Cave stratigraphy in western Norway; multiple Weichselian glaciations and interstadial vertebrate fauna
r r t t . t V L A R S E N . S T F I ) . i A R C i U L L I K S E N . S T E I N - t r R I K L A U R I T Z E N . R O I - F L I E . R t l l D A R l - O V L I E A N I ) J A N M A N ( ; E I t L ] T )
BOREAS
Skjonghellcren is a wave-cut cave ptlsitioned wcll above thc post-glacial nrarine limit. Like manv o t h e r c a v e s i n w e s t e r n N o r w a v ( H o l t c d a h l 1 9 8 4 ) i t thercfore must pre-clate thc last glaciation here.
R e u s c h ( l t l 7 7 a . b ) a n d U n d A s (1 9 4 2 ) d e s c r i b e d a t h i c k s e q u e n c e o f l a m i n a t c d c l a y a n d s i l t i n t h e c a v e . r v h i c h t h e v i n t c r p r e t c d t o h a v e b e e n c l e p o s i t e d i n a l a k e . d a n r m e d m a r g i n a l t o o r beneath the ice during the last glaciation. The interpretation has becn widelv acccpted. and is inclced the onc we still favour. Und:is (19'12) alstl found a bonc ttf a bird ( puflin) below the lanlinatecl s e d i m e n t s . s u g g e s t i n g t h e p o s s i b i l i t i e s o f f o s s i l - bearing strata of interstaclial or interglacial age.
L i r r s c n . E i l i r ' . ( i u l l i k s c n . S r c i n a r . L a u r i t z c n . S t c i n E r i k . L i c . I l o 1 1 . L d v l i c . R c i d a r & M a n g c r u d . . l a n 1 9 , 9 7 0 9 0 l : C a V e s t r r t i g r a p h y in w c s t c r n N o r w a v : m u l t i p l c W c i c h s c l i a n g l a c i a l i o n s a n t l i n t e r s t a d i a l I c r t c - b r a t c f r u n a . l J o r c z r . r . V o l . 1 6 . p p . 2 6 7 2 9 2 . O s k r ' I S S N { ) l ( ) ( ) 9 ' 1 8 3 .
S k j o n g h c ) l c r e n i s I r l a r i n c - c r r t c a r c $ ' i 1 h 1 5 l 0 m t l r i c k p r e - H 0 l t t c c n c s c c l i n e n l s . ( o l i n t s r n d c x u i r \ . t t i ( ) l l \ r e r e a l t h r c e b c d s o l c x t r c n c l \ U n c g r a i n e c i . l a n r i n a t c i l s c d i m c n l s a l t c r n r t i n g u ' i t h b l o c k l s c t l i n l i : n t s . T h c l l i m i n l r t e t l b c r l s a r c i n t c r p r e t e d a s g l a c i o l i r c u s l r i n c s e d i m c n t s c l c p o s i t c c l s u h g l i r c i a l l l a t t i n l c s \! h c n r ( 1 \ h c L ' t s c o r e r c r l t h e a r c r . s u g { c s t i n g a t l c r s t t h r c e g l a c i r t i o n s a l t c r t h c c a \ e \ \ ' r \ f o r n l e c l . T h e b l o c k r ' r l i r r m i c t i c s c t l i t n c n t s r v c r e lo r n t e d b \ f r o s t - s h l r t t c r c r l b l o c k s f n r m t l t c r o o i t t l t h c c a r c t l u r i n g i c e - f r e c p c r i o d s . a n c l n t i x i n g q i t h l h e t i n c s th r o u u h s k r u n t a s s m o v c n l c n t s a l o n g t h c l l o o r r l l t h c c a r c . I n t h c t l i r r l i c t i c \ c ( i l n l c n t b c n c a t h t h c u p p c r m ( ) s t l a m i n a t c d b e d . a l m o s t 7 . 0 0 0 b o n c a n d t c c t h f r a g r n c n t s o f t r i r t l s . n r a m m r l s a n t l f r s h
$ c r c l i r u n c l . Il i r t l s d o m i n r l e d . \ i t h l i l t l c a u k a n d b r u n n i c h s g u i l l c m o t a \ l h c m o s t l l . c q u e n t l \ , r c ( t l l t i n g s p c c i c s . A r c l i c f o x u r s t h e t l o n r i n a t i n g m a n t m r l . L ) u r i n g c l i r n r t i c o p t i m u m o i t h c i n t c r s t a d i a l . c r r n d i t i o n s s c c n t to h a r c b c c n s i n t i l i r r t 0 p r c s c n t - d r \ c o a s t i r t f i n n n t i r r k . r v i l h N o r t h A l l a n t i c u i t r n r \ \ ' a t c r c n t c r l n g t h c
\ q r g c g i l r l S c l r . T u o n r t l i o c l i r b o r t d l r t e s o n b o n c s r n c i t h r e c L l r a n i u n t s e r i c s c l l i t c s o n \ P c l e o t h c r n s l r o n l t h i s b r d l l t c l u s t c r a r o u D c l j 0 . 0 ( X ) I ] . I , . . i. c . . t h c c n d o l t h c A l c s u n t i in t e r s t a d i a l . A b o r c t h c u p p e r n r o \ l lr m r n a t c d 5 e d . t r q n c l r i r g n e n t s o l b i r t l s . ll s h r n d n r a m r r r a l s . t l c p o s i t c t l h c n r c c n r ' . 1 1 . 0 0 0 a n i l r ' 1 0 . ( } ( ) ( ) B . l ) . r v c r c i i r u n d . L i t t l c i r u k r l o m i n i r l e . T h c o c c u r r c n c c o l s q u i r r c l i s \ \ o r t h n o t i n g s i n c c i t i s l i n l i t c d m l i i n l \ t o l r r u r \ w l t h c o 6 il c r ( ) p s i o r c s t te d r r . T h e b c t l : b c l o r i t h e 3 ( 1 . 0 0 0 B . I ' . b c d r r c p o o r l r d a t e d o r u n d a l c d . b u t i t i \ t c n ta t i \ c l\
c o n c l u t l c t l t h a t r l t c c n l i r e s c c l i n t c n t \ c q u e n c c u ' r s d e p o s i t e c l d u r i n q t h c \ \ i c i c h s c l i t n s l a g c . Il \ c c n s t h r l t h c c a \ c \ \ ' a s Io l l t e d r l i r h i q h r c l a l i r e s e r - l e r c l s t r n d \ o n c l i m e d u t i n g t h c E a r t l W c i c h s c l i i r n . T u o r e c o l t l c d p a l a e o n r a u n c t i c e x c u r s i o n s s c c r n 1 o c ( ) r r c l a t e u i t h t h e L i r s c h r m p " O i b r a n d t h e L - r k c N { l l n ! o c V e n l s . r e \ p c c t r \ c l \ .
I i i | i t l ' u r ' s t t t ' ( i t ' o | t l q i t ' u | S u r u e l ' o / . \ o r l r t l . , I , . ( ) ' I : J o ' t . ] ( ) ( ) 6 '
I f u t | i , l l r l t i u | I ) u t i n ! I ' u | x l r u t t l t . r . ' Y ; 1 l , 1 . . , , \ o r x ' c g i t t t t I | ] s | i t u | ( ( ) | l t L ' | m o k l q l ' '
Nrrrrrrr,, St?iil-lrrik Laurit:art, I)(purtmcnt ol ('honistrt, Lrtiucr.sitt tt.l OsLo, P.O. llor l0.l.l. Blirttlern, N-03l6 Oslo.l, Nontul: Ilolf Lie, Zoologitul ivluseun. Liniatrsitt of Ilargcn. Muslplass -1, tt''-5000 Rerge rt, Nsntut; Rcidar Loulie, Geophl.sital ln.sritute, Settion C. Uniutrsltt'of Rergen. Alligt.70. N-5000 Bcrgen.
Nont'ut; Jun llungerud. Oeologital In.stitute. Settion B, Unioersitt ol Rergen, Alltgl. 11, N-5000 Btrgert, N o r . r l r r r ' . . l l s t O t t o b e r . 1 9 6 6 (r c t i s e d I l t l t F e b r u u r t . 1 9 8 7 ) .
The corings provecl a sediment depth of about 2 0 m , a s a l r e a d v s u g g e s t e d b 1 - R e u s t h ( 1 9 1 3 ) . a n d w e f o u n d t h r e e s c q u e n c c s o f l a m i n a t e d c l a y . s u g - gesting that the cave has survived at least three glaciations since its forntation. Four blocky units were formed in ice-frec periods prior to. betrveen.
and after the cle position of the laminated sequences. Bones were founcl in the upper. ptlst- g l a c i a l . b l o c k y u n i t . a n d t h o u s a n d s m o r c b o n e s werc found in the next upper bed. ciated by' r a d i o c a r b o n a n d U / T h t o a r o u n d 3 0 . ( X X ) B . P . T h e age is also supported bv palaeomagnetic results.
Coastal caves in Norwav were investigated at a n e a r l - v s t a g e (e . g . R e u s c h 1 U 7 7 a . 1 8 7 7 b . 1 9 1 3 :
268 Eiliu Lur.yen ct ul.
K a l d h o l 1 9 3 0 : U n c i l i s l9 ' 1 2 ) . b u t n e a r l v fo r g o t t e n b y g e o l o g i s t s . e x c e p t f o r t h c s t u d i e s b v I l o l t e d a h l ( 1 9 8 1 ) . ( ) u r i n v e s t i g a t i o n d e m o n s t r a t e s t h a t t h e s e cavcs mav hold extremelv r,.aluablc information on o n t h e L a t e Q u a t c r n a r y h i s t o r v o f t h c a r e a .
The cave
S k j o n g h c l l e r c n i s d e v c l o p e c l i n t o t h e s t c e p s l o p e forrning thc inner limit of the stranclflat (Larsen &
IJoltedahl l9li5) on the western side of thc island o f V a l d e r o v a ( F i g . l ) . T h e h i g h e s t mountain on Valderlaya is 231 m above sca lcvel. The fiord b e t w e e n t h e i s l a n d s V a l d e r o l u . G i s k c a n d V i g r a has a maximum clepth of 76 m. The bcdrock-on Valderoya consists rtf coarse crystallinc, grano_
dioritic gneissesl in nearby areas calcite_bearing g n e r s s e s a n d i n c l u s i o n s o f l i n t e s t o n e h a v e b e c n d e s c r i b e d ( C i j e l s v i k 1 9 5 1 ) . C a l c i t e i s a l s o fo u n d in t h c g n c i s s a t S k j o n g h e l l e r e n ( T a b l e l ) . T h e c a v e itself is formcd alons a lracture strikin-q 27-5.-095.
w i t h a n o r t h e r l v c l i p b e t w e c n -5 0 . a n c l d ) . ( F i g . 2 t . 'Ihe
cleepest part of the cave 1or maxtmum seclr_
m e n t t h i c k n e s s ) i s t h e r c f b r e a s s u m e d t o b e b e k r w t h c n o r t h e r n w a l l . T h e s c i s m i c p r o f i l e ( F i g . 3 ) i n d r - cates that the level of bednrck is 30 rr above se.
I e v e l a r r h e o p e n i n g (b c y o n d r h c limit of Fig. 3,1.
r n c r e a s l n g t o n c a r l v , l . 5 m a b o v e s e a l e v e l w i t h i n t h , cave. With the cave lioor at 63 m above sca level.
t h i s g i v e s a s e d i m e n t t h i c k n e s s o f c , . 2 0 m . T h e c a v e is a b o u t l ( X ) m l o n g ; it s in n e r 7() m are shown in Fig. 3. The great sediment thickness indicates that the cave continues beyond this posi_
tion. The height of the cave varies between 1 and 1 0 m . t h e w i d t h b e t w e e n 2 a n d 1 2 m . F r o m 0 to 25 m (as measured from the inner limit) the cave ls very narrow (Fig. 3) as a result of sediment_
fill; the bedrock cave, however, has a relatively c o n s t a n t w i d t h .
A l l h e i g h t s r e f e r t o m e a n s e a l e v e l ( F i g . 3) Chronostratigraphic nomenclature follows Man_
serud c1 al. (1971) except that the Middle/Late Weichselian boundary is rnovecl to 2-5.000 B.p, ( M a n g e r u d & t s e r g l u n d l9 7 g ) .
E x c a v a l i o n s a n d c o r i n g s
Thc manually excavated sites, with letter desig_
natlons of the walls, are shown in Fig. 3. The conngs were made by a mobile wire_line drilling unit utilizing both hammer and rotation principle.s
B C ) R h A S l 6 ( 1 9 U 7 )
/ , i g / K c 1 ' m a p o f N o r w a v w j t h namcs usctl in thc tcxt. A mapol t h c A l c s u n d a r c r w i t h t h c c a v e Skjonghellcrcn (cross,rrarkl on t h c is l a n d o f V a l d c r o v a is i n s c r t c d . I I l ) r i z o n t r l hal chintr is thc sca.
u s r n g 1 m l o n g s a m p l i n g tu b c s ( i n n e r diarneter between -51 and -56 mm). The corings wcre macje at three different angles from the base of excavation I in order to reach the deepest part of the cave at t h a t s i t e .
BOREAS 16 (1987) Caue stratigraphy in W Norway 269
Fig. 2. Yiew of the cave, developed along steeply dipping joints in the bedrock (gneiss). The opening is up to c. 30 m high. Photo towards east.
Excauation 1 and corings l, 2 and 3
The first excavation was near the opening, and nearly 5 m deep (Figs. 3 and 5). From earlier descriptions (Reusch 1877a, 1877b; Undhs 1,942;' Vibe-Miiller 1963) and a small accessible section, we knew that a relatively thick sequence of lami- nated sediments existed at the site (Fig. 4). UndAs (1942) reported a bone of puffin probably found in the bed we have labelled diamicton with bones G (Fig. 5). The corings extended from the base of excavation 1 down to bedrock. Coring was con- tinued for 3.8 m into bedrock in order to be con- fident that it was not a block. The sedimentological descriptions of the corings are preliminary, but additional information is unlikely to influence the stratigraphic interpretations.
Excauation 2
This 6 m deep excavation (Fig. 6) is near the inner end of the cave (Figs. 3 and 7). The excavation uncovered the most complete stratigraphy and the least post-depositional disturbances.
Excauation 3
Excavation 3 was a narrow trench made to facilitate lithostratigraphic correlation between excavations t and2 (Figs. 3 and 8). Within laminated clay F, individual lamina could be traced along most of the trench (Fig. 8), and also identified in excavations 1 and 2. Thus the sediments in the two main exca- vations can be correlated in great detail (Larsen et al. 1984). The correlations demonstrate that exca- vations 1 and 2 penetrated to the same stratigraphic level.
Lithostratigraphy and sedimentology
All lithostratigraphical units were defined in the field. The beds were given informal lithological designations. Letters were used for each bed described in the field (Figs. 5 and 6); the same letter corresponds to the same bed in each excavation.
Three groups of facies are recognized (Figs. 5 and 6): the facies associated with the fine-grained
210 Eiliu Larsen et al
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seciiments. those assocrated with the blockv sccli- m c n t s . a n d t h e s p e l e o t h c m s . T h e a l t e r n a t i o n s (cyclic) bet*'een the fine-grained ancl blockl'sedi- ments iirc interpreted to represerrt glacial vs. inter- stadial episocies.
The dtrmning o.l v,'ater
The extrernely finc-grained character of larninatecl clay L. I ancl F (Figs. -5 ancl 6) cle arlv proves depo- sition in quiet water; the complete lack of rnicro- lossils indicates a non-rrarine environntent. Tn'o alternatives for wate r in the cave can be seen: dam- ming b1' secliments or b1' glacier ice. A sandur below two tills on the islands of Godo.va and Vigra ( F i g . l ) i s d e s c r i b e d b y L a n d v i k & M a n g e r u d ( 1 9 8 5 ) . a n d p a l a e o c u r r e n t r e c o n s t r u c t i o n s c l e a r l y indicate that the sandur also extended to the lower parts of Valderova. This sandur could have dam- med the cave, causing deposition ofciay in a back- water pond. However. we Iind it highly improbable
\) :"
t h a t t h i s s i t u : r t i o n s h o u l d b e r e p e a t e d t h r c c t i m e s ( B e d s L . I . F . F i g s . 5 a n d 6 ) . A l s o . t h e c o m p l c t c lack of sancl in such thick finc-grained sequences is cliflicult to understand in a sandur environment.
A n i c e d a r n ( R e u s c h 1 9 1 3 ; U n d a s 1 9 4 2 ) s e e m s to bc the on11" possibilitl' to explain thc laminated s e d i n r e n l s . T h c l r r c l r h r r s h e e n e l i r c i i r t e r l l r n u m h e r o f t i m e s d u r i n g th e W e i c h s e l i a n ( M a n g e r u d 1 9 8 1 .
1 9 8 3 ; S c j r u p in p r e s s ) , s o th i s is a r c a s o n a b l c r e p e t i - t i v e m e c h a n i s m .
Fucies descriptiorts and irtterpretatiorts Larninated tluy Jacia.s. This facies completely d o m i n a t e s b e d s L . I a n d F ( F i g s . - 5 a n c l 6 ) ; i t i s n o t found in other beds. It is characterized by the fine grain size and the fining upwards laminations ( c o u p l e t s ) . N o r n t a l l v . th e l a m i n a th i c k n c s s v a r i e s b e t w e e n c . I m m a n d c . 2 c m . a n d i s o n a v e r a g c g r e a t e s t i n e x c a v a t i o n l . w h e r e a m a x i m u m th i c k -
S e d i m e n t c l o s e o c a v e -
_ --.__A_..
' ! Z F r
BOREAS 760987\
Caue stratigraphy in W Norway Z7I
Fig' 4' The cave in the area of excavation 1. The left wall of the excavation is shown in Fig. 5, as are the cores extending downwards from the base of the excavation. The fence is about 1 m hish.
ness of 5 cm occurs. The sediments also tend to be coarser in excavation 1 than in excavation 2. The .contact between couplets is normally sharp. The laminated sediments are draped on the underlying sediments (Fig. 9). This, in addition to post-depo- sitional compaction, control lamina dips. ihe compaction increases towards the north due to increasing sediment thickness. Small-scale faults accompany this general northerly dip. In exca_
vationz, average dip below bed G is higher than above, as one would expect (Fig. 6). The upper boundary of the laminated facies seqrrence is always erosional.
We have previously concluded that the lami_
nated sediments were deposited in an ice-dammed lake. The high clay content, the long continuous laminations and the lack of frost-shattered material from the roof (see below), indicate that the cave was totally water-filled. The topographic position of the cave makes it difficult to enviiaee a lateral lake with a water level high enough io completely fill the cave. We thus conclude that the sediments were deposited subglacially. The lack of till and glaciotectonic disturbances show.
however, that the glacier did not squeeze into the
cave. Probably the water in the cave had a hydro_
static pressure proportional to the thicknes of i.. . By accepting the total ice-cover model, still to be explained are the sediment provenance, the cause of the rhythmicity and the sediment dispersal and sedimentation mechanisms.
As expected, the grain size difference between the two excavations (Figs. 5 and 6) shows an inward transport component. An X-ray diffractogram from laminated clay F in excavation 1 (Fig. 10) showsverylittle orno evidence of montmorillonite or other 14 A minerals, which would be expected if the clay originated from the fracture above the cave (Carrol 1970). A SEM analysis of quartz grains from the same bed (Fig. 11) shows typically glacially-sculptured surfaces (Krinslev & Doorn_
kamp 1973 ; Whalley & Krinsley 1974; Strass I 97g).
We conclude that the sediments are glacialiy derived, and transported into the cave in water.
The rhythmic nature is not fully understood. It must be related to discharge and sediment load variations, but whether these variations are caused by climatic changes (annual?) or simply reflect subglacial channel migrations or channel overflows (Rcithlisberger 1972) is unclear.
272 Eiliu Lursen er al
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\
274 Eiliu Larsen et al. BOREAS 16 (1987\
Fig. T.Tlhecaveinthe area ofexcavation2. The exbavated site is in the foreground, the cave openingin the background. Photo looking west.
Some deductions can be made, however, about transportation of material within the cave and about the sedimentation process. An inwards transport component is well documented by grain size differences. Because of post-depositional deformation it is difficult to compare the depo- sitional levels between the sites. but laminated clav F was deposited in shallower water in excavation i further into the cave than in excavation 1. This implies that sediment transport occurred in the water column rather than as density currents. The draping (Fig. 9) supports the interpretation of deposition from suspension. The inferred trans- portation mechanisms suggests a very slow, lami- nar inward flow of the entire water column. A crude estimate of the maximum flow rate can thus be obtained by considering settling velocities. Dur- ing deposition of bed I, the height to the cave ceil- ing at excavation 2 was about 4 m. Most particles greater than 2 pm were deposited farther into the cave. It takes about 24 days for 2 pm particles to settle 4 m in still 0'C water. If we suppose that the ice dam was 70m farther away (Fig. 3), aZp.m particle could spend a maximum of 24 days over these 70 m. This reflects a horizontal flow rate of a
maximum of 3 m per day. This model suggests that the water drained through the cave, probably through fractures in the bedrock.
Laminated silt facies. - Some silt laminae exist in other beds, but the facies dominates only lami- nated silt J (Figs. 5 and 6). The bed is draped over block K. At the base there are a few clay-silt coup- lets with a gradational transition to mm-thin coup- lets composed mainly of silt, but with some fine sand (Fig. 5). A couple of clay-silt couplets are found c. 2 cm below the upper boundary. These are followed by a few silt to fine-sand laminae just below bed I. The laminae fine upwards. Normally the upper boundary is gradational, except for an unconformity in parts of excavation 1 caused by local slumping. The overall bed is thinner in the inner excavation (Figs. 5 and 6).
The gradual transition to laminated clay I sug- gests that this silt also was deposited in the ice- dammed lake. The greater contrast between lami- nae probably reflects greater discharge variations.
The coarser fraction reflects higher flow velocities, compared to the laminated clay facies. The bed was probably deposited at a higher altitude at the
B o n e b e a r i n g s i l t a n d b l o c k s B
a n o iLanuLale:d _c.ELq L a m a n a t e d c l a y F
e x c a v a t i o n
B O R E A S l 6 ( l 9 t r 7 ) Caue stratigraphy in W Norway 275
6 3 0
6 2 0
6 1 0
z t \ - ) 3 l a 3 7 o m
F i g . , \ . S l r r t i g r t p h l o f l h c s o u t h c r n rv a l l o f c x c r v a t i o n J . l h c n r a i n la m i n a c . rc c o g n i z c d i n l a m i n a t c d c l a l l - i n c x c a v a t i o n s I a n c l 2 . a r c i n d i c a t c t l r v i t h p a r a l l c l li n c s . r ' ( ' d a t c c l b o n c s . fr o m t h c t r a n s i t i o n z o n c b c t w c c n b c d s D a n d B . g a v c a n a g c o f 1 0 . 3 6 0 + 170 B.P.
p o s i t i o n o f e x c a v a t i o n I ( F i g s . - 5 a n c l 6 ) ; i t t h i n s a n d fines inwarcls. It is therefore probablc that at least the coarsest sizcs were transportcd ancl deposited b y d c n s i t v c u r r e n t s . T h e o c c u r r e n c e o f c l a v c o u p - lets indicates periocls of quiet lvater. and that the cavc might havc been totally water-filled. The observations suggcst that this facies was cleposited d u r i n g t h e i n i t i a l p h a s c s o f t h e l a k e w i t h s l a c i e r m a r g i n in t h e v i c i n i t v o f t h e c a v e . c a u s i n g a m o r e v a r i a b l e s e d i m e n t s u p p l v a n d g e n e r a l l v h i g h c r e n e r g y c n v l r o n m e n t s t h a n fa t h e r b a c k in t O t h e ic e . Larninate cl clily F is not unclcrlain by a larninated s i l t f a c i c s . In e x c a v a t i o t ' r 1 . h o w e v e r . th e b a s c o f t h e b e d h a s a 3 c m t h i c k z o n c o f l a m i n a t c d c l a v corrtaining subarrgular clasts of fine sand (Figs. -5 a n d l 2 ) . T h i s i n d i c a t c s a r c l a t i v e l v h i g h c n e r g y , l e v e I c l u r i n s t h e i n i t i a l p h a s e o f t h c l a k e .
('luv n,itlr introt:lust und granulation futit's. -Thc laminatecl clay facies is followecl bv thc intraclast r u n d g r a n u l a t i o n f a c i e s ( F i g s . 5 a n d 6 ) . T h e f a c i c s h a s a l o w c r e r o s i o n a l b o u n d a r v a n d i s b e s t d e v e l - opecl abo'"'e larninatccl clav F in e xcavation 2, where t h e E , a n d D b e c l s a r e d i s t i n g u i s h e d ( F i g . 9 ) . T h e f a c i c s is . h o w e v e r . a l s o c l e a r in t h e t o p o f b c d I (Fig. 6). Thc lou'er erosional bounclarv and the clitsts were probably formed bv water that drainecl out ofthe cave cluri ng dcglaciation. causing erosion a n d r e d e p o s i t i o n o i t h e c l a y in t h e c a v e .
Silt w,itlt lcntic'ulur luntinution.fucies. - This facies is reprcsentecl by becl I I in excavations i and 2 and b e d C i n e x c a v a t j o n 2 ( F i g s . -5 a n d 6 ) . I t i s c h a r - acterizecl by cliffusc. lenticular and non-persistent l a m i n a t i o n s ( F i g . l 3 ) . I n e x c a v a t i o n 1 . t h e l o w e r bounclary rvas crosional. but the facies lies con- dorclantlv upon thc unclerlyine bcds in excavation 2 .-fhe
sediment is presumcd to havc been deposited by sheet floods during thc final dririnins o l ' t h e c l r v c d u r i n L l t l e g l a r ' i a l i o n .
Clusl-supportetl blot'k f ucie.r. The term 'block' is used for large ( >2-56 nrrn ). angular rock fragments showing little or no modificatir)n bv transporting irgents. with a surfacc resulting from breaking of the parent mass ( Bates & Jackson I 980). An angu- larity distinguishes blocks from boulders. LJnits K a n d M a r e c o m p o s e d o f n u m e r o u s b l o c k s . b u t h e r c - after are called block K ancl block M. Block K by c l c f i n i t i o n i s e n t i r e l v o f t h i s f a c i e s . p r o b a b l y a l s o m o s t o f b e d M . a n d p o c k e t s i n b e d G .
Parts of block K were cxcavated at both sites I and 2. but thc bed is penetrated onl.v b1" the cores.
Large clasts of laminated cl av near thc basc of exca- v a t i o n 2 i n d i c a t e t h a t i t n c a r l v p e n e t r a t e d t o l a m i - natccl clav L. With the exception of the lorver and upper parts of the bed, practically no matrix exists b e t w e e n th e b l o c k s , b u t a t h i n v e n e e r o f c l a y i s common on the block surfaces. Block K is com- posed mainlv of angular blocks rind stones. The l a r g e s t b l o c k e n c o u n t e r e d ( c o r c d ) w a s a b o u t 2 . 4 m across. In the excavatcd part of site 1. block K is composed of one large block covered by an up to 3 8 c m t h i c k l: r y e r o f g r a v e l a n d s t o n e s ( F i g . 1 2 ) . A l l blocks and stones are the local gneiss, cxcept for the clasts of spele othems and vein calcites in exca- vation 2. The concentration ofthese clasts is greirt- cst near the basc of the bed, but they do occur throughout the bed. betwecn the other fragments.
Block M is almost,l m thick and is recorded only in cores (Fig. 5). The largcst block rvas sorne 8-5 cm across. Voicls cxistcd betrveen thc blocks. but clue to cooling water being usecl in the coring process.
l i t t l e i s k n o w n a b o u t t h e m a t r i x b e t w e e n b l o c k s . One of the cored fragments showccl some degrec of roundins. AII blocks har,'c been derived from the l o c a l b e d r o c k .
This lacies is interpreted to be blocks weathered from the roof. Most blocks apparentlv fell during colci periods with active frost r",eathcring. Few blocks werc found above the Holocene cultural remains, sutgesting that thick block beds represent
276 Eiliu Larsen et al.
r,:i,11$W
Frg. 9. Northern wall, excavation 2, showing beds I-B. Beds K and J are in the shadow.
long, cool periods. Due to the observation of one rounded boulder in block M and the stratigraphic position of this bed, it may have been exposed to marine action. In fact, it may be assumed that wave-abraded boulders grade upwards to frost- shattered blocks as a consequence of regression durins an interstadial.
BOREAS 16 (1987\
Matrix-supported block facles. - This facies con- sists of blocks similar in appearance and origin to the clast-supported block facies. The difference is that the blocks are supported by a fine-grained matrix. However, there are all transitions, from the openwork blocks without any matrix, to a silt with few floating blocks.
This facies dominates beds B and G, where the overwhelming number of bones were found. A stratigraphic description is therefore useful.
In bed G in the inner excavation (Fig. 6), the matrix is dominated by clay and silt, and the sedi- ment can best be described as a diamicton. In the middle to upper part of the bed, voids are common between the blocks. Well defined clasts of clay and silt are common. Atthis site. more than 6.000bone fragments and several fragments of speleothems and vein calcites were found. There are higher con- centrations of bones in the lower, mainly silty part of the bed. The amount of bones. decreases upwards, and there were none in the uppermost part. Speleothem fragments were found only in the lower and middle parts of the bed, but not as deep as the deepest bone fragments. A few very small fragments of charcoal were found in bed G in exca- vation 2. Two of these samples (el 83043 and -091) are supposed tobe Pinus andAlnus (L. M. Paulsen pers. comm. 1983). The first was actually found in laminated clay F, but was probably redeposited from bed G.
In excavation 1, bed G can be subdivided into a lower and an upper unit separated by an erosional boundary. The lower part is composed mainly of silt with fine sand and subangular clasts of clay. In the upper part, clay dominates. Stones, blocks and bone fragments are less frequent in excavation 1 than in excavation 2. Speleothems and vein calcites are not found in excavation 1.
In both excavations, the lower boundary of the facies is erosional.
The bone-bearing silt and blocks B in excavation 2 is dominated by silt, in which there are some floating clasts of clay, blocks, stones and bones.
The sediment is mainly massive, but with some diffuse, subhorizontal bands. Small folds exist along the boundary towards silt C. The bed is found only in a depression in the northern part of the excavation, and wedges out towards the east, west and south. Most bones were found in the upper part, but boneswere scattered throughoutthe bed.
In excavation 1, bed B is a silt and sand pocket where one bone fragment was found.
Inpit2 (Fig. 6), all beds have a strike parallel to
1
-r'j
{'l.
B O [ { E A S l 6 ( 1 9 8 7 )
the long axis of the cave (E-W), and a northerly clip which is greater below bed G than above it (Fig.
6). The lower boundary of bed G is erosional and the bed thickens towards the north. These obser- vations are best explained by originally horizontal beds being deformed towards greatest sediment thickness (north), and a simultaneous slow mass movement (solifluction) in the same direction. An incomplete vertical mixing of bed G, however. is indicated by a fauna development through the bed and the lack ofbones and speleothems in the upper- most part.
Bed B is folded. either by sliding or solifluction.
The fold axis is almost parallel to the long axis of the cave. Farther towards the north (outside the fold). bed B wedges out.
The matrix in the block facies derives from the underlying and overlying fine-grained sediments.
This is best seen from the inclusion of clasts of lami- nated clay in the matrix. Underlying clay was incor- porated by solifluction or simply by squeezing whcn blocks fell irom the roof . We assume that the bulk of the matrix was incorporated by solifluction, but some was also incorporated during deposition r r I th e o v c r l y i n g e Ia y h e d .
Speleothem facies. - This facies consists of spe- leothems, mainly carbonates, precipitated on the cave floor.
Only bed A (Fig. 6), and other post-glacial pre- cipitates on floor, ceiling and walls, are in situ.
However, this facies has also been repeated. as fragments are found as clasts in beds G and K.
'Ihese
clasts are formed by frost shattering. Bed A displays classic speleothem shapes (stalactites,
Caue stratigraphf in W Norway- 277 stalagmites and botryoidal forms). All remaining samples consist of tabular, frost-shattered clasts.
lacking stalactitic shapes. but may well have formed as crusts on the surfaces in the cave.
In addition to the speleothem clasts. beds G and K also contain clasts of vein calcite originally formed in the cavity above the cave. For chrono- logical purpt'rses it is essential to distinguish between the two groups of carbonates. because spe leothems formed during ice-free periods within the cave whereas vein calcite pre-dates the cave.
Speleothem deposition in non-carbonate caves is rare, but is previouslv reported from Norway (Schroder 19f1,1). The speleothems have a distinct internal structure (laminations. growth bands) dis- tinguishing thern from coarse crystalline vein frag- ments. They are either pure calcium carbonates (travertime A, Table I . Fig. 6) or they contain mix- tures of laumontite , rhodochrosite . K-feldspar and quartz in addition to calcium carbonate (samples el 83020. -l12. -307,4. -011, -142 and -221, Table 1 ) . K-feldspar and quartz obviouslv are impurities.
whereras laumontite and rhodochmsite are prob- ably formed as secondary precipitates along with the calcium carbonate. Laumontite and rhodo- chrosite have not been previously reported from s p e l e o t h e m s ( H i l l 1 9 7 6 ; W h i t e 1 9 7 6 ) . H o w e v e r , large, pink stalagmites and stalactite consisting of rhodochrosite do exist in one Bulgarian cave (Dr.
K. Spassov pers. comm. 1986).
The origin of the constituents in the speleothems may be discussed in detail . CaCO: is found both in t h e c a v i t y ( e l 8 3 1 0 7 . T a b l e l ) a n d i n t h e g n e i s s i t s e l f ( e l 8 3 1 0 i 3 a n d - 1 3 7 . T a b l e 1 ) . T h e m a i n C a C O r source is probably vein calcite. Both rhodochrosite
l'ablr, /. Results of X-ray tliffractomctry on bcdrock and spclcothcm sirmplcs
S a m p l c B c d / S i t c
Typc of
n n t c n a l M i n c r a l s
c l U 3 1 0 8 B c d r o c k , m o u n t a i n a b o v c G n c is s Clast of gnciss Vcin mincral Speleothem clast Speleothem clast Spclcothcm clast Clast of vein mineral Spclcothcm clast Spelcothem clast Spclcothcm clast 1n ri/u speleothem c z l v c
c l u 3 1 3 7 B c d G
cl 83107 Cavity abovc cavc cl 1t3020 Bcd K
c l l t 3 1 1 2 B c d K el 833074 Bcd K cl 833078 Bcd K cl 830,14 Bed G c l 8 3 1 4 2 B c d G cl ti322l Bed G
el 83023 Bcd A
Quartz, Fcldspar (Plagioclase. K-feldspar). Mica, C a l c i t e
Quartz, Fcldspar (Plagioclasc. K-fcldspar).
Chloritc, Calcitc Calcitc
Calcite. Laumontite C a l c i t e , L a u m o n t i t e Calcite, Laumontitc Calcite
Calcitc, Laumontitc
Calcitc. Laumontitc, Rhodochrositc?
Calcite, Rhodochrosite, Laumontite, Anorthite.
Quartz Calcitc
278 Eilio Larsen et al. BOREAS 16 (1987)
Frg. 11. Scanning electron nicroscope photo of quartz grain from laminated clay F, excavation 1 (sample el 83001). Grain shows conchoidal fractures and steps. Bar scale = 100 um.
there was no permafrost. Both frost shattering and speleothem formation rule out the possibility that beds M and K were deposited in an open cave under a cold-based glacier simply because both processes require water. Travertine A is found undisturbed overlying bed B (Fig. 6). It therefore seems that mass movements had ended when bed A was deposited some 8,500 years ago.
Dating
Absolute dates were obtained in excavations 2 (Fig. 6) and 3. The results are listed in Tables 3 and
4
Radiocarbon
Identified bones (Table 2) were selected for radiocarbon dating. All dates but one (T-5593) were performed on bones from several species.
Collagen was separated from the bones by the following method: After initial washing and crush- ing to fragments <2mm, the bone material was hydrolyzed with 3 N HCI at room temperature under reduced pressure. Insoluble residue was treated at 57o NaOH (room temperature) for 5 min and collagen dissolved in water at 90'C, adjusted to pH 3. 0-3. 5 with HCl. This ensured that
Fig. 10. X-ray diffractogram from laminated clay F, excavation 1 (sample el 83002).
and laumontite are foundin veins and as secondary precipitates (Berry & Mason 1959). The pre- cipitates may be an alteration product from plagio- clase and glass (Berry & Mason 1959). Sample el 833078 (Table 1) from bed K is a coarse crystalline vein calcite.
Local p alaeoenuironment
According to our interpretations, the sediment sequence reveals three periods of total ice cover (the fine-grained sediments) and, including the post-glacial, four ice-free periods (the blocky sedi- menis). The fining up from J to I and the lower part of F (Fig. 6) rnay indicate that sedimentation of the fine-grained sediments took place at least partly under advancing glaciers. Palaeomagnetic data support the interpretation of rapid sedimentation for bed F shortly after deposition of bed G. In the upper part of the laminated sequences, erosional and redepositional structures are attributed to draining of the cave when the damming glacier thinned. The magnitude of these erosional events is unknown, but is inferred to be small. The obser- vations suggest that the later phases of the glaci- ations were non-depositional.
Both solifluction and frost shattering (the blocky sediments) generally reflect a cold climate with repeated freeze-thaw cycles. The abundance of blocks in these beds, compared with the Holocene surface, the correlations (Fig. 16) and datings, indi- cate that the blocky sediments were formed in cool, but ice-free periods during the Weichselian. The formation of speleothems (beds K, G and B) reveals the existence of groundwater circulation.
This means that at least for parts of these periods
B O R E A S 1 6 ( 1 9 8 7 )
Tuble 2. List.rf spccics datcd bi' radiocarbon (Tablc 3)
Caue stratigraphy in W Norway 279
Specics names are given in Tables -5 and 6.
' r C Iaboratorv rcfcrcncc numbcr D a t c d s p c c i c s
T-5 l-56 Aloper lugopus
Uria lotnttiu ('ulidri.s muritimu Frater<'ulu urctit u ( tpphus grt llt Polluchius airens Alopex lagopus Pusu ltispida ( epphus grylle illelunittu fir.scu Lugopu.\ nlulLts 5o tt( t( r i( nto I I i s sirn u
Plautus slle C.eppltus grvlle Fruter<ttlu arLti<.u .\o rnuteriu s peoab i I is Lurus tnurinus Anurhicus lupu.s T-559 I
'I -559.1 T-5.i91
Phocidac Alcidac
Unidentilicd mammalia Unidcntificd aves Unidcntilicd pisccs
A n r t i d r c
U n i c l c n t i f i c d m a m r n a l i a Unidcntificci avcs U n i d c n t i l i c d p i s c c s
Uriu sp.
P h o c i d a c
U n i d c n t i l i c d m a n n t a l i r [-rnidcntificd avcs L ' n i d c n t i l i c d p i s c c s
contaminating humic acids not rentovecl bv the r r l k i l l i t r e a t m e n t w c r e p r c e i p i t i t t e d . I n s , , l u l . l c remains were removecl by centrifugation before cvapo!'atlon to rccover the gelatine. This was com_
busted to COz and counted in gas-proportional counters. The collagen separation technique elim_
i r e t c s c o n I a n r i n I t i o n e f f i c i e n t I y . W i t h t h i s c o l la g c n extractlon technique, a mammoth tusk from F h v a n g . e a r l i e r d a t e d a t 2 0 . 0 0 0 B . p . ( T - 1 2 3 9 ) , w a s d a t e d a t > 4 7 . 0 0 0 B . P . ( T - 2 8 0 1 . S . G u l l i k s e n . u n p u b l . ) .
Sample gas was analysed tbr r3C, ancl activity measurements normalized to 6lrc : -25%:a rel.
P D B . N t r c o r r e c t i o n f o r r c s e r v o i r a g e \ i l s il p p l i e d . The yield ofcarbon (Table 3) gives only a rough estimate ofthe collagen preservation status, as the extractlon proccdure is not designed for accurate deterrnination of the content. The flsures.
h o w c v c r . i l r e q u i t c c ( ) n \ i s t e n l w i t h t h e m e i r n v u l u e s
7ablc -1. Radiocarbon datcs on bonc samplcs.
obtained for regular bone sanrplcs clated in the laboratorl' (3.6 + 1 .97r )
Although radon contamination shoulcl not be a serious problem for gelatin samples, this possibility was investisated by measuring T-5 156 after normal storage time of 3 we eks and again after 16 weeks.
No significant difference was obseived between measurements.
At this site the possibility of introducing modern c a r h ( ) n i s : m a l l . a s th e s a m p l e s w e r c c o l l e r : l c L l m o r c than 7t) m from the opening of the cave. where no plant cover exists. Modern carbon might be trans_
ported in ground water through the cavitv above the cave, and introduced from cultural beds on too o [ t h e c x c r r r a t i o n . T h e d r t c d h e d . h , , w e v e r . is sealed by the overlving verv impermeable lami_
n a t e d c l a v F ( F i g . 6 ) . w h i c h e f f e c t i v e l y l i m i t s w a t e r penetration. The amount of water dripping from fractures in the cave ceiling is very little. and the
[ - a b o r a t o r \
r c l c r c n c c n u n t b c r S r n r p l e r e l c r c n u c A g c B . P . : i l o d r r C 0 , , 0 0 rc l . P D B Y i c l d a l g C ' - q B o n c T-5.59l
T-.5591 1 - - i 1 5 6 'f-559.1
B c d B c x c a v a t i o n Ilcd lJ cxcavation B c d G e x c a v a t i o n B e c l C i c x c a v r t i o n
I I . , 5 1 0 + 1 9 0 1 0 . 3 6 0 + 1 7 0 29.fiX) + lJ(x) 3:.1J00 + 800
- t 6 . 0
1 0 . . )
1 5 . 6
l . l .1..5 L.1 l . l
280 Eiliu Larsen et al BOREAS 16 (1987)
i
Frg. 12. Section wall A, excavation 1. In the lower left corner diamicton with bones G has slumped into laminated clay I. The same bed (G) is in the upper right corner. Above the two parts of G, at the base of laminated clay F, laminations with silt/snd clasts can be traced continuously. These laminations form the basis of a small basin in the lower left.
Fig. 13. Diamicton with bones G between silt H (lower left corner) and laminated clay F. In the centre a c. 5 cm long bone of ringed seal. Several of the white spots are speleothem fragments. From the northern wall, excavation 2
:
n - t .
it
t..l .
,
B O I t t : A S l 6 ( 1 9 8 7 )
ground-water table is far belor.v the dated bed. In addition. it is difficult to imagine how anv intro- duced modern carbon could form chemical com- pounds sulficicntly identical to collagen. or having sufficiently strong chernical bonds to it. to with- stand removal during the extraction process. We t h u s c o n c l u d e t h a t c o n t a m i n a t i o n i s a m i n o r p r o b - lem ancl that the age difference between the dates from bed G (Fig. 6) is real and caused b-v random selection of bones from a laver spanning some thousancl years.
Urattium serie.s
Seven speleothenr dates were obtained from exca- vation 2, onc of them a florvstonc crust (bed A) on t o p o f t h e s e d i m e n t s c q u e n c e . t h r e e o n f r a g m e n t s frorn becl G. and three on fragments from block K.
ln addition. one test was performed with uraniurn s e r i e s c l a t i n g o n b o n e s f r o m b e c l G ( e l 8 3 1 - 5 9 ) . a n d o n e s a n t p l e o f v e i n c a l c i t e ( e l t 3 3 3 0 7 B ) w a s d a t e d . The sarnples were dated by the r3OTh/IrU di\- equilibrium method. The mineralogv of the dated s a m p l e s i s p r e s e n t e d i n T a b l e l .
Spelcothems in non-carbonate cavcs are ttften exceptionallv rich in urarriurn duc tct the high uran- ium corrtcnt of the surrounding bedrock. Most of the prcsent sanrples have a high uranium content ('fable 4), consiclering that the materi:rl contains c.
3 0 % i n s o l u b l e s i l i c a t e s ( a l l s a r n p l e s e x c c p t e 1 8 3 0 2 3 a n d - 1 5 9 ) . T h e s a n r p l e s a r e t h c r e f o r e c o n s i d e r e d well-suitecl for ciating.
CaL;e stratigraphl" in W Nnrwuv 281 The dated sarnples rl'ere selectecl on the basis of t h e i r in t e r n a l s t r u c t u r e ( e . g . th e y r v e r e l a m i n a t e d . secondary deposits). distinguishing thcm from vein iragme nts. Sample el 83023 is a -5-10 mm thick botryoidal crust, taken in situ on top of bed B (Fig.
6). The remaining samples were angular clasts from beds G and K (Fig. 6). Sample el 830'14 showed secondary solution pitting ( I 2 rnm dia- meter). whereas thc other two had intiict surfaces.
All three samples showed ii similar internal lami- nation of white and pink bands.
The samples (2 7 g wcre cleane d in dilute acid prior to analysis. They were then digested in HNOr: the gelatinous residue from laumontite was then treated with HF/l lClOl until dissolution was complete. All leachiites were combined before further processing of each sample. U-concentra- tion, activity ratios of rrau/rrsu. r'r(rTh/|:Th 'nd rr0Th/:}U. were determined b-v the isotope dilu- tion technique. chemical separation of U and Th fractions. and radionletric cletermination bt' alpha particle spectrometrv. A Ir'Th/rirU qpike was usecl as the internal standard. This spike rvas calibrirted against a stanclard uraninite in l9Ul ancl 1983. and its activity ratio was calculated before each batch of samples. Furthermore. intcrlahttratory cali- brations reveal a good accurircy relative to other U-series laboratories. The spectra n'ere corrected for background and decay alter separation of the spike mother and daughter nucleides. The age was calculatecl from the activity ratios of Table '1. The e r r o r i s h i r s c d o n l y o n t h c c ( ) u n t i n g s t r r l i : t i c : .
f a b l e 4 . t l r a n i u m s c r i c s D i s c q u i l i b r i u m d a t c s o f s p c l c o t h c m s . v e i n c r l c i t c a n d b o n e s . ' l ' h c r r ' T h , / r r r U r a t i o o f c l u 3 l l l i s c o r r c c t c d l o r r r i T h tailing in thc spcctra. Maxinrunr tailing givcs 23.-5 k a . w h i c h i s t h c v o u n g c s t p o s s i b l e a g e . 8 0 . 1 k a i s t h c b c s t c s t i m i i t c . S a r r p l c c l
It3307ts shows cvidcncc of post-dcpositional lcaching of uranium
S a m p l c B c d M a t c r i a l U c o n c . p p n r r r L J / : r N U r r r r T h / r r r T h r r r ) T h / r r r f ' e g e ' A
e . t t t o cl 11302-l
el lll0,l4 c l 8 3 1 4 2 c l 8 3 2 2 I c l 1 1 3 1 5 9 cl 83020 c l 8 3 1 1 2
cl 833074 cl lJ3307B
lrr slla spclcothcn S p c l c o t h c m c l a s t S p c l c o t h c m c l a s t S p c l c o t h c m c l a s t Boncs of Pasc hispida Spclcothcm clast Spclcothcm clast
Spclcothcm clast Clast of vcin m a t c r i a l
u . 5 0 0 + 160 2 9 . 9 0 0 + t.u00 2 7 . 9 0 0 + 1.200 32.000 + 2.0(x) 1 1 . 8 ( X ) + 1 . 2 0 0 1 6 . 2 0 0 * 5(x)
+ 8 . 7 0 0 t l ) ' l { l l ' -
x . 2 r x t - 2 3 , 5 ( X ) + 3,30t) s s ? r x r + + ' o l } { l l . 9 l , l )
>350.000 G
G G
(;
K K
1 9 . 2 ,1.09
1 . 5 0 l u'l 62L7
5 . 6 1 3 . 3 5
0 . 9 u 5 0 . 9 1 6
L 3 0 1 .3 8 I .'16 L 5 5
1 . 3 6
| . 1 2
1 .5 0 1 . 3 5
> I .000
> I .000 28.7
> 1 .0(x)
> I .000 8 . 2
> l . ( x x )
2 6 2 l l . l
0 . 0 7 5 0 . 2 4 4 0 . 2 2 9 0 . 2 - s 9 0 . 1 0 , 1 0 . 1 , 1 0 0 . 5 3 8 0 . 1 9 7
0 . 4 I 2 L682 K
K
282 Eiliu Lar.sen et al.
The samples contain far more uranium than the lower detection limit of the metho<i (>0.05 pprn). Acceptable to high chernical yields (17-58%) of U and Th ensured sufficient aitivitv for counting. However, experiments with increas_
lng countlng tirnes and tail correction of the 2zETh and r'r0Th peaks suggest that a 2oerror should be used in correlation of the dates. Except for two samples. :30Th/2-r2Th rarios arc high (>2r)). indi_
catlng that contamination from detrital thorium is negligible. }aU/238U
ratios are fairly similar for all samples (mean ratio 1.42 + 0.011) and tvpical for t e r r e s t r i a l e n v i r o n n r e n t s ( S z a b o a R o s h o l t t V S 2 ) and other Norwegian speleothems. There is there_
fore no detectable evidence of post_depositional migration of uranium (except for veln calcite sample el 833078). The samples appear dense and crvstalline. satisfving the conditions fbr the requirement of a closed system since cleposition.
1n .il/rr speleothents are you lrge r than the su rface thev rest upon . I Ience. sample el g3023 post_dates bed B. Howe','cr. spele-othern clasts huve qrtrwn e l s e w h e r e a n d h a v e f r a g m c n t e d rr r n r e t i n t c a f t c r t h e v w c r e p r e c i p i t a t e d . I n g e n e r a l . t h e v a r e th e r e _ forc of equal or greater age than the surfacc the"
rest upon and olcler than the secliment rvhich burie.:
t h e n t . B e c a u s e t h e d i a n t i c t o n w i t h b o n e s G e x o c r i _ e n c e d r n l r s t n o \ c n t c n r \ . \ \ c c u n : l r y tl n l l l h a l t h c spelcotherns are of the samc age or older than the e n c l o s i n g s e d i m e n t .
The speleothem dates of this study support the widely-helcl assumption that speleothems grow p r e f e r e n t i a l l v u n c l e r n o n - g l a c i a l condition:
(Lauritzen & Gascoyne l9tj0. and references c i t e d t h e r e i n . L a u r i t z e n 1 9 8 . 1 ) .
Like rnollusks, bones do not contain mucl.r uran_
iunr ll rrlrro. the phosphate and organic matrix of bone acts as an effcctivc sca\/enger for uranium i n t h e p c r c o l a t i n s s r o u n d w a t c r o f t h e b u r i a l s i t e . A f t e r s o m e ti r n e (, r - ) . a n ' e q u i l i b r i u m ' i n
t h e u r a n _ i u m u p t a k e m a v b e a s s u n t e d . H c n c e . a u r a n i u m series date (t) always rcpresents a minimunt age.
s h c r c t h e ' l n t c i l t c i : I * . r \ e i t r s . (. r ) ,a 1 r . i r 1 t r r r n r l t f c \ \ k l r t r r a h t r u t l 5 k a l S z t r h o l q ) i ( l : S c h w l r r c l l 9 l l 2 ) . U r a n i u n t s c r i e s d a t i n g o f b o n e s h o u l d t h e r e _ fore rvork better tor oldcr than for vounser n t l l t c r i i r l .
B o n e s o f r i n g e d s e a l ( 3 0 g . s a m p l e e l g 3 l - 5 9 ) f r o m bed G were crushed. cleaned of internal clav bv l l t r t a t i o n a n d u r r s h i n r : . a n t l d r r t c d u s i n g a m o O i t i c c i extratlon procedure. The uranium yield was acceptable (I3.7tt). whereas the thoriunt vield
\ \ r s \ e r y lo u ( I . l ' i ) ( T r r h l e - l ). I n order to comprre
B O R E A S 1 6 ( t 9 u 7 ) this date with the radiocarbon dates of bones from the same bed (Fig. 6). the necessarl, value of (x) m u s t b e h i g h ( 1 8 - 2 0 k a ) . F u r t h e r discussion r s dependent on results from more samples.
Of the four siimples from the porous bed K. two may be rejected (el 83020 and el g3307B) because of probable 2i:Th contamination and/or evidence o f u r a n i u m l e a c h i n g (r r , , T h / : r r U > l . U ) . O f t h e remaining two samples, el g3307A is consiclered a n a l v t i c a l l y c o r r e c t . w h i l e s a m p l c e l g 3 l l 2 r e s u l t e d rn a spectrum with considerable tailine of the r:sTh peak. Tail correction vielded a bcst estinttte of 80 ka. rvhereas the voungest possible age (.worst c \ t i m i t t c ' ) i : 1 . 1 . 5 k r t .
P a l a e o m a g n e t i c p r o p e r t i e s
General results
Thc results of cletailecl palaeo-rockmagneric ano m a g n e t i c f a b r i c a n a l v s i s o f l l . l o r i e n t e d s u n r n l e . f r o n t b e d s J , I , I { a n c l F . p i t l . r c p ( ) r t e c l c l s e w h e r e ( L ( r v l i e & S a n d n e s 1 9 8 7 ) . can be summarized a s folktws : the clepositi<tnally-relatecl remanent mitg_
n e t i z a t i o n i n b c d s J . I a n r l F ( c a r r i c c l b v r n a r : n u t i t , . srains <2 prnt has probabll not hccn nrociitjetl hv p o s t - d e p o s i t i t r n i r l d i : t t t r t i o n \ ( ) r c ( ) l l p i r c l i , , n d u r _ i n g c o n s o l i c l a t i o n . P a l a e t r r n a e n c t i e d i i c c t i ( ) n s t h u s reflect genuine recorcls of the geornagnctic fielc.l.
Partiallv dentagnetized (therrlal/alternating h e ld ) . s i n . s l c c ( ) m p o n e n l d i r e t . t i , r n s c l c : t . r i h c h i r : l i a m p l i t u c l e v a r i a t i o n s o f i n c l i n a t i o n ( :u b - h o ri z o n t l l t o 8 0 ' ) , r e p r e s e n t e d b v d c c l i n a t i o n s d i s t r i t r u t c d b e t w e c n e a s t - s o u t h - w e s t ( F i g . l . l ) . T h e s e anorn_
a l o u s p a l a e o m a g n e t i c d i r e c t i o n s . w h i c h a r e n o t i n accord with a normal conflguration of the Late Quaternary geomaenetic field. arc interpreted to r c c r l r d t u o g e ( ) t n a u n e l i c c \ r . u r \ i ( r n s .
Bcd Il carries stecply-dipping palaeomagnetic d i r e c t i t r n s c o n t p l r l i h l c w i t h t l t e p r c s c n t g . , , , r r " g _ netic fielcl. The origin of magnetization in this becl, however. is not necessarill, relatecl to thc actual d e p o s i t i o n . a s f a l l i n g b l o c k s . c o n s t i t u t i n g b e c l G . m lr v h a r c i n d u c e d l r s h t r c k r e tn u n t n t n l r g r r e t i z i t t i o n p r r r u l l c l t o I h e a m h i c n t g e o n r r g n c r i c t i c i c l ( S y n r o n s et al. 1980). Bed II was probablv deposited clurinr t h e d r t i n i r r g o f l h e c a v c . p r e e c t l i n q r r c c u m u l r t i , r i of the blocky bed G. The palaeomagnetic direc_
tions in bed H thus record the geornagnetic field preceding or coinciding with the onset of the Alesund interstadial some 33 ka ago (Fig. 16).
Similar considerations also apply to the origin of the steeply-dipping palaeomagnetic inclinations
t s o R E A S l6 ( l 9 u 7 )
o E q - t N A r I 0 { 0
INCL I NAt l(l{
0
f '
/ , ) , g . / J . S t r i r t i u r a p h i c p l o t o f t r n i v c c t o r i a l p a l a c o n a g n c t i c d i r c c - t i ( ) n s i n e x c i r v a t i o t t I a f t c r p i r r t i a l a l t c r n r t i n g f i e l c l d c n t a g n c t i z a l i 0 n to - 1 0 r n f . L i t h o l o g i c u n i t s . b o l d l e t t c r s to t h c l c l t . r r c i n d i c a t t t l b t t r r o k c n li n c s .
in the laminated clay bed L, overlain by the blocky bed K.
G eomognetic excLtrsions
Virtual geomagnetic poles (VGP), based on five-
Caue stratigraphy in W Norway 283 points running mean directions (univectorial), define very consistent paths, as shown on the Mer- cator projection in Fig. 15. During formation of beds J and I (<56 ka). the VGP display two mer- idionally constrained paths situated around 90"W and at the site longitude. This characteristic of some transitional lleld geometries (Hoffman 1982). suggesting that the excursion may present an aborted geomagnetic reversal. The predomi- nantly non-dipole conliguration of the geomag- netic held during reversals implies that syn- chronous VGPs from different regions may not necessarily coincide. Hence, on a global scale an instability of the geomagnetic field is likely to be reflected by different VGP signatures. From these considerations. the excursion in beds J and I is cor- r e l a t c d w i t h t h c L a s c h a m p / O l b y e v e n l . d a t e d h y different mcthods to have occurred between 36 and 42 ka (Gillot et al. 1979). Within this time interval, additional regional records of inferred excursion have been encountered in Denmark (Rubjerg Iow- inclination excursion. Abrahamsen & Knudsen 1979) and in Arctic Ocean sediment cores (LOvlie et al. 1986).
The three counterclockwise VGP loops (Fig. 15) arc interpreted to represent the behaviour of the non-dipole lield during an aborted reversal.
Assuming a lifc-span of c. 1.(XX) years for a com- plete non-dipole cycle (Denham 1974). estimates for the duration of this high-resolutictn recorc 6
- t s
B
a
t . ' . '
l l
l e i '
t l
f t
f . :
I x " .
F :
| . " T
1 . . ' . .
l r
|' ,.,
t . . "
I r r ;
I 'r.
| . '
l ' r . .
| ' .
t '
Il r
t l
I t
l r ,
1 1 ,
L '
U
o .
t l
F F J
S K J O N G H E L L E R E N V G P P O S I T I O N S
0
L O N G I T U O E / ' l g . 1 - 5 . M e r c r t o r . p r o l c c t i o n o l
v i r t u l r l g c o n r a g n c t i c p o l c p o s i t i o n s fo r b e c i s . 1 . I a n d F . I r l r - e r l p r t 5 p o i n t ' r r r n r r i l L r r t e l r r t ( u n i \ e c t o r i a l ) .
100
4
B € 0 I { 5 6 - l 0 k o )
^ ^ B E o F ( 1 0 - 1 2 k o )
1 l 5 0 w 1 5
284 Eiliu Larsen et al.
range from 500 to 3.000 vears. depending on w h e t h e r t h e p a t h s a r e in t e r p r e t e d t o r e p r e s e n t 1 . 2 or 3 complete secular variation cycles, respec- t i v e l y .
None of the beds records a complete geo- magnetic cxcursion VGP path. but attention is put to the steeply-dipping inclinations residing in the beds deposited prior to (bed L) and after (bed H) deposition of beds J and I.
The gap in the VGP path between top bed J and base bed I evidences a short depositional hiatus b e t w e e n t h e t w o b e d s .
Bed F ( <29 ka) defines two equatorial, counter- clockwise VGP loops between 60" and 90'E, and 15'S and l0'N. Considering that this VGP path probably represents a high-resolution. incomplete record of geomagnetic excursion, the correlation with one synchronous VGP determination (spot- reading)for the Lake Mungo cxcursion ( Iire-place F l 2 , 2 8 , ( X ) 0 + 4 1 0 B . P . , 4 7 ' E , 6'5, Barbetti &
McElhinny 1976) is remarkably good. The oldest Lake Mungo event spans some 2.000 years (30 to 28 ka), and is represented by three spot-readings of equatorial VGPs covering 180" of longitude ( B a r b e t t i & M c E l h i n n y 1 9 7 6 ) . T h e t w o s m a l l amplitude VGP loops recorded in bed F are thus likely to represent a time span considerably less than 2,000 years.
Vertebrate fauna
Remains from vertebrate faunas older than 20.000 years are extremely rare in Norway (Mangerud 1981). Here, we have identified more than twenty speciesfrombedsdatedaround30,000 B.P. (Table 5 ) .
ldentification and description
The overwhelming percentage of the bones were found in bed G (Table 5), and most of them in excavation 2. The few bones in bed F are assumed to have been redeposited from G, and the bones ascribed to bed H could, in the field, be genetically related to bed G. Nearly 7,000 bones (Table 5) were collected from this level, being around 30,000 years old. Another group of approximately 1,000 bones (Table 6) were collected from bed B, being 10,000-12,000 years old.
No whole skeletonswere found. However, some bones belonging to the same animal, and parts of
UoREAS r6 ( 19ti7) jaws with several teeth were recovered. Bone sizes varied between a few mm and some 6 to 7 cm.
The samples were carefully washed on a 1 mm sieve and dried at room temperature. Clay par- ticles attached to bones were removed by careful brushing or scraping. Most bones were well pre- served and well suited for identilication. Identi- fications were carried out either with the naked eye or occasionally at 2-4x magnification; always comparing with a modern reference collection.
The level to which bones can be determined is mainly dependent on bone preservation and whether they contain diagnostic features. The more difficult bone fragments were identified by three persons working independently. This was the case for example when trying to distinguish between brunnich's guillemot and atlantic murre.
During most of the sampling the individual bone-bearing beds were sampled as one unit. But during the later period of the field work, bed G in excavation 2 was divided into a lower (L), a middle (M) and an upper (U) zone. Due to lack of strati- fication. the boundaries between the three zones are arbitrary and may have varied somewhat between persons during the sampling period.
The vast amount of bones from bed G are from birds, mostly little auk and brunnich's guillemot.
Arctic fox is the dominating mammal.
Six hundred and ninety-four fragments were col- lected from the transition zone between beds D and B in excavation 3, and are all included in bed B (Table 6). Birds dominate and little auk is the most common specles.
From the identified species, it appears that species diversity was lower during deposition of bed B than during bed G (Tables 5 and 6). Some species not identilied in the latter, however, are found in B : Mountain hare, squirrel, velvet scoter, eider duck, greater black-headed gull and four- bearded rockling.
Palaeoecology
Alesund interstadial (Figs.5 anci 6). According to our interpretations, the bones in beds F, G and H (Table 6) belong to the same ice-free period cen- tred around 30.000 8.P.. the Alesund interstadial (Fig. 6). From this level, about 17 times as many bones were found in excavation 2 as in excavation 1 (Table 5). The investigated volume of sediments from this bed was roughly comparable in the two excavations, but only a small volume was inves- tisated in excavation 3. We assume that differences
