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Sea-levelchansesand pollen stratigraphyon the outer
coast of Sunnmflre, western Norway
J O H N I N G E S V E N D S E N& J A N M A N G E R U D
Svendscn.J I.&Mangcrud,J.:Sea-lcvelchangesandpollenstratigraphyontheoutcrcoastofSunnmorc,
wcstcrn Norway. Norsk Geologisk ridsskrift, vol. 70. pp. ll1 134, oslo 1990. ISSN 0029-196x.
Thc sca-level history for the outcmost coast of Sunnmore was recorded by studying thc litho- and
palvnomorph stratigraphy in cight palaeo-lakes. Deglaciation occurred around 12,600Bp and was
followcd by a rapid emergcnce. Then. during thc late Allcrod and younger Dryas thcre was a longlasting stillstand. This suggestsa slow and even euslatic sea-level risc of less than l0 m during this time.
A subsequcnt cmergence startcd wilh thc onset of thc llolocenc climatic amelioration around 10.200Bp.
Radiocarbon dates from the Holoccnc wcre obtained from only one basin. Thc dates from this basin
indicatc that the Tapes transgressionculminated before 8000 BP; howevcr, manv dates from neighbouring
arcas suggest a culmination around 60fi)-7000 BP. Thc Late Weichselian pollcn stratigraphy has been
subdivided into four assemblagc zones which can casily be corrclated with established zoncs for thc
A l c s u n d a r c a . T h e s e i n c l u d e :R u m e r f o x y r i a ( 1 2 , 6 f i ) - l 2 , t n 0 B p ) . B e t u l a - E m p e t r u n ( 1 2 , 0 0 0 - 1 l . t u ) B p ) ,
Salix-Artemisia (11,000-10,200tsP) and Betula-Juniperrc-Empetram assemblage zones. Climatic
changcs instigatcd the changes in vcgctation associatcd with these zonc boundaries.
J. I. Suendsen & J. Mangerud, Ltni.uersityof Rergen, Dept. of Geologt, Sec. R, Alt$t.
This paper presentsa relative sea-levelcurve for
Lein0y basedon the litho- and pollen stratigraphy
from eight palaeo-lakessituatedto the southwest
of Alesund, western Norway (Fig. 1) (Svendsen
1985). The study forrhs part of an investigation of
sea-levelchangesin Sunrmore and partly relies
on previous work in the Alesund area (Mangerud
et al. 1984; Lie et al. 1983; Kristiansen et al.
1988). The objective was to extend the database
as far west as possible, to where the glacio-isostatic uplift was minimal in order to describe the
sea-level changes along a cross section of the
coast (Svendsen& Mangerud 1987). The pollen
stratigraphy diagrams were used primarily for
biostratigraphical correlation. They were, however, also used to reconstruct the veeetational
h i s t o r yo f t h e a r e a .
The study area includesthe islandsof Gurskoy,
Leinoy and Bergsoy (Fig. 1). The cored basins
are situated on the uneven strandflat which
encircles the central mountainous part of these
islands. The bedrock consistsofgneisses(Gjelsvik
1951) partly covered by a thin and patchy veneer
of till. All the studied basins- with the exceDtion
of Litlevatn and Dalevatn, which are still laies are bogs which are completely filled in with Holocene organic sediments.
tt,
N-5007 Bergen,
Methods
The sea-level curve was constructed accordins to
t h e c l a s s i c aSl c a n d i n a v i a m
n e t h o dw h i c h r e l i e so n
the stratigraphy in emerged lake basins situated
at different elevations(Fig. 3 in Svendsen& Mangerud 1987). First a Russian peat sampler was
used to map the lithostratigraphic units across
each basin and to locate appropriate coring sites.
Then samplesfor laboratory investigationswere
collected with a piston corer with a diameter of
110mm. which provided up to 2m long core
sectl0ns.
The age of the sea level correspondingto the
elevationof the outlet of each basinis determined
by identifying and dating the transitron between
brackish and lacustrine beds in the cores. In
this area these boundaries (isolation contacts)
coincide with major lithological transitions (Lie
et al. 1983) and were determined visually and
confirmed by means of pollen (phytoplancton)
and diatom analysis.
The chronostratigraphicterminology used in
this paper follows Mangerud et al. (1974), who
defined chronozones in radiocarbon vears.
Il2
J. I. Suendsen& J. Mangerud
NORSK GEOLOGISK TIDSSKRIFT 70 (1990)
Fig. 1. Location map of the study area with a key map of southernNorway. The investigatedsites are marked with dots. The
Younger Dryas isobasethrough FroystadmyraI, II and III is indicated.
Radiocarbondates
The radiocarbondates(Table 1) were calried out
at the Radiological Dating Laboratory, Trondheim under the supervisionof Reidar Nydal and
Steinar Gulliksen. Samplesof lacustrine gyttja
from directly above the isolation contact were
dated to obtain the time of emergenceof the
lakes. To avoid contamination from penetrating
roots from submergedplants (Kaland et al. 1984)
only the NaOH-solublefraction wasused(A after
the lab. no.). The errors due to the thicknessof
NORSK (;EOLOGISK TIDSSKRIFT 70 ( I990)
Sea leuel and pollen, W. Norwat
t13
f a b l . 1 R a d i o c a r b o nd a t c s l r o m t h c b a s i n sp r c s c n t c d i n t h i s p a p c r . A a f t e r t h c l a b . n o . m c a n s t h a t t h c N a O I I d i s s o l v c di r a c t i o n
i s d a t c c l . r r ( v a l u c s a r c g i v c n i n t h c P D t s s c a l c . A l l s a m p i c sa r c c o r r e c t c dl o r i s o t o p i cl r a c t i o n a t i o nt o i r ( - - 1 5 . ; i , . T h e n r a r i n c
s h e l l s a r e c o r r c c t c d l o t a r c s c r v o i r a g c o f , 1 , 1 0l c r r s . J h c n a r i n c i i n d b r a c k i s h s c d i n r e n t si l r c n o 1 c o r r c c t c d l o r r c s c r t o i r a g e .
b c c i l u \ c t h c p r o p ( ) r t i o no l t e r r c s t r i a l t o m a r i n c o r g a n i c m a l t c r i s u n k n o w n : s c c d i s c u s s i 0 ni n t c r i .
ll asrI
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T-,1967
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sediment slices used for radiocarbon dates (2
+ cm) were consideredto be in the order of 5f)1(X)vears as estimatedfrom a sedimentationrate
of 0.3--0.5mm vr r. All samples.with the exception rrt T-496'7 A and T-818-5 A from Frol'stadmvra l. give reasonabieagescompared \\'ith
weii-dated stratigraphicallevels. like the Vedde
Ash Becl (Manserucict al. 19E"i)and the Aiierod/
Younger Dryas and the YD/Preboreal transitions
(Kristransen et al. 1988). The two unsupportecl
date-sfrom the Holocene gyttja in Froystadmyra
I are discussedlater.
For one sampie from Kulturmyra (T--5150).
fragments of marine shells were dated and corrected for a marine reservoir age of 440 years
(Mangerud & Gulliksen 197-5).In addition to this
sheli date. one sample of marine sedimentsfrom
this core (T-5149 A) and two other sediment
samplesof a brackish origin from Froystadmyra
'fhe
I ('f-4969 A and T-4966A; were dated.
gvttja
ciates should be corrected for a reservoir age
corresponding to iheir content of marine components. The tirst-mentioned sample was taken
from a level 2-7 cm below the dated shells.T'he
dilTerence between these two dates is only ,s(l
years when the gyttja date is corrected lor a
similar marine reservoir age of 440 years. On the
other hand, the samplesof brackish origin from
Froystadmyra I both gave expected ages according to the litno- and pollenstratigraphy.Probablv
most of the organic material in these samples is
of lacustrine and/or terrestrial origin.
The sediment sequences were correlated bv
means of pollen-, litho- and tephra stratieraphy, which provided independent controi for
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evaluating the consrstencvof the radiocarhon
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Pollen analysisand diagrams
'fhe
sediment samples for pollen analysiswere
taken as a known volume of wet sedimentsand
Lycopodium tablets (Stockmarr 1971) were
added. An influx ciiagrarnhas been constructeci
( S v e n d s e n1 9 8 5 ) . b u t i s n o t p r e s e n t e di n t h i s
paper. I'he preparation procedures included
standard acetolysisand HF treatments. and the
identification procedures used are provided in
Kristiansenet al. (i98lti
A pollen diagram for most ol the Late Weicnselianis constructedfrom the lacustrinesediments
in F'roystadmyra II (Fig. -5). From the other
basinsonlv short seciimentsequencesaround the
marine/lacustrineboundarieswere analysed.
The number of polien grains counted (sum P)
was between 200 and 500. This polien sum
includes all pollen except for the limnophvtes.
'l'he
palynomorphsnot included in the sum P are
calculatedas the percentageof sum pollen -r the
actuai palynomorph.
In the pollen samplesthe occurrenceof freshwater green algae (Pediastrum, Botryococcus and
Tetrahedro n minimu m\ and marine dinofl agellate
cysts('Hystrix') was noted and used to determine
the marine/lacustrinetransitions,as shown in the
p o l l e n d i a g r a m s .T h e r e i s i n v a r i a h l v a d i s t i n c t
flourishing of the green algae directly above the
whereas dinoflagellate cysts
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Sealeuel and pollen, W. NorwaY 115
NORSK GEOLOGISK TIDSSKRIFT 70 (1990)
Kulturmyra and severalother lakes in the Alesund area) there is a marked increaseof pebbles
Diatom analysisfrom a few key beds in five of compared to the sedimentsof Aller@dage. The
the basinswas carried out by Bjorn Helge Seters- pebbleswere probably dropped from seaice.
moen, University of Bergen (Svendsen1985).
Well-definedred, red-brown and greenlamina
The results (not presented in this paper) were occur in the upper part of Formation B in Froyused to check the determination of the marine/ stadmyra I, Litlevatn and Skolemyra (Fig. 3).
lacustrinetransition.
These strongly coloured lamina are typical of a
brackish environment in this type of basin (Kristiansen et al. 1988;Krzywinski & Stabell 1984).
Diatoms
Lithostratigraphy
The stratigraphyfrom the coresis shown in Fig.
2. With the exceptionof Almestadmyra,the lithostratigraphyin these basinshas been subdivided
into formations and membersas definedby Kristiansen et al. (1988). Formations A and B are
marine/brackish sediments,whereasthe Langevig and Hatlen Formations are lacustrine sediments. The Langevig Formation is subdivided
into three members:MehukenAse and Leirstad.
An important marker horizon is the Vedde Ash
Bed (10,600-r60BP) (Mangerudet al. 1984),
which occursin both marine and lacustrinestrata'
A general description of the lithostratigraphic
units is given below. The lithostratigraphy of
Almestadrnyra is described in the section that
discussesthe individual basins.
Formation A. This formation comprises the
lowermost marine sedimentsand is underlain by
bedrock or till (Fig. 2). The sediment consists
mainly of grey silt with sandy beds in the lower
part. A low organiccontent is shownby a losson
ignition of lower than2Vo. Macrofossilsare not
found. The formation was most probably
depositedin a cold marine environmentsoonafter
deglaciation,which in this areais dated to arounc
12,600BP.
Formation B. This unit is a brownish grey to
grey gyttja silt. The main difference from the
underlying formation A is a higher organic
content. Marine shells occur frequently, and the
presenceof Mytilus edulis andModiola modiolus
from the baseof the formation indicate a warmer
environment. Two radiocarbon dates from Kulturmyra suggest an age of around -12,6008P
(Table 1) for the baseof the formation. In marine
beds from the Younger Dryas (FroystadmyraI,
The Langeudg Formation. This lacustrine formation has been found in all basinsexceptFroystadmyra I, Kulturmyra and Almestadmyra,
which where all isolated from the sea after its
formation (Fig. 2). The Mehuken Member was
only found in Dalevatn, which is located above
the marine limit and therefore hasonly lacustrine
sediments.This memberis characterizedby a very
low content of organic matter and was deposited
Core
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Fig. 3. Photograph of the marine/lacustrine boundary in Skolemyra. Note the lamination at the top of formation B.
Fig. 2. Lithostratigraphic successionsand radiocarbon dates obtained from the studied basins. On top of each core segment the
depth below the sediment'surface for that Palticular core is given
tl6
l. I. Suendsen& J. Mangerud
NORSK GEOLOGISK TIDSSKRIFT70 (1990)
Core
depth
(cm)
Pollen stratigraphyand vegetation
history
485-
tg)
The pollen stratigraphyis similar enoughto that
found in the Alesund area that the assemblage
zones defined by Kristiansenet al. (1988) are
applicableto this area. The following description
and discussionis basedmainly on the diagram
from FroystadmyraII (Fig. 5).
o
c
490 -
@
.+
{fi
5'
o
,ril 1 Rumex f Oxyria assemblage zone
(12,600-12,000
BP)
This zone is characterized by a high percentage
of Rumexf Oxyria anda low percent age of Betula.
495 The base of the zone was only identified in Dalevatn and it is assumedto be slightly younger than
deglaciation which occurred around 12,600BP.
f
A treeless arctic-alpine vegetation is suggested
@
for this zone. Rumexf Oxyria was an important
component of this vegetation, which together with
the Salix herbacea leaves present in the sediments
indicates the presence of extensive snow-beds in
this region at this time. A certain degree of differentiation is evident from the changes in the
composition of herbs above the marine/lacustrine
boundary in Froystadmyra II and III. The difFig. 4. Photographof the Leirstad Member in FroystadmyraII.
ferentiation includes the initial development of a
swamp vegetation around the lakes, as indicated
by the presence of Cyperaceae and Caltha type
contempo-raneously
with the marine Formation (Caltha palustris). The sea shore was probably
A. The Ase Member is a brownish silty algae occupied by a light demanding vegetation which
gyttja and the LeirstadMemberis a light greysilt included several mountain herbs (e.g. Cheno(Fig. a). The Leirstad Member was deposited podium, Sedum, Asteraceae sect. Asteroidae).
during the Younger Dryas and the boundariesare High values of Ranunculus (Anemone type) at
consideredto be isochronous
within the area.The the level directly above isolation contact are attriVedde Ash Bed is found near the centreof the buted to an aquatic species,probably Ranunculus
peltatus.
LeirstadMember.
U)
o
g
3
o
The Hatlen Formation. In the lower part, the
sedimentsconsistof a light brown, fine detritus
gyttja and this gradually becomes darker and
coarserupwards.The boundarybetweenthe Leirstad Member and the Hatlen Formation occursat
the samelevel as the distinct rise in the Betula
curves.In this studythis boundaryis assigned
the
minimum age of 10,200BP. However, a basal
date from the Hatlen Formation (T-5145A) in
Kulturmyra (Table 1) together with similar dates
from the Alesund area (Kristiansenet al. 1988),
may indicate a slightly older age (10,30010,500BP) for this boundary.
Al 2 getula-Empetrum assemblagezone
(12,000-11,000
BP)
The lowerboundaryis definedby a distinctrise
in the Betulacurve at the sametime as the values
of RumexfOxyria decline.This boundaryis dated
to around12,000BP (Kristiansenet al. 1988)and
we assumeit is roughly contemporaneouswithin
the entire Sunnmorearea.TheBetularise is probably due to the first occurrenceof the tree form of
Betula (Betulapubescens)at protected localities.
However, a relatively low influx indicates that
NORSKGEOLOGISK
TIDSSKRIF'|
70(1990)
real birch forests did not occur during the Late
Weichselian. A scanty heath vegetation is shown
by the appearance of a low percentage of Empetrum.
The changesin the vegetationat the Al tlAl Z
transition around 12,000BP couid possibly reflect
a natural successioninvolving soil maturation and
a closing in of the vegetation, independent of
climate. I{owever, after the preceding 600 ,vear
period, the changes seem to occur rapidly and
simultaneouslv throughout the entire region, suggestingthat climatic improvement instigatedthese
changes. The appearance of Filipendula (most
likely Filipenduala ulmaria) at this transition indicates a minimum mean July temperature of 8-9"C
(Kolstrup f979). By 11,500BP the occurrenceof
Myriophyllum spp. and Nymphaea indicates a
mean July temperature of not less than 10"C
(Kolstrup 19'79).The decline in the Betula curve
at the top of the zone is below the lithostratigraphic boundary, the difference corresponding
to some 50-100 years. This time lag is similar
to that found by Larsen et al. (1984) whereas
Kristiansen et al. (1988) found that only the influx
of Betula pollen declined before the sediment
changesat the lithostratigraphic boundary. A concurrent decline in the Poaceacurve together with
an increase in the percentages of Salix and
Rumexf Oxyria might indicate a moister climate
at the AlleradfYounger Dryas transition.
,ril 3 Sali"-Artemisi a assemblage zone
Sea leuel and pollen, W. Norway
117
the snowbed plant Salix herbacea and S. polaris.
Flowever, it is possiblethat part of the,Sallxpollen
is derived from willow as suggestedby Larsen et
al. (1984).
The changes in the pollen composition associated with the Salix-Artemisia zone were caused
by climatic deterioration in the Younger Dryas.
The decline in the Salix curve, a relatively low
influx of Rumexf Oxyria and the increasing importance of certain mountain herbs indicate a
gradual transition to a drier, more continental
type of climate.
Al 4 B etula-Juniperus-Empetrum
ussemblage
zone
The lower boundary coincideswith the baseof the
Hatlen Formation (10,200-10,300BP). Slightly
above, there is a marked increase in Empetrum
values and even further up a rise rn Juniperus
is noted. The arctic-alpine elements which were
common in the previous zone disappear.
From 490 to 472 cm there is a dramatic increase
(from 12 to 1100pollen cm-2 yr 1) in the influx
of Betula, and this is most likely due to the establishment of Betula pubescens, as suggested by
Kristiansen et al. (1983) for the Alesund area.
The influx of herb pollen was higher than during
At 3. ttrese changesin the pollen flora reflect the
development of an open birch forest where the
ground cover is dominated by grassesand ferns.
In open, well-drained areasEmpetrum heaths and
later juniper bushesdevelop.
(11,000-10,200
BP)
This zone is characterized by a low Betula curve,
a high percentage of Artemisia and a high percentageof Salix in the lower part of the zone. The
zone boundaries are close to the lithostratigraphic
boundaries of the Leirstad Member. The relative
importance of several herbs which are favoured
by unstable soil increases, such as Saxifraga
oppositifolia type, Sedum sp., Cerastium type.
Chenopodium, and Caryophyllaceae indicates a
reversion to open conditions. With the exception
of Artemisia the influx of most pollen species
decreasesand the total reaches a minimum (89
pollen cm 2 yr-1) at 492cm (influx diagram is not
presented). Salix was a dominant component of
the vegetation around the lake during the early
phase of the Younger Dryas. It is suggestedthat
a substantial amount of snow accumulated in
depressions and offered favourable habitats for
The investigatedbasins
Dalevatn, which is the only basin situated above
the marine limit and contains only lacustrine sediments, is described first. The other basinsused to
construct the sea-level curve (Fig. l7) are
described in the same order that they were isolated from the sea. These include Fr@ystadmyra
III, Froystadmyra II, Skolemyra, Litlevatnet followed by three basins, Froystadmyra I, Kulturmyra and Almestadmyra, which were isolated
at about the same time. With the exception of
Almestadmyra, the lithostratigraphic units in all
cored basins fit into a complete sequencewhere
the highest have more lacustrine beds and the
lower more marine beds (Fig. 2).
For each basin an'assumedage'is given for the
isolation of the lake. These proposed ages are
NORSK GEOLOGISK TIDSSKRIFf 70 (1990)
118 J. I. Suendsen& J. Mangerud
IT
FROYSTADMYRA
CALCULATIONBASIS:
P
a
uJ
u ) )
2 >
O <
N ( '
z z
)) ))
uJ
ul
o
20 40 60 807.
ffi
10 20 30 40
rrne detritusgyttia
50 60'/.
E
O
10 20 30 40 50%
F-l Diatomitesitt
r0
o
q
d
O
10 20 30
407.
ffi
r0
20 30
s,ttygyttlt
lig. -i. Pollcn diagram from Froystadmyra II
based on critical assessmentsof the individual
radiocarbon dates together with a correlation to
regional litho- and biostratigraphy (see Fig. 6 in
Svendsen& Mangerud 1987).
Daleuatn ( UTM coordinates 22801 I ),
30.5 m a.s.l.
The lake is situated in a valley at the southern
end of Gurskoy (Fig. 1) and it is surrounded by
bog from which the samples were taken. The
outlet is a rock threshold 30.5 m a.s.l. which has
recently been lowered by I-2 m. In this basin the
entire sequenceis most likely of lacustrine origin
(Fig. 2). The lower unit is massive silt of the
Mehuken Member.
The pollen diagran (Fig. 6) shows a noticeable
decreasein the Rumexf Oxyria curve between 668
and 658 cm at the same time that the percentage
of Betula increases from below ljVo to above
20%. This transition represents the boundary
between the RumexlOxyria and Betula-Empetrum assemblagezones. Provided there is a constant sedimentation rate throughout the Ase
Member this suggeststhat the lower boundary of
this unit is around 12,500-12,600 BP. No radiocarbon dates are available from this basin.
Sea leuel and pollen, W. NorwaY
NORSK GEOLOGISK TIDSSKRIFT70 (1990)
o
G
o
E
=
1'I9
q
- . ;
ii&e
j: oi ). 9
" =
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4=
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9
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n;e
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o
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o g 5 6
>
f9d sirrand ctay
confirm that the sediment is of marine origin. In
addition, the high trophic status as evident by
the flourishing of freshwater algae (Tetrahedron
diam
in
50
minimum and Pediastrum) at the base of the Ase
The almost circular basin is about
four
Member is assumed to be an effect of the isolation
about
is
only
area
meter and the catchment
times the basin area (Figs. 7, 8). The present of the basin.
The fact that Formation A is directly overlain
outlet is acrossa moraine threshold(22.2 m a's.1.)
the Ase Member indicates that the lake
m
durby
which seemsto have been lowered by 1-2
shortly after deglaciation and before the
original
emerged
The
area.
of
the
recent
cultivation
ing
commencement of sedimentation of the marine
threshold has been estimated to be 23 m a.s.l.
In this basin Formation A is directly overlain formation B. Provided a constant sedimentation
by the lacustrine Ase Member (Fig. 2). Very few rate for the Ase Member the transition level from
diatoms were found below the assumed isolation the RumexfOxyria to the Betula-Empetrum
contact, but frequent dinoflagellate cysts (Fig. 5) assemblage zone suggeststhat the marine/lacus-
III (UTM coordinates
Fr@ystadmyra
23 m a.s.l.
291147),
nA
N O R S KG E O L O G I S KT I D S S K R I F I 7 0 ( 1 9 9 0 )
& J. Mangeru.i
J. I. Suendsen
DALEVATNET
Calculatron
basis: { P
qJ
EI
e
C
-
-
Ni
U
c
o
c
o
-i
ol
?
a')
trl
6l
9 t> l
o
650
l
660
:
urol
I
l-
E
0)
2
q)
a
I
t-
F
uuJ
l -
i
l
6901
l
:
:
=
|
FilH sitty Erytla
]
.
m
liljil silt
fig. 5. Pollen <iiaglam frorn Dalevatn.
trine boundaryis between12,4frtand 12,550BP.
A gyttja sampie (765-77{)cm)frorn the level
directl,vabove the isolation contactwas radioto 12,22A! 370BP (T-5146A)" The
carbon-dated
assumedage of isolationis 12,50t)BF.
isolation contact occurs weil below the transition
frorn the Rumexf Oxyria to the Eetul{t assemblage
zones (Fig. 5). Lacustrine gyttja (524 527 cm)
from directly above the isolation contact was
radiocarbon-datedta 72,410I 180BP (T-4968,
IIA). The assumedage of isolation is 12,300BP.
II (uTM coordin{ttes
FrQystadmyra
300157),18 rn,a.s.!."
Skolemyra(UTM 262 162),i2.4 m a.s.l.
The bog is situated 1000m to the NE of FrQystadmyra III (Fig. 7). The basin is about
100 x 100 ni and at present is drained by a ditch
which cuts through a till threshold at the western
end of the bog. A considerable part of the surrounding area is now cultivated" There are no
brooks entering the lake and the main supply of
water is by means of surface runoff"
Fr@ystadmyra II has a thicker (1m) marine
sequencethan Froystadmyra III and includesFormation ts. The isolation contact coincides with
the lithological transition from Formation B to
the Ase Member (Figs. 2,5). Three sampleswere
analysed for diatoms across this boundary
between 530 and 525 cm. The brackish sediments
represent a narrow zone (less than 3 cm), indicating that the basin was isolated during a rapid
regression. The pollen stratigraphy shows that the
Fart of the basin {Fig. i0) was not available for
coring as it was filled in for the constr-r.lcticn
of a
school building. There are no brooks ri'hich drain
into the basin and the outlet is a bedrock threshold
at the southern end of tire Lrog.
Generally the lithostratigraphy in this basin
is similar to that in Fr@ystadmyra II (Fig. 2).
However, after 1 m of marine sediments a more
substantial brackish period is shown by welldefined red brown and green lamina (565-562 cm)
directly below the marine/lacustrine boundary
(Fig. 3). Only three samples(563, 560 and 555 cm)
were anaiysed for pollen, showing that the
marine/lacustrine boundary lies within the
Rumexf Oxyria zone (Fig. 11). This age is coniirmed by a radiocarbon date directly above the
isolation contact (72,090 4- 200 BP, T-5147 A).
The assumed age of isolation is 12,250BP.
NORSK GEOLOGISK TIDSSKRIFT 70 (1990)
Sealeuel and pollen, W. Norway 121
Froystadmyra
Fig. 7. A map of the bogsFroystadmyraI, II and III, Leinoy (Fig. 1). The basinsare shadedand the crossesmark coring points.
The location of the analysedcore is encircled.
t22 J. I. Suendsen& l
Mangerud
NORSK GEOLOGISK TIDSSKRIFT 70 (1990)
. :
Frg. 8. Photographof FroystadmyraIII viewed towards the wesr. The bog is
encircledby trees.
In the lacustrine sequencethere is a layer of
dark brown, ^coarsegyttja containing sediment
lumps of the Ase Member, terrestrial turf, stones
and gravel which rests on the Vedde Ash Bec
(Fig. 2). This mixture of sedimentsmust be the
result of an early Holocene slumping. The sedi_
ment aboveconsistof a dark brown, fine detritus
gyttja of the Hatlen Formation.
Litleuatn (UTM coordinates 349096),
1 9 . 2m a . s . l .
Litlevatn is a long and narrow lake basinbetween
low rock outcrops(Fig. 1). Most of the basinis
filled with lacustrinesedimentsand a layer of peat
on the top. The outlet is a bedrock threshold in
the northeasternend of the basin.
Unlike the preceding basins, which contain a
relatively thin marine sequence,this basin has
a long marine sequence(9I5q22.5cm) that is
overlain by a relatively thin layer of the Ase
Member (722.5--708.5cm)(Fig. Z). Distinct
brown, red and green lamina occurring in the
upper part of Formation B between 727 and
722.5cm suggestsa brackish transition period of
some duration. The pollen diagram shows that
the isolation contact is younger than the Rumexf
Oxyriaassemblage
zoneandwell into the Allergd
(Fig. I2). A sample of lacustrine gyttja (723_
719cm) from directly above the isolation contact was radiocarbondated to 11,510-+ 1208p
(T-5148 A). The assumedage of isolation is
1 1 , 5 0B
0 P.
Frlystadmyra I (UfM
6.2m a.s.l.
coordinates 295153).
The bog is situatedabout 500m to the southwest
of FroystadmyraII (Fig. 7). The basin is about
250m long and 100m wide with a bedrock
threshold in the western end. In the lower oart
there is 3.3 m of marine and brackishsediments
(Fig. 2). Becauseof a late isolationthe basindoes
not contain sedimentsof the Langevig Forma_
tion. The lithostratigraphicprofiles show that the
upper boundary of Formation B is an erosional
surfacewhich implies that the primary isolation
contact is missing in this basin (Fig. 13). Seven
NORSK GEOLOGISK TIDSSKRIFT 70 (1990)
Sea leuel and pollen, W. Norway
e L u c/ N f l l o d
r
uePunqeI
uouuos I
i
l
I
elpt
-
@
uorpaerlal
unrls€rpad
-
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F-r
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--.--.
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9
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aea9esou o
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)uuen
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souoz uollod
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(Luc)tllcloo
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(-)
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b;
I23
I24 J. I. Suendsen& J. Mangerud
NORSK GEOLOGISK TIDSSKRIFT 70 (1990)
:J ry"\\
Xl'liKY
> \\71
("1.
:a /
KuiturmYra
D\ i )&f*6***
Fig. 10. Map of the bogs Skolemyra and Kulturmyra,
The location of the analysed core is encircled.
Bergsoy (Fig. 1). The basins are shaded and the crosses mark coring points.
samples were analysed for diatoms between 494.5
and 540 cm in core 9 (Svendsen 1985) (Fig. 13).
These indicate that the upper part of the formation (from 540 cm and upwards) was deposited
in a brackish environment. The occurrence of
well-defined green and brown lamina between
533.5 and 51,3cm (Fig. 14) supports the interpretation of a long-term brackish environment.
The appearanceof laminationsuggests
a reducing
benthic environment with the absenceof burrowing organisms.This might haveresultedfrom
the sea leval falling below a certain threshold.
NORSK GEOLOGTSKTTDSSKRIFT70 (1990)
Sea leuel and pollen, W. Norway
IZ5
SKOLEMYRA
a
C a l c u l a t i o nb a s i s : E P
c
E
oE
E co
c
c
la
IO a
tr. l ( g c c
lo
lo
-c
tr
3
l a
l a
l<
N
c
E
N
11
.=
c
a
c
.F
C
: ; E
L
o- a
LL
.g
=C
o
;
a
c
o
a
a
F
.C
=
!_
PHYTOPL
HERBS
a
t
l
l
E
(E
E
c
o
o
c
4
llr
f
:
c
r
6
c
0 2 0
la,
i F
l o
l>o)
a
t"<
i
l.fr
Srltv qvttta
fl1+11
FLaminated
F4 silt and clav
rr^.,.
I srll ano cla!
,
F'ig. I l. Pollen diagram from Skolemyra.
The reappearance of massive sediments above
the laminated zone might representa minor transgressionwhich was not significantenough to atfect
the diatom composition in the basin.
Radiocarbon dates from the base of the laminated sequence (530-533 cm) and from the
top of the formation (496.5493.5 cm) were
10.980-F 160(T-4969A) and 10,510+ 190Bp (T4966 A) respectively (Fig. 14, Table 1). Both
dates agree with the expected age as suggested
from the pollen and lithostratigraphy. A decrease
in the percentage of Betula along with a distinct increase in the values for Artemisia, Salix
and Oxyriaf Rumex indicate that the AllerOdf
Younger Dryas transition occursbetween 540 ancl
530 cm (Fig. la). An age of around 10,300Bp is
suggestedfbr the upper boundary of the marine
formation (B) by assuming a constant sedimentation rate for the sequenceabove the Vedde
Ash Bed.
Above Formation B is an erosional unconformity (Figs. 13,14) covered by a layer of sorted
sand with diatoms of a marine/brackish origin.
Waves and/or strong currents associatedwith the
Tapes transgressionare the most plausible mechanisms for this severe erosion and subsequent
deposition of coarse sand. Abclve the sand is a
coarse gyttja layer consisting primarily of redeposited organic macro debris, mostly mosses
(Sphagnum). The terrestrial origin of these plant
remnants indicates that the sediment was washed
into the basin from the surrounding lake shore.
Above this coarseorganic layer is a thin silty layer
followed by gyttja of the Hatlen Formation. The
pollen of water plants shows that the sequence
above the sand layer was deposited in a lake (Fig.
14).
The lacustrine sediments have a completely
different pollen flora compared to the brackish/
marine sedimentsbelow (Fig. la). In the lacustrine sequencethe occurrenceof Corylus indicates
that the sediments post-date the Corylus rise
around 8300BP (Kristiansen et al. 1988). The
occurrence of 5% Alnus at 492cm indicates the
tentative presenceof alder. In the Bergen area to
the south the colonization of alder has been daterj
to 7600-7800BP (Kaland et al. 1984).The coarse
organic layer was radiocarbon to 8480 -f 160 Bp
(T-4967 A) and the base of the undisturbed lacutrine gyttja was dated to 8140 r- 110BP (T-8185).
The pollen data discussedabove suggestthat these
dates are too old; this problem is discussed in
more detail later. Regardless, the dates reveal
that there is a hiatus of at least 2000years between
the top of the marine and the baseof the lacustrine
sediments.
Kulturmyra (UTM coordinates262162),
2 . 5m a . s . l .
The bog is about 100 x 70 m and is a sub-basinof
Lake Myklebustvatnet (Fig. 10). It is separated
f26
NORSK GEOLOGISK TIDSSKRIF| 70 (1990)
J. I. Suendsen & J. Manserud
rJoNro
s^H..
sncco3oA.ilog
ld
i ro.uu,o.
urur uorpaerlal
urnrlserpad
orAHdl
u ul
+
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unruebredg
-a
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n
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1.,
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NORSK GEOLOGISK TIDSSKRIFI 70 (1990)
!!+
Sea leuel and pollen, W. Norway
I27
+ f
Core sites
oeptn-Jl
(m)
Fig. 13. Lithostratigraphic profile (W-E) acrossFr6ystadmyra I. The coring sites are shown in Fig. 7. Note the angular unconformity
beneath the sand bed.
from the lake by a bedrock threshold that is about
the same level as the lake. As in Froystadmyra I
the lacustrine Hatlen Formation directly overlies
a long marine sequenceconsisting of Formations
A and B (Fig. 2). Seven samples between 640
and 577 cm were analysedfor diatoms (Svendsen
1985) which indicate a long period of brackish
water prior to the isolation of the basin. The
presence of the Vedde Ash Bed between 612.5
and 612 cm shows that the transition from a marine to a brackish environment occurred prior to
10,600BP. The pollen analysis shows that the
isolation contact is contemporaneous or slightly
younger than the start of the Betula rise at I0,20010,300BP (Fig. 15). A sampleof lacustrinegyttja
(56G563 cm) directly above the isolation contact
was radiocarbon-dated to 10,500 -f 140 Bp (T5145 A), which seemsslightly too old. We assume
the age of isolation is 10,200BP, in accordance
with the pollen correlation.
The Tapes transgression is evident from
another marine sequence higher up in the core
(Fig. 2).
Almestadmyra
13.7m a.s.l.
( UTM
coordinates 269025 ),
The bog (Fig. 1) is situated in a valley that extends
from the head of the Gurskenfjorden. The exact
dimension of the basin was not determined, but
it is approximately 200 x 200 m. The bog has a
moraine threshold at the western end.
The lithostratigraphy (Fig. 16) was described
in the field based on only a few samples taken
with a Russian peat sampler and the lateral distribution of the layers is poorly known. The lithostratigraphy is to some degree different from the
other basins and it was not possible to correlate
all of the beds with the stratigraphic units in other
basins.
Formation B (82V771 cm) is a dark grey gyttja
silt which is stained by monosulphides. Small
fragments of Mytilus edulis andfor Modiolus
modiolus were found from the base and up to
790 cm. Few diatoms were found in the upper
part of Formation B, but the composition suggests
a brackish fmarine origin. Formation C is a gyttja
128 J. I. Suendsen & J. Mangerud
NORSK GEOLOGISK TIDSSKRIFI]70 (1990)
O()
(U9
&
a
c . .
) a
n
flffi]
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t^.]
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g uorleuJoJ
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NORSK GEOLOGISK TIDSSKRIFT70 (1990)
Sea leuel and pollen, W. Norway
s l
A I
ttrurelte
o l
" l l
I t-t-r
I
a
;
I
=
J
u o t l r u o tu o s s o l
Eig
'd'g) ourleP
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o
( v 9 r ! 9 - r ) o r r . o o 9 or
E.
cr
f
5
f
Y
sauoz uallod
,a;
oo
I29
130 J. L Suendsen& J. Mangerud
NORSK GEOLOGTSKTTDSSKRTFT
70 (1990)
rei:
d
t
I
J ]AP
2'1
t^l
o_
t/.1
(g
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=
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=
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t
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It.Lll li
.i
r-
u o r l t u out o s s o l
E<Br
R*ti
Hti
I
e
spag /suotleullol
o
t-
a
t!
J
ZlYrilY
.:
r'^
70(1990)
TIDSSKRIFf
NORSK(}EOLOGISK
silt characterized by distinct black and brown
lamina. The lower boundary is sharp whereasthe
upper boundary is more gradual. The presenceof
diatoms as well as the occurrence of green algae
(Pediastrum, Botryococcus) indicate a lacustrine
environment. However, atiew (3%) Dinophyceae
cysts('Hystrix') were also found. which may indicate that the lake environment was a little influenced by intrusion of sea water. The pollen
stratigraphy (Fig. 16) shows that this unit was
deposited during the late Allerod and early
Younger Dyras. Formation D (74G640cm) is a
mixture of grey silt and sand with a very low
content of organic material. The Vedde Ash Bed
(710 693 cm) occurs in the middle of this formation. A mixed diatom flora reflecting a brackish
environment was found at 746, 710, 664 and
646 cm, whereas only lacustrinetaxa were found
at 725 cm. Formation D is overlain by the lacustrine Hatlen Formation. There are no radiocarbon dates available from this sequence,but
the pollen stratigraphy shows that the isolation
contact coincides with the Betula rise at around
1 0 . 2 0 0B P .
Some 3-5cm up in the Hatlen Formation there
is a distinct sequenceconsistingof a well-defined
layer of sorted sand (608-606cm). a grey-brown
silty gyttja (60G603 cm) and brownish-greygyttja
silt (603-601cm). The diatoms are a mixture of
lacustrine and brackish flora. The origin of this
sequence is uncertain; however, it is not likely
that the basin was transgressedduring the Holocene because the elevation of the threshold is
more than 4 m above the Tapes level. The possibility that a tsunami causedthis sequenceis discussedbelow.
Sea level history
Sea leuel and pollen, W. Norway
131
rise. BecauseKulturmyra and FroystadmyraI are
situated too close to each other for a precise
determination of the isobase direction. the
Younger Dryas levels in these three basinswere
c o m p a r e dt o t h o s ei n t h e A l e s u n da r e a ( L i e e t a l .
1983).The direction of the isobasebetween Sula
and Leinoy was found to be N35'E with a shorel i n e g r a d i e n t o f c a . 1 . 3m / k m . T h i s a g r e e sw i t h
resultsbased on morphological criteria (Sollid &
Kjenstad 1980; Reite 1968). Reite (1968) and
Undns (1942) assumedthat the Younger Dryas
and the Tapes transgressionshorelines have a
similar isobasedirection. This has been conhrmed
by Svendsen& Mangerud (1987).
A sea-leuel curL)e for Lein@y
A relative sea-levelcurve (Fig. 17) has been constructed for FroystadvAgen,Leinoy (Figs. 1,7).
In order to use all basins to construct the
age-elevation diagram, the elevations of the
thresholdsfor Skolemyra, Kulturmyra and Litlevatn are corrected for differential uplift relative to
FroystadmyraI, II and III. The well-documented
Y o u n g e r D r y a s s h o r e l i n eg r a d i e n t o f 1 . 3m / k m
(Svendsen& Mangerud 1987) was used for all
basins. Thus, the threshold of Litlevatn (19.2m
a . s . l . ) ,w h i c h i s s i t u a t e d7 . 5 k m t o t h e e a s to f t h e
reference isobase (Fig. 1). is corrected by 10m
when usedfor constructionof this curve (Fig. 17).
Any divergencefrom this gradient for Litlevatn
is consideredinsignificant(less than 1 m), as the
lake was isolatedfrom the seaonly a few hundred
years before the Younger Dryas.
The curve (Fig. 17) is drawn visually as a
regressionline between the dated threshold elevations for each basin. These levels representthe
former high tide. The present tidal range is about
2-3 m and the mean sea level is estimated to be
at about 1-1.5 m below the curve.
Isobases
Isobasesare contours connecting sites of equal
emergence and define the strike direction for the
correspondingtilted shorelines.In this area the
Younger Dryas shoreline was defined by the
threshold elevations of Froystadmyra I, Kulturmyra and Almestadmyra (Fig. 1), which were
isolatedsimultaneouslyaround 10,200BP. A precise correlation of these basins was possible
because in each of them the Vedde Ash Bed
occurs in the brackish sediments and the marine/
lacustrine boundary corresponds to the Betula
The marine limit and the age of
deglaciation
From the basins studied the marine limit on
Leinoy could not be determined exactly because
the highest basin studied (Froystadmyra III,
2 3 m a . s . l . ) i s s i t u a t e db e l o w t h e m a r i n e l i m i t .
Assumingthat Leinoy was deglaciatedat the same
time as Gurskoy then the marine limit can be
bracketed between 23 and 28 m a.s.l. based on
the data from Dalevatn from Gurskoy. This figure
is also supported by field observations of the
l-12 .l. l. ,\pctttlst'n & J
Mangerud
N O R S KC ; E O l . O C i t sTKT D S S K R T F7 -0l ( 1 9 9 0 )
m.a.s.l.
F r o y s t a d m y r al l l
LEINOY
F r o y s t a d m y r al l
Skolemyra
Radiocarbon dates:
.
+
I
standard devialion
r_
Lacusltine sed above the boundary
to brackrsh / marine sed
Organic maller In mailne/
brackish sed.
H
Marine shell
1 0 3y e a r s 8 . P .
/ ' i g ' / z S c a l c v c l c u r v c f o r L c i n r , , v .f h c I l o r o c c n c p a r t
i s d c d ' c c d f r o m a s h u r c r i n cdiagram constructcd bv
Svcndscn
& lVlangcrud
( l9lJ7).
maxlmum elevation of beach sediments on
-fhe
Lcinoy.
m a r i n el i m i l w a s m o s rl i k e l vl o r m e d
i n r m e d i r t c l va [ r e rr h e c l e g l a c i a t i o nB., r t h i h e h a s a l
radiocarbon dates from the marine sedimentsin
Kulturmyra and the oldest dates of lacustrine
gyttja which were used to constructthe sea-level
curve (Fig. 17)suggestan ageof around 12,600Bp
for this event. This is in accordancewith dates
from the Alesund area, which lies farther inland_
and where a slightly younger age (12.3001 2 , 5 0 0 B P ) f o r t h e d e g l a c i a t i o nh a s b e e n s u g _
g e s t e d( K r i s r i r n s e nc t a l . l 9 8 t { ) .
Sea-leuel changes during the Late
Weichseliun
The curve shows a rapid emergence(more than
3 m/100 year) following deglaciationat approxi_
mately 12,600BP. From the late Allerdd ancl
during the Younger Dryas a prolongeclstandstill
is demonstrated. This standstiil is evident as a
brackishzone in FrOystadmyraI and Kulturmvra
w h i c h m u s t h a v el a s t e df o r s e v c r a lh u n d r c t lv e a r s .
T h e r a p i d l l t r l o c e n e c m e r g c n c ei s c r r n t e m p o r i-rnc()usto lhc Bttulu rise lnd the dcposition of
t h e l l u t l c n F o 1 6 x l i r n . f t r r w h i c ha m i n i m u ma s e
o f l U . 2 t ) t ) B Pw r r s u s c d . I f a s l i g h t l yo l d e r a g e
(10.300-10.-50
B0P ) i s u s e d t h e l e v e l l i n s o u t ; f
t h c s c t rl e v e lc u r v e i n t h e y o u n g e r D r y a sh . . o . . ,
shorter.
The stratigraphy recorded in Almestadmyra
i n d i c a t e st h r r rt h e s e a - l e v ehl i s t o r y i s s l i g h r l yc l i l ferent in the area farther south. The late Allerod
and early Younger Dryas sea levelswere appar_
ently below the 10,600BP shoreline.which means
that a small transgression occurred around
10.6008P. If the AllerOd and younser Drvas
isobasesare not exactly parallel in this southern
area (Svendsen& Mangerud l9g7) then this could
explain the transgression.This might indicate
t h a t t h e Y o u n g c r D r y a s t r l r n s g r c s s i , cwnh i c h i s
describedfurther south (Anundsen l9g5) besins
n c l r t h i s l a t i t u d e . R e g a r d l e s s .t h e f i n a l r a p i d
emergenceis assumedto [2yg occurred arouncl
10.200BP. as predicted by rhe curve.
Seu-leuel change.t during the Holocene
The l{olocene part of the sea-levelcurve is de_
duced from a shoreline diagram (Svendsen &
Mangerud 19ti7)and is not baseclon observations
from this particular area. The diagram predicts
that the Tapes transgressionon LeinOy culmin_
a t e d a t 8 m a . s . l . a r o u n d 6 0 0 0B p , w h i c h m e a n s
t h a t F r o y s t a d m y r aI ( 6 . 2 m a . s . l . ) w o u l d h a v e
been transgressed.This is supported by the pres_
ence of beach ridges associatedwith the Tapes
transgresslonmaximum around 10 m a.s.l. How_
ever, the radiocarbon dates from FroystadmvraI
(T-4976 A and T-818,5A) do not aeiee with the
d e d u c e dH o l t r c e n es e a - l e v ecl u r v e .
As describedabove, an unconformitv in Frov_
stadmyraI (Fig. l3) showsthat the earlv Holocene
s e d i m e n t sw e r e r e m o v c dh y e r o s i o n .u n d i t s e e m s
likely that this hiatus and the sand laver were
c a u s e db v t h e T a p e st r a n s g r e s s i o nC.o r i n g si n t h e
Alesund area have shown that in most basinsthe
Tapes transgressioneroded all of the soft earlv
H o l o c e n el a c u s t r i n eg y t t j a .
When the diagram was constructed.Svenclsen
70 ( l9tr0)
NoRSK GEOI-OGISK TIDSSKRIt--T
SealeueLan'dPollen, W' Norwav
133
transgression,that culminatedat a later date (Fig'
from
& M a n g e r u d ( 1 9 8 7 ) d i s r e g a r d e dt h e d a t e
17) or they can be confused with sediments
layer
the mixed sediments above the sand
deoosited as a result of the transgression' Further
(8480 + i60. T-4967 A) becauseit was from a bed
sample inland (e.g. the Alesund area) the transgression
including redeposited material Later' a
around
undis- maximum would pre-date tsunamis
from the base of the overlying, apparently
sediments
tsunami
possible
thus
and
BP,
7000
These
turbed, gyttja was submitted for dating'
s h o u l d b e m o r e e a s yt o d e t e c t '
lacustrine seiliments must have been deposited
I n A l m e s t a d m y r a ( 1 3 . 7m a ' s ' l ' ) w e h a v e
after the culminatitrn of the transgression
a sand layer interbedded in the lower
described
age
which caused the erosion. The obtained
Holocene lacustrine gyttja' The presthe
of
oart
t
h
e
w
i
t
h
( 8 1 4 0 + 1 1 0 , T - U 1 f l 5A ) i s c o n s i s t e n t
e n c e o f b r a c k i s hd i a t o m s i n d i c a t e ss o m e m a r i n e
former date. However, both dates are lncominfluence. According to the shoreline diagram
patible with the shoreline diagram in that they
(Svendsen& Mangerud 1987) The threshold.of
predicted
are 2000 3000 years older than the
this basin is 4 m above the Tapes transgresslon
transgressionmaximum (Fig' 17)'
(1987) maximum and this rules out the possibility that
As"discussedby Svendsen& Mangerud
rhe sand was dcposited as a result of a marine
an age around 6000-7000 BP for the culminatron
transgression.Even though this sand layer has
supported
of the Tapes transgressionon Lein@yis
not been dated or studied in detail, we propose
bv several radiocarbon dates from the outermost
that it may represent a tsunami deposit'
coast of Sunnmore (Bjerck 1982; Indrelid 1975;
I n S k o l e m y r a( 1 2 . 4m a . s . l . ) ,w h i c h i s s i t u a t e c
i983)'
Hafsten & Tallantire 1978;l-ongva et al'
5 m above the Tapes level and 6 m above
around
confirmed
In addition. this age has recently been
a the 7000BP level (Fig' 17), a disturbed layer
by three archaeologicaldates obtained from
which includes terrestrial turf is resting discorblach ridge (ca. l0 m a's'l'), which is correlative
dantly on the Vedde Ash Bed (Fig' 2)' This layer
the
with the Tapes transgressionmaximum on
occuis in the deepest part of the lake and is
island of Viilcleroya (Randers & Hoglin 1988)'
apparently the result of slumping' Because the
situatedsome 25 km to the northwestof Leindya'
suirounding topography is relatively flat and not
Even thclugh it is quite possible that the Tapes
conducive to slumping an external cause such as
transgressionin this area culminated somewhat
(ca' a tsunami is a plausible trigger for this slumptng
earlier than indicated on this deduced curve
as sug- event in this basin.
6000 BP). an age as old as 8000-U500BP'
with
conflicts
dates.
mentioned
two
the
by
gested
rrom
nearly all dates of the Tapes transgresslon
western Norway (Kaland 1984; Aksnes 1986; Conclusions
the
Svenclsen& Mangerud 1987)' The validity of
T h e L a t e W e i c h s e l i a ns e a - l e v ecl u r v e f o r L e i n o y
therefore
should
I
Froystadmvra
from
dates
two
depictsa similar courseof shoreline-displacement
b e c r i t i c a l l Yr e - e x a m i n e d '
as the other two curves from the Alesund area'
( S v e n d s e n&
S u l a ( L i e e t a l . 1 9 8 ' 1 )a n d S t e t l e
Mangerud 1987).Following deglaciation' all three
Possibleindications of a tsunami
curvJs show a rapid emergence followed by
a levelling out during the Younger Dryas'
In Scotland the occurrenceof sand layers tnterHowever. there are two minor differences' The
bedded in terrestrialpeat in a number of localities
e m e r g e n c eo n L e i n o y w a s s l i g h t l y s l o w e r ' a n d
t
s
u
n
a
m
i
h a s h e e n i n t e r p r e t e da s a r e s u l l o f a
duririg the Younger Dryas th-erewas a stillstand
(gigantic sea wave) dated to around 7000BP
in the Alesund area the,re
Long et al' 1989)' They on LeinOy whereas
ibo*.on et al. 198i1;
These differences can be
regression.
slight
a
was
ascribe this tsunami to large submarine slides
explained by the tilted shorelines and the increasfrom the continentalslopealong the westerncoast
ing intensity of the uplift towards the intertor
of Norway (Jansen et al. 1987) If these slides
the (Svendsen& Mangerud 1987)'
caused tsunamis of such a magnitude, then
As demonstrated by Svendsen & Mangerud
coast of western Norway must have been affected'
the shoreline geometry which accom(1987)
w
a
s
f
r
o
m
s
l
i
d
e
e v e n t h o u g h t h e d i r e c t i o no f t h e
modates these curves suggestsa slowdown of the
the coast. Along the outermost coast such
uplift rate during the Younger Dryas' most likely
depositscould have been removed by the Tapes
134 J. I. Suendsen & J. Mangerud
due to a halt in the retreat of the ice sheet. The
stillstand on Leinoy shows that the isostaticand
eustatic changes balance each other for nearly
a thousand-yearperiod. This indicates that the
eustatic rise during this interval was even and
smooth with no rapid high amplitude changes.
This curve is situated 80 km west of the Younger
Dryas ice sheet and the total glacio-isostatic
uplift
during this period is consideredto be small, suggestingthat the total eustaticrise was also small,
most likely less than 10 m. By the way of comparison the transgressionfrom 9000 to 8000Bp
required more than 20m of sea level rise. This
suggestsa marked increase in the rate of the
eustatic rise during the early Holocene.
Acknoulcdgernen rs.
This papcr rcsultcd from a projcct lcd by
J a n M a n g c r u d o n s c r - l e v e lc h a n g c si n S u n n m o r c w h i c h f o r m c r : i
part of lG(lP pro.jcct 2.1.Thc projcct was linanciallv supported
by thc Norwcgian Rcscarch Ciruncil lirr Scicncc and thc
I lumanitics (NAVF ) and thc Norwcgian Gcological Survcv.
Karl-JohanKarlscn. Svcin Erik Lic and Dag Hcrmanscn par
-l
t i c i p a t c d i n t h c f i c l d w o r k . h c p o l l e n a n a l y s i sw c r c c a r r i c d o u t
at thc Dcpartmcnt of Botanv. Univcrsity of Bcrgen. un.ler thc
guidcncc of Pcter Entil Kaland. All radiocarbon datcs wcrc
carricd out at thc Trondhcim laboratorvconductcdbv Rcidar
N v d a l a n d S t c i n a l C i u l l i k s c n .J a n c L , l l i n g s c na n d E l s e t . i c r m a d c
thc drawings. Pctcr Emil Krland and Svantc Bj(irk rcviewcd
t h c m a n u s c r i p t . T o t h c s c c o l l c a g u c sa n d i n s t i t u t i o n sw c o l l i r
o u r s i n c c r et h a n k s .
N l a n u s c r i p tr e c c i v c d D c c c r n b c r 1 9 1 J 9
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