Figure 2. Paleo-ice flow patterns Laurentide ice sheet,Foothills Erratics Train’ andlocation of Del Bonita uplandunglaciated area surroundedby terminal moraine.

Progressive westward expansion of North American continental ice sheets during the Quaternary and implications for the timing of initial human overland migration into the AmericasLionel E. Jackson, Jr. Geological Survey of Canada, Vancouver, B.C. and Department of Earth Sciences, Simon Fraser University, Burnaby, B.C., Canada. E-mail: lionelj@sfu.ca

ORIGIN OF THE ICE-FREE CORRIDOR CONCEPT AS AN EXPLANATION FOR INITIAL PEOPLING OF THE AMERICAS

The discovery of the Folsom and Clovis sites in 1927and 1932 respectively provided indisputable evidence of the co-existence of humans with extinct ‘ice age’ fauna. The question immediately arose as to how these hunters had reached the mid-latitudes of North America at a time when the northern half of the continent was apparently buried beneath the Laurentide and Cordilleran ice sheets. In 1933, W.A. Johnston (GSC) proposed that people could have reached the lands south of the ice via a passage between the montane and continental glaciers at the climax of the last glacial maximum (LGM). In 1935, Ernst Antevs coined the term 'ice-free corridor'. Testing of the existence of an ice-free corridor at the LGM was not completely settled until the advent of cosmogenic exposure dating of the Foothills Erratics Train (Fig. 1; Jackson et al. 1997). This in turn begged the question: “was to whether this coalesence was one of many coast-to-coast glaciations or a single unique event”. This question is now resolved based upon applications of advances in glacial sedimentology, AMS 14C dating and paleomagnetic investigation of glacial sediments (Jackson, Andriashek and Phillips, 2011).

ICE-FREE CORRIDORS ARE STILL OPTIONS FOR EARLY OVERLAND

ENTRY OF HUMANS INTO THE AMERICA--- BUT DURING ITS

CLOSING, NOT OPENING

Archaeological sites clearly predating the Clovis culture such as Paisley Cave in North America and Monte Verde in South America apparently predate the opening of a post-LGM ice-free corridor in the coast-to-coast ice covering Canada at the time. This has bolstered the idea that humans entered the Americas along the Pacific Coast.

However, older and, to some, controversial sites such as Meadowcroft (Adovasio and Peder, 2013), Cactus Hill (McAvoy and McAvoy,1997) and clusters of sites in the mid-west summarized by Holen and Holen (2013) (Fig. 6) support the presence of humans south of the ice sheets during the the LGM or earlier during the mid-Wisconsin (OIS 3). Humans occupation north of the Arctic Circle in western Beringia is now well established (Pitulko et al., 2013). Lifeways capable of allowing humans to flourish in the most rigourous periglacial conditions had been achieved by that time. Westward radiation of these people to eastern Beringia would have brought them into one or both of the ice-free corridors (Fig. 6) and the Americas to the south. If and when there is a consensus that humans were in the Americas prior to the LGM, ice- free corridors predating the coalesence of Cordilleran and Laurentide ice and indeed, the interior plateaux and valley systems of the Canadian Cordillera are viable overland routes of entry into the Americas (Jackson and Duk-Rodkin, 1996). Such passages may have existed until ca. 23,000 years ago or even later based upon the youngest pre-LGM ice-free 14C ages from the Interior Plains and the Cordillera.

Adovaso, J.M. and Pedler, D.R. (2013). Chapter 29. The ones that still won’t go away: more biased thoughts on the pre-Clovis peopling of the New World. C.V. Ketron and M.R. Waters (eds.) Paleoamerican odyssey, Center for the First Americans, College Station,

p. 511-520. Barendregt, R.W. and Duk-Rodkin, A.(2011). Chronology and extent of Late Cenozoic ice sheets in North America: A magnetostratigraphic assessment. In J. Ehlers and

P.L. Gibbard, editors: Quaternary glaciations--extent and chronology, Part II: North America. Developments in Quaternary Science, 2. Elsevier, Amsterdam, p. 1-8.Barendregt, R.W., Enkin, R.J. and Tesler, D.L. (2012). Magnetostratigraphy of Late Neogene Glacial, Interglacial,and Preglacial sediments in the Saskatoon and Regina areas, Saskatchewan, Canada. Studia Geophysica Et Geodaetica, 56 (2012), 705−724.Barendregt, R.W., Andriashek, L.D. and Jackson, L.E.(in press). Evidence for Early Pleistocene Glaciation obtained from borecores collected in East-Central Alberta, Canada. Abstracts, American Geophysical Union 2014 Fal l

meeting. Davis, N.K., Locke, W.W. III, Pierce, K.L., and Finkel, R,C. (2006). Glacial Lake Musselshell: Late Wisconsin slackwater on the Laurentide ice margin in central Montana,

USA. Geomorphology: 75, 330– 345.Fullerton, D.S., Colton, R.B., and Bush, C.A. (2004). Limits of mountain and continental glaciations east of the Continental Divide in northern Montana and northwestern

North Dakota, U.S.A. In: J. Ehlers and P.L. Gibbard (eds.), Quaternary glaciations—extent and chronology, part II. Developments in Quaternary Science 2b: North America.. Elsevier, Amsterdam, 131-150.

Holen,S.R. and Holen, K. (2013). Chapter. 25 The mammoth steppe hypothesis: the middle Wisconsin (oxygen isotope stage 3) peopling of North America. In K.E. Graf, C.V. Ketron and M.R. Waters (eds.) Paleoamerican odyssey, Center for the First Americans, College Station,

p. 429-444. Jackson, L.E. Jr. and Duk-Rodkin (1996). Quaternary geology of the ice-free corridor: glacial controls on the peopling of the New World. In: T. Akazawa and E. J. E.

Szathmary (eds.) Prehistoric Mongoloid dispersals. Oxford Science Publications, Oxford, 214-227.Jackson, L.E. Jr. and Little, E.C. (2004). A single continental glaciation of Rocky Mountain Foothills, south-western Alberta, Canada. In: J. Ehlers and P.L. Gibbard (eds.),

Quaternary glaciations—extent and chronology, part II. Developments in Quaternary Science 2b: North America. 29-38.Jackson, L.E. Jr., Andriashek, L.D. and Phillips, F.M. (2011). Limits of Successive Middle and Late Pleistocene Continental Ice Sheets, Interior Plains of Southern and Central Alberta and Adjacent Areas. In J. Ehlers, P.L. Gibbard and P.D. Hughes, editors: Developments in Quaternary Science, Vol. 15, Amsterdam, The Netherlands, 2011, pp. 575-589.Jackson, L.E. Jr., Phillips, F.M., Shimamura, K. and Little, E.C. (1997). Cosmogenic 36Cl dating of the Foothills erratics train, Alberta, Canada. Geology 25, 195-198. McAvoy, J.M., and McAvoy, L.D. (1997). Archaeological investigations of site 44SX202, Cactus Hill, Sussex County, Virginia. Research report series No. 8. Commonwealth of Virginia Department of Historical Resources, Richmond.Pitulko, V., Nikolskiy, P., Basilyan, A. and Pavlova, E. (2013) Chapter 2 Human habitation in Arctic western Beringia prior to the LGM.In K.E. Graf, C.V. Ketron and M.R. Waters (eds.) Paleoamerican odyssey, Center for the First Americans, College Station, p. 13-34.

In K.E. Graf,

Glenwood Erratic, one of the Foothills Erratics Train two 36Cl ages: 17 600+/-4 500 14 200+/- 4300

Arctic Ocean

Pacific Ocean

Generalized Cordilleran Ice Sheet,last glacial maximum

Laurentide Ice Sheet,

(ca. 11 000 years BP)

Arctic Ocean

Pacific Ocean

Atlantic Ocean

Arctic Ocean

Pacific Ocean

Speculative ice-capspredating fullbodied Cordilleran Ice Sheet

SpeculativeLaurentide Ice Sheet,

(ca. 25 000 years BP)

Arctic Ocean

Pacific Ocean

Atlantic Ocean

ICE- FREE C

ORRID

OR

ICE- FREE C

ORRID

OR

C

Rocky M

tns.

Mackenzi e Mtn

s.M

ac

kenzie v

al ley

Cana

dia

n Shield

200 km

Edmonton

CalgaryV

C

S

NW 49

49

49

120

O

O

O

O

O

Folsom

Folsom

Clovis

Clovis

S

Foothills erratics train

Origin of Foothills erratics train(Jasper National Park)

City

Archeological site

Generalized maximum limit of Laurentide Ice Sheet,last glacial maximum

Hudson Bay/Mississippi R.drainage divide

AB

B

Oldman

a. S sk. R.S

R.

Limit of glaciation

ALBERTA

CANADA

CANADA

USA

USA

MONTANA

BRITISHCOLUMBIA

Rocky Mtns.

Rocky M

ountains

NORTHWESTTERRITORIES

SA

SK

AT

CH

EW

AN

SA

SK

AT

CH

EW

AN

Watino

RD-S

Edmonton

Medicine Hat

o49 N

o49 No60 N

o120 W o110 W

o110 W

o114 W

o114 W

o108 W

o47 N

Wellsch Valley

Wellsch Valley

Lethbridge

Medicine Hat

Taber

Lethbridge

Hand Hills

CANADA

United States of America

o49 N

Hudson Bay

ArcticOcean

PacificOcean Atlanitic

Ocean

PacificOcean

Ungava

KeewatinMackenzie& Richardson mtns.

Smoking Hills

Gulf ofMexico

Glacial Lake Musselshell

Previously thought to be Illinoian (OIS stage 6 orolder: Fullerton et al. 2004))now known to be LateWisconsinan (OIS 2)

General area of Albertainferred to have been covered by the penultimate (Illinoian) ice sheet (westernlimit inferred).

Areas or locations with evidence of multiple glaciation

Areas dating glacialerratics to the LGM

Sites with evidence of a single (LGM) glaciation

? ? ? ?

? ?

Southern limit of glaciation

BrocketDel Bonita

Figure 3. Architectureof the Quaternary lithostratigraphy in central and northeast Alberta highlighting formations associated with multiple glaciations and illustrating the distribution of time-transgressive preglacial deposits oft he Empress Formation

in buried valleys. (GSC69-4)

Clay

SiltSand

Gravel

Diam

icton

Bedrock

Fl (10 m)

30 m

40 m

1 2 3 4 5 6 6A

45 m

50 m

55 m

60 m

Dmm(s)

Gm(i)

Gm

Gm

Sm

Sp(d)

Sp/Ds

Fm

Gms/Gm(i)Sm/Sp(d)

Dmm

Dms

Dmm

Dmm

Dmm

Dmm

Fm/Sm

Gm

Gm/Sm

Gm

Sm

Sm

Flv(d) (5m)Flv(d)

Flv(d)(s)

Flv

Flv

Fm (Holocene)

Fm (loess?)

Flv

R

R

R

Dmm(s)

Smp

S(f)/Gm(p)

S(s)

F/G(s)

Fl(d)(s)

Fl/Sh

Sm (Holocene soil)

S(s)

>37,000 y>34,000 y

37,000

Em

pre

ss G

rou

p

120 m

bedrock

Formation A

FormationB

FormationC

Selfpotential(mV) Resistance

upper

lower

>37,000 y >49,000 y >32,000 y

24,490+/- 20025,000+/-800 28,630+/-800

Sc

Sc?

Dms

Dms

Dmm(o)Gm

Sxl

Fl

Sl/Fl

Fl(d)

Dmm

Dmm

Dmm

Dmm

Dmm

Dmm

Dmm

Fl

Gm

GfuGfu

Sm (12 m)

Dmm (10 m)

Ds(s)

Fl/Dl

Fl

40 m

Fl(d)

Fl(d)Fm/Holocene soil

Montane glacialoutwash(Late Wisc.)

Montanetill (Late Wisc.)

Late Wisc.

LGM

Late Wisc.

Mid

dle

Wisco

nsin

an

Middle

Wisconsinan

LGM

Pen

ultim

ate

gla

cia

tion

Penultim

ate g

lacia

tion

Late Wisc.

Late

Wis

c.

Mo

nta

ne g

lacia

l ou

twash

(L. W

isc.)

Allo

cth

on

ou

s p

re-L

GM

bed

rock, g

lacia

l an

d n

on

gla

cia

l sed

imen

tsP

ost L

GM

gla

cio

lacu

strin

e a

nd

Ho

locen

e s

ed

imen

ts

Po

st

gla

cio

lacu

strin

e

an

d H

olo

cen

e

sed

imen

ts

Late

Wis

c. m

ax.

Oldman

Sas. k. R.

S

R.

CANADA

ALBERTA

USA

Rocky M

tns.

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hew

an

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h C

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mbia

o49 No110 Wo114 W

Medicine Hat

Taber

Lethbridge

Brocket

1

23

4

5 6,6A

Diamicton (contains Canadian Shield stones)

Diamicton (no Canadian Shield stones)

Sand

Silt and clay

LEGEND

Dropstone in silt and clay

Allochthonous bedrock block

In situ bedrock

Glaciogenic-sheared contact or zone

Radiocarbon age (years before present)

Erosional contact

Gradational contact

Conformable contact

Nature of contact uncertain?

Large intraclast in till

Roll-up structure in large intraclast

Gravel

?

?

Sources of sections: 1, 2--Jackson et al. 2009, sections O11, St3); 3--Jackson unpublished; 4--Stalker, 1962 (Kipp Section) and Jackson unpublished; 5--Stalker, 1962 (Taber section: plot by Jackson); 6--Proudfoot, 1985 (DNP-79-19: plot by Jackson); 6A--Stalker and Wyder, 1983

Pre OIS 2

OIS 1& 2 (includes allocthons of pre OIS 2 glacial sediments)

Pre OIS 2 glacialand non glacial sediments

Figure 4. Western limits of pre-OIS 2 glacial ice and stratigraphy along the Oldman River( from Jackson et al. 2011).

CALGARY

Lethbridge

Banff

Red Deer

Jasper

EDMONTON

Bow

River

Red D

eer r e Riv

htro

N

tcha ewk as naS

iverR

iverR

acsabahtA

114º W

49º 110º

52º

60º 60º

52º

B R

I T

I S

H C

O L

U M

B I A

S A

S

K

A T

C

H

E

W

A N

U.S.A.

Generalized distribution,

Foothills Erratics Train

Del Bonita

upland area

Paleo-glacier flowlines,

southern and central

Alberta: montane,

Laurentide ice sheet

(after Shaw et al., 2010)

ALBERTA

Pre LIS glacial limit

Figure 5. (A) Approximate areacovered by the penultimateLIS; area formerly mappedas Illinoian (OIS 6 or earlier) and location of siteswith 14C-dated stratigraphyshowing limits of pre-LGMglaciation(s)

ABSTRACTThere is extensive and robust stratigraphic and geomorphic evidence of progressive enlargement of North American (NA) continental ice sheets in a westerly direction during the glaciations of Quaternary Period. This culminated with a one-time coalescence of the Laurentide Ice sheet and valley glaciers from the Rocky and Mackenzie mountains and outlet glaciers from the Cordilleran Ice Sheet during marine isotope stage (MIS) 2. This singular coast-to-coast ice (CCI) event ended the pattern of broad ice-free corridors between Cordilleran and continental glaciers that was the norm during all previous Quaternary glacial maxima in North America. Recent discoveries of human settlements above the Arctic Circle in eastern Siberia during MIS 3 (~30 C14 ky BP) and an accumulation of archaeological sites in NA south of the limit of glaciation dating to MIS 3 (specifically <30 C14 ky BP to ~22 C14 ky BP) or contemporaneous with the CCI event during MIS 2 (specifically ~22 C14 ky BP to ~14 C14 ky BP) suggest that the limiting event for initial overland human migration into the Americas was the closing of the ice-free corridor rather than its opening as has been the orthodoxy.

** ** **** **

****

**

** ** ** **

****

**

**

**

EmpressFormationUnit1:time-transgressivepreglacialsandandgravel

Bedrock:undifferentiatedlithology

BonnyvilleFormation:diamict,minorstratifiedsediment

EthelLakeFormation:stratifiedsediment;clay,silt,sand,gravel

MarieCreekFormation:diamict,minorstratifiedsediment

SandRiverFormation:stratifiedsediment;dominantlysand

GrandCentreFormation:diamict,minorstratifiedsediment

GlacialLakeEdmontonsediments:sand,silt,clay

** -buriedoxidizedprofile

** -buriedoxidizedprofile

StratigraphicUnits

EmpressFormationUnit2:clayandsilt

BronsonLakeFormation:diamictandclay

MurielLakeFormation:stratifiedsediment;clay,silt,sand,gravel

EmpressFormationUnit3:glacialsandandgravel

%carbonateclasts,1-2mmsandfraction

%matrixcarbonate,silt-clayfraction

**

BuriedHelenaValley

BuriedWhitfordValley

BuriedBeverlyValley

No

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>25,550yrB.P.

26,000±1100yrB.P.

MarieCreekFm.

GrandCentreFm.

BonnyvilleFm.

ref.D.Jennings,1984ConsolidatedConcretePits#46,#47C14 agedates

27,730±1060yrB.P. CaribouAntler31,520± 450yrB.P. CervidAntler39,960±3950yrB.P.MammothTusk35,500±2530yrB.P.Wood35,760±2130yrB.P.Wood>39,690 Wood41,110±3570yrB.P.Wood41,400±3990yrB.P.Wood42,910±3940yrB.P.Wood

ref.Young,etal.1994

A A’Southwest Northeast

110011201140

540

550

560

MoostoosUplands

CookingLakeMoraine

ColdLake

Edmonton

LacLaBiche

N.SaskatchewanR.

Athab

asca

R.

Verticalexaggeration~750

Pre OIS 2(sediments from twoor more ice sheets)

OIS 2

Ele

vatio

nm

asl

Magneticallyreversed till

36 Cl ages erratics on moraine surrounding Del Bonita

Sample Zero erosion 1.1 mm/kyr 3.3 mm/kyr Age ± Age ± Age ±

JJO01419 15500 630 14800 580 13840 510JJO01420 14040 510 13430 460 12530 410JJO01421 19600 780 18240 680 16550 580JJO01423 11500 420 10990 380 10250 340JJO01425 22100 800 20600 700 18700 600JJO01429 21050 670 19660 590 18100 520JJO01433 20800 780 20750 770 20800 780JJO01435 30300 1160 28350 1030 26300 930

COAST-TO-COAST ICE WAS UNIQUE TO THE LAST GLACIAL MAXIMUM. THE EVIDENCE IS SUMMARIZED IN FIGS. 2-5. PRIOR

TO THE LGM, ICE-FREE CORRIDORS BETWEEN THE CORDILLERAN GLACIERS AND CANADIAN SHIELD CENTERED

ICE SHEETS WERE THE NORM.

PART 3--A PRE-LGM ICE-FREE CORRIDOR A VIABLE OPTION FOR OVERLAND ENTRY INTO THE AMERICAS

The Paleoamerican Odyssey conference in Santa Fe, New Mexico in October, 2013 marked the passing of the Clovis-first paradigm. At present, there is a consensus that we really don’t know when and how people arrived in the Americas. What we do know is that people were present in the Americas when what is now Canada and the adjacent parts of the USA were covered by coast-to-coast glacial ice. Some controversial sites suggest the presence of humans prior to the closing of the last ice-free corridor. The duration of this glacial cover was short: between ca. 22 and ca. 14 ky. This was the culmination of westward expansion of ice sheets during the late Neogene glaciations (Barendregt and Duk-Rodkin, 2004). Subsequent work has shown that the western margins of continental ice sheets first reached Saskatchewan and eastern Alberta during a glaciation(s) prior to the last magnetic reversal (~0.78 Ma) (Barendregt et al. 2012; Barendregt and Enkin, 2012; Barendregt et al in press). What is notable is that throughout the Pleistocene, there was always unglaciated land connecting the Arctic with the interior of North America.

PART 1-- INTRODUCTION

PART 2. EVIDENCE FOR ONE COAST-TO-COAST GLACIATION

PaisleyCave14-15 ka

Monte Verdesite 14.8-14.2 ka

Monte Verde, MV >33 kaI

CactusHil ca. 18-20 ka

Meadowcroft 16 ka+

8 sites datingto LGM or mid-Wisconsin(Holen and Holen,2013)

ICE

-F

RE

EC

OR

RID

OR

Figure 1 Post LGMice-free corridorand location of Foothills erraticstrain

Figure 6. A speculative distribution of open land and glacial ice ca. 25 ka BP. Ice-free corridors open for habitation and entry into the Americas are indicated. Sites with yellow dots indicate approximate synchroneity with the opening of the post LGM ice-free corridor. Those indicated byred indicate synchroneity with coast-to-coast glacial cover or pre- LGM ice-free corridors (afterJackson and Duk-Rodkin, 1996).

(from Jackson et al. 2011).

-