BOREN A continuous Eemian-Early Weichselian sequencecontaining pollen and marine fossils at Fjpsanger,western Norwav

A continuous Eemian-Early Weichselian sequence containing pollen and marine fossils at Fjpsanger, western Norwav

J A N M A N G E R U D , E I V I N D S " N S T E G A A R D , HANS-PETTER S E J R U P A N D S Y L V I H A L D O R S E N

BOREN

A complete interglacial cycle, named the Fjgsangcrian and correlated with the Eemian by means of its p o l l e n s t r a t i g r a p h y , is f o u n d i n m a r i n e s c d i m e n t s j u s t a b o v e the present day sea level outside Bergcn, w e s t c r n N o r s ' a y . A t t h e b a s c o f t h e s e c t i o n th e r e a r c t w o b a s a l t i l l s o f a s s u m c d Saalian (.rcrsr ult)) age i n w h i c h t h e m i n e r a l o g y a n d g e o c h c m i s t r y in d i c a t e lo c a l p r o v e n a n c e . A b o v e o c c u r beds of marinc silt.

s a n d a n d g r a v c l , d e p o s i t e d a t w a t e r d e p t h s o f b e t w c e n l 0 a n d - 5 0 m . T h e t e r r c s t r i a l p o l l c n a n d t h e m a r i n e firraminifera and mttlluscs indicate a cold-warm<old sequence with parallel devclopmenl of thc a t m o s p h c r i c a n d s c a s u r f a c e te m p e r a t u r e s . I n b o t h e n v i r o n m e n t s th e f l o r a / f a u n a in d i c a t c a n i n t e r g l a c i a l c l i m a t i c o p t i m u m a t l e a s t a s w a r m a s t h a t d u r i n g t h e H o l o c e n e . T h e h i g h r e l a t i v e sea lcvcl during thc E e m i a n ( a t l e a s t 3 0 m a b o v e s c a l e v e l ) r e q u i r c s y o u n g e r n e o t e c t o n i c u p l i f t . The uppermost marine beds a r e p a r t l y g l a c i o m a r i n e s i l t s , a s i n d i c a t e d b y t h e i r m i n e r a l o g y , d r o p stones and fauna, and partly i n t e r s t a d i a l g r a v e l s . T h c p o l l e n i n d i c a t e s a n o p e n v e g e t a t i o n t h r o u g h o u t these upper beds, and the c o r r e l a t i o n o f t h e d e s c r i b e d i n t e r s t a d i a l w i t h E a r l y W e i c h s e l i a n in t c r s t a d i a l s elsewhere is cssentially u n k n o w n . T h e s e c t i o n i s c a p p e d b y a n E a r l y W e i c h s e l i a n b a s a l t i l l containing rcdcposited fossils, s e d i m e n t s . a n d w e a t h c r i n g p r o d u c t s . S e v e r a l c l a s t i c d i k c s i n j e c t e d fr o m t h e g l a c i c r s o l e p e n c t r a t e the till a n d t h c i n t e r g l a c i a l s c d i m e n t s . R a d i o c a r b o n d a t e s o n w o o d a n d s h c l l s g a v e infinite ages. Amino acid epimerization ratios in molluscs support the infcned Eemian age of thc deposit. The Fj6sangcrian is c o r r e l a t e d w i t h t h e l l e m i a n a n d d e e p s c a o x y g e n i s o t o p e s t a g e - 5 e ; o t h e r p o s s i b l e corrclations are also d i s c u s s e d .

J u n M u n g a r u d u n d H a n s - P t t t e r S t j r u p , G t < l o g i s k i n s t i t u t t , d,d. B, Alterlt. 4t, N - 5 0 t 1 Btrgtn-Univcrsit(tct, Nt,rte); Ilit'ind Spnstegaard, Sogn og F.jordunc Distriktshqgsktb, Box J9, N-5801 Sogndal, Nonay; s1'bi Hultlorstn, Geologisktnstirut, Norgt's Lun<jbrukshotaskila, N-l$2 As, Norx ay; 27th M arch. 1 980.

I n t r o d u e t iu n F l x c a v a t i 0 n s L i l h ( ) \ t r a l ig r a p h y

M c l h o d s

T h e b c d r o c k a r o u n d l h e r i t e

Nomenclaturc of the lithostratigraphical units . . . . T h c S t r a u m e T i l l . . . .

T h c P a r a d i s T i l l . . . . . B ( ) u l d e r ) ' i l t h e d N S i l t b e d M

T o p o g r u p h y a n d h v d r o g r a p h l

S a n d b c d L . . . . . G r a v c l b e d K . . . . . .

1 3 8 P o l l e n s t r a t i g r a p h y . . . . . . 1 3 3 M e t h o d s

1 3 8 T h e d e v c l o p m e n t o f v e g e t a t i o n 139 Mollusc and foraminifera stratigraphy 1 3 9 M e t h o d s

1 4 0 D e s c r i p t i o n a n d d i s c u s s i o n o f t h e z o n e s l 4 l M a r i n e f a u n a in l u m p s o f g y t t i a f r o m t h e B l n e s T i l l l42 Conelation of Fjgsangerian with orher intcrglacials

14? Comments on the Quaternary stratigraphy of

143 Northwest Europe .

l 4 l C o r r c l a t i o n s b y m e a n s o f p o l l e n s t r a t i g r a p h y . . . . . 1 4 6 Z o o - b i o s t r a t i g r a p h i c a l c o r r e l a t i o n s w i t h E u r o p e a n

146 interglacials

1 4 7 C o n e l a t i o n w i t h t h e d e e p s e a s t r a t i g r a p h y . . . . . . . l4l Other interglacial sites in Norden

147 The Early Weichselian

1 4 9 T h e E e m i a n / W e i c h s e l i a n b o u n d a r y . . . .

153 The first glacial sediments

1 5 4 T h e F a n a l n t c r s t a d i a l

154 The Eikelund Stadial and thc first ice advance over Fjlsanger

S e a le v e l Acknowledgements References Appendix I A p p e n d i x l I

1 7 0 1 7 0 t 7 l 1 7 8 t 7 8 1 7 8 1 8 9 190 1 9 0 t 9 l

S a n d b e d J G r a v e l b e d I . . . . S i l t y g r a v e l b e d H S i l t b c d G

G r a v c l b c d F . . . . . . S i l t b e t l E

T h e B p n e r T i l l . . . .

T h e p r o v e n a n c e a n d s e d i m e n t a r y h i s t o r y o f t h e s i l t a n d c l a y f r a c l i u n \ . . . . . . .

T e c t o n i c \ l r u e t u r e \ G e o l e c h n i c a l a n a l Y s e : C h r o n o s l r a t i g r a p h y . . . . .

D a t i n g s .

Definition of losal chronostratigraphical units . . . . 1 5 8 1 6 4 1 6 6 1 6 6 1 6 6 1 6 9

192 l 9 l t94 194 t94 l9-s 1 9 5 t 9 6 1 9 6 1 9 8 t 9 8 201 205

138 Jan Munpcrud at ul.

Introduction

During the Quaternary glaciations Norway lav in a region of glacial erosion, so interglacial ie_

posits are extremely rare (Fig. l). Mangerud ( 1 9 7 0 a ) , w h e n o r i g i n a l l y d e s c r i b i n g f o s s i l s i n t h e till from Fjpsanger, came to the conclusion that this was the first find from Norway that demon_

strably belonged to an interglacial.

At Fjlsanger it is only the upper till, contain_

ing redeposited interglacial fossils, which can be s t u d i e d in a c c e s s i b l e s e c t i o n s . A c o r i n s i n l 9 7 t revealed that there were several differient beds below the till, but the samples obtained were so poor that we would have found it unrewarcline to c x a m i n e t h e m i n d e t a i l . I n s t e a d we decideJ to excavate by machine, which we started in 197-5 and continued in 1976 and lgi7. The result was the disclosure of a complete glacial_interglacial_

glacial sequence in which the interglaciaf layers contained pollen from the terrestrial vegetation and also marine fossils. We assume the aee to b e S a a l i a n ( s t ' n : ; r t la t t t ) - E e m i a n - W e i c h r e l i a n . Some of the results from the excavation have a l r e a d y b e e n p u b l i s h e d ( H a l d o r s e n et al. l97g:

Mangerud et al. 1977, 1979a\.

Tooogruphy und hydrography

l j p s a n g c r l i e s a t t h e e d g e o f t h e c i t y o f B e r g e n , in the midst of the fiord coastline of wesiern N o r w a y ( F i g . 2 ) . T h e s i t e lies near the present shoreline at the cnd of a small fiord known as Nordisvatn. Between this Sord and Bylorden, further north, there is a shallow valley along w.hich the town of Bergen now stretches ieig. :i.

The bedrock watershed between the two fi-oris i s o n l y 2 - 5 m a b o v e s e a level (Fig.4.y. On both sides of the valley there are high mountains up to 670 m above sea level.

At the Fj/sanger locality the side of the valley slopes steeply (20') up to 3-50 m above sea levej (Figs. -5 and 6). This is important for understand_

i n g t h e s e d i m c n t s : w i t h a h i g h e r s e a le v e l , s t o n e s and sand could roll and slide down to a consid_

e r a b l e d e p t h .

Nordisvatn is a 90 m deep glacially eroded lord with a sill only 3 m cleep, which means that the water in the fiord is distinctly layered. In the uppcr 20 m tcmperature and salinity vary greatly w i t h t h e s e a s o n s . B e l o w 2 0 m , s a l i n i t y is a p p r o r . 3 l % c t h r o u g h o u t t h e y e a r ( J o h a n n " r r . n - i 9 7 2 ) . R c d u c i n g ( a n a e r o b i c ) c o n d i t i o n s exist in the deepest parts with a high content of orsanic

L O W B O R T A

il"

l t g . / . L a s t I n t c r g l a c i a l ( E e m i a n ) sitcs (dots) in nurtherrr F i u r o p e a c c o r d i n g lo F r e n z e l il96g). In Norway. Swcden and F i n l a n d l a t e r d i s c o v c r e d sitcs are added: i F j 6 s a n g e r . 2 _ V o s s , J - K a r m d y . 4 - Mosvatn. -s _ Stcnberslt. O _ L c r s i l n i g p i . 7 \ o r t h e r n F i n l a n t l r r c r c r a l r i t c . ) . E _ R , ) v u . 9 _ N o v i n k y l d . T h e W c i c h s e l i a n ice maximum ilhick linc) is i n d i c a t e d a c c o r d i n g to B. G. Andcrscn ( l9g0). The z o o g e o g r a p h i c a l s u b d i v i s i o n {Feyling_Hanssen I9-s-5) o f t h c o c c a n i c s u r f a c e w a t e r i s also shown.

m a t e r i a l in t h e b o t t o m s e d i m e n t s (S t r 6 m I936).

At a higher sea level the hydrtrgraphy would be different. As noted above, with a sea level more than 2-5 m over today's level there would have been a channel running through the Bergen val_

l e y , i n w h i c h c a s e t h e l a y e r i n g of the water in NordAsvatn would have been broken clown (Fis.

4 ) .

Exco,tttttions

Before excavations were begun, seismic profiles u e r e t a k e n . lh e r e s u l t s i n d i c a l i n g r h a t r h e t l e p t h to the bedrock varied between 6 and l9 m in the area concerned. All thc excavations were carried out with excavators. Excavations l_4 (Fig. -5) were made during 197-5 and 1976, and -5_g in t 9 7 7 .

Excut,ation /. - We started at the same place that M a n g e r u d (1 9 7 0 a ) h a d w o r k e d p r c v i o u s l y in o r _ der to find out whether there were unctiiturbed beds directly under the fossil-bearing till. A silt bed (probably silt E) was reached about I m

B O R E A S t 0 ( r 9 8 1 )

^ . 1 \ C . ,.'N tr*"

, - o o o L A t : \ G ' "

M \ D - B O R E A L

B O R I - r A S l 0 ( 1 9 8 1 )

below the level of the road. Owing to technical difficulties we then moved to excavation 2.

I:-rcavution 2. - This is the main excavation;

nearly all the investigations of sediments and fossils were on samples taken from this site ( F i g s . 6 , 7 a n d 8 ) . W e d u g a d e e p n a r r o w t r e n c h which revcaled undisturbed sediments beneath thc till. We then proceeded to widen the trench i n o r d e r t o e x c a v a t e a s d e e p l y a s p o s s i b l e . B y the end of the season in 1975 we had reached dcrwn to bed L (Fig. 7). In l9'76 we widened the trcnch even more and reached the bedrock.

Altogether, more than 600 lorry loads of sedi- ment were removed from this excavation.

Excuvutions J-4. - Excavation 5 (Fig. 5) was s h a l l o w a n d r e v e a l e d m o s t l y B p n e s T i l l . I n e x c a - vation 4 only till was found. The dip of the beds i n c x c a v a t i o n 3 , h o w e v e r , in d i c a t e d th a t t h e t i l l in cxcavation 4 is below the interglacial beds, and thus is the Paradis or the Straume Till.

In excavation 6 (Fig. 9) the interglacial beds w c r c t h i n , i t b e i n g im p o s s i b l e t o d i s t i n g u i s h o n e f i ' o m t h e o t h c r . T h i s e x c a v a t i o n i s i m p o r t a n l . however. in so far as two thick beds of till were found at the bottom ( Fig. 9). E,xcavation 7 s h o w e d a r e l a t i v e l y c o m p l e t e s e q u e n c e a n d excavation 8 revealed a nearly complete se- q u e n c e (F i g s . 9 a n d l 0 ) .

1 9 7 I t r t r i n g . - A s m e n t i o n c d , c o r i n g w a s c a r r i c d o u t i n l 9 7 l s o m e w h a t s o u t h o f t h e e x c a v a t i o n sitcs (Fig. -5). The samples were taken at irregu- l a r i n t e r v a l s a n d e x a m i n e d i n 1 9 7 8 i n t h e l i g h t o f our experience from the excavations. We found t h e B o n e s T i l l , s i l t G a n d a l l b e d s b e n e a t h th i s d o w n t o g r a v e l K , a n d a t t h e b o t t o m a t i l l .

Lithostratigraphy

M<'th,tds

Ficldx'ork. - All the lithostratigraphical units were defined during the ficldwork and great cfforts were made to find unambiguous criteria for the boundaries of the beds. In excavation 2 the section walls were also measured precisely.

The fieldwork also took considcrable time on the practical side. There we re large masses of ma- terial to be removed; water had to be pumped out every day, the walls cleaned and fences put up, etc. In all, the fieldwork took 98 days with two or thrce men at work nearlv everv dav.

An Eemian-Early' Wcichsclian st'quancc 139 Grain-sizc distribution. - The analyses were m a d e a s d e s c r i b e d b y M a n g e r u d ( 1 9 7 7 ) . In t h e samples discussed in this article. CaCO,, was not removed. Some samples are shown on probality p a p e r ( F i g . 1 3 , e t c . ) a n d m o s t a r e p l o t t e d stratigraphically in Fig. ll. The curve had to be extrapolated for some of the clay rich samples in order to find the value for Q 16 to the parameters employed. A modified Wentworth scale was used with the clay-silt boundary at 2 microns, as proposed by Doeglas (1968).

Loss on ignition. - The samples were ignited for at least an hour at -5-50"C (Spnstegaard & Man- g e r u d 1 9 7 7 ) . T h e l o s s o n i g n i t i o n (F i g . l l ) g a v e a rough indication of the organic material content even though some of it was duc to other chemi- cal reactions.

CrtCO". - The CaCOr content was de termined by the addition of HrSOn to 0.2 g samples and measurements of thc gas pressure (Moum 1967).

M a t e r i a l u n d e r 4 m m w a s u s e d . i. e . w h o l e s h e l l s were not included. Thcre are. however. alscr many shell fragments in the shell-rich beds; the CaCOr curve (Fig. I l) therefore mainly indicatcs the content of shell and foraminifera.

Petntgruphl' oJ' thc pcbblcs. - Pebbles with a m i d - a x i s o f b e t w e e n I a n d l 0 c m , b u t m o s t l y between 2 and 4 cm, were used. Each sample c o n t a i n e d a p p r o x . 1 0 0 p e b b l e s . S i n c e t h e r c i s a gradual transition between many of the rock types in the area and it is difficult to distinguish between them. the rocks were divided into fcrur groups (Fig. l2). Rock identifications were car- ried out in the laboratory with the help of a magnifying glass, and all samples were checked b y c a n d . r e a l . A s b j p r n T h o n , w h o w o r k s w i t h t h e bedrock geology in the area.

R o u n d n c . y s . - R o u n d n e s s a n a l y s e s o f t h e p e b b l e samples were made before the rock types were d e t e r m i n e d . R o u n d n e s s . i n a c c o r d a n c e w i t h W a d e l l ' s ( 1 9 3 2 ) d e f i n i t i o n , w a s d e t e r m i n e d b 1 comparing with a type sample of nine classes ( 0 . l, 0 . 2 . e t c . ) i n w h i c h e a c h i n d i v i d u a l p c b b l e had been measured. The result was that for silt b e d G l t h e m e a n r o u n d n e s s w a s 0 . 2 8 . w h i l e t h a l for the rest of the samples was 0.20 or lower. Wc have therefore shown only the content of rounded and well rounded oebbles in each sam- p l e ( F i g . l 2 ) .

l4O Jan Mangerud et al' B O R E A S l0 ( 1 9 8 1 )

F i g ' 2 . A t o p o g r a p h i c a l m a p o f t h e B e r g e n a r e a . H o r i z o n t a l h a t c h i n g o n t h e s e a ' C o n t o u r i n t e r v a l l 0 0 m . T h e l e t t e r s a r e a b b r e v i a t i o n s f o r n a m e s u s e o i n t h e t e x t : F - F j / s a n g e r , B - B o n e s , P - - P a r a d i s , N - N o r d i s v a t n e t , s - s t r a u m e , H - H o p ' G - Grimstadfiorden, U - Ulriken. ihe ins"t mup is a simplified bedrock geology map of the Bergen-Nordisvatn area, with the same scale as the main maP.

Geochemistry and clay mineralogy. - Thirty-one samples from different beds were analysed' Each sample was divided into three subsamples, and the values given in Fig. 34 are the average of each set of subsamples. Separation of the frac- tions < 2 g,m, 4-8 pm, and 32-63 p.n was carried out in sedimentation cylinders after organic mat- ter was removed with dilute HrOr' Separation of different parts of the clay fraction was done by centrifugation. The geochemistry of each frac- tion was studied by atomic absorption spectro- photometry and flame photometry, and the re- iults are given as weight percentages of oxides (Fie. 3a).

The mineralogy of fractions < 2 g,m and 4-8 pm was also studied by X-ray diffractome-try, mainly by the methods used by Roaldset (1972) and Haldorse n (197 4). Semiquantitative calcula- tions of the mineral contents (Fig. 3a) are based on peak intensities' However, the area of the

3.18-3.20 A peak was halved to make the plagioclase values more comparable with those of illite and chlorite.

The bedrock around the site

The minerogenic components of the Fjlsanger deposits are supposed to have been derived muinly from bedrock within a few kilometres of Fjpsanger, which is therefore briefly described, mainly based on Kolderup & Kolderup (1940)'

The main valley extending from Nord6svatnet to Bergen is dominated by a complex of mica schist, green schist and zones of mylonite and phyllonite (Fie.2, inset) called the Minor Bergen Arc. Fj/sanger is situated within this bedrock complex, near its western boundary. The moun- tains east and west of the Minor Bergen Arc consist mainly of granite and gneiss. Further east

B O R E A S l0 f l 9 8 1 ) An Eemian-Early lV eichselian seque nce I4l

-J. An aerial photo towards north, ofthe Fjdsanger site (cf. Fig. 2). Excavations 2 and 8 are marked, for the others compare 5. Gulstein is the summit to the left of Ldvstakken, outside the picture.

Fig

F i o

there is an arc dominated by anorthosite and other gabbroid rocks (Fig. 2).

Great parts of the bedrock are exposed, particularly at the mountains and in the valley sides. The thickness ofthe unconsolidated sedi- ments in these areas rarely exceeds l-2 m. The till and also other unconsolidated sediments within the area are predominantly composed of locally derived material.

Nomenclature of the lith<tstratigraphical units

The marine beds at Fjgsanger are nearly all local, sublittoral facies which are quite obviously limited in extent. All the units are therefore classified as informal beds. During the fieldwork we used letters (A, B, C, and so on) to distin- guish the beds, beginning from the top. We have kept these designations here and have added a

2 A

0 - 2 4

1.0 - 6 0

- 8 0

1 0 0

Fig. 4. A longitudinal profile from Grimstadfiorden (Fig. 2) through the deepest part of Nordisvatnet and along the floor of the Bergen valley to Byforden. A little further out Bylorden is 450 m deep.

G n m s t a d f t a r d e n 1 \ , ^ N o r d d s v o t n e t

142 Jun Muttgt'rud ct ul.

Firi. -5. A dctailcd map ofthe Fii'lsangcr area All the excava- t i o n s a r e m a r k e d w i t h t h c n u m b c r s u s e d i n t h e t e x t . S t r a u m e v e g c n i s t h c n a m c o f t h c r o a d ( v c g e n : r o a d )

s i m p l e li t h o l o g i c a l d e s c r i p t i o n , e . g . s i l t E . g r a v e l F . e t c . ( F i g s . 7 a n d 9 ) .

The till beds have been given formal names, since their extent may well be greater. In cor- relating the tills, rcference must be made primarily to the lithostratigraphical units, while the marine beds can be correlated for the most part by means of the biostratigraphical or chronostratigraphical units. For the tills we have uscd geographical names beginning with the let- ter the till was identified with in the field, e.g.

till S is called the Straume Till.

The stratotypc (Hedberg l9'76:37) for both the Straume Till and the Paradis Till is excavation 6.

The geographical names originate from districts

B O R L , A S l0 ( l 9 8 l )

around Nordisvatn (Fig. 2). Straume lies around the outlet ofthe fiord, and Paradis is a suburb of Bergen just east of Fjpsanger. The stratotype for the B0nes Till is excavation 2. Bpnes lies along Nordisvatn, southwest of Fjpsanger'

The Straume Till

This till was found only at excavations 6 and 8 (Fig. 9). It is at least 4 m thick but the seismic profiles indicate that there could be a good 5 m more down to bedrock. The till is extremely hard and was difficult to excavate even with a large machine. It is unsorted and contains a fair pro- portion ofboulders; the clay content is over l0%

(Fig. 13). It is light grey in colour' No fossils were found. The pebble material is of local origin (Fig. l2) but the presence of greenschist indi- cates that some of the material was derived from the valley bottom to the east' The till is a basal till. It must be older than the FjOsangerian (Eemian) and is therefore most probably of Saalian (.sertstl /ttro) age.

On some of the stones in the Straume and Paradis tills and on the underlying bedrock there is a thin layer (under I mm) of diagenetically precipitated pyrites up to l0 cm2 in size. Apart from the reducing conditions, time is clearly an important factor in the formation of such large pyrite crystals. Similar pyrites in till have not previously been described from Norway, prob- ably mainly because most tills are not ncarly so o l d .

Thc Paradis Till

In excavation 6 (Fig. 9) the Paradis Till is 3 m thick and rests on the Straume Till, the boundary being well-defined. The Paradis Till is darker, looser, and contains far less clay than the S t r a u m e T i l l ( F i g s . l l a n d l 3 ) .

There is a till on the bedrock in excavation 2 which, in grain-size distribution (Fig. l3)' petrography of the pebbles (Fig' l2), and in the mineralogy of the silt (Fig. 34), resembles the Paradis Till in excavation 8 so closely that it would seem it was thc samc till; the gravel content in excavation 2 is higher than in excava- tion 8. however. Since the long axes of the stones are oriented parallel with the slope of the rock surface (Fig. l4) we assume that this till has slumped after primary deposition.

The surface of the bedrock (Fig. l-5) in cxcava- tion 2 slopes 32' towards E. On this surface there

5 0 m

Bones Titt (Weichsetion)/"

,eaft '

vi,i':'tiis"td n" sediments

'/////////////"

emion sediments

S e o l e v e { + F - 0 P o r o d r s l r l l l 5 0 0 l r o n l

Fig. 6. profile down the hillside excavation 2 (Fig. 5). Outside the excavation the depth to the bedrock is determined by seismic refraction measurements. The position ofFig. 7 is indicated. No vertical exaggeration.

B O R E A S l0 ( 1 9 8 1 ) E S E

are clearly identifiable glacial striae WSW (240'), which probably correspond with the ice move- ment that deposited the till. There are also older striae. 280'. in a direction across the valley. On the surface of the bedrock there is a one to several cm thick compact 'sand-layer' which is finer grained than the matrix in the remainder of the till.

There is no green schist in the Paradis Till (Fig. 12), which may indicate that the ice move- ment was more along the Bergen valley than during deposition of the Straume Till. We as- sume that the difference between the Paradis and Straume tills is because the ice movement changed direction. There is no indication of any substantial difference in the age or genesis of these two tills.

Bouldery silt bed N

Bouldery silt N is 20-30 cm thick and was found only in the westernmost part of excavation 2, where it wedges out some 17 m from the road.

The framework in this bed consists of boulders and cobbles, most of which were from 10 1o 20 cm in size though some were as large as 30 cm' The matrix is graded, with sand at the bottom and silt higher up. Locally in the matrix there are discontinuous lamina running parallel with the boundaries of the bed. The boundary with the Paradis Till is easily distinguishable by the great-

An Eemian-Early Weichselian sequence 143

er quantity ofboulders in bouldery silt N and by its better sorted and hne-grained matrix' It is obvious that the framework clasts were depos- ited first, either by being washed out of the till or by a landslide. Later the matrix filled the inters- tices between the boulders. No macrofossils were found in this layer, but dinoflagellate cysts and a few foraminifera show that the bed is marine. Pollen analyses (Fig. 4l) indicate that the matrix was deposited over a period of time.

Silt bed M

The lower boundary of silt M is defined by the appearance of a considerable element of sand and gravel in the matrix as compared with the top of bouldery silt N, which is richer in silt (Fig.

11). The boundary is sharp but wavy where it overlies the large boulders in bouldery silt N.

The thickness of silt M is on average 40 cm, but varies laterally.

Silt M consists for the most part of clay, silt and sand with pebbles and cobbles dispersed in this matrix. In the western part of excavation 2, the bed is distinctly subdivided into three zones with a more sandy layer at the bottom, silty in the middle, and sandy again at the top. The upper sandy layer is designated Ml (Fig. 11) and the other two as M2.

The bed changes colour from greyish-green at the bottom to a light brownish-green at the top.

144 Jan Mangerud et al.

m o . s , l .

D i s t o n c e f r o r i t h e r o q d

F i g . 7 . T h e s t r a t i g r a p h y o f t h e c e n t r a l p a r t o f t h e s o u t h e r n w a l l o f e x c a v a t i o n 2 i n 1 9 7 6

B O R E A S 1 0 (l 9 8 1 )

Cf. Figs. 6 and 8.

d " " ;

;i';..t"

i,,'.,t:::.it .

Flg. 8. Photo-mosaic of the southern wall of excavation 2. The wall is not straight, and the apparent thicknesses, dips, etc. of the beds are therefore not exactly true. Due to washing with a fire engine, the apparent cobble content in the sandy layers is too high.

The water level in the bottom is approximately I m above sea level

BOREAS l0 (1981) An Eemian-Early Weichselian sequence 145

EXCAVATION 6

.i\) ? z\(

^" rl\ - 66re' /Sond L

Stroume TiLl

We assume this is due to an increasing content of organic material, but this scarcely shows in the curve for loss on ignition (Fig. 1l).

Marine molluscs are present throughout the bed with the content increasing upwards (as appears from the CaCO, curve in Fig. 11). The silty zone of the western part of excavation 2 contains abundant Chlamys islandica. Silt M was also found in excavation 7 as a grey silt with some pebbles. Here, however, the bed cannot be subdivided.

Silt M marks the beginning of normal marine sedimentation. Interpretation of the marine units at Fjpsanger is closely linked with the sedimen- tation environment at the site. The mineroeenic

/ /

/ / /

/ / '

m o s l0

part of all the marine beds consists of two distinct components: (l) Material deposited through suspension. This material may have been brought out into the fiord by waves, rivers or glaciers and consequently may have been transported long diStances; (2) Coarser particles (sand, gravel, boulders), which were mainly de- rived from the shore above. It is so steep here (Fig. 6) that any particles coming out into the sea could roll, slide or fall through the water to considerable depths. Some stones could also have been transported by winter ice and, in glacial conditions, with icebergs.

The grain-size distribution in silt M is bimodal or polymodal. Fig. 16 (sample 653) shows a

EXCAVATION 8

t - - '

Distonce from the rood

Fig. 9. The stratigraphy ofthe southern walls ofexcavations 6 and 8, the eastern wall ofexcavation 3 and the northern wall of excavation 7. (Locations in Fig. 5.)

146 Jan Mangerud et al'

Fig- 10. The western wall of excavation.8' Some beds are mirt<ed wittr letters. Note the light clastic dike in the lower part.

typical example of the silty part of M2' It cor- ,irt, of u coaise population transported along the bottom (forming 567o of the sediment) and one or more fine-grained populations deposited from suspension.

ttt" ttlgtt proportion of fines (Fig' 11) may to some extent be due to the fact that the water was relatively deep on account of isostatic depres- sion from the former glaciation' Probably more

BOREAS l0 (1981) important, however, was the absence of dense vlietation on the freshly deglaciated land' with thJresult that erosion and thus the supply of silt was greater than later during the interglacial'

Sand bed L

In some places there is an even transition be- tween silf M and sand L, while in other places the boundary is sharp with a layer of gravel at the bottom of sand L. Sand L is easiiy disting- uished from all the beds below by its texture -

sorted sand and fine gravel (Fig' l7) with less boulders and less clay. The average thickness-is

""fV f S cm, but the bed is extensive and can be found ovet the whole of excavation 2 as well as in excavations 7 and 8.

As appears from Fig. l l the sediment changes

"hu.u"i". at the boundary between silt M and sand L. The mean grain size and kurtosis.in- creases. This is a consequence of the proportlon of sr,sp"nsion-deposited material being much less than in silt M. There is nevertheless still a tail of fine material (positive skewness)'

Gravel bed K

The boundary between gravel K and sand L is well defined by a layer of pebbles 2-10 cm in diameter at the bottom of gravel K' The mean thickness of gravel K is 30 cm' It can be found across ttre rw'hote of excavation 2 and also in excavations 7 and 8.

The framework in the bed consists of well- sorted gravel with the grain size decreasing towards the top. Throughout the bed the clasts are largest ln ttre western part decreasing downslJpe eastwards' This indicates that the bed has been deposited relatively close to the shore, the decreasing grain size being a result of increasing depth and distance from the shore'

The clasts are angular, i'e' there has been no rounding by wave action' This is similar to conditions --ihe in the fiord todaY'

matri* is grey-brown clay and silt with some organic material and many shell fragments' Th" ,"Ji-"nt is therefore markedly bimodal (Fig. 17) with a deficiency in the sand fraction' it seelms titat the matrix has been deposited mainly through suspension and has filled the pores between the gravel.

The bottom ofgravel K can be regarded as the

B O R E A S r 0 ( t9 8 t )

top ofa cnarsening-up sequence starting with the matrix in bouldery silt N (see grain-size distribu- t i o n a n d m e a n g r a i n s i z e , F i g . l l ) . T h e s i m p l c s t interpretation of this sequence is that there has becn a relative lowering of the sea level, caused by a glacial isostatic uplift. which also agrees w i t h t h e f o s s i l c o n t e n t .

Sund hcd J

The boundary with gravel K is sharp and defined b y t h e g r a v e l c o n t e n t b e i n g m u c h l e s s in s a n d J t h a n i n g r a v e l K , w h i l e t h e r e i s n o s u b s t a n t i a l c h a n g e i n t h c m a t r i x ( s i l t - c l a y ) .

S a n d J i s g r e y - b r o w n , 1 5 - 8 0 c m t h i c k , a n d c o n s i s t s o f w e l l - s o r t e d s a n d w i t h a c l a y - s i l t m a t r i x ( F i g . l 8 ) . T h e b e d i s c o m p a r a t i v e l y m a s - sive but there are some thin stripes of gravel (Fig. l9) which can be traced for many mctres parallel with the boundaries of the bed. In these stripes the grain size decreases down slope and flat stones lie parallel with the layer. indicating that the coarse particles have been transported from the shore.

In addition to the stratigraphical samples (Fig.

I l ) . w e a l s o m a d c g r a i n - s i z e d i s t r i b u t i o n analyses of a number of samples along thc bed ( F i g . 2 0 ) , f r o m b o t h t h e t o p and the bottom.

S i n c e th e b e d d i p s t o w a r d s th e c a s t ( F i g . 7 ) , t h c s e d i m e n t s i n t h e s e s a m p l e s h a v e b c e n d e p o s i t e d at different depths. The samples reveal an in- creasing content ofclay with increasing depth of s e d i m e n t a t i o n . w h i c h i n d i c a t e s t h a t t h e s e d i - m e n t s h a v e b e e n d e p o s i t e d i n s u c h s h a l l o w w a - ter that depth differences of only a couple of metrcs havc been significant for the sedimenta- tion cnvironment. We assume that the differ- ences in clay content are due morc to tidal currcnts than to waves. Thc samples also show ( F i g . 2 0 ) t h a t t h e r e i s l e s s c l a y a t t h e t o p o f the bcd than at the bottom.

S a n d J v a r i e s g r e a t l y in t h i c k n e s s . b u t s h o w s a general increase down the slope. At the eastern e n d t h i s i s b c c a u s e o f l a t e r fo l d i n g . T h e i n c r e a s e i n t h i c k n e s s , h o w e v e r , i s t o s o m e e x t e n t p r i - m a r y . T h i s c a n b e s e e n a t a b o u t 1 6 m f r o m t h e r o a d ( F i g . 2 l ) , w h e r e a t h i n l a y e r o f g r a v e l s t a r t s from the top of gravel K and runs into sand J.

This thin layer ofgravel also shows that gravel K and sand J are to some extent only different facies of the same sedimentation unit. the bot- tom of sand J in the east and the top ofgravel K in the west having been deposited at the same t i m e .

An Eemiun-Eurly l4cit hscliun scqut'n< a 147 Gruvel bcd I

T h e b o u n d a r y b e t w e e n s a n d J a n d g r a v e l I is transitional. In the field this bounclarv was de_

f i n e d b 1 a m a r k c d i n c r e a s e in g r . i r v c l p a r t i e l e r . T h e g r a i n - s i z e d i s t r i b u t i o n ( F i g . l l ) s h o w s t h a t the matrix also changes - clay disappears and silt i s m u c h r e d u c e d .

T h c g r a i n - s i z e d i s t r i b u t i o n is e x t r e m e l y c v e n t h r o u g h o u t t h e b e d . A t y p i c a l e x a m p l e is g i v e n i n F i g . 1 8 . T h e b e d i s m a s s i v e b u t i n a few places a t i i l f u s e la y c r i n g c a n b c l r . r e e d

The bcd is characterizcd by its biogenic com_

p o n e n t s : ( l ) a b r o w n i s h c o l o u r , a n d dark browrr a t t h c t o p b e c a u s e o f o r g a n i c m a t e r i a l ( F i g . I l ) , a n d ( 2 ) a h i g h c o n t e n t o f s h e l l , l a r g e r than the C a C O . , c u r v e ( F i g . l l ) i n d i c a t e s . s i n c e whole s h e l l s a r e n o t i n c l u d e d in t h e c a r b o n a t e a n a l v s i s . T h e s h a r p b o u n d " r i c s . m a x i m a e t e . in the ptlllcn d i a g r a m tF i g . 4 l ) s h o w t h a l t h c s r t l i m c n t r . r r r s d e p o s i t e d s l o w l y a n d s u c c e s s i v e l y w i t h o u t a n v I n l e r h o m o g c n i z a t i o n . F o s 1 f i s * . r c r r , . r n r . i t i , assumed that gravel I was depositcd deeper than t h e w a v e t r c t i o n z o n e . T h c g e n e r a l unguiar.ity , r f t h e s t o n e s a l s o in d i c a t e s t h i s ( F i c . 2 2 ) .

S i l t y g r u v e l b e d H

T h e l o w e r b o u n d a r y o f t h i s b e d i s d i s t i n c t a n d a h i a t u s p r o b a b l y e x i s t s h c r e . T h e s e d i m e n L c h a n g e s c h a r a c t e r c o m p l e t e l y c o m p a r e d w i t h t h c b e d b e l o w i t . T h e b o u n d a r y i s d e f i n e d b y t h e increase of both cobbles and silt/clay.

The framework in the bed consists of poorly roundcd cobbles and pcbbles of the local rock t y p e s ( F i g s . 2 a n d l 2 ) . T h e m a t r i x c o n s i s t s m a i n l y o f s i l t a n d e x t r c m e l y f i n c s a n d . T h e sediment is thus pronouncedly bimodiil with one modal class in the gravel fraction and the other at t h e b o u n d a r y b e t w c e n s i l t a n d s a n d . C o m p a r c d w i t h t h e b e d s b e l o w , t h e c o n t e n t o f C a C O . , is v e r y l o w . O n t h e o t h e r h a n d . t h e c o n t c n t o { ' organic material is higher and thc matrix is therefore a plastic silt-gyttja. Apart from this the bed is characterized by a quantity of flattencd chitin-tubes of polychaeta which hang in the s e c t i o n w a l l l i k e t h r e a d s (F i g . 2 3 ) .

I n e x c a v a t i o n 8 ( F i g . 9 ) t h e b e d i s o f a s i m i l a r character but the matrix contains much less organic material and the lower boundary is not a s d i s t i n c t a s i n e x c a v a t i o n 2 , p o s s i b l y b e c a u s e n o h i a t u s e x i s t s in t h i s e x c a v a t i o n (p . 1 7 0 ) .

In view of the high content of gravel and boulders, and also based on the foraminifera

148 Jan Mangerud et al. B O R E A S r 0 0 9 8 1 ) S o r t i n g o*- 08r- Sre_{Y 2}

2 3 4 5 6

G r a i n s i z e d i s t r i b u t i o n

1 1 5 6 3 m i c r o n

I I l o F l m q 6 4 ? 9 9

E i k e l u n d

G u t s t e i n

An Eemian-Early Weichselian sequence 149

BOREAS l0 (1981)

B O n $ T i l l Grovel F S i l r G l s i l t G 2 Silty srovel H Grovel I I l l

mylonite, phyl lonite, qudilzire

ffi c*r" Flllc*""schLr lA.onh"*e

Fi g. t 2. T o the left petrographical composition of pebbles from some beds. To the right the percent of rounded pebbles in the same samples.

fauna, we interpret the bed as having been depos- ited in shallow water. The high content of silt is probably because of severe erosion on land due to the deterioration of the climate and the en- suing deforestation. The organic matter is also mainly of terrigenous origin and is probably a local facies. Similar organic sediments can be seen in shallow bays along Norwegian fiords today.

Silt bed G

The lower boundary of this bed is relatively sharp and is defined by an increase in clay and silt and a decrease in the content of larger particles. The latter float in the matrix.

The bed has been divided into three parts (Fig.

7) by distinguishing a cobbly layer G2. The lowest part of the bed, G3, is extremely fine grained (Figs. ll and24). In places this layer is dark brownish-grey due to organic material' while in others it is a bluer grey. Higher up silt G is paler.

The transition from silty-gravel H to silt G has been interpreted as in the first place due to a large increase in the supply of minerogenic ma- terial deposited from suspension. It is, however, also possible that the water depth increased because of glacio-isostatic pressure.

The cobbly layer G2 consists mainly of stones from 3-10 cm in sizb, some even larger. Most of them float in the matrix. The matrix is rich in clay like G3 so that, sedimentologically, the fine

Fig. 11. The lithostratigraphy and some lithological parame- ters. Note the changing depth scale. The indicated thicknesses of the beds are the average thickness in excavation 2. Below the gap in the curves in the Paradis Till the thicknesses are from excavation 6. All the samples are from excavations 2 and 6.

1o-Boreas 2/El

150 Jan Mangerud et al.

a 8

Fig. I 3 . Typical grain-size distribution curves for the different tili beds. Nearly all samples from the Bones Till lie between the two given curves (51 and 59).

N

Fig. 14. Fabic of the long axis of 106 pebbles in the Paradis Tiil in excavation 2. The slope of the underlying bedrock surface and the direction of glacial striae on the surface are also indicated.

material in G2 and G3 can be regarded as one

unit. The long axes of the cobbles are parallel with the dip of the layer (Fig. 25). It looks as if the cobbly layer (Gr) has been deposited by a submarine slide which probably started from the shore. The rock types are local (Fig' l2) as in the beds below. There are more shells in G2 than in

Fip. /J. The Paradis Till in excavation 2, and the underlying bel<lrock. The simple anow indicates the youngest glacial striae, and the double-headed arrow the oldest' Much of the finest in the till was washed out through cleaning of the section with a fire engine.

the underlying G3, but hardly any of the shells in G2 were found in living position' The shells were probably carried down in the slide, so some of ih"- .uy be older. The species are about the same as in G3 and may indicate a more numer- ous fauna in shallower water. The cobbly layer appeared in excavations 2 and 7 but. not in the olh"... which indicates a fairly local slide'

The upper part of silt G, designated G I ' differs from the lower parts by containing considerably less clay (Figs. I I and 24). The grain-size dis- tributions of the silt and clay fractionp are very alike in all the samples from Gl, while the sand and gravel contents vary. Pebbles and cobbles are scattered except for a stripejust about in the middle of Gl, where the pebbles are more fre- quent (Fig. 7). Even in this stripe the distalce between each pebble is several cm' The petrography of the pebbles in G I is unlike any of ih" luy".. below (Fig. 12). There is far -more anorthosite, which in the bedrock is found further south and near the higher mountains (Gulfiellet) to the east. There is also more gneiss, whicir is found in the mountains on both sides of the valley. On the other hand there is less of all the rocks (mica schist, etc.) found in the bottom of the valley. The allochthone pebbles must have come in with floating ice. Theorbtically this could be winter ice. However, both the number and the petrography render this improbable and we conclude that the pebbles were dropped from icebergs.

Other arguments for Gl being a glaciomarine sediment include the likelihood that this thick silt bed was deposited from suspension in an ex-

B O R E A S l0 ( 1 9 8 1 )

I r o 0 0

6 5 1

t 6 3 1 6 3

- 3 , h l

) , - ) , :

I l , '

-r- +- t . / l

- 1 . . 1 -

z \

B O R E A S l0 ( 1 9 8 1 )

fiiln:;*l"ffi iij"",'F"'":jti.:,ijliifi :jl:

tionr.

An Eemian-Early Weichselian sequence 151

tA17 2

Fis. 18. Grain-size distribution curves for typical samples from sand J and gravel I.

Fis. 19. Gravel K, sand J with two thin gravel layers' and

"t""r"ii f"-ift" "*h wall of excavation 2' where sand J is only l0 cm thick.

- n 'l- 't"

8 t 6 3 1 6 3

l h

6 5 4

! 6 3 1 6 3 r o 9 l Vt

t4tt

l 2

' o , ) , , ' "

; : \ a a v t v * , o ' o o ' '

- L l | l -

1 2 a 8 t 6 3 1 6 3

Fig- I 7. Grain-size distribution curves for typical samples from Sand L and gravel K'

152 Jan Mangerud et al'

% ctoy

Fig. 20. Clay content in samples from sand J in excavation 2' talen paraliel with the dip of the bed. The scale for the abscissa is the horizontal distance from the road' Below that' the approximate height of the middle of the bed at each sampling point is given (cf. Fig. 7)'

Fig. 2 I . A detuled sketch from the southern wall of excavation 2 (Fie.7) showing a layer of pebbles extending from the top of gravel K into sand J. The scale for the abscissa is the distance from the road (no vertical exaggeration).

Fig.22. Pebbles from gravel I showing the poor roundness which is typical ofall beds except GI at Fjdsanger (seeFie' 12).

Fig.23. The silty-gravel H, and parts ofbeds G3 and I in the western wall of excavation 2. Note the threadlike remnants ofoolvchaeta in bed H.

Fig. 24. Typical grain-size distribution curves for different oarts of silt G.

1 6 3 1 6 3

B O R E A S l 0 ( l 9 8 1 )

/ B o s e o l t h e b e d

m f r o m t h e r o o d 0 . 5 m o s . l

B O R t T A S l0 ( l e 8 l )

l c i e . 2 5 . F a b r i c o f t h c l o n g a x i s o f 7 8 p e b b l c s fr o m s i l t C 2 .

tremely turbid fiord, that it contains drop stones, and that it has a poor marine fauna. Furth- ermore, the layer has a considerable horizontal e x t e n s i o n , s i n c e it i s f o u n d i n e x c a v a t i o n s 2 , 3 , 7 ' and 8 (Fig. 5) with about the same thickness and appearance. The geochemical analyses (Fig' 3a) reveal that the coarse silt (32-63 microns) in Gl has another provenance than that in the sedi- ments below. The most obvious explanation is increased transport from the anorthosite areas.

We therefore conclude that silt G I is a glaciomarine sediment deposited while glaciers were calving in the fjord only a few km from Fjpsanger. Our observations do not permlt our determining whether these were outlet glaciers from an ice sheet or from plateau glaciers on the adjacent mountains. Looking at the present snow line. however, it is obvious that if there w e r e a c o r r e s p o n d i n g d e t e r i o r a l i o n in l h e c l i - m a l c t o d a y . g l a c i e r s r . r o u l d c o m m e n c e t o d c - velop in the mountain areas east of Bergen. We assume thcrefore that during the deposition of s i l t G l ( n a m e d t h e G u l s t e i n S t a d i a l , p . 1 7 0 ) there were local glaciers in thc nearby moun- tains, though the development of an ice cap must also have begun in the higher mountainous areas of southern NorwaY.

Gravel hccl F

The lower boundary of this bed is defined by a great increase in sand and a corresponding de-

An Eemian-F,arly Weithselian seqttcncc 153

S I L I

3 0 2 0

5

T I

I

I

', ,/

. 4 _

,'/

S i l r E

Y

I L :

r V

G r o v e

T

76t i : ^

I ' - r l

-r / { /

, ) / t / .

.r'

/ /

l l l l

'ff-;',

. 4 + . . . n - r ' ) u

. t ;

' t l i r

riu tb3

M i d d e E o r e

/ /

, - * , /

, I ./ ',.t

r , / {

V /

'uiar

"

/.!

r'*4

/

//

./.r''

' / ' ../

l i

r 2

F i g . 2 6 . T y p i c a t g r a i n - s i z e d i s t r i b u t i o n c u r v e s f r o m g r a v e l F a n d s i l t E .

crease in silt. The boundary is relatively well marked. but a transition is evident as the content of sand and gravel increases in the upper part ot s i l t G ( F i C . ll ) , i n d i c a t i n g t h a t t h e r e is n o h i a t u s . Small deformation structures, e.g. load casting, occur here and there on the bed boundary.

Gravel F is characterized by an abundance of shells and foraminifera, and a correspondingly h i g h C a C O 3 c o n t e n t ( F i g . l l ) ' a n d a l s o b y t h e fact that the minerogenic part is nearly all sand and gravel with some boulders.

In excavation 2, where this bed was studied in detail. there is an internal zoning' At the bottom there is grey sand passing upwards into sandy gravel. This zone is 25-30 cm thick (samples ' / 5 3 J 5 7 , F i g s . l l a n d 2 6 ) ' A b o v e t h i s c o m e s l0-12 cm (sample 759) brownish-green silty sand containing a large quantity of small shell frag- ments. in addition to the unbroken shclls found throughout gravel F. Above this again there is sandy gravel (samples '761-762).

The petrography of the pebbles in gravel F is similar to that in the underlying beds' apart from Gl. This indicates a transport from the shore above. The same applies to the geochemistry of the coarse silt (32-63 microns, Fig. 34), which indicates that no more ice-eroded material was supplied.

G r a v e l F w a s f o u n d i n e x c a v a t i o n s 2 ' 3 . 6 , 7 , and 8 and is of about the same thickness and appearance in all the sections, even though the content of boulders varies somewhat. The bed

5 / 3 2 l 0 l 2 J t n l

1A1 i/6 \/s \ i/, I 2 r 3 nd

3 j 6 3 l O O 0

154 Jan Mangerud et al.

rr*

V , 4 ' ' - r , o : '

B O R E A S l0 ( 1 9 8 1 )

defined but with transition from gravel F in so far as there is more sand at the bottom of E than further up.

Silt E consists of almost pure silt and clay (Fig. 26) with a small content of pebbles. The bed is evenly thick, 40-60 cm throughout exca- vation 2 and about the same in excavations 3 and 7, where it was also found. In the main it is massive. However, there are a few long black, iron sulphide stained lenses parallel with the bed. In excavation 7 (Fig. 9) there is a zone of 15-20 cm at the bottom of the bed with much gravel in the silt.

Silt E is interpreted as a marine sediment since it contains both foraminifera and molluscs. The geochemistry of the coarse silt fraction (Fig. 3a) resembles silt G1 and thus indicates a transport of material from glaciers. Silt E is therefore probably glaciomarine.

The BOnes Till

The Blnes Till is characterized by its high con- tents of clay and silt, and also by the fact that it

I silfe,1," l ri

Fig. 27. Details from the boundary between silt E and the B/nes Till in the southern wall of excavation 2. Here the lower part of the till is full of small gyttja lumps (all the black spots). In the right part the boundary between the till and the silt is drawn. The till is (glaciotectonically) fingering into the silt. Boirndaries for lenses of till/gyttja in the silt are also drawn. The blade of the knife is

l 0 c m .

was traced from approx. 12 m above to about 2 m below sea level. Although this indicates a depth range ofat least 14 m during deposition, no significant lateral variations were found, and the bed everywhere conformably overlies silt G without any trace of erosion at the boundary.

Both these observations indicate that even the top of the bed must have been deposited at a depth of several metres.

Sedimentologically, gravel F can be compared with the early interglacial beds, sand L and gravel K, apart from the fact that there are coarser particles in gravel F. Gravel F is thus interpreted as having been deposited in an in- terstadial (Fana, p. 170) in which glaciers had retreated and in which the sedimentation condi- tions were almost the same as early in an inter- glacial period. This agrees with the interpreta- tion of the molluscs and foraminifera.

S i l t b e d E

The lower boundary is fixed where the matrix passes from sand into silt. The boundarv is well

t ] ' t n , ' t .

$

B O R E A S r 0 ( 1 9 8 1 )

contains redeposited wood, lumps of gyttja' shells, foraminifera, and other fossils' The till and its content of fossils have been described earlier by Mangerud (1970a).

Whether the Bdnes Till was deposited shortly after silt E or whether it is a hiatus at this boundary is of great interest. The boundary is well defined everywhere. In most places there is a transition zone of approx. 10 cm where there are subparallel lenses and tongues (Fig. 27) ofsilt E and Bpnes Till. This shows that the till has moved on the silt while both sediments have been plastic. There are no clear indications of erosion, however. There is also a strong stratigraphical argument against any erosion of superimposed beds or of silt E: a relatively complete marine sequence can be found in four of the excavations (2, 3 , 7 , and 8, Figs. 1 and 9) . In three of these, silt E is the youngest marine bed and its thickness is about the same every- where. It would be most surprising if glacial erosion had stopped at several different places just at this stratigraphical level, so we conclude that there is probably no erosional unconformity between silt E and the B0nes Till.

The Bgnes Till is unsorted but varies some- what in grain-size distribution (Fig. 13). The colour is brownish-grey. In one place fissility structures parallel with the lower boundary were observed. Apart from this, and some special features described below, the bed is massive. In excavation 2 (Fig.7) the till is 3-5 m thick. It was also found in excavations 1 and 3 and several places along the road.

In excavations 7 and 8 the upper till is more sandy than the typical B@nes Till, and in excava- tion 8 fewer fossils were found. We have there- fore not classified these tills as B@nes Till, even though parts of them are probably facies of the B g n e s T i l l .

Sitt BlC. - In the lower part of the B@nes Till there is an irregular silt layer which could be followed along the whole of excavation 2 (Fig.

7). During fieldwork, the till over this layer was called B, while the till under was called C. The two tills are indistinguishable by criteria other than their position over or under silt B/C (Fig' 28). An extension ofthe excavation to the north- west revealed that B/C is an overfolded and liquified part of silt E, a discovery which agreed with our interpretations of the structures, tfe lithology, and the fossil content of B/C. Here a thrust nearly cuts through gravel bed F (Fie. 29).

An Eemian-Early Weichselian sequence 155

Fg. 28. Silt E and the lower part of the Bones Till in excavation 2. The zone marked D in the lower part ofthe till is nearly brown of small gyttja lumps' B and C is the till, and B/C the silt layer (Fig. 7).

Flg.29. Sketch ofthe northern wall ofexcavation 2, where the glaciotectonic connection between silt E and silt B/C could be directly.seen. The letters refer to the designation of the beds (Fig. 7).

Below this thrust both E and F are strongly folded towards the southeast and silt E can be traced directly into B/C.

As mentioned, B/C is an irregular layer con- sisting of many lenses and laminae wedging into each other. A typical example is shown in Fig.

30. The fine-grained parts are almost identical

156 Jan Mangerud et al.

with silt E. There are also thin laminae and lenses of a diamicton (till), however, which in texture and fossil content are exactly the same as the B/nes Till. The structures indicate that this is a kind of mud flow or, in an often used term, a flow till.

The thrust and overfoldings show a movement downslope and might be interpreted as having been caused by the vertical load of the glacier.

As a result of the thrust, some silt E and till C have probably become fluid and moved down the hill as a mudflow. This assumes either that there was a space under the ice or that the mudflow occurred so close to the ice front that the glacier was floating. The latter assumption would more easily explain the fault and overfold- ing towards the southeast than the ice load being equal on the whole slope would. A fabric analysis in the Blnes Till 0-70 cm over B/C (Fig.

31) also indicates that the bottom of till B has moved downslope.

Lumps of gyttja. - The B/nes Till contains many lumps, up to 10 cm in size, of brown silty (Fig' 32) and clayey gyttja. The lumps occur through- out the till but are far more frequent at the base In most places here the till is quite speckled with small brown gyttja lumps up to a few cm in length (Fig. 28).

The lumps of gyttja contain foraminifera, mol- luscs, and dinoflagellate cysts, demonstrating a marine origin. Pollen analyses (Fig. aD showed that the lumps all contained mtch Picea but that some also had a high NAP. The gyttja is there- fore interpreted as a deep water facies of the upper part of gravel I and of the silty gravel H,

B O R E A S l0 ( l 9 8 1 )

Fig. 30. Sketch showing details of li- thology and structures of silt B/C. South- ern wall ofexcavation 2 in 1975.

Flg. 3/. Fabric ofthe long axis of 123 pebbles in the Bdnes Till' 0-70 cm above silt B/C.

Fig. 32. Two gyttja lumps in the B@nes Till. The size of each is 3-4 cm.

BOREAS l0 098r) An Eemian-Early lleichselian sequence 157

&

430

21,9

l-{

5 c m

Flg. 33. Pieces of wood. Sample 60 is Picea, 430 Alnas and 455 and,249 are Juniperus.

which both have similar pollen compositions to the lumps of gyttja, and where the organic con- tent maximum occurs (Fig. I l). The deposition of marine gyttja requires reducing conditions in the deeper water layers, something which at present is found in some small Norwegian fords with shallow thresholds, e.g. Nordisvatn (Strpm 1936;

Johannessen 1972; Myhre 1972). From this, together with the interpretation of the marine fossils, it can be deduced that, during the deposi- tion ofthe upper part ofgravel I, and silty gravel H, the relative sea level was so low that there was no tidal current through the Bergen valley.

Wood. - In all, 114 bits of wood and twigs were found in the Blnes Till (Fig. 33); the largest was 60 cm long with a diameter of 10 cm. Eighty-six of them were identified by Dr. Leif M. Paulssen, Oslo, according to methods described by Pauls- sen (1964). Seven pieces were determined as Larix. Since it is known that Larix is difficult to distinguish from Picea, they were also identified by Dr. Thomas Bartholin, Lund, using other methods (Bartholin 1979). Bartholin came to the conclusion that four ofthe seven were Picea,blI he could not say for certainty whether the re- maining three were Picea or Larix.

The results, when all the Larix are included in a Picea group are: 43 Picea, 35 Juniperus, I Pinus, 3 Alnus, 1 Corylus, 1 Betula and 2 Ericales. The Betula sample was found floating

in water at the bottom of the excavation and may thus be a 'pollution'. One sample (Picea) was found in the excavator shovel and is very prob- ably from silt G. Otherwise not a single piece of wood was found in the beds below the B/nes Till. Nearly all the other pieces were dug directly out of the till.

From a stratigraphical point of view two prob- lems of particular interest arise: how old are the pieces of wood and from which sediments were they picked up by the overriding glacier? As will be discussed later, thelaC datings all gave infi- nite dates.

The large number of Picea is a strong indica- tion that many ofthe pieces are from the younger part of the Fjlsangerian (Eemian). The high number of Juniperus can also agree with a Late Eemian/Early Weichselian age, even though Juniperus was even more common earlier in the Eemian (Fig. al). Juniperus has a particularly hard and resistant wood: as a whole. coniferous trees rot more slowly than deciduous trees be- cause of their higher resin content. From the preservation point of view one would therefore expect a higher content of Pinus too.

There are three types of sediment in particular from which the wood probably comes:

(l) Peat and limnic gyttjas. Wood preserves well in these sediments but one would then also expect to find, e.g., Quercus. We did not find