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QUATERNARY GLACIATIONS OF THE

WHITE RIVER VALLEY, ALASKA

WITH A REGI01JAL SYNTHESIS FOR THE

NORTHERN ·~T. ELIAS MOUNTAIN~,

ALASKA AND YUKCN TERRITORY

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GEORGE H. DENTON Department of Geological Sciences and Institute for Quaternary Studies, University of Maine, Orono, Maine 04473

Quaternary Glaciations of the White River \rq_lley, Alask2, with a Regional Synthesis for the Northern St. Elias Mountains, Alaska and Yukon Territory

ABSTRACT

During Quaternary ice ages, a complex piedmont glacier repeatedly formed north of the Sr. Elias Mountains in Yukon Terri­tory and Alaska. During the Macauley glaciation (the youngest), the White River valley in Alaska served as a conduit of ke that filled the valley to thicknesses of 850 to 1,150 ft (256 to 351 m) and flowed east­ward into Yukon Territory, where it fed the we$tern margin of the Macauley piedmont glacier. C14 dates fail to pinpoint M~cauley expansion in the valley, but they ~o indicate deglaciation by 11,270 yr B.P. and subse­quent spruce immigration by 8,020 yr B.P. On as many as five occasions prior to 37,000 yr B.P., pre··Macauley ice filled the valley; on at least three occasions, it spilled northward over the valley rim.

Along its upper surface, Macauley d:ift in the White River valley and .in the adja­cenr Snag-Kludan area (Rampton, 1971a) can be traced into Kluane Drift exposed farther east near Kluane Lake (Denton and Sruiver, 1966, 1967), rhus permitting re­r.onstruction of the Macauley-Kluane piedmont glacier. Near Kluane Lake, the main Kluane ice advance postdated 29,600 }'i B.P., but the initial Macauley advance in the Snag-Kiutlan area is not associated with finite C14 dates. The maximum Macauley­Kluane ice extent was attained ne~r Snag about 14,000 yr B.P. (Rampton, ~971a); subsequent recession was very rapid. Prior to the Kluane glaciation, Shakwak Trench was degbciated to the vicjr.iry of Kluane Lake during the Boutellier nonglacial inter­val (<29,000 to >49,000 yr B.P.). Whether similar recession characterized th(· Snag­Kiurlan area and White River valley is not kno\'m. The earlier Icefield glaciation (>49/)00 yr B.P. near Kluane Lake) corre­lates with, or is younger than, the Mirror Creek glaciation (>38,000 yr B.P. in the Snag-Klutlan area). The still older Silver nonglacial interval and the Shakwak glacia­tion in the Kluane Lake area cannot be c~)r­related now wirh other St. Elias events. Nor can pre-Macauley glaciati0ns in the White

River valley be con·elated yet on a regional basis.

The most striking late Wisconsin event in the St. Elias Mountains was the nearly complete disintegration of Macauley­Kluane ice within only 1,500 to 2,700 yr after attaining its rno.:ximum about 14,000 y'!' B.P. Several other alpine glacier systems in cordilleran North and South America showed -:imilar rapid recession, as did larger ice sheers to a less marked degree. Quite possibly, rhe behavior of tk:se sensi­tive alpine glaciers reflects an abrupt back­ground climatic event that essentially ter­minated ~he late Wisconsin glaciation shortly after 14,000 yr ago. Th~se data in­dicate that Termination I of Broecker and van Donk (1970) began shortly after 14,000 yr B.P. .

The glacial chronology of the nor;hern St. Elias Mountains suggesr.s tha-:- early man could have inhabited Shakwak Trench, perhaps using it as a route to British Co­lumbia or coastal southeastern Alaska, dur·· ing the Boutellier nonglacial interval, and agj.in by 11,000 to 12,000 yr B.P. at the end of t~1e Kluane-Macauley glaciation.

INTRODUCTION

Introductory Statement

Considu-able effort has been expended in deciphering the QuatG_1ary glacial stratig­raphy and chronology of the northern St. Elias Mountains in southwestern Yukon Territory (Fig. 1; Sharp, 195J, Bostock, 1952; Kindle, 1953; Rampton, 1969, 1970, 1971a, 1971b; Denton and Stuiver, 1966, 1967), The results indicate that, during the last several Quaternary ice ages, a complex piedmont glacier, which was fed by numer­ous v:Jlley glaciers, formed on the northern border of the St. Elias Mountains. This piedmont ~;lacier consisted entirely of St. Elias ice, e rt~n thoug..l, it merged along its eastern edge with the Cordilleran Ice Sheer. In view of the growing number of C14 dates associated with glacial drift units, the stratigraphic seq11ence in this region prom­ises eventually to provide a reasonably

Geological Soc1ecy of Amem:a Bulletin, v. 85, p. 871-892,1.3 ~gs., june 1974

871

complete late Quaternary chronology for an alpine glacier system in norrh-.-.•estern North America.

The initial sections of this paper sum­marize the Quaternary stratigraphy and chronology of the White River valley, which is iocated within Alaska immediately west of field areas previously srud~ed in southwestern Yukon Territorv. This vallev marking the boundary between th~ Wrangell and St. !·, 'i-as Mountains served both as a major COl• ~uit of Quaternary ice and as the northwesten'l margin of the youngest Quaternary piedmont glacier formed north of the mountains. In this re­spect, this report on the White River valley complete~ most of the areal studies neces­sary to reconstruct a preliminary configuration and chronology of Sr. Elias Quare ·nary glaciers. The final sections synthesi~e the Quaternary gla.:ial history of the northern St. Elias Mountains and sug­gest possible climatic implications.

Physical Setting

The St. Elias and Wrangell Mountains, as well as the neighboring Chugach Moun­tains, belong to the higb-mountair. system that borders the Gulf of Alaska and ;rends through northwestern British Colur.1bb, southwestern Yukon Territory, and south­central Alaska (Fig. 1). Geographic divi­sions between these individual mountain groups are somewhat Mbitrary, because the entire mountain system is geologically and physiographica!ly uniform. The Sr. Elias Mountains ext.!nd through northwestern British Columbia, southwestern Yukon Territory, and sout~-central Alaska; numerous rugged peaks exc-.:cd 14,000 ft (4,267 m) in altitude, and several are much higher. These mountains currenrlr support numerous glaciers. The Wrangell Moun­tains, located in south-centrnl Alaska ro the northwest of the St. Elias Mountains, are dominated by high, glacier-covered vol­canoes. The Chugach Mountains, also marked by high, glacier-dad peaks, lie along the Gulf of Alaska ro tht south of rhe Wrangell Mountains.

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ALASKA

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Rc:.mpton ) ( 1969, 1971a

K'uane Lake

d Stuiver oen·ton6 on6 19 67)

{ 19 f

100 k ilorr.tters

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I

Northway Rampton

{1969, 197la)

Kluane Lake

d Stuiver an ) Denton 66 1967 ( 19 J

ALASKA

0~----~~ ~I o.J"; O:>;k ~i lo;-;m~e~ters 0

. dexmapofSl. Fsgure 1. In Elias Mountams,

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I ·~

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•

r----~-----.---------_,_ ____________ .,~'··---------~--

61''301

>47,000(Y-2389) >47,000(''t ... 23 0~}

.----® 8020s:JZO!Y-2 302) 10,900s:JSO(Y-2301) II I I 00:&12i)(S!-1103) r37,0CO (GSC-1576)

~ Ptarmioan I 3533

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EXPLANATION

fOOOJ ~

........

Glacier ic:e Clnd band of surficial debris

Post- Macauley outwash

Neoglacial moraines

Macauley drift

Macauley recessional moraine

-< c:

" 0 z

-1 ITI ::0 ::0

I~ I l

131"30'

Ot------r--..&.5---.-----__.;..:10 miles 0 5 I 0 15 kilometers

rn Miocene-Pliocene tillites, outwash, and lava flows

___. 14 80201:120(Y-2302) C date

A ---- A"' Stratigraphic cross section

<D Locality referred to in text 141° '

Figerc: 2. G~acial deposits in White: River valley, St. Elias and Wrangell Mou!ltains, Alaska.

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874

A West

' - ... , --- --·-·~-__,..._, __ ....,_~--"'·-·-.... ~----~------.._..~...__.._..._...,_""'"'

G. H. DENTON

I ¥'/ /,. '/ /11 ~ I T rt----..

\ :>.. ! ' ''''U :--,.._ . ' ~~·I:, I ·: .. :.·.·. :'I;J I I ! I I i 'l j : ... ·: ;ll I l ! I I ~::A~ ~ :+ + l i ~ " j i I . • ' . l I . " I . I I : ! ; II r ~--~~ ·-~~ T~-1 ~--~ · : .. l :~ I i \ - , . 7J i~ 'f-------------3~

II 1 '"'I ll ll I' I I ' - -- 1- I i' T ,-! . ' ' ' j ll i i i l . J, ll 1! -II 1 l ! II I 1 I i ! I l l

Figure 3. White River stratigraphic section. See A-A'" in Figure 2 for location of section.

The White River valley is located in south-central Alaska on the northern flank of the St. Elias Mountains (Figs. 1 and 2). The Russell Glacier, Skolai and Chitistone .Passes, and the upper White River valley form the boundary between the St. Elias and Wrangell Mountains (Wahrhaftig, 1965). The Russell Glacier, a long valley glacier with manJ tributaries, flows north­ward from the flanks of Mr. Churchill (15,638 ft or 4,766 m) and Mr. Bona (16,421 ft or 5,005 m) f,J< .. 25 mi (40 km) to terminate at the head of the. White River valley. The upper 6.2 mi (10 km) of the val­ley trends from southwest to northeast, but the remainder of the valley within Alaska extends from west to east (Fig. 2). The val­ley floor slopes from 4,000 ft (1,}19 m) in altitude at the terminus of the Russell Glacier to 2,900 ft (88A m) at the Alaska-Yukon Territory boundary. The nonh flank of the valley is composed of rel­ar.ively gentle hills, which commonly form volcanic buttes up to 6,620 ft (2,0 18 m) high, except near Solo Creek where an ex­tensive and relatively flat, high-level area adjoins the valley. The steep north flank of

the St. Elias Mountains, dominated by Mr. Natazhat (13,435 ft or 4,095 m) and Mr. Sulzer (10,926 ft or 3,330 m), forms the south wall of the valley. Glaciers up to 12 mi long (19.3 km) originate in high ac­cumulation basins and flow down the north flank of the mountains to terminate near the floor of the White River valley; these in­clude the Giffin, Guerin, and Sheep Glaciers, as well as several that are un­named. Braided-stream patterns of the White River and its tributaries, which are fed by meltwater from several large glaciers, cover much of the valley floor. Trees in the valley consist mainly of white spruce, black spruce, and asp~n; spruce tree line varies from 4,000 to 4,200 ft ( 1,219 to 1,280 m) in altitude. Shrub tundra, sedge­moss tundra, and fell field occur above tree line.

Climates on the southern and northern flanks of the St. Elias, Wrangell, and Chugach Mountains contrast sharply, An­nual precipitation on the maritime southern flanks of the St. Elias and Chugach Moun­rains ranges up to 158 in. (400 :m), whereas extrapolated values on the north-

ern flank of the Wrangell ~nd Sr. Elias Mountains are about 10 in. (25 .4 em) or less (Post, 1969). Similarly, te;npe:atures show a sharp decline across the muuntains fro.n the maritime coastal regions to the continental interior. For example, at Yakutat near the coast, from 1941 to 1950 the mean annual temperature was 39.5° F (U.S. Weather Bureau, 1959, p. 826), whereas at Snag, located in Yukon Terri­tory north of the mountains, it was 22° F (-5.5° C) from 1943 to 1950 (Kendrew and Kerr, 1955). The White River valley lies on the interior flank of the mountains and has a cool, continental climate. Sum­mer is short and warm, spring and fall are also short, but winter is long and cold.

Firn limir£ on glaciers in the Sr. Elias Mountains reflect the transmountain cli­matic regimes. The firn unit near the Gulf of Alaska in the area of the Malasoina Glacier is at about 3,000 fr (914 m) ·in altitude, whereas the firn limit on the northern mountain flank is as high as 7,500 to 8,500 ft (2,286 to 2,591 mL The firn limit on glaciers that drain into the White River val­ley is at about 7,500 ft (2,286 m).

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QUATERNARY GLACIATIONS OF TI-IE WHITE RIVE<. VALLEY, ALASKA 875

I I! II I

I Ill

11 I

I I ~--rr--1 ... +++ .·~ ~·· .

! !'""'!""! ? . ! I I l TiT l

~~~~~~~~ I I I I l-4oo teet -{

i I I! l d. I l

I 100 EXPLANATION

50 feet D Outwash lJI[J Covered

100 200 "~ ~

Jill-fabric trend (North ~ Is vertical on cross section) Macauley till

a Outwash • ·c14 date

>~,OOO(GSC-1576) 25

maters

25 50

-• a

Slit

Pre-Mac\uley till

Ou?wash

QUATERNARY GLACIAL STRATIGRAPHY OF WHITE RIVER VALLEY

General Statement

Quaternary glaciations of the White River valley were preceded by a long suc­cession of pre-Quaternary glacial advances that occurred between 1.6 and 10 m.y. ago. The record for these advances is preserved in thick stratigraphic sequences of inter­bedded tillites, fluvial units, and lava flows that constitute foothills flanking the up­permost portion of the val! 1 These se­quences are described by Denton and Arm­strong (1969).

Resting on the floor and walls of the modern White River valley in Alaska are remnants of at least four, and perhaps six, Quaternary drift sheets, all probably rounger than the faulted and tilted tillires exposed in foothills in the upper reaches of the valley (Fig. 2). These drift sheets once may have mantled the entire valley floor, bur they have since been dissected by the braided streams of the White River and its tributaries. These braided streams have de-

posited outwash trains and large alluvial fans. These trains and fans cover the valley floor and project northward from glacier termini on the south wall of the vallev. As a result, extensive remnants of pre-Ho'locene drift now occur only on the valley flanks. The youngest drift sheet forms a nearly con­tinuous surface cover on the north flank of the valley and occurs in extensive patches along the southern flank; older drifts are exposed only in stream cuts.

For purposes of discussion, the drift bodies are considered in two groups. The youngest drift sheet is discussed separately because it occurs widely as surface deposits characterized by distinct morphology and commonly bounded by a moraine or by a sharp morphologic change. Theu· deposits are named Macauley drifr on the basis of firm correlation by physical tracing with Macauley drift mapped in adjacent Yukon Territory by Rampron (1969). All Quater­nary deposits older than Macauley drift are discussed as a second group, because their exposures are scattered and, hent.:e, cannot be correlated with confidence; they arc un­named. Particularly fine exposures along the north bank of the White River are dis-

Figure 3. (continued).

cussed separately in the following section because they reveal in juxtaposition most of the recognized Quaternary drift units.

White River .ltratigraphic Section

Closely spaced exposures along the north bank of the White River near Pingpong Mountain reveal in cross section extensive glacial deposits of Macauley and pre­Macauley age (A-A"' in Fig. 2 and Fig. 3). These exposures extend laterally for 7,800 ft (2,377 m); stratigraphic units are physi­cally traceable in the ravines between most exposures, as extensive slumped sediments are rare. Several isolated exposures that also exhibit extensive glacial sediments are downstream from the White River strati­graphic section.

The White River stratigraphic section re­veals two till units that crop our along nearly the entire length of the section (Fig. 3) and are separated by fluvial sediments except in two places where they are in jux­taposition. The upper till is Macauley in age and ranges in thickness fmm 12 tO 60 ft (3.7 to 18.3 m). It is medium gray {N5 on the Munsell color scale), very compact, nonstratified, and nonsorted; grain-size

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876 G. H. DENTON

TABLE 1. C~' Ilo\TIS USED IN TEXT AND IN FIGURES

Llboratory no.

ci- tilm! (yr B.P.)

Location (Fig. no. in text}

Stratigraphic position and significance of sample Ret.li!'el!Ce

~ 111ri.u Ri:vno VaLU]J, Al<uka

Y-2507 7,670 :t 120 2

Y-2302 8,020 ± 120 2

Y-2307 8,280 :1: 120 2

Y-2301 10,900 :1: tso 2

I-6092 10,980 :1: 150 2 SI-1103 11,100:1: 120 2 Y-2306 11,270 ± 200 2

G-~C-1576 >37,000 2 and 3

Y-2389 >47 ,000 2

Y-2305 >47,000 2

Y-2308 >47,000 2 aild 6

P'rcln Snag-EZ.ut!an aNa, :rukt:m Territory

GSt;-581 4,470 ± 140 10

GSC-580 4,550 ± 150 10

GSC-718 5,250 :1: 130 10

GSC-544 6,200 :1: 150 10

G-SC-932 6,500 j; 140 10

G-SC-777 7,760 ± 170 10

G-SC-776 9,360 ± 150 10

G-SC-714 11,000 ± 160 10

G-SC-1110 13,500 ± 300 10

G-SC-495 13,660 :1: 180 10

GSC-496 >36,000 9

ranges from clay to boulders. Clasts are predominantly andesite and limestone; many are faceted, polished, and striated. No weathering was noted along the upper surface of this till, A till fabric gave a dom­inant trend of N. 95° E. (Fig. 3), suggesting

$pruce wood

~skeg

Organic snt and muskeg Muskeg Orgllni c sit t Organic silt ar.!l muskeg llood nodules and basal parts of vascular plant stems Organic matter enclosed in silt bed; sample con­sists mainly gf wood nodules and vascu 1 ar p 1 ant stems

do.

do.

Sedge peat

Organfc detri~us

Wood

Organic detritus

Peat

Wood

Organic silt

Organic silt

Clayey silt with organic debris

Organic silt

Organic detritus

Sample from base of alluvial fan located adjacent to Holocene moraines fringing Guerin Glacier; sample affords mfnfmum age for recession of Hacau1ey fee from sampte·tocalfty Sample f$ lowermost spruce stump exposed fn thick muskeg section ~long north bank of White River; date gives minimum age for immigration of spruce into valley following recession of Macauley fee ~rom sample site Sample from lowennost organic matter from 1111skeg that rests on Macauley till; date affords minimum age for recession of Macauley fee from sample site

do.

do. do. do.

Sample from silt beds that rest directly on 1~.~r till exposed in White River stratigraphic secti,n; sample affords minimum age for underlying till

Sample from silt bed in a fluvial dep~sft that re~ts on a till exposed in north bank of North Fork Creek; s~~ple occurs 75 ft (23 m) above till and affords a minimum age for till

Sample from silt bed in a fluvial deposit that rests Dn a till exposed in nort~ bank of North Fork Creek; sample occurs fmmediat~iy 4bove till and affords minimum age fDr t'!ll Sample from a silt bed that fs located 3.9 ft (1.2 m) beneath upper till exposed in cross-section in banks of Solo Creek; .s~mple affords minimum age for under­lying tfll

Sample from base of sedge peat mat and dates initiation of organic accumulation in depression fn surface of Macauley drift Sampie from base of silt and gyttja on lake floor in ~iggerhead Lak~s ~egion; provides minimum age fo'l' underlying Macauley drift Sample from fluvial deposit located above present tree line; affords date for position of higher than present tree line Sample from base of silt and gyttja on lake floor in Niggerhead Lakes region; provides minimum age for underlying Macauley drift Sample from near base of a silty sand layer, that underlies 37 ft (11.3 m) uf gravel, silt, sand, and peat and that overlies 42.5 ft (12.7 H) of gravel and ~itt, that in turn rest on till; sample affords minimum age for this till Sample from base of bog that rests on a thick sequence of gravel and till; sample affords minimum age for Macauley drift Sample from base of peat bog that rests on till; affords minimum age for Macauley drift

do.

Samp1e from core in floor of Antifreeze Pond and was collected immediately above layer of Macauley loess; sample dates ces~ation of loess deposition and inferred concomitant recession of Macauley ice Sample from base of lacustrine organic silts that overlie laminated silt and sand; sample affords close limiting age on Macauley deglaciation Sample from base of bog immediately adjacent to Antifreeze Pond; bog rests on Mirror Creek drift and the1•efore date provides a minimum age for Mirror Creek drift

This paper

Stuiver, 196g, p. 561-562; this paper

Stuiver, 1969, p. 562; this paper

Stuiver, 1969, . p. 561; this paper This pap~:r

This paper Stuiver, 1969, p. 562; this paper This paper

This paper

Stuiver, 1969, p. 562; this paper

Stuiver, 1969, p. 562; tnis paper

R3l!'nton, l!tlla, p, ~94; Lowden and othet·s, 1!:67, p.175 Rampton, 1971a, p, 294; Lowdon and othet·s, 1967, p, 175 ~;:..,oton, 1969, p. 64

Rampton, 1971 a , p. 294; Lowden and others, 1967, p. 175 Lowdon and Blake, 1970, p. 81

Rampton, 197la, p. 294; Lowden and Blake, 1970, p. 79 Rampton, 197la, p. 294; lowden and Blake, 1970, p. 79 Ramp ton, 1971 a, p. 294; Lowdon a111:t Blake, 1970, p. 79 Rampton, 1971a, p. 295; Rampton, 1971b, p. 969

Rampton, 1~71a, p. 294-295

Ramp ton, 1971a, p. 293

Macauley ice flow parall~l to rhe valley axis at this locality.

The lower, pre-Macauley till, which is up to 40 ft (12 m) thick, crops our extensively and is compact, nonsorted, and composed predominantly of andesite and limestone

clasts, many of which are faceted and striated. Again, no weathering zone was observed on the till surface.

The fluvial sediments that separate the rwo tills are presumed to be outwash, as it is unlikely that the extensively glaciated

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QUATERNARY GLACIATIONS OF THE \VriiTE RIVER VALLEY, ALASKA

Laboratory no.

GSC-959

SSC-960

GSC-552

GSC-1579

GSC-995

GSC-799

GSC-924

GSC-962

GSC-919

c~> dat~ (yr B.P.}

>38,000

>38,!V'JO

>42,000

>40,000

>41,000

>:l9,000

>41,000

>40,000

>35,000

Frctr~ area of Rusty and Hcu.ard Glaci.wo

Y-2310 7,890:!: 120

Y-2313 B,200 :!: 140

Y-25G5 >50,.000

Location (Fig. no. in text}

9

9

9

9

9

9

9

9

9

10

10

9

Front aNa of Kaskalo1ulsh ana K1.uaM Glaeiel's

Y-1357 7,340:!: 140 10, as well as Plate 4 in Oeni:on and Stuir:·r, 1967

Y-1483 9,780 :!: 80 10

Y-1386 12,500 :!: 200 10

GSC-769 29,600 :!: 460 9

Y-1385 30,100 :!: 600 9, as ~ell as Plate 4 in Denton and Stuiver, 1967

Y-1488 33,400 :!: 800 9, as well as Plate 4 in Denton and Stuiver, 1967

Y-1356 37,700:!: l:~gg 9, as well as Plate 4 in Denton and Stuiver, 1957

SSC-734 >35,000 9

Y-1486 >49,000 9, as well as Plate 4 in Denton and Stufver, 1967

Y-1355 >46,400 9, as well as Plate 4 fn Oentorl and Stuiver, 1957

Y-1481 >49,000 9, as well as Plate 4 in Denton and Stuiver, 1967

TABLE 1 (continued)

Material

Peat and organic silt

Peat

Organic silt and silty ~at

Organic matter

Organic sflt and peat

Peat

Silty peat

Wood

Org~.nic elay

do.

fi,yttja

Wood

Grass and organic debris

Organic silt

Organic matter, including ~od

do.

do.

do.

do.

Peat

Organic matter, including ~oci

do.

Stratigraphic position and significance of sample

Sample frcm a succession of silt and peat layers that rest on Mirror Cree~ drift; affords minimum date for lo~ermost silt and peat lay~rs and for Mirror Creek drift Sample from base of thick deposits of organic silts that overlie Mirror Creek ou~ash; affords minimum age for underlying Mirror Creek o~~ash Sample from angular unconformitY be~een till &nd underlying gravel and sand

Sample from material deposited beneath Macauley drift

Sample from within a mudflow deposit that lies stratigraphically beneath a volcanic ash and gravel and till deposits, including till of Macauley ag~ Sample from ~~in layer of peat and volcanic ash that underlies a thick deposit of till of presumed Macauley age Sample from intertill deposit of alluvium and peat; overlying till is presumably Macauley in age. and thus date is maximum for deposition of Macauley till Sample from deltaic sand which is included in a thick succession of stratified materials that underlie Macaul ry ti 11

Sample from a olay bed which is included in a thick succession of stratified materials that underlie Macauley ti 11

Sample from base of peat bed that directly overlies Kluane (Macauley} till and that is overlain by Neoglacial till; affords minimum date for recession of Kluane (Macauley} ice from sample ar~a Sample from base of peat 7.9 ft (2.4 m) thick that rests on Kluane (Macauley} till; affords minimum d~te for recession of Kluane (Macauley) ice from sample area Sample from surface of gyttja buried beneath till sheet

Sample from silt bed in outwash that overlies Kluane till; affords minimum age for recession of Kluane ice from sample site Grass buried in place near base of Kluane loess; affords minimum age for recession of Kluane ice from sample site Sample from base of lacustrine siits that fill a kettle in Kluan~ ice-cQntact stratified drift; affords minimum age for ice recession Sample from silt bed in lcefield outwash 11, 4 ft (1.2 m} below upper surface of outwash II; dates portion of Boutellier nonglacial interval; sample from same locality as Y-1385 Sample from silt bed in Icefield outwash II, 4ft (1.2 m} bela~ upper surface of outwash II; dates portion of Boutellier nonglacial interval; sample from same locality as GSC-769 Sample from silt bed in lcefield ou~ash II, 12 ft (3.6 m) above lower sutface of ou~sh II; dates portion of Boutellier nonglacial interval Sample from silt bed in Iceffe1d outwash II, 12 ft (3.6 m) above lower surfac'; dates portion of Boutellier nonglacial intet~al; sample from same locality as GSC-734 Sample from silt bed in Icefield outwash II, 12ft (3.6 m} above lower surface; dates portion of Boutellier nonglacial interval; sample from same locality as Y--1356 Sample consists of sinuous stringers of peat enclosed in base of lcefield till; sample dates from before advance of Icefield glaciers, and presumably provides a maximum age for 1~ftiat1on of Icefield glaciatio" Sample from s11t bed located 10 ft (3 m) bel?W upper surface of snakwak outwash

Sample from silt bed located near blse of lceffeld ice-contact stratified drift: inferred to date initiation of Boute111er nonglacial lflter~al

•

877

Reference

Ramp ton, 1g71 a, p. 293; Lowdon and Blake, 1970, p. 80

Rampton, l97la, p. 293; Lowden and Blake, 1970, p. 77 Rampton, 1971a, p. 294; Lowdon and Blake, 1970, p. 79 Hughes and others, 1g72, p. 21 Hughes and others, 197Z, p. Zl

Rampton, 197la, p. 294; Lowdon and Blake, 1970, p. 77 Rampton, 1971a, p. 294; Lowdon and Bl~ke, 1970, p. 78 Rampton, 1971a, p p. 294; Lowdon. and Blake, 1970, p. 77 Rampton, 1971a, p. 294; Lowdon and Blake, 1970, p. 77

Stuiver, 196g, p. 560

Stuiver, 1969, p. 561

This paper

Denton and Stuiver, 1967. p. 506; Stuiver. 1981, p,SSB

Denton and Stuiver, 1967. p. 506; Stuiver, l96J, p.559 Denton and Stuiver, 1967, p. 506

Lowdon and Blake, 1970, p. 76

Denton and Stuiver, 1967. p. 506; Stuiver, 1969, p, 558

Denton and Stuiver, 1967. p. 506; Stuiver, 1969, p.560 Denton· and Stuiver, 1967, p. 506: Stuiver, 1969, p.557

Lowdon and Blat., 1970, p. 76

Denton and Stuiver, 19f7. p. 506; Stu!ver, 1969, p.55g

Denton and Stufver, 1967. p. 506; Sbfver, 1969, p.557 Denton and Stuive~. 1~. p. 506; Stuiver, 1969, p.559

high mountains at the head of the valley were free of ice at any time through the last several glacial cycles, for this would have required a firn-limit rise exceeding 8,500 ft (2,591 m). Deposition probably occurred when glacier termini were located in the

mountains, in analogy with the present situation. These sediments, which range up to 38 ft (11.6 m) in thickness, are poorly sorted, with clasts up to boulder size em­bedded in a fine matrix. They exhibit crude horizontal bedding; along their upper sur-

face, they grade into overlying Macauley rill. They are generally gray (5y 5/2) in color but in places have been oxidized by ground water and are yellow brown (10yr 5/4). In a few places, silt beds up to 6 ft ( 1.8 m) thick rest direct! y on the pre-Macauley till and

..

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..

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878 G. H. DENTON

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Figure 4. Vertical photograph showing outer limit of Macauley drift near Divide Creek {s~~ fig, ~ fgr loc.). Nmc hummocky morphology of Macauley drift.

separate .it from the overlying outwash sed- boulders which have fine-grained matrixes 41300 ft ( 1,311 m) near Solo Lake. Else­

iments; an organic layer within one ofthese or occur adjacent to well-sorted silt beds. where along the north flank of the va1ley, silt beds provided a C

14 date of >37,000 yr Such variability probably resulted from the outer limit of Macauley drift is marked

B.P. (GSC-1576; Figs. 1 and 3; Table 1), diurnal changes i!l capacity of meltwater by a distinct boundary between high-relief affording a minimum age for the pre- streams. - hummocky Macauiey drift with numerous Macauley till. These silts are interpreted as lakes and nonhummocky terrain charac-low-water or flood-phtin deposits. In anal... Macau)~;, Drift terized l:..y very few lakes (Fig. 4). ogy with present-day examples, the en- Although particularly well exposed in the Isolated patches of Macauley d,·ifr, some closed organic layer probably form~d when White River section, Macauley drift occurs hummocky, also occur on the south wall of a silt cover was deposited on the surface of elsewhere in the valley, both in cross section the valley. Here the outer limit of Macauley a flood-plain deposit that had been inactive and as a smface blanket over terrain not drift is marked by a moraine rhat trer long enough to develop a vegetation cover. occupied by modern outwash. On the north from 4,900 ft (1,491 m) in altitude ne

There is a thin layer of gray (5y 5/2), side of the valley, surficial Macauley drift Russell Glacier to 4,400 fr (1,341 m) ne: horizontally bedded, poorly sorted outwash exhibits distinct hummocky morphology Sheep Creek. Short outer moraine ridges that is unweathered through most of its ex• with a well-defined outer limit and with in- occur on the south valley wall between posure which sharply overlies Macauley rill dividual hummocks having relief up to 30 ft Sheep Creek and Guerin Glacier, and a in many localities. Fluvial sediments, again {2.2 m; figs. 3 and 4L SmaH lnkes fill prominent moraine ridge ar 4,400 ft (1,341 probably outwash deposited on the valley numerous depressions betWC!C!!1 hYmmQ!;ks. m) marks the upper limit of hummocky floor when glacier termini had retr~~red and thkk rt'iliskeg ~overs much of th€ drift Macauley drift benveen GuetiFI Gl:ider and into the mountains, underlie the pre- sheet, precluding accurate slope measure- the Alaska-Yukon Territory boundary. Macauley till. These fluvial sediments; some mcnts of the rypE performed by Rampton Macauley till crops our at an altitude of of which are stained with .iron oxide, arc (1969, 1971a). In the upper reaches of the 3,500 ft (1,067 m) at locality 1 in Figure 2 yellow (5y 5/2), exhibit crude horizontal valley, a large moraine ridge bounds and at 3,200 ft (975 m) at the White River bedding, and are very poorly sorted, Com- Macauley drift and decreases in altitude stratigraphic section (A-A"' in Fig. 2). monly, they exhibit beds of cobbles and from-4:4oo ft (1,341 m) near Lime Creek to These values, when compared with the al-

•

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I

QUATERNARY GLACIATIONS OF THE WHITE RIVER VALLEY, ALASKA 879

,, .. Figure 5. Post-Macaulcy muskeg and Macauley rill exposed along north bank of White River at locality 2 in

Figure: 2. Photograph shows central part of exposure where 48ft (14.6 m) of muskeg overlie Macauley till. Man in photograph i$ standing close: to contact between the two deposits, where C14 sample Sl-11 03 ( 11,100 ± 120 yr B.P.) was co!!~cted. Spruce: stumps can be seen preserved in muskeg. Horizomal shadowed area crossing muskeg 7 ft (2.1 m) below its upper position marks position of layer of nonh lobe of White River Ash, which has eroded back behind muskeg face.

titudes of the outer moraines, suggest a general .Macauley ice thickness in the val­ley, ranging from 850 to 1,150 ft (259 to 351 m). The increase in altitude of Macauley drift near present-day glaciers suggests slightly thicker Macauley ice near these former tributaries. Finally, expanded Macauley ice did not at any time merge

with Quaternary glaciers farther west in the Wrangell Mountains.

Several moraine ridges fall within the outer limits of Macauley drift (Fig. 2). Three small ridges occur inside of and parallel to the large outer lateral moraine between Lime Creek and So~o Lake. In ad­dition, two moraine segments trend down

the southeast wall of the valley near the Russell Glacier; their counterparts do not occur on the north valley wall. Moreover,

, several recessional moraines line the north­ern valley wall near Solo Creek. These are the only moraines that occur within the outer Macauley giacial limit in the White River valley.

The White River field area is contiguous with the Snag-Kiutlan area mapped by R<mpton (1971a) in adjacent Yukon Ter­ritory. Macauley drift mapped in the White River valley correlates well with that map­ped in the type area in Yukon Territory; all drift characteristics are similar, and the outer limits of Macauler drift mapped in both areas match perfedy. Thus) correla­tion of Macauley drift b!rween the areas is consideied firm on the basis of physical continuity.

Macauley drift is exposed in several small cutbanks, in addido11 to the White River section. In a bank near the confluence of North Fork Creek and the White River (Joe. 1 in Fig. 2), Macauley till is a minimum of 18 ft (5 .5 m) thick; here the till base is not exposed. However, the till is overlain sharply by 22ft (6.7 m) of muskeg with an ash layer that is 2 ft (0.61 m) thick and that belongs to the north lobe of the White River Ash (Lerbekmo and Campbell, 1969). Or­ganic matter from the till-muskeg interface afforded a C14 age of 10,980 ± 150 yr B.P. (1-6092 at Joe. 1 in Fig. 2).

A nearby exposure along the north bank of the White River (loc. 2 in Fig. 2), first de­scribed by Capps (1916, p. 69-75), shows 5 to 16ft (1.5 to 4.9 m) of Macauley rill over­lain by 39 to 48 ft (11.9 to 14.6 m) of fro­zen muskeg, which encloses White River Ash, as well as numerous megascopic spruce stumps (Fig. 5). This vertically ex­posed Macauley till-muskeg sequence ex­tends laterally for more than 600 ft (183 m), but its face changes constantly because of river erosion, C14 samples were obtained from two sires along the exposure. The first site, which yielded two samples collected in 1967, was near the western end of the ex­posure where 39 ft (11.9 m} of muskeg overlay more than 16 ft (4.9 m) of Macauley till. Organic matter from the muskeg-till interface gave a date of 10,900 + 160 yr B.P. (Y-2301), affording a minimum age for Macauley till. Addition­ally, the lowest 6 ft (1.83 m) of muskeg lacked megascopic spruce remains, whereas the upper 33 ft (10m) contained numerous spruce stumps. The lowermost spruce stump in the section provided a C14 dare of 8,020 ± 120 yr B.P. (Y-2302) and c-recur­red at an altitude of 3,500 ft (1,067 m), about 600 ft (183 m) below the current spruce tree line of about 4,100 ft (1,250 m). This date affords a minimum age for lure Holocene immigration of spruce into rhe

•

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j

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•

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880

B

U. H. DENTON

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EXPLANATION

•

Northeast

So I o

s'

~ t;;> Pre-Macauley ti II units ' e->47,000 (Y-2308) c14 date

Fluviol sediment• J/1 Till- fabric trend (North is vertical on cross section)

~ Organic- rich silt beds 40

10

[ill] Covered 20 feet meters

5

30 50 10

Figure 6. Stratigraphic section exposed along Solo Cw~k. Sec: B-B' in Fig:ne 2 for location of section. Layer of muskeg that rests on surface: is not shown in diagram.

White River valley following deposition of Macauley till. The second site, clearly re­vealed in 1970 by continued erosion of the central portion of the exposure, showed 48 ft (14.6 m) of muskeg overlying at least 3 ft (0.92 m) of Macauley till. Again the mus­keg en dosed a layer of the north lobe of the White River Ash. Basal muskeg here af­forded a date of 11,100 ± 120 yr B.P. (SI-1103).

One of the very early estimates for the age of the Wisconsin glaciation was ob­tained from this frczen muskeg-till section. Capps (1916, p. 70-74) used peculiar struc­tures in the root systems of the spruce

stumps to calculate a muskeg accumulation rate of 0.5 ft per 100 yr (0.15 m per 100 yr) through the last 400 yr. Applying this rate to a portion of the section that revealed 39 ft (11.9 m) of peat, he obtained an age of 7,800 yr for initial muskeg deposition, thus estimating a minimum date for ice recession from this sire. For several reasons, Capps considered that this value was quire con­servative and that ice recession actuallv oc . curred considerably earlier; Capps's esti;,at~" has turned out to be remarkably accurate .n light of present C14 dates.

Finally, small expos~:es of Macauley rill, again overlain by frozen muskeg containing

a layer o( the north lobe of the White River Ash, occur on the southeast bank of the upper White River (Joe. 3 in Fig. 2). An ex­posure located 2 mi (3.2 km) downstream from the Russell Glacier reveals 24 ft (7.3 m) of muskeg resting on at least 12 ft (3.7 m) of till. Basal muskeg from this section af­forded an age of 11,270 + 200 yr B.P. (Y-2306 at lor.. 3 in Fig. 2). This samplre site occurs on the proximal slope of one of the possible Macauley moraines mentioned above, which trend down the southeast wall of the valley near Wiley Creek. There­fore, the date is minimum both for till de­position and possibly for moraine construe-

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QUATERNARY GLACIATIONS OF THE WHITE RNER VALLEY, ALASKA 881

J.-. 4..-!11:~~::.--:. ~a-.:.~

Figur~ 7. ModC'rn development of organic-rich silt bed within outwash body. Photograph shows outwash depos­ited by high-water phase over vegetation mat that had grown on inactive portion of octwa£h plain. Much of pre­Macauley c••-dated organic material in northern St. Elias Mountains formed in place in this fashion.

tion. A second exposure, located 1.0 mi (1.61 km) downstream from the Russell Glacier (Joe. 4 in Fig. 2), provided a C14 age of 8,280 + 120 yr B.P. (Y-2307 at loc. 4 in Fig. 2) for basal organic material from a 5-ft-thick (1.5 m) muskeg section. Here the muskeg rests directly on Macauley till; and, thus, the date affords a minimum age for deglaciation of the sample site.

Pre-Macauley Quaternary Drift

Aside from deposits exposed in the White River stratigraphic section, pre-Macauley drift is found only in several isolated stream cuts. Even north of the valley where they extend beyond Macauley drift, the older deposits do not exhibit recognizable surface morphology and cannot be studied because they are subdued and covered with frozen muskeg. Examination of available exposures allowed delineation of the minimum extent of pre-Macauley drift, but logistic pr '1blems precluded mapping of the outer limt·~ of drift sheets. Within th,':! field area, the r1re-Macauley drifts cannot be corre­lated firmly and hence have not been as-

• 1 stgnc:u separate names.

On the banks of Solo Creek at B-B' in Figure 2, three till bodies are separated by fluvial sediments (Fig. 6), These tills must be pre-Macauley in age, for they lie north of the outer limit of Macauley drift. The up­permost till is 12ft (3.7 m) thick and is cov­ered by a thin layer of muskeg, whkh is not shown in Figure 6. This rill is underlain in succes~ion by fluvial sediments 16 ft (4.9 m) thick, ti1121 ft (6.4 m) thick, fluvial sed­iments 25 ft (7.6 m} thick, another till unit 15 ft (4.6 m) thick, and, finally, fluvial sed­iments more than 22 ft (6.7 m) thick. No

weathering profiles are present within the sequence. All the tills are gray (5y 5/2), compact, nonstratified, and nonsorted, with numerous faceted and striated clasts. A fabric on the upper till gives a preferred orientation of N. 20° E.; on the middle till, N. 15° E.; and on the lower till, N. 10° E. These fabrics, in conjun~tion with the local topography, suggest that pre-Macauley ice repeatedly spilled northward over the flank of the White River valley to deposit the riBs. The fluvial units separating the tills are gray (NS), horizontally bedded, and poorly sorted. They each contain several silt layers with enclosed organic matter. A C14 date of >47,000 yr B.P. (Y-2308) was obtained on organic matter collected from a silt bed lo­cated 4 ft (1.2 m) beneath the upper till (Figs. 2 and 6).

Several nonconsolidared stratigraphic units of pre-Macaule)· !1ge occur on the east bank of North Fork Creek (loc. 5 in Fig. 2). The lowermost unit is an oxidized fluvial deposit 25 ft (7.6 m) thick, orange (lOYR 6/6), hon ~omally bedded, and moderately well sorted. Overlying the oxidized fluvial deposit, there is a compact, poorlr sorted, brown (5YR 4/4) till unit 23 ft (7 m) thick, with particles ranging in size from boulders to clay and with numerous striated and polished clasts. This rill is overlain by gray fluvial sediments about 190 ft (58 m) thick, consisting of horizontally bedded sand, pebbles, and cobbles. These fluvial beds are ir.terrupred by several silt layers that con­rain enclosed organic matter. C 14 sample Y-2305 {>47,000 yr B.P.) comes from a silt layer immediately overlying the till, whereas sample Y-2389 (>47,000 yr B.P.) comes from a silt bed 75 ft (23 m) above the till.

DISCUSSION OF QUA TERNARY GLACIATIONS AND C14

CHRONOLOGY IN WHITE RIVER VALLEY

The areal configuration of the Macauley drift sheet indicates that glaciers in the drainage system of the upper White River expanded and coalesced in order to fill the valley and to flow eastward into Yukon Territory along the course of the current White River. At no time Was Macauley ice sufficiently thick ''O spill northward over the valley rim. No C14 dares from within the valley yet doe<lment initial Macauley ex­pansion or the maximum extent of Macauley ice. However, five C14 dares col­lected from the base of thick muskeg de­posits afford minimum ages for Macauley deglaciation (Table 1). They are 10,980 ± 150 (l-6092), 11,100 ± 120 (Sl-1103), 10,900 + 160 (Y--2301), 11,270 ± 200 (Y-2306), and 8,280 ± 120 yr B.P. (Y-2307). They are located, respectively, 10, 8.7, 8.7, 2, and 0.5 mi (16.1, 13, 13, 3.1, and 0.8 km), respectively, downstream from the present terminus of the Russell Glacier (Fig. 2). Additionally, a post­Macauley alluvial fan located near the Guerin Glacier contained organic matter in a silt layer near its base which provided a C14 age of 7,670 ± 120 yr B.P. (Y-2507 in Fig. 2). These dates point to nearly com­plete Macauley deglaciation of the White River valley prior to 11,270 yr B.P.

There were several major pre-Macauley Quaternary glaciations of the White River valley. Evidence from Solo Creek shows ice extension beyond the Macauley glacial limit on at least three occasions. The ab­sence of weathering zones within this stratigraphic sequence does not preclude significant nonglacial intervals, because frozen muskeg that inhibited weathering could always have covered the area. Till exposed at North Fork Creek correlates either with a till at Solo Creek or represents yet another pre-Macauley glacial fluctuation. Likewise, the lower till exposed along the White River section corresponds either to a till at Solo Creek or represents a younger, less extensive advance. Although it would be significant to distinguish be­tween these two possibilities, this cannot be done with present data.

Most pre-Macauley C 14 samples occur as thin, organic-rich silt beds located within outwash deposits. Such samples are com­mon not only in the valley but also farther cast near Kluane Lake in Yukon Territorv (Denton and Stuiver, 1967). Modern analogs, as illustruted in Figure 7, suggest that the organic material formed on an ounvash plain when small islands located between braided-stream channels remained undisturbed for several years and developed a vegetation cover. Subsequent changes in stream patterns or water volume innun-

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882

Glacial and nonolociol events c14 dotes ( ye art B, P.)

(not to scale)

--------Slims

e 7340o:t40 (Y-1357)

~ e 9780 t:80 (Y-1483)

f) 12,500 o: 200 (Y-1366)

i<luone otociotion

e 291600*460(GSC-769) e 30 1100*600(Y-1385)

Boutell fer • 33,400*800(Y-1488) e >35,000 (GSC-734)

nonolociol interval +1500 ( ) e 37,700 _1300 Y-1356

e >49 1000(Y-I481)

lcefleld

olocio!lon

e >49, 000( Y-1486)

Silver

nonoloclol interval

Shokwok e >46,400 (Y-1355)

glaciation

~-------

Figure 8, Quaternary glacial e\'(.'tlts and chronology in Kluane Lake area of Shakwak Trench (modified after Denton and Sruiver,1,67).

dated these islands and often covered the vegetation mat with silt. Hence, ancient or­ganic layers of this type formed in place. This interpretation is supported not only by modern analogs but also by the consistent internal relations of Y-1356, GSC-734, Y-1488, Y-1385, and GSC-769 from the exposures at Silver Creek near Kluane Lake (Table 1; Denton and Stuiver, 1967~ Pl. 4). Four dates of this type (GSC-1576, Y-2308, Y-2305, and Y-2389) from the White River valley indicate that all pre­Macauley tills exposed here have an age that is beyond the present capability of the C14 method.

QUATERNARY GLACIATIONS OF NORTHERN ST. ELIAS MOUNTAINS: A REGIONAL SYNTHESIS

Data from the upper White River valley, combined with that from adjacent Yukon Territory, permit a tentative reconstruction of Quaternary glaciations of the northern

G. H. DENTON

St. Elias Mountains. The chronology and the configuration of the youngest glaciation are known in some detail and therefore are emphasized in the following discussion. Older glaciations are harder to reconstruct because their deposits are scattered and be­cause associated finite C14 dates are nonex­istent.

Aside from the upper White River valley, several areas located within the former glacier system have been examined in detail (Fig. 1). One is in Shakwak Trench near the southeastern end of Kluane Lake (Denton and Stuiver, 1966, 1967) and another is near the Alaska-Yukon Territory border in the Snag and Klutlan Glacier area (Ramp­ton~ 1969, 1971a), which is adjacent to the White River area in Alaska. The Snag­Klutlan and KLJane Lake areas are not con­tiguous, but the intervening terrain has been examined in reconnaissance. Other areas examined in detail occur near the Kaskawulsh and Donjek Glaciers (Borns and Goldthwait, 1966; Denton and Sruiver, 1966, 1967), near the Steele Glacier (Sharp, 1951), and near the Hazard and Rusty Glaciers (Denton and Murray, in prep.).

In Shakwak Trench nea; the southeastern end of Kluane Lake, Denton and Stuiver (1967) recognized three glaciations sepa­rated by two nonglacial intervals. These events, somewhat modified after Denton and Stuiver (1967), are shown in Figttre 8. The geologic-climate units shown in Figure 8 are defined on the basis of rock­stratigraphic units exposed in cross section throughout the area and dated by C14 sam­ples, especially those coilected from strati­graphic sections along Silver and Outpost Creeks. In the Snag-Klutlan area, Rampton (1969, 1971a) recognized rwo glaciations on the basis of morphdstradgraphic fea­tures rather than on the basis of rock­stratigraphic units; these two glaciations, termed Macauley and Mirror Creek, are distinguished on the basis of mapping of two distinct outer moraine limits. In addi­tion, Rampton (1971a) inferred the exis­tence of :>lder glaciations from scattered glacial deposits located beyond the O';.lter limit of Mirror Creek drift.

Surficial drift of the youngest glaciation can be traced with reasonable certainty throughout the northern St. Elias region, This glaciation is called the Kluane in the Kluane Lake area, and the Macauley in the Snag-Klutlan area and in the upper White River valley, despite the fact that only one continuous glacier was involved at max­imum extent. Such a discrepancy in ter­minology was deemed necessary by Ramp­ton (1971a, p. 297) because the actual base of the Mac;;auley till in the Snag-Klutlan area has not been dared closely, despite a number of infinite C14 dares in subtill

stratigraphic units, whereas the base of Kluane till is associated with finite 0 4 dates along Silver Creek near Kluane Lake. Therefore, it is not known \f the lower por­tions of these drift sheets .:.re time correla­tive, although the upper portions can be traced physically through the regie,.

Figures 9 and 10 show the configuration of ice north of the St. Elias Mountains at the maximum of the Macauley-Kluane glaciation. The outer limit of the Macauley glaciation in the Snag-Klutlan area and in the White River valley is marked by distinct terminal moraines or by the outer limit of well-preserved hummocky drift. Former flow lines for the eastern t:lortion of the ex­panded glacier system ~re reconstructed from large-scale flutes which mark till sur­faces east of the Snag-Klutlan area (Fig. 11 ); flow lines for the western and northern margins of the former glacier must be in­ferred from topogra.phv, from the slopes of ice-marginal features, and from till fabrics, because drift surfaces there are hummocky rather than fl~ned.

Reconstruction of former ice-flow direc­tions of Macauley and Kluane Glaciers indi­cates that the current Kaskawulsh, Dusty, Lowell, and adjacent glaciers expanded northward through valleys dissecting the Kiuane Ranges and coalesced in Shakwak Trench. This coalescent ice mass was chan­neled northwest along Shakwak Trench through the Kluane Lake region; flow was constricted largely to Shakwak Trench by the confining high valley walls composed of the Kluane Rdnges to the southwest and the Ruby Range to the northeast (Bostock, 1952; Kindle, 1953; Denton and Sruiver, 1967, Fig. 6). The large glacier flowing northwest along Shakwak Trench merged with ice draining northwest through the Donjek River valley. In the Snag-Klutlan region, the unconfined ice from Shakwak Trench spread northward to form a com­plex piedmont glacier which was broken by sevr.ral large nunataks (Fig. 9} and which tf.'rminated north of Snag, where the Macauley (Kluane) ice limit is marked by the outer edge of well-preserved hummocky drift (Rampton, 1971a}. This large pied­mont ice sheet. fed entirely from Shakwak Trench, coa!esced with a smaller western lobe fed from the White River valley and from the Klutlan Glacier region (Fig. 9; k,ampton, 1971a).

Several C14 dates control riming of Kluane ice expansion into Shakwak Trench near Kluane Lake (Fig. 9 and Table 1; Den­ton and Sruiver, 1967}. Possibly a brief Kluane advance occurred between 33,400 ± 800 yr B.P. (Y-1488) and 29,600 ± 460 yr B.P. (GSC-769; Dentor and Sruiver, 196i, p. 505; Lowdon and Blake, 1970, p. 76). However, the main advance postdated

..

QUATERNARY GLACIATIONS OF THE WHITE RIVER VALLEY, ALASKA 883

Mirror Creek------­

Macauley Ridge

Anti freeze Pond >3G,OOO(GSC-496)-----~~

>38)000 (GSC-9

White Riv!lr Bridge Section '>42:000(GSC-55Z) >40,000(G S C-157 0 50 miles

~---------------·--~----------~

62°

>41, OOO(GSC-995) >4B,OOO(GSC-1615)

North Fork Creek >47,000(Y-23S >47,000 (Y-23 05)

Configuration of Mirror Cree~ glaciers

Configuration of Macculey- Kluane glaciers

Probable flow directions of Macauley-Kiuane

·- > 47,000 (Y-2308) cl4 date l...

0 50 lulometers

Outpost Creek > 49,000(Y-1481)

Silver Creek 29,60Qt:460(GSC-769) 3o,too =soo(Y-1385) 33,4oo:aoo (Y-1488) 37, 700±j~g(Y-1356) > 35,000(GSC-734) > 49,000(Y-1486) > 46,400(Y-1355} ", , Iuane

Figure 9. Configuration of Mirror Creek and Macauley-Kiuane glacial limits north of St. Elias Mountains (Rampton, 1969; Bostock, 1952; Denton and Stuiver, 1967; this paper). Probable flow lines of Macauley-Kiuane glaciers shown. Locations of CH dates of samples overlying Mirror Creek drift and underlying Macauley .:md Kluane drift indicated. See Table 1 for description of C14 samples.

29,600 ± 460 yr B.P. (GSC-769). There is no evidence of deglaciation of this portion of Shakwak Trench between the main Kluane advance and subsequent Kluane ice recession from the trench prior to 12,500 ± 200 yr B.P. (Y-1386). The timing of subse­quent initial Macauley expansion in the

Snag-Kiutlan area and in the White River valley is unknown, because here finite 0 4

dates from beneath Macauley till are nor available.

On the basis of two C 14 dates in critical stratigraphic position (Fig. 10 and Table 1), Rampron (1971a) inferred that the max-

imum of the Macauley glaciation in rhe Snag-Kiurlan area occurred shortly before about 13,660 yr B.P. Org:mic silt from the base of lacustrine sediments resting directly on Macauley drift afforded an age of 13t660 ± 180 yr B.P. (GSC-495); Ramp­ton (1971a, p. 295) felt that the dared sed-

..

• •

•

884

4470t:J40(GSC-581)

Anti freeze Pond 13,500~ 300 ( GSC-11 10)

13,660* ISO(GSC-495)

455Q:tJ50(GSC-580)---~~~;;;o>~

6200 :t 150(GSC-544)

7760*170 (GSC-777)

11,000t:ISO(GSC-71""~,. __ ~~~t2j:J;

II, IO(.h 120 (SI-ll

8020'* 120 {Y-230

Configuration of Mirror Craek. glaci•n

Configuration of Macauley-Kiuane glaciers

G. H. DENTON

Probable flow directions of Macauley-Kiuane g!ac;:iera

e.- 11,270 :t:200(Y-2306) c14 date 1....... r-... ..........

'·.J

0 50miles ~~-----------------r--------~ 0 50 kilometers

62°

Figure 10. Configuration of Mirror Creek and Macauley-Kluane glacial limits north of St. Elias Mountains. Flow lines of Macauley-Kluane glaciers shown. Locations of c•• dates of samples overlying Macauley and Kluane drih indicated. See Table 1 for description of C14 samples.

imenrs immediately postdated deglaciation. rion reached during late Wisconsin rime, for The cessation of Macauley loess deposition, C14 dares from organic debris resting on an event that probably coincided with Mirwr Crt:ek rill or outwash iocated close glacier recession (Rampron, 1971a, p. 295), to the Macauley glacial limit afforded ages was dared at 13,500 ± 300 yr B.P. of >38,000 (GSC-959), >35,000 (GSC-1110) in a core at Antifreeze Pond, (GSC-496), and >38,000 (GSC-960) yr The outer limit of Macauley drift in this B.P. area represents the maximum glacier posi- C14 dates from organic matter resting on

Macauley and Kluane drift are plotted in Figure 10 and are described in Table 1. All provide minimum values for deglaciation, bur the accuracy with which they date ice retreat varies widely. Samples Y -2301, Y-2306, Y-2307, Sl-1103, and l-6092 came from the base of thick muskeg de­posits overlying Macauley or Kluane drift

..

.. .

•

(Table 1). Samples GSC-581, GSC-777, GSC-776, and GSC-714 consisted of basal organic matter from bogs resting on Macauley drift (Rampton, 1971a, Table 2); samples GSC-580 and GSC-544 came from the base of lacustrine deposits resting on Macauley dnft (Rampton, 197la, Table 2); sample Y-1386 consisted of organic silt from the base of lacustrine sediments deposited in a kettle lake on Kluane drift; and sample Y-1483 was grass buried in place near the base of loess deposited dur­ing recession of Kluane ice (Denton and

Stuiver, 1967). The wide variation in ages of basal postglacial organic matter illus­trates the necessity of dating numerous samples to obtain a reasonably close limit­ing age for ice recession. Figure 10 shows that reliance on any one sample could well produce an anomalously young age for ice recession. Initial accumulation of basal or­ganic matter in bogs or lakes can be delayed long aftt..( general recession by preservation of isolated pice(· )f ice which ar;: mantled with a protective drift cover. Preservation of ice is well illustrated downstream from

the Russell Glacier, where large volumes of separated Neoglacial ice, dated to about 1,100 yr B.P. (Denton and Karlen, 1973), occur beneath supraglacial drift 3 to 6 ft (1 to 1.8 m} thick. Additionally, initial organic accumulation may be related to factors other than ice recession, such as sealing of lake bottoms by fine-grained sediments.

C14 dates plotted in Figure 10 show that Kiuane ice had retreated to within 1 i mi (27.4 km) of the current Kaskawulsh Glacier terminus prior to 12,500 ± 200 yr B.P. (Y-1386) and to the present terminal

..

• ..

•

886

posmon before 9,780 ± 80 yr B.P. (Y -1483). Farther west in the Snag-Kiutlan area, the oldest dare for Macauley ice reces­sion 1s llJ?OO ± 160 yr B.P. {GSC-714) from a locality about 14 mi (39 km) north of the current Kludan Glacier. Addition­ally, GSC-776 affords a minimum date of 9,360 ± 150 yr B.P. for ice recession im­mediately downstream from Kiutlan Glacier. Likewise, ice recession was rapid in the upper White River valley.

Geologic mapping of dri& bodies and glacial features has not produced convinc­ing evidence of major stillstands or read­vance during general Macauley-Kluane de­glaciation. The only features yet discovered t.hat may possibly represent breaks in the general deglacial pattern are a complex of ice-contact stratified dri& near Kluane Lake (Denton and Stuiver, 1967, p. 509), drift in Steele Creek valley (Sharp, 1951, p. 102-104), a spatuate-shape morainal com­plex near the Alaska-Yukon Territory bor­der (Rampton, 1971a, p. 296), moraine segments described earlier from the White River valley, and several moraine segments fronting other current glacier termini. However, none of these features has yet been shown to represent a widespread read vance.

Although the configuration of Macauley-Kiuane glaciers is known with reasonable accuracy, the interpretation of older glacier events is not straightforward and requires a review of the stratigraphy and C14 dating of ¥ertinent drift bodies. Kluane Drift fmms the surficial drift layer covering the floor of Shakwak Trench in the Kluane Lake area (Denton and Sruiver, 1967). Deposits of older glaciations and nonglacial intervals commonly crop our beneath Kluane till in curbanks throughout the area. These deposits are described in Denton and Stuiver (1967), and the events interpreted from them are shown in Figure 8. Only a stratigraphic section which needs reinterpretation is discussed below.

Quaternary drift sheets in the Kluane Lake area ar·e pamcularly well-exposed in cross section along Silver and Outpost Creeks (Fig. 9; Pl. 4 in Denton and Stuiver, 1967). Exposed along Silver Creek beneath Kluane tills I, II, and III are Kluane outWash I and Icefield outwash II sediments; Icefield oun.vash II, in turn, rests on the surface of Icefield till. The Boutellier Weathering Zone, which separates Icefield and Kluane Drifts, encompasses all products of subaer­ial weathering and dissection of icefield Drift (Denton and Stuiver, 1967, p. 497). The Boutellier nonglacial interval, whose name was derived from this weathering zone, was informally designated as the en­tire time-transgressive interval rh~'" ~epa­rated the lcefield from the Kluane glaciation

G. H. DENTON

{Denton and Sruiver, 1967, p. 498). Hence, at any one locality the duration of this in­terval is nor restricted to the formation of the weathering zone, but rather includes the entire rime between recession of Icefield glaciers and read vance of Kluane ice. ln this sense, the Boutellier nonglacial interval along Silve~ Creek encompasses Icefield out­wash II, which yielded C14 dares ranging from 29,600 ± 460 (GSC-769) near the top of the unit to < 37,700 ± l:3M (Y-1356) near the base.

Denton and Stuiver (1967, p. 497), plac­ing primary reliance on the interfingering of Icefield rill and outwash II at tWo localities along Silver Creek, originally thought that Icefield outwash II exposed here was deposited. as a fan dose to reced­ing Icefield glacie1s. They conceded {1967, p. 505) that the t.:.Prer portion of the out­wash may have been deposited by meltwa­ter from small glaciers in the Kluane Ranges, a situation that certainly occurred during the Slims nonglacial interval and that is prevalent today. Although this re­construction may be correct, Denton and Stuiver (1967) ignored the equally likely possibility that all outwash II exposed alor.g Silver Creek was deposited by melt­water from small glaciers in rhe Kluane Ranges and that the interfingering of Icefield rill and outwash II resulted from factors other than ice-terminal fluctuations, such as slumping of river banks composed of Icefield till over an adjacent Boutellier outWash plain. in this case, initial deposi­tion of outWash II need nor have occurred immediately after ice recession, for consid­erable rime could have elapsed before out­wash streams from small glaciers on rhe val­ley wall shifted to this locality and initiated fan deposition. Given the ambiguity in in­terpretation of this section, it now seems safest simply to state that recession of Icefield glaciers from this locality occurred >37,700 yr B.P.

Icefield till and ice-contact stratified drift have yielded two CH samples (Denton and Sruiver, 1967). One sample consisted of peat stringers enclosed in basal Icefield till exposed along Silvei Creek; this sample, which gave an age of >49,000 yr B.P. (Y-1486), was probably incorporated by the advancing Jcefield glacier. A second sample, collected from organic matter en­trapped in ice-contqCt stratified drift of Icefield age expused along Outpost Creek, probably formed in a kettle and was later enclosed by shifting of material over a melt­ing internal ice core. Hence, despite its posi­tion within Icefield ice-contact stratified drift, this sample afforded an age of >49,000 yr B.P. (Y-1481) for ice stagna­tion, presumably in the terminal phases of the Icefield glaciation (Demon and Sruiver,

•

1967, p. 505). If so, the duration of the Boutellier nonglacial interval should be ex·· tended to >49,000 yr B.P., a situation con­sistent with the reinterpretation of c:~e Silver Creek section. Such a revised dura­tion for rhe Boutellier nonglacial interval is used here, pending additional pertinent field and radiometric data.

In the Snag-Klurlan area, Rampton (1971a) recognized two glaciations on the basis of distinct moraines and morphologic glacial limits (Figs. 9 and 10). The older Mirror Creek glaciation was somewhat more extensive than the younger Macauley glaciation. Mirror Creek glacial deposits occasionally are up to 110 ft (34m) thick in places, but usually are considerably thinner. Their surface still exhibits hummocky ground moraine, which is less well pre­served than on adjacent Macauley drift. Oxidation and leaching of Mirror Creek deposits do not exceed depths of 1.1 and 1.7 fr (0.34 and 0.52 m), respectively (Rampton, 1971a, p. 287). 0 4 dates from basal peat or organic silt resting on the sur­face of Mirror Creek drift (Fig. 9) afforded values of >38,000 (GSC-959), >36,000 (GSC-496), and >38,000 yr (GSC-960; Rampton, 1971a).

A major difficulty arises in correlating older drifts betWeen the Snag-Klurlan and Kluane Lake areas; because organic matter located stratigraphically beneath Macauley till in the Snag-Kiutlan area hils not yielded finite CH dates, and therefore a correlc1tive of the Boureliier nonglacial interval has nor been defined. As Rampton (1971a, p. 297-298) pointed out, there are at least two possible explanations for this apparent discrepancy. First, extensive ice recession may nor have occurred in the Snag-Kiurlun area during the Bourellier interval. How­ever, this would have required a rather peculiar Boutellier deglacial pattern. The entire length of Shakwak Trench, at least back to the vicinity of Silver Creek near Kluane Lt.~ke, would have been deglaciated, whereas the major piedmont and valley­glacier complex in the Snag-Kiurlan area would have remained essentially intact. This is difficult to envision, because a major portion of the ice in the Snag-Kiutlan area during ·the Mirror Creek and Macauley glaciations entered the area from the southeast through Shakwak Trench (Rampton, 1971a, p. 292).

A second ~xplanation is chat the Snag­Klutlan area suffered Bourellier deglada­rionl bur pertinent C14 samples have not yer been found. 1 ';avor this Inner nlternative, both because of the difficulty in locating middle Wisconsin organic marerinl in any glaciated area and because of the limireJ numb'!r of control dates from beneath Macauley drift in the Snag~Kiurlan area.

• •

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•

QUATERNARY GLACIATIONS OF 11-IE \Xt'HITE RIVER VALLEY, ALASKA 887

Nine pertinent C14 samples have been dated (Fig. 9). Samples GSC-799 (>39,000 yr B.P.) and GSC-924 (>41,000 yr B.P.) ;!t'e from locations adjacent to the :Z!:Jdan Glacier and therefore do not bear directly on the question, for it is quite possible that extensive deglaciation of the Snag-Kiutlan arta occurred without exposing terrain fringing modern glaciers. Four samples were collected at the White River Bridge section about 26 mi ( 42 km) north of Klur­lan Glacier (Rampton, 1971a; Hughes and others, 1972, p. 20-23). These exposures are dis.conrinuous and local correlation is difficult. Organic materials buried beneath at least one till afforded ages of >41,000 yr B.P. (GSC-995), >40,000 yr B.P. (GSC-1579), and >42,000 yr B.P. (GSC-552; Hughes and others, 1972, p. 21). The fourth sample, which consisted of spruce wood collected from a mudflow that is difficult to place stratigraphically within the glacial sequence, affcrded an initial age of 48,000 ± 1,300 yr B.P. (GSC--752; Rampron, 1971a, p. 294). However, this sample may have been contaminated with. modern rootlets (Rampton, 1971a, p. 294), and a redating has provided a more reliable age of >48,000 yr B.P. (GSC-1615; Ramp­ron, 1972, written commun.); this sample shows that spruce invaded the area of the White River Bridge section during some nonglacial interval prior to the Macauley glaciation. Whether this interval corre­sponded with the Bourellier, or whether it is older, is not known. Therefore, although rhe stratigraphic data and C14 dates from the White River Bridge section do nor prove the existence of the Boute1lier nonglacial in­terval, neither do they deny it. As Rampton (1971a, p. 294) implied, there is no evi­dence to preclude the possibility that con­siderable rime elapsed between deposition of the dared organic materials and the over­lying Macauley rill. Furthermore, several tills possibly could be encompassed in the overlying drift, which are all assigned to the Macauley glaciation.

The two most critical samples, GSC-962 (>40,000 yr B.P.} and GSC-919 (>35,000 yr B.P.), come from a stratigraphic se<:don on Wolverine Creek (Fig. 9; Rampton, 1971a, Table 3). In essence, this section re­veals Macauley rill underlain by 80 fr (24.4 m) of sand and gravel. This, in turn, is un­derlain by a succession of sand and clay units that total 52.5 fr ( 15.9 m) and that yielded C14 samples GSC-962 (>40,000 yr B.P.) and GSC-919 (>35,000 yr B.P.). All these units are assigned to the Macauley glaciation and in turn are underlain by par­tially oxidized gravel and rill assigned a pre-Macauley age. However, indisputable evidence for the age assignment of =:he or­ganic horizons rhar produced the C14 sam-

ples to the Macauley glaciation is lacking. In analogy with the situation at Silver Creek (Denton and Stuiver, 1967), it is quite pos­sible that considerable time elapsed be­tween deposition of the organic units and the overlying Macauley till, for the two are separated by more than 80 fr (24 m) of sed­iments. Tht~ final sample, GSC-1576 (>37,000 yr l\.P.) from the White River val­ley in Alaska, has been discussed earlier and does not preclude ice recession during the Boutellier nonglacial interval. In summary, I feel that data are insufficient to state that the Snag-Klurlan area maintained an exten­sive glacier cover throughout the Boutellier nonglacial interval. In fact, deglaciation of Shakwak Trench, the major conduit of ice feeding the piedmont glacier in the Snag­Klutlan area, suggests that similar ice reces­sion probably occurred ar least in the Snag-Klutlan area and probably in the \Y/hite River valley in Alaska. However, final resolution of this problem must await additional data.

A combinatior 1f data from the White River valley, frorrJ the Snag-Klurlan area, and from Kluane Lake points to two firm conclusions: (1) Surficial Macauley and Kluane drift can be correlated on the basis of physical tracing; however, firm correla­tion of basal units of these two drifts is not yet possible. The Kluane glaciation began after 29,600 ± 460 yr B.P. (GSC-769) in the Kluane Lake area; however, it is not yet known when the Macauley glaciation beg:m in the White River valley and the Snag-Klurlan area. According to Rampton (1971a, p. 295), Macauley-Kiuane ice reached a maximum in the Snag-Klutlan area shortly before 13,660 ± 180 yr B.P. (GSC-495). Subsequent ice recession was widespread and rapid; deglaciation was es­sentially complete at least by 11,270 ± 200 yr B.P. (Y-2306) and perhaps by 12,500 ± 200 yr B.P. (Y-1386). (2) Shakwak Trench was largely ice free during the Bourellier nonglacial interval, dared here between <29,000 ± 460 yr B.P. (GSC-769) and >49,000 yr B.P. (Y-1481). The extent of simultaneous deglaciation, if any, in the Snag-Klutlan area and in the White Rjv~i valley in Alaska will remain unknown until additional peninent data become available. In addition to these firm conclusions, it can be stated with considerably less confidence that the Icefield till in the Kluane Lake area may correlate with the Mirror Creek rill, which projects north from beneath the Macauley drift in the Snag-Klurlan area. This tentative correlation is made because both tills predate Macauley or Kluane de­posits, because both ;;re older than about >3S,OOO yr B.P. and perhaps >49,000 yr B.P., and because both are relatively un­weathered in contrast to older Shakwak

deposits in the Kluane Lake area. However, it cannot be stated definitely that the Mirror Creek drift does not correlate with Shak­wak Drift, or some other drift not recog­nized in the Kluane Lake area. Further study of two parameters should clarify the correlation of pre-Macauley and pre­Kluane deposits in the northern Sr. Elias Mountains. First, electron-probe analyses might fingerprint volcanic materials present in the older deposits and hence facilitate correlation. Second, correlation eventually may be aided by pollen profiles from lake sediments on Mirror Creek drift and from organic material enclosed by Quaternary drifts.

On the basis of these conclusions, time­distance diagrams depicting termii'al fluctuations were constructed for two flov1

lines within the former glacier system (Fig. 12). One flow line extends 180 mi (290 km) from the head of the Kaskawulsh Glacier north and north\A.'est through Shakwak Trench ro the Macauley (Kiuane) and Mir­ror Creek terminal moraines near Snag; the other extends 47 m1 (75 km) from the head of the Russell Glacier in the upper White River valley eastward into Yukon Terri­tory, where it merges with flow lines from the Klutlan Glacier area and turns north­ward a short distance to terminate near the Alaska-Yukon Territory boundary. Hence the Kaskawulsh flow line represents the massive influx of ice from Shakwak Trench that entirely fed the large piedmont ice sheer in the Snag-Wellesley Lake area, whereas the White River flow line repre­sents the relatively minor influx of ice that fed the small lobe of the ice sheet near the border. The time-distance diagrams avoid the question of ice recession in the Snag­Klutlan area and the White River vallev in Alaska during the Bourellier nonglaciai in­terval. Likewise, they leave open the ques­tion of correlation of pre-Macauley glaciations.

The general sequence of Quaternary gla­cial events in the northern St. Elias Moun­tains renratively can be related to the well­known midcontinental glacial sequence as follows. In the Kluane Lake area, the Kluane glaciation, the Boutellier nonglacial interval, and the Icefield glaciation are as­signed to the Wisconsin glaciation on the basis of C14 dares, stratigraphic position, and lack of significant weathering zones. The Silver Weathering Zone represents the first intense weathering and may well dare ro the Sangamon (Eemian) interglacial. If so, this implies rhnr the Shakwak glaciation is pre-Wisconsin in age. In the Snag-Klutian area, the Macauley glaciation is Wisconsin in age and corresponds ar least in part ro the Kluane glaciation; in addition, I tenta­tively favor correlation of the Mirror Creek

..

•

•

888

WHITE RIVER FLOW LINE

10,980* 150 (1-6092)

I I 1100:!: 120(51-1103)

I 1,2 70%200(Y-2306)

> 37,000 (GSC-1576)"'

• •

>38,000(GSC-960)\

'> 36,000(GSC-496)

> ZS,OOO(GSC-95.6)

I I I I I I ?

0

I I I

? <>> > > > > >

.i--<..: Mirre>r Creek glaciation -------50 miles 25

100 kilomaten 50 f :

10

0

·20 ~ ~ =l

40

50

• ..

z a

"' n a ;;

Present terminus of Runell Glacier

Olslanee From Head Of Ruuell Glael•r

G. H. DENTON

KASK AWULSH-SH AKWA K FLOW L!N E

4470::t:I..O(GSC-5BI) ~:......:..:.:..:~~0

~4550*150(GSC-580) 9780::!:80(Y-!483)

.. /6200*150(GSC-544) '\. ~ 13,6e0.ZIBO(GSC-495) e e e '\. .. )

r;,ooo•ooot~~~"" IJ ,;,:~~!~~~\~:::!:~:~. •_/ ~ Ma'cauley r. glaciation !<Iuane glaciation

7760-k.I70(GSC-;:1j' 11 1000:1:.160(GSC-714)

29,600~:460 ( GSC-769) 30,100t:600(Y-1385)~ 331400t:800 (Y-1488)--.__.. ~­>35,000(GSC-734)-- . • 7

37,700:\~%% (Y-13!:6)-=:::::::: ()

Boutellier I nonglacial (

/

>38,000 (GSC-960) interval ) >36,000(GSC-496) <

/ ' /

>381000(GSC-959) )

> 49,000(Y-1481) -• ..S:: ------------• !!.c;::::~·~---~M~Iirr~ro;;r~C;reek ? -~on 0

lcefield glaciation

I ---1 > 4 91 0 0 0( Y- 148 ;:--:-) ---":':>""'co.:•~'/-

1 l> 1 Silver <"" 1 nonglacial ,

? interval > <>

? '> I ( I '-·16,400(Y-1355l-• ~ J, _____________ _

-=.-::.,:- Mirror Creek ? Shakwak --- glaciation glaciation

~00

-- 0 ------........

150 100 miles

200 kilometers 100

··~

Pr~sent term•nus of Kaakawulsh Glacier

:>lstaneo From Head Of Kaskowulah Glacier

0

0

10

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20 ~ if a ~ .. ,. 0

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40

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Figure 12. Time-distance diagrams of glacier fluctuations along two flow lines within Quaternary glacier system north of St. Elias Mountains. White River flow line extends from current head of Russell Glacier east along White River valley into Yukon Territory and north to terminal moraines ncar border (Figs. 9 and 10). Kaskawulsh flow line trends from head of Kaskawulsh Glacier north and northwest through Shakwak Trench to terminal moraines near Snag and Wellesley Lake (Figs. 9 :llld 10). See Figures 9 and 10 and Table 1 for location and description o£ C1~ samples. Only those C14 samples that lie close to the flow lines are used.

and the lcefield glaciations, and as­signment of both to the Wisconsin glacia­tion; however, it is equally likely that the Mirror Cred~ glaciation corresponds to the Shakwak glaciation and hence may be pre-Wisconsin in age. In the White River valley in Alaska, the Macauley glaciation can be tied in with the over-all sequence, but the older glaciations remain uncorre­lated. Therefore, Wisconsin time in the St. Elias Mountains probably was charac­terized by two major ice advances, one dur-

ing the early Wisconsin (Icefidd glaciation and possibly rhe Mirror Creek glaciation) and one during the late Wisconsin (Macauley-Kluane glaciation). In the Shakwak Trench, a long interval of reces­sion (Boutellier nonglacial interval) sepa­rated these rwo major advances. The Jcefield glaciation probably corresponds with the extensive early Wisconsin glacia­tion in the midcontinent that oc('urred be­tween the St. Pierre and Port Talbot inter­stadials and that is dated to >48,000 yr

B.P. The Boutellier nonglacial interval probably correlates with the Port Talbot and Plum Point interstadials.

The single long pollen profile available from the northern St. Elias Mountains (Rampton, 1971b) is from the floor of An­tifreeze Pond, which is situated on Mirror Creek drift near the Alaska-Yukon Terri­tory border (Figs. 9 and 10). The core ap­parently penetrated the entire thickness of lacustrine sediment, for it bottomed in gravel or tilL The CH dates from near the

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QUATERNARY GLACIATIONS OF THE WHITE RIVER VALLEY, ALASKA 889

base of the core range from 31,500 ± 700 (GSC-1048) to 27,100 ± 390 (GSC-1198) yr B.P., but they are not consistent strati­graphically. Organic silt from the base of a second test core taken adjacent to the pol­len core afforded an age of >36,000 yr B.P. (GSC-496). Thus, the pollen profile in­cludes at least the youngest part of the Boutellier nonglacial interval, and some of the profile may extend into an earlier part of the interval. The area of Antifreeze Pond was characterized by fell field or sedge­moss tundra during the interval that may possibly predate 31,000 yr B.P. (Rarr.pton, 1971b, p. 970). Subsequently, shrub rundra occurred 31,000 to 27,000 yr B.P., and sedge-moss tundra persisted from 27,000 to 10,000 yr B.P. Shrub tundra prl'!vailed from 10,000 to 8,700 yr B.P., and was succeeded by spruce woodland from 8,700 to 5,700 yr B.P. and by spruce forest from 5,700 yr B.P. to the present. Therefore, at this locality, tundra characterized the landscape at least during the end of the Boutellier nonglacial interval and through the Macauley-Kluane glaciation. Spruce apparently did not in­vade the region until well after disintegra­tion of the Macauley-Kluane piedmont glacier. The relatively late age for the ar­rival of spruce is supported by the date of 8,020 + 120 yr B.P. (Y-2302) on the low­ermost spruce stumps exposed in the mus­keg section in the upper White River valley in Alaska {Joe. 2 in Fig. 2 and Fig. 5). A change from spruce woodland to spruce forest characterized the Holocene.

CLIMATIC IMPLICATIONS Discussion of the climatic implications of

the ::it. Elias glacial sequence must be pref­aced with the remark that a number of cur­rent St. Elias glaciers undergo periodic surges. Although several recorded surges involved substantial displacement of ice, most were relatively minor pulses that often affected only tributaries and usually did not reach termini. Presumably, surging of the expanded Quaternary piedmont glacier in­volved only individual ice streams and probably did not drastically affect the ter­minus, although this possibility cannot be dismissed entirely. Surging of only parts of the expanded glacier is especially likely, in view of the fact that the Kaskawulsh Glacier, one of the main feeders of the Quaternary piedmont glacier, currently does not surge. Most likely, possible surges had litde effect on the broad conclusions reached in this section, which are concerned with major ice-volume changes and . not with individual terminal fluctuations.

The nature of most paleoclimatic indi­cators militates against recognition of ab­rupt climadc changes. Even if climates ameliorated rapidly, considerable time

•, .

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....................

Distance From Probable Center of Outflow ''(km)

:30 Laurentide Ice Sheet (Great Lakes Region) I I

2000 1500 1000 500 0

Scandinavian Ice Sheet (Southern Sector) ~-----r-----~-----~

1500 1000 500 0

· Cordilleran Ice Sheet (Southern Sector) ~·-·-·-·-·-·-·-·-···-·-·-·-·---·-·-·~

500 250 0

St. Elias Glaciers (Kaskawulsh Flow Line} r--------------------r-------------------, 300 150 0

Figure 13. Time-distance diagrams along flow lines within glacier systems of varying sizes; horizontal scale has been adjusted so that diagrams can be superimposed on each other. St. Elias data from this paper. Cordillera data from Armstrong and others (1965), Crandeli (1965), Crandell and others (1958), Easterbrook (1969, 1970), Fulton (1968, 1971), and Fyles (1963). Laurentide curve from Blake {1966), Broecker and Farrand (1963), Bryson ano others (1969), Dreimanis and others (1966), Farrand and others (1969), Frye and others (1965), Gadd (1964,1972), Goldthwait and others (1965), Hobson and Tcrasmae (1969), Hough (1958), McDonald (1971), Prest {1969), Ruhe (1969), Wright and Ruhe (1965), Wright and Wans (1969), Willman and Frye (1970), White (1968), and Wayne and Zumberge (1965). Scandinavian curve from Chebotareva (1969), Donner (1965), Hansen (1965), Hoppe (19 59), Lundqvist ( 1965), Sonesson ( 1968), Tauber (1970}, Hammen (1971 ), and Woldstedt ( 1967).

would be required for large ice sheets to melt and for vegetation to migrate and ad­just to new environments. Furthermore, large ice sheets tend to perpetuate them­selves and may continue to cool considera­ble portions of the globe. Moreover, 0 18

measurements from deep-sea cores may largely reflect large ice sheets, which in turn require considerable time to melt. Hence, these indicators tend to show smooth climatic curves when, in fact, the changes may have been rather abrupt. Such consid­erations suggest that alpine glaciers, be­cause of their relatively small size and rapid reaction to climatic change, may be espe­cially sensitive instruments capable of re­cording any possible rapid climatic amelio­ration, particularly at the end 0f a glacia-

tion. In this respect, the St. Elias glacial chronology, although it corresponds broadly with the midcontinental standard sequence of Wisconsin glacial events, em­phasizes one particularly dramatic event. If the interpretations of the stratigraphy and C 14 dates are correct, the Macauley-Kluane piedmont glacier attained its maximum ex­tent approximately 14,000 yr B.P., and shortly thereafter underwent rapid reces­sion that led to disintegration of the glacier system in less than 2;700 yr and perhaps within 1,500 yr. There is no evidence of widespread stillstands or readvances during this general recession. The behavior of St. Elias glaciers suggests that a decisive climat­ic change terminated the Macauley-Kiuane glaciation shortly after 14,000 yr B.P. This

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change represents the most marked event recognized in the late Wisconsin glacial record in this region. Corresponding to this scheme, relatively early alpine glacier reces~ sian at the end of the late Wisconsin glada~ tion was not restricted to the northern St. Elias A4ountains, but also occurred in Glacier Bay, Alask~ (Haselton, 1966; McKenzie and Goldthwait, 1971), and in Yellowstone Park, Wyoming (Richrr.ond, 1970, p. 20). Moreover, in the Southern Hemisphere, alpine glaciers in New Zea~ land (Suggate, 1965; Suggate and Moar, 1970) and in southern South America (Mercer, 1970, 1972) disintegrated rapidly shortly after 14,000 yr ago. In this respect, it is interesting to note that another sensi~ tive climatic indicator, the variations of the oxygen isotope ratio in deep ice cores, shows a very rapid end to late Wisconsin glacial dimates over northern Greenland about 13,000 yr B.P. (Langway and others, 1973, p. J17).

A dedsive change in glacier behavior shortly after 14,000 yr B.P. is indicated by larger ice sheets, as well as by alpine glaciers. Figure 13, which shows time~ distance diagrams for several Quaternary glacier systems of varying sizes in the Northern Hemisphere, records several fea~ tures not previously emphasized. First, all documented glaciers were at or near late Wisconsin maximum positions as late as 14~000 yr B.P. Second, the climatic amelio­ration shortly after 14,000 yr B.P. that is emphasized in the St. Elias glacial record is also shown by the larger glacier systems, al­though to a less marked degree. In all cases, glacier recession began very shortly after 14,000 yr B.P. and continued, with fluctuations, until glaciers disappeared or receded behind their present termini. The time required for complete dissipation after 14,000 yr B.P. was largely a function of ice volume. The Laurentide Ice Sheet (-26 X 10fl km3 of ice) required 8,000 yr; the Scan~ dinavian Ice Sheet (-13 X 106 km3), 5,500 yr; the Cordilleran lee Sheet (-3.5 X 106

km3), 4,000 yr; and the St. Elias glaciers

( <0.02 X 106 km3), 1,500 to 2,700 yr. The rapid dissipation of St. Elias glaciers)

as well as of other glaciers in the Northem Hemisphere shortly after 14,000 yr B.P , bears on the character of the termination l)f glaciations and on the important questictn of whether major glacial~intergladal dim at~ ic changes can occur abruptly. The availa­ble results suggest that the concept of an abrupt and widespread background event terminating the late Wisconsin glaciation is possible and deserves serious consideration. If further work on alpine moraine systems in both polar hemispheres tends to substan~ tiate this working hypothesis, it would sug~ gest intuitively that a widespread

G. H. DENTON

phenomenon affecting much of the Earth, such as a change in ~olar activity, termi­nated the last glaciation. £vern; :::.:bsequent to an abrupt termination may be related to a combination of {1) the substantial time required for the Earth's ocean~ice­atmosphere system to equilibrate with new boundary conditions, and (2) relatively minor climatic oscillations, such as those mentioned by Denton and Karlen (1973), superimposed on major glacial-interglacial changes. In any case, these data suggest that Termination I of Broecker and van Donk (1970) began shortly after 14,000 yr B.P.

The glacial history of the St. Elias Moun­tains also bears on more local problems. Morphologic and stratigraphic data, taken together with C14 dates, have not yet shown such major glacial events as rhe Younger Dryas readvances of the Scandinavian lee Sheet or the Cochrane-Cockburn read­vances of Laurentide ice. C14 dates show that Younger Dryas moraines, if they exist, are restricted to within a few kilometers of modern glacier termini or else have been overrun by Little Ice Age advances. Likewise, possible Cochrane-Cockburn moraines have been overrun by Little Ice Age advances. In any case, the dominant overprint is one of rapid recession, which might suggest that climates approaching those of the present time were obtained rel­atively early during late Wisconsin deglaci~ arion. If so, the tundra that persisted in Alaska until about 8,700 yr B.P. may have been relict and able to survive only until the immigration of spruce from far distant refugia.

IMPLICATIONS FOR EARLY MAN ARCHAEOLOGY

The history of St. Elias Quaternary glaciers has a direct bearing on early man studies in North America. These glaciers periodically filled Shakwak Trench, a prime possibility as a route through southwestern Yukon Territory from south-central Alaska to central British Columbi.,. or to the coast of southeastern Alask8. Moreover, together with the Cordilleran and Laurentide Ice Sheets, St. Elias glaciers formed a barrier across northwestern North America. The glacial chronology presented here indicates that Shakwak Trench was open for possible movement of early man during the Boutel­lier nonglacial interval from <29,600 to >49,000 yr B.P. Taken together with 0 4

dates that suggest recession of the Cordille­ran Ice Sheer in southern British Columbia during thl! correlative Olympia Interglacia­tion (Fulton, 1968, 1971), these data sug­gest the distinct possibility that during mid­dle Wisconsin time early man could have moved through southwestern Yukon Ter­ritory, and then southward through interior

. ..

British Columbia into what is currently r western United States. This route may ha been just as feasible as the ice-free corric.i route farther east berween the Cordiller and Laurentide Ice Sheets.

The rapid deglaciation of Shakw. Trench in late Wisconsin time pro\'id. early access to interior British Columbia to coastal southeastern Alaska across ti mountain passes currently followed by tl highway between Haines Junction ~ Yukon Territory and Haines in Alaska. Tl former route from Alaska to interior Briti~ Columbia could have been followed by ca. riers of the microblade tradition, where;:: the latter route could have been followed b the people who occupied Ground Hog Ba in southeastern Alaska about 10,180 ± 80r yr B.P. (WSU-412; Ackerman, 1968 p. 60).

ACKNOWLEDGMENTS The research reported here was financeL

by National Science Foundation Gran 21484, to the aur:hor at the University o Maine. I am gratef~! for this support, which allowed fieldwork in the White River valle\ in the summers of 1967, 1969, and 1970. The University of }.,1 '1e provided the time necessary for data 1 eduction and report preparation.

Minze Stuiver kindly processed 11 CH samples at the Yale Radiocarbon Labora­tory. The Geological Survey of Canada dared sample GSC-1576 through the cour­tesy of Weston Blake, Jr.; Robert Stucken~ rath of the Radiocarbon Laboraror: at the Smithsonian Institution dated sample SI-1103; and James Buckley at Teledyne­Isotopes, Inc., dated the remainder of the C'4 samples.

Douglas and Thomas Vaden supplied complete logistic support for the fieldwork, including air transport to the White River vailey from Anchorage and pack trains for transportation in the field area. Without their very expert help, the fieldwork could not have been carried out. I also thank Carl Weiman, Frederick B!"agdon, and Wibjorn Karlen for able assistance in rhe course of the fieldwork. The Icefield Ranges Research Project of the Arctic Institute of North America generously provided field equip­ment and allowed Frederick Bragdon to parckipate in the research program.

Additionally, I thank D. M. Hopkins, 'v. N. Rampron, H. R. Schmoll, and R. P. Sharp for their detailed and helpful com~ ments on an early draft of this paper.

REFERENCES CITED Ackerman, R. E., 1968, The archeology of the

Glacier Bay region, southeastern Alaska: Washingt'n State Univ., Laboratory of An­thropology Rept. lnv. no. 44, 123 p.

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QUATERNARY GLACIATIONS OF THE WHITE R~ER VALLEY, ALASKA 891

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G. H. DENTON

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MANUSCRIPT RECEIVED BY THE SOCIETY J~NE 18, 1973

REVISED MANUSCRIPT RECEIVED OCTOBER 26, 1973

Prtnted tn U.S A.

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