Kettle holes - stratigraphical archives for Weichselian geology and palaeoenvironment in northernmost Sweden

Kettle holes - stratigraphical archives for Weichselian ~~

geology and palaeoenvironment in northernmost Sweden ROBERT LAGERBACK AND ANN-MARIE ROBERTSSON

Lagerback, Robert & Robertsson, Ann-Marie 1988 1201: Kettle holes-stratigraphical archives for Weich- BOREAS selian . geology " and palaeoenvironment in northernmost Sweden. Bore@, Vol. 17, pp. 4 3 W . Oslo. ISSN 0300-9483.

An active search for pre-Holocene organic deposits in stratigraphically well-defined positions has proved to be a useful tool for reconstruction of glacial and non-glacial Weichselian development in northernmost Sweden. The investigations have been concentrated to kettle holes connected to eskers belonging to a morphologically prominent northwesterly glacial system characterized by extensive drumlinization. Organic deposits, radiocarbon-dated asolder than the Holocene, have been found at some 25 localities. Some sites display two organic-bearing sequences separated by a till bed. The pollen flora in the lowest organic bed reflects an interstadial vegetationaldevelopment: Arcticsbrub and herb tundra-subarcticlight birch forest- herb tundra with ericaceous shrubs and dwarf birch. This interstadial is correlated with Perapohjola in Finland. During the younger Tirendo Interstadial the vegetational development was similar, hut a more continental climate is indicated hy high values of steppe plants, e.g. Artemisiu and Chenopodiaceae. The Tarendo Interstadial, correlated with Odderade, wascharacterized by open, unstable soils due to periglacial processes such as cryoturbation and eolian activities. The Weichselian glaciation is divided into three glacial stades separated by ice-free interstadials in the area studied. Except for a zone with S S W drumlinization the impact of the two later ice sheets is insignificant.

Robert Lagerback & Ann-Marie Roberason, Geological Survey of Sweden, Box 670, S-751 28 Uppsala, Sweden; 7th March, 1988 (revised 2nd June, 1988).

Since Fredholm (1886) called attention to the area, the northeastern part of the County of Norrbotten has played an important role in the discussion of glacial development in northernmost Sweden. There are two regionally occurring systems of ice movement, an older ice flow from the northwest and a younger from the south or southwest. These two generations are represented by glacial striations and widely distributed drumlins (Figs. 1-4). In addition, there are indications of more westerly ice flows, but these appear to be of local importance or at least are not as extensive as the two dominating systems. The main question concerning the glacial development within the area is whether the systems described merely represent different phases within one glaciation, or two or more glaciations separated by ice-free periods.

A model including different glaciations, with one, or possibly two, ice-free periods in between, appeared to be the most probable explanation for the numerous observations of complex stratigraphy with different till beds and till-covered water- laid sediments. The different stratigraphical units, as well as the systems of ice flow, appear to be very well defined and without transitional stages.

Indications of successive veering of the ice flaw from one system to another have not been observed. An investigatory programme was started in 1982 in order to find conclusive evidence for deglaciation and ice-free conditions between the different generations of ice flow. This work was carried out by means of investigations of the Quat- ernary stratigraphy, including an active search for organic deposits in well-defined stratigraphical positions.

Organic sediments are indisputable criteria of ice-free conditions. Thus, if organic matter of interstadial age was found in primary position between the deposits belonging to the two main ice flows, it should be possible to demonstrate that the northwesterly flow belongs to a prior glaciation. Organic deposits formed in direct connection with morphologically pronounced features, such as drumlins and eskers, are most convincing. Such deposits were found and have been radiocarbon- dated and analysed with respect to their content of microfossils.

R. Lagerback initiated the investigations and is responsible for the field work including mapping and sampling, lithostratigraphicai interpretations

440 Robert Lagerback and Ann-Marie Robertsson BOREAS 17 (1988)

and presentation of glaciation models. A.M. Robertsson presents the biostratigraphical results and outlines the vegetational development and the changes in the sedimentation environment. We are jointly responsible for the interpretations of the results and for the conclusions concerning the chronostratigraphy of the different stratigraphical units. The aim of this paper is to emphasize the stratigraphical complexity of the region and the suitability of the applied methods for the reconstruction of the glacial development and the palaeoenvironment during non-glacial periods. The results of the investigations have partly been presented earlier in connection with meetings and symposia (e.g. Lagerback 1984, 1986, 1987; Robertsson 1984, 1987).

Quaternary deposits, geomorphology and stratigraphy The area studied (Fig. 1) covers some 15,000 km2 and is situated in the forested area of northernmost Sweden. Its southern parts are crossed by the Arc- tic Circle. The bedrock is dominated by granitic rocks of Precambrian age. Exposed bedrock constitutes only a few per cent of the area. The area is composed of an undulating plain, where scattered hills occur, and it is cut through by a few valleys of which that of the Kalix river is the most pronounced.

The area is situated between about 40 and 500 m above the present sea level, but altitudes between 100 and 350 mare most common. The terrain generally rises from the south towards the northwest and west. The southeastern part of the area is located below the Holocene highest coastline, which vanes between about 215 m in the southeastern part and 170 m in the north and northwest (cf. Fromm 1965: fig. 87).

Glacial till is the predominant Quaternary deposit. The tills generally have a sandy composition and often constitute morphologically prominent features such as hummocky moraines and drumlins. Hummocky moraine, mainly of so- called Veiki-type (Hoppe 1952), occurs in the far west of the area (Fig. 1).

The drumlinoid features, of the utmost importance for the reconstruction of glacial development within the area, mainly belong to two different systems of ice flow. An older, northwesterly system dominates the landscape. These drumlins are generally 1-3 km long, 200-500 m across and 10-20 m

o m m a 40 n k m __ Ice flow inferred + Site with interstadiai from drumlinization organic deposits

Eoker +, Site mentioned in the text 0 Hummocky moraine

Fig. 1. The glacial geology of the investigated area. Sites: (1) Riipiharju, (2) Onttoharjut, (3) Onttovaara, (4) Takanenrnan- nikko, (5) Hirvijarvi, (6) Vuottarauto.

high (Fig. 2). Rock dominated drumlins are often still larger. Features belonging to this system are spread over the entire area and partly developed as drumlin fields (Nordkalott Project 1986a).

The younger drumlinoid features, mainly representing an ice flow from the south or southwest (Fig. l ) , are generally less pronounced and occur as a weak fluting superimposed on the older, northwesterly drumlins (Figs. 3,4). The younger drumlinization is best developed in the east of the area (Fig. l), but faint features are locally found also in the west. In addition to these two main systems, more westerly drumlins occur locally. The relative age of these features compared with the main systems is not clear. Judging from observations of striations, either they may date from aperiod between these stages or postdate both (cf. Fromm 1965; Fagerlind 1981).

The glacial striations generally cluster in the same directions as the drumlins, supporting the interpretation that these represent well-defined systems of ice flow. In parts of the area there are striations representing a more northerly ice flow

BOREAS 17 (1988)

Fig. 2. Large NW drumlins, 20 km SSW of Tarendo, deriving from the first Weichselian ice sheet. The nearest drumlin measures 2,500 x 300 m and is about 15 m high (cf. Figs. 3 and 4). The photograph looks west. - Photo: R. Lagerback (1981).

Fig. 3. NW drumlins (thick arrow) superimposed and remoulded by younger drumlinization from SW (thin arrow) (cf. Figs. 2 and 4). Photograph taken 10 km NW of Korpilombolo, looking west. - Photo: R. Lagerback (1981).

Fig. 4. Intense small-scale drumlinization or fluting from SW (thin arrow). Older NW drumlins (thick arrow) occur as ghosts by the NW-SE rows of the younger features (cf. Figs. 2 and 3). Photograph taken 5 km NW of Korpilombolo, looking west. - Photo: R. Lagerback (1981).


older than the dominating northwesterly system. The younger, southwesterly striations are often very weakly developed and in vast areas there are no observations at all of striations younger than the northwesterly system.

Glaciofluvial deposits occur as eskers, and different types of marginal and extramarginal out- wash deposits. The glaciofluvial deposits mainly belong to the northwesterly glacial system (see orientation of eskers in Fig. 1) and are frequently, at least to some extent, till-covered. The till cover, although rarely more than a few dm thick, also occurs in areas without striations or other mor-

The morphology of hummocky moraine, drumlins, eskers and meltwater channels belonging to the northwesterly directed ice-flow system is generally fresh and there are few signs of glacial influence after formation. Many sharp-crested eskers are not eroded and air-photo interpretation scarcely suggests that the features observed pre- date the latest deglaciation (Figs. 5-7). Still, they appear to belong to the same system which in other areas can be demonstrated to have been overrun by ice from SW. Often the only indications of a pre- latest glacial age are a few erratics or a very thin cover of loose till-like material on the glaciofluvial deposits.

. phological evidence of younger ice movement.

Fig. 5. The Vuottarauto esker (Site 6 in Fig. 1) 30 km SSE of Nattavaara. Interstadial organic deposits were found at A and B. The esker derives from the deglaciation of the first Weichselian ice sheet and has survived two later glaciations. Photogaphlook- ing SE. -Photo: R. Lagerback (1987).

Glaciofluvial deposits associated with the younger, southwesterly directed ice flow system are few and generally of moderate size. On the other hand, this youngerice appears to have caused considerable glaciofluvial erosion in parts of the area. These circumstances, together with the thin till cover, are indicative of a sluggish glacier, to a great extent probably cold based, and only slightly loaded by debris.

The Quaternary stratigraphy within the area is complex. The section with two till beds described from Pajala by Jarnefors (1952) has proved to be typical of large parts of the region. Several sections with two till beds or with till-covered sediments have been reported by Fromm (1965) and Fager- lind (1981). Fagerlind found two till beds, often demonstrating fabrics which could be correlated with the ice flow generations (NW and SW), indicated by glacial striations and drumlinoid features.

Within the Nordkalott Project, and in connection with mineral exploration, some 300 machine made test pits have been examined within the area (cf. Nordkalott Project 1986~). Two or more till beds, often intercalated by water-laid sediments, appear to be the rule rather than the exception down to 4-6 m below ground surface. The most common sequence is one (or occasionally two) brown or greyish brown, fairly thin till bed resting on a thick, grey till. In the upper, brown till(s),oftennomorethanOS mthick, fabricanaly- ses generally suggest ice flow from the southwest, west or west-northwest. In the lower, grey till, which builds up the large northwesterly drumlins, fabric analyses demonstrate more divergence of the clasts, but typically a northwesterly ice flow is indicated. The till normally reaches to the bottom of the pits (4-6 m), but sometimes a rusty, very compact, weathered till bed is encountered. This lowermost till has been observed only at some 10 localities within the investigation area and it is dif- ficult to correlate to any certain system of glacial striations. In the south of the area it is believed to represent a northerly ice flow indicated by striations and a few drumlinoid features.

Research strategy to find Pre- Holocene organic deposits As described above, the deposits belonging to the northwesterly glacial system are extremely well preserved, although they have been exposed to younger ice movements (Figs. 5, 6, 7). Along eskers belonging to this system kettle holes of dif-

BOREAS 17 (1988) Kettle holes as stratigraphical archives 443

Fig. 6. The Onttoharjut esker 10 km NW of TTuend6. The Onttoharjut site is located at the small mire (see arrow) in the centre of the picture (cf. Figs:7,11). Photograph looking SE. -Photo: R. Lagerback (1987).

ferent sizes and shapes are found, i.e. depressions created by the melting of large ice blocks buried by glaciofluvial material in connection with the formation of the esker. These kettles were considered to be promising localities for demonstrating a pre- latest glacial age of the eskers and, thereby, also of the other deposits and morphological features deriving from the northwesterly ice flow. The kettle holes satisfy several important prerequi- sites:

The stratigraphical position is evident. The strata formed inside the kettle hole are younger than the glaciofluvial deposits in which the depression was created. The kettle hole offered good conditions for deposition and preservation of organic matter during ice-free periods. A deep depression situated close to a sharpesker provides the organic deposits with a good pro- tection against moderate glacial erosion or other erosive agents. As the kettle holes are often fairly deep, they afford good conditions for accumulation of thick sediments which will give good time resolution of the stratigraphical records. While the period

from the northwesterly ice flow to the Recent is generally represented by a thin till bed, the deposits in the kettle holes may exceed 10 m, the Holocene layers excluded.

For these reasons the efforts to find interstadial organic deposits were directed to kettle holes related to eskers of considerable extent and clearly belonging to the northwesterly glacial system. As the most favourable sites lay in remote areas, the investigations were carried out in winter when it is possible to transport drilling equipment by snow- scooter and drive excavators on the frozen mires. Most of the investigated sites have been explored by borings, at least as a first step. The equipment used is a light hand-held Cobra machine combined with 35mm rods and samplers of through-flow type, the biggest giving samples 500 X 33 mm in size.

Besides ease of transport, drilling in winter offers clean conditions with a minimal risk of contamination by recent pollen when the samples are treated in the field. After sampling for radiocarbon dating the cores were split into 5 or 10 cm pieces and put in plastic bags for further treatment at the laboratory.


Fig. 7. Aerial photograph (approx. scale 1:3O,ooO) showing the Onttoharjut esker 10 km NW of Thndb. A. The Onttoharjut site. B. The Onttovaara site. North is at the top of the picture (cf. Figs. 6 , l l ) . - Air-photo: National Land Survey of Sweden (1968).

BOREAS 17 (1988)

Methods for microfossil analyses Microfossil analyses of pollen and diatoms have been carried out on sample sequences collected at Riipiharju, Onttoharjut, Onttovaara and Tak- anenmannikko (Fig. 1). The samples were treated for pollen analyses according to a sedimentation- separation method (Pbsse 1976). This treatment was chosen as most of the material consists of fine- grained sedimentswith rather low organiccontent. The method is very effective and even till samples with low pollen frequenciescould be quantitatively analysed. The Holocene peat and gyttja samples from Riipiharju were prepared according to the acetolysis method (Faegri & Iversen 1975). The pollen diagrams (Figs. 8, 12, 15, 16) are constructed principally according to the model elab- orated by Berglund (Berglund 1966; Berglund & Lagerlund 1981 ; Berglund & Ralska-Jasiewiczowa 1986).

The treatment for diatom analyses follows the method described by Miller (1964). The diatoms were mounted in Naphrax with refractive index = 1.73. The diatom diagrams (Figs. 9,13) include the succession of the main diatom taxa. Life-form and pH spectra are shown in Figs. 10 and 14. The life- form groups are:

Kettle holes as stratigraphical archives 445

formed, themajority of whichdemonstrate infinite ages (>40,000 I4C-years B.P.). Parts of these datings are listed in Table 1 (see also Lagerback 1988a: table 1). The organic-bearing sequences are all situated above glaciofluvial deposits or glacial till belonging to the northwesterly glacial system. The lithostratigraphical records of several of these sites indicate two different ice-free periods with glaciationin between. Sequenceswith two organic- bearing beds intercalated by a till bed are found at four localities (Nos. 1, 2, 4, 6 in Fig. 1). Three of these sites are documented by microfossil analyses and will be more thoroughly discussed below. Six different lithostratigraphical units (A-F) have been distinguished. We have used the same letters on beds that we correlate between the different sites.

benthic = bottom living benthic-epiphytic = attached to the bottom epiphytic = attached to aquatic plants epiphytic-planktic = facultative pelagic or attached benthic-planktic = floating near the bottom planktic = floating, pelagic

The pH groups arranged according to Hustedt (1939) are: alkaliphilous (>7), indifferent (-7), acidophilous (S7) and acidobiontic (<7, optimum at 5.5 or lower).

Lithostratigraphy, biostratigraphy and radiocarbon datings from the kettle holes Since the start of the boring programme in 1982, some 70 sites have been explored, most of them kettle holes connected with glaciofluvial formations. Up to now, organic matter, radiocarbon- dated as significantly older than the Holocene, has been encountered at some 25 localities (Fig. 1). More than 100 radiocarbon datings have been per-

RIIPIHARJU (Site 1 in Fig. 1)

Thesite (67"35'N,22"49'E,270 mabovesealevel), located about 20 km NNE of Junosuando, is a circular kettle hole some 40 m in diameter. It is situated immediately to the west of the sharp ridge of the Riipiharju esker. The esker is about 8 km long; it is very pronounced, but in some parts cut by later glaciofluvial erosion. The highest parts of the esker are barely covered by till and there are no significant signs of glacial erosion. The lower and more level parts of the esker have a thin till cover, 0.5- 1 m thick, and with indications of division into two different beds.

The kettle hole was bored during winter 1985, and a few pits were excavated nearby in autumn the same year. Two parallel borings, close to each other, revealed the following stratigraphical sequence in the centre of the kettle hole:

Unit A1 0-3.0111 A2 3.0-3.8m

B 3 . 8 - c . 5 m

C c .5 -11 .7m

D 11.7-12.2111

E 12.2-12.3m F 12.3->13.0m

Peat (Holocene). Silt and gyttja, laminated. The organic content decreases down- wards. Diamicton (deformation till) composed of reworked sandy sediments with a low content of coarser clasts. Successively better sorted down- wards. Sand, laminated and organic- bearing. The organic content is fairly high throughout the bed. The macroscopic moss remains were extremely well preserved. Sandy till, impregnated by humic matter. Silty gyttja, with moss fragments. Sand and gravel, weU sorted and with fresh mineral grains.

446 Robert Lagerback and Ann-Marie Robertson BOREAS 17 (1988)

Table 1. Radiocarbon datings from localities mentioned in the text. The datings were made at the Laboratory for Isotope Geology, Stockholm and the Isotope Physics Laboratory in Groningen.

Site/material (unit 14C age B.P. Dating no. in parentheses) Depth (m) d13c9bo corrected for "C Remarks

St 10073 St 10074 St 10075 St 10076 St 10077 St 10078 St 10079 St 10080

St loo90

St 10094

St 10091 St 10092 St 10093 St 10098 St 10099

St 10100

St 10101 St 10095 St 10096 St 10097 St 8931 St 8932

St 9164 St 9165

St 9157 St 8684 St 8685 St 8639

St 8640

St 9158 St 9159 St 9160

St 9162 St 9161

St 8678 St 8679

Riipiharju

peat layers in sand (C) humus in sand (C) gyttja layers in sand (C) moss remains in sand (C) gyttja layers in sand (C) silty-sandy gyttja (C) humus in sand (C)

Onttoharjut humus and plant remains in sand (C) humus and plant remains in sand (C) piant remains (C) plant remains (C) plant remains (C) plant remains (C) plant remains (C)

plant remains (C)

plant remains (C) plant remains (C) peat (reworked) (D)

peat (All

peat (E) peat (E) peat (E)

peat (E) peat (El

Onttouaara

Takanenmiinnikko A humus in sand (C) humus in sand (C) peat (reworked) (D) peat (E)

peat (El

peat (El peat (E)

humus in silt and sand (E)

silty gyttja (E) silty gyttja (E)

Hiruijarui peat (reworked in till) (D) peaty gyttja (E) peat (reworked in till) (D) GrN-11963

GrN-11964 peat (E)

3.0 6.1-6.6 6.6-7.1 7.3-7.5 8.3-8.6 10.2-10.6 11.0-11.2 11.5-11.7

1.8

1.8

1.8 1.8 1.8 4.0 4.0

4.0

4.0 4.2 5.0 5.5 5.8 5.8

1.9 2.4

3.s3.5 3.4-3.9 4.7-4.9 6.0-6.4

6.04.4

6.14.2 6.2-6.4 6 .466 6.64.8 6.8-7.0

3.9 4.7 4.2 4.6

-26.6 f 0.5 -28.0 f 0.5 -27.6 f 0.5 -28.9 f 0.5 -26.4 f 0.5 -20.4 f 0.5 -27.6 f 0.5 -29.0 f 0.5

4,130 f 200 46,595 f 860 39,570 f 13,300 37,500 f 1,800 45 ,000 31,415 * 4,750 45,000 30.230 f 1,120

-25.9 zk 0.5 30,620 f 1,OOO

-25.3 f 0.5 32,505 f 1,280

38,090 t 2,925 33,885 f 5,480 33,630 f 1,400 37,850 f 9,000 28,160 f 2,160

-26.8 * 0.5 -26.9 f 0.5 -25.9 f 0.5 -26.5 f 0.5 -25.4 t 0.5

-24.0 f 0.5 38,700 f 6,700

-25.0 f 0.5 >45,000 -25.9 f 0.5 -26.5 f 0.5 >45,000 -25.4 f 0.5 -25.6 f 0.5 >50,000 -24.1 f 0.5 >50,000

36,290 f 8,495

36,065 f 2,165

-29.5 * 0.5 >50,000 -30.1 f 0.5 >50,000

-24.8 f 0.5 -25.0 f 0.5

38,600 f 6,700 36,370 f 4,590

33,900 f 1,750 - >45,000

-30.8 f 0.5

-30.1 f 0.5 >45,000

-26.3 f 0.5 -28.5 f 0.5 -29.4 t 0.5 >50,000 -25.0 f 0.5 >40,000 -14.8 f 0.5

40,600 f 3,250 45,200 f 4,400

32,550 2 2,700

-29.2 2 0.5 >45,000 -28.7 f 0.5 >45,000

>60,000 >64,ooo

Bulk sample Bulk sample Bulk sample, very low organic content Bulk sample, very low organic content Bulk sample, verL low organic content Bulk sample, very low organic content Bulk sample, very low organic content Bulk sample, very low organic content

Bulk sample

Bulk sample

>I mm fraction 0.5-1.0 mm fraction 0.25-0.5 mm fraction Bulk sample >0.5 mm soluble fraction

>0.5 mm insoluble fraction

Bulk sample Bulk sample Bulk sample Bulk sample Bulk sample Bulk sample

(warm NaOH)

(warm NaOH)

Bulk sample Bulk sample

Bulk sample Bulk sample Bulk sample Insoluble fraction (warm

NaOH) Soluble fraction (warm

NaOH) Bulk sample Bulk sample Bulk sample Bulk sample Bulk sample

Bulk sample Bulk sample


Pollen stratigraphy and vegetational lower than in the preceding zone. Spores of Lyco- development podiaceae have a small maximum. Pediastrum was

observed in most of the samples. Thirty-two samples have been analysed for their During the deposition of the sediments above content Of pollen and 'pores. Seven pollen blage

the till a continental climate prevailed. This is implied by the predominance ofArtemhi0 together have been distinguished (Fig.

8). with Chenopodiaceae. Among the Artemisia pollen two different types were observed: an 'arctical- type, including A. norvegica with prolate coarse sculptured pollen grains (cf. Liivrand 1969, 1971, 1987), and a smaller, spherical, smoother grain

Arctic-alpine tundra species such as saxifraga nana-type and (dwarf oppositifolia, Caryophyllaceae (Cerastium-type)

and R ~ ~ ~ ~ - o ~ ~ ~ ~ ~ has no modern analogue (Berglund 1966). The mixture of highly divergent ecological plant communities suggests a 'no-ana-

Unit E Artemisia-Ericales PAZ: 12.3 m.

20% pollen of Betula and Pinus. Shrubs include The lowermost spectrum (silty gyttja) contains type. The Occurrence of steppe plants parallel to

shrubs) reach 9%. Among herbs, which are represented with 55% 7 Artemisia, Gramineae, Cyper- aceae, C a r ~ o ~ h ~ l l a c e a e and Rumex-Ox~ria are

logue' environment (Birks 1986). The summers the most frequent. may have been as warm as 10-15"C, but the winters

Unit D very cold (down to -25'C) in NW Europe during Redeposited (Artemisia-Ericales-Betula nana- the Early and Middle Weichselian interstadials type) PAZ: 12.15-11.65 m. (Kolstrup & Wijmstra 1977; Kolstrup 1979,1980).

In the till layer the Pollen flora is redeposited Strong windsandlow precipitation resultedin arid, and derives from the underlying silty gyttja. The open landscapes, where cryoturbation created composition of the Pollen spectra is the Same as in fresh unstable soils. Later the climate changed and the previous PAZ. Only Pollen of Betula nana-type more favourable conditions allowed birch to reaches higher values. Among spores, PO~YPO- immigrate. The very low frequencies of Pinus pol- diaceae and Spagnum were noted. len suggest a great distance to pine forests, prob-

The pollen flora in the lowermost part of the ably Over 800 km (cf. Hicks 1977). sequence at 12.30-11.65 m indicates an Arctic- Subarctic treeless vegetation composed of dwarf Unit B birch, erkaceous shrubs and herbs, which include Redeposited (Betula-NAP) PAZ: 5.40, 4.50 and Artemisia, grasses, sedges, Caryophyllaceae and 3.85 m. Rumex-Oxyria. The silty gYttja was deposited In the disturbed (tectonized) upper part of the most probably during the end of an interstadid. sediments the pollen spectra show the same com-

position as in the PAZ below. Some redeposition Unit C may have occurred. Due to the low pollen fre- Artemisia-NAP-Salix PAZ: 11.35-8.05 m quencies and basic sums (about 100 pollen) only a

There is a very marked change in the pollen flora few herb taxa were noted. at 11.35 m. Pollen of Betula spp., bothpubescens- and nana-type and dwarf shrubs (Ericales) UnitA2 decrease. Herbs increase, mainly pollen of Arte- misia, which is present with 20-49%, except at 9.65 m. Chenopodiaceae, Caryophyllaceae, Rumex-Oxyria and Thalictrum occur with their highest values in this zone.

Betula-NAP PAZ: 7.85-5.50 m.

increases and together constitutes over 50% of the total pollen flora. Artemisia and other herbs decrease somewhat. Gramineae and Cyperaceae still reach high frequencies but generally somewhat

Betula-NAP PAZ: 3.75-3.05 m. This zone is dominated by Betula pollen (pub-

escens- andnana-type). Ericalesoccurs with2-3%. Pollen of herbs reaches moderate values but decreases upwards. Polypodiaceae and Lycopo- diaceae spores were observed.

PollenofBetulaspp. @ubescens- andnana-type) Unit A1 Betula-Pinus-Alnus PAZ: 3.00-2.95 m.

Pollen of Pinus increases markedly. Alnus pollen was registered with a few per cent. Shrubs and herbs together do not exceed 10%. The lowermost


Fig. 8. Pollen diagram from Riipiharju. See Fig. 11 for stratigraphical symbols.

,TRATIGRAPHICAL UNIT

ITHOSTR ATIGRAPHY

IADIOCARBON AGES B.P.

k p t h (m)

'etracyclus lacustris

:yctotella kutzingiana + v. radiosa

delosira I M. distans v. alplgena

M. lirata

iustulia rhomboides + varr.

iagihr ia I F. construens. pinnata.

brevistriata F. virescens

rabelhria fbcculosa+fenestral

khnanthes I A. kryophila EBZ A. austriaca.

rnarginulata + spp.

Navicub spp. (sect. minuscube)

Cymbelh

I c. spp.

C. cesatii

Neidium SOD.

Stauroneis I S. anceps

EBZ s. spp.

Pinnularia spp. (subcapitata, interrupta etc.)

Eunotia spp. (pectinalis, faba, robusta. diadema, tenelh etc.)

Cabneis SDD.

Nitzschia spp.

Gomphonerna spp.

E D = basic sum

DIATOM ZONE


partofthepeatat3.0 mwasdated4,130 f 200 B.P. which represents the beginning of the Subatlantic period.

During the first part of the Holocene, when sedimentation of silt and gyttja took place, the vegetation was dominated by birch, but later pine and alder spread. Probably there is a hiatus between the gyttja and peat at about 3.00m, according to the result of the I4C dating.

Diatom flora and sedimentation environment

Thirty-one samples between 12.40 and 3.10 m depth were analysed. At 20 of the levels only a few diatoms or fragments were observed. The results of 11 analysed samples are shown in Figs. 9 and 10. Six different diatom zones can be distinguished. Only freshwater diatoms are present.

Unit E Diatom zone 1: Melosira-Pinnularia spp. (12.30 m).

The zone is represented by only one spectrum, in which the planktic-benthicspecies Melosia lirata predominates with 52% of the total flora. Genera occurring frequently are Pinnularia and Eunotia. Melosira lirata indicates deposition of the lowermost silty gyttja (Zone 1) in an oligotrophic- dystrophic lake (Cleve-Euler 1951; Molder & Tynni 1967). The water was acid with a pH about 5.0, calculated according to Renberg’s formula (Renberg & Hellberg 1982). The genera Pinnu- laria, Eunotia, Neidium, Tetracyclus and Frustulia are represented by acidophilous taxa (Molder & Tynni 1969-1972; Tynni 1976; Cholnoky 1968). The dystrophic taxa are Tetracyclus lacustris and Frustulia rhomboides.

Unit C Diatom zone 2: Cyclotella kutzingiana-Melosira spp. (11.65 m).

The planktic Cyclotella kutzingiana and v. radiosa reach 29% in the spectrum at 11.65m. Melosia lirata and M. distans v. alpigena are together represented with47%. Inzone2 the water depth was greater than in zone 1, as the planktic taxa Cyclotella kutzingiana occurs frequently (29%). Melosira spp. together reach 47%. The pH was about 5, implied by the presence of inter alia Anomoeoneis serians v. brachysira and Frustulia rhomboides v. saxonica.

Diatom zone 3: Low frequencies, mostly fragments (11.55-8.05 m).

This zone is characterized by very few diatoms or fragments, which can be explained by a high sedimentation rate, unfavourable conditions for diatoms or dissolution of the frustules.

Diatom zone 4: Fragilaria spp. -Achnanthes spp. - Melosira distans v. alpigena (7.65-6.35 m).

Fragilaria spp. reach 35%, being represented by the alkaliphilous taxa F. construens, F. pinnata and F. brevistriata. Achnanthes spp., with values around 15%, include the acidophilous taxa A. kryophila, A . austriaca and A. linearis. At the different levels Pinnularia spp., Nauicula spp. (section minusculae), Eunotia spp. and Cymbella spp. reach about 5% each.

The sediments representing zone 4 were deposited in a littoral environment as the epiphytic genera Fragilaria, Achnanthes, Cymbella, and the benthic Pinnularia, Navicula and Stauroneis increase. Melosiraisstillpresentwith 17-27%. The pH of the water was 6.0-6.5, reflected by several alkaliphilous and indifferent taxa (Fig. 10). The rising pH value coincides with rising temperatures and the optimum of the interstadial. Dissolution of mineral salts in the soils surrounding the basin probably contributed to the rising pH of the water.

Zone 5: Achnanthes spp. - Cymbella spp. (6.00- 3.85 m).

Achnanthes kryophila is most common and reaches 20% at 5.65 m. Cymbella is represented by C. cesatii, C. latens and C. amphicephala. C. cesatii is very frequent, and constitutes 37% at 3.85 m. Pinnularia includes above all P. stauroptera, P. subcapitata, P. tenuis and P. borealis. Nitzschia spp. has its maximum in this zone, represented by the section lanceolatae.

The basin was filled in and the water depth decreased in Zone 5. Benthic and epiphytic taxa constitute over 80% of the flora. The predominant genera were the epiphytic Cymbella and Achnanthes. The sedimentation environment and its changes, however, can only be superficially interpreted according to results from a single sampling point in a lake. Uneven distribution and dissolution of frustules have been demonstrated to influence the fossil diatom flora in some lakes (Merillinen 1971).

Zone 6a: very few diatoms (3.8C3.35 m).

were observed. At 3.80-3.35 m very few diatoms or fragments

BOREAS 17 (1988) Kettle holes as stratigraphical archives

RllPlHARJU

50% t

pH - SPECTRA

451

1

117

141

90 80

I -

-~ ,~ - 200 - A A fig. 10. Diatom life-forms and E l ;E;-:, pH-spectra at Riipiharju A-M ROBERTSSON

Zone 6b: Pinnularia spp. - Stauroneis anceps - Eunotia spp. (3.25-3.10 m).

Zone 6b is dominated by Stauroneis anceps and Pinnularia spp. at 3.25m, and Pinnularia spp. together with Eunotia spp. at 3.10 m. In the laminated ‘Late-glacial’ silt, very few diatoms were registered. At 3.25 m diatoms occur rather frequently and the flora is represented by the benthic Pinnularia and Stauroneis anceps, together 71 % . In the uppermost Holocene spectrum at 3.10m Pinnularia still dominates but Eunotiu replaces Stauroneis. The pH of the water is calculated to have been about 5.6. Acid conditions prevailed at the beginning of the Holocene after the deglaciation (cf. Miller 1971).

Seven samples from different levels in the pre- Holocene interstadial sediments were radiocarbon dated and yielded infinite as well as finite ages (Fig. 8, Table 1).

ONTTOHARJUT (Site 2 in Fig. 1)

This site (67”12’N, 22”25’E, 195m above sea level), situated 10 km WNW of Tarendo, is a kettle hole, some 2&30 m across, located immediately NE of the very pronounced ridge of the Ontto- harjut esker (Figs. 6 and 7). The esker can be followed as a more or less continuous ridge for about 10 km and further to the northwest there are two more ridges belonging to the same train.

The site was bored in winter 1983 and a trench was made by excavator in winter 1985. The records from these investigations are shown in Fig. 11. The section demonstrates two organic-bearing beds older than the Holocene with a till bed in between. Another till unit, weakly developed and composed mainly of reworked sand and gravel, covers the upper organic bearing bed. On the highest parts of the esker there is almost no till cover but a few

452 Robert Lagerback and Ann-Marie Robertsson

sw

BOREAS 17 (1988)

NE 20

10

0

c. 1

C z m

A1 A2 B C

D E F

-

Om 50

Stratigraphical symbols:

silt

I 1 Sand

Till

peat lenses

scattered angular boulders. The deepest section, situated at the centre of the kettle hole, shows the following stratigraphy:

Unit A1 0-0.5 m Peat (Holocene). A2 0.5-1.3m Silt

B 1.3 m Erosive contact. A slab-shaped granitic boulder situated directly on the contact.

C 1.3 - 4.5 m Sandy sediments, laminated and mixed with well preserved brown mosses and gyttja layers. The organic content increases towards the bottom. The unit is discordantly cut at the top.

D 4.5-c.5.2m Sandy till, composed of reworked sand and gravel and mixedwith peat.

E c. 5.2-6.2111 Peat, with silty layers in the upper parts. Slightly tectonized at the top. The yellowish brown peat was composed mainly of mosses, very well preserved, and contained specimens of beetles.

F 6.2- >7.2 m Gravel and sand, partially rusty.

0

Fig. 1 . Cross-section through the Onttoharjut site (cf. Figs. 6,7) based on records from borings and excavations. The esker belongs to the N W ice flow (Fig. I) and is stratigraphically covered by two till beds separated from each other, and the esker, by two interstadid organic beds. The sequence described in the text originates from point A. The dimensions of the esker ridge are approximate. Height scale is exaggerated 2X.

Pollen stratigraphy and vegetational development

Analyses were performed on 12 samples. The peat at 6.2-5.2 m was sampled in 1983 and the interval 5.0 to 0.7 m in 1985. All pollen spectra are presented in one diagram (Fig. 12). Four PAZ were distinguished.

Unit E (+ reworked in unit D) NAP-Betula-Ericales PAZ: 6.2-5.9 m (5.0- 4.8 m).

Betula pubescens-type is the only tree pollen present except Pinus, which reaches a mere 5%. Shrubs include Betula nana-type, Salk and a few pollen of Juniperus. Ericales occur with 7.5- 10.5%. Among herbs, pollen of Cyperaceae, Gra- mineae and Artemisia predominate.

The peat at 6.0 m was deposited during an interstadial. The flora was dominated by shrubs and herbs, and birch trees only occurred in scattered corpses. Ericaceous dwarf shrubs, together with graminids, sedges and other herbs, dominated. The distance to pine forests was probably great (Hicks 1977; Robertsson & Garcia Ambrosiani 1988) as the Pinus pollen frequencies are extremely low. In the tundra today Pinus pollen transported from far away constitutes up to 20-30% of the total pollen flora (Aano 1940; Srodon 1960; Ritchie & Federovich 1967; Birks 1973).

Unit C NAP-Salk PAZ: 4.2 m and 4.0 m.

Betula pubescens-type is present with only 5%. Herbs (80% of the total pollen flora) are represented by Cyperaceae, Gramineae, Artemisia, Caryophyllaceae, Rumex-Oxyria and Cruciferae. Shrubs are dominated by Salk, which reaches 13%


llNn lV3IHdVtlE)llVtllS C

Fig. 12. Pollen diagram from Onttoharjut. See Fig. 11 for stratigraphical symbols.

454 Robert Lagerback and Ann-Marie Robertson BOREAS 17 (1988)

at 4.2m - at the same level Pediastrum has a maximum.

Artemisia-Salk PAZ: 1.9 m and 1.8 m. Artemisia increases and reaches very high

frequencies. Gramineae and Cyperaceae together constitute 3040%. Chenopodiaceae was recorded with 2.5% at 1.9 m. Other herbs observed only in this zone are Saxifraga oppositifolia and Thalictrum. Salix is present with 10-15%. The aquatic Batrachium-type has its maximum (2.5% at 1.9 m) and occurs together with Alisma.

During the non-glacial interval, represented by sand and silt with varying organic content at 4.5- 1.3 m, thevegetationconsistedofa herbandshrub tundra. Periglacial phenomena occurred, probably including eolian processes. The high frequencies of pioneer plants such as Artemisia indicate open, unstable soils, but also a continental climate, as pollen of Chenopodiaceae is present. During the interstadial optimum, birch was the only tree growing in the area. The flora can partly be compared with the arctic vegetation prevailing today on Spitsbergen and Greenland (Iversen 1945; Srodon 1960; Fredskild 1967).

Unit A2 Betula-NAP PAZ: 1.2 and 1.0 m.

Betula pubescens-type increases markedly and comprises some 50% of the flora. Ericales appear and approach 5%. Among herbs, Gramineae, Cyperaceae and Artemisia are most frequent. Polygonum viviparum-type and Compositae Tubuliflorae were observed only in this zone. The silt in Unit A2 was probably deposited in an ice- dammedlakeexistinginconnection with the deglaciation of the area. The early Holocene pioneer flora is reflected in the pollen spectra.

Moss remains

Analyses of mosses in the peat layer at 5.2-6.2 m have been carried out by Lars Hedenas, who identified the following species: Calliergon trifarium (Web. & Mohr) Kindb., Drepanocladus exannulatuslfluitans, D . sendtneri (Schimp.) Warnst., D . trichophyllus (Warnst.) Podp., Scor- pidium scorpioides (Hedw.) Limpr., Calliergon sarmentosum (Wg.) Kindb.

The most interesting species is Drepanocladlcs trichophyllus, which occurs submerged in small bodies of water such as kettle holes and isolated meander lakes (Sw. korvsjtjar). The main distri-

bution of the species today is northernmost Soviet Union, Finland and Sweden, where it is found as far south as Narke and Dalsland. Calliergon sarmentosum grows on lake shores, at springs and mires, often in running water. The species is rare in southern Sweden and occurs mainly in mountain areas in Europe. Calliergon trifarium, Drepano- cladus sendmeri and Scorpidium scorpioides are found on rich fens and mires and have been reported from nearly all parts of Sweden.

Diatom flora and sedimentarv environment

Seven samples from sequence 1985:A have been analysed (Figs. 13,14). At 1.5 and 1.2 m, veryfew diatoms were found. The most common genera in these two samples were Achnanthes and Cymbella at 1.5 m, and Eunotia and Pinnularia at 1.3 m. Three diatom zones have been distinguished (Fig. 13).

Unit E (+ reworked in Unit D ) Diatom zone 1: Achnanthes spp. - Eunotia spp. (5.5 and 5.0 m) 3.5 m - sample sequence B.

Achnanthes spp. are most frequent, including above all A . linearb, A . nodosa and A . lapponica. Eunotia spp. reach 20%. Other taxa occurring frequently are Tabellariaflocculosa, T. fenestrata and Nitzschia spp. section lanceolatae (N. fonticola, N. frustulum and others). Diatoms only appearing in zone 1 are Anomoeoneis serians v. brachysira, Frustulia rhomboides v. saxonica and Tetracyclus lacustris. The end of the interstadial, represented by the till-covered silty peat, was characterized by the benthic-epiphytic genera Eunotia, and the epiphytic Achnanthes. The peat was formed in the littoral part of a small oligotrophicwater body. The composition of the pH-spectra shows an acid water with a pH of about 5.7.

Unit C Diatom zone 2: Navicula spp. - Cymbella spp. - Stauroneis spp. 2.5,2.2 (1.5 m).

Navicula spp. are represented with 25%, including acidophilous, indifferent and alkaliphilous taxa. Cymbella spp. are dominated by C. ven- tricosa, C. cuspidata and C. caespitosa, all three indifferent to pH. Stauroneis anceps is frequent (about 10%). Gomphonema has a small maximum, and Caloneis and Amphora were recorded exclusively in this zone. At 1.5 m only 11 diatoms were noted, but among them Achnanthes and Cymbella were most frequent.

During the younger interstadial the sand with

I

Q

m 1 0 1 w Z ISTRATIGRAPHICAL UNIT

- Y ,. w L

w e -0 0 m m 0 vlyl 0

.- 8.W

3 N m - yio .v N(D

0 ylo

N

RADIOCARBON AGE B.P. - S DEPTH (m) 0

? ? O v) o m

= u 7 I Frustulia rhomboides v. saxonica

Tetracyclus lacustris

I Anomoeoneis serians v. brachysira+A. exilis

Melosira spp.

Nitzschia spp. (sect. ianc.1

~ Achnanthes spp.

Tabeilaria flocculosa+fenestrata

Eunotia spp.

' I w -

I - - w Cymbella spp.

Stauroneis anceps + Stauroneis phoenicenteron

Navicula spp.

- - 'I I Fragilaria spp.

Neidium spp.

Cahneis

A I N o IDIATOM ZONE I

0 Z -I -I 0 I D D t -I

L

A

LD m L" ? W


iJUT

LIFE - FORMS

= Benthic Epiphyticlplankt.

.- E Benthiclepiphytic Benthiclplankt.

I I- =Epiphytic Planktic P w n

-

very few diatoms l1 ?.OJ

I

pH - SPECTRA

Indifferent

I '

2

10% 50%

Fig. 14. Diatom lie-forms and pH-spectra at Onttoharjut and Takanenmhnikko.

organic material was deposited in a shallow littoral environment. Benthic diatoms constitute about 55%, represented by the genera Nauicula, Stau- roneis and Pinnularia (Fig. 14). Epiphytic taxa include Cyrnbella, Achnanthes and Gornphonerna. The water was slightly acid with a pH of 6.4 according to Renberg's formula.

Unit A2 Diatom zone 3 : Pinnularia borealis- Eunotia spp. - Hantzschia arnphioxys (1.2) 0.7 m.

At 1.2m only 10 diatom frustules were

observed, Eunotia being the most frequent. The aerophilous, terrestrial taxa Pinnularia borealis and Hantzschia arnphioxys together comprise 41 % at 0.7 m. This suggests influx of terrestrial material and/or that the basin was temporarily dry.

Fourteen radiocarbon datings have been carried out on samples from six levels between depths of 1.8 and 5.8 m (Table 1). In the 1.8 m sample the plant remains were separated into three different fractions, each dated separately. Two datings of bulk samples from the same depth were also made. The ages range from c. 30,000 to >45,000 B.P.

BOREAS 17 (1988)

ONTTOVAARA (Site 3 in Fig. 1)

The site consists of a minor kettle hole located on the eastern slope of the narrow, steep Onttoharjut esker, some 2 km SE of the Onttoharjut Site (Fig. 7). The stratigraphy is from the top:

Unit A 0- 0.2m Peat (Holocene). B or D 0.2 - 1.4 m Diamicton (deformation till) composed

mainly of reworked sand and gravel. C or El 1.4- 1.7 m Sand, undisturbed.

E l 1.7-1.9m Silt. E2 1.9-2.4m Peat. F 2.4->4m Gravel.

Fig. 15. Pollen diagram from


I N

t -

z 3

a s 0 I a

P I- Q [r I- cn -

E l

-

E 2

Pollen pora and vegetational development

Six samples of the peat at 2.40-1.90 m have been analysed. Two PAZ can be distinguished (Fig. 15).

Unit E2 Betula-NAP PAZ: 2.40-2.20 m.

Betula pubescens-type comprises over 50% of the pollen flora. Betula nana-type is present with approximately 10%. Among herbs, Gramineae and Cyperaceae are the most frequent. Ericales only reach about 2%.

Unit E2 and E l (1.80 m) NAP-Betula-Ericales PAZ: 2.10-1 .SO m.

Betula spp. decrease and shrubs are represented by Juniperus and Salk. Among herbs, Cyperaceae is the most frequent and reaches 16% at 1.8 m.

The pollen flora reflects the vegetational development during the later part of aninterstadial. The vegetation consisted of birch mixed with shrubs such as Betula nana and Juniperus, The herb pollen vegetation reflects wet areas covered by Cypera- ceae as well as heath vegetation with Encales and graminids.

The diatom flora was checked in one sample at 1.9 m depth. The dominant genera are Fragilaria (including the taxa F. construens and F. virescens), Pinnularia (15 %) and Melosira (12%). Pinnularia is primarily represented by P. interrupta and P. nodosa, and Melosira by M. distans v. alpigena and M. ambigua. The composition of the diatom flora is in accordance with that observed at Riipiharju and at Takanenmannikko. Two genera represented by several taxa are Navicula and Cymbella. According to the pH requirements of the different components, the indifferent and acidophilous groups together constitute about 75%. The only alkaliphilous taxa observed are Amphora avalis v. pediculus and Fragilaria construens. The acidophilous to acidobiontic diatoms present are Frustulia rhomboides v. saxonica, Anomoeoneis serians v. modesta and Tetracyclus lacustris. The

50 001

' 50 001

TOTAL POLLEN FLORA

0 TREES HERBS

0 Betula Artemisia

3 m

5

Yr gg

v) v)

z a

NAP

Betula

Ericales

-

-

Betula

NAP -

__ 'HI 198


Elc. 6.0- 6.2 m Siltandsand,laminatedandintercalated

E2 6.2-6.6m Peat. E3 6.6- 7.2 m Siltandsand,laminatedandintercalated

F 7.2- >8.6 m Sand and gravel, rusty.

by layers of organic matter.

by thin layers of organic matter.

abundance of Fragilaria construens in both the Onttovaara sequence and the other three sites is somewhat puzzling. F. construens is an alkaliphilous taxon usually occumng in eutrophic lakes. It often has a maximum at the isolation of basins from the sea and has been reported in 'late-glacial' sediments of Eemian, Early Weichselian and Late- Weichselian age (Miller 1971; Marciniak 1973; Florin 1977; Marciniak 8~ Kowalski 1978; Roberts- son 1973, 1986). The taxon, however, may be F. pseudoconstruens, registered in association with acidophilous diatoms such as Melosira lirata and M. distans (Marciniak 1982).

Radiocarbon datings of two peat samples at 1.9 and 2.4 m depth gave >50,000 B.P. (Table 1).

TAKANENMANNIKKO (Site 4 in Fig. 1)

This site (67"07'N, 22"18'E, 200m above sea level), located 15 km WSW of Tarendo, is a kettle hole associated with a20 km long, morphologically well-defined esker running NNW-SSE. The esker most probably belongs to a train of glaciofluvial deposits which can be followed some 100 km from north of Overkalix, along the Kalix river for some 40 km and further northwestwards to the hummocky moraine region NW of Tarendo (Fig. 1).

The circular kettle hole, measuring 3 0 4 0 m across, is situated immediately NE of the main esker ridge. The site was not visited during the summer season, but a low altitude flight over the locality revealed scattered erratics indicating a sheet of till covering the glaciofluvial deposits. In the early winter of 1982 borings were made at three points, two of which (A, B) were sampled for microfossil analyses and radiocarbon dating. The results of pollen analyses and radiocarbon datings are shown in Fig. 16 and Table 1. The stratigraphical record, based on sampling from seven boreholes situated very close to each other, demonstrates the following units at point A.

Unit A1 0- 1.0m B 1.0-c .2m

C c .2 -4 .4m

D 4.4-c.6.0m

Peat and gyttja (Holocene). Diamicton (deformation till), composed of reworked sandy sedimentsmixed with a low content of coarser clasts including boulders. Gradually changing into undisturbed sediments. Sandy sediments, laminated and mixed with organic matter. The organic content vanes from single moss fragments to fairly thick layers of peat or gyttja. Sandy till, to a high degree mixed with peat, especially in the lowest part where it grades into laminated silt and peat.

Pollen stratigraphy and vegetational development The results are presented as total pollen spectra in Fig. 16.

Unit E3 ArternisiaPAZ(A-6.85m, B-6.40111).

Artemisia is represented by values over 20%. Other herbs occurring frequently are Cyperaceae about 20%, Chenopodiaceae, Caryophyllaceae and Rumex, each around2% in both samples. Salk is present with 5 1 0 % .

NAP P A 2 (B - 6.05 and 5.65 m). Herbs dominate the total pollen spectra; Arte-

rnisia decreases but still reaches over 10%. Cyper- aceae was recorded with approximately 30%.

The Artemisia and NAP zones reflect the initial part of an interstadial. The flora included arctic- alpine plant communities and willow shrubs.

Unit E2 + El Betuia-NAP PAZ (A: 6.7-6.0 m, B: 5.25 m).

Betula pubescens-type is most frequent, represented with 4040%. Betula nana-type reaches 25- 30% in sample sequence A. Juniperus and Salk are present. This zone represents the cool interstadial optimum, during which tree birches and dwarf birch spread in the area.

Unit D Redeposited P A 2 (A: 5.9-5.1 m).

The pollen flora is reworked from the underlying sediments and peat (Unit E). The pollen spectrum at 5.6-5.7 m possibly reflects the end of the inter- stadia], when willows and herbs dominated the vegetation. Artemisia reaches over 20%, Cheno- podiaceae 3% and Caryophyllaceae 2%.

Unit C Gramineae-Artemisia PAZ (A: 4.15 and 3.25 m).

Pollen of herbs constitutes some 70% of the total flora, Gramineae and Artemkia together reach 4550%. Betula nana-type and Betula pubescens- type are both present with 1615% each.

The zone represents the initial phase of the

BOREAS 17 (1988)

TAKANENMANNIKKO A


Fig. 16. Diagram showing the total pollen spectra at Takanenmannikko See Fig. 11 for stratigraphical symbols.

- : 2 W

z

U 0

Q

a:

a Q a

38 600 f6700

36 370 i4590

40 600 f3250 45 200 f4400

>50 000

>40 000

32 550 f2700

-

- E - I I-

W n n -

1.0

1.0

5.0 ma

j.0

7.c

TAKANE N MAN NIK I

TOTAL POLLEN SPECTRA 1 TREES I....I SHRUBS W

0 Pinus HERBS

0 Betula = Artemisia z DWARF SHRUBS ! 2

10% 50% ! Graminsa

Artemisi i

-

0 ::. E E L 0::: A r f e m i s

Analyses: R.

> I a a: I-

I- cn

a 5? a a

s 8 I 0 -

E A R L Y

W E I C H S E L I A N

~

E A R L Y

W E I

C H S E L I A N

thi 198

younger interstadial. The vegetation was an arctic polar steppe with grasses and Artemisia. The climate was probably continental.

diatoms, sequence B - 6.05 m and A - 4.15 and 3.25 m (Figs. 13,14).

At 6.05 minsarnplesequenceB thefloraisdomi- nated by the genera Fragilaria, reaching 61% and represented by F. comtruens or F. pseudoconstruens (?). Other genera occurring with high fre- Diatoms and sedimentary environment

Three samples were checked for their content of quencies are Navicula, Pinnularia, Cymbella


15-

lo: 5

(together about 28%) including taxa preferably indifferent to pH. The acidophilous Melosira lirata and M. distans v. alpigena constitute 4% of the flora. The pH spectrum shows 70% alkaliphilous taxa, of which Fragilaria construens constitutes 66%.

The two uppermost diatom spectra from sequence A show great resemblances in composition. Navicula spp. predominate at both levels (25-30%), represented by N. subbacillum, N, spp. (section minusculae) andothertaxa. Euno- tia, Tabellaria, Pinnularia and Fragilaria occur frequently, 5-10%. At 4.15 m, Melosira distans and var. alpigena are present with 18%, in the upper spectra replaced by Achnanthes spp. and Cymbella spp. The life-form spectra consist of 50 and 75% benthic taxa (Fig. 14). According to the pH requirements of the diatoms recorded the water was acid.

A: 6.6 - 6.7 m r P = 100 :

Size measurements of Betula pollen Among the birch pollen, a Betulapubescens (alba)- type and a B. nana-type have been separated at the pollen analyses. As Betula was the only tree species growing in the area, it is of importance to elucidate the changing ratio of tree birches to dwarf birch.

Size measurements of the Betula pollen can be used to indicate the presence of birch trees and dwarf birch. However, the type of deposit and chemical treatment can influence the size of the fossil pollen grains (cf. Robertsson 1973). In the sequencessampled at Takanenmannikko A and B, four levels have been studied (Fig. 17). The size interval at the measurements was 1 pm from 17 pm to 30 pm. The size of fossil Betula nana grains in gyttja sediments is 16-26 pm and B. pubescens 23- 31 pm according to Florin (1969). In interglacial and interstadial peat and gyttja, Andersen obtained 23-25 pm and 27-29 pm as mean sizes for B. nana and B. pubescens, respectively (Andersen 1961).

A distinct change in the size distribution can be observed at the different levels analysed at Tak- anenmannikko (Fig. 17). In the lowermost part of sequence A at 6.7-6.6 m and 6.4-6.5 m, both B. nana and B. pubescens occur as there are two max- ima (around 20 pm and 25 pm). The sample from sequence B at 5.2m shows a maximum at 24- 27 pm, and high frequencies of grains 27-30 pm indicating the presence of both B. pubescens and B. tortuosa. In the uppermost sample, at 4 . S

TAKA N E N MAN N I KKO

1 * 18 20 22 24 i6 i8 jOpm

no A: 6.4 - 6.5 m

I P = 100

18 20 22 24 26 28 30pm


3.9 m, Betula nana-type dominates, as indicated by a maximum at 18-19 pm.

The results of the size measurements confirm the identification separation of a Betula nana-type by means of morphological features, e.g. circular pollen grains with small, less protruding pores.

Korpela (1969) concluded on the basis of size measurements that Betula nana, B. pubescens, B. uerrucosa and B. tortuosa were present during the Perapohjola Interstadial in N Finland.

Ten radiocarbon datings were performed, the ages ranging from c. 32,000 B.P. to >45,000 B.P. (Table 1).

Summary of kettle-hole stratigraphy, inferred development The sequences at Takanenmannikko, Onttoharjut and Riipiharju appear to be more or less identical

as regards both litho- and biostratigraphy. The main difference is that unit A2, silty deglaciation sediments, found at Riipiharju and Onttoharjut is missing at Takanenmannikko. The stratigraphical units, A-F, are thought to correspond to each other at the investigated localities described.

The following interpretation in terms of glacial and non-glacial development can be made. The litho- and biostratigraphical results are summa- rized in Fig. 18.

Unit F The sand and gravel represent the esker material. The rusty colour is due to the presence of oxy- genous water in the permeable gravel, and shows that the bore has penetrated the reducing environment of the organic bearing sediments within the kettle hole. The deposit was formed during the deglaciation of an Early Weichselian ice sheet with

:NVI-I LITHO - AND BIOSTRATIGRAPHY I c H R o N o s T R A T I G R A P H Y NORRBOT

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Fig. 18. Glacial and interstadial development during the Weichselianin northeastern Norrbotten, and tentative chronostratigraphical correlations with adjacent areas. The chronostratigraphy in northern Finland according to Hirvas ef al. (1981) and Hirvas & Nenonen (1987), central Sweden according to J. Lundqvist & Mook (1981), J. Lundqvist (1983) and Robertson (1988), in NW Germany according to Behre & Lade (1986). The range of the pollen samples analysed is marked for each site in the columns to the left of the PAZ.


ice movements from NW. This unit is correlated with the N W drumlins and striations.

Unit E 1-3 The water-laid sediments and peat were formed during aninterstadial. The amount of organic matter and the formation of peat suggest a fairly long period with stable conditions favourable for plant growth. The comparatively low content of minerogenic matter indicates a closed vegetational cover except perhaps for the beginning and end of the period.

Subunit E3 Initialpre-ternperate phase characterized by tundra covered with a rich herb flora including different plant communities such as arctic-alpine/pioneer plants, steppeelements, grasses, sedgesandwillow shrubs. This phase is represented at Takanen- mannikko B (6.45-5.65 m) by the Artemisia and NAP PAZ (Fig. 16). Silt and sand with organic material was deposited.

Subunit E2 Cool temperate optimum during which birches spread, first dwarf birch (Betula nana) and later tree birches (B. pubescens coll.). Birch was the only tree growingin the area, formingan open park tundra. The very low frequencies of Pinus pollen (below 3%) indicate that the distances to pine forest must have been large. Alternatively, prevailing winds were constantly northerly. Some admixture of junipers occurred, indicating open light vegetation. Many light-demanding pioneer plants imply the presence of fresh unstable soils. Peat was formed during this phase at Takanenmtinnikko, Onttovaara and Onttoharjut. The Betula-NAP PAZ at Onttovaara and Takanenmannikko reflects this phase.

Subunit El Post-temperate phase when tree birches were replaced by dwarf birch and ericaceous shrubs (Ericales). Herbs such as Artemisia, Gramineae, Cyperaceae, Rumex-Oxyria and Caryophyllaceae were important components of the flora. This phase is identified at Onttoharjut, Onttovaara and Riipiharju, where peat with silty layers or silty gyttja with moss fragments was formed. Pollen spectra representing this phase also occur re-

worked in the till bed rich in humus superimposing the peat at Onttoharjut and Riipiharju (Figs. 8, 15). The sedimentation took place in acid water with a pH of 5-6 according to the diatom floras.

Unit D The till was deposited by an ice sheet overrunning the area. The till bed is rather thin, thus the ice cannot have been heavily loaded with debris. The ice tectonized and incorporated the upper parts of the organic bed but did not alter the morphology of the eskers to any significant degree. There is no obvious correlation to any regional system of ice movement, but a westerly to west-northwesterly movement is inferred from till fabric analyses and scattered observations of striations. Reworked pollen and diatoms from unit E occur in the till.

Unit C The organic bearing laminated sandy sediments represent a second ice-free period. Judging from the pollen spectra, the climate was more continental than in the former ice-free period represented by unit E. The great accumulation of sandy sediments indicates a sparsely vegetated landscape with barren soils. The sand is perhaps partly of eolian origin (cf. Lagerback 1988b). Cryotur- bation and eolian activities occurred frequently. Acid or slightly acid waters prevailed according to the composition of the diatom flora.

The vegetational development during the inter- stadia1 can be outlined as follows:

Pre-temperate phase represented at Riipiharju, Onttoharjut and Takanenmannikko by Arte- misia-NAP-Salk, NAP-Salk and Gramineae- Artemisia PAZ respectively. The pollen flora reflects severe Arctic conditions with a vegetational cover consisting of dwarf shrubs (willows) and herbs. Even Betula nana was probably sparse, due to its sensitivity to strong winds and frost. The predominance of Artemisia (possibly including both tundra and steppe species) points to a continental climate. Cool temperate optimum-represented at Riipi- harju by the Betula-NAP PAZ (7.85-5.50 m). Dwarf birch and tree birches predominated. A small admixture of ericaceous shrubs, willows and junipers occurred. A tendency towards a climatic deterioration is mirrored in the undisturbed upper part of the sandy silty sediments


at 6.0-5.75 m. The Betula pubescens-type decreases and NAP (Gramineae, Cyperaceae) increases. The post-temperate phase is represented at Onttoharjut by the Artemisia-Salix PAZ. The birches disappeared (B. pubescens and B. nana) and were replaced by willows and herbs, including Artemisia, Caryophyllaceae, Gramineae and Cyperaceae.

Unit B The deformation of the upper sediments and the till-like character of this unit reflect the influence of a sluggish glaciation lasting for at least 30 to 40 millennia according to the radiocarbon age of unit C. The unit is correlated to the southerly to southwesterly ice flow represented by fluting and small drumlins in the east (Fig. l) , but older deposits escaped significant erosion in most of the area. The pollen flora is rebedded from unit C.

Unit A The laminated silt (Subunit A2) at Riipiharju and Onttoharjut was deposited in connection with the last deglaciation. Early Holocene immigration of plants is reflected (herbs, shrubs and birch). Acid waters prevailed according to the diatom flora. Peat (Al) was deposited when the area had become forested.

northwesterly during the main stage to a southwesterly at the deglaciation. The ice divide becomes still less perceptible compared with deductions from previous observations according to Fromm (1965:127, fig. 69).

By means of air-photo interpretation, Hoppe (1967) mapped the morphological tracks of the two main ice-flow generations of the area, i.e. the dominant system of drumlins and eskers from the northwest and the younger southerly drumlinization concentrated to a rather narrow zone west of Korpilombolo and Pajala (Fig. 1). Like Fromm (1965), Hoppe assigns the two systems to the latest glaciation, preferably the period of deglaciation, and suggests that the youngest ice flow, from S to SW, was successively developed in the course of deglaciation as the result of a recession of the ice front southwards from the area west of Pajala.

Comprehensive investigations crucial for the understanding of glacial development in the region have been carried out in northern Finland. A gen- eral outline of the Quaternary geology and the deglaciation of western Finnish Lapland was given by Kujansuu (1967). The discovery and description of the till-covered interstadial deposits in the Perapohjola region (Korpela 1969) was of the utmost importance for the interpretation of the local stratigraphy and glacial development. Two regional systems of ice movement (NW and W), separated by an ice-free period, were dif- ferentiated. The investigations by Korpela were followed by a comprehensive stratigraphical in- ventory programme in Finnish Lapland executed by Hirvas and co-workers, leading to a still more complex picture of the till stratigraphy and a model of the glacial development for not only the Weich- selian but also previous glaciations (Hirvas et af. 1976, 1977, 1981,.

Glacial and interstadial development in northeastern Norrbotten, correlations Previous investigations and interpretations

According to classical opinion, the investigation area is situated just south of a west-easterly oriented ice-divide zone during the last glaciation (e.g. G. Lundqvist (1961), J. Lundqvist (1974)). This ice-divide zone was inferred from the fact that to the north thereof the observed striations run mainly northeasterly while to the south the majority of the striations reflect an ice movement towards the southeast. In other words, the two directions of ice movement appeared to diverge from the zone more or less perpendicular to each other.

Fromm (1965) arrived at amore complex picture of glacial development in the area and suggested a shift of ice flow during the last glaciation from a

Fagerlind (1981), with support from the Finnish investigations, suggested that the two main systems of glacial movement (NW and SW) in the Pajala district were separated by an ice-free period, the Perapohjola Interstadial. Conclusive evidence for this standpoint did not exist in Sweden, but the interpretation was strongly supported by numerous observations of water-laid sediments separating the till beds deriving from the different phases of ice movement. Similar to Fromm (1965), but in contrast to Hoppe (1967), Fagerlind concluded that the southwesterly ice movement was regional and states that the ice divide zone during the last glaciation in this area should have been located some 100 km to the south


compared with the prevalent opinion. The southwesterly ice flow was interpreted to represent the main ice movement during the latest glaciation, while at the deglaciation the flow veered westerly. During the deglaciation, extensive damming of ice lakes occurred. It was suggested that the so-called Lainio arc (e.g. Tanner 1915; Hoppe 1952; G. Lundqvist 1961) was created in this period. This prominent formation of hummocky moraines should be attributed to the effect of the amount of glacier water available in the area (Fagerlind 1981 :82).

Znferred deuelopment f rom present investigations A summary of interpreted Weichselian development in this region and tentative correlations is given in Fig. 18. The similarity between the three sites Riipiharju, Onttoharjut and Takanenman- nikko must reflect glacial and non-glacial development of regional validity and, thereby, of great significance for the understanding of the Weichselian in this area and also other parts of Fennoscandia.

The broad outlines of the Weichselian development within the area according to the litho- and biostratigraphical information can be compiled as follows.

Thejirstglacialstude. -The first glaciation after the Eemian Interglacial is represented throughout the area by a thick till layer and glaciofluvial deposits (unit F). The northwesterly drumlins and eskers belong to this stadial phase and constitute the base for the interstadial deposits (unit El-3) dated as older than 45,000-50,OOO 14C years. By means of ice flow directions and till stratigraphy (Nord- kalott Project 1986b, c, d), the tilliscorrelatedwith tillbedIIIinFinland(e.g. Hirvasetal. 1981;Hirvas & Nenonen 1987). This till is stratigraphically situated between the Eemian Interglacial and the Perapohjola Interstadial.

An Early Weichselian age is also supported by the stratigraphy at the Leveaniemi site, located some 40 km SE of Kiruna, where a till, transported from the northwest, rests upon organic deposits interpreted to be of Eemian age (J. Lundqvist 1971). At Leveaniemi the NW-till is overlain by water-laid sediments, tentatively correlated with the Jamtland or Perapohjola Interstadial; on top of these there is a second till, transported from SW. This stratigraphy appears to correspond well with the main outlines in eastern Norrbotten.

However, one circumstance differentiates eastern Norrbotten from the Kiruna region to the west and Finnish Lapland to the east. In eastern Norrbotten the glacial and glaciofluvial deposits belonging to the northwesterly ice flow are often extremely well preserved and dominate the glacial landscape. The eskers more or less exclusively belong to this older system, while in the Kiruna region the situation is the opposite. In Finnish Lap- land less than 10% of the glaciofluvial deposits are interpreted as deriving from older glaciations and they are covered by a basal till (Makinen 1985).

Glacial striations from NW, representing this stadial, occur on many fresh outcrops in the investigation area and often it is the only direction represented. Obviously it was a very active glacier capable of remoulding the previous glacial landscape and forming large-scale morphological features all over the area. Probably the ice flow was directed by a culmination zone near to the mountain range to the west (cf. Nordkalott Project 1986d). The first Weichselian glacial stade is thought to have lasted c. 15,000 years, corre- sponding to isotope stage 5d (Mangerud 1988, in manuscript). In connection with the deglaciation large parts of the glacier became stagnant and developed dead-ice features. The widespread hummocky moraine terrain in the western parts of the investigation area (Fig. 1) was formed during this period (Lagerback 1988a).

Thejirst Early Weichselian interstadial. - The first ice-free period, represented by unit E at Tak- anenmannikko, Onttoharjut, Onttovaara and Riipiharju indicates a subarctic shrub tundra. The formation of peat and a low content of minerogenic matter in the organic deposits suggests stable soil conditions and the existence of a closed vegetational cover. The organic deposits are interpreted to represent the Perapohjola Interstadial (Korpela 1969; Hirvas et al. 1981; Donner et al. 1986). This correlation is based on pollen assem- blages, infinite radiocarbon datings and stratigraphical position directly on top of the deposits from the northwesterly ice flow. The same zonation and vegetational development as in E Norrbotten is indicated in some of the pollen diagrams from Finland. At Permantokoski, chosen as type locality for the Perapohjola Interstadial (Donner etal. 1986), the end of the pre-temperate phase is reflected in the sand below the peat layer (Korpela 1969: fig. 9). The climatic optimum is represented by a pronounced Betula maximum.


The end of the Perapohjola Interstadial, with a spread of heath vegetation, is reflected in the rebedded pollen spectra in the upper till bed with organic material. The zonation can also be traced in the pollen diagram from Pirttikoski (Korpela 1969: fig. 32). The pollen flora shows a successive development from herb and shrub tundra (Gra- mineae, Artemisia, Cyperaceae, Salix) tosubarctic birch forest, and a regression to Arctic conditions (Korpela 196951).

Diatom studies of interstadial sediments were carried out at three localities representing the Perapohjola Interstadial (Molder in Korpela 1969). At Permantokoski the same sedimentation environment prevailed as in the kettle holes studied here. The till-covered organic deposits were formed in a small freshwater basin with acid water, where the genera Eunotia, Pinnularia and Fra- gilaria were most common. But Tabellaria flocculosa, Anomoeoneis serians v. brachysira and Frustulia rhomboides v. saxonica were also frequent (Korpela 1969: table 1, 26-27).

The age of the interstadial is not quite clear. At Hirvijarvi the radiocarbon dating of peat formed during this interstadial (Fig. 1 and Table 1) gave >64,000 B.P. (GrN-11964). AccordingtoDonner etal. (1986), the Perapohjola Interstadial occurred at >60,000 B.P. and Mangerud (1988, in manuscript) correlates Perapohjola (Brcbrup) with isotope stage 5c, c . 105,00&93,000 B.P.

The second glacial stade. - Till unit D cannot be directly correlated with a regional system of ice movement. Fabric analyses of the thin till covering the northwesterly transported till often indicate ice flow from W-WNW. Glacial striations and sporadic drumlinization also indicate ice movements in these directions. There are westerly striations with a relative age between the northwesterly and southwesterly striations (e.g. Fromm 1965), but there are also observations of westerly striations younger than the southwesterly system (Fagerlind 1981). The westerly drumlins occur only in areas where the southwesterly system is weakly developed and are for this reason interpreted to pre-date the southwesterly ice movement. Hence, if a regional ice flow occurred during the deposition of unit D, it was most likely westerly to west-northwesterly.

No division of the post-Perapohjola glaciation, in the sense of two different glaciers divided by regional deglaciation, is known from adjacent parts of Finland. According to the established till

stratigraphy in Finnish Lapland, two till beds (I and 11) occur at many places intercalated by sand or gravel (e.g. Hirvas etal. 1981). No organic sediments have been found between the tills and the sand and gravel are assumed to date from the latest deglaciation, and attributed to oscillations of the ice margin (e.g. Hirvas et al. 1981; Hirvas & Nenonen 1987).

Concerning the geographical extent of this second glaciation there appear to be two possibilities. Either the glacier did not reach very far towards the east or its traces have never been seen in Finland, or, rather, no evidence for a second interstadial has been found. If the first alternative is accepted it implies that during the Perapohjola an ice advance occurred in at least parts of northern Sweden but not in northern Finland. At present we have to leave open the question of the extent of this second Weichselian glacier.

The second Early Weichselian interstadial. - The second ice-free period is represented by stratigraphical unit C at Takanenmannikko, Ontto- harjut and Riipiharju. The environment indicated is an open cold Arctic steppe, possibly partly com- parable to the situation in northern Greenland or Spitsbergen of today. The high content of minerogenic matter in the deposits, mainly sand, is indicative of barren soils, probably in combination with strong winds. Most probably severe periglacial conditions prevailed during at least parts of the period (cf. Lagerback 1988b).

The chronostratigraphical position of the interstadial is uncertain. It has no analogue described from northern Fennoscandia unless the different sequences assigned to the Perapohjola or Jamtland Interstadials actually represent two different ice- free periods. At Pilgrimstad the Jamtland Inter- stadial consists either of two interstadials (Brcbrup and Odderade) or one complex three-parted interstadial ( B r ~ r u p or Odderade) (Robertson 1988).

An ice-free period younger than the Jamtland Interstadial has been suggested by J. Lundqvist (1978) on the basis of radiocarbon datings ranging between about 30,000 and 40,000 14C years B.P. It is however hazardous to rely mainly on radiocarbon ages as a basis for chronostratigraphical correlations in this context. Concerning the Gal- livare site, mentioned by Lundqvist, a more recent dating, made on organic sediments in primary position, gave >45,000 B.P. (St 9761) and for lithostratigraphical reasons, too, can be correlated to


the older of the interstadials discussed in this paper, viz. the Perapohjola Interstadial. Samples from another site discussed by J. Lundqvist, at Juktan, were kindly placed at our disposal by Bo Linder of the Swedish State Power Board. These samples (till-covered organic sediments) have been analysed and clearly demonstrate an interglacial tree pollen flora with Picea, Pinus, Betula, Alnus and Corylus (cf. Robertson& Rodhe 1988).

Radiocarbon datings of the deposits belonging to the C-unit at Takanenmannikko, Onttoharjut and Riipiharju have given both finite and infinite ages (Table 1). The finite ages, ranging between c. 30,000 B .P. and c. 45,000 B .P., are disregarded and considered to be minimum ages asinfinite ages were obtained from the same deposits. The near surface position of these deposits, covered by peat, involves an obvious risk of contamination by humic colloids or rootlets of more recent origin. For these reasons it appears most likely that the age of the interstadial should beconsideredinfinite, i.e. more than 40,000-45,000 I4C years B.P.

Going outside Fennoscandia, the Odderade Interstadial appears to be the most likely correlate to this younger interstadial if the correlation between Perapohjola and BrQirup is accepted. According to Behre & Lade (1986), Odderade resembles BrQirup as regards the vegetational development and was, except for Brcbrup, the only Weichselian interstadial with a climate sufficient for development of forest in northern Germany.

The terrestrial 14C time-scale was extended by Grootes, who dated the three Early Weichselian Interstadials Amersfoort, Brcbrup and Odderade 73,000-56,000 B.P. (Grootes 1978), while Man- gerup (1988, in manuscript) correlates Odderade to isotope stage Sa, dated c. 85,000-75,000 B.P. At Grande Pile in France the uppermost part of Odderade was radiocarbon-dated c. 70,000 B.P. (Woillard & Mook 1982).

As no analogue to this younger interstadial is described from northern Fennoscandia we suggest the local name Tarendo Interstadial and the Riipi- harju site as type locality. The choice of Riipiharju is due to the high sedimentation rate of the inter- stadia1 deposits, resulting in a good time-resolution of the development.

The third and last glacial stade. - The youngest glacier left few traces in the area. The southerly to southwesterly ice flow probably occurred during a late phase and affected only the eastern parts of the area, where fluting, small drumlins and glacially

abraded bedrock are found. The previous glacial landscape was strongly altered only in a narrow zone west of Korpilombolo and Pajala (Figs. 1,4), where the Early Weichselian drumlins and eskers werepracticallyobliterated. In thewestern parts of the investigated area the older deposits are almost intact except for some glaciofluvial erosion dating from the deglaciation phase, and the very ground surface is largely preserved from the youngest of the two interstadials (Lagerback 1988b). The bor- der between unaffected and reshaped terrain is very distinct in some places. For instance, E of Tarendo the transition from perfectly preserved northwesterly drumlins to a strong drumlinization from the southwest occurs within a distance of a few km.

In all probability the ice sheet in this area was frozen to the ground practically throughout the time of its existence during the Middle and Late Weichselian. The ice probably started to grow by accumulation of snow in a periglacial environment and was cold-based from the outset (cf. Schytt 1974). Not until the end of the glaciation did the glacier start to erode the older deposits, and then only in parts of the area.

Concluding remarks Thus, from the stratigraphy recorded at Riipiharju, Onttoharjut and Takanenmannikko, it is concluded that the Weichselian glaciation was dividedinto (at least) three glacial stades separated by two ice-free interstadials in the area studied. Except for a zone with S-SW drumlinization, deriving from the last glacial stade, the impact of the two later ice sheets is modest and the deposits from the northwesterly ice Bow during the first Weichselian glaciation dominate the landscape. It can be stated that the classical west-easterly oriented ‘ice divide zone’ in northernmost Sweden never existed, and that it was constructed from glacial features deriving from two different glaciations separated by still another glaciation and two ice-free interstadials.

Acknowledgements. - This paper could not have been realized without the contributions and assistance of a great number of persons. Tobegin with, the collaboration withFinnish colleagues Heikki Hirvas, Pekka Huhta, Peter Johansson, Kalevi Makinen, Keijo Nenonen and Raimo Sutinen during stratigraphical investigations on both sides of the Finnish-Swedish frontier was most inspiring and of great importance for the interpretation of the stratigraphy on the Swedish side. Jan Olov Svedlund and Mats Edelryd generously shared the hardships during the field work in winter. The biostratigraphical preparations were carried out at


muit, Jakobshavn, West Greenland. Med&lekerfra Gronland 178:4. 54 pp.

Fromm, E. 1965: Beskrivning till jordartskarta over Norrbottens Ian nedanfor Lappmarksgransen. Soeriges geologiska undersokning Ca 39. 236 pp.

Grootes, P. M. 1978: Carbon 14 time scaleextended comparison of chronologies. Nature 200,ll-15.

Hirvas, H., Kujansuu, R. &Tynni, R. 1976: Till stratigraphy in Northern Finland. IGCP Project 73f1 f24 Quaternary Glaci- ations in the Northern Hemisphere. Report 3 , 256-273. Bellingham , Prague.

Hirvas, H., Alfthan, A. , Pulkkinen, E., Puranen, R. & Tynni, R. 1977: Raportti malminetsintaa palvelevasta maaperatut- kimukscsta Pohjois-Suomessa vuosina 1972-1976. Summary: a report of glacial drift investigations for ore-prospecting in northern Finland 1972-1976. Geological Survey of Finland. Report of Investigaiions 19. 54 pp.

Hirvas, H., Korpela, K. & Kujansuu, R. 1981: Weichselian in Finland before 15,000B.P. Boreus 10,423-431.

Hirvas, H. & Nenonen, K. 1987: The till stratigraphyof Finland. Geological Survey of Finland, Special Paper 3,49-63.

Hicks, S. 1977: Modern pollen rain in Finnish Lapland investigated by analysis of surface moss samples. New Phytologist 78,715-134.

Hoppe, G. 1952: Hummocky moraine regions with special reference to the interior of Norrbotten. Geogrqtiska Annaler34, 1-72.

Hoppe, G. 1967: Case studies of deglaciation patterns. Geo- graj'iska Annaler 49 A , 204-212.

Hustedt, F. 1939: Systematische und okologische Untersu- chungen iiber die Diatomeenflora von Java, Bali und Sumatra nach dem Material der Deutschen Limnologischen Sunda Expedition. Archiv fur Hydrobiologie. Supplement 15, 187- 295.

Iversen, J . 1945: Conditions and life for the large herbivorous mammals in the Late-Glacial Period. In Degerb01, M. & Iver- sen, J . (eds.): The Bison in Denmark. Danmarks geologiske unders@gelse II 73. 62 pp.

Jarnefors, B. 1952: A sediment-petrographic study of glacial till from the Pajala district, Sweden. Geologiska Foreningens i Stockholm Forhandlingar 74, 185-211.

Kolstrup, E. 1979: Herbs as July temperatureindicatorsfor parts of the Pleniglacial and Late-Glacial in the Netherlands. Geo- logic en Mijnbouw 58:3,377-380.

Kolstrup, E. 1980: Climate and stratigraphy in Northwestern Europe between 30,000B.P. and 13,000B.P. with specialref- erence to the Netherlands. Mededelingen Rijks Geologische Dienst 32-15, 181-253.

Kolstrup, E. & Wijmstra. T. A. 1977: A palynological investigation of the Moershoofd, Hengelo and Denekamp inter- stadialsin the Netherlands. Geologieen Mijnbouw56,85-102.

Korpela, K. 1969: Die Weichsel-Eiszeit und ihr Interstadial in Perapohjola (nordliches Nordfinnland) im Licht van sub- moranen sedimenten. A nnales Academiae Scientiarum Fen- nicae A III 99. 108 pp.

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Lagerback, R. 1986: WeichselistideninorraSverige. 17Nordhka Geolonmotet 1986, Helsingfors universitet 12-15.5. 1986.

the Micropaleontological Laboratory, Geological Survey of Sweden. The diatom analyses were made by Hikan Modig and the pollen analyses by Raija Sethi. Mats Edelryd and Anders Fredlund did the drawing work, Britta Lindkvist typed the manuscript and Theodosia Gray improved the English. Finally, Jan Mangerud thoroughly read a first draft of the manuscript and suggested important improvements. Our debt to these persons is gratefully acknowledged. The field work was carried out within the Nordkalott Project and the microfossil analyses were financed by the Documentation Programme of Quaternary deposits at the Geological Survey of Sweden. The aerial photographs are approved for publication.

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Documents

Kettle holes - stratigraphical archives for Weichselian geology and palaeoenvironment in northernmost Sweden