Lake Inarijärvi, Northern Finland: Sedimentation and Late Quaternary Evolution

TUTKIMUSRAPORTTI REPORT OF INVESTIGA TION 143

Raimo Kujansuu, Brita Eriksson & Tuulikki Grönlund

Lake Inarijärvi, northern Finland: Sedimentation and late Quaternary evolution

Espoo 1998 GEOLOGIAN TUTKIMUSKESKUS GEOLOGICAL SURVEY OF FINLAND

Tutkimusraportti 143 Report of Investigation 143

Raimo Kujansuu, Brita Eriksson & Tuulikki Grönlund

LAKE INARIJÄRVI, NORTHERN FINLAND: SEDIMENTATION AND LATE QUA TERNARY EVOLUTION

Espoo 1998 Kujansuu, Raimo, Eriksson, Brita & Grönlund, Tuulikki 1998. Lake Inarijärvi, northern Finland: Sedimentation and late Quaternary evolution. Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Fin land, Report of lnvestigation 143. 25 pages, 17 figures and one table. Lithostratigraphy, varves, diatom and pollen stratigraphies were studied 2 from the Lake Inarijärvi, the third largest lake (1386 km ) in Finland. Main stages during its Holocene history can be divided into: 1) the "late-glacial" stage ofvarved mineral matter and rapid sedimentation that lasted about 500 years, beginning as an ice-dammed lake, being later connected with the Arctic Ocean via the Paatsjoki river valley. Proto-Inari stage continued for as long as the meltwaters continued to f10w into the basin and affected the sedimentation there; 2) the "postglacial" stage of long and slow sedimenta tion, during which pine and birch forests similar to those occurring today were dominant. Diatoms represent gradual oligotrofication of water. Changes in c1imate and vegetation, e.g. paludification of the environment, caused minor changes in the properties of gyttja. The sediments in depressions underwent anaerobic decomposition under oligotrophie conditions, result ing in the formation of sulphide-bearing bands. Throughout the existence of the lake, 1 kg carbon per hectare, on average, has been bound to sediments annually.

Key words (GeoRefThesaurus, AGI): paleolimnology, lakes, lake sediments, varves, lithostratigraphy, diatoms, pollen analysis, biostratigraphy, glaciolacustrine sedimentation, carbon, Holocene, Lake Inarijärvi, Finland

Brita Eriksson, Tuulikki Gränlund & Raimo Kujansuu Geological Survey of Finland P.O. Box 96 FlN-02150 ESPOO, FlNLAND

E-mail: raimo.kujansuu@gsffi

ISBN 951-690-718-0 ISSN 0781-4240 Kujansuu, Raimo, Eriksson, Brita & Grönlund, Tuulikki 1998. Lake Inarijärvi, northern Finland: Sedimentation and late Quaternary evolution. Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Fin land, Report of Investigation 143. 25 sivua, 17 kuvaa ja yksi taulukko. 2 Inarijärven, Suomen kolmanneksi suurimman järven (1386 km ) pohjakerrostumista on tutkittu kerrosjärjestystä, raekoostumusta, humuspitoisuutta, lustoja, piileviä ja siitepölyjä. Järven holoseenikautinen kehitys voidaan jakaa kahteen vaiheeseen. Myöhäisglasiaalinen, nopean sedimentaationja lustosedimentin luonnehtima vaihe kesti noin 500 vuotta. Kerrostuminen alkoi Inarin altaan itäosassa mannerjäätikön reunan patoamaan jääjärveen, jonka pinta vähitell en laski jäätikön reunan vetäytyessä lounaaseenjajoka yhtyi lopulta lyhytaikaisesti Paatsjoen laakson kautta Pohjoiseen Jäämereen. Tämä Alku-Inari vaihe kesti niin kauan kuin mannerjäätikön sulamisvesiä virtasi Inarin altaaseen. Toisen vaiheen, jääkaudenjälkeisen pitkänja hitaan sedimentaation aikana nykyisen kaltaiset koivu- ja mäntymetsät olivat vallitsevia. Piilevät kuvastavat järven hidasta oligotrofoitumista. Ilmastonja kasvillisuuden muutokset, mm. soistuminen aiheuttivat vain vähäisiä muutoksia kerrostuvan sedimentin ominaisuuksiin. Syvänteiden sedimenteissä tapahtui oli gotrofisissa oloissa anaerobisia muutoksia,joiden tuloksena sedimenttiin syntyi sulfidipitoisia mustiajuovia. Järven olemassaolon aikana sen sedimentteihin on sitoutunut hiiltä keskimääriin noin yksi kilogramma hehtaaria kohden.

Asiasanat (Fingeo-sanasto, GTK): paleolimnologia,järvet,järvisedimentit, lustot, litostratigrafia, piilevät, si itepölyanalyysi , biostratigrafia, glasi lakustrinen sedimentaatio, hiili, holoseeni, Inarijärvi, Suomi

Brita Eriksson, Tuulikki Gränlund & Raimo Kujansuu Geologian tutkimuskeskus PL96 02151 ESPOO

E-mail: raimo.kujansuu@gsffi

CONTENTS

General ...... 7 Inarijärvi sediments ...... 10 Distribution and amount of lake sediments and the amount of contained carbon ...... 16 Biostrati graphy ...... 16 Pollen ...... 16 Diatoms ...... 19 Evolution of Inarijärvi ...... 2 1 Summary ...... 23 Acknowledgements ...... 24 References ...... 24

Geologian tutkimuskeskus, Tutkimusraportti - Geologica/ Survey 0/ Finland, Report o/ lnvesTigaTion 143, 1998 Lake Inarijärvi , northern Finland: sedimentati on and Quaternary evolution

GENERAL

2 2 Lake Inarijärvi, or Inari, is loeated in Finnish of 1386 km , of whieh about 300 km is eovered by Lapland, northeast of the fell are of Saariselkä (Fig. islands. Its maximum length is 80 km, width 41 km 1). Finland' s third largest lake, it has a surfaee area and depth 95 m. Two large rivers empty their

A 24° 26° 28° 30°

Fig. I. A. Northern Fennoseandia, showing the ID eati on of Inarijärvi, th e zone of Younger Dryas end moraines (hatehed), the withdrawal of the iee front in th e area of the Inarij ärvi basin (narrow lines) and the glaeial lakes with thei r di seharge ehanne ls that eontributed to the evolution of Inarijärvi (sehemati e): I) Suoli sjärvi , 2) Surnujärvi, 3) Nammijärvi, 4) Inari glaeial lake proper, 5) Kaamasjoki, 6) Repojoki and 7) Korsatunturi . B. Loeati on of eoring sites.

7 Geologian lUlkimuskesku s, TUlkimusraporlli - Geological Survey of Finland, Report of Investigatioll /43, /998 Raimo Kujansuu, Brita Eriksson & Tuulikki Grönlund waters into the lake, the Juutuanjoki from the west elongated depressions (fracture zones) in the wa and the Ivalojoki from the southwest. The outlet ters of Kasariselkä, Sammakkoselkä and Vasik channel of the lake is in the east, where the river kaselkä. Paatsjoki conducts the waters into the Arctic Ocean. There are two esker chains in the Inari lake Because of regulation, the water level in the lake lowland running roughly from southwest to north fluctuates between 117 and 119.5 m asl (mean east (deposition al direction): one following the water level 118 m). At its closest, the main water northwestern shore of the lake and the other in the divide is 25-30 km to the south and southwest ofthe southeast, a short distance from the lake (Fig. 3). lake. These subglacial meltwater systems that deposited The Inarijärvi basin (Inari lake lowland) is a the eskers terminated in the ancient Inarijärvi, kettle depression produced by Tertiary block fault Proto-Inari, at the deglaciation stage and thus con ing (Mikkola 1932, Tanner 1938). Boundaries be tributed to late-glacial sedimentation of the lake. tween the blocks, faults and fracture zones are East of the lake there are four small eskers (Fig. 3), visible in the present morphology as rectilinear or of which so me may start on the floor of the present gently winding valleys and bays ("vuonos", fjords), Inarijärvi. The till cover in the area tends to be straits ("nuoras") and lake depressions (Figs 2 and patchy and thin. There are numerous bedrock out 3). The dominant fractures strike southwest-north crops around the lake and the shores are particular east and northwest-southeast and are also clearly ly rocky. Depressions are usually occupied by visible in the orientation of lake shores. The de mires with only a thin pe at covering. pressions oriented in the dominant flow direction About 10 000 yr BP the front of the continental of the continental ice sheet, southwest-northeast, ice sheet withdrew from the end moraines (Fig. 2) are distinctly wider and flatter than those trending that had formed in Norway no more than 50-60 km in other directions (Ristiluoma 1968). The lake is from the Inarijärvi basin during the Younger Dryas. mostly less than 20 m deep; the few areas in which The Inarijärvi basin was liberated from the ice a few the depth exceeds 60 mare located in narrow and centuries later, probably about 9500 yr BP. The ages

~==l 0 m

r;w:'I- 20 ..

69'

o 10 km '-'-~---"

I 28 ' Fig. 2. Balhymelric map of Inarijärvi after Ristiluo ma ( 1968).

8 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Reporr o/ Investiga tion 143, 1998 Lake In arij ärvi, northern Finl and : sedimentation and Quaternary evolution referred to here are radiocarbon years and are onellaJormosa, Cyclotella stelligera, Melosira (= mainly based on the investigations of Hyvärinen Aulacoseira) distans and Tabellaria Jenestrata. (1975). Alhonen (1969) investigated the Bosmina, pollen Only a few studies have been published on Inari and diatom stratigraphies of Nanguvuono from a järvi and its sediments. Järnefelt (1956) studied the 125-cm-thick gyttja deposit resting on sand. He limnology and plankton population of Inarijärvi. divided the Nanguvuono gyttja into three pollen The most common plankton diatoms were Asteri- assemblage zones (I, II-III and IV). According to

Fi g. 3. Relief and eskers (g reen) in the northernmost Finl and to th e scale I: I 000 000. The shaded image has been produced from the elevation model data of National Land Survey of Fi nl and, li cence no. 287/MAR/98.

9 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Finland, Report of In vestigation 143, 1998 Raimo Kujansuu, Brita Eriksson & Tuulikki Grönlund

Table I. Studied cores from Inarijärvi: I) lithostratigraphy, 2) varves), 3) pollen, 4) diatoms, a nd 5) grain size and humus conte nt.

Core 2 3 4 5

Inari, I sola hti x Il Ina ri , Nanguvuono x x x x 111 Ina ri , Kasari selkä S x x IV Ina ri , Kasariselkä N x x x x x V I nari, Kasarisel kä x x VI Ina ri , Sammakkoselkä x x x x x VII Ina ri , Lusmanllora x x VIII Inari , Vasikkaselkä x x IX Inari, Vasikkaselkä N x x X Inari, Satapetäjäselkä x x x x XI Inari , Vas ikkaselkä W x x XII Inari, Sammakkoselkä N x x XIll In ari, Sammakkoselkä S x x x XIV In ari, Kaikunuora x x XV In ari, Kahkusaarensalmi x x XVI Inari, Ukonselkä x XVII Inari, Nang ll v ll o no S x x XV III Inari , Nanguvuono E x x x XIX In a ri , Nanguvuononselkä x x XX In ari, Moossinase lkä x x x XXI Inari, Kasariselkä W x the Bosmina and diatom analyses, the Nanguvuono present-day research. The results ofthe microfossil gyttja deposited in oligotrophic water although a studies, for instance, are therefore usually based on slightly alkaline stage prevailed at the onset of 100 determined specimens. Even so, the outcome deposition (Alhonen 1969). The present stage and gives a good overall picture ofthe Inarijärvi depos evolutionary trend of Inarijärvi was studied in its and their genesis. 1992-1997 (Marttunen et al. 1997). Twenty-six cores were taken with a piston corer The material presented here was collected in the from the floor of Inarijärvi; data on 21 are given 1970s and '80s in conjunction with the general here (Table 1). Owing to the shortage of relevant geological mapping of Quaternary deposits to the information (cf. Alhonen 1969), the coring was scale 1: 400000. The objective was to establish the planned on the basis of the bathymetric map com amount of sediments deposited on the lake floor piled by Ristiluoma (1968), as we assumed that the since glaciation and the extent to which they differ abundance of sediments was highest in the lake from those in the vicinity. The sampIes were stud depressions. We also attempted to study the mode ied in different years by various people. Conse of occurrence and distribution of sediments with an quently, when compiling the present paper we echo-sounder (Atlas Monograph), but due to the could no longer check or supplement the material large size of the lake the attempts were not alto or bring the results into li ne with the standards of gether successful.

INARIJÄRVI SEDIMENTS

The lithostratigraphy ofthe lake sediments turned usually, however, 2-5 mm. In the next layer the out to be very similar in all depressions (Figs 4 and grain size becomes finer upwards. The clay content 5). Eight cores reached till. Lowermost or resting increases to 65-75% (Fig. 6), and the thickness of on the till in all cores was a layer of varved sedi the varves is down to 0.5-1 mm. Finally the varves ment; six cores are more or less deformed. The can no longer be distinguished as the sediment me an thickness of the varved sediment is 113 cm gradually becomes increasingly homogeneous. This (range 44-235 cm). The layer is composed of three layer of fat clay is no more than 10 cm thick at its parts: lowermost there is a layer, 50 cm thick on maximum (Fig. 7) and is overlain by a distinctly average, of distinctly varved silt or lean clay, which varved lean clay with a sharp contact in between. shows that the sedimentation rate declined as the The grain size of this clay becomes slightly coarser ice sheet front withdrew from the area. The proxi upwards, implying an increase in the sedimenta mal varves are up to several centimetres thick, tion rate (varves up to 2-4 cm thick). After a thick

10 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Filliand, Report of lll vestigatioll 143, 1998 Lake Inarijärvi, northern Finland: sedimentation and Quaternary evolution

IV V VI VII VIII IX X XI XII XHI XIV XV XVI XVII XVIII XIX XX 0 m I I J I c, 2 D c, c,

~ 1 D [22:j 2 4 0 3 D § 4 D 5 ~5 [Q] 6 ~ 7 6

Fig. 4. Lithostratigraphy of cores investigated: J) c layey gyttja, 2) gyttja cJay, 3) homogeneous clay, 4) varved c lay/silt, 5) fat cJay, 6) deformations, 7) till. varve or varves the sedimentation rate declines to and vivianite precipitates visible to the naked eye the 1-2-mm level and the grain size becomes slight appear in the sediment. The humus content of the ly finer once again. According to colorimetric de glayey gyttja remains fairly constant, ranging only terminations, the abundance of organic matter in from 7.5% to 9%. The grain size, too, remains the whole varved sediment layer is 0.5-1 % (Fig. 6). constant right up to the surface. In the southwestern Separated by a moderately distinct contact, the part of the Inarijärvi basin, close to the present varved clay is overlain by 10 cm of homogeneous mouth of the river Ivalojoki (Fig. 6; XVIIland clay (Fig. 8), in which the humus content rapidly XX), the concentration of organic matter remains rises to over 2%. The clay layer grades upwards below 6%. The properties of the gyttja clay are into gyttja clay (2-6% humus), in the upper part of fairly constant right up to the surface. which there are occasional black sulphide bands The me an thickness of the gyttja clay/clayey and the mineral matter becomes less sorted in grain gyttja layer is almost 1.5 m, fluctuating between 20 size. The abundance of clay remains at 30% but that and 338 cm. At one coring point (XVI, Ukonselkä), of coarse silt and even fine sand increases slightly the gyttja clay/clayey gyttja layer is absent. at the expense of fine and medium silt. The gyttja In the Nanguvuono core studied by Alhonen clay layer, too, is often only 10 cm thick, and grades (1969) and taken from close to the shore, the clayey upwards into clayey gyttja (>6 % humus). In some gyttja layer is underlain by sand, and the varved cores the sediment remains gyttja clay up to the sediment is absent. According to loss-on-ignition surface. In the light of the four cores investigated determinations, the concentration of organic mat (Fig. 6; IV, VI, XVIII and XX), we may conclude ter is about 9% to start with but declines rapidly to that the organic matter transported to the open part 2%. The core reflects locallittoral conditions, and of the lake or formed there from plankton deposited the results obtained from it cannot be correlated mainly in depressions (Fig. 6; cores IV and VI). with those from depression cores. Owing to this accumulation of sediment in depres The total thickness of the deposits is estimated sions, the moderate production of organic matter in not to exceed 6 m (Fig. 4). The maximum length of the lake resulted in high humus concentrations. core (without deformations) taken with the piston The number of sulphide bands increases as the corer was 4.5 m, and it is possible that a few tens of concentration of organic matter rises to over 6%, centimetres of sediment are missing from the upper

11 Geologian tutkimuskeskus, TUlkimusraportti - Geological Survey of Finland, Report of In vestiga tion 143, 1998 Raimo Kujansuu, Brita Eriksson & Tuulikki Grönlund part. The sediment layers are thicker in the south deformed and for them, too, we had to assess the ern part of the lake. sedimentation rate from the mean varve thickness Varves were counted in 15 cores (Fig. 9). From in the nearest parts of the sediment that could be the lower part of core XXI we only had a photo at recognised reliably. Many of the cores, however, our disposal, and from this we could estimate the contained varves or groups of varves that could be number of varves in the lowermost varved clay. identified with certainty and on the basis of these Although most ofthe varves were distinct we could we were able to correlate the cores with each other. not count those in the fat clay unambiguously. For The first varve succeeding the deposition of fat the most difficult parts we estimated the number of clay, which, in all cores except those from Nangu varves from the thickness ofthe layer and the mean vuono (Figs IB and 9; 11, XVII and XVIII), proba thickness ofthe nearest varves. Not all cores reached bly represents the same depositional stage, is named the till , however, and we had to estimate the number varve 0 (Figs 5, 7 and 9). Depending on the core, of missing varves. Some cores had been heavily the fat clay layer might contain from 50 to 90 varves, consequently representing sedimentation from 50 to 90 years. cm A thick varve, named varve A (Figs 5, 9 and 10), o is recognisable in the upper varved clay, most distinctly in cores from the southwest of the lake (except in the Nanguvuono area) (Figs. IB and 9; cores IV, XII, XIII, XIV, XIX and XX). This varve 10 6 deposited about 122 varves later than varve 0 , and A was followed by another 113 varves; in other words, the last varve formed about 235 years after varve O. 20 On a large scale, the upper varved clay shows regular variations in sedimentation rate that are 5 6 visible in the Nanguvuono area but no longer in the Kasariselkä or Sammakkoselkä areas (Figs IB and 30 9; cores 11, XIV, XVII, XVIII, XIX and XX). 4 Despite the shortcomings in the varve count, large variations in sedimentation rate are visible in Nan 40 6 6 r guvuono core 11, too. An exceptionally thick varve, varve B, that is particularly prominent in the lower varved clay in the centre of the lake (Figs 1Band 9; cores V, VI, 50 IX and XIII) records a rapid sedimentation event. ·1 When the front of the ice sheet was roughly in the I line Kahkusaari (coring point XV) - Satapetäjäselkä 60 l (coring point X), a fairly large glacial lake im pounded in the headwaters of the Kaamasjoki dis charged its waters from the northwest. Since the 70 discharge is represented by only one varve, which is clearly thicker than the others, the maximum intensity of discharge did not last more than a year. ~ .. , I Thereafter the flow and sedimentation in the Inari 80 ...... järvi basin levelled off, corresponding to the pre j. vailing normal meltwater activity . .L- The closer the cores were to each other, the more 90 reliably they could be correlated, also for the lower varved clay. The correlation is fairly reliable be tween cores IV, V, XII, XIV, XV, XIX, XX and •• XXI. A relative ordinal number can be given to the 100 bottom varve ofthese cores, remembering, howev er, that onl y cores 111, XV, XIX and XX reached till. We did not attempt to estimate the number of Fig. 5. Pholograph of core XX containing the Followin g strati graphie unils: I) till , 2) lower varved elay, 3) Fat elay, 4) upper varved elay, missing varves in the lowermost part, but it was 5) homogeneous elay, 6) gyttja c1 ay/c1 ayey gyttja) and varves 0 and A. probably not very high. We delineated the posi-

12 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Finland, Report of In vestigation 143, 1998 Lake Inarijärvi, northern Finland: sedimentation and Quaternary evolution

INARI IV Kasariselka INARI VI Sammakkosetka INARI XVIII NanglNuono INARI xx Moossinaselka B c B c A B A B c

Fig. 6. Properties ofcores IV, VI, xvm and XX: I) lithostratigraphy, for symbols, see Fig. 4, 2) grain-size distribution and 3) humus content by colorimetry.

cm xv cm o o IV XV

5 5

20 25

Fig. 7. Detail of contact between fat clay and upper varved clay in Fig. 8. Detail of a layer of homogeneous clay between upper varved cores IV and XV. clay (below) and gyttja clay (above) in cores IV and XV.

13 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Report o/Investigation 143, 1998 Raimo Kujansuu, Brita Eriksson & Tuulikki Gränlund

IX N ~t : VA~IKKASELK.A

XI VASIKKASELKA w ~f : ~ ~ l : XII SAMMAKKOSELKA S

IV KASARISELKA N

V KASARISELKA

A o I ~ I XIII SAMMAKKOSELKA N

VI SAMMAKKOSELKA

xv KAHKUSAARENSALMI

XIV KA1KUNUOAA

XIX NANGUVUONONSELKA

XVIII NANGUVUONO E

11 NANGUVUONO

XVII NANGUVUONO S A : I I I +200 +100 -100

Fig. 9. Correlation of varve diagrams based on the change in sediment type at the contact between fat clay and the upper varved clay, varve o and di scharge varves A and B. The varve numbers downwards from varve 0 are provided with minus and those upwards with plus signs.

14 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Report o/Investigation 143, 1998 Lake Inarijärvi, northern Finland: sedimentation and Quaternary evolution tions of the ice front in the central parts of Inarij ärvi from the ordinal numbers of the bottom varves cm IV XIX XXI (Fig. 11). The coring sites are, however, too far o apart for reliable connections to be made. The varve diagrams were correlated on the basis of common features (Fig. 9). Rad the varve counts 5 been faultless, all varves 0 would be on the same vertical line and the distance to varve A of equal length in all cores. That this is not the case implies 10 that either we did not identify and count all the varves or that some of them had eroded away. The average number of varves counted in cores was 369 (range 329-412). Rowever, from the number of 15 varves we can deduce fairly reliably that deposition of the varved sediment in the Inarijärvi basin las ted about 400 years, in the northeastern part slightly 20 more and in the southwestern part slightly less.

40 Fig. 10. Detail of varve A, cores IV , XIX and XXI.

Fig. 11. Positions of continental ice sheet front in the Inarijärvi basin at I O-year periods according to varve count. Numbers show the positions before the deposition of the varve O.

15 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Finland, Report of Investigation 143, 1998 Raimo Kujansuu, Brita Eriksson & Tuulikki Grönlund

DISTRIBUTION AND AMOUNT OF LAKE SEDIMENTS AND THE AMOUNT OF CONT AINED CARBON

The echo-sounder and sediment data imply that and Nenonen 1967), the postglacial deposits are glacial sediments (varved silt/clay) are fairly com thickest in the western parts of the lake. Sampling mon throughout the Inarijärvi floor. Rocky and till demonstrated that postglacial deposits are absent dominant floor types occur on elevations and steep from only one coring point. West ofUkonselkä, off slopes (Fig. 12). The depth of the basin, however, Inari village, there was less than half a metre of clay does not seem to have had a marked effect on the on the floor. The average thickness of postglacial occurrence of sediments. We estimate that the sediments in the whole basin can be assumed to be average amount of varved sediments in the basin is 60 cm, since they seem to favour the basins more a good half of the mean thickness of these sedi than do the glacial sediments. Hence, their total ments in the cores studied, 113 cm, i.e. about 60 amount, too, is probably about 600-700 million m3. cm. Taking into account the surface area of 1000- Assuming that the glacial sediments contain, on 2 odd km , we deduce that the Inari basin contains average, 0.5% humus and 30% water and that the about 600-700 million m 3 of silt and clay, probably density of the dry matter is l.6 g/cm3 and further washed from glaciofluvial deposits and till while that the postglacial sediments contain 5% humus these were forming. and 60% water and that the density of dry matter is The thickest deposits of postglacial sediments 1.1 g/cm3 and humus contains 50% carbon we can (gyttja clay/clayey gyttja) are probably in basins calculate that the sediments in Inarijärvi contain where depositional conditions were tranquil, e.g. somewhat less than 10 million tonnes of carbon. in Nanguvuono and the depressions in large open This implies that, on average, 1 kg carbon per waters. As the allochthonous production, which is hectare has deposited in Inarijärvi annually during mainly humus, is more intense near the inlets of the 10 000 years that have elapsed since the last rivers, that ofthe Ivalojoki in particular (Kerminen glaciation.

50 m

Fig. 12. Echo-sounding profile (about 5 km long) across Kasari selkä from west to east between the coring sites IV and V showing the di stribution of the sediments on the lake floor. The lake sediments are mi ssin g onl y from the shallowest parts of the lake bottom.

BIOSTRATIGRAPHY

Pollen

Seven cores were submitted to pollen analysis to ments. All the pollen sequences reflect the same delineate the vegetation history and establish po historical development of forests; the proportion of tential palynostratigraphic markers in the sedi- the local pollen flora is very small, as the cores were

16 Geologian tutkimuskesku s, Tutkimusraportti - Geological Su rvey 01 Finland, Report olInvestigation 143, 1998 Lake Inarij ärvi, northern Finlan d: sedimentati on and Quaternary evolution taken far from the shore. We present here pollen Inarijärvi and its surroundings belong to the diagrams for two cores (Figs 13 and 14) : N anguvuo Forest-Lapland phytogeographical region of the no and Sammakkoselkä (Fig. 1B ; cores II and VI). north boreal vegetation zone (Alalammi 1988) The postglacial vegetation succession in Peräpoh• where only pine and birch form forests . Dry, nutri jola and Forest Lapland started with abrief period ent-poor lichen-predominant pine forests are com of open-land vegetation, after which birch forests mon; spruce is encountered only occasionally. North spread to the area, reaching their largest extent of and above the pine limit there are mountain birch 9000 yrBP (Auer 1927, Sorsa 1965, Hyvärinen 1975, forests and dwarf shrub heathlands. The climate is 1978, 1996). The rapid increase in pine prevalence mildly continental (Ahti et al. 1968), the me an that occurred about 8500-7500 yr BP is the most temperature in February ranging from -11 to -13 oe distinctive marker horizon in the pollen diagrams of and in July from +12 to +14 oe (Alalammi 1987). Lapland and Peräpohjola. As shown by pollen analy Three local pollen assemblage zones (P.A.Z.) can ses and the dates of subfossil pi ne trunks found in be distinguished in the pollen stratigraphy of the bogs and ponds (cf. Eronen & Huttunen 1993, Hy Inarijärvi cores, exemplified here by the diagrams of värinen 1993), the pine forests, when at their larg Nanguvuono and Sammakkoselkä (Figs 13 and 14). est - ca 7000-6000 yr BP - extended to the present Betula zone. The major part of the varved sedi birch zone on the fells and to the coast ofthe Arctic ment contains abundant redeposited, mainly arbo Ocean in the north. When the climate deteriorated real, pollen. Some ofthe pollen grains are probably around 5000 yr BP or shortly after, the tree Iines contemporaneous, having been transported by wind started to withdraw, a process that lasted for a from distant sources. In this part of the sediment, couple of thousand years, until they reached their which represents aperiod of only a few centuries, present positions. Spruce advanced to the north the relative pollen frequency is very low. The ernmost parts of its distribution about 3000 yr BP. contemporaneous vegetation was amosaic ofpark-

INARIII Nanguvuono ~ w w :::; L1i « w ~ => i3 (/) VJ W ü5 «w i5 i5 ~ 0 0 I 9 3d(/) L1i a: ~ !l. I- 0 Ü ~ !l. ~BETULA -{)- ALNUS >-a: => w w 0 !l. I a:w :::; LOCAL C§ !l. I- U ~ W I- O => ...J a: er: U 0 ::J AP -- PINUS -6- PICEA U O=> :::;NAP PAZ. !l. 0 « w :::;P 2 ~

POOR IN POLLEN \

% 10 20 30 40 50 60 70 80 90 5 5 5 10 20 10 10 10 10 10 20 10 20

I::;; APloo% I:::; P 1oo% I::;; AP 100% Anal. B. Eriksson 1970

Fig. 13. Abridged pollen diagram. Inari 11 , Nanguvuono. For sediment symbols, see Fig. 4.

17 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Reporr o/lllvesrigatiol1 143, 1998 Raimo Kujansuu, Brita Erikssol1 & Tuulikki Gränlund like birch forests and open-land vegetation col continuous birch forests. Distinct maxima of Poly onies in areas that had emerged fram the ice and podiaceae and Lycopodium spores at the border water. Salix, Ericaceae, Poaceae, Cyperaceae and between the Betula and Pinus-Betula-Alnus zones Artemisia predominated in the shrub and field lay are visible in all cores studied. The pollen series of er. The assemblage also included Asteraceae, Saxi the surroundings of Inarijärvi (Sorsa 1965, Seppälä fraga, Polygonum viviparum and Selaginella. The 1971, Hyvärinen 1975) demonstrate that lycopods Ericaceae pollen show a small maximum followed and fems were abundant in the area during the birch by a low and fairly continuous curve in the varved forest stage. Hyvärinen (1996) dates the Lycopodi N anguvuono and Sammakkoselkä sediment. In oth um subzone (lb) he separated fram the Betula zone er Inarijärvi cores, the abundances of Ericaceae to 9000-7500 yr BP. This pollen assemblage has no pollen are lower and the occurrence of pollen grains counterpart in the area of present birch forests is less regular. Hyvärinen (1996) defined aseparate (Hyvärinen 1975). The coincidence of the Lycopo Ericales sub zone Cl a) in the Betula zone Cl), dating dium maximum with the rise of the pine curve in the its termination to about 9000 yr BP. pollen stratigraphy of Inarijärvi is prabably due to The relative pollen frequency starts to increase long-distance transport by wind of pine pollen into in the upper part of the varved sediments, being the large water basin and/or the water transport of fairly high in the homogeneous clay and gyttja pollen from the catchment before pi ne became clay, where the abundance of redeposited pollen is prevalent in the area. very low. The pollen composition of the upper part Pinus-Betula-Alnus zone. The pollen assemblage of the Betula zone reflects vegetation dominated by of the clayey gyttja layer in the Nanguvuono and

INARI VI Sammakkoselkä U! « w w « ü w :::e ~ w ~ ~ => ~ Cf) ~w«~o 15 15 I 9 => «L5~~~ 0 0 >- -' Cl.. Cl.. Cl.. 0 -0-- BETULA -D-- ALNUS a: ü «r5z w I il: LOCAL~«gc-w ~ 0 0 c- o ü ::J AP --PINUS -6-- PICEA ü :::e NAP PAZ. G ~ ffi ~ :::e P ~ ~ m i5

P,INUS 102 BETULA I.!:I~~ 101 103

PINUS- 104

I 101 BETULA -

% 10 20

I ~ AP 100% I ~ P 100 % I ~ AP 100 % ANAL B. ERIKSSON 1971

Fig. 14. Abridged pollen diagram. Inari VI, Sammakkoselkä. For sediment symbols, see Fig. 4.

18 Geologian tutkimuskesku s, Tutkimusraportti - Geolo[!,ical Survey of Fillland, Report of lnvestigation 143, 1998 Lake In arij ärvi, northern Finland: sedimentation and Quaternary evolution

Sammakkoselkä cores reflects the occurrence of grains in the Inarijärvi cores are mainly due to pine and birch forests si rni 1ar to those of today. The distant transport by wind and possibly also by pollen values of Alnus are at their highest in this waters of the river Ivalojoki. The nearest spruee zone, implying that alder colonies grew on wetlands forests currently grow along the Ivalojoki and at and lake shores during the climatic optimum. The the same latitude close to the eastern national vegetation indicated by the pollen zone prevailed in border; however, the spruce limit runs north of the area 7500-3200 yr BP (Hyvärinen 1996). the area (Alalammi 1988; Fig. 5a). Since the Betula-Pinus-Picea zone. The arrival of spruce immigration of spruce the forests in the area have 3200 yr BP (Hyvärinen 1996) is not recorded in the been similar to those occurring today. Nanguvuono core. However, the eontinuous spruce The cores only occasionally contained Pota pollen curve of the Sammakkoselkä core shows mogeton pollen, Isoetes spores and Pediastrum that the species had spread to the Peräpohjola colonies; one pollen grain of Myriophyllum al phytogeographical region, to the south of Forest terniflorum was also found. ExceptionaIly, the Lapland. The pollen values are fairly high (maxi clayey gyttja in the Kasariselkä core (Fig. IB; III) mum 3.5-4.5%) compared with most of the other contained abundant Isoetes spores, most of all in Inarijärvi cores and with other cores studied from the upper part of the layer where their dominance the area (e.g. Sorsa 1965, Hyvärinen 1975). Since was over 20%. Isoi!tes lacustris and I. echinospora the northern spruce forest limit was then, as it is as weIl as Myriophyllum alterniflorum are sub now, south of the study area, the spruce pollen merged plants that grow in oligotrophie lakes.

Diatoms

Diatoms were studied in seven eores taken from similarity of the diatom stratigraphies the results of the central, eastern and southeastern parts of the only two cores (Figs IB; II and X) are given in lake (II, III, IV, VI, VII, VIII, X). Owing to the diagrams (Figs 15 and 16). The highest number of

[NAR l [[ ~anguvuono

FRESHWATER DIATOMS S

SMALL LAKE TAXA LARGE LAKE TAXA ~ "5~ 0. ~ "0 .t ~"" ~ .;;c '2 ,; ~ j ~ ~ " ~ ~ .~ g ~ " c ] .~ i ~ ] ~ c::

Fig. 15. Distribution of diatoms on the basis ofth eir habitat.lnari H, Nanguvuono. S = diatoms living under marine conditions and stratigraphy of selected taxa. For sedim ent sy mbols, see Fig. 16.

19 Geologian tutkimuskesku s, Tutkimusraportti - Geological Survey of Finland, Reporf of lnvestiga tion 143, 1998 Raimo Kujansuu, Brita Erikssol1 & Tuulikki Grönlund diatoms named from Inarijärvi was 255 taxalcore. cool, alkaline fresh water, poor in humic matter and A total of 436 diatom species from the seven cores with moderate content of electrolytes , such as studied were named (see Gränlund 1998). The water of the Ancylus Lake and the Baltic !ce Lake nomenclature was updated from the level of the of the Baltic Sea. The other freshwater diatoms repre 1970s (Williams et a1.1988, Round et a1.1990, sent small-Iake species. The presence of saline spe Round and Bukhtiyarova 1996 and Bukhtiyarova eies is marked with a cross in diagrams. and Round 1996). The diatom stratigraphies of the cores are very Apart from a few saline water diatoms found in similar, small-Iake species being dominant in all of lower parts of the cores and interpreted as redepos them. The lower parts of certain cores are poor in ited, the cores contain only freshwater diatoms. diatoms, and some of them may be secondary, at The diatoms have been grouped into large-Iake least those requiring a saline habitat. The abun and small-Iake species on the basis of their typical dance of diatoms starts to increase in the horizon in habitat. Large-lake diatoms are characteristic of which the concentration of humus starts to rise. The

INARI X Satapetäjäselkä

FRESHWATER DIATOM S S

SMALL LAKE TAXA LARGE LAKE TAXA g.0.. ...'"

-'". ~ 0- e ;::s '"- E..., + V> ~ :;:; .~'" " 0 ~ " 0.. ""- :;:; ~ g. "- e e g.0.. -'" E ,.. .~ .~ ·E .~ ~ ~ '-' 0 0 ~ .,'" s :3 c.> c.> -'" :S 0 0 .~ "- .s ~ :;'" :;'" ";::s " ... Cl'" ;:;'" < «: c:::" '"-'" <5'" 0 - r"" r MI - . I- ~ 210 ~ ~ 235 50 - - ~ I- 230 100 - ~ 200 I>- 225 150 - - ~ 200 200 i""- - 210 250 I-- =- 255 11~ ;=- 210 200 230 E 11 5 300 - -- - ~ Iii I---- + ~ ~ 140 I--- + I- I- ~ =- 63 r r -...,.., ''"l~ 20 40 60 80 100 20 40 60 80 20 40 20 40 400 % Anal. T. Gronlund 111 ~ 111 111 111 1. 2. 3. 4. 5.

Fig. 16. Distribution of diatoms on the basis of their habitat. Inari X, Satapetäjäselkä. S = diatoms living under marine conditions and stratigraphy of selected taxa. Sediment sy mbols: I) clayey gyttja, 2) gyttja clay, 3) homogeneous clay, 4) varved clay, 5) fat clay.

20 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 0/ Finland, Report o/Investigation 143, 1998 Lake Inarijärvi, northern FinJand: sedimentation and Quaternary evolution abundance of large-lake diatoms is at its highest in the ing) Rabenhorst are littoral large-lake species. upper part of the varved clay layer and in the lower The diatom flora in the uppermost clay gyttja / part of the gyttja clay/clayey gyttja layer. Aulacosei clayey gyttja does not show marked change in ra islandica (Müller) Simonsen (including the mor species. Small-lake species Cyclotella iris Brun, photype A. islandica ssp. helvetica (Müller) Si Tabellaria Jenestrata (Lyngbye) Kützing, T. jlocc monsen), Cyclotella bodanica Grunow and Stephan ulosa (Roth) Kützing and Aulacoseira, Eunotia odiscus neoastrea Hakansson & Hickel, all of which and Pinnularia species are common. live in plankton, are the most common large-lake Alkaliphilous species of the Fragilaria genus are species. Of them, the fIrst two are cool-water species, also abundant; the northem species, Fragilaria lap as is Cyclotella antiqua W. Srnith (Mölder & Tynni ponica Grunow, is particularly common. The in 1970), a species typical of oligotrophie lakes in crease in the abundance of Fragilaria species coin Lapland. Ellerbeckia arenaria (Ralfs & Moore) eides with or immediately follows the maximum of Crawford, Campylodiscus noricus Ehrenberg, Cym the large-lake diatoms, being clearest in cores VII and bella aspera (Ehren berg) Peragalli, C. lanceolata X. The mass occurrence of the Fragilaria genus is (Ehrenberg) Cleve and Gyrosigma attenuatum (Kütz- typical of the initial stage of the evolution of lakes.

EVOLUTION OF INARIJÄRVI

Tanner (1906, 1907, 1915, 1930), who studied deglaciation proceeded the basins at the highest Quaternary geology in the northem parts of Fenno elevations gradually joined those at lower eleva scandia, argued that during the deglaciation stage the tions, eventually joining the Inari glacial lake prop sea extended to the Inarijärvi basin. Synge (1969) er. To start with, its discharge channel was at the provided more detailed information on the highest northem end of the present lake Nitsijärvi, at a level shore and its characteristics in the Inarijärvi basin, slightly less than 130 m asl. From west of the lake, and came to the same conclusion as Tanner: the there are observations of a water level a few metres highest shore marks represent a marine transgression. above the highest shore li ne (Synge 1969); these It is nonetheless generally held that isostatic uplift are obviously from this glacial lake stage. In the exceeded the eustatic rise in sea level throughout course of deglaciation the ice front withdrew south the postglacial stage, except at the margins of the westwards and several small glacial lakes around uplift area (e.g. Pirazzoli 1991), thus precluding the eastern end of Inarijärvi drained into it. The the possibility of a transgressive stage. Morpho Inari glacial lake stage terminated when the ice logical observations show that the highest shore, front reached the starting point of the river Paats which at Virtaniemi - at the present outlet of the joki and the water level in the lake coincided with river Paatsjoki - is at 131 m asl, rises from the eastem that in the Ocean. This was the start of the Proto part of the lake southwestwards; thus at Nanguvuono Inari stage, which is characterised by the proximity it is at 145 m and 3 km east of Ivalo at 151.6 m asl. of the continental ice sheet, an abundance of melt These shore marks are located on the same tilted waters and the great amount of sediments trans plane, with a gradient of 0.47 m/km (Synge 1969). ported by these waters. The marine stage is not, however, recorded in the A few large glacial lakes developed in the vicin diatom stratigraphy of the lake, only a few saline ity of Proto-Inari, often draining suddenly into the water diatoms having been found in the sediment. Inarijärvi basin. This is visible in sediments as At least some of these are redeposited from older increased deposition (thick varves) and explains the sediments, such as Hemiaulus sp. and Triceratium great fluctuations in thickness of the proximal varves. trifoliatum Cleve, both of them probably Tertiary The correlation of an exceptionally thick varve with in origin (Grönlund 1977, Tynni 1982). Auliscus a given glacial lake stage in the lower varved clay is sculptus (W. Smith ) Ralfs, Biddulphia spp., Cos possible only for cores V, VI, XIII and X. At that time cinodiscus sp., Paralia sulcata (Ehrenberg) Cleve the ice front was slightly southwest of the sites from and P. sulcata var. sibirica (Grunow) Cleve are which these cores were taken and the waters of the probably from the Eernian interglacial. glacial lake impounded in the headwaters of the During deglaciation, small local lakes were im river Kaamasjoki drained from the northwest into pounded by the front of the ice sheet in the nOrth the Inarijärvi basin, depositing varve B. eastem part of the Inarijärvi basin, in basins now The sedimentation rate declined, however, when occupied by the lakes Surnujärvi, Suolisjärvi and the ice front withdrew southwestwards. Owing to Nammijärvi. Initially, these glacial lakes drained ice calving the withdrawal was fairly rapid. After over the water divide into the Arctic Ocean. As the ice front had reached the southwestern end of

21 Geologian tutkimuskes kus, Tutkimusraportti - Ge%gica/ Survey oi Fin/al1d, Report oi Ill vestigation /43, 1998 Raimo Kujansuu, Brita Eriksson & Tuulikki Grön/und the basin, the basin ae ted for some time in a flow glaeial lake waters that eame over the main water through capacity. Consequently, abundant silty and divide flowed to the headwaters of the Ivalojoki fine sand sediments were transported into the basin along the northern side of Korsatunturi fell. Dep and sedimentation remained fairly rapid. On reaeh osition of the glaeial (varved) sediments of Proto ing the supra-aquatie area west of the lake the iee Inari eame to an end when the iee front had front beeame stagnant for a while and the amount of withdrawn so far to the south of the water divide glaeial mineral matter declined, as shown by the that the meltwaters started to flow into rivers thinning of varves and reduetion in the grain size of heading southwards. The average sedimentation the sediment. The suddenly inereased sedimentation rate during the glaeial stage has been estimated at rate and the eoarsening of sediment (upper varved somewhat less than 3 mm/yr. clay) were due to an inerease in meltwater aetivity, As dedueed from varves, the withdrawal rate of as shown by the sudden thiekening of the varves. the iee sheet in the basin was 240-330 rn/yr (Fig. Provided that the observations of the transgres 11). It took the iee front from 400 to 500 years to sive nature of the highest shore are valid (Tanner withdraw from Vasikkaselkä in the eastern part of 1907, 1930, Synge 1969), the variation in sedimen Inari to the main water divide, a distanee of 120 tation rate eould also be explained by assuming that km, implying a rate of about 250-300 rn/yr. The the basin was at first a flow-through basin and that rate is slight1y high er than that estimated from the abundant silt and fine sand were transported into it. lateral drainage ehannels in the Saariselkä fell Onee transgression had reaehed its highest position, area (Tanner 1915, Penttilä 1963, Piirola 1982, at Virtaniemi, a large strait eontrolled the water flow Kujansuu and Hyyppä 1995, Johansson 1997). in the basin and flow-through beeame less intense. The time following deglaeiation is clearly re The sedimentation rate diminished as eoarse sedi eorded in the diatom stratigraphy, beeause the ments deposited in the deltas at river mouths and proximity of the iee sheet, its dynamies and the only clay was transported into the Inarijärvi basin. amount of meltwater affeeted the water, sedimen This eoneept eould also explain the shortage of tation and diatom flora of the basin. When sedi redeposited pollen in the fat clay layer (cf. Donner mentation was rapid, few mierofossils deposited, and Gardemeister 1971). The stage lasted 50-90 as demonstrated by the gaps in the pollen and years. As the water level fell, the flow ehanged and diatom stratigraphies. As weIl as small-Iake dia fraetions eoarser than clay started to enter the basin toms, the diatom flora eontained abundant large onee again. Meanwhile the iee front had withdrawn lake diatoms in the Proto-Inari stage. to the Saariselkä fells, and meltwaters aeeumulated The deposition of varved sediments with a in the Inarijärvi basin from an inereasingly large Betula-dominant pollen assemblage terminated area, earving ehannels and other erosional forms in about 9000 yr BP, and the independent Inarijärvi their bed. Coarse fraetions, gravel and sand deposit stage started. Homogeneous clay began to deposit ed in river valleys as large glaeiofluvial plains on the varved clay. The abundanee of organie (deltas, v sandurs, valley fills) and the finer fraetions matter in the clay inereased rapidly as the vegeta were transported by water into the Inarijärvi basin, tion in the environment beeame more den se, and further promoting sedimentation. The rise in the production started in the lake after the glaeial sedimentation rate of the upper varved clay bears influenee had eeased. At the same time the total testimony to this evolution. sedimentation declined markedly, being less than When the iee front had reaehed the water divide 0.2 mmlyr throughout postglaeial time (150 em in between the rivers flowing southwards to the Gulf of 9000 years). The deposition of gyttja clay/clayey Bothnia and the Ivalojoki, the glaeial lakes im gyttja has been very similar ever sinee. pounded beyond it diseharged for some time along Small-Iake diatoms are dominant in the diatom the river Vaskojoki and later along the Iva10joki to flora. After a brief, more alkaline stage the lake Inarijärvi. It is possible that the thiek varve that beeame oligotrophie and has eontinued its evolu formed 123 years after the upper varved clay had tion without great ehanges ever sinee; it is still started to deposit (A+122) is assoeiated with the oligotrophie today, although the quality of its drainage of a 1arge glaeia1 lake. For instanee, a water varies, being clearest and most oligotrophie glaeial lake diseharged through the headwaters of in the north and slightly brownish due to river the river Repojoki, and its waters deposited a large waters in the south and west (Marttunen et al. sandur east of Reposelkä. The intense flow through 1997). Aeidifieation eaused by atmospherie sul the headwaters of the Repojoki probably lasted a few phate fall-out eame to an end in the mid-1980s. years. Waters from glaeial lakes that had developed Diatom analyses on the surfieial parts of the sed south of the main water divide flowed into the iment imply slight eutrophieation sinee the late Inarijärvi basin for a good hundred years and the last 1980s (Puro et al. 1997).

22 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey of Fil1/ol1d. ReporI of 1l1 vesrigariol1 143, 1998 Lake lnarijärvi , northern Finland: sedimentation and Quaternary evolution

SUMMARY The eontinental iee sheet withdrew from the long and slow sedimentation, during whieh pine and northeastem end of the Inarijärvi basin southwest bireh forests similar to those oeeurring today were wards to the main water divide in 9700-9200 BP. dominant, the lake beeame oligotrophie and gyttja On the basis of sediments, the evolutionary history clay/clayey gyttja deposited on the lake floor as a of Inarijärvi (Fig. 17) ean be divided into two main result of its own produetion but also partly transported stages: 1) the "late-glaeial" stage of varved mineral by rivers diseharging their waters into the lake. Chang matter and rapid sedimentation that las ted about es in climate and vegetation, e.g. paludifieation of the 500 years, during whieh Proto-Inari, at first an iee environment, eaused rninor ehanges in the properties dammed lake, whieh diseharged at Sevetti over the of sediment. The sediments in depressions underwent water divide into the river Näätämöjoki, being later anaerobie deeomposition under oligotrophie eondi eonneeted with the Aretie Oeean via the Paatsjoki tions, resultingFig. 17. Environmental interpretations river valley. There is, however, no reeord in the and stratigraphie eorrelations of Inarij ärvi sedi diatoms of the brief eonneetion with the Oeean and ments. 1) lithostratigraphy, 2) humus eontent, 3) saline water even though the aneient shores imply sedimentation rate, 4) loeal pollen assemblage zones that it really did take plaee. Most likely, the vast and relative pollen frequenee, 5) diatoms, 6) devel amount of meltwater prevented the saline water opmental stages of Inarijärvi, 7) age in 14C yr BP. in from entering the Inarijärvi basin. The Proto-Inari the formation of sulphide-bearing bands. Through stage eontinued for as long as the meltwaters eon out the existenee of the lake, 1 kg earbon per tinued to flow into the basin and affeeted the heetare, on average, has been bound to sediments sedimentation there; 2) the "postglaeial" stage of annually.

1 2 3 4 5 6 7 o m I 5% 5mm Low Hgh Prcscnt Ina ri I Present I PitlllS, I I Be/lila, I Small Stable I ____ g:;E~.'!L_! Gyttja / lake diatoms I I I I common / I / I' / I / PiulJs- I / Belllla- I / AII/IIS / ~ Gradual 7500 / E / Gytlja c1ay oligotrophieation I ~ 3 Small "8;;' Homogeneous '" elay '" '" ~'E Sild large / '" - 9000 I '" lake / Upper I diatoms I varved I Proto-Inan elay I Belllla snd I eharaelcrized I redeposited I by meltwaters I I marine I from I taxa I eontinental 4 I Fat c1ay iee sheet

Lower varved c1ay 9500 4,5 Till Covercd by conlineilial ie. shee!

Fig. 17. Environmental interpretations and stratigraphie eorrelations oflnarijärvi sediments. 1) lithostratigraphy, 2) humus content, 3) sedimentation rate, 4) loeal pollen assemblage zones and relative pollen frequenee, 5) diatoms, 6) developmental stages of Inarijärvi, 7) age in " C yr BP.

23 Geologian tutkimuskeskus, Tutkimusraportti - Geological Survey 01 Finland, Report ollnvesrigarion 143, 1998 Raimo Kujansuu, Brira Eriksson & Tuulikki Grön/und

ACKNOWLEDGEMENTS

The cores were taken in cooperation with Esa digital image editing was done by lari Väätäinen, Kukkonen, Boris Winterhalter and the late Heikki the digital elevation model by laana larva and the Ignatius. Field and laboratory assistance was given text was translated into English by Gillian Häkli. i.a. by Eila Paavilainen, Pauli Kaijola, Arto Kiis To all of them we extend oUf sincere thanks.We are kinen, Risto Poil ari , Seppo Putkinen, Sauli Valka also grateful for the constructive comrnents given ma and the late Tauno Virtanen. Maps and illustra by Hannu Hyvärinen, the referee of the journal. tions were drawn by Satu Moberg, scanning and

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