinak Islands.

channelized fluvial braided-stream complexes. The 

conglomerates, which weather either reddish brown

or gray, contain well-rounded clasts ol volcanic rocks, 

vein quartz, argillite, graywacke, red chert, and granite;
22 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

the clasts are locally as long as 40-50 cm, generally 

5-10 cm. Paleocurrents measured from pebble or 

cobble imbrication and primary current lineation 

in flat-stratified sandstone indicate sediment transport toward the southeast, with a vector mean of 

114° and a standard deviation of 23°.

The siltstone and coal units consist of irregularly 

stratified carbonaceous siltstone to fine-grained 

sandstone that is thoroughly bioturbated and very 

poorly sorted (fig. 9G). The coal forms impure layers 

1-75 cm thick and locally contains coalified logs in 

vertical and horizontal positions (fig. 9H). The siltstone and fine-grained sandstone strata contain 

abundant plant fragments and fossil leaves. J. A. 

Wolfe (written commun., January 1977) identified 

specimens of Metasequoia cf. M. glyptostroboides 

Hu and Cheng and Alnus evidens (Holl.) Wolfe from 

collections taken in 1976. Well-stratified tongues 

of fine- to medium-grained sandstone, locally deformed by synsedimentary processes, extend into 

the siltstones (fig. 97).

The siltstone-coal units probably represent interchannel, lagoonal, and interdistributary bay deposits 

that probably form lens-shaped bodies enclosed 

within the conglomerate-sandstone units. As the 

channelized conglomerate-sandstone units migrated 

laterally, they cut into and eroded the laterally equivalent siltstone intervals. There are no marine fossils 

in the type section of the Sitkinak Formation; however, the fact that the mollusk-bearing Narrow Cape 

Formation is essentially conformable on the Sitkinak 

may suggest marginal marine sedimentation. During the summer of 1977, fine-grained beds of sandstone with marine trace fossils were observed in the 

southeasternmost exposure of the Sitkinak Formation 

within its central outcrop belt on Sitkinak Island.

At the main quarry directly west of and adjacent 

to the landing strip on Sitkinak Island, a sequence 

is exposed that demonstrates the stratigraphic 

relations between the conglomerate-sandstone and 

siltstone-coal units (fig. 12). Here the section consists 

of thin vertical cycles of red-weathering conglomerate overlain by gray-weathering conglomerate 

and, at places in the section, carbonaceous siltstone 

(fig. 9J). The basal contacts of the conglomeratesandstone units are erosional and indicate some 

channelization. The red-weathering conglomerate 

is imbricated (as is conglomerate on the south coast 

of the island) toward the southeast, with a vector 

mean of 111°, the presumed offshore direction. The 

gray-weathering conglomerate is imbricated toward 

the northwest, with a vector mean 278°, the presumed 

onshore direction. Within one thin sandstone bed, 

the long axes of scattered elongate pebbles are

20

10-

STRATA LITHOLOGY

Conglomerate, gray-weathering

Conglomerate, red-weathering

Bituminous shale and coal, interstratified siltstone, and finegrained sandstone

Sandstone, coarse-grained

Conglomerate, red-weathering

Coal

Sandstone, coarse-grained

Conglomerate, gray-weathering

Conglomerate, red-weathering

Shale, gray

Sandstone, coarse-grained

Coal

Shale, bituminous

EXPLANATION

Conglomerate

Sandstone

Siltstone

Shale

Coal

X

Covered interval

FIGURE 12.—Measured section of part of the Sitkinak Formation 

at quarry west of landing strip, Sitkinak Island.

orientated northeasterly (62°), a direction parallel 

to the approximate shoreline orientation. These 

fining-upward cycles suggest southeastward outbuilding of a major fan-delta complex in a marginalmarine setting, reworking by onshore currents, and
SEDIMENTARY PETROGRAPHY 23

subsidence yielding deposition of carbonaceous 

siltstone.

NARROW CAPE FORMATION 

BACKGROUND

The Narrow Cape Formation crops out at Narrow 

Cape on eastern Kodiak Island, its type locality, and 

on southern Sitkinak Island (Moore, 1967, 1969; 

fig. 2). At Narrow Cape, its age is early and middle 

Miocene (Allison, 1976) and the formation rests with 

angular unconformity on the Sitkalidak and Ghost 

Rocks Formations. On Sitkinak Island, it is late 

Oligocene or early Miocene in age (Allison, 1976) 

and is exposed in two northeast-trending synclines; 

here it rests without angular unconformity on the 

Sitkinak Formation, and its top is not exposed. At 

both localities, it consists of shallow-marine sandstone containing abundant molluscan fossils. 

Because the outcrops differ in age and are geographically separate, it is possible that future 

offshore subsurface information will provide a lithogenetic basis for subdividing the unit.

NARROW CAPE

At Narrow Cape, the formation is gently dipping 

and about 700 m thick (Moore, 1969). A fossiliferous 

basal sedimentary breccia and conglomerate contains angular to subangular sandstone clasts as 

large as 40 cm derived from the underlying vertical 

to overturned Sitkalidak Formation (fig. 13A). The 

breccia, 1-3 m thick, contains mainly disarticulated 

and broken molluscan fragments. Overlying the 

breccia is highly bioturbated massive silty finegrained sandstone and siltstone that constitutes 

more than 90 percent of the formation (fig. 13B). The 

largely unstratified but bioturbated sandstone (fig. 

13C) contains gastropods, pelecypods, scaphopods, 

and echinoids; it also includes articulated mollusks 

in apparent growth position throughout.

Interlayered with the silty sandstone and siltstone 

at irregular intervals are coarser deposits as thick as 

70 cm (fig. 13D) believed to have been deposited during 

storms. These layers contain well-rounded pebbles 

as large as 7 cm of granitic and volcanic rocks as well 

as clasts of the underlying Sitkalidak Formation and 

disarticulated, broken and partly rounded megafossil 

fragments. The conglomeratic or shelly layers are 

commonly graded, and their contact with the underlying bioturbated sandstone and siltstone is generally 

erosional. The upper part of the layers may consist of 

sandstone that contains parallel laminae or gently

inclined medium-scale cross-strata (fig. 13E). The 

upper contact with bioturbated sandstone or siltstone 

is gradational. In one storm layer, an eastward (88°) 

paleocurrent direction was measured from a crossbed. 

No preserved ripple marks were seen anywhere in 

the sequence.

The Narrow Cape Formation at its type locality, 

Narrow Cape, appears to represent a transgressive 

inner-shelf sequence deposited in generally quiet water 

beyond the surf zone. Allison (1976) suggests deposition at subtidal to neritic water depths and in subtropical or warm-temperate water temperatures. The 

local offshore direction may have been to the east, as 

inferred from the transport direction of a stormdeposited layer.

SITKINAK ISLAND

The general lithology of the Narrow Cape Formation on Sitkinak Island is similar to that at Narrow 

Cape. It consists of highly bioturbated siltstone 

and very fine grained sandstone with sporadic 

coarse-grained layers thought to have been deposited 

during storms. Coal-bearing siltstone of the Sitkinak 

Formation (fig. 14) is disconformable with the 

Narrow Cape Formation, here 150 m thick (Moore, 

1969). A 60-cm-thick pebble conglomerate with a 

siltstone matrix at the contact marks the disconformity. Small pebbles are scattered throughout 

the siltstone. The storm layers consist of wellrounded pebble conglomerate containing abundant 

clasts of sandstone derived from the Kodiak Formation and shelly layers of disarticulated and broken 

mollusk fragments (fig. 13F). Razor clams and 

other fossils in growth position are common in the 

bioturbated units (fig. 13G and H). Fossils are 

abundant, but species diversity is low: about 60 

percent of the fossils are ribbed clams, 30 percent 

razor clams, 5 percent smooth-shelled gastropods, 5 

percent turritellas, and less than 1 percent are ribbed 

gastropods. Allison (1976) concluded that the assemblage indicates middle or outer sublittoral 

(neritic) deposition probably in mild temperate 

waters, cooler conditions than for the somewhat 

younger assemblage in the Narrow Cape Formation 

at Narrow Cape.

SEDIMENTARY PETROGRAPHY 

By G. R. WlNKLER

Modal analyses of 21 thin sections of Cretaceous 

and Tertiary sandstone samples from Kodiak and 

adjacent islands indicate that most samples are 

subquartzose; that is, the percentage of quartzose
24 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

FIGURE 13.—Sedimentary fades, Narrow Cape Formation. A, 

Basal breccia-conglomerate resting unconformably on the 

Sitkalidak Formation, Narrow Cape. B, Massive bioturbated 

siltstone and fine-grained sandstone, Narrow Cape. C, Intengrains is generally less than 50 percent of all detrital 

constituents. Although plots of individual samples 

range widely on the quartzose-feldspar-lithic ternary 

diagram (fig. I5A), mean values for samples from 

the Kodiak (Upper Cretaceous), Ghost Rocks (Paleocene and Eocene), Sitkalidak (Eocene and Oligocene), 

and Sitkinak (Oligocene) Formations plot within the 

feldspatholithic field, and a mean value for the 

Narrow Cape (Oligocene? and Miocene) samples 

plots near the field boundary. A prominent trend 

through geologic time in the primary modes is an 

increase in total quartzose grains (Q) and a decrease 

in total feldspar grains (F) from the Kodiak Formation

D

sively bioturbated fine-grained sandstone, Narrow Cape. D, Thin 

storm layers in massive siltstone and finegrained sandstone, 

Narrow Cape.

to the Narrow Cape Formation. Moreover, there is an 

increasing diversity in types of lithic fragments 

(L) from older to younger samples. Volcanic and 

plutonic lithic fragments (V) constitute more than 

95 percent of Kodiak and Ghost Rocks lithic detritus 

(fig. 16A and B), about 75 percent of Sitkalidak and 

Sitkinak lithic detritus (fig. 16C and D), and 47 percent of Narrow Cape detritus. Most volcanic rock fragments have pilotaxitic, aphanitic, or porphyritic 

textures, and, though slightly altered, apparently 

were andesitic or basaltic; a smaller proportion are 

completely altered to silica, zeolite, prehnite, pumpellyite, or epidote. In the Sitkalidak and Sitkinak
SEDIMENTARY PETROGRAPHY 25

' '» J*a<$&£-?>VA-- '*1*t * "•:

FIGURE 13.—Continued. £, Low-angle cross-strata in fine-grained 

sandstone, Narrow Cape. F, Storm layers containing broken 

molluscan shells and fine pebbles, Sitkinak Island. G, ArticuH

ulated molluscan fossils in living positions below shelly storm 

layer, Sitkinak Island. H, Articulated molluscan fossils in 

living positions, Sitkinak Island.

Formations (fig. 16C and D), lithic fragments also 

include intraformational and extraformational sedimentary rock fragments (S) and, in small amounts, 

weakly foliated metamorphic rock fragments (M). 

In the Narrow Cape Formation, sedimentary rock 

fragments are the most abundant lithic constituent 

(fig- 16£).

The change in proportions of lithic constituents is 

accompanied by a marked change in the amount of 

chert and other polycrystalline quartzose grains 

(C), which increases from about 10 percent of total 

quartzose grains in the Kodiak and Ghost Rocks 

sandstone samples to more than 25 percent in

Sitkinak and Narrow Cape samples. A peculiar 

red-stained chert is particularly diagnostic of the 

younger formations. Much of the polycrystalline 

quartzose detritus probably was derived from 

strongly altered felsic volcanic rocks.

Texturally, a moderate contrast between the older 

and younger formations can be observed (fig. 151? 

and 16). Although all samples consist predominantly 

of framework grains, matrix is more abundant in 

some Kodiak and Ghost Rocks samples (fig. 16A 

and B), whereas carbonate or zeolite cement is more 

abundant in some Sitkalidak and Sitkinak samples. 

One sample from the Narrow Cape Formation is
26 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

APPROXIMATE 

THICKNESS. 

IN METERS

70 -

50-

40-

30 -

STRATA

6*. .

_: e?

10

UNIT

Narrow

Cape 

Formation

Sitkinak 

Formation

EXPLANATION

Gravelly and shelly 

storm layers 

with cross-strata 

at top

Coal

Molluscan fossils

FIGURE 14.—Approximate section at contact of Narrow Cape and 

Sitkinak Formations, south coast of Sitkinak Island.

tightly cemented, whereas the other two have abundant matrix. Most matrix appears to be composed 

of deformed weak detrital grains that in many cases 

are mineralogically altered. Such problematic interstitial material has been called "pseudomatrix" by 

Dickinson (1970). Samples with abundant matrix 

are tightly compacted with many sutured grain 

boundaries, indicating nearly complete eradication 

of primary porosity. Tightly cemented samples also 

have been compacted and altered; probably cementation occurred late in the diagenetic histories of 

such samples.

Heavy minerals are not abundant in samples 

from any of the formations. In almost every sample, 

biotite, epidote, muscovite, garnet, amphibole, 

sphene, chlorite, and zircon are present in minor 

amounts. Biotite is much more abundant in Sitkinak 

and Narrow Cape samples, and glauconite is present 

only in Sitkinak and Narrow Cape samples, in particular those containing abundant carbonaceous 

and glass-rich volcanic detritus.

Cretaceous and Tertiary sandstones from Kodiak 

Island were derived from volcanic sources similar 

to that of coeval rocks of the Shumagin Islands 

(Moore, 1973a), Alaska Peninsula (Burk, 1965), and 

Bristol Basin (Galloway, 1974). Because of their 

abundant volcanic detritus, these sandstones are 

not likely to be proximal equivalents of coeval 

turbidites on the Aleutian Abyssal Plain, as tentatively suggested by Stewart (1976). Some of the 

volcanic detritus may be recycled from older volcanic 

terranes, as it consists partly of prehnite-pumpellyite 

facies metavolcanic rock fragments. The ubiquity 

of detrital epidote, garnet, and weakly foliated 

quartz-mica clasts certainly indicates partial derivation from metamorphic terranes.

The marked upsection increase in polycrystalline 

and monocrystalline quartzose detritus indicates 

greater contribution through time from a quartz-rich 

provenance. Traces of myrmekite and antiperthite 

in the younger rocks indicate minor input from 

exposed plutons. Multiple sources are necessary to 

yield the varied detritus in the Cretaceous and Tertiary sandstones of Kodiak and adjacent islands. 

The persistence of dominant volcanic sources of 

detritus for perhaps 50 million years indicates that 

the volcanoplutonic arc of the Alaska Peninsula 

and southern Alaska Range remained a major and 

long-lived source of sediments that accumulated in 

adjoining basins.

SUMMARY AND CONCLUSIONS

Some tentative conclusions can be drawn regarding sedimentary environments, facies, and paleogeography of Upper Cretaceous to Miocene turbidites 

and associated sedimentary strata of Kodiak and 

adjacent islands, despite the briefness of our reconnaissance. These tentative conclusions are of 

particular value at the present time because of the 

pressing need for specific stratigraphic data in the 

evaluation of the hydrocarbon potential of the 

adjacent outer continental shelf. Many of the offshore stratigraphic problems were summarized 

by von Huene and others (1976) in relation to regional 

geology, geologic hazards, and the technological 

constraints of offshore exploration.

The Kodiak Formation represents a combination 

of slope (northwestern Kodiak Island) and basinplain (southeastern Kodiak Island) deposits. Within 

the slope deposits are thin basin-fill strata that form 

thin thickening-upward megasequences and sandstone-rich intervals. These deposits probably represent fillings of either local slope basins formed by 

downslope slumping and sliding or more extensive
SUMMARY AND CONCLUSIONS 27

FRAMEWORK GRAINS

Mean, Sitkalidak « 

Formation

\ \ MATRIX 

(gKMean, Kodiak Formation Mean, Ghost/Rocks Formatio

Lithofeldspathic Feldspatholithic

1:3 ROCK 

FRAGMENTS

FELDSPAR

FORMATION

Unit

Narrow 

Cape 

Formation

Sitkinak 

Formation

Sitkalidak 

Formation

Ghost 

Rocks 

Formation

Kodiak 

Formation

Shumagin 

Formation

n

3

4

3

8

3

61

GRAIN COMPOSITION, IN PERCENT

Mean

Range

Mean

Range

Mean

Range

Mean

Range

Mean

Range

Mean

Q

50

47-55

40

33-55

26

23-28

21

8-26

24

16-30

17 -

F

26

24-29

16

4-26

26

18-34

37

26-45

32

24-42

31

L

24

22-28

44

29-63

48

38-55

42

27-66

44

29-60

52

V

47

28-75

76

58-84

75

65-87

95

89-100

96

94-98

96

S

48

23-68

20

8-39

21

12-31

3

0-7

3

2-5

M

5

3-8

4

2-8

3

1-5

2

0-8

1

0-4

GRAIN RATIO

C/Q

0.25

.20-.29

.34

.10-.76

.16

.04-.28

.08

.03 -.15

.10

.05-. 15

.12

P/F

0.75

.6S-.83

.98

.93-1.0

.91

.S3-.98

.92

.80-.97

.95

.90-.99

.97

V/L

0.47

.28-.73

.75

.5 7-. 84

..74

.63-.87

.95

.89-1.0

.96

.94-.98

.95

CEMENT

EXPLANATION

Narrow Cape Formation 

Sitkinak Formation 

Sitkalidak Formation 

Ghost Rocks Formation 

Kodiak Formation 

Number of samples 

Total quart zose grains 

Polycrystalline quartzose 

grains

Total feldspar 

Plagioclase

Total rock fragments 

Volcanic and plutonic rock

fragments

Sedimentary rock fragments 

Metamorphic rock fragments

FIGURE 15.—Ternary diagrams showing sedimentary petrography 

of Upper Cretaceous to Miocene stratigraphic units, Kodiak 

and adjacent islands. A, Framework-grain compositions of 

21 point-counted sandstone samples from Kodiak Island, 

following classification schemes of Crook (1960) and Dickinson 

(1970). For comparison, mean values are shown for the 

Shumagin Formation (Moore, 1973a), a stratigraphic unit

depressions formed by tectonic processes (fig. 17). 

Relatively small basins (see fig. 17) may develop (1) 

at the edge of the shelf as a result of rapid sedimentation and subsidence; (2) in slope depressions formed 

at the base of scarps formed by downslope sliding

correlative with the Kodiak Formation. B, Textural characteristics of 21 point-counted sandstone samples from Kodiak 

Island. Note that matrix forms a minor component except in 

some samples from the Kodiak and Ghost Rocks Formations 

and that cement is a minor component except in some samples 

from the Sitkinak and Narrow Cape Formations.

and slumping, (3) in slope depressions formed 

between imbricated slide blocks, and (4) in truncated 

or abandoned canyons on the slope. Kelling and 

Stanley (1976) reviewed the geometry and development of slope basins on slump blocks.
28 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

FIGURE 16.—Selected photomicrographs of sandstone samples 

from the Kodiak, Ghost Rocks, Sitkalidak, Sitkinak, and 

Narrow Cape Formations. Plane-polarized light. A, Kodiak 

Formation. Poorly sorted, poorly rounded, and tightly appressed 

sandstone with considerable amount of interstitial matrix. B, 

Ghost Rocks Formation. Tightly appressed and strongly altered 

sandstone with sutured or indistinct grain boundaries. C,

In tectonically active slopes that develop adjacent 

to trenches defined by subduction zones, a variety 

of other types of small to large intraslope basins 

can form as a result of tectonic imbrication of 

underthrusted slices, as shown by Moore and Karig 

(1976) on Nias Island, or by folding of base-of-slope 

strata into ridge-and-valley topography, as shown 

by Carson, Yuan, Myers, and Barnard (1974) for the 

continental slope west of the state of Washington. 

It is probable that some intraslope basins of these 

types developed within the slope deposits of the 

Kodiak Formation, but more detailed structural

Sitkalidak Formation. Tightly packed sandstone composed of 

volcanic rock fragments (V), plagioclase (P), quartz (Q), and 

chert (C). D, Sitkinak Formation. Sandstone composed of 

diverse foliated metamorphic (M) and glass-rich volcanic (V) 

rock fragments, mudstone (S), quartz (Q), plagioclase (P), and 

chert (C).

and sedimentological studies would be required to 

demonstrate this.

Other types of intraslope basins may form in 

response to other processes, but they have not been 

recognized within the slope facies association of the 

Kodiak Formation. Intraslope basins may develop 

on abandoned segments of submarine canyons as 

described by Bouma, Smith, Sidner, and McKee 

(1976). Development of slope basins by processes of 

salt diapirism has been recently summarized by 

Amery (1976) and by Watkins, Worzel, and Ladd 

(1976). Deposition of large debris flows in intraslope
SUMMARY AND CONCLUSIONS 29

FIGURE 16.—Continued. E, Narrow Cape Formation. Tightly 

packed, poorly rounded sandstone with abundant dark, 

deformed mudstone fragments.

areas was most recently demonstrated by Embley 

(1976).

The mixture of slope and basin-plain fades to the 

exclusion of fan facies, as found within the Kodiak 

Formation, is not uncommon in deep-marine settings. Apparently not enough sediment was funneled 

through existing submarine canyons to feed or 

initiate the development of large deep-sea fans at 

the base of the slope. The canyons may not have 

extended all the way from shelf edge to base of slope 

owing to morphologic complications introduced by 

slumping or tectonic processes. Because consistent 

southwestward paleocurrents suggest sediment 

derivation from the northeast, deep-sea fan facies 

associations may be present to the northeast on 

the Kenai Peninsula or farther east in the Sitka area 

in rocks coeval with the basin-plain facies association of the Kodiak Formation (fig. 1).

The Kodiak Formation resembles other rocks of 

the structurally and stratigraphically similar 

Chugach terrane (Berg and others, 1972), which 

extends westward in an arc from near Sitka in southeastern Alaska across southern Alaska to Sanak 

Islands, 600 km southwest of Kodiak Island (fig. 1).

Shelf

Trench-floor 

basin plain

Sediment 

Arrows show direction of transport

Not to scale

Fault 

Arrows show relative movement

FIGURE 17.—Block diagram showing inferred paleogeography and depositional setting of the Kodiak Formation. (1) shelf-edge basin; 

(2) slide-scarp basin; (3) intraslide basin; (4) abandoned-canyon basin; (5) base-of-slope debris flow; (6) structurally produced basin; 

and (7) basin-plain turbidites. Arrows on the basin plain indicate direction of flow of turbidity currents.
30 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

Both J. C. Moore (1972, 1973a, b, 1974a) and Budnik 

(1974a, b) considered these rocks, on the Shumagin 

Islands and on the Kenai Peninsula respectively, to 

be Cretaceous trench sediments. Plafker, Jones and 

Pessagno (1977a, b) consider the Chugach terrane 

to represent turbidites accreted to the continental 

margin of southern Alaska by latest Cretaceous 

time. G. W. Moore and Bolm (1977) determined a 

subduction-slip azimuth from fold orientations of 

about N. 20° W. for the Kodiak Formation.

The origin of the extensive Chugach terrane and 

its relation to the associated melange terrane to its 

north and Paleogene turbidite terrane to its south 

remains the subject of extensive study. As more 

sedimentological data accumulate, constraints on 

the various proposed tectonic models become clearer. 

Progradation and outbuilding from the northwest 

of large deep-sea fans into the trench is not recorded 

by strata on Kodiak Island although it is possible 

that fans of this type may have subsequently been 

removed by subduction. If the basin-plain deposits 

did form in a trench from an upslope source, the 

consistent southwesterly paleocurrents suggest 

deflection into a trench whose axis sloped southwesterly.

Nilsen and Bouma (1977) concluded that the basinplain facies association of the Kodiak Formation 

more likely represents distal deposition of a major 

deep-sea fan complex that prograded south westward 

from a point source to the northeast; as such, it was 

deposited farther down the axis of a southwestplunging trench floor than more proximal fan 

deposits. The presence of inner- and middle-fan 

turbidites in the correlative Upper Cretaceous Valdez 

Formation in the Anchorage-Seward area, as reported by Nilsen and Bouma (1977), supports this 

concept. Paleocurrents in the Valdez Formation in 

this area indicate sediment transport to the southwest toward Kodiak Island (Nilsen and Bouma, 

1977). Reconnaissance examination of the coeval 

Sitka Graywacke in southeast Alaska by Nilsen 

and John Decker in 1978 indicated the presence of 

strata of the inner- to middle-fan facies associations 

in western or outboard outcrops and the slope facies 

association in eastern or inboard outcrops. This 

unit thus appears to represent the most proximal 

part of the axial trench fill, the coarsest and most 

thickly bedded part of the trench axis facies of the 

Chugach terrane. This scenario implies dominant 

filling of a trench floor by longitudinal transport 

from a major canyon and fan system developed 

northeast of Kodiak Island, probably traceable to 

southeast Alaska.

The basin-plain facies association of the Kodiak

Formation is thought to represent trench-fill rather 

than trench-slope-basin fill for several reasons:

(1) The very long and apparently continuous length 

of the Upper Cretaceous Chugach terrane (2,000 km) 

suggests the presence originally of a major tectonically controlled linear basin comparable to many 

modern continental-margin trenches, whereas trenchslope basins are more limited morphologic features;

(2) paleocurrents in the Chugach terrane are remarkably persistent in orientation toward the southwest, 

from the Shumagin Islands (Moore, 1973a) to Kodiak 

Island (this report) to the Kenai Peninsula (Nilsen 

and Bouma, 1977); and (3) the general petrography 

of sandstones from the various components of the 

Chugach terrane is similarly dominated by volcanic 

lithic fragments (fig. 15; Moore, 1974a, b; Budnik, 

1974a, b), implying a similar provenance for the 

terrane.

Part of the McHugh Complex (Clark, 1973) may 

represent the slope facies association of the Valdez 

Group, equivalent to the slope facies association of 

the Kodiak Formation (Nilsen and Bouma, 1977). 

Newly reported mapping in the McHugh Complex 

southeast of Anchorage by Tysdal and Case (1977) 

resulted in placement of strata previously mapped 

as McHugh Complex in the Valdez Group; these 

strata include mud-chip-bearing quartzofeldspathic 

sandstone, polymict conglomerate, and argillite— 

lithologies contained in the slope facies association 

of the Kodiak Formation. Nevertheless, the bulk 

of the McHugh Complex is certainly a melange 

terrane correlative with the Uyak Formation.

The Ghost Rocks Formation is sedimentologically 

difficult to interpret in terms of facies associations, 

mainly because of its extensive structural deformation. Paleocurrents are inconsistent in orientation; 

they have a slight preferential orientation toward 

the southwest. Because this formation is not clearly 

related stratigraphically to other units, it could 

represent a fragment of crust rafted in from a distant 

Pacific area during subduction. Yet the petrographic 

similarity of its sandstone turbidites to those of 

the Kodiak Formation suggests that it was derived 

from northwestern source terranes. The Ghost Rocks 

Formation may represent slope facies deformed by 

downslope gravitational movement as well as tectonic processes.

The Sitkalidak Formation appears to consist of 

middle- and outer-fan facies associations and some 

basin-plain deposits developed northeastward and 

south westward of the major submarine canyon and 

inner-fan channel complex formed by the Sitkinak 

Formation in the vicinity of central Sitkalidak 

Island (fig. 18). Subsequent work during the summer
SUMMARY AND CONCLUSIONS 31

Shoreline

"ope

i

Narrow

Sitkalidak Island 

Twoheaded Island 

Islands

Sediment 

Arrows show direction of transport

Outer fan lobes 

Fan channels

Not to scale 

FIGURE 18.—Block diagram showing inferred paleogeography and depositional setting of the Sitkalidak and Sitkinak Formations.

of 1977 revealed the existence of two additional 

major submarine canyon and inner-fan channel 

complexes on western Sitkinak and Chirikof Islands 

(Bouma and others, 1977); these areas also supplied 

sediment to the dominantly middle- and outer-fan 

complexes of the Sitkalidak Formation. Paleocurrents in the middle-fan deposits of Sitkalidak Island 

are variable; this variability indicates sediment 

transport to the northeast, southeast, and southwest. 

This paleocurrent pattern, together with the distribution of facies associations, suggests that the 

major submarine canyon northwest of Sitkalidak 

Island bifurcated northeastward and southwestward 

into inner- and middle-fan channels upon reaching 

the basin floor. Some of these channels transported 

sediment northeastward to outer-fan lobe deposits 

such as those cropping out at Narrow Cape; other 

channels transported sediment southwestward 

toward Twoheaded Island and Geese Islands.

Because deep-sea fan deposits of the Sitkalidak 

Formation apparently prograded or grew to the 

northeast and southwest rather than southeastward toward the Pacific Ocean (fig. 18), the tectonic 

setting of the basin in which the Sitkalidak Formation was deposited must have partly confined the 

growing fan system. One possible configuration 

that would explain the distribution of paleocurrents

and turbidite facies associations is a trench floor 

previously formed by a downgoing slab of oceanic 

crust that formed a northwest-sloping southeastern 

boundary to the trench (fig. 18). The general lack of 

subduction-related deformation in the Sitkalidak 

and Sitkinak turbidites suggests that if a trench 

floor formed the basin, active subduction was not 

taking place. A second possibility is deposition in 

an elongate trench-slope basin such as those described from Nias Island (Moore and Karig, 1976). 

Undoubtedly, other solutions that permit derivation of sediment from the northwest and outbuilding 

of fans toward the northeast and southwest are 

possible.

The Sitkinak Formation, defined by Moore (1969) 

for its numerous conglomerate beds, represents 

inner-fan channel or lower-slope canyon deposition 

on Sitkalidak Island (fig. 18). It probably represents 

fill of the same canyon and inner-fan channel system 

that fed the deep-sea fan deposits of the Sitkalidak 

Formation, and as such it is linked stratigraphically - 

to the Sitkalidak. The lack of a more marked stratigraphic break between the two units on Sitkalidak 

Island supports this tentative conclusion, as does 

the regularity of the upward passage from outer-fan 

to middle-fan deposits within the Sitkalidak Formation directly beneath the Sitkinak Formation. South-
32 CRETACEOUS TO MIOCENE STRATIGRAPHIC UNITS AND SEDIMENTARY FACIES, KODIAK ISLAND

eastward-directed paleocurrents within the Sitkinak 

Formation and the gradual upward increase in clast 

size through the sequence of the Sitkalidak and 

Sitkinak Formations here also suggest lateral 

continuity.

The Sitkinak Formation on Sitkinak Island represents a marginal-marine fan-delta complex of 

probably younger age than the deep-sea fan deposits 

of the Sitkalidak (fig. 18). The coalesced fan deltas 

of this sequence probably prograded to the east and 

may possibly represent younger very proximal 

top-of-slope deposition in the distributary system 

that fed the submarine canyon, fan, and basin-plain 

deposits of the Sitkalidak and Sitkinak Formations 

on Sitkinak Island. The fan-delta complex is probably 

preserved by downfaulting in the central graben on 

Sitkinak Island such that it is faulted against the 

older turbidite sequences (fig. 2). Part of the fan-delta 

distributary system may originally have traversed 

a narrow shelf cut by major southeast-trending 

submarine canyons. Funneling of sediment down 

the canyons then supplied material to the deep-sea 

fan deposits of the deep-marine part of the Sitkinak 

Formation and the Sitkalidak Formation.

The progressively more proximal environments 

represented by younger strata of the lower and 

middle Tertiary sequence of the southeastern flank 

of Kodiak Island suggest a major first-order offlapping or progradational depositional cycle similar 

to those described by Ricci Lucchi (1975). Such a 

cycle typically commences in vertical sequence with 

distal basin-plain turbidites, although on Kodiak 

Island the major cycle appears to commence with 

lobe-fringe and outer-fan lobe deposits of the lower 

part of the Sitkalidak Formation. During the summer 

of 1977, other basin-plain sequences were identified 

in the Sitkalidak Formation at various places. It is 

possible that deformed strata of the Ghost Rocks 

Formation might represent the most distal deposits 

of a major first-order cycle, but stratigraphic continuity between the Ghost Rocks and Sitkalidak 

Formations has not been demonstrated. Because 

the cycle includes marginal-marine to nonmarine 

deposits, it is even more inclusive than the turbidite 

cycles described by Ricci Lucchi.

The Narrow Cape Formation represents renewed 

transgression over the older Tertiary deposits following uplift and folding of the older rocks. On Sitkinak 

Island, the Narrow Cape Formation was deposited 

essentially conformably on the Sitkinak Formation, 

suggesting that the transgression took place across 

a low-relief marginal-marine area. At Narrow Cape, 

where the Narrow Cape Formation is younger than 

it is on Sitkinak Island, relief was greater and this

younger sequence of Narrow Cape Formation was 

deposited on the erosional edge of the overturned 

Sitkalidak Formation.

The entire Cretaceous to Miocene sequence on 

Kodiak Island in general resembles other sequences 

of circum-Pacific subduction zones, where structural 

units closest to the continent are the oldest, most 

deformed, most metamorphosed, and most clearly 

oceanic, and structural units farthest from the 

continent are progressively younger, less deformed, 

less metamorphosed, and more continental. The 

northwestward dip of most faults and axial planes 

of folds supports the concept of northwesterly subduction of oceanic crust. Changes in rate of convergence and angle of subduction, as suggested by Moore 

(1977), certainly may have controlled the varying 

amounts of deformation found in the Mesozoic and 

Cenozoic rocks of Kodiak Island.

On the basis of paleocurrent data and turbidite 

facies analyses, most of the units discussed in this 

paper appear to have been derived from source terranes to the northwest or northeast. Although most 

units may have accreted to the continental margin 

of Alaska by subduction-related processes, there is 

no evidence from the facies associations, paleocurrent patterns, sedimentary petrography, or 

paleogeographic reconstructions to support the 

hypothesis for long-distance transport of these 

accreted units; they must have accumulated at or 

adjacent to the Alaskan continental margin. Only 

the highly deformed Ghost Rocks Formation, separated from younger and older units by faults and 

containing pillow basalt and basalt breccia, appears 

to possibly represent a sequence derived from more 

distant terranes and transported to Kodiak Island 

by sea-floor motion. Yet, the petrographic similarity 

of its sandstone to rocks of the adjacent Kodiak 

Formation argues for a local Alaskan source. Largescale counterclockwise oroclinal bending or rotation 

of southern Alaska during Late Cretaceous or 

Paleogene time, as suggested by Plafker, Jones and 

Pessagno (1977a, b), would require revision of our 

concept of original geographic orientation of basin 

axes and paleocurrent orientations.

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GPO 689-035