# GEOLOGIC MAP OF ALASKA

# 

# COMPILED BY HELEN M. BEIKMAN

# 1980

# DESCRIPTION OF MAP UNITS

**STRATIFIED SEDIMENTARY SEQUENCE**

**Mainly marine. Includes some volcanic rocks.**

**In part metamorphosed**

Qh HOLOCENE DEPOSITS---Alluvial, glacial, lake, estuarine, swamp,
landslide, flood plain, and beach deposits

Q QUATERNARY DEPOSITS---Alluvial, glacial, lake, eolian, beach, and
volcanic deposits. Includes the marine Bootlegger Cove Clay

Qp PLEISTOCENE DEPOSITS---Alluvial, glacial, dune sand, loess, and
reworked sand and silt deposits

Tp PLIOCENE ROCKS---Sandstone, siltstone, and conglomerate. Includes
Tachilni Formation on the Alaska Peninsula and Tugidak Formation on
Tugidak and Chirikof Islands

uT UPPER TERTIARY ROCKS---Sandstone, siltstone, shale, mudstone, and
conglomerate of Miocene and Pliocene age. Includes upper part of the
Sagavanirktok Formation on the Arctic Coastal Plain, and the Yakataga
Formation in the Gulf of Alaska area

Tm MIOCENE ROCKS---Sandstone, siltstone, conglomerate, argillite,
graywacke, and basaltic rocks. As shown, includes Bear Lake Formation on
the Alaska Peninsula, Narrow Cape Formation (Oligocene or Miocene) on
Kodiak and Sitkinak Islands, and Chuniksak Formation (Miocene?) on Attu
Island

To OLIGOCENE ROCKS---Volcanic conglomerate, sandstone, volcanic breccia,
shale, and siltstone. As shown, includes the Meshik Formation and
Stepovak Formation of Burk (1965) on the Alaska Peninsular and the
Sitkinak Formation on Sitkalidak, Sitkinak, and Chirikof Islands

Te EOCENE ROCKS---Sandstone, siltstone, and shale interbedded with mafic
flows and sills of the Andrew Lake Formation on Adak Island

T TERTIARY ROCKS---Sedimentary rocks concealed beneath Quaternary cover
on Point Hope and volcanogenic sedimentary rocks and flows, dikes, and
sills on the Alaska Peninsula and Umnak Island

mT MIDDLE TERTIARY ROCKS---Siltstone, sandstone, organic shale, and
locally, volcanic rocks. Includes Poul Creek, Katalla, and Topsy
Formations ranging from Oligocene to Miocene age in Gulf of Alaska area

lT LOWER TERTIARY ROCKS---Interbedded sedimentary, volcanogenic, and
volcanic rocks of Paleocene, Eocene, and Oligocene age on the Alaska
Peninsula and Aleutian Islands and intensely deformed marine and
continental clastic rocks of Paleocene and Eocene age in the Gulf of
Alaska area. Includes the Tolstoi and Belkofski Formations of Burk
(1965) in the Alaska Peninsula; the Ghost Rocks Formation on Kodiak
Island; the Amchitka and Banjo Point Formations on Amchitka Island;
Gunners Cove Formation on Rat Island; the Krugloi Formation on Agattu
Island; and Kulthieth, Kustaka, and Tokun Formations and clastic rocks
of the Orca Group in the Gulf of Alaska area

uK UPPER CRETACEOUS ROCKS---Shale, sandstone, and conglomerate of the
Ninuluk Formation of the Nanushuk Group and Seabee and Schrader Bluff
Formations of the Colville Group in the Arctic Coastal Plain and
Foothills; nonmarine and marine clastic rocks, siltstone, and shale of
the Chignik and Hoodoo Formations on the Alaska Peninsula; graded beds
of sandstone and slate of the Kodiak Formation on Kodiak and Afgonak
Islands; sandstone and mudstone of Shumagin Formation on Shumagin and
Sanak Islands

K CRETACEOUS ROCKS---Volcanic graywacke, mudstone, and sandstone with
some coal-bearing rocks in the Yukon-Koyukuk province; graywacke and
shale of the Kuskokwim Group in the Kuskokwim Mountains; and shelf
deposits of sandstone, siltstone, shale, and limestone of the Kennicott,
Moonshine Creek, Schulze, Chititu, and MacColl Ridge Formations in the
southern Wrangell Mountains; the Matanuska Formation in the Matanuska
Valley; and the Kaguyak Formation on the Alaska Peninsula

lK LOWER CRETACEOUS ROCKS---Graywacke, sandstone, shale, siltstone, and
conglomerate of part of the Tiglukpuk Formation of former usage,
Okpikruak, Fortress Mountain, Torok, and Kukpowruk Formations in the
western Arctic Foothills; the Kongakut Formation, Bathtub Graywacke, and
Tuktu and Grandstand Formations in the eastern Brooks Range and Arctic
Foothills; unnamed graywacke, argillite, conglomerate, and minor
limestone southeast of the mouth of the Kuskokwim River; interlayered
submarine and subaerial andesitic fragmental volcanic rocks, flows,
tuffs, and volcaniclastic rocks of the Chisana Formation north of the
Wrangell Mountains; and unnamed graywacke, argillite, and minor andesite
on Etolin Island

KJ CRETACEOUS AND JURASSIC ROCKS---Argillite, shale, graywacke,
quartzite, conglomerate, lava, tuff, and agglomerate. Almost barren of
fossils and probably includes rocks ranging in age from Early Jurassic
to Late Cretaceous. In places moderately to highly metamorphosed
(amphibolite facies)

KJ~1~ LOWER CRETACEOUS AND UPPER JURASSIC ROCKS---Graywacke, slate,
argillite, minor conglomerate, volcanic detritus, and interbedded mafic
volcanic rocks. Includes Valdez and part of Yakutat Groups and Sitka
Graywacke. Mildly metamorphosed, locally to greenschist

KJ~2~ LOWER CRETACEOUS AND UPPER JURASSIC ROCKS---Shallow and deep water
clastic deposits (Oxfordian to Barremian) north of the Wrangell
Mountains; includes sandstone, arkose, siltstone, and limestone of the
Staniukovich Formation (Burk, 1965) and Herendeen Limestone on the
Alaska Peninsula; and slate, graywacke and conglomerate of the Seymour
Canal Formation on Admiralty and Kupreanof Islands

KJ~3~ CRETACEOUS AND UPPER JURASSIC(?) ROCKS---Melange of flysch,
greenstone, limestone, chert, granodiorite, glaucophane-bearing
greenschist, and layered gabbro and serpentinite. Melange consists of
Upper Jurassic(?) and Lower Cretaceous pelitic matrix enclosing blocks
several kilometers in dimension of Permian to lower Jurassic rocks.
Includes the Uyak Formation, McHugh Complex, melange within the Yakuktat
Group, and Waterfall Greenstone and Khaz Formation of the Kelp Bay
Group.

uJ UPPER JURASSIC ROCKS---Sandstone, siltstone, shale, and conglomerate
on the Alaska Peninsular, Cook Inlet area, and southern flank of the
Talkeetna Mountains. Includes the Chinitna and Naknek Formations

mJ MIDDLE JURASSIC ROCKS---Argillite, graywacke, and conglomerate
southeast of the Kuskokwim River and sandstone, shale, siltstone, and
conglomerate on the Alaska Peninsula and Cook Inlet area where it
includes the Kialagvik and Shelifkof Formations and Tuxedni Group

lJ LOWER JURASSIC ROCKS---Sandstone and argillite interbedded with
volcanic flows and pyroclastic rocks of the Talkeetna Formation in the
Cook Inlet area and southern Talkeetna Mountains

J JURASSIC ROCKS---Shale, siltstone ,and sandstone. Includes the Kingak
Shale along the northern front of the Brooks Range, Glenn Shale (which
includes rocks of Triassic and Cretaceous age) in the east-central part
of the State, the Nizina Mountain Formation and Kotsina Conglomerate
along the southern Wrangell Mountains, and unnamed slaty detrital rocks
on Gravina and Annette Islands.

JTr JURASSIC AND (OR) TRIASSIC ROCKS---Chert and argillite north of the
Porcupine River; limestone with minor dolomite, shale, and chert of the
Chitistone Limestone, Nizina Limestone, McCarthy Formation, and Lubbe
Creek Formation along the southern Wrangell Mountains; and hornfels and
phyllite of the Hazelton(?) Group in southeast Alaska

uTr UPPER TRIASSIC ROCKS---Limestone, shale, and chert of the Kamishak
Formation in the Cook Inlet area; a shelf facies of limestone, tuff,
tuffaceous conglomerate and breccias at the southern tip of the Kenai
Peninsula (west of the Border Ranges fault) and equivalent rocks of
Shuyak, Afognak, and Kodiak Islands; a deep water flysch and melange
facies of chert, pillow basalt and associated graywacke, argillite, and
minor ultramafic rocks (east of the Border Ranges fault) on the southern
Kenai Peninsula; chert, limestone, sandstone, and greenstone of the
Whitestripe Marble and Pinnacle Peak Phyllite (both Triassic?) on
Chichagof and Baranof Islands, of the Hyd Group on Admiralty Island and
Keku Straits area, and of the Nehenta and Chapin Peak Formations on
Gravina Island

Tr TRIASSIC ROCKS---Shale, chert, and limestone of the Shublik Formation
and quartzitic sandstone of the Karen Creek Sandstone on the north flank
of the Brooks Range

TrP TRIASSIC AND PERMIAN ROCKS---Sandstone, siltstone, and shale of the
Sadlerochit Group on the north flank of the Brooks Range; mafic volcanic
rocks, red beds, limestone, and calcareous argillite in the Chulitna
River area; argillite, limestone, siltstone, conglomerate, and abundant
gabbroic sills in the east-central Alaska Range where it includes the
upper part of the Mankomen Group; and schist, graywacke, slate,
conglomerate, phyllite, andesite flows and tuffs on Admiralty Island
where it includes the Barlow Cove Formation

JP JURASSIC, TRIASSIC, AND PERMIAN ROCKS---Shale, siltstone, and chert
and graywacke in the Brooks Range. Includes upper part of Nuka Formation
and Siksikpuk and Shublik Formations

MzPz MESOZOIC AND PALEOZOIC ROCKS---Sandstone, shale, chert, dolomite
and conglomerate, in a discordant rock sequence of unknown provenance
that includes rocks of Mississippian, Triassic, Jurassic, and Cretaceous
age in the western Brooks Range (includes Nuka Formation); Lower
Jurassic, Pennsylvanian, and Permian rocks, in part covered by Tertiary
sedimentary rocks and intruded by granitic rocks of Tertiary age in
north-central Chugach Mountains; and slate, quartzite, schist and
phyllite with interlayered beds of marble, layered gneiss and
amphibolite of Ordovician to Jurassic or Cretaceous age along the west
flank of the Coast Mountains

P PERMIAN ROCKS---Chert, shale, and siltstone of the Siksikpuk and
Echooka Formations in the central Arctic Foothills and volcanic
argillite and graywacke with local chert, pillow flows, limestone, and
dolomite of the Cannery, Pybus, and Halleck Formations on Admiralty,
Kuiu, and Kupreanof Islands

P\|P PERMIAN AND PENNSYLVANIAN ROCKS---Basaltic to andesitic lavas and
derivative volcaniclastic rocks, tuffs, minor gabbro, and local
shallow-water sedimentary rocks metamorphosed to greenschist facies, and
locally, amphibolite facies. Includes Skolai Group, Strelna Formation
(Permian), and Tetelna Volcanics in the Wrangell and Talkeetna
Mountains. Consists of unnamed phyllite, slate, schist, greenschist,
amphibolite, gneiss, and migmatite in St. Elias Mountains

\|P PENNSYLVANIAN ROCKS---Siltstone, sandstone, and limestone of the
Klawak Formation and Ladrones Limestone on Prince of Wales Island

\|PM PENNSYLVANIAN AND MISSISSIPPIAN ROCKS---Limestone, conglomerate,
shale, dolomite, and chert of the Kekiktuk Conglomerate and Kayak Shale
(both of Mississippian age) of the Endicott Group and the Alapah and
Wahoo Limestones of the Lisburne Group

M MISSISSIPPIAN ROCKS---Conglomerate, shale, limestone with subordinate
chert and dolomite of the Kekiktuk Conglomerate and Kayak Shale of the
Endicott Group and the Utukok Formation and Wachsmuth and Alapah
Limestones of the Lisburne Group on the northern flank of the Brooks
Range. Limestone, dolomite, and interbedded chert of the Iyoukeen
Formation on Chichagof Island and Peratrovich Formation on Prince of
Wales Island

JM JURASSIC TO MISSISSIPPIAN ROCKS---Unnamed slate and quartzite
northwest of Porcupine River and Lisburne and Sadlerochit Groups and
Kingak Shale at northeast front of Brooks Range

TrD TRIASSIC TO DEVONIAN ROCKS---Radiolarian chert, slate, and argillite

uPz UPPER PALEOZOIC ROCKS---Argillite, chert, shale, limestone, and
siltstone. Greenstone, limestone, shale, clastic sedimentary rocks,
schist, gneiss, and undifferentiated metamorphic rocks east of Juneau

Pz PALEOZOIC ROCKS---Limestone, marble, dolomite, and chert on Seward
Peninsula and St. Lawrence Island; limestone, slate, and conglomerate in
central Alaska Range; argillite and graywacke slightly metamorphosed
west of Chulitna River; flysch, conglomerate, limestone and pillow
basalt southwest of Mount McKinley; marble, in places containing
tremolite in Wrangell Mountains where it includes parts of a Devonian
section designated the Kaskawulsh Group in the Yukon Territory (Canada);
and sedimentary, metasedimentary, and metavolcanic rocks in southeastern
Alaska

MD MISSISSIPPIAN AND (OR) DEVONIAN ROCKS---Sandstone, graywacke,
quartzite, and conglomerate. Includes the Noatak Sandstone in western
Brooks Range and Kekiktuk and Kanayut Conglomerates in eastern Brooks
Range

D DEVONIAN ROCKS---Phyllite, hornfels, graywacke, and sandstone on the
Seward Peninsula; pyroclastic rocks and ash flows interbedded with
sedimentary rocks metamorphosed to schist and gneiss on north-central
flank of Alaska Range; limestone east of Kuskokwim Bay; clastic rocks
and limestone of the Kennel Creek Limestone (which may also include
Silurian rocks) and Cedar Cove Formation on Chichagof Island; schist,
phyllite, marble, and amphibolite of the Retreat Group and Gambier Bay
Formation on Admiralty and Kupreanof Islands and equivalent rocks to the
north and south; and limestone, shale, graywacke, conglomerate and
basaltic rocks of the St. Joseph Island Volcanics (Devonian?), Wadleigh
Limestone, and Port Refugio Formation on Prince of Wales Island

uD UPPER DEVONIAN ROCKS---Shale, sandstone, chert, conglomerate, and
quartzite in eastern and central Brooks Range and limestone and dolomite
in western Brooks Range. Includes Hunt Fork Shale, Kanayut Conglomerate,
Kugururok Formation, and Eli Limestone (Middle and Upper Devonian)

umD UPPER AND (OR) MIDDLE DEVONIAN ROCKS---Conglomerate, graywacke,
phyllite, shale, sandstone, siltstone, and limestone. Includes Nanook
Limestone in Shublik Mountains

DS DEVONIAN AND SILURIAN ROCKS---Limestone, dolomite, marble, and shale
of the Katakturuk Dolomite and the Skajit Limestone in Brooks Range and
Karheen Formation in Prince of Wales Island

S SILURIAN ROCKS---Graywacke, shale, siltstone, limestone, sandstone,
and argillite. Includes siltstone, mudstone, limestone, conglomerate,
sandstone, graywacke, minor red beds and volcanic rocks of the Rendu
Formation, and Willoughby Limestone in Glacier Bay area; the Point
Augusta Formation on Chichagof Island; Bay of Pillars Formation on
Admiralty, Kuiu, and Prince of Wales Island; and Kuiu Limestone and
Heceta Limestone on Prince of Wales Island

O ORDOVICIAN ROCKS---Limestone and shale on Seward Peninsula; argillite,
chert and limestone of the Hood Bay Formation on Admiralty Island

SO SILURIAN AND ORDOVICIAN ROCKS---Graywacke, conglomerate, shale,
siltstone, tuff, lava, and local limestone of the Descon Formation on
Prince of Wales Island

C CAMBRIAN ROCKS---Siltstone, sandstone, and phyllite

OpC ORDOVICIAN, CAMBRIAN, AND PRECAMBRIAN ROCKS---Phyllite, sandstone,
siltstone, limestone, chert, and quartzite

lPz LOWER PALEOZOIC ROCKS---Includes rocks of Cambrian through Devonian
age, in places metamorphosed to greenschist and amphibolite facies.
Sedimentary rocks include limestone, dolomite, argillite, chert, and
graywacke and metasedimentary rocks include schist, quartzite, slate,
greenstone, carbonate rocks, and phyllite. Includes Holitna Group in
Kuskokwim mountains, Tonzona Group along Kuskokwim River, rocks formerly
included in Birch Creek Schist in Yukon-Tanana Upland, unmetamorphosed
rocks of the Funnel Creek, Adams, Hillard, Road River, McCann Hill and
Hillard Formations, and Puppets Formation on Gravina and Annette Islands

lPzpC LOWER PALEOZOIC AND (OR) PRECAMBRIAN ROCKS---Sandstone, limestone,
shale, chert, phyllite, argillite, and quartzite of the Neruokpuk
Formation in the northeast Brooks Range; quartz-mica schist, mafic
greenschist, calcareous schist, chlorite schist, phyllite and quartzite
along south flank of Brooks Range and southwest through Kokrine-Hodzana
Highlands; schist and quartzite of the Birch Creek Schist of former
usage in Yukon-Tanana Highlands; highly metamorphosed clastic rocks
including the Keevy Peak Formation in the north flank of the Alaska
Range; and volcanogenic greenschist with interstratified marble in
Prince of Wales, Long and Dall Island, where it includes the Wales Group
and possibly Descon Formation

Z PRECAMBRIAN ROCKS---Siltite, phyllite, graywacke, quartz schist, and
graphitic schist of slate of the York region on Seward Peninsula;
schist, gneiss, and small amounts of amphibolite and marble east of
Kuskokwim Bay; quartz wacke, semi-schist, phyllite, and argillite,
slate, and siltstone east of Fort Yukon; and limestone, dolomite,
sandstone, shale, and basalt of the Tindir Group north of Tintina fault

Z~1~ YOUNGER PRECAMBRIAN ROCKS---Schistose, argillaceous, dolomitic
limestone and tactite on Seward Peninsula

Z~2~ OLDER PRECAMBRIAN ROCKS---Schist, gneiss, and migmatic and
metamorphic rocks, including rocks equivalent to slate of the York
region, in the Kigluai and Bendeleben Mountains on the Seward Peninsula

## CONTINENTAL DEPOSITS

Tpc PLIOCENE CONTINENTAL DEPOSITS---Pebble to boulder conglomerate,
coarse sandstone, siltstone, claystone, and thin lignite beds. Includes
Nenana Gravel (Pliocene?)

uTc UPPER TERTIARY CONTINENTAL DEPOSITS---Sandstone, siltstone,
claystone, minor conglomerate, and coal beds. Includes upper part of
Kenai Group in Cook Inlet area and Nenana Gravel and related unnamed
rocks in west-central Alaska Range. Rocks range in age from Oligocene(?)
through Pliocene

Tmc MIOCENE CONTINENTAL DEPOSITS---Sandstone, siltstone, shale,
claystone, conglomerate, and coal beds. Includes the Sanctuary,
Suntrana, Grubstake, and Lignite Creek Formations in central Alaska
Range and the Frederika Formation in Wrangell Mountains

mTc MIDDLE TERITARY CONTINENTAL DEPOSITS---Sandstone, siltstone,
claystone and coal beds. Includes the Healy Creek Formation in central
Alaska Range, the Gakona Formation in east-central Alaska Range, and the
Tsadaka Formation in Matanuska Valley. Rocks range in age from Oligocene
through Miocene

lTc LOWER TERTIARY CONTINENTAL DEPOSITS---Claystone, siltstone,
sandstone, conglomerate, and coal beds. Includes lower part of
Sagavanirktok Formation in the Arctic Coastal Plain and the Chickaloon
and Wishbone Formations in the Matanuska Valley. Rocks range in age from
Paleocene through Oligocene

Txc PALEOCENE CONTINENTAL DEPOSITS---Conglomerate, sandstone, coaly
shale, and shale. Includes Cantwell Formation in central Alaska Range

Tc TERTIARY CONTINENTAL DEPOSITS---Sandstone, coal, conglomerate and
shale of the Kootznahoo Formation on Admiralty, Kuiu, Kupreanof, and
Zarembo Islands

TKc TERTIARY AND CRETACEOUS CONTINENTAL DEPOSITS---Conglomerate,
breccia, sandstone, arkose, mudstone, shale, tuffaceous rocks, and
lignite. Includes Arkose Ridge Formation (Cretaceous?) in Matanuska
Valley.

uKc UPPER CRETACEOUS CONTINENTAL DEPOSITS---Sandstone and conglomerate
and interbedded shale, clay, silt, and bentonite of the Niakogon Tongue
of the Chandler Formation of the Nanushuk Group and the Prince Creek
Formation of the Colville Group on the Arctic Coastal Plain; shale and
siltstone in the Yukon-Koyukuk basin; and pebble conglomerate around the
margins of the basin

lKc LOWER CRETACEOUS CONTINENTAL DEPOSITS---Shale, claystone, siltstone,
sandstone, conglomerate, coaly shale and coal, ironstone, and bentonite.
Includes Corwin Formation (Lower and Upper Cretaceous) of the Nanushuk
Group and Killik Tongue of Chandler Formation of Nanushuk Group on
Arctic Coastal Plain

## METAMORPHIC ROCKS

lJm LOWER JURASSIC METAMORPHIC ROCKS---Intercalated blueschist, quartz
mica schist, greenschist with subordinate amphibolite, marble, and
metachert at southern tip of Kenai Peninsula and on Afognak Island

Mzm MESOZOIC METAMORPHIC ROCKS---Small masses of metamorphosed
sedimentary, volcanic, and igneous rocks, largely of pre-Cretaceous age,
scattered throughout the Aleutian Range batholith. Amphibolite facies
schist along north side of Matanuska Valley

JPm JURASSIC, TRIASSIC, AND PERMIAN METAMORPHIC ROCKS---Metasedimentary,
metaplutonic, and metavolcanic rocks near Anchorage and along south side
of Matanuska Valley

PzM PALEOZOIC METAMORPHIC ROCKS---Hornfels, schist, amphibolite, minor
marble, and undivided metamorphic rocks north of Icy Strait in
southeastern Alaska, and gneiss, schist, and phyllite, and
undifferentiated metasedimentary and metaigneous rocks in the
Yukon-Tanana Upland

PzpCm PALEOZOIC AND (OR) PRECAMBRIAN METAMORPHIC ROCKS---Metasedimentary
and metaigneous rocks, including schist and gneiss of many different
compositions, primarily of the greenschist and amphibolite facies, in
the Yukon-Tanana Upland. Formerly included the Birch Creek Schist

### REFERENCE

Beikman, H.M., 1980, Geologic map of Alaska: U.S. Geological Survey, 2
sheets, scale 1:2,500,000.