The Last Glacial Maximum on Spitsbergen, Svalbard

(1)

Q U A T E R N A R Y R E S E A R C H 3 8 , I-3I (I992)

T h e L a s t Glacial Maximum on Spitsbergen, S v a l b a r d

JeN MeNcr,Ruo, MacNe, BoLsr,A.o, ANNg Er_cr,nstrn, Dec Hr.lr_lxsp,N, J o N Y ' L R N o v l r , l Ioa L/NNe,' A""u KotRrNr. L y c r e , o r r o SRLvrcsr,N,*

Tov SeNoaHL, AND JoHN h.qcE SvE,NossN - -

universit:- tJ'Bergen, Department of Georogr-, Secri.n *Norv'egian porar B, Altigt.rr, N-5007 Bergan, Noru,uy: and Researtrt trttitutr,- p.o. io.r t5g, N-r3J0 o.sro Lufthavn, Norv,uy

R e c e i v e d April 4, l99l M o s t s c i e n t i s t s have concruded previousry

t h a t t h e west coast of Spitsbergen, Svarbard, r e _ m a i n e d i c e - l i e e during rhe late weichselia",

; . i ; ; . ; 2 _ 5 , 0 0 0 and 10.000 yr B.p.-we conclude rhar t h e g l a c i a t i o n was more extensive. Terraces'that

w e . e p o r t u t u t e a to have been ice-tiee are covered b y a t h i n ' late weichselian till' sudden drop in the marine r i m i t a n d basar radiocaroon dates of r a t s e d g l a c i o m a r i n e sediments demonstrates,t'ru,

r t r . g l a c i e r s in the main fords. lstjorclen and van M i j e n f i o r d e n ' terminated west (outside) of the flord'.outhr. B a s a l r a d i o c a r b o n - c i a t e s f r o m g l a c i - o m a r l n e clay above till in cores from the contineital l 2 ' - 5 0 0 y r B P'' from which we conclude that the ice extended s h e l f w e s t ofSpitsbergen yielded ages ofaboutt o t h e s h e l f e d g e . Base6 on the extent o f a m i n o acid diagenesis i n r a d i o c a r b o n - d a t e d

m o r l u s ; s . the duration of the maximum exlenslon o f t h e r a t e weichselian graciation was short, certainry r e s s t h a n 10,000 years. During the ice_free p e r r o d p r e c e d i n g that glaciation, at least uu.L to +o.iroo yr B . p . . r h e g l a c i e r s on .svatuard were not s i g n i f i c a n t l y rarger rhan at present. as shown by marine d e p o s i t s .r.* ," it. gl"lier snouts. Many r a d i o c a r b o n dates prace degraciation or,rr. ou,.. .oort u r u u o u t 12.-500 y r B.p-;; about 10,000 yr B P ' the rest of the archipelago rapidly became i;;-f;... q r e e r r i n i v e r s i r ! . . r w a r h i n s r . n .

I N T R O D U C T I O N

W h e n we started o u r in v e s t i g a t i o n s o f t h e g l a c i a l h i s t o r y of Svalbard i n l g g f *. o.

c e p t e d t h e view that the Barents I c e Sheet had covered eastern Svalbard and parts-of t h e Barenrs Sea (Fig. t) during if," tui.

W e i c h s e l i a n . T h i s view was rnurnty U o r . A on the classical argument of a majoi glacio_

i s o s t a t i c u p d o m i n g of the u..nip".iogo ( S c h y t t e t al., 1968), w i t h rhe dare io. ii"

100-m shoreline on Kongs@ya of 9g00 yr B . P . ( S a l v i g s e n , I g g t ) being i h e final proof t h a t this updoming w a s caused b y the late Weichselian glaciation. This inteipretafion has been reinforced by growing ""i0""..

from the sea floor of the Bareni, S"u fEI_

y e r h o i a n d S o l h e i m , l9g3; Vorren et ;., 1 9 8 8 ; E l v e r h Q i e t a l . , 1 9 9 0 ) , a n d i, n o * g . n _ e r a l l y accepted, e v e n though the areal ex_

' P r e s e n t adclress: Agricultural University of Nor_

w a y . D e p a r t m e n t o f S o i l S c i e n c e s . p . O . - g o x j g . N - 1 4 3 2 A s - N L H . N o r w a v .

t e n t a n d t h i c k n e s s of the Barents Ice Sheer i s s t i l l d e b a t e d .

A l t h o u g h t h e r e is a general consensus that a large ice sheet covered the northern a n d c e n t r a l Barents Sea during the laie Weichselian, a major disagreemeit ."rnuin, about the glacial limit on western Spitsber_

g e n . According to some reconstructions.

the entire archipelago was covered by the B a r e n r s Ic e Sheer (Grosswald. l9g0lb;;_

t o n a n d H u g h e s , lggl). However, all scien_

tists who had done field work in the area before we started. and indeed fut.., .on_

c l u d e d t h a t the extreme west coast re_

mained ice-free during the late Weichselian (Salvigsen, 1977, 1979: Salvigsen ""J Xl_

d a l , . l9 8 l : Salvigsen and @sterhof r n , f q S i ; Troitsky et at., 1979; Boulron, tS7g, 1990':

B o u l r o n e t at., t9g2: Miller, f SAZ; Iaille. "i al., 1989 Forman and Miller, f SS+; Fo._

m a n , 1 9 8 9 ) . S o m e s c i e n t i s t s a l s o c o n c l u d e d that the middle and inner parts of Isflorden a n d V a n M i j e n f i o r d e n w e r e 1 . . _ f . " "

0033-5894/92 $-s.00

Copyright a 1992 b] rhe Universjry ot Washington All rights of reproductjon in any f(rm reserved.

(2)

M A N G E R U D E T A L .

F r c . L M a p o f S v a l b a r d , g i v i n g p l a c e n a m e s o u t s i d e t h e a r e a s h o w n i n F i g u r e 2 . W e f o l l o w t h e official Norwegian naming; Svalbard is the name of the entire archipelago, whereas Spitsbergen is the m a i n i s l a n d o n l y . N u m b e r s g i v e r a d i o c a r b o n d a t e s th a t p r o v i d e m i n i m u m a g e s fo r t h e l a s t d e g l a c i a t i o n . The dates are given in 103 yr B.P., rounded off to the nearest hundred years. Original references for t h e d a t e s a r e g i v e n i n c i r c l e s , a n d a r e l i s t e d b e l o w . F o r m o s t o f t h e d a t e s , t h e a u t h o r s c o n c l u d e d t h a l t h e d a t e i n d i c a t e s t h e a g e o f d e g l a c i a t i o n , o r a m i n i m u m a g e l e s s t h a n 2 0 0 y r y o u n g e r t h a n t h e d e g l a c i a t i o n . H o w e v e r , b a s e d o n t h e r e s u l t s b y M a n g e r u d a n d S v e n d s e n ( 1 9 9 0 b ) , t h a t a s s u m p t i o n m a y b e t o o o p t i m i s t i c . R e f e r e n c e s : ( l ) Salvigsen, l98l: (2) Btidel, 1968; (3) Nacy, 1984; (4) Boulton, 1990;

( 5 ) Jonsson, 19831 ( 6 ) S a l v i g s e n . 1 9 7 8 ; ( 7 ) K a r l d n . 1 9 8 7 ; ( 8 ) Osterholm, 1986; (9) Blake. 1987; (10) B l a k e , l 9 8 l ; ( l l ) H o p p e , 1 9 8 7 ; ( 1 2 ) S a l v i g s e n a n d @ s t e r h o l m , 1 9 8 2 ; ( 1 3 ) S t a n k o w s k i e t a l . , 1 9 8 9 ; ( 1 4 \ F o r m a n e t a l . . 1 9 8 7 ( 1 5 ) L e h m a n a n d F o r m a n , l 9 9 l ; ( 1 6 ) F o r m a n , 1 9 9 0 . W e h a v e s u b t r a c t e d 1 4 0 y e a r s from whalebone dates cited from 14 and 16, see text. Ages without reference are from the present p a p e r .

(3)

L A S T G L A C I A T I O N OF SPITSBERGEN

( L a v r u s h i n , 1967, 1969; Troitsky et al., 1 9 7 9 ; T r o i t s k y , l98l; Boulron, 1979).

The main aim of this paper is to contrib_

ute to a resolution of the described contro_

versy on the limit of the last glacier, and ro provide an improved description and inter_

pretation of the late Weichselian glaciation on western Svalbard. Our evidence is based on extensive field work along the two main f i o r d s , V a n M i j e n f i o r d e n and Isfiorden ( F i g . 2t. This provided new stratigraphic and other geologic data for the reevaluation of earlier observations and interpretations, as well as samples for an extensive dating program. In this paper we also compile ear_

lier published results, especially the rele_

vant radiocarbon dates.

W h e n we started the field work we adopted the working hypothesis that the err_

tire study area had been ice-free, unless the opposite could be proven. One objective, therefore, has been to construct minimum models of the last glaciation. Our earlier re_

p o r t s d e m o n s t r a t e h o w o u r m o d e l h a s changed during the work: we soon found that there had been a glacier that extended at least to the mouth of Van Mijenfiorden ( M a n g e r u d e t a l . , 1984, l9g5; Landvik er al., 1987). Moving northward, we found that also Linn6dalen, at the mouth of Isfior_

d e n , had been glaciated. b u t i n that artlcte we kept open the possibility that lsfiorden remained ice-free (Mangerud et el., 19g71.

T h u s , to determine t h e g l a c i a l l i m i t , w e hao to study the sea floor sediments in the fiord a n d on the continental s h e l f . Our corrclu_

sion in this paper is that the entire Van Mi_

j e n f j o r d e n - I s { l o r d e n a r e a ( e x c e p t some s u m m i t s ) was ice-covered, a n d t h a t the western limit for the last glacial maximum was on the continental shelf (Svendsen el a l . . 199D.

W e r e s t r i c t the term the Barents lce Sheet to an ice sheet that was centered in t h e Barents Sea, including Kong Karls Land (Fig. l). We propose thar the term also be used for such ice sheets durins ear_

l i e r g l a c i a t i o n s . T h e B a r e n t s l c e S h e e i m a v h a v e f l o w e d o n t o l a n d i n E u r a s i a (e . g . .

Grosswald, 1980), and probably inundared most of Svalbard at some times. During other periods there were ice domes and/or separate glaciers situated on the main is_

l a n d s of Svalbard ( e . g . , Spitsbergen a n d Nordaustlandet) (Forman, l9g9). We do not include those glaciers in the Barents Ice Sheet, even though they might have been in physical contact with it. Such a conceptual distinction between the Barents Ice Sheet and glaciers on Svalbard is useful to under_

stand the glacial history of this area.

In this paper we first present the obser_

vations from the Van Mijenfiorden area, then Linnddalen and the coast around Is_

forden, and finally cores from the floor of Isfiorden and rhe conrinental shelf (Fig. 2).

M E T H O D S Field Work

This paper is based on stratigraphical in_

v e s t i g a t i o n s o f r a i s e d marine sediments, partly interbedded with tills. We spent days and weeks in digging sloped material to ot_

tain large sections that in addition to verti_

cal also provided lateral stratigraphic rela_

tionships. We also mapped glacial striae, s h o r e l i n e s , a n d moraines. M o r e detailed descriptions of some of the sites are given in unpublished (but available) candilates scientific theses (Master thesis) at the Uni_

versity of Bergen (Elgersma and Helliksen- 1 9 8 6 ; L p n n e , 1986; S a n d a h l , l 9 g 6 ; Bolstad, 1 9 8 7 ; L y c k e , 1987). E l e v a t i o n s w e r e mea_

sured either with a paulin barometer with l-m resolution, or leveled. Directions were measured with a 360" compass, corrected for magnetic deviation.

Radiocarbon Dates

All samples have been dated either at the

T r o n d h e i m Laboratory for Radioloeical

D a t i n g o r a t T h e S w e d b e r g L a b o r a t r v .

U p p s a l a U n i v e r s i t y . A t t h e T r o n d h e i m

Laboratory (prefix T-, on samples) dating is

performed by proportional counting, uring

CO, gas. We have submitted small samplei

to Uppsala (prefix Ua-), for acceleritor

(4)

MANGERUD ET AL.

ur

e J l

II

--ll I

rri

o

(,_

o

N

o o o c

6 CL

o l o lo l i o, o

t ;

. g - i D >' o - 9

E =a o

g e

r o C J 5

$ O

o o c ' I

. Y i

g ' iC E x 6o E

! o r

f ! E ' d ' = o

> d

l \

l

() ) >

s

E

o oo (!

o

. 9 =

o = ' i

. =

= L

l 9 ( 5 .

o > : - \

D

!

Io

dl

\ \ r

S x

o 9 l N I

+

@

sr

8_o"GR

:xTSU

('; gr=

tEto-

r$\+) \

'w...

+

a a a a a a a

Koil'

se

ilb"'9 iz;E

(5)

L A S T G L A C I A T I O N O F S P I T S B E R G E N

mass spectrometry (AMS) dating. For sam- ples with prefix TUa- the target was pre- paired in Trondheim, and the AMS mea- surements performed in Uppsala.

A l l s a m p l e s a r e r e p o r t e d a s r e c o m - mended by Stuiver and Polach (1977), in- cluding a correction for isotopic fraction- a t i o n t o - 2 5 p e r m i l r 3 C

o n t h e P D B s c a l e . A reservoir age of 440 yr is subtracted for all samples that have obtained their carbon f r o m s e a w a t e r ( s h e l l s , s e a w e e d , w h a l e - b o n e s , e t c . ) . T h i s i s a s t a n d a r d v a l u e u s e d b y t h e T r o n d h e i m L a b o r a t o r y f o r t h e coasts of Norway including Svalbard, and is based on measurements of many prein- dustrial shells from these waters (Mangerud a n d G u l l i k s e n , 1 9 7 5 ) ; 4 4 0 y r i s a l s o t h e mean reservoir age for the Svalbard area for the last 9000 yr according to Stuiver et a / . ( 1 9 8 6 ) . W h a l e s a c q u i r e t h e i r c a r b o n from larger oceanic areas and, thus, theo- retically they may have different reservoir ages compared to the stationary molluscs.

H o w e v e r , t h e r e s e r v o i r a g e s o b t a i n e d around the North Atlantic are nearly every- where 400-500 yr (Stuiver et al., 1986). We therefore use the same reservoir age for whales and shells. in contrast to Forman et al. (1987), who use 300 yr for whales and 425 yr for shells.

A m i n t t A r i t l D i u g e n a . s i s

In this paper we use amino acid diagene- sis for three purposes: (l) to ensure that r a d i o c a r b o n s a m p l e s o f s h e l l f r a g m e n t s consist of only one age population; (2) for a first-order age estimate of samples of "old"

or non-finite radiocarbon age; and (3) for

modeling of diagenetic temperatures (espe- cially ice-covered or not) for samples of postulated age.

All samples were analyzed at the Bergen laboratory (prefix BAL-). Full descriptions for some of the samples are given by Bol- s t a d ( 1 9 8 7 ) ; m e t h o d s f o l l o w M i l l e r a n d Mangerud (1986). ln this paper we report only the epimerization of isoleucine to allo- isoleucine for the total fraction, expressed as D/L ratios (by some labeled alle/Ile). All reported D/L ratios are from the species Mya truncata or Hiatella erctic:a, which h a v e s i m i l a r e p i m e r i z a t i o n r a t e s ( M i l l e r , 1 9 8 2 ) .

F o r p a l e o t e m p e r a t u r e e s t i m a t e s ( e s p e - cially the 87-m terrace in Linn6dalen and Kapp Ekholm) we have used a D/L ratio of 0 . 0 1 1 f o r l i v i n g s h e l l s , a n d t h e A r r h e n i u s parameters 28.1 kcalimole for the activa- t i o n e n e r g y a n d 1 6 . 4 5 f o r t h e i n t e r c e p t (Miller, 1985). For radiocarbon-dated shells that lived, and were uplifted, soon after de- g l a c i a t i o n ( l I , 5 0 0 to 1 0 , 0 0 0 y r B . P . ) , w e o b - tained a mean D/L value of 0.016 -f 0.003 for 42 analyses from different sites on the west coast of Spitsbergen. Solving the tem- perature equation for this D/L value (0.016) predicts an effective diagenetic tempera- t u r e o f - 3 . 7 ' C w h i c h i s c l o s e to t h e c u r r e n t mean annual temperature at Isfiord Radio, j u s t W of Linn6dalen (-4.7"C for 1951-

1 9 7 5 ; S t e f f e n s e n , 1 9 8 2 ) .

V A N M I J E N F J O R D E N _ B E L L S U N D Minimum Age of Deglaciation

Radiocarbon dates from the Bellsund-

Frc. 2. Map of the study area. Radiocarbon dates are given in l0r yr B.P. The ages are rounded off s l i g h t l y d i f f e r e n t c o m p a r e d t o F i g u r e l . I n t h i s m a p t h e f i r s t d i g i t i n t h e a s s a y i s g i v e n u n a l l e r e d , to make comparison with Tables l-6 easier. Thus, in this figure 9980 is cited as 9.9, whereas in Figure I i t i s c i t e d a s 1 0 . 0 . O n l y t h e o l d e s t d a t e s f r o m e a c h s i t e t h a t p r o v i d e m e a n i n g f u l minimum ages of deglaciation are cited. Dates in squares are from sediment subsequently overrun by ice. Location of cores from the sea floor are given by core number (03/04;01/02: and 144). Shaded areas show present day glaciers. Contour interval is 200 m both on the sea floor and on land. All names ending -d. are s h o r t e n i n g s fo r - d a l e n ( w h i c h m e a n s v a l l e y i n N o r w e g i a n ) . O t h e r s h o r t e n e d n a m e s a r e : B l o m e s l . , B l o m e s l e t t a l P e t . , P e t u n i a b u k t a ; B i l l e f i . , B i l l e f i o r d e n ; E k h o l m , K a p p E k h o l m ; B o h e m . f l . , Bohe- m a n n f l y a ; E r d m . f l . , E r d t m a n f l y a ; M i s e n . , M i s e n e s e t ( t h e s i t e S E o f t h e i s l a n d o f A k s e l g y a ) ; R e c h . f i . , Recherchefiorden.

(6)

6

l . R , q o r o c e n s o N D l r E s " r ' n o u B e l l s u N o , v A l M I : e N r r o n o r N , e N o A C l n o H n u x r n ( F t c . 2 )

A g e ( y r B . P . ) Material

Locality Field sample No. and descriptron T A B L E

Laboratory N o .

T-6000

Ua-280

T-5997

T-486-5

T-5995 T-5273

T - 5 7 1 l

T-4843

T-4842 T-5363

T-5362

T-5368

1 2 , 8 3 0 a 2 1 0

1 2 , 5 7 0 t 1 6 0

1 1 , 2 3 0 I 1 2 0

1 1 . 0 2 0 : t l l 0

10,U40 :t I l0 1 0 , 2 3 0 t 1 4 0

95U0 rt I l0

9640 ! 240

9600 t 180 1 0 , 3 3 0 t 1 4 0

10,040 r: 110

10,500 :! 200

S h e l l s

S h e l l s S h e l l s

S h e l l s

S h e l l s Seaweed

S h e l l s

Skilvika

Y t t e r d a l e n

Ytterdalen M d s e n e s e t

M i s e n e s e t

V a s s d a l e n

V a s s d a l e n Frysjadalen

Frysjadalen

Bromelldalen

T-5369 10, 130 :t 150 Shells

B r o m e l l d a l e n

Svalbard-84-747. Paired Nuculana pernula in a laminated, extremely finegrained clay, just a b o v e a t i l l .

Svalbard-84-225. Accelerator date of a similar sample as the conventional date T-6000 a b o v e .

Svalbard-84-426. Fragments of H iatellu arcti('a from a diamicton, interpreted as s l u m p - d e p o s i t , o v e r l y i n g t h e c l a y d e s c r i b e d under T-6000. Only fragments with D/L r a t i o s b e t w e e n 0 . 0 1 5 a n d 0 . 0 1 7 w e r e d a t e d . M!-a truncata and Hiatella nrclica related to

t e r r a c e a t 6 4 m a l t i t u d e ( L a n d v i k e l a 1 . , 1 9 8 7 ) .

A s T - 4 8 6 5 .

Sa-83-49 Hiatella arctica and Mya truncata tn living position in the lower part of foresets in a terrace at 40 m altitude. Just east of the main gully cutting through the large terrace.

H e l - E l g 2 4 0 - 8 3 . S h e l l f r a g m e n t s , m a i n l y Balanus, in low angle topsets ln terrace at 3 0 m a l t i t u d e . J u s t w e s t o f m a i n g u l l y . H e l - E l g 2 8 - 8 2 . F r o m s e c t i o n s a l o n g t h e

s e a s h o r e . s o u t h o f t h e m o u t h o f t h e r i v e r . Just above a basal till.

Hel-Elg 26-82. Mya trun(ata, and Hiatellu a r c t i c a . S i m i l a r p o s i t i o n t o T - 4 8 4 3 . H e l - E l g l 2 l - 8 3 . S e c t i o n a l o n g w e s t e r n m a r g i n

of present delta. Plant remains in silt, probably contorted by subsequent local ice advance. The sample had an estimated content of terrestrial plant remains of lV30%', therefore, a reservoir age of only 350 yr was subtracted.

Hel-Elg 324-83. Macoma calcarea in living position in undisturbed silt above the silt w i t h T - 5 3 6 3 .

Hel-Elg 266-83. Yoldiella lenticula, Portlandiu o r ( l i c d , N u c u l a l e n u i s ' M u ( o m u c a l c a r e u i n living position in a 50-cm thick clayey silt.

Above the silt is a diamicton, interpreted as a till deposited by a local Younger Dryas readvance down Bromelldalen. The section is situated 2.3 km from the sea, east side of t h e v a l l e y .

Hel-EIg 243-83. Macoma calcarea, and Mya truncata in living positions at the base of a silt just above the Younger Dryas till d e s c r i b e d u n d e r T - 5 3 6 8 .

(7)

T A B L E l - C o n t i n u e d

7

Laboratory

N o . A g e ( y r B . P . ) M a t e r i a l Locality F i e l d s a m p l e N o . a n d d e s c r i p t i o n

T-571 3 1 0 . 6 5 0 + 1 7 0

B r o m e l l d a l e n

B r o m e l l d a l e n S v e a g r u v a

K j e l l s t r @ m d a l e n

K j e l l s t r o m d a l e n

A g a r d h b u k t a

T - 5 1 0 9

T-5276 Tln- 146

T--57 l0

T-4844

T-4931

99U0 + 140

9 9 1 0 + 1 3 0 1 0 , 3 4 0 + I l 0

9590 + I l0

9050 + 130

9870 * 140

P l a n t

remalns

Shells

Wood S h e l l s

S h e l l s

P l a n t r e m a l n s

H e l - E l g 3 3 6 - 8 3 . S a m e s i l t b e d a s T - 5 3 6 9 , stratigraphically slightly higher. Small remnants of plants, mainly herbs and m o s s e s . b u t a l s o P i c e a a n d B e t u l a n a n u , f o u n d i n a l e n s e . C o m p a r e d t o t h e s h e l l dates, these long transporled plant remains y i e l d s l i g h t l y t o h i g h age

Hel-Elg 120-82. M,-u truncata, and, Macomu c a l c a r e a i n l i v i n g p o s i t i o n s , t o p o f t h e 6 - m t h i c k s i l t f r o m w h i c h T - 5 3 6 9 a n d T - 5 7 1 3 w e r e c o l l e c t e d .

S a 8 3 - 4 8 . P i c e u s p . , 3 0 m a l t i t u d e .

From 9 m below surface in a terrace at 40 m a l t i t u d e ( P u n n i n g e t a l . , 1 9 7 6 ) . A c c o r d i n g t o P u n n i n g ( p e r s o n a l c o m m u n i c a t i o n . 1 9 8 4 ) . the sample is not corrected for isotopic f r a c t i o n a t i o n . a n d t h u s h a s a " b u i l t - i n "

c o r r e c t i o n f o r r e s e r v o i r a g e o f 4 1 0 y r c o m p a r e d t o 4 4 0 y r f o r o u r s a m p l e s . H e l - E l g 1 2 3 - 8 2 . A l o n g t h e w e s t b a n k o f t h e

r i v e r f r o m L u n d s t r g m d a l e n i s 2 - 3 m silt a b o v e b e d r o c k . H i a t e l l u u r r c l i c a fr o m b a s e o f s i l t .

Hel-Efg 69-82. M,-a trun(ata and Hiatella nrr'Iica collected on the surface of a ridge at 4 9 m , s o m e t t w h u n d r e d m e t e r s w e s t o f T - 5 7 1 0 .

S a 8 2 - 1 7 . G r a s s a n d m o s s e s in d e l t a f o r e s e t s a t a p p r o x i m a t e l y 5 0 m a l t i t u d e i n

V a r i n g s d a l e n ( S a l v i g s e n a n d M a n g e r u d . l 9 9 l ) .

"

T h e d a t e s a r e l i s t e d f r o m w e s t t o e a s t . T h e t a b l e i n c l u d e s d a t e s g i v i n g minimum ages of the deglaciation.

T h u s , f o r b o t h t h i s a n d t h e f o l l o w i n g t a b l e s o n l y t h e o l d e s t dates obtained from each site are include{.

Van Mijenfiord area that give unambiguous m i n i m u m a g e s f o r t h e deglaciation a r e listed in Table l. Most of the samples were collected from the lower part of marine muds underlain by till, or from marine ter- race gravels that we infer were deposited shortly after deglaciation. The dates show a consistent pattern. We have obtained 20 dates from Van Mijenfiorden east of Ak- sel@ya (the island nearly blocking Van Mi- j e n f i o r d e n ; Fig. 2) giving ages between

1 0 , 6 5 0 a n d 9 5 0 0 y r B.P. The oldest a r e p l o t - ted in Figure 2. We conclude that deglacia- tion of Van Mijenfiorden occurred about 1 0 , 5 0 0 y r B.P. Both areas w e s t u d i e d w e s t of Aksel/ya yielded older minimum ages

of deglaciation (11,000 to 12,830 yr B.P.;

F i e . 2 ) .

Stratigraphy at Skilvika

Along the shore from Skilvika to Renar- dodden on the south coast of Bellsund (Fig.

2) are extensive sections in Quaternary sed-

i m e n t s ( F i g . 3) (Semevskij, 1 9 6 7 ; T r o i t s k y

et al., 1979). Our detailed investigations of

these sections will be reported in a forth-

coming paper by Landvik er a/. Above the

bedrock are two basal tills (formations I

and 2, Fig. 3) where tillfabric demonstrates

WNW ice flow. This flow direction shows

that the glacier that deposited the tills ter-

m i n a t e d w e s t of Bellsund. The tills are

(8)

F r c . 3 . S i m p l i f i e d l i t h o s t r a t i g r a p h y f o r t h e s i t e a t S k i l v i k a ( F i g . 2 ) . I c e f l o w d i r e c t i o n s ( t o t h e l e f t ) a r e based on till fabrics and foreset dip in formation 4. The y o u n g e s t fl o w d i r e c t i o n i n e a c h f o r m a t i o n i s s h o w n b y s t i p l e d a r r o w s . T h e y o u n g e r r a d i o c a r b o n d a t e s a r e g i v e n i n T a b l e l ; t h e n o n - f i n i t e d a t e s w i l l b e d e s c r i b e d i n a f o r t h c o m i n g p a p e r b y J . Y . L a n d v i k e l . z r l .

overlain by marine silts and sands (forma- tion 3) from which shell yielded non-finite radiocarbon ages of >49,000 yr B.P. (Fig.

3). The upper sand of formation 3 interfin- gers with the overlying formation 4, con- sisting of foresets of subangular boulders, which we interpret to have been deposited directly from the glacier terminus during an advance (toward the NE) by the local gla- c i e r S c o t t b r e e n . P a i r e d s h e l l s fr o m t h i s sand yielded non-finite radiocarbon ages also. Troitsky et al. (1919) interpreted the boulder bed (formation 4) to be of late We- ichselian age, based on a Tl-age of 26,000 yr. Our radiocarbon dates clearly contra- dict this assertion and show that the deposit is significantly older.

On top of formation 4 is an unconformity marked by cryoturbation and frost weath-

ering, representing a long ice-free period with low relative sea level (probably of mid- dle Weichselian age; see below). Above the unconformity is a till (formation 5) with fab- ric showing ice flow to the NNW in its lower part; thus, it was deposited by a gla- cier flowing out Rechercheforden (Fig. 2), and ice flow was to the NE (from Scott- breen) in the upper part of the till. Lami- nated clay, up to 5 m thick, occurs directly above this till. The clay contains only two mollusc species, mainly Nuculana pernula, w h i c h i s d a t e d to 1 2 , 8 3 0 a n d 1 2 , 5 7 0 y r B . P . (Table l), and very few Pecten groenlan- d i c u s . B o t h t h e u n d i s t u r b e d l a m i n a t i o n s and the extremely poor fauna indicate a stressed environment. We conclude that a glacier terminus was nearby, and that the last deglaciation occurred about 13,000 yr B.P. The till (formation 5) was probably de- posited by this glacier, although that age cannot be confirmed without dates beneath t h e t i l l .

Shoreline Data for

B e I I s u n d-V a n M ij e nfj o rd e n

Landvik et al. (1981) found that the di- rection of isobases north of Bellsund is ca.

150'. We placed the projection plane for a shoreline diagram for Van Mijenf orden at a right angle to these isobases, parallel to the d i r e c t i o n o f m a x i m u m t i l t o f t h e o l d e s t s h o r e l i n e s . T h e m a r i n e l i m i t s w e r e p r o - j e c t e d into that plane; the locations are plotted in Figure 4, and briefly described in the Appendix.

T h e t i l t o f t h e m a r i n e l i m i t s h o r e l i n e north of Bellsund is basically unknown, be- cause the entire mapped occurrence of the s h o r e l i n e i s p a r a l l e l w i t h t h e i s o b a s e s (Landvik et al.,1987). We correlate the ma- rine limit in this area (labeled Ytterdalen in Fig. 4) with a littoral gravel at Mflseneset (Appendix), but neither the exact tilt of the shoreline nor the correlation is significant to our conclusions. Landvik et al. (1981) a s s u m e d a n a g e o f 1 1 , 0 0 0 y r B . P . f o r t h e marine limit in Ytterdalen, which is a safe minimum age; possibly it is older. How-

H o o c e n e s u b l t t o r a s a n d

T I l r o m q l a c e r c u t R e c h e r c h e f l o r d e n . C r v o t u r b a l o n a n d w e a t h e r i n o B o u d e r y i o r e s e t s d e p o s r t e d f r o m S c o t t b r e e n S W o l t h e s t e

l " 4 a r n e s a n C a n o s l

(9)

Altitude oJ marine limit

Minimum elevation of marine limit Altitude of shoreline

in Ytterdalen

0

'

o i s t a n c e ( k m ) 5 0 9 0 k m

Ftc. 4. A shoreline diagram for Van Mijenfiorden. The sites are projected into a plane at right angle t o t h e i s o b a s e d i r e c t i o n f b u n d by Landvik et al. (19871. T h e I 1 , 0 0 0 y r B . P . s h o r e l i n e is clashed b e c a u s e i t s t i l t i s p o o r l y c o n s t r a i n e d . The important point is the drop in altitude from rhat line to the 10.300- l 0 ' 6 0 0 y r B . P . l i n e , w h i c h shows that the ice front stayed at Miseneset forthe period of that drop. The m a r i n e l i m i t l o c a l i t i e s a r e described in the Appendix and located in Fieure 2.

I

t

0

o ( ! 0

; > o a ; a : r {

c

. ) : G T :

i : > c t r

; i ; { 6 ;

> Y @ a

c (g

E

na cf

)

c 0) 6 o a l

ever, the exact age of this line does not in- fluence our main argument, namely, that there is a drop in the elevation of the marine limit around Aksel@ya (Fig. a). The only possible interpretation of that drop is that a glacier occupied Van Mijenfiorden when t h e m a r i n e limit west of Akset/ya was formed.

According to the radiocarbon dates (Fig.

2), the middle parts of Van Mijenfiorden were rapidly deglaciated about 10,500 yr B.P., or soon after. Indeed, all the marine limits along the fiord fit into a straight line that is drawn through both them and the 1 0 , 3 0 0 - 1 0 , 6 0 0 y r B.P. shoreline i n y t t e r - dalen (Fig. 4). This is a strong argument for that being the age of the deglaciation, and for rapid deglaciation in Van Mijenforden.

The very rapid emergence after 10,000 yr B.P. would clearly separate marine limits with age differences of some few hundreds of years, as demonstrated by the elevation of the 9600 yr B.P. shoreline (Fig. 4). The 9600 yr B.P. line is drawn through the ma- rine limit terrace in Lundstr0mdalen, indi- rectly dated to that age (Table l), and the elevation of the 9600 yr B.P. shoreline as

read out of the relative sea-level curve for Ytterdalen (Landvik et al., l98j\.

The Coast North of Bellsund

A well-developed gravel terrace at 64 m a l t i t u d e , r u n n i n g a l o n g the foothill and d a t e d t o a r o u n d 1 1 , 0 0 0 y r B . P . , r e p r e s e n t s the postglacial marine limit (Landvik et al.,

1987). The terrace is mapped along the en- t i r e c o a s t , a n d i n t o t h e v a l l e y s ; thus, the western coast between Bellsund and Isfior- d e n w a s c o m p l e t e l y ic e - f r e e I 1.000 yr" d.e.

at the latest. The area below the marine limit is mainly covered by a thin veneer of beach gravel, and some prominent beach ridges, that provides no clues as to whether the area was covered by ice or not during the last glacial maximum. Well-preserved glacial striae occur in some valleys (Fig. 2), which suggest a 'ryoung"

glaciation. No

"old"

marine deposits were found in the steep slopes above the postglacial marine l i m i t .

L I N N E D A L E N

Linn6dalen contains more pre-Holocene

sediments than any other area along outer

(10)

l 0

l s f j o r d e n . F u r t h e r m o r e , c o n t i n u o u s s e - quences of postglacial sediments have been recovered from Linn6vatnet, the largest lake on Svalbard. Linn6dalen is the west- ern-most tributary valley to Isfiorden and any glacier advance out of Isfiorden that passed beyond Linn6dalen terminated on the continental shelf.

At several sites in Linnddalen fresh gla- cial striae indicate ice flow to the north (Fig. 2). One of the sites is Nimrododden, protruding from the shore of lsfiorden, but still without westerly striae. Till is rare in the area. Below we describe a till covering a beach terrace at 87 m altitude, and a till in the sections along Linn6elva. ln both cases fabric and other directional indicators show deposition by a northward-moving glacier.

In all the tills, the clasts are derived from the bedrock in Linn6dalen. In fact. exotic rocks are extremely rare in other sediments in the area (Musial, 1985), so there exists no positive indication of glacial transport from the east and across the valley.

It seems quite clear that the last glacier in Linnddalen moved northward, downvalley in Linn6dalen. and terminated at the shore of lsfiorden. This may have been a deglaci- ation phase. However, evidence of ice flow out Isfiorden has not been recorded on land in this area.

Stratigraphy of Lake Linntvatnet

Beneath the Holocene lacustrine sedi- ments in Linn6vatnet is a sequence of ma- rine sediments that rests on till (Mangerud

a n d S v e n d s e n , 1 9 9 0 b ) . S u b b o t t o m e c h o - sounding profiles indicate that the till is but a thin veneer on the bedrock, and thus that the last glaciation removed most preexist- ing sediments. This glacier must have filled the entire valley and terminated north of the lake. Periods of nondeposition are un- likely in closed basins like those cored in Linn6vatnet, and we therefore postulate that the marine sedimentation started im- mediately after deglaciation. Radiocarbon samples from the lowermost marinc sedi- ments gave ages of around 12,300 yr B.P.

( T a b l e 2 , F i g . 5 ) . T h i s p r o v e s t h a t Linn6dalen was indeed glaciated during the late Weichselian, and that the final deglaci- a t i o n o c c u r r e d s h o r t l y b e f o r e 1 2 , 3 0 0 y r B . P . , o r , i f w e c o n s i d e r th e s t a n d a r d d e v i - ation of the dates, possibly as late as 12,000 y r B . P .

Pre-Late Weichselian Marine Terrac'es, Overrun by Glaciers

On the east slope of the Linnddalen val- ley there is a staircase of shorelines from present sea level up to 87 m altitude (Fig.

5 ) . R a d i o c a r b o n d a t e s d e m o n s t r a t e t h a t they are of Holocene or late-glacial age up to 65 m, and possibly up to 75 m. The high- est morphologically distinct terrace lies at 87 m (Fig. 6), and it is radiocarbon dated to ca. 36,000 yr B.P. (Table 3), which may be a minimum age. Our first assumption from the distinct morphology was that the ter- race had not been overrun by ice (Man- gerud et al., 1985), and thus that the area

T A B L E 2 . R n o r o c a n e o N D e r e s o p M e n r N e S u e l l s n n o v L I N N E o I I - c N G I v r N c M I N I v u v A c E s r o n D t c l a c r l r t o N

L a b o r a t o r y N o . A g e ( y r B . P . ) Sample

U a - l 3 5 1 Ua-730 Ua-729 Ua-291 Ua-290 Ua- I 350 Ua-732 Ua-279

1 1 , 7 4 0 + 1 3 0 I I ,560 :t 160 1 2 , 3 2 0 : ! 1 9 0 11,770 L l40 1 t , 4 9 0 t 1 5 0 1 1 , 6 4 0 t 1 3 0 12,300 + 190 11.000 :i 190

L i n n 6 v a t n e t , c o r e 0 1 , 7 8 0 c m ( M a n g e r u d a n d S v e n d s e n , 1 9 9 0 b ) . L i n n 6 v a t n e t , c o r e 0 1 , 8 4 5 c m ( M a n g e r u d a n d S v e n d s e n , 1 9 9 0 b ) . L i n n 6 v a t n e t , c o r e 0 1 , 9 2 8 c m ( M a n g e r u d a n d S v e n d s e n , 1 9 9 0 b ) . L i n n 6 v a t n e t , c o r e 1 4 , 1 , 1 6 0 c m ( M a n g e r u d a n d S v e n d s e n , 1 9 9 0 b ) . L i n n 6 v a t n e t , c o r e 1 4 , 1 , 1 7 9 c m ( M a n g e r u d a n d S v e n d s e n , 1 9 9 0 b ) . Linndvatnet, core 24,642 cm (Mangerud and Svendsen, 1990b).

Linn6vatnet, core 24, 686 cm (Mangerud and Svendsen, 1990b).

E valleyside, Svalbard 84-1174. One fragment of M1,u truncata from a terrace at 65 m altitude (Manserud et al., 1987).

(11)

LAST GLACIATION OF SPITSBERGEN

87 m terrace ^{' - i \ -}

l ' s o o o o (r-sz r r,t-oo r g ) (Mangerud et at. 1987)

M a r i n e li m i t ( 6 5 . 7 5 m a . s . 1 . )

y',:;:;

, - ' -

. l 1 0 0 0 i 1 9 0 ( U a - 2 7 9 ) ( M a n g e r u d el al. 1987) 1 1 0 2 0 a 1 1 0 ( T - 4 8 6 5 ) ( Y t t e r d a l e n , L a n d v i k e l a l . 1 9 8 7 )

Linnevatnet 12 m a.s.l.

Lac. sed:').-:

naarine sitt i-t and clay ',','-,'{

Titl

38060!s3o (ua 731) ?llf"X?Toll?,ll!0","*

FIc. 5. Schematic cross section ofLinnddalen. It has not been demonstrated in the field that the till covering the 87-m terrace is the same as the till that occurs on the floor ofthe lake. All dates above the till provide minimum ages for the deglaciation; the oldest are from the basal part of the marine sediments on the floor of the lake. From Mangerud and Svendsen (1990b).

11

r;, r;

; ! - . '

Bedrock

I easat oates from the marine J sed. in Linnevatnel

had been ice-free for at least 36,000 years.

This assumption was also compatible with the conclusions of, e.g., Lavrushin (1969), Troitsky (1981), and Boulton (1979), which were partly based on similar observations, including this terrace.

Morphologically identified shorelines have been used many places in the Arctic as evidence for a lack of glaciation after the

formation of the shoreline. Because we can now demonstrate that it has been overrun by ice, we will describe the 87-m terrace in some detail. The terrace is ca. 80 m long, 20 m wide, and has a l0 m high distal slope of gravel standing at the angle of repose. We dug four sections around the rim and two ditches in central parts of the terrace (Fig.

6). In all excavations two formations were

FIc. 6. Photo ofthe 87-m terrace toward south. The lake (Linn€vatnet, 12 m altitude) is seen to the

right. The three excavations in the northern end (marked l-3) show the width of the horizontal terrace

surface, which is 20 m. The heaps from excavations 4 and 5 in the central part are marked. Excavation

6 was in the southern end, 80 m south of excavations l-3.

(12)

t2

T A B L E 3 . R a o t o c l R s o N D e r c s nnou LlNNEoeleN PnEo,trrNc t.He Lnsr GlecrerroN oF THE Velrev

F i e l d r a m p l e N o . a n d d e s c r i p t i o n Laboratory

N o . A g e ( y r B . P . ) Material Locality

T--s2l I T-6618

T - 8 1 8 4

U a - 7 3 1

T-6003

T-6728

T-6001

T-6228 T-6226

T-6006

T-6224

3 6 , 1 0 0 + 8 0 0 35,900 + 500

40,600 + I 100

3 8 , 1 0 0 + 8 0 0

> 3 8 , 1 0 0

42,-500 + 1700 - 1400

> 4 3 . 1 0 0

50,200 + 4600 2900 28,600 + -500

>46,U00

>44,400

S h e l l s

W h a l e b o n e

S h e l l s

Seaweed S h e l l s

S h e l l s

L i n n 6 v a t n e t

L i n n d e l v a

L i n n 6 e l v a

L i n n d e l v a

found: (1) a lower gravel overlain by (2) a d i a m i c t o n .

(l) The lower formation is a gravel with rounded to subrounded pebbles which we

87 m terrace Sa 83-30. Mya trun(.atu collected one meter b e l o w t h e s u r f a c e ( M a n g e r u d er a/., l9g7).

87 m terrace Svalbard 1985-1001. Paired Mya trunceta from e x c a v a t i o n I ( F i g . 6 ) . ( M a n g e r u d el a/.,

I 9 8 7 ) .

Linn6breen Svalbard 1987-83. Fragments of Mya truncuta from beach sand at 83 m altitude just outside the Little Ice Age moraines of the glacier at the head of the valley (Mangerud a n d S v e n d s e n , 1 9 9 0 b ) .

Core 05, 843 cm. One fragment of M-ya trun(uttl in a diamicton at the base of the core (Mangerud and Svendsen, t990b).

Svalbard 1984-2001. Fragments of Mya truntata from the till (Fig. [l). Fragments with lowest D/L ratios were selected ( L @ n n e a n d M a n g e r u d , l 9 9 l ) . Svalbard 1985-2098. From the youngest

s e d i m e n t s b e l o w r h e t i l l ( F i g . 8) (Lgnne and M a n g e r u d , l9 9 l ) .

Svalbard 1984-2063. Paired Mat:oma calcurea f r o m f o r m a t i o n C ( F i g . 8) (L@nne and M a n g e r u d , l 9 9 l ) .

Svalbard 1984-2006. Formarion A (Fig. 8) ( L @ n n e and Mangerud, l99l).

S o l o v j e t s k i b S v a l b a r d 1 9 8 4 - 1 1 4 9 . S e v e r a l f r a g m e n t s , m a i n l y of M,-a truncata, from a slided silt in western part of Solovjetskibukta (Section 1 5 , i n S a n d a h l , 1 9 8 6 ) . S u b s e q u e n r obrained D / L r a t i o s o f 0 . 0 2 1 a n d 0.020

( B A L - 1 2 6 0 a , b ) from the same collection support a young age, as the shells are found o n l y l 9 m a l t i t u d e . H o w e v e r . the dated sample may represent a mixed age population of postglacial shells and n o n - f i n i t e o l d s h e l l s . F u r t h e r east in Solovjetskibukra shells (sample T-6006) from a similar silt yielded a non-finite age.

We are skeptical of this date, until it is reproduced on a single fragment.

Solovjetskib Svalbard 1984-1060. Fragments of Mya truncata from a silt that in section 4 (Sandahl, 1986) apparently is the youngest unit predating the ice advance.

Solovjetskib Svalbard 1984-1152. Several shell fragments f r o m a s i l t i n s e c t i o n 1 3 b (Sandahl, 1986) that is correlated with T_6006.

excavated to a depth of 2 m. The distinct

planar beds dip about 10"W. Scattered shell

fragments occur in the gravel. In a more

sandy facies in the NE part of the terrace

(13)

l 3 are frequent large Mya trunc.ata in living

position. We interpret the sandy gravel as a beachface facies developed on a small delta deposited from the brook immediately to the south of the terrace.

Before we discovered the till, we ob_

tained a radiocarbon age of36,100 I gl0 vr B . P . ( T - 5 2 1 l ) o n s h e l l s I m betow the ton Lf the gravel. We later recollected shells fiom the excavated section (No. l, Fig. 6), at least I m behind the original slope, and ob- tained an identical age of 35,900 t 500 vr B . P . ( T - 6 6 1 8 ) . T h e shells were buried be- neath a low-permeability diamicton, and the surface vegetation is extremely sparse, strongly decreasing the risk of contamina_

tion by young carbon. Still, we conserva- tively consider the dates to be minimum ases- T h e s h e l l s h a v e v e r y low amino aciO biL ratios (Fig. 9). In the Discussion we use these ratios to estimate the duration of the glaciation that deposited the till. The ques_

t i o n h e r e i s i f t h e low D/L values can be used to test whether the radiocarbon dates o f 3 6 , 0 0 0 y r B . P . g i v e realages or minimum ages only. No definite answer can be given, because at an annual temperature of, e.g., - 20'C the epimerization rate is so low that even the epimerization that occurs durins 100,000 yr is well inside one standard devil ation of the measurement precision.

(2) The upper formation is a diamicton- up to 60 cm thick, which thins toward the edges of the terrace. The boundary with the underlying gravel is sharp, and nearly hor_

izontal. The upper half of the diamicion is loose, and is probably frost disturbed or a s o l i f l u c t i o n d e p o s i t . The disturbed sedi_

ment was the only part seen along the rim of the terrace before the excavations.

The lower half of the diamicton is gray, matrix-supported, massive, and hard. The pebbles and boulders are generally suban_

gular, and significantly less-roundecl than in the gravel beneath. Several boulders in the d i a m i c t o n h a v e a d i s t i n c t s t o s s - a n d _ l e e morphology, typicalof lodgmenr tills (Boul_

ton, 1978). Figure 7 shows that the direc_

tion of glacial striae on boulders, and the long axis of both boulders and pebbles, all are parallel to the glacial striae in the valley.

T h e s e o b s e r v a t i o n s s h o w u n a m b i g u o u s i y that the diamicton is a basal till. We con_

c l u d e t h a t t h e t e r r a c e , despite its well_

preserved morphology, was overrun by a glacier moving NNW, down the valley.

The Sec'tion along Linnielva

Thick sections of Quaternary sediments are exposed along the lower course of the river Linn6elva (Fig. 8) (L@nne and Man_

g e r u d , l 9 9 l ) . Below the Holocene littoral

[ ] t - : . x Ll 3-5.%

L l s 7 . % L= 7 e.%

I t 9 . %

F t c ' 7 ' D i r e c t i o n a l elements in the diamicton (basal till) on the 87-m terrace. (A) Fabric of the long a x i s o f 1 0 0 p e b b l e s , excavation 2. schmidts net, lower hemisphere. (B) Fabric ofthe long axis o f 1 0 0 p e b b l e s ' in the central part ofthe terrace (excavation 5). (c) Squares show the fabnc ofthe l o n g a x i s o f l 4 b o u l d e r s ( > 2 0 cm) from different excavations. The lines.show the direction of glacial s t r i a e o n l 0 d i f f e r e n t b o u l d e r s . All directional elements show a NNW ice-flow direction, down the vallev.

(14)

l 4

sediments (formation E, Fig. 8) is a mas- sive, matrix-supported diamicton (forma- tion D) that contains frequent striated peb- bles. The diamicton is l-2 m thick and is mapped more or less continuously for 500 m along the sections. L6nne and Mangerud (1991) concluded that ir is a basal rill. Till fabric and glaciotectonic thrusting in the underlying sediments show that it was de- posited by a northward-moving (valley) gla- c i e r .

The youngest formation (C, Fig. 8) be- neath the till is interpreted to represent a prograding beach, deposited during a falling relative sea level that was at 28 m during the f i n a l s t a g e s of deposition. Formation C probably was deposited during the sea-level drop after the 87 m terrace was formed. The

C H R O N O . i T R A T I G R A P H Y

s

6E ]NTERPRETAT ON COMPOS TE STRAT GRAPHY

1 1 c DATES ( 1 0 3 y f B P )

HOLOCENEE S h o r e l i n e s e q u e n c e

1 0 . 2

' 3 8 . 1 4 2 . 5 , 4 3 . 1

50.2 L A T E

WE CHSET AN D T i i l

g aI

= -

.o

=

t o

d

P r o g r a d i n g n g n e n e r g y

s n o r e l n e

B

P r o g l a c i a : h a n n e l s a n d

o e D r l s

S h a l l o w m a n n e , p r o g L a c a l

t a n

F r c . 8 . C o m p o s i t e l i t h o s t r a t i g r a p h y for the section along Linn6elva, simplified from L14nne and Manserud i l 9 9 1 ) .

higher D/L ratios for formation C could be due to longer submergence (about 10,000 yr) at this lower level. Alternatively, forma- tion C might be older than the 87 m terrace.

In order to select the youngest fragments for (conventional) radiocarbon dating, the D/L ratios were measured for many shell fragments found in the till; the screened s a m p l e s t i l l y i e l d e d a n o n - f i n i t e a s e ( > 3 8 . 1 0 0 y r 8 . P . . T a b l e 3 ) . H e r e w e w ] l l also use the D/L ratios for till correlation.

Figure 9 shows that there is a significant difference in the D/L ratios from formations

1 5 l 2

I

F o m a t i o n D, till 0 . 0 2 5 I 0.005 (27)

3 2

I

F o m a l i o n A

0.027 I 0.003 (17)

! 1 - . 1 F n r m o r ' " n e I

= ' l l '

l i 7 m t c n e e

0.019 I 0.002 0 l )

u l r u 0 0 1 5 o " n o l r t

0 0 : 1 0 0 0 : 1 5 F r c . 9 . T h e a m i n o acid D/L ratios of the species Mya truncato and Hitttella urctica from described sec_

t i o n s i n L i n n d d a l e n . The "83 m sand" is from Man_

g e r u d a n d Svendsen (1990b), and is mentioned under D i s c u s s i o n . I n t h i s p l o t each individual measurement i s p l o t t e d , a l s o w h e n there are more than one measure- m e n t o n e a c h s p e c i m e n , e.g., the two low ratios in formation A are from one specimen. The means + I s t a n d a r d d e v i a t i o n and number of measurements in parentheses are given for each unit. The mean for for- m a t r o n s A , B , a n d C together is 0.028 + 0.003. For the t i l l ( D ) t h e m e a n f o r only M_va i s 0 . 0 2 3 + 0 . 0 0 5 . F o r the 8 7 - m t e r r a c e a r a t i o of 0.02U is omitted because new m e a s u r e m e n t s o n t h e s a m e s a m p l e g a v e 0.022; thus.

the mean is slightly lower than cited by Mangerud and S v e n d s e n ( 1 9 9 0 b ) . T h e 87 m terrace/83 m sand and formations A, B, and C represent two different D/L p o p u l a t i o n s ; both are included in the till.

8 3 n r smd 0 . 0 2 3 I 0.007 (1) 0 1 0

(15)

l 5 A, B, and C underlying the till in the Lin-

n6elva section and the ratios from the 87 m terrace/83 m sand (described in the discus- sion section). Possible causes for the differ- ent D/L ratios are discussed above. The point here is that both populations are rep- resented in the till (formation D) which therefore has to be younger than the 87-m terrace, and thus should be correlated with the till on that terrace.

T H E S H O R E S O F I S F J O R D E N S horelines

Boulton (1979) and Troitsky (1981) used

" o l d " s h o r e l i n e s w h i c h t h e y c o n c l u d e d were not overrun by ice to delineate the maximum limit of the last glacial advance.

As described for the 87-m terrace above.

and for the Kapp Ekholm section below, we can now demonstrate that some terraces that were assumed to have been beyond the late Weichselian ice limit, indeed have been overrun by ice. We do not know any "old"

shorelines along Isfiorden that can be con- v i n c i n g l y d e m o n s t r a t e d t o h a v e e s c a p e d elaciation.

Boulton (1979) used a postulated drop in altitude of the marine limit from high, pre- sumably pre-late Weichselian beaches in the outer fiord, to lower levels in the inner fiord, to delineate the last glacial maximum.

We cannot see that the high terraces are d o c u m e n t e d . O n t h e c o n t r a r y , i n L i n - n€dalen, and also in Van Mijenfiorden and Bellsund, we conclude that the postglacial marine limits were much lower than those compiled by Boulton (1979).

Stratigraphy at Kapp Ekholm

Within the middle and inner parts of Is- fiorden only a few known stratigraphic se- q u e n c e s p r e d a t e the last glaciation; the most important site is Kapp Ekholm (Figs.

2 and l0). This site was a key section that L a v r u s h i n ( 1 9 6 7 , 1 9 6 9 ) , T r o i t s k y ( 1 9 8 1 ) , and Troitsky et al. (1979) used to conclude that glaciers around Isfiorden never were m u c h l a r g e r t h a n t o d a y d u r i n g the last 40,000 years. Boulton and Rhodes (1974), Boulton (1979), and Boulton et al. 0982) used Kapp Ekholm as a key section for their reconstruction of a very limited and young late Weichselian glaciation. Some

North

u V ^South

8 5 9 9 4 4 0 l 4 s o l i ,ot o)1,

IV

8 7

ilv'l

H o i o c e n e

+ s g . j ' 1 1 0 / ' 9 4 / 9 7

3 0 m 2 0 1 0 o .- r1 Eem

9 0 0 m

L I T H O L O G Y :

W e r a v e l f o r e s e t s ( l i t t o r a t ) F . l v a r i n e s i t t a n d d i a m i c t o n

lJ:llll sano ffi rirr

lt-.Zl Gtaciotectonicatty deiormed f---l n.a,^"r l ? / l s i l t . s a n d a n d q r a v e l

F I c . 1 0 . A s i m p l i f i e d p r o t i l e o f t h e s e c t i o n s a t K a p p E k h o l m . T h e s t i p p l e d l i n e s b e t w e e n each section show the correlations made during field work. For the formations discussed in this paper (the glaciotectonically deformed and formations above) these correlations are supported by radiocarbon d a t e s a n d a m i n o a c i d D / L r a t i o s . R a d i o c a r b o n d a t e s a r e i n d i c a t e d i n l 0 r y r B . P . ; d e t a i l s f o r t h e Holocene dates are given in Table 4. The dates from older units will be described in a forthcoming p a p e r b y J . M a n g e r u d a n d J . I . S v e n d s e n . N o t e t h a t the youngest till is found in sections V and VI only, but an unconformity could be mapped to the south, between the deformed and Holocene f o r m a t i o n s .

(16)

l 6

preliminary results of our investigations are p r e s e n t e d in M a n g e r u d a n d S v e n d s e n (1990a). A full description will be given elsewhere; here we will present some re- sults that are relevant for the last glacial advance.

A s i m p l i f i e d s t r a t i g r a p h i c d i a g r a m is shown in Figure 10. In the upper part is a glaciotectonically deformed formation that we have correlated from section II to Vl. lt consists of silt, sand, and gravel, containing molluscs with radiocarbon ages between 5 0 , 0 0 0 a n d 3 7 , 0 0 0 y r B.P.; here we con- clude only that it is older than 40,000 yr B.P. The formation is not covered by till in sections II to IV. Troitsky and Punning h a v e o r a l l y c o n f i r m e d t h a t t h e i r a n d Lavrushin's ( 1969) section was measured at the site of our section Il, and the descrip- tions can indeed be compared. In this part the deformations are large thrust planes which are nearly parallel to the primary bedding planes. The thrusts can hardly be discerned without cleaning large parts of the section. Presumably these thrusts were not observed by Lavrushin (1969), Troitsky et al. (1979), or Boulton (1979), and cer- t a i n l y n o t b y M a n g e r u d a n d S a l v i g s e n ( 1 9 8 4 ) . L a v r u s h i n (1 9 6 9 ) , T r o i t s k y e t a / . (1979), and Punning and Troitsky (1984) concluded that the unit had not been cov- ered by ice, and as they also had obtained non-finite radiocarbon ages from this unit, they concluded the area had been ice-free during the entire late Weichselian.

The mean D/L ratio for 30 measurements on 22 individuals of Mya truncata from the deformed formation is 0.026 + 0.004. Un- der Discussion we use this ratio to calculate the duration of subsequent ice cover. Con- sidering that Kapp Ekholm is situated far inland and thus was covered longer by gla- ciers, and was submerged for longer peri- o d s d u r i n g g l a c i o i s o s t a t i c h i g h s e a - l e v e l stands. than most west coast sites, the de- formed formation should be correlated with s i t e s o n t h e w e s t c o a s t w i t h l o w e r D / L r a - tios. lt can most easily be correlated with the 87-m terrace in Linnddalen. If this is

correct, it will also support a correlation of the youngest till at both sites.

Most dates on shell from the lower part of t h e p o s t g l a c i a l s e q u e n c e g a v e a minimum age of deglaciation 9900-9700 yr B.P. (Ta- ble 4). One shell fragment yielded an age of 1 1 , 0 5 0 + 150 yr B.P. (tJa-912, T a b l e 4 ) . However, we subsequently obtained a date of 9410 -r 140 yr B.P. (TUa-71) from the s a m e l e v e l , a n d 9 7 3 0 + 1 8 0 y r B . P . ( T U a - 70) directly beneath that sample. Thus, ei- ther the shell fragment yielding I I,050 yr B.P. is redeposited, or the date is errone- ous. Boulton (1979) reported a similar date ( 1 1 , 0 3 0 - r 440 yr B.P., SRR-Ill, Table 5) from the upper till at his site I l, which is close to 140 m in Figure l0 (G. Boulton, personal communication, l99l). A possible interpretation is that there was a short ice- f r e e p e r i o d a b o u t 1 1 , 0 0 0 y r B.P., and that shells of that age were incorporated in the till and subsequently also redeposited in the postglacial sediments. Alternatively, both d a t e s o f I 1 , 0 0 0 y r B . P . a r e to o o l d . F o r e i - ther alternative, the final deglaciation is dated to just before 9900-9700 yr B.P.

Most folds and thrusts in the deformed u n i t s h o w t h r u s t i n g to t h e w e s t , t h a t i s nearly perpendicular to Billefiorden. The sections are situated south of the mouth of the tributary valley (Mathisondalen); thus, the deformations were not caused by a local glacier flowing out that valley. The simplest interpretation is that the westerly deforma- tions took place beneath a thick glacier that moved across Billefiorden. If this recon- struction is correct. there could not simul- taneously have existed an ice-stream out Billefi orden-Isfiorden. A further prediction from this ice flow direction is that the gla- cier also flowed across the land NW of Is- fiorden (Figs. I and 2), and that the ice front was located west of the coast between ls- fiorden and Kongsforden (Mangerud and S v e n d s e n , 1 9 9 0 a ) .

Minimum Dates for the Deglaciation

In Figure 2 and in Tables 4 and 5 are

compiled radiocarbon dates that give a min-

(17)

T A B L E 4 . R a o r o c a n s o N D e r e s F R o M T H E L o w e n P e n t o r t - H e P o s r c l e c r e l S e q u e N c e e r K e p p E x s o r - u

1 7

Laboratory

N o . A g e ( y r . t s . P . ) Material Section"

Ua-9'72 1 1 . 0 5 0 + 1 5 0 S h e l l s

Field sample No. and description

I, 110 Svalbard 1988-696. One shell fragment from the base of a 20-cm thick reddish-brown silt overlying till. The sample was collected just above sample -695 d e s c r i b e d b e l o w . S a m p l e s T U a - 6 9 , - 7 O , -1 1 , a n d - 7 2 were subsequently dated to test if the age obtained by U a - 9 7 2 c o u l d b e r e p r o d u c e d .

l, ll0 Svalbard 1988-695b. One shell fragment from a few millimeters thick sand layer beneath stones along the boundary between the underlying till and the reddish-brown silt. described above.

I, I l0 Svalbard 1988-695a. A thick fragment from the same c o l l e c t i o n a s T U a - 7 0 . T h e d a t e s h o w s t h a t t h i s fragment has been redeposited from older beds. The age has been calculated on the basis that infinite old calcite yields an age of 42,000 + 2500 yr B.P. with the same chemical preparation.

I, I l0 Svalbard 1988-697. One gastropode from exactly the same site as sample -696.

I. 130 Svalbard 1988-235. Paired Hiatella d,'clicc in sorted sand 5 cm above a l0- to 20-cm thick bed of r e d d i s h - b r o w n s i l t .

I , 1 6 0 S v a l b a r d 1 9 8 8 - 6 9 8 . B a l a n u s s i t t i n g o n a b o u l d e r i n a l0-cm thick lense of reddish-brown silt that was found i n t h e b o u n d a r y z o n e b e t w e e n t h e u n d e r l y i n g (interglacial) gravel foresets and the overlying H o l o c e n e s a n d .

II, 280 Svalbard 1998-78. Three individs of paired Hiatella arctica from the transition between a brownish silt a n d o v e r l y i n g f i n e s a n d . S a m p l e c o l l e c t e d l e s s t h a n l 0 cm above a bed of angular pebbles that are thought to b e t h e b a s e o f t h e H o l o c e n e a t t h i s l o c a l i t y .

I V , 5 5 0 S v a l b a r d 1 9 8 8 - 3 1 7 . O n e l a r g e i n d i v i d o f M , - u t r u n c a t a from a boulder bed interpreted as an erosional lag at t h e b a s e o f t h e H o l o c e n e .

V, 650 Svalbard 1988-447. One individ of Lepeta from a laminated silt with reddish and grayish lamina, at the base of the Holocene sequence.

V, 760 Svalbard 1988-438. One large individ of paired Mya truncata from the base of the Holocene. The u n d e r l y i n g t i l l i s m i s s i n g a t t h i s s i t e .

VI, 870 Svalbard 1988-758. On top of the youngest till is 20-30 cm reddish-brown silt. Small Lepeta from the base of t h e s i l t .

VI, 870 Sa 81-08. Paired Mya truncata in the lowest part of the sand following above the reddish-brown silt described under sample 1988-758. This sample was collected by Salvigsen and Mangerud in 1981, but can easily be plotted into the section measured in 1988.

Vl, 890 Svalbard 1988-522. Two large individs of Mya truncata in living position, from a zone rich in large Mya, 1.5 m a b o v e t h e t i l l .

TUa-70

TUa-69

T U a - 7 1 T-8322

T-8330

T - 8 3 1 9

T-8323

Ua-974

T-8326

TUa-'72

T-5666

9730 a 180

37.400 + 1600

S h e l l s

9690 I 70

S h e l l s

9470 ! 140

9730 + 120

9 8 1 0 + 7 0

8740 + 100

9 9 1 0 * 1 3 0

8560 + 60

9'760 + 140

9530 + I l0

S h e l l s

T-8_s34 9 0 8 0 + l l 0

Shells

" The column "Section" refers to Figure 10, where arabic numbers are meters along the horizontal scale Samoles are listed from south to north.

(18)

l 8

T A t s L E 5 . RenrocensoN DATE.s F R o M T H E S H o n e s or Isr:onoEN (Frc

2 )

Laboratory

N o . A g e ( y r . B . p . ) M a t e r i a l

T-6290

T-6282 T-6287 Lu-2364 T-4407

sl-4308

I t n - l / ' )

u - 1 3 2 u - 1 2 8

9 6 8 0 + l l 0 9 7 2 0 + l l 0 9 5 1 0 + 9 0 9690 + 140

S h e l l s S h e l l s S h e l l s S h e l l s

T-4406 t0,030 + 140 Wood

Gd-2772 11,940 + 200 Organic marter

Gd-5248 9730 + 70 Shells

imum age for deglaciation. A few of them are from silt just above a till, and thus should give an age close to the deglaciation.

Some are from terraces that are known to be lower than the marine limit, and thus somewhat younger than the deglaciation.

L o c a l i t y S a m p l e a n d description

Gr@nfiorden

Sa 84-19. Fragments of Mya trun(.ata and

H i a t e l l a a r d i c a at 12.5 m altitude in H o l o c e n e t i l l deposited by

Aldegondabreen.

E r d m a n n f l y a H i a t e l l a a r c t i ( . a , 2 6 m altitude (Salvigsen er a l . , t 9 9 0 .

Erdmannflya Shell fragments 47 m altitude (Salvissen cr a t . , 1 9 9 0 ) .

B o h e m a n n f l y a H i a t e l l a a r c t i c u , 2 0 m altitude (Salvrgsen et a t . , 1 9 9 0 ) .

L y c k h o l m d a l e n Sa 8l-g5. Mya trunc.ata in living position in s a n d , l 0 c m above a till. Sample altitude i s 3 2 m , but overlying beach sediments reach 4g m.

Blomesletta Myu trun(,ata from a beach ridge at 3l m a l r i t u d e ( p 6 w 6 er al., lgg}\.

A d v e n t d a l e n T e r r a c e a t 5 5 m altitude between L o n g y e a r b y e n and Todalen. (punnrns er u l . , 1 9 8 2 \ .

T e l t f e l l b e k k S h e l l s fr o m 5 6 m altitude (Feyling_Hanssen a n d O l s s o n , 1960).

K a p p E k h o l m S i t e c a l l e d n o r t h of phantomvika. same as o t h e r s c a l l Kapp Ekholm. Shells from 5l m a l t i t u d e ( F e y l i n g _ H a n s s e n a n d O l s s o n . I 9 6 0 ) .

K a p p E k h o f m W h o l e v a l v e s of M.va truncata (Boulton.

t979\.

Kapp Ekholm Fragment of Mucoma calcarea in lill ( B o u l t o n , 1979). According to G. Boulton ( p e r s o n a l communication, l99l), the site i s a t 1 6 0 m in our section (Fig. 101.

Kapp Ekholm Drifrwood of Larix ar 57 m attitlude. .t.houeht t o d a t e t h e 67_m terrace (Salvigsen. 19g4.).

Petuniabukta "A

weathering mantle enriched with organic matter has been recognized on bedrock making up the base of a marine terrace of l 0 m , , ( S r a n k o w s k i er a1., l9g9). We reJect this date, because if the area was ice_free that early, it was below sea level.

P e t u n i a b u k t a S h e l l s in t i l l from a postglacial readvance.

Most significant is that almost all dates are from land areas where glacial striae show that the last ice movement was from local glaciers in the hinterland, and thus give a m i n i m u m a g e of when these glaciers with_

drew from the shore.

9980 + 130 Shells

9780 + 80 Shells 9 4 8 0 + l l 0 S h e l l s

S R R - 1 0 9 9 7 1 0 : t 9 0 s R R - l l l 1 1 , 0 3 0 + 4 4 0

9840 + 150 9980 + 140

ry,* rr," our. r".r",.,9"y'1,1,"e ".,i"i,r,,,n "s,;;"#:#j*J** " uon"*

s e c t i o n a r e g i v e n in Table 4. Field sample numbeiis only given for unpublished d a t e s . F o r d a t e s from other laboratories than T-, U-. and Lu-, the corrections for reservoir age might be different fiom that used in this paper.