Deglaciation chronology in the mountain area bet- ween Suldal and Setesdal , southwestern Norway

Deglaciation chronology in the mountain area bet- ween Suldal and Setesdal , southwestern Norway

PER SLYSTAD &LOTTE SELSING

Slystad.P.& Seising.L.1988:Deglaciation chronologyin the mountainarea between Suldal and Setesdal.southweste rn Norw ay.Nor.geol.unaers. Bull.413.67-92.

Lithostratigraphic studies.14C dating andpollen analysiswere performed onsediments from six basins inthe mountain area between Suldaland Setesdal in order to establishthe deglaciation chronologyfor the area.The deglaciationof the YoungerDryasice sheetoccurredby10lOO:!:280 years S.P.at 720 m a.s.l.TheSkute thermomer occurred at 10100-9800 years S.P.•the Fidja cryomer at 9800-9700 years S.P..the Sandsaos thermom er at 9700-9300 years S.P. and the Sandsa cryomer at 9300-9100years S.P.The highmountainareaeastand northofthe terminal morainesof presumed Preboreal age was deglac iated by 8800years S.P.and probablythe high mountain areasof southern Norway weredeglaciated at this time or 100-200years later.The inlandvalley of Setesdalen seemstohavebeendeglaciated at aboutthe same time asthe high mountain area.This indicates that the wholeofsouthernNorwa ywas deglaciatedat some 8800- 8600years S.P.•mostprobably8800years S.P.

PerBlystad.NorwegianPetroleumDirectorate.P.O.Box 600.N-4001 Stavanger,Norway LotteSeIsing,ArkeologiskmuseumiStavanger.P.O.Box478,N-4001 Stavanger,Norway.

Introduction

Inthis paperwe try to establishthe deglacia- tion chronology for a mountainarea in south- western Norway (Fig. 1).

The bedrockin the area(Fig.2) ischaracte ri- zed by Precambrianmetamorphic rocks,main- ly gneiss , granite,metabasalt and meta-arko- se, the Ryfylke Schists, phyllite and mica schist,andtheCaledonianallochtonous gneis- ses ofPrecambrianage(Sigmond1975,1978).

The rocks of Precambrian age contain old carbon in local secondary deposited fissure fillings, and the Ryfylke Schists contain old carbon in graphite.

Quaternary sediments were investigated in the eastern part of the area (Blystad 1978).

In Setesdal ice-contact sediments dominate and are usually covered by a rather coarse melt-out till in the low er part of the valley.

Further up the valley sides ,basaltilldomina- tes. In the central part of the mountain pla- teau, on the watershed area, the bedrock is almost bare. Generally,there are more sedi- ments in the Ryfylke Schists area than in the Precambrian basement area.

The vegetation is monotonou s and poor in species.The distribution of Ryfylke Schists in bedrock and sediments gives richer and more varying plant communities in restricted areas of thenort hern andwestern regions. Thearea

liesin thelow alpinevegetationzone characte- rized by heather- and grass moor including part ofthesubalpine birch zone characterized by mountain birch forest Betula pubesce ns of nordic type.In the east it also liespartly in the mountain coniferous for est zone domina- ted by dense pine forest (Pinus sylves tris) mixed with some spruce (Picea abies). The forest limit comprises birch and rises east- wards from the western most areas at 750 m a.s.l.,reaching1050 m a.s.1.eastof the waters- hed in the Setesdalarea. It has beenlowered due to human influence. The pineforest limit, too, rises eastwards from 630 m a.s.1. in the westernmost areas and reaches 930 m a.s.1.

east of the watershed in the Setesdal area (Seising & Wishman 1984). The pine forest limithas presumably not been lowered to any notable extent (Seising 1983).

The investigated area is situated inside the terminalmorainesof presumed Younger Dryas age(Anundsen1972).Prominentend moraines oftheso-calledLysefjordstage,demonst rated to beof Younger Dryasage,have been descri- bed from the southern part of the area by Andersen (1954), who also described end moraines of the Trollgare nstage situatedeast of the Lysefjord stage end moraines. Seren- sen (1983) suggested a correlation betwee n

68 PerBtystea&LotteSeIsing

RECONSTR UC T ED ICE-FRO N T PO SIT IONS (Anund san 1972)

.- The Blllf j ell event _.-.- TheTr o ll g aren event --~- TheLysefjor den event

... Locality

Ccntcur mtarvat SOOm

NGU- BULL.413.1988

5~ '01

LOCA TI ON MAP

fO'

Fig.1.Map showing the locationofreconstructedice-fr ontpositions (Anundsen1972).The terminalmorainesof presumed Preborealagearelocated southofthemapintheSetesdalenarea.The threelocalitiesin the western part werechosen as closeaspossible to the icefront deposits.Twolocalitiesare from thehighmountainarea and onelocalityfrom theinland valleySetesdalen.

the Tro llgaren stage and the Aker moraine, Le.anearly Preborealage (Nydal1960,p.86).

Anundse n (1972) reco nstructed the glacier front variationsin the western part of theinves- tigated area, describing the Younger Dryas end moraines, the Trollgaren end moraines assumed to be of Preborealage,and the Bla- fjell end moraines assumed to be of either Prebo real or early Boreal age. No terminal mor aines youn ger than the Blatjell moraines are reported from the area of investigation.

Geologicalmapping of the glacial deposits in this area (Blystad 1978) shows that the last phase of deglaciation was character ized by downwastingglaciers inthe UpperSetesdalen valley and in the high mountain area.

Onlya few radiocarbon dates related to ice front positions are available from this area.

Anundse n(1977)interpr eted organic matterin clay,deposited close to the icefrontbetween Sandeidandel/en with"C-agesof 10 720±180

and 10 540±170 years B.P. as dating the maximum exten t of the Younger Dryas ice sheet. At Hjelmeland just to the south of the mou th of Jesentjorden,theglacierfront remai- ned for severalhundredsof years at the fjord mouth after 10 800 years B.P. (Blystad &

.Anundsen 1983). Neither theTrollgarenmorai- nes nor the Blatjell moraines were radiocar- bon-dated in this area.The Tro llgaren mor ai- nes are correlated withthe Odda - Eidfjord - Osa substage atthe southern part ofHardan- gervidda (Anundsen & Simonsen 1967). The early Odda - Eidfjord - Osa substage has been radiocarb on-dated to younge r than 9 680±90 years B.P. (Rye 1970) and to 9720±330 years B.P. on a basal gyttja from Busnes, in the innermost Hardangerfjord (Anundsen & Simonsen op.cit.).

Various authors have described end moral- nes of Preboreal age from the coastal and fjord areas of Western Norw ay (e.g. Vorren

NGU-B ULL.413.1988 Oeglaciation chronology 69

BEDROCK GEOLO GY (Sig mond1978)

1~ ~-o:1 ^Caledonianallocht honou s co mplexes

[ :-::.:;:J

^{The RyfylkeSchi sts,mai nl ymeta}

pelit es

D

^{Pr eca m b rian bas ement rocks}

"

se^ALE

10 20km

Con tou r mtervat:50 0m

6""

Fig.2.The bedrock in the investigation area(Sigmond 1978).

1973,Anderse n 1975, Berqstrern 1975). Two or three distinct zones of end moraines have been found, and the radiocarbon dates from many of these cluster around ca 9 900±100 years S.P., 9600±100 years S.P., and 9 300±100 years S.P. (Andersen 1980).

Methods

Site selection

Different criteria were used for selection of localit ies for chronology studies:

a) The locality should be close to the ice frontdepositsto ensurethe most reliableradio- carbon datings of the deglaciation.

b)Localitiesshouldpreferentiallybe outside the Ryfylke Schists areas, where one might encounter radiocarbon dating problems.

c) In the highmountain area,characte rized by exposed bedrock and a thin sediment co- ver, localities were favoured in areas with sediment cover. The sedimentat ionof organic matter could also thereby include debris from the vegetation surrounding the basin and not only algae and aquatic plants from the basin itself. The sedimentation rate of organic mat- ter would therefore theoretically be greater than in areas with exposed bedrock which would givea better resolution for pollen analy- sis and radiocarbon dating.

These circumstances reduced the range of poss ible sites for locations likely to reflect possibleclimatically induced vegetational alte- rations .

Approximately seventy basins were exami- ned bymeans of a Hiller sampler,a'Russian' peat corer (Tolonen 1967) or by an exploring stick. Basins with sediments presumed to have been deposited just after deglaciation

70 PerBlystad &Lotte Seising

were selected for preliminary palynological analyses . Based on pollen analytical dating of the basal organic sediments, studies were concentrated on ten localities. Six of these localitieswere chosen becausethe preliminary analysis of the pollen in the basal organic sediments indicated pioneer vegetation. Only theresults from these sites will be presented here.

Samp ling

A modified 11 cm piston corer (K. Krzywin- ski, pers. comm. 1978) was used in com- bination with digging of ditches for collecting the samples.

Uthostrat igraphy

In the pollen diagramsthe sediment and peat signat ures pro posed byFce gri& Gams (1937) are used.Loss-on-ignition was carriedout on the sediments to measure the variations in organic content. Loss-on-ignition was done at 550°C(Sensteqaard& Mangerud 1977:315), and the results are shown on the pollen dia- grams as weight percent loss-on-ignition .

Bios tratigraphy

Preparation ofthe palynologicalsamples main- ly followed the acetolysis method.A few ba- sal minerogenicsamples ateachlocality were treated withhydrofluor icacid (Fzeqri&Iversen 1975). Pollen analysis was carried out by means ofa Zeiss micr oscopewith phase con- trast object ives with analysis magnification 504x. Grains which were difficult to identify were exam inedat 1008x.Pollenidentifications are based mainlyonFcegri& Iversen (op.cit.).

Ericales pollen were determinedtogenus(Be- ug 1961).TheEricalescurve in thepollen dia- grams includesunidentifi ed tetrads.Thedeter- mination s of the trilete spores werebased on Moe (1974).

The pollen diagrams are percentage dia- grams. Aquatic pollen grains, spores and al- gae are not included in the basic sum (L P).

ThePolypodiaceae curve includesfern spores from all genera. The sediments have been subdivided into local and regional pollen zo- ne s . Th e procedure s sug g ested by Hedberg (1976), Mangerud et al. (1974) and Kaland (1984) are followed. The local pollen zones are pollenassemblagesandthe zone boundari- esare drawn between two spectrawhichindi- cate mark ed changes in the pollen compos iti-

NGU-BULL.413.1988

on. The regional pollen zones are used for biost ratigraphic dating and correlation. The boundaries of the chronozones are identified on thebasisof radiocarbo ndatedpollenlevels.

Ghronos tratigraphy

Twenty-tworadiocarbondateswereperformed by the RadiologicalDating Labor atoryinTrond- heim,Norway (Table 1).Results are reported in conventional"Cyears beforepresent(1950).

The radiocarbon dates are discu ssed in a separate paper (Blystad & Seising in manus) with emphasize on the dating errors.

Ages of the Gorylus and the Alnus rises

The ages of the Gory /us and the A/nus rises are importantin chronostratigr aphic subdivisi- on of theearlyHolocenebecausethey arethe principal palaeobotanical events.

The age of the Gory/us rise, 8800 years B.P., is based on the dates (Table 1) giving 8940 ::t 200 years B.P.(T-3486on macro sco- pic twigs) from the locality Langaneset just below the Gory /us rise and 9280 ::t 80 years B.P. (T-3489A, soluble fraction) from locality Sandsaos en 5 cm below the Gory /us rise.

These dates give a maximum ageon the rise of Gory/us . From locality Skreivatn the date of 8600 ::t 250 years B.P. (T-3487A, soluble fraction)provides aminimumage for theGo ry- /us rise.These dates indicate acontempor ary rise of Go ry/us in the eastern and western parts of theinvestigated areaandareinaccor- dance with the dating of the Gory /us rise in central Telemark (Heeq 1982) and the inner fjords of the Bergen district (Skar 1975).

The age of the initial A/nus rise,8400 and 8000 years B.P., in the western and the east- ern partsof the investigated area,respective- ly,are basedon3 dates from theinvestigated localities Sata, Skreivatn and Leyninq (Table 1). The age in the western part is about the same as the age at Eiger0Y at the south- westernmost coast of southwestern Norw ay (Simonsen pers.comm.).TheA/nus risein the eastern part of the investigated area is in accordance with Hoeq(1982)for centralTele- mark.

Site de scriptions and stra tig raphy

The six investigated localities are all topoge- nous overgrownor partly overgrownbogs si-

NGU-BULL.413.1988 Deglaciation chronology 71

Tabl e1.Radi ocar bon date s from the 6investi gat ed bas ins.

Locality(ma.s.l.) Sample:sediment Dep th below Weightof Radiocarbon AgeT'I,5570 ^a13C suggested Greenwichcoor. (Ioss-on-ignition). sediment sample date yearsB.P. '/ooPDB chronozone morphostratigraphy and eventdated surface,cm dated,9 reference

SATA(710) Sand with organic 207.5-210.0 2.1 T-3488A 10.100 ±280 -26.4 late YD/earlyPB

59°25 '50"N matter(3.6%), 68.4 T-3488B 11.210±150 -26.4

6°27'10"E deglaciation betweenYDand

Trollgaren ter.mor. Detritus gyttja with 205.5-207.5 1.3 T-3846A 9.610±210 -27.7 PB

sand(20%). 35.1 T-3846B 10.090±100 -24.5

Trollgaren stage

Detritus gyttjawith 203.5-205.0 3.8 T- 3847A 9.510±150 -26.6 PB

sand(10-20%),and 18.4 T-3847B 9.700±140 -25.2

0.5cm of sand with organic matter(6%), maximumageof BIAfellstage

Detritus gyttja(58%), 189.5-191.5 14.02 T-5687A 8.370±100 -26.4 late B Alnusrise

SANDSAOSEN(630) Detritus gyttja 220.5-222.0 6.4 T-3141A 9.650± 90 PB

59°23'30"N with sand(22-24%), 6°31 '50"E deglaciation between

Trollgarenand Detritus gyttja 219.0-221.0 8.7 T-3489A 9.280 ± 80 -29.5 late PB

Blafjellter.mor. withsand(24%), 12.9 T- 3489B 9.340 ±140 -28.0

BIAfjellstage

LANGANESET(610) Algae gyttja 371.0-372.0 12.7 T-3140A 10.210±180 latePB/ear lyB 59°25 'O"N (12%),

6°34'20" E deglaciat ion

just inside TWigs fromsilt, 372.0-384.0 0.9 T-3486 8.940±200 -26.1 latePB

BIAfjell ter.mor. deglaciation

Algae gyttja 321.0-323.0 5.42 T-5689 B 7.170±140 -28.1 late B/earlyA (45%),

Alnusimmigration onlocality

0VRESTORVT.(980) Detritus gyttja 139.5-141.0 3.5 T-3224A 8.640 ±120 earlyB 59°20'10"N (6%),

6°57'20"E deglaciation

inside BIAfjell Detritus gyttja 128.0-130 .0 30.17 T-5686 6.720± 90 -25.8 late B/early A

ter.mor.: (38-42%),

A/nusrise

SKREIVT.(1030) Siltydetritus 112.0-113.5 1.5 T-3487A 8.600±250 -26.4 earlyB

59°24 '20"N gyttja (4%), 70.8 T-3487B 9.020±210 -24.3

6°55'O"E deglaciation inside BIAfjell

ter.mor .

Detritusgyttja 94.0- 96.0 27.45 T- 5690A 8.280±100 -27.1 late B (28%),

Alnusrise

L0YNING (720) Siltygyttja and 476.0-478.5 3.7 T- 3139A 9.270±180 earlyB

59°2'30"N algae gyttja (6-24%), 7~23 '50"E deglaciation inside

Preboreal Plantremains of 470.0-476.0 0.5 T-4313 8.470±210 -29.8 B

ter.mo r. Pinusfrom algae 30.7 T-4314A 9.000±100 -29.4

gyttja,andalgae gyttja (24·32%)

Algaegyttja (38%), 461.5-463.5 8.15 T-5688B 7.900± 90 -29.4 lateB/earlyA A/nus rise

ANaOH soluble frac tion.Binsolublefraction,YD Younger Dryas cnronozone,PB Preborea/ chro nozone,B Bore al chronozo ne, A Atlanticcnronozone.ter.mor. terminalmoraines.

72 Per Blystad& Lotte Seising

Fig.3.Sata710 m a.s.1.is a partlyovergrowntarn situated between theYounger DryasandtheTrollgare nendmorai- nesin the subalpineopen birch forest. Thesite is defores ta- ted due toathin and scatteredsediment layerand topastu- ring.The samplesite is marked with anarrow.

SATA, Sul dal,Rogaland'''m..^.I.

Chro no- I

trat tgra phy.Lithostr atig raphy

NGU-BULL.413,1988

tuated at altitudes betw een 610 and 1030 m a.s.1. (Fig. 1).The positionsof the threewes- ternmost localities are closely related to the former positionof the icefronts.The twoloca- lities in the high moun tain area and the one in Setesdalen lay far east and north of the ice fronts of presumed Prebo realage.The localiti- es are described from west to east.

S ata

The locality (Fig. 3)is a partly overgrown tarn situated in the Ryfylke Schist zone betwee n the Younger Dryas and the Trollgare n end moraines atan altitude of 710ma.s.1.(Figs. 1

& 3). The youngest ice movement here was

towards SW.The bedroc k is covered with a thinandscatteredtill layer.Thepresentvegeta- tion is suba lpine open birch forest with an undervegetation dominated by bilbe rry. The recorded plant speciesat themire,e.g.Eriop- horum angustifo lium,ViolapalustrisandMeny- anthes tritoliata, indicate poorfen vegetation.

Bio s t ra tig raphy

Beds t.c ss-cn-

ig ni t ion E .e

To t a l polle n diagram M"n p hystOg-

nom lC;l ype l

no pollen

T,•••

calcu la tion ba sis :i Po lle n S"'t,ob.'''<1

<1• •,1''',,,,b.

5

u 0

,s,

, '90

•-:la Y

'""

Fig.4.Lithostratigraph yand pollenpercentage diagram from sata.The calculationbasisisshown on top of the diagram;x

ISspores,pollenfrom aquatic plants or algae.

NGU·BULL.413,1988 Oeglaciation chronology 73

Lithostratigraphy:At the base there is a grey, silty sand (Fig. 4) with a transition to poorly sorted sand with organic matter covered by dark brown coarse detritus gyttja with a mar- ked sandy gyttja layer in the lower part, and followed by Sphagnum peat at the to p.

Pollen analysis: The low est pollen zone Sa1 local zone (Fig. 4) is defined by high Betula values (50%), Salix values more than 5% and Rumex values just below 5% . The relatively highherb,shrub and dwarf shrub values (40%), e.g.Salix ,Juniperus,Empetrum,Rumex,Arte- misiaand Urtica,reflect an open pioneer veg- etation (et. Moe 1977, Simonsen 1980). The lowe r boundary of the Sa2 local zone is defi- ned by a depression of Betula dropping to 40% and by maxima in Juniperus and Rumex rising to 9% and 6%, respectively. Loss-on- ignition values stabilize at 16%. The lower

part of this assemblage zone is characterized

by a maximum in shrubs, dwarf shrubs and

herbs. The lower boundary of the Sa3 local zone is characterized by a rise in Betula to more than 50%. The AP-values rise. while shrubs- and dwarf shrubs-, and NAP-values decline.Gorylus rises inthe upper part ofthe zone.Thelowerpart of thiszone ischaracteri- zed by a depression in loss-on-ignitionvalues (9%) in a marked 1 cm-thick layer of sandy gyttja.The lower bounda ry ofthis sandy gytt- ja layer is interpreted to represent an uncon- formity repr esenting a hiatu s. Both the T- 3847 Aradiocarbon date and the pollen recor d abovethe sandy gyttjalayer indicate thatsedi- ments of late Preboreal age are missing.The low er boundary of the Sa4localzoneis defi- ned by the Gorylus rise to 21%.Betula decli- nes and stabilizes around 35%. The loss-on- ignition and the ratio between the main physi- ognomic types is stabilized at the lower boun- dary of this zone. The lower boundary of the SaS local zone is defined by the initial Alnus rise to 2%. Betula declines and Pinus rises

Bios tratigraphy

Total pollen di agr am calculationbas is:::i:poll en+x

Alg ae

-a.

I L

Spore plant s

1 \

III IL

l\j 11

I ^I1

I I

I

1

!\

/ I

I I I

76.

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ssa,., '0'

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I I

I

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.

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I I I

I I

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^I

1 H8-h i-..;....J-+-Hl--l-'-n+-t--H-+++-t-'I>-+-++-+---rl--t-+--n--- '"

+-+---,--+++-+--"--+--,1---1¹,'L.H-+--;-;-+-+++--+-l-+--;-;-t+-HI-

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:_E;e_• •_~ t £~ :3

~...

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19~-

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195- 1\

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,9O",

200-

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207- 208- 209.S-

".

KEYTO SEDIMENTTYPES: Silt

_ Detritus gyltlagenera lly

'..

_ Coarsedet ,itusgytlja

74 PerBlystad&Lotte Seising

Fig.5.Sandsaose n630m a.s.r,is a partly overgrowntarn situated between theTrollga renand theBIAtjellrnoraines.

just outside the BIAtjellmoraines in the subalpine open birch forest. The site is deforest ated due to a thin and scatte red sediment layer and to pasturing. The person marks the samplesite.

SANDSAOSEN,Suldal,Rogaland'>Om",.

NGU-BULL.413.1988

to more than 20%. Light demanding taxa are reduced except Cyperaceae and Poaceae.

Radiocarbon dating: Four levels of this core were "C-dated.

The two dates on the basal organic sedi- ment are presumed togivetheage ofthefirst organic material deposited in the basin after deglaciation (T-3488A and S, NaOH soluble and insoluble fractions, respectively) (Fig. 4).

The pollen record with high values of Betula indicates an early Preboreal age compared with the overlying pollen record, thus con- firming the radiocarbon date of the NaOH soluble fraction. Paus (1988) reported rising Betula values at 10 100 years S.P.

The nexttwo datesgive theminimumage of a drop inBetula,combined withmaximain the Juniperus and Rumex curves. This pollen re-

Chrono-I

trab9 raphYjLilh ostratigraphy

Beds t.ces-oe-

I^{igniti on}

Totat pollen diagram

Bio s t r atigra phy

cal c ul a ti on basis Tr•••

I I

~ Pollen

'"

.,

..

NGU-BUlL.413,1988 Deglaciationchronology 75

cord is interpreted to reflect a climaticdeterio- ration caused by the ice advance during the Trollgaren substage.The pollen recordindica- tes a Preboreal age and thus favours the date from the NaOH soluble fraction of 9610±210 years B.P. (Fig. 4).

The dates 9510±150 and 9700±140 years B.P. (NaOH soluble and insoluble fractions , respectively) give the maximum age of an expans ion in the Betula values, and where sand dominates the sediment. These dates are presumed to give the maximum age of a bio- and lithostratigraphic record which is in- terpreted as being caused by the Blatjell ice advancing and/or retr eatingin the area.These 2 radiocarbon datesthus givea maximum age of the Blafjellsubstage.The pollenrecordindi- cates a Preboreal age. Both dates seem to be toooldcompared withGorylus immigration at some 8800 year s B.P.,thus supporting the

previously discussed contention of a hiatus just below the Gorylus rise.

The uppermost radiocarbon dated levelcom- prising the initia lAlnus rise was performed in ordertoestablish the Boreal/Atlant icchronozo- ne boundary.The age 8370±100 years B.P.

(NaOH soluble fraction) is in accordance with the pollen record.

Sandsaosen

This locality (Fig.f»)is a part lyovergrown tarn situated 630 m a.s.1. in the Precambrianbase- ment gneiss,between the Trollgare nand Bla- fjell moraines,just outside the Blatjell moral- nes (Fig. 1).The sediment cover is scattered and thin, and the catchment area is entirely in the Precambrian zone. The youngest ice movement was towards the SW,draining out the Sandsa basin. The subalpine vegetation is characterized by heather and grassl and

I

^{Bio str atigraph y}

I I I !

I

calcu lationba si s:::l1:pollen+x Spor e pl ln U

f-,.,..c::rr.:;:-"-'-Irf-,--,---,---,-"m,"'-i-'- - - .---i

oo

. , .

m

11

I

I

, ..

1\

88. 1111

100 f

11

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⁶³³838

I

^e-a800 1156

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_{1 11}

calcu la tio n basi s :::l1: Poll e n

11

~

~ .~ ^,;

~ ~ ^~

¥

~ j l

: .

⁰

f "'"'

-""0"

"., 'Om

Fig.6. Lithostratigraphy and pollen percentage diagram from Sandsaosen.The calculationbasis is shownon thetop of the diagram;x is spores,pollen from aquatic plantsor algae.

76 PerBlystad&Lotte SeIsing

pasture. The recor ded plant species at the mire aro undthetarnindicate poo r fenvegeta- tion becauseof the absence of rich fen species and the presenceof e.g.Garexpaucifloraand Rubus chamaemorus.

Lithostrat igraphy:At thebase there is a poo r- ly sorted sand (Fig.6)in which a leaf of Salix herbacea was embedded,covered by brown, coarse and finedetritusgyttja with decreasing minerogen ic content upwards and followed by peat at the top.

Pollenanalysis:The Sa 1local zoneis defined by tree values at about 50%, and Empetrum, Salix and Rumex values more than 5%, 3%

and 2%,respectively.Loss-on-ignition is more

than 20% in the two bottom samples, which

is higher than in the bottom samples at the otherlocalities. Thismayindicateeither a slow sedimentation rate in the Sandsaosen basin in the time immediately follow ing deglaciation, a climaticameliorationand/or a relativelyhigh input of organic matter from an established vegetation close to the locality at the time of deglaciation . In the upper part of the assem- blage zone loss-on-ignition drops to 11%, Juniperus increases to more than 5% and Artemisia increases to a maximum value of 3% . Vaccinium has a maximimn of 2,5% in thiszone.Hippophaeis present,and Potamo- geton rises to values of more than 11%.The pollen flora reflects an openpioneer vegetati- on. The relative ly low frequ encies of treepol- len may indicate that the Pinus maximum in the middle of this zone is caused by a larger influx of long-distance pollen as a consequen- ce of lower local pollen production. In this pine maximum loss-on-ignition drop to 12%.

These changes are presumed to indicate a climatic deterioration. The Sa2 local zone is characterized byamaximumof Betula and the lower boundary is defined by a rise in Betula to 50%.The herbs, shrubs and dwa rf shrubs decline,due to a decline of the pioneer taxa.

Gorylus rises in the upper part of the zone. Loss-on-ignition is increased to about 50%.

The maxim um for Betulaisfoll ow ed byamini- mum in Pinus.Thelower boundary of theSa3 local zone is defined by a rise in Gorylus to 18% and a depres sion to about 30% in Betu- la correspond ing to higher values of Pinus.In the lowerpart ofthezonethereis a maximum inloss-on-ignition parallelto maximain Cypera- ceae and Sphagnum. Characteristic of this

NGU· BULL.413.1988

part of the zone is the early occurrence of a continuous curve of Alnus.In the upper part of the zone tree pollen rises to 80%.The lo- wer boundary of the Sa4local zoneisdefined by a rise in Alnus parallel to an increase in Pinus to more than 25% and a decline in Gorylus to20%.Sphag numincreasesto9%.

Radiocarbon dating: Two levels of this core were radiocarbon dated.

The "C-dating just above the basal poorly sorted sand without organic matter gave an age of 9650±90 years B.P. (NaOH soluble fraction) (Fig. 6) and ispresumed to give the age of the first organic material deposited in the basinafter deglaciationfromthe Trollgaren terminal moraines.Theageis thus considered a minimumage of deglaciationfromthe Trollga- ren moraines . This result agrees well with both the datingof the Trollgaren substage at Sataand withthe estimated age based on the bios tratigrap hyindicatinga pioneer vegetation and Preboreal Chronoz one.

The next two dates arederived from aparal- lel core and overlap the underlying date.The two cores were correlated by pollen.The da- tes gives theage of a maximum in Pinus,the maximum age of aminimum inloss-on-ignition andamaximum inArtemisia,Urtica and Junipe- rus.This Pinus maximum is presumed to be caused by lower local pollen production.and the bio-and lithostratigraphicrecor dprobably indicates a climat ic deterioration. The results of these radiocarbon determinations are 9280±80 and9340±140 years B.P. (T-3489A and B, soluble and unsoluble fraction s) (Fig.

6).The results of thedates arein accordance with a biost ratigraphic estimate indicating the late PreborealChrono zone.Theage diffe rence between these dates and the one just below seems,however,to reflecta greater sedimen- tation rate than is normal.

Langaneset

The locality(Fig. 7) is a partlyovergrowntarn situated justinside theBlatjellmor aines at 610 m a.s.1. lying within Precambrian basement granite. The sediment cover, mostly till, is continuous but rather thin.The youngest ice movement was towa rds SWout of the Sandsa basin.The subalpine vegetation is characteri- zed by open birch (Betula pubesce ns) forest mixed with heather and grassland pasture.

NGU·BULL. 413.1988

The plant speciesrecorded at themirearound the tarn indicate a rich fen vegetation,becau- se of the presence of e.g. Selaginellaselaginoi- des, Tofieldia pusilla and Saxifraga aizoides . A smallbrook drainsinto the basinoriginating from the steep mountainside southeastofthe locality. Here the Ryfylke Schists are foun d.

Lithostra tigraphy: At the base thereis a grey laminated silt (Fig. 8) with macroscopic plant remains (mainly parts of leaves and mosses, and small twigs from Betula sp. and Pinus) and stones covered by brow n algae gyttja.

Pollen analys is:The La 1 local zone (Fig. 8) is defined by tree values of about 60%and with Betula as the dominatingtaxon.Juniperus and Empetrum show maxima at 11% and 6%,re- spectively .Both Salix and unidentifiedEricales are present in relatively great amounts. The pioneer character of the vegetation is also indicated by the herb pollen of Rumex,Artemi- sia and Oxyria-type. The lower boundary of the La2 local zone is defined by a Betula rise to above 65%. Tree pollen rises through the zone to more than 80%,and Corylus rises in the upper part of the zone.The relatively low loss-on-ignition compared with the loss-on- ignition at the localities Sata and Sandsaosen may be caused bythe fact thatthis basinhas a greate r drainage area than the other two, allow ing a larger clastic sediment supply.The presence of diatoms will also contribute to this. Pollen from e.g. Rumex, Artem isia, Se- dum, Campanula, Ranunculaceae and Rubia- ceae indicate a relatively species-rich ground vegetation . Pediastrum has a maximum at 76,9% showing that the lake was eutrophic.

The lower bounda ry of the La3 local zone is defined by a rise of Corylus to 28% and a depression to below 40% in Betula values.

Tree pollen and loss-on-ignition values rise slowly through this zone,and the ratio betwe- en the main physiognomic types is stabilized in this zone. The lower boundary of the La4 local zone is defined by a rise in Pinus to 41%, an initial rise in Alnus and a decline in Corylus and Betula to 13%and 30%,respecti- vely. Alnus rises through the zone to 5%. A mixed birch and pine forest dominated the vegetation inthe period correspo ndingto this zone. The lower boundary of the La5 local zone is defined by an abrupt rise in Alnus to 43%, a temporary decline in Betula and Pi- nus, and the zone is characterised by tree

Deglaciation chronology 77

Fig.7.Langaneset610m a.s.1.isa partlyoverg rown tarn situated just inside the BIAfjell terminal moraines in the subalpine openbirch forest.The personmarks thesamp le site.

pollen values at about 90%.Alnus grew at the locality and dominated the vegetation around the tarn.

Radiocar bon dating: Three levels of this core were radiocarbon dated.

Based on pollenstratigraphyand dates from theothersites,the date of 10 210±180 years B.P.(T-3140A soluble fraction) (Fig. 8) on the basal organic sediment is mor e than 1000 years too old.Macroscopicremainsof terres- trial plants (leaves, seeds, twigs etc.), were therefore picked from the basalgreysilty clay infour new cores.The new radioca rbon date gave an age of 8940±200 years B.P.which is in accordancewith the biostratigraphicestima- te. This date is thus considered to give a minimum age of the deglaciationfrom the Bla- fjell substage.

The uppermost date (7170±140 years B.P.) gives the age of the Alnus immigration at the locality.The pollen flora with a dominance of Alnus and the I4C date support an early At- lantic age.

0vre Storvatn

This locality (Fig. 9) is a mire (an overgrown tarn) situated in the high mountain area, at an altitude of 980 m a.s.1. The bedrock is dominantlygneiss.The sedimentcover is relati- vely sparse and is found mainly in depress i- ons in thelandscape.The youngest ice move-

Total pollen diagram

78 PerBlrstad&Lotte Seising

LANGANESET,Suldal,Rogaland"Om . .,

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NGU· BULL. 413.1988

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NGU-BULL.413.1988 Deglaciation chronology 79

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x is spores,pollen from aquatic plantsoralgae.

80 PerBlystad & Lotte SeIsing

Fig.9.0vreStorvatn980ma.s.t, isa mire(an overgrown tarn)situatedin the highmountainareafarinside and north ofany recorded terminalmoraines ofpresumedPreboreal age.The sedimentcoveris relativelysparse.foundmainly indepressionsandthevegetationislow alpine.Theper- sonmarksthesample site.

ment was towards the SW. The localityissitua- tedwellinside and north of any recorded termi- nal morainesof presumed Prebo rea lage (Fig.

1).The low alpine vegetation is characterized by heather-andgrass moor.The plantspecies record ed at the mire indicate a poor fen veg- etation because of the presence of e.g.Eriop - horum angustifolium and Carex vaginata.

0VRESTO RVATN,Bykle,Ausl·Agd er,' ' ' m U.L

NGU-BULL.413.1988

Lithostratigraphy: At the base there is sorted sand coarsening upwards (Fig. 10) covered by dark bro wn detritus gyttja with a decrea- sing conten t of sand upw ards and followed by bro wn Eriophorumpeat atthe top.Angular sand and gravel particles are foun d at all le- vels inthe organic sediments.These are pro- bablyaproductof frost weath eringandsheet- wash.

Pollen analysis:The 051 local zone (Fig. 10) is defined by 8% Rumex. 3% Salix and a herb pollen florawith pioneer taxalikeArtemi- sia. Urtica. Caryophyllaceae and Thalictrum.

Characteristic ofthe zone are treepollen valu- es of 75%. Pinus is themain con stituent with 56%, while Betula and Corylus are present withrelativelysmall values(9and10%,respec- tively). Loss-on-ignition is 6%. The pollen re- cord indicates a low alp ine pioneer vegetati- on. Thelowerboundaryofthe 052localzone is defined by a decrease of Rumex to 3% , and anincreaseof treepollento around80%. This increase is primary caused by a rise in Corylus to 14% . The lower bounda ry of the 053 local zone is defined by an initial rise of Alnus.Pinusisthe mainconstituent among the tree po llen with values betwee n 52% and 43%. Betula constitutes betwee n 20% and

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NGU-BULL. 413,1988

13% .Gory/usgradually declines andCyperace- ae gradually increases through the zone.

Radiocarbo n dating: Two levels of this core were radiocarbon dated.

The pioneer characte r of the pollen flora indicates that the sandy gyttja was depositd shortly afte r deglaciation. The date from the lower part ofthis bed (8640±120years S.P.) (Fig. 10) was perfo rmedonthe NaOH soluble fraction,as contamination ofboth oldcarbon from the minerogenic part of the sediment, andyounger carbon from the verticalrootlets whichpenetrated the sediment,was conside- red possible. The obtained age is in agree- ment with the estimated age based on the pollen record, indicating a Soreal age. This age is also supported by the basal date at Skreivatndescribednext. Contaminationof the soluble fraction by carbon derived from the disintegrated part of the rootlets is therefore considered to be negligible. This dategivesa minimum age for the deglaciation of the high mountain area in the investigated area.

The upper dated level comprisesthe rise in A/nus, and was carried out to determine the age of the SoreallAtlantic boundary. The re- sultofthedetermination (6720±90 years S.P.)

Deg/aciationchronology 81

Fig. 11. Skreivatn 1030 m a.s.l.is a mire (an overgrown tarn) situatedin thehighmountainarea farinside andnorth of any recorded terminalmoraines ofpresumedPrebo real age. The sediment cover is thin and scattered and the vegetationislow alpine.Theperson marksthe sample site.

is somewhat younger than expected from the pollen record (see p. 70).

Skreivatn

This localityis a mire(an overgrow n tarn) situa- ted in the high mountain area 1030 m a.s.l, (Fig. 11)on graniticgneiss .The landscape is

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82 PerBlystad &Lot teSeising

SKREIVATN,Suld al,Rogaland,">Om. .'

Chrono- I I

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fairly flat in the vicinityof the locality and the sediment cover is thin and scatte red. The youngest ice movement was towards west.

The locality is situated far east and north of any record ed terminal mor aines of presumed Prebo real age.The scattered low alpine veg- etationis charact erized byheather- and grass- moor. Theplant species recorded at the mire indicatea poor fen vegetation because of the presence of e.g. Viola pelustris and Garex magellanica.

Lithostratigraphy:At the base thereis sorted sand (Fig.12)covered by browndetritus gytt- ja with a decreasing content of minerogenic matter upwar ds.

Pollenanalysis:The Sk 1 localzoneis defined by high Rumex values (16,6% in the basal

NGU-BULL.413.1988

Bio str a tigraphy

diagr am calculation basis

.00

sediment), by Salix (8% in the basal sedi- ment)dominating the shrubsand dwa rfshrubs and a herb pollen flora with pioneer taxa like Ar temisiaand Garyo phyllaceae (Fig.12).Tree pollen have amaximum of 72% in the middle of thezone.Pinus and Gorylusare thepromi- nent tree pollen, Pinus showing a rise in the bottom of the zone,whereloss-on-ignition is 4%. The pollen record indicates a low alpine pioneervegetation .The lower boundaryof the Sk2 lo cal zone is defined by an incr ease in Cyperaceae to 19% and in Poaceae to 11%.

while Rumex and Salix decline to 4 and 2%, respectively. Pinus dominates the tree pollen with values just below 40%. while Gorylus declines. The pollen record indicates a low alpine grassmoor.The lower boundary of the Sk3 local zone is defined by an increase in Cyperaceae to 31.5% and the initial Alnus ri-