BOREAS An Early or Middle Weichselian sequence ofproglacial, shallow marine sediments on westernSvalbard

An Early or Middle Weichselian sequence of proglacial, shallow marine sediments on western Svalbard

I D A L O N N E A N D J A N M A N G E R U D

BOREAS

A 2 0 m t h i c k s h a l l o w m a r i n c s c q u c n c c . c a p p c d b y a L a t e W e i c h s e l i a n lo d g c m c n t t i l l . i s c x p o s c d f o r 2(X) m along thc rivcr in Linnidalcn on thc wcst coast of Svalbard. Fivc formations arc rccognized:

F o r m a t i o n A . t h c o l d c s t . c o n s i s t s o f a s h a l l o w m a r i n c . p r o g l a c i a l fa n . o f c h a n n c l i z c d s a n d y t u r b i d i t c s , possibll fcd from an icc-contact dcposit. Formation B, a scqucnce of proglacial channels and icc-raftcd dcbris. was formcd during a small oscillation of the glacier. Formation C. r prograding, storm-dominatcd shorclinc scqucncc. was formcd during a sca level fall, assumcd to bc a rcsult of glacio-isostatic uplift.

F o r n r a t i o n D . a l o d g c m c n t t i l l f o r m e d d u r i n g t h e l a s t g l a c i c r a d v a n c c in L i n n 6 d a l c n a n d l o r m a t i o n E . a coarscning uprvards sctlucncc. wcre formcd during thc post-glacial sea lcvcl fall. Thc subtill sequcncc ( f n r . A . B a n d C ) i s d a t c d t o b c t w c c n ' 1 0 . 0 ( X ) B P ( r a d i o c a r b o n d a t c s ) a n d 1 2 0 . ( X n B P ( t h c r m o - l u m i n e s c c n c c a n d a m i n o a c i d D / L r a t r o s ) . T h c g l a c i c r lr o n t w a s 1 0 k m d o w n v a l l c y d u r i n g d c p o s i t i o n o f f o r m a t i o n s A a n d B . r e l a t i v e t o t h e p r c s c n t g l a c i c r t c r m i n u s . a n d m o r c t h a n l 2 k m d u r i n g t h c l a t c W c i c h s c l i a n m a x i m u m .

Ida L1nrte, Uniuersitt of Rerg,en, Department of Geologl,. Section B, AllQt. 11. N-5007 Bergen, Norway (prestnt uddress: Agriculturul Uniuersity o.f Norw,ay. Deparonent of Soil Scien<'es. P.O. Box 28. N-1132 Aus-NLH, Norwuy') and Jan Mungerud. Uniuersity of Bergen. Departrnent of Geologt. Section B, Alllgt.

11. N-5007 Bergen, Norwav; 29th May, 1990 (reuised 7rh Murc'h. 1991).

The history of Svalbard and the Barents Sea, prior to the Late Weichselian maximum (around 18,000 BP), is not well known. The problems have been discussed recently by Boulton (1979), Troitsky et al. (1979), Miller (1982) , Mlller er al.

(19t39) and Mangerud & Svendsen (1990a). They generally agree that western Svalbard was ice- free for long periods during the Early and Middle Weichselian; however, the age and duration of the ice-free periods and glacier advances are dis- puted.

In Linn6dalen. on the west coast of Svalbard (Fig. 1), a 20 m thick sequence of raised, shallow marine sediments, capped by a Late Weichselian till, is exposed along the river. This is one of the thickest marine sequences of Quaternary age exposed on the archipelago. Interlingering of facies suggests one depositional episode.

This paper documents the lithostratigraphy of the Linn6elva sequence, which was earlier inves- tigated by Lavrushin (1969). He described eight units which are correlated with our formations in Fis. 16. The aim of this discussion is an environ-

mental reconstruction of the pre-Late Weich- selian history in Linnddalen. focusing on the depositional environment and glacial and sea level history.

Methods

The slopes containing the Quaternary sequence were covered by slumped material, but 80 90%

of the steepest parts were excavated (Fig. 48) and investigated (Lonne 1986). The altitude of site 1 was precisely levelled, while a hand level was used within the sections. The style of the sediment logs is chosen to show the sedimentary structures observed in the field, so they contain details not discussed here. The scale of structures is slightly exaggerated. Grain size was determined in the field with a reference card. later calibrated with sieve analyses. Maximum particle size (MPS) is the average of the longest axis of the 10 largest particles. Clast roundness (R) (fraction 16- 32 mm) was determined using the method of K r u m b e i n ( 1 9 4 1 ) .

?sr v ' \

er ni

l u j v ' / r u

l

N O R W E G I A N SEA

N 1 0

7 r

/ _

\ - ) - .

l . ' A

86 Ida LPnne andlan Mangerud BOREAS 20 (1991)

Fig. 1. The Isfjorden area on the west coast of Svalbard. Location of the Linn6dalen valley is shown by the arrow. possible submarine end moraines (shaded) after Ohta (1982). Bathymetry in merres (from Map 503, Norsk polarin;titutt 1975).

Fig. 2. Oblique photo of the Linn6dalen valley towards the south (photo: Norsk Polarinstitutt 1936).

BOREAS 20 (1991)

Fig. 3. Map of the outer part of Linn6dalen, with location of the sections east of the river. Two sites with glacial striae show a northerly glacier movement. Boundaries of the local sedirnen- tation basin, as inferred from bedrock exposures, are cross- hatched. Asterisks show two sites of radiocarbon dates (in Table 1). Contours in metres (from Map 89, Norsk Pofarinstitutt 1955).

Shallow marine sedirnents. Soalbard 87

1 5 1 0

c

Fig' 4' The Linn6elva sequence, with section curved in a sector from N to sw. ! A. composite photo showing the numbered sites separated by gullies. tr B. sketcl of the section showing the excavated areas and some distinct lithological units. Arrows with site numbers show position of detailed logs; some of them are presented in this paper. fl c. GenerahzJ stratigraphy (v;rtical exaggeration is about 25/o), with lateral correlation of formations (capital letters) and members (numbers). tnt"."pr"tuiion oi tt "

formations is shown in Fig. 5.

1 B

til3 lda Lonne and Jan Mangerud

The Linn6elva sequence

The Linndelva sequence is exposed in a 200 m Iong and 30 m high section at the east side of the r i v e r ( F i g s . 2 , 3 , 1 ) . N u m e r o u s g u l l i e s a l l o w e d a three-dimensional control at most stratigraphic levels. The sites are numbered from 1 to l l (Fie.

, l t . T h e s e q u c n c e is tlivided into five inf,.lrmil formations (A to E) and subdivided into members ( A l . A 2 , e t c . ) ( F i g s . ,l C . - 5 ) . T h e s u b t i l l s e q u e n c e was deposited in a local basin, conlined by bed- r o c k t o t h e e a s t a n d w e s t ( F i g . 3 ) . i n a p e r i o d with high sea level (50-100 m above present).

Formations A and B were deposited below the base of wave erosion. while formation C was deposited during a fall in sea level. Petrographical analysis of fourteen samples suggests that bedrock in Linn6dalen is the onlv source for the sediments.

1 0 . - - - 7 0 - - - - 8 0 - - m e r r e s _{r - t : l}II

B O R E A S 2 0 ( 1 9 9 1 )

I N T E F P R E T A T I O ] \ J

L o d g e m e n t t i l l

P ro o r a d r n o . h lo h . e n e r g y s n o r e l t n e

s e q u e n c e

P r o g l c i a l c n a n n e l s a n d i c e r a l t e d d e b r i s

S h a lo w m a r i n e , p r o g a c i a l fa n

paired molluscs and abundant fritgntents of sea_

weed.

Member A2: Turbidites and associated deposits

Member A2 consists of a lenticular sand bodv ( F i g . 4 ) w i t h c h a n n e l i z e d e r r m n l c x c s o f s l l q c l g d sand becls interbedclecl with thinner silt u;its. It is interpreted as turbidites and associated deposits ( L o w e 1 9 7 5 . l g r i l : W a l k e r l 9 R 4 ; S t o w 1 a 8 5 . 1986). Single-flow deposits are traced laterall!

f r o m s o m c t e n s o f c n t u p t o 1 . 5 lt ) m . T h e r o f t e n f . r r m u p * o r d f i n i n g c o m p l c x e \ . u p t o s m th ck.

with channe I axes dipping towards W or NW (Fie.

5 ) . T h e f l r r w d g p 6 s 1 5 a r e d i v i t l e d in t o f i r ' e g r u r p i . based on sediment structures. sediment deform- a t i o n a n d b i o t u r b a t i o n .

2

( 1 ) R e w o r k e d s i l t - f l o w d e p o s i t s ( F i g s . 6 . 7 ) c o n - Formation A sist of lumps of silt together with crusheci shells

Formation A consists otwo members (Fig. 4c): ilt',fi}ff:lillill liitff:"":T:ljn.:l;:i

A silt (member Al) ,nd an overlving lenticular

(2) Thin-beldecl silt to silty sand turbidites (Fig.

s a n d b o d y ( m e m b e r 4 2 ) ' T h e l o w e r b o u n d a r v is 7 c ) . S i n g l e fl o u , d e p o s i t s a r e o f t e n a f e w centi- not exposed.

rnetres thick, and ihrcker complexes are com_

nronlv disturbed by sediment deformation. (3) Member AI: Glaciontarine silt Medium-grained turbidites. ur classical turbiclites

( S t o w 1 9 1 3 5 ) . A c o m p l e t e o r p a r t i a l B o u m a Up to 3 m of sandy silt is exposed at the base of sequence can be recognized, with co:lrser particles the section (sites 1 and 7, Fig. 5). The silt contains as shells, pebbles ani silt clasts at the base. T.he l e n s e s a n d h o r i z o n s o f s a n d . d r o p s t o n e s . f r e q u e n t t u r b i d i t e s a r e m o r e o r l e s s d e f o r m e d bv bro_

=,,

I arh,

B O R E A S 2 0 (1 e 9 1 )

'-t

l . l

F i g . - 5 . 1 1 1 5 n t 1 . u , i g r a p h v o f t h c L i n n i c l v a s c q u c n c c . ( T h c logs arc gcncratrzcd.) l l a r c m a r k c d b v d o t t e d l i n c s . Arrows indicatc cjircction ol dicp,rsrtlon.

turbation and sediment deformation (Fig. 7). (a;

Parallel-laminated sand, present in complexes with scattered pebbles and shell fragments along the lower boundaries (Figs. 7, 9), are interpreted a s t o p - a h s e n t c l a s s i c a l tu r b i d i t e s , and aie nor deformed. (5) Gravelly sand turbidites are present at the base of the thicker complexes of p a r a l l c l - l a m i n a r e d s a n d ( F i g . 8 D ) . u n d i f o r m e d , and commonly eroded deep into the substrate ( F i g s . 6 . 8 ) .

All transitions between these groups occur, and the lateral and vertical distributions are shown bv t h e l t r g s ( F i g s . o . 7 . t t . 9 . l 2 ; . M a r i n e f o s s i l s ancl the lack of wave structures suggest that the turbidite accumulation of member A2 was deposited in a shallow marine environment: here i t i s t e r m e d a f a n .

I rtte rp re ta ti ct n an d dis c' us s to n

The fan is mapped for 150 m along the section ( F i g . - l ) . A n e x c a v r r i o n l5 { ) m n o i t h t r f s i r e I (Fig. I 1) shows > 1(.) m of fine-grained turbidites.

tnterpreted as distal facies of member A2. The extension of the fan towards SW and NE is unknown. There is no available section west of the river. The exposed sand body (member A2) i s 1 4 m t h i c k a t s i t e s I a n d 2 . t h i n n i n s to 3 m at s i t c 7 ( F i g . 5 ) . T h e u p p e r p i r r r is e r o d c t l h v t h e c h l r n n e l s o [ f o r m r r l i o n B f r o m s i t e 4 t r r Z if.is.

Shallow marine sedintents, Sualbard 89

S o n t c t u r b i d i t c c o m p l c x c s in forntations A and

4 C ) . T h e d e c r e a s i n g a l t i t u d e of member ,A2 between sites 2 and 8 suggest that the fan surface slopes towards NW and SW. Four sub_environ_

m e n t s o f t h e f a n a r e d e f i n e d (F i g . l l).

A lun-channel. - The l4m thick sand at site 2 (Fig. 8) forms a l l m thick fining upward channel f i l l o v e r l r i n b y . l m o f p a r a l l e i l a m i n r r t e d s i r n d The three complexes of the channel fill are thin_

ning and fining upwards. They were deposited in a s t r a i g h r c h a n n c l d i p p i n g 1 2 . r o w a r d s N N W . w i t h m i n i m u m c h a n n e l w i d t h o f l - 5 m i n t h e lo w e r oart.

T h e c h a n n e l f i l l w a s f o r m e c l d u r i n g t h r e e d i s c r e r e e p i s o d e s . e a c h s t a r r i n g w i t h g r u i e l l y - s a n d rur_

bidity currents eroding deeply into the substrate, followed by sandy currents filling the ciepressions.

D r o p s t o n e s . f o s s i l s . s i l t h e d s and sedimenr deformation become more common towards the t o p . T h e c h a n n e l h o u n d a r i e s t r c n o t e x p o s e d . b u t t h e w e l l - d e v e l o p c d s y m m e t r y o f t h e t h r e e l o w e r complexes suggests a straight channel. and thus a fixed source of currents. The channel is locatecl at the thickest part of the fan. The high gradient of the turbidites. their high sand-to-silt ratio. sraded l o w e r p a r t s a n d p a r t i a l e r o s i t r n of f hc top oI the t u r h i d i t e s . s u g g e s t d e p o s i t i t r n c l o s e t o t h e : o u r c e . The undeformed parallel-laminated sancl in the lower part with no bioturbation suggests more o r l e s s c o n t i n u o u s f l o w o f s e d i m e n t s . T h e f i n i n g u p w a r d s is a r e s u l t o f r e t r e a t of thc source.rr i decrease in sediment supply.

90 Idu Lqnne antl Jan Mangerud

S I T E 1 A

I Beacn gravet

B O R E A S 2 0 ( l 9 9 l ) A lobe with high sedimentation rate. - The 72m thick sand at sites 1A and 18 is dominated by classical turbidites (Figs. 6, 7). The few silt lam- inae deposited from suspension and the fact that bioturbation is concentrated in thin zones suggest frequent currents. A lobe with high sedimentation rate is reconstructed NE of the fan-channel.

based on sites 1A and lB (Fig. 11). Together with the channel llll this comprises the thickest part of the fan, with the largest horizontal and vertical facies variations. Sedimentary deformation with abundant water-escape structures indicate a high rate of sedimentation.

A lobe with low sedimentation rate. - The 6 m thick sand at site 3 (Fig. 9), with well-preserved primary structures alternating with bioturbated horizons, suggests large variations in sediment supply. An upwards increase in bioturbation indi- cates reduced current frequency, which might be a result of local topographical changes of the fan surface. The 2 m of sand exposed at sites 4 and 5 (Fig. 12) is almost completely disturbed by bioturbation and water-escape structures. At site 7. the 3 m thick turbidite-sand shows well-defined upper and lower boundaries. Strong bioturbation and large numbers of the mollusc Macoma cal- cdrea suggest a low frequency of currents. A lobe with low sedimentation rate is reconstructed from sites 3 to 7. thinning in this direction, and with surface sloping towards NW and SW (Fig. 1l).

Pro-fan.sl/t. - Silt is exposed at sites I and 7. and probably continues subsurface below the sand body (member 42). The large number of seaweed fragments were probably eroded by sediment gravity flows or icebergs. and kept in suspension for some time before they settled in the low- energy pro-fan environment.

Depositional enuironment. - During high sea level, Linnddalen was a fjord. and the only poss- ible sediment source for this fan in the middle of the valley was a glacier (Fig. 10). The large amount of well-sorted sand in member A2 may partly be a result of the sand-dominated bedrock in Linn6dalen, and partly of sorting in the melt- water plume or on an ice-contact slope. Under present-day conditions, the meltwater drainage and sediment dispersal are restricted to the sum- mer months, while resedimentation dominates during most of the year. An accumulation proxi- mal to the fan. actine as a source for resedi- R e w o r k e d s l l t

S m a l l t u r b i d l t e f l e d c h a n n e l s w i t h s m a l

a n o r a r g e ' s c a e o e l o r m a l r o n s

T h i n b e d d e d s i l t t o s i l t y s a n d y t u r b i d i t e s

F i g . 7 C

3 m t h i c k t u r b i d l t e f l e d c h a n n e l . G r a v e l y s a n d y

t u r b d i t e s a t t h e b a s e a n d s a n d y . d e l o r m e d

t u r b d i t e s a t t o p

P a r a l l e l - l a m i n a t e d s a n d R e w o r k e d s l l t P a r a l l e l l a m l n a t e d s a n d

B i o t u r b a t e d t u r b l d t e s

, t q f r , a o l l r a n d

\ Y b r o l u r b a l i o n

Fig. 6. Lithological log from site 1A (position in Fig. 4B).

Membcr A2 shows thc vertical variations of turbidites and associatcd deposits in thc high-scdimentation lobc of thc fan R = clast roundness.

I

S a n dE

BOREAS 20 (1991) Shallow rnarine sedimen*, Sualbard 9t

tf7'',

, l. ..;r'

:, ,', '] i.

3;l " .-qo."a"e;i"

l - o - d c ; " , o c

Fig. 7. Z A. Lithological log from site 18, 20 m southwest of site 1A (see Fig. 48). Member Al showsthe pro-fansilt, and member A2 the vertical variations of turbidites and associated deposits in the high-sedimentation lobe of the fan. Positions of detailed figures are marked. ! B. Medium-grained turbidites, deformed by water escape. D C. Thin-bedded silt to silty sand turbidites (located in Fig. 6). Boundaries are indicated by arrows. n D- G. Deformation structures in the turbidites (member A2). ! D.

Fluid escape pipe which cuts the overlying turbidite complex.

! E. Top of turbidite complex, completely deformed by flu- idization. I F. Gravelly-sand turbidites, with loading associated with fluid escape into the overlying bed. ! G. Parallel-laminatcd sand with thin bioturbated horizons. Two flow deposits are completely disturbed, a third exhibits trace fossils together with Macoma calcarea and Pectinaria so.

92 Ida Lqnne and Jan Mangerud BOREAS 20 (1991)

Flg. 8. I A. Lithological log from site 2. R = clast roundness,

MPS=maximum particle size. !8. Parallel-laminated sand

with a small channel filled with sandy turbidites. The lower boundary is stippled. Lens cap for scale. n C. The boundary (arrows) betrveen the two lower turbidite complexes of the fan- channel. Gravelly sand turbidites are cut into parallellaminated sand. D D. Gravelly-sand turbidites with redeposited mollusc shells (member A2).

Beach grave Beds reworked by

in the beach zc Silt with diamicton

S u b m a r i n e s l i d e c

P a r a l l e l - l a m i n a sano-comptexes

pebbles at the b

Fining upwards turbidjte complex

M P S = 8 e m

h = U . C

F i g . 8 B

Fining upwards turbidite complex

M P S = 1 1 c m R = 0 . 5 F i g . 8 C

F i n i n g u p w a r d s t u r b i d i t e c o m p l e x

F i g . 8 D r='-:-

M P S = 1 4 c m R = 0 . 5

l l O R h A S 2 0 ( 1 9 9 1 )

SITE 3

)"aa*!b

Shallow marine sediments, SLtalbard 93 ness of the pebbles (Fig. 16). The position of the fan would then have been controlled by the distal slope of this deposit and the eastern basin bound- ary (Fig. 11). The sand lenses in the pro-fan silt may have been deposited directly from the meltwater plume. Investigations by Hoskin &

Burrell (1972), Elverhoi et al. (1980) and Mack- iewicz et a/. (1984) show that sands are deposited within 200 500 m of the glacier front. The fan was probably formed during retreat of the glacier, with strong turbidity currents forming the main channel at the maximum position of the glacier.

Formation B

Formation B is 0-5 m thick and exposed from sites 2 to tl and possibly at site I (Figs. 4. 5). Three members are defined (Fig. aC).

_ l

"T

--- l

ofl:

Beach gravel

Beds reworked by e r o s i o n i n t h e b e a c h

z o n e

R = 0 . 3

L a r g e c a s t oi lodge , m e n t 1 i l m e l t e d o u t - r r o m a q r o u f o e o

i c e b e r g R = 0 3 , G r a v e l d r o o o e d O l r o m i t o a l n g

i c e b e r g s R = 0 3

)

o

- ^ - -

i 9 --

S i l t w i t h m o l l u s c s a n d d r o p s t o n e s

P a r a l l e l l a m i n a t e d s a n d w i t h s c a t t e r e d p e b b l e s a n d s h e l l f r a g m e n t s a t

the base of each c o m p l e x

B r o t u r b a l e d t u r b i t i t e s

T h i n - b e d d e d s i l t t o s i l t y s a n d tu r b i d i t e s , partly bioturbated

R = 0 6

Fig. 9. Lithological krg from site 3. Mcmbcr A2 shows the v c r t i c a l v a r i a t i o n s o f t u r b i d i t c s a n d a s s o c i a t c d d c p o s i t s in t h c l o w - s c d i m c n t a t i o n l o b c o f t h c f a n . R - c l a s t r o u n d n c s s .

mentation, would buffer the variations in sediment input during the vear. and would also trap the coarsest particles. A situation like this could explain the elongated source area suggested by the variation in channel axes, the apparent continuous flow of sediments at site 2, the good sorting, the large number of seaweed fragments in both members A1 and A2. and the hieh round-

Member Bl: Channel fill sequence

Three stacked channel fills are cut into each other ( F i g s . 4 C , 5 ) , e a c h f i l l b e i n g 5 - 1 0 m w i d e w i t h straight axes dipping 10o towards north. The bed thickness increases from 0 to 2.5 m in the dip direction. At sites 4 and 5 the channel complex is up to 5 m thick and constitutes both the lower and the upper boundary of formation B (Fig. 5).

The lower channel fill (bed Bla) is cut 2 3 m into the underlying fan (member A2) (Figs. 4C, l2) and consists of medium-grained turbidites with pebbles and shells in the lower part, pro- gressively enriched with coarse-grained particles downstream. The rounded pebbles and the high content of Macoma calcarea suggest that the tur- bidites were eroded from underlying fan sedi- m e n t s ( f m . A ) .

The middle channel fill (bed Blb) is similar to the lower one, but has prograded relative to the latter and has cut 2 m into the substrate (site 4, Fig. 5). The deposits are dominated by frag- mented valves of Macoma calcarea, suggesting they were eroded from the underlying channel filt.

The axis ofthe upper channel fill (bed B1c) has the same direction as the two lower ones, and is eroded into these (Fig. aC). The bed thickness varies from 0 to 2.5 m in dip direction. The bed is dominated by fine-grained turbidites which are interbedded with silt towards the top of the bed.

The channel fill is characterized by small (<10 cm) clasts of red diamicton, a high number of sub-

94 ltltt L1tme und Jutt Mangcrud

angular cobbles. fragments of Macoma calcarea.

and high content of unbroken valves of Hiatella arctica. The silt towards the top of the bed (site 5), with numerous paired Hiutello arttica, was deposited in periods without flow in the channel.

a n d i n t e r l i n g e r s w i t h m e m b e r C l ( F i g . 5 ) .

Member 82: Lower diamicton antl associated ice-rafted deposits

The lower diamicton (bed B2a) is a reddish, matrix supported diamicton. present in different facies: Outside the channel svstem. a 10m long l e n s o c c u r s a t s i t e 3 ( F i g . 9 ) . a n d s r n a l l e r ( < 1 m ) clasts occur in the silt at sites 7 (Fig. 12) and tl.

Inside the channel system, a horizon of eroded diamicton grades laterally into a boulder lag (site 5 . F i g . 1 3 ) , a n d s m a l l (< 1 0 c m ) c l a s t s o f d i a m i c t o n are present in the upper channel fill (sites ;l and 5). This shows that the diamicton was deposited first at the stratigraphic level between the middle a n d u p p e r c h a n n e l s ( F i g . 5 ) .

A lens of diamicton at site 3 is 35-60 cm thick and covers an area 10 m x 10 m. Frequent striated and bullet-nosed shiiped pebbles and cobbles sug- gest that the clasts were transported subgtacially, and the characteristic reddish matrix colour and the petrography of the pebbles suggest it was furmed within Linnddalen. The diamicton is ovcr- consolidated and lacks flow structures. The sub- horizontal lower boundary suggests some degree of erosion of the substrate (fan surface) during deposition. A similar reddish diamicton with a subhorizontal lower boundarv is present at site -5, but here it is partly eroded by the upper channel (bed B1c). Clast fabric at site 3 (Fig. 16) and the lens formed shape of this unit indicate that this is

I J ( ) R I : A S l 0 ( l 9 9 l )

/'lg. 1//. Skctch ol Linncclalcn w i t h m a x i n u n r c x t c n s i o n o t t h c g l a c i c r d u r i n g d c p o s i t i o n o f f o r m a t i o n A . S c a l c v c l w a s 5 ( l l 1 ) 0 m a b o v e p r c s c n t . i t n d a v a l l c l g l a c i c r c o r c r e d t h c h k c ( i c e - f r c c c o n t l i t i o n s a r c s h o u n i n F i g . 3 ) . T h c f a n i s l o c a t e d b c l o w t h c m c l t $ ' a t e r p l u m c i n t h c s o u t h c a s l c r n p a r t o l t h c l o c a l s c d i m c n t a t i o n b a s i n ( s t i p p l c d ) .

not an irr .slta lodgement till. If wc distinguish between processes of formation and deposition (Shaw 1982). we assume that the diamicton was formed beneath a glacier in Linnddalen, but not deposited from an active slacier at this strati- e r a o h i c l e v e l .

l ) g . 1 / . R c c o n s t r u c t i o n o f t h c p r o u l a c i r l l a n ( f n . A ) \ \ i t i r t h c f o u r s u b e n r i r o n n e n t s : A f a n c h l i n n c l . r l o b c o 1 h i g h n t t e o l s c d i n c n t a t i o n . a k r b c o f l o u r i t t e o f s c d i m c n t a t i o n lt n d p r o f a n s i l t . ' l

h e a s t c r i s k s h o u ' s p o s i t i o n o f i t s m a l l s c c t i o n s t t u t h o f s i t e L C , ' n 1 1 ' n r . i t t m t l r r ' . i r l l ( r n l i r f ' h \ A l c r n ) . r t t {l q \ l l l

I

i , 4 s l t w a t e r o u t le t

I J ( ) R F A S l { r ( t e ( ) I )

SITE .5A

A 2

' : ' . . . . .

* r F : - + # - ;

"\"",\,"..

C l a s t s o f d i a m i c t o n lB2a) M P S 1 5 c m R 0 . 4

S I T E 58

j : <

-"'

== =.=a"=-:;

n D o " "

I

Shullow nnrine setlinrcnt.s, Suulburd 95

S I T E 7

B2a

" {

" {

{

B 1 b -

i.

t

, t

M P S 1 4 c m R = 0 . 5 -

B 1 q -

G l a c i o - t e c t o n i c t h r u s t s

F\*r,5.;;"*'-;

w RrS*

l R 0 . s

t ; z '

=:=;.

L

/ ' l g 1 2 t - i t h , k r g i c a l l. g s fr.m sircs 5A' -5B and T Thc latcral intcrfingcring

w i r h i n f . r r n a t i o n B is shown. u,ith thc rransili.n frLrrn u n c r . d c d d i a m i c t . n ( b e d lJ2a) at.sitc 7 to a b'uldcr lag at site 58. a n d c l a s t s o r d i a m i c t o n in ,n" rpp", channcr fiy ar sitc 5A.

Hi""t-""1":Hs rhc pn>fan silt Mcmbcr A2 shows thc cntirc rhickncss.f rhc fan ar this sirc. R - crast roundncss. MI)s =

96 lda Lpnne andJan Mangerud

Poorly sorted sand and gravel deposits (bed B2b) occur below (Fig. 9) and lateral to bed B1a at site 3 (Fig. 5), and are exposed for 1G-15 m before wedging out. The thickness varies from 0 to lm. Lenses of laminated sand, gravel and diamicton clasts wedge out in all directions. Cob- bles with vertical long axes have deformed the underlying laminated sand. Member 82 is inter- preted as an ice-rafted deposit.

Member 83: A submarine slide deposit A 0-2 m thick bed of alternating sand and silt, dipping slightly towards north, is exposed for 10 m between sites 2 and 3 (Fig. 5). Water-escape structures in the sand are associated with slight folding and fracturing of the silt horizons (Fig.

8A), suggesting sliding of unconsolidated sand with slightly consolidated silt. The unit contains no fossils, in contrast to the stratigraphically adjacent units (Fig. 15). Member 83 occurs lateral to member 82 (Fig. 5), indicating sliding more or less contemporaneous with deposition of member 8 2 .

Interpretation and discussion

The three members of formation B (81, B2 and 83) were all deposited on fan-sediments (member ,A.2) and overlain by the silt member C1 (Fig. 4C).

Member 81 constitutes both the lower and upper boundary of formation B (sites 4 and 5), showing that the episode started and ended with deposition

BOREAS 20 (1991)

Frg. 13. Boulder lag (bed B2a) at site 58 formed by erosion of the lower diamicton. Note the erosional unconformity between the boulder lag and the laminated fill of the middle channel (bed Blb).

of turbidites. The diamicton (bed B2a) was deposited between the upper two channels. The sand and gravel (bed B2b) are found below and lateral to bed B2a, and member 83 is found lateral to member 82.

The axes of the three channelized turbidite complexes (member 81) all have the same direc_

tion and are thus assumed to have the same source. The upward transition from predomi- nance of paired, transported Macomainthe lower channel, through fragments of Macoma in tlte middle, to fragmented Macoma and paired Hia- tella in the upper channel, suggests tirat the tur- bidity currents eroded the underlying or recently deposited sediments.

The lower diamicton (bed B2a) is eroded by the upper channel (bed Blc) between sites 4 ani 7. However, there are no indications of an active glacier at the stratigraphic level between the upper two channels. We interpret member 82 to represent a short, possibly catastrophic episode of ice rafting. Different facies of ice-rafted deposits occur: Large clasts of diamicton in silt (site 7) are assumed to have been dropped from floating ice.

The subhorizontal lower boundary of the dia- micton at sites 3 and 5 is probably the result of erosion by grounded icebergs. Ifthe diamicton at site 3 melted out from a stranded iceberg, this can explain the consolidation of gravel below the diamicton compared with the gravel lateral to it.

The thinning of sand and gravel (bed B2b) away from the diamicton suggests they were deposited from the same iceberg, possibly by sliding during

B O R E A S 2 0 ( l 9 9 l )

melting of the ice. This is supported by the fact that silt (member Cl) capping formation B is thinner where these icebergs are postulated.

This reconstruction suggests first two sub- sequent episodes of channelized turbidites on the lorver lobe of the fan (fm. A). The source of sediments was probably the underlying deposits.

The turbidite deposition was interrupted by an episode of ice rafting, and sliding of sediments.

A final pulse of channelized turbidites erodecl the ice-rafted deposits (between sites zl and 7), and the resultant turbidites were gradually replaced by silt deposited from suspension with numerous paired Hiatella arctica.

Formation C

A 0-10 m thick sequence coarsening upwards from silt to coarse-grained sand is exposed between sites 2 and l1 (Fig. 4). Two members are defined: A silt (member C1) interfingering with formation B. and overlain by a sand (member C2). Two beds between formations A and D at site I are named members C3 and Ca (Fig. 5).

Member CI: Glaciomarine silt

Member Cl consists of sandy silt with dropstones and contains frequent molluscs. The thickness increases towards the southwest, from a few centi- m e t r e s a t s i t e 2 t o m o r e t h a n 1 . 5 m a t s i t e 1 1 ( F i s . 5 ) . T h e l t r w e r h o u n d a r y in l e r f i n g e r s w i t h t h c s i l r in formation B (site -5). as described above.

Member C2: Coarsening upwards sand Bioturbated sand (bed C2a) consists of fine- grained, completely bioturbated sand with drop- s t o n e s a n d a h u n d a n t m o l l u s c s , a n d o . . u i , b e t w e e n s i t e s 4 a n d i 2 ( F i g . 5 ) . T h e d i s t i n c t l o w e r boundary matches an abrupt faunal change from Hiatella arctica in the silt to Maconta calcarea in t h e s a n d ( F i g . l - 5 ) .

Laminated and bioturbated sand (bed C2b) is w e l l d e v e l o p e d a t s i t e s 9 ( F i g . 1 4 ) a n d 1 1 ( F i g . 5). The subhorizontally laminated sand, which is partly bioturbated, is interpreted as hummocky cross-stratification (Howard & Reineck 1981;

Bourgeois & Leithold 19811; Greenwood & Sher- man 19t16).

Cross-stratified sand (bed C2c) is up to 3.5 m thick, and the lower boundary is defined bv the

Shollow nrurine sediment.s, Srtulhurtl 97 lowermost preserved scours (Fig. l4). The bouncl_

ary is sharp at sites 9 and 11, but is more diffuse a t s r t e s 4 t o 8 ( F i g . 5 ) , d u e t o b i o t u r b a t i o n . T h e bed is dominated by 0.-5-2 m wide scours.

enhanced by concentrations of pebbles and shells in the centre (Fig. l4,A, D). The bedform has the same geometry regardless of the orientation of sections. and is interpreted as swaley cross-stratl- fication (Leckie & Walker t9{t2). Only durins a few favourable days (wet sand and no wind) ias bedding seen between the scours. The flat to gently undulating laminae in the lower part is probably hummocky cross-stratification, with upwards transition to trough cross-bedding. Shal_

low depressions in the upper part of the bed are filled by laminated siltv sand. This low-energy filling might have occurred during periods with sea-ice cover.

Coarse-grained megarippled sand (bed C2d) is up to 90 cm thick and has an erosional lower boundary with scours and concentrations of cob_

bles (Fig. 14A, C). The lower part consists of 10 cm high and 60-90 cm long cross-beds. dipping 0-30' with alternating coarse- and meclium- g r a i n e d s a n d la m i n a e .

Parallel-laminated fine-grained sand (bed C2e) is 50 cm thick and dips 2-4" towards west (Fie.

l 4 , A . B ) . P e b h l e s a n d m i l l i m e r r e - l o n g s h c l l fr a g - ments are scattered throughout the bed.

Gravel (bed C2f) consisting of grain-supportecl pebbles with sand is present only at site 9 (Fig.

14,A. B) and is interpreted as an eroded beach.

The upward coarsening sequence of formation C is interpreted as a prograding shoreline sequence with four sub-environments recognized ( F i g . 1 4 ) : M e m b e r C l a n d b e d C 2 a a r e in t e r p r e t e d as offshore facies clepositcd below the base of wave erosion in a tributary fjord. Bed C2b is the offshore-transitional zone between the fairweather and storm wave bases. Bed C2c belongs to the shoreface (below low tide water level), and is influenced by waves every day. The megaripples (bed C2d) were formed close to the zone of breaking waves in the foreshore zone (the intertidal zone) and bed C2e in the swash zone, Gravel (bed C2f) is a beach eroded during the last glacial advance.

Members C3 and C4: Grauel and grauellv-

sand channel fill

A lm thick channel fill (member C4) at site 1 ( F i g . 5 ) c o n s i s t i n g o f n o r l h w a r d s d i p p i n g s a n d

98 lda LOnne and lan Mangerud

laminae with pebbles and shells (Fig. 7) is inter- preted as lateral accretion, possibly in a very shallow marine channel. A L m thick sandy chan- nel fill is traced 30 m into the gully between sites I and 2. The channel has eroded member 83 in the inner part of the gully and a small unit of gravel (member C3) at site 1 (Fig. 7). Members C3 and C4 are bracketed between member A2

BOREAS 20 (1991)

and formation D, but cannot be correlated by lateral mapping due to the northerly thinning of formations B and C (Fig. 5).

Interpretation and discussion

The coarsening upwards sequence of formation C suggests a simple progradational event sup-

Fig. 14. -A. Lithological log from site 9. !B. Parallel-laminated sand (bed C2e) and overlying beach gravel (bed C2f). !C.

CJarse-grained megaripples (bed C2d) formed in the foreshore, with a sharp erosive lower contact to fine-grained shoreface sand (bed C2;). tr D. Three stacked scours (lower boundaries are stippled) are cut into storm laminae (bed C2c).

B O R E A S 2 0 ( 1 9 9 1 )

ported by preservation of the upper shoreface and foreshore deposits, which are often eroded during a transgression (Kirk 19110). Large-scale cross- beds formed close to tide level, a sharp boundary between the shoreface and foreshore, and sparse bioturbation in the upper shoreface are charac- teristic of member C2. Howard & Reineck (1981) found this to be typical of a high energy shoreline sequence. This is supported by the presence of swaley- and hummocky cross-stratification, which are interpreted as high-energy forms, mainly storm-deposits (Leckie & Walker 19{.}2; Bour- geois & Leithold 1984). As pointed out by Massari

& Parea ( 1 98u) . a high frequency of scours formed during storms will reduce or even eliminate the fairweather deposits from the stratigraphic record. The last imprint of storm activity in for- mation C might have occurred during a short period of the year, but. due to the high energv, g i v e s th e i m p r e s s i o n o f a m o r e s e v e r e e n v i r o n - ment than was the case. Compared to other high- energy sequences (Howard & Reineck 1981;

McCubbin 1982), formation C is quite thin ( 10 m).

This may be explained by its formation during a sea-level fall, or during periods with minimal sediment supply (no fluvial erosion or sea-ice cover), and/or the presence of subhorizontal ero- sion surfaces (Hunter et al. 1979). We suggest that all these phenomena might be present during deposition of formation C. The regional recon- struction supports a fall from a high sea level ( 5 0 - 1 0 0 m ) t o 2 8 m a . s . l . d u r i n g d e p o s i t i o n o f formation C.

The shoreline sequence prograded into a basin controlled by the asvmmetrv ol the turbidite accumulation (formations A and B). The thickest and best-developed facies are preserved where the fan was thinnest and the basin deeoest (sites 9 a n d 1 1 . F i g . 5 ) .

Formation D

The upper diamicton; description and atscusstotl

Formation D is 0-3 m thick, with a sharp sub- horizontal lower boundarv. It is exposed along the entirc section (Fig. a) and mapped 500 m further to the south. where it slopes beneath the talus towards the prcsent river. The lower I m is a massive matrix-supported diamicton with fre- quent boulders. A brownish colour clearly dif-

Shallow marine sediments, Sualbard 99

tt

3

:

lt

E

=o

E3 E2 E 1 D c2l C2e c2d C2c c2b C2a c 1 B3 B2b

I I

r l t

I

t

t

psf I

p t I psf

p p

Y

t

* s 3

& s f $ $

S 3 i . t A E E r g e

s $ $ $ $ ! $ s $ $

B 2 a l l l

B 1 c I I p s f

B l b l I s f

B l a l l s f

A 2 l l l l l l t t p s f

A 1l l l p

I I I I

I I I I

t l I I

I Present I c o m m o n I Abundant

p Paired valves s Single valves f Fragments

F l g . 1 - 5 . D o m i n a t i n g t r c n d of macro-fossils in thc t_inncclr.a s c q u c n c c .

ferentiates it from the reddish lower diamicton ( b e d B 2 a ) . B a s e d o n t h e s u b a n g u l a r a n d com- monly striated pebbles. the distinct clast fabric (Fig. 16), and the deformational structures along the lower boundary, formation D is interpreted

l(X) lda Lqnne and Jun Mungerud I J O R E A S l 0 ( 1 9 9 l )

C H R O N O _ S I R A T I G R A P H Y

C O M P O S I T E S T R A T I G R A P H

L A S T F A B I ] A N O T H R U S T S

L I N N E D A L E N G L A C I A T I O N C U R V E D A T E S A M I N O

A C I D S O / L t o t a l l x 1 0 0 0 y s a r s

J 4 C T L

H O L O C E N E

L A T E

10.2 1 0 . 9

> 3 8

0 . 0 1 3 { n . 3 ) o . o 2 5

( n 1 9 )

W E I C H S E L I A N @ o

o o o

as a lodgement till. The upper boundary was disturbed during post-glacial fall of relative sea level. Soft sediment- and glaciotectonic deform- ation is found in the subtill sequence. A more than 10 m long thrust at site 5B (Fig. l2) is displaced 2- 3 m towards the north. parallel to the clast fabric in formation D (Fig. 16), which formed during the last glacier advance.

We conclude that the lodgement till (fm. D) and the underlying glaciotectonic deformation were formed by a northward moving glacier in Linnddalen. The till shows that the base of the glacier, at least for some of the time, was at the melting point. The glacier terminus probably reached Isfjorden. Even if only local directional elements are found (fabric, glaciotectonic thrusts, petrography), it is conceivable that this glacier was a tributary to a larger glacier in Isfjorden.

extending as far as the continental shelf (Fig. l).

2 . 5

> 4 3

Formation E

Formation E, comprises the post-glacial marine silt and littoral sediments overlying the upper diamicton. and is divided into three members.

E 1 , E 2 a n d E 3 . T h e l a t t e r t w o a r e s h o w n in F i g . 5. but are not discussed further here.

Macrofossils

The observations of fauna made during the litho- logical investigations are summarized in Fig. 15.

A more comprehensive fauna list was presented by Lavrushin (1969). The valves are well pre- served in the permafrost; both periostracum and siphons were found. We did not find any species suggesting that conditions were as warm as during the Holocene. This is supported by foraminifera

z

J

Ua I

9

- )

)

O s c i l l ;

\ L

\

\ r _{\ ,}

s c i l l a t i o n ) i :

/ / l

( i

I

F i g . 1 6 . C o m p o s i t c s t r a t i g r a p h v w i l h m a x i m u n r t h i c k n c s s o f c a c h l o r n r a t i o n . C ) u r p r o p o s c d c o r r c l a t i o n w i t h t h c u n i t s o l L a v r u s h r n ( 1 9 6 9 ) . w h o s c b o u n d a r i c s a r e n o t d c f i n c d . C l a s t f a b r i c ( t r - 1 ( X ) ) a n d g l a c i o t c c t o n i c t h r u s t s ( t r - f i ) r r c p l o t t c d i n S c h n i d t ' s n c t a n d W u l f f n c t . l o w c r h c m i s p h c r c . r c s p c c t i v c l v . A m i n o a c i d c p i m c r i z a t i o n : m c a n v a l u c s o f D , r L r a t i o s t o t a l f r a c t i o n f o r M r d tnut(utu for cach formation. (ilaciation rnd scr lcvcl crrrvcs as infcrrcd from thc scdimcntologr.

R E L A T I V E S E A L E V E L

I C E C O V E B

3 $ i l

' l r \ 11'o

:.1,.F

l l o R E A S l 0 ( 1 9 9 1 )

analyses (Lycke l9{37). Hntt et al. (1983) reported finds of Macoma baltita. however. we suggest this is irn incorrect determination of Macoma calcurea.

which is common at most stratigraphic levels.

Bones from three units were examined by R. Lie (written communication 19tt5): Member A2, site 3; three fragments from a 2(125kg cctd (Gadus morhua). Bed B 1c, site ,l: two fragments of shoul- der blades (sc'apula) of a Briinnich's guillemot (Uriu lomuia). Member C2. site 11: a dorsal uer- tebra frctm a young bottle-nosed whale (H_vp- erodon ampullatus). All three species live in the Svalbard rcgion today. Fossils shttw that even though the glacier in Linnddalen was considerably larger than at present. the sea ice was gone for much of the summer. The lateral and vertical uniformity of fossils support our conclusion that formations A. B and C were formed during one depositional episode without substantial inter- ruDtlons.

Dates

Radiocarbon date.r (Table l). - The sample from the till (T-6(X)3, fm. D) shows that most, probably all, incorporated shells have radiocarbon ages

Shollow nrurine setlintent.s. Sualbard l0l higher than 38.100 BP. Three dates are from the subtill sequence (fms. A and C. Fig. 16). The whalebone discussed above gave a finite age of 42.500 BP (T-672i1). Due to a low collagen content, we conservatively consider this as a mini- mum age. The sample was from the same strati- graphic level as T-6001. where paired molluscs vielded an infinite age. We conclude that for- mations A, B and C are older than 40.000 BP.

Thermoluminescence dates (Table 2). - Four samples were dated using the partial bleach method of Mejdahl (1988). Zeroing of the TL- signal of the sediments depends upon light exposure during deposition. The samples from the shoreface sand (R-852-511 and R-892-508) should be well exposed and give a reliable age, but questions could be raised about sufficient exposure of the turbidite sand in member A2 (R- 8525 l0 and R-882501). Age assessment by the TL method is not yet well understood for these types of sediments (papers in Townsend et al. 1988).

The main uncertainty is due to the zeroing of the Tl-signal during deposition, additional varying water content in the sediments through time, and to long-term fading. The consistent results from the four samples is an argument for an Early Weichselian age.

7 c h l c / . R a d i o c a r b o n d r t l c s lr o m t h c L i n n f c l v a s c c t i o n s ( c a r r i c d o u t b v R . N v d a h l a n d S . G u l l i k s c n a t t h c T r o n d h c i n l a b o n t o r v ) . Thc outcr 2(l3l)1 Ltf thc mollttsc shclls was rcmovcd bcli)rc dating. AII datcs arc corrcctcd litr a rcscrvoir agc of.1,10 vcars. For t h c b o n c . c o l l a g c n w a s c x t r a c t e d a n d d a t c d . S i t c s l 3 a n d 1 , 1 a r c l o c a t c d s o u l h o f t h c n a i n s c c t i g n s (F i e . 3 ) .

U n i l S a r r p l e n o . L a b . n o A g c B P S i t c R c m a r k s

E I E I D C2c

tl,1-20|i9 lJ.1-2097 1J.1,2(X) I lJ5 2091t

'I-6()()2 T-6229 T-6(X)3 T-6728 I -600 I T-622iJ

1 0 . 2 3 0 * I l 0 1 0 . 3 2 0 + I l 0 :'31.l. I 00 . 1 2 . 5 0 0 + 1 . 7 ( X )

2 . 6 ( X ) r'.13.1 (X) 50.200 + ,1.6(X)

2 . 9 ( X )

( 1 3 ) P a i r c c l m o l l u s c s . H i u t t l l u u r t t i t u ( l l ) M o l l u s c s in l i i i n g p o s i t i o n . M \ ' ( t r u n . q t u

I Shcll fragmcnts. Hiutcllu urttiru arul Mya truncutu

I I Whalcbt>nc. Hvperodott untpulltnus

6 P a i r c d m o l l u s c s . M u < ' c t t n u ( u l ( u r e u f S c a w c c d

C2 tl,1-2061

A2 ll.l-2(XXr

T i t b l t ' L T h c r n r o l u m i n c s c c n c e (T L ) d a t c s o b t r i n c d l r o m t h c N o r d i c L . a b o r a t u r i u m fo r T h c r m o l u m i n c s c c n c c D a t i n g . R i s o . D c n m a r k . l ' - o r a l l s a m p l c s . s a n d - s i z c d p o t a s s i u m l c l d s p a r w a s d a t c d f o l l o u i n g t h c s t a n d a r d p r o c c d u r c s ( M c i d a h l l 9 E 8 ) . T h c p l a t e a u i s r c p o r t c d w i t h a s t a n d a r d d c v i a t i o n o l . : 5 t ? .

L l n i l S a n r p l c n o L r b . n o A g c p l a t L ^ a u Agc IJP

C2r ( 2

ii,l-2 I 6{

i{t-l lt.l 2 l,l2 It.l 2 1,1 I

R-8525 l I R-lJ9250iJ R-lJtt250I R-u525 1 0

1.15-,175'C 290 .17(fC 1.15 .150'C 20(i-.1(xrc

I 1 8 . 0 0 0 * 12.(X)0 8 7 . ( X ) 0 a l 1 ) . 0 ( ) ( ) l l l . ( x ) 0 * 1 0 . ( x ) 0 1 2 0 . 0 0 0 * 12.0()()

5 I 0 I 2

102 lda L4nne and Jan Mangerud

Amino acid epimerization. - Samples of Macoma calcarea, Mya truncala and Hiatella arctica were analysed by Bolstad (1987). He found a faster epimerization rate for Macoma than for the other two species, thus we present here only the mean D/L value for the total fraction of Mya truncata from each formation (Fig. 16). The methods of analysis are described by Miller et ai. (1983). The Arhenius parameters (Miller 19it5) are used for age estimates. In this region verv different post- depositional temperatures and thus epimerization rates may occur. This can be exemplified as follows: At 0" C (below sea water or glaciers) a difference in DIL ratios of 0.01 between two samples would be attained in 10,000 years and a t - 5 " C ( p r e s e n t m e a n a n n u a l le m p e r a t u r e ) l n 28,000 years. At 18'C (possible ice age tem- perature) it would require more than 400.000 ye ars.

As formations A to C were deposited below sea level, the temperature during deposition was between -2 and +2" C. There are no differences

inDlL ratios between formations A and C, which suggests they were deposited in less than 600t) years. The D/L ratio 0.028 (Fig. 16) gives a post- Eemian age in all calculations using reasonable temperature histories. Miller et al. (1989) obtained a D/L-ratio >0.04 on Mya and Hiatella for Eemian sediments (episode C) at similar elev- ations on Broggerhalvoya. From their Weich- selian episode B (D/L ratios 0.026 to 0.037) they obtained a minimum age of 60,000 BP with both radiocarbon ancl U-series dating, and concluded it is only slightly older. We conclude that our formations A-C are either correlative or younger than their episode B.

Conclusions. - Radiocarbon dates of formations A. B and C demonstrate an age older than 40,000 BP, and amino acid D/L ratios suggest an age younger than the Eemian (120,000 BP). The time range given by the TL dates is also com- patible with the time span given by the amino acid analyses. If we interpret the TL dates with the constraints given by the amino acid method, an age around 110.000 BP (oxygen rsotope stage 5d) would be compatibie with the results of both methods. However, such an old age would require ground temperatures well below - 10'C for most of the post-depositional time to account for the low D/L ratios. We conclude that the ages of formations A-C are between 120,000 and 40,000 vears BP.

B O R E A S l 0 ( 1 9 9 1 )

Summary and conclusions

Formations A to E are mapped more or less continuously throughout the sections, thus the given stratigraphical relationships seem well established. Problems with correlation of member C3 and C4 are only of local significance and do not influence our geological history. Because of the interfingering of facies and the lack of major unconformities, we assume a continuous depo- sition of formations A. B and C. The base of the upper till (formation D) represents a hiatus of unknown duration.

A sandy turbidite-dominated proglacial fan (formation A) was deposited below the wave erosion base in a shallow fjord in front of a glacier filling Linn6dalen. The glacier terminus might have been as close as 200-500 m south of the section, as suggested by numerous sand lenses in the pro-fan silt. The fan was most likely formed during a retreat of the glacier. A sequence of proglacial channels and ice-rafted debris (for- mation B) was formed during a small oscillation of the glacier terminus. The glacier did not over- ride the section, but the high gradient of the channels suggests that the terminus was very close. The sediment gravity flows dominating these two formations (A and B) show only small horizontal and vertical changes in depositional direction, and thus a quite stable source area. The sand was trapped in the local basin of Linn6elva during this episode, and only suspended sedi- ments were transported into Isfjorden.

The fan-shaped surface of formations A and B controlled the facies distribution of the overlying prograding high-energy shoreline sequence (formation C). It was formed during a fall in sea level from 5O-100 m to 28 m a.s.l., suggested by beach gravel (bed C2f). The content of locally derived dropstones suggests a calving glacier front in the inner part of the submerged Linn6dalen during most of this period. However, formation C is the most glacier-distal facies present in the sequence.

The shallow marine sequence (formations A, B and C) is capped by a lodgement till (fm. D) formed beneath a northward moving glacier in Linn6dalen during Late Weichselian. The glacier probably advanced into a shallow marine or ter- restrial environment. There are no indications from Linnddalen that the glacier was confluent with a glacier filling Isfjorden, though this possi- bility cannot be excluded (Mangerud et al. 7997).

B O R E A S 2 0 ( 1 9 9 1 )

The shallow marine. subtill formations A, B and C are dated between 40,000 BP (radiocarbon dates) and 120.000 BP (amino acid racemization and thermoluminescence). Amino acid ratios of shell fragments from the upper till (fm. D) suggest that this represents a Late Weichselian advance (Mangerud et al. l99l).

The sea-level curve (Fig. 16) is based on the interpretation that formations A, B and the lower part of formation C were deposited below the wave erosion base. and thus during high relative sea level. This may correlate with the only known pre-Late Weichselian sea level in Linn6dalen, an 8 7 m t e r r a c e . r a d i o c a r b o n - d a t e d t o 3 6 . 0 0 0 B P , which might be a minimum age (Mangerud et al. 1987). A sea-level drop must have occurred during deposition of formation C. down to at least 28 m. During the Late Weichselian glaciation, the sea must have risen up to the post-glacial marine l i m i t b e t w e e n 6 5 a n d 7 8 m a . s . l . ( S a n d a h l 1 9 8 7 ) . which also gives the maximum sea level during deposition of the Holocene formation E.

A glaciation curve is shown in Fig. 16. The glacier in Linn6dalen was larger than present during most of the time represented by the sequence. Linnddalen is oriented at 90" to Isfjor- den (Fig. 1). Thus an ice-flow with far travelled debris from east would not be recorded unless the Isfjorden trough was completely filled with ice.

and the ice surface overtopped the mountains along the Linn6dalen valley. The oldest evidence of a glacier front position in Linnddalen is fbr- mations A and B, l0 km beyond the present ice front. This could be a late stage of a retreat from a more extensive glaciation. The eustatic sea level was lower in the Early to Middle Weichselian (Chappell & Shackleton 19t36). and as the relative sea level in Linnddalen was high, this suggests an isostatic depression. As we record only local glacial advances, the glacio-isostatic depression must have been caused by a large ice sheet to the east. Formation C indicates a retreat of the local glacier to an unknown position during a relative sea-level fall, which was probably caused by an isostatic uplift due to a deglaciation in the east.

The only recorded glaciation of the site was the Late Weichselian advance forming formation D, more than 1 2 km beyond the present glacier front.

The area was deglaciated about 12,500 BP (Man- gerud & Svendsen 1990b).

AcknowletlRements. - This work wits linancially supportcd by t h e N o r w c g i a n C o u n c i l f o r S c i c n c e a n d t h e I l u m a n i t i c s ( N A V F ) . D c n n o r s k c s t a t s o l j e s c l s k a p a . s . ( S t a t o i l ) . I . R .

Shullow ntarine sediments, Sualburd 103

H a l d o r s c n F o u n d a t i o n a n d t h c N o r w c g i a n P o l a r R c s c a r c h In s t i - tutc. Thc lattcr also providcd logistical support. During thc field work wc had coopcration and assistancc from O. Salvigscn, T . S a n d a h l . O . B . S a n d a h l . E . K . L o n n c a n d t h c c r c w a t l s f j t l r d R a d i o . M . B o l s t a d a n d I I . P . S c j r u p p c r f o r m e d t h c a m i n o a c i d a n a l y s e s . R . N y ' d a h l a n d S . G u l l i k s c n t h c r a d i o c a r b o n d a t i n g a n d V . l \ 4 c j d a h l t h c T L d a t i n g . R . L i c i d c n t i f i c d b o n c f r a g m c n t s . A. Borgan draftcd somc of thc figurcs. An carlicr vcrsion of t h c m a n u s c r i p t w a s c r i t i c a l l y r c a d b y J . Y . L a n d v i k a n d R . J . Stccl. Thc manuscript has bcncfltcd from critical rcvicws by A.

Elverhoi and R. Powcll. T'hc English languagc was corrcctcd b y M . B o v i s . T o a l l t h c s c p c r s o n s a n d i n s t i t u t i o n s w c g i v c o u r s i n c c r c th a n k s .

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