U.S. GEOLOGICAL SURVEY CIRCULAR 1026 

Late Cenozoic History 

of the Interior Basins 

of Alaska and the Yukon 

Proceedings of a cooperative workshop 

between earth scientists from Canada and 

the United States of America 
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Late Cenozoic His tory 

of the Interior Basins 

of Alaska and the Yukon 

L. DAVID CARTER, THOMAS D. HAMILTON, 

and JOHN P. GALLOWAY, Editors 

Proceedings of a cooperative workshop 

between earth scientists from Canada 

and the United States of America 

U.S. GEOLOGICAL SURVEY CIRCULAR 1026 
DEPARTMENT OF THE INTERIOR 

MANUEL LUJAN, JR., Secretary 

U.S. GEOLOGICAL SURVEY 

Dallas L. Peck, Director 

Any use of trade, product, or firm names 

in this publication is for descriptive purposes only 

and does not imply endorsement by the U.S. Government 

UNITED STATES GOVERNMENT PRINTING OFFICE, WASHINGTON : 1989 

Free on application to the 

Books and Open-File Reports Section 

U.S. Geological Survey 

Federal Center, Box 25425 

Denver, CO 80225 

Library of Congress Cataloging-in-Publication Data 

Late Cenozoic history of the interior basins of Alaska and the Yukon I L. 

David Carter, Thomas D. Hamilton, and John P. Galloway, editors. 

p. em.- (U.S. Geological Survey circular; 1026) 

Proceedings of a joint Canadian-American workshop hosted by the U.S. 

Geological Survey at Anchorage, AK, in Feb. 1987. 

Bibliography: p. 

Supt. of Docs. no.: I 19.4/2:1026 

1 . Geology, Stratigraphic-Quaternary-Congresses. 2. Geology-CanadaBeaufort Sea Region-Congresses. 3. Geology-Alaska-Beaufort Sea RegionCongresses. I. Carter, L. David. II. Hamilton, Thomas D. (Thomas Dudley), 

1936- . Ill. Galloway, John P. IV. Series: Geological Survey circular; 

1026. 

QE696.L286 1989 89-600059 

551.7'9-dc20 CIP 
CONTENTS 

INTRODUCTION 1 

L. David Carter and Thomas D. Hamilton 

WORKSHOP PROGRAM 3 

WORKSHOPPARTICIPANTS 4 

JOINT CANADIAN-AMERICAN INVESTIGATION OF THE CENOZOIC GEOLOGY 

OF THE LOWLANDS BORDERING THE BEAUFORT SEA 7 

Jean-Serge Vincent, L. David Carter, John V. Matthews, Jr., and David M. Hopkins 

PAPERS 

Late Pleistocene Spruce (Picea) in Northern Interior Basins of Alaska and the Yukon: 

Evidence from Marine Deposits in Northern Alaska 11 

L. David Carter and Thomas A. Ager 

Offshore Constraints on the Late Pleistocene Glacial History at the Mouth of the 

Mackenzie River 15 

Steve M. Blasco, Julie Bri.gham-Grette, and Philip R Hill 

Continental Ice Advances in Northwestern Canada and their Significance to Interior Basins 

in the Yukon 18 

Jean-Serge Vincent 

Was the Late Pleistocene Northwest Laurentide Ice Sheet Wet-Based? 22 

James Beget 

Quaternary Chronology, Yukon and Western District of Mackenzie 25 

Owen L. Hughes 

The Old Crow and Bluefish Basins, Northern Yukon: Development of the 

Quaternary History 30 

Charles E. Schweger 

Climatic Change in Eastern Beringia During Oxygen Isotope Stages 2 and 3: 

Proposed Thermal Events 34 

John V. Matthews, Jr., Charles E. Schweger, and Owen L. Hughes 

Paleosols of Northwestern Canada 39 

Charles Tamocai 

Upper Cenozoic Deposits, Kanuti Flats and Upper Kobuk Trench, Northern Alaska 45 

Thomas D. Hamilton 

Quaternary Deposits at Birch Creek, Northeastern Interior Alaska: The Possibility of 

Climatic Reconstruction 48 

Mary E. Edwards and Patricia F. McDowell 

Late Quaternary Paleofloods along the Porcupine River, Alaska: Implications for 

Regional Correlation 51 

Robert M. Thorson 

Contents Ill 
Late Cenozoic Sedimentary History along Major Fault Zones, Alaska 55 

Warren Y eend 

Paleoglaciology of the Selwyn Lobe of the Cordilleran Ice Sheet and Quaternary 

Stratigraphy of the East-Central Yukon 60 

Lionel E. Jackson, Jr. 

Late Cenozoic Stratigraphy and Sedimentology of Gravelly Deposits in Central and 

Southern Yukon 66 

Stephen R. Morison 

Quaternary Stratigraphy of the Fairbanks Area, Alaska 72 

Troy L. Pewe 

Pleistocene Glacial Events, Southeastern Copper River Basin, Alaska 78 

Donald R. Nichols 

A Working Glacial Chronology for the Western Copper River Basin, Alaska 81 

John R. Williams 

Glacial Lake Atna, Copper River Basin, Alaska 85 

Oscar J. Ferrians, Jr. 

History of Late Pleistocene and Holocene Vegetation in the Copper River Basin, 

South-Central Alaska 89 

Thomas A. Ager 

Pleistocene Vertebrate Localities in the Yukon 93 

C. Richard Harington 

Arctic Microtine Biochronology-Current Status 99 

Charles A. Repenning 

Comment on the Present Status of Dating Loess by Thermoluminescence 103 

Glenn W. Berger 

SUMMARIES OF DISCUSSION SESSIONS 1 0 7 

Geochronology 1 0 7 

Julie Brigham-Grette 

Neotectonics in Alaska and Northwestern Canada 1 0 8 

Robert M. Thorson 

Late Tertiary Events 1 0 9 

John V. Matthews, Jr. 

Early and Middle Pleistocene Events 11 0 

Thomas D. Hamilton 

Late Pleistocene Glacial Advances 111 

Jean-Serge Vincent 

Late Pleistocene Interstadial Intervals 112 

Charles E Schweger 

Canadian-American Collaborative Research 113 

L. David Carter 

IV Contents 
INTRODUCTION 

By L. David Carter and Thomas D. Hamilton 

This volume contains the proceedings of a joint Canadian-American workshop on the late Cenozoic history of 

the interior basins of Alaska and the Yukon, a meeting that 

was hosted by the U.S. Geological Survey at Anchorage, 

Alaska, in February 1987. The principal aim of the workshop was fostering communication between Canadian and 

American scientists on problems of late Cenozoic history 

common to both northwestern Canada and Alaska. 

The Anchorage workshop was the second in a planned 

series of meetings that are intended to be held at two- or 

three-year intervals. The first meeting of this series, which 

was hosted by the Geological Survey of Canada, was held 

in Calgary, Alberta, in April 1984. Its topic was the correlation of Quaternary deposits and events around the 

margin of the Beaufort Sea. A correlation chart that was 

assembled at the meeting and 16 short papers prepared by 

individual participants were published by the Geological 

Survey of Canada (Heginbottom and Vincent, 1986). 

During the Calgary meeting, it was agreed that a field 

trip would be held along the shore of the Beaufort Sea 

during the summer of 1985 and that a second workshop 

focusing on long geologic and climatic records of interior 

basins of Alaska and the Yukon would be held in Anchorage, Alaska, in the spring of 1987. 

The field trip was carried out in late July and early 

August 1985. Participants were Jean-Serge Vincent and 

John V. Matthews, Jr. (Geological Survey of Canada), 

David M. Hopkins (University of Alaska), and L. David 

Carter (U.S. Geological Survey). The group's objective 

was to study the chronology and geologic relations of 

deposits along the arctic coastal lowlands in order to clarify 

sea-level history and to resolve the age of late Tertiary and 

early to middle Pleistocene glacier advances (see Vincent 

and others, this volume). 

Planning for the subsequent Anchorage workshop was 

carried out jointly by members of the U.S. Geological 

Survey and the Geological Survey of Canada. Twentythree scientists from the Geological Survey of Canada, 

other Canadian government agencies, Canadian and United 

States universities, the Alaska Division of Mines and 

Manuscript approved for publication, January 5, 1989. 

Geology, and the U.S. Geological Survey participated in 

the meeting. Twenty of the following papers were prepared 

for the workshop and subsequently revised for publication; 

two additional papers were solicited after the workshop in 

order to expand coverage of topics that proved to be of 

particular interest. Brief synopses of the seven discussion 

sessions that followed the presentation of papers were 

prepared by discussion leaders, and these also are included 

in this volume. 

Some of the major rivers, tectonic basins, and faults 

referred to in the papers and discussion-session reports are 

shown in figure 1. More detailed maps showing all of the 

localities and geographic features mentioned in papers 

dealing with the Yukon can be found in Morison and Smith 

(1987, figs. 39, 41, and 42). 

One central theme that emerged from the workshop is 

the critical role of volcanic ash layers (tephras) in dating 

and correlating deposits of late Cenozoic age in Alaska and 

the Yukon. It is unfortunate that the age of one particularly 

widespread unit, the Old Crow tephra, is still unsettled as 

this volume goes to press. Most of the following topical 

reports and discussion summaries were written when an age 

of 86±8 ka was generally accepted for the Old Crow tephra 

(Wintle and Westgate, 1986), but subsequent age measurements indicate that it may be as old as 110±12 ka (Berger, 

this volume) or 149±13 ka (Westgate, 1988). 

In this volume, we follow the convention of using ka 

for "thousand years before present" and Ma for "million 

years before present" Timespans are designated as k.y. 

and m.y. for thousands and millions of years, respectively. 

Geologic-climatic units such as glaciations, interglaciations, stades, and interstades are considered informal stratigraphic units, as are all tephra layers discussed except the 

formally defined Ester, Dome, Wilber, Jarvis, and White 

River Ash Beds (Pewe, 1975). 

REFERENCES CITED 

Heginbottom, J.A., and Vincent, I-S., eds., 1986, Correlation of 

Quaternary deposits and events around the margin of the 

Beaufort Sea-Contributions from a joint Canadian-American workshop, April 1984: Geological Survey of Canada 

Open File Report 1237, 60 p. 

Introduction 
Morison, S.R., and Smith, C.A.S., eds., 1987, Guidebook to 

Quaternary research in Yukon; Xllth INQUA Congress field 

excursions A20a and A20b: Ottawa, National Research 

Council of Canada, 110 p. 

Pewe, T.L., 1975, Quaternary stratigraphic nomenclature in central Alaska: U.S. Geological Survey Professional Paper 862, 

CHUKCHI SEA 

32 p. 

Westgate, J.A., 1988, Isothermal plateau fission-track age of the 

late Pleistocene Old Crow tephra, Alaska: Geophysical 

Research Letters, v. 15, p. 376-379. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of Old Crow tephra in Alaska: Geology, v. 14, p. 594-597. 

300 

I I I 

BEAUFORT SEA KILOMETERS 

-· 

EXPLANATION 

D Basins Fault 

(!) Denali fault 

BB Bell Basin 

BfB Bluefish Basin ® Kaltag fault 

BPB Bonnet Plume Basin 

CRB Copper River Basin ® Kobuk fault 

KF Kanuti Flats @) Kugruk fault OCB Old Crow Basin 

YF Yukon Flats ® Tintina fault 

Figure 1. Some major geographic and geologic features of Alaska and the Yukon mentioned in papers and discussion-session 

reports in this volume. 

2 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
WORKSHOP PROGRAM 

Wednesday, February 11 

Welcome and Introduction 

L.D. Carter and T.D. Hamilton 

Resume of the joint Canadian-American field trip of 1985 

Vincent, Jean-Serge, and Carter, L. David 

Brief Presentations 

I. Northern Alaska, Yukon, and Mackenzie District 

Brigham-Grette, Julie 

Carter, L. David 

Vincent, Jean-Serge 

Beget, James E. 

II. Interior basins of northwest Canada 

Hughes, Owen L. 

Morison, Stephen R. 

Jackson, Lionel E., Jr. 

Tamocai, Charles 

Schweger, Charles E. 

III. Basins of central Alaska 

Hopkins, David M. 

Hamilton, Thomas D. 

Williams, John R. 

Edwards, Mary E. 

Pewe, Troy L. 

Williams, John R. 

Ferrians, Oscar, J., Jr. 

IV. Regional studies 

Thorson, Robert M. 

Yeend, Warren E. 

Repenning, Charles A. 

Judge, Alan S. 

Harington, C. Richard 

Ager, Thomas A. 

Matthews, John V., Jr. 

Thursday, February 12 

Discussion Sessions 

1. Geochronology 

Discussion Leader: Brigham-Grette, Julie 

2. Neotectonics 

Discussion Leader: Thorson, Robert M. 

3. Late Tertiary events 

Discussion Leader: Matthews, John V., Jr. 

4. Early and middle Pleistocene events 

Discussion Leader: Hamilton, Thomas D. 

Friday, February 13 

Discussion Sessions 

5. Late Pleistocene glacial advances 

Discussion Leader: Vincent, Jean-Serge 

6. Late Pleistocene interstadial intervals 

Discussion Leader: Schweger, Charles E. 

7. Canadian-American collaborative research 

Discussion Leader: Carter, L. David 

Workshop Program 3 
WORKSHOP PARTICIPANTS 

Thomas A. Ager 

Branch of Paleontology and Stratigraphy 

U.S. Geological Survey 

National Center-MS 970 

Reston, Virginia 22092 

James E. Beget 

Department of Geology and Geophysics 

408 Brooks Building 

University of Alaska 

Fairbanks, Alaska 99775-0760 

Julie Brigham-Grette 

Department of Geology 

University of Alberta 

Edmonton, Alberta 

Canada T6G 2E3 

Present address: 

Department of Geology and Geography 

University of Massachusetts 

Amherst, Massachusetts OI003-0026 

L. David Carter 

Branch of Alaskan Geology 

U.S. Geological Survey 

4200 University Drive 

Anchorage, Alaska 99508-4667 

Mary E. Edwards 

Marlboro College 

Marlboro, Vermont 05344 

Present address: 

Department of Geography 

University of Oregon 

Eugene, Oregon 97403-I2I8 

Oscar J. Ferrians, Jr. 

Branch of Alaskan Geology 

U.S. Geological Survey 

4200 University Drive 

Anchorage, Alaska 99508-4667 

Thomas D. Hamilton 

Branch of Alaskan Geology 

U.S. Geological Survey 

4200 University Drive 

Anchorage, Alaska 99508-4667 

C. Richard Harington 

National Museum of Natural Sciences 

Ottawa, Ontario 

Canada KIA ON8 

David M. Hopkins 

Department of Geology and Geophysics 

408 Brooks Building 

University of Alaska 

Fairbanks, Alaska 99775-0760 

Owen L. Hughes 

Geological Survey of Canada 

3303-33rd Street 

Calgary, Alberta 

Canada T2L 2A 7 

Lionel E. Jackson, Jr. 

Geological Survey of Canada 

IOO West Pender Street 

Vancouver, British Columbia 

Canada V6B IR8 

Alan S. Judge 

Geological Survey of Canada 

I Observatory Crescent 

Ottawa, Ontario 

Canada KIA OY3 

John V. Matthews, Jr. 

Geological Survey of Canada 

60I Booth Street 

Ottawa, Ontario 

Canada KIA OE8 

Stephen R. Morison 

Department of Indian and Northern Affairs 

200 Range Road 

Whitehorse, Yukon 

Canada YIA 3VI 

Troy L. Pewe 

Department of Geology 

Arizona State University 

Tempe, Ariwna 85287 

Richard D. Reger 

Alaska Division of Mining and Geology 

794 University Ave. 

Fairbanks, Alaska 9970I 

Charles A. Repenning 

Branch of Paleontology and Stratigraphy 

U;S. Geological Survey-MS 9I9 

Box 25046-Denver Federal Center 

Denver, Colorado 80225-0046 

4 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
WORKSHOP PARTICIPANTS-Continued 

Charles E. Schweger 

Department of Anthropology 

University of Alberta 

Edmonton, Alberta 

Canada T6G 2E3 

Charles Tarnocai 

Land Resource Research Institute 

Central Experimental Farm 

Ottawa, Ontario 

Canada KIA OC6 

Robert M. Thorson 

Department of Geology and Geophysics 

U-45, University of Connecticut 

Storrs, Connecticut 06268 

Jean-Serge Vincent 

Geological Survey of Canada 

601 Booth Street 

Ottawa, Ontario 

Canada KIA OE8 

John R. Williams 

Branch of Alaskan Geology-MS 917 

U.S. Geological Survey 

345 Middlefield Road 

Menlo Park, California 94025 

Warren E. Yeend 

Branch of Alaskan Geology-MS 917 

U.S. Geological Survey 

345 Middlefield Road 

Menlo Park, California 94025 

Other Contributors to this Volume 

Glenn W. Berger 

Department of Geology 

Western Washington University 

Bellingham, Washington 98225 

Steve M. Blasco 

Geological Survey of Canada 

Atlantic Geoscience Centre 

Bedford Institute of Oceanography 

P.O. Box 1006 

Dartmouth, Nova Scotia 

Canada B2Y 4A2 

John P. Galloway 

Branch of Alaska Geology-MS 917 

U.S. Geological Survey 

345 Middlefield Road 

Menlo Park, California 94025 

Philip R. Hill 

Geological Survey of Canada 

Atlantic Geoscience Centre 

Bedford Institute of Oceanography 

P.O. Box 1006 

Dartmouth, Nova Scotia 

Canada B2Y 4A2. 

Patricia F. McDowell 

Department of Geography 

University of Oregon 

Eugene, Oregon 97403-1218 

Donald R. Nichols 

Branch of Geologic Risk Assessment 

U.S. Geological Survey-MS 966 

Box 25046 Denver Federal Center 

Denver, Colorado 80225-0046 

Workshop Participants S 

JOINT CANADIAN-AMERICAN INVESTIGATION OF 

THE CENOZOIC GEOLOGY OF THE LOWLANDS 

BORDERING THE BEAUFORT SEA 

By jean-Serge Vincent, L. David Carter, John V. Matthews, Jr., and David M. Hopkins 

In late July and early August, 1985, we examined the 

geology of the lowlands along the margin of the Beaufort 

Sea in the Yukon and Northwest Territories of Canada and 

in Alaska (fig. 1). This field project was organized to 

address geologic problems identified during a joint Canadian-American workshop on the correlation of Quaternary 

deposits and events around the margin of the Beaufort Sea. 

The workshop was held in Calgary in 1984 and hosted by 

the Geological Survey of Canada (Heginbottom and Vincent, 1986). 

Suites of sediments along the Canadian margin of the 

Beaufort Sea record up to four advances of glaciers of 

Laurentide provenance and associated sea-level changes of 

glacioisostatic origin. Deposits of varied origin also record 

extensive nonglacial periods extending back at least to the 

Miocene. After meeting in Inuvik, we flew to Banks Island 

where the longest and most complete record exists. J.A. 

Westgate (University of Toronto) and Michel Lamothe 

(Geological Survey of Canada) accompanied us on this part 

of the trip in order to collect, respectively, tephra and 

thermoluminescence (TL) samples. At the Duck Hawk 

Bluffs, near Sachs Harbour, Upper Cretaceous marine 

sediments (Kanguk Formation) and Tertiary (Miocene and 

Pliocene?) fossil-bearing deltaic sand and gravel (Beaufort 

Formation) are overlain by preglacial mainly eolian and 

lacustrine sediments of the Worth Point Formation. The 

Worth Point Formation is overlain by a complex sequence 

composed of lower Pleistocene glacial and marine deposits 

associated with the Banks glaciation, interglacial middle 

Pleistocene lacustrine, fluvial, and paludal sediments of the 

Morgan Bluffs Formation, marine deposits associated with 

the late(?) middle Pleistocene Thomsen glaciation, interglacial lacustrine and paludal sediments of the Cape Collinson 

Formation, glacial and marine deposits of the early Wisconsin M'Clure stade of the Amundsen glaciation, and 

finally by Holocene deposits of varied origin (Vincent and 

others, 1983). Deposits of Late Wisconsin age crop out 

only on the east coast of the island. Our studies showed 

that (1) Cretaceous tephra reported from the Worth Point 

Formation had been ice-thrust from the Kanguk Formation 

over Beaufort Formation sediments during the Banks glaciation; (2) the Worth Point Formation is more complex 

than previously assumed; and (3) the Beaufort Formation 

contains a rich macroflora that includes many taxa not 

previously known from it. 

The group then moved to the Polar Continental Shelf 

Project Base at Tuktoyaktuk, on the mainland, and investigated various localities around Liverpool Bay, the Eskimo 

Lakes, and the Mackenzie River Delta. Glacial deposits of 

the middle(?) Pleistocene Mason River glaciation, of the 

Toker Point stade-Franklin Bay stade (early Wisconsin?), 

and of the Sitidgi stade (late Wisconsin) were briefly examined, but particular attention was given to pre-Toker Point 

stade nonglacial sediments (see Vincent, this volume, 

Hughes, this volume, and Rampton, 1982 for glacial limits 

and explanation of terminology). These nonglacial sediments include ancestral Mackenzie River sediments, eolian(?) sands of the Kittigazuit Formation, and complex 

sequences of middle Pleistocene and lower(?) upper late 

Pleistocene (Sangamon?) lacustrine, paludal, and marine 

deposits. Also investigated were marine shell-bearing sand 

and gravel that occurs on islands of the Mackenzie River 

Delta and postdates the Toker Point stade. Working out of 

Shingle Point, we examined exposures of the Buckland Till 

(= Toker Point stade), and the Flaxman Member of the 

Gubik Formation in Alaska (see Carter and Ager, this 

volume) was traced from the U.S.-Canada border east to 

Komakuk Beach, where it has been removed by erosion. 

From Shingle Point the group moved to Barter Island 

in Alaska. Working out of this base, the group examined 

excellent exposures of the Flaxman Member at Simpson 

Cove and Pokok Bay, and Pliocene(?) marine deposits of 

the Colvillian transgression (see Carter and others, 1986, 

for terminology of marine transgressions) were examined 

in coastal exposures between Pokok Bay and Pokok Lagoon. Poorly exposed Pliocene(?) marine deposits of the 

Fishcreekian transgression near the Niguanak River and 

along Carter Creek also were visited. At Carter Creek we 

sampled the well-exposed Tertiary Nuwok Member of the 

Sagavanirktok Formation (Detterman and others, 1975). 

We visited and extensively sampled fluvial gravelly sand 

that is exposed on a tributary of the Niguanak River and is 

older than the Fishcreekian transgression and possibly older 

than any of the recognized late Cenozoic marine transgressions. This site has yielded an intriguing flora and insect 

fauna that suggests a forest/tundra environment (unpublished Geological Survey of Canada macrofossil reports 

available on request from John Matthews). Unlike the 

present-day forest/tundra zone, it contained larch and fiveneedle pine in addition to spruce. Both tree and shrub 

Investigation of the Cenozoic Geology of the Lowlands Bordering the Beaufort Sea 7 
birches were present as well as some southern, nonboreal 

plants like honeysuckle (Lonicera). 

The group then moved west to Prudhoe Bay and examined a variety of deposits ranging in age from Eocene to 

Holocene including (1) Eocene deltaic(?) deposits with 

intercalated tephras and overlying coarse gravel beds that 

also contain tephras, (2) gravel pits excavated in lower(?), 

middle, and upper Pleistocene deposits near the Kuparuk 

River and near Milne Point, (3) larch-bearing fluvial deposits on the Kikiakrorak River, (4) thick Wisconsin eolian 

sand at Judy Creek, (5) Pliocene(?) marine deposits of the 

Fishcreekian transgression at Fish Creek, (6) Pliocene(?) 

marine deposits of the Bigbendian transgression near 

Ocean Point on the Colville River, and (7) sedimentary 

facies and structures in the bed of a drained lake near Fish 

Creek. 

Continuing west toward Barrow we stopped at the 

Kogru River to see Pelukian(?) and pre-Pelukian marine 

sediments and overlying marine sediments of the 

Simpsonian transgression (Flaxman Member of the Gubik 

Formation) at Cape Simpson. Out of Barrow, we spent two 

days studying the superposed Colvillian, Bigbendian, 

Fishcreekian, and Wainwrightian transgressions at Skull 

Cliff that were described by Brigham (1985). 

Some of the most important findings of our trip were 

the following: 

1. Plant macrofossils are widely present in the Beaufort 

and older parts of the Gubik Formations and will be 

useful in establishing a Neogene climatic framework of 

the margins of the Arctic Basin. 

2. The Worth Point Formation of Banks Island, which 

records an interval during the late Pliocene or early 

Pleistocene when larch, rather than spruce, formed the 

tree line, may correlate with deposits at various sites in 

Alaska that apparently also document the same type of 

vegetation. 

3. Similarly, the Banks glaciation, the oldest continental 

glacial event recognized in northwestern Canada, is 

probably recorded by glaciomarine deposits of late 

Pliocene or early Pleistocene age in Alaska. 

4. Determining the stratigraphic position at which shield 

erratics first appear in Gubik marine beds would establish a minimum age for the first Laurentide glacial 

episode in Canada. 

5. The widespread "brown sands" of the Kittigazuit Formation near Tuktoyaktuk, traditionally thought to be 

deltaic in origin, may instead be remnants of a large 

dune field. 

6. The glaciomarine Flaxman Member extends into Canada on the Yukon Coastal Plain at least to Komakuk 

Beach, and is either the same age as or younger than 

the Laurentide Buckland Till laid down during the 

0 

I 

0~ 

0 

BEAUFORT 

SEA 

CANADA 

I I 

KILOMETERS 

500 

I 

Figure 1. Location of places mentioned in text. N.W.T., Northwest Territories. 

8 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Buckland glaciation (=M'Clure stade of the Amundsen 

glaciation). 

7. Although most of the marine deposits in Canada represent high sea levels due to glacioisostatic depressions, some of the high sea-level events were likely 

eustatic in ongm. In particular, driftwood-bearing 

marine beds exposed along the northeast coast of 

Liverpool Bay were likely deposited during a eustatically higher sea level and may correlate with the Pelukian transgression of Alaska. In contrast, all Alaskan 

marine deposits formed during eustatic high sea level 

events, except perhaps part of the Flaxman Member. 

REFERENCES CITED 

Brigham, J.K., 1985, Marine stratigraphy and amino-acid geochronology of the Gubik Formation, western Arctic Coastal 

Plain, Alaska: U.S. Geological Survey Open-File Report 85-

381, 218 p. 

Carter, L.D., Brigham-Grette, Julie, and Hopkins, D.M., 1986, 

Late Cenozoic marine transgressions of the Alaskan Arctic 

Coastal Plain, in Heginbottom, J.A., and Vincent, J-S., eds., 

Correlation of Quaternary deposits and events around the 

margin of the Beaufort Sea: Geological Survey of Canada 

Open File Report 1237, p. 21-26. -

Detterman, R.L., Reiser, H.N., Brosge, W.P., and Dutro, J.T., Jr., 

1975, Post-Carboniferous stratigraphy, northeastern Alaska: 

U.S. Geological Survey Professional Paper 886, 46 p. 

Heginbottom, J.A., and Vincent, J-S., eds., 1986, Correlation of 

Quaternary deposits and events around the margin of the 

Beaufort Sea: Geological Survey of Canada Open File 

Report 1237, 60 p. 

Rampton, V.N., 1982, Quaternary geology of the Yukon Coastal 

Plain: Geological Survey of Canada Bulletin 317, 49 p. 

Vincent, J-S., Occhietli, S., Rutter, N., Lortie, G., Guilbault, J.P., 

and de Boutray, B., 1983, The late Tertiary-Quaternary stratigraphic record of the Duck Hawk Bluffs, Banks Island 

Canadian Arctic Archipelago: Canadian Journal of Earth 

Sciences, v. 20, no. 11, p. 1694-1712. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Investigation of the Cenozoic Geology of the Lowlands Bordering the Beaufort Sea 9 

Late Pleistocene Spruce (Picea) in 

Northern Interior Basins of Alaska and the Yukon: 

Evidence from Marine Deposits in Northern Alaska 

By L. David Carter and Thomas A. Ager 

The record of spruce (Picea) in upper Pleistocene 

sediments older than 20 ka in the northern interior basins of 

Alaska and the Yukon is poorly dated. The few finite 

radiocarbon dates on spruce occurrences have large analytical uncertainty (Hopkins and others, 1981b; Shackleton, 

1982) and thus are of uncertain validity. Most late Pleistocene sediments that contain spruce macrofossils or abundant spruce pollen are older than the range of radiocarbon 

dating, and there is debate about whether they represent 

interstadial or interglacial conditions (Pewe, 1975; 

Schweger and Matthews, 1985). Marine deposits on the 

Alaskan Arctic Coastal Plain provide evidence that during 

the last interglacial interval and during at least one and 

possibly two Wisconsin interstadials spruce was growing in 

northern interior basins. We discuss this evidence below 

and comment on its significance for the interpretation of 

the climatic and sedimentary record of northern interior 

basins. 

Marine deposits of the Alaskan Arctic Coastal Plain 

record at least two and possibly three late Pleistocene 

marine transgressions (Carter and others, 1986; Carter, 

unpub. data). The oldest of these was the Pelukian transgression, defined by Hopkins (1967) as producing shoreline 

features and deposits a few meters above present sea level 

that can be traced discontinuously around the coast of 

western and northern Alaska. Pelukian deposits on the 

Arctic Coastal Plain extend from Harrison Bay westward to 

near Barrow (fig. 1), and they are the youngest marine 

deposits that contain a fauna indicating more open water 

and warmer climatic conditions than exist at present 

(Hopkins and others, 1981a). Shells of the bivalve Hiatella 

arctica collected from Pelukian deposits yield amino-acid 

ratios that are barely distinguishable from those determined 

for modem specimens (Brigham and Miller, 1983), which 

supports Hopkins' ( 1967) conclusion that the Pelukian 

transgression occurred during the most recent pre-Holocene 

interglacial interval. 

In deep-sea sediment cores, the last interglacial period 

is generally equated with oxygen-isotope stage 5e, which 

peaked about 123 ka, and is the youngest Pleistocene 

oxygen-isotope stage in which the oxygen isotope compositions of the shells of benthic foraminifers are similar to 

Holocene isotopic compositions (Martinson and others, 

1987). We correlate the Pelukian transgression with stage 

5e because oxygen-isotope compositions of shells of the 

bivalve Astarte borealis from Pelukian deposits are about 

the same as those for modem A. borealis shells from the 

Beaufort Sea (Carter and others, 1985). This correlation is 

supported by six of eight thermoluminescence (TL) ages on 

Pelukian sediments. The six analyses are between 119 and 

134 ka and average about 124 ka (Carter, unpub. data). 

Two other TL ages of 89 and 140 ka fall outside the age 

range of oxygen-isotope stage 5e and may be spurious. 

Driftwood logs up to 25 em in diameter locally are 

common in Pelukian deposits of the Arctic Coastal Plain, 

and some of this wood has been identified as spruce (R.C. 

Koeppen, USDA Forest Products Laboratory, written 

commun., 1978). The most likely source for spruce driftwood is the Mackenzie River, but for the western part of 

the coastal plain a source in or north of the Yukon River 

drainage basin is also possible (Giddings, 1952), and a 

source on the North Slope of the Brooks Range cannot be 

ruled out. Spruce was thus almost certainly present in 

northern Alaska or northwestern Canada during the last 

interglacial interval. This conclusion was reached previously on the basis of the presence of spruce pollen, cones, 

and wood in interior basin sediments that were assumed to 

be of last-interglacial age (Hopkins, 1972; Pewe, 1975). 

However, the assumption of a last-interglacial age for these 

sediments was based in part on the presence of spruce 

pollen and macrofossils, and some of these same deposits 

have more recently been interpreted as much younger than 

125 ka (Hopkins, 1982; Schweger and Matthews, 1985). 

The next youngest transgression is informally named 

the Simpsonian transgression (Carter and others, 1986) and 

is represented by the Flaxman Member of the Gubik Formation, which occurs along the Beaufort Sea coast and 

inland to altitudes of about 7 m (fig. 1). The Flaxman 

Member is a glaciomarine deposit that contains ice-rafted 

erratics of Canadian provenance (Rodeick, 1979), with one 

of the source areas identified as Bathurst Inlet, about 1,000 

km to the east of figure 1 (J.-S. Vincent, Geological Survey 

of Canada, personal commun., 1985). Transportation of the 

erratics to the Beaufort Sea coast by icebergs records the 

ablation of an ice sheet in the Canadian Arctic. Remains of 

Pacific marine mammals collected from the Flaxman 

Member include ribbon seal (Histriophoca fasciata) and 

gray whale (Eschrichtius sp.) (Repenning, 1983) and show 

Late Pleistocene Spruce in Northern Interior Basins 11 
that, as now, a connection with the Bering Sea existed 

during the Simpsonian transgression. Marine mollusk shells 

from the Flaxman Member are enriched in 180 relative to 

modem specimens from the Beaufort Sea (Carter and others, 1985), indicating that there was more glacial ice during 

the Simpsonian transgression than there is today. The 180 

data also positively differentiate Simpsonian and Pelukian 

deposits. 

Preliminary results from 18 TL analyses of sediments 

from the Flaxman Member range from 50 to 86 ka and 

average about 70 ka (Carter, unpub. data). These analyses 

are supported by a uranium-series age of 75 ka determined 

on whalebone (J.L. Bischoff, U.S. Geological Survey, 

written commun., 1984). Radiocarbon ages on organic 

materials from the Flaxman Member range from about 19.5 

ka to indeterminate at more than 48 ka, and in some cases 

finite and indeterminate ages have been measured on pairs 

of samples from the same site (Sellmann and Brown, 1973; 

Stafford and others, 1987; Carter, unpub. data). For example, the uranium-series age cited above was measured on 

bone from a gray whale that previously had yielded radiocarbon ages of about 22.5 ka and >38 ka (Stafford and 

others, 1987). We conclude that fmite radiocarbon ages on 

organic materials from the Flaxman Member are probably 

minimum ages, and we tentatively accept the TL ages as 

approximating the time of the Simpsonian transgression. 

We emphasize, however, that analyses of the TL data are 

incomplete, and at this time we can say only that the data 

suggest that the Simpsonian transgression coincided with 

one of the two global high sea-level events dated on New 

Guinea as 59 and 81 ka (Chappell and Shackleton, 1986). 

148° 140° 

BEAUFORT SEA 

-4J? CriC SC Bl 

L. s.,.-'1( ' 

70"•·.......... Co-'1 ~r _;;.__ ~-.. ·. DB 

~~~::··::.~.~.-~:~:~:::::-rr·)::::::,··········\~0\\ 

68" 

···... -.. .... .· ~ 

••••••••••••••••••••••••••••••••••••••••••• ~p.NGE. ~o ~\ 

B~QOKS KILOMETERS 

EXPLANATION 

~ Pelukian transgression deposits 

.. Simpsonian transgression deposits (Flaxman Member) 

••••• Boundary of physiographic province 

Figure 1. Northern Alaska showing distribution of deposits of 

Pelukian transgression and Simpsonian transgression 

(Flaxman Member of Gubik Formation) and locations mentioned in the text (CS, Cape Simpson; SC, Simpson Cove; Bl, 

Barter Island; DB, Demarcation Bay). 

Spruce macrofossils (identified by J.T. Quirk, USDA 

Forest Products Laboratory, written commun., 1983) have 

been collected from the Flaxman Member at Cape Simpson 

and near Barter Island (fig. 1), and have been dated by 

radiocarbon as 35.75±0.68 ka (USGS-1850) and >48 ka 

(USGS-1855), respectively. As mentioned above, we 

consider the finite age as a minimum age. Of the several 

sediment samples from the Flaxman Member examined for 

pollen by T.A. Ager, only one sample was suitable for 

quantitative analysis. This sample contained 7.1 percent 

spruce pollen (table 1), which falls within the range of 

percentages of spruce pollen in the modem pollen rain 

(Nelson, 1979). These data suggest that during at least part 

of the Simpsonian transgression spruce forests may have 

been as close as the Mackenzie River valley, or valleys 

within or south of the Brooks Range, but probably not 

north of the Brooks Range. 

Evidence for possibly a third high sea-level event 

consists of marine sand that disconformably overlies the 

Flaxman Member at Demarcation Bay and at Cape 

Simpson. The marine sand could be merely a regressive 

facies of the Simpsonian transgression, but preliminary 

results of two TL analyses of the marine sand at Demarcation Bay are 41.5 and 48 ka (Carter, unpub. data), which 

suggests that it represents a separate sea-level highstand. 

Fine-grained organic detritus from the marine sand yielded 

a radiocarbon age of 29.39±0.24 ka (USGS-1856), but this 

age conflicts with the TL ages, and evidence from the 

Canadian Beaufort Sea shelf indicates that at about 27 ka 

relative sea level may have been as much as 140m below 

modem sea level (Hill and others, 1985). Furthermore, the 

marine oxygen-isotope record suggests that the time of 

minimum ice volume, and presumably highest sea level, 

during oxygen-isotope stage 3 occurred about 50 ka 

(Martinson and others, 1987). We thus provisionally accept the preliminary TL data, and adopt as a working 

hypothesis an age of about 45 or 50 ka for this unnamed 

and tentatively identified marine transgression. 

Small twigs identified as spruce (J.T. Quirk, USDA 

Forest Products Laboratory, written commun., 1983) occur 

in the marine sand at Demarcation Bay. They are localized 

in lenticular, organic-rich, cross-stratified beds that may be 

deltaic. If these beds are deltaic, then the spruce probably 

originated in the adjacent Brooks Range drainage. Otherwise, the most likely source for spruce driftwood on this 

part of the coastal plain is the Mackenzie River valley. 

Evidence from marine sediments of northern Alaska 

thus indicates that spruce was growing in northern interior 

basins during at least two and possibly three late Pleistocene marine transgressions: the Pelukian transgression of 

last-interglacial age (125 ka), the Simpsonian transgression 

of early or middle Wisconsin age, and a tentatively identified and unnamed transgression of middle Wisconsin age. 

A pollen or macrofossil record of spruce should be present 

in interior basin sediments that are correlative with these 

12 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Table 1. Pollen and spores from Flaxman Member of Gubik 

Formation at Simpson Cove 

[Analysis by T.A. Ager] 

Taxon Number of grains 

Pollen twe 

Betula (birch) ---------------------------------------- 49 

Picea (spruce) ---------------------------------------- 18 

Alnus (alder) ----------------------------------------- 33 

Salix (willow) ---------------------------------------- 8 

Myrica (sweet gale) -------------------------------- 1 

Ericaceae (blueberry/crowberry type) ----------- 7 

Rosaceae (rose family) ---------------------------- 1 

Shepherdia canadensis (soapberry) -------------- 2 

Caryophyllaceae {pink family) ----------------- 3 

Compositae (Asteraceae) 

Tubuliflorae type (for example, Aster) ---- 1 

Artemisia (wormwood) ------------------------- 6 

Cruciferae {Brassicaceae) (mustard family) ---- 12 

Cyperaceae (sedge family) ------------------------ 28 

Gramineae (Poaceae) (grass family) ------------ 75 

Polygonum sp. (buckwheat family) ------------- 2 

Ranunculaceae undiff. (crow foot family)------ 3 

Saxifragaceae undiff. (saxifrage family)-------- 2 

Unknown ----------------------------------------------- 3 

TOTAL POLLEN ------------------255 

Spore type 

Monolete type fern spores------------------------- 3 

Sphagnum moss spores----------------------------- 17 

Percent 

19.2 

7.1 

12.9 

3.1 

.4 

2.7 

.4 

.8 

1.2 

.4 

1.7 

4.7 

11.0 

29.4 

.8 

1.2 

.8 

1.2 

1.1 

6.2 

marine transgressions, and some upper Pleistocene sediments in interior basins do indeed contain spruce macrofossils and relatively high percentages of spruce pollen. 

Known occurrences of such sediments are in the Old Crow 

basin in Yukon Territory, and within Alaska on the Seward 

Peninsula, in the Koyukuk basin, the Chandalar valley, and 

in the Fairbanks area (Hamilton, 1979; Schweger and 

Matthews, 1985). These sediments are all stratigraphically 

above the Old Crow tephra, which has been dated by TL as 

86±8 ka (Wintle and Westgate, 1986) and 110±12 ka 

(Berger, 1987). These ages are concordant at two standard 

deviations and support earlier suggestions that the sprucebearing sediments above the tephra formed after oxygenisotope stage 5e and represent Wisconsin interstadial conditions (Hopkins, 1982; Schweger and Matthews, 1985). 

Some scientists, however, are reluctant to accept the TL 

ages for the tephra, because some of the overlying sprucebearing sediments contain evidence for climatic conditions 

as warm as or warmer than today, and they consider it 

unlikely that such climatic conditions have occurred since 

oxygen-isotope stage 5e (Pewe, this volume; D.M. 

Hopkins, University of Alaska, oral commun., 1987). If a 

correlation with stage 5e is correct, however, then there is 

no unequivocal record of Wisconsin-age spruce in sediments of northern interior basins. We thus prefer to accept 

the TL data for the age of the Old Crow tephra because of 

the likelihood that some of the overlying sediments that 

contain spruce macrofossils or abundant spruce pollen may 

correlate with Wisconsin-age marine deposits in northern 

Alaska. If we are correct, then climate in the northern 

interior basins of Alaska and the Yukon may have been as 

warm as or warmer than today during at least one Wisconsin interstadial event. 

REFERENCES CITED 

Berger, G.W., 1987, Thermoluminescence dating of the Pleistocene Old Crow tephra and adjacent loess, near Fairbanks, 

Alaska: Canadian Journal of Earth Sciences, v. 24, p. 

1975-1984. 

Brigham, J.K., and Miller, G.H., 1983, Paleotemperature estimates of the Alaskan Arctic Coastal Plain during the last 

125,000 years, in International Conference on Permafrost, 

4th, Proceedings, Fairbanks, Alaska, July 17-22, 1983: 

Washington, D.C., National Academy Press, p. 80-85. 

Carter, L.D., O'Neil, J.R., and Stipp, J.J., 1985, High sea level 

along the Alaskan arctic coast about 70 or 80 ka: Evidence 

for an Antarctic ice surge?: Arctic Land-Sea Interactions, 

14th Arctic Workshop, Dartmouth, Nova Scotia, November 

6-8, 1985,p. 22-24. 

Carter, L.D., Brigham-Grette, J., and Hopkins, D.M., 1986, Late 

Cenozoic marine transgressions of the Alaskan Arctic 

Coastal Plain, in Heginbottom, J.A., and Vincent, J-S., eds., 

Correlation of Quaternary deposits and events around the 

Beaufort Sea: Geological Survey of Canada Open File 

Report 1237, p. 21-26. 

Chappell, J., and Shackleton, N.J., 1986, Oxygen isotopes and sea 

level: Nature, v. 324, p. 137-140. 

Giddings, J.L., Jr., 1952, Driftwood and problems of Arctic sea 

currents: Proceedings of the American Philosophical Society, v. 96, p. 129-142. 

Hamilton, T.D., 1979, Quaternary stratigraphic sections with 

radiocarbon dates, Chandalar quadrangle, Alaska: U.S. 

Geological Survey Open-File Report 79-751, 17 p. 

Hill, P.R., Mudie, P.J., Moran, K., and Blasco, S.M., 1985, A sealevel curve for the Canadian Beaufort shelf: Canadian Journal of Earth Sciences, v. 22, p. 1383-1393. 

Hopkins, D.M., 1967, Quaternary marine transgressions in 

Alaska, in Hopkins, D.M., ed., The Bering Land Bridge: 

Stanford, Calif., Stanford University Press, p. 47-90. 

---1972, The paleogeography and climatic history of Beringia 

during late Cenozoic time: Internord, v. 12, p. 121-150. 

---1982, Aspects of the paleogeography of Beringia during 

the late Pleistocene, in Hopkins, D.M., Matthews, J.V., Jr., 

Schweger, C.E., and Young, S.B., eds., Paleoecology of 

Beringia: New York, Academic Press, p. 3-28. 

Hopkins, D.M., McDougall, K., and Brouwers, E., 1981a, Microfossil studies of Pelukian and Flaxman deposits, Alaska coast 

of the Beaufort Sea, in Smith, P.A., Hartz, R.W., and 

Hopkins, D.M., eds., Offshore permafrost studies and shoreline history as an aid to predicting offshore permafrost conditions: U.S. National Oceanic and Atmospheric Administration, Environmental Assessment of the Alaskan Continental Shelf, Annual Report, Task D-9, Research Unit 204 

and 273, April1979 to March 1980, Appendix G, p. 64-71. 

Hopkins, D.M., Smith, P.A., and Matthews, J.V., Jr., 1981b, 

Dated wood from Alaska and the Yukon: Implications for 

forest refugia in Beringia: Quaternary Research, v. 15, p. 

217-249. 

Martinson, D.G., Pisias, N.G., Hays, J.D., Imbrie, J., Moore T.C., 

Late Pleistocene Spruce in Northern Interior Basins 13 
Jr., and Shackleton, N.J., 1987, Age dating and the orbital 

theory of ice ages: Development of a high-resolution 0 to 

300,000-year chronostratigraphy: Quaternary Research, v. 

27, p. 1-29. 

Nelson, R.E., 1979, Quaternary environments of the Arctic Slope 

of Alaska: Seattle, University of Washington, M.S. thesis, 

141 p. 

Pewe, T.L., 1975, Quaternary geology of Alaska: U.S. Geological 

Survey Professional Paper 835, 145 p. 

Repenning, C.A., 1983, New evidence for the age of the Gubik 

Formation, Alaskan North Slope: Quaternary Research, v. 

19, p. 356-372. 

Rodeick, C.A., 1979, The origin, distribution, and depositional 

history of gravel deposits on the Beaufort Sea continental 

shelf, Alaska: U.S. Geological Survey Open-File Report 79-

234, 87 p. 

Schweger, C.E., and Matthews, J.V., Jr., 1985, Early and middle 

Wisconsinan environments of eastern Beringia: Stratigraphic 

and paleoecological implications of the Old Crow tephra: 

Geographie Physique et Quaternaire, v. 39, p. 275-290. 

Sellmann, P.V., and Brown, J., 1973, Stratigraphy and diagenesis 

of perennially frozen sediments in the Barrow, Alaska 

region, in The North American Contribution to the Second 

International Conference on Permafrost, Yakutsk, U.S.S.R., 

July 13-28, 1973: Washington, D.C., National Academy of 

Sciences, p. 171-181. 

Shackleton, J., 1982, Environmental histories from Whitefish and 

Imuruk Lakes, Seward Peninsula, Alaska: Ohio State University, Institute of Polar Studies Report No. 76, 49 p. 

Stafford, T.W., Jr., Jull, A.J.T., Brendel, K., Duhamel, R.C., and 

Donahue, D., 1987, Study of bone radiocarbon dating accuracy at the University of Arizona NSF Accelerator Facility 

for Radioisotope Analysis: Radiocarbon, v. 29, p. 24-44. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of the Old Crow tephra in Alaska: Geology, v. 14, p. 

594-597. 

Carter, l. David, Hamilton, Thomas D., and Galloway, John P., eds., 

1989, late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

14 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Offshore Constraints on the Late Pleistocene 

Glacial History at the Mouth of the Mackenzie River 

By Steve M. Blasco, julie Brigham-Grette, and Philip R. Hill 

The middle to late Pleistocene history of the Mackenzie River Delta, Mackenzie trough, and adjacent continental shelf of the Beaufort Sea has a direct bearing on the 

interpretation of Laurentide ice limits, which influenced the 

chronology of events in the upper Porcupine and Peel River 

valleys of the northern Yukon. The limit of the early 

Wisconsin Buckland glaciation as mapped by Rampton 

(1982; and see Vincent, this volume) extends offshore 

beyond Herschel Island, where Mackay (1959) originally 

described ice-thrusted sediments in coastal exposures coincident with this former ice limit. To the south, the Buckland limit has been traditionally extended by Hughes (see 

Hughes, 1986) to be correlative with the ice limits of the 

Hungry Creek glaciation (Hughes and others, 1981). Ice 

occupying this position in the north-central Yukon dammed 

the eastward drainage of the Peel River and impounded 

glacial lakes in the Old Crow, Bluefish, and Bell River 

basins just after 36.9 ka (Hughes and others, 1981). Discrepancies in the age and correlation of this maximum ice 

limit from Hungry Creek to the Beaufort Sea remain unresolved despite fieldwork in the intervening areas by Catto 

(1986), causing some to speculate that ice may have occupied a similar position more than once during the late 

Pleistocene. Alternate interpretations bring into question 

the age of the Buckland limit along the Yukon coast and 

the age of the Hungry Creek till. This abstract outlines 

ongoing work offshore that is relevant to determining the 

sequence and age of glacial events in the middle to late 

Pleistocene that influenced the stratigraphy of both the 

northern Yukon and the Beaufort Continental Shelf. 

The upper 80 to 100 m of sediment on the central part 

of the Beaufort Continental Shelf north of Richards Island 

and the Tuktoyaktuk Peninsula is composed of nearshore 

marine silt and clay overlain by glaciofluvial outwash sand, 

which is in turn overlain by a thin transgressive sequence 

that grades upward into a veneer of recent marine mud 

discharged from the modern Mackenzie River. This succession formed after 21 ka (Hill and others, 1985). Extensive seabed surveys by industry to locate offshore gravel 

and drift deposits as a source for construction materials 

have led to the identification of localized lag and barrier 

island deposits related to the last transgression, but no 

glacial tills or ice-contact deposits have been found. If 

present, such deposits must lie deeper than 80 m beneath 

the seabed. The glaciofluvial outwash complex of this 

succession was probably deposited fairly rapidly after 21 ka 

when an ice front was not far to the south. Seismic and 

chronologie evidence outlined by Hill and others (1985) 

suggests continued sea-level rise from at least 27 ka with an 

inflection around 15 ka, which is interpreted as indicating 

a slight readvance of the ice. The ice front was probably 

not far south of the present shoreline from late-middle 

Wisconsin time on, with a possible northward pulse about 

15 ka. 

On the western part of the Beaufort (or Yukon) Continental Shelf, northwest of Herschel Island, a discontinuous veneer of reworked sediments related to the last transgression and recent sedimentation unconformably overlies 

fine-grained sediments deposited before 53 ka (Julie 

Brigham-Grette, unpub. radiocarbon and thermoluminescence ages). Again, there is no evidence within this shallow sequence of an ice advance on the shelf. 

Between the central and western parts of the shelf lies 

the Mackenzie trough, a northwest-trending linear depression 80 km wide by 150 km long that is partly infilled by 

more than 300 m of sediment. Seismostratigraphic evidence suggests that the trough was excavated by the repeated action of ice tongues during the Pleistocene rather 

than forming as a graben, slump, or river valley (Blasco 

and others, in press). The base of the infilled trough is well 

defined by a smooth U-shaped angular unconformity 500 m 

below sea level, which rises to within 100m of the seafloor 

on the western shelf and lies about 200 m below the seabed 

at the edge of the central shelf (fig. 1). The chronostratigraphy of the Yukon shelf indicates that this basal unconformity formed before 53 ka. On the central shelf, extrapolated Holocene sedimentation rates suggest that the baseof-trough unconformity formed before 70 ka. 

Four seismostratigraphic units with a composite thickness of 300 m have been identified in the Mackenzie trough 

(fig. 1). Occupying a valley in the central section of the 

otherwise broad, flat base are unsampled sediments (unit 4) 

with a chaotic, hummocky acoustic character and a maximum thickness of 70 m. We believe that these sediments 

may be a basal till. This unit is overlain by an acoustically 

massive to poorly stratified sand (unit 3), as much as 200 

m thick, which rests directly on the basal unconfirmity over 

much of the trough. The contract between this sand and the 

overlying unit 2 is defined by a smooth, weak, trough-wide 

reflector which appears to terminate against the southwest 

wall of the trough and to rise into the shallow strata of the 

central shelf. The planar nature of this unconformity is 

Offshore Constraints on the Glacial History at the Mackenzie River 15 
interrupted along the western axis of the trough by a ridge 

with approximately 30m of relief. Unit 2 is an acoustically 

unstratified, trough-wide clay with a thickness that ranges 

from 40 to 60 m. The upper surface of this unit is well 

defined and can be mapped across the trough as a flat-lying 

to locally hummocky reflector. On the southwest wall, this 

event intersects the base-of-trough unconformity and rises 

higher in the section, truncating shallow sediments, to join 

with the present seafloor of the Yukon shelf. These 

seafloor sediments (beneath the thin discontinuous surficial 

veneer discussed above) were deposited before 53 ka. 

This reflector is traceable onto the central shelf, where 

it can be mapped at about 40 m below the seabed. Sediments at this depth are known to be of late Wisconsin age. 

Overlying this unconformity within the trough is unit 1, a 

late Wisconsin to Holocene sequence consisting of prograded deltaic bottomset, foreset, and topset beds, truncated 

at their upper surface by transgressive silt and clay, which 

is in tum overlain by thick recent marine mud. Unit 1 has 

a maximum thickness of 125 m. In the east-central part of 

the trough, 20 m of thick marine mud was deposited since 

9.5 ka. Palynological analysis suggests that the base of unit 

1 may have formed 12 to 14.6 ka (P.R. Hill, unpub. data) 

when compared with pollen sequences on land (Ritchie, 

1984). 

Tentative interpretation of the offshore stratigraphy 

suggests that the trough was excavated to its present maximum depth by a major ice advance during early Wisconsin 

time, or earlier, leaving a basal till deposit. The sand and 

clay (units 3 and 2) represent either a thick, fining-upward 

transgressive sequence related to the subsequent sea-level 

rise, or glacial deposits of succeeding advances. These 

sediments were subsequently overridden and marginally 

eroded by a limited middle(?) to late Wisconsin ice advance before 14 ka. Loading by ice may have deformed the 

underlying sand and clay units and destroyed their internal 

stratigraphy. This scenario correlates well with Beget's 

Sea level 

(1987) model of thin late Wisconsin ice in the Mackenzie 

River Delta. Ice retreat was followed by the deposition of 

a subaqueous deltaic sequence in which no ice-bonding has 

been observed. Transgression overtook progradation about 

12 ka in the central part of the trough. Rising sea levels 

truncated topset beds, and water depths became great 

enough for the deposition of marine mud about 9.5 ka. 

More than 10 m of marine sediments has been deposited in 

the central part of the trough over the last 6,800 years. 

In summary, a major ice advance during early Wisconsin time, or earlier, excavated the Mackenzie trough to its 

present maximum depth. The trough may have been subsequently reoccupied by ice at least once prior to the last 

advance. This middle to late Wisconsin ice margin was 

located not far south of the present shoreline. A thin ice 

tongue reoccupied the trough at this time but retreated by 

14 ka. 

The middle to late Pleistocene glacial history of the 

Beaufort Continental Shelf is very poorly constrained. In 

addition, evidence to support credible correlations with the 

onshore stratigraphy is clearly absent, making it difficult at 

present to contribute to the solution of the conflicting interpretations of the onshore record. 

REFERENCES CITED 

Beget, James, 1987, Low profile of the northwest Laurentide Ice 

Sheet: Arctic and Alpine Research, v. 19, p. 81-88. 

Blasco, S.M., O'Connor, M.J., Hill, P.R., and Fortin, G., (in 

press), Late Quaternary history of the Canadian Beaufort 

continental shelf, in Grantz, A., Johnson, L., and Sweeney, 

J., eds., The geology of the Arctic Ocean region: Boulder, 

Geological Society of America Decade of North American 

Geology. 

Catto, N.R., 1986, Quaternary sedimentology and stratigraphy, 

Peel Plateau and Richardson Mountains, Yukon and N.W.T.: 

Edmonton. University of Alberta, Ph.D. thesis, 358 p. 

Hill, P.R., Mudie, P.J., Moran, K., and Blasco, S.M., 1985, A sea 

level curve for the Canadian Beaufort Shelf: Canadian Jour0 --t---------- MACKENZIE TROUGH Sea level 

NE 

CENTRAL 

SHELF 0 

75 km wide 

200 

:§ 400 

J: 

.... 

a. 

w 

0 

600 (Dashed and queried where uncertain or unknown, respectively) 

200 

400 

600 

800 ~---------------------------------------------------------------------------~ 800 

Figure 1. Schematic cross section of Mackenzie trough at approximately 700 north. Seismostratigraphic units 1--4 discussed 

in text. 

16 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
nal of Earth Sciences, v. 22, p. 1383-1393. 

Hughes, O.L., 1986, Quaternary chronology of Yukon Territory 

and the western District of Mackenzie: Geological Survey of 

Canada Open File Report 1237, p. 13-17. 

Hughes, O.L., Harrington, C.R., Janssens, J.A., Matthews, J.V., 

Morlan, R.E., Rutter, N.W., and Schwege, C.E., 1981, Upper 

Pleistocene stratigraphy, paleoecology, and archaeology of 

the northern Yukon interior, eastern Beringia, 1. Bonnet 

Plume Basin: Arctic, v. 34, p. 329-365. 

Mackay, J.R., 1959, Glacier ice-thrust features of the Yukon 

coast: Geographical Bulletin, p. 5-21. 

Rampton, V.N., 1982, Quaternary geology of the Yukon Coastal 

Plain: Geological Survey of Canada Bulletin 317, 49 p. 

Ritchie, J.C., 1984, Past and present vegetation of the far northwest of Canada: Toronto, University of Toronto Press, 251 

p. 

Geological Survey of Canada Contribution 47188 

Carter, L. David, Hamilton, Thomas D., and Galloway, John P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Offshore Constraints on the Glacial History at the Mackenzie River 17 
Continental Ice Advances in Northwestern Canada and 

their Significance to Interior Basins in the Yukon 

By Jean-Serge Vincent 

On the basis of stratigraphic and chronologie evidence 

in the western District of Mackenzie, the Beaufort Sea 

coastal plain, and the southwestern Canadian Arctic Archipelago, it has been proposed that continental glaciers advanced westward to the Cordilleran mountain front at least 

four times during the late Cenozoic (fig. 1; Vincent, 1989). 

In the westernmost District of Mackenzie, weathered fluvial gravels along the Snake River, Peel River, and Rat 

River contain stones derived from the Canadian Shield 

(Catto, 1986). The possibly pre-Wisconsin tills in the 

Franklin Mountains (Rutter and others, 1973) provide 

additional evidence for early or middle Pleistocene continental ice advances to the Cordilleran mountain front. 

However, the westernmost extent of this ice has not been 

determined. 

In the late Pleistocene, two Wisconsin stadia! advances 

to the Cordilleran front are well recorded. The oldest of 

these is named the Hungry Creek glaciation in the Bonnet 

Plume Basin (Hughes and others, 1981), the Toker Point 

stade in the Tuktoyaktuk coastlands (Rampton, 1988), and 

the Buckland glaciation on the Yukon Coastal Plain 

(Rarnpton, 1982). It is this advance that is commonly 

thought to have been the most extensive ice advance on the 

mainland during the Pleistocene. However, because ice 

advances were distinctly more extensive in the southwestem Arctic Archipelago during the early Pleistocene Banks 

glaciation and the middle Pleistocene Thomsen glaciation 

than they were in late Pleistocene time (Vincent, 1986), it 

is possible that ice on the mainland, which carne from the 

same dispersal center, also was most extensive during early 

and middle Pleistocene advances. 

The younger Wisconsin stadia! advance is named the 

Sitidgi stade on the coastal plain (Rampton, 1989), the 

Russell stade in the southwestern Canadian Arctic Archipelago (Vincent, 1983), and the Tutsieta Lake phase in the 

District of Mackenzie (Hughes, 1987). The age of this 

advance is generally accepted as being latest late Wisconsin, but the age of the earlier ice advance is still the subject 

of some debate, particularly because of the seemingly 

divergent record of the Bonnet Plume and Rat River basins 

with that of the Beaufort Sea Coastal Plain (Vincent, 1989; 

Vincent and Prest, 1987; Blasco and others, this volume). 

In the Bonnet Plume and Rat River basins, as well as in the 

interior basins of the Yukon, radiometric ages on materials 

either predating the older Wisconsin ice advance or closely 

associated with it argue for a latest middle Wisconsin or 

earliest late Wisconsin age. In contrast, data from the 

coastal plain argue for a pre-middle Wisconsin age, perhaps 

during oxygen isotope stage 4. 

Whatever the chronology of Pleistocene continental 

ice advances, the evidence seems to indicate that ice repeatedly advanced to the Cordilleran front. This being the case, 

one can try to predict the potential impact of these successive continental ice advances on the interior basins of the 

Yukon, which were separated from Laurentide ice only by 

the relatively narrow barrier of the Richardson Mountains. 

It is then interesting to examine the documented record and 

see to what extent the predicted impacts have been recognized. 

The most obvious impact is certainly that of substantial 

climate and vegetation change due to the presence of the 

nearby ice. Other impacts, which I would like to discuss 

here, are the potential hydrological changes that would 

result from ice abutting the Cordilleran front. Several 

scenarios, which could each occur during any ice advance, 

can be proposed: (1) Drainage of any river flowing eastward across the Richardson Mountains from the interior 

basins of the Yukon toward the Mackenzie River basin 

would be impeded, and waters would be retained west of 

the ice front in lakes which would grow in size until the 

impounded waters could find an outlet to the north along 

the ice front or to the west in the unglaciated area toward 

Alaska. (2) Drainage of rivers on the east flank of the 

Richardson Mountains or those flowing into the Mackenzie 

River basin from the Ogilvie, Selwyn, or Mackenzie 

Mountains, via the Peel River, would be impounded into 

lakes and eventually diverted into basins in the Yukon if no 

outlet was present to the north within the Mackenzie River 

basin along the ice front. (3) Because of tilting resulting 

from the weight of continental glaciers, one could also 

envisage that headwaters of streams on the west side of the 

Richardson Mountains could be diverted into the Mackenzie River basin. There the waters could find their way 

north along an outlet at the margin of the ice front or be 

returned eventually to basins in the Yukon when pro glacial 

lakes overflowed to the west. (4) In any of the three scenarios mentioned above, advances or retreats of the ice 

margin could initiate or interupt drainage of waters into 

basins in the Yukon thus causing sporadic disruption of the 

hydrological regime in the interior basins. 

Although several cycles of major hydrologic changes 

could theoretically have occurred, based on the assumption 

18 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Q 

~. 

; 

[ 

;:; 

It 

f 

!l 

:r 

z 

!; 

f 

if 

:I 

~ 

~ 

... 

ID 

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I 

I 

I 

I 

I 

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I 

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I 

I 

I 

I 

I 

I 

I 

I 

/ - ·· - " -. Major retreat position \ '-

1 r=:::::J ' 1 r::::._____j Extent of late Wi sconsin-age ice 

j brrffifE!!i Extent of early Wiscons n-ag e 

/ ~Extent of Illinoian-age ice I 

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I k- ~ Extent of pre-Ill inoi an-age ice ~\ ~/t..>o ( rTT7TTTTTTTTTTT ~ \ '--riiiiii/111/IIIA , , . , > 9t- ( 

EXPLANATION 

1 .. 

Figure 1. Proposed limits and tentative ages of Quaternary continental ice in northwestern Canada. Limits queried where uncertain. 
that ice extended to the mountain front on several occasions 

during the Pleistocene, such changes are only well documented for the period spanning latest middle Wisconsin to 

late Wisconsin time. In the early Pleistocene a (single or 

multiple) lacustrine episode is well documented (the lower 

lacustrine unit in the Old Crow and Bluefish basins), but it 

is thought to be related to tectonic activity such as faulting 

or basin subsidence rather than glaciation (Schweger, this 

volume). No record of middle Pleistocene lacustrine events 

has thus far been documented. In latest middle Wisconsin 

to late Wisconsin time, ice advanced toward McDougall 

Pass (between the present headwaters of the Bell and Rat 

Rivers), caused the damming of the previously east-flowing 

Porcupine/Bell/Rat Rivers system, created a proglaciallake 

that occupied the upper Rat River and Bell, Bluefish and 

Old Crow Basins, and caused water to be diverted west into 

Alaska via the Ramparts (Catto, 1986; scenario 1 above). 

At the same time waters dammed in the Peel River basin 

were diverted north into the Yukon basin, via the Eagle 

River, cutting into Ford Lake Shale in the process and 

dispersing palynomorphs of Mississipian age into the basin 

area (scenario 2; see also Hughes, this volume; and 

Schweger, this volume). The two late Pleistocene events 

just mentioned above were likely contemporaneous, and 

they are the only ones which document a close link between known continental ice advances in the Mackenzie 

River basin and known major hydrological changes in the 

interior basins in the Yukon. 

The absence of hydrologic evidence in the interior 

basins in the Yukon for continental glacial events before 

middle Wisconsin time is somewhat surprising. Why are 

older events not recorded? Lacustrine sediments that 

formed prior to latest middle Wisconsin time occur in the 

Peel River basin (the Deception lacustrine sediments of 

Hughes and others, 1981), but no evidence of discharge 

into the Yukon basins has yet been recognized. Perhaps 

discharge during this event and all other probable early or 

middle Pleistocene advances was always east of the drainage divide along the mountain front? Are there still possibilities of finding, in the sedimentary record in the Yukon 

basins, clear evidence of hydrological changes related to 

the pre-late Wisconsin presence of continental ice? Attempts at answering these questions as well as at investigating the possible role of tilting due to ice loading east of the 

Richardson Mountains also should be made. 

Because of the increasingly detailed chronostratigraphic framework evolving for the interior basins, any direct 

link that can be made with glacial events east of the 

Richardson Mountains is critical to the establishment of the 

chronology of continental ice advances in North America. 

The interior basins of the northern Yukon, with their thick 

suite of nonglacial sediments, including marker beds such 

as widespread tephra layers, offer a unique opportunity for 

indirectly dating continental glacial events. The chronology derived from the basins for the latter part of late Pleistocene time has significant regional implications. For 

continental ice to be present in latest middle Wisconsin 

time at the Cordilleran front, which is far from the Keewatin dispersal center west of Hudson Bay, it must have 

developed considerably before that time over much of 

North America. Vincent and Prest (1987) have estimated, 

in their growth model of the Laurentide ice sheet, that at 

least 20,000 years would be needed to achieve this position 

from a Keewatin ice-dispersal center. If the chronology in 

the basins and the estimate for the growth period are correct, and if the dispersal center was located in Keewatin 

and not farther west in the District of Mackenzie, then 

much more ice existed over North America during middle 

Wisconsin time than is generally accepted. Dredge and 

Thorleifson (1987), partly on the basis of calculated global 

ice volumes, have argued for substantial coverage by the 

Laurentide ice sheet, particularly in northwestern North 

America, during middle Wisconsin time. These various 

considerations require a complete reevaluation of our concept of the chronology and understanding of Wisconsin 

glaciations. The record in the Yukon interior basins should 

provide much crucial information for this reevaluation. 

REFERENCES CITED 

Catto, N.R., 1986, Quaternary sedimentology and stratigraphy, 

Peel Plateau and Richardson Mountains, Yukon and NWT: 

Edmonton, University of Alberta, Ph.D. thesis, 728 p. 

Dredge, L.A., and Thorleifson, H., 1987, The Middle Wisconsinan history of the Laurentide Ice Sheet: Geographie Physique 

et Quaternaire, v. 41, p. 215-235. 

Hughes, O.L., 1987, Late Wisconsinan Laurentide glacial limits 

of northwestern Canada: The Tutsieta Lake and Kelly Lake 

phases: Geological Survey of Canada Paper 85-25, 19 p. 

Hughes, O.L., Harington, C.R., Janssens, J.A., Matthews, J.V., Jr., 

Morlan, R.E., Rutter, N.W., and Schweger, C.E., 1981, 

Upper Pleistocene stratigraphy, paleoecology, and archaeology of the northern Yukon Interior, eastern Beringia, 1. 

Bonnet Plume Basin: Arctic, v. 34, p. 329-365. 

Rampton, V.N., 1982, Quaternary geology of the Yukon coastal 

plain: Geological Survey of Canada Bulletin 317, 49 p. 

--1988, Quaternary geology of the Tuktoyaktuk Coastlands, 

Northwest Territories: Geological Survey of Canada Memoir 

423, 98 p. 

Rutter, N.W., Boydell, A.N., Savigny, K.W., and Van Everdingen, R.O., 1973, Terrain evaluation with respect to pipeline 

construction, Mackenzie Transportation Corridor, southern 

part, Lat. 60°-64°: Environmental-Social Committee Northem Pipelines, Report Number 73-36, 145 p. 

Vincent, J-S., 1983, La geologie du Quaternaire et la geomorphologie de l'ile Banks, Arctique canadien: Commission 

geologique du Canada Memoire 405, 118 p. 

--1986, Framework of Quaternary events of the northern 

Interior Plains of Canada, in Heginbottom, J.A., and Vincent, 

J-S., eds., Correlation of Quaternary deposits and events 

around the margin of the Beaufort Sea: Contributions from 

a joint Canadian-American Workshop, Apri11984: Geological Survey of Canada Open File Report 1237, p. 6-9. 

--1989, Quaternary geology of the northern Canadian interior plains, in Fulton, R.J., ed., Quaternary geology of Can20 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
ada and Greenland: Geological Survey of Canada, Geology 

of Canada Number 1. [Also Geological Society of America, 

The Geology of North America, v. K-1] 

Vincent, J-S., and Prest, V.K., 1987, The Early Wisconsinan 

history of the Laurentide Ice Sheet: Geographie Physique et 

Quaternaire, v. 41, no. 2, p. 199-213. 

Geological Survey of Canada Contribution 20887 

Carter, l. David, Hamilton, Thomas D., and Galloway, John P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Continental Ice Advances in Northwestern Canada 21 
Was the Late Pleistocene Northwest 

Laurentide Ice Sheet Wet-Based? 

By James Beget 

The Laurentide ice sheet was the largest glacier complex generated in the northern hemisphere. Few data are 

available on the thickness of much of the Laurentide ice 

sheet, principally because it originated and dispersed over 

areas of low relief. However, on both its northwestern and 

southwestern margins, Laurentide ice limits and glacier 

thicknesses for both the latest Pleistocene and penultimate 

glaciations can be reconstructed over reaches of hundreds 

of kilometers where the ice sheet terminated against the 

western Cordillera (Mathews, 1974; Beget, 1987). Field 

evidence in this region suggests that the Laurentide ice 

sheet was only 10 to 25 percent as thick as typical ice sheet 

profiles from Antarctica or Greenland. Typical basal shear 

stresses developed by the thin ice sheet margins were 1 to 

30 kPa, much less than the 100 kPa thought typical of ice 

sheets and generally used in theoretical ice sheet reconstructions (Beget, 1987). 

Boulton and Jones (1979) and Fisher and others (1985) 

suggested that in areas where the Laurentide ice sheet 

rested on weak, unconsolidated sediments the glacier's 

thickness would have been strongly influenced by the 

mechanical strength of the subglacial sediment. Although 

it is commonly assumed that basal tills are hard, dewatered, 

and overconsolidated at the time of deposition, sheared and 

water-saturated tills have much lower shear strength than 

ice. In situ measurements of till rheology at Breidamerkurjokull, Iceland, by Boulton and Jones (1979) showed 

that the strength of sheared till was only 20 to 26 kPa. The 

average cohesion (shear strength at zero normal stress) 

experimentally determined for poorly sorted clay-sand-silt 

mixtures similar to till range from only 6 to 28 kPa (Huang, 

1983; Selby, 1982). The average shear strength of 10 

representative tills when water saturated was only 10±10 

kPa (Milligan, 1976). The yield strength of sediments is 

strongly influenced by the grain size distribution and the 

amount and types of clay present in the sediment (Johnson, 

1970; Hampton, 1975; Rodine and Johnson, 1976), but the 

presence of water also plays a critical role in reducing shear 

strength of sediment. 

I have suggested that the low shear stress characteristic 

of the northwest Laurentide ice sheet in the Mackenzie 

River basin indicates that the glacier in this area was wetbased, and that subglacial tills were water-saturated and at 

low or zero effective normal stress due to high pore-water 

pressures (Beget, 1987). This inference is supported by 

independent, geomorphic evidence for a "warm-melting" 

subglacial thermal regime beneath the northwest Laurentide 

ice sheet (Sugden, 1977, 1978). 

The low profile of the northwest Laurentide ice sheet 

probably in part explains why the ice sheet was confined to 

the broad valley of the MacKenzie River, rather than overtopping the Richardson Mountains and entering the interior 

basins to the west. The history of lake formation in the Old 

Crow Basin may also be related to the dynamics of the 

Laurentide ice sheet. The field evidence seems to require 

a wet-based glacier, in spite of the extremely cold temperatures which characterized this area during Pleistocene glaciations. Here I examine possible mechanisms to generate 

water at or introduce water to the base of the northwest 

Laurentide ice sheet, and make frrst-order estimates of the 

amounts of water available. 

Possible sources of water beneath the late Pleistocene 

northwest Laurentide ice sheet 

Colder than modem air temperatures during the late 

Pleistocene probably had little significant effect on the 

amount of thermal energy introduced to the glacier by 

geothermal heating or mechanical heating during sliding or 

sediment deformation beneath the Laurentide ice. It is 

possible to estimate the magnitude of geothermal meltwater 

production (M) from the equation 

M = Y /pL g g 1 

(1) 

where Y, is the geothermal heat flux, pi is ice density, and 

L is the latent heat of fusion of ice. M in nonvolcanic g 

areas with average heat flow is typically on the order of 

0.005 to 0.01 m/yr. Similarly, if the value of Y •• or heat 

production due to sliding and (or) creep in basal sediment, 

were known, it would be possible to estimate meltwater 

production due to sliding (M) from the equation 

(2) 

The flow velocities of the northwest Laurentide ice 

sheet are poorly constrained, restricting the application of 

equation 2. The range of meltwater production due to 

internal energy dissipation (M.) in modem glaciers is 0.01 

to 0.4 m/yr (Drewry, 1986), and this serves as a good first 

approximation for the Pleistocene northwest Laurentide ice 

sheet. 

22 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Additional possible sources of water include rain during the ablation season. While it is generally agreed that 

the Alaskan and Canadian Arctic during Pleistocene glacial 

episodes was somewhat more arid than present, it is still 

likely that some rain fell directly on the marginal parts of 

the Laurentide ice sheet during summers. Current summer 

precipitation in northwest Canada is on the order of 10 em/ 

yr. Perhaps as much as several centimeters of rain may 

have fallen on the glacier each summer, some portion of 

which may have traveled to the base of the glacier via 

moulins or crevasses. Similarly, some input of water to the 

glacier system may have occurred from groundwater, or 

from runoff from surrounding nonglaciated areas to icemarginal streams. 

I have previously suggested that during the period of 

late Pleistocene deglaciation, if summer temperatures and 

atmospheric conditions were at all similar to those of today, 

as much as several meters of meltwater may have been 

produced annually during the ablation season from the 

surface of the northwest Laurentide ice sheet (Beget, 19g7). 

It is more difficult to approximate earlier Pleistocene conditions when the glacier was growing or in equilibrium, but 

ablation rates were almost certainly lower. If, as a first 

approximation, late Pleistocene ablation rates at latitude 

69° N. are assumed to have been similar to those of the 

northernmost glaciers known today at goo -82° N ., then 

ablation rates of 1.0 to 0.5 m/yr might be expected (Budd 

and Allison, 1975). Such ablation rates would be several 

times to an order of magnitude greater than the possible 

water production estimated above from all other sources. 

It is possible that surface meltwater reached the base of 

the Laurentide ice sheet via moulins, as has been suggested 

for the White Glacier on Axel Heiberg Island at goo N. 

(lken, 1972; Muller and Iken, 1973). The White Glacier is 

wet-based despite mean annual air temperatures well below 

freezing. Significant velocity increases were observed at 

this high-latitude glacier following periods of increased 

surface ablation, suggesting that surface meltwater was 

efficiently transmitted through the 200- to-300-m-thick 

glacier and distributed across the glacier base. 

Although most meltwater on the surface of the northwest Laurentide ice sheet probably refroze or ran off in 

surface drainage, the contribution of even a small percentage of the water available from surface melt to the glacier 

base would probably exceed the amount of water available 

from all other sources. The high heat capacity and latent 

heat of fusion of water would also introduce thermal energy 

to the glacier base. 

If water was present at the base of the northwest 

Laurentide ice sheet due to geothermal heating, frictional 

heating, surface meltwater influx, or some combination of 

these factors, then the rate of introduction of water to the 

glacier base, calculated by summing the individual estimates above, might have been as much as 1.5 m/yr. 

Groundwater charging and influx from marginal drainages 

might contribute still more. While much of any water at 

the glacier base undoubtedly exited the system as 

streamflow, this analysis suggests that sufficient sources of 

water existed during the Pleistocene for the northwest 

Laurentide ice sheet to have been wet-based. 

1Summary 

I 

Recent mapping indicates profiles of Pleistocene glacier lobes on the northwest perimeter of the Laurentide ice 

sheet were unusually thin. If the low profile of the northwest Laurentide ice sheet is due to subglacial deformation 

of low strength sediments in the MacKenzie River Delta 

area, then tills and subglacial sediments contained water 

and the glacier was wet-based. Possible sources for water 

at the glacier base might include geothermal or frictional 

melting of the glacier base, groundwater recharge, influx of 

ice-marginal drainage, or introduction of surface melt via 

moulins. The latter is potentially the most significant, and 

has been shown to be an important process at modem high 

latitude glaciers. 

I thank Professors D.M. Hopkins and M. Keskinen for 

reading early versions of the manuscript. 

REFERENCES CITED 

Beget, I.E., 1987, Low profile of the northwest Lamentide Ice 

Sheet: Journal of Arctic and Alpine Research, v. 19, p. 

81-88. 

Boulton, G.S., and Jones, A.S., 1979, Stability of temperate ice 

caps and ice sheets resting on beds of deformable sediment: 

Journal of Glaciology, v. 24, p. 29-43. 

Budd, W.F., and Allison, I.F., 1975, An empirical scheme for 

estimating the dynamics of unmeasured glaciers: International Association for Scientific Hydrology Publication No. 

104, p. 246-256. 

Drewry, D., 1986, Glacial geologic processes: London, Edward 

Arnold, 276 p. ' 

Fisher, D.A., Reeh, N., and Langley, K., 1985, Objective reconstructions of the late Wisconsin Laurentide ice sheet and the 

significance of deformable beds: Geographie Physique et 

Quaternaire, v. 39, p. 229-238. 

Hampton, M.A., 1975, Competence of fme-grained debris flows: 

Journal of Sedimentary Petrology, v. 45, p. 834-844. 

Huang, Y.H., 1983, Stability analysis of earth slopes: New York, 

Van Nostrand Reinhold, 305 p. 

Iken, A., 1972, Measurements of water pressure in moulins as part 

of a movement study of the White Glacier, Axel Heiberg 

Island, Northwest Territories, Canada: Journal of Glaciology, v. 11, p. 53-58. 

Johnson, A.M., 1970, Physical processes in geology: San Francisco, Freeman, Cooper, 577 p. 

Mathews, W.H., 1974, Surface proflles of the Laurentide Ice Sheet 

in its marginal areas: Journal of Glaciology, v. 13, p. 37-43. 

Milligan, V., 1976, Geotechnical aspects of glacial tills, in Legget, 

R.F., ed., Glacial till: Ottawa, Royal Society of Canada, p. 

269-291. 

Muller, F., and Iken, A., 1973, Velocity fluctuations and water 

regime of arctic valley glaciers: International Association of 

Scientific Hydrology, v. 95, p. 165-182. 

Rodine, J.D., and Johnson, A.M., 1976, The ability of debris, 

Was the Late Pleistocene Northwest Laurentide Ice Sheet Wet-Basedl 23 
heavily freighted with coarse clastic materials, to flow on 

gentle slopes: Sedimentology, v. 23, p. 213-234. 

Selby, M.J., 1982, Hillslope materials and processes: Oxford, 

Oxford University Press, 264 p. 

Sugden, D.E., 1977, Reconstruction of the morphology, dynamics, 

and thermal characteristics of the Laurentide ice sheet at its 

maximum: Arctic and Alpine Research, v. 9, p. 21-47. 

---1978, Glacial erosion by the Laurentide ice sheet: Journal 

of Glaciology, v. 20, p. 367-391. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

24 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Quaternary Chronology, Yukon and 

Western District of Mackenzie 

By Owen L. Hughes 

Local Quaternary chronologies for the Yukon and 

western District of Mackenzie have been evolving over a 

period of more than 30 years, beginning with a proposed 

chronology for the central Yukon by Bostock (1966; loc. 1, 

fig. 1). This was followed by chronologies for the Ogilvie 

Mountains (Vernon and Hughes, 1966; loc. 2, fig. 1) the 

northeastern St Elias Mountains of the southwestern Yukon (Denton and Stuiver, 1967; loc. 3, fig. 1), and the 

Snag-Klutlan area of the western Yukon (Rampton, 1971; 

loc. 4, fig. 1). A chronology of late Quaternary fluctuations 

of the western margin of the Laurentide ice sheet (loc. 5, 

fig. 1) and consequent major drainage changes in the area 

west of the ice sheet was offered by Hughes (1972) and 

modified by Hughes and others (1981). A chronology for 

the Yukon Coastal Plain was developed by Rampton (1982; 

loc. 6, fig. 1). 

The first attempt to correlate all of these local chronologies and to relate them to certain of the local chronologies of Alaska and more easterly areas of northern Canada 

arose from a workshop meeting held in Calgary in 1984 

(Hughes, 1986, table 6-1, p. 16; Heginbottom and Vincent, 

1986, correlation chart, p. 58). Those correlations are 

mostly unchanged (fig. 2), but substantial new data of 

diverse kinds serve to support parts of the correlation that 

were then speculative. 

Central and southern Yukon 

Of the fourfold glacial sequence of the Cordilleran ice 

sheet of the central Yukon (Bostock, 1966), the oldest 

event, the Nansen glaciation, was inferred from till at 

Nansen Creek (loc. 7, fig. 1). The next younger event, the 

Klaza glaciation, was inferred from a major glacial diversion of Klaza River (loc. 8, fig. 1). The succeeding Reid 

and McConnell glaciations were based on well-defined 

terminal moraines in the valley of the Stewart River (locs. 

9 and 10, fig. 1). The Mirror Creek and McCauley glaciations of the western Yukon (Rampton, 1971) are based on 

terminal moraine systems, as are the glaciations of the 

Ogilvie Mountains (Vernon and Hughes, 1966). Only the 

sequence for the southwestern Yukon (Denton and Stuiver, 

1967) is based entirely on rock-stratigraphic units. The use 

of morphostratigraphic units in some areas, rock-stratigraphic units in another, and mixtures of the two in one other 

area greatly complicates correlations between areas. In 

addition, within any one area there will likely always be 

some residual uncertainty as to correlations between glacial 

deposits seen in section and morphologically defined glaciations, or between stratigraphically defined glaciations 

and related moraine systems. With this cautionary note, 

recent developments in the chronology for the central 

Yukon and correlations with bordering areas are discussed 

below. 

Correlation of the Reid glaciation with the Delta glaciation of the Alaska Range is now strongly supported by 

recognition that tephra occurring above outwash of both 

Reid and Delta age is the Sheep Creek tephra (Hamilton 

and Bischoff, 1984; tephra identified by J.A. Westgate, 

University of Toronto, oral commun., 1986). Bones from 

immediately below the tephra at Canyon Creek, Alaska, 

have yielded uranium-series ages of about 75 to 80 ka 

(Hamilton and Bischoff, 1984), providing a minimum age 

for the Delta and Reid glaciations. This age, if valid, 

admits the possibility that the Reid and Delta glaciations 

are of early Wisconsin age (oxygen-isotope stage 5b or 5d). 

The intensity of soil development in the Diversion Creek 

paleosol developed on Reid drift (Tarnocai, this volume) 

suggests, however, that the soil is of Sangamon age and the 

drift of Illinoian age. 

Soil developed on moraines of "intermediate" age in 

the Ogilvie Mountains is essentially the same as the Diversion Creek paleosol developed on drift of Reid age (Tarnocai and others, 1985; Smith and others, 1986). This 

supports a correlation made originally on the basis of 

comparable preservation of glacial landforms. The preIllinoian Wounded Moose paleosols (Tarnocai, this volume) similarly support broad correlation between pre-Reid 

deposits of the Cordilleran ice sheet and deposits of "older 

glaciations" in the Ogilvie Mountains. 

Former ambiguity in the correlation between the Wisconsin history of the Cordilleran ice sheet and that of the 

piedmont glaciers of southwestern Yukon has been resolved by a finite accelerator radiocarbon date from beneath till of McConnell age at the Mayo Indian Village 

section (loc. 11, fig. 1). In the absence of a finite date it 

was possible to assume that the Cordilleran ice sheet had 

advanced to near its maximum position perhaps 40 to 50 ka 

and remained there until retreat began in late Wisconsin 

time, whereas piedmont glaciers of southwestern Yukon 

attained maximum positions after 29 ka, following an interstade that began before 30 ka. The new date from beneath 

Quaternary Chronology, Yukon and Western District of Mackenzie 25 
B~AUFORT SEA 

EXPLANATION 

Limit of pre-Reid and correlative glaciations 

Limit of Reid and correlative glaciations 

Limit of McConnell and correlative glaciations 

Laurentide maximum ( = Classical Wisconsin) west of Mackenzie River 

Early(?) Wisconsin Laurentide limit, Pleistocene coastal plain 

Late Wisconsin Laurentide ice-frontal positions 

Meltwater channel 

Isolated center of local glaciation 

Icefields, glaciers, (includes ice-free nunatak areas) 

0 200 km 

26 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
till of McConnell age (29 ,640±260, TO 292) suggests 

contemporaneity of advances in the two regions. 

The Laurentide ice sheet and northern Yukon basins 

Two Laurentide glaciations, the Deception glaciation 

of probable early Wisconsin age and the late Wisconsin 

Hungry Creek glaciation, have been recognized in the 

western District of Mackenzie from deposits at the Hungry 

Creek section (Hughes and others, 1981; loc. 12, fig. 1), 

and along Snake River (Catto, 1986; loc. 13, fig. 1). Although the Deception glaciation could be as old as Illinoian 

and therefore correlative with the Reid glaciation, it may be 

only a stade of the Hungry Creek glaciation. During the 

Hungry Creek glaciation, the most extensive glaciation in 

the northwestern sector of the Laurentide ice sheet, the Peel 

River was diverted northward into the Porcupine River 

drainage basin via the Eagle River discharge channel (loc. 

14, fig. 1). The Porcupine River, which formerly drained 

eastward through the Richardson Mountains via McDougall 

Pass (loc. 15, fig. 1), was blocked by a tongue of Laurentide ice that extended into the pass. The Bell, Bluefish, and 

Old Crow Basins (locs. 16 to 18, fig. 1) were inundated 

beneath interconnected glacial lakes that found a westward 

outlet to the Yukon River via the present-day Ramparts of 

the Porcupine River (loc. 19, fig. 1). Cyclic sediments in 

the Bell Basin suggest that there may have been many 

jokulhlaup-caused lowerings of the interconnected lakes 

through McDougall Pass before westward drainage was 

permanently established. 

The linkage between the Hungry Creek glaciation, 

diversion of the Peel River, reversal of the Porcupine River, 

and deposition of glacial lake sediments in the interconnected basins has recently been elucidated in two ways. 

First, the Eagle River discharge channel by which the Peel 

River was diverted northward is deeply incised into the 

Ford Lake Shale of Visean age. Anomalously large quantities of Visean palynomorphs appear abruptly in pollen 

profiles from all three basins, apparently providing a 

marker horizon that is correlative with initiation of the 

channel (Walde, 1985; C.E. Schweger, University of Alberta, unpub. data; J. Utting, Geological Survey of Canada, 

unpub. data). Second, radiocarbon dates at hand by 1984 

from beneath Hungry Creek Till and from beneath glaciolacustrine sediments of Bluefish and Old Crow Basins were 

Figure 1. Glacial limits of Cordilleran and Laurentide ice 

sheets, Yukon and Northwest Territories. General localities 

c.ited in the text are indicated by large numerals, and specific 

s1tes and features by smaller numerals. Dotted lines around 

localities 16-18 indicate Bell, Bluefish, and Old Crow Basins 

respectively. ' 

in agreement in placing the culmination of the Hungry 

Creek glaciation and the initiation of the glaciolacustrine 

stage at about 30 ka. However, dates from beneath glaciolacustrine sediments in the Bell Basin were all "greater 

than," suggesting an anomalous history for the Bell Basin. 

Recently acquired finite dates from beneath and within 

glaciolacustrine sediments of the southeast arm of the Bell 

Basin indicate a late Wisconsin history similar to that of the 

Bluefish and Old Crow Basins. Unresolved dating anomalies remain for the southwestern arm of the Bell Basin. 

Retreat following the Hungry Creek glaciation had 

begun by 16.4 ka (GSC-2690; Ritchie, 1982, table 15; 

Hughes and others, 1981, p. 358). On the Yukon Coastal 

Plain, where the last glaciation has been termed the Buckland glaciation by Rampton, there had been considerable 

retreat by 22 tea (Rampton, 1982, p. 25). Three late Wisconsin readvances, or perhaps significant stillstands during 

general retreat, have been inferred from moraines and other 

ice marginal features: the Sabine phase (Rampton, 1982, p. 

45) and the Tutsieta Lake and Kelly Lake phases (Hughes, 

1987). The Sabine phase is younger than 22 ka but is 

otherwise undated. The Tutsieta phase culminated 13 to 14 

ka and the Kelly lake phase before 10.6 ka. 

S.R. Morison (Department of Indian and Northern 

Affairs), J.V. Matthews, Jr. (Geological Survey of Canada), 

C.E. Schweger (University of Alberta), C. Tamocai (Land 

Resources Research Institute), and C.A.S. Smith (Land 

Resources Research Institute), have contributed much valuable discussion of the Quaternary stratigraphic history. A. 

Duk-Rodkin (Geological Survey of Canada) assisted in the 

preparation of figure 1 and S.R. Morison contributed additions and changes to figure 2. 

REFERENCES CITED 

Bostock, H.S., 1966, Notes on glaciation in central Yukon Territory: Geological Survey of Canada Paper 65-36. 

Catto, N.R., 1986, Quaternary sedimentology and stratigraphy, 

Peel Plateau and Richardson Mountains, Yukon and N.W.T.: 

Edmonton, University of Alberta, Ph.D. dissertation. 

Denton, G.H., and Stuiver, M., 1967, Late Pleistocene glacial 

stratigraphy and chronology, northeastern St. Elias Mountains, Canada: Geological Society of America Bulletin, v. 

78, p. 485-510. 

Hamilton, T.D., and Bischoff, J.L., 1984, Uranium series dating of 

fossil bones from the Canyon Creek locality in central 

Alaska: _p.S. Geological Survey Circular 939, p. 26-29. 

Heginbottom, J.A., and Vincent, J-S., eds., 1986, Correlation of 

Quaternary deposits and events around the margin of the 

Beaufort Sea: Contributions from a joint Canadian-American workshop, Calgary, April 1984: Geological Survey of 

Canada Open File Report 1237, 60 p. 

Hughes, O.L., 1972, Surficial geology of northern Yukon Territory and northeastern District of Mackenzie, N.W.T.: Geological Survey of Canada Paper 64-36. 

--1986, Quaternary chronology of Yukon Territory and 

western District of Mackenzie, in Heginbottom, J.A., and 

Quaternary Chronology, Yukon and Western District of Mackenzie 27 
Vincent, J-S., eds., 1986, Correlation of Quaternary deposits 

and events around the margin of the Beaufort Sea: Contributions from a joint Canadian-American workshop, Calgary, 

April 1984: Geological Survey of Canada Open File Report 

1237, p. 13-17. 

---1987, Late Wisconsinan Laurentide glacial limits of northem Canada: The Tutsieta Lake and Kelly Lake phases: 

Geological Survey of Canada Paper 85-25. 

Hughes, O.L., Harington, C.R., Janssens, J.A., Matthews, J.V., Jr., 

Morlan, R.E., Rutter, N.W., and Schweger, C.E., 1981, 

Upper Pleistocene stratigraphy, paleoecology, and archeolGENERAL zWcn ! wLw (I) 

~0~ _, 1) CORDILLERAN CHROMO- >t-c 11.1 0 

STRATIGRAPHY 

>COt- CJ (I) ICE SHEET o!!cn Cl: 

IL&J X X X X X • 1.2 ka oC!: 

.. _ 

.. 0 ' White River Ash Bed -..Lu 1 •• •o oo •• Nonglacial Interval ;z :t 

~ 

c;; 2 McConnell glaciation 

~ 

1&1 0 .... 

'Ill: Cl) 

(J -

3-Sd 

:;~] • 29.6ka .... ~ -. xxxxx Reid-McConnell 

115• :!!e \ nonglacial Interval 

SANGA- •u- Sheep Creek tephra liON Se ~ ':. Q • >42.6ka 128 

Lu 1&1 Reid glaciation 

C!: .... 

Lu Q 

(.) ~ 

0 ::e -a·; •• .... 1,~ Klaza-Reld 

(/) ~0 

- 0:1!!1 nonglacial Interval 

Lu == A. 

-.1 730 

Q. 

Klaza glaciation 

).. "" Nansen-Kiaza -a -:: .... ~=; nonglacial Interval,..--- ct ~g_; 1.08 ~ Fort Selkirk tephra Ma 

&u ;:~: X x~xx 'Y 0.86 Ma ... ~ 0 

ct 

Nansen glaciation (!) 

~ 

!!: 

~ 

,Lu Lij 

OC!: (I) 

_Lu - -..CJ 

Q. 

ogy of the northern Yukon interior, eastern Beringia, I. 

Bonnet Plume Basin: Arctic, v. 34, p. 329-365. 

Rampton, V.N., 1971, Late Pleistocene glaciations of the Snag 

Klutlan area, Yukon Territory, Canada: Arctic, v. 24, p. 

277-300. 

--1982, Quaternary geology of the Yukon Coastal Plain: 

Geological Survey of Canada Bulletin 317, 49 p. 

Ritchie, J.C., 1982, The modem and Late-Quaternary vegetation 

of the Doll Creek area, northern Yukon, Canada: The New 

Phytologist, v. 90, p. 563--603. 

Smith, C.A.S., Tamocai, C., and Hughes, O.L., 1986, Pedological 

2) ST. ELIAS PIEDMONT GLACIER 

2a) Snag-Kiutlan area 2 b) Silver Creek area 

x x x x~ White River Ash Bed 'tl - White River Ash Bed c: x x x x x ~· 1.2 ka Neoglaclatlon x x x x x • 1.2 ka N e o g I a c I a tl o n 0 

1.9 ka ll. 

Nonglacial Interval • Slims nonglacial Interval Ill 

.13.66ka • .12.5 ka • .:: 

.. McCauley glaciation c: 

'Ill: Kluane glaciation 

- • 29.6ka 

McCauley-Mirror Creek Boutelller 

nonglacial Interval nonglacial Interval 

• 37.7 ka / Old Crow tephra XX XXX • >48 ka 

Mirror Creek glaciation Icefields glaciation 

Silver nonglacial Interval 

(Shakwak glaciation?) 

(Shakwak glaciation?) 

PLIOCENE 

Figure 2. Correlation chart for Yukon and western District of Mackenzie. Modified from Heginbottom and Vincent (1986, 

correlation chart, p. 58; and Hughes, 1986, table 6-1, p. 16). Squares, radiocarbon ages; diamond, uranium-series age; triangle, fission-track age; inverted triangle, K-Ar age. 

28 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
investigations of Pleistocene glacial drift surfaces in the 

central Yukon: Geographie Physique et Quaternaire, v. 40, 

p. 29-37. 

Tamocai, C., Smith, C.A.S., and Hughes, O.L., 1985, Soil development on Quaternary deposits of various ages in the central 

Yukon Territory: Geological Survey of Canada Paper 

85-1A, p. 229-238. 

Vernon, P., and Hughes, O.L., 1966, Surficial geology of Dawson, 

Larsen Creek and Nash Creek map areas, Yukon Territory: 

Geological Survey of Canada Bulletin 136, 25 p. 

Walde, K., 1985, Pollen analysis and taphonomy of locality 15 al3) ALASKA RANGE 4) SOUTHERN OGILVIE 

RANGES 

/White River Ash Bed X X X X X • 1.9 ka 

Nonglacial Interval Nonglacial Interval 

Donnelly glaciation Last glaciation 

Nonglacial Interval Nonglacial Interval 

,Sheep Creek tephra xxxxx + 75-80 Ma 

Delta glaciation Intermediate glaciation 

Nonglacial Interval Nonglacial Interval, 

major stream 

entrenchment 

luvial sediments, Old Crow Basin, Yukon: Edmonton, 

University of Alberta, M.Sc. thesis. 

Geological Survey of Canada Contribution 40888 

Carter, L. David, Hamilton, Thomas D., and Galloway, John P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

5) DAWSON AREA 6) LAURENTIDE 

ICE SHEET 

/ White River Ash Bed xxxxx • 1.9 ka 

Nonglacial Interval 

= • Kelly Lake Phase 

~ • Tutsleta Lake Phase • 13 ka u Q, 

= Sltldgl Lake stade :II ,; Sabine Phase E Hungry Creek glaciation .... • • =Buckland f.laciaiton? 0 0 Deception _1i aclatlon? 

c - 0 "c:J • 36.9ka 

- • Nonglacial Interval -- !:: • 0 • • >53.9ka 0 Q, Q, 

• • XX XXX 

Q "c:J \ 

.. • Dawson tephra Deception glaciation? 

-

Major stream 

entrenchment 

YOUNGER HIGH TERRACE 

GRA~E!;_S-----

Darling Creek glaciation (Older glaciation?) ~---

Cl) 

..... IU...,. - Cl) ~~ 

....:~ Q WHITE CHANNEL Q:::::l IU <.!Jii CQ 

ltl( ~~ -o IU 

IU ~....: Q: oa 

0 GRAVELS ........... 

ltl( 

(Older glaciation?) ... 

....: 

..... 

..... . . . ..~ 

I I 

I I 

(NONGLACIAL} I I 

-

Figure 2. Continued. 

Quaternary Chronology, Yukon and Western District of Mackenzie 29 
The Old Crow and Bluefish Basins, Northern Yukon: 

Development of the Quaternary History 

By Charles E. Schweger 

The Old Crow and Bluefish Basins of northern Yukon 

contain thick sequences of unconsolidated fossil-rich sediments. Fieldwork carried out during the 1960's by O.L. 

Hughes (Geological Survey of Canada) led to the recognition of a long, "Late Tertiary into Quaternary time" record 

exposed along river bluffs in these basins. The accelerated 

research activity since that time is reviewed here by highlighting key developments that have led to our present 

understanding of the Quaternary history and chronology of 

this area. Much of these data are unpublished or in preparation, and some conclusions should be more properly 

called hypotheses. 

Hughes (1969, 1972) described, for the Bluefish Basin 

locality HH228, a sequence of two glaciolacustrine units 

separated by alluvial sand and silt (fig. 1). The upper lake 

unit was dated as forming between 12.5 and 32.4 ka, assuring correlation with the late Wisconsin glaciation when 

Keewatin ice dammed both the Peel River drainage and 

McDougall Pass, which is the former course of the Porcupine River through the Richardson Mountains. It was 

assumed that a similar glacial event during or before early 

Wisconsin time resulted in deposition of the lower lake 

unit. 

The discovery in 1966 of permineralized bone artifacts 

in the Old Crow Basin resulted in field surveys during 1967 

and 1970 by T.D. Hamilton (University of Alaska), who 

mapped shorelines, reported on stratigraphy, and evaluated 

features and processes of archeological importance in a 

series of unpublished maps and reports. Radiocarbon dating placed the ages of the bone artifacts between 27 and 35 

ka, thus bringing worldwide attention to the archeological 

potential of the region (Irving and Harington, 1973). Two 

multidisciplinary research groups took to the field during 

the summer of 1975. The Yukon Refugium Project, organized by R.E. Morlan (Archaeological Survey of Canada), 

has hypothesized a human presence in the Old Crow Basin 

to 35 ka (Morlan, 1986; but also see Nelson and others, 

1986), whereas the Northern Yukon Refugium program 

proposed a human presence to at least 150 ka (Irving and 

others, 1986). From the outset both groups relied heavily 

on the pioneering paleontological research of C.R. Rarington, who had systematically searched and collected in the 

Old Crow and Bluefish Basins since 1966 (Harington, 

1978). The Yukon Refugium Project, the work of which is 

stressed here, placed emphasis on detailed stratigraphy, 

recovery of in-place faunal remains, nested subsampling for 

paleoecological reconstruction, and geochronology. 

The Old Crow tephra (Westgate and others, 1981) was 

discovered in 1968 by Hughes at locality HH228 on the 

Porcupine River in the Bluefish Basin, and was collected 

and described by J.A. Westgate in 1976 (Westgate, 1982). 

Also in 1968, paleomagnetic studies indicated reversed 

geomagnetic polarity of most of the lower lake sediment, 

unit 3, at HH228 (Pearce and others, 1982). Because of 

subsequent dating of the Old Crow tephra and the prominent unconformity between units 3 and 4, unit 3 is thought 

to have been deposited before 730 ka, which is the timeboundary between the Brunhes Normal-Polarity and Matuyama Reversed-Polarity Chrons. Reversed geomagnetic 

polarity for unit 3 has since been verified at other locations. 

Unit 3 is known to be rich in pine as well as spruce pollen 

(Lichti-Federovich, 1974), unlike the modem pollen rain 

and certainly unlike the pollen found in unit 5, the upper 

glaciolacustrine unit This has led to the hypothesis that the 

lower lake unit is not of glacial origin but probably related 

to tectonic activity along faults, a conclusion supported by 

the detailed bedrock mapping of Norris (1981). Subsequent fieldwork in the Bluefish Basin indicated that unit 3 

may in fact represent three separate lake events. 

Fieldwork during 1977 at Old Crow River locality 

CRH 15 (fig. 1) led to the recognition there of the Old 

Crow tephra, disconformity A, and a defmition of the Old 

Crow Basin composite stratigraphy (Morlan and Matthews, 

1978). Over the next four years Morlan, together with 

colleagues and graduate students, concentrated fieldwork 

along the lower Old Crow River. Excavations at a number 

of river bluffs resulted in a large collection of vertebrate 

remains with well-documented stratigraphic context. These 

provided for the development of a taphonomic approach to 

Old Crow paleontology and archeology (Morlan, 1980; 

Morlan and Matthews, 1983). Thesis work on a wide 

variety of topics was carried out by University of Alberta 

students: Janssen, fossil bryophytes (1981); McCourt, 

palynology (1982); Walde, palynology (1985); Bombin, 

phytoliths (1984); and Hedlund, paleomagnetics (1986). 

Screening of large-volume sediment samples was undertaken in order to develop a paleoecological record based on 

plant and insect remains and augmented by fossil pollen 

studies. In 1980, fieldwork was expanded to include upper 

Porcupine River localities in the Bell Basin as well as sites 

of stratigraphic importance along the Porcupine River in 

Alaska (Thorson and Dixon, 1983). 

Tephra studies have come to play a dominant role in 

the developing geochronology. In 1981 the Little Timber 

30 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
tephra was discovered at locality CRH 94, Old Crow River. 

It has been characterized by Westgate and dated as forming 

before 1.2 Ma, depending upon the annealing factor. The 

Old Crow tephra was dated by fission track as less than 120 

ka (Naesser and others, 1982). 

An Old Crow River survey in 1983 by J.V. Matthews, 

Jr. (Geological Survey of Canada) and the author resulted 

in discovery of the Surprise Creek tephra at locality CRH 

47 (fig. 1), while the same year paleobotanist, Ruth Stockey 

(University of Alberta) initiated her research on the 

HH228, unit 1, cone flora. Extant species Pinus monticola, 

Pinus contorta, and Picea glauca have been identified, and 

the extinct forms Larix minuta and Picea sp. suggest a 

Pliocene age. This age placement is supported by paleosol 

Upper glaciolacustrine 

~ 

~~-------.... ~ 'Yx···v···· 

til Blake event 

;:C 115 ka 

~ :5 UNIT 4 

~ 

? 

vegetation 

---Mississippian-age spores 

mark glacial diversion , 

Koy-Yukon-- Old Crow tephra 86-94 ka 

'""'"'".....,....,..,...,.....Tundra ~.,..,.,..,..rTTTTrl 

vegetation 

sediments 

? 

OLD CROW RIVER 

SECTIONS 

UNIT 3 ~ 

Olduvai-age mammals J.Ll 

UNIT 1 

1.7 Ma U 

Surpnse Creek tephra! ~ ;:._tl) 

Boreal forest ·E ......., ...... vegetation .... ! ~ 

UNIT 2 <;; >o 

~ ~ l Ul 

CRH 47 

PORCUPINE RIVER 

SECTION HH228 CRH 94 

EXPLANATION 

y Ice-wedge pseudomorphs --------- Unconformity 

PLIOCENE UNIT 1 Pmus r:ontorta P1nus mont1co1a Lar1x mrnu'd 

P1cea glauca P1~ea sp -v----v- Paleosurface with ice-wedge ----- Lag on unconformity 

pseudomorphs 

~ Detrital logs 

Paleosol 

liin .tim Stumps 

~--= Cryoturbation 

X,)(,)(. Tephra Bedding 

Figure 1. Summary of Quaternary and uppermost Tertiary stratigraphy and geochronology for Old Crow and Bluefish 

Basins, northern Yukon. Old Crow tephra is an informal unit of Westgate and others (1981) and Westgate (1982). 11Biake event" is the Blake Reversed-Polarity Subchron of the Brunhes Normal-Polarity Chron; "Oiduvai" is the Olduvai 

Normal-Polarity Subchron of the Matuyama Reversed-Polarity Chron. 

The Old Crow and Bluefish Basins, Northern Yukon 31 
studies (Tarnocai, this volume) and pollen evidence 

(Schweger) from Bluefish River and Burnt Hill Bluffs (see 

Tarnocai, this volume). 

Walde (1985) demonstrated the paleohydrological significance of reworked palynomorphs from the Upper Mississippian Ford Lake Shale (Norris, 1984). These spores 

were dispersed throughout the northern Yukon Basins 

when ice blocked the Peel River and diverted water through 

the upper Eagle River valley, eroding overflow channels in 

the shale. Mississippian-age spores are found immediately 

above disconformity A, locality CRH 15, which has been 

recently dated at about 35 ka (R.E. Morlan, Archaeological 

Survey of Canada, oral commun., 1987). This new date for 

disconformity A plus other recent accelerator mass spectrometer radiocarbon dates in the Bell Basin have considerable regional significance, because they imply that Keewatin ice had approached its maximum western extent 

earlier than previously thought (Hughes and others, 1981). 

Glaciolacustrine unit 5 was deposited in a deep-water lake 

after 25 ka (14C age on tusk, Cadzow Bluff), through 21 ka 

(14C age on fine organics, Bluefish River section), and until 

just before 12.5 ka (14C age on bison bone, locality CRH 

11) by which time the lake had drained through the Ramparts of the Porcupine River to the west. The interval 

between the first blockage of the eastward drainage of 

Porcupine River and development of a deep glacial lake 

may have been characterized by lowerings of lake ·level in 

the basins via jokulhlaups through McDougall Pass. 

Stratigraphy, paleontology, and geochronology of locality HH228 has received considerable attention during 

and since 1983. Westgate and others (1985) documented 

the 115-ka reversal event marking the Blake ReversedPolarity Subchron (of the Brunhes Normal-Polarity Chron) 

below the Old Crow tephra, which has recently been dated 

by thermoluminescence as forming 86±8 ka (Wintle and 

Westgate, 1986). The stratigraphy and paleontology of 

upper unit 4 provides evidence of the Kay-Yukon thermal 

event, a period 50-60 ka in which climate in eastern Beringia was warmer than the present climate (Schweger and 

Matthews, 1985). 

Fieldwork during 1985 was centered on Old Crow 

River localities CRH 94 and CRH 47 (fig. 1), which are 

Little Timber and Surprise Creek tephra localities, respectively. Nearly five tons of sediment from near the Surprise 

Creek tephra at locality CRH 4 7 was screened for small 

mammals. C.A. Repenning (U.S. Geological Survey, oral 

commun., 1987) places this fauna near the base of the 

Pleistocene, within the Olduvai Normal-Polarity Subchron 

(of the Matuyama Reversed-Polarity Chron), which is dated 

at 1.7 Ma. This is corroborated by the fact that Surprise 

Creek tephra fell at a time of normal geomagnetic polarity 

when boreal forest was present in the Old Crow Basin. The 

stratigraphically lower Little Timber tephra was deposited 

on tundra vegetation at a time of reversed polarity. Considerable work remains to be done on these two important 

localities. 

At the present time, research continues on several 

fronts: small mammals, pollen, seeds, cones, insects, radiocarbon chronology, stratigraphy, paleosols, and tephrochronology. Over a decade after the Yukon Refugium 

Project was initiated, it has moved into a stage of synthesis, 

where large amounts of diverse information are being integrated into a comprehensive history of the region. The 

history of the Old Crow and Bluefish Basins is of regional 

significance because it links events in the District of 

Mackenzie to the east with those in interior Alaska to the 

west. These basins are now known to have the most 

complete Pliocene and early Pleistocene record in northwestern North America. The middle Pleistocene is poorly 

known, although R.E. Morlan's small-mammal record from 

Old Crow River locality CRH 11 has been placed between 

500 and 800 ka by C.A. Repenning (U.S. Geological Survey, oral commun., 1987) and sediments of similar age may 

be exposed at other sections (such as HH68-10). The 

history of the late Pleistocene is well established and dated 

and points up the fact that at no time during the Pleistocene 

did Keewatin ice extend as far westward as during the 

interval 35-12.5 ka. The research accomplished to date 

clearly points up the importance of joint multidisciplinary 

research with a high degree of information sharing and a 

long-term commitment to the region. 

REFERENCES CITED 

Bombin, M., 1984, On phytoliths, late Quaternary ecology of 

Beringia, and information evolutionary theory: Edmonton, 

University of Alberta, Ph.D. dissertation. 

Harington, C.R., 1978, Quaternary vertebrate faW'las of Canada 

and Alaska and their suggested chronological sequence: 

Ottawa, National Museums of Canada Syllogeus 15, 105 p. 

Hedlund, M.A.H., 1986, A Pleistocene high-latitude geomagnetic 

study: Edmonton, University of Alberta, M.A. thesis. 

Hughes, O.L., 1969, Pleistocene stratigraphy, Porcupine and Old 

Crow Rivers, Yukon Territory: Geological Survey of Canada Paper 69-1, p. 209-211. 

--1972, Surficial geology of northern Yukon Territory and 

northwestern District of Mackenzie, Northwest Territories: 

Geological Survey of Canada Paper 69-36. 

Hughes, O.L., Harrington, C.R., Janssens, J.A., Matthews, J.V., 

Jr., Morlan, R.E., Rutter, N.W., and Schweger, C.E., 1981, 

Upper Pleistocene stratigraphy, paleoecology, and archaeology of the northern Yukon Interior, eastern Beringia, 1, 

Bonnet Plume Basin: Arctic, v. 34, p. 329-365. 

Irving, W.N., and Harington, C.R., 1973, Upper Pleistocene radiocarbon-dated artifacts from the northern Yukon: Science, v. 

179, p. 335-340. 

Irving, W.N., Jopling, A.V., and Beebe, B.F., 1986, Indicators of 

Pre-Sangamon humans near Old Crow, Yukon, Canada, in 

Bryan, A.L., ed., New evidence for the peopling of the 

Americas: Orono, University of Maine, p. 49-63. 

Janssen, J.A.P., 1981, Subfossil bryophytes in eastern Beringia: 

Their paleoenvironmental and phytogeographic significance: 

Edmonton, University of Alberta, Ph.D. dissertation. 

Lichti-Federovich, S., 1974, Palynology of two sections of Late 

Quaternary sediments from the Porcupine River, Yukon 

Territory: Geological Survey of Canada Paper 74-23, 6 p. 

McCourt, G.H., 1982, Quaternary palynology of the Bluefish 

32 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Basin, northern Yukon Territory: Edmonton. University of 

Alberta. M.S. thesis. 

Morlan, R.E., 1980, Taphonomy and archaeology in the upper 

Pleistocene of the northern Yukon Territory: A glimpse of 

the peopling of the New World: National Museum of Man, 

Mercury Series, Archaeological Survey of Canada. Paper 94, 

380 p. 

---1986, Pleistocene archaeology in Old Crow Basin: A 

critical reappraisal, in Bryan, A.L., ed., New evidence for the 

peopling of the Americas: Orono, University of Maine, p. 

27-48. 

Morlan, R.E., and Matthews, J.V., 1978, New dates for early man: 

Geos, winter 1978, p. 2-5. 

---1983, Taphonomy and paleoecology of fossil insect assemblages from Old Crow River (CRH-15) northern Yukon 

Territory, Canada: Geographie Physique et Quaternaire, v. 

37, p. 147-157. 

Naeser, N.D., Westgate, J.A., Hughes, O.L., and Pewe, T.L, 1982, 

Fission-track ages of late Cenozoic distal tephra beds in the 

Yukon Territory and Alaska: Canadian Journal of Earth 

Sciences, v. 19, p. 2167-2178. 

Nelson, D.E., Morlan, R.E., Vogel, J.S., Southon. J.R., Harington, 

C.R., 1986, New dates on northern Yukon artifacts: Holocene not upper Pleistocene: Science, ·v. 232, p. 749-751. 

Norris, D.K., 1981, Geology; Old Crow, Yukon Territory: Geological Survey of Canada Map 1518A. 

---1984, Geology of the northern Yukon and northwestern 

District of Mackenzie: Geological Survey of Canada. Map 

1581A, scale 1:500,000. 

Pearce, G.W., Westgate, J.A., and Robertson. S., 1982, Magnetic 

reversal history of Pleistocene sediments at Old Crow, northwestern Yukon Territory: Canadian Journal of Earth Sciences, v. 19, p. 919-929. 

Schweger, C.E., and Matthews,. J.V., 1985, Early and middle 

Wisconsian environments of eastern Beringia: Stratigraphic 

and paleoecological implications of the Old Crow tephra: 

Geographie Physique et Quaternaire, v. 39, p. 275-290. 

Thorson, R.M., and Dixon. E.J., Jr., 1983, Alluvial history of the 

Porcupine River, Alaska: Role of glacial-lake overflow from 

northwest Canada: Geological Society of America Bulletin, 

v. 94, p. 576-589. 

Waide, K., 1985, Pollen analysis and taphonomy of locality 15 

alluvial sediments, Old Crow Basin, Yukon: Edmonton, 

University of Alberta, M.A. thesis. 

Westgate, J.A., 1982, Discovery of a large-magnitude, late Pleistocene volcanic eruption in Alaska: Science, v. 218, p. 

789-790. 

Westgate, J.A., Matthews, J.V., Jr., and Hamilton, T.D., 1981, Old 

Crow tephra: A new late Pleistocene stratigraphic marker 

across Alaska and the Yukon Territory: Geological Society 

of America Abstracts with Programs, v. 13, p. 579. 

Westgate, J.A., Walter, R.C., Pearce, G.W., and Gorton, M.P., 

1985, Distribution, stratigraphy, petrochemistry, and paleomagnetism of the late Pleistocene Old Crow tephra in Alaska 

and the Yukon: Canadian Journal of Earth Sciences, v. 22, 

p. 893-906. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of Old Crow tephra in Alaska: Geology, v. 14, p. 594-597. 

Carter, l. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

The Old Crow and Bluefish Basins, Northern Yukon 33 
Climatic Change in Eastern Beringia During Oxygen 

Isotope Stages 2 and 3: Proposed Thermal Events 

By John V. Matthews, Jr., Charles E. Schweger, and Owen L. Hughes 

Pollen and macrofossil data associated with recently 

acquired Accelerator Mass Spectrometer (AMS) and standard 14C dates in addition to recent thermoluminescence 

(TL) dates on the Old Crow and Sheep Creek tephras from 

Alaska and the Yukon allow us to discern new detail on 

climate during oxygen-isotope stages 2 and 3 in eastern 

Beringia (Alaska and the Yukon). At least three thermal 

"events" appear to have occurred. One of these, the 60 ka 

Koy-Yukon thermal event, has been discussed previously 

(Schweger and Matthews, 1985). The other two, the 25- to 

27-ka Sixtymile and the 18- to 22-ka Hanging Lake thermal 

events, are proposed here for the first time. The designation of these two new events conforms to the North American Stratigraphic Code (North American Commission on 

Stratigraphic Nomenclature, 1983). Like the earlier named 

Koy-Yukon thermal event (Schweger and Matthews, 1985), 

they have only regional importance and no formal chronostratigraphic significance. 

The Koy-Yukon thermal event 

Schweger and Matthews (1985) proposed the name 

Koy-Yukon thermal event for an interval of warmer-thanpresent summer climate which occurred after the deposition 

of both Old Crow tephra and Sheep Creek tephra, but prior 

to 59 ka. They estimated its age as about 60 ka, the start 

of isotope stage 3, when the marine record registers significant interstadial warming and when insolation curves indicate approximately 20 percent greater summer insolation 

than at present in the northern part of the northern hemisphere. The 59 ka minimum age is based on a minimum 

limiting age on wood from the Eva Formation (Fairbanks 

area, Pewe, 1975), deposition of which was penecontemporaneous with the interval of deep thawing in the Fairbanks 

region that Schweger and Matthews (1985) assigned to the 

Koy-Yukon thermal event A TL date on sediments associated with the Old Crow tephra implies that it could be as 

young as 86±8 ka (Wintle and Westgate, 1986). The age 

of the Sheep Creek tephra is still poorly known, but 

Hamilton and Bischoff (1984) estimated it to be slightly 

younger than 80 ka, whereas a recent TL date suggests it is 

75±7 ka (T.L. Pewe, Arizona State Univ., oral commun., 

1987). If these dates are correct, the Sheep Creek tephra 

was deposited during isotope stage 4, a conclusion supported by the pollen data from the Ash Bend site in the 

northern Yukon (C.E. Schweger, unpub. data). The Sheep 

Creek tephra occurs in the Gold Hill Loess at Fairbanks, 

which means that it predates the Eva Formation and the 

interval of thawing associated with the Koy-Yukon thermal 

event 

As indicated above, several lines of evidence show that 

the Koy-Yukon thermal event postdates the last interglaciation (stage 5e) and stage 4, yet its fauna and flora clearly 

suggest that summer climate was warmer than at present. 

This is best shown by fossils from unit 4c at the 

Twelvemile Bluff exposure in the northern Yukon. The 

fluvial and lacustrine deposits within that unit contain plant 

macroremains of species like Carex sychnocephala and 

Chenopodium gigantospermum, neither of which extend as 

far north today. A similar pattern is exhibited by some of 

the insect taxa (such as Bradycellus lecontei and Bembidion 

quadrimaculatum), and the presence of traces of Corylus 

and Typha in the pollen spectra. Furthermore, it is now 

clear that the extremely high frequencies of spruce shown 

in Lichti-Federovich's (1973) pollen diagram for the 

Twelvemile Bluff section occur in unit 4c. Unit 4c cuts out 

another unit containing a series of large ice-wedge pseudomorphs which probably reflect regional thawing. Higher in 

the sequence, above the beds indicative of the warming of 

the Koy-Yukon thermal event, is another series of icewedge pseudomorphs, which formed before 37 ka and may 

also mark regional thawing. 

Sixtymile thermal event 

Pollen and macrofossils (fig. 1) from an alluvial unit 

below late Wisconsin (McConnell glaciation) till at the 

Mayo Indian Village section near the town of Mayo in the 

central Yukon suggest a period of dry, arctic climate during 

which trees were absent or existed only as isolated groves 

in the lowlands. Today the region is well forested. Fossil 

seeds of Corispermum hyssopifolium (bugseed), a plant 

very likely to have been growing on the floodplain at the 

time of deposition, are dated by the AMS radiocarbon 

method at 29.6±0.3 ka (T0-292). Some of the more 

important macrofossils from the dated level are listed in 

figure 1. The insect assemblage implies at least a cold, dry 

local floodplain climate and probably an arctic regional 

climate. Like some others from Beringia, the insect assemblage includes at least one beetle, Harpalus amputatus, 

which is normally an occupant of grassland areas. Another 

species, the weevil Connatichela artemisiae Anderson (fig. 

34 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
1) feeds on sage (Artemisia), a plant which is well represented in the pollen diagram and probably grew on the 

flood plain at 29.6 ka. 

Spruce percentages rise slightly above the dated level, 

suggesting slight climatic amelioration. The best evidence 

for such a trend comes from a site in the Sixtymile District 

near Dawson City. A spruce stump in growth position 

from that region has been dated at 26.08±0.3 ka (B-13870) 

(C.R. Harington, Canada National Museum of Natural 

Sciences, oral commun., 1986). It shows that climate had 

warmed enough for growth of spruce in the valley bottoms 

of the central Yukon, unlike the situation at 29.6 ka. 

We believe that these data may signify a period of 

slightly warmer climate--the Sixtymile thermal eventwhich occurred between about 25 and 27 ka. As indicated 

in figure 2 this conclusion appears to be supported by (1) 

an AMS age on mosses from the northern Yukon Bell 

Basin that implies that meltwater levels in the Bell Basin 

were fluctuating between 25 and 26 ka, probably due to 

changes of the Laurentide ice margin on the east side of the 

Richardson Mountains; (2) pollen spectra indicative of 

interstadial conditions at Harding Lake in central Alaska 

(Nakao and Ager, 1985); and (3) ages in the 25- to 27-ka 

range on soils and wood in the Alaska Range (Hamilton 

c~ 

o E 

-ro(() 

u ~ co 0 

{J)~ 

- 0... 

(ii~ 

c 

c c 

0 0 

o·.;::: 

u u ~ (].) 

~(/) 

:-:: 0 S e 

20 10 10 20 

and Thorson, 1983). The Sixtymile thermal event was 

followed at about 24 ka by climatic deterioration and renewed glaciation in both Alaska and the Yukon (Hamilton 

and Thorson, 1983; Hamilton, 1986; Klassen, 1986; fig. 2). 

Hanging Lake thermal event 

Several sites in eastern Beringia yield circumstantial 

evidence for an interval of warmer climate between 18 and 

22 ka. Cwynar (1982) first recognized this event in his 

discussion of the pollen sequence at Hanging Lake in the 

northern Yukon (fig. 3), hence the designation "Hanging 

Lake thermal event." Climatic warming evidently occurred 

at about the same time in western Alaska, judging from the 

pollen sequence at Kaiyak Lake in northwestern Alaska 

(Anderson, 1985; fig. 3). Other probable indicators of 

contemporaneous warming include (1) dates and macrofossils from the Rat Pass area near the Yukon-Northwest 

Territories border that suggest spruce may have been growing near there at about 21.3 ka (Matthews and Hughes, 

unpub. data); (2) an abrupt peak of Ericaceae pollen and 

slightly higher percentages of Picea, Alnus, and Betula at a 

level now dated at 20.8±0.2 ka (GSC-3946) in the pollen 

record from the northern Bluefish Basin (HH75-24) section 

e 

20 40 10 

!P--lants 

Carex spp. 

Corispermum 

Oxyria digyna 

Caryophyllaceae 

Potamogeton spp 

n s e c t s 

Amara alpina 

Amara glacialis 

Harpalus amputatus 

Cryobius 

Bembidion hasti 

Morychus 

Lepidophorus 

lineaticollis 

Connatichela 

, artemisiae L __ _ 

POLLEN, IN PERCENT 

• = Less than 2 percent 

Figure 1. Summary of pollen from base of the Mayo Indian Village section, including insect and plant macrofossils identified from the same level as the 29.6-ka Accelerator Mass Spectrometer 14C date on Corispermum hyssopifolium seeds. 

Identifications: pollen, C.E. Schweger; macrofossils, j.V. Matthews, Jr. 

Climatic Change in Eastern Beringia During Oxygen Isotope Stages 2 and 3 35 
(summarized in fig. 4, which is based on data in McCourt, 

1982); (3) presence of paleosols and indicators of cessation 

of alluviation and stabilized periglacial features in the Wind 

River and Koyukuk regions of Alaska (fig. 2) (Hamilton, 

1986). However, we note that there is also contradictory 

evidence of warming; for example, T.A. Ager (in Weber 

and Ager, 1984) found only traces of spruce pollen in a 

sample from interior Alaska that is associated with the 

Mount Harper ash, which was deposited about 21 ka. 

Discussion 

We have attempted to point out several facts that seem 

to indicate minor climatic oscillations during oxygen-isotope stages 2 and 3. We acknowledge that the evidence is 

~nic:<)oo 

.c:!: 0 13 ka 

- .::t:. ::::sC:::::s 

~~> <)oo 

13 ka 

<)oo 

12.4 ka 

<)oo 

11.7 ka 

Tundra at 

Fairbanks 

<)oo 

12.4 ka 

18 20 22 24 

at best circumstantial, but believe that by proposing names 

for the presumed climatic fluctuations we will stimulate the 

research and discussion necessary to test the validity of our 

proposal. 

Paleoecologists working in east Beringia have often 

expressed regret that there was no unequivocal interglacial 

fauna and flora with which to compare middle Wisconsin 

faunas and floras. As indicated above, the deposits assigned to the Koy-Yukon thermal event include the expected interglacial biotic elements, yet appear to be much 

younger than stage 5e. Work now under way at the Birch 

Creek exposure by Mary Edwards and colleagues (Edwards, this volume) may resolve this dilemma. In our 

view, the Birch Creek section is the key to clarifying the 

record of climatic events during both stages 3 and 5 be26 

===~> 

Tundra (Antifreeze Pond) ::::::;:> 

_.....,.;t__ Meltwater lakes ___r-......___ 

-...........r- in Bell Basin ---,.........--

28 

~arb tundra (Titilak) 

c:::=::::::;E=nd:::J~f interstadial 

in John Valley 

30 32 

THOUSANDS OF YEARS (ka) BEFORE PRESENT 

Figure 2. Plot of 14C dates on phenomena thought to imply existence of Sixtymile and Hanging Lake thermal events in 

eastern Beringia (from various sources). Bars with vertical hash mark represent 14C dates and 1 or 2 r7 error values. 

Arrows signify duration of glaciations or other climatically related phenomena; arrows dashed where approximate and 

queried where uncertain. Black 14C bars and black arrows signify dates or events that suggest climatic warming. 

36 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
cause it contains sediments bracketing those stages as well 

as several paleosols and another undated tephra older than 

the Old Crow tephra. 

Age 

7.9 ka 

14.3 ka 

21.6 ka 

Age 

7.8 ka 

9.2 ka 

10.9 ka 

12.4 ka 

15.8 ka 

20.3 ka 

20 20 20 

POLLEN. IN PERCENT 

B 

POLLEN, IN PERCENT 

Figure 3. Summary of pollen from (A) Kaiyak Lake, 

northwestern Alaska (modified from Anderson, 1985), 

and (B) Hanging Lake, northern Yukon (modified from 

Cwynar, 1982), showing pollen fluctuations at around 

20 ka that are thought to reflect warming associated 

with the Hanging Lake thermal event 

REFERENCES CITED 

Anderson, P.M., 1985, Late Quaternary vegetational change in the 

Kotzebue Sound area, Northwestern Alaska: Quaternary 

Research, v. 24, p. 307-321. 

Cwynar, L.C., 1982, A late-Quaternary vegetation history from 

Hanging Lake, northern Yukon: Ecological Monographs, v. 

52, p. 1-24 

Hamilton, T.D., 1986, Late Cenozoic glaciation of the Central 

Brooks Range, in Hamilton, T .D., Reed, K.M., and Thorson, 

R.M., eds., Glaciation in Alaska: The geologic record: 

Anchorage, Alaska Geological Society, p. 9-49. 

Hamilton, T.D., and Bischoff, J.L., 1984, Uranium series dating of 

fossil bones from the Canyon Creek locality in central 

Alaska: U.S. Geological Survey Circular 939, p. 26-29. 

Hamilton, T.D., and Thorson, R.M., 1983, The Cordilleran ice 

sheet in Alaska, in Porter, S.C., and Wright, H.W., Jr., eds., 

Late-Quaternary environments of the United States; v. 1, The 

late Pleistocene: University of Minnesota Press, p. 38-52. 

Klassen, R.W., 1986, Tertiary-Pleistocene stratigraphy of the 

Liard Plain, southeastern Yukon Territory: Geological SurAge 

Cl) 

m 

Cl) 

Picea Betula 

u 

m 

u 

·.:: Alnus w 

20 20 20 20 

POLLEN, IN PERCENT 

e = Less than 2 percent 

~ 

ro 

c 

(» 

iii 

:::::J en Oa> 

cD 0 "-C. 

a... en 

50 100 

PERCENT OF 

POLLEN & 

PORES 

Figure 4. Summary of pollen percentages in upper part of 

Bluefish Basin (loc. HH75-24) that may signify slightly 

warmer climate shortly after 20.8 ka-the Hanging Lake 

thermal event. From McCourt (1982) and j.V. Matthews, Jr. 

(unpub. data). 

Climatic Change in Eastern Beringia During Oxygen Isotope Stages 2 and 3 37 
vey of Canada Paper 86-17, 16 p. 

Lichti-Federovich, S., 1973, Palynology of six sections of late 

Quaternary sediments from the Old Crow River Yukon 

Territory: Canadian Journal of Biology, v. 51, p. 553-564. 

McCourt, G.H., 1982, Quaternary palynology of the BluefiSh 

Basin. northern Yukon Territory: Edmonton. University of 

Alberta, M.S. thesis, 165 p. 

Nakao, K., and Ager, T.A., 1985, Climatic changes and vegetational history of the Interior Alaska inferred from drilled 

cores at Harding Lake, in Nakao, K., ed., Hydrological regime and climatic changes in the Arctic Circle; Report of the 

Alaskan Paleohydrology Research Project-1982/83: Japan, 

Hokkaido University, Laboratory of Hydrology, Department 

of Geophysics, Faculty of Science, p. 43-52. 

Pewe, T.L., 1975, Quaternary stratigraphic nomenclature in unglaciated central Alaska: U.S. Geological Survey Professional 

Paper 862, 32 p. 

Schweger, C.E., and Matthews, J.V., Jr., 1985, Early and Middle 

Wisconsinan environments of eastern Beringia; Stratigraphic 

and paleoecological implications of the Old Crow tephra: 

Geographie Physique et Quaternaire, v. 39, no. 3, p. 

275-290. 

Weber, P.R., and Ager, T.A., 1984, Glacial-lake deposits in the 

Mt. Harper area, Yukon-Tanana Upland, in Coonrad, W.L., 

and Elliott, eds., The United States Gelogical Survey in 

Alaska; Accomplishments during 1981: U.S. Geological 

Survey Circular 868, p. 68-70. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of Old Crow tephra in Alaska: Geology, v. 14, p. 594-597. 

Geological Survey of Canada Contribution 20687 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

38 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Paleosols of Northwestern Canada 

By Charles Tarnocai 

Paleosols were investigated in three areas in northwestem Canada: the central Yukon, the Old Crow area, and the 

Mackenzie Mountains. In the central Yukon, the work 

focused on paleosols developed on old glacial materials. In 

the unglaciated Old Crow area, paleosols developed on a 

variety of parent materials were studied in both the Old 

Crow Basin and the Bluefish River uplands. In the Mackenzie Mountains, paleosols were studied in the Little Bear 

River section, which is composed of Cordilleran and Laurentide glacial deposits of Pleistocene age. The brief discussion of these paleosols given below includes information concerning the relationship of their development to 

past climates. 

Paleosols of the central Yukon 

Paleosols in the central Yukon formed during the 

Pleistocene (table 1). Paleosols that formed during the 

early Pleistocene are called Wounded Moose paleosols, 

whereas those that developed during the late Pleistocene 

are called Diversion Creek paleosols (Smith and others, 

1986). The morphological and analytical data presented in 

tables 2 and 3 include not only the data for these paleosols, 

but for comparison also include data for the Stewart soils, 

which developed during the Holocene on materials derived 

from the late Wisconsin McConnell glaciation (Smith and 

others, 1986). 

Early Pleistocene paleosols 

The Wounded Moose paleosols developed during preIllinoian time on both till and glaciofluvial materials deposited during the pre-Reid glaciations (table 1). 

A maximum solum thickness of 2m was reported for 

those soils developed on pre-Reid outwash (Tamocai and 

others, 1985). The colors of the upper paleo-argillic (Bt) 

horizons of these paleosols are SYR for outwash and 7 .SYR 

for till (table 2). These paleosols developed strongly 

weathered Bt horizons with thick clay skins. Clay skins 

occur as coatings on ped and pebble surfaces and form 

bridges between sand grains. As a result of cryoturbation, 

the clay skins in the upper B horizon are usually fragmented and dispersed. The Wounded Moose paleosols are 

strongly leached. The uppermost paleo Bt horizon has 

average pH values ranging between 4.7 and 4.8. This 

horizon also has a somewhat higher concentration of exchangeable cations than the uppermost paleo B horizons in 

the Diversion Creek paleosols developed on corresponding 

materials. Carbon and nitrogen values are low in this 

horizon, and the average sodium pyrophosphate extractable 

Fe + AI values are 0.10 percent (table 3). 

According to Foscolos and others (1977), Wounded 

Moose paleosols contain kaolinite, illite, and montmorillonite-kaolinite mixed-layer clay minerals. Chlorite and 

vermiculite are absent. Although chloritic intergrades are 

present, they are not as conspicuous as in the Diversion 

Creek paleosols. These chloritic intergrades decrease with 

depth, and no such intergrade was found in the IIC horizon. 

The montmorillonite-kaolinite mixed-layer clay minerals 

were identified below a depth of 190 em in these paleosols 

(Foscolos and others, 1977). 

Most Wounded Moose paleosols display strong 

cryoturbation in the form of disrupted and displaced soil 

horizons and oriented stones. Sand wedges and sand involutions of various sizes are also common. The sand wedges 

are much wider and more common in these paleosols than 

in ihe Diversion Creek paleosols. Ventifacts are commonly 

found at the paleosol surface. During the early Pleistocene, 

when development of Wounded Moose paleosols began, 

the climate was probably warm and subhumid and grassland and shrub vegetation predominated (Foscolos and 

others, 1977; Rutter and others, 1978). These conditions, 

in contrast to modern soil-forming conditions, promoted 

strong weathering, leaching, and soil development and the 

formation of montmorillonite. This was followed by a 

more temperate and humid climate that induced the degradation of montmorillonite to kaolinite through an intermediate step of mixed-layer montmorillonite-kaolinite. This 

latter type of climate was probably responsible for the red 

colors and very thick Bt horizons that characterize these 

paleosols. These two climatic regimes produced the rubification, deep sola, eluviated clay, and thick clay skins of 

the Wounded Moose paleosols. During subsequent glacial 

periods, Wounded Moose paleosols were affected by strong 

erosional and cryogenic processes as a result of the cold 

arctic climate. Thermal cracking caused the development 

of sand wedges and sand involutions, and cryoturbation 

produced discontinuous and displaced soil horizons and 

oriented features. 

Late Pleistocene paleosols 

The Diversion Creek paleosols developed on deposits 

formed during the Reid glaciation, with soil formation 

beginning during the Sangamonian interglacial period 

Paleosols of Northwestern Canada 39 
Table 1. Paleosols of northwestern Canada 

[Time scale used in this table is that of Heginbottom and Vincent (1986)] 

General chronostratigraphy Paleosols 

TIIYle Period Epoch 

(Mal 

HOLOCENE 

Stage 

Ice sheets 

(glaciations) Central Yukon Old Crow 

area 

Little Bear 

River section 

Major soil-forming processes and soil features 

Weak Brunisolic development in the central Yukon, 

Cryosolic development in the Old Crow area. 

0.010-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

z McConnell Moderate cryogenic processes with the development of 

- IA1E and periglacial features in a permafrost environment. 

Buckland Severe erosion and the formation of ventifacts. 

0.023 

0.064 

0.115 

z 

< u z 

0 

z 

0 MIDDlE 

u l.IJ ell----------------

SANGAMONIAN Diversion Creek 

Old Crow 

paleosols 

Paleosol 5 

Old Crow paleosols: Cryosolic soil development with 

formation of patterned ground and permafrost. 

Diversion Creek paleosols: Moderate Brunisolic and 

weak Luvisolic soil development, leaching of 

carbonates, moderate Bm and weak Bt horizon 

development, occasional thin clay skins, moderate 

weathering. 

0.128 

Paleosol 5: Moderate Brunisolic soil development with 

moderately thick Bm horizons, very little leaching, 

slight rubification in the Bm horizon. 

f- -----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------

0.320 < 

0.730 

1.10 

1.70 

Q pJ 

Q 

ll.llNOIAN 

>- PRE-llllNOIAN 

....:& 

Reid 

Pre-Reid 

glacial 

and 

interglacial 

periods 

Wounded 

Moose 

paleosols 

Paleosol 4 

Paleosol 3 

Paleosol 2 

Paleosol 1 

Strong cryogenic processes with the development of 

periglacial features in a permafrost environment. 

Severe erosion and formation of ventifacts. 

INTERGLACIAL PERIODS: 

Wounded Moose paleosols: Strong Luvisolic soil 

development, leaching, development of Bt horizons 

with red colors (2.5YR and 5YR) and clay skins, 

strong weathering, deep sola. 

Paleosols 1 to 4: Strong Brunisolic and weak Luvisolic 

soil development, some leaching and development of 

moderately thick Bm horizons with slightly reddish 

colors in Paleosol 4 and moderate rubification in 

paleosols 1 to 3, some argillans in paleosol 3. 

GLACIAL PERIODS: 

Strong cryogenic processes with the development of 

periglacial features in a permafrost environment. 

Severe erosion and formation of ventifacts on the 

Wounded Moose paleosols. 

pJ 

z 

u.l 

u 

0 

Burnt Hill 

and 

Bluefish 

River 

paleosols 

Burnt Hill and Bluefish River paleosols: Luvisolic and 

Podzolic soil development, leaching of carbonates, 

development of strong colors (5YR) and clay 

accumulation in the B horizon. 

5.00 

(table 1). They are found on both till and glaciofluvial 

materials. 

These paleosols are associated with a moderately well 

developed B horizon, and the dominant color of the uppermost B horizon is 7 .5YR (table 2). The Bt horizons, which 

are found only in Diversion Creek paleosols developed on 

till, are associated with thin clay skins on ped surfaces and 

clay bridges between sand grains. These Diversion Creek 

paleosols have leached sola. The uppermost paleo B horizons have average pH values ranging between 4.6 and 5.3 

and a low concentration of exchangeable cations. The 

carbon and nitrogen values are low in these horizons and 

the sodium pyrophosphate extractable Fe + AI values are 

generally less than 0.11 percent (table 3). Sand wedges are 

present in these paleosols but not common. Ventifacts are 

regularly observed on the surfaces of Diversion Creek 

paleosols. Cryoturbated features such as oriented stones, 

silt cappings, and distorted horizons are more common on 

40 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Table 2. Summary of-soil morphologies of the central Yukon soils 

[For definition of soil horizons see Agriculture Canada Expert Committee on Soil Survey (1987); solum thickness is mean thickness with range of values 

in brackets; equal sign means equal proportions] 

Dominant color hue 

in Munsell soil notation Dominant primary structure Coarse fragments 

Soil and Solum Soils Ill Soils Soils 

parent thickness Uppermost lower Type Grade with118t horizons with sand with strong Degree of Frost Ventifacts 

material (em) Ill Ill horizons with wedps and CI)IOturbation weathering orientation 

clay skins involutions 

(pet) (pet) (pet) (pet) 

Wounded Moose 109 5YR 7.5YR Blocky Weak to 100 100 34 50 Strong Common Common 

(outwash) (58-205) moderate chemical 

altention 

Wounded Moose 91 7.5YR 7.5YR Blocky= Modente to 100 100 15 100 St1011g Common Common 

(till) (50-123) granular strong chemical 

alteration 

Diversion Creek 45 7.5YR 7.5YR Blocky= Weak to 20 80 20 0 Moderate Oc:casional Abundant 

(outwash) (9-90) platy moderate chemical 

alteration; 

frost shattering 

Diversion Creek 56 10YR 10YR Blocky= Weak to 33 83 0 20 Moderate Common Common 

(till) (14-106) gnnular moderate chemical 

alteration; 

frost shattering 

Stew an 21 10YR Variable Weak None None None None Weak chemical None None 

(drift) (0-40) altention; 

some frost 

shattering 

Table 3. Average values of various parameters for the uppermost B horizons and the C horizons in the central Yukon soils 

Soil and Soil Number CaC03 pH c N Sodium Exchangeable cations Total 

parent horizon of equiv. (pet) (pet) pyrophosphate (meqilOO g) 

material samples (pet) (Fe+Ail Sand 

Wounded Moose Iffit 14 0.0 4.8 0.22 0.01 

(outwash) IIC 6 .0 5.3 .12 .01 

Wounded Moose Imt 6 .0 4.7 .23 .02 

(till) IIC 3 .0 5.0 .09 .00 

Diversion Creek IIBm 6 .23 5.3 .26 .01 

(outwash) IIC 2 .00 5.8 .13 .00 

Diversion Creek IIBm 9 .00 4.6 .30 .02 

(till) IIBt 6 .00 4.7 .30 .03 

IIC 10 .00 5.3 .57 .03 

Stewart IIBm 3 .00 4.3 .53 .04 

(outwash) IIC 4 .00 4.8 .22 .20 

Stewart IIBm 8 .94 5.3 .73 .04 

(till) IIC 8 1.68 6.3 .33 .01 

the Diversion Creek paleosols developed on till than on 

those developed on outwash. Weathering of coarse fragments in these paleosols is moderate and frost -shattered 

coarse fragments are common. 

Foscolos and others (1977) and Rutter and others 

(1978) suggested that a cool and humid climate during this 

period was responsible for the development of Brunisols 

(paleo) or weak Luvisols (paleo). This cooler climate 

resulted in a weaker soil development than is found in the 

Wounded Moose paleosols. The Diversion Creek paleosols 

were exposed to only one glacial period, the McConnell 

(pet) 

0.10 

.06 

.10 

.06 

.08 

.05 

.11 

.11 

.07 

.12 

.06 

.28 

.08 

Silt Clay 

(pet) (pet) (pet) 

Ca Mg K AI 

7.19 3.85 0.09 0.34 57.2 23.0 19.8 

2.46 .84 .05 .16 90.4 5.0 4.6 

10.70 3.85 .09 .25 50.9 30.3 18.7 

6.80 1.73 .10 .00 81.5 11.8 6.7 

3.30 1.10 .09 .07 74.2 19.2 6.5 

1.70 .45 .03 .00 91.0 6.7 2.3 

2.84 .85 .07 .15 63.5 31.1 5.3 

7.02 1.90 .18 .13 53.7 32.5 13.7 

3.80 .25 .14 .02 66.1 26.0 7.9 

1.63 .40 .08 .98 56.6 38.9 4.5 

1.37 .40 .07 .03 84.0 14.9 1.1 

1.92 .43 .06 .30 62.5 3.9 6.6 

2.23 .42 .02 .04 17.2 27.8 6.4 

glaciation, and thus cryogenic features are also weaker and 

fewer than those found in the Wounded Moose paleosols. 

Paleosols of the Old Crow area 

Late Pliocene and Pleistocene paleosols 

Paleosols examined in the Old Crow area, a portion of 

the Yukon that was never glaciated, include examples of 

possible late Pliocene age from the Bluefish River valley, 

the Bluefish River uplands, and the Burnt Hill section along 

Paleosols of Northwestern Canada 41 
the Old Crow River. Other paleosols of early to middle 

Wisconsin age were examined in sections in the Old Crow 

Basin (table 1). Although most of these paleosols were 

buried by thick fluvial deposits, some of them are covered 

only by a thin loess cap. 

A paleosol examined at the Burnt Hill exposure along 

the Old Crow River had a well-developed reddish (5YR 3/ 

3) B horizon and a leached Ae horizon. Analysis of pollen 

from this soil indicated that the area had been dominated by 

spruce, pine, alder, birch, Corylus sp., ericaceous shrubs, 

and moss species. The pine pollens were identified as 

Haploxylon types (white pine), Pinus monticola, and Diploxylon types. Small amounts of Tsuga and Abies pollen 

were also present. The pollen assemblage found in this 

paleosol indicates that the vegetation was a mixed, closedcanopy forest with a dense alder layer. The understory was 

dominated by Corylus sp., ericaceous shrubs, and moss 

species. The presence of white pine, Corylus, and Tsuga 

point to a climate much warmer than at present. Similar 

pollen assemblages, dated as late Pliocene (Nelson and 

Carter, 1985), were found in the Gubik Formation, at the 

Ocean Point site in Alaska, although no Corylus was found 

at that site and Salix pollen was much less common than in 

the Burnt Hill paleosol. The similarity of the pollen assemblage indicates that the Burnt Hill paleosol also developed 

in the late Pliocene (Schweger, in press). 

Paleosols in the Bluefish River area developed from 

calcareous materials derived from limestone bedrock. They 

have a well-developed B horizon with strong colors, dominantly 5YR 4/5 moist. The B horizon contains a significant 

clay accumulation (table 4). The Bluefish River paleosols 

have average pH values of 7.4 in the uppermost paleo Bt 

horizon and 7.5 in the Ck horizon, which would normally 

indicate that very little leaching has occurred. The difference in the concentration of calcium carbonate in these two 

horizons, however, indicates that a significant amount of 

leaching has taken place. The average calcium carbonate 

concentration in the Ck horizon is 63.5 percent while in the 

Bt horizon it is 17.0 percent. These paleosols contain high 

amounts of total carbon. Since the concentration of carbon 

is generally higher in the parent material than in the overlying Bt horizons, this carbon is most likely derived from 

the bedrock (table 4). The Burnt Hill paleosol (table 5), on 

the other hand, has developed on noncalcareous fluvial 

materials. Its morphology reflects the effects of advanced 

podzolization processes. Although the sodium-pyrophosphate-extractable Fe and AI values are lower than in 

the contemporary (Holocene) Podzols (Agriculture Canada 

Expert Committee on Soil Survey, 1987), the ammoniumoxalate-extractable Fe and Al values are very similar. This 

would indicate that the use of the sodium-pyrophosphateextractable Fe and Al criteria developed for recent Podzols 

is questionable when attempting to identify podzolization 

in paleosols. It is possible that the sodium-pyrophosphateextractable Fe and AI values change with time. In modern 

Podzols occurring in southern Canada, the sodium-pyrophosphate-extractable Fe is approximate! y 50 percent of the 

ammonium-oxalate-extractable Fe (Wang and McKeague, 

1982; McKeague and others, 1983). In the the Burnt Hill 

paleosol this ratio is much less, possibly because the sodium-pyrophosphate-extractable Fe, which is bound in an 

iron-organic complex (McKeague and others, 1971), has 

oxidized into an amorphous hydrous iron oxide. The 

concentration of this form of amorphous iron is determined 

by the ammonium oxalate test. 

Most of these paleosols were buried under various 

sediments in the Bluefish River valley. In one case, 

however, a strongly truncated paleosol was found on the 

Bluefish River uplands. Soil material from the surface 

horizon of a buried paleosol was analyzed for pollen. It 

had essentially the same pollen assemblage as did the 

paleosol at the Burnt Hill exposure. The development of 

paleosols found in the Bluefish River uplands, the Bluefish 

River valley, and the Burnt Hill exposure are very similar. 

The soil development and, especially, the pollen data suggest that the Bluefish River paleosols are also of late Pliocene age. 

The most recent paleosols in the Old Crow area were 

found buried within a dominantly fluvial succession overlain by late Wisconsin lake sediments in the Old Crow 

Basin. These Cryosols (paleo), which had developed in a 

permafrost environment, were associated with gleyed horizons, mottles, cryoturbated features, patterned ground, and 

ice wedges. A bone buried in this soil yielded a radiocarbon age of 42±1.2 ka (R.E. Morlan, Archaeological Survey 

of Canada, oral common., 1987). 

Paleosols of the Little Bear River section 

The Little Bear River lies near the boundary between 

the Mackenzie Plain and the Mackenzie Mountains, in a 

zone of overlap between the former extent of local montane 

glaciers originating in the Canyon Ranges of the Mackenzie 

Mountains and the maximum extent of the Laurentide ice 

sheet. The Little Bear River section is located at latitude 

64° 27.5' N. and longitude 126° 42' W. at an elevation of 

approximately 900 m. Tills of montane origin overlain by 

the Laurentide boulder gravel can be differentiated in this 

section. These tills and boulder gravel,. which are underlain 

by bedrock of the Franklin Mountain Formation, have an 

aggregate thickness of approximately 40 to 50 m. 

Five paleosols were identified in association with five 

different montane tills (table 1). In addition, a modern soil 

developed on boulder gravel of Laurentide origin occurs on 

the surface. Paleosols developed on the top of each till 

indicate prolonged intervals of soil formation during the 

interglacial periods (Hughes and others, in press). 

Spruce logs found in a buried peat deposit on the top 

of paleosol 4 gave a radiocarbon age greater than 4 7 ka 

(Hughes and others, in press). Pollen data obtained from 

42 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Table 4. Average values of various parameters for the uppermost B horizons and the C horizons in the 

Bluefish River paleosols 

Soil and Soil Number CaC03 pH c N parent material horizon of samples equiv (pet) (pet) 

(pet) 

Bluefish River IIBt 3 17.0 7.4 2.13 0.06 

(residual) liCk 3 63.5 7.5 7.68 .24 

Table 5. Analytical data for the Burnt Hill paleosol 

[*, calculated] 

Soil and Soil Number CaC03 pH c N Dithionite 

parent horizon of equiv. (pet) (pet) citrate 

material samples (pet) 

Fe AI 

(pet) (pet) 

Burnt Hill AI! 0.0 4.6 0.06 0.02 0.43 0.04 

(fluvial) Bf .0 6.7 .31 .02 3.94 .04 

BC .0 6.7 .23 .02 .81 .04 

c .0 6.4 .23 .01 .75 .04 

this same deposit indicate that the area was covered by a 

closed-canopy coniferous forest at that time (Hughes and 

others, in press). The area is now alpine tundra, just above 

treeline. This information and the degree of soil development indicate that paleosols 1 to 4 probably developed 

during pre-Illinoian stages whereas paleosolS likely developed during the Sangamonian Stage (table 1). 

The uniqueness of the Little Bear River section is that 

it contains, in one location, five distinctly different paleosols developed on similar parent materials. The greater 

solum and B horizon thicknesses, the increase of redness in 

the B horizons, and the occurrence of some argillans in the 

older paleosols indicate stronger soil development with age 

(table 6). This suggests that, since the formation of the 

oldest paleosols, the climate has steadily cooled. The lack 

of evidence for cryoturbation, especially in Gleysols 

(paleo), indicates that these paleosols developed in a permafrost-free environment 

All of these paleosols developed in a relatively dry 

environment in which the precipitation was probably similar to that occurring today, but because of the higher ternperatures and thus correspondingly higher rate of 

evapotranspiration, the environment was drier than at the 

present time. Paleosols 1 and 2 developed under a slightly 

warmer climate than did paleosols 3, 4, and 5, which 

developed in a boreal environment dominated by closedcanopy coniferous forest vegetation. The modern soil has 

developed in a permafrost environment, the coldest of all 

the climates under which these soils have developed. 

Dithionite Ammonium Sodium Total 

citrate oxalate pyrophosphate 

Sand Silt Clay 

(Fe+Ail (Fe+AI) (Fe+AI) (pet) (pet) (pet) 

(pet) (pet) (pet) 

1.76 0.27 0.05 51.5 30.8 18.0 

.79 .11 .03 43.9 44.8 11.3 

Ammonium -Sodium C.E.c.• Total 

oxalate pyrophosphate meqllOOg 

Sand Silt Clay 

Fe AI Fe AI (pet) (pel) (pet) 

(pel) (pet) (pet) (pet) 

0.31 0.03 0.05 0.01 2.80 92.9 5.5 1.6 

3.54 .03 .02 .00 3.90 91.7 5.9 2.3 

.97 .03 .05 .00 3.93 92.5 5.6 2.0 

.92 .03 .05 .00 2.87 89.7 8.5 1.7 

Summary 

1. The older the paleosol, the stronger the soil development Paleosols developed during the late Pliocene 

and the pre-Illinoian stages of the Pleistocene have 

stronger soil development than those developed in the 

Sangamonian and early part of the Wisconsinan 

Stages of the Pleistocene. 

2. This stronger soil development in the late Pliocene 

and the pre-Illinoian stages of the Pleistocene is primarily due to the warmer and moister climate and, to 

a lesser degree, to the great length of time during 

which weathering took place. 

3. All pre-Wisconsin paleosols began developing in a 

permafrost-free environment 

4. Cryogenic features found in all pre-Wisconsin paleosols, except those which were buried, result from the 

cold climate which existed during the subsequent 

glacial periods. 

5. Early Wisconsin paleosols in the Old Crow Basin 

began developing in a permafrost environment. 

REFERENCES CITED 

Agriculture Canada Expert Committee on Soil Survey, 1987, The 

Canadian system of soil classification: Research Branch, 

Agriculture Canada, Publication No. 164, second edition, 

164 p. 

Foscolos, A.E., Rutter, N.W., and Hughes, O.L., 1977, The use of 

pedological studies in integrating the Quaternary history of 

Paleosols of Northwestern Canada 43 
Table 6. Average values of the uppermost 8 horizons in the Little Bear River paleosols 

[Redness rating = [(10-H)xO]N, where H is the YR hue, C is the chroma and Vis the value (forrent and others, 1980, 1983] 

Number Tolal Color Redness pH CaC03 

of B horizon rating (pet) 

pedons thickness 

(em) 

Paleosol 1 0 

Paleosol 2 2 68 5YR 4/4 3.1a 7.2 1.3 

7.5YR 4/2 

Paleosol 3 95 7.5YR 4/2 1.2 7.4 1.4 

Paleosol4 68 10YR 3/2 .0 7.4 18.2 

Paleosol 5 3 81 7.5YR 4/6 1.2a 7.3 .6 

10YR 4/6 

IOYR 4/6 

Modem soil 42 10YR 4/6 .0 6.4 .0 

8Meanvalue. 

central Yukon: Geological Survey of Canada, Energy, Mines 

and Resources Canada, Bulletin 271, 48 p. 

Heginbottom, J.A., and Vincent, J-S., eds., 1986, Correlation of 

Quaternary deposits and events around the margin of the 

Beaufort Sea; Contributions from a joint Canadian-American 

Workshop, April 1984: Geological Survey of Canada Open 

File Report 1237, 60 p. 

Hughes, O.L., Tamocai, C., and Schweger, C.E., in press, Pleistocene stratigraphy, paleopedology and paleoecology, Little 

Bear River section, western District of Mackenzie: Geographie Physique et Quaternaire. 

McKeague, J.A., Brydon, I.E., and Miles, N.M., 1971, Differentiation of forms of extractable iron and aluminum in soils: 

Soil Science Society of America, Proceedings, v. 35, p. 

33-38. 

McKeague, J.A., Wang, C., Coen, G.M., DeKimpe, C.R., Laverdiere, M.R., Evans, L.J., Kloosterman, B., and Green, A.J., 

1983, Testing chemical criteria for spodic horizons on 

podzolic soils in Canada: Soil Science Society of America 

Journal, v. 47, p. 1052-1053. 

Nelson, R.E., and Carter, L.D., 1985, Pollen analysis of a late 

Pliocene and early Pleistocene section from the Gubik Formation of arctic Alaska: Quaternary Research, v. 24, p. 

295-306. 

Rutter, N.W., Foscolos, A.E., and Hughes, O.L., 1978, Climatic 

trends during the Quaternary in central Yukon based upon 

pedological and geomorphological evidence, in York Quaternary Symposium on Quaternary Soils, 2d, Proceedings: 

N c Dithionite Ammonium Sodium Clay 

(pet) (pet) citrate oxalate pyroposphate (pet) 

(fe+AI) (fe+AI) (Fe+AI) 

(pet) (pet) (pet) 

0.10 0.16 1.29 0.13 0.03 10.9 

.01 .28 1.92 .19 .06 8.3 

.05 2.32 1.92 .46 .06 26.8 

.03 .29 1.90 .25 .06 20.6 

.16 2.63 2.33 1.15 .56 18.7 

Norwich, England, Geo Abstracts, p. 309-359. 

Schweger, C.E., in press, Late Tertiary-early Pleistocene palynology, Old Crow-Bluefish Basins, northern Yukon, Canada: 

Proceedings of a Workshop on Neogene Environments, 

Denver, October 1987. 

Smith, C.A.S., Tamocai, Charles, and Hughes, O.L., 1986, Pedological investigations of Pleistocene glacial drift surfaces in 

the central Yukon: Geographie Physique et Quaternaire, v. 

15, p. 29-37. 

Tamocai, C., Smith, S., and Hughes, O.L., 1985, Soil development on Quaternary deposits of various ages in the central 

Yukon Territory: Geological Survey of Canada Paper 

85-1A, Current Research, Part A, p. 229-238. 

Torrent, J., Schwertmann, U., and Schulze, D.G., 1980, Iron oxide 

mineralogy of some soils of two river terrace sequences in 

Spain: Geoderma, v. 23, p. 91-208. 

Torrent, J., Schwertmann, U., and Alferez, F., 1983, Quantitative 

relationships between soil color and hematite content: Soil 

Science, v. 136, p. 354-358. 

Wang, C., and McKeague, J.A., 1982, Illuviated clay in sandy 

podzolic soils of New Brunswick: Canadian Journal of Soil 

Science, v. 62, p. 79-89. 

Carter, l. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

44 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Upper Cenozoic Deposits, Kanuti Flats and 

Upper Kobuk Trench, Northern Alaska 

By Thomas D. Hamilton 

Tectonic deformation has caused the Kanuti Flats and 

upper Kobuk trench (fig. 1) to be continuing foci of late 

Cenozoic deposition. The Kanuti Flats, a broad lake-dotted 

plain within the Koyukuk River valley (Wahrhaftig, 1965, 

p. 26), has been subjected to late Cenozoic subsidence 

which continues to the present day (T.D. Hamilton, unpub. 

field mapping, 1985 and 1987). Its geologic record spans 

about two million years and includes glacial and glaciolacustrine deposits correlated with all of the major glacial 

events defined for the central Brooks Range (Hamilton, 

1986a, 1986b). From oldest to youngest, these are the 

Gunsight Mountain, Anaktuvuk River, Sagavanirktok 

River, and Itkillik glacial episodes. The upper Kobuk 

trench is part of a structural feature that extends west to the 

Bering Sea (Grantz, 1966); activity along its bounding 

faults has continued into the Holocene (Hamilton, 1984). 

The record from the upper Kobuk trench extends into the 

Matuyama Reversed-Polarity Chron and includes deposits 

of Anaktuvuk River through Itkillik ages. 

Drift of presumed Tertiary age correlated with Gunsight Mountain glacial advances forms a subdued, arcuate, 

probable end moraine about 4 to 5 km wide that is traceable 

for nearly 100 km along the south margin of the Kanuti 

Flats (fig. 2). The moraine is thickly covered by loess and 

lacustrine silt of Quaternary age, but concentrations of 

erratic boulders along river channels that cut the moraine 

attest to its glacial origin. 

Glacier advances of Anaktuvuk River age occurred 

prior to about 0.8 Ma throughout the central Brooks Range 

on ancient landscapes 50 m or more above levels of modem 

streams (Hamilton, 1986b, 1986c). Glaciers that flowed 

south from the Brooks Range coalesced into broad piedmont lobes in lowlands around the present-day Kobuk and 

Koyukuk Rivers (fig. 2). Glacial lobes terminated in a 

large proglacial lake in the Kanuti Flats, where subdued 

arcuate end moraines generally are covered by eolian and 

lacustrine silt more than 15 m thick. Knolls and ridges 

along moraine crests contain wave-washed gravel mixed 

with larger glacial clasts. River bluffs expose strongly 

jointed, compact till and stony glaciolacustrine silt that are 

strongly oxidized along joint planes. Glaciers in the Kobuk 

valley coalesced into an extensive ice body that extended 

west to Kotzebue Sound and probably was contemporaneous with the early Pleistocene Nome River advance of the 

Seward Peninsula (Kaufman and Hopkins, 1986). 

Glaciation of Anaktuvuk River age was followed by a 

long nonglacial interval during which drainage systems 

within the Brooks Range became adjusted to levels close to 

those of modem flood plains and structural troughs developed along the south flank of the range (Hamilton, 1986a). 

Bluffs and knolls within the Koyukuk-Kobuk region expose rounded, quartzose, pebble-small-cobble gravel that 

filled east-west-trending structural troughs to measured 

thicknesses as great as 55 m during a long interval of 

reduced glaciation in mountain valleys. Paleomagnetic 

determinations indicate that deposition of nonglacial fine 

gravel in the upper Kobuk trench began during the Matuyama Reversed-Polarity Chron and continued into the 

Brunhes Normal-Polarity Chron (Hamilton, 1986a, 1986c). 

Glacier flow patterns of Sagavanirktok River age were 

similar to those of the Anaktuvuk River glacial interval, but 

glaciers were markedly smaller. Glaciers filled structural 

troughs along the south flank of the Brooks Range (fig. 2) 

and extended south beyond the troughs along major valleys, within which they commonly terminated in lakes. 

Drift is not as broadly eroded as is drift of Anaktuvuk River 

age, and it occurs close to modem valley floors. Multiple 

end moraines and stratigraphic relations suggest two major 

ice advances in some valleys. The Sagavanirktok River 

glaciation is much younger than the early Pleistocene 

Anaktuvuk River glaciation and is separated by a major 

ARCTIC OCEAN 

tl 

\ 

500 km 

Figure 1. Northern Alaska, showing Kanuti Flats (KF), upper 

Kobuk trench (KT), and area of detail map (fig. 2). 

Upper Cenozoic Deposits, Kanuti Flats and Upper Kobuk Trench, Northern Alaska 45 
interglacial period from succeeding glacial advances of 

Itkillik age. Because of evidence for multiple advances in 

some valleys, "Sagavanirktok River" is considered a generic term for multiple ice advances of middle Pleistocene 

age. 

All glacial deposits of late Pleistocene age are assigned 

to the Itkillik glaciation, which is divisible into two or three 

major phases. The outer border of Itkillik drift is the most 

striking discontinuity in the entire Brooks Range glacial 

succession; it separates subdued older glacial deposits from 

steeper, stonier, and more irregular drift with drainage 

derangements and discontinuous vegetation. 

During Itkillik I time, glaciers extended through southern valleys of the Brooks Range and terminated 25-45 km 

beyond the range along the north margin of the Kanuti 

Flats. Glaciers farther west were smaller and generally did 

not extend into the upper Kobuk trench. Moraines have 

smooth, somewhat flattened, hummocky crests that support 

open vegetation; moist depressions are covered by dense 

muskeg. All ice advances of Itkillik I age are older than the 

effective range of radiocarbon dating, and stratigraphic 

relations described in Westgate and others (1983) suggest 

that the maximum advance may have taken place shortly 

before deposition of the Old Crow tephra about 86±8 ka 

(Wintle and Westgate, 1986). A younger major advance 

occured sometime between about 86 and 55 ka. Driftmantled glacier ice persisted for long intervals in many 

valleys, and relict ice of Itkillik I age is still locally present 

(Hamilton, 1982). 

Drift of Itkillik II age formed during late Wisconsin 

time between about 24 and 11.5 ka. Rugged end moraines 

commonly are located at the south flank of the Brooks 

Range, where they enclose elongate lakes or lacustrine 

plains. Younger end moraines formed within mountain 

valleys during a major read vance of glaciers between 13 ka 

and 11.5 ka. 

Many glaciers of Sagavanirktok River and Itkillik age 

either terminated in standing water or extended to within a 

few kilometers of large lakes in the upper Kobuk trench 

and the Kanuti Flats (Hamilton, 1986a). Some moraines 

are anomalously broad and flat, and they consist either of 

fine-grained glaciolacustrine sediment with dropstones or 

of deltaic sand with steeply dipping foreset beds. Outwash 

trains in other cases extend southward and become deltas at 

concordant altitudes that reflect former lake levels. Because the lakes were not dammed by glaciers or by any 

EXPLANATION 

Glaciers of Itkillik age 

Terrace gravel 

DRIFT LIMITS--Dashed where inferred 

Drift of Sagavanirktok River age (sdl 

Drift of Anaktuvuk River age (ad) 

Drift of Gunsight Mountain age (gmdl 

Figure 2. Glacier limits and drift deposits, Kanuti Flats and upper Kobuk trench, northern Alaska. 

46 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
other known physical agents, and because their reconstructed surfaces rise northward toward the Brooks Range, 

their origin must be the result of isostatic deflection and 

drainage reversals within the low-gradient Kobuk and 

Koyukuk drainage systems. 

REFERENCES CITED 

Grantz, Arthur, 1966, Strike-slip faults in Alaska: U.S. Geological 

Survey Open-File Report 267, 82 p. 

Hamilton, T.D., 1982, Relict Pleistocene glacier ice in northern 

Alaska, in Arctic workshop, 11th. March 1982, Institute of 

Arctic and Alpine Research: Boulder, University of Colorado, p. 25-26. 

---1984, Late Quaternary offsets along the Kobuk and related 

fault zones, northwestern Alaska: Geological Society of 

America Abstracts with Programs, v. 16, p. 288. 

---1986a, Late Cenozoic glaciation of the central Brooks 

Range, in Hamilton, T.D., Reed, K.M., and Thorson, R.M., 

eds., Glaciation in Alaska-The geologic record: Anchorage, Alaska Geological Society, p. 9-49. 

---1986b, Glaciation of the Brooks Range, in Heginbottom, 

J.A., and Vincent, J-S., eds., Correlation of Quaternary 

deposits and events around the margin of the Beaufort Sea: 

Geological Survey of Canada Open File Report 1237, p. 

27-29. 

---1986c, Correlation of Quaternary glacial deposits in 

Alaska, in Richmond, G.M., and Fullerton, D.S., eds., Quaternary glaciations in the United States of America: Quaternary Science Reviews, v. 5 (Quaternary Glaciations in the 

Northern Hemisphere), p. 171-180. 

Kaufman, D.S., and Hopkins, D.M., 1986, Glacial history of the 

Seward Peninsula, in Hamilton, T.D., Reed, K.M., and 

Thorson, R.M., eds., Glaciation in Alaska-The geologic 

record: Anchorage, Alaska Geological Society, p. 51-77. 

Wahrhaftig, Clyde, 1965, Physiographic divisions of Alaska: U.S. 

Geological Survey Professional Paper 482, 52 p. 

Westgate, J.A., Hamilton, T.D., and Gorton, M.P., 1983, Old 

Crow tephra-A new late Pleistocene stratigraphic marker 

across north-central Alaska and western Yukon Territory: 

Quaternary Research, v. 19, p. 38-54. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of Old Crow tephra in Alaska: Geology, v. 14, p. 594-597. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Upper Cenozoic Deposits, Kanuti Flats and Upper Kobuk Trench, Northern Alaska 47 
Quaternary Deposits at Birch Creek, 

Northeastern Interior Alaska: 

The Possibility of Climatic Reconstruction 

By Mary E. Edwards and Patricia F. McDowell 

Extensive sections of Quaternary sediments, exposed 

by rivers or mining activities, offer excellent opportunities 

to study Quaternary paleoenvironments in unglaciated interior Alaska. Thick accumulations of loess containing 

paleosol complexes occur in the Fairbanks area and the 

Yukon Flats (Pewe, 1975; McDowell and Edwards, 1984). 

Woody and organic-rich units ("forest beds") and lacustrine 

sediments are also present. Tephra layers provide a means 

of correlation and dating (Westgate and others, 1983). 

We suggest that a sequence of climatic oscillations is 

recorded in such sections. If a chronology can be established and records correlated, the inferred climatic sequence may extend the terrestrial proxy climate record 

through marine oxygen-isotope stage 5 and beyond, and 

provide independent data for the testing of paleoclimatic 

models. Ritchie and others (1983) have demonstrated that 

the paleoecological record in northwest Canada reflects a 

climatic warming about 10 ka, attributable to increased 

summer insolation at high latitudes (Milankovitch, 1941). 

Other insolation maxima controlled by orbital elements 

occurred about 50, 80 to 90, and 130 ka (Berger, 1978). 

The known values of important climate boundary conditions such as ice volume, sea-surface temperature, and sea 

level suggest that warm intervals could have been associated with these maxima (P.J. Bartlein, University of Oregon, oral common., 1987), but few data are available to test 

this hypothesis. 

This report describes a 45-m-high river-cut section of 

Quaternary deposits on Birch Creek, near Circle, Alaska 

(fig. 1). We briefly discuss the stratigraphy of this site, 

problems associated with dating the sediments, and the application of our data to paleoclimatic reconstruction. 

Study area 

The Yukon Flats tectonic basin (altitude 150 to 250m) 

contains a marginal upland surrounding a central lowland, 

through which flows the Yukon River (Williams, 1962; fig. 

1 ). The southern marginal upland is mantled by loess as 

thick as 35 m, which overlies gravel or bedrock. Williams 

(1962) suggested that the loess is of Pleistocene age, derived from the flood plain of the Yukon and its tributaries 

in glacial periods. The present surface of the southern 

marginal upland is characterized by numerous lakes. 

The modem climate is cold continental (Fort Yukon 

July mean temperature is 17 °C; January mean is -28 °C; 

annual precipitation is <20 em). Discontinuous permafrost 

underlies the region. Below 700 m altitude the vegetation 

is boreal forest dominated by spruce (Picea), birch (Betula), alder (Alnus), poplar (Populus), and willow (Salix). 

The present boreal forest developed during the early 

Holocene, according to late Quaternary pollen diagrams for 

the Yukon Flats (Edwards and Brubaker, 1984) and the 

Tanana lowland (Ager, 1975). Full-glacial pollen assemblages are characterized by herbaceous taxa such as 

Poaceae, Cyperaceae, Artemisia, and ChenopodiaceaeAmaranthaceae and suggest tundra vegetation. 

Section BC-1 

Section BC-1 (fig. 2) faces east and south and is 

exposed for about 400 m along Birch Creek. We sampled 

a 45-m-high part of the section that is free from large ice 

masses, and where slumping is confined to the lowermost 

2.5 m of the section. The basal sediments, units A and B, 

from 2.5 to 14m above creek level, are fluvial deposits of 

silt, sand, and gravel that include organic lenses and pieces 

of detrital wood. The presence of pollen of Picea, Alnus, 

and Betula and the absence of palynomorphs characteristic 

of Tertiary sediments suggest that the deposits are of Pleistocene age. Unit A contains a white ash layer that is 1 to 

3 em thick. Its composition suggests a source in the 

Wrangell Mountains, but the ash has not been dated and is 

not yet chemically or petrographically characterized (J.A. 

Westgate, University of Toronto, written common., 1987). 

Between 14 m and 31 m above river level are three 

units of silt. The lowermost (unit C) probably consists of 

retransported loess; units D and E are massive silts, probably undisturbed or slightly retransported loess. The uppermost part of units B, C, and D contain relatively large 

amounts of disseminated organic matter and macrofossils 

(such as rootlets and pieces of wood), and are either 

leached of carbonates, and(or) display roots, bioturbation, 

and zones resembling soil horizons, suggesting that they 

are paleosols. A 10-cm-thick volcanic ash layer 25 m 

above river level has been identified as the Old Crow 

tephra (Westgate and others, 1985). 

Above unitE is an unconformity overlain by 12m of 

lacustrine sediment and peat (unit F). The lowermost part 

48 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
of unit F consists of a layer of detrital, beaver-chewed 

Picea, Salix, and Populus wood. Approximately 9 m of 

lacustrine sediments lies above the woody layer and is in 

turn overlain by about 3 m of silty peat The section is 

capped by several meters of loess (unit G). 

Pollen has been extracted from units E and F. Unit E 

contains Chenopodiaceae-Amaranthaceae, Poaceae, other 

herbs, and high frequencies of indeterminable pollen 

(>100-grain counts from loess). Abundant pollen of Picea, 

Betula, and Alnus, with minor quantities of Populus, 

Poaceae, Cyperaceae, and Typha characterizes unit F 

(>300-grain counts from lacustrine silt). 

Chronology 

Three radiocarbon ages (QL-1897, QL-1898, 

QL-1899) on unit Fare older than 50 ka. A maximum age 

for unit E is provided by the Old Crow tephra, which 

occurs widely in eastern Beringia (Westgate and others, 

1985). Fission-track data indicate a maximum age of 120 

ka (Naeser and others, 1982; Westgate and others, 1985). 

Thermoluminescence dating of bracketing loess has given 

an age of about 86 ka (Wintle and Westgate, 1986), and 

110 ka (Berger, 1987). This would suggest that unit E 

loess deposition and subsequent lake development occurred 

after 120 ka and before 50 ka. Holocene lake sedimentation rates of 1 m/2,000 yr to 1 m/6,000 yr determined from 

modem lakes in the study area (M. Edwards, unpub. data) 

suggest that the lake or pond represented by unit F was 

present for a considerable interval of time. 

0 so I I I I ' 

km 

148° 

~c., ,_. -- 67° 00 ) 

<Q~ ( .._ 

/ 

Figure 1. Central Alaska, showing location of Birch 

Creek section. Dashed line is boundary of Yukon 

Flats. 

Implications for paleoclimatic reconstruction 

In a survey of early- and mid-Wisconsin paleoenvironmental data from eastern Beringia, Schweger and Matthews 

(1985) showed that a phase of cold, treeless conditions 

followed the deposition of the Old Crow tephra. A subsequent warm period is marked variously at sites across 

eastern Beringia by increased pollen frequencies of boreal 

forest taxa, deep thawing, and macrofossil evidence of 

forested conditions. The BC-1 stratigraphy shows a similar pattern, with loess characterized by a herbaceous pollen 

assemblage overlying the Old Crow tephra, and a subsequent warm period represented by unit F. 

The boreal forest vegetation indicated by the unit F 

pollen spectra, and the presence of Typha, which today 

reaches its northern limits in the study region, imply a very 

warm interval, probably of interglacial character. If the 

dating of the Old Crow tephra is correct, this interval 

occurred in early Wisconsin time, and perhaps reflects an 

insolation maximum at 80 to 90 ka or about 50 ka (approximately oxygen-isotope stages 5a+5c or 3). However, we 

suggest that the age of the Old Crow tephra must be further 

METERS 

50-

>55- 2 ka 

>53.4 ka 

40-

>58 ka 

30-

20-

10-

0-

01 d Crow 

tephra 

tephra -

Tan massive silt 

Peat 

Beaver Jog layer 

Gray blocky silt 

Paleosol 

Tan massive silt 

Paleosol 

Tan silt with 

faint laminations 

Paleosol 

Gray massive silt 

with few pebbles 

Dark organic silt 

Gravelly sand 

Dark organic silt 

Gravel 

UNIT G 

Prirt1ary loess 

UNIT F 

Lacustrine sequence 

UNIT E 

Primary loess 

UNIT D 

Primary loess 

UNIT C 

Retransported silt 

UNIT B 

Fluvial deposits 

UNIT A 

Fluvial deposits 

Figure 2. Summary stratigraphic diagram of section BC-1, 

including Old Crow tephra of Westgate and others (1985). 

Quaternary Deposits at Birch Creek, Northeastern Interior Alaska 49 
studied. The fission-track method is at the lower limit of 

its range, and dating therefore rests heavily on two thermoluminescence results. It is critical that the age of the 

Old Crow tephra be more firmly established. If it is actually much older, the very warm interval represented by unit 

F would probably correspond to the last interglacial (130 

ka; oxygen-isotope stage 5e). 

At BC-1, determining the age of the basal tephra in 

unit A is crucial for dating the lower part of the section; 

work is in progress to date the tephra and to characterize it 

chemically and petrographically. Further plans for work at 

BC-1 involve a detailed analysis of the paleosols and the 

extraction of pollen from the lower units in an attempt to 

describe environments of earlier parts of the Pleistocene. 

This work was funded by National Science Foundation 

Grant DPP 8303734. We thank PJ. Bartlein (University of 

Oregon), D.M. Hopkins (University of Alaska), J.V. Matthews, Jr. (Geological Survey of Canada), and C.E. 

Schweger (University of Alberta) for helpful discussions 

and advice. Robert Anderson (University of Washington) 

and P.W. Dunwiddie (University of Washington) provided 

field assistance, P.W. Dunwiddie made the fossil wood 

identifications, L.B. Brubaker (University of Washington) 

provided laboratory facilities, and Mulu Malmo (University 

of Washington) provided technical help. 

REFERENCES CITED 

Ager, T.A., 1975, Late Quaternary environmental history of the 

Tanana River valley, Alaska: Columbus, Ohio State University, Institute of Polar Studies Report No. 54, 117 p. 

Berger, A.L., 1978, Long-term variations of caloric insolation 

resulting from the Earth's orbital elements: Quaternary 

Research, v. 9, p. 139-167. 

Berger, G.W., 1987, Thermoluminescence dating of the Pleistocene Old Crow tephra and adjacent loess, near Fairbanks, 

Alaska: Canadian Journal of Earth Sciences, v. 24, p. 

1975-1984. 

Edwards, M.E., and Brubaker, L.B., 1984, A 23,000-year pollen 

record from northern interior Alaska: Boulder, Colorado, 

American Quaternary Association, VIII Biennial Meeting 

Abstracts, p. 35. 

McDowell, P.F., and Edwards, M.E., 1984, Loess stratigraphy and 

landscape development, Yukon Flats area, interior Alaska: 

Boulder, Colorado, American Quaternary Association, VITI 

Biennial Meeting Abstracts, p. 81. 

Milankovitch, Milutin, 1941, Canon of insolation and the ice-age 

problem: Belgrade, Koniglich Serbische Akademie Geogr. 

Spec. Publ. 132, 484 pp. (franslated by Israel Program for 

Scientific Publications, Jerusalem, 1969.) 

Naeser, N.D., Westgate, J.A., Hughes, O.L., and Pewe, T.L., 

1982, Fission-track ages of late Cenozoic distal tephra beds 

in the Yukon Territory and Alaska: Canadian Journal of 

Earth Sciences, v. 29, p. 2167-2178. 

Pewe, T.L., 1975, Quaternary geology of Alaska: U.S. Geological 

Survey Professional Paper 835, 145 p. 

Ritchie, J.C., Cwynar, L.C., and Spear, R.W., 1983, Evidence 

from northwest Canada for an early Holocene Milankovitch 

thermal maximum: Nature, v. 305, p. 126-128. 

Schweger, C.E., and Matthews, J.V., Jr., 1985, Early and middle 

Wisconsinan environments of eastern Beringia: Stratigraphic 

and paleoecological implications of the Old Crow tephra: 

Geographie Physique et Quaternaire, v. 39, p. 275-290. 

Westgate, J.A., Hamilton, T.D., and Gorton, M.P., 1983, Old 

Crow Tephra: A new late Pleistocene stratigraphic marker 

across north-central Alaska and western Yukon Territory: 

Quaternary Research, v. 19, p. 38-54. 

Westgate, J.A., Walter, R.C., Pearce, G.W., and Gorton, M.P., 

1985, Distribution, stratigraphy, petrochemistry, and paleomagnetism of the late Pleistocene Old Crow Tephra in 

Alaska and the Yukon: Canadian Journal of Earth Sciences, 

v. 22, p. 893-906. 

Williams, J.R., 1962, A geologic reconnaissance, Yukon Flats 

district, Alaska: U.S. Geological Survey Bulletin 1111-H, p. 

290-331. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of the Old Crow tephra in Alaska: Geology, v. 14, p. 

594-597. 

Carter, l. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

50 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Late Quaternary Paleofloods along the Porcupine River, 

Alaska: Implications for Regional Correlation 

By Robert M. Thorson 

A preliminary overview of the alluvial history of the 

Porcupine River valley was presented by Thorson and 

Dixon (1983). In that paper, we described erosional and 

depositional evidence for exceptionally high discharges 

through the Porcupine canyon that resulted from intermittent drainage of lakes that were impounded in basins of 

Yukon Territory by the Keewatin sector of the Laurentide 

ice sheet We concluded that at least two paleoflood episodes, separated by an interval of local aggradation, occurred within approximately the last 35,000 radiocarbon 

years. 

This report presents additional stratigraphic and erosional evidence for the Porcupine River paleofloods and 

provides preliminary paleohydrologic estimates for peak 

discharge, mean channel velocity, and flood duration. I 

compare features along the Porcupine River to those reported for the Channeled Scabland of Washington (Bretz, 

1969; Baker and Nummendal, 1978), the Snake River 

canyon (Malde, 1968), and torrential flood deposits in 

mountain valleys (Costa, 1983). Nearly every feature 

described in these areas is present along the Porcupine 

River upstream from the Yukon Flats (fig. 1). High-water 

marks are recognized on aerial photographs by either pronounced erosional discontinuities or by massive eddy-bars 

along reentrants (figs. 2, 3). Constricted reaches are characterized by steep waterline gradients, trough-shaped cross 

sections, and hanging tributaries (fig. 4 ). Expanded reaches 

exhibit low gradients and broad longitudinal gravel bars 

that were subsequently segmented by narrow canyons. 

Specific features interpreted as having been formed by 

Porcupine River paleofloods include the following: 

1. Hexagonally jointed basalt boulders to 3 m in intermediate diameter have been transported more than 1 

km from the nearest outcrop. 

2. A thin sheet of gray pelitic pebble-cobble gravel was 

spread uniformly across uneroded loess-mantled fmegrained alluvium in Fishhook Bend (fig. 1), which is 

the broadest of the expanded reaches. 

3. An anastomosing plexus of steep bedrock channels 

(coulees) of at least 14 m average depth characterizes 

the lowest 30 km of the canyon. 

4. A 700-m-wide amphitheatre-shaped vertical headwall 

at the mouth of Rapid River in the upper Ramparts 

(fig. 1) is interpreted as a plunge-pool cataract created 

by westward drainage (fig. 2). 

5. A 20-m-high gravel bar 1 km west of the Canadian 

border, whose full height is dominated by steeply dipping coarse foreset beds, is similar to the pendant bars 

described for both the Snake River and Missoula 

flood tracts. 

6. A scour channel 32 m deep, 1 km south of Rapid 

River that is alternately filled with open-work coarse 

gravel and matrix -supported boulders may have been 

emplaced during alternating episodes of scour and 

deposition from suspension, respectively. Large 

(about 1 m in diameter) chaotically oriented rip-up 

clasts of Tertiary clay and lignite fill the lower 15 m 

of the channel. 

Yukon 

Flats Lower Ramparts Fishhook Bend Howling Dog 

Canyon Upper Ramparts 

0 5 10 15km 

--- Figure 1. Northeastern Alaska and northern Yukon showing location of study area and geographic features mentioned in 

text (modified from Thorson and Dixon, 1983). Site locations (circles and triangles) are not mentioned in the text, but are 

discussed in Thorson and Dixon (1983). 

Late Quaternary Paleofloods along the Porcupine River, Alaska 51 
7. Scalloped irregular topography (scabland) characterized by scour depressions occupied by lakes and by 

eminences up to 7 min height occurs on many bedrock surfaces below the high-water mark (whaleback 

eminences at the mouth of Salmon Trout River (fig. 

1) are streamlined parallel to the paleo flow direction, 

transverse to lithologic trends). 

8. Evidence for negligible slopes of the high-water mark 

upstream from tightly constricted reaches may indicate hydraulic impoundment. 

9. Stratified sediments characterized by rhythmically 

interbedded silt and ripple-drift cross-laminated sand 

occur near the base of Tusk Bluff in Fishhook Bend 

(fig. 1) and near the mouths of several tributaries. 

These resemble slack-water sediments reported from 

other paleofloods. 

Preliminary estimates for paleohydrologic parameters 

were obtained using a simplified version of the slope-area 

method outlined by Baker (1973, p. 17). A constricted 

reach at White Mountain Creek (fig. 4) was used to infer 

channel geometry. Maximum and minimum flow depths 

were obtained from the vertical interval defined by the 

cataract and scour channel at Rapid River, respectively. 

The energy gradient was estimated from the slope of the 

EXPLANATION 

-- High-water mark 

Canyon wall 

Terrace scarp 

~ Cataract 

.,_... Scour lake 

c=:::J Gravel bar 

N 

l 

Figure 2. Geomorphic map showing features associated with 

paleofloods along the Porcupine River near Rapid River. 

A-A' shows location of cross-valley profile (fig. 4). 

high-water mark for 10 km down valley from the measured 

constricted reach. Using conservative (minimizing) estimates for Manning roughness (0.040), energy slope 

(0.0026), hydraulic radius (26.3 m), and channel area 

(15,360 m2), peak di~harge could have exceeded 134,000 

m3 s-1• Using the average channel depth of 26 m, and 

assuming uniform flow, mean velocity should have exceeded 8.7 m s-1• These minimum estimates for discharge 

and average velocity are comparable to those determined 

by Malde (1968) for the Bonneville Flood and to the highest peak flows of the Amazon River (Oltman and others, 

1964), but are substantially lower than the most conservative estimates for Missoula outburst flooding (Beget, 1986). 

Use of the DuBoys equation for boundary shear (Baker, 

1973, p. 23) and estimates based on unit stream power 

(Costa, 1983) confrrm that strong flows of this magnitude 

are required to transport the large boulders found in flood 

alluvium along the Porcupine River. 

Thorson and Dixon (1983) inferred that the drainage of 

glacial lakes in the Yukon Territory was required to explain 

their observations. Determination of the duration of sustained flow from estimates of the lake volume can be used 

to test this hypothesis. Using the combined area of Old 

Crow and Bluefish Basins (5,700 km2) and an average 

depth of only 30.5 m (100 ft), flow at peak discharges 

could have been sustained for 15 days. Direct drainage of 

Keewatin meltwater across the northern Yukon without 

impoundment is a highly improbable alternative explanation because the flood discharge required greatly exceeds 

the probable steady-state meltwater flux. For example, 

assuming a mean ablation rate of 0.5 m/yr (water equivalent of ice), an ablation area larger than all of Canada 

would have been required to supply the needed discharge. 

Flood discharges along the Porcupine River should 

have had a dramatic effect on downstream areas. The large 

fan with braided surface morphology below John Herberts 

Village in the Yukon Flats is at least partially a result of 

flood deposition, and may have indirectly caused aggradation of rivers draining the southern Brooks Range. Hydraulic ponding at the Ramparts of the Yukon River and at 

other constrictions may have initiated temporary lacustrine 

slackwater sedimentation in such alluvial basins. The flux 

and character of sediment load to the lower Yukon River 

the continental shelf, and the Bering Sea may also have 

been impacted. For example, Griggs and others (1970) 

reported that fluvial gravel resulting from Missoula flooding reached abyssal depths more than 600 km from the 

outburst flood source. First appearances of retransported 

palynomorphs (such as the Mississippian-age spores marking disconformity A in the Old Crow Basin (Schweger, this 

volume)) could be used as marker horizons to supplement 

lithologic, geomorphic, and isotopic correlations of 

paleoflood horizons. 

Outburst flooding of glacially impounded lakes in the 

northern Yukon Territory might provide a unique opportu52 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
nity to link previously disjointed stratigraphic records 

across the whole of eastern Beringia. Although speculative, possible correlations could be made for several 

paleoflood episodes linking (1) the westward-advancing 

Keewatin sector of the Laurentide ice sheet, (2) lacustrine 

sediments and erosional channels within and between 

Yukon lakes, (3) the terrace stratigraphy within the middle 

Porcupine River valley, (4) the Yukon Flats and its southdraining tributaries, (5) altered sedimentation regimes of 

the continental shelf, and (6) abyssal sedimentation in the 

Bering Sea. More detailed analysis of Porcupine River 

en 

a: 

w 

1-

w 

~ 

~ 

ui' 

0 

:::> 

1-

i= 

_J 

<( 

WEST 

400 

300 

200 

Fishhook 60 

Bend 

Basin 

40 Rapid 

River 

outburst flooding is in progress. Many questions remain, 

particularly those dealing with the number and timing of 

flood events and with changing channel characteristics. 

REFERENCES CITED 

Baker, V.R., 1973, Paleohydrology and sedimentology of Lake 

Missoula flooding in eastern Washington: Geological Society of America Special Paper 144, 79 p. 

Baker, V.R., and Nummendal, Dag, 1978, The Channeled Scabland: Washington, D.C., National Aeronautics and Space 

Administration Planetary Geology Program, 186 p. 

Canada 

border 

EAST 

Old Crow 

Basin 

DISTANCE, IN KILOMETERS 

Figure 3. Longitudinal profile of the Porcupine River (lower line) and the high-water mark (upper line) associated with the highest paleoflood. Location of channel cross section A-A (fig. 4) and points used to estimate 

maximum and minimum flow depths shown. 

c 

~ Q)C~ 

.'!:::: :::1 Q) .!:QQ) 

A s:~u A' 

en I High-water mark 296m a: 300 

1-

UJ 

UJ Minimum 260 m 0 ~j :E --~~ ~ Maximum 234m~~ ~ UJ- .......... j 0 

:::::> 0 

1- 200 "" i= 

«( 

_J ~-Porcupine River ~ 

0 100 200 300 400 500 

DISTANCE, IN METERS 

Figure 4. Cross-valley profile of the Porcupine River canyon at White Mountain Creek showing 

high-water mark and minimum and maximum depths of flood flows. No vertical exaggeration. 

Location of section shown on figures 1 and 2. 

Late Quaternary Paleofloods along the Porcupine River, Alaska 53 
Beget, J.E., 1986, Comment on "Outburst Floods from Glacial 

Lake Missoula" by Clarke, G.K.C., Mathews, W.H., and 

Pack, R.T. (letter to the editor): Quaternary Research, v. 25, 

p. 136-138. 

Bretz, J H., 1969, The Lake Missoula floods and the Channeled 

Scabland: American Journal of Science, v. 77, p. 505-543. 

Costa, I.E., 1983, Paleohydraulic reconstruction of flash flood 

peaks from boulder deposits in· the Colorado Front Range: 

Geological Society of America Bulletin, v. 94, p. 986-1004. 

Griggs, B.B., Kulm, L.D., Waters, A.C., and Fowler, G.A., 1970, 

Deep-sea gravel from Cascadia Channel: Journal of Geology, v. 78, p. 611-619. 

Malde, H.E., 1968, The cataStrophic late Pleistocene Bonneville 

flood in the Snake River Plain, Idaho: U.S. Geological 

Survey Professional Paper 596, 52 p. 

Oltman, R.E., Sternberg, H. O'R., Ames, F.C., and Davis, L.C., 

Jr., 1964, Amazon River investigations-Reconnaissance 

measurements of July 1963: U.S. Geological Survey Circular 486, 15 p. 

Thorson, R.M., and Dixon, E.J., 1983, Alluvial history of the 

Porcupine River, Alaska: Role of glacial-lake overflow from 

northwest Canada: Geological Society of America Bulletin, 

v. 94, p. 576-589. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1 026. 

54 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Late Cenozoic Sedimentary History Along 

Major Fault Zones, Alaska 

By Warren Yeend 

The presence of small, isolated, commonly faultbounded outcrops of clastic rocks of known or suspected 

Tertiary age throughout much of interior Alaska is puzzling. Were these rocks once part of a large blanket deposit 

covering an extensive area, which subsequently was faulted 

and eroded to such an extent that only small remnants are 

left of the original deposit? Or were they deposited only in 

small basins or trenches such as might occur along faults, 

and which could explain their common spatial association 

with major fault zones today? The age of the clastic rocks 

is rarely well documented, but plant fragments and pollen 

of Tertiary age are found in fine-grained beds associated 

with some clastic units. Many of the clastic rocks are goldbearing and, although of low unit value (less than $0.10/yd3 

at $400/oz), appear to have been a source of gold for a few 

Pleistocene and Holocene placers. Four specific locations 

of such clastic rocks (fig. 1) are discussed below, and 

one-the Tintina fault zone in the Circle quadrangle-is 

suggested as a modem depositional analog for the others. 

The Denali fault zone roughly parallels the Alaska 

Range in the Mount Hayes quadrangle (fig. 2). Tertiary 

sandstone and conglomerate form scattered outcrops south 

of the main strand of the Denali fault; these units are goldbearing and are referred to, at least in the Slate Creek area, 

as ~'Round Wash" (Yeend, 1981). The Tertiary clastic 

rocks are extensively fragmented at this locality. Many 

have beds that dip up to 60°, are bounded by steeply dipping faults with vertical offsets of more than 400 m, and in 

places are thrust beneath older rocks. The sandstones are 

light-colored and are interbedded with conglomerate, gray 

siltstone, shale, mudstone, sparse white rhyodacite ash, and 

thin coal layers. Abundant crossbedding, ripple marks, and 

pebble imbrication imply a high-energy alluvial environment; and the geometry of the deposits suggests that they 

probably formed as alluvial fans. A potassium-argon hornblende age of 5.4 Ma for interbedded white rhyodacite ash 

(Bond, 1976; Turner and others, 1980) and plant leaves of 

Sequoia from beds immediately above and below 

rhyodacitic ash indicate a Pliocene or latest Miocene age 

(J.A. Wolfe, U.S. Geological Survey, unpub. data cited in 

Turner and others, 1980) for at least some of these deposits. 

The conglomerates, which are stratigraphically below the 

sandstones, have clasts up to 30 em diameter of both local 

and foreign rock types. Thin beds of coal are present 

locally in intercalated sandstone layers. Plant fossils 

resembling Alnus evidens suggest a late Oligocene age 

(Stout, 1976). Minimum thickness of both the sandstone 

and conglomerates is on the order of 300 to 500 m (Nokleberg and others, 1982). 

Outcrops of Tertiary rocks associated with placer gold 

deposits are present in the vicinity of the Kaltag fault in the 

eastern part of the Tanana quadrangle (fig. 3). The Kaltag 

fault here has probably exerted a strong control on the 

present position of the Yukon River. Rocks of Tertiary and 

suspected Tertiary age crop out at several localities on both 

sides of the fault, although they may be even more prevalent beneath the alluvium-covered lowland next to the river. 

The high-level gravel associated with the fault is chiefly 

pebble to small-cobble size with some sand and silt. Clasts 

are subrounded to well rounded, semi-consolidated, and 

consist of local rock types. South of the Yukon River the 

gravel is in part auriferous (Mertie, 1937) and is believed 

to be of late Tertiary and perhaps early Quaternary age 

(Chapman and others, 1982). The rocks believed to be 

Tertiary are poorly to well consolidated, interbedded 

polymictic pebble conglomerate, boulder conglomerate, 

grit, and sandstone, with some siltstone, shale, and lignite. 

Plant fossils and pollen suggest an early Tertiary and 

ALASKA I 

\ 

\~ '"'? 

c 

'"'? 

km 

Figure 1. Index map of Alaska showing location of figures 

2-5. 

Late Cenozoic Sedimentary History Along Major Fault Zones, Alaska 55 
Miocene age, respectively (Chapman and others, 1982). 

Thickness of the rocks in the western part of the map area 

is possibly as much as 1,500 m (Paige, 1959). These isolated exposures of gently folded Tertiary rocks have definitely been offset by movement along the Kaltag fault. 

On the eastern side of the Seward Peninsula, the 

Kugruk fault zone generally trends north-south and is 10 to 

22 km wide (fig. 4). Only a few outcrops of Tertiary and 

0 10 

L 

) 

EXPLANATION ' ) 

(~ 

... Tertiary rocks 

:J: t c;· 

;;( ~ 

Fault ="\ .... ~,~ 

• • • Thrust fault--Sawteeth on OliO 

upper plate -< ) :I 

63° 

suspected Tertiary aged sediments have been identified 

within the fault zone, but these rocks probably are more 

prevalent beneath the Pleistocene and Holocene deposits 

that cover most of the fault zone. The Tertiary(?) rocks 

consist of both fine-grained clastics and conglomerate 

composed of carbonate clasts. The fme-grained clastics 

that occur in the north half of the fault zone are tan to lightgray siltstone, sandstone, and pebbly sandstone, friable to 

Figure 2. Outcrops of Tertiary rocks along the Denali fault zone, Mount Hayes quadrangle. 

EXPLANATION 

Upper Pleistocene sediment 

cover 

Lower Pleistocene and Tertiary 

rocks 

6lf' Tertiary rocks 

--Fault trace 

0 

~ 

0 

0 

~ 

10 KILOMETERS 

Figure 3. Outcrops of Tertiary and lower Pleistocene rocks along the Kaltag fault zone, Tanana quadrangle. 

56 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
well-indurated with calcite cement Beds are 5 to 60 em 

thick and commonly are graded; sedimentary structures 

include channels, small-scale ripples, and crossbeds. 

Siltstone layers are locally rich in carbonaceous plant 

debris, and coal seams are present. Clasts are derived from 

local rocks. Pollen of both Cretaceous and Tertiary (Eocene to early Miocene?) age has been identified from this 

unit (Till and others, 1986). The conglomerate is poorly 

sorted, with rounded and subrounded cobbles of carbonate 

rocks up to 72 em in diameter. Bedding is rarely discernible, but local sandy interbeds and crude bedding are present. No age-diagnostic fossils have been obtained, although conodonts from the clasts have been assigned an 

age range of Ordovician to Devonian. Deposition may 

have been as a series of small alluvial fans (Till and others, 

1986). Both of the clastic units are strongly deformed, with 

dips locally vertical. 

The Tintina fault zone is a topographic low about 10 

km wide that trends northwest-southeast across the Circle 

quadrangle (fig. 5). Rocks of suspected Tertiary age crop 

out rarely; however, it is believed that much of the fault 

trench is underlain by Tertiary gravel and conglomerate. 

Recent placer mining within the fault trench in the vicinity 

of Crooked Creek has exposed orange-colored, deeply 

decomposed, gold-bearing Tertiary(?) gravel. The gravel is 

truncated by the Hot Springs fault at the one locality where 

it is exposed at the fault contact. Elsewhere, Tertiary(?) 

rocks consist of both conglomerate and sandstone. The 

conglomerate is well to poorly consolidated, poorly stratified, and consists of well-rounded clasts up to 45 em in 

diameter. The sandstone is fine to coarse grained, locally 

argillaceous, and commonly has a "salt and pepper" appearance; its minimum thickness is 90 m. Poor to moderately well preserved plant material and impressions are 

present, including Metasequoia and broadleaf types. Lignite and coal are found in float associated with the conglomerate and sandstone. Beds dip up to 55 degrees 

(Foster and others, 1983). The age is uncertain but presumed to be Tertiary (Mertie, 1937). 

Tertiary(?), Pleistocene, and Holocene age alluvial 

fans have been deposited in the Tintina fault trench, in 

places obscured by overlying loess, alluvium, and undifferentiated silt (fig. 6), and this topographic and geologic 

environment may be a modern analog of conditions that 

have existed at some time along many other major fault 

zones in Alaska. The situation along this portion of the 

Tintina fault zone--that of a topographic low bounded by 

topographic high areas-is ideal for the generation of alluvial fan debris which eventually fills the fault trench. In 

time this topographic situation will be altered through 

changing fault activity, erosion will occur, and the area will 

no longer be suitable for receiving sediment. It then might 

resemble some of the older fault zones where the Tertiary 

fan detritus has been fragmented and only isolated exposures are apparent The Denali fault zone where it extends 

through the Mount Hayes quadrangle is near the divide of 

the Alaska Range, and is, obviously, not similar topographically to the Tintina fault zone in the Circle quadrangle. 

Therefore, it is no longer an environment of fan deposition, 

except very locally. The Kaltag fault zone in the Tanana 

EXPLANATION 

Tertiary rocks 

Kugruk fault-zone 

boundaries 

--- Fault--Dashed where 

concealed 

Figure 4. Outcrops of Tertiary rocks within the Kugruk fault 

zone, Seward Peninsula. 

Late Cenozoic Sedimentary History Along Major Fault Zones, Alaska 57 
quadrangle is better situated for receiving contemporary fan 

deposits, as the Yukon River flows in a topographic low 

that is bounded by highlands. The Kugruk fault zone does 

not seem to exert much control over topography where it 

crosses the Seward Peninsula. Drainages cut across the 

zone as well as run parallel to it, and it is not receiving 

much sediment except very locally. 

~ 

~ 

G7Z_al 

~ 

-

[_ _j 

----

Holocene and Pleistocene alluvium, 

undifferentiated 

Holocene and Pleistocene alluvial 

fan deposits 

Tertiary(?) rocks 

Pre-Tertiary bedrock 

Contact--Dashed where inferred 

Fault--Dashed where inferred or 

concealed 

REFERENCES CITED 

Bond, G.C., 1976, Geology of the Rainbow Mountains-Gulkana 

Glacier area, eastern Alaska Range, with emphasis on upper 

Paleozoic strata: Alaska Division of Geological and Geophysical Surveys Geologic Report 45, 47 p. 

Chapman, R.M., Yeend, Warren, Brosge, W.P., and Reiser, H.N., 

1982, Reconnaissance geologic map of the Tanana quad1450 

10 KILOMETERS 

Figure 5. Simplified geologic map of a part of the Tintina fault zone, Circle quadrangle (modified from Foster and others, 

1983). A-A', line of cross section in figure 6. 

A 

Mastodon 

Mountain 

- / 

- Quartzite and schist 

.. - _.-

0 5 ~----·_j 

KILOMETERS 

/ / 

/ 

/ 

/ 

, / 

TINTINA FAULT ZONE 

Crazy 

Mountains 

Figure 6. Cross section near center of Circle quadrangle across Tintina fault zone. location on figure 5. 

58 late Cenozoic History of the Interior Basins of Alaska and the Yukon 

A' 
rangle, Alaska: U.S. Geological Survey Open-File Report 

82-734. 

Foster, H.L., Laird, Jo, Keith, T.E.C., Cushing, G.W., and Menzie, W.D., 1983, Preliminary geologic map of the Circle 

quadrangle, Alaska: U.S. Geological Survey Open-File 

Report 83-170-A, scale 1:250,000. 

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

Geological Survey Bulletin 872, 276 p. 

Nokleberg, W.J., and others, 1982, Geologic map of the southern 

Mount Hayes quadrangle, Alaska: U.S. Geological Survey 

Open-File Report 82-52. 

Paige, R.A., 1959, Tertiary geology of the Cheyenne Creek area, 

Alaska: Seattle, University of Washington, M.S. thesis, 66 p. 

Stout, J.H., 1976, Geology of the Eureka Creek area, east-central 

Alaska Range: Alaska Division of Geological and Geophysical Surveys Geologic Report 46, 32 p. 

Till, A.B., Dumoulin, J.A., Gamble, B.M., Kaufman, D.S., and 

Carroll, P.l., 1986, Preliminary geologic map and fossil data, 

Solomon, Bendeleben, and southern Kotzebue quadrangles, 

Seward Peninsula, Alaska: U.S. Geological Survey OpenFile Report 86-276, scale 1:250,000. 

Turner, D.L., Triplehorn, D.M., Naeser, C.W., and Wolfe, J.A., 

1980, Radiometric dating of ash partings in Alaskan coal 

beds and upper Tertiary paleobotanical stages: Geology, v. 

8, p. 92-96. 

Yeend, Warren, 1981, Placer gold deposits, Mount Hayes quadrangle, Alaska, in Silberman, Miles, and others, eds., Proceedings of the symposium of mineral deposits of the Pacific 

Northwest: U.S. Geological Survey Open-File Report 

81-355, p. 74-83. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1 026. 

Late Cenozoic Sedimentary History Along Major Fault Zones, Alaska 59 
Paleoglaciology of the Selwyn Lobe of the 

Cordilleran Ice Sheet and Quaternary Stratigraphy 

of the East-Central Yukon 

By Lionel E. Jackson, Jr. 

This paper reports the results of surficial geologic 

mapping and investigation of the Quaternary stratigraphy in 

east-central Yukon carried out between 1980 and 1986 by 

Jackson (1982, 1986a, 1986b, 1987a, 1987b), Jackson and 

others (1984, 1985), and Duk-Rodkin and others (1986), 

and by previous workers in the same or contiguous areas 

(Campbell, 1967; Klassen, 1978, 1982; Klassen and Morison, 1981; Dyke, 1981). The region discussed includes an 

area which was covered by the Selwyn lobe of the Cordilleran ice sheet during the McConnell glaciation (Hughes 

and others, 1969). The morphology, modes of flow, and 

deglaciation of the ice sheet are discussed along with regional Quaternary stratigraphy and chronology. 

Setting 

Figure 1 shows the context of the Selwyn lobe within 

the limits of the McConnell glaciation and older glaciations 

in southern Yukon Territory, and figure 2 outlines the 

portion of the region formerly covered by the Selwyn lobe 

for which data exist to permit its detailed reconstruction. 

This region includes the Glenlyon Range, the MacMillan 

River basin sector of the Yukon Plateau, parts of the 

Tintina Trench and Pelly Mountains, and the Selous Mountains, which are part of the Selwyn Mountains. 

The surface of the Yukon Plateau within the MacMillan River basin is incised by two sets of valleys. Broad 

southwest-trending valleys were incised during preglacial 

times, and are occupied predominantly by underfit streams. 

Narrower northwest-trending valleys were created by glacial and glaciofluvial erosion during the Quaternary and 

contain major streams. The result is a pattern of anastomosing valleys surrounding island-like table lands that are 

surmounted by small mountain ranges. Valley bottoms 

range in elevation from 640 to 760 m, the plateau surface 

from 1,070 to 1,370 m. Mountain summits may have an 

additional 600 m of relief with maximum elevations up to 

about 2,130 m. 

Evidence of past glaciation is ubiquitous. Plateau 

areas and the sides of larger valleys are marked by whaleback ridges and crag-and-tails which allow past ice-flow 

directions to be easily determined. Valley bottoms contain 

complexes of glaciofluvial deposits or thick fills of glaciolacustrine sediments. The gravelly floors of channels that 

were walled by ice form flights of terraces that commonly 

extend from mountain summits to valley bottoms. 

The valleys are extensively mantled by boreal forest 

whereas much of the plateau surfaces lie above tree line 

and are vegetated by thick brush. Alpine areas are vegetated by tundra or are barren. The entire region is within 

the zone of discontinuous permafrost. 

Paleoglaciology of the Selwyn lobe 

The Selwyn lobe is the name given by Hughes and 

others (1969) to a sector of the Cordilleran ice sheet that 

flowed west to northwest across 5 degrees of longitude and 

between latitudes 61 o and 64° N. in east to east-central 

Yukon Territory (fig. 1). It was separated from the Cassiar 

lobe on the south by the Pelly Mountains. The two lobes 

interacted near their termini. The Selwyn lobe shared 

divides with glaciers flowing east and south into the Mackenzie River Valley. The largest of these flowed into the 

Liard River basin and is named the Liard lobe. 

During the McConnell glaciation, isolated mountain 

summits stood above the Selwyn lobe as nunataks 

(Campbell, 1967; Duk-Rodkin and others, 1986). Glacial 

deposits surrounding these former nunataks have a fresh 

morphology characteristic of deposits of McConnell age 

elsewhere in the territory, in contrast to the subdued morphology typical of deposits of Reid and older glaciations 

(Bostock, 1966; Hughes and others, 1969). The maximum 

McConnell terminus (fig. 2) is well defined by moraines 

and incised ice-marginal channels. 

Duk-Rodkin and others (1986) constructed a generalized profile of the distal part of the Selwyn lobe (fig. 3), 

based upon geomorphic features indicative of ice limits 

around former nunataks. Profile slopes were 0°30' over the 

outer 50 km, 0°19' over the next 53 km, and 0°03' farther 

east. The profile of the Selwyn lobe was flatter than profiles of the contemporary Greenland and Antarctic ice 

sheets (Paterson, 1981, p. 153--167). The best numerical 

approximation to the measured profile is the curvilinear 

profile of a valley glacier modeled by Shilling and Hollin 

(1981) after Nye (1952a, 1952b). This finding is not surprising, because flow in the Selwyn lobe was similar to 

flow in a valley glacier; shear stress occurred not only 

along the sole of the ice sheet but along the sides of high60 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
relief roughness elements (valley and mountain sides). 

Flow within the ice sheet, based upon ice flow indicators 

such as whalebacks and crag-and-tails, occurred as anastomosing ice streams that followed major east-west-trending 

valleys such as the Tintina trench and the MacMillan River 

valley (fig. 2). Ice flow was entirely channeled by underlying topography rather than predominantly independent of 

it, as is largely the case in the contemporary ice sheets of 

Greenland (Flint, 1971, p. 51-54) and Antarctica (Denton 

and others, 1971). 

Deglaciation of the Selwyn lobe 

The Selwyn lobe disappeared rapidly at the close of the 

McConnell glaciation through a combination of downI 

I 

J 

i 

i 

I 

I 

i 

DAWSON 

• 

.. -.: 

\ .., 

wasting and stagnation. Many cirques in the Selwyn and 

Pelly Mountains have ice-stagnation landforms on their 

floors which are continuous with similar features in adjacent valleys. It can be concluded from these relationships 

that ice stagnated in these cirques during or before stagnation in adjacent valleys. These stagnation features occur up 

to altitudes of 1,830 m. Consequently, it appears that early 

in the deglaciation of the Selwyn lobe, the equilibrium line 

rose significantly above an altitude of 1,830 m and remained above it until the present day (Jackson, 1986b). 

This rise in the equilibrium line above the ice sheet resulted 

in the wholesale starvation of the Selwyn lobe. The resulting thinning of the ice sheet is documented along many 

valley sides by flights of terraces that once were the floors 

of ice-walled channels. Ice in valleys oriented transverse to 

Unmapped 

\28 0 0 

L 64 

!-', r 

I ' '-- / ' 

' ' 

\-? 

\< 

\ 

I 

I • WHITEHORSE 

EXPLANATION 

Pre-Reid glaciation , - ' Mountain ice cap, .,<....-~,... I complex ice-flow directions 

~ Reid glaciation Generalized divide in the +++ Cordilleran ice sheet 

~ McConnell glaciation 

__...... Generalized ice-flow direction 

Figure 1. Glacial limits and ice divides in southern Yukon Territory. 

Paleoglaciology of the Cordilleran Ice Sheet and Quaternary Stratigraphy of the Yukon 61 
the general direction of glacial flow stagnated between ice 

streams and gave rise to extensive complexes of stagnation 

landforms. 

A succession of progressively lower and younger lakes 

was ponded within the Pelly Mountains and mountain 

ranges to the north during the period of downwasting of the 

Selwyn and Cassiar lobes (figs. 4A and 4B). 

Quaternary stratigraphy and chronology 

The deposition of Quaternary sediments within the 

region formerly occupied by the Selwyn lobe was controlled chiefly by topography. Lodgement and meltout tills 

are the dominant sediments on plateau remnants; ice-stagnation gravels are extensive in valleys oriented transverse 

to former ice flow, and glaciolacustrine sediments occur in 

valleys which were fortuitously blocked by ice during 

138' 

deglaciation. Only the Tay and Pelly River valleys (Tintina 

Trench) were sufficiently wide and deep enough to accumulate and preserve sediments representing more than one 

glacial interval. Figure 5 summarizes the stratigraphy of 

the most informative sections within the region covered by 

the Selwyn lobe. Of these, sections along the Pelly River 

and Lapie Canyon (14686 S-1 and 7686 S-2, respectively, 

on fig. 4A), provide the most complete record of depositional and erosional events of two glacial intervals. The 

age of the lowest till (PM) is unknown. The recession 

following deposition of the lowest till was marked by glaciolacustrine sedimentation in both the Tay River and Pelly 

River valleys (sections 23685 C-3 and 14686 S-1, fig. 4B). 

In the Pelly River valley, glaciolacustrine sediments are 

unconformably overlain by horizontally stratified gravel 

deposited during a subsequent period of fluvial aggradation 

and prior to the McConnell glaciation. Gravel beds in an 

EXPLANATION 

Limit ot McConnell glaciation 

Nunatak above McConnell glaciation 

Projected McConnell glaciation limit 

--

- Limit of Reid glaciation 

Nunatak above Reid glaciation 

Direction of ice flow 

Figure 2. Generalized glacial limits, Carmacks (11S 1), Glen lyon (1 OS L), and lay River (1 OS K) map areas, Yukon Territory. 

w 

1500-t 

1QQQ I 

500l 

Glenlyon 105 L map area 

50 

EXPLANATION 

~ Topographic profile 

100 

km 

Tay River 105 K map area e It 

·····~:~~~ _ _J2000 

150 200 

Surface of the Cordilleran ice sheet during McConnell glaciation -- Dotted where projected 

Positions of ice marginal features of McConnell glaciation 

Figure 3. Generalized topographic profile oriented east-west across area of figure 2 showing reconstructed upper limit 

of the McConnell glaciation (from Duk-Rodkin and others, 1986). Profile constructed by projecting eight separate eastwest profiles onto single plane. Vertical exaggeration x 6. 

62 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
analogous stratigraphic position below McConnell-age till 

at the Ketza site (fig. 4A) yielded bone fragments from 

Bison sp. (perhaps B. priscus) and a cheek tooth from 

Mammuthus primigenius (identified by C.R. Harington, 

Canada National Museum of Natural Sciences, written 

commun., 1986). A radiocarbon date on a B. priscus radius 

fragment from this site yielded an age of 26.35±0.28 ka 

(T0-393). This provides a maximum age for the overlying 

McConnell till (M in fig. 5). 

The succession above the McConnell-age till is essentially a repeat of stratigraphy seen above the lower till: 

glaciolacustrine sedimentation in the Pelly and Tay River 

valleys and massive to horizontally bedded gravelly outwash in adjacent areas. Radiocarbon dates from the continental divide in the Selwyn Mountains indicate that ice had 

disappeared from the divide area before about 9 ka 

(MacDonald, 1983; Jonasson and others, 1983). 

134° 133° 0 

62°45'-t--r='-------=~-_L__ ___________ 1--I- 31 

A 

~· 

Nisutlin L. 

o,_-=-=c==w===--=-~50~-=---=~-==1~00 km 

Holocene events 

As has been demonstrated elsewhere in glaciated regions of the Cordillera, geomorphic events during the 

Holocene have reflected the readjustment of slopes and 

streams from a glacial to a nonglacial regime (Ryder, 

1971a, 1971b; Church and Ryder, 1972; Jackson and others, 1982; Ritter and Ten Brink, 1986). Alluvial fans built 

predominantly of debris-flow diamictons are ubiquitous 

Holocene landforms. These were graded to braided flood 

plains. As glacially deposited sediments were progressively eroded from stream basins, sediment loads decreased 

and debris-flow activity waned. Paraglacial fans became 

inactive and were incised from head to toe as braided 

stream courses were incised. Incision of outwash plains in 

the Pelly River valley began before 8 ka (Jackson, unpub. 

data). Near the town of Ross River, the Pelly River had 

incised to 14 m above its present flood plain, by 5.92±0.7 

ka (T0-196). The White River Ash Bed (Pewe, 1975, p. 

79-81), which formed about 1.4 ka, is within the overbank 

sediment of the present floodplain. At some point between 

about 6 and 1 ka, the Pelly River changed from a braided 

planform to a meandering one. This change in channel 

planform in the post middle-Holocene has been documented elsewhere in the Cordillera (Jackson and others, 

1982). 

The initiation and spread of blanket bog throughout the 

region is second only to paraglacial sedimentation in its 

modification of the land surface during the Holocene. Bog 

bottom dates from Selwyn Mountains indicate that blanketbog expansion was well under way by 8.8 ka (Jackson, 

1987b). 

Figure 4. Distribution and surface elevations of glaciolacustrine sediments deposited in glacial lakes during deglaciation 

of Selwyn and Cassiar lobes in areas adjacent to Pelly 

Mountains. A, Distribution of sediments (patterned areas). 

Heavy dashed line and numbered localities show plane of 

stratigraphic section in figure 5. Single letters designate glaciolacustrine surface elevations shown in 8. 8, Surface elevations of glaciolacustrine sediments shown in A (letters) 

projected onto north-south plane at longitude 133° W. 

Dashed line separates lake basins under influence of Selwyn 

lobe from those under influence of Cassiar lobe. 

CASSIAR LOBE 

PELLY MOUNTAINS 

I 

South 

1500 

1000 

1240 

cA---

800 820 

BF--

1370 

0--

1250 

1100 

I 

N--

850 

1040 HSELWYN LOBE 

730 

1430 p -

North 

1500 

910 0--__::__:__ __ 

1000 

a------------------

8 500 t---------------,------------...,-------------,-----_j 500 

100 150 km 

Paleoglaciology of the Cordilleran Ice Sheet and Quaternary Stratigraphy of the Yukon 63 
0'\ 

""' 

r-

;. 

Q 

:I 

2 

C> 

;;· 

:::1: 

Iii' 

6' 

-< 

C> 

-l 

5" 

!i 

c;· 

.. 

= el 

;· 

(II 

C> 

-i!:: 

el 

£r 

i 

~ I'D 

-< c 

S'" 

:I 

EXPLANATION 

(modified from Eyles and Miall, 1984) 

Diamictons 

Dmm .... Matrix supported and massive 

Dms ...... Matrix supported and stratified 

Gravels 

Gm ....... Massive 

Gt. ........ Trough crossbedded 

Gmc ...... Massive with meltout structures 

Gg ......... Normally graded 

Sand 

Sm ......... Massive 

Sh .......... Horizontally bedded, laminated 

Sr .......... Trough crossbedded 

Sp .......... Planar crossbedded 

Sd .......... Soft sediment deformation 

St. ......... Trough crossbedded 

Sdd ........ Sheared with dropstones 

Silt and clay 

Fm ........ Massive 

Fs .......... Sheared 

Fsd ........ Sheared with drops tones 

Pd ......... With soft sediment deformation 

structures 

Fh .......... Horizontally bedded, laminated 

Fld ......... Laminated with dropstones 

\\\\ 

X u v u u v 

~ 

k i,"; oJ 

CJ 

CJ 

Shear planes 

Conjugate faults 

Soft sediment deformation structures 

Diamicton 

Gravel 

Sand 

Silt and clay 

PELLY RIVER 

14686 S-1 

METERS fvm"'NJ,.,I 

TAY RIVER 50 

23685 C-3 PELL Y RIVER 

28685 S-5 ~ Sr 

Gm 45 Sd Sr 

~~~h • 

Sp,Sh Sd 

Gm 

Gm r ; AO§js~~d 40 i . OH~ LAPIE CANYON 

Gm ""' !.?h,Sd ~ 3 Sh 7686 S-2 5mm 

Sh,Sd 

6-:JDmm 

g~m 35 I .;1 I '~I Gm 

Sd 

LAPIE CANYON 

19686 S-1 

Dmm j ~ ~VI 6 Dmm Fs M 6 Oms ... ' 

Fsd I ''''I ~30 6 A , •••• · g~," Gm 

Sh 

Obscured I ] ,3 Gm ~ Sm 

25 °J Sdd 

Gmc 

Sm Sd 

\ J Gm 

Sh White River Ash Bed 20 i . -~ \ 

Contacts : I · · : J Sp,Sr I ~·-~ Gg 

-t-- Gradational 

Sh 

Abrupt 15 Sd Fh,Dmm,Sr 

,....,_,..._, Erosional ~~ 

\.1""\.f'\ Loaded 6 

66 

10 6~~ Dmm I PM -:-t.t Dmm 

PM :~~ 661 

.61 5 -1 6 I 6/lj 

~ Obscured 

6~ 6Aj 

61 0 I A I 

Fld 

Sd 

Sh 

Sr Gm Sp 

Sp Gm 

Gm 

Sp Gm 

Sp Gm 

Dmm 

Obscured 

Figure 5. Lithostratigraphic cross section from Tay River valley to Lapie River valley (line of section shown in fig. 4A). Section constructed using top of till of McConnell 

glaciation (M) as datum. PM denotes till that predates pre-McConnell glaciation. 
REFERENCES CITED 

Bostock, H.S., 1966, Notes on glaciation in central Yukon Territory: Geological Survey of Canada Paper 65-56, 18 p. 

Campbell, R.B., 1967, Reconnaissance geology of Glenlyon map 

area, Yukon Territory: Geological Survey of Canada 

Memoir 352, 92 p. 

Church. M., and Ryder, J.M., 1972, Paraglacial sedimentation: A 

consideration of fluvial processes conditioned by glaciation: 

Geological Society of America Bulletin, v. 83, p. 3072-3095. 

Denton, G.H., Armstrong, R.L., and Stuiver, M., 1971, The late 

Cenozoic glacial history of Antarctica, in Turekian, K.K., 

ed., The late Cenozoic glacial ages: New Haven, Yale 

University Press, p. 267-306. 

Duk-Rodkin, A., Jackson, L.E., Jr., and Rodkin, 0., 1986, A 

composite profile of the Cordilleran ice sheet during McConnell Glaciation, Glenlyon and Tay River map areas, Yukon 

Territory: Geological Survey of Canada Paper 86-1B, Current Research, Part B, p. 257-262. 

Dyke, A.S., 1981, Surficial geology of Francis Lake map area 

(105 H): Geological Survey of Canada Open File Report 898, 

scale 1:125,000. 

Eyles, N., and Miall, A.D., 1984, in Walker, R.G., ed., Facies 

models, Geoscience Canada reprint series 1: Toronto, Geological Association of Canada, Glacial facies, p. 15-38. 

Flint, R.F., 1971, Glacial and Quaternary geology: New York, 

Wiley, 892 p. 

Hughes, O.L., Campbell, R.B., Muller, I.E., and Wheeler, J.O., 

1969, Glacial limits and flow patterns, Yukon Territory south 

of 65 degrees north latitude: Geological Survey of Canada 

Paper 68-34, 9 p. 

Jackson, L.E., Jr., 1982, Terrain conditions, Nahanni (105 1): 

Geological Survey of Canada Open File Report 886, scale 

1:125,000. 

---1986a, Terrain inventory Finlayson Lake map area (105 

G), Yukon Territory: Geological Survey of Canada Open 

File Report 1379, scale 1:125,000. 

---1986b, Terrain inventory, Tay River map area (105 K): 

Geological Survey of Canada Open File Report 1380, scale 

1:125,000. 

---1987a, Terrain inventory, Quiet Lake map area (105 F): 

Geological Survey of Canada Open File Report 1536, scale 

1:125,000. 

---1987b, Terrain inventory and Quaternary history of the 

Nahanni map area, Yukon and Northwest Territories: Geological Survey of Canada Paper 86-18, 23 p. 

Jackson, L.E., Jr., MacDonald, G.M., Foscolos, A.E., and Clarke, 

A.H., 1985, An occurrence of pre-McConnell nonglacial 

sediments, Selwyn Mountains, Northwest Territories: Geological Survey of Canada Paper 85-1B Current Research, 

Part B, p. 169-175. 

Jackson, L.E., Jr., MacDonald, G.M., and Wilson, M.C., 1982, 

Paraglacial origin for terraced river sediments in Bow Valley, Alberta: Canadian Journal of Earth Sciences, v. 19, p. 

2219-2231. 

Jackson, L.E., Jr., Morison, S.R., McKenna, K., and Duk, A., 

1984, Terrain inventory, Sheldon Lake map area (105 J): 

Geological Survey of Canada Open File Report 1033. 

Jonasson, I.R., Jackson, L.E., and Sangster, D.F., 1983, A Holocene zinc orebody formed by the supergene replacement of 

mosses: Journal of Geochemical Exploration, v. 18, p. 

189-194. 

Klassen, R.W., 1978, A unique stratigraphic record of late Tertiary-Quaternary events in southeastern Yukon: Canadian 

Journal of Earth Sciences, v. 15, p. 1884-1886. 

--1982, Surficial geology Wolf Lake map area (105 A): 

Geological Survey of Canada Map 14-1982, scale 1:250,000. 

Klassen, R.W., and Morison, S.R., 1981, Surficial geology Watson Lake (105 B): Geological Survey of Canada Map 

21-1981. 

MacDonald, G.M., 1983, Holocene vegetation history of the 

upper Natla River area, Northwest Territories, Canada: 

Arctic and Alpine Research. v. 15, p. 169-180. 

Nye, J.F., 1952a, The mechanics of glacier flow: Journal of 

Glaciology, v. 2, p. 103-107. 

---1952b, A comparison between the theoretical and the 

measured long profile of the Unteraar Glacier: Journal of 

Glaciology, v. 2, p. 103-107. 

Paterson, W.S.B., 1981, The physics of glaciers (2d ed.): New 

York, Pergamon Press, 380 p. 

Pewe, T.L., 1975, Quaternary geology of Alaska: U.S. Geological 

Survey Professional Paper 835, 145 p. 

Ritter, D.F., and Ten Brink, N.W., 1986, Alluvial fan development and the glacial-glaciofluvial cycle, Nenana Valley, 

Alaska: Journal of Geology, v. 94, p. 613-625. 

Ryder, J.M., 1971a, The stratigraphy and morphology of paraglacial alluvial fans in south central British Columbia: Canadian Journal of Earth Sciences, v. 8, p 279-298. 

---1971b, Some aspects of morphology of paraglacial alluvial 

fans in south central British Columbia: Canadian Journal of 

Earth Sciences, v. 8, p. 1252-1264. 

Shilling, D.H., and Hollin, J.T., 1981, Numerical reconstructions 

of valley glaciers and small ice caps, in Denton, G.H., and 

Hughes, T.J., eds., The last great ice sheets: New York, 

Wiley-Interscience, p. 207-220. 

Geological Survey of Canada Contribution 17487 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Paleoglaciology of the Cordilleran Ice Sheet and Quaternary Stratigraphy of the Yukon 65 
Late Cenozoic Stratigraphy and Sedimentology 

of Gravelly Deposits in Central and Southern Yukon 

By Stephen R. Morison 

Placer deposit studies in west-central and southern 

Yukon have shown that discrete periods of sedimentation 

of gold-bearing gravel occurred in five generalized settings 

(table 1). These settings occurred in both unglaciated terrain and in glaciated terrain during interglacial and glacial 

intervals, and thus form important components of the late 

Cenozoic history of the Yukon. This paper represents a 

first attempt at relating types of fluvial gravelly sedimentation to the late Cenozoic history of the Yukon. It therefore 

is very general and forms only a working framework. 

Pliocene to early Pleistocene 

Pliocene to lower Pleistocene gravelly sequences are 

preserved as high-level terraces in unglaciated terrain and 

areas within the limits of pre-Reid glaciations. Examples 

include terraces proximal to the upper limit of glaciation in 

the Clear Creek drainage basin and the high-level terraces 

in the Klondike placer district (fig. 1). 

In the Clear Creek drainage basin, preglacial fluvial 

gravel is found stratigraphically below till units that were 

Table 1. Stratigraphy and general characteristics of placer gold deposits in Canada (from Morison, in press) 

TERTIARY QUATERNARY 

AGE 

I PUOCENE PLEISTOCENE HOLOCENE 

ENVIRONMENT Buried alluvial Preglacial or Interglacial valley fill Glacial benches of Valley bottom alluvial 

AND GEOMORPffiC sediments in benches nmglacial buried alluvial sediments; proglacial and ice plains and terraces; 

LOCATION OF above valley floors alluvial sediments in alluvial terraces cmtact deposits; colluvium and slope 

PLACERS benches above valley tenninal valley deposits 

floors; valley fill moraines and alpine 

alluvial sediments; drift 

alluvial terraces 

GENERAL Mature sediments; Locally derived gravel Mixed gravel Regionally derived Mixed gravel 

SEDIMENT well-sorted alluvium lithology; moderately lithology; moderately gravel lithology; lithology; moderately 

CHARACfERISTICS with a diverse to well sorted alluvimn to well sorted variable sorting and to well sorted 

assemblage of which is crudely to alluvium, crudely to stratification depending alluvium, crudely to 

sediment types distinctly stratified distinctly stratified upon type of glacial distinctly stratified; 

drift poorly sorted, massive 

slope deposits 

GOLD Greater concentration Discrete concentrations Discrete cmcentrations Dispersed throughout Discrete cmcentrations 

DISTRIBUTION with depth throughout to pay throughout to pay throughout to pay 

streaks at base of streaks at base of streaks at base of 

alluvium alluvium alluvium; pay streaks 

follow slope morphology 

MJNING PROBLEMS Thick overburden Thick overburden; Variable grade Low grade and larger Variable grade and 

variable grade volmne of material small volume of 

auriferous sediment 

EXAMPLES "White Channel Preglacial fluvial Interglacial stream Glaciofluvial gravel in Valley bottom creek 

Gravel" of the gravels, Oear Creek gravels in Allin and Oear Creek drainage and gulch placers in 

Klondike area Yukon drainage basin and Cariboo areas, British basin, Yukon Territory Oear Creek drainage 

Territory unglaciated terrain and Columbia basin, Yukon Territory 

Sixtymile River area, 

Yukon Territory 

66 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
deposited prior to the Reid glaciation (fig. 2). The stratigraphy and sedimentology of this sequence suggests that 

gold-bearing fluvial gravel was buried by melt-out till, 

possibly basal, which was subsequently covered by redeposited ice-marginal sediments (Morison, 1985a). Glacial 

sediments in this sequence are not auriferous, which demI 

onstrates minimal subglacial erosion of underlying fluvial 

gravel and supports deposition through meltout of the 

overlying drift. 

High-level terraces in the Klondike placer area are 

composed of White Channel placer gravel deposits that are 

overlain by non-auriferous sequences of either the KionEXPLANATION 

0 McConnell glacial deposits 

~ Reid glacial deposits 

w~~ 'Y1 Pre-Reid glacial deposits 

Hungry Creek or Buckland glacial deposits 

• lcefields , glaciers 

D Undifferentiated nonglacial deposits 

Cordilleran ice sheet 

umit of McConnell glaciation 

!late Wisconsin) 

Limit of Reid glaciation 

llllinoian7) 

Limit of pre-Reid glaciationlsl 

Laurentide ice sheet 

Limit of Hungry Creek lor Buckland) 

glaciation II ate Wisconsin 7) 

and also the maximum Laurentide 

limit 

General direction of ice movement 

* Major placer mining areas 

1 Klondike 

2 Sixtymile 

3 Fortymile 

4 Clear Creek 

5 Mayo 

6 Big Creek 

7 Burwash 

8 Livingston Creek 

0 

KILOMETERS 

100 

Figure 1. Glacial limits in Yukon Territory (modified from Hughes and others, 1983, and Tarnocai, 1987). 

Late Cenozoic Stratigraphy and Sedimentology in Central and Southern Yukon 67 
dike Gravel (McConnell, 1907), which is glaciofluvial in 

origin (Hughes and others, 1972), or younger Pleistocene 

fluvial gravel such as the iron-stained sequence in the lower 

part of the Hunker Creek drainage basin (Dufresne and Morison, 1985; Morison, 1985b). White Channel alluvium is 

characterized by 14 lithofacies types which range from 

laminated silt and clay to massive and disorganized boulder 

gravel (Morison, 1985b). Cryogenic features such as icewedge casts are found in the upper part of the White 

Channel sequence and indicate climatic cooling, which may 

coincide with the Pliocene-Pleistocene boundary. White 

Channel alluvium was deposited in a braided river environment (fig. 3) that included the following main components 

(Morison and Hein, 1987): (1) a main valley proximal 

setting which was dominated by high discharge and flood 

channels in a crudely braided environment; (2) main valley 

medial to distal settings which formed well-defined braided 

sequences of channels and low-relief bars; and (3) debris 

flows from valley walls in association with either tributary 

alluvial fan sedimentation or as independent gravity flows. 

Pleistocene 

Gravel deposits in unglaciated terrain 

In unglaciated terrain, placer gravel deposits are found 

as valley-bottom fill and low to high terraces. An example 

is the Miller Creek area in the Sixtyrnile River placer area 

(fig. 1), where four distinct stages in drainage-basin evolution have been identified (Hughes, 1986; Hughes and others, 1987). These stages (fig. 4A-D) consist of: (1) 

downcutting and tributary-valley widening; (2) main valley 

braidplain sedimentation and alluvial fan aggradation, 

which was completed before 40 ka (GSC-3934 and 

GSC-4032); (3) debris-flow sedimentation, which began 

approximately 26 ka (Beta-13870), and a change in the 

main valley channel pattern from braided to meandering; 

0 

2 

3 

4 

Ul 

a: 5 w 

1-

w 

:::!: 

~ 6 

::c 

t 

w 7 a 

8 

9 

10 

11 

12 

3 

Quartz-chloritic schist 

Unit 1--Diamicton which has a silt-to-sand matrix and contains 

both local bedrock fragments and glacial erratics. 

Bottom contact is sharp and follows underlying slope 

morphology. Unit is interpreted as colluvium. 

Unit 2--Stratified sequence of massive diamicton and sorted fine 

clastic sediment. Diamicton has a matrix texture which 

ranges from silty sand to fine sand and contains 

subangular to subrounded clasts. Fine clastic interbeds 

range from clay to fine sand, and lower contact for this 

unit is gradational. Sequence is interpreted as a series of 

resedimented melt-out till units. 

Unit 3--Diamicton which has a matrix texture of clayey silt and 

contains subrounded to rounded clasts. Sedimentary 

structures include intrabeds and lenses of sorted sand 

and silt. Bottom contact is characterized by an irregular 

bed of laminated silt and fine sand. Unit is interpreted as 

a melt-out till. 

Unit 4--Preglacial fluvial gravel which is auriferous. Gravel is 

clast supported, matrix filled, and trough cross-stratified. 

Occasional disorganized openwork gravelly beds and 

cross-stratified sandy beds are also present. Gravels 

were deposited in a multichanneled river environment. 

Figure 2. Stratigraphy and sedimentology of buried placer deposit at mouth of Left Clear Creek, Yukon. Sediment 

texture shown diagrammatically by relative horizontal extent of units. 

68 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
(4) loess and colluvial sedimentation, and establishment of 

the modem Sixtymile River flood plain. Although it is 

difficult to estimate the age of incision and the development of gravelly terraces, major changes in stream channel 

patterns are thought to indicate rejuvenated downcutting 

through gravelly deposits. 

Interglacial gravel deposits 

In glaciated terrain, drainage basins that were not 

eroded by subsequent Cordilleran glacial advances contain 

placer gold deposits that were concentrated through resedimentation by interglacial streams. Examples are not well 

documented; however, in the Livingstone Creek placer area 

(fig. 1), gold-bearing gravelly alluvium is found below drift 

of the McConnell glaciation (Bostock and Lees, 1960). 

Also, valley-bottom gravelly fill was deposited and preserved in areas of pre-Reid glaciation, such as the Big 

Creek drainage basin (placer area 6, fig. 1), which were not 

occupied by ice of the subsequent Reid and McConnell 

glaciations. 

Significant stream entrenchment occurred in the Klondike placer area (fig. 1) between the Old (pre-Reid?) and 

Intermediate (Reid?) glaciations of the southern Ogilvie 

Range (Hughes and others, 1972, 1983; and Vernon and 

Hughes, 1966). Following deposition of drift from the Old 

FLOW DIRECTION 

~ 

EXPLANATION 

Muddy facies 

Sandy facies 

Gravelly facies 

Crude stratification 

Distinct stratification 

Trough cross-stratification 

Planar cross-stratification 

~ 

~ 

OJ:] 

~ 

1-1 

~-:2 

~ 

Bar foreset margin 

Diffuse sheet margin 

Gravelly dunes 

Sandy dunes 

Abandoned bar form 

Swamp 

Debris flow 

Figure 3. Interpreted paleoenvironmental setting for White Channel deposit, Klondike area, Yukon, showing fully developed gravelly braided river flanked by alluvial fans and debris flows from colluvial slopes. 

late Cenozoic Stratigraphy and Sedimentology in Central and Southern Yukon 69 
EXPLANATION 

~ Diffuse gravel sheet 

[@] Bar with slipface 

5:§] Sandy dunes 

I ::::J) I Debris flows 

Abandoned bar 

Swamp 

~ Terrace 

Figure 4. Sketches showing Pleistocene evolution of unglaciated terrain. 

A, Fluvial environments of Sixtymile 

River and Miller Creek prior to fan 

aggradation. Note initiation of tributary valley widening and braidplain 

environment of main Sixtymile River 

valley. Stream flow is left to right. 8, 

Aggradation of Miller Creek alluvial 

fan, which was complete before 40 

ka. Note erosion of distal fan sediments by Sixtymile River. C, Debrisflow sedimentation and terrace development 26 ka. Miller Creek is being 

diverted to southwest side of valley, 

and Sixtymile River has changed 

channel pattern from braided to 

meandering. 0, Post-terrace development with active debris-flow sedimentation, valley widening at mouth of 

Miller Creek, and establishment of 

D modern Sixtymile River flood plain. 

70 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
glaciation (for example, Flat Creek beds and Klondike 

Gravel), the Klondike River and North Klondike River 

were incised to approximately present-day stream levels 

before the Intermediate glaciation (Hughes and others, 

1983). This represents downcutting of approximately 200 

m below the drift surface of the Old glaciation (Hughes and 

others, 1983). 

Glacial gravel deposits 

During glacial intervals, ice-marginal and proglacial 

processes deposited gravelly sequences which incorporated 

placer gold from regional bedrock or paleoplacer sources. 

Examples are found in areas glaciated during pre-Reid 

glaciations such as the Clear Creek drainage basin (placer 

area 4, fig. 1), where placer gold occurs in glaciofluvial 

sediments (Morison, 1985a). Drift of the Reid and McConnell glaciations does not usually contain placer gold because bedrock or paleoplacer sources were largely eroded 

and dispersed or covered by drift during the pre-Reid glacial intervals. 

Holocene 

Holocene gravelly deposits with concentrated placer 

gold include colluvium (for example, Dublin Gulch, near 

the Mayo placer area), valley-bottom alluvial blankets in 

gulches and streams (for example, the Clear Creek drainage 

basin), and bar deposits in major rivers (fig. 1). Gulch and 

stream placer deposits are generally thin (less than 5 m), 

and gravelly sediments are poorly sorted, angular, and 

locally derived. 

REFERENCES CITED 

Bostock, H.S., and Lees, E.J., 1960, Laberge map-area: Geological Survey of Canada Memoir 217, 32 p. 

Dufresne, M.B., and Morison, S.R., 1985, Stratigraphy and alteration of the White Channel Gravel at Dago Hill, A progress 

report, Klondike area, Yukon; Yukon Exploration and Geology 1983: Exploration and Geological Services Division, 

Northern Affairs Program, Yukon, p. 55-59. 

Hughes, O.L., Rampton, V.N., and Rutter, N.W., 1972, Quaternary geology and geomorphology, southern and central 

Yukon (Northern Canada): International Geological Congress, 24th Excursion, Guidebook All, 59 p. 

Hughes, O.L., Van Everdingen, R.O., and Tamocai, C., 1983, 

Regional setting-Physiography and geology, in French, 

H.M., and Heginbottom, J.A., eds., Guidebook to permafrost 

and related features of the northern Yukon Territory and 

Mackenzie Delta, Canada: Guidebook 3, International 

Conference on Permafrost, 4th, p. 5-12. 

Hughes, R.L., Morison, S.R., and Hein, F.J., 1987, Placer gravels 

of Miller Creek, Sixtymile area, 116B-116C: Yukon Geology, v. 1, Exploration and Geological Services Division, 

Northern Affairs Program, Yukon, p. 5a-55. 

Hughes, R.L., 1986, Sedimentology of the Sixtymile River placer 

gravels, Yukon Territory: Edmonton, University of Alberta, 

M.S. thesis, 210 p. 

McConnell, R.G., 1907, Report on gold values in the Klondike 

high level gravels: Geological Survey of Canada Publication 

no. 884, p. 1-71. 

Morison, S.R., 1985a, Placer deposits of Clear Creek drainage 

basin 115P, central Yukon; Yukon Exploration and Geology 

1983: Exploration and Geological Services Division, Northem Affairs Program, Yukon, P. 88-93. 

--1985b, Sedimentology of White Channel placer deposits, 

Klondike area, wests-central Yukon; Edmonton, University 

of Alberta, M.S. thesis 149 p. 

--in press, Placer deposits in Canada, in Geology and economic minerals of Canada: DNAG Quaternary Volume, 

Geological Survey of Canada Publication. 

Morison, S.R., and Hein, F.J., 1987, Sedimentology of the White 

- Channel Gravels, Klondike area, Yukon Territory: Fluvial 

deposits of a confmed valley, in Ethridge, F.G., Flores, RM., 

and Harvey, M.D., eds., Recent developments in fluvial 

sedimentology: Society of Economic Paleontologists and 

Mineralogists Special Publication no. 39, p. 205-216. 

Tamocai, C., 1987, Quaternary soils of Yukon Territory: Guidebook to Quaternary Research in Yukon, Field Excursions 

A20a and A20b, XTI INQUA Congress, Ottawa, July-August 

1987, 110 p. 

Vernon, P., and Hughes, O.L., 1966, Surficial geology of Dawson, 

Larsen Creek and North Creek map areas, Yukon Territory: 

Canadian Geological Survey Bulletin 136, 25 p. (includes 

Maps 1170A, 1171A, 1172A, scale 1:250,000). 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Late Cenozoic Stratigraphy and Sedimentology in Central and Southern Yukon 71 
Quaternary Stratigraphy of the Fairbanks Area, Alaska 

By Troy L. Pewe 

A geologic record of the past 2 million years or more 

is preserved in the nonglacial sediments of the Fairbanks 

area in central Alaska (fig. 1). Perennially frozen gravel, 

rich in placer gold, and loess and retransported loess with 

several interbedded tephra layers preserve a rich floral and 

faunal history. This paper summarizes an earlier synthesis 

of the stratigraphy, age, and paleoclimatic significance of 

these sediments (Pewe, 1975a), especially the Gold Hill 

Loess, and then discusses more recent tephrochronology 

and thermoluminescence (TL) data and their bearing on the 

previous interpretations. These data include preliminary 

results, and the interpretations presented represent my opinions as of March 1987. The tephrochronology studies were 

initiated in 1971, when J.A. Westgate (University of 

Toronto) began studying many tephra samples that I had 

previously collected from the loess. In 1983, Westgate, 

G.W. Berger (Western Washington University), Ann 

Wintle (Cambridge University), and I began joint field 

investigations to refine the age and stratigraphic interpretations of the loess by expanding detailed tephrochronology 

studies and initiating TL and paleomagnetic studies. The 

reader is referred to Pewe (1975a) and references therein 

for detailed descriptions of individual stratigraphic units 

and their contained fossils. 

Stratigraphy 

The oldest unconsolidated deposit in the Fairbanks 

vicinity is the Cripple Gravel (Pewe, 1975a); a gold-rich, 

brownish, coarse sandy gravel with angular clasts that is 

preserved on buried bedrock benches (fig. 2). The Cripple 

Gravel is thought to be late Pliocene and (or) early Pleistocene in age, but no fossils have been reported from it It 

is interpreted as composed of solifluction debris that was 

produced in a periglacial climate and partly reworked by 

streams. The Cripple Gravel formed when drainage directions were different from those of today. 

After modern drainageways had been established by 

rejuvenated streams, a gold-bearing, poorly stratified gravel 

named the Fox Gravel (Pewe, 1975a) accumulated in valley 

bottoms. The Fox Gravel is believed to be laterally equivalent to the Tanana Formation, which consists of unsorted 

and angular fractured and weathered bedrock fragments in 

a silty-sandy matrix and is interpreted as a solifluction 

deposit. Both the Fox Gravel and the Tanana Formation 

are thus thought to have formed during an interval of rigorous periglacial climate. The Fox Gravel contains large 

bones of mammoth and bison that are thought to be of early 

Pleistocene age. At various locations, the Fox Gravel is 

overlain by the Dawson Cut Formation, Gold Hill Loess, or 

Goldstream Formation (fig. 2). 

The Dawson Cut Formation (Pewe, 1975a) is a silt unit 

1 to 3 m thick that contains peat lenses, logs, and forest 

beds. Logs are as much as 30 em in diameter and are 

weathered, flattened, and iron stained. Spruce stumps as 

much as 20 em in diameter are rooted in peaty soil. The 

Dawson Cut Formation is believed to represent a pre-Illinoian interglacial interval. 

The next younger formation is the Gold Hill Loess 

(Pewe, 1975a), which is as much as 55 m thick and includes conspicuous folds, contortions, and fault blocks that 

are 2 to 35m across. Because of the uniformity in texture 

and composition of the silt, even prominent structural features are seen only as displacements of tephra layers, organic-rich beds, iron-stained layers, or paleosols. Several 

conglomerate layers composed of silt clasts in a silt matrix 

occur at topographic breaks in cliff faces developed in the 

Gold Hill Loess, especially in the middle of the formation 

at Gold Hill mining cut, Sheep Creek mining cut, and 

"Ester Island" (Pewe, 1952, and unpub. data, 1956), and 

these may record significant interruptions in the record. 

These topographic breaks have become prominent in the 

last 15 to 20 years as the silt cliffs thawed and retreated due 

to weathering and erosion. One of these silt-conglomerate 

layers occurs just above the Ester Ash Bed, which is described below. 

Figure 1. Map of Fairbanks area showing localities mentioned in text 

72 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Remains of small arctic and alpine mammals occur 

throughout the Gold Hill Loess, and tree pollen is rare. 

Bones of large mammals such as mammoth, horse, and 

bison are common but not abundant, and no mammal carcasses have been found. Retransported loess with abundant 

mammal fossils probably accumulated in valley bottoms 

during or shortly after deposition of the Gold Hill Loess. If 

so, then most of the valley-bottom accumulations must 

have been removed by the major valley streams prior to 

deposition of the late Pleistocene Goldstream Formation, 

except in rare downfaulted areas such as the one near Ester 

island (fig. 1) known as Cripple Sump, where retransported 

loess correlative with the Gold Hill Loess is preserved. 

The retransported loess at Cripple Sump is rich in fossils, 

including remains of Praeovibos, the only Pleistocene large 

mammal that may have been restricted to pre-Wisconsin 

time in Alaska. 

A prominent tephra layer, the Ester Ash Bed (Pewe, 

1955), occurs 2.8 m above the base of the Gold Hill Loess 

at several localities. A persistent tephra layer named the 

Dome Ash Bed (Pewe, 1975a) also occurs near the top of 

the Gold Hill Loess in many exposures near Fairbanks and 

as far away as 200 km. This bed is commonly faulted. 

More than one ash bed is present in some exposures, and 

recent studies have shown that some of these are distinct 

from both the Ester Ash Bed and the Dome Ash Bed and 

provide new and important marker horizons. 

Based on sedimentological and paleontological studies, 

I proposed that the Gold Hill Loess represented a long 

interval of rigorous periglacial climate when treeline was 

EXPLANATION 

Orb--Ready Bullion Formation 

Oen--Engineer Loess. Includes: 

Oenj, Jarvis Ash Bed 

Qenwi, Wilber Ash Bed 

Qgs--Goldstream Formation. Includes: 

Ogsc, Chatanika Ash Bed 

Oev--Eva Formation 

Qgh--Gold Hill Loess. Includes: 

Qghd, Dome Ash Bed 

Qghe, Ester Ash Bed 

Qfd--Fairbanks Loess 

Ode--Dawson Cut Formation; forest bed 

Ota--Tanana Formation 

Qfx--Fox Gravel 

OTc--Cripple Gravel 

Bedrock 

QUATERNARY 

} 

QUATERNARY 

AND (OR) 

TERTIARY 

450 to 600 m lower than today (Pewe, 1975a). Because 

sedimentological breaks were not thought to represent significant time intervals, and no major environmental 

changes were recognized in the floral and faunal record, the 

Gold Hill Loess was believed to have formed during a 

single major glaciation, which was interpreted as Illinoian 

in age. 

The long sedimentary record represented by the Gold 

Hill Loess is rarely preserved in its entirety at any one 

exposure. On upper slopes the loess is more easily eroded 

and only the upper part of the record is preserved. In valley 

bottoms most of the loess was removed by erosion during 

the last major warm period (interglacial interval). Only on 

low hills near the Tanana River (7 km to the south), or on 

middle slopes, is the most complete record available. 

Exposures at Gold Hill, Sheep Creek, and Ester island 

exhibit the thickest deposits and the longest record. 

Mter deposition of most or all of the Gold Hill Loess, 

large blocks of this silt with tephra layers were locally tilted 

into the valley by slumping, presumably in response to 

erosion of the loess. Prior to and during erosion, the iron 

coating on minerals in the upper part of the deposit was 

reduced from the ferric to the ferrous state, probably by 

percolating ground water. The thickness of the silt with 

ferrous iron is about 10 to 20m. These relations, plus the 

absence of ice wedges and mammal carcasses, indicate a 

major interval of erosion and thawing of permafrost during 

a climate warmer than now. Frozen carcasses and ice 

wedges of Wisconsin age exist in the silt of the Fairbanks 

area under the modern climate. 

Alti pIa nation 

terraces 

0 100 METERS 

L___......___~ 

VERTICAL EXAGGERATION X4 

Figure 2. Schematic composite cross section of creek valley near Fairbanks illustrating stratigraphic relations of Quaternary 

deposits (from Pewe, 1975a). 

Quaternary Stratigraphy of the Fairbanks Area, Alaska 73 
Unconformably overlying the Gold Hill Loess is the 

Eva Formation (Pewe, 1975a), a forest bed 1 m thick that 

contains rooted stumps and prostrate logs of white spruce 

and birch up to 25 em in diameter and 3 m long. These 

remains appear to indicate a climate at least as warm as 

now. The forest bed probably formed during the latter part 

of the warm interval that caused the erosion and slumping 

of the Gold Hill Loess. Radiocarbon ages show that this 

warm interval occurred before 57 ka, and it is presumed to 

be of Sangamon (last interglacial) age (Pewe, 1975a, 

1975b), which is now equated with oxygen-isotope substage 5e (Richmond and Fullerton, 1986; Edwards and 

others, 1987). 

Overlying the Eva Formation is the Goldstream Formation (Pewe, 1975a), a widespread deposit of perennially 

frozen, poorly bedded, organic-rich, gray to black retransported loess that is 10 to 35 m thick. Vertebrate remains 

including mammoth, horse, and bison are common in this 

deposit, and rare frozen carcasses also are present. Palynological analyses and studies of small-mammal fossils 

indicated that trees were rare on the landscape during 

deposition of the Goldstream Formation. All of these 

characteristics, plus the presence of large ice wedges, are 

interpreted as indicating a rigorous periglacial climate. 

Large, flat-topped ice wedges in the upper middle part of 

the unit probably formed during a short warming interval. 

The Chatanika Ash Bed (Pewe, 1975a), dated as forming 

about 14 ka, occurs near the top of the Goldstream Formation and is deformed by large ice wedges. Numerous 

radiocarbon ages have been obtained on organic materials 

from this deposit; they range from about 10 ka near the top 

of the unit to more than 38.5 ka near the middle, and so the 

Goldstream Formation was thought to be Wisconsin in age. 

Unconformably overlying the Goldstream Formation is 

the Engineer Loess (on hill slopes) and the Ready Bullion 

Formation (in valley bottoms). Both of these units are of 

Holocene age and have basal radiocarbon ages of about 10 

ka (Pewe, 1975a). The Engineer Loess contains at least 

four tephra layers: the Wilber, Jarvis, and White River Ash 

Beds (Pewe, 1975a) and an unnamed ash bed. The Ready 

Bullion Formation is a poorly to well-stratified, perennially 

frozen, organic-rich, retransported loess. Prior to deposition of the Ready Bullion Formation, ice wedges at the top 

of the Goldstream Formation thawed downward 0.5 to 1 m, 

and faulting and slumping occurred over and adjacent to 

them. These relations were interpreted to indicate that a 

brief interval of thawing and erosion occurred about 10 ka. 

Later, the permafrost table rose into the Ready Bullion 

Formation and now is about 0.25 to 0.5 m below the surface. Active ice wedges locally are present (Hamilton and 

others, 1983). 

The Fairbanks Loess (Pewe, 1958) is the most widespread Quaternary deposit in the Fairbanks area. It is 

defined to consist of all the loess on hilltops and upper 

slopes that cannot be identified as either Gold Hill Loess or 

Engineer Loess, and it is in part correlative with the retransported silt of the Goldstream Formation. 

Tephrochronology studies 

Naeser and others (1982) reported a fission-track age 

of greater than 450 ka for the Ester Ash Bed. Detailed 

work on (1) tephra layers at the Gold Hill, Dawson, and 

Cripple Sump mining cuts that formerly were interpreted as 

correlative with the Ester Ash Bed (Pewe, 1975a), and (2) 

a tephra bed at Eva Creek also thought to correlate with the 

Ester Ash Bed, revealed that each tephra layer is chemically and petrologically distinct and that all are older than 

the Ester Ash Bed (J.A. Westgate, University of Toronto, 

written commun., 1984). Two of the tephra layers occur at 

the Cripple Sump (south side of Ester Island, fig. 1) and 

Dawson mining cuts (West Dawson and Dawson cut, fig. 

1). The lower of these two beds is here informally termed 

the Cripple Sump tephra, and the upper bed is informally 

termed the Dawson tephra. The tephra layer near the base 

of the Fairbanks Loess at Gold Hill (fig. 1; Pewe, 1975a) 

is here informally termed the Canal tephra, and the one at 

Eva Creek (fig. 1) is informally termed the Weigh Scale 

tephra. The stratigraphic positions of the Canal tephra and 

the Weigh Scale tephra relative to one another and to the 

Cripple Sump and Dawson tephras are not clear. According to the recent application of the term "illinoian" to the 

time period from 302 to 132 ka (Richmond and Fullerton, 

1986), all five tephra layers and the lower part of the Gold 

Hill Loess are pre-Illinoian in age. I suggest that the loess 

record in the Fairbanks area may extend back 1 m.y. 

Petrographic and chemical examination of tephras 

thought to correlate with the Dome Ash Bed have revealed 

that they may comprise as many as seven different tephra 

layers (J.A. Westgate, University of Toronto, written 

commun., 1985) (fig. 3). Thus, contrary to previous interpretations (Pewe, 1975a), the Dome Ash Bed is not present 

in all exposures of the upper part of the Gold Hill Loess. 

However, preliminary examination of tephra samples from 

Eva Creek, Dawson Cut, and at West Dawson (fig. 1) 

suggests that the Dome Ash Bed is present at these localities (J.A. Westgate, University of Toronto, written commun., 1980). 

A tephra layer present at Sheep Creek (fig. 1) is petrographically and chemically distinct from those mentioned 

above and has been informally termed the Sheep Creek 

tephra (Westgate and others, 1982, 1985). This tephra bed 

also has been identified at Dawson Cut and Eva Creek (fig. 

1). At Canyon Creek, about 85 km southeast of Fairbanks, 

the Sheep Creek tephra occurs as angular retransported 

fragments (Weber and others, 1981), which are associated 

with mammal bones dated by the uranium-series method as 

about 80 ka (Hamilton and Bischoff, 1984). The Sheep 

Creek tephra also has been identified in Yukon Territory 

(Hughes, this volume). 

7 4 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
The thickest and perhaps most widespread of the group 

of tephras in the middle and upper parts of the Gold Hill 

Loess is the informally termed Old Crow tephra (Westgate 

and others, 1981; Westgate, 1982). It occurs in several 

places in Alaska and the Yukon (Westgate and others, 

1985), and some of the thickest known occurrences are near 

Fairbanks, where it is 10 to 30 em thick. It has been 

identified by petrographic and chemical analyses at Eva 

Creek, Gold Hill, and Sheep Creek near Fairbanks (fig. 1), 

at the Halfway House locality on the Parks Highway about 

35 km west of Fairbanks, and in an exposure on the 

Richardson Highway about 100 km southeast of Fairbanks 

(Westgate and others, 1985). 

At the Halfway House locality, a tephra layer stratigraphically above the Old Crow tephra is here informally 

termed the Halfway House tephra. The Halfway House 

tephra also has been identified at West Dawson (J .A. 

Westgate, University of Toronto, written common., 1985) 

(fig. 1). 

In addition to the tephra beds described above, at least 

three other tephra layers occur in the middle and upper 

parts of the Gold Hill Loess. Thus there are at least seven 

tephra beds in the middle and upper parts of the Gold Hill 

Loess. However, except for the relationship of the Old 

Crow tephra and the Halfway House tephra, the stratigraphic position of any one tephra bed relative to the others is 

unknown (fig. 3). 

Thermoluminescence studies 

To refine age interpretations for the upper part of the 

Gold Hill Loess and its enclosed tephras in the Fairbanks 

area, a TL sampling program was begun in 1983. Loess 

immediately above the Sheep Creek tephra yielded a TL 

AGE GLACIATION UNITS (AND ADDITIONAL COMMENTS) SEQUENCE 

z 

UJ ~ """' Rl•w Aoh Z:READY BULLION 

~ ~~~~::~ FORMATION UJ INTERGLACIAL ENGINEER LOESS (.) 

0 ...__ Unnamed teptn ( < 1 0 ka ) 

MJ z 

~ ~:Jl ~ ~ .,.- Chatanlka Ash Bed 0 

0 1-< T (14ka) (f) (f)~ 

i Oa: 

.Jo gu. 

INTERGLACIAL EVA FORMATION (>56.9 ka) 

~ 

Seven tephra& shown diagrammatically; 

~ stratigraphic relatione not 

z ............... completely known. One unit Is the formally UJ c( 

z 0 ---- ) named Dome Ash Bed #; three are Informally UJ 

(.) z termed the Sheep Creek #; Old Crow #; 

0 :J xxxxxxxxxxxxxxx and Halfway House tephras #; 1- :::! (f) 

'\-opographlc break In cliff facies en three remain unnamed. 

w (f) 

w-- ..J 

Q. 0 

.J~ 

:::: '-V" TL ages (In k a) for tephra• 

-? I: from Fairbanks area: 

0 Sheep Creek - 71 on loess 

.J Old Crow - 88 on loess 0 

~ Possible unconformity Old Crow 110 on ash z 

c( I 

0 xxxxxxxxxxxx 

z ~ .-:::::: Ester Ash Bed # (>450 ka} 

:J 

..J Four Informally termed tephra& that are older than the 

lJI T } Ester Ash Bed are shown here diagrammatically: 

a: 

UJ --..... 

--..r ~ ~ Weigh Scale #, Canal #, Dawson #, and Cripple Sump tephraa #. Q. 

UJQ INTERGLACIAL DAWSON CUT FORMATION Z..J 

UJO.. 

o- oa: 

t-0 GLACIAL FOX GRAVEL 

en-

-c 

~z GLACIAL CRIPPLE GRAVEL Q.c( 

Figure 3. Generalized stratigraphic section of Quaternary deposits in Fairbanks area. 

Symbol (#} indicates tephra layers that have been petrographically and chemically 

characterized. 

Quaternary Stratigraphy of the Fairbanks Area, Alaska 75 
age of 71±3ka (Ann Wintle, Cambridge University, written 

commun., 1987). Lower and upper age limits of 130 and 

220 ka and a probable age of 150 ka were determined by 

TL analyses of glass from the Old Crow tephra at the 

Halfway House locality (Berger and Huntley, 1985), but 

techniques used in these analyses are now considered invalid, and more recent TL analyses produced an age of 

110±12 ka (Berger, 1987; and this volume). Loess immediately above the tephra has been dated by TL as 108±16 

ka (Berger, 1987; and this volume), and, using a different 

technique, loess above and below the tephra yield TL ages 

of about 86±8 ka (Wintle and Westgate, 1986). 

The TL ages support recent interpretations of an early 

Wisconsin age for the Old Crow tephra, the upper part of 

the Gold Hill Loess, and the overlying Eva Formation (for 

example, Hopkins, 1982). However, some scientists now 

question the applicability of TL dating to sediments older 

than 100 ka (Debenham, 1985; Wintle, 1987), and some 

geologists have concluded that the TL method severely 

underestimates the age of loess in the central United States 

that is beyond the range of radiocarbon dating (Norton and 

Bradford, 1985; McKay, 1986; Canfield, 1985; Canfield 

and Mickelson, in press). Therefore, I still believe that a 

Sangamon age for the Eva Formation and an Illinoian age 

for the upper part of the Gold Hill Loess is most logical. 

The Eva Formation and the deep thawing of permafrost that 

I believe was concurrent with its deposition represent the 

warmest climatic interval of middle and late Pleistocene 

time, and it seems most likely that this warm interval is of 

Sangamon age. 

I deeply appreciate comments by the following persons 

on critical points of earlier drafts of the manuscript: G.W. 

Berger (Western Washington University), OJ. Ferrians, Jr. 

(U.S. Geological Survey), D.M. Hopkins (University of 

Alaska), J.V. Matthews, Jr. (Geological Survey of Canada), 

R.D. Reger (Alaska Division of Geological and Geophysical Surveys), J.A. Westgate (University of Toronto), and 

A.G. Wintle (Cambridge University). Support for my work 

in central Alaska is presently provided by the U.S. Geological Survey through the Arctic Environmental Studies Project and by the National Science Foundation. 

REFERENCES CITED 

Berger, G.W., 1987, Thermoluminescence dating of the Pleistocene Old Crow tephra and adjacent loess, near Fairbanks, 

Alaska: Canadian Journal of Earth Sciences, v. 24, p. 

1975-1984. 

Berger, G.W., and Huntley, D.J., 1985, A thermoluminescence 

date for the Old Crow tephra: Geological Society of America Abstracts with Programs, v. 17, no. 6, p. 341. 

Canfield, H.E., 1985, Thermoluminescence dating and chronology 

of loess deposition in the central United States: Madison, 

University of Wisconsin, M.S. thesis, 159 p. 

Canfield, H.E., and Mickelson, D.M., in press, Thermoluminescence dating of loess in the central United States: Quaternary Research. 

Debenham, N.C., 1985, Use of UV emissions in TL dating of 

sediments: Nuclear Tracks, v. 10, p. 717-724. 

Edwards, R.L., Chen, J.H., Ku, T.L., and Wasserburg, C.J., 1987, 

Precise timing of the last interglacial period from mass spectrometer determination of thorium-230 in corals: Science, v. 

236, p. 1547-1553. 

Hamilton, T.D., Ager, T.A., and Robinson, S.W., 1983, Late 

Holocene ice wedges near Fairbanks, Alaska, U.S.A.: Environmental setting and history of growth: Arctic and Alpine 

Research, v. 15, p. 157-168. 

Hamilton, T.D., and Bischoff, J.L., 1984, Uranium-series dating 

of fossil bones from the Canyon Creek vertebrate locality in 

central Alaska: U.S. Geological Survey Circular 939, p. 

26-29. 

Hopkins, D.M., 1982, Aspects of the paleogeography of Beringia 

during the late Pleistocene, in Hopkins, D.M., Matthews, 

J.V., Jr., Schweger, C.E., and Young, S.B., eds., Paleoecology of Beringia: New York, Academic Press, p. 3-28. 

McKay, E.D., 1986, lllinoian and older loesses and tills at the 

Maryville Section: Illinois State Geological Survey 

AMQUA Guidebook, p. 21-30. 

Naeser, N.D., Westgate, J.A., Hughes, O.L., and Pewe, T.L., 

1982, Fission-track ages of late Cenozoic distal tephra beds 

in the Yukon Territory and Alaska: Canadian Journal of 

Earth Sciences, v. 19, p. 2167-2178. 

Norton, L.D., and Bradford, J.M., 1985, Thermoluminescence 

dating of loess from western Iowa: Soil Science Society of 

America Journal, v. 49, p. 708-712. 

Pewe, T.L., 1952, Geomorphology of the Fairbanks area, Alaska: 

Stanford, California, Stanford University, Ph.D. Thesis, 220 

p. 

--1955, Origin of the upland silt near Fairbanks, Alaska: 

Geological Society of America Bulletin, v.66, p. 699-724. 

--1958, Geology of the Fairbanks D-2 quadrangle, Alaska: 

U.S. Geological Survey Geologic Quadrangle Map GQ-110, 

scale 1:63,360. 

--1975a, Quaternary stratigraphic nomenclature in central 

Alaska: U.S. Geological Survey Professional Paper 862, 32 

p. 

--1975b, Quaternary geology of Alaska: U.S. Geological 

Survey Professional Paper 835, 145 p. 

Pewe, T.L., and Reger, R.D., 1983, Guidebook to permafrost and 

Quaternary geology along the Richardson and Glenn Highways between Fairbanks and Anchorage, Alaska: Alaska 

Division of Geological and Geophysical Surveys, Guidebook 

1, International Conference on Permafrost, 4th, 263 p. 

Richmond, G.M., and Fullerton, D.S., 1986, Introduction to 

Quaternary glaciation in the United States of America, in 

Sibrava, Vladimir, Bowen D.Q., and Richmond, G.M., eds., 

Quaternary glaciations in the Northern Hemisphere: Quaternary Science Reviews, v. 5, p. 3-10. 

Weber, F.R., Hamilton, T.D., Hopkins, D.M., Repenning, C.A., 

and Haas, Herbert, 1981, Canyon Creek: A late Pleistocene 

vertebrate locality in interior Alaska: Quaternary Research, 

v. 16, p. 167-180. 

Westgate, J.A., 1982, Discovery of a large-magnitude, late Pleistocene volcanic eruption in Alaska: Science, v. 218, p. 

789-790. 

Westgate, J.A., Matthews, J.V., Jr., and Hamilton, T.D., 1981, Old 

Crow tephra-A new late Pleistocene stratigraphic marker 

across Alaska and the Yukon Territory: Geological Society 

of America Abstracts with Programs, v. 13, p. 579. 

Westgate, J.A., Pewe, T.L., and Gorton, M.P., 1982, Tephrachronology of the Gold Hill Loess in central Alaska: Geological Society of America Abstracts with Programs, v. 14, 

76 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
no. 7, p. 645-646. 

Westgate, J.A., Walter, R.C., Pearce, G.W., and Gorton, M.P., 

1985, Distribution, stratigraphy, petrochemistry, and paleomagnetism of the late Pleistocene Old Crow tephra in Alaska 

and the Yukon: Canadian Journal of Earth Sciences, v. 22, 

p. 893-906. 

Wintle, A.G ., 1987, Thermoluminescence dating of loess: Catena 

Supplement 9 (in press). 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of Old Crow tephra in Alaska: Geology, v. 14, p. 594-597. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Quaternary Stratigraphy of the Fairbanks Area, Alaska 77 
Pleistocene Glacial Events, 

Southeastern Copper River Basin, Alaska 

By Donald R. Nichols 

The deeply incised Copper River and its principal 

tributaries form bluffs that expose thick sequences of glacial, glaciofluvial, glaciolacustrine, fluvial, colluvial, eolian, and volcanic deposits. These deposits record a long 

Quaternary history probably extending back to early Pleistocene time. Pre-Quaternary rocks (Jurassic and older) are 

rarely exposed (Winkler and others, 1981) and, where they 

are observed, they usually are covered only by relatively 

young Quaternary deposits; presumably deposits of intermediate age have been eroded. 

The onset of glacial conditions during each major 

Pleistocene glaciation resulted in the advance of valley 

glaciers that blocked the Copper River, which flows in a 

deep trench through the Chugach Mountains (fig. 1). For 

example, near the head of the Copper River Delta, the 

Miles, Childs, and Allen Glaciers currently front in the 

Copper River, and ice advances of less than 10 km would 

likely dam the Copper River, at least temporarily. As 

glaciers filled the Copper River trench during each glaciation, they created an ice dam, which formed a lake that 

backed up into the Copper River Basin. Glaciers draining 

the large snow and ice fields of the Chugach and Wrangell 

Mountains, and even the Alaska Range, flowed down their 

respective valleys and terminated in the lake. The Chitina 

River valley, fed by one of the largest ice fields in Alaska, 

was occupied by a huge trunk glacier that flowed down the 

valley to the town of Chitina where it was joined by ice 

filling the Copper River trench in the Chugach Mountains. 

This enlarged trunk glacier then flowed up the Copper 

River valley; its terminus probably floated at times in the 

proglacial lake filling the basin. 

Five apparently stratigraphically distinct drift sheets 

are exposed in the Pleistocene sediments of the southeastem part of the basin (Nichols, 1965). All appear to be 

separated by fluvial deposits indicative of nonglacial or 

nonlacustrine environments that suggest ice positions were 

no farther advanced than at present in the Chugach Mountains. The three youngest drift sheets are expressed both 

geomorphically and stratigraphically, but the older two are 

believed to be represented only stratigraphically. Glaciolacustrine sediments are associated with all but the oldest 

drift sheet. All radiocarbon samples collected from beneath 

the youngest drift sheet have yielded ages beyond the 

maximum radiocarbon dating range, generally older than 

40 ka. However, two K-Ar age determinations on plagioclase in a near-surface lava flow, which was scoured by ice 

of at least the last major glaciation, indicate an age of no 

older than about 200 ka (Yehle and Nichols, 1980). The 

oldest near-surface fmite dates in the southeastern Copper 

River Basin are no greater than about 9.4 ka (Rubin and 

Alexander, 1960, p. 171-172, W-714; Ferrians, 1963, p. 

C121). Thus this youngest drift is considered equivalent to 

late Wisconsin, or possibly even the entire Wisconsin time 

as defmed by Richmond and Fullerton (1986). 

No direct evidence has been found to indicate the 

extent of the ice sheet that deposited the oldest drift sheet. 

Based on relative intensities of European and mid-continent 

United States glaciations, where older ice sheets generally 

equaled or extended beyond the limits of younger drift 

(Flint, 1957, p. 327), it is speculated that ice of the oldest 

drift sheet probably filled the Copper River Basin and then 

flowed outward through low divides and drainages in the 

surrounding mountains-Tahneta Pass, S usitna River Canyon, Delta River, Mentasta Pass, and the Copper River 

trench. The apparent lack of widespread lacustrine conditions associated with this drift also suggests that the glaciers may have formed a massive ice cap centered in the 

basin and that deglaciation probably began along the periphery of the basin with ice persisting in the center until a 

late stage of deglaciation. 

The next-to-oldest preserved drift is commonly made 

up of two diamicton units, distinguishable by color and 

texture (Nichols, unpub. data), and separated by a persistent 

bedded wne or layer of pebbles or cobbles. The dual 

nature of the drift and the association with lacustrine deposits above and below the drift, and locally interbedded 

within it, is interpreted as representing an advance of ice 

into the basin, a partial retreat, but not removal of the ice 

dam, and readvance into the basin. This scenario may 

indicate a restricted distribution of the ice, which probably 

did not completely fill the basin even though it may have 

covered the basin floor. 

I arbitrarily correlate the third youngest, stratigraphically exposed drift sheet with the oldest drift having geomorphic expression. Geomorphically, it is represented by 

erratics and highly modified morainal remnants, which lie 

on high, relatively flat or gently sloping surfaces of the 

northern slopes of the Chugach Mountains and above the 

limits of the two youngest drift sheets. Stratigraphically, 

till of this ice advance appears more uniform in texture and 

composition than that of other drifts. Where exposed, it 

forms steep, prominent ledges and pinnacles, commonly 

78 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
about midway in bluff faces along the Copper River and in 

tributary valleys. The till generally is underlain by lacustrine deposits; thus, ice probably advanced into a lake-filled 

basin. However, the presence of coarse fluvial deposits 

immediately above the till in most exposures indicates that 

melt water from the ice probably drained off subaerially, 

rather than subglacially into a proglacial lake. The high 

altitude of erratics and erosional evidence of south-flowing 

ice over the tops of 1,525-m-high mountains also suggest 

that ice filled the basin and flowed outward from a central 

ice cap. Consequently, deglaciation is inferred to have 

begun in the mountains peripheral to the basin and to have 

progressed toward the center of the basin, as was suggested 

for retreat of the oldest ice advance. 

The next-to-youngest drift sheet is represented by the 

widespread distribution of dual diamicton units and associated lacustrine deposits that are arbitrarily correlated with 

the higher of two sets of prominent moraines blocking 

small tributary valleys in the northern Chugach Mountains. 

The higher, slightly dissected and modified set of moraines 

decreases in altitude from between 1,056 and 1,160 m in 

altitude between Tonsina and Tonsina Lake to 975 to 1,056 

m north of the Klutina River. The strong similarity in the 

character of this drift to that of the next-to-oldest drift 

suggests that this younger ice advance was also somewhat 

limited in extent and was characterized by a major recession followed by a significant readvance. Although the ice 

may have covered most, if not all, of the basin floor, it may 

never have been very thick near the center. 

Ice that produced the fifth and youngest drift sheet 

flowed northward up the Copper River about as far as the 

mouth of the Gulkana River and fronted in Glacial Lake 

Atna (Nichols, 1965), the youngest of the succession of 

proglacial lakes formed by repeated invasions of glaciers 

~~\~ ::-: c .. > 

I 

I 

\ 

I 

I 

"V s \ 

' I 

GULF OF ALASKA 

100 km 

-----------~b--------------~~----------ll59" 141" 

148" 144" 

Figure 1. Index map of Copper River Basin (enclosed by dashed line) and adjacent areas, Alaska. 

Pleistocene Glacial Events, Southern Copper River Basin, Alaska 79 
into the basin or along its margins. Ferrians (1984) presented evidence that the lake level was below an altitude of 

655 m between 31.3 and 28.3 ka, and subsequently rose 

above that altitude in the central Copper River Basin. This 

youngest glaciation is represented by two major, littlemodified morainal systems along the western flank of the 

Wrangell Mountains. The higher, slightly older moraines 

and related features decrease in altitude from about 1,220 m 

along the southwest side of Mount Drum to about 975 m 

along the northwest side. The lower moraine decreases in 

altitude from about 1 ,070 m to about 700 m over the same 

distance. Similar, but slightly lower, north-sloping moraines are present along the northern flank of the Chugach 

Mountains. 

REFERENCES CITED 

Ferrians, O.J., Jr., 1963, Glaciolacustrine diamicton deposits in 

the Copper River Basin, Alaska, in Geological Survey Research 1963: U.S. Geological Survey Professional Paper 

475-C, p. C120-C125. 

---1984, Pleistocene glacial history of the northeastern Copper River basin, Alaska: Geological Society of America 

Abstracts with Programs, v. 16, no. 5, p. 282. 

Flint, R.F., 1957, Glacial and Pleistocene geology: New York, 

Wiley, 553 p. 

Nichols, D.R., 1965, Glacial history of the Copper River Basin, 

Alaska [abs.]: International Association for Quaternary 

Research, 7th Congress, Fairbanks, Alaska, 1965, Proceedings, Lincoln, Nebraska Academy of Sciences, p. 360. 

Richmond, G.M., and Fullerton, D.S., 1986, Introduction to 

Quaternary glaciations in the United States of America, in 

Sibrava, V., Bowen, D.Q., and Richmond, G.M., eds., Quaternary glaciations in the northern hemisphere: International 

Union of Geological Sciences and UNESCO, Report of the 

International Geological Correlation Programme, Project 24, 

Pergamon Press, 513 p. 

Rubin, Meyer, and Alexander, Corrine, 1960, U.S. Geological 

Survey radiocarbon dates V, in Flint, R.F., and Deevey, E.S., 

Jr., eds., Radiocarbon supplement: American Journal of 

Science, v. 2, p. 129-185. 

Winkler, G.R., Silberman, M.L., Grantz, Arthur, Miller, R.J., and 

MacKevett, E.M., Jr., 1981, Geologic map and summary 

geochronology of the Valdez quadrangle, southern Alaska: 

U.S. Geological Survey Open-File Report 80-892-A, 2 

sheets. 

Yehle, L.A., and Nichols, D.R., 1980, Reconnaissance map and 

description of the Chetaslina volcanic debris flow (new 

name), southeastern Copper River Basin and adjacent areas, 

south-central Alaska: U.S. Geological Survey Miscellaneous 

Field Studies Map MF-1209, scale 1:250,000. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

80 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
A Working Glacial Chronology for the 

Western Copper River Basin, Alaska 

By John R. Williams 

Pleistocene piedmont glaciers advanced into the westem Copper River Basin from the Chitina-Copper River 

valley, and also from the surrounding Chugach and 

Talkeetna Mountains and from the Alaska Range (fig. 1). 

They filled the basin, perhaps to overflowing, during earlier 

advances that are marked by erratics, formless drift, and the 

Daisy Creek moraine system along the eastern flank of the 

Talkeetna Mountains (fig. 2). During the last major glaciation, equivalent to most if not all of Wisconsin time, glaciers advanced from the Talkeetna Mountains, the Chugach 

Mountains, and the Alaska Range. They coalesced in the 

northwestern part of the Copper River Basin during the 

early phase of glacier expansion, but advances during a 

later phase were less extensive by about 40 km. Each 

glacial phase was associated with extensive glacial lakes, 

termed glacial Lakes Susitna and Atna, respectively (fig. 

1). The western Copper River Basin has been studied 

intermittently by the U.S. Geological Survey since 1952, 

and this summary of the glacial chronology is based on the 

distribution, stratigraphy, and radiocarbon dating of the 

Quaternary deposits (Williams and Galloway, 1986). 

Older glaciations of the western Copper River Basin 

are recognized by erratic clasts and patches of drift, lacking 

morainal form, that lie above and beyond the Daisy Creek 

(oldest) moraine system in areas farthest from modem 

glaciers in the eastern Talkeetna Mountains. Although 

erratics are difficult to identify in many areas of the eastern 

Talkeetna Mountains that are underlain by disaggregated 

Jurassic and Tertiary conglomerate, their distribution west 

of the Oshetna River on Twin Hills (TH on fig. 2) to more 

than 1,730 m above sea level is 400 m above the oldest 

moraine nearby. East of the Oshetna River (near TC, fig. 

2) drift and erratics seem to be absent above 1 ,296 m along 

the eastern front of the Talkeetna Mountains, suggesting a 

possible driftless area. Thick, stratified gravel (OG, fig. 2) 

farther south lies above 1 ,219 m altitude; the gravel is 

slightly lithified and contains clasts derived from the 

Chugach Mountains, which suggests (Grantz, 1960 and 

Grantz, U.S. Geological Survey, written commun., April 

12, 1957) that it is outwash, rather than Tertiary conglomerate. 

The Daisy Creek moraine (fig. 2) is the oldest moraine 

along the eastern front of the Talkeetna Mountains; it is a 

lateral moraine formed by Chugach glaciers that stands 

beyond and 122m higher than Tyone Creek, which is the 

marginal channel bordering the Curtis Lake moraine of the 

early phase of the last major glaciation. Exposures on the 

west bank of Tyone Creek (TC, fig. 2) are of organic-rich 

fluvial overbank deposits at river level, overlain by gravel 

that is capped by glaciolacustrine diamicton of glacial Lake 

Susitna. Daisy Creek drift is assumed to lie stratigraphically below the organic-rich deposits. Dating the organic 

material by radiocarbon methods provided an age greater 

than 35 ka (W-357). Ager (this volume) found pollen of 

spruce, birch, alder, and other plants in the organic beds; 

the flora was similar to the present low land spruce forest 

and also to the interglacial Goose Bay peat, near Anchorage. Daisy Creek drift is pre-interglacial (Illinoian?), or 

less likely early Wisconsin(?) in age, and formed immediately preceding a very warm climatic interval. 

During the early phase of the last major glaciation, 

glaciers from the Talkeetna Mountains moved northward to 

form the Oshetna moraine system, glaciers from the Alaska 

Range advanced southward to form the Tysus moraines, 

and Chugach glaciers moved northward to form the Tolson 

Creek and Curtis Lake moraines and to merge with the 

Alaska Range glaciers to form the Heartland Ridge interlobate moraine (HR) against the northward moving ChitinaCopper piedmont glacier (fig. 2). Based on radiocarbon 

ages from Thaw and Tyone Bluffs (TB, fig. 2) (Thorson 

and others, 1981), the drift of the Tysus moraines, although 

not exposed, is believed to lie below river level and to be 

older than the sediments of glacial Lake Susitna(?), which 

are at least as old as 32±2.73 ka (Beta-1820). Glacial Lake 

Susitna (fig. 2) expanded during retreat of the ice of the 

early phase of the last major glaciation. The lake was 

blocked by ice in the lower Susitna River canyon (R&M 

Consultants, 1981) and, during retreat of the glaciers, the 

lake extended up the Susitna River an unknown distance 

beyond the Hatchet Lake moraine, northeastward up the 

Maclaren River, eastward to where dammed by piedmont 

ice east of Heartland Ridge, and south to and perhaps 

beyond the Lake Louise sandur (LL) and Old Man moraine 

of the late phase of the last glaciation. Its level, 914 to 975 

m, was controlled by spillways at the southwestern end of 

Fog Lakes lowland, such as Chunilna Creek (CS, fig. 2) 

near the site of the ice dam in Susitna canyon. Glacial 

Lake Susitna had drained, perhaps completely, but at least 

to some unknown level below 705 m by 29.45±0.61 ka 

(Beta-1820), which is the radiocarbon age of a mammoth 

bone embedded in subaerial gravel above the lake sediments at that altitude. 

A Working Glacial Chronology for the Western Copper River Basin, Alaska 81 
During the late (Old Man) phase of the last major glaciation glaciers from the Chugach Mountains advanced 

northward in two lateral lobes, the western or Little Nelchina lobe up the Little Nelchina River, and the eastern, or 

Old Man lobe, up Mendeltna Creek and beyond Old Man 

Lake to the Lake Louise sandur (LL, on fig. 2); a trunk 

glacier also moved eastward down the Tazlina River valley. 

Meltwater drainage from the Little Nelchina lobe cut 

through deposits of glacial Lake Susitna and into the underlying Curtis Lake moraine (fig. 2). This outwash stream 

formed a gravel kame terrace at about 792 m altitude 

against ice along the western edge of the Lake Louise 

sandur of the Old Man lobe. The kame terrace was deposited when lake level was lower than 792 m but higher than 

777 m, because the lake deposits do not cover the kame 

terrace but do cover the sandur and recessional ice-contact 

features and feeder eskers to the south. This lake, associated with the maximum of the late phase of the last major 

glaciation, was apparently held between 777 to 792 m by a 

short-lived Tyone spillway (TSp on fig. 2). 

As the ice retreated from the outer Old Man moraine 

of the Little Nelchina lobe and from the Lake Louise sandur to the Old Man moraine of the Old Man lobe, succes-

~MTNS, ~ I 

~fL)\ .. ·· ... ··.·. 0 I 

*-«) ·········••·· •. · I -<.,.'t-v cz:9 .... 

0 50 

sive marginal drainage channels from the interlobate area 

were graded to delta-like features at 774 m, 762 m, and 747 

m altitude; the minimum age of the outwash leading to the 

762-m delta is 13.28±0.4 ka (W-583). By the time the lake 

level had fallen to 747 m, the lake was receiving outwash 

from the Old Man moraine (fig. 2), and the lake was draining across the present Susitna-Copper divide through a 

single outlet, connecting the valley of the West Fork 

Gulkana River to the Tyone River. The 747-m shoreline 

was more stable or longer lived than any of the others, and 

it is widespread and locally prominent on both sides of the 

Copper River Basin. The lake thus formed has been called 

glacial Lake Atna (see Ferrians, this volume). In the northeastern end of Lake Atna (fig. 1) wood exposed in lake 

bottom sediments was dated at 17.6±0.4 ka (W-1184); that 

this age may closely approximate the age of the highest 

stand of glacial Lake Atna in that area at 747 m was among 

the possible correlations listed by Schmoll (1984). This 

correlation would permit assignment of an 18 ka age to the 

747-m lake level, related outwash, and the Old Man moraine. 

In the Susitna River valley the ice advanced southward 

to the Hatchet Lake moraine, which is similar morphologiANG~ MENTASTA 

PASS 

100 KILOMETERS 

Figure 1. South-central Alaska showing boundary of western Copper River Basin (dashed lines), existing glaciers (dot 

pattern), glacial Lake Susitna (circle pattern), and glacial Lake Atna (cross pattern). 

82 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
cally to the Old Man moraines and like them in being about 

40 km within the morainal boundaries of the older phase of 

the last major glaciation. The Hatchet Lake moraine, 

described by Kachadoorian and others (1955), lies above 

lacustrine deposits, presumably of glacial Lake Susitna 

(Reuben Kachadoorian, U.S. Geological Survey, written 

commun., 1959). The moraine, however, has not been 

covered by these or younger lake deposits. The upper 

stratigraphic units at Tyone and Thaw Bluffs (TB), dated 

between 11.53±0.14 ka (Beta-1821) and 21.73±0.39 ka 

(DIC-1861) by Thorson and others (1981), are reinterpreted here as glaciolacustrine deposits; they are at elevations of 709 to 722 m, which is above the 29.45 ka gravel 

that separates the younger lake deposits from those of 

glacial Lake Susitna. These younger lake sediments also 

seem equivalent in age to the Hatchet Lake moraine. 

0 50 

Exactly how these deposits can be linked to the history of 

lakes and receding Chugach glaciers, given above, is not 

known; however, it is possible that a lake at this elevation 

existed separately or in connection with that above the 

Tyone spillway. 

Both the late and early phases of the last major glaciation are represented by a single drift unit exposed in sections along the Nelchina River near the front of the 

Chugach Mountains (N, fig. 2). This drift lies locally on a 

discontinuous organic layer that has alpine tundra vegetation (Ager, this volume) and is older than 38 ka (W-842). 

Gravel underlying the organic layer can be traced for 11 km 

at a gradient and direction of flow comparable to the present Nelchina River, down to an altitude of 615 m near 

Tazlina Lake. The gravel, apparently an advance outwash, 

lies on lacustrine sand and silt that also are older than 38 

100 KILOMETERS 

EXPLANATION 

CS Chunilna Creek spillway 

H R Heartland Ridge 

LL Lake Louise sandur 

M G Matanuska Glacier bog 

section 

N Nelchina River section 

OG High-level gravel 

TB Thaw and Tyone Bluff 

section 

TC Tyone Creek section 

TH Twin Hills 

TSp Tyone spillway (777 m) 

TT Tazlina terraces 

0 Location of section 

m 

~ 

D 

0 

Deposits of Lake Susitna, 

914-975 m 

Deposits of intermediate 

lake, 774-747 m 

Deposits of Lake Atna, 

747 m and below 

Existing glacier 

Boundaries of moraines 

Daisy Creek and early 

phase of last major 

glaciation 

Outer boundary of late 

phase (Old Man) of 

last major glaciation 

Direction of ice movement--

Based on drumlinlike 

features beneath lake 

sediments (eastern 

part of map area) 

Figure 2. Western Copper River Basin, showing distribution of glacial-lake deposits and successive positions of glaciers during 

last major glaciation (hachures). Mor., moraine. 

A Working Glacial Chronology for the Western Copper River Basin, Alaska 83 
ka (W-295). The lacustrine sediments contain a sparse 

pollen assemblage characteristric of spruce forest, suggesting a warm interstadial or interglacial climate (T.A. Ager, 

U.S. Geological Survey, written commun., March 1985). 

Retreat of the ice from the Old Man moraine first 

involved bifurcation of the glacier into discrete Tazlina and 

Nelchina glaciers, the uncovering of the Nelchina-Matanuska divide, advance of the Matanuska and Southeast 

Fork Glacier eastward up Matanuska River valley toward 

the divide, and formation of moraines at the mountain front 

in valleys tributary to the divide area (fig. 2). Drainage 

from Nelchina Glacier across the divide was ponded east of 

the extended Matanuska Glacier. A local readvance or halt 

of Nelchina Glacier about 20 km from its present terminus 

was later covered by lake waters at least as high as 700 m 

altitude. Lake Atna, therefore, persisted at very high levels 

until the retreating glaciers were within 17 km of their 

present positions. The Matanuska Glacier and others in the 

coastal mountains (Williams, 1986) had been no more than 

a few kilometers beyond their present terminal positions in 

the last 10 to 13 ka. The level of the ice in the Copper 

River canyon near Tiekel River had been lowered to about 

500 m altitude before 14 ka (Sirkin and Tuthill, 1987), 

based apparently on the age of the basal peat in a nearby 

bog. These data strongly suggest that Lake Atna in the 

western Copper River Basin was lowered significantly or 

drained through the Copper River canyon, the only outlet 

available lower than about 708 m, slightly before 14 ka or 

soon thereafter. 

Drainage of Lake Atna created an independent lake 

basin at Tazlina Lake. The lake's outlet, the modem 

Tazlina River, cut a deep canyon through the lip of the 

hanging valley and deposited alluvium now preserved as 

terraces bordering the river downstream. Shorelines of 

Tazlina Lake were initially 20m above the present lake. In 

the upper Matanuska River valley the Matanuska Glacier 

advanced 2 to 8 km down valley west of its present terminus 

(MG, fig. 2) (Williams and Ferrians, 1961) before 13 ka 

(Williams, 1986). This glacial advance blocked streams 

from the east and north to create local lakes. 

Holocene advances of Matanuska Glacier were 1.6 km 

beyond the present terminus at 4 ka and a later advance 

about 0.4 km from the present terminus in the past few 

hundred years (Williams and Ferrians, 1961). The Holocene deposits are similar to deposits of the Tustumena and 

Tunnel advances of the Kenai Peninsula (Karlstrom, 1964 ). 

In summary, the ages of two phases of the last major 

glaciation are 11.53 to about 21.73 ka for the younger and 

more than 32 ka for the older. Both phases are represented 

by a single drift sheet near the mountains. This drift is 

probably equivalent to the deposits of the last major glaciation in the northeastern Copper River Basin, which at 

Gakona represents the last of three depositional cycles 

(Ferrians, 1963 and this volume) and began before 55 ka. 

Drift of the last major glaciation is similar to the uppermost 

drift of the southeastern Copper River Basin, where basal 

dates are also greater than 38 ka; this drift postdates the 

lava flows, volcaniclastic debris flows, mud flows, ash 

flows and tephra emanating from the volcanic Wrangell 

Mountains to the east (Nichols, 1984, Nichols and Yehle, 

1985). 

REFERENCES CITED 

Ferrians, O.J., Jr., 1963, Glaciolacustrine diamicton deposits in 

the Copper River Basin, Alaska: U.S. Geological Survey 

Professional Paper 475-C, p. C120-C125. 

Grantz, Arthur, 1960, Geologic map of the Talkeetna Mountains 

(A-1) quadrangle and the south third of the Talkeetna 

Mountains (B-1) quadrangle, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-314, scale 

1:48,000. 

Kachadoorian, Reuben, Hopkins, D.M., and Nichols, D.R., 1955, 

A preliminary report of geologic factors affecting highway 

construction in the area between the Susitna and Maclaren 

Rivers, Alaska: U.S. Geological Survey Open-File Report 

92, 74 p., scale 1:40,000. 

Karlstrom, T.N.V., 1964, Quaternary geology of the Kenai Lowland and glacial record of the Cook Inlet region, Alaska: 

U.S. Geological Survey Professional Paper 443, 69 p. 

Nichols, D.R., 1984, Quaternary events in the southeastern Copper River Basin, Alaska: Geological Society of America 

Abstracts with Programs, v. 16, no. 5, p. 325. 

Nichols, D.R., and Yehle, L.A., 1985, Volcanic debris flows, 

Copper River Basin, Alaska: International Conference and 

Field Workshop on Landslides, 4th, Proceedings, Tokyo, p. 

365-372. 

R&M Consultants, Inc., 1981, Terrain unit maps, photointerpretation, subtask 5.02: Acres Inc., Report on Susitna Hydroelectric Project, Alaska Power Authority, 1980-81, Geotechnical 

Report, v. 2, Appendix J, Final draft, 21 sheets. 

Schmoll, H.R., 1984, Late Pleistocene morainal and glaciolacustrine geology in the upper Copper River-Mentasta Pass area, 

Alaska: Geological Society of America Abstracts with 

Programs, v. 16, no. 5, p. 332. 

Sirkin, L.A., and Tuthill, S.J., 1987, Late Pleistocene and Holocene deglaciation and environments of the southern Chugach 

Mountains, Alaska: Geological Society of America Bulletin, 

v. 99, p. 376-384. 

Thorson, R.M., Dixon, E.J., Jr., Smith, G.S., and Batten, A.R., 

1981, Interstadial Proboscidean from south-central Alaska: 

Implications for biogeography, geology, and archaeology: 

Quaternary Research, v. 16, no. 3, p. 404-417. 

Williams, J.R., 1986, New radiocarbon dates from the Matanuska 

Glacier bog section, in Bartsch-Winkler, Susan, and Reed, 

K.M., eds., Geologic studies in Alaska by the U.S. Geological Survey during 1985: U.S. Geological Survey Circular 

978, p. 85-88. 

Williams, J.R., and Ferrians, O.J., Jr., 1961, Late Wisconsin and 

Recent history of the Matanuska Glacier, Alaska: Arctic, v. 

14, no. 2, p. 83-90. 

Williams, J.R., and Galloway, J.P., 1986, Map of western Copper 

River Basin, Alaska, showing lake sediments and shorelines, 

glacial moraines, and location of stratigraphic sections and 

radiocarbon-dated samples: U.S. Geological Survey OpenFile Report 86-390, 30 p., scale 1:250,000. 

Carter, L. David, Hamilton, Thomas D., and Galloway, John P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

84 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Glacial Lake Atna, Copper River Basin, Alaska 

By Oscar J. Ferrians, Jr. 

The Copper River Basin, located in south-central 

Alaska, is a large intermontaine basin surrounded by high 

glacier-clad mountains-the Alaska Range to the north, the 

Talkeetna Mountains to the west, the Chugach Mountains 

to the south, and the Wrangell Mountains to the east (fig. 

1). The basin is approximately 13,000 km2 in areal extent, 

and most of it is drained by the Copper River, which heads 

in the northern Wrangell Mountains, flows in a semicircular course around the west side of the mountains to their 

south side, then cuts through the Chugach Mountains in a 

deep canyon and flows into the Gulf of Alaska. Within the 

Chugach Mountains, the Copper River is bordered on both 

sides by ice fields. Several glaciers, which include the 

Allen, Miles, and Childs Glaciers, emanate from the ice 

fields and terminate along the margin of the river. This 

relation suggests that during any major glaciation the 

Copper River would be dammed by advancing glaciers, 

causing the formation of an extensive proglaciallake in the 

basin. Stratigraphic evidence from high river bluff exposures in the basin confmns this, indicating that lakes did 

form during each major glaciation, and that the lakes 

drained when the glaciers retreated during each major interglaciation (Ferrians and Nichols, 1965; Ferrians and others, 

1983). 

Previous investigations 

In 1898, Schrader (1900) made a reconnaissance study 

in the Copper River Basin and concluded that the unconsolidated Pleistocene sediments in the central part of the 

basin were much finer than those at the edges, and that this 

relation suggested that the fme-grained sediments were 

deposited in a large body of standing water (either an 

"inland lake" or an "arm of the sea") with encroaching 

glaciers depositing gravel and till around the edges. 

However, Schrader and Spencer (1901, p. 58), after additional studies in the southeastern part of the Copper River 

Basin, decided that the fine-grained deposits probably are 

present only in limited areas and are surrounded by coarser 

deposits. Mendenhall (1905, p. 62-72), who studied the 

Pleistocene deposits of the central Copper River region, 

concurred with Schrader and Spencer in concluding that 

fine-grained sediments were deposited only in several isolated lakes, similar to the present-day Tazlina and Tonsina 

Lakes. Moffit (1954, p. 159) also concluded that the lake 

sediments in the Copper River Basin were deposited in 

several small lakes; however, he stated that "the topographic setting for a large lake seems favorable, but evidence for it has not been recognized." Subsequent studies 

demonstrated that a large proglacial lake formed in the 

Copper River Basin during the last major glaciation. These 

studies form the basis for the following discussion. 

Glacial Lake Atna 

Extent and strand lines 

The lake that formed in the Copper River Basin during 

the last major glaciation has been named glacial Lake Atna 

(Nichols, 1965). Evidence in the northeastern Copper 

River Basin indicates that this lake covered more than 

5,200 km2 of the basin floor, and that numerous glaciers 

and sediment-laden, glacier-fed streams debouched into it 

(Ferrians, 1984). Locally, prominent strandlines occur at 

altitudes of approximately 800, 745, 700, and 640 m, and 

less prominent ones occur at intermediate and lower levels. 

These strandlines indicate periods of relatively stable lake 

level, separated by periods of lowering of lake level. 

Several maps show the extent of the lake or the distribution of lake sediments throughout or in various parts of 

the Copper River Basin (Karlstrom and others, 1964; 

Coulter and others, 1965; Nichols and Yehle, 1969; Ferrians, 1971a, 1971b; Richter and others, 1979; Williams and 

Johnson, 1980; Yehle, 1980, 1981; Williams, 1985; Emery 

and others, 1985; and Williams and Galloway, 1986). 

Isostatic effects 

Obviously, the tremendous additional weight of the 

waters of glacial Lake Atna and of the glaciers that advanced into the basin depressed the basin isostatically, and 

conversely, when the glaciers retreated and the lake 

drained, the loss of weight resulted in rebound. 

Because the shoreline features are not preserved continuously, and because precise measurements of the altitudes of the features have not been made, it is difficult to 

determine whether or not there has been tilting of the basin 

floor. The apparent general agreement of the altitudes of 

shoreline features in many different areas of the basin 

suggests that the rebound was somewhat uniform and that 

tilting was not great within any one area. 

One line of evidence that suggests that some tilting 

occurred in the northeastern Copper River Basin is as follows. The Indian Creek delta gravel, 65 km northeast of 

Gakona, represents the highest recognizable glacial Lake 

Atna deposit in this local area, and it is at an altitude of 745 

m. The Meiers Lake delta gravel, 50 km west of the Indian 

Glacial Lake Atna, Copper River Basin, Alaska 85 
Creek deposit, represents the highest Glacial Lake Atna 

deposit in this local area, and it is at an altitude of 800 m. 

If one concludes that these two features are coeval, then the 

55 m difference in altitude would be a measure of the 

difference in isostatic rebound between these two sites. If 

the tilt were uniform, it would be only a little more than 1 

m per kilometer of horizontal distance, which would be 

very difficult to detect in routine geologic field mapping. 

Possibly the apparent anomalous situation of the highest 

shoreline features formed during the last major glaciation 

occurring at different altitudes in different parts of the basin 

might be explained, in part, by this kind of differential 

isostatic rebound. For example, lacustrine deposits or 

shoreline features occur up to altitudes of 945-975 min the 

northwestern Copper River Basin (Williams, 1984; Williams and Galloway, 1986, p. 1) and in the adjacent Denali 

area (Nichols and Yehle, 1961, p. 1067), but up to altitudes 

of only 745 min the eastern part of the basin (Ferrians and 

Schmoll, 1957; Nichols and Yehle, 1969). 

Character of sediments 

The deposits of Glacial Lake Atna consist of numerous 

diamicton units, which are interbedded with stratified lacustrine sediments (Ferrians, 1963a, 1963b). The character, stratigraphic relations, and distribution of these diamicton units indicate that many of them were deposited by 

turbidity currents and subaqueous mudflows. Others were 

formed by rapid deposition of massive, fine-grained sediment with numerous ice-rafted stones included. They 

range in thickness from a few centimeters to 50 m. Most 

of the diamicton is nonsorted and till-like in character. 

GULF OF ALASKA 

/) 

59" 

-----------~=----------------~;----------14141" 148" 

Figure 1. Index map showing setting of Copper River Basin (approximate boundary shown by dashed line). 

86 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Other diamicton deposits are poorly sorted and relatively 

fme grained, with the coarser fraction generally limited to 

sizes smaller than cobbles. Locally, these poorly sorted 

deposits show well-developed graded bedding. Numerous 

units of nonsorted till-like diamicton alternate in vertical 

sequence with bedded lacustrine sediments and with poorly 

sorted diamicton. Locally, the alternation repeats itself 

several times within a stratigraphic thickness of a meter. 

Generally, the contacts between these units are sharp; the 

beds immediately underlying the diamicton units generally 

are not deformed, even though deformation is common 

within the entire lacustrine sequence. Nichols (1960) described two types of contorted bedding in horizontal zones 

within the thin-bedded lacustrine sand, silt, and clay, and he 

concluded that this deformation was caused by slumping 

generated by earthquakes. Studies of the orientation of 

phenoclasts in the laminated lacustrine deposits by Schmoll 

( 1961) indicated that there are two preferred orientations of 

the clasts. The dominant orientation, which is nearly horizontal, resulted from ice-rafted stones being dropped on the 

relatively firm bottom of the lake. The second preferred 

orientation, which is weak and which varies between 

samples of different ages, probably was caused by water 

currents. According to Eyles (1984), late Quaternary glaciolacustrine deposition in the Copper River Basin and in 

Lake Ontario, Canada, is analogous to distal glaciomarine 

sedimentation on the continental shelves. 

Age 

The age of Glacial Lake Atna is indicated by radiocarbon dates of samples collected from high river-bluff sections at Gakona in the northeastern Copper River Basin. 

Organic material buried with sediments deposited during 

the early phase of lake formation when the ancestral Copper River valley was being flooded was dated at greater 

than 38 ka (sample W-531). Organic material immediately 

overlying the lacustrine sediments and buried by cliff-head 

dune deposits was dated at 9.4±0.3 ka (W-714). 

Because of the scientific importance of dating the initiation of the lake and the last major glaciation in the 

Copper River Basin, a very large sample of the older organic material was collected and submitted to the Groningen Laboratory, which uses the carbon-enrichment method 

to extend the range of radiocarbon dating. Unfortunately, 

the results were not conclusive. One measurement gave an 

absolute age of 43.44±0.25 ka (GrN-4086}, but because 

this age was younger than two dates on nonenriched parts 

of the same sample (>46 ka and >49 ka, GrN-4165 and 

GrN-4448, respectively) the laboratory concluded that the 

sample was contaminated during the enrichment process. 

Consequently, the analysis was repeated and the sample 

yielded an absolute age of 58.6±1.1 ka (GrN-4798). 

Under the circumstances, it is difficult to accept the 

age determination of 58.6±1.1 ka without corroborating 

evidence, but the series of dates by the Groningen Laboratory does suggest that the lake started to form before 50 ka, 

and the 9.4±0.3 ka age determination provides a good 

minimum date for lake draining. Additional age determinations of organic material collected from bluffs along the 

Sanford River, 17 km east of Gakona, indicate that the lake 

level was below 655 m between 31.3±1 ka (W-843) and 

28.3±1 ka (W-1343). Thorson and others (1981) and 

Thorson (1984) presented evidence that subaerial conditions existed in the northwestern comer of the Copper 

River Basin at an altitude of approximately 700 m between 

32 and 21 ka. Also, lake deposits exposed at 670 m altitude 

in a bluff along the Copper River at Slana, 80 km northeast 

of Gakona, are dated at about 17 ka (17.6±0.4, W-1134) 

(Schmoll, 1984). All of these dates, in conjunction with the 

stratigraphic relations, indicate that glacial Lake Atna and 

the last major glaciation in the Copper River Basin are, at 

least in part, comparable in age to the Wisconsin glaciation 

of central North America. 

REFERENCES CITED 

Coulter, H.W., Hopkins, D.M., Karlstrom, T.N.V., Pewe, T.L., 

Wahrhaftig, Clyde, and Williams, J.R., compilers, 1965, Map 

showing extent of glaciations in Alaska: U.S. Geological 

Survey Miscellaneous Geologic Investigations Map 1-415, 

scale 1:2,500,000. 

Emery, P.A., Jones, S.H., and Glass, R.L., 1985, Water resources 

of the Copper River Basin, Alaska: U.S. Geological Survey 

Hydrologic Investigations Atlas HA-686, 3 sheets. 

Eyles, Nicholas, 1984, Sediments in large late Quaternary glaciolacustrine basins (Copper River, Alaska and Great Lakes, 

Canada): Application to pre-Quaternary sequences: Geological Society of America Abstracts with Program, v. 16, 

no. 5, p. 282. 

Ferrians, O.J., Jr., 1963a, Till-like glaciolacustrine deposits in the 

Copper River Basin, Alaska: Geological Society of America 

Special Paper 73, p. 151. 

--1963b, Glaciolacustrine diamicton deposits in the Copper 

River Basin, Alaska, in Geological Survey Research 1963-

Short papers in geology and hydrology, 1963: U.S. Geological Survey Professional Paper 475-C, p. C121-C125. 

--1971 a, Preliminary engineering geologic maps of the 

proposed trans-Alaska pipeline route, Gulkana quadrangle: 

U.S. Geological Survey Open-File Report 71-102 (494), 

scale 1:125,000, 2 sheets. 

--1971b, Preliminary engineering geologic maps of the 

proposed trans-Alaska pipeline route, Valdez quadrangle: 

U.S. Geological Survey Open-File Report 71-104 (495), 

scale 1:125,000, 2 sheets. 

--1984, Pleistocene glacial history of the northeastern Copper River Basin, Alaska: Geological Society of America 

Abstracts with Programs, v. 16, no. 5, p. 282. 

Ferrians, O.J., Jr., and Nichols, D.R., 1965, Copper River Basin, 

in Schultz, C.B., and Smith, H.T.U., eds., Guidebook for 

Field Conference F, central and south-central Alaska: Nebraska Academy of Sciences, International Association for 

Quaternary Research, VII Congress, Lincoln, Nebr., p. 

93-114. 

Ferrians, O.J., Jr., Nichols, D.R., and Williams, J.R., 1983, Copper River Basin, in Pewe, T.L., and Reger, R.D., eds., GuideClacial Lake Atna, Copper River Basin, Alaska 87 
book to permafrost and Quaternary geology along the 

Richardson and Glenn Highways, between Fairbanks and 

Anchorage, Alaska: Alaska Division of Geological and 

Geophysical Surveys Guidebook 1, p. 137-175. 

Ferrians, O.J., Jr., and Schmoll, H.R., 1957, Extensive proglacial 

lake of Wisconsin age in the Copper River Basin, Alaska: 

Geological Society of America Bulletin, v. 68, no. 12, p. 

1726. 

Karlstrom, T.N.V., and others, compilers, 1964, Surficial geology 

of Alaska: U.S. Geological Survey Miscellaneous Geologic 

Investigations Map 1-357, scale 1:584,000. 

Mendenhall, W.C., 1905, Geology of the central Copper River 

region, Alaska: U.S. Geological Survey Professional Paper 

41, 133 p. 

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

Range and adjacent area: U.S. Geological Survey Bulletin 

989-D, 218 p. 

Nichols, D.R., 1960, Slump structures in Pleistocene lake sediments, Copper River Basin, Alaska, in Geological Survey 

Research 1960--Short papers in the geological sciences 

1960: U.S. Geological Survey Professional Paper 400-B, p. 

B353-B354. 

---1965, Glacial history of the Copper River Basin: International Association for Quaternary Research, 7th Congress, 

Fairbanks, Alaska, 1965, Proceedings, Abstract volume, 

Lincoln, Nebraska Academy of Sciences, p. 360. 

Nichols, D.R., and Yehle, L.A., 1961, Mud volcanoes in the 

Copper River Basin, Alaska, in Raasch, G.O., ed., Geology 

of the Arctic: Toronto, University of Toronto Press, v. 2, p. 

1063-1087. 

---1969, Engineering geologic map of the southeastern Copper River Basin, Alaska: U.S. Geological Survey Miscellaneous Geologic Investigations Map 1-524, scale 1:125,000. 

Richter, D.H., Smith, R.L., Yehle, L.A., and Miller, T.P., 1979, 

Geologic map of the Gulkana A-2 quadrangle, Alaska: U.S. 

Geological Survey Geologic Quadrangle Map GQ-1520, 

scale 1:63,360. 

Schmoll, H.R., 1961, Orientation of phenoclasts in laminated 

glaciolacustrine deposits, Copper River Basin, Alaska, in 

Geological Survey Research 1961-Short papers in the 

geological and hydrological sciences: U.S. Geological Survey Professional Paper 424-C, p. C192-C195. 

---1984, Late Pleistocene morainal and glaciolacustrine geology in the upper Copper River-Mentasta Pass area, Alaska: 

Geological Society of America Abstracts with Programs, v. 

16, no. 5, p. 332. 

Schrader, F.C., 1900, A reconnaissance of a part of Prince William Sound and the Copper River district, Alaska: U.S. 

Geological Survey 20th Annual Report, 1898-99, Pt. VIIExploration in Alaska in 1898, p. 341-423. 

Schrader, F.C., and Spencer, A.C., 1901, The geology and mineral 

resources of a portion of the Copper River district, Alaska: 

U.S. Geological Survey Special Publication, 94 p. 

Thorson, R.M., 1984, Pattern and chronology of late Quaternary 

glaciation, northwest Copper River Basin: Geological Society of America Abstracts with Programs, v. 16, no. 5, p. 337. 

Thorson, R.M., Dixon, E.J., Jr., Smith, G.S., and Batten, A.R., 

1981, Interstadial Proboscidean. from south-central Alaska: 

Implications for biogeography, geology, and archeology: 

Quaternary Research, v. 16, no. 3, p. 404-417. 

Williams, J.R., 1984, Late Wisconsin glacial retreat and lake 

levels, western Copper River Basin, Alaska: Geological 

Society of America Abstracts with Programs, v. 16, no. 5, p. 

340. 

---1985, Engineering-geologic map of the southwestern 

Copper River Basin and upper Matanuska River valley, 

Alaska: U.S. Geological Survey Open-File Report 85-143, 

scale 1:125,000, 2 sheets. 

Williams, J.R., and Galloway, J.P., 1986, Map of western Copper 

River Basin, Alaska, showing lake sediments and shorelines, 

glacial moraines, and location of stratigraphic sections and 

radiocarbon-dated samples: U.S. Geological Survey OpenFile Report 86-390, scale 1:250,000. 

Williams, J.R., and Johnson, K.M., compilers, 1980, Map and 

description of late Tertiary and Quaternary deposits, Valdez 

quadrangle, Alaska: U.S. Geological Survey Open-File 

Report 80-892C, scale 1:250,000, 2 sheets. 

Yehle, L.A., 1980, Preliminary surficial geologic map of the 

Valdez C-1 quadrangle, Alaska: U.S. Geological Survey 

Miscellaneous Field Studies Map MF-1132, scale 1:63,360. 

---1981, Preliminary surficial geologic map of the Valdez 

B-1 quadrangle, Alaska: U.S. Geological Survey Miscellaneous Field Studies Map MF-1364, scale 1:63,360. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

88 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
History of Late Pleistocene and Holocene Vegetation 

in the Copper River Basin, South-Central Alaska 

By Thomas A. Ager 

This paper provides an outline of vegetation history for 

the Copper River Basin of south-central Alaska (fig. 1) 

during the late Pleistocene and Holocene. Vegetation reconstructions are based upon analyses of pollen and spore 

assemblages from lacustrine sediment cores and outcrop 

samples from scattered sites within the basin and in adjacent areas. The chronology of vegetation changes is based 

upon radiocarbon-dated organic materials from these 

samples. 

The glacial and glaciolacustrine deposits of the Copper 

River Basin have been the subject of several investigations 

during the past four decades. Results of these studies have 

been summarized recently by Ferrians and others (1983), 

Hamilton and Thorson (1983), and Williams and Galloway 

(1986). 

Palynological investigations were begun in this region 

by Hansen (1953), who analyzed arboreal pollen in shallow 

peat cores from roadside muskegs found along the 

Richardson and Glenn Highways. The cores lacked radiocarbon control, however, and very few palynological data 

were included in the publication. What is presently known 

about the Quaternary vegetational history of the Copper 

River Basin is based upon recent work by Connor (1984), 

Ager and Brubaker (1985), and Ager (unpub. data). Sirkin 

and Tuthill (1987) summarized results of palynological and 

glacial geologic studies in the lower Copper River valley, 

but most of that area is outside the region included in the 

present paper. 

The small number of sites investigated within the 

Copper River Basin is inadequate to permit as detailed areconstruction of vegetation history as has been carried out in 

other areas of Alaska (Ager and Brubaker, 1985). The data 

are sufficient, however, to permit construction of a fragmentary history for the basin during the late Pleistocene, 

and of a nearly complete Holocene history. The pre-Holocene record is pieced together from radiocarbon-dated 

outcrop samples from scattered sites in the basin. These 

samples were collected by J.R. Williams, OJ. Ferrians, Jr., 

CL. Connor, and T.A. Ager (all with the U.S. Geological 

Survey). The largest set of dated outcrop samples used in 

this palynological investigation was collected by J.R. Williams during fieldwork that spanned more than three decades (Williams and Galloway, 1986). 

The Holocene record for the region is based upon 

lacustrine sediment cores from Seventymile Lake (Ager 

and Brubaker, 1985), Grizzly Lake (Ager, unpub. data), 

Tangle Lakes in the Gulkana Upland (Ager and Sims, 

1981; Schweger, 1981), and Watana Pond (local usage) in 

the middle part of the Susitna River valley (Ager, unpub. 

data) (fig. 1). The pollen records from these cores are 

supplemented by radiocarbon-dated outcrop samples from 

several localities (Williams, 1986; Williams and Galloway, 

1986; Ager, unpub. data). 

The oldest known pollen samples of Pleistocene age 

from the region are from outcrops on the Dadina River 

(Connor, 1984) and Tyone Creek (Williams and Galloway, 

1986). The samples from the Dadina River locality (fig. 1) 

yielded pollen assemblages dominated by Picea (spruce), 

Betula (birch), and Alnus (alder), along with Ericaceae 

(heaths), Cyperaceae (sedge), and various herbs (Connor, 

1984). The sampled units have yielded infinite radiocarbon 

ages of >33.5 (1-12,321) and >40 ka (I-12,320; I-12,322). 

Connor (1984) interpreted these samples to represent boreal 

forest vegetation that occupied the lowlands of the Copper 

River Basin during a warm climate interval within the midWisconsin interstadial, presumably during the early part of 

the interstadial. Interpretations of the chronology for a core 

from Imuruk Lake in western Alaska (Shackleton, 1982) 

suggested that an unusually warm interval may have occurred in Beringia in early mid-Wisconsin time. Other 

evidence from Beringia in support of Shackleton's interpretation was recently presented by Matthews and Schweger 

(1985) and in this volume. 

Outcrop samples from Tyone Creek (fig. 1) collected 

by J .R. Williams (Williams and Galloway, 1986) also are 

associated with an infmite radiocarbon age of > 35 ka 

(W-357), and their pollen assemblages are dominated by 

Picea, Betula, Alnus, and Cyperaceae (Ager, unpub. data). 

These assemblages are quite similar to those described by 

Connor (1984) from Dadina River. It is likely that the 

Tyone Creek and Dadina River pollen assemblages are 

correlative. Pollen data from both sites represent lowland 

boreal forest vegetation, and that they suggest climate conditions quite similar to those of the present day. It remains 

in the realm of speculation whether this interval of boreal 

forest development represents an unusually warm interval 

during the early mid-Wisconsin interstadial, or whether it 

represents an older interglacial interval. 

An outcrop sample from Nelchina River (fig. 1) collected by J .R. Williams yielded a radiocarbon determination of >38 ka (W-842) (Williams and Galloway, 1986). 

The sampled horizon is overlain by till and overlies gravel 

History of Late Pleistocene and Holocene Vegetation in the Copper River Basin, Alaska 89 
outwash. The dominant pollen types in that sample (Ager, 

unpub. data) were herbaceous taxa such as Cyperaceae, 

Caryophyllaceae, and Gramineae. This assemblage suggests that treeless herbaceous tundra, probably a moist 

sedge meadow, covered at least some lowlands within the 

Copper River Basin before 38 ka. A nearby outcrop along 

the Nelchina River yielded a peat sample from a stratigraphically lower position than that which yielded a tundra 

pollen assemblage. The lower sample was from a sandy 

deltaic unit underlying the outwash unit. The peat yielded 

a radiocarbon determination of >38 ka (W-295). The 

pollen assemblage contained in the lower sample from 

Nelchina River was dominated by spruce pollen. This 

suggests boreal forest vegetation similar to that from Tyone 

Creek. It is not known, however, if the Nelchina sample 

with spruce pollen is the same age as those with boreal assemblages from Tyone Creek or Dadina River. 

Figure 1. Map of Copper River Basin and adjacent areas, 

south-central Alaska. Numbers refer to localities discussed in 

text: 1, Watana Pond (Ager, unpub. data); 2, Tyone Bluff 

(Thorson and others, 1981 ); 3, Tangle Lakes (Ager and Sims, 

1981; Schweger, 1981 ); 4, Grizzly Lake (Ager, unpub. data); 

5, Sanford River (Ferrians and others, 1983; Ager, unpub. 

data); 6, Dadina River (Connor, 1984); 7, Chitina area (Ager, 

unpub. data); 8, Seventymile Lake (Ager and Brubaker, 1985); 

9, Nelchina River (Williams and Galloway, 1986; Ager, 

unpub. data); 10, Tyone Creek (Williams and Galloway, 

1986; Ager, unpub. data); 11, Matanuska Glacier (Williams, 

1986; Ager, unpub. data). 

An interstadial deposit from the Sanford River (fig. 1) 

was sampled for pollen analysis in 1985 by OJ. Ferrians, 

Jr. (U.S. Geological Survey). The slightly peaty fme sand 

and silt unit had been previously sampled for radiocarbon 

dating, and those samples had yielded bracketing ages of 

31.3±1 ka (W-843) near the base of the unit and 28.3±1 ka 

(W-1343) near the top of the unit (Williams and Galloway, 

1986; Ferrians and others, 1983). The sediments were 

deposited late within the mid-Wisconsin interstadial, at 

what may have been the only time during the entire Wisconsin when the shoreline of the large proglacial lake that 

occupied much of the basin dropped sufficiently to expose 

the Sanford River site subaerially, thus permitting vegetation to colonize. 

The pollen data from eight samples collected from this 

interstadial unit provide important new evidence about the 

nature of lowland vegetation of this region during the final 

phase of the Wisconsin interstadial. The assemblages are 

dominated by pollen of Cyperaceae, Gramineae, 

Caryophyllaceae, Artemisia, Phlox, and other herbs. This 

indicates that lowland areas of the Copper River Basin that 

are now occupied by boreal forest (mostly spruce) were 

vegetated by treeless alpine tundra between about 28 and 

31 ka. This evidence is consistent with limited plant 

macrofossil evidence reported previously from a site of 

approximately the same age at Tyone Bluff on the western 

edge of the basin (fig. 1; Thorson and others, 1981). 

No evidence has yet been found that serves as a basis 

for reconstructing full-glacial vegetation in the region. 

Most of the Copper River Basin was covered by glacier ice 

and lake waters, limiting potential sites for plant colonization to nunataks and relatively small areas of lowlands 

above lake level. In view of the poiien evidence from 

Sanford River interstadial deposits, it is highly likely that 

any vegetation types that developed on nunataks during full 

glacial times were herbaceous tundra communities. 

The vegetation that developed during late Wisconsin 

deglaciation can be reconstructed from samples taken at 

several localities in the Copper River Basin (Williams and 

Galloway, 1986). The Holocene record is based upon a 

combination of samples from outcrops and two lacustrine 

sediment cores (Ager and Brubaker, 1985; Ager, unpub. 

data). 

The earliest known vegetation to develop in the basin 

during the waning of late Wisconsin glaciers was herbshrub tundra dominated by Cyperaceae and dwarf Betula. 

This vegetation is known to have developed in the region 

as early as 13.28±0.4 ka (W-583)(Williams and Galloway, 

1986; Connor, 1984; Ager, unpub. data). A somewhat 

older age of 13.9±0.4 ka (I-3796) was reported for the 

lower Copper River valley by Sirkin and Tuthill (1987). 

Betula percentages abruptly increased during deglaciation, indicating the development of shrub tundra dominated 

by dwarf birch. Shrub tundra and shrub-herb tundra 

communities dominated the lowland landscape of the basin 

until early Holocene time, when Populus (balsam poplar or 

90 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
aspen trees) and Alnus (alder) shrubs rapidly invaded. The 

lowlands and lower slopes of uplands developed vegetation 

cover of poplar and willow stands, alder and willow shrub 

communities, and shrub tundra. 

Current evidence indicates that Picea first invaded the 

Copper River Basin from the north by at least 9 ka Picea 

apparently invaded from the Tanana River valley via 

Mentasta Pass and the Delta River valley (fig. 1) and 

spread rapidly westward and southward (Ager and 

Brubaker, 1985). Picea glauca (white spruce) was present 

at Tangle Lakes (fig. 1) by about 9.1 ka (Schweger, 1981). 

Picea reached the valleys of the northern Chugach Mountains (fig. 1) soon thereafter. Pollen evidence and radiocarbon ages bracket the arrival of Picea in that area between 

8.48±0.13 ka (I-11,397)(Williams and Galloway, 1986; 

Ager, unpub. data) and 9.02±0.2 ka at 70 Mile Lake 

(W-5336) (Ager and Brubaker, 1985). Recently published 

evidence from the upper Matanuska River valley (fig. 1) 

indicates that Picea reached that area at least as early as 

8.95±0.15 ka (I-14,096) (Williams, 1986). A buried spruce 

stump exposed in place near Chitina (fig. 1) yielded a 

radiocarbon date of 7.23±0.15 ka (W-5335, Ager, unpub. 

data). That age provides a minimum age for Picea in the 

Chitina and lower Copper River valleys. 

With the establishment of spruce-dominated boreal 

forest in the lowlands of the Copper River Basin, the available evidence suggests that only minor vegetation changes 

occurred thereafter in the region. There is some suggestion 

of lowering of treeline in the vicinity of Seventymile Lake 

during the Neoglacial (Ager and Brubaker, 1985), but there 

is also puzzling evidence from the Gulkana Upland that 

suggests a local spruce reinvasion near altitudinal tree line 

at about the same time (Ager and Sims, 1981). 

The studies done thus far provide only an outline of the 

region's history (fig. 2), but they reveal that the Quaternary 

deposits of the Copper River Basin contain a rich record of 

past environments and climates. Future palynological research that is needed in this region includes detailed studies 

of the Quaternary records in the vicinity of Mentasta Pass, 

and the central and northwestern areas of the basin. 

Much of the data discussed in this paper were derived 

from analyses of samples collected by J.R. Williams and 

OJ. Fenians, Jr. (U.S. Geological Survey). I gratefully 

acknowledge their willingness to share their samples and 

field data .. 

REFERENCES CITED 

Ager, T.A., and Brubaker, L., 1985, Quaternary palynology and 

vegetational history of Alaska, in Bryant, V.M., Jr., and 

Holloway, R.G., eds., Pollen records of late-Quaternary 

North American sediments: American Association of Stratigraphic Palynologists Foundation, Dallas, p. 353-384. 

Ager, T.A, and Sims, J.D., 1981, Holocene pollen and sediment 

record from the Tangle Lakes area, central Alaska: Palynology, v. 5, p. 85-98. 

Connor, C.L., 1984, Late Quaternary glaciolacustrine vegetational 

history of the Copper River Basin, south-central Alaska: 

University of Montana, Ph.D. thesis, 115 p. 

Ferrians, O.J., Jr., Nichols, D.R., and Williams, J.R., 1983, Copper River Basin, in Pewe, T.L., and Reger, R.D., eds., 

Richardson and Glenn Highways, Alaska: Guidebook to 

permafrost and Quaternary geology: Guidebook 1, International Conference on Permafrost, 4th, University of Alaska, 

Fairbanks, July 18-22, 1983: State of Alaska Department of 

Natural Resources, Division of Geological and Geophysical 

Surveys, p. 137-175. 

Hamilton, T.D., and Thorson, R.M., 1983, The Cordilleran ice 

sheet in Alaska, in Porter, S.C., ed., Late Quaternary environments of the United States: v. 1, The late Pleistocene: 

Minneapolis, University of Minnesota Press, p. 38-52. 

Hansen, H.P., 1953, Postglacial forests in the Yukon Territory and 

Alaska: American Journal of Science, v. 251, p. 505-542. 

Matthews, J.V., Jr., and Schweger, C.E., 1985, Old Crow tephra: 

Its significance for understanding the early and middle 

Wisconsinan climate history of eastern Beringia, in Rarington, C.R., ed., Climate change in Canada: Syllogeus, no. 55, 

p. 453-459. 

Schweger, C.E., 1981, Chronology of Late Glacial events from 

the Tangle Lakes, Alaska Range, Alaska: Arctic Anthropology, v. 18, p. 97-101. 

Yr B.P. 

X 10 3 Pollen zone 

Picea-AinusBetula 

zone 

Vegetation type 

Boreal 

forest 

Climatic type 

Present 

interglacial 

Latest 

Cll 

c: 

Cll 

u 

0 

0 

:I: 

Cll 

c: 

Cll 

u 

0 

iii 

'i 

a: 

Cll 

iV 

...I 

Figure 2. Summary of late Pleistocene and Holocene vegetational history of Copper River Basin and adjacent areas, 

south-central Alaska. 

History of Late Pleistocene and Holocene Vegetation in the Copper River Basin, Alaska 91 
Shackleton, J., 1982, Environmental histories from Whitefish and 

hnuruk Lakes, Seward Peninsula, Alaska: Columbus, Ohio 

State University, Institute of Polar Studies Report 76, 50 p. 

Sirkin, L.A., and Tuthill, S.J., 1987, Late Pleistocene and Holocene deglaciation and environments of the southern Chugach 

Mountains, Alaska: Geological Society of America Bulletin, 

v. 99, p. 376-384. 

Thorson, R.M., Dixon, E.J., Jr., Smith, G.S., and Batten, A.R., 

1981, Interstadial proboscidean from south-central Alaska: 

hnplications for biogeography, geology, and archaeology: 

Quaternary Research, v. 16, p. 404-417. 

Williams, J.R., 1986, New radiocarbon dates from the Matanuska 

Glacier bog section, in Bartsch-Winkler, Susan, and Reed, 

K.M., eds., Geologic studies in Alaska by the U.S. Geological Survey during 1985: U.S. Geological Survey Circular 

978, p. 85-88. 

Williams, J.R., and Galloway, J.P., 1986, Map of western Copper 

River Bas in, Alaska, showing lake sediments and shorelines, 

glacial moraines, and location of stratigraphic sections and 

radiocarbon-dated samples: U.S. Geological Survey OpenFile Report 86-390, scale 1:250,000, 30 p. 

Carter, L. David, Hamilton, Thomas D., and Galloway, John P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

92 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Pleistocene Vertebrate Localities in the Yukon 

By C. Richard Harington 

Among ice-age vertebrate localities in Canada, those in 

unglaciated parts of the Yukon are most productive of 

fossils (Harington, 1985). The National Museum of Natural Sciences (NMNS) has been carrying out a long-term 

project of collecting and studying Pleistocene vertebrate 

fossils in the Yukon since 1966. Its collections from the 

Old Crow area have been greatly augmented by those of the 

Northern Yukon Research Program and the Y uk:on Refugium Project, both of which began about 1975. The following sections present previously unrecorded faunal lists 

(table 1) and radiocarbon ages (table 2) on Yukon Pleistocene vertebrates, as well as comments on evidence for early 

humans at Yukon localities (fig. 1). 

Old Crow Basin 

The Old Crow Basin (area 2 on fig. 1) is the richest 

area for collecting Pleistocene vertebrate remains in Canada, having yielded some 40,000 specimens representing 

nearly 60 mammal species, at least 7 fish species (Crossman and Harington, 1970; Cumbaa and others, 1981), and 

at least 33 bird species (G. R. Fitzgerald, NMNS, oral 

commun., 1985) during the last 20 years. Approximately 

150 fossil localities are known within the basin. Remains 

of taxa found in place between Lower Lake (pre-Sangamon?) and Upper Lake (late Wisconsin) clays, as well as 

those recovered by intensive collecting at a productive 

point bar (loc. 11A) are listed in table 1 (Harington, 1977, 

1985; Morlan, 1980b, 1984; Jopling and others, 1981). 

Abundant remains of large-homed bison that apparently 

died catastrophically about 12 ka have been collected in 

place above the Upper Lake clay at locality 11(1) (see 

Harington (1977) for locations of numbered vertebrate 

localities in the Old Crow Basin). Woolly mammoths 

survived in the basin until about that time, because a partial 

skeleton of a young individual collected in 1985 from 

locality 92 yielded a radiocarbon age of 13.82±0.84 ka 

(Beta-13867). Among the most interesting mammals represented are Jefferson's ground sloth, giant pika, giant 

beaver, short-faced bear, short-faced skunk, hyena, scimitar 

cat, gigantic camels, and the primitive Soergel's muskox. 

When did people frrst reach the Yukon? Jopling and 

others (1981) claim that specimens of bone interpreted to 

be artifacts from the reworked Lower Lake beds at locality 

12 are of pre-Sangamon age. A caribou antler pestle has 

been dated by radiocarbon at about 24.5 ka at the Chalk 

River accelerator mass spectrometer (AMS) of Atomic 

Energy Canada Ltd. (R.E. Morlan, Archaeological Survey 

of Canada, oral commun., 1984). However, recent AMS 

radiocarbon determinations on several artifacts that were 

thought to provide evidence for late Pleistocene human 

occupation of the Yukon have all given late Holocene ages 

(Nelson and others, 1986). For example, a caribou tibia 

fleshing tool originally dated at about 27 ka (Irving and 

Harington, 1973) and the jaw of a domestic dog from 

locality 11A (Beebe, 1980b) are now dated at 1.35±0.15 

and 2.11±0.4 ka, respectively. A fragmentary mandible of 

a child from locality 11A, considered to be of possible 

Pleistocene age (Irving and others, 1977), needs similar 

checking, as does a caribou antler punch from Hunker 

Creek in the Dawson area, because a caribou antler in the 

same collection and in similar condition yielded a radiocarbon age of 23.9±0.47 ka (I-8580) (Harington, 1975). 

Despite the fact that no Pleistocene living floors with artifacts have been found so far, there is still strong circumstantial evidence for human Pleistocene occupation of the 

Yukon (for example, Morlan, 1980a, .Harington, 1980). 

Bluefish Caves 

Bluefish Caves I-III (area 3 on fig. 1) have yielded a 

Pleistocene vertebrate fauna. Apparently the caves resulted 

from solution and congelifraction of ancient mixed limestone breccia. The fossils, from a loess bed underlying 

peaty material, yield radiocarbon ages between about 25 

and 12 ka. Relatively recent specimens of small horse 

(12.9±0.1 ka, GSC-2881), mammoth (15.5±0.13 ka, 

GSC-3053), and saiga antelope have been collected here. 

The partial skull of the saiga gave an AMS radiocarbon age 

of about 13 ka (Jacques Cinq-Mars, Archaeological Survey 

of Canada, oral commun., 1986), suggesting the existence 

of steppe-like conditions toward the close of the last glaciation. Evidently most of the fossils accumulated in grassy 

tundra surroundings (Cinq-Mars, 1979, 1982). Artifacts 

found in the loess unit indicate that humans occupied the 

caves, perhaps hunting and butchering many of the large 

mammalian species, near the end of the last glaciaton. 

Sixtymile 

Since 1975, a gold placer site (Sixtymile locality 3) has 

yielded hundreds of excellent specimens, including remains 

of the relatively rare western camel (23.32±0.64 ka, 

Beta-8864), helmeted muskox, and tundra muskox 

(21.16±0.28 ka, Beta-13869). Carcasses of black-footed 

ferret from this site, and arctic ground squirrel (Walker, 

Pleistocene Vertebrate Localities in the Yukon 93 
\0 

oil- Table 1. Ice Age vertebrate taxa recorded for various fossil localities in the Yukon Territory 

[x, present;-,not collected or identified so far; cf., closely comparable specimen identified; *, extinct; **, extinct in Yukon Territory or reintroduced] r-

~ ~ 

("') 1. Herschel 2. Old Crow basin (stratigraphic) Locality 3. Bluefish 4. Sixtymile 5. Dawson 6. Dawson 7. Dublin 8. Big Creek ~ Island 11A Caves 1-111 locality 3 locality 10 localities Gulch localities :I 

0 (7 localities) 32-33 locality 1 1-3 N Reworked Base of Upper Mixed Loess zone Hunk« Creek Gold Run 0 

;;· lower interlake interlake (80 Pup) Creek 

:t: (Sangamonl lake beds beds beds (early (middle (middle 

(ij" to late (latest (Sangamonl (early Pleistocene (apptox. to late (late to late (middle (middle 

S' Wisconsin) lllinoianl) 120ka) Wisconsin) to Holocene) 25-10 ka) Wisconsin) Wisconsin) Wisconsin) Wisconsin) Wisconsin) 

-< 

0 Fishes X X X X X -:r WhiteflSh (Coregonus sp.) X X X 

~ Broad whitefish (Coregonus 110SUS) X X X 

:;- lnconnu (SteNJdus leucicthys) cf. X - cf. 

1! Arctic grayling (Thymallus arcticus) - X X 

~- Pike (Esox sp.) X cf. 

Sucker (Catostomus sp.) X X X 

= Longnose Sucker (Catostomus catostomus) X X 

~ 

:r Burbot (Lota Iota) X X 

Ill Sculpin (Cottus sp.) X 

0 

-;I> Bird~ X X X X X X 

~ Loon (Gavia sp.) X 

~ Horned Grebe (Podiceps auritus) X ~ 

~ Ducks and geese (Anatidae) X X X X 

:I Goose (Chen sp.) cf. cf. c. American widgeon (Mareca americana) cf. 

:r 

~ Oldsquaw (Clanglua hyemalis) X 

-<: Scoter (Melanitta sp.) X 

c Ptarmigan and grouse (fetraonidae) cf. X X X X ~ 

0 Shorebirds (Charadriiforrnes) - cf. :I Perching birds (Passeriforrnes) X X 

Mammals X X X X X X X X X X X 

Shrews (Soricidae) X X X X X 

*Plains shrew (Planisorex dixonensis) - cf. 

Shrew (So rex sp.) X 

Humans (Homo sp.) - X 

*Jefferson's ground sloth (Megalonyxjeffersonil) X 

*Giant pika (Ochotona cf. whartoN) X X X X 

Pika (Ochotona princeps) X X X 

Snowshoe hare (Lepus americanus) X X X X X 

**Arctic hare (Lepus arcticus) X X X X X - - - cf. 

Woodchuck (Marmota monax) X 

Arctic ground squirrel (Spermophilus parryi) X X X X X X 

Beaver (Castor canadensis) X X X X 

*Giant beaver (Castoroides ohioensis) X X X X 

*Primitive lemming (Predicrostonyx sp.) - X 

Collared lemming (Dicrostonyx sp.) X X X X X 

Brown lemming (Lemm.us sibiricus) X X X X X 

Red-backed vole (ClethrioNJmys rutilus) X X X 

Muskrat (Ondatra zibethicus) X X X X X 

Heather vole (Phenacomys intermedius) - X X 

Singing vole (Microtus miurus) X X X X X 

Meadow vole (Microtus pennsylvanicus) - X 

Tundra vole (Microtus oeconomus) cf. cf. 

Yellow-cheeked vole (Microtus xanthoganthus) X cf. X X X 
Large whale (Cetacea cf. Balaena mysticetus) X 

Coyote (Canis latrans) - X 

Wolf(Canis lupus) cf. X X X X X X cf. 

Domestic dog (Cani.s familiaris) - X cf. 

Arctic fox (Alopex lag opus) X X X X X X 

Red fox (Vulpes vulpes} - X X 

*Yukon short-faced bear (Arctos simus yukonensis) - X X X 

Bear (Ursus sp.) X X cf. cf. - X 

Black bear (Ursus america1U4S) X 

Brown bear (Ursus arctos) cf. X 

Ermine (Mustela erminea) X X X 

Least weasel (Musti!la nivalis) X 

**Black-footed ferret (Mustela nigripes) - X X 

Noble marten (Martes nobilis) X 

American marten (Martes americana) X X 

Fisher (Martes peMtmtl) X X 

Wolverine (Gulo gulo) X X X 

**Badger (faxidea ta.xus) X X 

*Short-faced skunk (Brachyprotoma obtusata) X cf. 

Otter (Lutra can.a.cknsis) - X 

*Hyaena (Adcrocuta sp.) X 

Mountain lion (Felis coN:olor) X 

Lynx (Felis can.a.cknsis) cf. X 

*American lion (?anthera leo atrox) X X X X X X X X 

• American scimitar cat (/I omotherium serum) X 

Small seal (Phoca_sp.) X 

• American mastodon (M ammut america""'") X X 

*Mammoth (Mammuthus sp.) X X X X X X X X X cf. X 

*Southern mammoth (Mammuthus meritlionalis) - X - - - - *Woolly mammoth (Mammuthus primigenius) X cf. X X X cf. X X X cf. X 

**Horse (Equus sp.) X X X X X X X X X X X 

*Large horse (Equus verae) X X X X cf. cf. 

*Scott's horse (Equus scott1) cf. - cf. 

*Small horse (Equus lambe1) X - X X X X X X X 

**Kiang (Equus (Asinus) k.iang) - - X 

"" *Large camel (Camelini) X X ii" 

c;;· *Western camel (Camelops hesternus) - - X 

0 **Wapiti (Cervus elaphus) - X X X 

n Moose (Alces sp.) X X X X X X X X tD 

::2 

tD *Giant moose (Alces latifrons) X - < American moose (Alces alces) X cf. X X cf. cf. 

tD Caribou (fian.gifer taran.dus} X X X X X X X X X X ;. **Bison (Bison. sp.) X X X X X X X X X X c-

.. *Large-homed bison (Bison. priscus) cf. X cf. X X X cf. X 

~ *Alaskan bison (Bison. alaslunsis) X X tD 

r- **Saiga antelope (Saiga tatarica) - X 

n 

0 *Muskoxen (Ovibovini) X X X X X X - X 

S: *Soergel's muskox (Soergelia sp.) X - - X 

;;· *Helmeted muskox (Symbos cavifrons) X - X X - cf. (II *Staudinger's muskox (Praeovibos priscus) X 

:;· **Tundra muskox (Ovibos moschatus) X - - X X X 

~ Dall sheep (Ovis dall1) - X X X - X X 

tD 

-< 

c Note: In addition to species mentioned here: flat-headed peccary (Platygonus compressus) has been recorded fran Old Crow locality 74 (Beebe. 1980a); steppe mammoth (Mammuthus armeniacus or M. columb,) is ~ 

0 known from various Old Crow localities, including locality 22, as well as Dawson locality 8 (Quartz Creek) (Harington, 1977, 1980); dhole (Cuon. sp.) is recorded from Old Crow locality 14N (Harington, 1977); western biscn ::2 (Bison bison occickntalis) is reported from Old Crow River (Gilmore, 1908) and the Dawson area (Haringtm, 1977); black-footed ferret (Mustela nigripes) is tentatively considered to be conspecific with Mustela 

eversmanni(Old Crow localities 65 and 83); and Bootherium sargenti is cmsidered to be a female of and conspecific with the Helmeted muskox (Symbos cavifrons). 

\D 

U1 
Table 2. Radiocarbon ages for fossil vertebrates and plant 

macrofossils from the Yukon 

Fossil 

Old Crow Basin 

Mammoth 

Domestic dog 

Bluefish Caves 

Small horse 

Mammoth 

Sixty mile 

Western camel 

Tundra muskox 

Black-footed ferret 

Arctic ground squirrel 

Brown bear 

Mastodon 

Spruce wood 

Dawson Area 

Caribou 

Brown bear 

Short-faced bear 

Grass (ground squirrel nest) 

Alaskan bison 

Long-homed bison 

Mammoth 

Dublin Gulch 

Horse 

Big Creek 

Willow wood 

Ketza River 

Bison 

Herschel Island 

Small horse 

Radiocarbon 

age 

13.820±840 

2.110±40 

12.900±100 

15.500±130 

23.320±640 

21.160±280 

39.560±490 

47 .500±1.900 

36.500±1.150 

24.980±1.300 

26.080±300 

23.900±470 

41.000±1.050 

29.600±1.200 

12.200±100 

>39.000 

22.200±1.400 

32.350±1.750 

laboratory 

number 

Beta-13867 

T0-276 

GSC-2881 

GSC-3053 

Beta-8864 

Beta-13869 

T0-214 

Beta-16157 

Beta-16162 

Beta-16163 

Beta-13870 

I-8580 

Beta-16159 

1-11037 

GSC-2641 

1-5405 

1-3570 

I-4226 

31.450±1.300 1-10935 

48.100±1.100 GSC-3032-2 

26.350±280 T0-393 

16.200±150 SFU:RIDDL-765 

1984) from Sixtymile locality 4, a few kilometers away, 

gave AMS radiocarbon ages of 39.56±0.49 ka (T0-214) 

and 47.5±1.9 ka (Beta-16157), respectively (Youngman 

1987). Brown bear bones from Sixtymile locality 3 and 

from Dawson locality 16 (Hunker Creek) yielded radiocarbon ages of 36.5±1.15 ka (Beta-16162) and 41±1.05 ka 

(Beta-16159), respectively, indicating that this species 

lived in the west-central Yukon before the peak of the last 

glaciation. Of particular interest is a radiocarbon age of 

26.08±0.3 ka (Beta-13870) on a spruce stump in growth 

position-one of many such stumps in similar stratigraphic 

position at the site. In this regard, it is worth noting that a 

mastodon tooth from nearby Sixtymile locality 5 yielded a 

radiocarbon age on collagen of 24.98±1.3 ka (Beta-16163). 

Since American mastodons evidently preferred open spruce 

forest habitat, I am examining the possibility that spruce 

pockets existed in this region just before the peak of the last 

glaciation, if not later. 

Dawson Area 

Ice-age vertebrate remains near Dawson, like those at 

Sixtymile, Dublin Gulch, and Big Creek, are mainly exposed during placer mining for gold. Approximately 50 

localities are recorded in the region. Most of the fossils, 

when found in place, occur in frozen organic silt just above 

the surface of gold-bearing gravel, and most date to the 

latter half of the Wisconsin glaciation (about 30 to 15 ka). 

Generally, fossils from this area are more complete than 

those from Old Crow Basin. Faunas from Hunker Creek 

(80 Pup) and Gold Run Creek are typical of the Dawson 

area. 

Collecting at 80 Pup (Dawson loc. 10) began in 1973 

and has continued to the present. During that period, about 

260 ice-age mammal bones have been collected. Approximately 90 percent of the finds comprise large-homed bison 

(46 percent), small horse (19 percent), mammoth (11 percent), Dall sheep (11 percent), and caribou (3 percent). Of 

14 bones found in place, their average height above the 

surface of the gold-bearing gravel is 1.5 m. Rarely, bones 

are found up to 5 m above the gravel. A humerus of a 

short-faced bear found in place in frozen organic silt 3 em 

above the surface of the gold-bearing gravel yielded a 

radiocarbon age of 29 .6±1.2 ka (1-11 037), indicating the 

presence of this unusually long-limbed species in the region 

before the peak of the last glaciation (Harington, 1980). 

Most specimens are incomplete, but many good skulls of 

large-homed bison, Dall sheep, woolly mammoth, and one 

of an American lion, have been collected here. An interesting find in 1984 consisted of a nearly complete cranium 

of a young woolly mammoth with teeth and tusks (the latter 

about 53 em long) from the interface of the gold-bearing 

gravel and the organic silt. Several skulls of arctic ground 

squirrels have been recovered, as well as their droppings 

and nesting grasses from nests frozen in the organic silt 

some 3.7 m above the surface of the gold-bearing gravel. 

Grasses from a ground squirrel nest on nearby Dominion 

Creek yielded a radiocarbon age of 12.2±0.1 ka 

(GSC-2641), which may give an idea of the age of the 

nests at 80 Pup. Pathological signs are occasionally noted 

too, for example a bison mandible with lesions on the 

ascending ramus, and a series of eight bison thoracic vertebrae with offset neural spines. 

Gold Run Creek (Dawson locs. 31 through 33) is about 

50 km southeast of Dawson. The area remained unglaciated during the Pleistocene, and constituted the southeastern extremity of the Beringian refugium. Two important 

specimens from this locality were described more than 70 

years ago: the type skull of the Yukon short-faced bear 

(Lambe, 1911) and the type skull of the small horse (Hay, 

1917). Other specimens of interest are badger, American 

mastodon, a nearly complete skull of a mammoth which 

was exhibited in Dawson in 1907 (Quackenbush, 1909), the 

first kiang horse described from Beringian Pleistocene 

deposits, and Alaskan bison (Harington and Clulow, 1973). 

96 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
The badger, represented by a humerus, is the ftrst record for 

the Yukon, and is signiftcant because it indicates a former 

grassland link between the northern prairies and the interior 

of the Yukon and Alaska. Unfortunately a 1986 attempt at 

AMS radiocarbon dating of another badger specimen from 

Dominion Creek (Dawson loc. 28) failed It is still a priority to establish when badgers entered and lived in the 

Yukon, because of the important paleoenvironmental and 

paleoclimatic implications. The deeply buried Alaskan 

bison horncore yielded an age of >39.9 ka (1-5405), one of 

the few non-finite dates on Pleistocene mammal bones 

from the region. If a North American ancestor for the giant 

bison (Bison latifrons) is sought, the Alaskan bison would 

be a good choice. Large-horned bison and mammoth bones 

from Gold Run Creek gave radiocarbon ages of 22.2± 1.4 

ka (1-3570) and 32.35±1.75 ka (1-4226), respectively. 

Dublin Gulch 

In 1967 I collected an astragalus of a small ungulate at 

Dublin Gulch, north of Mayo. About 70 bones of ice-age 

mammals subsequently were collected during the summer 

of 1977, presumably from an organic unit underlying glacial till and colluvium, and all but seven (kept as a representative sample in the Paleobiology Division of NMNS) 

were sent to the Kluane Museum of Natural History at 

Burwash Landing after identiftcation. Species most commonly represented are small horse (38 percent), bison (36 

percent), Dall sheep, and caribou (10 percent each). A 

horse metatarsal from the site has a radiocarbon age of 

31.45±1.3 ka (1-10935), indicating that this fauna occupied 

the Mayo area during the last interstadial. This locality, 

like Big Creek and Ketza River, is of greater interest than 

usual because it has been glaciated. 

Big Creek 

So far, Pleistocene vertebrate remains have been collected from three tributaries of Big Creek: (1) Revenue 

Creek, where American lion, large-horned bison, and parts 

of a woolly mammoth skeleton were recovered in 1979 

from nonglacial peaty beds that may be of last interstadial 

age (willow wood from the frozen peat yielded a radiocarbon age of 48.1±1.1 ka; GSC-3032-2); (2) Happy Creek, 

where mammoth, horse, caribou, large-horned bison, and 

Dall sheep were recorded in 1980 and 1983; and (3) Boliden Creek, where brown bear, woolly mammoth, small 

horse, caribou, bison, and Dall sheep remains were recorded in 1983. The brown bear cranium is in excellent 

condition and should be radiocarbon-dated. 

Ketza River 

About 40 fragmentary specimens of mammals, including hare, ground squirrel, collared lemming, mammoth, 

small horse, moose, and bison were collected in 1986 and 

1987 from Wisconsin interstadial deposits underlying till of 

the McConnell glaciation. Bison bone found in place 

yielded an AMS radiocarbon age of 26.35±0.28 ka 

(T0-393). This is the most southerly Pleistocene vertebrate locality yet recorded in the Yukon. 

Herschel Island 

In contrast to Ketza River, Herschel Island Pleistocene 

vertebrate sites are the most northerly in the Yukon, and are 

the only ones that have produced in-place marine mammal 

remains. Although none of the marine mammal bones has 

been dated, a possible bowhead whale specimen was in 

place in "preglacial" (pre-early Wisconsin?) marine sand, 

and a seal scapula fragment came from oxidized organic 

deposits (including marine mollusk shells) approximately 5 

m above present sea level, which I suspect are of last interglacial age (Harington, 1977). On the northeastern coast of 

the island, a partial cranium of a small horse from silty sand 

that postdates the Buckland glaciation of inferred early 

Wisconsin age has yielded an AMS radiocarbon age of 

16.2±0.15 ka (SFU:RIDDL-765). Because seven scattered 

fossil sites were discovered during a relatively short period 

of time, a systematic investigation for ice-age vertebrate 

remains is planned for Herschel Island. 

140" 135" 130" 120" 

70" 

Figure 1. Yukon Territory (dashed outline), showing main 

Pleistocene vertebrate sites referred to in text: 1, Herschel 

Island; 2, Old Crow Basin; 3, Bluefish Caves; 4, Sixtymile; 5, 

Dawson area (80 Pup); 6, Dawson area (Gold Run Creek); 7, 

Dublin Gulch; 8, Big Creek; 9, Ketza River. 

Pleistocene Vertebrate Localities in the Yukon 97 
Acknowledgments 

I am most grateful to the following people for their 

assistance: Old Crow Basin-P. Lord, C. Thomas, and 

G.R. Fitzgerald for field assistance; B.F. Beebe, R.E. 

Morlan, and W.N. Irving for their great paleobiological 

contributions; W .N. Irving and T .N. Friesen for supplying 

their list of taxa from locality llA; Bluefish Caves-J. 

Cinq-Mars for supplying a current list of species from the 

loess unit (RE. Morlan identified the microtine rodent 

remains and P.M. Youngman the small carnivores) and 

generously allowing me to quote some radiocarbon dates he 

obtained; Sixtymile-W. Yaremcio, A. Brisebois, and particularly C. and L. McDougall for their great generosity in 

donating important specimens and for their continued hospitality; the late R. Hughes, a most helpful coworker on the 

geology of the site; Dawson (80 Pup)-E. Raguth, V. Hall, 

and particularly T. Kosuta for donation of important specimens and hospitality; Dawson (Gold Run Creek)-L. Ross, 

J. Lamontagne, S. Mynott, and particularly E. Schink for 

donating important specimens and hospitality; W.Y. Watson and F.V. Clulow were instrumental in purchasing many 

specimens from the site and ultimately donating the bulk of 

them to the NMNS in July 1980; Dublin Gulch-F. Taylor, 

and particulary D. Duensing and R. Holway for collecting 

the specimens; M. Rogers (Kluane Museum, Burwash 

Landing) for donating a representative sample to the 

NMNS; R.E. Morlan for providing a copy of his 1977 field 

notes on the locality; Big Creek-R. McCauley and particularly K. Djukastein and G. MacPherson for donating 

important specimens and hospitality; Stephen Morison, 

O.L. Hughes, and R.W. Klassen for stratigraphic and radiocarbon information, and R.L. Debicki for arranging transportation to the site in 1980; Ketza River-L.E. Jackson, 

Jr., for discovering the locality, collecting and transferring 

important fossils to the NMNS, and supplying critical stratigraphic information; Herschel Island-D. Gill, M. 

Bouchard, V. Rampton, J. Hunston, R. Collier, S. Dallimore, and S. Wolfe; and the Canadian Wildlife Service for 

allowing me to accompany their biologists on a flight from 

Old Crow to Herschel Island in 1973. 

REFERENCES CITED 

Beebe, B.F., 1980a, Pleistocene peccary, Platygonus compressus 

LeConte, from Yukon Territory, Canada: Canadian Journal 

of Earth Sciences, v. 17, p. 1204-1209. 

--1980b, A domestic dog (Canis familiaris L.) of probably 

Pleistocene age from Old Crow, Yukon Territory, Canada: 

Canadian Journal of Archaeology, v. 4, p. 161-168. 

Cinq-Mars, J., 1979, Bluefish Cave 1: A Late Pleistocene Eastern 

Beringian cave deposit in the northern Yukon: Canadian 

Journal of Archaeology, v. 3, p. 1-32. 

--1982, Les grottes du Poisson-Bleu: Geos, v. 11, no. 1, p. 

19-21. 

Crossman, E.J., and Harington, C.R., 1970, Pleistocene pike, Esox 

lucius, and Esox sp., from the Yukon Territory and Ontario: 

Canadian Journal of Earth Sciences, v. 7, p. 1130-1138. 

Cumbaa, S.L., McAllister, D.E., and Morlan, R.E., 1981, Late 

Pleistocene fish fossils of Coregonus, Stenodus, Thymallus, 

Catostomus, Lota and Cottus from Old Crow Basin, northern 

Yukon, Canada: Canadian Journal of Earth Sciences, v. 18, 

no. 11, p 1740-1754. 

Gilmore, C.W., 1908, Smithsonian exploration in Alaska in 1907 

in search of Pleistocene fossil vertebrates: Smithsonian 

Miscellaneous Collection, v. 51, no. 3, p. 1-38. 

Harington, C.R., 1975, A bone tool found with ice age mammal 

remains near Dawson City, Yukon Territory: Arctic Circular, v. 23, no. 1, p. 1-5. 

---1977, Pleistocene mammals of the Yukon Territory: 

Edmonton, University of Alberta, Ph.D. thesis, 1060 p. 

--1980, Radiocarbon dates on some Quaternary mammals 

and artifacts from northern North America: Arctic, v. 33, no. 

4, p. 815-832. 

--1985, Comments on Canadian Pleistocene mammals: 

Acta Zoologica Fennica, v. 170, p. 193-197. 

Harington, C.R., and Clulow, F.V., 1973, Pleistocene mammals 

from Gold Run Creek, Yukon Territory: Canadian Journal of 

Earth Sciences, v. 10, p. 697-759. 

Hay, O.P., 1917, Description of a new species of extinct horse, 

Equus lambei, from the Pleistocene of Yukon Territory: 

Proceedings of the United States National Museum, v. 53, p. 

435-443. 

Irving, W .N., and Harington, C.R., 1973, Upper Pleistocene radiocarbon-dated artefacts from the northern Yukon: Science, v. 

179, p. 335-340. 

Irving, W.N., Mayhall, J.T., Melbye, F.J., and Beebe, B.F., 1977, 

A human mandible in probable association with a Pleistocene 

faunal assemblage in eastern Beringia: A preliminary report: 

Canadian Journal of Archaeology, v. 1, p. 81-93. 

Jopling, A.V., Irving, W.N., and Beebe, B.F., 1981, Stratigraphic, 

sedimentological and faunal evidence for the occurrence of 

pre-Sangamonian artefacts in northern Yukon: Arctic, v. 34, 

no. 1, p. 3-33. 

Lambe, L.M., 1911, On Arctotherium from the Pleistocene of 

Yukon: Ottawa Naturalist, v. 25, p. 21-26. 

Morlan, R.E., 1980a, Taphonomy and archaeology in the Upper 

Pleistocene of the northern Yukon Territory: A glimpse of 

the peopling of the New World: National Museum of Man 

Mercury Series, Archaeological Survey of Canada Paper No. 

94, p. 1-380. 

--1980b, Yukon Refugium Project, in Marois, R.J., ed., 

Archaeological Survey of Canada Annual Reviews 

1977-1979: National Museum of Man Mercury Series, Archaeological Survey of Canada Paper No. 95, p. 65-68. 

--1984, Biostratigraphy and biogeography of Quaternary 

microtine rodents from northern Yukon Territory, Eastern 

Beringia: Carnegie Museum of Natural History Special 

Publication No. 8, p. 184-199. 

Nelson, D.E., Morlan, R.E., Vogel, J.S., Southon, J.R., and Harington, C.R., 1986, New dates on northern Yukon artifacts: 

Holocene not upper Pleistocene: Science, v. 232, p. 

749-751. 

Quackenbush, L.S., 1909, Notes on Alaskan mammoth expeditions of 1907 and 1908: Bulletin of the American Museum 

of Natural History, v. 26, p. 87-130. 

Walker, L., 1984, The "moon-egg" that contained an arctic 

ground squirrel: BlOME, v. 4, p. 1. 

Youngman, P.M., 1987, Freeze-dried mummies are hot items with 

paleontologists: BlOME, v. 7, no. 2, p. 4. 

Carter, l. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

98 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Arctic Microtine Biochronology-Current Status 

By Charles A. Repenning 

The microtine rodents include the lemmings, muskrats, 

meadow mice, and similar small-eared, usually short-tailed 

mice; the name derives from their small ears. They live, 

and have lived, only in the Northern Hemisphere. The 

microtines are polyphyletic and include five lineages that 

derive from different, large-eared ancestors within the 

Family Cricetidae. Most of these lineages have evolved 

faster than any other mammal whose history is known; as 

a result, they are noted for recognizable changes in shorter 

periods of time than are other mammals. This makes their 

biochronology more precise for interpreting geologic time. 

The biochronology of the microtine rodents of the 

Northern Hemisphere spans the past 6.5 m.y. and was first 

reconstructed about 10 years ago (Repenning and Feijfar, 

1977). Subsequently, its factual foundations and its network of correlations with other methods of inferring geologic time have been greatly enlarged and the confidence of 

dates based upon the microtine biochronology has been 

accordingly strengthened. 

Because of varying precision of temporal control, the 

6-m.y.-long microtine biochronology is stronger during 

some intervals than in others. However, on the average, 

this biochronology can distinguish time differences as brief 

as 250 k.y., and this is sufficient to identify magnetic polarity events. Microtine dates combined with polarity determinations are significantly refmed in dating precision; in 

many cases the uncertainty is reduced by half. Under ideal 

conditions, with both associated magnetic and climatic 

sequences, this biochronology enables a correlation of climatic changes on the continents with the oxygen-isotope 

stages in the oceans. In such cases, the uncertainty in 

dating is nearly reduced to the errors necessitated by the 

assumptions of constant depositional rates in oceanic deposits. 

Most microtine rodents evolved in the Arctic region, 

and the microtine biochronology is very applicable there. 

The Beringian segment of the Arctic Ocean borderland is 

unique in that there the "microtine east" meets the "microtine west." Thus Beringia holds many of the biochronologic 

keys of the entire Arctic Ocean borderland, and these keys 

are significant also to the biochronologies of other parts of 

the Northern Hemisphere at lower latitudes. Because of 

this intermediate position, an understanding of only North 

American (Rcpenning, 1987) or of only Eurasian microtine 

biochronology is not enough to fully comprehend the 

temporal significance of Beringian fossil microtines. 

Twenty years ago the Arctic Ocean borderland was an 

area completely devoid of information about pre-Pleistocene, or even pre-Illinoian, land mammal faunas. No information was known about Arctic microtine rodents older 

than latest Pleistocene until 1971, when Guthrie and Matthews described the Cape Deceit fauna from the Seward 

Peninsula. At that time, there was only a suspicion in a few 

minds that microtine rodents mighf provide a worldwide 

biochronology, and thus the temporal significance of the 

Cape Deceit fauna could not be realized. In addition, the 

taxonomic composition of the fauna had little chance of 

being fully recognized. 

The breakthrough in Beringian microtine biochronology came in 1979 through the efforts of A.V. Sher, the 

principal student of the Kolyma lowlands in eastern 

Yakutia, U.S.S.R., and his associates, particularly V.S. 

Zazhigin, the microtine specialist. Sher directed an interdisciplinary study of the Krestovka section in the Kolyma 

lowlands that identified many significantly primitive microtine faunas. These were tied to paleomagnetic determinations and to climate indicators. Today the Krestovka 

section is the "key" to the microtine biochronology of 

Beringia and the Arctic Ocean borderland (see fig. 1). 

The microtine faunas of the Krestovka section that 

have sufficient temporal control to be of use in biochronology are from that part of the section that is between 3 and 

2 Ma. Faunal assemblages younger than 2 Ma are present 

in the Krestovka section, but paleomagnetic correlations are 

not clear, and the faunas are not sufficiently definitive to 

indicate age. The useful faunas are the biochronologic 

basis for understanding the age of the Cape Deceit fauna 

and of a fauna from Fish Creek on the Alaskan North Slope 

(Repenning and others, 1987; see fig. 1). 

Through the Krestovka section an intercontinental 

biochronologic correlation network has been established 

that is the foundation for future research. The network also 

provides insight into the evolutionary pattern of several 

lineages that explains anomalous faunal relations that have 

hampered interpretation of arctic faunas, as well as of 

faunas in lower latitudes. These anomalies include the 

earlier record in Asia of many lineages, the abrupt appearance of many genera, as Microtus, Phenacomys, Mictomys, 

Pitymys, Allophaiomys, and Dicrostonyx in both Europe 

and North America with no record of where they evolved, 

and the asynchronous appearance of evolutionary lineages 

in different parts of the Arctic Ocean borderland. 

The earliest records of at least four microtine genera 

are found in the Krestovka section of western Beringia. 

These records are between 200 and 400 k. y. older than the 

oldest records in Europe and North America (Repenning, 

Arctic Microtine Biochronology 99 
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FAUNAL AND 

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ICE AGES 

Galerian fauna 

---'"- I Laurentide ice 

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Figure 1. Current status of arctic microtine biochronologic correlations. Oxygen isotope records replotted from original data (Iceland: Shackleton and others, 1984; 

Ponape: Shackleton and Opdy~ 1976) to a common temporal scale; no paleomagnetic control intended below the Olduvai event for site V28-239 nor above it for site 

552 A. J, Jaramillo Normal-Polarity Subchron; 0, Olduvai Normal-Polarity Subchron; R, the two brief events of the Reunion Normal-Polarity Subchron; K, Kaena 

Reversed-Polarity Subthron; and M, Mammoth Reversed-Polarity Subchron. 
1984), which clearly confirms previous interpretations that 

these four genera must have been immigrants to lower 

latitudes, presumably from Siberia (Kowalski, 1966). 

Delays in the dispersals of some microtines from 

Asiatic Beringia to North American Beringia can now be 

demonstrated, and similar delays for dispersal of some 

large mammals from Beringia to other areas of the Northern Hemisphere are also beginning to be recognized as a 

result of Sher's study in the Kolyma lowlands. Such 

understanding of the origins and dispersals of faunas provides a clearer concept of the historic framework of biochronology, particularly the biochronology of the Arctic 

Ocean borderland. Many mammalian types evolved in this 

region, and they have an older temporal significance here 

than in lower latitudes. 

In direct contrast to what was possible as little as three 

years ago, it is highly likely that any adequate microtine 

fauna found in the Canadian-Alaskan arctic can be convincingly dated to within about 200 ka if it is between 3 and 2 

Ma. Dating with even greater precision is possible if the 

paleomagnetic pattern is known; dating with still greater 

precision is feasible if the climatic pattern is also known. 

However, the same cannot be said of micro tine faunas 

between 2 and 1 Ma, because there is no as yet "key" 

section for this period of time. Even in the well-known 

areas of Europe and the conterminous United States, 

mammalian biochronology is weak for the period between 

the Olduvai and Jaramillo Normal-Polarity Subchrons of 

the Matuyama Reversed-Polarity Chron. The beginning 

and the end of this time are well dated and are easily identifiable in the lower latitudes by the immigration of microtines that completely alter the faunal composition, but there 

is as yet no well-documented biochronology for the intervening 500 k.y. These immigrants came from the north, 

and their ancestors are found in older sediments of Beringia. Microtines of the older immigration have been found 

in Beringian deposits older than 2 Ma. Those of the 

immigration 850 ka are still poorly known in the Arctic, but 

should be found in Beringian deposits that formed between 

2 and 1 Ma. At present only one Beringian locality in 

Canada (Old Crow locality 47; R.E. Morlan, oral commun., 

1985), and one in Yakutia (type locality of the Olyor Suite; 

Sher, 1971) are known that date from this time span, but 

studies of these two localities are already improving biochronologic understanding of this vague period (see fig. 1). 

In fact, the correlation of events during this period, at 

present, is better understood in the Arctic Ocean borderland 

than it is in lower latitudes (Repenning, 1987). 

This long period of poorly known microtine history 

ended 850 ka with the southward dispersal of arctic microtines and other mammals. In North America, this dispersal included both large and small mammals and appears 

to have resulted from the southward advance of the first of 

the several "Nebraskan" ice sheets. In Eurasia, the southward dispersal of microtines was accompanied by a conspicuous dispersal of large mammals from Beringian and, 

presumably, other Siberian areas. This was called the 

"End-Villafranchian" dispersal event by Azzaroli (1983). 

The large-mammal fauna was present in western Beringia 

before the "End-Villafranchian" dispersal event. 

There were two subsequent dispersals into the conterminous United States, and a greater number into Europe. 

These introduced new species to the faunas of these lowlatitude areas, but the species were of lineages whose 

evolution is difficult to understand. The evolution of some 

seems to be evident in the younger faunas of the Old Crow 

Basin, Yukon Territory, Canada, but much work remains 

before this is understood. The dates of the arrival in the 

conterminous United States of these new species, coupled 

with an understanding of their stage of evolution derived 

from study of the Old Crow or other material, may assist in 

approximating the age of these arctic faunas and help establish the later microtine biochronology of the Arctic Ocean 

borderland. 

Figure 1 illustrates the current status of microtine 

correlations in the Arctic Ocean borderland, based upon the 

microtine biochronology as correlated with climatic and 

paleomagnetic evidence. Kap Kobenhavn is in northernmost Greenland, and the Old Crow sections are in eastern 

Beringia in the Yukon Territory, Canada. Study of these 

two sites is in progress, and there appears to be considerable time that is not represented. Fish Creek and the lower 

Colville River are in the central part of the North Slope of 

Alaska, and Cape Deceit is on the Seward Peninsula of 

Alaska, central Beringia. The Krestovka sections and the 

type section of the Olyor Suite are in eastern Yakutsk 

A.S.S.R., western Beringia. 

REFERENCES CITED 

Azzaroli, Augusto, 1983, Quaternary mammals and the "EndVillafranchian" dispersal event-A turning point in the history of Eurasia: Paleogeography, Paleoclimatology, 

Paleoecology, v. 44, p. 117-1139. 

Guthrie, R.D., and Matthews, J.V., Jr., 1971, The Cape Deceit 

fauna-Early Pleistocene mammalian assemblage from the 

Alaskan arctic: Quaternary Research, v. 1, p. 474-510. 

Kowalski, Kazimierz, 1966, The stratigraphic importance of 

rodents in the studies on the European Quaternary: Folia 

Quatemaria, Krakow, no. 22, 16 p. 

Repenning, C.A., 1984, Quaternary rodent biochronology and its 

correlation with climatic and magnetic stratigraphies, in 

Mahaney, W.C., ed., Correlation of Quaternary chronologies: 

Norwich, England, Geo Books, p. 105-118. 

--1987, Biochronology of the microtine rodents of the 

United States, in Woodbume, M.D., ed., Cenozoic mammals 

of North America: Geochronology and biochronology: 

Berkeley, University of California Press, p. 236-268. 

Repenning, C.A., Brouwers, E.M., Carter, L.D., Marincovich, 

Louie, Jr. and Ager, T.A., 1987, The Beringian ancestry of 

Phenacomys (Rodentia: Cricetidae) and the beginning of the 

modem Arctic Ocean borderland biota: U.S. Geological 

Survey Bulletin 1687, 31 p. 

Repenning, C.A., and Feijfar, Oldrich, 1977, Holarctic correlaArctic Microtine Biochronology 1 01 
tions of microtid rodents, in Sibrava, Vladimir, ed., Quaternary glaciations in the Northern Hemisphere: Report 4, On 

the session in Stuttgart, Federal Republic of Germany, September 1976: Prague, Czechoslovakian Geological Survey, 

p. 234-259. 

Shackleton, N.J., and Opdyke, N.D., 1976, Oxygen-isotope and 

paleomagnetic stratigraphy of Pacific core V28-239: Late 

Pliocene to latest Pleistocene: Geological Society of America Memoir 145, p. 449-464. 

Shackleton, N.J., and others, 1984, Oxygen isotope calibration of 

the onset of ice-rafting and history of glaciation in the North 

Atlantic region: Nature, v. 307, p. 620-623. 

Sher, A.V., 1971, Pleistocene mammals and stratigraphy of the far 

northeast U.S.S.R. and North America: Moscow, U.S.S.R. 

Academy of Science (in Russian; translation in International 

Geology Review, 1974, v. 16, nos. 7-10, separate pagination, 

284 p.) 

Sher, A.V., Kaplina, T .N., Koumetsov, Yu.V., Virina, E.l., and 

Zazhigin, V.S., 1979, Late Cenozoic of the Kolyma Lowland: XIV Pacific Science Congress, Tour Guide XI, Academy of Sciences U.S.S.R., Moscow, 115 p. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eds., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

1 02 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Comment on the Present Status of 

Dating Loess by Thermoluminescence 

By Glenn W. Berger 

T.L. Pewe (this volume) has pointed out the ambiguities in the chronology of sediments (mostly loess and ash) 

in the Fairbanks region, and has mentioned the present 

confusion about the reliability of the thermoluminescence 

(TL) dating methods as applied to loess. This comment 

addresses problems of TL methodology and suggests probable causes for these problems. 

Considering all the published indirect arguments (for 

example, stratigraphic and paleoclimatic) for assigning 

ages to the Sheep Creek tephra (Hamilton and Bischoff, 

1984) and Old Crow tephra (Westgate and others, 1985), 

one is left with the realization that the true ages could be 

anywhere within the respective time ranges of 60 to 110 ka 

and 80 to 160 ka (Hughes, this volume; Matthews and 

others, this volume). Adding to this confusion are reported 

discrepant TL age estimates for the Old Crow tephra of 

about 85 ka (Wintle and Westgate, 1986) and about 150 ka 

(Berger and Huntley, 1985). Clearly, it is important to 

resolve the questions about the accuracy of present TL 

methods, because TL appears to offer the only direct means 

for dating the relevant deposits. 

Methodology and discordancies 

The view here is that improper application of previously introduced techniques (Wintle and Huntley, 1980), 

coupled with lack of rigor in tests for anomalous fading and 

for sensitivity changes, has created the present confusion 

about the reliability of the current TL dating methods. 

Consider first the data in figure 1, where all published 

results using two TL methods are plotted. Almost all of the 

partial bleach data are from Norton and Bradford (1985). 

A few of these are incorrect, probably because of failure to 

recognize and correct for anomalous fading, overbleaching 

of laboratory samples, and use of linear extrapolations to 

dose-response curves for older samples. These are my 

inferences based on experiments with fine-grained sediments (see Berger, 1986), because no reasons for the incorrect results were discussed by Norton and Bradford. 

Whatever the causes for the scatter of these few partial 

bleach results, there is far more discordancy in the regeneration results of Debenham (1985). 

Now this discordancy is interesting because these data 

are from the same set used by Debenham to hypothesize a 

physical phenomenon (decay of luminescence centers) to 

explain the discordancy of another part of this data set 

(those results for deposits thought to be older than 80 to 

100 ka). This hypothesis predicts that all TL results (by 

any method) for deposits younger than about 50 ka should 

undershoot the correct age by <10 percent. Debenham did 

not comment on the evident inconsistency of a large 

number of his own results (fig. 1) with this prediction of his 

hypothesis. 

My view in this note is that uncorrected sensitivity 

changes (for example, Rendell and others, 1983) and (or) 

anomalous fading have led to the incorrect results in figure 

1, and very probably to all of the remaining discordancies 

reported by Debenham (notwithstanding that some of the 

"known ages" of De benham's samples are questionable 

(Mejdahl, 1986)). Thus, Occam's Razor has not been 

applied to the interpretation of these (and other) published 

discordancies. 

40 I-

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0: 

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0 20 40 

KNOWN AGE (ka) 

Figure 1. Plot of published thermoluminescence (TL) 

age estimates versus known ages (mostly associated C14 

dates, when accurate to less than 1 0 percent) for loess. 

Results from partial bleach method (dot, from Norton 

and Bradford, 1985; square, from Wintle and Brunnacker, 1982) and regeneration method (x, from 

Prosynska, 1983; circle with an x, from Debenham, 

1985). Results between outermost dashed lines are 

accurate to within 15 percent of the known age of the 

sample. 

Comment on the Present Status of Dating Loess by Thermoluminescence 1 03 
Probable assignable causes 

The above view is supported by the following arguments. First, when the regeneration dose-response curve 

becomes sublinear, the practice of several workers to estimate sensitivity changes (Debenham, 1985; Canfield, 1985; 

Singhvi and others, 1987) has been to compare the slopes 

of tangents to this curve with those to an additive-dose 

curve. Esoteric arguments can be made why this practice 

may be invalid, but it is questionable for a more obvious 

reason-the choice of tangential slope is subject to very 

large relative errors, partly due to the limited reproducibility of TL data. Consequently, the uncertainties in these 

slopes have been as large as 40 percent(!) and typically are 

20 to 30 percent (Debenham, 1985; Canfield, 1985; Singhvi 

and others, 1987). Yet these authors have dismissed this 

variation as insignificant, even though for sublinear growth 

curves small changes in the interpolated TL can lead to 

large changes in the estimated equivalent dose values (for 

example, Wintle, 1985). The obvious way to test this explanation is to apply the partial bleach method to the same 

samples that have yielded underestimated regeneration 

ages, because the partial bleach method is not subject to 

this type of sensitivity change. This test has not been done, 

probably for the reasons stated below. 

Second, anomalous fading (up to 25 percent) has been 

reported for the same samples of loess from the Fairbanks 

region (Berger and Huntley, 1985; Berger, 1987) for which 

Wintle and Westgate (1986) reported none. Also, several 

other workers have reported no significant anomalous fading in loess. The reason for this discrepancy is likely 

methodological rather than geological. In particular, few if 

any reports have stated how such tests were made, and 

some workers have not even mentioned such tests, despite 

the early admonishment of Wintle and Huntley (1982). It 

is commonly believed that any significant fading in loess 

would be detectable within a few days of laboratory irradiatons. Yet Berger and Huntley (1985) and Berger (1987) 

have shown that storage tests up to at least several weeks 

were required. The routinely used short (room temperature) storage intervals may have caused anomalous fading 

in loess often to go undetected. An uncorrected 20 to 30 

percent fading component may account for much of the 

underestimation of loess ages by TL dating. 

Complicating these aspects of methodology is the 

misconception that the partial bleach method is invalid 

when dose-response curves are not linear (for example, 

Aitken, 1985, p. 266; Wintle and others, 1984). This 

misconception persists despite the evidence of many successful applications of this technique to waterlaid sediments, when the dose-response curves are unambiguously 

sublinear, and even saturating (for example, Berger, 1986; 

Berger and others, 1987). Feldspars dominate the TL signal in both loess and waterlaid sediments, and there is no 

reason to suppose that the TL properties of the feldspars in 

these sediments differ in any unknown way. Indeed, these 

successes motivated the application of this method (results 

described below) to the loess lying just above the Old Crow 

ash layer. 

Thus, there are many reasonable methodological arguments for not accepting Debenham' s hypothesis, and for 

believing that the regeneration method is in any case presently unreliable for loess older than about 50 ka. Even so, 

this method continues to be applied without independent 

age checks (for example, Singhvi and others, 1987). There 

are thus compelling arguments for applying only the partial 

bleach technique when coupled with rigorous regression 

analyses. 

Concluding remarks 

To close this comment, some new results (Berger, 

1987) should be outlined. By careful laboratory techniques, a significant anomalous fading component has been 

eliminated from both the Old Crow tephra and a contiguous 

(ash-free) loess. Combined with appropriate extrapolations 

of saturating-exponential growth curves (contrast with the 

linear extrapolations of Wintle and Westgate, 1986), this 

empirical correction for anomalous fading has led to concordant TL age estimates of 110±12 ka for the Old Crow 

tephra and 108±16 ka for loess just above this ash layer. 

The average of about 150 ka of Berger and Huntley (1985) 

is invalid because in those preliminary experiments the 

results for bulk ash were averaged with those of a glass-rich 

fraction, and because the plateau test was not satisfied for 

the experiments on loess. 

In conclusion, successful applications of the present 

TL methods require analytical care. For loess, the partial 

bleach method of Huntley (in Wintle and Huntley, 1980) is 

the preferred technique, even though it is more laborious 

than other methods. 

REFERENCES CITED 

Aitken, M.J., 1985, thermoluminescence Dating, New York, 

Academic Press, 351 p. 

Berger, G.W., 1986, Dating Quaternary deposits by luminescence--recent advances: Geoscience Canada, v. 13, p. 

15-21. 

--1987, Thermoluminescence dating of the Pleistocene Old 

Crow tephra and adjacent loess, near Fairbanks, Alaska: 

Canadian Journal of Earth Sciences, v. 24, p. 1975-1984. 

Berger, G.W., Clague, J.J., and Huntley, D.J., 1987, Thermoluminescence dating applied to glaciolacustrine sediments from 

central British Columbia: Canadian Journal of Earth Sciences, v. 24, p. 425-434. 

Berger, G.W., and Huntley, D.J., 1985, A thermoluminescence 

date for the Old Crow tephra: Geological Society of America Abstracts with Programs, v. 17, p. 341. 

Canfield, H., 1985, Thermoluminescence dating and the chronology of loess deposition in the central United States: Madison, University of Wisconsin, M.S. thesis, 159 p. 

Debenham, N.C., 1985, Use of UV emissions in TL dating of 

104 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
sediments: Nuclear Tracks, v. 10, p. 717-724. 

Hamilton, T.D., and Bischoff, J.L., 1984, Uranium-series dating 

of fossil bones from the Canyon Creek vertebrate locality in 

central Alaska, in Reed, K.M., and Bartsch-Winkler, Susan, 

eds., The United States Geological Survey in Alaska: Accomplishments during 1982: U.S. Geological Survey Circular 939, p. 26-29. 

Mejdahl, V., 1986, Thermoluminescence dating of sediments: 

Radiation Protection Dosimetry, v. 17, p. 219-227. 

Norton, L.D., and Bradford, J.M., 1985, Thermoluminescence 

dating of loess from western Iowa: Soil Science Society of 

America Journal, v. 49, p. 708-712. 

Prosynska, H., 1983, TL dating of some subaerial sediments from 

Poland: PACT Journal, v. 9, p. 539-546. 

Rendell, H.M., Gamble, I.J.A., and Townsend, P.D., 1983, Thermoluminescence dating of loess from Potwar Plateau, northem Pakistan: PACT Journal, v. 9, p. 555-562. 

Singhvi, A.K., Bronger, A., Pant, R.K., and Sauer, W., 1987, 

Thermoluminescence dating and its implications for the 

chronostratigraphy of loess-paleosol sequences in the Kashmir Valley (India); Isotope Geoscience, v. 65, p. 45-56. 

Westgate, J.A., Walter, R.C., Pearce, G.W., and Gorton, M.P., 

1985, Distribution, stratigraphy, petrochemistry, and paleomagnetism of the late Pleistocene Old Crow tephra in Alaska 

and the Yukon: Canadian Journal of Earth Sciences, v. 22, 

p. 893-902. 

Wintle, A.G., 1985, Sensitization of TL signal by exposure to 

light: Ancient TL, v. 3, p. 16-21. 

Wintle, A.G., and Brunnacker, K., 1982, Ages of volcanic tuff in 

Rheinhessen obtained by thermoluminescence dating of 

loess: Naturwissenschaften, v. 69, p. 181-183. 

Wintle, A.G., and Huntley, D.J., 1980, Thermoluminescence dating of ocean sediments: Canadian Journal of Earth Sciences, 

v. 17, p. 348-360. 

---1982, Thermoluminescence dating of sediments: Quaternary Science Reviews, v. 1, p. 31-53. 

Wintle, A.G., and Westgate, J.A., 1986, Thermoluminescence age 

of Old Crow tephra in Alaska: Geology, v. 14, p. 594-597. 

Wintle, A.G., Shackleton, N.J., and Lautridou, J.P., 1984, Thermoluminescence dating of periods of loess deposition and 

soil formation in Normandy: Nature, v. 310, p. 491-493. 

Carter, L. David, Hamilton, Thomas D., and Galloway, john P., eels., 

1989, Late Cenozoic History of the Interior Basins of Alaska and the 

Yukon: U.S. Geological Survey Circular 1026. 

Comment on the Present Status of Dating Loess by Thermoluminescence 1 05 

SUMMARIES OF DISCUSSION SESSIONS 

Following the presentation of individual papers, a 

series of two-hour discussions was held on topics that were 

considered to be of particular interest to the participants. 

The following summaries were prepared by individual 

discussion leaders for incorporation in this volume. 

Geochronology 

Julie Brigham-Grette 

Accurate dating is essential for piecing together the 

Quaternary stratigraphy of any area and for correlating 

sequences in separate drainage basins. During our discussions, it was clear that some stratigraphic problems will 

remain unresolved until we can distinguish between real 

gaps in the preserved record and disagreements caused by 

inadequate age control. For example, differences in the 

glacial record from the Brooks Range, the Alaska Range, 

and the northern Yukon may reflect differences in the style 

and intensity of glaciation or differences in the preservation 

potential of ice marginal features from different areas 

(Gibbon and others, 1984). Direct matching of series of 

glacial or periglacial events may mislead us into false 

correlations unless they can be supported by adequate age 

control. 

The discussion focused largely on the problems and 

reliability of standard radiocarbon dating, accelerator radiocarbon dating, and thermoluminescence dating. Time did 

not permit adequate discussion of other dating methods 

such as amino acid, fission track, K-Ar, uranium series, and 

paleomagnetism. 

Several researchers presented examples of significant 

discrepancies in radiocarbon dates on organic materials 

from the same deposit. David Carter reported seven ages 

ranging from about 13 to 30 ka on different size fractions 

of a detrital organic deposit from northern Alaska. Successively finer fractions yielded successively older ages (Nelson and others, 1988). Lake sequences in Alberta yield 

basal ages on moss that are consistently older than wood at 

the same horizon, according to Lionel Jackson. The basal 

ages on moss and peat generally are too old because of 

bicarbonate enrichment soon after deglaciation. 

Owen Hughes emphasized that there is a fundamental 

need to carefully define what reseachers mean by "peat," 

because this term commonly is used for disseminated organics in fine-grained sediments as well as for densely 

compressed plant macrofossils. Charles Schweger commented that most palynologists use the classification 

scheme outlined by Troels-Smith (1955; see also Aaby and 

Berglund, 1986) and suggested that perhaps Quaternary geologists should adopt the same system. Moreover, we must 

concern ourselves more with studies of the taphonomy of 

organic material. Articles by Arundale (1981), Clayton and 

Moran (1982), Stuckenrath and others (1979), and Fowler 

and others (1986) were cited as useful guides to sample 

selection. 

Robert Thorson discussed problems in recognizing 

organic material out of stratigraphic context in terrace 

sequences along the upper Yukon River drainage. For 

example, wood and other plant debris may become lodged 

in a deep thermo-erosional niche at the base of a river bluff. 

If the bluff face then slumps or settles to close such a niche, 

the inset deposit may appear stratigraphically older than 

undisturbed organic layers higher in the bluff. 

Discussion then turned to the maximum age limits of 

radiocarbon dating. David Carter presented a series of unpublished radiocarbon ages from the Flaxman Member of 

the Gubik Formation on the North Slope of Alaska. Initial 

analyses of seal bone, mollusks, and whale bone all yielded 

finite ages in the range of 19.6 to 22.6 ka, but subsequent 

ages on whale bone collagen yielded ages of > 38 and >48 

ka and a uranium-series age on the same material was about 

75 ka. Thomas Hamilton reported that radiocarbon ages 

from the permafrost tunnel near Fairbanks and from Epiguruk bluff in northwest Alaska were stratigraphically consistent back to about 37 ka but that the ages became erratic 

beyond that point Richard Harington reviewed the dating 

of a bone tool of presumed Pleistocene age from the Old 

Crow Basin, Yukon Territory. Initial radiocarbon dating of 

the apatite fraction of this specimen yielded an age of about 

27 ka, but recent accelerator dating of the collagen fraction 

of the same specimen produced an age of about 1.5 ka (see 

Harington, this volume). Recent studies (for example, 

Hassan and Ortner, 1977; Hassan and others, 1977) have 

discredited dating of bone apatite. 

Most participants agreed that the reliable range of the 

radiocarbon method may be less than that stated by the 

laboratories, and that accelerator dating has not extended 

the useful age range but provides only a means of dating 

small samples. The accelerator technique also enables us to 

date several fractions of a sample to reveal whether they 

represent a detrital mixture. Whereas wood may be recommended most often as the best material to date, John 

Matthews pointed out that it also generally preserves well 

and, therefore, is commonly redeposited in Arctic stratigraphic sequences. Radiocarbon dating of modern marine 

shells from the Canadian Beaufort Sea and adjacent Arctic 

Islands also is needed to regionally assess the reservoir age 

of such materials. 

Thermoluminescence (TL) dating is gradually becoming an important dating tool in Alaska and the Yukon, 

particularly for subdividing stratigraphy in unglaciated 

Summaries of Discussion Sessions 107 
regions. No commercial laboratories do TL dating, and it 

was agreed that the method is still at the research stage. TL 

dating of the Old Crow tephra is critically important because the tephra forms a nearly instantaneous time datum 

for subdividing the stratigraphy of a very broad region of 

Alaska and the Yukon. Charles Schweger summarized 

evidence from a variety of sites which place age estimates 

on the tephra using different dating methods (Schweger and 

Matthews, 1985). Radiocarbon analyses of samples from 

the Koyukuk River valley and the Fairbanks region provide 

minimum age estimates of >56 and >60 ka, whereas a 

fission-track analysis provides a maximum age limit of 

about 120 ka. A maximum age limit of 100--125 ka is also 

provided by the occurence of the Blake Reversed-Polarity 

Subchron of the Brunhes Normal-Polarity Chron below the 

tephra at three localities (Shackleton, 1982; Westgate and 

others, 1985). Extrapolation of sedimentation rates places 

the age of the Old Crow tephra between at 87 and 105 ka 

(Schweger and Matthews, 1985) whereas recent TL dating 

of loess above and below the tephra at Halfway House 

limits the age to 86±8 ka (Wintle and Westgate, 1986). In 

addition, a TL age of 110±12 ka has been obtained by Glen 

Berger (this volume). Given the range of ages for the Old 

Crow tephra, Schweger proposed that perhaps the best age 

estimate on the tephra is between 87 and 94 ka. Most 

participants agreed that this was a reasonable age bracket to 

use until additional geochronology is available. Accurate 

TL and fission-track dating of other tephras found in Pleistocene sequences of Beringia is equally crucial to provide 

synchronous datums for regional correlation. 

It was concluded that problems of geochronology, 

including the reliability of datable material and the need for 

more accurate methods, provide the greatest obstacle to 

determining and correlating the late Cenozoic glacial and 

periglacial record of Alaska and the Yukon. 

Neotectonics in Alaska and 

Northwestern Canada 

Robert M. Thorson 

Neotectonics was defined as the effects, both direct 

and indirect, of regional or local crustal movements that are 

either part of the Neogene stratigraphic record or have 

influenced it in some way. The discussion revolved around 

four principal themes: glacio-isostasy, fault zones and 

relations to placer deposits, non-isostatic regional warping, 

and Holocene faulting and fault-related activity. 

The isostatic record 

Thomas Hamilton presented evidence from the Brooks 

Range for warping of late-glacial shorelines. He concluded 

that glacial loading caused at least 100 m of differential 

uplift between upper mountain valleys and the range front. 

Lionel Jackson confmned the isostatic deflection of mountain valleys by presenting evidence for upwarping of extensive proglacial shorelines that formed during ice recession 

in southern Yukon Territory. 

Robert Thorson and Thomas Hamilton suggested that 

shorelines in the Copper River Basin should be substantially warped because glacier complexes around the basin 

were larger than those of the Brooks Range. Evidence 

from aerial photographs indicates to Hamilton that strand 

lines near the Tangle Lakes in the northern Copper River 

Basin may have stood as high as 900 m altitude owing to 

crustal depression during the last glaciation. Other participants agreed that crustal warping should have occurred, but 

they argued that the present shoreline record is too fragmentary and the topographic data base is too imprecise to 

provide firm evidence for warping. A specific study of 

shoreline facies and an accurate survey of their altitudes 

should be a future research priority. 

Thorson raised the possibility that young radiocarbon 

ages on deglaciation at low altitudes around the Gulf of 

Alaska could reflect isostatic submergence. However, 

Thomas Ager and several others pointed out that other 

factors such as Holocene faulting could have caused the 

apparent hiatus between deglaciation and basal ages. 

Fault zones and placer deposits 

Stephen Morison provided evidence for hydrothermal 

alteration and thrusting associated with Neogene fault displacements in the Dawson area. Owen Hughes confirmed 

such observations, noting that similar features also exist in 

the Tintina Trench, and that a true fault scarp in this area 

cuts till of the Reid glaciation of Bostock (1966). Warren 

Yeend also described surface scarps and fault-related stratigraphy in the Alaskan sector of the Tintina Trench, and 

cited the work of Weber and Foster (1982) who demonstrated Quaternary faulting near Circle. All of the discussants agreed that there is a strong link between Neogene 

tectonism and placer development, and that displacements 

have continued into the Quaternary. 

Non-isostatic regional warping 

Richard Reger opened the discussion by pointing out 

that the Alaska Range did not exist as an obstacle to southward drainage from central Alaska during early Tertiary 

time and that its uplift history dates from the late Cenozoic. 

David Hopkins stated that the Cenozoic history of all 

master drainages in Alaska is almost completely unknown. 

Owen Hughes discussed the high strath terrace along the 

Yukon River, noting that it rises eastward (downriver) in 

altitude to about 220 m near the Fortymile River and then 

descends toward the Yukon Flats. John Williams and 

Robert Thorson correlate this high strath terrace with the 

high terrace flanking the Yukon Flats. 

1 08 late Cenozoic History of the Interior Basins of Alaska and the Yukon 
Much of the discussion focused on the "White Gravels" described by Stephen Morison in the Yukon. Charles 

Schweger suggested that the arkosic (grus-like) character of 

the gravel could reflect the rapid deposition of mechanically disintegrated regolith into newly formed Tertiary 

basins. Robert Thorson pointed out that similar gravels 

along the Porcupine River are interbedded with lava flows, 

zeolitized argillic paleosols, and lignitized organic horizons. John Williams indicated that lava is overlain by 

white arkosic gravel at the western border of the Yukon 

Flats, and that the modem Yukon River is incised below 

these deposits. Lionel Jackson suggested that the petrology 

of one occurrence of these basalts is consistent with rifting. 

Julie Brigham-Grette pointed out that significant tectonic 

activity also occurred in the Canadian Arctic Islands during 

this interval. The discussants concluded that one or more 

protracted episodes of substantial uplift, volcanism, and 

formation of basins occurred broadly across the region 

during the Tertiary. 

Holocene faulting and fault-related activity 

Several participants described evidence for large landslides and rockfall avalanches in recently deglaciated terrain. They speculated that many of these events may have 

been seismically induced, but the instability and steepness 

of recently deglaciated slopes must have been an important 

factor as well. James Beget also mentioned that high seismicity might be expected as a natural consequence of 

unloading during rapid deglacation. 

John Williams and Richard Reger described peats of 

early Holocene age that are presently submerged more than 

10 m below sea level near Valdez, suggesting either 

isostatic or tectonic deformation. This raised the question 

of the expected lag time between deglaciation and peat 

formation, especially in coastal areas. Charles Schweger 

emphasized that peat is a botanical deposit, and is controlled by moisture, acidity, and climate as well as by time. 

He suggested that throughout northwestern North America 

3,000 to 4,000 years may elapse following deglaciation or 

coastal uplift before peat is able to form or be preserved. 

Specific research questions that developed during our 

discussion included: What was the impact of basin subsidence and movement along flanking border faults on the 

lacustrine history of the northern Yukon basins? How do 

regional tectonic warping and glacial isostasy affect the 

marine transgressive record? How and when did Neogene 

faulting affect fluvial placer deposits? Are tectonic and 

volcanic records obtainable from the distribution of seismically initiated rockfalls and volcanic debris flows, respectively? Can the sedimentology, distribution, and fauna of 

the Bootlegger Cove Formation be used to infer a coastal 

isostatic record for upper Cook Inlet? Can the regional 

slope of full-glacial lacustrine shoreline features be used to 

infer ice thickness and distribution in the Brooks Range and 

the Yukon? What evidence exists for glacioisostatic deformation in the Copper River Basin? How did regional 

tectonism influence the Neogene fluvial incision of interior 

uplands and the formation of high-level placer benches? 

Three general research problems were considered to be 

particularly important: 

1. The long-term history of regional drainage systems 

and interior basins remains obscure. This history 

should be studied through correlation and dating of 

high level strath terraces, interstratified lava flows, 

tephra, and fluvial-lacustrine associations. 

2. Isostatic effects of Pleistocene glaciation were significant and measurable throughout Alaska and the 

Yukon, as indicated by raised marine deposits in 

coastal areas and warped lacustrine strandlines. 

Systematic data need to be collected to determine 

mechanisms of glacio-isostatic loading and the seismic and tectonic effects of subsequent unloading. 

3. Interpreting and dating fluvial and tectonic records at 

placer localities is important for mineral exploration 

and development and also for broader assessment of 

Cenozoic stratigraphy in interior basins. 

Late Tertiary Events 

John V. Matthews, Jr. 

The interior basins of Alaska and the Yukon contain a 

rich record of late Neogene and early Pleistocene time, 

which has important implications for paleoclimatology and 

biogeography. Our discussion focused on fauna and flora 

of the late Neogene, involving such subsidiary questions as 

(1) the first development of lowland tundra, (2) the character of the early boreal forest, (3) correlaton and dating 

based on floral and faunal data, and ( 4) past vegetation 

zones. Much of the discussion centered on the origin of 

lowland tundra David Carter, David Hopkins, Charles 

Repenning, and others believe that the earliest manifestation of tundra vegetation in the lowlands of the Northern 

Hemisphere is recorded at the Krestovka site in northern 

Siberia, and that tundra environments were present shortly 

afterward at some Alaskan localities as represented in 

exposures of the Gubik Formation. Matthews maintains 

that floras of the Beaufort Formation on Meighen Island 

represent a lowland tundra-like environment that is older 

than that represented by the Gubik Formation. The flora of 

the Kap Kobehnavn site in northern Greenland figures 

prominently in this argument. There is a problem, however, because if Kap Kobenhavn is ofOlduvai age (Olduvai 

Normal-Polarity Subchron of Matuyama Reversed-Polarity 

Chron) as Repenning suggests, then sites farther south that 

are presumed to be of similar age should display a much 

richer boreal flora and fauna. One such site in the Old 

Crow Basin has flora and fauna that apparently are less 

diverse than at Kap Kobenhavn. The basic assumption 

Summaries of Discussion Sessions 1 09 
implicit in such arguments is that the latitudinal diversity 

gradient of the Neogene was similar at least in trend to that 

of the present. Thomas Ager noted that it is very difficult 

to know what northern Alaskan equivalents of the Cook 

Inlet floras should be like because of the unknown effect of 

latitudinal diversity. In other words, should we expect 

Seldovian-type (Seldovian Stage of Wolfe and others, 

1966) pollen floras from northern Alaska to be the same 

age as those from the Seldovian type locality in southern 

Alaska? Charles Repenning stated that the geologic record 

no longer supports a clear division between forested conditions in east Beringia during the late Tertiary and widespread tundra at the beginning of the Quaternary. 

Another topic considered was Neogene climates and 

their proxy indicators: glaciation, vegetation changes, and 

dispersal events. Most discussion concerned earliest glacial 

advances. David Hopkins stated that the earliest record on 

the Seward Peninsula probably is at 2.4 Ma at California 

Creek on the Seward Peninsula. Thomas Hamilton mentioned the Gunsight Mountain glacial interval of Hamilton 

(1979) as a probable equivalent in the Brooks Range, and 

Troy Pewe stated that the Browne glaciation of Wahrhaftig 

(1958) was probably also older than 2 Ma. Robert Thorson 

presented possible evidence in the Alaska Range for a preBrowne glaciation, which led to a discussion of the record 

of Tertiary ice rafting in the Yakataga Formation of the 

Prince William Sound region and the question of possible 

Miocene glaciations in the Wrangell Mountains. It is clear 

there were major and possibly successive glacial events in 

east Beringia prior to the Quaternary. 

Marine and terrestrial relationships were discussed 

briefly, mostly in conjunction with the degree to which 

Pacific mollusks swamped the resident Arctic (North Atlantic) fauna when the Bering land bridge was first 

breached in late Pliocene time. An important question is 

how long an interval was required for total replacement (in 

other words, are there faunas that contain a mixture of 

Atlantic and Pacific mollusks?). 

A final question raised during the discussion concerned 

the reason for apparently distinct modem arboreal floras on 

either side of Bering Strait. The Bering land bridge existed 

for nearly all of Neogene time, and boreal forest occurred 

in Alaska and East Siberia for nearly all of that interval. 

Hopkins stated that exchange of arboreal taxa during that 

interval is indicated by comparison of North American 

fossils to those from Siberia. Matthews noted that recent 

work has shown that some of the shrubs and herbs that 

were present in Neogene Siberian forests are now known 

from the Be3;ufort Formation in North America. So perhaps the east and west Beringian forests were similar during the Neogene. Why are they different today? 

One joint Canadian-American research project that 

would go far to clarifying some of our Neogene problems 

would involve drilling boreholes in both the Old Crow 

Basin and the Yukon Flats. Alan Judge stated that his 

group had been looking into the feasibility of putting in 

holes on Old Crow Mountain and in the adjacent basin. 

John Williams described an earlier study at Fort Yukon, 

and suggested that it might be the best locality for a new 

borehole. Ideally, boreholes in the Old Crow Basin and the 

Yukon Flats should be drilled in the same year, using the 

same scientific sampling team and possibly the same drilling crew. 

Early and Middle Pleistocene Events 

T.D. Hamilton 

We followed international convention in assigning to 

the early Pleistocene those events that took place between 

1.65 Ma and the boundary between the Matuyama Reversed-Polarity Chron and the Brunhes Normal-Polarity 

Chron at about 790 ka (Richmond and Fullerton, 1986). 

Middle Pleistocene events are those that occured after this 

polarity reversal and before the peak of the last interglaciation (marine oxygen-isotope substage 5e) at about 125-130 

ka. Our discussion covered glacial and sea-level records, 

biogeographic and evolutionary changes in flora and fauna, 

drainage history, tectonic records, development of permafrost and sea ice, and paleosol formation. 

Glacial sequences of inferred early through middle 

Pleistocene age have been reported from the Brooks Range 

(Hamilton, 1986), Seward Peninsula (Kaufman and 

Hopkins, 1986), and the Yukon-Tanana Upland (Weber, 

1986), but glacial records farther to the south and east 

generally are more fragmentary owing to active tectonism 

and to overlap of older drift sheets by younger glacial 

deposits. Correlations between relatively continuous and 

fragmentary sequences are tenuous at present. Although 

several sea-level highstands are known from the Bering and 

Chukchi Sea regions, the Arctic Coastal Plain close to the 

Canadian border contains no elevated strandlines younger 

than late Tertiary and older than Pelukian (substage 5e in 

age). Expansion of the tundra biome continued during 

early Pleistocene time and, according to Charles Repenning, evolution of microtine rodents provides a time scale 

valid to within about 200 ka for some fossiliferous Pleistocene deposits. A general history of drainage evolution in 

the central and western Brooks Range has been inferred 

from Thomas Hamilton's detailed mapping of drift sheets 

deposited by sequential glacial advances of early and 

middle Pleistocene age. Drainage evolution elsewhere in 

Alaska and the Yukon during this interval is poorly known, 

according to Stephen Morison and Warren Yeend, but the 

widespread occurrence of economically important placer 

deposits makes this research field of particular interest. 

Tectonism altered relief and drainage patterns of many 

areas and impacted others through changes in wind patterns, precipitation values, and regional drainage. Few 

quantitative data are available on the timing or rates of 

110 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
faulting and other tectonic changes during this interval, but 

the topic is of great importance to studies of crustal dynamics and to assessment of geologic hazards as well as to 

Quaternary geology. Development and expansion of permafrost in northern Alaska and Arctic Ocean ice cover 

probably occurred during late Pliocene time, but details are 

little known. Studies applicable to permafrost and sea-ice 

history include paleoecology of fossil taxa, deep thermal 

profiles in permafrost boreholes, and history of kettle formation in ice-cored glacial deposits. Detailed studies of 

paleosols in Yukon Territory by Charles Tarnocai show 

that these fossil soils reflect the ages and environments of 

their formation. Mapping of similar paleosols should be 

carried out in central Alaska as an aid to dating surficial 

deposits and extending correlations across the international 

boundary. 

Absolute ages of early and middle Pleistocene events 

are provided by K-Ar, thermoluminescence, and fissiontrack dating and by paleomagnetism; amino-acid analyses 

provide a means of relative-age dating and correlation. 

Absolute-dating approaches show that the very extensive 

Anaktuvuk River-Nome River drift complex of northern 

and northwestern Alaska formed shortly before 790 ka 

according to David Hopkins, and TL dating by J .A. 

Westgate (University of Toronto) and Troy Pewe shows 

that the Gold Hill Loess around Fairbanks began to form 

about 450 ka. 

A major problem in both Alaska and the Yukon is the 

age of the youngest glacial event that preceded late Wisconsin glaciation. Data from northern Alaska suggest an 

age younger than the last interglacial maximum (substage 

5e) according to Thomas Hamilton, and a comparable history has been reported from the eastern Canadian Arctic 

(Andrews and others, 1985). On the other hand, examination of soils in the Yukon by Charles Tarnocai suggest that 

seemingly correlative drift may be older than substage 5e. 

This controversial topic was covered more extensively in 

the following discussion session. 

Late Pleistocene Glacial Advances 

Jean-Serge Vincent 

The workshop participants were asked to present the 

crucial data which enabled them to recognize the existence 

and chronology of glacial advances during late Pleistocene 

time (132 to 10 ka) in their individual study areas. The 

informal time divisions presented in table 1 were followed 

to ensure a uniform chronologie framework. 

In the Brooks Range, according to Thomas Hamilton, 

three major ice advances have occurred since marine oxygen-isotope substage 5e. In the southern Brooks Range the 

oldest and most extensive advance, termed the SirzJk Creek, 

occurred prior to deposition of the Old Crow tephra and 

overlying forest beds. This advance is younger than oxidized interglacial gravels, and probably took place during 

Table 1. Informal time subdivisions of late Pleistocene time 

used in discussion 

Marine Glaciation{mterglaciation Age oxygen-isotope Epoch (in ka) stages and Stage Substage substages 

HOLOCENE 0-10 

PLEISTOCENE 

Late Wisconsin 10-23 2 

WISCONSIN Middle Wisconsin 23-65 3 

Early Wisconsin 65-80 4 

Late Sangamon 80-122 5a 

5b 

SANGAMON 5c 

5d 

Early Sangamon 122-132 5e 

substage 5d and (or) 5b. The early(?) Wisconsin Chebanika advance (>35 ka) and the late Wisconsin Walker Lake 

advance, dated at between 25 and 12 ka, followed. In the 

northern Brooks Range, after a period of weathering and 

soil formation assigned to marine oxygen-isotope substage 

5e, ice of the Itkillik IA glaciation of Hamilton (1986) 

advanced in phase with the Siruk Creek advance in southem valleys. The subsequent Itkillik IB and Itkillik II glacial advances probably took place during oxygen isotope 

stages 4 and 2, respectively. Glaciations may well have 

occurred during Sangamon time (substages 5d and (or) 5b) 

because at that time the oceans were warmer and the 

summers cooler on land. Abundant moisture sources, 

therefore, were available for snowfall, but summer ablation 

would have been inhibited. 

According to Thomas Hamilton, the glacial record in 

the Yukon-Tanana Upland (Weber, 1986) is very similar to 

that of the Brooks Range. He also stated that at Canyon 

Creek, outwash of the Delta glaciation of Pewe (1953), 

derived from the Alaska Range, is overlain by sediments 

that contain bones with uranium-series ages of about 80 ka. 

This suggests that glaciation of late Sangamon age took 

place in the Alaska Range as well. 

Late Wisconsin glacial advances are well documented 

in the Alaska Range and the Canadian Cordillera, but the 

existence of early Wisconsin or late Sangamon ice advances is still subject to controversy. Glacial deposits 

underlie nonglacial sediments that are older than the time 

range of radiocarbon dating and that contain the Old Crow 

and Sheep Creek tephras. These glacial deposits may date 

from the early part of the late Pleistocene but they could 

also be older. On the basis of data at the Ash Bend locality 

in the Yukon, for example, Owen Hughes now believes that 

the Reid glaciation of Bostock (1966) is much older than 

Summaries of Discussion Sessions 111 
the Sheep Creek tephra and may predate the Sangamon. 

According to Charles Tarnocai, this older age assignment is 

also supported by the stratigraphic position of the Diversion 

Creek paleosols, of probable Sangamon age, which overlie 

Reid till. In the Alaska Range, the age of the pre-late 

Wisconsin Delta glaciation, generally correlated with the 

Reid glaciation, is uncertain. Thomas Hamilton believes 

that two advances of Delta age may have occurred respectively during late Sangamon and early Wisconsin time. 

However, Troy Pewe argues that the Delta glaciation may 

be middle Pleistocene in age because ( 1) interglacial soils 

are developed on its till, (2) tephras correlated with the Old 

Crow and Sheep Creek tephras found in loess linked with 

the ice advances are providing ages of 120 ka or older, and 

(3) in at least three localities the Blake geomagnetic excursion (Blake Reversed-Polarity Subchron of Brunhes Normal-Polarity Chron), which occurred about 115 ka, is recorded in sediments overlying the till. In the Watson Lake 

area of the Yukon, Lionel Jackson observed no sediments 

recording Sangamon through middle Wisconsin events. 

The existence or nonexistence of an extensive glaciation in 

the early part of the late Pleistocene remains an open 

question. Julie Brigham-Grette suggested that the apparent 

absence of a record of glaciation in the Cordillera during 

oxygen-isotope stages 5 to 3 is perhaps due to the fact that 

late Wisconsin ice advances of the McConnell or Donnelly 

glaciations (of Bostock, 1966, and Pewe, 1953, respectively) were so extensive that they obliterated the earlier 

glacial record. In the Brooks Range the record is preserved 

because the earlier ice advances of the late Pleistocene 

were stronger than the later ones. 

The chronology of lacustrine filling of the interior 

basins of the Yukon seems to indicate that Laurentide ice 

was strong enough to advance to the Cordilleran mountain 

front (thus blocking eastward drainage and impounding 

waters) only in the later part of the late Pleistocene (after 

about 35 ka). No earlier record of such an event seem to 

be recorded in the basins or at the ramparts which served 

as spillways for the glacier-dammed lake basins. 

Two late Pleistocene ice advances are documented in 

the Northern Interior Plains, both on land on the coastal 

plain (by Jean-Serge Vincent) and offshore on the shelf (by 

Julie Brigham-Grette). There is a general consensus that 

the youngest ice advance, the Tutsieta Lake phase of Owen 

Hughes, took place during late Wisconsin time and was 

confined on land. The age of the earlier and more extensive late Pleistocene ice advance, which extended to the 

continental shelf, is controversial. This event, which has 

been assigned to the Hungry Creek glaciation in the Bonnet 

Plume area by Owen Hughes and to the Buckland glaciation on the Yukon Coastal Plain by Rampton (1982), could 

be as old as late Sangamon (marine oxygen-isotope substage Sd or Sb) or as young as middle Wisconsin in age. 

Because of the lack of adequate dating techniques for 

deposits beyond the range of the radiocarbon method, most 

of our age assignments for deposits older than about 35 ka 

commonly rest on the assignment of associated organicbearing nonglacial deposits to the Sangamon interglaciation 

or the middle Wisconsin nonglacial period. The presence 

of tephras or geomagnetic events permits better age assignments in some instances. Glacial advances of stages 5 and 

4 age may be present in the Brooks Range, but are more 

dubious in regions farther to the east and south such as the 

Alaska Range, the northwest Yukon, and the periphery of 

the Laurentide ice sheet. If a major ice advance did not 

occur at this time, what then is the age of the well-documented glaciogenic deposits found stratigraphically below 

glacial deposits of late Wisconsin age? Do these predate 

the Sangamon or were they laid down during late Sangamon or early Wisconsin time? These important research 

problems deserve particular attention. 

Late Pleistocene Interstadial Intervals 

Charles E. Schweger 

Interstades must be considered as unique time periods 

of considerable biological and climatic significance rather 

than merely as warm periods that bracket glacial stades. To 

initiate discussion, Charles Schweger described evidence 

for the Koy-Yukon thermal event, a period when treelines 

advanced and active layers deepened through much of interior Alaska and the Yukon. Dated at between 50 and 60 

ka, it occurred during the insolation maximum that initiated 

marine oxygen-isotope stage 3. Troy Pewe pointed out that 

evidence from the Fairbanks area indicates this may have 

been the warmest climatic interval in the past 500 k.y. If 

it is of stage 3 age, he asked, why is this event more prominent than the Sangamon (the last major interglacial interval) and how does one use a climatic signal for distinguishing interglacials from interstadials? 

Mary Edwards demonstrated the usefulness of the 

marine oxygen isotope and Milankovitch insolation records 

for testing paleoclimatic reconstructions. Marine oxygenisotope stage 1 (Holocene), stage 3 (in part Koy-Yukon 

thermal event), and substage Se (Sangamon) represent three 

late Pleistocene warm periods with different insolation 

budgets and duration. The length of the warm period may 

be of great importance because the migration lag of many 

boreal forest species may be considerable, as demonstrated 

by the Holocene record. Because of its long duration, stage 

3 might appear to have a warmer climatic signal than 

substages Sa, Sc, or Se. In addition, the boreal forest can 

create its own climate through changes in albedo, surface 

wind shear effects, and snow depth. Once established, the 

forest could conceivably enhance or reinforce the results of 

a warmer and possibly more moist climate. Several participants suggested that the interval represented by marine 

oxygen-isotope substage Se may never have seen the full 

development of boreal forest vegetation, and therefore it is 

poorly represented in the stratigraphic record. David 

Hopkins, however, noted that substage Se is represented on 

112 Late Cenozoic History of the Interior Basins of Alaska and the Yukon 
the Seward Peninsula by higher sea levels and an apparent 

westward advance of boreal treeline (see Hopkins, 1967). 

The botanical record of interstadials is rapidly developing and points to the need for more autecological studies. 

Typha (cattail) is known to have greatly expanded its range 

during the Koy-Yukon thermal event and the early Holocene, indicating higher summer water temperatures and (or) 

higher nutrient status. Alnus seems to have been present in 

the interior during the Koy-Yukon thermal event but not 

during other interstadials. Thomas Ager expressed a cautionary note by pointing out that ecotypic evolution may 

have occurred during the course of the late Pleistocene, 

making modem autecological data less reliable. 

Knowledge of interstadial, interglacial, and stadia! 

faunas is much less precise, and we need to follow a more 

strict stratigraphic approach to vertebrate studies. Richard 

Harington added that many of the so-called "arctic" species 

appear to have existed throughout the late Pleistocene 

seemingly without regard for the differences between stadia! and interstadial conditions. This led David Hopkins to 

suggest that past interstadial vegetation may have had a 

more open character than that of true interglaciations. 

Thomas Hamilton criticized reliance on very old radiocarbon ages based on isotope enrichment, and several discussants commented on the wide range of ages assigned to 

the Old Crow tephra in regional chronologies. An age 

range of 87 to 94 ka for the Old Crow tephra (see "Geochronology" discussion) allows the tephra to be placed in 

substage 5c, which satisfies the pollen evidence. 

There is also special interest in events occurring 

around 35 ka (late stage 3). Pollen studies over eastern 

Beringia point out the existence at this time of an east-west, 

as well as the more familiar north-south, climatic and 

ecological gradient. This period also seems to have been 

the time of pronounced westward expansion of the Laurentide ice sheet, with resulting proglacial flooding through 

northern Yukon basins and the Porcupine River. This 

episode of ice growth and expansion during middle Wisconsin time challenges our assumptions about interrelations 

between climate and glacial events. Data presented by 

John Matthews and Thomas Hamilton suggest that the late 

Wisconsin (stage 2) may have included warm oscillations. 

Mary Edwards pointed out that the type of study site will 

greatly influence the record of paleovegetation, and that 

many different sites will be needed to adequately represent 

regional vegetation and therefore synoptic paleoclimate. 

Canadian-American Collaborative Research 

L. David Carter 

In the final discussion session we reviewed ongoing 

research projects involving Canadian and American scientists, identified topics and specific problems that are best 

addressed through joint Canadian-American research, and 

discussed field excursions in Alaska and the Yukon that 

would provide information necessary for a preliminary 

evaluation of some of these problems. 

Ongoing Canadian-American collaborative research 

includes studies of the Quaternary stratigraphy and tephrochronology of central Alaska being carried out by Troy 

Pewe, J.A. Westgate (University of Toronto), and A.G. 

Wintle (Cambridge University). Their work focuses on the 

resolution of many long-standing stratigraphic problems 

through thermoluminescence dating of loess, fission-track 

dating of tephra, petrographic and geochemical correlation 

of tephras, radiocarbon dating of shells, wood, peat, and 

bone, and paleomagnetic stratigraphy of loess. Charles 

Schweger and John Matthews, in collaboration with Pewe 

and Westgate, are correlating tephras across Alaska and the 

Yukon and using them as datums in order to reconstruct 

spatial variation in paleoecological conditions during instants of geologic time. 

Topics and problems that seem particularly appropriate 

for collaborative research initiatives include: 

1. Application of the stratigraphy and sedimentology of 

placer gravels established for the Yukon (see Morison, this volume) to studies of the origin and distribution of placer gravels in eastern and central Alaska. 

2. A taxonomic study of the Cripple Sump fauna of 

central Alaska. This would augment the ongoing 

placer research projects in both Alaska and the 

Yukon. 

3. Coring through the deep sediments that fill the Yukon 

Flats and the Old Crow basins, and instrumenting the 

coreholes for precise temperature measurements. 

This will allow comparison of the depositional histories of these tectonic basins, and provide important 

information on heat flow; permafrost temperature, 

history, and thickness; and climatic change for northeast Alaska and the Yukon. 

4. Tracing high-level terraces of the Yukon River into 

Alaska and determining their relation to climatic 

change and tectonism. 

5. Comparing the Pleistocene glacial sequence in the 

Yukon with those established for the Brooks Range, 

Alaska Range, and Yukon-Tanana Upland. 

6. Determining the size and number of late Pleistocene 

catastrophic floods of the Porcupine and Yukon rivers, and comparing this record with the history of 

sedimentation in the Bering Sea to identify floodgenerated pulses of sedimentation. 

7. Developing a soil chronosequence for glacial and 

nonglacial deposits in Alaska that can be compared 

with the soil chronosequence established for the 

Yukon (see Tarnocai, this volume). This would allow 

correlation of geomorphic surfaces between Alaska 

and the Yukon. 

8. Determining radiometric ages of Cenozoic lavas on 

the east side of the Yukon Flats that are interbedded 

Summaries of Discussion Sessions 113 
with organic-rich deposits. Samples of the organicrich deposits are in hand and are being studied by 

Thomas Ager and Charles Schweger. Dating the 

lavas will provide a record of vegetation change that 

can be extended into the Yukon and correlated with 

the Tertiary floral stages established for the Cook 

Inlet region. 

It was the unanimous opinion of the workshop participants that joint Canadian-American field excursions be 

organized for the summer of 1988 to evaluate several of the 

research opportunities enumerated above and examine 

some of the localities discussed at the workshop that are 

most critical to the interpretation of late Cenozoic deposits 

and events in Alaska and the Yukon. The excursions 

should include examination of key stratigraphic sections on 

the Stewart, Porcupine, and Yukon Rivers via riverboat, 

and in the Whitehorse and Dawson areas and the Tanana 

River valley by automobile or van. 

COMBINED REFERENCES CITED 

Aaby, B., and Berglund, B.E., 1986, Characterization of peat and 

lake sediments, in B .E. Berglund, ed., Handbook of 

palaeoecology and palaeohydrology: New York, Wiley, p. 

231-246. 

Andrews, J.T., Aksu, A., Kelly, M., Klassen, R., Miller, G.H., 

Mode, W.N., and Mudie, P., 1985, Land/ocean correlations 

during the late interglaciaVglacial transition, Baffin Bay, 

northwestern North Atlantic-A review: Quaternary Science 

Reviews, v. 4, p. 333-355. 

Arundale, W.H., 1981, Radiocarbon dating in eastern arctic archaeology: A flexible approach: American Antiquity, v. 46, 

p. 244-271. 

Bostock, H.S., 1966, Notes on glaciation in central Yukon Territory: Geological Survey of Canada Paper 65-36, 18 p. 

Clayton, L., and Moran, S.R., 1982, Chronology of late Wisconsinan glaciation in middle North America: Quaternary Science Reviews, v. 1, p. 55-82. 

Fowler, A.J., Gillespie, R., and Hedges, R.E.M., 1986, Radiocarbon ~ating of sediments by accelerator mass spectrometry: 

Physics of the Earth and Planetary Interiors, v. 44, p. 15-20. 

Gibbons, A.B., Megeath, J.D., and Pierce, K.L., 1984, Probability 

of moraine survival in a succession of glacial advances: 

Geology, v. 12, p. 327-330. 

Hamilton, T.D., 1979, Late Cenozoic glaciations and erosion 

intervals, north-central Brooks Range, in Johnson, K.M., and 

Williams, J.R., eds., The United State Geological Survey in 

Alaska-Accomplishments during 1978: U.S. Geological 

Survey Circular 804-B, p. B27-B29. 

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Range, in Hamilton, T.D., Reed, K.M., and Thorson, R.M., 

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114 late Cenozoic History of the Interior Basins of Alaska and the Yukon 

GPO 685-041 /9793 
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